andy pugh wrote: > On 27 November 2012 20:21, Przemek Klosowski > <przemek.klosow...@gmail.com> wrote: > > >> OK, but there's very little consequence if the engine controls get it >> wrong, correct? it'd just keep turning over and fire on another TDC. >> Whereas rigid tapping would go quite wrong if it was off by a revolution. >> > > No, as long as it is exactly one rev, it's all fine in the case of > rigid tapping. > Not if the tap is buried in the workpiece at the time! This happens every time the tap reaches full depth, the spindle is reversed and the tap is brought out in sync with the thread. If it even looses a couple teeth (depending on tooth count/ rev) it will break the tap or maul the workpiece. If it misses the index pulse (the missing tooth) that is pretty benign, but if there is a loss of one or more teeth at reversal, that would be bad.
My specific concern with this whole scheme is if the reversal happens right over the missing tooth, you CANNOT compute your way out of it by timing alone. It seems impossible to detect the difference between the time between tooth crossings right at reversal and know whether that contained the missing tooth or not. Maybe you can do it by always maintaining the count up/down and knowing when the next tooth is the missing one, but that incurs a jump when you were going forward, say, and the next tooth should be the missing one, and then you detect the first tooth showing the pulse width that indicates the reverse direction. Suddenly, you have to shift the spindle position by two teeth. If the encoder has pretty high resolution, that doesn't represent a lot of degrees, but if it has a fairly low tooth count, then it does. Jon ------------------------------------------------------------------------------ Keep yourself connected to Go Parallel: INSIGHTS What's next for parallel hardware, programming and related areas? Interviews and blogs by thought leaders keep you ahead of the curve. http://goparallel.sourceforge.net _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
