ARRANGEMENT FOR CONTROLLING THE SPEED AND POSITIONING OF AN ELECTRIC MOTOR

A direct-current electric motor (29) used for, for example, positioning a printing device in an office machine, is controlled by an arrangement comprising a microprocessor (40) which causes the motor digitally to perform accelerations and/or decelerations to maintain it close to a desired speed programmed in relation to the distance to be completed. Control between the actual speed of the motor and the desired speed is effected utilizing the timing signals (FTA, STB) generated by a transducer (35) connected to the motor. During a first phase, the microprocessor compares the times taken to complete a series of angular steps of rotation, the steps following a schedule of decreasing size with stored reference times and effects accelerations and decelerations of durations proportional to any discrepancies. Once the motor is near enough to its target position to be on a monotonic segment of one of the timing signals (FTA) which is sinusoidal, control switches to a position feedback loop bringing the motor to a standstill with FTA zero.