Electrical power tool having a motor control circuit for providing control over the torque output of the power tool
First Claim
1. A portable power tool having an output spindle, an electric motor for driving the output spindle and a control system for controlling the operation of the motor including a power source and a power switching device interconnecting the power source to the motor for applying a constant frequency PWM drive signal from the power source to the motor, and a controller for controlling the power switching device and monitoring at least one operating characteristic of the power tool and reducing the frequency of said PWM drive signal in response to a predetermined change in said operating characteristic to thereby cause said power tool to enter a ratchet mode of operation.
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Accused Products
Abstract
A power tool such as an electric drill typically contains a gear train that couples the output spindle of the motor to the tool bit-receiving chuck. The control circuit for the power tool is operable in a ratcheting or pulse mode that causes the output spindle to rotate in discrete incremental amounts. Corresponding methods for controlling the operation of the electric motor of a power tool are also disclosed.
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Citations
58 Claims
- 1. A portable power tool having an output spindle, an electric motor for driving the output spindle and a control system for controlling the operation of the motor including a power source and a power switching device interconnecting the power source to the motor for applying a constant frequency PWM drive signal from the power source to the motor, and a controller for controlling the power switching device and monitoring at least one operating characteristic of the power tool and reducing the frequency of said PWM drive signal in response to a predetermined change in said operating characteristic to thereby cause said power tool to enter a ratchet mode of operation.
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11. A control system for a portable power tool having an output spindle driven by an electric motor of the type that is responsive to the total power supplied to the motor via a drive signal for controlling the speed of the motor, said drive signal having associated therewith a frequency, the control system comprising:
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an operator actuable trigger switch for controlling the speed of the motor; a power switching device interconnecting the motor to a power source for applying said drive signal to said motor; and a controller for monitoring an operating characteristic of the power tool and adjusting the frequency of the drive signal in accordance with a predetermined change in said operating characteristic to cause the motor to enter a ratchet mode of operation; wherein said controller further controls the amount of power supplied to the motor by controlling a characteristic of said drive signal in accordance with the actuated position of said trigger switch. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A power tool having an electric motor for driving an output spindle, a first operator actuable device for controlling the speed of the motor, and a control circuit for modulating the power supplied to the motor in accordance with the actuation of said first operator actuable device;
- the improvement comprising a second operator actuable device connected to the control circuit for selectively causing said control circuit to operate the motor in a pulse mode that produces substantial cyclical variations in the torque applied to said output spindle.
- View Dependent Claims (24, 25, 26, 27, 28, 29, 35)
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30. A power tool having an electric motor for driving an output spindle, a first operator actuable device having a plurality of non-OFF positions, and a control circuit connected to said first operator actuable device and to said electric motor, said control circuit controlling the amount of electrical power supplied to the motor by modulating an electrical signal in accordance with the position of said first operator actuable device;
- the improvement comprising a second operator actuable device connected to said control circuit for selectively causing said control circuit to operate said motor in a pulse mode by cycling the power supplied to the motor ON and OFF with the intervening OFF periods being of sufficient duration to cause discontinuous incremental rotation of said output spindle.
- View Dependent Claims (31, 32, 33, 34)
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36. A power tool having an electric motor for driving an output spindle having a tool holder operatively coupled thereto, an operator actuable switch for controlling the amount of power applied to the motor, and a control circuit for modulating the power supplied to the motor in accordance with the position of said switch by varying the duty cycle of a constant frequency, pulse width modulated (PWM) direct current (d.c.) control signal generated by the control circuit to thereby control the speed of the motor;
- the improvement wherein said control circuit further controls the power to the motor, with said switch in a substantially fixed position, by cyclically turning the power ON and OFF at a frequency of less than 50 Hz.
- View Dependent Claims (37, 38)
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39. A power tool having an electric motor for driving an output spindle having a tool holder operatively coupled thereto, an operator actuable switch for controlling the amount of power applied to the motor, and a control circuit for modulating the power supplied to the motor in accordance with the position of said switch by varying the duty cycle of a constant frequency, pulse width modulated (PWM) direct current (d.c.) control signal generated by the control circuit to thereby control the speed of the motor;
- the improvement wherein said control circuit in a first operating mode generates said PWM d.c. control signal to cause said motor to provide a substantially smooth application of torque to said output spindle over substantially the entire duty cycle range of said control signal, and in a second operating mode generates said PWM d.c. control signal to cause said motor to provide bursts of torque to said output spindle that produce substantial variation in the speed of rotation of said output spindle between successive bursts of torque.
- View Dependent Claims (40, 41, 42)
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43. A method of controlling a power tool having an electric motor for driving an output spindle having a tool holder operatively coupled thereto and a control circuit that is responsive to a first operator actuable device for controlling the amount of power applied to the motor, the method comprising the steps of:
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modulating the power to the motor in accordance with the position of said first operator actuable device by varying the duty cycle of a constant frequency, pulse width modulated (PWM) direct current (d.c.) control signal generated by the control circuit to thereby control the speed of the motor; and cyclically turning said PWM d.c. control signal ON and OFF at a sufficiently low frequency to cause the motor to provide bursts of torque to said output spindle that produce substantial variation in the speed of rotation of said output spindle between successive bursts of torque. - View Dependent Claims (44, 45)
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- 46. In a power tool having a variable speed electric motor for driving an output spindle, the method of selectively operating the power tool in either a first continuous mode wherein power is supplied to the motor in accordance with an operating characteristic of a drive signal so that the rotational speed of the motor varies in response to changes in the operating characteristic of the drive signal, or in a second mode wherein power is supplied to the motor in a manner that imparts a non-uniform application of torque to said output spindle of sufficient variation to cause said output spindle to rotate in a series of discontinuous increments.
- 49. In a power tool having a variable speed electric motor for driving an output spindle and a control circuit for controlling the rotational speed of the motor, the method of controlling the electric motor by pulsing the motor so that a series of discontinuous torque bursts are imparted to the output spindle of the tool, said torque bursts causing said output spindle to rotate in a corresponding series of discontinuous increments each of which is less than a full revolution of said output spindle.
- 51. In a power tool having a variable speed electric motor for driving an output spindle, the method of selectively operating the power tool in either a first continuous mode wherein power is supplied to the motor in accordance with an operating characteristic of a drive signal so that the rotational speed of the motor varies in response to changes in the operating characteristic of the drive signal, or in a second mode wherein power is supplied to the motor in a manner that imparts bursts of torque to said output spindle that produce substantial variation in the speed of rotation of said output spindle between successive bursts of torque.
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55. A portable power tool having an output spindle, an electric motor for driving the output spindle, and a control circuit for controlling the operation of the motor including a power switching device interconnecting a power source to the motor for controlling the application of power to the motor, said control circuit producing a drive signal that is supplied to said power switching device to control the operation of said power switching device so that the motor drives the output spindle in a pulse mode that causes substantial cyclical variation in the rotational speed of the output spindle;
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wherein said control circuit is further adapted to produce a drive signal that causes the motor to drive the output spindle in a continuous rotational mode wherein the rotational speed of the motor is varied in accordance with an operating characteristic of the drive signal. - View Dependent Claims (56, 57, 58)
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Specification