Sorry, but the pawl is essential to how it operates. The counter rotation is limited by the pawl to the exact position where the tool should rest. These tool turrets will only work with the spindle rotating in the normal direction, pushing the tool back against the pawl, but they do work well for such a simple design. They were used by Southbend, Emco Maier, and many others.
Steve Stallings > -----Original Message----- > From: Stuart Stevenson [mailto:stus...@gmail.com] > Sent: Sunday, July 25, 2010 6:33 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Lathe ATC integration > > I don't know the physical requirements. If the pawl is not > needed for rigidity but is only used for positioning then > with an encoder the pawl can be removed. > > On Sun, Jul 25, 2010 at 5:10 PM, Chris Radek > <ch...@timeguy.com> wrote: > > > On Sun, Jul 25, 2010 at 06:44:31PM +0100, John Prentice wrote: > > > > > For an 8 position turret you have a ratchet with 8 teeth and a > > spring-loaded > > > pawl. Assuming you know where you are now (say tool 2) and each > > > click > > needs > > > 100 steps. > > > > > > To move to tool 5 you output 330 steps. You now know that > ratchet is > > about > > > 30 steps after a "click". Send 40 reverse steps. The > stepper stalls, > > > as > > you > > > say, but you are in the known position for tool 5. Next > move to say > > > tool > > 6 > > > just outputs 130 steps forward and 40 back. > > > > OK, that's kind of what I was afraid of. Sounds like you need a > > position mode stepgen, so you can issue the particular > number of steps > > you want. But when you are done with your +130 and -40, > your position > > mode stepgen doesn't know the position anymore because the > motor has > > stalled. > > > > The position commands for the next tool change would then > have to be > > slipped by 10 steps worth of position to make up for the lossage > > (which you assume is 10 but probably isn't exactly.) > > > > I don't see a good way to do this with the stock stepgen. Maybe a > > totally different component is needed. You still have the > problem of > > not knowing what position it's in when you start up (or > even if it's > > in a valid position). If it starts between positions, it won't > > correct itself. > > > > Now let me continue on with what I'd do in this position: > > > > If you add an encoder with index, all these problems are > solved. Upon > > startup you can seek the index position. Once you have > done that, you > > have exact position information forever, no matter what the stepper > > does. You can use velocity mode stepgen then, and you know exactly > > when (at what position) you have to reverse to find the pawl. You > > know whether the tool change has completed successfully because the > > turret will be in the correct position. > > > > Then the tool change procedure would look like: > > > > 1. If you have not yet found index this run, do that, then > continue on > > 2. Turn forward until the reversal position for the > requested tool 3. > > Turn backward until the lock position for the requested > tool 4. Tell > > stepgen to stop 5. If still at the lock position, report > that the tool > > change is OK > > > > Note that between 4 and 5, the stepgen will decelerate to a > stop, so > > extra steps will be issued. If the pawl didn't lock for > some reason, > > step 5 will fail and you won't go on to crash with an > unlocked turret. > > > > While you can manage without feedback, I think adding it > would change > > this troubled design into a system that works reliably and safely. > > > > After typing all that I see that neither configuration is > going to be > > very simple to set up. > > > > Chris > > > > > > > ---------------------------------------------------------------------- > > -------- This SF.net email is sponsored by Sprint What will you do > > first with EVO, the first 4G phone? > > Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > -- > dos centavos > -------------------------------------------------------------- > ---------------- > This SF.net email is sponsored by Sprint What will you do > first with EVO, the first 4G phone? > Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://ad.doubleclick.net/clk;226879339;13503038;l? http://clk.atdmt.com/CRS/go/247765532/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
