On Mon, 03 Oct 2005 23:12:29 GMT, Howard Eisenhauer
wrote:
O.K., today's silly question- Maybe I'm missing something here but
how does the readout know to count up or down with only the raw
clocking out from the encoder? Seems to me that without the
quadrature info the display won't know whether to increment or
decrement-
O.K, so lets say I have missed something in the discussion & the unit
is counting in the right direction, if you reverse the encoder's
rotation how many pulses does it have to generate before it knows it's
going backwards??
Enquiring Minds want To Know-
H.
Howard,
The encoders I'm using have a clear disc with a bunch of lines
arranged radially and measure about .1" long from the edge toward the
center. The two line detectors ( A and B) are arranged in a "phased
array". This means that the detectors are placed such that first A
detects the leading edge of a line, then B detects this edge, then A
detects the trailing edge of the line, then B detects this line.
Actually, the line A and B use can be different lines as long as the
detectors are placed properly and the lines are evenly spaced (which
they are). It works like this:
The detector A would see the dark leading edge of the line, then as
the disc turns detector B sees this edge but sees it before the disc
has turned enough for A to see the trailing edge. Then the disc turns
a little more and A sees the trailing edge. Then B sees this edge but
sees it before A sees the leading edge of the next line. Kinda wordy
explanation. Surely someone here can say it better and clearer. OK,
now that we know the pattern of detection we can see that A will lead
B when the disc turns one direction and B will lead A when turning the
other direction. So that's how the display knows the direction. This
detection scheme also allows both single and quadrature pulses to be
read by the display. If the display only increments one count on the
leading edge of A then the number shown will be the number of lines
that have passed A. But if done the way explained above the display is
able to count 4 pulses for each line passed. I don't know, but I
suppose that the display still uses detectors A and B to tell which
direction the disc is turning, even when it is only showing the actual
number of lines that have passed one detector.
Eric
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