A novel nonlinear compensator based on digital acceleration control

In this paper, we propose two nonlinear compensators for controlling mechanical systems. The high nonlinearity of typical multi-body mechanical systems arises form the effects of gravity, friction, joint interactions, and other factors. Such non-linearity limits the accuracy of the proportional-integral-derivative (PID) control, but does not affect the integrity of the digital acceleration control (DAC). Previously, we proposed a control system combining PID and DAC (PID-DAC) and confirmed its validity. However, PID-DAC is of limited accuracy when controlling an object with high acceleration. To solve this problem, we modified DAC to compensate for nonlinear effects only. Essentially, the new compensators compensate for nonlinearity while PID controls the object position. The effectiveness of the proposed methods is investigated through experiments on a two-link robot manipulator. The controller performs well in the presence of nonlinear forces, and is easily applied to PID to enhance object control.