GB1440371A - Electric motor controlling system - Google Patents

Abstract

1440371 Automatic control of lifts HITACHI Ltd 13 Aug 1973 [14 Aug 1972] 38297/73 Heading G3N [Also in Division H2] A light system has high speed and low speed motor sections driving the lift and energizable to give respectively motoring and braking torques and controlled such that an improved response is obtained when approaching the rest position by providing both motoring and braking torques together. In the arrangement shown the lift is driven by induction motors HM and LM having lower and higher pole numbers respectively. The high speed motor is energized through primary voltage controller WR and the low speed motor is energized either directly from the mains supply (for inspection shown running) or, when braking is required, from controllable rectifier arrangement VR. A tacho-generator mounted on the motor shaft provides an actual speed signal for comparison with a speed signal produced by a pattern generator. The comparators are biased at B1 and B2 whereby the torque curves of the two motors are made to overlap, see Fig. 4, and thus the system has high gain and thereby a high speed of response even at the zero point. An additional feedback of braking current CD is made to the comparators CP1, CP2 controlling the high speed motor. Around the zero speed condition both motors are simultaneously energized to provide oppositely directed torques as can be seen from Fig. 4. The pattern generator provides an increasing speed signal for acceleration, decreasing speed signal for deceleration and includes a priority circuit which passes the lower valued signal as its output. A positional detection arrangement comprising fixed sensors 91 and moving probe P provides a step output when decelerating. The two motors may be provided as a single structure with separate motoring and braking windings.