KR20220142910A - 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 deformation comprises: a first conductive composite capable of bending; a dielectric body capable of bending and compressive deformation; and a second conductive composite capable of bending. Provided is the composite material capable of measuring bending deformation, wherein the first conductive composite and the second conductive composite are laminated on each of both surfaces of the dielectric body and the height of the first conductive composite from the dielectric body and the height of the second conductive composite from the dielectric body are different.

Description

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

The present invention relates to a composite material capable of measuring bending deformation, a spring including the same, and a method for manufacturing the same, and more particularly, to measure bending deformation with the composite itself without adding a separate sensor in the composite material used for parts that are deformed such as a spring. It relates to a composite material capable of measuring bending deformation, a spring including the same, and a method for manufacturing the same, having the effect of storing and releasing elastic energy generated according to bending in addition to the weight reduction effect.

Composite materials not only have excellent mechanical properties including specific strength and specific stiffness, but also have a high elastic energy storage rate. It is being used as

In particular, the composite material spring is applied to a traveling robot to realize weight reduction and at the same time store and release elastic energy to further improve driving performance. In addition, it is possible to derive driving data such as ground reaction force and ankle, knee, and hip joint angles from the dynamic deformation of the composite spring according to the movement of the robot. If the motor is controlled in real time according to the driving data, the driving performance of the robot can be further maximized.

An additional sensor is generally required to detect the dynamic deformation of a composite spring, and an externally attached sensor or a composite embedded sensor is usually used. Among them, the externally attached sensor is very vulnerable in terms of durability when it undergoes rapid dynamic deformation such as robot driving because the sensor itself is directly exposed to the external environment. Another composite embedded sensor includes a piezoelectric ceramic sensor and a fiber bragg grating (FBG) sensor.

However, since these sensors are relatively brittle compared to composite materials, they are easily broken in structures with large deformations such as springs. In addition, since sensors embedded in composite materials have relatively large diameters and lower mechanical properties compared to reinforcement fibers, stress concentration phenomenon easily occurs, thereby lowering the mechanical properties of the structure itself. In addition, both methods using an externally attached sensor or a built-in embedded sensor have a disadvantage in that additional sensor installation is required.

Therefore, a composite material and a spring using the same that store and release elastic energy that plays a role in improving the driving performance of the robot, and at the same time detect the structural bending deformation through capacitance change without an additional sensor. development is needed

An object to be solved by the present invention is to provide a new composite material that can be used for springs, etc. by detecting bending deformation by itself and a method for manufacturing the same.

In order to solve the above problems, the present invention provides a composite material capable of measuring bending strain, comprising: a first conductive composite capable of being bent; bendable and compressively deformable dielectrics; and a second bendable conductive composite, wherein a first conductive composite and a second conductive composite are laminated on each of both sides of the dielectric, wherein heights of the first conductive composite and the second conductive composite from the dielectric are different. To provide a composite material capable of measuring the bending strain.

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

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

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

In an embodiment of the present invention, the dielectric is a compressible foam, and the dielectric foam is PVC (Polyvinyl chloride), PU (Polyurethane), Melamine, PMI (Polymethacrylimide), PET (Polyethylene terephthalate) and PVDF (Polyvinylidene). fluoride), including any one or more selected from the group consisting of.

In one embodiment of the present invention, the first and second conductive composites are conductive carbon fiber reinforced plastics, and the first and second conductive composites are uni directional carbon fiber composites, carbon fabric composites. It includes any one or more selected from the group consisting of a material (carbon fabric composite), a short carbon fiber composite (short carbon fiber composite).

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

The present invention provides a spring including the composite material described above, 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 comprising the above-mentioned spring.

The present invention provides a method for manufacturing the above-described composite material, comprising the steps of: molding carbon fiber-reinforced plastics of different thicknesses and bending them 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 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 when the spring of the composite material according to the present invention is utilized, the structure itself can be moved without an externally attached sensor or a composite material embedded sensor. Bending deformation can be detected through capacitance change. In addition, by fabricating a sandwich composite spring using foam as a core, it is possible to realize weight reduction and secure spring stiffness.

Furthermore, when the composite material according to the present invention is used as an ankle spring of a traveling robot, it serves to store and release elastic energy generated by bending, thereby improving the running performance of the robot, and at the same time, the capacitance of the structure. It has the advantage of being able to obtain driving data such as ground reaction force or ankle knee hip joint angle in real time from the change.

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

Hereinafter, a composite material capable of measuring bending strain according to the present invention, a spring including the same, and a manufacturing method thereof will be described with reference to the accompanying drawings. Unless otherwise defined, all terms in this specification have the same general meaning as understood by those of ordinary skill in the art to which the present invention belongs. 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 will be omitted. Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

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

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

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

Referring to FIG. 1, the prior art disclosed in Prior Art 1 Intrinsic 3 is a structural capacitor through a film serving as a dielectric and a plate-shaped carbon fiber reinforced plastic (CFRP) serving as an electrode. was the way to use it.

In this case, rather than detecting deformation, most of the composite materials were used to secure structural safety by increasing the mechanical properties of the capacitor. In addition, since this structure has a very small thickness-direction deformation according to structural deformation, there is a problem in that sensitivity to change in capacitance is also very low.

Referring to FIG. 2 , this prior art disclosed in Prior Art 4 uses a conductive composite material separated from each other as an electrode, and the overlapping area is changed according to the relative positions of the two composite material electrodes, and the capacitance changing accordingly to detect

However, this prior art has a low degree of capacitance change because there is no clear dielectric between the electrodes, and since the composite materials are separated from each other, there is a limit in measuring the deformation of the structure itself.

In order to solve this problem, the present invention provides a so-called sandwich-type composite by inserting a dielectric asymmetrically between the composite materials, whereby sensing, weight reduction, and elastic energy release are possible through the composite material itself.

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 deformation according to an embodiment of the present invention includes a first bendable conductive composite 110 ; a bendable, compressible dielectric 120; and a second bendable conductive composite 130 , wherein the first conductive composite 110 and the second conductive composite 130 are laminated on both surfaces of the dielectric 120 .

In an 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 to 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. By positioning the dielectric asymmetrically in the direction of the outer diameter of the curvature with respect to the mid-plane of the composite, the compressive deformation dominates, thereby increasing the degree of capacitance change. Here, "dominant" means that the deformation in the height direction is greater than the deformation 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 a compressible foam.

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

In addition, the dielectric foam core may include at least one 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, making it possible to store and release spring elastic energy.

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

Referring to FIG. 4 , the composite conductive composite, which is a conductive carbon fiber reinforced plastic serving as a conductive composite, hand lay-up carbon fibers on a mold with a constant curvature shape to have a leaf spring shape, and apply epoxy. Impregnated or prepreg prepreg impregnated with epoxy is directly laid up by hand, and then manufactured by hot press molding or autoclave molding.

At this time, two carbon fiber-reinforced plastics were fabricated with different thicknesses to make a sandwich composite material having a core stacked asymmetrically with respect to the mid plane. As used herein, “asymmetric” means that the dielectric core is oriented in one direction from the center of the entire composite.

After that, 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 made through methods such as adhesive application, use of an adhesive film, simultaneous curing, etc. In this case, as described above, a relatively thick carbon fiber-reinforced plastic is applied in the inner diameter direction in terms of curvature, and a thin carbon fiber Place the reinforced plastic in the direction of the outer diameter.

The composite material according to the present invention produced in the above manner has a foam core sandwich structure, and stores and releases elastic energy while undergoing bending deformation. In addition, 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 detect the bending deformation of the composite material spring by itself through the structural shape without an additional sensor, and by using a foam-type core, the overall structure can be lightened, and the relative weight with carbon fiber reinforced plastics Through the difference in mechanical properties, the degree of change in capacitance can be increased by further maximizing the deformation in the thickness direction of the dielectric due to bending deformation.

In addition, by placing the foam core in the outer radial direction with respect to the mid plane and stacking it asymmetrically, compressive deformation in the thickness direction occurs predominantly to increase the capacitance change, and at the same time, tension at the adhesive interface, which is vulnerable to tension. Deformation was minimized. In addition, since most of the stress caused by bending deformation is applied to the face sheet rather than the core, the change in the bending stiffness of the structure itself due to the foam core is insignificant. can increase the mechanical strength of

A composite according to the present invention can be prepared by the steps of: preparing two composites having different thicknesses; And both sides of the foam core are manufactured in such a way that the two composite materials are respectively bonded.

Referring to FIG. 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 to have different thicknesses are hand laid up on a metal mold in the shape of a leaf spring, or carbon fiber is hand laid up and then impregnated with epoxy.

After that, molding is performed under constant curing conditions through hot press or autoclave, and carbon fiber reinforced plastic with a thick thickness is placed in the inner diameter direction with a dielectric foam interposed therebetween, and carbon fiber reinforced plastic with a thin thickness is placed in the outer diameter direction, and then A foam core composite sandwich spring is fabricated by bonding under curing conditions. In this case, the adhesion may be performed through methods such as applying an adhesive, using an adhesive film, and simultaneous curing.

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

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

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

Referring to FIG. 7 , the strain in thickness direction according to the bending deformation shows that the tensile strain at the interface between the core form and the composite material, which is vulnerable to tensile deformation in the thickness direction, is increased as the dielectric core form is asymmetrically positioned toward the outer diameter. decrease can be seen. This means that the overall structure safety can be increased in the composite material according to the present invention, which is a sandwich structure.

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

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

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

Claims (16)

As a composite material capable of measuring bending strain,
a first bendable conductive composite;
bendable and compressively deformable dielectrics; and
a bendable second conductive composite;
A first conductive composite and a second conductive composite are laminated on each side of the dielectric,
A composite material capable of measuring bending strain, characterized in that the heights of the first conductive composite and the second conductive composite are different from the dielectric. The method of claim 1,
A composite material capable of measuring bending deformation, characterized in that deformation in the thickness direction of the dielectric is dominant according to the bending deformation of the composite material. The method of claim 1,
The height ratio of the first conductive composite and the second conductive composite is, the bending strain measurement possible composite material, characterized in that the dielectric is configured to be located closer to the first conductive composite direction than the second conductive composite. The method of claim 1,
The first conductive composite and the second conductive composite are a composite material capable of measuring bending deformation, characterized in that the carbon fiber reinforced plastic. The method of claim 1,
The composite material has a first conductive composite on the inner diameter and the second conductive composite on the outer diameter based on the curvature, and the second conductive composite is thinner than the first conductive composite. The method of claim 1,
The dielectric is a composite material capable of measuring bending deformation, characterized in that the compressible foam (foam). 7. The method of claim 6,
The dielectric foam is a foam comprising at least one selected from the group consisting of PVC (Polyvinyl chloride), PU (Polyurethane), Melamine, PMI (Polymethacrylimide), PET (Polyethylene terephthalate) and PVDF (Polyvinylidene fluoride). Composite materials capable of measuring bending strain. The method of claim 1,
The first and second conductive composites are capable of measuring bending deformation, characterized in that the conductive carbon fiber reinforced plastic. 9. The method of claim 8,
The first and second conductive composites are any one selected from the group consisting of a uni-directional carbon fiber composite, a carbon fabric composite, and a short carbon fiber composite. A composite material capable of measuring bending strain, comprising at least one. The method of claim 1,
The first conductive composite and the second conductive composite are in a curved shape. The method of claim 1,
A composite material, characterized in that the dielectric has a lower density than the first conductive composite and the second conductive composite. A spring comprising the composite material according to any one of claims 1 to 11. An attachable robot comprising a spring according to claim 12 . 14. The method of claim 13,
The spring composite material stores elastic energy generated as the spring is compressed in the dielectric and then releases it again upon recovery. A method for manufacturing a composite material according to any one of claims 1 to 11,
forming first and second conductive composites by molding and bending carbon fiber reinforced plastics of different thicknesses; and
bonding the conductive assembly to each of the cross-sections of both sides of the dielectric, wherein the dielectric is a compressible foam. 16. The method of claim 15,
The carbon fiber reinforced plastic is a composite material manufacturing method, characterized in that manufactured by laminating a plurality of carbon fibers and then impregnating the epoxy.

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