On Thu, Sep 16, 2010 at 10:36 AM, Jon Elson <[email protected]> wrote: > Igor Chudov wrote: >> Jon, siggen is very nifty. Thanks. >> >> I spent some time adjusting Z parameters yesterday. A change of P from >> 300 to 550 has made the servo motor a lot stiffer, and now the best I >> can do by hand, is move the Z axis by about 0.0003" or so. I can live >> with it. >> > Yes, that sounds pretty good for a hobby/home shop machine. Mine is > down in that > region until I overpower the servo amps.
Good to know. >> So, what would you say, does velocity mode provide in extra benefits? >> Precise speed control at low speed? >> > Yes, it theoretically enables the machine to retain smooth motion at > speeds where the > encoder counts are coming in VERY slow. I did some testing WAYYY back > in the > EMC1 days, when I was setting up my own servo amps, back about 1998, > where I was > getting smooth motion down to where the encoder counts were coming in at > 3 per > second. Below that, stick-slip friction became dominant, but I'm not > sure the encoder > counts were the cause. > > I BELIEVE, but can't prove it, that a torque-mode system would not be > able to keep > this smooth motion down that low. You can do some tests, like put an > ultra-fine point > pen in the spindle, and tape paper to a block in the vise. Then program > an arc of as > large a diameter as will fit, or just an arc sector including where an > axis will reverse > direction. This makes the stairsteps pretty visible. If not > stairsteps, then it should be > good enough. My encoders have 1024 counts, or 4096 pulses per revolution. One revolution is 2.5mm table motion. This means that one pulse is .000024 inch or 0.00061 mm per count. It is a little hard to figure out how miscalculations of speed from discrete pulse counts affect positioning, but it may be acceptable enough for what I do. At a speed of 0.1 IPM, for example, the encoder will see 68 pulses per second. I would be surprised to need to move at a slower rate. I will definitely try to scribe a circle at a low speed, it sounds fun. ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
