WO2006129391A1

WO2006129391A1 - Apparatus for detecting contaminants in food

Info

Publication number: WO2006129391A1
Application number: PCT/JP2005/021621
Authority: WO
Inventors: Shinji Hashizume; Yasuhiro Ikkai
Original assignee: Mayekawa Mfg.Co., Ltd.
Priority date: 2005-06-03
Filing date: 2005-11-18
Publication date: 2006-12-07
Also published as: JP2008541007A; CN101194161A; TW200643402A; CN101194161B; TWI339727B

Abstract

A foreign matter detecting apparatus 10 for detecting foreign matter existing in food 20 is provided, the apparatus comprising:a transfer means for transferring the food through an inspection zone, a plurality of lighting means for illuminating the food at least from two sides of said inspection zone, a photographing means for photographing one of the surface of the food when it passes through said inspection zone, and an image processing means for processing the picked up image of the surface of the food including converting the image into a binary-valued image, whereby an abnormal picture element exceeding a pre-established threshold value of darkness is detected in the binary-valued image obtained through image processing by said image processing means, then picture elements adjacent said abnormal picture element are inspected whether abnormal or not, and when abnormal picture element continues to said abnormal picture element, it is judged that foreign matter exists. When abnormal picture elements exist continuing linearly, it is judged that fibrous foreign matter such as a hair exists. When abnormal picture elements form an aggregate area, it is judged that area-type foreign matter such as a vermin exists.

Description

DESCRIPTION

APPARATUS FOR DETECTING CONTAMINANTS IN FOOD

Technical Field

The present invention relates to an apparatus for detecting contaminants in food, specifically for detecting foreign matter (materials unacceptable for food) such as fibrous substance like hair, etc. or area-type foreign matter such as vermin, etc. adhered to the surface of food.

Background Art

From the viewpoint of hygienics , it is demanded in food manufacturing factories to remove foreign matter existing in food product material or come to exist in food products in the process of manufacturing for distributing the food products as articles to be sold. Foreign materials largest in number existing in food products are various types of vermin, and hairs in the second place. These two kinds of foreign matter make up about 50% of all the foreign matter.

As a cause of existing of hair in food can be cited the case hairs faϊien-off from the workers exist in the food or hairs adhering to the clothes of the workers drop out and exist in the food in the process in which workers are involved, or the case hairs already being fallen on the floor, etc. adhere to wraps by static electricity, etc. and exist in the food byway of the wraps . Many of the existing of foreign matter in food occurs in the process of cooling, handling after placing in service dishes, or wrapping of food articles.

On the other hand, as a case of existing of .vermin in food can be cited the case dead bodies of adult vermin exist in food material, or the case that eggs of them exist in food materials or the eggs of vermin such as cockroaches already existing in food material hatch therein, or the case that a vermin which comes flying from outside the factory exists in the food material. Conventionally, detection of foreign matter in food has been done by visual inspection by workers, which has taken a lot of labor, and moreover there has been a problem in accuracy.

In these years a variety of automated apparatuses for detecting foreign matter in food were proposed and have been put into practical use. Among these are apparatuses using electromagnetic waves , those using X-rays , and those utilizing image processing using visible light.

There are restrictions in the purpose of use when applying an apparatus using electromagnetic waves, for it is applicable only for detecting foreign matter which reacts to electromagnetic waves .

An apparatus using-X rays detects foreign matter by color difference on a monochrome image obtained by X-ray transmission through food. With an X-ray type detecting apparatus currently used in general, metal such as iron, etc. can be detected easily because color difference is large, but foreign mater which is composed of ingredients (protein) similar to food can not be detected, so it is difficult to apply it to detecting foreign matter of protein such as hairs, vermin, etc. Since area of more than 1 mm² of foreign matter of is necessary for it to be detected by the X-ray type detector, it is difficult to detect long thin fibrous foreign matter such as a hair, etc.

Apparatuses utilizing image processing using visible light are disclosed in patent literature 1 ( JP-A-H05-22395 ) , patent literature 2 ( JP-A-2001-21499 ) , and patent literature 3 ( JP-A-2004-245695 ) .

Patent literature 1 discloses an apparatus for detecting a hair existing in packed food, in which an optical image of the food is picked up by an imaging device, the shape of the hair is extracted as a partial salient feature from the data of the optical image converted to binary-valued data, and it is judged whether the extracted data is pertinent to a fibrous matter having a length longer than a certain length or not. By this, the hair existing in the food can be specified.

In patent literature 2 is recited an apparatus, in which food material such as sake lees or noodle dough formed into a plain belt-like shape of a certain thickness is transferred vertically and rayed from one lateral side thereof to receive the light transmitted through the plate-like food in the other lateral side, and the transmitted optical image is processed to detect foreign matter in the food material.

Further, in patent literature 3 is disclosed an apparatus , in which a gap is provided between a carrying-in conveyor and carrying-out conveyor, a transmitting-illumination means and a line sensor imaging camera are located at positions opposite to each other sandwiching the gap, and the image of the subject of inspection obtained by scanning by the line sensor imaging camera is processed to be converted to binary-valued data to detect easily the foreign matter in the subject.

It has become possible to detect a variety of foreign matter existing in food by analyzing optical image of subject food with these apparatuses.

However, the apparatus recited in patent literature 2 is restricted in application only to food material which can be formed into plate shape, not applicable to foodmolded into complicated shape such as packed refrigerated noodles , refrigerated boiled rice, steam-baked meat pie, shao-mai, etc .

With the apparatus according to patent literature 1, there appear many shadow parts in the photographed image when the molded food articles are not uniform in their shapes and have patterned indented surfaces, and the shadow parts might be misidentified as foreign matter when detecting foreign matter from the binary-valued data of the image. The apparatus recited in patent literature 3 is applicable only to subjects permeable to light, and in this apparatus also, when applying to subjects having patterned indented surfaces, shadow parts appear in the photographed image and the rate of misidentification of foreign matter is high, resulting in decreased accuracy of detection.

Further, it was necessary to clear problems of hygiene when applying these apparatuses to food different from the case they were applied to subjects other than food.

Disclosure of Invention

The present invention was made in light of the problems mentioned above, and the object is to provide an apparatus for detecting contaminants, or foreign matter (materials unacceptable for food) in food with which foreign matter can be detected with high accuracy even if the food to be inspected has an irregular surface, or patterned indented surface.

To solve the problems, the present invention proposed an apparatus for detecting contaminants in food comprising : a transfer means for transferring the food through an inspection zone, a photographing means for photographing one of the surface of the food when it passes through an inspection zone, a plurality of lighting means for illuminating the food from one side or both sides of said inspection zone across said transfer means, and an image processing means for processing the picked up image of the surface of the food including converting the image into a binary-valued image, whereby an abnormal picture element exceeding a pre-established threshold value of darkness is detected in the binary-valued image obtained through image processing by said image processing means, then picture elements adjacent said abnormal picture element are inspected whether abnormal or not, detection of abnormal picture element or elements adjacent the detected abnormal picture element or elements is repeated, and when abnormal picture elements continue to said first detected abnormal picture element, it is judged that foreign matter exists .

According to the invention, it becomes possible to detect foreign matter in food, detection of which with high accuracy has been difficult heretofore. Since shades due to the existence of concaves and convexes on the surface of the food do not appear on the photographed image of the food and the foreign matter adhered to the food article is brought into relief as compared with the surface around the foreign matter by illuminating at least in two directions sandwiching the inspection zone, detection of foreign matter is possible even if the food has a complicated shape with concaves and convexes on the surface thereof.

When said abnormal picture elements appear continuing linearly, it is judged that fibrous foreign matter such as a hair exists.

By detecting continuity of abnormal picture elements exceeding a pre-established threshold value concerning the length and thickness or boldness of the linear shape of the binary-valued picture elements in the binary-valued image obtained by processing the photographed image and judging the existence of foreign matter only when the abnormal picture elements appear continuing linearly, fibrous foreign matter is selectively determined.

When said abnormal picture elements appear bordering on each other by the side thereof to form an aggregate area of abnormal picture elements, it is judged that area-type foreign matter exists.

By detecting continuity of abnormal picture elements exceeding a pre-established threshold value concerning area of the binary-valued picture elements in the binary-valued image obtained by processing the photographed image and judging the existence of foreign matter only when the abnormal picture elements appear bordering on each other by the side thereof to form an aggregate area of abnormal picture elements, area- type foreign matter is selectively determined.

Here, foreign matter having a certain width and length or occupies an area larger than certain area is referred to as area-type foreign matter.

Further, a first lighting means located in said photographing means side among said lighting means are means to radiate visible light and a second lighting means located in the other side across the transfer conveyor is a means to radiate infrared light .

By the irradiation of infrared rays from the side opposite to the imaging means across the transfer conveyor, shades which will appear in the photographed image due to concaves and convexes on the surface of the food can be almost eliminated. Further, it is preferable that the first lighting means consists of 2 or more lighting devices so that the imagingmeans side surface of the food is irradiated in two or more directions.

In the first lighting means, one of red, blue, green, and white light which is the mixture of red, blue, and green light can be selected in accordance with the kind of food.

By selecting a light color in accordance with the kind of food, it is photographed clearer and detection of foreign matter with high accuracy is possible.

Further, it is suitable that said photographing means is a CCD camera having focus length of 500 mm to 900 mm, preferably 800 mm to 900 mm.

By this, the image of the food can be brought into focus when the surface of the food is irregular with conspicuous concaves and convexes or when there is a considerable distance between the food and the bottom of the tray containing the food.

A cleaning means is provided for cleaning the part of the transfer means which will be brought into contact with the food, and at least either of said lighting means is movable so that it can be accommodated in a storage box provided apart therefrom when cleansing is carried out by the cleaning means .

By providing the cleaning means, hygienically safe and reliable food articles can be produced, and by composing such that the lighting means can be accommodated in the storage box, occurrence of problems caused by splashing of water or cleansing liquid against the lighting means can be prevented. It is suitable that the lighting means movable to be accommodated in the storage box is said first lighting means.

The second lighting means is accommodated in a fluid-tight storage box with the side thereof facing the transfer means being formed of material permeable to infrared light, and a cooling means is provided for cooling the inside of the storage box.

By this, occurrence of problems caused by splashing of water or cleansing liquid against the second lighting means can be prevented, and when the apparatus is composed such that the second lighting means is located under the gap between transfer conveyors , foreign particles or fragments of food falling through the gap and adhered to the storage box can be easily cleaned.

The transfer means includes two conveyor belts arranged side by side in parallel to each other, transfer directions of the two conveyor belts being opposite to each other, a turn-over means for turning over food thereon is provided at an end of the paralleling conveyor belts, the topside surface is inspected to detect foreign matter on one of said conveyor belts, and reverse side surface is inspected to detect foreign matter on the other of said conveyor belts .

By composing the transfer conveyor to have forwardly and backwardly transferring belts arranged side by side in parallel to each other, both the top side surface and reverse side surface of the food can be inspected for detecting foreign matter with a single detecting device, and inspection time period can be reduced.

The foreign matter is a substance containing protein as a chief ingredient .

The apparatus of the invention can detect foreign matter containing protein as a chief ingredient which a conventional X-ray type detecting apparatus has been unable to detect.

As has been described in the foregoing, it is possible according to the invention to detect foreign matter such as a hair and vermin which it has been difficult to detect hitherto. By illuminating the food at least from two sides of the inspection zone, shades due to concaves and convexes on the surface of the food disappear in the photographed image and foreign matter is brought into relief from the surrounding surface of the food, so that it is prevented that the shades are misjudged as foreign matter. Further, by detecting continuity of binary-valued picture elements exceeding a pre-established threshold value of darkness, fibrous or area-type foreign matte can be selectively detected.

Further, by providing a cleaning means for cleaning the transfer means, food articles safe and reliable from the sanitary point view can be produced, and by composing such that the lightingmeans can be accommodated in a storage box, the lighting means can be protected from splashing of water or cleansing liquid.

Further, by composing the transfer conveyor to have forwardly and backwardly transferring belts arranged side by side in parallel to each other with both the transfer belts being connected by a turn-over means for turning over the food thereon, both the top side surface and reverse side surface of the food can be inspected for detecting foreign matter with a single detecting device, and inspection time period can be reduced.

Brief Description of Drawings

FIG.l is a front view of an embodiment of the apparatus for detecting foreign matter according to the present invention .

FIG.2 is a side view of the apparatus of FIG.l.

FIG.3 is a schematic front view of the apparatus showing when a cleaning means is provided.

FIG.4 is a schematic front view of another embodiment of the apparatus for detecting foreign matter.

FIG.5 is a schematic plan view of another embodiment of transfer conveyor.

FIG.6a shows binary-valued images obtained in the image processing device when a fibrous foreign material is detected.

FIG.6b shows binary-valued images obtained in the image processing device when an area-type foreign material is detected.

Best Mode for Carrying Out the Invention

A preferred embodiment of the present invention will now be detailed with reference to the accompanying drawings . It is intended, however , that unless particularly specified, dimensions, materials, relative positions and so forth of the constituent parts in the embodiments shall be interpreted as illustrative only not as limitative of the scope of the present invention.

Subject of inspection in the embodiments is food including bare food or food contained in a tray and wrapped . Kinds of food are not limited particularly. Subject of inspection may be boiled rice, noodles, shao-mai, steam-baked meat pie, etc., and they may be in a frozen state, ordinary temperature state, or heated state . Foreign matter (materials unacceptable for food) to be detected is a hair, vermin, etc.

FIG.l is a front view of an embodiment of the apparatus for detecting foreign matter according to the present invention, FIG.2 is a side view of the apparatus of FIG.l, FIG.3 is a schematic front view of the apparatus showing when a cleaning means is provided, FIG.4 is a schematic front view of another embodiment of the apparatus for detecting foreign matter , FIG .5 is a schematic plan view of another embodiment of transfer conveyor, and FIG.6 shows binary-valued images obtained in the image processing device . A foreign matter detecting apparatus 10 shown in FIG.l and FIG.2 comprises as main components a transfer conveyor 11 for transferring food through an inspection zone A, an imaging camera 12 for photographing the surface of the food placed on the transfer conveyor 11, an image processing device 13 for processing the surface image photographed by the imaging camera 11 to detect foreign matter, and an upper and lower lighting devices 14, 15 which illuminate the food in the inspection zone A from two different directions across the transfer conveyor 11. The inspection zone A nearly coincides with the field of view of the imaging camera 12.

Further, it is preferable that the foreign matter detecting apparatus 10 includes a monitor 22 for displaying the image of the surface of the food taken by the imaging camera 12, a touch panel 23 and operation keys 24 for operating the apparatus 10 , lifting handle 25 for adjusting height position of the upper lighting device 14 in accordance with the dimension of the food to be inspected in order to improve operationality .

The transfer conveyor 11 has a driving roller lib connected to a motor, and a conveyor belt 11a runs between the driving roller lib and a follower roller.

Configuration of the transfer conveyor 11 is shown in FIG.3.

In the drawing, the conveyor belt 11a is made of material permeable to infrared light, and the lower lighting device 15 is located at the inspection zone A below the upside running conveyor belt. It is suitable to make the conveyor belt of transparent or semitransparent material such as urethane for example. There may be a case the conveyor belt of white color group is permissible depending on the kind of food. Another configuration of transfer conveyor is shown in FIG.4, in which a plurality of conveyor belts 11a are arranged in series, a gap is provided at a position corresponding to the inspection zone A, and the lower lighting device 15 is provided below the gap. In this case. the conveyor belts need, not be permeable to infrared light , the belt is not restricted to be made of specific material.

The lighting means consists of upper lighting devices 14 located above the transfer conveyor 11 and a lower lighting device 15 located between the upper side running belt and lower side running belt or below the conveyor 11.

The upper lighting device 14 is positioned above the inspection zone A as is the imaging camera 12 such that the devices illuminate the food article to be inspected from both sides . Foreign matter adhered to the food article is brought into relief as compared with the surface around the foreign matter by the illumination from the upper lighting devices 14 and the existence and position of foreign matter is recognized. For example, when foreign matter is a hair, as its cross section is circular, the hair can be distinguished from the food material around it by illuminating both lateral sides of the hair. When foreign matter is a vermin, as its cross section has a dimension larger than a certain size, it can be distinguished from the food material around it by illuminating sideways at it. In the case of other foreign matter, the foreign matter can be distinguished from the food material around it by adopting an appropriate method suitable according to the shape of the foreign matter.

The upper lighting devices 14 radiate visible light, and when illuminating foreign matter, light color can be selected from among four colors of light , i . e . three primary colors and white light which is a mixture of three primary colors so that foreign matter can be best brought into relief with the food material around the foreign matter as a background.

When foreign matter is a hair, it exists near the black part in the binary-valued image of black and white. First, a target domain is determined to include the black part and picture elements belonging to the domain are picked up as objects of inspection. This process is the same also when the color of the hair is white. When foreign matter is a vermin, it exists near the black part in the binary-valued image of black and white. Therefore, first a target domain is determined to include the black part and picture elements belonging to the domain are picked up as objects of inspection as done in the case of a hair.

The positions from which visible light is irradiated are preferable to be near the food as far as possible. As the food placed on the transfer conveyor 11 moves passing under the upper lighting devices 14 as mentioned later, it is necessary to secure a certain distance between the top of the food and the lower ends of the upper lighting devices .

However, a problem arises when utilizing four colors of light of the upper lighting devices 14 only. Because, when visible light illuminates food having an irregular surface, or patterned indented surface from the imaging camera 12 side, there is possibility that shades appeared in the photographed image are misjudged as foreign matter. Therefore, it is needed to find an art not to allow shades to appear in the photographed image. Inventors of the present invention found out that the shades can not be eliminated completely by illuminating the food from the imaging camera 12 side. In order to solve the problem, a lower lighting device 15 is provided to illuminate the food from the side opposite to the imaging camera 12.

A lighting device which radiates infrared rays is adopted as the lower lighting device. The food is placed on the transfer conveyor 11 and photographed by the imaging camera 12 while being transferred passing through the inspection zone A as mentioned later, and its image is analyzed by the image processing device 13 to detect foreign matter, whereby the infrared rays is radiated from the lower lighting device 15 to illuminate the rear face of the food through the conveyor belt .

Therefore, shades caused by the irregular surface of the food do not appear or faintly appear in the photographed image. When the food is formed of transparent materials. or materials not transparent but permeable to infrared rays , for example, boiled rice and noodles, shades do not appear at all. When the food is formed of materials almost impermeable to infrared rays , reflected infrared rays exist in the concaves and convexes on the surface of the food and shades are eliminated in the photographed image.

A CCD imaging camera or the like is used as the imaging camera 12. The focal length of the imaging camera 12 is preferable to be long. With long focal length, the imaging camera can be easily focused on the surface of the food even when the surface is very irregular or when the distance between the surface of the food and the bottom of the tray is large. Good result was obtained when the focal length is in a range of 500 mm~900 mm, preferably 500 mm~800 mm, when the field of view to be picked up is 300 mm X 300 mm on the food surface and said distance is 40 mm.

The larger the number of picture elements is , the smaller the area that one picture element can pick up. For example, a liair has a diameter of about 100 μ m , a vermin is larger than 100 μm. When picking up a field of view of 300 mm X 300 mm by a CCD imaging camera of 4 million pixel, the pixel dimension is 150 μ m X 150 μ m . With this pixel dimension, a hair or vermin can be picked up as foreign matter. Of course, a imaging camera of 6 million pixel, 12 million pixel are available and can be applicable to the embodiment of the invention, but they are expensive, and a imaging camera of 4million pixel is more preferable.

The image processing device 13 is a device to perform image processing including converting the image of the food picked up by the imaging camera 12 into a binary-valued image .

Here, methods of determining (1) a black hair, (2) a vermin will be described as examples.

(1) Method of determining black hair

In the conversion of an image into a binary-valued image of black-and-white, a picture element darker in blackness than all of picture elements around said picture element exists and this picture element is determined as a reference picture element. Then a picture element which is abnormal in darkness similar to said reference picture element is searched from among picture elements surrounding said reference picture element. On this occasion, threshold value for converting into a binary-valued image is established beforehand, and a picture element of which the darkness exceeds the threshold value is detected and denoted by reference numeral 41. Blackness of picture elements denoted by reference numerals 40 is within the threshold value. Then anther picture element 41 abnormal in blackness adjacent said reference picture element is recognized. Then next picture element 41 abnormal in blackness is searched on the basis of said another picture element as a new reference picture element. This process is performed sequentially, and when picture elements 41 abnormal in blackness exist continuing linearly as shown in FIG.6 (a), it is determined that black, fibrous foreign matter exists. A black hair can be detected in this way. On the other hand, wire-like food such as hijiki(black seaweed of diameter of about 2-3 mm) will be judged as black, fibrous foreign matter. Therefore, it is preferable to determine beforehand a standard of thinness to be judged as foreign matter. By this, wire-like food such as hijiki can be excluded as non-foreign matter . Pig bristles, black vegetable fibers are also included in black fibrous matter. Further, when detecting only hairs, the case in which picture elements 41 abnormal in blackness appear in a large area as shown in FIG.6(b) is not judged as foreign matter exists .

Method of determining white hair is similar to that of determining black hairs except that the search for foreign matter is started from determining a picture element stronger in whiteness than all of picture elements around said picture element .

(2) Method of determining vermin

In the conversion of an image into a binary-valued image of black-and-white, a picture element darker in blackness than all of picture elements around said picture element exists and this picture element is determined as a reference picture element . Saidpicture element stronger in blackness corresponds to a part of the vermin . Then a picture element which is abnormal in darkness similar to said reference picture element is searched from among picture elements surrounding said reference picture element. On this occasion, threshold value for converting into a binary-valued image is established beforehand, and a picture element of which the darkness exceeds the threshold value is detected and denoted by reference numeral 41. Blackness of picture elements denoted by reference numerals

40 is within the threshold value. Then anther picture element 41 abnormal in blackness adjacent said reference picture element is recognized. Then next picture element

41 abnormal in blackness is searched on the basis of said another picture element as a new reference picture element . This process is performed sequentially, and when picture elements 41 abnormal in blackness border on each other and form an area as shown in FIG.6(b), it is determined that black, area-type foreign matter exists. A vermin can be detected in this way. A burned part of the food and foreign matter of black color other than a vermin are also included in black, area-type foreign matter. Further, when detecting only area-type foreign matter such as a vermin, the case in which picture elements 41 abnormal in blackness exist continuing linearly as shown in FIG.6(a)isnot judged as foreign matter exists.

Further, the embodiment of the foreign matter detecting apparatus 10 is composed to be particularly suited for inspecting food. An embodiment in which the imaging camera 12 is located above the transfer conveyor 11 will be explained referring to FIG.3. The imaging camera 12, upper lighting device 14, transfer conveyor 11, and lower lighting device 15 are positioned from on high downward in this order. Bare food or food contained in a tray is placed on the transfer conveyor 11 and transferred through the inspection zone A passing through under the upper lighting device 14. Apparatuses for handling food must be maintained clean from sanitary point of view. Therefore, at least the part of the transfer conveyor where the food or tray contacts is needed to be cleansed. In the embodiment , a cleaning means30 is provided for cleansing the surface of the transfer belt 11a with water or cleaning liquid as shown in FIG.3.

There is possibility, when the clearance between the upper lighting device 14 located above the transfer belt 11a and the surface of the transfer belt 11a is so narrow as to allow only the food to pass through the clearance, that the upper lighting devices 14 is splashed with liquid when the transfer belt 11a is cleansed by splashing water or cleansing liquid . In the embodiment , the upper lighting devices 14 are provided movable so that they are accommodated in a storage box 17 provided near them or storage boxes provided near each of them respectively and the opening of the storage box is sealed in order to evade splashing of liquid against the upper lighting devices when cleansing the transfer belt 11a. The upper lighting devices 14 are provided movable on a rail 18(see FIG.2). It is suitable to compose so that the storage box 17 can accommodate the imaging camera 12 too.

There is also possibility that the lower lighting device 15 located below the upside running conveyor belt is splashed with liquid when cleaning the transfer belt 11a with liquid spouted from the cleaning means 30. In the embodiment, a fluid-tight storage box 19 is provided in which the lower lighting device 15 is accommodated. The upper face of the box 19 facing the transfer belt is provided with a window 19a permeable to infrared rays. The infrared light permeable window 19a is suitably made of a transparent plastic plate such as polycarbonate plate, for example.

As the lower lighting device 15 is always lighted in the closed storage box 19, temperature rises in the box. So, a cooling means (not shown in the drawing) is provided to cool the inside of the storage box 19. A forced cooling means is suitable for cooling the inside of the storage box 19, which is composed such that piping is connected to the box 19 so that outside air is introduced into the box 19 and exhausted outside, for example.

Further, in the case a plurality of transfer conveyors 11 are provided as shown in FIG .4 , it is suitable to provide an infrared light permeable plate 31 between the lower lighting device 15 and the transfer conveyors 11. By this, splashing of cleansing liquid or water against the lower lighting device can be prevented. Further, it is suitable to provide a cleaning device 32 form which air is blasted against the upper surface of the infrared light permeable plate 31. By this, even if foreign particles or fragments of food fall through the gap between the transfer conveyors 11, they are received on the upper surface of infrared permeable plate 31 and can be blown off with the air blasted from the cleaning device 32, and permeability of the plate 31 can be maintained sufficiently.

Further, the embodiment of foreign matter detecting apparatus 10 is preferably provided with a mechanism for removing the food which is judged that foreign matter is existing in it. Food 20 is supplied to the entrance of the transfer conveyor 11 to be transferred continuously, and when it is judged that foreign matter is existing in any of the food by the result of detection of foreign matter by means of the image processing device 13, the signal of judgment is sent to the food removing mechanism, and only the food judged to contain foreign matter is removed.

Next, the method of detecting foreign matter using the foreign matter detecting apparatus 10 will be explained as an example. The image processing device 13 provided to the foreign matter detecting apparatus 10 has a performance so far as it can detect the foreign matter adhered to the surface of food in the photographed image thereof . The image processing device 13 demands 0.8 seconds to 1.5 seconds for image processing to detect foreign matter in an image plane, so it can search 75-40 planes of plane dimension of 300 mm X 300 mm in one minute. When a food article to be inspected occupy one plane, 75-40 articles can be inspected. Generally, a plane of 300 mm X 300 mm can cover two trays of food, so 150-80 trays can be inspected. With this speed of inspection, the apparatus can be adopted easily to conventional food production line.

By the apparatus according to the embodiment, a hair (including a black hair, white hair, or hair of other color) , pigbristle or hair(black, white) , vegetable fiber, area-type foreign matter such as a worm, moth, other vermin , could be detected. As target food for detecting foreign matter can be cited raw meat , processed meat , ham, sausage, meatballs, boiledrice, noodles, buckwheat noodles , bread, sandwiches, packed lunches, shao-mai, steam-baked meat pies, other Chinese food, tempura( Japanese fried food), fried prawns, hamburgers, vegetables, fruits, salads, filleted fish, sliced cuttlefish rings, etc.

Another embodiment of the transfer conveyor 11 is shown in FIG.5. In the drawing, the transfer conveyor 11 consists of two transfer conveyors HA and HB arranged parallel adjacent to each other and their transfer directions are opposite to each other. These two transfer conveyors HA and HB are connected to a turn-over means 28 for turning over the food thereon. The surface of food 20 transferred on the transfer conveyor HA is inspected when it passes through an inspection zone A, then it is turned over on the turn-over means 28 and shifted to the transfer conveyor HB to be reversed in its transfer direction so that the food is transferred with the reverse side up on the transfer conveyor HB in the direction opposite to that of the transfer conveyor HA. So, the reverse side of the food 20 is inspected in turn when it again passes through the inspection zone A.

By composing the transfer conveyor 11 like this, foreign matter adhering to the food 20 can be detected on both sides by a single inspection means, and inspection time period can be reduced. Industrial Applicability

According to the present invention, misjudging of foreign matter can be decreased to a minimum even when inspecting food of complicated shape by illuminating the food from at least two sides, and foreign matter such as a hair and vermin which has been difficult to be detect hitherto can be detected with high accuracy by detecting continuity of abnormal binary-valued picture elements obtained by converting a photographed image into an image composed of binary-valued picture elements , thus a variety of foreign matter existing in food of every kind can be detected.

Claims

1. An apparatus for detecting contaminants in food comprising: a transfer means for transferring the food through an inspection zone, a photographing means for photographing the surface of the food from one side of said inspection zone when it passes through said inspection zone, a plurality of lighting means for illuminating the food from one side or both sides of said inspection zone across said transfer means, and an image processing means for processing the picked up image of the surface of the food including converting the image into a binary-valued image, whereby an abnormal picture element exceeding a pre-established threshold value of darkness is detected in the binary-valued image obtained through image processing by said image processing means, then picture elements adjacent said abnormal picture element are inspected whether abnormal or not, detection of abnormal picture element or elements adjacent the detected abnormal picture element or elements is repeated, and when abnormal picture elements continue to said first detected abnormal picture element, it is judged that foreign matter exists.

2. An apparatus for detecting contaminants in food according to claim 1, wherein when said abnormal picture elements appear continuing linearly, it is judged that fibrous foreign matter such as hair exists.

3. An apparatus for detecting contaminants in food according to claim 1, wherein when said abnormal picture elements appear bordering on each other by the side thereof to form an aggregate area of abnormal picture elements, it is judged that area-type foreign matter exists.

4. An apparatus for detecting contaminants in food according to claim 1 , wherein a first lighting means located in said photographing means side among said lighting means is a means to radiate visible light and a second lighting means located in the other side across said transfer conveyor is a means to radiate infrared light.

5. An apparatus for detecting contaminants in food according to claim 4, wherein one of red, blue, green, and white light which is the mixture of red, blue, and green light can be selected in said first lighting means in accordance with the kind of food.

6. An apparatus for detecting contaminants in food according to claim 1, wherein said photographing means is a CCD camera having focus length of 500 mm to 900 mm.

7. An apparatus for detecting contaminants in food according to claim 1 , wherein a cleaning means is provided for cleaning the part of the transfer means which will be brought into contact with the food, and at least either of said lighting means is movable so that it can be accommodated in a storage box provided apart therefrom when cleansing is carried out by said cleaning means.

8. An apparatus for detecting contaminants in food according to claim 4, wherein said second lighting means is accommodated in a fluid-tight storage box with the side thereof facing the transfer means being formed of material permeable to infrared light , and a cooling means is provided for cooling the inside of said storage box.

9. An apparatus for detecting contaminants in food according to claim 1, wherein said transfer means includes two conveyor belts arranged side by side in parallel to each other, transfer directions of the two conveyor belts being opposite to each other, a turn-over means for turning over food thereon is provided at an end of the paralleling conveyor belts, the topside surface is inspected to detect foreign matter on one of said conveyor belts, and reverse side surface is inspected to detect foreign matter on the other of said conveyor belts.

10. An apparatus for detecting contaminants in food according to claim 1, wherein said foreign matter is a substance containing protein as a chief ingredient.