The process of welding the tailgate on the Corsa at Opel Eisenach has been overhauled without any compromise to safety, with automation expert Pilz
Like most body shops the one at Opel Eisenach is heavily automated, almost a 100 per cent in fact, save for eight workstations on the body assembly line. And when Opel decided to reconfigure them it did so with the objective of making them more ergonomic and economical, and increasing productivity.
The automation had to be simple to use, offer maximum diagnostic capability and have a modular design that brought a high level of flexibility to the planned extension of the production facility.
These criteria also went for the safety-related automation components, which is where Pilz came in with its multifunctional safety system PNOZmulti.
Among the Opel models assembled at Eisenach is the three and five-door Corsa. The vehicle’s tailgate is built in the body shop’s first production zone, where up to eight workers attach the doors to the body with the help of welding jigs. Once the doors have been assembled, the wings and engine bonnet are added to the vehicle body before it is transported to the finish line.
Before the production zone for manual door welding was redesigned, two interconnected pairs of light-beam devices monitored the left- and right-hand sides of the production line. The self-resetting five-beam and one-light beam devices were positioned 30cm horizontally and vertically above the floor and monitored the danger zone along its whole length.
The body could only move to the next production zone if all eight workers had left the danger zone and had signalled that the conveyor could start by pressing the enable buttons. Ultimately, the slowest worker determined the pace and therefore the productivity of the whole production zone. Thus the fact that four workstations to the left and right of the production line were “linked” to only two safety sensors was a problem that needed changing.
As a first step in the reconfiguration, the production zone was extended by two buffer zones. These spaces were set up after the first and before the last manual station, giving workers time to react to the variations that occur in finishing the work stages.
As a result of splitting the workstations it became necessary to separate the safety sensors in order to achieve a clear increase in productivity.
Four light beam devices were replaced by ten people scanners, with one scanner assigned to each workstation with a welding jig. Two scanners were also assembled in the final manual station area where residual welding work is completed if necessary.
Opel engineers decided on Pilz’s PNOZmulti system to monitor the ten scanners, plus the E-stop grab wires for the conveyor system.
This modular safety system monitors multiple safety functions with one unit and can also undertake standard control functions. Plus, safety functions are no longer implemented through the wiring but are easy to configure using a configuration tool on the PC.
“Eplan macros were available right at the start of the planning phase. This was a great help to us during planning and design,” said Bernd Köllner, Project Engineer at Hörmann, the German door maker supplying Eisenach.
One PNOZmulti-base unit replaced multiple individual safety relays, which would have been costly and timeconsuming to wire together.
The functions provided by the safety system were tailored exactly to suit the application: 44 inputs, four semiconductor outputs and 26 relay outputs with a maximum 6A load, all of which could be configured via the software. The safety system was easy to configure which meant the upgrade of the production zone was completed in just four days.
Production efficiency and uptime is directly related to the diagnostic capabilities of the automation components within the application. Safety related automation solutions that don’t provide diagnostics on a fully-integrated basis are no longer acceptable to users long term.
What Pilz ultimately equipped the safety engineers at Opel Eisenach with is a redundant, micro processorbased safety system that provides the whole range of communication channels — including all the common fieldbus systems. For Eisenach engineers, it is easy to transmit data to the process control PLC, including input/output status or run/stop operating conditions. Not only are communication modules available – in Eisenach’s case, to connect to Profibus DP – but 24 virtual outputs can also be activated.
“The fact that Pilz also provides the necessary GSD files simplifies the process enormously,” says Frank Seiferth, Managing Director of SEITEC, which provided the software for the project.
With the help of a COM-Server, a Serial/Ethernet converter, the system can also feed all internally generated information into an Ethernet-TCP/IP network or area network.
Operators at the Eisenach plant are now able to perform online diagnostics and view help texts from any PC containing the pre-installed PNOZmulti service tool software. These remote diagnostics, together with detailed, descriptive diagnostic messages in the form of a dynamic program display, help to reduce plant downtime significantly. Maintenance personnel don’t even have to attend the affected production zone; they can access an area network PC, which may even be remote from the production process, to obtain information about the cause of a problem and take targeted action.
The system can not be accidentally reconfigured according to Pilz. The PNOZmulti service tool is a reduced version of the PNOZmulti configuration software – it does not contain the extensive editing functions – and as such it can confidently be used for remote diagnostics.
Optimisation of the production flow and logistics, combined with modern, safe automation technology, enabled an intelligent, economical solution.
All requirements were met with total success, including the productivity increase. The plant has now been operating for more than six months without problem and production managers are delighted with the considerable increase in productivity and subsequent rise in output.