Tightening tool

• US 5,289,885 A
• Filed: 09/08/1993
• Issued: 03/01/1994
• Est. Priority Date: 01/23/1992
• Status: Expired due to Term

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Sakoh, Masahiko
• Primary Examiner(s): SMITH, SCOTT A
• Application Number:
  US08/117,940
• Time in Patent Office: 174 Days
• Field of Search: 173/2, 173/4, 173/5, 173/10, 173/11, 173/176, 173/20, 173/109, 173/178, 173/128, 173/206, 173/180, 81/467, 81/468, 81/469, 364/474.19, 364/508
• US Class Current: 173/2
• CPC Class Codes: B25B 23/1405 for impact wrenches or screwdrivers
• CPC Class Codes: B25B 23/1475 for impact wrenches or screwdrivers
• CPC Class Codes: B25B 23/15 having a mechanism to mark the work when the selected torque is applied to the work

Abstract

A tightening tool includes a hammer for impacting on an anvil which drives a nut etc. A microphone is provided for converting impact sounds of the hammer on the anvil into an electric signal. A counting device counts the number of pulses of the electric signal. A setting device is provided for setting a set number of impacts to be obtained. A switch device compares the counted number of pulses with the set number and stops a motor for driving the hammer when the number of pulses coincides with the set number.

Claims

1. A tightening tool, comprising:

a hammer rotatably driven by drive means;

an anvil driven by said hammer in such a manner that said hammer is rotated idly when the torque transmitted from said hammer to said anvil exceeds a predetermined value and that said hammer impacts on said anvil so as to rotate said anvil when said hammer is rotated by a predetermined angle after said hammer has been rotated idly;

a microphone for converting impact sounds of said hammer on said anvil into an electric signal;

comparing means for comparing the level of the electric signal with a reference level;

detecting means for detecting timing when the level of the electric signal exceeds the reference level;

period calculating means for calculating a period of the timing based on at least two numbers of the detected timing;

counting means for counting the number of impact from the number of timing when the level of the electric signal exceeds the reference level, said counting means being operable to compensate the counted number of impact based on the period calculated by said period calculating means;

setting means for setting a set number of impact to be obtained; and

switch means for comparing the number counted by said counting means with the set number set by said setting means and for stopping said drive means when the counted number coincides with the set number.

2. The tightening tool as defined in claim 1 and further including latch means for keeping the result of comparison by said comparing means during a time TC, the time TC being determined to be slightly shorter than a possible shortest impact period.

3. The tightening tool as defined in claim 2 and further including means for determining as to whether the result of comparison has been once changed immediately after said latch means has kept the result of comparison, and means for changing the reference level when said determining means determines that the result has been once changed.