The Advantages of Velocity Control for Reactive Robot Motion

At the hardware level, servo drives are traditionally controlled in the position or velocity domain. Frequently, roboticists do not recognize the significance of selecting one control domain over the other. This paper argues that velocity control is the clear choice for reactive trajectory modification and online motion planning. Velocity control provides smoother motion, is more suitable for low control frequencies, more robust to control signal variation, and it reduces collision forces more effectively. The primary advantage of position control is inherent safety with regards to signal delays. To support these points, this paper presents mathematical, graphical and experimental evidence. New experimental results explore the robustness of velocity control with regards to low-frequency control signals and signal delay. The experiment is based on a cooperative manipulation task performed with stiff industrial manipulators. Position and velocity control are also directly compared using a one-DOF linear actuator force control task using total work performed as a performance metric.