Messages

81

Video P*r*o*b*i*n*g / Re: Calibration

« on: June 25, 2008, 01:23:33 AM »

Hello Brett,

> Tom, get to play with it anymore since the workshop?

No. My video probe attended the CNC Workshop but I did not. With luck, I will get my probe back Thur night at our local amateur metalworking club (http://www.cams-club.org/) meeting.

> You really post some informative information. 

Thanx. In the 1980's I made my living designing non contact measurement equipment. Some used laser triangulation like these 3d video probes.

Others used trilateration by tracking a spherical glass cateye retroreflector about the size of a baseball. We could locate the cateye within 0.001 inch up to a range of 70 feet. We counted quarter wavelengths of red laser so we could have nailed the location within a wavelength of light if it were not for the mechanical tolerances of the gimbaled tracking equipment.

Tom Hubin
thubin@earthlink.net

82

Video P*r*o*b*i*n*g / Scan Direction

« on: June 19, 2008, 07:55:46 PM »

Hello,

For scanning an area or a volume I would like to have the user specify:

(xFirst, xLast, xStep, xOrder)
(yFirst, yLast, yStep, yOrder)
(zFirst, zLast, zStep, zOrder)

Where First designates the first point for that axis and Last designates the end of the scan. This would allow for scanning in either a positiive or negative axis direction.

Step designates the scan step size for that axis. This would be shown unsigned or the sign shown taken from the direction from First to Last. An alternative might be to specify the number of steps rather than the step size.

The Order designates the order in which the axes are incremented. Order=1 would be the innermost loop and order=3 would be the outermost loop for three axes. Zero would mean to exclude that axis from motion. 
 
Tom Hubin
thubin@earthlink.net

83

Video P*r*o*b*i*n*g / Calibration

« on: June 19, 2008, 07:51:30 PM »

Hello,

My probe is at the CNC Workshop in Illinois this week so I cannot do any serious testing until I get it back. However, I have given calibration some thought and I did do a few simple experiments during the brief time that I had it.

The present calibration scheme requires a square bar of known dimensions to be placed on the table parallel to the Y axis, and the camera and laser in the YZ plane and the target scan in the XY plane. No motion is used in the calibration so data is captured in a single position.

This static scheme does not allow for:
misorientation of the probe,
misorientation of the calibration bar,
inaccurate calibration bar dimensions,
radial distortion due to camera lens,
rectangular distortion due to non-square detector pixel layout,
keystone distortion due to laser and camera axes not perpendicular,
preferring a different arrangement of probe and target.

I would propose using a single point as a target. This could be the pointy end of a nail or pin or it could be the apex of a cone. If it is a cone then the apex angle would have to be sharp enough that the camera cannot see where the laser hits the cone except at the point. For example, in my setup at http://www.machsupport.com/forum/index.php/topic,5023.msg42913.html#msg42913, with the laser 30 degrees off the Z axis, the calibration target cone point would need to be less than 60 degrees.

I would jog until the point shows up near one corner of the screen then save the (X,Y,Z) coordinate from the machine axes and the (H,V) pixel horizontal and vertical coordinate from the CCD array where the center of the bright spot appears. I would do this for three corners to get three points as far apart as possible. This would create the data set:

(X1, Y1, Z1, H1, V1)
(X2, Y2, Z2, H2, V2)
(X3, Y3, Z3, H3, V3)

Three points are sufficient to define a plane so this is sufficient to define (H,V) points on the CCD plane in terms of the (X,Y,Z) points of the machine axes.

More than three points would permit a least squares fit which would be more accurate. Many more points, spread over the array, would allow for correction of distortion.

This scheme allows the probe to be installed in any orientation, even off axis orientations to get better data from odd shaped targets.

The probe could even be installed on the Z axis and pointed toward the front of the machine rather than down at the table. For this arrangement the point used for calibration would have to be setup so that it is pointed at the Z column. Then scanning the side of something would be possible.

Or side scan a target on a rotary table.

Or hang the probe on an articulating arm any way you wish.

Tom Hubin
thubin@earthlink.net 

84

Video P*r*o*b*i*n*g / Re: MachCloud point viewer program

« on: June 19, 2008, 06:34:07 AM »

Hello Hbaba,

> I'm doing the 90 deg setup now and the results are poor in a variety of ways.

What item are you scanning? Is it recognizable? Is it distorted? Is there a lot of unknown or unwanted stuff cluttering the scan?

What camera are you using? Can you setup AGC for Peak rather than the more common Average? If not, can you set the exposure time very low so that the laser is visible while the background is black?

If camera is upside down, did you select mirror and flip options in the Mach3 camera setup? If not, calibration is screwy and I have no idea what that does to the math. If not sure, post a screen shot with your calibration bar in place right after you calibrate.

Try scanning your calibration bar. Does the point cloud look like a square bar? If so, can you determine the size of the square bar from the point cloud?

Can you post some of your results?

Some stuff that would be informative:
Photo of your camera/laser setup.
Screen shot of probe video on Mach3.
Output (text file) from a scan that you are not happy with.
JPEG file showing views from various angles from MachCloud or other software.

> Do you have any before/after scans to share that came out well?

Not sure what you mean by "before/after" but I only have that one good scan of the key. I do have one of a penny but it does not show enough detail to say that it is anything but a disc.

My only probe is out of my hands at the moment. Should be able to do more next week when I get it back or maybe make another probe if I find time.

BTW, another camera that looks promising is the Playstation "Eye Toy". It does not have Peak AGC but does have the ability to turn AGC off and set exposure time very short. Not short enough to black out the background so it works better with house lights out or at least very dim.

Tom Hubin
thubin@earthlink.net

85

Video P*r*o*b*i*n*g / Re: MachCloud point viewer program

« on: June 19, 2008, 01:22:40 AM »

Hello Sid,

> Laser is almost directly above camera- offset maybe a few degrees
> (there is a photo I posted of this in another thread) 
>http://www.machsupport.com/forum/index.php/topic,4777.20.html

I See the laser but I don't see the camera. Is there a photo that shows them both at the same time?

> Camera angle is around 20 Deg

Are the laser and camera axes intersecting at 90 degrees?

Tom Hubin
thubin@earthlink.net

86

Video P*r*o*b*i*n*g / Re: MachCloud point viewer program

« on: June 19, 2008, 01:12:03 AM »

Hello Hbaba,

> I've been working with the plugin off and on for a while now but can't get dimensionally
> good results. I can get detail just not proportions that are usable.

> Can you share with me your Scan setup...

Here is a drawing of my setup. I show the camera and and laser axes in the XZ plane but Mach3's 3d Probe Plugin presumes that the camera and laser axes are in the YZ plane.

http://www.machsupport.com/forum/index.php/topic,5023.msg42913.html#msg42913

It is important that the laser and camera axes intersect at 90 degrees so that the laser plane is parallel to the camera lens detector planes.

> Laser angle to object

Laser angle is 30 degrees clockwise from Z axis.

> Camera angle to object

Camera angle is 60 degrees counter clockwise from Z axis.

> Camera distance to object

See drawing for layout.

-Camera Model/Spec

3Com Watchport/V CCD USB Webcam with 648h by 480v square pixels for VGA format. I use a 12mm focal length f/2 lens. This gives the camera a 14 x 18 degree field of view. At the target that is about 1/2 inch square.

> Also, any plugin settings you can share would be awesome.

I use a 1/4 inch square bar to calibrate. The corners are slightly rounded since this is just extruded stock. I have a scan of a key.  http://www.machsupport.com/forum/index.php/topic,6596.msg44274.html#msg44274

Calibration would be more accurate if I milled the calibration bar so that the bar surfaces intersect at a sharp 90 degrees. I have not measured anything in the point cloud so cannot yet comment on precision. My probe is being shown at the CNC Workshop in Illinois right now. I will have it back in a week or two and will then be able to do more testing. 

Tom Hubin
thubin@earthlink.net

87

Video P*r*o*b*i*n*g / Re: Post your Point Clouds Here!

« on: June 15, 2008, 11:36:01 PM »

Here is the point cloud that goes with the mailbox key JPEG that I posted previously.

Tom Hubin
thubin@earthlink.net

88

Video P*r*o*b*i*n*g / Re: Video plugin crashing windows?

« on: May 21, 2008, 03:39:09 AM »

Hello,

Last night I tried a Play Station 2 "Eye Toy" USB camera for the Mach3 3d Video Probe plugin on a Dell Inspiron 8000, 850 MHz laptop, Windows 2000.

Mach3 seemed to be ok. Jogged at the normal speed. That is all the testing that I have done so far.

There are at least three manufacturers for the "Eye Toy" and each has its own downloadable driver. I will give details on the exact camera model I used, later, since I do not have the camera with me right now.

Tom Hubin
thubin@earthlink.net

89

Video P*r*o*b*i*n*g / Re: Video plugin crashing windows?

« on: May 17, 2008, 12:29:29 PM »

Hello Mark,

> The Kworld usb device is a video converter (and a cheap one) that takes PAL/NTSC input
> video and converts it to ...MPEG? (can't remember) and ports it to the usb connection.

Something to keep in mind is to avoid loss of data since the distribution of the points is what we are processing.

For example, JPEG changes some of the data to make the file more compact while, hopefully, keeping it visually similar. I would avoid JPEG compression. GIF files compress and decompress with all original data intact. I do not know if MPEG is lossy or lossless.

Tom Hubin
thubin@earthlink.net

90

Video P*r*o*b*i*n*g / Re: Video plugin crashing windows?

« on: May 16, 2008, 05:53:05 PM »

Hello Sid,

> Usually the video driver crash/error dialog would pop up when I closed the 3D video window,
> tried to access the 'source' button on the plugin  or stopped a scan in the middle of its process.
>  I wasn't really happy with the results from this camera and decided to switch to a camera that
> did not require any kind of special driver software package (i.e. plug it in and windows detects
> it and it works)  Nothing fancy, just a 'plain jane'.

> Since the camera change, I have not had any problems with the stopped scans in process since I
> saw this problem and have not had this problem since.  Things just simply got a lot more stable
> with a different camera/driver combo.

I have wondered about my camera drivers as well. The 3Com Watchport/V was first sold in the mid 1990's. Several manufacturers and improvements later it is now sold as the Digi International Watchport/V2 or Watchport/V3. I am using the older cameras, the /V version. I have to install from the CD or from a downloaded file. If not, Windows has no knowledge of the camera.

The /V2 and /V3 versions were created about 2002 so Windows might have built in drivers for those. These sell for about $150 so I don't have any. I have several of the old /V version because they are on eBay for $10 to $30 and they worked under Mach3 on a friend's Windows XP desktop that I have occasional access to.

Perhaps the ticket is to find a camera with which Windows is already familiar...one that does not require an installation CD. What camera did you end up using? Please be specific enough that I could borrow or buy one just like it if I chose to do so.

Where is there a list of cameras for which Windows 2000 or XP is ready to go?

Tom Hubin
thubin@earthlink.net