Patent GB-1243377-A (GB)
Title: Improvements in or relating to electronic control systems
Inventor: REDFEARN ROBERT NEVILLE
IPC: D06F34/08
Filed: 1969-01-22
Abstract: 1,243,377. Control of D.C. motors. FISHER-BENDIX Ltd. 14 Nov., 1969 [22 Jan., 1969], No. 3657/69. Heading H2J. [Also in Division G3] A washing machine drum is driven by a motor whose armature is regulated by a semi-conductor device receiving signals from a cyclically intermittent on-off control circuit C and a progressive control circuit D. Reversing and braking arrangements for the motor are actuated by relays. The circuit C is associated with an oscillator E, multivibrator G, and short duration oscillator F. The circuit D receives a spin signal from a programming unit, this signal being applied through diode D11 to capacitor C13 and then converted in an integrating circuit to a control signal for accelerating the motor from the washing speed through a distribution speed to a high-speed spin. The oscillator E comprises switch SCS1 which conducts at a predetermined voltage level on capacitor C6 whereby a reduced voltage appears across capacitor C10 of the controlled semi-conductor device. When switch SCS1 conducts, the device does not feed the armature. A signal from the switch SCS1 switches-off either transistor T2 or T3 and causes the bi-stable circuit G to go into its other stable state. When transistor T2 is non-conductive, a time delay capacitor C1 switches transistor T1 to energize relay RL1 and reverse the motor. While switch SCS1 is non-conductive a capacitor C8 is charged until switch SCS2 conducts to discontinue the feed to the motor. This circuit is disconnected when the programme unit separates connections STC, ST. The voltage developed across capacitor C13 is applied to transistor T4 whereby switch SCS1 conducts throughout the operation of the circuit D. Transistor T4 ensures that relay RL1 is operated during operation of the circuit D, but at other times the transistor T4 is non- conductive. The voltage on capacitor C13 is also applied to transistors T5, T6, T7, an integrating base input circuit for the transistor T7 comprising capacitor C12 and resistor R37 which is adapted to be shunted by normallyclosed contacts RL1/2 to disable the circuit D if the relay RL1 has not been operated. The transistor T7 provides a progressively increasing voltage, a limited voltage being applied to the semi-conductor device through resistors R33, R28 so that the motor accelerates slowly to a distribution speed. A Zener diode Z2 is introduced by contact ALL of the programme unit to hold motor at this speed. Otherwise, the non-limited progressively increasing voltage at the emitter of the transistor T7 is fed to the base of transistor T6 which conducts when a bias is overcome to reduce the voltage-drop across collector load resistor R29 of transistor T5. This voltage is fed to a tachometer circuit T which provides an alternative input to the semi-conductor device to provide a medium speed. As the progressive voltage further increases, a Zener diode Z1 breaks down to reduce the rate of acceleration. A contact HS of the programme unit disables this circuit. The circuit T controls the motor speed by offsetting the progressive voltage, since the tachometer diverts current through diode D7. A diode D6 provides current limitation. On failure of the supply, capacitor C12 discharges to reduce the speed, the capacitor C1 holding the relay RL1 for a period to allow the field to collapse before the motor connections are reversed. The semi-conductor device for energizing the motor comprises a buffer stage and an oscillator which supplies firing pulses in antiphase to two controlled rectifiers in a bridge circuit with a pair of diodes. The rectifier bridge feeds its output through change-over contacts to reverse the armature or field connections. For braking the motor is connected to a load resistor. An interlock solenoid holds the door of the washing machine until the motor reaches a low speed.