I got the first pass on my Bridgeport X axis working and I am having trouble with tuning. I am using a brushed DC motor with a 3:1 belt ratio between the motor and ballscrew. The motor is driven by a Pico PWM amp and controlled by a Pico UPC and EMC 2.1.7. Because a glass slide was already mounted, I used it for my encoder. My primary concern was to do a sanity check on the motor because it is a cheap treadmill motor and not a true servo motor. The motor seems to have no trouble driving the axis at my theoretical rapid of 390"/minute or 6.5"/second. My next consideration is the low speed performance, which seems much more dependent on the system tuning than just raw system power. Since I have a similar system on my lathe, I started with its tuning parameters. I need to post pictures and Halscope plots but some general issues came to mind.
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? I seem to have a consistent (non-self energizing) oscillation across a wide P range (30 to 280). I am wondering, is this is due to the .002" screw backlash, or this backlash being on the motor side of the encoder, the relatively low encoder (slide) resolution or all of the above? Which has the greater influence? The end position always seems to come to within an encoder count (0.0005") but the rate seems to vary widely during the traverse. Anyway, I need to document and post better information, but if anyone has any thoughts, I'd appreciate hearing them. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- 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
