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Perfect Packaging with PC Control

20 January 2009

Multivac, the packaging machinery specialists with headquarters in Wolfertschwenden, Germany, manufactures thermoformers which are considered by many in the packaging industry to be the best in the world.

Multivac R 535
Multivac R 535

For control technology, Multivac relies not on programmable controllers, but on PC-based control.

The development, design, manufacture and mounting of the packaging machines at Multivac (www.multivac.com) is carried out exclusively in-house, so that all development and production processes dovetail precisely. Total commitment to quality is Multivac’s recipe for success.

THERMOFORMERS

In general, thermoformers provide the most diverse packaging solutions for food, industrial and consumer products and sterile medical goods: from the high-speed packaging line for 40,000 hypodermic needles or 3,000 kilograms of meat per hour, to the flexible packaging centre for small batches with programmable format change.

Moulding, filling, sealing and cutting take place inline on the same machine, but at successive stations. The packing material for the lower web is pulled from a roll, heated in a moulding tool and shaped into cavities. The cooled packing cavities are filled manually or automatically.

The upper web packing material (lid film) is pulled from a second roll and positioned on the filled cavities. In the sealing station, the air is evacuated; if necessary, a protective atmosphere is added and the package is sealed using heat and pressure. Finally, the web of packs is divided up, first cross-wise and then length-wise.

MULTIVAC R 535 THERMOFORMER

The Multivac R 535 thermoformer series fully and automatically packs the most varied food products, such as sausage, fish and cheese, but also industrial goods and sterile medical goods in – depending on requirements – vacuum, protective gas, skin or blister packs.

“With a cut-off length of 1,600 mm and up to 30 cycles per minute, the R 535 is currently the best thermoformer on the market,” says Alois Allgaier, division manager for control technology at Multivac.

One of the many ways the R 535 sets itself apart from previous thermoformers is its innovative control technology.

When choosing the control technology, Multivac says it investigated a total of 10 leading companies in the automation industry. The selection requirements were: modularity with a wide range of functionality, optimum networking capability, scalability, reliability, ease of maintenance, simple operation and open architecture.

The decision was finally made in favor of Beckhoff.

“We were able to implement all the requirements set out in our specification book for the ‘New Generation of Control Technology’ project using the Embedded PC solution from Beckhoff,” explains Mr. Allgaier.

“PC-based technology has been tried and tested for years and is widely used," he says.

Using Beckhoff, we are confident not only of meeting our current requirements, but also of being able to react early and quickly to new trends and rising market demands looming in the future, guaranteeing our technical advantage,” Claus Botzenhardt, departmental manager for software development at Multivac, explains the decision, adding: “Naturally, the impressive price-to-performance ratio was also a deciding factor.”

EMBEDDED PCS AT THE CORE OF THE CONTROL SYSTEM

Multivac now employs PC-based control technology in all fully automated machines in its production range. At the core of the machine control systems are Embedded PCs from the CX series loaded with Windows XP Embedded as the operating system and TwinCAT automation software.

“It all began with the development of the new R 535 thermoformer,” recalls Claus Botzenhardt. “At the end of 2005 we used the CX1000 Embedded PC in our first prototypes. We have gone into large-scale production since the beginning of 2007 and have so far delivered approximately 1,500 packaging machines equipped with the CX1020 Embedded PC.”

The space-saving CX1020 controller for the terminal stations is located in the control cabinet. “Depending on the complexity of the machines and the control technology, we install an Embedded PC with the appropriate performance level. We use it for the PLC, Motion Control and our visualisation developed in Java. Installing the PC Control technology with Microsoft Embedded operating system provided the opportunity for integrating the HMI in the control system. This meant we could do without an additional PC for visualisation,” explains Mr. Allgaier.

The Multivac operating panel is connected to the CX via DVI/USB. The Ethernet interfaces allow integration into the company network and provide the Internet connection, giving the option of remote maintenance.

The Multivac product series ranges from small machines for manual packaging up to complex packaging plants for large-scale production. In the fully automatic machines, the Embedded PC used as the central control unit ensures optimum machine processes. Due to the CX being directly connected to the I/O terminals, an additional fieldbus is unnecessary in the more compact models. A local control system with several Embedded PCs can be supplied for very large and complex packaging plants.

MODULARITY PERMITS INDIVIDUALISED OFFERINGS

“Our packaging machines are a standard product to a large extent, however no one automated packaging line is like another. We develop our packaging solutions flexibly and in accordance with our customers' requirements,” Mr. Allgaier explains. “Our machines are constructed on a modular basis so that we can individually configure customised solutions and adapt the modules in the best possible way.”

CX1020 embedded computer
CX1020 embedded computer

In the R 535, Multivac integrates Beckhoff Bus Terminals and sensors for temperature recording using thermocouples or odometers with SSI sensor interfaces as well as ancillary equipment for printing or cutting the film in the control system. For example, special function I/O terminals are used to position the stepper motors in the printers. Communication terminals and the wide range of Bus Couplers can also integrate devices with serial interfaces and other fieldbuses such as CANopen or DeviceNet.

TWINSAFE: SAFETY SIMPLIFIED

Safety components such as emergency stop switches and protective coverings provide the necessary safety elements for packaging machines. Previously, Multivac wired the safety components in a conventional way.

In the R 535, the safety functions are integrated directly in the Bus Terminal system using TwinSAFE terminals. The safety data are recorded on site and evaluated in the TwinSAFE Logic Terminal. The certified TwinSAFE protocol ensures secure communication.

“TwinSAFE drastically reduces the costs and time involved in wiring,” says Mr. Allgaier. “The benefits of the modular, scalable technology are obvious here too. We select the necessary TwinSAFE terminals depending on the machine and integrate them in the control system. This is simple, convenient and cost-effective as well.”

Multivac changed its control system to EtherCAT, the ultra fast Ethernet-based fieldbus for industrial applications.

“EtherCAT brings us a big step forward technologically. The signals are captured more quickly and the machine cycle times are optimised. This enables us to better exploit the potential of the PC-based control system with its high-performance processors and to control the axis modules of our plant more rapidly and precisely,” said Mr. Allgaier.

IMPLEMENTING COMPLEX PROCESSES SIMPLY WITH TWINCAT

The R 535 thermoformer machines package large batches of product with optimum heat-sealed seam strength and functionally diverse labelling in a short space of time. TwinCAT controls the complex packaging processes such as moulding, filling, sealing and cutting very precisely and reliably in real-time and synchronises them.

However, Multivac uses TwinCAT not only as a control platform, but also as a development environment.

“Programming our new modular software architecture according to IEC 61131 using structured text was managed without difficulty by our experienced C programmers. The debugging functions in the TwinCAT PLC controls in particular saved time in the case of complex function blocks,” explains Mr. Allgaier.

PLC libraries with blocks based on PLCopen Motion Control and the OMAC PackSoft standard (PackAL) facilitate programming. Standards such as the OMAC Packaging Guidelines offer a consistent interface for packaging machines worldwide.

Important parameters for the quality of the packaging are well moulded cavities, a precise positioning of the lower film in relation to the upper film and strong sealed seams. This requires precise control of temperature, time, and pressure and printing mark control.

For the controllers, Multivac makes use of the TwinCAT libraries. The temperature controller sets the heating temperature for moulding the cavities and for sealing. In thermal sealing, the temperature is controlled in such a way that a homogeneous temperature distribution is produced and as a result, reliable and strong sealed seams can be made even under conditions which are not quite optimal.

Positioning of the lower and upper films with one another is carried out using the printing mark control system. By stretching the upper film, the product imagery is aligned with the cavity and is positioned on the packaging with great precision.

ONE MACHINE, MANY DIVERSE APPLICATIONS

Repeated change-overs are no problem for the R 535. Depending on the packaged goods, one machine can produce both round, angular and oval packages as well as tall or flat ones.

The machines are equipped with several format settings for this. A change of format can be initiated at the touch of a button i.e. the moulding plate and the sliding sealing unit are exchanged and new instructions are loaded and started in the machine control system.

“Using TwinCAT we are able to perfectly co-ordinate all components and configurations in the machine. This results in high reliability and perfect packaging results all the time,” says Mr. Botzenhardt and adds: “Independent of the hardware, we are able to use applications developed using TwinCAT on different types of packaging machines.”

For example, Multivac transferred the application software for the R 535 thermoformers to chamber machines in the Multivac TC range, which are based on a different functional principle.

“This level of flexibility is unique to-date. We equip simpler machines with an existing, more complex software and achieve additional functionalities as well as standards which enable completely new applications,” adds Mr. Allgaier.

For instance, it was possible to integrate the temperature controller for the thermoformer into the chamber machine in the TC range in order to achieve validation of the sealing temperature.

Twinsafe Terminals
Twinsafe Terminals

In addition, the operating software for the chamber machine supports customers in complying with the strict US FDA regulations, CFR21 Part 11 “Guidance for Industry Part 11, Electronic Records; Electronic Signatures – Scope and Application.”

The FDA (US Food and Drug Administration) is a public authority and is responsible for US legislation on food, drugs and cosmetics. This means that the chamber machines in the TC range can be used in medical technology without restriction.

THE KING OF CLEAN

The food and medical industries in particular demand the highest cleanliness and sterility standards. For the R 535, Multivac developed a novel cleaning process, currently unique to thermoformers, the CIP self-cleaning system (Clean in Place).

The CIP automates the chemical cleaning of chain carriers, chain profiles and internal components using a comprehensive system of nozzles and pipes. After pre-cleaning, a simple touch of a button starts a standardised cleaning program which proceeds in clearly-defined stages. The process is automated and logged in the machine control system using TwinCAT.

Users can employ a set cleaning program from Multivac or define one of their own and integrate it into TwinCAT. Depending on the program selected, TwinCAT loads the correct instructions and processes them. The cleaning process proceeds in full each time with consistent thoroughness and can be documented and followed at all times.

NETWORKED AND RELIABLE

Packaging alone is not enough – only integration with upstream and downstream components leads to a complete packaging line. Depending on the application, the automatic packaging machines are combined with slicers and infeed, dosing, weighing, labeling, testing and discharge systems of all kinds. The additional modules are registered in TwinCAT and integrated in the machine process sequence.

Additional test programs for optimising individual parameters and fine adjustment can be integrated in TwinCAT. The machine control synchronises all the modules, irrespective of whether they are before, on or after the machine, and controls the timing.

The automated packaging machines must be able to operate with high productivity and reliability. Current machine data, production volume, current process status and errors must be recorded, analysed and evaluated.

The Embedded PC records all machine data and stores it for further applications. The data can be accessed via the Internet for remote maintenance of the machine.

The recorded data can be exchanged between the machine control of a packaging plant and production data acquisition (PDA) using Ethernet and the optional TwinCAT OPC interface. Here, data is stored, evaluated and visualised. The easily operated process control enables rapid recognition of deviations from the desired condition so that counter-measures can be taken immediately. This guarantees permanently stable machine performance and consistently high daily reproducible packaging quality with more calculable running costs.

EFFICIENT DEVELOPMENT WITH A LOW ERROR RATE

All the software for every Multivac packaging machine is developed by in-house programmers.

“Programming with TwinCAT is very easy and intuitive thanks to the user-friendly operating interface,” says Mr. Botzenhardt. “In addition, it was easy to integrate TwinCAT in our development process.”

The Multivac programmers develop one part of the code automatically and transfer it to the machine control using TwinCAT. Multivac reduces the development time using Test Driven Design (TDD): during development, the I/O level is simulated and the machine tested using the simulated input values. The results are analysed and fed into the optimisation process in the machine control system in TwinCAT. TwinCAT’s dynamic diagnostic functionality assists in error minimisation. A version management system manages the software versions.

PACKAGING LONG-TERM SUCCESS

Thanks to its presence in over 100 countries with almost 60 of its own marketing companies and decentralised spare parts distribution, Multivac guarantees on-schedule delivery, a reliable spare part supply with availability even after 20 to 30 years, as well as rapid response to market requirements. In line with this, Multivac also places obligations on its suppliers to adhere to a demand-oriented component supply in accordance with the Kanban principle.

Claus Botzenhardt says he is satisfied with the control system solution for the R 535:

“This new generation of machines – and the control technology which goes with them – is significantly more complex than our earlier range of models. But despite the higher complexity, we can offer the dependability and process reliability typical of Multivac automatic packaging machines using the PC based control system.”

“This control solution also has the considerable advantage for us that a system with such scalable capacity also meets our economic requirements. Due to the modular design we can react in a flexible way to future demands,” concludes Mr. Allgaier.

Author -- Dr.-Ing. Ursula Frank, Beckhoff Automation GmbH


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