Position detection apparatus

Details Position detection apparatus Position detection apparatus

2003-06-23

2004-07-27

Young, Brian (Department: 2819)

Coded data generation or conversion

Digital pattern reading type converter

Plural types of codes on single carrier

C341S011000, C341S015000

Reexamination Certificate

active

06768426

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a position detection apparatus, used in e.g. machine tools or industrial machines, for detecting the position which has been varied due to linear movements or rotational movements. This application claims priority of Japanese Patent Application No. 2002-190773, filed on Jun. 28, 2002, the entirety of which is incorporated by reference herein.
2. Description of Related Art
Among the position detection apparatus, used in e.g. machine tools or industrial machines, for detecting changes in the positions caused by e.g. linear movements, there are those disclosed in Japanese Laying-Open Patent Publications Nos.S50-99564, S63-177019 and H1-152314.
Such a position detection apparatus
120
, shown in
FIG. 12
, includes one absolute track, referred to below as an ABS track
121
, and a detection unit for the ABS track, referred to below as an ABS detection unit
124
, having n heads for the absolute track, referred to below as ABS heads
123
-
1
,
123
-
2
, . . . ,
123
-
n
. It should be noted that the ABS heads
123
-
1
,
123
-
2
, . . . ,
123
-
n
, if collectively referred to, are termed ABS heads
123
-
1
to
123
-
n.
The ABS track
121
is a pattern of micro-sized areas represented by [0] and by [1], arrayed in accordance with the degree-n cyclic code. The micro-sized areas represented by [0] and by [1] differ from each other as to physical properties. For example, if the position detection apparatus
120
detects the position of the ABS detection unit
124
by exploiting the magnetism, micro-sized areas represented by [1] are magnetized, while those represented by [1] are not magnetized.
The ABS detection unit
124
is movable is movable along the longitudinal direction of the ABS track
121
, indicated by arrow Y in the drawing. The ABS heads
123
-
1
to
123
-
n
are provided facing the ABS track
121
. Moreover, the ABS heads
123
-
1
to
123
-
n
are provided at an interval &lgr; from one another, where &lgr; is the pitch of the micro-sized areas.
The ABS head
123
-
1
includes magnetizable devices
123
-
1
a
and
123
-
1
b
. The magnetizable devices may, for example, be MR devices. The ABS head
123
-
1
also includes a wiring and is in operation by the current flowing therein. Meanwhile, the ABS heads
123
-
2
to
123
-
n
are of the same structure as the ABS head
123
-
1
.
In the above-described position detection apparatus
120
, in which the ABS track
121
is of a pattern having an array conforming to the degree n cyclic code, the n-bit codes, detected by the ABS detection unit
124
, referred to below as ABS values, assume different values, as the position of the ABS detection unit
124
relative to the ABS track
121
is changed, despite the fact that the ABS track provided is one track. Thus, the position detection apparatus
120
is able to detect the position of the ABS detection unit
124
relative to the ABS track
121
, based on the ABS value as detected by the ABS detection unit
124
.
With the position detection apparatus
120
, in which the ABS track provided is one track, it is possible to reduce the size along the width-wise direction of the ABS track
121
, indicated by arrow Z in the drawing. That is, the position detection apparatus
120
can be reduced in size.
In the above-described position detection apparatus
120
, there is raised a demand for higher definition and higher resolution in order to measure position changes of the ABS detection unit
124
relative to the ABS track
121
more precisely. Among the methods for further improving the definition and the resolution, there is a method for decreasing the pitch of the micro-sized areas. When the pitch of the micro-sized areas is reduced, it becomes necessary to diminish the gap between the ABS heads
123
-
1
to
123
-
n.
However, when the gap between the ABS heads
123
-
1
to
123
-
n
is diminished, the ABS heads
123
-
1
to
123
-
n
need to be arranged congested. When the ABS heads
123
-
1
to
123
-
n
are arranged congested, the state of
FIG. 13
results for n=4, as an example, as a result of which the magnetizable devices
123
-
1
a
to
123
-
4
a
and
123
-
1
b
to
123
-
4
b
, provided to the ABS heads
123
-
1
to
123
-
4
, are congested.
The ABS heads
123
-
1
to
123
-
n
are in operation by the current flowing therein. For example, the respective ABS heads
123
-
1
to
123
-
n
are determined to be facing the micro-sized areas represented by [1] or the micro-sized areas represented by [0] by measuring the resistance values thereof. That is, the current flows in the respective ABS heads
123
-
1
to
123
-
n.
Thus, when the ABS heads
123
-
1
to
123
-
n
are congested, the intensity of the current flowing per unit area is increased in an area of high degree of congestion of the magnetizable devices provided to the ABS heads
123
-
1
to
123
-
n
, with the result that the heat evolution in the area is increased. If, in the area of high degree of congestion of the magnetizable devices provided to the ABS heads
123
-
1
to
123
-
n
, the amount of heat evolution per unit area is increased, the ABS heads
123
-
1
to
123
-
n
are deteriorated in characteristics, or are destroyed.
Moreover, if the ABS heads
123
-
1
to
123
-
n
are congested, the wiring provided to these ABS heads
123
-
1
to
123
-
n
is concentrated, with the result that the wiring needs to be reduced in diameter, thus increasing the possibility of line breakage or the current leaking to the neighboring ABS heads.
If the ABS heads
123
-
1
to
123
-
n
are deteriorated in characteristics or destroyed, or if line breakage of the wiring or the current leakage to the neighboring ABS heads occurs, the possibility of malfunctioning of the position detection apparatus
120
increases, and hence the position detection apparatus
120
is deteriorated in operational reliability.
SUMMARY OF THE INVENTION
In view of the above depicted status of the art, it is an object of the present invention to provide a position detection apparatus in which, when the pitch of the micro-sized areas is diminished to improve the definition and resolution, it is possible to realize high operational reliability.
The present invention provides a position detection apparatus comprising an absolute track composed of a string of a number of micro-sized areas each indicated by a code of [0] and a number of micro-sized areas each indicated by a code of [1] in accordance with a maximum length sequence generated by a degree-n primitive polynominal, n being a natural number not less than 2, and a detection unit for the absolute track movable relative to the absolute track, the detection unit including n heads for the absolute track, arrayed facing the absolute track, for detecting the physical properties of the absolute track. The micro-sized areas each indicated by a code of [1] differ in physical properties from the micro-sized areas each indicated by a code of [0]. The n heads for the absolute track are arrayed under a condition satisfying the equations 1 and 2 if n is an even number and under a condition satisfying the equations 1 and 3 if n is an odd number:
&lgr;
1
=m&lgr;, m being an integer not less than 2  (1)
&lgr;
1
≠k
(2
n/2
+1)&lgr;, k being a natural number  (2)
&lgr;
1
≠k
(2
n
+1)&lgr;  (3)
where &lgr; is a pitch of the micro-sized areas and &lgr;
1
is the separation between neighboring ones of the n heads for the absolute track.
With the position detection apparatus, the n ABS heads are arranged under the conditions satisfying the equations (1) and (2) or under the conditions satisfying the equations (1) and (3) when n is even or odd, respectively. By arraying the n ABS heads under these conditions, the separation between neighboring ones of the ABS heads in the position detection apparatus of the present invention can be 2&lgr; or larger.
With the positi

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