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Cerotti a velocità record
«Plasters at record speed»

AUTOMAZIONE OGGI n°290 — April 2006
VNU business publications www.vnu.it

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When we use a plaster, certainly we do not imagine how complex the technology for its production is. The machines producing these items, that are so important for our health, are very exigent as far as speed, control precision and product quality are concerned.

R.C.A. Bignami (www.rcabignami.com), Varese-based company established on an ancient craft tradition in the punch and printing field, is perfectly aware about it. The professional competence gained in this thirty-year activity, combined with a working environment always open to the application of state-of-the-art technologies, enabled the company to manufacture some of the most interesting plaster production line machines in this kind of market.

The latest machine manufactured by Bignami is the fastest one of its sector: during the production cycle it can reach a speed of 50 m/min. with 15-mm wide plasters (that is to say more than 3300 plasters per minute).

In the past the automation of Bignami machines was managed by special CNC solutions. But for this new challenge Bignami entrusted the Biella-based company Motion Engineering, Siemens System Partner for Motion Control applications (www.motion-eng.it), with the complete redesign of the control architecture, making use of its experience of many years in the field of fast machines and motion systems.

If you have a look at the Bignami machine, what leaps immediately to the eye is the large quantity of coils made of different materials involved in the process. In fact a plaster is composed of different more or less “technical” superimposed materials (such as silicon paper, hydroxocolloid, gauzes, adhesive supports etc.). So the machine axle control must be able to adjust with extreme accuracy the unwinding speed of the different layers, allowing afterwards a precise and very fast cut in order to obtain the “finished” and wrapped plaster.
All this was obtained by means of the most innovative and dynamic Motion Control system available among Siemens range of products: SIMOTION. Simotion is an automation system designed for the motion control and available in three different hardware versions: controller-based, PC-based and drive-based. The project manager can choose the most suitable configuration according to the type of solution to be adopted (centralized or distributed) and to required performance.

For the Bignami machine a SIMOTION D445 control (the most powerful among Simotion’s Drive-based CPUs) was selected that controls 18 axles of the new SINAMICS family. The CPU manages, in addition to the machine logic, the part concerning coilers and uncoilers, the rotating knives for plaster cutting as well as the phasing with regard to the cut position and is able to carry out this performance with a 2 ms elaboration cycle only. Moreover Motion Engineering has implemented a register control with a superimposed cam profile on the normal gearing movement in order to centre precisely the cut as regards the plaster print (printed plasters are especially appreciated by children).

The Simotion D/Sinamics combination has proved to be particularly suitable, as far as hardware configuration compactness and control system power are concerned. In addition to the machine logic, all necessary motion control functions have been programmed by means of SCOUT, the Simotion engineering tool. The management of SINAMICS drives is totally integrated in the Simotion project.

This driving gear family presents a completely innovative architecture: the single power parts (engine modules) are not equipped with the electronics managing the current and speed regulation because this is centralized in one CPU only working for all axles involved. The core of the system is represented by the Drive CLiQ communication link which connects all components (also engines) and is able to transfer a huge quantity of data at a speed of 100MBaud. Thanks to the Drive CLiQ the control is able to get automatically the electronic labels of all components, carrying out its own configuration consequently. The easiness and speed advantages during the initial installation are as huge as the system diagnostic potentials. These latter are underlined by SCOUT’s powerful debugging tools which enable the user to carry out a fast and precise failure search.

All brushless drives of the 1FK7 series are supplied by Siemens with low-clearance reducers that are already coupled.

Eng. Lucio Bonandini of Motion Engineering, who has developed the project, says that the flexibility allowed by SCOUT programming system has proved to be essential for the success of the application. In particular the possibility of arranging the most used routines in Functional Blocks (FB), allows a considerable program modulation, creating code parts that can be reused as you like thanks to the management “on request”.

This mode has been extensively used for the different coilers and uncoilers of the machine: they are all managed choosing the same FB for different axles.

It is a couple limitation indirect control (without retroaction on the material tension) with a sensor on each coil able to measure its diameter.

In particular the coiler/uncoiler mathematic model has been studied, implementing also the coil (variable) inertia compensation during machine acceleration and deceleration transient phases.

In a similar way functional blocks have been developed that are able to manage in parallel the scrap of non-complying pieces. These latter are detected by means of contrast control fast photocells and are put into FIFO structures composed of max. 512 elements for the final outgoing scrap. There are in total twelve scrap reasons, but the implemented routine is “universal”.

The presence of specific technological devices for the management of diameter sensor inputs was also much appreciated: these ready-to-use software functions contain all necessary elements to filter and process the signals in order to make them available for the calculation regulation.

The interface with the operator, based on a Simatic MP370 touch panel and designed with Pro Tool/Pro, is up to the machine as well: functional and nice video pages guide the operator during the planning phase of all production data.

Finally, thanks to the power factor correction function of all axles during the starting phase (absolute coordinate electric shaft combined with absolute multirevolution encoders) it is possible to obtain a very fast and reliable restart after any anomalous situation.

Mr. Bignami, owner of the company, expressed his satisfaction for the collaboration with Motion Engineering and for the results obtained with Siemens electronics.

The machine, developed for a foreign plant of a big German group, is now arousing the interest of other important companies active in the field of medical and sanitary products and probably it will become a true model to follow in this sector.



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