JP7641444B2 - Torque Sensor - Google Patents

Description

The present invention relates to a torque sensor, and in particular to technology that is useful when applied to a torque sensor that detects strain in the direction of rotation of the central axis between an outer ring and an inner ring.

As a torque sensor that detects strain in the direction of rotation, Patent Document 1 (JP 2007-40774 A) and Patent Document 2 (JP 2019-174325 A) describe a torque sensor having an outer ring, an inner ring, and a strain detection means (torque detection means) attached to the spokes (torque members) between them.

JP 2007-40774 A JP 2019-174325 A

Typically, a torque sensor is composed of an outer ring, an inner ring, and spokes equipped with a strain detection means, and has a symmetrical structure with two pairs of spokes so that strains generated by moments other than the torque around the central axis of the outer and inner rings can be offset by output calculations. Therefore, only the torque around the central axis can be measured. However, for example, due to the influence of contact between the torque sensor and its mounting partner, torque sensor fastening variations, or the influence of the asymmetric shape of the mounting partner, if moments other than the torque around the central axis (crosstalk) are superimposed as asymmetric strain components that cannot be offset by output calculations, the measurement accuracy of the torque sensor decreases.

Therefore, in order to avoid the influence of forces other than the torque around the central axis, it is necessary to devise a way to ensure that the torque sensor's measurement values are not affected by these loads.

Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

A brief overview of the representative embodiments disclosed in this application is as follows:

In one embodiment, the torque sensor has an outer ring, an inner ring, two or more spokes connecting the outer ring and the inner ring, and a strain detection element provided on the spokes, and the spokes have a mounting portion for the strain detection element, a first peripheral portion connecting the mounting portion and the outer ring, and a second peripheral portion connecting the mounting portion and the inner ring, and the rigidity of each of the first peripheral portion and the second peripheral portion is lower than the rigidity of the mounting portion.

According to one embodiment, the performance of the torque sensor can be improved.

FIG. 1 is a plan view showing a torque sensor according to an embodiment. FIG. 1 is a perspective view showing a portion of a torque sensor according to an embodiment. 2 is a cross-sectional view taken along line AA in FIG. 1. 2 is a cross-sectional view taken along line BB in FIG. 1. 13 is a graph showing the relationship between the mounting portion thickness/peripheral portion thickness ratio and the strain change rate. FIG. 11 is a plan view showing a torque sensor according to a first modified example of the embodiment. FIG. 11 is a perspective view showing a portion of a torque sensor according to a first modified example of the embodiment. 7 is a cross-sectional view taken along line AA in FIG. 6. FIG. 11 is a plan view showing a torque sensor according to a second modified example of the embodiment. FIG. 11 is a perspective view showing a portion of a torque sensor according to a second modified example of the embodiment. FIG. 11 is a plan view showing a torque sensor according to a third modified example of the embodiment. 12 is a cross-sectional view taken along line AA in FIG. 11. FIG. 11 is a plan view showing a torque sensor according to a fourth modified example of the embodiment. FIG. 11 is a perspective view showing a portion of a torque sensor according to a fourth modified example of the embodiment. FIG. 13 is a plan view showing a torque sensor according to a fifth modified example of the embodiment. 16 is a cross-sectional view taken along line AA in FIG. 15. FIG. 13 is a plan view showing a torque sensor according to a sixth modified example of the embodiment. 18 is a cross-sectional view taken along line AA in FIG. 17. FIG. 1 is a perspective view showing a torque sensor as a comparative example.

The following describes in detail an embodiment of the present invention with reference to the drawings. In all drawings used to explain the embodiment, the same reference numerals are used for components having the same functions, and repeated explanations will be omitted. In addition, in the embodiment, explanations of the same or similar parts will not be repeated as a general rule, unless particularly necessary.

The thickness here refers to the length of each component in the direction along the central axis of the outer ring and inner ring that make up the torque sensor (hereinafter referred to as the axial direction). Plan view refers to the case where each component is viewed in the axial direction.

(Embodiment 1)
<Torque sensor structure>
FIG. 1 shows an example of a disk-shaped torque sensor 1 according to the present embodiment. The torque sensor (torque meter) 1 includes an outer ring (first structure) 2, an inner ring (second structure) 3, a plurality of spokes (third structure) 4, and a plurality of mounting parts (measurement parts, sensor parts) 4a. The inner ring 3 and the outer ring 2 are formed in an annular shape, and the diameter of the outer ring 2 is larger than the diameter of the inner ring 3. The outer ring 2 is arranged concentrically with the inner ring 3. The inner ring 3 and the outer ring 2 are connected to each other by spokes 4 as a plurality of beam parts arranged radially around their axes (hereinafter referred to as central axes). The spokes 4 transmit torque between the inner ring 3 and the outer ring 2. Each spoke 4 has a mounting part 4a equipped with a strain detection element (sensor element, strain sensor) 5. The mounting part 4a is a part that generates strain due to an external force, that is, a strain generating body. This external force is a force (torque around the central axis) that rotates the inner ring 3 or the outer ring 2 about its axis. When this external force is applied to one or both of the inner ring 3 and the outer ring 2, a strain is generated in the mounting portion 4a, and the torque is detected by the strain detection element 5.

That is, when the robot arm is driven, a force about the central axis is applied to the torque sensor 1. The outer ring 2 of the torque sensor 1 is displaced in the direction about the central axis (circumferential direction) relative to the inner ring 3. As the outer ring 2 is displaced relative to the inner ring 3, electrical signals are output from the two strain detection elements 5 that sandwich the central axis, allowing the torque sensor 1 to detect torque. Here, the inner ring 3 has an annular structure, but the inner ring 3 may also be a circular plate without a central hole.

The torque sensor 1 of this embodiment is used by being assembled to, for example, a multi-joint robot, that is, a rotatable joint portion of a robot arm. For example, one of the outer ring 2 or the inner ring 3 is fixed to a first arm constituting a robot arm, and the other is fixed to a second arm constituting a robot arm and rotatable with respect to the first arm. A hand or various tools is attached to the second arm. The outer ring 2 or the inner ring 3 is fixed to the first arm or the second arm to which the torque sensor 1 is attached by a plurality of bolts. The outer ring 2 and the inner ring 3 have a plurality of circular holes 6 that penetrate them in the axial direction (central axis direction), and the bolts fasten each arm and the outer ring 2 or the inner ring 3 through the holes 6. The plurality of circular holes 6 are arranged in a circumferential direction in each of the outer ring 2 and the inner ring 3.

The outer ring 2, the inner ring 3, and the spokes 4 are made of metal (e.g., stainless steel), but materials other than metal can be used as long as sufficient mechanical strength can be obtained against the applied torque. The outer ring 2 and the inner ring 3 have, for example, the same thickness in the axial direction. In the radial direction of the outer ring 2 and the inner ring 3, one end of the spoke 4 is joined to the inner ring 3, and the other end is joined to the outer ring 2. The outer ring 2, the inner ring 3, and the spokes 4 are integral with each other here, and are formed, for example, by cutting out one member. In the vicinity of the connection between the spoke 4 and the outer ring 2 and the connection between the spoke 4 and the inner ring 3, the width of the spoke 4 in the circumferential direction is expanded in order to increase the strength of each connection, and the outer shape of these connection parts has an arc shape.

As shown in FIG. 2, the spoke 4 has a mounting portion 4a and an annular peripheral portion 4b that surrounds the entire periphery of the mounting portion 4a in a plan view. The peripheral portion 4b includes a peripheral portion (connecting portion) 42 that connects the mounting portion 4a and the outer ring 2, and a peripheral portion (connecting portion) 43 that connects the mounting portion 4a and the inner ring 3. In other words, the peripheral portions 42 and 43 constitute the peripheral portion 4b. The thickness, filling degree, and material of the peripheral portion 4b are the same as those of the peripheral portions 42 and 43. As shown in FIG. 3 and FIG. 4, the overall thickness of the mounting portion 4a is almost constant, and the cross-sectional shape of the mounting portion 4a is rectangular. The overall thickness of the peripheral portion 4b is also almost constant. However, the corners of the connection portion between the mounting portion 4a and the peripheral portion 4b may be provided with an arc (a connection portion having a curved surface) or the like to avoid stress concentration. The thickness of the peripheral portion 4b is smaller than the thickness of the mounting portion 4a. The mounting portion 4a and the peripheral portion 4b are integral with each other here, and are formed, for example, by cutting out from a single member.

Of the parts constituting the spoke 4, all parts other than the mounting part 4a (peripheral part 4b) have a constant thickness. Here, the peripheral part 4b constitutes both ends of the spoke 4 in the circumferential direction. In other words, the thickness of both ends of the spoke 4 in the circumferential direction is smaller than the thickness of the mounting part 4a.

As shown in Fig. 3, the peripheral portion 4b and the peripheral portions 42 and 43 shown in Fig. 2 each have a first surface b1 on one side in the axial direction and a second surface b2 on the opposite side of the first surface b1. The mounting portion 4a has a first protruding portion in contact with the protruding strain detection element 5 relative to the first surface b1 of the peripheral portion 4b in the axial direction, and a second protruding portion spaced apart from the protruding strain detection element 5 relative to the second surface b2 of the peripheral portion 4b.

As shown in FIG. 1, the spokes 4 with mounting portion 4a are formed as a pair on either side of the central axis in a plan view, and have a symmetrical structure, so that distortions caused by moments other than the torque around the central axis can be offset by output calculation. Therefore, at least two spokes 4 with mounting portion 4a are provided as shown in FIG. 1. Two or more pairs of spokes 4 with mounting portion 4a may be provided. In addition to the spokes 4 with mounting portion 4a, multiple spokes that connect the outer ring 2 and the inner ring 3 and do not have mounting portion 4a may be provided.

In a plan view, the mounting portion 4a is completely surrounded by the peripheral portion 4b, so that the mounting portion 4a is separated from both the outer ring 2 and the inner ring 3. The peripheral portion 4b, which is made of the same material as the mounting portion 4a, has a smaller thickness than the mounting portion 4a, so that the rigidity of the peripheral portion 4b is lower than that of the mounting portion 4a. One of the main features of this embodiment is that the mounting portion 4a is surrounded by the peripheral portion 4b, which is thinner than the mounting portion 4a, so that the peripheral portion 4b has a lower rigidity than the mounting portion 4a.

In the axial direction, the strain detection element 5 is attached (glued) to one surface of the mounting portion 4a. The strain detection element 5 is arranged in a symmetrical position with respect to the center (the torque action center) of the outer ring 2 and the inner ring 3. The two strain detection elements 5 are arranged on a diameter sandwiching the center of the annular inner ring 3 and the outer ring 2. The strain detection element 5 may be a metal or semiconductor strain gauge, or an optical fiber type element. Although the strain detection element 5 is shown in a small grain shape in FIG. 1, the shape of the strain detection element 5 is not limited to this, and may be a sheet shape along the surface of the mounting portion 4a in the axial direction, for example, it may extend in the radial direction. In addition, the planar shape of the mounting portion 4a shown in FIG. 1 is close to a square, but it may be a rectangle or an ellipse without being limited to this.

<Effects of the embodiment>
The torque sensor has a pair of spokes arranged symmetrically so that distortions caused by moments other than the torque around the central axis can be offset by output calculations. Therefore, only the torque around the central axis can be measured. However, for example, due to the influence of contact with the object to which the torque sensor is attached, the variation in fastening of the object to which the torque sensor is attached, or the influence of an asymmetric shape of the object to which the torque sensor is attached, moments other than the torque around the central axis (crosstalk) are superimposed as asymmetric distortion components that cannot be offset by output calculations, resulting in a decrease in the measurement accuracy of the torque sensor.

19, the torque sensor of the comparative example has a mounting portion 4x provided on the spoke 4 connecting the outer ring 2 and the inner ring 3, which is formed with a constant thickness between the outer ring 2 and the inner ring 3. In this case, among the parts constituting the spoke 4, the second moment of area of the mounting portion 4x having the strain detection element 5 and its surrounding portion (periphery) is constant, or the mounting portion is less than or equal to the surrounding portion, and the strain detection element is directly affected by the asymmetric strain components due to crosstalk.

In contrast, the torque sensor of this embodiment has an outer ring, an inner ring, two or more spokes connecting the outer ring and the inner ring, and a strain detection element provided on the spoke, and the spoke has a mounting portion for the strain detection element and a peripheral portion that surrounds the mounting portion in a plan view. A main feature is that the rigidity of the peripheral portions that make up the spokes is lower than the rigidity of the mounting portion.

Here, if the outer or inner ring undergoes asymmetric deformation due to a moment other than the torque around the central axis, the second moment of area of the peripheral part is made lower than that of the mounting part, causing the peripheral part to elastically deform, thereby reducing the effect of asymmetric deformation on the mounting part and suppressing a decrease in measurement accuracy.

That is, in this embodiment, in the axial direction (torque measurement axial direction), there is a difference in thickness between the peripheral part and the mounting part (mounting part > peripheral part). Here, the strain due to crosstalk is divided by the square of the thickness of the spoke, and becomes small. On the other hand, the strain due to the torque around the central axis becomes small in inverse proportion to the thickness of the spoke. In this embodiment, the peripheral part of the components of the spoke is formed thinner than the mounting part, so that the deformation caused by the measurement torque (torque around the central axis) is transmitted to the strain detection element, but the deformation caused by moments other than the measurement torque is difficult to transmit to the strain detection element. In other words, by making the rigidity of the peripheral part lower than the rigidity of the mounting part, the influence of asymmetric deformation caused by moments other than the torque around the central axis can be reduced, and the deterioration of measurement accuracy can be suppressed.

Figure 5 shows a graph of the relationship between the mounting part thickness/peripheral part thickness ratio (horizontal axis) and the strain change rate (vertical axis). The mounting part thickness/peripheral part thickness ratio, which is the horizontal axis of Figure 5, is the ratio of the thickness of the mounting part 4a to the peripheral part 4b shown in Figure 2. In Figure 5, the torque around the central axis is shown by a circle plot and a solid line graph, the moment other than the torque around the central axis (crosstalk) is shown by a triangle plot and a dashed line graph, and the difference in strain change rate is shown by a square plot and a dashed line graph.

As shown in FIG. 5, when the peripheral portion 4b is thinned, the torque around the central axis is reduced by a large amount compared to the torque around the central axis when the mounting portion thickness/peripheral portion thickness ratio is higher than 1:1. This also shows that by forming the peripheral portion 4b thinner than the mounting portion 4a, the influence of moments other than the torque around the central axis can be reduced. As shown in FIG. 5, this effect can be obtained if the mounting portion thickness/peripheral portion thickness ratio is greater than 1. However, if the mounting portion thickness/peripheral portion thickness ratio is greater than 4, the amount of strain is excessively reduced. In addition, since there are restrictions on the dimensions of the mounting portion 4a, it is desirable that the thickness ratio of the mounting portion 4a to the peripheral portion 4b is greater than 1 and equal to or less than 4.

<Modification 1>
6 to 8 show a torque sensor 1a according to a first modified example in which reinforcing portions 4c are formed on both ends of the spokes 4. FIG.

In this modified example, the spoke 4 has a mounting portion 4a, an annular peripheral portion 4b that surrounds the entire periphery of the mounting portion 4a in a plan view, and a pair of reinforcing portions 4c that sandwich the mounting portion 4a and the peripheral portion 4b in the circumferential direction of the outer ring 2 and the inner ring 3. Each of the pair of reinforcing portions 4c is formed between the outer ring 2 and the inner ring 3. The peripheral portion 4b connects the mounting portion 4a and the reinforcing portion 4c. The thickness of the reinforcing portion 4c is approximately equal to the thickness of each of the outer ring 2 and the inner ring 3. As shown in FIG. 8, the thickness of the mounting portion 4a is smaller than the thickness of the reinforcing portion 4c. The mounting portion 4a, the peripheral portion 4b, and the reinforcing portion 4c are integral with each other here. Here, the reinforcing portion 4c constitutes both ends of the spoke 4 in the circumferential direction. In a plan view, the periphery of the mounting portion 4a is completely surrounded by the peripheral portion 4b, so that the mounting portion 4a is separated from all of the outer ring 2, the inner ring 3, and the reinforcing portion 4c.

Even if the reinforcing portion 4c is present as in this modified example, by making the rigidity of the peripheral portion 4b lower than the rigidity of the mounting portion 4a, the effects of asymmetric deformation due to moments other than the torque around the central axis can be reduced, and a decrease in measurement accuracy can be suppressed.

<Modification 2>
9 and 10 show a torque sensor 1b in which the peripheral portions 42, 43 constituting the spokes 4 do not entirely surround the periphery of the mounting portion 4a.

In this modified example, the spoke 4 has a mounting portion 4a, a peripheral portion (connecting portion) 42 that connects the mounting portion 4a to the outer ring 2, and a peripheral portion (connecting portion) 43 that connects the mounting portion 4a to the inner ring 3. The mounting portion 4a is interposed between the peripheral portion 42 and the peripheral portion 43, and the peripheral portion 42 and the peripheral portion 43 are spaced apart from each other. The side surface of the mounting portion 4a in the circumferential direction is exposed and is spaced apart from the peripheral portions 42 and 43. The thickness of the peripheral portions 42 and 43 is the same as the thickness of the peripheral portion 4b shown in FIG. 2 and is smaller than the thickness of the mounting portion 4a. Therefore, the rigidity of the peripheral portions 42 and 43 is lower than the rigidity of the mounting portion 4a.

Even if the peripheral portions 42, 43 do not surround the entire periphery of the mounting portion 4a as in this modified example, by making the rigidity of the peripheral portions 42, 43 lower than the rigidity of the mounting portion 4a, the effects of asymmetric deformation due to moments other than the torque around the central axis can be reduced, and a decrease in measurement accuracy can be suppressed.

Here, in addition to the spokes 4 equipped with the strain detection elements 5, a plurality of spokes 7 are provided that connect the outer ring 2 and the inner ring 3 and are not equipped with the mounting portion 4a and the strain detection elements 5. The spokes 7 may be provided in the embodiment described using Figures 1 to 5 and in Modifications 4 to 7 described below.

<Modification 3>
11 and 12 show a torque sensor 1c having a peripheral portion 4b and a peripheral portion 4d. The peripheral portion 4b is made of the same material as the mounting portion 4a, the reinforcing portion 4c, the outer ring 2, and the inner ring 3.

The peripheral portion 4d, which is made of a material different from the mounting portion 4a, the peripheral portion 4b, the reinforcing portion 4c, the outer ring 2, and the inner ring 3, is embedded in the step between the mounting portion 4a and the peripheral portion 4b. In other words, the peripheral portion 4d is embedded in a recess provided by the peripheral portion 4b being thinner than the mounting portion 4a. The peripheral portions 4b and 4d overlap each other in a plan view, and the two peripheral portions 4d cover both surfaces of the peripheral portion 4b in the axial direction. The total thickness of the peripheral portion 4b and the two peripheral portions 4d is, for example, equal to the thickness of the mounting portion 4a.

In this modified example, by making the average rigidity of the overlapping peripheral portions 4b, 4d in a planar view lower than the rigidity of the mounting portion 4a, the effects of asymmetric deformation due to moments other than the torque around the central axis can be reduced, and a decrease in measurement accuracy can be suppressed.

Here, in addition to the spokes 4 equipped with the strain detection element 5, a plurality of spokes 7 are provided that connect the outer ring 2 and the inner ring 3 and do not have a mounting portion 4a and a strain detection element 5.

<Modification 4>
13 and 14 show a torque sensor 1d in which a part of a spoke 4 is embedded in the outer ring 2 and the inner ring 3. FIG.

The inner circumference of the outer ring 2 and the outer circumference of the inner ring 3 are not perfectly circular, but have recesses (notches) on the outer peripheral surface, and the radial ends of the spokes 4 are connected to these recesses. A peripheral portion 4b is formed within the recess. Also, a mounting portion 4a, a reinforcing portion 4c, or a part of the strain detection element 5 may be formed within the recess.

In this way, even if a portion of the spoke 4 is embedded in the outer ring 2 and the inner ring 3, by making the rigidity of the peripheral portion 4b lower than the rigidity of the mounting portion 4a, the effects of asymmetric deformation due to moments other than the torque around the central axis can be reduced, and a decrease in measurement accuracy can be suppressed.

<Modification 5>
15 and 16 show a torque sensor 1f in which the mounting portion 4a is configured with a protruding portion that protrudes toward the strain detection element 5 side with respect to the peripheral portion 4b.

The peripheral portion 4b has a first surface b1 on one side in the axial direction and a second surface b2 opposite the first surface. The mounting portion 4a has a first protruding portion that protrudes toward the strain detection element 5 in the axial direction relative to the first surface b1 of the peripheral portion 4b and contacts the strain detection element 5. The surface of the mounting portion 4a opposite the surface that contacts the strain detection element 5 is continuous with the second surface b2 of the peripheral portion 4b to form a single flat surface.

In other words, in this modified example, the mounting portion 4a is configured with a protrusion that protrudes only on one surface side of the peripheral portion 4b in the axial direction, making the thickness of the mounting portion 4a greater than the thickness of the peripheral portion 4b.

In this modified example, by making the rigidity of the peripheral portion 4b lower than the rigidity of the mounting portion 4a, the effects of asymmetric deformation due to moments other than the torque around the central axis can be reduced, and a decrease in measurement accuracy can be suppressed.

<Modification 6>
17 and 18 show a torque sensor 1g in which the mounting portion 4a is configured with a protruding portion that protrudes from the peripheral portion 4b on the side opposite to the strain detection element 5 side.

The mounting portion 4a has a second protruding portion that protrudes in the axial direction relative to the second surface b2 of the peripheral portion 4b and is spaced apart from the strain detection element 5. Of the surfaces of the mounting portion 4a, the surface that contacts the strain detection element 5 is continuous with the first surface b1 of the peripheral portion 4b to form a single flat surface.

In other words, in this modified example, the mounting portion 4a is configured with a protrusion that protrudes only on one surface side of the peripheral portion 4b in the axial direction, making the thickness of the mounting portion 4a greater than the thickness of the peripheral portion 4b.

In this modified example, by making the rigidity of the peripheral portion 4b lower than the rigidity of the mounting portion 4a, the effects of asymmetric deformation due to moments other than the torque around the central axis can be reduced, and a decrease in measurement accuracy can be suppressed.

The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the present invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention.

For example, the embodiment described using Figures 1 to 5 may be combined with its variants 4, 5, or 6, and each variant may be combined with each other, except for the combination of variants 5 and 6.

Reference Signs List 1, 1a to 1g Torque sensor 2 Outer ring 3 Inner ring 4, 7 Spokes 4a, 4x Mounting portion 4b, 4d Peripheral portion 4c Reinforcement portion 5 Detection element 6, 8 Hole portion 42, 43 Peripheral portion (connection portion)
b1 First surface b2 Second surface

Claims (2)

The bearing comprises an outer ring, an inner ring, two or more spokes connecting the outer ring and the inner ring, and strain detection elements provided on the spokes,
each spoke includes a mounting portion for the strain detection element, a first peripheral portion connecting the mounting portion and the outer ring, a second peripheral portion connecting the mounting portion and the inner ring, and a third peripheral portion surrounding the mounting portion in a plan view;
The rigidity of each of the first peripheral portion and the second peripheral portion is lower than the rigidity of the mounting portion,
the first peripheral portion and the second peripheral portion constitute the third peripheral portion,
A torque sensor, wherein the rigidity of the third peripheral portion is lower than the rigidity of the mounting portion. 2. The torque sensor according to claim 1 ,
a fourth peripheral portion overlapping the first peripheral portion in a plan view, and a fifth peripheral portion overlapping the second peripheral portion in a plan view,
the fourth peripheral portion and the fifth peripheral portion are made of a material different from that of the mounting portion,
A torque sensor in which the average rigidity of the fourth peripheral portion and the first peripheral portion that overlap in a planar view is lower than the rigidity of the mounting portion, and the average rigidity of the fifth peripheral portion and the second peripheral portion that overlap in a planar view is lower than the rigidity of the mounting portion.

Images