Delay compensation in a dual-rate cascade visual servomechanism

The paper presents a simple technique for a compensation of a one-sampling-period delay in the outer (position) loop in a cascade visual servomechanism with the inner feedback loop taking care of a velocity. The result presented in the paper is mainly relevant for visual servoing applications, since the velocity sensors such as tachometers or gyros usually achieve much higher sampling rate compared to computer vision systems playing the role of position sensors. The technique is based on the concept of a modified Smith compensator wherein the undelayed output of a mathematical model is replaced by a measured value of a signal from the inner loop. Casting this intuitive solution as a special instance of a theoretical methodology not only gives an insight but also suggests a generalization based on a multirate estimation theory, which might offer yet some more improvement.