Analysis of a 6-DOF redundantly actuated 4-legged parallel mechanism

Abstract

In this paper, we propose a new 4-legged 6-DOF redundantly actuated UPS parallel mechanism. Kinematics, singularity and dynamics analyses of the proposed mechanism are addressed. Inverse kinematics has a closed-form solution, whereas the forward kinematics has a semi-closed form solution. Also, the Jacobian matrix has been determined using the concept of reciprocal screws. Using the principle of virtual work and minimum norm method, a general formulation for the inverse dynamics of redundantly actuated parallel manipulator is presented.Moreover, the proposed redundant mechanism has been compared with a similar but nonredundant mechanism in three aspects: reachable points, and actuation forces under static and dynamic conditions. We show that the redundancy decreases singular points, and dramatically reduces the actuators' forces and torques.

Exploiting Higher Kinematic Performance - Using a 4-Legged Redundant PM Rather than Gough-Stewart Platforms

“…A rotary actuator and a linear actuator are used to actuate each leg. The rotary actuators, whose shafts are attached to the lower parts of the linear actuators through the universal joints, are placed on the corners of the fixed platform (Abedinnasab & Vossoughi, 2009;Aghababai, 2005). The spherical joints connect the upper parts of the linear actuators to the moving platform.…”

“…Performance comparison between 3-legged mechanism, 4-legged mechanism, Stewart 6-6, and Stewart 3-6 6.3 Singularity analysis of 3-legged and 4-legged mechanisms Several types of workspace can be considered. For example, the 3D constant orientation workspace, which describes all possible locations of an arbitrary point P in the moving system with a constant orientation of the moving platform, the reachable workspace (all the locations that can be reached by P), the orientation workspace (all possible orientations of the end-effector around P for a given position) or the inclusive orientation workspace (all the locations that can be reached by the origin of the end-effector with every orientation in a given set) (Abedinnasab & Vossoughi, 2009). Out of those types, we have used the inclusive orientation workspace, where for every position in a fixed surface, the moving platform is rotated in every possible orientation to determine if that configuration is singular or not.…”

A Study on Vibrations of Hexarot-Based High-G Centrifugal Simulators

“…Newton-Euler approach, [1][2][3][4][5][6][7] Euler-Lagrange approach, [7][8][9][10][11][12] and the principle of virtual work. [13][14][15][16][17][18] All the approaches that use classical mechanics result in equivalent dynamic formulations as they are describing the same manipulator; however, the obtained equations have different complexities and applications. For example, the Newton-Euler approach considers the internal forces and moments applied to different parts of the manipulator.…”

Performance Evaluation of Redundant Parallel Manipulators Assimilating Motion/Force Transmissibility

“…Actuation redundancy consists of two categories: the activation of passive DOFs in the joint space, and the introduction of new and active DOFs in the joint space [15]. Actuation redundancy in PKMs can decrease or eliminate singularity, increase manipulability [15], increase payload and acceleration of the mobile platform [16], further improve the efficiency and reliability by eliminating actuator singularity or force-unconstrained configurations [4,17], and improve the repeatability by controlling the direction of the internal forces to reduce the effects of joint backlashes [18]. Actuation redundancy can improve the transmission properties and yield an optimal load distribution among actuators by increasing the homogeneity of force transmission and manipulator stiffness [16].…”