Force sensor

Abstract

To provide a force sensor capable of measuring force according to deformation of an elastic hinge with high sensitivity.SOLUTION: A force sensor 11 includes: a pair of elastic hinges 22a, 22b in which a movable body (link material 16) deforming relatively to a fixing body 12 is connected to the fixing body 12, which has a shape of regulating the deformation of the movable body around a reference axis 21, and which is provided with a gap S in an axial direction of the reference axis 21; and a piezoelectric element 25 which is provided between the elastic hinges 22a, 22b, whose one end is fixed to the fixing body 12, and whose the other end is fixed to the movable body.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a force sensor that connects a movable body that displaces relative to the fixed body to a fixed body and includes an elastic hinge that has a shape that restricts the displacement of the movable body around a reference axis. [Background technology]

[0002] Patent Document 1 discloses a load sensor that uses a quartz crystal oscillator. The oscillation frequency of the quartz crystal oscillator shifts linearly when subjected to an external force. The load sensor has high rigidity, high sensitivity, and a wide dynamic measurement range, so it can measure loads in the same dynamic range as a force sensor while measuring minute forces at the level of a conventional tactile sensor. This sensor is expected to be used in a variety of applications in the future. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6941874 [Non-patent literature]

[0004] [Non-Patent Document 1] A&D Co., Ltd., Introduction to Load Cells, Chapter 2: Measurement Principles of Load Cells, [online], [Retrieved March 22, 2024], Internet<https: / / www.aandd.co.jp / products / loadcell / introduction / cell_intro02.html> Summary of the Invention [Problem to be solved by the invention]

[0005] As disclosed in Non-Patent Document 1, a load cell having a strain gauge attached to a strain-generating body is known. The strain-generating body has an elastic hinge that connects a fixed body to a movable body that displaces relative to the fixed body. The elastic hinge is divided into a plane parallel to a reference axis and a curved surface formed by a generatrix parallel to the reference axis and that restricts displacement of the movable body around the reference axis. The strain gauge is attached to the plane parallel to the reference axis. When an external force acts on the movable body, the strain gauge measures the magnitude of the external force in accordance with the deformation of the elastic hinge.

[0006] In this load cell, the stiffness of the strain body can be adjusted according to the magnitude of the external force. The material and shape of the strain body are designed to set the stiffness. However, in this load cell, if the stiffness is increased, sufficient sensitivity cannot be ensured with the strain gauge. In particular, according to the analysis of the inventors, stress concentration occurs on the curved surface of the elastic hinge, and therefore a mechanism for efficiently converting the deformation of the elastic hinge into an electrical signal was found to be necessary.

[0007] An object of the present invention is to provide a force sensor that can measure force with high sensitivity in accordance with the deformation of an elastic hinge. [Means for solving the problem]

[0008] A force sensor according to one embodiment of the present invention includes a fixed body connected to a movable body that is displaceable relative to the fixed body, a pair of elastic hinges that have a shape that restricts displacement of the movable body around a reference axis and are arranged at a distance in the axial direction of the reference axis, and a piezoelectric element that is arranged between the elastic hinges and has one end fixed to the fixed body and the other end fixed to the movable body.

[0009] A force sensor according to another aspect of the present invention comprises a first link member having one end connected to a fixed body by a first hinge and the other end connected to a movable body by a second hinge; and a second link member having the same length as the first link member and extending parallel to the first link member, having one end connected to the fixed body by a third hinge and the other end connected to the movable body by a fourth hinge, and cooperating with the first link member to realize parallel movement of the movable body, wherein at least one of the first hinge, the second hinge, the third hinge, and the fourth hinge has a shape that restricts displacement of the movable body around a reference axis during the parallel movement, and has a pair of elastic hinges arranged at a distance in the axial direction of the reference axis, and a piezoelectric element is arranged between the elastic hinges, one end of which is fixed to the fixed body or the movable body and the other end of which is fixed to the first link member or the second link member. [Effects of the Invention]

[0010] As described above, according to the present invention, a force sensor can be provided that can measure a force with high sensitivity in accordance with the deformation of an elastic hinge. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view schematically illustrating a structure of a force sensor according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged perspective view schematically showing the structure of the first hinge (or the second hinge). [Figure 3] FIG. 10 is an enlarged perspective view schematically showing the structure of the third hinge (or the fourth hinge). [Figure 4] FIG. 2 is an enlarged plan view of a first hinge. [Figure 5] FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. [Figure 6] 3A and 3B are schematic diagrams illustrating the operation of a force sensor. [Figure 7] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] FIG. 1 shows a schematic structure of a force sensor 11 according to an embodiment of the present invention. The force sensor 11 includes a fixed body 12 and a movable body 13 connected to the fixed body 12 so as to be relatively displaceable and subjected to an external force. To achieve this relative displacement, a parallel link mechanism 14 is established between the fixed body 12 and the movable body 13. The parallel link mechanism 14 includes a first link member 16 having one end connected to the fixed body 12 at a first hinge 15a and the other end connected to the movable body 13 at a second hinge 15b, and a second link member 18 having the same length as the first link member 16 and extending parallel to the first link member 16. The second link member 18 has one end connected to the fixed body 12 at a third hinge 17a and the other end connected to the movable body 13 at a fourth hinge 17b. The parallel link mechanism 14 enables the movable body 13 to move in a parallel direction. The parallel link mechanism 14 functions as a strain-generating body. The fixed body 12 does not necessarily have to be fixed immovably, but only needs to support an external force acting on the movable body 13. Therefore, the first link member 16 and the second link member 18 function as movable bodies relative to the fixed body 12. Similarly, the first link member 16 and the second link member 18 function as fixed bodies relative to the movable body 13.

[0014] As shown in FIG. 2, the first hinge 15a has a shape that restricts displacement of the movable body 13 about the reference axis 21, and includes a pair of first elastic hinges 22a, 22b that are spaced apart in the axial direction of the reference axis 21. To restrict displacement, the first elastic hinges 22a, 22b are divided by a flat surface 23 that is parallel to the reference axis 21 and a curved surface 24 that is formed by a generatrix that is also parallel to the reference axis 21 and restricts displacement of the movable body 13 about the reference axis 21. An elastically deformable thin-walled solid body is formed between the flat surface 23 and the curved surface 24. A piezoelectric element 25 is disposed between the first elastic hinges 22a, 22b. One end of the piezoelectric element 25 is fixed to the fixed body 12, and the other end of the piezoelectric element 25 is fixed to the first link member 16.

[0015] The fixed body 12, the first elastic hinges 22a, 22b, and the first link member 16 are continuous; that is, they are molded as a single unit. Metallic materials such as aluminum or stainless steel can be used as the material. Machining processes such as cutting and polishing, or wire electric discharge machining can be used for molding. To separate the first elastic hinges 22a, 22b, a slit 26 extending parallel to the reference axis 21 is formed in the integrally molded material. The piezoelectric element 25 has a width W in the axial direction of the reference axis 21 that is smaller than the distance S between the first elastic hinges 22a, 22b.

[0016] The second hinge 15b is configured similarly to the first hinge 15a. Referring to FIG. 2, the second hinge 15b has a shape that restricts displacement of the movable body 13 about a reference axis 27 and includes a pair of second elastic hinges 28a, 28b that are spaced apart in the axial direction of the reference axis 27. To restrict displacement, the second elastic hinges 28a, 28b are divided by a flat surface 29 that is parallel to the reference axis 27 and a curved surface 31 that is formed by a generatrix that is also parallel to the reference axis 27 and restricts displacement of the movable body 13 about the reference axis 27. An elastically deformable thin-walled solid body is formed between the flat surface 29 and the curved surface 31. A piezoelectric element 32 is disposed between the second elastic hinges 28a, 28b. One end of the piezoelectric element 32 is fixed to the movable body 13 and the other end is fixed to the first link member 16. Piezoelectric element 32 is coupled to piezoelectric element 25 on first link member 16 .

[0017] The movable body 13, second elastic hinges 28a, 28b, and first link member 16 are continuous; that is, they are molded as a single unit. Metal materials such as aluminum or stainless steel can be used as the material. Machining processes such as cutting and polishing, or wire electric discharge machining can be used for molding. To separate the second elastic hinges 28a, 28b, a slit 33 extending parallel to the reference axis 27 is formed in the integrally molded material. The piezoelectric element 32 has a width W in the axial direction of the reference axis 27 that is smaller than the distance S between the second elastic hinges 28a, 28b.

[0018] As shown in FIG. 3 , the third hinge 17a has a shape that restricts displacement of the movable body 13 about a reference axis 37 and includes a pair of third elastic hinges 38a, 38b spaced apart in the axial direction of the reference axis 37. To restrict displacement, the third elastic hinges 38a, 38b are divided by a flat surface 39 parallel to the reference axis 37 and a curved surface 41 formed by a generatrix parallel to the reference axis 37 and restricting displacement of the movable body 13 about the reference axis 37. An elastically deformable thin-walled solid body is formed between the flat surface 39 and the curved surface 41. A piezoelectric element 42 is disposed between the third elastic hinges 38a, 38b. One end of the piezoelectric element 42 is fixed to the fixed body 12 and the other end is fixed to the second link member 18. However, the piezoelectric element 42 may be omitted.

[0019] The fixed body 12, the third elastic hinges 38a, 38b, and the second link member 18 are continuous; that is, they are molded as a single unit. Metallic materials such as aluminum or stainless steel can be used as the material. Machining processes such as cutting and polishing, or wire electric discharge machining can be used for molding. To separate the third elastic hinges 38a, 38b, a slit 43 extending parallel to the reference axis 37 is formed in the integrally molded material. The piezoelectric element 42 has a width W in the axial direction of the reference axis 37 that is smaller than the distance S between the third elastic hinges 38a, 38b.

[0020] The fourth hinge 17b is configured similarly to the third hinge 17a. Referring to FIG. 3, the fourth hinge 17b has a shape that restricts displacement of the movable body 13 about the reference axis 44 and includes a pair of fourth elastic hinges 45a, 45b that are spaced apart in the axial direction of the reference axis 44. To restrict displacement, the fourth elastic hinges 45a, 45b are divided by a flat surface 46 that is parallel to the reference axis 44 and a curved surface 47 that is formed by a generatrix that is also parallel to the reference axis 44 and restricts displacement of the movable body 13 about the reference axis 44. An elastically deformable thin-walled solid body is formed between the flat surface 46 and the curved surface 47. A piezoelectric element 48 is disposed between the fourth elastic hinges 45a, 45b. One end of the piezoelectric element 48 is fixed to the movable body 13 and the other end is fixed to the second link member 18. The piezoelectric element 48 is combined with the piezoelectric element 42 on the second link member 18. If the piezoelectric element 42 is omitted, the piezoelectric element 48 is omitted.

[0021] The movable body 13, the fourth elastic hinges 45a, 45b, and the second link member 18 are continuous; that is, they are molded as a single unit. Metal materials such as aluminum or stainless steel can be used as the material. Machining processes such as cutting and polishing, or wire electric discharge machining can be used for molding. To separate the fourth elastic hinges 45a, 45b, a slit 49 extending parallel to the reference axis 44 is formed in the integrally molded material. The piezoelectric element 48 has a width W in the axial direction of the reference axis 44 that is smaller than the distance S between the fourth elastic hinges 45a, 45b.

[0022] As shown in FIG. 4, the piezoelectric element 25 includes an upper electrode 51 and a lower electrode 52 that are stacked and sized to fit between the fixed body 12 and the first link member 16. Here, the upper electrode 51 and the lower electrode 52 are formed to the same shape and have overlapping contours. As shown in FIG. 5, a piezoelectric plate material 53 is sandwiched between the upper electrode 51 and the lower electrode 52. The piezoelectric material is made of, for example, a quartz crystal oscillator. The quartz crystal oscillator exhibits a piezoelectric effect in the area sandwiched between the upper electrode 51 and the lower electrode 52. Alternatively, aluminum nitride, lead zirconium titanate, barium titanate, lead zirconium titanate, or lead zirconium titanate may be used for the piezoelectric material.

[0023] A first contact 54 is formed on the surface of the plate 53, continuing from the upper electrode 51 and extending to the edge of the plate 53. The upper electrode 51 and the first contact 54 are composed of a Cr layer laminated on the surface of the plate 53 and an Au layer laminated on the surface of the Cr layer. A second contact 55 is formed on the back surface of the plate 53, continuing from the lower electrode 52 and extending to the edge of the plate 53. Similarly, the lower electrode 52 and the second contact 55 are composed of a Cr layer laminated on the surface of the plate 53 and an Au layer laminated on the surface of the Cr layer. The second contact 55 is located as far away from the first contact 54 as possible. Here, a Ti layer may be used instead of the Cr layer, and a Pt layer may be used instead of the Au layer.

[0024] A surface cover layer 56 is laminated on the surface of the plate material 53. The surface cover layer 56 covers the upper electrode 51 and the first contact 54 on the surface of the plate material 53. The surface cover layer 56 is adhered to the surface of the plate material 53. During this adhesion, a space 57a that accommodates the upper electrode 51 is defined in the adhesive layer 57. The upper electrode 51 is separated from the adhesive layer 57. The surface cover layer 56 may be bonded to the surface of the plate material 53 based on intermolecular interactions.

[0025] Similarly, a back cover layer 58 is laminated on the back surface of the plate material 53. The back cover layer 58 covers the lower electrode 52 and the second contact 55 on the back surface of the plate material 53. The back cover layer 58 is adhered to the back surface of the plate material 53. During this adhesion, a space 59a that accommodates the lower electrode 52 is defined in the adhesive layer 59. The lower electrode 52 is separated from the adhesive layer 59. The back cover layer 58 may be bonded to the back surface of the plate material 53 based on intermolecular interactions.

[0026] A detection circuit 61 is connected to the first contact 54 and the second contact 55. The detection circuit 61 includes an oscillation circuit having negative resistance and capacitive reactance that causes self-excited oscillation of the piezoelectric material. The plate 53 oscillates in response to the application of voltage. When strain is generated in the plate 53, the oscillation frequency shifts. The detection circuit 61 detects the shift in the oscillation frequency. The amount of change in the oscillation frequency is proportional to the magnitude of the external force applied to the plate 53.

[0027] The piezoelectric element 25 is fixed to the fixed body 12 and the first link member 16 with thermosetting polyimide resin. An adhesive layer 62 made of thermosetting polyimide resin is sandwiched between the rear cover layer 58 of the piezoelectric element 25 and the fixed body 12. An adhesive layer 63 made of thermosetting polyimide resin is sandwiched between the rear cover layer 58 of the piezoelectric element 25 and the first link member 16. When the fixed body 12, first elastic hinges 22a, 22b, and first link member 16 are formed from aluminum, an anodized film 64 is formed on the surfaces of the fixed body 12 and the first link member 16. The adhesive layers 62, 63 penetrate into the pores of the anodized film 64. A wedge effect is achieved. Alternatively, when the fixed body 12, the first elastic hinges 22a, 22b, and the first link member 16 are made of stainless steel or aluminum alloy, a wedge effect film 64 can be formed on the surfaces of the fixed body 12 and the first link member 16 by precipitation hardening and selective corrosion. The adhesive layers 62, 63 are entangled with the wedge effect film 64, thereby achieving the wedge effect.

[0028] Next, the operation of the force sensor 11 will be described. The fixed body 12 is fixed to, for example, a stationary structure 65. The detection circuit 61 applies a voltage at a predetermined frequency to the quartz oscillator plate 53. The plate 53 oscillates in response to the applied voltage. As shown in FIG. 6, when an external force F acts on the movable body 13, the movable body 13 is displaced in a predetermined direction by the action of the parallel link mechanism 14. As the movable body 13 displaces, the first elastic hinges 22a and 22b at the first hinge 15a elastically deform. In response to the deformation of the first elastic hinges 22a and 22b, the first link member 16 (corresponding to the movable body of the present invention) displaces around the reference axis 21 relative to the fixed body 12. The displacement of the first link member 16 causes deformation of the piezoelectric element 25. A tensile force acts on the piezoelectric element 25 at the first hinge 15a. The second elastic hinges 28a and 28b at the second hinge 15b elastically deform. In response to the deformation of the second elastic hinges 28a and 28b, the movable body 13 is displaced around the reference axis 27 relative to the first link member 16 (corresponding to the fixed body of the present invention). The displacement of the movable body 13 causes the deformation of the piezoelectric element 32. In the second hinge 15b, a compressive force acts on the piezoelectric element 32. Symmetrical and complementary tensile and compressive forces are generated in the piezoelectric elements 25 and 32.

[0029] In the first hinge 15a, strain is generated in the plate material 53 in response to the deformation of the piezoelectric element 25. The oscillation frequency shifts to a higher frequency by a fixed amount based on the tensile force. The detection circuit 61 detects the amount of change in the oscillation frequency. The amount of change in the oscillation frequency is proportional to the magnitude of the external force F applied to the plate material 53. Since the piezoelectric element 25 deforms between the fixed body 12 and the first link material 16 in accordance with the deformation of the first elastic hinges 22a, 22b, strain is generated in the piezoelectric element 25 more efficiently than when the piezoelectric element 25 is attached to the surface of the first elastic hinges 22a, 22b. The external force F can be converted well into an electrical signal output from the piezoelectric element 25. The external force F can be measured with high sensitivity.

[0030] In the second hinge 15b, strain is generated in the plate material 53 in response to the deformation of the piezoelectric element 32. The oscillation frequency shifts to a lower frequency by a fixed amount based on the compressive force. The detection circuit 61 detects the amount of change in the oscillation frequency. The amount of change in the oscillation frequency is proportional to the magnitude of the external force F applied to the plate material 53. Since the piezoelectric element 32 deforms in accordance with the deformation of the second elastic hinges 28a, 28b between the first link member 16 and the movable body 13, strain is generated in the piezoelectric element 32 more efficiently than when the piezoelectric element 32 is attached to the surface of the second elastic hinges 28a, 28b. The external force F can be efficiently converted into an electrical signal output from the piezoelectric element 32. The external force F can be measured with high sensitivity.

[0031] Here, first link member 16 and second link member 18 constitute a parallel link mechanism 14 that realizes parallel movement of movable body 13. Unlike when movable body 13 is connected to fixed body 12 by a single link, no rotational force component acts on movable body 13 even if movable body 13 is displaced. First elastic hinges 22a, 22b and second elastic hinges 28a, 28b can be released from the influence of bending moments. The strain of piezoelectric elements 25, 32 can reflect the magnitude of external force F with high accuracy.

[0032] In the two hinges 15a, 15b combined on the first link member 16, the piezoelectric elements 25, 32 can generate symmetrical and complementary tensile and compressive stresses. The difference between the tensile and compressive stresses can achieve double the sensitivity. Furthermore, when using the force sensor 11, the effects of disturbances such as parasitic capacitance from the environment, electromagnetic noise, and temperature fluctuations can be complementarily canceled out. In the force sensor 11, the piezoelectric elements 42, 48 of the two hinges (third hinge 17a and fourth hinge 17b) combined on the second link member 18 may be used to measure force. Similarly, in the two hinges 17a, 17b, the piezoelectric elements 42, 48 can generate symmetrical and complementary tensile and compressive stresses. A compressive force acts on the piezoelectric element 42, while a tensile force acts on the piezoelectric element 48.

[0033] In the first hinge 15a, the piezoelectric element 25 has a width W in the axial direction of the reference axis 21 that is smaller than the distance S between the first elastic hinges 22a and 22b. Interference between the piezoelectric element 25 and the first elastic hinges 22a and 22b can be avoided between the fixed body 12 and the first link member 16. The tensile stress acting on the piezoelectric element 25 can be increased. Similarly, in the second hinge 15b, the piezoelectric element 32 has a width W in the axial direction of the reference axis 27 that is smaller than the distance S between the second elastic hinges 28a and 28b. Interference between the piezoelectric element 32 and the second elastic hinges 28a and 28b can be avoided between the first link member 16 and the movable body 13. The compressive stress acting on the piezoelectric element 32 can be increased. Similarly, in the third hinge 17a, interference between the piezoelectric element 42 and the third elastic hinges 38a and 38b can be avoided between the fixed body 12 and the second link member 18. In the fourth hinge 17b, interference between the piezoelectric element 48 and the fourth elastic hinges 45a, 45b between the second link member 18 and the movable body 13 can be avoided.

[0034] In the first hinge 15a, the upper electrode 51 and lower electrode 52 of the piezoelectric element 25 are sized to fit between the fixed body 12 and the first link member 16. In the piezoelectric element 25, deformation of the plate member 53 in the region sandwiched between the upper electrode 51 and the lower electrode 52 contributes to the generation of an electrical signal. If the upper electrode 51 and the lower electrode 52 fit between the fixed body 12 and the first link member 16, stress concentration can be effectively induced in the plate member 53 in the region sandwiched between the upper electrode 51 and the lower electrode 52. An external force F acting on the movable body 13 can be efficiently converted into an electrical signal. In this case, the rigidity of the force sensor 11 can be adjusted depending on the material and structure of the first elastic hinges 22a and 22b. The sensitivity of the force sensor 11 can be adjusted by adjusting the distance between the fixed body 12 and the first link member 16 relative to the size of the upper electrode 51 and the lower electrode 52. The rigidity and sensitivity can be effectively adjusted without changing the piezoelectric element 25. Similarly, in the piezoelectric element 32 of the second hinge 15b, the upper electrode 51 and the lower electrode 52 are located between the first link member 16 and the movable body 13, so that stress concentration can be effectively induced in the plate material 53 in the area sandwiched between the upper electrode 51 and the lower electrode 52.

[0035] In the first hinge 15a, one end of the piezoelectric element 25 is fixed to the fixed body 12 with thermosetting polyimide resin. An adhesive layer 62 fixes one end of the piezoelectric element 25 to the fixed body 12. The other end of the piezoelectric element 25 is fixed to the first link member 16 with thermosetting polyimide resin. An adhesive layer 63 fixes the other end of the piezoelectric element 25 to the first link member 16. Because thermosetting polyimide resin has high mechanical bonding strength, displacement of the first link member 16 effectively causes strain in the piezoelectric element 25. Mechanical losses such as plasticity and viscoelasticity can be suppressed. An external force F can be efficiently converted into strain in the piezoelectric element 25. Because thermosetting polyimide resin has electrical insulating properties, the piezoelectric element 25 can be effectively insulated from the fixed body 12 and the first link member 16. Leakage of electrical signals can be effectively prevented. Similarly, in the second hinge 15b, an adhesive layer 63 made of thermosetting polyimide resin fixes the piezoelectric element 32 to the first link member 16 or the movable body 13. Mechanical losses such as plasticity and viscoelasticity can be suppressed. The external force F can be efficiently converted into strain in the piezoelectric element 32.

[0036] When the fixed body 12, the first link member 16, and the movable body 13 are made of aluminum, an anodized coating 64 that receives the piezoelectric elements 25, 32 is formed on the surfaces of the fixed body 12 and the first link member 16. High adhesion can be established between the piezoelectric element 25 and the fixed body 12 and the first link member 16, and between the piezoelectric element 32 and the first link member 16 and the movable body 13. Depending on the adhesion, the piezoelectric element 25 can be firmly fixed to the fixed body 12 and the first link member 16. Similarly, depending on the adhesion, the piezoelectric element 32 can be firmly fixed to the first link member 16 and the movable body 13. An external force F can be efficiently converted into strain of the piezoelectric elements 25, 32.

[0037] Alternatively, when the fixed body 12, the first link member 16, and the movable body 13 are formed from stainless steel or an aluminum alloy, a wedge-effect film 64 that receives the piezoelectric elements 25, 32 is formed on the surfaces of the fixed body 12 and the first link member 16. High adhesion can be established between the piezoelectric element 25 and the fixed body 12 and the first link member 16, and between the piezoelectric element 32 and the first link member 16 and the movable body 13. Depending on the adhesion, the piezoelectric element 25 can be firmly fixed to the fixed body 12 and the first link member 16. Similarly, depending on the adhesion, the piezoelectric element 32 can be firmly fixed to the first link member 16 and the movable body 13. An external force F can be efficiently converted into strain of the piezoelectric elements 25, 32.

[0038] In this embodiment, the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b can be formed from aluminum or stainless steel, which has increased strength due to precipitation strengthening. In aluminum or stainless steel, which has increased strength due to precipitation strengthening, grain boundary migration and dislocation line growth can be effectively suppressed. Accumulation of plastic strain can be prevented in the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b. Even if the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b are subjected to repeated deformation, strain can be effectively generated in the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b. The durability of the force sensor 11 can be improved. Similarly, the third elastic hinges 38a, 38b and the fourth elastic hinges 45a, 45b can be formed from aluminum or stainless steel, which have increased strength due to precipitation strengthening.

[0039] Additionally, the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b can be formed from amorphous metal or metallic glass. In amorphous metal or metallic glass, migration of crystal grain boundaries and growth of dislocation lines can be avoided. Accumulation of plastic strain can be prevented in the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b. Even if the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b are subjected to repeated deformation, strain can be effectively generated in the first elastic hinges 22a, 22b and the second elastic hinges 28a, 28b. The durability of the force sensor 11 can be improved.

[0040] The inventors analyzed the stress acting on the piezoelectric element based on a simulation. As shown in FIG. 7, a simulation model similar to the first hinge 15a was constructed for the simulation. As a comparative example, a simulation model of an elastic hinge was constructed. In the comparative example, an elastic hinge was established over the entire area between the fixed body and the movable body. As a result of the analysis, stress concentration was confirmed at the two first elastic hinges 22a and 22b when the movable body (first link member 16) was displaced around the reference axis 21. In the piezoelectric element 25, stress concentration was confirmed between the fixed body 12 and the movable body (first link member 16). [Explanation of symbols]

[0041] 11 Force sensor 12 Fixed body 13 Movable body 15a First hinge 15b Second hinge 16 First link material 17a Third hinge 17b 4th hinge 18 Second link material 21 Reference axis 22a Elastic hinge (first elastic hinge) 22b Elastic hinge (first elastic hinge) 25 Piezoelectric element 27 Reference axis 28a Elastic hinge (second elastic hinge) 28b Elastic hinge (second elastic hinge) 32 Piezoelectric element 37 Reference axis 38a Elastic hinge (third elastic hinge) 38b Elastic hinge (third elastic hinge) 42 Piezoelectric element 44 Reference axis 45a Elastic hinge (fourth elastic hinge) 45b Elastic hinge (fourth elastic hinge) 48 Piezoelectric element 62 Adhesive layer 63 Adhesive layer 64 Anodized film or wedge effect film S interval W (piezoelectric element) width

Claims

1. a pair of elastic hinges that connect a movable body that displaces relative to the fixed body to the fixed body, have a shape that restricts displacement of the movable body around a reference axis, and are arranged at an interval in the axial direction of the reference axis; a piezoelectric element disposed between the elastic hinges, one end of which is fixed to the fixed body and the other end of which is fixed to the movable body; A force sensor comprising:

2. The piezoelectric element has a width in the axial direction of the reference axis that is smaller than the interval. The force sensor of claim 1 .

3. The piezoelectric element is formed to a size that can be accommodated between the fixed body and the movable body, and is stacked, and includes a pair of electrodes that sandwich a plate material of the piezoelectric body. The force sensor according to claim 2 .

4. The piezoelectric element is made of a quartz crystal. The force sensor according to claim 3 .

5. An adhesive layer is provided which is made of a thermosetting polyimide resin and fixes the piezoelectric element to the fixed body or the movable body. The force sensor of claim 1 .

6. The fixed body and the movable body are made of aluminum, and an anodized film that receives the piezoelectric element is formed on the surfaces of the fixed body and the movable body. The force sensor according to claim 5 .

7. The fixed body and the movable body are formed from stainless steel or aluminum, and a wedge-effect film that receives the piezoelectric element is formed on the surfaces of the fixed body and the movable body by precipitation hardening and selective corrosion. The force sensor according to claim 5 .

8. The elastic hinge is formed from aluminum or stainless steel, which has increased strength due to precipitation strengthening. The force sensor according to claim 5 .

9. a first link member having one end connected to the fixed body by a first hinge and the other end connected to the movable body by a second hinge; a second link member having the same length as the first link member and extending parallel to the first link member, one end of which is connected to the fixed body by a third hinge and the other end of which is connected to the movable body by a fourth hinge, and which cooperates with the first link member to realize parallel movement of the movable body; At least one of the first hinge, the second hinge, the third hinge, and the fourth hinge is a pair of elastic hinges each having a shape that restricts displacement of the movable body around a reference axis during the parallel movement, the elastic hinges being spaced apart in an axial direction of the reference axis; A piezoelectric element is disposed between the elastic hinges, the piezoelectric element having one end fixed to the fixed body or the movable body and the other end fixed to the first link member or the second link member. Force sensor.

10. The first hinge, the second hinge, the third hinge, or the fourth hinge, which is combined with any one of the first hinge, the second hinge, the third hinge, and the fourth hinge on the first link member or the second link member, a pair of second elastic hinges each having a shape that restricts displacement of the movable body around a reference axis during the parallel movement, and arranged at an interval in an axial direction of the reference axis; A piezoelectric element is disposed between the second elastic hinges, the piezoelectric element having one end fixed to the fixed body or the movable body and the other end fixed to the first link member or the second link member. The force sensor of claim 9.

11. The piezoelectric element includes a quartz crystal unit sandwiched between a pair of electrodes. The force sensor of claim 10.

12. An adhesive layer is formed from a thermosetting polyimide resin and fixes the piezoelectric element to the fixed body, the movable body, the first link material, or the second link material. The force sensor of claim 9.

13. The fixed body, the movable body, the first link material, or the second link material is formed from aluminum, and an anodized coating that receives the piezoelectric element is formed on the surface of the fixed body, the movable body, the first link material, or the second link material.

13. The force sensor of claim 12.

14. The fixed body, the movable body, the first link material, or the second link material is formed from stainless steel or aluminum, and a wedge effect film that receives the piezoelectric element is formed on the surface of the fixed body, the movable body, the first link material, or the second link material based on precipitation hardening treatment and selective corrosion.

13. The force sensor of claim 12.

15. The elastic hinge is formed from aluminum or stainless steel, which has increased strength due to precipitation strengthening.

13. The force sensor of claim 12.

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