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#1 2014-12-05 17:03:20

vhubbard
Beta User
From: Dallas, TX
Registered: 2004-11-11
Posts: 220
Website

Bell Curve ACC/DEC calculations

We have been working to get accurate times from Vericut for years.  We change the Acceleration settings for Rapid, Feed, and the Various High Speed modes in the control.  (new function added about 2 years ago)  You can get close on time depending on the job, but never close enough.   "Apply Acceleration to Cycle Time" enables the ACC/DEC calculation for each move in Vericut.  Times get longer with this enabled, which is more accurate.

Acceleration and Deceleration, ACC/DEC,  as calculated by Vericut is linear  from what I was told.   On most machines it is a bell curve ACC/DEC.  Bell curve ACC is much slower at the start of the move, but accelerating in a non-linear fashion.   The same for DEC, Decelerating in a non linear fashion, much slower at the end.  The Linear ACC/DEC used by Vericut will often report shorter machining times. 
 
When you have longer moves, 1"/25mm or more and very few short moves,  Vericut can get within 5-15%.   With a high percentage of short moves, .1" /2.5mm or less and high feed rates Vericut will show the moves much faster than they are at the machine.   Vericut will report times up to 50% shorter than actual run time.

On a job with 1 million moves and the majority of the moves being in the .04/1mm range and feeds of 400-1000IPM/10-25MM,  Vericut is off 30-40%.

When there are many small moves and relatively high feeds, Vericut time calculations are not accurate.  I don't see time calculations getting better until Vericut can simulate Bell Curve ACC/DEC.

Turned in as an enhancement Feb 14, 2014  ER 11985

Last edited by vhubbard (2014-12-05 17:21:20)

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#2 2015-01-15 19:46:39

Verifun
Senior Member
From: U.S.
Registered: 2005-03-31
Posts: 351
Website

Re: Bell Curve ACC/DEC calculations

I´d like to see it too... However I wonder if manufacturers would share that info with customers, and if so, in which format... Quite often we realize they don´t know that much about the physics behind their product, or that we can´t get the answers from that geek that designed the thing but from the "business" guys...


Daniel Santos

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#3 2015-01-31 19:54:20

DaveF
Senior Member
From: Valencia, CA
Registered: 2005-08-20
Posts: 304

Re: Bell Curve ACC/DEC calculations

I agree

No mater what the $$  machine shop... managment wants $$ to know how things are going to end before you start.  The $$ problem we are trying to solve is there really is not an $$ Accurate software package I know of... at least.

If Vericut was $$ to provide a solution, that would make a lot of people happy.  It's SO IMPORTANT.... my guess is.... white shirts would actually pay $$ 2 thousand  for and add on the Machine simulation, to cover the development costs. I would  $$ put my neck on the line, and recomend it...........if it was accurate.

Imagine as we explore $$  pocket roughing algerithms.  The cycle time before Optimath is way off.  After OP, still way off.  $$

Dave Frank


Dave Frank
Aerospace Dynamics International, PCC
Valencia Ca
"Where else can you have this much fun,.......and get paid???."

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#4 2016-02-19 15:35:55

vhubbard
Beta User
From: Dallas, TX
Registered: 2004-11-11
Posts: 220
Website

Re: Bell Curve ACC/DEC calculations

To answer Verifun,  if there was bell curve support, the parameters the machine uses can be read from the parameter tables for Fanuc machines.

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#5 2016-03-11 14:28:43

mcam
Beta User
From: Planet Earth
Registered: 2007-06-10
Posts: 81

Re: Bell Curve ACC/DEC calculations

Modifying the accel/decal values in Vericut has never had any effect on returned cycle times in my experience. Is there something I am missing in this process? Should I be switching this on via a macro or macros?

Interestingly, our Okuma MB56VA machine/control model returns very accurate cycle times in 3 axis, but when we use 4 axis, it blows the times out hugely. None of other other machines (all Okumas) are close. This is something I would really like to address at some stage.


New Zealand Vericut Reseller

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#6 2016-03-14 17:25:33

vhubbard
Beta User
From: Dallas, TX
Registered: 2004-11-11
Posts: 220
Website

Re: Bell Curve ACC/DEC calculations

3 things have to be set.
ACC/DEC values for each axis. must be defined for the machine.  Values in inch are inches per second per second.   Machines can be set with values from 9-38 for feed inch mode.   Equivalent to  .025-.1G. which is what most feed mode is.   Rapids on some machines can get to 1G.   
Full cycles must be enabled.
Setup, C-Code, "Apply Acceleration to Cycle Time" has to be enabled.   (for all time not just cycles)

It does make a difference.  More in faster feed materials than in slow feed cutting materials.     If you are cutting under 20ipm/400mmm then acc/dec is a very small part of the overall time.   at 1000ipm/25Mm it can have a significant effect on time.

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