Hello Mark,
Taking a break from sorting income tax info.
> Still trying to pull up the specs of the other camera
Not important unless we talk specifics about this camera.
> it doesn't have all that alarm and image masking hardware (which may be handy in excluding all
> the laser line except the region of interest)
I would think that the meshing software will allow you to delete regions that are properly measured but not of interest...like the table that the object is sitting on. There should be no data outside the laser plane bounded by the camera's field of view. The laser is so much brighter than any other lighting that a short exposure time, like 1ms, will black out everything but the laser wherever it intersects the object.
> It has an adjustable shutter from off to 1/20000
If auto exposure is used it should be based on peak value and not the customary average over the entire view. Peak AGC would show the laser and black out everything else.
> The lens image is fine at this distance with no discernible distortion but I haven't looked
> that close. I have been playing with angles while imaging a steel ruler obliquely to get a
> sharp focus across the full frame.
> I didn't intend on having the laser plane along the Z but more in line with what you have
> been saying with the camera and lens setup in an adjustable mount to tilt the image plane
> correctly onto the CCD.
The payoff to allowing the CCD to be tilted is that you can locate the laser just about any way that you want to. Consider a simple laser pointer that is pointed straight down the Z axis and focused to a small diameter on the target 100mm below. Locate the lens off to the left of the laser about 75mm. Point the lens optical axis at the laser waist at the target. The object distance is 125mm since the laser and the lens and the target form a 3:4:5 right triangle.
Calculate the image distance and the image tilt.
clfl = camera lens focal length
od = object distance
id = image distance
latm = lateral magnification
otilt = object tilt (zero degrees is perpendicular to the optical axis)
itilt = image tilt (zero degrees is perpendicular to the optical axis)
Given:
cfl = 50mm
od = 125mm
Calculate:
id = 1/(1/clfl - 1/od) = 1/(1/50mm - 1/125mm) = 83.333333mm
latm = -id/od = -83.333333mm/125mm = -0.667
otilt = atan(100mm/75mm) = 53.1301 degrees
itilt = atan(m*tan(otilt)) = atan(-0.889) = -41.634 degrees
Since the laser is the center of symmetry the camera can be located on the left or the right or front or rear or several cameras all around.
> I'll check out that site for line generators as the good ones at Edmund don't come cheap.
Also checkout Thorlabs. Not cheap there either but many more choices for laser, housing, lens combinations.
> BTW I have access to a Beamscan XY spot size meter so when I do get a laser
> (in the 670nM range) I'll be able to tell you exactly how gaussian and wide my beam is
.
That is great. I don't suppose we are neighbors. I am in Laurel MD (between DC and Baltimore MD).
> The main disadvantage I see with using my current lenses is that range of Z measurements
> will be greatly reduced than with a wider angle lens.
You can expect to get accuracy about 1% of your fov. To get better than that you will need to design and build everything just right. Since you are scrounging and making compromises you should be proud if you get 1% of your fov as accuracy.
> If I have a 90 degree included angle between the laser plane and the optical axis
> (equally spread each side ie. laser plane intersects the table at 45 degrees) then
> that will only give me sqrt 2 (1.4) times my measured FOV of 15mm or around
> 20mm of Z depth measurable.
Actually, I think you need to divide by the square root of two. That makes it closer to 10.6mm z combined with 10.6mm x.
>This would be increases the more oblique the optic axis to the bed became but there
> are limits with this too as one need the camera not to run into the object its scanning
> not be too blind to the shadow area... decisions decisions.
This is the way that I am doing mine. A 90 degree included angle means that you really cannot have the laser vertical because that would require the camera to be horizontal. I am setting the laser 30 degrees cw of the vertical and setting the camera 60 degrees ccw of the vertical. The advantage to this approach is that I can swap lenses to change my fov since the ccd array is not tilted with respect to the optical axis. And since I am interested in teaching it is easier for amateurs to copy and vary. The disadvantage is that x and z both depend on the h and v camera coordinates.
However, the professional method is to point the laser straight down the z axis. Then z depends on either the camera h or v coordinate (depending on camera orientation) while x and y are just taken from the cnc machine's DRO. The disadvantages are that it is more difficult to understand and design and build, the image will be distorted (but predictable) so must be corrected in software, changing the lens focal length changes the image tilt.
> Depending on what I wish to scan this may be way too small I would be happier with am max
> depth scanable of 150mm. One could do slices by indexing the scan head down but again I am
> not sure how either Arts s/w would cope with this or how I would join the separate meshes
> latter (probably using Gmax or similar)
You get accuracy by having a small fov and scanning over as large a volume as necessary, as you suggest, to accumulate the point cloud shifted by machine coordinates so that it is relative to absolute space.
Also, accuracy depends on methodology. Two points can be uncertain by 0.010 inches and used to define a straight line. It would be best if those two points are as far apart as possible. Even better, many points taken along the length of the line reduce random error by a factor equal to the square root of the number of points. So 100 points along the line can reduce the error by a factor of 10.
> I really need to get the plugin working so that i can figure it out for myself but I've been
> concentrating on building my machine of late and I now have a windows\driver\mach3 conflict
> somewhere on my new laptop that crashes big time everytime I launch a video plugin from
> mach (blue screen of death) . I'll probably fall back onto the old desktop to experiment.
I am about to do that myself. I now have three laptops that will run Mach3, or the camera vendors software, or both side by side. I can access the camera with the Mach3 video window plugin but after that Mach3 slows to about 1% of its normal speed. I have to exit Mach3 and restart it to get it working right again.
> What kind of ballpark numbers for laser plane and optical axis (plus FOV ) are you shooting for?
Similar to yours. I started with a goal of one inch but scaled it down a bit so that I could make a one piece frame on my little Sherline 5410 CNC mill.
Tom Hubin
thubin@earthlink.net
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Instead I used a setting in the camera driver to 'flip' the image so it appeared correctly on the screen.