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Fast Start Up for PROFINET IO

Authors Kostyantyn Shcherbina, Hilscher Gmbh, and Jens Bürger, Murrelektronik GmbH, explain why fast start up (less than 500 ms between “power on” and receipt of IO data) was critical to automobile manufacturers who chose PROFINET as their Industrial Ethernet standard.

Aw 2908 09 06 Fast Profinet Io
Industrial Ethernet communication systems, with advantages such as higher data rate, vertical communication and the ability to coexist with established IT standards, have had a profound impact on the world of automation. As a flexible, robust and rapidly advancing technology, PROFINET covers all areas of automation and distinguishes itself from other Industrial Ethernet standards by its ability to replace the traditional fieldbus systems and adapt to new challenges.

Based on 20 years of successful experience with PROFIBUS, PROFINET incorporates technology that will become the common industrial communication system for the future. Easing the way is the development of the Fast Start Up (FSU) technique for PROFINET IO, which makes it possible for an IO device to go instantly from power on to cyclic data exchange with an IO controller. Such functionality is a high priority requirement for specific applications in factory automation. This article describes the FSU technique from different points of view—from development up to the application.

Faster tool changes

During the last decades, industrial robots have become very important for efficient factory automation. Modern robots, with their capability of automatic tool changing, increase the flexibility of production lines and reduce the total amount of robots per cell. This allows reduction of costs and required space, and may also shorten the production cycle, provided the tool changing time is as short as possible. Every delay while uncoupling one tool and coupling the other one should be minimized. A tool, and thus the whole robot, is only ready for operation if all corresponding IO peripherals are in cyclic data exchange with the PLC. This means that the time required for the establishment of the communication between the IO device on the tool and a PLC will negatively impact the productivity.

In 2004 the Automation Initiative of German Automobile Manufacturers (AIDA) made a decision to use PROFINET IO as the basic communication standard for the factory automation. However, all Industrial Ethernet standards had the handicap of a very slow start-up time compared to the traditional fieldbuses. The typical start-up time was in the range of seconds. This disadvantage prevented the use of Industrial Ethernet systems on robots with automatic tool changing.

Since the automotive industry had always pushed for the development of new factory automation technologies, such as automatic tool changing (ATC) for robots, AIDA proposed the additional requirement for PROFINET IO that an IO device had to start up faster than 500 milliseconds. The Fast Start Up technique (FSU) was specified in order to meet that requirement.

The basic rule of FSU, which is described in the latest specification of PROFINET IO, is that the time between the power-on and the first cyclic input data is received should not exceed 500 ms. The benefits of FSU may be used from the second start up because during the first start up the IO Device is parameterized and configured.

These enhancements remove the protocol-specific delays. Furthermore the start up of a device can be optimized through the use of the corresponding hardware.

The protocol optimizations are standardized:
•    Using fixed transmission parameters (only for copper wires), instead of automatic detection, which reduces the start-up time up to three seconds.
•    Network address is not passed to the IO device on each start up, but only on the first start up. These parameters are saved within the permanent memory of the IO device. On every following start up the parameters are retrieved from the permanent memory and reused. This optimization may save several seconds.
•    IO device announces the readiness to build up the communication instead of waiting for the IO controller to search for it. It is possible to save up to one second this way.

Gateway and wireless solutions

The transmission of the signals in the present-day ATCs is mostly based on traditional fieldbuses, such as PROFIBUS, DeviceNet and INTERBUS, which have typical start-up times in the area of a few hundred milliseconds. For a long time Industrial Ethernet communication systems were not able to keep up with the conventional fieldbuses in terms of start-up time.

The market, however, set new performance requirements that resulted in the development of compromise solutions, the most noticeable being gateway and wireless solutions. PROFINET IO, in contrast to the other common Industrial Ethernet systems, standardizes the way the devices can reach start-up times faster than 500 ms. The devices available on the market guarantee a start-up time of approximately 400 ms. Development experiences showed that considerably lower times can be easily reached.

In the recently established gateway concept, the proven fieldbuses enable fast ATC, while the Industrial Ethernet systems take care of the vertical communication. The crucial drawback of the concept is the increased complexity of the whole system due to the utilization of two different standards. This has a noticeable negative effect on maintenance and service.

Wireless devices solve the problem of a start up either through keeping the communication up all the time or utilizing the technique of communication establishment shortly before the tool is coupled.

The advantage of the wireless solutions is the absence of idle times during the start up and cable-caused problems (for instance, line disruption or short circuit due to damage to the cable or connectors). The disadvantages of the wireless technique are safety risks and interferences that lead to higher jitter, longer cycle times, additional planning effort, and a limited number of transmitting devices in the local area.

In summary, wireless technique will be used where:
•    Cable usage is not economical or not possible.
•    The mentioned disadvantages play a negligible role.

Future developments

One of the worldwide leading German car manufacturers is currently planning its future production line and needs to select the communication peripherals for its robots with ATC. The typical operations of the robots in the application are welding and gripping. The time for the car body’s production in a robot cell is as low as 45 seconds, which includes the delay for tool changing.

The automobile manufacturer has specified the following:
•    FSU devices with a start-up time less than 500ms are required.
•    Gateway concepts will not be used due the mentioned disadvantages.
•    The use of wireless components is limited because the cycle times are usually not satisfactory.

The German automotive industry has said that the next step for the communication components manufacturers is for them to implement the PROFIsafe and PROFIenergy profiles in their devices. The safe environment for a human and a machine is a fundamental pre-condition for the use of future industrial communication systems. PROFIsafe fulfills this requirement. PROFIenergy, which is in the specification stage at the moment, provides for cost effective energy utilization.

With start-up times lower than 500ms, nothing stands in the way of PROFINET IO utilization for robot ATC. Based on AIDA’s choice and the advantages in comparison to the alternative solutions, PROFINET IO becomes an approved standard for ATC systems.

To see more whitepapers on PROFINET technology, please click here.

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