Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-11-04
2001-12-04
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06326577
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a wire cut electrical discharge device which processes a work piece by generating a discharge between a wire cut electrode and a work piece while conveying the wire electrode along a wire conveying path while a predetermined tension is applied to it. More particularly, the invention relates to a wire cut electrical discharge device which is provided with a device which controls the tension applied to the wire electrode while it travels along the wire conveying path.
BACKGROUND OF THE INVENTION
In most wire cut electrical discharge processing devices, the wire electrode travels in a direction which is nearly vertical to the X-Y plane between a pair of wire guides while one of the wire electrode and work piece moves on the X-Y plane relative to the other. During processing, a voltage pulse is applied to a gap which is formed between the wire electrode and the work piece and the work piece is processed by the wire by generating a discharge in this gap. This type of wire cut electrical discharge processing device is used for precise processing applications.
The wire electrode, typically having a 0.1 to 0.3 mm diameter, is conveyed from a wire spool through a pair of wire guides disposed respectively above and below the work piece, via a device comprising a number of pulleys which apply tension to the wire. In addition, the wire electrode is conveyed to an appropriate recovery device, usually via a wire take-up device comprising a number of pulleys. The wire take-up device is controlled so that the traveling speed of the wire electrode is maintained at a set value. The tension applying device is controlled so that the tension applied to the wire electrode is a set value. The tension on the wire electrode is set, for example, so that it corresponds to the diameter and material of the wire electrode as well as the type of processing. If the tension is set to a large value, good straightness of the wire electrode between the pair of wire guides is achieved. However, excessive force may cause the wire to break, which is undesirable.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a wire cut electrical discharge processing device which accurately maintains the tension on the wire electrode at a set value.
It is another object of the present invention to provide a wire cut electrical discharge processing device which reduces fluctuations in the tension on the wire electrode.
Yet another object of the present invention is explained partially in the explanation which follows and will partially become clear to one of skill in the art by practice of the invention.
In order to attain the above-mentioned and other objects, a wire cut electrical discharge processing device according to the present invention comprises a device which conveys the wire electrode so that the wire electrode travels along a conveying path, a servo motor which applies tension to the wire electrode while it travels, a NC device which generates signals which indicate the set value for the tension, a tension detection device which detects the tension applied to the wire electrode and generates signals which indicate the value detected, and a tension control device which revises the speed command signals which direct the rotating speed of the servo motor based on the difference between the set value of the tension and the detected value of the tension. The tension control device comprises two notch filters which stop the different frequencies which are continuously connected.
The tension control device may comprise an unnecessary frequency setting device which sets the minimum value of the unnecessary frequencies to one of the two notch filters and sets the maximum value of the unnecessary frequencies to the other of the two notch filters.
The wire cut electrical discharge processing method in the present invention which processes the work piece by generating a discharge in the gap between the wire electrode and the work piece while the wire travels along a conveying path while tension is applied to it by a motor, comprises:
a step of generating signals which indicate a set value of the tension to be applied to the wire electrode;
a step of conveying the wire electrode along a conveying path;
a step of generating speed command signals to direct the rotation speed of the motor;
a step of detecting the tension which is applied to the traveling wire electrode and generating signals which indicate the detected value;
a step of revising the speed command signals based on the difference between the set value and the detected value of the tension applied to the wire electrode;
a step of determining a the minimum value and a maximum of unnecessary frequencies which cause the force applied to the wire to fluctuate based on the signals which indicate the detected value of the tension applied to the wire electrode; and
a step of providing a cascade connection between a notch filter which checks the minimum value of the unnecessary frequencies and a notch filter which checks a maximum value of the unnecessary frequencies.
REFERENCES:
patent: 4298781 (1981-11-01), Inoue
patent: 6028282 (2000-02-01), Toyonaga et al.
patent: 2-185321 (1990-07-01), None
patent: 5-312657 (1993-11-01), None
patent: 7-60552 (1995-03-01), None
patent: WO98/39128 (1998-09-01), None
International Search Report.
Minamikawa Masateru
Toyonaga Tatsuo
Devinsky Paul
Evans Geoffrey S.
McDermott & Will & Emery
Sodick Co. Ltd.
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