Electric heating – Metal heating – Cutting or disintegrating
Patent
1989-05-26
1991-10-15
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
B23H 702
Patent
active
050576623
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a spark erosion machine, comprising a travelling wire electrode and an optical measuring means to measure the deflection of the travelling wire electrode, the measuring means comprising a light source, a sensor assembly for measuring the light beam which comes from the light source and is shaded by the travelling wire electrode, as well as an evaluation circuit connected downstream of the sensor assembly.
Such an electric erosion machine is known from DE-PS 28 26 270. For each measuring plane, this known arrangement comprises a light source and two sensor elements disposed behind the travelling wire electrode in the direction of the light beam. These sensor elements are located laterally spaced from each other. As long as the travelling wire electrode is in a zero position, its shadow falls between the two sensor elements so that both are illuminated and provide an electrical signal. As the travelling wire electrode is deflected by a predetermined minimum value, one of the two sensor elements is shaded by the travelling wire electrode so that a conclusion may be drawn from the changing output signal of this sensor element as to the displacement of the erosive wire from its zero position. Therefore, what can be determined with this known arrangement is primarily whether or not the travelling wire electrode is in zero position. No precise measurement of the deflection is possible in a very narrow range. However, this known machine does not need a precise measurement, because a control of the position of the wire electrode is only performed with respect to the Zero-position of the sensor. Therefore, it is not possible to avoid faults in the cutting process.
A similar electric erosion machine is known from JP-OS 51-137 193. In that case the sensor arrangement consists of a group of parallel side-by-side light conducting fibers supplied with light from a light source. Again, the travelling wire electrode is positioned between the light source and the light conducting fibers. A photoelectric transducer element is connected to each light conducting fiber, and is each connected, in turn, to a summing circuit generating an output signal when at least a predetermined number of light conducting fibers is irradiated by the light source. As long as the travelling wire electrode is in a required position, its shadow conceals such a great number of light conducting elements that the summing circuit does not respond. When the travelling wire electrode is deflected out of the range of detection of this sensor arrangement all the light conducting fibers are irradiated by the light source so that the summing circuit does respond. The output signal of the summing circuit, therefore, likewise indicates only whether or not the travelling wire electrode is within its required range.
Optical measuring means which scan the contour of an object are known in other technical fields, for example, from DE-OS 19 30 111, U.S. Pat. No. 3,901,604, DE-OS 26 46 674. However, the shadow casting technique is not applied in those cases. Instead, either the deflection of a light beam is measured (U.S. Pat. No. 3,901,604) or a mark applied to the object to be measured is scanned optically (DE-OS 26 46 674, DE-OS 19 30 111), the mark having an absorbance or reflectivity which differs from the background of the object to be measured.
As regards the technical background, reference is further made to the following publications: JP-AS 58-217225, JP-OS 60-29231, JP-OS 57-178618, JP-OS 60-221221, and JP-OS 59-142021.
Cylindrical lenses having a parabolic distribution of the refractive index have been known in the market for some time. In principle, these lenses have the same optical characteristics as conventional spherical lenses, plus the additional advantage of having planar end surfaces. These lenses are used preferably for coupling light into light conducting fibers (cf. company publication entitled "Selfoc" by Messrs. TS-Optoelectronic, 8000 Munich 22). ("Selfoc" is a registered trademark by Messrs. Nippon Sheet Glass Co.,
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Beltrami Ivano
Bertholds Axel
Wehrli Peter
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