Claims
- 1. 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 application of power 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 pulse width modulated (PWM) control signal generated by the control circuit; the improvement wherein the frequency of the PWM control signal generated by said control circuit is less than 50 Hz.
- 2. The power tool of claim 1 wherein said frequency is within a range of between 10 Hz and 50 Hz.
- 3. 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 application of power 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 pulse width modulated (PWM) control signal generated by the control circuit; the improvement wherein said control circuit is adapted to selectively generate said PWM control signal at a first frequency that is sufficiently high 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, or at a second frequency that is sufficiently low to cause said motor to provide uneven bursts of torque to said output spindle over a substantial portion of the duty cycle range of said control signal.
- 4. The power tool of claim 3 further including a second operator actuable device for selectively setting the frequency of said PWM control signal.
- 5. The power tool of claim 4 wherein said second operator actuable device comprises a second switch for selectively setting the frequency of said PWM control signal to either a first high frequency greater than 1 KHz or a second low frequency less than 50 Hz.
- 6. The power tool of claim 4 wherein said second operator actuable device is adapted to selectively vary the frequency of said PWM control signal within a range that includes 10 Hz-50 Hz.
- 7. 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 application of power to the motor, and a control circuit for modulating the power supplied to the motor in accordance with the position of said switch; the improvement wherein said control circuit is adapted to modulate the power supplied to said motor while said switch is in a substantially fixed position so that the motor produces substantial variations in the torque applied to said output spindle.
- 8. The power tool of claim 7 wherein said control circuit is adapted to modulate the power supplied to the motor by varying the duty cycle of a pulse width modulated (PWM) control signal generated by the control circuit, and further wherein the frequency of said PWM control signal is less than 50 Hz.
- 9. 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 application of power to the motor, and a control circuit for modulating the power supplied to the motor in accordance with the position of said switch; the improvement wherein said control circuit is adapted to modulate the power supplied to the motor such that with said switch in a substantially fixed position and the tool under an operative load condition, the motor produces a plurality of torque pulses that causes the output spindle of the tool to intermittently come substantially to a stop between successive torque pulses.
- 10. The power tool of claim 9 wherein said control circuit is adapted to modulate the power supplied to the motor by varying the duty cycle of a pulse width modulated (PWM) control signal generated by the control circuit, and further wherein the frequency of said PWM control signal is less than 50 Hz.
- 11. 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 application of power to the motor; the method comprising the steps of:
modulating the power to the motor in accordance with the position of said first operator actuable device by varying the duty cycle of a pulse width modulated (PWM) control signal generated by the control circuit; and setting the frequency of said PWM control signal sufficiently low to cause the motor to provide uneven bursts of torque to said output spindle over a substantial portion of the duty cycle range of the control signal.
- 12. The method of claim 11 wherein the frequency of said PWM control signal is set to a frequency less than 50 Hz.
- 13. 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 application of power to the motor; the method comprising the steps of:
controlling the average level of power supplied to the motor in accordance with the position of said first operator actuable device; and with said first operator actuable device in a substantially fixed position, varying the power supplied to the motor so that the motor produces substantial variations in the torque applied to said output spindle.
- 14. The method of claim 13 wherein the position of said first operator actuable device determines the duty cycle of a pulse width modulated (PWM) control signal generated by the control circuit, and further wherein the frequency of said PWM control signal is less than 50 Hz.
- 15. The method of claim 14 wherein said control circuit includes a second operator actuable device, and further including the step of setting the frequency of said PWM control signal in accordance with the position of said second operator actuable device.
- 16. 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 application of power to the motor; the method comprising the steps of:
controlling the average level of power supplied to the motor in accordance with the position of said first operator actuable device; and with said first operator actuable device in a substantially fixed position and the tool under an operative load condition, varying the power supplied to the motor so that the motor produces a plurality of torque pulses that causes the output spindle of the tool to intermittently come substantially to a stop between successive torque pulses.
- 17. The method of claim 16 wherein the position of said first operator actuable device determines the duty cycle of a pulse width modulated (PWM) control signal generated by the control circuit, and further wherein the frequency of said PWM control signal is less than 50 Hz.
- 18. The method of claim 17 wherein said control circuit includes a second operator actuable device, and further including the step of setting the frequency of said PWM control signal in accordance with the position of said second operator actuable device.
- 19. A power tool having an electric motor and a control circuit for modulating the power supplied to the motor by varying the duty cycle of a pulse width modulated (PWM) control signal generated at an output of the control circuit; the output of said control circuit being operative to switch from a first state to a second state when the magnitude of an input signal supplied thereto is less than a first threshold value and from said second state to said first state when the magnitude of said input signal exceeds a second threshold value greater than said first threshold value by a predetermined amount; an input circuit including a capacitor for producing said input signal in accordance with the charge on a first side of said capacitor and further including a charge circuit for charging the capacitor when the output of said control circuit is in said second state and a discharge circuit for discharging said capacitor when the output of said control circuit is in said first state; and a frequency control circuit for controlling the frequency of said PWM control signal by supplying a voltage signal to the other side of said capacitor the magnitude of which is substantially equal to zero when said capacitor is discharging and selectively variable between substantially zero and a value less than said predetermined amount when said capacitor is charging.
- 20. The power tool of claim 19 wherein said frequency control circuit includes a first diode having its cathode connected to said other side of said capacitor and its anode connected to a ground potential and a second diode having its anode connected to said other side of said capacitor and its cathode connected to receive said voltage signal.
Parent Case Info
[0001] This application is a continuation-in-part of pending U.S. application Ser. No. 08/087,932, filed Jul. 6, 1993.
Continuations (2)
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Number |
Date |
Country |
Parent |
08834774 |
Apr 1997 |
US |
Child |
10166805 |
Jun 2002 |
US |
Parent |
08369497 |
Jan 1995 |
US |
Child |
08834774 |
Apr 1997 |
US |
Continuation in Parts (1)
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Number |
Date |
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Parent |
08087932 |
Jul 1993 |
US |
Child |
08369497 |
Jan 1995 |
US |