GB1317673A - Motor stop control system - Google Patents

Abstract

1317673 Control of D.C. motors INTERNATIONAL BUSINESS MACHINES CORP 28 May 1971 [22 June 1970] 17801/71 Heading H2J In order that a member e.g. a carriage for a selective printer, may be brought to rest in a specified distance irrespective of variations in the deceleration characteristic of its driving motor the motor is first braked until its speed has dropped to a predetermined value, is then allowed to "coast" for an automatically varied time and finally is braked again to standstill. When the carriage is a predetermined distance from a desired stopping point a stop signal is applied to a logic circuit (Fig. 3, not shown) which immediately initiates reverse energization of the motor (which is a D.C. printed circuit machine) and also starts a fixed time "reference single shot". A speed detector connected across a resistor (31) in series with the motor produces a signal when the speed has dropped to half its initial value. This terminates braking and also starts a "proportional single shot" device comprising a capacitor which charges until a second signal is applied when the reference single shot times out, whereupon the capacitor discharges at a fixed rate, e.g. at the same rate at which it was charged, and produces a signal to re-start braking when fully discharged. Thus, if deceleration is more rapid than normal, due to the motor being cold for example, the motor coasts for a longer period at half speed as shown in Fig. 5. In an alternative arrangement of the logic circuit (Fig. 6, not shown) account is taken of the possibility of the reference single shot timing out before half speed is reached. In this embodiment the motor is driven by pulses from an oscillator (32) applied through a variable duty cycle device (34). The initial braking is by continuous current and the second stage by pulses.