Drive apparatus
First Claim
1. A variable drive apparatus, comprising:
- a stepper motor having a rotor and a plurality of coils;
power supply means arranged to supply pulses to said coils in sequence to cause sustained rotation of said rotor;
means for modulating the width of said pulses for varying the power applied to said coils;
signal generating means for generating a variable rate signal;
signal producing means for receiving said variable rate signal and producing a first signal, the timing of which controls the timing of the centers of said pulses, and a second signal, which controls progress through said sequence, the first and second signals having a predetermined timing relationship to each other and each having a timing and a frequency determined by said variable rate signal;
means to supply a control signal having a timing in accordance with the phase position of said rotor; and
means to enable the generation of the variable rate signal by said signal generating means to be effected by said control signal so as to maintain the centers of said pulses substantially coincident with the positions of the rotor relative to the coils at which maximum torque is generated.
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Accused Products
Abstract
Drive apparatus, particularly for a twin polygon thermal scanner, utilizes a stepper motor driven by pulses of variable width timed, relative to the rotational position of the motor, so that the pulses are substantially centred on the maximum torque position of the motor. This minimizes power consumption. The control circuitry for the motor performs a start sequence, which is aborted and reinitiated in the event that the motor fails properly to start and in which the frequency of the pulses applied to the stopper motor is increased as the motor accelerates. Any excessive increase in the rate of increase of frequency of the pulses is detected and corrected. When the motor is running up to speed, the power applied to the motor is controlled by a phase detector which detects variations in phase between a referenced pulse train and a pulse train generated by the rotation of the motor.
26 Citations
19 Claims
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1. A variable drive apparatus, comprising:
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a stepper motor having a rotor and a plurality of coils; power supply means arranged to supply pulses to said coils in sequence to cause sustained rotation of said rotor; means for modulating the width of said pulses for varying the power applied to said coils; signal generating means for generating a variable rate signal; signal producing means for receiving said variable rate signal and producing a first signal, the timing of which controls the timing of the centers of said pulses, and a second signal, which controls progress through said sequence, the first and second signals having a predetermined timing relationship to each other and each having a timing and a frequency determined by said variable rate signal; means to supply a control signal having a timing in accordance with the phase position of said rotor; and means to enable the generation of the variable rate signal by said signal generating means to be effected by said control signal so as to maintain the centers of said pulses substantially coincident with the positions of the rotor relative to the coils at which maximum torque is generated. - View Dependent Claims (2, 15, 16, 17, 18, 19)
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- 3. Drive apparatus comprising a stepper motor, power supply means for supplying drive pulses to said motor for effecting sustained drive of said motor, and start control means operable to perform a start sequence in which it causes the power supply means to supply said drive pulses initially at a low frequency and said frequency is increased at a relatively low rate for an initial period determined by the speed of rotation of the motor and subsequently at a relatively high rate.
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7. Drive apparatus comprising a stepper motor, power supply means for supplying pulses to said motor for effecting sustained drive of said motor, start control means operable to control said power supply means to perform a start sequence for said motor, detector means to detect whether said motor has started, and timing means for providing a time out signal at the end of a time-out interval from the beginning of the start sequence, said control means being responsive to said detector means and said timing means to restart the start sequence and reset said timing means in the event the said timing means provides said time-out signal before said start control means receives a signal from the detector means indicating the the motor has started.
- 8. Drive apparatus comprising a motor, means for supplying a first signal at a reference frequency representing a speed at which said motor is to be driven, means for supplying a second signal having a frequency representing the actual speed of the motor, first and second counters arranged for receiving respectively said first and said second signals, means for obtaining a further signal representing the difference in the number of cycles of said first and second signals counted by said first and second counters respectively, and means for controlling the speed of the motor in dependence upon the value of said further signal.
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14. Drive apparatus comprising a motor, means for supplying a first signal at a reference frequency representing a desired frequency of revolution of said motor, means for providing a second signal having a frequency representing the actual frequency of revolution of said motor, said frequencies of both of said first and second signals being at least 100 times said frequency of revolution, first detector means for detecting the difference between said frequencies of said first and second signals, second detector means for detecting a phase difference between said first and second signals, third detector means for detecting whether the frequency difference is within predetermined limits, and control means responsive to the third detector means to control the speed of the motor in accordance with said frequency difference when said frequency difference is outside predetermined limits and in accordance with said phase difference when said frequency difference is within said predetermined limits.
Specification