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Author Topic: Odd glitch in movement?  (Read 7639 times)

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Offline BR549

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Re: Odd glitch in movement?
« Reply #20 on: April 27, 2014, 03:58:44 PM »
HIGH speeds are only good for LARGE tables were you have to jog a long distance sometimes. It is a waste on small tables and will bite you one day jogging at high speed on a small table.

Here I limit the table to 200IPM at 30IPS/s accel. That does a great jog on 99.99% of all cutting we do. That would be from 28 guage up to 3/4" Steel and 28ga to 3/8" alum plate AND we cut a lot of each.

YOUR parameters will be dependant on your table design , rigidity, drives and motor and Feed mechanics ( screw,rack/pinion,belt) type.

(;-) TP

Offline Davek0974

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Re: Odd glitch in movement?
« Reply #21 on: April 27, 2014, 04:07:14 PM »
Brilliant, thanks

Looks like I'm shooting too high on the speed and too low in acceleration.

Does my tuning strategy seem correct?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline BR549

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Re: Odd glitch in movement?
« Reply #22 on: April 27, 2014, 05:00:14 PM »
IF you go with a lower Vel then your acel is not as sensitive to lost steps.

Your sweet spot will be based on YOUR machines ability to Acell under load.

TEST,Tune,Test,Tune

(;-) TP

Offline Davek0974

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Re: Odd glitch in movement?
« Reply #23 on: April 28, 2014, 06:46:18 AM »
Just out of curiosity, and I know it's machine specific, but what sort of figure do you have for relative G force on your setup??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline Davek0974

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Re: Odd glitch in movement?
« Reply #24 on: April 28, 2014, 10:33:39 AM »
OK, educational half hour for me...

Speed was set at 3300mm/min in the file, THC codes removed, all CV config boxes cleared, THC turned on and ignored by me ;)

In the first picture we have, from the back, acceleration values of 2000, 1500, 1000 & 900mm/s/s

As you can see, the higher the acceleration, the worse is the ripple effect caused by my belt drive system or machine design being taxed too hard.

Once I hit 1000mm/s/s I dropped to the smaller increment to see what happens and the 900 seems to be pretty acceptable i think?

The second picture shows the 900mm/s/s cut face-on and the nasty exit slope seems to be all but gone now which is good.


A question..

Is it worth going any lower on acceleration as the quality likely will not improve much as it seems pretty good bearing in mind this is the thinnest/fastest material I have (1mm)?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline stirling

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Re: Odd glitch in movement?
« Reply #25 on: April 28, 2014, 10:47:16 AM »
CV rounding < accel > Jerk.

i.e. accels right there somewhere between CV rounding and Jerk. What's the best accel for your machine? Looks like your close on finding it. To me those cuts look pretty darn good. Good work.

Ian

Offline Davek0974

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Re: Odd glitch in movement?
« Reply #26 on: April 28, 2014, 01:15:12 PM »
Well at least I'm getting somewhere now thanks to all the help :)

I might try and se what happens if I knock it back another 50 maybe, just for reference purposes but as it is, I think it's a 100% better.

Question - as it is I now know it will work at 3300mm.min on 1mm sheet very nicely. If I then go for thicker metal, say cutting at 700mm.min, will the acceleration have less 'bite' than it does at this higher speed.?

My guess is it will be gentler as there is less speed to reach but I'm still a bit foggy on how it affects the process.

:)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline BR549

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Re: Odd glitch in movement?
« Reply #27 on: April 28, 2014, 04:33:36 PM »
The question remains is the chatter in the cut related to the belt drive rebounding OR is it THC osillation due to the THC coming back online after the arc ??  I would lower the THC SPEED a bit and go back up on acell just to see IF it is any better.

Here that cut would be a nice sharp corner about as sharp as it it drawn .BUT that is this machine not yours. Here the settings are Vel 200 Acell 30IPS/S. It would depend on the drives/motors here everything runs from nema 34 high torque motors and gecko drives and the CLong axis has 2 slaved nema 34's.

Looking better though, (;-) TP

Offline Davek0974

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Re: Odd glitch in movement?
« Reply #28 on: April 28, 2014, 05:02:38 PM »
I could run the same speed and part with THC off to prove the point, but I'm fairly certain it's belt flex. I have the THC rate very low, 8 or 10% i think! I don't think it would react fast enough to oscillate that rapidly. Plus the sheet is pretty flat so I doubt THC is doing much at all in this instance.

Will try tomorrow though just for confirmation.

It's more likely because I have under specified my belts, they are only 10mm wide, Y has two and Z has one. To make matters worse, they are full loops too so are about 2m long each. I could have halved that by mounting the motor on the gantry and using the belt as a rack but that would make the gantry far heavier which I thought would be a worse situation.

Live and learn, it's almost pretty damn good and that will be good enough for my uses I think, little bit more fiddling and learning should have it nailed.



Just thinking on, my settings for vel and acc are higher than yours, would I not get exactly the same results as you by setting them the same?
Just wondering.
« Last Edit: April 28, 2014, 05:04:56 PM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline stirling

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Re: Odd glitch in movement?
« Reply #29 on: April 29, 2014, 04:34:54 AM »
Question - as it is I now know it will work at 3300mm.min on 1mm sheet very nicely. If I then go for thicker metal, say cutting at 700mm.min, will the acceleration have less 'bite' than it does at this higher speed.?

Not sure what you mean by "bite" but if you mean "jerk" then...

(Jerk is not just an arbitrary term btw - it's the pukka name for the rate of change of acceleration).

As acceleration is constant in Mach - so is Jerk. (There used to be a planner that used S-curve accel to reduce jerk - but that's another story).

Or to put it another way - any lack of rigidity presents the same issues at any speed.

Not sure if that answers your question.