Position transducer

Details Position transducer Position transducer

2003-02-21

2004-08-03

Bui, Bryan (Department: 2863)

Data processing: measuring, calibrating, or testing

Measurement system

Dimensional determination

C702S104000, C702S150000, C702S151000

Reexamination Certificate

active

06772088

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position transducer used in the fields of machine tools, industrial machinery, etc. to detect a position changed due to a rectilinear movement, rotational movement or the like.
This application claims the priority of the Japanese Patent Application No. 2002-064566 filed on Mar. 8, 2002, the entirety of which is incorporated by reference herein.
2. Description of the Related Art
The position transducers used in th fields of machine tools, industrial machinery, etc. to detect a position changed due to a rectilinear movement or the like are known from the disclosure in the Japanese Unexamined Application Publication Nos. 99564 of 1985, 177019 of 1988, 152314 of 1989, etc.
Referring now to
FIG. 1
, there is schematically illustrated in the form of a block diagram a conventional position transducer with one absolute track. The position transducer is generally indicated with a reference
120
. As shown, the position transducer
120
is composed of one absolute track
121
and an ABS head
124
including
n
absolute track detectors
123
1
,
123
2
, . . . ,
123
a
. It should be noted that in the following explanation, the absolute track will be referred to as “ABS track” and the ABS track detector be referred to as “ABS detector”.
The ABS track
121
is formed from a pattern in which micro-areas each represented by “0” and ones each represented by “1” are laid in array according to an a-order cyclic code. The micro-area represented by “0” and one represented by “1” are different in physical property from each other. For example, for the position transducer
120
to magnetically detect the position of the ABS head
124
, the micro-areas “1” are magnetized but the micro-areas “0” are not.
The ABS head
124
is movable longitudinally of the ABS track
121
as indicated by an arrow Y in FIG.
1
. Each of the ABS detectors
123
1
to
123
a
is provided in a position opposite to the ABS track
121
. Also, when the micro-areas are laid at a pitch &lgr;, the ABS detectors
123
1
to
123
a
are spaced a distance &lgr; corresponding to the micro-area pitch &lgr; from each other.
In the aforementioned position transducer
120
, since the ABS track
121
is formed as the pattern in which the micro-areas each represented by “0” and ones each represented by “1” are laid in array according to the a-order cyclic code, as the ABS head
124
moves in relation to the ABS track
121
, the ABS head
124
will detect ABS values all different from each other irrespectively of the fact that only the ABS track
121
is included in the position transducer
120
. Therefore, the position transducer
120
can detect the position of the ABS head
124
in relation to the ABS track
121
on the basis of the ABS values detected by the ABS head
124
.
The position transducer
120
can have the ABS track
121
reduced in size in a direction indicated by an arrow Z in
FIG. 1
because it has only one ABS track
121
. That is, the position transducer
120
can be designed smaller.
In the position transducer
120
having only the ABS track
121
, when the position of the ABS head
124
varies, signals outputs from two or more of the ABS detectors
123
1
to
123
n
will possibly be switched from one to another. Specifically, signal outputs from two or more of the ABS detectors
123
1
to
123
n
are switched from “0” to “1” or vice versa.
It is difficult to provide all the ABS detectors
123
1
to
123
n
having quite the same capability of detecting a physical property and outputting a signal. Also it is difficult to provide all the micro-areas spaced at quite the same pitch &lgr; (as shown in
FIG. 1
) from each other when producing the ABS track
121
.
Therefore, when each of the ABS detectors
123
1
to
123
n
is opposite to near the edge of a micro-area, it is difficult for the ABS head
124
to accurately detect a code from the ABS track
121
because the ABS detectors
123
1
to
123
n
output signals at different times, respectively.
Also, when each of the ABS detectors
123
1
to
123
a
is opposite to near the edge of a micro-area, the magnetic field to be detected is influenced by the adjacent micro-areas. Therefore, when a magnetized micro-area is adjacent to a micro-area not magnetized, there will take place near the edge of each micro-area an area where it is difficult for the ABS detector to stably output “1” or “0” signal.
Namely, when each of the ABS detectors
123
1
to
123
a
is near the edge of a micro-area, it will be difficult for the position transducer
120
to accurately detect the position of the ABS head
124
in relation to the ABS track
121
.
Position transducers capable of detecting the position of the ABS head in relation to the ABS track without error include two types which will be described below.
The first one of the two types of position transducers is disclosed in the Japanese Unexampled Application Publication No. 1990-21216, Japanese Patent No. 2679207 and Japanese Unexamined Application Publication No. 1988-152314, respectively. This position transducer does not detect signal output from each of the ABS detectors that is opposite to near the edge of a micro-area but detects signal output from each of the ABS detectors that is opposite to near the center of the micro-area (which area will be referred to as “stable area” hereunder).
FIG. 2
is also a block diagram of a variant of the aforementioned conventional position transducer. This conventional position transducer is generally indicated with a reference
140
. As shown, in the position transducer
140
, an incremental track
142
having a pattern of constant-wavelength, alternating magnetic fields is juxtaposed with the ABS track
121
. Also, the position transducer
140
includes, in addition to the ABS head
124
, an incremental track head
144
having two incremental track detectors
143
1
and
143
2
.
The position transducer
140
is adapted such that judging from a signal output from the incremental track head
144
that each of the ABS detectors
123
1
to
123
a
is in the stable area, it detects signal outputs from the ABS detectors
123
1
to
123
a
.
When each of the ABS detectors
123
1
to
123
a
is not in the stable area, however, the aforementioned position transducer
140
cannot detect any position of the ABS head
124
in relation to the ABS track
121
.
Therefore, for example, to detect the position of the ABS head
124
in relation to the ABS track
121
the moment the power is applied to the position transducer
140
, each of the ABS detectors
123
1
to
123
a
have to be in the stable area at that moment. If none of the ABS detectors
123
1
to
123
a
are in their respective stable areas, the position transducer
140
cannot detect any position of the ABS head
124
in relation to the ABS track
121
before the ABS head
124
is moved until each of the ABS detectors
123
1
to
123
a
moves into the stable area. Namely, the position transducer
140
can hardly detect the position of the ABS bead
124
in relation to the ABS track
121
the movement it is applied with the power.
The second type of position transducer is disclosed in the Japanese Patent Nos. 2571393, 2571394, 3063044 and 3103266. The positional transducer includes
a
sets of ABS detectors, each set including two ABS detectors. In this position transducer, signal output from one of the two ABS detectors that is opposite to the stable area is used to detect an a-bit code.
In this position transducer, however, the ABS head includes 2n ABS detectors to detect an n-bit code indicating an a-bit code. That is, the position transducer will have a larger number of ABS detectors for the number of bits in a code the ABS head detects. Since many ABS detections are made in the position transducer, the ABS head will possibly have to be designed large and corresponding addition of wires and the like will possibly cause the circuit to be more complicated. Therefore, this position transducer can hardly be designed compact. Also, since the position transducer

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