Device and method for measuring a double fold of a can

Abstract

Method for measuring a double fold of a can, in which an electromagnetic radiation source of a measuring device emits electromagnetic radiation, the double fold modifies the emitted electromagnetic radiation, a sensor of the measuring device detects the modified electromagnetic radiation and provides a sensor signal dependent on the detected electromagnetic radiation, and a measuring module of the measuring device determines a fold width of the double fold depending on the provided sensor signal, as well as a device for measuring a double fold of a can.

Description

[0001] The invention relates to a method for measuring a double seam of a can, in which a fully closed can is provided, comprising a can body and a can lid and having a double seam arranged on an outer side of the can and permanently connecting an edge of the can lid to an edge of an opening of the can body, a first measuring point on an inner surface of the double seam, a second measuring point on an outer surface of the double seam opposite the inner surface, a measuring axis extending through the first measuring point and the second measuring point, and a thickness of the double seam to be determined during the measurement are defined as a distance of the second measuring point from the first measuring point, and an end face of the double seam is brought into contact with a reference surface of a device, and an electromagnetic radiation source of the device emits light as electromagnetic radiation.The double seam modifies the emitted electromagnetic radiation, a sensor of the device detects the modified electromagnetic radiation and provides a sensor signal dependent on the detected electromagnetic radiation, and a measuring module of the device determines the distance based on the provided sensor signal. Furthermore, the invention relates to a device for measuring a double seam of a can, in short, a measuring device for a double seam of a can.

[0002] Cans within the meaning of the invention comprise metal containers that can be constructed in two or three parts, with parts of the can being made of, for example, aluminum or tinplate or comprising aluminum or tinplate. The cans are used for storing and / or transporting beverages or long-life foodstuffs and, depending on their precise intended use, can be referred to as beverage cans or food cans.

[0003] The tightness of a can is a key criterion for its quality. The tighter the can, the better protected the contents are from leaking into the can's surroundings or from substances from the surroundings entering the can, and the longer the contents will last.

[0004] Two-piece cans comprise a deep-drawn, ironed can body and a can end for closing one opening of the deep-drawn, ironed can body. Three-piece cans comprise a tubular can body and two can ends for closing two opposite openings of the tubular can body.

[0005] The can body is sealed by permanently connecting one edge of each lid to the edge of an opening in the can body using a double seam. The can's tightness depends largely on the quality of the double seam. The quality of the double seam correlates with the width of the double seam, or seam thickness.

[0006] The seam width is defined as a thickness of the double seam, i.e. a material thickness relative to a measuring axis that extends from an inner side of the double seam facing the can end through all layers of the double seam to an outer side of the double seam facing away from the can end. The measuring axis defines a first measuring point arranged on an inner surface of the double seam and a second measuring point arranged on an outer surface of the double seam as the respective intersection points of the measuring axis with the inner surface and the outer surface, respectively. Measuring devices provided for measuring the double seam use sensors to detect the respective positions of the two measuring points defined in this way and determine the seam width as a distance between the two measuring points along the measuring axis.

[0007] The measuring axis can be standardized by an angle of the measuring axis relative to a reference plane, a so-called measuring angle, and a height of the first measuring point above the reference plane, a so-called measuring height, which is also referred to below as the first probing height. For example, the measuring angle can be 6° and the measuring height 1.2 mm. However, the invention is not limited to currently standardized measuring axes.

[0008] To ensure the quality of the double seam, individual cans are randomly selected during can production, and the width of the double seam is measured for each selected can. During the measurement, the can is filled and completely closed. Therefore, non-destructive measurement methods are preferred.

[0009] For non-destructive measurement of the fold width, a device can be used that directly mechanically scans the double fold. Alternatively, the fold width can be determined based on the transmissivity of the double fold measured using X-rays.

[0010] Apart from that, measurement methods for optically measuring objects are known. For example, DE 10 2018 209 365 A1 discloses an optical measurement method in which the completeness of an annular seal on the closure of a detergent and dishwashing liquid bottle is determined by illuminating the closure with UV light and capturing the light reflected from the closure using a telecentric camera.

[0011] DE 200 17 739 U1 discloses an optical measuring method in which an object arranged on a translucent support surface is illuminated and measured by means of reflected incident light or transmitted light captured by cameras.

[0012] DE 10 2016 004 713 A1 discloses an optical measuring method in which a closure cap arranged on a translucent support surface is illuminated and a mean circle diameter and a quality of the closure cap are determined by means of a silhouette of the closure cap.

[0013] From JP 2012-159321 A an optical measuring method is known in which an end face of a can is illuminated by means of a ring light, a camera captures an image of the illuminated end face and a computing device determines a thickness of a double seam of the can arranged on the end face as a distance of a circular inner edge from a circular outer edge of the imaged double seam.

[0014] A similar optical measuring method is described in JP 2024-129676 A. In this method, deviations from a perfect circular shape of the inner edge or the outer edge of the double fold are detected as defects in the double fold.

[0015] JP 2001-050716 A discloses an optical measuring method that can be integrated into automated can production. A double seam of a can transported on a conveyor belt is illuminated simultaneously from at least two directions in a sensor-detected position. An optical sensor arranged above one end of the can captures a grayscale image of the illuminated double seam, which is used to determine the thickness of the double seam using image processing.

[0016] However, known devices and methods for measuring a double seam, in short measuring devices or measuring methods, tend to be subject to systematic errors due to unavoidable mechanical wear, cannot be integrated into an automatic production of cans or can only be integrated with great effort and / or provide insufficient accuracy of the measured seam width.

[0017] It is therefore an object of the invention to propose a method for measuring a double seam of a can that enables the thickness of the double seam of a fully closed can to be determined reliably with high accuracy and can be easily integrated into an automated can production process, i.e., allows inline measurement. A further object of the invention is to provide a device for measuring a double seam of a can.

[0018] The invention relates to a method for measuring a double seam of a can, in which a completely closed can is provided, which comprises a can body and a can lid and has a double seam which is arranged on an outer side of the can and permanently connects an edge of the can lid to an edge of an opening of the can body, a measuring axis extending through the double seam with a first measuring point on an inner surface of the double seam and a second measuring point on an outer surface of the double seam opposite the inner surface, and a thickness of the double seam to be determined during the measurement is defined as a distance of the second measuring point from the first measuring point, and an electromagnetic radiation source of a device emits electromagnetic radiation, the double seam modifies the emitted electromagnetic radiation,A sensor of the device detects the modified electromagnetic radiation and provides a sensor signal dependent on the detected electromagnetic radiation, and a measuring module of the device determines the distance based on the provided sensor signal. The fully closed can is an end product of an automated production process and contains a content, for example, a beverage or food. The method does not depend on whether the can lid forms a bottom of the can or a top of the can. The distance is to be understood as the shortest distance connecting the first measuring point and the second measuring point and is located entirely within the double seam. The distance is therefore equal to the length of the shortest distance connecting the two measuring points. The measuring axis is to be understood as a straight line that extends collinearly with the shortest distance.

[0019] According to the invention, an end face of the double seam is aligned parallel to a reference plane defined by the device, and light is emitted as the electromagnetic radiation. For example, the end face of the double seam can be brought into contact with a reference surface of the device extending in the reference plane in order to align the end face of the double seam parallel to the reference plane. Alternatively, an end face of the can opposite the double seam to be measured can be brought into contact with a reference surface of the device extending at a distance from and parallel to the reference plane. The opposite end face can have another double seam or a deep-drawn base ring.

[0020] Light within the meaning of the invention refers to electromagnetic waves that include infrared radiation, visible light, and ultraviolet radiation. In other words, electromagnetic radiation with higher frequencies or shorter wavelengths, such as X-rays, or electromagnetic radiation with lower frequencies or longer wavelengths, such as radar or microwave radiation, is not light within the meaning of the invention. In other words, the method according to the invention is an optical method that enables ray-optical measurement of the double seam using geometric optics. This is because the dimensions of the can, in particular of the double seam, are very large compared to a wavelength of light.

[0021] Furthermore, the optical beam measurement is contactless and therefore reliable, i.e. systematic errors due to mechanical wear of the measuring device or deformation of the double fold by the measuring device are avoided.

[0022] Furthermore, the optical beam measurement of the can seam is carried out at a distance equal to the distance of the double seam, and thus the can, from the electromagnetic radiation source and the sensor. Accordingly, the measurement method according to the invention can be integrated into a can production line without affecting a production rate of more than 1,000 cans per minute. This significantly reduces production waste, resulting in significantly greater efficiency and cost-effectiveness of the production line.

[0023] Typically, a measurement is required to have a measurement uncertainty where the total measurement uncertainty range is at most 20% and preferably at most 10% of a manufacturing tolerance of an object to be measured.

[0024] Double folds typically have a fold width in the range of 1.0 mm to 1.5 mm and are manufactured with a manufacturing tolerance of ±0.05 mm = ±50 µm. In other words, the double folds should vary by a maximum of 100 µm. The measurement uncertainty for the fold width of the double fold should therefore be within a range of ±3 µm and ±7 µm, i.e., in particular, not exceed ±7 µm. The measurement method according to the invention can achieve such a low measurement uncertainty.

[0025] The two measurement points are freely definable and can be defined according to a standard. Due to the freely definable nature of the measurement points, the measurement points can deviate from any standard. Consequently, the method according to the invention is suitable for establishing a new standard.

[0026] In one embodiment, the sensor detects light reflected from the double fold as the modified electromagnetic radiation. The double fold modifies the light emitted by the electromagnetic radiation source by means of diffuse reflection, i.e., the double fold diffusely reflects the emitted light. In diffuse reflection, emitted light is reflected from a surface simultaneously in a plurality of directions.

[0027] The light can be emitted and detected collinearly or parallel to the measurement axis. Ideally, the emitted light is reflected from the first measurement point or the second measurement point. For example, a distance of the sensor from the first measurement point or the second measurement point along the measurement axis can be determined using a chromatic confocal distance measurement. In particular, two sensors can simultaneously measure a first distance d1 or a second distance d2 from the first measurement point and the second measurement point. If the distance d S of the two sensors along the measuring axis, the measuring module determines the thickness d D of the double fold according to d D = d S - d1 - d2. Such a measuring device can be used by means of a calibration piece with a highly accurate known thickness d K which is placed between the two sensors instead of the double fold: d1 + d2 = d S - d K .

[0028] In particular, a drive device of the device can move the electromagnetic radiation source and the sensor synchronously, allowing the moving electromagnetic radiation source to emit the light and the moving sensor to detect the modified electromagnetic radiation. In this way, a section of the inner surface of the double fold, which includes the first measuring point, and a section of the outer surface of the double fold, which includes the second measuring point, can be measured, thereby more reliably determining the quality of the double fold.

[0029] Advantageously, the inner surface or the outer surface is brought into contact with a probing means of the device extending transversely to the reference plane, and the measuring module determines a distance of the second measuring point or the first measuring point from the electronic radiation source. The probing means is brought into contact with a first probing point on the inner surface of the double fold or a second probing point on the outer surface of the double fold, whereby ideally the first probing point coincides with the first measuring point or the second probing point coincides with the second measuring point. A possible distance of the first probing point from the first measuring point or of the second probing point from the second measuring point is only included in the determination of the fold width as a second-order measurement error. Accordingly, exactly one electromagnetic radiation source orexactly one sensor is required, which is arranged opposite the sensing device in relation to the double fold.

[0030] The sensor can detect a distance of 1 / 2 from the first measuring point or the second measuring point. If the distance d S of the sensor is determined by the probing means along the measuring axis, the measuring module determines the thickness d D of the double fold according to d D = d S - d 1 / 2 . Such a measuring device can be used by means of a calibration piece with a highly accurate known thickness d K which is placed between the two sensors instead of the double fold: d 1 / 2 = d S - d K .

[0031] Alternatively, the light can be emitted and detected perpendicular to the reference plane. The electromagnetic radiation source and the sensor are arranged opposite the can lid or the double seam, respectively, relative to the reference plane. In particular, the electromagnetic radiation source can emit structured light, i.e., the emitted light has a spatial structure or, in other words, is not spatially homogeneous.

[0032] Furthermore, the emitted light can be deflected to the inner surface and the outer surface by means of an optical imaging system and the diffusely reflected light can be deflected to the sensor by means of the optical imaging system. The optical imaging system can comprise one or more lenses, one or more mirrors and / or one or more gratings. If the electromagnetic radiation source is designed as a surface light and has a surface which, relative to the measuring axis, has a greater thickness than the fold width to be measured and the double fold is arranged centrally relative to the surface light, the optical imaging system can deflect the light emitted by the electromagnetic radiation source to the inner surface and the outer surface of the double fold and light reflected from the inner surface and the outer surface, i.e. also from the first measuring point and the second measuring point, to the sensor.In other words, the sensor records the first measuring point and the second measuring point simultaneously.

[0033] If the electromagnetic radiation source is designed as a surface light and has a surface that is larger than the can lid and the can lid is arranged centrally with respect to the surface light, the optical imaging system can deflect the light emitted by the electromagnetic radiation source parallel to the can lid. In particular, the electromagnetic radiation source can be designed as a ring light whose axis of symmetry coincides with the axis of symmetry of the double fold, i.e., an axis of symmetry of the ring light and an axis of symmetry of the double fold are coaxial. The emitted light is also reflected by the inner and outer surfaces of the double fold. The optical imaging system deflects the light diffusely reflected from the inner and outer surfaces, i.e., also from the first measuring point and the second measuring point, to the sensor.In other words, the sensor detects the can lid and the double seam with the first measuring point and the second measuring point simultaneously.

[0034] It is also possible for the electromagnetic radiation source to be designed as a ring sector light, i.e., only one sector of the double seam is illuminated by the electromagnetic radiation source. The measured sector of the double seam can, for example, have an approximately rectangular shape with side lengths of 2 mm or 3 mm. The ring sector light allows for a higher spatial resolution of the reflected light detected by the sensor. Furthermore, a significantly larger number of double seams can be measured with an inline measurement, and measured double seams of different cans can be particularly easily compared with one another using the image difference method, thus enabling statistical image analysis. Statistical image analysis further increases measurement accuracy.

[0035] In particular, a camera acting as the sensor can capture an image of the double seam comprising the first and second measurement points, and the measuring module can determine the distance based on the captured image. In particular, an artificial neural network of the measuring module or a traditional pattern recognition algorithm of the measuring module can evaluate the captured image and identify the first and second measurement points. The detection of the two measurement points occurs automatically and requires little computing time. Accordingly, a larger sample of double seams can be measured, thereby improving the quality of the manufactured cans.

[0036] In an alternative embodiment, the sensor detects a first shadow contour caused by the double fold and comprising the second measuring point and a second shadow contour caused by a shadow means of the device as the modified electromagnetic radiation, and the measuring module determines the distance based on a distance of the first shadow contour from the second shadow contour along the measuring axis. Alternatively, the sensor detects a light line that is bounded at the end by the second measuring point and the shadow means as the modified electromagnetic radiation, and the measuring module determines the distance as a length of the detected light line. The second shadow contour comprises an intersection point of the measuring axis with the second shadow contour. For determining the distance, i.e., the thickness of the double fold, the distance d Q of the intersection point of the second measuring point along the measuring axis is decisive.

[0037] If the distance d S of the sensor is determined by the probing means along the measuring axis, the measuring module determines the thickness d D of the double fold according to d D = d S - d Q . Such a measuring device can be used by means of a calibration piece with a highly accurate known thickness d K be calibrated, which is brought into contact with the probing device instead of the double fold: d Q = ds - d K .

[0038] Preferably, the light is emitted and detected perpendicular to the measuring axis and parallel to the reference plane. The electromagnetic radiation source and the sensor are arranged opposite one another with respect to the double fold, i.e., light detected by the electromagnetic radiation source and the sensor reaches the sensor directly without reflection.

[0039] Advantageously, an emission direction of the electromagnetic radiation source and an immission direction of the sensor are collinear. In other words, one beam path of the light is telecentric. This ensures that the first and second shadow contours detected by the sensor are perspectively undistorted. Accordingly, the measurement module can evaluate the first and second shadow contours without perspective correction.

[0040] The can body can have an at least substantially cylindrical shape, the can lid at least substantially a circular disc shape, and the double seam at least substantially a circular ring shape. Such cans are widely used as beverage cans or food cans, thus offering a wide range of possible applications for the invention. However, other can shapes are also compatible with the method according to the invention, for example, cans with a substantially rectangular can lid with rounded corners.

[0041] Another subject of the invention is a device for measuring a double seam of a can, comprising an electromagnetic radiation source for emitting electromagnetic radiation, a sensor for detecting the emitted electromagnetic radiation, and a measuring module operatively connected to the electromagnetic radiation source and the sensor for determining a thickness of the double seam to be determined during the measurement. The measuring module can be embodied as a known computing device and comprise a memory with a computer program and a processor that executes the computer program.

[0042] According to the invention, the device defines a reference plane for the double fold, and the electromagnetic radiation source is configured to emit light as the electromagnetic radiation. To measure the double fold, an end face of the double fold is aligned parallel to the reference plane. The reference plane enables the definition of a measuring axis, i.e., a measuring angle and a measuring height of a measuring point relative to the reference plane. The electromagnetic radiation source is configured as a light source to emit infrared, visible, or ultraviolet light. The device is therefore designed for ray-optical measurement of the double fold using geometric optics.

[0043] Preferably, the device is configured to carry out a method according to one of the preceding claims. In this way, the device can be integrated into a can production line and enables reliable and highly accurate determination of the seam width of a double seam of a can.

[0044] In one embodiment, the device comprises a distance sensor comprising the electromagnetic radiation source and the sensor. The distance sensor combines the electromagnetic radiation source and the sensor such that the respective optical axes, i.e., an emission direction of the electromagnetic radiation source and an immission direction of the sensor, extend collinearly. The distance sensor is preferably designed as a chromatic-confocal distance sensor for chromatic-confocal distance measurement. The chromatic-confocal distance measurement allows a distance of a measuring point from the sensor to be determined, wherein the electromagnetic radiation source of the distance sensor emits light, the emitted light is reflected at the measuring point, and the reflected light is detected by the sensor of the distance sensor.The device may include two distance sensors arranged opposite one another and aligned in such a way that their respective optical axes extend collinearly. For measurement, the double fold is placed between the two distance sensors.

[0045] The device may include a drive device for moving the distance sensor. The drive device is preferably designed to move the distance sensor in a movement plane perpendicular to the reference plane, through the measuring axis and perpendicular to the measuring axis. During the movement, the optical axes of the electromagnetic radiation source and the sensor remain parallel to the measuring axis and scan an intersection line of the movement plane with the double fold, i.e., an inner fold contour and an outer fold contour, wherein the intersection line encompasses the measuring point. If the device comprises two distance sensors, the two distance sensors are moved synchronously.

[0046] In a further embodiment, the device comprises a sensing means for positioning the double fold, a shadow means for generating a shadow contour, and / or an optical imaging system that is fixed relative to the electromagnetic radiation source and the sensor. The sensing means positions the double fold by bringing a first measuring point arranged on an inner surface of the double fold into contact with the sensing means, or by bringing a second measuring point arranged on an outer surface of the double fold into contact with the sensing means. The sensing means replaces a distance sensor and is arranged opposite the remaining distance sensor. For measurement, the double fold is arranged between the distance sensor and the sensing means, or between the shadow means and the stop means.

[0047] The optical imaging system can collimate light emitted by the electromagnetic radiation source to create a shadow contour of the can seam or the shadowing agent, which is detected by the sensor. Alternatively, the optical imaging system can focus light emitted by the electromagnetic radiation source in such a way that an inner surface, an end surface, and an outer surface of the double seam are simultaneously illuminated.

[0048] The probing means and the shadow means can each have a spherical or cylindrical shape and / or be fixed relative to the reference plane. The spherical and cylindrical shapes enable a nearly point-like contact with the can seam, thereby preventing or at least reducing first-order measurement errors caused by the probing means. It is understood that the measuring axis extends through the fixed probing means or shadow means, and the contours of the probing means or shadow means are measured with high accuracy.

[0049] The electromagnetic radiation source can be fixed relative to the reference plane. Relative fixation refers to a height relative to the reference plane and / or a position relative to the measurement axis.

[0050] Alternatively or additionally, an emission direction of the electromagnetic radiation source can extend collinearly, parallel or perpendicular to the measuring axis or perpendicular to the reference plane. The collinear or parallel extension is advantageous for a device in which the light emitted by the electromagnetic radiation source is diffusely reflected by the double fold and the diffusely reflected light is used for a distance measurement. The extension perpendicular to the measuring axis is advantageous for a device in which the light emitted by the electromagnetic radiation source is used to generate a shadow contour of the double fold. The extension perpendicular to the reference plane is advantageous for a device in which the light emitted by the electromagnetic radiation source is diffusely reflected by the double fold and the diffusely reflected light is used to image the double fold.

[0051] The sensor can be fixed relative to the reference plane. Relative fixation refers to a height relative to the reference plane and / or a position relative to the measurement axis.

[0052] Alternatively or additionally, an immission direction of the sensor can extend collinear, parallel, or perpendicular to the measuring axis or perpendicular to the reference plane. The collinear or parallel extension is advantageous for a device in which the light emitted by the electromagnetic radiation source is diffusely reflected by the double fold, and the diffusely reflected light is used for a distance measurement. The extension perpendicular to the measuring axis is advantageous for a device in which the light emitted by the electromagnetic radiation source is used to generate a shadow contour of the double fold. The extension perpendicular to the reference plane is advantageous for a device in which the light emitted by the electromagnetic radiation source is diffusely reflected by the double fold, and the diffusely reflected light is used to image the double fold.

[0053] A significant advantage of the method according to the invention is that a thickness of the double seam of a completely closed can is reliably determined with a high degree of accuracy and that integration into an automatic production of cans is possible.

[0054] Further features and advantages of the invention will be described using several embodiments and with reference to the accompanying drawings. They show: Fig. 1 is a partial cross-sectional view of a can with a double seam; Fig. 2 a partial view of a device according to a first embodiment of the invention for measuring the double fold of the Fig. 1 can shown; Fig. 3 a partial view of a device according to a second embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 4 a partial view of a device according to a third embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 5 a partial view of a device according to a fourth embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 6 a partial view of a device according to a fifth embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 7 one of the Fig. Image captured by the device shown in Figure 6; Fig. 8 is a partial view of a device according to a sixth embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 9 a partial view of a device according to a seventh embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 10 is a partial view of a device according to an eighth embodiment of the invention for measuring a double fold of the Fig. 1 can shown; Fig. 11 one of the in Fig. Image captured by the device shown in Figure 10.

[0055] Fig. 1 schematically shows a partial cross-sectional view of a can 2 with a double seam 3. The can 2 comprises a can body 20 and a can lid 21. The double seam 3 is arranged on an outer side of the can 2 and permanently connects an edge of the can lid 21 to an edge of an opening of the can body 20. The can body 20 has, for example, an at least substantially cylindrical shape, the can lid 21 at least substantially a circular disk shape and the double seam 3 at least substantially a circular ring shape.

[0056] A measuring axis 35 is defined which extends through the double fold 3 and has a measuring angle 36 relative to a reference plane 10. The measuring axis 35 comprises a first measuring point 31 on an inner surface 33 of the double fold 3. The first measuring point 31 is defined by the measuring axis 35 and has a first probing height 37 relative to a reference plane 10 defining a reference plane, which is usually referred to as the measuring height. Furthermore, the measuring axis 35 comprises a second measuring point 32 on an outer surface 34 of the double fold 3 opposite the inner surface. The second measuring point 32 is defined by the measuring axis 35 and has a second probing height 38 relative to the reference plane 10.

[0057] In addition, a thickness of the double fold 3 to be determined during the measurement, ie a fold width, is defined as a distance 30 of the second measuring point 32 from the first measuring point 31.

[0058] Fig. Fig. 2 shows schematically a partial view of a device 1 according to a first embodiment of the invention for measuring the double fold 3 of the double fold of the Fig. 1. The device 1 comprises two electromagnetic radiation sources 13 for emitting electromagnetic radiation and two sensors 14 for detecting the emitted electromagnetic radiation. The electromagnetic radiation sources 13 are configured to emit light as the electromagnetic radiation.

[0059] The electromagnetic radiation sources 13 are fixed relative to the reference plane 10. Emission directions of the electromagnetic radiation sources 13 extend collinearly with the measuring axis 35. The sensors 14 are fixed relative to the reference plane 10. Immission directions of the sensors 14 extend collinearly with the measuring axis 35. Ideally, the device 1 comprises two distance sensors, each comprising an electromagnetic radiation source 13 and a sensor 14.

[0060] The device 1 further includes a measuring module 15 operatively connected to the electromagnetic radiation sources 13 and the sensors 14 for determining a thickness of the double fold 3 to be determined during the measurement. The device 1 further defines a reference plane 10 for the double fold 3.

[0061] The device 1 is configured to measure the Fig. 1 shown can 2 to carry out a method according to an embodiment of the invention as follows.

[0062] The fully closed can 2 is prepared. One end face of the double seam 3 is aligned parallel to the reference surface 10 of the device 1.

[0063] The electromagnetic radiation sources 13 of the device 1 emit electromagnetic radiation, with light being emitted as the electromagnetic radiation. The light is emitted collinearly with the measurement axis 35.

[0064] The double fold 3 modifies the emitted electromagnetic radiation. The sensors 14 of the device 1 detect the modified electromagnetic radiation, more precisely, a light diffusely reflected by the double fold 3 as the modified electromagnetic radiation, and provide a sensor signal dependent on the detected electromagnetic radiation. The measuring module 15 of the device 1 determines the distance 30 based on the provided sensor signals.

[0065] Fig. 3 shows schematically a partial view of a device 1 according to a second embodiment of the invention for measuring a double fold 3 of the Fig. 1 shown can 2. The device 1 has the same basic structure as the one shown in Fig. 2. Additionally, the device 1 comprises a drive device 16 for moving the distance sensors. However, the emission directions of the electromagnetic radiation sources 13 and the immission directions of the sensors 14 extend parallel to the measuring axis 35.

[0066] To measure the double seam 3 of the can 2, the light is emitted parallel to the measuring axis 35, the drive device 16 of the device 1 moves the electromagnetic radiation sources 13 and the sensors 14 synchronously, the moving electromagnetic radiation sources 13 emit the light and the moving sensors 14 detect the modified electromagnetic radiation.

[0067] Fig. 4 shows schematically a partial view of a device 1 according to a third embodiment of the invention for measuring a double fold 3 of the Fig. 1 shown can 2. The device 1 has the same basic structure as the one shown in Fig. 1. Deviating from this, the device 1 comprises precisely one electromagnetic radiation source 13 and precisely one sensor 14, i.e., precisely one distance sensor. In addition, the device 1 comprises a sensing means 11 for positioning the double fold 3. The sensing means 11 is fixed relative to the reference plane 10 and arranged opposite the distance sensor and extends transversely to the reference plane 10.

[0068] The sensing element 11 has a spherical shape. Relative to the double fold 3, the distance sensor is arranged on an outer side, and the sensing element 11 is arranged on an inner side of the double fold 3, opposite the outer side.

[0069] To measure the double seam 3 of the can 2, the inner surface 33 is brought into contact with the probe 11 of the device 1. The measuring module 15 determines the distance of the second measuring point 32 from the electronic radiation source 13.

[0070] Fig. Fig. 5 shows schematically a partial view of a device 1 according to a fourth embodiment of the invention for measuring a double fold 3 of the Fig. 1 shown can 2. The device 1 has the same basic structure as the one shown in Fig. Device shown in Figure 4.

[0071] In contrast, the sensing element 11 has a cylindrical shape. Furthermore, with respect to the double fold 3, the distance sensor is arranged on the inside and the sensing element 11 is arranged on the outside.

[0072] To measure the double seam 3 of the can 2, the outer surface 34 is brought into contact with the probe 11 of the device 1. The measuring module 15 determines the distance of the first measuring point 31 from the electronic radiation source 13.

[0073] Fig. Fig. 6 shows schematically a partial view of a device 1 according to a fifth embodiment of the invention for measuring a double fold 3 of the Fig. 1 shown can 2. The device 1 comprises an electromagnetic radiation source for emitting electromagnetic radiation, a sensor for detecting the emitted electromagnetic radiation and a measuring module operatively connected to the electromagnetic radiation source and the sensor for determining a thickness of the double fold 3 to be determined during the measurement. The electromagnetic radiation source is configured to emit light as the electromagnetic radiation.

[0074] The electromagnetic radiation source and the sensor are arranged opposite each other in front of and behind the section plane, i.e., outside the plane of the paper, and therefore, like the measuring module, are not shown in the figure. The electromagnetic radiation source is fixed relative to the reference plane 10. An emission direction of the electromagnetic radiation source 13 extends perpendicular to the measurement axis 35. The sensor is fixed relative to the reference plane 10. An immission direction of the sensor extends perpendicular to the measurement axis 35.

[0075] The device 1 further comprises a reference plane 10 for the double fold 3, a sensing means 11 for positioning the double fold 3, and a shadow means 12 for generating a shadow contour. The sensing means 11 and the shadow means 12 each have a spherical shape and are fixed relative to the reference plane 10.

[0076] The electromagnetic radiation source is designed as a surface light source and arranged such that the measuring axis 35 lies in a light volume emitted by the electromagnetic radiation source.

[0077] To measure the double seam 3 of the can 2, the light is emitted and detected perpendicular to the measuring axis 35 and parallel to the reference plane 10. The sensor detects light diffusely reflected from the double seam 3 as the modified electromagnetic radiation. An emission direction of the electromagnetic radiation source and an immission direction of the sensor are parallel.

[0078] A camera as the sensor captures an image 4 of the double fold 3 comprising the first measuring point 31 and the second measuring point 32. The measuring module 15 determines the distance 30 based on the captured image 4.

[0079] Fig. 7 shows a Fig. Image 4 captured by the device 1 shown in Figure 6.

[0080] The sensor 14 detects a first shadow contour 40 caused by the double fold 3 and encompassing the second measuring point 32, and a second shadow contour 41 caused by a shadowing means 12 of the device 1 as the modified electromagnetic radiation. The measuring module determines the distance 30 based on the distance between the first shadow contour 40 and the second shadow contour 41 along the measuring axis 35.

[0081] Fig. Fig. 8 shows schematically a partial view of a device 1 according to a sixth embodiment of the invention for measuring a double fold 3 of the Fig. 1 shown can 2. The device 1 has the same basic structure as the one shown in Fig. The device shown in Figure 7.

[0082] Deviating from this, the electromagnetic radiation source is designed as a line light source and arranged such that the measuring axis 35 lies in a light plane emitted by the electromagnetic radiation source.

[0083] The sensor detects a light line 42, which is bounded at the end by the second measuring point 32 and the shadowing device 12, as the modified electromagnetic radiation. The measuring module determines the distance 30 as the length of the detected light line 42.

[0084] Fig. 9 shows schematically a partial view of a device 1 according to a seventh embodiment of the invention for measuring a double fold 3 of the Fig. 1. The device 1 comprises an electromagnetic radiation source 13 for emitting electromagnetic radiation and a sensor 14 for detecting the emitted electromagnetic radiation. The electromagnetic radiation source 13 is configured to emit light as the electromagnetic radiation. The device 1 further defines a reference plane 10 for the double fold 3.

[0085] The electromagnetic radiation source 13 is fixed relative to the reference plane 10. An emission direction of the electromagnetic radiation source 13 extends perpendicular to the reference plane 10. The sensor 14 is fixed relative to the reference plane 10. An emission direction of the sensor 14 extends perpendicular to the reference plane 10.

[0086] The device 1 further includes an optical imaging system 17, which is fixed relative to the electromagnetic radiation source 13 and the sensor 14, and a measuring module 15 operatively connected to the electromagnetic radiation source 13 and the sensor 14 for determining a thickness of the double fold 3 to be determined during the measurement. The optical imaging system 17 can comprise one or more lenses, one or more mirrors and one or more gratings.

[0087] The electromagnetic radiation source 13, the sensor 14 and the optical imaging system 17 are configured to measure exclusively a circular ring section of the double fold 3.

[0088] To measure the double seam 3 of the can 2, the light is emitted and detected perpendicular to the reference plane 10. An emission direction of the electromagnetic radiation source 13 and an immission direction of the sensor 14 are parallel. The emitted light is deflected by the lens 17 toward the inner surface 33 and the outer surface 34, and the diffusely reflected light is deflected by the lens 17 toward the sensor 14.

[0089] The sensor 14 detects the light diffusely reflected by the double fold 3 as modified electromagnetic radiation. A camera acting as the sensor 14 captures an image 4 of the double fold 3 comprising the first measuring point 31 and the second measuring point 32. The measuring module 15 determines the distance 30 based on the captured image.

[0090] Fig. 10 shows schematically a partial view of a device 1 according to an eighth embodiment of the invention for measuring a double fold 3 of the Fig. 1 shown can 2. The device 1 has the same basic structure as the one shown in Fig. The device shown in Figure 9.

[0091] Deviating from this, the device 1 does not comprise an optical imaging system 17 and the electromagnetic radiation source 13 and the sensor 14 are configured, in particular in a ring shape or a ring sector shape, to measure the entire circular ring arc of the double fold 3 or a sector of the circular ring arc.

[0092] Fig. 11 shows a Fig.10. Image 5 comprises a circular line 50 of first measuring points 31 and a circular line 51 with second measuring points 32. Furthermore, image 5 comprises a third circular line 52 corresponding to a circumferential contour of the can body 20 and a fourth circular line 53 corresponding to a groove of the can lid 21. Alternatively, a ring-sector-shaped image section 54 can be captured as image 5. List of reference symbols 1 device 10 Reference plane 11 probing devices 12 shade products 13 electromagnetic radiation source 14 Sensor 15 measuring module 16 Drive device 17 optical imaging system 2 cans 20 can bodies 21 can lids 3 double fold 30 distance 31 first measuring point 32 second measuring point 33 inner surface 34 exterior surface 35 measuring axis 36 measuring angles 37 first contact height 38 second probing height 4 Image 40 first shadow contour 41 second shadow contour 42 Light line 5 Image 50 first circle line 51 second circle line 52 third circle line 53 fourth circle line 54 Image detail

Claims

[1] Method for measuring a double seam (3) of a can (2), in which - a completely closed can (2) is provided, which comprises a can body (20) and a can lid (21) and has a double seam (3) which is arranged on an outer side of the can (2) and non-detachably connects an edge of the can lid (21) to an edge of an opening of the can body (20); - a first measuring point (31) on an inner surface (33) of the double fold (3), a second measuring point (32) on an outer surface (34) of the double fold (3) opposite the inner surface (33), a measuring axis (35) extending through the first measuring point (31) and the second measuring point (32) and a thickness of the double fold (3) to be determined during the measurement are defined as a distance (30) of the second measuring point (32) from the first measuring point (31); - an end face of the double fold (3) is brought into contact with a reference surface (10) of a device (1); - an electromagnetic radiation source (13) of the device (1) emits light as electromagnetic radiation, the double fold (3) modifies the emitted electromagnetic radiation, a sensor (14) of the device (1) detects the modified electromagnetic radiation and provides a sensor signal dependent on the detected electromagnetic radiation, and a measuring module (15) of the device (1) determines the distance (30) depending on the provided sensor signal. [2] Method according to claim 1, characterized by that the sensor (14) detects a light diffusely reflected from the double fold (3) as the modified electromagnetic radiation. [3] Method according to claim 2, characterized by that the light is emitted and detected collinearly or parallel to the measuring axis (35). [4] Method according to claim 3, characterized by that a drive device (16) of the device (1) moves the electromagnetic radiation source (13) and the sensor (14) synchronously, the moving electromagnetic radiation source (13) emits the light and the moving sensor (14) detects the modified electromagnetic radiation. [5] Method according to claim 3, characterized by that the first measuring point (31) or the second measuring point (32) is brought into contact with a stop means (11) of the device (1) extending transversely to the reference surface (10) and the measuring module (15) determines a distance of the second measuring point (32) or the first measuring point (31) from the electronic radiation source (13). [6] Method according to claim 2, characterized by that the light is emitted and detected perpendicular to the reference plane (10). [7] Method according to claim 6, characterized bythat the emitted light is deflected by means of a lens (17) to the inner surface (33) and the outer surface (34) and the diffusely reflected light is deflected by means of the lens (17) to the sensor (14). [8] Method according to claim 6 or 7, characterized by that a camera as the sensor (14) captures an image of the double fold (3) comprising the first measuring point (31) and the second measuring point (32) and the measuring module (5) determines the distance (30) based on the captured image. [9] Method according to claim 1, characterized byin that the sensor (14) detects a first shadow contour (40) caused by the double fold (3) and comprising the second measuring point (32) and a second shadow contour (41) caused by a shadow means (12) of the device (1) as the modified electromagnetic radiation and the measuring module (15) determines the distance (30) based on a distance of the first shadow contour (40) from the second shadow contour (41) along the measuring axis (35) or the sensor (14) detects a light line (42) which is delimited at the end by the second measuring point (32) and the shadow means (12) as the modified electromagnetic radiation and the measuring module (15) determines the distance (30) as a length of the detected light line (42). [10] Method according to claim 9, characterized by that the light is emitted and detected perpendicular to the measuring axis (35) and parallel to the reference plane (10). [11] Method according to one of claims 1 to 10, characterized bythat an emission direction of the electromagnetic radiation source (13) and an immission direction of the sensor (14) are collinear. [12] Method according to one of claims 1 to 11, characterized by that the can body (20) has an at least substantially cylindrical shape, the can lid (21) has at least substantially a circular disk shape and the double seam (3) has at least substantially a circular ring shape. [13] Device (1) for measuring a double seam (3) of a can (2), which device comprises a contact surface (10) for the double seam (3), an electromagnetic radiation source (13) for emitting electromagnetic radiation which is configured to emit a light as the electromagnetic radiation, a sensor (14) for detecting the emitted electromagnetic radiation and a measuring module (15) which is operatively connected to the electromagnetic radiation source (13) and the sensor (14) for determining a thickness of the double seam (3) to be determined during the measurement and is configured to carry out a method according to one of the preceding claims. [14] Device according to claim 13, characterized by a distance sensor comprising the electromagnetic radiation source (13) and the sensor (14). [15] Device according to claim 14, characterized by a drive device (16) for moving the distance sensor. [16] Device according to one of claims 13 to 15, characterized by a stop means (11) for positioning the double fold (3), a shadow means (12) for generating a shadow contour (41) and / or a lens (17) which is fixed relative to the electromagnetic radiation source (13) and the sensor (14). [17] Device according to claim 16, characterized by that the stop means (11) has a spherical shape or a cylindrical shape and / or is fixed relative to the reference surface (10). [18] Device according to one of claims 13 to 17, characterized by that the electromagnetic radiation source (13) is fixed relative to the reference surface (10) and / or an emission direction of the electromagnetic radiation source (13) extends collinearly, parallel or perpendicular to the measuring axis (35) or perpendicular to the reference surface (10). [19] Device according to one of claims 13 to 18, characterized bythat the sensor (14) is fixed relative to the reference surface (10) and / or an emission direction of the sensor (14) extends collinearly, parallel or perpendicular to the measuring axis (35) or perpendicular to the reference surface (10).

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