Machsupport Forum
Mach Discussion => Mach4 General Discussion => Topic started by: KatzYaakov on September 22, 2021, 06:34:54 PM
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hello every one
i use mach 4 for about 3 years more then 20 cnc
i always had acceleration problems ,but i always blame the chines structure
until we open our work shop and start produce our cnc ,but ...same problem cant get normal value for the acceleration without having vibration
today we found the at least the reason
mach don't support S curve
i know this the reason because when we use the driver filter(its act similar as S curve)this vibration go even with high level of acceleration
after this long story i ask mach engineer ,please try put attention for this
its very very important(solve it by the driver its not correct way)please try solve this point
thanks
yaakov
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Hi,
Mach3 and Mach4 have second order trajectory planners, ie they suffer from 'jerk'
There was talk, development and discussion about a third order planner but it was never implemented in Mach4.
https://www.machsupport.com/forum/index.php?topic=12042.0 (https://www.machsupport.com/forum/index.php?topic=12042.0)
Craig
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I understand ,but until yesterday i didn't understand how important is this s curve ,its critical ...i give you sample ,we had many times that CV wizard got "crazy" and was far from original tool path,when i sent it to mach to cheack always conclusion from there side was that my acceleration /deccelration so poor that CV can't calculate well
But now i understand why it was do poor ,it was so poor because mach system not support s curve and without s curve you got very big vibration on other axis while you accelerated
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Hi,
complete rubbish......CNC machines were for decades second order planners, its only since the advent of highly capable
computers that third order planners became possible or even desirable.
You are confusing a third order trajectory with CV settings....they have commonalities but a third order planner has
minimal impact on toolpath following.
Craig
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Craig
As i remember you use the cnc for electric cards ,so its probably small table with screw lead system ,in that case s curve real not critical,my field its woodworking ,rack and pinion system with big table ,s curve its very very and one more very important
So only question i can't answer its if more user use as me ( wood or sighn engraving) or like you ,but if there many user like me its critical 100 %
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Hi,
my new mill has 32mm diameter ballscrews in 115kg cast iron axis beds, accelerating at 2.5ms-2 up to 25m/min,
so its a heavy machine accelerating hard. Yes, I would like a third order planner but that has very little bearing on toolpath following.
Craig
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Hi,
with big table ,s curve its very very and one more very important
Wrong, still the majority of industrial machines still use a second order planner....your issue with toolpath following is more to do with limited acceleration
of your machine and the limitations that places on the CV algorithm.
Craig
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Hi,
this is one of many articles:
https://www.pmdcorp.com/resources/type/articles/get/mathematics-of-motion-control-profiles-article (https://www.pmdcorp.com/resources/type/articles/get/mathematics-of-motion-control-profiles-article)
It concludes that trapezoidal, that is second order planners are still the fastest but the S-curve, that is third order planners can be tuned to be
smoother......but note neither second or third order planners have ANY ADVANTAGE with respect to toolpath following. That is determined
by the CV algorithm alone.
As I said before....yes.....having a third order motion planner in Mach4 would be nice....but that's all it is......nice.
If you want to ensure the best toolpath following look to the CV algorithm.
Craig
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Ill give you some numbers
When i use without s curve i can max use accl in mach 500, while max speed 70 m/min
When i use s curve i csn use 2500
Total in time ehrn i cut parts size about 500"400 mm different in time its more then double
This without notice about pocket ( we use alot "pocket in woodworking" then time difference much much higher
And i not take also the following errors in cv that we have because poor acceleration
So again ,im not sure how many users are woodworking cnc or sigh ,but i guess not few,and for us its not only important its critical
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Hi,
then unless you can persuade NFS developers to redo Mach's trajectory planner the you'll have to buy another control solution,
a Siemens 840 should do the trick, and probably not much more than $20,000 either!
Craig
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Syntec,Tpa,Weihong.... and much more that i not remember names now ,cost about 1000-2000$ and all of them have jerk
I normally solve many thing by myself ,like modbus... interface...2 machine's parallel... all I solve with c# but this jerk i can't find any way to solve without mach help
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As Craig has said, if you want ‘S’ curve then you need to be using a different software / planner or alternately wait for it to be incorporated within Mach4 (which could be a long wait).
Back in the days of Mach3 – Art developed the Tempest trajectory planner which did incorporate the ‘S’ curve and it was, at that time, intended to become Mach4. However, it was later decided to develop Mach4 from the ground up and the ‘S’ curve was subsequently dropped from the planner.
Art then went on to develop another trajectory planner software ‘Auggie’ which does incorporate the ‘S’ curve and this software can be downloaded from Art’s website http://www.gearotic.com/index.html
Although Auggie was intended as an addon to Gearotic Motion I believe it can be run as a stand-alone program. If you have the time then check it out.
Tweakie.
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Thanks
As i told on first post ,i found way to solve ,im not sure its will handle all working typs ,but for now up to 3 axiss simoltan its look ok
I use the s curve option in the servo drive