Foreword
On Brückner Maschinenbau GmbH & Co. KG's LISIM® biaxially oriented film production line, over 700 clamping mechanisms hold plastic films together, simultaneously stretching them biaxially. These clamps are pulled by magnetic fields, much like a maglev train on rails, made possible by 728 linear motors generating this moving magnetic field. Recently, Brückner adopted B&R ACOPOS series drives for this motion control, enabling synchronous communication via a POWERLINK bus. By adopting B&R technology, the Chiemgau-based machinery manufacturer in Germany has been able to significantly reduce drive equipment costs, shorten cycle times, simplify hardware and software maintenance, and replace proprietary drive systems and bus technologies with off-the-shelf solutions.
On the LISIM® biaxially oriented film production line, a synchronous stretching system driven by linear motors pulls hundreds of clamping mechanisms on two annular guide rails to stretch the film at speeds up to 6.6 m/s. After the plastic film emerges from the extruder and calender rolls, these clamping mechanisms grip both sides for accelerated lateral stretching. The two guide rails are not parallel; their spacing increases as the production line extends. Simultaneously, the film is stretched longitudinally, with absolutely no scratches allowed. During stretching, the film passes through an oven; the high temperature determines the molecular structure of the material, thus determining the film's physical properties, such as shrinkage under stretching. After stretching, the clamping mechanisms release the film, allowing it to idle back to the system's starting position. Unusable film edges are trimmed before winding.
Bruckner thin film production equipment, which employs advanced B&R drive technology, boasts extremely short cycle times.
In practice, only a limited number of clips are driven, while hundreds of undriven clips not only improve the stress distribution on the membrane but also prevent sagging during stretching. The driven clips are designed as secondary aspects (rotors) of the linear motor, thus featuring permanent magnets on their traction surfaces. The primary components (stator windings) are symmetrically positioned above and below the permanent magnets on the traction surfaces to further improve stress distribution. The windings are distributed along guide rails in regions of varying lengths, ensuring that only one clip is driven in each region.
728 individually controlled windings
Each zone is individually controlled by an inverter. Bruckner's new LISIM® system relies on B&R drive technology: along a 65-meter length, there are 728 zones, controlled by 384 B&R ACOPOS series single/dual-axis inverter modules and 14 power modules, communicating synchronously via a POWERLINK bus. The longer the zone distance, the greater the power required, thus necessitating drive types ranging from 2.6A to 22A with a rated power of 5kW.
“The machine concept is built on linear motors. We created this concept 15 years ago, but it remains very advanced today. The machine has been continuously improved due to the increasing demand for special films in the packaging and LCD panel industries. The drive technology we've been using is indeed outdated,” said Günter Oedl, Electrical Manager of Automation Development at Brückner Maschinenbau GmbH & Co. KG, when discussing the switch to the B&R system. “It was also developed specifically for us and uses a proprietary bus, making new development both difficult and expensive.”
This machinery manufacturer is able to replace proprietary products with cost-effective standard solutions by using ACOPOS modules and POWERLINK buses, and these standard solutions can be further developed to meet the needs of different users.
Achieve precise synchronization via POWERLINK
“The POWERLINK bus enables precise synchronization of hundreds of network nodes while providing high data throughput. On the one hand, we have been able to significantly reduce the cycle time – now only 400μs. On the other hand, we have been able to move large software blocks from the driver to the global driver controller,” Günter Oedl explained. “This significantly simplifies software maintenance.”
All 398 ACOPOS modules (power supply modules and inverter modules) in the system are synchronized by 12 APC810 series industrial PCs. Each PC is equipped with three POWERLINK cards and can control up to 13 modules. The PCs communicate with each other via another POWERLINK card or connect to a higher-level APC810 running Bruckner motion control software. For example, the factory control system responsible for controlling the oven is connected to the B&R industrial PC via a PROFIBUS interface.
398 ACOPOS modules achieve precise synchronous control of the clamp mechanism via the POWERLINK bus.
The control cabinet of the LISIM® biaxially oriented film production line contains a total of 398 ACOPOS modules, which are synchronously controlled by 12 APC810 series industrial computers.
POWERLINK features extremely short cycle times and extremely low jitter rates, enabling Bruckner to achieve precise area positioning. As confirmed by the company's electrical development director, "These individual areas combine to have a consistent topology with tolerances far less than one millisecond specified in the application project."
Another advantage of POWERLINK for machine manufacturers is that it is not a proprietary bus system, but an open-source solution, thus gaining support from numerous manufacturers and adopting a variety of solutions, including professional diagnostic tools.
Energy and space saving
Bruckner's management was impressed with ACOPOS's extensive product portfolio, particularly the ability to control two shafts or windings with just one inverter module, as Günter Oedl noted. "We don't need 728 inverter modules; 398 modules are sufficient to accomplish this, reducing both costs and space."
Bruckner's management also paid particular attention to cooling technology. "The risk of air cooling is that clogged filters cannot be replaced in time, or worse, they may have been removed or no longer needed," warned Bruckner's engineering manager. "Therefore, we wanted to use plate cooling, and in our initial discussions with B&R, they showed a very positive willingness to cooperate and developed an ideal solution for us." Even during subsequent project development, B&R remained very dedicated to service: the company replicated the entire drive system at its technical center in Eggelsberg for further development.
ACOPOS inverters do not require thermal paste, an advantage that has been crucial for Bruckner's adoption of B&R's drive technology. "Inverter replacement used to take an hour during equipment maintenance, but now it can be done in half an hour," said Günter Oedl. But that's not all: for drives with cooling plates, rack-mounted cooling is far more efficient than water or oil cooling. This avoids peak temperatures and large temperature fluctuations, extending the equipment's lifespan. Adding coolant to the existing cooling system further enhances overall efficiency compared to traditional cooling methods.
Sensorless closed-loop control offers higher efficiency and robustness.
Switching from open-loop to closed-loop winding control significantly improves energy efficiency. To achieve this, Bruckner had to abandon the use of sensors, as they cannot be installed near the oven. "Thanks to the sensorless control method, we were able to reduce the power consumption of each system by 100 to 150 kW," claims Günter Oedl. This control method has higher damping characteristics compared to weakly damped magnetic shaft systems, thus sensorless controlled machinery is better able to prevent process deviations or film tearing. "The advantages of sensorless closed-loop control are quite significant. Therefore, we very much welcome B&R to continue providing us with ideal solutions in the future," concludes the Engineering Manager at Bruckner.
