Servo control improves flexibility of shrink wrapper

One of Italy’s leading manufacturers of packaging machinery, MIMI Srl, has incorporated high-accuracy servo drives from Control Technologies for its latest MITO shrink wrapper.

High precision and highly repeatable movements required by this shrink wrapper are delivered by servo drives.
High precision and highly repeatable movements required by this shrink wrapper are delivered by servo drives.

MIMI is part of the Tosa group, famous for making wine bottling machinery. Its MITO automatic shrink-wrapping machine is designed as an end-of-line machine for the wrapping of different configurations and pack sizes of bottles, cartons, cans, or tubs, and its key selling point is its flexibility. The incorporation of highly accurate and synchronized Digitax ST servo drives into three critical areas of the machine—throughput speed, film cutting, and control of wrapping action—have resulted in an increase in throughput and versatility to the process in this new machine.

Control Techniques Italy worked closely with MIMI to produce a machine that can quickly and easily be set-up for different bundle/pack sizes, different configurations and even different products. For example, it can be changed in seconds from a format for wrapping 6 1.5-L bottles of mineral water to 24 0.5-L litre packs at a throughput of up to 40 packs a minute. The machine can also be supplied with a carton pad dispenser or with a tray-maker.

Bottles or other containers are fed into the machine by conveyor and marshaled by a pneumatic separator into blocks of the specified number. At this point, a chain driven by a brushless motor conveys the bundle into the wrapping area. The heat-shrinkable plastic film is unwound under controlled tension from a roll; the film is cut from underneath into pre-determined lengths using a rotary cutter mechanism driven by brushless motor. The cut edge is drawn forward and held precisely 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, where it shrinks into a secure package, and on to the after-cooler. This wrapping action is also controlled by brushless motor.

Each of these actions requires high precision and highly repeatable movements. The advancing bundle of products must synchronize with the cutting stroke and the cut film must meet the advancing bundle at the right moment.

The trajectory described by the film when looped up and over the bar of the wrapping section must be co-coordinated precisely with the speed of the bundle in order to meet the film at the correct point. Each of these movements is critical to the machine quality of the packaging, eliminating bubbles, swelling, or creases. It also ensures the correct placement of the end-user’s logo and copy, so that the finished pack can be merchandised correctly and attractively.

For the control of the three brushless motors in the MITO shrink wrapper, MIMI engineers selected Digitax ST servo drives, which not only provide precise control, but also allow fast and straightforward re-configuring of each of the brushless motors to accommodate different configurations of product. Each drive incorporates an SM-Application module that provides PLC functionality at drive level. For instance, the CAM-profiles are stored on board, reducing the overall level of PLC control and giving the end user maximum versatility of control. This also gives the machine designer flexibility in choosing the communication bus to suit the needs of the client as the drives operate downstream of the bus.

The Digitax ST range encompasses four models, each with industry-leading features, extremely compact in size and having full compatibility with Control Techniques’ existing range of function and communication modules. It is optimized for servo applications requiring high peak torque, exceptional dynamic response, faster installation and start-up as well as ease of integration. Four product variants make up the range—Base, Indexer, EZ Motion and Digitax ST Plus chosen for the MITO shrink wrapper.

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

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