Re: [CAD_CAM_EDM_DRO] stepper encoders

In a message dated 12/2/2002 12:16:26 PM Central Standard Time,
mmiami2002@... writes:

> All I realy know is the pin outputs +vcc, gnd , ch a, ch a not, ch b, ch b
> not, index, index not.
>
> Could someone explain the basics of hooking up these connections?

Troy: I have been reading about encoders and "feedback" on machine-control
for years (and gave up and stuck with steppers with great success!), so I can
tell you about these connections, though surely some others "in here" like
Mariss or Jon could do so much more eruditely:

"+Vcc" means the Plus DC supply, PROBABLY 5.0 VDC. Gnd is "common" to DC and
all outputs. There are "three outputs", Channels A and B, and Index. The
"Not" for each is simply the INVERTED version of that output. For example,
if "A" is HI, then "A not" would be LO, and vice-versa. SOME counters "want"
inverted inputs, and I suppose some might be configured to "want" both, but I
can't imagine why!

Now, to what "A", "B", and "Index" are: You have an "incremental encoder"
with "quadrature outputs, plus index". That means that A and B are "ninety
degrees out-of-phase with each other. That is, B changes state (HI to LO, or
LO to HI) in the MIDDLE of the HI (or LO) of A. In other words, if A has
"gone HI", then B can "go HI" after that, but BEFORE A "goes LO" again.

The Counter the encoder signals is a "bi-directional counter", that is, it
can count UP or DOWN. It counts UP when B goes HI when A is HI, and counts
DOWN when B goes LO when A is HI. Or, if the counter can also count when A
is LO, it has to "remember" which direction is which, so that it counts DOWN
when B goes HI when A is LO, and so on. This can get complex with out
face-to-face explanation with PAPER and pencil in front of the explainer!
There ARE books covering the topic, with diagrams, but it can get "hairy" for
a non-digital-logic-person, at first!

The INDEX generally makes ONE pulse, often the same "width" as, say, one HI
pulse of B, but ONLY one time per turn, and ALWAYS at the same position in
that full turn, say "12:00 o'clock". Then, this "index pulse" can be used by
the counter to "make sure" it has "kept up" with all the up/down counts, so
that ITS total-count is "syncronized" to the full-turn of the shaft, etc. It
is difficult to describe very clearly in words, particularly by THIS ignernt
old dummy!

HTH! Jan Rowland


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