Anti-kickback and breakthrough torque control for power tool

• US 6,479,958 B1
• Filed: 10/22/1996
• Issued: 11/12/2002
• Est. Priority Date: 01/06/1995
• Status: Expired due to Fees

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Patel, Falgun, Thompson, Stephen S., Huber, Paul G.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/736,020
• Time in Patent Office: 2,212 Days
• Field of Search: 318/430, 318/432, 318/433, 318/434, 318/630, 318/431, 388/937
• US Class Current: 318/430
• CPC Class Codes: B25F 5/00 Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for
• CPC Class Codes: H02H 7/0854 responsive to rate of change of current, couple or speed, e.g. anti-kickback protection H02H7/0851 takes precedence
• CPC Class Codes: H02H 7/0858 by reversing, cycling or reducing the power supply to the motor
• CPC Class Codes: Y10S 388/937 Hand tool

Abstract

A rapid increase in motor current (di/dt above a predetermined threshold) causes the motor control system to enter pulse mode operation in-which the motor current is pulsed on and off rapidly to dislodge the workpiece obstruction or binding condition that would otherwise lead to a motor stall. When the workpiece obstruction or binding has been cleared, the motor resumes normal operation.

Claims

1. A method of controlling a power tool having a motor that imparts torque to an output spindle when actuated by an operator actuable switch, the power tool having a characteristic natural resonant frequency, comprising:

sensing a motor parameter indicative of the onset of an impending stall condition; and

in response to the sensed onset of an impending stall condition and while the switch remains actuated, pulsing the motor a plurality of times at a frequency substantially harmonically related to said natural resonant frequency to deliver a series of torque pulses having peak torque substantially greater than the average torque delivered during the series.

2. A motor control circuit for an electric power tool having a characteristic natural resonant frequency, comprising:

drive circuit coupled to said motor for controlling the application of current to said motor;

a processor coupled to said drive circuit and providing a processor output signal for controlling said drive circuit;

a current sensor coupled to said drive circuit for sensing a parameter indicative of motor current and coupled to said processor for providing first processor input signal;

said processor having first means for detecting when the rate of change in the value of said first processor input signal exceeds a predetermined limit for detecting the onset of a stall condition;

said processor further having second means for using said processor output signal to apply current pulses to said motor at a frequency that is substantially harmonically related to said natural resonant frequency in response to the detected onset of a stall condition.