I am a control freak - and this helps my affliction... I don't what to assume that the step/dir servo is following the path - I want to know for sure. IIRC atleast the older gecko drives won't error until 128 encoder counts. Yikes! I agree with everything said below... :)
Also - the buying cheap ebay stuff with generic drives (amc, copley and such) makes this hobby pretty inexpensive for the quality system you can build. On 1/25/2017 6:03 AM, Les Newell wrote: > Using analog should be more accurate. With step/dir the drive has to > estimate the commanded speed and position based on the steps. LCNC has > much more accurate commanded position and velocity figures. It can also > use tricks like feed forward. > > IMHO using step/dir negates some of the advantages of using servos. If > your machine is moved with the drives off LCNC has no way of detecting > this. That means you have to home each time you disable the drives. I > have also found setting up and fault finding step/dir servo systems is > more difficult than if the loop is in LCNC. For example the scope > function in LCNC beats every servo drive equivalent I have used. Even a > little thing like an error message on the screen saying 'Following error > on X axis' is a lot clearer than a drive flashing 'E42' when you can't > find the drive manual. Having the loop in LCNC also allows you to do > tricks like varying the following error limit depending on what you are > doing. For instance on my lathe I have very tight limits for when the > machine is stationary but looser limits when it is moving. This allows > it to detect problems such as a broken encoder cable very quickly. As I > often use the machine in combined CNC/manual mode (it has two jog wheels > in place of the traditional hand wheels) I am often working a lot closer > to the machine than you would in pure CNC mode so it is very important > to detect a runaway quickly. > > Les > > On 25/01/2017 11:17, Andrew wrote: >> Nice! The ferror might be larger when machining, though. >> Since we're talking about following error, one question has been puzzling >> me for some time. >> Say, we have some (pretty advanced) servo drives like Yaskawa or similar, >> with analog and step/dir input, so we can connect them either way (to 7i76 >> or 7i77). What is the best way to minimise ferror - use LinuxCNC pid with >> analog control or servo drive's internal pid with step/dir? I guess some >> cheaper Chinese servos can be tuned better with LinuxCNC, but what about >> more advanced servo drives like Sigma 5 or 7? > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
