Method and apparatus for detecting leaks in sealed containers

Abstract

A method for detecting fluid leakage in a sealed container, comprising the following steps: defining a detection zone (13) in which a sealed container (CT) is to be placed; connecting the detection zone (13) to at least one gas sensor (19; 219a, 219b) via at least one pipe (21); introducing flushing gas into the detection zone (13) via the at least one pipe (21); placing the container (CT) in the detection zone (13); and extracting gas from the detection zone (13) via the pipe (21) and transmitting it to the sensor (19; 219a, 219b) to determine whether there is a gas leak in the container (CT).

Description

Technical Field

[0001] The present invention relates to a method and device for detecting leakage of a sealed container. According to the method and device of the present invention, it is possible to detect whether there is fluid leakage in a fluid from a sealed container. More specifically, but not exclusively, the fluid can be in a gas or vapor state, and can be composed of a gas or a gas mixture, or a vapor or a vapor mixture, or a gas and a vapor mixture. The container can be a rigid container, such as a glass jar or a bottle, or a container with at least one flexible wall portion, such as different types of plastic barrels, bags and flexible packaging. Background Art

[0002] Currently, many beverages and products used as food or for other purposes are preserved mainly by one of the following packaging methods.

[0003] According to a first approach, which is mainly used for the storage of liquids, a rigid or semi-rigid container is filled with the substance to be stored through a suitable opening provided on the container. Subsequently, the opening is sealed by a suitable closing element, such as a lid. In other cases, the product to be stored is wrapped with a tape or film or introduced into a flexible plastic material tube, and the package thus obtained is subsequently sealed by welding along one or more connecting lines. In other cases, it is known to use a preformed plastic material barrel. This barrel is filled through an opening provided thereon, and the opening is subsequently sealed by a plastic film welded to the barrel wall.

[0004] More generally, food products, but not only food products, are stored in sealed packaging with the aim of preserving for as long as possible the chemical and physical characteristics that the product had when it was packaged.

[0005] Therefore, one of the main problems encountered when applying the above methods is how to obtain an optimal seal of the package to avoid contamination by the external environment. In many applications, the optimal seal leads to the closure having to be substantially airtight at the external pressure to which the package is maintained or at the pressure to which it is subjected during normal use, transportation and storage. For example, in the case of food products, the package must be substantially airtight at atmospheric pressure to prevent the environment inside the package from communicating with the external environment, thereby causing the transfer of substances and air from one environment to the other, thereby preventing the risk of contamination of the packaged product and its organoleptic properties from spoiling.

[0006] In the case of containers sealed by welding, a poor weld, for example due to an incorrect execution of the welding process, can compromise the hermetic seal of the package. Errors in setting the welding temperature, incorrect selection of adhesive welding materials, poor flatness of the contact surface in the weld area, and the presence of impurities or foreign matter in the weld area are all factors that can affect the hermetic seal of the container.

[0007] In case of rigid or semi-rigid containers, such as bottles closed by a cap as is well known, the hermetic seal may be compromised due to, for example, deformities of the cap or bottle in the area where the cap is to be applied, or due to operating problems of the capping machine, such as alignment problems during the cap application step.

[0008] Usually, a careful operator can easily detect even by visual inspection the loss of the substance of a container that occurs due to a noticeable defect in the container closure. Such a defect usually results in a noticeable escape of the substance from the container. Therefore, in this case, the careful operator who is responsible for supervising the packaging line can easily identify the defective containers and, if necessary, remove them immediately downstream of the filling and sealing steps, mainly in order to discard them to prevent them from being provided to consumers, or to submit them for further inspection or repair.

[0009] It is easy to understand that leak detection of containers is more difficult for operators the smaller the leaks are, for example, due to micro cracks and micro holes. These leaks are defined as micro leaks, i.e. very small leaks on the container. Since they do not lead to obvious spillage of liquid or other substances, they cannot be detected immediately, but in the long run they can damage product quality. Such micro leaks are usually caused by cracks of about 10 microns and even as small as a few microns, such as 3-7 microns.

[0010] In order to solve the problem of how to effectively detect whether a sealed container has micro-leakage, several solutions have been proposed so far.

[0011] A first known solution is disclosed, for example, in US 3708949 (A) for detecting the problem of leaks in heat-sealed containers. This document discloses a method and a device for forming and subsequently checking the tightness of a heat-sealed envelope. The method disclosed in this document essentially comprises: a step of sealing the container after the introduction of a modified atmosphere; a step of subjecting the container to mechanical pressure in order to reduce the volume enclosed by the container wall and thus increase the pressure of the gas enclosed in the container, thereby promoting the escape of microcracks if they are present; a step of a gas detector detecting the presence of a tracer gas present in the modified atmosphere outside the container; and a step of removing containers that fail the inspection.

[0012] Another known method for testing the tightness of heat-sealed containers is disclosed in WO2013 / 011329 (A2). According to the teachings of this document, the container is filled with a tracer gas and subjected to compression to promote the escape of gas through microcracks that may be present in the sealing area. Suitable detectors, including paired electrodes, are located near the container area where gas micro-leaks are more likely to occur. Changes in the voltage on the detector electrodes enable the presence of the tracer gas to be detected.

[0013] WO2017125386 (A2) discloses a method in which a chemical substance, usually in the form of a strip, is applied to a container. The physical and / or chemical properties of the substance vary depending on the concentration of a gas, such as oxygen, that comes into contact with the substance. The change in the properties of the substance causes a change in the frequency, wavelength or phase of the emitted electromagnetic radiation, which can be detected by a detector located outside the container.

[0014] DK201570808 (A1) discloses a device for detecting gas leakage from a sealed container into which a tracer gas has been introduced. The device comprises: an analysis chamber in which the container is contained during a gas-tight seal test; and a device capable of generating a vacuum in the analysis chamber. A gas detector is arranged to communicate with the analysis chamber to detect the presence of the tracer gas.

[0015] Therefore, according to the teachings of the prior art, the step of detecting micro-leakages is usually carried out by means of a tracer gas, usually carbon dioxide (CO2), helium (He) or hydrogen (H2), introduced into the container before the container is sealed. Usually, the detection of the presence of the tracer gas outside the container is by a detector, such as usually by electrodes to detect liquids or tracer gases such as He, or by a detector operating based on non-dispersive infrared (NDIR) technology or other technologies to detect CO2 leaks.

[0016] In the field of detecting gas leaks in squeezable sealed containers, a further known problem is how to clean the area where the sample to be checked is placed from possible undesired gas traces, which originate, for example, from the passage of previous samples or from contamination by gases from the external environment surrounding the detection zone.

[0017] EP2755015 (A1) teaches the use of so-called compressed air curtains to clean the detection zone. In addition, the document also teaches the use of multiple air curtains to shield the detection zone from possible external gas flows, in particular CO2, which could contaminate the detection zone and thus alter the leak detection. According to the description of this document, the air from a compressed air source is delivered to the device through a dedicated pipe circuit and enters the detection zone through a set of nozzles, which are configured to define corresponding air curtains or air knives, that is, air flows that, when diffused through openings or slits of appropriate shape, are essentially spread out on a plane and, thanks to the flow rate, maintain this configuration within a certain distance from the diffuser.

[0018] Air curtains are used for cleaning, also called flushing, of the detection zone. However, the air curtains are located at the start and end of the measuring channel and they cannot be located near the extractor fan for obvious reasons of functional interference. The effectiveness of the air curtains is therefore only local and even assuming that they could be located near the extractor fan - which is only a theoretical assumption - they cannot flush the interior of the suction duct. Therefore, according to currently known technology, the flushing performed by the air curtains is limited to the detection zone, while other parts of the device, which are usually present in such devices, for example, the ducts communicating with the detector, do not undergo any air change and can therefore be contaminated with foreign gases which can be detrimental to the correct detection of leaks in the sample container, especially if the leaks are small or very small and the test is to be carried out very quickly, for example in order not to slow down the product advancement line of an industrial plant.

[0019] FR2522820 (A1) discloses a method and a device for detecting gas leakage in a container, wherein a detection area near the container is surrounded by a bell. During the gas leakage measurement step, the bell is connected in a closed loop, which includes a detector capable of measuring the concentration of the gas to be detected. More specifically, the closed loop includes a first pipe connecting the detector outlet to the bell inlet and a second pipe connecting the bell outlet to the detector inlet. A circulator connected in the first pipe between the detector and the bell circulates the gas in the loop. The container is kept under the bell for a long time, so that the amount of gas to be measured gradually increases and accumulates, and these gases can circulate several times in the loop, passing through the detector. In order to be able to clean the detector and the bell before a new measurement, the closed loop is opened and a gas different from the gas to be measured is allowed to flow in the first pipe. However, this gas does not flow in the second pipe, so it may still be contaminated by the gas previously measured.

[0020] Thus, the aforementioned method provides homogenization of the gas to be tested by repeatedly passing the same gas in a closed loop. In addition, the method taught has the disadvantage that it does not allow for efficient and rapid cleaning of the entire device, resulting in a slowdown in operation between the measurement of a gas leak in one container and the measurement of a subsequent gas leak in the container.

[0021] A first object of the present invention is to provide a method and apparatus for detecting the presence of leakage in a sealed container which is not affected by the above-mentioned limitations and disadvantages of the prior art.

[0022] Another object of the invention is to provide a method and a device of the above type capable of detecting leaks from different kinds of containers, whether rigid or flexible, whether or not the container is subjected to mechanical compression, and even small or very small leaks, i.e., corresponding to micro-leaks and caused by openings of a few micrometers.

[0023] Another object of the present invention is to provide a method and device for detecting whether there is a leak in a sealed container, which can improve the operating speed compared with the prior art, that is, if there is a leak, it is a method and device that can detect the leak more quickly, thereby maximizing the operating speed of the production or container processing plant.

[0024] It is a further object of the present invention to provide a method and an apparatus of the above type which can achieve leak detection with high accuracy even when the conditions of the surrounding environment are disturbed or changed.

[0025] A further but not last object of the invention is to provide a method and an apparatus which are reliable and can be used inexpensively, thereby making them applicable industrially on a large scale.

[0026] The above and other objects are achieved by the method and apparatus as claimed in the accompanying claims. Summary of the invention

[0027] A method for detecting leakage of a sealed container mainly comprises the steps of placing a sealed container to be detected in a detection zone, and sucking the air present in the detection zone through at least one suction pipe connected to the detection zone. According to the present invention, the suction step is preceded by a step of flushing the pipe and the detection zone, and the flushing step is performed by introducing a flushing gas into the detection zone and making the flushing gas flow through the same pipe in a direction opposite to the direction of the air sucked in the suction step. In addition, it is preferred that the detection zone is connected to the atmosphere.

[0028] In one embodiment of the invention, the suction step and the flushing step are performed respectively by an exhaust fan having a suction port connected to the pipeline and by a blower having an outlet connected to the same pipeline. An electromechanical valve, such as a three-way valve, is further provided so that the pipeline is connected to the exhaust fan during the suction step and to the blower during the flushing step. The same three-way valve closes the connection between the pipeline and the blower during the suction step and closes the connection between the pipeline and the exhaust fan during the flushing step. Therefore, according to this embodiment, the suction of air from the detection zone and the flushing are carried out by two separate and independent units, namely, an exhaust fan and a blower, which are separately connected to the pipeline and the detection zone, respectively, for example, by a three-way valve. Preferably, in the introduction step, the flushing gas introduced into the detection zone is taken from a controlled environment containing the flushing gas, and in the suction step, the gas sucked from the detection zone is discharged to an uncontrolled environment.

[0029] In an alternative embodiment of the invention, the extraction of air from the detection zone and the flushing are performed by a single unit, which thus acts both as an extractor and as a blower. The unit is connected to a circuit equipped with a valve for:

[0030] - communication between the duct communicating with the detection zone and the inlet of the unit, and between the outlet of the unit and the external environment (during the step of sucking air from the detection zone), or, in the alternative

[0031] - Communication between the conduit communicating with the detection zone and the outlet of the cell, and communication between the inlet of the cell and a controlled environment containing a flushing gas or gas mixture (during the flushing step).

[0032] In another embodiment of the invention, the extraction of air and flushing from the detection zone are performed by a single reversible unit that can alternately operate as an extractor or a blower by reversing the movement of the blades of a single impeller. Also in this embodiment, it is preferred that the single reversible unit discharges the extracted gas to the external environment during the extraction step, while during the flushing step it obtains flushing gas from the controlled environment containing it.

[0033] According to a preferred embodiment of the present invention, at least one gas sensor is arranged along the suction and flushing pipeline between the detection zone and the suction unit or blower, and the sensor is arranged to generate an electrical signal indicating the presence of a given gas or gas mixture in the air flow, which flows through the pipeline from the detection zone and touches the sensor.

[0034] Therefore, according to the present invention, the method for detecting leakage preferably comprises the following steps:

[0035] Define the inspection area where the sealed containers will be placed;

[0036] Connecting the detection area to the gas sensor through a pipeline;

[0037] introducing a flushing gas or gas mixture into the detection zone by flowing the flushing gas or gas mixture through the conduit in a first direction;

[0038] placing a container in the detection zone;

[0039] A gas sample is drawn from the detection zone and conveyed to the sensor to determine if a gas leak exists in the container, the gas being conveyed from the detection zone to the sensor by flowing the gas through the conduit in a second direction opposite to the first direction.

[0040] According to the invention, the step of placing the container in the detection zone can be performed before or after the flushing gas is introduced. However, preferably, the introduction of flushing gas into the detection zone is stopped after the container to be detected has been placed in the detection zone.

[0041] According to a particular aspect of the invention, a step of defining a detection zone arranged to receive a sealed container to be detected and a flushing step are performed to produce a detection zone gas atmosphere having a constant concentration and substantially without turbulence in said detection zone. According to the invention, an atmosphere containing one or more gases at a constant concentration and without turbulence can be obtained by forming an environment with a mixture of gases having a concentration as similar as possible to that in the atmosphere, or preferably by introducing a gas or a gas mixture from a controlled environment into the detection zone with the aid of a diffuser, wherein the controlled environment does not contain the gas to be detected or the gas is present therein in a limited and stable concentration. According to the invention, the gas flow introduced into the detection zone must preferably be a gas flow that is as laminar as possible and without turbulence.

[0042] According to a preferred embodiment of the invention, the containers are moved on a conveyor in a channel provided with one or more diffusers, preferably positioned to analyze the entire profile of the sample as the conveyor advances, in order to monitor any part of the same container for possible leaks.

[0043] Furthermore, according to the invention, a squeezing device is preferably provided to promote possible gas escape from the container when the container is in the detection zone. Furthermore, a device for discarding the container according to the result of the inspection performed may be provided downstream of the detection zone.

[0044] According to this first aspect, the present invention can detect a gas micro-leak from a sealed container when the tracer gas concentration in the atmosphere within the container is different from the tracer gas concentration in the surrounding environment.

[0045] Furthermore, the invention optionally provides the possibility to change the concentration of the gas mixture present in the atmosphere near the container. Thus, the invention is able to detect gas micro-leaks from the container when the tracer gas concentration in the atmosphere inside the container is the same as the tracer gas concentration in the surroundings before said change.

[0046] By way of example, taking CO2 as an example of a tracer gas introduced into the container before sealing the container, according to the first aspect described, the invention provides that the concentration of CO2 present in the container exceeds the CO2 concentration in the atmosphere (typically 400 ppm), and according to the second aspect described, the invention provides that the CO2 concentration is substantially the same as the CO2 concentration of the atmosphere. In the second case, as previously described, the invention provides that a modified atmosphere is defined in the detection zone, i.e., an atmosphere with a reduced CO2 concentration or without CO2. The second aspect of the invention can be achieved, for example, by introducing a pure gas, such as nitrogen, into the detection zone.

[0047] In the following, CO 2 is often referred to as the tracer gas to be detected; however, the present invention may use any other tracer gas, such as O 2 , H 2 and other gases or gas mixtures suitable for this purpose.

[0048] According to the present invention, the sealed container to be inspected is preferably placed in the inspection zone by a positioning assembly, the positioning assembly comprising at least one conveyor belt, or a turntable, or a transporter or any other device capable of conveying the container to the inspection zone. The positioning assembly further preferably comprises a pair of side guides for correctly placing the container in the inspection zone.

[0049] The positioning assembly also preferably includes a pair of conveyor belts for respectively introducing or causing the container to enter the detection zone and removing or causing the container to exit the detection zone.

[0050] A pressing assembly is optionally provided in the detection zone, which, if micropores are present, is capable of pressing the sealed container to be inspected to promote gas escape. The pressing assembly preferably comprises a pair of rotatable rollers, which are preferably arranged transversely relative to the direction of advance of the product to be inspected and have a rotation axis substantially parallel to the plane of the product advance. When the product to be inspected advances on the conveyor belt, the rotatable rollers are preferably arranged so that their rotation axes are transverse to the direction of advance of the belt and are located in a plane parallel to the plane of the belt. In a preferred embodiment, each roller is suspended on a pair of floating arms, which are connected to corresponding cylinders, which are capable of applying a pressure suitable for squeezing the container located in the detection zone to the arm and thus to the roller. A motor is provided on the pivot axis of each arm to rotate the roller through a transmission belt. The pivot axis of the arm is fixed relative to the structure of the detection device, and the spatial position of the rotation axis of the roller can be changed according to the pressure applied by the cylinder when the container passes through the detection area. The described assembly includes the arm, the cylinder and the associated rollers of the pressing assembly, which generally define a three-stage lever. An angular potentiometer capable of generating an electrical signal indicative of the angular position of the arm, and thus of the position of the roller relative to the sample container at that moment in the detection zone, is arranged at the pivot axis of each arm on the fixed structure of the device. The angular displacement indicates the presence of the sample container to be submitted for detection. The angular displacement of the arm and the roller indicates that the sample is present and has been squeezed. If the sample is not squeezed, for example, the sample is in a highly compressed state, the same sample is discarded.

[0051] According to a preferred embodiment of the invention, the roller of the extrusion assembly comprises a cylindrical body in which a central portion is defined, delimited by a pair of end plates for lateral protection. On the outside of one of the end plates there is provided a grooved pulley engaged by a belt transmitting the movement imparted by a motor positioned in a position corresponding to the pivot axis of one of the floating arms suspending the roller.

[0052] Preferably, when viewed in cross section and radially outward from the inside, the central part of the roller comprises: a substantially rigid and hollow inner central sleeve, for example made of steel or aluminum; a soft layer, for example made of foam rubber; and an outer coating of non-slip material, i.e. a material with high grip, for example natural rubber, capable of exerting strong friction on the surface of a passing sample container to advance it without slipping. A shaft is arranged inside the central sleeve, the ends of which are integral with the end plates and the outer pulleys.

[0053] In an alternative, the roller of the squeezing assembly comprises a hollow rubber sleeve having an outer surface with anti-slip properties and a cavity which provides a certain softness and compressibility due to an external radial thrust, which is due to the squeezing resistance encountered when the sample container passes under the roller.

[0054] According to a preferred embodiment of the present invention, a suction head comprising a plurality of slits for extracting gas is located in the detection zone. Advantageously, when the sample container passes through the detection zone, the slits are arranged along a peripheral band that substantially surrounds the entire sample container. The slits are advantageously distributed on the peripheral band that is located in a plane that is substantially perpendicular to the direction of advance of the sample. Therefore, in general, the slits are arranged along the upper surface, two side surfaces and the bottom surface of the peripheral band. For example, three upper grooves and three bottom grooves can be provided, and one side groove is provided for each side surface, for a total of two side grooves. In addition, each groove is connected to a corresponding pipeline and, in turn, to a gas sensor.

[0055] The detection area is also equipped with diffusers, through which an air curtain or air knife is blown, which helps to isolate the detection area from contamination by gases from the surrounding environment.

[0056] Considering that, according to a preferred embodiment of the present invention, the detection head extends along a peripheral belt substantially surrounding the entire sample container passing through the detection zone, the conveyor belt is preferably interrupted so as to create a free zone for air to flow in and out of the slits in the bottom surface of the slit belt at the interruption. The conveyor belt therefore preferably comprises: an input portion, advancing in a direction towards the detection zone, for placing the sample into the zone and passing it through the inside of the slit belt; and an output portion, advancing in a direction away from the detection zone, for removing the sample from the zone to a subsequent destination in the container processing plant. The slits in the bottom surface of the peripheral belt corresponding to the interruption of the conveyor belt are located between the end of the input portion and the beginning of the output portion. Alternatively, the conveyor belt can be made of an air-permeable material, or other means for allowing air to flow into and out of the detection zone can be used to convey the sample product.

[0057] Preferably, the slits located on the upper surface of the detection head and along the sides are height-adjustable to accommodate the presence of containers of different sizes.

[0058] Preferably, the slits positioned along the upper surface are arranged obliquely relative to the periphery of the peripheral band and are inclined at an angle of about 15° to 30° relative to the plane of the band. Preferably, the slits positioned along the sides of the peripheral band are arranged substantially perpendicular to the corresponding sides and parallel to the sample advance direction. Preferably, the slits located on the bottom surface are parallel to the bottom surface and perpendicular to the sample advance direction. Preferably, the bottom slit is defined in a suction assembly, for example, having three channels, one channel for each slit. The bottom suction assembly has an elongated body with a trapezoidal cross-sectional shape. The cavity connecting the corresponding slits to the corresponding gas outlet is defined inside the elongated body. In this case, three slits are arranged as a whole, their lengths are shorter than the length of the elongated body, and are arranged on two parallel lines. In addition, the slits are offset to ensure the continuity of suction over the entire length of the elongated body. The internal cavity of the elongated body defines a suction duct for conveying the fluid sucked through the slits to the corresponding outlet, which is configured to avoid sharp angles and promote laminar flow of the fluid flowing therethrough.

[0059] The slit located on the upper surface is defined in an upper suction assembly having two channels, one channel for each slit. The upper suction assembly has an elongated body of approximately parallelepiped shape. Two cavities connecting the respective slits with the respective gas outlets are defined inside the elongated body. The two slits are arranged as a whole, their lengths are less than the length of the elongated body and are arranged obliquely so that the projections of the slits on a plane perpendicular to the direction of advance of the sample overlap to ensure the continuity of suction over the entire width of the elongated body. The internal cavity of the elongated body defines a suction duct for conveying the fluid sucked through the slit to the respective outlet port, which is configured to avoid sharp angles and promote laminar flow of the fluid flowing therethrough.

[0060] Preferably, the slits on each side are defined in a corresponding side suction assembly having a channel, one assembly being provided for each side. The side suction assembly is a prism having a substantially parallelepiped shape. A cavity connecting the respective slits with the respective gas outlets is defined within the body. There is a single slit having a length substantially the same as that of the suction body and arranged parallel to the direction of advance of the sample. The internal cavity of the elongated body defines a suction tube for conveying the fluid sucked through the slit to the respective outlet, which is configured to avoid sharp angles and promote laminar flow of the fluid flowing therethrough.

[0061] A first advantage of the invention is that the flushing of the detection zone is carried out through the same conduit as the conduit through which the gas is sucked from the detection zone. Thus, according to the invention, the conduit is used in a bidirectional manner, i.e., both for sucking gas from the detection zone and conveying it to the sensor and for introducing the flushing gas or gas mixture into the detection zone. This arrangement makes it possible to flush away the unwanted gas in a rapid manner from the detection zone through which the sample passes and from the zone defined by the conduit arranged between the detection zone and the sensor and between the sensor and the exhaust fan, which is more critical for the possible presence of unwanted gases. In addition, this can speed up the operation without having to wait for the unwanted gas to leave the zone by non-forced diffusion to the external environment. In addition, always thanks to this arrangement, the space in which the sensor is located and the internal space of the same sensor are also flushed due to the action of the flushing gas or gas mixture. Thanks to this arrangement, the risk of the environment through which the sample passes and the conduit conveying the gas to the sensor being contaminated by unwanted gases due to the passage of the previous sample is minimized, thus significantly improving the ability to detect trace leaks, i.e. micro leaks.

[0062] Advantageously, the present invention is capable of detecting leakage of gas or gas mixtures, even small amounts, i.e. micro-leaks, from small-sized holes, i.e. micro-pores, of the order of a few micrometers, e.g. 3-7 μm, which occur accidentally in the flexible wall of a container.

[0063] Furthermore, the invention optionally provides the possibility of implementing a detection method capable of significantly increasing the sensitivity of the detection itself. Such a detection method can advantageously increase the detection sensitivity, thus making it possible to detect low tracer gas concentrations present in the atmosphere in the detection zone due to micro-leaks of said tracer gas from the sample container.

[0064] Thus, the invention is able to detect gas micro-leaks from containers where the tracer gas concentration is slightly higher than the gas concentration in the external environment. According to the invention, such a detection method can be implemented without or in combination with a function that changes the composition of the gas mixture near the container.

[0065] According to such a further embodiment of the invention, at least two sensors are provided, which are arranged to generate respective signals indicative of the presence of the tracer gas. The same gas flow drawn from the detection zone passes through the two sensors in series, whereby the second sensor, i.e. the sensor located downstream of the first sensor, generates a delayed signal relative to the first sensor.

[0066] In an alternative to this embodiment, a single sensor is provided and the delay is achieved by passing the same airflow from the detection zone through the same sensor first in one direction and then in the opposite direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Some preferred embodiments of the present invention will be provided by way of non-limiting examples with reference to the accompanying drawings, in which:

[0068] Figures 1A-1F is a schematic diagram of many embodiments of the present invention;

[0069] Figure 2A is a side perspective view of a device according to a preferred embodiment of the present invention.

[0070] Figure 2B yes Figure 2A Side perspective view of the detection zone of the device shown.

[0071] Figure 2C yes Figure 2A Side plan view of the detection zone of the illustrated device.

[0072] Figure 2D yes Figure 2A Top view of the detection area of ​​the device shown.

[0073] Figure 3A is a perspective view of a squeeze roller according to the first embodiment.

[0074] Figure 3B yes Figure 3A A perspective view of a squeeze roller shown in , with the end plates removed.

[0075] Figure 4 is a cross-sectional perspective view of a squeeze roller according to a modified embodiment.

[0076] Figure 5A is a top perspective view of a first diffuser;

[0077] Figure 5B yes Figure 5A A perspective view of the diffuser shown in ;

[0078] Fig. 6A is a side plan view of a second diffuser;

[0079] Figure 6B yes Fig. 6A Bottom view of the diffuser shown.

[0080] Figure 6C yes Fig. 6A A perspective view of the diffuser shown in ;

[0081] Fig. 7A is a plan side view of the third diffuser;

[0082] Figure 7B yes Fig. 7A Bottom view of the diffuser shown.

[0083] Figure 8is a schematic diagram of a second embodiment of an apparatus according to the present invention;

[0084] Figures 9A-9E is a graph of many tracer gas concentration signals;

[0085] Fig.10 is a graph comparing two tracer gas concentration signals of different intensities;

[0086] Figures 11A-11C is a graph of as many gas concentration signals as possible that do not indicate a leak;

[0087] Fig.12 is a comparison circuit diagram of the second embodiment of the present invention.

[0088] Fig.13 is a graph of a pair of gas concentration signals generated by a pair of sensors in a second embodiment of the present invention.

[0089] Throughout the drawings, the same reference numbers are used to indicate identical or functionally equivalent components. DETAILED DESCRIPTION

[0090] Reference Figure 1A , which schematically shows a detection device 11 manufactured according to a preferred embodiment of the present invention and comprising a detection zone 13. The detection zone 13 is arranged to receive a sealed container CT, which is to be checked to determine whether there is a possible leak, i.e. an opening enabling the contents of the container CT to communicate with the surrounding environment outside the container. According to a preferred embodiment of the present invention, the detection zone 13 is defined by a support structure 15 including a frame 17, and it communicates with the external environment.

[0091] The device 11 also comprises a gas sensor device 19, which is arranged to generate an electrical signal indicating the presence of a specific gas in the gas mixture passing through the sensor 19. In a specific embodiment of the invention, the gas is CO2 and the sensor 19 is an infrared CO2 sensor, which comprises a measuring cell equipped with an IR emitter and a corresponding photodetector. The gas mixture to be analyzed, when passing through the measuring cell in the sensor 19, causes a change in at least one parameter of the electrical signal passing in the circuit associated with the photodetector. This change is proportional to the amount of CO2 present, i.e. proportional to the CO2 concentration in the mixture passing through the sensor 19. In other embodiments, different types of gas sensors can be provided to detect CO2 with different modalities, or to detect different types of gases, such as He or H2. Such sensors are known to those skilled in the art and will not be described in more detail.

[0092] The device 11 also includes a conduit 21 connected to the detection zone 13 and the gas sensor 19. According to the present invention, and as will become more apparent from the following description, in the step of extracting gas from the detection zone 13, the gas flows from the detection zone 13 to the sensor 19 through the conduit 21 in a first direction (arrow f1), and in the gas flushing step, the gas flows from the sensor 19 to the detection zone 13 through the conduit 21 in a second direction (arrow f2) opposite to the first direction.

[0093] according to Figure 1A In the embodiment of the invention depicted in , the device 11 comprises a flushing gas blower 23 having an outlet 23a from which flushing gas is discharged, and an inlet 23b, which is in communication with the duct 21; the inlet 23b serves as an inlet for the sucked gas and is connected to a controlled environment (not shown) containing the flushing gas. In the embodiment shown, the device 11 also comprises an exhaust fan 25, which has an inlet 25a for sucking air, which is in communication with the duct 21; and an outlet 25b for exhausting the sucked air into an uncontrolled environment, such as the external environment. Always referring to the embodiment shown, the duct 21 comprises a first section 21a connected between the detection zone 13 and the sensor 19, a second section 21b connected between the sensor 19 and the first port of the three-way switching valve 27, and two sections 21c and 21d connected between the second port 27b of the valve 27 and the blower 23 and between the third port 27c of the valve 27 and the exhaust fan 25, respectively.

[0094] In this preferred embodiment of the invention, the segment 21a is in communication with the detection zone 13 via a diffuser 29. According to the invention, a single detection zone 13 may be equipped with a plurality of diffusers 29. For example, the diffuser 29 may be arranged around the container CT passing through the zone 13 so that substantially the entire side surface of the container CT passing through the zone 13 is affected by the air suction of the diffuser 29.

[0095] Reference Figure 1B In a particular embodiment of the invention, the diffuser 29 is in communication with a single sensor 19 via a corresponding section 21a of the parallelly arranged conduits 21 .

[0096] Reference Figure 1C In another embodiment, a plurality of diffusers 29 are provided, each diffuser belonging to an independent and separate detection system equipped with its own sensor 19 , blower 23 , exhaust fan 25 and valve 27 .

[0097] Reference Figure 1DIn yet another embodiment of the present invention, a configuration between the aforementioned configurations is provided, wherein each diffuser 29 is equipped with a dedicated sensor 19 and each sensor 19 is connected to a single valve 27 associated with a single blower 23 and a single exhaust fan 25 through a corresponding section 21b of the duct 21.

[0098] Still according to the invention, other embodiments are conceivable, for example resulting from combinations of the arrangements described above.

[0099] Furthermore, each diffuser 29 may preferably be configured and oriented to suit the geometry of the zone 13 and the geometry of the containers CT to be inspected passing through the zone 13 .

[0100] Preferably, the controlled environment from which the blower 23 draws gas contains a mixture of specific gases, such as a gas different from the tracer gas present in the container to be inspected, or a gas mixture wherein the concentration of that type of gas present in the container to be inspected is lower than the concentration of the same gas in the container.

[0101] Back to Figures 1A to 1D , shows an embodiment of the invention in which a blower 23 and an exhaust fan 25 are provided for each duct 21. The blower 23 has an outlet 23a which communicates with the duct 21 through a section 21c of the duct 21, and the exhaust fan 25 has an inlet or suction port 25a which communicates with the duct 21 through a section 21d of the same duct 21. A three-way valve 27 is also provided to connect the duct 21 with the exhaust fan 25 during the suction step and to connect the duct 21 with the blower 23 during the flushing step. The same three-way valve 27 closes the connection between the duct 21 and the blower 23 during the suction step and closes the connection between the duct 21 and the exhaust fan 25 during the flushing step. Thus, according to this embodiment of the invention, the suction of air and flushing from the detection zone 13 are performed by two separate and independent units 23, 25 which exclusively connect the duct 21 and the detection zone 13 through the three-way valve 27.

[0102] Reference Figure 1E , which schematically and partially shows an alternative embodiment of the device 11 of the invention, in which the suction of air from the detection zone 13 and the flushing step are performed by a single unit 31, which thus acts both as an extractor and as a flushing gas blower. The unit 31 comprises a valve 33, which is arranged so that the duct 21 communicating with the detection zone 13 is alternately connected to the inlet / outlet 31a or the outlet / inlet 31b of the unit 31. The unit 31 can, for example, consist of a reversible blower unit or a compressor. Moreover, during the suction step, the single unit 31 discharges the sucked gas to the external environment, while in the flushing step it takes the flushing gas from a controlled environment containing the flushing gas.

[0103] Reference Figure 1F , schematically and partially shows another alternative embodiment of the device 11 of the present invention, in which the air suction from the detection zone 13 and the flushing step are performed by a single unit 31 ', which thus acts both as an exhaust fan and as a flushing gas blower. The unit 31 ' is preferably connected to the valve 27 ' via a five-way valve, which is configured as follows:

[0104] connecting the section 21b of the duct 21 with the inlet 31'a of the unit 31', and connecting the outlet 31'b of the unit 31' with the external environment (during the step of sucking air from the detection area 13), or, in the alternative

[0105] The section 21b of the pipe 21 is connected to the outlet 31'b of the cell 31', and the inlet 31'a of the cell 31' is connected to the controlled environment containing flushing gas (during the flushing step).

[0106] In another embodiment of the invention, the extraction of air and flushing from the detection zone 13 are performed by a single reversible unit which can be operated as an extractor or a blower by reversing the direction of its operating movement.

[0107] Reference Figures 2A-2D According to the embodiment shown in the present invention, the sample container to be tested is placed in the detection zone 13 defined in the device 11 by the positioning assembly 51. According to this embodiment, the positioning assembly 51 includes a pair of conveyor belts 53, 55, which are respectively used to introduce or allow the container to enter the detection zone 13 and to remove or allow the container to exit the detection zone 13. Preferably, the positioning assembly 51 also includes a pair of side guides 55a, 55b for correctly positioning the container in the detection zone 13, preferably in the center of the zone 13.

[0108] Still referring to this embodiment, a pressing assembly 57 is also provided in the detection zone 13, comprising a pair of rotatable rollers 59a, 59b arranged transversely to the direction of advancement "d" of the conveyor belts 53, 55 and having an axis of rotation "S1" substantially parallel to the plane defined by said belts 53, 55 on which the sample containers to be tested are placed. Each roller 59a, 59b is suspended on a pair of floating arms 61, each of which is connected to a respective cylinder 63 capable of applying a pressure suitable for pressing the container located in the detection zone 13 to the arms 61 and therefore to the rollers 59a, 59b and, if there is an opening in said container, promoting the leakage of gas from the interior of the container to the surrounding environment in the zone 13.

[0109] A motor 65 for rotating the rollers 59a, 59b by means of a drive belt 67 is arranged in correspondence with the pivot axis "S2" of each arm 61. The position of the pivot axis "S2" of the arm 61 is fixed relative to the structure 15 of the device 11, while the position of the axis of rotation "S1" of the rollers 59a, 59b can be varied according to the pressure exerted by the pneumatic cylinder 63 when the container passes through the detection zone 13. The assembly comprising the arm 61, the corresponding pneumatic cylinder 63 and the rollers 59a, 59b associated with the arm of the described pressing assembly 57, defines as a whole a three-stage lever. An angular potentiometer 69 capable of generating an electrical signal indicating the angular position of the associated arm 61 and therefore the position of the rollers 59a, 59b relative to the sample container present at this moment in the detection zone 13 is arranged on the frame 17 of the fixed structure 15 of the device 11 in correspondence with the pivot axis "S2" of each arm 61. The angular displacement indicates the presence of a sample container to be checked in the zone 13. Angular displacement of the arm 61 and associated rollers 59a, 59b indicates that the sample is present in the region 13 and that the sample has been locally deformed by the pressing assembly 57. For example, if the container arrives very flat due to a severe leak causing it to collapse or shrivel, the sample will no longer be pressed and the same sample will be discarded.

[0110] A plurality of diffusers 29a, 29b, 29c, 29d are located in the detection zone 13, each of which comprises a corresponding suction head 71a, 71b, 71c, 71d equipped with a plurality of slits 73 for sucking gas. The slits 73 are generally arranged along a peripheral band substantially surrounding the sample container when the sample container moves in the detection zone 13. In addition, the peripheral band is arranged on a plane "P1" substantially perpendicular to the advancing direction "d" of the sample on the bands 53, 55. The slits 73 are generally arranged along the upper surface, a pair of side surfaces and the bottom surface of the peripheral band. Two slits 73 are located on the upper surface and belong to the upper diffusion head 71a; four slits 73 are located on the bottom surface and belong to the bottom diffusion head 71d. A slit 73 is provided on each side, and there are two side slits 73 in total, belonging to the side diffusion heads 71b and 71c, respectively. In addition, each slit 73 is connected to a corresponding pipe formed in a corresponding head provided with a slit, which in turn is connected to the gas sensor 19 through a port 75. According to the arrangement described and related to this particular embodiment of the invention, each slot 73 along the peripheral band is associated with a corresponding port 75. Figures 1A-1D In one of the depicted embodiments, port 75 may be connected to as many sensors 19 as desired, or to a single sensor 19 .

[0111] The detection zone 13 is also equipped with an auxiliary diffuser 77 which blows an air curtain or air knife which helps to isolate the detection zone 13 from contamination by gases from the surrounding environment.

[0112] Reference Figure 3A and 3B, the rollers 59a, 59b of the extrusion assembly 57 comprise a cylindrical body 81 defining a central portion 81a bounded by a pair of lateral end plates 81b, 81c. A grooved pulley 83 is provided on the exterior of one of the end plates for engaging with a conveyor belt 67 to transmit the motion imparted by a motor 65 located corresponding to the pivot axis "S2" of one of the floating arms 61 from which the respective roller 59a, 59b is suspended.

[0113] When viewed in cross section and looking radially outwards from the inside, the central portion 81a of the rollers 59a, 59b comprises: a substantially rigid and hollow inner central sleeve 85a, for example made of steel or aluminum; an intermediate soft layer 85b, for example made of foam rubber; and an outer coating 85c made of a non-slip material, i.e., having a high grip, such as natural rubber, i.e., capable of exerting a strong friction force on the surface of a passing sample container so as to advance it without slipping when squeezed in the detection zone 13. The ends of the shaft 87, which is arranged in the central sleeve 85a, are integral with the side end plates 81b, 81c and the outer pulley 83.

[0114] In the alternative, refer to Figure 4 The rollers 59a and 59b of the extrusion assembly 57 include a hollow rubber sleeve 91. Thanks to the properties of the sleeve material, the outer surface 91a of the sleeve has anti-slip properties, and due to the reverse extrusion resistance of the sample container when passing under the rollers 59a and 59b, the internal cavity 91b of the sleeve determines that the sleeve 91 has a certain softness and compression capacity through the external radial thrust.

[0115] Back to Figures 2A to 2D , it is necessary to interrupt the conveyor belt, taking into account that the detection zone 13 includes a peripheral belt of suction slits 73 surrounding the sample container when the sample container passes through the detection zone 13. Therefore, the conveyor belt 53, 55 includes: an input part 53, which advances in the direction towards the detection zone 13 to place the sample into the zone 13 and pass it through the inside of the belt of slits 73; and an output part 55, which advances in the direction away from the detection zone 13 to move the sample out of the zone 13 to a destination downstream of the zone 13 in the container processing plant. The destination can be a preferred destination including containers in a packaging plant or a special destination, where containers with defective hermetic sealing are discarded. The slit 73 in the bottom surface of the peripheral belt belonging to the bottom diffusion head 71d is located at the interruption of the conveyor belt, between the end of the input part 53 and the beginning of the output part 55. Thus, the portions 53, 55 will be spaced apart from each other in the longitudinal direction of the conveyor belt advance by a distance sufficient to allow the bottom diffuser head 71d to draw air but without affecting the smooth transfer of the sample containers, i.e. in such a way that the interruption does not cause blockage or change the direction of the sample.

[0116] The slits 73 located on the upper surface and the side of the peripheral band are height-adjustable to cope with sample containers of different sizes in the detection area 13 .

[0117] The slits 73 belonging to the upper head 71a are therefore positioned along the upper surface of the peripheral strip, arranged obliquely with respect to the plane of the strip and inclined at an angle of about 15° to 30° with respect to said plane. The grooves 73 belonging to the side heads 71b, 71c are therefore positioned along the sides of the peripheral strip, arranged substantially perpendicular to the plane of the strip and parallel to the direction of advancement "d" of the sample. The slits 73 belonging to the bottom head 71d are therefore positioned along the bottom surface of the peripheral strip, parallel to the plane of the strip and perpendicular to the direction of advancement "d" of the sample.

[0118] As can be seen from Figure 5A and 5B Better understood, the bottom slit 73 is defined in a suction head or assembly 71d having four channels, one slit 73 for each channel. The bottom suction assembly 71d has an elongated body having a substantially trapezoidal cross-sectional shape. Four separate cavities 101 are defined inside the elongated body, communicating the corresponding slits 73 with corresponding gas outlets 75. Overall, four slits 73 are provided in the bottom suction head 71d, their lengths being shorter than the length of the elongated body, and arranged on two parallel lines, with a pair of slits on each line. In addition, the slits 73 are offset to ensure the continuity of suction over the entire length of the elongated body of the head 71d. The internal cavity 101 of the elongated body defines a suction conduit for conveying the fluid sucked through the slits 73 to the corresponding outlet 75, which is configured to avoid acute angles and promote laminar flow of the fluid flowing therethrough.

[0119] Reference Figures 6A to 6C , the slit 73 located on the upper surface of the peripheral band is defined in an upper head 71a or an upper suction assembly having two channels, one slit 73 for each channel. The upper suction assembly 71a has an elongated body of approximately parallelepiped shape. Two cavities 105 are defined inside the body, connecting the corresponding slits 73 with the corresponding gas outlets 75. Overall, two slits 73 are provided, their lengths are shorter than the length of the elongated body of the head 71a, and are arranged obliquely so that the projections of the slits on a plane perpendicular to the advancing direction "d" of the sample overlap to ensure the continuity of suction over the entire width of the elongated body of the upper head 71a. The internal cavity 105 of the elongated body defines a suction duct for conveying the fluid sucked through the slit 73 to the corresponding outlet 75, which is configured to avoid sharp angles and promote laminar flow of the fluid flowing therethrough.

[0120] Reference Fig. 7A and 7BAs shown, the slit 73 located on each side is defined in a corresponding side head 71b, 71c or a side suction assembly having a channel, one assembly on each side. The side suction assemblies 71b, 71c have a prism with a roughly parallelepiped shape. A cavity 109 is defined inside the body, connecting the corresponding slit 73 with the corresponding gas outlet 75. There is a single cavity 73 in each side head 71b, 71c, the length of which is roughly the same as the corresponding suction body and is arranged roughly parallel to the forward direction "d" of the sample. The internal cavity 109 of the elongated body defines a suction conduit for conveying the fluid sucked through the slit 73 to the corresponding outlet 75, which is configured to avoid sharp angles and promote laminar flow of the fluid flowing therethrough.

[0121] Back to Figure 1A , a preferred embodiment of the method for detecting whether there is leakage in a sealed container according to the present invention will be described below.

[0122] The method mainly comprises: a step of placing the container to be checked for leaktightness in a detection zone 13; and a step of sucking the air present in the detection zone 13 through at least one suction duct 21 connected to the detection zone. According to the invention, the suction step is preceded by a step of flushing the duct 21 and the detection zone 13, which step is performed by reversing the airflow flowing through the same duct 21.

[0123] According to a first aspect, the invention consists in defining a predetermined gas atmosphere, preferably substantially free of turbulence, in the detection zone 13, wherein such a tracer gas enclosed in the container is present in a constant concentration. Advantageously, the shape and arrangement of the diffuser 29 described above enable the desired results to be obtained with respect to the absence of turbulence in the zone 13. According to such a first aspect, the invention enables the detection of gas micro-leaks from the container when the tracer gas concentration inside the container differs from the tracer gas concentration in the surrounding environment.

[0124] Furthermore, the invention also optionally provides the possibility of changing the composition of the gas mixture in the vicinity of the container in the detection zone 13 by means of a flushing step, thereby changing the gas concentration corresponding to the tracer gas enclosed in the sealed container. Thus, the invention enables the detection of gas micro-leaks from the container when the gas composition is substantially the same as the gas composition in the surrounding environment before the change during the flushing step.

[0125] By way of example, CO2 is introduced as a tracer gas into the container before sealing the container, and according to the first aspect described, the invention provides a CO2 concentration in the container that exceeds the CO2 concentration in the atmosphere (typically 400 ppm), and, according to the second aspect described, provides a CO2 concentration that is substantially the same as the CO2 concentration in the atmosphere. In the second case, as previously described, the invention provides for defining a modified atmosphere, i.e. an atmosphere with a reduced CO2 concentration or without CO2, in the detection zone 13 by means of a flushing step. The second aspect of the invention can be achieved, for example, by introducing a pure gas, such as nitrogen, into the detection zone.

[0126] In a preferred embodiment of the present invention, the suction step and the flushing step are respectively performed by a suction fan 25 having a suction port 25a communicating with the duct 21 and by a blower 23 having an outlet 23a communicating with the same duct 21. A three-way valve 27 is further provided to connect the communication duct 21 with the suction fan 25 during the suction step and to connect the communication duct 21 with the blower 23 during the flushing step. The same three-way valve 27 closes the communication between the duct 21 and the blower 23 during the suction step and closes the communication between the duct 21 and the suction fan 25 during the flushing step.

[0127] According to the invention, the gas sensor 19 is arranged along the suction and flushing conduit 21 between the detection zone 13 and the suction unit 25 or the blower 23 and is arranged to generate an electrical signal indicating the presence of a given gas in the gas flow flowing in the conduit 21 coming from the detection zone and touching said sensor 19. Advantageously, the arrangement of the gas sensor 19 adjacent to the detection zone 13 increases the measurement sensitivity of the gas sensor. In fact, the gas sucked from the detection zone 13 by the suction unit 25 reaches the gas sensor 19 directly without having to flow through the suction unit 25 beforehand, which will homogenize the gas to be detected in the sucked gas sample.

[0128] Therefore, according to the present invention, the method for detecting whether there is a leak mainly and preferably comprises the following steps:

[0129] defining a detection zone 13 in which the sealed container is to be placed;

[0130] The detection area 13 is connected to the gas sensor 19 through the pipeline 21;

[0131] introducing the flushing gas or the gas mixture into the detection zone 13 by causing the flushing gas or the gas mixture to flow through the conduit 21 in a first direction;

[0132] Placing the container in the detection zone 13;

[0133] A gas sample is drawn from the detection zone 13 and conveyed to the sensor 19 to determine if there is a gas leak in the container by causing the gas to flow through the same conduit 21 in a second direction opposite to the first direction, from the detection zone 13 to the sensor 19.

[0134] Furthermore, it is preferred that the aspiration step is started immediately after stopping the flushing step, ie in a substantially seamless manner.

[0135] Optionally, the method according to the present invention comprises a step of subjecting the sample container to a compression or squeezing step to facilitate possible gas escape. Preferably, the squeezing step is performed by the squeezing assembly 57 described above.

[0136] Now refer to Figure 8 A preferred embodiment of a device 11 ′ made according to a particular embodiment of the invention will now be described, said device 11 ′ being arranged to implement a detection method capable of significantly improving the sensitivity of the detection itself.

[0137] exist Figure 8 In the figure, reference numerals 219a and 219b denote two gas sensors connected in series in the same pipeline 21. According to this embodiment of the present invention, the pipeline section 21e connects the two sensors 219a, 219b, and when detecting the tracer gas mixed with the gas mixture from the detection area 13 and flowing in the pipeline 21, the signal generated by the sensor 219b will be delayed relative to the signal generated by the sensor 219a located downstream of the pipeline section 21e.

[0138] In the following, the operating principle of a variant of the detection method according to the present invention will be explained in more detail.

[0139] Reference Fig. 9A , shows that by referring to Figures 1A-1E A graph showing the CO2 concentration over time as measured by an indicative signal generated by a CO2 sensor 19 of the type implemented in the first embodiment of the present invention is described. Fig. 9A The graph in relates to the operating cycle of the device 11 of the invention when there is no sample to be tested, or when the sample is completely sealed, ie there is no leakage at all.

[0140] According to a preferred embodiment of the method of the present invention, at time T0, a flushing gas stream from a blower 23 reaches the detection zone 13 of the device 11 manufactured according to the present invention. The flushing gas may be, for example, nitrogen or a gas mixture with a high nitrogen concentration. The flushing gas stream is introduced into the detection zone 13 through a diffuser 29. The flushing gas stream flows through the duct 21 in the direction of the detection zone 13 and hits the gas sensor 19, which detects 0 ppm CO2, because nitrogen is essentially the only gas that contacts the gas sensor.

[0141] At time T1, the flushing gas flow is stopped and, in a substantially seamless manner, an extraction step is started to extract air from the detection zone 13, always through the same diffuser 29 through which the zone 13 has been flushed. Furthermore, the air extracted from the detection zone 13 by the exhaust fan 25 flows through the same duct 21 through which the flushing gas flow previously flowed and is intercepted by the sensor 19, which detects, for example, 400 ppm, i.e. a typical atmospheric CO2 concentration.

[0142] At time T2, the pumping step stops and the flushing step starts again, in which nitrogen from the blower 23 is introduced into the detection zone 13. The nitrogen again flows through the same duct 21 in the opposite direction to the air pumped in the previous step and is intercepted by the sensor 19, which again detects 0 ppm CO2, since nitrogen is again the only gas touching said sensor 19. At time T3, the cycle stops.

[0143] Reference Fig. 9B , reference is now made to a sample container to be tested passing through the detection zone 13 of the device 11, the container containing a tracer gas, presumably CO2.

[0144] Fig. 9B The graph of the CO2 concentration measured by the indication signal generated by the CO2 sensor 19 over time is shown. The operation cycle is basically the same as the above case, but at time T1, the sample container to be tested with the micropores leaking CO2 is passed through the detection area 13 at a constant speed. Fig. 9B It can be seen that the sensor 19 is at time T 1- The CO2 leak is detected in the interval between T2. ​​The CO2 concentration at the sensor 19 gradually increases to a maximum value and then decreases as the sample and the micropores passing through move away from the detection zone 13. At time T2, when the container under test has passed the detection zone 13 and the microleak has therefore moved out of the diffuser 29 for aspirating the gas, the aspiration is stopped and the flushing step of introducing pure nitrogen, i.e. a gas containing substantially 0 ppm CO2, is started again. At time T3, the cycle stops.

[0145] Reference above Fig. 9A and 9B The operating cycle of the device 11 described can also be achieved by using compressed air (400 ppm, Fig. 9B The dashed line in the figure) replaces pure nitrogen ( Fig. 9B solid line in the figure) as flushing gas, or by using another gas mixture with a CO2 concentration lower than the detected CO2 concentration due to the micro-leak.

[0146] Reference Fig. 9C, shows the variation of the CO2 concentration measured by the sensor 19 over time in the case where two samples passing through show different amounts of gas leakage, namely a small amount (dashed line) and a large amount (solid line). It can be understood that in the example shown, the shape of the signal curve indicating the variation of the tracer gas CO2 concentration is essentially always the same. It will become more obvious from the following description that the experiments carried out can actually determine that the graphical appearance of the signal indicating the gas concentration in the interval T1-T2 has a Gaussian-like behavior. What is obviously different is the signal intensity, which depends on the size of the opening causing the leak, the tracer gas concentration in the gas mixture overflowing from the container, and if there is a squeeze assembly 57, whether the sample squeezes the assembly 57 mechanical pressure and the size of the mechanical pressure (the stronger the squeeze, the higher the leak intensity detected by the sensor 19).

[0147] Reference Fig.9D and 9E , shows a graph of the CO2 concentration changing with time when the tracer gas in zone 13 in the interval T1-T2, i.e., the ambient CO2 concentration in the example shown, is disturbed while the sample passes through at a high speed.

[0148] Special reference Fig.9D , shows a graph of the CO2 concentration measured at sensor 19 varying with time when a very high and constant background value of the tracer gas CO2 in this particular case with a variable offset appears in the interval T1-T2, in the case where two passing samples exhibit different amounts of gas leakage, namely a small amount (dashed line) and a large amount (solid line).

[0149] Special reference Fig.9E , shows a graph of the CO2 concentration measured by sensor 19 varying over time when a very high and highly fluctuating background value of the tracer gas CO2 with strong turbulence and variable offset in the specific case occurs in the interval T1-T2, when two passing samples show different amounts of gas leakage, namely a small amount (dashed line) and a large amount (solid line).

[0150] from Fig.10 It can be seen that the detection method based on a fixed threshold value for the tracer gas concentration has a number of limitations. Firstly, due to the fixed threshold value, this detection method is very sensitive to background gas excursions. Secondly, the moment at which the signal from the sensor, indicating the tracer gas concentration, exceeds the fixed threshold value and thus signals the presence of a leak depends on the tracer gas concentration, i.e. on the amount of the leak. Always refer to Fig.10 , where signals indicating a small leak (dashed line) and a large leak (solid line) are shown, and the threshold is identified by the horizontal solid line Th. The moment when the leak signal is emitted actually has a time shift T→T' that varies with the tracer gas concentration.

[0151] Furthermore, this method of setting a fixed threshold value relative to the signal generated by the gas sensor has little excellent performance in the case of a very small amount of micro-leakage and may cause a false alarm problem, i.e., a false signal that a leak has occurred. Fig.11A , shows an example where a small change in tracer gas concentration at the gas sensor due to a micro-opening in the container is not sufficient to identify that the container is not properly sealed and is therefore likely to be discarded. Fig. 11B An example is shown in which a concentration fluctuation of the same type of gas as the tracer gas introduced into the container, due to causes external to the container, is misinterpreted as a leak because it is sufficient to generate a signal at the gas sensor whose value exceeds a set fixed threshold. Fig. 11C shows an example similar to the previous one, where background gas turbulence due to causes external to the vessel is misinterpreted as a leak.

[0152] Therefore, fixing the threshold too low results in the practical impossibility of distinguishing transitions caused by micro-leaks from those caused by background noise in most cases. The presence of background noise therefore forces the threshold to be set to a value significantly different from zero and, in any case, whose absolute value is higher than the noise "peak". In the specific case, this therefore means that a leak will only be detected if the amount of the leak is much larger than the background fluctuations.

[0153] The detection method according to an alternative embodiment of the invention, which makes it possible to significantly increase the sensitivity of the detection itself, uses the principle of being able to accurately establish the moment, i.e. the time, at which a leak occurs. Establishing an accurate and reproducible time at which a leak occurs can significantly shorten the analytical interval of measurements on a moving sample near the channel of the sample container affected by the leak to be detected. The precise choice of time makes the detection method less sensitive to environmental turbulence, even though environmental turbulence can generate signals that are very similar to the signal characteristics of a leak and can therefore be misinterpreted as a leak indication signal.

[0154] As previously referenced Fig.10As described, by assuming a fixed threshold value Th, the exceeding of which triggers a signal indicating the presence of tracer gas, the delay of the moment T, T' at which the leak signal is emitted due to exceeding the threshold value varies as the amplitude of the signal indicating the presence of gas caused by the leak changes. More specifically, the delay increases as the amplitude of the signal decreases. Assuming that the signal generated by the sensor 19 is sent to a comparator device, which is set so that the comparator generates a logic signal "0" when the input signal strength of the comparator is below the set threshold and generates a logic signal "1" when the input signal of the comparator exceeds the set threshold, due to the delay indicated above, the time interval between the transition from the logic state "0" to "1" does not correspond to the correct time interval of the change of the tracer gas concentration at the sensor. This effect of the timing being dependent on the signal amplitude is called the "walking" effect in the scientific literature, and as mentioned above, the timing techniques based on fixed thresholds are subject to a significant "walking" effect.

[0155] Furthermore, the signals generated by gas sensors are often affected by significant background noise, which can lead to equally significant "jitter" effects, i.e. fluctuations, in time.

[0156] The basic similarity of the shape of the signal curve indicative of the tracer gas concentration in the gas mixture reaching the sensor, despite variations in the signal amplitude, advantageously allows the use of a substantially wander-free timing technique comprising a transition of the time-logic signal occurring when the signal exceeds a threshold, wherein, ideally, for each signal, the threshold adapts itself to a defined portion of the maximum value of the curve, for example when the signal reaches half of its final amplitude.

[0157] Setting this "floating" threshold is equivalent to what is called "constant fraction timing" or "constant fraction discrimination" (CFD).

[0158] Now we will refer to Figure 8 A preferred embodiment of a device 11 ′ made according to a particular embodiment of the invention is described, which is arranged to implement a detection method capable of significantly improving the sensitivity of the detection itself.

[0159] As previously mentioned, the device 11 ' comprises a pair of sensors 219a and 219b connected to each other by a pipe section 21e, the internal volume of which is known: that is, the length and cross-sectional dimensions of said pipe section 21e are known and constant. This pipe section 21e separating the sensors 219a and 219b essentially forms a corresponding delay line for the gas propagating along the pipe 21.

[0160] Also refer to Fig.12, the corresponding signals M1 and M2 from the two sensors 219a and 219b are sent to the comparator 210, and at the same moment when the signal of the second sensor 219b exceeds the floating threshold determined by the variable signal of the first sensor, the output signal M3 of the comparator 10 will indicate that a leak has occurred in the container passing through.

[0161] This technique advantageously allows for a discrimination time point that is independent of amplitude and less sensitive to jitter and wander.

[0162] Furthermore, CFD discrimination enables higher performance of the system in the case of low-intensity leak signals and improves the measurement sensitivity. In addition, the detection method is less affected by external CO2 background variations or turbulence effects. In addition, the detection technology prevents false alarms, i.e., external fluctuations are misinterpreted as measured leaks.

[0163] exist Fig.13 In the example shown, two switches, i.e. two transitions 0 → 1 of the comparator, occur in the appropriate measurement interval. However, this switching occurs at a different point in time than the moment when the reading is taken. If the switching occurred too close in time, the system would think that they were caused by background noise and not by an event determined by a CO2 leak.

[0164] In an alternative embodiment of the device made according to this particular embodiment of the invention, the signal of the second sensor is replaced by the second signal of the first sensor, wherein the airflow is made to pass a second time in the opposite direction. In other words, according to such an alternative embodiment, the airflow from the detection zone 13 flows through the first sensor 19 by flowing along the duct in a first direction towards the exhaust fan 25 and then in the opposite direction towards the sensor 19. Obviously, in this embodiment, even a single and exclusive sensor can be provided.

[0165] In the following a specific signal processing mode will be described which can be applied to an embodiment of the present invention in which at least two gas sensors, preferably six sensors, are provided in parallel and arranged to intercept the gas flow from the detection zone 13 along the corresponding duct 21. This signal processing mode can be applied, for example Figure 1C 1. This particular processing mode correlates the signals of multiple sensors in parallel by a convolution technique applied to the sensor pairs. If the correlation exceeds a certain factor (e.g. >+0.8 or <-0.8), a pre-processing operation is performed on the signals, allowing the subtraction of a noise signal or an external disturbance signal that is common to multiple sensors and appears as a constant offset or a linear (increasing or decreasing) signal from each signal.

[0166] The preprocessing step includes sampling the signals of the two channels, thereby sampling the signal strengths SS1 and SS2 of the two gas sensors. Each signal SS i Once digitized, it can be represented as an array of points whose length depends on the duration of sampling and measurement. The Pearson correlation coefficient is defined as the covariance divided by the product of the standard deviations σ of the two variables and is considered for each signal pair:

[0167] ρ SS1 SS2 =σ SS1 SS2 / (σ SS1 ,σ SS2 )

[0168] where σ SS1 SS2 is the covariance between the two signals SS1 and SS2, σ SS1 and σ SS2 is two standard deviations.

[0169] When the Pearson coefficient is above +0.8 or below -0.8, there is a strong correlation. The Pearson coefficient is the value of the N Calculated over all combinations of .

[0170] N represents the number of channels, and the independent combination is represented by (N . (N-1)) / 2 is given.

[0171] For example, if N=6 (ie, 6 is the number of independent channels according to the preferred embodiment of the present invention), the following fifteen pairs are obtained: (1 2)(1 3)(1 4)(1 5)(1 6) (2 3)(2 4)(2 5)(2 6) (3 4)(3 5)(3 6) (4 5)(4 6)

[0176] For all combinations, if all Pearson coefficients are above +0.8 or below -0.8, the signals are correlated, indicating the presence of background variation.

[0177] In this case, all signals from SS n Subtract the average signal SS of all channels from m Array, *SS N The new value of will be

[0178] *SS1:=SS1–SS m

[0179] *SS2:=SS2–SS m

[0180] …………

[0181] *SS n :=SS n –SS m

[0182] According to the invention, this detection method can be implemented without modifying or in combination with the above disclosed function of the gas mixture in the vicinity of the container and can be initiated during the flushing step.

[0183] Industrial Applicability

[0184] The invention has industrial applications in a variety of fields for detecting leaks and micro-leaks in substantially any type of container, whether the container is compressible or rigid. The invention can also be used to detect leaks of liquids, such as water or beverages, from pressurized rigid containers.

[0185] The invention as described and illustrated is susceptible of numerous variations and modifications within the same inventive principle.

Claims

1. A method for detecting leakage of a sealed container, It is characterized in that The method comprises the following steps: defining a test zone (13) in which the sealed container (CT) is to be placed; connecting the detection zone (13) to a pair of gas sensors (219a, 219b) via a conduit (21), wherein the sensors (219a, 219b) are connected in series with each other via a segment (21a) of the conduit (21), wherein the internal volume of the segment (21a) is known and a corresponding delay line in the propagation of the gas along the conduit (21) is determined; introducing the flushing gas into the detection zone (13) by flowing the flushing gas through the conduit (21) in a first direction; placing a container (CT) in the detection zone (13); aspirating gas from the detection zone (13) and conveying it to the pair of sensors (219a, 219b) to determine whether there is a gas leak in the container (CT), conveying the gas from the detection zone (13) to the pair of sensors (219a, 219b) by causing the gas to flow through the conduit (21) in a second direction opposite to the first direction; obtaining a corresponding signal (M1, M2) from each of the pair of gas sensors (219a, 219b) and sending each corresponding signal to a comparator; An output signal (M3) is obtained from the comparator, and when the signal (M2) of the second sensor (219b) of the pair of gas sensors exceeds the floating threshold determined by the variable signal (M1) of the first sensor (219a) of the pair of gas sensors at the same time, the output signal (M3) indicates that there is a leak in the container present in the detection area (13).

2. The method according to claim 1, Features: The detection area (13) is connected to the atmosphere.

3. The method according to claim 1 or 2, Features: A step is also provided for subjecting said container (CT) to compression when placed in said detection zone (13) in order to promote the fluid to escape from said container (CT) through an opening that may be present on said container.

4. The method according to claim 1, Features: The introducing and aspirating steps are respectively performed by means of a flushing gas blower (23) and an aspirator (25) which are connected to the detection zone (13) through the pipeline (21).

5. The method according to claim 4, Features: In the introducing step, the flushing gas introduced into the detection zone (13) is obtained from a controlled environment containing the flushing gas, and in the suction step, the gas sucked from the detection zone (13) is discharged to an uncontrolled environment.

6. The method according to claim 1, Features: The introduction and aspiration steps are carried out by a single unit (31) which acts both as an exhaust fan and as a flushing gas blower by means of a gas flow reversal circuit provided with a switching valve (33) and connected to the detection zone (13) via the duct (21).

7. The method according to claim 1, Features: The introduction and suction steps are carried out by a single unit (31') acting both as an extractor and as a blower, wherein the single unit (31') is connected to a circuit equipped with a valve (27') configured such that: In the suction step, the pipe (21) connected to the detection area (13) is connected to the inlet (31'a) of the single unit (31'), and the outlet (31'b) of the single unit (31') is connected to the external environment, or In the introducing step, the pipe (21) connected to the detection area (13) is connected to the outlet (31'b) of the single unit (31'), and the inlet (31'a) of the single unit (31') is connected to the controlled environment containing flushing gas.

8. A device for detecting leakage of a sealed container, It is characterized in that The device comprises: a detection zone (13) adapted to receive a sealed container (CT); a pair of gas sensors (219a, 219b); The pipeline (21) is in communication with the detection area (13) and the pair of gas sensors (219a, 219b); a flushing gas blower (23) provided with an outlet (23a) for the flushing gas, the outlet (23a) being in communication with the duct (21), the blower (23) being configured to introduce the flushing gas into the detection zone (13) by causing the flushing gas to flow through the duct (21) in a first direction; an exhaust fan (25) having an inlet (25a) for sucking air, the inlet (25a) being in communication with the duct (21), the exhaust fan (25) being configured to suck gas from the detection area (13) by causing the gas to flow through the duct (21) in a second direction opposite to the first direction; The sensors (219a, 219b) are connected in series with each other through a segment (21a) of the pipeline (21), wherein the internal volume of the segment (21a) is known and a corresponding delay line in the propagation of gas along the pipeline (21) is determined, and wherein a corresponding signal (M1, M2) is obtained from each sensor of the pair of gas sensors (219a, 219b), and each corresponding signal is sent to a comparator, and an output signal (M3) is obtained from the comparator, and when the signal (M2) of the second sensor (219b) of the pair of gas sensors exceeds a floating threshold value determined by the variable signal (M1) of the first sensor (219a) of the pair of gas sensors at the same time, the output signal (M3) indicates that there is a leak in the container present in the detection zone (13).

9. The device according to claim 8, Features: The exhaust fan (25) is connected to an uncontrolled environment to which it discharges the gas sucked from the detection area (13), and the flushing gas blower (23) is connected to a controlled environment from which the flushing gas is taken.

10. The device according to claim 8, Features: The blower and the exhauster are a single unit (31') connected to a circuit equipped with a valve (27') configured to: connecting the pipe (21) to the inlet (31'a) of the single unit (31'), and connecting the outlet (31'b) of the single unit (31') to the external environment, or The communicating pipe (21) is connected to the outlet (31'b) of the single unit (31'), and the inlet (31'a) of the single unit (31') is connected to a controlled environment containing flushing gas.

11. The device according to claim 10, Features: The pair of gas sensors (219a, 219b) are positioned along the duct (21) between the detection zone (13) and the exhaust fan (25) or the blower (23).

12. The device according to claim 8, Features: The pipeline (21) is connected to the detection area (13) through at least one diffuser (29).

13. The device according to claim 8, Features: A suction head (71a...71d) including a plurality of slots (73) for suctioning and introducing gas is arranged in the detection area (13).

14. The device according to claim 13, Features: The slots (73) are arranged along a peripheral band around the entire sample container as it passes through the detection zone (13).

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