Robot Modeling and Control, 2nd Edition

CHAPTER 8INDEPENDENT JOINT CONTROL

8.1 Introduction

The control problem for robot manipulators is to determine the time history of joint inputs required to cause the end effector to execute a commanded motion. The joint inputs may be joint forces and torques, or they may be inputs to the actuators, for example, voltage or current inputs to the motors, depending on the model used for controller design. The commanded motion is typically specified either as a sequence of end-effector positions and orientations, or as a continuous path.

There are many control techniques and methodologies that can be applied to the control of manipulators. The particular control method used can have a significant impact on the performance of the manipulator and consequently on the range of its possible applications. For example, continuous path tracking requires a different control architecture than does point-to-point motion.

In addition, the mechanical design of the manipulator itself will influence the type of control scheme needed. For example, the control problems encountered with a Cartesian manipulator are different from those encountered with an elbow manipulator. This creates a so-called hardware/ software trade-off between the mechanical structure of the system and the architecture/programming of the controller.

Technological improvements are continually being made in the mechanical design of robots, which in turn improves their performance potential and broadens their range of applications. ...