U.S. patent application number 09/834616 was filed with the patent office on 2001-09-13 for induction-type position measuring apparatus.
This patent application is currently assigned to Mitutoyo Corporation. Invention is credited to Miyata, Toshiharu.
Application Number | 20010020846 09/834616 |
Document ID | / |
Family ID | 26475241 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010020846 |
Kind Code |
A1 |
Miyata, Toshiharu |
September 13, 2001 |
Induction-type position measuring apparatus
Abstract
An inductive linear encoder (10) has a position sensor (1) and
scale (2) which are movably disposed relative to each other. The
sensor (1) is with a drive wire (3) to which an alternating current
is supplied, and one set of detection wires (4a-4d) at right angles
to the drive wire (3) in the same plane. The scale (2) is
configured including an elongate substrate (7) having its surface
on which a series combination of conductive closed loop patterns
(8) are periodically arranged at equal intervals. These conductive
closed loop (8) are linearly laid out on the substrate (7) in the
relative movement direction. Each loop (8) consists essentially of
a reception conductor segment (8a) and signal transmit conductor
segments (8b, 8c) integral with the former (8a). The receive
conductor segment (8a) is responsible for generation of an induced
current due to a first variable magnetic field creatable from the
drive coil (3). The transmit conductor segments (8b, 8c) are to
create second variable magnetic fields that are opposite in
polarity to each other and are perpendicular to the first magnetic
field. Creation of such second magnetic fields results in flow of
an induced current in the detector wire (4) of sensor (1), which in
turn acts as a position detection output current.
Inventors: |
Miyata, Toshiharu;
(Kawasaki-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Mitutoyo Corporation
|
Family ID: |
26475241 |
Appl. No.: |
09/834616 |
Filed: |
April 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09834616 |
Apr 16, 2001 |
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09197419 |
Nov 23, 1998 |
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6259249 |
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Current U.S.
Class: |
324/207.17 |
Current CPC
Class: |
G01B 7/003 20130101;
G01D 5/2093 20130101; G01D 5/2086 20130101 |
Class at
Publication: |
324/207.17 |
International
Class: |
G01B 007/14; H01F
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 1997 |
JP |
9-333249 |
May 25, 1998 |
JP |
10-143537 |
Claims
What is claimed is:
1. An induction-type position measuring apparatus comprising: a
first member; a second member having a measurement axis and being
movably arranged along the measurement axis with a predefined gap
between the first and second members; a drive wire disposed on the
first member and having a predetermined length along the
measurement axis, for producing a first variable magnetic field
upon receipt of an alternating current from a drive signal source;
an array of electromagnetic coupling devices laid out on the second
member along the measurement axis at constant intervals, each of
the electromagnetic coupling devices generating an induced current
due to couplement with the first variable magnetic field generated
by the drive wire, and generating a second variable magnetic field
substantially perpendicular to the first variable magnetic field in
response to the induced current at a position physically spaced
apart from a coupling portion with the first variable magnetic
field; and a variable magnetic field detecting device which has at
least one detection wire disposed on the first member substantially
perpendicular to the drive wire, for providing an output signal due
to couplement with the second variable magnetic field from the
electromagnetic coupling devices, the output signal being variable
with relative displacement of the first and second members.
2. The apparatus according to claim 1, wherein the drive wire is
wound into a drive coil, and wherein the detection wire is wound
into a detector coil with its axis substantially perpendicular to
the drive coil.
3. The apparatus according to claim 1, wherein the first member
includes an insulative block letting the drive wire and the
detection wire be wound therearound into a drive coil and a
detector coil respectively.
4. The apparatus according to claim 1, wherein the first member
includes an insulative substrate, and the drive wire and the
detector wire are formed of patterned conductive leads on the top
and bottom surfaces of the insulative substrate and conductive
through-going leads extending through the substrate for electrical
interconnection of the patterned inductive leads as to serve as
drive coil and detector coil, respectively.
5. The apparatus according to claim 1, wherein each of the
electromagnetic coupling device comprises a conductive closed loop
pattern having a receiver conductor segment lying substantially
parallel to the drive wire for being coupled with the first
variable magnetic field as generated by the drive wire, and a
transmit conductor segment integral with the receiver conductor for
creation of the second magnetic field.
6. The apparatus according to claim 5, wherein the conductive
closed loop pattern is of a rectangular shape with the receiver
conductor segment lying at right angles to the transmit conductor
segment.
7. The apparatus according to claim 5, wherein the conductive
closed loop pattern is shaped letting each of the receiver
conductor segment and the transmit conductor segment resemble a
circular arc in shape.
8. The apparatus according to claim 5, wherein each the conductive
closed loop pattern includes two spaced-apart receiver conductor
segments with a distance equivalent to half of a layout period of
the electromagnetic coupling devices for permitting flow of induced
currents in opposite directions at right angles to the drive wire,
and wherein the variable magnetic field detector device includes at
least one set of four detection wires in combination, the wires
being laid out in a range corresponding to the length of the drive
wire at specified intervals each being quarter of the layout period
of the electromagnetic coupling devices for coupling with a
variable magnetic field created from the transmit conductor segment
of each the conductive closed loop pattern to thereby provide
four-phase output signals each being shifted of 90.degree. from
another.
9. The apparatus according to claim 5, wherein each the conductive
closed loop pattern includes two spaced-apart transmit conductor
segments at intervals each equal to half of a layout period of said
electromagnetic coupling devices for permitting flow of induced
currents in opposite directions at right angles to the drive wire,
and wherein the variable magnetic field detector devices includes
at least one set of four first detection wires in combination being
laid out in a range corresponding to the length of the drive wire
at specified intervals each being quarter of the layout period of
the electromagnetic coupling devices for coupling with a variable
magnetic field from the transmit conductor segment of each the
conductive closed loop pattern to thereby provide four-phase output
signals each being shifted of 90.degree. from another, at least one
set of four second detection wires as disposed within a range of
the length of the drive wire at intervals each equal to a quarter
of the layout period of the electromagnetic coupling devices with a
predefined phase shift relative to the first detection wires for
coupling with variable magnetic fields from the transmit conductor
segments of each the conductive closed loop pattern to thereby
provide four-phase output signals each being shifted of 90.degree.
from another, the predefined phase shift being substantially equal
to .lambda./2N, where .lambda. is the layout period of the
electromagnetic coupling devices, and N is an odd number greater
than or equal to 3.
10. The apparatus according to claim 1, wherein each the
electromagnetic coupling device is formed of a conductive pattern
responsive to receipt of the first variable magnetic field from the
drive wire for permitting induction of an eddy current therein.
11. The apparatus according to claim 1, wherein each the
electromagnetic coupling device is formed of a magnetic material
pattern for modulating a magnetic flux density of the first
variable magnetic field generated from the drive wire.
12. A position measurement apparatus having an inductive position
sensor for sensing a position of an object to be measured, the
position sensor comprising: a drive coil for generating a variable
magnetic field upon receipt of an alternating current from a drive
current source; a detection coil disposed adjacent to the drive
coil for generating an induced current due to coupling with a
variable magnetic field created by the drive coil in response to
displacement of the object; and a support body for immovably
holding the drive coil and the detection coil, wherein the drive
coil and said detection coil are arranged so that in absence of the
object no electromagnetic coupling is made, while electromagnetic
coupling with the detection coil occur due to modulation in
distribution of the variable magnetic field as generated by the
drive coil depending upon displacement of the object.
13. The apparatus according to claim 12, wherein the drive coil and
the detection coil are disposed having axes at right angles to each
other.
14. The apparatus according to claim 12, wherein the inductive
position sensor is adaptable for use as a proximity sensor by
letting the drive coil and the detection coil be laid out having
axes at right angles to each other and by comprising a contactor
movably disposed as the object along a bisector line of the axes of
the drive coil and the detection coil for modulation of a variable
magnetic field generatable from the drive coil in accordance with a
position.
15. The apparatus according to claim 12, wherein the inductive
position sensor is adaptable for use as a linear encoder by letting
the drive coil and the detector coil be disposed having axes at
right angles to each other and by comprising an elongate scale
movably penetrating the detection coil as the object and having
thereon an array of periodically disposed magnetic field modulation
units for modulating a variable magnetic field distribution from
the drive coil during movement of the scale.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an induction-type position
measuring apparatus for performing position measurements based on
electromagnetic coupling principles.
[0003] 2. Description of the Related Art
[0004] One prior known magnetic encoder employing transformers is
configured including a displacement sensor and a scale structure
operatively associated therewith. The displacement sensor typically
has two coils: a primary coil (i.e. drive coil), and a secondary
coil (detection coil). The scale is placed adjacent to the sensor
and is movable relative thereto. The scale is responsible during
movement for modulating the magnetic flux as generated from the
drive coil. Upon activation of the drive coil by supplying an
alternating drive current thereto, variable magnetic flux might
take place, which is then modulated by the scale resulting in
coupling with the detection coil. This magnetic coupling causes
induction of a corresponding voltage at the detector coil. The
induced voltage is variable in potential with movement of the
scale, and thus is employable as a detection output indicative of a
position measured.
[0005] With the prior art magnetic encoder thus arranged, the drive
coil and its associative detector coil are coaxially disposed. Such
coaxial coil layout must permit presence of electromagnetic
coupling components (cross-talk) between the spaced-apart drive
coil and detector coil, which components remain independent of the
relative position of the scale and are hardly affected from it.
Presence of such crosstalk results in inclusion of certain offset
components in a detection output of the detector coil, which again
are hardly affectable by relative movements of the scale. These
offset components can badly behave to cause significant measurement
errors in cases where high-precision position detection is
performed by dividing a wavelength of the scale into portions.
[0006] One typical approach to removal of such offset components is
to differentiate two detection voltages of which phases are reverse
with each other. This approach, however, suffers from difficulty in
offset removal due to the fact that offset components are
significantly affectable from to the alignment accuracy of the
drive and detector coils along with uniformity of materials
employed therefor, resulting in the offset value experiencing
non-negligible amount of variations among individual products.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to provide such an
inductive position measurement apparatus capable of effecting
high-accuracy position measurements that offset components are not
generated in principle.
[0008] In accordance with one aspect of the instant invention, an
induction-type position measurement apparatus comprises a first
member; a second member having a measurement axis and being movably
arranged along the measurement axis with a predefined gap between
the first and second members; a drive wire disposed on the first
member and having a predetermined length along the measurement
axis, for producing a first variable magnetic field upon receipt of
an alternating current from a drive signal source; an array of
electromagnetic coupling devices laid out on the second member
along the measurement axis at constant intervals, each of the
electromagnetic coupling devices generating an induced current due
to couplement with the first variable magnetic field generated by
the drive wire, and generating a second variable magnetic field
substantially perpendicular to the first variable magnetic field in
response to the induced current at a position physically spaced
apart from a coupling portion with the first variable magnetic
field; and a variable magnetic field detecting device which has at
least one detection wire disposed on the first member substantially
perpendicular to the drive wire, for providing an output signal due
to couplement with the second variable magnetic field from the
electromagnetic coupling devices, the output signal being variable
with relative displacement of the first and second members.
[0009] A respective one of the electromagnetic coupling devices may
typically be configurable from a conductive member providing
therein a closed loop current flow path. This closed loop conductor
has a receiver conductor segment and more than one transmitter
conductor segment. The receiver conductor segment lies
substantially parallel to the drive wire, and is coupled with the
first variable magnetic field as produced by the drive wire. The
transmit conductor segment is formed continuously with the receiver
conductor segment, for creation of the second variable magnetic
field. More practically, each loop conductor is structured
including two transmit conductor segments which are spaced apart
from each other by a distance that is equivalent to half of the
layout period or "pitch" of the electromagnetic couplers. These
segments are at right angles to the drive wire in a plane, and may
derive electromagnetically induced current components flowing
therethrough in opposite directions perpendicular to the drive
wire.
[0010] The variable magnetic field detector device may be such that
it includes at least one set of four detection wires lying parallel
to one another. These parallel detector wires are laid out within a
coverage corresponding to the length of the drive wire at
predefined intervals each equal to quarter of the layout period of
the electromagnetic couplers. Upon coupling with one or more
variable magnetic fields generatable from the transmit conductor
segments of each loop conductor, the detector wires provide
four-phase output signals, each of which is offset by 90.degree.
from another.
[0011] In accordance with another aspect of the invention, there is
provided an induction-type position measurement apparatus with an
inductive position sensor for use in measuring a present location
of an object of interest under measurement. The inductive position
sensor comprises a drive coil for generating a variable magnetic
field upon receipt of an alternating current from a drive current
source; a detection coil disposed adjacent to the drive coil for
generating an induced current due to coupling with a variable
magnetic field created by the drive coil in response to
displacement of the object; and a support body for immovably
holding the drive coil and the detection coil, wherein the drive
coil and said detection coil are arranged so that in absence of the
object no electromagnetic coupling is made, while electromagnetic
coupling with the detection coil occur due to modulation in
distribution of the variable magnetic field as generated by the
drive coil depending upon displacement of the object.
[0012] In the former position measurement apparatus of the
induction type in accordance with the first aspect of the
invention, the drive wire and detection wire are disposed at right
angles to each other on the first member so that any variable
magnetic fields generatable due to alternating current flow in the
drive coil will no longer be directly coupled with the detector
wire. A first variable magnetic field generated by AC-driving the
drive wire causes the electromagnetic coupler devices on the second
member to produce an induced current. Each electromagnetic coupler
is typically configurable from a conductive closed loop pattern
having a receive conductor segment lying parallel to the drive wire
and more than one transmit conductor segment extending
perpendicular thereto. An induced current generatable in the
receive conductor segment attempts to flow in this conductive loop
producing a second variable magnetic field at right angles to the
first variable magnetic field at a specific location physically
distant from the receive conductor segments. Detecting this second
magnetic field by the detector wire makes it possible to obtain a
detection output changeable depending on relative displacement
between the first and second members.
[0013] With the scheme of this invention, no electromagnetic
coupling activities take place in principle between the drive and
detector wires due to the fact that these wires are disposed at
right angles to each other. Thus, no offset components are
generatable unlike prior art systems. This may in turn enable
achievement of high-precision position measurements required.
[0014] In the induction-type position measurement apparatus in
accordance with the second aspect of the invention, the position
sensor's drive coil and detector coil are disposed so that these
are in the state that no electromagnetic coupling is present in the
absence of any object of interest to be measured at right angles to
each other, while permitting creation of electromagnetic coupling
with the detector coil due to modulation of the drive coil's
generated variable magnetic field distribution in response to the
object's displacement. Accordingly, with this apparatus also, it
becomes possible to obtain offset-free detection outputs, leading
to an ability to attain high-precision position measurements.
[0015] These and other objects, features and advantages of the
invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram showing a principal configuration of a
linear encoder in accordance with one preferred embodiment of this
invention.
[0017] FIG. 2A is a diagram showing a perspective view of a
combination of magnetically coupled drive wire and conductive
closed loop pattern as used in the linear encoder shown in FIG. 1,
and FIG. 2B depicts a perspective view of the conductive loop and
its associated detection wires for explanation of the
electromagnetic coupling therebetween.
[0018] FIG. 3 depicts a plan view of a prototype linear encoder
including a sensor and a scale structure.
[0019] FIG. 4A shows a perspective view of the sensor used in the
encoder of FIG. 3, and FIG. 4B is a diagrammatic representation of
a configuration of equivalent circuitry of the sensor.
[0020] FIG. 5 is a graph showing a detection output signal waveform
of the encoder shown in FIGS. 3-4B.
[0021] FIG. 6 illustrates another exemplary configuration of the
sensor.
[0022] FIG. 7 depicts equivalent circuitry of a linear encoder
embodying the invention.
[0023] FIG. 8 is a block diagram of a signal processor circuit
adaptable for use in the embodiment linear encoder.
[0024] FIG. 9 is a block diagram of another signal processor
circuit usable in the linear encoder.
[0025] FIG. 10 depicts a configuration of equivalent circuitry of
an embodiment linear encoder with its transmit and receive stages
reversed.
[0026] FIGS. 11A to 11D are diagrams each showing an exemplary
structure of the scale shown in FIG. 1.
[0027] FIG. 12 depicts another exemplary structure of the sensor of
FIG. 1.
[0028] FIGS. 13A and 13B are diagrams showing an embodiment of the
invention adapted for use with a rotary encoder.
[0029] FIGS. 14A-14C are illustrations each for explanation of a
configuration of a sensor also embodying this invention.
[0030] FIG. 15 depicts an exemplary configuration of the embodiment
sensor.
[0031] FIG. 16 a waveform diagram showing a way of reducing
harmonic wave distortion in the embodiment sensor.
[0032] FIGS. 17A-17C are illustrations each showing a modified
sensor configuration of the embodiment sensor.
[0033] FIG. 18 shows a principal structure of an induction-type
position sensor in accordance with a further embodiment of the
invention.
[0034] FIGS. 19A-19B are diagrams for explanation of the operation
principle of the position sensor of FIG. 18.
[0035] FIGS. 20-23 are diagrams each showing a configuration of an
induction-type position sensor also incorporating the principles of
the invention.
[0036] FIG. 24 illustrates, in cross-section, a proximity sensor
module employing the position sensor of FIG. 18 in accordance with
a further embodiment of the invention.
[0037] FIG. 25 illustrates in perspective view a linear encoder
structure employing the FIG. 18 sensor in accordance with a still
further embodiment of the invention.
[0038] FIGS. 26A-26C are diagrams for explanation of an operation
of the linear encoder of FIG. 25.
DETAILED DESCRIPTION OF TEE PREFERRED EMBODIMENTS
[0039] Referring now to FIG. 1, there is illustrated in perspective
view a principal configuration of an electromagnetic linear encoder
10 in accordance with one embodiment incorporating the first
principle of the invention. As shown herein, the encoder 10
includes in combination a sensor 1 (as a first member), and a scale
2 (as a second member). The sensor 1 and scale 2 are disposed
opposing each other with a predetermined distance or gap defined
between them. The scale 2 is relatively movable reciprocally along
a preset measurement axis X, which is set in the longitudinal
direction of the scale 2. The sensor 1 includes a drive wire 3
having a preselected length, which extends in the measurement axis
X. The sensor 1 also includes parallel spaced-apart detection wires
4 that lie perpendicular to the drive wire 3 in the same plane.
These wires act as detection wires, and are illustratively formed
from four wires 4a-4d as one unitary group or set. The layout
interval or pitch between adjacent ones of such detection wires 4
is designed to be quarter of the scale pitch .lambda. (i.e.,
.lambda./4) as will be later discussed in the description. The
length of drive wires 3 is such that it is at least equal to the
scale pitch A when four ones 4a-4d of the detection wires 4 are
grouped into one set. The drive wire 3 is connected to a drive
signal source 6, which is operable to drive the wire 3 causing an
alternating current to flow in wire 3. Alternate ones of detector
wires 4 are coupled to two-input differential amplifiers 5a, 5b in
a way such that alternate wires 4a, 4c are coupled to the inverting
and non-inverting inputs of amplifier 5a, whereas the remaining
alternate wires 4b, 4d are to the inputs of amplifier 5b as shown
in FIG. 1.
[0040] The scale 2 is structured from an electrically insulative or
dielectric elongate substrate 7, and a preselected number of closed
conductive loops 8 each being patterned providing a closed-loop
current flow path therein. These conductive loops 8 are laid out in
a linear array on the top surface of the scale substrate 7 with a
specified scale pitch .lambda. along the measurement axis X. Each
loop conductor 8 functions as an electromagnetic coupler device,
which derives an induced current generated by a variable magnetic
field--say, "first" variable magnetic field--creatable upon
AC-driving of the drive wire 3, for creation of another variable
magnetic field ("second" variable magnetic field) perpendicular to
the first variable magnetic field at locations apart from the
position immediately beneath drive wire 3. Each loop conductor 8 is
illustratively patterned into a rectangular frame shape. One short
side portion 8a immediately underlying the drive wire 3 in almost
parallel thereto serves as a signal receiver conductor segment,
which provides an induced current when coupled with the first
variable magnetic field generatable from driver wire 3. The
opposite long sides 8b, 8c extending at right angles to such
receive conductor segment 8a are disposed lying parallel to segment
8a thereby to make up signal transmitter conductor segments for use
in producing, upon receipt of the induced current, the second
variable magnetic field as coupled with detector wires 4. The
transmit conductor segments 8b, 8c of each loop 8 are spaced apart
from each other at a distance of .lambda./2.
[0041] A position measurement operation of the linear encoder 10
thus arranged will be explained with reference to FIG. 2A-2B. FIG.
2A illustrates in perspective view one state of electromagnetic
coupling between the drive wire 3 on sensor 1 and one of the
conductive loop patterns 8 on scale 2, while FIG. 2B depicts the
state of electromagnetic coupling between the loop conductor 8 and
its associated detector wires 4a-4d. As shown in FIG. 2A, when
letting an AC drive current flow 11 in drive wire 3, a first
variable magnetic field 12 is created around wire 3. One loop
conductor 8 adjacent to this wire 3 becomes coupled at its signal
receipt conductor segment 8a with the first variable magnetic field
12, producing therein an induced currents 13. This current 13
attempts to flow circularly in loop 8 along its closed-loop path.
The induced current 13 flows in two transmit conductor segments 8b,
8c of loop 8 extending at right angles to the receipt conductor
segment 8a, providing current components flowing in the opposite
directions, which create second variable magnetic fields 14a,
14bperpendicular to the first magnetic field 12 around segments 8b,
8c respectively as shown in FIG. 2B.
[0042] A distance between the first and third ones 4a, 4c of four
detection wires 4 on the sensor 1 is equal to the distance between
two transmit conductor segments 8b, 8c in one loop conductor 8,
which should measure .lambda./2. As shown in FIG. 2B, supposing
that these wires 4a, 4c are immediately over transmit conductors
8c, 8b, the second variable magnetic fields 14a, 14bcreated around
such two transmit conductors 8b, 8c are electromagnetically coupled
strongly with detection wires 4c, 4a respectively to derive induced
currents 15a, 15b that flow in wires 4c, 4a in the opposite
directions. As the scale 2 moves, the electromagnetic coupling
between detector wires 4 and loop conductor 3 varies in magnitude.
Thus, the resulting induced currents 15a, 15b in detector wires 4c,
4a vary substantially sinusoidally in magnitude along the opposite
directions with motion of scale 2. This will be true for the second
and fourth ones 4b, 4d of the detector wires 4: these wires 4b, 4d
will exhibit, with a constant phase difference, an induced-current
variation in reply to scale 2's motion in a way similar to that in
the wires 4a, 4c.
[0043] With such scale motion-dependent electromagnetic coupling
variation at each part, one set of four detection wires 4a-4d
provide four-phase output currents A, AB, B, BB each of which is
shifted in phase by 90.degree. degrees from its neighboring one.
Accordingly, by connecting the detector wires 4 to the differential
amplifiers 5a, 5b in a way such that a pair of wires 4a, 4c which
are exactly out of phase with each other are coupled to one
amplifier 5a whereas the other pair of wires 4b, 4d being exactly
out of phase with each other are to the remaining amplifier 5b as
shown in FIG. 1, and then applying differential processing thereto,
it becomes possible to obtain signal voltages PHA, PHB which are
phase-shifted by 90.degree. from each other.
[0044] Referring to FIG. 3, there is illustrated in plan view one
practical configuration of the sensor 1 and scale 2 used in the
embodiment linear encoder 10 shown in FIG. 1. FIG. 4A depicts in
perspective view the structure of sensor 1, whose equivalent
circuity is visible in FIG. 4B. The sensor 1 shown includes a
dielectric block 20 made of a chosen resin material with a drive
coil 21 being wound around it in a direction parallel to the
longitudinal direction of scale 2, and also with detector coils 22
wound in the perpendicular direction thereto. As better depicted in
FIG. 4A, the resin block 20 has vertical through-going holes 23
preformed therein at locations distant from the drive coil 21,
which holes are for winding of detector coils 22 perpendicular to
drive coil 21. Electrical leads are wound through such holes 23
providing independent rectangular detector coils 22a-22,
respectively. A respective one of drive coil 21 and detector coils
22a-22d has a predefined number of parallel spaced-apart wire
portions at equal intervals on the bottom surface of resin block
20, which may correspond respectively to the drive wire 3 and
detector wires 4 shown in FIG. 1.
[0045] The scale 2 is formed from a printed circuit board that has
a metallic thin-film layer as patterned forming an array of the
loop conductors 8. Optionally, the scale 2 may be arranged using a
glass substrate, ceramic substrate or the like other than the print
board, each having on its surface a conductive film patterned
through etching treatment into a similar array of loop
conductors.
[0046] A prototype encoder structure was prepared letting the scale
pitch .lambda.=24 [mm] and the gap between the sensor 1 and scale 2
be 2 [mm] with a drive signal source voltage set at 12 [v] having a
frequency of 1 [MHz]. The encoder includes differential amplifiers
corresponding to those 5a, 5b of FIG. 1, which are each designed to
provide at its output a signal voltage PHA, PHB through twenty-time
amplification of a voltage indicative of a difference between
corresponding detection outputs from detector wires (4a, 4c; 4b,
4d) that are exactly out of phase with each other. The resultant
signal voltage waveforms are shown in FIG. 5. The signal voltages
PHA and PHB are plotted as effective net voltages in the unit of
"mVRMS." As apparent from FIG. 5, its has been affirmed that a
signal offset is as small as 0.6 [%] of the signal amplitude, or
stays below.
[0047] While in the foregoing explanation the detector wires 4 are
arranged with four wires grouped into one set for purposes of
convenience in illustration and discussion herein, it will be
preferable that a greater number of detector wire sets be provided
with similar phase relationship maintained. See FIG. 6, which shows
one example wherein the sensor 1 includes two sets of such detector
wires. More specifically, a first set consists of four parallel
detector wires 4a4d, and a second set consists of four ones 4a-4d.
Those "same-phase" wires in respective sets which are exactly in
phase with each other are serially connected together in a manner
which follows. The wire 4a in the first set is series-connected to
its corresponding one 4a in second set. The second wire 4bin first
set is series-coupled to wire 4bin second set. The third wire 4c in
the former set is to wire 4c in the latter; the last wire 4d in
first set is to wire 4d in second set. The four wires 4a-4d of
second set have their ends common-coupled to ground. The wires
4a-4d of first set have opposite ends as detection output terminals
for A, AB, B and BB phase outputs. It would be readily appreciated
by those skilled in the art that with such plural detector wire
sets used for the sensor 1, the drive wire associated therewith
should be elongated to have an extended length covering the widened
region of such detector wires increased in number.
[0048] Providing multiple sets of detector wires in the way stated
above may permit further enhancement of the position measurement
accuracy due to the averaging effect expected.
[0049] Turning now to FIG. 7, there is illustrated electrical
equivalent circuity of a linear encoder 10 of this embodiment. As
shown herein, the drive wire 3 on the sensor 1 and the receive
conductor segment 8a of loop conductor 8 on the scale 2 make up a
transformer thereby permitting flow of an induced current in loop
conductor 8. Another transformer is configured between the transmit
conductor segment 8b, 8c of loop 8 on the scale 2 and the detector
wire 4 on the sensor 1 with the aforementioned specific phase
relationship established, thereby causing a variable magnetic field
created by the induced current from receive conductor 8a to couple
the detector coil 4.
[0050] See also FIG. 8, which depicts a configuration of signal
processing circuitry for use in determining displacement. Letting a
voltage of the drive signal source 6 be defined as C=sin(.omega.t),
two resultant detection signal voltages PHA, PHB may be given as:
PHA=sin(kx).multidot.sin(.omega.t),
PHB=cos(kx).multidot.sin(.omega.t). Here, the amplitude is set at 1
for purposes of convenience in explanation only. The signal voltage
PHA and A.C. drive voltage "C" are supplied to a multiplier circuit
81a which multiplies them together; the voltage PHB and AC drive
voltage C are passed to another multiplier 81b for multiplication.
Output signals of multipliers 81a, 81b are then fed to low-pass
filter (LPF) circuits 82a, 82b respectively, for removal of any
high frequency components contained therein. Whereby, sinusoidal
wave components sin(kx) of displacement x may be extracted along
with its cosine wave components cos(kx). These components are then
input to digital volt meters (DVMs) 83a, 83b for detection of
corresponding voltage amplitude values. The resulting amplitudes
are routed to an arithmetic processor circuit 84, which executes
arc tangent (ATAN) function processing to thereby numerically
determine the value of displacement x.
[0051] See FIG. 9. This diagram shows one exemplary configuration
of another signal processor circuitry for use in obtaining the
displacement x. This circuitry shown is composed of a phase-shift
circuit 91, a differential amplifier 92, and a phase-difference
measurement/detection circuit 93. Upon receipt of two detection
signal voltages PHA and PHB, one of them, PHB is supplied via the
phase-shifter 91, for effectuation of 90.degree. phase shifting, to
the inverting input of differential amplifier 92 while letting the
remaining voltage PHA be input directly to the non-inverting input
of amplifier 92. Whereby, the differential amplifier 92 provides at
its output a signal indicative of the value of cos(kx+.omega.t).
The differential amplifier 92's output is passed to a first input
of the phase-difference detector 93. This detector has a second
input to which a reference signal is fed which is potentially
representative of a predefined voltage level, i.e. the AC drive
voltage C=sin(.omega.t). Based on such input signals,
phase-difference detector 93 operates to detect a difference in
phase between them obtaining a displacement x component
required.
[0052] Note that in the above embodiment, the drive wire 3 and
detector wire 4 of the linear encoder 10 are reversible in
relation. More specifically, where appropriate, the encoder will be
modified so that while AC-driving the detector wire 4, the drive
wire 3 is alternatively used as a detector wire providing the
inverse electromagnetic coupling opposite in direction to the case
stated supra; in this case also, similar position measurements may
be achievable. Equivalent circuitry in this case is shown in FIG.
10. The loop conductor 8 on the scale 2 is such that its receive
conductor segment 8a functions as the transmit conductor, whereas
two transmit conductor segments 8b, 8c serve as the receive
conductors. An AC signal from drive signal source 6 is supplied so
that it progressively passes through 90.degree. phase shifters
101-103 in this order providing four phase-shifted signals, each of
which is angularly "offset" by 90.degree. from another. These
four-phase signals are given to four wires 4a-4d, respectively.
When this is done, at one pair of alternate wires 4a and 4c,
variable magnetic fields opposite in phase to each other (each
corresponding to the "second" variable magnetic field in the
aforementioned embodiment) are created therearound. When the loop
conductor 8's two receive conductors 8c, 8d are present immediately
beneath such magnetic fields, corresponding antiphase currents are
induced which are opposite in phase to each other. These induced
currents are of the same direction within the conductive loop 8,
and also act to flow into the transmit conductor 8a producing a
variable magnetic field (corresponding to the "first" variable
magnetic field in the prior embodiment) at here. The same goes with
the wires 4b, 4d. Then, the variable magnetic field of transmit
conductor 8a in turn permits generation of an induced current in
the wire 3, which will become a detection output.
[0053] In other words a difference of this embodiment merely lies
in that the electromagnetic coupling activity herein becomes
reversal in order of sequence, which has been explained in FIG. 2
as follows: the drive current 11.fwdarw.variable magnetic field
12.fwdarw.induced current 13.fwdarw.variable magnetic fields 14a,
14b.fwdarw.induced current (detection current) 15a, 15b. This lets
the wire 3 be responsive to a presently detected displacement x for
providing a signal output as given by sin(.omega.t+kx). This output
is then passed to a phase difference detector circuit 104 for
detection of its phase difference from the AC signal sin(.omega.t),
thereby enabling numerical determination of a displacement
required.
[0054] There are shown in FIGS. 11A-11D other exemplary structures
of the scale 2 that couples electromagnetically with the sensor 1.
With a structure of scale 2 shown in FIG. 11A, each loop conductor
8 is formed to have an ellipse-like (or circle-like) loop pattern
as a whole with its transmit and receive conductor segments being
of the arc shape. With such ellipse-patterned loop conductors, if
the drive wire 3 and detector wires 4 mounted on the sensor 1 are
designed having the linear shape as in the embodiment discussed
previously, then the resultant area or coverage as magnetically
coupled with them becomes smaller than would be in the prior
embodiment; fortunately, such reduction of magnetic couplement is
avoidable by employing the coils shown in FIG. 3 as the drive wire
3 and detector wires 4 with the number of wire turns increased
appropriately, which permits achievement of the required
electromagnetic coupling that is sufficiently significant for
practical implementations.
[0055] A structure of scale 2 shown in FIG. 11B is such that it
employs as the electromagnetic couplers an array of rectangular
conductive "island" patterns 111, each being substantially the same
in area to the individual loop conductor 8 typically illustrated in
FIG. 1. With such rectangular "solid" islands 111, the magnetic
coupling activities similar to those in the embodiment stated supra
may also be attainable because an induced current 13 behaves to
flow as "eddy" current in a loop path indicated by arrow in FIG.
11B, as in the prior embodiments.
[0056] A scale plate 2 shown in FIG. 11C is structured from a
tape-like conductive substrate 112 made of copper or the like
having an array of multiple rectangular openings or windows 113
along its measurement axis at equal intervals, which are formed by
known machining processes such as for example punching techniques.
Use of such "ladder"-shaped scale structure results in
accomplishment of functionally equivalent conductive patterns 114
each of which is between adjacent ones of the window openings 111
in substrate 112, and thus offers substantially the sam
functionality as the conductive islands patterns 111 of FIG.
11B.
[0057] A scale 2 shown in FIG. 11D is such that its tape-like
conductive substrate 112 comes with a unique surface configuration
on the top thereof, wherein rectangular raised portions 115 and
recess portions 116 are laid out alternately along the measurement
axis of scale 2. Such "serpentine" surface configuration may be
fabricated by currently available mechanical or chemical machining
process technologies including but not limited to carving,
engraving or sculpture techniques. The raised or protuberance
portions 115 are expected to be the same in function as the
rectangular islands 111 of FIG. 11B. The remaining, recess portions
116 will hardly be contributed to electromagnetic coupling
activities due to the fact that these are significant in distance
or gap between themselves and the sensor 1 operatively associated
therewith.
[0058] Note that the conductive islands 111 of FIG. 11B may be
magnetic patterns made of ferromagnetic metals by way of example.
Similarly, for the scale structures of FIGS. 11C-11D, the
conductive substrate 112 may be replaced with a magnetic substrate
when necessary. In such cases, the magnetic coupling in the order
of the sensor 1.fwdarw.scale 2.fwdarw.sensor 1 is established in a
way as follows: while the induced current 113 hardly flows therein,
the use of ferromagnetic metals with increased magnetic flux
permeability causes the magnetic flux of a variable magnetic field
created from a drive coil to periodically receive modulation due to
the periodical layout of ferromagnetic metal patterns, which may be
sensed by associative detector coils used.
[0059] Another exemplary structure of the sensor 1 is depicted in
FIG. 12. Whereas in FIGS. 3-4 the sensor 1 is formed by winding a
wire around the resin block 20, the sensor of FIG. 12 is designed
including a double-face printed circuit board 121. The print board
121 has its opposite metal films which are patterned so that the
upper and lower (top and bottom) lead patterns (122, 123; 124, 125)
are formed on the top and bottom board surfaces overlying each
other with a dielectric layer sandwiched therebetween. The upper
and lower leads 122, 123 forming a pair are electrically connected
together via vertical through-going interconnect leads 126 at the
terminate ends thereof, thus providing a vertically oriented loop
that corresponds to the drive coil 21 of FIG. 3. Similarly, each of
four parallel lead pairs extending at right angles to the looped
lead pair 122, 123 consists of an upper lead 124 and lower lead 127
which are likewise electrically connected together via vertical
through-going leads 127 at the opposite ends of such lead pair,
which is thus equivalent in function to the detector coil 22 shown
in FIG. 3 or better depicted in FIG. 4A.
[0060] With such an arrangement, it becomes possible to allow the
sensor 1 to have an "integrated" structure smaller in size with
reduced thickness without use of any "discrete" electrical parts or
components, such as separate coil wires. The scale 2 may also be
structured by use of the scheme as discussed in conjunction with
FIG. 3. Employing these fabrication schemes in combination makes it
possible to manufacture a highly integrated encoder structure with
its scale pitch minimized at enhanced accuracy and reliability.
[0061] Optionally, the printed circuit board 121 of FIG. 12 may
alternatively be a glass substrate, ceramic substrate, or other
suitable similar substrates if needed.
[0062] Turning now to FIGS. 13A-13B, there are illustrated in
schematic plan view a stator 131 and rotor 132 of a rotary encoder
incorporating the principles of the invention. As shown, the stator
131 which may correspond to the sensor 1 discussed above includes a
round disk-like plate having one surface opposing the rotor 132, on
which surface a ring-like drive wire 3 and multiple detection wires
4 are formed. The driver ring 3 circumferentially extends along the
outer periphery of the disk. The detector wires 4 extend radially
within driver ring 3 on the disk surface at equal angular pitches
.lambda./4. Four successive ones of detector wires 4 are organized
into a group or "set." Stator 131 of FIG. 13A is immovably placed
opposing the rotor 132 shown in FIG. 13B with a predefined thin
space or gap kept therebetween. Rotor 132 may be a similar round
disk-like plate having a surface opposing stator 131, on which
surface a circular array of equally spaced-apart sector-like
conductive loops 8 are laid out at angular pitch .lambda. so that
each loop 8 is electromagnetically coupled with a corresponding set
of four detector wires 4 and its associated part of driver ring 4
on stator 131. As in the prior embodiments, the individual loop
conductor 8 has a receive conductor segment 8a opposing driver ring
3, and transmit conductor segments 8b, 8c facing corresponding ones
of detector wires 4 on stator 131.
[0063] With such a sensor structure, the same principles of
operation as in the prior embodiments are employable for
measurement of rotational angular displacement x.
[0064] The foregoing sensor/scale structures embodying the
invention may offer several advantages which follow.
[0065] (1) Principally, no direct electromagnetic coupling
activities are found between the driver wire 3 and detector wires 4
in the absence of the scale 2 due to the fact that driver wire 3
and each detector wire 4 are laid out at right angles to each
other. Accordingly, unlike prior known schemes, any attendant
crosstalk hardly occurs letting no offset components be contained
in output signals.
[0066] (2) The electromagnetic coupling along the "route" of the
driver wire and scale plus detector wires in this order is
increasable in magnitude by arranging the scale 2 so that it has
thereon its receive conductor 8a magnetically coupled to drive wire
3 with the rectangular or similarly shaped loop conductors
(closed-loop coil) 8 having transmit conductor segments 8b, 8c
coupled with such detector wires 4.
[0067] (3) The sensor 1 and its associative scale 2 may be designed
as separate or "discrete" electrical components by mounting or
"integrating" the drive wire 3 and detector wires 4 together on the
sensor 1 while providing the loop conductors 8 on the scale 2. In
addition, the sensor 1 alone requires extra electrical lead wiring
for transmission of input/output signals, which may in turn
facilitate electrical interconnections required.
[0068] (4) Use of multiple sets of detector wires 4 may enable
position measurement with further enhanced accuracy due to
resultant averaging effect among them.
[0069] (5) The sensor 1 and scale 2 may be structured employing
printed circuit boards, glass substrates, ceramic substrates or any
equivalents thereto with more than one metallic film formed
thereon, which offers enhanced ability to form by etching
treatments any desired electrical lead patterns including the drive
wire 3 and detector wires 4 as well as loop conductors 8. This in
turn makes it possible to fabricate high-accuracy encoders while
reducing complexities in the manufacture thereof.
[0070] The foregoing embodiment structures are aimed at achievement
of high accuracy of measurement due to the averaging effect, which
is obtainable by disposing the sensor 1's detector wires 4 (or
detector coils 22) so that these are 90.degree. phase-shifted from
each other with four wires or coils as a unit for addition of
negative-phase or antiphase output signals together. This scheme
also offers secondary harmonic distortion reducibilities, and
moreover enables establishment of further improved low-distortion
characteristics. One exemplary configuration of a sensor 1
employing this low-distortion attaining scheme will be explained
below with reference to FIGS. 14-16.
[0071] See first FIG. 14A. This diagram depicts one layout example
of first detection wires 41 with a phase difference of .lambda./4
(=90.degree.) between adjacent ones of them. Four ones 4a1, 4b1,
4c1, 4d1 of these detector wires are organized into a group or
"set." See FIG. 14B, which illustrates an exemplary layout of
second detector wires 42 (4a, 4b2, 4c2, 4d2) with a phase offset of
A /6 (=60.degree. ) relative to the configuration of FIG. 14A. The
individual one of such wires may be the same in function as a
corresponding one of the wires in the embodiments stated supra. The
wire layout patterns of FIGS. 14A-14B are combined together
obtaining a composite wire layout shown in FIG. 14C. More
specifically, the first detector wires 41 and the second ones 42
are disposed formulating into a single overlap pattern with the
latter wires being phase-shifted by 60.degree. from the former. The
"pattern-synthesized" first and second detector wires 41, 42 are
within a spatial coverage equivalent in dimension to the length of
the driver wire 3.
[0072] Referring to FIG. 15, there is shown one exemplary wire
configuration in the case the first and second detector wires 41,
42 of FIG. 14C are designed so that each constitutes a detection
coil. Appropriate interconnections are made so that respective
outputs of A-phases (A1, A2) of the first and second detector wires
41, 42 are added together whereas the remaining antiphase outputs
of AB-phases (AB1, AB2) opposite in phase to each other undergo
subtraction therebetween. The same goes with B-phases (B1, B2) and
BB-phases (BB1, BB2) being exactly out of phase therewith.
Subtracting an AB-phase output from A-phase output may correspond
to the differentiation processing as effected at the differential
amplifiers 5a, 5b discussed previously in conjunction with FIG. 1.
Whereby, both the offset reducibility due to the averaging effect
and the secondary harmonic distortion suppressibility are
obtainable at a time. Adding together A-phase (A1, A2) outputs with
a 60.degree. phase shift therebetween and addition of AB-phase
(AB1, AB2) outputs result in a decrease in tertiary harmonic
distortion (more generically, odd-number ordered harmonic
distortion). The same is true for B and BB phases.
[0073] FIG. 16 shows conceptually a way of reducing harmonic
distortion in accordance with this embodiment. As shown herein,
four different phase-shifted output waveforms are such that with
respect to an A1-phase output depicted on the top, an A2-phase
output is phase-shifted by 60.degree.; similarly, an AB2-phase
output shown on the bottom in FIG. 16 is 60.degree. phase-shifted
from an AB1-phase output. By adding together the waveforms of A1-
and A2-phase outputs, tertiary harmonic distortion components are
cancelled out; likewise, adding together AB1- and AB2-phase outputs
results in cancellation of tertiary harmonic distortion components.
Furthermore, subtracting from the A1-phase output the AB1-phase
output--this is exactly out of phase with the former--while
subtracting from A2-phase output the AB2-phase output which is
exactly out of phase therewith may enable cancellation of secondary
harmonic distortion components. The same goes with the B- and
BB-phase outputs.
[0074] FIGS. 17A-17C show some modifications of the layout of the
detector wires 41, 42 shown in FIGS. 14-15. In FIG. 17A the first
detector wires 41 include a first set 41a and second set 41b, which
are arranged so that the A-phase wires, i.e. A1- and AB1-phase
wires, are exactly in phase with each other in the sets 41a and
41b, whereas B-phase wires (B1- and BB1-phase ones) have the
reverse phase with each other in the sets 41a and 41b. The second
detector wires 42 include a first set 42a and a second set 42b,
which are disposed so that these are 60.degree. phase-shifted from
the wire sets 41a, 41b of first detector wires 41. In this case,
A-phase outputs are taken out after being added together, while
B-phase outputs are taken after being subject to subtraction
therebetween.
[0075] A detector wire configuration of FIG. 17B may be similar to
that shown in FIG. 17A with the wire sets 41a, 42a, 41b, 42b being
disposed at increased intervals or pitches. More specifically, the
distance between neighboring wire sets 41a, 42a is increased from
.lambda./6 (FIG. 17A) up to 5 .lambda./12. The distance between the
next neighboring sets 42a, 41b is increased from .lambda./12 to
.lambda./3. The distance between sets 41b, 42b is increased to 5
.lambda./12 from .lambda./6. A wire layout pattern of FIG. 17C is
such that while four phase ones A1, BB1, AB1, B1 of the first
detector wires 41 are disposed at intervals of 270', the second
detector wires 42 containing four phase ones B2, A2, BB2, AB2--each
is 60.degree. -shifted in phase from another--are laid out so that
each is between adjacent ones of second wires 41.
[0076] Any one of the detector wire layout patterns shown in FIGS.
17A-17C is similar to the prior discussed embodiments in that the
plural sets of first detector wires 41 are disposed so that these
are the same in phase with respect to at least one of A- and
B-phases while at the same time causing the second detector wires
42 to be disposed in the state of 60.degree. phase-shift relative
to such first wires 41.
[0077] With the layout patterns of FIGS. 17A-17C also, it is
possible to obtain the intended output signals with harmonic
distortion greatly suppressed or minimized.
[0078] Although the foregoing description is drawn to removal of
tertiary harmonic distortion, the phase difference between the
first and second detector wires should not exclusively be limited
to the angle value 60.degree. (.lambda./6), such value may
generically be set at .lambda./2N (where N is an odd number greater
than or equal to 3). With such value settings, it is possible to
remove N-order harmonic distortion.
[0079] FIG. 18 illustrates a principal structure of an
induction-type position sensor 140 in accordance with the second
aspect of the instant invention. The inductive position sensor 140
shown is structured including a drive coil 141 as its primary coil,
and a detector coil 142 as the secondary coil. These coils 141, 142
have their axes a, b at right angles to each other with a single
center point owned in common. Drive coil 141 is electrically
connected to an AC signal source 143, which is operable as a
magnetization exciter or magnetizer for coil 141. Detector coil 142
is connected to a detector circuit 144. Drive coil 141 and detector
coil 142 are immovably supported and adherently secured to a
support structure (not shown). When an object to be measured (i.e.,
a target body) is absent as in the state depicted in FIG. 18,
variable magnetic flux lines created during AC-driving of drive
coil 141 hardly interlink detector coil 142 as shown in FIG. 19A,
resulting in provision of no detection outputs at detector coil
142. This is reworded such that in the absence of a target body, no
electromagnetic coupling activities are found between drive coil
141 and detector coil 142.
[0080] On the contrary, suppose that a magnetic body (or conductor)
145 which is the target body being measured approaches the
cross-coupled coils 141, 142 along a bisector line c of the axes a,
b thereof as shown exemplarily in FIG. 19B. Variable magnetic flux,
i.e. magnetic lines of force, from the drive coil 141 is modulated
behaving to partly cross or interlink detector coil 142. This
allows coil 142 to derive a corresponding detection output. The
foregoing is the principle of position measurement, which is
employable for implementation of proximity sensors and linear
encoders as will be described later.
[0081] The sensor structure of FIG. 18 is modifiable in several
ways as shown in FIGS. 20-22. See first FIG. 20. A sensor structure
shown herein includes its drive coil 141 and detector coil 142.
While the center points of these coils are far from each other,
these yet maintain the relationship that the axis a of drive coil
141 is at 90.degree. to the axis b of detector coil 142. As long as
this relation is satisfied, no electromagnetic coupling is between
drive coil 141 and detector coil 142 in the absence of any target
body to be measured, thereby enabling effectuation of offset-free
position measurements based on the same principle as in the case of
FIG. 18.
[0082] A sensor structure of FIG. 21 is such that its detector coil
142 is disposed not simply on the axis a of driver coil 141;
rather, coil 142 neighbors upon drive coil 141 in a plane 171
containing therein the axis a of coil 141, and has its own axis b
perpendicular to plane 171. In this case also, variable magnetic
flux from drive coil 141 will no longer be coupled with detector
coil 142 in the absence of a target body being measured: only when
such target body appears, variable magnetic flux is modulated
permitting couplement with detector coil 142.
[0083] A sensor structure of FIG. 22 is designed including a
detector coil 142 disposed to have its axis b extending at
90.degree. to a specific one 181 of magnetic flux lines produced
from a driver coil 141 in the absence of a to-be-measured object,
which one is in a predefined direction. In this case also, the
magnetic flux from drive coil 141 is modulated by the object under
measurement permitting obtainability of a detection output due to
electromagnetic coupling with detector coil 142 in such event
only.
[0084] In the sensor structures discussed above, both the drive
coil 141 and detector coil 142 are designed into the circular or
ring-like shape, which may alternatively be modified so that these
coils are rectangular in shape as shown in FIG. 23.
[0085] A further embodiment is shown in FIG. 24, wherein the
position sensor 140 of FIG. 18 is adapted for use with a proximity
sensor 200. This proximity sensor 200 includes a drive coil 141 and
a detector coil 142 operatively associated therewith. These coils
are mounted to a support structure 201, which in turn is immovably
received within a housing 202. Housing 202 has an elastic top cover
plate member 203 that has a vertical though-hole as centrally
defined therein, into which a contactor (or a touch probe) 204 is
inserted and attached as an object under measurement in such a
manner as to lie along a bisector line as defined by equally
dividing an angle between the axis a of drive coil 141 and the
detector coil 142's axis b. Contactor 204 may be a magnetic or
conductive material.
[0086] Unless the contactor 204 is in contact with a target object
being measured (not shown), this contactor is kept spaced apart by
a specified distance from both the drive coil 141 and detector coil
142 so that those components of the variable magnetic field from
drive coil 141 intersecting detector coil 142 stay negligible in
magnitude. This is a steady or standby state. When contactor 204
comes into contact at its distal end with the target object, the
elastic plate 203 behaves to likewise bend downwardly. The variable
magnetic flux of drive coil 141 is thus modulated causing its
interlinkage components with detector coil 142 to increase
accordingly. Thus, such physical contact can be detectes by
determining a detection output of coil 142 through comparison with
a preset threshold value as a reference level therefor, by way of
example.
[0087] A linear encoder device 210 also embodying the invention is
shown in FIG. 25, which employs the electromagnetic position sensor
140 of FIG. 18 therein. The linear encoder 210 is held by a support
structure (not shown). Encoder 210 also includes a scale plate 211
operatively associated with position sensor 140 formed from its
ring-like drive coil 141 and detector coil 142. These coil rings
141, 142 are spatially engaged in a way such that coil 142 is
inside of coil 141 with their axes at 90.degree. to each other. For
such cross-coupled coils 141, 142, the scale 2 is mounted as an
object to be measured to laterally extend through the upstanding
coil 142 and is relatively movable in a direction indicated by
arrow x in FIG. 25, which direction is parallel to the axis of
detector coil 142. Scale 211 has thereon an array of periodically
disposed coin-shaped conductors 212 for modulation of variable
magnetic flux from drive coil 141. These conductors 212 may
optionally be magnetic materials.
[0088] In the linear encoder 210 of FIG. 25, as the scale 211
exhibits relative movement, the variable magnetic flux from drive
coil 141 is modulated periodically due to the periodic layout of
equally spaced conductive (or magnetic) round islands 212 on scale
211 thus letting detector coil 142 derive detection outputs
periodically.
[0089] See FIGS. 26A-26C, which illustrate in side view some of the
major steps during linear movement of the scale 211 relative to the
stationary cross-coupled drive coil 141 and detector coil 142, each
step corresponding to one state of coupling of magnetic flux from
coil 141 with respect to coil 142 at an instant. In this drawing
two adjacent conductor islands 212a, 212b are considered while
scale 211 is moving in the rightward direction. In the state of
FIG. 26A, conductor 212b has almost completely escaped from the
magnetic flux region of drive coil 141 whereas the next conductor
212a is approaching detector coil 142. At this time certain
components of variable magnetic flux from drive coil 141 are
attracted to conductor 212a as indicated by dotted lines in FIG.
26A. In other words, part of the magnetic flux from drive coil 141
comes to couple or interlink detector coil 142. Scale 211 is keep
moving rightwardly. When conductor 212a enter inside of the core of
detector coil 142 as shown in FIG. 26B, magnetic flux from drive
coil 141 is modulated uniformly with respect to the right and left
sides thereof to ensure that no magnetic flux lines cross detector
coil 142. As scale 2 further moves rightward, the magnetic flux
lines from drive coil 141 are attracted to meet together at
conductor 212a only, resulting in creation of magnetic flux
crossing detector coil 142 in a direction opposite to that in FIG.
26A.
[0090] Accordingly, during linear movement of the scale 2 through
the steps shown in FIGS. 26A-26C, the detector coil 142 provides
different outputs in polarity at different stages, including a
positive (or negative) polarity output, zero output, and then
negative (or positive) polarity output in this order of sequence.
With such operation, a sinusoidal wave signal is obtainable at
detector coil 142 as the scale 2 moves linearly. Counting the cycle
or period of this sine wave signal may result in accurate detection
of displacement concerned.
[0091] It has been described that the inductive position
measurement apparatus of the first type incorporating the
principles of this invention includes its drive wire and detection
wires as disposed at right angles to each other to ensure that any
variable magnetic fields creatable by AC driving of the drive coil
are no longer directly coupled with the detection wire in any
events. The first variable magnetic field generatable through AC
driving of the drive wire in turn allows the electromagnetic
couplers to produce an induced current, which in turn permits
creation of the second variable magnetic field which is at 90# to
the first magnetic field. Detecting the second variable magnetic
field using the detection wires results in provision of a detection
output which is variable depending upon relative displacement
between the first and second members. With this scheme of this
invention, no electromagnetic coupling activities are present
between the drive wire and detection wire in principle; thus, no
offset components are generated unlike prior art schemes. This in
turn makes it possible to achieve high-accuracy position
measurements.
[0092] In accordance with the inductive position measurement
apparatus of the second type also incorporating the principles of
the invention, the drive coil and detector coil of a position
sensor are specifically arranged in layout so that these are free
from electromagnetic coupling activities in the absence of a target
object to be measured, whereby the drive coil's generated variable
magnetic field is modulated in distribution in a way responding to
displacement of the target body resulting in creation of
electromagnetic coupling with the detector coil. This apparatus is
also capable of obtaining the intended detection output free from
any offset components, thus enabling accomplishment of position
measurements with increased accuracy and enhanced reliability.
[0093] While the present invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made without departing from the spirit, scope,
and teaching of the invention. Accordingly, the disclosed invention
is to be considered merely as illustrative and limited in scope of
coverage only as specified in the appended claims.
[0094] The entire disclosure of Japanese Patent Applications No.
9-333249 filed on Dec. 3, 1997 and No. 10-143537 filed on May 25,
1998, including specification, claims, drawings and abstract are
incorporated herein by reference in its entirety.
* * * * *