Torque sensor

Abstract

This torque sensor comprises: an annular first structure; an annular second structure positioned inside the first structure; a plurality of third structures that are flexible and connect the first structure and the second structure; a strain-generating body having a long, plate-like shape, with one end in the longitudinal direction fixed to the first structure and the other end fixed to the second structure; a strain measurement element that is installed on the strain-generating body and measures the strain of the strain-generating body; and a temperature measurement element that is installed within a range in the longitudinal direction in which the strain and the position in the longitudinal direction at each point on the strain-generating body exhibit a linear relationship, and measures the temperature of the strain-generating body.

Description

Torque sensor

[0001] The present invention relates to a torque sensor.

[0002] Patent Document 1 discloses a sensor in which two Wheatstone bridge circuits for strain detection and temperature detection are formed using a plurality of identical thin film resistors having a high gauge factor and a high temperature coefficient on a single insulating thin film substrate. One of the thin film resistors having a high gauge factor and a high temperature coefficient that constitutes one side of the Wheatstone bridge circuit for strain measurement is formed in the strain generation direction, and the other thin film resistors are formed at right angles to the strain generation direction.

[0003] Patent Document 2 discloses a load cell unit provided with a strain generating body having a plurality of strain generating portions. Each strain gauge is a temperature sensitivity compensation type gauge and is arranged at a corresponding strain generating portion. The bridge circuit is formed by the strain gauges. The zero point compensation element compensates the zero point of the bridge circuit according to the temperature of the strain generating body and roughly corrects the output of the bridge circuit. The temperature sensitive resistor is a temperature sensor that detects the temperature of the strain generating body. These zero point compensation elements and temperature sensitive resistors are provided in a thick portion sandwiched between adjacent strain generating portions. The signal processing unit finely corrects the output of the roughly corrected bridge circuit.

[0004] Japanese Patent Application Laid-Open No. 5-34182, Japanese Patent Application Laid-Open No. 2008-64497

[0005] The torque sensor is provided, for example, at a joint of a robot arm and measures the torque accompanying the rotation of the joint. The measurement of torque is realized by measuring the strain of a strain generating body that is strained along with the torque by a strain measurement element such as a strain gauge. Since the strain measurement element is installed on the strain generating body and causes a change in resistance value along with the strain of the strain generating body, the strain is measured by measuring the resistance value of the strain measurement element.

[0006] Since the resistance value of a strain measuring element also changes with temperature, a torque sensor in which a temperature measuring element is placed on the strain generating body is desirable. A torque sensor with a temperature measuring element on the strain generating body allows for temperature compensation to correct for errors due to temperature changes. However, the configuration of Patent Document 1 cannot be applied when strain occurs two-dimensionally on the surface of the strain generating body. Also, the configuration of Patent Document 2 requires a thick section and cannot be applied to a typical plate-shaped strain generating body.

[0007] Therefore, the present disclosure aims to provide a torque sensor with a novel configuration that includes a temperature measuring element on a strain generating body.

[0008] One embodiment of the torque sensor according to the present disclosure comprises: an annular first structure; an annular second structure located inside the first structure; a plurality of flexible third structures connecting the first structure and the second structure; a strain generating body having a long plate shape, with one end in the longitudinal direction fixed to the first structure and the other end fixed to the second structure; a strain measuring element installed on the strain generating body for measuring the strain of the strain generating body; and a temperature measuring element installed within a range in the longitudinal direction where the longitudinal position and strain at each point on the strain generating body show a linear relationship, for measuring the temperature of the strain generating body.

[0009] Another embodiment of the torque sensor according to this disclosure comprises the first structure, the second structure, the plurality of third structures, the strain generating body, the strain measuring element, and a temperature measuring element installed within the central range of the non-fixed range in the longitudinal direction of the strain generating body, which occupies 40% of the total length of the strain generating body.

[0010] According to this disclosure, a new torque sensor configuration is realized in which a temperature measuring element is mounted on a strain generating body.

[0011] Figure 1 is a perspective view showing the torque sensor. Figure 2 is a top view showing the torque sensor. Figure 3 is a diagram showing an example of the measurement unit. Figure 4 is a diagram showing a modified example of the measurement unit. Figure 5 is a graph showing the strain generated in strain body No. 1. Figure 6 is a table showing the dimensions of the strain bodies used for verification. Figure 7 is a graph showing the strain generated in strain body No. 2. Figure 8 is a graph showing the strain generated in strain body No. 3. Figure 9 is a graph showing the strain generated in strain body No. 4. Figure 10 is a graph showing the strain generated in strain body No. 5.

[0012] Embodiments of the torque sensor of this disclosure will be described in detail below with reference to the attached drawings. However, in order to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art, more detailed explanations than necessary may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. In addition, elements shown in the previously described drawings may be referred to as appropriate in the later descriptions of the drawings.

[0013] <Configuration of Torque Sensor> Figure 1 is a perspective view showing a torque sensor 100 according to one aspect of the present disclosure, and Figure 2 is a top view showing the torque sensor 100. The torque sensor 100 is a sensor that detects torque of a moment with the central axis 300 as the axis of rotation. The torque sensor 100 is mounted on, for example, a robot to detect the rotational torque of the robot's joints.

[0014] The torque sensor 100 comprises a first structure 110, a second structure 120, a plurality of third structures 130, and a measuring unit 140. In this specification, "to comprises" means to be provided in some form, whether as an independent object or as part of an object, unless the context clearly indicates otherwise. In contrast, in this specification, "to have" generally means to have as part of an object. The first structure 110 has an annular shape that encircles the central axis 300 of the torque sensor 100. The second structure 120 is located inside the first structure 110 and has an annular shape that encircles the central axis 300 of the torque sensor 100. The first structure 110 and the second structure 120 are, for example, annular in shape, and for example, are located concentrically with each other.

[0015] Each of the multiple third structures 130 is flexible and is arranged, for example, radially between the first structure 110 and the second structure 120, connecting the first structure 110 and the second structure 120 to each other. The radially arranged multiple third structures 130 suppress the strain on the strain-generating body 201 (see Figure 3) of the measuring unit 140 caused by forces other than the moment around the central axis 300 of the torque sensor 100.

[0016] The first structure 110, the second structure 120, and the third structure 130 are formed, for example, as a single elastic body. The first structure 101, the second structure 120, and the third structure 130 are formed, for example, from a metal such as stainless steel by machining. The first structure 110, the second structure 120, and the third structure 130 may be formed from materials other than metal (such as resin) as long as they have sufficient mechanical strength against applied forces such as torque.

[0017] The torque sensor 100 has one of its two structures, the first structure 110 and the second structure 120, attached to a load that receives torque, and the other attached to a power source that generates torque. The power source side is the torque input side, such as a motor or a gearbox. The load side is the torque output side, such as a robot's hand or arm.

[0018] The measuring unit 140 is located between the first structure 110 and the second structure 120. The measuring unit 140 is protected by a cover 141. The cover 141 covers the top of the measuring unit 140 without contacting it. The measuring unit 140 is a measuring element for electrically measuring the torque applied to the torque sensor 100 and the ambient temperature of the torque sensor 100.

[0019] The measuring unit 140 may be provided as one unit per torque sensor 100, or multiple units may be provided. Preferably, multiple measuring units 140 are provided symmetrically with respect to the central axis 300 of the first structure 110 and the second structure 120. In Figure 2, eight measuring units 140 are provided symmetrically as an example.

[0020] <Configuration of the Measurement Unit> Figure 3 shows an example of the measurement unit 140. Figure 3 shows XY coordinates as a reference for direction. The XY plane defined by the X and Y axes is a plane perpendicular to the central axis 300 of the torque sensor 100, and the X direction represents the longitudinal direction of the measurement unit 140, regardless of the orientation of the measurement unit 140 in relation to the torque sensor 100.

[0021] The measuring unit 140 includes a strain generating body 201, a strain gauge 202, and a temperature sensor 203. The strain generating body 201 is, for example, a metal plate that extends along the XY plane and is elongated in the X direction. When the strain generating body 201 is fixed to the torque sensor 100, it is fixed such that the direction in which the plate shape extends (XY plane) is perpendicular to the direction of the central axis 300 of the torque sensor 100 (Z direction). One end of the strain generating body 201 in the longitudinal direction is fixed to the first structure 110, and the other end in the longitudinal direction is fixed to the second structure 120. That is, the fixed regions A2 at both ends in the X direction are fixed to the first structure 110 or the second structure 120. The unfixed region A1 between the fixed regions A2 is the region where strain is generated. The unfixed region A1 is also elongated in the X direction.

[0022] It is desirable that the strain generating body 201 has a shape that is symmetrical with respect to one end and the other end in the longitudinal direction. That is, it is desirable that the strain generating body 201 has a shape that is symmetrical with respect to the center line Cx that indicates the center in the X direction. In the example shown in Figure 3, the strain generating body 201 has a rectangular shape, so it is symmetrical with respect to both the longitudinal and transverse directions. That is, the strain generating body 201 is symmetrical with respect to the center line Cx that indicates the center in the X direction, and also symmetrical with respect to the center line Cy that indicates the center in the Y direction.

[0023] When torque is applied to the torque sensor 100, the fixed regions A2 located at both ends of the strain generating body 201 are each displaced in the Y direction, and displaced in opposite directions to each other. As a result, a strain is generated in the non-fixed region A1 of the strain generating body 201, distributed two-dimensionally along the surface of the strain generating body 201. Specifically, the strain is large near the corners of the non-fixed region A1, the surface of the strain generating body 201 is compressed by the strain near the two diagonally opposite corners, and the surface is stretched by the strain near the other two corners.

[0024] The strain gauges 202 are installed in the non-fixed region A1 of the strain generating body 201, and in particular, near the corners mentioned above. Figure 3 shows four strain gauges 202 as an example, but only one strain gauge 202 may be installed, or two or three may be installed. Alternatively, five or more strain gauges 202 may be installed.

[0025] The strain gauge 202 is an example of a strain measuring element as described in this disclosure, and its resistance changes as it expands and contracts in response to the strain of the strain generating body 201. Other strain measuring elements may be installed in the measurement unit 140. The strain of the strain generating body 201 is measured by measuring the resistance of the strain gauge 202 via the electrode 204, thereby measuring the torque. However, since the resistance of the strain gauge 202 also changes with temperature, it is desirable that the measured value from the strain gauge 202 be temperature compensated. Temperature compensation may be applied to any of the measured resistance, strain, or torque.

[0026] The temperature sensor 203 corresponds to an example of a temperature measuring element as described in this disclosure. The temperature sensor 203 has a temperature-sensitive material whose resistance value changes with temperature changes, and the ambient temperature is measured by measuring the resistance value of the temperature sensor 203 via the electrode 204. In the example shown in Figure 3, the resistance value of the temperature sensor 203 is measured in the short direction of the strain generating body 201.

[0027] Figure 4 shows a modified example of the measurement unit 140. The modified measurement unit 140 shown in Figure 4 also includes a temperature sensor 205, and the temperature sensor 205 shown in Figure 4 also has a temperature-sensitive material. In the modified example shown in Figure 4, the resistance value of the temperature sensor 205 is measured in the longitudinal direction of the strain-generating body 201.

[0028] In the examples shown in both Figure 3 and Figure 4, the resistance value of the temperature-sensing material of the temperature sensors 203 and 205 changes as it is strained in accordance with the strain of the strain-generating body 201. For this reason, the temperature sensors 203 and 205 are required to be installed in locations where the influence of the strain of the strain-generating body 201 is small, but in the measurement unit 140, the arrangement of the strain gauges 202 and electrodes 204 takes priority. Therefore, the following section will examine the installation range of the temperature sensors 203 and 205 where the influence of the strain of the strain-generating body 201 is small.

[0029] <Temperature Sensor Placement Range> Figure 5 is a graph showing the strain generated in the strain-generating body 201. The graph in Figure 5 shows the strain at various positions on the edge 210 extending in the X direction of the strain-generating body 201 shown in Figure 4. The horizontal axis of the graph in Figure 5 indicates the position in the X direction, and the 0 mm position corresponds to the position of the corner of the strain-generating body 201. The vertical axis of the graph indicates the amount of strain. As will be described later, Figure 5 shows the strain generated in the strain-generating body 201 with a dimension of 7.8 mm in the X direction. In considering the installation range of the temperature sensors 203 and 205, the focus was placed on the edge 210 where the strain is large, rather than the vicinity of the center line Cy extending in the X direction.

[0030] On the horizontal axis of the graph, the ranges of 0 mm to 1 mm and 6.8 mm to 7.8 mm correspond to the fixed region A2, where basically no strain occurs in the strain generating body 201. When opposing forces in the Y direction are applied to the fixed regions A2 at both ends of the strain generating body 201, large strains occur at both ends of the unfixed region A1 of the strain generating body 201. At one end of the unfixed region A1, the surface of the strain generating body 201 is compressed, while at the other end, the surface of the strain generating body 201 is stretched.

[0031] Since the strain-generating body 201 and the non-fixed region A1 have symmetrical shapes at one end and the other end in the longitudinal direction, the strain distribution is also symmetrical, and the amount of strain is zero in the center of the non-fixed region A1. Furthermore, with the center of the non-fixed region A1 in the longitudinal direction, one end experiences compressive strain, and the other end experiences tensile strain.

[0032] In the range RL1, which includes the center of the non-fixed region A1, the relationship between strain and position is linear. In this range RL1, the increase in strain is gradual even when moving away from the center of the non-fixed region A1. Therefore, it is considered that the effect of strain is small when temperature sensors 203 and 205 are installed within the range RL1, where the relationship between strain and position is linear.

[0033] In the case of the strain-generating body 201, whose strain is shown in the graph of Figure 5, the range RL1 in which the amount of strain and position show a linear relationship occupies approximately 40% of the total length of the non-fixed region A1 in the X direction. Hereinafter, the total length of the non-fixed region A1 in the X direction will be referred to as the "effective length," and the range in which the amount of strain and position show a linear relationship will be referred to as the "linear range."

[0034] Next, we examine the ratio of the linear range to the effective length for several strain bodies 201 with different length and width dimensions. Figure 6 is a table showing the dimensions of the strain bodies 201 used in the examination. Strain bodies 201 with longitudinal dimensions of 6.8 mm, 7.8 mm, and 8.8 mm were prepared. For strain bodies 201 of all dimensions, the fixed region A2 is the 1.0 mm at both ends in the longitudinal direction, so the effective lengths are 4.8 mm, 5.8 mm, and 6.8 mm.

[0035] Furthermore, for the strain body 201 with a longitudinal dimension of 7.8 mm, transverse dimensions of 2.6 mm, 3.4 mm, and 4.8 mm were also prepared. Thus, a total of five different dimensions of strain bodies 201 were prepared, and the numbers 1 through 5 used to distinguish each strain body 201 are listed in the table in Figure 6. The variation range of the non-fixed region A1 in the strain bodies 201 used for verification, expressed as the ratio of the longitudinal to transverse dimensions, is between 1.2 and 2.3.

[0036] The graph in Figure 5 shows the strain in strain body 201 number 1 shown in the table in Figure 6. Figure 7 is a graph showing the strain in strain body 201 number 2 in the table in Figure 6, and Figure 8 is a graph showing the strain in strain body 201 number 3 in the table in Figure 6. Figure 9 is a graph showing the strain in strain body 201 number 4 in the table in Figure 6, and Figure 10 is a graph showing the strain in strain body 201 number 5 in the table in Figure 6.

[0037] Similar to the graph in Figure 5, the horizontal axis of the graphs in Figures 7 to 10 indicates the position in the X direction, and the vertical axis indicates the amount of strain. Each graph in Figures 7 to 10 shows linear ranges RL2, RL3, RL4, and RL5, and each of these linear ranges RL2, RL3, RL4, and RL5 accounts for approximately 40% of the effective length. Therefore, regardless of the dimensions of the strain generating body 201, if the temperature sensors 203 and 205 are installed within the central range, which accounts for 40% of the effective length, the effect of strain is considered to be small. If the shape of the strain generating body 201 is asymmetrical between one end and the other in the longitudinal direction, the strain distribution will also be asymmetrical, and the linear range may be biased from the center. Therefore, it is desirable that the shape of the strain generating body 201 be symmetrical between one end and the other in the longitudinal direction. Furthermore, if the shape of the strain generating body 201 is rectangular, the strain distribution will also be symmetrical in the width direction, and the range in which the temperature sensors 203 and 205 can be easily determined.

[0038] Furthermore, since the strain of the strain-generating body 201 is considered to be greater in the longitudinal direction due to compression and extension than in the short direction, it is preferable to arrange the temperature sensor 203, which measures resistance in the short direction, as shown in Figure 3. However, if it is possible to arrange the temperature sensor 205, which measures resistance in the longitudinal direction, as shown in Figure 4, if it is possible to arrange it sufficiently close to the center line Cx indicating the center in the longitudinal direction, it is also acceptable to arrange the temperature sensor 205, which measures resistance in the longitudinal direction.

[0039] While the above example of how the torque sensor of this disclosure can be used is torque detection in a robot, the torque sensor of this disclosure is not limited to the above-mentioned use and can be used in a wide range of applications, such as torque detection of steering and drive shafts in automobiles, torque detection on the rotating shafts of motors and pumps, and torque detection on the gear shafts of electric assist bicycles.

[0040] Furthermore, the embodiments described above should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the embodiments described above, and all modifications within the meaning and scope of the claims are intended to be included. The technology can be configured as follows:

[0041] (1) A torque sensor comprising: an annular first structure; an annular second structure located inside the first structure; a plurality of flexible third structures connecting the first structure and the second structure; a strain generating body having a long plate shape, with one end in the longitudinal direction fixed to the first structure and the other end fixed to the second structure; a strain measuring element installed on the strain generating body to measure the strain of the strain generating body; and a temperature measuring element installed within the longitudinal range in which the longitudinal position and strain at each point on the strain generating body show a linear relationship, to measure the temperature of the strain generating body.

[0042] (2) An annular first structure, an annular second structure located inside the first structure, a plurality of third structures having flexibility and connecting the first structure and the second structure, a strain generating body having a long plate shape, one end in the longitudinal direction being fixed to the first structure, and the other end with respect to the one end being fixed to the second structure, a strain measurement element installed on the strain generating body for measuring the strain of the strain generating body, and a temperature measurement element installed within a central range occupying 40% of the total length of the non-fixed range in the longitudinal direction of the strain generating body for measuring the temperature of the strain generating body, a torque sensor comprising these components.

[0043] (3) The torque sensor according to (1) or (2), wherein the temperature measurement element measures the temperature by measuring the resistance value of a temperature-sensitive substance whose resistance value changes with temperature change in the short side direction of the strain generating body.

[0044] (4) The torque sensor according to (1) or (2), wherein the temperature measurement element measures the temperature by measuring the resistance value of a temperature-sensitive substance whose resistance value changes with temperature change in the longitudinal direction of the strain generating body.

[0045] (5) The torque sensor according to any one of (1) to (4), wherein the strain generating body is distorted by receiving a force along the direction in which the plate shape spreads.

[0046] (6) The torque sensor according to any one of (1) to (5), wherein the strain generating body has a symmetric shape on the one end side and the other end side in the longitudinal direction.

[0047] (7) The torque sensor according to any one of (1) to (6), wherein the strain generating body has a rectangular plate shape.

[0048] (8) The torque sensor according to any one of (1) to (7), wherein the dimensional ratio of the longitudinal direction to the short side direction in the non-fixed range is 1.2 or more and 2.3 or less.

[0049] 100: Torque sensor 110: First structure 120: Second structure 130: Third structure 140: Measurement unit 141: Cover 201: Strain generating body 202: Strain gauge 203, 205: Temperature sensor 204: Electrode 210: Edge 300: Central axis RL1, RL2, RL3, RL4, RL5: Linear range

Claims

1. A torque sensor comprising: an annular first structure; an annular second structure located inside the first structure; a plurality of flexible third structures connecting the first structure and the second structure; a strain generating body having a long plate shape, with one end in the longitudinal direction fixed to the first structure and the other end fixed to the second structure; a strain measuring element installed on the strain generating body to measure the strain of the strain generating body; and a temperature measuring element installed within the longitudinal range where the longitudinal position and strain at each point on the strain generating body show a linear relationship, to measure the temperature of the strain generating body.

2. A torque sensor comprising: an annular first structure; an annular second structure located inside the first structure; a plurality of flexible third structures connecting the first structure and the second structure; a strain generating body having a long plate shape, with one end in the longitudinal direction fixed to the first structure and the other end fixed to the second structure; a strain measuring element installed on the strain generating body for measuring the strain of the strain generating body; and a temperature measuring element installed within a central range occupying 40% of the total length of the non-fixed range in the longitudinal direction of the strain generating body for measuring the temperature of the strain generating body.

3. The torque sensor according to claim 1 or 2, wherein the temperature measuring element measures the resistance of a temperature-sensitive material whose resistance changes with temperature in the short direction of the strain-generating body to measure the temperature.

4. The torque sensor according to claim 1 or 2, wherein the temperature measuring element measures the resistance of a temperature-sensitive material whose resistance changes with temperature, in the longitudinal direction of the strain-generating body to measure the temperature.

5. The torque sensor according to claim 1 or 2, wherein the strain-generating body is deformed by a force along the direction in which the plate shape expands.

6. The torque sensor according to claim 1 or 2, wherein the strain generating body has a symmetrical shape at one end and the other end in the longitudinal direction.

7. The torque sensor according to claim 1 or 2, wherein the strain generating body has a rectangular plate shape.

8. The torque sensor according to claim 1 or 2, wherein the ratio of the dimensions in the longitudinal direction to the short direction in the non-fixed range is 1.2 or more and 2.3 or less.

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