DESIGN AND ANALYSIS OF A 6-AXIS REVOLUTE JOINT ROBOT

Abstract

This project sets out to design and build a 6-axis robot. It gathers experience on the technical know-how, using CAD/CAM to aid the design and building processes. It also provides a platform for the many academic interests on robotics that may arise in the future. The 6-axis manipulator first took its shape on the CATIA solid modelling package. This package allows its inertia, weight and joint limits to be predetermined with ease and with accuracy of ±15 %. The experience of sizing motors for the joints, selecting suitable tolerance for the mechanical hardware and finding means to minimise backlashes in the motion transmission has been acquired in the course of this project. A 3-axis wrist with concurrent axes was designed and built for the robot. The kinematics of this wrist is such that it simplifies the mathematical analysis.

The robot controller was built with a dedicated architecture based on the MC 6809 processor. It is a local controller and a motion control module, the host controller being the MicroVAX. The communication facilities were designed such that they allow maximum sharing of information within the local controller modules and between the local and host controllers. A simple library of motion control and planning software was written to support the hardware for future use as standard routines.

With this hardware, experiments showed that the sampling rate in the control loop of a joint cannot go beyond I00 Hz without encountering limitation in computing speed. Preliminary control performance analyses were carried out on the robot base axis. With experimental results gathered, and from conclusions provided by computer simulation studies, a proportional controller function was derived.

Recommendations were also included for further research to develop faster and more efficient control algorithms and to implement active force control strategy.