device circuitale for the food of a motor to corren you still excited in series with dc pulse

摘要

1400845 Automatic control of speed ROBERT BOSCH GmbH 13 Oct 1972 [16 Oct 1971] 47230/72 Heading G3R [Also in Division H2] A motor control circuit for a D.C. series motor in a pedestrian controlled battery operated fork lift truck comprises a pulse generator including an operational amplifier operating as a relaxation oscillator for applying pulses having a controllable pulse duty ratio to a transistor switch for connecting the motor to the battery where the desired speed valve voltage is applied to the amplifiers non-inverting input and the back e.m.f. of the motor is applied to the inverting input after smoothing. As shown motor 11 is connected to battery 20 through transistor switch 18 and resistor 19 and its field windings, for reversible operation, are connected through their respective contacts 15, 16 to the other supply lead 24. The desired speed is set by potentiometer 25 which is fed to the non-inverting input of adder 26 and added to the motor voltage fed to the inverting input through a smoothing circuit including a capacitor (295) and a resistor (296). The resultant signal controls the mark/space ratio of pulses from generator 27 up to a 50% duty ratio when the pulse frequency is decreased and the mark/space ratio further increased. Resistors (292, 293) in the feedback path provide a limiting arrangement for motor speed allowing the top speeds to be condition dependent. Two switching circuits 40, 30 are provided for short-circuiting the error signal and the desired speed signal respectively. The circuit 40 provides motor over-current protection and measures the voltage drop across resistor 19. Switch 31 is operated by a brake switch (52) or collision switch 34 and requires that selector 25 is returned to zero before bi-stable 31 can be reset. In the case of collision switch operation the motor is automatically reversed and made to run at slow speed in the opposite direction. A bi-metal switch (253) is used to shut down the arrangement by switch 32 if the germanium transistors used in switch 18 overheat. A battery voltage monitoring circuit (36) is provided to adjust the operating point of the transistor in switch 32. Switch 32 also operates when the reversing switch is operated. Free-wheeling diodes 22, 21 are provided across the whole motor and across the motor armature respectively, the latter is provided so that reverse current braking can be used. The current supply circuit for the control system comprises a blocking oscillator.