An improved trajectory planner for redundant manipulators in constrained workspace

Abstract

This paper studies the trajectory planning of redundant robots performing tasks within enclosed workspace. Configuration control of kinematically redundant manipulators using pseudo-inverse with null-space projection method is a well-known scheme. A switching objective function is proposed. We modify Liegeois' (1997) joint angle availability objective function so that the midpoints of each joint are switched at a series of pre-specified key path points for the end-effector to achieve. These key path points are planned beforehand according to the geometry of constrained workspace. The trajectory planning problem can then be viewed as a series of proper postures determination problems at key path points. The proper postures are determined using a combination of potential field method and elastic model method, which take into account the joint operating ranges and motion tendency of end-effector. A variable weighting technique to achieve the proper postures effectively is also presented. Simulations of a planar 8-link robot in constrained workspace illustrate the effectiveness of this approach.