Electrical power tool having a motor control circuit for providing control over the torque output of the power tool

• US 20020153856A1
• Filed: 06/11/2002
• Published: 10/24/2002
• Est. Priority Date: 07/06/1993
• Status: Active Grant

• Current Assignee: Alan A. Gilmore
• Original Assignee: Alan A. Gilmore
• Inventors: Gilmore, Alan A.
• Granted Patent: US 6,836,614 B2
• Time in Patent Office: Days
• US Class Current: 318/599
• CPC Class Codes: B23P 19/066 by electrical means
• CPC Class Codes: B25B 21/00 Portable power-driven screw or nut setting or loosening tools; details or components, e.g. casings, bodies, of portable power-driven tools not particularly related to the operation performed B25F5/00; for mounting or dismounting wheels B60B29/006; Attachments for drilling apparatus serving the same purpose machines B23P19/06
• CPC Class Codes: B25B 21/004 of the ratchet type
• CPC Class Codes: B25B 23/1415 Break members; Arrangements specially adapted for break-bolts break-bolts per se F16B31/00
• CPC Class Codes: B25B 23/147 specially adapted for electrically operated wrenches or screwdrivers
• CPC Class Codes: B25F 5/001 Gearings, speed selectors, clutches or the like specially adapted for rotary tools
• CPC Class Codes: Y10S 388/93 Load or torque
• CPC Class Codes: Y10S 388/937 Hand tool

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 and has associated therewith a degree of looseness which must be taken up before torque from the motor is applied to the tool bit. The control circuit for the power tool increases the effective torque output of the tool after a predetermined torque level is attained, by alternately turning the motor on and off, with the duration of the off-time sufficient to permit the gear train to relax, thus giving the motor a “running start” when power is reapplied. Various alternative schemes for transitioning to this ratcheting mode of operation are disclosed including the sensing of a predetermined threshold current, a predetermined increase in motor current, and a predetermined rate of deceleration in motor speed. The control circuit preferably provides the operator with means for adjusting the transition point as well as for varying the duration of the on-time in the ratcheting mode. Additional alternative embodiments of the present invention are disclosed that permit the power tool to be continuously operated in a low frequency mode to advantageous effect. Corresponding methods for controlling the operation of the electric motor of a power tool are also disclosed.

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.

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.

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.

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.

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.

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.

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.