Textile is an important pillar of China's national economy and an important source of foreign exchange earning. Modern weaving equipment is the guarantee for high-quality and high-yield textile production. Modern weaving equipment integrates precision machining, electrical and electronic, hydraulic, pneumatic, instrumentation, oil bath, central lubrication, computer control, and the latest achievements in the development of multi-disciplinary technology. The sizing process is the heart of the textile mill. "The sizing is one minute, the cloth machine is a class." There is also a good yarn in foreign countries, which is equivalent to the half of the cloth weaving. However, the sizing machine is the basis for achieving the goal of the sizing process. As the "neural system" in the sizing machine, various sensors are the primary link for realizing automatic detection and control of various technological goals, and are the modernization of cutting-edge electronic technology in mechatronics. The concrete embodiment of the textile field is an important symbol that distinguishes modern sizing machines from traditional sizing machines. One of the development trends of modern sizing machines is automation (automatic detection and control) and informationization (timely, accurate, comprehensive, digital, graphical, networked feedback and processing of data). The use of sensors is a prerequisite for the automation and information construction of modern sizing machines. Textile engineering and technical personnel should abandon the concept of “separation of mechanical maintenance and electrical maintenance from each other, separation of management personnel, process personnel and equipment maintenance personnelâ€, in order to adapt to the new “mechatronics, process and equipment mutual penetration, mutual integration†situation. Mastering the high-tech application of the sensor on the sizing machine can help technicians master the comprehensive performance of the equipment and lay the foundation for equipment maintenance, technical transformation and product upgrade. Therefore, it is necessary to discuss the specific application of the sensor from the sizing machine.
1 Main types and performance evaluation of sensors used in slashers
1.1 Definitions and main types According to the national standard GB7665-87, the sensor is defined as a device or device that can be measured and converted into a usable signal according to a certain rule, usually composed of a sensitive component and a conversion component. The sensor is a detection device and meets the requirements of information transmission, processing, storage, display, recording and control, and thus is the premise of detection and automatic control and informationization. The sensor used in the new sizing machine is divided into electric resistance (mainly heat sensitive, humidity sensitive, etc.), inductance, Hall, ultrasonic, strain gauge, photoelectric and other sensors. According to the measured physical quantity: sensors with force, displacement, speed, temperature, humidity and angle.
1.2 Performance Evaluation The performance of the sensor is measured by its static and dynamic characteristics. The main parameters of the static characteristics are linearity, sensitivity, resolution and hysteresis. Dynamic characteristics are commonly used for step response and frequency response representation.
2 sensors in the application of the new sizing machine
The sensor is used on the new sizing machine for the unwinding diameter of the warp beam, the moisture regain, the temperature of the drying cylinder and the slurry tank, the tension of each zone, the elongation of each zone, the running speed, and the detection.
2.1 Platinum thermal resistance temperature sensor for temperature detection and control 2.1.1 Sensor selection In industrial applications, temperature detection, there are two forms of thermocouple and thermal resistance, thermocouple is generally suitable for measuring 500 ° C The higher temperature above. For medium and low temperatures below 500 °C, the thermoelectric potential of the output of the thermocouple is very small, which requires high requirements for amplifiers and anti-interference measures of the secondary instrument, otherwise it is difficult to achieve accurate measurement; and in the lower temperature region, The relative error caused by the change in the cold junction temperature is also very prominent. Therefore, it is more suitable to use a thermal resistance temperature measuring instrument for measuring medium and low temperatures. The drying temperature of the drying drum of the sizing machine is generally lower than 150 ° C, and the slurry temperature is less than or equal to 100 ° C, so a thermal resistance type sensor can be adopted.
2.1.2 Temperature measurement principle and selection of the thermal resistance sensor The thermal resistance is based on the thermal effect of the resistance, that is, the resistance value of the resistor changes with temperature. Therefore, as long as the resistance change of the temperature sensitive resistor is measured, the temperature can be measured. There are two main types of metal thermal resistance and semiconductor thermistor. Metal thermal resistance is characterized by accurate measurement, good stability and reliable performance, and is widely used in engineering control.
The resistance value and temperature can generally be approximated by the following:
Rt=Rt0[1+α(t_t0)]
Where: Rt is the resistance value at temperature t; Rt0 is the corresponding resistance value at temperature t0 (usually t0=O°C); α is the temperature coefficient.
2.1.3 Application of platinum thermal resistance sensor on sizing machine The sizing machine mainly uses metal platinum thermal resistance sensor. Zhengfang machine GA308, SUCKER-S432 sizing machine, and other sizing machines use Pt-100 platinum thermal resistance, measuring range 0 ~ 200 ° C, maximum current 20 mA, relative to copper resistance, platinum resistance accuracy, suitable for Neutral and oxidizing medium, good stability, certain nonlinearity, the higher the temperature, the smaller the rate of change of resistance.
The platinum thermal resistance temperature sensor detects and combines the control unit to control the slurry temperature and drying temperature within the process range. This sensor is a thermistor sensor.
2.1.4 Platinum thermal resistance sensor method for detecting temperature The temperature of the drying cylinder or slurry detected by the platinum thermal resistance temperature sensor passes through the bridge output voltage signal proportional to the temperature, and enters the A/D converter through the operational amplifier to apply the voltage. The analog signal is converted into a digital signal and sent to the microprocessor CPU through the photoelectric isolator. The difference between the actual temperature and the predetermined temperature is calculated and output by the CPU according to a certain rule, and an analog current signal is formed after the photoelectric isolator, the D/A converter and the driver; The control unit adopts the disconnection type or the position control mode. The disconnection control mode controls the opening and closing of the membrane valve by the solenoid valve, and opens the steam when the temperature is lower than the set value. In this way, for a drying cylinder with a large thermal inertia, the detection accuracy is very poor, and it has been replaced by a position control method with a PID adjustment function.
GA308, KARL MAYER, Tsudakoma HS20, HS40, Zucker S432 sizing machine, etc. adopt this method, which is characterized by linear adjustment of cylinder valve opening degree by proportional valve and control of steam flow, that is, the closer to the set value, the steam valve The smaller the opening, the smaller the vice versa, to control the temperature. The block diagram is shown in Figure 1.
2.2 Ultrasonic displacement sensor is applied to the detection of the unwinding diameter of the warp beam. It is an important part of the sizing process control to ensure the unwinding tension of the warp yarns between the warp beams in the unwinding zone. The traditional sizing machine uses the kilometer paper strip combined with the warp clamp to adjust the braking force to control the unwinding tension of the warp beam, ensuring that the warp tension of each warp beam is uniform and uniform, so as to reduce the whitening back, the new slurry of Zucker SUCKER-S432 The AB tension adjuster of the yarn machine uses the mechanical tension detecting device to detect the unwinding tension. The feedback to the pneumatic proportional control valve is compared with the set value, and the air pressure signal is output to adjust the unwinding tension. It is still a mechanical feedback and control device.
Zheng Textile's GA301 sizing machine uses ultrasonic sensors to detect the unwinding diameter of the warp beam. The computer control automatically adjusts the air pressure of the brake cylinder to keep the unwinding tension constant. The ultrasonic sensor utilizes the reflection characteristics of the ultrasonic waves for spatial measurement and positioning. Since the test distance is short, the attenuation is negligible.
2.3 Wet sensor is used for the detection and feedback of moisture regain. The sizing moisture regain is an important indicator to measure the quality of sizing. The moisture regain rate directly affects the elasticity of the serosa, the abrasion resistance of the sizing, the clarity of the weaving opening, and the high moisture regain is also caused by the narrow length of the cloth. Therefore, the detection and control of moisture regain is of vital importance. The sizing machine uses a humidity sensitive resistance sensor to test the sizing moisture regain.
2.3.1 Test principle The conductivity of textile materials varies with water content. The moisture regain and sizing resistance are as follows:
W=A+Blg R
Where: W is the sizing moisture regain (%); R is the sizing resistance (MΩ); A, B is a constant, determined by the type of fiber and the density of the yarn.
Since the resistance is proportional to the logarithm of the moisture regain, when the regain rate changes little, the resistance value varies greatly, so the measuring instrument designed according to this principle can achieve high sensitivity and precision.
2.3.2 Test method As the humidity measuring electrode of the humidity sensor, a certain amount of measuring voltage is applied to the sizing yarn. As the moisture regaining rate changes, the sizing resistance changes, and the current passing through the sizing yarn also changes accordingly. It is amplified and converted into a voltage signal in the controller, compared with the preset moisture regain voltage, and then the pulse signal is sent by the control circuit to control the speed of the sizing machine (in combination with the Hall tachogenerator) to control the moisture regain.
The GA301 sizing machine adopts the M601 moisture meter produced by Strandberg Company of the United States; the Zucker SUCKER-S432 sizing machine adopts the RMSR-7K moisture meter, etc., all of which belong to the humidity sensitive resistance sensor.
2.4 Resistance strain gauge tension sensor detects the tension of each zone of sizing tension sizing is the important process content of sizing. The control principle of tension of each sizing zone is: small unwinding tension, microslurry tension, uniform drying tension, medium Split tension, large winding tension. In order to achieve this purpose, it is necessary to test the various regions of the sizing, which is the premise of the process adjustment control.
2.4.1 Application of strain gauge tension sensor The strain gauge tension sensor is used to detect the tension of each zone of the sizing machine (slurry tank, drying, splitting and winding), and uses a hyperbolic cannon (such as Zucker) SUCKER-S432 sizing machine), hyperbolic iron gun + XP1 (such as Taiwan Daya TAYA500, Zhengfang machine GA301 sizing machine, etc.) and more advanced frequency converters control the unit motor speed (such as Zhengfang machine GA308, Suzhou Shengyuan ASGA368) adjusts the ratio of each zone to adjust the tension.
KARL MAYER and Tsudak sizing machines use strain gauge pressure sensors to detect the unwinding tension. The resultant force of the warp tension acts on the pressure sensor at the bottom of the detection roller bearing. The current or voltage signal from the sensor is input into the control system. The control system will The measured value and the set value are compared and calculated, the control current or voltage of the electronically controlled proportional valve is changed, and the output air pressure of the proportional valve is adjusted, so that the pressurized cylinder changes the brake damping to the warp beam until the measured value and the set value equal. Thus, the unwinding tension is kept constant. This type of control is fixed by the detecting roller and does not need to be swung, so that the influence of inertia can be reduced, and the sensitivity is higher than that of the Zucker sizing machine.
2.4.2 Working principle of resistance strain sensor Based on the principle of resistance strain effect, a resistance strain gauge is made of metal resistance wire and pasted on the elastic body. During the measurement, when the elastic body is deformed by force, the sensitive grid of the strain gauge is also deformed, and the resistance value changes correspondingly, and is converted into a voltage or current change by the conversion circuit.
The resistance strain gauge converts the mechanical strain into ΔR/R (ΔR is the absolute value of the resistance value, and R is the resistance value). Strain resistance changes are generally small, so that small resistance changes are difficult to measure directly and are not directly processed. Therefore, a conversion circuit must be used to convert the ΔR/R change of the strain gauge into a voltage or current change. This conversion is usually done using a Wheatstone bridge circuit.
The advantages of the Wheatstone bridge are to suppress the effects of temperature changes, suppress interference, and facilitate compensation. The bridge is shown in Figure 2. U0 is the bridge supply voltage, R1, R2, R3, and R4 are the bridge arms, and Usc is the bridge output voltage. When Usc=0, the bridge balances, then the equilibrium condition is: R1/R2=R4/R3 or R1R3=R2R4. This means that to balance the bridge, the ratio of the adjacent two arm resistors should be equal or equal to the product of the two arm resistors. . The strain gauge is connected to the bridge circuit as the arm resistance. When the elastic force is deformed, the resistance value of the strain gauge changes correspondingly, and the bridge is out of balance. Usc≠0, the absolute value of the bridge output voltage is proportional to the force of the sensor.
2.5 Proximity switch sensor and photoelectric encoder for sizing machine elongation detection and speed detection Elongation is an important process parameter for sizing. Excessive elongation will make the sizing elasticity too much, and the yarn will be weaved. The ability to resist repeated loads is reduced, resulting in an increase in the rate of breakage during weaving.
The elongation can be detected using a proximity switch sensor or a photoelectric encoder.
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