Process of determining torque output and controlling power...

Details Process of determining torque output and controlling power... Process of determining torque output and controlling power...

1998-12-03

2001-11-06

Smith, Scott A. (Department: 3721)

Tool driving or impacting

Processes

C173S177000, C173S180000, C173S181000, C173S183000, C073S862230

Reexamination Certificate

active

06311786

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to processes for determining torque output and controlling power impact tools using impulse. The invention also relates to a mechanical impact wrench having electronic control.
2. Related Art
In the related art, control of power impact tools has been accomplished by directly monitoring the torque of impacts of the tool. For instance, in U.S. Pat. Nos. 5,366,026 and 5,715,894 to Maruyama et al., incorporated herein by reference, controlled impact tightening apparatuses are disclosed in which complex processes involving direct torque measurement are used. Direct torque measurement involves the measurement of the force component of torsional stress, as exhibited by a magnetic field about a tool output shaft, at the point in time of impact. From this force component, related art devices directly determine the torque applied during the impact, i.e., torque T=force F times length of torque arm r. As exemplified by FIG. 10 of U.S. Pat. No. 5,366,026, however, torque measurements fluctuate, even after a large number of impacts are applied. This phenomena is caused by the inconsistent nature of the force component of the impact. In particular, some devices measure torque at a given point in time, such that the torque measured is based on whatever force is being applied at that point in time. In other cases, the force is monitored as it rises, and is measured for peak at a point in time at which a force decrease is detected. In either case outlined above, the force may not be the peak force and, hence, the peak torque derived may not be accurate.
To rectify this problem, related art devices use weighting factors, or peak and/or low pass filtering of torque peak measurement, and/or assume, even though it is not the case, a constant driving force from the motor. For instance, in U.S. Pat. No. 5,366,026, torque measurements are used to calculate a clamping force based on the peak value of a pulsatory torque and an increasing coefficient that represents an increasing rate of a clamping force applied. Unfortunately, torque measurement accuracy remains diminished. Accordingly, there exists a need for better processes of operating power impact tools and, in particular mechanical impact tools (i.e., those with mechanical impact transmission mechanisms), with greater accuracy of torque measurement. There also exists a need for more accurate torque measurement.
Another shortcoming of the related art is the lack of an electronic control in a mechanical impact wrench.
SUMMARY OF THE INVENTION
In a first aspect of the invention a process is provided for determining the torque applied by a power impact tool, comprising the steps of: determining the impulse of a tool impact; and calculating a torque value of the tool from the impulse. This aspect provides a more accurate measurement of torque applied by a power tool by deriving the torque from an impulse determination of each impact during, for example, the tightening process of a threaded fastener joint. Because impulse determinations include a time parameter, fluctuations of force over time, which are not accounted for in direct torque measurements, can be taken into account. As a result, the measured torque values derived from the measured impulse values allow for more precise operation of the tool and more precise action on a workpiece.
In a second aspect of the invention a process is provided for controlling a power tool that applies repetitive torque impacts to a workpiece, comprising the steps of: determining an impulse value from a measured force value of each tool impact; calculating a torque value of the tool from the impulse value; determining whether the torque value meets a torque standard for the workpiece; and stopping operation of the tool when the torque value violates the standard. This aspect provides the overall operational process for operating an impact tool using impulse determinations. As an alternative to this aspect, the number of tool impacts and the time duration of operation may be monitored for further precision.
In a third aspect of the invention a process is provided for controlling a mechanical impact tool, comprising the steps of: determining an impulse value of each tool impact; calculating a torque value of the tool from the impulse; determining whether the torque value meets a torque standard for the workpiece; and stopping operation of the tool when the torque value violates the standard. This aspect provides the same advantages of the second aspect but on a mechanical impact tool.
In a fourth aspect of the invention a mechanical impact wrench is provided comprising: a motor; a mechanical impact transmission mechanism coupled to the motor to repetitively transmit an impact to the output shaft; and an electronic control to control operation of the mechanical impact wrench. This aspect provides the never before furnished electronic control of a mechanical impact wrench so as to provide increased accuracy, longevity, and lower costs over prior art devices.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.


REFERENCES:
patent: 5181575 (1993-01-01), Maruyama et al.
patent: 5285857 (1994-02-01), Shimada
patent: 5289886 (1994-03-01), Shikata et al.
patent: 5315501 (1994-05-01), Whitehouse
patent: 5351555 (1994-10-01), Garshelis
patent: 5366026 (1994-11-01), Maruyama et al.
patent: 5465627 (1995-11-01), Garshelis
patent: 5492185 (1996-02-01), Schoeps et al.
patent: 5708216 (1998-01-01), Garshelis
patent: 5715894 (1998-02-01), Maruyama et al.
patent: 5937370 (1999-08-01), Lysaght
Differing Torque Sensing Technologies, pp. 4-17, 1998 Magna-lastic Devices, Inc.

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