3d Accelerometers - Will they do position sensing??

[hs92]

does anyone know much about the 3D accelerometers that are on here for sale?

I am looking to use one for a positioning system possibly using one of the arduino boards.

I need to be able to work out where my device is at a given time, eg, its distance travelled since last calculation in all three dimensions.

If anyone can help me out i would be very grateful and if you need to know any more info just ask away,

Thanks,

Henry

[i-Bot]

Accelerometer measure acceleration exactly as they say. To get position you have to integrate the signal output twice. Integration intoduces large errors which accumulate to make the measurement of position almost useless. Accelerometers also detect the acceleration due to gravity, so are best for determining orientation about a vertical axis, which is why they are used so much in robotics.

Measuring distance travelled is better done with a direct position measurement. This depends on the scale (millimetres, metres, kilometers) and the relationship of the device to its surroundings ( wheels, known environment, fixed or autonomous). Different techniques can then be used including encoders, cameras, gps, laser, IR.

So I don't think accelerometers will do it for you, but there is usually a way.

[hs92]

Thanks for the reply. I am looking at a device that will be travelling down a pipe in a sealed unit whilst a medium is flowing. So the device will need to know where it is whilst travelling down the pipe.

From what you are saying, an accelerometer will tell me the orientation of my device, in terms of x-y-z coords.

But to measure the position in the pipe at a given time will require something else...Could you possibly suggest anything that may work?

Thanks.

[hs92]

Could you not use the acceleration in the direction of travel, over a given time to calculate the distance travelled?

Cheers,

[SK]

Could you not use the acceleration in the direction of travel, over a given time to calculate the distance travelled?

Cheers,

Well you could try that, but I´d strongly suggest you don´t get your hope too high that it works for more than a very short time (seconds). After all, you´d be still integrating noise twice.
Of course, one could use (Kalman) filtering for fusing data from the accelerometers with some other measurement device that might give less frequent but more accurate updates (RFIDs spring to my mind for example).
It´s probably a good idea to read up on Kalman Filters, INS/IMU systems and low cos inertial sensors before trying anything

[hs92]

Thanks for the reply.

So it would be best to use another means for the distance travelled.

If i want to know the position in the pipe of the device at any one time in terns of x-y coords, ie height in pipe and position across the pipe, would accelerometers give me what i want or would i have to use some other means?

Cheers.

[SK]

Well I haven´t tried such an application myself, so I can only state my other experience with low cost accelerometers which basically says "don´t use them for unaided position estimation for timespans larger than a few seconds max".

A potentially useful article dealing with 1D accelerometer filtering is this:
http://www.gamasutra.com/view/feature/1 ... alman_.php