Dynomotion

Group: DynoMotion Message: 48 From: m37grady Date: 9/8/2009
Subject: Lead screw comp
with the talk of backlash comp using linear and rotary
encoders I was wondering if you have room in your device
to enable lead screw comp instead
with both encoders and a home switch
you could map the screw for pitch errors
and backlash
the EMC guys have it
as EMC is open source if you wanted you could use their
algorithms here is a description of the EMC comp

> The leadscrew compensation algorithm lets you specify two different
> compensation profiles, one for each direction of travel. The
> difference
> between the two represents the backlash. Using this approach you can
> compensate for a screw that has more backlash near the center where
> the
> wear is bad, and less near the ends where there is less wear.
mike
Group: DynoMotion Message: 51 From: TK Date: 9/8/2009
Subject: Re: Lead screw comp

I would think if your system has glass scales it would be better to use that to close the loop rather than to try to map errors.

 

Our KMotionCNC software supports a 2.5D nonlinear geometric correction table, but it doesn’t allow different tables for different directions.  See:

 

http://dynomotion.com/Help/KMotionCNC/ToolSetupScreen.htm#Geo_File

 

TK

 

 

Group: DynoMotion Message: 53 From: mike Date: 9/17/2009
Subject: Re: Lead screw comp
-
>
> I would think if your system has glass scales it would be better to use that
> to close the loop rather than to try to map errors.

that way you are always chasing the backlash
be ok if I was running with nice new screws with nearly zero backlash
even then new cnc machine tools will have the screws mapped to microns with a laser interferometer
as most of us are using 4th hand old NC machines or cobbled together systems with variable backlash/pitch errors over the travel
and mach not being able do anything but a fixed amount of
backlash comp

with the screw being mapped you are ahead of the backlash
the scales would then only have to eliminate any accumuated backlash
from inaccurate mapping I can buy the Chinese .0002 lin scales for all 3 axis cheaper than I could get one screw rebuilt

could be used without lin scales and mapped with gage blocks
and a .0001 indicator as long as you re homed it occasionally


mike