Pauses in motion on the M10/M11 commands

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Re: Pauses in motion on the M10/M11 commands

Postby Robertspark » Mon Oct 30, 2017 8:20 am

I think you are misunderstanding a few things, but I do know what you mean and think I can explain what it's doing.

The "stop at angle degrees" that I think you are refering to (89 degrees) does not actually do what I think you thought it does, it only affects the tradjectory planner, have a read of the extract of the manual below. It does not physically change from CV to exact stop where an angle is over 89 degrees (which is what I think you think this probably did). It is how UCCNC plans the tradjectory.

There is a new thread on here that has just started up and you are probably best to follow that as cncDrive / Balazs may have something to add or explain as the thread develops.
viewtopic.php?f=4&t=830
___________________________________________________________________________________

Back to the item being discussed here....

joining arcs and motion slowing / stopping under CV control.

I think I understand what the problem is, but I don't think it can be "fixed" unless you run the macroloop I posted in the other thread and set the feedrate adjust to 100 (100%) for plasma it is set to 60 (60%) which is the acceptable slow down for corners or changes in direction.

The tradjectory planner is very much dependant upon the "corner error max" setting and this very much affects the slowdown from one line of motion (linear motion (G1) or arc (G2 / G3))

Picture this for a moment, when the tradjectory planner gets to the end of an arc it only knows that its feedrate is say 10000 units / min, and it does not know the angle that is formed by the end of the motion and the next segment (line or another arc). It could have a G02 followed by a G03 motion (directly back on it's self) the best way that it knows to make the turn correctly is to slow the feedrate down to meet the centripetal acceleration limiting radius (corner error max) and then whatever comes next will be arrived at correctly within the parameters {you} set.

hence if youve got the default 0.03 units the slowdown is going to be huge if you are running at 10meters / min because it has to be.

Try the following codes in metric or imperial, adjust the X and I numbers and feedrate acording to your preferences (setting F as high as possible will emulate your machine running at its max velocity setting even if F is higher than the set number)

In short, use the macro I posted and set the asjustment in feedrate (%) alowable velociy change accroding to you preferences.
I don't think there is a fix for what you are asking for as it does not need a fix, you are the one who set the imiting / allowable corner error max setting statically, the macroloop just makes this dynamic.

METRIC Code:
Code: Select all
G91
M98 P200 L10
G90
M30

O200
G02 X20 Y0 I10 J0 F10000
G02 X-10 Y0 I-5 J0
G03 X-10 Y0 I-5 J0
G03 X20 Y0 I10 J0
G03 X-10 Y0 I-5 J0
G02 X-10 Y0 I-5 J0
M99






IMPERIAL (INCHES) code:
Code: Select all
G91
M98 P200 L10
G90
M30

O200
G02 X2 Y0 I1 J0 F10000
G02 X-1 Y0 I-0.5 J0
G03 X-1 Y0 I-0.5 J0
G03 X2 Y0 I1 J0
G03 X-1 Y0 I-0.5 J0
G02 X-1 Y0 I-0.5 J0
M99
Rob

Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
UC400eth, UC300eth, UCCNC v1.2046, Neuron Lite.
UCCNC Macro Manual
Robertspark
 
Posts: 617
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Location: Nr Liverpool, England

Re: Pauses in motion on the M10/M11 commands

Postby Robertspark » Mon Oct 30, 2017 10:55 am

The best simple explanation I've found for centripetal acceleration is here:
https://www.khanacademy.org/science/phy ... celeration

Look specifically at example 1 and expand for the solution.

Image

given it is made up of only 3 parameters:
- velocity
- acceleration
- radius

It is quite easy to consider and use.

In UCCNC we have defined a fixed radius tolerance (Corner Error Max = r) {unless you have a got at using the macroloop I put forward}
the acceleration is a function of your machine setup and is a fixed value.

the velocity is really the variable number even though you define a feedrate that is a TARGET feedrate only if the distance of the move is too short and the defined acceleration of the machine is too long (even on a linear G1 / G0) move the Target feedrate will never be achieved.

with using the macroloop that I put forward, essentially what you are doing is varying the corner radius achievable and attempting to fix the feedrate (acceleration is still a fixed parameter). The trade off is that the corners will not be so sharp but you now have near constant velocity once accelerated up to the velocity. I only thought of this being useful in plasma cutting where the feedrates are high and acceleration is high and it may benefit with reducing jolt or jerk in blended motion. I did not think it would be useful in milling where precision corners were preferred, especially outside corners where the macro will round external corners, but with plasma cutting these are "normally" looped so will be sharp corners anyway, and the inside corners are more acceptable to be rounded relative to the feedrate, material and material thickness and to a degree masked by the kerf.... and most will probably be welding whatever is plasma cut so its less of an issue for a sharp corner internally and it will actually provide a stronger corner by having a slight radius anyway.
Rob

Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
UC400eth, UC300eth, UCCNC v1.2046, Neuron Lite.
UCCNC Macro Manual
Robertspark
 
Posts: 617
Joined: Sat Sep 03, 2016 4:27 pm
Location: Nr Liverpool, England

Re: Pauses in motion on the M10/M11 commands

Postby RJS » Wed Nov 01, 2017 8:52 pm

Robertspark,

Perhaps not as well as you do, but I do understand the physics. I have tried the macroloop macro from your other post and it adjusts the corner error max from 0.03 to 0.64222222222 and I have also tried manually setting it as high as 30 and it makes no difference. The spindle significantly slows down at every arc->arc transition. The only thing that seems to help is to set the acceleration to an extreme value which tells me UCCNC is purposely slowing down and speeding up and at least in my case unnecessarily. I cannot believe this is by design and I am hoping the UCCNC team can either tell me this is by design or that it can be fixed.

Thanks,

RJS
RJS
 
Posts: 20
Joined: Tue Jan 10, 2017 12:16 am

Re: Pauses in motion on the M10/M11 commands

Postby Robertspark » Thu Nov 02, 2017 9:33 am

What slows down, the spindle (rpm) or axis federate.

The macro loop only adjusts the feedrate of the X&y axis.

Doesn't do anything for the spindle.

I am out of ideas, over to cncdrive
Rob

Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
UC400eth, UC300eth, UCCNC v1.2046, Neuron Lite.
UCCNC Macro Manual
Robertspark
 
Posts: 617
Joined: Sat Sep 03, 2016 4:27 pm
Location: Nr Liverpool, England

Re: Pauses in motion on the M10/M11 commands

Postby RJS » Thu Nov 02, 2017 10:53 pm

Robertspark,

The spindle RPM does not change, it is just the x and Y movements, I think the Z axis is affected as well but I am not worried about that it as much.

Thanks,

RJS
RJS
 
Posts: 20
Joined: Tue Jan 10, 2017 12:16 am

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