Spring constant variable force sensor and measurement method

Abstract

To provide a force sensor capable of changing a spring constant.SOLUTION: There is provided a force sensor that has a distorted body and a stage and a variable spring constant. The distorted body has a fixed section, a spring section connected to the fixed body, and a beam connected to the spring section, the beam extends horizontally from the spring section, and one end of the beam has a magnet and the end in the opposite side that does not have the magnet in the beam is a soft actuator. The stage has at least one stage side magnet, and hence the force sensor has a spring constant obtained by adding up the spring constant of the distorted body and a spring constant because of restoration force of the magnet between the stage side magnet and the magnet of the beam. The stage can adjust the distance between the stage side magnet and the magnet of the beam, thus changing the spring constant because of the restoration force of the magnet with the magnet of the beam.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a force sensor and a measurement method using the same. [Background technology]

[0002] In recent years, there has been active development of soft actuators using polymer gels and other materials, with a view to application to underwater robots and soft robots. Soft actuators excel at the flexible and complex movements required for underwater robots. However, there are no clear indicators that allow for a quantitative evaluation of their performance, making it difficult to select them. In selecting rotary motors for use in conventional robots, the performance diagram showing torque-rotation characteristics is used as the most common indicator of performance. If a similar indicator for performance evaluation could be established for soft actuators, more quantitative selection would be possible.

[0003] In order to quantitatively create a performance diagram for a soft actuator, it is necessary to evaluate the relationship between the force and displacement of the actuator according to the load. For this reason, in conventional soft actuators, the force and displacement when pressing force sensors with different spring constants have been measured. However, it is difficult to prepare multiple force sensors with different spring constants and measure each sensor. In addition, using multiple force sensors with different spring constants leads to increased costs. Furthermore, in artificial tissues with cultured cells on their surface, it is impossible to peel off the culture layer on the surface of a force sensor with a certain spring constant and reattach the culture layer to the surface of a force sensor with a different spring constant.

[0004] Non-Patent Document 1 describes a MEMS (Micro Electro Mechanical Systems) device that uses the Lorentz force to tune the resonance frequency of a cantilever. The disclosed cantilever has a thickness on the order of nanometers.

[0005] Patent Document 1 discloses a force sensor including a beam layer supported at one end by a spacer, a functional fluid layer in contact with the beam layer and having a functional fluid sealed within an elastic body, an application unit that applies an electromagnetic field to the functional fluid, and a detection unit that detects the amount of deflection of the beam layer. This determines the spring constant of the functional fluid layer by the electromagnetic field, and sets the measurement range of an external force.

[0006] Patent Document 2 discloses a force sensor device having a deformable body that is capable of being deformed and that maintains a deformed state. A shape memory material or a shape memory polymer is used as the deformable body. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-141720 (Patent No. 6769342) [Patent Document 2] Patent Publication No. 2023-123902 [Non-patent literature]

[0008] [Non-Patent Document 1] "Cantilever with 10-fold tunable spring constant using Lorentz force" MEMS 2016, Shangai, CHINA, 24-28 January 2016 (DOI: 10.1109 / MEMSYS.2016.7421767) Summary of the Invention [Problem to be solved by the invention]

[0009] The device described in Patent Document 1 requires a special functional fluid whose spring constant changes when an electromagnetic field is applied. This limits the measurement range that can be changed. In addition, the electromagnetic field generated may cause noise interference with measuring equipment, so the situations in which it can be used are also limited. In addition, since the magnetic fluid needs to be sealed, it is not suitable for miniaturization.

[0010] The device described in Patent Document 2 requires a shape-memory material. The shape-memory material maintains the deformed state. In order to return the changed shape of the deformed body to its original state, the temperature of the deformed body must be raised to a temperature higher than the reverse transformation starting temperature, which is a complicated operation. In addition, the device cannot be used in situations where it cannot be exposed to high temperatures.

[0011] In one embodiment, the present invention aims to provide a force sensor with a variable spring constant that can at least partially solve the above problems. In one embodiment, the present invention aims to provide a force sensor with a variable spring constant that does not require a functional fluid and does not require a shape memory material. [Means for solving the problem]

[0012] As a result of extensive research into solving the above problems, the inventors have developed, as an example, a variable spring constant force sensor that utilizes the restoring force of a magnet, and have completed the present invention, which includes this as one embodiment.

[0013] The present invention includes the following embodiments. [1] A force sensor having a variable spring constant, the force sensor having a strained body and a stage, the strained body has a fixed portion, a spring portion connected to the fixed portion, and a beam connected to the spring portion; The beam extends from the spring section to the left and right. One end of the beam has a magnet; The opposite end of the beam, which does not have a magnet, is a soft actuator; the stage has one or more stage-side magnets, and the force sensor has a spring constant that is a sum of a spring constant of the strained body and a spring constant due to a restoring force of the magnet between the stage-side magnet and the magnet of the beam; The stage can adjust the distance between the stage side magnet and the magnet of the beam, thereby changing the spring constant due to the restoring force of the magnet between the stage side magnet and the magnet of the beam. The force sensor has a variable spring constant. [2] A force sensor as described in embodiment 1, wherein the stage has two stage side magnets, a first stage side magnet being positioned above the beam magnet and a second stage side magnet being positioned below the beam magnet. [3] A force sensor as described in embodiment 2, in which when no force is applied to the beam, the distance between the beam magnet and a first stage side magnet above the beam is r1, and the distance between the beam magnet and a second stage side magnet below the beam is r2, the two stage side magnets are positioned above and below the beam magnet so that r1 and r2 are equal. [4] The force sensor according to any one of embodiments 1 to 3, wherein the beam magnet and the stage side magnet are configured so that a repulsive force acts between the beam magnet and the stage side magnet. [5] The force sensor according to any one of embodiments 1 to 3, wherein the beam magnet and the stage side magnet are configured so that an attractive force acts between the beam magnet and the stage side magnet. [6] The force sensor according to any one of embodiments 1 to 5, wherein the beams extending to the left and right from the spring portion deform symmetrically in the up and down directions with the center of the beam as a fulcrum. [7] A method for measuring a force applied to a soft actuator using the force sensor according to any one of embodiments 1 to 6. [8] A force sensor having a variable spring constant, the force sensor having a strained body and a stage, the strained body has a fixed portion, a spring portion connected to the fixed portion, and a beam connected to the spring portion; The beam extends from the spring section to the left and right. One end of the beam has a magnet; The opposite end of the beam, which does not have a magnet, is a soft actuator; the stage has one or more stage-side magnets, and the force sensor has a spring constant that is a sum of a spring constant of the strained body and a spring constant due to a restoring force of the magnet between the stage-side magnet and the magnet of the beam; The stage can adjust the distance between the stage side magnet and the magnet of the beam, thereby changing the spring constant due to the restoring force of the magnet between the stage side magnet and the magnet of the beam. providing a force sensor having a variable spring constant; and A step of changing a spring constant due to a restoring force of a magnet between the stage side magnet and the magnet of the beam by adjusting a distance between the stage side magnet and the magnet of the beam; A method for varying a spring constant of a force sensor, comprising: [9] A method for changing the spring constant of the force sensor by the method described in embodiment 8, and measuring the force applied to the soft actuator using the force sensor with the changed spring constant. Effect of the Invention

[0014] An advantage of the present invention is that it is possible to evaluate a force with a single sensor, without using a plurality of force sensors having different spring constants. [Brief description of the drawings]

[0015] [Figure 1-1] A strained body 10 is shown. [Figure 1-2] A strained body 10 is shown. [Diagram 2] Shows stage 20. [Figure 3-1] The magnet 14 of the beam of the object 10 to be distorted and the stage side magnets 21, 21' are shown. [Figure 3-2] The displacement d of the beam 13 is shown. [Figure 4] The principle of an eddy current displacement sensor is shown. [Diagram 5] A strained body 10 and a stage 20 are shown. [Figure 6] 1 is a photograph of the experimental setup. [Figure 7] The results of measuring the spring constant of the strain target 10 using the force sensor of the present invention are shown below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will now be described in detail with reference to the drawings.

[0017] The force sensor of the present invention has a beam portion that deforms and a portion that measures the displacement. The beam portion that deforms and the portion that measures the displacement are separated from each other. FIG. 1 shows an example of the beam portion that deforms of the force sensor of the present invention. In this specification, the beam portion that deforms is sometimes referred to as the strained body. Also, in this specification, the portion that measures the displacement of the beam is sometimes referred to as the stage. In FIG. 1, the strained body 10 has a fixed portion 11 for fixing the strained body 10 to a base, a spring portion 12 connected to the fixed portion, and a beam 13 extending from the spring to the left and right. One end of the beam 13 has a magnet 14. In one embodiment, the magnet 14 is embedded in one end of the beam. In another embodiment, the magnet 14 is removable and attached to one end of the beam. The opposite end of the beam 13 that does not have a magnet serves as a soft actuator in the force sensor of the present invention. Therefore, the end of the beam 13 that does not have a magnet is sometimes referred to as a soft actuator 15 in this specification.

[0018] The object to be distorted 10 is distorted when a force is applied to the soft actuator 15. For example, when a downward force is applied to the upper part of the soft actuator 15, the opposite end of the beam 13 having the magnet 14 rises. The spring constant of the object to be distorted 10 at this time is k1. Unless otherwise specified, the spring constant k1 is constant in this specification. In one embodiment, the beam 13 extending to the left and right from the spring portion 12 deforms symmetrically up and down with the center of the beam 13 as the fulcrum.

[0019] The portion for measuring the displacement of the beam, i.e., the stage 20, has one or more magnets 21 different from the magnet 14 of the beam. In this specification, the magnet 21 different from the magnet 14 of the beam may be referred to as a stage-side magnet. In one embodiment, the stage-side magnet may be placed above or below the magnet 14 of the beam. In one embodiment, the force sensor of the present invention has two stage-side magnets. In this case, one stage-side magnet 21 may be placed above and one below the magnet 14 of the beam. In addition, the two stage-side magnets may be placed so as to be equidistant from the magnet 14 of the beam. In other words, when the distance between the magnet 14 of the beam and the stage-side magnet 21 above the beam is r1 and the distance between the magnet 14 of the beam and the stage-side magnet 21' below the beam is r2 in a state where no force is applied to the beam, the two stage-side magnets may be placed above and below the magnet 14 of the beam so that r1 and r2 are equal. See FIG. 3-1.

[0020] In one embodiment, the beam magnet 14 and one or more, for example two, stage side magnets 21 are configured to repel each other. This repulsive force can be adjusted by changing the distance between the beam magnet and the stage side magnet. In another embodiment, the beam magnet and one or more, for example two, stage side magnets are configured to attract each other. This attractive force can be adjusted by changing the distance between the beam magnet and the stage side magnet. For example, in FIG. 3-1, the magnitudes of r1 and r2 can be changed by moving the initial positions of the stage side magnets 21, 21' above and below the beam magnet 14 while making r1 and r2 equal, thereby changing the value of the magnetic force at the beam displacement d. In other words, the restoring force of the magnets can be adjusted. See FIG. 3-2 for the beam displacement d.

[0021] The magnetic force at a beam displacement d, i.e., the value of the magnet's restoring force f, is expressed by the following equation.

[0022]

number

[0023] In one embodiment, the displacement d of the beam can be detected or measured by a displacement sensor. In one embodiment, the displacement sensor for detecting or measuring the displacement d of the beam is an eddy current displacement sensor 22. That is, in one embodiment, the force sensor of the present invention has one or more, for example two, eddy current displacement sensors 22. The eddy current displacement sensors 22 can be located only above, only below, or both above and below the magnet 14 of the beam. The displacement d can then be measured by the eddy current displacement sensor 22, and f can be calculated from the above formula.

[0024] The eddy current displacement sensor 22 passes a current through a coil inside the sensor, generating a magnetic field 26. When a measurement target is present in the magnetic field, an eddy current flows due to electromagnetic induction, and the impedance of the coil inside the sensor changes. This makes it possible to measure the distance to the target. See Figure 4 for the principle of the eddy current displacement sensor 22.

[0025]

number

[0026]

number

[0027] In another embodiment, the sensor for detecting or measuring the displacement d of the beam can be a laser displacement sensor. In an embodiment, the force sensor of the present invention can comprise a laser displacement sensor.

[0028] An attractive or repulsive force acts between the beam magnet 14 and the stage-side magnet 21. In either case, the restoring force of the magnet can be likened to a spring. For convenience, the restoring force of the magnet is treated as a spring constant in this specification. If the spring constant due to the restoring force of the magnet is k2, the relationship between the displacement x of the soft actuator 15 and F when a force F is applied to the soft actuator 15 is expressed by the following equation.

[0029]

number

[0030] In the above formula, k1 is fixed, but by adjusting k2, the spring constant of the entire force sensor can be made variable, thereby realizing a variable spring constant force sensor.

[0031] In one embodiment, the displacement x of the soft actuator 15 when a force F is applied can be measured by a displacement meter. Examples of the displacement meter include, but are not limited to, a contact-type displacement meter, an eddy current displacement meter, and a laser displacement meter. A contact-type displacement meter is a displacement meter that measures displacement by a contactor coming into direct physical contact with an object to be measured. In one embodiment, the force sensor of the present invention includes a displacement meter for measuring the displacement x of the soft actuator 15. In another embodiment, the force sensor of the present invention does not include a displacement meter for measuring the displacement x of the soft actuator 15.

[0032] In the force sensor of the present invention, the shape of the spring portion 12 and the fixed portion 11 of the strained body 10 is not particularly limited. In one embodiment, the strained body 10 is preferably shaped so that the end having the magnet 14 is easily displaced upward when a downward force is applied to the soft actuator 15. In one embodiment, the strained body 10 is preferably shaped so that the end having the magnet 14 is not easily displaced downward when a downward force is applied to the soft actuator 15. In one embodiment, the beam 13 is connected to the spring portion 12 having a spiral shape. In one embodiment, the spring portion 12 may have an Archimedes spiral. The Archimedes spiral refers to a spiral in which the radius r is equal to the deflection angle θ (r=θ). However, the spring portion 12 is not limited to this structure, and may have any shape as long as the end having the magnet 14 of the beam is displaced upward with a constant spring constant k1 when a downward force is applied to the soft actuator 15.

[0033] In some embodiments, the thickness of the beam is not on the order of nanometers. In some embodiments, the thickness of the beam is on the order of millimeters. In some embodiments, the thickness of the beam is 0.5 mm or more, 1 mm or more, 2 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 6 mm or more, 7 mm or more, 8 mm or more, 9 mm or more, for example, 10 mm or more. In some embodiments, the variable spring constant force sensor of the present invention does not include a functional fluid whose spring constant changes upon application of an electromagnetic field. In some embodiments, the variable spring constant force sensor of the present invention does not include a shape memory material.

[0034] A method of using the force sensor of the present invention will now be described. First, the object to be distorted 10 is placed on the stage 20, the magnet 21 (and magnet 21' in some cases) is placed, and the eddy current displacement sensor 22 is placed. Next, a force F is applied to the soft actuator 15 by the load cell 30, and the displacement x is measured by the displacement meter 31. Here, it is assumed that the absolute values ​​of the displacement d of the beam and the displacement x of the soft actuator are equal. Then, d in equation 1 and x in equation 4 are the same. Therefore, k2 can be calculated by the following equation.

[0035]

number

[0036] Also, k1 is known. Next, the distance r between magnet 21 (and magnet 21' in some cases) and magnet 14 of the beam is adjusted, and k2 at that distance is calculated. In this manner, the relationship between the distances r between various magnets and k2 is determined (or the relationship between r and k1+k2 is determined). Next, the displacement d of the beam when an unknown force F is applied to the soft actuator 15 is measured by the eddy current displacement sensor 22, and F can be determined using the predetermined k2 and the known k1 (or using the predetermined k1+k2).

[0037] The variable spring constant force sensor of the present invention does not require a shape memory material. The variable spring constant force sensor of the present invention does not require a special functional fluid whose spring constant changes when an electromagnetic field is applied. The present invention provides a simple force sensor with a variable spring constant that utilizes the restoring force of a magnet. The variable spring constant force sensor of the present invention can make the spring constant larger (using the attractive force of a magnet) or smaller (using the repulsive force of a magnet) than the original spring constant k1 of the strained body 10, simply by adjusting the distance between the stage-side magnet and the beam magnet. EXAMPLES

[0038] The present invention will be described in more detail below with reference to examples. is not intended to be limited in any way by these examples.

[0039] In this example, we will use an actuator that produces a force of about 10 mN. Also, measurements will be taken at a displacement of about 1 mm, at which point the spring's elasticity is maintained. Therefore, the spring constant will be 10 N / m or more.

[0040] experiment The dimensions of the strained body 10 were 60 mm in the longitudinal direction of the beam 13, 2.0 mm in thickness in the vertical direction, and 10 mm in length in the horizontal direction. The spring portion 12 was an Archimedes spiral (spiral constant a=1 mm / rad). The strained body 10 was manufactured using a fused deposition modeling 3D printer (Ultimaker S5, Ultimaker). A magnet 14 with a diameter of 5.0 mm and a magnetic flux density of 150 mT was embedded in the tip of the beam. The spring constant of the strained body 10 manufactured in this embodiment was 13 N / m. As shown in FIG. 3, L-shaped jigs 25 were attached to the upper and lower stages 20, and magnets 21, 21' with a diameter of 13 mm and a magnetic flux density of 60 mT were embedded in them. A stand that moves up and down was installed on the soft actuator 15 side of the beam. A load cell (LVS-100GA, Kyowa Denki) and a displacement meter 31 were attached there as strain-generating bodies. A photograph of the experimental setup including the load cell 30 and the displacement gauge 31 is shown in FIG.

[0041] result An experiment was carried out to measure the spring constant of the fabricated strained body 10. Figure 7 shows the results of the experiment. The distance between the stage-side magnet 21 and the beam magnet 14 was adjusted in 1 mm increments using the stage 20. The spring constant was calculated from the value obtained from the output voltage of the load cell and the amount of displacement. The experiment was carried out under two magnetic force conditions: repulsive and attractive. While the original spring constant of the strained body 10 was 13 N / m, a range of values ​​from 4.4 N / m to 17 N / m was obtained depending on the magnetic force.

[0042] In one embodiment, the present invention provides a force sensor in which the spring constant is variable using magnetic force. According to the present invention, the spring constant of the strained body is variable by changing the distance between the magnets. [Industrial Applicability]

[0043] The present invention allows for the evaluation of forces using a single sensor, which can be used, for example, to evaluate the performance of soft actuators.

[0044] Numerous documents, including patent applications and manufacturer's manuals, are cited in this specification. The disclosures of these documents are not considered relevant to the patentability of this invention, but are incorporated herein by reference in their entirety. More specifically, all referenced documents are incorporated herein by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0045] 10 Distorted object 11 Fixed part 12 Spring part 13. Beam 14. Magnets 15 Soft Actuator 20 Stages 21 Magnet 21' Magnet 22 Eddy current displacement sensor 25 L-shaped jig 26 Magnetic Field 30 Load Cells 31 Displacement gauge d Beam displacement F force x Displacement of the soft actuator when a force F is applied r Distance between the beam magnet and the stage magnet r1: Distance between the beam magnet and the stage magnet above the beam r2 Distance between the beam magnet and the stage magnet underneath the beam

Claims

1. A force sensor having a variable spring constant, the force sensor including a strained body and a stage, The strained body has a fixed portion, a spring portion connected to the fixed portion, and a beam connected to the spring portion, The beam extends from the spring section to the left and right. One end of the beam has a magnet; The opposite end of the beam, which does not have a magnet, is a soft actuator; the stage has one or more stage-side magnets, whereby the force sensor has a spring constant that is a sum of a spring constant of the strained body and a spring constant due to a restoring force of the magnet between the stage-side magnet and the magnet of the beam; The stage can adjust the distance between the stage side magnet and the magnet of the beam, thereby changing the spring constant due to the restoring force of the magnet between the stage side magnet and the magnet of the beam. The force sensor has a variable spring constant.

2. 2. The force sensor of claim 1, wherein the stage has two stage side magnets, a first stage side magnet positioned above the beam magnet and a second stage side magnet positioned below the beam magnet.

3. The distance between the beam magnet and the first stage magnet above the beam when no force is applied to the beam is r 1 The distance between the beam magnet and the second stage magnet under the beam is r 2 Then, r 1 andr 2 3. The force sensor of claim 2, wherein two stage magnets are positioned above and below the beam magnet such that .function..times ...

4. 2. The force sensor according to claim 1, wherein the beam magnet and the stage side magnet are configured so that a repulsive force acts between the beam magnet and the stage side magnet.

5. 2. The force sensor according to claim 1, wherein the beam magnet and the stage side magnet are configured such that an attractive force acts between the beam magnet and the stage side magnet.

6. 2. The force sensor according to claim 1, wherein the beams extending laterally from the spring portion deform symmetrically in the up and down directions with the center of the beam as a fulcrum.

7. A method for measuring a force applied to a soft actuator using a force sensor according to any one of claims 1 to 6.

8. A force sensor having a variable spring constant, the force sensor including a strained body and a stage, The strained body has a fixed portion, a spring portion connected to the fixed portion, and a beam connected to the spring portion, The beam extends from the spring section to the left and right. One end of the beam has a magnet; The opposite end of the beam, which does not have a magnet, is a soft actuator; the stage has one or more stage-side magnets, whereby the force sensor has a spring constant that is a sum of a spring constant of the strained body and a spring constant due to a restoring force of the magnet between the stage-side magnet and the magnet of the beam; The stage can adjust the distance between the stage side magnet and the magnet of the beam, thereby changing the spring constant due to the restoring force of the magnet between the stage side magnet and the magnet of the beam. providing a force sensor having a variable spring constant; and A step of changing a spring constant due to a restoring force of a magnet between the stage side magnet and the magnet of the beam by adjusting a distance between the stage side magnet and the magnet of the beam; A method for varying a spring constant of a force sensor, comprising:

9. A method for measuring a force applied to the soft actuator by varying a spring constant of the force sensor according to the method of claim 8 and using the force sensor with the varied spring constant.

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