RE: stepper pulse rate idea

["Steve Stallings" <stevesng-at-newsguy.com>]

Ray,

On the topic of your proposed speed shift for
steppers driven by EMC.....

I think Jon's PPMC is a good solution the
problem, as would be the Gecko 2002 or any
similar hardware based step generator. Yes, I
know, this is avoiding the issue.

If you do implement a speed shift, then EMC
or the hardware will have to keep track of the
fractional parts (in fine mode) so that you
can put them back after shifting. This should
be possible with a pulse multiplier such as
is used in the Gecko 210 and 340. The chips
used in the Xylotex board actually change
micro-stepping resolution internally and
will "round" the current position to the
nearest full step position when you shift
from micro-step to full step.

My personal feeling is that, if you are going
to add hardware to solve the problem, then
the added hardware should be a step generator
which would solve the problem for all brands
of motor driver.

Regards,
Steve Stallings



> ------------------------------
>
> Date: Thu, 13 Mar 2003 15:57:47 -0600
> From: Ray Henry <rehenry-at-up.net>
> Subject: stepper pulse rate idea
> Message-ID: <200303140000.h2E00hvr027043-at-btc3.up.net>
>
>
>
> List
>
> Those of you who have applied the EMC to steppers that run
> from the parport
> know that you have to design into the machine a compromise
> between speed and
> resolution.
>
> This compromise is fixed in part by Jon's PPMC stepper rate
> generator card.
> This card goes a long way toward expanding the range of
> stepper powered
> machines to which the EMC can be applied.  (this is not
> just a blatant
> advertisement but an attempt to clarify where the rest of
> this post is going
> or not going.)  I'm thinking here of a direct parport driven system.
>
> What I'd like you to think about is a two scale pulse train
> for each axis.
> One pulse train would run at a low rate for high speed
> travel, the other at a
> high rate for low speed resolution.  Let me suggest a
> couple of ini variables
> because that may be the easiest way to think about this.
>
> INPUT_SCALE_RAPID =  5000 0000
> OUTPUT_SCALE_RAPID = 5000 0000
>
> and
>
> INPUT_SCALE_FEED = 50000 0000
> OUTPUT_SCALE_FEED = 50000 0000
>
> As I see it we would not change the resolution of the axis
> hardware itself.
> We would change the resolution that the EMC sees or
> imagines to se out there
> at the machine.  I think this thought experiment has
> software, hardware, and
> value components.
>
>
> 1 - Software
>
> What kind of a nightmare would we create for the software
> if we ran the 5000
> step scale for any rapid move and the 50000 step scale for
> any feedrate move?
> The example is deliberately exaggerated to show that there
> will be a rather
> slow feedrate above which you can not cut.
>
> Some sort of scaling would have to happen in several places
> including
> accel/decel, following error, position, world model, etc.
>
> Some sort of output would have to tell the hardware to
> change the pulse
> scaling.
>
>
> 2 - Hardware
>
> I spoke with Mariss at Geckodrive this morning about
> applying this notion to
> his step and direction servo with the pulse multiplier card
> (G340).  His
> initial response was, "don't even go there."  I suspect
> that pretty well
> matches the initial thinking of most the readers of this post.
>
> As you can see from the scale numbers above this is a ten
> to one ratio.  This
> is one of the ratios available with the Gecko card.  Others
> are two and five
> times the input rate.
>
> Mariss listed a dozen reasons why it couldn't be done and
> then came up with a
> couple of ways that it could.  In fact he even thought
> about building a new
> pulse multiplier card that would do it.  In typical "Ray
> steps in IT again"
> fashion, I offered to be an alpha/beta test site for such
> an animal.  There
> would need to be some small delay (70 ms in worst case) for
> the pulse
> multiplier to complete it's work before the pulse train
> from the other scale
> begins.
>
> Although I have not spoken with Jeff at Zylotek, I suspect
> that it would be
> as easy to accomplish the same thing with that board except
> that the scaling
> would be full, half, quarter, eighth and you would be dealing with
> microstepping rather than servo stepping.  You could do the
> same thing with
> the G210 from Gecko.
>
> Or we could simply build a small pulse multiplier card that
> would do the work
> somewhere between the PC's parport and whatever step and
> direction device we
> have out there.  Matt would be incined to build one of
> these into one end of
> a parport cable or one of those little Radio Shack db25
> jumper boxes.
>
>
> 3 - Value ( your chance to vote or express your thoughts)
>
> 3 - a  Do you see any value to such an approach to
> expanding the range of
> stepper speeds that the emc can reach?
>
> 3 - b  Assuming that we can accomplish the hardware side of
> this in one of
> several ways, would it be worth doing on the software side?
>
> 3 - c  Ray needs to reduce his caffeine intake?
>
> (snip replies to save)
>
> Ray
>
>