Torque detector

Abstract

To be non-sensitive to strain occurring by a bending moment to be applied to a straining part upon torque detection.SOLUTION: A straining part 111 of an I cut is adopted, and a revolving torque to be applied to a revolving shaft 110 is detected by acquiring a change in resistance values of strain sensitive resistors Ga1 and Ga2 affixed to a plane part 111a of the straining part 111 and resistance values of strain sensitive resistors Gb1 and Gb2 affixed to a plane part 111b of the straining part 111. Upon such detection, as for the strain sensitive resistors Ga1 and Ga2, they are affixed to the plane part 111a so that a direction having them affixed is a direction where they are non-sensitive to strain occurring by a bending moment to be applied to the straining part 111. Also, upon such detection, as for the strain sensitive resistors Gb1 and Gb2, they are affixed to the plane part 111b so that a direction having them affixed is a direction where they are non-sensitive to strain occurring by a bending moment to be applied to the straining part 111.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] This invention relates to a torque detector. [Background technology]

[0002] Various technologies have been proposed to detect the torque of a rotating shaft. One such proposed technology directly measures the torsion of the rotating shaft using a strain gauge. In this technology, a thin-walled strain-generating section is provided on the rotating shaft, and a strain gauge is attached to this section. The torque of the rotating shaft is then detected by measuring the resistance of the filament when the strain gauge deforms due to the torsion of the strain-generating section.

[0003] Here, the shape of the strain gauge attached to the strain generating part to detect the torque of the rotating shaft is such that, in order to accurately detect not only the torsion of unidirectional rotation but also the torsion of reverse rotation, a pair of strain gauges as shown in Figure 7 of Patent Document 1 is generally used (hereinafter referred to as the conventional example). In this conventional example, the strain generating part has a circular outer shape in cross-section formed by a plane perpendicular to the axial direction of the rotating shaft, and two strain gauges whose maximum sensitivity directions intersect at a 90-degree angle. Gauges in which the sensitivity directions of two strain gauges intersect in this way are called biaxial shear gauges, and each gauge is arranged side by side without gaps so as to face each other symmetrically in the direction of the center line of the rotating shaft (axial direction). In the conventional biaxial shear gauge, the pair of strain gauges are inclined at 45 degrees symmetrically with respect to a line perpendicular to the axial direction of the rotating shaft. Hereafter, the conventional biaxial shear gauge will also be referred to as the "45-degree inclined biaxial shear gauge". Furthermore, the filaments (resistors) that constitute a 45-degree inclined biaxial shear gauge are also referred to as "45-degree inclined strain-sensitive resistors" as a higher-level concept. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-077172 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, strain gauges consist of a filament ("strain-sensitive resistor," "sensing element"), a gauge base made of polyimide, and other materials. When the humidity of the environment in which the torque detector is used increases, the polyimide absorbs moisture from the surroundings, and the thickness of the gauge base increases.

[0006] Here, when a 45-degree inclined biaxial shear gauge is attached to a strain generating section (also referred to as a "round bar-type strain generating body") whose cross-section is circular due to a plane perpendicular to the axial direction of the rotating shaft, as the humidity of the operating environment increases, the polyimide absorbs surrounding moisture and swells according to the curvature of the round bar, increasing the thickness of the gauge base. As a result, tension is applied to the filament. In this case, if the filament is attached symmetrically to the round bar-type strain generating body, the effect of the tension applied to the filament due to the expansion of the gauge base is compensated for. However, if there is even a slight deviation in this symmetry, the output value when no torque is applied, that is, the zero-point output of the torque detector, will fluctuate, and unwanted signals other than torque will be included when detecting torque. For this reason, when a round bar-type strain generating body is used, it was sometimes not possible to accurately detect torque in a high-humidity environment.

[0007] To avoid such situations, for example, a round bar-shaped strain generating body can be processed to create a strain generating section with two planar portions that are oriented 180 degrees apart from each other and parallel to the axial direction. In this case, the cross-section of the strain generating section formed by the plane perpendicular to the axial direction of the rotation axis will be "I" shaped (hereinafter, this strain generating section will also be referred to as the "I-cut strain generating section"). Then, a configuration can be considered in which a biaxial shear gauge inclined at 45 degrees is attached to each planar portion so that the line of symmetry is parallel to the axial direction. When this configuration is adopted, since the gauge base is attached to the planar portion, tension is not applied to the filament of the biaxial shear gauge even if the thickness of the gauge base increases. As a result, when the biaxial shear gauge is attached to the planar portion, the expansion and contraction of the filament due to changes in humidity is smaller compared to when it is attached to a cylinder or cylindrical body, which is convenient for torque detection.

[0008] However, the thickness of the strain-generating portion sandwiching the two planar sections is thinner than the diameter of the non-planar portion of the strain-generating portion. This thinner portion has a smaller section modulus with respect to bending moment compared to the thicker portion. Therefore, when the rotation axis angle is around the angle where the section modulus is small, it is affected by the bending moment, which interferes with torque detection. Due to this influence of the bending moment, which interferes with torque detection and changes in the rotation axis angle, it becomes difficult to discriminate the measured torque. Here, if the pair of filaments of the biaxial shear gauge are perfectly symmetrical with respect to the bending moment axis, the influence of the bending moment can be compensated for. However, if the pair of filaments cannot be made perfectly symmetrical with respect to the bending moment axis, the influence of the bending moment appears as an interfering signal to torque detection that varies with the rotation angle. Therefore, it becomes impossible to measure the torque accurately.

[0009] Therefore, there is a strong demand for a technology that can detect torque while minimizing the influence of bending moment, especially when employing a strain-generating section capable of accurately detecting torque in high-humidity environments. Meeting this demand is one of the problems that this invention aims to solve.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a torque detector that does not detect strain caused by bending moment applied to the strain-generating part when detecting torque. [Means for solving the problem]

[0011] The present invention relates to a torque detector comprising a rotating shaft that is rotatably supported and has an elastically deformable strain-generating portion, and a strain-sensitive resistor attached to the strain-generating portion, wherein the strain-sensitive resistor is attached in a direction that does not sense the strain generated by the bending moment applied to the strain-generating portion, and the torque acting on the strain-generating portion is detected based on the output of a circuit including the strain-sensitive resistor. [Brief explanation of the drawing]

[0012] [Figure 1] This is an external view of a torque detector according to an embodiment of the present invention. [Figure 2] This is a view (part 1) of the inside of the torque detector of FIG. 1. [Figure 3] This is a view (part 2) of the inside of the torque detector of FIG. 1. [Figure 4] This is a cross-sectional view of the torque detector of FIG. 1. [Figure 5] This is a view of the rotating shaft of FIG. 2. [Figure 6] This is a plan view of a pair of strain gauges attached to the strained portion of the rotating shaft of FIG. 5. [Figure 7] This is a configuration diagram of a Wheatstone bridge circuit including a strain gauge and its surroundings in FIG. 6. [Figure 8] This is a diagram for conceptually explaining the state of the strained portion when the rotating shaft of FIG. 5 is twisted. [Figure 9] This is an external view when evaluating the bending moment of the torque detector of FIG. 1, and a diagram for conceptually explaining the state of the strained portion when a bending moment is applied. [Figure 10] This is a diagram for conceptually explaining the deformed state of the strained portion when a bending moment is applied. [Embodiments for Carrying Out the Invention]

[0013] Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. In the following description and drawings, the same or equivalent elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

[0014] [Configuration] FIG. 1 shows an external view of a torque detector 100 according to an embodiment. The coordinate system (X, Y, Z) for explaining the torque detector 100 is defined as shown in the figure.

[0015] Figures 2 and 3 show internal diagrams of the torque detector 100. Here, Figure 2 is a perspective view of the inside of the torque detector 100. Figure 3(A) is a view of the torque detector 100 shown in Figure 2 from the +Z direction, and Figure 3(B) is a view of the torque detector 100 shown in Figure 2 from the -Y direction. Figure 4 shows a cross-sectional view of the torque detector 100 when cut by the XZ plane P passing through the rotation axis of the torque detector 100 shown in Figure 1.

[0016] Furthermore, Figure 5 shows an external view of the rotating shaft portion of the torque detector 100. Here, Figure 5(A) is an external view of the rotating shaft portion of the torque detector 100 shown in Figure 2, with the +Z direction side of the rotating shaft visible. Figure 5(B) is an external view of the rotating shaft shown in Figure 5(A) rotated 180 degrees, with the -Z direction side of the rotating shaft visible.

[0017] As comprehensively shown in Figures 1 to 5, the torque detector 100 comprises a rotating shaft (rotating shaft member) 110, housings 121 to 123, and a cover portion 124. The rotating shaft 110 is provided with a strain generating portion 111. The torque detector 100 also includes strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2 attached to the strain generating portion 111. Furthermore, the torque detector 100 includes a rotating substrate 310, fixed substrates 321 and 322, a primary core 211, a secondary core 221, and the like.

[0018] The rotating shaft (rotating shaft member) 110 described above is a roughly cylindrical metal member whose shape changes in stages along the axial direction AX (X direction). Both ends of the rotating shaft 110 protrude from housings 121 and 122, which are parallel to the YZ plane, so that they can be connected to a load device and a drive device (not shown). The rotating shaft 110 is rotatably supported by housings 121 and 122 via bearings 131 and 132.

[0019] The strain-generating portion 111 provided on the rotation axis 110 has an I-cut shape with two planar portions 111a and 111b that are parallel to each other. These planar portions 111a and 111b are planes that include a line segment parallel to the axial direction AX and are provided at positions equidistant from the central axis of the rotation axis 110. Here, in Figure 5(A), the planar portion 111a is visible, and in Figure 5(B), the planar portion 111b opposite to the planar portion 111a is visible.

[0020] Strain-sensitive resistors Ga1 and Ga2 (hereinafter, a resistor containing a pair of strain-sensitive resistors Ga1 and Ga2 will also be referred to as a "strain-sensitive resistor pair Ga") are attached to the planar portion 111a of the strain-generating section 111. Strain-sensitive resistors Gb1 and Gb2 (hereinafter, a resistor containing a pair of strain-sensitive resistors Gb1 and Gb2 will also be referred to as a "strain-sensitive resistor pair Gb") are attached to the planar portion 111b of the strain-generating section 111. By acquiring the change in the resistance values ​​of the strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2, the rotational torque applied to the rotating shaft 110 can be detected. The configuration of the strain-sensitive resistors Ga1 and Ga2 and their attachment to the planar portion 111a, and the configuration of the strain-sensitive resistors Gb1 and Gb2 and their attachment to the planar portion 111b will be described later.

[0021] The housings 121 to 123 described above cover the internal components of the torque detector 100 and protect them from the external environment. Housings 121 and 122 are planar members parallel to the YZ plane and are paired. Housings 121 and 122 are provided with holes through which the rotating shaft 110 passes. Housings 121 and 122 rotatably support the rotating shaft 110 via paired bearings 131 and 132. Housing 123 is a hollow rectangular parallelepiped member with an opening.

[0022] The cover portion 124 described above is a planar member parallel to the XY plane and is secured with screws to close the opening in the housing 123. The cover portion 124 covers the internal components of the torque detector 100 and, together with the housings 121-123, protects the components of the torque detector 100 from the external environment.

[0023] The rotating substrate 310 described above has a hole in its center through which the rotating shaft 110 passes, and has a ring-shaped disc form. The rotating substrate 310 is passed through the rotating shaft 110 and fixed to the rotating shaft 110 by being sandwiched between a rotating shaft flange 112 with a step and a nut 125. Multiple electrical and electronic components, including a rotating-side optical element 331, are mounted on the rotating substrate 310. If there is an imbalance in the rotation of the rotating substrate 310, it will affect the detection of the rotational torque of the rotating shaft 110, so multiple electrical and electronic components are arranged considering rotational balance. The rotating-side optical element 331 placed on the rotating substrate 310 emits infrared light. The rotating substrate 310 is also equipped with an amplification circuit 311, an AD conversion circuit 312, a rotating-side CPU 313 (see Figure 8), and the like.

[0024] The fixed substrates 321 and 322 are electrically connected via a substrate-to-substrate connector (not shown). The fixed substrates 321 and 322 are also mechanically connected and fixed in place by spacers (not shown) to maintain their relative positions. The fixed substrate 322 is then screwed to the housings 121-123 to secure it in a predetermined position. The fixed substrate 321 is equipped with a fixed-side optical element 332, which receives infrared light emitted by the rotating-side optical element 331. The fixed substrates 321 and 322 also include a switching circuit, a fixed-side CPU, a DA (Digital to Analogue) conversion circuit, and other components.

[0025] The fixed substrate 322 is provided with the primary side of a separable rotary transformer for non-contact power supply to the rotating substrate 310. Specifically, a ferrite primary side core 211 with a U-shaped cross-section and protrusions at both ends is attached to the fixed substrate 322 via a core holder 213. A primary side coil 212, made of copper wire wound around the protrusions of the primary side core 211, is provided between the two protrusions.

[0026] On the other hand, the secondary side of the separate rotary converter is provided on the rotating shaft 110. Specifically, the secondary core 221 is attached to the rotating shaft 110 via the secondary core space 223. A secondary coil 222, made of copper wire wound around the outer circumference of the secondary core 221, is provided. The primary core 211 and the secondary core 221 are arranged facing each other.

[0027] Here, contactless power supply to the rotating substrate 310 will be described. The torque detector 100 is connected to an external control device (not shown) via a connector 340. This control device is connected to fixed substrates 321 and 322, and a switching circuit provided on the fixed substrate converts the DC current supplied from the control device into AC current. This switching circuit is connected to the primary coil 212 and outputs the converted AC current to the primary coil 212. The AC current sent from the switching circuit to the primary coil 212 generates an AC magnetic field in the primary coil 212, and this AC magnetic field passes through the rotating secondary core 221, inducing a current in the secondary coil 222.

[0028] Therefore, the secondary coil 222 can receive power from the primary coil 212 without contact. The current thus induced is converted into a DC voltage by the rectifier circuit and stabilization circuit in the rotating substrate 310, and this DC voltage is supplied to the amplifier circuit 311, AD conversion circuit 312, rotating CPU 313, etc., which are provided on the rotating substrate 310.

[0029] <Configuration of strain-sensitive resistors Ga1 and Ga2> Figure 6(A) shows a plan view of a strain-sensitive resistor pair Ga, including strain-sensitive resistors Ga1 and Ga2. As shown in Figure 6(A), the strain-sensitive resistor pair Ga has resistors and wiring patterned on a base film-like substrate a0, and comprises strain-sensitive resistor Ga1, strain-sensitive resistor Ga2, and terminal portions a1, a2, a3. The strain-sensitive resistors Ga1 and Ga2 and terminal portions a1, a2, a3 are arranged on the substrate a0 (on the same plane). The strain-sensitive resistors Ga1 and Ga2, terminal portions a1, a2, a3, and substrate a0 form a biaxial shear strain gauge.

[0030] In this embodiment, the substrate a0 is, for example, a dielectric polyimide film. The strain-sensitive resistors Ga1 and Ga2, and the terminals a1, a2, and a3 are made of metal, for example, an alloy of copper and nickel. One end of the strain-sensitive resistor Ga1 is connected to terminal a1 via a wiring section, and the other end of the strain-sensitive resistor Ga1 is connected to terminal a3 via a wiring section. One end of the strain-sensitive resistor Ga2 is connected to terminal a2 via a wiring section, and the other end of the strain-sensitive resistor Ga2 is connected to terminal a3 via a wiring section. Furthermore, if necessary, the strain-sensitive resistors Ga1, Ga2, the wiring sections, etc., are covered from above with a protective layer.

[0031] Each of the strain-sensitive resistors Ga1 and Ga2 is configured to include a folded pattern of multiple parallel linear resistors for strain detection, and the line width of the resistors is set to be relatively small. The strain-sensitive resistor Ga1 is disposed in region Ra1 of the base material a0, and the strain-sensitive resistor Ga2 is disposed in region Ra2 of the base material a0, and the strain-sensitive resistors Ga1 and Ga2 are arranged symmetrically along a line segment OB parallel to the axial direction AX.

[0032] The strain-sensitive resistor Ga1 is a single thin, linear resistor designed to detect strain with maximum sensitivity in direction pa1, and multiple linear resistors are arranged parallel to direction pa1 by a folded pattern. The strain-sensitive resistor Ga2 is a single thin, linear resistor designed to detect strain with maximum sensitivity in direction pa2, and multiple linear resistors are arranged parallel to direction pa2 by a folded pattern. The angle θ between directions pa1 and pa2 (angle from the linear direction perpendicular to the axial direction AX of the rotation axis) will be described later.

[0033] <Configuration of strain-sensitive resistors Gb1 and Gb2> Figure 6(B) shows a plan view of a strain-sensitive resistor pair Gb, including strain-sensitive resistors Gb1 and Gb2. As shown in Figure 6(B), the strain-sensitive resistor pair Gb is configured similarly to the strain-sensitive resistor pair Ga described above, with resistors and wiring patterned on a film-like substrate b0, and comprises strain-sensitive resistor Gb1, strain-sensitive resistor Gb2, and terminal portions b1, b2, b3. The strain-sensitive resistors Gb1 and Gb2 and terminal portions b1, b2, b3 are arranged on the substrate b0. A biaxial shear strain gauge is formed by the strain-sensitive resistors Gb1 and Gb2, terminal portions b1, b2, b3, and substrate b0.

[0034] In this embodiment, the substrate b0 is, for example, a dielectric polyimide film. The strain-sensitive resistors Gb1 and Gb2, and the terminals b1, b2, and b3 are made of metal, for example, an alloy of copper and nickel. One end of the strain-sensitive resistor Gb1 is connected to terminal b1 via a wiring section, and the other end of the strain-sensitive resistor Gb1 is connected to terminal b3 via a wiring section. One end of the strain-sensitive resistor Gb2 is connected to terminal b2 via a wiring section, and the other end of the strain-sensitive resistor Gb2 is connected to terminal b3 via a wiring section. In addition, if necessary, the strain-sensitive resistors Gb1, Gb2, the wiring sections, etc. are covered from above with a protective layer.

[0035] Each of the strain-sensitive resistors Gb1 and Gb2 is configured to include a folded pattern of multiple parallel linear resistors for strain detection, with the line width of the resistors being relatively small. The strain-sensitive resistor Gb1 is disposed in region Rb1 of the base material b0, and the strain-sensitive resistor Gb2 is disposed in region Rb2 of the base material b0, and the strain-sensitive resistors Gb1 and Gb2 are arranged symmetrically along a line segment OB parallel to the axial direction AX.

[0036] The strain-sensitive resistor Gb1 is a thin, linear resistor designed to detect strain with maximum sensitivity in direction pb1, and multiple linear resistors are arranged parallel to direction pb1 by a folded pattern. The strain-sensitive resistor Gb2 is a thin, linear resistor designed to detect strain with maximum sensitivity in direction pb2, and multiple linear resistors are arranged parallel to direction pb2 by a folded pattern. The angle θ of directions pb1 and pb2 (angle from the linear direction perpendicular to the axial direction AX of the rotation axis) will be described later.

[0037] <Configuration of a Wheatstone bridge circuit including distortion-sensitive resistors Ga1 to Gb2> Next, the configuration of the Wheatstone bridge circuit and peripheral circuits, including the strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2, will be described. Figure 7 shows the configuration of the Wheatstone bridge circuit and peripheral circuits, which are composed of strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2 attached to the strain-generating portion 111 of the rotating shaft 110. As shown in Figure 7, in addition to the Wheatstone bridge circuit, the circuit includes the aforementioned amplification circuit 311, the AD conversion circuit 312, and the rotating side CPU 313.

[0038] In a Wheatstone bridge circuit, terminal a4 of a pair of strain-sensitive resistors Ga1 and Ga2 is connected to terminal T1, and terminal b4 of a pair of strain-sensitive resistors Gb1 and Gb2 is connected to terminal T3. Additionally, terminal a1 of strain-sensitive resistor Ga1 is connected to terminal T4, terminal a2 of strain-sensitive resistor Ga2 is connected to terminal T2, terminal b1 of strain-sensitive resistor Gb1 is connected to terminal T2, and terminal b2 of strain-sensitive resistor Gb2 is connected to terminal T4.

[0039] When the output of the Wheatstone bridge circuit, which includes strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2 attached to the strain-generating portion 111 of the rotating shaft 110, is sent to the amplification circuit 311, the amplification circuit 311 amplifies the analog signal sent from the Wheatstone bridge circuit and sends it to the AD conversion circuit 312. Next, the AD conversion circuit 312 converts the analog signal sent from the amplification circuit 311 into a digital signal and sends it to the rotating-side CPU 313. Subsequently, the rotating-side CPU 313 processes the digital signal sent from the AD conversion circuit 312, causes the rotating-side optical element 331 to emit light, and transmits a data signal corresponding to the torque value using infrared light.

[0040] The infrared light emitted by the rotating optical element 331 is received by the stationary optical element 332. The stationary optical element 332 sends the reception result to the stationary CPU, which processes the reception result and sends it to the DA (Digital to Analogue) conversion circuit. The DA conversion circuit then converts the digital signal sent from the stationary CPU into an analog signal. The resulting analog signal, corresponding to the torque value, is sent to an external control device via the connector 340.

[0041] <State of the planar portions 111a and 111b when the rotation axis 110 is twisted> Here, we will explain the state of the planar portions 111a and 111b (strain-sensitive resistor pairs Ga and Gb) of the strain-generating portion 111 when the rotation axis 110 is twisted. Figure 8 conceptually shows the state of the planar portion 111a of the strain-generating portion 111 when the rotation axis 110 is twisted in the direction τ shown. The dotted line represents the state before the rotation axis 110 is twisted, and the solid line represents the state when the rotation axis 110 is twisted. As shown in Figure 8, when the rotation axis 110 is twisted in direction τ, the line connecting points H2 and U1 stretches, and the line connecting points H1 and U2 contracts. Here, the dotted line represents the state before the rotation axis 110 is twisted, and the solid line represents the state when the rotation axis 110 is twisted. Here, [T] represents stretching, and [C] represents contraction. The planar portion 111b of the strain-generating portion 111 also undergoes deformation similar to that of the planar portion 111a when the rotation axis 110 is twisted in the direction τ shown in the figure.

[0042] As shown in Figures 6(A), (B) and 8 above, when the rotation axis 110 twists in direction τ and the strain-generating portion 111 deforms, in the strain-sensitive resistor pair Ga, the multiple resistors constituting the strain-sensitive resistor Ga1 stretch and the multiple resistors constituting the strain-sensitive resistor Ga2 contract. Similarly, in the strain-sensitive resistor pair Gb, the resistors constituting the strain-sensitive resistor Gb1 stretch and the multiple resistors constituting the strain-sensitive resistor Gb2 contract.

[0043] <Radial evaluation test> Figure 9(A) shows an example of a bending moment evaluation test for the torque detector 100. In the bending moment evaluation test shown in Figure 9(A), the torque detector 100 is placed on a stand STD set on a table TBL, and a rod ROD is attached to the rotation axis 110 of the torque detector 100. A weight connecting member JIN, which is connected to a weight receiving plate PLT, is attached to the tip of the rod ROD, and the weight receiving plate PLT is suspended vertically downward. Then, the weight of the weight WGT placed on the weight receiving plate PLT is changed, and a bending moment evaluation test is performed.

[0044] Figure 9(B) shows an exaggerated diagram of the state of the strained portion 111 on the rotating shaft 110 when the bending moment is evaluated in this way. As shown in Figure 9(B), when a bending moment is applied, the strained portion 111 deforms as shown.

[0045] Therefore, if the strain-sensitive resistors attached to the flat portion are a pair of strain-sensitive resistors tilted at 45 degrees, the strain component of the strain-generating portion 111 due to bending moment will also be detected when detecting torque.

[0046] <Angles θ between directions pa1, pa2, and directions pb1, pb2> Therefore, we will explain how to calculate the angles θ (angles from a linear direction perpendicular to the axial direction AX of the rotation axis) of directions pa1, pa2 and pb1, pb2 in which the strain component of the strain-generating portion 111 due to the bending moment is not felt.

[0047] Figure 10(A) shows a conceptual diagram of a pair of strain-sensitive resistors Ga attached to the planar portion 111a of the strain-generating portion 111 when a bending moment is applied. In Figure 10(A), the dotted rectangle represents the outer circumference of the pair of strain-sensitive resistors Ga when no bending moment is applied to the strain-generating portion 111, and the solid rectangle represents the outer circumference of the pair of strain-sensitive resistors Ga when a bending moment is applied to the strain-generating portion 111. Thus, when a bending moment is applied to the strain-generating portion 111, the outer circumference of the pair of strain-sensitive resistors Ga deforms from the outer circumference of the dotted line passing through points H1, U1, B, U2, H2, H1 to the outer circumference of the solid line passing through points V1, W1, C, W2, V2, V1. That is, the planar portion 111a of the strain-generating portion 111 extends in the +X direction. Regions Ra1 and Ra2 deform symmetrically with respect to the line OB parallel to the axial direction AX.

[0048] In the region Ra1 where the strain-sensitive resistor Ga1 is placed, let Q1 be a point on the line segment (V1-W1) that is deformed by the bending moment, and let P1 be a point on the line segment (H1-U1) before deformation. The strain-sensitive resistor Ga1 is then positioned such that the direction of maximum sensitivity of the strain-sensitive resistor Ga1 is oriented at an angle where the length of the line segment connecting point O and point Q1 is equal to the length of the line segment connecting point O and point P1 (see Figures 10(B)(iii),(iv)).

[0049] In the region Ra2 where the strain-sensitive resistor Ga2 is placed, let Q2 be a point on the line segment (V2-W2) that is deformed by the bending moment, and let P2 be a point on the line segment (H2-U2) before deformation. The strain-sensitive resistor Ga2 is then positioned such that the direction of maximum sensitivity of the strain-sensitive resistor Ga2 is oriented at an angle where the length of the line segment connecting point O and point Q2 is equal to the length of the line segment connecting point O and point P1 (see Figures 10(B)(i) and (ii)).

[0050] Here, strain-sensitive elements Ga1 and Ga2 are arranged symmetrically with respect to a line segment OB parallel to the axial direction AX. Furthermore, due to the bending moment, regions Ra1 and Ra2 deform symmetrically with respect to the line OB parallel to the axial direction AX. Therefore, the length of the line segment connecting points O and Q1 in strain-sensitive element Ga1 is the same as the length of the line segment connecting points O and Q2 in strain-sensitive element Ga2 (let's call this length L1). Similarly, the length of the line segment connecting points O and P1 in strain-sensitive element Ga1 is the same as the length of the line segment connecting points O and P2 in strain-sensitive element Ga2 (let's call this length L2). Consequently, the angle at which lengths L1 and L2 are equal is the same for both strain-sensitive elements Ga1 and Ga2 (let's call this angle θ).

[0051] The fact that lengths L1 and L2 are equal means that the amount of strain on the strain-sensitive resistor is the same before and after deformation due to the bending moment. This means that even if a radial load is applied to the rotation axis 110, generating a bending moment in the strain-generating portion 111, and causing axial elongation of the strain-generating portion 111, the strain-sensitive resistor will not be sensitive to that elongation (hereinafter also referred to as "elongation insensitive"). The angle θ at which lengths L1 and L2 are equal can be determined as follows.

[0052] In Figures 10(B)(i) and (iii), length z is the length that defines the angle θ (directions pa1, pa2). Length a is the length in the direction perpendicular to the axial direction AX (X direction) in regions Ra1 and Ra2 before the bending moment is applied. Furthermore, ν is the Poisson's ratio of the strained portion 111, and k is the elongation in the X direction.

[0053] In this case, the length L1 is given by the following equation (1). L1=[(1-kν) 2 ×a 2 + (1+k) 2 ×z 2 ] 1 / 2 …(1) Furthermore, the length L2 is given by the following equation (2). L2=[a 2 + Z 2 ] 1 / 2…(2)

[0054] (1), (2), and (L1) 2 = (L2) 2 From the relationship of, the following (3) holds. (1 - kν) 2 × a 2 + (1 + k) 2 × z 2 = a 2 + z 2 …(3) Therefore, the length z is given by the following (4). z = ± [((2 - kν) × ν) / (k + 2)] 1 / 2 × a …(4)

[0055] From the relationship tanθ = z / a, the angle θ is given by the following (5). θ = tan -1 [((2 - kν) × ν) / (k + 2)] 1 / 2 …(5)

[0056] When the Poisson's ratio ν of the strained portion 111 is 0.3 and the elongation rate k is 0.1, from (5), θ = 27.9 degrees. At this time, the shear strain that the strain-sensitive resistor can detect is τsin2θ in the Mohr's circle (τ: shear stress), so multiply the output by (1 / sin2θ) to obtain a value corresponding to the actual shear strain. Therefore, the strain-sensitive resistors Ga1 and Ga2 are strain-sensitive resistors that have no sensitivity to the expansion and contraction in the axial direction AX of the strained portion 111 and have sensitivity to the strain of the rotation axis 110 (strain-insensitive strain-sensitive resistors).

[0057] The angle θ of the directions pb1 and pb2 of the strain-sensitive resistor pair Gb attached to the planar portion 111b in the strained portion 111 is also obtained in the same manner as for the strain-sensitive resistor pair Ga. And the angle θ of the directions pa1, pa2 and the directions pb1, pb2 is the above-mentioned (5). Therefore, the strain-sensitive resistors Gb1 and Gb2 are strain-sensitive resistors that have no sensitivity to the expansion and contraction in the axial direction AX of the strained portion 111 and have sensitivity to the strain of the rotation axis 110 (strain-insensitive strain-sensitive resistors).

[0058] Therefore, by using strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2, torque can be measured accurately without interference even when a radial load is applied to the rotation axis 110 of the torque detector 100.

[0059] Furthermore, even if there are slight deviations in the axial symmetry of strain-sensitive resistors Ga1 and Ga2, and in the axial symmetry of strain-sensitive resistors Gb1 and Gb2, the effect of bending moment can be eliminated compared to a strain-sensitive resistor tilted at 45 degrees.

[0060] As described above, in this embodiment, an I-cut strain generating section 111 is employed, and the rotational torque applied to the rotating shaft 110 is detected by acquiring the change in the resistance values ​​of the strain-sensitive resistors Ga1 and Ga2 attached to the planar portion 111a of the strain generating section 111, and the strain-sensitive resistors Gb1 and Gb2 attached to the planar portion 111b of the strain generating section 111.

[0061] In this detection process, the strain-sensitive resistors Ga1 and Ga2 are attached to the planar portion 111a in such a direction that they do not sense the strain caused by the bending moment applied to the strain-generating portion 111. Similarly, in this detection process, the strain-sensitive resistors Gb1 and Gb2 are attached to the planar portion 111b in such a direction that they do not sense the strain caused by the bending moment applied to the strain-generating portion 111. This direction is determined by the Poisson's ratio of the strain-generating portion 111. In other words, the strain-sensitive resistors Ga1, Ga2, Gb1, and Gb2 are insensitive to the axial stretching and contraction of the strain-generating portion 111, but are sensitive to the strain of the rotation axis 110.

[0062] Therefore, in this embodiment, even in a high-humidity environment, the strain-generating portion 111 of the I-cut can be brought into contact with the bending moment, reducing the influence of bending moment and enabling accurate torque measurement.

[0063] Therefore, according to this embodiment, when detecting torque, it is possible to avoid sensing the strain caused by the bending moment applied to the strain-generating part. [Variations of the Embodiment] The present invention is not limited to the embodiments described above, and various modifications are possible.

[0064] In the above embodiment, a pair of strain-sensitive resistors was attached to the two planar portions of the I-cut strain-generating section, but it is also possible to attach the strain-sensitive resistor to a single planar portion surface.

[0065] Furthermore, in the above embodiment, the shape of the strain-generating portion was an I-cut having two planar portions, but it may also have one or three or more planar portions.

[0066] Furthermore, in the above embodiment, a round bar-shaped strain generating body was processed to create a strain generating section (I-cut strain generating body) with two planar portions parallel to the axial direction and oriented 180 degrees apart from each other. In contrast, a round bar-shaped strain generating body was processed to create a strain generating section with four planar portions parallel to the axial direction and oriented 90 degrees apart from each other (quadrilateral strain generating body). At least one of these four surfaces may be fitted with the elongation-insensitive strain-sensitive resistor of this embodiment. In this case as well, the axial elongation caused by the bending moment of the strain generating section is not detected, and the torque applied to the rotating shaft can be detected with high accuracy.

[0067] Alternatively, the cylindrical strain generating body may be configured with the elongation-insensitive strain-sensitive resistor of this embodiment attached. In this case, the torque detector employing the cylindrical strain generating body is insensitive to the bending moment, thereby improving measurement accuracy.

[0068] Furthermore, although the above embodiment employs a biaxial shear strain gauge having two strain-sensitive resistors, a strain gauge consisting of a single strain-sensitive resistor may be attached to each planar or curved portion of the strain-generating area. Alternatively, if a configuration is adopted in which a single strain gauge consisting of a single strain-sensitive resistor is attached to the strain-generating area, the strain-sensitive resistor may be placed on one side of the Wheatstone bridge circuit, and fixed-value resistors may be placed on the other three sides of the Wheatstone bridge circuit. [Explanation of Symbols]

[0069] 100 ... Torque sensor 110 ... Rotation axis 111 … Strain part 112 ... Rotating shaft flange 111a,111b … Plane part 121, 122, 123… enclosure 124 … Lid 125... Nut 131,132… bearings 211 … Primary core 212 … Primary coil 213 … Core folder 221 … Secondary core 222 … Secondary coil 223 … Secondary core space 310 ... Rotating circuit board 311 ... Amplifier circuit 312 … AD conversion circuit 313 ... Rotating CPU 321,322 … Fixed substrate 331 ... Rotating optical element 332 … Fixed-side optical element 340… Connector AX … Axial direction Ga, Gb… Distortion-sensitive resistive pairs Ga1, Ga2, Gb1, Gb2 ... Distortion-sensitive resistors Ra1,Ra2 … area a0,b0 … Base material a1,a2,a3,b1,b2,b3...Terminal section pa1,pa2,pb1,pb2 … direction

Claims

1. A rotating shaft that is rotatably supported and has a partial strain generating portion; A strain-sensitive resistor having a substrate for attachment to the strain-generating portion; Equipped with The strain-generating portion is A flat portion is provided so that a bending moment is applied to the rotating shaft when a load in a radial direction with respect to the axial direction of the rotating shaft occurs, and the flat portion is capable of elastically deforming the rotating shaft and allowing the base material to be attached; The strain sensitive resistor is A folded pattern based on a linear resistor having a predetermined length is provided on the substrate; The folding pattern is The resistor is arranged so that the resistor is folded back in sequence along the middle of the stretched resistor, and a plurality of inclined lines extending in parallel are formed in accordance with a line direction having a predetermined inclination with respect to a virtual direction perpendicular to a virtual line along the axial direction, The predetermined inclination line direction is: the maximum sensitivity in the sense of sensation when no bending moment is applied to the strain-flexing part, which is an angle of distortion compared to the inclination angle from the virtual line, is determined according to a calculated angle obtained by a calculation in which a value related to the elongation rate in the axial direction when the bending moment is applied is given, A torque detector, characterized in that a torque acting on the strain-flexing part is detected based on an output of a circuit including the strain-sensitive resistor.

2. The line direction of the predetermined inclination is: performing the calculation using a predetermined formula that multiplies the Poisson's ratio of the strain-generating portion to a value related to the elongation rate of the strain-generating portion in the axial direction; The torque detector according to claim 1, characterized in that the calculated angle is determined based on the calculation, and the inclined line is made to be sensitive so as not to affect the axial expansion and contraction that occurs when the bending moment is applied.

3. A torque detector as described in claim 1 or 2, characterized in that an arithmetic process is performed in which the result that the circuit can output is multiplied by 1 / sin2Θ, thereby enabling a value corresponding to shear strain to be calculated.

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