Power wrench

US6161629A · kind A · utility

Inventors

• Jörg Hohmann · Meschede, DE
• Frank Hohmann · Warstein, DE

Key dates

• Filing date: Jul 16, 1999
• Grant date: Dec 19, 2000
• Expiry date: Jul 16, 2019

Classification

• Technology area (CPC B): Performing Operations; Transporting
• CPC primary: B25B23/14
• WIPO field: Machine tools
• WIPO sector: Mechanical engineering

Abstract

A power screwdriver has a drive unit and an input circuit for inputting screw size, material quality, pitch, and clamping length of a screw. An evaluation circuit is provided for determining a nominal prestress force based on input screw size, material quality, and clamping length, for determining a nominal torque based on the nominal prestress force and the pitch, and for determining the screw clamping angle resulting from the nominal prestress force and the pitch. A sensing device for sensing the actual torque is provided, and a further sensing device for sensing the actual screw clamping angle is present. A control and switch-off device controls further rotation of the drive unit when the actual torque coincides with the nominal torque and switches off the drive unit when the actual screw clamping angle coincides with the nominal screw clamping angle. The nominal torque, based on which the additional rotation o f the drive unit is controlled until the nominal screw clamping angle is reached, is set to a value which is smaller than the torque corresponding to the nominal pretension force. An additional rotation angle of the drive unit, for reaching the nominal screw clamping angl…