Motor makes like a stage thanks to novel encoder

Feb. 17, 2005
A servomotor mimics the performance of much more expensive rotary stages with help from a superhigh-res encoder having a tiny Z height.

The Mercury encoder (foreground) has a small Z-height which lets the HO Series stage keep its axial dimension at a minimum. Encoder maker MicroE Systems produced custom largethrough-hole rotary scales for the motors.

A servomotor mimics the performance of much more expensive rotary stages with help from a superhigh-res encoder having a tiny Z height.

Applimotion Inc. in Loomis, Calif. (, designed its HO Series servos to have many of the same qualities found in high-precision stages. The servos incorporate ABEC-7 bearings and sport a through-hole in the motor shaft. A precision grind on the motor shaft gives the HO Series the run-out specs of a stage though it fits in an ordinary NEMA-23 housing.

Built into the HO Series motor is a Mercury encoder from MicroE Systems, Natick, Mass. ( The encoder lets the hybrid stage operate at resolutions up to 7.37M CPR thanks to integer selectable interpolation levels from X4 to X256.

Applimotion also assembles the servomotor before installing the encoder's glass grating on the motor shaft. This helps give the device a point-to-point absolute accuracy of 20 to 30 arc-sec and lets the encoder account for any nonlinearities in the bearings or other parts of the motor assembly.

Typical applications for the HO Series are in controlling apertures of optical inspection systems used in automated lines. The servos also generate less heat than the stepmotors ordinarily used in rotary stages for such systems. Heat can be problematic for holding necessary tolerances during focusing and imaging tasks.

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