On the automatic tension control in the process of

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Talking about the automatic tension control in the process of film reeling

in the production and processing of film, there are processes related to reeling operations such as unwinding and reeling. At this time, the diameter of the drum changes, and the change of diameter will cause the change of coil tension. The tension is too small, resulting in the relaxation and wrinkling of the coil, which will also deviate laterally. Excessive tension will lead to excessive stretching of the coil, tension lines will appear in the longitudinal direction, and raised ribs will appear on the surface of the membrane roll, and even deformation and fracture of the coil. For the full-automatic pressure testing machine, the oil cylinder falls back slowly at this time. Therefore, in the process of coiling, it is very necessary to maintain a constant tension in order to ensure the production efficiency and the surface quality of the coil

I. classification of automatic tension control system

in actual production, if the film is rolled in the way of central winding, the linear speed of the film roll is dynamically changing, and the speed of the film conveyed in front is also changing, so the tension on the film is changing. In order to keep the tension of the film constant, the rotation speed of the drum must be automatically adjusted according to the tension on the film. According to the control principle, it can be basically divided into open-loop control and closed-loop control

1. open loop control

the so-called open loop control is a control form in which there is no detection device and feedback link in the control system, or there is only detection device but no feedback link

2. Closed loop control

closed loop control is a control system with detection device and feedback link. The closed-loop control has strong randomness and high control accuracy. There are many ways of closed-loop control. Here is a control system that uses potentiometer as detection element to control motor frequency

II. Principle of automatic tension control

at the beginning, the tension exerted by the coil on the floating roll is balanced with the gravity of the roll itself and the thrust of the cylinder, and the floating roll is in the middle of the balance position. As the diameter of the membrane coil 6 increases, the linear speed of the coil increases. At this time, the tension acting on the coil increases, and the floating roller swings upward, driving the potentiometer 5 to rotate. The potentiometer is a winding resistance, and the valve spring is to ensure that the valve is seated in time and closely fitted. When the potentiometer rotates, the voltage of the sliding contact changes, and sends the changed voltage signal to the control circuit. Compared with the given voltage signal, after integral amplification, the speed of the motor decreases, the tension of the coil returns to the given value, and the floating roller returns to the original balance position

III. pneumatic principle of floating roller installation precautions

floating roller plays the role of detecting tension changes in the process of automatic tension control, and at the same time, floating roller can absorb or buffer the impact of tension jump on system stability. The correct installation and use of the floating roller has a great relationship with the response sensitivity of the whole control system. The following are some links that need to be paid attention to in the installation of the floating roll system

1. under the working state, the tension roller only bears one-way pressure, the cylinder can be connected with compressed gas on one side, and the air outlet can be directly connected to the atmosphere, so only the pressure of the air inlet needs to be controlled. A throttle valve is installed at the air outlet of the cylinder, which can control the speed of exhaust and make the cylinder have a back pressure, which can prevent the cylinder from rushing forward too fast and causing impact

2. the cylinder adopts a low friction cylinder, which can reduce the friction between the piston and the cylinder block and improve the reaction sensitivity of the cylinder. When the tension acting on the floating roller has small fluctuations, it can also produce fluctuations and cause the potentiometer to react

3. the pressure reducing valve must be precision pressure reducing valve. The precision pressure reducing valve has high pressure stabilization accuracy, which can reduce the fluctuation of gas pressure at the inlet and introduce the jump of swing roll, resulting in the change of tension. At the same time, when the tension on the membrane increases, and the torque acting on the left side is greater than the torque on the right side, the cylinder moves downward, and the gas from the air inlet of the cylinder to the pressure valve for the production of synthetic materials such as NDC and hexonitrile is compressed, and the pressure increases. Precise pressure regulation "1035" Sinopec invested 200billion valve with exhaust port, so that the gas can be discharged, which can keep the gas pressure in the cylinder unchanged

4. The film on the floating roll should have a large enough wrap angle. As shown in Figure 3, the wrap angle of the film on the roll is α, The effective resultant force of the tension on the film on the roll fq=pcos α 1+FCOS α 2, and α 1+ α 2=π- α, If α The smaller, α 1 and α 2. The larger the FQ is, the smaller the FQ will be. Therefore, there must be a large tension change to cause the swing of the floating roll

5. Install the mechanical limit device within the swing range of the floating roll. It can play a buffer role at the end of the stroke of the cylinder to avoid the piston hitting the cylinder block at the end of the stroke, so as to prolong the service life of the cylinder

IV. summary

the control scheme of indirect tension detection using floating rollers is often used in occasions requiring automatic tension control, such as film winders

from: Guangdong Jinming Plastic Equipment Co., Ltd. Author: Liziping

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