Special configurations of robot-arms via screw theory

SUMMARY Part 1 of the paper* was concerned with the Jacobian of serial robot-arms and its matrix of cofactors; part 2 emphasizes the end-effector's velocity characteristics as affected at special configurations. The displacement about a ‘fixture-point’ is extended dually to a ‘fixture-plane’, and then to a ‘fixture-line’. These fixture-elements serve to highlight the prolixity of special configurations. Reciprocal screws lead to a complete survey of how the end-effector can ‘twist’ when one freedom is lost; extension to loss of more freedoms is explained. Then the fixture-elements are given elementary displacements that allow common requirements to be studied with the minimum of complications. Further investigation is thought to have promise for robot-control.