Beckhoff EtherCAT measurement technology
Industrial Ethernet Book Issue 75 / 43
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Wireless replacement for monorail contact wire system

The use of Ethernet communications and an industrial wireless LAN instead of Profibus contact wires means that the central electric monorail system in the production of polyurethane (PU) molded skins for dashboards is to a great extent maintenance-free and the availability of the system is significantly improved. The change minimizes the number of faults, raises productivity and maximizes the ability to deliver.

Tools opened for preparation or removal of the finished molded skins.

Due to continuous friction, contact wire systems naturally wear out. They must be regularly checked and, sooner or later, they must be replaced. In an application at the automotive supplier Faurecia Innenraumsysteme located in Germany, dimensional tolerances at the segment transitions caused increased contact burn-off, frequently resulting in short-circuits which in turn caused problems for the power rail boosters for the Profibus communications.

As the number of operating hours stacked up, first the number of communication errors increased and then the failures which meant that the overall system required more intensive maintenance and had to be completely overhauled at specific intervals. Finally there was a switchover to Ethernet communications via an industrial wireless LAN (IWLAN) system that solved the problem.

In the production of special high-quality polyurethane molded skins for dashboards for the Mercedes S Class, 24 automated mold carriers are transported through a multi-stage process using an oval 2-rail monorail about 210 meters in length. Within the oval, there are four offset areas that enable components to be delivered to a number of parallel processing stations. Via another offset station outside the core process, several set-down rails and cabins are linked for the laser cleaning of the molds, for tool changes and repairs.

The power supply and the data exchange between the mold carrier trolleys and the higher-level plant control were previously implemented by means of 13 contact wire tracks shared between two packages, a common technology at the time the plant was constructed in 2004. By the end of 2008 when a comprehensive regular maintenance was due again, it was time to install wireless or contactless communication. The changeover created system-related advantages using an IWLAN solution, based on Siemens components, compared to the previously utilized contact wire concept.

Mold carriers are transported using a two-rail monorail through the multi-stage molding process and communicate with the main controller via an industrial wireless LAN.

Potential obstacles facing the project were the metallic structures in the hall which proved to be less critical than anticipated following a field trial. Alfred Kautzki, Technology Business Manager for Intronyx, the project's system integrator, said "we installed an IWLAN Access Point at various locations in the extensive plant, connected a notebook computer with an IWLAN client and travelled the routes of the mold carriers with a laboratory truck in order to see what level of radio coverage and signal strengths could be achieved with which configurations."

Kautzki said the results were good, with at least 75 percent at every location, which meant that the plant operator was also convinced from a technical viewpoint and immediately gave the green light for the conversion.

High-quality molded skins

According to Kautzki, Faurecia is the only manufacturer in the world to master the series production of polyurethane (PU) molded skins with particularly fine radii. The process comprises several stages through which the mold carriers have to travel. The mold carriers are equipped in groups with tools for various components of a dashboard (upper section, lower section and glove box lid for both right and left-hand drive vehicles). The upper and lower sections of the tools can be inserted vertically into the mold carriers and pivoted into various positions for the manual removal of the molded skins and the subsequent cleaning.

The first stage is the application of form release agent onto both halves of the molding tool. The top coat on the visible side that is then applied by a painting robot is completely taken up by the molded skin. This is followed by the also robot-controlled injection of the twin-component PU system that hardens in about three minutes and cools to the extent that the finished molded skins can be removed by hand and visually inspected.

Once the two halves of the tool have been cleaned, the form carrier is ready for the next cycle. After a number of production runs, mold carriers are automatically ejected from the production cycle and transported via the offset station to one of the cleaning stations where they are intensively cleaned by laser before being returned into the circuit.

EtherCAT digital positioner

The entire production sequence is controlled from a central Simatic S7 300 (CPU S7 317 2 DP) head controller in the main control cabinet above the plant. By means of additionally integrated CP343-1 communications processors, Scalance X108 unmanaged Ethernet switches and IWLAN components of the Scalance W series the head controller communicates wirelessly with the Simatic controllers on the mold carriers.

For safety-related tasks in the stationary section including light curtains, light barriers and safety switches for doors, there is also a Simatic S7 300F (CPU S7 315F 2 DP) in a remotely located control cabinet that maintains a connection to the main controller. In this way, the signals for the safety system are also evaluated for visualization and plant management purposes. The respective positions of all mold carriers are also recorded precisely by means of an absolute position sensor system installed recently as part of the conversion.

Safe radio coverage

"In order to play really safe and also have a certain degree of redundancy, we have installed a total of six Scalance W788 1Pro access points with omnidirectional antennas (5 GHz) in the plant, although only three are ever actively in use", said Gerhard Korunka, the Intronyx business manager.

In the event of faults or failure of an active access point, the nearest standby device automatically takes over communications, although this has not been necessary so far. Data security if an event occurs is achieved by buffering the data. As soon as new data is received and successfully checked, buffered data is deleted again. The counterparts in the control cabinets on the mold carriers are Scalance W746-1Pro IWLAN clients each with two external omnidirectional antennas. The internal connection to the associated controller is by means of a Simatic CP343 1 Lean Industrial Ethernet communications processor. Current status and process data, such as alarm and fault messages or shutdown times, paint and injection quantities etc. are exchanged, also for the purpose of quality verification for the end customer. The interface to the plant operators is a central, PC-based visualization system.

IWLAN technology advantages

The new IWLAN installation has been running since the installation without any faults, according to Edmund Weigel from the Technical Service at Faurecia. Communications have been more reliable and faster, and system availability has risen by at least 15 to 20 percent. At the same time, maintenance costs have been slashed because parts can be replaced and no longer require regular periodic maintenance.

All in all, this has reduced the planned downtimes for service and maintenance and unplanned downtimes due to failures by a full 16 shifts over the whole year. Apart from saving time, the conversion also saves hardware. This includes five complete copper rail tracks as well as 35 power rail booster. Overall, the project provided a complete return on the invested capital in just the second year after acquisition of the IWLAN system, as the project work by Intronyx had forecast.

For the power supply, the original contact wire system would still be a good choice. But in terms of communications and connectivity, the new IWLAN technology offers a series of additional benefits not only for the operator, but also for the automation engineer and system integrator. These include considerably more fault-proof communications through determined signal processing.

Extensive options for remote maintenance are also available by modem via a TeleService Adapter IE. This allows remote access from home, for example, and convenient local troubleshooting using a programming device integrated into the IWLAN. Another convenient feature is the ability to connect simultaneously with as many as 10 mold carriers in parallel. Previously, it was necessary to make individual connections to each mold carrier which caused interruptions, especially when the carriers were passing the boundaries between rail segments. A final benefit is simple integration into the company network and access to production data from the corporate management level.

The Faurecia integrated automation solution is 210m long with offset areas for parallel production.

Reiner Windholz works for Siemens Industry, Automation und Drive Technologies.

Source: Industrial Ethernet Book Issue 75 / 43
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