Clamping device for tool holder

A clamping device arranged for releasably holding a tool holder shank, the clamping device comprising:

• a housing;
• a spindle rotatably mounted inside the housing and having a front end, a rear end and a bore which intersects the front end and extends rearwardly therefrom, wherein a mounting portion for receiving the tool holder shank is provided at a front end of the bore;
• a drawbar slidably mounted inside the bore so as to be reciprocally moveable in the bore along a longitudinal axis thereof between an advanced releasing position and a retracted locking position;
• a plurality of engagement members arranged around the drawbar at a front end thereof, wherein the engagement members, under the effect of a movement of the drawbar from the advanced releasing position to the retracted locking position, are moveable from a first position, in which the engagement members allow the tool holder shank to move into and out of said mounting portion of the bore, to a second position, in which the engagement members are in locking engagement with the tool holder shank and keep the tool holder shank secured to the spindle;
• an actuating member arranged inside the housing, wherein the actuating member is slidably mounted to the spindle so as to be moveable in relation to the spindle in the axial direction thereof,
• a motion transferring mechanism arranged inside the housing, wherein the motion transferring mechanism is mounted to the spindle and configured to transfer a movement of the actuating member in a first axial direction in relation to the spindle into a movement of the drawbar from the advanced releasing position to the retracted locking position;
• two or more hydraulic actuators arranged in or mounted on the housing on different sides of the spindle and configured to move the actuating member axially in relation to the spindle, wherein each hydraulic actuator includes one or more piston members, each of the piston members being slidably received in a space of the hydraulic actuator at the side of and at a distance from the spindle so as to be hydraulically moveable axially in this space in parallel with the longitudinal axis;
• and
• a connecting element at least partly arranged inside the housing and configured to form a connection in radial direction between the actuating member and the piston members of the hydraulic actuators, wherein the connecting element is configured to transfer an axial movement of the piston members in relation to the housing into a corresponding axial movement of the actuating member in relation to the spindle, wherein the connecting element includes a central part through which the connecting element is connected to the actuating member, and several arms, one for each hydraulic actuator, through which the connecting element is connected to the piston members of the hydraulic actuators, wherein each arm is fixed to the central part and projects from the central part in radial direction, and wherein each hydraulic actuator includes two piston members the two piston members being first and second piston members, the first and second piston members being arranged opposite each other and in alignment with each other, wherein each one of said first and second piston members has a first side facing the other piston member and an opposite second side facing away from the other piston member, wherein a first hydraulic chamber is formed in said space of the hydraulic actuator on the second side of the first piston member and a second hydraulic chamber is formed in this space on the second side of the second piston member, wherein each one of said arms of the connecting element has a part received in an interspace between the first and second piston members of the associated hydraulic actuator, and wherein the connecting element is moveable in said first axial direction by feeding of hydraulic fluid into the first hydraulic chamber of each hydraulic actuator and in an opposite second axial direction by feeding of hydraulic fluid into the second hydraulic chamber of each hydraulic actuator.