PULSE RATE CONTROL MOTOR SPEED CONTROL SYSTEM WITH FEEDBACK

摘要

1342849 Automatic control of speed CUTLER-HAMMER INTERNATIONAL FINANCE Inc 22 Feb 1972 [22 Feb 1971] 8089/72 Heading G3R An electric motor is energized with constant width pulses, the space between the pulses being determined by a capacitor circuit which is charged during the "on" pulses and discharges initially at a predetermined rate and then at a rate determined by the back e.m.f. of the motor so that the total "off" time depends upon motor speed which is hence kept constant. In the embodiment a shunt or permanent magnet field motor A is energized from a D.C. source via switching transistors Q4, Q5 which are turned on by Q2 during the charging of the capacitor C1 from a Zener diode regulated source 6. Charging ceases when a unijunction transistor Q1 conducts and discharge begins at a relatively slow rate. A further transistor Q3 has been conductive during this time so that point 12 is substantially at earth potential. The "on" pulse also charges a further capacitor C2; at the end of this pulse C2 commences to discharge via R8 at the predetermined rate until its voltage drops below that of the back e.m.f. Diode D3 then conducts and slows down the rate of discharge of C2. When the voltage on it is insufficient to maintain Q3 in a conducting state this turns off and rapidly completes the discharge of C1 by raising the potential at 12, thereby turning off Q1 and causing the cycle to repeat. Thus, the "off" time depends upon the discharging rate of C2 and hence upon back e.m.f. A bias circuit R7 ensures adequate control at low speeds and speed adjustment is made by potentiometer 16.