On 5 May 2010 15:47, John Kasunich <jmkasun...@fastmail.fm> wrote: > Just because a particular motor works well driving the spindle > in lathe mode does NOT mean it will be even close to good enough > for direct drive positioning.
A good point, I have only been discussing what is technically possible in EMC. I am fairly sure that various lathes do exactly what is being proposed, but how much such spindle drives cost is something I could not even speculate on. This machine does it, it also looks quite expensive :-) http://www.youtube.com/watch?v=JZcFMjLmjZc&feature=related <thinking aloud> I would guess that there is a risk of the flute-frequency setting off oscillations in the controller. For the proposed application (rough-milling cams) the rotary stiffness requirements might not be all that exacting. I suppose in principle, with a fast-enough X axis and enough low-speed spindle torque you can machine cams with a conventional turning operation and spindle-synchronised motion. I think this might be one of those applications where a small-budget proof-of concept might be a good idea, though the problem here is that it might be something where you need the expensive stuff (high torque servo, high-count encoder) to make it work. > Good PID tuning might be able to reduce the steady state error, > but when an individual flute of a spinning end mill applies a > brief force to the axis, the axis will move. Only after it moves > will there be a position error that the PID can use to drive the > axis back to the proper position. I wonder if a Resolver (and high-resolution interface electronics) might be a better bet than an encoder? http://www.analog.com/en/other-products/militaryaerospace/ad2s80a/products/product.html Is a 16-bit converter and claims +/- 2 arcmin resolution. on 50mm diameter material I think that is 0.015mm (0.0005") tangential resolution. Say 4 counts to produce a PID response and it is probably good enough for end-mill roughing a cam with live tooling, but not for some other operations you might think of. (I am imagining the cutter axis at right angles to the spindle axis and on the same plane, the stiffness requirements with the axes parallel strike me as more of a challenge) -- atp ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
