Laser Surface Scanner

[raptor1956]

A while back I asked about methods and materials to make a flat surface as part of an optical measurement system and it occurred to me that perhaps the better approach would be to do a more basic and less costly machining for flatness and then scan the part with a laser scanner.  So, even if the machined part is off by +/- 250um a laser scanner with, say, 10um accuracy and point spacing of, say, 5mm x 5mm, would permit a calibration table that would compensate and allow a final output near the accuracy of the laser scanner or about 10um.  More likely the resultant accuracy might be more like 20um and that would be more than adequate for my application.  In fact, a final accuracy of 35um would probably be enough.

So, what options are there for laser scanners to permit scanning of a 230mm x 150mm plate and to do so within 10 seconds and preferably quicker?  About what would something like this cost?


Brian

[LaserSteve]

Google Zygo interferometer...


Steve

[Marco]

Even structured light scanners can get near that.

[Nauris]

Maybe you should re-check your numbers? 20um flattness on that small surface requires only very basic and cheap machining.

[daqq]

For industrial stuff, check out https://www.micro-epsilon.com/2D_3D/

[Conrad Hoffman]

Are you machining with a butter knife and a file? 20 um is more than half a thou, easily done with a common facing head or fly cutter.

[CopperCone]

This design makes me angry. I can't imagine the confusion it would cause if someone tried to repair it. To require a look up table for a flat surface. Unless its the most cutting edge thing ever 

Even for a surface plate they will send it for resurfacing if it gets bad enough that you have to avoid certain areas.

Also a poorly machined surface is going to be ripe with asparities and such that will cause serious problems if you load or use bolts to mount anything precise. Torque will be unstable. And I suspect that glue will have a hard time adhering because machining oil will be able to penetrate the voids and such. It is difficult to clean. It will generally have low performance IMO.

[LaserSteve]

Showing you the errors with  a very cheap interferometer based on a home made wavelength stabilized diode laser or HENE laser is easy. Its when you want the digital  read out of the magnitude and direction of major segments  of the plate in ten seconds that drives the cost bananas.

A good piece of float glass can hit +/- 30 um  before polishing. Float glass is made by passing  the molten glass over a bath of molten tin to get a very nice surface with no molds or pinch rollers.

Steve

[raptor1956]

There's lots of things that make getting a cheaply machined part super flat.  First, any stress can cause warpage.  Second, if the part is bowed or crowned a bit and the clamping eliminates or reduces it then you may have a perfectly flat part after machining but as soon as you remove from the vise/clamp it's bowed or warped again.  If the part was nearly perfectly flat before machining the clamping to machine the part will tend to distort it and once removed the part will tend to rebound.  Lastly, if the part is relatively thin in vertical cross section then gravity alone will tend to distort the part -- yes, this should be small but is one of several things that add up.  It's not enough to have a mill that's perfectly aligned as the clamping process effects the part, particularly when it's of relatively thin cross section.

The idea is to minimize the manufacture cost and then account for the limitations by scanning.


Brian

[_Wim_]

What you are looking for is a "Profilometer". These devices scan a line really fast and accurate (so multiple points at once). By placing a couple next to each other (warning, not cheap!) it should be possible to scan the entire width of your piece in one scan. By moving the piece under the scanners, or moving the scanners over the piece (in a continous way) you could scan the entire surface quite accurate. Example sensor:

https://www.keyence.com/products/measure/laser-2d/lj-g/variations/index.jsp