Application of photoelectric sensors in automated production lines

Introduction

Photoelectric Sensor It uses photoelectric elements as detection elements, first converts the measured change into the change of signal, and then further converts the optical signal into electrical signal with the help of photoelectric elements. Photoelectric sensors are generally composed of three parts: light source, optical path and photoelectric element. Photoelectric detection method has the advantages of high precision, fast response, non-contact, etc., and can measure many parameters. The sensor has a simple structure, flexible and diverse forms, and small size. In recent years, with the development of photoelectric technology, photoelectric sensors have become a series of products, and their varieties and output are increasing. Users can choose various specifications of products according to their needs, and they are widely used in various light industrial automatic machines. 1 Photoelectric strip deviation detector The strip deviation detector is used to detect the size and direction of the strip material deviating from the correct position during processing, so as to provide a correction signal for the correction control circuit. It is mainly used in the production process of printing and dyeing, paper feeding, film, and tape. The principle of the photoelectric strip deviation detector is shown in Figure 1. The light emitted by the light source is converged into a line beam through lens 1, projected to lens 2, and then converged to the photoresistor. On the way of the parallel light beam reaching the lens 2, part of the light is blocked by the strip being measured, so that the light flux transmitted to the photoresistor is reduced.

Figure 1 Working principle of strip deviation detector

Figure 2 is a simplified diagram of the measurement circuit. R1 and R2 are photoresistors of the same type. R1 is installed under the strip as a measuring element, and R2 is covered with a light shield to compensate for temperature. When the strip is in the correct position (middle position), the bridge composed of R1, R2, R3, and R4 is balanced, so that the amplifier output voltage U0 is 0. When the strip deviates to the left, the shading area decreases, the resistance of the photoresistor R1 decreases, and the bridge loses balance. The differential amplifier amplifies this unbalanced voltage, and the output voltage is negative, which reflects the direction and size of the strip deviation. On the contrary, when the strip deviates to the right, U0 is positive. The output signal U0 is displayed on the display on the one hand, and sent to the actuator on the other hand to provide a correction signal for the correction control system.

Figure 2 Strip deviation detector measurement circuit

2 Packaging filling height detection

In addition to a certain error range requirement for weight, finished products measured by volumetric method generally also have certain requirements for filling height to ensure the appearance quality of the product. Finished products that do not meet the filling height will not be allowed to leave the factory. Figure 3 shows the principle of controlling the filling height with the help of photoelectric detection technology. When the filling height h deviates too much, the photoelectric connector has no electrical signal, that is, the actuator pushes the packaged items out for processing.

Figure 3: Using photoelectric detection technology to control filling height

3 Photoelectric color quality detection

Figure 4 shows the principle of photoelectric color quality detection of packaging materials. If the base color of the packaging items is specified to be white, and some of them appear yellow due to poor quality, the color quality will be detected by photoelectric detection before the product is packaged. When the items turn yellow, a comparative voltage difference will be output, and the solenoid valve will be turned on, and the yellowed items will be blown out by compressed air.

Figure 4 Principle of photoelectric color quality detection of packaging materials

4 Color plastic packaging bag making plastic film position control

Figure 5 shows the principle of the plastic film position control system of the packaging machine. The rolled plastic film is printed with trademarks and texts, and has a positioning color mark. When packaging, the trademark and text must be accurately positioned, and the pattern must not be cut off in the middle. The position of the trademark on the film is detected by the photoelectric system and amplified to control the electromagnetic clutch. When the color mark on the film (a small opaque area, usually black) does not reach the positioning color mark position, the photoelectric system makes the electromagnetic clutch energized and attracted because the light of the projector can pass through the film, and the film can continue to move. When the color mark on the film reaches the positioning color mark position, the light of the projector is blocked by the color mark and a signal is sent out. After the signal is converted and amplified by the photoelectric conversion, the electromagnetic clutch is disconnected and the film stops accurately at the position and continues to move after being cut off.

Figure 5 Schematic diagram of film position control system

When the color mark on the film does not reach the photoelectric tube, the photoelectric relay coil has no current, the servo motor rotates, and the film continues to move forward. When the color mark reaches the photoelectric tube position, the photoelectric relay coil has current, the servo motor stops immediately, and the film stops at that position. When the cutting action is completed, the servo motor continues to rotate. As shown in Figure 6.

Figure 6 Schematic diagram of film position control

5 Other applications

Photoelectric switches can also be used to count the production on the production line, to detect whether the assembly parts are in place and the assembly quality, such as whether the bottle cap is pressed on during filling, whether the trademark is missing (see Figure 7), and whether the feeding mechanism is broken (see Figure 8).

Figure 7 Schematic diagram of bottle filling detection Figure 8 Schematic diagram of feeding mechanism detection

In addition, the presence and width of fabric can be detected by using reflective photoelectric sensors (see Figure 9). The droop of fabric can be detected by using shielded photoelectric sensors, and the result can be used to adjust the tension of fabric during transmission. Empty boxes with missing products can be found by using reflective photoelectric sensors installed on the frame, and the empty boxes can be pushed out by using a cylinder.

6 Conclusion

It can be predicted that with the rapid development of automation technology, photoelectric sensors will be used more and more widely as detection devices in light industrial automatic production lines. References [1] Wang Jiaxiang. Light Industry Machinery Design. Beijing: China Light Industry Press, 1996 [2] Zhang Zhengwei. Sensor Principles and Applications. Beijing: China Central Radio and Television University Press, 1991 [3] Peng Jun. Sensors and Detection Technology. Xi'an: Xi'an University of Electronic Science and Technology Press, 2003