[ahmed4040]

Dears

We are trying to install a liner scale to X axis to improve its accuracy. (boring machine)
After editing the below parameters, we got a strange problem which is as follow:

the motor of X axis move backward 0.08 mm after reaching the desired position (suppose that we need to move 100.00 mm, so X axis goes to 100.00 mm then wait for 3 seconds then go back (-0.08 mm), so the final position become 99.92 mm.(but CNC position screen shows 100.00 mm) this action happen in all modes (MPG, JOG, MDI .... etc) (video attached)

the machine is equipped with reducer (X axis ball screw is not directly coupled to X axis motor, BUT, the machine tool builder is using a belt which connecting between ball screw and servo motor) (reduction ratio is 1/3)

the problem reason 100% sure not a mechanical problem because when we restore the original parameters, this backward movement does not happen.

The parameters we changed was:

MP 1815 from 00110000 to 00000010
MP 1820 from 20 to 2
MP 1821 from 100000 to 12000
MP 1905 from 00000000 to 01000000
MP 1936 from 0 to 1
MP 2024 from 12500 to 3300
MP 2085 from 30 to 1

* controller is Fanuc 0IMD
* Pulse coder type : Beta i A 128 "A860-2020-T301" "photo attached"
* linear scale brand " NEWALL - SHG-AF series"
* linear scale resolution is 0.001mm
* gear reduction ratio is 1/3

We need to know why the motor moves backward that distance equal to 0.08 mm when linear scale parameter is active.

And how to fix this problem ??

Thank you all in advance

[guhl]

didn't see your parameters
may be backlash compensation still active?

[underthetire]

Or could be a value other than zero in drift comp.

Sent from my SM-T813 using Tapatalk

[ahmed4040]

Dears ..

All backlash was set to "0"

and about drift comp. i do not know this function!!

is that function could be enable or disable? what its parameter number and i will see its value

[guhl]

I think drift compensation only being used for CNC with analogue drives
what is showed in servo error register? Seemingly 800 or 801 register in diagnostics

[zavateandu]

Dears ..

All backlash was set to "0"

and about drift comp. i do not know this function!!

is that function could be enable or disable? what its parameter number and i will see its value

did you try in the other direction too?is the same?
Go in the middle of the stroke and go 50mm one direction and 50mm other direction.is the same amount 0.08mm?

[spark-el]

Try a setting of "1" for CMR, para. 1820.

[ahmed4040]

yes same in the two direction

[ahmed4040]

no drift compensation in this controller

[ahmed4040]

Try a setting of "1" for CMR, para. 1820.

same results .... error 0.08mm

[guhl]

same results .... error 0.08mm

what do you see in error registers?

[ahmed4040]

what do you see in error registers?

what is error register?

[hanermo]

I suspect it is 99% likely a mechanical problem ..
semi-adjusted out via sw settings, in some cases.

Under load, a ballscrew is == like a spring and twists = tensions.
Once relaxed, it springs back.
The same applies to belts, screw mounts, etc.

This would be easy to test.
Install encoders on both ends of screw with a simple readout.
Add 2-3 digital dtis, of 0.001 mm resolution, to bs mounts, yoke, endpoint.

Repeat the same operation.
Let us know the results.
It is 99% likely you will immediately see one, or more, errors in various mechanical parts..
and 98% likely You can fix them relatively easily and cheaply after that.

Never change many parameters at once.
Always test before and after, on a suspected issue, for repetition.

There are endless possibilities for *why* the error happens ... but only by measuring one-at-a-time or several-at-once, can you definitely fix the actual errors.
Once You really *know* the errors, the fixes can usually be 20$ in parts and 2 hours of work in a practical non-factory manner.

Tension screws/mounts, add shims to mounts, or nuts, or ballnuts, or bearings, fix pulleys or belts, etc.
Be very careful with belts and pulleys.
Timing belts should be (very) tight .. but too tight will hurt/break the servos.

[guhl]

what is error register?

System screen -> W.DGNS

it shows position deviation (error)