Many manufacturers associate a major change in technology with significant cost savings and performance increases. However, hesitation regarding implementation is often based on fears of unpredicted expenses or difficult and time-consuming engineering challenges. One situation where such doubts proved unfounded was the conversion of an edge banding machine from Beckhoff''s fiber optic fieldbus, Lightbus, to Ethernet-based EtherCAT at IMA Klessmann. A smooth changeover for the company opened up a straightforward path into the industrial Ethernet world.
Based in Lubbecke, Germany, IMA Klessmann GmbH manufactures special purpose machines for the furniture industry -- in particular, edge banding machines and processing centers. The edge banding machines are high-performance systems that apply edges to sheet material such as chipboard or varieties of light building board (honeycomb board). While passing through the machine, workpieces are milled, an edge is banded and trimmed at the ends, and edges and contours are finished and polished. Intermediate stations are sometimes required, depending on the board material, the type of edge, and the shape of the workpiece.
The Novimat Concept from IMA is a single-sided, automatic edge banding machine specially developed for jointing, edge banding, and edge finishing in through-feed operation. "Single-sided" in this context means that one edge of the workpiece is processed while it passes through the machine.
The Novimat Concept consists of several modularly configurable processing units, such as a milling and edge banding unit, an edge banding magazine, a trimming unit, a finishing unit (a scraper, for example), and a smoothing unit. The system allows several workpieces to be processed at the same time, with workpiece positions monitored and controlled precisely via continuous path control. Accordingly, the automation behind the Novimat Concept is complex, involving around 250 I/O points, 12 axes, and 30 path signals.
The previous Lightbus-based automation technology in IMA''s woodworking machines used PC-based visualization and control. Each machine unit featured a Beckhoff Bus Terminal I/O station coupled via Lightbus, servo drives coupled via PROFIBUS for the actual processing, and actuators communicating via CAN.
Ethernet Evolved
In the previous Novimat Concept model, IMA used a Beckhoff PC controller with DOS operating system. Since the other IMA machines already use a Windows-based automation platform, the company wanted to take another step toward the latest in PC technology.
"As part of the modernization, we used the machine as a pilot application for EtherCAT since we intend to use this Ethernet-based fieldbus as our standard in the future," said Gunter Redeker, director for electrical design at IMA. There are many reasons for this.
"We have very complex machines with several thousand I/Os and more than 100 axes in total. In order to control these machines via fieldbus systems, we previously used up to four Lightbus strands that collected or transferred a wide range of data with the sampling rate required for the machine. This was the only way to achieve the required performance," Redeker said. "However, a good deal of computing power was required for handling the large amount of data, since the processor had to copy the data from Lightbus into the memory and back again. It also had to sort the input/output data according to the process image. With EtherCAT, this is not necessary since the DMA controller deals with the data traffic between the Ethernet interface and the memory, resulting in a significant improvement for us."
While the speed of currently available fieldbus systems tends to be adequate for many applications, significantly higher bandwidth and better integration are called for in many cases, due to the continuously increasing complexity of machines.
"The additional potential offered by EtherCAT is particularly useful for continuous path control. It enables the workpieces to be tracked in the machine for precise control during the passage, or for synchronizing parts for flying machining," Redeker said. "The workpieces move through the machine with a speed of up to 60 m/min, corresponding to 1 mm of travel and an associated potential deviation per millisecond. At 2 ms for continuous path control, the resulting inaccuracy over a machine length of 60 m is already 2 mm. This is a borderline value, especially since the precision requirements are continuously increasing. Only a high-performance fieldbus such as EtherCAT and a powerful computer can help reduce cycle times in this situation."
New Technology Introduced in Stages
IMA implemented the changeover from "conventional" fieldbus technology to the real-time Ethernet solution in two stages. During the first phase, the BK2000 Lightbus I/O bus couplers were replaced with BK1120 EtherCAT couplers. During the second phase, the bus terminal I/O was replaced with EtherCAT terminals. The EtherCAT terminals maintain the Ethernet protocol down to the individual I/O terminals without the need for a further sub-bus.
The introduction of EtherCAT also led to a significant simplification of the machine automation system -- a fieldbus card is no longer required in the PC. This means that fewer slots are needed in the computer, and the PCs can be smaller in size. Replacing traditional fieldbus systems with EtherCAT can also significantly reduce the effort required for installation and training. Additionally, problems caused by the cycle times were no longer an issue.
Not surprisingly, Gunter Redeker is satisfied with the progress of the pilot project.
"The test phases at IMA have already been completed. The machine runs quite robustly at three pilot customer locations. We will start converting the machine type fully in order to ensure that staff and distribution partners can be trained accordingly," he said. Another aim is integration of the drives, which are currently coupled via PROFIBUS, into the EtherCAT-based system. This also applies to the intelligent auxiliary servo drives that are operated via CAN bus, which will then be integrated via an EtherCAT/CAN gateway.
"We will continue to monitor developments in this area and use servo drive technology that supports EtherCAT in the future. Several different drive suppliers already support EtherCAT," Redeker noted.
Redeker sees long-term potential in a full EtherCAT implementation, which enables the utilization of the latest, most powerful industrial computer technology. The largest machine lines currently require two computers -- one for the user interface and one for real-time control.
"In the future, we expect one PC to be sufficient even for these systems. Engineering and service will also be simplified if only one fieldbus has to be dealt with," Redeker concluded.