GB1522522A - Electric windscreen wiper systems - Google Patents

Abstract

1522522 Automatic control of D.C. motors GENERAL MOTORS Ltd 30 April 1976 [29 May 1975] 23387/75 Heading H2L A windscreen wiper system comprises a pair of D.C. motors 28, 30 which drive respective wiper arm and blade assemblies and are controlled by respective transistor switching circuits 46, 48 and 52, 54, whose transistors 46, 52 are controlled by the outputs of similar operational amplifiers 34, 38 to whose inputs are applied signals from potentiometers 24, 26 having tappings notionally movable with respective rotary members driven by the respective motors, the signals thus varying in accordance with the motor positions and speeds and controlling the motors to run in synchronism, the arrangement being such that, when the motors are in the same position, both amplifiers 34, 38 produce outputs to switch on their respective motors and, if one motor (say 28) runs faster than the other, then the signals to amplifier 34 differ to cause it to switch off transistors 46, 48 and motor 28, which slows down until motor 30 catches up to restore the signal equality at amplifier 34 and so allow it to switch on motor 28. Each potentiometer 24, 26 comprises an annular resistance track (14) located between and connected at respective ends to annular contact tracks (12, 16), the three tracks being carried on one face of a gear wheel (10) driven by the motor and being connected to the positive and earth terminals and to the output to the amplifiers by means of reflective contact arms (20, 18, 22), Fig. 1 (not shown). The invention may be applied to control more than two motors, for example three motors whose operational amplifiers are each supplied with the signal from its respective motor and a signal from a different one of the other two motors.