Sensor Fusion

Donald Heer11/10/10

The Questions

Can two things happen at the ‘same’ time?Can the same thing be observed ‘identically’ by two different observers?

Example

You are designing a system that measures ‘instantaneous power’ of a AC circuit. You are using a current sensor and a voltage sensor fed into a microcontroller. Can you display ‘instantaneous power’?Discuss in your groups

What Contributes to Timing Error?

ADC Timing Microcontroller ProcessingWire delay

Does it even matter though? Discuss.

What is ‘instant enough’?

Depends on specifications

Another Example

You are tasked with building a dead reckoning device. This system has a digital compass, a GPS, a 3 axis accelerometer, and a 3 axis gyroscope. The device will be installed on an off road buggy the can reach speeds of 60mph.

Specifics

GPS – Accurate with in 10M, 10Hz refreshAccelerometers – Accurate with in .001Gs, 1KHz refresh rateGyroscopes – Accurate within .1ft/sec/sec, 1KHz refresh rateDigital Compass – accurate with in 1 degree, 100Hz refresh rate

Come up with some rules to combine these inputs into a single ‘picture’ of where the buggy is. Discuss

Which Sensors are More Useful?

GPS? Only on rough terrain or when moving fastAccelerometers? Update fast, but noisyGyroscopes? Measures rotation, but drifts over timeDigital Compass? Only gives direction

Take Away

Be sure you know if you need ‘simultaneous’ measurements, or what error you can acceptIf needed, use one sensor to confirm another