Direct current motor speed control
First Claim
1. A DC motor speed control circuit comprising:
- a DC motor inducing a back EMF;
a sample and hold means coupled to said motor for developing a signal having a 1-χ
relationship to the back EMF of said motor where is χ
the back EMF;
a means for measuring and comparing said developed signal with a predetermined reference signal indicative of the desired motor speed;
a means for producing a gating signal indicative of the relationship of said developed signal to said reference signal;
a gated control means coupled to regulate electrical power to said motor;
said control means being responsive to said gating signal to permit power flow to said motor when said developed signal is at one relationship to said reference signal and to restrict power flow to said motor when said developed signal is at a second relationship to said reference signal.
1 Assignment
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Accused Products
Abstract
The motor speed control circuit senses average back EMF as a measure of motor speed. The back EMF charges a capacitor circuit which accumulates charge and develops a voltage indicative of the motor speed. A sample and hold circuit may be used to sample the back EMF when the motor is switched off during each cycle. This voltage is compared with a reference voltage indicative of the desired motor speed. An error signal is generated by comparing the desired speed with the actual speed and this error signal is used to generate a variable duty cycle pulse train which gates the power controlling transistor on and off to control motor speed. A logic gated or SCR gated voltage boosting circuit operates in synchronism with the gating pulse train to drive the power transistor hard into saturation. This lowers the resistance of the power transistor, causing less energy dissipation as waste heat. The motor speed control circuit produces a family of torque-speed curves which maintain speed constant until a break point is reached, whereupon speed falls inversely proportional to torque. A torque control circuit monitors the motor current and maintains that current at a user selected level to thereby select a desired output torque.
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Citations
14 Claims
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1. A DC motor speed control circuit comprising:
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a DC motor inducing a back EMF; a sample and hold means coupled to said motor for developing a signal having a 1-χ
relationship to the back EMF of said motor where is χ
the back EMF;a means for measuring and comparing said developed signal with a predetermined reference signal indicative of the desired motor speed; a means for producing a gating signal indicative of the relationship of said developed signal to said reference signal; a gated control means coupled to regulate electrical power to said motor;
said control means being responsive to said gating signal to permit power flow to said motor when said developed signal is at one relationship to said reference signal and to restrict power flow to said motor when said developed signal is at a second relationship to said reference signal. - View Dependent Claims (2, 3, 4)
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5. A DC motor speed control circuit comprising:
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a DC motor inducing a back EMF; an energy storage means coupled to said motor for developing a signal indicative of the back EMF of said motor; a means for measuring and comparing said developed signal with a predetermined reference signal indicative of desired motor speed; a means for producing a first gating signal indicative of the relationship of said developed signal to said reference signal; a gated control means coupled to regulate electrical power to said motor;
said control means being responsive to said first gating signal to permit power flow to said motor when said developed signal is at one relationship to said reference signal and to restrict power flow to said motor when said developed signal is at a second relationship to said reference signal;a means for sensing current flow through said motor and for providing a current level signal; a means for comparing said current level signal to a second predetermined reference signal indicative of desired motor torque; a means for producing a second gating signal indicative of the relationship of said current level signal to said second reference signal; said gated control means being responsive to said second gating signal to regulate power flow to said motor in response to said current flow through said motor to thereby control the torque output of said motor. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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12. A DC motor speed control circuit comprising:
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a DC motor having an operating current and inducing a back EMF; a sample and hold means coupled to said motor for developing a signal indicative of the back EMF of said motor; a means for measuring and comparing said developed signal with a predetermined reference signal indicative of desired motor speed; a capacitor means charged by said operating current of said DC motor for producing a variable frequency gating signal wherein said frequency is indicative of the relationship of said developed signal to said reference signal;
wherein said sample and hold means further comprises buffer amplifier coupled to said energy storage means for coupling to said means for measuring and comparing;a gated control means coupled to regulate electrical power to said motor;
said control means being responsive to said gating signal to permit power flow to said motor when said developed signal is at one relationship to said reference signal and to restrict power flow to said motor when said developed signal is at a second relationship to said reference signal. - View Dependent Claims (13, 14)
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Specification