John Kasunich wrote: > > > It sounds like Brian already has a fairly good idea of the > flow of positions through the motion controller, but to help > clarify things, take a look at > http://linuxcnc.org/docs/2.2/html/code_Code_Notes.html#r3_2 > > Thank you John, I was looking for this!
<snip> OK, I am answering ahead of Brian, but I do believe you have the machine setup and wanted features correct. > In CNC mode (stepper drives enabled), you want it to: > > 1) display where the table actually is, as measured by > the linear scale > This is trivial, assuming the encoder is accurate. > 2) move the table exactly where it is told to move, > in spite of backlash and screw error > Screw error should just be canceled out by the positioning loop, leaving backlash as the sole issue. > In manual mode (stepper drives disabled), you want it to: > > 3) display where the table actually is, as measured by > the linear scale > Again, trivial. > 4) allow you to turn the cranks to move the table > Of course. > And finally, you want to be able to: > > 5) transition between manual and CNC modes without > re-homing or moving during a transition > Should be no problem. So, the only thing that could be a problem is backlash. And, the fact that the backlash varies from spot to spot may cause trouble using the single backlash offset value. We still don't know how much backlash Brian's machine has. If it is .001" it may not be much of a concern, of it is .015" then it would be a disaster. I still think that one way or other, fixing the backlash has to be the best approach. I still believe the whole thrust of this debacle is that Brian feels that using the error comp table with different values for left and right will totally resolve the backlash issue in software, and that it can only work in open-loop mode. I sort of see the argument about how it only works in open loop, as adding the correction to the already very accurate linear scale throws positioning off to fix backlash. But, I feel STRONGLY, this is a complete misunderstanding of the whole SYSTEM, and thinking that you can fix backlash in software is a major fallacy. We have certainly hashed this over before, and I suspect you agree, John, on that one. What Brian is trying to do would work on a positioning-only system, ie. for drilling holes, but it won't work for milling, the backlash will seriously get in the way. Now, we have to convince Brian that he is following a mistaken notion. (Without sounding like "We know better than you, and we're not listening LA LA LA!") Jon ------------------------------------------------------------------------------ This SF.net email is sponsored by Make an app they can't live without Enter the BlackBerry Developer Challenge http://p.sf.net/sfu/RIM-dev2dev _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
