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Digital Speed Control of DC Motor

IP.com Disclosure Number: IPCOM000052062D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Sjostedt, J: AUTHOR [+2]

Abstract

A circuit is provided where the motor speed is controlled by a differen amplifier having a first input from a motor tacho-generator and a second input from a digitally stepped counter. The amplifier compares and synchronizes the motor speed with the electronic frequency of the input signals to the counter. The circuit provided is preferably used to synchronize the clock rate of an optical character reader system with the document driving speed.

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Digital Speed Control of DC Motor

A circuit is provided where the motor speed is controlled by a differen amplifier having a first input from a motor tacho-generator and a second input from a digitally stepped counter. The amplifier compares and synchronizes the motor speed with the electronic frequency of the input signals to the counter. The circuit provided is preferably used to synchronize the clock rate of an optical character reader system with the document driving speed.

In the figure, a digital tacho-generator 1 feeds a signal FG to a zero-crossing detector A2. The pulse length of the output signal TG from A2 defines the speed of the motor 2, and TG enters a differential amplifier A1. The leading edge of the motor speed signal TG also enters a counter 3 as a load pulse over a gate G1. A latch LTH1 is used to open the gate G1 only for the leading edge of the TG signal. The counter is preset by a digital load value and stepped by a clock pulse FC. The carry output line 4 of the counter resets a second latch LTH2 which is set by the TG leading edge signal. The output of the latch LTH2 is gated through a start gate G2 and provides, as a signal TC, the second input to the differential amplifier A1.

The difference in pulse length of TC and TG generates a differential input voltage to A1. If TG is longer than TC, the output voltage from A1 to two transistors Q1 and Q2 increases and the motor voltage WM increases. If TG is shorter than TC, motor voltage WM decrea...