JP2010145166A - Magnetic encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic encoder capable of detecting a moving direction (a rotating direction) by a single bridge circuit. <P>SOLUTION: The magnetic encoder 1 is characterized in constitution that a center-to-center distance T1 between each first magnetic resistance effect element 5a and each second magnetic resistance effect element 5b is different from an integer multiple of a magnetic pole pitch λ and a relative moving distance for maintaining the saturation state of a free magnetic layer differs between when an outer magnetic field H1 is applied and when an outer magnetic field H2 is applied. Accordingly, since an output waveform in a CW and an output waveform in a CCW are different from each other, it is possible to detect a moving direction (a rotating direction) even by a single bridge circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic encoder capable of detecting a moving speed (rotational speed), a moving direction (rotating direction), and the like.

  FIG. 12 is a schematic diagram showing a configuration of a conventional magnetic encoder 20. The magnetic encoder 20 includes a magnet 21 and a magnetic sensor 22. In FIG. 12, the magnet 21 has a rod shape extending in the X1-X2 direction, and the magnetic sensor 22 relatively moves in the X1 direction.

  The magnetic sensor 22 is provided with eight magnetoresistive elements A1, A2, B1, and B2. Of these, two magnetoresistive effect elements A1 and two magnetoresistive effect elements A2 constitute an A phase bridge circuit, and two magnetoresistive effect elements B1 and two magnetoresistive effect elements B2 constitute a B phase bridge circuit. (See FIG. 13).

  As shown in FIG. 12, the magnetized pitch of the magnet 21 (the distance between the centers of the N pole and the S pole) is λ, while the magnetoresistive element A1 and the magnetoresistive element that form a bridge circuit with the magnetic sensor 22 The distance between the centers of A2 and the distance between the centers of the magnetoresistive effect element B1 and the magnetoresistive effect element B2 are also λ.

  As shown in FIG. 1, when the magnetic sensor 22 relatively moves, an external magnetic field H <b> 1 and an external magnetic field H <b> 2 act from the magnetized surface 21 a of the magnet 21 toward the magnetic sensor 22. The external magnetic field H1 is an external magnetic field that acts on the magnetic sensor 22 when the magnetic sensor 22 relatively moves from the S pole side toward the N pole side. The external magnetic field H2 is the magnetic field of the magnetic sensor 22 from the N pole side to the S pole. This is an external magnetic field that acts on the magnetic sensor 22 when it moves relative to the side.

Based on the output obtained from the A-phase bridge circuit shown in FIG. 13 and the output obtained from the B-phase bridge circuit, the movement amount and the movement speed can be detected, and the output timing of the A phase and the B phase are shifted. The moving direction can also be detected by the phase relationship.
Japanese Patent Laid-Open No. 3-125918

  However, the conventional magnetic encoder 20 shown in FIG. 12 requires two bridge circuits to know the moving direction. 12 shows only a magnetoresistive effect element and a substrate on which these magnetoresistive effect elements are mounted, but actually has a package structure in which an ASIC for generating an output is also mounted. In the conventional configuration, two circuits having the same configuration are required on the ASIC side.

  From the above, there is a problem that the manufacturing cost of the magnetic sensor 22 increases. There is also a problem that the size of the magnetic sensor 22 is increased.

  FIG. 12 shows the linear magnetic encoder 20, but the same problem occurs even with a rotary magnetic encoder.

  Accordingly, the present invention is to solve the above-described conventional problems, and in particular, an object of the present invention is to provide a magnetic encoder that can detect a moving direction (rotational direction) with a single bridge circuit.

The present invention provides a magnetic field generating member having a magnetized surface in which N and S poles are alternately magnetized in the relative movement direction, and disposed at a position away from the magnetized surface of the magnetic field generating member. A magnetic sensor having a plurality of magnetoresistive elements utilizing a magnetoresistive effect whose electrical resistance value changes with respect to an external magnetic field,
One bridge circuit is configured by the plurality of magnetoresistive elements,
Each magnetoresistive effect element connected in series via the output terminal is arranged at a center-to-center distance different from a positive integer of the magnetic pole pitch λ in the relative movement direction,
When the magnetic sensor relatively moves from the S pole side to the N pole side on the magnetized surface of the magnetic field generating member, and the external magnetic field H1 acts on the magnetoresistive element, the magnetoresistive element A relative movement distance L1 for maintaining the saturation state of the magnetization fluctuation layer of the effect element;
When the magnetic sensor relatively moves from the N-pole side to the S-pole side on the magnetized surface of the magnetic field generating member, and the external magnetic field H2 acts on the magnetoresistive element, the magnetoresistive element The relative movement distance L2 for maintaining the saturation state of the magnetization fluctuation layer of the effect element is different.

  With the above configuration, the moving direction (rotating direction) can be detected even with one bridge circuit. As described above, according to the present invention, a single bridge circuit can be provided and the number of elements can be reduced as compared with the prior art, so that the manufacturing cost and the size of the magnetic sensor and thus the magnetic encoder can be reduced.

  In the present invention, it is preferable that the magnetization strength in each magnetic pole formed on the magnetized surface is magnetized so as to be different on both sides in the relative movement direction. Thereby, the above-mentioned relative movement distance L1 and relative movement distance L2 can be easily made different.

  In the present invention, it is preferable that the distance between the centers of the magnetoresistive elements is smaller than the magnetic pole pitch λ. This makes it possible to more effectively reduce the size of the magnetic sensor, and thus the magnetic encoder.

  In the present invention, the output waveform obtained from the bridge circuit has either a rising side or a falling side of the output between the minimum output line and the maximum output line, and has a shape with a step in the middle. It is preferable that the other has a continuous shape without the step. Thereby, a moving direction (rotation direction) can be detected with high accuracy.

  According to the magnetic encoder having the magnetic sensor and the magnetic field generating member of the present invention, the moving direction (rotational direction) can be detected even with one bridge circuit. As described above, according to the present invention, a single bridge circuit can be provided and the number of elements can be reduced as compared with the prior art, so that the manufacturing cost and the size of the magnetic sensor and thus the magnetic encoder can be reduced.

  1 is a perspective view of a magnetic encoder according to the present embodiment, FIG. 2 is a partial cross-sectional view of a magnetoresistive effect element, FIG. 3 is a configuration of a conventional example, and FIG. FIG. 4B is an output waveform diagram for normal magnetization, FIG. 4C is an output waveform diagram for offset magnetization, FIG. 4 is the configuration of the first embodiment, and FIG. Is a schematic diagram showing the positional relationship between a magnet and a magnetoresistive effect element, (b) is an output waveform diagram for normal magnetization (comparative example), and (c) is an output waveform diagram for offset magnetization (example). 5A and 5B show the configuration of the second embodiment, wherein FIG. 5A is a schematic diagram showing the positional relationship between a magnet and a magnetoresistive element, and FIG. 5B is an output waveform diagram for normal magnetization (comparative example). , (C) is an output waveform diagram (example) for offset magnetization, and FIG. Graph showing the magnetic field intensity changes with respect to the relative movement direction when the multi magnetized, (b) are graphs, showing the magnetic field intensity changes with respect to the relative movement direction when the offset magnetized.

  Each direction of the X1-X2 direction, the Y1-Y2 direction, and the Z1-Z2 direction in each figure has a relationship orthogonal to the remaining two directions. The X1-X2 direction is a relative movement direction of the magnet 2 and the magnetic sensor 3. In this embodiment, unless otherwise specified, the “relative movement direction” refers to the relative movement direction of the magnetic sensor 3. In this embodiment, the relative movement direction of the magnetic sensor 3 is the X1 direction. Therefore, when the magnet 2 is fixed and the magnetic sensor 3 moves, the magnetic sensor 3 moves in the X1 direction, and when the magnet 2 moves while the magnetic sensor 3 is fixed, the magnet 2 moves in the X2 direction. Note that both the magnet 2 and the magnetic sensor 3 may move. The Y1-Y2 direction is the width direction of the magnetic sensor 3 orthogonal to the relative movement direction in the plane of the substrate 4. The Z1-Z2 direction is a height direction in which the magnet 2 and the magnetic sensor 3 face each other with a predetermined interval.

  As shown in FIG. 1, the magnetic encoder 1 includes a magnet (magnetic field generating member) 2 and a magnetic sensor 3.

  For example, the magnet 2 has a rod shape extending in the X1-X2 direction shown in the figure, and the magnetized surface 2a in which the surface facing the magnetic sensor 3 is alternately magnetized with N and S poles with a predetermined width in the X1-X2 direction shown in the figure. It is. The pitch between the magnetic poles (the distance between the centers of the N pole and the S pole) is λ. For example, λ is 0.5 to 4.0 mm.

  As shown in FIG. 1, the magnetic sensor 3 includes a substrate 4 and a plurality of magnetoresistive elements 5 a and 5 b provided on a surface (a surface facing the magnet 2) 4 a of the common substrate 4. The

  In the magnetoresistive effect element, reference numeral 5a is a first magnetoresistive effect element, and reference numeral 5b is a second magnetoresistive effect element. Each of the first magnetoresistive effect element 5a and the second magnetoresistive effect element 5b is provided in two, and is composed of a total of four magnetoresistive effect elements.

  The two first magnetoresistive elements 5a are arranged at an interval in the Y1-Y2 direction. Similarly, the two second magnetoresistive elements 5b are arranged at an interval in the Y1-Y2 direction.

  As shown in FIG. 1, each first magnetoresistive element 5a and each second magnetoresistive element 5b are opposed to each other with an interval in the X1-X2 direction. The center-to-center distance between the element 5a and each second magnetoresistive element 5b is T1.

  In the present embodiment, the center-to-center distance T1 is different from a positive integer multiple of the magnetic pole pitch λ.

  These magnetoresistive elements 5a and 5b constitute a full bridge circuit similar to that shown in FIG. However, in the present embodiment, a configuration of a half bridge circuit in which one magnetoresistive effect element 5a and 5b is provided and connected in series via an output terminal may be employed.

  Each of the magnetoresistive elements 5a and 5b has, for example, a meander shape in which a plurality of element portions formed in an elongated shape in the Y1-Y2 direction are arranged in the X1-X2 direction and ends of each element portion are connected. Preferably it is formed.

  As shown in FIG. 2, each magnetoresistive effect element 5a, 5b includes an antiferromagnetic layer 7, a pinned magnetic layer 8, a nonmagnetic layer 9, a free magnetic layer (magnetization varying layer) 10, and a protective layer 11 in this order. It is formed with the structure laminated | stacked by. However, the stacked structure in FIG. 2 is an example. For example, the pinned magnetic layer 8 may be formed with a laminated ferrimagnetic structure. For example, the antiferromagnetic layer 7 is made of IrMn, the pinned magnetic layer 8 is made of CoFe, the nonmagnetic layer 9 is made of Cu, the free magnetic layer 10 is made of NiFe, and the protective layer 11 is made of Ta.

  The magnetoresistive effect elements 5 a and 5 b include a laminated portion in which at least the pinned magnetic layer 8 and the free magnetic layer 10 are laminated via the nonmagnetic layer 9. An exchange coupling magnetic field (Hex) is generated between the antiferromagnetic layer 7 and the pinned magnetic layer 8, and the magnetization of the pinned magnetic layer 8 is pinned in one direction.

  On the other hand, the magnetization direction of the free magnetic layer 10 is not fixed and fluctuates due to the external magnetic field H.

  In the present embodiment, the interface between the free magnetic layer 10 and the nonmagnetic layer 9 constituting the magnetoresistive effect elements 5a and 5b is a plane direction (XY plane direction) parallel to the magnetized surface 2a of the magnet 2. Facing.

The above configuration is a configuration of a giant magnetoresistive effect element (GMR element) in which the nonmagnetic layer 9 is formed of Cu. For example, when the nonmagnetic layer 9 is formed of an insulating material such as Al ₂ O ₃ or MgO. And configured as a tunnel type magnetoresistive effect element (TMR element). The magnetoresistive elements 5a and 5b may be anisotropic magnetoresistive elements (AMR elements).

  In this embodiment, the fixed magnetization direction (PIN direction) of the fixed magnetic layer 8 of each magnetoresistive element 5a, 5b is the X1 direction or the X2 direction.

  When the magnetic sensor 3 moves relative to the magnet 2 in the X1 direction, the external magnetic fields H1 and H2 enter the magnetoresistive elements 5a and 5b from the magnetized surface 2a of the magnet 2. As shown in FIG. 1, the directions of the external magnetic field H1 and the external magnetic field H2 are different (opposite directions), and when the magnetoresistive element is positioned on the magnetic pole, the magnetic field component is a vertical magnetic field with respect to the magnetoresistive element. It becomes dominant and the external magnetic field becomes zero (no magnetic field).

  When an external magnetic field in the same direction as the magnetization direction of the pinned magnetic layer 8 enters the magnetoresistive effect elements 5a and 5b, and the free magnetic layer 10 faces the same direction as the magnetization direction of the pinned magnetic layer 8, the electric resistance value is It becomes the minimum value. On the other hand, when an external magnetic field in the direction opposite to the magnetization direction of the pinned magnetic layer 8 enters and the free magnetic layer 10 faces in the direction opposite to the magnetization direction of the pinned magnetic layer 8, the electric resistance value becomes the maximum value.

  When the magnetic sensor 3 relatively moves from the N pole side of the magnet 2 toward the S pole side, the external magnetic field acting on the magnetic sensor 3 is H2, and the magnetic sensor 3 is N pole from the S pole side of the magnet 2. The external magnetic field that acts on the magnetic sensor 3 when moving relative to the side is H1.

  With the relative movement of the magnetic sensor 3, it is possible to detect the movement amount, the movement speed, and the movement direction.

  The magnetic encoder 1 according to the present embodiment is different from the first embodiment in that the center-to-center distance T1 between each first magnetoresistive element 5a and each second magnetoresistive element 5b is different from a positive integer multiple of the magnetic pole pitch λ. There is a characteristic configuration in that the relative movement distance for maintaining the saturation state of 10 is different between when the external magnetic field H1 is applied and when the external magnetic field H2 is applied.

  To make the relative movement distance for maintaining the saturated state of the free magnetic layer 10 different between when the external magnetic field H1 is applied and when the external magnetic field H2 is applied, "offset magnetization" is applied. Can be achieved.

  FIG. 6A shows a change in magnetic field strength of normal magnetization. The horizontal axis indicates the distance or time in the relative movement direction with respect to the magnetized surface of the magnetic sensor. The vertical axis represents the magnetic field strength of the external magnetic field generated from the magnetized surface.

  As shown in FIG. 6A, the upper side of the horizontal axis indicates, for example, the change in the magnetic field strength of the external magnetic field H2, and the lower side of the horizontal axis indicates the change in the magnetic field strength of the external magnetic field H1.

  As shown in FIG. 6A, the maximum magnetic field strength H1a of the external magnetic field H1 and the maximum magnetic field strength H2a of the external magnetic field H2 are substantially the same, and the magnetic field strength change curve of the external magnetic field H1 and the external magnetic field H2 The magnetic field strength change curve is a symmetrical shape with the horizontal axis as the axis of symmetry.

  The magnetic field strengths H1b and H2b at the dotted line positions shown in FIG. 6A are lower limit values for magnetic saturation of the free magnetic layer 10 constituting the magnetoresistive effect elements A1 and A2.

  When a strong external magnetic field of a certain level or more acts on the free magnetic layer 10, the whole is directed to the external magnetic field and reaches magnetic saturation. At this time, if the magnetization of the free magnetic layer 10 is directed to the magnetization direction of the pinned magnetic layer 8, the electric resistance value gradually decreases, and eventually reaches a minimum value when magnetic saturation is reached. Further, when the magnetization of the free magnetic layer 10 is directed to the magnetization direction of the pinned magnetic layer 8, the electric resistance value gradually increases, and eventually reaches a maximum value when the magnetic saturation is reached.

  In the normal magnetization of FIG. 6A, the relative movement distance L3 (saturation time) for maintaining the saturation state of the free magnetic layer 10 of the magnetoresistive effect element when the external magnetic field H1 is acting on the magnetoresistive effect element. ) And the relative movement direction distance L4 (saturation time) for maintaining the saturation state of the free magnetic layer 10 of the magnetoresistive element when the external magnetic field H2 is acting on the magnetoresistive element. ing.

  FIG. 6B shows a change in magnetic field strength of offset magnetization. The horizontal axis indicates the distance or time in the relative movement direction with respect to the magnetized surface of the magnetic sensor. The vertical axis represents the magnetic field strength of the external magnetic field generated from the magnetized surface.

  As shown in FIG. 6B, the upper side of the horizontal axis shows, for example, the change in the magnetic field strength of the external magnetic field H2, and the lower side of the horizontal axis shows the change in the magnetic field strength of the external magnetic field H1.

  As shown in FIG. 6B, the maximum magnetic field strength H1c of the external magnetic field H1 and the maximum magnetic field strength H2c of the external magnetic field H2 are different in magnitude, and the magnetic field strength change curve of the external magnetic field H1 and the external magnetic field H2 The magnetic field strength change curve is an asymmetric shape when the horizontal axis is the axis of symmetry. The magnetic field strength change curve in the offset magnetization of FIG. 6B is, so to speak, a waveform obtained by moving the magnetic field strength change curve in the normal magnetization of FIG. 6A to the external magnetic field H2 side with a constant offset amount. It has become.

  The magnetic field strengths H1d and H2d at the dotted line positions shown in FIG. 6B are lower limit values for magnetic saturation of the free magnetic layer 10 constituting the magnetoresistive elements A1 and A2. These magnetic field strengths H1d and H2d are the same magnitude as the magnetic field strengths H1b and H2b in FIG.

  6B, the relative movement distance L1 (saturation time) that maintains the saturation state of the free magnetic layer 10 of the magnetoresistive effect element when the external magnetic field H1 is acting on the magnetoresistive effect element. ) And the relative movement direction distance L2 (saturation time) for maintaining the saturation state of the free magnetic layer 10 of the magnetoresistive element when the external magnetic field H2 is acting on the magnetoresistive element.

  FIG. 3A shows the configuration of a conventional magnetic encoder. That is, although it is the structure of the magnetic encoder shown in FIG. 12, in order to make it easy to explain, the magnetoresistive effect element mounted on the magnetic sensor 22 includes the A-phase magnetoresistive effect elements A1 and A2 one by one. . The distance between the centers of the magnetoresistive elements A1 and A2 is the same as the magnetic pole pitch λ.

  FIG. 3B shows a first output waveform based on the electrical resistance change of the magnetoresistive effect element A1 with respect to the normal magnetization described in FIG. 6A, and a second output waveform based on the electrical resistance change of the magnetoresistive effect element A2. , And a differential output waveform (Total output) obtained by connecting the magnetoresistive effect element A and the magnetoresistive effect element A2 in series.

  FIG. 3C shows a first output waveform based on the electrical resistance change of the magnetoresistive effect element A1 with respect to the offset magnetization, a second output waveform based on the electrical resistance change of the magnetoresistive effect element A2, and the magnetoresistive effect element A. The differential output waveform obtained by connecting the magnetoresistive effect element A2 in series is shown.

  As shown in FIG. 3B, in normal magnetization, the rise timing of the first output and the fall timing of the second output are the same timing, and the fall timing of the first output and the second output The rise timing is the same timing. The duty ratio of the output waveform in FIG. 3B is approximately 50%.

  On the other hand, as shown in FIG. 3C, in offset magnetization, the rising timing of the first output is different from the falling timing of the second output, and the falling timing of the first output is The rising timing of the second output is different from the timing. The duty ratio of the output waveform in FIG. 3C is less than 50%, and the rising timing and falling timing of the first output are always when the second output is the minimum output line.

  As shown in FIG. 3C, the differential output waveform obtained by connecting the magnetoresistive effect element A and the magnetoresistive effect element A2 in series in the offset magnetization is the differential output waveform in the normal magnetization ( This is different from FIG. Here, CW indicates the clockwise direction, and CCW indicates the counterclockwise direction. This is based on the assumption of a rotary magnetic encoder as shown in the embodiment of FIG. 11. In the case of linear movement, CW indicates linear movement in one direction, and CCW is in the opposite direction to CW. Indicates a straight line movement.

  As shown in FIG. 3C, the differential output change has the same waveform in CW and CCW. Therefore, if the distance between the centers of the magnetoresistive elements A1 and A2 is the same as the magnetic pole pitch λ, the moving direction (rotating direction) cannot be detected with only one bridge circuit even with offset magnetization.

  On the other hand, FIG. 4A shows an embodiment in which the center distance T1 between the first magnetoresistive element 5a and the second magnetoresistive element 5b is smaller than the magnetic pole pitch λ.

  FIG. 4B shows a first output waveform based on a change in electrical resistance of the first magnetoresistance effect element 5a with respect to normal magnetization, a second output waveform based on a change in electrical resistance of the second magnetoresistance effect element 5b, and The differential output waveform (Total output) obtained by connecting the 1st magnetoresistive effect element 5a and the 2nd magnetoresistive effect element 5b in series is shown.

  FIG. 4C shows a first output waveform based on a change in electrical resistance of the first magnetoresistance effect element 5a with respect to offset magnetization, a second output waveform based on a change in electrical resistance of the second magnetoresistance effect element 5b, and The differential output waveform obtained by connecting the 1st magnetoresistive effect element 5a and the 2nd magnetoresistive effect element 5b in series is shown.

  In the normal magnetization of FIG. 4B, the first output waveform based on the electrical resistance change of the first magnetoresistance effect element 5a and the second output waveform based on the electrical resistance change of the second magnetoresistance effect element 5b are In both cases, the duty ratio is approximately 50%, but the output timing is shifted. The obtained differential output waveform (Total output) has a symmetric shape, which is almost the same shape as the differential output waveform shown in FIG. Therefore, in normal magnetization, even if the center distance T1 between the first magnetoresistive element 5a and the second magnetoresistive element 5b is smaller than the magnetic pole pitch λ, the moving direction (rotating direction) can be detected. I can't.

  On the other hand, in the offset magnetization of FIG. 4C, the first output waveform based on the electrical resistance change of the first magnetoresistance effect element 5a and the second output waveform based on the electrical resistance change of the second magnetoresistance effect element 5b. Both output waveforms have a duty ratio smaller than 50%. At this time, as shown in FIG. 4C, the fall timing a of the output waveform of the first output is shifted from the rise timing b of the output waveform of the second output. As shown in FIG. 4C, the rising timing c of the output waveform of the first output and the falling timing d of the output waveform of the second output are the same timing.

  As shown in the differential output waveform of FIG. 4C, the differential output waveform at CW rises up to the maximum at the rising timing e, and the falling timings f and g become two steps through the steps. ing. For this reason, the differential output waveform in CW has an asymmetric shape. The differential output waveform in the CCW has a shape obtained by inverting the differential output waveform in the CW. Thus, since the differential output waveform at CW and the differential output waveform at CCW are different, the center-to-center distance T1 between the first magnetoresistive effect element 5a and the second magnetoresistive effect element 5b is defined as the magnetic pole pitch. By making it smaller than λ and performing offset magnetization, it is possible to detect the moving direction (rotating direction) even with one bridge circuit.

  FIG. 5A shows an embodiment in which the center distance T1 between the first magnetoresistive element 5a and the second magnetoresistive element 5b is larger than the magnetic pole pitch λ.

  FIG. 5B shows a first output waveform based on a change in electrical resistance of the first magnetoresistance effect element 5a with respect to normal magnetization, a second output waveform based on a change in electrical resistance of the second magnetoresistance effect element 5b, and The differential output waveform (Total output) obtained by connecting the 1st magnetoresistive effect element 5a and the 2nd magnetoresistive effect element 5b in series is shown.

  FIG. 5C shows a first output waveform based on a change in electrical resistance of the first magnetoresistance effect element 5a with respect to offset magnetization, a second output waveform based on a change in electrical resistance of the second magnetoresistance effect element 5b, and The differential output waveform obtained by connecting the 1st magnetoresistive effect element 5a and the 2nd magnetoresistive effect element 5b in series is shown.

  In the normal magnetization of FIG. 5B, as in FIG. 4B, the center-to-center distance T1 between the first magnetoresistive element 5a and the second magnetoresistive element 5b is made larger than the magnetic pole pitch λ. However, the moving direction (rotational direction) cannot be detected.

  On the other hand, in the offset magnetization of FIG. 5 (c), as shown in FIG. 5 (c), the differential output waveform at CW reaches the maximum at the two-stage rise timings h and i through the steps. It falls to the minimum at a stretch at the rising and falling timing j.

  For this reason, the differential output waveform in CW has an asymmetric shape. The differential output waveform at the CCW has a shape obtained by inverting the differential output waveform at the CW by 180 degrees. Thus, since the differential output waveform at CW and the differential output waveform at CCW are different, the center-to-center distance T1 between the first magnetoresistive effect element 5a and the second magnetoresistive effect element 5b is defined as the magnetic pole pitch. By making it larger than λ and performing offset magnetization, it is possible to detect the moving direction (rotating direction) even with one bridge circuit.

  As described above, in the present embodiment, one bridge circuit is sufficient to detect the moving direction (rotating direction), so that the number of magnetoresistive elements 5a and 5b mounted on the magnetic sensor 3 can be reduced as compared with the prior art. . In addition, since a single bridge circuit is sufficient, the circuit configuration of the ASIC can be made simpler than before. Therefore, the manufacturing cost of the magnetic sensor 3 and thus the magnetic encoder 1 can be reduced as compared with the prior art.

  As shown in FIG. 4, if the center distance T1 between the first magnetoresistive effect element 5a and the second magnetoresistive effect element 5b is made smaller than the magnetic pole pitch λ, the magnetic sensor is more effective than the conventional one. 3. As a result, the magnetic encoder 1 can be reduced in size. The center distance T1 is preferably 0.5 mm or more and smaller than λ.

  As shown in FIG. 5, even when the center distance T1 between the first magnetoresistive element 5a and the second magnetoresistive element 5b is larger than the magnetic pole pitch λ, the center distance T1 is 3λ / 2 (3λ / 2 can be formed smaller than the distance between the centers of the magnetoresistive effect elements arranged on both sides shown in the conventional example of FIG. 12, and the magnetic sensor 3 can be made smaller than the conventional one.

  The center distance T1 between the first magnetoresistive element 5a and the second magnetoresistive element 5b is the relative movement that maintains the saturation state of the free magnetic layer 10 of the magnetoresistive element described with reference to FIG. Adjustment is performed based on the distances L1 and L2 (saturation time). In particular, as shown in FIG. 4 (c), the rising timing c of the first output is the same as the falling timing d of the second output, or as shown in FIG. 5 (c). It is preferable to adjust the center-to-center distance T1 (or the relative movement distances L1 and L2) so that the first output fall timing k and the second output rise timing l are the same timing. As a result, the differential output waveform obtained from the bridge circuit consisting of a plurality of magnetoresistive elements has a step in the middle of either the rising or falling side of the output between the minimum output line and the maximum output line. The other is a continuous shape without the step (FIGS. 4C and 5C). Thereby, a moving direction (rotation direction) can be detected with higher accuracy.

  The differential output waveforms in FIGS. 3 to 5 are digitized analog signals obtained, but the analog signals can be used as detection signals in the movement direction (rotation direction) as they are. In the case of a digital signal, for example, as shown in FIG. 4C, a first threshold level LV1 is defined between the intermediate output line and the maximum output line, and a second threshold is set between the intermediate output line and the minimum output line. Level LV2 is defined. In the stop state of the magnetic sensor 3 and the magnet 2, the control is always performed so as to be positioned on the intermediate output line, and when the magnetic sensor 3 starts to move relative to the magnet 2, the output is the first value. The moving direction (rotating direction) can be detected depending on whether it exceeds the threshold level LV1 or falls below the second threshold level LV2.

  Next, an offset magnetization method will be described. Note that the following three examples are merely examples and do not exclude other methods of offset magnetization.

  7A is a plan view and a side view of the magnet, FIG. 7B is a change in magnetic field strength in the rotation direction in normal magnetization, FIG. 7C is a change in magnetic field strength in the rotation direction in offset magnetization, (d ) Is a schematic diagram of a magnetized surface and a yoke surface showing a method of offset magnetization.

  When the magnetized surface and the yoke surface are magnetized in parallel, normal magnetization shown in FIG. 7B is obtained. On the other hand, if the yoke surface is tilted with respect to the magnetized surface as shown in FIG. 7D, the magnetization intensity in each magnetic pole formed on the magnetized surface is not uniform, and each magnetic pole Magnetization patterns having different magnetization strengths on both sides in the rotation direction are obtained. As a result, as shown in FIG. 7C, offset magnetization is generated in which a predetermined offset amount is generated from the normal magnetization in FIG. 7B.

  8A is a perspective view and a side view of the magnet, FIG. 8B is a change in magnetic field strength in the rotation direction of a magnet without inclination (a magnet with a flat magnetized surface), and FIG. 8C is a magnet with a gradient. The magnetic field strength changes in the rotation direction.

  As shown in FIG. 8A, an inclined surface inclined in the rotation direction is formed on the magnetized surface of each magnetic pole. Then, as in the conventional case, the magnet is magnetized with the yoke facing in parallel to the magnet, and as shown in FIG. 8C, a predetermined offset amount is obtained from the normal magnetization in FIG. 8B. The resulting offset magnetization.

  FIG. 9 is a plan view and a side view of the magnet. The magnet in FIG. 9 is magnetized with the magnetized surface and the yoke surface parallel to each other as in the prior art. As shown in FIG. 9, the distance (Airgap) between the magnet and the magnetoresistive effect element mounted on the magnetic sensor is changed to 1.0 mm, 1.5 mm, 2.0 mm, and 2.5 mm, and the magnet The magnetic sensor was moved relative to the magnet in a state where the magnetic sensor was opposed to each other at an inner peripheral position (R0 mm) of the inner peripheral position and positions of 1 mm, 2 mm, and 3 mm from the inner peripheral position toward the outer periphery. . Similar to FIGS. 4 and 5, the magnetic sensor includes the first magnetoresistive element 5a and the second magnetoresistive element 5b. The center-to-center distance T1 between these magnetoresistive elements 5a and 5b is: It was 2.0 mm. FIG. 10 shows each output change (analog output) when the distance between the magnetic sensor and the magnet (Airgap) and the facing position of the magnetic sensor are changed as described above. As shown in FIG. 10, if the distance (Airgap) between the magnetic sensor and the magnet is 2.5 mm, the output waveform is the CCW output waveform in FIG. 4C or the CW in FIG. 5C. It turned out to be almost the same as the output waveform. Further, if the opposing position of the magnetic sensor is the inner peripheral position (R0 mm) of the magnet or 1 mm from the inner peripheral position, it is preferable because the intermediate output line (step position) extends long in parallel.

  As described above, when the distance (Airgap) between the magnetic sensor and the magnet is increased, the magnetic field strength acting on the magnetoresistive effect element from the magnet becomes weaker, and a subtle magnetization offset becomes obvious and differential output The change can be formed into an asymmetric waveform.

  Although FIGS. 7 to 9 are forms in which a ring-shaped magnet is axially magnetized, it can also be applied to radial magnetization.

The perspective view of the magnetic encoder of this embodiment, Partial sectional view of magnetoresistive effect element, It is a structure of a prior art example, (a) is a schematic diagram which shows the positional relationship of a magnet and a magnetoresistive effect element, (b) is an output waveform figure with respect to normal magnetization, (c) is an output with respect to offset magnetization. Waveform diagram, It is a structure of 1st Embodiment, (a) is a schematic diagram which shows the positional relationship of a magnet and a magnetoresistive effect element, (b) is an output waveform figure (comparative example) with respect to normal magnetization, (c) is , Output waveform diagram for offset magnetization (Example), It is a structure of 2nd Embodiment, (a) is a schematic diagram which shows the positional relationship of a magnet and a magnetoresistive effect element, (b) is an output waveform figure (comparative example) with respect to normal magnetization, (c) is , Output waveform diagram for offset magnetization (Example), (A) is a graph showing a change in magnetic field strength relative to the relative movement direction when normal magnetization is performed, (b) is a graph showing a change in magnetic field strength relative to the relative movement direction when offset magnetization is performed, It is an example of offset magnetization, (a) is a plan view and a side view of a magnet, (b) is a change in magnetic field strength in the rotation direction in normal magnetization, (c) is a rotation direction in offset magnetization. Magnetic field strength change, (d) is a schematic diagram of a magnetized surface and a yoke surface showing a method of offset magnetization, It is an example of offset magnetization, (a) is a perspective view and a side view of a magnet, (b) is a magnetic field strength change in the rotation direction in a non-tilt magnet (magnet with a flat magnetized surface), (c ) Is the change in magnetic field strength in the direction of rotation with a tilted magnet, An example of offset magnetization, a plan view and a side view of a magnet, As shown in FIG. 9, a graph showing each output change (analog output) when the distance between the magnetic sensor and the magnet (Airgap) and the facing position of the magnetic sensor are changed, A perspective view of a rotary magnetic encoder in the present embodiment, Schematic diagram (perspective view) showing the configuration of a conventional magnetic encoder, A block diagram of the A-phase and B-phase bridge circuit,

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic encoder 2 Magnet 3 Magnetic sensor 5a, 5b Magnetoresistive effect element 7 Antiferromagnetic layer 8 Fixed magnetic layer 9 Nonmagnetic layer 10 Free magnetic layer (magnetization fluctuation layer)

Claims (4)

A magnetic field generating member having a magnetized surface in which N and S poles are alternately magnetized in the relative movement direction, and a position away from the magnetized surface of the magnetic field generating member, and disposed on the substrate surface against an external magnetic field A magnetic sensor having a plurality of magnetoresistive elements utilizing a magnetoresistive effect that changes in electrical resistance value,
One bridge circuit is configured by the plurality of magnetoresistive elements,
Each magnetoresistive effect element connected in series via the output terminal is arranged at a center-to-center distance different from a positive integer of the magnetic pole pitch λ in the relative movement direction,
When the magnetic sensor relatively moves from the S pole side to the N pole side on the magnetized surface of the magnetic field generating member, and the external magnetic field H1 acts on the magnetoresistive element, the magnetoresistive element A relative movement distance L1 for maintaining the saturation state of the magnetization fluctuation layer of the effect element;
When the magnetic sensor relatively moves from the N-pole side to the S-pole side on the magnetized surface of the magnetic field generating member, and the external magnetic field H2 acts on the magnetoresistive element, the magnetoresistive element A magnetic encoder characterized in that the relative movement distance L2 for maintaining the saturation state of the magnetization fluctuation layer of the effect element is different.   The magnetic encoder according to claim 1, wherein the magnetic strength in each magnetic pole formed on the magnetized surface is magnetized so as to be different on both sides in the relative movement direction.   The magnetic encoder according to claim 1 or 2, wherein a distance between centers of the magnetoresistive elements is smaller than the magnetic pole pitch λ.   The output waveform obtained from the bridge circuit is such that either the rising or falling side of the output between the minimum output line and the maximum output line has a shape with a step in the middle, and the other is the step. The magnetic encoder according to any one of claims 1 to 3, wherein the magnetic encoder has a continuous shape.

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