On Thu, 6 Dec 2007, Kirk Wallace wrote: > Date: Thu, 06 Dec 2007 11:43:27 -0800 > From: Kirk Wallace <[EMAIL PROTECTED]> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: [Emc-users] Slides, Endoders and Resulotion > > 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? >
One way is to use dual feedback, Dont know if EMC supports this or not. > 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? I would say the backlash would be the major source of the oscillation. Even with dual feedback, It would be problematic to prevent 'hunting' . I guess it would be simpler to use a rotary encoder and have EMC do the backlash compensation. What is your deadzone? > > 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 > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------- 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
