On Sunday 06 May 2007, Chris Radek wrote: >On Sun, May 06, 2007 at 09:03:19PM -0400, Gene Heskett wrote: >> >* fix constraint violation right after a probing move >> >> I don't believe I hit that one, what might the symptoms be? > >On steppers, a joint following error. The violation was minor so I >doubt it would have been noticed on a servo machine. > No such thing once I got the tuning somewhere near right.
>> >* abort if the probe does not trip before a probing move ends >> >> Now that's going to be a problem, Chris. I have it doing a probe right >> now, that will probably still be running this time tomorrow. In order to >> get the edges of an irregular shaped piece, like the floor plate of my >> deer rifle, it is going to be a total miss for about 10% of the probes. >> If it aborts on a full miss, then my 48 line program will have to be >> broken down into numerous additional subroutines to prevent its ever going >> off the edge of the piece. So this is one item that should somehow be >> selectable so it can be disabled. > >I'm sorry to hear this fix causes you trouble. It may have been a >mistake for me to put it in 2.1.5. > >The danger of not having it is that if an error is not signalled when >your probe doesn't touch anything, you get a reading anyway (the end >of the probe move), even though that's some random point in the air. That's fine as it gives a consistently flat reference surface in the output data. >The RS274NGC authors definitely wanted it to be an error: > >"If the probe does not trip ... an error is signalled." I do not know if its recording the misses or not. After 2 hours of running, and several hundred probes, the filename I gave it is still zero length. So it looks like I won't know if I have a good recording till its done. I'll be a bit put out if its empty. :( As its running now, I only probed deep enough to get the full surface. My probe is flexible enough that it slides off the edge if the point itself misses, I can see it springing as it slides off by about 0.020", still a heck of a lot more accurate than any other way I might have tried to model it. repeatability seems to be about a thou. >http://www.linuxcnc.org/handbook/RS274NGC_3/RS274NGC_33a.html#1001097 That's an older version I think. The one I was pointed at when I asked about some obviously old text in the printout I had of rs-274, and I printed it newly 3 days ago, does not contain that phraseology. It states on the cover page that it is V2.1 User Handbook, dated April 26, 2007. Which are we to use as reference then? >Judging from this and their example uses of finding a hole center, >finding a hole diameter, and testing parallelism in various planes, I >suspect they did not intend/forsee that people would want to use G38.2 >to probe a huge grid of points to digitize a complex shape. As you >know, doing this works pretty badly since you have to go to the max >height for each point. The routine I have running only lifts z about 0.010" off the surfaces maximum height, so the total z motion for this particular job won't exceed 0.125", ever. >John and I have briefly discussed what it would take to allow a much >smarter shape probing, which would march the probe over the shape >with very little extra motion, instead of what we have to do now. Wouldn't that require some sort of a bearing to keep the probe from scratching the finish as it slid along? I'm not saying its not doable, but the probe gets a bit pricier, I might have a $10 bill in this one. Steel tip, polished with rouge to both dull it and reduce the possibility of dimpling the finish. The spring in mine needs about a pound to reach the 0.020" up trip point, so that's quite a heavy push in terms of psi at the point considering its blued finish I'd rather not damage any worse than it is. It was the only one that would fit at Ace Hdwe. >I've added this to the list of discussion topics planned for the >upcoming CNC workshop (June). We may get a chance to work on it if >there's time and interest. One obstacle is that I don't think we have >a probe among us. Dean's little optical gizmo is pretty easy to make, if I get a chance I'll knock out a couple more. I went back to town and bought 3 foot sticks of the tubing, and I've still got 4 opto assemblies. But its not terribly rigid in the xy direction, so the probe points either need to be flatter, or sewing needle sharp, my 95 degree angle tends to slide a bit when its hitting the edge of something away from the point itself. When I get another made, I'll yelp for a shipto address. Ping me occasionally so I don't forget. :-) Humm, I was going to ssh into that box and check progress, but apparently sshd isn't running, connection refused. Grrrr. >Chris Thanks for the thoughtfull reply Chris. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) "When the only tool you have is a hammer, you tend to treat everything as if it were a nail." -- Abraham Maslow ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
