Detection and control circuit is one of the core technologies of automatic control system. Its sensitivity, accuracy, service life, safety, stability and other factors directly determine the advantages and disadvantages of automatic control process. Through the investigation of cotton textile enterprises, it is found that some spinning equipment still use on-site manual quality inspection, which can not guarantee the output of high-quality sliver and cotton yarn. In addition, one spinning machine inputs cotton sliver and outputs 96108120 cotton yarns at the same time. Due to the manual test, the timely splicing of cotton sliver and the stability of cotton yarn diameter can not be guaranteed, resulting in the problems of low product quality and production efficiency. In order to ensure the improvement of product quality and efficiency, the Electromechanical Research Institute of Zhengzhou aviation academy has designed, studied and developed a high-precision detection and control system. The control system effectively transformed the domestic fa431 and fa541 series high-speed roving frames, increased the production efficiency by 25% – 35% and greatly improved the product quality. Certified by experts, the modified fa431 is superior to the fl16 roving frame of Toyota in cost performance. The system can not only be used in textile machinery, but also be used in traditional forging machines and machine tools through the adjustment of system accuracy, sensitivity and measurement range, so as to effectively ensure personal safety. Because infrared ray has strong penetration ability and anti-interference ability, it is not easy to scatter and cause crosstalk. The system is based on infrared sensing and uses modulation / demodulation technology to complete the signal transmission and reception design of the system. 2. The signal flow and principle of the system are the main channel of processing unit signal from infrared transmitter to relay control equipment to stop and start. In the main channel, the electrical signals are transmitted in the order shown in Figure 1.
The infrared light emitting tube and the infrared receiving tube are separated on both sides of the photoelectric detection area and rarely need maintenance. Infrared receiving tube is a light sensing current source. The light sensing current increases with the increase of light flux. When the light sensing current charges the capacitor, the electrical signal that changes with the change of light flux can be obtained. When there is no shelter, the optical path is unobstructed, and the light sensing current is the maximum; When a shelter passes through the detection area, the light path is blocked, and the output potential increases. The larger the shading area, the higher the output potential . Using this principle, through the sensitivity adjustment of the detection system and the measurement and control of the diameter or area of the measured object, the function of quality inspection or safety protection can be realized. The installation position and structure of the system are shown in Figure 2. Multi station monitoring can be realized through connectors.
In this design, the generation and pickup of infrared light adopt pulse modulation and synchronous demodulation technology respectively. Compared with DC light, pulse modulated light, on the one hand, enhances the ability to resist environmental stray light and electromechanical interference in the workshop. On the other hand, because the LED works in the pulse state, its service life is relatively prolonged. When an obstruction enters the detection area, the light intensity received by the infrared receiving tube will suddenly change. Therefore, any changing light can be used as an occlusion signal. The traditional safety protector is prone to misoperation. For example, when the lamp is turned on or off, the signal processing unit will judge it as a shelter signal and misoperate. In the design of the system, pulse modulation / synchronous demodulation is adopted to make the infrared light-emitting tube emit signal for a period of time and turn off signal for a period of time, that is, emit infrared light in the form of pulse. Similarly, the infrared receiving tube only works when the infrared light emitting tube transmits a pulse signal. The light emission and reception are synchronized in time, so only the light emitted by the infrared light-emitting tube can be detected, and the external stray light is completely screened out, so that the anti-interference ability of the control system is greatly improved and the misoperation is greatly reduced. 3 design of main functional modules
The control is mainly composed of the following circuit modules: high stability and low power DC power supply system, signal generation system, infrared pulse transmitting system, electronic self-locking switch system, infrared receiving system, signal processing system, status indication panel, etc. This paper only explains the design principle of the important functional modules of the system. 3.1 The infrared pulse transmits the square wave from the signal generator. After buffering, amplification and frequency conversion, the pulse wave with small duty cycle is obtained to drive the infrared transmitting tube. In this way, the infrared light emitting tube works in the pulse state, which greatly prolongs its service life. The principle block diagram is shown in Figure 3.
In order to meet the working requirements of the device, more than two infrared light-emitting tubes can be connected in series to improve the output power and action distance, and reduce the required current. 3.2 infrared receiving when there is no shelter in the detection area, the pulse light emitted by the infrared transmitting tube is received by the receiving tube without shelter, and a negative photosensitive voltage is generated on the pre capacitor. This voltage is equal to the voltage at both ends of the pre capacitor, and the direction is opposite, and no signal passes through the post capacitor; When an obstruction enters the detection area, the intensity of the infrared light received by the receiving tube changes, so that a signal enters the subsequent signal processing unit through the post capacitor. The electric signal output by the receiving tube is very weak, so the electric signal passing through the post capacitor is very small, which needs to be demodulated and then amplified. In order to meet the working requirements, an infrared filter can be installed at the front end of the receiving tube to remove the visible light, so that the infrared receiving tube forms the maximum light receiving area. An electric filter is added at the front end of the amplifier to eliminate low-frequency interference and high-frequency interference. Through the signal comparison circuit, the new level signal is output for processing . The principle block diagram is shown in Figure 4.
3.3 the signal processing system adopts a four operational amplifier integrated chip with low power consumption, high gain and internal frequency compensation . When no shelter enters the detection area, there is only DC signal in the circuit, which cannot pass through the DC isolation capacitor; When an obstruction enters the detection area, the receiving circuit outputs a sudden change electrical signal, which is transmitted through the capacitor relay circuit, preliminarily amplified by the triode, and then sent to the amplification circuit for secondary amplification. The principle block diagram is shown in Figure 5.
Because the demodulated square wave is synchronized with the operation of the infrared transmitting tube in time, and the electronic switch is only turned on when the infrared transmitting tube is working, only the optical signal from the infrared transmitting tube is received, and the stray light is blocked. The square wave signal passing through the electronic switch is filtered and smoothed by the resistance capacitance network, leaving the DC component, so the light blocking area signal of the shelter is restored, that is, the light blocking area of the shelter is large, the left DC component is also large, the light blocking area of the shelter is small, and the left DC component is also small. The resistance network is used to adjust the high and low level of the pulse signal to obtain the appropriate voltage to drive the subsequent circuit. Based on the negative feedback principle of integrated operational amplifier, a sensitivity subsystem circuit is added to the signal processing circuit to adjust the detection accuracy. After adjusting the accuracy, the system can be widely used in other quality inspection and safety protection mechanical equipment, such as the transformation of traditional machine tools and forging machines without safety protection devices. 4 the test results and data analysis, the schematic drawing, simulation debugging and PCB diagram of the detection system are designed by EDA (Protel) software , and all parts are selected, debugged and welded. Under the normal temperature, humidity and fluorescent lighting environment, the measured object is detected by using the infrared sensor probe. Several groups of experimental data are obtained by changing the measurement distance and the diameter of the measured object, as shown in Table 1.
It can be seen from the experimental data that due to the long-distance propagation of infrared light emitted by infrared emission tube in the air, beam divergence and other effects such as air flow, dust and density difference, the diameter of test object decreases with the increase of test distance, which can not achieve the expected test results. By increasing the transmitting power and improving the demodulation and detection function of the receiving end, the detection distance is 30m, the diameter of the test object is 2mm, and the detection accuracy is 95%. However, the accurate detection rate below 1mm is low. Therefore, how to improve the accuracy of the detected object is the focus of the future research and development of the project, and it is also the key to continue to expand the detection field. Considering that the infrared sensing element is greatly affected by the performance of ambient temperature, illumination and humidity, adjust the stability of ambient temperature, humidity, illumination and light stroboscopic detection system. Within the range of ambient illumination ≤ 20000lx, ambient temperature – 15 ~ 60 ℃, ambient humidity ≤ 90% RH and stroboscopic ≤ 1500 rpm, the test detection rate (correct parking percentage) shall not be less than 90%. The test data are shown in Figure 6.
The domestic fa431 object detection device, high-speed roving frame (body 15075mm), was reformed and debugged. 32 cotton yarns (less than 50mm) were output. Infrared detection probes were installed on both sides of the body for on-site work detection. The automatic shutdown rate of cotton yarns beyond the allowable range of 32 diameters was more than 95%, which effectively ensured the product quality and improved the production efficiency.
The detection system works with 380 or 220V, 50-60Hz AC, and has good universality with traditional spinning machinery and equipment, without additional power supply; The mounting frame is easy to install, and the light display circuit is used to adjust the ejaculation degree of the transmitting tube and receiving tube, which is simple and fast; The transformation of traditional mechanical connection is simple, and the circuit of mechanical part is controlled to be on and off. In the actual working environment, for example, fa431 high-speed roving frame includes 96 spindles, 108 spindles, 120 spindles and other multi-channel simultaneous detection. In order to meet the simultaneous detection or safety protection of multiple stations, the system can be realized through connector connection. Based on infrared sensing technology, the high-precision detection system can be used in the fields of product quality monitoring and safety protection in textile, machinery and food production, effectively ensuring the improvement of product quality and the normal progress of production. This system has a wide application prospect.
Responsible editor; zl