Method for improving torque accuracy of a discrete energy tool

• US 20030009262A1
• Filed: 06/18/2001
• Published: 01/09/2003
• Est. Priority Date: 06/18/2001
• Status: Active Grant

• Current Assignee: Ingersoll-Rand Industrial U.S., Inc. (Ingersoll Rand, Inc.)
• Original Assignee: Ingersoll-Rand Company (Trane Technologies plc)
• Inventors: Colangelo, Louis J. III, Linehan, John L., Cooper, Timothy R.
• Granted Patent: US 6,668,212 B2
• Time in Patent Office: Days
• US Class Current: 700/275
• CPC Class Codes: B25B 23/145 specially adapted for fluid operated wrenches or screwdrivers
• CPC Class Codes: B25B 23/1453 for impact wrenches or screwdrivers
• CPC Class Codes: B25B 23/1456 having electrical components

Abstract

A method for improving the accuracy and repeatability of torque applied by discrete energy tools subjected to a wide variety of joint conditions. The method includes relating air pressure to output torque and compensating for temperature and aging variations. Additionally, the method may include a process for detecting previously tightened fasteners.

Claims

1. A method of controlling an air driven tool to provide a desired torque to a fastener, the method comprising the steps of:

establishing an air pressure profile for a plurality of torque values;

determining a calibration factor for the tool;

multiplying the desired torque by the calibration factor to determine a calibrated torque value; and

supplying the tool with air at the air pressure profile corresponding to the calibrated torque value.

2. The method of claim 1 wherein the step of determining a calibration factor includes the steps of:

measuring a temperature of the tool; and

establishing an expected torque value (T_EXP) based on the tool temperature.

3. The method of claim 2 wherein the step of determining a calibration factor further includes the steps of:

accessing a nominal torque value (T_NOM) for the tool which was established by applying a standard tool to a calibration joint at a nominal air pressure (P_NOM) and a nominal temperature (Temp_NOM); and

calculating a temperature calibration factor (C_T) by dividing the nominal torque value (T_NOM) by the expected 1 torque value (T_EXP).

4. The method of claim 3 wherein the temperature of the tool is measured at a given interval and averaged over a given amount of time.

5. The method of claim 4 wherein the given interval is equal to 5 minutes and the given amount of time is equal to 30 minutes.

6. The method of claim 2 wherein the step of determining a calibration factor further includes the steps of:

measuring a measured torque value (T_MEA) for the tool by applying the tool to a calibration joint at a nominal air pressure (P_NOM); and

calculating a tool age calibration factor (C_A) by dividing the expected torque value (T_EXP) by the measured torque value (T_MEA).

7. The method of claim 6 wherein the step of measuring the measured torque value (T_MEA) includes measuring peak values of torque blows for a fixed time or a fixed number of blows and averaging the measured peak values.

8. The method of claim 7 wherein the step of measuring peak values includes filtering the measured peak values to attenuate signals above a corner frequency.

9. The method of claim 6 further comprises the step of automatically setting the air supply pressure to a value equal to the nominal air pressure (P_NOM) prior to application of the tool to the calibration joint.

10. The method of claim 2 wherein the step of determining a calibration factor further includes the steps of:

accessing a nominal torque value (T_NOM) for the tool which was established by applying a lab standard tool to a calibration joint at a nominal air pressure (P_NOM);

measuring a measured torque value (T_MEA) for the tool by applying the tool to the calibration joint at the nominal air pressure (P_NOM);

calculating a temperature calibration factor (C_T) by dividing the nominal torque value (T_NOM) by the expected torque value (T_EXP);

calculating a tool age calibration factor (C_A) by dividing the expected torque value (T_EXP) by the measured torque value (T_MEA); and

calculating a total calibration factor by multiplying the temperature calibration factor (C_T) by the tool age calibration factor (C_A).

11. The method of claim 10 wherein the expected torque value (T_EXP) is calculated using the formula:

T_EXP=A₀+A₁*temperatur+A₂*temperature²+A₃*temperature³

wherein temperature is equal to a current or averaged temperature value and the A'"'"'s are coefficients established using laboratory data relating to measured values under standard conditions.

12. The method of claim 11 wherein the coefficients are found by using a least squares fit to the laboratory data.

13. The method of claim 11 wherein the coefficients, using a lab standard tool manufactured by Yakota Industries under model no. YEX-1900 at a P_NOM of 70 psi with a resultant T_NOM of 108.6 ft. lbs., have the following values:

A₀=6.766E1

A₁=1.537E0

A₂=−

1.813E-2

A₃=6.462E-5

14. The method of claim 10 further comprising the step of storing the nominal torque value (T_NOM), the nominal air pressure (P_NOM) and the coefficients in an associated control system.

15. The method of claim 2 wherein the nominal torque value (T_EXP) is calculated using the formula:

T_EXP=A₀+A₁*temperature+A₂*temperature²+A₃*temperature³

wherein temperature is equal to a current or averaged temperature value and the A'"'"'s are coefficients established using laboratory data relating to measured values under standard conditions.

16. The method of claim 1 wherein at least one torque value has a linear pressure profile.

17. The method of claim 16 wherein each linear pressure profile has a constant pressure value.

18. The method of claim 1 wherein at least one torque value has a non-linear pressure profile.

20. The method of claim 19 wherein a calibration factor is utilized in establishing the maximum air pressure value.

21. The method of claim 19 wherein a calibration factor is utilized in establishing the intermediate air pressure value.

22. The method of claim 19 wherein the desired rate is equal to 1 psi per impulse blow.

23. The method of claim 19 further comprising the steps of:

establishing a finish air pressure value equal to the air pressure value at the time the torque applied to the fastener is within the predetermined range of the desired torque; and

supplying the tool with air at an additional air pressure value less than the finish air pressure value for a limited time.

24. The method of claim 23 wherein the additional air pressure value is calculated as a percentage of the finish air pressure value.

25. The method of claim 23 wherein the additional air pressure value is a predetermined value related to the desired torque.

26. The method of claim 19 further comprising the step of:

supplying the tool with air at a starting air pressure value greater than the intermediate air pressure value and less than or equal to the maximum air pressure value for a limited time prior to supplying of air beginning at the intermediate air pressure value.

27. The method of claim 26 wherein a calibration factor is utilized in establishing the starting air pressure value.

28. The method of claim 26 further comprising the steps of:

measuring a torque value at the limited time;

comparing the measured torque value at the limited time with a limit torque having a predetermined value; and

designating a pre-tightened condition if the measured torque value at the limited time is greater than or equal to limit torque value.

29. The method of claim 28 wherein the limit torque value is calculated as a percentage of the desired torque.

30. The method of claim 29 wherein the percentage is in a range of 91-100 percent.

31. The method of claim 28 wherein a calibration factor is utilized in establishing the predetermined value.

19. A method of controlling an air driven tool to provide a desired torque to a fastener, the method comprising the steps of:

establishing a maximum air pressure value;

repeatedly measuring the torque applied to the fastener;

supplying the tool with a continuous supply of air beginning at an intermediate air pressure value that is less than the maximum air pressure value and continuously increasing the air pressure at a desired rate until the torque applied to the fastener is within a predetermined range of the desired torque.

32. A method of controlling an air driven tool to provide a desired torque to a fastener, the method comprising the steps of:

establishing an air pressure profile for a plurality of torque values, each air pressure profile having;

a maximum value;

an intermediate air pressure value that is initially less than the maximum air pressure value and continuously increases at a desired rate until the torque applied to the fastener is within a predetermined range of the desired torque; and

a starting air pressure value that is greater than the intermediate air pressure value and less than or equal to the maximum air pressure and which is applied for a limited time prior to supplying of air at the intermediate air pressure value;

determining a calibration factor for the tool;

multiplying the desired torque by the calibration factor to determine a calibrated torque value; and

supplying the tool with air at the air pressure profile corresponding to the calibrated torque value.