CN118329109A - A stacking structure multimodal flexible tactile sensor - Google Patents

Abstract

The present invention provides a structural design and preparation method of a stacked multimodal flexible tactile sensor, which mainly includes a temperature sensing unit and a pressure sensing unit. The temperature sensing unit specifically adopts a composite material made of carbon nanofibers with thermosensitive properties and polyvinyl alcohol as a thermosensitive layer, and metallic silver as a conductive electrode. The pressure sensing unit is based on the pressure-capacitive effect, and uses a composite material mixed with gallium-indium alloy liquid metal and polyvinyl alcohol as an electrode, and a composite of liquid metal and water-based polyurethane as a dielectric layer. The stacking structure design of the temperature sensing unit and the pressure sensing unit ensures that there is no signal crosstalk and coupling between the two. The flexible tactile sensor of the invention has a simple manufacturing process and low cost, and is expected to create new possibilities for future wearable devices and has huge application potential.

Description

A stacking structure multimodal flexible tactile sensor

Technical Field

The present invention relates to the field of flexible sensor technology, and in particular to a stacking type structure multi-modal flexible tactile sensor.

Background technique

Human skin is not only our largest organ, but also plays the role of a complex sensory system. It can sense a variety of environmental stimuli such as pressure and temperature. This perception ability is crucial to our daily life. It not only allows us to identify and manipulate objects, but also helps protect our bodies from harm. However, the sensory ability of human skin is not perfect. For example, when faced with two objects of different temperatures but the same weight, we may misjudge their weight. This phenomenon reveals the limitations of the skin's perception system, which is mainly due to the delayed response of the mechanical receptors in the skin to thermal stimuli and pressure, and the nonlinear differences in our perception of different pressure ranges.

It is particularly important to create a flexible tactile sensor that can sense and accurately interpret pressure and temperature, two key environmental signals, especially in the field of healthcare. Accurate signal detection and analysis can not only promote the development of medical technology and improve the accuracy of disease diagnosis, but also improve the treatment and rehabilitation process of patients.

At present, despite certain progress in the field of flexible multimodal tactile sensors, a single device still faces major challenges in achieving simultaneous detection and differentiation of different environmental signals such as temperature and pressure. Overcoming this challenge is particularly critical for the development of efficient healthcare equipment. In order to circumvent complex manufacturing processes and high production costs, the use of multifunctional sensing capabilities integrated in a single device has become an efficient solution for building electronic skin. By optimizing sensing materials and designing structures, high sensitivity and accurate differentiation of different types of signals can be achieved, thereby providing more complex and detailed sensing capabilities.

Summary of the invention

The present invention proposes an innovative solution to the above technical problems, namely, a stacking-type multimodal flexible tactile sensor. The sensor can effectively convert temperature and pressure changes into two independent electrical signals by utilizing the thermal resistance effect and the pressure capacitance effect, thus realizing instant sensing of temperature and pressure signals. This design allows the sensor to directly distinguish signals, avoiding the need to separate different stimulus-related signals through a complex decoupling process, and greatly reducing crosstalk between signals.

The purpose of the present invention is achieved as follows: the multimodal flexible tactile sensor is composed of temperature and pressure sensing units, the temperature sensing unit uses a composite material made of carbon nanofibers (CNF) with thermosensitive properties and polyvinyl alcohol (PVA) as a thermosensitive layer, and metal silver (Ag) as a conductive electrode. The pressure sensing unit is based on the pressure-capacitive effect, and a composite material made of a mixture of gallium-indium alloy liquid metal (LM) and PVA is used as an electrode, and a composite of LM and waterborne polyurethane (WPU) is used as a dielectric layer. The stacking structure design of the temperature sensing unit and the pressure sensing unit ensures that there is no signal crosstalk and coupling between the two.

The object of the present invention is achieved by: a stacking structure multi-modal flexible tactile sensor, comprising the following steps:

(1) The preparation process of the temperature sensing unit is as follows:

a. PVA solid particles were placed in deionized water, allowed to stand at room temperature for 12 hours, and then stirred evenly with a magnetic stirrer under heating in a water bath to prepare a PVA solution.

b. Add polyvinylpyrrolidone (PVP) particles into ethanol and obtain a PVP solution by stirring.

c. Add CNF particles into PVP solution and perform ultrasonic treatment to obtain CNF suspension. The main purpose of PVP here is to better disperse CNF.

d. PVA solution was mixed with CNF suspension in different proportions and stirred by magnetic force to prepare CNF/PVA suspensions with different concentrations.

e. The obtained CNF/PVA suspension was poured into a glass mold and dried at room temperature.

f. The dried CNF/PVA film was cut to a specific size and coated with conductive silver paste at both ends and dried at room temperature to form a CNF/PVA temperature sensing unit with Ag electrodes.

(2) The preparation of the pressure sensing unit includes the following steps:

a. Add LM into ethanol and disperse it by ultrasonic to obtain LM suspension.

b. The LM suspension and the PVA solution obtained in step (1) a are mixed in a certain proportion, and after being magnetically stirred to obtain a LM/PVA suspension.

c. Pour the LM/PVA suspension into the same glass mold as used in step (1) e, and let it stand and dry at room temperature to obtain a LM/PVA film. Then cut the film into the same size as the CNF/PVA film in step (1) e to obtain a LM/PVA electrode.

d. Add LM to the PVP solution in step (1) b and disperse by ultrasonic to obtain a LM@PVP suspension.

e. The LM@PVP suspension and WPU were mixed in different proportions, and LM/WPU suspensions with different concentration ratios were obtained by magnetic stirring.

f. Pour the obtained LM/WPU suspension into a glass mold of the same size as that used in step (1) e, and let it stand and dry at room temperature to obtain a LM/WPU film. Then cut the film into the same size as the CNF/PVA film in step (1) e, and finally obtain a LM/WPU dielectric layer.

g. Place the LM/WPU dielectric layer between two LM/PVA electrodes of the same size, ensuring sufficient contact between the electrodes and the dielectric layer, thereby obtaining a complete LM/PVA-LM/WPU pressure sensing unit.

The present invention provides a stacking-type multimodal flexible tactile sensor, which can convert separate pressure and temperature signals to achieve direct signal discrimination, so there is no need for a complex decoupling process to separate the signals associated with each stimulus, and the manufacturing process is simple, easy to operate, and low in cost. In this design, the temperature sensing unit uses a composite material of CNF and PVA to construct a self-supporting structure that is highly sensitive to temperature changes. The simplification of this structural design not only improves the temperature response capability of the sensor, but also ensures insensitivity to pressure changes, thereby avoiding the interference of pressure changes on temperature detection. For the pressure sensing unit, a mixture of LM and PVA is used as the electrode material. Through the cross-linking of PVA and LM, a self-supporting LM/PVA thin film electrode with exposed conductors is formed, which exhibits excellent flexibility compared to traditional rigid electrodes. A mixture of LM and WPU is selected as the dielectric layer of the pressure sensing unit. When subjected to compression force, the LM particles will deform from a spherical shape to an olive shape, which not only increases the conductive area, but also reduces the gap between the LM particles. According to the capacitance formula of the parallel plate capacitor:

Where ε is the dielectric constant, A is the electrode area, and d is the gap between the electrodes, which will lead to an increase in capacitance, thereby increasing the sensitivity of the sensor to pressure changes. The pressure sensing unit achieves a high degree of insensitivity to temperature changes, effectively avoiding the impact of temperature changes on pressure detection accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a stacking-type multi-modal flexible tactile sensor constructed in Example 1 of the present invention.

FIG. 2 is a schematic structural diagram of the LM/WPU dielectric layer in the pressure sensing unit of the present invention in the original state and under the condition of force compression.

FIG. 3 is a schematic diagram showing an equivalent circuit model of a pressure sensing unit in the present invention.

FIG. 4 is a schematic diagram of a 3*3 array of multimodal flexible tactile sensors according to Example 2 of the present invention.

Figure 5 is a schematic diagram of a measurement circuit of a 3*3 array of stacked multimodal flexible tactile sensors in Example 2 of the present invention. Figure 6 is a schematic diagram of the sensor array attached to a human body and used as an electronic skin to monitor temperature and pressure changes between the body and the external environment.

In the accompanying drawings: 1-Ag electrode, 2-CNF/PVA thermosensitive layer, 3-PVA top insulating layer, 4-LM/PVA top electrode, 5-LM/WPU dielectric layer, 6-LM/PVA bottom electrode, 7-PVA bottom insulating layer, 8-LM particles, 9-WPU, 10-equivalent capacitance between adjacent LM particles, 11-stacking structure multimodal flexible tactile sensor, 12-PET film, 13-flexible tactile sensor array, A-I-3*3 flexible tactile sensor numbering in the array.

Detailed ways

In the following sections, we will introduce the embodiments of the present invention in detail through relevant diagrams. It should be noted that the embodiments shown here represent only one of many possible implementations of the present invention. Based on these descriptions, professionals in the field can derive or implement other variations of the present invention without the need for innovative efforts. These derived implementations also fall within the scope of protection of the present invention.

Example 1 A stacking structure multi-modal flexible tactile sensor

The method specifically comprises the following steps:

(1) First, 5 g of PVA solid particles were placed in 100 ml of deionized water and allowed to stand at room temperature for 12 hours. Thereafter, the solid particles were placed in a 90° C. water bath and stirred at 1000 rpm for 30 minutes using a magnetic stirrer to prepare a PVA solution.

(2) 250 mg of PVP particles were added to 50 ml of ethanol and stirred with a magnetic stirrer at 1000 rpm for 5 min to obtain a PVP solution.

(3) 50 mg of CNF particles were added to 5 ml of the PVP solution prepared in step (2), and ultrasonic dispersion was performed in a 120 W ultrasonic cleaning machine for 15 minutes to obtain a CNF suspension.

(4) Add 10 ml of the PVA solution prepared in step (1) to the CNF suspension prepared in step (3), and stir the mixture at 1000 rpm for 10 minutes using a magnetic stirrer to prepare a CNF/PVA suspension.

(5) Pour the CNF/PVA suspension obtained in step (4) into a glass mold with a size of 100 mm x 100 mm x 10 mm and dry it at room temperature. The dried CNF/PVA film is cut into a size of 20 mm x 20 mm and coated with a 20 mm x 2 mm conductive silver paste at both ends. After drying at room temperature, a CNF/PVA temperature sensing unit with a Ag electrode is formed.

(6) 0.5 g of LM was added to 2 ml of ethanol and subjected to ultrasonic dispersion treatment in a 120 W ultrasonic cleaning machine for 10 min to obtain a LM suspension.

(7) The LM suspension obtained in step (6) was added to 5 ml of the PVA solution obtained in step (1), and stirred at 1000 rpm for 15 minutes using a magnetic stirrer to obtain a LM/PVA suspension.

(8) Pour the LM/PVA suspension prepared in step (7) into a glass mold of 100 mm*100 mm*10 mm in size, and allow to dry at room temperature to obtain a LM/PVA film. The film is then cut into a size of 20 mm*20 mm to obtain a LM/PVA electrode.

(9) 0.5 g of LM was added to 2 ml of the PVP solution obtained in step (2), and ultrasonic dispersion was performed in a 120 W ultrasonic cleaning machine for 10 minutes to obtain a LM@PVP suspension.

(10) The LM@PVP suspension obtained in step (9) was mixed with 5 g of WPU and stirred at 1000 rpm for 15 min using a magnetic stirrer to obtain a LM/WPU suspension.

(11) The LM/WPU suspension prepared in step (10) is poured into a glass mold of 100 mm×100 mm×10 mm in size and placed at room temperature to dry naturally to form a LM/WPU film. After drying, the film is cut into 20 mm×20 mm to obtain a LM/WPU dielectric layer. The schematic diagram of the structure is shown in FIG2 .

(12) The prepared LM/WPU dielectric layer is placed between two LM/PVA electrodes of the same size, ensuring close contact between the electrodes and the dielectric layer, and assembled into a complete LM/PVA-LM/WPU pressure sensing unit. Then, the pressure sensing unit is encapsulated in a PET film together with a CNF/PVA temperature sensing unit equipped with an Ag electrode to form a multimodal flexible tactile sensor with a stacking structure. The schematic diagram of its structure is shown in Figure 1.

Example 2

On the basis of the construction of Example 1, a 3*3 array of multimodal flexible tactile sensors is further designed, as shown in Figure 4. This array ensures that each sensing unit in the array can maintain electrical isolation, effectively avoiding the occurrence of electrical crosstalk. The signal acquisition circuit design of the sensor array in this embodiment is shown in Figure 5. Design a capacitance acquisition circuit, and use the CDC chip to measure 9 pressure sensing units at the same time. At the same time, for the resistive sensor of the temperature sensing unit, design an R/V conversion circuit to convert the temperature sensor output resistance signal into a voltage, and then use the ADC chip to measure 9 temperature sensing units at the same time. Afterwards, the temperature sensing signal and the pressure sensing signal are transmitted to the host computer respectively through the microprocessor, and the host computer collects and analyzes the output signals of the pressure sensing module and the temperature sensing module.

This design allows the sensor array to accurately detect pressure and temperature changes on multiple contact points at the same time without interfering with each other. By adopting an integrated and modular design, the sensor array can identify and distinguish the weight, temperature and pressure distribution of different objects placed on its surface. When two objects with different weights and temperatures act on the tactile sensor array at the same time, each individual sensing unit can independently respond to the specific pressure and temperature changes applied to it. In this way, not only can the weight and temperature of each object be accurately measured, but these objects can also be distinguished and identified based on the measurement results. As shown in Figure 6, through further integration, the sensor array can be used as an electronic skin to monitor the temperature and pressure changes between the body and the external environment. This electronic skin can simulate the temperature and tactile perception functions of the skin, and through its temperature and pressure sensing units, it can capture and respond to small changes in the outside world in real time. The integrated design not only enhances the practicality and scope of application of the sensor, but also provides new solutions for wearable devices, intelligent robots and medical health monitoring by simulating the perception ability of human skin.

Claims (1)

1. The multi-mode flexible touch sensor is characterized by comprising a temperature sensing unit and a pressure sensing unit, wherein the temperature sensing unit is formed by taking a composite material made of carbon nano fibers with thermal sensitivity and polyvinyl alcohol as a thermal sensitive layer and metal silver as a conductive electrode, the pressure sensing unit comprises a top electrode and a bottom electrode which are made of a composite material made of gallium indium alloy liquid metal and polyvinyl alcohol, and a dielectric layer which is a composite of liquid metal and aqueous polyurethane, and the temperature sensing unit and the pressure sensing unit are adjacent up and down to form a stacking structure.