Hydraulic drive for a tool head

A hydraulic drive for adjustment, feed, and return movements of a toolhead of a machine tool, the hydraulic drive comprising:

• a hydraulic motor including a movable drive element fixedly coupled to the toolhead, said drive element being drivable by alternative pressurization and pressure relief of drive pressure chambers in accordance with tool movements;
• a follow-up control valve operating in response to an electromechanically controllable reference position value setting for the movable drive element and mechanical actual position value return indication;
• means for setting a reference position value and return indication of an actual position value including a threaded spindle and a spindle nut fashioned as a hollow shaft and meshing with a thread of the spindle, one of the threaded spindle and the spindle nut forming a reference value setting element, one of the threaded spindle and spindle nut being adapted to be driven by an electric motor in a direction of rotation of the electric motor in accordance with a setting of the reference position value, and the other of the threaded spindle and spindle nut being adapted to be axially displaced by a drive element in accordance with an actual position value return indication;
• an electronic control unit provided with an interface for an NC or a CNC control for producing signals required for motion control of the electric motor;
• a rotational and angular position pickup system for producing output signals containing information relating to a total number of revolutions by the reference value setting element as well as the azimuthal position of the reference value setting element within each revolution;
• and
• an electronic displacement pickup system providing output signals which constitutes a direct measure for axial deflections of the reference value setting element and a valve operating member of the follow-up control valve also executing these axial deflections from a rest position and providing a measure for the lag error by which at lest one of the toolhead or the drive element of the hydraulic motor trails with respect to a reference position.