Gear cutting – milling – or planing – Milling – Cutter spindle or spindle support
Reexamination Certificate
1998-12-02
2001-09-11
Wellington, A. L. (Department: 3722)
Gear cutting, milling, or planing
Milling
Cutter spindle or spindle support
C279S900000, C279S155000
Reexamination Certificate
active
06287059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a machine tool. More particularly, the invention relates to a clamping device for holding a tool holder such that the tool can be released to a hollow rotating spindle.
BACKGROUND TECHNOLOGY
In general, tapered shank tool holders having a knob on the tapered end are releasably held within a tapered socket on a complementary, hollow rotating spindle. The spindle has an axial hole which penetrates through the tapered socket, collet fingers which grip the tapered shank tool holder knob, and a draw bar connected to the collet fingers, housed so as to be able to slide in the shaft hole. The collet fingers are turnable in the space between the knob-gripping clamped position and the knob-releasing unclamped position. The draw bar is movable in the axial direction of the spindle between an operating position in which the tool holder is held in the spindle tapered socket and a non-operating position, in which the tool holder is released from the tapered socket.
In order to reliably hold the tool holder in the spindle tapered socket, a bias is normally applied on the draw bar toward the operating position by a strong spring force. At this point, the collet finger rotation is arrested, and the collet fingers are stopped in the clamped position. By this means, the knob held by the collet fingers is pulled toward the draw bar operating position, and the tapered shank is tightly fit into the tapered socket.
When machining by a given tool is completed, the machine tool controller generates a tool release signal, which releases the tool from the spindle. In response to this tool release signal, a tool changing device grips the tool holder which has been inserted in the spindle using an arm. When the controller receives a confirmation signal indicating that the tool changing arm has gripped the tool holder, it commands the draw bar to move against the spring force to the non-operating position using appropriate motion means, such as an air cylinder. By moving the draw bar to the non-operating position, tensile force from the spring is removed form the knob. The arresting of the rotation of the collet fingers ends with the movement of the draw bar. Nevertheless, the tool holder remains in the grip of the tool changing device arm, so that it will not fall down due to its weight.
However, a machine tool controller of this type cannot command the draw bar to move until a confirmation signal has been received. This is because when the draw bar moves to the non-operating position, i.e., until the tool changing device arm has gripped the tool holder, the weight of the tool holder causes the knob thereof to be released from the collet fingers, and a tapered shank may separate from the spindle tapered socket inside surface. Thus, in order to reliably prevent the tool holder from falling, the machine tool controller must wait for a confirmation signal. This wait time reduces tool changing operation efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a clamping device which reliably holds a tool holder so that it can be released, without reducing the efficiency of the tool changing operation.
Other objects of the present invention are presented in the description which follows, or will be apparent to practitioners of the art by practice of the invention.
In order to achieve the above and other objects, of the invention a machine tool clamping device according to the present invention, which holds a tool holder having a knob onto a spindle having an axial a shaft hole in such a way that it can be released, comprises:
multiple collet fingers housed in the spindle axial hole so as to be turnable between a clamped position in which the tool holder is clamped and an unclamped position in which the knob is released;
a collet sleeve for arresting the turning of the collet fingers;
an air cylinder for moving the collet fingers and the collet sleeve relative to each other in the spindle axial direction to permit rotation of the collet fingers;
a first plate spring for applying a strong force to bias the knob against the spindle through the collet fingers;
an air cylinder for removing the biasing force of the first plate spring; and
a second plate spring which maintains the collet fingers in a clamped position in opposition to the tool holder weight, even when the collet fingers rotate and the first plate spring is removed.
REFERENCES:
patent: 3568566 (1971-03-01), Weidig
patent: 3762271 (1973-10-01), Poincenot
patent: 4075927 (1978-02-01), Frazier
patent: 4620824 (1986-11-01), Eckstein et al.
patent: 4628586 (1986-12-01), Yoshimi et al.
patent: 4997325 (1991-03-01), Heel et al.
patent: 3-4323 (1991-01-01), None
patent: 6-170623 (1994-06-01), None
patent: 7-13923 (1995-04-01), None
patent: 8-174315 (1996-07-01), None
Hashidate Akitake
Misawa Keita
Cadugan Erica E
Devinsky Paul
McDermott & Will & Emery
Sodick Co. Ltd.
Wellington A. L.
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