Re: Jerk Control in machines
Originally Posted by
peteeng
since the velocity/accel (hence eng jerk) can be calculated by the CAM system and velocity profile are generated by the CAM then the whole thing can be controlled in the code. This presumes the motors and machine can follow the required path and velocity profile independent of the inertial conditions eg volumill
hy peteeng my sugestion is to focus 1st on mcs, and leave cam system where it is
even if a cam takes as input some speed, acc, in order to do whatever with it ( like smoothing and cycle estimation ), most results are bull***t
cam is extensions, is not critical; is not like take this toolpath, it will work; no, is like it should work if you don't push the machine too much
my dear petteng, your thinking is ok, thus like tring to smooth things out as much as possible before creating the g-code, but truth is that actual stage of things is not like that, otherwise there wouldn't be so much complains about shaking/screaming machines
smoothnes is required to push machines, but achieving that top smoothness is not because of cam software
then some sort of feedback loop needs to be used
the feedback loop... this is it
yes, but let's leave this a bit for latter, to smooth out waters at actual discusion, otherwise it won't fit in
please, i sugest this, because it requires a perspective shift with 180 degrees : you see, most cam are extensions, simply doing something and what you see is what you get, but there are things really tailored to an mcs
Hi All - The issue with cnc machine control is that there are three main domains to control. rapids ie no tool load, roughing and finishing.
1) rapids - we want very fast AtoB motion without overshooting or exciting the machine ie minimise settling time
2) Roughing - don't need accuracy but do need to maximise MRR. Heavy MRR will lead to vibration so smoothing jerk minimises delta Accel which minimises inertial forces which means better cutting (generally speaking)
3) finishing - we need position accuracy but at max speed so path accuracy and smooth paths require smooth accels. Constant velocity machining means we will have pathway accels due to inflections in path eg lines to rads
close, but no cigar ... machine has not clue if it sees finish, roughing, inertia or a crash
yes, those are different scenarios, but also different scenarios are these :
... trapez vs S motions
... read ahead of 4 lines or 50 lines
... diff 0 or diff 1
this enumaration above has things in common with your enumaration ( rapid rough finish )
again, here we are, discussing the mcs / kindly
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