ES2368574T3 - X-RAY INSPECTION SYSTEM - Google Patents

Abstract

An x-ray inspection system (198) arranged to inspect at least one object (212) and comprising: a radiation source (200); a detector (216), which in use is capable of detecting the radiation that passes through an irradiation zone (214) and of generating a periodic data output thereof; where the detection is arranged so that the radiation is detected when a period of accumulation passes; processing circuitry arranged to process the output generated by the detector (216); a speed determining means arranged, in use to determine and send to the processing circuit the speed at which an object (212) passes through the detector; where the processing circuitry is arranged to vary the period (T) of the detector output (216) according to the output of the speed determining means, characterized in that the period (T) of the detector output (216) comprises the accumulation period (C) and a restart period (R) and the accumulation period (C) is maintained as a substantially constant period.

Description

X-ray inspection system.

This invention relates to an x-ray inspection system and related methods of inspecting items using x-rays.

There is a continuing need to inspect items, be it the inspection of luggage at an airport or other transportation-related situation, or at the exit of a production process. For example, it is common in the food industry to inspect the actual content of the article to determine that the food content is as desired and does not contain any foreign bodies such as stones, bone fragments, metal from the machines used in food production , or the like.

A typical x-ray inspection apparatus comprises a conveyor arranged to transport the objects to be inspected through the apparatus. Inside the apparatus there is an x-ray source with a collimator associated therewith arranged to produce a narrow irradiation zone that extends across the width of the conveyor. Under the conveyor there is a detector capable of detecting the x-rays that have passed through an object that passes over the conveyor through the irradiation zone.

The detector generally comprises a linear array of photodiodes that extend across the width of the conveyor, next to the irradiation zone. The photodiodes are generally provided with a series of modules, each of which contains a plurality of photodiodes. There is a phosphorescent strip mounted on top of the photodiodes inside a module, and the x-rays that affect the phosphorescent strip cause the emission of light. The intensity of the light emitted by the phosphorescent strip is proportional to the amount of x-rays that affect it, and the light emitted is detected by the photodiodes.

Therefore, the output of the photodiodes can be used to give an indication about the amount of x-rays that are reaching the phosphorescent strip through the irradiation zone. The amount of x-rays that the phosphorescent tape reaches will be dependent on the nature of the object that is passing through the irradiation zone; Denser materials such as bone, metal, stone and the like will absorb more x-rays than materials such as meat or other foods. Similarly, the absence of material, for example due to a hole, will absorb less x-rays than meat or other foods. Therefore, the amount of x-rays that reach the phosphorescent strip can be used to determine if there is foreign matter in the product, or in fact also if there is absence of matter.

The output of the photodiodes is normally converted to a video signal and / or processed to determine if the object that is passing through the irradiation zone meets predetermined criteria.

In general, the detector (for example, photodiodes) is kept in a fixed orientation and the object / product to be scanned is moved past the detector by means of a conveyor. Some applications that allow the use of such an x-ray inspection system vary the speed of the conveyor. These applications include the monitoring of drug or food packaging lines to ensure that the container is correctly filled with the drug / food; monitoring of fluids or solids in a pipe (for example, soup or minced meat respectively); and other similar applications.

The processing circuitry arranged to process the detector output is generally calibrated at the speed at which the object to be scanned passes through the detector. Therefore, if the conveyor speed is altered, the speed at which the object passes through the detector is modified, and the calibration of the processing circuitry becomes incorrect.

Many x-ray inspection systems work to automatically reject objects that do not meet predetermined criteria. Therefore, if the calibration is not inaccurate, some objects may be unnecessarily rejected, or even worse, some objects that should be rejected may not be. Therefore, respectively there would be wasted objects or objects of inferior quality that would pass the filter.

EP 0 198 276 describes an x-ray inspection system in which the scanning speed of the detector depends on the speed of the conveyor.

US 2004/0251415 describes a system that can measure the variable speed of a target and measure the radiation that passes through the target to generate a distortion-free image of the target's contents.

According to a first aspect of the invention, there is provided an x-ray inspection system arranged to inspect at least one object and comprising:

a source of radiation;

a detector, which in use is capable of detecting the radiation that passes through an irradiation zone and of generating a periodic data output thereof;

where the detection is arranged such that radiation is detected when a period of accumulation occurs;

processing circuitry arranged to process the output generated by the detector;

a speed determining means arranged to, during use, determine and send to the processing circuitry the speed at which an object passes through the detector, where

the processing circuitry is arranged to modify the period of the detector output according to the output of the speed determining means,

characterized in that the period of the detector output comprises the accumulation period and a restart period and the accumulation period is maintained in a substantially constant period.

According to a second aspect of the invention, a method is provided for monitoring a product comprising:

measure the speed at which the product passes through an irradiation zone in which the x-rays generated by an x-ray source affect; detect the amount of x-rays that pass through the product using a detector adjacent to the irradiation zone and that detects a periodic radiation output when an accumulation period occurs; where the method comprises adjusting the period of the exit of the detector according to the speed at which the object passes through the irradiation zone, characterized in that the period of the exit comprises a period of accumulation and a period of restart and the Accumulation period is maintained in a substantially constant period.

According to a third aspect of the invention, a machine-readable medium is provided that contains instructions that, when read by a processing circuitry, cause said processing circuitry to carry out the method of the second aspect of the invention, or when read by a processing circuitry in an x-ray inspection system, they cause the system to function as an x-ray inspection system in accordance with the first aspect of the invention.

The computer-readable medium of any of the above aspects of the invention can be any of the following: a flexible disk; a CD ROM, a DVD (including + R / + RW, -R / -RW, RAM); a hard disk, a memory (including memory sticks and the like); a tape: a transmitted signal (including an Internet download, an ftp transfer and the like); a cable; or similar.

The following is only an example of a detailed description of the present invention with reference to the attached figures, in which:

Figure 1 shows an arrangement of photodiodes within an x-ray inspection system;

Figure 2 shows a typical arrangement of the components of an x-ray inspection system;

Figure 3 shows a 3-dimensional view of the array of a photodiode array

Figure 4 shows a time diagram of the circuitry used to drive the array of photodetectors shown in the previous figures.

Figure 1 is used to describe an arrangement of a prior art x-ray inspection system that typically comprises a photodiode array made of discrete diodes arranged according to a single row. A photodiode array typically comprises 64 diodes and in Figure 1 four of the diodes 10-16 of matrix 8 are shown. One skilled in the art will readily appreciate that the photodiode array can comprise any number of photodiodes, where the number used It will be determined by the application.

Figure 2 shows a general arrangement of an x-ray inspection system 198. This Figure is intended to put the embodiments of the invention in context, although it may also be applicable to prior art systems. The system is intended to inspect objects to ensure that the object inspected is adequate and / or safe for its purpose. If the object were a food or a drug, then the inspection could be used to determine if there are foreign bodies or holes in them, or the absence of product in the container. If the object is a piece of luggage, then the inspection can be used to determine if there are prohibited products in the luggage; for example, to inspect luggage before a flight.

The system comprises an x-ray source 200, which provides a radiation source, which is fed by a high-voltage power source 202. The x-ray source is cooled by a refrigerator 204 to ensure that its temperature is maintained within a certain operating range. The power supply 202 and the refrigerator 204 are controlled by the processing circuitry of a controller 206 described below.

The x-rays produced by the x-ray source 200 are collimated, in a known manner, to provide a narrow beam of x-rays, generally fan-shaped 208 (whose shape can best be seen in Figure 3) and which typically has a width of about 1 mm. In Figure 2, the fan shape is shown from the side and represented by a row of dots.

A conveyor 210, which has an end 224 upstream from which objects flow and an end 226 downstream to which objects flow, is arranged to move an object 212 to be inspected through an irradiation zone 214 located in a region under the x-ray source 200 and on the x-ray detector 216, comprising a plurality of detector elements, each arranged to generate a periodic output. In Figure 2 the conveyor 216 is shown as a conveyor belt, but it could be any other type of suitable mechanism arranged to transfer objects 212 through the irradiation zone 214, such as Bandolier or band type transport mechanisms. It will be appreciated that if the direction of movement of the conveyor 210 is reversed, then the upstream end 224 will become the downstream end 226 and vice versa.

Some transport mechanisms may use the packaging of the object as a transporter (as in the packaging of drugs). Other transport mechanisms may have conduits for fluids, such as soups or the like. In such embodiments, the object to be inspected is the fluid. However, it will normally be desirable to inspect the contents of the objects transported by said transport mechanisms to ensure that the product is adequate and / or safe for release.

The detector 216 is arranged to generate data indicative of the amount of x-rays incident therein. The x-rays emitted from the source 200 generally pass through the object 212 when it is in the irradiation zone 214, but are attenuated by the object 212 according to its composition, and are then detected by the x-ray detector 216. The amount of x-rays received at a point along the detector (that is, in or out of the page as shown in Figure 2) gives an indication of the composition of object 212 at that point along the detector 216 at that moment of time.

As the object 212 (which can be a fluid, or a container that should contain an object) is displaced through the irradiation zone 214 by the conveyor 210, a two-dimensional image can be constructed from the data generated by the detector 216. That is, the data generated by the detector can be taken at predetermined intervals (typically about 1 ms) and linked together to form an image after proper processing. In this embodiment, the processing circuitry of the controller 206 processes an output 218 of the detector 216 to generate a video image that is displayed by a screen 220.

In some examples, already known and described to improve the understanding of the invention as a whole, the controller 206 can also perform another processing of the data generated by the detector 216, for example to determine whether the product being scanning should be rejected by activating an "exit rejection mechanism" 222. In such embodiments, if controller 206 determines that the object being scanned is below a predetermined standard (it may be because it contains a foreign body above a predetermined size, it contains a gap, a portion of the container is not full, or similar), then it can cause the rejection mechanism to remove that object from the conveyor 210. Such rejection mechanisms are well known and will not be described further.

In some examples, the screen 220 can be omitted and the machine can perform an automatic inspection of an object that passes through the irradiation zone 214. During automatic inspection, if the controller 206 determines that a product falls outside the acceptable criteria, then the output to the rejection mechanism 222 can be used to remove the product from the conveyor 210.

The processing circuitry of controller 206 typically comprises a processor such as an InterTM PentiumTM, AMDTM AthlonTM, IBMTM PowerPCTM, or other similar processor. However, in other embodiments the processing circuitry may also comprise dedicated electronic devices provided by one or more Specific Application Integrated Circuits (or the like).

The processor is configured to execute a code stored in a memory accessible by the processor. The memory may or may not be disposed in the system 198 and may be accessible through a network connection of the system 198. Moreover, the memory may comprise a volatile portion (for example, a RAM) and a non-portion volatile (for example, a ROM, EPROM, hard disk or similar).

The screen 220 is typically a Liquid Crystal Display (LCD) but could be any other type of screen, such as a Cathode Ray Tube (CRT) screen, a Light Emitting Polymer (LEP) screen or the like.

In Figure 1, four elements 10, 12, 14, 16 detectors are shown. A detector element would generally be a photodiode. The detector elements are arranged in modules that are configured to constitute the detector. Typically a module would contain 64 photodiodes, but it does not need to be so, and 32 and 128 diode modules are also known. It is possible that a module contains any number of photodiodes.

As with known systems, which are described for clarity, in one example there are fourteen modules in the detector 216. However, other examples may have different numbers of detector modules that constitute the detector 216. In effect, the detector may not comprise modules The number of modules in generally sufficient to provide detection along the width of the conveyor 210 that is used to transport the objects 212 through the irradiation zone 214. Current examples generally have approximately 4 to 20 modules. However, some examples have up to 72 modules and it is possible to use more detectors or fewer modules. Therefore, a system that uses 72 modules, each of which has 64 detector elements, would use 4608 detector elements (for example, photodiodes).

The image shown by the screen 220 is by nature pixelated, as is the corresponding image that is maintained in the memory of the processing circuitry of the controller 206 due to the digital nature of the electronics used.

In one example, when an image is processed, it is assumed that any object 212 on the conveyor 210 has moved a predetermined distance between samples taken from the outputs of the detector 216. Therefore, a fixed conveyor speed is assumed. It is convenient that this speed be calculated so that it is the length of the diodes in the direction of movement of the conveyor 210 multiplied by the scan rate:

(1) speed = height (h) X scan rate

Using the example in Figure 1, the diodes have a height (h) in the direction of movement of the conveyor of 0.8 mm and the system has a scan rate of 1000 scans / s (i.e. a period of 1 ms ). Therefore, in the system of Figure 1 an object would appear correctly on the screen (and in memory) if the conveyor 210 were moving at 0.8 mm x 1000 scans / s - that is, 800 mm per second. Dividing the scanning speed by up to 500 scans / s would reduce the speed of the conveyor to which the system is set (ie, for which no correction is required) to 400 mm / s.

If such a fixed speed is assumed and the conveyor 210 travels at a speed greater than that speed, then the objects would appear on the screen shorter than they should. Likewise, if the conveyor 210 travels at a slower speed, then the objects 212 will appear to be larger than they should. This can be problematic for the processing carried out by the controller 206 of the data generated by the detector

216. For example, the system may be arranged to process the data generated by the detector 216 to obtain a volume of an object (for example, a chocolate bar, etc.). If the length of the bar varied due to the variation in conveyor speed, then the volume would appear to fluctuate, which would lead to a potential rejection of objects with an acceptable volume and / or the maintenance of objects with an unacceptable volume. Moreover, embodiments of the system can be used to determine whether foods (eg, chocolate), drugs or the like fill each portion of the package. A variable conveyor speed can lead to controller 206 determining that a food, drug, etc. It is in a position that it does not really occupy, that is, it has moved.

The following is explained with reference to Fig. 4 which embodiments of the invention can be used to correct the processing of the data generated by the detector 216 according to the speed of the conveyor 210. Each of the detector elements is generally a photodiode with the which is associated with a layer of scintillating material usually a phosphor strip). This is well known in the art.

In addition, photodiodes are generally inversely polarized, so that they function as a charged coupled device: when x-rays strike the scintillator layer, light is generated; the light generated causes a charge to be stored in the photodiode; the magnitude of the charge on any photodiode is read according to a predetermined interval (as such, the detector's output is periodic); and after reading the charge level, the diode is reset so that the accumulated charge in it is removed. The charge level of any photodiode read in this way gives an indication of the amount of x-rays that hit the scintillator material in a region above that photodiode. Therefore, the photodiodes of the detector 216 are reset at regular intervals, which are generally kept constant so that the load measured by the photodiode is measured over a constant time interval.

Figure 4a shows a waveform 900 suitable for resetting the photodiodes of the detector. The waveform has a period T comprising a low period 902 reset pulse R used to reset the photodiode and a high period C pulse that allows the charge to accumulate in the diode; Period C can be considered as a measurement pulse. The detector output is generally read at an end region of this measurement pulse before the detector restarts. It will be seen that the period T is substantially constant for the waveform 900, so that the edges of the reset pulse occur at a predetermined time.

To accommodate a variable conveyor speed, the person skilled in the art might think that it would be enough simply to alter the period T of the waveform 900, so that an object 212 on the conveyor moves a predetermined distance between each reset pulse 902 . However, there are complex calibration problems and if the T period is altered the system must be recalibrated to keep the detector output 216 constant. This is not a practical solution, particularly in system applications where the speed of the conveyor 210 varies continuously. Such applications include drug packaging in blister packs comprising a plurality of blister packs; the filling of dust bags, or the like, the monitoring of fluids (such as soup) or pumped solids (such as minced meat) in a pipe; and the like

In embodiments of the invention the processing that is carried out with the data generated by the detector 216 is compensated according to a method and apparatus described in relation to Figures 4a and 4b.

It is assumed that the apparatus is fundamentally as described in relation to Figure 2, although the person skilled in the art will understand that the teachings of the invention in relation to Figures 4a and 4b could be applied to apparatus with a different configuration. To carry out the method, the maximum speed at which it will be desired for the conveyor 210 to travel is determined and the controller 206 is configured to process the data generated by the detector 216 properly. Part of this configuration is done to establish the periods T, C and R; the total period (T), the period during which charge is allowed to accumulate (C), and the restart period (R). In the described method, T and R vary, while C remains constant. Period C is established during the initial calibration of system 198 and is calculated to achieve the required exposure of x-rays to the detector during the measurement period (i.e. period C). Once period C has been established, periods T and R can be modified without affecting the calibration of system 198, since the detector will continue to receive the required exposure in each period of the detector's output (for example, period T ).

In one embodiment of the invention, period C is kept constant and period R is varied as described below; therefore, the period T (that is, the period of the detector output) also varies. Therefore, in this embodiment the duration of the reset pulse that is applied to the detector is controlled. For example, period C may typically be established as a period of approximately 1 ms, although other values approximately similar to the following may also be suitable: 100 µs, 500 µs, 1.5 ms, 5 ms, 10 ms or any value between these values

As mentioned above, in period C of waveform 900, charge is accumulated in the photodiodes of the detector 216. The calibration of the outputs of the individual photodiodes, the gain of the detector as a whole, and the like, require that Period C remains constant. However, if the conveyor speed varies then the scan speed of the detector output data must also change so that the conveyor speed matches the scan speed according to equation (1) above.

Therefore, if the conveyor speed is reduced by half (for example, from 800 mm / s to 400 mm / s), then the scan rate would also be reduced by half; that is, the period T would have to double. To achieve this, the period R is increased to achieve the desired period T, keeping C constant (note that R + C = T). This is shown in Figure 4b.

For example, assuming the height h of 0.8 mm in Figure 1, a conveyor speed of 800 mm / s that would result in a scanning speed of 1 m / s (i.e. 1000 scans / s), one could assume that C is 990 µs and R is 10 µs. Therefore, the sum of R and C gives a period of 1 ms which is the required scan rate. If the conveyor speed slows down to 400 mm / s, the scan rate should be reduced by half (that is, T becomes 2 ms), but C remains constant and therefore R becomes 1010 µs. Therefore, controller 206 can accommodate a variable speed conveyor without recalibrating the system. Figure 4b shows an example in which period T has doubled compared to Figure 4a, but in which period C remains constant.

Because when the system 198 is initialized, the maximum conveyor speed is determined, and the system is properly designed, then the period T should never be reduced below this initial setting. Therefore, when the conveyor 210 slows down, the period T is increased in proportion to the speed drop of the conveyor 210. If the speed of the conveyor 210 descends again, then the period can be reduced again. To achieve this, the system 198 comprises a speed detector 228. The speed determining means 228 may be any suitable device, such as an optical encoder, a ferromagnetic winding, capacitive sensors, a switch (such as a micro switch, a reed switch or the like) or other device.

Therefore, in use the system 198 using the method described with reference to Figure 4 can be used for an application in which the speed of the conveyor 210 varies periodically.

In a particular example, the x-ray inspection system 198 is used to examine blister packs where each of the blister packs in the package should have been filled with a capsule during the packaging process. If the controller 206 determines, by processing the output data of the detector 210, that one or more of the blister packs of the package does not contain any capsule, then an output of the "Output rejection mechanism " 222 to reject that blister pack. The peak speed of the conveyor 210 in this system is 60 m / s, but the average speed is 40 m / s. Therefore, it is likely that a blister pack is accelerating when it passes through the irradiation zone 214. The method of varying the period R described in relation to Figure 4 allows the processing circuitry of the controller 206 to correctly process the output data of the detector 216 to identify whether each blister in the blister pack is full and avoid any of the problems described. previously.

Claims (9)

1. An x-ray inspection system (198) arranged to inspect at least one object (212) and comprising: a radiation source (200); a detector (216), which in use is capable of detecting the radiation that passes through an irradiation zone (214) and of generating a periodic data output thereof; where the detection is arranged so that the radiation is detected when a period of accumulation passes; processing circuitry arranged to process the output generated by the detector (216); a speed determining means arranged, in use to determine and send to the processing circuit the speed at which an object (212) passes through the detector; where the processing circuitry is arranged to vary the period (T) of the detector output (216) according to the output of the speed determining means, characterized in that the period (T) of the detector output (216) comprises the accumulation period (C) and a restart period (R) and the accumulation period (C) is maintained as a substantially constant period.

2.

A system (198) according to claim 1 wherein the processing circuitry is arranged to vary the period (T) of the detector output (216) by controlling the duration of a reset period (R) applied to the detector (216) .

3.

A system (198) according to claim 1 or 2, wherein the processing circuitry is arranged to measure the output of the detector (216) at an end region of the accumulation period (C).

Four.

A system (198) according to any of the preceding claims, wherein the detector (216) comprises a plurality of photodiodes (10, 12, 14, 16).

5.

A method for monitoring a product comprising: measuring the rate at which the product (212) passes through an irradiation zone (214) in which the x-rays generated by an x-ray source are affected; detect the amount of x-rays that pass through the product (212) using a detector (216) next to the irradiation zone and detect periodic output radiation when the accumulation period (C) occurs; where the method comprises adjusting the period (T) of the detector output (216) according to the speed at which the object (212) passes through the irradiation zone, characterized in that the period of the output (T) of the detector

(216) comprises a period (C) of accumulation and a period (R) of restart and the period (C) of accumulation is maintained as a substantially constant period.

6.

A method according to claim 5 which controls the duration of the reset period (R) applied to the detector to adjust the period (T) of the detector output (216).

7.

A method according to claim 5 or claim 6 that reads the output of the detector (216) at an end region of the accumulation period (C).

8.

A method according to any of claims 5 to 7, which establishes the duration of the period (T) of the detector output (216) according to the maximum speed at which the object (212) will pass through the zone irradiation (214).

9.

A computer-readable medium containing instructions that, when read by a processing circuitry, causes a processing circuitry to carry out the method of any of claims 5 to 8 or when read by a processing circuitry in a system X-ray inspection causes the system to function as an x-ray inspection system according to any one of claims 1 to 4.