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.
['Tzu-Chen Liang', 'Jing-Sin Liu']
An improved trajectory planner for redundant manipulators in constrained workspace