Motor speed control circuit with electronic clutch
First Claim
1. A motor control circuit for supplying energy from a power source to a motor to deliver a user-selected torque, comprising:
- a solid-state switching device having ON and OFF states and having first and second semi-conductor terminals connected in series with said motor between said power source and ground for conducting drive current through said motor when said switching device is in said ON state, a third semi-conductor terminal for controlling the conductive state of said switching device, and a fourth semi-conductor terminal for producing a low current sense signal the magnitude of which is related to the current flowing across said first and second semi-conductor terminals and hence through said motor;
modulator circuit means coupled to said third semi-conductor terminal and responsive to said sense signal for supplying a speed control signal to said third semiconductor terminal to control the conductive state of said switching device, said modulator circuit means varying a characteristic of said speed control signal in accordance with said sense signal;
user-settable means for providing a torque signal indicative of a user-selected torque; and
torque control comparator means coupled to said user-settable means and to said fourth semi-conductor terminal of said switching device for comparing said torque signal and said sense signal and for causing said modulator circuit means to place said switching device in its OFF state when said sense signal bears a predetermined relationship to said torque signal.
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Accused Products
Abstract
The pulse width modulated DC motor speed control circuit indirectly senses motor current using sense MOSFETs and a peak detector circuit with storage capacitor for deriving an average motor current signal. The average motor current signal is used both in the feedback loop of the pulse width modulated speed control circuit and also in the motor shutoff or clutch circuit. The clutch circuit shuts off power to the motor when a user-settable torque is reached. The motor speed control circuit is therefore adapted for use in hand-held DC power tools such as screwdrivers and nutdrivers which stop rotation at a predefined torque.
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Citations
20 Claims
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1. A motor control circuit for supplying energy from a power source to a motor to deliver a user-selected torque, comprising:
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a solid-state switching device having ON and OFF states and having first and second semi-conductor terminals connected in series with said motor between said power source and ground for conducting drive current through said motor when said switching device is in said ON state, a third semi-conductor terminal for controlling the conductive state of said switching device, and a fourth semi-conductor terminal for producing a low current sense signal the magnitude of which is related to the current flowing across said first and second semi-conductor terminals and hence through said motor; modulator circuit means coupled to said third semi-conductor terminal and responsive to said sense signal for supplying a speed control signal to said third semiconductor terminal to control the conductive state of said switching device, said modulator circuit means varying a characteristic of said speed control signal in accordance with said sense signal; user-settable means for providing a torque signal indicative of a user-selected torque; and torque control comparator means coupled to said user-settable means and to said fourth semi-conductor terminal of said switching device for comparing said torque signal and said sense signal and for causing said modulator circuit means to place said switching device in its OFF state when said sense signal bears a predetermined relationship to said torque signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of controlling a motor supplied with energy from a power source to deliver a controlled torque and controlled speed, comprising:
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producing a desired motor speed signal; producing a desired torque signal; supplying drive current to said motor through an electronically controlled switching circuit; sensing the amount of drive current supplied to said motor and deriving a motor current signal; developing a first control signal from said motor current signal having a characteristic related to the actual speed of the motor; developing a second control signal from said motor current signal having a characteristic related to the actual torque of the motor; comparing said first control signal to said desired motor speed signal and controlling said electronically controlled switching circuit in accordance with the difference between said signals to control the speed of the motor; and comparing said second control signal to said desired torque signal and causing said electronically controlled switching circuit to interrupt the supply of drive current to the motor when said second control signal bears a predetermined relationship to said desired torque signal. - View Dependent Claims (17, 18, 19, 20)
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Specification