Re: encoder head pitch, or, quit your griping.

Hi,

Yes, this is the same principle. The point is that with gratings crossed
at an angle movement of one relative to the other produces a series of
dark bands which move at right angles to the movement. Changing the
angle effectively allows you to space these out as much as you like and
so it would become practical to make a reading head containing, say, 10
phototransistors equally spaced over 6 inches, then, by arranging it so
that the length of this set of sensors corresponds with 9 or 11 dark
bands, you get a vernier effect which magnifies the resolution.

Ian

Bill & Joyce Ammons wrote:

>
> From: Bill & Joyce Ammons <ammonsbj@...>
>
> Ian,
> What you described reminds me of a shaft encoder design that utilizes two
> discs with equal width opaque and transparent sections and the total number
> of sections for each disc to be different by one opaque section. One disc
> is stationary and the other is rotated. If the pair is illuminated from
> one side, interference produces a pattern that is dark at one angle and
> lighter as you progress across the diameter to the opposite (180 degrees)
> side. This pattern rotates 360 degrees as one disc is advanced one
> dark/light increment. So resolution is multiplied by the number of light
> sensors. For instance, discs with 100 and 99 dark lines and 10 equally
> spaced sensors looking through the discs, (parallel to the rotation axis),
> would yield a resolution of 1000 states per revolution.

Best wishes

Ian

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Ian W. Wright LBHI
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