can linuxcnc use easson dro for feedback?
I am trying to decide whether to use steppers or servo's on my mill when I put ball screws on later this year, so I would like to know if linuxcnc can use the signals from the easson dro as position feedback? It would seem a shame to have very accurate position information there and not use it.
If it can then I would guess servo's would be the way to go, but being a complete novice at this, I need all the advice I can get. Price is a big consideration- being retired, there's not a lot of money to throw around- but there is a lot of time available!
I tried searching the forum, but came up blank- though I find it hard to believe that the word "easson" doesn't appear anywhere in nearly 60,000 posts?
Ken.
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I tried searching the forum, but came up blank- though I find it hard to believe that the word "easson" doesn't appear anywhere in nearly 60,000 posts?
I had never heard of Easson before. Newall, Accurite, Mitutoyo etc but not them
However appears a lot of UK stockists now sell their scales and complete kits
The important thing to know about your Easson scales is that they are glass scales outputting a 5 volt TTL Quadrature signal
With that knowledge, there is a post of quite recently that should help you
www.linuxcnc.org/index.php/english/forum...cales?start=20#53438
regards
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these are at least the common pinouts used
you may find other information that may be helpful here
www.yuriystoys.com/p/msp430-launchpad-quadrature-dro.html
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Is this a relatively simple thing to do or is some programming needed?
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now how do I tell it to use the information for position feedback so it is not relying purely on the number of steps it send the motors for correct positioning?
If it were that simple everyone would do it.
With steppers all you will get is a system that knows with greater accuracy when you have lost steps.
Unless the commands are controlled by the actual position relative to desired position,
closed loop does not work.
I am trying to decide whether to use steppers or servo's on my mill
If you use servos, you can have a proper closed loop.
regards
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and quite a bit of scripting files
however using encoders with say a mesa 5i25 /7i76 for steppers or with 7i77 for servo is for the most part painless
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If it were that simple everyone would do it.now how do I tell it to use the information for position feedback so it is not relying purely on the number of steps it send the motors for correct positioning?
With steppers all you will get is a system that knows with greater accuracy when you have lost steps.
Unless the commands are controlled by the actual position relative to desired position,
closed loop does not work.
A possible half-way-house is to use velocity-mode stepgens and a PID loop. Effectively this becomes a system that says "Make steps in the correct direction until I am in the right place on the scales".
The problem is that high-error = high-speed-pulses = low-torque.
As long as the speed is capped to well within the safe range the effect should give accurate position control to the scales. How much this helps depends on how much movement there is in the mechanical chain from the scale to the cutting tool and the workpiece. Slack in the ways and flex in the frame won't be compensated for.
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