Impact wrench having speed control circuit

• US 5,526,460 A
• Filed: 04/25/1994
• Issued: 06/11/1996
• Est. Priority Date: 04/25/1994
• Status: Expired due to Term

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: DeFrancesco, Angelo J., Elligson, Daniel M., Kunz, Michael P.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/232,559
• Time in Patent Office: 778 Days
• Field of Search: 388/825, 388/826, 388/827, 388/828, 388/829, 388/830, 388/831, 388/838, 388/839, 318/434, 318/256, 318/257, 318/258, 318/268, 318/269, 318/289, 318/293, 318/379
• US Class Current: 388/831
• CPC Class Codes: B25B 23/1475 for impact wrenches or screwdrivers
• CPC Class Codes: H02P 7/29 using pulse modulation

Abstract

An impact wrench having a speed limiting control circuit to allow an operator of the wrench to controllably limit the maximum speed of the wrench to a predetermined value when a trigger thereof is fully engaged. The impact wrench includes a manually adjustable speed limiting control protruding from an outer surface of the impact wrench which is conveniently manually adjustable. The speed limiting control is coupled to the wiper arm of a speed limiting potentiometer which is electrically coupled to a speed control circuit within the impact wrench. The speed limiting potentiometer limits the maximum speed of the motor of the impact wrench (and thus the maximum torque which can be generated by the impact wrench 10) to an operator selected percentage of the maximum motor speed which would otherwise be produced when the trigger is fully engaged. In the preferred embodiment the speed limiting potentiometer is electrically coupled in series between a capacitor and speed control potentiometer, which are each coupled to a 555 CMOS timer which controls the duty cycle of an FET used to drive the motor. The speed limiting potentiometer enables the operator to further limit the maximum duty cycle of the output of the timer, which is a pulse-width-modulated like output, to a percentage of that which would otherwise be produced when the trigger is fully engaged.

Claims

1. A variable speed impact wrench having an operator settable maximum speed control to limit the maximum torque applied to a tool bit holder of the wrench, said impact wrench comprising:

a motor for driving the tool bit holder;

a speed control circuit for controlling the speed of said motor;

a trigger engageable by an operator, said trigger being operably coupled to said speed control circuit to allow said operator to generate a speed control signal in relation to the degree of actuation of said trigger;

a speed limiting device electrically communicating with said speed control circuit and manually adjustable by said operator for enabling said operator to electrically limit a maximum speed at which said motor can be driven when said trigger is fully engaged.

2. The impact wrench of claim 1, wherein said speed limiting device for adjusting the maximum speed of said motor comprises a speed limiting potentiometer for limiting a maximum voltage which may be applied to said motor.

3. The impact wrench of claim 2, further comprising a battery pack releasably securable to said impact wrench for powering said motor.

4. The impact wrench of claim 1, wherein said speed control circuit comprises a 555 CMOS timer.

5. A variable speed electric impact wrench having an operator engageable trigger for permitting the operator to vary the speed of the impact wrench in accordance with the degree of engagement of the trigger, a maximum speed limiting control for allowing the operator to set a maximum speed at which a motor of the wrench may be driven regardless of the degree of engagement of the trigger, said impact wrench comprising:

a variable speed circuit operably associated with said trigger to produce a motor drive signal for driving said motor of said impact wrench at a speed in proportion to the degree of engagement of said trigger up to a maximum speed when said trigger is fully engaged; and

a speed limiting device adjustable by said operator and in electrical communication with said variable speed circuit, for enabling said operator to limit said motor drive signal to a maximum value, to thereby limit said motor speed to a speed less than said maximum speed when said trigger is fully engaged by said operator.

6. The impact wrench of claim 5, wherein said speed limiting device comprises a potentiometer manually adjustable by said operator.

7. The impact wrench of claim 5, wherein said variable speed circuit generates a pulse-width-modulated like motor drive signal;

and

wherein operator adjustment of said speed limiting device operates to limit a duty cycle of said pulse-width-modulated like motor drive signal to said maximum value, to thereby limit operation of said motor to said speed which is less than said maximum speed.

8. A variable speed impact wrench comprising:

a tool bit holder;

a motor for driving said tool bit holder rotationally;

a speed control circuit including a speed control potentiometer,for generating a pulse width modulated like motor drive signal having a controllably variable duty cycle for driving said motor;

an operator engageable trigger for allowing a user to control said duty cycle, and therefore the speed of said motor; and

a speed limiting potentiometer manually adjustable by said user and operably coupled to said speed control circuit for enabling said user to limit said duty cycle to a desired percentage of a maximum value when said trigger is in a fully engaged position.

9. The impact wrench of claim 8, further comprising a releasably coupled, rechargeable battery pack for powering said motor.

10. The impact wrench of claim 8, wherein said speed control circuit comprises:

a CMOS timer circuit;

said speed control potentiometer mechanically coupled to said trigger and electrically coupled to said CMOS timer circuit; and

a capacitor; and

wherein an RC time constant provided by said speed control potentiometer and said capacitor is further modified by the resistance provided by said speed limiting potentiometer to thereby controllably limit said duty cycle.

11. A variable speed impact wrench comprising:

a tool bit holder;

a motor for driving said tool bit holder rotationally;

a speed control circuit comprising a CMOS timer circuit, a speed control potentiometer mechanically coupled to an operator engageable trigger and electrically coupled to said CMOS timer circuit, and a capacitor, for generating a pulse width modulated like motor drive signal having a controllably variable duty cycle for driving said motor;

said operator engageable trigger for allowing the user to control said duty cycle, and therefore the speed of said motor; and

a speed limiting potentiometer manually adjustable by said user and operably coupled to said speed control circuit for providing resistance to an RC time constant provided by said speed control potentiometer and said capacitor to controllably limit said duty cycle to a desired percentage of a maximum value when said trigger is in a fully engaged position.