Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2002-01-22
2003-09-30
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207180, C324S207240, C340S870320, C336S045000, C336S129000
Reexamination Certificate
active
06628115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electromagnetic induction-type absolute position transducer in which variation of the signal strength depending on positions on a scale is small. More particularly, the present invention relates to an electromagnetic induction-type absolute position transducer comprising a scale with a plurality of scale loops functioning as coils, the scale loop having a set of loop portions including at least two loop portions, which are arranged along a measuring axis at different wavelength intervals to constitute a plurality of tracks arranged along the measuring axis at different wavelengths, and a connecting pattern portion connecting the corresponding two loop portions with each other. The electromagnetic induction-type absolute position transducer is suitably used in an electronic caliper, an electronic micrometer, an indicator, a linear scale, a linear gauge, and the like.
2. Description of the Related Art
The assignee of the invention has proposed an electromagnetic induction-type absolute position transducer having N (N≧2) tracks of different wavelengths, in Japanese Patent Unexamined Publication No. 2000-180209 (filed based on U.S. patent application Ser. No. 09/213,268). As shown in
FIG. 10
, the proposed transducer has a scale
10
and a readhead
20
which are relatively movable along a measuring axis X. The readhead
20
includes at least one magnetic flux sensor (receiving coils
22
and
24
). The scale
10
has a plurality of closed-loop coupling loops (hereinafter, referred to as scale loops) which extend along the measuring axis. The scale loops function as coils. Each of the scale loops includes a first loop portion
12
, a second loop portion
14
, and a connecting pattern portion
16
connecting the first and second loop portion with each other. The first loop portions
12
are arranged at intervals corresponding to a first wavelength &lgr;
1
along the measuring axis. The second loop portions
14
are arranged at intervals corresponding to a second wavelength &lgr;
2
which is different from the first wavelength &lgr;
1
.
In
FIG. 10
a driving circuit
30
selectively outputs a time-varying drive signal to either a first transmitting coil
26
or a second transmitting coil
28
. An amplifying circuit
32
amplifies signals from the receiving coils
22
and
24
. A calculation device
34
A/D-converts an output of the amplifying circuit
32
and calculates an absolute position from the phase difference between the tracks.
In
FIG. 10
, the first loop portions
12
are arranged on one side of the second loop portions
14
. The first loop portions
12
may be alternately arranged on both the sides of the second loop portions
14
as shown in FIG.
11
.
FIG. 12
enlargedly shows connecting stats of 0-th and n-th first loop portions
12
and second loop portions
14
in the scale loops of FIG.
10
.
FIG. 13
shows variation of the signal strength with respect to the length of the scale loop (hereinafter, referred to as scale length). As shown in
FIGS. 12 and 13
, in the electromagnetic induction-type absolute position transducer of the related art, the connecting pattern portion
16
, which connects loop portions (the first loop portion
12
and the second loop portion
14
) of each scale loop in the scale
10
, is longer as the scale length is larger. Accordingly, if the pattern widths of the scale loops (pattern widths A of the first and second loop portions, and pattern widths B of the connecting patterns
16
) are kept to be constant along the measuring axis as shown in
FIG. 12
, an output signal of the readhead
20
is lowered in strength as indicated by the solid line A in
FIG. 14
as the scale length is larger. That is, the output signal of the readhead is lowered in strength as the readhead moves away from the position of the scale loop having the shortest length connecting pattern portion (hereinafter, referred as 0-th scale loop) Here, the scale pattern of the 0-th scale loop is referred as shortest connecting pattern.
When the signal strength is changed depending on the scale position as described above, the setting range of the gap between the scale and the readhead is inevitably narrowed in order to ensure a sufficient signal strength even when the signal strength is reduced. Therefore, the accuracy of components and an assembling process must be enhanced. Further, in the case where, as proposed by the assignee of the invention in U.S. patent application Ser. No. 09/804,300, an erroneous operation due to, for example, the readhead or a breakage of the scale is detected on the basis of the signal strength, the detection sensitivity cannot be set to be high.
SUMMARY OF THE INVENTION
The invention has been conducted in order to solve the problems of the related art. It is an object of the invention to provide an electromagnetic induction-type absolute position transducer in which variation of an output signal depending on positions on the scale is small.
To achieved the above-mentioned object of the invention, there is provided with an electromagnetic induction-type absolute position transducer comprising a scale with a plurality of scale loops functioning as coils, the scale loop having a set of loop portions including two loop portions, which are arranged along a measuring axis at different wavelength intervals to constitute a plurality of tracks arranged along the measuring axis at different wavelengths, and a connecting pattern portion connecting corresponding two loop portions with each other. In the electromagnetic induction-type absolute position transducer, at least part of pattern widths constituting the scale loops are changed in accordance with the length of the connecting pattern portion (hereinafter, as referred as connecting pattern length). With such configuration, a change of the signal strength due to a change of the connecting pattern length is prevented from occurring.
In the above-mentioned electromagnetic induction-type absolute position transducer, it is preferable that at least part of the pattern widths may be gradually increased as the connecting pattern length becomes longer with respect to a shortest connecting pattern.
Further, according to the present invention, there is provided a position measuring device which uses the above-mentioned electromagnetic induction-type absolute position transducer.
In the electromagnetic induction-type absolute position transducer and the position measuring device using the same according to the present invention, in the scale pattern where the loop portions are arranged at constant pitches (in the related art, the first loop portions are arranged at the pitch &lgr;
1
, and the second loop portions at the pitch &lgr;
2
), at least part of the pattern widths constructing the scale loop are changed depending on the connecting pattern length without changing the pitches and the loop center distances of the first and second loop portions. For example, at least part of the pattern widths is stepwisely (gradually) increased as the connecting pattern length becomes longer with respect to the shortest connecting pattern (in this example, the 0-th scale loop: also referred to as a scale coil). According to this configuration, the amount of the attenuation of the signal strength due to increase of the scale length such as that indicated by the solid line A in
FIG. 14
can be complemented by increasing the current flowing through the scale loop. Therefore, attenuation of the signal strength depending on increase of the connecting pattern length is prevented from occurring, whereby the strength of the output signal of the readhead can be kept to be constant as indicated by the solid line B in FIG.
14
.
REFERENCES:
patent: 5886519 (1999-03-01), Masreliez et al.
patent: 6329813 (2001-12-01), Andermo
patent: 2002/0030484 (2002-03-01), Kiriyama et al.
patent: 2002/0030485 (2002-03-01), Gleixner
patent: 62-211501 (1987-09-01), None
Hayashi Nobuyuki
Sasaki Kouji
Shiraishi Yoshiaki
Mitutoyo Corporation
Patidar Jay
Rankin, Hill Porter & Clark LLP
LandOfFree
Scale loops for electromagnetic induction-type absolute... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Scale loops for electromagnetic induction-type absolute..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scale loops for electromagnetic induction-type absolute... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3020915