Power tools with multi-stage tightening torque control

Details Power tools with multi-stage tightening torque control Power tools with multi-stage tightening torque control

1991-08-26

1992-10-13

Yost, Frank T.

Tool driving or impacting

Automatic control of power operated means

Drive means responsive to torque or speed condition

81469, 7386223, 73862331, 173179, 173180, B25B 23147, B23Q 1709

Patent

active

051542420

ABSTRACT:
A power tool includes a DC motor for tightening a fastener through three consecutive stages. In the first stage, the motor is rotated at a high speed to tighten the fastener to a pre-seated condition which is acknowledged by the tool. Then, the motor is temporarily stopped and restarted at a low speed for tightening the fastener to its seated condition to complete the second stage. At the third stage, a control is made to gradually increase a field current in a feedback manner by constantly monitoring the field current flowing through the motor up to a predetermined current limit determined as directly related to an intended tightening torque at which the fastener is tightened past the seat condition. After the field current reaches the current limit, the motor is stopped to complete the tightening cycle. By monitoring the field current during the third stage to control the field current in the feedback manner, it is possible to accurately determine the final tightening torque which is related substantially directly to the field current, assuring to tighten the fastener accurately to a desired final torque. The tool is also capable of increasing the field current at differing rates up to the current limits of different values within a constant period of time so as to complete the tightening of the fastener within substantially the same perod of time irrespective of the differing requirements for the final tightening torque.

REFERENCES:
patent: 3892146 (1975-07-01), Yasoshima
patent: 3962910 (1976-06-01), Spyridakis et al.
patent: 4249117 (1981-02-01), Leukardt et al.
patent: 4562389 (1985-12-01), Jundt et al.
patent: 4685050 (1987-08-01), Polzer et al.
patent: 4813312 (1989-03-01), Wilhelm
patent: 4908926 (1990-03-01), Takeshima et al.
patent: 4987806 (1991-01-01), Lehnert
patent: 5014793 (1991-05-01), Germanton et al.

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