Method and apparatus for detecting imperfections during sealing of a package containing a film - Patents.com

Abstract

The invention relates to a method for detecting defective sealing of a package, which comprises positioning the film and other parts of the package between two sealing bars and successively closing and opening the sealing bars, at least during the closing of the sealing bars, the distance between both sealing bars or between the sealing bar and the sealing bar holder is measured by means of a distance sensor, a unitless measure of deviation at a certain time T is calculated and compared with a threshold value, the unitless measure of deviation being calculated from the relative measure of the distance between both sealing bars or between the sealing bar and the sealing bar holder. The invention also relates to an apparatus and an application.

Description

[Technical field]

[0001] The invention relates to a method for detecting imperfections during the sealing of packages containing a film, in particular when the sealing is performed using two sealing bars. Summary of the Invention

[0002] prior art A wide range of products are packaged in hermetically sealed packages to extend the shelf life of the product, to ensure quality and / or to maintain sterility. Such products range from food and beverages to various medical products, electronic products and pharmaceuticals. A key point in the packaging process is to ensure high quality sealing of the package. One of the factors that determines the quality of the seal is the tightness. This is certainly a very important aspect in the case of food and beverages, where poor sealing quality can lead to a very rapid deterioration of the quality of the packaged product. Other possible factors that affect the quality of the seal are for example the presence of inclusions in the seal. As a result, the strength of the seal is reduced, which can also directly affect the tightness of the seal. In the packaging industry, poor quality seals are a common problem when films are used to seal packages. Therefore, devices and methods are used in the packaging industry to automatically detect imperfections during the sealing of packages with films.

[0003] Such an apparatus is known in particular from EP 2 804 742 (EP'742). EP'742 describes an apparatus and a method for detecting imperfections during sealing of a package with a film. The apparatus comprises at least one distance sensor for measuring the distance between two sealing bars during sealing of the package with a film. The measured distance is measured during sealing and compared with a predefined reference value. If at least one measured distance exceeds at least one predefined reference value, a signal is generated. This signal is indicative of an insufficient quality of the seal.

[0004] The known device and method have the disadvantage that they are only suitable for use with packaging machines which allow the device and method to measure the distance between two sealing bars. Devices for automatically detecting imperfections are often installed later on in the packaging machine. Depending on the construction of the packaging machine, it is not always possible to install a distance sensor in the packaging machine so that the distance between the sealing bars can be effectively measured, so that the use of the device and method from EP'742 is not feasible. In addition, the method described in EP'742 does not take into account transition effects which may occur, for example, when starting up the packaging machine, or variations in, for example, the thickness of the film, the temperature of the packaging machine or the temperature of the sealing bars.

[0005] The present invention aims to address at least some of the above problems or shortcomings.

[0006] Summary of the Invention In a first aspect, the present invention relates to a method according to claim 1.

[0007] This method is very advantageous because it is possible to detect imperfections during sealing of a package containing a film, both when the distance between two sealing bars can be measured and when the packaging machine has such a structure, and it is not possible to measure the distance between the sealing bars directly or indirectly by a distance sensor. The detection of imperfections during sealing is based on the relative displacement of the sealing bars, or on the relative displacement of the sealing bars with respect to the sealing bar holder, if it is not possible to measure the distance between the sealing bars directly or indirectly. Since the method works with the relative displacement, it is not necessary to know the absolute distance between the sealing bars.

[0008] Preferred embodiments of the method are described in claims 2 to 11, including claim 11.

[0009] A particular preferred embodiment relates to the method according to claim 2.

[0010] This preferred embodiment is advantageous since two relative displacements are taken into account, namely the displacement along the trajectory A and the rotation around the axis E. As a result, the inaccuracies that may occur when it is not possible to measure the distance between the sealing bars are almost completely compensated for. An additional advantage is that imperfections can also be detected, in which, for example, in the middle of the sealing bar, a similar displacement along the trajectory A is obtained according to the longitudinal direction of the sealing bar as in the case of correct sealing of packages containing a film, while more towards the end of the sealing bar there are inclusions, which in fact do not result in a quality seal.

[0011] A particular preferred embodiment relates to the method according to claim 7.

[0012] This preferred embodiment has the advantage that when calculating the item of unitless measurement of deviation, the dynamic behavior during sealing of the package containing the film is taken into account, e.g. due to heating of the packaging machine, due to an increase or decrease in the thickness of the film, due to an increase or decrease in the tension on or in the film, due to temperature changes of the packaging machine or the sealing bar, etc. As a result, defects can be detected with a higher sensitivity, since the dynamic behavior at a certain threshold value needs to be taken into account less or not at all.

[0013] In a second aspect, the invention relates to an apparatus according to claim 12.

[0014] This embodiment is advantageous because the apparatus comprises the distance sensors necessary to perform the method and because this results in an integrated apparatus for detecting imperfections in the sealing of packages containing a film even when it is not possible to determine the absolute distance between the sealing bars.

[0015] Preferred embodiments of the device are set out in the dependent claims 13 to 16, inclusive.

[0016] In a third aspect, the present invention relates to the use according to claim 17.

[0017] This use results in improved packaging of food products, since possible imperfections during the sealing of food packages are automatically detected, even when using packaging machines whose construction does not allow measuring the distance between the sealing bars of the packaging machine. This prevents food products that may quickly spoil, for example because they are not airtight packaged, from entering the food chain, with the risk of food poisoning for example. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 shows a schematic representation of an arrangement of distance sensors in a sealing bar holder of a device according to an embodiment of the invention. [Diagram 2] FIG. 2 shows a schematic representation of the arrangement of distance sensors in a sealing bar holder of a device according to an alternative embodiment of the invention. [Diagram 3] FIG. 3 shows a schematic representation of an arrangement of distance sensors in a sealing bar holder of an apparatus according to yet another alternative embodiment of the invention. [Figure 4] FIG. 4 shows a three-dimensional representation of the arrangement of distance sensors in a sealing bar holder of a device according to another alternative embodiment of the invention. [Diagram 5] FIG. 5 shows a diagram of a method according to an embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Detailed Description Unless otherwise specified, all terms used in the description of the invention, including technical and scientific terms, have the meanings commonly understood by one of ordinary skill in the art to which the invention pertains. In order to better understand the description of the present invention, the following terms are expressly explained.

[0020] In this document, "a," "an," and "the" refer to both the singular and the plural, unless the context dictates otherwise. For example, "a segment" means one or more segments.

[0021] The terms "comprise," "comprising," "consist of," "consisting of," "provided with," "include," "including," "contain," and "containing" are synonymous and are inclusive or open-ended terms indicating the presence of what is below and do not exclude or preclude the presence of other components, features, elements, materials, or steps that are known from or disclosed in the prior art.

[0022] Citations of numerical intervals by endpoints include all integer, fractional and / or real numbers between the endpoints, including the endpoints.

[0023] Moreover, terms such as "first," "second," "third," etc. are used in the specification and claims to distinguish between like elements and do not necessarily denote a sequential or chronological order, unless specified. The terms so used are interchangeable, under appropriate circumstances, and it is understood that the embodiments of the invention described herein may operate in sequences other than those described or illustrated herein.

[0024] In this document, two distance sensors lying symmetrically with respect to an axis in a plane means that the vertical distance from the first distance sensor to the projection of said axis on said plane differs from the vertical distance from the second distance sensor to said projection by at most 10%, preferably at most 5%, more preferably at most 2%, even more preferably at most 1% and even more preferably at most 0.5%.

[0025] In a first aspect, the invention relates to a method for detecting imperfections during sealing of a package containing a film.

[0026] According to a preferred embodiment, the method comprises the following steps: - positioning the film and the other parts of the package containing the film between two parallel sealing bars; - moving one or both sealing bars towards each other along trajectory A so that a connection is formed between the film and other parts of the film-containing package; - moving one or both sealing bars along trajectory A so that the sealing bars are separated from each other; - and remove the sealed package.

[0027] Non-limiting examples of packages containing a film are a tray sealed with a film, a preformed pouch with one open side, and a pouch formed by sealing a tubular film at two ends. A tubular film is a seamless film with two open ends. The film is folded closed to package an article in the tubular film. Alternatively, the tubular film is formed from a flat film around a tube, and the two edges of the film are sealed together along the length of the tube. The tubular film is sealed at a first end, and then the article to be packaged is placed in the pouch and the second end is sealed. It is not until the article is packaged in the tubular film that the tubular shape is created. In the case of a preformed pouch with one open side, the pouch is first filled with the article to be packaged and then sealed at the open side. In the case of a tray, the other part of the package containing the film is, for example, the protruding edge of the tray to which the film is adhered. In the case of a pouch, the film and other portions of the package including the film are the two opposing sides of a tubular film that has been folded closed. In the case of a preformed pouch having one open side, the film and other portions of the package including the film are the two opposing sides of a preformed pouch.

[0028] Non-exhaustive examples of imperfections include product or other packaging material in the seal, creases in the seal, a seal that is too narrow or too wide, no seal, a seal that is not straight, and the like.

[0029] The two sealing bars extend in a longitudinal direction. The sealing bar therefore has a longitudinal direction, a height direction and a lateral direction. The longitudinal direction determines the maximum dimension of the sealing bar. The two sealing bars are parallel along the longitudinal direction. Each sealing bar is mounted on its own sealing bar holder. The sealing bars are preferably releasably mounted on the sealing bar holder. This is advantageous for cleaning and replacement of the sealing bars. The sealing bar is moved by moving its own sealing bar holder. The sealing bar includes a longitudinal axis. The longitudinal axis is parallel to the longitudinal direction.

[0030] Said longitudinal direction of the sealing bar is transverse to the line represented by the trajectory A during the movement of one or both sealing bars along the trajectory A. The trajectory A may be represented by a straight line, a circular arc or any other suitable curve. Preferably, the trajectory A is a straight line. By moving one or both sealing bars towards each other along the trajectory A, the film and the other part of the package containing the film are clamped together. Now, a connection is formed between the film and the other part of the package containing the film, for example in the case of a tray, because a layer of glue is applied to the edge of the tray and because the clamping causes the film to adhere to the edge of the tray. Another possibility is that the film and the edge of the tray are clamped together between two sealing bars and the two sealing bars are heated, so that the film and the edge of the tray are welded together. For example, in the case of a preformed pouch or tubular film with one open side, the two opposing faces of the folded closed tubular film or preformed pouch are clamped together at the ends of the respective open sides between two sealing bars, and the two sealing bars are heated, resulting in the two opposing faces being welded together. When sealing a package containing a film by heating the sealing bar, the sealing bar can be heated either continuously or pulsed. An alternative is that the sealing bar is an ultrasonic sealing jaw. Depending on the design of the packaging machine, multiple packages containing a film can be sealed simultaneously between the two sealing bars.

[0031] It will be clear to a person skilled in the art that if both sealing bars are moved, then both sealing bars are moved in opposite senses along the trajectory A. It will also be clear to a person skilled in the art that during the sealing bars are moved away from each other, they are moved in the opposite direction as during the movement of the two sealing bars towards each other. It will also be clear to a person skilled in the art that if only one sealing bar is moved, then preferably the same sealing bar is always moved.

[0032] During the step of moving at least one or both sealing bars towards each other, the distance between the sealing bars or between the sealing bar and the sealing bar holder is measured using a number of distance sensors, non-limiting examples of suitable distance sensors include laser distance meters, ultrasonic transceivers, capacitive distance sensors and inductive distance sensors.

[0033] Preferably, the distance between both sealing bars is measured using multiple distance sensors. If this is not possible, for example due to the mechanical structure of the packaging machine, the distance between the sealing bar and the sealing bar holder is measured using multiple distance sensors. That is, the distance between the sealing bar and its sealing bar holder is measured using multiple distance sensors. The distance between the sealing bar and the sealing bar holder is measured for one or both sealing bars. Preferably, the distance between the sealing bar and the sealing bar holder is measured for both sealing bars. When the distance between the sealing bar and the sealing bar holder is measured, the sealing bar and the sealing bar holder are attached to each other in a spring-loaded manner. That is, by moving the sealing bar holder along the trajectory A, the sealing bar attached to it is also moved along the trajectory A, and when both sealing bars come into contact with each other or with a package containing a film, the sealing bar moves along the trajectory A when there is a further displacement of its own sealing bar holder relative to its own sealing bar holder due to the pressure of one or more springs.

[0034] A plurality of distance sensors for measuring the distance between two sealing bars or between a sealing bar and its sealing bar holder are advantageous for determining a measurement of the displacement of a point D of two sealing bars relative to each other along a trajectory A or a measurement of the displacement of a point D of a sealing bar relative to its own sealing bar holder along a trajectory A, where the point D is in the center of the sealing surface of the sealing bar. The sealing surfaces of both sealing bars are the surfaces which are in contact with the film or other parts of the film-containing package, all or part of which are clamped between them, during the sealing of the film-containing package. The film-containing package is usually sealed in the center between the sealing bars, which is advantageous for determining a measurement of the displacement along the trajectory at the point D. Due to the mechanical structure of the packaging machine, it is often practically impossible to install a distance sensor at or near the point D. The measurement of the displacement along the trajectory can easily be determined, for example, by calculating a weighted average of the distances measured by the distance sensors, the weights for the distances in the weighted average depending on the longitudinal distance from the distance sensor to point D. A distance sensor that is equidistant longitudinally from point D is advantageous because it is not necessary to know the exact longitudinal distance between the distance sensor and point D.

[0035] Measuring the displacement along trajectory A is advantageous for detecting imperfections in the sealing of packages containing the film.

[0036] For example, if there is an inclusion of a packaged product, e.g., food, between the film and other parts of the film-containing package, the two sealing bars can be moved towards each other less than normal along path A. If the sealing bar is attached to its own sealing bar holder in a spring-loaded manner, the sealing bar will be moved more towards its own sealing bar holder along path A. Thus, even if the distance between both sealing bars cannot be measured, by measuring the distance between the sealing bar and its own sealing bar holder, a measurement of the displacement along path A can be determined, which can be used to detect imperfections during sealing.

[0037] The method includes the additional steps of calculating a unitless measurement of deviation at a time T and comparing the unitless measurement of deviation with a predefined threshold. If the unitless measurement of deviation is equal to or less than the predefined threshold, the resulting seal is considered a correct sealing of the package including the film. The time T is in a time interval in which the measured distance changes or has changed due to the movement of one or both sealing bars towards each other. The time T is before the time when one or both sealing bars are moved away from each other. That is, the unitless measurement of deviation is calculated simultaneously at the time T when the package including the film is or has already been sealed by the sealing bars. Only one unitless measurement of deviation is calculated.

[0038] A unitless measurement of deviation is calculated from the relative measurement of the distance between both sealing bars or between the sealing bar and the sealing bar holder.

[0039] A relative measurement value for the distance between both sealing bars or between a sealing bar and its sealing bar holder is calculated from the previously described measurements of the displacements along the trajectory A of the points D of the two sealing bars relative to each other or from the previously described measurements of the displacements along the trajectory A of the points D of a sealing bar relative to its own sealing bar holder, respectively, relative to an expected value for the distance between the two sealing bars and relative to an expected value for the distance between a sealing bar and its own sealing bar holder. Alternatively, a relative measurement value for the distance between both sealing bars or between a sealing bar and a sealing bar holder is calculated as a difference between an expected value for the distance between the two sealing bars or between a sealing bar and its own sealing bar holder, respectively, and said measurement value for the displacement along the trajectory A, relative to a set variance for said difference. The expected value for the distance and / or the set variance is preferably determined based on statistical data on the distances measured using a distance sensor.

[0040] The method according to the present embodiment is very advantageous because it is possible to detect imperfections during sealing of a package containing a film both when the distance between two sealing bars is measurable and when the packaging machine has such a structure that it is not possible to directly or indirectly measure the distance between the sealing bars by a distance sensor. The detection of imperfections during sealing is based on the relative displacement of the sealing bars relative to each other, or, if it is not possible to directly or indirectly measure the distance between the sealing bars, on the relative displacement of the sealing bar relative to its own sealing bar holder. Since the method works with the relative displacement, it is not necessary to know the absolute distance between the sealing bars.

[0041] According to a preferred embodiment, the unitless measure of deviation is the root of a weighted square sum of at least two terms. The first term is a relative measure of the distance between both sealing bars or between a sealing bar and a sealing bar holder. The relative measure of the distance between both sealing bars or between a sealing bar and its sealing bar holder is the same as in the previous embodiment. The second term is a relative measure of the rotation of the sealing bar around axis E.

[0042] Thus, a unitless measure of deviation is calculated according to the following formula:

number

[0043] A number of distance sensors are advantageous for determining a measurement of the rotation of the sealing bar around the axis E at a time when the axis E intersects the sealing bar, the axis E being transverse to the trajectory A and transverse to the longitudinal direction of the sealing bar. Transverse to the trajectory A means transverse to a line representing the trajectory A at the position on the trajectory where the sealing bar is located at said time. The axis E preferably passes through the point D of the sealing bar. For example, the measurement of the rotation around the axis E is determined by calculating the difference between the distances measured by distance sensors located on either side of the point D in the longitudinal direction and / or at different longitudinal distances from the point D. This difference is proportional to the rotation. If the distance sensors are not equidistant from the point D along the longitudinal direction, the measured distances are given a weight that depends on the distance from the distance sensor to the point D in the longitudinal direction. This difference can be converted into a rotation angle. However, as will become clear from the further description, this is not necessary for the method. Distance sensors located equidistant from, and on different sides longitudinally of, point D are advantageous because it is not necessary to know the exact longitudinal distance between the distance sensors and point D. Since no rotation angle is used, it is also not necessary to know the exact longitudinal distance between the distance sensors and point D.

[0044] Measurements of displacement along trajectory A and of rotation about axis E are particularly advantageous for detecting imperfections in the sealing of packages containing the film.

[0045] The advantages of measuring the displacement along trajectory A are similar to those in the previously described embodiment.

[0046] In the case of inclusions located mostly on one side of the sealing bar along the longitudinal direction, the sealing bars will each rotate about axis E when moving towards each other, for example along trajectory A. This rotation is due to the spring-loaded mounting of the sealing bars to their own sealing bar holders and / or due to mechanical tolerances of the mounting of the sealing bars to the sealing bar holders. When measuring the distance between both sealing bars, the measurement of the rotation about axis E is a measurement of the combined rotation of both sealing bars. Thereby, it is irrelevant in the method which rotation each sealing bar undergoes individually. For a sealing bar that is spring-loaded mounted to its own sealing bar holder, the sealing bar will move more towards its own sealing bar holder at one end than at the other end. Thus, even if it is not possible to measure the distance between both sealing bars, by measuring the distance between the sealing bar and its own sealing bar holder, it is possible to determine a measurement of the rotation about axis E and use this to detect imperfections during sealing.

[0047] The second term is then calculated from said measured value of the rotation of the sealing bar around the axis E against an expected value of the rotation of the sealing bar around the axis E. As mentioned before, the rotation is not necessarily expressed in degrees. This is also not necessary for the expected value of the rotation. Alternatively, the second term is calculated as the difference between the expected value of the rotation of the sealing bar around the axis E and said measured value of the rotation of the sealing bar around the axis E in conjunction with a set variance of said difference. The expected value of the rotation and / or the set variance are preferably determined on the basis of statistical data on distances measured by means of a distance sensor.

[0048] Weight w i is preferably an item term calculated based on a preliminary test in which a package containing the film is sealed by a packaging machine. iThe packaging machine is determined based on statistical data regarding the packaging machine being the same or similar to the packaging machine that will be used to seal the package containing the film.

[0049] In the case of a weighted sum of squares of only the first and second terms, the weighted sum of squares can be considered as the equation of an ellipse. As mentioned before, if the unitless measure of deviation is below a predefined threshold, the resulting seal is considered a correct sealing of the package containing the film. This can be compared to checking whether the unitless measure of deviation is within or on an ellipse, where the length of the axis of the ellipse is the weight w in the weighted sum of squares. i and by a predefined threshold.

[0050] The relative sizes are advantageous because they allow equal or nearly equal thresholds to be used for similar packaging machines, without precise distances being required in this regard.

[0051] This embodiment is particularly advantageous, since two relative displacements are taken into account, namely the displacement along the trajectory A and the rotation around the axis E. As a result, possible inaccuracies when it is not possible to measure the distance between the sealing bars are almost completely compensated for. An additional advantage is that imperfections can also be detected, in which, for example in the middle of the sealing bar, a displacement along the trajectory A is obtained that is similar to that in the case of correct sealing of a package containing a film, according to the longitudinal direction of the sealing bar, but towards the end of the sealing bar there are inclusions, whereby in fact a good quality seal is not obtained.

[0052] According to a preferred embodiment, the first term is the difference between the expected value for the distance between both sealing bars or between a sealing bar and a sealing bar holder, respectively, and the calculated distance between both sealing bars or between a sealing bar and a sealing bar holder, divided by a set variance for the determined difference between the expected value for the distance and the calculated distance. And the calculated distance between both sealing bars or between a sealing bar and a sealing bar holder is a measurement for the displacement along the trajectory A of the points D of the two sealing bars relative to each other or of the central point D of a sealing bar relative to its own sealing bar holder. The set variance is preferably determined based on a preliminary test in which a package containing the film is sealed on a packaging machine, which is the same or similar to the packaging machine that will be used to seal the package containing the film. Preferably, the variance of said difference is calculated after the test is completed for a seal judged by the operator to be of sufficient quality. The calculated variance is preferably based on a Gaussian distribution. The set variance is preferably at most 5 times the calculated variance, more preferably at most 4 times the calculated variance, even more preferably at most 3 times the calculated variance, even more preferably equal to 3 times the calculated variance. The expected value for distance is a weighted average of the calculated distances between the two sealing bars and between the sealing bar and the sealing bar holder, respectively, in case of correct sealing of the package containing the film. Preferably, more weight is given to the more recently calculated distances. The expected value for distance is preferably a weighted average of the calculated distances for sealings that are initially judged to be of sufficient quality by the operator after tests are completed or when the packaging machine is started up.

[0053] Therefore, the first term 1 ) is calculated according to the following formula:

number

[0054] This embodiment is advantageous because it allows the calculation in a simple manner of relative measurements of the distance between two sealing bars or between a sealing bar and its sealing bar holder. Relative sizes are advantageous as mentioned above because they allow equal or nearly equal predetermined thresholds to be used for similar packaging machines. Exact distances are not necessary in this regard.

[0055] According to a preferred embodiment, the second term is the difference between the expected value for the rotation of the sealing bar around the axis E and the calculated rotation of the sealing bar around the axis E, divided by a set variance for said difference between the expected value for the rotation around the axis E and the calculated rotation around the axis E. As mentioned before, there is no need to convert the rotation into a rotation angle. And the calculated rotation of the sealing bar around the axis E is a measurement of the rotation of the sealing bar around the axis E. The set variance is preferably determined based on a preliminary test of sealing a package containing the film with a packaging machine, the packaging machine being the same or similar to the packaging machine that will be used to seal the package containing the film. Preferably, after the test is completed for sealings judged by the operator to be of sufficient quality, the variance of said difference is calculated. The calculated variance is preferably based on a Gaussian distribution. And the set variance is preferably at most 5 times the calculated variance, more preferably at most 4 times the calculated variance, even more preferably at most 3 times the calculated variance, even more preferably equal to 3 times the calculated variance. The expected value for rotation about axis E is a weighted average of the calculated rotations about axis E for correct sealing of the package containing the film, preferably with more weight given to more recently calculated distances. The expected value for rotation about axis E is preferably initially a weighted average of the calculated rotations about axis E for seals that are judged to be of sufficient quality by the operator after testing is completed or when the packaging machine is started up.

[0056] Therefore, the second term 2 ) is calculated according to the following formula:

number

[0057] This embodiment is advantageous because it allows the relative measurements of the rotation of the sealing bars around the axis E to be calculated in a simple manner. The relative sizes are advantageous as mentioned above because they make it possible to use predetermined thresholds that are equal or nearly equal for similar packaging machines. No exact angle or distance of rotation is necessary in this regard.

[0058] According to one embodiment, the weighted sum of squares includes two terms. The two terms are the first and second terms mentioned above. Since only the first and second terms are used, only a limited number of weights need to be determined for the weighted sum of squares. If set variances are required in calculating the first and second terms, as in the previously described embodiment, only two set variances need to be determined. As a result, in this embodiment, only a limited number of variables need to be determined before imperfections during sealing of a package containing a film can be detected. This embodiment is particularly advantageous when measuring the distance between both sealing bars or between one sealing bar and its sealing bar holder.

[0059] According to a preferred embodiment, the weighted sum of squares includes at least three terms, two of which are the first and second terms mentioned above, and the third term is a relative measure of the rotation of the sealing bar about its longitudinal axis.

[0060] Rotation around the longitudinal axis of the sealing bar indicates the presence of inclusions, e.g. of the packaged product, e.g. food, between the film and other parts of the package containing the film. If these inclusions, seen in a transverse direction to the longitudinal direction, are located mainly on one side of the sealing bar, this may lead to rotation around the longitudinal axis of the sealing bar, depending on mechanical tolerances. Therefore, measuring the rotation of the sealing bar around its longitudinal axis is advantageous for detecting imperfections during sealing of the package containing the film.

[0061] For example, the rotation of the sealing bar around its longitudinal axis can be detected using three distance sensors, the three distance sensors and the point D of the sealing bar not being in one plane. Three distance sensors are necessary to simultaneously determine the second and third terms. For example, the measurement of the rotation around the longitudinal axis is determined by calculating the difference between the distances measured by the distance sensors, at least two of which are arranged in a direction transverse to the longitudinal direction of the sealing bar at different distances from the point D of the sealing bar and / or on different sides of the sealing bar. This difference is proportional to the rotation. If the distance sensors according to said direction transverse to the longitudinal direction are not equidistant from the point D, the measured distances are given a weight according to the distance from the distance sensors to the point D as seen according to said direction transverse to the longitudinal direction. This difference can be converted into a rotation angle. However, this is not necessary for the method. A distance sensor equidistant from point D according to said direction transverse to the longitudinal direction is advantageous because it is not necessary to know the exact distance according to said direction transverse to the longitudinal direction between the distance sensor and point D. Since no rotation angle is used, it is also not necessary to know the exact distance according to said direction transverse to the longitudinal direction between the distance sensor and point D. It will be clear that in the case of simultaneous rotations around axis E and around the longitudinal axis, the measurements of both rotations can be determined by solving simultaneous equations. The third term is calculated from the measurement of the rotation of the sealing bar around its longitudinal axis to the expected value of the rotation of the sealing bar around its longitudinal axis. As mentioned before, the rotation is not necessarily expressed in degrees. This is also not necessary for the expected value of the rotation. Alternatively, the third term is calculated as the difference between an expected value for the rotation of the sealing bar about its longitudinal axis and a determined measured value of the rotation of the sealing bar about its longitudinal axis in conjunction with a set variance for said difference. The expected value for the rotation and / or the set variance are preferably determined based on statistical data on distances measured by means of a distance sensor.

[0062] This embodiment is advantageous for obtaining greater sensitivity and accuracy in detecting imperfections during the sealing of packages containing the film, which is particularly advantageous on packaging machines where there are mechanical tolerances that limit the rotation of the sealing bars about their longitudinal axes.

[0063] According to a further embodiment, the third term is the difference between the expected value of the rotation of the sealing bar around its longitudinal axis and the calculated rotation of the sealing bar around its longitudinal axis, divided by a set variance for said difference between the expected value of the rotation of the sealing bar around its longitudinal axis and the calculated rotation of the sealing bar around its longitudinal axis. As mentioned before, there is no need to convert the rotation into a rotation angle. And the calculated rotation of the sealing bar around its longitudinal axis is a measure of the rotation of the sealing bar around said longitudinal axis. The set variance is preferably determined based on a preliminary test of sealing a package containing the film on a packaging machine, the packaging machine being the same or similar to the packaging machine that will be used to seal the package containing the film. Preferably, the variance of said difference is calculated after tests have been completed for sealings judged by the operator to be of sufficient quality. The calculated variance is preferably based on a Gaussian distribution. and the set variance is preferably at most 5 times the calculated variance, more preferably at most 4 times the calculated variance, even more preferably at most 3 times the calculated variance, even more preferably equal to 3 times the calculated variance. The expected value for the rotation about the longitudinal axis of the sealing bar is a weighted average of the calculated rotations about the longitudinal axis of the sealing bar for correct sealing of the package containing the film. Preferably, more recently calculated distances are given more weight. The expected value for the rotation about the longitudinal axis of the sealing bar is preferably initially a weighted average of the calculated rotations about the longitudinal axis of the sealing bar for sealings judged as of sufficient quality by the operator after tests are completed or when the packaging machine is started up.

[0064] Therefore, term 3 3 ) is calculated according to the following formula:

number

[0065] This embodiment is advantageous because it allows the calculation in a simple manner of relative measurements of the rotation of the sealing bar around its longitudinal axis. Relative sizes are advantageous as mentioned above because they allow equal or nearly equal predetermined thresholds to be used for similar packaging machines. No exact angle or distance of rotation is necessary in this regard.

[0066] According to one embodiment, the weighted sum of squares includes three terms, the three terms being the first, second and third terms mentioned above. This embodiment is particularly advantageous when measuring the distance between both sealing bars or between only one sealing bar and its sealing bar holder in order to obtain the best possible sensitivity and accuracy in detecting imperfections during sealing of a package containing a film, while still requiring a limited number of variables to be determined.

[0067] According to one embodiment, the weighted sum of squares includes six terms. The three terms are the first, second and third terms mentioned above. These terms are calculated for the first of both sealing bars. The fourth, fifth and sixth terms are calculated for the second of both sealing bars. The fourth term corresponds to the first term, but is calculated for the second sealing bar. The fifth term corresponds to the second term, but is calculated for the second sealing bar. The sixth term corresponds to the third term, but is calculated for the second sealing bar. This embodiment is advantageous when the distance between the sealing bar and its sealing bar holder is measured for both sealing bar holders, in order to obtain a higher possible sensitivity and accuracy when detecting imperfections during sealing of packages containing a film, compared to the previously described embodiment in which the weighted sum of squares includes three terms.

[0068] According to one embodiment, the weighted sum of squares includes four terms. Two of the terms are the first and second terms mentioned above. These terms are calculated for the first of both sealing bars. The fourth and fifth terms are calculated for the second of both sealing bars. The fourth term corresponds to the first term, but is calculated for the second sealing bar. The fifth term corresponds to the second term, but is calculated for the second sealing bar. This embodiment, compared to the previously described embodiment in which the weighted sum of squares includes two terms, is advantageous when the distance between the sealing bar and its sealing bar holder is measured for both sealing bar holders in order to obtain a higher sensitivity and accuracy in detecting imperfections during the sealing of a package containing a film.

[0069] According to a preferred embodiment, after calculating the terms for the correct sealing of the package containing the film, the variance of the calculated distance or rotation for the correct sealing is calculated. The calculated variance is preferably based on a Gaussian distribution. According to any of the previously described embodiments, the terms are calculated for the first, second, third, fourth, fifth or sixth terms, and the difference between the expected value for the distance or rotation and the calculated distance or rotation is divided by the set variance for the difference. If each of the calculated distances and rotations is within the interval of the current expected value ± the calculated variance, a new expected value for each of the calculated distances and rotations is calculated.

[0070] This preferred embodiment has the advantage that, when calculating the unitless measurement term of the deviation, the dynamic behavior during sealing of the package containing the film is taken into account, for example due to heating of the packaging machine, due to an increase or decrease in the thickness of the film, due to an increase or decrease in the tension on or in the film, due to temperature changes of the packaging machine or the sealing bar, etc. As a result, defects can be detected with a higher sensitivity, since the dynamic behavior at a certain threshold does not have to be taken into account less or not at all. A further advantage is that the calculation of the expected value does not take into account correct sealing of packages containing films that are outside or within the current expected value ± the calculated variance. These correct sealings can be seen as values ​​that deviate from the current expected value (outliers), which are not representative of the dynamic behavior.

[0071] According to a further embodiment, a transition model for a set of expected values ​​for distance or rotation is created depending on the number of sealings performed. The transition model is preferably created based on preliminary tests of sealing packages containing the film on a packaging machine, which is the same or similar to the packaging machine that will be used to seal the packages containing the film. For example, the transition model is an asymptotic function that is fitted through the expected values ​​for distance or rotation depending on the number of sealings performed, the expected value being a weighted average. Preferably, only correct sealings are used to calculate the weighted average. The new expected value for each of said distance or rotation is corrected using the transition model. This is done by adding the ideal expected value for said distance or rotation, respectively, based on the transition model and subtracting the weighted average of the ideal expected values ​​for said distance or rotation, respectively, based on the transition model.

[0072] This embodiment is particularly advantageous for compensating for transient phenomena when starting up a packaging machine. At start-up, the packaging machine is cooler than in normal operation, which means that for example the tolerances between the mechanical parts of the packaging machine may be larger or smaller, or the tensions in the film may be larger or smaller. By taking these transient phenomena into account, it is also possible to accurately detect imperfections in the sealing of packages containing the film during start-up, since there is no need to set a large predetermined threshold value for the unitless measurement of deviation, whereby during start-up the unitless measurement of deviation in case of correct sealing is also below the threshold value.

[0073] According to an embodiment, the measured distance is filtered using a low-pass filter. The low-pass filter preferably has a cut-off frequency of at most 4.5 kHz, more preferably has a cut-off frequency of at most 4.0 kHz, even more preferably has a cut-off frequency of at most 3.5 kHz, even more preferably has a cut-off frequency of at most 3.0 kHz. The low-pass filter is a Butterworth filter, a Chebyshev filter, a Bessel filter, or an elliptic filter. Preferably, the low-pass filter is a Chebyshev filter. Preferably, the measured distance using the distance sensor is oversampled. The sampling frequency is preferably at least 9 kHz, more preferably at least 10 kHz, even more preferably at least 11 kHz, even more preferably at least 12 kHz. This embodiment is advantageous for removing high frequency measurement noise from the measured distance.

[0074] According to one embodiment, the measured values ​​of the distance sensor are linearized. The measured values ​​of the distance sensor are linearized using a high order polynomial, which is of at least degree 3, preferably at least degree 4, more preferably at least degree 5. This embodiment is advantageous because some distance sensors have a non-linear response as a function of the measured distance. Linearizing the measured values, and thus the response near the operating point, allows measurements from the distance sensor near the operating point to be processed using linear techniques, simplifying the processing of the measured distances.

[0075] According to a preferred embodiment, after measuring the distance between both sealing bars or between the sealing bar and the sealing bar holder, a constant value is added. The constant value is calculated at a certain time T 1 is proportional to the difference between the measured distances at the time T 1 T is the time interval during which the distance measured by moving one or both sealing bars toward each other changes. 1 is not necessarily a fixed point in time after one or both sealing bars start to move towards each other. It depends on the accuracy of the clock used to sample the readings from the distance sensor. With a less accurate clock or a lower clock frequency, the change in the measured distance compared to starting to move one or both sealing bars towards each other may differ by, for example, several milliseconds. 1 is determined, for example, as a fixed time point after the first change in the measured distance or as the middle of a time interval during which the measured distance changes due to one or both sealing bars moving toward each other. The constant value can be a single value that is added to the distance measured by a single distance sensor. The constant value can take multiple values, each value being specific to a distance sensor. The constant value can also be negative.

[0076] This embodiment is advantageous because it does not require positioning all of the distance sensors with sub-millimeter accuracy at the same height along an axis perpendicular to the sealing surface. If there is a small deviation in height along the axis, the distance sensors will measure different distances. With certain distance sensors, e.g. inductive distance sensors or capacitive distance sensors, the distance sensors will start measuring the distance at different times. By adding a constant value to the measured distance, the flanks of the measured distance as a function of time compensate for the difference in height along the axis, but leave a difference in the distance in the height of the distance sensors between the two sealing bars or between a sealing bar and its sealing bar holder at the time T 1 The electrodes can be arranged so as to overlap each other at

[0077] According to one embodiment, the time T is the reference point T when the distance between both sealing bars is measured. 0 It is determined as a fixed point in time. 0 is the point that indicates the transition between the changing distance between the sealing bars and the stable distance. For example, T 0 is the intersection point of a line fitted through the varying measured distances with a horizontal line fitted through the constant measured values. For example, the fixed point is T 0 This embodiment is advantageous for determining the appropriate point in time for calculating a unitless measure of deviation when an inaccurate clock or a clock with too large a period is used to sample readings from the distance sensor.

[0078] According to one embodiment, the time T is determined as a point in the time interval at which, when the distance between the sealing bar and its sealing bar holder is measured, the measured distance changes due to the movement of one or both sealing bars towards each other. The time T is, for example, the time at which the first measured distance changes or a fixed point in time after the time at which the first measured distance changes. Alternatively, the time T is the middle of the time interval at which the measured distance changes due to the movement of one or both sealing bars towards each other. This embodiment is advantageous for determining the appropriate time for calculating the unitless measurement of deviation when an inaccurate clock or a clock with too large a period is used to sample the readings from the distance sensor.

[0079] According to a preferred embodiment, if the unitless measurement of deviation exceeds a predefined threshold, the film is not cut. This embodiment is particularly advantageous when the package containing the film is a tubular film. If the predefined threshold is exceeded, it is clear that the seal is defective. As a result, when the film is cut, the product may fall out of the formed pouch and contaminate the packaging machine or the blade that cuts the film. Contamination may adversely affect the cutting of the film. A dirty blade may get stuck on the sealing bar. In that case, the blade must be removed, cleaned and reattached, which means lost production time. By not cutting the film, two consecutive pouches remain together, preventing the product from falling out of one of them. The product may only be transferred from one pouch to another.

[0080] According to one embodiment, if the unitless measurement of deviation exceeds a predetermined threshold, a signal is generated that is advantageous for use by other systems or by packaging machines for automatic ejection, removal or marking of packages containing films with defective sealing.

[0081] In a second aspect, the invention relates to an apparatus for detecting imperfections during sealing of a package containing a film.

[0082] According to a preferred embodiment, the device comprises two sealing bars, a number of distance sensors for measuring the distance between both sealing bars or between the sealing bar and the sealing bar holder, and a processing unit for processing the distances measured by means of the number of distance sensors.

[0083] The two sealing bars extend in a longitudinal direction. Thus, the sealing bar has a longitudinal direction, a height direction and a transverse direction. The longitudinal direction determines the maximum dimension of the sealing bar. The two sealing bars are parallel along the longitudinal direction. Each sealing bar is attached to its own sealing bar holder. The sealing bars are preferably releasably attached to the sealing bar holder. This is advantageous for cleaning and for replacing the sealing bars. One or both sealing bars are movable along a trajectory A. The said longitudinal direction of the sealing bars is transverse to a line represented by the trajectory A during the movement of the one or both sealing bars along the trajectory A. The trajectory A is represented by a straight line, a circular arc or any other suitable curve. Preferably, the trajectory A is a straight line. The sealing bar is movable by its own sealing bar holder. The sealing bar includes a longitudinal axis. The longitudinal axis is parallel to the longitudinal direction.

[0084] Those skilled in the art will appreciate that the device may include several pairs of sealing bars, for example two pairs, three pairs or even more pairs.

[0085] The processing unit comprises means for carrying out the method according to the first aspect. This embodiment is advantageous as the apparatus comprises the distance sensors necessary to carry out the method and as this results in an integrated apparatus for detecting imperfections in the sealing of a package containing a film.

[0086] According to a preferred embodiment, at least two of the distance sensors are arranged in a plane B. The trajectory A is a straight line, which of the trajectory A is transverse to said longitudinal direction. The plane B is parallel to said longitudinal direction of both sealing bars. The plane B is parallel to the straight line of the trajectory A. The at least two of the distance sensors are arranged symmetrically in the plane B with respect to an axis C. The axis C is parallel to the straight line of the trajectory A. The axis C passes through a point D. The point D is in the centre of the sealing surfaces of the sealing bars. The sealing surfaces of both sealing bars are the surfaces which are in total or partial contact with a film or other part of the film-containing package during sealing of the film-containing package, between which the film and other part of the film-containing package are clamped.

[0087] This device has the advantage, in particular, that due to the symmetrical positioning of the at least two distance sensors with respect to the axis C in the plane B, it is possible to determine two relative displacements of the sealing bars with respect to each other and with respect to the sealing bar holder, when the distance between the sealing bars cannot be measured directly or indirectly: a linear displacement along the trajectory A and a rotation about an axis E, which intersects the sealing bars and the axis C, is transverse to the axis C and is transverse to the longitudinal direction of the sealing bars, which relative displacements are suitable for detecting imperfections during the sealing of packages containing a film, even when the absolute distance between the sealing bars cannot be determined.

[0088] According to a further embodiment, two distance sensors are mounted on a first sealing bar holder and two targets for the two distance sensors are mounted on a second sealing bar holder. The two distance sensors are symmetrical in plane B with respect to axis C. The two sealing bars are preferably not mounted on the sealing bar holder in a spring-loaded manner. This embodiment is advantageous for measuring the distance between both sealing bars. The measured distance corresponds to the distance between the distance sensor and the corresponding target. This embodiment is also advantageous for determining the rotation of the sealing bar around axis E.

[0089] According to an alternative embodiment, two distance sensors are attached to the first sealing bar holder and two targets for the two distance sensors are attached to the first sealing bar. The first sealing bar is mounted in a spring-loaded manner on the first sealing bar holder in a direction parallel to the straight line of the trajectory A. The two distance sensors are symmetrical in plane B with respect to axis C. This embodiment is advantageous for measuring the distance between the sealing bar and its sealing bar holder. The measured distance corresponds to the distance between the distance sensor and the corresponding target. This embodiment is also advantageous for determining the rotation of the sealing bar around axis E.

[0090] According to a further embodiment, two distance sensors are attached to the second sealing bar holder and two targets for the two distance sensors are attached to the second sealing bar. The second sealing bar is attached to the second sealing bar holder in a spring-loaded manner in a direction parallel to the straight line of the trajectory A. The two distance sensors are symmetrical in the plane B with respect to the axis C. This embodiment is advantageous for measuring the distance between the first sealing bar and its sealing bar holder and the distance between the second sealing bar and its sealing bar holder. The measured distances correspond to the distances between the distance sensors and the corresponding targets. This embodiment is also advantageous for determining the rotation of the first sealing bar about its axis E and the rotation of the second sealing bar about its axis E.

[0091] A person skilled in the art will appreciate that the method according to the first aspect is preferably carried out using an apparatus according to the second aspect, and that the apparatus according to the second aspect is preferably configured for carrying out the method according to the first aspect. Thus, each of the features described herein above and below may relate to any of the three aspects of the invention.

[0092] In a third aspect, the invention relates to the use of the method according to the first aspect and / or the apparatus according to the second aspect for sealing a food package.

[0093] This use results in improved packaging of food products, because possible imperfections during the sealing of food packages are automatically detected, even when using packaging machines with a construction that does not allow measuring the distance between the sealing bars of the packaging machine, which prevents food products, e.g. which are not airtightly packaged and therefore may quickly spoil, e.g. which pose a risk of food poisoning, from entering the food chain.

[0094] In the following, the invention is described by means of non-limiting figures illustrating the invention, which are not intended and should not be construed as limiting the scope of the invention.

[0095] Description of the drawings FIG. 1 shows a schematic diagram of an arrangement of distance sensors in a sealing bar holder of an apparatus according to an embodiment of the present invention.

[0096] The figure shows a cross-section of the device in plane B (B). The device comprises two sealing bars (1), each of which is attached to its own sealing bar holder (2). The two sealing bars (1) are preferably removably attached to their own sealing bar holder (2). The two sealing bars (1) have a fixed position relative to their own sealing bar holder (2). The two sealing bars (1) are parallel. The two sealing bars (1) extend in a longitudinal direction (6). One or both sealing bars (1) are movable along a trajectory A (A) by the movement of their own sealing bar holder (2). The trajectory A (A) is represented by a straight line. A distance sensor (3) is attached at both ends to the first sealing bar holder (2). The second sealing bar holder (2) has a target (4) attached at both ends. The distance sensor (3) is in plane B (B). A plane B (B) passes through both sealing bars (1) and is parallel to the longitudinal direction (6) and to the straight line of the trajectory A (A). Two distance sensors (3) are arranged symmetrically in the plane B (B) with respect to an axis C (C). The axis C (C) is parallel to the straight line of the trajectory A (A). The axis C (C) passes through a point D (D) in the center of the sealing surface of the sealing bar (1) mounted on the first sealing bar holder (2). It will be clear that the axis C (C) coincides when the point D (D) is in the middle of the sealing surface of the sealing bar (1) mounted on the second sealing bar holder (2). The distance sensor (3) is suitable for measuring the distance between both sealing bars (1) by measuring the distance between the distance sensor (3) and a target (4) lying opposite each other in a direction parallel to the straight line of the trajectory A (A). The measured distances are suitable for calculating the first and second terms of a weighted squared sum, the first term being a relative measure of the distance between the two sealing bars (1) according to said direction parallel to the straight line of the trajectory A (A) and the second term being a relative measure of the rotation of the sealing bars (1) around the axis E (E) which intersects the sealing bars (1) and the axis C (C) and is transverse to the axis C (C) and transverse to the longitudinal direction (6).Axis E (E) in this embodiment passes through point D (D). Point D (D) and axis E (E) are shown as circles in FIG.

[0097] FIG. 2 shows a schematic diagram of the arrangement of distance sensors in a sealing bar holder of a device according to an alternative embodiment of the present invention.

[0098] The figure shows a cross-section of the device in plane B (B). The device comprises two sealing bars (1), each of which is attached to its own sealing bar holder (2). The two sealing bars (1) are preferably removably attached to their own sealing bar holder (2). The two sealing bars (1) are attached to their own sealing bar holder (2) by means of a spring-loaded attachment (5). By means of the spring-loaded attachment (5), the sealing bar (1) can be moved relative to its own sealing bar holder (2). The two sealing bars (1) are parallel. The two sealing bars (1) extend in a longitudinal direction (6). One or both sealing bars (1) can be moved along a trajectory A (A) by movement of their own sealing bar holder (2). The trajectory A (A) is represented as a straight line. Two distance sensors (3) are attached to the first sealing bar holder (2). Two targets (4) are attached to the sealing bar (1), which is attached to the first sealing bar holder (2). The targets (4) are attached to parts of a spring-loaded attachment (5) that has a fixed position relative to the sealing bar (1). The distance sensors (3) lie in a plane B (B), which passes through both sealing bars (1) and is parallel to the longitudinal direction (6) and to the line of the trajectory A (A). The two distance sensors (3) are arranged symmetrically in the plane B (B) with respect to an axis C (C), which is parallel to the line of the trajectory A (A). The axis C (C) passes through a point D (D) in the middle of the sealing surface of the sealing bar (1) that is attached to the first sealing bar holder (2). It will be apparent that if point D (D) is in the centre of the sealing surface of the sealing bar (1) mounted on the second sealing bar holder (2), then axis C (C) will coincide.The distance sensor (3) is suitable for measuring the distance between the first sealing bar holder (2) and the sealing bar (1) attached to the first sealing bar holder by measuring the distance between the distance sensor (3) and a target (4) lying opposite in a direction parallel to the straight line of the trajectory A (A). The measured distances are suitable for calculating the first and second terms of a weighted squared sum, the first term being a relative measurement of the distance along said direction parallel to the straight line of the trajectory A (A) between the first sealing bar holder (2) and the sealing bar (1) attached to the first sealing bar holder (2), and the second term being a relative measurement of the rotation about the axis E (E) of the sealing bar (1) attached to the first sealing bar holder (2). The axis E (E) intersects the sealing bar (1) and the axis C (C), is transverse to the axis C (C) and is transverse to the longitudinal direction (6). The axis E (E) in this embodiment passes through the point D (D). In FIG. 2, point D (D) and axis E (E) are shown as circles.

[0099] FIG. 3 shows a schematic diagram of an arrangement of distance sensors in a sealing bar holder of an apparatus according to yet another alternative embodiment of the present invention.

[0100] The device is very similar to the device of figure 2. In this embodiment, distance sensors (3) are attached to both sealing bar holders (2) and targets (4) are attached to both sealing bars (1). This makes it possible to calculate both the first and second terms for the first sealing bar (1) and both the fourth and fifth terms for the second sealing bar (1), the fourth term corresponding to the first term but calculated for the second sealing bar (1) and the fifth term corresponding to the second term but calculated for the second sealing bar (1). It will be clear that the point D (D) and the axis E (E) can be determined for both sealing bars (1).

[0101] FIG. 4 shows a three-dimensional representation of the arrangement of distance sensors in a sealing bar holder of a device according to another alternative embodiment of the invention.

[0102] The device is very similar to the device in Figure 1. The main difference is that the distance sensor (3) and the target (4) are not attached to the end of the sealing bar holder (2) and they are not all symmetrical about the axis C (C). The key to this alternative embodiment is that the distance sensor (3) and the target (4) are not coplanar with the point D (D). This allows for the simultaneous calculation of the second and third terms.

[0103] FIG. 5 shows a diagram of a method according to one embodiment of the present invention.

[0104] In a first step (21) the signal from the distance sensor is sampled. The signal from the distance sensor is sampled during the movement of at least one or both sealing bars towards each other. The sampled signal is proportional to the distance between both sealing bars or between a sealing bar and its own sealing bar holder.

[0105] In a second step (22), the sampled signal is filtered using a low pass filter, for example a Chebyshev filter, which removes high frequency measurement noise from the sampled signal.

[0106] In a third step (23), the measured values ​​of the distance sensor are linearized. The measured values ​​are sampled signals. By linearizing the measured values, the measured values ​​of the distance sensor can be processed in subsequent steps using linear techniques.

[0107] In a fourth step (24), a constant value is added to the measured distance. The constant value can be negative. The constant value is calculated at a certain time T 1 is proportional to the difference between the measured distances at a given time T 1is the time interval during which the measured distance changes by moving one or both sealing bars towards each other. If there is a small deviation in the height between the distance sensors along an axis perpendicular to the sealing surface of the sealing bars, the distance sensors will measure a different distance. By adding a constant value to the measured distance, the rise and fall of the measured distance as a function of time compensates for the difference in height along said axis, but leaves behind a difference in the distance in the height of the distance sensors between the two sealing bars or between a sealing bar and its sealing bar holder, at the time T 1 The electrodes can be arranged so as to overlap each other at

[0108] In a fifth step (25) measurements of the displacement of the points D of the two sealing bars relative to each other along the trajectory A or of the displacement of a point D of a sealing bar relative to its own sealing bar holder along the trajectory A and of the rotation of the sealing bars about the axis E are determined for every time point at which the signals from the distance sensors are sampled.

[0109] In a sixth step (26), a time point T is determined at which a unitless measurement of the deviation is calculated. The time point T corresponds to the reference point T when the distance between the sealing bars is measured. 0 It is determined as a fixed point at a later time. T 0 is a point that indicates a transition between a changing distance between both sealing bars and a stable distance. Time point T is determined as a point in the time interval where, when the distance between a sealing bar and its sealing bar holder is measured, the measured distance changes due to the movement of one or both sealing bars towards each other. Time point T may be, for example, the time at which the first measured distance changes or a fixed point in time after the time at which the first measured distance changes. Alternatively, time point T may be the middle of the time interval where the measured distance changes due to the movement of one or both sealing bars towards each other.

[0110] In a seventh step (27) the measurements of displacement of the points D of the two sealing bars relative to each other along the trajectory A or the measurements of displacement of the points D of a sealing bar relative to its own sealing bar holder along the trajectory A and the measurement of the rotation of the sealing bar about the axis E are determined. Optionally, the measurement of the rotation of the sealing bar about its longitudinal axis is also determined. It will be clear that if the sealing bars are mounted in a spring-loaded manner in the sealing bar holder and the distance between the sealing bar and its own sealing bar holder is measurable for both sealing bars, it is possible to determine for both sealing bars the measurements of displacement along the trajectory A, the measurements of rotation about the axis E and, optionally, the measurements of rotation about the longitudinal axis of the sealing bar.

[0111] In an eighth step (28), a unitless measure of deviation at time T is calculated. The unitless measure of deviation is the root of a weighted squared sum of at least two terms. The first term is a relative measure of the distance between the two sealing bars or between a sealing bar and a sealing bar holder. The second term is a relative measure of the rotation of the sealing bar about its axis E. Optionally, the weighted squared sum includes a third term, which is a relative measure of the rotation of the sealing bar about its longitudinal axis. It will be clear that if the sealing bars are attached to the sealing bar holder in a spring-loaded manner and the distance between the sealing bar and its own sealing bar holder is measurable for both sealing bars, the weighted squared sum can include four terms and optionally six terms. The three terms are the first term calculated for the first sealing bar, the second term for the first sealing bar, and optionally the third term for the first sealing bar. The fourth term corresponds to the first term, but is calculated for the second sealing bar. The fifth term corresponds to the second term, but is calculated for the second sealing bar. The optional sixth term corresponds to the optional third term, but is calculated for the second sealing bar. In calculating the different terms, the expected values ​​for distance and rotation, respectively, from step 7 (27) are used. After calculating the unitless measure of deviation, the unitless measure of deviation is compared to a predefined threshold. If the unitless measure of deviation is equal to or less than the predefined threshold, the resulting seal is considered a correct sealing of the package including the film.

[0112] In a ninth step (29), new expected values ​​for each of the distances and rotations from the seventh step (27) are calculated. For this purpose, the variance of the calculated distances or rotations in case of correct sealing of the package including the film is calculated for the corrected sealing case. If each of the calculated distances and rotations is within the interval of the current expected value ± the calculated variance, a new expected value for each of the calculated distances and rotations is calculated.

[0113] After this, the method starts again with the first step (21) with a new detection of imperfections in the sealing of the package containing the film.

[0114] The numbered elements in the diagram are as follows: 1 Sealing bar 2 Ceiling Bar Holder 3 Distance Sensor 4. Target 5 Spring-loaded attachment 6 Longitudinal sealing bars 21 First Step 22 Second Step 23 Third Step 24 Fourth Step 25 5th Step 26 Sixth Step 27 Seventh Step 28 Eighth Step 29 9th Step A Orbit A B plane B C axis C D Center point D E axis E

Claims

1. A method for detecting defects during the sealing of a package including a film, - A step of positioning the film and other parts of a package including the film between two parallel sealing bars, the sealing bars extending in the longitudinal direction; - A step of moving one or both sealing bars toward each other along track A, such that a connection is formed between the film and the other part of the package including the film; - A step of moving one or both of the sealing bars along the track A, wherein the sealing bars are separated from each other; - The step of removing the sealed package, A method characterized in that, during the movement of at least one or both of the ceiling bars toward each other, the distance between the two ceiling bars or the distance between the ceiling bars and the ceiling bar holder is measured by several distance sensors, and the method comprises the additional step of calculating a unitless measurement of the deviation at time T and comparing the unitless measurement of the deviation with a predetermined threshold, wherein time T is in a time interval in which the measured distance changes or changes by moving one or both of the ceiling bars toward each other, and before the one or both of the ceiling bars are separated from each other, and the unitless measurement of the deviation is calculated from relative measurements of the distance between the two ceiling bars or between the ceiling bars and the ceiling bar holder.

2. The method according to claim 1, wherein the unitless measurement of the deviation is the square root of the weighted sum of squares of at least two terms, the first being a relative measurement of the distance between the two sealing bars or between the sealing bar and the sealing bar holder, and the second being a relative measurement of the rotation of the sealing bar around axis E, wherein axis E intersects the sealing bar, is perpendicular to the trajectory A, and is perpendicular to the longitudinal direction of the sealing bar.

3. The method according to 2, characterized in that the weighted sum of squares comprises at least three terms, the third of which is a relative measurement of the rotation of the sealing bar around the longitudinal axis of the sealing bar.

4. The method according to 3, wherein the third term is the difference between an expected value of the rotation of the sealing bar around the longitudinal axis of the sealing bar and a calculated rotation of the sealing bar around the longitudinal axis of the sealing bar, divided by a set variance of the difference between the expected value of the rotation of the sealing bar around the longitudinal axis of the sealing bar and the calculated rotation of the sealing bar around the longitudinal axis of the sealing bar, wherein the expected value of the rotation of the sealing bar around the longitudinal axis of the sealing bar is a weighted average of the calculated rotations of the sealing bar around the longitudinal axis in the case of proper sealing of the package including the film.

5. The first term is the difference between an expected value relating to the distance between the two sealing bars or between the sealing bars and the sealing bar holder and the calculated distance between the two sealing bars or between the sealing bars and the sealing bar holder, divided by a set variance relating to the predetermined difference between the expected value relating to the distance and the calculated distance, wherein the expected value relating to the distance is a weighted average of the calculated distance between the two sealing bars or between the sealing bars and the sealing bar holder, respectively, in the case of proper sealing of the package including the film.

6. The method according to claim 1, wherein the second term is the difference between an expected value for the rotation of the sealing bar around the axis E and a calculated rotation of the sealing bar around the axis E, divided by a set variance relating to the difference between the expected value for the rotation around the axis E and the calculated rotation around the axis E, wherein the expected value for the rotation around the axis E is a weighted average of the calculated rotations around the axis E in the case of proper sealing of the package including the film.

7. The method according to any one of 4 to 6, characterized in that, in the case of correct sealing of the package including the film, after calculating the term, the variance of the calculated distance or rotation in the case of correct sealing is calculated, and if each of the calculated distance or rotation is within the interval of current expected value ± the calculated variance, a new expected value for the distance or rotation is calculated.

8. The method according to 7, characterized in that a transition model is created for a series of expected values ​​relating to distance or rotation in proportion to the number of seals performed, and the new expected values ​​relating to distance and rotation are corrected using the transition model by adding the ideal expected values ​​relating to distance or rotation based on the transition model and subtracting the weighted average of the ideal expected values ​​relating to distance or rotation based on the transition model.

9. The method according to any one of 1 to 6, characterized in that the film is not cut if the unitless measurement value of the deviation exceeds the predetermined threshold.

10. After measuring the distance between both sealing bars or the distance between the sealing bar and the sealing bar holder, a certain value is added, and this certain value is at time T １ The difference between the distances measured at time T is proportional to the difference between the distances measured at time T １ The method according to any one of 1 to 6, characterized in that the measured distance changes at time intervals in which one or both sealing bars are moved toward each other.

11. The method according to any one of 1 to 6, characterized in that a signal is generated when the unitless measurement value of the deviation exceeds the predetermined threshold.

12. An apparatus for detecting defects during sealing of a film-containing package, comprising: two parallel sealing bars, the sealing bars extending in the longitudinal direction and one or both sealing bars movable along a track A; a plurality of distance sensors for measuring the distance between the two sealing bars or the distance between the sealing bars and a sealing bar holder; and a processing unit for processing the distance measured using the plurality of distance sensors, wherein the processing unit comprises means for performing the method according to claim 1.

13. The apparatus according to claim 12, wherein at least two of the several distance sensors are located in a plane B, the trajectory A is a straight line, the straight line of the trajectory A is perpendicular to the longitudinal direction, the plane B is parallel to the longitudinal direction and to the straight line of the trajectory A, and at least two of the plurality of distance sensors are arranged symmetrically in the plane B with respect to the axis C, the axis C is parallel to the straight line of the trajectory A, the axis C passes through point D, and point D is at the center of the sealing surface of the sealing bar.

14. The apparatus according to claim 13, characterized in that two distance sensors are attached to a first sealing bar holder, two targets relating to the two distance sensors are attached to a second sealing bar holder, and the two distance sensors are symmetrical in the plane B with respect to the axis C.

15. The apparatus according to claim 13, characterized in that two distance sensors are attached to a first sealing bar holder, two targets relating to the two distance sensors are attached to a first sealing bar, the first sealing bar is attached to the first sealing bar holder by a spring load in a direction parallel to the trajectory A, and the two distance sensors are symmetrical in the plane B with respect to the axis C.

16. The apparatus according to claim 15, characterized in that two distance sensors are attached to a second sealing bar holder, two targets relating to the two distance sensors are attached to a second sealing bar, the second sealing bar is attached to the second sealing bar holder by a spring load in a direction parallel to the trajectory A, and the two distance sensors are symmetrical in the plane B with respect to the axis C.

17. Use of the method according to any one of claims 1 to 6 and / or the apparatus according to any one of claims 12 to 16 for sealing food packaging.

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