Line shaft couplings simplify gantry designs

• eliminates separate drives
• eliminates intermediate support bearings

Traditional gantry designs used in industrial automation have employed a motion system consisting of an independent drive for each of the two guides, racks, linear motors, etc., that serve as the rails along which the bridge is driven. With this method, design, maintenance and operation can become unnecessarily complicated as motion must be synchronized between the two drives for smooth travel of the gantry bridge. Failure of only one of the independent drives can pose a serious hazard and cause excessive damage as only one side of a rigidly supported bridge will attempt to travel. The cost of manufacturing such a system can be quite high in comparison to newer, simpler solution — using a single drive with line shaft couplings from R+W America, precise motion can be transferred across the bridge mechanically rather than electrically. The result is a safer, more efficient, and more reliable gantry system. 

These line shaft couplings can precisely transmit torsional loads of up to 4000 Nm (35,000 in.lbs) and can traverse bridges up to 6 meters wide. Lightweight, precision balanced tubing is supported by gimbals on each end, eliminating the need for intermediate support bearings, which would be required if heavier steel shafting were to be used. Backlash-free flexible bellows protect the remaining bearings from the restoring forces resulting from slight shaft misalignments in system assembly. The balancing and a low mass moment of inertia allows line shafts to achieve speeds of up to 8000 rpm.

One of the more popular line shaft design possibilities involves one ball screw actuator driven directly through a dual output gearbox. The second output of this gearbox, positioned at a right angle from the first, is used to drive a line shaft coupling, spanning the entire length of the bridge. The other end of this line shaft couples to a second right angle gearbox, which is used to drive the second ball screw actuator. The line shaft coupling traversing the bridge is backlash free, and settling time approaches zero as a result of high torsional rigidity. In other designs where a more traditional rail system is used, such as a rack and pinion system, a motor can actually be mounted on the center of the bridge of the gantry system with a dual output gearbox driving each pinion gear through a line shaft coupling.