Camera alignment system

[carlosfandango]

Dear All, I haven't posted for a long time on the forum although I am a regular 'lurker'. I'm posting up something I've tried over the past couple of days - I've no idea if anyone has already done this before (wouldn't be surprised if they had) or if it's 'old hat' in some way, but I couldn't find anything after a quick search. So, apologies if I'm treading old ground here.

I built my CNC a couple of years ago with a HUGE amount of help from this forum (thankyou, thankyou everyone), and the machine has undergone a number of revisions since then. Mainly, to stop it leaking coolant all over the floor of my workshop(!), but also to increase stiffness etc. I use it for many different things, personal and commercial, and it's now settled quite nicely into a production tool for me.

BUT - there always has to be a but - I've always had problems with alignment of one sort or another. Most two-sided machining issues can be solved with appropriate fixtures of course, and I have used this method quite sucessfully. The problems come from what happens if the fixture is moved and then replaced, finding a reliable machine zero position, etc. To try and solve this I purchased a laser alignment tool, which fits in the spindle. This rather expensive piece of gear ended up being somewhat useless, as the laser was not concentric with the part that fitted in the spindle, and despite having adjustment capability, could not be made so. After an extensive analysis of the device I complained, got a replacement which was the same, and - eventually - got refunded. I still have the laser, but it's not really of much use.

So, disappointed by this, I considered other methods of alignment. Over the past weekend I thought 'how about using a camera?'. That's how I came to build the unit I show here. It's basically a miniature security camera in a sealed aluminium housing with an acrylic lens. This attaches to my mill controller PC via a WinTV card from Hauppage. Using some free software, it's possible to overlay an image on the camera view - that's what you can see in some of these images. Any image could be used, but I'm using a cross with some concentric circles here.

Using a pointed tool such as engraving bit, and after ensuring that the camera is parallel to the spindle of course (important! Use a mirror until the camera's lens is centred on the cross in the image), I machined a small pinpoint in a workpiece. Then I moved the pinpoint to the centre of the cross in the image, and made a note of the offset. Testing shows that [using the kit I have here - and it was all lying around my house, by the way, I didn't buy anything special] I can achieve positional accuracies of around 0.1mm. I don't think that's too bad for my needs, but this could no doubt be considerably improved with better equipment / narrower field of view.

Once the offset is obtained, this can be used to find any position on any fixture or workpiece, a desired position, such as the workpiece centre, is then very simply obtained. Because I placed the camera somewhat arbitrarily the offset is quite stupid, something like -105.6 / -20.9 (mm) but again this could be made a proper whole number of units by positioning the camera using vernier adjustment or similar.

Anyway, that's it. The software I used is called ManyCam and is really designed to allow you to attach wigs to your image using a webcam (ha ha), but it does this job quite nicely. I'm on the lookout for something more scientific though, if anyone knows of anything.

-CF

[ozzie34231]

Hi Carlos,
At one time there was much discussion of this system on the Mach 3 group. In fact Mach 3 has the facility to put the image right on its own window, without added software, including cross hairs.
The offset can be taken care of by writing a simple VB macro and attaching the macro to a screen button,so it really doesn't matter how weird the offset numbers are.
There are also systems that combine lasers and a camera.
As you already said the results depend on how much you are willing to spend on the "stuff".
For me it seems a better approach to use Mach 3 's probe facility, G31 I think. There has been quite a discussion of it, I think somewhere on this site. I'll try to find it for you. With some simple probes that you can cobble yourself for no money, you can obtain near "dead on" accuracy for edges, centering over a point or feature, centering within an existing hole, and even tool height.
Ozzie

[ozzie34231]

Again Carlos,
I think this will take you to the probe discussion.
http://www.cnczone.com/forums/showthread.php?t=56079

Don't be put off by the need to write some simple VB. nearly all you need is right there in this discussion.
Ozzie

[carlosfandango]

Originally Posted by ozzie34231 Hi Carlos, At one time there was much discussion of this system on the Mach 3 group. In fact Mach 3 has the facility to put the image right on its own window, without added software, including cross hairs. The offset can be taken care of by writing a simple VB macro and attaching the macro to a screen button,so it really doesn't matter how weird the offset numbers are. There are also systems that combine lasers and a camera. As you already said the results depend on how much you are willing to spend on the "stuff". For me it seems a better approach to use Mach 3 's probe facility, G31 I think. There has been quite a discussion of it, I think somewhere on this site. I'll try to find it for you. With some simple probes that you can cobble yourself for no money, you can obtain near "dead on" accuracy for edges, centering over a point or feature, centering within an existing hole, and even tool height. Ozzie

Hi Ozzie

I did find a few references to similar things after I'd posted this, including a link to a camera installed in a spindle collet. It hardly surprises me that it has been done previously, as it seems like an obvious approach to the problem. Still, it might be interesting to anyone considering doing something similar, as it plainly works well and (in my case) effectively cost nothing. I think even buying all of the same equipment new today would only cost $100 or so.

I didn't know that Mach3 could handle the video in any way - I'll certainly be looking into that, but thanks greatly for the link to the thread concerning the probe method. Mach3 does seem to have some amazing capabilities, and I've only really scratched the surface with it despite using it for a couple of years! Hats off to those guys.

-CF