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-----Original Message-----
From: Jon Elson [mailto:jmelson@...]
Sent: Sunday, June 06, 1999 6:10 PM
To: CAD_CAM_EDM_DRO@...
Subject: Re: [CAD_CAM_EDM_DRO] EMC & Linux


From: Jon Elson <jmelson@...>



Matt Shaver wrote:

[There are other documents like the NCMS (National Center for

Manufacturing

Sciences) Next Generation Controller Part programming Functional
Specification (RS274/NGC), which, unfortunately, only exist as paper
documents. This one is 127 pages and I have a Xerox which also has Tom
Kramer's handwritten notes in the margins regarding the

inconsistencies in

the document. I'd scan it and html it if I had the time. I

can't imagine how

long it would take to OCR it and then as slow as I type, we'll

all be dead

before I could finish, plus, what do I do with Tom's handwritten notes?
Footnotes? Appendix?]

I have this document, too. I could scan it, but it would have to
be published
as an image. There is so much henscratching all over it, no OCR could
read the original printed text (which is wrong in many places, hence the
henscratches).

Paraphrasing NCMS:

G09 Exact Stop (Non-Modal) Causes an exact stop before the next

move begins.

G61 Exact Stop Mode (Modal) Same as G09, except it doesn't affect rapid
moves.
G64 Contouring Mode (Modal) Default mode where the next move

begins when the

previous move has reached a position within the "tolerance

band" specified by

the machine builder. (I wonder where this tolerance is in the

EMC, and how to

change it?)

Unfortunately, they don't seem to work.

Right, I was pretty sure from some email with Fred that this was
a permanently
active feature, right now. There is no 'tolerance'. The next
move starts as
soon as the deceleration of the current move begins. Since the
deceleration
is a linear ramp at a fixed rate, if you slow the feedrate, the
decel begins closer
to the end point. So, if this is a problem, you can program or
override the
feedrate at these points to prevent rounded corners (or crashes!) where it
matters.

Unfortunately, they don't seem to work. The reason for the

blending in the

first place (as explained to me by Fred, and which I hope I remember
correctly) is that the heritage of the EMC is the robotics

family, not the

machine tool control family. There are three variables involved

in motion

control:

1. Desired Velocity (feed rate)
2. Maximum Acceleration Rate
3. Path Geometry

<snip>

The immediate problem with all this is that the stepper guys

(and that will

be me soon as well) have acceleration limits low enough that

they are getting

blending at machining feed rates. This could cause there to be

radiuses where

none are expected! Either they will need to hop up the hardware to allow
faster acceleration (higher supply voltage Tim?), or G61 needs

to work, or

you need a dwell between every move (the other alternative of

limiting the

feed rate isn't a good answer).

Well, I see it on my fairly responsive servo system, especially
when I have
some non-cutting moves above 45 IPM.

Jon


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