Re: [CAD_CAM_EDM_DRO] Re: Newall sperosyn encoders

ccs@... wrote:

> I don't believe you can read magnetic tape with the normal heads
> unless it is moving in relation to the readhead. Ie, there is a
> current induced that is dependent on the rate of change of the
> magnetic field. If you were moving an axis at extremely low velocity,
> the induced current could well be too small to detect. It may work
> under normal use, but I'd be afraid it would miss any kind of slow
> creep, say in an axis that was nominally locked...

But, magneto-resistive (MR) sensors do not respond to the CHANGE
in magnetic flux, they sense the flux itself. These have been used for
years in some positioning systems, but now are used by the millions
in the read heads of high-end hard drives. (Yes, they have a write
coil, and an MR sensor for reading in the same head. The MR sensor
is used because it has no inductance and is much more sensitive
that the tiny coil of wire that would be needed otherwise.)

> I think the balls-in-a-tube system works inductively - ie, the read head
> generates a changing magnetic field and determines how much ferrous
> metal is inside the tube there. Balls are used because they can be
> cheaply had at great precision - just drop them into precision drawn
> tubing (or maybe even force them into slightly undersize tube) and
> all the hard stuff is in the read head.

Yup, and that, indeed, is the problem. The hard stuff is really hard
without Newall's custom IC.

Jon