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Author Topic: Constant velocity  (Read 40241 times)

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Offline Chaoticone

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Re: Constant velocity
« Reply #20 on: September 27, 2007, 12:21:49 PM »
NP Ian, I understand.

Brett
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Re: Constant velocity
« Reply #21 on: September 27, 2007, 12:23:46 PM »
Ian,
CV angle is only telling mach3 that it must come to a full stop at the intersection point of the two moves...

Run this as a test
(Machine needs to be at X0 Y0)
G01 X100 F5000000
Y50 X50

IF the CV angle is at 90 you shoudl not get any rounding of the corner... test it with CV on and CV off. What do you see??

thanks
Brian
Fixing problems one post at a time ;)

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Offline stirling

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Re: Constant velocity
« Reply #22 on: September 27, 2007, 12:58:21 PM »
Hi Brian

I ran your code with angle set to 90°.
With CV mode on I get rounding. With CV mode off I get no rounding which is exactly what I'd expect. Why do you say I shouldn't see any rounding?

Ian

Offline stirling

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Re: Constant velocity
« Reply #23 on: September 27, 2007, 01:02:08 PM »
Sorry Brian - strike that last answer - it's NOT what I'd expect - but I DO get rounding. I'm getting confused now!!!!

Offline jimpinder

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Re: Constant velocity
« Reply #24 on: September 27, 2007, 03:01:56 PM »
I have read through this post and I am getting a little confused as to what we are trying to achieve.
As far as I understand, CV is a system that comes into play when the motors cannot decelerate and accelerate quickly enough to achieve instantaneous speeds required, constantly. The computer therefore decelerates one axis as it accelerates the other so the speed of the tool is overall constant. I don't know if anybody has studied the resultant curve or not  - is it circular, parabolic or what. I dont suppose it matters.

You can turn this effect on or off - and the off position should result in a sharp angle of cut.
A question - IF THE COMPUTER CAN ACHIEVE A SHARP CUT, WILL IT DO IT REGARDLESS OF WHETHER CV IS ON OR OFF

I understand that you are able to alter CV Distance and CV Feedrate. I can only assume that these two parameters only come into play if CV is ON - if it is off the computer will decelerate to 0 and then accelerate up again. I cannot see that you need both parameters - the computer will compute its dec/acceleration from either the distance it is told to start from, or the feedrate it is told to maintain round the shape - I cannot see how it can do both.

As far as the angle is concerned - Stirling - keep it simple.
Try a right angle and run with CV mode on.
I assume the feed rate must be pushed fairly high or the motor will be able to start and stop quickly enough - and up it until you are clearly getting a rounded corner.
I would try the Stop CV on angles, and try ENTERING from 88 to 92 - it may be that at 90 - if it is programed to stop when angle >90, it doesnt catch it - and see where the change from round to sharp occurs (if it does).

I cant see this diatribe will help much, but I cleared it up a bit in my mind, anyway.

 
Not me driving the engine - I'm better looking.

Offline stirling

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Re: Constant velocity
« Reply #25 on: September 28, 2007, 03:34:38 AM »
Jim - you tell me to keep it simple. I thought that's what I was doing when I sent the two short examples to Brian. I have not undertaken this post lightly - I NEED CV to work for me. I spent several hours yesterday doing nothing else but testing the "Stop CV on angles >" and I've done all the simple stuff like you've suggested.

Let me nail my colurs to the mast here. I think that the way that "Stop CV on angles >" has been implemented in the latest version of Mach (R2.45 as of the 5th Sep) is wrong and does NOT do what Art intended.

Brian gave me a code snippet in his last post, told me to set "Stop CV on angles >" to 90, and asked me what I saw. Well, I saw rounding with CV on and a sharp point when CV was off.

So let me ask you to test it and see what you get. I'd be very interested in your results. Note that units are in mm.
Re: Constant velocity
« Reply #26 on: September 28, 2007, 04:17:20 AM »
I am on the road today and will be back at the end of the day... when I get back I will have a look at CV again.
thanks
Brian
Fixing problems one post at a time ;)

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Offline stirling

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Re: Constant velocity
« Reply #27 on: September 28, 2007, 08:39:49 AM »
Brian

I think I've found the problem.

Just to make sure we're on the same page, when we say "Stop CV on angles > 90 degrees. The angle we're referring to as being greater than 90 degrees is the obtuse angle.

Note: We've used 90 degrees as our limit in our discussion but the following holds true for any angle we care to use.

If we refer to the direction of the obtuse angle as being from the first line to the second line then:

For clockwise angles Mach succeeds. i.e. it blends when it should and doesn't blend when it shouldn't.

BUT For anti-clockwise angles Mach fails. i.e. it doesn't blend when it should and does blend when it shouldn't.

If you run the code fragment you posted to me you'll see that it blends (when it shouldn't) but if you cut exactly the same two lines starting from the other end, Mach works fine. I've tried it with loads of examples and the above seems to hold.

The attached pic might help.

Thanks

Ian

Offline stirling

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Re: Constant velocity
« Reply #28 on: October 02, 2007, 10:51:25 AM »
is there no further interest in this from the forum?
Re: Constant velocity
« Reply #29 on: October 02, 2007, 12:19:53 PM »
I have seen your post and can not look at the problem at this time :( I have an OEM that I am working with and as soon as they are done I hope to get into that section of code to see if we can find the trouble...


Thanks
Brian
Fixing problems one post at a time ;)

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