Spinning Tension Monitoring System Based on LabVIEW and C8051F350

0 Introduction
Yarn tension is an important parameter that affects product quality and processing efficiency during spinning, false twisting and other processing processes. The greater the fluctuation of yarn tension, the worse the product quality, and it will affect the appearance and comfort of the subsequent processed products. Therefore, it is necessary to monitor and control the yarn tension during the production process to reduce the fluctuation of yarn tension. At present, most of the domestic monitoring of yarn tension is still at the stage of random sampling, with low monitoring accuracy and low efficiency; some foreign monitoring equipment can realize real-time monitoring of yarn tension, but it is expensive and the technology is confidential. Therefore, it is urgent to independently research and design a set of yarn tension online monitoring system.

1 Overall operation mechanism of the system
The spinning online tension monitoring system based on LabVIEW and C8051F350 single-chip microcomputer adopts a domestically developed special tension sensor, an embedded mixed signal microprocessor chip 8051F350 single-chip microcomputer as the lower computer, and a virtual instrument graphical development platform LabVIEW as the upper computer to build a simple, practical, accurate and reliable spinning tension monitoring system.
Figure 1 is the overall structure diagram of the system. The overall operation mechanism is as follows:
(1) The tension sensor obtains the yarn tension signal during the spinning, false twisting and other processing processes, and the output signal enters the signal conditioning circuit for processing. (2
) After the signal conditioning is completed, it is input to the controller, and the output signal is processed by the single-chip microcomputer to complete the closed-loop control. The information is transmitted to the upper computer through the serial port.
(3) The upper computer uses the powerful LabVIEW graphical programming to complete the parameter setting and the tension online monitoring display. Among them, the display content includes the set tension value, the measured tension value, the tension controller operation status (manual, automatic and parameter setting status), etc.

2 System Hardware Design
2.1 Processor Selection
According to the tension control principle, this paper adopts the weighing method to realize tension detection and control. It requires two sensor input signals and one constant current output control signal, and performs A/D and D/A conversion on the signals. To this end, the system controller needs to use an embedded mixed signal microprocessor chip with A/D and D/A functions to avoid using off-chip A/D and D/A converters, thereby simplifying the circuit and reducing costs. Based on the above needs, this paper selects C8051F350 MPU as the embedded processor, which contains a fully differential 24-bit ∑-△ A/D, with analog multiplexer, 2 8-bit current output DACs, and has multiple functions such as on-chip calibration and extraction filter, internal voltage reference and 8 gain settings. Among them, D/A uses the programmable counter array (PCA) pulse width modulation (PWM) function of C8051F350, has 16-bit conversion accuracy, and is convenient for photoelectric isolation. Hardware implementation parameters include SPI, SMBus/IIC and 1 UART serial interface, 8 KB in-system programmable FLASH memory, 768 B (512+256) on-chip RAM, on-chip watchdog timer, 1 comparator, as well as VDD monitor and temperature sensor, 17 I/O ports, -40～+85℃ industrial temperature range, 2.7～3.6 V operating voltage. [page]

2.2 Tension sensor and signal conditioning circuit design
The sensor selection is mainly based on the analysis of the principles and types of wire tension sensors. The resistance strain type tension sensor is selected. The FK6 tension sensor (Tension Sensor) can replace the imported tension sensor. It has the advantages of superior and stable indicators, no calibration, accurate measurement, and low price. It has targeted anti-interference ability for the elastic application environment, strong anti-destruction ability, maintenance-free, and long life. Its performance indicators are as follows:
FK6 tension measurement range CN0-80/0-120/0-180; comprehensive error %FS1.2; long-term zero drift %FS1.2; one-year long-term gain drift %FS1.2; one-year zero drift %FS1.2≥48 h (same as above); temperature drift %FS/10℃0.325～70℃; nonlinearity %FS1.2. The output of the FK6 sensor is a DC 4～20 mA standard instrument signal (or voltage signal DC 0～10 V/0～5 V), and the interface circuit form is relatively simple. Here, the strain gauge sensor circuit using the weighing method is mainly described, and Figure 2 is its interface circuit diagram.

The bridge circuit composed of strain gauges includes two forms of constant voltage power supply and constant current power supply. The design adopts the constant current power supply form, and the circuit adopts the OP07 operational amplifier form. The circuit forms a constant current power supply mainly by connecting the operational amplifier in the same phase to a 2 V voltage regulator tube, and the voltage applied to the inverting terminal resistor R2 (68 Ω) of the operational amplifier U1 is also 2 V. Therefore, the current flowing through the resistor R2 does not change due to load changes. In addition, during the winding and unwinding process, the bridge circuit will be unbalanced due to tension changes, and a voltage signal will be output. The output voltage signal is amplified by the instrument amplifier AD623 and transmitted to the A/D
converter of the MPU. Among them, W1 is a gain adjustment potentiometer; W0 is a zero level adjustment potentiometer. The control circuit and communication interface mainly use constant current signal output control, and the microcontroller communicates with the host computer through the MAX 232 serial interface.

3 System software design
3.1 Control program design
The tension controller software uses the PID control method to complete the control of each functional module, and realizes functions such as parameter calibration, setting, tension measurement, and constant current signal output. After the software completes the initialization setting, it performs data acquisition and processing of the tension signal, constant current control output, etc. According to the actual working conditions, the tension signal data acquisition needs to be filtered, and the filtering algorithm based on the lifting framework is used for simulation experiments. The experimental results show that the algorithm can effectively eliminate various types of noise and has certain advantages compared with the relevant technologies of foreign products.
The control algorithm adopts integral separation PID control to prevent the integral accumulation of PID operation when the deviation is large, and to avoid the control amount exceeding the maximum action range of the brake. When the deviation between the control amount and the set value is large, the integral action is cancelled; when the control amount is close to the set value, the integral action is added to eliminate the static error and improve the control accuracy. In actual operation, the differential adjustment effect can also be cancelled according to actual needs. Figure 3 is a program flow chart.

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3.2 Communication module design
The host computer uses a PC, and the communication between the controller and the host computer uses RS 232 serial communication. The data collected by the controller is sent to the host computer through serial communication to realize automatic data upload. Dual-channel multiple conversion is adopted, and multiple sampling of the two channels is performed to obtain the average value. The time interval of data acquisition is completed by the timer, and the sending and receiving of data are realized by interruption.
3.3 Host computer software platform LabVIEW and software design
The host computer software platform uses NI's LabVIEW. LabVIEW adopts data flow programming. The data flow between nodes in the program flowchart determines the execution order of the program. LabVI-EW uses icons to represent functions and lines to represent data flow. It provides many controls that look similar to traditional instruments, which can easily create user interfaces. The user interface is called the front panel in LabVIEW. Figure 4 shows the front panel of the spinning tension monitoring system, which shows the monitoring 1 status interface, and the monitoring 2 interface includes a table to display multiple tension signal data.

The system design uses form files to store and record data. It has powerful file I/O functions, which can store the collected data in a certain format in the file to meet the different file operation needs of users. The form file can convert the data array into ASCII code and store it in the spreadsheet file. The design will use the measurement date as the file name, and the data measured every day will be stored in a table. Users can enter the date through the front panel interface to view historical data, and can also view it through third-party software such as Excel. Other interface selection cards can display the spinning reel doffing records, tracking and debugging, and system information, and the tracking and debugging interface design parameter modification interface. When the doffing or broken wire is dropped, the system generates a doffing record, and the record information includes product-related production information, tension information, etc. At the same time, the doffing record and abnormal point data are uploaded to the network database, and then the network analysis system uses the above original collected information as the basis for statistical analysis, and provides different analysis reports and charts according to the current manufacturer's analysis requirements for output and quality.

4 Conclusion
(1) The fully differential 24-bit ∑-△ analog-to-digital converter and decimation filter of C8051F350 can effectively suppress the influence of various interference factors, and can stably perform tension signal acquisition and constant current control output;
(2) The host computer control software is developed using the LabVIEW graphical development platform, which can easily and quickly realize the control system and human-machine interface design;
(3) The tension control system has been proved by experiments and actual operation to have a simple system structure and reasonable design, and has achieved the required tension control.