TORQUE SENSOR

Abstract

The invention provides a torque sensor capable of detecting torque with high accuracy, even when a force other than torque is applied. The torque sensor 10 comprises a first structure 11, a second structure 12, a plurality of third structures 13, a strain gauge 21, and a fourth structure 24. The third structures 13 are connected between the first and second structures. The strain gauge 21 is located between adjacent third structures and contains a plurality of sensor elements and is coupled between the first and second structures. A fourth structure 24 is located between adjacent third structures and is connected between the first and second structures. The width of the fourth structure 24 widens from a midpoint along its longitudinal axis towards the first and second structures.

Description

Technical area

[0001] Embodiments described herein generally relate to a torque sensor installed, for example, in a joint of a robot arm. General state of the art

[0002] The torque sensor includes a first structure to which torque is applied, a second structure to which torque is output, a plurality of third structures connecting the first and second structures, and a plurality of strain gauges between the first and second structures. A plurality of strain gauges are located on each strain gauge (see, for example, JP 2018-091813 A and JP 2017-172983 A). Brief description of the inventionTechnical problem

[0003] For example, the first and second structures of the torque sensor are ring-shaped. When torque and forces other than torque are applied to the torque sensor, the first and second structures may be deformed into an elliptical shape. In this case, the parts of the first and second structures are not deformed evenly, and thus the strain gauges between the first and second structures are also not deformed evenly. Therefore, output signals from strain gauges provided with each of the strain gauges include signals due to forces other than torque, reducing the accuracy of torque detection.

[0004] The present application provides a torque sensor that can detect torque with high accuracy even when a force other than torque is applied. Solution to the problem

[0005] The torque sensor of the present 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, wherein a width of the fourth structure (length parallel to planes of the first structure and the second structure intersecting a longitudinal direction of the fourth structure) widens from a center of the longitudinal direction of the fourth structure toward the first structure and the second structure. Short description of the drawings Fig. 1 is a plan view illustrating a torque sensor of one embodiment with some parts removed. Fig. 2 is a plan view of the torque sensor of the embodiment in a deformed state. Fig. Figure 3 illustrates a fourth structure, which is a cross-sectional view along the line III-III of Fig. 1 is. Fig. Figure 4 illustrates the fourth structure, which is an enlarged plan view of a part indicated by A in Fig. 2 is specified. Fig. 5 a degree of deformation of the structures of the embodiment and other examples. Mode of implementation of the invention

[0006] The embodiment will be described below with reference to the drawings. In the figures, the same elements or parts with the same function are designated by the same reference numerals.

[0007] Fig. Figure 1 illustrates a torque sensor 10 of the present embodiment. The configuration of the torque sensor 10 is not limited to this and can be applied to torque sensors of various configurations. It is also possible to apply the present embodiment not only to torque sensors but also to force sensors using strain gauges.

[0008] In Fig. 1, the torque sensor 10 includes, for example, a first structure 11, a second structure 12, a plurality of third structures 13, a plurality of waterproof caps 14, a housing 15, a socket 16, a cable 17, a plurality of strain sensors 20, a plurality of flexible plates 23, a plurality of fourth structures 24, and a plurality of waterproof caps 25.

[0009] 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 third structures 13 and fourth structures 24 as a plurality of radially arranged supports. Each fourth structure 24 is evenly spaced and located between adjacent third structures 13.

[0010] As described below, the fourth structure 24 is arranged in correspondence with the strain sensor 20, and the number of strain sensors 20 and fourth structures 24 is, for example, eight each. The number of strain sensors 20 and fourth structures 24 is not limited to eight.

[0011] The first structure 11 is connected, for example, to a measuring object and the second structure 12 is connected to another structure, which is not shown. The third structures 13 transmit torque (in Fig. 2) from the first structure 11 to the second structure 12. Conversely, the second structure 12 may be connected to the measurement object, the first structure 11 may be connected to another structure not shown, and the torque may be transmitted from the second structure 12 to the first structure 11 via the third structures 13.

[0012] The first structure 11, second structure 12 and third structure 13 are made of metal, e.g. stainless steel, but materials other than metal may be used if sufficient mechanical strength for the applied torque can be achieved.

[0013] The second structure 12 has a hollow portion 12a, and the housing 15 is attached to the second structure 12 around the hollow portion 12a. A processing circuit, not shown, is provided inside the housing 15. The processing circuit processes the electrical signal supplied from the strain sensor 20 and generates a torque detection signal as a sensor signal.

[0014] The socket 16 is provided with a part of the housing 15 and holds the cable 17. One end of the cable 17, not shown, is connected to a processing circuit in the housing 15, and the other end of the cable 17 is passed through, for example, the hollow part 12a. The cable 17 supplies external power to the processing circuit and outputs sensor signals processed by the processing circuit to the outside. The configuration of the processing circuit is not essential to the present embodiment and will not be described.

[0015] Each strain sensor 20 arranged corresponding to every fourth structure 24 is covered by the cap 14. The configuration of the portion covered by the cap 14 is identical. To illustrate the fourth structure 24, the strain sensor 20, the flexible substrate 23, and the cap 25, Fig. 1 shows the four caps 14 and other components that are not necessary for the explanation are removed and the components that are necessary for the explanation are exposed.

[0016] The strain sensor 20 is provided between the first structure 11 and the second structure 12. That is, one end of the strain sensor 20 is coupled to the first structure 11, and the other end of the strain sensor 20 is coupled to the second structure 12, as described below.

[0017] In particular, the first and second structures 11 and 12, which correspond to the fourth structure 24, have an integrated recess 30.

[0018] A hole 30a is provided approximately in the center of the portion of the recess 30 corresponding to the first structure 11, and a hole 30b is further provided approximately in the center of the portion thereof corresponding to the second structure 12.

[0019] The strain sensor 20 is provided between the first and second structures 11 and 12 in the recess 30. The strain sensor 20 includes, for example, a metallic strain body 21 and a plurality of strain gauges 22 as sensor elements arranged on the surface of the strain body 21.

[0020] The expansion body 21 has, for example, a rectangular shape, and the length of the expansion body 21 is longer than the length of the third structure 13 and shorter than the length between the holes 30a and 30b. One longitudinal end of the expansion body 21 is placed on the surface of the first structure 11 in the recess 30, and the other longitudinal end of the expansion body 21 is placed on the surface of the second structure 12 in the recess 30. One end of the expansion body 21 is fixed to the first structure 11 by a fastener 40a located in the recess 30 and a screw 41a inserted into the hole 30a from the back of the first structure 11 and screwed into the fastener 40a.The other end of the expansion body 21 is fixed to the second structure 12 by a fixing member 40b located in the recess 30 and a screw 41b inserted into the hole 30b from the back of the second structure 12 and screwed to the fixing member 40b.

[0021] The strain gauges 22 are, for example, thin-film resistor elements whose resistance value changes with the deformation of the strain body 21. The strain gauges 22 form a bridge circuit (not shown), and a change in the resistance value is detected by the bridge circuit as an electrical signal. The 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 in the housing 15. The electrical signal output from the bridge circuit is supplied to the processing circuit via the flexible substrate 23, and a torque detection signal is generated in the processing circuit as a sensor signal.

[0022] The cap 14 is attached to the recess 30 and seals the recess 30. The cap 25 is positioned between the expansion body 21 and the fourth structure 24, covering the fourth structure 24 to seal the openings 26 on both sides of the fourth structure 24. The strain sensor 20 is protected from moisture by the cap 14 and the cap 25. Specifically, the cap 14 prevents moisture from entering the front of the expansion body 21, and the cap 25 prevents moisture from entering the back of the expansion body 21.

[0023] Fig. 2 shows an example of deformation due to force detected by the torque sensor 10. For example, in the torque sensor 10 in which eight strain sensors 20 are arranged, when a force other than torque is applied and the first and second structures 11 and 12 are deformed into an elliptical shape, as shown by the dashed line, the strain bodies 21 of the eight strain sensors 20 are not deformed uniformly. In this case, the output signal of the bridge circuit including a plurality of strain gauges arranged on the surface (plane) of the strain bodies 21 includes signals corresponding to the force other than torque. Thus, the detection accuracy of the torque Mz decreases.

[0024] The present embodiment prevents a reduction in the accuracy of torque detection by increasing the rigidity of the first and second structures 11 and 12 against forces other than torque, with the fourth structures 24 arranged in correspondence with each of the strain sensors 20.

[0025] Fig. 3 shows a cross section along the line III-III Fig. 1, which shows cross sections of two of the third structures 13, the fourth structure 24 placed therebetween, and the expansion body 21.

[0026] Each of the two third structures 13 arranged in a direction intersecting the longitudinal direction of the expansion body 21 has a side surface 13a parallel to the side surface 21a along the longitudinal direction of the expansion body 21. In particular, the longitudinal directions of the third structure 13 and the expansion body 21 are arranged in the same direction. The width (length in the direction parallel to the plane 11a of the first structure 11 (as shown in Fig. 1) and the plane 12a of the second structure 12, which intersects the longitudinal direction of the third structure 13) of the section of the third structure 13 parallel to the expansion body 21 is constant. The length of the section of the third structure 13 parallel to the expansion body 21 is, for example, 25 to 40% of the total length of the third structure 13.

[0027] The width of the third structure 13 at both ends in the longitudinal direction is widened toward the first and second structures 11 and 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.

[0028] The fourth structure 24 is positioned parallel to and away from the expansion body 21. That is, the surface 24b of the fourth structure 24 (parallel to the plane 11a of the first structure 11 and the plane 12a of the second structure 12) is parallel to and opposite the rear surface 21c of the expansion body 21.

[0029] In the plane 24b of the fourth structure 24, the width of the central portion in the longitudinal direction is narrower than the widths of the 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 expansion body 21 (in the intersection direction with the plane 11a of the first structure 11 and the plane 12a of the second structure 12). That is, as in Fig. 1, a circular opening 26 is formed between the fourth structure 24 and the two adjacent third structures 13, and the side surface 24a of the fourth structure 24 is arcuate. Therefore, the width of the plane 24b of the fourth structure 24 widens from the longitudinal center of the fourth structure 24 toward the first structure 11 and the second structure 12. In other words, the width W4 of the connecting portion of the fourth structure 24 between the first structure 11 and the second structure 12 is wider than the width W1 in the center of the longitudinal direction (W4>W1).

[0030] The connecting parts of the fourth structure 24 with the first structure 11 and the second structure 12 are separated from the two third structures 13 adjacent to the fourth structure 24. Thus, the fourth structure 24 can function as a support independently of the two third structures 13 adjacent to the fourth structure 24.

[0031] It should be noted that the shape of the opening 26 is not limited to a circle, but may have an oval or other shape as long as the shape of the flat surface 24b of the fourth structure 24 can widen from the longitudinal center of the fourth structure 24 toward the first structure 11 and the second structure 12.

[0032] The thickness T1 of the fourth structure 24 is thicker than the thickness T3 of the expansion body 21 and thinner than the thickness T2 of the third structure 13 (T3 < T1 < T2). The width W1 of the longitudinal center of the fourth structure 24 is narrower than the width W3 of the expansion body 21 and wider than the width W2 of the third structure 13 (W3 > W1 > W2). However, these width ratios are examples and are not limited thereto, and can be varied.

[0033] Here, the thickness is the length of the third structure 13, the fourth structure 24 and the expansion body 21 in a direction perpendicular to the planes of the first and second structures 11 and 12, and the width is the length of the third structure 13, the fourth structure 24 and the expansion body 21 in a direction parallel to the planes of the first and second structures 11 and 12, which intersects the length direction.

[0034] If no force is applied to the torque sensor 10, as shown in Fig. 4 the two third structures 13 adjacent to the fourth structure 24 and the first and second structures 11 and 12 form a rectangle as shown by the dashed line B.

[0035] With the above configuration, when a force (other than torque Mz) that deforms the torque sensor 10 into an elliptical shape (a force other than the torque Mz) is applied to the torque sensor 10, the fourth structure 24 functions as an X-shaped support between the first and second structures 11 and 12. Thus, the rigidity of the fourth structure 24 suppresses the deformation of the two third structures 13 adjacent to the fourth structure 24 and the first and second structures 11 and 12 with respect to forces other than the torque Mz. Therefore, the output of signals due to forces other than the torque can be reduced, and the torque can be detected with high accuracy by suppressing interference in other axes.

[0036] On the other hand, when the torque Mz is applied to the torque sensor 10 described above, the two third structures 13 adjacent to the fourth structure 24, the first structure 11, and the second structure 12 are deformed into a parallelogram as shown by the dashed line C. At this time, the rigidity of the fourth structure 24 suppresses the deformation of the strain body 21 compared to a case without the fourth structure 24. However, the width of the central part of the fourth structure 24 in the longitudinal direction is narrower than the width of the connecting part with the first structure 11 and the connecting part with the second structure 12. Therefore, in response to the torque Mz, the central part of the fourth structure 24 deforms, thereby deforming the strain body 21 and enabling the torque Mz to be detected with high accuracy.

[0037] Fig. 5 shows results of the analysis of the stiffness of the first and second structures 11 and 12 with respect to deformation (elliptical deformation) when forces other than torque are applied to the different support structures of the torque sensor 10.

[0038] In particular, Fig. 5 represents a degree of deformation when elliptical deformation occurs in the first and second structures 11 and 12 due to forces other than torque. Thus, as the value of the degree of deformation becomes smaller, the stiffness becomes higher, indicating that inference in other axes can be suppressed by forces other than torque.

[0039] It should be noted that the beams include two third structures 13 and one structure in between, and the width of the beams is adjusted so that each model has equal stiffness in the torque direction.

[0040] Model 1 is a case of a beam without a fourth structure 24 or any other structure between the two third structures 13. In this case, the degree of deformation of the first and second structures 11 and 12 due to forces other than torque with respect to an elliptical deformation is 0.771.

[0041] Model 2 is a case of a beam connected by a thin metal material between two third structures 13 and between the first and second structures 11 and 12. In this case, the degree of deformation of the first and second structures 11 and 12 due to forces other than torque with respect to an elliptical deformation is 0.707.

[0042] Model 3 is a case of a beam of the present embodiment having a fourth structure 24 connecting the first and second structures 11 and 12 between the two third structures 13. In this case, the degree of deformation upon elliptical deformation of the first and second structures 11 and 12 due to forces other than torque is 0.624.

[0043] Thus, according to the embodiment, it can be seen that the rigidity of the first and second structures 11 and 12 is high with respect to forces other than torque. Thus, a plurality of strain bodies 21 can be uniformly deformed with respect to forces other than torque, and the output signal from a plurality of strain gauges provided on each strain body 21 can reduce the output signal due to forces other than torque. Therefore, interference in other axes can be suppressed and torque can be detected with high accuracy. (Effect of the embodiment)

[0044] The torque sensor 10 of the present embodiment forms a quadrilateral by the first and second structures 11 and 12 and two third structures 13, and includes, inside the quadrilateral, a strain body 21 as a strain sensor 20 coupled between the first and second structures 11 and 12, and a fourth structure 24 connecting the first and second structures 11 and 12. The fourth structure 24 has a width in the center of the longitudinal direction that is narrower than the widths at both ends of the longitudinal direction. Therefore, when a force in a direction other than torque is applied to the torque sensor 10, the fourth structure 24 increases the rigidity of the first structure 11 and the second structure 12 with respect to elliptical deformation.Therefore, when a force in a direction other than torque is applied to the torque sensor 10, the signal output due to a force other than torque can be reduced, and torque can be detected with high accuracy by suppressing interference in other axes.

[0045] Moreover, since the width of the central portion of the fourth structure 24 in the longitudinal direction is narrower than the widths of the two ends in the longitudinal direction, torque can be detected with high accuracy when a force in the torque direction is applied to the torque sensor 10 because the rigidity of the fourth structure 24 is low.

[0046] It should be noted that the present invention is not limited to the embodiments described above, but the individual elements of the invention can be modified in various ways without departing from the spirit and scope of the invention. Furthermore, various aspects of the invention can be obtained by any suitable combination of a variety of components disclosed in the embodiments. Some components may be omitted from all components disclosed in the embodiments. The components described in different embodiments can be combined in any way. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2018-091813 A

[0002] JP 2017-172983 A

[0002]

Claims

[1] Torque sensor, comprising: 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, wherein a width of the fourth structure (length parallel to planes of the first structure and the second structure intersecting a length direction of the fourth structure) widens from a center of the length direction of the fourth structure toward the first structure and the second structure. [2] The torque sensor according to claim 1, wherein a longitudinal direction of the third structure adjacent to the strain body is parallel to a longitudinal direction of the strain body. [3] Torque sensor according to claim 1, wherein a shape of the expansion body is rectangular with a side surface along a direction intersecting the planes of the first structure and the second structure, and the third structure includes a side surface parallel to a side surface of the expansion body. [4] The torque sensor according to claim 2 or 3, wherein a length of a part of the third structure that is parallel to the expansion body is 25 to 40% of a total length of the third structure. [5] The torque sensor according to claim 1, wherein a thickness of the fourth structure perpendicular to the planes of the first structure and the second structure is thinner than a thickness of the third structure perpendicular to the first structure and the second structure. [6] The torque sensor of claim 5, further comprising a cap disposed between the strain body and the fourth structure, the cap sealing a space between the adjacent third structures and the fourth structure and a space between the first structure and the second structure. [7] A torque sensor according to claim 6, wherein one of the surfaces of the fourth structure is arranged parallel to the planes of the first structure and the second structure such that it faces the other of the surfaces of the strain body parallel to the planes of the first structure and the second structure. [8] Torque sensor according to claim 7, wherein the expansion body includes a surface and a back surface that are parallel to the planes of the first structure and the second structure, and the fourth structure includes a surface and a back surface that are parallel to the planes of the first structure and the second structure, while the surface of the fourth structure is arranged to face the back surface of the expansion body. [9] The torque sensor according to claim 8, wherein a connecting part of the fourth structure and the first structure and a connecting part of the fourth structure and the second structure are spaced from the third structure adjacent to the fourth structure.

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