KR102624982B1 - Composite material capable of measuring bending deformation, spring including the same, and manufacturing method thereof - Google Patents

Abstract

A composite material capable of measuring bending strain, comprising: a first bendable conductive composite;
Dielectric capable of bending and compression deformation; and a bendable second conductive composite, wherein a first conductive composite and a second conductive composite are stacked on each of both sides of the dielectric, and the heights of the first conductive composite and the second conductive composite from the dielectric are different. A composite material capable of measuring bending strain is provided.

Description

Composite material capable of measuring bending deformation, spring including the same, and manufacturing method thereof}

The present invention relates to a composite material capable of measuring bending deformation, a spring containing the same, and a manufacturing method thereof. More specifically, the present invention relates to a composite material capable of measuring bending deformation, and more specifically, to measuring bending deformation by the composite itself without adding a separate sensor within the composite material used for deformable parts such as springs. It relates to a composite material capable of measuring bending deformation, which has the effect of storing and releasing elastic energy generated by bending in addition to the effect of reducing weight, a spring containing the same, and a method of manufacturing the same.

Composite materials not only have excellent mechanical properties including specific strength and specific stiffness, but also have a high elastic energy storage rate, so they can be used in various types of springs such as coil springs, leaf springs, and wave springs. It is being utilized as.

In particular, composite material springs are applied to driving robots to achieve weight reduction and at the same time store and release elastic energy to further improve driving performance. In addition, driving data such as ground reaction force and ankle, knee, and hip joint angles can be derived from the dynamic deformation of the composite spring as the robot runs. If the motor is controlled in real time according to such driving data, the robot's driving performance can be further maximized.

Additional sensors are generally required to detect dynamic deformation of composite springs, and externally attached sensors or sensors built into composite materials are usually used. Among these, externally attached sensors are very vulnerable in terms of durability when undergoing rapid dynamic deformation, such as when a robot runs, because the sensor itself is directly exposed to the external environment. Other composite material-embedded sensors include piezoelectric ceramic sensors and fiber bragg grating (FBG) sensors.

However, because these sensors are relatively brittle compared to composite materials, they easily break in structures that undergo large deformations, such as springs. In addition, since composite material-embedded sensors have a relatively large diameter and low mechanical properties compared to reinforcement fibers, stress concentration phenomenon easily occurs, deteriorating the mechanical properties of the structure itself. Additionally, both methods using an externally attached sensor or a built-in inserted sensor have the disadvantage of requiring additional sensor installation.

Therefore, a composite material that stores and releases elastic energy, which plays a role in improving the robot's driving performance, and at the same time detects structural bending deformation through changes in capacitance without an additional sensor, and a spring using the same. development is needed.

The problem that the present invention aims to solve is to provide a new composite material that can be used for springs, etc. by detecting bending deformation by itself, and a method of manufacturing the same.

In order to solve the above problem, the present invention provides a composite material capable of measuring bending deformation, comprising: a first bendable conductive composite; Dielectric material capable of bending and compression deformation; and a bendable second conductive composite, wherein a first conductive composite and a second conductive composite are stacked on each of both sides of the dielectric, and the heights of the first conductive composite and the second conductive composite from the dielectric are different. Provides a composite material capable of measuring bending deformation.

In one embodiment of the present invention, deformation of the dielectric in the thickness direction is dominant according to bending deformation of the composite material.

In one embodiment of the present invention, the height ratio of the first conductive composite and the second conductive composite is such that the dielectric is located closer to the direction of the first conductive composite than the second conductive composite. Measurement of bending strain, characterized in that This possible composite material.

In one embodiment of the present invention, the first conductive composite and the second conductive composite are carbon fiber reinforced plastic, and the composite is provided with the first conductive composite on the inner diameter and the second conductive composite on the outer diameter based on curvature, The second conductive composite is thinner than the first conductive composite.

In one embodiment of the present invention, the dielectric is compressible foam, and the dielectric foam is PVC (Polyvinyl chloride), PU (Polyurethane), Melamine, PMI (Polymethacrylimide), PET (Polyethylene terephthalate), and PVDF (Polyvinylidene) fluoride) and contains at least one selected from the group consisting of

In one embodiment of the present invention, the first and second conductive composites are conductive carbon fiber reinforced plastic, and the first and second conductive composites are uni directional carbon fiber composite, carbon fabric composite. It includes one or more materials selected from the group consisting of carbon fabric composite and short carbon fiber composite.

In one embodiment of the present invention, the dielectric has a lower density compared to the first conductive composite and the second conductive composite.

The present invention provides a spring containing the above-described composite material, and the composite material of the spring stores elastic energy generated as the spring is compressed in the dielectric and then releases it again upon recovery.

The present invention also provides an attachable robot including the spring described above.

The present invention is a method of manufacturing the above-described composite material, comprising the steps of forming and bending carbon fiber-reinforced plastics of different thicknesses to form first and second conductive composites; and bonding the conductive assembly to each of the cross-sections of both sides of the dielectric, wherein the dielectric is a compressible foam, and the carbon fiber reinforced plastic is manufactured by laminating a plurality of carbon fibers and then impregnating them with epoxy.

The composite material according to the present invention has a structure including a dielectric asymmetrically positioned between the composite materials constituting the composite material, and by utilizing the spring of the composite material according to the present invention, the structure itself can be used without an externally attached sensor or a sensor built into the composite material. Bending deformation can be detected through changes in capacitance. In addition, by manufacturing a sandwich composite spring using foam as the core, it is possible to achieve weight reduction and secure spring rigidity at the same time.

Furthermore, when the composite material according to the present invention is used as an ankle spring for a traveling robot, it plays a role in storing and releasing elastic energy generated by bending to improve the driving performance of the robot and at the same time increases the electrostatic capacity of the structure. The advantage is that driving data such as ground reaction force or ankle-knee-hip joint angle can be obtained from changes in real time.

Figure 1 is a schematic diagram of a conventional structural capacitor using a composite material, and Figure 2 is a schematic diagram of a method for detecting capacitance using the separated composite material of Figure 1 as an electrode.
Figure 3 is a cross-sectional view of a composite material according to an embodiment of the present invention.
Figure 4 is a schematic diagram showing the structure of a sandwich composite spring having an asymmetric dielectric foam core proposed in the present invention.
Figure 5 is a diagram illustrating a method of making a curved conductive composite according to an embodiment of the present invention.
Figure 6 is a simulation result of the degree of deformation in the thickness direction of the foam core, which is a dielectric, according to the bending deformation of the composite material.
Figure 7 is a comparative analysis result of strain according to the relative position of the core form.
Figure 8 is a diagram showing an experimental method according to an embodiment of the present invention, and Figure 9 is a diagram explaining a method of obtaining ground reaction forces (GRFs) values through actual machine learning.

Hereinafter, a composite material capable of measuring bending deformation according to the present invention, a spring containing the same, and a method of manufacturing the same will be described with reference to the attached drawings. Unless otherwise specified, all terms in this specification have the same general meaning as understood by a person with ordinary knowledge in the technical field to which the present invention pertains, and if there is a conflict with the meaning of the terms used in this specification, it shall be written in this specification. According to the definition used. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention are omitted. Throughout the specification, when a part "includes" a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

In order to solve the above-mentioned problems, the present invention provides an integrated sandwich composite material having an asymmetric dielectric and a spring using the same. In one embodiment of the present invention, the effect of reducing the weight of the composite material was achieved by using a foam core as the dielectric, but the scope of the present invention is not limited to the type of specific dielectric described below.

The composite material according to the present invention uses capacitance to measure bending deformation, and capacitance is defined by the thickness, width, and dielectric constant of the dielectric located between two electrodes.

Figure 1 is a schematic diagram of a conventional structural capacitor using a composite material, and Figure 2 is a schematic diagram of a method for detecting capacitance using the separated composite material of Figure 1 as an electrode.

Referring to Figure 1, the prior art disclosed in Prior Art 1 and Embedded 3 is a structural capacitor through a film that acts as a dielectric and a plate-shaped carbon fiber reinforced plastic (CFRP) that acts as an electrode. The method was to use .

In this case, rather than detecting deformation, most of the progress was made to secure structural safety by increasing the mechanical properties of the capacitor using composite materials. In addition, this structure has a problem in that the sensitivity to changes in capacitance is also very low because the deformation in the thickness direction of the dielectric due to structural deformation is very small.

Referring to FIG. 2, the prior art disclosed in prior art 4 uses conductive composite materials separated from each other as electrodes, and the overlapping area changes depending on the relative positions of the two composite electrodes, and the capacitance changes accordingly. detects.

However, this prior art not only has a low degree of capacitance change due to the lack of a distinct dielectric between electrodes, but also has limitations in measuring the deformation of the structure itself because the composite materials are separated from each other.

To solve this problem, the present invention provides a so-called sandwich-type composite by inserting a dielectric asymmetrically between composite materials, which enables sensing, weight reduction, and elastic energy release through the composite material itself.

Figure 3 is a cross-sectional view of a composite material according to an embodiment of the present invention.

Referring to FIG. 3, the composite material capable of measuring bending strain according to an embodiment of the present invention includes a first bendable conductive composite 110; bendable, compressible dielectric (120); and a bendable second conductive composite 130, wherein the first conductive composite 110 and the second conductive composite 130 are stacked on both sides of the dielectric 120, respectively.

In one embodiment of the present invention, the heights of the first conductive composite and the second conductive composite are different, and the height ratio is configured such that the dielectric is located closer in the direction of the first conductive composite than the second conductive composite, whereby the dielectric becomes symmetrical in one direction.

At this time, the height (d1) of the first conductive composite 110 from the dielectric 120 is different from the height (d2) of the second conductive composite 120 from the dielectric 120, and the present invention is as follows. By positioning the dielectric asymmetrically in the direction of the outer diameter of curvature based on the middle surface of the composite, compressive deformation occurs predominantly, increasing the degree of capacitance change. Here, “dominant” means that the strain in the height direction has a greater degree of strain than the strain in the length or other directions.

In one embodiment of the present invention, the first conductive composite and the second conductive composite are carbon fiber reinforced plastics (CFRP), and the dielectric is compressible foam.

In one embodiment of the present invention, the first and second conductive composites may be conductive carbon fiber reinforced plastic, in this case, uni directional carbon fiber composite, carbon fabric composite. ), any one or more selected from the group consisting of short carbon fiber composite materials can be used as a conductive composite material.

In addition, the dielectric foam core may include one or more selected from the group consisting of PVC (Polyvinyl chloride), PU (Polyurethane), Melamine, PMI (Polymethacrylimide), PET (Polyethylene terephthalate), and PVDF (Polyvinylidene fluoride). , In particular, the density is lower than that of the conductive composite, allowing storage and release of spring elastic energy.

Figure 4 is a schematic diagram showing the structure of a sandwich composite spring having an asymmetric dielectric foam core proposed in the present invention.

Referring to Figure 4, the composite conductive composite, which is a conductive carbon fiber reinforced plastic that serves as a conductive composite, is made by hand laying up carbon fiber on a mold with a constant curvature shape to have a leaf spring shape and applying epoxy. It is manufactured by hand laying up prepreg that is impregnated or already impregnated with epoxy, and then through hot press molding or autoclave molding.

At this time, two carbon fiber reinforced plastics are manufactured with different thicknesses to create a sandwich composite material with a core that is asymmetrically laminated based on the mid plane. As used herein, “asymmetry” means that the dielectric core is deviated in one direction from the center of the entire composite material.

Afterwards, a foam core with dielectric properties is placed between two fiber-reinforced plastics, and then bonded under certain curing conditions to produce a foam core composite sandwich composite.

In one embodiment of the present invention, adhesion may be achieved through methods such as applying an adhesive, using an adhesive film, simultaneous curing, etc. In this case, as described above, a relatively thick carbon fiber reinforced plastic is placed in the inner diameter direction from the curvature standard, and a thin carbon fiber is applied. Position the reinforced plastic in the outer diameter direction.

The composite material according to the present invention manufactured in the above manner has a foam core sandwich structure and stores and releases elastic energy while undergoing bending deformation. Additionally, at this time, the foam core is deformed in the thickness direction due to the overall bending deformation, resulting in a change in capacitance.

The composite material according to the present invention can independently detect the bending deformation of the composite spring through its structural shape without an additional sensor, and can lighten the overall structure by using a foam-shaped core, and can reduce the weight of the overall structure compared to carbon fiber reinforced plastic. Through differences in mechanical properties, the degree of capacitance change can be increased by further maximizing the deformation in the thickness direction of the dielectric due to bending deformation.

In addition, the foam core is placed in the outer diameter direction based on the mid plane and stacked asymmetrically, causing compression deformation in the thickness direction to dominate, thereby increasing the change in capacitance and at the same time reducing tension at the adhesive interface, which is vulnerable to tension. Deformation was minimized. In addition, since most of the stress due to bending deformation is applied to the skin layer (face sheet) rather than the core, the change in bending stiffness of the structure itself due to the foam core is minimal. This minimizes the decline in mechanical properties of the material due to stiffness deterioration, etc. The mechanical rigidity can be increased.

The composite material according to the present invention includes the steps of manufacturing two composite materials with different thicknesses; And both sides of the foam core are manufactured by bonding two composite materials, respectively. Figure 5 is a diagram illustrating a method of making a bent-shaped conductive composite according to an embodiment of the present invention.

Referring to Figure 5, the steps for manufacturing a sensor-integrated foam core sandwich composite spring capable of measuring bending deformation are as follows.

First, two carbon fiber reinforced plastic prepregs with different thicknesses are hand laid up on a metal mold in the shape of a leaf spring, or the carbon fibers are hand laid up and then impregnated with epoxy.

Afterwards, molding is performed under certain curing conditions through a hot press or autoclave, and then the thick carbon fiber reinforced plastic is placed in the inner diameter direction with the dielectric foam in between, and the thin carbon fiber reinforced plastic is placed in the outer diameter direction, and then the thin carbon fiber reinforced plastic is placed in the outer diameter direction. Foam core composite sandwich springs are manufactured by bonding under curing conditions. At this time, adhesion can be performed through methods such as applying adhesive, using adhesive film, simultaneous curing, etc.

Figure 6 is a simulation result of the degree of deformation in the thickness direction of the foam core, which is a dielectric, according to the bending deformation of the composite material.

Referring to Figure 6, it can be seen that the sandwich-type composite spring according to the present invention is predominantly deformed in the thickness direction according to bending deformation.

Figure 7 is a comparative analysis result of strain according to the relative position of the core form.

Referring to FIG. 7, the strain in the thickness direction due to bending deformation shows that the more asymmetrically the dielectric core form is positioned toward the outer diameter, the more the tensile strain at the interface between the core form and the composite material, which is vulnerable to tensile strain in the thickness direction, increases. You can see that it is decreasing. This means that the stability (safety) of the overall structure can be increased in the composite material according to the present invention, which has a sandwich structure.

The present invention further provides an attachable robot equipped with a composite spring according to the present invention, and measures strain due to deformation from the spring without a separate sensor. To this end, in one embodiment of the present invention, while wearing an exoskeleton robot and performing a running test on a treadmill, the capacitance value of the composite material spring according to the present invention is measured and the ground surface in the vertical/horizontal direction is measured. Reaction forces (GRFs) values were measured using a force plate built into the treadmill.

Figure 8 is a diagram showing an experimental method according to an embodiment of the present invention, and Figure 9 is a diagram explaining a method of obtaining ground reaction forces (GRFs) values through actual machine learning.

Referring to Figures 8 and 9, according to the present invention, the ground reaction force value (output) can be derived from the capacitance value (input) sensed according to the deformation of the composite spring capable of self-sensing, using an artificial intelligence model, This ultimately proves that various variables, including ground reaction force values, can be measured from the deformation of the spring itself according to the present invention without a separate sensor.

Claims (16)

A spring comprising a composite material capable of measuring bending strain,
a first bendable conductive composite;
Dielectric capable of bending and compression deformation; and
comprising a bendable second conductive composite,
A first conductive composite and a second conductive composite are stacked on each of both sides of the dielectric,
The heights of the first conductive composite and the second conductive composite from the dielectric are different,
The composite material is provided with a first conductive composite on the inner diameter and the second conductive composite on the outer diameter based on curvature,
The height ratio of the first conductive composite and the second conductive composite is configured such that the dielectric is located closer in the direction of the first conductive composite than the second conductive composite, thereby causing compressive deformation to occur dominantly, thereby increasing the degree of capacitance change. A spring containing a composite material capable of measuring bending strain, characterized in that it increases. According to clause 1,
A spring comprising a composite material capable of measuring bending deformation, characterized in that the deformation of the dielectric in the thickness direction is dominant according to the bending deformation of the composite material. delete According to clause 1,
A spring comprising a composite material capable of measuring bending deformation, wherein the first conductive composite and the second conductive composite are carbon fiber reinforced plastic. delete According to clause 1,
A spring comprising a composite material capable of measuring bending strain, wherein the dielectric is compressible foam. According to clause 6,
The dielectric foam is characterized in that it is a foam containing at least one selected from the group consisting of PVC (Polyvinyl chloride), PU (Polyurethane), Melamine, PMI (Polymethacrylimide), PET (Polyethylene terephthalate), and PVDF (Polyvinylidene fluoride). , springs containing composite materials capable of measuring bending deformation. According to clause 1,
A spring comprising a composite material capable of measuring bending deformation, wherein the first and second conductive composites are conductive carbon fiber reinforced plastic. According to clause 8,
The first and second conductive composites are any selected from the group consisting of uni directional carbon fiber composite, carbon fabric composite, and short carbon fiber composite. A spring comprising a composite material capable of measuring bending deformation, characterized in that it includes one or more. According to clause 1,
A spring comprising a composite material capable of measuring bending deformation, wherein the first conductive composite and the second conductive composite are in a bent shape. According to clause 1,
A spring comprising a composite material capable of measuring bending deformation, wherein the dielectric has a low density compared to the first conductive composite and the second conductive composite. delete An attachable robot comprising the spring according to any one of claims 1, 2, 4, and 6 to 11.
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