Webcam centre / edge / hole finder

[scubasteve_911]

Switcher,

It's funny that you mention that because I had run into problems tonight during experimentation with another image processing algorithm. The problem occurs when thresholding the image to a binary format meant for shape recognition, it simply thinks that the reflection is what should be thresholded.

I have decided that I want to pursue this application further and develop some advanced code. I want to provide a means of automatic centering along edges and holes. The program must be calibrated via a white card with a black square. It also needs information about where your X and Y step-dir signals are located on the parallel port. I want the program to self-calibrate, then find the correct hole (based upon approximate diameter input from user), then move to either an edge, corner, or center of a hole.

The entire concept is fairly complex, but it seems doable. I will let people know how progress is going as I continue. As I had said, I really need to get the hardware up and running first.

Steve

[CarbideBob]

Steve,
Welcome to the world of machine vision, I've got a little experience in this. A couple of thoughts.
Unless you use optics designed for measuring your magnification (and calibration) will be different at the sides of the image than in the center.
If you use telecentric optics you will not see the sides of the hole when it is off center.
Cheapo sensors are CMOS color devices. These use a color filter to split the RGB across 3 photosites. Because of this the measuring capability is less than than the sensor resolution.
Your sensor will not be square. Be aware that you will need different calibrations for X and Y.
Edmund Optics is the best source for optics and calibration masters. Get one of their catalogs. Full of good information on lenses, calibration, and lighting techniques.
Yes, this is very doable. I'll be interested to hear about your progress.
Bob

[scubasteve_911]

Hi Bob,

Thanks very much for your input and encouragement, first-hand advice is always appreciated.

I'm having to draw the line here in terms of cost and availability. I have learned very painfully from experience that things can always be done better and it nearly always comes at an exponential cost. 1.3M webcams are extremely cheap and readily available, albeit extremely cheap plastic optics and the problem of RGB splitting on the array itself.

Edmund optics does make excellent stuff, I must admit. Their prices are fairly reasonable with the exception of the more highly integrated things. I was actually sponsored by Edmund when I was 17 to build a laser range finder, they're great people!

I had once used a Micron 1.3M B&W CMOS image sensor capable of full resolution at 30FPS on a custom-made four layer PCB with a FPGA for interface and processing. I remember how much of a pain it was to find focusing optics that would fit the sensor.. It ended up costing well over 100$US just for the sensor and cheapie optics. If I had wanted to go all out, I could have gotten a housing machined and used some high grade optics from Edmund and would have spent over 250$US. That would probably be an ideal solution for this project, but I don't really want to get into having to make a USB / slow RS232-based interface.

I guess I am going to try my best with software and determine whether or not it is acceptable by experimentation.

Steve

[scubasteve_911]

Hi Bob,

I found an okay webcam to use, which is a step above a typical webcam. It's a cheapo chinese webcam, but I think it will be fine.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=120148423323

The unequal lighting kind of upsets me, but I guess it is better than having to make a mount for LEDs and my own dimming circuit. Apparently, the lens is "German-Made" and is glass. It's funny, I used to work as a Kitchen Appliance salesman (another lame student job) and we used to use that line "It's German-made" and people would be immediately impressed! To me, where something is made and the brand name means nothing, just specifications count.

We will just have to see how this pans out, I will keep updating, maybe in my own post

Steve

[abasir]

Found this thread recently... Just to share my setup ... USD15 webcam quickly modified for the purpose... works very well... will be making a new mounting soon... more details at my blog...

[lvittori]

Here is my version. I do a lot better with this than a center finder.

[joejared]

Hey,

131.7250 269.2802
382.2941 261.6078
394.4105 101.8659
586.1414 96.4520

This is my no means an optimal setup and once I get the hardware finished (another month), then it will be clear whether or not the program will work.

Steve

Speaking as someone who has designed laser and structured light 3d scanners, I find it difficult to believe anything from the 3rd digit on, especially given the size of the holes you are centering over. You might get some improvement using subpixel resolution, but at best you'll probably get no more than 1/4 pixel improvement. My own edge finder implementation is described on http://www.oretek.com/micromill/user.shtml#edge and works in conjunction with a proximity sensor to provide a means of setting depth without making actual contact with the end of the tool. See also: http://www.oretek.com/micromill/user.shtml#proxy . For purpose of calibration, I simply "touch down" on the proximity sensor with the edge finder, change tools, and touch down onto the proximity sensor with the tool to be used. At this point, an offset is applied per previous calibrations determined by performing the same action onto a digital depth gauge and recording the results. The only real downside is that there is a minimum limit to the diameter of cutting tools that can be used, and if there's a hole in the middle of the tool, there's nothing to reference. For tools with a hole in the middle, it would be a simple matter to design an alternative proximity sense with an offset so that the sensor is in close proximity with the actual metal. As for accuracy, it would appear from test results that I can get within +-0.0015" in terms of accuracy with this method for depth, and whatever the accuracy of the edge finder is in terms of X and Y. The only real problems I've found with the electronic edge finders is in the fowler brand. Typically, I have yet to find one more accurate than 0.005 and have indicated them on my lathe to confirm they are not well made. The ball style from PEC tools is much better, but also much more fragile. I'm tempted to make a repairable form of the ball type for just this reason.

My high quality camera lcd busted but in the mean time, here are some cell phone videos, just barely clear enough to show the operation:

http://www.oretek.com/micromill/edge.mp4
http://www.oretek.com/micromill/proxysetup.mp4


Normal proximity operations are purely vertical as it is simply a machine setup issue to center onto the proximity sensor. I don't really know how critical the magnetic field is but suspect it's a good idea to have the tool centered over the sensor to provide repeatability and reliability.

As for centerfinding, I simply position the edge finder inside of the hole to be centered, after at first possibly hopscotching from known corners and then issue a command from my own software:

edge c+ 0.00

The above is functionally equivilent to edge x+ edge x- and centering on the results, and then performing the same operation for the y axis. Generally, I perform this command twice for greater precision.


I wouldn't have the first clue how to implement a similar command in G codes and only know just enough to be really dangerous when it comes to those codes.

As to cost, it's mostly the cost of the electronic edgefinder itself. I've used everything from the cheap $20.00 barely electronic units to the $70.00 unit from wttool.com. It hurts more when the idiot doing the programming for it breaks one. (me)

[dang]

There's one on Ebay selling for between $199 and $900.00. AND it doesn't appear to be able to be adjusted either. It's got some software that was custom written for it and can be outfitted with a laser for edge finding.

It doesn't look quite as fancy as some I've seen here. But it does come with a magnet and a convenient carrying case.

[luky luke]

Hello Everyone,
I take very little speech on the Forum, however, I read your posts carefully and I had not seen this one, have you solved the problem now, I guess yes!

I too faced the problem of accurate alignment.
A friend told me about a German software he used with his Webcam, " NC-Eye-1.39 ", the Company ANKOTEC, he obtained a good result with the Webcam sold at CNC4PC mounted cone MK3.

I originally bought the laser pointer to CNC, I pointed to a room and mounted the laser clip ER20 I leave it, I mounted on the milling machine and rule for a point as small as possible and I set the laser at the center, and I blocked the X and Y axes, then to my great surprise I fell exactly in my score, just as with the laser, of course I have refined the pixels, and adjust Z but this material is really good, pity he is not thought to be an addon like this on MACH3, because each setting should appeal to the NC-Eye software, unless any of you, to merge all of the two programs would make a great plugin ?

Even after all this time, I'll be curious to know your results, I am available, or perhaps you're better than this equipment (expensive sold on Ebay, which does not seem higher, but It is true that the presentation is nice for the price) ... If so my system works but it is tedious, so I'm interested of you !!!

Best Regards.
Luky.

[Tim Hyde]

It seems that I have gone through the same process as many others in this thread, wish I had looked for this some time ago - how to use a webcam for optical alignment?

Well I came up with a software solution to make the most out of a cheap endoscope webcam available on eBay to provide an accuracy of about 0.01mm. The software allows you to zoom right in, add a cross-hair overlay, but most importantly - lets you use it whilst in your CNC application (whatever your preference). See CNC Cam for more information about CNC Cam or to get the download (free but does have a nag screen).

Hope that this is useful for someone!

[iwebnet]

Hi Bob,

I found an okay webcam to use, which is a step above a typical webcam. It's a cheapo chinese webcam, but I think it will be fine.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=120148423323

The unequal lighting kind of upsets me, but I guess it is better than having to make a mount for LEDs and my own dimming circuit. Apparently, the lens is "German-Made" and is glass. It's funny, I used to work as a Kitchen Appliance salesman (another lame student job) and we used to use that line "It's German-made" and people would be immediately impressed! To me, where something is made and the brand name means nothing, just specifications count.

We will just have to see how this pans out, I will keep updating, maybe in my own post

Steve

I agree with you.I guess it is better than having to make a mount for LEDs and my own dimming circuit