DIY Laser levelling using webcam and laser level

[Kitwn]

I suspect this is not the greatest limitation on the acuracy of your system. Making the concrete floor of your shed more rigid should be a higher priority.

[devmonkey]

I suspect this is not the greatest limitation on the acuracy of your system. Making the concrete floor of your shed more rigid should be a higher priority.

You may think that Kit, however I believe the (presumably linear) interpolation on the sensor is messing with my non-linear intensity fitting algorithms. It makes no sense to resolve down to sub-pixel resolution when 75% of the sensor information is estimated (Nyquist would have a fit).

For example imagine the raw intensity at the peak of our gaussian laser line looks like this:
100, 100, 101, 101, 100, 100
Now if this falls under the bayer filter on a green+red filter line arranged as:
G, R, G, R, G, R, G

With only red laser light, nearest neighbour linear interpolation would look like this:
100, 100, 100, 101, 100, 100

If the bayer filter is offset 1 pixel the other way you would get
100, 100, 101, 100, 100, 100

Therefore you have 1 pixel (3um) uncertainty and this is for a green+red filter line. I think is worse for a green+blue filter line where all the information is interpolated, i.e the information rate is zero.

I have some ideas to detect and strip this out but it is guess work without a datasheet for the camera chip, or maybe just reduce the resolution of the system from 1 pixel to say 4 pixels (6um).

I have a few RPIs here with cameras which I can get the raw bayer data from and just use the red pixels (can't get the raw data from a webcam), might we worth an experiment but would need entirely new code.

An alternative would be to use an IR laser as the bayer filter is transparent to IR therefore the sensor will behave as monochrome at full resolution, but then you couldn't see the laser for rough alignment.

Monochrome usb cameras (that are made without the bayer filter) are expensive as there is no mass demand.

[Michael Gilligan]

Wow ... I stopped visiting this thread on page_15 when it went quiet after my post.

I have a lot of reading to do !!

MichaelG.

[Michael Gilligan]

An alternative would be to use an IR laser as the bayer filter is transparent to IR therefore the sensor will behave as monochrome at full resolution, but then you couldn't see the laser for rough alignment...

May I also mention that, for the same reason, they are very dangerous things to have around.

MichaelG.

[devmonkey]

Been a bit busy with other jobs, however I have been playing around with a raspberry pi version of this system. I took a PI zero W (with builtin wifi), a small TFT screen and an OV5647 (pi camera v1) and wrote some more software. This will form a simple standalone unit and addresses a number of the problems I was having with a simple webcam, specifically:

1. I access the raw camera sensor directly, read the bayer data and only use the red pixels. This removes a load of noise that was being introduced by the blue an green channels and interpolation. There is no interpolation done at all on the sensor using it this way which means I get the true intensity per (red) pixel. Pixel pitch is 1.4um and 1/4 are red so system resolution is 2.8um.
2. Vertical range is much improved around 4mm.
3. With lens removed there is no glass (or a very very thin glass maybe) over the pixel array unlike the VGA webcam which had about 0.5mm of glass which gave some diffraction patterns.
4. I put in an algo to dynamically adjust the exposure, this means I increase exposure until the detected gaussian starts to clip (sensor saturates) then back it down a bit. This makes things much more accurate and repeatable at varying distances from the laser source.
5. No more cables!

I printed a case for it today and mounted the camera to a piece of Aluminium, still need to fix it all together. It has a lipo cell on board that I salvaged from a dead rc pack, a usb charger / ups and lasts for about 3 hrs before needing recharging.






Cheers, Joe

[Michael Gilligan]

That’s a great development, Joe

Will we be able to select our colour ?
... methinks green would be worth a try.

MichaelG.

[Michael Gilligan]

This monochrome camera [with 2.2 micron pixels] may be of interest:

https://www.e-consystems.com/ar0521-...nir-camera.asp

MichaelG.

[devmonkey]

Work has been getting in the way of progressing my machine, but where I left off the laser system is working well enough to perform the operation (particularly with the raspberry pi version) however the process of position a jig and routing the steel frame into plane with a trim router was highly error prone.

1. It was difficult to level the jig since I didn't use concentric adjustment and clamping bolts,
2. The process requires that the laser doesn't move, the trim router height gauge doesn't move and the cutting tool doesn't break or chip throughout otherwise it has to be started over. Also the jig has to remain a planar plate and not wear, since I used tooling plate the surface got quite a lot of wear from the trim router.

This is what stopped me attempting it across the whole machine frame.

So I've had a bit of a rethink and come up with a different process that is hopefully a bit more forgiving and controlled. Rather than attempt to level the frame by grinding it the new processes will attempt to attach rail bearing sub plates to the frame such that these sub-plates are planar.

I'm thinking of using 10mm aluminium for the sub-plates. The plates would run the full length of the X axis on top of each steel beam and eventually the rails will be bolted to these plates. The plates will themselves be bolted to the steel frame in an adjustable manor such that they can be brought into plane using the laser, then they will be permanently fixed in place with a potting compound taking up the gap between plate and frame.

A few people have tried this using set screws to level the plates which seems quite fiddly unless you go the trouble of making concentric adjustment/locking bolts.

What I'm proposing is to take each plate and drill two sets of holes along the centre line. The first set will be counterbored and used to bolt the plate down to the steel frame, the second set will be used to inject the potting compound. To allow the plates to float above the frame but also be held accurately in height by the bolts I'm thinking a compressible gasket could be run down each side of the plate. As the bolts are tightened the gasket would compress pushing the plate up hard against the bolt, this is simpler than grub screws and locking bolts.

To prevent the two plates (one for each X rail) tilting they would be coupled together with lengths of angle during the process.

The laser would be setup and both plates adjusted into plane using the bolts, once everything is level potting compound would be injected through the remaining holes. The compressed gasket will now act to contain the potting compound.

I think this has a number of advantages,
1. The entire leveling process can be completed before making a permanent adjustment to the machine,
2. I would be directly leveling the final machine surface (the sub-plate) rather than some tool that is then used to machine the frame.

I have sketched this up, would welcome thoughts on it.

[driftspin]

Work has been getting in the way of progressing my machine, but where I left off the laser system is working well enough to perform the operation (particularly with the raspberry pi version) however the process of position a jig and routing the steel frame into plane with a trim router was highly error prone.

1. It was difficult to level the jig since I didn't use concentric adjustment and clamping bolts,
2. The process requires that the laser doesn't move, the trim router height gauge doesn't move and the cutting tool doesn't break or chip throughout otherwise it has to be started over. Also the jig has to remain a planar plate and not wear, since I used tooling plate the surface got quite a lot of wear from the trim router.

This is what stopped me attempting it across the whole machine frame.

So I've had a bit of a rethink and come up with a different process that is hopefully a bit more forgiving and controlled. Rather than attempt to level the frame by grinding it the new processes will attempt to attach rail bearing sub plates to the frame such that these sub-plates are planar.

I'm thinking of using 10mm aluminium for the sub-plates. The plates would run the full length of the X axis on top of each steel beam and eventually the rails will be bolted to these plates. The plates will themselves be bolted to the steel frame in an adjustable manor such that they can be brought into plane using the laser, then they will be permanently fixed in place with a potting compound taking up the gap between plate and frame.

A few people have tried this using set screws to level the plates which seems quite fiddly unless you go the trouble of making concentric adjustment/locking bolts.

What I'm proposing is to take each plate and drill two sets of holes along the centre line. The first set will be counterbored and used to bolt the plate down to the steel frame, the second set will be used to inject the potting compound. To allow the plates to float above the frame but also be held accurately in height by the bolts I'm thinking a compressible gasket could be run down each side of the plate. As the bolts are tightened the gasket would compress pushing the plate up hard against the bolt, this is simpler than grub screws and locking bolts.

To prevent the two plates (one for each X rail) tilting they would be coupled together with lengths of angle during the process.

The laser would be setup and both plates adjusted into plane using the bolts, once everything is level potting compound would be injected through the remaining holes. The compressed gasket will now act to contain the potting compound.

I think this has a number of advantages,
1. The entire leveling process can be completed before making a permanent adjustment to the machine,
2. I would be directly leveling the final machine surface (the sub-plate) rather than some tool that is then used to machine the frame.

I have sketched this up, would welcome thoughts on it.

Hi devmonkey,

I think you might need 2 rows of bolts rather then the 1 row in the middle.

This will allow for correction of axial deviations.

Did you calculate the expected flex of the plate in relation to the gasket compression forces? This would dictate the number of bolts in relation to the maximum expected compression.

As said before all thing look like made out of gummy now we can measure things in microns.

I might be able to start measuring my machine tomorrow unless shmbo thinks of something more important.

Grtz Bert.



Verstuurd vanaf mijn SM-A320FL met Tapatalk

[devmonkey]

Hi devmonkey,

I think you might need 2 rows of bolts rather then the 1 row in the middle.

This will allow for correction of axial deviations.

Did you calculate the expected flex of the plate in relation to the gasket compression forces? This would dictate the number of bolts in relation to the maximum expected compression.

As said before all thing look like made out of gummy now we can measure things in microns.

I might be able to start measuring my machine tomorrow unless shmbo thinks of something more important.

Grtz Bert.



Verstuurd vanaf mijn SM-A320FL met Tapatalk

Hi Bert,

I was hoping that bolting the two sub-plates together with angle would go a large way to reducing the axial deviation (twist), but we'll have to see.

I will calculate the compression forces required after measuring various gasket materials by squashing them with a known mass. If I start with plate that is relatively flat then most of the adjustment will be bringing these two flats into plane, not so much will be bending the plates into plane which requires significantly more force from the gasket. It maybe that a combination of gasket and hard shims under plate bends is required.

Will go hunting for some 10mm aluminium tomorrow and some gasket materials.

Cheers, Joe