Output Feedback Tracking Controllers

All the position tracking controllers presented in Chapter 3 required fullstate feedback (FSFB). That is, the control implementation requires the measurement of the position and velocity of the mechanical system. Since the cost of implementing a FSFB controller for achieving position tracking would typically include the cost of motion sensors, this chapter addresses the problem of position tracking under the constraint of minimizing the sensor count (i.e., elimination of velocity measurements). Hence, we are motivated to investigate means of constructing velocity signal surrogates for use in closed-loop, position tracking control strategies, i.e., output feedback (OFB) controllers. A standard approach for removing velocity measurements is to apply the so-called backwards difference algorithm to the position measurements. Even though this method of eliminating velocity may provide reasonable performance, the use of this discrete-time velocity approximation is not satisfying from a theoretical viewpoint since the dynamics of the backwards difference algorithm are normally not included during the closed-loop stability analysis.