On Saturday 22 November 2008, Andrew Ayre wrote: >Gene Heskett wrote: >> On Saturday 22 November 2008, Andrew Ayre wrote: >>> Jon Elson wrote: >>>> Andrew Ayre wrote: >>>>> Hi, I've been happily generating g-code files and cutting them with >>>>> AXIS. I'm using EMC2 pre-2.2 CVS HEAD. Yes, I know it's old but I have >>>>> everything working and I am reluctant to change it right now as I am >>>>> trying to get Christmas gifts made as quickly as possible. >>>>> >>>>> With a new g-code file I get "Joint 0 Following Error" at the same >>>>> point every time in the file. Line 161 I believe. The g-code file is >>>>> here: >>>>> >>>>> http://files.britishideas.com/public/emc2/jointerror1.ngc >>>>> >>>>> On April 17th, 2007 Chris Radek said this about the error message: >>>>> >>>>> "It means the difference between the commanded position and feedback >>>>> position differ by more than the allowed following error." >>>>> >>>>> I am using a simple, HobbyCNC card with steppers, three axis, no >>>>> feedback. I have backlash compensation set in the emc2 ini file. I have >>>>> cut lots of g-code files without a problem until now. Can anyone give >>>>> me some hints on how to solve this? Is it a problem with the g-code? >>>> >>>> A following error in this case means that the commanded velocity >>>> required more steps/second than the step generator could produce, with >>>> the settings of your system. It may be possible to make the step >>>> generator run faster by decreasing the value of BASE_PERIOD in the >>>> [EMCMOT] section of your .ini file. Warning! If you make this value >>>> too small, your system will freeze up when you start EMC. A quick check >>>> would be to set your feed override to 50% and see if the program gets >>>> past this spot. I didn't see anything near line 161 that looked like a >>>> sudden fast and long move. I do notice some G00 moves at other spots, >>>> which would command the fastest motion permitted by the .ini file >>>> parameters. That would be where I'd expect to see a following error. A >>>> 50% feed override ALSO affects G00 moves, so all motion should slow to >>>> 50%, and it should get past the bad spot. If it is really tripping on a >>>> G00 move, then you need to lower the MAX velocity in your .ini file >>>> (unless speeding up the BASE_PERIOD is possible.) >>> >>> Thanks for the detailed reply. I set the feed override to 44% and it >>> works (slowly), but I would like to better understand this so I can >>> avoid this in the future. >>> >>> I've set the BASE_PERIOD based on the latency test, and it is the >>> maximum my machine can run at. It gives me a max speed of 71.6 IPM. I >>> can't decrease this value, unfortunately. >> >> And why not? All it takes is an editor to change that value in the .ini >> file, it is in (I think) nanoseconds, and a 25% upward increment should >> still work just fine if your limit is 30 ipm. For steppers though, 30 ipm >> is pushing them, and torque at that speed, unless you have lots higher >> voltages available than I, is going to be well below the motors rated >> value. > >I meant decrease the BASE_PERIOD. Sorry if what I wrote was confusing. > >My steppers have a max torque of 305 oz-in at 3A and I am running them >at 2A (36VDC input I believe). Do you know of a formula or graph that >allows me to work out the optimal cutting speed for the most torque? My >machine is quite small - 18" x 12" x 3" cutting area. I assumed the >motors I have are overkill for this size of machine (when cutting wood), >but maybe that is wrong?
Chuckle, bigger than mine. Gantry style? If I had room to play, I cvould be tempted to do one, about an 12x48 work area, with an A axis to turn stock blanks as they art carved. :) As far as overkill, no, its never overkill till the machine can't support the weight of them. :) 30 ipm is going to be down the far side of the torque curve. Particularly if carving wood, whose dust can raise the friction of the movements pretty badly. I've had my micromill seize up and stall at 8 ipm after using it to do a couple dozen 3/8" x 1.5" x .8" deep mortises in cherry. Sure does make neat mortises though when using an 1/8" upcut carbide mill. :) >30 IPM is an arbitrary value that I picked that I didn't feel >comfortable going above. If I knew I could run it faster I would, but >I'm just starting out. One of the problems that pushes the speed up is that the cuttings are part of the bit cooling, they carry away the heat. Cut too thin (on either edge) and the bits get hot too fast. If you are seeing burns, slow the bit rpms down, speed up the move, or replace the bit, its getting dull. >>> The g-code file is supposed to limit the speed to 30 IPM, and you can >>> see this when running the file in AXIS. >>> >>> However I now notice that when the file is running in AXIS the velocity >>> occasionally and only for a split second displays a value of 71.6 IPM. >>> This raises two questions for me: >>> >>> - why would a movement cause the velocity to go beyond the maximum of >>> 30 IPM that I set? Is that a problem with AXIS/EMC2 or the g-code? >> >> What version of emc, and what backlash settings please? > >pre-2.2 CVS HEAD. The backlash settings are: > You may want to update that. Someplace in about that time frame I believe the backlash handling was changed to put them under the control of the MAXVEL and MAX_ACCEL settings, where prior versions did them as fast as possible, which led to following errors at direction reversals for me if the backlash setting exceeded the max error. It also caused lost steps. It doesn't do that now for a while. >X: 0.005375" This could be adjust down I'd think. Wear? >Y: 0.0025" >Z: 0.0003" Head weight is the preload? Not always realistic when pushing on a drill bit to bore a hole. The hole won't be quite as deep as you told emc to do in that case. >The backlash was measured with a dial indicator. > >As I mentioned before, I've cut lots of g-code files without a problem >using the same settings. But I think this g-code file has more small >rapid movements than the others. > >thanks, Andy This isn't iron clad advice of course, but are areas to investigate according to Gene. For whatever that might be worth. :) -- 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) Why does New Jersey have more toxic waste dumps and California have more lawyers? New Jersey had first choice. ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
