Preparation for the self-construction of a carousel changer

I have added an additional "U" axis to my sim, as Joint 4.
I can also bring the U axis home.

When I move it, nothing changes in the preview at U, only DTG counts down the path. The preview moves the travel of the X axis!
I hope I could express myself understandably!

I think that is not what I want.
I want to have an independent axis, which has nothing to do with the X axis! only that it moves in the same plane, it should move the changer.

 

When I move the U axis I always get the error "joint 4 following error".
no matter what I set in the ini!

ini setting:
[AXIS_U]
MAX_VELOCITY = 125
MAX_ACCELERATION = 150
MIN_LIMIT = -0.001
MAX_LIMIT = 500

[JOINT_4]
TYPE = LINEAR
HOME = 0.0
MIN_LIMIT = -0.001
MAX_LIMIT = 500
MAX_VELOCITY = 125.0
MAX_ACCELERATION = 150.0
STEPGEN_MAXVEL = 62.5
STEPGEN_MAXACCEL = 937.5
SCALE = 80
FERROR = 1
MIN_FERROR = .25
HOME_OFFSET = 0
HOME_SEQUENCE = 2

The same settings I have but with the other axes also and there is no problem!
Could this be an error in the simulation in connection with the u axis?

Geometry is:
KINEMATICS = trivkins coordinates=XYZYU kinstype=BOTH

So the missing entries in the Hal I have now made and the error is gone ...

I have also entered the geometry in the [DISPLAY] section
GEOMETRY = X Y Z
Unfortunately the U axis still moves when I move the U axis.
I have made two pictures.
Once with U = 120 moved and once with U =0
 
 

I have made a sketch so that I can better explain my project.

I have a portal milling machine with X YY Z

I want to be able to move the carousel changer on an axis parallel to X!
In the sketch as axis U drawn.

 

It is not necessary that the U axis moves back to 0.

Is there another possibility to integrate an independent axis which I can move with a G-code command?
It does not have to be displayed visually!