Electrical driving system for machine tool

A machine tool ELECTRICAL DRIVING SYSTEM comprising:

• a housing installed to be fixed to a main body of a machine tool;
• a hollow tubular spindle rotatably installed with respect to the housing inside the housing;
• a drive pulley rotatably installed with respect to the spindle outside the spindle;
• a spindle motor configured to rotate the drive pulley;
• a drawbar installed to be linearly movable in an axial direction inside the spindle and configured to be rotatable together with the spindle;
• a motion conversion unit configured to convert a rotary motion of the drive pulley into a forward-rearward linear motion of the drawbar;
• a clutch unit installed outside the spindle to selectively connect the spindle to the drive pulley and the housing;
• a position detection unit including a first encoder pulley fixed to the drive pulley, a second encoder pulley installed in the housing, a timing belt wound around the first encoder pulley and the second encoder pulley to transmit a rotational force of the first encoder pulley to the second encoder pulley, and an encoder axially coupled with the second encoder pulley to detect an amount of rotation and a rotation position of the drive pulley;
• and
• a controller configured to perform a position adjustment process of rotating the drive pulley based on position information of the clutch unit detected by the position detection unit immediately before a spindle operation mode in which the spindle is connected to the drive pulley by the clutch unit is switched to a clamping operation mode in which the spindle is connected to the housing and immediately before the clamping operation mode is switched to the spindle operation mode, and aligning the drive pulley to the position of the clutch unit,
• wherein the clutch unit includes:
• a fixed clutch fixed to a front surface of the drive pulley and having a fixed serration formed along a circumferential direction,
• a movable clutch formed in a ring shape and slidable on an outer surface of the spindle in the axial direction, wherein the movable clutch is non-rotatable relative to the outer surface of the spindle,
• a front coupler installed on a front surface of the movable clutch and having a front serration configured to engage with a housing serration formed behind the housing in the clamping operation mode,
• a rear coupler installed on a rear surface of the movable clutch and having a rear serration configured to engage with the fixed serration of the fixed clutch in the spindle operation mode, and
• a clutch driving unit configured to linearly move the movable clutch in the axial direction of the spindle in the clamping operation mode,
• wherein the controller is configured to rotate the drive pulley based on the position information detected by the position detection unit immediately before the spindle operation mode is switched to the clamping operation mode to align a position of the movable clutch to an initial original position, and the controller is configured to rotate the drive pulley to finely adjust a position of the fixed clutch in a clamping direction and align the fixed serration of the fixed clutch with the rear serration of the movable clutch based on the position information detected by the position detection unit immediately before the clamping operation mode is switched to the spindle operation mode.