Kinematic and dynamic accuracy of spherical mechanisms

Abstract

Abstract. Among parallel robots, spherical robots occupy an important place. Most applications of spherical manipulators can be found in orienting devices, such as camera orienting and medical instrument alignment. A spherical parallel robot is, in general, made up of the base platform and the moving platform. This mobile platform and base are connected by three equally spaced legs, each consisting of revolute joints only. The axes of all joints intersect at a common point, which is called the center of rotation. The motion of the moving platform is confined on the surface of a sphere centered at the rotation center. A spherical parallel robot provides 3 degrees of freedom of pure rotations. These robots have been the subject of many papers dealing with the structure, the problems of position and velocity, workspace modeling, singularity analysis, and some problems with the dynamic analysis. However, not all the important problems have been solved. These concern the problem of accuracy. This paper presents accuracy of the spherical parallel. In the considered spherical manipulator, each leg consists of five kinematic pairs. The kinematic accuracy is determined on the kinematic problem. The dynamic accuracy is estimated on the equation of motion. Examples of solving the problem of determining the positioning error of the output level are presented.

Optimal design and experiments of a novel bobbin thread-hooking mechanism with RRSC (revolute–revolute–spherical–cylindrical) spatial four-bar linkage

“…Crank 0 rotates clockwise, and the motion trajectory of the looper tip P is formed under the synthetic motion of axial movement motion and radial oscillation motion of rocker 2. Therefore, the oscillation angular displacement θ 3 and movement displacement S 2 of rocker 2 is solved, and the displacement equations of the looper tip P is established (Liu et al, 2019;Vo et al, 2022;Rodríguez-González et al, 2020;Bai et al, 2021;Mohan and Corves, 2017).…”