Die cutter drives forward

Rotoflex International of Ontario, Canada, has for some time used electronic servo drives to control the reversing path movement for label die cutting by a magnetic rotational system on its Vericut machines. But the technology has reached its limits. Looking for a modular expandable solution the company found it in the Siemens drive based Simotion D motion control system and the matched Sinamics drives. Not only the flexibility and the performance, but also the speedy implementation has convinced the Rotoflex managers to equip future machine generations in a similar way.

The atypical operation of the Vericut is achieved by the construction of the label die cutting unit. At its heart is a continuously turning magnetic roller (up to 240rev/min) on which the flexible die cutting plates are placed - held only by the magnetic force. This is much simpler and more economic than using a separate cutting roller for each label format. Depending on label format, the magnetic plates wrap around the roller circumference from 300 – 360 degrees. This obviously may produce a gap in the plate. To prevent gaps in the cutting pattern the label web has to operate in an intermittent motion – for each rotation of the magnetic roller at the correct time the substrate web travels briefly in the direction opposite to the production direction. At the end of the plate gap it is re-synchronized to the roller.

The reversing motion is controlled using an output cam. The exact die cutting positions are recorded with sensors using registration marks on the web. Within a fraction of a second they are transferred to the controller in order to correct any deviations immediately. The individually driven dancer rollers situated before and after the die cutting station decouple the reverse motion of the web in this area from what is fundamentally the continuous motion of the line determined by the two winders. The winder also regulates web tension.

The servo drive of the magnetic roller acts as master for the complete line. This all means that the machine manufacturer has to provide for a die cutter positioning accuracy of ± 0.1mm at a maximum web speed of more than 90m/min.

The Canadian company was able to implement this immediately with a high performance control and drive system from Siemens, claims the drives and controls specialist. The most important component here is the Simotion D445 motion control system that integrates the motion control, the technology and the plc functionality in the compact construction of the Sinamics S120 drive family and permits cycle times in the millisecond range without requiring the usual interfaces.

The converters of the modular Sinamics S120 series, which drive servomotors of the 1PH7 and 1FT6 series, are connected using the digital interface of the system. The first Vericut machine equipped with the new technology includes nine servo controlled axes. A Simatic Multi Panel MP270 Touch is used for the operator control and monitoring of all the processes.

More axes possible

The main reason for the conversion to the Simotion D445 was the limitation of 18 axes on the old control system. Additional axes would have required the use of an additional controller. Now, in contrast, a maximum of 64 drives can be connected to the new Siemens motion controller that gives the manufacturer the necessary breathing space for future extensions. This allows lines (even by retrofitting) to be augmented with additional modules, for example, for laminating and for lateral or cross cutting, and thus quickly and economically satisfy specific customer requirements.

It is also possible to pre-configure these modules in a standard controller software that covers all requirements, which can then be activated as required. This concept helps greatly to simplify not only the engineering, but also the commissioning and the software maintenance.

The relationship of the positions of the magnetic roller and the label web changes with the contact angle of the die plate and therefore has to be recalculated for each label format change. The Simotion controller allows this relationship to be described very precisely using a simple output cam comprising a linear and an exact sinusoidal component rather than the previous system's individual interpolation points. This reduces the time for the on-line calculation to a fraction of a millisecond so that the operator has practically no waiting time.

Downtime on format changes is further reduced. And, thanks to the smoother, more harmonic motion control, the new control and drive solution provides significantly improved running and a ± 0.05mm positioning accuracy of the die cutter. This, in turn, gives the manufacturer additional reserves; their machines not only cut labels more precisely, but also at higher web running speeds.

The use of standardized blocks developed by Siemens for a wide range of "converting" tasks also simplifies configuring. These blocks provide all the functionality required for the specific task of the used "winder" block, for example, various control modes, such as dancer roller position control, tension control with torque limitation and speed correction or torque control (indirect tension control). The blocks are claimed to be easy to parameterize and no longer need complex programming by the user.

In addition, and this is a significant difference to the previous solution, the blocks are completely open. This allows the manufacturer to make changes itself and customize the functionality to specific factors. Before the system change, even small changes to one of the blocks required (paid) program changes by the controller manufacturer.

"Because Rotoflex wanted to present its modified machine at a trade exhibition, the conversion to the new control and drive concept needed to be completed in just over four weeks," said Stefan Müller, application developer in the converting industry group at Siemens in Erlangen. “Thanks to the extensive co-operation of the machine manufacturer with Siemens application specialists from Canada and Germany, the project was successfully completed in this tight time frame. And the upgraded label die cutter immediately found two customers at the exhibition!”

This was reason enough for the Canadian company to make the Simotion D and Sinamics combination its new standard for the second generation of Vericut lines currently being developed. These machines with initially 22 axes already provide for significantly higher demands. "For future developments, we will be able to include innovations not possible for the first project because of the limited time available", emphasized Stefan Müller.

Ready to go

With the Converting Toolbox, Siemens has a tailored package of ready-to-use software functions and applications specially developed for converting. This allows recurring tasks to be taken from the proverbial drawer and implemented with significantly reduced engineering effort and thus at a lower cost, it explains. They have been tested in use, are fully documented and can be put together in any combination. The open functions of the Converting Toolbox can be easily adapted to specific requirements and easily moved to different target platforms, concludes Siemens.