A system for partitioned control of a robot

Abstract

Many robots contain a microprocessor controller per axis, linked to a supervisory minicomputer contained within the manufacturer's package. In the paper it is proposed that a defined bus structure and protocol can give public access to similar controllers, enabling the supervisory and geometric computations to be performed on a standard desk-top machine of the current commercial type. The proposed protocol allows for evaluation of a cubic interpolation function in the controller cards, so that a fit can be made to two past and two future sets of target co-ordinates. A command coding scheme is suggested which will give close liaison between controllers and a supervisory computer. Design details are given of an ongoing practical project based on adding such a controller to the mechanical portion of the Mitsubishi RM-501 robot. Kinematic equations are derived, showing the restriction of the 5-axis robot. Expressions are found for evaluating coefficients to be used in a simple recursive computation, giving an exact cubic fit to a succession of four target points. An outline is given of the hardware structure of the interface, of the handshake which synchronises the movements of the various axes, and of the interrupt levels assigned to the controllers' tasks.