Acceleration of U-Axis asynchronous to XYZ
25 Jun 2012 14:35 - 25 Jun 2012 14:40 #21303
by poolspieler
Acceleration of U-Axis asynchronous to XYZ was created by poolspieler
Hi @all,
I am trying to get my 3D-Printer running with LinuxCNC 2.5.0
I am using a wades extruder ( reprap.org/wiki/Wade's_Geared_Extruder ) on my CNC.
As a matter of principle it is running fine BUT:
The extruder is NOT generating the correct amount of PLA during acceleration/deceleration of the axis.
Please note the attached picture of the result:
The higher I set the Axis-speed, the higher I get bad printing results.
For the left print I reduced the XYZ-speed to 10mm/s --> this ist too slow for bigger prints (they would take more than 10 hours...)
For the right print I used 30mm/s and got this bad result...
Question:
Is there a way to get the U-Axis moving (accelerating) BEFORE the XYZ-Axis are moving for each G1-command?
Of course I would have to configure the time or something else for this asynchronous moves.
I already downloaded the source code on LinuxCNC - and tried to find the section for acceleration - but it does not look as simple as meant...
Do you need further information?
Could someone help me? Thanks!
Best Regards,
poolspieler
I am trying to get my 3D-Printer running with LinuxCNC 2.5.0
I am using a wades extruder ( reprap.org/wiki/Wade's_Geared_Extruder ) on my CNC.
As a matter of principle it is running fine BUT:
The extruder is NOT generating the correct amount of PLA during acceleration/deceleration of the axis.
Please note the attached picture of the result:
The higher I set the Axis-speed, the higher I get bad printing results.
For the left print I reduced the XYZ-speed to 10mm/s --> this ist too slow for bigger prints (they would take more than 10 hours...)
For the right print I used 30mm/s and got this bad result...
Question:
Is there a way to get the U-Axis moving (accelerating) BEFORE the XYZ-Axis are moving for each G1-command?
Of course I would have to configure the time or something else for this asynchronous moves.
I already downloaded the source code on LinuxCNC - and tried to find the section for acceleration - but it does not look as simple as meant...
Do you need further information?
Could someone help me? Thanks!
Best Regards,
poolspieler
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25 Jun 2012 14:41 #21304
by poolspieler
Replied by poolspieler on topic Re:Acceleration of U-Axis asynchronous to XYZ
Here is the picture:
... its a little bit complicated to attach a picture to a post...
... its a little bit complicated to attach a picture to a post...
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25 Jun 2012 16:17 #21308
by poolspieler
Replied by poolspieler on topic Re:Acceleration of U-Axis asynchronous to XYZ
Hi,
thank you for your answers!
A snippet of my ini-file:
But at acceleration, the extruder takes some time to increase its internal preasure. I would say, this takes about 100-400 milliseconds.
This time depends on the acceleration of the extruder. At very low speeds I don't see this behavior.
An "off-topic question":
Would it better to use the A-axis in stead of the U-axis?
--> If I use the U-axis, the 3D-graph is not correct. there is a displacement in the x-axis
I attached to screenshots...
Thank you for your support!
Do you need further information?
Best Regards,
Andy
thank you for your answers!
A snippet of my .hal File:How is the extruder "axis" set up?
net xdir => parport.0.pin-02-out
net xstep => parport.0.pin-03-out
setp parport.0.pin-03-out-reset 1
net ydir => parport.0.pin-04-out
net ystep => parport.0.pin-05-out
setp parport.0.pin-05-out-reset 1
net zdir => parport.0.pin-06-out
net zstep => parport.0.pin-07-out
setp parport.0.pin-07-out-reset 1
net udir => parport.0.pin-08-out
setp parport.0.pin-08-out-invert 0
net ustep => parport.0.pin-09-out
setp parport.0.pin-09-out-reset 1
net charge-pump => parport.0.pin-16-out
net estop-ext <= parport.0.pin-11-in
net all-home <= parport.0.pin-13-in
setp stepgen.0.position-scale [AXIS_0]SCALE
setp stepgen.0.steplen 1
setp stepgen.0.stepspace 0
setp stepgen.0.dirhold 35000
setp stepgen.0.dirsetup 35000
setp stepgen.0.maxaccel [AXIS_0]STEPGEN_MAXACCEL
net xpos-cmd axis.0.motor-pos-cmd => stepgen.0.position-cmd
net xpos-fb stepgen.0.position-fb => axis.0.motor-pos-fb
net xstep <= stepgen.0.step
net xdir <= stepgen.0.dir
net xenable axis.0.amp-enable-out => stepgen.0.enable
net all-home => axis.0.home-sw-in
setp stepgen.1.position-scale [AXIS_1]SCALE
setp stepgen.1.steplen 1
setp stepgen.1.stepspace 0
setp stepgen.1.dirhold 35000
setp stepgen.1.dirsetup 35000
setp stepgen.1.maxaccel [AXIS_1]STEPGEN_MAXACCEL
net ypos-cmd axis.1.motor-pos-cmd => stepgen.1.position-cmd
net ypos-fb stepgen.1.position-fb => axis.1.motor-pos-fb
net ystep <= stepgen.1.step
net ydir <= stepgen.1.dir
net yenable axis.1.amp-enable-out => stepgen.1.enable
net all-home => axis.1.home-sw-in
setp stepgen.2.position-scale [AXIS_2]SCALE
setp stepgen.2.steplen 1
setp stepgen.2.stepspace 0
setp stepgen.2.dirhold 35000
setp stepgen.2.dirsetup 35000
setp stepgen.2.maxaccel [AXIS_2]STEPGEN_MAXACCEL
net zpos-cmd axis.2.motor-pos-cmd => stepgen.2.position-cmd
net zpos-fb stepgen.2.position-fb => axis.2.motor-pos-fb
net zstep <= stepgen.2.step
net zdir <= stepgen.2.dir
net zenable axis.2.amp-enable-out => stepgen.2.enable
net all-home => axis.2.home-sw-in
setp stepgen.6.position-scale [AXIS_6]SCALE
setp stepgen.6.steplen 1
setp stepgen.6.stepspace 0
setp stepgen.6.dirhold 35000
setp stepgen.6.dirsetup 35000
setp stepgen.6.maxaccel [AXIS_6]STEPGEN_MAXACCEL
net upos-cmd axis.6.motor-pos-cmd => stepgen.6.position-cmd
net upos-fb stepgen.6.position-fb => axis.6.motor-pos-fb
net ustep <= stepgen.6.step
net udir <= stepgen.6.dir
net uenable axis.6.amp-enable-out => stepgen.6.enable
net all-home => axis.6.home-sw-inA snippet of my ini-file:
[TRAJ]
AXES = 8
COORDINATES = X Y Z U
MAX_ANGULAR_VELOCITY = 360.00
DEFAULT_ANGULAR_VELOCITY = 36.00
LINEAR_UNITS = mm
ANGULAR_UNITS = degree
CYCLE_TIME = 0.010
DEFAULT_VELOCITY = 4.00
MAX_LINEAR_VELOCITY = 40.00
[EMCIO]
EMCIO = io
CYCLE_TIME = 0.100
TOOL_TABLE = tool.tbl
[AXIS_0]
TYPE = LINEAR
HOME = 418.0
MAX_VELOCITY = 38.0
MAX_ACCELERATION = 240.0
STEPGEN_MAXACCEL = 260.0
SCALE = 400.0
FERROR = 1
MIN_FERROR = .25
MIN_LIMIT = 0.0
MAX_LIMIT = 420.0
HOME_OFFSET = 420.000000
HOME_SEARCH_VEL = -20.000000
HOME_LATCH_VEL = 1.000000
HOME_SEQUENCE = 1
[AXIS_1]
TYPE = LINEAR
HOME = 478.0
MAX_VELOCITY = 38.0
MAX_ACCELERATION = 240.0
STEPGEN_MAXACCEL = 260.0
SCALE = 400.0
FERROR = 1
MIN_FERROR = .25
MIN_LIMIT = 0.0
MAX_LIMIT = 480.0
HOME_OFFSET = 480.000000
HOME_SEARCH_VEL = -20.000000
HOME_LATCH_VEL = 1.000000
HOME_SEQUENCE = 2
[AXIS_2]
TYPE = LINEAR
HOME = 128.0
MAX_VELOCITY = 38.0
MAX_ACCELERATION = 240.0
STEPGEN_MAXACCEL = 260.0
SCALE = 400.0
FERROR = 1
MIN_FERROR = .25
MIN_LIMIT = 5.0
MAX_LIMIT = 130.0
HOME_OFFSET = 130.000000
HOME_SEARCH_VEL = -20.000000
HOME_LATCH_VEL = 1.000000
HOME_SEQUENCE = 0
[AXIS_6]
TYPE = LINEAR
HOME = 0
MAX_VELOCITY = 40.0
MAX_ACCELERATION = 240.0
STEPGEN_MAXACCEL = 260.0
SCALE = 746.1
FERROR = 1
MIN_FERROR = .25
MIN_LIMIT = -999999
MAX_LIMIT = 999999
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = 1.000000
HOME_LATCH_VEL = 1.000000
HOME_SEQUENCE = 0Can you paste a snippet of the G-code?
G17
G90
G54
G92 U0
G0 U0
G21
G64 P0.1 Q0.1
G92 U0
G0 U0
G21
G1 X-5.803 Y0.915 Z0.5 F1200.0
G1 F1200.0
G1 U1.05
G1 F1200.0
G1 X-5.601 Y21.154 Z0.5 F450.0 U2.3486
G1 X-2.404 Y24.74 Z0.5 F450.0 U2.6569
G1 X0.915 Y25.803 Z0.5 F450.0 U2.8805
G1 X21.347 Y25.6 Z0.5 F450.0 U4.1915
G1 X25.62 Y21.327 Z0.5 F450.0 U4.5792
G1 X25.654 Y-1.186 Z0.5 F450.0 U6.0237
G1 X21.417 Y-5.599 Z0.5 F450.0 U6.4161
G1 X0.915 Y-5.803 Z0.5 F450.0 U7.7316
G1 X-2.234 Y-4.794 Z0.5 F450.0 U7.9438
G1 X-4.794 Y-2.234 Z0.5 F450.0 U8.1761
G1 X-5.803 Y0.915 Z0.5 F450.0 U8.3882The extruder should give a constant volume-per-mm.What is required is for the extruder to extrude at a rate proportional to axis speed to give a constant volume-per-mm
But at acceleration, the extruder takes some time to increase its internal preasure. I would say, this takes about 100-400 milliseconds.
This time depends on the acceleration of the extruder. At very low speeds I don't see this behavior.
I just looked around the code --> and I AGREEIt might be worth tweaking the U-axis accelleration settings to see if you can make an improvement. Unfortunately I don't think you can do this live.
How can I do this. Is there a documentation or a HOWTO somewhere?There are other possible approaches, you could pass X and Y velocities into the "hypot" HAL function to convert to a linear velocity, and then scale that and pass it as an extrusion rate to a velocity-mode stepgen connected to U.
This sounds good. Could you give me an example - or a link to a documentation?Since it looks like the error is a phase lag in the extruder,
I would be tempted to delay the motion axis a fixed number
of servo cycles (fixed time) but leave the "U" calculation in
real time so the extruder rate is "ahead" of the mechanics
a hal comp with a circular buffer could generate a variable
(in servo thread increments) delay in the commanded positions
An "off-topic question":
Would it better to use the A-axis in stead of the U-axis?
--> If I use the U-axis, the 3D-graph is not correct. there is a displacement in the x-axis
I attached to screenshots...
Thank you for your support!
Do you need further information?
Best Regards,
Andy
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25 Jun 2012 17:42 - 25 Jun 2012 17:45 #21312
by poolspieler
Replied by poolspieler on topic Re:Acceleration of U-Axis asynchronous to XYZ
Hi Andy,
I added "GEOMETRY = XYZ" to my DISPLAY-Section - now everything is displayed right. Thank you!
Whithout the G64 the results really awful!
I attached two screenshots of the HAL oscilloscope --> a really nice tool. I didn't know this up to now
In my opinion - it is doing everything right - doesn't it?
--> But this is the problem. Axis6 (the extruder) shold move before the other axis are moving...
Best Regards,
Andy
I added "GEOMETRY = XYZ" to my DISPLAY-Section - now everything is displayed right. Thank you!
The G64 command is a very good improvement - but only for lower speeds.The first thing to try is probably to make sure that the axis acellerations are as high as possible, so that your machine slows less for corners.
I was going to suggest G64, but you have already done that.
Whithout the G64 the results really awful!
I can imagine a HAL component that would modify the extruder speed dependant on axis accelleration, but I am not clear if it would work or not.
It is probably worth graphing X, Y and U in Halscope to make sure that the U move is properly coordinating.
I attached two screenshots of the HAL oscilloscope --> a really nice tool. I didn't know this up to now
In my opinion - it is doing everything right - doesn't it?
--> But this is the problem. Axis6 (the extruder) shold move before the other axis are moving...
Best Regards,
Andy
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25 Jun 2012 19:10 #21315
by poolspieler
Replied by poolspieler on topic Re:Acceleration of U-Axis asynchronous to XYZ
Hi PCW,
thank you for your answer!
I am sorry, I overlooked the hint for plotting velocities instead of positions.
--> Could you say me, the exact pin for velocities in the HAL scope - I am not able to find them
Sorry for this stupid question: HOW can I enable or use the hypot comp?
At linuxcnc.org/docs/html/hal/components.html I found, that hypot is a "Three-input hypotenuse (Euclidean distance) calculator."
--> But how to install and use it?
Best Regards,
Andy
thank you for your answer!
I am sorry, I overlooked the hint for plotting velocities instead of positions.
--> Could you say me, the exact pin for velocities in the HAL scope - I am not able to find them
Sorry for this stupid question: HOW can I enable or use the hypot comp?
At linuxcnc.org/docs/html/hal/components.html I found, that hypot is a "Three-input hypotenuse (Euclidean distance) calculator."
--> But how to install and use it?
Best Regards,
Andy
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