Motion Index Drives, Inc. was tasked with designing, engineering, and manufacturing a linear transfer shuttle that is a cross between a robot transfer unit and a tool tray transfer unit. The machine builder gave specific constraints in regards to payload to transfer, speed, overall dimensions, and critical maximum height.

The design constraints that proved to be the most challenging were to have a unit capable of moving almost 2.5 tons over a 5 meter distance in ~10 seconds, with a maximum height of 314mm to the floor, including space for leveling the unit. A tubular steel structure was designed with thick wall steel tubing to be rigid. The leveling feet were place on the same plane as the bottom tube structure to achieve a lower profile, and a machined carriage plate was engineered to achieve this low height. Heavy duty versions of a 45 series linear bearing were used to handle the load, as well as mounting a high torque extreme low backlash (less than 1 arc-min) reducer to handle moving the load smoothly and accurately.

For the accuracy, we were tasked to obtain +/-0.25mm positional accuracy in all directions. The rack and pinion system used provides 100% repeatability, with an accuracy of +/-0.1mm. But, to be 100% confident in the positioning, an additional linear encoder system was used that also achieves a positional feedback accuracy of +/-0.1mm. This is especially useful as the position is absolute, so if the motor was ever removed or altered, the linear position is always still known.