Optics: measuring and testing – By configuration comparison – With photosensitive film or plate
Patent
1997-10-07
1998-11-24
Pham, Hoa Q
Optics: measuring and testing
By configuration comparison
With photosensitive film or plate
356386, 25055924, G01B 1108
Patent
active
058415424
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an opto-electronic measuring apparatus for checking geometric features of a workpiece according to the shadow casting technique, including a first support, defining a supporting location for the workpiece, a second support, coupled with the first support, with two portions oppositely arranged with respect to said supporting location, a first generating system for generating optical radiations for providing a first beam of light with a section directed towards the workpiece, a first photosensitive linear system coupled to one of the two oppositely arranged portions for receiving said first beam after it is intercepted by the workpiece, a second generating system for generating optical radiations for providing a second beam of light with a section directed towards the workpiece, a second photosensitive linear system for receiving said second beam after it is intercepted by the workpiece and detecting and control circuits connected to the first and the second photosensitive linear system and adapted to receive the signals from the first and the second photosensitive linear system and to combine said signals for achieving a measurement of the workpiece in a single cross-section.
BACKGROUND ART
Various types of opto-electronic devices for checking the geometric features of workpieces are well known. These devices are based on various principles, among which the <<shadow casting>> technique.
Fundamentally, a shadow casting device comprises an emitter unit emitting a beam of light and directing it towards a workpiece, arranged at a prefixed position. The workpiece partially intercepts, depending on its dimensions, the beam. The non-intercepted portion of the beam reaches a detector-processor unit that detects the portion of the beam and, by means of electronic processings, calculates the dimensions of the workpiece, or its deviation with respect to a nominal value.
Among the shadow casting measuring apparatuses, those for measuring, in an absolute and flexible way, diameters and axial distances of rotationally symmetrical workpieces, as rings, hubs and elongate workpieces, like shafts, are particularly important. The term flexibility for similar apparatuses means, for example, the possibility of measuring workpieces with even considerably different nominal dimensions, workpieces with portions having dimensions, as the diameters thereof, differing, or workpieces of different types, without there being the need to modify the structure of the apparatus. For these purposes, it is necessary that the opto-electronic system cover a broad measuring range. Since the opto-electronic components available on the market, in particular the detecting devices, such as the devices with linear arrays of photodiodes, "CCD" ("Charge Coupled Devices") arrays, or similar ones, cover relatively small measuring ranges, it is necessary to envisage solutions enabling to broaden the range of a single component. In this connection, it is necessary to bear in mind that if several detecting devices are arranged aligned, one after the other, the resulting measuring range is discontinuous, as there are zones, corresponding to the passage from one device to the following one, that do not overlap.
A first solution foresees the use (in the case of diameter checking) of just two detecting devices, precision positioning slides for displacing the elements of the opto-electronic apparatus and measuring systems for accurately measuring the slide displacements. A similar solution, adopted in the measuring apparatus disclosed in European patent application EP-A0216587, is subject to drawbacks due to the difficulty of performing and measuring to a high degree of accuracy the displacements of the elements of the opto-electronic system and to the lengthy measuring cycles.
Another solution, according to the apparatus disclosed in U.S. Pat. No. 4,854,707, foresees the use of two rows of emitters and two rows of detectors, oppositely arranged with respect to the workpiece axis. The two rows of em
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See 1 in Addendum.
English language translation of International Publication No. WO 86/05583.
Graziani Giovanni
Milana Emilio
MARPOSS Societa' per Azioni
Pham Hoa Q
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