FEATURE COVER STORY
FOR MORE POWER IN THE ARMS cycloidal gearboxes in crossbar feeder
Cycloidal gearboxes from Nabtesco must withstand extremely high loads when installed in a crossbar feeder used for the safe and fast handling of parts in automotive manufacturing
arms of the crossbar feeder the minimal play of less than one angular minute, even at high loads, is an advantage. Transmission of force via rollers without gears (typical for cycloidal gearboxes) enables high efficiency and permits fast and precise positioning movements with high loads without overshoot. Thus high repeatability and path accuracy are achieved. In addition, the rolling friction of all elements participating in the transmission of force enables an extremely low breakaway torque.
I
n automobile production sheet metal parts run through a forming process at
multiple stations before exiting the press line as doors or side elements. Schuler is equipping its press lines with the crossbar feeder - a robot-like transport device for fast and safe handling of parts. In this process the cycloidal gearboxes from Nabtesco installed in the axes must withstand extremely high loads. Schuler is the largest manufacturer of presses in the world. Its first crossbar feeder for press automation achieves a production rate unmatched by any comparable machine on the market. Nabtesco’s cycloidal gearboxes contribute to the outstanding capacity of the machine. "Nabtesco was immediately the
competent contact on site,” says Diplom Ingenieur Eduard Lenhardt. “Thus our collaboration quickly picked up speed.”
COST-EFFICIENT PRODUCTION
The crossbar feeder transports sheet metal parts automatically from press to press without intermediate placement. The latest crossbar feeder B benefits
from openings between individual presses having been reduced from 6600 mm for the first model via 5200 mm for the second variant to 4700 mm for the smallest device. Because the crossbar feeder is a central reach system the presses can be built more compact, lowering the material costs for plant
6 MARCH 2015 | FACTORY EQUIPMENT
construction. Production and cycle rates along with energy efficiency have increased significantly for the new models. The second generation of the crossbar feeder offers seven degrees of freedom, three rotation axes and four linear axes in an extremely rigid and short compact design. Basically the crossbar feeder enables
fast, fully automatic tool change and free access to the press opening. It moves with high repeatability so that the sheet metal elements can be taken up and set down with precise positioning. The crossbar feeder resembles a robot yet it can move on preprogrammed paths precisely and faster. Moreover, it can appropriately position the components for the next work step through tilting and rotary movements In this regard the transport weight can be up to 130 kg.
COMPACT BUT POWERFUL In the arm axes of the latest generation of the crossbar feeder Schuler uses the Nabtesco RV-F, RV-E, and RV-N series gearboxes in cycloidal design which are used successfully around the world by many robot manufacturers. For older models of the crossbar feeder only RV-F and RV-E gearboxes were installed. The gearboxes are characterised by a compact, lightweight design and high positioning accuracy, rigidity and output density. Moreover, when used in the long
The crossbar feeder resembles a robot yet it can move on preprogrammed paths precisely and faster
LONG SERVICE LIFE DESPITE HIGH LOADS In the press line the gearboxes must withstand unusual stresses including high ambient and operating temperatures, impacts and vibrations at high cycle rates as well as a round-the-clock duty cycle. In this regard high-level shock resistance up to five times the rated torque ensures extensive safety reserves and a long service life of the precision gearbox. For fast movements of the crossbar feeder maximum turning moments of the RV-N gearbox are frequently reached. "In terms of speed and load with the crossbar feeder we are working in the limit areas,” explains Lenhardt. “Thus we can differentiate ourselves from the competition. To this point we have not been disappointed in Nabtesco because the gearboxes often even exceed the specified catalog values.” Fast and easy maintenance mean that
plant downtimes are minimised. Thanks to the high MTBF (mean time between failures) the gearboxes offer quality and profitability for positioning, handling and assembly in automotive manufacture. "Nabtesco has established a high level of trust at our company, particularly through the good consulting," concludes Lenhardt. "A further advantage of the RV-N gearbox is that it can always be modularly adapted to meet the requirements of our customers". This is why Schuler will rely on Nabtesco gearboxes for future new developments in the crossbar feeder area.
Nabtesco Precision Europe T: +49 (0)211 17379-0
www.nabtesco.de/en
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