Manoeuvring highly redundant manipulators

Abstract

A task based approach to the issue of redundant robots starts from thepremise that there are obstacles that cannot be removed from the working areaand which therefore must be avoided. This statement produces the requirement fora device with a certain degree of mobility, and stresses the need to ensure thatthe aim is twofold: reach the goal and avoid obstacles. But avoiding obstaclesis not the same objective as keeping as far away from an obstacle as possible;the primary goal is still to reach the target. In fact humans use soft contactto reach targets that are at the periphery of their reach. This soft distributedcontact has the effect of smoothing the surface of the object and hence there isan element of only being interested in obstacle detail at the appropriate scaleto achieve the task.

This paper describes a new approach to collisionavoidance based on using a global path finding algorithm, in this case usingLaplacian potential fields, in conjunction with a simple local geometricallybased algorithm for avoiding obstacles and maximising the use of manoeuvringspace in a manner which is not limited by digital computation resolution issues.This extra technique is in some ways analogous to the human soft contactapproach.

Three examples are presented to illustrate the robustness ofthe algorithm. In order to be able to compare results with other techniques, anenvironment measurement scheme is defined which gives an indication of thedifficulty of the trajectory being followed.