Re: [Emc-users] Fwd: backlash compensation

[Jeff Epler]

On Fri, Oct 30, 2015 at 11:03:30PM -0400, Tom Easterday wrote:
> Thanks Jeff.  I was using a dial indicator and moving back and forth
> before and after setting "BACKLASH = 0.0005" and found no difference.  I
> think I was homed but will verify next time I am at the machine and will
> also try your method to see what the hal pins believe.  Is the "+" and
> "-" optional?
> -Tom

"+" denotes what I added, and "-" denotes what I removed:
> >   [AXIS_0]
> >   ...
> >   -BACKLASH = 0.000
> >   +BACKLASH = 0.100
> > 

so I removed the line that said
BACKLASH = 0.000
and added the one that said
BACKLASH = 0.100
or in other terms, changed 0.000 to 0.100.

This is a typical way that changes are denoted by software developers,
and it slipped into my e-mail without me considering my audience well enough.

(you're not putting in the line that says "..." either)

Jeff

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Re: [Emc-users] Fwd: backlash compensation

[Gene Heskett]

On Friday 30 October 2015 21:33:34 andy pugh wrote:

> On 31 October 2015 at 00:58, Tom Easterday  wrote:
> > Can anyone verify that backlash compensation has no effect for
> > jogging or MDI commands in 2.7.1?
>
> Just so that you don't think you are being ignored, I don't know, and
> I don't understand the question.

I do Andy, but the only 2.7.1 install in these here parts is the axis.sim 
on this machine.  The other 3 machine movers are all a 2.80-pre, and it 
appears to be working as I just went thru the g0704, adjusting the 
backlash comp until I got as exactly as close to a 5 thou jog in 
alternate directions as I could get, then played with scale's until 1" 
was 1" on a well aligned dial.

I don't have measuring tools to get any closer than that. the .ini file 
backlash entries are all above 2 thou even with these cheap Chinese ball 
screws.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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[Emc-users] Fwd: backlash compensation

[Tom Easterday]

Can anyone verify that backlash compensation has no effect for jogging or MDI 
commands in 2.7.1?
-Tom


Begin forwarded message:

> From: Tom Easterday 
> Date: October 29, 2015 at 2:10:50 PM EDT
> To: "Enhanced Machine Controller (EMC)" 
> Subject: [Emc-users] backlash compensation
> Reply-To: "Enhanced Machine Controller \(EMC\)" 
> 
> 
> I have 0.0005” of backlash in my Y axis.  I added a parameter to the Y-axis 
> section of my .ini file: BACKLASH = 0.0005 (also tried 0.001).  I also 
> increased my STEPGEN_MAXVEL to 25% more than my MAXVEL, and STEPGEN_MAXACCEL 
> to 100% more than my MAXACCEL.  This doesn’t seem to have any affect on 
> backlash when I am jogging or issuing G1’s in MDI window.  Should it?
> -Tom
> 
> 
> 
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Re: [Emc-users] Fwd: backlash compensation

[andy pugh]

On 31 October 2015 at 00:58, Tom Easterday  wrote:
> Can anyone verify that backlash compensation has no effect for jogging or MDI 
> commands in 2.7.1?

Just so that you don't think you are being ignored, I don't know, and
I don't understand the question.

-- 
atp
If you can't fix it, you don't own it.
http://www.ifixit.com/Manifesto

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Re: [Emc-users] Fwd: backlash compensation

[Jeff Epler]

For the following testing, I used the 2.7 branch at ref
v2.7.1-26-g21ae480 (26 commits past the most recent release, 2.7.1)

I tested backlash compensation by modifying configs/sim/axis/axis.ini to
add backlash to the X axis:

[AXIS_0]
...
-BACKLASH = 0.000
+BACKLASH = 0.100

I started with that configuration, homed all axes, and went into MDI
mode.

I approached X0 first from the positive direction, and then used halcmd
to look at the relationship between the joint command and the motor
command:
[MDI in axis]
g0 x1
g0 x0

[in a terminal window]
$ halcmd show pin axis.0.motor-pos-cmd axis.0.joint-pos-cmd
Component Pins:
Owner   Type  Dir Value  Name
23  float OUT 0  axis.0.joint-pos-cmd
23  float OUT   0.93955  axis.0.motor-pos-cmd ==> Xpos

And then I approached from the negative direction:
[MDI in axis]
g0 x-1
g0 x0

[in a terminal window]
jepler@babs:~$ halcmd show pin axis.0.motor-pos-cmd axis.0.joint-pos-cmd
Component Pins:
Owner   Type  Dir Value  Name
23  float OUT 0  axis.0.joint-pos-cmd
23  float OUT   1.03955  axis.0.motor-pos-cmd ==> Xpos

In this case, I see that the motor positions differ by .1 inch depending
on the direction of approach.  So the result of my testing is that
backlash compensation seems to operate as expected in at least one
situation.

I got similar results when using incremental and continuous jogs -- the
difference between joint-pos-cmd and motor-pos-cmd was either 1.03955 or
0.93955 depending on the direction of the last motion.

(The specific values 1.03955 and 0.93955 depend on the details of how
the machine was homed and would differ from run to run at least on a
real machine)

And now idle speculation as to why backlash compensation might be seen
not to operate at all for some users: I believe backlash compensation is
not activated until all axes are homed. So if you are using a
configuration that permits MDI & AUTO mode without homing, you might see
this happen (but this is just a memory of how linuxcnc used to work at
some time in the past and may not be accurate information for 2.7)

Jeff

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Re: [Emc-users] Fwd: backlash compensation

[Tom Easterday]

Thanks Jeff.  I was using a dial indicator and moving back and forth before and 
after setting "BACKLASH = 0.0005" and found no difference.  I think I was homed 
but will verify next time I am at the machine and will also try your method to 
see what the hal pins believe.  Is the "+" and "-" optional?
-Tom

> On Oct 30, 2015, at 10:25 PM, Jeff Epler  wrote:
> 
> For the following testing, I used the 2.7 branch at ref
> v2.7.1-26-g21ae480 (26 commits past the most recent release, 2.7.1)
> 
> I tested backlash compensation by modifying configs/sim/axis/axis.ini to
> add backlash to the X axis:
> 
>   [AXIS_0]
>   ...
>   -BACKLASH = 0.000
>   +BACKLASH = 0.100
> 
> I started with that configuration, homed all axes, and went into MDI
> mode.
> 
> I approached X0 first from the positive direction, and then used halcmd
> to look at the relationship between the joint command and the motor
> command:
>   [MDI in axis]
>   g0 x1
>   g0 x0
> 
>   [in a terminal window]
>   $ halcmd show pin axis.0.motor-pos-cmd axis.0.joint-pos-cmd
>   Component Pins:
>   Owner   Type  Dir Value  Name
>   23  float OUT 0  axis.0.joint-pos-cmd
>   23  float OUT   0.93955  axis.0.motor-pos-cmd ==> Xpos
> 
> And then I approached from the negative direction:
>   [MDI in axis]
>   g0 x-1
>   g0 x0
> 
>   [in a terminal window]
>   jepler@babs:~$ halcmd show pin axis.0.motor-pos-cmd axis.0.joint-pos-cmd
>   Component Pins:
>   Owner   Type  Dir Value  Name
>   23  float OUT 0  axis.0.joint-pos-cmd
>   23  float OUT   1.03955  axis.0.motor-pos-cmd ==> Xpos
> 
> In this case, I see that the motor positions differ by .1 inch depending
> on the direction of approach.  So the result of my testing is that
> backlash compensation seems to operate as expected in at least one
> situation.
> 
> I got similar results when using incremental and continuous jogs -- the
> difference between joint-pos-cmd and motor-pos-cmd was either 1.03955 or
> 0.93955 depending on the direction of the last motion.
> 
> (The specific values 1.03955 and 0.93955 depend on the details of how
> the machine was homed and would differ from run to run at least on a
> real machine)
> 
> And now idle speculation as to why backlash compensation might be seen
> not to operate at all for some users: I believe backlash compensation is
> not activated until all axes are homed. So if you are using a
> configuration that permits MDI & AUTO mode without homing, you might see
> this happen (but this is just a memory of how linuxcnc used to work at
> some time in the past and may not be accurate information for 2.7)
> 
> Jeff
> 
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Re: [Emc-users] Fwd: backlash compensation

[Tom Easterday]

I entered a value in my ini file assuming that when I moved back and forth the 
movements would be compensated by the value in the ini file.  But at least for 
jogging and issuing G1 movements in MDI, nothing changes - that is the backlash 
is still present.   I haven't ever used it before so I was guessing that this 
is how it was supposed to work so I don't know if my expectations are wrong or 
it is broken (at least in 2.7.1)?

> On Oct 30, 2015, at 9:33 PM, andy pugh  wrote:
> 
>> On 31 October 2015 at 00:58, Tom Easterday  wrote:
>> Can anyone verify that backlash compensation has no effect for jogging or 
>> MDI commands in 2.7.1?
> 
> Just so that you don't think you are being ignored, I don't know, and
> I don't understand the question.
> 
> -- 
> atp
> If you can't fix it, you don't own it.
> http://www.ifixit.com/Manifesto
> 
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