On Thu, 2007-12-06 at 11:43 -0800, Kirk Wallace wrote: > Glass slides do not seem to be recommended for CNC applications. Could > someone remind me why? I would think for positioning accuracy you would > want as little as possible between the tool and the mechanism doing the > position measuring. On the other hand for motor control, you would want > as little as possible between the motor shaft position and the > controller. Is there a way to cater to both?
The one thing you don't want to do with a glass scale into the EMC is add backlash compensation. As long as your axis has no mechanical backlash you should be able to tune to it. What the backlash comp does is ignore a few encoder pulses assuming that they are inside the range of backlash. Since the scale does not move during any mechanical lash the comp is all wrong. The motor winds up then finally pushes the scale and the final position is off by the amount of comp. With any mechanical lash the motor winds up while seeing no pulses and then when it sees pulses it tries to stop. Any DC motor worth it's salt will hunt between adjacent pulses so the motor will always be winding up then reversing. This effect is much worse with some lash and linear scales. You can not do it with the PICO system but an encoder on the motor connected to a commercial amp will fix hunting and a proper velocity control loop. A linear scale to the EMC would nicely close the position loop. HTH Rayh ------------------------------------------------------------------------- SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
