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
