Showing papers on "Parallel manipulator published in 2002"

Jacobian Analysis of Limited-DOF Parallel Manipulators

Abstract: This paper presents a methodology for the Jacobian analysis of limited degrees-of-freedom (DOF) parallel manipulators. A limited-DOF parallel manipulator is a spatial parallel manipulator which has less than six degrees-of-freedom. It is shown that a 6 × 6 Jacobian matrix, which provides complete information about singularities, can be derived by making use of the theory of reciprocal screws. The 3-UPU and 3-RPS parallel manipulators are used as examples to demonstrate the methodology.Copyright © 2002 by ASME

General Methodology for Type Synthesis of Symmetrical Lower-Mobility Parallel Manipulators and Several Novel Manipulators

Abstract: In the area of parallel robots, the use of lower-mobility parallel manipulators for many tasks requiring fewer than six degrees of freedom (DoF) has drawn a lot of interest. This paper treats one fundamental problem in the study of lower-mobility parallel manipulators: type synthesis. Using reciprocal screw theory, we define the mechanism constraint system and limb constraint system. We then investigate the relations between the mechanism constraint system and the limb constraint system under different geometrical conditions. Three tables describing the relations are presented. Based on the three tables, we propose a constraint-synthesis method for type synthesis of symmetrical lower-mobility parallel manipulators. The method used in the paper to construct the kinematic structure of the limb of lower-mobility parallel manipulators with prescribed DoF is simple and systematic. Examples are included to illustrate the application of the method and some novel lower-mobility parallel manipulators with 3-, 4- a...

Structure Synthesis of a Class of 4-DoF and 5-DoF Parallel Manipulators with Identical Limb Structures

Abstract: In this paper, a systematic approach is developed for the structural synthesis of a class of four-degrees-of-freedom (4-DoF) and 5-DoF overconstrained parallel manipulators with identical serial limbs. The theory of screws and reciprocal screws is employed for the analysis of the geometric conditions that must be met by the limbs of such parallel manipulators. Limb structures that can be used for constructing 4-DoF or 5-DoF parallel manipulators are enumerated according to the reciprocity of the twist and wrench systems. The assembly conditions of a parallel manipulator built by using identical C- or F-limbs are discussed. Several 4-DoF and 5-DoF parallel manipulators are sketched as examples.

Type Synthesis of 3-DOF Spherical Parallel Manipulators Based on Screw Theory

Abstract: A spherical parallel manipulator (SPM) refers to a 3-DOF parallel manipulator in which the moving platform has only three pure rotational degrees of freedom of motion relative to the base. A method is proposed for the type synthesis of SPMs based on screw theory. The wrench systems of a spherical parallel kinematic chain (SPKC) and its legs are first analyzed. A general procedure is then proposed for the type synthesis of SPMs. The type synthesis of legs for SPKCs, the type synthesis of SPKCs, as well as the input validity check of SPMs are dealt with in sequence. SPKCs with and without inactive joints are synthesized. The number of over-constraints of each SPKC is also given. The phenomenon of dependent joint groups in a SPKC is revealed for the first time. The input validity check of SPMs is also simplified.Copyright © 2002 by ASME

Design Optimization of a Cartesian Parallel Manipulator

Abstract: This paper introduces a new 3-DOF translational parallel manipulator named the Cartesian Parallel Manipulator (CPM). The manipulator consists of a moving platform that is connected to a fixed base by three limbs. Each limb is made up of one prismatic and three revolute joints and all joint axes are parallel to one another. In this way, each limb provides two rotational constraints to the moving platform and the combined effects of the three limbs lead to an over-constrained mechanism with three translational degrees of freedom. The manipulator behaves like a conventional X-Y-Z Cartesian machine due to the orthogonal arrangement of the three limbs. Two actuation methods are analyzed. However, the rotary actuation method is discarded because of the existence of singularities within the workspace. For the linear actuation method, there exists a one-to-one correspondence between the input and output displacements of the manipulator. However, each limb structure is exposed to a relatively large moment about an axis perpendicular to the prismatic joint axis. In order to compensate for this shortcoming, a method to maximize the stiffness is suggested. Finally, a numerical example of the optimal design is presented.Copyright © 2002 by ASME

Kinematics and Singularity Analysis of a Novel Type of 3-CRR 3-DOF Translational Parallel Manipulator:

Abstract: A new three-degrees-of-freedom (3-DOF) translational parallel manipulator (TPM) with linear actuators, i.e., 3-CRR TPM, is first proposed. The rotation singularity analysis, the inverse kinematics, the forward kinematics, and the kinematic singularity analysis of the 3-CRR TPM are then performed. The analysis shows that the proposed TPM has the following kinematic merits over previous TPMs. (1) The forward displacement analysis can be performed by solving a set of linear equations. (2) The Jacobian matrix of the TPM is constant. The inverse of the Jacobian matrix can be pre-calculated, and there is no need to calculate repeatedly the inverse of the Jacobian matrix in performing the forward displacement analysis and forward velocity analysis. (3) There is no rotation singularity. (4) There is no uncertainty singularity. (5) The TPM has a fewer number of links or joints. The geometric condition for a 3-CRR TPM to be isotropic is also revealed. Two additional kinematic merits exist for the isotropic 3-CRR TP...

Design of spherical parallel mechanisms for application to laparoscopic surgery

Abstract: This paper addresses an optimal study of workspace for spherical parallel mechanism for laparoscopic surgery. The spherical parallel manipulator has been selected because of its characteristics. Two designs have been studied for maximizing their workspaces; a haptic device, as part of training system, and a laparoscope holding mechanism. The laparoscope holding mechanism has to satisfy additional constraints by minimizing the occupied space above the patient. The objective is to solve design problem to offer the maximal workspace for such mechanisms. The design of a haptic interface and the laparoscope holding mechanism based on the optimal parameters are presented. This paper presents a Genetic Algorithm (GA) approach for selecting optimal design parameters for maximizing workspace of spherical parallel mechanism.

A comparison study of two 3-DOF parallel manipulators: one with three and the other with four supporting legs

Abstract: This paper presents a comparison study of the well-conditioned workspace and stiffness properties of two 3 degree-of-freedom (DOF) parallel manipulators, one with three supporting limbs and the other with four supporting limbs. The inverse kinematics and Jacobian of these two mechanisms are analyzed. The well-conditioned workspace of each mechanism is maximized and the stiffness properties are determined. A comparison of the results indicates that the Tricept manipulator out performs the 3-UPU parallel manipulator.

The 3-RRS Wrist: A New, Very Simple and Not Over-Constrained Spherical Parallel Manipulator

Abstract: Orientating a rigid body without changing its position is required in many technical applications. This manipulation task is accomplished by manipulators (spherical manipulators) that are just able to make the end effector move according to controlled spherical motions. Spherical manipulators can be either serial or parallel. Parallel architectures are usually more stiff and precise than the serial ones, whereas their structures are more complex than the serial ones. This paper presents a new three-equal-legged spherical parallel manipulator, named 3-RRS wrist. The 3-RRS wrist is not overconstrained and exhibits a very simple architecture employing just three passive revolute pairs, three passive spherical pairs and three actuated revolute pairs adjacent to the frame. The kinematic analysis of the 3-RRS wrist is addressed and fully solved. Finally, its singularity conditions are written in explicit form and discussed. The results of this analysis lead to the conclusion that the new manipulator has only two types of singularities both easy to be identified with geometric reasoning.Copyright © 2002 by ASME

A Family of Novel Orientational 3-DOF Parallel Robots

Abstract: This paper presents a family of novel orientational 3-dof parallel robots, which are not overconstrained whereas most of the previously described mechanisms are. Using equivalencies that stem from the algebraic structure of Lie group of the set of Euclidean displacements, we have found many new tripod limbs and some of them are truly amazing by including prismatic pairs.

Optimal design for the micro parallel robot MIPS

Abstract: MIPS is a micro robot with a parallel mechanical architecture having three degrees of freedom (one translation and two orientations) that allow fine positioning of a surgical tool. The purpose of MIPS is to act as an active wrist at the tip of an endoscope and to provide to the surgeon an accurate tool that may furthermore offers a partial force-feedback. The current prototype has a diameter of 7 mm for a length of 2.5 cm and includes all the necessary hardware. We will explain why a parallel architecture has be chosen, the method of optimal design that has been used for determining the dimensions of the robot and present the current prototype.

Cartesian parallel manipulators

Abstract: A manipulator (10) for receiving and displacing an object, comprising a moving portion (11), adapted for receiving the object. Three articulated support legs (A, B, C) each extend between the moving portion (11) and a ground (12) for supporting the moving portion (11). The articulated support legs (A, B, C) are connected to the ground (12) by a first joint member (JA1, JB1, JC1) and to the moving portion (11) by a second joint member (JA3, JB3, JC3). The first joint member (JA1, JB1, JC1) and the second joint member (JA3, JB3, JC3) in the articulated support legs (A, B, C) are interconnected by a third joint member (JA2, JB2, JC2). The articulated support legs (A, B, C) each have at least one rotational degree of freedom and have constraints in the joint members operable to restrict movement of the moving portion (11) to three translational degrees of freedom and to constrain a relationship between linear displacement of the first joint members (JA1, JB1, JC1) and output of the moving portion (11) to be linear. Three linear actuators (13) are operatively connected each to a different one of the first joint members (JA1, JB1, JC1) for controlling the movement of the moving portion (11) in any of the three translational degrees of freedom. With each actuator (13) controlling exclusively one of the three translational degrees of freedom of the moving portion (11), i.e., the movement of the moving portion (11) along one of three orthogonal directions, the manipulator (10) is said to be decoupled. With the relationship being equal for a linear displacement of any one of the first joint members (JA1, JB1, JC1) and a displacement output of the moving portion (11), the decoupled manipulator (10) is said to be isotropic.

The constant‐Jacobian method for kinematics of a three‐DOF planar micro‐motion stage

Abstract: This paper concerns the development of a class of devices that generate end-effector motion in the range of less than 100 μm and with sub-nanometer resolution; in particular, a parallel manipulator configuration that generates a planar x-y-γ motion is considered. The parallel manipulator is implemented as a compliant mechanism. A problem with parallel manipulators is that the forward kinematics is usually too complex, which can hinder the implementation of advanced control algorithms. The contribution of this paper is that a simple method, called the constant-Jacobian (CJ) method, is developed based on the pseudo-rigid body (PRB) approach to compliant mechanisms. The experiment validates the CJ method. © 2002 John Wiley & Sons, Inc.

A new family of spherical parallel manipulators

Abstract: In the literature, 3-RRPRR architectures were proposed to obtain pure translation manipulators. Moreover, the geometric conditions, which 3-RRPRR architectures must match, in order to make the end-effector (platform) perform infinitesimal (elementary) spherical motion were enunciated. The ability to perform elementary spherical motion is a necessary but not sufficient condition to conclude that the platform is bound to accomplish finite spherical motion, i.e. that the mechanism is a spherical parallel manipulator (parallel wrist). This paper demonstrates that the 3-RRPRR architectures matching the geometric conditions for elementary spherical motion make the platform accomplish finite spherical motion, i.e. they are parallel wrists (3-RRPRR wrist), provided that some singular configurations, named translation singularities, are not reached. Moreover, it shows that 3-RRPRR wrists belong to a family of parallel wrists which share the same analytic expression of the constraints which the legs impose on the platform. Finally, the condition that identifies all the translation singularities of the mechanisms of this family is found and geometrically interpreted. The result of this analysis is that the translation singularity locus can be represented by a surface (singularity surface) in the configuration space of the mechanism. Singularity surfaces drawn by exploiting the given condition are useful tools in designing these wrists.

Evaluation of a Cartesian Parallel Manipulator

Abstract: This paper describes a new 3-DOF translational parallel manipulator named a Cartesian Parallel Manipulator (CPM). The machine behaves like a conventional X-Y-Z Cartesian machine due to the orthogonal arrangement of the three supporting limbs. It is shown that there exists a one-to-one correspondence between the input and output of the manipulator. Three possible arrangements of the Z actuator are evaluated by stiffness mapping. A method for compensating actuator misalignment is described.

Nonlinear PD control for trajectory tracking with consideration of the design for control methodology

Abstract: This paper presents a study of examining nonlinear PD (NPD) control of multi-degree-of-freedom parallel manipulator systems for a generic task, i.e., trajectory tracking. The motivation of this study is the well-known observation that NPD control method can offer a means to improve the performance of plant systems. This study is also to examine how the mechanical structure of the manipulator affects dynamic performance. The design of mechanical structure follows the design-for-control (DFC) principle, and in particular it renders to a full force balanced mechanism. Simulation studies confirm that the concurrent consideration of mechanical structure design and NPD control can obtain good trajectory tracking performance for the parallel manipulators.

Geometric Analysis of Overconstrained Parallel Manipulators with Three and Four Degrees of Freedom

Abstract: This paper investigates the constraint characteristics of parallel manipulators with three and four degrees of freedom. An analytical method of using equivalent screw groups is developed in the study based on the linear independence of screw systems and reciprocal screw systems. A procedure for determining overconstraints in spatial parallel mechanisms with fewer six degrees of freedom is given. With this method, the constraint characteristics of four parallel mechanisms with three or four degrees of freedom, i. e. 3-RRC, 3-CPR, 3-URU/SPS and 4-UPU mechanisms, are revealed. The constraint characteristics of three types of parallelogram linkage unites are then discovered, which gives the corresponding equivalent representations in terms of serial mechanisms. The approach is further applied to the geometric analysis of parallel mechanisms with hybrid limbs including 3-R(4U)RPP and 3-R(4S)RRRP mechanisms.

A General Approach to the Dynamics of Nonholonomic Mobile Manipulator Systems

Abstract: This paper studies the dynamic modeling of a nonholonomic mobile manipulator that consists of a multi-degree of freedom serial manipulator and an autonomous wheeled mobile platform. The manipulator is rigidly mounted on the mobile platform, and the wheeled mobile platform moves on the ground subjected to nonholonomic constraints. Forward Recursive Formulation for the dynamics of multibody systems is employed to obtain the governing equation of the mobile manipulator system. The approach fully utilizes the existing equations of motion of the manipulator and that of the mobile platform. Furthermore, terms representing the dynamic interactions between the manipulator and the mobile platform can be observed. The resulting dynamic equation of the mobile manipulator has the minimum number of generalized coordinates and can be used for the purpose of dynamic simulation and control design, etc. The implementation issues of the model are discussed.

Cable suspended robots: feedback controllers with positive inputs

Abstract: Cable-suspended robots are structurally similar to parallel actuated robots but with the fundamental difference that cables can only pull the end-effector but not push it. From a scientific point of view, this feature makes feedback control of cable-suspended robots a lot more challenging than their counterpart parallel-actuated robots. This paper describes the structure of two closed-loop asymptotic controllers that assure positive cable tensions. These controllers are based on the Lyapunov design technique and feedback linearization, respectively. The effectiveness of the approach is demonstrated through simulation and experiments on a six degree-of-freedom cable suspended robot.

Motion planning for mobile manipulator with keeping manipulability

Abstract: Our research goal is to realize a motion planning for an intelligent mobile manipulator. To plan a mobile manipulator's motion, it is popular that the base robot motion is regarded as manipulator's extra joints, and the whole system is considered as a redundant manipulator. In this case, the locomotion controller is a part of the manipulator controller. However, it is difficult to implement both controllers as one controller, in our implementation experience, because of difference of actuators' character. In this research, we focus on a path planning algorithm for a mobile base with keeping manipulability at the tip of the mounted manipulator. In this case, the locomotion controller is independent from the manipulator controller, and a cooperative motion is realized by a communication between both controllers. In this paper, we propose a motion planning algorithm for a mobile manipulator, and report several experimental results.

Design of a battery-powered multi-purpose bipedal locomotor with parallel mechanism

Abstract: This paper describes the design of a battery driven bipedal robot, which uses 6-DOF parallel mechanisms for its each leg. We have designed this considering a bipedal robot as the leg module that is sufficient for practical use as a multi-purpose locomotor of the robot system. This robot is applicable to various fields, such as medical, welfare and entertainment. In the design of the robot, we have reduced the weight to the maximum extent, taking advantage of the features of the parallel mechanism where the mechanism rigidity is high. Using the developed bipedal locomotor, dynamic walking with the step time of 0.96 sec/step and the step length of 0.2 m/step was conducted, and the effectiveness of its mechanism was confirmed.

Dynamic modeling of structurally-flexible planar parallel manipulator

Abstract: This paper presents a dynamic model of a planar parallel manipulator including structural flexibility of several linkages. The equations of motion are formulated using the Lagrangian equations of the first type and Lagrangian multipliers are introduced to represent the geometry of multiple closed loop chains. Then, an active damping approach using a PZT actuator is described to attenuate structural vibration of the linkages. Overall dynamic behavior of the manipulator, induced from structural flexibility of the linkage, is well illustrated through simulations. This analysis will be used to develop a prototype parallel manipulator.

Optimal design of CaPaMan (Cassino Parallel Manipulator) with a specified orientation workspace

Abstract: CaPaMan (Cassino Parallel Manipulator) is a 3-Degree Of Freedom spatial parallel manipulator that has been designed at the Laboratory of Robotics and Mechatronics, in Cassino. In this paper we present a formulation for an optimum design for CaPaMan architecture when the orientation workspace is suitably specified.

Design and Singularity Analysis of a 3-Translational-DOF In-Parallel Manipulator*

Abstract: In this work, we shall present a novel design of a 3-translational-DOF in-parallel manipulator having 3 linear actuators. Three variable length legs constitute the actuators of this manipulator, whereas two other kinematic chains with passive joints are used to eliminate the three rotations of the platform with respect to the base. This design presents several advantages compared to other designs of similar 3-translational-dof parallel manipulators. First, the proposed design uses only revolute or spherical joints as passive joints and hence, it avoids problems that are inherent to the nature of prismatic joints when loaded in arbitrary way. Second, the actuators are chosen to be linear and to be located in the three legs since this design presents higher rigidity than other. In the second part of this paper, we addressed the problem of kinematic analysis of the proposed in-parallel manipulator. A mixed geometric and vector formulation is used to show that two solutions exist for the forward kinematic analysis. The problem of singularities is also investigated using the same method. In this work, we investigated the singularities of the active legs and the two types of singularity were identified: architectural singularities and configurational singularities. The singularity of the passive chains, used to restrict the motion of the platform to only three translations, is also investigated. In the last part of this paper we built a 3D solid model of the platform and the amplitude of rotation due to the deformation of the different links under some realistic load was determined. This allowed us to estimate the orientation error of the platform due to external moments. Moreover, this analysis allowed us to compare the proposed design (over constrained) with a modified one (not over constrained). This comparison confirmed the conclusion that the over constraint design has a better rigidity.

Multiple degree of freedom substrate manipulator

Abstract: A system for manipulating a planar substrate such as a semiconductor wafer is provided. The manipulator is typically used in conjunction with an XY stage to focus and planarize a wafer with respect to a tool. The manipulator employs redundant actuators of different types and a control system that uses low-bandwidth, high efficiency actuators to provide low frequency forces and high-bandwidth, but less efficient, actuators to provide all other forces. The manipulator provides support and manipulation of a substrate while minimizing errors due to thermal distortion.

The synthesis of planar parallel manipulators with prismatic joints for an optimal, singularity‐free workspace

Abstract: The synthesis of three-degree-of-freedom planar parallel manipulators is performed using a genetic algorithm. The architecture of a manipulator and its position and orientation with respect to a prescribed workspace are determined. The architectural parameters are optimized so that the manipulator's constant-orientation workspace is as close as possible to a prescribed workspace. The manipulator's workspace is discretized and its dexterity is computed as a global property of the manipulator. An analytical expression of the singularity loci (local null dexterity) can be obtained from the Jacobian matrix determinant, and its intersection with the manipulator's workspace may be verified and avoided. Results are shown for different conditions. First, the manipulators' workspaces are optimized for a prescribed workspace, without considering whether the singularity loci intersect it or not. Then the same type of optimization is performed, taking intersections with the singularity loci into account. In the following results, the optimization of the manipulator's dexterity is also included in an objective function, along with the workspace optimization and the avoidance of singularity loci. Results show that the end-effector's location has a significant effect on the manipulator's dexterity. © 2002 John Wiley & Sons, Inc.