Method and device for controlling a hydraulically operated power wrench

US8056426B2 · kind B2 · utility

Inventors

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

Key dates

• Filing date: Apr 17, 2009
• Grant date: Nov 15, 2011
• Expiry date: Jul 21, 2030

Classification

• Technology area (CPC B): Performing Operations; Transporting
• CPC primary: B25B23/1456
• WIPO field: Machine tools
• WIPO sector: Mechanical engineering

Abstract

In a method for controlling a hydraulic power wrench with a pivotable lever pivoted by a piston-cylinder unit and a ratchet arrangement for stepwise rotation of a ratchet bushing by advancing and return strokes, parameters such as nominal torque or pre-load or screw parameters are entered into an electronic input unit. Nominal pressure corresponding to the parameters is determined by an electronic evaluation unit and generated by the pump. The piston-cylinder unit is pressure-loaded for performing a pre-stroke until the nominal pressure is reached followed immediately by a return stroke. A time interval from beginning of pressure loading until reaching nominal pressure or until reaching an initial pressure after pressure relief is measured. Pressure loading and measuring are repeated. The measured time intervals are compared. Pressure loading cycles are stopped when at least the last measured time interval is shorter than at least the penultimate measured time interval.