Design of a Computer Controlled Manipulator for Robot Research

Abstract

The purpose of this paper is to describe the Jet Propulsion L aboratory Robot Research Project's manipulator, including the rationale behind the design and the detailed design trade - offs that were made. It is intended to assist ot her wor kers in Artificial Intelligence ( AI) w h o need to develop manipulators for their own use. A discussion is presented of the constra int s and requ irements imposed on th e manipulator which led to the basic design, which was developed by Stanford Uni vers it y's Artificial Intelli gence Project. Furth er, detai l is pres en ted on the implementation of the basic conf igur ation. The end result is a man i pulator which reproduces th e flexibility and speed of a human arm. The manipulator is designed t o be integrated with a vehicle and is complete ly computer controlled. Human comman ds are inje c ted only a t the gross instruction level, with a digital computer generating th e contro l leve l commands. The JPL requirements are for the manipulator t o pick up irregular objects from the laboratory working area , or surface, and move them t o an arbitrary position e ither on or o ff the veh icl e, while avoiding any obstacles. The manipulator ( Fig. l) has 6 degrees of freedom whic h allow the grasping device (h and ) to be placed in any arbitrary position with great flexibility. Th e joints from the base to the hand co nsist o f two rotary joints, one linear joint a nd three rotary joints (2R, lL, 3R using the nomenclature of Ref. 1). This allows the hum an waist, shoulder, arm and wrist motions to be reproduced. Manipulator reach is a maximum of 52" and an object of abou t 5 pounds may be lifted. The manipulator may reach an ob je ct in any part o f a sphere that is not occup ied (i. e. , by the vehicle, floor, etc.). System resp onse allows a maximum motion to be accomplished in about 5 seconds. P ower is supplied by 6 permanent magnet DC torque motors geared directly to each link. For th e first four inner rotary joints, harm on i c drive gearing is used, w it h rack and pini o n drive for th e linear joint. For the o ut er rotary joint, spur gearing is used. DC power is provided through analog DC amplifiers t o minimize electrical n oise. Analog position and rat e fe edback inf orma ti on is provided. B rakes are used in each joint to pr ovide holding torque.