METHOD AND DEVICE FOR DETECTING DIRT AS PRESENT ON ARTICLES, FOR EXAMPLE EGGS

Abstract: Method and device for detecting dirt on articles, in particular axially symmetrical articles, for example eggs, the method comprising, exposing said articles to ultraviolet light, imaging said exposed articles resulting in images, said images being built up of pixels, and determining within said images surface areas of dirt by correlating data of contrast and data of position of said pixels. Such a method enables selecting and subsequently removing articles for which too large surface areas of dirt are determined. Such a method and device can be applied advantageously for white and brown eggs in egg sorting machines.

Description: Title: Method and device for detecting dirt as present on articles, for example eggs The present invention relates to a method and device for detecting dirt as present on articles, in particular axially symmetrical articles, for example eggs. In particular the invention concerns a method and a device for selecting and sorting eggs upon which dirt is detected. In the field of industrial activity of egg processing it is well known to examine eggs and subsequently to select eggs on certain characteristics for which well-defined criteria are set. Said characteristics are mainly weight and crack. In present times of very large and still growing egg processing plants standards on hygienic in treatment of food products are increased more and more. In particular dirt on eggs is concerned. Remnants of dirt, in particular remnants of albumen and yolk, and also traces of excrements, can cause unwanted infections and consequently can be very disadvantageous during and after processing of eggs. Before removing dirt on eggs, or even to remove dirty eggs as well, it is necessary to detect said dirt adequately and to incorporate this detection in egg sorting procedures. Already for a long time, see for example the German patent DE937956, eggs are inspected, more in particular "candled 1 , before said eggs are sorted. This means that during conveying by a sorting machine the eggs are exposed from below to white light, mainly in order to make blood spots or cracks visible. Then eggs can be either labelled or removed by hand. In case of sorting such labels are taken into account . From US patent 4662469 it is known to detect remnants of rotten albumen by exposing eggs to ultraviolet light, for example rotten albumen originating from broken eggs. It has appeared that such remnants are fluorescent. In OSRAM-catalogue, named "Lichtprogramm 97/98", page 6.12, high-pressure mercury lamps are shown as ultraviolet light sources to be used for recognizing remnants of dirt on fruit, meat, fish, etc. From that document it is not clear to what extent contrasts in fluorescent image areas can be distinguished. The main object of the present invention is to take measures in order to satisfy the above-mentioned standards and criteria, thereby also remedying the shortcomings of the methods and devices known thus far. Therefore the present invention involves a method as mentioned above, further comprising, - exposing said articles to ultraviolet light, - imaging said exposed articles resulting in images, said images being built up of pixels, and - determining within said images surface areas of dirt by correlating data of contrast and data of position of said pixels . Furthermore the invention concerns a method, comprising, - supplying the articles to be selected, - exposing said articles to ultraviolet light, - imaging said exposed articles resulting in images, said images being built up of pixels, - determining within said images surface areas of dirt by correlating data of contrast and data of position of said pixels, - comparing said areas to reference areas having a limit value which represents an acceptable amount of dirt, - determining articles for which said limit has been exceeded, - selecting said articles for which said limit has been exceeded, and - removing said articles after said selecting. In addition to the above the present invention relates to devices for applying the above-mentioned methods, in particular devices detecting dirt on articles such as there are fruit, eggs, and vegetables, and devices for sorting articles such as eggs. It has appeared that for both brown and white eggs when exposing to ultraviolet light, egg shells are clearly fluorescent rather than dirt surface areas looking black. The resulting differences in fluorescense at different parts of the egg surface allow to obtain contrast data for article surface areas. Consequently by having such data, such surface parts can be compared with preset standards and suitably decisions about further treatment and processing can be taken. Advantageously the invention can be applied for automatic sorting and selecting procedures for large amounts of articles such as eggs. Differences caused by interpretation or tiredness of operators who sorted such articles thus far by hand, can be avoided. Moreover different settings according to correspondingly different requirements, for example as to brightness, can be employed in an easy way. Another advantage of the present invention is found in inspection of articles already cleaned. Thus dirt which hardly could be observed thus far can be traced. In another embodiment of the present invention said articles are positioned upon rollers of a conveyor or a conveyor belt in that said articles are rotating about an axis. Either continuous, intermittent, or pulswise exposure, or even combinations, can be employed advantageously in the set-up of the present invention. Hereinafter the invention will be explained in detail, thereby referring to, figure 1, showing schematically the device in accordance with the present invention, and figure 2, giving a scheme for processing signals as obtained when imaging said articles in accordance with the present invention. In figure 1 articles, in particular eggs 1, are shown schematically while placed on a conveyor (not shown in detail) , the conveyor moving in the direction as given by arrow A. Usually eggs placed on such a conveyor are rolling about their main axis . During transport said eggs are passing a source 2 of ultraviolet light. For example a source comprises a light box which supports several lamps or a combination of one or more lamps and one or more mirrors . The light reversing from the eggs, mainly fluorescent light from the egg shells, is imaged by image receiving means of at least one camera 3. For a skilled person it will be clear that many types of lamps or light sources irradiating ultraviolet light having emission spectra at least with wavelenghts between 250 and 400 nm can be used. In special cases, for example for certain types of eggs, such as brown eggs, filters for blocking light having wavelengths which will disturb the inspection results, are employed advantageously. Suitably filters which filter wavelenghts between 400 and 800 nm are applied. Preferably for brown eggs filters filtering wavelenghts between 620 and 720 nm are employed. Furthermore in figure 1 exemplary positions for two cameras arranged adjacent to a conveyor are shown. Generally CCD type cameras which are sensitive for said fluorescent light can be employed. Filters as mentioned before can be arranged on said cameras . It will be clear to those skilled in the art that the fluorescent light sensitiveness of the cameras has to be set in accordance with the situation of either unwashed or cleaned eggs. Of course there is the possibility for detecting and sorting blends of washed and cleaned eggs in one run . In figure 2 a scheme for processing image signals as obtained by means of the above described cameras when imaging said articles is shown. Fluorescent light 10 strikes one or more cameras 100. The image signals thus obtained represent image data 20 comprising information on values of black levels and positions of all the pixels. Said data are processed in an image data processing unit 200 resulting in processed data 30. Subsequent to such processing, said data 30 are supplied to a unit 300 for comparing said data 30. Further to comparison said unit 300 is also capable for selecting said data, thus resulting in comparison data or selection data 40 respectively. Said data 40 are used for control of for example an article sorting machine or a selection unit. For those skilled in the art it will be clear that unit 200, generally being a computer, is capable for taking into account effects of shadowing in case of multiside exposure, and consequently for carrying out standardising said data 30 over the whole image field. Also corrections can be made for border effects i.e. effects of dirt present at the image border, thereby using well-known methods for projecting image data and comparing said projected data with well known egg characteristics. The values of black levels as mentioned before allow to determine contrast data for the pixels. After standardising these contrasts for the whole image, details within said image can be made visible. In order to obtain well usable images a background materials should have suitable colour and light reflecting characteristics. Advantageously non- fluorescent materials are chosen. Said contrast data allow determination of both total egg surface areas and dirt surface areas . For example methods for elimination of well-defined grey values are applied in order to arrive at suitable images . By means of unit 300, preferably being a computer, for example a personal computer or a main frame computer, further determinations such as checking said contrast data with regard to limit or threshold values, are carried out. This means that by exceeding such limit or threshold values articles are considered no longer suitable for use or consumption and consequently have to be selected and sorted out . All kinds of combinations of rotating the eggs and exposing the eggs to continuously, intermittently or pulswise irradiated light, or even combinations, can be employed. Corresponding data processing is used. In this respect continuous is self-evident, both for rotating and for irradiating. For pulswise irradiating all kinds of pulses can be applied, i.e. shorter or larger pulse durations, and high and low frequency pulses. Intermittent is defined as positioning the eggs in subsequent well-defined positions and imaging said eggs only in said positions. Furthermore well known pattern recognition algorithms for dirt or crack can be applied. Further to the kinds of articles mentioned also toys or sweets are comprised. For a skilled person it may be clear that slight deviations from the method and device as explained above are also comprised by the present invention and by the appending claims .

Claims: Claims 1. A method for detecting dirt on articles, in particular axially symmetrical articles, for example eggs, comprising, - exposing said articles to ultraviolet light, - imaging said exposed articles resulting in images, said images being built up of pixels, and - determining within said images surface areas of dirt by correlating data of contrast and data of position of said pixels . 2. A method for selecting dirty articles, in particular axially symmetrical articles, for example dirty eggs, comprising, - supplying the articles to be selected, - exposing said articles to ultraviolet light, - imaging said exposed articles resulting in images, said images being built up of pixels, - determining within said images surface areas of dirt by correlating data of contrast and data of position of said pixels , - comparing said areas to reference areas having a limit value of an acceptable amount of dirt, - determining articles for which said limit has been exceeded, - selecting said articles for which said limit has been exceeded, and - removing said articles after said selecting. 3. Method according to claim 1 or 2 , wherein for each article the total surface area is imaged. 4. Method according to anyone of the claims 1 - 3 , wherein during imaging said articles are exposed from at least two sides. 5. Method according to claim 4, wherein the articles are exposed continuously during rotation about an axis. 6. Method according to claim 4, wherein the articles are exposed intermittently during rotation about an axis 7. Method according to claim 6, wherein the articles are exposed after every angle of rotation of 90°. 8. A device for detecting dirt on articles, in particular axially symmetrical articles, for example eggs, comprising, - support means for said articles, - a source of ultraviolet light for exposing said articles, - a camera for imaging said articles for obtaining images of said articles, - an image processing means for determining data of contrast and data of position of pixels building up said images, and - data processing means for correlating said data of contrast and said data of position in order thereby determining surface areas of dirt of said supported articles. 9. A device for selecting dirty articles, in particular axially symmetrical articles, for example eggs, comprising, - means for supplying and removing said articles, in particular a conveyor or conveyor belt, for selecting and selected articles respectively, - a source of ultraviolet light for exposing said articles, - a camera for imaging said articles for obtaining images of said articles, - an image processing means for determining data of contrast and data of position of pixels building up said images, and - data processing means for correlating said data of contrast and said data of position in order thereby determining surface areas of dirt of said supported articles, - means for comparing said surface areas of dirt to reference areas having a limit value of an acceptable amount of dirt, - means for determining articles for which said limit has been exceeded, and - means for selecting said articles for which said limit has been exceeded. 10. Device according to claim 9, wherein said articles are conveyed by means of a conveyor and rotate about an axis 11. Device according to claim 9 or 10, wherein said articles are exposed continuously. 12. Device according to claim 9 or 10, wherein said articles are exposed intermittently. 13. Device according to claim 9 or 10, wherein said source is a light pulse generator. 14. Device or method according to one of the foregoing claims, wherein filters for filtering out light with wavelengths between 400 and 800 nm, preferably wavelengths between 620 and 720 nm, are arranged.

Inventors: BOLLINGER PETER, POMREHN WOLFGANG, BOLLINGER, PETER, POMREHN, WOLFGANG
Applicants: BOLLINGER PETER, FOOD PROCESSING SYSTEMS, POMREHN WOLFGANG, BOLLINGER, PETER, FPS FOOD PROCESSING SYSTEMS B.V., POMREHN, WOLFGANG
Application year: 1998
Main classification: G01N33
IPC codes: A01K43, B07C5, G01N21, G01N33