I recently came across a cool innovation in servo technology from a little company called QuickSilver Controls. The Mosolver is a servo motion actuator that infuses a position feedback sensor into the structure of a high-pole-count AC motor. This combination eliminates the need for an encoder and resolvers, and it results in robust closed-loop motion control.
For further precision, the servo's designers have added sense coils within the motor. Voltages are induced by these sense coils from a combination of the pulse-width modulation current ripple and the flux steering as a result of the rotor and stator interaction. The design removes a separate feedback device to make the overall package smaller (along with the overall bill of materials). And having everything packaged together increases the system's reliability. Many more details are available in the data sheet.
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