Method and apparatus for shutting off a power screwdriver

US4463293A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Friedrich Hornung · Stuttgart, DE
• Wolfgang Jundt · Ditzingen, DE
• Fritz Schadlich · Echterdingen, DE
• Hans-Joachim Vogt · Stuttgart, DE
• Steffen Wunsch · Waldenbuch, DE

Key dates

• Filing date: Mar 22, 1983
• Grant date: Jul 31, 1984
• Expiry date: Mar 22, 2003

Classification

• Technology area (CPC B): Performing Operations; Transporting
• CPC primary: B25B21/00
• WIPO field: Machine tools
• WIPO sector: Mechanical engineering

Abstract

A power screwdriver that is equipped with a spring coupling between the motor drive and the tool spindle, a signal that indicates that a certain value of torque has been overstepped, at which the screwdriver must be sopped, first causes reversal of the motor, but before the motor appreciably turns in the reverse direction, powers shut-off, allowing the motor to coast. After another brief interval, power is reapplied to the motor in the original direction, again briefly. In this way it is possible for the final shut-off to occur when the motor is stopped and the spring is unstressed, avoiding oscillations of the motor-spring system. A triac bridge circuit makes possible quick reversals and brief applications of power. In such a bridge circuit, precautions must be taken to be sure one pair of triacs is extinguished before the other pair is ignited.