Load sensor

Abstract

To provide a load sensor that can be reduced in size.SOLUTION: A load sensor 1 comprises: a pressure-receiving core 2 made of a magnetostrictive material on which a load to be detected F acts; non-pressure-receiving cores 3a, 3b made of a magnetic material, concentrically arranged with the pressure-receiving core 2, and on which the load to be detected F does not act; detection coils 51, 52 generating magnetic fluxes passing through the pressure-receiving core 2 by energizing; and references coils 71, 72, when energized, generating magnetic fluxes not passing through the pressure-receiving cores 2, 2a, 2b and passing through the non-pressure-receiving cores 3a, 3b.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a load sensor.

Background Art

[0002] Patent Documents 1 and 2 disclose load sensors that detect the magnitude of a load using a magnetostrictive material whose permeability changes according to the magnitude of an externally applied load.

[0003] Each of the load sensors described in Patent Documents 1 and 2 includes a detection shaft portion made of a magnetostrictive material on which a load acts, a reference shaft portion on which no load acts, and a plurality of coils for load detection wound around each of the detection shaft portion and the reference shaft portion. In the load sensor described in Patent Document 1, the detection shaft portion and the reference shaft portion are arranged side by side in the axial direction of the plurality of coils, and in the load sensor described in Patent Document 2, the detection shaft portion and the reference shaft portion are arranged side by side in a direction orthogonal to the axial direction of the plurality of coils.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In each of the load sensors described in Patent Documents 1 and 2, there is a risk of enlargement in the arrangement direction of the detection shaft portion and the reference shaft portion.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a load sensor capable of achieving miniaturization.

Means for Solving the Problems

[0007] To achieve the above objective, the present invention provides a load sensor comprising: a pressure-receiving core made of a magnetostrictive material on which the load to be detected acts; a non-pressure-receiving core made of a magnetic material, arranged concentrically with the pressure-receiving core and on which the load to be detected does not act; a detection coil that generates a magnetic flux passing through the pressure-receiving core when energized; and a reference coil that generates a magnetic flux passing through the non-pressure-receiving core but not through the pressure-receiving core when energized. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a load sensor that can be miniaturized. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the load sensor in the first embodiment. [Figure 2] This is an enlarged view of the area indicated by the dashed line in Figure 1. [Figure 3] This is an exploded perspective view of the load sensor in the first embodiment. [Figure 4] This is a circuit diagram of the load sensor in the first embodiment. [Figure 5] This is a cross-sectional view of the load sensor in the second embodiment. [Figure 6] This is a cross-sectional view of the load sensor in the third embodiment. [Figure 7] This is a cross-sectional view of the load sensor in the fourth embodiment. [Modes for carrying out the invention]

[0010] [First Embodiment] A first embodiment of the present invention will be described with reference to Figures 1 to 4. The embodiments described below are presented as preferred specific examples for carrying out the present invention, and while some parts specifically illustrate various technically preferable technical matters, the technical scope of the present invention is not limited to these specific embodiments.

[0011] Figure 1 is a cross-sectional view of the load sensor 1 in this embodiment. Figure 2 is an enlarged view of the area shown by the dashed line in Figure 1. Figure 3 is an exploded perspective view of the load sensor 1.

[0012] The load sensor 1 comprises a pressure-receiving core 2, first and second non-pressure-receiving cores 3a and 3b, first and second detection coils 51 and 52 wound around a detection bobbin 4, and first and second reference coils 71 and 72 wound around a reference bobbin 6. The pressure-receiving core 2 is made of magnetostrictive material and is the core on which the load to be detected acts. The first and second non-pressure-receiving cores 3a and 3b are made of magnetic material (specifically soft magnetic material), are arranged concentrically with the pressure-receiving core 2, and are cores on which the load to be detected does not act. The first and second detection coils 51 and 52 are coils that generate a magnetic flux φ1 passing through the pressure-receiving core 2 when energized. The first and second reference coils 71 and 72 are coils that generate a magnetic flux φ2 passing through the first and second non-pressure-receiving cores 3a and 3b without passing through the pressure-receiving core 2 when energized.

[0013] The load sensor 1 comprises, in order from the inner circumference, a first non-pressure-receiving core 3a, first and second reference coils 71 and 72 wound around a reference bobbin 6, a second non-pressure-receiving core 3b, first and second detection coils 51 and 52 wound around a detection bobbin 4, and a pressure-receiving core 2. Each of the first non-pressure-receiving core 3a, reference bobbin 6, second non-pressure-receiving core 3b, detection bobbin 4, and pressure-receiving core 2 is formed in a cylindrical shape and arranged concentrically. Concentric means a state in which multiple members are arranged in layers in the radial direction, and is not limited to the case where the centers of each member coincide. The load sensor 1 in this embodiment is attached to the mounting target 100 and is used to detect a load F acting on the pressure-receiving core 2 from the opposite side of the mounting target 100. The parts of the load sensor 1 will be described in detail below, starting with the parts located on the inner circumference.

[0014] The first non-pressure-receiving core 3a is made of a magnetic material as described above. In this embodiment, the first non-pressure-receiving core 3a is made of the same material as the pressure-receiving core 2 (i.e., the magnetostrictive material described later), and its magnetic permeability is the same as that of the pressure-receiving core 2. However, the first non-pressure-receiving core 3a may be made of a different material than the pressure-receiving core 2, or it may be made of a magnetic material other than the magnetostrictive material. Furthermore, in this embodiment, the first non-pressure-receiving core 3a is shown as being cylindrical, but it is not limited to this, and may be a solid member such as a columnar shape.

[0015] Shot peening is applied to the surfaces of the first non-pressure core 3a facing the first and second reference coils 71 and 72 (in this embodiment, the outer circumferential surface of the first non-pressure core 3a). This allows for martensitic transformation (diffusion-free transformation) to occur in the retained austenite near the surfaces of the first and second reference coils 71 and 72 facing the first non-pressure core 3a. As a result, the amount of non-magnetic austenite in the first non-pressure core 3a is reduced and the amount of ferromagnetic martensite is increased. This increases the magnetic region of the first non-pressure core 3a. A reference bobbin 6 is positioned to surround the first non-pressure core 3a from the outer circumferential side.

[0016] The reference bobbin 6 is made of, for example, an insulator. The first and second reference coils 71 and 72 are wound around the outer surface of the reference bobbin 6. Alternatively, the first and second reference coils 71 and 72 may be wound directly around the outer surface of the first non-pressure-receiving core 3a without using the reference bobbin 6. However, from the viewpoint of improving load detection accuracy, it is not desirable for the first and second reference coils 71 and 72 to be in direct contact with the first non-pressure-receiving core 3a, and it is preferable to use the reference bobbin 6 to form a predetermined gap between them.

[0017] The first and second reference coils 71 and 72 have the same winding direction and the same energization direction as each other. In FIG. 2, the first reference coil 71 and the second reference coil 72 are distinguished by reversing the direction of the hatching. FIG. 2 shows an example in which the first and second reference coils 71 and 72 are bifilar-wound around the reference bobbin 6. Bifilar winding is a winding method in which the same turns when winding the windings of a plurality of coils are along each other. Note that the first and second reference coils 71 and 72 may be layer-wound on the outer peripheral surface of the reference bobbin 6 instead of bifilar winding. Layer winding will be described later. The second non-pressure core 3b is arranged between coils adjacent in the radial direction (in this embodiment, between the first and second reference coils 71 and 72 and the first and second detection coils 51 and 52), and constitutes a yoke 8 in which both magnetic fluxes φ1 and φ2 generated by energizing each of the adjacent coils are formed. By providing the yoke 8, the magnetic paths of the magnetic fluxes φ1 and φ2 are separated within the yoke 8, and it becomes difficult for the magnetic flux φ1 and the magnetic flux φ2 to interfere with each other. Also, by providing the yoke 8, the magnetic resistance of the magnetic paths where the magnetic fluxes φ1 and φ2 are generated becomes low, and it becomes easier to improve the load detection accuracy by the load sensor 1.

[0018] The second non-pressure core 3b is arranged between coils adjacent in the radial direction (in this embodiment, between the first and second reference coils 71 and 72 and the first and second detection coils 51 and 52), and constitutes a yoke 8 in which both magnetic fluxes φ1 and φ2 generated by energizing each of the adjacent coils are formed. By providing the yoke 8, the magnetic paths of the magnetic fluxes φ1 and φ2 are separated within the yoke 8, and it becomes difficult for the magnetic flux φ1 and the magnetic flux φ2 to interfere with each other. Also, by providing the yoke 8, the magnetic resistance of the magnetic paths where the magnetic fluxes φ1 and φ2 are generated becomes low, and it becomes easier to improve the load detection accuracy by the load sensor 1.

[0019] From the viewpoint of facilitating separation of the magnetic paths of the magnetic fluxes φ1 and φ2 within the yoke 8, the magnetic permeability of the yoke 8 is preferably the same as or greater than the magnetic permeability of each of the first non-pressure core 3a and the pressure core 2. In this embodiment, the yoke 8 can be, for example, a powder core formed by compressing magnetic metal powder such as iron. Note that the yoke 8 can be omitted, and for example, a gap or the like can be provided between the reference bobbin 6 and the detection bobbin 4. The detection bobbin 4 is arranged so as to cover the yoke 8 from the outer peripheral side.

[0020] The detection bobbin 4 is made of, for example, an insulator. The first and second detection coils 51 and 52 are wound around the outer surface of the detection bobbin 4. Alternatively, the first and second detection coils 51 and 52 may be wound directly around the outer surface of the yoke 8 without using the detection bobbin 4. However, from the viewpoint of improving the accuracy of load detection, it is not preferable for the first and second detection coils 51 and 52 to be in direct contact with the yoke 8, and it is preferable to use the detection bobbin 4 to form a predetermined gap between them.

[0021] The first and second detection coils 51 and 52 are wound in the same direction and have the same current-conducting direction. The winding direction and current-conducting direction of the first and second detection coils 51 and 52 may be the same as or opposite to the winding direction and current-conducting direction of the first and second reference coils 71 and 72, respectively, but Figure 2 shows the case where they are the same. In Figure 2, the first detection coil 51 and the second detection coil 52 are distinguished by the direction of the hatching. Figure 2 shows an example in which the first and second detection coils 51 and 52 are bifilar wound on the detection bobbin 4. Note that the first and second detection coils 51 and 52 may be layer-wound on the outer surface of the detection bobbin 4 instead of bifilar-wound. Layer winding will be described later. A pressure-receiving core 2 is arranged to cover the detection bobbin 4 on which the first and second detection coils 51 and 52 are wound from the outer surface.

[0022] The pressure-receiving core 2 is made of a magnetostrictive material as described above. The pressure-receiving core 2 may be made of steel, such as chromium steel or chromium-molybdenum steel, more specifically, SCr420H or SCM420H according to JIS standards. The entire pressure-receiving core 2 may be subjected to carburizing, quenching, and tempering treatment. This can increase the mechanical strength, including the toughness, of the pressure-receiving core 2 and suppress the decrease in load detection accuracy caused by hysteresis occurring in the pressure-receiving core 2. Although no load is applied to the first non-pressure-receiving core 3a, the same treatment may be applied to the first non-pressure-receiving core 3a.

[0023] Shot peening is applied to the surfaces of the pressure-receiving core 2 on the sides of the first and second detection coils 51 and 52 (in this embodiment, the inner circumferential surfaces of the pressure-receiving core 2). This allows for martensitic transformation (diffusion-free transformation) of the retained austenite near the surfaces of the pressure-receiving core 2 on the sides of the first and second detection coils 51 and 52. As a result, the amount of non-magnetic austenite in the pressure-receiving core 2 is reduced and the amount of ferromagnetic martensite is increased. This increases the magnetic region of the pressure-receiving core 2 and improves the load detection accuracy of the load sensor 1. Furthermore, applying shot peening to the pressure-receiving core 2 also increases its rigidity. This suppresses the decrease in load detection accuracy caused by hysteresis in the pressure-receiving core 2.

[0024] In this embodiment, the pressure-receiving core 2 is configured to receive the load F to be detected in the axial direction. The load F to be detected acts in the axial direction on the receiving surface 21 of the pressure-receiving core 2 opposite to the mounting target 100 when the load sensor 1 is attached to the mounting target 100. To facilitate the application of the load to the receiving surface 21, the receiving surface 21 is located on the opposite side from the mounting target 100 than the first and second non-pressure-receiving cores 3a and 3b when the load sensor 1 is attached to the mounting target 100. In this embodiment, the first non-pressure-receiving core 3a, the reference bobbin 6, the yoke 8 (i.e., the second non-pressure-receiving core 3b), the detection bobbin 4, and the pressure-receiving core 2 are each mounted so as to contact a flat portion of the mounting target 100 on the surface facing the mounting target 100, and the pressure-receiving core 2 is formed to be axially longer than each of the first non-pressure-receiving core 3a, the reference bobbin 6, the yoke 8, and the detection bobbin 4, so that the receiving surface 21 is located on the opposite side from the mounting target 100 than the other components constituting the load sensor 1, excluding the pressure-receiving core 2.

[0025] Although not shown in the diagram, for example, by making the part of the mounting target 100 facing the pressure-receiving core 2 an annular protrusion, it is possible to achieve a configuration in which the receiving surface 21 of the pressure-receiving core 2 is located on the opposite side of the mounting target 100 from the other parts of the load sensor 1, even if the axial length of the pressure-receiving core 2 is not longer than the axial length of the other parts of the load sensor 1. Furthermore, even in a configuration in the load sensor 1 in which the pressure-receiving core 2 does not protrude in the axial direction, it is possible to achieve a configuration in which the load F acts only on the pressure-receiving core 2 by, for example, forming a protrusion on the member that applies the load F to the receiving surface 21 so as to contact only the pressure-receiving core 2 among the components of the load sensor 1.

[0026] Furthermore, in order to suppress the transmission of the load F acting on the pressure-receiving core 2 to the first and second non-pressure-receiving cores 3a and 3b, which would reduce the load detection accuracy, it is preferable that the pressure-receiving core 2 and the first and second non-pressure-receiving cores 3a and 3b are physically separated. For example, it is preferable that a gap be formed at least at one location between the pressure-receiving core 2 and the detection bobbin 4, and between the detection bobbin 4 and the yoke 8. If the pressure-receiving core 2 and the first and second non-pressure-receiving cores 3a and 3b are physically separated, some of the components constituting the load sensor 1 may be fixed to each other.

[0027] The positional relationship of each component of the load sensor 1 can be fixed when the load sensor 1 is attached to the mounting object 100. For example, in the state shown in Figure 1, the positional relationship of each component of the load sensor 1 can be fixed by fixing the axial surface of each component of the load sensor 1 to the mounting object 100 by adhesive or the like. Alternatively, for example, a flange portion that extends radially can be formed on at least one of the reference bobbin 6 and the detection bobbin 4, and the components of the load sensor 1 can be placed on and fixed to this flange portion to position the components of the load sensor 1.

[0028] Furthermore, in this embodiment, the axial length of the load sensor 1 is smaller than the maximum length in the direction perpendicular to the axial direction (in this embodiment, the diameter of the pressure-receiving core 2). This allows the load sensor 1 to be made compact in the axial direction.

[0029] Next, the circuit configuration of the load sensor 1 in this embodiment will be described with reference to Figure 4. Figure 4 is a circuit diagram of the load sensor 1 in this embodiment.

[0030] The first and second detection coils 51, 52 and the first and second reference coils 71, 72 form a bridge circuit 10. The bridge circuit 10 has a first series circuit section 101 in which the first detection coil 51 and the first reference coil 71 are connected in series, and a second series circuit section 102 in which the second reference coil 72 and the second detection coil 52 are connected in series. The first series circuit section 101 and the second series circuit section 102 are connected in parallel. The first series circuit section 101 is connected to the first detection coil 51 side, and the second series circuit section 102 is connected to the second reference coil 72 side. An AC voltage is applied to the electrodes 11, 12 at both ends of the bridge circuit 10 from an AC power supply 15 outside the load sensor 1.

[0031] The first midpoint 101a between the first detection coil 51 and the first reference coil 71 in the first series circuit section 101 is connected to the first output terminal 13, and the second midpoint 102a between the second reference coil 72 and the second detection coil 52 in the second series circuit section 102 is connected to the second output terminal 14. These first and second output terminals 13 and 14 are connected to an external voltage measuring unit 16, and the voltage between the first midpoint 101a and the second midpoint 102a is measured by the voltage measuring unit 16.

[0032] When an AC voltage from the AC power supply 15 is applied to the bridge circuit 10, current flows through the first and second detection coils 51, 52 and the first and second reference coils 71, 72, and magnetic fluxes φ1, φ2 (see Figure 2) are formed. The magnetic flux φ1 generated by the energization of the first and second detection coils 51, 52 is formed to pass through the pressure-receiving core 2 and the yoke 8, while the magnetic flux φ2 generated by the energization of the first and second reference coils 71, 72 does not pass through the pressure-receiving core 2 but is formed to pass through the first non-pressure-receiving core 3a and the yoke 8.

[0033] When no load F is acting on the pressure-receiving core 2, the inductances of each coil constituting the bridge circuit 10 are designed to be equal. As a result, when no load F is acting on the pressure-receiving core 2, no voltage is generated between the first midpoint 101a and the second midpoint 102a. On the other hand, when a load F is acting on the pressure-receiving core 2, the permeability of the pressure-receiving core 2 changes according to the magnitude of the load F, and the inductances of the first and second detection coils 51 and 52 change. As a result, the voltage between the first midpoint 101a and the second midpoint 102a changes according to the magnitude of the load F acting on the pressure-receiving core 2, and the magnitude of the load F acting on the pressure-receiving core 2 can be detected based on the voltage between the first midpoint 101a and the second midpoint 102a. The voltage measurement unit 16 may also include a differential amplifier circuit that amplifies the voltage between the first midpoint 101a and the second midpoint 102a in order to remove the common-mode component and detect only the differential component, and a detection circuit that detects the output signal of the differential amplifier circuit.

[0034] As described above, in this embodiment, the first non-pressure-receiving core 3a and the pressure-receiving core 2 are made of the same material, and their magnetic permeability is equivalent. This makes it easy to match the impedances of the first reference coil 71, the second reference coil 72, the first detection coil 51, and the second detection coil 52, for example, by adjusting the number of turns of each coil. Here, the statement that the magnetic permeability of the first non-pressure-receiving core 3a and the pressure-receiving core 2 are equivalent includes cases where they were designed to have the same magnetic permeability, but they differ slightly due to manufacturing tolerances, etc.

[0035] Furthermore, the winding method of the first and second reference coils 71 and 72 on the outer surface of the reference bobbin 6, and the winding method of the first and second detection coils 51 and 52 on the outer surface of the detection bobbin 4, is not limited to bifilar winding, but may be layer winding. Layer winding is a winding method in which multiple coils are wound alternately in layers. For example, on the outer surface of the reference bobbin 6, the first reference coil 71 is wound on the odd-numbered layers and the second reference coil 72 is wound on the even-numbered layers, and on the outer surface of the detection bobbin 4, the first detection coil 51 is wound on the odd-numbered layers and the second detection coil 52 is wound on the even-numbered layers. In the case of layer winding, it is preferable to make the impedance of the first detection coil 51 and the impedance of the second reference coil 72 equal to each other, and to make the impedance of the first reference coil 71 and the impedance of the second detection coil 52 equal to each other, by making the layer positions of the first detection coil 51 and the second reference coil 72 the same. That is, for example, if the first detection coil 51 is wound on the 1st and 3rd layers, it is preferable that the second reference coil 72 is also wound on the 1st and 3rd layers, and if the first reference coil 71 is wound on the 2nd and 4th layers, it is preferable that the second detection coil 52 is also wound on the 2nd and 4th layers.

[0036] (Operation and effects of the first embodiment) In this embodiment of the load sensor 1, the pressure-receiving core 2 and the first and second non-pressure-receiving cores 3a and 3b are arranged concentrically. This makes it possible to miniaturize the load sensor 1.

[0037] Furthermore, at least one of the pressure-receiving core 2 and the non-pressure-receiving cores (i.e., the first and second non-pressure-receiving cores 3a and 3b) is positioned between radially adjacent coils among the plurality of coils constituting the first and second detection coils 51 and 52 and the first and second reference coils 71 and 72 (in this embodiment, between the first and second reference coils 71 and 72 and the first and second detection coils 51 and 52), and has a yoke 8 on which both magnetic fluxes φ1 and φ2 generated by energizing each of the adjacent coils are formed. Therefore, the magnetic flux φ1 generated by energizing the first and second detection coils 51 and 52 and the magnetic flux φ2 generated by energizing the first and second reference coils 71 and 72 are less likely to interfere with each other, and a decrease in load detection accuracy can be suppressed.

[0038] Furthermore, the permeability of the yoke 8 is greater than or equal to the permeability of the pressure-receiving core 2 and the first and second non-pressure-receiving cores 3a and 3b other than the yoke 8 (i.e., the pressure-receiving core 2 and the first non-pressure-receiving core 3a). Therefore, interference between the magnetic flux φ1 generated by energizing the first and second detection coils 51 and 52 and the magnetic flux φ2 generated by energizing the first and second reference coils 71 and 72 is further suppressed, improving the load detection accuracy.

[0039] Furthermore, the load F to be detected acts axially on the receiving surface 21 at one end of the pressure-receiving core 2 in the axial direction. By configuring the pressure-receiving core 2 to receive loads from the axial direction in this way, the durability of the pressure-receiving core 2 can be improved.

[0040] Furthermore, when mounted on the mounting target 100, the receiving surface 21 is located on the opposite side from the mounting target 100 to the first and second non-pressure-receiving cores 3a and 3b. Therefore, it is easy to suppress the load F of the object to be detected from acting on the first and second non-pressure-receiving cores 3a and 3b while allowing the load of the object to be detected to act on the pressure-receiving core 2 from the receiving surface 21. In this embodiment, since the axial length of the pressure-receiving core 2 is longer than the axial length of the first and second non-pressure-receiving cores 3a and 3b, it is easy to realize a configuration in which the receiving surface 21 is located on the opposite side from the mounting target 100 to the first and second non-pressure-receiving cores 3a and 3b.

[0041] As described above, this embodiment makes it possible to provide a load sensor that can be miniaturized.

[0042] [Second Embodiment] Figure 5 is a cross-sectional view of the load sensor 1 in this embodiment. This embodiment has the same basic structure as the first embodiment, but is designed to prevent external magnetic flux from entering the load sensor 1. If external magnetic flux enters the load sensor 1, it becomes difficult to accurately detect the change in the permeability of the pressure-receiving core 2 in accordance with the magnitude of the load on the pressure-receiving core 2, which may reduce the load detection accuracy. This embodiment aims to eliminate this concern.

[0043] In this embodiment of the load sensor 1, a shielding member 9 is arranged on at least one side in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72. The shielding member 9 is made of a material that has a magnetic shielding effect. As a material that has a magnetic shielding effect, for example, a conductor that generates eddy currents as magnetic flux passes through can be used, and both magnetic and non-magnetic materials can be used. As an example, the shielding member 9 can be made of an iron-based metal such as permalloy.

[0044] In this embodiment, shield members 9 are arranged inside each of the openings at both ends of the pressure-receiving core 2. The two shield members 9 are each formed in a disc shape and are provided to close the two openings. For example, the shield members 9 may be formed in an annular shape with a through hole that communicates with the inner space of the first non-pressure-receiving core 3a. In this embodiment, an example is shown in which the shield members 9 are arranged on both sides in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72, but for example, the shield members 9 may be arranged only on one side in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72.

[0045] Each shield member 9 is not fixed to at least one of the pressure-receiving core 2 and the first and second non-pressure-receiving cores 3a and 3b, thereby making it difficult for the load F to be transmitted from the pressure-receiving core 2 to the first and second non-pressure-receiving cores 3a and 3b via the shield member 9.

[0046] In this embodiment, the receiving surface 21 of the pressure-receiving core 2 is located further away from the mounting target 100 than the shielding member 9 located on the opposite side of the mounting target 100. This suppresses a decrease in load detection accuracy caused by the transmission of load F to the first and second non-pressure-receiving cores 3a and 3b via the shielding member 9.

[0047] The other configurations of this embodiment are the same as those of the first embodiment. In addition, among the reference numerals used in the second embodiment and subsequent embodiments, those that are the same as those used in the previously described embodiments represent the same components, etc., as those in the previously described embodiments, unless otherwise specified.

[0048] (Operation and effects of the second embodiment) In this embodiment, the first and second detection coils 51, 52 and the first and second reference coils 71, 72 are covered from at least one side in the axial direction by a shielding member 9 having a magnetic shielding effect. Therefore, magnetic flux present near the load sensor 1 is prevented from entering the load sensor 1 and affecting load detection by the load sensor 1. Furthermore, it has the same functions and effects as the first embodiment.

[0049] [Third Embodiment] Figure 6 is a cross-sectional view of the load sensor 1 in this embodiment. This embodiment is a configuration in which the radial arrangement of each component is reversed compared to the first embodiment. That is, in this embodiment, the components are arranged in order from the inner circumference side: a pressure-receiving core 2, first and second detection coils 51 and 52 wound around a detection bobbin 4, a second non-pressure-receiving core 3b constituting the yoke 8, first and second reference coils 71 and 72 wound around a reference bobbin 6, and a first non-pressure-receiving core 3a.

[0050] In this embodiment, the pressure-receiving core 2 is located at the innermost circumference of each component constituting the load sensor 1, and when mounted on the mounting object 100, the receiving surface 21 of the pressure-receiving core 2 is located on the opposite side from the mounting object 100 than the other components constituting the load sensor 1. In this embodiment, the inductance of the first and second detection coils 51 and 52, and the first and second reference coils 71 and 72, which are located on the inner circumference side, changes in response to the change in the magnetic permeability of the pressure-receiving core 2. Otherwise, it is the same as in the first embodiment.

[0051] (Operation and Effects of the Third Embodiment) In this configuration, the pressure-receiving core 2, on which the load F acts, has a smaller diameter than the first and second non-pressure-receiving cores 3a and 3b, making it easier to improve the durability of the pressure-receiving core 2 against the load F. Furthermore, it has the same functions and effects as the first embodiment.

[0052] [Fourth Embodiment] Figure 7 is a cross-sectional view of the load sensor 1 in this embodiment. This embodiment has the same basic structure as the third embodiment, but is designed to prevent external magnetic flux from entering the load sensor 1. In this embodiment, the load sensor 1 has a shielding member 9 added to at least one side in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72.

[0053] In this embodiment of the load sensor 1, a shield member 9 is provided on at least one side in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72. The material of the shield member 9 is the same as in the second embodiment.

[0054] In this embodiment, two shield members 9 are provided. Each of the two shield members 9 is formed in an annular shape and is fitted onto both ends of the pressure-receiving core 2. Each shield member 9 is positioned to cover the detection bobbin 4, yoke 8, reference bobbin 6, and the first non-pressure-receiving core 3a from the axial direction. In this embodiment, an example is shown in which the shield members 9 are arranged on both sides in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72. However, for example, the shield member 9 may be arranged only on one side in the axial direction of the first and second detection coils 51, 52 and the first and second reference coils 71, 72.

[0055] Each shield member 9 is not fixed to at least one of the pressure-receiving core 2 and the first and second non-pressure-receiving cores 3a and 3b, thereby making it difficult for the load F to be transmitted from the pressure-receiving core 2 to the first and second non-pressure-receiving cores 3a and 3b via the shield member 9.

[0056] In this embodiment, the receiving surface 21 of the pressure-receiving core 2 is located further away from the mounting target 100 than the shielding member 9 located on the opposite side of the mounting target 100. The other configurations of this embodiment are the same as those of the third embodiment.

[0057] (Operation and effects of the fourth embodiment) In this embodiment, the first and second detection coils 51, 52 and the first and second reference coils 71, 72 are covered from at least one side in the axial direction by a shielding member 9 having a magnetic shielding effect. Therefore, magnetic flux present near the load sensor 1 is prevented from entering the load sensor 1 and affecting load detection by the load sensor 1. Furthermore, it has the same functions and effects as the third embodiment.

[0058] [Other embodiments] In the embodiments described above, examples were shown in which a bridge circuit was constructed using four coils, but the invention is not limited to this. For example, a circuit may be adopted in which the second reference coil 72 and the second detection coil 52 shown in Figure 4 are each replaced with an impedance element other than a coil (e.g., a resistor). Alternatively, the first detection coil 51 and the second reference coil 72 shown in Figure 4 may each be replaced with an impedance element other than a coil. The impedance element other than a coil may be provided, for example, outside the load sensor 1 (e.g., in the voltage measurement unit 16). In such a case, the load sensor 1 will have a configuration comprising one detection coil and one reference coil. The load sensor 1 can adopt various circuit configurations as long as the detection coil can detect a change in magnetic permeability corresponding to the magnitude of the load on the pressure-receiving core.

[0059] In the embodiments described above, the examples in which the pressure-receiving core, non-pressure-receiving core, reference bobbin, and detection bobbin are each formed in a cylindrical shape are not limited to these, and other shapes such as polygonal cylinders may be adopted.

[0060] Furthermore, in the first and second embodiments, the direction in which the load acts on the pressure-receiving core may be radial. In this case, the permeability of the pressure-receiving core changes as it is compressed radially, and the magnitude of the load acting on the pressure-receiving core is detected according to this change in permeability.

[0061] (Summary of the embodiments) Next, the technical concept understood from the embodiments described above will be described using the reference numerals and other symbols from the embodiments. However, the reference numerals and other symbols in the following description are not limited to the components in the claims that are specifically shown in the embodiments.

[0062] [1] A load sensor (1) comprising: pressure-receiving cores (2, 2a, 2b) made of magnetostrictive material on which the load (F) to be detected acts; non-pressure-receiving cores (3a, 3b, 3c) made of a magnetic material, arranged concentrically with the pressure-receiving cores (2, 2a, 2b), on which the load (F) to be detected does not act; detection coils (51, 52) that generate a magnetic flux (φ1) passing through the pressure-receiving cores (2, 2a, 2b) when energized; and reference coils (71, 72) that generate a magnetic flux (φ2) passing through the non-pressure-receiving cores (3a, 3b, 3c) but not through the pressure-receiving cores (2, 2a, 2b) when energized.

[0063] [2] The load sensor (1) according to [1], wherein at least one of the pressure-receiving cores (2, 2a, 2b) and the non-pressure-receiving cores (3a, 3b, 3c) is positioned between radially adjacent coils among a plurality of coils constituting the detection coils (51, 52) and the reference coils (71, 72), and has a yoke (8) on which both magnetic fluxes (φ1, φ2) generated by energizing each of the adjacent coils are formed.

[0064] [3] The permeability of the yoke (8) is equal to or greater than the permeability of the pressure-receiving cores (2, 2a, 2b) and the non-pressure-receiving cores (3a, 3b, 3c) other than the yoke (8), as described in [2].

[0065] [4] The load (F) to be detected is a load sensor (1) according to any one of [1] to [3], which acts in the axial direction on a receiving surface (21) at one end of the axial direction of the pressure receiving core (2, 2a, 2b).

[0066] [5] The load sensor (1) according to [4], wherein, when attached to the mounting target (100), the receiving surface (21) is located on the opposite side from the mounting target (100) than the non-pressure receiving core (3a, 3b, 3c).

[0067] [6] The load sensor (1) described in [5], wherein the axial length of the pressure-receiving core (2, 2a, 2b) is longer than the axial length of the non-pressure-receiving core (3a, 3b, 3c).

[0068] [7] The load sensor (1) according to any one of [1] to [6], wherein the detection coils (51, 52) and the reference coils (71, 72) are covered from at least one side in the axial direction by a shielding member (9) having a magnetic shielding effect.

[0069] [8] The load sensor (1) according to any one of [1] to [7], wherein the detection coil (51, 52) has a first detection coil (51) and a second detection coil (52), the reference coil (71, 72) has a first reference coil (71) and a second reference coil (72), the first detection coil (51) and the first reference coil (71) are connected in series, the second reference coil (72) and the second detection coil (52) are connected in series, and the first reference coil (71) and the first detection coil (51) and the second reference coil (72) and the second detection coil (52) are connected in parallel to form a bridge circuit (10).

[0070] (Note) Although embodiments of the present invention have been described above, the embodiments described herein do not limit the invention as defined in the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. Moreover, the present invention can be implemented with appropriate modifications without departing from its spirit. [Explanation of Symbols]

[0071] 1...Load sensor 10...Bridge circuit 100... Mounting target 2... Pressure receiving core 2a...First pressure-receiving core 2b...Second pressure-receiving core 21... receiving surface 3a... first non-pressure receiving core 3b...Second non-pressurized core 3c...Third non-pressurized core 51...Detection coil 51...First detection coil 52...Second detection coil 71...First reference coil 72...Second reference coil 8...Yoke 9... Shielding component

Claims

1. A pressure-receiving core made of magnetostrictive material, on which the load to be detected acts, A non-pressure-receiving core made of a magnetic material, arranged concentrically with the pressure-receiving core, and on which the load of the object to be detected does not act, A detection coil that generates a magnetic flux passing through the pressure-receiving core when power is applied, The system includes a reference coil that generates a magnetic flux that passes through the non-pressure-receiving core but not through the pressure-receiving core when energized, Load sensor.

2. At least one of the pressure-receiving core and the non-pressure-receiving core is positioned between radially adjacent coils among a plurality of coils constituting the detection coil and the reference coil, and has a yoke into which both magnetic fluxes generated by energizing each of the adjacent coils are formed. The load sensor according to claim 1.

3. The permeability of the yoke is greater than or equal to the permeability of the pressure-receiving core and the non-pressure-receiving core other than the yoke. The load sensor according to claim 2.

4. The load to be detected acts axially on the receiving surface at one end of the pressure-receiving core in the axial direction. The load sensor according to claim 1 or 2.

5. When mounted to the object to be mounted, the receiving surface is located on the side opposite to the object to be mounted, relative to the non-pressure-receiving core. The load sensor according to claim 4.

6. The axial length of the pressure-receiving core is longer than the axial length of the non-pressure-receiving core. The load sensor according to claim 5.

7. The detection coil and the reference coil are covered from at least one side in the axial direction by a shielding member having a magnetic shielding effect. The load sensor according to claim 1 or 2.

8. The detection coil comprises a first detection coil and a second detection coil. The aforementioned reference coil comprises a first reference coil and a second reference coil. The first detection coil and the first reference coil are connected in series, the second reference coil and the second detection coil are connected in series, and the first reference coil and the first detection coil and the second reference coil and the second detection coil are connected in parallel to form a bridge circuit. The load sensor according to claim 1 or 2.

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