introduction
China's label printing industry has achieved considerable development in the past decade. According to statistics from relevant data, the annual growth rate of China's label market in recent years has been as high as 15% -20%, which is far higher than the average growth rate of the national economy. As an important branch of the printing industry, pharmaceutical label printing is accompanied by the development of China's medical and health undertakings and the modernization and internationalization of the pharmaceutical industry. The production requirements of its products have also shifted from high output and high efficiency to high quality and efficiency. In the label printing of certain health care medicines, the printed patterns are more exquisite and diverse, and the quality requirements are much higher than traditional medicines. At the same time, due to the intensification of industry competition, the profits of pharmaceutical label printing companies are getting thinner, but the labor costs are getting higher and higher. For a pharmaceutical packaging and printing enterprise dedicated to meeting higher customer requirements and long-term development, these changes and developments cannot be ignored.
In the traditional quality control process, the detection of print quality is done manually with the naked eye. There are two aspects to the drawbacks. One is that manual detection is affected by factors such as emotion, physical health, fatigue, and interference from the surrounding environment. The detection standards cannot be well grasped and implemented, and the consistency of quality control is poor; The second is that for some special defects (such as reflective, some defects on transparent materials), it is difficult to find when the human eye observes at a fixed position, and it is necessary to continuously adjust the observation position or the direction of the viewing angle to find these defects, which increases the labor. The degree of fatigue is also more difficult to guarantee the test results. Many printing companies I contacted, because of the pressure of customer complaints, the quality inspection department had to adopt the method of manual inspection of the same product multiple times to ensure the test results, but the results were not ideal due to the instability of manual inspection and other factors.
Machine vision printing quality inspection is an automated inspection method that simulates manual inspection methods and judgment logic, but at the same time has higher inspection accuracy and better consistency. It can not only meet the high quality and high efficiency requirements of modern pharmaceutical label printing, but also have good flexible adjustment functions to meet the individual testing requirements of label customers; at the same time, from the perspective of enterprise production management, its special testing results are stored and analyzed And the communication function can be easily embedded in the enterprise ERP system, to achieve digital quality management that manual detection simply cannot achieve.
1. Features of machine vision inspection
1. Introduction to machine vision inspection technology
Machine vision, in short, uses machines to replace humans for target recognition, judgment, and measurement. It is the intersection and integration of modern optics, electronics, software engineering, signal processing and system control technology. The following figure is the workflow of machine vision inspection:
Figure 1 Machine vision inspection workflow Click here to view all news pictures
Optical acquisition equipment: It consists of hardware such as industrial cameras, light sources and supporting image acquisition cards. The main function is to obtain the digital image of the label passing through the collection position, and to provide materials for subsequent analysis and processing, which is equivalent to the eyes detected manually.
Judgment and recognition: It consists of industrial control computer and embedded image processing and analysis software and control software. It is the core part of visual inspection, which ultimately forms a defect judgment and can issue instructions to subsequent actuators.
Automatic control: the results of the detection system are finally converted into specific hardware, such as common sound and light alarms, scrap rejection devices or marking devices (such as inkjet machines, labeling machines, etc.).
In addition, the printing inspection equipment must also have a stable mechanical transmission control platform. For the online inspection system installed on the printing machine, the transmission platform is the printing machine; for the offline inspection system, the transmission platform needs to be configured separately. Such as rewinding machine, single sheet transmission platform, etc. [next]
2. Principles of printing defect detection
Printing defect detection mainly depends on the method of image comparison. As shown in Figure 2, the upper image is a real-time image collected by the camera, while the lower image is a standard image collected and stored in advance. During detection, firstly, the two images are superimposed by positioning and other methods, and then the color (or brightness difference) is compared point by point (pixel by pixel). When the difference between them exceeds the preset range, it is judged as a defect.
Figure 2 Schematic diagram of defect detection Click here to view all news pictures
There are two defect points (1 and 2) that may be found in the picture, but because the area of ​​2 is small and the difference in brightness is less than the preset difference, it is not judged as a defect.
3. Features of machine vision inspection
A high-quality machine vision inspection system must have the following prerequisites:
1) High-quality imaging system
The imaging system is called the "eye" of the visual inspection device, so the recognition ability of the "eye" is the most critical index for evaluating the imaging system. Generally, the evaluation indicators of imaging systems are mainly reflected in three aspects:
Can you find the defects
For the detection based on the image method, the most original and the only data that can be based on is the color (or brightness) change on the acquired image. In addition to this, there is no other information to refer to. Therefore, a high-quality imaging system should first be an imaging system that can fully express the color change of the surface of the detected object. Therefore, in addition to choosing a high-definition camera and lens, the lighting design used to create the imaging environment is also very important, and sometimes a lighting system specially designed for special defects will appear. What we often refer to as a 100% quality inspection system actually refers to a 100% full inspection in an image that can fully express various defects.
The smallest size of defect that can be found
The smallest unit of measurement for digital images is pixels, which does not represent the actual size of the subject. corresponding,
The relationship between the actual size of the subject and the pixels is accomplished by a physical quantity called resolution. Resolution refers to the actual object size represented by each unit pixel. The smaller the resolution value, the higher the fineness of the image, the smaller the defect size that the inspection system can find, and the higher the inspection accuracy.
Can the image be captured fast enough
Just as the human eye sees a moving object, when the object moves fast enough, the human eye can no longer clearly observe all of the object. The "eyes" of the machine vision inspection system-the camera also has an upper limit for the shooting speed, which is the main frequency of the camera. When the running speed of the subject exceeds the upper limit of the main frequency of the camera, the camera cannot obtain a clear and complete image, and the detection cannot continue normally. The higher the main frequency of the camera, the faster the acquisition speed, and the detection can be carried out efficiently. Therefore, whether a sufficiently high-frequency camera is used is also a key factor in evaluating whether an imaging system is of high quality.
2) Mature image processing and analysis algorithm
The image processing and analysis algorithm is equivalent to the human brain's judgment thinking during manual detection in the entire detection system. Since machine vision is a highly practical discipline, evaluating the quality of an algorithm is more dependent on the verification of actual application It is not to investigate whether more advanced or sophisticated theories are used in the algorithm. Therefore, a stable and efficient image processing and analysis algorithm that can fully simulate the human brain judgment process and method is what we need, which is the so-called mature processing and analysis algorithm. Therefore, when designing the processing algorithm, it is necessary to fully analyze the human judgment process and convert it into the language of the computer.
3) Good operability
Good operability mainly requires that the application operation of the testing equipment should be simple, convenient and easy to understand. For example, the system has a friendly human-computer interaction interface and a good directional operation design.
4) Stable other supporting facilities
Other ancillary facilities refer to facilities other than the inspection system, such as transmission control platforms and defect processing devices (rejection, alarm, marking, etc.). The requirements for supporting facilities must be stable operation, timely and rapid signal response. [next]
Second, the testing needs of pharmaceutical labels
At present, China's pharmaceutical label printing as a whole has the characteristics of large batch size and relatively simple printing content. But this does not mean that the quality inspection is less difficult than other labels. On the contrary, due to the particularity of the use of medical labels and the continuous strengthening of the national standardization of medical product management, the surface printing quality of medical labels has to some extent more stringent testing requirements than other daily-use and electronic labels.
The testing requirements for pharmaceutical labels are mainly reflected in:
1. The detection accuracy of key areas on the label is high. For example, the detection of small-name areas such as the name of the medicine and the dosage required requires that it must be detected and that no missed inspections can occur. For some small font labels, missing font strokes or missing decimal points are mandatory content, which is a challenge to the detection accuracy of the detection system.
2. Due to the large volume of products, the inspection efficiency must be guaranteed to truly play the role of inspection equipment to replace manual. The traditional "stop-and-error" mode of operation is more difficult to meet the needs of efficient detection.
3. As the national drug regulatory authorities increase the supervision of drugs, electronic supervision codes are an inevitable trend in the printing of pharmaceutical labels. It is impossible to complete the inspection of supervision codes by relying on manual or simple printing inspection systems. The main reason is that the electronic supervision code is unique, and each label is different. At present, most of the detection equipment on the market rely on the method of comparing with the standard image to detect. The electronic supervision code cannot use this method.
3. Application status of domestic medical label testing equipment
It has been nearly ten years since visual label testing equipment entered China. Some foreign-funded daily chemical label printing companies first brought foreign testing equipment into China through the channels of setting up factories in China. Afterwards, due to factors such as competition, the larger domestic label printing companies gradually began to choose similar testing equipment. However, the application of foreign testing equipment in the field of electronic and pharmaceutical labels with high quality requirements is relatively small. The main reason is that the requirements for label quality in electronics, pharmaceuticals and other industries are quite different from daily chemical labels. In terms of detection accuracy, special defects and detection efficiency, foreign equipment does not meet the needs of domestic and domestic users.
After 2007, the market share of domestic label inspection equipment has exceeded 60%, becoming the mainstream. At present, in the domestic pharmaceutical label printing industry, the market share of domestic equipment has reached 90%, and domestic equipment has been widely accepted.
From the point of view of equipment performance characteristics, the domestic medical label inspection equipment represented by Daheng Image mainly meets the needs of users in three aspects: fine defect detection, electronic supervision code recognition and phase detection, and equipment application efficiency. First of all, in view of the high requirements for small defects such as text and dirty spots in medical labels, domestic equipment can achieve a detection accuracy of up to 0.04mm, which fully meets the defect detection requirements of the lowest specification products of medical label printing enterprises. Has reached the limit of human eye observation. It fully guarantees the precise requirements of medical labels for numbers and text. Secondly, the electronic supervision code is a common concern in medical labels. The electronic supervision code detection module currently developed not only can identify the barcode and number of the electronic supervision code, but also has the function of variable data area quality detection. This function is very good to meet the quality requirements of high-end medical label customers for electronic supervision codes. In addition, in response to the outstanding problem of many offline shutdowns and low efficiency of the label, domestic equipment has also launched a variety of shutdown modes such as single-point and re-examination. Through long-term practical testing by customers, the flexible defect processing mode of domestic equipment can improve the detection efficiency of similar equipment by more than 50%. This makes the domestic testing equipment have a better input-output ratio, further reducing the threshold for equipment use.
After the unremitting efforts and practice of domestic visual equipment providers, domestic visual inspection equipment has become the first choice for Chinese medical label printing enterprises!
Figure 3 Application of Daheng image printing inspection equipment in medical label printing enterprises Click here to view all news pictures
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