Ries, that is great experience and an interesting post - thanks!

Laser distance sensing is done by at least 2 different methods:
- the triangulation method (as per the modules mentioned earlier, and Ries's sketch)
- time of flight method (typically longer range, above what we need for CNC)

Both methods employ a beam transmitter with a sensor mounted closely beside it, and therefore they both have a triangle effect. From Ries's sketch above, it can be seen that the sensor(camera) view can be blocked by ridges(hills) standing up from the profile. So, we want to keep the point of the triangle as sharp as possible, to reach down into the details of the "valleys". This is why I like the pre-packaged laser&sensor modules.

(Some commercially available scanning systems have a pair of sensors, one to either side of the laser beam, to increase the chances of the sensor being able to see the spot, but it doesn't totally solve the problem)

My gut feel says it would be nice to mount one of these modules about 6" above the y-car, so that it reads something on the table that is between 14" to 20" away. The angle at the sense point will only be about 3 degrees.

Reading that site I see that measuring distance is adjustable, in one model via a pot, that may mean the depth of focus of these lasers is very shallow which for our use is not a good thing.

Pablo, I cannot see what you are seeing......which site are you talking about?

From the link you posted I went back in the same section, here for example model FHDK 10 and many others.

compact housing, small beam diameter, sensing distance adjustable via potentiometer, IP 67

The model FDHK 10 does not give an output value of the distance. You use the pot to set the "trigger" point . . . . .it behaves like a proximity switch. If the the target is nearer than the set point it could close a switch, and open it again when further away. (It also is not a laser).

One has to select the device very carefully between the many options!

What Ries described at his post about laser scanning with a camera,
has been done by this guy : http://www.david-laserscanner.com/

Though the only thing you probably need from his site is the software which is
priced at 230 euros (ouch).

Sergio,

the method I described is not the same, they just use the same tools :)
The difference is that david 3d scanner measures a contour of object and calibrates the angle of the laser with a background board. Knowing the angle it knows more about the objects form based on the contour lines. It's actually a very clever method and easy to do it DIY.

The method described here, and what we talk about really tries to measure the depth. The laser depth measurements calculates the depth by triangulation, it really knows a distance and can do this very accurately, if the laser pointer is fine enough.
BEcause of this we need to have the MM move over X and Y to know the objects surface.

Ries

Hi Ries

So to get it straight what you are saying is something like the
depth finder we use at boats for viewing a 2 dimentional sea bottom graph but instead of pulse emition you use laser beams and cameras in a fixed distance ?

Sergio,

a depth finder on boats usually usually uses 'time of flight', on a boat this is done using sound. you emit a pulse from your boat, then wait how long it times it comes back. That time will tell you something about the location of the seabed.

With (single device) laser distance meters that need to be very accurate <1mm, triangulation is used, that's what we discuss here, it also means your measuring distance is short. Time of flight is rather hard for short distances (possible though, just very expensive due to electronics used) time of flight with a accuracy <5mm is hard, you need very fast and noise free electronics.

Laser distance meters for long distances can use time of flight, just don't expect to measure up to or smaller then 1 mm, >5mm, still possible, just electronics are very expensive when accuracy increases.

For us we need something in the sub mm accuracy, our MM can also be that accurate and the objects we can need to be milled that accurate, we also need to take into account any noise during scanning, so we need to have something in the order of +- 0.1mm-0.2mm accurate.

The laser distance meters discussed here can be that accurate, and with the MM moving over X and Y we can scan large objects very accurate. People with a latè can also scan around a object.

Each method has it's advantages, and disadvantages.


David laser scanner is : fixed camera and moving laser to capture contours.
We discuss here : moving camera/CCD, moving laser to capture distance by triangulation.

The advantage of 'our' method is that we can be accurate over large distances. If you have a MM of 2400x1200mm, then over the complete MM you can measure the object at a sub-mm level. If you need to copy ornamentals for restoration, this can be ideal, large areas but still very accurate unto detail, client would be very happy!

David laserscanner loses accuracy when the object size increases, but increases accuracy when the objects get's smaller. This is the reason they can scan complete sofa's, but also coins in very small detail. A other advantage of DL is that they you can scan a object where there are 'shadows' are, making it more suitable for scanning true 3D objects like a head, bust or a shoe ( see gallery) .




Ries

Ries

First sorry for repeating David's method as i jumped to your post and didn't see that the thread was started with David's laserscanner :D:D
I should start reading from No.1 next time.

I understood about the advantages disadvantages you mentioned above
(or at least i think i did).

So to my conclusion is that we could possibly use DL as a method for
scanning but with a diferent software that would allow us to have the camera
moving at the whole extend of the table and not fixed in a prealligned position.

Something like this : http://www.creaform3d.com/en/handysc...s/default.aspx
but in an affordable DIY budget.

Please take me back to first principles so I can better follow this thread (it's of interest to me, but let me get a cutting head going first :-).
The scanning device is mounted on the head and then the head is "driven" by software through a xy grid over the object?

Surely if we "drive" the head, then we know where it is, so can reconstruct the height of the head from the object (conversely the Z height of the surface at any xy point)?

More complex: If there is much z variation in the scanned object then this is "eyeballed" and the grid modified to roughly follow xyz needed to keep the scanner within its required distance from the object, but high enough so the head does not hit the object?

Red, you have it exactly right. The reading head stays at a fixed height, on the y-car, above the bottom of the gantry, which means it cannot crash into the object.

One of those scanner to hook up onto the gantry. 20110-00 South African ? money
http://www.cncsolutions.co.za/laser%20scanner.html

ZAR ( SA curency) to USD $ = +/- 0.145
So = +/- 2910 us$
Robert ;)

Hi,
I have not built the Mechmate yet but i can offer free laser Scanning services to all of the forum members of this great community...
www.free3dscans.blogspot.com
Regards

Thanks Khalid!

I have one question, are you using David scanner? Your results are fantastic!

I've seen Khalid's posts on the ArtCAM and CNCzone forums, and he does do good work. He uses the David scanner.

I wish I could find more information on Streamline Automation's products, including their scanner.

Here is on Streamline automation
http://3dcutting.com/

Not sure this would have the resolution you might want but the x box kinect is being used as a 3d scanner. There's lots of info on the Web. I picked one up used for $30 to use - but just have too many other things going on right now to have played with it and report any results...

I have used a number of different scan methods for use just as Streamline does.
Actually, modified #5 do cut large statues based on their large machine with removable table and 4th axis.

Streamlines "frog" based series of things uses technology similar to the David principle with a custom interface. Any IR / 2 head scanning system would work for what I see in this discussion thread.

Personally, the hand held david version has always worked well for me for small/med size objects that did not have really super high detail.

2 cents.
Sean