RU2754028C1 - Method for preform optical quality control of the preform - Google Patents

Abstract

FIELD: packaging materials.

SUBSTANCE: invention relates to the production of packaging materials, namely to a method for quality control of a preform used later for the production of colorless and colored plastic bottles. The method for optical quality control of the preform includes the exposure of the molded preform to radiation from an optical radiation source. Reception of optical radiation passing through the preform is then compared with the reference optical radiation that passed through the suitable product, and then a conclusion is made about the validity of the manufactured preform. Exposure of the walls of the preform to radiation is carried out using a flat circular fan beam of optical radiation, the plane of which is perpendicular to the longitudinal axis of the preform, for which an optical radiation source is placed inside the preform, and an optical radiation receiver with a flat circular radiation reception area is placed outside. The optical control process itself is carried out by simultaneously synchronously moving the source and receiver of optical radiation relative to the preform in such a way as to scan the entire side surface of the preform and obtain a scan of its optical density, which is then compared with the optical density of the side surface of the reference preform.

EFFECT: higher accuracy of quality control of the preform.

5 cl, 8 dwg

Description

The invention relates to the production of packaging materials, and in particular to a method for quality control of a preform used in the future for the production of colorless and colored plastic bottles directly during the production of the preform.

Currently, preforms are widely used for the production of plastic bottles, each of which is a thick-walled glass with a molded bottle neck. To obtain a plastic bottle, the preform is placed in a vacuum blowing machine, where it is heated and blown into the shape of a specific bottle. The quality of bottle blowing is determined by the presence of existing defects in the geometry of the preform, as well as by the observance of technological and thermal conditions during its blowing.

The active use of PET bottles for packaging various types of drinks has led to the creation of high-performance equipment for blowing PET bottles from a preform. The capacity of this equipment is 30-50 thousand bottles per hour. Such speeds impose extremely stringent requirements on the quality of PET preforms, since getting into the blowing machine even one preform with an internal defect, for example, incomplete melting, air bubble, color inhomogeneity or specks in the body of the preform lead to a stop of the blowing machine, irreversible losses of a large amount of heat tunnel of the preform and, accordingly, large production losses.

There is a known method of monitoring the quality of the preform (see Specifications "Kit for plastic bottles" TU-2297-001-47213996-97, 1997), including control of the guaranteed geometry of the preform, its weight and transparency. But the known method, firstly, does not guarantee the high quality of inflated bottles, especially from colored preforms. This is due to the lack of control over the characteristics of the thermal conductivity of the material of the painted preforms.

Secondly, the known method is not intended to detect such defects in the body of the preform as "gas bubbles in the body", "non-melting", "specks" and the like.

Also known is a method for controlling the quality of the preform, described in US patent No. 7541556, class. В07С 5/00, 2009. The method provides for the transportation of the obtained workpieces along a given trajectory of movement, while along this trajectory an optical device is installed, suitable for forming an image of each of the workpieces, which compares the workpiece with a given standard, and when the workpiece deviates from the standard, it rejected.

The known method has one significant drawback, which is that the quality control of the preform is carried out after the completion of the manufacture of the preform and therefore is an additional production procedure and, accordingly, requires additional resources such as personnel, production premises, packaging materials and production time.

The closest to the claimed technical solution is a method of quality control of the color characteristics of the preform during the production process, described in the patent "Injection molding machine (ILM) with a system of automatic control and correction of coloring of products" (see patent RU No. 2306222, class В29С 45 / 00, G05D 7/00, 2005). The method includes double-sided transillumination of the molded preform with a source of optical radiation, receiving the optical signal passed through the preform, which is compared with a reference signal corresponding to a usable product.

In the known device, thanks to the method of optical control of preforms in the process of their production, objective control over the technology of preform coloring and correction of the supply of the required dose of dye is realized.

The known method allows for complete or selective control of products directly in the process of their manufacture with the possibility of making technological adjustments to the process, but it has three significant drawbacks.

First, as seen in FIG. 5 of patent specification No. 2306222, the optical emitter and the optical receiver are separated from each other by two walls of the PET preform, which, when working with dyed products, greatly reduces the sensitivity and contributes to the skipping of defects in the preform.

Secondly, (see Fig. 7 of this application) in the prototype when the preform is translucent, part of its wall remains in the shadow, i. E. in the dark area, which can contain more than 50% of the preform wall area. If the defect falls into the shadow zone, it will not be detected.

Thirdly, the known method has limited functionality, since provides control and adjustment of only color parameters of the preform, but is not able to fix in the preform body such defects as incomplete melting, air bubbles, black dots that appear when burnt or foreign material gets into the preform body.

The technical result of the proposed method for controlling the quality of a preform in the process of its production is the elimination of the indicated disadvantages of the known solution, namely:

- increasing the sensitivity of the preform control method, especially when working with painted products, which practically eliminates the skipping of a defective preform;

- exclusion of the shadow zone and, as a consequence, an increase in the number of detected preform defects;

- expanding the functionality of the method, in particular, identifying defects in the preform body such as incomplete melting, air bubbles, black dots, etc.

The specified technical result in the method of optical quality control of the preform, including the transillumination of the molded preform with a source of optical radiation, reception of the optical radiation passed through the preform, which is then compared with the reference optical radiation that passed through the good product, after which a conclusion is made about the suitability of the manufactured preform, is achieved by that the transillumination of the walls of the preform is carried out with a flat circular fan beam of optical radiation, the plane of which is perpendicular to the longitudinal axis of the preform, for which an optical radiation source is placed inside the preform, and an optical radiation receiver with a flat circular radiation receiving zone is placed outside, and the process of optical control itself is carried out by simultaneous synchronous movement of the source and receiver of optical radiation relative to the preform in such a way as to scan the entire side surface of the preform and obtain a scan of its optical density, which is then compared thread with the optical density of the lateral surface of the reference preform.

The specified implementation of the proposed method of optical quality control of the preform allows you to solve several problems at once.

First, to double the sensitivity of the method, because only one wall of the preform is visible, and not two as in the prototype.

Secondly, the shadow zone is completely excluded, which means that the entire surface of the preform is controlled by thoroughly viewing the full scan of the optical density of its lateral surface.

Thirdly, the functionality of the proposed method is significantly expanded, which controls not only the color parameters of the preform, but is also able to fix in the body of the preform such micro defects as incomplete melting, air bubbles, black dots that appear when burnt or foreign material gets into the body of the preform.

It is advisable to place a point emitter on the axis of the preform, for example, a miniature glow lamp, the filament of which is located in the center of a flat circular zone for receiving optical radiation, or an LED, the emitting surface of which is located in the center of a flat circular zone for receiving optical radiation. In this case, the flat annular diaphragm plays the role of a spatial filter that cuts out the most informative glow plane (with the maximum width of the radiation spectrum).

It is advantageous to place an annular optical emitter around the axis of the preform, the annular emitting surface of which is aligned with the plane of the flat circular zone for receiving optical radiation, while as the annular emitting surface it is possible to use, for example, the lateral surface of a mirror cone having an angle at the base equal to 45 degrees and fixed to its own apex at the end of a light guide rod installed along the axis of the preform and illuminated from the side of the apex of the cone by a parallel beam of optical radiation.

It is promising to make a flat circular radiation receiving area by installing a flat annular diaphragm, the diameter of which exceeds the maximum diameter of the preform and allows it to move freely along the entire height of the preform, while inside the diaphragm, place a fan of open ends of optical fibers installed radially in the plane of the circle.

Thus, the inventive method of optical quality control of preforms makes it possible to control their quality directly in the production process, while by increasing its sensitivity and excluding shadow zones from the control area, it is possible to significantly increase not only the quality of control, but also to exclude the omission of defective preforms with such defects in the body, such as incomplete melting, air bubbles, color inhomogeneity or specks and, thus, excludes further stopping of the blowing machine and significant production losses, which has no analogues among the known methods of quality control of preforms directly in the process of their production, which means that it corresponds criterion "inventive step".

The essence of the proposed method is illustrated by the drawings in FIG. 1-7.

FIG. 1 shows a figure explaining the implementation of the proposed method for monitoring the quality of a preform with a point light source located inside the preform and synchronously with it moved relative to the preform, an annular slotted receiver of optical radiation installed outside the preform, where: 1 - controlled preform, fixed inside the optical unit 2 (block body is shown conditionally); placed inside the preform 1 rod 3 with a microlight 4 fixed at its end, emitting light in various directions 5 around itself; mounted outside the preform 1 receiver of optical radiation 6 with a flat annular diaphragm 7, inside which is placed a flat fan of optical fibers 8, collected at the output of the optical unit in the beam 9; 10 - the mechanism for moving the preform 1 inside the optical unit (shown conventionally).

FIG. 2 shows a drawing of the view A-A (see Fig. 1), explaining the direction of light from the microlamp 4 through the walls of the preform 1 to the optical fibers 8 located inside the flat annular diaphragm.

FIG. Figures 3a and 3b illustrate a variant of the implementation of the proposed method for monitoring the quality of a preform with an annular optical emitter located inside the preform and synchronously moved relative to the preform, an annular slotted receiver of optical radiation installed outside the preform, where: 11 is a controlled preform fixed inside the optical block 12 (block body is shown conditionally); inside the preform 11 there is a rod-light guide 13 with a light source fixed at one end thereof, consisting of a lamp 14 and a biconvex lens 15 with an output parallel beam 16 passing inside the rod-light guide 13, at the other end of which there is a mirror straight cone 17 with an angle of inclination forming to the base equal to 45 degrees, which reflects a parallel beam of light 16 incident on it at an angle of 90 degrees, converting the light into a flat true beam 18 directed towards a flat annular diaphragm 19, inside which a flat fan of optical fibers 20 of an optical radiation receiver 21 ; at the output of the optical block 12, all optical fibers are collected in a bundle 22; 23 - a mechanism for moving the preform 11 inside the optical unit (shown conventionally).

FIG. 4 shows a drawing of the type B-B (see Fig.3a), explaining the direction of light from the lamp 14, converted into a parallel beam of light 16, passing through the glass rod-light guide 13 to the mirror cone 17, which reflects the parallel beam of light 16 incident on it at an angle of 90 degrees, converting the light into a flat, faithful beam 18, which then, passing through the wall of the preform 11 and the diaphragm 19, enters the entrance of the optical fibers 20.

FIG. 5 shows a diagram of the transmission of an optical image to the receiving window of the CCD matrix (matrix of charge coupled devices), including: an annular diaphragm 19; optical fibers 20; a collector of optical fibers 24, which is optically connected to the photodetector 25, the output of which is connected to the data bus 26.

FIG. 6 shows a block diagram of an optoelectronic converter 27 consisting of a photodetector 25 connected by a data bus 26 to a control unit 28. Also in FIG. 6 shows a block diagram of a computer device 30, to the input of which signals from an optoelectronic converter 27 are received via the data transfer bus 29. The computer device 30 includes: a processor 31; input-output device 32; RAM (random access memory) 33; ROM (Read Only Memory) 34; as well as external devices - keyboard 35 and monitor 36.

FIG. 7 is a drawing explaining the occurrence of a shadow zone (dark zone) that occurs when using the method taken as a prototype.

We will consider the implementation of the proposed method by examples using various options for its implementation.

Option 1.

First, consider the implementation of the proposed method using the device shown in Fig. 3a. The device participates in every working cycle of the ILM. When transferring products from the transfer robot to the cooling unit, it performs a full scan of the preform body to detect the presence of defects in the preform body such as incomplete melting, air bubbles, color irregularities or specks. When registering the presence of a defective preform in the device, a signal is sent to the rejection system and the defective product is dumped into a separate container for defective preforms. Let us consider in more detail the operation of an optical device that controls the quality of the preform I, which is scanned by moving it relative to the annular light source 18 (the luminous ring on the lateral surface of the cone 17) and, together with it, the moving annular optical radiation receiver 21. A distinctive feature of this embodiment of the method is the fact that the light source is a lamp 14 located outside the preform and located in the focus of a biconvex lens 15, which converts the divergent light lamp 14 into a parallel beam of light 16, which, passing inside the light guide rod 13, falls on a mirror straight cone 17 with an angle of inclination of the generatrix to the base, equal to 45 degrees. The cone reflects a parallel beam of light 16 incident on it at an angle of 90 degrees, converting the light into a flat, faithful beam 18, which passes through the wall of the preform 11, and then the radial light flux proportional to the transparency of the wall of the preform enters the receiving diaphragm 19, in which the open end of the optical fiber is located 20. Section B-B (see Fig. 4) schematically shows the azimuthal arrangement of the receiving ends of the optical fibers 20, which transmit the luminous flux to the slotted plane of the radial emitting collector 24 (see Fig. 5). The luminous flux leaves the end sections of the optical fibers 20, arranged in an orderly manner on the radial emitting collector 24 and enters the photodetector unit 25, consisting of optical lenses 25a, transferring this image to the receiving window of the CCD matrix 256. The CCD matrix is an analog integrated circuit consisting of light-sensitive photodiodes and using CCD technology - charge coupled devices. Thus, the image of the projection of the slit light flux passed through the wall of the preform 11 along its perimeter is transferred to the receiving window of the CCD matrix 256, which converts the light fluxes of various intensities coming from the optical fibers 20 into electrical signals proportional to the density of individual sections of the lateral surface of the preform. The control unit 28 (see Fig. 6) continuously polls the CCD matrix 256, and the electrical signals received from the CCD matrix via the data transfer bus 29 transmits to the input of the computer device 30, which then compares these signals with the signals of the reference preform stored in its ROM 34. If the received signals do not exceed the tolerance limit with reference signals, a conclusion is made about the suitability of the product. Option 2.

The inventive method operates in a similar manner using the device shown in FIG. 1. The difference from option 1 is that the presented diagram of the device for optical quality control of the preform operates with a point light source located inside the preform and a slotted optical radiation detector installed outside the preform. The light source and the slit receiver also move together relative to the preform. Since the point source 4 emits light 5 around itself in different directions, the optical radiation receiver 6 is equipped with a flat annular diaphragm 7, which transmits only that part of the radiation 5 that passes through the body of the preform 1 and corresponds to the width of the entrance slit of the diaphragm 7, inside which the optical fiber 8. Due to this, we control the annular cut of the preform 1, equal to the width of the inlet slit of the diaphragm 7.

For the technical implementation of the proposed technical solution, a mock-up of the device was developed, shown in Fig. 1. Below are the main technical characteristics of the device layout.

1. An XBHAWT-00-0000-000LT60E1 white light-emitting diode was used as a point light source 4.

2. A fan of optical fibers in the amount of 150 pieces was used as a receiver of optical radiation 6, forming an annular fan-shaped receiver with a diameter of 47 mm, which was 4 mm higher than the maximum diameter of the preform. The width of the entrance slit of diaphragm 7 corresponded to 1.5 mm.

3. A point light source and an optical radiation detector were fixed on a common movable platform, which scanned the preform to the full height (110 mm) in a time equal to 0.7 sec.

4. An ILX751B microcircuit (manufactured by Sony Corporation) with a resolution of 2048 pixels was used as a CCD matrix.

5. An objective based on lenses AL5.934.020 and AL7.554.010 was used as an objective 25a projecting light pulses onto a CCD matrix.

6. The signals from the CCD matrix were read out by a standard electronic circuit based on the TMDSLCDK138 microprocessor assembly from TEXAS INSTRUMENTS.

7. A personal computer of the brand "DELL Optiplex 5070" was used as a computer device 30: processor: Intel Core i7 9700T; processor frequency: 2 GHz (4.3 GHz, in Turbo mode); RAM: SO-DIMM, DDR4 8192 MB 2666 MHz; video card: Intel UHD Graphics 630; SSD: 256GB; operating system: Windows 10 Professional.

The layout of the device fully confirmed the advantages of the proposed method in comparison with the prototype, especially in terms of identifying such manufacturing defects as incomplete melting, air bubbles, black dots, color irregularities or specks.

Claims (5)

1. A method of optical quality control of a preform, including transillumination of a molded preform with a source of optical radiation, reception of optical radiation that has passed through the preform, which is then compared with the reference optical radiation that has passed through a suitable product, after which a conclusion is made about the suitability of the manufactured preform, characterized in that transillumination the walls of the preform are carried out with a flat circular fan-shaped beam of optical radiation, the plane of which is perpendicular to the longitudinal axis of the preform, for which an optical radiation source is placed inside the preform, and an optical radiation receiver with a flat circular radiation receiving area is placed outside, and the optical control process itself is carried out by simultaneous synchronous movement relative to the preform of the source and receiver of optical radiation in such a way as to scan the entire side surface of the preform and obtain a scan of its optical density, which is then compared with the optical density the lateral surface of the reference preform. 2. The method according to claim 1, characterized in that a point optical emitter, such as a miniature glow lamp, is placed on the axis of the preform, the filament of which is located in the center of a flat circular zone for receiving optical radiation. 3. The method according to claim 1, characterized in that a point optical emitter, such as an LED, is placed on the axis of the preform, the emitting surface of which is located in the center of a flat circular zone for receiving optical radiation. 4. The method according to claim 1, characterized in that an annular optical emitter is placed around the preform axis, the annular emitting surface of which is aligned with the plane of a flat circular optical radiation receiving area, while, for example, the lateral surface of a mirror cone can be used as the annular emitting surface having an angle at the base equal to 45 degrees, and fixed with its apex at the end of a light guide rod installed along the axis of the preform and illuminated from the side of the apex of the cone by a parallel beam of optical radiation. 5. The method according to claim 1, characterized in that the flat circular zone for receiving radiation is carried out by installing a flat annular diaphragm, the diameter of which exceeds the maximum diameter of the preform and allows it to move freely along the entire height of the preform, while a fan of open ends of optical fibers is placed inside the diaphragm installed radially in the plane of the circle.

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