新型六自由度平行机构设计和运动学参数的优化外文文献翻译、中英文翻译

1、 MECHANICAL DESIGN AND KINEMATIC OPTIMIZATION OF A NOVEL SIX-DEGREE-OF-FREEDOM PARALLEL MECHANISM Antonio Frisoli, Fabio Salsedo, Diego Ferrazzin, Massimo Bergamasco PERCRO Simultaneous Presence, Telepresence and Virtual PresenceScuola Superiore S. AnnaVia Carducci, 40 56127 PISA, ItalyE-mail: anton

2、ysssup.it, bergamascopercro.sssup.itABSTRACT A six-degree-of-freedom hand controller with force feedback capabilities has been designed. The proposed mechanism new design is fully parallel and actuator redundant. Actuator redundancy refers to the addition of more actuators than strictly necessary to

3、 control the mechanism without increasing the mobility. A new cable transmission is used to drive each of the six degrees of freedom, allowing all actuators be fixed to ground. Kinematic optimization of the dexterity and redundant actuation analysis of the manipulator has been developed. The mechani

4、cal design of a prototype version is shown.KEYWORDS Haptic Interface, Tendon Transmission, Six Dof Parallel ManipulatorINTRODUCTION Parallel manipulators have been extensively studied for their favorable properties in terms of structural stiffness, position accuracy and good dynamic performance (Mer

5、let 1990). Their well-known counterbalance is lack in workspace dimensions and more complex direct kinematics law. Several parallel manipulators proposed in the literature are based on octahedral geometry kinematics (Fichter 1986, Albus et al. 1993) With the adoption of such a kinematics, the geomet

6、ric coincidence between two joints leads to a lack of the one-to-one correspondence between leg points on platform and base. The legs form a “zigzag triangulated pattern” (Hunt and McHaree 1998) that connect the base to the mobile platform. With this kinematics the manipulator can support external l

7、oads with increased stiffness and avoid the singularity configurations, with a consequent average improvement in kinematic performance. The novel manipulator, presented in this paper, has been devised to realize a six-degree of freedom haptic interface. Requirements of low friction and no backslash

8、are critical in the design of force feedback devices (Hayward,1995). Moreover a uniform kinematic behavior of the mechanism over the workspace is required. A six-degree of freedom haptic device can be used to replicate the most of the physical interactions in Virtual Environments (VE). The aim of th

9、is research has been to design an Haptic Interface for the simulation in VE of all tasks involving dexterous manipulation and precise execution, e.g. Surgery, with the replication of all the components of the interaction wrench. The new manipulator design is composed of a mobile platform connected b

10、y four legs to a fixed platform. Two motors located on the base actuate each leg by a novel tendon drive system. Since eight tendons are used to control six degree-of-freedom, the configuration of the tendon driven system according to (Jacobsen et al. 1989) is redundant of type N+2. The tendon drive

11、 modifies the kinematic behavior of the system, so that it becomes statically equivalent to a mobile platform connected to the base by eight pistons, disposed in a triangulated pattern. By means of this static analogy, the mechanical architecture of the system recalls an octahedral like geometry wit

12、h two more linear actuators. But with respect to the octahedral parallel manipulator classical designs, the mechanical system is implemented by DC iron-less motors and steel cables, yielding an high fidelity force-feedback desktop device. KINEMATIC DESCRIPTION OF THE MECHANISM The kinematics of the

13、legs of the parallel manipulator is based on the closed 5-bar mechanism. An innovative tendon transmission has been devised to drive the closed 5-bar mechanism. It is composed of two tendons routed orderly over the pulleys mounted on each joint axis, as shown in figure 1. All the pulleys are idle, e

14、xcept the final driven pulleys of each tendon transmission that are bolted to the base link.Figure 1: Scheme of the closed-loop tendon drive The pulley radii are the same for all the joints, but with different winding directions. So differently from classical tendon transmissions used in serial mani

15、pulators, the final driven pulley is grounded and it is not connected to a moving driven link. This new tendon drive design allows, by properly choosing the tendon routing, to improve the kinematic performance of the closed 5-bar linkage, i.e. avoiding the singularities and improving the kinematic d

16、exterity. The closed-loop tendon drive We shall analyze now the properties of the tendon drive. Since the sum of the internal angles of a triangle is p, it is easy to show that for the angles of figure 1 the following differential relations hold: (1) Since the tendon branch tangent to two consecutiv

17、e pulleys is constant independently from the close 5 bar posture, the displacement dvi of the starting terminal of the tendon is determined only by the variations of the joint angles: (2) So by using the differential expressions (1) we obtain: (3) The above equation is very meaningful. Since (4) by

18、the duality principle between statics and kinematics, the action of the two tendon tensions T1 and T2 is equivalent to two linear actuators directed along QP and RP with thrusts: (5) But since tendon can generate only tension forces, the previous static analogy is incomplete and, depending by the im

19、plemented routing, the equivalent pistons can either only pushing upwards or pulling downwards. So the kineto-static behavior of a tendon driven closed 5-bar linkage can be reduced to one of the equivalent mechanisms showed in figure 2.Figure 2: Equivalent class of mechanisms This mechanical analogy

20、 is very worthwhile, since it permits to explain clearly the force capability of the tendon driven 5-bar linkage. The forces applied at the End Effector (EF) must be comprised in the angle formed by the two equivalent thrust vectors QP and RP, with the sign determined by the routing. Comparative ana

21、lysis We have studied the differential kinematics of the closed 5-bar linkage both with the direct drive of base joints and with the new tendon drive, in order to point out the difference in kinematics performance. Figure 3: Manipulability ellipses for the base joints drive Figure 4 : Manipulability

22、 ellipses for the closed-loop tendon drive Kinematics performance have been compared computing over all the workspace the manipulability ellipses of the two drive systems. The results of an exemplifying case study are reported in figures 3 and 4. The manipulability ellipses for the tendon driven 5-b

23、ars mechanism have a rounder shape than t-hose of the 5-bars mechanism actuated at the joints. So the proposed driving system improves the kinematics isotropy of the mechanism. The manipulability, i.e the ellipsis area, is also greater in the closed-loop tendon driven mechanism. Extension to six deg

24、rees-of-freedom kinematics The mechanical designs of both closed 5-bar linkages with a pushing type drive and with a pulling type drive have been developed. Then these two mechanisms have been assembled with a ball joint and with a rotational joint, as shown in figure 5, to give raise to two types o

25、f six-degree of freedom kinematic components, later on called for sake of simplicity pushing and pulling legs. Figure 5: CAD model of a 6-dof leg Then four legs have been assembled with a mobile platform and a fixed platform in a six degree-of-freedom parallel manipulator. Such a parallel manipulato

26、r is redundant in the actuation since eight command variables, namely eight tendon tensions or displacements, are independently used to control six degrees of freedom (Kurtz 1990). On the other side, the constraint on the positive sign of the tendon tension (Jacobsen 1989 ) limits the actuation capa

27、bility of the HI. The equation ruling the statics of the HI is the dual of the Jacobian equation: Figure 6: General kinematic architecture with F and t being the external force and torque on the moving platform and t being the eight-dimensional vector of tendon tensions. The HI can exert forces and

28、torques of arbitrary directions if and only if the kernel of contains a vector whose components are all positive. The points of the workspace where such a condition is verified belong to the controllable workspace. Our aim has been to enlarge the controllable workspace to the kinematically reachable

29、 workspace of the mechanism. So we have studied all the possible symmetric spatial arrangements of four legs, to find the most suitable architecture for an HI design maximizing the controllable workspace. Figure 7: Instantaneous kinematic equivalenceWe have chosen the architecture of fig. 6. The leg

30、s are located with an axial symmetry of 90 around an axis normal to the base plane; the base axes of the legs lay in the base plane; both the pushing and the pulling legs are two; the pulling and pushing legs are placed in alternate way around the symmetry axes. The mechanical analogy can be extende

31、d to the 6-dof parallel manipulator. Istantaneously the system is equivalent to the one depicted in figure 7. The equivalent pistons are disposed in a triangulated pattern. Parallel Architecture Geometric Analysis There is a geometric interpretation of the problem of controllability. Figure 8: Force

32、 closure in pure translations It can be shown that a given configuration belongs to the controllable workspace , if in that configuration the four legs can apply to the coupler a statically balanced system of forces. This problem is known in literature as the force-closure problem and it is related

33、with the study of stable grasps in robotics hands (Nguyen 1988). We can regard the four legs of the HI as four fingers that are grasping in four contact points without friction (corresponding to the ball joints) the coupler. In this way the legs can apply to the coupler four forces.From line geometr

34、y (Phillips 1984), it is known that four forces can be statically balanced if their lines of action belong to: a plane ; a bundle of lines; the system of lines constituted by two planar pencils of lines with a common generator; the Regulus of a hyperboloid (the general screws 3-system of null pitch

35、). In the controllable workspace the legs are always capable of applying to the coupler forces whose lines of action belong to one of the listed systems of lines and so statically balanced. In particular for the selected architecture, if we put aside the angular limitation and the sign limitatio-ns

36、of the forces which each legs can exert, it is always possible to find four forces exertable by the HI whose action lines belong to the simplified system of the type 3. Moreover it can be demonstrated that such architectures every pure translation of the mechanism from the initial position, belongs

37、to the controllable workspace. This property is true because there exists always a point to which the lines of actions of the leg thrusts converge, as shown in fig. 8. So it exists a system of lines of the type 2 aforementioned. KINEMATIC OPTIMIZATION AND MECHANICAL DESIGN The six kinematics paramet

38、ers which define the HI kinematics have been dimensioned aiming at maximizing the total volume W of the controllable workspace. The maximum controllable workspace volume has been computed for 7920 different kinematic configurations, ranging overall the search space of kinematic parameters. The analy

39、sis of the results has given the following indications. Figure 9: Translational workspace with zero orientation The smaller is the dimension of the base platform the larger is the controllable workspace. This dimension is lower bounded by the length of the base links of the 5-bars, since they cannot

40、 interfere. The base links dimensions depend on the dimensions of the mechanical components of the base joints of the 5-bars, including the transmission mechanisms. These values have then been chosen as the smallest possible. Larger controllable workspaces are obtained for larger values of the linea

41、r dimensions of the 5-bars links, which is related to the dimension of the legs workspaces. This value has then been chosen in order to meet the workspace requirements, but designing a compact mechanism with dimensions compatible with the requirements. The controllable workspace of the optimal solut

42、ion has been so estimated: in the zero orientation position the admitted translations are depicted in figure and range in -200;200 mm in the xy-plane and in -130;+130 mm in the vertical direction; the maximum and minimum admissible rotations around an axis in the horizontal plane have been estimated

43、 to 35 and when the mobile platform is in the zero-translation position. A maximum force of 20 N can be exerted in the plane with a motor torque of 500 mNm. The mechanical design of the solution addressed by the optimization process has then been designed in a CAD environment. The CAD model of the m

44、anipulator is shown in figure 1.Figure 10: CAD model of the Haptic Interfac Interference between parts has been assessed in the parametric solid CAD model.CONCLUSIONS The general kinematic description of a new six-degree-of-freedom tendon driven manipulator has been reported. Important properties of

45、 the system descend from the chosen kinematics architecture and can be deducted using elements of line geometry. An exhaustive search of all the possible kinematics solution has been numerically implemented. Finally the parameters of the kinematics architecture that yield the maximum controllable wo

46、rkspace have been determined. 桂林电子科技大学图书馆电子资源镜像站点SpecialSciDBS(国道数据)新型六自由度平行机构设计和运动学参数的优化摘要带有力反馈能力的六自由度机构已经问世。与计划中的机械设计完全相同而且有额外的传动装置。额外的传动装置是指在不增加动力的情况下，在机械控制上增加传动装置。现在，新型的电缆传输已经用于六自由度装置中的每一个自由度驱动，允许所有的传动装置置于地面。机械手灵敏性的运动学参数优化和额外装置已有所发展。这里所要展示的是机械设计的雏形。关键字接触面， 关节运动， 六自由度平行机构手引言 平行机械手因其显著的性能（刚度好、位置精确

47、、良好的动力性能）而被广泛的研究。其众所周知的平衡配比在工作空间大小及复杂的动力学规则中是不足的。 少数平行机械手在文献中都是基于八面体几何系统而设计的。采用这一动力学原理，连接处的几何一致性导致了平台与腿关节，基座与腿关节之间的不一致。腿部形成的“锯齿形三角图案”连接着基座与运动平台。根据该动力学原理，机械手通过增强刚度来支持外载荷，能基本改善动力工作情况的特殊结构。 论文中讨论的新型机械手，是为实现六自由度运动而设计的，要求低摩擦，无齿隙及力反馈装置的严密设计。此外还需要要求机械装置在一定的工作空间内运动。六自由度操作装置在虚拟环境（VE）中的模拟能反复用于大多数的物理效应。研究的目的是通

48、过虚拟环境（VE）的模拟来设计灵巧和精度的结构，如：碰撞情况，各元件间的相互扭转。 新机械手的设计由可动平台通过四条支腿与固定平台相连而组成。两台电动机被设置在基座上，通过新的关节驱动系统来激励腿部的运动。由于八个关节控制六自由度，关节驱动系统的结构参照应为N+2型。 关节驱动限制了系统的运动行为，所以是静态的，等同于运动平台通过八个活塞与基座相连的三角形图案。 借助静态分析，系统的机械结构恢复八面体的几何系统，并带有两个以上的线形传动装置。顾虑到八面体平行机械手的典型设计，机械系统是由直流电动机，钢丝绳来执行，产生一个高逼真的力反馈到上一级的装置。机械装置的动力学描述 平行机械手的支腿的运动

49、是基于封闭五杆机构的。 新型关节传动的设计是为了驱动封闭五杆机构的。 该机构在每个关节轴线上各安装有一个滑轮，如图1所示。除了最后一个驱动滑轮外，其它滑轮空转并用螺栓固定在连杆上。图1：封闭关节驱动的示意图 所有关节上的滑轮半径都相同。但旋转方向不同。与典型关节传动不同，用于连续的机械手，最后的驱动滑轮是基础，且不与运动的驱动连杆相连结。新关节的驱动设计允许在选择合适的关节路线时，改善封闭五杆联动装置的运动工况，如：避免异常情况和提高运动的灵活性。封闭关节的驱动 现在我们应分析一下关节驱动的特性。 由于内角的总和为P，容易看出图1中各角度的不同关系包括： （1） 由于关节部分相邻的两个滑轮相对

50、封闭五杆机构是独立的，关节的起始极限位移dvi只是连接角度的变化量而确定的： （2）将（1）式代入，得： （3）以上方程意味着： （4）由于静力学和运动学间的二元性原理，两关节上的作用力T1和T2是相等的，沿QP 和 RP的轴向压力为： （5） 但由于关节处产生了张力，先前的静态分析是不完全的，且有赖于执行路线，等效的活塞要么只能向上推，要么只能向下拉。 所以关节驱动的封闭五杆联动装置可以简化为图2所示的等效装置。 图2： 等效装置 机械分析是值得的，因为它可以将关节驱动的五杆联动装置的力的能力解释得非常清楚。力支持的终端操纵装置（EF）必须包括沿推力矢量QP 和 RP方向生成的夹角，并作上记号。相对分析： 我们研究了封闭五杆联动装置上基座关节处的直接驱动和新关节驱动在动力学上的差异，为的是指出运动工作情况的不同。 以计算机模拟的两个驱动系统的椭圆工作图来比较其运动工作情况。例证结果的研究图3和图4。 图3：基座关节驱动的椭圆工作图 图4：封闭关节驱动