Nonlinear Direct Error Compensator for Visual Servo Trajectory Tracking Under Image Sensor Delay on a Moving Platform

In this article, a nonlinear direct error compensator (NDEC) control method is proposed to reject high-frequency nonlinear disturbances, for a visual servo trajectory tracking system on a moving platform with time delays. First, direct error compensation with finite tracking bandwidth is used in the position loop, complex disturbances induced by dynamic lag are counteracted. In addition, to address transient error spikes from velocity reversals and target lifting, a nonlinear saturation constraint-based compensation method is introduced in the velocity loop. Essentially, a saturation function is incorporated into the servo control law to reshape the amplitude of velocity errors and directly compensate for them, thereby enabling accurate trajectory tracking error regulation. Furthermore, to elucidate the saturation performance of the proposed compensator and the relationship between the filter bandwidth and system stability, the influence of the saturation function threshold is analyzed, following which the selection rules of parameters are also provided. Simulation and experimental results on a moving platform demonstrate that the NDEC scheme can be easily implemented and exhibits excellent performance in trajectory tracking and high-frequency disturbance rejection.