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Optically measuring a part (Scanning)

clutch

Hot Rolled
Joined
Feb 12, 2006
Location
Northern LP of Michigan
Are there systems other than cameras that suffer from perspective distortion that can measure a part in say a 16x16 inch envelope looking horizontally and from above?

What key words do I need to use to find such a system?

Thanks,

Clutch
 
Photogrammetry!
But you need at least 3 pictures from different angles for every point (one picture can have many points of course).
This method is astonishingly accurate. You can get resolution well above 5000:1 (10000:1 is not at all utopic) with a standard camera (after calibration). 5000:1 means, a 5m object can be measured with 1 mm accuracy. Of course, you need one dimension to be taken off of the object for proper scaling.

Professional cameras (they co$t) give a by magnitudes better resolution.


Search for Photomodeler.


HTH,
Nick
 
Ive not been here for a while, so I hope this is still relevant.
Disclosure: I work for Phase Vision, we make fringe projection systems.

With a little more info I can probably point you in the correct direction, as I work in that area.
Fringe Projection Systems might be able to do what you want, take a look at Phase Vision - Optical Inspection Solutions for some more details, but basically they project a series of patterns and take pictures of them, then mathematically reverse the information contained in the pictures to produce a 3d point cloud of the object.
Our systems typically scan areas in the range of 0.5 - about 2 meters square. Other fringe projection systems tend to be setup for smaller areas.
Laser Line Scanners might also work for you, usually on the end of a faro arm of similar, but they are slower to acquire the data. You can however also point probe into holes with them. Most optical systems can only measure what they can see. This means deep holes or slots can cause them to miss sections of the data. You end up with holes in the data, but you can usually get round this by moving the part or scanner to scan from a different angle.
Another problem for most optical systems is shiny / machined surfaces. At Phase Vision we have a number of patented algorithms to help cope with this. Lasers systems can have particular problems with shiny, as it can cause the laser to reflect back up the laser output and cause overloading (Im not a laser tech, so this might not be quite the accurate description, but its close).
A lot of optical inspection companies will spray a shiny object with NDT developer spray (white talc) to 'dull' and give a nice to measure surface.

If you have any questions just ask, if I cant help either I will know someone, or someone here probably will...

Dave
 
Photogrammetry

A second vote for photogrammetry.

Photomodeler is about the lowest price package.

The top end for terrestrial packages is probably Adamtech.

http://www.adamtech.com.au/Blog/

If you have a pattern of circles on the background which are known distances apart, you can use them for scaling and for orientating the images. you need at least 3 and preferably 5 or 6 common points in adjoining images.

a DSLR or rangefinder with a good quality lens (and no fancy shake reduction) is almost as stable as the big sheet film cameras which used to be used.
 
Optical Gaging Products here in Rochester might have something useful. We use one of their video inspection systems at work and the accuracy is very good.

There are special lenses that don't suffer from perspective distortion over a limited area, but I can't for the life of me remember the name for them. I know they show up in the Edmund Optics listings.

Happy New Year!
Conrad
 
There are special lenses that don't suffer from perspective distortion over a limited area, but I can't for the life of me remember the name for them.

Conrad et al. --

I believe the optical design term in question is "telecentric in object space". Here is the associated Wikipedia link:

http://en.wikipedia.org/wiki/Telecentric_lens

Since you mentioned Edmund Scientific as a resource, the following is a link to their on-line description:

What is Telecentricity? - Edmund Optics

... which may also prove informative.

Hope this helps,

-- Jim
 








 
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