Brian wrote:
> EMC adds the screw compensation to the measured value from the
> encoder before it is interpreted as actual joint position. Therefore,
> if I want to use screw comp and scale feedback at the same time, it
> wont work.
>
The whole POINT of the screw comp table is to correct for
Dave wrote:
> Who really cares where your motors are at if you can accurately control
> the actual position
> via the scales?Backlash will not be compensated but the velocity
> mode stepgen won't care. The PID loop will try and compensate.
>
Yes, but with larger amounts of backlash, the m
Andy Pugh wrote:
> On 8 August 2010 22:25, Jon Elson wrote:
>
>
>> And that's what I SIMPLY don't understand. I have two servo-controlled
>> machines.
>>
>
> And I think he has none, if I have been reading right.
>
> I am fairly sure this is a stepper machine that is fitted with linear
>
Brian,
If you have a closed loop system and are using scales then using screw
comp really doesn't make any sense since the outer loop is closed to the
scales.
Screw comp only makes sense if you are relying on the screws accuracy.
You will be relying on the scales accuracy, not the screws.
Yo
> And that's what I SIMPLY don't understand. I have two servo-controlled
> machines.
>
> Jon
Jon,
EMC adds the screw compensation to the measured value from the
encoder before it is interpreted as actual joint position. Therefore,
if I want to use screw comp and scale feedback at the same tim
Do you really need screw correction AND backlash comp?
I'm not so sure you do.
I would turn off any backlash comp and screw comp and setup the feedback
loop with the linear scales and try and tweak the position loop to get
what you want. Use a velocity mode stepgen and feed that with a PID loo
Ron Bean wrote:
> I read somewhere (maybe on the Gumstix site) that the easiest way to set
> them up is to recompile the bootloader, and have it set them up the way
> you want them. The Beagleboard expansion cards have a ROM that tells the
> bootloader how to set things up, which is nice if you're
Jon Elson wrote:
> Ron Bean wrote:
>
>> Are the Beagleboard and the Gumstix Overo-Water similar enough that
>> the Beagleboard port is likely to run on the Overo?
>>
>>
>>
> Maybe. The CPI is the same.
Typo - that should be CPU
Jon
--
Brian wrote:
>> He wants the displayed position to have the screw error (and backlash)
>> correction applied. Even if EMC2 doesn't do this now, making the
>> displayed position show the corrected value sounds like a couple hours
>> of work and a new HAL component. The most difficult part is to ar
On 8 August 2010 22:25, Jon Elson wrote:
> And that's what I SIMPLY don't understand. I have two servo-controlled
> machines.
And I think he has none, if I have been reading right.
I am fairly sure this is a stepper machine that is fitted with linear
scales. My understanding is that leadscrews
Brian wrote:
> I am quite happy with the way EMC handles screw comp and lash. I am
> not interested in changing my machine or EMC in these regards. The
> ONLY reasons backlash and screw comp have been mentioned at all in
> this thread is because it is the reason I can't feed my scale feedback
> i
Brian wrote:
> Dave,
>
> I simply want axis to be able to utilize my scale feedback as actual
> joint position. Thats all.
>
And that's what I SIMPLY don't understand. I have two servo-controlled
machines.
One is a converted manual Bridgeport mill, the other a converted 150Lb
minimill.
The
Jon Elson writes:
>Yup, few people use bare GPIO, and the documentation, all 3700 pages of
>it, has the info but it is REALLY hard to figure out how to set up the
>GPIO pins to use them.
I read somewhere (maybe on the Gumstix site) that the easiest way to set
them up is to recompile the bootload
Ahh, I see your point.
I know it doesn't solve your problem, but perhaps something like a PYVCP DRO
like the one shown here would be a good short term or alternative solution
http://wiki.linuxcnc.org/emcinfo.pl?PyVCP ( A big DRO from Goslowjimbo) I
haven't played with it much because my machine ca
>
> How about axis.N.motor-pos-fb?
>
> from the integrators manual:
>
> axis.N.motor-pos-fb (float, in) The actual position for this joint.
>
> as opposed to:
>
> axis.N.joint-pos-fb (float, out) The joint (as opposed to motor) feedback
> position.
>
Because the screw comp gets added to that value
> The motion controller copies feedback to command while in the machine
> off state. The stepgen also updates its internal command position while
> it is disabled (which it should be in machine off). The motion
> controller shouldn't do anything when it's enabled (it might, and that
> would be a
On Sun, Aug 8, 2010 at 12:27 PM, Stephen Wille Padnos wrote:
> Andy Pugh wrote:
> > On 8 August 2010 19:04, Stephen Wille Padnos wrote:
> >
> >
> >> Wait a second. You said in your original email that you couldn't
> >> connect the scale feedback to axis.n.joint-pos-fb - have you actually
> >> tr
Andy Pugh wrote:
> On 8 August 2010 19:04, Stephen Wille Padnos wrote:
>
>
>> Wait a second. You said in your original email that you couldn't
>> connect the scale feedback to axis.n.joint-pos-fb - have you actually
>> tried doing that?
>>
> axis.N.joint-pos-fb is an output:
>
> 9 fl
On 8 August 2010 19:04, Stephen Wille Padnos wrote:
> Wait a second. You said in your original email that you couldn't
> connect the scale feedback to axis.n.joint-pos-fb - have you actually
> tried doing that?
axis.N.joint-pos-fb is an output:
9 float OUT -9.566617 axis.0.joint-pos-fb
Brian wrote:
> Jon,
>
>
>> Well, I simply don't understand why this doesn't work.
>>
> It quits working when the motors are disabled. Once you do that, the
> wiki method wont track the table position with a stepper machine.
>
Wait a second. You said in your original email that you c
Ron Bean wrote:
> Are the Beagleboard and the Gumstix Overo-Water similar enough that
> the Beagleboard port is likely to run on the Overo?
>
>
Maybe. The CPI is the same. The Beagle has a video interface, I'm not
clear if the Gumstix boards have that. If not, just make sure that X11
doesn
> He wants the displayed position to have the screw error (and backlash)
> correction applied. Even if EMC2 doesn't do this now, making the
> displayed position show the corrected value sounds like a couple hours
> of work and a new HAL component. The most difficult part is to arrange
> the code
Jon,
> Well, I simply don't understand why this doesn't work.
It quits working when the motors are disabled. Once you do that, the
wiki method wont track the table position with a stepper machine.
> Now, the screw mapping with backlash may not work at all for manual
> moves. I believe the co
Andy Pugh wrote:
> Am I right in thinking that your request is basically that
> axis.N.joint-pos-fb should be read/write (or split into
> joint-pos-fb-in and joint-pos-fb-out?). Then what is displayed on the
> screen is the actual position from the scales?
> My impression is that you are happy with
Dave wrote:
> Backlash is a difficult thing to handle and it just gets worse when you
> try and put a PID loop around it.
>
> Backlash is like having a loose shaft coupling with slop in it.
>
> Pretty much a control nightmare.
>
Yes, a simple control algorithm requires a linear function between
Brian wrote:
> Jon,
>
> If I had encoders on the screws, the method described on the wiki
> would work. This is basically what Dave suggested a few replies back,
> and what my config already does to some degree. This method will also
> work with steppers, until the motors are disabled, and you
Dave,
I simply want axis to be able to utilize my scale feedback as actual
joint position. Thats all.
Brian
On Sun, Aug 8, 2010 at 12:28 PM, Dave wrote:
> Ok... I guess I don't understand what you are trying to do.. or what
> the issues are.
>
> I thought this was a control issuethat y
Ok... I guess I don't understand what you are trying to do.. or what
the issues are.
I thought this was a control issuethat you want the control to
compensate for backlash and possibly a screw that that has some pitch
errors, and also close the position loop with
some direct reading scale
Andy,
You and I are now on the same page. That is EXACTLY what I would
like to see. It would be simple, and would solve all the other BS
that has been errantly discussed in this thread.
In addition to splitting the joint-pos-fb PIN as you mention, it
would be cool that add a PIN that has th
Are the Beagleboard and the Gumstix Overo-Water similar enough that
the Beagleboard port is likely to run on the Overo?
I'm disappointed in the small number of GPIO pins available on the
Beagleboard. Oddly, I haven't been able to find a straightforward
breakout board for the OMAP 3530-- they al
Dave writes:
>The only way around this is to run your machine very slowly, which some
>would say, negates a lot of the benefits of CNC'ing your machine.
I would disagree, although it depends on what you're doing.
>At some point fixing the machine is more productive than trying to work
>around a
On 8 August 2010 07:57, Brian wrote:
>
> In the HAL component axis, joint position and motor position are
> thought of as separate concepts. Joint position is related to motor
> position through the compensation logic, but otherwise they are their
> own entities. This is good design, because in
Steve's suggestion of using a velocity stepgen with a PID loop and then
using the scale feedback to close the loop - works. I have that running
on an actual machine and at high speeds - 1100 ipm. The machine is
running two shifts right now and is very reliable.
There is no need to add anythin
Hi
I don't know anything about the inner workings of EMC. I do know a bit
about control systems. I think I understand the question raised here.
If you want to combine the measured joint position and use this
information to figure out what the motor needs to do to maintain control
of the j
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