Wire tension controlling method in a wire cut electric discharge

Details Wire tension controlling method in a wire cut electric discharge Wire tension controlling method in a wire cut electric discharge

1990-03-23

1991-06-11

Evans, Geoffrey S.

Electric heating

Metal heating

Cutting or disintegrating

219 6917, 36447404, B23H 710, B23H 720

Patent

active

050234200

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

1. Background of the Invention
The present invention relates to a wire cut electric discharge machine adapted to control the wire tension by means of an electric bracke, and more particularly, to a wire tension controlling method capable of preventing occurrences of wire breakage at the time of starting and releasing application of the wire tension, and changing the same.
2. Background Art
In general, a wire cut electric discharge machine includes an apparatus for controlling the tension applied to a wire electrode (hereinafter referred to as a wire). Typically, the wire tension controlling apparatus includes an electromagnetic powder brake for applying a braking force to a braking roller arranged in contact with the wire. An operation voltage of the powder brake is changed to adjust the braking force applied to the braking roller, to thereby control the wire tension. However, according to the wire tension controlling apparatus of this type, there is a possibility of the wire being broken or disconnected upon start of the application of the wire tension and upon increase of the wire tension. Further, the wire may be slacked when the application of the wire tension is released and the wire tension is reduced, so that occurrence of the wire breakage may be erroneously detected by a wire breakage detection apparatus disposed in the vicinity of the wire path. In addition, there is a possibility that the wire may vibrate upon start and release of application of the wire tension, and upon increase and decrease of the wire tansion, badly influencing various operating sections of the electric discharge machine.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a wire tension controlling method capable of controlling a wire tension, and of preventing wire breakage, an erroneous determination in wire breakage detection, and vibration of a wire, which may occur upon start and release of application of the wire tension and upon change of the wire tension in a wire cut electric discharge machine.
In order to achieve the above object, a wire tension controlling method of the present invention, which is applied to a wire cut electric discharge machine adapted to control a wire tension applied to a wire electrode by means of an electric brake, comprises steps of: (a) predictively determining, when a wire tension setting/updating instruction is delivered, presence/absence of a possibility of an actual wire tension being excessively changed if the electric brake is operated in accordance with the instruction; (b) changing a target wire tension by a predetermined amount so as to prevent an excessive change of the actual wire tension when the presence of the posibility of the actual wire tension being excessively changed is determined; and (c) periodically effecting the step (b) until the target wire tension reaches an instructed wire tension.
As described above, according to the present invention, when there is a possibility of the actual wire tension being excessively changed if the electric brake is operated in accordance with the wire tension setting/updating instruction, the target wire tension is gradually changed until it reaches the instructed wire tension. Therefore, the wire tension can be controlled to the target value, during an abnormal operation of the electric brake at the time of setting/updating the wire tension without the operation of the electric discharge machine being interrupted, which abnormality causes an excessive change of the wire tension which may incur wire breakage, erroneous determination of wire breakage detection, and vibration of the wire.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a wire delivery apparatus of a wire cut electric discharge machine to which a wire tension controlling method according to an embodiment of the present invention is applied, and peripheral equipment of the wire delivery apparatus;
FIG. 2 is a flowchart showing wire tension setting/updating process executed by the electric discharge machine of

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