First, the photoelectric detection technology in the packaging process
Photoelectric detection mainly uses photoelectric sensors to measure. The working principle of photoelectric sensor is that the light source generates luminous flux, and the parameters of luminous flux (such as the cross-sectional area of radiant energy flow, spectral composition, luminous intensity, etc.) are controlled by the measured object, and then converted into changes of electrical parameters by photoelectric devices for measurement. Different light sources can be used in different working environments, such as incandescent lamps, lasers, light emitting diodes and so on. Sometimes the controlled object itself is the signal source, such as the sign line on the packaging bag.
In general, the directly detected signal is weak and lacks stability, so amplification and shaping circuits are often added to the control circuit to improve the practical operation ability of the system. The measuring mechanism includes an indicator, an alarm, a digital display and a product classification device, which displays the relevant measured values of products or automatically classifies products. Usually, in order to automatically adjust the production process to keep the controlled quantity unchanged or change according to certain rules (such as automatically adjusting the cutting position of packaging bags), it is necessary to add a feedback circuit to the circuit.
The invention has the advantages of simple structure, long detection distance, high precision, fast response speed and long service life. It has its unique advantages in pattern recognition. Non-contact detection can be realized, no force and moment act on the measured object, and even if the measured object has a great impact force, the detection instrument will not be damaged. Similarly, some products that require high packaging technology, such as food and medicine, can also be measured through their non-contact characteristics.
The photoelectric detection circuit is composed of electronic components or integrated circuits, which has the advantages of low cost, high sensitivity, fast measurement speed, objective indication and easy automation. With the development of computer technology and machinery industry, the combination of light, machinery and electricity can be realized, and data processing, verification, logical judgment and storage can be realized, so as to adjust the precision of packaging process and realize synchronous feeding.
To illustrate the problem, here is an example of position detection and positioning in the process of automatic packaging control:
In the process of packaging operation, the radius of the drum is decreasing, the tension of the wrapping paper changes, the friction coefficient between the paper feeding roller and the wrapping paper fluctuates due to the influence of environmental temperature and humidity, and the actual tangent of the knife roller deviates from the specified position due to trademark printing errors and differences in paper feeding, longitudinal sealing and cutting. Although each error is small, due to the long-term accumulation of high-speed operation of the machine, the tangent will be seriously deviated, which will reduce the packaging quality and even cause waste products. Therefore, it is necessary to add automatic photoelectric positioning detection control equipment to the system.
The photoelectric detection and positioning system uses photoelectric tracking to detect the positioning color mark on the packaging paper, and outputs corresponding control signals by comparing the error between the paper feeding speed and the transverse sealing cutting speed, so as to push the actuator to automatically position or compensate the error. In order to detect reliably, it is required that the background color of the positioning color label is obviously different from that of the packaging paper, and the greater the contrast, the more sensitive the detection is. The color code requires bright colors, uniform ink and a certain area. Generally, color codes are rectangular, and the ratio of length to width should be appropriate. According to different packaging materials, photoelectric detection can be divided into transmission and reflection. Transmission type is used for the detection of transparent materials, and the packaging materials pass between the emitting head and the reflecting head. In this way, even if the packaging material jumps in the feeding process, the detection sensitivity will not be affected, and it is not easy to be disturbed by ambient light. Reflective, the emitting head and the reflecting head are in the same direction, and the focused light beam is required to form a focus on the packaging material or the reflecting plate, so the packaging material is not allowed to have a big jump when passing through the detection part. According to different packaging forms and packaging requirements, the photoelectric detection and positioning devices used for feeding, bag making and sealing and cutting on the packaging machine are also different.
Second, the application of laser technology in printing and plate making
Laser is a new discipline and high technology. Since its birth in the early 1960s, it has attracted the attention of all countries in the world and developed rapidly. The application scope of laser is expanding, and many corresponding fields have undergone profound changes. The printing industry around the world, like other industries, actively adopts this new technology. Laser has applications in electronic plate making, color separation, laser phototypesetting and holographic printing technology, and greatly optimizes the printing system. Limited by space, this paper only discusses the application of laser in plate making. Printing plate is an indispensable part in the printing process, and it is the medium to transfer ink to the substrate. The quality of printed matter is directly related to the quality of printed matter. The printing industry has been working hard to improve the plate-making process, so as to make printing plates as quickly and as well as possible, and at the same time reduce the labor intensity and plate-making cost. In the early days, gravure printing, relief printing and offset printing were mainly made by manual, mechanical, chemical etching, electrophotographic technology and so on. However, these methods have some defects, such as unstable operation and long plate-making time. Since the birth of laser, these problems have been solved. Using the high intensity, high coherence and monochromaticity of laser, printing plates can be made quickly and reliably.
Laser engraving printing plate is to aim the focused laser beam at the printing plate, melt the printing plate in a specified range, and then remove the unnecessary parts to make a convex-concave image. The shape, size and size of the image can be controlled by electronic modulation. Generally speaking, when the power density of laser reaches
When 10-lOw/cm, plate-making materials (including ceramics) need to be melted or gasified, and the power density value obtained at the focal point after the medium-intensity laser beam is focused by the lens is much greater than the above value, so the laser is more suitable for engraving printing plates. Because of its good monochromaticity, high energy and good coherence, laser has shown strong advantages in engraving and plate making, especially the development and application of modern purple laser technology, which makes the production of printing plates more perfect. High laser intensity can not only melt and etch nonmetallic materials (such as imaging films, photosensitive resin plate and plastic plates). ), but also can melt metal materials (such as nickel, lead, steel, chromium and other plates). Even ceramic rollers with high fire resistance can be etched. Compared with other methods, the etching range is wider. Laser plate making is fast and of good quality. Generally, the carving time is about 3 minutes. If the purple laser technology with shorter wavelength is used, the time will be shorter, which can improve the resolution and ensure the dot quality. Because the laser has good coherence and concentrated energy, the engraving efficiency is high and the total energy consumption is low. Laser plate making is not perfect, but the problem lies in the poor effect of laser engraving metal directly. Because the ink holes etched by laser are not smooth and have burrs, and the metal surface has great reflection on laser light, it can only be carved with high-power laser. The general solution to this problem is to cover the metal drum with a resin or plastic sleeve, and the laser does not directly engrave on the metal plate. The laser technology in modern plate-making industry is mainly manifested in CTP technology and purple laser technology.
Third, the conclusion
Both photoelectric detection technology and laser technology can belong to the category of photoelectric technology. The emergence and development of modern new technologies and new equipment is no longer the development of a single discipline, but the result of mutual penetration and complementarity of multiple disciplines. Photoelectric technology for printing and packaging is a comprehensive technology based on optics, electronic technology, atomic physics, quantum mechanics and other disciplines, and developed on the basis of information theory, cybernetics and system theory. Their development will certainly bring good economic and social benefits to the printing and packaging industry.