Hi again Thanks for the various links and info, I will have to sit down and try to get my head around them and work out the best strategy
John and Steve are correct about the way it operates. It is a Boxford 240F and really it does not matter whether the motor loses steps when locking back. The important thing is to know where the ATC is, ie locked back against a pawl on tool no X, not where the motor is. The holding torque of the stepper is more than enough to ensure the ATC does not move once up against the pawl. In Mach, I just set the tool number up to the current tool at startup. Then the macro moved x amount for each tool position and having reached the required one, it moved back y amount to lock back against the pawl. This worked fine, especially as the distance between each tool is not even, from cutting tool to drill is slightly shorter than drill to tool. Odd to even moves were one amount and even to odd another. 360 degrees divided by 8 would have been too easy! I could put an indexing switch by tool 1 and 'home' the ATC at startup. This is the arrangement it had originally with a Fanuc control. However that proximity switch and just about every other bit of low voltage stuff was burnt out, the control had suffered a power outrage. Does EMC store the current tool number somewhere that can be read and written to, or will I have to implement that? Thanks again, I'll see what I can come up with. regards ArcEye > > I admit that I don't quite see how these tool changers are supposed to > > work. When the stepper backs up against the stop, doesn't it stall > > and lose position? Is there some kind of feedback available? When > > you start up, how do you know what position it's in? > > > > I have never seen a machine with a tool changer that operates like > > this. > > > Boxford in UK used this for small and medium sized changers. 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. John Prentice 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 ------------------------------------------------------------------------------ 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
