Dynamic effects in visual closed-loop systems

In this paper we argue that the focus of much of the visual servoing literature has been on the kinematics of visual control and has ignored a number of fundamental and significant dynamic control issues. To this end the concept of visual dynamic control is introduced, which is concerned with dynamic effects due to the manipulator and machine vision sensor which limit the performance. These must be explicitly addressed in order to achieve high-performance control. The paper uses simulation and experiment to investigate the feedback control issues such as the choice of compensator, and the use of axis position, velocity or torque controlled inner-loops within the visual servo system. The limitations of visual feedback control lead to the investigation of target velocity feedforward control, which combined with axis velocity control, is shown to result in robust and high performance tracking.