Load sensor

Abstract

A load sensor (1) comprises: a base member (50); a plurality of sensor units (40) that are installed on the upper surface (51) of the base member (50) and are separated by a gap (GP) extending radially from the center (51a) of the base member (50); a cover member (20) that covers the upper surface (41) of the plurality of sensor units (40); and a support member (30) that is interposed between the base member (50) and the cover member (20) in a portion of a gap (GP) including at least the center (51a), the support member (30) being capable of rolling relative to the base member (50).

Description

Load Sensor

[0001] The present invention relates to a load sensor that detects an externally applied load based on a change in capacitance.

[0002] Load sensors for detecting applied loads have been used in various fields. For example, Patent Document 1 (Patent Document 1) describes a detection device including a sensor substrate having a detection area where multiple pressure sensors are arranged, elastic protrusions that elastically deform in response to an external force, and an actuation substrate on whose underside the elastic protrusions are provided. In this detection device, the elastic protrusions arranged on the underside of the actuation substrate deform in response to the direction and magnitude of an external force applied to the upper surface of the actuation substrate, causing the center of gravity of the elastic protrusions to move from the reference point of the multiple pressure sensors provided on the sensor substrate. The pressure sensors detect the external force using a resistive or capacitive method, and the X-, Y-, and Z-axis directional components of the external force are calculated based on the detected values ​​of the multiple pressure sensors.

[0003] JP 2013-142613 A

[0004] In the load sensor having the above configuration, the elastic projections and the biasing substrate must be provided outside the sheet-like sensor substrate, which makes the load sensor thick and complicated in configuration.

[0005] In view of the above problem, an object of the present invention is to provide a load sensor that is thin and simple in configuration and that can detect load components in a direction perpendicular to a surface receiving the load and in a direction parallel to this surface.

[0006] A load sensor according to a main aspect of the present invention comprises a base member, a plurality of sensor units installed on the upper surface of the base member and separated by gaps extending radially from the center of the base member, a cover member covering the upper surfaces of the plurality of sensor units, and a support member interposed between the base member and the cover member in at least the portion of the gap including the center and capable of rolling relative to the base member.

[0007] According to the load sensor of this aspect, when a load is applied in a direction perpendicular to the top surface of the cover member (the surface receiving the load), the load is applied to the top surfaces of the multiple sensor units via the cover member, and the vertically applied load can be detected based on the detection signals of the multiple sensor units. On the other hand, when a load is applied obliquely to the top surface of the cover member (directions perpendicular and parallel to the surface receiving the load), the support member rolls and tilts in the direction of the applied load, causing the portion of the cover member supported by the support member to tilt as well. This changes the distribution of the loads applied to the top surfaces of the multiple sensor units via the cover member, resulting in a difference in the loads detected by each sensor unit. Therefore, based on this difference, the load parallel to the surface receiving the load can be detected, and the load perpendicular to the surface receiving the load can be detected based on the sum of the loads detected by the multiple sensor units. Therefore, the load components perpendicular to the surface receiving the load and parallel to the surface can be detected. Furthermore, because the support member is disposed between the base member and the cover member in the gap separating the multiple sensor units, the load sensor can be constructed thin and simple.

[0008] As described above, according to the present invention, it is possible to provide a load sensor that is thin and simple in configuration and that can detect load components in directions perpendicular to a surface receiving the load and in directions parallel to this surface.

[0009] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0010] FIG. 1 is an exploded perspective view schematically illustrating the configuration of a load sensor according to the first embodiment. FIG. 2(a) is a perspective view schematically illustrating the configuration of a support member according to the first embodiment. FIG. 2(b) is a view schematically illustrating a CS1-CS2 cross section according to the first embodiment. FIG. 3 is an exploded perspective view schematically illustrating the configuration of one sensor unit according to the first embodiment. FIGS. 4(a) and 4(b) are cross-sectional views schematically illustrating the sensor unit in an unloaded state and a loaded state according to the first embodiment, respectively. FIG. 5 is a perspective view schematically illustrating the configuration of a load sensor according to the first embodiment. FIG. 6 is a plan view schematically illustrating the configuration of a load sensor according to the first embodiment. FIGS. 7(a) and 7(b) are cross-sectional views schematically illustrating the load sensor in an unloaded state and a loaded state according to the first embodiment, respectively. FIG. 8(a) is a perspective view schematically illustrating a load profile according to a simulation of the first embodiment. FIG. 8(b) is a perspective view schematically illustrating the configuration of a load sensor of Comparative Example 1 according to a simulation of the first embodiment. FIGS. 9( a) and 9(b) are perspective views schematically illustrating the configurations of load sensors of Comparative Examples 2 and 3, respectively, in the simulation of Embodiment 1. FIGS. 10(a) and 10(b) are perspective views schematically illustrating the configurations of load sensors of Comparative Examples 4 and 5, respectively, in the simulation of Embodiment 1. FIGS. 11(a) and 11(b) are perspective views schematically illustrating the configurations of the load sensors of the Reference Example and Embodiment 1, respectively, in the simulation of Embodiment 1. FIGS. 12(a) and 12(b) are graphs illustrating the simulation results under Conditions 1 and 2, respectively, in the simulation of Embodiment 1. FIGS. 13(a) and 13(b) are graphs illustrating the simulation results under Conditions 3 and 4, respectively, in the simulation of Embodiment 1. FIG. 14 is a graph illustrating the simulation results under Condition 5, respectively, in the simulation of Embodiment 1. FIG. 15 is an exploded perspective view schematically illustrating the configuration of a load sensor according to Embodiment 2. FIGS. 16(a) to 16(c) are cross-sectional views schematically illustrating the configurations of the support members of the load sensor according to Embodiment 2, respectively, in the simulation of Embodiment 2. FIG. 17 is a graph showing the simulation results under condition 2 according to the simulation of the second embodiment.FIGS. 18( a) and 18(b) are cross-sectional views each schematically showing the configuration of a support member according to Modification Example 1. FIG. 19 is a perspective view each schematically showing the configuration of a support member according to Modification Example 2. FIG. 20(a) is a plan view each schematically showing the configuration of a load sensor according to Modification Example 3. FIG. 20(b) is a perspective view each schematically showing the configuration of a support member according to Modification Example 3. FIG. 21(a) is a plan view each schematically showing the configuration of a load sensor according to Modification Example 4. FIG. 21(b) is a perspective view each schematically showing the configuration of a support member according to Modification Example 4. FIG. 22 is a plan view each schematically showing the configuration of a load sensor according to Modification Example 5. FIG. 23 is a perspective view each schematically showing the configuration of a load sensor according to Modification Example 6. FIG. 24 is an exploded perspective view each schematically showing the configuration of one sensor unit according to Modification Example 7. FIGS. 25(a) and 25(b) are cross-sectional views each schematically showing the sensor unit in an unloaded state and a loaded state according to Modification Example 7, respectively.

[0011] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0012] The load sensor according to the present invention can be applied to systems and electronic devices that perform processing in response to loads applied in planar and vertical directions.

[0013] An example of such a system is a transfer system using a robot hand. In this case, a load sensor is installed on the gripping surface of the robot hand to detect loads in two-dimensional directions parallel to the gripping surface and in directions perpendicular to the gripping surface. From the detection results, the weight, posture, etc. of the object gripped by the robot hand can be obtained.

[0014] Examples of electronic devices include game controllers, touch panels, electronic pens, etc. In electronic devices, a load sensor is provided in an input unit that receives input from a user in a planar direction and a vertical direction.

[0015] The load sensor in the following embodiments is a capacitance type load sensor that is typically provided in the load sensors of the above-mentioned systems and electronic devices. Such load sensors are also sometimes called "capacitive pressure sensor elements," "capacitive pressure detection sensor elements," "pressure-sensitive switch elements," etc.

[0016] The load sensor in the following embodiment is connected to a detection circuit, and the load sensor and the detection circuit constitute a load detection device. The following embodiment is one embodiment of the present invention, and the present invention is not limited to the following embodiment.

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, each drawing is labeled with X, Y, and Z axes that are orthogonal to one another. The Z axis direction is the height direction of the load sensor. For convenience, the X-Y plane will be referred to as the horizontal plane, the positive direction of the Z axis will be referred to as the upward direction, the negative direction of the Z axis will be referred to as the downward direction, and the Z axis direction will be referred to as the vertical direction.

[0018] First Embodiment FIG. 1 is an exploded perspective view schematically showing the configuration of a load sensor 1 according to a first embodiment.

[0019] The load sensor 1 includes a plate-shaped member 10, a cover member 20, a support member 30, four sensor units 40, and a base member 50. A central axis CA is illustrated in Fig. 1. The central axis CA is an axis that passes through the center of the load sensor 1 in a plan view and is parallel to the Z-axis direction.

[0020] The plate-shaped member 10 has a square shape in a plan view. The plate-shaped member 10 is symmetrical in the X-axis direction and the Y-axis direction about a central axis CA. The top surface 11 and bottom surface 12 of the plate-shaped member 10 are parallel to a horizontal plane. The central axis CA passes through the center 11a of the top surface 11. In the first embodiment, the plate-shaped member 10 is smaller than the cover member 20 in a plan view. This prevents the plate-shaped members 10 of adjacent load sensors 1 from abutting against and interfering with each other when multiple load sensors 1 are arranged side by side. The material constituting the plate-shaped member 10 is an electrically insulating material, such as polyethylene terephthalate, polycarbonate, or polyimide.

[0021] The plate-like member 10 does not necessarily have to be included in the load sensor 1, and the upper surface 21 of the cover member 20 may be the surface onto which an external load is applied to the load sensor 1. When the plate-like member 10 is omitted in this way, the load sensor 1 can be configured to be thinner.

[0022] The cover member 20 has a square shape in a plan view. The plate-like member 10 has a shape that is symmetrical in the X-axis direction and the Y-axis direction about the central axis CA. The upper surface 21 and the lower surface 22 of the cover member 20 are parallel to the horizontal plane. The cover member 20 is disposed opposite the upper surfaces 41 of the four sensor units 40. The cover member 20 is made of a flexible and electrically insulating material, such as ethylene propylene diene rubber (EPDM).

[0023] The support member 30 has a plus (+) shape in a plan view. The support member 30 has a shape that is symmetrical in the X-axis direction and the Y-axis direction about the central axis CA. The upper surface 31 of the support member 30 is a surface parallel to the horizontal plane, and the lower surface 32 of the support member 30 has a curved shape. The configuration of the support member 30 will be described later with reference to Figures 2(a) and (b). The upper surface 31 of the support member 30 is attached to the lower surface 22 of the cover member 20 with an adhesive or the like.

[0024] The support member 30 is made of a material that does not substantially deform under loads within the detection range of the load sensor 1. Materials that make up the support member 30 include, for example, polyethylene terephthalate, polycarbonate, polyimide, or resins or metals that have rigidity equal to or greater than these engineering plastics. Because the support member 30 is disposed in close proximity to the four sensor units 40 as described below, it is preferably made of a non-conductive material to prevent electrical conduction between the four sensor units 40.

[0025] The sensor units 40 are sensors for detecting loads in the Z-axis direction. Each sensor unit 40 has a square shape in a plan view. The configuration of the sensor units 40 will be described later with reference to FIGS. 3 to 4(b).

[0026] The base member 50 has a square shape in a plan view. The base member 50 is symmetrical in the X-axis direction and the Y-axis direction with respect to a central axis CA. The upper surface 51 and the lower surface 52 of the base member 50 are parallel to the horizontal plane. The central axis CA passes through the center 51a of the upper surface 51. The material constituting the base member 50 is an electrically insulating material, and is, for example, the same as the material constituting the plate-like member 10.

[0027] Fig. 2A is a perspective view that schematically illustrates the configuration of the support member 30. In Fig. 2A, the support member 30 is shown upside down from the state in Fig. 1, and the positive direction of the Z axis faces downward.

[0028] The central axis CA1 of the support member 30 is parallel to the Z-axis direction and coincides with the central axis CA (see FIG. 1 ) of the load sensor 1. The lower surface 32 of the support member 30 has a convex shape that protrudes in the negative Z-axis direction at the center 32a of the lower surface 32. Specifically, the lower surface 32 has a curved shape similar to the surface shape of a true sphere. The central axis CA1 passes through the center 32a of the lower surface 32. The support member 30 has four arms 30a that extend from the central axis CA1 in the positive X-axis direction, negative X-axis direction, positive Y-axis direction, and negative Y-axis direction, respectively.

[0029] FIG. 2B is a diagram schematically showing the CS1-CS2 cross section of FIG.

[0030] The distance (height) between the lower surface 32 and the upper surface 31 in the Z-axis direction is longest at the center 32 a, H1, and shortest at the end furthest from the center 32 a, H2. The height H1 at the center 32 a of the support member 30 is the same as the height of the sensor unit 40.

[0031] If the height H1 of the support member 30 is lower than the height of the sensor unit 40, as will be described later with reference to FIG. 7B, the load is not transmitted from the cover member 20 to the support member 30, the support member 30 does not roll, and the horizontal load component cannot be detected. On the other hand, if the height H1 of the support member 30 is higher than the height of the sensor unit 40, most of the Z-axis component of the load applied to the load sensor 1 is supported by the support member 30, and the Z-axis load component cannot be properly detected. Therefore, it is preferable that the height H1 of the support member 30 be approximately the same as the height of the sensor unit 40.

[0032] FIG. 3 is an exploded perspective view showing a schematic configuration of one sensor unit 40. As shown in FIG.

[0033] The sensor unit 40 includes a substrate 110, a first electrode 120, a dielectric 130, a second electrode 140, and a substrate 150. The substrate 110, the first electrode 120, the dielectric 130, the second electrode 140, and the substrate 150 all have substantially the same square shape in plan view.

[0034] The substrate 110 is a plate-shaped member. An upper surface 111 and a lower surface 112 of the substrate 110 are parallel to a horizontal plane. The upper surface 111 is the upper surface 41 of the sensor unit 40. The material that constitutes the substrate 110 is, for example, polyethylene terephthalate, polycarbonate, polyimide, or the like.

[0035] The first electrode 120 is made of a conductive metal material. The material of the first electrode 120 is, for example, In. ２ O ３ , ZnO and SnO ２ The first electrode 120 is provided with a conductor (not shown) for connecting to a detection circuit external to the load sensor 1. The dielectric 130 is made of an electrically insulating material. Examples of the material for the dielectric 130 include polypropylene resin, polyethylene terephthalate resin, polyimide resin, polyphenylene sulfide resin, and Al. ２ O ３ and Ta ２ O ５ etc.

[0036] The second electrode 140 includes a base portion 141 and a plurality of protrusions 142. The base portion 141 has a plate shape, and the protrusions 142 are formed to protrude upward from the upper surface of the base portion 141. The base portion 141 and the protrusions 142 are integrally formed. The plurality of protrusions 142 are arranged in a lattice pattern. In the example shown in FIG. 3 , a total of 36 protrusions 142 are formed on the upper surface of the base portion 141, six in the X-axis direction and six in the Y-axis direction. The cross-sectional area of ​​the protrusions 142 decreases as they progress in the positive direction of the Z-axis. A surface 142a parallel to the horizontal plane is formed at the tip of each protrusion 142. The protrusions 142 have a truncated cone shape obtained by cutting a predetermined cone shape at the position of the surface 142a.

[0037] The second electrode 140 is composed of a non-conductive elastic material and a conductive filler mixed into the elastic material. The elastic material that constitutes the second electrode 140 is a resin, rubber, or the like, such as silicone rubber. The conductive filler that constitutes the second electrode 140 is a conductive metal, such as carbon (C). The conductive filler is dispersed within the elastic material. This makes the base portion 141 and the protrusions 142 conductive and elastic. A conductor (not shown) is installed in the base portion 141 for connecting to a detection circuit external to the load sensor 1.

[0038] The substrate 150 is a support member for placing the first electrode 120, the dielectric 130, and the second electrode 140. The material constituting the substrate 150 is, for example, the same as the material constituting the substrate 110.

[0039] When assembling the sensor unit 40, the second electrode 140 is placed on the upper surface 151 of the substrate 150. The dielectric 130 is formed on the lower surface of the first electrode 120, for example, by coating. A structure consisting of the first electrode 120 and the dielectric 130 is overlaid on the upper surface of the second electrode 140 so that the dielectric 130 faces the second electrode 140. Then, the substrate 110 is placed on top of the first electrode 120, and the periphery of the substrate 110 is attached to the substrate 150 by an attachment member. In this manner, the sensor unit 40 is completed.

[0040] Fig. 4(a) is a cross-sectional view schematically showing the sensor unit 40 in an unloaded state (a state in which no load is applied). Fig. 4(b) is a cross-sectional view schematically showing the sensor unit 40 in a loaded state (a state in which a load is applied). Figs. 4(a) and 4(b) show a cross-section of the sensor unit 40 when cut along a plane parallel to the X-Z plane passing through the center of the protrusion 142. In Figs. 4(a) and 4(b), for convenience, the number of protrusions 142 aligned in the X-axis direction is five.

[0041] As shown in Fig. 4(a), in the initial state where no load is applied, only the surface 142a at the tip of the protrusion 142 contacts the dielectric 130. When a load is then applied to the upper surface 111 of the substrate 110, the protrusion 142 contracts in response to an increase in the load, as shown in Fig. 4(b). This increases the contact area between the protrusion 142 and the dielectric 130, and shortens the distance between the dielectric 130 and the base portion 141.

[0042] When the contact area between the protrusion 142 and the dielectric 130 and the distance between the dielectric 130 and the base portion 141 change with the load, the capacitance between the first electrode 120 and the second electrode 140 changes with the load. This capacitance is proportional to the total contact area between the dielectric 130 and the second electrode 140, and inversely proportional to the thickness of the dielectric 130 and the distance between the dielectric 130 and the base portion 141. The potential reflecting this change in capacitance is measured in an external control circuit, thereby detecting the load applied to the sensor portion 40 in the negative direction of the Z axis.

[0043] Returning to FIG. 1 , when assembling the load sensor 1, the four sensor units 40 are placed on the upper surface 51 of the base member 50 while being spaced apart from one another via the gap GP. Next, the upper surface 31 of the support member 30 is placed on the lower surface 22 of the cover member 20. Then, the cover member 20 is placed on the upper surface 41 of the four sensor units 40 so that the support member 30 is positioned within the gap GP. The periphery of the cover member 20 and the periphery of the base member 50 are bonded together, for example, via a spacer. The plate-like member 10 is placed on the upper surface 21 of the cover member 20 with an adhesive or the like. In this way, the load sensor 1 is completed.

[0044] FIG. 5 is a perspective view schematically showing the configuration of the load sensor 1. As shown in FIG.

[0045] The lower surface of the load sensor 1 (lower surface 52 of the base member 50) is placed on a surface that is the target of load detection. When a load is applied to the upper surface of the load sensor 1 (upper surface 11 of the plate-like member 10) in a direction perpendicular to the upper surface 11 and a direction parallel to the upper surface 11, the applied load is transmitted to the four sensor units 40 via the plate-like member 10 and the cover member 20. At this time, the load applied to the load sensor 1 is detected based on the load detected by the four sensor units 40.

[0046] A single load sensor 1 may be installed on a surface that is the target of load detection, or multiple load sensors 1 may be installed side by side. When multiple load sensors 1 are installed, the load applied to a large surface that is the target of load detection can be detected based on the loads detected by the multiple load sensors 1.

[0047] Fig. 6 is a plan view schematically showing the configuration of the load sensor 1. For convenience, the plate-like member 10 and the cover member 20 are omitted from Fig. 6.

[0048] The four sensor units 40 are spaced apart from one another via a gap GP. The gap GP has a shape that extends radially from the center 51a of the upper surface 51 of the base member 50. Specifically, the gap GP has two straight line portions GP1 that intersect at the center 51a, one of which extends parallel to the X-axis direction and the other of which extends parallel to the Y-axis direction. As a result, the gap GP has a plus (+) shape in a plan view, and the four sensor units 40 are arranged in a grid pattern so as to be aligned in the X-axis and Y-axis directions.

[0049] The support member 30 is disposed in the gap GP so that the center 32a of the lower surface 32 of the support member 30 coincides with the center 51a of the base member 50 in a plan view. As a result, the two arms 30a extending in the X-axis direction of the support member 30 are disposed on the straight line portion GP1 extending in the X-axis direction, and the two arms 30a extending in the Y-axis direction of the support member 30 are disposed on the straight line portion GP1 extending in the Y-axis direction.

[0050] In the first embodiment, the lengths of the support member 30 in the X-axis direction and the Y-axis direction are shorter than the lengths of the region consisting of the four sensor units 40. That is, in a plan view, the support member 30 is smaller than the region consisting of the four sensor units 40. In this case, the support member 30 can be configured compactly and can roll efficiently based on the load applied near the center 51a. Note that the lengths of the support member 30 in the X-axis direction and the Y-axis direction may be equal to the lengths of the region consisting of the four sensor units 40 in the X-axis direction and the Y-axis direction.

[0051] Next, the behavior of the load sensor 1 when a load is applied to the load sensor 1 will be described.

[0052] Fig. 7(a) is a cross-sectional view schematically showing the load sensor 1 in a no-load state (a state in which no load is applied). Fig. 7(b) is a cross-sectional view schematically showing the load sensor 1 in a loaded state (a state in which a load is applied). Figs. 7(a) and 7(b) are diagrams schematically showing a cross section of the load sensor 1 taken along the X-Z plane passing through the central axis CA.

[0053] 7A, in the initial state where no load is applied, only the center 32a located at the lowest position on the lower surface 32 of the support member 30 contacts the upper surface 51 of the base member 50. When a load including a component in the negative Z-axis direction and a component in the horizontal direction is then applied to the upper surface 11 of the plate-like member 10, the support member 30 rolls.

[0054] As shown in FIG. 7B , when the horizontal load component includes a component in the positive X-axis direction, the plate-like member 10 receives a load obliquely inclined from the negative Z-axis direction toward the positive X-axis direction, causing the support member 30 to roll in the X-axis direction. At this time, the contact position between the lower surface 32 of the support member 30 and the upper surface 51 of the base member 50 moves from center 32a to position 32b, causing the arm 30a on the positive X-axis side to descend and the arm 30a on the negative X-axis side to ascend. This pulls down the lower surface 22 of the cover member 20 near the arm 30a on the positive X-axis side, and pushes up the lower surface 22 of the cover member 20 near the arm 30a on the negative X-axis side. The load acting on the two sensor units 40 located on the positive X-axis side becomes greater than the load acting on the two sensor units 40 located on the negative X-axis side. Therefore, in the case of Figure 7 (b), the component of the load in the X-axis direction can be detected based on the degree of imbalance between the load detected by the two sensor units 40 located on the positive side of the X-axis and the load detected by the two sensor units 40 located on the negative side of the X-axis.

[0055] Similarly, when the horizontal load component includes a Y-axis component, the support member 30 rolls in the Y-axis direction. This makes it possible to detect the Y-axis load component based on the degree of imbalance between the load detected by the two sensor units 40 located on the positive side of the Y axis and the load detected by the two sensor units 40 located on the negative side of the Y axis.

[0056] In this way, when a load including a downward component and a horizontal component is applied, the rolling direction and amount of rolling of the support member 30 changes depending on the direction and magnitude of the horizontal load component. In this case, the direction and magnitude of the horizontal load component can be detected based on the degree of load imbalance detected by the four sensor units 40. Furthermore, the downward load can be detected based on the sum of the loads detected by the four sensor units 40.

[0057] 6, the sensor unit 40 located on the positive side of the X-axis and the positive side of the Y-axis is designated as sensor unit SR1, the sensor unit 40 located on the positive side of the X-axis and the negative side of the Y-axis is designated as sensor unit SR2, the sensor unit 40 located on the negative side of the X-axis and the positive side of the Y-axis is designated as sensor unit SR3, and the sensor unit 40 located on the negative side of the X-axis and the negative side of the Y-axis is designated as sensor unit SR4. The loads detected by sensor units SR1, SR2, SR3, and SR4 are designated as Ld1, Ld2, Ld3, and Ld4, respectively.

[0058] The load component in the X-axis direction is detected based on the absolute value of (Ld1 + Ld2) - (Ld3 + Ld4), and whether the load component in the X-axis direction is in the positive or negative X-axis direction is detected based on the sign of this difference. The load component in the Y-axis direction is detected based on the absolute value of (Ld1 + Ld3) - (Ld2 + Ld4), and whether the load component in the Y-axis direction is in the positive or negative Y-axis direction is detected based on the sign of this difference. The load component in the negative Z-axis direction is detected based on Ld1 + Ld2 + Ld3 + Ld4. The load components in the X-axis direction, Y-axis direction, and negative Z-axis direction are detected in a control circuit external to the load sensor 1.

[0059] Alternatively, the load component in the direction from the center 51a toward the sensor unit SR1 may be detected based on Ld1-Ld4, and the load component in the direction from the center 51a toward the sensor unit SR2 may be detected based on Ld2-Ld3. In this case, the load components in the directions from the center 51a toward the sensor units SR1 and SR2 (directions forming angles of ±45° with respect to the X-axis direction) are detected in a control circuit external to the load sensor 1.

[0060] <Load detection simulation> Next, the inventors performed the following simulation to verify whether the load components in the negative Z-axis direction and horizontal direction can be properly detected when a load is applied diagonally to the Z-axis direction.

[0061] FIG. 8A is a perspective view that schematically shows a load profile according to this simulation.

[0062] In this simulation, a common load was applied evenly in a diagonal direction to the plate-shaped member 10 for each of the load sensors of Comparative Examples 1 to 5, Reference Example, and Embodiment 1. Specifically, the load component Fz in the negative Z-axis direction was set to 1 N, the load component Fx in the X-axis direction was set to 0.1 N, and the load component Fy in the Y-axis direction was set to 0.1 N. When the thickness of the plate-shaped member 10 was set to zero under the conditions described below, the same load as above was applied evenly in a diagonal direction to the region of the lower surface 12 of the plate-shaped member 10.

[0063] Fig. 8(b) is a perspective view that schematically shows the configuration of the load sensor CE1 of Comparative Example 1. In Fig. 8(b), for convenience, the plate-shaped member 10 and the cover member 20 are shown in a see-through state.

[0064] In the load sensor CE1 of Comparative Example 1, the thickness H3 of the plate-shaped member 10 was set to 0 mm or 1.0 mm depending on the conditions described below. The thickness H4 of the cover member 20 was set to 0.5 mm. The length L1 of one side of the lower surface 12 of the plate-shaped member 10 was set to 13 mm. The thickness H5 of the sensor unit 40 was set to 1.0 mm, and the length L2 of one side of the sensor unit 40 was set to 8.0 mm. The interval W1 between two adjacent sensor units 40 in the X-axis direction or Y-axis direction, i.e., the width of the straight portion GP1 of the gap GP (see FIG. 6), was set to 2.0 mm.

[0065] 9(a) to 11(b) are perspective views each schematically illustrating the configuration of a load sensor CE2 of Comparative Example 2, a load sensor CE3 of Comparative Example 3, a load sensor CE4 of Comparative Example 4, a load sensor CE5 of Comparative Example 5, a load sensor RE of the reference example, and a load sensor EM1 of Embodiment 1. In Fig. 9(a) to Fig. 11(b), for convenience, the cover member 20 is shown in a see-through state, the plate-like member 10 is not shown, and the underside 12 is indicated by a dotted line.

[0066] 9A, the load sensor CE2 of Comparative Example 2, unlike Comparative Example 1, includes a cylindrical support member 60 in the center of the gap GP. The upper and lower surfaces of the support member 60 are parallel to the horizontal plane. The upper surface of the support member 60 is fixed to the lower surface of the cover member 20, and the lower surface of the support member 60 is not fixed to the base member 50. In Comparative Example 2, the diameter Φ of the support member 60 is 1 mm, and the height H6 of the support member 60 is 1 mm.

[0067] 9B, the load sensor CE3 of Comparative Example 3 differs from Comparative Example 2 in the diameter of the support member 60. In Comparative Example 3, the diameter Φ of the support member 60 was set to 2 mm.

[0068] 10A, the load sensor CE4 of Comparative Example 4 differs from Comparative Example 2 in the shape of the four sensor units 40 in a plan view and in the diameter of the support member 60. The sensor units 40 of Comparative Example 4 have an octagonal shape in a plan view, with the corners of the sensor units 40 of Comparative Example 2 cut out. This makes the center of the gap GP larger than in Comparative Example 2. In Comparative Example 4, the diameter Φ of the support members 60 is 5 mm.

[0069] 10B, the load sensor CE5 of Comparative Example 5 includes a support member 70 instead of the support member 60 of Comparative Example 2. The support member 70 has a shape similar to the support member 30 of Embodiment 1 in a plan view. However, the lower surface of the support member 70 is parallel to the horizontal plane. In Comparative Example 5, the width L3 of the support member 70 is 8 mm, the width of the arm portion 70a of the support member 70 is 1 mm, and the height H7 of the support member 60 is 1 mm.

[0070] 11A, the load sensor RE of the reference example is different from the comparative example 2 in that it further includes four support members 80 around the central support member 60. The four support members 80 are respectively arranged on linear portions GP1 located on the X-axis positive side, the X-axis negative side, the Y-axis positive side, and the Y-axis negative side of the central support member 60. In the reference example, like the central support member 60, the diameter Φ of each support member 80 is 1 mm, and the height of each support member 60 is 1 mm.

[0071] 11B, the load sensor EM1 of the first embodiment includes the support member 30 shown in FIGS. 1 to 2B at the center of the gap GP, in comparison with the comparative example 1. In the first embodiment, the width L3 of the support member 30 is 8 mm, the width of the arm portion 30a of the support member 30 is 1 mm, and the heights H1 and H2 of the support member 30 (see FIG. 2B) are 1 mm and 0.8 mm, respectively.

[0072] In this simulation, each load sensor was configured as shown in Figures 8(b) to 11(b), and a load was applied to each load sensor as shown in Figure 8(a). At this time, the configuration of each load sensor was changed according to conditions 1 to 5, and the simulation results shown in Figures 12(a) to 14 were obtained under conditions 1 to 5.

[0073] The support member of each load sensor was a rigid body under conditions 1 to 4, i.e., a member that did not deform in the simulation, and was rubber under condition 5, i.e., a member that deformed in the simulation. The elastic modulus of the support member under condition 5 was set to the same elastic modulus as ethylene propylene diene rubber (EPDM). The coefficient of friction between each support member and the base member 50, and between the cover member 20 and the sensor unit 40, was set to 0 under condition 1, and 0.1 under conditions 2, 4, and 5. The thickness H3 of the plate-like member 10 was set to 0 mm under conditions 1 to 3 and 5, and 1.0 mm under condition 4.

[0074] In the following simulation results, the "X direction" indicates the difference between the sum of the loads detected by the sensor units SR1 and SR2 (Ld1 + Ld2) and the sum of the loads detected by the sensor units SR3 and SR4 (Ld3 + Ld4). The "Y direction" indicates the difference between the sum of the loads detected by the sensor units SR1 and SR3 (Ld1 + Ld3) and the sum of the loads detected by the sensor units SR2 and SR4 (Ld2 + Ld4). "Diagonal 1" indicates the difference between the load Ld1 detected by the sensor unit SR1 and the load Ld4 detected by the sensor unit SR4. "Diagonal 2" indicates the difference between the load Ld3 detected by the sensor unit SR3 and the load Ld2 detected by the sensor unit SR2.

[0075] In the following simulation results, "vertical load" indicates the negative Z-axis component Fz (1 N in this simulation) of the load applied to the load sensor. The left axis of the graphs showing the simulation results is the horizontal load detection rate. The horizontal load detection rate is the value obtained by dividing the values ​​in the X direction, Y direction, diagonal 1, and diagonal 2 by the vertical load. In each figure, the horizontal load detection rate is shown as a bar graph. The right axis is the vertical load detection rate. The vertical load detection rate is the value obtained by dividing the total value of the loads Ld1, Ld2, Ld3, and Ld4 detected by the four sensor units 40 by the vertical load. In each figure, the vertical load detection rate is shown as a line graph.

[0076] 12(a), the vertical load detection rate of the load sensors CE1 to CE5 under condition 1 is slightly higher than that of the load sensors RE and EM1, but the horizontal load detection rate of the load sensors CE1 to CE5 under condition 1 is low at 0.4% or less. The reason for the low horizontal load detection rate is that the lower surface of the support member is parallel to the upper surface 51 of the base member 50, so the support member hardly rolls in response to a horizontal load, and there is almost no load imbalance among the four sensor units 40. Therefore, it can be said that while the load sensors CE1 to CE5 under condition 1 can detect a load in the Z-axis direction, it is difficult to properly detect a horizontal load.

[0077] On the other hand, for the load sensor EM1 under Condition 1, the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 3% to 4%. That is, the difference values ​​in the X direction, Y direction, and diagonal 1 were approximately 3% to 4% of the actual applied vertical load (Fz = 1 N). In this case, a horizontal load acts on the top surface 21 of the cover member 20. This horizontal load imparts torque to the support member 30 via the cover member 20, causing the support member 30 to roll in response to the diagonal load, resulting in a greater imbalance in the load distribution acting on the four sensor units 40. This results in a high horizontal load detection rate. Furthermore, since the actual applied loads in the X-axis and Y-axis directions (Fx = 0.1 N, Fy = 0.1 N) are 10% of the vertical load (Fz = 1 N), the horizontal difference value of approximately 3% to 4% as described above can be said to be sufficient for detecting a horizontal load.

[0078] Furthermore, the horizontal load detection rate for diagonal 2 was low at about 0.5%, which corresponds to the fact that no load was applied in the direction indicated by diagonal 2. Furthermore, the vertical load detection rate for load sensor EM1 under condition 1 was 65%. That is, the total load value acquired by the four sensor units 40 was about 65% of the actually applied vertical load (Fz = 1 N), which was a value sufficient for detecting the load in the Z-axis direction.

[0079] Therefore, it can be said that the load sensor EM1 of condition 1 can properly detect the load in the Z-axis direction and the horizontal direction.

[0080] Even with the load sensor RE under condition 1, the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 3% to 4%, which is sufficient for detecting horizontal loads, while the horizontal load detection rate for diagonal 2 was appropriately low at approximately 0.5%. Furthermore, the vertical load detection rate was approximately 78%, which is sufficient for detecting loads in the Z-axis direction. Therefore, it can be said that the load sensor RE under condition 1 can also appropriately detect loads in the Z-axis direction and horizontal direction.

[0081] In addition, since the lower surfaces of the support members 60, 80 (see FIG. 11(a)) of the load sensor RE are parallel to the upper surface 51 of the base member 50, the support members 60, 80 do not roll at all in response to a horizontal load. However, since the coefficient of friction between the cover member 20 and the sensor units 40 is 0 under condition 1, it is believed that the cover member 20 moves relative to the four sensor units 40 due to the load, causing a load imbalance among the four sensor units 40. For this reason, it is believed that the horizontal load detection rate was high even in the load sensor RE under condition 1.

[0082] 12(b), the load sensors CE1 to CE5 under condition 2 have a slightly high vertical load detection rate but a low horizontal load detection rate, similar to condition 1 in Fig. 12(a). Therefore, it can be said that the load sensors CE1 to CE5 under condition 2 can detect loads in the Z-axis direction, but have difficulty in properly detecting loads in the horizontal direction.

[0083] On the other hand, in the load sensor EM1 under condition 2, similar to condition 1 in Figure 12(a), the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 3% to 4%, which is sufficient for detecting horizontal loads, and the horizontal load detection rate in diagonal 2 was appropriately low at approximately 0.5%. In addition, the vertical load detection rate was approximately 65%, which is sufficient for detecting loads in the Z axis direction. Therefore, it can be said that the load sensor EM1 under condition 2 can appropriately detect loads in the Z axis direction and horizontal direction.

[0084] 12A, the horizontal load detection rate in the X direction, Y direction, and diagonal 1 of the load sensor RE under condition 2 is slightly lower than that under condition 1. The reason for this is thought to be that the coefficient of friction between the cover member 20 and the sensor units 40 is larger than that under condition 1, making it difficult for the cover member 20 to move relative to the four sensor units 40 due to the load, and making it difficult for an imbalance in the load to occur among the four sensor units 40.

[0085] As shown in Fig. 13(a), the load sensors CE1 to CE5 under condition 3 have a slightly high vertical load detection rate but a low horizontal load detection rate, similar to condition 1 in Fig. 12(a) and condition 2 in Fig. 12(b). Therefore, it can be said that the load sensors CE1 to CE5 under condition 3 can detect loads in the Z-axis direction, but have difficulty in properly detecting loads in the horizontal direction.

[0086] On the other hand, for the load sensor EM1 under condition 3, similar to condition 1 in Figure 12(a) and condition 2 in Figure 12(b), the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 3% to 4%, which is sufficient for detecting horizontal loads, and the horizontal load detection rate for diagonal 2 was appropriately low at approximately 0.5%. Furthermore, the vertical load detection rate was approximately 65%, which is sufficient for detecting loads in the Z-axis direction. Therefore, it can be said that the load sensor EM1 under condition 3 can appropriately detect loads in the Z-axis direction and horizontal direction.

[0087] 12B, the horizontal load detection rate in the X direction, Y direction, and diagonal 1 of the load sensor RE under condition 3 is even lower than that under condition 2. This is thought to be because the coefficient of friction between the cover member 20 and the sensor unit 40 is even higher than that under condition 2.

[0088] As shown in FIG. 13(b), the load sensors CE1 to CE5 under condition 4 have a higher horizontal load detection rate of approximately 3% in the X direction, Y direction, and diagonal 1 compared to condition 2 in FIG. 12(b). This is because, compared to condition 2, the thickness of the plate-shaped member 10 is greater, resulting in a longer distance between the force point of the load applied to the load sensor (the top surface 11 of the plate-shaped member 10) and the fulcrum supporting the load (the top surface 21 of the cover member 20). This generates a moment on the plate-shaped member 10, which in turn causes a bias in the load distribution on the top surface 21 of the cover member 20 and a bias in the load acting on the four sensor units 40. This is thought to be the reason for the higher horizontal load detection rate. Therefore, it can be said that the load sensors CE1 to CE5 under condition 4 can properly detect loads in the Z-axis direction and horizontal direction. However, depending on the thickness of the plate-shaped member 10, the horizontal load detection rate of the load sensors CE1 to CE5 can be significantly lower, as shown in conditions 1 to 3.

[0089] On the other hand, for the load sensor EM1 under condition 4, the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 5% to 6.5%, which was sufficient for detecting horizontal loads, while the horizontal load detection rate for diagonal 2 was appropriately low at approximately 0.7%. Furthermore, the vertical load detection rate was approximately 55%, which was sufficient for detecting loads in the Z axis direction. In this case, too, the distance between the force point of the load applied to the load sensor EM1 (the top surface 11 of the plate-shaped member 10) and the fulcrum supporting the load (the top surface 21 of the cover member 20) was long. This caused a moment to be generated in the plate-shaped member 10, which in turn caused a bias in the load distribution on the top surface 21 of the cover member 20, resulting in a bias in the load acting on the four sensor units 40. Furthermore, as described above, since a horizontal load acts on the top surface 21 of the cover member 20, the horizontal load applies torque to the support member 30 via the cover member 20, causing the support member 30 to roll in response to the diagonal load, resulting in a greater imbalance in the load distribution acting on the four sensor units 40. For the above reasons, the horizontal load detection rate is even higher compared to condition 2 in Figure 12(b). Therefore, it can be said that the load sensor EM1 under condition 4 can properly detect loads in the Z-axis direction and horizontally.

[0090] In the load sensor RE under condition 4, the distance between the point of application of the load to the load sensor RE (upper surface 11 of the plate member 10) and the fulcrum supporting the load (upper surface 21 of the cover member 20) is also long. This causes a moment to be generated in the plate member 10, which in turn causes a bias in the load distribution on the upper surface 21 of the cover member 20, resulting in a bias in the load acting on the four sensor units 40. This is thought to have resulted in an even higher horizontal load compared to condition 2 in Figure 12(b).

[0091] As shown in Figure 14, for the load sensors CE1 to CE5, RE, and EM1 under condition 5, the vertical load detection rate is high, but the horizontal load detection rate is almost 0%. The reason for this is thought to be that the support members of each load sensor are made of an elastic body, so the load applied to each load sensor is absorbed by the support members and the support members do not contribute much to the load imbalance. From this result, it can be said that it is preferable to make the support members out of a rigid body.

[0092] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0093] The plurality of sensor units 40 are mounted on the upper surface 51 of the base member 50 and are separated by gaps GP extending radially from the center 51a of the base member 50. The cover member 20 covers the upper surface 41 of the plurality of sensor units 40. The support member 30 is interposed between the base member 50 and the cover member 20 in the portion of the gap GP that includes at least the center 51a, and is rollable relative to the base member 50.

[0094] With this configuration, when a load is applied in a direction perpendicular to the top surface 21 (the surface receiving the load) of the cover member 20, the load is applied to the top surfaces 41 of the multiple sensor units 40 via the cover member 20, and the vertically applied load can be detected based on the detection signals of the multiple sensor units 40. On the other hand, when a load is applied obliquely to the top surface 21 of the cover member 20 (directions perpendicular and parallel to the surface receiving the load), the support member 30 rolls and tilts in the direction of the applied load, causing the portion of the cover member 20 supported by the support member 30 to tilt as well. This changes the distribution of the loads applied to the top surfaces 41 of the multiple sensor units 40 via the cover member 20, resulting in a difference in the loads detected by each sensor unit 40. Based on this difference, the load parallel to the surface receiving the load can be detected among the oblique loads. Based on the sum of the loads detected by the multiple sensor units 40, the load perpendicular to the surface receiving the load can be detected among the oblique loads. Therefore, the load components perpendicular to the surface receiving the load and parallel to the surface receiving the load can be detected. Furthermore, since the support member 30 is disposed between the base member 50 and the cover member 20 in the gap GP that separates the multiple sensor units 40, the load sensor 1 can be configured to be thin and simple.

[0095] As shown in FIGS. 2A and 2B, the lower surface 32 of the support member 30 has a curved shape.

[0096] With this configuration, when a load is applied in an oblique direction, the support member 30 smoothly rolls and tilts, thereby stably changing the distribution of the loads applied to the multiple sensor units 40. Therefore, it is possible to accurately detect loads in a direction parallel to the surface receiving the load.

[0097] 6, the gap GP has two straight line portions GP1 that intersect at a center 51 a. The support member 30 has an arm portion 30 a that extends along at least one of the straight line portions GP1 and is rollable relative to the base member 50 in the direction in which the one straight line portion GP1 extends.

[0098] With this configuration, when a load is applied in the direction in which one straight section GP1 extends, the support member 30 rolls, and the arm section 30a on one side moves down and the arm section 30a on the other side moves up in the direction in which one straight section GP1 extends, as shown in Figure 7(b). This allows for a greater change in the distribution of the loads applied to the multiple sensor sections 40, making it possible to accurately detect loads in a direction parallel to the surface receiving the load.

[0099] Furthermore, the support member 30 has an arm portion 30a that extends along the other straight portion GP1 and is rollable relative to the base member 50 in the direction in which the other straight portion GP1 extends.

[0100] This configuration allows for accurate detection of loads in any direction parallel to the load-receiving surface. Also, horizontal loads that are diagonal to both the X-axis and Y-axis directions can be detected as the resultant force of the X-axis load and the Y-axis load.

[0101] The support member 30 is made of a material that does not substantially deform under a load in the detection range.

[0102] As shown in the simulation results for condition 5 in Figure 14, if the support member 30 is made of an elastic material, the horizontal load detection rate will be nearly 0%. In contrast, if the support member 30 is made of a material that does not substantially deform under loads within the detection range, the support member 30 will roll properly, and a difference in height will occur between the ends of the support member 30 on both sides in the rolling direction. This will allow for proper detection of loads parallel to the surface receiving the load.

[0103] The load sensor 1 further includes a plate-like member 10 placed on the upper surface 21 of the cover member 20 .

[0104] 13(b), compared to when the plate-shaped member 10 is not provided, this configuration generates a moment in the plate-shaped member 10, which causes a bias in the load distribution on the upper surface 21 of the cover member 20 and a bias in the load acting on the four sensor units 40. Therefore, it is possible to detect the load in a direction parallel to the surface receiving the load with even greater accuracy.

[0105] As shown in FIG. 3, the sensor unit 40 includes a first electrode 120 (electrode), a second electrode 140 (conductive elastic body) facing the first electrode 120 (electrode), and a dielectric 130 arranged between the first electrode 120 (electrode) and the second electrode 140 (conductive elastic body).

[0106] According to this configuration, the sensor unit 40 can be configured thin and simple.

[0107] <Embodiment 2> In embodiment 1, the support member 30 disposed in the gap GP is formed with an arm portion 30a extending along the linear portion GP1. In contrast, in embodiment 2, the support member disposed in the gap GP is not formed with an arm portion extending along the linear portion GP1. That is, embodiment 2 is an embodiment that focuses on the fact that the lower surface of the support member has a curved shape.

[0108] FIG. 15 is an exploded perspective view schematically showing the configuration of the load sensor 1 according to the second embodiment.

[0109] The load sensor 1 of the second embodiment differs from the first embodiment in that it includes a support member 90 instead of the support member 30. The support member 90 has a perfect circular shape in a plan view. The central axis CA1 of the support member 90 is parallel to the Z-axis direction and coincides with the central axis CA of the load sensor 1. The support member 90 has a rotationally symmetric shape about the central axis CA1. The upper surface 91 of the support member 90 is a surface parallel to the horizontal plane, and the lower surface 92 of the support member 90 has a curved shape. Specifically, the lower surface 92 has a spherical surface shape. The central axis CA1 of the support member 90 passes through the center 92a of the lower surface 92. The upper surface 91 of the support member 90 is attached to the lower surface 22 of the cover member 20 with an adhesive or the like. The support member 90 is made of the same material as the support member 30 of the first embodiment.

[0110] In the second embodiment as well, when a load including a downward component and a horizontal component is applied, the rolling direction and amount of rolling of the support member 30 change depending on the direction and magnitude of the horizontal load component. At this time, the direction and magnitude of the horizontal load component can be detected based on the degree of load imbalance detected by the four sensor units 40. Furthermore, the downward load can be detected based on the sum of the loads detected by the four sensor units 40.

[0111] <Load detection simulation> Next, the inventors performed the following simulation to verify whether the load components in the negative Z-axis direction and horizontal direction can be properly detected when a load is applied diagonally to the Z-axis direction.

[0112] In this simulation, a load similar to that shown in FIG. 8(a) was applied to the load sensor CE1 of Comparative Example 1 (see FIG. 8(b)), the load sensor EM1 of Embodiment 1 (see FIG. 11(b)), and three types of load sensors EM2-1, EM2-2, and EM2-3 of Embodiment 2 (see FIGS. 16(a) to 16(c)).

[0113] 16A to 16C are cross-sectional views each showing a schematic configuration of the support member 90 of the load sensors EM2-1, EM2-2, and EM2-3 of the second embodiment.

[0114] The lower surfaces 92 of the support members 90 of the load sensors EM2-1, EM2-2, and EM2-3 had the same spherical surface shape. The diameters Φ of the support members 90 in a plan view were 1 mm, 2 mm, and 5 mm, respectively. The height H1 of the center 92a of the lower surface 92 of each support member 90 was 1 mm.

[0115] The configuration of the load sensors EM2-1, EM2-2, and EM2-3, excluding the support member 90, is the same as that shown in Fig. 8(b). However, in the load sensor EM2-3, the diameter of the support member 90 is large and it cannot be placed in the center of the gap GP, so the sensor unit 40 has an octagonal shape with the corners cut out in a plan view, similar to the case of Fig. 10(a).

[0116] In this simulation, the load sensors CE1, EM2-1, EM2-2, EM2-3, and EM1 were configured as described above, and a load was applied to each load sensor as shown in FIG. 8(a). At this time, the configuration of each load sensor was set to Condition 2 described in the simulation of Embodiment 1. Under Condition 2, the support member was a rigid body, the friction coefficient was 0.1, and the thickness of the plate-like member 10 was 0 mm. Then, under Condition 2, the simulation results shown in FIG. 17 were obtained.

[0117] 17, for the load sensor CE1 under condition 2, the vertical load detection rate was high, but the horizontal load detection rate was low at approximately 0% to 0.5%. For the load sensor EM1 under condition 2, the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 3%, which is sufficient for detecting a horizontal load, the horizontal load detection rate for diagonal 2 was appropriately low at approximately 0%, and the vertical load detection rate was approximately 68%, which is sufficient for detecting a load in the Z axis direction. This result is almost the same as the result described under condition 2 of the simulation of embodiment 1 (see FIG. 12(b)).

[0118] In the load sensor EM2-1 under condition 2, the vertical load detection rate was high, but the horizontal load detection rate was about 0%. This shows that when the diameter of the support member 90 is small, about 1 mm, it is difficult to properly detect horizontal loads even if the lower surface 92 has a spherical surface shape.

[0119] For the load sensor EM2-2 under condition 2, the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 3%, which was sufficient for detecting a horizontal load, the horizontal load detection rate for diagonal 2 was appropriately low at approximately 0.1%, and the vertical load detection rate was approximately 95%, which was sufficient for detecting a load in the Z-axis direction. For the load sensor EM2-3 under condition 2, the horizontal load detection rates in the X direction, Y direction, and diagonal 1 were approximately 1.5% to 2.1%, which was sufficient for detecting a horizontal load, the horizontal load detection rate for diagonal 2 was appropriately low at approximately 0.3%, and the vertical load detection rate was approximately 79%, which was sufficient for detecting a load in the Z-axis direction. Therefore, it can be said that the load sensors EM2-2 and EM2-3 under condition 2 can appropriately detect a horizontal load as well as a load in the Z-axis direction by making the lower surface 92 a spherical surface shape.

[0120] Furthermore, the reason why the horizontal load could not be detected by the load sensor EM2-1 is thought to be that the diameter of the support member 90 is small, so even if the support member 90 rolls, the effect of tilting the cover member 20 is small, and there is almost no change in the distribution of the load acting on the four sensor units 40. In addition, it can be assumed that the reason for this is that the diameter of the support member 90 is small, so the distance between the support member 90 and the sensor units 40 is large, and the tilt of the cover member 20 caused by the rolling of the support member 90 does not affect the sensor units 40.

[0121] Therefore, in the configuration of embodiment 2, it can be said that the diameter of the support member 90 and the curved shape of the lower surface 92 need to be set so that the support member 90 can roll smoothly due to horizontal load, and so that the tilt of the cover member 20 due to this rolling can spread to the sensor unit 40.

[0122] <Effects of Second Embodiment> According to the second embodiment, the following effects are achieved.

[0123] The support member 90 has a columnar shape with a convexly inclined lower surface 92, and is disposed in the gap GP near the center 51a of the base member 50.

[0124] Even with this configuration, the load components in the direction perpendicular to the load-receiving surface and the direction parallel to this surface can be detected with a simple configuration. However, as shown in the simulation results of FIG. 17 , if the diameter of the support member 90 is small compared to the width of the gap GP, the horizontal load cannot be detected properly. Therefore, it is preferable that the diameter of the support member 90 be somewhat larger than the width of the gap GP. Furthermore, with the above configuration, the configuration of the support member 90 is simpler than the support member 30 of embodiment 1, making it easier to mold the support member 90.

[0125] The lower surface 92 of the support member 90 has a curved shape that is symmetrical with respect to the central axis CA1 of the support member 90.

[0126] This configuration allows the support member 90 to roll smoothly in all circumferential directions.

[0127] <Modification 1> In the first embodiment, the lower surface 32 of the support member 30 has a spherical surface shape, but is not limited to this. The lower surface 32 may have a conical side shape with the center 32 a as the apex and protruding downward (in the negative Z-axis direction).

[0128] 18(a), the lower surface 32 has a single type of conical side shape that protrudes in the negative direction of the Z axis. In this case, when a load is applied to the load sensor 1, the contact point between the lower surface 32 and the upper surface 51 of the base member 50 does not move from the center 32a, and the support member 30 rolls with the center 32a as the fulcrum. As a result, as in the first embodiment, a bias occurs in the loads detected by the four sensor units 40, making it possible to detect the horizontal load component.

[0129] 18(b), the lower surface 32 has a shape formed by combining the side shapes of multiple cones that have a vertex at the center 32a and protrude in the negative direction of the Z axis. In a plan view, the lower surface 32 has a circular region A1 centered on the center 32a and an annular region A2 centered on the center 32a. Region A1 of the lower surface 32 and region A2 of the lower surface 32 both have a conical side shape, and the inclinations of regions A1 and A2 are different from each other. In this case, too, the point of contact between the lower surface 32 and the upper surface 51 of the base member 50 does not move from the center 32a, and the support member 30 rolls with the center 32a as a fulcrum.

[0130] 18(a) and 18(b), the lower surface 92 of the support member 90 may have one or more conical side surfaces projecting downward, with the center 92a as the apex. In addition, in FIG. 18(b), the support member 30 may roll so that the contact point between the lower surface 32 and the upper surface 51 of the base member 50 fluctuates in the region A1.

[0131] <Modification 2> In the first embodiment, the lower surface 32 of the support member 30 has only a curved shape, but this is not limiting, and as shown in FIG. 19, a recess may be formed in part of the lower surface 32.

[0132] In the example shown in FIG. 19 , a notch 32c is formed in the lower surface 32 of each of the four arms 30a. The notch 32c is recessed in the positive direction of the Z axis relative to the lower surface 32. The support member 30 has a shape that is symmetrical in the X-axis and Y-axis directions relative to the central axis CA1. In this case, if the contact point between the lower surface 32 and the upper surface 51 of the base member 50 is at the notch 32c, the support member 30 will not roll smoothly. However, similar to the first embodiment, a horizontal load component can be detected in response to the rolling of the support member 30. However, in order to allow the support member 30 to roll smoothly across the entire lower surface 32, it is preferable that the lower surface 32 be configured with a continuously curved shape, as in the first embodiment.

[0133] In the second embodiment, the lower surface 92 of the support member 90 may also have a ring-shaped notch centered at the center 92a.

[0134] <Modification 3> In the first embodiment, the load sensor 1 is configured to be able to detect the load components in the X-axis direction and the Y-axis direction, but it may be configured to be able to detect only the load component in one direction (for example, the load component in the Y-axis direction) among the horizontal load components.

[0135] Fig. 20(a) is a plan view schematically showing the configuration of the load sensor 1 according to this modified example. For convenience, the plate-like member 10 and the cover member 20 are omitted from Fig. 20(a).

[0136] In the support member 30 of this modified example, the two arms 30a extending in the X-axis direction are omitted compared to the first embodiment. That is, the two arms 30a extending in the Y-axis direction are arranged in the straight portion GP1 of the gap GP extending in the Y-axis direction, and no arms 30a are arranged in the straight portion GP1 extending in the X-axis direction.

[0137] FIG. 20B is a perspective view that schematically shows the configuration of the support member 30 according to this modified example.

[0138] The lower surface 32 of the support member 30 in this modified example has a cylindrical side surface shape with a generatrix parallel to the X-axis direction. In this case, the thickness of the support member 30 is greatest at a position on the lower surface 32 that passes through the center 32 a and extends in the X-axis direction.

[0139] According to this modified example, because the support member 30 rolls only in the Y-axis direction, it is possible to detect only the Y-axis load component among the horizontal load components. In this case, as in the first embodiment, the Y-axis load component can be detected based on the difference between the load detected by the two sensor units 40 on the Y-axis positive side and the load detected by the two sensor units 40 on the Y-axis negative side.

[0140] <Modification 4> In Modification 3, four sensor units 40 are arranged to detect only one directional load component among the horizontal load components, but two sensor units 40 may also be arranged.

[0141] FIG. 21A is a plan view schematically showing the configuration of the load sensor 1 according to this modified example.

[0142] The support member 30 of this modified example includes two arms 30a extending in the Y-axis direction, similar to modified example 3. Also, unlike modified example 3, this modified example has two sensor units 40 arranged on the upper surface 51 of the base member 50. The two sensor units 40 are arranged spaced apart in the X-axis direction with a gap GP interposed therebetween, and the gap GP consists only of a straight line portion GP1 extending in the Y-axis direction.

[0143] FIG. 21B is a perspective view schematically showing the configuration of the support member 30 according to this modified example.

[0144] The lower surface 32 of the support member 30 in this modified example has a cylindrical side surface shape with a generatrix parallel to the Y-axis direction. In this case, the thickness of the support member 30 is greatest at a position on the lower surface 32 that passes through the center 32 a and extends in the Y-axis direction.

[0145] According to this modification, since the support member 30 rolls only in the X-axis direction, it is possible to detect only the component of the load in the X-axis direction among the horizontal load components. In this case, the component of the load in the X-axis direction can be detected based on the difference between the load detected by the sensor unit 40 on the positive side of the X-axis and the load detected by the sensor unit 40 on the negative side of the X-axis.

[0146] <Modification 5> In the first embodiment, the four arms 30a of the support member 30 extend in the positive X-axis direction, the negative X-axis direction, the positive Y-axis direction, and the negative Y-axis direction, but the directions in which the multiple arms 30a extend are not limited to this.

[0147] FIG. 22 is a plan view schematically showing the configuration of the load sensor 1 according to this modified example.

[0148] The support member 30 of this modified example has three arms 30a extending radially from the center 51a of the base member 50. The directions in which the three arms 30a extend form an angle of 120° with respect to each other in a plan view. In addition, in this modified example, three sensor units 40 are arranged spaced apart from each other by a gap GP. The gap GP is made up of three linear portions GP2 extending radially from the center 51a, and two adjacent sensor units 40 are arranged spaced apart by one linear portion GP2. The lower surface 32 of the support member 30 of this modified example has a spherical surface shape that protrudes downward, similar to the first embodiment.

[0149] According to this modified example, the support member 30 rolls in three directions relative to the center 51a. In this case, the load component in the direction in which one arm 30a extends is detected based on the difference between the load detected by the two sensor units 40 arranged on either side of that direction and the load detected by the other sensor unit 40. As a result, the load component in the horizontal direction can be detected as the resultant force of the loads in the directions in which the three arms 30a extend.

[0150] <Modification 6> In the first embodiment, the load sensor 1 includes the plate-shaped member 10 , but the plate-shaped member 10 does not necessarily have to be included in the load sensor 1 .

[0151] FIG. 23 is a perspective view schematically showing the configuration of the load sensor 1 according to this modified example.

[0152] In this modified example, the load sensor 1 does not include the plate-shaped member 10, as compared to the first embodiment shown in FIG. 5 . In this case, the upper surface 21 of the cover member 20 is the surface to which an external load is applied to the load sensor 1. In this case, too, for example, when a load is applied to the upper surface 21 over an area similar to that of the lower surface 12 of the plate-shaped member 10, the Z-axis and horizontal components of the applied load can be properly detected, as shown in the above simulation in which the thickness of the plate-shaped member 10 is 0 mm. Furthermore, by omitting the plate-shaped member 10, the load sensor 1 can be configured even thinner than the first embodiment.

[0153] <Modification 7> The sensor unit 40 for detecting the load is not limited to the configuration shown in FIG. 3, and may have other configurations.

[0154] FIG. 24 is an exploded perspective view showing a schematic configuration of one sensor unit 40 according to this modified example.

[0155] The sensor unit 40 of this modified example includes a substrate 210 , a conductive elastic body 220 , a conductor wire 230 , and a substrate 240 .

[0156] The substrate 210 is configured in the same manner as the substrate 110 of the first embodiment. The conductive elastic body 220 has a square shape in a plan view. Like the second electrode 140 of the first embodiment, the conductive elastic body 220 is configured from a non-conductive elastic material and a conductive filler mixed into the elastic material. The conductive elastic body 220 is configured from the same material as the second electrode 140 of the first embodiment. A cable 221 electrically connected to the conductive elastic body 220 is installed in the conductive elastic body 220. The cable 221 is connected to a detection circuit external to the load sensor 1.

[0157] The conductor wire 230 is composed of a conductive member 231 and a dielectric member 232 formed to cover the conductive member 231. The conductive member 231 is a linear member. The conductive member 231 is made of a conductive metal material, for example, copper. The dielectric member 232 is made of the same material as the dielectric member 130 of the first embodiment. The conductive member 231 is connected to a detection circuit external to the load sensor 1. The substrate 240 is configured in the same manner as the base member 50 of the first embodiment.

[0158] When assembling the sensor unit 40, the conductive elastic body 220 is formed on the lower surface 212 of the substrate 210 by a printing method such as screen printing, gravure printing, flexographic printing, offset printing, or gravure offset printing. The conductor wire 230 is arranged on the upper surface 241 of the substrate 240, a structure consisting of the substrate 210 and the conductive elastic body 220 is placed on the upper surface 241 of the substrate 240, and the periphery of the substrate 210 is installed on the substrate 240 by an installation member. As a result, the conductor wire 230 is sandwiched between the conductive elastic body 220 and the substrate 240. In this way, the sensor unit 40 of this modified example is completed.

[0159] Fig. 25(a) is a cross-sectional view schematically showing the sensor unit 40 in an unloaded state (a state in which no load is applied) according to this modified example. Fig. 25(b) is a cross-sectional view schematically showing the sensor unit 40 in a loaded state (a state in which a load is applied) according to this modified example. Figs. 25(a) and (b) show a cross-section of the sensor unit 40 when cut along a plane parallel to the YZ plane passing through the center of the sensor unit 40.

[0160] As shown in Fig. 25(a), in the initial state where no load is applied, the force acting between the conductive elastic body 220 and the conductor wire 230 is almost zero. When a load is subsequently applied to the upper surface 211 of the substrate 210, as shown in Fig. 25(b), the conductive elastic body 220 is deformed by the conductor wire 230 in response to an increase in the load. This increases the contact area between the conductive elastic body 220 and the dielectric 232.

[0161] When the contact area between the conductive elastic body 220 and the dielectric 232 changes with the load, the capacitance between the conductive elastic body 220 and the conductive member 231 also changes with the load. This capacitance is proportional to the total contact area between the conductive elastic body 220 and the dielectric 130. The potential reflecting this change in capacitance is measured in an external control circuit, thereby detecting the load applied to the sensor unit 40 in the negative direction of the Z axis.

[0162] As a result, the sensor unit 40 of this modified example can detect the load acting on the sensor unit 40, similarly to the sensor unit 40 of embodiment 1. Therefore, based on the load detected by the four sensor units 40 of this modified example, similarly to embodiment 1, it is possible to detect the load components in the direction perpendicular to the surface receiving the load and in the direction parallel to this surface with a simple configuration.

[0163] <Other Modifications> The configuration of the load sensor 1 can be modified in various ways in addition to the configurations shown in the first and second embodiments and the first to sixth modifications.

[0164] In the first embodiment and the second and fifth modifications, the lower surface 32 of the support member 30 has a spherical surface shape, but is not limited thereto and may have a curved surface shape other than a spherical surface shape (for example, an oval surface shape). Furthermore, in the first embodiment and the second and fifth modifications, the lower surface 32 at the position corresponding to each arm portion 30a may be configured with different flat surfaces. That is, the lower surface 32 may have a pyramidal side surface shape. However, the support member 30 can roll more smoothly if the lower surface 32 has a curved surface shape.

[0165] In Modifications 3 and 4, the lower surface 32 has a cylindrical surface shape, but is not limited thereto and may have a curved surface shape other than a cylindrical surface shape (for example, the side shape of an elliptical cylinder, the surface shape of a perfect sphere, the surface shape of an ellipsoidal sphere, etc.). Also, in Modifications 3 and 4, the lower surface 32 at the position corresponding to each arm portion 30a may be formed of different flat surfaces. That is, the lower surface 32 may have a pyramidal side shape. However, a curved lower surface 32 allows the support member 30 to roll more smoothly.

[0166] In the first embodiment and the first to fifth modifications, the arms 30a have the same length, but the arms 30a may have different lengths. However, the arms 30a having the same length can stably roll the support member 30.

[0167] In the second embodiment, the support member 90 has a cylindrical shape except for the lower surface 92, which has a spherical surface shape. However, the present invention is not limited to this, and the support member 90 may have a truncated cone shape except for the lower surface 92. The lower surface 92 may have a curved shape other than a spherical surface shape (for example, an ellipsoidal surface shape).

[0168] In the first embodiment, the support member 30 is adhesively fixed to the underside 22 of the cover member 20, but if misalignment of the support member 30 is not a problem, the support member 30 does not need to be fixed to the underside 22 of the cover member 20. However, if the support member 30 rolls, the arm portion 30a that drops downward cannot lower the cover member 20 in the vicinity of the arm portion 30a, and the load detected by the sensor unit 40 in the vicinity of the arm portion 30a cannot be increased. Therefore, it is preferable that the support member 30 be fixed to the underside 22 of the cover member 20.

[0169] In the first and second embodiments and the first to sixth modifications, the sensor unit 40 for detecting the load is a capacitance type sensor, but is not limited to this and may be, for example, a resistance type sensor.

[0170] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims.

[0171] In the above-described reference example, as shown in FIG. 11A, the support member 60 is disposed at the center of the gap GP, and the support members 80 are disposed at four positions in the gap GP excluding the center position. However, this is not limiting, and the number and positions of the support members 80 disposed at positions other than the center of the gap GP can be changed as appropriate as long as they can properly detect both the vertical load and the horizontal load. Furthermore, as in the fourth modification shown in FIG. 21, when the horizontal load to be detected is only the load component in the X-axis direction, it can be assumed that the horizontal load in that direction can be properly detected by distributing multiple support members 60, 80 in the gap GP in a predetermined layout.

[0172] <Supplementary Notes> The above description of the embodiments discloses the following techniques.

[0173] (Technology 1) A load sensor comprising: a base member; a plurality of sensor units installed on an upper surface of the base member and separated by gaps extending radially from the center of the base member; a cover member covering the upper surfaces of the plurality of sensor units; and a support member interposed between the base member and the cover member in at least a portion of the gap including the center, and capable of rolling relative to the base member.

[0174] According to this technology, when a load is applied perpendicularly to the top surface of the cover member (the surface receiving the load), the load is applied to the top surfaces of the multiple sensor units via the cover member. The vertically applied load can be detected based on the detection signals of the multiple sensor units. On the other hand, when a load is applied obliquely to the top surface of the cover member (directions perpendicular and parallel to the surface receiving the load), the support member rolls and tilts in the direction of the applied load, causing the portion of the cover member supported by the support member to tilt as well. This changes the distribution of the loads applied to the top surfaces of the multiple sensor units via the cover member, resulting in a difference in the loads detected by each sensor unit. Therefore, based on this difference, the portion of the oblique load parallel to the surface receiving the load can be detected. Based on the sum of the loads detected by the multiple sensor units, the portion of the oblique load perpendicular to the surface receiving the load can be detected. Therefore, the load components perpendicular to the surface receiving the load and parallel to the surface can be detected. Furthermore, because the support member is disposed between the base member and the cover member in the gap separating the multiple sensor units, the load sensor can be constructed thin and simply.

[0175] (Technology 2) The load sensor according to Technology 1, wherein the lower surface of the support member has a curved shape.

[0176] With this technology, when a diagonal load is applied, the support member smoothly rolls and tilts, which stably changes the distribution of the loads applied to the multiple sensor units, thereby enabling accurate detection of loads in a direction parallel to the load-receiving surface.

[0177] (Technology 3) A load sensor according to Technology 1 or 2, characterized in that the gap has two straight portions that intersect at the center, and the support member has an arm portion that extends along at least one of the straight portions and is rollable relative to the base member in the direction in which the one straight portion extends.

[0178] According to this technology, when a load is applied in the direction in which one of the straight sections extends, the support member rolls, causing one arm to lower and the other arm to rise in the direction in which the straight section extends. This increases the distribution change of the loads applied to the multiple sensor sections, allowing for accurate detection of loads in a direction parallel to the surface receiving the load.

[0179] (Technology 4) In the load sensor described in Technology 3, the support member has an arm portion that extends along the other straight portion and is rollable relative to the base member in the direction in which the other straight portion extends.

[0180] This technology makes it possible to accurately detect loads in any direction parallel to the load-receiving surface.

[0181] (Technology 5) The load sensor according to Technology 1, wherein the support member has a columnar shape with a convexly inclined lower surface, and is disposed in the gap near the center.

[0182] According to this technique, the structure of the support member is simplified, and therefore the support member can be easily formed.

[0183] (Technology 6) The load sensor according to Technology 5, wherein the lower surface of the support member has a curved shape that is symmetrical with respect to the central axis of the support member.

[0184] This technique allows the support member to roll smoothly in all circumferential directions.

[0185] (Technology 7) The load sensor according to any one of Technologies 1 to 6, wherein the support member is made of a material that is not substantially deformed by a load within the detection range.

[0186] This technology allows the support member to roll properly, creating a difference in height between the ends of the support member in the rolling direction, allowing the load in a direction parallel to the load-receiving surface to be detected properly.

[0187] (Technology 8) The load sensor according to any one of Technologies 1 to 7, further comprising a plate-like member disposed on an upper surface of the cover member.

[0188] According to this technology, a moment is generated in the plate-like member compared to when no plate-like member is provided, and this moment causes a bias in the load distribution on the top surface of the cover member, which in turn causes a bias in the load acting on the multiple sensor units, thereby enabling more accurate detection of loads in a direction parallel to the load-receiving surface.

[0189] (Technology 9) A load sensor according to any one of technologies 1 to 8, characterized in that the sensor unit comprises an electrode, a conductive elastic body facing the electrode, and a dielectric body arranged between the electrode and the conductive elastic body.

[0190] This technique allows the sensor section to be configured thin and simple.

[0191] (Technology 10) A load sensor comprising: a base member; a plurality of sensor units installed on an upper surface of the base member and separated by gaps extending radially from the center of the base member; a cover member covering the upper surfaces of the plurality of sensor units; and a plurality of support members interposed between the base member and the cover member so as to be scattered at the center and in the gaps other than the center.

[0192] According to this technology, as shown in the above-mentioned reference example, it is possible to detect load components in the direction perpendicular to the load-receiving surface and in the direction parallel to this surface. In addition, since the support member is disposed between the base member and the cover member in the gap that separates the multiple sensor units, the load sensor can be configured thin and simple.

[0193] REFERENCE SIGNS LIST 1 Load sensor 10 Plate-like member 20 Cover member 21 Upper surface 30 Support member 30a Arm portion 32 Lower surface 40 Sensor portion 41 Upper surface 50 Base member 51 Upper surface 51a Center 60 Support member 90 Support member 92 Lower surface 120 First electrode (electrode) 130 Dielectric 140 Second electrode (conductive elastic body) 220 Conductive elastic body 231 Conductive member (electrode) 232 Dielectric CA1 Central axis GP Gap GP1 Straight portion

Claims

1. A load sensor comprising: a base member; a plurality of sensor units mounted on an upper surface of the base member and separated by gaps extending radially from a center of the base member; a cover member covering the upper surfaces of the plurality of sensor units; and a support member interposed between the base member and the cover member in at least a portion of the gap including the center, and capable of rolling relative to the base member.

2. A load sensor as claimed in claim 1, characterized in that the lower surface of the support member has a curved shape.

3. A load sensor as described in claim 1, characterized in that the gap has two straight portions intersecting at the center, and the support member has an arm portion extending along at least one of the straight portions and capable of rolling relative to the base member in the direction in which the one straight portion extends.

4. A load sensor as claimed in claim 3, characterized in that the support member has an arm portion which extends along the other straight portion and is capable of rolling relative to the base member in the direction in which the other straight portion extends.

5. A load sensor as claimed in claim 1, characterized in that the support member has a columnar shape with a convexly inclined lower surface, and is disposed in the gap near the centre.

6. A load sensor as claimed in claim 5, characterized in that the lower surface of the support member has a curved shape symmetrical with respect to the central axis of the support member.

7. A load sensor according to claim 1, characterized in that the support member is made of a material that is not substantially deformed by a load within the detection range.

8. The load sensor according to claim 1, further comprising a plate-like member disposed on the upper surface of said cover member.

9. A load sensor as claimed in any one of claims 1 to 8, characterized in that the sensor section comprises: an electrode; a conductive elastic body facing the electrode; and a dielectric body arranged between the electrode and the conductive elastic body.

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