Author Topic: CV bad behaviour need improvement  (Read 14959 times)

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Offline nik

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CV bad behaviour need improvement
« on: March 07, 2012, 08:50:37 AM »
hello
finally I found a spindle with higher RPM and endmill which allow me to increase the feedrate
unfortunately I found several problems with CV mode when feedrate increased over 3m/min
in some situations it have terribly badly behavior where step motors will definitely loose position
Im using servo drive where sudden stop with lower speed is executed relatively well, the whole machine is shaking and vibrating badly where high elastic deformation occur in my construction but the machine continue and I can observe what is happening

so here is my configuration
maximum speed on X and Y axis - 15 m/min
acceleration - 0.4s to reach maximum speed
CV distance 1mm
CV angle 10 degrees

what I found is that CV angle in not as shown in CV notes

please see the attached file

on second and third image Gcode points are shown with circles, where the distance between each point is slightly lower than CV distance - 1mm
if no sudden stop occur then the rounding is obvious

after sudden stop is fixed I think rounding can be reduced significantly and keep high speed if more options are added:

if CV angle < 1 degrees then CV distance = 10mm
if CV angle < 2 degrees then CV distance = 5mm
if CV angle < 5 degrees then CV distance = 2mm
if CV angle < 10 degrees then CV distance = 1mm
if CV angle < 20 degrees then CV distance = 0.1mm
if CV angle > 45 degrees then CV off - exact stop or plasma mode
if not possible to keep same speed in next 10 or 50 lines then start deceleration early or exact stop on next point and then start over with CV or any similar algorithm

all numbers need to be entered manually for any specific machine and configuration


I guess even if you found a good ideas will take long time to fix it
is there any chance I can improve it myself? probably with custom brain or something else which can be done quickly than waiting for next release?
please advice
thanks
« Last Edit: March 07, 2012, 09:00:04 AM by nik »

Offline nik

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Re: CV bad behaviour need improvement
« Reply #1 on: March 07, 2012, 03:36:19 PM »
I was not able to edit my message again
I tried to generate G code with different tolerance(resolutiron)
but when lower resolution - low number of points used, then arcs with large radius are represented as lines, if they are longer than CV distance then they are executed with exact stop, where the machine is shaking even if the radius is so large, almost straight line
when higher resolution used then slightly better but still strange movement, therefore I we need to set different CV distance for different angles on next line

so here is the exact Gcode for the second image

X205.786 Y44.396
X205.583 Y43.434
X205.376 Y42.473
X205.165 Y41.513
X204.951 Y40.553
X204.732 Y39.595
X204.510 Y38.637
X204.284 Y37.680
X204.054 Y36.724
X203.821 Y35.769
X203.583 Y34.815
X203.342 Y33.862
X203.098 Y32.910
X202.849 Y31.959
X202.597 Y31.009
X202.577 Y30.941
X202.554 Y30.873
X202.527 Y30.805
X202.496 Y30.738
X202.462 Y30.671
X202.424 Y30.606
X202.382 Y30.542
X202.337 Y30.480
X202.288 Y30.420
X202.236 Y30.362
X202.181 Y30.307
X202.122 Y30.254
X202.062 Y30.205
X201.998 Y30.159
X201.933 Y30.116
X201.865 Y30.077
X201.796 Y30.041
X201.725 Y30.010
X201.653 Y29.982
X201.581 Y29.958
X201.508 Y29.938
X201.435 Y29.922
X201.362 Y29.909
X201.290 Y29.901
X201.218 Y29.895
X201.147 Y29.894
X18.983  

next Gcode is third image on top:

G0 X32.480 Y173.046
G1   Z0.000 F2000
G1 X187.651   F3000
X187.953 Y173.044
X188.255 Y173.039
X188.557 Y173.029
X188.860 Y173.016
X189.163 Y172.999
X189.466 Y172.977
X189.769 Y172.952
X190.071 Y172.924
X190.374 Y172.891
X190.677 Y172.854
X190.979 Y172.813

gcode third image bottom

X191.266 Y30.233
X190.966 Y30.189
X190.665 Y30.149
X190.365 Y30.112
X190.064 Y30.080
X189.763 Y30.051
X189.462 Y30.026
X189.161 Y30.005
X188.861 Y29.988
X188.560 Y29.975
X188.260 Y29.965
X187.960 Y29.960
X187.661 Y29.958
X32.480 Y29.958

here is G code similar to third image bottom but the last point is at the end of the curve:

X28.278 Y172.673
X28.577 Y172.725
X28.877 Y172.772
X29.177 Y172.816
X29.477 Y172.857
X29.778 Y172.893
X30.079 Y172.925
X30.379 Y172.954
X30.680 Y172.978
X30.981 Y172.999
X31.281 Y173.016
X31.581 Y173.029
X31.881 Y173.039
X32.181 Y173.044
X32.480 Y173.046
G0   Z10.000
« Last Edit: March 07, 2012, 03:48:37 PM by nik »

Offline nik

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Re: CV bad behaviour need improvement
« Reply #2 on: March 12, 2012, 05:28:53 AM »
anybody there?

Offline BR549

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Re: CV bad behaviour need improvement
« Reply #3 on: March 12, 2012, 01:31:59 PM »
CV is NOT going to fix your floppy machine. YOU have to do that part(;-) AS to LOST steps that is a simple point that the mootrs cannot go any faster or quicker in accel and they loose steps. May need to repower the machine with stronger motors/drives.

OR just slow things down within the boundaries of your machine capabilities.

There IS info here on the use of CV it was written by "Stirling" DO a search and read up on it.

Just a thought, (;-) TP
« Last Edit: March 12, 2012, 01:34:24 PM by BR549 »

Offline nik

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Re: CV bad behaviour need improvement
« Reply #4 on: March 12, 2012, 04:05:43 PM »
hi
as I mentioned ALREADY for that machine I use servo motors, not steppers
the motors are powerful enough to move the machine in opposite direction on higher speeds and accel
that problem occur when I use higher feeds - over 5m/min
I read all information about CV and I understand completely how it should work, but it is not, in the situations I mentioned above is not decelerating early as it should be, therefore I need to improve it, so I can use the full potential of my machine
mach3 do not drive properly in some situations, therefore I tried to explain the problem as clear as possible - what and when is going wrong, and I will be very happy if anybody well grounded in can help me to solve it
thanks
« Last Edit: March 12, 2012, 04:17:06 PM by nik »

Offline nik

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Re: CV bad behaviour need improvement
« Reply #5 on: March 13, 2012, 07:36:05 AM »
1 week no reply from customer support
very disappointing
I will look for another solution
thanks for the missing technical support

Offline BR549

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Re: CV bad behaviour need improvement
« Reply #6 on: March 13, 2012, 01:01:05 PM »
YOU have been given ALL the info available on CV. It is what it is. FOr most applications It works BEST if you don't try to outsmart it.
AND again it is not there to FIX your machine from being FLEXABLE (floppy) .

Thousands of users all over the world use it successfully every day so something must be right about it.

Just a thought, (;-) TP

Offline nik

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Re: CV bad behaviour need improvement
« Reply #7 on: March 13, 2012, 06:20:33 PM »
all machines in the world are flexible, 1mm or 0.00000001mm they are always flexible
therefore mach3 should use ramps, slow accelerating and decelerating, ALWAYS, not only some time
CV is great, and most of the times works perfect, but some time it forget to decelerate, anyway.... if there is no technical support then I have to look for another solution to avoid these sudden stops
« Last Edit: March 13, 2012, 06:26:04 PM by nik »

Offline BR549

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Re: CV bad behaviour need improvement
« Reply #8 on: March 13, 2012, 07:28:42 PM »
I would turn on CV and turn off all the extra settings, that puts it in native mode and it works 100% of the time.

Mach3 runs a bang bang tragectory (trapazoidal) it does NOT run an S curve. There are settings for accelleration of the motors as well as max velocity.

Perhaps you need to tune the motors DOWN a bit in accelleration to help avoid the sudden stops(;-) or plan your Gcode for a better use of the machine capabilities.

Just because a drive/motor combination can rattle the machine it doesn't mean you should.

Just a thought, (;-) TP

Offline nik

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Re: CV bad behaviour need improvement
« Reply #9 on: March 15, 2012, 06:31:07 AM »
you are explaining like beginner to beginner, Im not sure about you but Im not, and Im not going to explain same thing again and again just because nobody is reading  :'(
the motors are tuned already, and they accelerate and decelerate properly , the machine run nice and smoothly
but as I already explained SEVERAL !!!!!!!!  times - some time mach3 DO NOT DECELERATE !!!!!!!!!!!!!!!!!! this is the only problem that do not allow me to use higher feed than 3m/min, because when mach3 STOP WITHOUT DECELERATION !!!!!!!!!!!! with 5 or 6 m/min the machine is shaking and this reduce the quality

it is definitely a bug in CV algorithm because it is happening in identical situations, but as you can see nobody care about that.... very sad
« Last Edit: March 15, 2012, 06:39:36 AM by nik »