Most of the feedback algorithms used in current control systems are implementations of a proportional plus derivative (PD) control. In industrial robots, a local PD feedback control law is applied at each joint independently. The advantages of using a PD controller are the following:
On the other hand, there are some disadvantages of using a PD controller instead of the dynamic equations such as:
Some ideas have been suggested to enhance the usability of the local PD feedback law for trajectory tracking. One idea is to add a lag-lead compensator using frequency response analysis [1]. Another method is to build an inner loop stabilizing controller using a multi-variable PD controller, and an outer loop tracking controller using a multi-variable PID controller [9]. In general, using a local PD feedback controller with high update rates can give an acceptable accuracy for trajectory tracking applications. It was proved that using a linear PD feedback law is useful for positioning and trajectory tracking [3].