Textiles are an important pillar of our economy and a significant source of foreign exchange earnings from exports. Modern weaving equipment is the guarantee for high-yield textile production. Modern weaving equipment integrates precision machining, electrical and electronic, hydraulic, pneumatic, instrumentation, oil bath, lubrication, and computer control, combining the achievements of multidisciplinary technological development. The sizing process is the heart of a textile factory. "One minute of sizing, one shift of fabric machine". There is also a saying that good yarn slurry is equivalent to half weaving the fabric. However, the sizing machine is the foundation for achieving the goals of the sizing process. As various sensors of the "nervous system" in the sizing machine, they are essential for achieving automatic detection and control of various process goals. It is a concrete manifestation of electronic technology in the modern textile field of mechatronics, and an important symbol that distinguishes modern sizing machines from traditional ones. One of the development trends of modern sizing machines is automation (automatic detection and control) and informatization (timely, accurate, comprehensive, textual, graphical, networked feedback and processing). The use of sensors is a prerequisite for the automation and information construction of modern sizing machines. Textile engineering technicians should abandon the previous concept of separating mechanical and electrical maintenance from each other, and separating management personnel, process personnel, and equipment maintenance personnel, in order to adapt to the new situation of "mechatronics integration, mutual infiltration and integration of process and equipment". Mastering the specific application of high-tech sensors in sizing machines can help technicians grasp the comprehensive performance of the equipment, laying a foundation for equipment maintenance, technical transformation, and product upgrading. Therefore, it is necessary to explore the specific application of sensors on self sizing machines.

1. The main types and performance evaluation of sensors used in sizing machines

1.1 Definition and Main Types

According to the national standard GB7665-87, a sensor is defined as a device or apparatus that can sense the measured signal and convert it into a usable signal according to a certain pattern. It usually consists of a sensitive element and a conversion element. Sensors are detection devices that meet the requirements of information transmission, processing, storage, display, recording, and control, and are therefore a prerequisite for detection, automatic control, and informatization. The sensors used in the new sizing machine are divided into resistance sensors (mainly thermal and humidity sensitive), inductance sensors, Hall sensors, ultrasonic sensors, strain gauges, photoelectric sensors, etc. according to their working principles. According to the measured physical quantities, sensors such as force, displacement, velocity, temperature, humidity, and angle are classified.

1.2 Performance evaluation

The performance of sensors is measured by their static and dynamic characteristics, with the main parameters of static characteristics including linearity, sensitivity, resolution, and hysteresis. Dynamic characteristics are commonly represented by step response and frequency response.

2. Application of sensors in new sizing machines

Sensors are used on the new sizing machine for measuring the diameter of the warp and weft rewinding, moisture regain, temperature of the drying cylinder and pulp tank, tension and elongation in each zone, operating speed, and detection.

2.1 Platinum resistance temperature sensor for temperature detection and control

2.1.1 Selection of Sensors

In industrial applications, temperature detection comes in two forms: thermocouples and thermistors. Thermocouples are generally suitable for measuring higher temperatures above 500 ℃. For medium and low temperatures below 500 ℃, the thermoelectric potential output of the thermocouple is very small, which requires high requirements for the amplifier and anti-interference measures of the secondary instrument, otherwise it is difficult to achieve measurement; Moreover, in lower temperature regions, the relative error caused by changes in the cold end temperature is also very prominent. So it is more suitable to use a thermistor thermometer for measuring medium and low temperatures. The drying temperature of the drying cylinder of the sizing machine is generally below 150 ℃, and the slurry temperature is less than or equal to 100 ℃, so a thermal resistance sensor can be used.

2.1.2 Temperature Measurement Principle and Selection of Thermistor Sensor

Thermistor is a temperature measurement method based on the thermal effect of resistance, which refers to the characteristic of the resistance value of a resistor changing with temperature. Therefore, as long as the resistance change of the thermistor is measured, the temperature can be measured. There are mainly two types of thermistors: metal thermistors and semiconductor thermistors. The characteristics of metal thermistor are accurate measurement, good stability, and reliable performance, and it is widely used in engineering control.

The approximate relationship between resistance value and temperature can generally be expressed as follows:

Rt=Rt0［1+α（tt0）］

In the formula: Rt is the resistance value at temperature t; Rt0 is the corresponding resistance value at temperature t0 (usually t0=O ℃); α is a temperature system.

2.1.3 Application of Platinum Thermistor Sensor in sizing Machine

The sizing machine mainly uses metal platinum thermistor sensors. Zhengzhou Textile Machinery GA308, SUCKER-S432 sizing machines, and other sizing machines use Pt-100 platinum thermistors with a measurement range of 0-200 ℃ and a maximum current of 20mA. Compared to copper resistors, platinum resistors have high accuracy and are suitable for neutral and oxidizing media. They have good stability and a certain nonlinearity, and the resistance change rate decreases with higher temperature.

The platinum resistance temperature sensor detects and combines with the control unit to control the slurry temperature and drying temperature within the process range. This sensor is a thermistor sensor.

2.1.4 Method for detecting temperature using platinum resistance sensors

The temperature of the drying drum or slurry detected by the platinum resistance temperature sensor is output as a voltage signal proportional to the temperature through a bridge. The voltage analog signal is converted into a word signal through an operational amplifier and sent to the microprocessor CPU through a photoelectric isolator. The difference between the actual temperature and the predetermined temperature is calculated and output by the CPU according to a predetermined rule. After passing through the photoelectric isolator, D/A converter, and driver, an analog current signal is formed; The control unit adopts a disconnect or position control mode. The disconnect control mode is controlled by an electromagnetic valve to open and close the diaphragm valve. When the temperature is below the set value, the steam is turned on. This method has poor detection accuracy for drying cylinders with high thermal inertia, and has now been replaced by positional control methods with PID regulation function.

GA308、 Karl Mayer, Tsudakoma HS20, HS40, Zuke S432 sizing machines and others adopt this method, which is characterized by the ability to linearly adjust the cylinder valve opening through a proportional valve to control the steam flow rate. That is, the closer it is to the set value, the smaller the steam valve opening, and vice versa, to control the temperature.

2.2 Application of ultrasonic displacement sensor in detecting the diameter of warp and weft winding

Ensuring the tension of the warp yarn rewinding between each warp axis in the rewinding area is an important aspect of sizing process control. Traditional sizing machines use kilometer clip paper strips combined with warp clips to adjust braking force to control the unwinding tension of the warp, ensuring uniform unwinding tension of each warp to reduce machine white rewinding. The AB tension regulator of the Zuke SUCKER-S432 new sizing machine uses a mechanical tension detection device to detect the unwinding tension, and after comparing the feedback pneumatic proportional control valve with the set value, outputs an air pressure signal to adjust the unwinding tension, which is still a mechanical feedback and control device.

The GA301 sizing machine of Zhengzhou Textile Machinery uses ultrasonic sensors to detect the rewinding diameter of the warp shaft, and the computer controls the automatic adjustment of the air pressure of the brake cylinder to maintain a constant rewinding tension. Ultrasonic sensors utilize the reflection characteristics of ultrasonic waves for spatial measurement and positioning. Due to the short testing distance, its attenuation can be ignored.

2.3 Moisture sensors are used for detecting and providing feedback on moisture regain

The moisture regain of sizing is an important indicator for measuring the quality of sizing. The moisture regain directly affects the elasticity of the sizing film, the wear resistance of the sizing, the clarity of the weaving opening, and excessive moisture regain can also lead to narrow and long fabric. Therefore, the detection and control of moisture regain are of great significance. The sizing machine uses a moisture sensitive resistor sensor to test the moisture regain of the sizing.

2.3.1 Testing principle

The conductivity of textile materials varies with moisture content, and the moisture regain and sizing resistance follow the following relationship:

W = a + blgr

In the formula: W is the moisture regain of the sizing (%); R is the sizing resistance (M Ω); A. B is constant, determined by the type of fiber and yarn density.

Due to the proportional relationship between resistance and moisture regain, when there is a small change in moisture regain, the resistance value changes greatly. Therefore, measuring instruments designed based on this principle can achieve high sensitivity and accuracy.

2.3.2 Testing Methods

As a moisture sensor, the moisture meter adds a quantitative measurement voltage to the sizing machine. With the change of moisture regain, the sizing resistance changes, and the current passing through the sizing machine also changes accordingly. The changing current is amplified and converted into a voltage signal in the controller, which is compared with the preset moisture regain voltage. Then, the control circuit sends a pulse signal to control the speed of the sizing machine (combined with a Hall tachometer generator) to control the moisture regain.

The GA301 sizing machine adopts the M601 moisture meter produced by Strandberg Company in the United States; The Zuke SUCKER-S432 sizing machine adopts RMSR-7K moisture meter and other sensors, all of which are humidity sensitive resistance sensors.

2.4 Resistance strain gauge tension sensor for detecting sizing tension

The tension in each area of sizing is an important process content of sizing. The control principles for tension in each area of sizing are generally: small unwinding tension, micro sizing groove tension, uniform drying tension, medium separation twisting tension, and large winding tension. To achieve this process goal, it is necessary to inspect each area of the sizing, which is a prerequisite for process adjustment and control.

2.4.1 Application of Strain Gauge Tension Sensor

The strain gauge tension sensor is used to detect the tension in each area of the sizing machine (pulp trough, drying, twisting and winding), and the hyperbolic iron cannon (such as Zuke SUCKER-S432 sizing machine), hyperbolic iron cannon+XP1 (such as Taiwan, China Daya TAYA500, Zheng Textile GA301 sizing machine, etc.) and the relatively variable frequency governors in each area control the motor speed of each unit (such as Zheng Textile GA308, Suzhou Shengyuan ASGA368) to adjust the speed ratio of each area to adjust the tension.

The Karl Mayer and Tsuda Jusu yarn spinning machines use strain gauge pressure sensors to detect unwinding tension. The resultant force of warp tension acts on the pressure sensor located at the bottom of the detection roller bearing. The current or voltage signal emitted by the sensor is input into the control system, which compares and calculates the measured value with the set value, changes the control current or voltage of the electronic proportional valve, adjusts the output air pressure of the proportional valve, and causes the pressure cylinder to change the braking damping of the warp shaft. The measured value is equal to the set value. In order to maintain a constant unwinding tension, this control form requires swinging due to the fixed detection roller, which can reduce the influence of inertia and has higher sensitivity than the Zuk 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 an elastic body. When measuring, when the elastic body deforms under stress, the sensitive grid of the strain gauge also deforms, and its resistance value changes accordingly, which is converted into changes in voltage or current through a conversion circuit.

Resistance strain gauges convert mechanical strain into Δ R/R (where Δ R represents the change in resistance and R represents the resistance value). The changes in strain resistance are usually very small, making it difficult to directly measure and handle such small changes in resistance. Therefore, a conversion circuit must be used to convert the Δ R/R variation of the strain gauge into voltage or current variation. This conversion is usually achieved using a Wheatstone bridge circuit.

The advantages of Wheatstone bridge are the suppression of temperature changes, interference, and convenient compensation. The bridge is shown in Figure 2, where U0 is the power supply voltage for the bridge, R1, R2, R3, R4 are the bridge arms, and Usc is the output voltage of the bridge. When Usc=0, the balance condition of the bridge is: R1/R2=R4/R3 or R1R3=R2R4. This indicates that in order to balance the bridge, the ratio of adjacent arm resistances should be equal or the product of the relative arm resistances should be equal. Connect the strain gauge as an arm resistor to the bridge circuit. When the elastic force deforms, the resistance value of the strain gauge changes accordingly, causing the bridge to lose balance, Usc≠0， The output voltage of the bridge is directly proportional to the force acting on the sensor.

2.4 Resistance strain gauge tension sensor for detecting sizing tension

The tension in each area of sizing is an important process content of sizing. The control principles for tension in each area of sizing are generally: small unwinding tension, micro sizing groove tension, uniform drying tension, medium separation twisting tension, and large winding tension. To achieve this process goal, it is necessary to inspect each area of the sizing, which is a prerequisite for process adjustment and control.

2.4.1 Application of Strain Gauge Tension Sensor

The strain gauge tension sensor is used to detect the tension in each area of the sizing machine (pulp trough, drying, twisting and winding), and the hyperbolic iron cannon (such as Zuke SUCKER-S432 sizing machine), hyperbolic iron cannon+XP1 (such as Taiwan, China Daya TAYA500, Zheng Textile GA301 sizing machine, etc.) and the relatively variable frequency governors in each area control the motor speed of each unit (such as Zheng Textile GA308, Suzhou Shengyuan ASGA368) to adjust the speed ratio of each area to adjust the tension.

The Karl Mayer and Tsuda Jusu yarn spinning machines use strain gauge pressure sensors to detect unwinding tension. The resultant force of warp tension acts on the pressure sensor located at the bottom of the detection roller bearing. The current or voltage signal emitted by the sensor is input into the control system, which compares and calculates the measured value with the set value, changes the control current or voltage of the electronic proportional valve, adjusts the output air pressure of the proportional valve, and causes the pressure cylinder to change the braking damping of the warp shaft. The measured value is equal to the set value. In order to maintain a constant unwinding tension, this control form requires swinging due to the fixed detection roller, which can reduce the influence of inertia and has higher sensitivity than the Zuk 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 an elastic body. When measuring, when the elastic body deforms under stress, the sensitive grid of the strain gauge also deforms, and its resistance value changes accordingly, which is converted into changes in voltage or current through a conversion circuit.

Resistance strain gauges convert mechanical strain into Δ R/R (where Δ R represents the change in resistance and R represents the resistance value). The changes in strain resistance are usually very small, making it difficult to directly measure and handle such small changes in resistance. Therefore, a conversion circuit must be used to convert the Δ R/R variation of the strain gauge into voltage or current variation. This conversion is usually achieved using a Wheatstone bridge circuit.

The advantages of Wheatstone bridge are the suppression of temperature changes, interference, and convenient compensation. The bridge is shown in Figure 2, where U0 is the power supply voltage for the bridge, R1, R2, R3, R4 are the bridge arms, and Usc is the output voltage of the bridge. When Usc=0, the balance condition of the bridge is: R1/R2=R4/R3 or R1R3=R2R4. This indicates that in order to balance the bridge, the ratio of adjacent arm resistances should be equal or the product of the relative arm resistances should be equal. Connect the strain gauge as an arm resistor to the bridge circuit. When the elastic force deforms, the resistance value of the strain gauge changes accordingly, causing the bridge to lose balance, Usc≠0， The output voltage of the bridge is directly proportional to the force acting on the sensor.

2.5.2 Optical encoder used for measuring the elongation of sizing

A photoelectric encoder is an angle (angular velocity) detection device that converts the angle input to the shaft into corresponding electrical pulses or words using the principle of photoelectric conversion. A typical photoelectric encoder consists of a code wheel, a detection grating (Mask), a photoelectric conversion circuit (including a light source, a photosensitive device, and a signal conversion circuit), mechanical components, etc.

2.5.2 Optical encoder used for measuring the elongation of sizing

A photoelectric encoder is an angle (angular velocity) detection device that converts the angle input to the shaft into corresponding electrical pulses or words using the principle of photoelectric conversion. A typical photoelectric encoder consists of a disk (see Figure 3), a detection grating (Mask), a photoelectric conversion circuit (including light source, photosensitive device, signal conversion circuit), mechanical components, etc.

The inner loop is a current loop, mainly used to improve the dynamic characteristics of the system, maintain the maximum constant current during startup to achieve fast startup, etc. The outer loop is the speed loop, which forms a closed-loop speed control system for a DC motor with DC speed measurement feedback. The speed value measured by the DC tachometer generator is compared with the set value through a speed feedback loop, and negative feedback is performed to correct the speed.

Zhengzhou Textile Machinery GA301 adopts a variable frequency speed regulation transmission system. During the sizing process, the DC tachometer generator converts the actual speed of the motor into a DC voltage signal. The measured value is compared with the set value by a feedback comparator, and the deviation is sent to the microcontroller through A/D conversion to adjust the frequency of the control signal, so as to stabilize the actual speed of the motor at the set value, improve the speed regulation accuracy, and eliminate the speed change of the motor caused by the load variation during sizing operation.

3. Conclusion

Various electronic sensors are a prerequisite for the process parameter control of modern sizing machines and an important symbol of modern sizing machines.

The drying temperature of the sizing machine is detected by a platinum thermistor temperature sensor; Ultrasonic displacement sensors are used for detecting the diameter of the warp and weft winding; The detection of moisture regain adopts a humidity sensitive resistance sensor; The tension measurement of sizing is carried out using a resistance strain gauge sensor; The elongation rate of sizing and vehicle speed can be detected by proximity switch sensors and photoelectric encoders; Hall speed generator is applied to the speed control system of sizing machine.