Steppers & Linear encoders

tommylight wrote: Rod, are you gona be using encoders?

No I won't. I did buy one to experiment with but good encoders are awfully expensive. I thought a better approach was to enable boost only during acceleration/deceleration via a separate component. In a lot of instances, this would be for only a very short period most of the time so the drive could idle once at cruising velocity . That seemed to be more the way Lam suggested how to use the feature.

OK, waiting patiently for the results.

Great info and interested to see where you get with things Rod.

Aciera wrote: I use steppers in closed loop with glass scales on my mill with a 7i76E. Works fine.

Aciera - i note from a post elsewhere that you are using 5um scales like me. Would you be willing to post your hal and ini files? Keen to check my setup/connections and values against another working config. Also interested in any observations on accuracy, tolerances you typically get.

I found Metalmusings build thread as well and have been looking at his setup.

Cheers,
J.

Just to let people know I cracked things. I now have the two MPG encoders on the 7i76 in mode 2 linked up to 5um glass scales on X and Y axis providing closed loop feedback into the stepper PIDs.

Tests are showing following error is typically 0.02mm the vaste bulk of the time when cutting and is within 0.05mm during rapids. Also test cuts of aluminium on this small BF20 mill (G0704 equivalent) look to be within 0.02mm. This includes external cuts and internal pockets. An internal circular pocket was done as a "tough test" with the diameter coming within 0.02mm of target. There were also no signs of backlash or transition marks.

cheers,
James.

Dear James,
thank you very much for pinging your success back to this Forum, this makes your answer to the following question very valuable to this forum.

With your knowledge today, how would you do it "again":
If you would get a new (stiff) machine, having standard lead-bearing-screws on all Axis, and successfully added CNC-Steppers & Optical Linear Encoders on these axis... and hooked them up to your current LinuxCNC hardware.... What procedure did/would you follow today, to get to a working Feedback-loop going, where the encoders are actually the input to LinuxCNC to get to the wanted position ?

I ask you this, as I simply can't find any guidance here, why and what to edit in Linux-CNC from start to end, to get to a basic full-feedback-looped Machine.

Any feedback is very welcome, even if it is a rough one.

Best regards,

Ronald