Faced with the challenge of doubling the throughput of a film coating line for a transfer printing operation, the Mitsubishi’s FR-A700-A1 inverter’s winder function proved to be an excellent control solution requiring only simple parameter settings.

Jim O’Neill runs a bespoke machinery design-and-build company, Jim O’Neill Engineering, and was developing a coating line for a transfer printing operation. “We wanted to double the output but increasing the throughput speed by a factor of two was not feasible due to the nature of the coating operation,” he recalls. “We were using nip rollers to apply the coating material to the film web then passing it through a heater section to cure it. The time required in the heater set the transfer speed.

“So we switched from a 300mm wide web to a 600mm one and added a slitter after the coating and drying stations. Of course this meant we had to add a second, or auxiliary, rewind/unwind station as well.”

A film role weighs 25kg and needs to unwind through the coater and dryer at a speed of 40m/min and with a tension of 35kgf.  Reel diameters vary from 25mm to 350mm as they wind and unwind, requiring the drives to constantly control the motor torque.  Identifying the correct power rating for each motor was critical as the motor torque would define web tension.

By using diameter calculation and compensation for friction and roll inertia, the drives enable the motors to maintain constant tension into the web. Low ratio gearing was needed to minimise efficiency losses and the gearing would have to allow back-driving of the spindle.

The optimum systems configuration used four motors: a rewind motor; an unwind motor; auxiliary station, and a master motor running in speed control. The rewind and auxiliary station inverters were connected to the three-phase supply and the others to the DC Bus of each of these inverters. This allowed the continuous regenerative energy from the unwind sections to be used in the motoring inverters. It also meant that the regenerated energy could be recovered, so reducing energy costs.

Overall control was provided by a Mitsubishi Q-series PLC with a CC-Link communication network controlling and monitoring each of the inverters. As well as control of the drives, the PLC runs the process control of the coating station, maintains the temperature of the dryers and checks product flow to the application rollers.

For simple, easy to use operator/machine interface with additional information to assist with fault diagnosis a Mitsubishi HMI (human machine interface) was programmed to carry out several important functions including set point controls, alarm diagnostics and recipe handling.

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