Power tool used for fastening screw or bolt

Abstract

In a power impact tool for fastening a screw or a bolt, malfunction that driving of a motor is stopped before the screw or the bolt is fastened completely can be prevented. A fastening judger judged that the fastening operation is completed at least when a torque variation ratio becomes substantially zero and a reference index becomes equal to or larger than a threshold value of trouble judgment. The reference index is a number of impact of a hammer in a term in which the torque variation ratios take positive values, and the threshold value of trouble judgment is calculated with using a maximum value of the torque variation ratio in the term. Since the number of the impact of the hammer due to trouble in fastening operation is smaller than that due to the screw or the bolt is fastened completely, it is possible to distinguish the increase of the torque in the former case from the increase of the torque in the latter case.

Description

technical field [0001] The present invention relates to an electric tool for fastening screws or bolts, such as an impact screwdriver or an impact wrench. Background technique [0002] In general, an electric tool that tightens a screw or a bolt using the driving force of a motor has a function of automatically stopping the driving of the motor when the torque required for tightening the screw or the bolt reaches a predetermined value because the screw or the bolt has been completely tightened. Function. [0003] In the first conventional power tool for fastening screws, such as an impact wrench disclosed in Japanese Patent Application Laid-Open Publication No. 4-322974, the impact value of a hammer is detected, and when the impact The drive of the motor is automatically stopped when the value reaches a predetermined reference value. [0004] In the second conventional electric impact tool disclosed in Japanese Patent Application Laid-Open Publication No. 9-285974, the rot...

AI Technical Summary

Problems solved by technology

[0011] However, in this fourth conventional electric impact tool, it is difficult to distinguish between a temporary increase in torque in torque variation due to a malfunction in the tightening operation and a torque increase due to the bolt being completely tightened, because corresponding to Depending on the combination of the bolt and the workpiece to be fastened, the change in torque when the bolt is tightened is irregular

Therefore, there is a possibility that the driving of the motor stops before the bolts are fully tightened

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