SERA Actuator/Summer Revision 2007

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Isometric view of the design proposed over the summer.

Side view of the design proposed over the summer.

This design was created during the summer of 2007 by Gui Cavalcanti working independently. Recognizing the problems with his previous design due to tolerances and stiction, he simplified the design substantially by considering using a frameless motor stator with a slightly larger, linearly-free rotor mounted directly on the shaft with the worm. To sense the linear and rotational location of the shaft and therefore torque and angle of the output shaft, he planned to put helical magnetics on the main shaft with increasing helix angle and using hall effect sensors to detect the rotational and helical angle and therefore the linear position and rotational position of the shaft. The above version does not include this, instead using the Austrian Microsystems 5046 magnetic rotary encoder as both a linear sensor and a rotational sensor. The shaft was designed to move slowly, and therefore the shaft was held in place by buhings; the shaft was allowed to move axially between Belleville washers which provided the spring between the shaft and the case.

The design was to be housed in a case machined out of aluminum and would have cost on the order of a thousand dollars per unit in prototype state for parts alone without machining due to the high cost of frame-less motors. This cost was the primary reason why the team left this iteration to look for alternatives.

Iteration: Sense K_m dynamically

An iteration was considered where a different linear sensing mechanism was used. Rather than having the rotor and stator be mismatched to enable a constant motor constant despite linear motion, Gui considered sensing torque and current directly and calculating the motor constant to infer linear displacement. This has the obvious difficulty that the sign of the displacement is still unknown, so an additional sensor would be needed.

Copyright Notice

The contents of this page are Copyright © 2007 Matthew Aasted, Guilherme Cavalcanti, Jeffrey DeCew, Christopher Dellin, Gill Pratt, Kevin Sihlanick, and Jon Tse.