By Jim Montague, Executive Editor
Unless youre the butter on an English muffin, its never easy to get into the nooks and crannies. You expect DIY house painters will find it hard to get into the corners, especially when theyre on ladders. However, even if youve painted as many car bodies as Stuttgart, Germany-based Dürr Paint Systems GmbH, youre still all about achieving as much accuracy and coverage as possible. And you want to do it safely, too.
Dürr Paint Systems inverted its robot design, so it could be installed on walls and ceilings for better access, more accurate painting and better coverage.
In 1997, Dürr migrated from its traditional spray-bell machines, which atomized paint in the shape of a bell, to its first robot on a standard meter-wide pedestal. It used to take 12-18 atomizers for one paint station. However, users found over time they still couldnt get the accuracy and coverage they wanted. Some customers asked if the robot could be inverted and installed on a rail on the wall or ceiling of their paint booths. Dürr later confirmed that locating its robot on the wall or ceiling could give users better access to the inside of bodies being painted, and also enabled users to handle more varied body sizes and styles. This innovation became a major part of EcoPaints redesign into Eco RPE 32 and 33.
Saving Paint and Time
The auto industry wanted solutions that wouldnt consume so much paint, especially when changing colors, so the technology moved to using fewer atomizers, says Jurgen Jost, Dürrs electrical systems director. Now, we have only four to six atomizers, and EcoRPEs wall and ceiling mounting allows more flexibility of movement, and reaches nearly every location on a car body.
To further ease color changes, the 24 color lines and valves leading to EcoRPE meet at a common channel, where a 8-10 mm pigging system uses a ball to pushes the old paint out of the hose. The software monitors the amount of paint needed for a particular body, and this allows us to start the pig in coordination with when a paint job will end, and so we can have almost no paint loss, says Jost.
EcoRPEs off-the-floor mounting only requires four 50-cm holes. This means its easy for older paint shops to install because they dont have to reconfigure or find new space on the floor of their painting booths. Having to renovate or rebuild a typical aluminum and glass paint booth and rebuild its clean room capabilities can take two months, adds Jost. Because much of EcoRPEs components can be build outside the booth, it can be implemented in two weekends, one for installation and one for commission and training.
Seeking, Securing Safety
To protect operators and maintenance staff, Dürr previously used safety PLCs with its self-built Safety Box terminal box, which collects safety signals from the robots, and typically is installed at the entrance and exit of each booth. However, connecting the needed one to four emergency pushbuttons to the Safety Box required a significant amount of hardwiring.
Dürr selected Rockwell Automations GuardLogix controller with DeviceNet Safety because the software makes pushbuttons easier to commission and activate, it can deliver more data to operators, and its PLC can identify their specific locations. Because EcoRPE expects car bodies to come through in a programmed sequence, an e-stop can be programmed to occur when that sequence is interrupted unexpectedly.
If the light curtain is disturbed by a person mistakenly entering the booth, that data is transmitted by DeviceNet Safety, GuardLogix recognizes that sequence is wrong, and it orders stops for all four robots via the safety I/O, says Jost. We used to have separate safety panels, safety relays, and hardwire to do this, but now its all in the software, and our safety I/O communications can go over our regular infrastructure.
