While most x-y-z gantries have a horizontal orientation, sometimes the job calls for a vertical system. We recently produced just such a system for a test-and-measurement application. At 3-meters tall and 2.8-meters wide, this vertical gantry was constructed from ServoBelt™ Linear Medium stages with two different chassis sizes—90 x 180-mm on the horizontal linear stages and 45 x 90-mm on the vertical linear stage. A ServoBelt™ Rotary 100 unit provided an additional rotational axis at the end of the secondary horizontal axis—or what would have been the the z-axis in a horizontal x-y-z gantry.
The I's Have It
The main reason we call attention to this stage is its "I-shaped" structure with a single linear stage for the vertical axis. The natural design inclination for these vertical gantries would be to go with an "H-shaped" design in which two vertical stages would be connected by a moving bridge.
That H-shape at first glance seems to offer more rigidity, but it actually makes the design more susceptible to three problems:
- Deflection of the bridge.
- Positioning errors related to motor synchronization and racking of the bridge between two vertical members.
- High costs due to the additional complexity.
In this case, the I-shaped design was the way to go. The rigidity of ServoBelt Linear stage made it possible to execute the design with fewer moving parts—and less opportunity for error.