Assembly in Action: Cartesian Systems Enable Flexibility
July 19, 2007
In addition to being flexible enough to handle multiple, small production runs, the behr GmbH (Blaichach, Germany) system needed to be built in such a way that it would dovetail smoothly with seven existing machines.
Machine-builder behr GmbH (Blaichach, Germany) recently received a contract to build an automated optical lens manufacturing line. In addition to being flexible enough to handle multiple, small production runs, the system needed to be built in such a way that it would dovetail smoothly with seven existing machines. Central to the line’s success would be a pick-and-place system capable of manipulating the various dies that are used to fabricate a range of contact lenses.
To solve this problem, behr constructed a high-speed Cartesian system using a battery of CMS Multiple Axis Motion Systems modules from automated equipment manufacturer Bosch Rexroth Corp. (Hoffman Estates, IL). These modules can be integrated into a number of different configurations employing one, two or three axes. Based on Rexroth’s Compact Module CKK concept, each module comes complete with motors, cables and servo drives, as well as ports for all commonly used fieldbus systems.
“When appropriately designed, Cartesian motion systems are more flexible than robots,” says behr GmbH Managing Director, Uwe Behr. “It is substantially less expensive than other solutions. What is most important, Rexroth offers plug-and-play solutions with its CMS, which considerably cuts our project planning and startup costs.”
In the contact lens manufacturing line, behr engineers included three injection-molding machines, which produce eight parts in four different designs per cycle using die halves with the exact negative contours of the lenses. A pick-and-place system positions the dies, which are 15 millimeters in diameter, on workpiece trays that are equipped with 32 compartments each. A conveyor system carries these filled pallets to a transfer system where four separate Cartesian systems slot the die pairs into grouped, vertical storage “towers” for further processing.
The Cartesian systems provide speeds up to 1 meter per second, and a stroke of 500 millimeters in the X-axis and 400 millimeters in the Y-axis. Behr engineers also developed a special gripper for the Z-axis. Each CKK module includes a compact precision-extruded aluminum profile with an aluminum cover plate. A continuous gap seal protects the modules’ internal mechanisms. These mechanisms include a pair of integrated ball rail systems and a centrally oriented ball-screw drive, which delivers positional accuracy of 0.01 millimeter, with 0.005-millimeter-per-axis repeatability.
The ball rail systems and ball screw drive have a one-point lubrication system, which is accessible from either side, facilitating maintenance. An aluminum fixed bearing block with preloaded angular-contact ball bearings and a floating bearing block with double ball bearings ensures backlash-free operation. A locating feature and threaded mounting holes facilitate motor mounting.
For additional information on linear motion, call 800-739-7684 or visit www.boschrexroth-us.com.