U.S. patent application number 10/790624 was filed with the patent office on 2004-12-02 for bearing equipped with magnetic encoder and sensor including aligned sensing elements.
Invention is credited to Desbiolles, Pascal, LaCroix, Mark E., Santos, Alfred John.
Application Number | 20040239311 10/790624 |
Document ID | / |
Family ID | 9544378 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040239311 |
Kind Code |
A1 |
Santos, Alfred John ; et
al. |
December 2, 2004 |
Bearing equipped with magnetic encoder and sensor including aligned
sensing elements
Abstract
The invention relates to a bearing provided with an annular
means generating magnetic pulses and with a device for detecting
these pulses, wherein the detection device comprises a plurality of
aligned sensitive elements.
Inventors: |
Santos, Alfred John;
(Farmington, CT) ; LaCroix, Mark E.; (New
Hartford, CT) ; Desbiolles, Pascal; (Thorens Glieres,
FR) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
3773 CORPORATE PARKWAY
SUITE 360
CENTER VALLEY
PA
18034-8217
US
|
Family ID: |
9544378 |
Appl. No.: |
10/790624 |
Filed: |
March 1, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10790624 |
Mar 1, 2004 |
|
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|
09549634 |
Apr 14, 2000 |
|
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|
6700367 |
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Current U.S.
Class: |
324/165 ;
324/207.25 |
Current CPC
Class: |
G01P 3/443 20130101;
F16C 41/007 20130101; G01D 5/145 20130101 |
Class at
Publication: |
324/165 ;
324/207.25 |
International
Class: |
G01B 007/30; G01P
013/00; G01P 003/52 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 1999 |
FR |
99-04658 |
Claims
1. A bearing provided with an annular means generating magnetic
pulses and with a device for detecting these pulses, wherein the
detection device comprises a plurality of aligned sensitive
elements (5).
2. The bearing as claimed in claim 1, wherein the sensitive
elements are chosen from among the groups comprising Hall-effect
probes, magnetoresistors, giant magnetoresistors.
3 The bearing as claimed in claim 1 or 2, wherein the sensitive
elements are placed equidistantly from one another.
4. The bearing as claimed in any one of claims 1 to 3, wherein the
pulse generating means is an annular member which is made of a
synthetic material laden with ferrite particles and is formed by a
plurality of contiguous domains having reversed direction of
magnetization of a given domain with respect to the two domains
which are contiguous with it.
5. The bearing as claimed in any one of claims 1 to 4, wherein the
detection device comprises an even number 2N of sensitive
elements.
6. The bearing as claimed in claim 5, wherein the assembly of 2N
sensitive elements is divided into two subassemblies (8, 9) of N
elements, each sensitive element (5) of the first subassembly (8)
being connected to a first adder (10), each sensitive element (5)
of the second subassembly (9) being connected to a second adder
(11), the two sums (S.sub.1, S.sub.2) emanating from the first and
second adders (10, 11) being connected to the input of a third
adder (12), the output (S.sub.1) of the first adder (10) and, via
an inverter (13), the output (S.sub.2) of the second adder (11)
being connected to the input of a fourth adder (14), the signals
SIN=S.sub.1+S.sub.2 and COS=S.sub.1-S.sub.2 emanating from the
third (12) and fourth adders (14) being processed by a circuit so
as to deduce the direction of rotation and/or the speed or rotation
and/or the position of the pulse generating means with respect to
the detection device.
7. The bearing as claimed in claim 6, wherein the polar length (Lp)
of the encoder is substantially equal to the product of the number
(2N) of sensitive elements (5) times the distance (d) between
sensitive elements, the signals SIN and COS then being in
substantially perfect quadrature and of substantially like
amplitude.
8. The bearing as claimed in claim 6, wherein the polar length (Lp)
of the encoder is less than the product of the number (2N) of
sensitive elements (5) times the distance (d) between sensitive
elements.
9. The bearing as claimed in claim 6, wherein the polar length (Lp)
of the encoder is greater than the product of the number (2N) of
sensitive elements (5) times the distance (d) between sensitive
elements.
10. The bearing as claimed in claim 9, wherein, by programming, an
even number (2M) of sensitive elements, less than the total number
(2N) of these elements (5) is employed to form two subassemblies of
M elements, each sensitive element (5) of the first subassembly
being connected to a first adder, each sensitive element of the
second subassembly being connected to a second adder, the two sums
emanating from the first and second adders being connected to the
input of a third adder, the output of the first adder and, via an
inverter, the output of the second adder being connected to the
input of a fourth adder, the signals emanating from the third and
fourth adders being processed by a circuit so as to deduce the
direction of rotation and/or the speed or rotation and/or the
position of the pulse generating means with respect to the
detection device, said signals being in substantially perfect
quadrature.
11. The bearing as claimed in claim 10, wherein the programming is
carried out by EEPROM.
12. The bearing as claimed in claim 10, wherein the programming is
carried out by Zener Zapping.
13. The bearing as claimed in claim 8 or 9, wherein an amplifier
circuit is able to re-establish an identical amplitude for the
signals emanating from the third and fourth adders.
14. The bearing as claimed in one of claims 1 to 13, wherein the
detection device comprises a number of sensitive elements (5) which
is a multiple of four.
15. The bearing as claimed in claim 14, wherein the assembly of 4P
sensitive elements is divided into four subassemblies of P
elements, each sensitive element (5) of the first subassembly with
P elements being connected to a first adder supplying a signal
S.sub.1; each sensitive element (5) of the second subassembly with
P elements being connected to a second adder supplying a signal
S.sub.2; each sensitive element (5) of the third subassembly with P
elements being connected to a third adder supplying a signal
S'.sub.1; each sensitive element (5) of the fourth subassembly with
P elements being connected to a fourth adder supplying a signal
S'.sub.2; a circuit of adders and of inverters supplying two
signals SIN and COS respectively equal to:
SIN=(S.sub.1-S.sub.2)-(S'.sub.- 1-S'.sub.2);
COS=(S.sub.1+S.sub.2)-(S'.sub.1+S'.sub.2); these signals SIN and
COS being devoid of magnetic offset.
16. The bearing as claimed in claim 15, wherein the detection
device comprises an interpolator increasing the resolution of these
output signals.
17. The bearing as claimed in any one of claims 1 to 16, wherein
the sensitive elements are integrated on an ASIC type circuit
support.
18. The bearing as claimed in claim 17, wherein the detection
device is incorporated within an ASIC type customized integrated
circuit.
19. The bearing as claimed in one of claims 1 to 18, wherein the
pulse generating means is integrated into a preassembled assembly
forming a seal.
20. The bearing as claimed in claim 19, wherein the detection
device is secured in a possibly removable manner to the fixed race.
Description
[0001] The invention relates to the technical domain of bearings
provided with a rotating means generating pulses, and referred to
as an "encoder", a detection device, referred to as a "sensor",
make it possible to obtain information, such as for example, the
speed of rotation, the angular position and the direction of
rotation of a bush comprising such a bearing with built-in
encoder.
[0002] Such bushes may, for example, be employed for the wheels of
motor vehicles provided with a wheel anti-lock system.
[0003] The invention relates more particularly, but not
exclusively, to bearings with built-in magnetic encoder, the
functionally associated sensor being of magnetoresistor or
Hall-effect probe type.
[0004] The expression "Hall-effect probe" here designates sensors
comprising at least one sensitive element, generally a
semiconductor in wafer form, such that, when a current I flows
through it, whilst being subjected moreover to an induction B
making an angle .theta. with the current, a voltage V equal to
V=K.I.B. sin .theta. appears in a direction perpendicular to the
current I and to the induction B, K being referred to as the "Hall
constant", and being characteristic of the material and of the
geometry of the sensitive element, K varying with temperature.
[0005] The expression "magnetoresistor" here designates a varistor
sensitive to the intensity of a magnetic field, or in other words a
resistor made of a semiconductor material whose ohmic value varies
alongside a variation in the intensity of a unidirectional magnetic
field applied perpendicularly to the direction of the current
flowing through the resistor.
[0006] Hall probes are regarded as active sensors, insofar as the
information delivered is related to the electromotive force.
[0007] When these Hall probes are used for conveying position or
displacement, the magnet which creates the induction is the test
body on which the primary value to be measured acts, modifying the
secondary measurand, namely conventionally the normal component of
the induction, to which measurand the probe is directly
sensitive.
[0008] Numerous designs of bearings with built-in magnetic encoder
and sensors of Hall-effect probe or magnetoresistor type are
already known in the prior art.
[0009] Reference may be made for example to the following
documents:
[0010] French patent applications 2 667 947, 2 669 432, 2 669 728,
2 671 633, 2 678 691, 2 678 692, 2 690 989, 2 693 272, 2 694 082, 2
702 567, 2 710 985, 2 718 499;
[0011] European patent applications 375 019, 420 040, 420 041, 438
624, 487 405, 488 853, 498 298, 518 157, 521 789, 522 933, 531 924,
557 931, 557 932, 647 851, 693 689, 701 132, 701 133, 714 029, 745
857, 751 311, 753 679, 767 385.
[0012] Reference may be made, likewise by way of example, to the
following documents emanating from the applicant:
[0013] French patent applications 2 639 689, 2 640 706, 2 645 924,
2 730 283, 2 732 458, 2 717 266, 2 701 298;
[0014] European patent applications 371 836, 376 771, 484 195, 394
083, 607 719, 616 219, 619 438, 631 140, 652 438, 671 628, 725 281,
735 348.
[0015] When one wishes to ascertain both the speed of rotation of
the inner race or of the outer race of the bearing and also the
direction of rotation of this race, it is known practice to utilize
two signals electrically out of phase by 90.degree. to define the
direction of rotation.
[0016] For the sake of clarity, it is recalled here that two
sinusoidal signals of like frequency are said to be in quadrature
when the signals are out of phase by .pi./2 or 90.degree., i.e. a
quarter of a cycle, that is to say when one of the signals is at
its peak value while the other is passing through zero.
[0017] Thus, for example, the document FR-A-2 599 794, emanating
from the applicant, describes a bush or bearing with information
sensor comprising a fixed element supporting, in one embodiment,
two Hall sensors or magnetoresistors angularly offset by an
interval of n+0.5 n, in which n is the length of a magnet.
[0018] The document EP-A-395 783 describes a bush with a sensor for
measuring the speed of rotation and/or the angle of rotation,
comprising one or more Hall-effect sensors.
[0019] In the devices of the type mentioned above, the out-of-phase
signals emanate from two Hall-effect sensitive elements or
magnetoresistors, placed on a substrate or implanted directly on
silicon with a defined and fixed distance between them, this
distance being dependent on the encoder.
[0020] Given the inter-element distance fixed by the very principle
of the sensor, in the case where the polar distance is not
suitable, the digital signals emanating from the sensitive elements
are not in quadrature.
[0021] Hence, the devices known from the prior art have the
following drawbacks:
[0022] the polar length span, and therefore the encoder span which
can be used with a dual sensor (that is to say having two sensitive
elements), whose polar length is fixed, is limited by the tolerance
in the quadrature of the digital output signals;
[0023] for a polar length corresponding to the inter-element
distance, the tolerance in the output signals is dependent on the
technology of the sensor and on the accuracy of placement of the
sensitive elements;
[0024] in the case of a dual sensor delivering analog signals
associated with an interpolation principle such as described in the
document WO-97/01660 or in the document FR-97/12033, the accuracy
required with regard to the quadrature of the analog signals limits
the use of such a sensor to magnetic encoders whose polar distance
corresponds accurately to the inter-element distance.
[0025] The invention relates to a device for detecting the
direction of rotation of an outer race or of an inner race of a
bearing, this device also allowing the detection of the angular
position and of the speed of rotation of the said race, the said
device allowing adaptation to various polar lengths and
cancellation of the magnetic offset.
[0026] For this purpose, the subject of the invention is a bearing
provided with an annular means generating magnetic pulses and with
a device for detecting these pulses, the detection device
comprising a plurality of aligned sensitive elements.
[0027] The aligned sensitive elements are, for example, chosen from
among the group comprising Hall-effect probes, magnetoresistors,
giant magnetoresistors and are placed equidistantly from one
another.
[0028] According to one embodiment, the pulse generating means is
an annular member which is made of a synthetic material laden with
ferrite particles and is formed by a plurality of contiguous
domains having reversed direction of magnetization of a given
domain with respect to the two domains which are contiguous with
it.
[0029] In a first embodiment, the detection device comprises an
even number 2N of sensitive elements, for example divided into two
subassemblies of N elements, each sensitive element of the first
subassembly being connected to a first adder, each sensitive
element of the second subassembly being connected to a second
adder, the two sums S.sub.1, S.sub.2 emanating from the first and
second adders being connected to the input of a third adder, the
output S.sub.1 of the first adder and, via an inverter, the output
S.sub.2 of the second adder being connected to the input of a
fourth adder, the signals SIN=S.sub.1+S.sub.2 and
COS=S.sub.1-S.sub.2 emanating from the third and fourth adders
being processed by a circuit so as to deduce the direction of
rotation and/or the speed or rotation and/or the position of the
pulse generating means with respect to the detection device.
[0030] In a first variant, the polar length Lp of the encoder is
substantially equal to the product of the number 2N of sensitive
elements times the distance d between sensitive elements, the
signals SIN and COS then being in substantially perfect quadrature
and of substantially like amplitude.
[0031] In a second variant, the polar length Lp of the encoder is
less than the product of the number 2N of sensitive elements times
the distance d between sensitive elements.
[0032] In a third variant, the polar length Lp of the encoder is
greater than the product of the number 2N of sensitive elements
times the distance d between sensitive elements.
[0033] By programming an even number 2M of sensitive elements, less
than the total number 2N of these elements is employed to form two
subassemblies of M elements, each sensitive element of the first
subassembly being connected to a first adder, each sensitive
element of the second subassembly being connected to a second
adder, the two sums emanating from the first and second adders
being connected to the input of a third adder, the output of the
first adder and, via an inverter, the output of the second adder
being connected to the input of a fourth adder, the signals
emanating from the third and fourth adders being processed by a
circuit so as to deduce the direction of rotation and/or the speed
or rotation and/or the position of the pulse generating means with
respect to the detection device, the said signals being in
substantially perfect quadrature.
[0034] The programming can be carried out by EEPROM or by Zener
Zapping.
[0035] In one envisageable subvariant, an amplifier circuit is able
to re-establish an identical amplitude for the signals emanating
from the third and fourth adders.
[0036] In a second embodiment, the detection device comprises a
number of sensitive elements which is a multiple of four, for
example divided into four subassemblies of P elements,
[0037] each sensitive element of the first subassembly with P
elements being connected to a first adder supplying a signal
S.sub.1;
[0038] each sensitive element of the second subassembly with P
elements being connected to a second adder supplying a signal
S.sub.2;
[0039] each sensitive element of the third subassembly with P
elements being connected to a third adder supplying a signal
S'.sub.1;
[0040] each sensitive element of the fourth subassembly with P
elements being connected to a fourth adder supplying a signal
S'.sub.2;
[0041] a circuit of adders and of inverters supplying two signals
SIN and COS respectively equal to:
[0042] SIN=(S.sub.1-S.sub.2)-(S'.sub.1-S'.sub.2);
[0043] COS=(S.sub.1+S.sub.2)-(S'.sub.1+S'.sub.2);
[0044] these signals SIN and COS being devoid of magnetic
offset.
[0045] As a variant, the detection device comprises an interpolator
increasing the resolution of these output signals.
[0046] In another embodiment, the sensitive elements are integrated
on an ASIC type circuit support the detection device is
incorporated within an ASIC type customized integrated circuit.
[0047] According to one embodiment, the pulse generating means is
integrated into a preassembled assembly forming a seal, the
detection device being secured in a possibly removable manner to
the fixed race.
[0048] Other subjects and advantages of the invention will become
apparent in the course of the following description of embodiments,
which description will be given with reference to the appended
drawings in which:
[0049] FIG. 1 is a partial schematic representation of a pair of
poles of an encoder and of the substantially sinusoidal magnetic
induction which it delivers at the working gap;
[0050] FIG. 2 represents an embodiment of the detection device
according to the invention;
[0051] FIG. 3 represents a second embodiment of a detection device
according to the invention.
[0052] A bearing with built-in magnetic encoder comprises a
multipole rotating means generating magnetic pulses and referred to
as the "encoder", and a device for detecting this magnetic field,
referred to as the "sensor".
[0053] The encoder comprises an even number of poles and is
disposed, either on the circumference of a rotating race, or
integrated into a pre-assembled assembly forming a seal.
[0054] For example, the multipole magnetized encoder can be an
annular member, made of a synthetic material laden with particles
of Barium ferrite or of Strontium ferrite, or of some other hard
ferromagnetic material, and is formed by a plurality of contiguous
domains having reversed direction of magnetization of a given
domain with respect to the two domains which are contiguous with
it.
[0055] The polar length Lp of the sensor is defined as the length
of a magnetic pole measured at the relevant reading radius.
[0056] In such a configuration, the magnetic induction delivered by
the encoder can be regarded as sinusoidal at the relevant gap.
[0057] FIG. 1 schematically illustrates a period 1 of a component,
for example normal, of the said induction B, for a pair of poles 2,
3 of the encoder.
[0058] The detection device 4 comprises an even number 2N of
sensitive elements 5 of magnetoresistor or Hall-effect probe type,
placed an equal distance d apart, these elements 5 being disposed
substantially along a straight line D, for example the sensitive
elements 5 can be disposed on an arc of a circle which can be
approximated to a straight line.
[0059] In the embodiment represented in FIGS. 2 and 3, twenty-four
sensitive elements 5 are provided.
[0060] This arrangement defines a strip 6 of sensitive elements 5
of length equal to (2N-1)d.
[0061] The detection device also comprises an electronic circuit 7
making it possible to process the analog signals emanating from the
various sensitive elements 5 so as to obtain information such as
for example the speed, and/or the direction and/or the angle of
rotation of the multipole magnetic encoder, and, thereby, the speed
and/or the direction and/or the angle of rotation of the race of a
bearing supporting this encoder.
[0062] The detection device can be used integrated on a silicon
substrate or the like for example AsGa, so as to form an
application specific customized integrated circuits, which is
sometimes designated by the term ASIC (Application Specific
Integrated Circuit) so as to refer to the integrated circuits
designed partially or entirely on the basis of requirements.
[0063] In the embodiment of FIG. 2, the assembly of sensitive
elements 5 is divided into two subassemblies 8, 9 of N elements
(N=12, in the embodiment of FIG. 2).
[0064] Each sensitive element 5 of the first subassembly 8 is
connected to a first adder or addition circuit 10, such as the
amplifier, ensuring the summation of the signals Se.sub.1,
Se.sub.2, . . . , Se.sub.N, emanating from the first N sensitive
elements 5.
[0065] Likewise, each sensitive element 5 of the second subassembly
9 is connected to a second adder or addition circuit 11, such as an
amplifier, ensuring the summation of the signals Se(.sub.N+1),
Se.sub.(N+2), Se.sub.(N+3), . . . , Se.sub.2N, emanating from the
other N sensitive elements.
[0066] Two sum signals are thus obtained:
[0067] S.sub.1=Se.sub.1+ . . . +Se.sub.N
[0068] S.sub.2=Se.sub.(N+1)+ . . . +Se.sub.2N.
[0069] The two sums S.sub.1 and S.sub.2 from the first and second
adder means are connected to the input of a third adder means or
addition circuit 12.
[0070] The output S.sub.1 of the first adder means and, via an
inverter, the output S.sub.2 of the second adder means are
connected to the input of a fourth adder means or addition circuit
14.
[0071] Let:
[0072] Se.sub.1=sin(wt-.alpha./2)
[0073] Se.sub.2= . . .
[0074] . . .
[0075] Se.sub.(2N-1)= . . .
[0076] Se.sub.2N=sin(wt-(1/2+2N-1).alpha.)
[0077] Where .alpha. corresponds to the phase shift between two
sensitive elements (.alpha.=.pi./2N.Lp0/Lp) and the length Lp0=2Nd
is directly related to the length of the strip of sensitive
elements.
[0078] Two sinusoidal signals:
[0079] S.sub.1+S.sub.2 (referred to hereinafter as "SIN") and
[0080] S.sub.1-S.sub.2 (referred to hereinafter as "COS")
respectively then appear at the outputs of the third 12 and fourth
adder means 14 with
[0081]
SIN=(sin(.pi.Lp0/2Lp).sin(wt-.pi.Lp0/2Lp)/sin(.pi./2/Lp.Lp0/2N)
[0082] COS=2
sin.sup.2(Lp0/4Lp).cos(wt-.pi.Lp0/2Lp)/sin(.pi./2/Lp.Lp0/2N)
[0083] d being the distance between sensitive elements.
[0084] According to the two formulae above, it is apparent that,
when the polar length Lp is equal to 2Nd, the detection device
delivers two signals of like amplitude SIN and COS in perfect
quadrature. It is therefore apparent that Lp0=2Nd is the reference
length for which the amplitudes of the SIN and of the COS are
identical.
[0085] The device therefore makes it possible to circumvent the
tolerances in the placement of the sensitive elements, as for
example when the sensitive elements are placed on a substrate.
[0086] Moreover, when the polar length Lp of the encoder is not
suited to the sensor, only the amplitude of the signals is
modified, the phase of these signals being kept constant.
[0087] Hence, if the device is implemented with no electronic
interpolation system, that is to say if the digital signals have an
identical resolution to that of the magnetic encoder, the
quadrature of the signals SIN and COS is preserved, for a wide
range of polar lengths Lp.
[0088] With a view to the use of an interpolator increasing the
resolution of the output signals from the detection device,
described for example in patent application FR-2 754 063, the
analog signals must fulfill the following conditions so as to
ensure interpolated digital signals of good quality:
[0089] be in perfect quadrature;
[0090] be of like amplitude;
[0091] be devoid of magnetic and electronic offset.
[0092] A second embodiment of the invention proposes a detection
device which delivers analog signals fulfilling these three
conditions within a wide range of polar lengths Lp.
[0093] The detection device described above delivers signals in
perfect quadrature.
[0094] The ratio of the amplitudes of the analog signals SIN and
COS is given by the formula:
[0095] R=amp(COS)/amp(SIN)=tan(.pi.Lp0/4Lp)
[0096] It is apparent that when the length Lp0 is greater than the
polar length Lp, the amplitude of the SIN signal is less than that
of the COS signal.
[0097] When Lp0 is equal to Lp, the amplitudes of the SIN and COS
signals are equal.
[0098] When Lp0 is less than Lp, the amplitude of the SIN signal is
greater than that of the COS signal.
[0099] In a first variant embodiment, and when Lp0 is greater than
Lp, a means of increasing the number of polar lengths usable and of
reducing the length of the strip to 2M elements used out of the 2N
(M being less than N), by programming, for example of EEPROM or
Zener Zapping type.
[0100] Here, EEPROM designates an electrically erasable
reprogrammable memory, each of whose cells is for example formed of
an MNOS or DIFMOS transistor or the like, with read and write
transistors, the MNOS transistors (Metal Nitride Oxide
Semiconductor), derived from MOS transistors, forming a
semiconductor memory.
[0101] The expression Zener zapping conventionally designates Zener
trimming, that is to say a correcting of any error in voltage
delivered by a digitizer in respect of a specified input binary
word, by selectively short-circuiting reverse-biased Zener diodes
powered by constant-current sources of increasing intensity, the
total intensity of the circuit thus obtained creating the necessary
correction voltage across the terminals of a resistor.
[0102] A strip of thirty sensitive elements spaced 0.1 mm apart can
thus be usable for polar length of between 3 and 1 mm with a
spacing of 0.2 mm (values below 1 mm are in theory usable, but
deliver little magnetic fields).
[0103] Consequently, the programming of the sensor renders them
usable when faced by 11 different polar lengths in this case.
[0104] In a second variant embodiment, one of the two signals can
be electronically amplified with respect to the other so as to
recover an identical amplitude for the SIN and COS signals.
[0105] The magnetic and electric offset corresponds to a continuous
component (the magnetic offset is for its part assumed to be
uniform over the assembly of sensitive elements) which are added to
the signals detected.
[0106] Since the COS is obtained by subtracting the signals S.sub.1
and S.sub.2, the continuous component related to the magnetic
offset of each of the two terms is thus eliminated.
[0107] This is not true for the SIN, which for its part is obtained
by summing all the signals emanating from the sensitive
elements.
[0108] One solution making it possible to circumvent the magnetic
offset in the SIN, and illustrated in FIG. 3, consists in splitting
the strip up into four quadrants with P sensitive elements, the
strip being composed of 4 P sensitive elements, and using an
electronic circuit, for example based on adder amplifiers and on
inverters, to form the following combinations:
[0109] SIN=S.sub.1-S.sub.2-(S'.sub.1-S'.sub.2)
[0110] COS=S.sub.1+S.sub.2-(S'.sub.1+S'.sub.2)
[0111] In the example illustrated in FIG. 3, the strip composed of
4P sensitive elements covers a complete magnetic period, that is to
say:
[0112] Lp0=2Lp with Lp0=2Pd
[0113] Given the fact that the SIN signal is henceforth obtained by
differencing two differences, the continuous component related to
the magnetic offset is thus eliminated.
[0114] The analog signals used in the interpolator are therefore
devoid of magnetic offsets. The electronic component can be
reduced, moreover, by other means which are not described in the
present patent application.
[0115] When the strip is made up of 4P sensitive elements covering
a complete magnetic period, the splitting of the strip into four
quadrants, such as represented in FIG. 3, leads to SIN and COS
signals with the following expressions: 1 SIN = - 4 sin ( / 8 Lp0 /
Lp ) sin ( 4 Lp0 / Lp ) SIN ( / 2 Lp Lp0 / 4 N ) sin ( wt - Lp0 /
Lp COS = 2 sin 2 ( / 4 Lp0 / Lp ) sin ( / 2 / Lp Lp0 / 4 N cos ( wt
- Lp0 / Lp )
[0116] The canceling of the magnetic offset, by virtue of this
splitting into four quadrants, is compatible with the amplifying of
the SIN or COS signal so as to increase the allowable polar
lengths, when the polar length Lp is less than the length Lp0.
[0117] The value of the gain is then given by the following
formula:
[0118] R=amp(COS)/amp(SIN)=sin(.pi.Lp0/4Lp)/2 sin(.pi.Lp0/8Lp).
[0119] The device according to the invention makes it possible to
measure the magnetic field delivered by a multipole magnetic
encoder and to deliver two analog signals which are always
90.degree. out of phase electrically, and to do so independently of
the polar length of the sensor.
[0120] The processing of these two analog signals by an ad-hoc
circuit, not represented, makes it possible to deduce the direction
of rotation of the multipole magnetic encoder, even for a low
rotation speed.
* * * * *