Impact tool control method and apparatus and impact tool using the same

• US 20010032726A1
• Filed: 12/15/2000
• Published: 10/25/2001
• Est. Priority Date: 12/16/1999
• Status: Active Grant

• Current Assignee: Methode Electronics Incorporated
• Original Assignee: Magna-Lastics Devices Inc.
• Inventors: Jones, Christopher, Cripe, David W.
• Granted Patent: US 6,655,471 B2
• Time in Patent Office: Days
• US Class Current: 173/1
• CPC Class Codes: B25B 23/14 Arrangement of torque limiters or torque indicators in wrenches or screwdrivers couplings for transmitting rotation or clutches F16D; devices for measuring torque per se G01L
• CPC Class Codes: B25B 23/1405 for impact wrenches or screwdrivers

Abstract

An impact tool control method and apparatus and an impact tool using the same. Pulses of torque applied to a fastener by the impact tool are measured. The duration and magnitude of the torque pulse are subtracted from a torque signal and the resulting difference is integrated over time to obtain a fastener angular velocity signal. The angular velocity signal is integrated over time to obtain a displacement signal which can be converted to a torque signal. The impact tool can be controlled based on the value of the torque signal.

Claims

1. A method for determining torque applied to a fastener comprising the steps of:

applying torque pulses to a fastener;

measuring the values of amplitude and duration of each torque pulse applied to the fastener; and

processing the amplitude and duration of the torque pulses to obtain the total torque applied to the fastener.

2. A method as recited in

claim 1

, wherein said processing step comprises processing the values of amplitude and duration in accordance with the following relationships:

3. A method as recited in

claim 2

, further comprising the step of terminating said applying step when V_n exceeds a predetermined threshold.

4. A method as recited in

claim 3

, wherein the threshold is determined in accordance with the following relationship:

5. A method as recited in

claim 4

, further comprising the step of imputing a value of desired fastener torque.

6. A method as recited in

claim 1

, wherein said processing step comprises the steps of:

generating a torque pulse signal based on the torque pulses;

subtracting a torque signal from the torque pulse signal to generate a difference signal;

integrating the difference signal to obtain a fastener angular velocity signal;

integrating the velocity signal to obtain a fastener angular displacement signal; and

converting the angular displacement signal to the torque signal representing torque on the fastener.

7. A method as recited in

claim 6

, wherein said step of integrating the difference signal is accomplished only when the difference signal has a value of greater than zero.

8. A method as recited in

claim 6

, further comprising the steps of:

comparing the value of the torque signal to a preset threshold value; and

terminating said applying step when the value of the torque signal equals or exceeds the threshold value;

9. A method as recited in

claim 8

, wherein the threshold value is a value of desired torque of the fastener.

10. A method as recited in

claim 6

, wherein said generating step comprises:

producing a magnetic field based on the torque in a shaft of a tool applying the torque pulses;

inducing a voltage in a detector with the magnetic field; and

integrating the voltage.

11. A method as recited in

claim 10

, wherein said producing step is accomplished by a magnetoelastic transducer disposed on the shaft.

12. An impact tool comprising:

a body;

an output shaft adapted to be coupled to a fastener;

means for applying torque pulses to said output shaft;

a torque transducer coupled to said output shaft;

and means for processing the output of the torque transducer to obtain torque on the fastener.

13. An impact tool as recited in

claim 12

, wherein said means for processing comprises:

means for generating a torque pulse signal based on the output of the torque transducer;

means for subtracting a torque signal from the torque impulse signal to generate a difference signal;

means for integrating the difference signal to obtain a fastener angular velocity signal;

means for integrating the velocity signal to obtain a fastener angular displacement signal; and

means for converting the angular displacement signal to the torque signal representing torque on the fastener.

14. An impact tool as recited in

claim 13

, wherein said means for generating a torque pulse signal, said means for subtracting a torque signal from the torque pulse signal, said means for integrating the difference signal, said means for integrating the velocity signal, and said means for converting all comprise a programmable microprocessor based controller.

15. An impact tool as recited in

claim 13

, wherein said means for generating a torque pulse signal, said means for subtracting a torque signal from the torque pulse signal, said means for integrating the difference signal, said means for integrating the velocity signal, and said means for converting all comprise an analog circuit controller.

16. An impact tool as recited in

claim 13

, wherein said means for integrating the difference signal is activated only when the difference signal has a value of greater than zero.

17. An impact tool as recited in

claim 13

, further comprising:

means for comparing the value of the torque signal to a preset threshold value; and

means for terminating said means for applying when the value of the torque signal equals or exceeds the threshold value.

18. An impact tool as recited in

claim 17

, wherein the threshold value is a value of desired torque of the fastener.

19. An impact tool as recited in

claim 13

, wherein said means for generating comprises:

means for producing a magnetic field based on the torque in said shaft;

means for inducing a voltage in a coil with the magnetic field; and

means for integrating the voltage.

20. An impact tool as recited in

claim 19

, wherein said means for producing comprises a magnetoelastic transducer coupled to said output shaft.

21. An impact tool as recited in

claim 13

wherein, said means for subtracting a torque signal from the torque pulse signal comprises a differential amplifier, said means for integrating the difference signal comprises an op amp integrator, and said means for integrating the velocity signal comprises an op-amp integrator.

22. A controller for an impact tool comprising:

a substraction circuit having an output, a first input and a second input, the first input being configured to accept a value representing calculated torque on a fastener being tightened by the impact tool and the second input being configured to accept a value of torque impulse being applied to the fastener;

a velocity circuit having an output and an input coupled to the output of said substraction circuit and configured to integrate the value of the output of said substraction circuit over time to obtain a value indicating angular velocity of the fastener;

a torque circuit having an output and an input coupled to the output of said velocity circuit and configured to integrate the value of the output of said velocity circuit over time to obtain the value indicating calculated torque on the fastener, the output of said torque circuit being coupled to the first input of said substraction circuit; and

a threshold comparing circuit having an input coupled to the output of the torque circuit and being configured to generate a control signal for controlling the impact tool when a predetermined relationship between the value of the output of the torque circuit and threshold value exists.

23. A retrofit system for an impact tool of the type comprising a body and an output shaft adapted to be coupled to a fastener, said retrofit system comprising;

a shaft extension having a first end and a second end, said first end being adapted to be coupled to the output shaft and said second end being adapted to be coupled to the fastener;

a torque transducer coupled to said shaft extension;

and means for processing the output of the torque transducer to obtain torque on the fastener.

24. A retrofit system as recited in

claim 23

, wherein said means for processing comprises:

means for generating a torque pulse signal based on the output of the torque transducer;

means for subtracting a torque signal from the torque impulse signal to generate a difference signal;

means for integrating the difference signal to obtain a fastener angular velocity signal;

means for integrating the velocity signal to obtain a fastener angular displacement signal; and

means for converting the angular displacement signal to the torque signal representing torque on the fastener.

25. A retrofit system as recited in

claim 24

, wherein said means for generating a torque pulse signal, said means for subtracting a torque signal from the torque pulse signal, said means for integrating the difference signal, said means for integrating the velocity signal, and said means for converting all comprise a programmable microprocessor based controller.

26. A retrofit system as recited in

claim 24

, wherein said means for generating a torque pulse signal, said means for subtracting a torque signal from the torque pulse signal, said means for integrating the difference signal, said means for integrating the velocity signal, and said means for converting all comprise an analog circuit controller.

27. A retrofit system as recited in

claim 24

, wherein said means for integrating the difference signal is activated only when the difference signal has a value of greater than zero.

28. A retrofit system as recited in

claim 24

, further comprising:

means for comparing the value of the torque signal to a preset threshold value; and

means for terminating said means for applying when the value of the torque signal equals or exceeds the threshold value.

29. A retrofit system as recited in

claim 24

, wherein the threshold value is a value of desired torque of the fastener.

30. A retrofit system as recited in

claim 24

, wherein said means for generating comprises:

means for producing a magnetic field based on the torque in said shaft extension;

means for inducing a voltage in a detector with the magnetic field; and

means for integrating the voltage.

31. A retrofit system as recited in

claim 30

, wherein said means for producing comprises a magnetoelastic transducer coupled to said shaft extension.

32. A retrofit system as recited in

claim 24

wherein, said means for subtracting a torque signal from the torque pulse signal comprises a differential amplifier, said means for integrating the difference signal comprises an op amp integrator, and said means for integrating the velocity signal comprises an op-amp integrator.