An end of line automatic shrink wrapping machine has been produced for Italian company MIMI. In development, Control Techniques worked with MIMI to produce a machine that can quickly and easily be set-up for different bundle/pack sizes, and different configurations and products. Accurate synchronised Digitax ST servo drives from Control Techniques have been incorporated into three areas: speed of throughput, film cutting, and control of the wrapping action.

In operation, bottles or other containers are fed into the machine by conveyor and marshalled by a pneumatic separator into blocks of the specified number. A chain driven by a brushless motor then conveys the bundle into the wrapping area. The heat-shrinkable plastic film is unwound under controlled tension from a roll and cut into pre-determined lengths using a rotary cutter mechanism driven by brushless motor. The cut edge is drawn forward and held in place by toothed suction belts – a bar lifts the leading edge of the film up, over and behind the advancing bundle of products – and it moves into the shrink tunnel then on to the after-cooler. This wrapping action is also controlled by brushless motor. Each action requires high precision, highly repeatable movements. The advancing bundle of products must synchronise with the cutting stroke and the cut film must meet the advancing bundle at exactly the right moment. The trajectory described by the film when looped up and over the bar of the wrapping section must be co-ordinated precisely with the speed of the bundle. Each movement is critical to the quality of the packaging.

The ST servo drives are being used to control the three brushless motors in the machine, which not only provide precision control but also allow fast and straightforward re-configuring of each of the motors. Each drive has an SM-Application module that provides PLC functionality at drive level.

The MITO’s shrink tunnel is available in different sizes to suit the application and it can be supplied with an in-feed gating system, a twin-film feed unit, print centring unit, anti-stick bars and pneumatic discharge of the pack.