EP4070084A1

EP4070084A1 - Method for checking a wall thickness of a container made of an at least partially transparent material

Info

Publication number: EP4070084A1
Application number: EP20796498.2A
Authority: EP
Inventors: Andreas Stopfer; Stefan Piana
Original assignee: Krones AG
Current assignee: Krones AG
Priority date: 2019-12-02
Filing date: 2020-10-14
Publication date: 2022-10-12
Also published as: US20230003508A1; DE102019132655A1; WO2021110308A1; CN114761790A

Abstract

The invention relates to a method for checking a wall thickness of a container made of an at least partially transparent material, for example a bottle made of PET, the method comprising: irradiating the container with a measuring beam of an irradiation device at a plurality of measurement points along a measurement direction, wherein for each measurement point, a signal indicative of the wall thickness of the container at the measurement point is obtained by means of an optical detector, wherein by means of an evaluation device, the plurality of measurement points are compared with a reference curve that specifies the wall thickness of a reference container along the measurement direction, wherein if the comparison results in agreement between the plurality of measurement points and the reference curve it is determined that the wall thickness of the container corresponds to a predefined wall thickness and wherein if the comparison does not result in agreement between the plurality of measurement points and the reference curve it is determined that the wall thickness of the container does not correspond to a predefined wall thickness.

Description

Method for checking a wall thickness of a container made of an at least partially transparent material

The present invention relates to a method for checking a wall thickness of a container made of an at least partially transparent material, for example a bottle made of PET, according to claim 1, and an inspection device for checking a wall thickness of a container according to independent claim 12.

State of the art

Methods are known from the prior art with which the wall thickness of containers used for example in the beverage processing industry or the cosmetics industry can be checked after their manufacture.

Processes for checking the wall thickness of containers manufactured using stretch blow molding processes are particularly relevant here. This is due to the fact that in the manufacture of these containers from preforms, errors can occur during manufacture, which can also have a negative effect on the wall thickness of the container and thus on the overall stability of the container. If such a container is transported further and then filled, for example, this can lead to the container tearing, which would result in considerable contamination of the entire system. Even if the container does not tear, the defect in the wall thickness can lead to deformations of the container when the container is filled, which makes it impossible to transport the container (for example due to an undesirable lengthening of the container or the formation of bulges). This can also lead to impairments and even damage to the system.

In addition, such a defective container cannot be delivered to the customer because it does not meet the desired quality standards.

From EP 2 676 127 a method for detecting defects in the material distribution in transparent containers is known, in which the material strength is deduced from the inclusion of light reflected by the outer wall both on the outside and on the inside and a corresponding value is compared with a reference value to determine whether the material thickness has the desired value.

This method is quite advantageous for uniformly shaped containers. However, the difficulty arises that containers commonly used today have a relief structure on their surface that leads to different material thicknesses in different areas of the container. Containers that are aligned differently to the inspection device will therefore provide different measured values for the wall thickness, even though they have the same wall thickness outside or between the reliefs incorporated into the material.

A reliable statement as to whether such a container then has the desired wall thickness at all is not possible.

task

Based on the known prior art, the technical problem to be solved consists in specifying a method for checking the wall thickness of a container which reliably allows the wall thickness to be determined even in the case of containers that are not uniformly shaped.

solution

This object is achieved according to the invention by the method for checking the wall thickness of a container made of an at least partially transparent material according to claim 1 and an inspection device for performing the method according to claim 12. Before partial further developments of the invention are covered in the subclaims.

The method according to the invention for checking the wall thickness of a container made of an at least partially transparent material, for example a bottle made of PET, comprises irradiating the container with a measuring beam from an irradiation device at a plurality of measuring points along a measuring direction, with one for each measuring point a wall thickness of the container at the measuring point indicative signal is obtained by means of an optical detector, the plurality of measuring points being compared with a reference curve, which indicates the wall thickness of a reference container along the measuring direction, by means of an evaluation device; the plurality of measuring points with the reference curve results, it is determined that the wall thickness of the Behäl age corresponds to a predetermined wall thickness and if the comparison does not result in agreement of the plurality of measuring points with the reference curve, it is determined that the The wall thickness of the container does not correspond to the specified wall thickness. It can be provided here that the irradiation device is formed according to known radiation devices for checking the wall thickness of a transparent container and transmits light into the wall of the container, this light being reflected from the outer surface and the inner surface and on the optical Detector hits. The detector can be formed as a camera or a similar device.

The reference curve is to be understood as a curve that also contains a large number of measurement points along the desired measurement direction or was determined (using a reference container) from a large number of such specific measurement points by, for example, extrapolation and / or interpolation between the measuring points and possibly beyond the measuring points.

The reference curve for the container will preferably not only contain measurement points that correspond to a measurement of a container once positioned with respect to the irradiation device and the optical detector, but the reference curve corresponds to a measurement of a container that is also in different positions (in different positions Alignments or rotations approximately around its longitudinal axis in a measurement direction that runs perpendicular to the longitudinal axis) was positioned with respect to the irradiation device. This means that there are reference points on the reference curve even with the most varied of relative arrangements of the container relative to the irradiation device, so that the corresponding reference curve can be used regardless of the precise orientation of the container to carry out such a comparison.

It goes without saying that not only one measuring beam but also (simultaneously) several measuring beams can be used, for example, for measuring the wall thickness along different (possibly parallel to one another) measuring directions.

The checking of the wall thickness is therefore independent of the actual alignment of the container relative to the irradiation device and the optical detector.

This method can therefore be used particularly advantageously in containers provided with an outer contour in which the wall thickness of the container changes along the measuring direction.

It can be provided that if the comparison does not result in a match between the plurality of measurement points and the reference curve, the evaluation device undertakes a transformation (translation, possibly also rotation) of the reference curve and a new comparison of the Measurement points is carried out with the transformed reference curve, wherein, if the comparison of the measurement points with the transformed reference curve results in a match, it is determined that the wall thickness of the container corresponds to the specified wall thickness and, if the comparison of the measurement points with the If the transformed reference curve does not match, it is determined that the wall thickness of the container does not correspond to the specified wall thickness.

The transformation can in particular consist in that a section of the reference curve is shifted to such an extent that this section corresponds to the recorded area of the container with the irradiation device or the optical detector and a corresponding comparison is then carried out. Whether the range of the reference curve after the transformation corresponds to the recorded measured values can again only be determined by means of a comparison, so that within this embodiment it can also be envisaged that several transformations of the reference curve are carried out until either a match is found or it is determined that there is no match.

This embodiment is particularly advantageous in the case of containers with a surface structure which is not symmetrical with regard to a rotation of the container about the longitudinal axis, since it is nevertheless possible to reliably check the wall thickness.

In one embodiment it is provided that the irradiation device irradiates or irradiates the container at each measuring point with at least one measuring beam.

In a further embodiment, the measuring beams can have different wavelengths per measuring point, the wall thickness being determined by calculating the at least two different wavelengths.

Since the wall thickness changes in the case of containers provided with a surface structure, the transmission and reflection behavior of the material of the container with regard to certain wavelengths can also change in these areas. If at least two wavelengths are used for the irradiation, changes that could affect the measured wall thickness as systematic errors can be compensated.

Furthermore, it can be provided that the measuring direction runs perpendicular to a longitudinal axis of the container or that the measuring direction runs parallel to a longitudinal axis of the container. With this embodiment, fundamentally relevant changes in the wall thickness of the container in the transverse direction and in the longitudinal direction can be examined, which in particular also enables simple measurement of the container in order to produce a complete or almost complete wall thickness profile of the entire container.

In one embodiment, the transformation comprises shifting the reference curve along the measuring direction by a value D, the value D being significantly less than 0.1 D or less than 0.05D, where D is the extension of the container along the measuring direction.

The reference curve can be understood, for example, as a function which assigns a specific wall thickness W (X) to a position X along the measuring direction. As already mentioned above, the corresponding function of the measured container is dependent on the actual alignment of the container relative to the irradiation device and / or to the optical detector. If, when comparing the reference curve and the measured values, it is found that there is no agreement, such a slight modification of the argument X in the function W (X) by replacing X with X + D can lead to a shift in the reference curve for the measured location X is compared with the measured values. This procedure can be carried out quickly in a computer, which usually forms the evaluation device, and requires little computing power, so that a large number of these transformation steps can be carried out for each container in order to determine whether the wall thickness of the container corresponds to the reference curve. This ensures a technically simple method for transforming the reference curve and thus a still quick check of the measured values, which makes this method also suitable for the ongoing operation of container treatment machines with several 1000 to several 10,000 containers per hour.

In a further embodiment, the transformation is carried out as a function of a characteristic point of the plurality of measurement points and / or a measurement curve derived therefrom and / or as a function of a characteristic point of the reference curve.

Characteristic points are, for example, the points at which there is a transition from an area of the container with a thin wall thickness to an area of the container with a thicker wall thickness, since the material thickness here is usually thicker than in all usual areas. These are expressed in the measured values and in the reference curve as a maximum or minimum and characterize the course of the entire curve (regardless of whether it is the reference curve or a curve generated from the measuring points. delt). If the transformation is carried out in such a way that a characteristic point occurring in the measuring points is brought into agreement with a characteristic point occurring in the reference curve (for example, as above, by transforming the argument X in the function W (X) of the reference curve such that the characteristic points of the reference curve and the measured values coincide), only a single transformation is necessary to compensate for any alignment of the container with respect to the irradiation device or the optical detector and to make a comparison with the reference curve to enable meaningful. If it is then determined that the measured values do not match the reference curve, it can be determined that the wall thickness does not meet the requirements.

This method significantly reduces the number of transformation steps, but can possibly involve increased computational effort, since an analysis of the measured values on the one hand and the reference curve on the other hand with regard to characteristic points is necessary.

This increased computational effort can be reduced by the fact that the position of the characteristic points of the reference curve is already stored in a memory (for example together with the reference curve), so that only an analysis of the measurement points or a curve extrapolated therefrom with regard to characteristic points must take place and then a difference is formed between the positions of these points in the measuring direction in order to carry out the transformation of the reference curve.

The method can be carried out for a container along different, optionally parallel measuring directions. This enables a very precise measurement of the container and, in particular, of its wall thickness.

It can also be provided that the comparison of the measurement points with the reference curve and the transformed reference curve takes place taking into account a measurement tolerance of the measurement points and / or taking into account a tolerance of the reference curve and / or the transformed reference curve .

Since, in particular, the determination of the measuring points, but also the determination of the reference curve, for example from a reference container, are subject to certain errors, taking these errors into account within the framework of tolerances can avoid the incorrect identification of supposedly non-matching or matching wall thicknesses. The method is preferably carried out by an inspection device comprising the irradiation device, the optical detector and the evaluation device and the containers are fed to the inspection device by means of a transport device and transported away by the transport device and in the event that the measurement points do not match the reference curve and the transformed reference curve is determined, the operation of the transport device is stopped. This can ensure that any error that occurs, which is expressed in the change in the wall thickness of a container, is first identified and, if necessary, rectified before the machine continues to operate. This can be advantageous in particular for downstream machines, such as filling devices for filling the container, and avoid damage or contamination.

In the event that the measurement points do not match the reference curve and the transformed reference curve, information can be output to an operator. A warning can be issued to the operator, for example, that the measured wall thickness no longer corresponds to the specified wall thickness. The operator can then decide for himself, for example, whether the operation of the machine is to be continued or whether he should stop the operation of the machine and carry out a repair or replacement of parts or a more detailed error analysis.

As an alternative or in addition, a container can also be automatically diverted in the event that it is determined that the wall thickness does not correspond to the specified wall thickness or corresponds to this within the scope of the measuring accuracy. The Auslei th can take place, for example, by a pusher that ejects the container from the transport device and pushes it into a collecting container provided for this purpose. Other implementations for diverting the container from neck handling, such as star or clamp, are also conceivable here.

As an alternative or in addition, a preferably wirelessly transmitted message can also be sent automatically to the operator or maintenance personnel in the event that it is established that the wall thickness does not match the specified wall thickness. A message to a tablet, mobile phone or wearble is preferred, machine data, setpoints and measured values being particularly preferably transmitted.

The measured wall thickness is particularly preferably assigned to the treatment organs, so that it is known with which cavity, heating mandrel, heating zone, gripping element the container was treated or produced. This allows in a closed loop process in the event of a target Deviating wall thicknesses in the (design) embossed area (relief, support structure, etc.) an influence can be exerted on the treatment organs in order to lead the material distribution back to the target wall thickness. This can either be done automatically or support / guide a machine operator.

At least some of the measurement points and / or the result of the comparison of the measurement points with the reference curve and / or the result of the comparison of the measurement points with the transformed reference curve can be stored in a memory associated with the evaluation device. In this way, for example, a later error analysis can be carried out by evaluating the data stored in the memory.

The inspection device according to the invention for checking a wall thickness of a container comprises an irradiation device, an optical detector and an evaluation device, whereby the container leads to the inspection device via a transport device and can be transported away from the inspection device by the transport device, the transport device and the irradiation device and the optical detector are arranged in relation to one another in such a way that a container transported in the transport device can be irradiated by the irradiation device at at least a plurality of measuring points along a measuring direction and the optical detector the light reflected and / or transmitted by the container along the measuring points the measuring direction can receive, wherein the inspection device is designed to carry out the method according to one of the previous embodiments. This inspection device is particularly suitable before geous to carry out the method according to the invention.

The irradiation device can be designed to emit light with at least two different wavelengths and the optical detector being designed to detect at least light of these two different wavelengths. Any errors due to a changing transmission and / or reflection behavior of the container wall for a specific wavelength when the wall thickness changes can thus be compensated for.

Furthermore, the irradiation device can be designed in such a way that it can irradiate a container with light for generating a multiplicity of measuring points along different measuring directions. This means that the inspection devices can be used flexibly not only for measuring an entire container, but also for measuring containers of different shapes. In a further development of this embodiment, the irradiation device is designed to be displaceable along at least one axis. The displacement of the irradiation device can consist of an actual physical displacement of the entire irradiation device, but it can also include a deflection of the emitted light, for example by mirrors or other optics, which is usually to be carried out more quickly than a complete displacement of the irradiation device. With this embodiment, it is not only possible to change the measuring direction for an individual container, but also to adapt the inspection devices to different containers, for example by adapting the measuring direction to a changing shape or size of the container.

Brief description of the figures

Fig. 1 shows a schematic representation of an inspection device according to the invention

Fig. 2 shows the course of the wall thickness of a container and the resulting measurement points

Fig. 3 shows an embodiment of a transformation of a reference curve for checking the wall thickness of a container

4 shows a variant in which the reference curve and the measurement points do not match

FIG. 5 shows an embodiment of a height-adjustable irradiation device. FIG. 6 shows a further embodiment of an inspection device

Detailed description

In Fig. 1, an inspection device 100 is shown, which can inspect containers according to the inventive method. This inspection device comprises or is assigned at least one transport device 140, in which containers 130 can be transported. The transport device can be, for example, a conveyor belt, but also any other known type of container transport. The containers are usually bottles or small cans that are basically made of transparent material, in particular plastic, such as PET. For the transport of these containers either stand plates or turntables in connection with centering devices that clamp the container between the centering device and the plate, but also clamp grippers have been established which grip the container in the area of a support ring or at least in the mouth area, so that the container is transported hanging.

Since it is essential for the invention that the material of the container can be irradiated in at least one area, a transport is preferred in such a way that at least a large part of the wall of the container is exposed, so that grippers and centering devices with associated standing plates or turntables are particularly advantageous can.

However, the transport device 140 is not limited in this regard.

For the further explanation of the method according to the invention, however, it is essential that the container 130 (here only partially shown as a cross-section in plan view) has a wall 133. This wall, ie the wall of the container, has an outer upper surface 131 and an inner surface 132. The inner surface 132 is the surface of the container that faces the interior of the container, which is usually filled with the medium to be filled into the container becomes. The outer wall or outer surface of the container 131 is then the surface 131 of the wall 133 opposite the inner surface 132.

In the embodiment shown here, the wall 133 of the container comprises different thick areas, such as the area 134, which extends relatively long along the circumference of the container and has a constant wall thickness, and the areas 135, which are approximately as notches in the Surface of the container are formed and in which the wall thickness of the container is smaller. Areas with a greater wall thickness extend between these areas.

This is not absolutely necessary, but the method according to the invention is particularly advantageous for containers 130 which, for example, do not have a constant wall thickness in relation to a cross section of the container.

The inspection device 100 furthermore comprises an irradiation device 121. This can for example comprise one or more incandescent filaments in order to form a diffuse light source. The filament can be operated in such a way that, depending on its temperature, it has an emission spectrum that emits electromagnetic radiation, especially in the infrared range. The filament can also be operated with a slightly red glow. It is also conceivable to operate the incandescent filament (or a filament) at a temperature at which it emits white light, i.e. its emission maximum is in the visible range. That of this one Light emitted from one or more incandescent filaments then strikes the wall of the container. Alternatively, one or more diodes, in particular laser diodes, can also be used to apply electromagnetic radiation (infrared light or visible light) 151 in the direction of the wall of the container. Furthermore, an optical detector 122 is provided, for example in the form of a camera, which can detect the light reflected by the container and / or transmitted through the container.

In the embodiment shown here, detector 122 and irradiation device 121 are located on the same side of the container or the transport device, so that at least partially reflected light from the container is detected in the detector. In this case, light is not only reflected from the outer surface 131 of the container, but also reflected from the inner surface due to the transparency of the container and transmitted through the outer surface 131 in the direction of the optical detector 122.

In a variant in which the detector records the light transmitted through the container, the detector 122 is arranged on the opposite side with respect to the transport device 140 than the irradiation device 121. In the plan view shown in FIG. 1, the transport device is then located between the irradiation device 121 and the detector 122, so that a container to be inspected is also positioned between the irradiation device 121 and the detector 122.

It can be provided that the irradiation device can specifically emit light of different wavelengths, for example light in the infrared spectral range, rich in the red spectral range and / or light in the blue spectral range. By using light of different wavelengths it is achieved that random effects, such as constructive interference or destructive interference of the portions of the light emitted by the irradiation device which are reflected and / or transmitted from the inside and outside of the container and which affect the measurement result of the Wall thickness could inadvertently affect, can be compensated. Alternatively, it can also be provided that the irradiation device emits white light (or only infrared light or red light and infrared light), as was described for the incandescent filament, for example, and the optical detector has several (at least 2) color filters or corresponding color filters in between the radiation device formed in this way and the container are arranged. These can be filters, for example, of which one only allows blue and one only red light to pass through. Here too, the above-described effect of avoiding undesirable effects can be achieved. Regardless of whether the light is transmitted or reflected by the bottles 152 (reflected from the inner surface 132) and 153 (reflected from the outer surface 131), these then strike the optical detector 122 Material thickness or wall thickness of the container so that the amount of transmitted (reflected) light and thus the optical signal arriving at the optical detector (depending on the wall thickness) is stronger or smaller. The optical detector 122 can then transmit a signal indicative of the wall thickness of the container (for example, a brightness signal or an interference signal or the like) to an evaluation device 123. This evaluation device can be connected to the optical detector, for example via a cable connection 124, but also via a wireless connection or in any suitable manner for transferring data at least from the optical detector to the evaluation device, but preferably bidirectionally.

As will also be described in greater detail with reference to FIGS. 3 and 4, a reference curve is stored in the evaluation device 123 or can be called up by it. This reference curve corresponds to signals indicative of the wall thickness of the container at certain points of the container in the measuring direction and can be generated, for example, by measuring a reference container whose wall thickness is known. As an alternative or in addition, a large number of reference containers can of course be measured in order to obtain a reference curve that avoids systematic errors as much as possible. A simulated ideal container can also serve as the basis for the reference curve.

How the reference curve was ultimately determined is not relevant to the method according to the invention. The reference curve preferably extends over an area which is larger than the area usually measured for an individual container. If, for example, the container is moved upright past the irradiation device 121 and not rotated relative to the irradiation device, the wall thickness is measured only in the portion of the surface of the container facing the irradiation device. The reference curve which is available to the evaluation device 123, however, preferably comprises values for the wall thickness or values which are indicative of the wall thickness of the container and which cover the entire surface of the container.

In this regard, it should be mentioned that the irradiation device irradiates the container along a measuring direction (for example along the cross-sectional direction of the container shown here in FIG. 1) in order to generate a large number of measuring points. For exactly this measuring direction is then in the Evaluation device preferably stored a reference curve. This is described in more detail in FIG. 5. The irradiation can either take place in that the container is guided past the irradiation device and the container is irradiated point by point. However, it can also be provided that the container is positioned in such a way that the light from the irradiation device strikes exactly one point on the container (for example when a turntable is used together with a centering device). The container is then rotated (either by part of its entire circumference or by a full rotation) and a corresponding signal is generated in the detector for different measuring points along the measuring direction.

The first method has the advantage that the machine can be operated continuously. But above all in the areas of the container which, due to its cross-sectional shape, curve strongly towards the lighting device or away from it, only partially meaningful results. The second method allows the wall thickness to be determined with high accuracy, but requires the inspection device to be operated cyclically.

By comparing the reference curve with the measured values recorded along the measuring direction, which are indicative of the wall thickness of the container, it can then be determined whether the wall thickness of the container corresponds to the expected values for the wall thickness. This can be done, for example, by determining a match between the reference curve or a part of the reference curve (if this covers a larger area of the surface of the container than is checked during the inspection with the inspection device). This correspondence can of course also take possible error tolerances into account. It can thus be taken into account that the resolution and the determination of the signals in the optical detector is only possible with a certain degree of accuracy. In addition, it can be taken into account that the manufacture of the container itself is subject to certain tolerances, so that, for example, slight deviations in the wall thickness from the reference value are still acceptable. The determination of the correspondence between the reference curve and the measured values is therefore essentially to be understood as meaning that there is agreement within the specified tolerances.

For a more precise illustration of the measuring process with the inspection device 100, an example container and the resulting measured values are described in FIG. 2.

The container section shown here, which may have been included, for example, at a certain height of the loading container, represents part of the cross section of the container and the longitudinal axis of the container is preferably perpendicular to this cross section. The section of the surface of the container shown here does not have a constant wall thickness. In one area, the wall thickness (also due to the curvature of the surface of the container) is considerably greater with d1 than, for example, in area d2. The area with a thin wall thickness slowly becomes thicker approximately in the area d3 until it has the thickness d4 in this area. The wall thickness then drops again, with the ascertainable wall thickness d5 again being greater due to the curvature of the container and increasing up to wall thickness d6 (again due to the curvature of the container).

In this context it should be noted that due to the irradiation with the irradiation device 121 and the reception of the signal in the optical detector 122 and due to the curvature of the container that is usually present (these usually have a round or at least curved cross section), ultimately a "wall thickness" is determined, which is also influenced by the curvature of the container. As shown on the left in FIG. 2, the wall thickness d1 does not extend approximately perpendicular to the surfaces 131 and 132, but is indicated with an angle thereto, so that it is greater than the actual wall thickness. This is due to the fact that the light from the irradiation device does not usually strike the surface of the container at right angles, but rather hits it at an angle which can also change as a function of the curvature of the container. Strongly curved areas, in particular the areas shown on the left and right in the left-hand part of Figure 2, which curve sharply in the direction of the lighting device or away from it, usually deliver a result that is not reliable because the light passes through more material than the actual wall thickness would be the case with perpendicular light incidence on the surface of the Behäl age. These areas can be left out when comparing the measured values with the reference curve later. The image shown in FIG. 2 is based on the fact that the container is simply moving past the lighting device. As described above, it can also be provided that the container is positioned in the area of the lighting device so that only one point of the container is irradiated (for example, preferably so that the incidence of light occurs perpendicular to the surface). In the meantime, the container is rotated so that measuring points indicative of the wall thickness of the container can be recorded at least over a section of the circumference of the container (in some embodiments also around the entire circumference of the container).

Regardless of this, the illustration shown on the right in FIG. 2 shows the corresponding image for the signals recorded by the optical detector 122, which are at least indicative (although not synonymous with) the wall thickness of the container. The area d1 shows the relatively thick measured wall thickness, whereas the areas d2 and d3 can be seen in the thinner area of the container. The wall thickness d4 is measured in the again thicker area and the wall thicknesses d5 and d6 increase despite the actual wall thickness actually remaining constant due to the curvature of the container and its relative orientation to the irradiation device.

While the signals measured here are indeed at least partially indicative of the wall thickness of the container, they are not identical to the wall thickness, since other influences such as the already discussed curvature of the container also have an influence.

Nevertheless, the measurement curve shown on the right in Fig. 2 can be used to draw conclusions about the actual wall thickness of the container.

For this purpose, the reference curve available in the evaluation device 123 can be used, which, as already described, preferably represents more than just a section of the surface of the container in the measuring direction.

This is described in FIG. 3.

The “measurement curve” 361 resulting from a multiplicity of measurement points along a measurement direction is shown in FIG. 3. This can be understood as an interpolation between a large number of measuring points along the measuring direction. Instead of this continuous curve, a series of measuring points could also be displayed.

It goes without saying that the curve 361 shown here will also have a certain error in accordance with the measurement points actually recorded. This could also be supplemented here by error bars, as shown in FIG. 2, in order to obtain information on the accuracy of the curve. However, because of the clarity, this has not happened here.

In addition to the measurement curve of the real container resulting from the measurement values along the measurement direction, the reference curve 362 is shown. In the illustration shown on the left in FIG. 3, this is obviously different from the resulting measurement curve 361 Maxi mum is separated. With a larger argument X, the reference curve 362 grows again. Upon first observation, the person skilled in the art will come to the conclusion that the reference curve 362 and the curve 361 resulting from the measurement points do not match. As already mentioned, the measured values obtained by the method for checking the wall thickness according to the invention differ from one another, however, depending on how the container is oriented relative to the irradiation device and / or to the optical detector of FIG.

As a clear example of this, it can be imagined that to generate the reference curve, the surface of the container is unrolled so that the entire circumference of the container is shown as a straight line. The corresponding wall thicknesses can be plotted as a reference curve over the entire circumference of the container. The beginning of the unrolling of the surface of the container can be arbitrarily set to the value 0 as location X0. However, the actual orientation of a container to be measured relative to the irradiation device and relative to the optical detector of FIG. 1 and thus the location X1 of the real container to be measured is usually not known and can vary. The start of the measurement does not have to coincide with the location XO as the beginning of the rolling of the surface of the container for the imaginary generation of the reference curve, but it can be, for example, at location X1, which differs from location X0 by the value D. While the measured container or the wall thicknesses obtained for this container are identical to the reference curve in the corresponding area, there is a shift between the measured and the reference curve by exactly the amount D.

This can be seen in the illustration on the left in FIG. 3 from the fact that the two maxima of the measured values are spaced apart by the distance D.

In one embodiment of the method according to the invention, it can now be provided that the reference curve is transformed when the comparison is made between the measured values with the reference curve, if in a first comparison step there is no agreement between the reference curve (without transformation) and the measured values is obtained. This transformation can lie in a shift of the reference curve 362 with respect to the curve 361, for example. According to the invention, there are now two possibilities, each of which, taken individually, offers certain advantages.

On the one hand, the reference curve can be transformed by shifting the reference curve by a fixed amount D, the amount D preferably being significantly smaller or significantly smaller than the extent of the container or the reference container along the measuring direction. If the measuring direction is parallel to the circumferential direction of the container, it is Expansion of the tank the perimeter. If the expansion of the container along the measuring direction is denoted by D, then D can preferably be smaller than 0.1 D and particularly preferably smaller than 0.05D, particularly preferably smaller than 0.005D.

This shift of the reference curve by an absolute amount is computationally easy to implement and thus requires little processor power. However, in a first step, such a shift may not immediately lead to a correspondence between the reference curve and the measured values being achieved, although this is indeed present when viewed objectively. This can be due to the fact that the difference between the values X1 and X0 is greater than the fixed D, so that, for example, several transformation steps (2, 3, 4, 5, etc.) may be necessary until the present agreement is established. In extreme cases, this can make it necessary to move a length that reduces the expansion of the container in the measuring direction by the length of the section of the actually measured container in the measuring direction in individual sub-steps D until a final judgment is reached the present agreement or mismatch of the measured points with the reference curve is obtained. This can be time-consuming and, despite the actually low computer resources required for a single transformation, considerable effort.

As an alternative to this, the shift D by which the reference curve must be shifted in order, if necessary, to be brought into line with the measured values, can also first be calculated before the shift or transformation is carried out.

This process is shown in FIG. 3. As can be seen in the left figure in Fig. 3, both the reference curve and the curve 362 and 361 resulting from the measured values (or the large number of measuring points) have a pronounced maximum at points 371 (for the measured curve) and 372 (for the reference curve). It can be known that the container on which FIG. 3 is based must always have such a pronounced maximum because, for example, it has a material thickening that is not reached in any other area and thus has a wall thickness in no other area. The position of this point, if included in the measurement curve, clearly defines the distance D between points X0 and X1 (see above). If the measurement curve contains this characteristic point (the maximum 371), its relative position with respect to the maximum 372 of the reference curve 362 can be used to determine the necessary shift D for the transformation of the reference curve. To determine the curve. Then the reference curve can then be transformed with the resulting D resulting in the image shown on the right in FIG. 3. After the transformation, the reference curve and the measurement curve coincide and it can be seen that the measurement curve, formed from the individual measurement values along the measurement direction, agrees with the reference curve, i.e. the wall thickness corresponds to the expectations.

This method is of course only applicable if the section of the container that was measured in example in FIG. 1 (unless it is the entire circumference of the container) also contains the relevant characteristic point. If this is not the case (which can be determined, for example, in the course of a first analysis of the measured values), the previously described method can be used by transforming the reference curve by a specific, fixed value D in order to nevertheless compare the measured values with to enable the reference curve.

It can be provided that the characteristic point 372 or a plurality of characteristic points along the reference curve (for example a series of maxima or minima) are stored in a memory assigned to the evaluation device and each of these characteristic points can be compared with the measurement curve in order to determine which of these characteristic points can be found on the measurement curve in order to determine the necessary shift D of the reference curve.

If the container is measured along its entire circumference in the inspection device (e.g. when using a turntable), the described method of determining the characteristic points and deriving the displacement D can always be used, since any characteristic points that may be present are also recorded during the measurement.

If no characteristic point is recognized, the evaluation device can also determine here directly that the course of the wall thickness does not correspond to the course of the reference curve or, in general, that the wall thickness does not correspond to expectations.

4 shows a case in which even a transformation of the reference curve does not provide any correspondence between the measurement curve or the measured values and the reference curve.

In FIG. 4, the measurement curve 361 of a measured container and the reference curve 362 are shown again. Both have a maximum 371 and 372, respectively. This was used, if necessary, to set the reference curve in accordance with the measured values or the measurement curve Bring 361. Although the relative alignment of the measurement curve and reference curve in FIG. 4 was determined on the basis of the maxima and a corresponding transformation was carried out, it can be seen in the area 490 that the measurement curve 361 differs from the reference curve 362 itself, taking into account the The error bar shown in the area differs, so there is no match in any case.

Correspondingly, in this embodiment, the comparison between the reference curve and the measurement curve or measured values leads to the determination that these do not match, not even within the scope of the error tolerance, regardless of any transformation carried out for the relative arrangement of the reference curve and the measurement curve.

FIG. 5 shows an embodiment of the invention in which the containers are measured along different measuring directions.

In FIG. 5, the container 130 is shown on the transport device (shown here as a standing plate or rotary plate 140). In this embodiment, the irradiation device 121 is movably mounted along the axis 570, which can be arranged on a module housing 571 of the inspection device, so that the irradiation device 121 can be moved up and down along the double arrow shown. In this embodiment, the irradiation device can thus emit the light 151 at different heights (along the longitudinal axis of the container).

A large number of measured values can then be determined in each case along the measuring direction 581, 582, 583 and 584 by a corresponding movement of the irradiation device 121. In the embodiment shown here, several measuring points along the three different measuring directions 581 to 583 have been recorded in the neck area or shoulder area of the container, in which the container can usually have a strong curvature of the surface and possibly also relief structures.

An additional measurement in the belly region of the container along the measurement direction 584 can be provided. It is also possible to use more or less than the four different measuring directions described here. Thus, a measuring direction can also run perpendicular to the measuring directions shown here or include a specific angle different from 90 ° and 0 ° with them.

While only the irradiation device 121 is moved vertically in FIG. 5, it can also be provided that the optical detector is moved accordingly in order to ensure that that the light reflected by the container at different heights is actually detected by the optical detector.

As an alternative to moving the optical detector and / or the irradiation device as a whole, it can also be provided that only an optical system, for example an arrangement of mirrors or lenses, is moved in order to carry out the different measurements of the container along the differently illustrated measuring directions 581 to 584 . In this way, the number of components to be moved and in particular the movement amplitude can be kept as low as possible.

Furthermore, it can also be provided that (separate) irradiation devices are arranged at different heights relative to the transport device (and thus relative to a container transported therein) or the irradiation device extends over a corresponding vertical extent. Correspondingly, one or more detectors are then provided which can detect the light transmitted or reflected through the container at the corresponding heights.

A corresponding embodiment is shown in FIG.

In the embodiment shown in FIG. 6, a container 130 is on the far left in the picture, which has a varying wall thickness 631, for example due to an embossed or embossed pattern. On the left in FIG. 6, the container is only shown from one side, with it being shown “unrolled” in the middle of the illustration in FIG. 6, that is to say its entire surface is shown by rolling the bottle onto a plane. The change in material thickness 631 is also shown here. In connection with the middle picture, the course of the wall thickness along the entire circumference of the container is also shown.

On the right in FIG. 6, an embodiment of the inspection device 600 is shown, in which case the transport device 140 and the containers 130 can also be configured in accordance with the variants described in FIG. 1, for example.

However, here the detector 622 and the irradiation device 621 are arranged on opposite sides of the transport device, so that the light emitted by the irradiation device irradiates the container completely and the light transmitted through the container is then recorded.

This corresponds to the variants already described in FIG. 1, as an alternative to receiving reflected light. FIG. 6 also shows the wall thickness measured at different heights or measurement directions 681 to 684, with the measurement curve 694 shown for the measurement direction 684 along the entire circumference of the container.

The measurement curve actually recorded by the detector 622 can possibly only represent a section of this reference curve 694.

According to the method described in the previous figures, the reference curve can then be shifted relative to the measurement curve in order to determine whether there is a match here.

The method for this is analogous to the method designated in FIGS. 3 and 4 for determining a match or determining that ultimately no match can be achieved between the reference curve and the measurement curve even through transformation.

In the embodiments described in FIGS. 3 to 6, reference was made to reference curves for the wall thickness, which have mapped the entire surface of the container, which results in a function w (cp) for the wall thickness that is dependent on only one parameter, where cp can be approximately the angle of rotation of the container about its longitudinal axis with respect to any starting position.

In Figures 5 and 6, two-dimensional information about the behavior of the wall thickness in the circumferential direction and in the longitudinal direction of the container can also be obtained by (simultaneously) recording different measurement curves (i.e. in different vertical positions along the circumference of the container). While the reference measurement curves that have been discussed so far only represent a function w (cp), which indicate the wall thickness w as a function of the position cp along the measuring direction, this information can also be designed as a function depending on two parameters. For example, points on the surface can be assigned a wall thickness depending on their vertical position (in the longitudinal direction of the container) and depending on their position along the circumference of the container, so that the wall thickness function w (l, cp) depends on two variables, e.g. the angle of rotation cp depends on any starting position or zero position of the container and the vertical position I along the longitudinal direction of the container. Such a function can also be stored for the entire surface of the container and used in accordance with the above method to check whether the measurement curve (which can then also be two-dimensional, but does not have to) and the reference curve match.

While it was always assumed here that a corresponding reference curve is then also available for the entire available parameter range (i.e. for the entire angle of rotation cp, i.e. along the entire circumference), this is not absolutely necessary.

Since the inspection device can usually be arranged after a container cleaning machine and / or a blow molding machine or similar machine for producing the containers, it can result that the containers are always fed to the inspection device essentially in the same way with respect to any normal orientation. For example, a normal orientation of the containers can be specified as the “mean value” of all containers dispensed from the container cleaning machine and / or a blow molding machine, with the actual orientation of the containers around this mean value by +/- 10 degrees, +/- 20 degrees or any value in between or any larger or any smaller values fluctuates.

For example, containers that are produced with a blow molding machine can always be output from this machine in the same orientation and fed to the inspection device. If they are not rotated further about their longitudinal axis during transport from the blow molding machine to the inspection device, the orientation of all containers essentially corresponds to that when they leave the blow molding machine and this is practically the same for all containers.

If this fluctuation is known with sufficient accuracy and is reliably adhered to by all containers, it is no longer necessary to provide a reference curve that maps the entire surface of the container and assigns a value for the wall thickness to a point on the surface of the container ( at least along one or more measuring directions). It can then also be sufficient to store a corresponding section of the container around this normal alignment as a reference curve and to use it for the comparison with the measurement curves of the individual containers. Alternatively, it is also possible to relate a reference curve (expectation range) to the measurement result by means of a second known feature. In the case of a plastic container, this can be the container seam or the pentaloid base, which have a fixed angular relationship to the design elements.

Claims

1. A method for checking a wall thickness of a container made of an at least partially transparent material, for example a bottle made of PET, the method comprising irradiating the container with a measuring beam from an irradiation device at a plurality of measuring points along a measuring direction, with for each measuring point a signal indicative of a wall thickness of the container at the measuring point is obtained by means of an optical detector, the plurality of measuring points being compared with a reference curve which indicates the wall thickness of a reference container along the measuring direction by means of an evaluation device Comparing a correspondence of the plurality of measuring points with the reference curve results, it is determined that the wall thickness of the container corresponds to a predetermined wall thickness and, if the comparison does not result in a correspondence of the plurality of measuring points with the reference curve, it is determined that the wa The thickness of the container does not correspond to the specified wall thickness.

2. The method according to claim 1, wherein if the comparison does not result in a match between the plurality of measurement points and the reference curve, the evaluation device transforms the reference curve and the measurement points are compared again with the transformed reference curve, wherein If the comparison of the measurement points with the transformed reference curve results in a match, it is determined that the wall thickness of the container corresponds to the specified wall thickness and, if the comparison of the measurement points with the transformed reference curve does not result in a match, it is established becomes that the wall thickness of the container does not correspond to the specified wall thickness.

3. The method according to claim 1 or 2, wherein the irradiation device irradiates and / or irradiates the container at each measuring point with two measuring beams and the measuring beams have different wavelengths.

4. The method according to any one of claims 1 to 3, wherein the measuring direction runs perpendicular to a longitudinal axis of the container or wherein the measuring direction runs parallel to a longitudinal axis of the container.

5. The method according to any one of claims 2 to 4, wherein the transformation comprises shifting the reference curve along the measuring direction by a value D, the value D is significantly less than 0.1 D or less than 0.05D, where D is the extension of the container along the measuring direction.

6. The method according to any one of claims 2 to 5, wherein the transformation is carried out as a function of a characteristic point of the plurality of measurement points and / or a measurement curve derived therefrom and as a function of a characteristic point of the reference curve.

7. The method according to any one of claims 1 to 6, wherein the method is carried out for a container along different, optionally parallel measuring directions.

8. The method according to any one of claims 1 to 7, wherein the comparison of the measurement points with the reference curve and the transformed reference curve taking into account a measurement tolerance of the measurement points and / or taking into account a tolerance of the reference curve and the transformed reference -Curve takes place.

9. The method according to any one of claims 1 to 8, wherein the method is carried out by an inspection device comprising the irradiation device, the optical detector and the evaluation device and the containers are supplied to the inspection device by means of a transport device and transported away from the transport device and in which case that no agreement of the measuring points with the reference curve and the transformed reference curve is found, the operation of the transport device is stopped.

10. The method according to any one of claims 1 to 9, wherein, in the event that the measurement points do not match the reference curve and the transformed reference curve, information is output to an operator and / or in which case that no correspondence of the measuring points with the reference curve and the transformed reference curve is determined, the container is diverted from the transport device.

11. The method according to any one of claims 1 to 10, wherein at least some of the measurement points and / or the result of the comparison of the measurement points with the reference curve and / or the result of the comparison of the measurement points with the transformed reference curve in one of the Evaluation device associated memory is stored.

12. Inspection device for checking a wall thickness of a container, the inspection device comprising an irradiation device, an optical detector and an evaluation device, wherein the container can be supplied to the inspection device via a transport device and transported away from the inspection device by the transport device, the transport device and the irradiation device and the optical detector are arranged to each other so that a container transported in the transport device can be irradiated by the irradiation device at at least a plurality of measuring points along a measuring direction and the optical detector transmitted the reflected and / or transmitted from the container Can receive light of the measuring points along the measuring direction, wherein the inspection device is designed to carry out the method according to one of claims 1 to 11.

13. Inspection device according to claim 12, wherein the irradiation device is ausgebil det to send out light with at least two different wavelengths or broadband and wherein the optical detector is designed to detect at least light of two different wavelengths ver.

14. Inspection device according to claim 12 or 13, wherein the irradiation device is designed such that it can irradiate a container with light for generating a plurality of measuring points along different measuring directions.

15. Inspection device according to claim 14, wherein the irradiation device is designed to be displaceable along at least one axis.