Keeping bread fresh with POWERLINK and Linux
De la Ballina specializes in packaging industrially produced baked goods. When developing its latest generation of machines, the French company decided to implement an integrated automation solution. POWERLINK was the only network protocol that was up to the task. The exceptional openness of this Ethernet standard was among the winning arguments in its favor.
De la Ballina has been producing packaging lines for some 20 years now. The French packaging specialist provides high-tech solutions involving vision systems and robotics for packaging industrially produced baked goods and pastries. The optical scanners and image processing components they use need to provide high-precision and fast response times. In order to meet these requirements in the past, De la Ballina used hardwiring and low-end fieldbus solutions.
Five years ago, they decided to re-evaluate the automation architecture of their systems. The goal was to pursue long-term competitive advantages and adapt to changing market demands. De la Ballina had a very clear idea of what they were looking for in the new automation solution: Increased performance, productivity and energy efficiency, along with reduced costs for implementation and maintenance.
With such ambitious goals, the company was well aware that the selection of the communication protocol, which forms the foundation for an integrated automation architecture, would be a key decision. The main criteria for the network technology were that it should be deterministic (precision < 1 ms) and especially powerful.
With precision down to 10 ns, cycle times as fast as 100 µs and response times well below 1 ms, POWERLINK meets these requirements with ease. There was no question that this real-time protocol would be perfect for the new generation of machines. In comparison, an ASIC-based solution proved too risky for long-term development. "Using technology built on the standard network secured our investment," explains De la Ballina's head of vision system development, Emmanuel Dumas, continuing: "Custom Ethernet solutions based on ASICs are too risky in the long-term. With future Ethernet developments, the cost of redesigning ASICs can lead down a technological dead-end street."
Upon discovering B&R, De la Ballina was confident they would need to look no further. "Choosing a network is a key strategic decision when developing a new machine architecture. The selection of POWERLINK harmonizes perfectly with our vision of an integrated automation solution," emphasizes Dumas. "Unlike proprietary solutions, with open source technology there is no risk of hidden design flaws. This is the great advantage of the white box principle behind open source products," Dumas elaborates. Since 2010, every De la Ballina machine installed around the world has been based on POWERLINK.
De la Ballina's image processing system, developed in-house and based on a PC with a Linux operating system, has also been integrated via POWERLINK. The open structure of POWERLINK makes integration a breeze. "Worldwide, we've installed a total of 90 POWERLINK-based systems that are in operation 24 hours a day, 7 days a week," explains Dumas.
Communication protocols are comprised of a number of layers. The OSI model introduced by the International Organization for Standardization (ISO) is comprised of seven layers, each dedicated to a specific communication requirement. For the bottom two layers (1 and 2), POWERLINK uses the IEEE802.3 Ethernet standard.
Layers 3 through 6 provide the POWERLINK-specific features such as real-time capability and hot-plugging. These layers also ensure that only one node at a time is able to access the network. The specification defines CANopen for the seventh layer. This makes it easy to integrate standard CANopen applications on a POWERLINK network.
A POWERLINK device can be used as either a master or a slave. A master controls all network activity, while all the other devices function as slaves. Communication on a POWERLINK network takes place cyclically, and each cycle begins with a frame being sent by the master.
Immediately following this first frame, the master sends a query to each slave. The addressed slaves respond to the query, and this response can be received by every master and slave on the network. This prevents network collisions and also allows for deterministic timing. A fixed time in the network cycle is reserved for asynchronous data. This can be used for image processing, diagnostics or firmware upgrades, for example. Any Ethernet frame can be sent as an asynchronous frame.
POWERLINK for maximum efficiency
POWERLINK completely fulfilled every aspect of De la Ballina's requirements. It paved the way for a completely integrated and highly efficient automation architecture for the new generation of machines. And because POWERLINK is an open solution, integration of the existing image processing system was both inexpensive and extremely effective at improving its performance.
De la Ballina's next step will be to consider switching to FPGA technology for the image processing system. With POWERLINK, that would be no problem at all. POWERLINK requires so little space, they could use the same FPGA for both the image processing algorithm and the POWERLINK network connection.
The Open Source Automation Development Lab eG (OSADL) is actively working on developing a real-time preempt patch. To evaluate its real-time capability, the OSADL is equipping a real-time Linux test system with a POWERLINK master kernel module. This is connected to a POWERLINK I/O node on the B&R X20BC0083 bus controller and continuously sends data from the cyclic system at an interval of 500 µs. The packet stream is monitored by a real-time capable Ethernet network analyzer. The results of the stress test show that the jitter remains in the microsecond range, even with a very high load on the CPU.