Open-loop control

The initial stages of system design are concerned with steady-state performance; the choice of stepping motor and drive circuit is mainly dictated by the maximum tolerable position error and the maximum required stepping rate. When this task of selection is completed, the designer must consider how the motor and drive are to be controlled and interfaced to the remainder of the system. The open-loop control schemes discussed in this chapter have the merits of simplicity and consequent low cost. Digital phase control signals are generated by the microprocessor and amplified by the drive circuit before being applied to the motor. Although the system illustrated receives its phase control signals from a microprocessor a number of alternatives are presented later in this chapter.