Experimental evaluation of feedforward and computed torque control

Trajectory tracking errors resulting from the application of various controllers have been experimentally determined on the MIT Serial Link Direct Drive Arm. The controllers range from simple analog PD (proportional-derivative) control applied independently at each joint to feedforward and computed torque methods incorporating full dynamics. It was found that trajectory tracking errors decreased as more dynamic compensation terms were incorporated. There was no significant difference in trajectory tracking performance between the feedforward controller using independent digital servos and the full computed torque controller. Implementing the model-based controller highlights the need for accurate control of joint torque, accurate joint position and velocity sensing, and adequate sampling rates