DC motor control using frequency and pulsewidth modulation
First Claim
1. A control system for controlling the flow of power from a DC power source to a DC motor in order to control the speed of said motor, said control system comprising:
- a frequency modulator having first and second inputs and an output;
a first pulse generator for generating first pulses at a first frequency and a first duty cycle and for applying said first pulses to said first input of said frequency modulator;
a second pulse generator for generating second pulses at a second frequency and a second duty cycle and for applying said second pulses to said second input of said frequency modulator, wherein said first frequency is substantially lower than said second frequency, so that said frequency modulator produces a frequency modulated output signal at the output of said frequency modulator by superimposing said first pulses on said second pulses;
a power circuit for applying power to said motor in response to the frequency modulated output signal of said frequency modulator; and
a control circuit for varying the duty cycle of said first pulses in response to a signal representing the desired speed of said motor.
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Accused Products
Abstract
The flow of power through a field effect transistor to a DC motor is controlled by the output of a frequency modulator having a low frequency pulsed signal applied to one input thereof and a high frequency pulsed signal applied to a second input thereof. The pulse width of each "on" pulse of the low frequency pulsed signal is varied in response to a signal representing a desired motor speed. Optionally, the pulse width of each "on" pulse of the high frequency pulsed signal can also be varied in response to the signal representing the desired motor speed. A filter circuit can be employed to prevent rapid changes in the pulse width of the low frequency pulsed signal. Similarly, a filter circuit can be used to avoid rapid changes in the pulse width of the high frequency pulsed signal. A freewheeling diode can be used to minimize inverse voltage spikes across the motor.
26 Citations
33 Claims
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1. A control system for controlling the flow of power from a DC power source to a DC motor in order to control the speed of said motor, said control system comprising:
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a frequency modulator having first and second inputs and an output; a first pulse generator for generating first pulses at a first frequency and a first duty cycle and for applying said first pulses to said first input of said frequency modulator; a second pulse generator for generating second pulses at a second frequency and a second duty cycle and for applying said second pulses to said second input of said frequency modulator, wherein said first frequency is substantially lower than said second frequency, so that said frequency modulator produces a frequency modulated output signal at the output of said frequency modulator by superimposing said first pulses on said second pulses; a power circuit for applying power to said motor in response to the frequency modulated output signal of said frequency modulator; and a control circuit for varying the duty cycle of said first pulses in response to a signal representing the desired speed of said motor. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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2. A control system for controlling the flow of power from a DC power source to a DC motor in order to control the speed of said motor, said control system comprising:
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a frequency modulator having first and second inputs and an output; a first pulse generator for generating first pulses at a first frequency and a first duty cycle and for applying said first pulses to said first input of said frequency modulator; a second pulse generator for generating second pulses at a second frequency and a second duty cycle and for applying said second pulses to said second input of said frequency modulator, wherein said first frequency is substantially lower than said second frequency; a power circuit for applying power to said motor in response to the output of said frequency modulator; and a control circuit for varying the duty cycle of said first pulses in response to a signal representing the desired speed of said motor; wherein said control circuit comprises a manually positionable lever for indicating a desired speed of said motor, a power setpoint circuit for producing a voltage signal representative of the thus indicated desired speed, and a connection for applying said voltage signal to an input of said first pulse generator to modify the duty cycle of said first pulses in response to said voltage signal. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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20. A control system for controlling the flow of power from a battery to a DC motor in order to control the speed of said motor, said control system comprising:
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a frequency modulator having first and second inputs and an output; a low frequency pulse generator for generating a low frequency pulsed output signal and for applying said low frequency pulsed output signal to said first input of said frequency modulator; a high frequency pulse generator for generating a high frequency pulsed output signal and for applying said high frequency pulsed output signal to said second input of said frequency modulator, so that said frequency modulator produces a frequency modulated output signal at the output of said frequency modulator by superimposing said low frequency pulsed output signal on said high frequency pulsed output signal; a power circuit for applying power from said battery to said motor in response to the frequency modulated output signal of said frequency modulator; and a control circuit for varying the on-off ratio of the pulses of said low frequency output signal in response to a signal representing the desired speed of said motor.
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21. A control system for controlling the flow of power from a battery to a DC motor in order to control the speed of said motor, said control system comprising:
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a frequency modulator having first and second inputs and an output signal; a low frequency pulse generator for generating a low frequency pulsed output signal and for applying said low frequency pulsed output signal to said first input of said frequency modulator; a high frequency pulse generator for generating a high frequency pulsed output signal and for applying said high frequency pulsed output signal to said second input of said frequency modulator; a power circuit for applying power from said battery to said motor in response to the output signal of said frequency modulator; and a control circuit for varying the on-off ratio of the pulses of said low frequency pulsed output signal in response to a signal representing the desired speed of said motor; wherein the length of each cycle of the output signal from said frequency modulator corresponds to the length of a cycle in the low frequency pulsed output signal, with each cycle of the output signal from said frequency modulator having an "off" cycle portion and an "on" cycle portion, with the "on" cycle portion of said output signal from said frequency modulator comprising a plurality of pulses having a frequency corresponding to the frequency of said high frequency pulsed output signal. - View Dependent Claims (22, 23, 24, 25)
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26. A process for controlling the flow of power from a DC power source to a DC motor in order to control the speed of said motor, said process comprising the steps of:
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generating first pulses at a first frequency and a first duty cycle; generating second pulses at a second frequency and a second duty cycle, wherein said first frequency is substantially lower than said second frequency; generating, responsive to said first pulses and said second pulses, a frequency modulated signal by superimposing said first pulses on said second pulses; applying power to said motor in response to said frequency modulated signal; and varying the duty cycle of said first pulses in response to a signal representing the desired speed of said motor. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33)
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Specification