Design of Tension Control System of Coiler Based on Single Chip Microcomputer

Tension control, popularly speaking, is to control the force that keeps objects elongated or tightened with each other when coiling objects. Tension is widely used in light industries such as papermaking, fiber, plastic film, wire, printing, tape and so on. The winding tension of strip or wire plays a vital role in the quality of products. In the process of winding and unwinding, it is very important to maintain constant tension in order to ensure the quality and efficiency of production.

1 Introduction and basic principle of tension control system

In metallurgy, papermaking, textile and other industries, in the processing process or after the processing is completed, the last process is generally to wind the processed goods into a cylinder. In this process, the quality of winding will be the key to determine the product quality. If the winding is too tight, it is easy to deform and break the fabric, and if the winding is too loose, it is easy to make the winding not compact, which is not conducive to handling and transportation. Therefore, in order to make the winding compact and ensure the quality of products, it is required to establish a certain tension on the fabric during the winding process and keep the tension at a constant value, The system that can realize this function is called tension control system. According to the principle of measurement and control, there are three kinds of tension control systems currently used: indirect tension control system; Direct tension control system; A compound tension control system with both indirect method and direct method.

In terms of control mode, tension control can generally be divided into manual, semi-automatic and full-automatic; The coil diameter control mode can automatically detect the coil diameter, so as to adjust and compensate the actuator of tension and realize the constant tension. The coil diameter control mode belongs to semi-automatic control mode. Its outstanding feature is that it eliminates the relatively expensive tension sensor, has simple installation, and can easily obtain taper tension control. It is especially suitable for slitting and winding machines and equipment in metallurgy, printing, packaging, papermaking, printing and dyeing and other industries. Figure 1 is the schematic diagram of winding.

In Figure 1, R0 is the radius of the unwinding shaft; Rx is the radius of unwinding material; R1 is the radius of winding drive shaft; V is the linear speed of coil operation.

When the reel speed is constant, the torque f · RX generated by tension is equal to the braking torque generated by magnetic particle brake. Therefore, if f is kept constant, it is only necessary to detect the rotational angular speed of the unwinding shaft and the driving spindle, calculate Rx, and realize the constant tension control of the unwinding shaft by controlling the braking current of the magnetic particle brake. Among them, the pulse signal is obtained through the proximity switch or rotary encoder installed on the rotating shaft (this design adopts the proximity switch). The single chip microcomputer can accurately calculate the angular speed of the shaft to be detected by counting the frequency of the pulse signal. Because the on-line speeds of the two rolling shafts are equal, it can be obtained:

Where: ω 1 is the angular speed of the winding drive shaft; ω 0 is the angular velocity of the unwinding shaft; K is the characteristic coefficient of magnetic particle brake.

2 Application of proximity switch

Proximity switch belongs to a position sensor with switching value output. It is divided into capacitive type and inductive type according to different working principles. The basic principle block diagram of proximity switch is shown in Figure 2.

In this design, inductive proximity switch is used to accurately measure the rotation angular velocity of unwinding shaft and spindle. The two proximity switches detect the angular velocity of the unwinding shaft and the winding drive shaft, which is used to generate the pulse square wave signal, which is transformed into the level pulse signal that can be read by the single chip microcomputer through the photoelectric isolation switch.

3 magnetic particle brake, the actuating part of tension control

In the tension control system, magnetic powder brake is widely used because of its small volume, light weight, small exciting power and good control characteristics. The relationship between torque and exciting current of magnetic particle brake is generally referred to as static characteristic. It is the relationship between the excitation current and output torque of the magnetic particle brake when the driving end speed n is constant and the driven end is braked. The torque current characteristic curve is shown in Figure 3.

As can be seen from Figure 3, the torque curve of magnetic particle brake can be divided into three parts: nonlinear section, linear section and saturation section. The magnetic powder brake has good constant torque characteristics, and there is a good linear relationship between the output torque of the magnetic powder brake and the excitation current of the magnetic powder coil. As long as the excitation current is adjusted linearly, the dynamic control of the field tension can be realized, and the performance of the magnetic powder brake is also very stable when the speed is very low. The application of magnetic particle brake in coiling tension control system is shown in Figure 4. Compared with the previous control system, the scheme of controlling tension with magnetic particle brake has the characteristics of simple structure, low cost of execution unit and easy control. In particular, the actual tension is directly adjusted by current, which changes the manual operation process of other adjustment devices, making the operation simple and accurate. Adding dynamic current compensation is conducive to further improve product quality.

4 single chip microcomputer tension control system

4.1 system function overview

(1) Detect the angular speed of the unwinder and the angular speed, linear speed and radius of the coiler, and display the test results of each parameter with a nixie tube.

(2) If the parameter detection result exceeds the upper and lower limits, the alarm will be realized.

(3) According to the detected parameters, after calculation through the designed control algorithm, the control value is output as the input voltage of the trigger pulse circuit of the thyristor to control the torque of the magnetic particle brake of the actuator.

(4) Establish a real-time clock and display the clock with nixie tube.

(5) By pressing different function keys, man-machine dialogue is carried out to realize various operation functions.

4.2 system hardware block diagram

The system hardware block diagram is shown in Figure 5.

4.3 system software design

The system software design mainly includes the following aspects:

(1) Realize various initialization, including AVR chip initialization, timer / counter o initialization, clock initial value input, on / off, timer / counter startup, etc.

(2) Realize display (display clock or various different parameters according to man-machine dialogue function).

(3) Continuously scan the key to determine whether there is a key pressed. If there is no key pressed, it will return to the display; If a key is pressed, the corresponding man-machine dialogue function will be realized according to the key.

The flow chart of the main program system is shown in Figure 6.

5 Conclusion

This paper introduces the basic concept and implementation mode of the tension control system, and studies the basic principle and working characteristics of the magnetic particle brake as the main executive part. Then, the hardware and software design of the single chip microcomputer tension automatic control system are carried out by using the indirect tension control technology based on radius detection. The practice shows that the system has good anti-interference performance, can complete the control effect well, and the operation is stable and reliable.

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