Flexible foam piezoresistive tactile sensor and pressure imaging system

Abstract

The embodiment of the utility model provides a flexible foam piezoresistive tactile sensor and a pressure imaging system. The flexible foam piezoresistive tactile sensor comprises a conductive sensing layer, an interdigital electrode layer, an insulating diaphragm layer and a thin film packaging layer, a hole array is engraved on the insulating diaphragm layer; the conductive sensing layer, the interdigital electrode layer and the insulating diaphragm layer are located between the two thin film packaging layers, and the conductive sensing layer, the insulating diaphragm layer and the interdigital electrode layer are stacked in sequence; the flexible or telescopic foam is used as the substrate, so that the sensor has better flexibility and stretchability and can perfectly fit a human body. Besides, based on the structure, the size and the shape of the sensor, high-precision measurement of the surface pressure between the two contact surfaces is realized, and multi-dimensional pressure imaging can be realized. By introducing the foam material, the advantages of the traditional piezoresistive sensor are maintained, the limitation of the traditional piezoresistive sensor is overcome, and the applicability and the performance of the sensor are improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of sensors, and in particular to a flexible foam piezoresistive tactile sensor and a pressure imaging system. Background Art

[0002] Flexible pressure sensors are key components of flexible electronic products and are widely used in human health monitoring, medical equipment and other fields.

[0003] Piezoresistive sensors have a simple structure and good performance. Piezoresistive sensors are often composed of two electrodes and an elastic conductive material. However, most traditional piezoresistive sensors are made of rigid materials. Due to the high rigidity of the materials, they are often not flexible enough and cannot adapt to complex environments. There are also some limitations in the application, such as being easily restricted by the shape and size of the target object, which makes it difficult for traditional piezoresistive sensors to achieve multi-dimensional accurate pressure imaging. Utility Model Content

[0004] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0005] The purpose of the present application is to solve one of the technical problems existing in the related art to at least a certain extent, and the embodiments of the present application provide.

[0006] An embodiment of the first aspect of the present application is a flexible foam piezoresistive tactile sensor, comprising: a conductive sensing layer, an interdigitated electrode layer, an insulating diaphragm layer and a thin film packaging layer; the insulating diaphragm layer is engraved with a hole array; the conductive sensing layer, the interdigitated electrode layer and the insulating diaphragm layer are located between two layers of the thin film packaging layers, and the conductive sensing layer, the insulating diaphragm layer and the interdigitated electrode layer are stacked in sequence.

[0007] According to an embodiment of the first aspect of the present application, the conductive sensing layer is made of polydimethylsiloxane, a curing agent, sodium chloride, and polydiallyldimethylammonium chloride.

[0008] According to an embodiment of the first aspect of the present application, the insulating diaphragm layer is made of polyimide, polyester resin, polyvinyl chloride or polyethylene.

[0009] According to an embodiment of the first aspect of the present application, the thin film encapsulation layer is made of polyimide, polyester resin, polyvinyl chloride or polyethylene.

[0010] According to an embodiment of the first aspect of the present application, the thickness of the insulating diaphragm layer is in a range of 15 μm to 50 μm, and the radius of the holes of the hole array is in a range of 0.2 mm to 0.8 mm.

[0011] According to an embodiment of the first aspect of the present application, the porosity of the conductive sensing layer is in a range of 55% to 78%, and the thickness is in a range of 1 mm to 5 mm.

[0012] According to an embodiment of the first aspect of the present application, the line width of the interdigitated electrode layer ranges from 0.5 mm to 1 mm, and the spacing ranges from 0.5 mm to 1 mm.

[0013] An embodiment of the second aspect of the present application is a pressure imaging system, comprising a flexible foam piezoresistive tactile sensor and a pressure analysis and processing unit, wherein the flexible foam piezoresistive tactile sensor is arranged into a sensing matrix; the sensing matrix is ​​used to collect pressure information, and the pressure analysis and processing unit is used to obtain a pressure value based on the pressure information.

[0014] According to an embodiment of the second aspect of the present application, the flexible foam piezoresistive tactile sensor is connected to a proportional amplification circuit.

[0015] According to an embodiment of the second aspect of the present application, the proportional amplification circuit includes an operational amplifier and a feedback resistor, one end of the flexible foam piezoresistive tactile sensor is connected to the negative phase terminal of the operational amplifier, the other end of the flexible foam piezoresistive tactile sensor is grounded, one end of the feedback resistor is connected to the negative phase terminal of the operational amplifier, and the other end of the feedback resistor is connected to the output terminal of the operational amplifier.

[0016] The above scheme has at least the following beneficial effects: the use of soft or stretchable foam as a substrate makes the sensor more flexible and stretchable, and can perfectly fit the human body. In addition, based on the structure, size and shape of the sensor, high-precision measurement of the surface pressure between the two contact surfaces is achieved, and multi-dimensional pressure imaging can be achieved. By introducing foam materials, while maintaining the advantages of traditional piezoresistive sensors, its limitations are overcome, and the applicability and performance of the sensor are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide further understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0018] Figure 1 is a step diagram of a method for preparing a flexible foam piezoresistive tactile sensor;

[0019] Figure 2 It is the stress-strain curve of the foam regulated according to the porosity;

[0020] Figure 3 It is the relationship curve between drying temperature and mechanical factors of foam skeleton;

[0021] Figure 4 is a structural diagram of a flexible foam piezoresistive tactile sensor;

[0022] Figure 5 is a structural diagram of the interdigitated electrode layer;

[0023] Figure 6 It is a structural diagram of the insulating diaphragm layer;

[0024] Figure 7 is the relationship curve between the pore size of the insulating diaphragm layer and the performance of the flexible foam piezoresistive tactile sensor;

[0025] Figure 8 It is a schematic diagram of the sound test of the flexible foam piezoresistive tactile sensor;

[0026] Fig. 9 is a schematic diagram of a cyclic test of a flexible foam piezoresistive tactile sensor;

[0027] Fig.10 is a schematic diagram of a distributed circuit;

[0028] Fig.11 is a schematic diagram of a distributed circuit sandwich diaphragm;

[0029] Fig.12 It is a schematic diagram of the sensor unit acquisition circuit;

[0030] Fig.13 It is the circuit diagram of the sensing unit acquisition circuit. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] It should be noted that, although the functional modules are divided in the device schematic diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flowchart. The terms "first", "second", etc. in the specification, claims or the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0033] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0034] An embodiment of the present application provides a flexible foam piezoresistive tactile sensor.

[0035] Reference Figure 4The flexible foam piezoresistive tactile sensor comprises: a conductive sensing layer 3, a forked electrode layer 4, an insulating diaphragm layer 2 and a thin film packaging layer 1; the insulating diaphragm layer 2 is engraved with a hole array; the conductive sensing layer 3, the forked electrode layer 4 and the insulating diaphragm layer 2 are located between two thin film packaging layers 1, and the conductive sensing layer 3, the insulating diaphragm layer 2 and the forked electrode layer 4 are stacked in sequence.

[0036] The insulating membrane layer 2 is made of polyimide, polyester resin, polyvinyl chloride or polyethylene. The thin film encapsulation layer 1 is made of polyimide, polyester resin, polyvinyl chloride or polyethylene.

[0037] Reference Figure 6 The thickness of the insulating membrane layer 2 is in the range of 15 μm to 50 μm, and the radius of the holes in the hole array is in the range of 0.2 mm to 0.8 mm.

[0038] The porosity of the conductive sensing layer 3 is in the range of 55% to 78%, and the thickness is in the range of 1 mm to 5 mm. The conductive sensing layer 3 is chemically modified with a polydiallyldimethylammonium chloride (PDDA) solution, and the concentration of the polydiallyldimethylammonium chloride (PDDA) solution is in the range of 0.1 wt % to 1 wt %.

[0039] Reference Figure 5 The line width of the interdigital electrode layer 4 is in the range of 0.5 mm to 1 mm, and the spacing is in the range of 0.5 mm to 1 mm.

[0040] Specifically, the interdigital electrode layer 4 has a line width of 1 mm and a spacing of 1 mm. The thickness of the insulating diaphragm layer 2 is 17 μm. The concentration of the PDDA solution is 0.1 wt%. Figure 7 , Figure 7 : is a curve showing the relationship between the pore size of the insulating diaphragm layer 2 and the performance of the flexible foam piezoresistive tactile sensor; the radius of the holes in the hole array of the insulating diaphragm layer 2 is 0.4 mm.

[0041] A flexible foam piezoresistive tactile sensor was prepared according to the following preparation method.

[0042] Reference Figure 1 , the preparation method includes but is not limited to the following steps:

[0043] Step S100, preparing a foam skeleton;

[0044] Step S200, preparing a conductive sensing layer 3 using a foam skeleton;

[0045] Step S300, connecting the wire to the interdigital electrode layer 4;

[0046] Step S400, engraving a hole array on the insulating membrane layer 2;

[0047] Step S500, assemble the foam skeleton, the conductive sensing layer 3, the interdigitated electrode layer 4, the insulating diaphragm layer 2 and the thin film packaging layer 1, and make the conductive sensing layer 3, the interdigitated electrode layer 4 and the insulating diaphragm layer 2 located between two layers of the thin film packaging layer 1, and the conductive sensing layer 3, the insulating diaphragm layer 2 and the interdigitated electrode layer 4 are stacked in sequence.

[0048] For step S100, a foam skeleton is prepared, and the process is as follows.

[0049] Pour a polydimethylsiloxane (PDMS) prepolymer and a curing agent into a container, wherein the mass ratio of the polydimethylsiloxane (PDMS) prepolymer and the curing agent is 10:1, and mix them uniformly under magnetic stirring to obtain a first PDMS mixture.

[0050] A certain amount of salt particles are weighed and added to the mixed first PDMS mixture, and mechanically stirred again to make them uniformly dispersed in the first PDMS mixture to obtain a second PDMS mixture.

[0051] The second PDMS mixture after being stirred evenly was transferred to a 3D printed mold. The customized mold size was 10 mm long × 10 mm wide × 2 mm high, and the second PDMS mixture was pressed and shaped.

[0052] The mold and the second PDMS mixture in the mold are placed in an oven and cured at 120° C. for 2 to 10 hours. Preferably, the curing time is 3 hours. The PDMS cured product is obtained.

[0053] The solidified product is washed in 80° C. water for 1 to 10 hours. Preferably, the washing time is 3 hours to ensure that the salt particles are completely removed, and then dried again to obtain a foam skeleton.

[0054] For step S200, the conductive sensing layer 3 is prepared by using the foam skeleton, and the process is as follows.

[0055] A polydiallyldimethylammonium chloride (PDDA) solution having a concentration of 0.1 wt % was prepared.

[0056] The foam skeleton was immersed in the PDDA solution under vacuum conditions for 20 minutes to allow the surface of the PDMS foam and its internal pores to fully absorb.

[0057] The foam skeleton is placed in an oven and dried at 120° C. for 2 to 10 hours. Preferably, the drying time is 3 hours.

[0058] The MXene dispersion and the MWCNTs dispersion were mixed together at a weight ratio of 1:1 and magnetically stirred for 20 minutes to obtain a mixed dispersion.

[0059] The completely dried foam skeleton is immersed in the mixed dispersion for 20 minutes under vacuum to allow the foam skeleton to be fully loaded with conductive particles.

[0060] The foam skeleton soaked in the mixed dispersion was placed in an oven and dried twice at 120°C.

[0061] The foam skeleton is ultrasonically cleaned to remove particles adsorbed on the surface of the foam skeleton.

[0062] The foam skeleton after ultrasonic cleaning is dried to obtain a conductive sensing layer 3.

[0063] Reference Figure 5 , use silver paste to connect the DuPont wire to the interdigital electrode layer 4 to serve as a lead.

[0064] Stick the bottom of the distributed circuit onto the film tape.

[0065] Reference Figure 6 A hole array with a hole radius of 0.4 mm is photoetched on the insulating diaphragm layer 2 using a laser engraving machine. The side with glue is in contact with the electrode and fixed by hot pressing.

[0066] The conductive sensing layer 3 is placed on the insulating diaphragm layer 2 .

[0067] The conductive sensing layer 3 is fixed with a film tape and laminated with the film tape of the bottom layer to obtain a single sensing unit, namely, a flexible foam piezoresistive tactile sensor.

[0068] Reference Figure 2 , Figure 2 The stress-strain curve of the foam is adjusted according to the porosity. Figure 3 , Figure 3 The relationship curve between the drying temperature and the mechanical factors of the foam skeleton is shown in Figure 2. The performance of the flexible foam piezoresistive tactile sensor can be adjusted by the porosity and drying temperature according to actual needs.

[0069] Using soft or stretchable foam as a substrate gives the sensor better flexibility and stretchability, allowing it to fit the human body perfectly. In addition, based on the structure, size and shape of the sensor, high-precision measurement of the surface pressure between the two contact surfaces is achieved, and multi-dimensional pressure imaging can be achieved. By introducing foam materials, the system overcomes the limitations of traditional piezoresistive sensors while maintaining their advantages, improving the applicability and performance of the sensor.

[0070] The flexible foam piezoresistive tactile sensor was tested for sound. Figure 8 Schematic diagram of sound testing of the flexible foam piezoresistive tactile sensor shown.

[0071] The flexible foam piezoresistive tactile sensor was tested cyclically and the following results were obtained: Fig. 9 Schematic diagram of the cyclic test of the flexible foam piezoresistive tactile sensor shown.

[0072] The flexible foam piezoresistive tactile sensor uses a distributed circuit with a proportional amplification circuit to form a sensing unit acquisition circuit. Fig.10 , Fig.10 is a schematic diagram of a distributed circuit; refer to Fig.11 , Fig.11 is a schematic diagram of a distributed circuit interlayer diaphragm; refer to Fig.12 , Fig.12 It is a schematic diagram of the sensor unit acquisition circuit.

[0073] Reference Fig.13 , Fig.13 This is the circuit diagram of the sensor unit acquisition circuit. x Place it between the negative phase terminal of the op amp and the ground, and give V to the positive phase terminal ref The reference voltage is fed through the feedback resistor R f Perform voltage feedback amplification to obtain the op amp output voltage V out The voltage obtained at this time is an analog signal, which is then output as a digital signal through the ADC. The sensor resistance and the op amp output voltage V out The relationship is:

[0074] Positive terminal V ref The voltage is output by a voltage follower composed of a voltage proportional amplifier circuit in the same direction. The voltage follower can play a role in voltage isolation, so that the input signal and the output signal are isolated from each other, thereby improving the stability and anti-interference ability of the circuit and keeping the output voltage stable at V ref In the same-direction proportional amplifier circuit, an analog switch is used to select at the enable end: one end is grounded and the other end is open. The open connection avoids the possibility and accuracy of circuit crosstalk that is easy to occur under ideal conditions. By cyclically controlling the analog switch in each column channel to ground the channel, the AD chip collects the voltage data of the current column in parallel. When the AD chip receives the conversion completion instruction, the channel of the current column is cut off and the channel of the next column is turned on for parallel data collection, achieving the effect of the row-column collection area. In the circuit collection process, the V out Then infer the sensor resistance value. To reduce the error, use the op amp output V out According to the characteristics of piezoresistive sensors, as pressure increases, resistance decreases, and the current flowing through the sensor increases. The current of the sensor is related to the output voltage V out The relationship is as follows:

[0075] At the positive phase terminal V ref and feedback resistor R fUnder the premise of being fixed, the current increases, and the op amp output voltage V out Increases, and then becomes manifested as the voltage change rate across the operational amplifier increases with the increase of pressure, and the resistance change rate of the sensor resistor is obtained.

[0076] The pressure imaging system uses determinant area scanning technology to achieve high-precision detection of the pressure value of the object. The system includes a sensing array, an analog switch circuit, and a pressure analysis processing unit. The sensing array uses piezoresistive foam flexible tactile sensors arranged in a matrix. The sensing array covers a specific area of ​​the object to be detected. Each sensing unit can sense the pressure exerted on it by the object and generate a corresponding pressure value, and sense the pressure changes in different areas in real time. By controlling the conduction state of each analog switch, the sensing array can collect pressure information of each area one by one. The pressure analysis processing unit analyzes the data according to the preset threshold, and the intelligent algorithm accurately measures and records the pressure values ​​of different areas.

[0077] The working process of the pressure imaging system is as follows: the pressure information is collected through the sensing matrix, and the pressure analysis processing unit calculates the partition pressure value of the detection area of ​​the object according to the preset pressure calculation rules and pressure information, and determines the surface pressure distribution according to the preset pressure threshold and the partition pressure value. The surface pressure distribution is presented in the image of the object according to the point position to obtain a real-time response to the dynamic pressure.

[0078] The system determines the contour of the object based on the pressure value of the sensing unit. The sensing unit array is arranged in a matrix shape and can sense the pressure exerted on it by the object. The data processing unit receives the pressure value data, analyzes the contour of the object, considers the position relationship between the sensing units and the pressure distribution change trend, accurately restores the shape of the object, and generates multi-dimensional contour information. Then, the multi-channel data in the area is integrated, and the pressure data is presented in two-dimensional and three-dimensional images according to the point level, realizing real-time response of dynamic pressure.

[0079] The pressure imaging system provides sensor data collection methods, including but not limited to serial port methods. It is also very easy to replace it with other communication modes later. You only need to replace the corresponding code to complete the type conversion. However, when receiving specific data, corresponding adjustments are required. Since the data format transmitted by the hardware cannot be guaranteed, only one method is listed here, and the actual situation can be flexible.

[0080] After the system collects the data from the sensor, it can further classify and process the data. All data can be regionalized, and both fixed points and regions can be changed arbitrarily, so as to achieve the effect of module classification or overall processing. While receiving the data, data can be screened according to actual needs, invalid data can be eliminated, and only valid data can be retained.

[0081] The above is a specific description of the preferred implementation of the present application, but the present application is not limited to the embodiments. Technical personnel familiar with the field can make various equivalent modifications or substitutions without violating the spirit of the present application. These equivalent modifications or substitutions are all included in the scope defined by the claims of the present application.

Claims

1. A flexible foam piezoresistive tactile sensor, characterized in that: include: A conductive sensing layer, an interdigitated electrode layer, an insulating diaphragm layer and a thin film packaging layer; the insulating diaphragm layer is engraved with a hole array; The conductive sensing layer, the interdigital electrode layer and the insulating diaphragm layer are located between the two thin film encapsulation layers, and the conductive sensing layer, the insulating diaphragm layer and the interdigital electrode layer are stacked in sequence.

2. The flexible foam piezoresistive tactile sensor according to claim 1, characterized in that: The insulating membrane layer is made of polyimide, polyester resin, polyvinyl chloride or polyethylene.

3. The flexible foam piezoresistive tactile sensor according to claim 1, characterized in that: The thin film encapsulation layer is made of polyimide, polyester resin, polyvinyl chloride or polyethylene.

4. The flexible foam piezoresistive tactile sensor according to claim 1, characterized in that: The thickness of the insulating membrane layer ranges from 15 μm to 50 μm, and the radius of the holes of the hole array ranges from 0.2 mm to 0.8 mm.

5. The flexible foam piezoresistive tactile sensor according to claim 1, characterized in that: The porosity of the conductive sensing layer ranges from 55% to 78%, and the thickness ranges from 1 mm to 5 mm.

6. The flexible foam piezoresistive tactile sensor according to claim 1, characterized in that: The line width of the interdigital electrode layer ranges from 0.5 mm to 1 mm, and the spacing ranges from 0.5 mm to 1 mm.

7. A pressure imaging system, characterized in that: It comprises a flexible foam piezoresistive tactile sensor and a pressure analysis processing unit as described in any one of claims 1 to 6, wherein the flexible foam piezoresistive tactile sensor is arranged into a sensing matrix; the sensing matrix is ​​used to collect pressure information, and the pressure analysis processing unit is used to obtain a pressure value according to the pressure information.

8. A pressure imaging system according to claim 7, characterized in that: The flexible foam piezoresistive tactile sensor is connected to a proportional amplification circuit.

9. A pressure imaging system according to claim 8, characterized in that: The proportional amplification circuit includes an operational amplifier and a feedback resistor, one end of the flexible foam piezoresistive tactile sensor is connected to the negative phase end of the operational amplifier, the other end of the flexible foam piezoresistive tactile sensor is grounded, one end of the feedback resistor is connected to the negative phase end of the operational amplifier, and the other end of the feedback resistor is connected to the output end of the operational amplifier.

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