Inspection system for controlling the laying of a string or layer of a fluorescent material on a metal piece

Abstract: An optical inspection system for controlling the laying of a string or layer of a fluorescent material on a metal piece comprises an optical inspection station including wall means (5) movable between an open condition and a closed condition in which said means define a dark chamber (6) wherein the piece (3) to be controlled is confined. With said wall means (5) there are associated Wood lamps (9) which light the piece (3) ensuring an optimal inspection by the video camera (8).

Description: The present invention relates to an optical inspection system for controlling the laying of a string or layer of a fluorescent material on a metal piece. In motor-vehicle components, it is now a conventional technique to use so-called "structural" sealing materials and adhesives interposed between the elements of a structure, for example between the crank-case and the sump of an internal combustion engine in order to obtain both the required sealing effect and the required degree of strength of the structure. Among the materials which are used, there are structural adhesives, for example an adhesive marketed under the trade-mark "Loctite 573", which have fluorescence properties. In a mass production, where such materials are laid by means of automated systems, it is then necessary to provide a quality check of the laying of the string or layer of adhesive. It has already been proposed to achieve the above-mentioned result by optical means comprising a vision system with a black-and-white video camera which inspects the piece while it is illuminated by a strong light, typically a neon light. However, the results achieved by such technology are not always satisfactory because the string, which usually has a surface with an irregular shape or in any case not uniform in cross-section, has a position relative to the light rays from the lamp which originates areas with an excess of light, particularly on the string, altering thereby the grey level sensed by the video camera. This originates great difficulties for the vision system which may sense such areas in different possible ways giving results which are not correct or have a low degree of reliability. Furthermore, the pieces on which the sealing material is laid have irregular shapes with different depth. This originates a play of reflected light which affects the clearness of the contrast between the string and the piece. EP A 0 458 474, discloses an apparatus for detecting the presence of a layer on a substrate. In this known apparatus, a video camera is used to inspect fluorescent radiation coming from the layer within a stationary dark chamber, as a result of ultraviolet light impinging on the layer. Document US-A-4 778 999, reveals an apparatus is known for inspecting the base of plastic bottles to confirm the presence of adhesive, which includes photosensors for receiving fluoresced light coming from the adhesive as a result of the impinging on the adhesive of ultraviolet light. In order to overcome such problems and considering that the materials in question have fluoresence properties, the present invention provides an optical inspection system having the features set forth in Claim 1. Due to said features, the system according to the invention is able to enhance the contrast string-piece and to eliminate almost completely the plays of reflected light caused by the shape of the piece itself, greatly increasing the reliability and reducing the errors at minimum. At the same time, the wall means are able to define rapidly a dark chamber surrounding a piece to be inspected along the line, the Wood lamp(s) and the video camera means also being supported by said wall means, so that inspection can be carried out quickly and easily. The invention will be now described with reference to the annexed drawings, given purely by way of non limiting example, in which: figure 1 is a perspective diagrammatic view of a piece bearing a string of a fluorescent structural adhesive, and figure 2 is a diagrammatic elevational view of the system according to the invention. With reference to the drawings, numeral 1 generally designates a transport line with pallets 2 each carring a metal piece 3 (figure 1) on whose upper surface there has been previously laid for example by a robot, a string of an adhesive, such as Loctite 573. The string is indicated by reference numeral 4 in figure 1. With specific reference to figure 2, numeral 5 generally designates a casing adapted to define a dark chamber 6 which is movable between a lowered position (illustrated in figure 2) and a raised position with respect to a support structure 7. The upper wall of casing 5 supports a video camera 8 which is to perform the optical inspection of string 4, whereas the side walls support a plurality of Wood lamps 9 adapted to light piece 3 by ultra-violet light once the latter has been confined within dark chamber 6. In operation, line 1 is advanced intermittently, so as to stop each piece 3 in the position illustrated in figure 2 to allow optical inspection of the string 4. During movement of line 1, casing 5 is in its raised position. When a piece 3 is stopped in the inspection station, casing 5 is lowered in the position illustrated in figure 2 so as to confine piece 3 within dark chamber 6, whereupon the lamps 9 are turned on (they could also be kept constantly on) to light piece 3 by ultra-violet light, ensuring thereby an optimal optical inspection of the string by the video camera 8. The output signals by the video camera are processed by electronic means 10 (which form part of the vision system) to provide data on the quality of the laying of the string 4. Tests conducted by the applicant have shown that the above-described system achieves efficient result both in case the fluorescent material forms a layer spread on the metal piece, for example with a thickness of about 0.1 mm and in case it forms a string with a thickness of about 1-2 mm and a width of 3-5 mm. Under the light of the Wood lamps, the fluorescent string takes a colour tending to a very pale green, and is clearly visible by the video camera 8. Naturally, the principle of the invention remaining the same, the construction details and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of the present invention.

Claims: An optical inspection system for controlling the laying of a string or a layer of a fluorescent material on a metal piece, including ultraviolet light source means for lighting said string or layer and video camera means for inspecting the string or layer illuminated thereby, said system comprising: a transport line (1) with piece-supporting pallets for transporting pieces (3) to be controlled, an optical inspection station located on the path of said line (1), said station comprising: wall means (5) movable between an opened condition and a closed condition in which said means define a dark chamber wherein the piece to be controlled is confined, said ultraviolet light source means including at least a Wood lamp (9) located on said wall means to light said piece (3) by ultra-violet light after that said piece has been confined within said dark chamber (6), said video camera means (8) being also supported by said wall means (5) for optically inspecting the string of a fluorescent material (4) on said piece (3), illuminated by the ultra-violet light of said Wood lamps (9), and electronic means for processing output signals from said video camera means (8) and to provide data on the quality of the laying of the string of fluorescent material (4). An optical inspection system according to claim 1, characterized in that said wall means (5) include a casing (5) opened downwardly, slidably mounted on a support structure (7) between a raised position and a lowered position, said casing (5) having an upper wall carrying said video camera (8) and side walls carrying said Wood lamps (9).

Inventors: BONGI ADOLFO, BONGI, ADOLFO
Applicants: COMAU SPA, COMAU S.P.A.
Application year: 1993
Main classification: G01N21
IPC codes: G01N21