Feteris Components gyros provide the enabling technology at the heart of the Segway PT
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The Segway PT is instantly recognisable across the world as a unique and alternative means of transport. Its press launch in December 2001 attracted enormous attention. Its key design element - the balancing technology - had been developed and delivered by our supplier. This close relationship stemmed from previously providing the balancing gyros for the IBOT®, the equally novel balancing wheelchair, from the same inventor.Technically speaking, the Segway design is classic implementation of the 'inverted pendulum control theory' – balancing a broomstick on your fingertip is another example of the same thing.
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But to enable an automatically-balancing system based on this theory demands the availability of sensing, processing and actuation, all of which are fast and accurate enough. And for a commercially-viable product to emerge, this further demands the availability of these technologies at affordable prices, with sufficient robustness and reliability, and being of a suitable size. The overall system concept demanded that the Segway PT could always continue to balance if a component fails, whilst providing alarms and reversionary action to ensure that the rider is able to dismount safely.
Being involved from the very early days, they were able to propose and develop an innovative design, to be called the Balance Sensor Assembly, in which the size, reliability and affordability criteria were met through use of VSG3-based silicon MEMS gyro technology. A key requirement was at least dual redundancy in balance sensing – and the desire for triple redundancy in at least the pitch axis. Although not immediately obvious, the other two axes of yaw and roll also required to be sensed for the situation in which the Segway PT is balancing on a slope.
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The resulting solution is ingenious. Rather than providing dual and triple redundancy on each axis separately, the gyros are set at angles such that, by applying trigonometry to any pair of gyros, it is possible to deduce pure pitch, roll or yaw in more than one way. In summary, the solution provides three ways of measuring pitch and two each of measuring yaw and roll. To complete the module, two dual-axis liquid tilt sensors are included which sense the true 'down' direction and thus the pitch and roll angles. Processing within the BSA – again duplicated both electrically and physically – continuously checks the sensor data and monitors for any failures.
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