Pressure and tactile sensor made of carbon nanotube yarn

Abstract

To provide a sensor capable of converting strain, pressure changes, and tactile sensations applied to a ribbon tape made of elastic fibers to electrical signals by weaving a high-purity, homogeneous, and flexible CNT yarn with mechanical strength into an accordion-like pattern on the ribbon tape.SOLUTION: In a CNT yarn ribbon tape sensor, a single continuous CNT yarn is woven or knitted into a ribbon tape. The continuously woven CNT yarn is arranged in parallel at approximately regular intervals and bends into a U-shape at both ends of the ribbon tape, with each CNT yarn not in contact with the others. Changes in the electrical resistance or impedance of this ribbon tape sensor are measured as electrical signals. When the surface of the ribbon tape is pressed vertically and flexed, the spacing between the CNT yarns changes. This results in a change in the electrical resistance or impedance of the ribbon, thereby converting the strain or elongation applied to the ribbon tape into an electrical signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a highly sensitive pressure and touch sensor in which carbon nanotube yarn (CNT yarn), which has mechanical strength equivalent to that of carbon fiber spun from carbon nanotubes (CNT) and physical properties equivalent to those of clothing fibers, is woven or knitted into a fiber ribbon tape. [Background technology]

[0002] As an interface between humans and machines, many technologies have been proposed that use artificial intelligence (AI) to numerically process movements detected by various sensors and image processing, digitizing and recording human movements, and then playing them back. These sensors and image recognition devices are being used to understand health conditions, remote medical diagnosis, and motion simulations, as well as to make the movements of robots and humanoids more similar to those of humans.

[0003] These technologies have enabled remote control of robotic arms and fingers, enabling them to grasp objects securely and with precision. This has greatly improved unmanned workplace processes, such as robotic surgical equipment and crane operation at construction sites. However, tactile sensors, which sense the touch felt by human fingertips and the pressure and friction felt by skin, are often based on conventional semiconductors, which are hard and inflexible like silicon wafers. While surface sensors employing semiconductor chip manufacturing and flexible substrate technologies have been developed, consisting of numerous tiny semiconductors mounted on a resin film, resin films lack the flexibility of fabrics, making them difficult to fit to complex three-dimensional shapes like the human body. Therefore, they are limited to handling objects with specific shapes and surface conditions.

[0004] W. Huang et al. reported a soft, sponge-like pressure sensor (Non-Patent Document 1). They mixed CNTs into a resin to create a sponge-like mass and successfully measured the pressure applied to this mass as an on / off electrical signal. However, because the material has a sponge-like structure, the dielectric constant of the entire mass changes when it absorbs water, which alters the electrical response, making practical application difficult. H. Lee et al. reported a method in which CNTs were mixed into a silicone rubber elastomer to create a rubber-like sheet, measured in-plane strain at multiple points vertically and horizontally, and converted the pressure applied to the surface into an electrical signal by numerically processing the two-dimensional dynamic information (Non-Patent Document 2). This elastomer sheet cannot detect deformation beyond a certain level, and the two-dimensional multi-point dynamic processing requires a high-performance computer. This requires a large-capacity power supply, making it difficult to reduce the size and weight. Furthermore, it cannot detect the touch or friction of the sheet surface. Hata et al. attempted to develop a stretchable sensor by attaching a CNT sheet to a stretchable substrate (Non-Patent Document 3). They were successful in capturing foot movement as an electrical signal for strain sensing in one-way stretching and contraction measurements, but were unable to detect pressure changes or tactile sensations.

[0005] Meanwhile, in the industrial technology field, there are applications related to pressure and tactile sensing as a sensor technology for robot control. Patent Document 1 proposes electrically detecting the pressure and distribution applied to the surface of an elastomer sheet by filling it with metal fibers in the thickness direction. This method requires a large number of wiring lines to measure changes in the electrical resistance of numerous metal fibers, making practical application difficult. Patent Document 2 proposes a piezoelectric film using vinylidene fluoride film, and Patent Document 3 proposes a piezoelectric film using vinylidene fluoride and tetrafluoroethylene copolymer film. This detects electricity generated by applying pressure or strain to a film made of piezoelectric material. It is intended for application in electronic devices such as capacitors and piezoelectric panels using thin, high-temperature films. Since the structure generates electricity through strain across the entire surface, it is not a sensor for detecting localized pressure or tactile sensation on a sheet. Patent Document 4 converts pressure applied to a surface into air pressure using a membrane, and pressure changes are detected by a pressure sensor device installed at a location separate from the measurement point. It proposes a device that uses air pressure to cancel out residual pressure stresses that occur in semiconductor pressure sensors. Patent Document 5 proposes a material for use as a surface tactile sensor, in which piezo tape is wrapped around a core wire made of twisted metal wires, which is then covered with an insulating film and a mesh-like metal shield wire, and the wire is then covered with an insulating material and woven or knitted. However, since a large number of sensor wires are used both vertically and horizontally, the calculations become multidimensional input analysis, which is the square of the number of wires, and the calculations become complicated, requiring a high-performance computer and its driving power.

[0006] Although robot hand structures have been proposed that can grasp objects by enveloping them with deformable materials such as balloons or bead chairs, a soft, thin, fabric-like sensor like artificial skin is desirable in order to convert pressure and tactile sensations into electrical signals, as with human fingertips or skin, and to directly detect the force applied when grasping three-dimensional or soft objects with the tip of a robot's finger using a sensor attached to the finger. On the other hand, providing multiple measurement points in a vertical and horizontal mesh pattern to sense two-dimensional surfaces, as in Patent Document 5 and Non-Patent Document 3, results in multi-point input control, which complicates the control function and requires a high-performance computer and a large-capacity drive power supply. This inevitably makes the entire computer device larger and more complex.

[0007] Therefore, what is required for pressure and tactile sensing is a fabric-like sensor that can obtain signals from one or several outputs, is highly durable, can be used even when wet, which occurs in everyday life, and also responds to friction, etc. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication S59-3234 [Patent Document 2] WO2017 / 014123 [Patent Document 3] Patent No. 6760404 [Patent Document 4] Special publication 2020 / 510201 [Patent Document 5] WO2019 / 117037 [Patent Document 6] Patent No. 7083996 Public Relations [Non-Patent Document 1] Huang,W.,et al.(2017):Flexible and Lightweight Pressure Sensor Based on Carbon Nanotube / Thermoplastic Polyurethane Aligned Conductive Foam with Superior Compressibility and Stability.ACS Applied Materials & Interfaces,2017,9,48,42266-42277. [Non-patent document 2] Lee,H.et al.(2017):Soft Nanocomposite Based Multipoint,Multi-directional Strain Mapping Sensor Using Anisotropic Electrical Impedance Tomography.Scientific Reports,7:39837. [Non-patent document 3] Kenji Hata, Strategic Basic Research Promotion Program CREST "Creation of Functional Nanosystems through Process Integration: Soft Nano-MEMS Devices Using Functional and Composite CNT Elements Created by Self-Assembly Processes," Research Final Report, October 2008 - March 2014. [Non-patent document 4] Chui, RW, Fosdick, A., Conner, R., Jiang, J., Bruenner, BA and Vargas, HM (2009): Assessment of two external telemetry systems(PhysioJacket and JET) in beagle dogs with telemetry implants.J Pharmacol Toxicol Methods 60,58-68. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a sensor that converts strain, pressure changes, and tactile sensations applied to a ribbon tape into electrical signals by weaving highly pure, homogeneous, flexible, and mechanically strong CNT yarns into a ribbon tape made of elastic fibers in a bellows pattern. [Means for solving the problem]

[0010] CNTs are inorganic artificial nanomaterials, and their novel physicochemical properties make them promising as new technology platform materials. Recently, it has been reported that it has become possible to produce homogeneous yarns of CNTs with lengths of approximately 1 km or more, which are fibrous materials with lengths of tens to hundreds of micrometers, do not contain metal impurities, and have uniform lengths and diameters (Patent Document 6). This homogeneous CNT yarn can be manufactured in 10 5 It has a conductivity of over S / m, high flexibility and mechanical strength, so it can be handled in the same way as silk thread or synthetic fibers.

[0011] The sensor's configuration and measurements measure changes in resistance and capacitance as impedance changes in a conductor made of ribbon tape woven or braided with CNT yarns in a bellows pattern. By pressing the ribbon tape surface vertically and bending it, the spacing between the CNT yarns changes, which changes the impedance of the ribbon, and the strain or stretch applied to the ribbon tape is measured as an electrical signal. When the ribbon tape is twisted, a different electrical signal waveform is observed than when it is pressed. Furthermore, when a conductive object such as skin comes close to or comes into contact with it, a change in impedance waveform is also observed.

[0012] Furthermore, when two of these ribbon tapes are overlapped with a semiconductor or insulating polymer film sandwiched between them, the pressure change can be measured numerically based on the difference in impedance that occurs in each ribbon tape due to minute differences in the shape of the two ribbon tapes.

[0013] The polymer film may be a thin flexible thermoplastic resin sheet or paper, or may be a polyvinylidene film for food storage.

[0014] The CNT yarn woven or knitted (hereinafter collectively referred to as "CNT yarn woven") ribbon tape used in the present invention is capable of detecting changes in impedance, which is the sum of capacitance and electrical resistance, with very little power, so the signal detection device can be small, and since the output is electrical, existing signal detection and analysis software such as ARDUINO can be used for signal analysis, making it highly versatile.

[0015] In the CNT yarn according to the present invention, the diameter of the CNTs is preferably 2 to 10 nanometers or less, and more preferably 2 to 5 nanometers.

[0016] The CNT yarn according to the present invention is preferably a homogeneous CNT yarn spun from CNTs of uniform length and diameter that do not contain metal impurities.

[0017] When connecting the ends of the CNT yarns woven into the ribbon tape to metal wires or metal terminals, it is desirable to use a method that enables soldering by crimping or by electrolytic copper plating of the CNT yarn ends. [Effects of the Invention]

[0018] This invention is a sensor that aims to convert strain, pressure changes, and tactile sensations applied to an elastic fiber ribbon tape into electrical signals by weaving highly pure, homogeneous, flexible, and mechanically strong CNT yarn into the ribbon tape in a bellows pattern.Unlike conventional solid semiconductor sensors or pressure sensors that use gas pressure or incompressible liquids, this sensor realizes sensing using an extremely thin, fabric-like sensor, making it possible to digitize pressure changes and tactile sensations as electrical signals that are closer to skin sensations.

[0019] By replacing the control of the finger movements of industrial robots with a woven ribbon tape made from the CNT yarn of this application, the mechanical methods, such as complex camera image processing and detection of the rotation angle of operating gears, can be replaced with a method that is more suited to the skin's response to stimulation in living organisms, making the movement of grasping complex-shaped objects more similar to human senses, leading to improved workability and efficiency.

[0020] The ultra-thin pressure sensor, which is made by layering the CNT yarn woven ribbon, has a soft structure like skin, but is able to convert minute pressures and frictions into electrical signals, enabling control that is close to human sensations.

[0021] When various robots of different sizes are introduced to work at height or in dangerous work sites, the robots can be made to perform autonomous tasks with the same level of sophistication as humans. [Brief explanation of the drawings]

[0022] [Figure 1] CNT yarn woven ribbon tape. 11: Ribbon tape made of polyurethane warp and polyester weft fibers. 12: Continuous CNT yarn woven into the ribbon tape.

[0023] [Figure 2] This shows a pressure and touch sensor in which a polymer film is sandwiched between two ribbon tapes woven with CNT yarn. 21: CNT yarn woven ribbon tape, 22: polymer film, 23: CNT yarn woven ribbon tape.

[0024] [Figure 3] This is a graph showing the change in the elongation and resistance value of the CNT woven ribbon tape (50 mm long) shown in Figure 1 when it is stretched.

[0025] [Figure 4]Photographs of a demonstration of actual measurement using the tactile sensor in Figure 2. Photograph A shows the state when the tactile sensor is not being touched. Photograph B shows the state when the tactile sensor is being touched with the index finger of the left hand. 31, 34: Tester. The displayed number is kΩ. 32, 35: A pressure / tactile sensor consisting of two CNT yarn sensors (approximately 0.1 mm thick) proposed in this application sandwiching a polymer film (approximately 0.08 mm thick). 33, 36: Measurement terminals are each connected to the CNT part on the right end of the CNT yarn sensor, and a finger is pressing the insulating part of the terminal. 37: The index finger of the left hand pressing the surface of the CNT yarn sensor. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below are preferred examples for carrying out the present invention, and therefore various technical limitations are imposed thereon. However, the present invention is not limited to these embodiments unless otherwise specified in the following description to limit the present invention.

[0027] Figure 1 shows a CNT yarn ribbon tape sensor in which a single continuous CNT yarn is woven into a ribbon tape with polyurethane fibers as the warp and polyester fibers as the weft. The continuously woven CNT yarns are arranged parallel to each other at approximately regular intervals, and are bent in a U-shape at both ends of the ribbon tape, with the CNT yarns not touching each other.

[0028] Because woven or knitted fiber fabrics are elastic, the ribbon tape expands and contracts, and the spacing between the CNT yarns changes in response to this expansion and contraction. When elastic fibers such as polyurethane are used for the warp, the relationship between the amount of stretch in the ribbon tape and the electrical resistance value is shown as an almost linear relationship. As shown in Figure 3, the resistance value changes almost linearly in the 2 to 13 mm range in which the ribbon tape is stretched (approximately 40% stretch of the natural length), making it easy to measure the amount of strain.

[0029] Furthermore, as shown in Figure 2, when pressure or strain is applied to two ribbon tapes sandwiching an insulating polymer film between them, the change in electrical resistance or impedance that occurs in each ribbon tape due to the minute difference in the expansion and contraction of the two ribbon tapes can be measured numerically. When using ribbon tapes with a thickness of 0.2 mm or less and polymer films of 0.1 mm or less, the total thickness must be 0.5 mm or less. It is even more desirable for the total thickness to be 0.2 mm or less.

[0030] The insulating film may be a thin flexible thermoplastic resin film or paper, or may be a polyvinylidene film used for storing food.

[0031] When a conductive object such as skin comes close to or touches the sensor, the change in capacitance is observed as an electrical signal.

[0032] Figure 3 plots the change in resistance value and the amount of elongation of the ribbon tape (50 mm long) shown in Figure 1 when the ribbon tape is stretched, illustrating how the electrical resistance value changes roughly in proportion to the stretching of the ribbon tape from 2 to 14 mm.

[0033] Figure 4 shows photos of a demonstration of the pressure and touch sensor made by layering the CNT yarn ribbon tape shown in Figure 2. Photo A shows the electrical resistance of 3.406 kΩ before the sensor is pressed with a finger. Photo B shows 3.432 kΩ after the sensor is touched with a finger, indicating a significant change in electrical resistance compared to the state in Photo A.

Claims

1. A sensor for detecting strain, pressure, or touch made of a CNT yarn ribbon tape in which a single continuous carbon nanotube yarn is woven or knitted into a ribbon tape made of fibers, the continuous CNT yarn being arranged parallel to one another at approximately equal intervals, and bent into a U-shape at both ends of the ribbon tape, with the CNT yarns not in contact with each other.

2. 2. A tactile sensor according to claim 1, wherein the tape width is 10 mm or less, preferably 8 mm or less, more preferably 5 mm or less.

3. 2. The sensor of claim 1, wherein the fibers other than carbon nanotubes are synthetic fibers.

4. 2. The sensor of claim 1, wherein the fibers other than carbon nanotubes are made of an elastomer and a non-elastomer.

5. 2. The sensor according to claim 1, wherein the one-dimensional expansion and contraction and the three-dimensional deformation are electrically output as changes in electrical resistance or impedance.

6. A pressure sensor characterized by having a structure in which multiple sensors according to claim 1 are sandwiched between a thermoplastic resin film, paper, or nonwoven fabric, and by measuring the difference in electrical resistance or impedance between the multiple sensors to detect three-dimensional deformation due to strain, pressure change, or friction as an electrical signal.

7. 7. The pressure sensor according to claim 6, wherein the thickness is 1 mm or less, preferably 0.5 mm or less, and more preferably 0.3 mm or less.

8. A pressure sensor having a control circuit and data transmission unit for a strain, tactile or pressure sensor, characterized in that the control circuit and data transmission unit that detect changes in the electrical resistance or impedance of the ribbon tape of claim 1 weighs 30 grams or less, is driven by 3 V to 3.7 V, is capable of converting analog electrical signals from the CNT yarn into digital signals, has a sampling rate of 50 to 4000 Hz, and is capable of wirelessly transmitting and receiving data with general-purpose electronic devices such as personal computers via Bluetooth or Wi-Fi, and has a function of logging data within the control circuit and data transmission board.

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