Adaptive Pulse Width Control of Structurally Flexible Systems

1. Motivation The performance of manufacturing machines of all sorts depends upon precise control of the position of some sort of end-effector. Mechanical friction has forever been the thorn in the side of the developers of these machines [1,4]. Consider the simplest of all possible cases, the problem of controlling the position of the rigid-body plant shown in Figure 1. Except when the mass m and the stiction and Coulomb friction levels are known exactly, feedforward plus proportional-derivative feedback control of the position of the mass, y, even when y is measured exactly, results in a steady-state position error. This error occurs when the stiction sticks the plant at a position close enough to the desired position that the proportional gain of the controller multiplied by the position error is not large enough to overcome the stiction force. This error can be reduced by increasing the proportional feedback gain, but, in an application to a physical plant with flexible-body dynamics, the requirement for closed-loop stability places an upper bound on the value of this gain [7,19].