Dave Engvall wrote: > Hi, > > It is indeed possible to use linear scales with emc. With backlash > they do not tune as well as encoders on the > ballscrew. If the ballscrews are very tight the performance should be > excellent. Recently there was a proposal by someone on the list > (JMK?) to use encoders on the ballscrew/servo motor for velocity and > rough positioning and then use the linear scale to drive final > position. AFIK there is no software at present to do implement this > but it is certainly a cute idea. I believe you could probably mock this up with HAL components (possibly might need to add a new math function along the way, but the set of components is getting quite robust) to merge the two encoder inputs. The math shouldn't be very complex.
But, a caution: Knowing position via the glass scales doesn't eliminate the backlash problem. The real problem is that the position of the table is not constrained in both directions by the servo. it is only constrained in one direction at a time, and the motor cannot hop from one side of the backlash to the other instantly, therefore cutting forces and inertia can flip it from one side to the other faster than the motor can compensate. This can lead to messed-up parts, broken tools and general foul language around the shop. So, don't think the glass scales are some kind of panacea that allows you to do precision work with sloppy leadscrews. Jon ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
