2017 Volume 6 Issue 4 Pages 278-285
This paper addresses the joint limit avoidance problem in kinematic control of redundant manipulators. A kinematically redundant manipulator has more Degrees of Freedom (DOFs) than are required to perform a given task. An inverse kinematic problem for such a manipulator admits an infinite number of solutions. In its kinematic control, by utilizing the redundant DOFs of the solutions, we can compose a primary task in consideration of a constraint condition. We usually select one of the solutions by introducing a Performance Criterion Function (PCF). The PCF performs a secondary task that has no effect on a primary task. Thus, we can introduce, e.g., joint limit avoidance as a secondary task to the design of a PCF. However, it is hard to perform joint limit avoidance in the case where a joint behaves in the close vicinity of the limit. In this paper, we propose a new PCF for avoiding joint limits. The main feature of the function is to admit the joint range of motion maximally. We adopt the proposed function in the gradient projection method to obtain the redundancy resolution. The effectiveness of the function is demonstrated by both numerical and experimental results. The differences among the proposed and conventional functions are also discussed.
