Understanding Smart Sensors - Nomads.usp

208 Understanding Smart SensorsFigure 9.4 Rotary wedge stepper motor. (Courtesy of Sandia National Laboratories.)9.2.4 MicrodynamometersThe first steps have been taken to achieve a functional planar microdynamometer[9]. A dynamometer consists of a motor, a coupling gear train, a generatorto act as an active load, and associated electronics. The LIGA process (discussedin Chapter 2) with the addition of a sacrificial layer (SLIGA) was used to fabricatemechanical components of the microdynamometer. Magnetic actuationwas chosen for the micromotor and generator windings. As shown in Figure9.6, a two-pole-pair motor with three windings per pole (upper right corner)and a generator with six windings were fabricated using electroplated nickel.Photodiodes integrated into the design can be used to determine the position ofthe rotor in the motor and the generator. Among the issues that must beresolved to realize a functional microdynamometer are magnetic materialsproblems.A microtransmission fabricated using surface micromachining canincrease the power from a microengine by a factor of 3 million when the frictionis neglected [10]. Researchers coupled six identical transmission systems,each with a 12:1 reduction ratio to achieve the total increase. That level could