14 QP Based Encoder Feedback Control

Given they have more DOF than required to perform a given end-effector primary task, redundant robot manipulators can achieve subtasks such as obstacle avoidance, fault tolerance, repetitive motion planning, joint limits, and singularity avoidance. Existing optimal control methods for path planning and control of robot manipulators can be roughly categorized into two types: First, optimal control methods that can handle each robot link separately without regard to robot dynamics by computing set points for low-level (e.g., position- or velocity-level) single-input single-output controllers; Second, optimal control methods that can handle the robot directly by considering robot dynamics and computing motor torques for high-level controllers, specifically, torque-level controllers. The former methods pertain to the description of motion (position, velocity, acceleration, etc.). These methods can perform well if the desired motion is not too fast and does not require large acceleration. The latter methods are related to the explanation of motion in terms of forces and torques and are applicable to numerous practical manipulators. The level at which path planning and control is performed may depend on the type of robot controller. For example, if joints are driven by positionor velocity-controlled servo motors, then a path planning and control scheme at the position or velocity level will generally suffice. However, if controllers can be driven by joint torque or actuator force, then the path planning and control scheme will be designed at the torque level. The computer simulations and experiments in this chapter are based on a six-DOF planar redundant robot manipulator.The manipulator is operated and controlled by pulse signals transmitted from the host computer. Manipulator joints are operated by position- and velocity-controlled servo or stepper motors, and the resultant joint variables (i.e., joint angle and joint velocity) should be converted into pulse per second (PPS) for manipulator control. In consideration of these points, the former optimal control method, which is better suited and much simpler than the latter methods, is exploited to control the six-DOF planar redundant robot manipulator.