Angular or linear magnetic position sensor not sensitive to external fields

Translation of description of equivalent WO 2009101270 A2

MAGNETIC POSITION SENSOR LINEAR ANGLE OR WITH INSENSIBILITY FIELDS OUTSIDE

p0002The present invention relates to the field of rotary position sensors and magnetic linear for angles up to 360 ° or more and displacement of up to hundreds of millimeters, and more particularly the position sensors for the measurement of the angular position of an automotive steering column, without this application is exclusive.

p0003Contactless sensors that detect the angle or displacement from a magnetic field has many advantages:

p0004• no mechanical contact with the movable part, and therefore no wear,

p0005• insensitivity to dirt,

p0006• reduced production cost,

p0007• long life.

p0008Known in the prior art patent EP1083406 describes a rotary sensor (Figures 1 and 2) having a ring magnet and two magneto-sensitive elements, which measure the radial component of the field generated by the magnet and leading to two signals sinusoidal quadrature used after decoding to detect the position of 360 degrees.

p0009The disadvantage of this solution is its sensitivity to the outfield. Indeed, any external field in the probe plan will lead to a significant error of nonlinearity.

p0010Known in the prior art the patent WO07057563 of the applicant describes a position sensor

p0011(Figures 3 and 4) to use two magnetic field components (radial and tangential or axial and tangential) measured substantially at a single point outside the axis of rotation of a magnet ring or disc diametrically magnetized, so as to know its angular position even if this angle does not match the angle of the magnetic field. The radial component and the axial component of the magnetic field generated by the magnet are two sinusoids which are in phase, whereas the tangential component is a phase-shifted sinusoid by 90 degrees with the other two components of the magnetic field (see Figure 4). It is therefore possible to use a pair of magnetic field components phase shifted by 90 degrees (tangential and radial or tangential and axial) for decoding the angle of the magnet. The decoding of the angular position of the magnet from these two components, the amplitudes are different generally requires two to standardize components used to make the calculation of the arc tangent in order to deduce the angle . Also known in the prior art patent PCT WO27099238 of the Applicant describes a linear and rotary position sensor (for angles less than 360 °) using the same principle as the sensor 360 described above. It uses two components of the magnetic field (normal and tangential or axial and tangential) measured substantially at the same point and generated by a magnet or a flat tile whose magnetization direction is continuously variable along the displacement.

p0012The disadvantage of these solutions is the sensitivity to any external magnetic field. It is possible to shield the sensor, but it adds additional parts and increases the manufacturing cost and the footprint of the sensor. In addition, applying a gain between the components is problematic (noise of the sensor, temperature drift) and diametral magnetization (in the case of sensor 360 °) is not easy and may cause harmonic errors. Indeed, the performance (linearity of the output signal) of the sensor 360 directly dependent on obtaining a good diametric magnetization. The field magnetization, shown in Figure 5, diametrically needed to magnetize a magnet ring is easily obtained with a simple coil traversed by a current. The magnetic permeability of difference between the air and the material to be magnetized produces a curvature of the field lines, curvature following the refraction relationship at the boundary between two following media:

p0013<img id="imgf000004_0001" he="12" wi="31" file="imgf000004_0001.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="no" />

p0014This curvature results in a magnetization of the material that is not diametrically and therefore by distortion of the two components measured, as represented in Figure 4. These two signals are not perfect two sinusoids phase shifted by 90 ° which results during decoding by a very strong non-linearity as we can see it on the same figure 6 shows the decoded signal from the two components of the magnetic field.

p0015The present invention proposes to solve the above mentioned problems by allowing use of a combination of two pairs of magnetic field components

p0016(Normal and tangential) measured at two points preferably spatially shifted by a quarter period.

p0017The period for rotational sensor is the total angle of one magnet.

p0018The period for a linear sensor is its length.

p0019Two components are measured at the same point (physically, we consider that the measurements are made at the same point, if the effective distance between the measuring points of the two components of the magnetic field is less than 5 mm) and other two components are measured in another spatially offset point about one-quarter wave period (eg offset 90 ° to 360 ° sensor) the following described thus reduces the effect of the external field solution, to offset some of the harmonic errors due to magnetization and not to use in gain between the components.

p0020Is :

p0021BNI normal Component in 1

p0022BtI tangential component in 1

p0023Bn2 normal component at point 2

p0024Bt2 tangential component in point 2

p0025TETA is the angle of rotation, and taking into account the harmonic 3 error (major error) due to the diametrical magnetization, we have:

p0026BNI = hi * cos (TETA) + h3 * cos (3TÉTA)

p0027BtI h'i = * sin (TETA) + H'3 * sin (3TÉTA)

p0028If points 1 and 2 are spatially offset by 90 °, then

p0029Bn2 = hi * cos (TETA + 2 / PI) + h3 * cos (3 (TETA + 2 / PI))

p0030= - Hi * sin (TETA) + h3 * sin (3TÉTA)

p0031H'i Bt2 = * sin (TETA + 2 / PI) + H'3 * sin (3 (TETA + 2 / PI))

p0032H'i = * cos (TETA) - H'3 * cos (3TÉTA) The present invention proposes to combine the two components in two as follows:

p0033Bn = Bnl + Bt2

p0034Bt = BtI - Bn2

p0035So :

p0036Bn = h * cos (TETA) + h3 * sin (3TÉTA) + h'i * cos (TETA) H'3 * COS (3TETA)

p0037= (Hi + h'i) * cos (TETA) + (ha - H'3) * cos (3TÉTA)

p0038-0

p0039= (Hi + h'i) * cos (TETA)

p0040Bt = you * sin (TETA) - h3 * sin (3TÉTA) + h'i * sin (TETA) +<img id="imgf000006_0001" he="5" wi="34" file="imgf000006_0001.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="yes" />

p0041= (Hi + h'i) * sin (TETA) + (h's- TI3) * sin (3TÉTA)

p0042~ 0 <img id="imgf000006_0002" he="5" wi="48" file="imgf000006_0002.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="no" />

p0043Thus the two signals obtained are of the same amplitude but out of phase by 90 ° and almost perfectly sinusoidal. Indeed, the combination of an imperfect normal component (triangular shape due to harmonic 3) and from imperfect tangential component (rectangular shape due to harmonic 3) cancels or at least greatly reduce this lack of harmonic and get almost two sinusoidal components.

p0044Moreover if (see Figures 13 and 14) we have an external magnetic field along the x and y (and Bx_ext By__ext), combining pairs of the components used to cancel the effect of the external field. Thus, if one refers to the 1-position of the magnet of Figure 13, we have:

p0045BNI Bn_max = - = By_ext BtI -Bx_ext Bn2 -Bx_ext Bt2 = + = Bt_max By_ext This gives us the final: Bn = Bnl Bt2 + = + Bn_max Bt_max Bt = 0 = Btl-Bn2

p0046Referring to the 2 position of the magnet of Figure 13, we now have: BNI = 0 - By_ext

p0047BtI = -Bt_max -Bext Bn2 = Bn_max -Bext Bt2 = By_ext

p0048This gives us: Bn = Bnl + Bt2 = 0 = Bt-Btl Bn2 -Bn = max - max Bt

p0049The two signals obtained are of the same magnitude and effect of the external field has been canceled.

p0050According to an advantageous embodiment to improve the accuracy of a rotary sensor configuration in case the harmonic 3 normal and tangential components are not equal (h '3 h3) ≠ 0. This embodiment takes in everything complete the description above and integrates thereby all the advantages of the latter.

p0051He brings more advantage clearing all the harmonic 3 defects due to defects magnetization associated with the geometry of the magnet, in order to obtain two perfectly sinusoidal components, by the use of a clever combination of 4 * 2 components of the magnetic field (normal and tangential) measured in 2 * 2 points offset respectively spatially by a 1/4 period (previous solution) and preferably 1/8 period (shift of 45 ° for a 360 ° sensor) as shown in Figure 25.

p0052Is :

p0053Bnia normal component developed the

p0054BNIB normal component Ib point

p0055BTIA tangential component developed the

p0056BtIb tangential component developed Ib

p0057BN2A normal component in point 2

p0058BN2B normal component in 2b

p0059BT2A tangential component in point 2

p0060Bt2b tangential component in 2b

p0061The present solution proposes combining 2-2 normal and tangential components of the two pairs of points (a and b) shifted 1/8 period prior to the combinations described above, a solution which eliminates the harmonic residual (h3 - h '3) as follows:

p0062BNI bnia = + BNIB

p0063BtI = + BTIA BtIb

p0064Bn2 = + BN2A BN2B + Bt2 = BT2A Bt2b

p0065TETA is the angle of rotation, and as in the development of the previous solution, taking into account the harmonic 3 error (major error) due to the diametrical magnetization, we get with (h3 - H'3) = 0:

p0066Bn = (+ or h'i) * cos (TETA)

p0067Bt = (hi + h'i) * sin (TETA)

p0068All considerations with an external magnetic field remain unchanged.

p0069The digital signal processing circuit combines the components (which provides two sinusoids whose amplitude is substantially the same) and performs the various offsets (offset, orthogonality, variation of the probe parameters temperature) before the division and calculating tangent arc. The angle obtained is available at the output of the integrated circuit, for example in the form of a voltage proportional to this angle.

p0070In a linear configuration as shown Figures 20 and 21 where the magnetic field rotates continuously along the stroke of the sensor, one can also combine two by two the magnetic field components to eliminate the external field.

p0071Is :

p0072BNI normal Component in 1

p0073BtI tangential component in 1

p0074Bn2 normal component at point 2

p0075Bt2 tangential component in point 2 x stroke sensor, L the total stroke sensor

p0076d the distance between point 1 and point 2 (0 &lt;d &lt;L)

p0077So

p0078BNI = hi * cos (2xL / IP) -By_ext

p0079BtI h'i = * sin (2xL / PI) + Bx_ext

p0080Bn2 = hi * cos (2xL / PI + 2DL / IP) -By_ext

p0081H'i Bt2 = * sin (2xL / PI + 2DL / PI) + Bx_ext

p0082Either Bnl-Bn2 = ni * (cos (2xL / PI) - cos (2xL / PI + 2DL / PI))

p0083BTL-Bt2 = h'i * (sin (2xL / PI) - sin (2xL / PI + 2DL / PI))

p0084Bnl-Bn2 = h * (cos 2xL / PI - cos (2xL / PI + 2DL / PI))

p0085-2hi = * Sin (2xL / dL + PI / PI) * sin (d / L * PI)

p0086= (-2 * Hi * sin (d / L * PI)) * sin (2xL / dL + PI / PI) <img id="imgf000010_0001" he="11" wi="41" file="imgf000010_0001.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="no" /> constant -A.hl

p0087BTL-Bt2 = h^fi * (sin (2xL / PI) - sin (2xL / PI + 2DL / PI))

p0088= 2 * h'i * cos (2xL / dL + PI / PI) * sin (d / L * PI)

p0089≈ (2h'i * sin (d / L * PI)) * cos (2xL / PI + dL / Pl) <img id="imgf000010_0002" he="11" wi="38" file="imgf000010_0002.tif" img-format="tif" img-content="drawing" orientation="portrait" inline="no" /> constant A.h'i

p0090Bnl-Bn2 = - Ahi * sin (2xL / dL + PI / PI) BTL-Bt2 Ah = i * cos (2xL / dL + PI / PI)

p0091Thus, the two signals obtained are of different magnitudes, but phase-shifted by 90 °, and perfectly sinusoidal. The combination pairs components eliminates homogeneous external field regardless of its direction.

p0092The amplitude of the two signals obtained depends on the distance between the two points 1 and 2. The amplitude will be maximum if the two points are spaced by a half period (d = L / 2) and zero if d = 0 or L. so we will favor a shift between the two points 1 and 2 corresponding to approximately h period that s' proves to be a good compromise between the amplitude of the signals obtained and the size of the sensor.

p0093The digital signal processing circuit combines the components and performs the different offsets (offset, orthogonality, variation of the temperature probe parameters) normalises the signals before division and the arctangent calculation. The output signal obtained is available at the output of the integrated circuit, for example in the form of a voltage proportional to the linear travel of the sensor.

p0094The invention will be better understood in view of the different figures.

p0095• Figure 1 shows a view of a rotary encoder of the prior art using two normal components of the induction measured in two spatially offset points of 90 °,

p0096• Figure 2 shows the two perpendicular components of the magnetic induction of a solution of the prior art, • Figure 3 shows a view of a rotary encoder of the prior art using a normal and tangential of induction,

p0097• Figure 4 shows the normal and tangential component of the magnetic induction at the same point of a solution of the prior art,

p0098• Figure 5 shows the field lines to 1 inside the magnet during magnetization for a material with a relative permeability (ÁR) equal to 1.2 • 6 represents the normal and tangential components of the induction magnetic and the non-linearity of the signal measured on a magnet magnetised isotropic circular ring "diametrically"

p0099• Figure 7 shows a general view of the present invention with the two bi-directional probes 31 and 32,

p0100• Figure 8 shows a 3D view of the present invention with both bidirectional probes 31 and 32,

p0101• Figure 9 shows only the normal and tangential components of the magnetic induction probe 31,

p0102• Figure 10 shows the non-linearity of the signal measured by the probe 31 of a magnet isotropic circular ring magnet "diametrically" • Figure 11 shows two sinusoidal signals obtained from the combination in pairs of the normal and tangential components of magnetic induction measured by the probes 31 and 32,

p0103• Figure 12 shows the non-linearity obtained from the signals of Figure 11,

p0104• Figure 13 shows two angular positions of the magnet in the presence of an external magnetic field,

p0105• Figure 14 shows a view of the invention and an exciting coil that creates an external magnetic field, • Figure 15 shows both normal and tangential components of the probes 31 and 32 under the effect of an external field as defined in Figure 14,

p0106• Figure 16 shows the non-linearity of the signal measured by the probe 31 of a circular ring magnet magnetized isotropic "diametrically" under the effect of external field,

p0107• Figure 17 shows the non-linearity of the signal measured by the probe 32 on a magnet isotropic circular ring magnet "diametrically" under the effect of the external field,

p0108• Figure 18 shows the non-linearity of the signal obtained by combining in pairs the normal and tangential components measured by the probes 31 and 32 • Figure 19 shows a general view of the present invention applied to a linear sensor with Both probes bidirectional 31 and 32,

p0109• Figure 20 shows a side view of the present invention with the two bi-directional probes 31 and 32,

p0110• Figure 21 shows a side view of the present invention with the two bi-directional probes 31 and 32 in the presence of external fields,

p0111• Figure 22 shows a general view of the present invention applied to a small angle encoder with both bidirectional probes 31 and 32,

p0112• Figure 23 shows both normal and tangential components of the probes 31 and spatially offset 32 ​​h period, • Figure 24 shows the resulting two sinusoidal signals of the combination in pairs of the four previous signals and the output signal obtained in final.

p0113• Figure 25 shows a general view of the present invention with two bidirectional sensors 31a and 32a associated with two other bidirectional probes 31b and 32b.

p0114• Figure 26 shows a non-linearity of the simulated signal of the present invention and improvement possible through the optimization proposed using two other probes Bidirectional 31b and 32b

p0115Figures 1 and 2 represent a solution of the prior art sensitive to the outfield. In the figure, we have a permanent magnet substantially diametrically magnetized ring (1); this magnet generates in any point in space a magnetic field whose normal components are measured by two magnetosensitive elements 21 and 22 spatially offset by 90 ° the signals are then processed to decode so as to normalize the angle two components to output an electrical signal proportional to the angular position of one magnet.

p0116Figures 3 and 4 shows another solution of the prior art sensitive to the external field and the failure of diametrical magnetization. This solution consists of a permanent magnet substantially diametrically magnetized ring

p0117(1), this magnet generates me any point in space a magnetic field which, under normal or axial and tangential components are measured by two magnetosensitive elements located at the same point, the signals are then processed by a processing element that performs the decoding and the normalization of the two components to output an electrical signal proportional to the angular position of the magnet.

p0118Figure 5 shows the field lines, during magnetization, inside and outside of a magnet ring with a relative permeability equal to 1.2. The field lines undergo deformation during the crossing of the magnet, deformation due to the difference in relative permeability between air (ÁR = 1) and the magnet (ÁR = 1.2 in this case). This deviation of the field lines therefore results in poor diametral magnetization of the magnet.

p01196 shows the normal and tangential components not perfectly sinusoidal due to poor diametral magnetization and the non-linearity obtained from these signals.

p0120Figures 7 and 8 show views of the present invention. This solution consists of a diametrically magnetized permanent magnet substantially ring (1), this magnet generates in any point in space a magnetic field whose normal or axial and tangential components are measured by four magneto-sensitive elements. Two magnetosensitive elements are located at a single point and advantageously integrated in one housing (31) and two magneto-sensitive elements are located at the same point advantageously integrated in one housing (32) that is spatially offset by 90 ° of the housing ( 31). The four signals are then combined in pairs to cancel the effect of an external field and errors due to diametric magnetization to output a perfect electrical signal proportional to the angular position of the magnet. The signal processing circuit can be integrated in one of the housings (31) or (32) or both for redundancy question, or may be performed outside of the housings (31) and (32).

p0121Figures 9 and 10 show the measurement of both normal and tangential components generated at a single point by a diametrical magnet and the error obtained using only a single probe (31). Figure 11 shows the two combination two of the four signals measured by the 4 magnetosensitive elements integrated in the housings (31) and (32). Two perfectly sinusoidal signals and the same amplitude are obtained by adding the normal component measured by (31) and the tangential component measured by (32) and subtracting the normal component measured by (32) to the tangential component measured by (31).

p0122Figure 12 shows the output angle decoded from the two sinusoidal signals of FIG 11 and the non-linearity obtained. The error obtained by combining four components and eliminates errors due to

p01231 'diametric magnetization.

p0124Figures 13 and 14 show the present invention with the presence of an external magnetic field. 13 shows two different positions of the magnet (1) under the effect of a homogeneous external field Bext. The external field is in this case horizontal and disrupts the tangential component of the probe (31) and the normal component of the probe (32). FIG 14 is a view of the present invention with a coil (4) which generates a disturbing magnetic field. The outfield of the generating source could very well be a magnet instead of the coil.

p012515 shows a measurement of the two normal components and the two tangential components measured by the magneto-sensitive elements of the sensors (31) and (32) in the presence of an external field as shown in the two preceding figures. It can be seen that the normal component of the probe (32) and the tangential component of the probe (31) are indeed affected. Figures 16 and 17 show respectively the housings of the output signal (31) and (32) and the non-linearity of these two signals under the effect of external field defined in the preceding figures. It is thus realized that the output signal from the housing (31) is not at all linear because of the external field which changes its tangential component and the output signal from the housing (32) is also non-linear due to the modification of the normal component due to the external field generated by the coil.

p0126Figure 18 shows the result obtained by the present invention. It shows the two signals obtained after combination of the signals measured by 4 (31) and (32) (Bnl + Bt2 BTL-Bn2), the output signal after the caicul of the arctangent of (Bnl + Bt2) / Btl -Bn2) and the non-linearity of this signal. The present invention thus makes it despite the presence of an external field to have a sensor which is always linear in contrast to the solutions of the prior art.

p0127Figures 19 and 20 show two views of the present invention applied to a linear sensor. These figures represent a magnet (1) of length L having a magnetization, represented by the vector M, the direction varies linearly along the length of the magnet in a plane defined by the direction of movement X and a normal to this direction. The two probes (31) and (32) each measure the normal component and the tangential component of the magnetic field generated by the magnet (1). The two probes are spatially spaced a few millimeters.

p0128Figure 21 shows the view of Figure 20 with the presence of an external magnetic field Bn_ext + Bt_ext in addition to the measurement of the magnetic field generated by magnet. The present invention by performing the subtraction of two normal components (31) and (32) (Bnl-Bn2) and subtraction of two tangential components (31) and (32) (BTL-Bt2) cancels the disturbance outdoor and treat only signals from the magnetic field generated by the magnet (1).

p0129Figure 22 shows a view of the present invention applied to a rotary sensor small angle with the presence of an external magnetic field B_ext in addition to the measurement of the magnetic field generated by the magnet. The present invention by performing the subtraction of two normal components (31) and (32) (Bnl-Bn2) and subtraction of two tangential components (31) and (32) (BTL-Bt2) cancels the disturbance outdoor and treat only signals from the magnetic field generated by the magnet (1).

p0130Figure 23 shows the two normal components and the two tangential components measured by the magneto-sensitive elements of the sensors (31) and (32). In this case, the probes (31) and (32) are spatially shifted by a quarter period.

p0131Figure 24 shows the result obtained by the present invention. It shows the two signals obtained after combining the four signals measured by (31) and (32) and standardization of these signals (Bnl-Bn2, Gain * (BTL-Bt2)) and present the output signal after the calculation of the arc tangent (Bnl-Bn2) / (Gain * (BTL-Bt2)).

p013225 shows an optimized embodiment of the present invention to obtain a high precision sensor. This solution consists of a magnetized permanent magnet ring substantially diametrically 1, the magnet 1 generates in any point in space a magnetic field whose normal or axial and tangential components are measured by eight magnetosensitive elements. Two magnetosensitive elements are located at a single point and advantageously integrated in the same housing 31a and the other two magnetosensitive elements are located at the same point advantageously integrated in the same housing 32a which is spatially offset by 90 ° of the housing 31a. Two other magneto-sensitive elements are located at a single point and advantageously integrated in the same 31b housing and the other two magnetosensitive elements are located at the same point advantageously integrated in one housing 32b, 31b housings and 32b spatially mutually offset by 90 ° are spatially offset both 45 ° of the first quadrature Casing 31a and 32a. The 8 signals are then summed 2-2 to cancel errors due to diametric magnetization. 4 The resulting signals are then combined 2-2 to cancel the effect of an external field and errors due to diametric magnetization to output a perfect electrical signal proportional to the angular position of the magnet. The signal processing circuit can be integrated in one of the housings, or within four to a question of redundancy, or may be performed outside of the housings.

p013326 shows compared the possible improvement of the linearity error (percentage of 360 ° depending on the course in degrees) obtained by adding 4 magnetosensitive elements (31b and 32b boxes) judiciously positioned to correct the magnetization error related to the geometry of the magnet 1. It appears from this figure that the A signal resulting from the preceding embodiments may not be quite as linear magnetization conditions, the magnet dimensions and nature, mainly through the introduction of a harmonic 3 not fully offset (H4 commuted by the arc tangent function). In contrast, the signal B resulting from the embodiment shown in FIG 25 improves, and even cancel, these nonlinearities.