Re: Ecoder resolution terms

Jon,

I thought pulses meant the "whole" square wave. Which means either 200
(one channel) or 400(both channels)PPR for a 200 line encoder?

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> Mina Aboul Saad wrote:
>
> >Hi,
> >
> >I just need to know the difference between several encoder
resolution terms.
> >I read the Gecko requirement and it mentioned a min. 200 line
encoder
> >Searching to buy the encoders, I found the following resolution
terms:
> >- Count per Revolution (CPR)
> >- Pulse per Revolution (PPR)
> >
> >Could someone please explain the difference between the 3 terms.
> >
> >
> This is a great big mess. The only terms that you can be certain
about
> are cycles/rev or lines/rev, they are equivalent. When
abbreviated,
> however,
> you have a problem. Does C mean Cycles or counts? That's when the
> trouble starts.
>
> One cycle or line on the encoder produces 4 edge transitions, so any
> quadrature decoder that decodes all transitions (counts all edges,
etc.)
> will give 4 counts for the full cycle. So, a 1000 CYCLE/rev encoder
> is a 4000 COUNT/rev encoder. COUNT and Pulse are equivalent, in
> most cases. But, CPR is totally meaningless, unless you know what
> tht "C" stands for.
>
> The 200 LINE encoder mentioned above should give 800 COUNTS/Rev.
> Also, in Gecko terms, this is not a hard and fast number. I
suspect a
> Gecko 320 could be hooked to a very small motor with a 16 CYCLE/Rev
> encoder and made to perform acceptably. It wouldn't do so well on a
large
> motor connected to a large machine, of course.
>
> Don't look at the encoder first. First, find the motor that is
capable of
> driving the machine in question with acceptable torque and speed.
> Determine the belt reduction ratio, if one is needed. THEN, figure
out
> the revolutions of the motor/unit of linear measure, and figure out
> what encoder resolution you need. For instance, if you want to
describe
> positions in units of .0001", it would be good to have resolution
of as
> close
> to .00001" as possible. If a wood router only needed .005"
accuracy,
> than a .0005" resolution would be good enough. This is an old
machine
> tool "rule-of-thumb" and is not very strict, but a good guideline.
>
> Jon