CN108613758A - A kind of capacitance type touch sensor based on zero Poisson's ratio structure - Google Patents

Abstract

The invention discloses a capacitive touch sensor based on a zero Poisson's ratio structure, which comprises an upper electrode layer, a lower electrode layer and a dielectric layer with a zero Poisson's ratio structure between the two electrode layers; the zero Poisson's ratio structure The dielectric layer is composed of several cellular structures; the cellular structures are arranged in an array, and the upper surface of the cellular structure of the top layer is a layer of smooth and flexible photosensitive resin layer, which is used to connect with the upper electrode layer; The lower surface of the structure is a layer of smooth flexible photosensitive resin layer, which is used to connect with the lower electrode layer; the longitudinal section of each cell structure is a convex structure, and the lower bottom surface of the convex structure is concave; the outer cell wall of the cell structure The included angle with the vertical direction is always α; when the sensor is stimulated by positive pressure, since the value of α is always constant, the transverse strain perpendicular to the load direction is always zero, and only the strain in the load direction is generated, which is equivalent to Poisson ratio is always zero.

Description

A Capacitive Tactile Sensor Based on Zero Poisson's Ratio Structure

technical field

The invention relates to a tactile sensor, in particular to a capacitive tactile sensor based on a zero Poisson's ratio structure for measuring positive pressure.

Background technique

The tactile sensor is an essential medium for the robot to directly interact with the external environment. It can directly measure various properties of objects and environments. With the progress of human life, the cooperation between robots and humans is getting closer and closer, and the research on robots is getting deeper and deeper. Giving them corresponding vision and touch is of great significance to achieve better cooperation between robots and humans. At present, the development of vision is relatively mature, but the development of touch is still under continuous research and development. The sense of touch is particularly important to realize the intelligence of the robot, and it will directly reflect various information of the surrounding environment to the robot. However, the tactile skin sensor currently studied is mainly used to sense mechanical external force and lacks flexibility.

Existing studies have shown that adding different forms of microstructures in the dielectric layer improves the sensitivity of the tactile sensor due to its mechanical properties under tactile stimuli. At present, most of the dielectric layer materials used are polydimethylsiloxane (PDMS), and the liquid-solid conversion characteristics of PDMS materials are used to realize different structure preparations. However, as the raw material for the production of the dielectric layer of the electronic skin, the PDMS material is not soft enough. The dielectric layer printed by flexible photosensitive resin has better softness.

The document with the application number 201610644815.2 discloses a sandwich-type flexible capacitive pressure sensor and its preparation method. The processing and preparation method of the pressure sensor is complicated, and multi-electrode capacitance is used at the same time, which will produce a high signal-to-noise ratio, and the influence of parasitic capacitance is relatively large. Large, and the method of binding silver paste is used as the lead, which requires high processing technology and is not easy to process on a large scale.

Contents of the invention

Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a capacitive touch sensor based on a zero Poisson's ratio structure.

The technical solution of the present invention to solve the technical problem is to provide a capacitive tactile sensor based on a zero Poisson's ratio structure, which is characterized in that the sensor includes an upper electrode layer, a lower electrode layer and a zero Poisson's ratio between the two electrode layers. Dielectric layer with a loose ratio structure; the dielectric layer with a zero Poisson’s ratio structure is composed of several cellular structures; the cellular structures are arranged in an array, and the upper surface of the cellular structure on the top layer is a smooth layer of flexible photosensitive resin layer, used to connect with the upper electrode layer; the lower surface of the bottom cell structure is a layer of smooth flexible photosensitive resin layer, used to connect with the lower electrode layer; the longitudinal section of each cell structure is a convex structure, convex The bottom surface of the glyph structure is sunken; the angle between the outer cell wall of the cell structure and the vertical direction is constant; when the sensor is stimulated by positive pressure, the value of the angle is always constant.

Compared with the prior art, the present invention has the beneficial effects of:

1. The dielectric layer in the middle is made of flexible photosensitive resin, which is printed by photocuring technology and has a certain degree of flexibility. Through reasonable structural design, Poisson's ratio is zero, and when positive pressure is detected, the lateral strain is reduced. To avoid the error caused by lateral strain on the analysis of force, its mechanical characteristics will effectively improve the sensitivity of the sensor, convert the pressure into capacitance to the maximum extent, measure the capacitance more accurately, and improve the pressure detection accuracy.

2. The design of the zero Poisson's ratio structure is determined by the definition of Poisson's ratio ν=-ει/ε, where ν represents Poisson's ratio, which is defined as the absolute value ratio of the transverse normal strain ει to the axial normal strain ε. Therefore, the transverse normal strain needs to be zero and only the longitudinal strain is required, so that the detection accuracy and sensitivity of the tactile sensor can be improved.

3. The upper and lower electrode layers of the sensor and the dielectric layer are integral structures, which reduces the measurement error caused by the poor sealing and bonding between the three-layer structures.

Description of drawings

Fig. 1 is the overall structure schematic diagram of an embodiment of the capacitive touch sensor based on zero Poisson's ratio structure of the present invention;

2 is a schematic diagram of a dielectric layer structure of an embodiment of a capacitive tactile sensor based on a zero Poisson's ratio structure of the present invention;

3 is a schematic axonometric view of the cell structure of the dielectric layer of an embodiment of the capacitive touch sensor based on the zero Poisson's ratio structure of the present invention;

4 is a schematic front view of the cell structure of the dielectric layer of an embodiment of the capacitive touch sensor based on the zero Poisson's ratio structure of the present invention;

Fig. 5 is the schematic diagram of the cell principal view structural parameters of the dielectric layer of an embodiment of the capacitive touch sensor based on the zero Poisson's ratio structure of the present invention; (in the figure: 1, upper electrode layer; 2, zero Poisson's ratio Structural dielectric layer; 3, lower electrode layer);

Detailed ways

Specific examples of the present invention are given below. The specific embodiments are only used to further describe the present invention in detail, and do not limit the protection scope of the claims of the present application.

The present invention provides a capacitive tactile sensor based on a zero Poisson's ratio structure (see Fig. 1-5, referred to as the sensor), which is used to measure the magnitude of positive pressure, and is characterized in that the sensor includes an upper electrode layer 1, a lower electrode layer 3 and a zero Poisson's ratio structure dielectric layer 2 located between the two electrode layers; the zero Poisson's ratio structure dielectric layer 2 is composed of several cellular structures 21; the cellular structures 21 are arranged in an array, and the top layer The upper surface of the cellular structure 21 is a smooth flexible photosensitive resin layer, which is used to connect with the upper electrode layer 1 by screen printing technology; the lower surface of the underlying cellular structure 21 is a smooth flexible photosensitive resin layer , used to connect with the lower electrode layer 3 by screen printing technology; the longitudinal section of each cell structure 21 is similar to a convex structure, and the lower bottom surface of the convex structure is concave; the angle between the upper part of the convex structure and the vertical direction Always be α, that is, the angle between the outer cell wall of the cellular structure 21 and the vertical direction is always α, and the cell wall ratio coefficient is K=M/L (wherein M represents the length of the inner cell wall, and L represents the length of the outer cell wall, K is a constant value); when the sensor is stimulated by positive pressure, since the value of α is always constant, the strain perpendicular to the load direction is always zero, that is, the transverse strain is zero, so that the load on the sensor only produces the strain in the load direction , that is, the pressure can be completely converted into a change in capacitance, satisfying that the equivalent Poisson's ratio is always zero.

Converting the Poisson's ratio formula ν=-ει/ε into the equivalent Poisson's ratio formula containing only α and K is: Among them, cosα>1/2K; when K≤0.5, 0<α<arcsinK; when K>0.5, arccos(1/2k)<α<arcsinK; under this precondition, let K=0.5, μ=0 Bring into the equivalent Poisson's ratio formula to obtain α=27° (α takes 0-30°); so under this condition, when α=27°, the equivalent Poisson's ratio of the cellular structure is 0;

Both the upper electrode layer 1 and the lower electrode layer 3 are based on a flexible resin, and a layer of graphene conductive film is coated on the flexible substrate to form a conductive graphene electrode;

The dielectric layer 2 with zero Poisson's ratio structure is made of flexible photosensitive resin, and is 3D printed by photocuring technology to obtain a microstructure with an equivalent Poisson's ratio of zero.

The thickness of the sensor is 5mm±1mm.

The working principle and work flow of the capacitive tactile sensor based on the zero Poisson's ratio structure of the present invention are:

When the sensor is stimulated by positive pressure, the strain generated by the compression increases continuously, the upper electrode layer 1 is deformed, and the dielectric layer 2 of the zero Poisson's ratio structure is deformed, but the structural particularity of the cellular structure 21 makes neither There will be lateral expansion and no lateral contraction, only longitudinal compression, the equivalent Poisson's ratio of the zero Poisson's ratio structure dielectric layer 2 is zero, and the distance between the upper electrode layer 1 and the lower electrode layer 3 Since the material of the dielectric layer 2 of the zero Poisson's ratio structure is flexible resin, its modulus of elasticity is constant, so the generated deformation is proportional to the pressure. According to the principle of the capacitive touch sensor, the distance between the parallel plates will affect the capacitance change, so that the pressure change can be converted into the capacitance change, and the pressure can be determined by measuring the capacitance change. When the external detection circuit collects capacitance signals, since the distance between the upper electrode layer 1 and the lower electrode layer 3 changes, the capacitance will change accordingly, thereby detecting the change of pressure.

During the experiment, place a 20g weight on the sensor, lead out the electrode through the wire, connect it to the terminal of the data acquisition card of the industrial computer of NI Company, perform program control in the Labview environment, and realize the capacitance measurement through the data acquisition card. signal collection. A positive pressure is applied to the sensor by using a digital display tension and pressure testing machine, and the collected capacitance and pressure are calibrated, so as to realize the detection of pressure. The size of the sensor is 100*100*5mm, the model of the data acquisition card is NI PXI-6251, the model of the industrial computer is NI PXIe-1065, and the model of the digital tensile tester is ZQ-21B-1.

What is not mentioned in the present invention is applicable to the prior art.

Claims (5)

1. A capacitive touch sensor based on a zero Poisson's ratio structure, characterized in that the sensor comprises an upper electrode layer, a lower electrode layer and a zero Poisson's ratio structure dielectric layer positioned between two electrode layers; said zero Poisson's ratio The dielectric layer of the Songbi structure is composed of several cellular structures; the cellular structures are arranged in an array, and the upper surface of the cellular structure of the top layer is a layer of smooth flexible photosensitive resin layer, which is used to connect with the upper electrode layer; the bottom layer The lower surface of the cellular structure is a layer of smooth flexible photosensitive resin layer, which is used to connect with the lower electrode layer; the longitudinal section of each cellular structure is a convex structure, and the lower bottom surface of the convex structure is concave; the cellular structure The angle between the outer cell wall and the vertical direction is a constant value; when the sensor is stimulated by positive pressure, the value of the angle remains unchanged. 2. the capacitive tactile sensor based on zero Poisson's ratio structure according to claim 1, is characterized in that Poisson's ratio formula v=-ει/ε is transformed into the equivalent Poisson's ratio formula that only contains α and K as : Among them, the cell wall ratio coefficient K=M/L, M represents the length of the inner cell wall, L represents the length of the outer cell wall, and K is a fixed value; cosα>1/2K; when K≤0.5, 0<α<arcsinK; when K When >0.5, arccos(1/2k)<α<arcsinK; under this precondition, let K=0.5, μ=0 into the equivalent Poisson’s ratio formula, and get α=27°; so under this condition, When α=27°, the equivalent Poisson's ratio is 0. 3. The capacitive touch sensor based on zero Poisson's ratio structure according to claim 1, characterized in that the upper electrode layer and the lower electrode layer are all based on flexible resin, and one layer of graphene is coated on the flexible substrate Conductive films to form conductive graphene electrodes. 4. The capacitive tactile sensor based on a zero Poisson's ratio structure according to claim 1, wherein the dielectric layer of the zero Poisson's ratio structure is made of a flexible photosensitive resin, which is equivalent to obtained by 3D printing using photocuring technology. A microstructure with a Poisson's ratio of zero. 5. The capacitive tactile sensor based on a zero Poisson's ratio structure according to claim 1, characterized in that the thickness of the sensor is 5mm±1mm.