On Saturday, June 09, 2012 09:23:07 AM John Thornton did opine: > John, > > Do you know if the same algorithm is used for G76? > > Thanks > John > I would have to assume so since I was using G76 when I made the discovery.
Re-reading this many times, I may have come up with a solution of sorts though. This assumes that the backlash is at least consistent, and that sufficient air is allowed for. Backlash moves would still be at the stepgen maxaccel and if lots of backlash, you would still hear the motor overspeed a bit at the peak of the backlash move. I have managed to reduce the backlash enough that I wasn't hearing that overspeed "gwow" at z start yesterday. Here is my thought experiment: Rather than assume a lagging index angle at the synch point, why not do that same math, but use it to advance the start of motion to be that same lag value, but used to issue the start motion at that calculated angle in front of the _next_ index pulse, maintaining the phase at effectively zero for all speeds at the time expense of using 2 index pulse periods, 2 revs of the spindle to get started for each pass. Or has this approach already been explored and turned down in the back room for other perfectly valid reasons? Chris? > On 6/8/2012 12:56 PM, John Kasunich wrote: > > On Fri, Jun 8, 2012, at 09:20 AM, gene heskett wrote: > > I first observed this problem on my lathe a few months > > after G33 was added. I could hear strange noises as the > > motor first accelerated to higher than the proper speed, > > then decelerated again. I also got bad threads on the > > end of my part, because the sync process was using a lot > > more Z distance than it should. I described the problem > > to Chris Radek (who implemented G33) and he worked out > > the following fix, which is in there now: > > > > At the beginning of each G33 pass, LinuxCNC uses the spindle > > speed and the machine limits to calculate how long it will > > take Z to accelerate, and determines how many degrees the > > spindle will rotate during that time. It then adds that > > angle to the index position and computes the Z position > > using the corrected spindle angle. That means that Z will > > reach the correct position just as it finishes accelerating > > to the proper speed, and can immediately begin cutting a > > good thread. Z will never have to move faster than you > > would expect given the spindle speed and thread pitch. > > > > The downside of this fix is that the offset is different > > if the spindle speed is different. I was worried about > > that at the time, and argued with Chris about it. But > > I couldn't come up with a better way to solve the problem. > > It has been at three or four years now (maybe longer?), > > and this is the first time someone has been bitten by > > this particular behavior, so I think Chris was right. > > ------------------------------------------------------------------------ > ------ Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. > Discussions will include endpoint security, mobile security and the > latest in malware threats. > http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users 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) My web page: <http://coyoteden.dyndns-free.com:85/gene> Dealing with failure is easy: Work hard to improve. Success is also easy to handle: You've solved the wrong problem. Work hard to improve. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
