I don't know if you're set up to do this but you could use your shaft encoder for feedback to a drive and your linear encoder for feedback to EMC. That's what my Anilam controls do (one has been replaced with EMC, works great) but they use tach feedback to the drives. The drives are tuned to the motor and I use mostly P gain and a little I from the EMC PC. I can have backlash and the system is still stable though it delays getting in position. Roger N
----- Original Message ----- From: "Kirk Wallace" <[EMAIL PROTECTED]> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Sent: Friday, December 07, 2007 2:30 AM Subject: Re: [Emc-users] Slides, Encoders, and Resolution > On Thu, 2007-12-06 at 12:09 -0800, Kirk Wallace wrote: >> (Dooh, fixed title spelling) >> >> On Thu, 2007-12-06 at 11:43 -0800, Kirk Wallace wrote: >> > 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. >> > > > I jury rigged an encoder to the motor and it tunes fairly well now, > but > now the travel end points are affected by the backlash. I am looking > at > getting the MicroKinetics ballscrew kit. > > http://www.microkinetics.com/convkit.htm (at the bottom of the page) > > which appears to have adjustable double nuts. With zero backlash, it > seems that it shouldn't matter whether I use the linear slide encoder > or > the shaft encoder, though my shaft encoder has much higher resolution. > > -- > 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 ------------------------------------------------------------------------- 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
