氣動柔性驅動器FPA的特性

1、氣動柔性驅動器 FPA的特性及其在多指靈巧手設計中的應用研究摘要末端執(zhí)行器作為機器人與外界環(huán)境互相作用的最后執(zhí)行部件一直受到研究 人員的關注。除了傳統(tǒng)的剛性驅動和執(zhí)行機構以外，氣動人工肌肉PMA乍為一種 新型的驅動器，以其結構簡單、功率 / 重量比大等優(yōu)點得到眾多學者的關注，相 繼研制出氣動肌肉關節(jié)、仿人手臂等。但是PMA還需要其他輔助機構才能構成關 節(jié)和手臂，使用中增加了體積、重量，也給結構設計和控制帶來不便。本課題組 研究的新型氣動柔性驅動器 FPA既是驅動器也是執(zhí)行器，可以直接構成各種關 節(jié)。本文在以往研究的基礎上，進一步深入研究了 FPA及各種關節(jié)的特性，研制 了氣動柔性三指手爪、提出

2、了氣動柔性多指靈巧手的設計思路，為FPA及柔性關 節(jié)的研究和應用奠定基礎。本文首先綜述了 McKibben型PMA三自由的FMA旋轉型氣動柔性驅動器、 柔性流體驅動器以及新型氣動柔性驅動器 FPA的國內外研究現(xiàn)狀，深入分析了上 述幾種典型氣動柔性驅動器的特點；進一步綜述并分析了多指靈巧手的研究現(xiàn) 狀，重點分析了基于典型氣動柔性驅動器的柔性多指靈巧手的研究進展。 根據文 獻綜述及分析，指出進行FPA及其在多指靈巧手中應用研究的理論和實際意義。本文簡要介紹了氣動柔性驅動器 FPA的結構原理，詳細描述了 FPA及其橡膠 管及零件的選材、設計和加工制作過程。對FPA的靜態(tài)模型和基本特性進行了深 入的研

3、究。詳細分析了 FPA平均半徑和橡膠管壁厚的變化情況及其對 FPA特性的 影響，分析了 FPA的彈性模量問題，基于上述三個因素的分析建立了 FPA的靜態(tài) 模型。根據建立的FPA靜態(tài)模型，詳細分析了 FPA的恒輸出力特性、恒壓特性和 恒長特性，得出：FPA內腔壓力較高、輸出力較大時，F(xiàn)PA的剛性較大，其特性 更趨于滿足虎克定律的彈性固體、 當橡膠管伸長量較小或輸出力較大時， 恒壓特 性曲線的線性度較好、橡膠管的伸長量越小，則 FPA輸出力越大等結論。分析 了 FPA在外力作用下的壓桿穩(wěn)定性問題，得出 FPA壓桿穩(wěn)定的臨界力偏小，不 宜把FPA直接作為軸向輸出力驅動器的結論?；跉鈩酉到y(tǒng)動力學建立

4、FPA充放氣過程的動態(tài)模型，并分析了各種參數對動態(tài)過程的影響， 分析了 FPA充放氣 動態(tài)過程存在差異性的原因，得出FPA動態(tài)過程迅速并且受管接頭出口面積、FPA 內腔容積等因素影響較大的結論。 建立了 FPA基本特性實驗平臺，對FPA的模型 和基本特性進行了實驗研究， 驗證了建立的數學模型， 并分析了理論模型與實驗 結果之間誤差的主要原因。在氣動柔性驅動器 FPA 的橡膠管壁內嵌入約束鋼絲，得到氣動柔性彎曲關 節(jié)，該關節(jié)可以實現(xiàn)平面內的彎曲運動。 參考FPA的平均半徑分析和壁厚分析方 法，總結得出彎曲關節(jié)平均半徑和壁厚變化對其性能的影響， 進而分析建立彎曲 關節(jié)的數學模型， 靜態(tài)模型是基于對

5、彎曲關節(jié)端截面的力平衡和力矩平衡分析得 到；分析了關節(jié)壁厚、長度、半徑等結構參數對彎曲角度的影響，得出彎曲關節(jié) 的彎曲角度隨其內腔壓力增大而增大、 關節(jié)的彎曲角度隨著橡膠管壁厚的增大而 逐漸減小、關節(jié)的彎曲角度隨著橡膠管長度的增大而增大、 關節(jié)的彎曲角度隨著 橡膠管半徑的增大而增大等結論； 基于氣動系統(tǒng)動力學建立彎曲關節(jié)的動態(tài)模型 并進行仿真分析， 仿真結果表明彎曲關節(jié)動態(tài)過程的時間相對很短， 可以忽略不 計。對彎曲關節(jié)的靜態(tài)模型和特性進行實驗研究， 結果表明：彎曲關節(jié)的充放氣 過程存在一個明顯的滯環(huán)， 分析說明了滯環(huán)產生的原因， 并進一步分析理論模型 與實驗數據之間存在誤差的原因。氣動柔性扭

6、轉關節(jié)是FPA的另一個應用，扭轉關節(jié)主要由兩個弧形的FPA構成，可以在平面內形成旋轉運動。 在彎曲關節(jié)模型推導的基礎上， 建立扭轉關 節(jié)的靜態(tài)模型，并分析了扭轉關節(jié)內腔壓力、初始轉角、橡膠管平均半徑、橡膠 管壁厚等參數對關節(jié)轉角的影響，得出扭轉關節(jié)的轉動角度與充入 FPA 內腔的 壓縮氣體壓力之間基本呈線性關系、 扭轉關節(jié)的轉角隨初始角度和橡膠管平均半 徑的增大而增大、 扭轉關節(jié)的轉角隨橡膠管壁厚的增大而減小的結論； 建立了扭 轉關節(jié)的動力學方程，仿真實驗表明FPA的充放氣過程與扭轉關節(jié)的動力學過程 相比時間極短， 在實際系統(tǒng)設計和控制過程中可以忽略不計； 分析討論橡膠管壁 厚、平均半徑、初始

7、角度、氣體節(jié)流口面積、轉動慣量、粘性阻尼系數等因素對 扭轉關節(jié)動態(tài)特性的影響，得出橡膠管初始壁厚的變化對扭轉關節(jié) FPA 內腔壓 力的動態(tài)響應幾乎沒有影響而對關節(jié)轉角的響應曲線影響比較明顯，壁厚較小 時，關節(jié)可以得到較大的轉角，并且轉角的響應曲線沒有超調，但上升時間長， 壁厚較大時，關節(jié)轉角變小，響應加快，但是有超調和輕微振蕩現(xiàn)象、橡膠管平 均半徑越大，得到的關節(jié)轉角越大，但是轉角響應的超調量也隨之增大、FPA的 初始角度越大，關節(jié)的轉角越大，并且超調量減小，振蕩減弱，但是上升時間增 大、管接頭出口面積的大小對關節(jié) FPA 內腔壓力的建立過程影響較大，但對關 節(jié)轉角的動態(tài)響應幾乎沒有影響、轉動

8、慣量和粘性阻尼系數對 FPA 內腔壓力的 動態(tài)過程幾乎沒有影響而對扭轉關節(jié)轉角有較大影響等結論。 對扭轉關節(jié)進行了 實驗研究， 驗證了建立的靜態(tài)模型， 并根據實驗結果和最小二乘法原理引入修正 項，對扭轉關節(jié)的靜態(tài)模型進行修正處理；對扭轉關節(jié)進行了開環(huán)控制和PID控制實驗研究，實驗結果表明用修正后的靜態(tài)模型進行開環(huán)控制能夠較好地達到 期望值，PID控制能夠有效地消除系統(tǒng)的靜態(tài)誤差，克服了靜態(tài)模型的不準確性， 使得扭轉關節(jié)穩(wěn)定地到達期望值，提高控制精度，但是PID控制存在明顯的滯后 性，詳細分析了其產生的原因。在以上研究的基礎上， 研制了氣動柔性三指手爪， 該手爪以氣動柔性彎曲關 節(jié)作為爪指， 以

9、扭轉關節(jié)構成腕部， 可以實現(xiàn)抓握和轉腕動作。 分析建立了三指 手爪的數學模型： 爪指的數學模型即是彎曲關節(jié)的模型、 腕部的數學模型即是扭 轉關節(jié)的模型， 建立氣動柔性三指手爪的坐標系統(tǒng)， 詳細分析建立了爪指指端的 運動學方程， 得出其位姿表達式。 根據三指手爪的結構， 把手爪的抓持模式分為 兩種：夾持和抓握，結合前面研究的彎曲關節(jié)模型詳細分析了手爪的抓持模式， 建立抓取簡單形狀目標時的數學模型， 并進行了仿真和實驗驗證， 結果表明：在 夾持模式下， 目標物體的重力與所需要的爪指內腔壓力基本上成線性關系， 爪指 內腔壓力隨著目標物體半徑的增大先減小而后突然增大； 在抓握模式下， 目標物 體重量與

10、所需要的爪指內腔壓力成線性關系， 但目標重力對爪指內腔壓力的影響 沒有夾持模型下的影響大， 內腔壓力隨著目標物體半徑的增大先減小而后逐漸增 大。最后，本文在氣動柔性彎曲關節(jié)和氣動柔性球關節(jié)研究的基礎上， 提出了五 自由度手指的設計， 由一個球關節(jié)和兩個彎曲關節(jié)串聯(lián)得到一個五自由度的柔性 手指。在氣動柔性扭轉關節(jié)、 三自由度手指和五自由度手指的基礎上， 提出了模 擬人手結構和功能的氣動柔性多指靈巧手，總結了氣動柔性多指靈巧手的特點， 并分析了多指靈巧手設計的可行性及研究思路。關鍵詞：氣動柔性驅動器FPA氣動柔性彎曲關節(jié)，氣動柔性扭轉關節(jié)，氣動柔 性手爪，多指靈巧手，PID控制RESEARCH O

11、N CHARACTERISTICS OF FLEXIBLEPNEUMATIC ACTUATOR FPA AND ITS APPLICATION INMULTI-FINGERED DEXTEROUS HAND DESIGNABSTRACTAs final executing manipulator for robot to interact with outside environment, the terminal actuators have been paid much attention. Besides the traditional rigid driving and executi

12、ng devices, many researchershave great interests in pneumatic artificial muscle PMA, which has quite a few characteristics, such as simple structure, high power/weight ratio etc. Pneumatic muscle joint and anthropomorphic arm had been developed based on PMA. However, assistant devices are neededto c

13、onstruct joint or arm with PMA, which increases the volume and weight. This makes the structure bigger and the control more difficult. The new type flexible pneumatic actuator FPA, developed by our researching group, is a kind of actuator as well as manipulator. Different joints can be designed usin

14、g FPA. Based on the previous research, properties of FPA and joints are studied profoundly in this paper. Flexible pneumatic 3-fingered hand and dexterous multi-fingered hand are proposed based on FPA. All the work in this paper lays the foundation of research and application of FPA and flexible joi

15、nts.Firstly, the researching status of McKibben PMA, three degrees of freedom FMA, Pneumatic Rotary Soft Actuator, Flexible Fluidic Actuator and the novel flexible pneumatic actuator FPA is reviewed. The characteristics of these typical flexible pneumatic actuators are analyzed. Furthermore, the res

16、earching status of multi-fingered hands is reviewed and analyzed. The researching situation of soft multi-fingered hand based on typical flexible pneumatic actuators is emphatically studied. Based on the reviews and analysis, the theoretical and application significances of FPA and its application i

17、n multi-fingered hand are pointed out.The structure and principle of flexible pneumatic actuator FPA are briefly introduced. The materials choosing, design and manufacturing of FPA rubber tube and other parts are described in detail. The static model and basical properties of FPA are profoundly stud

18、ied. The changing principles of average radius and shell thickness of rubber tube are analyzed in detail, the elastic modulus of FPA is discussed. Based on the above analysis, the static model of FPA is built. Based on the established static model, the isoforce property, isobaric property and isomet

19、ric property of FPA are analyzed and the following conclusions are drawn: when the air pressure inside the FPA is high and the output force is high, the stiffness of FPA is high and its properties are similar to elastic solid which meets the hookes law; when the extended length is small or the outpu

20、t force is high, the linearity of isobaric is pretty good; when the extended length is small, the output force of FPA is high. Besides, the stability of FPA striker under out force is researched and it is concluded that the critic force of FPA striker is small, so FPA cannot be directly used as axia

21、l force actuator. The dynamic models of inflating and deflating for FPA are built based on pneumatic hydrodynamics. The effects of different parameters on the dynamic process of FPA are analyzed. The reasons of the discrepancy between the inflating and deflating process of FPA are analyzed and it is

22、 concluded that the dynamic process of FPA is very fast and it is greatly affected by the section area of air connector and the volume of FPA chamber. Experiment platform is established. Experiments were carried out to verify the mathematic model and test the basic properties of FPA. The reasons for

23、 the error between the theoretical model and experimental data are analyzed.Adding constraining wire in FPA rubber tube results in the flexible pneumatic bending joint. This kind of joint can softly realize bending movement in a plane. According to the average radius and shell thickness analysis met

24、hods, the effects of average radius and shell thickness of bending joint on its properties are analyzed. The model analysis and building is the key work for research of bending joint. Based on the force balance and moment balance analysis of the end section of bending joint, the static model is dedu

25、ced, which was also verified by experimental result. The effects of shell thickness of rubber tube, length, and average radius on the bending angle are discussed. The following conclusions are reached: the bending angle of bending joint will increase as its inside air pressure increase, the bending

26、angle of bending joint will decrease as its shell thickness increase, the bending angle of bending joint will increase as its length increase, the bending angle of bending joint will increase as its average radius increase. Based on pneumatic hydrodynamics, the dynamic model of bending joint is buil

27、t and its simulation is done. The simulating results of dynamic model show that the time of pneumatic process is quite short, so it can be ignored in actual system control. Experiments are done to test the static model and properties of bending joint. The experimental results show that there is an o

28、bvious hysteresis in the curve of inflating and deflating data. The reasons for the hysteresis are given and the reasons for the error between theoretical model and experimental data are analyzed.Flexible pneumatic torsion joint is another application of FPA. A torsion joint is mainly composed of tw

29、o arcual FPAs, which can realize turning movement in a plane. The static model of torsion joint is based on that of bending joint. The effects of structure parameters inside air pressure, initial angle, rube average radius, rube shell thickness on the turning angle are analyzed and the following con

30、clusions are drawn: the relationship between the angle of torsion joint and the inside air pressure is basically linear, the angle of torsion joint increaseswith the initial angle and rube average radius, the angle of torsion joint decreaseswhile the rube shell thickness increases. The kinetic equat

31、ion is built for torsion joint. Simulating experiment implies that the time of inflating and deflating process is extremely shorter than that of kinetic process. So the pneumatic process can be ignored in actual system design and control. The factors that affect the dynamic features of torsion joint

32、, such as shell thickness of rubber tube, average radius, initial angle, connecto'sr outlet area, moment of inertia and viscous damping coefficient, are analyzed and the following conclusions are drawn: the change of rube shell thickness has no effects on the dynamic process of FPA inside air pr

33、essure while greatly affects the turning angle of torsion joint; when the rube shell thickness is small, the torsion joint has a bigger turning angle, no overshoot and long risetime, when the shell thickness is big, the turning angle of torsion joint is small, but has high response speed, overshoot

34、and low shock; when the rube average radius increases, the turning angle of torsion joint increases and the overshoot increases too; when the initial angle of torsion joint is big, the turning joint is big, the overshoot is small and shock is low, but the risetime is big; the connector's outlet

35、area affects the dynamic process of FPA inside air pressure greatly, but has no effects on the dynamic process of turning angle; moment of inertia and viscous damping coefficient have no effects on the dynamic process of FPA inside air pressure, but affect the dynamic process of turning angle greatl

36、y. Experiments are done to study the torsion joint. The established static model is verified and modified by adding correction terms according to the experimental data and least square method. Open-loop and PID control experiments are done for the torsion joint. The controlling results imply that op

37、en-loop control with the modified static model can reach the expected target value pretty good. The PID control can effectively avoid the system static error, which overcomes the inaccuracy of the static model, stabilizes the torsion joint at the expected value and promotes the controlling precision

38、. But the PID control method has obvious posterity, the reasons of which are analyzed.Based on the research described above, a kind of flexible pneumatic 3-fingered hand is proposed. In the 3-fingered hand structure, three bending joints are used as fingers and a torsion joint is used as wrist. This

39、 hand can grasp, hold objects and turn wrist. The mathematic model of 3-fingered hand is built. The mathematic model of fingers is that of bending joint and the mathematic model of wrist is that of torsion joint. The coordination system for flexible pneumatic 3-finged hand is established and the kin

40、ematics equation of finger tips is deduced. The mathematic equation for the finger-tip 's position and gesture is given. According to the structure of 3-fingered hand, the grasping model of the hand can be divided into two types: grip and hold. Combined with the mathematic model of bending joint, the grasping model is analyzed in detail and the mathematic models for grasping simple objects are built. Simulation and experiments are done for the h