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Offline Scott

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Re: New CV features
« Reply #30 on: December 09, 2006, 01:18:19 PM »
Ok you two, now you're just messin' with my head!  :D  I see you turned that less than into a greater than for Stop CV On Angles!  The operator or less than sign wasn't the problem, it's the way that the numbers are being handled.  A 90 degree angle is less than a 91 degree angle so if I have a setting of Stop CV On Angles < (less than) 91, it should stop.  If I have a setting of less than 89, it shouldn't.  By changing the sign to > (greater than) you're saying to stop on angles greater than say 90 on up to what, 360...?  It needs to be the way it was (less than) and the handling of the values should be reversed.  ;)

That aside, with my sample file below, with any setting for angle, the machine basically acts as if it's in exact stop mode.  Depending on the angle setting, it may or may not stop CV on the 90 degree angle, but it always hesitates at the transition of the G01's and G02/3's.  Also, with Stop CV On Angles unchecked and CV Distance Tolerance checked with a value of 0.1, as you raise the feed speed, it starts to hesitate in the same manner.  This will happen on files other than just my sample.

Regards,
Scott
Re: New CV features
« Reply #31 on: December 10, 2006, 05:55:02 PM »
I have been thinking about this problem that you are having and I think I know what it is... It is the acceleration that is your trouble but the more accel that you have the more you don't like the axis starting and stopping... it is not "smooth". If you take the derivative of acceleration it is known as "Jerk"... this is known as jerk because it is the change in the Rate of change... What the heck is that! you say... Well if you look at the graph of mach3's accel it would look like this:

 -----------
|          |
|          |

The vertical walls are telling us that we are getting very high Jerk and will get a shock into the machine when we start and stop a move. The worst would be to Reverse direction!

You would like to see an accel that looks like this:

   ------------
  /              \
 /                  \

This will make for a move that will not give the sharp shock into the system.

Now for the bad news :( there is nothing that we can do at this time to make this work for you... You need to have Scurve acceleration to get the jerk out of the system OR you need to have more mass to stop the shock (can't be stopped as fast, and is not a good fix). If you were running a Galil we could use the S curve accel in it to smooth out the accels in your table, but that would be about 1200.00 min to get set up :(

Just wanted to tell you where I think you are getting the problem from.
Brian
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com
Re: New CV features
« Reply #32 on: December 10, 2006, 06:24:42 PM »
Cant the S curve acceleration be implemented within Mach?
Best regards
Fernando

Offline Scott

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Re: New CV features
« Reply #33 on: December 10, 2006, 08:36:02 PM »
Brian,

I'm not sure that we're on the same page.  At least I hope not.

If you take a look at the attached jpg and see the red and blue segments of the toolpath, they each represent one line of code.

Here's the senario;

CV on with Distance Tolerance unchecked (off) and Angle limit unchecked (off), run at 120ipm and 150ipm.  Motion is just fine. Albeit with some corner rounding (understood).

Next, CV Distance Tolerance checked and a value of 0.1 applied.  120ipm runs okay and 150 ipm hesitates at each segment (red, blue, red,.....)  If you raise the Distance Tolerance value, you can get to the point where it doesn't hesitate, but you have then negated the limit on corner rounding by raising the value.

Next, CV Distance Tolerance checked or unchecked (doesn't make a difference) and Angle limit checked with a value of 89 (again, it doesn't matter what value you put in there except for the 90 degree angle in the toolpath), it will hesitate at each segment again.  Feed speed makes no difference here.

Why do we need to stop at each segment?  The angle isn't acute by any means and there's little to no need to acel or decel in this situation.  Now if I have a lot of small curves and segments back to back, I can definitely see the need for ramping the speed up and down as it goes through them, but not to hesitate at each line ever unless you have chosen to run in Exact Stop mode.

I have also noticed that V-carving is affected by corner rounding and running a v-carve file in exact stop mode is something that is impossible.

I don't know how I can describe the situation any better and I truly hope that we aren't talking about the same thing, just in different words, because if we are, for a great share of my work on my machine, Mach will become unusable.  :-[

Regards,
Scott
Re: New CV features
« Reply #34 on: December 10, 2006, 10:12:19 PM »
yup we are not on the same page but we are looking at the same problem... You need to run a heigher accel to get closer to the path in CV mode BUT your router can't take the "jerk" that is being devloped by the acceleration (makes a gouge form deflection). The CV distance mode woudl work for you if you had a mill type machine that had mass and a good amout of steps per unit. I wish you could see mach 3 run a mill becasue it is SO smooth.

Brian
Fixing problems one post at a time ;)

www.newfangledsolutions.com
www.machsupport.com

Offline Chip

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Re: New CV features
« Reply #35 on: December 10, 2006, 11:30:54 PM »
Hi, Scott

Would you post your Steps Per, Vel. and Acceleration values.

I have read some of the posts hear and have had some simillar issues early on.

Your values I read were vel 780 acc. 13.

Try setting your Vel to Max speed just where you start to miss steps then back it off some.

Then set your acc. to as fast as you can from a dead stop to missing steps then back this off some also.

You can set the speed to lower than your Acceleration start speed with your F settings, or over-ride.

I had this problem with a Water-jet cutter being Jerky also this smoothed it out, dual overhead gantry.

Give this a try let us now.

Thanks, Chip

Offline Scott

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Re: New CV features
« Reply #36 on: December 10, 2006, 11:54:40 PM »
Thanks, I'll check into it more tomorrow, but right now I'm pretty sure that my Steps Per are 1834.864039 for XY, Velocity at 817.2 (the top of the scale for 25000) and the Acceleration has been tried at 13 to 15.  15 makes it more crisp, but also gives a aftershock that will leave ripples on any edges that are affected by it.

I have been able to run as high of a velocity as it will go at the 35000 setting, but that seems a bit fast.  I have run for quite a while with it at 840, but then out of the blue, it will loose steps big time during a jog with quite a bit of racket as things try to catch up.  I'll get everything reset and it will be fine again for another day or two before it happens again.  So I just set it back down, but it has happened at the lower setting too.  Seems like something all of a sudden causes the loss and then is gone for a while again, making it hard to pin point and find a setting that I can set and forget.  :(  I'm running a slightly overclocked Athlon XP 2500+ with 512 ram.

Regards,
Scott

Offline Chip

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Re: New CV features
« Reply #37 on: December 11, 2006, 12:24:08 AM »
Hi, Scott

I looked at your sample.Tap File, It dosn't have a F value set for your G01, G02, G03, so there running at 100 % speed.

Do your other files have F speeds in them. ?

Could you post an actual file your having problems with and describe your machine in a little more detail, stepper-servo, size, photos.?

Thanks, Chip
« Last Edit: December 11, 2006, 12:37:17 AM by afn09556 »

Offline Scott

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Re: New CV features
« Reply #38 on: December 14, 2006, 07:50:39 AM »
Hi Chip,

Sorry for the delay here.  My machine is a six year old ShopBot PRT96 (48" x 96") with Oriental Motors 3.6:1 steppers.  The gantry is relatively light and does flex or wiggle in the Y direction, thus the difficulty with high acceleration.  I've done some modifications to stiffen things up, but it needs to have the X car reinforced or redone in order to stiffen that up and probably a second Y motor on the opposite side.

I just stripped the Z moves and F values from the sample file and just manually set the feed rate up and down.

Here's one of a number of gun box files that I have been running lately.  This particular one gets the rear site notch rounded out and the muzzle end also get the detail removed while a sharp corner at the front of the grip is just fine.  High acceleration makes the the direction changes too harsh.  Adding in a CV distance of 0.1 is about as low as I seem to be able to go without Mach stopping at each line of code like it was in exact stop mode and still rounds corners.  I don't understand why we have to hesitate between two lines of code that need little to no ramping between them like along the underside of the barrel and the back of the handle (these hesitations just introduce more vibes).  A stop CV on angle limit of any value just results in an exact stop condition and an overheating tool.

The attached photo is the same gun, just a different type of box.  This one was done with my old controller.  I wouldn't even attempt the design on the cover at this moment, in fear of it rounding out every detail, even if it's just a scratch path on the line.

V-carving files seem to need another whole different setting that I haven't found yet.  :(

I've come to the point where I don't have time to fart & fiddle with it anymore and just need to get stuff done now.  I'll have to do some machine modifications after the holidays and hope for something closer to exact path w/ramping, like I've been used to, in the future.  ;)

Regards,
Scott

Offline Chip

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Re: New CV features
« Reply #39 on: December 14, 2006, 08:25:20 PM »
Hi, Scott

Thanks for the photos nice work.

As far as the problems go, I didn't mention.

Have you try-ed setting the LookAhead value down in Config. General Logic.

Setting the Step & Dir Pulse up some in Motor Tuning, some stepper cards need this.

Change the Dir & Step Low Active  to opposite state in Ports & Pins, Motor Outputs, some stepper cards need this also.

You can Reverse Axis Direction in Home & Limits page (Reverse box), Its really the proper place to do this, well in My opinion.

May-be one of these will Help, Chip