The importance of the right packaging

EQUATIONS If packaging plays a strategic role for companies operating in the field of consumer products and good packaging can be achieved thanks to an adequate motion control... then motion control is strategic. This is demonstrated by Control Techniques’ intervention on the company Mimi’s Mito shrink-wrapping machine.

Any company that today operates in the consumer goods industry needs to provide its products with a proper, good quality packaging, in order to preserve and protect the same, but also to give greater visibility to the company logo and brand. The packaging is, in short, a veritable calling card, with which companies present themselves to consumers.

Based at Canelli (AT), Mimi (Tosa Group) is a company that has been building and manufacturing shrink-wrapping machines since 1978. These machines automatically shrink-wrap all kinds of product (jars, cans, bottles, packs of rice and foodstuffs in general, but also newspapers, magazines and furniture): the bundle made is subsequently passed through a shrink tunnel for a perfect closure.

One of Mimi’s most recent creations is the Mito shrink-wrapper, designed for the mineral water industry and, more generally, for liquids packaged in bottles, bricks, cartons, cans, flacons or jars. Mito’s special feature lies in its ability to flexibly vary the bundle format, going from the classic type (six 1.5 l bottles) to that of twenty-four 0.5 l bottles, or any other kind of container, and hence vary the size of finished bundle. Control Technique’s servodrives contributed towards achieving these results.
 
The importance of brushless motors
The workcycle of a shrink-wrapping machine is a delicate and precise play of kinematics, and Mito is obviously no exception: the advancing bundle must synchronize with the cutting stroke and the cut film which in turn must meet up in the right instant with the selfsame bundle; likewise 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 in order to meet the film at the correct point.

To this one must add the aim that Mimi’s engineers set themselves when designing Mito: flexibility, to be able to easily vary the size of the bundles. That is why brushless motors have been located at the focal points of the machine, where the true control of the kinematics lies: the bundle drive chain has an adjustable speed depending on the type of bundle, the same way as the second brushless motor on the cutting unit guarantees the phasing of the rotating blade, depending on the size and pitch of the bundles in transit, thus conforming to the size of the film edge to be cut.

Lastly, the unit that wraps the film around the bundles, this too operated by the brushless motor, enables the creation of the speed, acceleration and deceleration profiles appropriate to the bundle being processed. In this phase system accuracy and synchronization are of vital importance to gain a perfectly finished bundle: the right quantity of accurately positioned film ensures that there are no bubbles, swelling or creases on the pack. It also ensures the correct positioning of the logos that, to the consumer’s eye, will be perfectly aligned on all bundles displayed along the supermarket shelves.
 
Flexible motion control strategies
For the control of the three brushless motors aboard the Mito, Mimi’s engineers chose Control Techniques’ Digitax ST servo drives, particularly suited for driving brushless motors operating on industrial machinery, which not only provide precision control, but also allow fast and straightforward re-configuring of each of the brushless motors, to accommodate different product configurations. As seen, it is a question of creating trajectories of circular motion around the pack advancing in rectilinear motion, with appropriate speed and acceleration profiles; in other words, electronic cams have been created according to the dimensions of the various bundles to be wrapped.
The result was achieved thanks to the Digitax STs equipped with SM Application modules. Thus the software codes for the motion control and the electronic cams have been incorporated in the drive instead of directly on the machine PLC. This has enabled the logical motion control functions to be separated from the choice of PLC, giving added flexibility to the Mito and allowing Mimi’s technicians to concentrate the specific characteristics of the shrink-wrapper - such as space and axial management, control of movement and of the various available cams according to the bundle to be wrapped - in the allotted drive in the SM Application module.
Likewise, the Mito’s communication fieldbuses can be varied without problems: again thanks to the SM Application modules, any possible change of fieldbus has no impact on the code developed on the Digitax drive, as the drives operate downstream of the bus, without hence affecting the logical functions of the PLC and the data type that the bus has to administer.