气动柔性驱动器FPA的特性

1、气动柔性驱动器 FPA的特性及其在多指灵巧手设计中的应用研究摘要末端执行器作为机器人与外界环境互相作用的最后执行部件一直受到研究 人员的关注。除了传统的刚性驱动和执行机构以外，气动人工肌肉PMA乍为一种 新型的驱动器，以其结构简单、功率 / 重量比大等优点得到众多学者的关注，相 继研制出气动肌肉关节、仿人手臂等。但是PMA还需要其他辅助机构才能构成关 节和手臂，使用中增加了体积、重量，也给结构设计和控制带来不便。本课题组 研究的新型气动柔性驱动器 FPA既是驱动器也是执行器，可以直接构成各种关 节。本文在以往研究的基础上，进一步深入研究了 FPA及各种关节的特性，研制 了气动柔性三指手爪、提出

2、了气动柔性多指灵巧手的设计思路，为FPA及柔性关 节的研究和应用奠定基础。本文首先综述了 McKibben型PMA三自由的FMA旋转型气动柔性驱动器、 柔性流体驱动器以及新型气动柔性驱动器 FPA的国内外研究现状，深入分析了上 述几种典型气动柔性驱动器的特点；进一步综述并分析了多指灵巧手的研究现 状，重点分析了基于典型气动柔性驱动器的柔性多指灵巧手的研究进展。 根据文 献综述及分析，指出进行FPA及其在多指灵巧手中应用研究的理论和实际意义。本文简要介绍了气动柔性驱动器 FPA的结构原理，详细描述了 FPA及其橡胶 管及零件的选材、设计和加工制作过程。对FPA的静态模型和基本特性进行了深 入的研

3、究。详细分析了 FPA平均半径和橡胶管壁厚的变化情况及其对 FPA特性的 影响，分析了 FPA的弹性模量问题，基于上述三个因素的分析建立了 FPA的静态 模型。根据建立的FPA静态模型，详细分析了 FPA的恒输出力特性、恒压特性和 恒长特性，得出：FPA内腔压力较高、输出力较大时，FPA的刚性较大，其特性 更趋于满足虎克定律的弹性固体、 当橡胶管伸长量较小或输出力较大时， 恒压特 性曲线的线性度较好、橡胶管的伸长量越小，则 FPA输出力越大等结论。分析 了 FPA在外力作用下的压杆稳定性问题，得出 FPA压杆稳定的临界力偏小，不 宜把FPA直接作为轴向输出力驱动器的结论。基于气动系统动力学建立

4、FPA充放气过程的动态模型，并分析了各种参数对动态过程的影响， 分析了 FPA充放气 动态过程存在差异性的原因，得出FPA动态过程迅速并且受管接头出口面积、FPA 内腔容积等因素影响较大的结论。 建立了 FPA基本特性实验平台，对FPA的模型 和基本特性进行了实验研究， 验证了建立的数学模型， 并分析了理论模型与实验 结果之间误差的主要原因。在气动柔性驱动器 FPA 的橡胶管壁内嵌入约束钢丝，得到气动柔性弯曲关 节，该关节可以实现平面内的弯曲运动。 参考FPA的平均半径分析和壁厚分析方 法，总结得出弯曲关节平均半径和壁厚变化对其性能的影响， 进而分析建立弯曲 关节的数学模型， 静态模型是基于对

5、弯曲关节端截面的力平衡和力矩平衡分析得 到；分析了关节壁厚、长度、半径等结构参数对弯曲角度的影响，得出弯曲关节 的弯曲角度随其内腔压力增大而增大、 关节的弯曲角度随着橡胶管壁厚的增大而 逐渐减小、关节的弯曲角度随着橡胶管长度的增大而增大、 关节的弯曲角度随着 橡胶管半径的增大而增大等结论； 基于气动系统动力学建立弯曲关节的动态模型 并进行仿真分析， 仿真结果表明弯曲关节动态过程的时间相对很短， 可以忽略不 计。对弯曲关节的静态模型和特性进行实验研究， 结果表明：弯曲关节的充放气 过程存在一个明显的滞环， 分析说明了滞环产生的原因， 并进一步分析理论模型 与实验数据之间存在误差的原因。气动柔性扭

6、转关节是FPA的另一个应用，扭转关节主要由两个弧形的FPA构成，可以在平面内形成旋转运动。 在弯曲关节模型推导的基础上， 建立扭转关 节的静态模型，并分析了扭转关节内腔压力、初始转角、橡胶管平均半径、橡胶 管壁厚等参数对关节转角的影响，得出扭转关节的转动角度与充入 FPA 内腔的 压缩气体压力之间基本呈线性关系、 扭转关节的转角随初始角度和橡胶管平均半 径的增大而增大、 扭转关节的转角随橡胶管壁厚的增大而减小的结论； 建立了扭 转关节的动力学方程，仿真实验表明FPA的充放气过程与扭转关节的动力学过程 相比时间极短， 在实际系统设计和控制过程中可以忽略不计； 分析讨论橡胶管壁 厚、平均半径、初始

7、角度、气体节流口面积、转动惯量、粘性阻尼系数等因素对 扭转关节动态特性的影响，得出橡胶管初始壁厚的变化对扭转关节 FPA 内腔压 力的动态响应几乎没有影响而对关节转角的响应曲线影响比较明显，壁厚较小 时，关节可以得到较大的转角，并且转角的响应曲线没有超调，但上升时间长， 壁厚较大时，关节转角变小，响应加快，但是有超调和轻微振荡现象、橡胶管平 均半径越大，得到的关节转角越大，但是转角响应的超调量也随之增大、FPA的 初始角度越大，关节的转角越大，并且超调量减小，振荡减弱，但是上升时间增 大、管接头出口面积的大小对关节 FPA 内腔压力的建立过程影响较大，但对关 节转角的动态响应几乎没有影响、转动

8、惯量和粘性阻尼系数对 FPA 内腔压力的 动态过程几乎没有影响而对扭转关节转角有较大影响等结论。 对扭转关节进行了 实验研究， 验证了建立的静态模型， 并根据实验结果和最小二乘法原理引入修正 项，对扭转关节的静态模型进行修正处理；对扭转关节进行了开环控制和PID控制实验研究，实验结果表明用修正后的静态模型进行开环控制能够较好地达到 期望值，PID控制能够有效地消除系统的静态误差，克服了静态模型的不准确性， 使得扭转关节稳定地到达期望值，提高控制精度，但是PID控制存在明显的滞后 性，详细分析了其产生的原因。在以上研究的基础上， 研制了气动柔性三指手爪， 该手爪以气动柔性弯曲关 节作为爪指， 以

9、扭转关节构成腕部， 可以实现抓握和转腕动作。 分析建立了三指 手爪的数学模型： 爪指的数学模型即是弯曲关节的模型、 腕部的数学模型即是扭 转关节的模型， 建立气动柔性三指手爪的坐标系统， 详细分析建立了爪指指端的 运动学方程， 得出其位姿表达式。 根据三指手爪的结构， 把手爪的抓持模式分为 两种：夹持和抓握，结合前面研究的弯曲关节模型详细分析了手爪的抓持模式， 建立抓取简单形状目标时的数学模型， 并进行了仿真和实验验证， 结果表明：在 夹持模式下， 目标物体的重力与所需要的爪指内腔压力基本上成线性关系， 爪指 内腔压力随着目标物体半径的增大先减小而后突然增大； 在抓握模式下， 目标物 体重量与

10、所需要的爪指内腔压力成线性关系， 但目标重力对爪指内腔压力的影响 没有夹持模型下的影响大， 内腔压力随着目标物体半径的增大先减小而后逐渐增 大。最后，本文在气动柔性弯曲关节和气动柔性球关节研究的基础上， 提出了五 自由度手指的设计， 由一个球关节和两个弯曲关节串联得到一个五自由度的柔性 手指。在气动柔性扭转关节、 三自由度手指和五自由度手指的基础上， 提出了模 拟人手结构和功能的气动柔性多指灵巧手，总结了气动柔性多指灵巧手的特点， 并分析了多指灵巧手设计的可行性及研究思路。关键词：气动柔性驱动器FPA气动柔性弯曲关节，气动柔性扭转关节，气动柔 性手爪，多指灵巧手，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