Re: [CAD_CAM_EDM_DRO] Balls in tube DRO Resolver to Digital

vrsculptor wrote:

>A while back there was discussions about using ball bearings in a
>tube for a DRO scale.
>

The maker of this is Newall.

The tube would have to be completely transparent to the AC magnetic
field, and I'm not
at all clear on the geometry of the exciting winding and the sense
windings. They would need
to produce a very accurate sine wave variation in sensed signal strength
as the read head was
moved, or the interpolation will not produce accurate position information.

> The reader used several excited loops to read
>its position? I'm not an analog type but would the resolver to
>digital converter metioned previously:
>
>http://products.analog.com/products/info.asp?product=AD2S90
>
>allow you to build a ball encoder? Is it easy or a stretch? Any
>volunteers to design one? Cost seems reasonable, I'd be happy to
>spend $89 for the possibility of an arbitrary length DRO.
>
>AD2S90-EB PRODUCTION Evaluation Boards - COMMERCIAL $89.06
>AD2S90AP PRODUCTION PLASTIC LEAD CHIP CARRIER 20 COMMERCIAL $29.16
>
>

Indeed, these have come WAY down! Yes, this is the type of circuit to
read these signals.
Making an Inductosyn seems a LOT simpler, as the geometry is pretty
straightforward.
It has a planar square wave exiting winding which forms the scale, and 2
planar square
wave sense windings which have the same wave length as the exciting
winding, but they
are placed such that there is a 90 degree phase shift between the two
windings. These can be
made by printed circuit technology. You just hook it all to the 2S90
series of chips.

Unless I'm missing something simple, you'd have to work out the geometry
and magnetic
field patterns of the windings and balls to get the correct response
depending on motion.
Maybe this is all written down in Newall's patent application.

Jon