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

Abstract

The invention relates to a method for checking the wall thickness of a container made of 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 measuring points along a measurement direction, wherein for each measuring point a signal is obtained by an optical detector which is indicative of the wall thickness of the container at the measuring point, wherein the plurality of measuring points is compared by an evaluation device to a reference curve of the wall thickness of a specified reference container along the measurement direction, wherein if the comparison yields a conformity between the plurality of measuring points and the reference curve, it is determined that the wall thickness of the container corresponds to a predetermined wall thickness, and wherein if the comparison does not yield a conformity between the plurality of measuring points and the reference curve, it is determined that the wall thickness of the container does not correspond to the predetermined wall thickness.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for checking the wall thickness of a container made of at least partially transparent material, for example a bottle made of PET, according to claim 1, and an inspection device for checking the wall thickness of a container according to independent claim 12. BACKGROUND

[0002] In the prior art, methods are known for checking the wall thickness of containers after their manufacture, for example in the beverage processing industry or in the cosmetics industry.

[0003] Of particular relevance in this regard is a method for checking the wall thickness of containers manufactured in the stretch blow molding process. This is because the manufacture of these containers from preforms can have defects during manufacture which adversely affect the wall thickness of the container and thus also the overall stability of the container. If such a container is further conveyed and subsequently filled, it can lead to the container breaking, which would cause considerable contamination of the entire facility. Even if the container does not break, a wall thickness defect can cause the container to deform during filling, so that the container cannot be further conveyed (for example due to an undesired elongation or the formation of a bulge of the container). This can also lead to damage or even destruction of the system.

[0004] In addition, such a defective container cannot be delivered to the customer, since it does not meet the desired quality standards.

[0005] From EP 2 676 127 a method for detecting material distribution defects in a transparent container is known, in which the material thickness is inferred on the basis of images of light reflected by the outer wall on the outside and on the inside and the corresponding values are compared with reference values in order to determine whether the material thickness has the desired value.

[0006] This method is advantageous for containers of uniform shape.

[0007] However, it is difficult when today's commonly used containers have a relief pattern on their surface, which leads to different material thicknesses in different regions of the container. Thus, a container oriented differently towards the inspection device will give different wall thickness measurements, even if they have the same wall thickness on the outside or between the material of the relief.

[0008] Any reliable statement as to whether such a container will have the desired wall thickness is not possible. SUMMARY

[0009] Task

[0010] Starting from the known prior art, the technical task to be solved is therefore to provide a method for checking the wall thickness of a container, so that it is possible to reliably determine the wall thickness even in the case of shape-uniform containers.

[0011] Solution

[0012] According to the application, this task is achieved by a method for checking the wall thickness of a container made of at least partially transparent material according to claim 1 and by an inspection apparatus for carrying out the method according to claim 12. Advantageous further developments of the application are described in the dependent claims.

[0013] The method for checking the wall thickness of a container made of at least partially transparent material, for example a bottle made of PET, according to the application comprises: irradiating the container with a measuring beam of an irradiation apparatus at a plurality of measuring points along a measuring direction, wherein for each measuring point a signal is obtained by an optical detector which is indicative of the wall thickness of the container at the measuring point, wherein by an evaluation apparatus the plurality of measuring points is compared with a reference curve of the wall thickness of a specified reference container along the measuring direction, wherein if the comparison yields a conformity between the plurality of measuring points and the reference curve, it is determined that the wall thickness of the container corresponds to a predetermined wall thickness, and wherein if the comparison does not yield a conformity between the plurality of measuring points and the reference curve, it is determined that the wall thickness of the container does not correspond to the predetermined wall thickness.

[0014] Here, it can be provided that the irradiation apparatus is configured according to known irradiation apparatuses for checking the wall thickness of transparent containers and, for example, transmits light into the wall of the container, wherein the light is reflected from the outer surface and the inner surface and impinges on the optical detector. The detector can be configured as a camera or a similar apparatus.

[0015] The reference curve is to be understood as a curve which also contains a plurality of measuring points along the desired measuring direction or which has been determined from a plurality of such specific measuring points, for example by extrapolation and / or interpolation between and possibly beyond the measuring points (using a reference container).

[0016] Preferably, the reference curve of the container will not only contain measuring points which correspond to measuring values of the container positioned once relative to the irradiation apparatus and the optical detector, but the reference curve will rather correspond to measuring values of the container which have also been positioned in different positions with respect to the irradiation apparatus (in different orientations or rotations around its longitudinal axis, for example with the measuring direction perpendicular to the longitudinal axis). Thus, the reference points on the reference curve exist even in the case of various relative arrangements of the container relative to the irradiation apparatus, so that such a comparison can be carried out using the corresponding reference curve, regardless of the exact orientation of the container.

[0017] Thus, for measuring the wall thickness, not only one measuring beam can be used, but also a plurality of (simultaneously) measuring beams along different measuring directions (optionally parallel to each other).

[0018] Thus, the wall thickness is checked independently of the actual orientation of the container with respect to the illumination device and the optical detector.

[0019] The method is thus particularly advantageously suitable for containers having an outer contour, in which case the wall thickness of the container varies along the measurement direction.

[0020] It can be provided that, if the comparison does not result in a conformity of the plurality of measurement points with the reference curve, the evaluation device performs a transformation (translation, if necessary also rotation) of the reference curve and performs a renewed comparison of the measurement points with the transformed reference curve, wherein, if the comparison of the measurement points with the transformed reference curve results in a conformity, it is determined that the wall thickness of the container corresponds to the predetermined wall thickness, and wherein, if the comparison of the measurement points with the transformed reference curve does not result in a conformity, it is determined that the wall thickness of the container does not correspond to the predetermined wall thickness.

[0021] In particular, the transformation can comprise a displacement of a section of the reference curve until this section corresponds to the recorded region of the container with the illumination device or the optical detector, and then a corresponding comparison is performed. Whether the region of the transformed reference curve corresponds to the recorded measurement values can again only be determined by means of a comparison, so that in this embodiment too it is conceivable to perform a plurality of transformations of the reference curve until a conformity is determined or until a non-conformity is determined.

[0022] This embodiment is particularly advantageous for containers which have a surface structure which is not rotationally symmetrical about the longitudinal axis of the container, since this embodiment can still reliably check the wall thickness in this case.

[0023] In one embodiment, it is provided that the illumination device illuminates through the container and / or illuminates the container at each measurement point with at least one measurement beam.

[0024] In a further embodiment, the measurement beam can have a different wavelength for each measurement point, wherein the wall thickness is determined by setting at least two different wavelengths relative to one another.

[0025] Since the wall thickness of the container with the surface structure varies, the transmission and reflection behavior of the container material with respect to certain wavelengths can also vary in these regions. If at least two wavelengths are used in the illumination, these variations can be compensated, which can influence the measured wall thickness as a systematic error.

[0026] Furthermore, it can be provided that the measurement direction extends perpendicular to the longitudinal axis of the container or that the measurement direction extends parallel to the longitudinal axis of the container.

[0027] By this embodiment, in principle, a correlation of the wall thickness of the container in the transverse direction and in the longitudinal direction can be investigated, which in particular also enables a simple measurement of the container, for example, to generate a complete or almost complete wall thickness profile of the entire container.

[0028] In one embodiment, the transformation comprises a shift of the reference curve along the measurement direction by a value Δ; wherein the value Δ is substantially smaller than 0.1 D or smaller than 0.05 D; wherein D is the extension of the container along the measurement direction.

[0029] For example, the reference curve can be understood as a function which assigns a certain wall thickness W(X) to a position X along the measurement direction. As mentioned above, the corresponding function of the container which is measured depends on the actual orientation of the container with respect to the illumination device and / or the optical detector. If, when comparing the reference curve and the measured values, a discrepancy is found, this slight modification of X in the function W(X) by replacing the argument X by X+△ can lead to a shift of the reference curve which is then compared to the measured values of the position X. This procedure can be performed quickly in a computer, which usually forms the evaluation device, and requires little computing power, so that a plurality of these transformation steps can be performed for each container to determine whether the wall thickness of the container coincides with the reference curve. Thus, a simple procedure for transforming the reference curve is ensured, which in turn ensures a quick check of the measured values, which makes this procedure also suitable for continuous operation of a container processing machine with 1000 to about 10000 containers per hour.

[0030] In a further embodiment, the transformation is performed as a function of characteristic points of the plurality of measurement points and / or of a measurement curve derived from the plurality of measurement points and / or as a function of characteristic points of the reference curve.

[0031] Characteristic points are, for example, points at which a transition from a region of the container with a thin wall thickness to a region of the container with a thick wall thickness occurs, since here the thickness of the material is usually thicker than in all common regions. These are therefore represented in the measured values and in the reference curve, for example, as a maximum or minimum value, and characterize the course of the entire curve, whether this is the reference curve or a curve generated from the measurement points. If the transformation is performed such that the characteristic points occurring in the measurement points correspond to the characteristic points occurring in the reference curve (for example, as described above, by transforming the argument X in the function W(X) of the reference curve such that the characteristic points of the reference curve coincide with the measured values), only a single transformation is required to compensate for any alignment of the container with respect to the illumination device or the optical detector and to enable a comparison with the reference curve in a useful manner. If it is then determined that the measured values do not correspond to the reference curve, it can be determined that the wall thickness does not meet the requirements.

[0032] This procedure greatly reduces the number of transformation steps, but can involve a greater computational effort, since on the one hand the measured values are analyzed and on the other hand the reference curve is analyzed with respect to the characteristic points.

[0033] This greater computational effort can be reduced by the fact that the positions of the characteristic points of the reference curve are already stored in the memory (approximately together with the reference curve), so that only the analysis of the measured points or of the curve with respect to the characteristic points extrapolated from these measured points has to be carried out, and then the difference between the positions of these points in the measurement direction is formed in order to carry out the transformation of the reference curve.

[0034] This procedure can be carried out on the container along different, optionally parallel, measurement directions. In this way, a very precise measurement of the container, in particular of its wall thickness, can be achieved.

[0035] It can also be provided that, for the comparison of the measured points with the reference curve and the transformed reference curve, a measurement tolerance of the measured points and / or a tolerance of the reference curve and / or the transformed reference curve is taken into account.

[0036] In particular since the determination of the measured points, and also the determination of the reference curve, for example from the determination of a reference container, are influenced by certain errors, the taking into account of these errors in the context of a tolerance can prevent a false recognition of wall thicknesses which are considered to be inconsistent or consistent.

[0037] The method is preferably carried out by an inspection device, which comprises the illumination device, the optical detector and the evaluation device, and the container is supplied to the inspection device and carried away from the transport facility, and wherein, in the event of a determination that the measured points are inconsistent with the reference curve and the transformed reference curve, the operation of the transport facility is stopped. This can serve to ensure that any errors which can occur, i.e. extreme values in the wall thickness variation of the container, are first identified and, if necessary, eliminated before the machine continues to operate. This is particularly advantageous for machines arranged downstream, such as filling devices for filling the containers, and can prevent damage or contamination.

[0038] In the event that no consistency of the measured points with the reference curve and the transformed reference curve is detected, an information can be issued to an operator. For example, a warning can be issued to the operator that the measured wall thickness no longer corresponds to the predetermined wall thickness. The operator can then decide independently, for example, whether to continue the machine operation or whether to stop the machine operation and, for example, carry out a repair or replacement of parts or a more detailed fault analysis.

[0039] Alternatively or additionally, the container can also be diverted automatically in the event that the wall thickness is determined not to correspond to the specified wall thickness within the measurement accuracy or not to correspond thereto. To divert the container, a pusher can be used, which pushes the container out of the transport facility and into a collection container provided for this purpose. Other implementations for diverting the container from a neck handling device, such as a star wheel or a gripper, are also conceivable here.

[0040] Alternatively or additionally, a message, preferably wirelessly transmitted, can be automatically sent to an operator or maintenance personnel in the event that the wall thickness is determined not to correspond to the predetermined wall thickness. Preferably, the message is sent to a tablet, a cell phone or a wearable device, while in particular machine data, target values and measured values are transmitted.

[0041] It is particularly preferred that the measured wall thickness is assigned to the filling device in order to understand which cavity, heating mandrel, heating zone, clamping element the container was processed or produced with. Thus, in a closed-loop process, in the event of a deviation of the wall thickness of the (design) embossed area (relief, support structure, etc.) from the target, the filling device can be influenced in order to restore the material distribution to the target wall thickness. This can be done automatically or support / guide the machine operator, on the one hand.

[0042] At least a part of the measurement points and / or the comparison of the measurement points with the reference curve and / or the comparison of the measurement points with the transformed reference curve can be stored in a memory associated with the evaluation device. This can be used, for example, to perform a subsequent error analysis by evaluating the data stored in the memory.

[0043] The inspection device for inspecting the wall thickness of a container according to the application comprises an illumination device, an optical detector and an evaluation device, wherein the container can be supplied to the inspection device via a transport facility and carried away from the inspection device by the transport facility, wherein the transport facility and the illumination device and the optical detector are arranged relative to one another such that a container conveyed in the transport facility can be illuminated by the illumination device at at least a plurality of measurement points along a measurement direction and the optical detector can receive light reflected and / or transmitted by the container from the measurement points along the measurement direction, wherein the inspection device is configured to carry out the method according to one of the preceding embodiments. This inspection device is particularly advantageous for carrying out the method according to the application.

[0044] The illumination device can be configured to emit light having at least two different wavelengths, and wherein the optical detector is configured to detect at least the two different wavelengths of light. Thus, any errors that arise due to a changed transmission and / or reflection behavior of the container wall for a particular wavelength when the wall thickness changes can be compensated for.

[0045] Furthermore, the illumination device can be configured to illuminate the container with light to produce a plurality of measurement points along different measurement directions. This allows for a flexible use of the inspection device, not only measuring the entire container, but also containers of different shapes.

[0046] In a further development of this embodiment, the illumination device is configured to be slidable along at least one axis. The displacement of the illumination device can consist of an actual physical displacement of the entire illumination device, but can also include, for example, a deflection of the emitted light (for example, by means of mirrors or other optical means), which is usually performed faster than a complete displacement of the illumination device. With this embodiment, not only a change of the measurement direction for a single container can be realized, but also an adaptation of the inspection device to different containers, for example, by adapting the measurement direction to a varying shape or size of the container. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 A schematic representation of an inspection device 1 according to the application is shown;

[0048] Figure 2 The wall thickness of a container and the resulting measurement points are shown;

[0049] Figure 3 An embodiment of a transformation of a reference curve for inspecting the wall thickness of a container is shown;

[0050] Figure 4 A variant is shown in which the reference curve and the measurement points do not coincide with each other;

[0051] Figure 5 An embodiment of a vertically adjustable illumination device is shown;

[0052] Figure 6 A further embodiment of an inspection device is shown. DETAILED DESCRIPTION

[0053] Figure 1 An inspection device 100 according to the embodiment, with which a container can be inspected, is shown. The inspection device comprises or is associated with at least one transport facility 140 in which the containers 130 can be conveyed. For example, the transport facility can be a conveyor belt, but also any other known way of conveying containers. The containers are usually bottles or cans, which are made of a transparent material, in particular plastic, such as PET. In order to convey these containers, a support plate or carousel is usually combined with a centering facility, which clamps the container between the centering facility and the plate, and with claws that grip around the container, for example, in the area of a support ring or at least in the area of the mouth. The containers are thus conveyed hanging.

[0054] Since it is essential for the present application that the material of the container can be irradiated in at least one region, it is preferred to be fed in such a way that at least a large part of the wall of the container is exposed, so that a gripper and a centering device with an associated support plate or carousel can be particularly advantageous.

[0055] In this respect, the transport facility 140 is not limited.

[0056] However, in order to further explain the method according to the application, it is necessary that the container 130 (here only shown in a top view as a cross section) has a wall 133. This wall (of the container) has an outer surface 131 and an inner surface 132. Here, the inner surface 132 is the surface of the container facing the inner space of the container, which is usually filled with the medium to be filled into the container. The outer wall or outer surface of the container 131 is then the surface 131 of the wall 133 which is opposite the inner surface 132.

[0057] In the embodiment shown here, the wall 133 of the container comprises regions of different thickness, such as a region 134 which extends relatively long along the outer circumference of the container and has a constant wall thickness, and a region 135 which is formed, for example, as an indentation in the surface of the container and in which the wall thickness of the container is smaller. Between these regions, in turn, regions with a greater wall thickness extend.

[0058] This is not absolutely necessary, but the method according to the application is particularly advantageous for containers 130 which do not have a constant wall thickness (for example, with respect to the cross section of the container).

[0059] The inspection device 100 further comprises an irradiation device 121. For example, the irradiation device can comprise one or more glow filaments to form a diffuse light source. The glow filaments can be operated such that they have an emission spectrum corresponding to their temperature, which emits electromagnetic radiation mainly in the infrared range. The glow filaments can also be operated to emit micro-red light. It is also conceivable to operate the glow filaments (or filaments) at a temperature at which they emit white light, i.e. with an emission maximum in the visible range. The light emitted by this one or more filaments then impinges on the wall of the container. Alternatively, one or more diodes, in particular laser diodes, can be used to emit electromagnetic radiation (infrared light or visible light) 151 to the container wall. Furthermore, an optical detector 122 is provided, for example in the form of a camera, which can detect light reflected and / or transmitted through the container.

[0060] In the embodiment shown here, the detector 122 and the irradiation device 121 are located on the same side of the container or the transport facility, so that the light reflected from the container is at least partially detected in the detector. In this case, the light is not only reflected from the outer surface 131 of the container, but due to the transparency of the container, light is also reflected back from the inner surface and transmitted through the outer surface 131 to the optical detector 122.

[0061] In a variant in which the detector records light transmitted through the container, the detector 122 is arranged on the side opposite the irradiation device 121 with respect to the transport facility 140. Thus, in the top view shown in Figure 1 the transport facility is then located between the irradiation device 121 and the detector 122, so that the container to be checked is also located between the irradiation device 121 and the detector 122.

[0062] It can be provided that the irradiation device can selectively emit light of different wavelengths, such as light in the infrared spectral range, light in the red spectral range and / or light in the blue spectral range. By using light of different wavelengths, random effects such as constructive or destructive interference of the part of the light emitted by the irradiation device that is reflected and / or transmitted from the inside and outside of the container, which can unintentionally influence the measurement of the wall thickness, can be compensated for. Alternatively, it can also be provided that the irradiation device emits white light (or only infrared light or red and infrared light), for example as described for the light filament, and that the optical detector has a plurality of (at least 2) color filters, or corresponding color filters are arranged between the thus configured irradiation device and the container. These color filters can be light filters, for example, one of which allows only blue light to pass through, one of which allows only red light to pass through. With this, too, the effect of avoiding the above-mentioned adverse effects can be achieved.

[0063] Whether the light beam 152 (reflected from the inner surface 132) and the light beam 153 (reflected from the outer surface 131) is transmitted or reflected by the bottle, it hits the optical detector 122. Usually, due to the material thickness or the wall thickness of the container, the amount of light transmitted (reflected) and thus the light signal reaching the optical detector (depending on the wall thickness) is stronger or smaller. The optical detector 122 can then transmit a signal (for example, a brightness signal or an interference signal, etc.) corresponding to the container wall thickness to the evaluation device 123. To this end, the 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 at least from the optical detector to the evaluation device, but preferably bidirectionally.

[0064] The reference curve is stored in or can be retrieved from the evaluation device 123, which will also be described in more detail with reference to Figure 3 and Figure 4 The reference curve corresponds to an expected signal indicating the container wall thickness at a specific location on the container in the measurement direction and can be generated, for example, by measuring a reference container whose wall thickness is known. Of course, alternatively or additionally, for this purpose a large number of measurements of reference containers can be carried out in order to obtain from these measurements a reference curve that avoids errors as systematically as possible. An idealized container can also be used as a basis for the reference curve.

[0065] However, how the reference curve is ultimately determined is independent of the method according to the application. Preferably, the reference curve extends over a larger area than the area which is usually measured for a single container. For example, if the container is moved in an upright position past the illumination device 121 and does not rotate relative to the illumination device, the measurement of the wall thickness only takes place in the local area of the container surface which faces the illumination device. However, the reference curve available to the evaluation device 123 preferably comprises values for the wall thickness or values which are indicative of the wall thickness of the container which cover the entire surface of the container.

[0066] In this connection, it should be mentioned that the illumination device illuminates the container along a measurement direction, such as along the cross-sectional direction of the container as shown in Figure 1 Fig. 1. The reference curve is then preferably stored in the evaluation device for precisely this measurement direction. This is described in more detail in Figure 5 Fig. 2. The illumination can take place by moving the container past the illumination device and illuminating the container point by point. However, it can also be provided that the container is positioned such that the light from the illumination device hits exactly one point on the container (for example, if a turntable is used together with a centering device). The container is then rotated (a part of its entire circumference or a full rotation) so that a corresponding signal is generated in the detector for each measurement point along the measurement direction.

[0067] The advantage of the first method is that the machine can be operated continuously. However, the first method only provides limited useful results, especially in areas of the container which curve strongly towards or away from the illumination unit due to the cross-sectional shape of the container. The second method allows the wall thickness to be recorded with high accuracy, but requires the inspection device to be operated in cycles.

[0068] By comparing the reference curve with the measurement values recorded along the measurement 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 value of the wall thickness. This can be done, for example, by detecting the conformity of the reference curve or of a part of the reference curve, if it covers a larger surface area of the container than the surface area during the inspection using the inspection device. Of course, any error tolerance can be taken into account. Thus, it can be taken into account that the resolution and certainty of the signal in the optical detector can only be made with a certain accuracy. Furthermore, it can be taken into account that the production of the container itself is influenced by certain tolerances, so that, for example, a slight deviation of the wall thickness from the reference value is still acceptable. Establishing conformity between the reference curve and the measurement values should therefore essentially be understood as establishing conformity within the expected tolerance range.

[0069] For a more detailed description of the measurement process using the inspection device 100, Figure 2 An example container and the resulting measurement values are described.

[0070] The container cross-section shown here (e.g., it may be cut at a certain height of the container) represents a portion of the container's cross-section, and the container's longitudinal axis is preferably perpendicular to this cross-section.

[0071] The portion of the container surface shown here does not have a constant wall thickness. In one region, the wall thickness (also due to the curvature of the container surface) is much greater in region d1 than in region d2. Regions with thinner wall thicknesses gradually thicken around region d3 until they reach a thickness d4 in that region. Thereafter, the wall thickness decreases again, where, again due to the curvature of the container, a definite wall thickness d5 is larger and increases to a wall thickness d6 (also due to the curvature of the container).

[0072] In this context, it should be noted that the “wall thickness,” which is also affected by the container’s curvature, is ultimately determined by the illumination from the irradiation device 121 and the reception of signals in the optical detector 122, and by the curvature typically present in the container (which usually has a circular or at least curved cross-section). Figure 2 As shown on the left, the wall thickness d1 does not extend approximately perpendicular to surfaces 131 and 132, but is represented at an angle to them, and is therefore greater than the actual wall thickness. This is because light from the irradiation device typically does not strike the container surface perpendicularly, but rather at an angle that can also vary depending on the curvature of the container. The highly curved regions, particularly... Figure 2 The areas shown on the left and right sides of the left-hand section, which curve sharply towards or away from the lighting unit, generally provide unreliable results because the light passes through more material here than would occur if the light fell perpendicularly onto the container surface due to the actual wall thickness. These areas can be omitted, for example, when comparing measurements to a reference curve later. However, Figure 2 The images shown assume the container simply moves past the lighting unit. As mentioned above, it can also be specified that the container is positioned in the area of ​​the lighting device such that only one point of the container is illuminated (e.g., preferably with the incident light perpendicular to the surface). Simultaneously, the container is rotated such that measurements indicating the container wall thickness can be recorded on at least a portion of the container's outer periphery (in some embodiments, around the entire outer periphery of the container).

[0073] Despite the above regulations, Figure 2 In the diagram shown on the right, the corresponding image of the signal recorded by optical detector 122 at least indicates the wall thickness of the container (although not synonymous). Region d1 shows the relatively thick measured wall thickness, while regions d2 and d3 can be seen in the thinner regions of the container. The wall thickness d4 is measured in the again thicker region, and the wall thicknesses d5 and d6 increase due to the curvature of the container and its relative orientation to the irradiation facility, but the actual wall thickness remains unchanged.

[0074] Thus, while the signals measured here are at least partially indicative of the wall thickness of the container, they are not identical to the wall thickness, since other influences discussed above, such as the curvature of the container, also have an effect here.

[0075] Nonetheless, Figure 2 The measurement curve shown on the right in the middle can be used to draw conclusions about the actual wall thickness of the container.

[0076] For this purpose, a reference curve available in the evaluation device 123 can be used, which, as described above, preferably represents not only a portion of the container surface in the measurement direction.

[0077] This is described in Figure 3 .

[0078] Figure 3 A "measurement curve" 361 is shown, which is generated from the plurality of measurement points along the measurement direction. This can be understood as an interpolation between the plurality of measurement points along the measurement direction. Thus, in addition to this continuous curve, a series of measurement points can also be displayed.

[0079] It is to be understood that the curve 361 shown here will also have some errors, which correspond to the actually recorded measurement points. This can be supplemented here in addition by error bars, as Figure 2 shown in the middle, to provide an indication of the accuracy of the curve. However, for the sake of clarity, this is not done here.

[0080] In addition to the measurement curve of the actual container resulting from the measurements along the measurement direction, a reference curve 362 is also shown. This is clearly different from Figure 3 the resulting measurement curve 361 shown in the diagram on the left in the middle. It thus not only comprises a maximum and a minimum, but also a further maximum to the left of the significant maximum, separated from the significant maximum by a further minimum. For larger independent variables X, the reference curve 362 grows again.

[0081] The person skilled in the art will conclude from a first glance that the reference curve 362 and the curve 361 resulting from the measurement points do not coincide. However, as described above, the measurement values obtained according to the method for checking the wall thickness according to the application differ from one another depending on how the container is oriented with respect to Figure 1 the illumination device and / or the optical detector.

[0082] As an illustrative example thereof, it is conceivable that, in order to generate the reference curve, the surface of the container is unfolded such that the entire circumference of the container is shown as a straight line. The corresponding wall thickness can be plotted as a reference curve over the entire circumference of the container. The beginning of the roll of the container surface can be arbitrarily set to the value 0 as the position X0. However, the container to be measured is oriented with respect to Figure 1the illumination device and the actual orientation of the optical detector relative to Figure 1 The actual position X1 of the container to be measured is thus generally unknown and can vary. The start of the measurement thus does not necessarily at all coincide with the position X0 as the start of the rolling of the container surface (for the virtual generation of the reference curve), but it can be located, for example, at a position X1 that differs from the position X0 by a value Δ. Although the container being measured or the wall thickness obtained for this container is identical to the reference curve in the corresponding region, the displacement between the measured and the reference curve is exactly the amount Δ.

[0083] This can be seen in the left-hand illustration in Figure 3 where two maxima of the measured values are separated by a distance Δ.

[0084] In one embodiment of the method according to the application, it can now be provided that, if no agreement is obtained between the reference curve (without transformation) and the measured values in the first comparison step, the reference curve is transformed when comparing the measured values with the reference curve. This transformation can be, for example, a displacement of the reference curve 362 with respect to the curve 361. According to the application, there are now two possibilities here, each of which has certain advantages.

[0085] On the one hand, the transformation of the reference curve can be performed by displacing the reference curve by a fixed amount Δ, wherein the amount Δ is preferably significantly smaller or substantially smaller than the extension of the container or the reference container in the measurement direction. If the measurement direction is parallel to the peripheral direction of the container, the extension of the container is the periphery. If the extension of the container in the measurement direction is denoted by D, then preferably, Δ can be smaller than 0.1 D, more preferably smaller than 0.05 D, and particularly preferably smaller than 0.005 D.

[0086] This displacement of the reference curve is simple to implement computationally in terms of the absolute amount, thus requiring little processor power. However, this displacement in the first step can not immediately lead to an agreement between the reference curve and the measured values, but it is objectively very likely that this is the case. This can be because the difference between the values X1 and X0 is greater than the fixed Δ, so that, for example, it can be necessary to perform several transformation steps (2, 3, 4, 5, etc.) until an agreement is established at present. In the extreme case, this can thus require a displacement of the following length in each partial step Δ until a final conclusion is reached with respect to the current agreement or disagreement of the point being measured with the reference curve, wherein the length corresponds to the extension of the container in the measurement direction minus the length actually measured of the container cross section in the measurement direction. Although little computer resources are actually required, this can be very time-consuming and require considerable effort for the individual transformation.

[0087] Alternatively, the displacement Δ necessary to shift the reference curve to coincide with the measured values can also be calculated first, if necessary, before performing the displacement or transformation.

[0088] The procedure is shown in Figure 3 . As shown in the left-hand graph in Figure 3 , the reference curve and the curve resulting from the measured values 362 and 361 (or a plurality of measured points) have a significant maximum at point 371 (for the measured curve) and 372 (for the reference curve). It can be known Figure 3 that the container on which the reference curve is based must always have such a significant maximum, since, for example, it has a material thickening and thus a wall thickness in a certain region that is not reached in any other region. The position of this point, if included in the measured curve, thus clearly defines the distance between points X0 and X1 (see above). Thus, if the measured curve contains this characteristic point (maximum 371), the relative position of its maximum 372 with respect to the reference trace 362 can be used to determine the displacement Δ necessary for the transformation of the reference curve. The reference curve can then be transformed with the resulting Δ and the picture shown on the right in Figure 3 is obtained. After the transformation, the reference curve and the measured curve coincide and it is shown that the individual measured values or the measured curve formed from these measured values along the measurement direction correspond to the reference curve, i.e. the wall thickness is in accordance with the expected.

[0089] Of course, this method is only applicable if Figure 1 the cross section of the container in is measured, for example, if not the entire circumference of the container, also contains the characteristic point in question. If this is not the case, for example, it can be determined in the initial analysis of the measurement, the above-described method can be used by transforming the reference curve by a certain fixed value Δ in order to be able to compare the measured values with the reference curve.

[0090] 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 associated with the evaluation device and each of these characteristic points can be compared with the reference curve in order to determine which of these characteristic points is approximately found on the reference curve in order to determine the necessary displacement Δ of the reference curve.

[0091] If the container is measured along its entire circumference in the examination device, for example, when a turntable is used, the described method of determining the characteristic point and deriving the displacement Δ always applies, since all characteristic points that can possibly exist are also recorded during the measurement.

[0092] If no characteristic point is detected, it can also be determined directly by the evaluation device that the course of the wall thickness does not correspond to the course of the reference curve or, generally, that the wall thickness does not correspond to the expected.

[0093] Figure 4 This illustrates a situation where even a transformation of the reference curve cannot provide consistency between the measured curve or the measured value and the reference curve.

[0094] Figure 4 The measurement curve 361 and reference curve 362 of the measured container are shown again. Both have maximum values ​​371 and 372, respectively. This is used, where appropriate, to align the reference curve with the measured value or measurement curve 361. Thus, although the value has been determined based on the maximum value... Figure 4 The relative orientation of the measurement curve and the reference curve has been adjusted and the corresponding transformation has been performed, but it can be seen in region 490 that the measurement curve 361 is different from the reference curve 362, even taking into account the error bars shown in this region, that is, there is no consistency under any circumstances.

[0095] Therefore, in this embodiment, the comparison between the reference curve and the measured curve or measured value determines that they are inconsistent (even if within the error tolerance), regardless of any transformation made to the relative arrangement of the reference curve and the measured curve.

[0096] Figure 5 An embodiment of the invention is shown, in which the container is measured along different measurement directions.

[0097] exist Figure 5 In the diagram, container 130 is shown positioned on a transport facility (here shown as a support plate or turntable 140). In this embodiment, the irradiation device 121 is movably supported along axis 570, which may be an axis disposed on the module housing 571 of the inspection device, allowing the irradiation device 121 to move up and down along the indicated bidirectional arrows. In this embodiment, the irradiation device can thus emit light 151 at different heights (along the longitudinal axis of the container).

[0098] Then, by correspondingly moving the irradiation device 121, multiple measured values ​​can be determined along measurement directions 581, 582, 583, and 584, respectively. Thus, in the embodiment shown here, multiple measurement points along three different measurement directions 581 to 583 have been recorded in the neck or shoulder region of the container, where the container may typically have a strong surface curvature and may also have an embossed structure if necessary.

[0099] Additional measurements can be provided along measurement direction 584 in the main body region of the container. More or fewer of the four different measurement directions described herein may also be used. Thus, the measurement directions may also be perpendicular to the measurement directions shown herein or include specific angles about them that differ from 90° and 0°.

[0100] Although Figure 5In this case, only the irradiation device 121 moves vertically, but it can also be specified that the optical detector moves accordingly to ensure that the light reflected from different heights of the container is actually detected by the optical detector.

[0101] As an alternative to the overall moving optical detector and / or illumination device, it is also possible to specify moving only the optical system, such as a mirror or lens array, to achieve different measurements of the container along different depicted measurement directions 581 to 584. In this way, the number of components to be moved, and in particular the magnitude of the movement, can be kept as low as possible.

[0102] Furthermore, it can be specified that (separate) irradiation devices are arranged at different heights relative to the transport facility (and thus relative to the containers transported therein), or that the irradiation devices extend on corresponding vertical extensions. Therefore, one or more detectors are then provided that can detect light transmitted or reflected through the container at the appropriate height.

[0103] exist Figure 6 The corresponding embodiments are shown in the figure.

[0104] exist Figure 6 In the embodiment shown, container 130 is shown on the far left of the image. Container 130 has a varying wall thickness 631, for example, due to embossing or stamping patterns. Figure 6 On the left side, the container is shown only from one side, and... Figure 6 The center of the illustration is shown as "unfolded," meaning the bottle is unfolded onto a flat surface to show its entire surface. The variation in material thickness 631 is also shown here. Combined with the middle image, the wall thickness trend along the entire outer perimeter of the container is also shown.

[0105] exist Figure 6 On the right side, an embodiment of the inspection equipment 600 is shown, and here, the transport facility 140 and container 130 can also be configured, for example, according to... Figure 1 The variants described in the text are used for arrangement.

[0106] However, the detector 622 and the irradiation device 621 are arranged on opposite sides of the transport facility, so that the container is completely irradiated by the light emitted by the irradiation device, and then the light transmitted through the container is received.

[0107] This corresponds to Figure 1 The variant already described is an alternative to the recorded image of reflected light.

[0108] Figure 6 The wall thickness measured at different heights or in measurement directions 681 to 684 is also shown, and the measurement curve 694 for the entire outer perimeter of the container in measurement direction 684 is shown.

[0109] The measurement curve actually recorded by the detector 622 can represent only a part of this reference curve 694.

[0110] According to the procedure described in the previous figures, the reference curve can then be shifted with respect to the measurement curve in order to determine whether a correspondence exists or not.

[0111] In this respect, the procedure is similar to the one described in Figure 3 and Figure 4 for determining a correspondence or determining that no final correspondence between the reference curve and the measurement curve can be achieved even by a transformation.

[0112] In the embodiment described in Figures 3 to 6 , a reference curve is essentially referred to which maps the entire surface of the container, giving a wall thickness function which depends only on one parameter wherein may be approximately the angle of rotation of the container about its longitudinal axis with respect to any initial position.

[0113] In Figure 5 and Figure 6 , by recording different measurement curves (i.e. at different vertical positions along the outer circumference of the container) at the same time, also two-dimensional information about the behavior of the wall thickness in the circumferential direction of the container and in the longitudinal direction can be obtained. While the reference trace discussed so far is only a function which indicates the wall thickness w as a function of the position along the measurement direction, this information can also be arranged as a function of two parameters. For example, the wall thickness can be assigned to points on the surface which depends on their vertical position (in the longitudinal direction of the container) and which depends on their position along the outer circumference of the container, so that the wall thickness function depends on two variables, one being the angle of rotation about any initial position or zero position of the container and the vertical position l along the longitudinal direction of the container.

[0114] Such a function can also be stored for the entire surface of the container and used according to the procedure described above to check the correspondence between the measurement curve (which can then also be two-dimensional, but does not have to be) and the reference curve.

[0115] While it has been assumed here that the corresponding reference curve is also available for the entire range of available parameters (e.g. for the entire angle of rotation i.e. along the entire circumference), this is not absolutely necessary.

[0116] Since the inspection device can usually be located downstream of the container cleaning machine and / or blow molding machine or similar machine for producing the containers, it can be made sure that the containers are always supplied to the inspection device in substantially the same orientation with respect to any normal orientation. For example, the normal orientation of the containers can be specified as the "average" value of all containers output from the container cleaning machine and / or blow molding machine, the actual orientation of the containers varying around this average value by + / - 10 degrees, + / - 20 degrees or any value in between, or any greater or lesser value.

[0117] For example, the containers produced by the blow molding machine can always be output from this machine in the same orientation and supplied to the inspection device. If the containers are not further rotated around their longitudinal axis during the transport from the blow molding machine to the inspection device, the orientation of all containers is substantially the same as the orientation when they leave the blow molding machine, which is practically the same for all containers.

[0118] If this variation is known with sufficient accuracy and is reliably observed for all containers, it is not necessary to provide the following reference curve any more, wherein this reference curve maps the entire surface of the container and assigns wall thickness values to the points on the container surface (at least along one or more measurement directions). It is then sufficient to store the corresponding cross section of the container around this normal orientation as the reference curve and to use it for the comparison with the measurement curves of the individual containers.

[0119] Alternatively, the reference curve (expected area) can also be related to the measurement results by a second known feature. In the case of plastic containers, this second known feature can be the container seam or the pentagonal 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 at least partially transparent material, the method comprising: irradiating the container at a plurality of measurement points with a measurement beam of an irradiation device along a measurement direction, wherein for each measurement point a signal indicative of a wall thickness of the container at the measurement point is obtained by an optical detector, wherein by an evaluation device the plurality of measurement points is compared to a reference curve of wall thicknesses of a specified reference container along the measurement direction, wherein if the comparison yields a conformity between the plurality of measurement points and the reference curve, it is determined that the wall thickness of the container corresponds to a predetermined wall thickness, and wherein if the comparison does not yield a conformity between the plurality of measurement points and the reference curve, it is determined that the wall thickness of the container does not correspond to the predetermined wall thickness, wherein when the comparison does not yield a conformity of the plurality of measurement points and the reference curve, the evaluation device performs a transformation of the reference curve and performs a re-comparison of the measurement points to the transformed reference curve, wherein if the comparison of the measurement points to the transformed reference curve yields a conformity, it is determined that the wall thickness of the container corresponds to the predetermined wall thickness, and wherein if the comparison of the measurement points to the transformed reference curve does not yield a conformity, it is determined that the wall thickness of the container does not correspond to the predetermined wall thickness.

2. The method of claim 1, wherein, the container is irradiated at each measurement point by the irradiation device with two measurement beams through and / or with, and the measurement beams have different wavelengths.

3. The method of any one of claims 1-2, wherein, the measurement direction extends perpendicular to a longitudinal axis of the container; or wherein the measurement direction extends parallel to a longitudinal axis of the container.

4. The method of any one of claims 1 to 2, wherein, the transformation comprises a displacement of the reference curve along the measurement direction by a value Δ; wherein the value Δ is smaller than 0.1 D; wherein D is an extension of the container along the measurement direction.

5. The method of any one of claims 1-2, wherein, the transformation is performed as a function of feature points of the plurality of measurement points and / or of a measurement curve derived from the plurality of measurement points and / or as a function of feature points of the reference curve.

6. The method of any one of claims 1 to 2, wherein, the method is performed on the container along different measurement directions.

7. The method of any one of claims 1 to 2, wherein, the comparison of the measurement points to the reference curve and to the transformed reference curve is performed taking into account measurement tolerances of the measurement points and / or taking into account tolerances of the reference curve and / or of the transformed reference curve.

8. The method of any one of claims 1 to 2, wherein, the method is performed by an inspection device, the inspection device comprising the irradiation device, the optical detector and the evaluation device, and the container is supplied to the inspection device by a transportation facility and is transported away from the transportation facility, and wherein in case it is determined that the measurement points do not conform to the reference curve and to the transformed reference curve, an operation of the transportation facility is stopped.

9. The method of claim 8, wherein, in case it is determined that the measurement points do not conform to the reference curve and to the transformed reference curve, an information is output to an operator, and / or wherein in case it is determined that the measurement points do not conform to the reference curve and to the transformed reference curve, the container is guided out of the transportation facility.

10. The method of any one of claims 1 to 2, wherein, At least a part of the measurement points and / or the comparison results of the measurement points with the reference curve and / or the comparison results of the measurement points with the transformed reference curve are stored in a memory associated with the evaluation device.

11. The method of any one of claims 1 to 2, wherein, The container is a bottle made of PET.

12. The method of claim 4, wherein, The value delta is less than 0.05 D.

13. The method of claim 6, wherein, The different measurement directions extend parallel to each other.

14. An inspection apparatus for inspecting a wall thickness of a container, wherein, The inspection device comprises an illumination device, an optical detector and an evaluation device, wherein the containers can be supplied to the inspection device via a transport facility and transported away from the inspection device by the transport facility, wherein the transport facility and the illumination device and the optical detector are arranged relative to each other such that a container conveyed in the transport facility can be illuminated by the illumination device at at least a plurality of measurement points along a measurement direction and the optical detector can receive light reflected and / or transmitted by the container from the measurement points along the measurement direction, wherein the inspection device is configured to carry out the method according to any one of claims 1 to 13.

15. The inspection apparatus of claim 14, wherein, The illumination device is configured to emit light having at least two different wavelengths or broadband light; and wherein the optical detector is configured to detect at least two different wavelengths of light.

16. The inspection apparatus of claim 14 or 15, wherein, The illumination device is configured to illuminate a container with light to produce a plurality of measurement points along different measurement directions.

17. The inspection apparatus of claim 16, wherein, The illumination device is configured to be slidable along at least one axis. The illumination device is configured to emit light having at least two different wavelengths or broadband light; and wherein the optical detector is configured to detect at least two different wavelengths of light.

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