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

• US 6,836,614 B2
• Filed: 06/11/2002
• Issued: 12/28/2004
• Est. Priority Date: 07/06/1993
• Status: Expired due to Fees

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Gilmore, Alan A.
• Primary Examiner(s): DUDA, RINA I
• Application Number:
  US10/166,805
• Publication Number:
  US 20020153856A1
• Time in Patent Office: 931 Days
• Field of Search: 318/432, 318/434, 318/599, 388/809, 388/811, 388/819, 388/815, 388/907.5, 388/930, 388/937, 388/814, 173/4, 173/5, 173/7, 173/11, 173/176, 173/178, 738/620.8, 814/67, 814/69
• US Class Current: 388/811
• 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. 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.

Claims

1. A power tool having an electric motor, having associated therewith a response time, 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 the period of the PWM d.c. control signal generated by said control circuit is greater than the response time of the motor.

2. 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 generates said PWM d.c. control signal at a frequency that is sufficiently low to cause said motor to provide, over a substantial portion of the duty cycle range of said control signal, bursts of torque to said output spindle that cause substantial variation in the speed of rotation of said output spindle between successive bursts of torque.

3. The power tool of claim 2 wherein said frequency is within a range between 10 Hz and 50 Hz.

4. The power tool of claim 2 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.