Stepper motor control circuit
First Claim
1. A stepper motor control circuit responsive to a variable step rate demand signal, said circuit comprising a waveform generator circuit arranged to generate a pair of substantially stepless symmetrical periodic waveforms of constant amplitude and of frequency determined by said variable step rate demand signal received thereby, the waveforms being 90°
- out of phase, a pair of pulse width modulation circuits arranged to drive the motor windings, each modulation circuit receiving one of said waveforms as a current demand signal and a feedback signal related to the instantaneous current in the associated ones of the motor windings, wherein said waveform generator circuit is a triangular waveform generator circuit in which the slopes of the leading and trailing flanks of the waveform are equal during steady speed running of the motor.
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Accused Products
Abstract
A stepper motor control circuit includes a waveform generator circuit which produces two identical substantially stepless symmetrical waveforms (preferably a triangular configuration) at a frequency which can be varied on demand. Each waveform is used as a current demand signal for a pulse width modulator with a push-pull output stage controlling current in the motor windings. The pulse width modulator runs at a fixed frequency an order of magnitude higher than the maximum required stepping frequency. A current sensing resistor provides a feed-back signal which is fed back to input of the modulator to balance the demand signal.
42 Citations
15 Claims
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1. A stepper motor control circuit responsive to a variable step rate demand signal, said circuit comprising a waveform generator circuit arranged to generate a pair of substantially stepless symmetrical periodic waveforms of constant amplitude and of frequency determined by said variable step rate demand signal received thereby, the waveforms being 90°
- out of phase, a pair of pulse width modulation circuits arranged to drive the motor windings, each modulation circuit receiving one of said waveforms as a current demand signal and a feedback signal related to the instantaneous current in the associated ones of the motor windings, wherein said waveform generator circuit is a triangular waveform generator circuit in which the slopes of the leading and trailing flanks of the waveform are equal during steady speed running of the motor.
- View Dependent Claims (2, 3, 4, 5, 12)
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6. A stepper motor control circuit responsive to a variable step rate demand signal, said circuit comprising a waveform generator circuit arranged to generate a pair of substantially stepless symmetrical periodic waveforms of constant amplitude and of frequency determined by said variable step rate demand signal received thereby, the waveforms being 90°
- out of phase, a pair of pulse width modulation circuits arranged to drive the motor windings, each modulation circuit receiving one of said waveforms as a current demand signal and a feedback signal related to the instantaneous current in the associated ones of the motor windings, wherein each pulse width modulator has an output stage operating in push-pull between positive and negative supply rails at a frequency at least an order of magnitude higher than the maximum required stepping frequency.
- View Dependent Claims (7, 9, 10, 11)
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8. A stepper motor control circuit as claimed in 7 in which the output stage comprises a complementary pair of power FETs.
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13. A stepper motor control circuit comprising a waveform generator circuit arranged to generate a pair of substantially stepless symmetrical periodic waveforms of constant amplitude and of frequency determined by a variable step rate demand signal received thereby, the waveforms being 90°
- out of phase, a pair of pulse width modulation circuits arranged to drive the motor windings, each modulation circuit receiving one of said waveforms as a current demand signal and a feedback signal related to the instantaneous current in the associated ones of the motor windings, a phase detector circuit connected to said modulation circuit and operating to provide a signal related to the difference between the phases of the voltage applied to and the current flowing in the motor, and means connected to said phase detector circuit and to said waveform generator circuit to reduce the frequency of the waveforms independently of said step rate demand signal when a predetermined out of phase condition is detected by said detector circuit.
- View Dependent Claims (14, 15)
Specification