mesa7i76e + 7i85s stepper motor + encoder feedback

Good morning everyone ,

My 3-axis xyz milling machine is equipped with stepper motors that work properly.
However, sometimes it happens that the Z axis loses steps due to the weight of the axis.
To improve the situation I added an encoder
to the ball screw.
Now I would like to add feedback to the z axis....
I tried to study the linux cnc documentation, if I understood it I'll highlight the lines of the hal file that I should modify.

net z-pos-fb     <= hm2_7i76e.0.stepgen.02.position-fb ( actual configuration)

net z-pos-fb     <= hm2_7i76e.0.encoder.xx.position (future configuration)

where xx is the encoder number

logically then I will also modify the ini file to scale the encoderAm I on the right path?
Thanks everyone for the help





 

What you suggest there will detect following errors, but will not recover from lost steps.

You probably need to modify the hardware too. (Bigger stepper, lower gearing, closed-loop stepper, pneumatic countrbalance, something else)

Thanks for the suggestion, the motor is a very large 12A, reduced 3:1 and the accelerations are also low.

How should I modify the hal file to also have a recovery of lost steps?

What drives are you using?
The only open loop drives that are capable of actually doing something to compensate for lost steps are Lam Technologies drives, the DS series being the entry level, they have a Boost pin that can be used to send more current (programmable) to motors in case of lost steps/feed error, i did test that and it works properly.
Otherwise, with normal drives if the stepper stalls, sending more steps at the same rate or higher will not help, sending slower rates might help.
Maybe something can be done in hal to stop the stepgen and start it from 0 to try to move again after stall, but i never tried this.

Why not using a pid controller if you already have an encoder,
you can add a pid loop to the hal

thank you meister ,
That's exactly the idea, but how is it configured?
Can you direct me to some specific document?