JP2017101783A - Bearing with rotation detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing with a rotation detection device which exactly positions a magnetic sensor capable of detecting a high resolution or an absolute angle even if using a printed board having flexibility to a sensor housing, and can facilitate work for fixing the printed board to the sensor housing.SOLUTION: This bearing with a rotation detection sensor comprises a magnetic encoder 7 fixed to an inner ring 3, a sensor housing 9 fixed to an outer ring 2, and a flexible printed board 12. A reinforcing plate 16 is arranged at a rear surface 12b at a side opposite to a magnetic sensor mounting face of the printed board 12. A reference face 17 for pressing a surface 16a of the reinforcing plate is formed at the sensor housing 9. Positioning means for positioning a magnetic sensor 13 to an axial direction or a peripheral direction is arranged at the sensor housing 9. The printed board 12 or the reinforcing plate 16 is fixed to the sensor housing 9 in a state that the reinforcing plate 16 is pressed against the reference face 17.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bearing with a rotation detection device equipped with a rotation detection device on the bearing, and more particularly to a technique applied when fixing a flexible printed board on which a sensor element is mounted.

Conventionally, a rolling bearing with a rotation sensor can be mounted in a limited space such as a peripheral wall of a sensor housing by bending the substrate by using a flexible plastic substrate as an electric circuit substrate, for example, and shortening its axial length (Patent Document 1).
In another rolling bearing with a rotation sensor, the electric circuit board is formed of a plastic film, and the ratio of the outer diameter radius of the bearing outer ring to the thickness of the film is set within a certain range (50 to 200). Circuit board disconnection and the like are prevented (Patent Document 2).

JP 2002-296289 A JP 2004-125455 A

  The bearings with rotation sensors disclosed in Patent Documents 1 and 2 can reduce the axial length of the sensor housing by using a flexible substrate as an electric circuit substrate (printed substrate). The A detection element (sensor element) and an electronic component are mounted on a flexible substrate, and the substrate is fitted into an arc-shaped groove provided in the sensor housing. Thereafter, a resin molding material is usually poured into the groove to fix the electric circuit board in the sensor housing.

However, since the flexible substrate is thin and flexible, it is assumed that stress due to bending occurs in the detection element portion and solder cracks occur. Further, even if an attempt is made to adjust the gap between the magnetic sensor (detecting element) and the magnetic encoder after inserting a flexible substrate into the groove provided in the sensor housing, it is difficult to align the sensor.
In particular, when using a magnetic sensor capable of high-resolution detection or absolute angle detection that can process magnetic signals inside the magnetic sensor and output more pulses than the number of pole pairs, the position of the magnetic sensor and the magnetic encoder Matching (gap, eccentricity) is important because it affects detection accuracy.

  In addition, the groove formed in accordance with the thickness of the flexible substrate on which the detection element and the electronic component are mounted is designed to be narrow in consideration of so-called “backlash” that suppresses rattling of the detection element. For this reason, in order to pour the resin mold material into the groove, it is necessary to use a filling needle with a small nozzle diameter, and it is also assumed that the groove bottom may not be filled firmly.

  An object of the present invention is to accurately position a magnetic sensor capable of high-resolution detection or absolute angle detection with respect to a sensor housing even when using a flexible printed circuit board, and to fix the printed circuit board to the sensor housing. It is an object of the present invention to provide a bearing with a rotation detection device that can facilitate the above.

A bearing with a rotation detector of the present invention includes a magnetic encoder fixed to a rotating ring of the bearing, a sensor housing fixed to the fixed ring of the bearing, and a flexible printed board provided in the sensor housing,
The magnetic encoder has a magnetic sensor having a magnetic track in which N poles and S poles are alternately magnetized, and a magnetic sensor facing the magnetic track with a gap is mounted on the printed circuit board. ,
A reinforcing plate is provided on the back surface of the printed circuit board opposite to the mounting surface on which the magnetic sensor is mounted,
A reference surface that presses the surface of the reinforcing plate against the sensor housing is formed,
The sensor housing is provided with positioning means for positioning the magnetic sensor in the axial direction and the circumferential direction with respect to the sensor housing,
The printed circuit board or the reinforcing plate is fixed to the sensor housing in a state where the reinforcing plate is pressed against a reference surface.

  According to this configuration, since the reinforcing plate is provided on the back surface of the printed circuit board opposite to the mounting surface on which the magnetic sensor is mounted, even if the printed circuit board is bent, stress is generated in the solder connection portion of the magnetic sensor. Therefore, the occurrence of solder cracks can be avoided. Further, only by pressing the surface of the reinforcing plate against the reference surface of the sensor housing, the gap between the magnetic track and the magnetic sensor is secured by a predetermined size. For this reason, it becomes easy to adjust the gap.

The positioning means positions the magnetic sensor relative to the sensor housing in the axial direction and the circumferential direction. For this reason, position adjustment at the time of adhering a reinforcement board to a printed circuit board becomes unnecessary, and a process can be simplified. Since positioning accuracy of the magnetic sensor is improved by the positioning means, even when a magnetic sensor capable of high resolution detection or absolute angle detection is used, it is output with high accuracy.
Further, when the resin mold material is filled in order to fix the printed circuit board to the sensor housing, the width of the groove provided in the sensor housing becomes wide at the portion where the reinforcing plate is inserted, so that the filling operation is facilitated.

  The surface of the reinforcing plate and the reference surface of the sensor housing may be in surface contact. In this case, the magnetic sensor is prevented from being undesirably tilted with respect to the sensor housing reference plane, and the parallelism between the magnetic encoder and the magnetic sensor is maintained.

An opening for inserting the magnetic sensor is formed in the sensor housing, and the positioning means includes an axial positioning portion that forms a bottom surface of the opening that is in contact with one axial end surface of the magnetic sensor; It is good also as what has the circumferential direction positioning part which comprises the circumferential direction side surface in the said opening part which a side surface contacts.
In this case, the axial end of the magnetic sensor relative to the sensor housing can be easily positioned by bringing the axial end of the magnetic sensor into contact with the bottom surface of the opening of the sensor housing. Positioning of the magnetic sensor in the circumferential direction with respect to the sensor housing can be easily performed by contacting the side surface of the magnetic sensor with the circumferential side surface of the opening of the sensor housing.

A wiring drawing pattern region is provided on one of the mounting surface and the back surface of the printed circuit board, and a reinforcing member is provided on a surface of the printed circuit board opposite to the wiring drawing pattern region. Also good.
In this case, the rigidity of the flexible printed circuit board is increased, and the wiring soldering operation is facilitated. Further, when the resin mold material is filled in order to fix the printed circuit board to the sensor housing, the width of the groove provided in the sensor housing becomes wide even at the portion where the reinforcing member is inserted, so that the filling operation is facilitated.

  The magnetic sensor may include interpolation means that performs electrical interpolation and outputs a pulse that is larger than the number of pole pairs of the N pole and the S pole. Since the positioning unit improves the positioning accuracy of the magnetic sensor, the detection accuracy can be improved even if the interpolating unit outputs more pulses than the N pole and S pole pairs.

  The magnetic encoder has a plurality of magnetic tracks magnetized with different numbers of magnetic poles, and the magnetic sensor has a function of detecting an absolute angle of the rotating wheel from magnetic signals detected from the plurality of magnetic tracks. It is good also as what has. In this case, the positioning accuracy of the magnetic sensor with respect to the sensor housing affects the detection accuracy of the absolute angle. However, since the positioning accuracy of the magnetic sensor is improved by the positioning means, the detection accuracy of the absolute angle can be improved.

  A bearing with a rotation detection device of the present invention includes a magnetic encoder fixed to a rotating ring of the bearing, a sensor housing fixed to the fixed ring of the bearing, and a flexible printed circuit board provided on the sensor housing, The magnetic encoder has a magnetic track having a magnetic track in which N poles and S poles are alternately magnetized, and a magnetic sensor facing the magnetic track with a gap is mounted on the printed circuit board. A reinforcing plate is provided on the back surface of the printed board opposite to the mounting surface on which the magnetic sensor is mounted, and a reference surface for pressing the surface of the reinforcing plate against the sensor housing is formed on the sensor housing. Is provided with positioning means for positioning the magnetic sensor with respect to the sensor housing in an axial direction and a circumferential direction, and the reinforcing plate In a state of being pressed against the reference surface, the printed circuit board or the reinforcing plate is fixed to the sensor housing. For this reason, even when using a flexible printed circuit board, a magnetic sensor capable of high resolution detection or absolute angle detection is accurately positioned with respect to the sensor housing, and the work for fixing the printed circuit board to the sensor housing is facilitated. It becomes possible to do.

It is sectional drawing of the bearing with a rotation detection apparatus which concerns on embodiment of this invention. It is II-II sectional view taken on the line of the bearing with the same rotation detection device. (A) is the top view seen from the component mounting surface in the printed circuit board of the bearing with the rotation detection apparatus from the opposite side, (B) is a side view of the printed circuit board. It is sectional drawing which extracted only the sensor housing from the bearing with a rotation detection apparatus of FIG. It is sectional drawing which extracted only the sensor housing from FIG. It is sectional drawing of the bearing with a rotation detection apparatus which concerns on other embodiment of this invention. It is explanatory drawing which shows the signal processing example which performs absolute angle detection in the bearing with the rotation detection apparatus.

A bearing with a rotation detection device according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the bearing with the rotation detection device includes a bearing 1 and a rotation detection device Ks.
First, the bearing 1 will be described.
In this example, the bearing 1 is a rolling bearing made of a deep groove ball bearing. The bearing 1 includes an outer ring 2 that is a fixed ring, an inner ring 3 that is a rotating ring, a plurality of rolling elements 4 interposed between the inner and outer rings 3 and 2, a cage 5 that holds the rolling elements 4, And a seal 6.

  The seal 6 is provided on the opposite surface where the rotation detection device Ks is provided, and closes the bearing space between the inner ring 3 and the outer ring 2. The seal 6 is, for example, a contact seal that is attached to the outer ring 2 and has a seal tip that contacts a seal groove of the inner ring 3. However, the seal 6 may be in contact with the outer diameter surface of the inner ring 3, and is not limited to other contact seals, and may be a non-contact seal.

The rotation detection device Ks will be described.
As shown in FIGS. 1 and 2, the rotation detection device Ks includes a magnetic encoder 7 and a sensor unit Su. In the bearing 1, the magnetic encoder 7 and the sensor unit Su are provided on the side opposite to the seal 6 in the axial direction. The magnetic encoder 7 has an annular cored bar 7a and a magnetic track 7b provided on the entire outer periphery of the cored bar 7a. A tip portion of the inner peripheral surface of the cored bar 7a is fitted and fixed to a portion on one end side in the axial direction on the outer diameter surface of the inner ring 3. The cored bar 7a is made of, for example, a sintered member or another metal member. The magnetic track 7b is a rotating element in which N poles and S poles are alternately magnetized, and is formed in a substantially cylindrical shape.

  The sensor unit Su is obtained by fixing a sensor housing 9 containing a magnetic sensor 13 to a metal ring 8. The metal ring 8 includes a cylindrical metal ring main body 8a, a flange portion 8b, and a fitting cylinder portion 8c. The flange portion 8b extends from the one end in the axial direction of the metal ring body 8a to the inner diameter side. The fitting tube portion 8c extends from the inner diameter edge of the flange portion 8b into the axial bearing space to form a step shape. The sensor unit Su is fixed to the outer ring 2 by press-fitting the outer peripheral surface of the fitting cylinder portion 8 c into a portion of the inner diameter surface of the outer ring 2 on one end side in the axial direction. Further, the one side surface of the flange portion 8b abuts against the end surface of the outer ring 2, whereby the sensor unit Su is positioned relative to the bearing 1 in the axial direction.

  The sensor housing 9 is made of, for example, an annular shape made of resin. A sensor housing 9 is attached to the inner peripheral surface of the metal ring body 8a, and the metal ring 8 and the sensor housing 9 are provided concentrically. The sensor housing 9 is provided with a bottomed arc-shaped groove 10 and a concave opening 11 communicating with the groove 10. A flexible printed circuit board 12 is mounted in a curved manner in the groove 10 in the sensor housing 9.

  The printed circuit board 12 is, for example, a film having a thickness of approximately 200 μm made of polyethylene terephthalate having excellent electrical insulation. A magnetic sensor 13 that is a detection element, other electrical components 14, and a cable 15 are mounted on the printed circuit board 12. Examples of the electrical component 14 include passive components such as resistors and capacitors. The cable 15 outputs a signal from the magnetic sensor 13 to the outside.

  A magnetic sensor 13 is inserted and positioned in a concave opening 11 in the sensor housing 9 (described later). The magnetic sensor 13 faces the magnetic track 7b with a gap δ defined in the radial direction. The magnetic sensor 13 has interpolation means 13c that performs electrical interpolation and outputs a pulse that is larger than the number of pole pairs of the N pole and S pole of the magnetic track 7b.

A reinforcing plate 16 is provided on the back surface 12b of the printed board 12 opposite to the mounting surface 12a on which the magnetic sensor 13 is mounted. The reinforcing plate 16 is, for example, a glass epoxy substrate.
3A is a plan view of the printed circuit board 12 as viewed from the side opposite to the component mounting surface 12a, and FIG. 3B is a side view of the printed circuit board 12. FIG.

As shown in FIGS. 3A and 3B, the reinforcing plate 16 has a larger area than the magnetic sensor 13 and is formed on the back surface 12 b of the printed circuit board 12 so as to overlap the position of the magnetic sensor 13. Glued and fixed.
On the component mounting surface 12 a of the printed circuit board 12, a wiring drawing pattern area Pa for soldering the cable 15 is provided. A reinforcing member 18 is fixed to a surface of the printed board 12 opposite to the wiring drawing pattern area Pa, that is, the back surface 12b.

  As shown in FIGS. 1 and 2, the sensor housing 9 is provided with a reference surface 17 connected to the vicinity of the middle in the circumferential direction in the bottomed arc-shaped groove 10. The reference surface 17 is a flat surface that serves as a reference for pressing the surface 16 a of the reinforcing plate 16. The surface 16a of the reinforcing plate 16 and the reference surface 17 of the sensor housing 9 are in surface contact. The thickness of the reinforcing plate 16 is such that when the reinforcing plate 16 is pressed against the reference surface 17, the gap δ is secured by a predetermined size (design gap).

  4 is a cross-sectional view of only the sensor housing 9 extracted from the bearing with the rotation detection device of FIG. FIG. 5 is a cross-sectional view of only the sensor housing 9 extracted from FIG. As shown in FIGS. 4 and 5, the sensor housing 9 includes a positioning means 21 for positioning the magnetic sensor 13 (FIG. 1) mounted on the flexible printed circuit board 12 in the axial direction L <b> 1 and the circumferential direction L <b> 2 with respect to the sensor housing 9. Is provided.

  The positioning means 21 has an axial direction positioning part and a circumferential direction positioning part. As shown in FIGS. 1 and 4, the axial positioning portion forms a bottom surface 20 in the opening portion 11 with which the axial end surface 13 b of the magnetic sensor 13 abuts. The one end surface 13 b in the axial direction of the magnetic sensor 13 abuts against the bottom surface 20 of the opening 11 in the sensor housing 9, whereby the magnetic sensor 13 is positioned in the depth direction, that is, the axial direction L <b> 1 with respect to the sensor housing 9.

  As shown in FIGS. 2 and 5, the circumferential positioning portion forms left and right side walls (circumferential side surfaces) 19, 19 in the opening portion 11 with which the left and right side surfaces 13 a, 13 a of the magnetic sensor 13 abut. The left and right side surfaces 13 a, 13 a of the magnetic sensor 13 abut on the left and right side walls 19, 19 of the opening 11 in the sensor housing 9, so that the magnetic sensor 13 is positioned in the eccentric direction, that is, the circumferential direction L 2 with respect to the sensor housing 9. Is done.

  Of the groove 10 of the sensor housing 9, the circumferentially middle portion is set to have a wider groove width than the circumferentially neighboring portion on which the electrical component 14 is mounted, because the reinforcing plate 16 is accommodated. Further, in the groove 10 of the sensor housing 9, the vicinity of the reinforcing member 18 and the wiring drawing pattern area Pa is also set to have a wider groove width than the vicinity of the circumferential direction where the electrical component 14 is mounted. Yes. Further, in order to fix the printed circuit board 12 to the sensor housing 9, the groove 10 is filled with a resin molding material (not shown).

The effect will be described.
Since the reinforcing plate 16 is provided on the back surface 12b of the printed circuit board 12 opposite to the mounting surface 12a on which the magnetic sensor 13 is mounted, stress is applied to the solder connection portion of the magnetic sensor 13 even if the printed circuit board 12 is curved. It does not occur, and the occurrence of solder cracks can be avoided. Further, only by pressing the surface 16a of the reinforcing plate 16 against the reference surface 17 of the sensor housing 9, the gap δ between the magnetic track 7b and the magnetic sensor 13 is ensured by a predetermined size. For this reason, it becomes easy to adjust the gap δ.

  The positioning means 21 positions the magnetic sensor 13 with respect to the sensor housing 9 in the axial direction L1 and the circumferential direction L2. That is, the axial end L <b> 1 of the magnetic sensor 13 can be easily positioned with respect to the sensor housing 9 by contacting the bottom end 20 of the magnetic sensor 13 with the bottom surface 20 of the opening 11 of the sensor housing 9. By positioning the left and right side surfaces 13a and 13a of the magnetic sensor 13 in contact with the left and right side walls 19 and 19 in the opening 11 of the sensor housing 9, the positioning of the magnetic sensor 13 in the circumferential direction L2 with respect to the sensor housing 9 can be easily performed. Can do. For this reason, the position adjustment at the time of bonding the reinforcing plate 16 to the printed circuit board 12 becomes unnecessary, and the process can be simplified. Since positioning accuracy of the magnetic sensor 13 is improved by the positioning means 21, even when the magnetic sensor 13 capable of high resolution detection or absolute angle detection is used, the magnetic sensor 13 is output with high accuracy.

When the resin mold material is filled into the groove 10 to fix the printed circuit board 12 to the sensor housing 9, the width of the groove 10 provided in the sensor housing 9 is wide at the place where the reinforcing plate 16 is inserted. Becomes easier. In a state where the reinforcing plate 16 is pressed against the reference surface 17, the resin mold material is filled and the printed circuit board 12 and the reinforcing plate 16 are fixed to the sensor housing 9. Therefore, the positioning accuracy of the magnetic sensor 13 can be improved and the magnetic sensor 13 is securely fixed to the sensor housing 9. In addition, since the filling process can be facilitated, the manufacturing cost of the bearing with the rotation detecting device can be reduced.
Since the surface 16a of the reinforcing plate 16 and the reference surface 17 of the sensor housing 9 are in surface contact with each other, the magnetic sensor 13 is prevented from being undesirably inclined with respect to the reference surface 17 of the sensor housing 9, and the magnetic encoder 7 and the magnetic sensor 13 are prevented. The parallelism with is maintained.

  A wiring drawing pattern area Pa is provided on the component mounting surface 12a of the printed board 12, and a reinforcing member 18 is provided on the back surface 12b of the printed board 12 opposite to the wiring drawing pattern area Pa. For this reason, the rigidity of the flexible printed circuit board 12 becomes high and the soldering work of wiring becomes easy. Further, when filling the resin mold material to fix the printed circuit board 12 to the sensor housing 9, the width of the groove 10 provided in the sensor housing 9 is wide even at the portion where the reinforcing member 18 is inserted, so that the filling operation is facilitated. .

  The magnetic sensor 13 includes an interpolation unit 13c that performs electrical interpolation and outputs a pulse that is larger than the number of pole pairs of N and S poles. Since the positioning unit 21 improves the positioning accuracy of the magnetic sensor 13, even if the interpolating unit 13c outputs more pulses than the number of pole pairs of the N pole and the S pole, the detection accuracy can be improved.

Another embodiment will be described.
In the following description, the same reference numerals are assigned to portions corresponding to the matters described in the preceding embodiment, and overlapping descriptions are omitted. When only a part of the configuration is described, the other parts of the configuration are the same as those described in advance unless otherwise specified. The same effect is obtained from the same configuration. Not only the combination of the parts specifically described in each embodiment, but also the embodiments can be partially combined as long as the combination does not hinder.

  As shown in FIG. 6, the magnetic encoder 7 may have a plurality (two in this example) of magnetic tracks 7b1 and 7b2, and these magnetic tracks 7b1 and 7b2 may be magnetized with different numbers of magnetic poles. . For example, the first magnetic track 7b1 having 32 pole pairs and the second magnetic track 7b2 having 31 pole pairs can be used. However, it is not limited to the number of these magnetic pole pairs. The magnetic sensor 13 can detect the absolute angle of the inner ring 3 that is a rotating wheel from the magnetic signals detected from the first and second magnetic tracks 7b1 and 7b2.

  FIG. 7 is an explanatory diagram showing an example of signal processing for performing absolute angle detection in the bearing with the rotation detection device of FIG. When the phase difference between the phase outputs obtained from the magnetic sensors 13 facing the first and second magnetic tracks 7b1 and 7b2 in two rows is taken, a signal with an electrical angle of 360 degrees is obtained in one rotation. Based on this value, the absolute angle is calculated. Further, the resolution is improved by electrically multiplying the magnetic signal obtained from one cycle including the NS poles of the first magnetic track 7b1.

As the printed circuit board 12, other thermoplastic plastic films excellent in electrical insulation, such as polyethylene, polyimide, and vinyl chloride, can be used. These plastic films can be formed by a conventional film forming method by roll processing or extrusion processing.
In each embodiment, the configuration may be such that the reinforcing member 18 is removed from the printed circuit board 12.
The rotating wheel may be the outer ring 2 and the fixed wheel may be the inner ring 3.
Bearing types other than deep groove ball bearings are also applicable.

  As mentioned above, although the form for implementing this invention based on embodiment was demonstrated, embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 ... Bearing 2 ... Outer ring (fixed ring)
3 ... Inner ring (rotating wheel)
7 ... Magnetic encoders 7b, 7b1, 7b2 ... Magnetic track 9 ... Sensor housing 11 ... Opening 12 ... Printed circuit board 13 ... Magnetic sensor 13c ... Interpolating means 16 ... Reinforcing plate 18 ... Reinforcing member 21 ... Positioning means

Claims (6)

A magnetic encoder fixed to a rotating ring of the bearing, a sensor housing fixed to the fixed ring of the bearing, and a flexible printed circuit board provided in the sensor housing,
The magnetic encoder has a magnetic sensor having a magnetic track in which N poles and S poles are alternately magnetized, and a magnetic sensor facing the magnetic track with a gap is mounted on the printed circuit board. ,
A reinforcing plate is provided on the back surface of the printed circuit board opposite to the mounting surface on which the magnetic sensor is mounted,
A reference surface that presses the surface of the reinforcing plate against the sensor housing is formed,
The sensor housing is provided with positioning means for positioning the magnetic sensor in the axial direction and the circumferential direction with respect to the sensor housing,
A bearing with a rotation detecting device, wherein the printed circuit board or the reinforcing plate is fixed to the sensor housing in a state where the reinforcing plate is pressed against a reference surface.   The bearing with a rotation detection device according to claim 1, wherein the surface of the reinforcing plate and the reference surface of the sensor housing are in surface contact.   The bearing with a rotation detection device according to claim 1 or 2, wherein an opening for inserting the magnetic sensor is formed in the sensor housing, and the positioning means abuts one end surface in the axial direction of the magnetic sensor. A bearing with a rotation detection device, comprising: an axial positioning portion that forms a bottom surface of the opening portion; and a circumferential positioning portion that forms a circumferential side surface of the opening portion on which the side surface of the magnetic sensor abuts.   The bearing with a rotation detecting device according to any one of claims 1 to 3, wherein a pattern region for wiring drawing is provided on either one of the mounting surface and the back surface of the printed circuit board, A bearing with a rotation detecting device, wherein a reinforcing member is provided on a surface of the substrate opposite to the wiring drawing pattern region.   5. The bearing with a rotation detection device according to claim 1, wherein the magnetic sensor performs electrical interpolation and outputs a pulse output larger than the number of pole pairs of the N pole and the S pole. Bearing with rotation detecting device having interpolated means. The bearing with a rotation detection device according to any one of claims 1 to 5, wherein the magnetic encoder has a plurality of magnetic tracks magnetized with different numbers of magnetic poles, and the magnetic sensor includes: A bearing with a rotation detection device having a function of detecting an absolute angle of the rotating wheel from magnetic signals detected from a plurality of magnetic tracks.

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