U.S. patent application number 16/568604 was filed with the patent office on 2020-01-02 for inductive position sensor designed to measure the angular position of a shaft or the like.
The applicant listed for this patent is Continental Automotive France, Continental Automotive GmbH. Invention is credited to Alain Fontanet, Jean-louis Roux.
Application Number | 20200003584 16/568604 |
Document ID | / |
Family ID | 56684068 |
Filed Date | 2020-01-02 |
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United States Patent
Application |
20200003584 |
Kind Code |
A1 |
Fontanet; Alain ; et
al. |
January 2, 2020 |
INDUCTIVE POSITION SENSOR DESIGNED TO MEASURE THE ANGULAR POSITION
OF A SHAFT OR THE LIKE
Abstract
An inductive position sensor designed to measure the angular
position of a shaft or the like and includes a support on which are
realized, on the one hand, a primary winding, and on the other
hand, at least two secondary windings in phase opposition with
respect to each other. Each secondary winding is defined by a set
of at least two loops in phase with each other. The secondary
windings are connected in series and each arranged symmetrically
with respect to a middle line so as to form each time a pattern on
either side of this middle line, the two patterns having a
separation between them in the area of said middle line. An
assembly including such a sensor and a target with two oppositely
directed helices.
Inventors: |
Fontanet; Alain; (Muret,
FR) ; Roux; Jean-louis; (Brax, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Continental Automotive France
Continental Automotive GmbH |
Toulouse
Hannover |
|
FR
DE |
|
|
Family ID: |
56684068 |
Appl. No.: |
16/568604 |
Filed: |
September 12, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16307274 |
Dec 5, 2018 |
|
|
|
PCT/FR2017/051394 |
Jun 2, 2017 |
|
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16568604 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01D 5/2291 20130101;
G01D 5/2275 20130101; G01D 5/2053 20130101 |
International
Class: |
G01D 5/22 20060101
G01D005/22; G01D 5/20 20060101 G01D005/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2016 |
FR |
1655109 |
Claims
1. A method for noncontact measurement of the angular position of a
shaft, comprising: providing the outer surface of the shaft with
two helices of opposite directions, the helices being distant from
one another, along the angular measurement range, by a
predetermined distance which is a function of the estimated axial
displacement of the shaft, furnishing an inductive position sensor
with one primary winding and at least two secondary windings, one
secondary winding being defined by a set of at least two loops in
phase with each other, arranging the loops of each secondary
winding facing the helices so that when the angular position of the
shaft varies by a value, then on the one hand for one secondary
winding the variation in flux induced in the loops facing one helix
is identical to that of the flux induced in the loops facing the
other helix, and on the other hand the variation in flux induced in
the loops of one secondary winding facing one helix is identical
but opposite the variation in flux induced in the loops of the
other secondary winding, the loops facing one helix being separated
from the loops facing the other helix by a distance corresponding
to the distance separating the helices along the angular
measurement range, exciting the primary winding and measuring the
signal on the secondary windings, and determining the angular
position of the shaft, the measured signal corresponding to an
angular value of the position of the shaft independent of an axial
displacement of the latter.
2. The method as claimed in claim 1, wherein it also makes it
possible to measure an axial displacement of the shaft and further
comprises: providing the sensor with at least two additional
secondary windings, arranging the loops of each additional
secondary winding facing the helices so that when the angular
position of the shaft varies by a value, then on the one hand for
one secondary winding the variation in flux induced in the loops
facing one helix is identical but opposite to that of the flux
induced in the loops facing the other helix, and on the other hand
the variation in flux induced in the loops of one secondary winding
facing one helix is identical to that of the flux induced in the
loops of the other secondary winding, the loops facing one helix
being separated from the loops facing the other helix by a distance
corresponding to the distance separating the helices along the
angular measurement range measuring the signal on the additional
secondary windings, and determining the axial position of the
shaft, the signal measured in the area of the additional secondary
windings corresponding to position of the shaft independent of the
angular position of the latter.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 16/307,274 filed Dec. 5, 2018 which is the U.S. National
Stage Application of PCT International Application No.
PCT/FR2017/051394, filed Jun. 2, 2017, which claims priority to
French Patent Application No. 1655109, filed Jun. 6, 2016, the
contents of such applications being incorporated by reference
herein.
FIELD OF THE INVENTION
[0002] The present invention concerns an inductive position sensor
designed to measure an angular position of a shaft or the like.
[0003] This type of sensor has the advantage of making it possible
to determine the position of a mechanical part, or any other
element, without the need for a contact with the part whose
position is to be found. This advantage means that the applications
of such sensors are very numerous in all types of industries. Such
sensors are likewise used in mass market applications such as the
field of automobiles within which aspects of the present invention
have been realized. However, it can be used in other diverse and
varied fields.
BACKGROUND OF THE INVENTION
[0004] The principle of operation of an inductive sensor is based
on the variation in coupling between a primary winding and
secondary windings of a transformer operating at high frequency and
without the use of a magnetic circuit. The coupling between these
windings varies as a function of the position of a movable
conductor (of electricity) piece, generally known as a "target".
Currents induced in the target will in fact modify the currents
induced in the secondary windings. By adapting the configuration of
the windings and knowing the current injected in the primary
winding, measuring the current induced in the secondary windings
makes it possible to determine the position of the target.
[0005] Document EP0182085, incorporated herein by reference,
describes the principle of such an inductive sensor.
[0006] In order to integrate such an inductive sensor in a device,
especially an electronic device, it is known how to make the
aforementioned transformer on a printed circuit card. The primary
winding and the secondary windings are then formed by tracks traced
on the printed circuit card. The primary winding is then energized
for example by an external high-frequency source and the secondary
windings are then the site of currents induced by the magnetic
field created by the circulation of a current in the primary
winding. The target, which is a conductive piece, such as metal,
can have a simple shape. For example, it may be a piece cut out
from a metal sheet. In order to make a linear sensor, the cutout to
form the target is for example rectangular, while for a rotary
sensor this cutout will be for example in the form of an angular
sector with radius and angle suited to the movement of the
piece.
[0007] Generally, two sets of secondary windings are designed to
accomplish sine and cosine functions of the target position in one
complete run of the sensor. Such functions (cos and sin) are well
known and can be easily processed by an electronic system. By
forming the ratio of the sine to the cosine and then applying an
arc tangent function, one obtains an image of the position of the
target. The argument of the sine and cosine functions is a linear
(or affine) function of the position of the target whose course
then represents a more or less large portion of the spatial period
of these trigonometric functions.
[0008] From a physical standpoint, the modification of the coupling
between the primary circuit and the secondary circuits is realized
thanks to the phenomenon of the electromagnetic skin effect, known
to the person skilled in the art. The primary circuit being
energized by a high-frequency source, the phenomena taking place in
the entire sensor are high-frequency phenomena. The target whose
position is to be found is a massive conductor piece and is the
site of significant induced currents. The depth of penetration of
these induced currents is relatively shallow (hence the term skin).
For example, it is in the order of 50 .mu.m in the case of an
aluminum target. Thus, the induction does not penetrate into the
target and the magnetic flux produced by the primary circuit thus
bypasses the target. Due to this fact, the field lines are strongly
modified. This modification is perceived by the secondary circuits
which, depending on the position of the target, receive more or
less flux. These fluxes are variable as a function of the position
of the target and also variable as a function of time and therefore
generate a voltage at the terminals of the secondary circuits. By
measuring these voltages, one thus obtains a signal which, when
analyzed, lets one know the position of the target.
[0009] When it is not possible to place a sensor at the end of a
shaft to determine the angular position of that shaft, it is known
how to provide the shaft with a helix which is placed opposite a
linear sensor. In fact, if one looks at a helix in rotation
relative to a fixed point, one sees from this fixed point a surface
in axial displacement. Thus, it is as if the target were moving
linearly in front of the sensor.
[0010] Thus, a linear sensor can give an indication as to the
angular position of a shaft by adapting the shape of the target.
However, when the shaft whose angular position is to be determined
is moving axially, even if it is only parasitic movements, the
angular measurement is falsified on account of this axial
movement.
SUMMARY OF THE INVENTION
[0011] Therefore, an aspect of the present invention is to enable a
measuring of the angular position of a shaft or the like in
inductive technology (no contact), in radial position, that is, by
being positioned at the side of the shaft and not at its end, being
insensitive to the axial play.
[0012] Preferably, the sensor enabling this measurement will have a
reduced footprint.
[0013] Advantageously, such a sensor will also allow measuring a
longitudinal displacement (along the axis of rotation of the
shaft). This will allow, for example, measuring at the same time of
an angular position and/or a speed of rotation and an axial
displacement. Such a measurement of longitudinal displacement could
likewise be used in order to quantify a parasitic longitudinal
movement.
[0014] For this purpose, an aspect of the present invention
proposes an inductive position sensor designed to measure the
angular position of a shaft or the like, comprising a support on
which are realized, on the one hand, a primary winding and, on the
other hand, at least two secondary windings in phase opposition to
each other, each secondary winding being defined by a set of at
least two loops in phase with each other.
[0015] According to an aspect of the present invention, the
secondary windings are connected in series and are each arranged
symmetrically with respect to a middle line so as to form each time
a pattern on either side of this middle line, the two patterns
having a separation between them in the area of said middle
line.
[0016] Such a sensor is designed to work with a double helix having
two helices one alongside the other, the two helices being of
opposite direction and spaced apart from one another. The two
patterns defined above are separated so that, even if the shaft
carrying the target in the form of a double helix is moving
longitudinally--for example, parasitic vibrations--each pattern can
remain opposite a helix without being influenced by the other
one.
[0017] The proposed sensor thus makes it possible to obtain a
signal depending solely on the angular position of the shaft
carrying the target while being insensitive to any variation in
longitudinal position, parasitic or desired. In fact, it is
possible to cancel out the variations in flux due to longitudinal
displacements in the loops of the secondary circuit proposed.
[0018] In a first embodiment, the inductive position sensor
described above is such that each pattern is constituted of a first
set of loops of a first winding adjacent to a second set of loops
of a second winding, the loops of the first winding having a form
similar to the loops of the second winding and the number of loops
of the first set being equal to the number of loops of the second
set.
[0019] In one alternative embodiment of the position sensor
described above, each pattern is constituted of a first set of
loops of a first winding adjacent to a second set of loops of a
second winding and to a third set of loops of the second winding,
the loops of the first winding having a surface which is double
that of the loops of the second winding, the number of loops being
equal for the three sets and the loops of the first set of loops
being disposed between the loops of the second set of loops and
those of the third set of loops in order to form an alignment of
loops perpendicular to the middle line.
[0020] In order for the inductive position sensor described to be
able moreover to perform a measurement of longitudinal position,
this sensor advantageously comprises moreover at least two
additional secondary windings in phase opposition with respect to
each other and connected in series with each other; each additional
secondary winding is defined by a set of at least two loops in
phase with each other; the loops of an additional secondary winding
are disposed in symmetrical manner to the loops of the other
additional secondary winding in respect of said middle line, and
the loops of one additional secondary winding form, on one side of
the middle line with the loops of the other additional secondary
winding located on the same side of the middle line, a pattern
separate from the pattern formed by the other loops of the
additional secondary windings.
[0021] An aspect of the present invention likewise concerns an
assembly formed by an inductive position sensor and a target,
distinguished in that the position sensor is a position sensor as
described above, in that the target comprises two helices of
opposite pitches, and in that the inductive position sensor is
disposed facing the target such that on the one hand one pattern of
the secondary windings is situated facing one helix and the other
pattern of the secondary windings is located facing the other
helix, and on the other hand so that each helix (18, 20) is located
facing both a first secondary winding and facing a second secondary
winding in phase opposition with the first secondary winding.
[0022] Finally, an aspect of the present invention concerns a
method for noncontact measurement of the angular position of a
shaft, distinguished in that it involves the following steps:
[0023] providing the outer surface of the shaft with two helices of
opposite directions, the helices being distant from one another;
along the angular measurement range, by a predetermined distance
which is a function of the estimated axial displacement of the
shaft, [0024] furnishing an inductive position sensor with one
primary winding and at least two secondary windings, one secondary
winding being defined by a set of at least two loops in phase with
each other, [0025] arranging the loops of each secondary winding
facing the helices so that when the angular position of the shaft
varies by a value, then on the one hand for one secondary winding
the variation in flux induced in the loops facing one helix is
identical to that of the flux induced in the loops facing the other
helix, and on the other hand the variation in flux induced in the
loops of one secondary winding facing one helix is identical but
opposite the variation in flux induced in the loops of the other
secondary winding, the loops facing one helix being separated from
the loops facing the other helix by a distance corresponding to the
distance separating the helices along the angular measurement
range, [0026] excitation of the primary winding and measurement of
the signal on the secondary windings, [0027] determination of the
angular position of the shaft, the measured signal corresponding to
an angular value of the position of the shaft independent of an
axial displacement of the latter.
[0028] In order to facilitate the implementing of this method, one
may for example arrange for the helices to be disposed on a
cylindrical surface of the shaft symmetrically with respect to a
transverse plane of said cylindrical surface.
[0029] Advantageously, such a method also makes it possible to
measure an axial displacement of the shaft. For this purpose, it
may then involve also the following steps: [0030] providing the
sensor with at least two additional secondary windings, [0031]
arranging the loops of each additional secondary winding facing the
helices so that when the angular position of the shaft varies by a
value, then on the one hand for one secondary winding the variation
in flux induced in the loops facing one helix is identical but
opposite to that of the flux induced in the loops facing the other
helix, and on the other hand the variation in flux induced in the
loops of one secondary winding facing one helix is identical to
that of the flux induced in the loops of the other secondary
winding, the loops facing one helix being separated from the loops
facing the other helix by a distance corresponding to the distance
separating the helices along the angular measurement range [0032]
measuring the signal on the additional secondary windings, [0033]
determination of the axial position of the shaft, the signal
measured in the area of the additional secondary windings
corresponding to position of the shaft independent of the angular
position of the latter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Details and advantages of aspects of the present invention
will better appear from the following description, made in
reference to the appended schematic drawing, in which:
[0035] FIG. 1 is a side view of a shaft on which a measurement of
angular position (and possibly axial position) is to be done,
[0036] FIG. 2 is a cross sectional view of the shaft of FIG. 1
illustrating a noncontact position sensor,
[0037] FIG. 3 illustrates schematically a primary winding which can
be used for the sensor illustrated in FIG. 2,
[0038] FIGS. 4 to 7 illustrate schematically secondary windings
which can be used for the sensor illustrated in FIG. 2,
[0039] FIG. 8 illustrates very schematically secondary windings
facing a shaft for which the angular position is being measured
along a given range (less than 360.degree.),
[0040] FIG. 9 illustrates very schematically secondary windings
facing a shaft for which the angular position is being measured
along a range of 360.degree., and
[0041] FIGS. 10 and 11 are views similar to FIGS. 8 and 9 for
variant embodiments of the shaft on which the measurement of
angular position is realized.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] FIG. 1 illustrates a shaft 12 of longitudinal axis 14. This
shaft 12 is driven in rotation and its angular position is given by
an angle .theta.. It is able to move in a lateral translation _62
in the longitudinal direction corresponding to the longitudinal
axis. The displacement in translation can be a parasitic
displacement (which is then in the order of a tenth of a
millimeter, for example) and/or a controlled displacement.
[0043] For example, this may be a camshaft of a motor vehicle. This
shaft 12 has a cylindrical zone 16 on which a first helix 18 and a
second helix 20 are produced. These two helices in the preferred
embodiment illustrated here have the same characteristics and are
disposed symmetrically to a transverse plane of the shaft 12. Thus,
these two helices have the same pitch, but opposite directions. It
is assumed here that they extend for 360.degree. about the
cylindrical zone 16. It is assumed that the maximum lateral
displacement of the shaft 12 along the longitudinal axis 14 is
.delta.. The first helix 18 will then be spaced from the second
helix 20 by a distance at least equal to 2.delta..
[0044] The first helix 18 and the second helix 20 cooperate with a
position sensor 22 realized on an integrated circuit board, itself
being mounted on a support 24 associated with a connector 26. The
position sensor 22 is mounted in a plane parallel to the
longitudinal axis 14 of the shaft 12 facing the helices and in
proximity to them, yet without having contact with them. FIG. 2
illustrates in transverse section with regard to the shaft 12 the
position of the position sensor 22 in relation to the shaft. A free
space in the order of a millimeter (from 0.5 to 5 mm) remains
between the helices and the position sensor 22.
[0045] The position sensor 22 is adapted, first of all, to
determine the angular position of the shaft 12 independently of its
lateral position, that is, independently of its position along the
longitudinal axis 14. Furthermore, as an option, it is provided to
determine the position of the shaft 12 likewise along its
longitudinal axis 14.
[0046] In order to determine the angular position (angle .theta.),
the position sensor 22 is an inductive sensor comprising a primary
circuit 28 (FIG. 3) associated with a secondary circuit (FIG. 4 or
FIG. 5). In a way known to the skilled person, the primary circuit
28 is excited by a high-frequency signal and a target, here the
helices (first helix 18 and second helix 20) realize a coupling
with the corresponding secondary circuit. By measuring the
electrical voltage (signal) on the terminals of the secondary
circuit, it is possible to learn the position of the helices in
relation to the position sensor 22 and thus the angular position of
the shaft 12.
[0047] Like the primary circuit, the secondary circuit is printed
on a board, also called a PCB (Printed Circuit Board). A first form
of secondary circuit is illustrated in FIG. 4 and a variant
embodiment is illustrated in FIG. 5.
[0048] In the embodiment of FIG. 4, the secondary circuit has two
windings connected in series and in phase opposition to each other.
One notices in this FIG. 4 the presence of four loops numbered 1 to
4. The loops 1 and 4 form a first winding: they are connected in
series and are in phase. Likewise, the loops 2 and 3 form a second
winding: they are connected in series and are in phase. The first
winding is connected to the second winding and is in phase
opposition with the second winding.
[0049] The four loops 1, 2, 3 and 4 are aligned along an axis
parallel to the longitudinal axis 14 of the shaft 12. They each
have substantially the same surface so that the flux induced by the
primary circuit in each of them in the absence of the target has a
same absolute value. The loops 1 and 2 are designed to face the
first helix 18 while the loops 3 and 4 are designed to face the
second helix 20. The loops 1 and 2 form a pattern M which is
symmetrical to the pattern M formed by the loops 3 and 4 in
relation to a middle line AA'. In a same pattern M (1 and 2 or 3
and 4), each time there is at least one loop in phase opposition
with another loop of the same pattern. It is further noticed that
the two patterns M are separated. The separation distance between
the two patterns (corresponding in FIG. 4 to the separation
distance between the loop 2 and the loop 3) is the same as the
distance separating the first helix 18 from the second helix 20,
for example 2.delta..
[0050] FIG. 5 illustrates a variant embodiment of the secondary
circuit shown in FIG. 4. One finds here six loops numbered 5 to 10.
The secondary circuit is formed by two windings connected in series
and in phase opposition relative to each other. The loops 5, 7, 8
and 10 form a first winding: they are connected in series and are
in phase. The loops 6 and 9 form a second winding. They are
connected in series and are in phase but are in phase opposition to
the loops 5, 7, 8 and 10.
[0051] Here as well, the loops of the secondary circuit are aligned
along an axis parallel to the longitudinal axis 14 of the shaft 12.
The loops 5, 6 and 7 form a first pattern M' symmetrical with a
second pattern M' formed by the loops 8, 9 and 10, along the middle
line AA'. These two patterns are symmetrical in regard to the
middle line AA' and are separated from one another by a distance
which corresponds here as well to the distance separating the first
helix 18 from the second helix 20, or 2.delta..
[0052] In each of the patterns, the surface of the loops of a
winding is equal to the surface of the loops of the other winding.
Thus, we have here in the first pattern the loops 5 and 7, each one
having a surface substantially equal to half the surface of the
loop 6. Thus, the flux induced in the loops of a winding in a
pattern by the primary circuit is, in absolute value, the same as
that induced by the primary circuit in the loops of the other
winding.
[0053] The measurement principle for the angular position .theta.
of the shaft 12 with the aid of the position sensor 22 is explained
in reference to FIG. 8. In this figure, it is assumed that the
position sensor 22 comprises the primary circuit 28 of FIG. 3
superimposed on the secondary circuit of FIG. 4.
[0054] In FIG. 8, which is a very schematic figure, there is
represented the first helix 18, the second helix 20 and only the
secondary circuit of FIG. 4 with its four loops 1, 2, 3 and 4.
There is represented in this figure an abscissa axis Z and the
ordinate axis corresponds to the angular position .theta.. It is
assumed that the secondary circuit (loops 1, 2, 3 and 4) is fixed.
The helices are each represented by an inclined band: this
corresponds to what is perceived by the sensor (secondary circuit)
of the helices 18, 20 when the shaft 12 is rotating in front of
it.
[0055] FIG. 8 corresponds to one angular position and one axial
position of the shaft 12. If the shaft 12 is rotating, then the
inclined bands representing the helices rise or fall along the
ordinate axis in FIG. 8. If the shaft 12 moves axially, then the
inclined bands are displaced in relation to the sensor along the
abscissa axis.
[0056] In the specific case of FIG. 8, it is assumed that the
measurement of the angular position is done in a predetermined
range, less than 360.degree..
[0057] When the shaft 12 is rotating and .theta. increases, the
free surface of the loop 1 diminishes. When the shaft 12 is
displaced toward the increasing Z, the free surface of the loop 1
increases. Say that .PHI.1 is the flux induced in the loop 1. This
flux will be inversely proportional to the angle .theta. and
proportional to the longitudinal position Z. Since the loop 1 is
assumed to be in phase opposition with the primary circuit, one
chooses a negative constant (-.PHI.0) to determine .PHI.1.
[0058] One will then have:
.PHI.1=-.PHI.0(-.theta.+Z)
[0059] Applying the same reasoning to the other loops, one
obtains:
.PHI.2=.PHI.0(.theta.-Z)
.PHI.3=.PHI.0(.theta.+Z)
.PHI.4=-.phi.0(-.theta.-Z)
[0060] The signal measured on the terminals of the secondary
circuit will be proportional to the sum of the fluxes circulating
in the loops 1, 2, 3 and 4.
[0061] One thus has:
.SIGMA..PHI.=+.PHI.1+.PHI.2+.PHI.3+.PHI.4
.SIGMA..PHI.=.PHI.0(.theta.-Z+.theta.-Z+.theta.+Z+.theta.+Z)
or
.SIGMA..PHI.=4.PHI.0*.theta.
[0062] It thus emerges that the signal on the terminals of the
secondary circuit is proportional to the angular position of the
shaft 12 and insensitive to an axial displacement Z of the shaft
12.
[0063] A similar demonstration can be done with the secondary
circuit illustrated in FIG. 5. This leads to the same result: the
signal is proportional to the angle of rotation of the shaft and
insensitive to a variation in axial position Z of this shaft
12.
[0064] In the preceding calculation, it was assumed that each time
there was only a single loop 1, a single loop 2, a single loop 3
and a single loop 4. In order to obtain a greater sensitivity, it
is clear that one can superimpose each time several loops to
increase the induced flux and thus obtain a better sensitivity.
[0065] It also emerges from the preceding calculation that it is
advisable to have each helix permanently facing the two windings at
the same time (1, 4 and 2, 3 in the embodiment of FIGS. 4 and 8) so
as to obtain the above calculated flux compensation in regard to a
displacement in translation. It is sufficient here to adapt the
geometry of the windings to that of the helices. The size, and the
position, of the loops are adapted to the pitch of the helices, to
their width, to their position and to their maximum displacement in
translation along the measurement range in question. Thus, each
helix is located along the angular measurement range facing both a
first secondary winding and a second secondary winding in phase
opposition with the first secondary winding.
[0066] FIG. 9 illustrates a measurement of the angular position
over 360.degree.. The measurement principle here remains the same.
The shape of the ends of the helices is adapted so that the
variation in induced flux remains the same for the same angular
variation along the entire measurement range, that is, 360.degree..
Thus, one arranges here for the helices to extend for 360.degree.
about the shaft 2 and for their ends of the helices to be situated
in a radial plane with respect to the shaft 12. It is likewise
advisable to make sure that the cylindrical zone 16 does not have
any bosses or the like forming a target at a distance less than 6
from the ends of the helices.
[0067] As illustrated in FIG. 10, it is possible to join the
helices to form a chevron. For a measurement performed for several
poles, such as a shaft with a motor having several poles, it is
possible to provide several helices or chevrons in the area of the
cylindrical zone 16 provided for the measurement of position.
[0068] The transverse displacement along the longitudinal axis 14
of the shaft 12 can be a parasitic movement. However, it may be a
controlled movement and it is then of interest to likewise be able
to measure the displacement of the shaft 12 along its longitudinal
axis Z.
[0069] Thanks to the presence of the two helices, of opposite
direction, one can likewise measure the longitudinal displacement
of the shaft 12. It is proposed here to superimpose an additional
secondary circuit on the secondary circuit used to measure the
angular position and on the primary circuit 28.
[0070] It is proposed here to use an additional secondary circuit
such as that illustrated in FIG. 6 or in FIG. 7.
[0071] The additional secondary circuits proposed here are similar
to the secondary circuits of FIGS. 4 and 5. One again finds two
windings in phase opposition and two patterns each with loops of
one winding and loops of the other winding such that in one pattern
the surface of the loops of one winding corresponds to the surface
of the loops of the other winding. As compared to the secondary
circuits of FIGS. 4 and 5, the additional secondary circuits of
FIGS. 6 and 7 again have the same pattern on one side, but the
other pattern, likewise separated from the first pattern by a
distance corresponding to the distance separating the helices, is
in phase opposition. One can thus define the second pattern here as
being the same pattern as the first pattern but offset along the
longitudinal axis by a distance corresponding to the length of the
pattern increased by the distance separating the two helices.
Described in another way, one may consider that one loop of one
winding of one pattern is symmetrical to one loop of the other
winding of the other pattern.
[0072] In short, as appears clearly by comparing FIG. 4 with FIG.
6, the loops of the additional secondary circuit of FIG. 6 again
have the same shape as the loops of the secondary circuit of FIG. 4
but the connection between the two patterns is inverted. One thus
denotes the loops of FIG. 6 as: 1, 2, 3' and 4'. Likewise, in FIG.
7, one will have loops 5, 6, 7, 8', 9' and 10'.
[0073] The signal on the terminals of the additional secondary
circuit corresponds to the flux induced by the primary circuit 28
in the loops of this circuit. As already done above, one calculates
the fluxes in each of the loops of the additional secondary
circuit. As per the above, one will again find the same flux for
the loops 1 and 2 and an inverted flux for the loops 3' and 4' (in
relation to the loops 3 and 4). One thus has:
.PHI.1=-.PHI.0(-.theta.+Z)
.PHI.2=.PHI.0(.theta.-Z)
.PHI.3'=-.PHI.0(.theta.+Z)
.PHI.4'=.PHI.0(-.theta.-Z)
[0074] The signal measured on the terminals of the additional
secondary circuit will be proportional to the sum of the fluxes
circulating in the loops 1, 2, 3' and 4'.
[0075] One thus has:
.SIGMA..PHI.=.PHI.1+.PHI.2+.PHI.3'+.PHI.4'
.SIGMA..PHI.=.PHI.0(.theta.-Z+.theta.-Z-.theta.-Z-.theta.-Z)
or
.SIGMA..PHI.=-4.PHI.0*Z
[0076] It thus emerges that the signal on the terminals of the
additional secondary circuit is proportional to the longitudinal
position of the shaft 12 and it is insensitive to a displacement in
rotation .theta. of the shaft 12.
[0077] Thus, by superimposing on the position sensor 22 a primary
circuit 28 with a secondary circuit as illustrated in FIG. 4 or in
FIG. 5 and moreover an additional secondary circuit as illustrated
in FIG. 6 or in FIG. 7, it is possible to measure with precision,
on the one hand, the angular position .theta. of the shaft 12 and
on the other hand its axial position Z.
[0078] The above embodiment thus makes possible at the same time a
measurement of the angular position .theta. of a shaft without
being influenced by its axial position Z while also enabling a
measurement of the axial position Z of this shaft. Thus, the same
position sensor is able to perform two measurements of position
(angular and longitudinal). Such a double measurement with a single
sensor has not yet been accomplished to the knowledge of the
inventors at the time of the filing of the patent application.
[0079] The position sensor (angular and/or longitudinal) proposed
is of reduced footprint. It can also be used to produce a sensor of
angular velocity of the shaft (also known as a "resolver").
[0080] The preferred embodiment proposed is to have targets in the
shape of helices, the two helices having the same pitch but being
opposite in direction. One could contemplate having a different
pitch for the two helices, by then adapting the loops.
* * * * *