Suggest a Transducer..!

[Torben]

Morning Torben,
I have seen people trying to develop something similar to this idea.

Its not easy, it can be done using accelerometers to calculate the offset distance from the Datum.
We did a 'heave compensation' system for Inshore Survey vessels, it does work, but its not cheap and the accuracy we had was about +/-0.1mtr at best.

A stationary, scanning laser leveller [very narrow beam] is positioned at a known height ref point, from which the remote receivers measure their offset, to do what GB is trying.

The accelerometer idea occurred to me but it would seem a little hard to make work right.

The stationary scanning reference beam seems like it would be easier to make work, at least as a prototype.


Torben

 

[ericgibbs]

The stationary scanning reference beam seems like it would be easier to make work, at least as a prototype.
Torben

hi,
As some other posts have pointed out, he dosnt need to rotate the complete lasing head.
An oscillating mirror or prism is usually enough to cover the area where the mechanical grader is working.

All he needs to check the feasibilty of is idea, is get a highish powered laser pointer, as used in a classroom.
As these are about 5cm long he could oscillate the pointer in an horizontal plane.
Using sensitive, multipoint vertical detectors at the grader, it should be able to 'see' the beam as it flashes past.

BTW I have never seen an area graded to +/-4 mm.

 

[Mikebits]

What about a barometric transducer that you zero at ground zero, and then measure pressure change to compute elevation. I really do not know if pressure sensors have that much accuracy. Just brainstorming...

 

[Torben]

hi,
As some other posts have pointed out, he dosnt need to rotate the complete lasing head.
An oscillating mirror or prism is usually enough to cover the area where the mechanical grader is working.

Yup--to paraphrase my original reply: "don't spin the laser, spin the beam".

All he needs to check the feasibilty of is idea, is get a highish powered laser pointer, as used in a classroom.
As these are about 5cm long he could oscillate the pointer in an horizontal plane.
Using sensitive, multipoint vertical detectors at the grader, it should be able to 'see' the beam as it flashes past.

I agree completely. I've read of some robot projects which use a camera directed straight up as the sensor. Immediately above the camera's lens is a conical mirror, which reflects a 360 degree image down into the lens. Image processing software picks the relevant information out of the image data.

For a quick prototype, something more akin to a line-following robot's control software might be easier though.

BTW I have never seen an area graded to +/-4 mm.

I think some of the baseball diamonds we play on are graded to about +/- 50cm.


Torben

 

[Torben]

What about a barometric transducer that you zero at ground zero, and then measure pressure change to compute elevation. I really do not know if pressure sensors have that much accuracy. Just brainstorming...

I have no idea how barometric sensors operate, but it seems like weather changes would render them untrustworthy for a task like this. Not 100% on that though.


Torben

 

[ericgibbs]

What about a barometric transducer that you zero at ground zero, and then measure pressure change to compute elevation. I really do not know if pressure sensors have that much accuracy. Just brainstorming...

hi Mike,

Problem is the baro pressure is changing very quickly with time.
I think +/-4mm is a no,no.

The difference in water level in a harbour can change more than a metre due to baro highs/lows

 

[Mikebits]

That is why I suggested it must be zeroed first.

 

[Torben]

That is why I suggested it must be zeroed first.

Right, but you're zeroing it to a changing standard. If you zero it, then as soon as the ambient pressure changes I'd think that you'd need to re-zero it to the new conditions. And the ambient pressure changes constantly with the weather. What I'm not sure about is how sensitive these sensors are to this sort of thing.


Torben