1. Constant tension control principle
The essence of constant tension control in the process of winding and unwinding is to know the change of winding diameter during the operation of the load. Because of the change of winding diameter, in order to maintain the operation of the load, the output torque of the motor needs to change with the change of winding diameter. For V series inverter, because it can do torque control, it can complete the control of constant tension. V series inverter provides three analog input ports, AUI, AVI and ACI. These three analog inputs can be defined as multiple functions. Therefore, one of them can be selected as the torque setting and the other as the speed limit. 0 ~ 10V corresponds to the inverter output 0 ~ motor rated torque, so the constant tension can be controlled by adjusting the voltage of 0 ~ 10V. And Duyu slitting machine, the calculation of coil diameter is calculated through the tension controller, of course, using PLC architecture to achieve is no problem. In other words, the tension can be set on the man-machine or text, and the winding diameter can be calculated by PLC, t = f * D / 2, so the torque output of the motor can be calculated, and it can be connected to the torque given end of V series inverter through analog output.

2. Synchronous speed calculation
Because we know that when the inverter works at low frequency, the AC asynchronous motor of slitter has poor characteristics, low activation torque and linear, so we should try to avoid the winding motor working below 2Hz in the whole process of winding. Therefore, the winding motor has a minimum speed limit. For the four stage motor, the synchronous speed is calculated as follows: N1 = 30f1 / P = N1 = 1500r / min = 2Hz / 50Hz = n / 1500 = n = 60rpm / min
(F1 is the rated frequency, P is the number of poles, N1 is the synchronous speed)

3. Speed limit operation
When the maximum winding diameter is reached, the lowest speed of the whole winding process can be calculated
V=π*D*n/i=Vmin=3.14*1.2*60/9=25.12m/min
In tension control, the slitter should limit its speed, otherwise it will run at a speed limit.

4. Calculation of tension and torque
If f * D / 2 = t / I (F -- tension, D -- winding diameter, T -- torque, I -- reduction ratio), = f = 2 * t * I / D, the rated torque of 3.7KW AC motor is calculated as follows: T = 9550 * P / N = t = 24.88n. M, so Fmax = 2 * 24.88 * 9 / 0.6 = 74.64n (T -- rated torque of motor, P -- rated power of motor,