Rotary shaft

Abstract

This rotary shaft (1) comprises a shaft body (30) and a torque sensor (10) for detecting torque generated in the shaft body (30). The torque sensor (10) includes: a first support part (11c); a second support part (11d) disposed so as to face the first support part (11c) at a distance therefrom; and a strain body (21) having a first end part attached to the first support part (11c), a second end part attached to the second support part (11d), and a plurality of strain gauges disposed on the surface thereof. The first support part (11c), the strain body (21), and the second support part (11d) are disposed along the axis of rotation of the shaft body (30). When defining the linear expansion coefficient of the strain body (21) as α1, the linear expansion coefficient of the shaft body (30) as α2, and the linear expansion coefficients of the first support part (11c) and the second support part (11d) as α3, α1>α2>α3 or α1<α2<α3.

Description

Rotating shaft

[0001] An embodiment of the present invention relates to a rotating shaft provided with a torque sensor.

[0002] In the automotive field, it is generally known to provide a torque sensor to detect torque generated in a rotating shaft. For example, a torque detection device in which a strain sensor is mounted on a protrusion on the outer circumferential surface of a shaft member is disclosed (see Patent Document 1). Torque sensors are also used in fields other than automotive. For example, a torque sensor that detects torque applied to the output shaft of a motor is disclosed in an actuating unit used in a robot or the like (see Patent Document 2). Furthermore, a robotic surgical system is disclosed in which multiple strain gauges are provided on the shaft of a manipulator to detect torque (see Patent Document 3). However, when a torque sensor is provided on the rotating shaft to be measured, if the rotating shaft deforms due to temperature changes, this deformation may reduce the accuracy of torque measurement.

[0003] Japanese Patent No. 6216879 Japanese Patent Application Laid-Open No. 2020-067295 Special Publication No. 2009-522016

[0004] An embodiment of the present invention provides a rotating shaft in which the effect of temperature changes on the measurement accuracy of a torque sensor is reduced. The rotating shaft of this embodiment includes a shaft body having a cylindrical outer shape and rotating, and a torque sensor that detects torque generated in the shaft body, wherein the torque sensor includes a first mounting portion attached to a surface of the shaft body, a second mounting portion attached to the surface of the shaft body, a first support portion provided on the first mounting portion, a second support portion provided on the second mounting portion and arranged to face the first support portion at a distance, and a flexure element having a first end attached to the first support portion and a second end attached to the second support portion, and a plurality of strain gauges arranged on a surface thereof, wherein the first support portion, the flexure element, and the second support portion are arranged along a rotation axis of the shaft body, and wherein, where α1 is a linear expansion coefficient of the flexure element, α2 is a linear expansion coefficient of the shaft body, and α3 is a linear expansion coefficient of the first support portion and the second support portion, α1 > α2 > α3 or α1 < α2 < α3.

[0005] FIG. 1 is a schematic diagram showing the configuration of a rotating shaft according to a first embodiment of the present invention. FIG. 2 is a plan view showing the configuration of a torque sensor according to the first embodiment. FIG. 3 is a cross-sectional view taken along line II-II shown in FIG. 2. FIG. 4 is a plan view showing a sensor main body according to the first embodiment. FIG. 5 is a cross-sectional view showing the configuration of a strain gauge according to the first embodiment. FIG. 6 is a cross-sectional view showing a torque sensor provided on the inner circumferential surface of a shaft main body of the rotating shaft according to the first embodiment. FIG. 7 is a schematic diagram for explaining the operation of the torque sensor according to the first embodiment. FIG. 8 is a schematic diagram for explaining the rigidity of the torque sensor according to the first embodiment. FIG. 9 is a plan view showing a sensor main body according to a first modified example of the first embodiment. FIG. 10 is a plan view showing a sensor main body according to a second modified example of the first embodiment. FIG. 11 is a cross-sectional view showing a first mounting configuration of a torque sensor according to a second modified example of the first embodiment. FIG. 12 is a cross-sectional view showing a second mounting configuration of a torque sensor according to the second modified example of the first embodiment. FIG. 13 is a perspective view showing a rotating shaft according to a third modified example of the first embodiment. FIG. 14 is a cross-sectional view showing a rotating shaft according to the third modified example of the first embodiment. Fig. 15 is a diagram showing the configuration of a rotary shaft according to a second embodiment of the present invention, and Fig. 16 is a cross-sectional view taken along line III-III shown in Fig. 15.

[0006] 1 is a schematic diagram showing the configuration of a rotary shaft 1 according to a first embodiment of the present invention. In the drawings, the same parts are denoted by the same reference numerals.

[0007] The rotating shaft 1 is a shaft that is rotated by a motor or the like. The rotating shaft 1 is equipped with a torque sensor 10 that detects torque generated by the rotation of the rotating shaft 1 itself. For example, the rotating shaft 1 is a shaft that serves as the rotation axis of the tires of an electric vehicle. Note that the rotating shaft 1 is not limited to the automotive field and may be used in any industry, such as robotics.

[0008] The rotating shaft 1 includes a shaft body 30 and a torque sensor 10. Note that the rotating shaft 1 may be provided with a plurality of torque sensors 10.

[0009] The shaft body 30 has a circular cross section and an elongated cylindrical shape like a rod. The shaft body 30 may be a hollow cylindrical shape with a hollow center, or a solid cylindrical shape with a filled center (columnar shape).

[0010] The torque sensor 10 is attached to the shaft body 30. The torque sensor 10 detects torque generated by rotation of the shaft body 30. For example, the torque detected by the torque sensor 10 is transmitted as an electrical signal to a control device that controls the rotation of the shaft body 30.

[0011] The torque sensor 10 according to this embodiment will be described with reference to Figures 2 to 4. Figure 2 is a plan view showing the configuration of the torque sensor 10. Figure 3 is a cross-sectional view taken along line II-II shown in Figure 2. Figure 4 is a plan view showing the sensor main body 11.

[0012] The torque sensor 10 includes a sensor body 11 and a strain sensor 20 attached to the sensor body 11 .

[0013] For example, the sensor body 11 has an overall rectangular plate shape. For example, the sensor body 11 is made of a metal such as stainless steel. The sensor body 11 may be formed by punching a metal plate or may be manufactured by other methods.

[0014] The sensor body 11 includes a first mounting portion 11a, a second mounting portion 11b, a first support portion 11c, a second support portion 11d, a first beam 11e, and a second beam 11f.

[0015] The first mounting portion 11a and the second mounting portion 11b are portions that are attached to the shaft body 30 by screws 27 and 28, respectively. The first support portion 11c is provided so as to protrude from the first mounting portion 11a. The second support portion 11d is provided so as to protrude from the second mounting portion 11b. The first beam 11e and the second beam 11f are provided on both sides of the first support portion 11c and the second support portion 11d, between the first mounting portion 11a and the second mounting portion 11b.

[0016] The strain sensor 20 is disposed between the first support portion 11c and the second support portion 11d. The strain sensor 20 includes a flexure body 21 and a plurality of strain gauges 22 disposed on the surface of the flexure body 21. For example, the flexure body 21 has a rectangular plate shape.

[0017] The mounting position of the torque sensor 10 on the shaft body 30 will be described with reference to FIG. 1 . The torque sensor 10 is mounted on the outer surface of the shaft body 30. The torque sensor 10 is mounted so that the longitudinal direction of the torque sensor 10 is aligned with the axis A (rotation axis or rotation center) about which the shaft body 30 rotates. Specifically, when the shaft body 30 is stationary (when no torque is applied), the first mounting portion 11a, first support portion 11c, strain element 21, second support portion 11d, and second mounting portion 11b, which are arranged in a straight line, are aligned along the axis A of the shaft body 30. In other words, the first support portion 11c, strain element 21, and second support portion 11d, which are arranged in series, are aligned parallel to the axis A of the shaft body 30.

[0018] In the torque sensor 10 arranged as described above, when torque is applied to the shaft body 30 in the direction of the arrow T in the figure, a twist occurs in the surface of the shaft body 30 in the same direction as the torque. That is, the shaft body 30 twists by an angle θ with respect to the axis A, causing a displacement Δ on the surface of the shaft body 30. As a result, the first support portion 11c of the torque sensor 10 is displaced in the direction of the arrow T relative to the second support portion 11d. This causes a distortion in the strain element 21, and this distortion is detected by the multiple strain gauges 22.

[0019] Two or more torque sensors 10 may be arranged symmetrically with respect to the shaft body 30. For example, two torque sensors 10 may be arranged on opposite sides of the axis A (180° from the axis A). This makes it possible to eliminate components other than torque based on the detection values ​​of the two torque sensors 10 by utilizing the symmetry of the arrangement of the two torque sensors 10, and to more accurately determine the detection value of only the torque component.

[0020] An example of the shape of the sensor main body 11 will be described with reference to Fig. 4. The length Lc of the first support portion 11c and the length Ld of the second support portion 11d are equal (Lc = Ld), and the first support portion 11c and the second support portion 11d are spaced a predetermined distance apart. Therefore, the tip of the first support portion 11c and the tip of the second support portion 11d face each other at a predetermined distance in the longitudinal direction of the sensor main body 11.

[0021] A first slit 11g is provided between the first beam 11e and each of the first support portion 11c and the second support portion 11d. A second slit 11h is provided between the second beam 11f and each of the first support portion 11c and the second support portion 11d. Therefore, both longitudinal side surfaces of the first support portion 11c and both longitudinal side surfaces of the second support portion 11d are spaced apart from the first beam 11e and the second beam 11f.

[0022] The first beam 11e and the second beam 11f are provided to maintain a constant distance between the first support portion 11c and the second support portion 11d. Therefore, in order to avoid affecting the torque detection sensitivity, it is preferable that the width of the first beam 11e and the second beam 11f (the length in the direction perpendicular to the longitudinal direction of the torque sensor 10) is as narrow as possible and the rigidity of the first beam 11e and the second beam 11f is as small as possible.

[0023] The widths of the first beam 11e and the second beam 11f are narrowed by providing the first slit 11g and the second slit 11h, respectively, so that the rigidity of the first beam 11e and the second beam 11f is smaller than the rigidity of the strain body 21. Note that only one of the first beam 11e and the second beam 11f may be provided.

[0024] The first mounting portion 11a includes a plurality of holes 11i into which a plurality of screws 27 are inserted in a direction perpendicular to the longitudinal direction of the sensor body 11. The second mounting portion 11b includes a plurality of holes 11j into which a plurality of screws 28 are inserted in a direction perpendicular to the longitudinal direction of the sensor body 11.

[0025] The first support portion 11c includes a screw hole 11k into which the screw 24 is screwed. The second support portion 11d includes a screw hole 11l into which the screw 26 is screwed.

[0026] The configuration of the strain sensor 20 will be described with reference to Figures 2 and 3. The strain sensor 21 is made of a metal such as aluminum. However, the strain sensor 21 may be made of a metal other than aluminum, or ceramic, etc. Four strain gauges 22 are arranged along the diagonal of the rectangular strain sensor 21. The four strain gauges 22 form a bridge circuit. However, any number of strain gauges 22 may be provided, any arrangement may be made, and any type of electrical circuit may be formed.

[0027] As shown in FIG. 3, the thickness Ta of the flexure body 21 (the length in the direction perpendicular to the plane of the flexure body 21) is thinner than the thickness Tb of the first support portion 11c and the second support portion 11d (the length in the direction perpendicular to the plane of the first support portion 11c and the second support portion 11d) (Ta<Tb).

[0028] As shown in FIG. 2, the width Wa of the strain element 21 is narrower than the width Wb of the first support portion 11c and the second support portion 11d (Wa<Wb).

[0029] The configuration of the strain gauge 22 will be described with reference to Fig. 5. The strain gauge 22 is not limited to the configuration described here, and may be configured in any way.

[0030] The strain gauge 22 includes an elastic body 22a, an insulating film 22b, a thin-film resistor (strain-sensitive film) 22c, an adhesive film 22d, thin-film wiring 22e, an adhesive film 22f, and a glass film 22g as a protective film. Specifically, the insulating film 22b is provided on the elastic body 22a, and the thin-film resistor 22c is provided on the insulating film 22b. For example, the thin-film resistor 22c is made of a Cr—N resistor. A thin-film wiring 22e serving as an electrode lead and made of a conductive material such as copper is provided on the end of the thin-film resistor 22c, with the adhesive film 22d interposed therebetween. An adhesive film 22f is provided on the thin-film wiring 22e. The insulating film 22b, the thin-film resistor 22c, and the adhesive film 22f are covered with a glass film 22g. The adhesive film 22d improves adhesion between the thin-film wiring 22e and the thin-film resistor 22c. The adhesive film 22f improves adhesion between the thin-film wiring 22e and the glass film 22g. The elastic body 22a is made of a metal such as stainless steel or an aluminum alloy, or a silicon substrate, etc. The adhesive films 22d and 22f are films containing chromium (Cr) or the like.

[0031] A specific method for attaching the torque sensor 10 to the shaft body 30 will be described with reference to FIG.

[0032] A first end of the strain sensor 20 (flexure element 21) is disposed on the first support portion 11c. A second end of the strain sensor 20 is disposed on the second support portion 11d. The first end of the strain sensor 20 is fixed to the first support portion 11c by a first fixing member 23 and a screw 24 disposed on the first support portion 11c. The second end of the strain sensor 20 is fixed to the second support portion 11d by a second fixing member 25 and a screw 26 disposed on the second support portion 11d.

[0033] The first fixing member 23 contacts the upper surface of the first support portion 11c at the first protrusion 23a and contacts the first end of the strain sensor 20 at the second protrusion 23b. The second protrusion 23b is shorter than the first protrusion 23a. A hole 23c is located between the first protrusion 23a and the second protrusion 23b of the first fixing member 23.

[0034] The screw 24 is inserted into the hole 23c and threaded into the screw hole 11k of the first support portion 11c, whereby the first protrusion 23a is fixed to the first support portion 11c and the second protrusion 23b is brought into line contact with the first end of the strain sensor 20. In this way, the first end of the strain sensor 20 is fixed to the first support portion 11c.

[0035] The configuration of the second fixing member 25 is similar to that of the first fixing member 23, and includes a third protrusion 25a that contacts the upper surface of the second support portion 11d, a fourth protrusion 25b that contacts the second end of the strain sensor 20 and is shorter in length than the third protrusion 25a, and a hole 25c located between the third protrusion 25a and the fourth protrusion 25b.

[0036] The screw 26 is inserted into the hole 25c and threaded into the screw hole 111 of the second support portion 11d, whereby the third protrusion 25a is fixed to the second support portion 11d and the fourth protrusion 25b is brought into line contact with the second end of the strain sensor 20. In this way, the second end of the strain sensor 20 is fixed to the second support portion 11d.

[0037] The torque sensor 10 having the above configuration is attached to the surface of the shaft body 30 by inserting screws 27 into each of the multiple holes 11i provided in the first mounting portion 11a and screws 28 into each of the multiple holes 11j provided in the second mounting portion 11b.

[0038] Therefore, the relationship between the length between the fixed portions of the strain body 21 (the length between the second protrusion 23 b and the third protrusion 25 b, or the effective length of the strain body 21) La and the length between the first mounting portion 11 a and the second mounting portion 11 b (the length between the center of the screw 27 and the center of the screw 28, or the effective length of the sensor body 11) Lb is La<Lb.

[0039] 1, the torque sensor 10 is attached to the outer surface (outer circumferential surface) of the shaft body 30, but this is not limiting and the torque sensor 10 may be attached to the inner surface (inner circumferential surface) of the shaft body 30. Specifically, in FIG. 3, the surface of the shaft body 30 on which the torque sensor 10 is provided may be the inner circumferential surface of the shaft body 30. FIG. 6 is a cross-sectional view of the torque sensor 10 provided on the inner circumferential surface of the shaft body 30, as viewed from the direction of the axis A. When the torque sensor 10 is provided on the inner circumferential surface of the shaft body 30, the wiring of the torque sensor 10 (for example, the wiring of the strain gauge 22) can be arranged in a cavity inside the cylinder of the shaft body 30, thereby making effective use of the internal space of the shaft body 30.

[0040] The operation of the torque sensor according to this embodiment will be described with reference to Figures 1 and 7. Figure 1 shows a schematic diagram of the positions of the shaft body 30 and the torque sensor 10.

[0041] The first support portion 11 c, the strain element 21, and the second support portion 11 d, which are arranged in series in the torque sensor 10, are arranged in parallel along the axis A of the shaft body 30.

[0042] Since the rigidity of the first support portion 11c and the second support portion 11d is sufficiently greater than the rigidity of the strain body 21, the displacement X1 of the first support portion 11c relative to the second support portion 11d is not greater than the displacement X2 of the first attachment portion 11a relative to the second attachment portion 11b. Specifically, the displacement of the first support portion 11c relative to the second support portion 11d and the displacement of the first attachment portion 11a relative to the second attachment portion 11b are substantially the same.

[0043] On the other hand, the effective length La of the flexure body 21 is sufficiently shorter than the effective length Lb of the sensor main body 11 (the length between the center of the screw 27 and the center of the screw 28). Therefore, the torsion angle θ1 of the flexure body 21 is larger than the torsion angle θ2 of the sensor main body 11. Therefore, the flexure body 21 deforms more than the sensor main body 11, and the amount of strain received by the flexure body 21 is larger than the amount of strain received by the sensor main body 11, resulting in amplified strain. Therefore, a large amplified signal is output from the multiple strain gauges 22 arranged on the flexure body 21.

[0044] Here, we will explain the rigidity of the first support portion 11c, the second support portion 11d, and the strain body 21. One end of the first support portion 11c and one end of the second support portion 11d are connected to the first attachment portion 11a and the second attachment portion 11b, respectively. Therefore, the first support portion 11c and the second support portion 11d can be considered to be deformed cantilevers.

[0045] In the cantilever beam shown in FIG. 8, if the length of the beam is L and the displacement of the beam when a load P is applied to the free end of the beam is ymax, ymax is expressed by the following equation (1).

[0046] ymax = PL3 / 3EI (1) where I: moment of inertia E: Young's modulus Transforming equation (1) gives equation (2): P = 3EIymax / L3 (2) 3EI / L3 is like a spring constant, and can be thought of as equivalent to rigidity.

[0047] In this embodiment, the value of 3EI / L3 is set to be larger in the first support portion 11c and the second support portion 11d (sections of length Lc and length Ld (Lc=Ld)) than in the strain element 21 (section of effective length La).

[0048] Specifically, the value of 3EI / L3 can be found by substituting the Young's moduli of the flexure element 21, the first support portion 11c, and the second support portion 11d into E, and substituting the geometrical moment of inertia of the flexure element 21, the first support portion 11c, and the second support portion 11d into I (the geometrical moment of inertia in the direction perpendicular to the plane in the plan view shown in FIG. 2).

[0049] For example, if the cross sections of the first support portion 11c and the second support portion 11d are rectangular, the thickness in the direction perpendicular to the plane is t, and the width in the direction perpendicular to the longitudinal direction is W, the second moment of area Is of the section of lengths Lc and Ld of the first support portion 11c and the second support portion 11d is expressed by equation (3).

[0050] Is=tW3 / 12 (3) Because the sections of lengths Lc and Ld of the first support portion 11c and the second support portion 11d are divided into two sections with the strain element 21 in between, the value equivalent to the rigidity is the sum of the rigidities of the sections of lengths Lc and Ld. Therefore, the rigidity of the section of lengths Lc and Ld is expressed by equation (4).

[0051] 2(3EI / L3) ... (4) As described above, the configurations of the flexure body 21, the first support portion 11c, and the second support portion 11d can be defined. In this embodiment, the relationship between the rigidity of the flexure body 21 and the first support portion 11c and the second support portion 11d is such that the rigidity of the flexure body 21 is smaller than the rigidity of the first support portion 11c and the second support portion 11d (rigidity of the flexure body 21<rigidity of the first support portion 11c and the second support portion 11d).

[0052] Specifically, the sensor body 11, including the strain body 21 and the first and second support portions 11 c and 11 d, is made of metal, such as stainless steel. The thickness Ta of the strain body 21 is thinner than the thickness Tb of the first and second support portions 11 c and 11 d, and the width of the strain body 21 is narrower than the width of the first and second support portions 11 c and 11 d.

[0053] The materials of the strain element 21 and the sensor body 11 can be combined with other materials as long as the above-mentioned rigidity relationship is satisfied.

[0054] The strain body 21 is fixed to the first support portion 11c and the second support portion 11d using the first fixing member 23, the second fixing member 25, and the screws 24, 26, respectively, but this is not limitative and the strain body 21 may be fixed using an adhesive, welding, or the like.

[0055] The sensor body 11 is fixed to the shaft body 30 using a plurality of screws 27, 28, but this is not limitative and the sensor body 11 may be fixed using adhesive, welding, or the like.

[0056] (Regarding Linear Expansion) In this embodiment, the first support portion 11c, the flexure body 21, and the second support portion 11d are arranged in series and are disposed on the shaft body 30. If the shaft body 30, the first support portion 11c, the flexure body 21, and the second support portion 11d are made of the same material, the coefficients of linear expansion with respect to temperature changes are equal, and therefore no expansion or compression force is generated in the flexure body 21.

[0057] However, depending on the material of the flexure body 21, it may be difficult to form a film of the strain gauge 22 on the flexure body 21, and it may be difficult to form the flexure body 21, the shaft body 30, the first support portion 11c, and the second support portion 11d from the same material. If these materials are different, a tensile force or a compressive force will be generated in the flexure body 21 due to temperature changes, and the torque measurement accuracy will decrease.

[0058] Therefore, in this embodiment, the relationship between the linear expansion coefficients of the strain body 21, the first support portion 11c, the second support portion 11d, and the shaft body 30 is adjusted to be strain body 21 < shaft body 30 < first support portion 11c, second support portion 11d.

[0059] Specifically, when the temperature changes by ΔT, if the sum of the linear expansion Lex1 of the shaft main body 30, the linear expansion Lex2 of the strain body 21 of the torque sensor 10, and the linear expansion Lex3 of the first support portion 11 c and the second support portion 11 d is equal (Lex1 = Lex2 + Lex3), no force is generated in the strain body 21.

[0060] Here, Lex1 = α2 Lb ΔT Lex2 = α1 La ΔT Lex3 = α3 (Lb - La) ΔT La: effective length of flexure body 21 Lb: length of shaft body 30 between first attachment portion 11a and second attachment portion 11b (effective length of shaft body 30) Then, Lex1 = Lex2 + Lex3 α2 Lb ΔT = α1 La ΔT + α3 (Lb - La) ΔT Therefore, if the following formula (5) is satisfied, no force due to temperature change will be generated in the flexure body 21. La = Lb (α2 - α3) / (α1 - α3) ... (5) In this case, the relationship of the linear expansion coefficients will be α1 > α2 > α3 or α1 < α2 < α3.

[0061] For example, the flexure element 21 may be made of stainless steel, the shaft body 30 may be made of aluminum alloy, and the first support portion 11c and the second support portion 11d may be made of zinc alloy. In this case, the linear expansion coefficient α2 of the aluminum alloy is greater than the linear expansion coefficient α1 of stainless steel (α1<α2) and less than the linear expansion coefficient α3 of the zinc alloy (α2<α3). Therefore, the first support portion 11c and the second support portion 11d, which have a large linear expansion coefficient, and the flexure element 21, which has a small linear expansion coefficient, can bring the overall linear expansion of the flexure element 21, the first support portion 11c, and the second support portion 11d closer to the linear expansion of the shaft body 30. This improves the accuracy of torque measurement in response to temperature changes.

[0062] Effect of the Embodiment According to the rotating shaft 1 of this embodiment, the strain body 21 including multiple strain gauges 22 is joined between the first support portion 11c and the second support portion 11d of the sensor main body 11, and torsion of the shaft main body 30 is detected by converting it into displacement between the first support portion 11c and the second support portion 11d, and into displacement of the strain body 21. In other words, the displacement of the first support portion 11c and the second support portion 11d has the effect of magnifying the amount of torsion of the shaft main body 30. This allows the multiple strain gauges 22 provided on the strain body 21 to output a large signal. This therefore allows for improved torque measurement accuracy compared to when multiple strain gauges are provided directly on the surface (outer or inner peripheral surface) of the shaft main body 30 to detect slight strain.

[0063] Furthermore, first slits 11g are provided between the first beam 11e and the first support portion 11c and the second support portion 11d, and second slits 11h are provided between the second beam 11f and the first support portion 11c and the second support portion 11d. This allows the rigidity of the first beam 11e and the second beam 11f to be smaller than the rigidity of the strain body 21, thereby increasing the displacement of the first mounting portion 11a and the second mounting portion 11b. This also increases the displacement of the strain body 21 between the first support portion 11c and the second support portion 11d, allowing larger signals to be output from the multiple strain gauges 22 and improving the torque measurement accuracy.

[0064] Furthermore, the relationship between the linear expansion coefficient α1 of the strain body 21, the linear expansion coefficient α3 of the first support portion 11c and the second support portion 11d, and the linear expansion coefficient α2 of the shaft body 30 satisfies α1>α2>α3 or α1<α2<α3, so that no force due to temperature changes is generated in the strain body 21. This improves the accuracy of measuring torque relative to temperature changes.

[0065] 9 shows a sensor body 11 according to a first modification of the present embodiment. The basic sensor body 11 shown in FIG. 4 includes a first beam 11e, a second beam 11f, a first slit 11g, and a second slit 11h between the first mounting portion 11a and the second mounting portion 11b.

[0066] In contrast, the sensor body 11 of the first modified example does not include the first beam 11e, the second beam 11f, the first slit 11g, and the second slit 11h, but includes an opening 11m between the first support portion 11c and the second support portion 11d.

[0067] In the first variant, the rigidity of the sensor body 11 and the first support portion 11c and second support portion 11d is higher than that of the basic form, so that the displacement of the first support portion 11c and second support portion 11d in response to twisting of the shaft body 30 is smaller than that of the basic form, but an effect almost the same as that of the basic form can be obtained.

[0068] 10 shows a sensor body 11 according to a second modification of this embodiment. The sensor body 11 according to the second modification is separated into a first body 111 and a second body 112.

[0069] In the second modified example, because the first body 111 and the second body 112 are separated, the first body 111 and the first support portion 11c are displaced in the same manner, and the second body 112 and the second support portion 11d are displaced in the same manner in response to a twist of the shaft body 30. Therefore, the strain element 21 joined between the first support portion 11c and the second support portion 11d undergoes a larger displacement than in the basic form. Therefore, the multiple strain gauges 22 can output a larger signal than in the basic form, improving the torque measurement accuracy.

[0070] In the case of the second modified example, it is necessary to maintain a constant distance between the first body 111 and the second body 112 .

[0071] FIG. 11 shows a first mounting configuration of the torque sensor 10 according to the second modified example of this embodiment. In FIG. 11 , the shaft body 30 has a first protrusion 30a as a first engagement portion and a second protrusion 30b as a second engagement portion on its surface. The first protrusion 30a and the second protrusion 30b are arranged at a predetermined distance along the axial direction A of the shaft body 30 and define the distance between the first body 111 and the second body 112. That is, the side surface of the first body 111 facing the first mounting portion 11a is arranged in contact with the first protrusion 30a, and the side surface of the second body 112 facing the second mounting portion 11b is arranged in contact with the second protrusion 30b. The rest of the configuration is the same as the mounting configuration of the basic type.

[0072] In this way, by providing the first protrusion 30a and the second protrusion 30b on the surface of the shaft body 30, the separated first body 111 and second body 112 can be positioned a predetermined distance apart, thereby improving the dimensional accuracy between the first body 111 and the second body 112.

[0073] 12 shows a second mounting configuration of the torque sensor 10 according to the second modified example of the present embodiment. In FIG. 12, the shaft body 30 has a recess 31c on the surface and a cover 31d that covers the recess 31c.

[0074] The longitudinal direction of the recess 31c is arranged along the axis A of the shaft body 30, and the longitudinal length Le of the recess 31c defines the distance between the first body 111 and the second body 112. The side surface of the first body 111 on the first mounting portion 11a side is arranged in contact with one longitudinal side surface (first engagement portion) of the recess 31c, and the side surface of the second body 112 on the second mounting portion 11b side is arranged in contact with the other longitudinal side surface (second engagement portion) of the recess 31c. The other configurations are the same as the mounting configuration of the basic form.

[0075] In this way, by providing a recess 31c on the surface of the shaft body 30, the separated first body 111 and second body 112 can be positioned a predetermined distance apart, thereby improving the dimensional accuracy between the first body 111 and the second body 112.

[0076] Furthermore, the recess 31c displaces in response to applied torque in the same manner as the surface of the shaft body 30, so torque can be measured in the same manner as with the basic shape.

[0077] In the second mounting configuration, a torque sensor 10 having a sensor body 11 of the second modified example shown in Figure 10 is placed in the recess 31c, but this is not limited to this, and it is also possible to place a torque sensor having a sensor body 11 of the basic type or the first modified example.

[0078] 13 and 14 show a rotating shaft 1 according to a third modified example of the present embodiment. Fig. 13 is a perspective view showing the rotating shaft 1. Fig. 14 is a cross-sectional view of the rotating shaft 1 shown in Fig. 13 taken along a plane that is parallel to and passes through the axis A, so as to cut the rotating shaft 1 shown in Fig. 13 together with the strain sensor 20 in the longitudinal direction.

[0079] The sensor main body 11 of the third modified example is composed of a first main body 111a and a second main body 112a. The first main body 111a and the second main body 112a correspond to the first main body 111 and the second main body 112, respectively, of the sensor main body 11 of the second modified example shown in FIG.

[0080] As in the second modification, the first body 111a and the second body 112a are arranged at a predetermined distance from each other, and the strain sensor 20 is arranged to straddle the first body 111a and the second body 112a at a predetermined distance from each other.

[0081] The sensor body 11 is formed as a whole in a ring shape that covers the entire outer circumferential surface of the shaft body 30. That is, the sensor body 11 is formed so as to wrap around the shaft body 30 around the axis A. The surface of the sensor body 11 on which the strain sensor 20 is provided is plate-shaped, and a cavity is formed between the sensor body 11 and the shaft body 30.

[0082] The end portions of the surfaces of the first body 111a and the second body 112a are bent perpendicularly toward the shaft body 30. This allows the end portions of the surfaces of the first body 111a and the second body 112a to be fixed to the outer circumferential surface of the shaft body 30. The first body 111a and the second body 112a may be fixed to the outer circumferential surface of the shaft body 30 by any method, such as screws, adhesive, or welding.

[0083] Even when the third modification is adopted, it is possible to obtain substantially the same effect as the second modification. Furthermore, if the distance between both ends of the sensor main body 11 (the end of the first main body 111a and the end of the second main body 112a) is Lb and the distance between the first main body 111a and the second main body 112a is La, the amplification factor of the strain detected by the strain sensor 20 is Lb / La.

[0084] Second Embodiment Fig. 15 is a diagram showing the configuration of a rotating shaft 1A according to a second embodiment of the present invention. Fig. 16 is a cross-sectional view taken along line III-III shown in Fig. 15. Note that in Fig. 15, the cross section is the same as in Fig. 3 except for the fixing member 40, in order to make the attachment state easier to understand.

[0085] In the rotating shaft 1 of the first embodiment, the sensor body 11 was fixed to the shaft body 30 by screws 27 and 28, but in the rotating shaft 1A of this embodiment, the sensor body 11A is fixed to the shaft body 30 by two fixing members 40.

[0086] The sensor body 11A according to this embodiment is similar to the sensor body 11 according to the first embodiment, except that the holes 11i and 11j through which the screws 27 and 28 are inserted are removed, and a linearly extending protrusion 11Aa that is parallel to the axis A (the longitudinal direction of the shaft body 30) and makes line contact with the shaft body 30 is provided on the back surface of the sensor body 11 (the contact surface with the shaft body 30). Here, the sensor body 11 according to the first embodiment, which serves as the base for the sensor body 11A according to this embodiment, may be any of the basic form, the first modified form, or the second modified form. Note that the protrusion 11Aa may be modified to any shape or may not be present.

[0087] The fixing member 40 includes an upper frame 41, a lower frame 42, and two screws 43. The upper frame 41 and the lower frame 42 are semi-cylindrical, formed by dividing a cylinder into two halves along the axial direction. The inner circumferential surfaces of the upper frame 41 and the lower frame 42 are curved so that, when the upper frame 41 and the lower frame 42 are aligned with a small gap between them, a cylindrical space is formed inside to accommodate the shaft body 30. A rectangular recess 41a is formed in each inner circumferential surface of the upper frame 41 and the lower frame 42, into which the first mounting portion 11a or the second mounting portion 11b of the sensor main body 11A is fitted. Rectangular plate-like protrusions 41b and 42b are formed at both circumferential ends of the upper frame 41 and the lower frame 42, respectively. Threaded holes into which the screws 43 are threaded are formed in the protrusions 41b and 42b.

[0088] 15 and 16 , a method for attaching the torque sensor 10 to the shaft body 30 using the fixing member 40 will be described. Here, a method for attaching two torque sensors 10 to the shaft body 30 will be described, but any number of torque sensors 10 greater than or equal to one may be attached to the shaft body 30.

[0089] Two torque sensors 10 are arranged at attachment positions on the outer circumferential surface of the shaft body 30. For example, the two torque sensors 10 are arranged at positions 180° apart from the axis A of the shaft body 30. In other words, the two torque sensors 10 are arranged so that they are directly opposite each other. When arranging multiple torque sensors 10, arranging them at equal intervals on the outer circumferential surface of the shaft body 30 makes it easier to eliminate forces other than those being measured and to determine only the torque of the object being measured. However, the torque sensors 10 may be arranged in any manner.

[0090] After placing the two torque sensors 10 in predetermined positions, the shaft body 30 is sandwiched from above and below between the upper frame 41 and the lower frame 42 together with the first mounting portion 11a or the second mounting portion 11b of each sensor body 11A of the two torque sensors 10, thereby fixing the two sensor bodies 11A to the shaft body 30.

[0091] The first mounting portion 11a located at one longitudinal end of each of the two sensor bodies 11A is fixed with one fixing member 40, and the second mounting portion 11b located at the other longitudinal end of each of the two sensor bodies 11A is fixed with another fixing member 40. By threading screws 43 into screw holes provided in the protrusions 41b, 42b of the upper frame 41 and lower frame 42 of each of the two fixing members 40, the upper frame 41 and the lower frame 42 are fixed so that contact between the shaft body 30 and the two sensor bodies 11A is maintained. The sensor bodies 11A are fixed in line contact with the outer circumferential surface of the shaft body 30 parallel to the axis A by protrusions 11Aa provided on the back surface of each of the sensor bodies 11A.

[0092] According to this embodiment, in addition to the same effects as those of the first embodiment, the following effects can be obtained.

[0093] By using the fixing member 40 to fix the torque sensor 10 to the shaft body 30, there is no need to perform processing (for example, forming a screw hole) to fix the torque sensor 10 to the shaft body 30.

[0094] The sensor main body 11A and the shaft main body 30 are not joined by welding or screwing, but are fixed in a contacting state, so that the sensor main body 11A is less likely to be deformed by longitudinal deformation of the shaft main body 30. This reduces the influence of longitudinal deformation of the shaft main body 30 (deformation unrelated to torque), and improves the measurement accuracy of the torque of the object to be measured.

[0095] By providing a protrusion 11Aa on the sensor body 11A and fixing the sensor body 11A and the shaft body 30 in a line contact state, the influence of deformation of the shaft body 30 due to temperature changes on the torque measurement accuracy can be reduced. Specifically, by bringing the outer peripheral surfaces of the sensor body 11A and the shaft body 30 into line contact in the longitudinal direction (parallel to the axis A), the coefficient of friction between the sensor body 11A and the shaft body 30 in the longitudinal direction is low, and the coefficient of friction between the sensor body 11A and the shaft body 30 in the longitudinal direction and perpendicular directions is high. As a result, the sensor body 11A is less likely to deform when the shaft body 30 is deformed in the longitudinal direction (deformation unrelated to torque), but is more likely to deform when the shaft body 30 is deformed in the longitudinal direction and perpendicular directions (deformation related to torque). Therefore, the influence of deformation in the longitudinal direction of the shaft body 30 due to forces unrelated to torque is reduced, making it easier to measure the torque of the object to be measured.

[0096] Even if the sensor main body 11A does not have the protrusion 11Aa, line contact can be achieved by bringing the planar back surface of the sensor main body 11A into contact with the outer circumferential surface of the shaft main body 30. Therefore, similar to the case where the protrusion 11Aa is provided, the effect of reducing the influence of deformation in the longitudinal direction of the shaft main body 30 can be obtained.

[0097] Although each embodiment has been described with reference to a configuration in which a torque sensor that detects only torque is provided, each embodiment is not limited to a torque sensor that detects only torque. For example, a configuration in which a torque sensor (e.g., a force sensor) that measures torque and forces in directions other than torque is provided may also be provided.

[0098] Furthermore, the present invention is not limited to the above-described embodiments, and in the implementation stage, the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

Claims

1. A rotating shaft comprising: a rotating shaft body having a cylindrical outer shape; and a torque sensor that detects torque generated in the shaft body, wherein the torque sensor comprises: a first attachment portion attached to the surface of the shaft body; a second attachment portion attached to the surface of the shaft body; a first support portion provided on the first attachment portion; a second support portion provided on the second attachment portion and arranged to face the first support portion at a distance; and a flexure element having a first end attached to the first support portion and a second end attached to the second support portion and having a plurality of strain gauges arranged on its surface, wherein the first support portion, the flexure element, and the second support portion are arranged along the axis of rotation of the shaft body, wherein, where the linear expansion coefficient of the flexure element is α1, the linear expansion coefficient of the shaft body is α2, and the linear expansion coefficients of the first support portion and the second support portion are α3, α1>α2>α3 or α1<α2<α3.

2. The rotating shaft according to claim 1, wherein the following relationship is satisfied: La = Lb · (α2 - α3) / (α1 - α3), where La is the effective length of the strain element and Lb is the effective length of the shaft main body.

3. A rotating shaft as described in claim 1, further comprising at least one beam connecting the first mounting portion and the second mounting portion, and at least one slit provided between the at least one beam and the first support portion and between the at least one beam and the second support portion, wherein the width of the at least one beam is smaller than the widths of the first support portion and the second support portion.

4. The rotary shaft according to claim 1, wherein the surface of the shaft body is the outer circumferential surface of the shaft body.

5. The rotary shaft according to claim 1, wherein the surface of the shaft body is an inner peripheral surface of the shaft body.

6. A rotating shaft as described in claim 4, comprising: a first fixing member that fixes the first support portion and the surface of the shaft body in contact with each other and accommodates the first attachment portion and the shaft body inside; and a second fixing member that fixes the second support portion and the surface of the shaft body in contact with each other and accommodates the second attachment portion and the shaft body inside.

7. A rotating shaft according to claim 6, wherein the first support portion and the surface of the shaft body are fixed in line contact, and the second support portion and the surface of the shaft body are fixed in line contact.

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