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Best laser setup: Translating or rotating laser?

Questions, problems, comments and tips regarding the 3d scanning process.

Best laser setup: Translating or rotating laser?

Postby motordude » Fri Jul 06, 2007 9:08 am

Hello all.
To get the most accurate results, what is the best setup of the laser?

1. Laser on a tripod, laser rotating to brush the object. The angle to the object varies. Distance is fixed.
2. Laser on a gantry moving over the object. The angle and distance to the scanned object is fixed.

Suggestion 2 fits me better as I have milling machines where this can easily be arranged. Scan envelope will be 500x500 (mm) approx.

In setup 2, what would be the prefered laser distance to the object, and camera and laser angle to the object?

Thanks!
John
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Postby WalterMo » Fri Jul 06, 2007 11:41 am

Hello John,
Because you already have a milling machine I would use it as a translation stage for the laser.
The best distance laser to object depends a bit on the magnitude of the profile you intend to scan. For small differences in magnitude I would propose a shorter distance because the line width of the laser can be finer focused. (If you have a focusable laser of course). But in this case the depth of focus of the laser line is relative small.
I would not use a constant angle of the laser beam during scanning. Better is to change it between the single scans at about 60° and 120°. Thereby slots will be better illuminated.
The distance of the camera to the object depends of course on the size of the calibration corner.
May I ask what kind of objects you are planning to scan?

Walter
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Postby motordude » Fri Jul 06, 2007 1:04 pm

Hello Walter!
Thanks for your reply. I don`t know if the laser is focusable, just ordered it today LD532-5-3(20x80) 532 nm 5 mw. Still waiting for the web camera, so I haven`t tried scanning anything just yet.

If I understand you correctly, scan several passes over the surface and change the angle after each pass? Then perhaps change the camera position and repeat the procedure?

I will be using the scanner for reverse engineering. I have a machineshop and foundry, so the scanfiles (STL) will be sent to my 3D printers (3D Systems ThermoJet) and a wax print will be made. This will be used for investment casting in any material, except Titanium. Castings will be mostly industrial items such as covers, propellers, engine parts etc. So accuracy is rather important.

When the laser setup is ready I`ll 3D print files and send pics to the forum if any interest.

Best regards
John
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Postby WalterMo » Fri Jul 06, 2007 2:06 pm

Hello John,
Of course we are interested of your results.
I think such an industrial application was not presented before here in the forum.
The angle of the laser need not to be changed after each pass but two times during all passes. (one half at about 60° and the other at 120°).
Important: The position of the camera in relation to the calibration corner must not be changed after calibration!
If your object cannot find space in the calibration corner you can also use my suggestion which I presented by scanning a car tyre.

Best regards

Walter
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Re: Best laser setup: Translating or rotating laser?

Postby masterkielbaster » Tue Jul 10, 2007 7:44 am

motordude wrote:1. Laser on a tripod, laser rotating to brush the object. The angle to the object varies. Distance is fixed.

John


In fact interesction angle is more constant than in second case.
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Postby WalterMo » Sat Jul 14, 2007 8:13 pm

I think it's not so important to work at a preferably constant angle of the laser beam.
In some cases it might be advantageous to vary the angle to get a better illumination of cavities etc.
Secondly: If the laser rotats in hand, fixed at the rotating axis of a stepper or on a tripod the focal distance to the object changes. Specially at a short distance when the depth of focus is relative small this effect is visible but unavoidable.
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