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Magnetic and optical vernier encoder

IP.com Disclosure Number: IPCOM000030031D
Original Publication Date: 2004-Jul-23
Included in the Prior Art Database: 2004-Jul-23
Document File: 4 page(s) / 41K

Publishing Venue

IBM

Abstract

A magnetic encoder uses the vernier principle for increased resolution. This design allows an air-gap between the magnetic disc and the GMR sensor array so that no abrasion occurs.

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THIS COPY WAS MADE FROM AN INTERNAL IBM DOCUMENT AND

NOTNOT

FROM THE PUBLISHED BOOK

DE820030170 Fritz Teufel/Germany/IBM Stefan Goeldner, Hans-Guenter Kraemer, Thomas Albrecht

Magnetic and optical vernier encoder

Summary of Invention:

The rotary magnetic encoder uses a magnetic media on a rotating disk and a GMR (Giant Magneto Resistive) sensor array. The technical design of sensor array and magnetic disc pattern follows the vernier principle. This principe allows large magnetic bit-sizes and thus a large distance between sensor array and magnetic disc - numerical simulations show, that the length of a magnetic bit has to be in the same order of magnitude like the distance between magnetic track and sensor . In the proposed encoder the sensor array has no contact to the magnetic media and hence no abrasion is possible neither on the magnetic disk nor on the sensor array . The whole system is encapsulated in a dust-tight housing.

sensor chips with 250 sensors

magnetic disc with 400 flux changes

base plate

Fig 1

Fig 1 shows that a low number of magnetic flux-changes is available. To obtain a high resolution, the sensor chip consists not only of a single sensor, but of an array of sensors (e.g. 250 sensors and 400 flux changes for a 100000/2Pi resolution).

The principle of a nested vernier-sensor array is shown in the next schematic:

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General considerations - sensor chip geometry

d

The distance between two sensors in any row S differs from the distance lp of two consecutive flux changes byand, a number of k sensor-stacks is convoluted to one sensor array Sk,n, where n*=lP.

E xam p le: A ssu m p tion

* resolution of the encoder R = 100.000C P R


* m in im u m p a tte rn le n g th lmin ~ 110µm
* d ia m e te r o f th e p a tte rn w h e e l d = 1 4 m m

Pp

NNNNNN NNN

SSS SSS SSS

S 1,n

S 2,n

S k,n

lP

xS

Geom etry

num ber of flux changes N P

num ber of sensors N S to achieve R

πN P

d

=⋅=4 0 0

l

m in

NRS N

==2 5 0

P

2

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