Closed-loop application of VFD (Variable-frequency Drive) in tension control of sizing machines

The ZGA-203 double tank sizing machine used in a cotton spinning mill can sizing a variety of yarns. The original transmission scheme of the equipment adopts a single frequency conversion + mechanical stepless speed regulation, that is, the speed of the main traction motor is adjusted through a VFD (Variable-frequency Drive), and the main traction motor is then transmitted to other respective transmissions through four mechanical stepless speed regulators. points to form a speed chain to maintain tension in each section. In the winding part, the main motor drives the pneumatic mechanical stepless speed regulator, and the winding tension is adjusted by manually adjusting the air pressure, and the winding tension is automatically stabilized. After using this equipment for a period of time, many problems occurred one after another. The main problem was that the pneumatic mechanical stepless speed regulator in the winding part was easily worn, causing the winding tension to be unstable. Either the yarn tension is too low and causes curling, or the yarn tension is too high and causes breakage. At the same time, the maintenance of this part is time-consuming and laborious, which seriously affects the output and quality of subsequent weaving.

The TD3300 series tension control dedicated VFD (Variable-frequency Drive) launched by Emerson in the United States has an internal roll diameter calculation module, which can automatically calculate roll diameter changes, and can independently form a tension control system to complete open-loop and closed-loop constant tension control; at the same time, the The series VFD (Variable-frequency Drive) has a tension taper control function, which can ensure the uniform shape of each layer after winding, greatly improves the accuracy and speed of tension control, and improves production efficiency. The cotton spinning mill used Emerson's TD3300 tension control dedicated VFD (Variable-frequency Drive) to transform the winding part of the sizing machine and achieved satisfactory results.

The specific requirements for using VFD (Variable-frequency Drive) for tension control are: transformation ratio 11.73; roll diameter range 110~780mm; speed adjustment range 3~60m/min; tension adjustment range 800~3000N. The winding line speed must be synchronized with the main line speed and adjustable. The winding yarn tension must be kept constant during the winding constant speed, speed adjustment and start and stop processes.

TD3300 VFD (Variable-frequency Drive) tension control has 3 control modes, namely tension open-loop torque mode, tension closed-loop speed mode and tension closed-loop torque mode.

The tension open-loop torque mode does not require the installation of a tension sensor and is widely used in situations where tension control requirements are not high. However, it is required that the minimum output torque of the motor should be controlled at more than 10% of the rated torque of the motor. Since different yarn products require different tensions to be controlled, when selecting a motor, the rated output torque of the motor must be calculated based on the maximum winding diameter and maximum tension given value. Through calculation, it can be seen that the VFD (Variable-frequency Drive) operating frequency is between 0.3 and 67.2Hz. It is best to use a variable frequency motor for the winding motor to ensure the safe use of the motor. Therefore, a 22kW four-pole variable frequency motor (rated torque 140N) is selected as the winding motor, and TD3300-4T0220G is selected as the winding VFD (Variable-frequency Drive). The minimum output torque of the motor is calculated based on the minimum roll diameter and minimum tension given value. If the tension open-loop torque mode is selected, the minimum output torque of the motor is only 2.7% of the rated output torque of the motor, which is far lower than the 10% requirement. In this way, when producing small tension yarn, it is very difficult to ensure constant winding tension of small winding diameter. That is to say, when performing tension control, both the tension is required to be constant, and the adjustable range of tension is required to be large. It is difficult to meet the control requirements using the tension open-loop torque mode.

Then the control scheme can only choose the tension closed-loop mode. Tension closed-loop mode is divided into tension closed-loop speed mode and tension closed-loop torque mode. Although the tension closed-loop speed mode has a certain dependence on the PID parameters, compared with the tension closed-loop torque mode, the debugging is relatively simple and can fully meet the control requirements. Therefore, this control scheme adopts the tension closed-loop speed mode, adding a tension sensor (24VDC power supply, 4-20 mA current signal output), tension roller and angle roller between the winding roller and the yarn pressure roller, and realizes it through the signal feedback of the tension sensor Tension closed-loop control to achieve constant winding tension.

It should be noted that it is necessary to ensure that the motor has sufficient output torque at large roll diameter, large tension, low speed or zero speed to prevent the motor from insufficient torque at low speed and zero speed causing the winding roller to roll back. TD3300 should be set It is a closed-loop vector control mode to increase the low-frequency output torque of the motor. This requires a rotary encoder to be installed on the motor.

When using VFD (Variable-frequency Drive) for tension control, if both the tension is required to be constant and the tension adjustable range is large, it is best to use the tension closed-loop mode. After the transformation of the ZGA-203 double tank sizing machine using TD3300 VFD (Variable-frequency Drive), the on-site configuration is simple, the operation is stable, and the debugging is convenient. The actual winding effect is also very ideal. The user has been using it for a long time and is impressed by the transformation results. Quite satisfied.