Beckhoff: Get ready for the next automation revolution
Industrial Ethernet Book Issue 93 / 11
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Compact and high-precision glass cutting machines

Machines for glass cutting are using PC-based controls to provide versatile, easily adaptable controls. ADS communication is utilized for production planning and optimization, order entry and inventory management, as well as "transparent production" that has been developed using the framework of Industry 4.0.

GLOBAL MACHINE BUILDER, LiSEC, has a main objective of polyvalent, versatile machines which can be easily adapted and parameterized to a respective application as a stand-alone system or system module.

To achieve these goals, the approach has been to use PC-based controls and highly scalable, flexible technology which, as the glass cutting machine "base Cut" clearly illustrates, is extremely compact and facilitates precise machining procedures.

An Austrian company, LiSEC Maschinenbau GmbH has specialized in flat glass processing for over 50 years. Their portfolio ranges from glass cutting systems to glass processing, such as technology for smoothing and grinding glass edges, to production lines for insulating glass. In recent years, LiSEC has increasingly reinforced its leading position as a supplier of automated complete systems, with complementary operator expertise through a separate glass processing division.

Other key features include a separate software program connected to Beckhoff′s TwinCAT software via ADS communication for production planning and optimization, along with order entry and inventory management, as well as "transparent production" developed using the framework of Industry 4.0.

Scalable controls simplify machines

PC-based control technology has resulted in numerous advantages for LiSEC, as Dr. Markus Schoisswohl, Head of Automation at LiSEC, explains: "Since system visualization requires one anyway, also using a PC as the controller was a no-brainer for us. In addition, there is the exceptional scalability and high flexibility of PC Control. This is very important to us, because it enables us to implement machine automation as economically as possible. Finally, our systems offer a huge number of configuration options that go hand-in-hand with the best possible support from a control technology standpoint. Also, TwinCAT makes it easy to keep new systems updated to the latest software version without reprogramming."

According to Andreas Rohrweck, head of L1 (PLC) & L2 (Visualization) at LiSEC another advantage is scalability. "The fact that the processes are quite similar in different machines means that we can be more efficient with uniform control programs."

For example, the new "base CUT" glass cutting machine (as a standalone machine with basic functionality) uses the same control program as a high-end system in the system network. Plus the automation solution can be scaled, both in terms of software as well as with regard to the drive technology used. The TwinCAT System Manager provides support for this by adding a layer of abstraction for the programming and hardware levels.

According to Schoisswohl, speed and openness are also central properties of effective PC control. "Due to the increasing modernization of our division, the demand for advanced automation systems is rising. That is why a flexible solution for system-wide communication that accommodates different networks is so important to us. The EtherCAT industrial Ethernet system handles the communication tasks and forwarding of the real-time data transfers among the machines. Non-time critical data are transferred by client-server technology via TCP/IP, for example, to a higher level line coordinator," Schoisswohl said.

Rohrweck added that "the speed of EtherCAT also benefits us in the area of motion control. The servo-axes are operated in 1 ms clocks, for example, to meet the especially high requirements in the CNC machining of glass edges. This is supported by TwinCAT NC I software, which also facilitates highly dynamic controls."

Modern control and drive technology provides the necessary high precision for each movement. "There is a broad distribution here with respect to the processing steps and the range of machinery, beginning with relatively less critical single-axis positioning tasks (simple point-to-point movements), to complex machine tools operated in the CNC environment," Rohrwecks said.

"In the process, the grinding and the boring of holes or milling require much greater precision than glass cutting. For example, a cutting tolerance of 0.2 mm is sufficient for base CUT; for machines that polish edges on the other hand, this value lies in the hundredth of a millimeter range. TwinCAT NC I can handle all of this, supported by ready-made function blocks for smooth starting after an S-shaped ramp and much more," he added

By mounting the control cabinet IPC (bottom right) directly in the operator terminal, the servomotors (top left) could be placed in the cutting table under restricted space conditions, saving an enormous amount of space.

Space-saving control components

Tasks accomplished with PC Control using base CUT and a 2-axis NC with auxiliary axis include: automatic search for workpiece zero point, automatic detection of workpiece position with corresponding correction in the NC program, automatic measurement of unknown glass plates as well as standard PLC tasks such as tilting the table up.

The heart of the control system is a Beckhoff C6930 control cabinet Industrial PC (IPC), which according to Rohrweck, excels due to its very compact and robust design: "Due to its low space requirements we could integrate this IPC directly into the operator terminal in the base CUT. In addition, the C6930 has all the necessary interfaces for our machines as well as the option of to use high availability SLC flash memory. Also, high scalability through numerous options is a decisive factor for us, since the C6930 is employed in our entire range of machinery."

Since the operator terminal for base CUT is placed directly on the machine, LiSEC also stresses the importance of space saving components here. In Rohrweck′s view, the compact drive technology is also a major contributor in this because the X and Y axes are jointly controlled via a AX5206 2-channel EtherCAT Servo Drive.

In addition to this, the EL7201 servomotor terminal for the Z-axis is integrated directly in the EtherCAT I/O system. Both of these save space in control cabinets. One Cable Technology (OCT) provides an ability to connect the AM8000 servomotors ensures compact design and reduced installation efforts. The same goes for the safety engineering directly integrated in the PC Control architecture via the TwinSAFE terminals, the AX5801 TwinSAFE drive option card and the Safety over EtherCAT protocol, with which the functions ′Control On′, ′Emergency Stop′ and ′Safe Stop of Axes′ are implemented in base CUT.

TwinSAFE terminals (left) and the servomotor EtherCAT terminal (right) seamlessly integrated both safety and drive technology into the PC-based control system.

Computing power & online changes

Due to its computing capabilities, the C6930 IPC can process several runtimes simultaneously. As Rohrweck explains: "Like all LiSEC machines, the basic system of the base CUT can be upgraded and networked. For example, the cutting table can be augmented by downstream glass crushing systems. To this end, up to two additional runtimes are available on the C6930 from base CUT, so that additional systems requiring only a few user interventions do not need a separate IPC. This reduces costs and engineering time while eliminating a cross-controller and expensive axis synchronization."

According to Schoisswohl, the Online Change feature first implemented through TwinCAT is also an important function for system operation.

"The ability to load a new program on the controller on the fly is tremendously important to us, in particular with very large processing systems. This makes machine prototyping and adjustments as well as remote maintenance of systems much easier," Schoisswohl said. "This is an advantage, in particular for end customers, since they can benefit from program updates without stopping production."

Leo Büchinger, Drive Technology, Beckhoff Austria.

Source: Industrial Ethernet Book Issue 93 / 11
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