Friday, July 2, 2010

We're falling for gyros

Back in the early days of aviation and aerospace, gyroscopes were bulky mechanical devices which, despite their size and weight, were amazingly fragile.

Anyone who's ever played with a spinning top understands the basics of a gyroscope.

One of the most common demonstrations of gyroscopic stability is a childs spinning top.

When not turning, the spinning top will never balance on the narrow point that is its base. No matter how carefully you try to get it balanced and level, when you release it, it quickly falls to the side until it is resting on that point and the edge of the disk.

However, spin that top up and it will quite happily sit, steady as a rock on that tiny point in the center. Even if you give it a good shove, it will still maintain an upright stance and continue to pivot on its base.

The wonders if gyroscopic force go far beyond a simple child's toy however. Gyroscopes have long been at the very cornerstone of our ability to build and fly aircraft, rockets and orbiting satellites.

And now, thanks to the inexorable tide of miniaturisation and advances in solid-state technology, gyroscopes, and their close cousins called accelerometers, are now built into a growing number of consumer electronic devices.

What's the difference between an accelerometer and a gyroscope?

An accelerometer detects an acceleration (such as the force of gravity or a change in the speed of an object) in a single plane. A gyro detects an change in angular movement (rotation).

To draw an analogy -- let's say you mount a gyro and an accelerometer on your head...

Now, if you are standing and you crouch, then return to standing position, the accelerometer will have been able to measure the forces that were created by that movement and when connected to a suitably programnmed computer, could even produce a graph that ploted the vertical position of your head against time. However, the gyroscope would not have even noticed the movement because there was no rotation involved.

Yet, if you twisted your body and head around so as to look behind you, the accelerometer would read nothing but gyroscope attached to your head would be able to tell you just how many degrees it had rotated and (with the right computer/software) could plot a graph of your head's rotational position against time.

So just how are gyros and accelerometers being used these days?

Cameras with "Optical Image Stabilisation" which promises to reduce the effects of camera-shake, usually contain either gyros (to detect the small rotations of the lens-angle when your hand wobbles) and/or accelerometers (to detect vertical/horizontal displacements of the camera). The signal from the movement sensor is then used to adjust the angle of a small mirror or prism to compensate for the movement, effectively eliminating or greatly reducing the effect of that camera-shake.

If you've got an iPhone or iPad then you'll know that these devices have accelerometers in them that allow the display to recognise whether it's being held in landscape or portrait mode.

Users of the Wii console will be very well acquainted with just how accelerometers can convert the direction and speed of a movement into a game-input.

And of course, we've all see the Segway which relies heavily on gyros and accelerometers to maintain its upright position and allow control inputs to be made simply by leaning forwards or backwards.

So where are the big, heavy spinning wheels that used to make up the gyros of yester-year?

Well they've been replaced by tiny etched slithers of silicon which vibrate at a high frequency and in the case of a gyro, rely on something called Coriolis Effect.

Accelerometers use a small strip of silicon which is bent by the force of acceleration, effectively changing the gap between it and surrounding bits of silicon. When a high frequency signal is passed through this arrangement, the amount of deflection (hence the acceleration) can be very accurately measured.

Both these bits of clever stuff are what's called MEMS devices (Micro Electro Mechanical Systems) and form part of a family known as motion sensors. Most of these devices are smaller than a fingernail, making them ideal for today's ultra-compact consumer electronics.

They're already making huge (often covert) inroads into our hi-tech appliances and you can expect to see a lot more features and functions that rely on them as we wake up to the potential they offer to clever and innovative technology designers.

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