Stretch wrapping is a common enough process in any manufacturing or distribution business using palletised loading, but the task of automating the wrapping procedure relies on sophisticated control. This is why, for its latest automated wrapping machine, Easywrapper, Nissen Packaging specified Hitachi drives and PLCs from HID.
The machine has two axis drives with 0.55kW AC induction motors controlled by L100 inverters. One motor controls a rotary turntable on which the pallet to be wrapped is placed. The second controls the rise and fall of the roll of stretch film material on its vertical linear axis using a chain drive.
A Seeka photocell detects whether a pallet is loaded on the machine, and then identifies when the film roll has reached the top of the pallet. When the top of the pallet is detected, a routine enables the film carrier to lower slightly to allow a top sheet to be placed on the load before completing the wrapping. Where no top sheet is required, the roll continues to rise a discrete amount to give a finishing overlap wrap to the top edge of the loaded pallet. The logic functions of the programs are controlled by a Hitachi EC28HRP PLC with 28 I/O, and all 14 outputs are used on the machine.
The two drives are pre-programmed to each give seven speeds and there are five recipes also pre-programmed to provide for just about any wrapping sequence. The recipes include different speeds for single and double wrapping, different film overlaps and so on.
The drives and the Hitachi EC28 PLC are interfaced with a plain English menu operation Horner MMI which is also where program selection is made. The L100 drives have an RS422 communications port and seven inputs – of which five are programmable – and two programmable outputs, as well as an alarm output.
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