Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: grahamatcadcam on April 18, 2007, 05:04:48 PM
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Hi
We are developing a new machine and part of it is an XY table moving in a circular motion.
Using code listed below.
At 12 and 6 oclock on the graphics we can see a disturbance on the feedrate DRO. This shows in the servo motion as a blip and spoils the smooth motion we need.
I have tried faster PC's = makes no difference
Slowed feed speed down to 100mm/min - still present
It would appear as if at the point of calculating the G03 the pulse output gets disturbed
We are using version .062
Can you provide any ideas as to how to avoid this issue
Regards
Graham
G0 G49 G40 G17 G80 G50 G90
M6 T1 (TOOL DIA. 2)
G21 (mm)
M03 S100
G64
G00G90X0.Y0.
G00G90Z5.
G01G90Z0.F100.
G91G03Y19.Z-0.05R9.5F100.
G03J-19.Z-0.1 F1000
G03J-19.Z-0.1
G03J-19.Z-0.1
G03J-19.Z-0.1
G03J-19.Z-0.1
G03J-19.Z-0.1
G03J-19.Z-0.1
G03J-19.Z-0.1
G03J-19.Z-0.1
G03Y-19.Z-0.05R9.5
G00G91Z.254
G90Y0.
Z5.
M30
%
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Hey Graham,
What do you have your lines look ahead set to? In is in General config. Also, have you checked the backlash on your machine?
Brett
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Thanks for reply
Backlash and mechanical issues were checked and they are not a factor.
The look ahead was at default val (20 I think) - I tried 2&5 and 100 as alternatives. No difference
Regards
Graham
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What is it like if you remove the G64 from the code and replace it with G61.
Graham.
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Write yor program in G90 mode and see if you have a problem...
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Hi
Thanks for replies,
To Brian, I have tried abs code same behaviour
To Graham, will try G61 later today. Thanks for idea
Regards
Graham
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What are your Accel settings? and what Vel are you looking to use? I Have tested your path and it runs smooth here...
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Hi
I have just got back from the workshop. Its about 8Km away and not always accessible due to production isues.
I have deleted the G64 (having tried G61) G61 was worse, removing the G64 seemed to of made a slight improvement. Not sure what this did as its not in the manual. I had assumed it was a smoothing function or look ahead!!.
F1000 is what we are running, we would like to run up to about 1600 if possible.
In the motor settings I have 1280 pulses per unit, maxed out Velocity, about 1800 (from memory) Acc is set to 150
As a last resort I un ticked the Advanced Compensation Analysis. This seemed to be a further improvement.
However we can still see (and feel) a variation at the 12 and 6 oclock positions.
Ran at 35,000 then tried 45,000 pulse setting.
Task Manager showed a distinct increase in CPU demend. In all cases we have tried to use no more than 80% cpu demand.
I can try scope and Freq Meter. However in the past its been very difficult to follow the pulse output trains as they vary from 0to max in 90deg rotation of the table.
Its getting a bit fustrating. I have had 3 months of wiring, setting up and changing the servo's and drives till we got sets that work. Solving this issue appears to be the last before we can change mode to production of some samples and move to a next phase.
Regards and appreciate all help.
Graham
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Graham,
I have sent you a personal message.
Brett
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As a test please run the program at 500 and tell me if it feels better?
Also You need to know that Vel = Accel * Time (From a stop) and that Mach3 looks at every move from a stop and smooths them from there...
Okay... so if you have a move that you would like to be 1000 Units per sec and Accel of 150..
Vel/Accel = Time
(1000 / 60 )/150 = .11111 sec accel
and will take .5*Accel*Time^2 units to get to velocity
.5*150*.11111^2 = .92592 units to get to vel... if you are over a dis of .92592 you should feel a nice smooth path...
The only way that you will not is if you have played with some of the CV settings... Post your XML from the machine and I will see what I can find
Thanks
Brian
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I had the same problem with backlash compensation enabled on the y axis, it is doing its little shift for the backlash at those two points.
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Hi, Graham
I loaded your Settings and Code, steps 1280, vel. 1800, acc. 150, To achieve vel of 1800, You need kernel speed of 45K, Re-boot Reguired after changing.
I dont see any slowdown at 6 pos, But the 12 pos has a pause, It's Caused by the Gcode line change.
Mach ramps down using your Acc. setting even in CV mode.
There is a relationship between Steps, Vel, and Acc. settings, Hear is an example.
I have a Sherline mill with a 4th Axis, 10 micro steep controls.
X, Y, Z settings, S 7500, V 40, A 18
4th Axis, S 400.2, V 2500, A 500
Give this a try, set your Kernel speed to 45K re-boot if needed, S 1280, V 1800, A 350 - 450.
The way I setup from scratch is set slow Vel. Acc., Calibrate the Steps required to move 1 unit, Inch/MM.
Set the velocity up to a speed that you trip/lose steps or it's just too scary!!, Then back it off some.
Set the Acceleration up to a speed you trip/lose steps then back it off some.
This will give you a Max speed for your G00 Moves, F- Setting for G01, G02 & G03.
Note: You need to do some X, Y, Blended moves to determin whether you lose steps with multi axis moves.
You may need to reduce the Max Vel. and Acc. some, If your start / return position is off.
G00 X0 Y0
G00 X10 Y10 ( adjust to distance to get max blended Vel. to display)
G00 X0 Y0
M30
Additionally you may need to reduce your Acc., If it's to fast for the material your cutting.
It's all a balancing act any way.
Hope this Helps, Chip