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Dc Motor Servo System

IP.com Disclosure Number: IPCOM000099471D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 3 page(s) / 71K

Publishing Venue

IBM

Related People

Jaw, ACS: AUTHOR [+4]

Abstract

A low-cost, reliable servo system for driving a constant throughput mechanism is attained by using a brush-type DC motor with constant on-time pulses to maintain optimum velocity through sampled control by a shared microprocessor. The DC motor receives drive pulses of constant on-time or width, but the frequency of application varies according to the encountered load. Since the motor integrates the applied pulses, its input power and velocity are controlled by the frequency- modulated drive signal.

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Dc Motor Servo System

       A low-cost, reliable servo system for driving a constant
throughput mechanism is attained by using a brush-type DC motor with
constant on-time pulses to maintain optimum velocity through sampled
control by a shared microprocessor. The DC motor receives drive
pulses of constant on-time or width, but the frequency of application
varies according to the encountered load.  Since the motor integrates
the applied pulses, its input power and velocity are controlled by
the frequency- modulated drive signal.

      The overall system is shown in Fig. 1. The driver circuit is
shown in Fig. 3A, in which a chopper type of driver uses transistors
1 and 2 to control the current to motor 3.  A motor drive signal from
a microprocessor fires single shot 4 that determines the width of the
drive pulse. An on-time compensation network, including capacitor 5
and voltage divider resistors 6 and 7, varies the single shot on time
slightly to compensate for motor supply voltage fluctuations.

      Motor velocity is monitored by a stationary magnetic sensor
adjacent to a pair of magnets on a suitable output shaft of the
driven mechanism.  This arrangement produces two pulses per
revolution, and the mechanical inertia requires only infrequent
sampling by the shared microprocessor.  The microprocessor makes
frequency adjustments over a twelve-step range.  The small on-time
pulse-width adjustment in response to the supply voltage level
assists in keeping...