Re: mouse encoder

Hi Weyland, Tony,

Talking about making encoder disks by drilling them, I posted a JPG
about a year ago, using a jig to drill holes in a brass plate:

http://groups.yahoo.com/group/sherline/files/IndexJig.jpg

The disk was for a robot's wheel encoder, I made the disks about 14 or
so years ago, when I bought my Sears/Sherline mill. I used a
photo-interrupter type sensor, and calculated the ring circle for the
center to center hole distance I wanted. Then I used a plastic timing
belt pulley to index the ring of holes I drilled. Worked OK, probably
less light transmitted through holes then slots, and alignment was
harder. Before CNC!

Alan KM6VV


Tony Jeffree wrote:

>
> At 01:12 22/08/2001 +0000, you wrote:
> >Simply excellent, Tony.
> >Bravo.
> >This is indeed *exactly* what I was thinking.
> >Did your parts come out of a mouse?
>
> No - this is a mouse-free design
>
> >Also, a word on the slots.
> >In thinking this over, it occurred to me that one could just as easily
> >(if not more easily) simply drill holes in the disc.
> >Upon looking at it, it would appear that they put slots in
> >only to make it easier to account for not-so-perfect alignment.
>
> That is part of the reason - the other part (which is important for a
> quadrature encoder like in the mouse) is that a slot gives a better defined
> mark-space ratio to the generated signal.
>
> >If one were to calculate the width of the slot, pick a suitably close
> >drill diameter, and drill the holes with a like distance between the holes,
> >wouldn't this do the same thing, and be much easier and quicker to make?
> >(in other words .031 holes, .062 apart)
>
> This would work fine for a simple sensor like the one in my RPM meter, but
> I wouldn't go that way if I was building a sensor that woud generate a
> quadrature output.
>
> >I'm thinking that with a 200 step per rev motor, you simply plot the bolt
> >hole circle
> >for the correct size disc and hole, and start drilling away.
> >This seems much simpler and quicker.
>
> If you have the technology to divide the circle (dividing head, rotary
> table, CNC mill...), cutting slots vs drilling holes is not that much more
> difficult.
>
> Regards,
> Tony