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<!DOCTYPE article PUBLIC "-//NLM//DTD Journal Publishing with OASIS Tables v3.0 20080202//EN" "https://jats.nlm.nih.gov/nlm-dtd/publishing/3.0/journalpub-oasis3.dtd">
<article xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:oasis="http://docs.oasis-open.org/ns/oasis-exchange/table" xml:lang="en" dtd-version="3.0" article-type="research-article">
  <front>
    <journal-meta><journal-id journal-id-type="publisher">MS</journal-id><journal-title-group>
    <journal-title>Mechanical Sciences</journal-title>
    <abbrev-journal-title abbrev-type="publisher">MS</abbrev-journal-title><abbrev-journal-title abbrev-type="nlm-ta">Mech. Sci.</abbrev-journal-title>
  </journal-title-group><issn pub-type="epub">2191-916X</issn><publisher>
    <publisher-name>Copernicus Publications</publisher-name>
    <publisher-loc>Göttingen, Germany</publisher-loc>
  </publisher></journal-meta>
    <article-meta>
      <article-id pub-id-type="doi">10.5194/ms-15-63-2024</article-id><title-group><article-title>Dynamic analysis of a box-structured satellite deployment mechanism with self-actuated torsion joints</article-title><alt-title>Dynamic analysis of a satellite deployment mechanism with self-actuated torsion joints</alt-title>
      </title-group><?xmltex \runningtitle{Dynamic analysis of a satellite deployment mechanism with self-actuated torsion joints}?><?xmltex \runningauthor{D.~Sheng~et~al.}?>
      <contrib-group>
        <contrib contrib-type="author" corresp="yes" rid="aff1">
          <name><surname>Sheng</surname><given-names>Dongping</given-names></name>
          <email>shengdp@czu.com</email>
        <ext-link>https://orcid.org/0000-0002-5414-0362</ext-link></contrib>
        <contrib contrib-type="author" corresp="no" rid="aff2">
          <name><surname>Ma</surname><given-names>Renzhe</given-names></name>
          
        </contrib>
        <contrib contrib-type="author" corresp="no" rid="aff1">
          <name><surname>Su</surname><given-names>Chun</given-names></name>
          
        </contrib>
        <aff id="aff1"><label>1</label><institution>School of Aeronautical and Mechanical Engineering, Changzhou Institute of Technology (11055), Changzhou, 213032, China</institution>
        </aff>
        <aff id="aff2"><label>2</label><institution>Faculty of Engineering and Physical Sciences, University of Leeds, Woodhouse Lane,<?xmltex \hack{\break}?> Leeds, LS29JT, United Kingdom</institution>
        </aff>
      </contrib-group>
      <author-notes><corresp id="corr1">Dongping Sheng (shengdp@czu.com)</corresp></author-notes><pub-date><day>6</day><month>February</month><year>2024</year></pub-date>
      
      <volume>15</volume>
      <issue>1</issue>
      <fpage>63</fpage><lpage>76</lpage>
      <history>
        <date date-type="received"><day>28</day><month>October</month><year>2023</year></date>
           <date date-type="accepted"><day>17</day><month>December</month><year>2023</year></date>
           <date date-type="rev-recd"><day>30</day><month>November</month><year>2023</year></date>
      </history>
      <permissions>
        <copyright-statement>Copyright: © 2024 Dongping Sheng et al.</copyright-statement>
        <copyright-year>2024</copyright-year>
      <license license-type="open-access"><license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p></license></permissions><self-uri xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024.html">This article is available from https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024.html</self-uri><self-uri xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024.pdf">The full text article is available as a PDF file from https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024.pdf</self-uri>
      <abstract><title>Abstract</title>

      <p id="d1e103">This paper designed a kind of satellite deployment mechanism with a boxed structure and passive torsion joints. This deployment mechanism has significant strengths, including a high base frequency and stiffness, a high ratio of deployed and folded space occupation ratios, and self-actuated joints without needing any external power to drive. In order to analyze the dynamic characteristics of this mechanism, a simplified governing equation is proposed and dynamic behavior is studied systematically, including impact response, harmonic response, and modal analysis. Through systematic research, several conclusions are drawn. Firstly, when the deployment mechanism reached the ending stage of unfolding driven by passive torsional joints, the load base installed on top of the deployment mechanism generated a first-order sharp reaction force and multiple low-order shocks followed, and the system entered a stable state after a certain time of vibration. Secondly, the system can generate a high vibration magnitude at low-frequency excitation when the mechanism is in a fully deployed state and at high-frequency excitation when the mechanism is in a folded state. Thirdly, the first sixth-order natural frequency and vibration shape with different wall thicknesses are obtained by modal analysis. The result shows that only with a 2.5 <inline-formula><mml:math id="M1" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness can the connecting rod satisfy the design requirement. Through dynamic behavior research, the structure characteristics are obtained which can be used for structure optimization and to provide an effective solution for the design of a box-structured satellite-unfolding mechanism with self-actuated torsion joints.</p>
  </abstract>
    
<funding-group>
<award-group id="gs1">
<funding-source>Nanjing University of Aeronautics and Astronautics</funding-source>
<award-id>HTL-O-20K01</award-id>
</award-group>
</funding-group>
</article-meta>
  </front>
<body>
      

<sec id="Ch1.S1" sec-type="intro">
  <label>1</label><title>Introduction</title>
      <p id="d1e123">A space-folding mechanism is a new type of foldable and deployable space equipment, which adapts to the development of spacecraft in the direction of a large scale (Meguro et al., 2006; Angeletfi et al., 2019). The research and development of space-folding mechanisms can solve the space constraints in spacecraft navigation and carry as many tools and equipment as possible with the limited space and weight. At the same time, this can realize the compact layout of spacecraft components, improve the load capacity and use of space, and reduce production and transportation costs significantly.</p>
      <p id="d1e126">NASA began studying the application of space-folding mechanisms as early as the 1960s. In the space exploration project of the United States, the space-folding mechanism is widely used in the development and construction of satellites, space stations, and probes (Ma et al., 2018; Liu et al., 2018; Hu et al., 2022). With the requirement of satellite miniaturization, Choi proposed a high-precision extension arm design scheme (Arita et al., 2018; Choi et al., 2019), which is mainly used for space optical telescopes. The extension arm was based on a quadrangular column and was equipped with an upper panel and a lower panel, a connecting rod, and a supporting module. In order to further improve the folding and unfolding accuracy of the mechanism, a special assembly mold was developed, and based on the precision detection platform built by five contactless laser displacement sensors, the unfolding accuracy of the mechanism was experimentally studied and the micro-unfolding accuracy was achieved. In<?pagebreak page64?> the 1990s, ATK Company developed a kind of UltraFlex solar wing (Spence et al., 2006; Eacre and White, 2010), which mainly consists of a flexible triangle film, a center hub, a compression band, and an expansion mechanism. The expansion principle is similar to that of a folding fan, the torsion spring located at the center is used to expand, and the shape is circular after expansion.</p>
      <p id="d1e129">The European Union and the European Space Agency have also conducted a lot of research on space-folding mechanisms, mainly applied to the expansion and contraction of solar panels as well as the construction of satellites and space vehicles. The European Space Agency and a number of research institutions such as Georgia Technical University (Datashvili, 2013; Medzmarlashvili et al., 2013) jointly developed a conical-ring deployable antenna with a diameter of up to 6 <inline-formula><mml:math id="M2" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">m</mml:mi></mml:mrow></mml:math></inline-formula> after development. The antenna is composed of a number of trapezoidal components, including upper and lower V-shaped folding rods, vertical rods, synchronous hinges, driving springs, and cable components. An extended arm of a triangular prism with the triangular prism as the unfolding unit was proposed (Sahn et al., 2018), which was composed of a rigid triangular frame, an upper and lower folding arm, a diagonal cable, and other structures. The device is located in the middle of the upper and lower folding arm and uses the transmission mode combined with the motor and the screw to tighten the diagonal cable when deployed, thereby increasing the rigidity of the device.</p>
      <p id="d1e140">A triangular prism extension arm with a super-elastic hinge was proposed (Yang et al., 2016, 2018). The extension arm was also a modular unit with a triangular prism, and its main components include a longitudinal rod, a rope, a triangular frame, casing, and a super-elastic hinge. An expandable triangular prism type extension arm composed of a longitudinal rod, a beam, a tension cable, and a hinge was proposed (Gao et al., 2020). The extension arm is driven by a spring taking into account the load. The whole is made of lightweight materials, the longitudinal rod is made of carbon fiber, and the other parts are made of aluminum alloy. After the extension arm is unfurled and fixed, the longitudinal rod supports the extension arm, and at the same time, the tension cable is tightened to increase the strength of the extension arm. China's Shijian-20 satellite is equipped with the solar wing with the largest area and longest wingspan at present, which is composed of six solar panels, i.e., four transverse solar panels and two longitudinal solar panels (Cui and Tang, 2020). Based on the traditional folding fan principle, a deep study of the fan solar wing was made (Jian and Ce, 2020), and the synchronous mechanism, self-locking hinge, and driving mechanism were designed and used the multi-body dynamics software to simulate and analyze the kinematics and dynamics of the mechanism. Based on the scissor's mechanism, the configuration method of the rib-element folding mechanism was proposed (He et al., 2021), and the rib-element folding mechanism and expansion method of the multi-modular folding mechanism were proposed based on the envelope cone method, which verified that the method was designed. A series of analyses and experiments was conducted in the face of the demand to replace the ultra-thin aluminum honeycomb materials used in manufacturing solar panels (Guan et al., 2023). A surface defect detection method for flexible solar wing piano hinges was proposed based on deep learning (Wang et al., 2023). In this method, cameras are used to record the hinges, and a big-data analysis method is utilized to analyze the recorded data, which not only reduces the performance requirements of computers, but also improves the detection accuracy and efficiency.</p>
      <p id="d1e144">In this paper, a box-structured satellite-unfolding mechanism based on a precision positioning self-actuated torsion joint is designed, and the dynamic simulation of the folding mechanism is carried out in three aspects based on multi-body dynamics, including shock response, modal analysis, and vibration analysis. Through multi-angle dynamic analysis, the structural dynamic response is obtained, and based on the response, the structure is optimized, which provides a reliable solution for the analysis and optimal design of this kind of structure.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F1" specific-use="star"><?xmltex \currentcnt{1}?><?xmltex \def\figurename{Figure}?><label>Figure 1</label><caption><p id="d1e149">Unfolding process of the deployable mechanism. <bold>(a)</bold> Fully folded; <bold>(b)</bold> half-deployed; <bold>(c)</bold> fully deployed.</p></caption>
        <?xmltex \igopts{width=284.527559pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f01.png"/>

      </fig>

</sec>
<sec id="Ch1.S2">
  <label>2</label><title>Physical model and dynamic equation</title>
<sec id="Ch1.S2.SS1">
  <label>2.1</label><title>Physical model</title>
      <p id="d1e182">Figure 1 shows the unfolding process of the mechanism, Fig. 1a shows the fully folded state, Fig. 1b shows the half-deployed state, and Fig. 3c shows the fully deployed state. In addition, it can be seen that the unfolding mechanism mainly includes a load base, a connecting rod, and a torsion joint, and the four joints located on the bottom of the unfolding mechanism are installed on the satellite body. The load base is used to install the deep space exploration lens and to drive with the connecting rods and self-actuated joints. In addition, it should be noted that the connecting rod is made of carbon fiber considering its characteristics of high strength and low weight.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F2" specific-use="star"><?xmltex \currentcnt{2}?><?xmltex \def\figurename{Figure}?><label>Figure 2</label><caption><p id="d1e187">Unfolding process of joints.</p></caption>
          <?xmltex \igopts{width=284.527559pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f02.png"/>

        </fig>

      <p id="d1e196">Figure 2 shows the detailed unfolding process and structure of the self-actuated joint, which has an energy storage unit to unfold the mechanism. As seen in Fig. 2a, each joint is bonded with two connecting rods in parallel. Under the driver of the joint, which has a custom-designed torque spring inside, the angle between the rods is increased from 0 to 180<inline-formula><mml:math id="M3" display="inline"><mml:msup><mml:mi/><mml:mo>∘</mml:mo></mml:msup></mml:math></inline-formula> gradually. After strict testing, the driven torque of the joint behaved near-linearly and from 0.9 to 0.3 <inline-formula><mml:math id="M4" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Nm</mml:mi></mml:mrow></mml:math></inline-formula> when the rod angle increased from 0 to 180<inline-formula><mml:math id="M5" display="inline"><mml:msup><mml:mi/><mml:mo>∘</mml:mo></mml:msup></mml:math></inline-formula>.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F3"><?xmltex \currentcnt{3}?><?xmltex \def\figurename{Figure}?><label>Figure 3</label><caption><p id="d1e228">Simplified model of the deployable mechanism. </p></caption>
          <?xmltex \igopts{width=236.157874pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f03.png"/>

        </fig>

      <?xmltex \floatpos{p}?><fig id="Ch1.F4" specific-use="star"><?xmltex \currentcnt{4}?><?xmltex \def\figurename{Figure}?><label>Figure 4</label><caption><p id="d1e239">Dynamic unfolding process. <bold>(a)</bold> Folded state; <bold>(b)</bold> half-deployed; <bold>(c)</bold> fully deployed.</p></caption>
          <?xmltex \igopts{width=312.980315pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f04.png"/>

        </fig>

      <?xmltex \floatpos{p}?><fig id="Ch1.F5" specific-use="star"><?xmltex \currentcnt{5}?><?xmltex \def\figurename{Figure}?><label>Figure 5</label><caption><p id="d1e259">Time vs. impact force diagram.</p></caption>
          <?xmltex \igopts{width=426.791339pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f05.png"/>

        </fig>

</sec>
<sec id="Ch1.S2.SS2">
  <label>2.2</label><title>Dynamic equation</title>
      <?pagebreak page66?><p id="d1e276">In order to analyze the dynamic behavior and characteristics, the dynamic equation is proposed. For the spatial multi-degree-of-freedom mechanism, the Lagrange equation is used to establish the dynamic equation as follows:
            <disp-formula id="Ch1.E1" content-type="numbered"><label>1</label><mml:math id="M6" display="block"><mml:mrow><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mi mathvariant="normal">d</mml:mi><mml:mrow><mml:mi mathvariant="normal">d</mml:mi><mml:mi>t</mml:mi></mml:mrow></mml:mfrac></mml:mstyle><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover></mml:mrow></mml:mfrac></mml:mstyle><mml:mo>-</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mo>=</mml:mo><mml:msub><mml:mi>Q</mml:mi><mml:mi>j</mml:mi></mml:msub><mml:mo>,</mml:mo></mml:mrow></mml:math></disp-formula>
          where <inline-formula><mml:math id="M7" display="inline"><mml:mi>T</mml:mi></mml:math></inline-formula> is kinetic energy, <inline-formula><mml:math id="M8" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> is generalized coordinates, <inline-formula><mml:math id="M9" display="inline"><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover></mml:math></inline-formula> is generalized velocity, and <inline-formula><mml:math id="M10" display="inline"><mml:mrow><mml:msub><mml:mi>Q</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> is generalized force.</p>
      <p id="d1e382">The box-structured space-folding mechanism consists of the same four modules as seen in Fig. 1, and a single-side module is adopted for analysis. The mechanism is simplified into four rigid rods connected in sequence from end to end. In order to facilitate the construction of the dynamic equation, the intermediate layer and the load plate are simplified as mass points, and the simplified model is shown in Fig. 3.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F6" specific-use="star"><?xmltex \currentcnt{6}?><?xmltex \def\figurename{Figure}?><label>Figure 6</label><caption><p id="d1e387">Frequency response diagram (1 <inline-formula><mml:math id="M11" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting rod). <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f06.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F7" specific-use="star"><?xmltex \currentcnt{7}?><?xmltex \def\figurename{Figure}?><label>Figure 7</label><caption><p id="d1e413">Frequency response diagram (2 <inline-formula><mml:math id="M12" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting rod). <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f07.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F8" specific-use="star"><?xmltex \currentcnt{8}?><?xmltex \def\figurename{Figure}?><label>Figure 8</label><caption><p id="d1e438">Frequency response diagram (3.5 <inline-formula><mml:math id="M13" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting rod). <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f08.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F9" specific-use="star"><?xmltex \currentcnt{9}?><?xmltex \def\figurename{Figure}?><label>Figure 9</label><caption><p id="d1e463">Frequency response diagram (1 <inline-formula><mml:math id="M14" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting rod). <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(c)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f09.png"/>

        </fig>

      <p id="d1e486"><inline-formula><mml:math id="M15" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> represents the angle between the <inline-formula><mml:math id="M16" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod and the <inline-formula><mml:math id="M17" display="inline"><mml:mi>y</mml:mi></mml:math></inline-formula> axis. <inline-formula><mml:math id="M18" display="inline"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> represents the torque acted on the <inline-formula><mml:math id="M19" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod, as shown in Fig. 3. Similarly, it can be seen that <inline-formula><mml:math id="M20" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M21" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M22" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, and <inline-formula><mml:math id="M23" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>=</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>.</p>
      <p id="d1e604">During the process of deployment, the four rods are all in plane motion, and the motion state of each rod at any time can be represented by four generalized coordinates, so the position of the centroid of the first rod at any time can be described as
            <disp-formula id="Ch1.E2" content-type="numbered"><label>2</label><mml:math id="M24" display="block"><mml:mfenced open="{" close=""><mml:mtable class="cases" rowspacing="0.2ex" columnspacing="1em" columnalign="left" framespacing="0em"><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>r</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>l</mml:mi><mml:mo>⋅</mml:mo><mml:mfenced close="]" open="["><mml:mrow><mml:msubsup><mml:mo movablelimits="false">∑</mml:mo><mml:mrow><mml:mi>j</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow><mml:mi>i</mml:mi></mml:msubsup><mml:mfenced open="(" close=")"><mml:mrow><mml:mi>sin⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mfenced><mml:mo>-</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mi>sin⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle></mml:mstyle></mml:mrow></mml:mfenced><mml:mo>,</mml:mo></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>r</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>y</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mi>l</mml:mi><mml:mo>⋅</mml:mo><mml:mfenced close="]" open="["><mml:mrow><mml:msubsup><mml:mo movablelimits="false">∑</mml:mo><mml:mrow><mml:mi>j</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow><mml:mi>i</mml:mi></mml:msubsup><mml:mfenced open="(" close=")"><mml:mrow><mml:mo>(</mml:mo><mml:mo>-</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:msup><mml:mo>)</mml:mo><mml:mrow><mml:mi>j</mml:mi><mml:mo>+</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow></mml:msup><mml:mi>cos⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mfenced><mml:mo>+</mml:mo><mml:mo>(</mml:mo><mml:mo>-</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:msup><mml:mo>)</mml:mo><mml:mi>j</mml:mi></mml:msup><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mi>cos⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle></mml:mstyle></mml:mrow></mml:mfenced><mml:mo>,</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced></mml:math></disp-formula>
          where <inline-formula><mml:math id="M25" display="inline"><mml:mrow><mml:msub><mml:mi>r</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> is the horizontal coordinate of the <inline-formula><mml:math id="M26" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod, <inline-formula><mml:math id="M27" display="inline"><mml:mrow><mml:msub><mml:mi>r</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>y</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> is the vertical coordinate of the <inline-formula><mml:math id="M28" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod, and <inline-formula><mml:math id="M29" display="inline"><mml:mi>l</mml:mi></mml:math></inline-formula> is the length of the rod: <inline-formula><mml:math id="M30" display="inline"><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">2</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">3</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">4</mml:mn></mml:mrow></mml:math></inline-formula>; <inline-formula><mml:math id="M31" display="inline"><mml:mrow><mml:mi>j</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">2</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">3</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">4</mml:mn></mml:mrow></mml:math></inline-formula>.</p>
      <p id="d1e854">Using vector <inline-formula><mml:math id="M32" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="bold-italic">r</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> as the displacement of the center of the <inline-formula><mml:math id="M33" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod,
            <disp-formula id="Ch1.E3" content-type="numbered"><label>3</label><mml:math id="M34" display="block"><mml:mtable class="split" rowspacing="0.2ex" displaystyle="true" columnalign="right left"><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>v</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>=</mml:mo><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>r</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>=</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="bold-italic">r</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="bold-italic">r</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="bold-italic">r</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="bold-italic">r</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd/><mml:mtd><mml:mrow><mml:mo>=</mml:mo><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>,</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
          where <inline-formula><mml:math id="M35" display="inline"><mml:mrow><mml:msub><mml:mi>v</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> represents the velocity of the center of the <inline-formula><mml:math id="M36" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod; and <inline-formula><mml:math id="M37" display="inline"><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M38" display="inline"><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M39" display="inline"><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>, and <inline-formula><mml:math id="M40" display="inline"><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> represent the line velocity of the <inline-formula><mml:math id="M41" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod under the generalized coordinates of <inline-formula><mml:math id="M42" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M43" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M44" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, and <inline-formula><mml:math id="M45" display="inline"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>.</p>
      <p id="d1e1229">Using <inline-formula><mml:math id="M46" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> as the angle displacement of the i<inline-formula><mml:math id="M47" display="inline"><mml:msup><mml:mi/><mml:mrow><mml:mi>t</mml:mi><mml:mi>h</mml:mi></mml:mrow></mml:msup></mml:math></inline-formula> rod,
            <disp-formula id="Ch1.E4" content-type="numbered"><label>4</label><mml:math id="M48" display="block"><mml:mtable rowspacing="0.2ex" class="split" displaystyle="true" columnalign="right left"><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi mathvariant="italic">ω</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>=</mml:mo><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>=</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd/><mml:mtd><mml:mrow><mml:mo>=</mml:mo><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>+</mml:mo><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:mrow></mml:msub><mml:mover accent="true"><mml:mrow><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mo>.</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula></p>
      <p id="d1e1481">The linear velocity of each bar can be calculated by the motion equation of the centroid of each rod. In order to facilitate the calculation, we can decompose it into scalars in the <inline-formula><mml:math id="M49" display="inline"><mml:mi>x</mml:mi></mml:math></inline-formula> direction and <inline-formula><mml:math id="M50" display="inline"><mml:mi>y</mml:mi></mml:math></inline-formula> direction. The linear velocity of the centroid of the <inline-formula><mml:math id="M51" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod relative to the <inline-formula><mml:math id="M52" display="inline"><mml:mi>j</mml:mi></mml:math></inline-formula>th generalized coordinate in the <inline-formula><mml:math id="M53" display="inline"><mml:mi>x</mml:mi></mml:math></inline-formula>- and <inline-formula><mml:math id="M54" display="inline"><mml:mi>y</mml:mi></mml:math></inline-formula>-axis directions can be described as follows.
            <disp-formula id="Ch1.E5" content-type="numbered"><label>5</label><mml:math id="M55" display="block"><mml:mtable class="split" rowspacing="0.2ex" displaystyle="true" columnalign="right left"><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>j</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>=</mml:mo><mml:mfenced open="{" close=""><mml:mtable rowspacing="0.2ex" class="cases" columnspacing="1em" columnalign="left left" framespacing="0em"><mml:mtr><mml:mtd><mml:mn mathvariant="normal">0</mml:mn></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>&lt;</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle></mml:mstyle><mml:mi>l</mml:mi><mml:mi>cos⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mi>l</mml:mi><mml:mi>cos⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>&gt;</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>j</mml:mi><mml:mi>y</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>=</mml:mo><mml:mfenced open="{" close=""><mml:mtable columnspacing="1em" class="cases" rowspacing="0.2ex" columnalign="left left" framespacing="0em"><mml:mtr><mml:mtd><mml:mn mathvariant="normal">0</mml:mn></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>&lt;</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mo>-</mml:mo><mml:mi>l</mml:mi><mml:mi>sin⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">3</mml:mn><mml:mtext> and </mml:mtext><mml:mi>i</mml:mi><mml:mo>&gt;</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mi>l</mml:mi><mml:mi>sin⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">2</mml:mn><mml:mo>,</mml:mo><mml:mn mathvariant="normal">4</mml:mn><mml:mtext> and </mml:mtext><mml:mi>i</mml:mi><mml:mo>&gt;</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle></mml:mstyle><mml:mi>l</mml:mi><mml:mi>sin⁡</mml:mi><mml:msub><mml:mi mathvariant="italic">φ</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula></p>
      <p id="d1e1734">The angular velocity <inline-formula><mml:math id="M56" display="inline"><mml:mrow><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>j</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> of the <inline-formula><mml:math id="M57" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod with respect to the <inline-formula><mml:math id="M58" display="inline"><mml:mi>j</mml:mi></mml:math></inline-formula>th generalized coordinate is
            <disp-formula id="Ch1.E6" content-type="numbered"><label>6</label><mml:math id="M59" display="block"><mml:mrow><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>j</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mfenced open="{" close=""><mml:mtable class="cases" rowspacing="0.2ex" columnspacing="1em" columnalign="left left" framespacing="0em"><mml:mtr><mml:mtd><mml:mn mathvariant="normal">1</mml:mn></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mi>j</mml:mi><mml:mo>,</mml:mo></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mn mathvariant="normal">0</mml:mn></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>≠</mml:mo><mml:mi>j</mml:mi><mml:mo>.</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced></mml:mrow></mml:math></disp-formula></p>
      <p id="d1e1810">The kinetic energy <inline-formula><mml:math id="M60" display="inline"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mtext>ni</mml:mtext></mml:msub></mml:mrow></mml:math></inline-formula> of the <inline-formula><mml:math id="M61" display="inline"><mml:mi>i</mml:mi></mml:math></inline-formula>th rod during the unfolding process can be written as
            <disp-formula id="Ch1.E7" content-type="numbered"><label>7</label><mml:math id="M62" display="block"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mtext>ni</mml:mtext></mml:msub><mml:mo>=</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle><mml:msub><mml:mi>m</mml:mi><mml:mi>i</mml:mi></mml:msub><mml:msubsup><mml:mi>v</mml:mi><mml:mi>i</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mstyle displaystyle="true"><mml:mfrac style="display"><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle><mml:msub><mml:mi>J</mml:mi><mml:mi>S</mml:mi></mml:msub><mml:msubsup><mml:mi mathvariant="italic">ω</mml:mi><mml:mi>i</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>,</mml:mo></mml:mrow></mml:math></disp-formula>
          where <inline-formula><mml:math id="M63" display="inline"><mml:mrow><mml:msub><mml:mi>v</mml:mi><mml:mi>i</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> is the line angle of the mass center of the rod, and <inline-formula><mml:math id="M64" display="inline"><mml:mrow><mml:msub><mml:mi>j</mml:mi><mml:mi mathvariant="normal">s</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> is the moment of inertia.</p>
      <p id="d1e1906">The total kinetic energy <inline-formula><mml:math id="M65" display="inline"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi mathvariant="normal">n</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> of the unfolding system can be written as
            <disp-formula id="Ch1.E8" content-type="numbered"><label>8</label><mml:math id="M66" display="block"><mml:mtable rowspacing="0.2ex" class="split" displaystyle="true" columnalign="right left"><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi mathvariant="normal">n</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:munderover><mml:mo movablelimits="false">∑</mml:mo><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow><mml:mn mathvariant="normal">4</mml:mn></mml:munderover><mml:msub><mml:mi>T</mml:mi><mml:mtext>ni</mml:mtext></mml:msub><mml:mo>=</mml:mo></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mspace linebreak="nobreak" width="0.25em"/><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">11</mml:mn></mml:msub><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">22</mml:mn></mml:msub><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">33</mml:mn></mml:msub><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">44</mml:mn></mml:msub><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd/><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">12</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">13</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">14</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd/><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">23</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">24</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">34</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>,</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:math></disp-formula>
          where <inline-formula><mml:math id="M67" display="inline"><mml:mrow><mml:msub><mml:mi>j</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>j</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> is the coefficient of the inertia and is written as
            <disp-formula id="Ch1.E9" content-type="numbered"><label>9</label><mml:math id="M68" display="block"><mml:mrow><?xmltex \hack{\hbox\bgroup\fontsize{9.5}{9.5}\selectfont$\displaystyle}?><mml:msub><mml:mi>J</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>j</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mfenced open="{" close=""><mml:mtable columnspacing="1em" class="cases" rowspacing="0.2ex" columnalign="left left" framespacing="0em"><mml:mtr><mml:mtd><mml:mrow><mml:msubsup><mml:mo movablelimits="false">∑</mml:mo><mml:mrow><mml:mi>j</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow><mml:mn mathvariant="normal">4</mml:mn></mml:msubsup><mml:mfenced open="(" close=")"><mml:mrow><mml:mi>m</mml:mi><mml:msubsup><mml:mi>u</mml:mi><mml:mrow><mml:mi>j</mml:mi><mml:mi>i</mml:mi><mml:mi>x</mml:mi></mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mi>m</mml:mi><mml:msubsup><mml:mi>u</mml:mi><mml:mrow><mml:mi>j</mml:mi><mml:mi>i</mml:mi><mml:mi>y</mml:mi></mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mi>j</mml:mi></mml:msub><mml:msubsup><mml:mi>i</mml:mi><mml:mrow><mml:mi>j</mml:mi><mml:mi>i</mml:mi></mml:mrow><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mfenced></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mi>j</mml:mi><mml:mo>,</mml:mo></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:msubsup><mml:mo movablelimits="false">∑</mml:mo><mml:mrow><mml:mi>k</mml:mi><mml:mo>=</mml:mo><mml:mn mathvariant="normal">1</mml:mn></mml:mrow><mml:mn mathvariant="normal">4</mml:mn></mml:msubsup><mml:mfenced open="(" close=")"><mml:mrow><mml:mi>m</mml:mi><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>k</mml:mi><mml:mi>i</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>k</mml:mi><mml:mi>j</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:mi>m</mml:mi><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>k</mml:mi><mml:mi>i</mml:mi><mml:mi>y</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>u</mml:mi><mml:mrow><mml:mi>k</mml:mi><mml:mi>j</mml:mi><mml:mi>y</mml:mi></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mi>i</mml:mi></mml:msub><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>k</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>i</mml:mi><mml:mrow><mml:mi>j</mml:mi><mml:mi>k</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfenced></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mi>i</mml:mi><mml:mo>≠</mml:mo><mml:mi>j</mml:mi><mml:mo>.</mml:mo></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced><?xmltex \hack{$\egroup}?></mml:mrow></mml:math></disp-formula></p>
      <?pagebreak page68?><p id="d1e2379">By substituting <inline-formula><mml:math id="M69" display="inline"><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi mathvariant="normal">n</mml:mi></mml:msub></mml:mrow></mml:math></inline-formula> into Eq. (<xref ref-type="disp-formula" rid="Ch1.E1"/>), the system of governing equations can be obtained as follows.
            <disp-formula id="Ch1.E10" content-type="numbered"><label>10</label><mml:math id="M70" display="block"><mml:mfenced open="{" close=""><mml:mtable columnspacing="1em" class="cases" rowspacing="0.2ex" columnalign="left left" framespacing="0em"><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">11</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">12</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">13</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">14</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">12</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow/></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">13</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">14</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>Q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">21</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">22</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">23</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">24</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">21</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow/></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">23</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">24</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>Q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">31</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">32</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">33</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">34</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">31</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow/></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">32</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">34</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>Q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">41</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">42</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">43</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">44</mml:mn></mml:msub><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">41</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow/></mml:mtd><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">42</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mstyle displaystyle="false"><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn mathvariant="normal">43</mml:mn></mml:msub></mml:mrow><mml:mrow><mml:mo>∂</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mstyle></mml:mstyle><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>Q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced></mml:math></disp-formula></p>
      <p id="d1e3073">Without considering gravity and friction, there are only four driving torques and systems, and the generalized force can be expressed as
            <disp-formula id="Ch1.E11" content-type="numbered"><label>11</label><mml:math id="M71" display="block"><mml:mrow><mml:msub><mml:mi>Q</mml:mi><mml:mi>i</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:munderover><mml:mo movablelimits="false">∑</mml:mo><mml:mrow><mml:mi>j</mml:mi><mml:mo>=</mml:mo><mml:mi>i</mml:mi></mml:mrow><mml:mn mathvariant="normal">4</mml:mn></mml:munderover><mml:mfenced close=")" open="("><mml:mrow><mml:mo>(</mml:mo><mml:mo>-</mml:mo><mml:mn mathvariant="normal">1</mml:mn><mml:msup><mml:mo>)</mml:mo><mml:mrow><mml:mi>i</mml:mi><mml:mo>+</mml:mo><mml:mi>j</mml:mi></mml:mrow></mml:msup><mml:mo>⋅</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mi>j</mml:mi></mml:msub></mml:mrow></mml:mfenced><mml:mo>.</mml:mo></mml:mrow></mml:math></disp-formula></p>
      <?pagebreak page69?><p id="d1e3127"><?xmltex \hack{\newpage}?>By substituting Eqs. (<xref ref-type="disp-formula" rid="Ch1.E9"/>) and (<xref ref-type="disp-formula" rid="Ch1.E11"/>) into Eq. (<xref ref-type="disp-formula" rid="Ch1.E10"/>), the governing equation can be simplified further and written as follows.
            <disp-formula id="Ch1.E12" content-type="numbered"><label>12</label><mml:math id="M72" display="block"><mml:mrow><?xmltex \hack{\hbox\bgroup\fontsize{8.9}{8.9}\selectfont$\displaystyle}?><mml:mfenced open="{" close=""><mml:mtable rowspacing="0.2ex" class="cases" columnspacing="1em" columnalign="left" framespacing="0em"><mml:mtr><mml:mtd><mml:mrow><mml:mfenced open="(" close=")"><mml:mrow><mml:mn mathvariant="normal">4</mml:mn><mml:msup><mml:mi>l</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msup><mml:mo>+</mml:mo><mml:mi>e</mml:mi></mml:mrow></mml:mfenced><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mi>a</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mi>b</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mi>c</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:mi>a</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mi>b</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mo>-</mml:mo><mml:mi>c</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow/></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mi>a</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mfenced open="(" close=")"><mml:mrow><mml:mn mathvariant="normal">3</mml:mn><mml:mi>m</mml:mi><mml:msup><mml:mi>l</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msup><mml:mo>+</mml:mo><mml:mi>e</mml:mi></mml:mrow></mml:mfenced><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mi>b</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mi>c</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:mi>a</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>-</mml:mo><mml:mi>b</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mo>+</mml:mo><mml:mi>c</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">4</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow/></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mi>b</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:mi>b</mml:mi><mml:mi>c</mml:mi><mml:mi>cos⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">¨</mml:mo></mml:mover><mml:mn 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mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>+</mml:mo><mml:mi>c</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msub><mml:mo>-</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">2</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup></mml:mrow></mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mrow><mml:mo>-</mml:mo><mml:mi>c</mml:mi><mml:mi>sin⁡</mml:mi><mml:mo>(</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">3</mml:mn></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>q</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub><mml:mo>)</mml:mo><mml:msubsup><mml:mover accent="true"><mml:mi>q</mml:mi><mml:mo mathvariant="normal">˙</mml:mo></mml:mover><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:msubsup><mml:mo>=</mml:mo><mml:msub><mml:mi>T</mml:mi><mml:mn mathvariant="normal">4</mml:mn></mml:msub></mml:mrow></mml:mtd></mml:mtr></mml:mtable></mml:mfenced><?xmltex \hack{$\egroup}?></mml:mrow></mml:math></disp-formula>
          <inline-formula><mml:math id="M73" display="inline"><mml:mrow><mml:mi>a</mml:mi><mml:mo>=</mml:mo><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mn mathvariant="normal">7</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle><mml:mi>m</mml:mi><mml:msup><mml:mi>l</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M74" display="inline"><mml:mrow><mml:mi>b</mml:mi><mml:mo>=</mml:mo><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mn mathvariant="normal">5</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle><mml:mi>m</mml:mi><mml:msup><mml:mi>l</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula>, <inline-formula><mml:math id="M75" display="inline"><mml:mrow><mml:mi>c</mml:mi><mml:mo>=</mml:mo><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mn mathvariant="normal">3</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle><mml:mi>m</mml:mi><mml:msup><mml:mi>l</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula>, and <inline-formula><mml:math id="M76" display="inline"><mml:mrow><mml:mi>d</mml:mi><mml:mo>=</mml:mo><mml:mstyle displaystyle="false"><mml:mfrac style="text"><mml:mn mathvariant="normal">1</mml:mn><mml:mn mathvariant="normal">2</mml:mn></mml:mfrac></mml:mstyle><mml:mi>m</mml:mi><mml:msup><mml:mi>l</mml:mi><mml:mn mathvariant="normal">2</mml:mn></mml:msup></mml:mrow></mml:math></inline-formula>.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F10" specific-use="star"><?xmltex \currentcnt{10}?><?xmltex \def\figurename{Figure}?><label>Figure 10</label><caption><p id="d1e4207">Frequency response diagram (2 <inline-formula><mml:math id="M77" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting rod). <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f10.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F11" specific-use="star"><?xmltex \currentcnt{11}?><?xmltex \def\figurename{Figure}?><label>Figure 11</label><caption><p id="d1e4232">Frequency response diagram (3.5 <inline-formula><mml:math id="M78" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting rod). <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f11.png"/>

        </fig>

</sec>
</sec>
<sec id="Ch1.S3">
  <label>3</label><title>Dynamic behavior analysis</title>
<sec id="Ch1.S3.SS1">
  <label>3.1</label><title>Impact dynamic analysis</title>
      <p id="d1e4271">Considering that the deployment mechanism is driven by a self-actuated torsion joint, the initial driven torsion is 0.9 <inline-formula><mml:math id="M79" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Nm</mml:mi></mml:mrow></mml:math></inline-formula> and the final driven torsion is 0.3 <inline-formula><mml:math id="M80" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Nm</mml:mi></mml:mrow></mml:math></inline-formula>, respectively. When the deployment mechanism starts to deploy, the velocity of the load base increases gradually. The mechanism will lock in an instant while fully deployed, and the kinetic energy absorbed by the mechanism will have an impact on the satellite body, which may damage the satellite body. So, it is necessary to analyze the influence and find the solution if an unacceptable<?pagebreak page70?> result is generated. Figure 4 shows the process from a folded state to a fully deployed state.</p>
      <p id="d1e4290">Figure 5 shows the time vs. impact force diagram, and it can be seen that, after 0.65 <inline-formula><mml:math id="M81" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">s</mml:mi></mml:mrow></mml:math></inline-formula> stable deployment with zero impact force, the load base reached the limiting position, and a sharp peak reaction force was generated and almost reached 9800 <inline-formula><mml:math id="M82" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math></inline-formula>. After that, the load base started negative displacement, and the reaction force returned to zero and generated a small peak force again about 0.15 <inline-formula><mml:math id="M83" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">s</mml:mi></mml:mrow></mml:math></inline-formula> later. The system reached a stable state.</p>
      <p id="d1e4317">The critical point of this impact analysis is to check whether the mechanism can bear the first-order impact reaction force. The damper would be added when the first-order impact force could generate damages.</p>
</sec>
<sec id="Ch1.S3.SS2">
  <label>3.2</label><title>Harmonic response analysis</title>
      <p id="d1e4328">The satellite works in space, and unpredictable excitation happens normally. However, the excitation frequency is random, and thus harmonic response analysis in a wide frequency range is a necessary option. In this section, the responses of the load base and connecting rod at wide-range harmonic excitation are shown.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F12" specific-use="star"><?xmltex \currentcnt{12}?><?xmltex \def\figurename{Figure}?><label>Figure 12</label><caption><p id="d1e4333">Frequency response of the first layer of the connecting rod. <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f12.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F13" specific-use="star"><?xmltex \currentcnt{13}?><?xmltex \def\figurename{Figure}?><label>Figure 13</label><caption><p id="d1e4350">Frequency response of the second layer of the connecting rod. <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f13.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F14" specific-use="star"><?xmltex \currentcnt{14}?><?xmltex \def\figurename{Figure}?><label>Figure 14</label><caption><p id="d1e4368">Frequency response of the third layer of the connecting rod. <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f14.png"/>

        </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F15" specific-use="star"><?xmltex \currentcnt{15}?><?xmltex \def\figurename{Figure}?><label>Figure 15</label><caption><p id="d1e4385">Frequency response of the fourth layer of the connecting rod. <bold>(a)</bold> Frequency vs. magnitude diagram. <bold>(b)</bold> Frequency vs. phase diagram.</p></caption>
          <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f15.png"/>

        </fig>

<sec id="Ch1.S3.SS2.SSS1">
  <label>3.2.1</label><title>Harmonic response of the load base under the folded condition</title>
      <?pagebreak page71?><p id="d1e4407">To get the optimal design parameter of the connecting rod, the thickness of the rod is chosen as a variable. Figure 6 shows the frequency response diagram at the center of the load base, with 1 <inline-formula><mml:math id="M84" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting the rod under the folded condition.</p>
      <p id="d1e4418">Figure 6a shows the frequency vs. magnitude diagram, and Fig. 6b shows the frequency vs. phase diagram. It can be seen that, in Fig. 6a, the system suffers two significant increases in vibration amplitude at frequencies of 16 and 34 <inline-formula><mml:math id="M85" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula>, respectively, and the phase angle also increased a lot at these two points, as seen in Fig. 6b. At the same time, only a positive phase angle was generated.</p>
      <p id="d1e4429">Figure 7 shows the frequency response diagram of the center of the load base, with a 2 <inline-formula><mml:math id="M86" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting the rod under the folded condition. It can be seen that the first-order resonant frequency is about 35 <inline-formula><mml:math id="M87" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula> and that the second-order resonant frequency is about 65 <inline-formula><mml:math id="M88" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula>. By comparing Figs. 7a and 6a, the resonant frequency is almost doubled when the wall thickness increased to 2 <inline-formula><mml:math id="M89" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula>. The magnitude is decreased from 60 to 40 <inline-formula><mml:math id="M90" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula>, and both positive and negative phase angles are generated under this condition.</p>
      <p id="d1e4472">Similarly, Fig. 8 shows the frequency response diagram of the center of the load base, with a 3.5 <inline-formula><mml:math id="M91" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness connecting the rod under the folded condition. It can be found that the main resonant frequency is about 55 <inline-formula><mml:math id="M92" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula> but, differently from Figs. 7 and 8, several subharmonic responses were generated and the phase angle became negative in all the frequency ranges.</p>
</sec>
<sec id="Ch1.S3.SS2.SSS2">
  <label>3.2.2</label><title>Harmonic response of the load base under the fully deployed condition</title>
      <p id="d1e4499">The analysis in Sect. 3.2.1 only exists in the workshop or during the trip to orbit, which is not the normal state of the<?pagebreak page72?> deployment mechanism. However, the fully deployed condition has the dominant status.</p>
      <p id="d1e4502">Figures 9–11 show the harmonic response of the load base at the center of mass with different wall thicknesses of the connecting rod under the fully deployed working condition.</p>
      <p id="d1e4505">As seen in Figs. 9–11, it can be found that, in the frequency range of 0 to 1000 <inline-formula><mml:math id="M93" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula>, only the first-order main resonant frequency response was generated, and the magnitude of vibration increased with frequency until the resonant point.</p>
      <p id="d1e4516">Additionally, the resonant point gradually became larger with the increase in the connecting rod's wall thickness, and the magnitude of vibration decreased. In addition, it can be seen that the phase angle transition point also increased simultaneously.</p>
</sec>
<sec id="Ch1.S3.SS2.SSS3">
  <label>3.2.3</label><title>Harmonic response of the connecting rod under the fully deployed condition</title>
      <p id="d1e4527">The deployment mechanism has four layers of connecting rods according to Fig. 1. Obviously, those connecting rods play a critical role in the system performance. It is quite necessary to find the vibration response to avoid the critical external excitation.</p>
      <p id="d1e4530">Figures 12–15 show the diagrams of frequency vs. magnitude and frequency vs. phase angle for different layers of connecting rods. By comparing the diagrams of frequency vs. magnitude, it can be seen that the trend of the curve behaved similarly but gradually decreased in magnitude. Additionally, as seen in Figs. 12b–15b, the phase angle also behaves similarly except for several transition points.</p>

      <?xmltex \floatpos{t}?><fig id="Ch1.F16" specific-use="star"><?xmltex \currentcnt{16}?><?xmltex \def\figurename{Figure}?><label>Figure 16</label><caption><p id="d1e4535">Meshed model of the deployable mechanism.</p></caption>
            <?xmltex \igopts{width=369.885827pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f16.png"/>

          </fig>

      <?xmltex \floatpos{t}?><fig id="Ch1.F17" specific-use="star"><?xmltex \currentcnt{17}?><?xmltex \def\figurename{Figure}?><label>Figure 17</label><caption><p id="d1e4547">Modal distribution diagram.</p></caption>
            <?xmltex \igopts{width=483.69685pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f17.png"/>

          </fig>

      <?xmltex \floatpos{p}?><fig id="Ch1.F18" specific-use="star"><?xmltex \currentcnt{18}?><?xmltex \def\figurename{Figure}?><label>Figure 18</label><caption><p id="d1e4558">First sixth-order vibration shape under different natural frequencies. <bold>(a)</bold> First-order vibration shape. <bold>(b)</bold> Second-order vibration shape. <bold>(c)</bold> Third-order vibration shape. <bold>(d)</bold> Fourth-order vibration shape. <bold>(e)</bold> First-order vibration shape. <bold>(f)</bold> Sixth-order vibration shape.</p></caption>
            <?xmltex \igopts{width=426.791339pt}?><graphic xlink:href="https://ms.copernicus.org/articles/15/63/2024/ms-15-63-2024-f18.png"/>

          </fig>

</sec>
</sec>
<?pagebreak page73?><sec id="Ch1.S3.SS3">
  <label>3.3</label><title>Modal analysis</title>
      <p id="d1e4595">One important way to conduct structure optimum design is to obtain a system's natural characteristics, including natural frequency and vibration shape. Before starting modal analysis, all components need to be set as flexible parts, and the wall thickness is chosen as a variable. Figure 16 shows the meshed model under a fully deployed condition, and the folded meshing model can be obtained in the same way.</p>
<sec id="Ch1.S3.SS3.SSS1">
  <label>3.3.1</label><title>Frequency response analysis under the folded condition</title>
      <p id="d1e4605">Table 1 shows the frequency and damping ratio of the structure with different wall thicknesses under the folded condition. It should show that, according to the design specification, the first-order natural frequency should be no less than 115 <inline-formula><mml:math id="M94" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula>, and the only available design with the available wall thickness is 2.5 <inline-formula><mml:math id="M95" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula>.</p>

<?xmltex \floatpos{t}?><table-wrap id="Ch1.T1" specific-use="star"><?xmltex \currentcnt{1}?><label>Table 1</label><caption><p id="d1e4627">Frequency and damping ratio with different wall thicknesses under the folded condition.</p></caption><oasis:table frame="topbot"><oasis:tgroup cols="7">
     <oasis:colspec colnum="1" colname="col1" align="left"/>
     <oasis:colspec colnum="2" colname="col2" align="right"/>
     <oasis:colspec colnum="3" colname="col3" align="right"/>
     <oasis:colspec colnum="4" colname="col4" align="right" colsep="1"/>
     <oasis:colspec colnum="5" colname="col5" align="right"/>
     <oasis:colspec colnum="6" colname="col6" align="right"/>
     <oasis:colspec colnum="7" colname="col7" align="right"/>
     <oasis:thead>
       <oasis:row>
         <oasis:entry colname="col1">Order</oasis:entry>
         <oasis:entry rowsep="1" namest="col2" nameend="col4" align="center" colsep="1">Natural frequency </oasis:entry>
         <oasis:entry rowsep="1" namest="col5" nameend="col7" align="center">Damping ratio </oasis:entry>
       </oasis:row>
       <oasis:row rowsep="1">
         <oasis:entry colname="col1"/>
         <oasis:entry colname="col2">1 <inline-formula><mml:math id="M96" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col3">2.5 <inline-formula><mml:math id="M97" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col4">3.5 <inline-formula><mml:math id="M98" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col5">1 <inline-formula><mml:math id="M99" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col6">2.5 <inline-formula><mml:math id="M100" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col7">3.5 <inline-formula><mml:math id="M101" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
       </oasis:row>
     </oasis:thead>
     <oasis:tbody>
       <oasis:row>
         <oasis:entry colname="col1">1</oasis:entry>
         <oasis:entry colname="col2">52.5226</oasis:entry>
         <oasis:entry colname="col3">118.534</oasis:entry>
         <oasis:entry colname="col4">35.564</oasis:entry>
         <oasis:entry colname="col5">0.00110694</oasis:entry>
         <oasis:entry colname="col6">0.00219123</oasis:entry>
         <oasis:entry colname="col7">0.00127327</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">2</oasis:entry>
         <oasis:entry colname="col2">79.661</oasis:entry>
         <oasis:entry colname="col3">269.246</oasis:entry>
         <oasis:entry colname="col4">45.4194</oasis:entry>
         <oasis:entry colname="col5">0.000372739</oasis:entry>
         <oasis:entry colname="col6">0.0240956</oasis:entry>
         <oasis:entry colname="col7">0.00179502</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">3</oasis:entry>
         <oasis:entry colname="col2">242.625</oasis:entry>
         <oasis:entry colname="col3">281.261</oasis:entry>
         <oasis:entry colname="col4">174.911</oasis:entry>
         <oasis:entry colname="col5">0.790152</oasis:entry>
         <oasis:entry colname="col6">0.0282781</oasis:entry>
         <oasis:entry colname="col7">0.783862</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">4</oasis:entry>
         <oasis:entry colname="col2">229.48</oasis:entry>
         <oasis:entry colname="col3">344.033</oasis:entry>
         <oasis:entry colname="col4">177.947</oasis:entry>
         <oasis:entry colname="col5">0.760871</oasis:entry>
         <oasis:entry colname="col6">0.0259809</oasis:entry>
         <oasis:entry colname="col7">0.742891</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">5</oasis:entry>
         <oasis:entry colname="col2">154.934</oasis:entry>
         <oasis:entry colname="col3">443.292</oasis:entry>
         <oasis:entry colname="col4">240.815</oasis:entry>
         <oasis:entry colname="col5">0.0193153</oasis:entry>
         <oasis:entry colname="col6">0.0470947</oasis:entry>
         <oasis:entry colname="col7">0.0214783</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">6</oasis:entry>
         <oasis:entry colname="col2">251.218</oasis:entry>
         <oasis:entry colname="col3">462.649</oasis:entry>
         <oasis:entry colname="col4">287.545</oasis:entry>
         <oasis:entry colname="col5">0.188274</oasis:entry>
         <oasis:entry colname="col6">0.0461821</oasis:entry>
         <oasis:entry colname="col7">0.0305008</oasis:entry>
       </oasis:row>
     </oasis:tbody>
   </oasis:tgroup></oasis:table><?xmltex \gdef\@currentlabel{1}?></table-wrap>

</sec>
<sec id="Ch1.S3.SS3.SSS2">
  <label>3.3.2</label><title>Frequency response analysis under the fully deployed condition</title>
      <p id="d1e4893">Table 2 shows the frequency and damping ratio of the structure with different wall thicknesses under the fully deployed condition. Similarly, under the fully deployed condition, the first-order natural frequency should be no less than 20 <inline-formula><mml:math id="M102" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">Hz</mml:mi></mml:mrow></mml:math></inline-formula>. It can be found that, according to Table 2, the available design with proper wall thicknesses is 2.5 and 3 <inline-formula><mml:math id="M103" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula>, respectively.</p>

<?xmltex \floatpos{t}?><table-wrap id="Ch1.T2" specific-use="star"><?xmltex \currentcnt{2}?><label>Table 2</label><caption><p id="d1e4915">Frequency and damping ratio with different wall thicknesses under the unfolded condition.</p></caption><oasis:table frame="topbot"><oasis:tgroup cols="7">
     <oasis:colspec colnum="1" colname="col1" align="left"/>
     <oasis:colspec colnum="2" colname="col2" align="right"/>
     <oasis:colspec colnum="3" colname="col3" align="right"/>
     <oasis:colspec colnum="4" colname="col4" align="right" colsep="1"/>
     <oasis:colspec colnum="5" colname="col5" align="right"/>
     <oasis:colspec colnum="6" colname="col6" align="right"/>
     <oasis:colspec colnum="7" colname="col7" align="right"/>
     <oasis:thead>
       <oasis:row>
         <oasis:entry colname="col1">Order</oasis:entry>
         <oasis:entry rowsep="1" namest="col2" nameend="col4" align="center" colsep="1">Natural frequency </oasis:entry>
         <oasis:entry rowsep="1" namest="col5" nameend="col7" align="center">Damping ratio </oasis:entry>
       </oasis:row>
       <oasis:row rowsep="1">
         <oasis:entry colname="col1"/>
         <oasis:entry colname="col2">1 <inline-formula><mml:math id="M104" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col3">2.5 <inline-formula><mml:math id="M105" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col4">3.5 <inline-formula><mml:math id="M106" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col5">1 <inline-formula><mml:math id="M107" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col6">2.5 <inline-formula><mml:math id="M108" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
         <oasis:entry colname="col7">3.5 <inline-formula><mml:math id="M109" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula></oasis:entry>
       </oasis:row>
     </oasis:thead>
     <oasis:tbody>
       <oasis:row>
         <oasis:entry colname="col1">1</oasis:entry>
         <oasis:entry colname="col2">18.0605</oasis:entry>
         <oasis:entry colname="col3">20.0555</oasis:entry>
         <oasis:entry colname="col4">29.1763</oasis:entry>
         <oasis:entry colname="col5">0.00144546</oasis:entry>
         <oasis:entry colname="col6">0.00229639</oasis:entry>
         <oasis:entry colname="col7">0.00509782</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">2</oasis:entry>
         <oasis:entry colname="col2">18.7344</oasis:entry>
         <oasis:entry colname="col3">20.142</oasis:entry>
         <oasis:entry colname="col4">29.3584</oasis:entry>
         <oasis:entry colname="col5">0.00159535</oasis:entry>
         <oasis:entry colname="col6">0.00231231</oasis:entry>
         <oasis:entry colname="col7">0.00520071</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">3</oasis:entry>
         <oasis:entry colname="col2">29.265</oasis:entry>
         <oasis:entry colname="col3">30.2742</oasis:entry>
         <oasis:entry colname="col4">42.3297</oasis:entry>
         <oasis:entry colname="col5">0.00197595</oasis:entry>
         <oasis:entry colname="col6">0.00290489</oasis:entry>
         <oasis:entry colname="col7">0.00613632</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">4</oasis:entry>
         <oasis:entry colname="col2">109.525</oasis:entry>
         <oasis:entry colname="col3">114.669</oasis:entry>
         <oasis:entry colname="col4">133.154</oasis:entry>
         <oasis:entry colname="col5">0.0090971</oasis:entry>
         <oasis:entry colname="col6">0.0132825</oasis:entry>
         <oasis:entry colname="col7">0.024076</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">5</oasis:entry>
         <oasis:entry colname="col2">113.329</oasis:entry>
         <oasis:entry colname="col3">115.946</oasis:entry>
         <oasis:entry colname="col4">134.137</oasis:entry>
         <oasis:entry colname="col5">0.00998474</oasis:entry>
         <oasis:entry colname="col6">0.0135798</oasis:entry>
         <oasis:entry colname="col7">0.0246054</oasis:entry>
       </oasis:row>
       <oasis:row>
         <oasis:entry colname="col1">6</oasis:entry>
         <oasis:entry colname="col2">152.4</oasis:entry>
         <oasis:entry colname="col3">151.484</oasis:entry>
         <oasis:entry colname="col4">167.276</oasis:entry>
         <oasis:entry colname="col5">0.0104177</oasis:entry>
         <oasis:entry colname="col6">0.0146563</oasis:entry>
         <oasis:entry colname="col7">0.0249745</oasis:entry>
       </oasis:row>
     </oasis:tbody>
   </oasis:tgroup></oasis:table><?xmltex \gdef\@currentlabel{2}?></table-wrap>

</sec>
<sec id="Ch1.S3.SS3.SSS3">
  <label>3.3.3</label><title>Vibration shape response analysis under the fully deployed condition</title>
      <p id="d1e5181">According to Sect. 3.2.1 and 3.2.2, it could be that the first-order natural frequency under the folded condition is much higher than the fully deployed condition, which also means that the mechanism could generate high vibration at low frequency. So, the fully deployed condition becomes the key research object in this section.</p>
      <p id="d1e5184">Figure 17 shows the modal distribution diagram, and Fig. 18 shows the vibration shape under the first sixth-order natural frequency excitation. It can be seen that, in Fig. 18a and b, the deployment mechanism swings as one part in two horizontal directions. When the system is at high-level natural frequency excitation, system vibration changed into twist or higher-level swing.</p>
</sec>
</sec>
</sec>
<sec id="Ch1.S4" sec-type="conclusions">
  <label>4</label><title>Conclusion</title>
      <p id="d1e5197">In this paper, a box-structured satellite-unfolding mechanism with a brand-new self-actuated torsion joint is proposed, and a physical model and a dynamic equation are established. The system dynamic behavior is studied systematically, including impact dynamic analysis, harmonic response analysis, and modal analysis. The analysis enables us to draw the following conclusions. <list list-type="order"><list-item>
      <p id="d1e5202">The system could generate a sharp peak reaction force value when the load base reaches the limiting position during the process of unfolding. After the main impact, several sub-peak forces followed and went into a stable state finally, which shows that the first-order main impacting force is the key parameter for checking whether the additional joint damper is needed.</p></list-item><list-item>
      <p id="d1e5206">The harmonic responses of the load base and connecting rod in the folded and fully deployed states are seen, and the wall thickness is set as a structure optimization variable. The result shows that the system generates a high vibration magnitude at low-frequency excitation when the mechanism is in the fully deployed state and at high-frequency excitation when the mechanism is in the folded state.</p></list-item><list-item>
      <p id="d1e5210">The first sixth-order natural frequency and vibration shape with different wall thicknesses are obtained by modal analysis. The result shows that only with a 2.5 <inline-formula><mml:math id="M110" display="inline"><mml:mrow class="unit"><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math></inline-formula> wall thickness can the connecting rod satisfy the design requirement.</p></list-item><list-item>
      <p id="d1e5222">The static and dynamic test research is scheduled to be conducted in a space-like center to verify the validity of the theoretical research, and the fatigue life, as the most important parameter, will be tested and researched based on the previous static and dynamic study. Additionally, the dynamic behavior research with more rod thicknesses will be studied in future work.</p></list-item></list></p>
</sec>

      
      </body>
    <back><notes notes-type="dataavailability"><title>Data availability</title>

      <p id="d1e5230">The data used to support the findings of this study are included within the article and are accessible on request to the corresponding author.</p>
  </notes><notes notes-type="authorcontribution"><title>Author contributions</title>

      <p id="d1e5236">DS performed the methodology and formal analysis, wrote the original draft, and acquired the funding. RM performed the formal analysis and data curation. CS carried out the writing, review and editing.</p>
  </notes><notes notes-type="competinginterests"><title>Competing interests</title>

      <p id="d1e5242">The contact author has declared that none of the authors has any competing interests.</p>
  </notes><notes notes-type="disclaimer"><title>Disclaimer</title>

      <p id="d1e5248">Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors.</p>
  </notes><ack><title>Acknowledgements</title><p id="d1e5254">This work is supported by the National Key Laboratory of Science and Technology on Helicopter Transmission (Nanjing University of Aeronautics and Astronautics) (grant<?pagebreak page76?> no. HTL-O-20K01) and the Changzhou Science and Technology Planning Project (grant no. CE20225067).</p></ack><notes notes-type="financialsupport"><title>Financial support</title>

      <p id="d1e5259">This research has been supported by the National Key Laboratory of Science and Technology on Helicopter Transmission (Nanjing University of Aeronautics and Astronautics) (grant no. HTL-O-20K01) and the Changzhou Science and Technology Planning Project (grant no. CE20225067).</p>
  </notes><notes notes-type="reviewstatement"><title>Review statement</title>

      <p id="d1e5265">This paper was edited by Daniel Condurache and reviewed by two anonymous referees.</p>
  </notes><ref-list>
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