GB2185101A - Detection of surface defects in glass containers - Google Patents

Abstract

A method of detecting flaws in the neck finish 1 of a glass container 2, especially "line overfinishes", comprises illuminating the neck finish 1 by means of a light source 3, via a half-silvered mirror 4 mounted at an angle to the axis of the container, and reflecting the image of the neck finish via a rotating dove prism 7 to an image detector 10. The detector 10 may comprise two detector cells placed adjacent each other so as to view part of the rotating annular image of the neck finish 1. A flaw in the neck finish is indicated when the intensity of light falling on one of the cells differs from that falling on the other. <IMAGE>

Description

SPECIFICATION Detection of surface defects in glass containers This invention relates to the detection of surface defects in glass containers, e.g. glass bottles, and is especially concerned with a method and apparatus for detecting flaws in the sealing surfaces of such containers.

The use of optical scanning forthe detection of flaws orfaults in glass containers is nowwidespread and devices are obtainableforthe high speed scanning of the base, body and finish of such containers. Broadly speaking, these devices all involve the use of a light source which irradiates that portion of the container being checked, and a detection element which observes the amount of lightscattered ortransmitted by the respective portion being checked. The detection element, which mayforexample comprise avideo camera oran array of phototransistors, wi 11 normally be linked to suitable electronics whereby a container detected as being flawed can be automatically removed from, for example, a filling line conveyor on which it is travelling.

In one known device for the checking of flaws in the bases of glass bottles, the bases are irradiated by a light source situated vertically axially beneath them through a light diffuser, and a rotating image of the bases is projected onto a photocell matrix situated vertically axially above the bottles via static lenses in conjunction with a dove prism rotating at high speed. The signals emanating from the photocell matrix are analysed electronically to detect faulty bottles which are automatically removed from the line.

Defects or "checks" in the neck finishes ofglass bottles are usually detected by the use of light sources, e.g. light emitting diodes, situated above and radially-outwardlyofthe neck finish, and light detectors, e.g. photocells, situated correspondingly to the light sources to pick up, or not, the light reflected from the light sources by the neckfinishes.

The light falling on the light detectors is electronically processed and if a faulty bottle is detected it is automatically removed from the line.

The present invention is especially concerned with the detection of bottles having faulty neck finishes.

Such may be categorised as "line overfinish", which isduetothemarkcaused by the shear during the production process; as "blister overfinish", caused by the dope used to treat the moulds used in manufacture; as "chipped finish", caused by mechanical damage to the finish; and as "unfilled finish", which is due to an incomplete press during the pressing stage of the manufacturing process; inter alia. The invention is particularly, but not exclusively, concerned with the first-mentioned type offault.

The use of a rotating dove prism for detecting faults in the bases of glass containers is highly effective, and itwould beofconsiderablevalueinthe glass industry if a system could be evolved whereby this type of prism could be used to detect faults in the neckfin.shes of glass containers. It is the object of the invention to provide such a system.

According to the invention a method of detecting flaws in the neck finish of a glass container comprises illuminating said neck finish by means of a light source above said finish, via a half-silvered mirror mounted at an angle to the axis ofthe container, the image of said neck finish being reflected via a rotating dove prism to an image detector.

The invention also includes apparatus for use in this method, including a light source, a half-silvered mirror, a rotating dove prism and an image detector, all arranged in relation to a container being inspected so as to enable said method to be performed.

A major advantage of the system proposed by the present invention is that it is not necessary to rotate the glass containers being inspected. This is a feature of all presently-used detection systems, and is a substantial practical inconvenience. As stated, the present invention does away with this need.

In a preferred embodiment of the invention, the image of the neck finish of the container being inspected is reflected from the half-silvered mirror through a collimating lens, then through the rotating dove prism, and then an object lens to the image detector.

The image impinging on the image detector is an annular ring oflightwhich, because the dove prism is rotating, moves past the detection system in a circular motion,thus enabling thewhole ofthe neck finish to be examined in detail. When it is required to examine a flat sealing surface, e.g. in the case of spirits or beverage containers, the' illuminating light source may be situated vertically above the container, i.e. itwill illuminatetheflattopsealing surface along a plane substantially perpendicular to that sealing surface. When a "crown" finish is to be inspected, the sealing surface being both top and side, the illumination of the side sealing surface will also be necessary.

The angle at which the half-silvered mirror is mounted relative to the axis of the container being inspected is preferably in the range 35" to 60 , most preferably 45" to 48 .

The image of the neck finish is, as mentioned above, an annular ring of light moving past the detection system. Any fault will appear as a dark line tending to the radial direction and of small width.

The image detector may be of any suitable construction, and may for example comprise a TV camera, or a photodiode array camera, or a photocell matrix. The effect of passing light through a dove prism is to cause the intensity of the light to vary in sympathy with the rotation of the prism due to reflection from the end faces. In typical applications involving the use of dove prisms, electronic filtering is employed to extract a defect signal from the background signal, and such may be used in practising the invention. However, it is important that the defect signal, which can vary, is notfiltered out, and thus can be accomplished, according to a further preferred feature of the invention, by using, as the image detector,two detector cells placed adjacent each other and accessing the annular image.The changing intensity of the light issuing from the dove prism is thus cancelled out. The signals obtained from the two photocells, which are in effect viewing and comparing a continuous ring of radial strips, will only differ when a defect is observed, and such a difference will then initiate a container-rejection procedure in known manner.

The accompanying drawing, which is very diagrammatic in nature, illustrates an embodiment ofthe present invention, Figure 1 being a sketch of the component parts of the detection system, and Figure2a sketch of the image received bythe image detector.

ReferringtoFigurel,theneckfinish 1 of a container 2 passing along a linear conveyor (not shown) isto be inspected. Mounted above the conveyor, so as to be vertically above container 2, is a light source 3. Between lightsource3 and the container finish lisa half-silvered mirror 4, mounted atan angleato a plane parallel to that of neckfinish 1 of approximately 45", In practice it may be convenientto situate the light source a few degrees off the vertical, and the mirror a few degrees off450.

To the side ofthe conveyor, and mounted so as to receive the reflection of the image of the neckfinish 1, is a lens system 5, consisting of a collimating lens 6, a rotating above prism 7 and an object lens 8. The detector cell 10, which "sees" the image as a moving annulus of light, one cell seeing the image fractionally beforethe other. When there is no defect in the finish the ceils "see" identical images; when there is a defect, the cells "see" different images. The detection of such a difference is caused to initiate the rejection of the defective containerfrom the conveyor.

The above is a description of an embodiment of the present invention, and is byway of example only.

Modification and departures from the above are possible while still remaining within the scope ofthe invention.

Claims (7)

1. A method of detecting flaws in the neckfinish of a glass container comprising illuminating said neck finish by means of a light source above said finish, via a half-silvered mirror mounted at an angle to the axis ofthe container, the image of said neck finish being reflected via a rotating dove prism to an image detector.

2. A method as claimed in claim 1 wherein the image of the neck finish is reflected to the image detector via a collimating lens, a rotating dove prism, and an object lens.

3. A method as claimed in claim 1 or claim 2 wherein the half-silvered mirror is mounted at an angle in the range 35" to 600 relative to the axis ofthe container being inspected.

4. A method as claimed in claim 3 wherein said angleisinthe range42 to48 .

5. Method as claimed in any of claims 1 to 4 in which the image detector comprises two adjacent detector cells.

6. A method as claimed in claim 1, substantially as described with reference to the drawing.

7. Apparatus for detecting flaws in the neckfinish of a glass container, comprising a light source, a half-silvered mirror, a rotating dove prism and an image detector, all arranged in relation to a container being inspected so as to enable the method of any preceding claim to be performed.