August 16, 2011 — At the École Polytechnique Fédérale de Lausanne (EPFL) Integrated Actuactors Laboratory (IAL), researchers have constructed an electromagnetic three-phase motor that could make watches 3x more efficient and add telephony, compass navigation, and other applications to time keeping.
The micro electro mechanical system (MEMS) based device at the core of this watch technology outputs 3x as much energy as a traditional motor. It differs from typical MEMS, based on electrostatics. This MEMS is an electromagnetic drive system that uses a fixed magnet and three phases instead of a single phase.
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Fabrication took place in a cleanroom in 24 operations. This method produces components at a lower cost than traditional methods, according to Yves Perriard, head of LAI. Fixed parts of the motor were engraved in silicon wafers in bulk, simultaneously. This cut down on the form factor of a three-phase motor as well. LAI reinvented configuration and geometry for the motor, Perriard notes.
Researchers had to redesign the command electronics to handle a three-phase motor. The motor needs to "locate the rotor, or the rotating part, at any point in time," to tell time accurately, explains Perriard. Sensors would accomplish the task, but be prohibitively expensive. Instead, signal processing techniques use the motor’s voltage and current to derive location.