Compensation of trajectory tracking errors introduced by sampling in computer-control implementations of model-based robot control

Trajectory following control of robot manipulators requires the online evaluation of the robot dynamic model. It is known that the continuous (analog) implementation of model-based (also called inverse dynamics or computed-torque) control can provide perfect tracking under perfect knowledge of the robot dynamic model. The model describing the robot dynamic behavior is highly nonlinear and computationally complex. Its complexity necessitates online evaluation of the robot dynamic model digitally either via VLSI/hardware implementation or under computer (software) control. Digital implementations require sampling of robot states and zero-order-hold (ZOH) actuations which introduce trajectory tracking errors. Modeling errors further add tracking errors due to inexact cancellation of robot dynamics resulting in a still-coupled and nonlinear system. Modeling errors come from parameter errors as well as unmodeled dynamics