Low-Cost Brushless DC Motor Rate Sensor (MFS-31143)
The new brushless DC motorbased rate sensor addresses the drawbacks associated with other rotation sensor technologies. The mechanical brushes on brush-type tachometers produce electrical arcing and wear out relatively quickly, requiring that the device be replaced. Although prior technology using brushless DC motors/tachometers addresses this issue, most alternatives must be used in conjunction with position sensors and require that wires be added to excite the position sensor. Resolver-developed rate sensors also require wires for an excitation signal. Additionally, they usually require differentiation, which is quite noisy, to produce rate information. Finally, encoder-developed rate sensors¿ accuracy degrades at low rates because of the discrete nature of encoder outputs. NASA¿s technology is a brushless motor-based rate sensor that produces a DC output that is proportional to the rotation rate of a shaft. Windings sense the back electromagnetic force from the shaft, and these windings are coupled with circuits that calculate the DC output. This new device is inherently linear and produces accurate rotation rate signals. The instrument is a stand-alone sensor, requiring neither electrical excitation nor an additional position sensor. Furthermore, this direction-sensitive device has a simple design that requires no mechanical brushes.
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