Study On Revamping Of Control System Of Coating Machine

Composite reverse osmosis membrane is a new kind of polymeric material, whose quality depends much on the coater. But with a lot of problems in the control system of the imported coater, the quality of reverse osmosis membrane could not be guaranteed.The improvement of the electrical control system of the coater is presented. The industrial computer is replaced by the PLC that is more friendly for programmer and easier to maintain, and the DC speed controller was replaced by inverter.Only with the tensions of all the segments is constant during the operation, the quality of the products can be guaranteed. For the unwinding system, we use a system that includes tension feedback and magnetic powder clutch. The tension will not variate with a change of the unwinding roll's diameter.The speed of mid motor is regulated with constant torque rule. The motor with basic speed is controlled with speed feedback. Encoder and High speed counter tests the speed value, the PID calculated by PLC.The tensions of the middle segments are controlled by feedforward control and feedback control. The feedforward portion is proportional to the basic speed, the feedback is supplied by the PID controllers. With the feedforward control, the dynamic performance of the tension control is improved when speed is up or down.On the rewinding segment, the reverse osmosis membrane requires almost no tension, otherwise it will be mechanically damaged. But it is very difficult for tension feedback control to meet this requirement. The tension of rewinding system is controlled by torque motor. The input voltage of the torque motor is controlled according to the diameter of the rewinding roll, so the above requirement can be met.The control system uses the touch screen as the HMI that can make it more convenient for operators. And with the alert of the HMI, the failure can be found as soon as possible.After the improvement, the stability of the control system is much better. The phenomena of the products trembling and the damage disappeared and the quality of the products improved greatly.