PC-based control for photovoltaic production
Industrial handling of crystalline silicon wafers
Jonas & Redmann Group GmbH, Germany
As an energy source, photovoltaics has developed from a niche application into an established globally used alternative to fossil fuels. Most solar power plants are based on crystalline silicon technology. In this process, silicon is extracted from quartz sand in several melting and cleaning steps, and it is then further processed into blocks commonly known as ingots. These are then sawn into thin slices known as wafers. In wire sawing solutions, a wire encrusted with diamonds is stretched over rollers to form a wire field, so that only minimal cutting losses occur when cutting the wafers. Beckhoff offers the ideal automation products for this process. However, the technological know-how in the selection of servomotors and drives is also of great importance: In order to reduce energy consumption when cutting the wafers, the braking energy of the motors for the diamond wire saws is fed back. The wafers are further processed into solar cells, which convert the sun's rays into solar power. In the first step, saw damage to the wafers is eliminated by means of wet chemical processes and optimized by the texturing process. The cells are then fed to the PECVD process. Plasma-enhanced chemical vapor deposition (PECVD) machines for passivation and anti-reflective coating processes in solar cell production have been revolutionized by the use of PC-based control. The machines controlled in this way are characterized by excellent process performance and low operation costs.
Contacts are subsequently applied to the solar cell using the screen printing process. The electricity generated in the solar cells is discharged via metallic electrodes. This gives the surface of the cell a fine contact grid. The solar cells then run through a furnace to sinter the solar cell metal contacts. Due to the optimized unloading of the furnace by means of PC-based control, the solar cells can be fed to the downstream test systems in an optimized cycle. The solar cells are further processed into solar modules through connection by means of soldering bands called strings. The electrical connection between them takes place in the laminator. The strings are positioned on the glass and encapsulation material (layup) and thus form the solar cell matrix. In order to protect the solar cells against environmental influences, the individual layers are connected together and framed in a vacuum. In the final assembly, the finished solar module is equipped with the electrical connections and tested for power, voltage and electroluminescence.
Beckhoff technology highlights for the photovoltaic production
The PC-based control principle
Mechanical engineering for the photovoltaic industry is under constant performance and cost pressures. The further developments in solar module technology as well as the networking of the machines up to the cloud connection are the challenges that companies have to face in the industrial production of solar modules. On the part of mechanical engineering, therefore, there is a necessity to integrate new technologies in order to increase plant efficiency and transparency. It is therefore important to identify the cost drivers and to regularly test them: a wide variety of special hardware and software components, which perform their service reliably for the moment, not only causes high procurement costs, but is also complex and costly in engineering, networking, and maintenance as well as in long-term spare parts maintenance. If the functional extension of a machine necessitates a design change of this special hardware, all of the above factors come into play once again.
A way out is offered by PC-based control as an open platform: a large number of hardware and software providers, as well as services, standardized and inexpensive interfaces and, most importantly, unimaginably high performance make the PC controller an indispensable helper in all aspects of automation technology. Beckhoff addresses the industrial requirements for PC-based control through the consistent in-house development and production of its Industrial PCs, including the motherboards, TwinCAT automation software and the EtherCAT real-time fieldbus system. The long-term availability of hardware, industrial design, real-time qualification, a high degree of diagnostics and scalability form the foundation of PC-based control by Beckhoff. Continuous advances in the PC sector, e.g., in terms of microprocessor technology, are constantly incorporated into the development process of Beckhoff Industrial PCs, thus guaranteeing an organic and automatic increase in performance for the future
The inherent scalability of all components in terms of price, performance and design makes it possible to use the same control technology throughout, i.e. from a simple wafer and cell handling machine to a diffusion furnace. The result is: consistent system from one machine class to the next, no specialized development teams and an unbeatably large portfolio of modular hardware and software that covers almost every area of use and application case. Mechanical engineering for the photovoltaic industry is no longer imaginable without PC-based control.
Due to the power of modern microprocessors, such as those that Beckhoff uses in all of its PC series, even complex automation operations can be integrated into the controller at any time without changing the system: image processing systems (TwinCAT Vision), special software modules created with Matlab®/Simulink®, special know-how implemented by the customer in the C/C++ programming language, machine learning and many other computationally intensive applications can easily be executed from the PC controller. But what if the PC cannot cope with the load? Choose the next larger Industrial PC from Beckhoff. The system architecture and the required know-how remain the same, and the software implemented in TwinCAT is taken along.
EtherCAT: the global standard for mechanical engineering in photovoltaics
More than 6,000 companies worldwide have joined forces as members of the EtherCAT Technology Group (ETG) to support the technology developed by Beckhoff, which is the basis today for almost all leading-edge photovoltaic machines. With cycle times well below 1 ms, outstanding synchronization accuracy, flexible network topology selection, extensive diagnostics and simple configuration, EtherCAT is ideal for mechanical engineering in photovoltaics and has established itself here as a communication standard. The real-time fieldbus handles all communication and is an I/O, safety and drive bus system all in one. Due to its widespread use around the world, many EtherCAT-compatible devices, sensors and actuators are available on the market, ensuring a high level of investment security and guaranteeing a suitable solution for every problem.
The high speed of EtherCAT results in a higher cycle time while at the same time increasing the accuracy of the processes. EtherCAT shows its strengths in two ways: the high-precision acquisition and output of signals down to the nanosecond range (XFC technology) leads to a precise detection of the solar wafers and cells. The resulting control of the machine platform for loading and unloading is carried out with the highest accuracy. When using EtherCAT, manufacturers of photovoltaic machines are fully in control. They do not have to consider the communication structures at all. The plant is planned and built; EtherCAT fits in with the selected plant topology. Line, star or tree topology is fully supported by EtherCAT without impacting performance. And best of all: standard TCP/IP-based devices such as scanners, barcode/QR code printers or other devices from the classic IT landscape can be simply connected via EtherCAT.
EtherCAT P minimizes assembly times
Each cable is one too many, provided there is a technologically better alternative to it. Cables are a not inconsiderable cost factor in mechanical engineering in photovoltaics – they have to be procured, configured, connected and, in the worst case, assembled. In subsequent operation, cables are a source of error, especially when they are moved. Bending and torsional movements in drag chains and robots lead to wear. EtherCAT P significantly reduces this expenditure. It combines EtherCAT communication with the power supply for the connected consumers in a 4-wire standard Ethernet cable. All benefits of EtherCAT are retained, including free choice of topology, high speed, optimum bandwidth utilization, dynamic processing of telegrams, high-precision synchronization and extensive diagnostics. This makes EtherCAT P the ideal system for sensors and actuators in mechanical engineering in photovoltaics. The result: less wiring, fewer parts to maintain, reduced complexity and lower costs without loss of functionality.
XFC increases the performance of your machine
The processing of solar cells is a dynamic process. Many processing operations on the cells take place without a stop, on the fly. It is therefore crucially important that the position of the solar cells to be processed is exactly known before and during processing. Thus, the processing machines can be switched on and off exactly without damaging the solar cell; the more precisely this happens, the higher the quality of the cells. TwinCAT automation software and the EtherCAT high-speed communication system are the basic function blocks for this. Cycle times in the lower millisecond or even sub-millisecond range allow fast reaction and response times; nevertheless, these times cannot be completely eliminated.
The XFC (eXtreme Fast Control) technology helps with its Distributed Clocks (DC) functionality: this technology provides the machine with a nanosecond-precise system time. All signals from the field and calculations within the controller are referenced to this time. On this basis, the time for controlling the machine can be calculated with high precision and sent together with the actual signal information to an EtherCAT output terminal. PLC and fieldbus-related delays, which are always bound to occur, can thus be compensated almost completely in this application.
Another property of XFC, oversampling, is also used to improve the process. This technology is used whenever it comes to acquiring or outputting signals from the machine with an even higher resolution, despite PLC cycle times that have already been set very short. The trick: in an EtherCAT cycle, up to 100 temporally equidistant values of a signal are transmitted at a stroke; the temporal resolution of the signal is also appropriately increased by this factor. Accuracy in the detection of wafer and/or solar cells increases and the stringing of the solar cells can be done without additional hardware.
TwinSAFE: the open and scalable safety technology
TwinSAFE from Beckhoff provides a universal safety concept that integrates safety functionalities into the standard control platform: from the PLC via I/Os to the drive technology. All safety functions such as emergency stop, safety door monitoring, two-hand operation, safety mat evaluation and muting, safe position, safely limited speed, etc. can be programmed and/or configured on the integrated TwinCAT engineering platform. Safety technology is seamlessly integrated into the terminal segment via the TwinSAFE I/O modules, whereby safe signals can be mixed with standard signals as required.
The typical safety functions can be programmed or configured according to the safety requirements in an EL6910 TwinSAFE Logic Terminal or the EK1960 compact safety controller on the basis of standard safety function blocks. All Beckhoff safety controllers are suitable for applications up to SIL 3 according to IEC 61508 / Performance Level e of ISO 13849-1. The EL6910 and EK1960 safety controllers support complex, safe analog evaluations.
With the help of the TwinSAFE SC (Single Channel) technology, it is possible to use standard signals for safety tasks in any network. For this purpose, corresponding EtherCAT Terminals are available for the acquisition and safe transport of these signals via EtherCAT.
Large networked machine applications pose major challenges for all parties involved, especially with regard to safety technology. Many networked machines with their own safety areas, spread over large production areas, hinder the overview and make subsequent extensions and adaptations a Herculean task. TwinSAFE offers the option to completely or partially decentralize the safety application as required. Each machine can easily be equipped with its own safety logic. The TwinSAFE logic is part of every safe input or output terminal and also of many drive components. It makes it easy to create autonomous safety areas that can communicate with one another. During production and commissioning, individual machines can be verified and validated in terms of safety by the respective department.
Beckhoff product highlights for the photovoltaic production
Modular Industrial PCs for the DIN rail
With the CX series of Embedded PCs, Beckhoff combines PC technology with the modular I/O level on the DIN rail in the control cabinet. By adding individual modules and interfaces, only the components that the user needs for the respective application are installed. In this way, the Embedded PCs open up a wide range of applications – from solar wafers to solar module production.
Due to their ruggedized design, the compact Embedded PCs from the CX series are suitable for use as powerful and reliable controllers in industrial conditions. The fine scalability in different device classes allows users to select exactly the right performance category for their applications. High-performance machine controllers with multi-core processor technology are available in the CX5100 and CX5200 Embedded PCs. The devices in this performance class are suitable, for example, for the control of machines for anti-reflection coating. The CX20x0 and CX20x2 device series are high-end controllers for demanding applications, such as the integration of image processing, the realization of Machine Learning or the aggregation of large amounts of data.
Another advantage of the Embedded PCs series – as with Beckhoff's entire Industrial PC portfolio – is the long-term availability of spare parts, which offers the customer a high level of investment security.
Extremely space-saving, flexibly expandable and built to last: the new generation of ultra-compact Industrial PCs
Vibration, power supply fluctuations and high currents transmitted via a variety of cables, which are often high-frequency and loaded with harmonic components – these factors result in electromagnetic interference fields, the invisible enemy of every control technology. This is the typical environment in solar module production and the conditions in which machines and plants must function reliably.
Beckhoff meets these requirements with the C60xx Industrial PC series (e.g. C6015 and C6032). As always with Beckhoff, the device, which is developed in-house including a motherboard, power supply and a complete housing concept, is ruggedized by design. Among other things, this allows the devices to operate at ambient temperatures up to 55°C despite high power. These temperatures typically do not occur in an air-conditioned control cabinet, but outside these air-conditioned zones, close to heat-producing units and in countries with extreme weather conditions, they quickly become a real challenge. However, durability in the industrial environment is not the only credo. The Industrial PC diagnostics provide the machine manufacturer and operator with comprehensive information about the operating state of the device at all times: this information is accessible via a simple web browser and can be evaluated directly in the PLC and displayed in the plant visualization as required.
These data also include the state of the storage media (SSD) used, which can operate in RAID mode, for example, if two storage media are used. And should a change of a storage medium be necessary after a long period of operation: despite the compactness of the device, simple and fast maintainability is ensured.
One of the biggest challenges is fluctuations in the IPC supply voltage. There can be various reasons for this: a high number of consumers within an industrial company with a high demand for power and consequently the possible occurrence of incalculable peak currents is a common reason. Regardless of the cause, the consequences are severe, especially in the case of linked production plants. There may be hundreds of workpieces in different machining states in the plants, which often extend over entire halls. If an Industrial PC ceases to operate during full production due to a voltage fluctuation or even a complete failure of the supply voltage, the restart is associated with a high expenditure of time and cost. Therefore, the Industrial PCs from the C60xx series can optionally be extended by a CU81xx UPS. The UPS ensures that important control and operating data are saved securely in the event of major voltage drops and that the Industrial PC is shut down in a controlled manner. A quick restart of the plant and thus a high availability is guaranteed.
EtherCAT I/O modules integrate temperature control, energy measurement and safety technology into the control platform
In 1995, Beckhoff launched the Bus Terminal, which has since become one of the most important technology standards in automation technology. That was followed in 2003 by the development of the EtherCAT fast communication system. Launched by Beckhoff as an open system, it became a global standard in automation within a few years. An extensive EtherCAT I/O Terminal portfolio is available to users that is extremely well suited for automating every functionality in plastics machines and their peripherals in terms of both its performance and variance.
EL3318 for temperature measurement
- The EL3318 EtherCAT Terminal is ideal for temperature measurement via thermocouples. The 8-channel input terminal with integrated cold junction compensation is very compact in its design and measures temperatures with high accuracy and high signal-to-noise ratio.
EL3403 for power measurement
- The EL3403 3-phase power measurement terminal can monitor the energy consumption of a continuous furnace. In combination with TwinCAT 3, the EL3403 provides cost-effective monitoring of the fire zones in the continuous furnace.
EL6910 and EL3124-0090 for safety monitoring
- The EL6910 TwinSAFE Logic integrates safety technology into the controller. Due to its scalability, the Beckhoff safety solution is suitable for complex machines with distributed I/Os as well as for use in smaller solar wafers and cell handling machines. One TwinSAFE terminal is sufficient here to realize the complete safety Technology.
- The EL3124-0090 analog EtherCAT input terminal processes signals in the range of 4 to 20 mA. With the help of the TwinSAFE SC (Single Channel) technology, it is possible to use standard signals for safety tasks. This technology is ideally suited for monitoring machines for passivation and anti-reflection coating processes such as those used in the production of solar cells.
Highly dynamic, modular, scalable: Beckhoff drive technology
The photovoltaic industry requires a high degree of precision: Each step in the production of solar wafers and cells, the lamination of the solar modules and the various handling processes must be carried out with high accuracy in order to produce high-quality solar modules. Any deviation comes at the expense of quality or leads to complex post-processing or even to scrap, with a negative effect on the yield.
In combination with the TwinCAT Motion Control software and EtherCAT, the fast communication system, the scalable Beckhoff drive system completely covers the high requirements profile of the photovoltaic industry: The integrated, fast control technology of the AX8000 and AX5000 servo drive series supports fast and highly dynamic positioning tasks. In the lower performance range, the EL7xxx EtherCAT drive terminals represent an inexpensive and compact alternative.
The extensive range of linear and rotary servomotors is tailored to the servo drives. The AM8000 motor series is characterized by the One Cable Technology, in which power and feedback are combined in a standard cable. For applications with simple positioning drives, Beckhoff offers the full range of drives, such as stepper motors or DC motors.
TwinCAT 3: the universal engineering and control platform
TwinCAT 3 integrates all engineering and control functions into one universal software platform. This applies to programming, configuration, real-time environment and all runtime modules. By programming in the common IEC PLC dialects and the integration of C/C++ algorithms, the photovoltaic machine manufacturer can freely choose the most suitable programming method, depending on the programmers' task and the service strategy. With the integration of MATLAB®/Simulink®, control concepts are developed on a model basis and thus make their contribution to virtual machine design. The TwinCAT 3 interfaces to Machine Learning algorithms allow the use of AI methods in the traditional control environment. Through the use of Microsoft Visual Studio® as a uniform programmer workbench, different versioning systems are supported and team work is simplified. With the Automation Interface, TwinCAT 3 offers open interfaces for the integration of commercial IT systems for programming machines for series production.
- Extensive TwinCAT libraries for motion control save development time thanks to tested and optimized algorithms. The TwinCAT 3 PTP and TwinCAT NC I supplements are ideally suited for handling applications with Cartesian robots. Ready-to-run solutions are available with TwinCAT Kinematic Transformation for other robot kinematics, such as SCARA, Delta and articulated arm.
- Commissioning and service processes are accelerated and improved with TwinCAT Scope, a software oscilloscope fully integrated into the TwinCAT system architecture, and thus contribute to increasing machine quality.
- TwinSAFE software-based safety technology simplifies the wiring of complex systems; variants can be mapped in software. This allows, for example, the modular development and commissioning of production cells. Documentation is also simplified and adaptations to additional customer requirements can be implemented quickly.
- The integrated, browser-based TwinCAT HMI visualization solution enables convenient development and maintenance of visualization objects. The information is presented either on the machines and systems or via the internet using a web browser.
- TwinCAT 3 IoT provides the prerequisite for data aggregation in the cloud or locally in the edge controller. For this purpose, TwinCAT 3 includes standardized communication protocols for cloud applications. TwinCAT 3 Analytics can be used to evaluate the collected data.