The present disclosure relates to a magnetic linear position detector capable of detecting a position of a mover that moves linearly.
There are known magnetic linear position detectors capable of detecting a position of a mover that moves linearly. In a magnetic linear position detector, one of a mover and a stator is provided with a magnetic detector, and the other is provided with a magnet. Patent Literature 1 discloses a position detector including a magnet with alternately arranged S poles and N poles, and a magnetic sensor including a magnetoresistive element whose resistance value changes depending on a direction of a magnetic field received from the magnet.
Patent Literature 1: Japanese Patent No. 5343001
However, magnetic lines of force from the N pole to the S pole can have a shape close to an elliptical arc. In the case of elliptical-arc-shaped magnetic lines of force, some areas in which the change in the direction of the magnetic field is small with respect to the change in the relative position between a magnet and a magnetic detector can be generated. In this case, since the change in the resistance value of the magnetic detector also becomes small, the accuracy of position detection can be lowered. In particular, as the distance between the N pole and the S pole is increased in order to secure the stroke amount of a mover, the shape of the magnetic lines of force becomes an elliptical arc shape long in the moving direction of the mover, and areas in which the change in the magnetic field is small tend to be easily generated.
The present disclosure has been made in view of the above, and an object of the present disclosure is to obtain a magnetic linear position detector capable of improving the accuracy of position detection while using a magnetoresistive element whose resistance value changes depending on the direction of a magnetic field.
In order to solve the above problems and achieve the object, the present disclosure includes a stator and a mover that is movable along a first direction with respect to the stator. One of the stator and the mover is provided with a magnetic detector. The other of the stator and the mover is provided with a magnet having a first face facing the magnetic detector. The first face is magnetized in such a manner that a magnetization direction changes in an arc shape around a magnetization center point. The magnetic detector is an element whose output changes depending on a direction of a magnetic field.
A magnetic linear position detector according to the present disclosure has an effect of being capable of improving the accuracy of position detection of a mover while using a magnetoresistive element whose resistance value changes depending on the direction of a magnetic field.
Hereinafter, a magnetic linear position detector according to an embodiment of the present disclosure is described in detail with reference to the drawings. Note that, this disclosure is not limited by the embodiments.
The magnet 4 has a first face 4a facing the magnetic detector 3. Note that a Z axis perpendicular to the first face 4a is defined. In addition, a Y axis perpendicular to the X axis and the Z axis is defined. In the following description, the direction along the X axis is referred to as a lateral direction, and the direction along the Y axis is referred to as a longitudinal direction.
The first face 4a is a rectangle having a long side parallel to the X axis, and the ratio of the long side to the short side is 2:1.
The magnet 4 is a polar anisotropic or isotropic magnet. The first face 4a of the magnet 4 is polar-anisotropically magnetized around a magnetization center point 5, and the magnetization direction is arc-shaped as indicated by an arrow 6. In the first embodiment, there is one magnetization center point 5, and the magnetization center point 5 is positioned at the center portion of one long side of the first face 4a.
The magnetic detector 3 is an element whose output changes with respect to the direction of the magnetic field received from the magnet 4. For example, the magnetic detector 3 is a spin valve giant magnetoresistance (GMR), a spin valve tunnel magnetoresistance (TMR), a rotation detection anisotropic magnetoresistance (AMR), or the like. Such a magnetic detector 3 is generally inexpensive, and the manufacturing cost of the magnetic linear position detector 20 can be suppressed.
As illustrated in
Here, as in the configuration disclosed in, for example, Patent Literature 1, when the same direction of the magnetic field appears a plurality of times with respect to the displacement of the magnet, the same output also appears a plurality of times from the magnetic detector. Therefore, for example, a sensor for identifying the same output that appears a plurality of times or a sensor for detecting the magnet being at the origin is further needed. In the first embodiment, since a sensor for identification as described above is unnecessary, the manufacturing cost of the magnetic linear position detector 20 can be suppressed. In addition, the operation of returning to the origin is unnecessary when the power of the magnetic linear position detector 20 is turned on, and the start-up operation of a drive device equipped with the magnetic linear position detector 20 can be further simplified, which means that the workability can be improved.
In addition, since the direction of the magnetic field changes in an arc shape, it is unlikely to generate areas in which the change in the direction of the magnetic field is small with respect to the change in the relative position between the magnet 4 and the magnetic detector 3, unlike the case with change in the direction of the magnetic field in an elliptical arc. Therefore, it is possible to detect the position of the mover more accurately regardless of the displacement of the magnet 4.
In addition, by setting the ratio of the long side to the short side of the first face 4a of the magnet 4 to 2:1, the diameter of the arc can be set to the length in the long side of the magnet 4, and the radius of the arc can be set to the length in the short side of the magnet 4 as illustrated in
A magnet 40 included in a magnetic linear position detector 21 according to the second embodiment is provided with two magnetization center points 5a and 5b. The magnetization direction in an arc shape around the magnetization center point 5a is counterclockwise. The magnetization direction in an arc shape around the magnetization center point 5b is clockwise.
A first face 40a of the magnet 40 is a rectangle having a long side parallel to the X axis, and the ratio of the long side to the short side is 4:1. The magnetization center points 5a and 5b are each positioned at ΒΌ of one long side of the first face 40a.
As illustrated in
In addition, since the direction of the magnetic field changes in an arc shape, it is unlikely to generate areas in which the change in the direction of the magnetic field is small with respect to the change in the relative position between the magnet 40 and the magnetic detector 3, unlike the case with change in the direction of the magnetic field in an elliptical arc. Therefore, it is possible to detect the position of the mover more accurately regardless of the displacement of the magnet 40.
In addition, by setting the ratio of the long side to the short side of the first face 40a of the magnet 40 to 4:1, twice the diameter of the arc can be set to the length in the long side of the magnet 40, and the radius of the arc can be set to the length in the short side of the magnet 40 as illustrated in
As the magnetization method, an electric wire is arranged at each of the magnetization center points 5a and 5b, and a linear current is caused to flow in the electric wire similarly to the first embodiment. At this time, by making the current-applying direction different between the electric wire arranged at the magnetization center point 5a and the electric wire arranged at the magnetization center point 5b, the magnetization direction can be made different between the arc around the magnetization center point 5a and the arc around the magnetization center point 5b.
In addition, three or more arc-shaped magnetic fields may be provided side by side although a sensor or the like for identifying the same output appearing a plurality of times from the magnetic detector is needed, because the same direction of the magnetic field appears a plurality of times with respect to the displacement of the magnet. That is, three or more magnetization center points may be provided. For example, if three arc-shaped magnetic fields are provided side by side, the ratio of the long side to the short side of the first face 40a of the magnet 40 is set to 6:1, whereby the magnet 40 can be efficiently magnetized to have the arc-shaped magnetic fields. Therefore, when the number of arc-shaped magnetic fields is n (n is an integer), the ratio between the long side and the short side of the first face 40a of the magnet 40 is preferably 2n:1.
The configurations described in the above embodiments are merely examples and can be combined with other known techniques, the above embodiments can be combined with each other, and a part of the configurations can be omitted or changed without departing from the gist of the present disclosure.
1 stator; 2 mover; 3 magnetic detector; 4, 40 magnet; 4a, 40a first face; 5, 5a, 5b magnetization center point; 6 arrow; 10 electric wire; 20, 21 magnetic linear position detector.
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/010356 | 3/10/2020 | WO |