WO2003002992A2 - Method and apparatus for inspecting containers - Google Patents

Abstract

Method and apparatus (1) for inspecting containers (5) with optical vision means (2) in combination with planar convex and/or double convex lenses (6) having non spherical section so shaped and positioned as to deviate according to predetermined angles light rays coming from the container (5), to allow the simultaneous vision, in a single image, both of parts of the container (5) that are directly visible, and of parts of the container (5) that are not directly visible by said vision means (2).

Description

METHOD AND APPARATUS FOR INSPECTING CONTAINERS

TECHNICAL FIELD AND BACKGROUND ART.

The present invention relates to a method and an apparatus for inspecting containers, in particular bottles, cans and/or jars, by means of optical vision means positioned in correspondence with the container to be inspected. As is well known, in the field of bottling and canning, the containers, be they bottles or jars or cans, must meet certain requirements in terms of integrity, hygiene and aesthetics. It is therefore necessary to inspect the containers, to verify their cleanliness, to identify mechanical flaws, typically dents or shape imperfections, and any defects on caps or on the positioning or graphic appearance of labels that are usually applied to the containers. US Patent 4,691,231 discloses a system for inspecting bottles that provides for the use of three pairs of television cameras positioned at 60° in front of a conveyor belt whereon bottles are fed, at a sufficient mutual distance to avoid causing image interference.

Behind the belt is provided a wall for diffusing the light emitted by lamps positioned behind said wall. Thanks to the high number and the disposition of the television cameras, the image of a superficial part of the bottle exceeding 180° is obtained whilst the bottle is in a certain position.

An embodiment variation provides for the use of three pairs of mutually parallel television cameras, distanced and perpendicular to the conveyor belt, which derive the image of individual bottles and of the respective labels in three successive positions obtained by rotating the bottles themselves, hi this case, distancing the bottles is not necessary. Between a television camera and the successive one, the bottle is rotated by using a movable lateral belt and a fixed rear abutment between which the bottle is held. Both described embodiments, however, require using a plurality of television cameras, positioned at a pre-set distance from each other, to obtain the necessary information on the labels.

The patent EP 0415154 discloses a device for inspecting objects that comprises an input conveyor in correspondence with which there is a first inspection station, an output conveyor in correspondence with which there is a second inspection station, and an intermediate conveyor in correspondence with which there is a station for inspecting the bottom of the objects. The intermediate conveyor comprises two parallel conveyor belts actuated at different speeds in such a way as to cause the objects to rotate on themselves during their advance. This patent also teaches the use of multiple, mutually distanced television cameras.

When checking labels and bottle caps to assess their proper positioning and the absence of flaws in said labels or capsules, there is a particularly pressing need to reduce the complexity of the machines and methods necessary for the aforesaid operations. A typical problem of the prior art is given by the distortion and deformation of the image in correspondence with the edges of the bottle by effect of the curvature of the surface of the bottle itself, which forces to reconstruct the image via software, with the added complication of the paucity of information available. Another factor causing a lack of precision in the image is represented by the possible lateral motions of the bottle during its transport, which cause variations in the distance between bottles and television cameras. This can be solved by installing lateral guides, which however need to be adjusted and changed every time the type and format of the bottles to be checked is changed.

An additional drawback, in the case of multiple television cameras simultaneously observing the same bottle from different angles, is given by the need to position the bottles at a considerable mutual distance to prevent contiguous bottles from contanrinating the image (by means of invisible areas or areas where the image cannot be processed because of the superposition of the elements to be inspected.

The patent application for industrial invention no. PR94A000011 discloses an inspection device that allows simultaneously to acquire the image of the entire lateral surface of an object. Said acquisition takes place by means of a plurality of television cameras positioned around the object or by means of a single television camera and a plurality of reflecting mirrors so positioned as simultaneously to reflect in the television camera the image of the entire lateral surface of the object. Said device, however, forces to inspect sufficiently distanced bottles and requires a diffuse lighting, uniformly distributed on all the space around the object, which is technically difficult to achieve.

Currently, some inspection apparatuses also provided for the use of optical lenses, solely for the purpose of enlarging the vision of critical or particularly small parts of the container, thereby increasing the resolution of the image obtained by the television camera. Said lenses, moreover, do not provide for differentiated or preferred enlargements, in that the entire area covered by the lens is enlarged identically.

Some systems provide for the presence of a television camera that takes the image of the bottle from above to identify its orientation and command the movement of a pair of lateral belts between which the bottle is rotated until it assumes the desired position, in alignment with an additional television camera that checks the label frontally. This system still requires bottles provided with an identifying reference element visible from above and the frontal television camera is not able to obtain a sufficiently ample image of the bottle surface.

DISCLOSURE OF INVENTION.

The aim of the present invention is to eliminate the aforesaid drawbacks making available an apparatus and a method for inspecting containers that allow both the inspection of the outer walls, and the inspection of the inner walls by means of transparency or reflection.

Another aim of the present invention is to propose an apparatus and a method that allow to inspect containers having any cross section, typically circular, oval, square and/or rectangular with or without rounded corners. An additional aim of the present invention is to make available an apparatus and a method that allow to inspect containers without requiring them to be moved or rotated and possibly with a single television camera or at most two. Said aims are fully achieved by the apparatus and the method of the present invention, which are characterised by the content of the claims set out below and in particular in that they provide for the use of planar-convex and/or double convex lenses with non-spherical section, so shaped and positioned as to deviate, according to predetermined angles, light rays coming from a container to be inspected, to allow the simultaneous viewing, in a single image, both of directly visible parts of the container, and of parts of the container that are not directly visible by said vision means. BRIEF DESCRIPTION OF DRAWINGS.

These and other aims shall become more readily apparent from the following description of a preferred embodiment illustrated, purely by way of non limiting indication, in the accompanying drawing tables, in which:

Figure 1 shows a perspective view of an apparatus for inspecting containers according to the present invention;

Figure 2 shows a plan view of the apparatus of Figure 1; Figure 3 shows a first example of operation of the apparatus according to the invention;

Figure 4 shows a second example of operation of the apparatus according to the invention;

Figure 4a shows, by contrast, a type of inspection according to the prior art.

Figure 5 schematically shows the lens calculation methodology. BEST MODE FOR CARRYING OUT THE INVENTION. With reference to Figures 1 and 2, the apparatus for inspecting containers is globally indicated with the number 1 and comprises optical vision means 2, typically a television camera 3 and a illuminator 4 oriented on the container 5, in the illustrated example a bottle, to be inspected. The apparatus 1 is originally provided with at least a planar convex, or double convex, lens 6, with non-spherical section and preferably obtained by moulding or machined by removing material starting from a block of glass, optical glass or transparent plastic material having a homogeneous refraction index throughout the volume of the block.

Said lens 6 is so shaped as to deviate according to predetermined angles light rays coming from a container, to allow the simultaneous viewing, in a single image, both of parts of the container 5 that are directly visible, and of parts of the container that are not directly visible by said vision means 2. In particular, the directly visible parts are those substantially perpendicular to the container-television camera axis, whilst the parts that are not directly visible are those located substantially parallel to said television camera- container axis, typically the edge portions, whose visibility is limited by the presence of the curvature of the surface.

In the illustrated embodiment, the light rays coming from the container 5 are refracted light rays, since the illuminator 4 is positioned at the opposite side of the television camera 3 relative to the container itself, which is illuminated by transparency.

The lens 6 is positioned between the container 5 and the television camera 3, which is located in raised position relative to the containers. To allow the television camera 3 to capture the image of the containers, a mirror 7 is used, positioned in such a way as to reflect upwards the light rays that traverse the lens 6 and that come from the containers.

In an embodiment not illustrated herein, it is possible to position the illuminator 4 between the container 5 to be inspected and the television camera, or behind the television camera, thereby exploiting light rays that are reflected and not refracted by the containers. In the illustrated embodiment, the containers to be inspected are positioned on a container belt 8 able to slide and positioned between the lens 6 and the illuminator 4.

Said lens 6, moreover, is so shaped that, on the image captured by the television camera, to equal portions of the container correspond equal portions on the image itself. Specifically, the portions of the container that are visible with very low resolution, because they are located, for instance, in positions where the curvature of the surface is very marked, are amplified by the lens 6 until reaching dimensions and resolution that are comparable to the more visible parts of the container.

In an embodiment not illustrated herein, there are provisions for using a plurality of planar convex and/or double convex lenses 6 with non -spherical session positioned along the same optical axis, in order to increase the deviation of said light rays. The planar convex and/or double convex lenses with hon spherical section used in the present invention allow to obtain a non-constant angular deviation of the light rays coming from the object to be inspected, said angular deviation allowing to amplify the vision of parts of the container that otherwise, with a constant angular deviation (as is the one achieved by a prism), would be viewed with a very modest resolution level, insufficient for inspection and greatly inferior to that of the more visible parts. In an embodiment non illustrated herein, to effect an inspection of the lateral walls over their 360°, there are provisions for using two mutually opposite television camera - lens apparatuses. The lens 6 is dimensioned exploiting the fundamental relationships of optics relating to the angular deviation undergone by light rays when they traverse means with different refraction indexes.

The computing method followed is based on Snell's law in combination with the condition that the minimum deviation angle be achieved. This condition guarantees the best result from the optical viewpoint (the best stigmatism is obtained).

Snell's law, together with the condition of a minimum deviation angle, is repeatedly applied starting from the outermost point of the lens, progressively approaching the axis of the lens itself. The angular and lens thickness parameters are computed in a first point, the outermost one where the maximum angular deviation is normally obtained; thereafter, one proceeds moving towards the axis of the lens by a pre-set quantity and the angular and thickness parameters are computed in this new point as a function of the angular deviation to be achieved in said new points, of the angular parameters and of the thickness computed in the previous point and so on. One thereby obtains the section of the required non spherical bi-convex lens. Alternatively, if it is required for one of the surfaces of the lenses to be planar and perpendicular to the axis of the lens, the section of the required non spherical planar convex lens is obtained in similar fashion. In an embodiment not illustrated herein, to compensate for the chromatic dispersion caused by the variation of the index of refraction of the lenses as the wavelength of light changes, there are provisions for using monochrome television cameras in combination with narrow-band filters mounted on the lens of the television camera or, alternatives, the container to be inspected is illuminated with a narrow-band light like the one generated by LED illuminators.

With reference to Figure 3, a first example of operation of the present invention is shown.

In the embodiment illustrated in Figure 3, the television camera is positioned above the object to be inspected and the lens 6 is interposed between the object and the television camera itself. In particular, the object to be inspected is a bottle of significant height, provided with two labels positioned at a preset distance from each other, for instance a sparkling wine bottle. Figure 2 shows that vision of the label ET2 is amplified on the plane of the lens by effect of the angular deviation operated thereby; the CD segment on the plane of the lens is equal to the height of the label ET2. In the absence of a lens with the ability to effect a non constant angular deviation, the label ET2 would be seen by the television camera with a far lesser height, equal to about half the actual height of the label in question. In order to see the label ET1 with a 1:1 scale height too, however, it is necessary to use a second lens, able to effect a non constant angular deviation and exploit a second television camera.

It should be stressed that use of a second lens in combination with a second television camera is not always necessary and depends on the type of container to be inspected, on the characteristics to be measured and on the degree of accuracy to be achieved.

With reference to Figure 4, a second example of operation of the present invention is illustrated. In particular, the possibility is shown of using the aforesaid apparatus simultaneously to inspect the mouth, the thread, the bottom and part of the inner walls of containers, in particular bottles, jars and/or cans. To execute this inspection mode, the vision means and the lenses are positioned above the object to be inspected, aligned therewith. As illustrated in Figure 4 by the segments AB and CD, use of a planar convex or double convex lens allows to inspect, amplifying their vision, the bottom, part of the inner walls, the mouth and the thread of a bottle, employing a single television camera provided with a normal lens.

Figure 4A shows how, in the absence of a lens of the type described, it is not possible simultaneously to inspect the bottom, part of the inner walls, the mouth and the thread of the bottle. In particular, Figure 4A shows how, with conventional optics, even the simple inspection of the bottom is very limited, with the consequent loss of information especially about the edge portions of the bottom, and of the inner lateral walls. The method of the present invention provides for the use of optical vision means, typically at least a television camera and an illuminator, in combination with planar convex and/or double convex lenses with non spherical section shaped and positioned in such a way as to deviate according to pre-set angles light rays coming from the container, to allow the simultaneous vision in a single image, both of directly visible parts of the containers, and of parts of the container that are not directly visible by said vision means.

The lenses used are so shaped as to amplify the visions of predetennined parts of containers, typically those not directly visible by the vision means, in order to enhance image resolution. The method of the present invention provides for the possibility of using a plurality of said lenses positioned along the same optical axis, in order to increase the deviation of said light rays, to capture larger portions of containers and/or to enhance image resolution. The invention achieves important advantages. First of all, an apparatus and a method according to the invention allow both the inspection of the outer walls, and the inspection by transparency or reflection of the inner walls of a container.

Secondly, such an apparatus can be used to inspect containers of any shape and size. Another advantage is represented by the fact that, since the containers are not subjected to movements or rotations during the inspection, the acquired image is precise and no errors or superpositions with other images are generated. A further advantage is given by the ability to use an optical apparatus according to the present invention simultaneously to inspect the mouth, the thread, the bottom and part of the inner and outer walls of containers, in particular bottles, jars and/or cans. To effect this mode of inspection, the vision means and the lenses are located above the object to be inspected, aligned therewith. Said inspection apparatus allows for a considerable reduction of costs and bulk, since normally this inspection mode is effected exploiting a plurality of television cameras, typically at least three.

Figure 5 is applicable to the total inspection (360°) of the lateral surface of a container using two lenses and two opposite television cameras, each whereof sees a "deformed" development of the container of 180°. The circumference arc AB, corresponding to 90°, is subdivided into n equal arcs and the A'B' segment is subdivided into n equal segments (one proceeds in similar fashion for the arc AC to complete the 180°); the ends of the arc are joined with the ends of the segments and then with O, i.e. with the focal point of the television camera lens. The purpose therefore is to develop the part of lateral surface of the container represented by the circumference arc on a plane represented by the segment A'B'; the television camera sees the "deformed" image (in the sense that is more clearly highlighted than the image that would be directly visible without the interposition of the lens) of the container on that plane and not the container directly. Hence, the television camera also sees lateral areas that otherwise, without lens, it could not see.

Development on the plane is nearly linear since to equal arcs correspond equal segments; an amplification of the image of the lateral surface of the container is also achieved. The dimensioning of the lens can be performed as follows. Starting from the point B', the outermost one of the segment, Snell's law of refraction (previously mentioned) is applied to obtain an angle of deviation like the desired one which is given by the line joining the points BB'O. To obtain such an angle of deviation, it is necessary to consider the index of refraction of the material of the lens. In essence, once the angle of deviation to be obtained and the index of refraction of the material of the lens are known, Snell's law is used to obtain the angle of aperture of the section of the lens in the point B'. Having determined the angle, knowing the inclination of the segment BB' and of the segment BO relative to the segment A'B', the direction of the upper and lower profile of the initial part of the double convex lens is determined. Moving on the line bisecting the angle of aperture, one approaches A' to compute the second angle of aperture and hence two points of the profile of the double convex lens, one above and one below the segment A'B'.

Moving on the line bisecting said second angle, one again approaches A' to compute the third angle and hence two other points of the profile of the lens.

And so on.

From an image quality standpoint, it is preferable to use double convex lenses.

The method indicated above is in any case similar for planar convex lenses except, naturally, for the condition that the angle of aperture computed on each occasion be totally to one side of the segment A'B' and that one of the points of each computed pair be on the segment itself.

After obtaining the co-ordinates of the points of the profile of the lens, its profile is drawn. To do so, it is possible to use circle arcs whose equations are obtained from triads of points of the profile, or one can obtain, with polynomial interpolation, the analytical function of the profile and then draw it using the function itself.

The lenses thereby obtained normally have sizeable thickness, of several tens of millimetres. In those cases when a high level of optical quality is not necessary, thickness can be reduced using the same profiles but obtained as in Fresnel lenses.

Since the lenses normally have diameters of hundreds of millimetres and since they are used in all their surface and not only in the paraxial part, chromatic aberration can be relevant. To limit its effects, the objects can be illuminated with narrow-band light or more economically narrow-band filters can be used in front of the lenses of the television cameras.

It can also be conceivable to use combinations of two or three lenses so dimensioned as to correct chromatic aberration in correspondence with the focus of the television camera optics.

Claims

1. Method for inspecting containers (5) with optical vision means (2), characterised in that it provides for the use of planar convex and/or double convex lenses (6) with non spherical section, so shaped and positioned as to deviate according to pre-set angles light rays coming from the container (5), to allow the simultaneous vision, in a single image, both of parts of the container (5) that are directly visible, and of parts of the container (5) that are not directly visible by said vision means (2).

2. Method as claimed in claim 1 , characterised in that said lenses (6) are so shaped as to amplify the vision of predetermined parts of containers (5), to enhance image resolution.

3. Method as claimed in claim 2, characterised in that said predetermined parts of containers (5) are those not directly visible by the vision means (2).

4. Method as claimed in claim 1, characterised in that it provides for the use of a plurality of said lenses (6) positioned along a same optical axis to increase the deviation of said light rays.

5. Method as claimed in claim 1 , characterised in that said vision means (2) comprise at least a television camera (3) and an illuminator (4).

6. Apparatus (1) for inspecting containers (5) comprising optical vision means (2), characterised in that it comprises at least a planar convex, or double convex, lens (6), with non spherical section, so shaped and positioned as to deviate according to predetermined angles light rays coming from a container (5), to allow the simultaneous vision, in a single image, both of parts of the container (5) that are directly visible, and of parts of the container (5) that are not directly visible by said vision means (2).

7. Apparatus as claimed in claim 6, characterised in that it comprises a plurality of planar convex and/or double convex lenses (6) with non spherical section positioned along a same optical axis to increase the deviation of said light rays.

8. Apparatus as claimed in claim 6, characterised in that said lens (6) is so shaped as to amplify the vision of predetermined parts of containers (5) to enhance image resolution.

9. Apparatus as claimed in claim 8, characterised in that said predetermined parts of containers (5) are those not directly visible by the vision means (2).

10. Apparatus as claimed in claim 6, characterised in that said lens (6) is so shaped that, on the image captured by the vision means (2), to equal portions of the container (5) correspond equal portions on the image itself.

11. Apparatus as claimed in claim 6, characterised in that said vision means (2) comprise at least a television camera (3) and an illuminator (4).