Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-02-28
2001-12-04
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C242S419900
Reexamination Certificate
active
06326578
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a wire electric discharge machine for machining a conductive workpiece by causing electric discharge between a traveling wire electrode and the conductive workpiece, and more particularly to a tension applying device for applying tension to the traveling wire electrode.
BACKGROUND OF THE INVENTION
A wire electrode is normally supplied to a workpiece from a wire bobbin, running along a fixed wire conveying path including a tension applying device, to take-up rollers from which used wire electrode is discharged to an appropriate bucket. If a voltage pulse is applied between the wire electrode and the workpiece, electric discharge is caused between the wire electrode, as it is held in tension while traveling between a pair of wire guides and the workpiece. A wire electric discharge machine causes the wire electrode and the workpiece to move relative to each other within a horizontal X-Y plane in order to form the workpiece into a desired profile. The speed of travel of the wire electrode is controlled by a motor causing rotation of the take-up rollers, and tension on the wire electrode is provided by the tension applying device. In many instances, a wire electrode having a diameter of about 0.20 to 0.35 mm is used, but sometimes, a fine wire, having a diameter of about 0.15 to 0.05 mm, is used. The tension applying device adjusts the tension according to the diameter of the wire electrode. For example, a tension of about 1200 g may be applied to a wire electrode having a diameter of 0.20 mm, and a tension of about 50 g may be applied to a wire electrode having a diameter of 0.03 mm. In order to improve surface roughness and dimensional accuracy, a tension applying device has been proposed in order to accurately apply the appropriate tension according to the diameter to the wire electrode, and to prevent variations in tension.
Japanese Patent 8-336 discloses a tension applying device provided with a brake roller
47
linked to a high torque electromagnetic brake
3
via a clutch
7
, and a pinch roller
46
which contact(s) a peripheral surface of the brake roller
47
and which is linked to a low torque electromagnetic brake
1
, as shown in
FIG. 10. A
wire electrode
6
is wound in an S-shape around the rollers
46
and
47
. When a relatively thick wire electrode
6
is used, the relatively large braking torque of the high torque electromagnetic brake
3
is transmitted to the brake roller
47
. On the other hand, when a fine wire electrode
6
is used, the clutch
7
is disengaged and only the relatively small braking torque of the low torque electromagnetic brake
1
is transmitted to the pinch roller
46
.
As shown in
FIG. 11
, Japanese Patent No. 2686783 discloses a tension applying device having a switch
8
for connecting a brake roller
47
to a large brake
3
when a relatively thick wire electrode
6
is used, and for connecting the brake roller
47
a small brake
1
when a thin wire electrode
6
is used. A similar device is also disclosed in U.S. Pat. No. 5,422,454.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a tension applying device capable of accurately applying appropriate tension to a wire electrode according to the diameter, and provided with only one brake means.
Additional objects, advantages and novel features of the invention will be set forth in the description that follows, and in part will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by practicing the invention as recited in the appended claims.
In order to achieve the foregoing and other objects, a first embodiment of tension applying device for a wire electric discharge machine according to the present invention may comprise brake means having controllable torque, a rotatable tension roller around which a wire electrode is wound, and a drive roller directly linked to the brake means and pressed against the peripheral surface of the tension roller, the drive roller having a diameter smaller than the diameter of the tension roller.
Another embodiment of tension applying device for a wire electrode discharge machine according to the present invention may comprise a brake means having controllable torque, a rotating tension roller around which a wire electrode is wound, an intermediate roller having substantially the same diameter as the tension roller and formed integrally with the tension roller, and a drive roller directly linked to the brake means and pressed against the peripheral surface of the intermediate roller, the drive roller having a diameter smaller than the diameter of the tension roller.
REFERENCES:
patent: 5268551 (1993-12-01), Kawanabe et al.
patent: 5422454 (1995-06-01), Kajitori
patent: 2-100829 (1990-04-01), None
patent: 2-205415 (1990-08-01), None
patent: 3-239422 (1991-10-01), None
patent: 8-336 (1996-01-01), None
patent: 2686783 (1997-08-01), None
Devinsky Paul
Evans Geoffrey S.
McDermott & Will & Emery
Sodick Co. Ltd.
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