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Bidirectional PWM Motor Speed Control

IP.com Disclosure Number: IPCOM000074943D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Coburn, RL: AUTHOR [+3]

Abstract

This closed-loop motor speed servomechanism provides bidirectional rotation of direct current motor 1 utilizing pulse width modulation techniques.

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Bidirectional PWM Motor Speed Control

This closed-loop motor speed servomechanism provides bidirectional rotation of direct current motor 1 utilizing pulse width modulation techniques.

When forward rotation is desired, a command signal is provided on conductor 2 and switch 3 is closed. For reverse rotation, a command signal is provided on conductor 4 and switch 22 is closed. View B discloses the waveform on conductors 5, 6, and 7 for forward and reverse commands, time t0 designating the occurrence of such a command.

Assuming a command for forward rotation, the signal on conductor 5 goes positive at time t0. This voltage turns on transistor 8 and the resultant positive signal on conductor 7 causes servo amplifier 9 to draw current from negative supply 10 through resistor 11. The resultant voltage drop across resistor 11 drives power amplifier 12, causing the motor to be energized to rotate in a forward direction. Negative voltage feedback is provided by resistor 13.

A command for reverse rotation causes conductor 6 to go negative at time t0, as shown in View B. This voltage turns on transistor 14 and causes conductor 7 to go negative. This negative signal causes the servo amplifier 9 to draw current from positive supply 15 through resistor 16. Power amplifier 17 then energizes the motor for reverse rotation.

The motor shaft begins to rotate and after a small angular distance has been traversed, an output pulse appears from digital tachometer 18. These pulses occur each time the m...