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





 

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?

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?

Hi Raban,
not realy, i can show you my related part of the .hal
but don't know how to do this with mesa and how to do the real PID-tuning

```
setp pid.0.Pgain [JOINT_0]P
setp pid.0.Igain [JOINT_0]I
setp pid.0.Dgain [JOINT_0]D
setp pid.0.bias [JOINT_0]BIAS
setp pid.0.FF0 [JOINT_0]FF0
setp pid.0.FF1 [JOINT_0]FF1
setp pid.0.FF2 [JOINT_0]FF2
setp pid.0.deadband [JOINT_0]DEADBAND
setp pid.0.maxoutput [JOINT_0]MAXOUTPUT
setp rio.stepdir15.velocity-scale [JOINT_0]SCALE_OUT
setp rio.stepdir15.position-scale [JOINT_0]SCALE_IN
net j0vel-cmd <= pid.0.output => rio.stepdir15.velocity
net j0pos-cmd <= joint.0.motor-pos-cmd => pid.0.command
net j0pos-fb <= rio.stepdir15.position => joint.0.motor-pos-fb
net j0pos-fb => pid.0.feedback
net j0enable <= joint.0.amp-enable-out => rio.stepdir15.enable
net j0enable => pid.0.enable

```

```
[JOINT_0]
# stepdir15
P = 50.0
I = 0.0
D = 0.0
BIAS = 0.0
FF0 = 0.0
FF1 = 0.0
FF2 = 0.0
DEADBAND = 0.01
MAXOUTPUT = 300
```

Raban wrote:

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

If you use pncconf to create the original hal/ini files, a PID loop will already be setup for each joint.
Changing the joint feedback source and tuning parameters are needed for encoder feedback.
(along with getting the encoder feedback in the correct direction and scaled properly)

Tuning can be done live using the calibrate menu.

_BUT_ as others have mentioned, simple adding encoders to a step/dir system will not solve a
missed step issue (though it can halt the system if this occurs) This is because when a missed
step occurs, the drive had insufficient torque and skipped one or more pole positions (1/50th of a turn)
Having the controller simply add more steps will not fix this (and least not without slowing the motion
significantly so the torque becomes higher)

Thanks PCW, it's very clear.
the goal is for the milling machine to stop if for some reason the z axis stalls.
otherwise, a rapid crossing with the z in the wrong position can cause a disaster