Torque Sensor

Abstract

To provide a torque sensor capable of detecting torque with high accuracy even when a force other than torque is applied.SOLUTION: A torque sensor 10 includes a first structure 11, a second structure 12, a plurality of third structures 13, a strain body 21, and a fourth structure 24. The plurality of third structures 13 are connected between the first structure and the second structure. The strain body 21 including a plurality of sensor elements is located between adjacent third structures and coupled between the first structure and the second structure. The fourth structure 24 is located between adjacent third structures and connected between the first structure and the second structure. The width of the fourth structure 24 increases as it approaches the first structure and the second structure from the center in the length direction of the fourth structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a torque sensor provided in a joint of, for example, a robot arm. [Background technology]

[0002] The torque sensor has a first structure to which torque is applied, a second structure to which torque is output, a plurality of third structures connecting the first structure and the second structure, and a plurality of strain generating bodies provided between the first structure and the second structure, with a plurality of strain gauges arranged on the surfaces of these strain generating bodies (see, for example, Patent Document 1 and Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-091813 [Patent Document 2] Japanese Patent Application Publication No. 2017-172983 Summary of the Invention [Problem to be solved by the invention]

[0004] The first and second structures of the torque sensor are, for example, annular. When torque or a force other than torque is applied to this torque sensor, the first and second structures may be deformed into an elliptical shape. In this case, each portion of the first and second structures does not deform evenly, and therefore the multiple strain gauges provided between the first and second structures also do not deform evenly. Therefore, the output signals of the multiple strain gauges provided on each strain element include signals due to forces other than torque, which reduces the torque detection accuracy.

[0005] The embodiments of the present invention provide a torque sensor that can detect torque with high accuracy even when a force other than torque is applied. [Means for solving the problem]

[0006] The torque sensor of this embodiment includes a first structure, a second structure, a plurality of third structures connected between the first structure and the second structure, a strain body located between adjacent third structures and including a plurality of sensor elements coupled between the first structure and the second structure, and a fourth structure located between adjacent third structures and connected between the first structure and the second structure, and the width of the fourth structure (the length parallel to the planes of the first structure and the second structure and intersecting the longitudinal direction of the fourth structure) increases from the center of the longitudinal direction of the fourth structure toward the first structure and the second structure. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a partially removed plan view showing the torque sensor according to the embodiment. [Figure 2] FIG. 4 is a plan view illustrating a deformed state of the torque sensor according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, showing a fourth structure according to the present embodiment. [Figure 4] 4 is an enlarged plan view of a portion indicated by A in FIG. 2, shown for explaining a fourth structure according to the embodiment. FIG. [Figure 5] 10A and 10B are diagrams showing deformation amounts of structures in this embodiment and other examples. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings. In the drawings, the same parts or parts having the same functions are designated by the same reference numerals.

[0009] 1 shows a torque sensor 10 according to this embodiment. The configuration of the torque sensor 10 is not limited to this, and the present embodiment can be applied to torque sensors of various configurations. Furthermore, the present embodiment can be applied not only to torque sensors, but also to force sensors using strain gauges.

[0010] In FIG. 1, the torque sensor 10 includes a first structure 11, a second structure 12, a plurality of third structures 13, a plurality of waterproof caps 14, a case 15, a bushing 16, a cable 17, a plurality of strain sensors 20, a plurality of flexible substrates 23, a plurality of fourth structures 24, a plurality of waterproof caps 25, etc.

[0011] The first structure 11 and the second structure 12 are annular, and the diameter of the second structure 12 is smaller than the diameter of the first structure 11. The second structure 12 is arranged concentrically with the first structure 11, and the first structure 11 and the second structure 12 are connected by a third structure 13 and a fourth structure 24 serving as a plurality of beams arranged radially. The fourth structures 24 are arranged at equal intervals and are disposed between adjacent third structures 13.

[0012] As will be described later, the fourth structures 24 are arranged corresponding to the strain sensors 20, and the number of the strain sensors 20 and the fourth structures 24 is, for example, eight. The number of the strain sensors 20 and the fourth structures 24 is not limited to eight.

[0013] The first structure 11 is connected, for example, to a measurement object, and the second structure 12 is connected to another structure (not shown). The plurality of third structures 13 transmit torque (moment (Mz) shown in FIG. 2) from the first structure 11 to the second structure 12. Conversely, the second structure 12 may be connected to a measurement object, and the first structure 11 may be connected to another structure (not shown), and torque may be transmitted from the second structure 12 to the first structure 11 via the plurality of third structures 13.

[0014] The first structure 11, the second structure 12, and the plurality of third structures 13 are made of metal, for example, stainless steel, but materials other than metal can also be used as long as they have sufficient mechanical strength to withstand the applied torque.

[0015] The second structure 12 has a hollow portion 12a, and the case 15 is attached to the second structure 12 around the hollow portion 12a. A processing circuit (not shown) is provided inside the case 15. The processing circuit processes the electrical signal supplied from the strain sensor 20 and generates a torque detection signal as a sensor signal.

[0016] The bushing 16 is provided in a part of the case 15 and holds a cable 17. One end of the cable 17 (not shown) is connected to a processing circuit inside the case 15, and the other end of the cable 17 is passed through, for example, the hollow portion 12a. The cable 17 supplies power to the processing circuit from an external source and outputs a sensor signal processed by the processing circuit to the outside. The configuration of the processing circuit is not essential to this embodiment, so a description thereof will be omitted.

[0017] Each strain sensor 20 arranged corresponding to each fourth structure 24 is covered by a cap 14. The configuration of the portions covered by the caps 14 is the same. In order to show the fourth structure 24, the strain sensor 20, the flexible substrate 23, and the caps 25, FIG. 1 removes the four caps 14 and configuration not necessary for explanation, and exposes the configuration necessary for explanation.

[0018] The strain sensor 20 is provided between the first structure 11 and the second structure 12. That is, as will be described later, one end of the strain sensor 20 is joined to the first structure 11, and the other end of the strain sensor 20 is joined to the second structure 12.

[0019] Specifically, the first structure 11 and the second structure 12 corresponding to the fourth structure 24 have recesses 30 formed integrally therewith.

[0020] A hole 30a is provided in the approximate center of the portion of the recess 30 corresponding to the first structure 11, and a hole 30b is provided in the approximate center of the portion corresponding to the second structure 12.

[0021] The strain sensor 20 is provided in the recess 30 between the first structure 11 and the second structure 12. The strain sensor 20 includes a strain element 21 made of, for example, metal, and a plurality of strain gauges 22 as sensor elements arranged on the surface of the strain element 21.

[0022] The flexure element 21 is, for example, rectangular, and the length of the flexure element 21 is longer than the length of the third structure 13 and shorter than the distance between the holes 30a and 30b. One longitudinal end of the flexure element 21 is placed on the surface of the first structure 11 within the recess 30, and the other longitudinal end of the flexure element 21 is placed on the surface of the second structure 12 within the recess 30. One end of the flexure element 21 is fixed to the first structure 11 by a fixing member 40a arranged within the recess 30 and a screw 41a inserted into the hole 30a from the back surface side of the first structure 11 and screwed into the fixing member 40a. The other end of the flexure element 21 is fixed to the second structure 12 by a fixing member 40b arranged within the recess 30 and a screw 41b inserted into the hole 30b from the back surface side of the second structure 12 and screwed into the fixing member 40b.

[0023] The strain gauges 22 are, for example, thin-film resistor elements, and their resistance value changes in response to the deformation of the strain body 21. The multiple strain gauges 22 form a bridge circuit (not shown), which detects the change in resistance value as an electrical signal. The multiple strain gauges 22 are connected to one end of a flexible substrate 23 provided in the center of the strain body 21. The other end of the flexible substrate 23 is connected to a processing circuit within the case 15. The electrical signal output from the bridge circuit is supplied to the processing circuit via the flexible substrate 23, and the processing circuit generates a torque detection signal as a sensor signal.

[0024] The cap 14 is attached to the recess 30 and seals the recess 30. The cap 25 is disposed between the flexure element 21 and the fourth structure 24 so as to cover the fourth structure 24 and seals the openings 26 provided on both sides of the fourth structure 24. In the strain sensor 20, the cap 14 protects the front surface side of the flexure element 21 from moisture intrusion, and the cap 25 protects the back surface side of the flexure element 21 from moisture intrusion.

[0025] 2 shows an example of deformation due to a force applied to the torque sensor 10. For example, in a torque sensor 10 having eight strain sensors 20 arranged therein, if a force other than torque is applied and the first structure 11 and the second structure 12 are deformed into an elliptical shape as shown by the dashed line, the strain bodies 21 of the eight strain sensors 20 will not deform uniformly. In this case, the output signal of the bridge circuit formed by multiple strain gauges arranged on the surface (plane) of the strain body 21 will include a signal corresponding to a force other than torque. This reduces the detection accuracy of the torque Mz.

[0026] In this embodiment, a fourth structure 24 is arranged corresponding to each strain sensor 20, thereby increasing the rigidity of the first structure 11 and the second structure 12 against forces other than torque, thereby preventing a decrease in torque detection accuracy.

[0027] FIG. 3 shows a cross section taken along line III-III in FIG. 1, illustrating two third structures 13, a fourth structure 24 disposed between them, and a flexure element 21.

[0028] Each of the two third structures 13 arranged in a direction intersecting the longitudinal direction of the flexure body 21 has a side surface 13a parallel to a side surface 21a along the longitudinal direction of the flexure body 21. Specifically, the longitudinal direction of the third structures 13 and the longitudinal direction of the flexure body 21 are arranged in the same direction. The width of the portion of the third structure 13 parallel to the flexure body 21 (the length in the direction parallel to the plane 11a (shown in FIG. 1 ) of the first structure 11 and the plane 12a of the second structure 12 and intersecting the longitudinal direction of the third structure 13) is constant. The length of the portion of the third structure 13 parallel to the flexure body 21 is, for example, 25% to 40% of the overall length of the third structure 13.

[0029] The width of both ends of the third structure 13 in the longitudinal direction is increased toward the first structure 11 and the second structure 12. In other words, at both ends of the third structure 13 in the longitudinal direction, the surfaces corresponding to the planes of the first structure 11 and the second structure 12 have curved portions 13b.

[0030] The fourth structure 24 is disposed parallel to the flexure body 21 and spaced apart from the flexure body 21. That is, a surface 24b of the fourth structure 24 (a surface parallel to the plane 11a of the first structure 11 and the plane 12a of the second structure 12) is parallel to the back surface 21c of the flexure body 21 and faces the back surface 21c of the flexure body 21.

[0031] In the plane 24b of the fourth structure 24, the width of the longitudinal center portion is narrower than the width of both ends in the longitudinal direction. In other words, the fourth structure 24 has a side surface 24a that is not parallel to the side surface 21a of the flexure element 21 (a surface in a direction intersecting the plane 11a of the first structure 11 and the plane 12a of the second structure 12). That is, as shown in FIG. 1 , a circular opening 26 is formed between the fourth structure 24 and two adjacent third structures 13, and the side surface 24a of the fourth structure 24 is arc-shaped. Therefore, the width of the plane 24b of the fourth structure 24 increases from the longitudinal center of the fourth structure 24 toward the first structure 11 and the second structure 12. That is, the width W4 of the connection portion of the fourth structure 24 between the first structure 11 and the second structure 12 is wider than the width W1 of the longitudinal center (W4>W1).

[0032] Furthermore, the connection portion of the fourth structure 24 with the first structure 11 and the connection portion of the fourth structure 24 with the second structure 12 are spaced apart from the two third structures 13 adjacent to the fourth structure 24. Therefore, the fourth structure 24 can function as a beam independent of the two third structures 13 adjacent to the fourth structure 24.

[0033] The shape of the opening 26 is not limited to a circle, and may be an oval or other shape as long as the shape of the plane 24b of the fourth structure 24 is such that the width increases from the longitudinal center of the fourth structure 24 toward the first structure 11 and the second structure 12.

[0034] The thickness T1 of the fourth structure 24 is greater than the thickness T3 of the strained body 21 and less than the thickness T2 of the third structure 13 (T3 < T1 < T2). The width W1 at the longitudinal center of the fourth structure 24 is narrower than the width W3 of the strained body 21 and wider than the width W2 of the third structure 13 (W3 > W1 > W2). However, these width relationships are merely examples and are not limited thereto, and are deformable.

[0035] Here, the thickness is the length in the direction perpendicular to the planes of the first structure 11 and the second structure 12 of the third structure 13, the fourth structure 24, and the strained body 21, and the width is the length in the direction parallel to the planes of the first structure 11 and the second structure 12 of the third structure 13, the fourth structure 24, and the strained body 21 and intersecting the length direction.

[0036] As shown in FIG. 4, when no force is applied to the torque sensor 10, the two third structures 13 adjacent to the fourth structure 24, the first structure 11, and the second structure 12 form a quadrilateral as indicated by the broken line B.

[0037] When a force (a force other than the torque Mz) that deforms the torque sensor 10 into an elliptical shape is applied to the torque sensor 10 configured as described above, the fourth structure 24 acts as an X-shaped beam provided between the first structure 11 and the second structure 12. For this reason, due to the rigidity of the fourth structure 24, the deformation of the two third structures 13 adjacent to the fourth structure 24, the first structure 11, and the second structure 12 is suppressed against a force other than the torque Mz. Therefore, the output of a signal due to a force other than the torque can be reduced, and cross-axis interference can be suppressed to detect torque with high precision.

[0038] On the other hand, when torque Mz is applied to the torque sensor 10 configured as described above, the fourth structure 24 and the two adjacent third structures 13, the first structure 11, and the second structure 12 are deformed into a parallelogram as shown by dashed line C. At this time, due to the rigidity of the fourth structure 24, deformation of the flexure element 21 is suppressed compared to when the fourth structure 24 is not present. However, the width of the central portion of the fourth structure 24 in the longitudinal direction is narrower than the width of the connection portion with the first structure 11 and the width of the connection portion with the second structure 12. For this reason, when torque Mz is applied, the central portion of the fourth structure 24 deforms, and the flexure element 21 deforms, allowing torque Mz to be detected with high accuracy.

[0039] FIG. 5 shows the results of an analysis of the rigidity of the first structure 11 and the second structure 12 against deformation (elliptical deformation) when a force other than torque is applied to different beam structures of the torque sensor 10.

[0040] Specifically, Fig. 5 shows the amount of deformation when elliptical deformation occurs in the first structure 11 and the second structure 12 due to a force other than torque. Therefore, the smaller the numerical value of the amount of deformation, the higher the rigidity, indicating that other-axis interference due to a force other than torque can be suppressed.

[0041] The beam includes two third structures 13 and a structure provided therebetween, and the width of the beam is adjusted so that the stiffness in the torque direction is equal for each model.

[0042] Model 1 is the case of a beam in which there is no fourth structure 24 or the like between two third structures 13. In this case, the amount of deformation with respect to the elliptical deformation of the first structure 11 and the second structure 12 due to a force other than torque is 0.771.

[0043] Model 2 is the case of a beam in which a thin metal material connects two third structures 13 and the first structure 11 and the second structure 12. In this case, the amount of deformation with respect to the elliptical deformation of the first structure 11 and the second structure 12 due to a force other than torque is 0.707.

[0044] Model 3 relates to this embodiment and is the case of a beam in which a fourth structure 24 that connects the first structure 11 and the second structure 12 is provided between two third structures 13. In this case, the amount of deformation with respect to the elliptical deformation of the first structure 11 and the second structure 12 due to a force other than torque is 0.624.

[0045] As described above, it can be seen that in this embodiment, the first structure 11 and the second structure 12 have high rigidity against forces other than torque. Therefore, the multiple strain gauges 21 can be uniformly deformed against forces other than torque, and the output of signals due to forces other than torque can be reduced from the output signals of the multiple strain gauges provided on each strain gauge 21. Therefore, it is possible to suppress other-axis interference and detect torque with high accuracy.

[0046] (Effects of the embodiment) The torque sensor 10 of this embodiment is configured such that a first structure 11, a second structure 12, and two third structures 13 form a quadrangle, and is provided inside the quadrangle with a strain sensor 20 (a strain element 21) bonded between the first structure 11 and the second structure 12, and a fourth structure 24 connecting the first structure 11 and the second structure 12. The width of the fourth structure 24 at its longitudinal center is narrower than the widths at both longitudinal ends. Therefore, when a force in a direction other than torque is applied to the torque sensor 10, the fourth structure 24 can increase the rigidity of the first structure 11 and the second structure 12 against elliptical deformation. Therefore, when a force in a direction other than torque is applied to the torque sensor 10, the signal output due to the force other than torque can be reduced, and other-axis interference can be suppressed, enabling torque to be detected with high accuracy.

[0047] Furthermore, since the width of the longitudinal center of the fourth structure 24 is narrower than the width of both longitudinal ends, when a force in the torque direction is applied to the torque sensor 10, the rigidity of the fourth structure 24 is low, and therefore the torque can be detected with high accuracy.

[0048] 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. [Explanation of symbols]

[0049] 11...first structure, 12...second structure, 13...third structure, 20...strain sensor, 21...flexural element, 22...strain gauge, 24...fourth structure, 25...waterproof cap.

Claims

1. a first structure; a second structure; and a plurality of third structures connected between the first structure and the second structure; a strain-generating body located between adjacent third structures and including a plurality of sensor elements coupled between the first structure and the second structure; a fourth structure located between adjacent third structures and connected between the first structure and the second structure; Equipped with A torque sensor characterized in that the width of the fourth structure (the length parallel to the plane of the first structure and the second structure and intersecting the longitudinal direction of the fourth structure) becomes wider as it approaches the first structure and the second structure from the center of the longitudinal direction of the fourth structure.

2. 2. The torque sensor according to claim 1, wherein a longitudinal direction of the third structure adjacent to the flexure element is parallel to a longitudinal direction of the flexure element.

3. the strain element is rectangular and has a side surface in a direction intersecting with a plane of the first structure and the second structure, 2. The torque sensor according to claim 1, wherein the third structure has a side surface parallel to the side surface of the strain element.

4. 4. The torque sensor according to claim 2, wherein the length of the portion of the third structure parallel to the strain-generating body is 25% to 40% of the entire length of the third structure.

5. 2. The torque sensor according to claim 1, wherein a thickness of the fourth structure in a direction perpendicular to a plane of the first structure and the second structure is thinner than a thickness of the third structure in a direction perpendicular to the plane of the first structure and the second structure.

6. 6. The torque sensor according to claim 5, further comprising: a cap provided between the strain body and the fourth structure, the cap closing a space between the adjacent third structure and fourth structure and a space between the adjacent first structure and second structure.

7. 7. The torque sensor according to claim 6, wherein one of the surfaces of the fourth structure parallel to the plane of the first structure and the second structure is disposed opposite to the other surface of the strain element parallel to the plane of the first structure and the second structure.

8. the strain-generating body has a front surface and a back surface parallel to the planes of the first structure and the second structure, 8. The torque sensor according to claim 7, wherein the fourth structure has a front surface and a back surface parallel to planes of the first structure and the second structure, and the front surface of the fourth structure is disposed opposite the back surface of the strain element.

9. 9. The torque sensor according to claim 8, wherein a connection portion of the fourth structure with the first structure and a connection portion of the fourth structure with the second structure are spaced apart from the third structure adjacent to the fourth structure.

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