DE102016118670B4 - Process and device for testing preforms - Google Patents

Abstract

Method for testing the condition of preforms (2) immediately following the manufacturing process of the preforms, comprising the steps
- Transporting the preforms (2) to be tested by means of a first transport device (3),
- Transporting the tested preforms (2) by means of a second transport device (5),
- Transferring the preforms (2) from the first to the second transport device (3, 5) at a transfer point (4),
- Recording thermal images of the preforms (2) using a thermal imaging camera (6) during the transfer of the preforms (2),
- Processing the thermal images in such a way that the temperature distribution on the surface of the preforms (2) is determined and anomalies in the temperature distribution on the surface of the preforms (2) are revealed by comparing the temperature distribution of the recorded thermal image with a reference thermal image for the respective, produced preform is compared.

Description

• - Transportieren der zu prüfenden Preforms mittels einer ersten Transporteinrichtung,
• - Transportieren der geprüften Preforms mittels einer zweiten Transporteinrichtung,
• - Übergeben der Preforms von der ersten an die zweite Transporteinrichtung an einer Übergabe.

The invention relates to a method for checking the condition of preforms immediately following the manufacturing process of the preforms, comprising the steps

• - Transporting the preforms to be checked by means of a first transport device,
• - Transporting the tested preforms using a second transport device,
• - Transferring the preforms from the first to the second transport device at a transfer point.

• - eine erste Transporteinrichtung eingerichet zum Transportieren der zu prüfenden Preforms,
• - eine zweite Transporteinrichtung eingerichtet zum Transportieren der geprüften Preforms,
• - eine Übergabe zum Übergeben der Preforms von der ersten an die zweite Transporteinrichtung.

The invention also relates to a device for checking the condition of preforms immediately following the manufacturing process of the preforms

• - a first transport device set up for transporting the preforms to be tested,
• - a second transport device set up for transporting the tested preforms,
• - A transfer for transferring the preforms from the first to the second transport device.

In the production of containers, in particular bottles, what are known as preforms, ie preforms, are generally first produced and these preforms are then further processed to form the finished containers. These preforms are typically made of plastic, especially PET (polyethylene terephthalate) using an injection molding process. PET bottles are usually manufactured in two process steps. In a first step, the preforms are manufactured using the injection molding process. In a second step, the PET bottles are made from the preforms using the stretch blow molding process.

The two manufacturing steps can be carried out directly in the plastics processing plant in a one-step process. However, the two-step process with a separation of the injection molding process from the stretch blow molding process is more common.

Because faulty preforms force production to be interrupted, in the prior art the preforms are checked for the presence of faults before they are fed to the second processing step. Possible defects in the manufactured preforms are, above all, imprecise dimensions, areas in the container wall that are too thin or too thick, pinholes, burns, inclusions or an incorrect color quality.

Image processing systems have established themselves for checking preforms. The preforms are moved past a digital camera, taking one or more images of each preform. An electronic processing device compares the recordings with a reference image and determines whether the respective preform is error-free or has certain defects. If a defect is detected, the image processing system can use a separate device to sort out preforms that have been identified as defective.

Such an image processing system is described by INTRAVIS GmbH, Rotter Bruch 26 a, 52068 Aachen, in their brochure "INTRAVIS Vision Systems, Image Processing Systems Preforms" in Version 09/2013 A. The image processing system configured there as an inline system checks the preforms for all geometric features and material defects in both the body and the mouth area of the preform at speeds of up to 72,000 objects per hour.

Furthermore, from the WO 2014/147176 A1 a method and a device for checking the color quality of preforms is known, in which the objects to be checked can be fed to a digital image recording device in a disordered manner. As a result, the device can be easily integrated into existing production machines for preforms without corresponding devices for aligning and orderly feeding the preforms to the digital image recording device. When leaving a transport device, the preforms are transferred into a receiving vessel in a disordered manner, with the preforms being picked up between leaving the transport device and the receiving vessel. The test method that can be carried out with the device described makes it possible to discover preforms with color defects without having to align them beforehand. In addition, it only requires a small adjustment of the existing production machine for the preforms.

The DE 100 47 269 A1 discloses a method and a device for determining a temperature distribution of bulk material. When handling and processing such bulk materials, particles agglomerate, some of which retain very high temperatures inside for a long time. If the agglomerations come into an oxygen-rich environment, fires can occur, sometimes with considerable consequential costs. It is therefore proposed to determine the temperature distribution of the bulk material in a spatially resolved manner in a measuring range of a fall distance in order to prevent fires in bulk material.

The WO 2013/087762 A1 discloses a method and associated system for inspecting articles provided with a gas barrier layer. An infrared camera takes an image of each object and processes these images using a processing module in such a way that defective objects are identified and eliminated.

The DE 198 46 995 A1 relates to a method for the non-contact detection of structural and/or surface defects in plate-shaped materials. For fast, non-contact and non-destructive detection, it is proposed that thermal energy is continuously introduced into the surface of the test specimen, which is continuously moved relative to the heat source, via a heat source, and that one thermal image or several thermal images are then continuously recorded line by line from the previously heated surface of the test specimen.

The WO 2011/137264 A1 discloses a system and method for non-destructive testing and detection of thickness and structural variations in opaque and semi-opaque non-metallic composites and plastic materials using infrared thermographic techniques.

The US 2002/0033943 A1 discloses an apparatus and method for detecting flaws in colored plastic articles comprising irradiating the article in the near infrared, measuring radiation reflected from or transmitted through the article and analyzing the reflected or transmitted radiation to obtain defect data for provide the item.

The U.S. 2008/0022632 A1 discloses a method and apparatus for taking thermal images of heat-sealed seams produced in heat-sealing stations when sealing containers with tear-open foils. To determine the airtightness of the heat seal, a thermal image of the seam is taken while the seam is still hot. By evaluating the image, it can be determined whether the temperature of the seam is within a range that ensures a proper seam, or has exceeded an upper or lower limit for the temperature, which indicates a faulty heat seal seam. Defective objects can then be sorted out on the basis of the evaluation of the thermal image.

Based on this prior art, the invention is based on the object of creating a method for testing the condition of preforms that can be easily integrated into existing production systems, in particular injection molding systems for preforms, and enables early detection of faults in the production process or the Manufacturing plant allows, especially before defects show up in the preforms. In addition, a device for carrying out the method is to be specified.

The solution to this task is based on the application of passive thermography. With the help of imaging processes, the temperature distribution on the surface of the preforms is recorded immediately after the manufacturing process. In contrast to active thermography, the preforms to be tested are not thermally excited in order to generate additional heat flow in the preforms.

The object is achieved in detail by a method having the features of independent claim 1 and a device having the features of independent claim 10 . During the transfer of the preforms from a first to a second transport device, thermal images of the preforms are recorded using at least one thermal imaging camera. The recorded thermal images are processed in an electronic processing device in such a way that the temperature distribution on the surface of the preforms is determined and anomalies in the temperature distribution on the surface of the preforms are revealed. For this purpose, the temperature distribution of the recorded thermal image is compared with a reference thermal image for the respective preform to be produced. If there are deviations that exceed specific tolerance values stored in the processing device, this is detected by the processing device. Such deviations indicate that temperatures that are too high or too low occur in the manufacturing process. This can occur due to local overheating in the cavities of the injection molding machine or insufficient after-cooling after the injection molding process. The preforms produced in the injection molding machine in the first step are selectively cooled using different devices. In particular, the body and the thread arranged on the neck of the preform are cooled on the inside and outside. Cooling errors can occur if the preforms are not positioned correctly in relation to a cooling device. From the temperature distribution between the body and the neck of each preform, it can be seen, for example, whether the preforms are properly cooled.

Although the known testing methods for the freedom from defects of preforms by means of digital image recording devices do not yet signal an error, problems can already occur at an early stage with the method according to the invention revealed during the manufacturing process of the preforms.

In one embodiment of the invention, the preforms to be tested are transported in an unordered manner by means of the first transport device and are transferred to the second transport device in free fall. This procedure allows the unproblematic integration of the device for checking the condition of preforms in existing production plants for preforms. Furthermore, any anomalies in the temperature distribution of the preforms can be recorded without the preforms previously coming into contact with devices for sorting and/or aligning the preforms, which can influence the surface temperature and thus the thermal image. The recording of the preforms by means of the thermal imaging camera in free fall is preferably carried out immediately at the beginning of the free fall, as long as the speed of the preforms is still low.

In order to increase the time window for recording thermal images of the preforms, in one embodiment of the invention the preforms are transferred along an inclined plane. The transfer along the inclined plane takes place, for example, with a chute that reduces the speed of the preforms during transfer.

However, in order to record the temperature distribution of as many preforms recorded on the thermal images as possible, the preforms are preferably first aligned during transfer and only then recorded using the thermal imaging camera. The electronic processing device is preferably set up in such a way that an alignment of the preforms in the longitudinal direction is sufficient, it being irrelevant whether the dome or the neck of the preform is at the front in the transport direction. Such an alignment of the preforms can take place, for example, by means of a chute which is arranged between the first and second transport direction and has channels running in the longitudinal direction, which are set up for aligning the preforms. The at least one thermal imaging camera is aligned with the transfer in such a way that only thermal images of the aligned preforms are recorded, preferably immediately after leaving the chute.

So that the thermal images are only slightly distorted by the atmosphere between the preforms and the thermal imager, the thermal images are recorded at a maximum distance of two meters between the thermal imager and the preforms. Furthermore, the thermal imaging camera preferably works in a limited wavelength range in which the atmosphere hardly emits or absorbs its own radiation.

In order to prevent the thermal images from being falsified by external heat sources, the thermal images are preferably recorded in front of a background with a surface with a homogeneous temperature distribution. A plate with liquid-carrying channels, for example, can be considered as the background. In this case, it is not necessary for the plate to be cooled to temperatures below ambient temperature by means of the liquid. It is crucial that the plate through which liquid can flow has a homogeneous temperature distribution on the surface. The surface is preferably non-reflective in order to avoid reflection of surrounding, warm objects in the thermal image.

Above absolute zero temperature, each preform emits thermal radiation with an emissivity ε < 1, which depends on the material of the preform, in this case PET. The spectrum of the thermal radiation emitted depends on the temperature. With increasing temperature, the emitted spectrum shifts to shorter wavelengths (Wien's shift law). Depending on the material-dependent emissivity and the temperature-dependent emission spectrum of the preforms to be examined, the preferably limited wavelength range of the thermal imaging camera is matched to the emitted spectrum of the preforms, in particular in such a way that the limited wavelength range of the thermal imaging camera corresponds at least partially with the expected emission spectrum of the preforms preferably completely overlaps.

For preforms with surface temperatures between 20 and 100 degrees Celsius, the thermal imaging camera has a limited wavelength range of around 8 to 14 µm (long-wave infrared - LWIR). In principle, a thermal imaging camera with a wavelength range between 3 and 5 µm (mid-infrared - MWIR) could also be considered. In this wavelength range, however, the radiant power is significantly lower at the specified temperatures of the preforms. Thermal imaging cameras therefore preferably use the long-wave infrared spectral range.

In principle, uncooled and cooled thermal imaging cameras can be considered as thermal imaging cameras. Cooled cameras count the photons of energy in a specific wavelength, typically in the infrared range between about 3 - 5 µm. The photons hit the individual sensors in the array, which are electronically controlled. The thermal sensitivity (temperature resolution) cooled cameras is significantly higher compared to uncooled cameras. The cooled camera's detectors must be cooled to operating temperature. If the cooling fails, the thermal imaging camera cannot work properly. In addition, the cooling requires a start-up time. In addition, the advantage of a higher thermal sensitivity is paid for by the high acquisition and operating costs of the cooled cameras.

For economic reasons, an uncooled thermal imaging camera is therefore preferably used in a device for carrying out the method according to the invention. The sensors of the uncooled camera are made of a material whose resistance changes significantly with temperature. Such uncooled thermal imaging cameras do not require expensive cooling devices. They are therefore significantly smaller and cheaper than the cooled thermal imaging cameras.

• 1 Eine schematische Seitenansicht einer Vorrichtung zur Prüfung von Preforms gemäß einer ersten Ausführungsform der Erfindung,
• 2 eine schematische Seitenansicht einer Vorrichtung zur Prüfung von Preforms gemäß einer zweiten Ausführungsform der Erfindung sowie
• 3a eine schematische perspektivische Ansicht einer dritten Ausführungsform der Erfindung mit Einrichtungen zum Ausrichten der Preforms an der Übergabe sowie
• 3b eine schematische Darstellung der ausgerichteten Preforms während der Übergabe.

The invention is explained in more detail below with reference to the figures. The figures show:

• 1 A schematic side view of a device for testing preforms according to a first embodiment of the invention,
• 2 a schematic side view of a device for testing preforms according to a second embodiment of the invention and
• 3a a schematic perspective view of a third embodiment of the invention with devices for aligning the preforms at the transfer and
• 3b a schematic representation of the aligned preforms during transfer.

1 shows a device (1) for testing the condition of preforms (2), which are produced by means of an injection molding machine, not shown, and then selectively cooled. The device (1) comprises a first transport device (3), which is designed as a conveyor belt in the exemplary embodiment. The upper run of the conveyor belt of the transport device (3) transports the preforms (2) to be checked from the injection molding machine (not shown) to a transfer (4) for transferring the preforms (2) from the first transport device (3) to a second transport device (5) for Transport of the inspected preforms (2).

The device (1) also includes a thermal imaging camera (6) which is aimed at an upper area of the transfer (4), ie the area directly below the deflection (3a) of the conveyor belt. The thermal imaging camera (6) is connected to an electronic processing device (7), for example a personal computer, which is set up to process the thermal images of the preforms (2) recorded by the thermal imaging camera (6).

The second transport device (5) is also designed as a conveyor belt. Of course, other continuous conveyors, such as in particular roller conveyors or vibratory conveyors, can also be used as transport devices. The first transport device (3) is arranged in a first transport level and the second transport device (5) in a second transport level below the first transport level.

The preforms (2) are transferred in free fall, as is the case with the free-falling collective (2a) of the preforms (2) in 1 is indicated. The thermal images are recorded using the thermal imaging camera (6) in front of a background (8) with a surface (8a) with a homogeneous temperature distribution. The homogeneous temperature distribution of the surface (8a) is generated by a cavity (8b) through which fluid can flow, which is arranged on the rear side of a plate and through which a temperature-controlled medium can flow continuously. The temperature is preferably controlled by the medium in such a way that the surface (8a) has a surface temperature corresponding to the ambient conditions.

The embodiment of the device for testing the condition of preforms (2) according to 2 differs according to the device 1 essentially in that the preforms (2) are transferred to the second transport device (5) along an inclined plane. In this embodiment, the background (8) also forms the inclined plane on which the preforms (2) slide. Due to the temperature control of the surface (8a) of the background (8) by means of the cavity (8b) through which fluid can flow, a homogeneous temperature distribution on the surface (8a) is permanently ensured. Local heating of the background (8) and thus a heat signature on the surface (8a) of the background (8) that would falsify the thermal images are avoided by maintaining the homogeneous surface temperature. The temperature control also allows the use of a cheaper thermal imaging camera with a lower resolution.

Both after the device 1 as well as the device 2 the transfer of the preforms (2) from the first transport device (3) to the second transport device (5) takes place in an unordered form, as can be seen from the group (2a) of preforms shown schematically and located in the area of the transfer (4). is. The thermal image of individual preforms (2) of the collective (2a) may therefore be incomplete under certain circumstances, since it is completely or partially overlaid by other preforms. In addition, individual preforms (2) can be at an angle to the background (8) in the thermal image, with the result that the temperature distribution of only part of the surface can be seen on the thermal image.

In the embodiment after 2 With the transfer of the preforms (2) along the inclined plane created by the background (8), it is already largely ensured that the preforms are recognized by the thermal imaging camera over their entire length, since the longitudinal axis of the preform is usually parallel to the thermal imaging at the moment the thermal image is recorded aligned with the surface (8a) of the background.

However, the above statements make it clear that the devices according to the 1 and 2 do not allow all preforms (2) to be subjected to an inspection, since some preforms are always in a position during free fall or sliding down the inclined plane during the recording of the thermal image, which precludes a meaningful evaluation by the processing device.

As part of the processing of the thermal images, those recorded preforms are identified whose position on the thermal image is suitable for comparison with a reference thermal image. In the event of deviations from the reference thermal image, for example local overheating of the preform, a faulty manufacturing process in the injection molding machine and/or faulty after-cooling can be inferred.

in the in 3a, b In the device shown, the preforms (2) are aligned during transfer, immediately after leaving the first transport device (3), with the aid of an inclined chute (9) with channels (9b) running in the longitudinal direction (9a).

At the end of the chute section, the aligned preforms (2) leave the chute (9) and in front of the background (8) are in free fall from the in 3a not shown thermal imaging camera (6) added. The collective (2a) of the aligned preforms (2) presents itself, for example, as in 3b implied. All the preforms are aligned in three rows in the longitudinal direction (9a), it being irrelevant for the thermal image recording whether the neck (2b) or the dome (2c) of the preform (2) points downwards.

Due to the parallel alignment of the longitudinal axes of the preforms (2) to the surface (8a) of the background (8), a perfect thermal image recording of the aligned preforms (2) of the collective (2c) is guaranteed.

Through the device after 3a it is therefore possible to check the temperature distribution on the surface of all preforms. This further increases the reliability of the early detection of any problems in the upstream manufacturing machine for manufacturing the preforms.

Reference List

1

contraption

2

preforms

2a

Collective

2 B

Neck

2c

dome

3

First transport device

3a

deflection

4

handing over

5

Second transport device

6

Thermal camera

7

processing facility

8th

background

8a

surface

8b

cavity

9

slide

9a

longitudinal direction

9b

gutters

Claims (18)

Method for testing the condition of preforms (2) immediately following the manufacturing process of the preforms, comprising the steps - transporting the preforms (2) to be tested using a first transport device (3), - transporting the tested preforms (2) using a second transport device (5), - transferring the preforms (2) from the first to the second transport device (3, 5) at a transfer (4), - taking thermal images of the preforms (2) using a thermal imaging camera (6) during the transfer of the preforms (2), - Processing the thermal images in such a way that the temperature distribution on the surface of the preforms (2) is determined and anomalies in the temperature distribution on the surface of the preforms (2) are revealed, in which the temperature distribution of the revealed taken thermal image is compared with a reference thermal image for the respective preform to be produced. procedure after claim 1 , characterized in that the preforms (2) to be tested are transported in a disordered manner by means of the first transport device (3). procedure after claim 1 or 2 , characterized in that the preforms (2) are passed in free fall. procedure after claim 1 or 2 , characterized in that the preforms (2) are transferred along an inclined plane. procedure after claim 3 or 4 , characterized in that the preforms (2) are initially aligned during transfer and only then are thermal images of the aligned preforms taken. Procedure according to one of Claims 1 until 5 , characterized in that the thermal images are recorded at a maximum distance of 2 meters between the thermal imaging camera (6) and the preforms (2). Procedure according to one of Claims 1 until 6 , characterized in that the thermal images are recorded in front of a background (8) with a surface with a homogeneous temperature distribution. Procedure according to one of Claims 1 until 7 , characterized in that the wavelength range of the thermal imaging camera is limited in the infrared spectrum. procedure after claim 8 , characterized in that the wavelength range of the thermal imaging camera (6) at least partially overlaps with the emission spectrum of the preforms (2), which depends on the emissivity and the temperature window to be expected. Device (1) for checking the condition of preforms (2) immediately following the manufacturing process of the preforms - a first transport device (3) set up for transporting the preforms (2) to be tested, - a second transport device (5) set up for transporting the tested preforms (2), - a transfer (4) for transferring the preforms (2) from the first to the second transport device (3, 5), - a thermal imaging camera (6) set up to record thermal images of the preforms (2) during the transfer of the preforms, - a processing device (7) connected to the thermal imaging camera (6) set up for processing the thermal images in such a way that the temperature distribution on the surface of the preforms (2) is determined and anomalies in the temperature distribution on the surface of the preforms are revealed, in which the temperature distribution of the recorded thermal image is compared with a reference thermal image for the respective preform to be produced. device after claim 10 , characterized in that the first and / or second transport device (3, 5) are designed as a conveyor belt. device after claim 10 or 11 , characterized in that the first transport device (3) are arranged in a first transport plane and the second transport device (5) in a second transport plane below the first transport plane. device after claim 12 , characterized in that the transfer (4) is set up for a free fall of the preforms (2) between the first and second transport device. device after claim 12 , characterized in that the transfer (4) comprises a chute (9) which is set up for the transfer of the preforms along an inclined plane between the first and second transport level. device after Claim 14 , characterized in that the chute (9) has channels (9b) running in the longitudinal direction, which are set up for aligning the preforms (2) in the longitudinal direction and the thermal imaging camera (6) is oriented towards the transfer (4) in such a way that only thermal images of the aligned preforms (2) are recorded. Device according to one of Claims 10 until 15 , characterized in that the thermal imaging camera (6) is arranged at a maximum distance of 2 meters from the transfer (4). Device according to one of Claims 10 until 16 , characterized in that it has a background (8) with a surface (8a) with a homogeneous temperature distribution. device after Claim 17 , characterized in that the background (8) is an integral part of the transfer (4).

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