Segway gyroscope: Silicon Sensing keeps PT in balance


UPDATED: 2 January 2013 (see “Segway ‘thumbs-up’ for PinPoint” below)

This little box is a key ingredient in the special sauce that keeps that Segway Personal Transporter (PT) poised upright and self-balancing, as if by magic.

Silicon Sensing makes the gyroscopes used in the Segway PT.

These are not large, physical gyroscopes like you might find on a ship or aeroplane, or as an educational toy. They are micro-electrical-mechanical systems (MEMS), or gyroscopes-on-a-microchip. While relatively rare and expensive when the first Segway PT was revealed in 2001, these days such chips are encountered on a daily basis in iPhones and other smartphones, Nintendo Wii and Sony Playstation controllers, etc. As Silicon Sensing notes on their website page dedicated to the work they did with Segway, Inc:

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. 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.

Dean Kamen and his team desired the Segway PT to have triple redundancy in the pitch axis (tilting forward/back), and double-redundancy in the roll and yaw axes (sideways tipping and twisting/rotation). While it is obvious that the Segway PT needs to know about pitching, roll and yaw are important when balancing on a slope.

Silicon Sensing 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 our 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.

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….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.

First Generation Segway PTs could be made to “get giddy” by deliberately rotating at high speed on the spot until the centripetal motion affected the liquid filled tilt sensors (ie: confusing what way is being sensed to be straight up and down). When the rider stops spinning, the PT “feels a little drunk” for a few moments, before pulling itself together as the liquid filled sensors and solid state gyros work out what you’ve been up to!
ARTICLE UPDATE: 2 January 2013

Silicon Sensing issued the following press release on 12 September 2012:

Segway ‘thumbs-up’ for PinPoint®

After a year of development, and rigorous testing and trials at Segway’s facility in Bedford, New Hampshire (USA), Silicon Sensing’s PinPoint® precision navigation and pointing MEMS gyro has been given a ‘thumbs up’ for use in the Balance Sensor Assembly for Segway’s latest generation of ground breaking self-balancing Personal Transporters (PT).

Silicon Sensing was heavily involved in the original development and manufacture of the BSA for Segway over ten years ago, using its VSG (Vibrating Structure Gyroscope). PinPoint® uses the latest generation of this unique vibrating ring gyro technology and delivers the same high reliability angular rate sensing but in a device which is a tiny fraction of the size, power consumption and cost of the original.

One of the key factors for Segway is the high performance and integrity of the sensors produced by Silicon Sensing. PinPoint® CRM100 is an automotive grade gyro sensor and the technology is used in passenger car navigation, safety and braking systems.

Production deliveries of CRM100 units have already begun.

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