氣動(dòng)機(jī)械手的畢業(yè)設(shè)計(jì)翻譯

1、“軟”2-自由度平面氣動(dòng)機(jī)械手的設(shè)計(jì)m. van damme, r. van ham, b. vanderborght, f. daerden, and d.lefeber機(jī)器人和多體力學(xué)研究團(tuán)隊(duì),機(jī)械工程學(xué)系, 比利時(shí)布魯塞爾市中心的自由大學(xué)michael.vandammevub.ac.be摘要本文提出這樣一個(gè)的概念，即使是重量很輕的機(jī)械手也能夠直接和操作員一起，協(xié)助他處理沉重的貨物。該系統(tǒng)的優(yōu)點(diǎn)是：符合人類工程學(xué)、重量輕、成本低、操作簡(jiǎn)便并且能很好的保護(hù)操作人員的安全。執(zhí)行機(jī)構(gòu)采用了褶皺式氣動(dòng)人工肌肉。我們提供一種使用這種執(zhí)行機(jī)構(gòu)設(shè)計(jì)的機(jī)械手的小型模型，以及用于該機(jī)構(gòu)的滑?？刂破鳌ｊP(guān)鍵詞:

2、氣動(dòng)人工肌肉,滑模控制。1引言徒手搬運(yùn)物料的工作,比如搬起和移動(dòng)重物,或搬運(yùn)重物的時(shí)候長(zhǎng)時(shí)間保持一個(gè)姿勢(shì)是導(dǎo)致常見(jiàn)的腰部疾病和其他健康問(wèn)題的原因。事實(shí)上，人工搬運(yùn)已與大部分腰部受傷，占所有工人傷病賠償?shù)?6-19，同時(shí)也是所有與工作相關(guān)的賠償?shù)?3-411。這個(gè)問(wèn)題不但使得受傷工人的生活質(zhì)量受到很嚴(yán)重影響，而且它也是一個(gè)很大的經(jīng)濟(jì)的支出。傳統(tǒng)的解決方案是使用市售的機(jī)械手系統(tǒng)。這些系統(tǒng)大多采用配重，這就限制了它用于一些特定的重量負(fù)荷的工作。為了提高安全性和工人的生產(chǎn)力，在機(jī)器人專業(yè)領(lǐng)域已經(jīng)在研究其他幾種機(jī)器人輔助操縱的方法 2，3，4。在這些研究過(guò)程中開(kāi)發(fā)的設(shè)備都是屬于一些材料處理設(shè)備，這些設(shè)備

3、被稱為智能輔助裝置（iads）。然而，這些設(shè)備大多是沉重的，不僅結(jié)構(gòu)復(fù)雜而且造價(jià)昂貴。在本文中，我們提到的機(jī)械手初步的設(shè)計(jì)和控制，最終將結(jié)合人體工程學(xué)，操作安全，成本低，重量輕和易于操作和控制。所有這一切都可以通過(guò)布魯塞爾自由大學(xué)的機(jī)械工程系開(kāi)發(fā)的褶皺氣動(dòng)人工肌肉（ppam）5執(zhí)行機(jī)構(gòu)來(lái)實(shí)現(xiàn)，這是一種一由壓縮空氣驅(qū)動(dòng)的可收縮的裝置。我們正努力實(shí)現(xiàn)讓這個(gè)系統(tǒng)能做到這樣一點(diǎn)：當(dāng)操作員希望移動(dòng)機(jī)器手上的重物,那么他/她就可以像沒(méi)有機(jī)械手一樣開(kāi)始移動(dòng)它。該系統(tǒng)通過(guò)測(cè)量肌肉壓力表的壓力值，可以不斷估計(jì)由操作員應(yīng)用的力量，并協(xié)助他/她在完成所需的負(fù)荷動(dòng)作。操作員和負(fù)載（不含中介控制工具）之間的直接互動(dòng)，可

4、以實(shí)現(xiàn)非常精確的定位。在人們眼中使用任何機(jī)械設(shè)備的主要要求就是安全。 ppam驅(qū)動(dòng)器非常有助于提高操縱系統(tǒng)的整體安全性：它允許輕量的工作，沒(méi)有觸電的危險(xiǎn)，最重要的是，肌肉本身和它是相容的。在本文中，為了證明這種機(jī)械手而設(shè)計(jì)了一個(gè)小型的概念模型，模型由兩個(gè)ppam驅(qū)動(dòng)的反肘裝配鏈接組成，為一個(gè)滑?？刂破鞯南到y(tǒng)進(jìn)行開(kāi)發(fā)和測(cè)試。系統(tǒng)顯示如圖1。圖1。機(jī)械手的規(guī)模模式2機(jī)器人的設(shè)計(jì)2.1簡(jiǎn)介我們的目標(biāo)是設(shè)計(jì)一個(gè)在垂直平面內(nèi)能提供幫助的機(jī)器。這意味著就兩個(gè)驅(qū)動(dòng)能滿足自由度的要求。我們考慮了三種可能的連接配置：肘，反肘和菱形。由于設(shè)計(jì)上考慮到重量應(yīng)盡可能輕，結(jié)構(gòu)盡可能簡(jiǎn)單，這樣的話菱形的配置顯然是不適合的

5、。作為操作員將可以直接和機(jī)械手互動(dòng)，這一點(diǎn)也非常重要，機(jī)器手臂不能妨礙到操作員的動(dòng)作。出于這個(gè)原因，我們選擇了肘這種配置。為了方便開(kāi)發(fā)和測(cè)試，并獲得與這種類型的系統(tǒng)的經(jīng)驗(yàn)，我們決定先開(kāi)發(fā)一個(gè)小型機(jī)器人。選擇兩個(gè)環(huán)節(jié)的長(zhǎng)度是30厘米。2.2設(shè)計(jì)圖2顯示了逆肘配置中的兩個(gè)環(huán)節(jié)的的示意圖。圖中還包括約定了一個(gè)慣例，本文剩余的部分是如何定義兩個(gè)關(guān)節(jié)角度和如何對(duì)不同氣動(dòng)肌肉進(jìn)行編號(hào)的。圖2 逆肘的配置因?yàn)槲覀冇兴膫€(gè)ppams，有8個(gè)附著點(diǎn)。每個(gè)點(diǎn)的位置可以由兩個(gè)坐標(biāo)來(lái)描述。每塊肌肉有兩個(gè)參數(shù)（長(zhǎng)細(xì)比和最大長(zhǎng)度）。這意味著有一共有24個(gè)待定參數(shù)。確定最好的設(shè)計(jì)意味著需要在全球24維參數(shù)空間中發(fā)現(xiàn)一個(gè)最好的

6、，受到條件影響，如產(chǎn)能，空間沖突的情況下，避免肌肉過(guò)度負(fù)荷，確保有足夠大的工作區(qū)，.這已被證明是難以計(jì)算的。因此，不同的參數(shù)進(jìn)行手動(dòng)選擇，主要是經(jīng)過(guò)廣泛的計(jì)算機(jī)實(shí)驗(yàn)之后便于生產(chǎn)。2.2.1轉(zhuǎn)矩特性一旦所有附著點(diǎn)的位置和ppam參數(shù)能夠確定下來(lái)，我們就可以判斷這兩個(gè)關(guān)節(jié)的扭矩特性。由于ppam肌肉使用非線性收縮壓力的關(guān)系（見(jiàn)5，6），那么由肌肉產(chǎn)生的扭矩可以寫(xiě)成 (1)=肌肉1和2與=肌肉3和4。方程（1）證實(shí)了在兩個(gè)確定扭矩因素之間有一個(gè)明顯的差別：表面壓力和扭矩函數(shù)m之間的關(guān)系取決于其設(shè)計(jì)參數(shù)和兩者的位置。扭矩功能表示如圖3。在7中可以找到更多細(xì)節(jié)。圖3扭矩功能3 控制3.1 簡(jiǎn)介我們所使用

7、的褶皺氣動(dòng)人工肌肉，它的控制器的設(shè)計(jì)并不簡(jiǎn)單。在設(shè)計(jì)控制器時(shí)所遇到的困難包括以下內(nèi)容：機(jī)械臂及其驅(qū)動(dòng)器具有很強(qiáng)的非線性系統(tǒng)。ppams上的測(cè)量也表明在力-壓力特性上略有滯后。這使得當(dāng)僅僅提供壓力測(cè)量值的情況下難以估算它的驅(qū)動(dòng)力。驅(qū)動(dòng)器的壓力表壓力可以采取一個(gè)比較長(zhǎng)的時(shí)間來(lái)實(shí)現(xiàn)（大約需要100毫秒較大的壓力來(lái)進(jìn)行操作）。執(zhí)行機(jī)構(gòu)的外觀和數(shù)據(jù)（細(xì)長(zhǎng)）不是很知名。在本文中，我們描述了一個(gè)滑動(dòng)模式的方法控制系統(tǒng)。3.2 p-方法必須計(jì)算執(zhí)行器輸出，以減少數(shù)量，p的方法適用于6,8。這涉及到平均壓力，使用一對(duì)針對(duì)性的肌肉和控制器，通過(guò)一個(gè)肌肉增加一個(gè)（p +p）并且另一個(gè)肌肉減去一個(gè)（p-p），來(lái)計(jì)算壓

8、力差p。的選擇影響符合，同時(shí)p可以用于判斷關(guān)節(jié)位置。驅(qū)動(dòng)機(jī)構(gòu)自己處理壓力都是通過(guò)現(xiàn)成的比例壓力調(diào)節(jié)閥內(nèi)部的pid控制器來(lái)進(jìn)行控制的。3.3 控制器2自由度平面機(jī)械臂的動(dòng)力學(xué)模型是眾所周知的，并且可以寫(xiě)成： （2）其中 為關(guān)節(jié)角度的載體，h是慣性矩陣，c是離心力矩陣（離心力和科里奧利力）和g是引力的載體。 為代表執(zhí)行器的扭矩矢量，可以寫(xiě)成： （3）肌肉i與壓力表的壓力 （i= 1.4),還有與肌肉的扭矩功能 （見(jiàn)2.2.1節(jié)）。壓力表的壓力是由壓力調(diào)節(jié)閥來(lái)控制的。為簡(jiǎn)單起見(jiàn)，我們?yōu)橐浑A系統(tǒng)的閥門(mén)進(jìn)行建模。 p的方法相結(jié)合，這給了我們以下的閥門(mén)模型： （4）將p1和p2分別輸入上下臂關(guān)節(jié)。并且結(jié)合

9、方程（2），（3）和（4），這樣就為我們提供了完整的控制系統(tǒng)來(lái)進(jìn)行建模。這個(gè)系統(tǒng)不是一個(gè)允許直接應(yīng)用滑模控制技術(shù) 9中所述的技術(shù)（siso系統(tǒng)）是假設(shè)系統(tǒng)的形式為 ，它的狀態(tài)向量為，x為輸出的標(biāo)量和u為輸入的標(biāo)量。因此，狀態(tài)向量只包含輸出和第n-1個(gè)衍生物，和一個(gè)具有區(qū)分輸入輸出量的n次方出現(xiàn)（這意味著該系統(tǒng)具有嚴(yán)格的相對(duì)次數(shù)n10）。我們的系統(tǒng)的狀態(tài)向量還包含壓力表的壓力，這當(dāng)然沒(méi)有系統(tǒng)的關(guān)節(jié)角度（輸出）的衍生物。的形式，正如在實(shí)例9中的介紹。為了解決這個(gè)問(wèn)題，我們把兩個(gè)（耦合）siso系統(tǒng)組成的系統(tǒng)，把他們寫(xiě)成： （5） （6）與i= 1，2（上臂1，下臂2）， 的狀態(tài)向量， 標(biāo)量輸入和

10、的系統(tǒng)的輸出?，F(xiàn)在，我們可以改變這些系統(tǒng)在10中描述的的一般使用程序形式。坐標(biāo)分別寫(xiě)成 ， ， ， 與 滿足 代表了f 關(guān)于h的李導(dǎo)數(shù)。，我們就可以得到以下兩個(gè)系統(tǒng)（i = 1，2）：跟 、 和 一起。為了設(shè)計(jì)滑?？刂破骺梢允沟眠@些系統(tǒng)跟蹤各自所需的輸出軌跡 ，我們使用 來(lái)定義滑動(dòng)面 ： （7） （8）從上述公式（7）（8）當(dāng)中，我們已經(jīng)確定了一個(gè)事實(shí)，即這兩個(gè)系統(tǒng)有嚴(yán)格的相對(duì)程度3（見(jiàn)10），這意味著 和 。選擇系數(shù) 和 以便湊成赫爾維茨 一個(gè)有正系數(shù)并且根是為負(fù)數(shù)，或者有成對(duì)的共軛負(fù)實(shí)部的多項(xiàng)式。多項(xiàng)式 。如果軌跡的滑動(dòng)面（如si= 0），錯(cuò)誤往往會(huì)呈指數(shù)性的消失。通過(guò)選擇控制規(guī)律，在初始

11、條件有限的時(shí)間內(nèi)使滑動(dòng)面的吸引，我們可以實(shí)現(xiàn)我們的控制目標(biāo)。其中的一種可能性是（見(jiàn)10）：如果k是大到足以克服系統(tǒng)的不確定性和擾動(dòng)，si將在有限時(shí)間內(nèi)趨于零。為了減少抖振，引入邊界層，并且（見(jiàn)9）將sgn(si)替換為sat(si/i)，i是一個(gè)由邊界層的寬度決定的常數(shù)。3.4 結(jié)果為了評(píng)估以及為滑?？刂破鞯母櫺阅芴峁┙ㄗh，滑膜控制器被用來(lái)跟蹤一個(gè)處在x-y空間圓圈。需要在5秒內(nèi)進(jìn)行軌跡跟蹤。為了處理抖振，必須要有一個(gè)重大邊界層（1= 4，2= 3），當(dāng)然這會(huì)增加一些跟蹤誤差。由此產(chǎn)生的路徑如圖4所示。圖4 空間跟蹤路徑。4 結(jié)論提出了一個(gè)小規(guī)模的，輕盈褶氣動(dòng)人工肌肉驅(qū)動(dòng)的機(jī)械臂設(shè)計(jì)。還對(duì)滑

12、動(dòng)模跟蹤系統(tǒng)控制器提出了建議，并提出初步跟蹤結(jié)果。關(guān)于抖振的問(wèn)題，只要能夠限制跟蹤精度可以達(dá)到需求。參考文獻(xiàn)1. w.s. marras, k.p. granata, k.g. davis, w.g. allread, and m.j. jorgensen (1999) effects of box features on spine loading during warehouse order selecting. ergonomics, vol. 42, no. 7, pp. 980996.2. kevin m. lynch and caizhen liu (2000) designing

13、 motion guides for ergonomic collaborative manipulation. ieee international conference on robotics and automation.3. h. kazerooni (1996) the human power amplifier technology at the university of california, berkeley. journal of robotics and autonomous systems, vol. 19, pp. 179187.4. jae h. chung (20

14、02) control of an operator-assisted mobile robotic system. robotica, vol. 20, no. 4, pp. 439446.5. daerden f. and lefeber d. (2001) the concept and design of pleated pneumatic artificial muscles. international journal of fluid power, vol. 2, no. 3, pp. 4150.6. frank daerden (1999) conception and rea

15、lization of pleated pneumatic artificial muscles and their use as compliant actuation elements. ph.d. thesis, vrije universiteit brussel.7. van damme m., daerden f., and lefeber d. (2005) a pneumatic manipulator used in direct contact with an operator. in proceedings of the 2005 ieee international c

16、onference on robotics and automation, barcelona, spain, pp. 45054510.8. daerden f., lefeber d., verrelst b., and van ham r. (2001) pleated pneumatic artificial muscles: actuators for automation and robotics”. in ieee/asme international conference on advanced intelligent mechatronics, como, italy, pp

17、. 738743.9. j.-j. slotine and w. li (1991) applied nonlinear control. prentice hall.10. sastry, s. (1999) nonlinear systems analysis,stability and control. springer.英文原版design of a “soft” 2-dof planar pneumatic manipulatorm. van damme, r. van ham, b. vanderborght, f. daerden, and d.lefeberrobotics a

18、nd multibody mechanics research group, department of mechanical engineering, vrije universiteit brussel, belgium michael.vandammevub.ac.beabstractthis paper presents the concept of a lightweight manipulator that can interact directly with an operator in order to assist him in handling heavy loads. t

19、he advantages of the system, ergonomics, low weight, low cost, ease of operation and operator safety are a consequence of the use of pleated pneumatic artificial muscles as actuators. the design of a smalls cale model of such a manipulator using these actuators is presented, as well as a sliding mod

20、e controller for the system.keywords: pneumatic artificial muscles, sliding mode control.1 introductionmanual material handling tasks such as lifting and carrying heavy loads, or maintaining static postures while supporting loads are a common cause of lower back disorders and other health problems.

21、in fact, manual material handling has been associated with the majority of lower back injuries, which account for 16-19% of all workers compensation claims, while being responsible for 33-41% of all work-related compensations 1. the problem has an important impact on the quality of life of affected

22、workers, and it presents an important economic cost.the traditional solution is using a commercially available manipulator system. most of these systems use a counterweight, which limits their use to handling loads of a specific mass.in order to increase safety and productivity of human workers, sev

23、eral other approaches to robot-assisted manipulation have been studied in the robotics community 2, 3, 4. the devices developed in the course of these studies belong to a class of materials handling equipment called intelligent assist devices (iads). most of these systems, however, are heavy, comple

24、x and expensive.in this paper we present the initial design and control of a manipulator that will eventually combine ergonomics, operator safety, low cost, low weight and ease of operation. all of this can be achieved through the use of an actuator, developed at the department of mechanical enginee

25、ring at the vrije universiteit brussel: the pleated pneumatic artificial muscle (ppam) 5, a contractile device operated by pressurized air.we are working towards a system that behaves as follows: when the operator wants to move a load attached to the manipulator, he/she starts moving it as if there

26、were no manipulator. by measuring the muscle gauge pressures, the system continuously estimates the forces applied by the operator and assist him/her in accomplishing the desired load movement. the direct interaction between operator and load (without intermediary control tools) allows for very prec

27、ise positioning.the main requirement for any mechanical device that is used in the immediate environment of people is safety. the ppam actuators greatly contribute to the overall safety of the manipulator system: they allow for a lightweight construction, there is no danger of electrocution and, mos

28、t important of all, the muscles are inherently compliant.in this paper, the design of a small-scale proof-of-concept model of such a manipulator, consisting of two ppam actuated links in inverse elbow configuration, is presented and a sliding-mode controller for the system is developed and tested. t

29、he system is shown in fig. 1.fig. 1. the manipulator scale model.2 manipulator design2.1 introductionthe goal is to design a machine that will provide assistance in the vertical plane. this means that two actuated degrees of freedom are sufficient. three possible link configurations were considered:

30、 elbow, inverse-elbow and rhombic. since the design should be as lightweight and simple as possible, the rhombic configuration isnt suitable. as operator and manipulator will be interacting directly, its important that the manipulator doesnt obstruct the operators movements. for this reason, the elb

31、ow-up configuration was chosen.for easier development and testing, and to gain experience with this type of system, we decided to develop a small-scale manipulator first. the length of both links was chosen to be 30 cm.2.2 designfig. 2 shows a schematic representation of the two links in inverse elb

32、ow configuration. the conventions used in the rest of this document regarding to how both joint angles are defined and how the different pneumatic muscles are numbered are also included in the figure.fig. 2. the inverse elbow configuration.since we have four ppams, there are eight attachment points.

33、 the location of each of these points can be described by two coordinates. each muscle has two parameters (slenderness and maximum length). this means there are a total of 24 parameters to be determined. determining the best design means finding a global optimum in a 24- dimensional parameter space,

34、 subject to conditions such as producibility, absence of space conflicts, avoiding excessive muscle loading, ensuring a large enough working area,. this has proven to be computationally intractable. therefore, the different parameters were chosen manually, mainly with ease of production in mind, aft

35、er extensive computer experiments.2.2.1 torque characteristicsonce all attachment point locations and ppam parameters are known, we can determine the torque characteristics of both joints. using the nonlinear force-pressure-contraction relation of the ppam muscle (see 5, 6), torque generated by a mu

36、scle can be written as (1)with = for muscles 1 and 2 and = for muscles 3 and 4. equation (1) provides a clear separation between the two factors that determine torque: gauge pressure and a torque function m, that depends on the design parameters and the position. the torque functions are shown in fi

37、g. 3. more details can be found in 7.fig. 3. torque functions.3 control3.1 introductionwhen using pleated pneumatic artificial muscles, controller design is not straightforward. difficulties encountered when designing a controller include the following: both the manipulator and its actuators are str

38、ongly nonlinear systems. measurements on ppams also show a slight hysteresis in the force-pressure characteristic. this makes it hard to estimate actuator force when only pressure measurements are available. actuator gauge pressures can take a relatively long time to settle (around 100 ms for large

39、pressure steps). actuator paramters (slenderness) are not very well known.in this paper, we describe a sliding mode approach to control the system.3.2 p - approachto reduce the number of actuator outputs that have to be calculated, the p-approach was used 6, 8. this involves choosing an average pres

40、sure pm for both muscles of an antagonistic pair, and having the controller calculate a pressure difference p that is added in one muscle (p+p) and subtracted in the other (pp). the choice of pm influences compliance while p determines joint position. the control of the actuator pressures themselves

41、 is handled by off the shelf proportional pressure regulating valves with internal pid controllers.3.3 controllerthe dynamical model of a 2-dof planar arm is well known, and can be written as (2)where q = q1 q2t is the vector of joint angles, h is the inertia matrix, c is the centrifugal matrix (cen

42、trifugal and coriolis forces) and g is the gravitational force vector. is a vector representing the actuator torques, and can be written as (3)with pi (i = 1. . . 4) the gauge pressure in muscle i, and mi the torquefunction associated with that muscle (see section 2.2.1).the gauge pressures are dete

43、rmined by the pressure regulating valves. for simplicity, we model the valves as first order systems. combined with the p-approach, this gives us the following valve model: (4)p1 and p2 are the inputs for upper and lower arm joints, respectively. combining equations (2), (3) and (4) gives us the com

44、plete model of the system to be controlled.this system is not in a form that allows direct application of sliding mode control techniques1, such as described in for instance 9. to solve this, we treat the system as consisting of two (coupled) siso systems, writing them as(5)(6)with i = 1, 2 (1 for u

45、pper arm, 2 for lower arm), xi = qi qi p2i1 p2i the state vector, ui = pi the scalar input and yi = hi(xi) = qi the system output. we can now transform these systems to the normal form using a procedure described in 10. written in the coordinates i1 = hi (xi), i2 = lfihi (xi), i3 = lfi (lfihi) (xi)

46、= l2fi hi (xi), i (xi) with i (xi) satisfying lgii (xi) 0 2, we get the following two systems (again, i = 1, 2): with bi (i, i) = l3 fi hi (xi), ai (i, i) = lgil2 fi hi (xi) and ri (i, i) = lfii (xi).to design a sliding mode controller that makes these systems track their respective desired output t

47、rajectories yim (t) = qim (t), we use ei0 (t) = yim (t) yi (t) to define the sliding surfaces si (xi, t):(7) (8)in going from (7) to (8), we have used the fact that both systems have strict relative degree 3 (see 10), which implies lgiqi = 0 and lgilfiqi =1 the technique outlined in 9 (for a siso sy

48、stem) supposes the system is in the form x(n) = f(x)+b(x)u, with state vector x = hx x · · · x(n1)it , x being the scalar output and u the scalar input. thus, the state vector only contains the output and its first n1 derivatives, and one has to differentiate the output n times for th

49、e input to appear (which means the system has strict relative degree n 10). our systems state vector also contains the gauge pressures, which are of course no derivatives of the joint angles (outputs) of the system.2 lfh (x) = hxf stands for the lie derivative of h with respect to f. 0. the coeffici

50、ents i0 and i1 are chosen so that the polynomials p2 + i1p + i0 are hurwitz3. if the trajectory is on the sliding surface (if si = 0), the error will tend to zero exponentially. by selecting a control law that makes the sliding surface attractive to the initial conditions in finite time, we can achi

51、eve our control objective. one possibility is (see 10):if k is large enough to overcome system uncertainty and perturbations, si will tend to zero in finite time. to reduce chattering, a boundary layer (see 9) is introduced by replacing sgn (si) with sat(si/i), whereand i are constants determining t

52、he width of the boundary layers.3.4 resultsto evaluate the tracking performance of the proposed sliding mode controller, it was used to track a circle in xy space. the desired trajectory was tracked in a period of 5 seconds. in order to deal with chattering, significant boundary layers were necessar

53、y (1 = 4, 2 = 3), which of course increases tracking error. the resulting path is shown in fig. 4.fig. 4. spatial tracking behaviour.3 a polynomial with real positive coefficients and roots which are either negative or pairwise conjugate with negative real parts.4 conclusionthe design of a small-scale, lightweight manipulator actuated by pleated pneumatic artificial muscles was presented. a sliding mode tracking controll