Patent ID: 8382405

Claim:
A spindle device for a machine tool, comprising: a spindle having an attaching hole which opens in a front end surface and a rear end surface of the spindle and penetrates through the spindle along an axis of the spindle, the spindle having a tool attaching portion to which a tool is attached formed at a front end portion of the attaching hole; a first housing having a retaining hole and supporting the spindle within the retaining hole so that the spindle is rotatable about the axis thereof; a first drive motor for rotating the spindle; clamping means for clamping the tool attached to the tool attaching portion of the spindle to fix the tool to the tool attaching portion; control means for controlling an action of the first drive motor; the first drive motor comprising: a cylindrical first rotor installed securely on an outer circumferential surface of the spindle; and a first stator installed securely on an inner circumferential surface of the retaining hole of the first housing, the first stator being disposed at a distance from the first rotor radially outwardly of the first rotor; and the clamping means comprising: a drawing member which is disposed within the attaching hole of the spindle so as to be movable in forward and backward directions along an axis thereof, and which moves in the backward direction to draw the tool into the tool attaching portion and clamp the tool; and a drive mechanism which is placed on a rear-end side of the spindle, and which moves the drawing member in the forward direction to unclamp the tool clamped to the tool attaching portion by the drawing member, wherein the spindle device for a machine tool further comprises: a second housing which is formed to have a hollow portion therein and which is connected to a rear portion of the first housing so that a rear end portion of the spindle is positioned within the hollow portion; a second drive motor which is disposed within the hollowing portion of the second housing and an action of which is controlled by the control means, the second drive motor comprising: a cylindrical second rotor which is disposed coaxially with the spindle on the rear-end side of the spindle and which is supported so as to be rotatable about an axis thereof; and a second stator installed securely on an inner circumferential surface of the hollow portion of the second housing, the second stator being disposed at a distance from the second rotor radially outwardly of the second rotor; and a connecting mechanism which is disposed within the second housing and has at least a first member installed securely on the second rotor and a second member installed securely on the rear end portion of the spindle, which connects the spindle and the second rotor by connecting the first member and the second member and releases the connection between the spindle and the second rotor by releasing the connection between the first member and the second member, and an action of which is controlled by the control means, and the drive mechanism is disposed within the second rotor.