Patent ID: 8721238

Claim:
A tool clamping device for a work spindle of a machine tool, comprising: an actuating member, positioned within the tool clamping device, which is displaceable between a first position in which the tool clamping device is in a clamping position and a second position in which the tool clamping device is in a releasing position; a sensor, disposed within the tool clamping device for detecting an axial position of the actuating member, the sensor including a capacitive element whose value depends on an axial position of the actuating member; at least one portion of the actuating member is electrically conductive and forms at least one electrode of the capacitive element; and the capacitive element further includes two annular and mutually coaxial electrodes arranged next to one another in an axial direction and having external terminals, wherein an annular and electrically conducting portion of the actuating member covers the two electrodes coaxially and thereby forms with these two electrodes a series circuit of two capacitors, and wherein a cross section of the electrically conductive portion of the actuating member covering the two electrodes varies in the axial direction so that the capacitance value depends on the axial position of the electrically conductive portion of the actuating member.