Singularity Avoidance and the Control of an Eight-Revolute-Joint Manipulator

Abstract

The "optimum" 6R manipulator's singular configurations are used to develop the "best" 4R orientation and 4R regional structures for singularity avoidance. For comparison with the "best" 4R regional structure, the kinematics of a second 4R regional structure is explored. Conceptually, the control algo rithms for the 4R orientation and two 4R regional structures begin in primary mode with three actuator screws apiece. In primary mode the traditional position kinematics approach is used. However, when either the orientation or regional struc ture has difficulty following its Cartesian trajectory, control for that structure goes into secondary mode, where the redundant actuator is called on. The algorithms maintain a sixth-order screw system for an 8R manipulator with bounded actuator rates and well-behaved actuator values. The numerical com putations for an 8R manipulator are comparable to those for the "optimum" 6R manipulator and can be implemented in real time.