Pulse-width-modulating control of a nonlinear electromagnetic actuator

The performance of a fast, nonlinear, clapper-type electromagnetic actuator used in impact printing is controlled by real-time measurement and feedback. The objective is to regulate flight time, which is the time from start to actuation to impact. Toward this end, control is applied digitally via pulse-width modulation of a series of coil-driving pulses, which together propel the armature through its trajectory. Each pulse is modulated individually based on state-variable errors measured on its rising edge. The functional relationships between the measured state-variable errors and the required pulse-width modulations are derived systematically, using a computer-controlled method involving trial-and-error experimentation followed by statistical regression. The resulting control law accounts for both mechanical and electrical perturbations and is expressed in an analytic format that can be applied either by look-up tables or by direct computation. Using look-up tables, typical closed-loop operation is shown to achieve dramatic reductions in flight-time error when compared with open-loop operation. >