You don't need a joint at all.  You can just have an encoder
channel that doesn't connect to any joint.  You can then
net encoder.xx.count to your display widget.  You could also
net a button widget to encoder.xx.reset to reset the count.
If you are wanting to scan into a point cloud, you could use
halsampler to capture the x, y, z encoder or stepgen counts
and probe encoder counts to a file.

I used this method to map errors of a stepper leadscrew actuator
with a 1um linear encoder borrowed out of an ancient manual
CMM.

-- Ralph
________________________________________
From: Thaddeus Waldner [[email protected]]
Sent: Thursday, February 24, 2022 8:43 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Auxiliary axis DRO only

CAUTION: This email originated from outside the Walla Walla University email 
system.


> That is likely because motion is aware its moving, but there is no
> feedback of a signal showing that it has moved to show motion it is
> following orders.  I have a pair of 100 ppr dials on my sheldons
> replacement apron, which I use to drive it since there are no cranks on
> mine, motors having replaced the cranks.  And I just spent 20 mins
> studying my hal file to find that coupling, but that hal file is now
> several years old, and apparently not well enough commented to let me get
> my ancient head back into what I was thinking back then. At 87, can I
> plead oldtimers?

I suspect you connected them as MPGs, as that would be the most logical thing 
to do. I don’t think I want MPGs because the axis need to move during NC moves.

Perhaps if I were more clear as to what the purpose is of this axis …

I plan to use this axis with the linuxCNC probe features to automatically 
record the profile of a surface as the Y axis moves across that surface. The 
probe will have a roller on the end, which will be held in contact of the 
surface by gravity or a spring.

At this point, I am trying to find the correct hook to feed the 
position/velocity from the encoder into the joint, as Gene suggested, to get 
rid of the following error. Do I even need the stepgen? Can I have a joint 
without a motor? Can I configure the joint to ignore the following error and 
still get good position feedback?

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