Apparatus for fixing workpieces to be machined and method of fixing a workpiece by means of that apparatus

In a method of fixing a workpiece in a machine tool for machining the workpiece, which comprises

• initially moving two clamping jaws operable to move toward and away from each other along respective displacement paths into engagement with the workpiece with a respective actuator associated with each one of the clamping jaws and operable to move each one of said jaws individually to position the jaw along the displacement path thereof,
• fixing one of the jaws serving as a backing jaw in an initial position wherein it engages the workpiece and
• moving the other one of the jaws serving as pressure-applying jaw along the displacement path thereof toward the backing jaw to apply clamping pressure to the engaged workpiece and causing a yielding movement of the backing jaw along the displacement path thereof,
• the improvement comprising the steps of
• (a) picking up the respective positions of the backing jaw along the displacement path thereof before and after the yielding movement and generating position signals corresponding to the respective positions,
• (b) transmitting the position signals to a controller incorporating a stored control program, and
• (c) delivering displacement signals to the actuator of the backing jaw, the displacement signals being a function of the received position signals in accordance with the stored control program whereby the actuator moves the backing jaw back to the initial position along the displacement path over a distance corresponding to the yielding movement and determined by the received position signals, the backing jaw being released during the back movement and then fixed again.