Transcript
Most smartphones contain gyroscopes to detect the orientation of the screen and help figure out which way it is facing, but their accuracy is poor. They’re the reason why phones often incorrectly indicate which direction a user is facing during navigation.
It doesn’t matter much to a human on the street or behind the wheel, but a driverless car could get lost quickly with a loss of GPS signal. Inside their backup navigation systems, autonomous vehicles currently use high-performance gyroscopes that are larger and much more expensive.
However, high-performance gyroscopes are a bottleneck, and they have been for a long time. And now, a small, inexpensive, and highly accurate gyroscope developed at the University of Michigan can remove this bottleneck by enabling the use of high-precision and low-cost inertial navigation in most autonomous vehicles. The new gyroscope is 10,000 times more accurate but only ten times more expensive than the gyroscopes now used in your typical cell phone. Importantly, this gyroscope is 1,000 times less expensive than much larger gyroscopes with similar performance.
It could form the core of an improved backup navigation system that could help soldiers find their way in areas where GPS signals have been jammed. Or, in a more mundane scenario, accurate indoor navigation could speed up warehouse robots.
The device that enables navigation without a consistent orienting signal is called an inertial measurement unit. It is made up of three accelerometers and three gyroscopes, one for each axis in space. But getting a good read on which way you’re going with existing inertial measurement units is so expensive that they have been out of range for most applications, even for applications as expensive as autonomous automobiles.
The key to making this affordable is a small gyroscope with a nearly symmetrical mechanical resonator. It looks like a one centimeter wide “Bundt pan” crossed with a wine glass. As with wine glasses, the duration of the ringing tone produced when the glass is struck on the quality of the glass — but instead of being an aesthetic feature, the ring is crucial to the gyroscope’s function. The complete device uses electrodes placed around the glass resonator to push and pull on the glass, making it ring and keeping it going.
The glass resonator vibrates in a specified pattern, and if you suddenly rotate it, the vibrating pattern wants to stay in its original orientation. So, by monitoring the vibration pattern, it is possible to directly measure the rotation rate and angle. The way that the vibrating motion moves through the glass reveals when, how fast and by how much the gyroscope spins in space.
To make their resonators as perfect as possible, the Michigan team starts with a nearly ideal sheet of pure glass, known as fused-silica, about a quarter of a millimeter thick. They use a blowtorch to heat the glass and then mold it into a Bundt-like shape — known as a “birdbath resonator” since it also resembles an upside-down birdbath.
Then, they add a metallic coating to the shell and place electrodes around it that initiate and measure vibrations in the glass. The whole thing is encased in a vacuum package, about the footprint of a postage stamp and half a centimeter tall, which prevents air from damping out the vibrations.
The research, funded by DARPA, was recently presented at the 7th IEEE International Symposium on Inertial Sensors & Systems.
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