Schaublin 125-CNC retrofit.

common on servo drives is analog control, because you do usually an velocity control. means the position control loop is extern. The drives does only current and velocity loop.

Many drives can do positioning at there own, then step/dir input makes sence. normaly this is not used in cnc control. because in position mode the drive normaly has its own accel and deccel control. This is usefull for stand alone axis oder handling devices.

In the CNC World we need syncronous axis for interpolation use. So if you want to use the drives position loop, something is need like an externclock that all drives are synced and know exactly at which time of the task they have to accept your commanded postion.

I think there exists drives out there which can interpolate the speed command from an step/dir input, but this would not be the common way. For accurancy, precision and fast reaction an well tuned analog input would always be the better choise.

But if you decide to take new AC Servos and drives, i would take a look at an bus controlled drive like Ethercat.... No interface needed, only cat cable between pc and drives, no stres with analog noise or dc offset, no need to wire encoder signals back to the control, no control wires need, no space waste for breakout boards etc...

That is an excellent explanation thanks. I watched old Tony's used of Leadshine ELP EC750Z ethercat drivers, and noted that each driver offered a bit of extra I/O.

Is Ethercat fully supported by LinuxCNC? I haven't really followed that. I looked at the wiki and it still mentioned that it is under development. I would still expect to need some Mesa hardware for the user module, MPG's etc.

Mark

oh, there are answers in beetween....

Step/dir or analog or bus has nothing to do with tuning!

Tuning you position control is always the same. on a digital (bus system) it is easier because you define an controll window then send a command 1000 and the drives does 1000. At analog control you additionally have to do with Voltage calibration or dc offset.

If there people outside who tells that they need no tuning for step/dir control. then they don'T know what there talking about... Because with no need for tuning the drive does the position, and at an interpolation path the path following would be horrible.

linuxcnc-ethercat is fully stable working. Sascha (the developer/programmer) , myself and many others i know using this in industrial projects.....

It is not offically part of linuxcnc, but behaves as every other external hardware driver...

back then, when this was brand new (approx 10 years ago.. time for anniversary party), there have been discussions on the mailing lists about integration and sometime saschi lost lust to beg again...

That’s good to know for future projects. I was considering it but lost track and got confused. I saw TOT use ethercat for his Maho conversion and thought this would be handy but was not sure If I could get it running with LinuxCNC.
In the End I sticked to Analog Servo drives cause this is what I have already done.

anfänger wrote: Most prefer Step/Dir to avoid tuning.....and you can tune without the servos actual attached to the machine.

You should still tune your servos with the machines installed, whether you go step/dir or analogue 0-10V. There seems to be a myth that step/dir somehow works optimally regardless of what you attach to it. The default settings may be generally stable for most applications but that simply tells you that you have a suboptimal setup unless you take the time to tune the response.