f error settings in .ini

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23 Jul 2011 22:33 #11785 by fabworx
out of curiousity what are some of your guys ferror settings in your ini file. im not sure if im done tuning my loops and would like to know what kind of numbers i should be shooting for here. right now i have a min ferror of 0.00075 and a max ferror of 0.0075. does that sound feezable. this is my first machine i have set up with servos and getting this pid loop thing down is troublesome to say the least. by the way these numbers are for a rapid of 250 inch per minute on a kasuga knee mill the same size as the bigger shizoukas. with numbers like this what kind of accuracy can i expect to get?

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24 Jul 2011 04:12 #11792 by aike
Replied by aike on topic Re:f error settings in .ini
Hi
If there is the difference between the command and actual position - ferror will let you to prevent futher moving.
For example. If your axe is too inerts and the command to move executed with some delay, the "join N follow error" mesage appears.
Increase MIN_FERROR in this case.
MIN_FERROR - it is the starting max possible value with the speed = 0.
FERROR - it is the max possible value in maximum speed.
The EMC each time calculate the FEROR value due the current axe speed.
It is true for closed loop (servo drive). If you have open loop (no encoder feedback) stay ferror as you want.

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25 Jul 2011 04:35 #11814 by fabworx
Replied by fabworx on topic Re:f error settings in .ini
ok i get that, thanx but what is a feesable number. to allow and what kind of tolerance will be held on the part. im not sure if i need to increase my min ferror or keep tuing my pid loop cause from where im sitting ive about pulled all of my hair out with these pid loops.

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25 Jul 2011 07:15 #11815 by aike
Replied by aike on topic Re:f error settings in .ini
Hi!
You can see my lathe in
www.microcnc.ru/research/1325F30.php
Hear is the sample of ini file with FERROR values.

#********************
# Axis X
#********************
[AXIS_0]
TYPE = LINEAR
HOME = 0.0
#experiment 2010-12-17
FERROR =10.5
#experiment 2010-12-17
MIN_FERROR = 10.5
MAX_VELOCITY = 120.0
MAX_ACCELERATION =240.0
#Added by hand 2010-11-16
P = 50.0
I = 0.0
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.001
OUTPUT_SCALE = 500.0
OUTPUT_OFFSET = 0.0
MAX_OUTPUT = 140.0
#??? SCALE
#the sign may be "-" or "+", it depends of encoder wires connect
#if the servo drive has fatal error [ferror] then change the sign to opposit
INPUT_SCALE =-2500.0

# these are in nanoseconds
DIRSETUP = 1000
DIRHOLD = 1000
STEPLEN = 1000
STEPSPACE = 1000
#??? SCALE
SCALE = 2500.0
MIN_LIMIT = -338.0
MAX_LIMIT = 2.0
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = -20.500000
HOME_LATCH_VEL = -1.50000
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = YES
HOME_SEQUENCE = 1

#********************
# Axis Z
#********************
[AXIS_2]
TYPE = LINEAR
HOME = 0.0
#experiment 2010-12-17
FERROR = 10.5
#experiment 2010-12-17
MIN_FERROR = 10.5
MAX_VELOCITY = 120.0
MAX_ACCELERATION = 240.0
#Added by hand 2010-11-16
P = 50.0
I = 0.0
D = 0.0
FF0 = 0.0
FF1 = 1.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.001
OUTPUT_SCALE = 250.0
OUTPUT_OFFSET = 0.0
MAX_OUTPUT = 140.0
#change sign 2010-11-16
#???
#the sign may be "-" or "+", it depends of encoder wires connect
#if the servo drive has fatal error [ferror] then change the sign to opposit
INPUT_SCALE =2500.0


# these are in nanoseconds
DIRSETUP = 1000
DIRHOLD = 1000
STEPLEN = 1000
STEPSPACE = 1000
#???
SCALE = 2500.0
MIN_LIMIT = -300.0
MAX_LIMIT = 2.0
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = -20.500000
HOME_LATCH_VEL = -1.50000
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = YES
HOME_SEQUENCE = 0

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25 Jul 2011 10:12 #11817 by cmorley
Replied by cmorley on topic Re:f error settings in .ini
As I read it you could have as much as .00075 error at slow feed speeds before EMC will throw an error.
That almost 1 thousands of an inch. I would think you want better. whether you can depends on many things such as encoder resolution and servo amplifiers. Are your Servo amps closing a velocity loop of their own? Are they tuned right?
Is the machine in good mechanical shape?

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25 Jul 2011 15:59 #11834 by andypugh
fabworx wrote:

with numbers like this what kind of accuracy can i expect to get?


Well, EMC2 will try to get you to zero error. The f-error numbers are the error at which an error is flagged, and the machine is stopped. Reducing the numbers won't make the machine any more accurate, but it will eventually give you spurious f-err shutdowns.

So, the first thing to find out is what your current f-error is. You can plot f-error during a move by using Halscope. Have a loot at how big it is at during very slow moves and during rapids, and set the f-error limits to be some multiple of that. 2x 3x, 10x, your choice.
The following user(s) said Thank You: Dubmfg

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