Workspace Of Parallel Mechanism Research Articles

Design and Analysis of a Flexible, Elastic, and Rope-Driven Parallel Mechanism for Wrist Rehabilitation.

This paper proposes a bionic flexible wrist parallel mechanism to simulate human wrist joints, which is characterized by a rope-driven, compression spring-supported hybrid mechanism. Specifically, to realize the movement of the wrist mechanism, a parallel structure is adopted to support the mobile platform and is controlled by a cable, which plays the role of wrist muscles. Because the compression spring is elastic, it is difficult to directly solve inverse kinematics. To address this problem, the external force acting on the moving platform is firstly equivalent to the vector force and torque at the center of the moving platform. Then, based on inverse kinematic and static analyses, the inverse motion of the robot model can be solved according to the force and torque balance conditions and the lateral spring bending equation of the compression spring. In order to verify the proposed method, kinematics, statics, and parallel mechanism workspace are further analyzed by the software MATLAB. The obtained results demonstrate the effectiveness and feasibility of the designed parallel mechanism. This work offers new insights into the parallel mechanism with flexible joints in replicating the movements of the human wrist, thus promoting the development of rehabilitation robots and rope-driven technology to some extent.

Determining the maximal singularity-free circle or sphere of parallel mechanisms using interval analysis

SUMMARYThis paper proposes a systematic algorithm based on the concept of interval analysis to obtain the maximal singularity-free circle or sphere within the workspace of parallel mechanisms. As case studies the 3-RPR planar and 6-UPS parallel mechanisms are considered to illustrate the relevance of the algorithm for 2D and 3D workspaces. To this end, the main algorithm is divided into four sub-algorithms, which eases the understanding of the main approach and leads to a more effective and robust algorithm to solve the problem. The first step is introduced to obtain the constant-orientation workspace and then the singularity locus. The main purpose is to obtain the maximal singularity-free workspace for an initial guess. Eventually, the general maximal singularity-free workspace is obtained. The main contribution of the paper is the proposition of a systematic algorithm to obtain the maximal singularity-free circle/sphere in the workspace of parallel mechanisms. The combination of a maximal singularity-free circle or sphere with the workspace analysis by taking into account the stroke of actuators, as additional constraint to the latter problem, is considered. Moreover, the center point of the circle/sphere is not restrained to a prescribed point.

The Research about Parallel Mechanism Workspace for Quenching

To research 3-DOF parallel mechanism institutions applying to the process of plasma arc surface strengthening, the author establishes an inverse kinematics of institutions mathematical model, and then, basing on its structural constraints and using the boundary finding, draws the workspace. It has guiding significance for the establishment of robotic the plasma arc surface strengthening process.

Determination of Singularity-Free Zones in the Workspace of Planar Parallel Mechanisms with Revolute Actuators

The singularity-free workspace of parallel mechanisms is important in the trajectory planning and the kinematic design of the mechanisms. The planar parallel mechanism with revolute actuators, which the expression for the singularity locus and the algorithms for determining the singularity-free zones involve both the Cartesian and the joint variables, has been studied in the paper. Algorithms are proposed here to simplify the determination of the singularity-free zones in Cartesian space. The methodology and procedures for determining the singularity-free zones of planar parallel mechanisms with revolute actuators are introduced. The numerical results show that the simplified algorithms and the techniques are correct and efficient in determining singularity-free zones in the workspace of planar parallel mechanisms.

Workspace Analysis of New Type Parallel Mechanism with Serial Input

A new 4 DOF parallel mechanism with serial input limb is presented ——2UPS-RPU parallel mechanism, the limb with serial input is a less contrained active branched-chain,the number of its DOF is less than six,that is to say,the limbs not only transmitting driving force but also constraint force at the same time.Compared with traditional parallel mechanisms,the mechanism with serial input has greater number of DOF than the number of limbs and don’t lose the property of parallel mechanism. The inverse solutions to positions of the mechanism are modeled by inverse kinematic analysis in this paper, then the constraint conditions are established according to factors influencing the workspace of parallel mechanism,such as the limits of the hinge angle and the parallel link length.The workspace of 2UPS-RPU parallel mechanism can be obtained by using exetreme-boundary numerical algorithm in Matlab,the volume of workspace can be quantified by means of computation,and analyzing the impact of rod length ,circumradius of moving and fixed platform and motion pair rotation angle on the workspace.

Workspace Analysis and Simulation of 3-PCR Parallel Mechanism

Inverse position equations of 3-PCR parallel mechanism were obtained by coordinate conversion method, based on the influence factors to the workspace of parallel mechanism, workspace volume under a certain size was worked out with method of polar coordinates boundary searching. According to mathematical model, using MATLAB software, solid figure and cross-section diagram of the mechanism in a certain range of size were presented. Finally, characteristics of workspace were analyzed through diagrams. Workspace analysis can provide necessary preconditions for the design and manufacture of parallel mechanism.

GEOMETRIC OPTIMIZATION OF PLANAR 3-RPR PARALLEL MECHANISMS

To pursue the maximal singularity-free workspace of parallel mechanisms is a very important concern for robot designers. This paper focuses on the case of planar 3-RPR parallel mechanisms. First, a relatively simple singularity equation of any point on the platform is derived. The obtained singularity equation shows that the singularity locus of any point on the platform is a circle of the same size, as long as the base and the platform are similar triangles. Furthermore, the three centres of the workspace circles lie exactly on the singularity circle. With these useful observations, the singularity-free workspace as well as the maximal leg length ranges can be determined. For a base of unit area, it is found that robots with equilateral triangle base and platform can obtain the maximal singularity-free workspace. Three case studies demonstrate this observation. Finally, a procedure for this kind of robot geometric design is provided.