JP2015102507A - Force sensor, force detection device using the same and force detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a force sensor capable of reducing the thickness thereof, a force detection device using the same and a force detection method.SOLUTION: The force sensor includes: a core 4 which is formed of a magnetic material including a central hollow part 400; and a coil 5 attached to the core 4. When the power is supplied to the coil 5, a magnetic path M1 of a magnetic flux is formed on the core 4 along a circumferential direction of the hollow part 400. The core 4 has a load reception part 40 for receiving a load, which is formed on one face in a direction crossing the face on which the magnetic path M1 is formed.

Description

  The present invention generally relates to a force sensor, and more particularly to a force sensor that detects a load applied to a magnetic body by utilizing the inverse magnetostriction effect of the magnetic body, a force detection device using the same, and a force detection method.

  2. Description of the Related Art Conventionally, a magnetostrictive load sensor that detects a load applied to a magnetic body based on a change in magnetic permeability accompanying a distortion of the magnetic body magnetized by a current flowing through a coil is known. Yes. A magnetostrictive load sensor described in Patent Document 1 includes a load receiving portion of a ferromagnetic body that receives an external load, a coil that is wound around the load receiving portion, and a ferromagnetic body that houses the load receiving portion and the coil. And at least the case. Further, the coil is housed in a bobbin made of resin disposed around the load receiving portion.

  The load receiving portion has a rod shape, and an axially symmetric region including the central axis in the height direction is penetrated to form a cylindrical hollow portion. The load receiving portion receives a load applied in the axial direction of the rod-shaped member by inserting a rod-shaped member such as a wire or cable in close contact with the hollow portion.

  When a load is applied to the load receiving portion, the magnetic permeability of the load receiving portion changes due to the inverse magnetostrictive effect, and the impedance of the circuit including the coil inductance changes. This magnetostrictive load sensor detects (detects) a load caused by the movement of a rod-shaped member inserted into the hollow portion of the load receiving portion by measuring a voltage change at both ends of the coil accompanying this impedance change.

JP 2004-226196 A

  However, the conventional magnetostrictive load sensor (force sensor) requires a ferromagnetic case that prevents the magnetic flux generated by the current flowing through the coil from leaking outside in order to reduce the influence of the external magnetic field. For this reason, the conventional magnetostrictive load sensor requires a space for providing a ferromagnetic case, and it is difficult to reduce the thickness.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a force sensor that can be thinned, a force detection device using the force sensor, and a force detection method.

  The force sensor of the present invention includes a core having a hollow portion formed of a magnetic material and a coil attached to the core, and the core is generated when the coil is energized along a circumferential direction of the hollow portion. A magnetic path through which a magnetic flux passes is formed, and the core includes a load receiving portion that receives a load on one surface intersecting a surface on which the magnetic path is formed.

  This force sensor preferably includes a structure that avoids a load applied to the coil.

  In this force sensor, the structure is a structure in which the core has a smaller dimension in the intersecting direction than the other part in the attachment part to which the coil is attached, and the dimension of the attachment part in the intersecting direction is It is preferable that the coil is set so as to be within the dimension of the other part in the crossing direction.

  In this force sensor, it is preferable that the structure is a protective portion that covers at least the coil on the load receiving portion side in the intersecting direction.

  The force sensor preferably includes a bobbin attached to a part of the core, and the coil is configured by winding a conductive wire around the core via the bobbin.

  In this force sensor, it is preferable that the core has a gap in a part in a circumferential direction of the hollow portion, and the bobbin is attached to the core so as to cover the gap.

  In this force sensor, it is preferable that the force sensor includes a shielding portion that is made of a metal material and covers at least a part of the core.

  A force detection device according to the present invention includes any one of the force sensors described above and a detection circuit that detects a load applied to the load receiving portion based on a change in inductance of the coil.

  A force detection device according to the present invention includes any one of the force sensors described above and a detection circuit that detects a load applied to the load receiving portion based on a change in conductance of the coil.

  According to the force detection method of the present invention, in any one of the force sensors described above, the step of supplying a current to the coil and the load in the cross direction applied to the load receiving portion are detected based on a change in inductance of the coil. And a step of performing.

  According to the force detection method of the present invention, in any one of the force sensors described above, the step of supplying a current to the coil and the load in the cross direction applied to the load receiving portion are detected based on a change in conductance of the coil. And a step of performing.

  In the force sensor of the present invention, the core is configured such that a magnetic path (closed magnetic path) through which the magnetic flux generated when the coil is energized passes along the circumferential direction of the hollow portion. For this reason, in the force sensor of the present invention, leakage of magnetic flux from the core to the outside hardly occurs, and there is no need to use a ferromagnetic case as in the conventional example. Therefore, the force sensor of the present invention does not require a space for providing a ferromagnetic case, and thus can be reduced in thickness.

1A is a schematic diagram of a force detection device according to an embodiment of the present invention, FIG. 1B is a schematic plan view of a force sensor according to an embodiment of the present invention, and FIG. 1C is a schematic cross-section of the configuration shown in FIG. 1B. FIG. 2A is a schematic diagram of a detection circuit in the force detection device according to the embodiment of the present invention, and FIG. 2B is a diagram illustrating a load applied to the load receiving portion, the inductance of the coil, and the conductance in the force sensor according to the embodiment of the present invention. FIG. It is the schematic which shows the conventional force sensor. 4A is a schematic plan view of a configuration provided with a protrusion in the force sensor according to the embodiment of the present invention, and FIG. 4B is a schematic cross-sectional view of the configuration shown in FIG. 4A. In the force sensor which concerns on embodiment of this invention, it is a schematic sectional drawing of the structure which wound the conducting wire around the core and provided the coil, without providing an attaching part. In the force sensor which concerns on embodiment of this invention, it is a schematic sectional drawing of the structure provided with the protection part. 7A is a schematic plan view of a configuration including a bobbin in the force sensor according to the embodiment of the present invention, and FIG. 7B is a schematic cross-sectional view of the configuration shown in FIG. 7A. 8A is a schematic plan view of a configuration in which the core has a gap in the force sensor according to the embodiment of the present invention, and FIG. 8B is a schematic cross-sectional view of the configuration shown in FIG. 8A. 9A is a schematic plan view of a configuration in which the dimensions of the bobbin are changed in the force sensor according to the embodiment of the present invention, and FIG. 9B is a schematic cross-sectional view of the configuration shown in FIG. 9A. 10A is a schematic plan view of a configuration in which the dimensions of the bobbin are further changed in the force sensor according to the embodiment of the present invention, and FIG. 10B is a schematic cross-sectional view of the configuration shown in FIG. 10A. In the force sensor which concerns on embodiment of this invention, it is a schematic sectional drawing of the structure provided with the shielding part. FIG. 12A is a schematic diagram of a force detection device in an embodiment of the present invention, and FIG. 12B is an explanatory diagram of a method of using the force detection device in an embodiment of the present invention.

  As shown in FIGS. 1B and 1C, the force sensor 2 according to the embodiment of the present invention includes a core 4 having a hollow portion 400 formed of a magnetic material, and a coil 5 attached to the core 4. In the core 4, a magnetic path M <b> 1 through which a magnetic flux generated when the coil 5 is energized is formed along the circumferential direction of the hollow portion 400. And the core 4 is equipped with the load receiving part 40 which receives a load in one surface of the cross | intersection direction which cross | intersects the surface where the magnetic path M1 is formed.

  Moreover, the force detection apparatus 1 which concerns on embodiment of this invention is provided with the force sensor 2 and detection circuit 3 of this embodiment, as shown to FIG. 1A. The detection circuit 3 detects a load applied to the load receiver 40 based on a change in inductance (or conductance) of the coil 5.

  The force detection method according to the embodiment of the present invention includes a step of supplying a current to the coil 5 in the force sensor 2 of the present embodiment. Further, the force detection method of the present embodiment includes a step of detecting a load in the cross direction applied to the load receiving portion 40 based on a change in inductance (or conductance) of the coil 5.

  Hereinafter, a force sensor 2 according to an embodiment of the present invention, a force detection device 1 using the same, and a force detection method will be described in detail. The force detection device 1 according to the present embodiment includes a force sensor 2 and a detection circuit 3 as shown in FIG. 1A.

  As shown in FIGS. 1B and 1C, the force sensor 2 includes a core 4 having a hollow portion 400 and a coil 5 attached to the core 4. The core 4 is formed in an annular shape from a magnetic material such as Ni (nickel) -Zn (zinc) ferrite. In addition, the core 4 should just be formed with the magnetic body which has a reverse magnetostriction effect, when a load is added to the core 4. FIG. The inverse magnetostriction effect is an effect in which the magnetized core 4 is distorted when a load is applied, and the permeability of the core 4 changes due to the distortion.

  The coil 5 is configured by winding a conducting wire around a part of the core 4 so as to alternately pass through the hollow portions 400 and the outside of the core 4. In addition, as a conducting wire, it is desirable to use a copper wire (for example, enameled wire) coated with an insulating material. In the following description, a portion where the conducting wire is wound in the core 4 (that is, a portion where the coil 5 is attached) is referred to as an “attachment portion 41”.

  As shown in FIG. 1B, magnetic flux generated when the coil 5 is energized passes through the core 4. For this reason, a magnetic path (magnetic circuit) M <b> 1 along the circumferential direction of the hollow portion 400 is formed in the core 4. This magnetic path M1 is a closed magnetic path.

  The core 4 includes a load receiving portion 40 that receives a load on one surface (upper surface in FIG. 1C) of the thickness direction (vertical direction in FIG. 1C). In other words, the core 4 includes the load receiving portion 40 on one surface in the intersecting direction intersecting the surface on which the magnetic path M1 is formed. In the force sensor 2 of the present embodiment, the core 4 includes a load receiving portion 40 on one surface in a direction orthogonal to the surface on which the magnetic path M1 is formed. Note that “orthogonal” is an expression including not only complete “orthogonal” but also “substantially orthogonal”.

  As shown in FIG. 2A, the detection circuit 3 includes an oscillation circuit 30, a period measurement circuit 31, a squaring circuit 32, a temperature compensation circuit 33, and a signal processing circuit 34. The oscillation circuit 30 is configured to maintain the oscillation of the resonance circuit 50 including the coil 5. The oscillation circuit 30 is configured to output an oscillation signal that oscillates at a frequency corresponding to the resonance frequency of the resonance circuit 50. The period measurement circuit 31 is configured to measure the period of the oscillation signal output from the oscillation circuit 30 and output a signal corresponding to the measured period. The square circuit 32 is configured to calculate and output the square value of the signal output from the period measurement circuit 31. The temperature compensation circuit 33 is configured to suppress temperature fluctuation of the signal output from the squaring circuit 32 by temperature compensation processing. The signal processing circuit 34 is configured to detect a change in load applied to the load receiving portion 40 of the core 4 based on a signal output from the temperature compensation circuit 33.

  As shown in FIG. 2A, an equivalent circuit of the resonance circuit 50 is configured by a parallel circuit of a series circuit of an inductor L1 and a resistor R1 and a capacitor C1. Here, the inductance of the inductor L1 is equivalent to the inductance of the coil 5. Further, the resistance value of the resistor R1 is equivalent to the resistance value of the winding resistance of the coil 5. Further, the capacitance value of the capacitor C1 is equivalent to the parasitic capacitance of the coil 5. That is, in the force detection device 1 of the present embodiment, the resonance circuit 50 is configured by only the coil 5. The resonance circuit 50 may be configured by electrically connecting a capacitor (not shown) in parallel with the coil 5. In this configuration, the capacitance value of the capacitor C1 is equivalent to the combined capacitance of the parasitic capacitance of the coil 5 and the capacitance value of the capacitor connected in parallel with the coil 5.

  Here, the force detection method according to the embodiment of the present invention will be described. The force detection method of the present embodiment includes a step of supplying a current to the coil 5 in the force sensor 2 of the present embodiment. In addition, the force detection method of the present embodiment includes a step of detecting a load in the intersecting direction (here, the vertical direction in FIG. 1C) applied to the load receiving unit 40 based on a change in the inductance of the coil 5. Hereinafter, the force detection method of the present embodiment will be described by describing the operation of the force detection device 1 of the present embodiment.

  First, an external power source (not shown) supplies current to the coil 5. Here, the oscillation circuit 30 of the detection circuit 3 supplies a current to the coil 5. Then, the core 4 is magnetized by the magnetic flux generated when the coil 5 is energized. In the core 4, a magnetic path M1 shown in FIG. 1B is formed. Next, when a load is applied to the load receiving portion 40 of the core 4 in the direction in which the core 4 is pushed (the direction of the arrow shown in FIG. 1C), the magnetic permeability of the core 4 varies depending on the magnitude of the load due to the inverse magnetostrictive effect. Change. For this reason, the inductance of the coil 5 changes as the magnetic permeability of the core 4 changes.

  That is, as shown in FIG. 2B, the inductance of the coil 5 changes according to the load applied to the load receiving portion 40. 2B shows the amount of change in the inductance of the coil 5 according to the load, where the inductance of the coil 5 when no load is applied to the load receiving portion 40 is 100%.

  When the inductance of the coil 5 changes, the resonance frequency of the resonance circuit 50 including the coil 5 changes. In the detection circuit 3, as described above, the oscillation circuit 30 outputs an oscillation signal having a frequency corresponding to the resonance frequency of the resonance circuit 50, and the period measurement circuit 31 outputs a signal corresponding to the period of the oscillation signal. Here, the period of the oscillation signal is represented by the square root of the product of the inductance of the inductor L1 and the capacitance value of the capacitor C1 in the equivalent circuit. And since the square circuit 32 calculates and outputs the square value of the output signal of the period measurement circuit 31, the output signal of the square circuit 32 changes linearly with respect to the change of the inductance of the coil 5. Here, the output signal of the squaring circuit 32 is corrected for temperature fluctuations by the temperature compensation circuit 33, but the output signal of the temperature compensation circuit 33 also changes linearly with respect to the change in the inductance of the coil 5.

  The signal processing circuit 34 calculates the inductance of the coil 5 based on the output signal of the temperature compensation circuit 33, and calculates the load applied to the load receiving portion 40 from the obtained amount of change in the inductance of the coil 5. That is, the detection circuit 3 detects a load applied to the load receiving portion 40 of the core 4 based on a change in inductance of the coil 5.

  As described above, in the force sensor 2 of the present embodiment, the core 4 is configured such that the magnetic path M1 (closed magnetic path) through which the magnetic flux generated when the coil 5 is energized passes along the circumferential direction of the hollow portion 400. Has been. For this reason, in the force sensor 2 of this embodiment, the leakage of the magnetic flux from the core 4 to the outside does not easily occur, and there is no need to use a ferromagnetic case as in the conventional example. Therefore, the force sensor 2 of the present embodiment does not require a space for providing a ferromagnetic case, and thus can be thinned.

  By the way, Japanese Patent Laid-Open No. 2003-194639 (hereinafter referred to as “reference example”) discloses a force sensor 100 that does not require a ferromagnetic case. As shown in FIG. 3, the force sensor 100 includes two iron cores 101, a magnetostrictive member 102, an excitation coil 103, and a detection coil 104.

  Each iron core 101 is integrally formed with iron leg portions 101A at both ends in the longitudinal direction (left and right direction in FIG. 3). A gap (gap) 105 is provided between each iron core leg portion 101A of one iron core 101 and each iron core leg portion 101A of the other iron core 101. The magnetostrictive member 102 is formed in a cylindrical shape from a magnetic material and is sandwiched between two iron cores 101. The exciting coil 103 is wound around each iron core leg portion 101A on one side (left side in FIG. 3) of each iron core 101, and by supplying an alternating current, a magnetic flux is applied to each iron core 101 and the magnetostrictive member 102. generate. The detection coil 104 is wound around each core leg 101A on the other side (right side in FIG. 3) of each iron core 101, and detects a magnetic flux passing through each iron core 101.

  Hereinafter, the operation of the force sensor 100 will be described. When an alternating current is passed through the exciting coil 103, the magnetic path M2 of the magnetic flux passing through the iron core leg 101A-gap 105-the iron core leg 101A, and the magnetic path of the magnetic flux passing through the iron core leg 101A-gap 105-magnetostrictive member 102. M3 is formed. Here, when a load is applied to one of the iron cores 101 (upper side in FIG. 3) in the axial direction (vertical direction in FIG. 3) of the magnetostrictive member 102, the load is applied to the magnetostrictive member 102 via the iron core 101. The magnetostrictive member 102 is compressed. At this time, as the load increases, the magnetic resistance of the magnetic path M3 increases and the magnetic resistance of the magnetism M2 decreases, so that the magnetic flux passing through the magnetic path M2 increases. Therefore, since the magnetic flux detected by the detection coil 104 increases, the induced voltage also increases. In the force sensor 100, the load is calculated from the voltage induced in the detection coil 104.

  In this force sensor 100, magnetic paths M2 and M3 passing through each iron core 101 and the magnetostrictive member 102 are closed magnetic paths. However, in the force sensor 100, the surface on which the magnetic paths M2 and M3 are formed and the direction in which the magnetostrictive member 102 receives a load (vertical direction in FIG. 3) are parallel. For this reason, in order to secure the magnetic path length required by the magnetic paths M2 and M3, it is necessary to adjust the dimension of each iron core 101 in the height direction (vertical direction in FIG. 3). Therefore, it is difficult to reduce the thickness of the force sensor 100 in the direction in which a load is received.

  On the other hand, in the force sensor 2 of the present embodiment, as shown in FIGS. 1B and 1C, the surface on which the magnetic path M1 is formed and the direction in which the load receiving portion 40 of the core 4 receives a load (up and down direction in FIG. 1C). Intersect with each other. For this reason, in order to secure the magnetic path length required by the magnetic path M1, the dimension in the circumferential direction of the core 4 may be adjusted. It does not depend on the magnetic path length. Therefore, the force sensor 2 of the present embodiment can be thinned in the direction of receiving a load, compared to the force sensor 100 disclosed in the reference example.

  In the force sensor 2 of the present embodiment, the shape of the core 4 is not limited to an annular shape, and may be an annular shape having rounded corners as shown in FIG. 8A, for example. That is, the core 4 may have a shape in which a magnetic path (closed magnetic path) through which the magnetic flux generated when the coil 5 is energized passes along the circumferential direction of the hollow portion 400.

  In the force detection device 1 of the present embodiment, the detection circuit 3 does not include the squaring circuit 32 and the temperature compensation circuit 33, and the signal processing circuit 34 changes the load based on the signal output from the period measurement circuit 31. The structure which detects this may be sufficient. Further, the configuration of the detection circuit 3 illustrated in FIG. 2A is an example, and the detection circuit 3 may have another configuration as long as the load is detected based on a change in inductance of the coil 5.

  Further, as shown in FIG. 2B, the conductance of the coil 5 also changes in accordance with the change in the load. Therefore, the detection circuit 3 may be configured to detect the load based on the change in the conductance of the coil 5. 2B shows the amount of change in the conductance of the coil 5 according to the load, with the conductance of the coil 5 being 100% when no load is applied to the load receiving portion 40. FIG. In this case, the force detection method according to the present embodiment includes a step of supplying a current to the coil 5 and a load in the cross direction applied to the load receiving portion 40 in the force sensor 2 according to the present embodiment. And detecting based on.

  In the force sensor 2 of the present embodiment, the load receiving portion 40 is one surface in the thickness direction (cross direction) of the core 4 and is configured as a plane, but the load receiving portion 40 is not necessarily configured as a plane. It does not have to be. For example, as illustrated in FIGS. 4A and 4B, the load receiver 40 may have a configuration in which one or a plurality of protrusions 42 are provided on one surface of the core 4 in the thickness direction (cross direction). The protrusion 42 is formed in a hemispherical shape and protrudes in a direction opposite to the direction in which the load is received (upward in FIG. 4B). In addition, the shape of the protrusion 42 is not limited to a hemispherical shape, and may be another shape. Moreover, you may form the protrusion 42 with the material which has elasticity, for example.

  By the way, for example, as shown in FIG. 5, when the coil 5 is configured simply by winding a conducting wire around the core 4, a part of the coil 5 is more than the load receiving portion 40 in the thickness direction (cross direction) of the core 4. Protruding. In this configuration, when a load is applied to the load receiving portion 40, a load is also applied to the coil 5, and the coil 5 may be disconnected. In this configuration, the load receiving portion 40 includes a portion from which a part of the coil 5 protrudes and another portion. For this reason, in this configuration, there is a possibility that the load is not uniformly applied to the load receiving portion 40 and the load cannot be detected with high accuracy.

  Therefore, the force sensor 2 of the present embodiment may be configured to have a structure that avoids a load applied to the coil 5. In the force sensor 2 of the present embodiment, this structure is a structure in which the core 4 has a smaller dimension in the thickness direction (crossing direction) of the core 4 than the other parts in the mounting portion 41 (FIG. 1B, FIG. 1C). As shown in FIG. 1C, the mounting portion 41 is configured such that the dimension T2 of the coil 5 is smaller than the dimension T1 of the core 4 in the thickness direction of the core 4. In other words, the dimension of the attachment portion 41 in the intersecting direction is set such that the coil 5 is within the dimension of the other part in the intersecting direction. For this reason, in this configuration, part of the coil 5 does not protrude beyond the load receiving portion 40 in the thickness direction (cross direction) of the core 4. Therefore, in this configuration, it is possible to avoid applying a load to the coil 5 and to prevent the coil 5 from being disconnected. Further, in this configuration, since the load is easily applied uniformly to the load receiving portion 40, the load can be detected with high accuracy.

  In addition, in the force sensor 2 of this embodiment, the structure provided with the protection part 6 instead of providing the attachment part 41 may be sufficient as shown in FIG. The protection unit 6 is formed in a plate shape by, for example, a resin material, and is installed on both sides in the thickness direction of the core 4. For this reason, the part which protrudes rather than the load receiving part 40 of the coil 5 is covered with the protection part 6. That is, the protection part 6 is configured to cover at least the coil 5 on the side of the load receiving part 40 in the intersecting direction.

  In this configuration, since a load is applied to the load receiving portion 40 via the protection portion 6, it is possible to avoid a load from being directly applied to the coil 5 and to prevent the coil 5 from being disconnected. Further, the protective portion 6 is provided with a recess 60 that avoids the coil 5 at a portion facing the coil 5. For this reason, since it is hard to touch the coil 5 and the protection part 6 directly, it can avoid more that a load is added to the coil 5. FIG.

  In addition, in the force sensor 2 of this embodiment, as shown to FIG. 7A and 7B, the structure provided with the bobbin 7 attached to a part of core 4 may be sufficient. The coil 5 may be configured by winding a conducting wire around the core 4 via the bobbin 7. The bobbin 7 is formed of an insulating material (for example, a resin material). Further, as shown in FIG. 7B, the bobbin 7 is formed in a C-shaped cross-section with a part thereof opened (upper part in FIG. 7B). The bobbin 7 is attached to the core 4 by being fitted into the core 4 through the opening. And the coil 5 is comprised by winding a conducting wire around the bobbin 7 in the state which attached the bobbin 7 to the core 4. FIG.

  In this configuration, since the coil 5 is configured by winding a conducting wire around the core 4 via the bobbin 7, the bobbin 7 can prevent the core 4 and the coil 5 from being short-circuited. For this reason, in this configuration, the core 4 can be formed of a highly conductive material. The core 4 can be formed of a metal material such as iron, chromium, or nickel. The core 4 can be formed of an alloy such as Mn (manganese) -Zn (zinc) ferrite or permalloy, for example. In particular, when the core 4 is formed of an alloy, the strength of the core 4 can be increased, so that further thinning can be achieved while ensuring the strength.

  Moreover, in the force sensor 2 of this embodiment, as shown to FIG. 8A and FIG. 8B, the structure which has the space | gap 43 in the circumferential part of the hollow part 400 may be sufficient as the core 4. FIG. Then, instead of the bobbin 7, the bobbin 8 may be attached to the core 4 so as to cover the gap 43. As shown in FIG. 8A, the core 4 is formed in a C shape in plan view by cutting out a part thereof. A gap 43 is provided between one end 44 of the core 4 and the other end 45. The bobbin 8 is formed of an insulating material (for example, a resin material). The bobbin 8 is formed in a cylindrical shape as shown in FIGS. 8A and 8B. Therefore, unlike the bobbin 7, the bobbin 8 does not have an opening. The bobbin 8 is attached to the core 4 via the gap 43 so that the end portions 44 and 45 of the core 4 fit into the hollow portion.

  In this configuration, the bobbin 8 in which the conducting wire constituting the coil 5 is wound in advance can be attached to the core 4 via the gap 43. Therefore, in this configuration, the step of winding the conductive wire around the core 4 is unnecessary, and the coil 5 can be easily attached to the core 4. In this configuration, the air gap 43 is interposed in the middle of the magnetic path M1. That is, in this configuration, air having a low magnetic permeability is interposed in the middle of the magnetic path M1, so that variations in inductance of the coil 5 can be reduced. FIG. 8C shows the amount of change in the inductance (and conductance) of the coil 5 according to the load, assuming that the inductance (and conductance) of the coil 5 when no load is applied to the load receiving portion 40 is 100%. Yes.

  9A and 9B, the bobbin 8 may be formed so as to fit within the width dimension D1 of the core 4. In this case, as shown in FIG. 9B, the width dimension D <b> 2 of each end portion 44, 45 may be reduced so that each end portion 44, 45 of the core 4 fits into the hollow portion of the bobbin 8. Further, as shown in FIGS. 10A and 10B, the dimension T2 of the wound coil 5 is the dimension of the core 4 in the thickness direction of the core 4 so that the bobbin 8 does not protrude from the load receiving portion 40 of the coil 5. You may form so that it may become smaller than T1. In this case, as shown in FIG. 10B, the thickness dimension T <b> 3 of each end portion 44, 45 may be reduced so that each end portion 44, 45 of the core 4 fits into the hollow portion of the bobbin 8.

  In addition, in the force sensor 2 of this embodiment, the structure provided with the shielding part 9 may be sufficient as shown in FIG. The shielding part 9 is formed in a plate shape from a metal material, and is installed on both sides in the thickness direction of the core 4. In this configuration, the shielding unit 9 can reduce the influence of an external magnetic field. Here, the hole 90 is provided in the shielding part 9 in order to pass an object (for example, a bolt or the like) for detecting the load through the hollow part 400 of the core 4, but it is not always necessary to provide it. That is, if it is not necessary to pass the object through the hollow portion 400 of the core 4, the hole 90 may not be provided in the shielding portion 9. Moreover, when providing the shielding part 9, it is desirable to provide a fixed space | interval between the coil 5 and the shielding part 9 so that the core 4 and the coil 5 may not short-circuit via the shielding part 9. FIG.

  By the way, the force sensor 2 of the present embodiment can be reduced in thickness as compared with the conventional magnetostrictive load sensor and the force sensor 100 disclosed in the reference example, so that it is used instead of, for example, a washer. Is possible in the future. For this reason, the force detection apparatus 1 using the force sensor 2 of the present embodiment can be used for detecting a tightening axial force when, for example, a bolt is tightened on a ceiling or a wall.

  Hereinafter, an example of detecting the tightening axial force of the bolt B1 using the force detection device 1 of the present embodiment will be described with reference to FIG. The tightening axial force refers to a load along the axial direction of the bolt B1 applied to the construction material A1 (for example, a wall or a ceiling) when the bolt B1 is tightened with the nut N1 (see FIG. 12B).

  In this embodiment, the force detection device 1 is configured by housing a force sensor 2 and a substrate 300 on which the detection circuit 3 is mounted in a case 10 as shown in FIG. 12A. The case 10 is formed of, for example, a resin material, and includes a semi-disc-shaped first case 10A that protects the force sensor 2 and a flat rectangular parallelepiped second case 10B that protects the substrate 300. Unlike the conventional ferromagnetic case used for reducing the external magnetic field, the case 10 does not participate in the formation of the magnetic path M1. Therefore, the case 10 only needs to have a strength capable of withstanding the load, and can be formed thin.

  The first case 10A is provided with a circular through hole 10C in plan view in order to pass the shaft portion B10 of the bolt B1. The shaft portion B10 of the bolt B1 passes through the through hole 10C and the hollow portion 400 of the core 4.

  Hereafter, the usage method of the force detection apparatus 1 in this Example is demonstrated. First, the bolt B1 is passed from the back side (the lower side in FIG. 12B) of the building material A1. In FIG. 12B, the head of the bolt B1 is not shown. Next, the through hole 10 </ b> C and the hollow portion 400 of the core 4 are passed through the shaft portion B <b> 10 protruding to the front side (upper side in FIG. 12B) of the building material A <b> 1. Then, the nut N1 is passed through the shaft portion B10 and tightened so as to sandwich the first case 10A with the building material A1. Then, the tightening axial force of the bolt B1 is applied to the load receiving portion 40 of the core 4 via the first case 10A. Therefore, the force detection device 1 can detect the tightening axial force of the bolt B <b> 1 by detecting the load applied by the detection circuit 3 to the load receiving portion 40.

  As described above, the force sensor 2 of this embodiment can be used instead of a washer. Therefore, for example, if the force sensor 2 of the present embodiment is attached as a washer to an anchor bolt (not shown) used to suspend the ceiling plate of the tunnel, the tightening axial force of the anchor bolt is monitored at a location away from the site. It is also possible to do.

DESCRIPTION OF SYMBOLS 1 Force detection apparatus 2 Force sensor 3 Detection circuit 4 Core 40 Load receiving part 400 Hollow part 41 Mounting part 43 Air gap 5 Coil 6 Protection part 7, 8 Bobbin 9 Shielding part M1 Magnetic path

Claims (11)

A core having a hollow portion formed of a magnetic material, and a coil attached to the core,
In the core, a magnetic path through which a magnetic flux generated when the coil is energized is formed along the circumferential direction of the hollow portion,
The core is provided with a load receiving portion for receiving a load on one surface in a crossing direction intersecting a surface on which the magnetic path is formed.   The force sensor according to claim 1, further comprising a structure that avoids a load applied to the coil. In the structure, the core is a structure in which the dimension in the intersecting direction is made smaller than other parts in an attachment portion to which the coil is attached,
3. The force sensor according to claim 2, wherein a dimension of the mounting portion in the intersecting direction is set so that the coil is within a dimension of the other portion in the intersecting direction.   The force sensor according to claim 2, wherein the structure is a protective portion that covers at least the coil on the load receiving portion side in the intersecting direction. Comprising a bobbin attached to a portion of the core;
The force sensor according to any one of claims 1 to 4, wherein the coil is configured by winding a conducting wire around the core via the bobbin. The core has a gap in a part of the hollow portion in the circumferential direction,
The force sensor according to claim 5, wherein the bobbin is attached to the core so as to cover the gap.   The force sensor according to any one of claims 1 to 6, further comprising a shielding portion that is made of a metal material and covers at least a part of the core.   A force detection device comprising: the force sensor according to any one of claims 1 to 7; and a detection circuit that detects a load applied to the load receiving portion based on a change in inductance of the coil. .   A force detection device comprising: the force sensor according to any one of claims 1 to 7; and a detection circuit that detects a load applied to the load receiving portion based on a change in conductance of the coil. . In the force sensor according to any one of claims 1 to 7, supplying a current to the coil;
And a step of detecting a load in the crossing direction applied to the load receiving portion based on a change in inductance of the coil. In the force sensor according to any one of claims 1 to 7, supplying a current to the coil;
And a step of detecting a load in the crossing direction applied to the load receiving portion based on a change in conductance of the coil.

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