torque sensor

Abstract

A torque sensor (1) is provided with: an outer peripheral portion (2) and an inner peripheral portion (3) which are circular ring-shaped, are arranged apart in the radial direction and concentrically; a plurality of double support beam-shaped connecting beam portions (4) which are arranged apart in the circumferential direction and connect between the outer peripheral portion (2) and the inner peripheral portion (3); and detection portions (5), (20) which detect a torque around a central axis (A) applied between the outer peripheral portion (2) and the inner peripheral portion (3). The two side surfaces in the circumferential direction of the connecting beam portion (4) have a concave curved surface shape, and when viewed from the direction of the central axis (A), the radii of curvature of the curved surface shape gradually increase from the inner peripheral surface of the outer peripheral portion (2) and the outer peripheral surface of the inner peripheral portion (3) toward the center in the length direction of the connecting beam portion (4), respectively.

Description

Technical Field

[0001] This invention relates to torque sensors. Background Technology

[0002] Previously, a measuring device was known, comprising: an annular outer peripheral portion; an annular inner peripheral portion disposed radially inward of the outer peripheral portion; and an annular middle portion disposed between the outer peripheral portion and the inner peripheral portion (for example, see Patent Document 1).

[0003] Multiple rigid adjustment holes, elongated in shape and extending circumferentially, are evenly spaced in the middle section. Thus, between adjacent rigid adjustment holes, multiple double-support beam-like sections radially connecting the outer and inner circumferences are arranged at intervals. A torque measuring device is constructed by attaching a strain gauge to the radial center of each double-support beam-like section.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-25956 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Because in each of the double-support beam-shaped portions in Patent Document 1, the two circumferential sides are formed by the arc surfaces at the ends of rigid adjustment holes in the shape of elongated holes, the circumferential width dimension is too large in the connection portion with the outer and inner circumferential portions, resulting in a decrease in the torque detection sensitivity.

[0009] On the other hand, by reducing the radius of the arc surface, the sensitivity of torque detection is improved, but stress concentration is more likely to occur.

[0010] Therefore, it is desirable to reduce stress concentration in the double-supported beam section while suppressing the decrease in torque detection sensitivity.

[0011] Solution for solving the problem

[0012] One aspect of the present invention is a torque sensor comprising: an annular outer peripheral portion and an inner peripheral portion, which are radially spaced apart and concentrically arranged; a plurality of double-supported beam-shaped connecting beam portions, which are circumferentially spaced apart and connect the outer peripheral portion and the inner peripheral portion; and a detection unit that detects the torque applied between the outer peripheral portion and the inner peripheral portion about a central axis, wherein the two circumferentially side surfaces of the connecting beam portions have concave curved surface shapes, and when viewed from the direction of the central axis, the radius of curvature of the curved surface shapes gradually increases from the inner peripheral surface of the outer peripheral portion and the outer peripheral surface of the inner peripheral portion toward the center of the length direction of the connecting beam portion. Attached Figure Description

[0013] Figure 1 This is a top view illustrating a torque sensor according to one embodiment of the present invention.

[0014] Figure 2 It means Figure 1 A partial enlarged view of the connecting beam of the torque sensor.

[0015] Figure 3 It means to Figure 1 The figure shows an example of a torque sensor installed on a robot's joint.

[0016] Figure 4 It means in the future Figure 2 A diagram of a portion of the analytical model where the contour shape of the two sides of the connecting beam is set as an elliptical arc.

[0017] Figure 5 It means in the future Figure 2 A diagram of a portion of the analytical model where the contours of the two sides of the connecting beam are set to arcs.

[0018] Figure 6 It means to Figure 2 A graph showing the analytical results of the relationship between the profile shape (minor diameter R = R1) of the two sides of the connecting beam and the rate of change of the maximum stress value of the connecting beam.

[0019] Figure 7 It means to Figure 2 A graph showing the analytical results of the relationship between the profile shape (minor diameter R = R2) of the two sides of the connecting beam and the rate of change of the maximum stress value of the connecting beam.

[0020] Figure 8 It means to Figure 2 A graph showing the analytical results of the relationship between the profile shape (minor diameter R = R3) of the two sides of the connecting beam and the rate of change of the maximum stress value of the connecting beam.

[0021] Figure 9 It means to Figure 2 A graph showing the analytical results of the relationship between the profile shape (minor diameter R = R1) of the two sides of the connecting beam and the rate of change of the deformation of the connecting beam.

[0022] Figure 10 It means to Figure 2 A graph showing the analytical results of the relationship between the profile shape (minor diameter R = R2) of the two sides of the connecting beam and the rate of change of the deformation of the connecting beam.

[0023] Figure 11 It means to Figure 2A graph showing the analytical results of the relationship between the profile shape (minor diameter R = R3) of the two sides of the connecting beam and the rate of change of the deformation of the connecting beam.

[0024] Figure 12 It means Figure 2 A graph showing the ratio of the profile shape (minor diameter R = R1) of the two sides of the connecting beam, the rate of change of the maximum stress value, and the rate of change of the deformation.

[0025] Figure 13 It means Figure 2 A graph showing the contour shape of the two sides of the connecting beam (minor diameter R = R2), the ratio of the rate of change of the maximum stress value to the rate of change of the deformation.

[0026] Figure 14 It means Figure 2 A graph showing the ratio of the profile shape (minor diameter R = R3) of the two sides of the connecting beam, the rate of change of the maximum stress value, and the rate of change of the deformation.

[0027] Figure 15 It means Figure 1 A partial enlarged view of the connecting beam of the first modified example of the torque sensor.

[0028] Figure 16 It means Figure 1 A partially enlarged view of the connecting beam of the second modified example of the torque sensor. Detailed Implementation

[0029] Hereinafter, a torque sensor 1 according to one embodiment of the present invention will be described with reference to the accompanying drawings.

[0030] The torque sensor 1 of this embodiment includes: a sensor body 10, which is formed by punching a metal plate of a certain thickness along the thickness direction; and a strain gauge (detection unit) 20, which is mounted on the sensor body 10.

[0031] like Figure 1 As shown, the sensor body 10 includes: an annular outer peripheral portion 2, which is centered on an axis (central axis) A; and an annular inner peripheral portion 3, which is arranged concentrically and at intervals to the radially inward of the outer peripheral portion 2. The sensor body 10 has an annular gap that is equally spaced around the axis A between the outer peripheral portion 2 and the inner peripheral portion 3, and a plurality of, for example, four connecting beams 4 and for example four detection beams (detection sections) that connect the outer peripheral portion 2 and the inner peripheral portion 3 radially in a double-support beam manner.

[0032] The outer periphery 2 has a plurality of through holes 6a spaced apart circumferentially, extending through the thickness of the plate. The inner periphery 3 has a plurality of threaded holes 6b spaced apart circumferentially, extending through the thickness of the plate.

[0033] like Figure 2 As shown, each connecting beam portion 4 has a long axis B extending radially along a straight line passing through axis A. One end of the long axis B of each connecting beam portion 4 is connected to the inner peripheral surface 2a of the outer peripheral portion 2, and the other end is connected to the outer peripheral surface 3a of the inner peripheral portion 3.

[0034] The outline shape of the two circumferential side surfaces 4a of each connecting beam portion 4, viewed from the direction of axis A, is symmetrical with respect to the major axis B. The outline shape of each side surface 4a is formed by a concave curve consisting of an elliptical arc comprising a half-circumference portion of an ellipse with its major axis aligned parallel to the major axis B. The major axis of the elliptical arc has the same length as the radial distance between the inner circumferential surface 2a of the outer circumferential portion 2 and the outer circumferential surface 3a of the inner circumferential portion 3.

[0035] Thus, each side 4a becomes a curved surface shape with the radius of curvature gradually increasing from both ends toward the center along the major axis B.

[0036] Each detection beam 5 is disposed between a pair of circumferentially adjacent connecting beams 4 and radially connects the outer peripheral portion 2 and the inner peripheral portion 3. The cross-sectional area of ​​the detection beam 5 is sufficiently small compared to the cross-sectional area of ​​the connecting beam 4, and has a shape that is easily deformable when a circumferential torque is applied between the outer peripheral portion 2 and the inner peripheral portion 3. Therefore, the strength of the torque sensor 1 is mainly borne by the connecting beam 4, and the detection beam 5 does not affect the strength of the torque sensor 1.

[0037] Strain gauges 20 are individually attached to the surface of each detection beam 5. Each strain gauge 20 is, for example, a thin-film resistive element, and its resistance value changes according to the deformation of the detection beam 5 to which it is attached.

[0038] In addition, each strain gauge 20 forms a bridge circuit (not shown) and detects changes in resistance as changes in voltage.

[0039] The operation of the torque sensor 1 configured as described in this embodiment will be explained below.

[0040] like Figure 3 As shown, torque sensor 1 is installed, for example, on a joint 100 of the robot, to detect the torque output by the actuator 110 provided on the joint 100.

[0041] exist Figure 3In the example shown, torque sensor 1 is mounted with its axis A aligned with the rotation axis of output shaft 112 between the output shaft 112 of the reducer 111 of the actuator 110 constituting the robot joint 100 and the robot arm 120 fixed to the output shaft 112. Specifically, the outer peripheral portion 2 is fixed to the output shaft 112 of the reducer 111 using bolts 7 passing through the through hole 6a, and the inner peripheral portion 3 is fixed to the robot arm 120 using bolts 8 fastened to the threaded hole 6b of the inner peripheral portion 3.

[0042] Therefore, the torque sensor 1 is directly fixed between the reducer 111, which is the object being detected, and the robot arm 120.

[0043] In this state, if the output shaft 112 of the reducer 111 rotates around axis A, a circumferential torque around axis A acts between the outer peripheral portion 2 and the inner peripheral portion 3, and the outer peripheral portion 2 and the inner peripheral portion 3 undergo slight displacement relative to each other in the circumferential direction. In addition, due to the slight displacement of the outer peripheral portion 2 and the inner peripheral portion 3, each detection beam portion 5 also deforms.

[0044] Therefore, by using each strain gauge 20 attached to each detection beam 5, the voltage value corresponding to the deformation of the detection beam 5 can be detected, and the magnitude of the torque generated by the rotation of the output shaft 112 of the reducer 111 can be detected.

[0045] In this case, when a torque around axis A acts between the outer peripheral portion 2 and the inner peripheral portion 3, stress is generated in each connecting beam portion 4 that connects the outer peripheral portion 2 and the inner peripheral portion 3. In particular, greater stress is generated at both ends of each connecting beam portion 4 in the direction of the major axis B. On the other hand, almost no stress is generated near the center in the direction of the major axis B.

[0046] Here, the relationship between the shape of each side 4a of the connecting beam 4, the magnitude of the stress generated in the connecting beam 4, and the ease with which the connecting beam 4 deforms will be explained.

[0047] Figure 4 This represents a part of the analytical model when the profile shape of one end of the two sides 4a of the connecting beam 4, viewed from the axis A, is set as an elliptical arc. Figure 5 Indicates that in Figure 4 This is part of the analytical model when the elliptical arc is converted into a circular arc. For both analytical models, the maximum stress and deformation generated in the connecting beam 4 when a predetermined circumferential force is applied to the other end of the connecting beam 4 in the direction of its major axis B are calculated separately.

[0048] exist Figures 6 to 8 The solid line in the middle represents the middle. Figure 4In the analytical model, the minor axis R of the elliptical arc is fixed at R1, R2, and R3 (R1 > R2 > R3), and the major axis Ra is varied along the major axis B, representing the rate of change of the maximum stress value. Additionally, dashed lines represent the maximum stress value under these conditions. Figure 5 The radius Ra in the analytical model corresponds to Figure 4 The rate of change of the maximum stress value when the major axis Ra changes in the analytical model. Similarly, Figures 9 to 11 The graph is obtained by comparing the rate of change of deformation of the connecting beam 4 in the two analytical models.

[0049] Figures 6 to 11 The rate of change in Ra refers to dividing the maximum stress value or deformation in each major axis Ra or radius Ra by the value in the range specified in the original text. Figure 4 In the analytical model, when the major axis Ra is equal to the minor axis R, Figure 5 The value obtained by setting the radius Ra to R in the analytical model is the maximum stress or deformation.

[0050] according to Figure 6 The analytical results shown indicate that when the maximum stress value generated in the connecting beam 4 is reduced to a predetermined proportion P, Figure 5 In the case of the analytical model, the radius Ra needs to be increased from R (=R1) to Ra1. On the other hand, it is known that in Figure 4 In the case of the analytical model, it is not necessary to increase the size of the minor axis R (=R1), but only to increase the major axis Ra to Ra2, which is larger than Ra1.

[0051] Therefore, by setting the outline shape of the two ends of the two sides 4a of the connecting beam 4 in the direction of the major axis B as an elliptical arc when viewed from the direction of the axis A, it is possible to reduce the stress concentration of the connecting beam 4 without increasing the width of the two ends of the connecting beam 4 in the direction of the major axis B in the direction orthogonal to the major axis B.

[0052] In addition, according to Figure 9 The analysis results shown maintain Figure 4 The rate of change of deformation of the connecting beam 4 under the condition that the minor diameter R (=R1) of the analytical model is increased to Ra2 is greater than that under the condition that the major diameter Ra is increased to Ra2. Figure 5 The rate of change of deformation of the connecting beam 4 when the radius Ra of the analytical model is increased to Ra1.

[0053] That is, by comparison, the maximum stress value generated in the connecting beam 4 is reduced to a predetermined proportion P. Figure 4 Analytical model and Figure 5 Analytical model, Figure 4 The analytical model can maintain the ease of circumferential deformation of the connecting beam in four directions and suppress excessive increase in stiffness.

[0054] It can be known that according to Figure 7 and Figure 10 as well as Figure 8 and Figure 11 The same effect as described above can also be achieved.

[0055] Thus, according to the torque sensor 1 of this embodiment, the relative circumferential displacement between the outer peripheral portion 2 and the inner peripheral portion 3 and the deformation of each detection beam portion 5 can be maintained to a greater extent while reducing stress concentration generated in the connecting beam portion 4 when the circumferential torque is applied between them.

[0056] Therefore, the torque sensor 1 of this embodiment has the following advantages: it can improve the strength of the connecting beam 4 while suppressing the decrease in torque detection sensitivity.

[0057] In addition, Figures 12 to 14 In, with Figures 6 to 11 Similarly, it represents the ratio of the rate of change of the maximum stress value of the connecting beam 4 to the rate of change of the deformation when the major diameter Ra or radius Ra in the two analytical models changes.

[0058] like Figure 12 As shown, in Figure 4 In the analytical model, when only the major axis Ra of the elliptical arc is increased, and the flatness ratio f is increased to 57%, the rate of change of deformation of the connecting beam 4 and the rate of change of maximum stress change at roughly the same rate. In contrast, in Figure 5 In the analytical model, when the radius Ra is increased, the rate of change of deformation greatly exceeds the rate of change of the maximum stress value.

[0059] In addition, Figure 13 as well as Figure 14 In the middle, too, Figure 4 The flattening factor f of the elliptical arc in the analytical model is greater than 0% and less than 57%, and... Figure 5 Compared with the analytical model, the rate of change of the maximum stress value of the connecting beam 4 is much greater than the rate of change of the deformation.

[0060] Based on these results, it can also be said that by setting the outline shape of the two ends of the two sides 4a of the connecting beam 4 in the direction of the major axis B as elliptical arcs when viewed from the direction of the axis A, it is possible to mitigate the stress concentration of the connecting beam 4 while suppressing the excessive increase in the circumferential stiffness of the connecting beam 4, regardless of the value of the flatness ratio f.

[0061] In addition, in this case Figure 4 In the analytical model, the flatness f of the elliptical arc is preferably 0% to 57%, and more preferably 20% to 55%.

[0062] Furthermore, in this embodiment, the profile shape of each side 4a of the connecting beam 4, viewed from the axis A, is formed by an elliptical arc comprising half the circumference of an ellipse with its major axis arranged parallel to the major axis B. Instead, as... Figure 15 As shown, the outline shape of the two sides 4a of the connecting beam 4, when viewed from the direction of axis A, can also be formed as a shape consisting of a straight line parallel to the major axis B at the center in the direction of major axis B, and elliptical arcs with major axes parallel to the major axis B at both ends in the direction of major axis B.

[0063] Therefore, only the necessary minimum range at both ends of the major axis B direction, where stress is most easily concentrated, on both sides 4a of the connecting beam 4, is formed by a surface with an elliptical arc profile when viewed from the axis A direction. This allows for a smaller suppression of the increase in circumferential stiffness of the connecting beam 4 around axis A, and also reduces stress concentration in the connecting beam 4.

[0064] In addition, in this embodiment, the outline shapes of the two ends of each side 4a of the connecting beam 4, viewed from the axis A direction, may be different.

[0065] Thus, for example, if it is anticipated that the stress distribution at both ends of the connecting beam 4 in the direction of the long axis B will be uneven, the curved surfaces at both ends of each side 4a of the connecting beam 4 in the direction of the long axis B can be set to the optimal shape according to the anticipated stress distribution.

[0066] In addition, in this embodiment, such as Figure 16 As shown, the outline shape of each side 4a of the connecting beam 4, viewed from the direction of axis A, can also be formed by a portion of an elliptical arc with its major axis arranged in a direction inclined relative to the major axis B.

[0067] In addition, in this embodiment, the connecting beam 4 is set to four beams, but it can also be two, three or more beams.

[0068] In addition, in this embodiment, the detection beam 5 is set as part of the sensor body 10. However, instead, the detection beam 5 can be set separately from the sensor body 10 and fixed between the outer peripheral part 2 and the inner peripheral part 3 using bolts or the like across the radial direction.

[0069] In this embodiment, the strain gauge 20 is attached to the surface of the detection beam 5. However, it can also be attached one by one to the surface of each connecting beam 4. In this case, the detection beam 5 can be omitted, thus simplifying the structure of the torque sensor 1.

[0070] In addition, as a component for detecting the deformation of the detection beam 5, a resistive strain gauge 20 is given as an example, but it is not limited to this. Other sensors of any kind, such as capacitive sensors, optical sensors, or magnetostrictive sensors, can also be used.

[0071] For example, when using a capacitive sensor, a pair of opposing electrodes can be configured such that the distance between the electrodes or the opposing area changes according to the circumferential torque acting between the outer peripheral portion 2 and the inner peripheral portion 3.

[0072] In addition, in this embodiment, the outline shape of each side 4a of the connecting beam 4 as viewed from the axis A direction is formed by elliptical arcs. However, it can also be formed by any concave curve with the radius of curvature gradually increasing from both ends toward the center in the direction of the major axis B of the connecting beam 4.

[0073] Explanation of reference numerals in the attached figures:

[0074] 1: Torque sensor

[0075] 2: Peripheral part

[0076] 2a: Inner circumferential surface

[0077] 3: Inner periphery

[0078] 3a: outer peripheral surface

[0079] 4: Connecting beam section

[0080] 4a: Side view

[0081] 5: Inspection of the beam section (inspection department)

[0082] 20: Strain gauge (Testing Department)

[0083] A: Axis (Central Axis)

[0084] f: Flatness

[0085] Ra: Major axis

Claims

1. A torque sensor, characterized in that, have: The outer and inner circumferences are arranged concentrically and are spaced apart radially; Multiple double-supported beam-shaped connecting beams, spaced circumferentially and connecting the outer and inner peripheral portions; and The detection unit detects the torque applied between the outer peripheral portion and the inner peripheral portion around a central axis. The two circumferential sides of the connecting beam have concave curved surfaces. When viewed from the central axis, the radius of curvature of the curved surface gradually increases from the inner circumferential surface of the outer circumferential part and the outer circumferential surface of the inner circumferential part towards the center of the length direction of the connecting beam. The curved surface shape is formed by a portion of an ellipse in which the major axis is arranged parallel to the length direction of the connecting beam.

2. The torque sensor according to claim 1, characterized in that, The curved surface shape of each of the circumferential sides of the connecting beam, from the outer periphery to the inner periphery, is formed by a portion of a single ellipse.

3. The torque sensor according to claim 1, characterized in that, In each of the circumferential sides of the connecting beam, the curved surface shape from the inner circumferential surface of the outer circumferential portion toward the center of the connecting beam in the length direction is different from the curved surface shape from the outer circumferential surface of the inner circumferential portion toward the center of the connecting beam in the length direction.

4. The torque sensor according to claim 1, characterized in that, The flatness of the ellipse is greater than 0% and less than 57%.

5. The torque sensor according to claim 1, characterized in that, The flatness of the ellipse is between 20% and 55%.

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