using HAL to correct axis errors
16 Feb 2018 21:54 #106047
by pgf
Replied by pgf on topic using HAL to correct axis errors
Your suggestions work(ed) well! Thanks again.
I realized that I also need to do a reverse transformation for the feedback path.
So now my component looks like this:
and my custom.hal looks like this:
and after an X traverse from 0 to 10, the signals look like this, which leads to one more question.
Should I be rounding off the math, perhaps to the nearest .0001, to ensure that I don't accumulate precision errors of some sort? Or is this kind of trace discrepancy eliminated elsewhere in the code? I don't want to someday get a "following error" because of floating point inaccuracy.
paul
I realized that I also need to do a reverse transformation for the feedback path.
So now my component looks like this:
component nonsquare_table;
license "GPL"; // GPL v2 or later
pin in float x-in;
pin in float y-in;
pin out float y-out;
function cmd;
pin in float x-fb-in;
pin in float y-fb-in;
pin out float y-fb-out;
function fb;
;;
FUNCTION(cmd){
y_out = y_in + x_in * 0.007;
}
FUNCTION(fb){
y_fb_out = y_fb_in - x_fb_in * 0.007;
}
and my custom.hal looks like this:
loadrt nonsquare_table
addf nonsquare-table.0.cmd servo-thread
addf nonsquare-table.0.fb servo-thread
delsig ypos-cmd
net xpos-cmd => nonsquare-table.0.x-in
net ypos-cmd axis.1.motor-pos-cmd => nonsquare-table.0.y-in
net ypos-cmd-adjusted nonsquare-table.0.y-out => stepgen.1.position-cmd
delsig ypos-fb
net xpos-fb => nonsquare-table.0.x-fb-in
net ypos-fb-adjusted stepgen.1.position-fb => nonsquare-table.0.y-fb-in
net ypos-fb nonsquare-table.0.y-fb-out => axis.1.motor-pos-fband after an X traverse from 0 to 10, the signals look like this, which leads to one more question.
Should I be rounding off the math, perhaps to the nearest .0001, to ensure that I don't accumulate precision errors of some sort? Or is this kind of trace discrepancy eliminated elsewhere in the code? I don't want to someday get a "following error" because of floating point inaccuracy.
paul
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16 Feb 2018 22:28 #106050
by pgf
Replied by pgf on topic using HAL to correct axis errors
The DROs look like I was never here, except that the Y position shows a -0 due to the floating point errors:
It was the DROs that reminded me I needed to modify the feeback path -- because when I jogged X, Y was changing too. Not good.
paul
It was the DROs that reminded me I needed to modify the feeback path -- because when I jogged X, Y was changing too. Not good.
paul
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17 Feb 2018 13:47 #106073
by pgf
Replied by pgf on topic using HAL to correct axis errors
Thanks, and thanks for your help and encouragement. I'm pretty thrilled that I don't have to disassemble and try and realign my MDF-and-drawer-slide bed in order to try to adjust things. It wouldn't go well, I'm sure. (Though it will take some time to get used to seeing the Y stepper ticking over slowly while jogging in X alone.)
I'd actually forgotten how superb the linuxcnc architecture is. It simply fantastic that I was able to make this kind of customization at all. My thanks to all designers and hard workers, whether you ever read this or not!
Here's one more version of my component, for the record. It's now documented, and takes the deviation value as a parameter for ease of tuning. After tuning my value ended up at .011 -- the axes were off by about 7/64" at 10" out.
This isn't actually my first foray into the depths of HAL. When I first built my mill, the controller was practically a direct pass-through of parallel port pins to stepper coils. When I switched from the original DOS software that came with mill's plans to EMC (2004?), there wasn't yet a HAL driver for that, so I had to write my own, and get the sequencing right. Correcting my axis errors was way easier than that!
Here are some pictures of my mill, which don't include a recent upgrade with threaded inserts in the bed and a masonite wasteboard on the top, which together finally give me proper hold-downs. I think the pictures also don't include the ACME screw upgrades for X and Y, which sent my top jog speed from 18 IPS to a whopping 54 IPS! pgf's mill
paul
I'd actually forgotten how superb the linuxcnc architecture is. It simply fantastic that I was able to make this kind of customization at all. My thanks to all designers and hard workers, whether you ever read this or not!
Here's one more version of my component, for the record. It's now documented, and takes the deviation value as a parameter for ease of tuning. After tuning my value ended up at .011 -- the axes were off by about 7/64" at 10" out.
component nonsquare_table """Adjusts for non-square X-Y tables.
The value of Y is modified linearly based on the value of X,
i.e. newY = Y + X * deviation. Pins are provided for doing
both the forward and reverse (feedback) transform. Should
be inserted between axis and stepgen (or equivalent) components.
The 'deviation' multiplier is supplied as a parameter, and
defaults to 0.0.""";
license "GPL"; // GPL v2 or later
option singleton yes;
pin in float x-in;
pin in float y-in;
pin out float y-out "y-out = y-in + x-in * deviation";
function cmd;
pin in float x-fb-in;
pin in float y-fb-in;
pin out float y-fb-out "y-fb-out = y-fb-in - x-fb-in * deviation";
function fb;
param rw float deviation = 0.0;
;;
FUNCTION(cmd){
y_out = y_in + x_in * deviation;
}
FUNCTION(fb){
y_fb_out = y_fb_in - x_fb_in * deviation;
}
This isn't actually my first foray into the depths of HAL. When I first built my mill, the controller was practically a direct pass-through of parallel port pins to stepper coils. When I switched from the original DOS software that came with mill's plans to EMC (2004?), there wasn't yet a HAL driver for that, so I had to write my own, and get the sequencing right. Correcting my axis errors was way easier than that!
Here are some pictures of my mill, which don't include a recent upgrade with threaded inserts in the bed and a masonite wasteboard on the top, which together finally give me proper hold-downs. I think the pictures also don't include the ACME screw upgrades for X and Y, which sent my top jog speed from 18 IPS to a whopping 54 IPS! pgf's mill
paul
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