Automating film wrapping at full stretch

Stretch wrapping is a commonplace enough process in any manufacturing or distribution business using palletised loading, but the task of automating the wrapping procedure relies on sophisticated control. Which is why shrink and stretch wrapping specialist Nissen Packaging selected Hitachi drives and PLCs from HID Limited for its latest automated wrapping machines.

Nissen's latest Easywrapper machine has two axis drives with 0.55kW AC induction motors controlled by Hitachi 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 is employed to detect whether a pallet is loaded on the machine and then to identify when the film roll has reached the top of the pallet. Once 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 pallet before completing the wrapping. Alternatively, 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 28I/O. Surprisingly, for what appears to be a relatively simple process, all 14 outputs are employed in the Nissen machine.

The two Hitachi L100 inverter drives are pre-programmed by Nissen 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 forth. Programs are selected via a simple MMI from Horner, which has a plain English menu operation. Clearly, if the recipes provided are insufficient for an application, the machine can be reprogrammed by a supervisory engineer or by Nissen if required. A further level of control is provided by fitting an electromagnetic clutch to the film roll holder that enables film tension to be adjusted via a simple potentiometer knob adjacent to the operator panel.

The Hitachi L100 inverter drives and the Hitachi EC28 PLC are interfaced with the MMI. The Hitachi L100 inverter drives have an RS422 communications port and there are seven inputs, of which five are programmable, and two programmable outputs as well as an alarm output. Access to the terminal rails is by opening the hinged front case.

Nissen Packaging commented, "HID has been extremely helpful and supportive both during the design stages of the machine and afterwards. The company has also assisted in automating the machine through its PLC programming and work carried out to identify and then interface with the Horner MMI." Unusually, the Easywrapper is made largely from standard off-the-shelf components from UK sources.

Hitachi L100 inverter drives are used on Nissen's semi-automatic machines and there is also a larger Easywrapper machine that uses 0.75kW Hitachi L100 inverters. In conjunction with the Hitachi inverter drives, Nissen are using Hitachi's latest Windows-based programming software for the Hitachi L100 inverters, making multiple programme storage for various machines possible.

Nissen began in the UK as a sales subsidiary of a Swedish film packaging company in 1971. Six years ago, the company was established as an independent British company as the result of a management buyout. About three years later Nissen designed and manufactured its first semi-automatic stretch film wrapping machines at its Leighton Buzzard premises.

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