Design of a computer controlled manipulator for robot research

The purpose of this paper is to describe the Jet Propulsion Laboratory 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 other workers in Artificial Intelligence (AI) who need to develop manipulators for their own use. A discussion is presented of the constraints and requirements imposed on the manipulator which led to the basic design, which was developed by Stanford University's Artificial Intelligence Project. Further, detail is presented on the implementation of the basic configuration. The end result is a manipulator which reproduces the flexibility and speed of a human arm. The manipulator is designed to be integrated with a vehicle and is completely computer controlled. Human commands are injected only at the gross instruction level, with a digital computer generating the control level commands. The JPL requirements are for the manipulator to pick up irregular objects from the laboratory working area, or surface, and move them to an arbitrary position either on or off the vehicle, while avoiding any obstacles. The manipulator (Fig.1) has 6 degrees of freedom which allow the grasping device (hand) to be placed in any a rbitrary position with great flexibility. The joints from the base to the hand consist of two rotary joints, one linear joint and three rotary joints (2R, 1L, 3R using the nomenclature of Ref. 1). This allows the human waist, shoulder, arm and wrist motions to be reproduced. Manipulator reach is a maximum of 52 and an object of about 5 pounds may be lifted. The manipulator may reach an object in any part of a sphere that is not occupied (i.e., by the vehicle, floor, etc.). System response allows a maximum motion to be accomplished in about 5 seconds. Power is supplied by 6 permanent magnet DC torque motors geared directly to each link. For the first four inner rotary joints, harmonic drive gearing is used, with rack and pinion drive for the linear joint. For the outer rotary joint, spur gearing is used. DC power is provided through analog DC amplifiers to minimize electrical noise. Analog position and rate feedback information is provided. Brakes are used in each joint to provide holding torque.