WO1997033160A1

WO1997033160A1 - Process and device for the automatic radioscopic quality control of foodstuffs

Info

Publication number: WO1997033160A1
Application number: PCT/EP1997/000513
Authority: WO
Inventors: Günther KOSTKA; Peter Schmitt; Randolf Hanke; Norbert Bauer
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1996-03-08
Filing date: 1997-02-05
Publication date: 1997-09-12
Also published as: AU1600997A

Abstract

In a process for the automatic radioscopic quality control of foodstuff items (104), an item (104) to be controlled is taken past an X-radiation source (100) and the X-radiation (100a-100c) passing through said item (104) to be controlled is detected. A chargeimage is generated from the detected X-radiation (100a-100c) by means of a sensor (108) having a plurality of sensor units (102a-102c) by shifting generated charges (110, 112, 114) over several sensor units (102a-102c) synchronously with a direction (106) and speed of movement of the item (104) to be controlled and imaged on the sensor (108) and by adding the partial charges generated by the sensor units (102a-102c) to the charge image. The foodstuff item to be controlled is then assessed by means of the charge image.

Description

Method and device for automatic radioscopic quality control of food

description

The present invention relates to a method and a device for automatic radioscopic quality control of foods, in particular to the automatic X-ray inspection for foreign bodies and other incorrect fillings of industrially produced foods at high object speeds by means of line or surface X-ray cameras and fast automatic image processing.

In the industrial production of foodstuffs, foreign bodies can be admixed before or during the filling process, or other incorrect filling, such as, for example, an insufficient filling quantity or water filling. If injuries to the body of harmful foreign bodies in the food occur, this leads to claims for recourse by the consumer against the manufacturer. In order to ensure the flawless quality of the products, many manufacturers nowadays have to subject their products to 100% quality control with regard to the admixture of foreign bodies or incorrect filling.

For foods that due to their packaging or consistency with conventional methods such. B. an optical test or a test using ultrasound, are not testable, for example cans or the like, radioscopic test methods are increasingly being used. Since foreign bodies appearing in the food generally from materials with compared to food itself higher radiation attenuation coefficients exist, these can be recognized and classified on the basis of gray value differences occurring in a transmission image or charge image. In this case, the packaging unit is illuminated with the food by radiation, for example an X-ray or gamma radiation, then the resulting image is imaged by means of suitable detectors or by means of a suitable detector and converted into an electronic gray-scale image, which in turn is converted is visually evaluated by human examiners or by a computer-aided automatic evaluation unit with regard to the relevant error criteria. The packaging units identified as defective on the basis of the specified quality regulations are discarded accordingly.

Typical material flow velocities realized in the production lines are in the order of approx. 10 to 20 packaging units per second, i.e. converted in the range of conveyor belt speeds of approx. 1 m / sec to 2 m / sec with an assumed packaging extension of approx. 10 cm in the longitudinal direction of the belt. Since the production facilities are generally in operation around the clock, it is expedient to carry out the quality inspection with the same cycle times in which a foodstuff to be inspected is guided past the inspection station. It has been found that these high clock rates are no longer manageable by human auditors.

Due to blurring effects, fast-moving objects can only be poorly imaged by area image sensors. Therefore, in such cases, so-called line cameras are used for data acquisition, the pixel information of which is read out, digitized and processed in an evaluation system in a specific line cycle.

A disadvantage of X-ray inspection systems used hitherto is the relatively low test speed that can be achieved, which is about 10 times lower than the production clock lies. For a 100% check, it is therefore necessary to branch the material flow and have it checked by several inspection systems. This increases the costs for quality assurance considerably, so that only a few manufacturers can operate this relatively large cost.

The test speed is essentially determined by the detection sensitivity of the camera system and the maximum possible line clock rate, i.e. on the readout and processing speed. With conventional X-ray line cameras, maximum line clock rates of approx. 200 lines / sec can be realized at approx. 1000 pixels / line and 250 mm line length. In order to detect foreign objects with a minimum extension of 1 mm in the direction of movement at an object speed of 1 m / sec, a line cycle of at least 2 kHz with a line resolution of 0.5 mm is necessary. In other words, a line frequency which is a factor of 10 higher than is required by the conventional technology is required.

In the X-ray examination, the X-ray detection sensitivity of the sensor, ie the quantum yield, should be as high as possible in order to enable short exposure times at low X-ray intensities with a sufficient signal-to-noise ratio (SNR). The x-ray detection sensitivity essentially depends on the active input area per pixel, ie on the pixel length and width, and on the thickness and effectiveness of the scintillator material. In a conventional line camera, the geometry is determined by the required image resolution parallel and perpendicular to the scanning direction. A widening of the line area would lead to a loss of spatial resolution in the vertical line direction, ie in the direction of movement. The geometry of the line detector used, which is determined by the required sensitivity and imaging properties, leads to a relatively large electrical capacity of the sensor. a reading of the pixel information practically prevented at higher frequencies. In summary, it can be stated that with conventional line camera technology a compromise must be found between the largest possible input area for high sensitivity and the smallest possible dimension of the targets for high readout speed and spatial resolution. This conflict generally prevents use at correspondingly high read-out speeds, as is required for food testing or other high-speed testing tasks.

Proceeding from this prior art, the present invention is based on the object of creating a method and a device for automatic radioscopic quality control of foodstuffs which can achieve test speeds of more than 1 m / sec with a spatial resolution of approximately 0. 5 mm allows.

This object is achieved by a method according to claim 1 and by an apparatus according to claim 9.

The present invention provides a method for the automatic radioscopic quality control of foodstuffs, with the following steps:

- guiding a food to be checked past an X-ray source;

Detecting the x-rays that penetrate the food to be checked;

Generating a charge image from the detected X-ray radiation by means of a sensor having a plurality of sensor elements, the generation of the charge image comprising the following steps:

- Shifting the generated charges over several sensor elements synchronously with a direction of movement and Speed of movement of the food to be checked which is imaged on the sensor; and

Adding the partial charges generated by the sensor elements to the charge image; and

Assess the quality of the food to be checked using the charge image.

The present invention provides a device for carrying out the method for automatic radioscopic quality control of foods

a transport device that moves a food to be checked into a transport device;

an X-ray source that irradiates the food to be checked;

an X-ray radiation detection device, by means of which a charge image can be generated from the detected X-ray radiation, which penetrates the food to be checked, by means of a sensor having a plurality of sensor elements;

an assessment device which assesses the quality of the food to be checked on the basis of the charge image; and

a control device which, depending on the assessment of the quality of the food to be checked, generates a signal which causes the food to be separated.

According to a preferred embodiment, a charge image is generated by means of a TDI X-ray line camera (TDI = Time Delayed Integration = time-delayed integration). Preferred developments of the present invention are defined in the subclaims.

Preferred exemplary embodiments of the present invention are described in more detail below with reference to the accompanying drawings. Show it:

1 is a schematic diagram illustrating the acquisition of a charge image of a food to be checked according to the present invention;

2 shows a basic diagram of a device for radiological quality control of foods by means of a TDI X-ray line camera; and

3 shows a preferred exemplary embodiment of the device according to the invention for automatic quality control of foods.

In the following description with reference to the accompanying drawings, the same elements are provided with the same reference symbols in the individual drawings.

The method according to the invention for automatic radioscopic quality control of foods is described in more detail below with reference to FIG. 1. In Fig. 1 a), c), e) three lines I-III of a sensor of an X-ray line camera are shown, and in Fig. 1 b), d), f) are schematic representations of a device for generating a charge image 1, the passage of a food to be checked is shown schematically in FIGS. 1 b), d) f).

1b) shows an X-ray radiation source (RQ) 100 and an X-ray camera (RK) 102. The x-ray source 100 emits x-rays, which is schematically represented by the arrow 100a in FIG. 1b). It is Obviously, the X-ray source 100 emits a large number of X-rays, however, in order to maintain clarity, no further X-rays have been shown, since these are not necessary for the following explanation of the functional principle of the present invention. The x-ray camera 102 has a plurality of sensor elements (A, B, C) 102a-102c. A foodstuff 104 to be checked, which is arranged, for example, within a metallic can, is moved between the x-ray source 100 and the x-ray camera 102 in a direction of movement, which is indicated by the arrow 106.

In this case, as shown in FIG. 1 b), the food 104 is penetrated by the X-ray beam 100a and the sensor element (A) 102a generates a charge from the X-ray beam incident on the sensor element. This is shown in more detail in FIG. 1 a), which shows the sensor 108 of the X-ray camera 102 in more detail, which comprises a plurality of lines, in the illustrated case three lines. The sensor element (A), which is illuminated by the X-ray beam 100a, stores a partial charge 110, which is represented by the black area in the sensor element (A).

If the food 104 is now moved further between the X-ray source 100 and the X-ray camera 102, the situation results, which is shown in FIG. 1 d), in which the food 104 is penetrated by a first X-ray beam 100a and a second X-ray beam 100b . In this case, two sensor elements (A, B) 102a, 102b receive the rays 100a, 100b which penetrate the food 104. It is pointed out that the designation of the individual sensor elements 102a-102c with (A) or (B) serve to clarify the method according to the invention. As can be seen in FIG. 1 c), the partial charge 110 shown in FIG. 1 a) in the sensor element (A) 102a is now shifted into the sensor element 102b, but for clarification is still referred to as sensor element (A). Sensor element ^• 102a, which is now referred to as sensor element (B), in turn converts a received X-ray beam 100a into a partial charge 110, as shown in FIG. 1 c). To make this possible, according to the present invention, the partial charge 110 shown in FIG. 1 a) in the sensor element 102a is shifted from the sensor element 102a into the sensor element 102b synchronously with the direction of movement 106 and the speed of movement of the food 104, and that by the sensor element 102b Charged charge is added to the partial charge already located in sensor element 102b, or partial charges 110, 112 are integrated, so that an added charge 112 is represented by the filled area of sensor element 102b in FIG. 1 c) is.

1 e) and 1 f) show a further situation in which the food 104 is completely between the X-ray source 100 and the X-ray camera 102. The partial charges 110, 112 located in FIGS. 1 c) and 1 d) of the sensor element 102b and 102a are shifted into the sensor elements 102c and 102b, and the partial charges generated by the respective sensor elements 102b and 102c already become those Partial loads located in the sensor elements are added, so that the situation arises as shown in FIG. 1e). The sensor element (A) now contains an added partial charge 114, which results from the partial charges 110 and 112 and from the newly generated charge due to the incidence of the X-ray beam 100c on the sensor element 102c. The partial charges 110 and 112 are generated in the sensor elements (B) and (C) in the manner described above. The rows I-III shown in FIG. 1 a), c), f) thus result. After the state shown in FIG. 1, line I is read out from the sensor and the information represented by the charge 114 is made available to an image processing system. It is pointed out that the method according to the invention was described by way of example only with reference to FIG. 1, in particular a sensor with only three lines and three sensor elements was assumed to simplify the description, it being obvious that an actual one X-ray camera has a variety of sensor elements and lines.

In other words, the basis of the method according to the invention for the radioscopic quality control of foods at high belt speeds is the use of X-ray line cameras which are based on CCD area sensors and work in the so-called TDI mode. As has already been described with reference to FIG. 1, the electrical charges generated by the radiation are in the individual pixels (pixels, which are represented in FIG. 1 by sensor elements (A), (B) and (C) ), which represent the image information, on the surface sensor 108 during the irradiation in synchronism with the object 104, ie with the corresponding direction 106 and speed, perpendicular to the line direction, also moved over all the image lines I, II, III and added up. The image information is then read out line by line and made available to an image processing system. As a result, the active input area of the sensor 108 increases from a single line, as is present in a conventional line sensor, to almost any number of lines, depending on the sensor type selected. Accordingly, the input sensitivity of the signal-to-noise ratio also increases with otherwise identical exposure conditions.

A device which uses a TDI X-ray line camera is described in more detail below with reference to FIG. 2. An x-ray source 100 emits an x-ray radiation 100a, 100b which penetrates an object 104. The x-ray camera 102 comprises an input window which is defined by an aperture 116, behind which a scintillator layer 118 is arranged, which contains the x-ray radiation impinging on it changes into visible light. The light emitted by the scintillator layer 118 is imaged onto an optical input window 122 by means of a fiber optic 120. The generated light reaches the CCD sensor 124 from the optical input window 122. Control electronics 126 are provided in the X-ray camera 102, which controls the readout method from the CCD sensors 124 described above with reference to FIG. 1.

In addition to the fiber optics 120 described with reference to FIG. 2, the light-sensitive CCD sensor surface 124 can be coupled to the scintillator-coated X-ray-sensitive input screen 118 by means of a conventional X-ray image intensifier technology or by other light-transmitting imaging components. Through the choice of the geometry of the coupling element 120, any uni- or biaxial enlargement or reduction of the active input surface can be achieved within certain limits without the CCD sensor surface itself having to be changed to this size. This enables the high readout speed of CCD sensors of approximately 10 MHz to be used, so that the required feed and line read cycles can be realized in this way.

The use of TDI-CCD sensors thus enables simultaneously high line feed and read speeds with high input sensitivity and a correspondingly adapted input area.

The data material obtained by the TDI-CCD X-ray camera in the manner described above can, after an analog-to-digital conversion, directly from a correspondingly powerful computer system either line by line (one-dimensional or two-dimensional) by means of suitable algorithms corresponding error criteria are checked. The computer takes over both the image evaluation and the control of the corresponding hardware components, the removal and communication with a computer network. Factory of the quality system for permanent error feedback. For extremely computing-intensive evaluation algorithms, the system can also be expanded by additional image processing hardware.

In addition to the readout speed to be implemented, the performance and reliability of the algorithms for error detection are essential for the evaluation of a method and a device for automatic quality control of foods. Under the error criteria, such as Foreign bodies, water filling or underfilling, the most important type of error is the presence of foreign bodies in the food. Due to the usual inhomogeneity of the food, e.g. Bone and cartilage parts in the dog food, the problem arises of selecting these components of actual foreign bodies that are intentionally introduced. Foreign bodies usually cause due to the higher radiation attenuation coefficients of the materials, e.g. Metal, glass, ceramic, stone, compared to the food, which generally consists of over 90% water, reduced radiation intensities at the detector and can be determined by the difference in contrast generated, i.e. through darker areas in the image, recognize and classify.

A preferred exemplary embodiment of the present invention is described in more detail below with reference to FIG. 3. 3 shows a device for the automatic radio-scopic quality control of animal feed cans 104, which have a diameter of 100 mm and a height of 170 mm. The test cycle to be implemented is 10 cans / sec, which leads to a belt speed of the transport device 128 of 1 m / sec when the cans 104 are guided individually.

In this exemplary embodiment, foreign bodies made of metal, glass, stone or ceramic with a minimum expansion of 1 mm, as well as an insufficient filling, ie incorrect filling, and a water filling can be detected.

The cans 104 stand vertically on the conveyor belt 128 and are occasionally guided by a pressure radiation arrangement. The x-ray line camera 102 is arranged such that its longitudinal orientation is perpendicular to the direction of movement and parallel to the can axis. The beam entry window is parallel to the direction of movement next to the band 128. The x-ray source 100 is directly opposite the line camera 102 on the other side of the band 128. The x-ray beam is oriented perpendicular to the band movement, the beam focal point being just above the band plane, see above that the can base is irradiated almost in parallel in order to make it possible to image foreign bodies that have sunk onto the base without being switched off by the can base. In approximate parallel beam geometry, i.e. the distance between the source and the can is much greater than the height of the cans, the cans 104 are guided as close as possible, preferably about 6 cm, past the line camera 102 on the belt 128, so that there is a magnification value of about 1.1 results. The resolution is almost independent of the focal spot size of the X-ray source 102 and is essentially determined by the pixel size of the X-ray camera 102.

The required tape speed (lm / sec) and the required detail resolution (0.5 mm / pixel), when enlarged by a factor of 1.1, force an effective line read cycle with at least 2.2 kHz. As a suitable light coupling component between the X-ray-sensitive input screen (118, FIG. 2) of 200 mm in length and the actual sensor surface, which in a preferred exemplary embodiment is 1024 x 256 pixels with a pixel area of 26 μm x 26 μm and a length of 27 mm and a width of 6.7 mm, an obliquely cut fiber optic is used, as is shown for example in FIG. 2, which causes a uniaxial, ie one-dimensional, enlargement of the sensor input surface by a factor of 7.5, which means that the individual pixels correspondingly have a line width of 26 μm ₁ 95 μm can be enlarged. A grouping of groups, which is also referred to as binning, of three successive pixels each when reading out the line leads to an effective pixel size of 885 μm on the input screen and of approximately 530 μm on the object.

The line feed speed on the sensor 108 is determined from the object speed multiplied by the magnification factor. Since the pixels cannot be enlarged in the direction perpendicular to the line, the direction of movement of the cans 104, 20 lines on the TDI sensor can be combined into an effective line by simple addition before reading, which is also called 16 - is called line binning. The effective line width in this case is 520 μm or 470 μm on the object, i.e. on the can 104.

The TDI sensor described above has 256 lines, with a line width of 26 μm resulting in a total width of approximately 6.7 mm. Compared to a standard line width of 0.5 mm, this means an enlargement of the active input area and thereby an increase in sensitivity and a factor of approx. 13.3 without impairing the spatial resolution.

In the preferred exemplary embodiment described above, an evaluation device 130 is provided which executes an evaluation algorithm which enables a qualitative evaluation of the three-dimensional extent and the absorption properties of a foreign body, regardless of its relative position and orientation. For this purpose, the recorded data are first corrected for the mean, so that the shape-related thickness variation has no influence on the intensity values. Then all pixels of a line with an intensity value smaller than a certain lower bound are added up, namely both the number of pixels and the amount of the intensity difference from the mean. The evaluation result of a line is the expansion of a potential tial foreign body along the line and the strength of the intensity attenuation, which depends on the depth and the beam attenuation coefficient of the material. If this evaluation is repeated for all successive lines, an integral value results over the entire error. If there are several foreign bodies, they can be selected accordingly and evaluated separately.

A can that is only filled with water, for example, can be detected within the rows by the absence of the intensity modulation that normally occurs due to the inhomogeneity of the can content.

A can, for example, which is only partially filled, can be detected by the resulting jump in intensity to high values within the lines in a defined range, within which no such jump is normally to be expected.

FIG. 3 also shows a control device 132 which, depending on the result of the evaluation, outputs a signal in the evaluation device 130, which causes a processing stage following the quality control to reject the can 104 classified as defective.

Claims

claims

1. Process for the automatic radioscopic quality control of foodstuffs, with the following steps:

- guiding a food (104) to be checked past an X-ray source (100);

Detecting the x-ray radiation (100a-100c) which penetrates the food (104) to be checked;

Generating a charge image from the detected X-ray radiation (100a-100c) by means of a sensor (108) having a plurality of sensor elements (102a-102c), the generation of the charge image comprising the following steps:

- Shifting the generated charges (110, 112, 114) via a plurality of sensor elements (102a-102c) synchronously with a direction of movement (106) and speed of movement of the foodstuff (104) to be checked which is imaged on the sensor (108); and

Adding up the partial charges (110, 112, 114) generated by the sensor elements (102a-102c) to the charge image; and

Assess the quality of the foodstuff (104) to be checked on the basis of the charge image.

2. The method as claimed in claim 1, in which the food (104) to be checked is imaged on the sensor (108) by means of an optical system (120), the generated charges (110, 112, 114) being shifted at a speed which through the movement speed multiplied by a magnification factor of the optics (120) is determined.

3. The method of claim 2, wherein the optics (120) is fiber optics.

4. The method according to any one of claims 1 to 3, in which the sensor elements (102a-102c) are arranged side by side next to one another, the generation of the charge image including reading the charges line by line.

5. The method according to claim 4, wherein the reading of the charges is carried out with a clock frequency of at least 2.2 kHz.

6. The method according to any one of claims 1 to 5, wherein the assessment of the quality comprises the detection and classification of contrast differences in the charge image generated.

7. The method according to any one of claims 1 to 6, wherein the food (104) is obtained in a can.

8. The method according to any one of claims 1 to 7, wherein the sensor is a CCD sensor, wherein the X-radiation is converted by means of a scintillator-coated screen (118) into the rays which are applied to the CCD sensor (124) hit.

9. The method according to any one of claims 1 to 8, wherein the charge image is generated by means of a TDI-CCD X-ray line camera.

10. Device for performing a method for automatic quality control of food according to one of the preceding claims, with

- a transport device (128) which is to be con- trolling food (104) moved in a transport direction;

an X-ray source (100) which irradiates the food (104) to be checked;

an X-ray radiation detection device (102), by means of which a charge image can be generated from the detected X-ray radiation, which penetrates the food (104) to be checked, by means of a sensor (108) having a plurality of sensor elements (102a-102c);

an assessment device (130) which uses the load image to assess the quality of the food to be checked; and

a control device (132) which, depending on the assessment of the quality of the food to be checked, generates a signal which causes the food (104) to be rejected.

11. The device according to claim 9, wherein the X-ray radiation detection device (100) is a TDI-CCD X-ray line camera.

12. The apparatus of claim 8 or 9, wherein the transport device (128) moves the food (104) at a speed of 1 m / sec.