Blister forming is also called vacuum forming. Blister packaging products belong to the category of thermoformed packaging products. It is a kind of plastic sheet that will be processed by secondary processing. It is preheated and vacuum blistered on a certain mold to form a certain type. Shaped packaging products 1. Cutting is an important process in the production process of blister packaging. The main purpose of cutting is to cut and separate the individual blister packaging or to cut the blister packaging, that is, the whole piece processed. The blister pack is cut and separated to obtain a single packaged product, or the desired blister packaged product is trimmed and the waste side treated.
Shaped blister packaging uses blister packaging technology to package irregularly shaped objects. Since the three-dimensional shape and the planar projection shape of the shaped object are irregular shapes, the individual's cutting boundary is irregular.
At present, the cutting of blister packaging products is mostly done by mechanical cutting, that is, cutting into a model knives or forming knives according to a pre-designed graphic or mold. The traditional cutting production die cutter is combined into a cutting blade according to the design requirements of the product design, and the packaged product is cut under the action of pressure (using a punching machine) to realize cutting separation or edge removal treatment. The traditional cutting method requires custom-made model cutters. For complex blister packs or shaped blister packs, the cut stencils are quite complicated to produce and have a long production cycle. A set of molds can only correspond to one set of products. The system has a low degree of flexibility, some special shapes (such as small angle acute angles), the use of die-cutting methods can not achieve the top, etc. Pan Yushu Na and Yu Zhongcai research B117 cutting 0. At the same time, due to the limitations of the pressure cutting process, cut During the cutting process, there are problems such as bending and wrinkling at the edge of the package, and burrs on the trimming edge. With the continuous development and maturity of laser processing technology, the introduction of laser cutting in the cutting process will solve the problems of the traditional process. In this paper, the laser cutting method for the shaped blister packaging cutting is studied, and the traditional die cutting knives are replaced by machine vision, the images of the blister packaging are collected by the industrial camera, and the image processing is used to obtain the cutting outline or boundary of the packaging individual. At the same time, the method of generating the laser cutting path of the blister packaging was studied.
1 Application of laser cutting in shaped blister packaging 1.1 Laser cutting principle Laser cutting uses a high power density laser beam after focusing to illuminate the workpiece. At this time, the heat input by the beam input is much higher than that reflected, conducted or diffused by the material. In part, the material to be irradiated is quickly melted, vaporized, ablated or reaches a burning point, and the workpiece is pierced to form a small hole, and as the beam and the material move relatively linearly along a certain trajectory, the small holes are connected to form a slit, and at the same time The high-speed airflow coaxial with the beam blows off the molten material, thereby achieving the hot cutting of the workpiece. Laser cutting is a combination of melting and vaporization. The factors affecting the cutting quality mainly include hardware factors and software factors. The hardware factors mainly refer to the machine tools, processing materials, etc., and the software factors are mainly related to the computer-aided process design, including: the selection of the cutting initial position or the punching point; the setting of the main cutting path; the setting of the auxiliary cutting path; the laser beam Radius compensation and idle stroke processing; optimized layout of machined workpieces; path optimization after considering actual machining factors.
1.2 Principle of laser-cut shaped blister packaging The materials of special-shaped blister packaging include thermoplastic sheets of ABS, PVC, PP, PE, PS, etc. The laser cutting is a laser-cut non-metallic material during the cutting process, and the cutting mechanism is vaporization. Cutting. The non-metallic material is a good absorber of a C2 laser beam having a wavelength of 10.6. Due to the small thermal conductivity of the material, the heat conduction loss is small, it can absorb most of the incident beam energy, and quickly evaporate the material, forming a starting hole from the spot irradiation, and entering the cutting process. Vaporization cutting means that when a high power density laser is irradiated onto the surface of the workpiece, the material is heated to a vaporization point in a very short period of time, and part of the material is vaporized to form a slit. Most organic materials and ceramics are vaporized and cut. H. For the cutting of plastic materials in shaped blister packaging, laser cutting uses its high energy density vaporization adhesive to rapidly destroy the polymer chain of polymer materials to achieve plastic products. laser cutting. For the low-melting thermoplastic material, the laser cutting process is controlled, and the burr-free bottom edge can be obtained, and the slit is smooth and flat. When cutting the blister packaging of PVC materials, it is necessary to pay attention to the harmful gases generated during the cutting process.
1.3 Advantages of laser-cut shaped blister packaging Laser cutting is a more advanced cutting method in industrial cutting processing. It is also the most mature technology in laser processing technology. It is applied in the cutting process of shaped blister packaging, replacing traditional The mechanical cutting method can reflect many advantages, as described below.
Laser cutting is a kind of non-contact cutting. There is no mechanical extrusion and punching during the cutting process. It does not cause extrusion and bending of the blister packaging. The blister packaging has no mechanical deformation and no wrinkles at the edges.
Laser cutting has a high power density, a small slit width, a neat cutting edge and no burrs. Due to the short laser action time, the heat affected zone around the workpiece is small. At the same time, for different materials, cutting can be carried out, and the adaptability is strong.
When laser-cut shaped blister packaging, there is no problem of tool wear in traditional cutting, so the steps of tool maintenance and tool change can be omitted.
Laser cutting requires only positioning, no need to tighten, scribe and other preparation processes, so the blister packaging has no mechanical stress and surface damage.
The use of laser cutting to cut shaped blister packaging can be easily combined with automated equipment to improve the flexibility of the cutting system without the need for custom molds. It can carry out large-scale production cutting, and can also perform edge-cutting and plastic cutting of single body and small quantity of blister packaging.
The use of laser cutting to cut the shaped blister packaging allows the cutting to be separated from the mold. The cutting system can be combined with the computer and CAD software to completely control the cutting path autonomously, and the packaging boundary of any complex shape can be cut. Achieve a boundary or shape that cannot be cut in the traditional way, with unlimited contour cutting ability.
Especially for the special-shaped blister packaging, due to the irregularity, multi-change and complexity of the packaging shape, and the single-piece and small-batch trial cutting, the traditional mold cutting method is difficult to achieve the precision and complex adaptability of the cutting. This makes the advantages of laser cutting more vivid in the cutting of shaped blister packaging.
2 machine vision-assisted laser cutting traditional blister packaging cutting method depends on the mold stencil, especially the shaped blister packaging, due to its irregular shape, complex edge shape, resulting in a large mold stencil production Difficult, and some special shape cuts can not be completed. In the process of laser cutting instead of the traditional mechanical cutting of blister packaging, machine vision technology can be used instead of the traditional template, which makes the cutting out of the template, making the cutting of the shaped blister packaging more flexible. , greatly improving the flexibility of the cutting system.
In the process of laser cutting the blister packaging sheet, the moving path of the laser head mainly includes two parts: a processing trajectory generated according to the contour of the part to be processed (ie, a laser cutting path) and an auxiliary connecting path between the respective cutting paths (including the starting point). , the auxiliary path of the end, and the connection path between the contours of each part. 5. In the process of machine vision-aided laser cutting of the shaped blister package, it is necessary to apply machine vision and image processing to accurately generate the contour cutting trajectory of the part to be machined. According to the arrangement of the parts to be processed, each auxiliary connection track is automatically generated, and the connection trajectory is ensured to be reasonable and effective.
2.1 Generation of profiled blister packaging products The formation of profiled blister packaging includes cutting and separating a plurality of processed blister packs to obtain a full-cut cut of individual packaged products, and The individual blister packaging products are trimmed and the waste-treated monomer is removed for cutting. In both types of cutting, it is necessary to obtain a contour trajectory of the product to be cut before laser cutting to generate a laser cutting processing trajectory. According to the characteristics of the shaped blister packaging cutting, the laser cutting system is improved, the machine vision system is added into the system, and the image of the workpiece to be cut is obtained by the industrial camera. Based on this, the image is processed to obtain the workpiece. The contour trace, this is the actual cutting path of the laser.
There are many kinds of boundary contour extraction algorithms in image processing, including Sobel operator, Log operator, Lapalce transform, Robert operator, Can-ny operator, etc. These operators are divided into two cores by two-dimensional discrete micro-division, supplemented by correlation. Filtering and processing to achieve edge extraction.
Through the comparison of the experimental and processing results, the Canny operator is selected as the algorithm for generating the laser cut contour trajectory in the shaped blister packaging. The Canny algorithm has an edge detection optimal filter that filters both noise and edge characteristics, and uses a first-order differential filter. This algorithm uses the order derivative of the two-dimensional Gaussian function in any direction as a noise filter, and performs filtering by convolving with the image; then, the filtered image is used to find the local maximum of the image gradient to determine the edge of the image. According to the measurement of the signal-to-noise ratio and the positioning product, the optimal approximation operator is obtained. 63. At the same time, all the contour traces obtained are screened, and only the outermost contour of the packaged product is retained, which is the actual cutting path of the laser.
Since the actual cutting path of the laser is a closed contour curve, the cutting of each contour trajectory starts from a certain point on it, and returns to this point after cutting the circumference along the closed contour trajectory. This is used as the cutting starting point and is also the cutting end point of each individual contour trajectory. In this way, this point also becomes a marker point for each contour trajectory, that is, a contour trajectory can be determined by a certain cutting starting point, and the cutting starting point also represents the positional relationship of the contour with other contours. After the image is acquired for the contour trajectory, the starting cut point of each contour trajectory is automatically generated according to the processing process needs. 2.2 Generation of auxiliary connection path In the process of automatically generating the cutting path, it is necessary to accurately generate the contour cutting trajectory of the part to be machined, and automatically generate the auxiliary connection trajectory according to the arrangement of the parts to be processed, and ensure the connection. The plausibility of the trajectory. For the cutting of ordinary flat sheets, the generation of the auxiliary connection path is relatively easy. Usually, the problem is transformed into the traveling agent TSP (Traveling Salesman Problem) problem 7-8, which is solved according to the shortest path principle to ensure the processing efficiency. For the special-shaped blister packaging products, since the plastic sheets are subjected to plastic processing, space protrusions are formed, and the shapes and heights are different. Therefore, in addition to the shortest path principle, the laser head must be considered to avoid the convex portions of the materials, that is, Tool avoidance problems.
In this paper, the A algorithm in the field of artificial intelligence is applied to realize the generation of laser cutting auxiliary connection path and automatic obstacle avoidance.
The A algorithm belongs to a heuristic search algorithm in the field of artificial intelligence. Heuristic search is an improvement on the breadth-first search in the state space search method. The main idea is to filter all the nodes of the next layer through a valuation function and then determine the direction of the search. 8. The core of the heuristic search algorithm is the evaluation function /U): f (the actual cost from the initial state to the current state; h(n) is the estimated cost from the current state to the target state in the state space. When expanding the state node, first Calculate the valuation function f(n) of each node, and then select the node with the smallest evaluation function f(n) to expand. If a search algorithm can find the best solution path, it is called adoptability.
(n) is the valuation function; g(n) is the actual cost from the initial state to the current state in the state space; h(n) is the estimated cost from the current state to the target state in the state space. Since f cannot be known in advance, it is approximated by the previous evaluation function f(n); g(n) is approximated by g(n), but g(n)g(n) is required; h(n) is h() n) Approximate, but requires h(n)>h(n). It has been mathematically proven that the valuation function that satisfies these conditions can find the shortest path, that is, it is acceptable, so the A algorithm is acceptable.
For the full-page separation cutting and the single-edge cutting in the cutting of the special-shaped blister packaging, the A-algorithm can be used to automatically generate the auxiliary connection path. At the same time, for the single edge cutting, laser cutting and A algorithm auxiliary processing can be used to cut one package at a time, or manually place multiple single packages randomly on the cutting table for multiple times of cutting. Single packaging to improve processing efficiency.
The A algorithm can be used to generate an auxiliary connection path between the contour traces of each package and the randomly arranged single package contour traces. The start and end points of the auxiliary connection path are respectively the two contour traces of the successive cuts. The starting point of the cut. These two cutting starting points are also the starting node and the target node in the A algorithm.
Therefore, only the coordinates of the starting node and the target node are known, and the A-algorithm can automatically generate an auxiliary connection path between the two package unit contour trajectories, and at the same time ensure that the automatically generated connection path is the optimal solution, and the package There is no interference in the raised area.
3 Shaped blister packaging laser cutting system composition and processing according to the application of laser cutting profiled blister packaging process characteristics, coupled with machine vision equipment, the overall shaped blister packaging laser cutting system composition block diagram.
In the laser cutting system, the image acquisition system is an information input system, and the image information of the shaped blister packaging product to be processed is collected by an industrial camera. The processing system is a processing system for inputting information, and processing processing algorithms such as image processing, boundary extraction, and trajectory generation generate processing trajectory data that can be recognized and read by the laser numerical control system. The laser control system is the control core of this system, which realizes the post processing of the processing track, the configuration and optimization of the processing parameters and the actual control of the system. The laser cutting system is the execution part of this system, and the cutting of the shaped blister packaging products is realized by laser cutting.
Select the shaped blister packaging products that need to be cut and cut by the unit for processing, see -3. Among them, the image of the special-shaped blister packaging products collected by the image acquisition system, the black area is the shaped blister packaging. Boundary and internal coverage area (after pre-processing), the laser cutting trajectory obtained by applying Canny algorithm and A algorithm (including the actual edge of the contour and the auxiliary processing trajectory, in order to avoid confusion, the retraction trajectory is not shown; 2 picture periphery The black border is not the processing track in order to display the border of the image.
4 Conclusions The application of machine vision and laser cutting to cut the shaped blister packaging has been studied. It is proposed that the combination of image processing and A algorithm can replace the reliance on the template in traditional cutting, which can solve complex contours well. The cutting problem of the irregular shaped blister packaging products with irregular contours has achieved good results in practical applications. Under different industrial environments and noise interference, the method of processing the collected blister packaging images still needs further research to improve the system adaptability and processing accuracy.
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