Three-dimensional tactile sensor with asymmetric structure and method for manufacturing same

Abstract

The application belongs to the field of tactile sensors, and relates to a three-dimensional tactile sensor with an asymmetric structure and a preparation method thereof. The three-dimensional tactile sensor comprises, from top to bottom, an upper packaging layer, an upper electrode, a medium layer, a lower electrode and a lower packaging layer. The number of the upper electrode is one, the upper electrode is a common electrode, and the upper electrode is a square electrode. The number of the lower electrode is three, including a first lower electrode, a second lower electrode and a third lower electrode. The three lower electrodes are square electrodes, and the side lengths of the three lower electrodes are equal. The side length of the upper electrode is greater than the side length of a single lower electrode. When the three-dimensional tactile sensor works, the three lower electrode plates are fixed and immovable, and the upper electrode moves after being stressed. According to the electrode arrangement of the three-dimensional tactile sensor and in combination with displacement data of the upper electrode after being stressed, the size and direction of a tangential force and the size of a Z-direction force applied to the upper electrode are calculated and obtained.

Description

Technical Field

[0001] This invention belongs to the field of tactile sensor technology, specifically relating to an asymmetric three-dimensional tactile sensor and its fabrication method. Background Technology

[0002] Regarding the dimension of force detection by sensors, research on single-dimensional force is currently extensive and mature:

[0003] Wo Hualei of Zhejiang University (Wo Hualei. Design and fabrication of capacitive three-dimensional force flexible tactile sensor [D]. Zhejiang University, 2019.) proposed a cross-shaped upper and lower capacitor plate pair structure to address the issues of interlayer alignment deviation and the slight offset of the upper capacitor plate relative to the lower capacitor plate during measurement. In this design, each individual capacitor plate is rectangular, and the facing area of ​​the upper and lower capacitor plates is square, with equal area margins in each of the four tangential directions (+x, X, y, y). The drawback is that this three-dimensional sensor can only measure the magnitude and direction of the force in the Z-direction or tangential direction, and cannot truly achieve three-dimensional force detection, i.e., simultaneously measuring the direction and magnitude of any force. The structure and working principle are also complex.

[0004] The research group of Cheng-Yao Luo (Ochtar Chandra, Da-Jeng Yao, Rongshun Chen, Cheng-Yao Lo. Spatial resolution maximization for capacitive tactile sensors[C].MEMS2016:881-884.) has done a lot of research on the design and arrangement of asymmetric capacitor plates. They used rectangular capacitor plates with staggered upper and lower layers to replace the traditional square capacitor plate structure. However, the electrode plate arrangement in this technology has defects, requiring eight electrode plates to meet the requirements.

[0005] Zhang Shuyan (Zhang Shuyan, Zhang Jinhong, Zhao Lirui. Design of a simple capacitive three-dimensional force flexible tactile sensor [J]. Electronic Devices, 2018, 41(1):5.) proposed a sensor structure. This structure comprises three layers: the first layer is a sensing electrode soldered onto a printed circuit board (PCB); the second layer is an insulating material that provides an air gap; and the top layer is a flexible hemispherical object composed of two parts of silicone rubber with a dielectric constant of 3–4. The bottom of the PCB is a ground layer. The disadvantages of this technology are its complex structure, low electrode utilization, and inability to simultaneously measure the magnitude and direction of forces in the Z-direction and tangential directions.

[0006] Wang Can (Wang Can. Fabrication and Signal Acquisition Circuit Design of Flexible Tactile Sensor Based on PDMS) from the University of Electronic Science and Technology of China invented a capacitive sensor. When this capacitive sensor is subjected to a force or force component parallel to the surface of the electrode plate, the dielectric and electrode plate will undergo tangential displacement of different magnitudes due to the different force conditions of each layer of the sensor. This causes the effective area (facing area) between the upper and lower electrode plates of the capacitor to change, and the corresponding capacitance value will also change. To detect the direction of the tangential force, three capacitors are used to reflect the direction of the tangential force. When subjected to a tangential force in a certain direction, the capacitance value of one capacitor can increase, decrease, or remain unchanged. A sensitive unit composed of three capacitors has a total of nine states, which can just reflect the nine directions of the tangential force (no force, force along the positive and negative directions of the X and Y axes, and force not along the X and Y axes). However, this electrode arrangement can only measure the magnitude of the force in the Z direction alone or measure the magnitude and direction of the tangential force alone.

[0007] Based on current development trends, the tactile system of robots must incorporate more comprehensive tactile sensors. The flexible tactile sensors equipped with these sensors should not only be able to detect the magnitude of vertical pressure, but also detect the magnitude of horizontal tangential force when pressure is applied. In this way, when the robot grasps an object, it will receive pressure and tangential force in different directions to determine the shape of the object. Alternatively, when the robot comes into contact with some rough-surfaced materials, it can determine the specific material by the curve relationship between pressure and tangential force. It is clear that the single-dimensional force tactile sensors in the current technology do not meet the requirements.

[0008] Research on flexible tactile three-dimensional force is of great importance and significance for the future of robotics, aerospace, and medical technologies.

[0009] Existing capacitive 3D tactile sensors mainly suffer from the following problems:

[0010] (1) Incomplete functionality: It cannot simultaneously measure the magnitude and direction of the Z-direction force and the tangential force;

[0011] (2) The utilization rate of the electrodes is not high: Although there are many electrodes, the decoupling problem between the tangential force and the Z-direction force has not been truly solved, and the role of each electrode plate has not been fully utilized.

[0012] (3) Complex electrode arrangement: The electrodes are arranged not only horizontally but also vertically, which greatly increases the difficulty of sensor manufacturing.

[0013] (4) Complex electrode arrangement: In order to measure the direction and magnitude of the tangential force, the electrodes need to be arranged in a complex manner when the utilization rate of multiple electrode plates is not high. Summary of the Invention

[0014] To address the aforementioned technical problems, this invention provides an asymmetric three-dimensional tactile sensor and its fabrication method. The three-dimensional tactile sensor provided by this invention, starting from the distribution of the capacitor's electrode plates, combines the electrode arrangement of the three-dimensional tactile sensor with the displacement data of the upper electrode after being subjected to force, enabling simultaneous measurement of the magnitude and direction of the Z-direction force and the tangential force, thus making it a true capacitive three-dimensional force sensor.

[0015] The technical solution adopted in this invention is as follows:

[0016] A three-dimensional tactile sensor with an asymmetric structure, the three-dimensional tactile sensor comprising: an upper encapsulation layer, an upper electrode, a dielectric layer, a lower electrode, and a lower encapsulation layer arranged from top to bottom;

[0017] The number of upper electrodes is one, which is a common electrode, and the upper electrode is a square electrode; the number of lower electrodes is three, including a first lower electrode, a second lower electrode, and a third lower electrode; all three lower electrodes are square electrodes, and the side lengths of the three lower electrodes are equal; the side length of the upper electrode is greater than the side length of a single lower electrode.

[0018] The first lower electrode and the third lower electrode are horizontally parallel, and the second lower electrode and the third lower electrode are vertically parallel;

[0019] When the three-dimensional tactile sensor is working, the three lower electrode plates are fixed at the bottom, and the upper electrode moves after being subjected to force. Based on the electrode arrangement of the three-dimensional tactile sensor and the displacement data of the upper electrode after being subjected to force, the magnitude of the longitudinal force applied to the upper electrode, i.e., the Z-direction force, and the magnitude and direction of the tangential force applied to the upper electrode are calculated.

[0020] Furthermore, the initial electrode arrangement of the three-dimensional tactile sensor is specifically as follows:

[0021] The distance between the first lower electrode and the third lower electrode and the distance between the second lower electrode and the third lower electrode are equal, each being half the side length of a single lower electrode;

[0022] The distance between the upper boundary of the third lower electrode and the first lower electrode and the upper boundary of the upper electrode is equal to half the side length of a single lower electrode; the distance between the left boundary of the third lower electrode and the second lower electrode and the left boundary of the upper electrode is equal to half the side length of a single lower electrode; the first lower electrode and the second lower electrode are respectively bisected by the right boundary and the lower boundary of the upper electrode;

[0023] The distances between the upper boundary of the upper electrode, the left boundary of the upper electrode, the right boundary of the first lower electrode, the lower boundary of the second lower electrode, and the boundary of the encapsulation layer are all equal to half the side length of a single lower electrode.

[0024] The side length of the lower electrode ranges from 3mm to 4mm; the side length of the upper electrode is 2.5 times that of the lower electrode.

[0025] In this invention, by limiting the electrode arrangement of the three-dimensional tactile sensor, the electrode efficiency can be improved (using only four electrode plates); with high electrode efficiency, true three-dimensional force detection can be achieved; in this electrode arrangement, the electrode plates are arranged horizontally, which simplifies the manufacturing process; and the electrode arrangement is simple, and the position parameters of the electrode plates are easy to set.

[0026] Furthermore, when the three-dimensional tactile sensor is in operation, the upper electrode can move along the positive and negative x-axis, along the positive and negative y-axis, and along the negative z-axis after being subjected to force.

[0027] The maximum distance the upper electrode can move along the positive x-axis, negative x-axis, positive y-axis, and negative y-axis is equal to half the side length of a single lower electrode.

[0028] Furthermore, the upper encapsulation layer, the lower encapsulation layer, and the dielectric layer are all prepared using polydimethylsiloxane (PDMS) and a crosslinking agent.

[0029] Furthermore, the capacitance between the upper electrode and the first lower electrode is defined as the first capacitor C1, the capacitance between the upper electrode and the second lower electrode is defined as the second capacitor C2, and the capacitance between the upper electrode and the third lower electrode is defined as the third capacitor C3.

[0030] After being subjected to force, the upper electrode produces a downward displacement Δd; the magnitude of the Z-direction force F applied to the upper electrode and the downward displacement Δd are derived using the following formulas:

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037] In the formula: C3 is the initial capacitance value of the third capacitor C3 corresponding to the initial electrode arrangement state; C3′ is the capacitance value of the third capacitor C3 after the upper electrode is subjected to force; ε is the dielectric constant corresponding to the dielectric layer; b is the side length of the lower electrode; d is the electrode plate spacing; F is the longitudinal force, i.e. the magnitude of the force in the Z direction; R(f) is the responsivity; S(f) is the pre-measured longitudinal sensitivity of the three-dimensional tactile sensor, i.e. the responsivity per unit force.

[0038] Furthermore, the method for calculating the magnitude and direction of the tangential force applied to the upper electrode is as follows:

[0039] When the upper electrode is subjected to force, it generates X-direction displacement Δx and Y-direction displacement Δy along the X-axis and Y-axis, respectively; Δx and Δy are derived using the following formulas:

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] In the formula: Δx is the displacement of the upper electrode along the X-axis; Δy is the displacement of the upper electrode along the Y-axis;

[0047] C1 is the initial capacitance value of the first capacitor C1 corresponding to the initial electrode arrangement; C1′ is the capacitance value of the first capacitor C1 after the upper electrode is subjected to force; C2 is the initial capacitance value of the second capacitor C2 corresponding to the initial electrode arrangement; C2′ is the capacitance value of the second capacitor C2 after the upper electrode is subjected to force; b is the side length of the lower electrode, and a is half the side length of the lower electrode, i.e., a=0.5b;

[0048] The magnitude of the tangential force is obtained by measuring the tangential force and displacement response curves corresponding to the three-dimensional tactile sensor in advance.

[0049] Furthermore, the three-dimensional tactile sensor is installed on the surface of the robot's fingers, or on a large area of ​​the robot's body surface.

[0050] A novel method for fabricating a capacitive sensor, used to fabricate the three-dimensional tactile sensor, the method comprising:

[0051] Preparation of upper and lower encapsulation layers: A mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent is dropped onto a spin coater slide. The spin coating speed is adjusted according to the target thickness of the encapsulation layer. After annealing and semi-curing, the upper and lower encapsulation layers are obtained.

[0052] According to the initial electrode arrangement of the three-dimensional tactile sensor, the upper electrode mask and the lower electrode mask are respectively covered on the annealed and semi-cured upper and lower encapsulation layers; the electrode material is selected as nano-silver or graphene-doped nano-silver wire, the electrode material solution is sprayed, and the conductive copper wire is led out.

[0053] Remove the upper electrode mask and the lower electrode mask respectively, and anneal them to cure the upper and lower encapsulation layers.

[0054] A mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent was dropped onto the encapsulation layer on which the electrode had been sprayed. The spin coater was adjusted to a suitable speed to spin coat the dielectric layer. After spin coating was completed, the layer was annealed for semi-curing.

[0055] The lower electrode is aligned with the semi-cured dielectric layer and bonded together to complete the packaging and fabrication of the three-dimensional tactile sensor.

[0056] Furthermore, the method for preparing the mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent is as follows:

[0057] According to the mass ratio of polydimethylsiloxane PDMS: crosslinking agent = (5-15):1, the polydimethylsiloxane PDMS and crosslinking agent are mixed and stirred using a magnetic stirrer. The mixed solution is placed in a vacuum chamber and vacuumed to remove air bubbles in the solution, thereby obtaining the mixed solution of polydimethylsiloxane PDMS and crosslinking agent.

[0058] Furthermore, a pyramid structure is photolithographically etched on the contact surface between the dielectric layer and the upper electrode.

[0059] Beneficial technical effects of the present invention:

[0060] This invention provides a three-dimensional tactile sensor. Based on the electrode arrangement and combined with the displacement data of the upper electrode after being subjected to force, it can simultaneously measure the magnitude and direction of the force in the Z direction and the magnitude and direction of the tangential force, making it a true capacitive three-dimensional force sensor.

[0061] The asymmetric three-dimensional tactile sensor provided by this invention starts from the distribution of the electrode plates of the capacitor. The manufacturing process of the electrode plates of the capacitor is currently quite mature, which can easily realize the simultaneous measurement of the magnitude and direction of the Z-direction force and the tangential force. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the southwest isometric structure of a single three-dimensional tactile sensor in an embodiment of the present invention;

[0063] Figure 2 This is a side view schematic diagram of the three-dimensional tactile sensor in an embodiment of the present invention;

[0064] Figure 3 This is a top view of the three-dimensional tactile sensor in an embodiment of the present invention;

[0065] Figure 4 This is a top view of the three-dimensional tactile sensor array in an embodiment of the present invention;

[0066] Figure 5 This is a schematic diagram showing the position of the upper electrode (C4) in the three-dimensional tactile sensor of this invention after moving the maximum distance along the negative X-axis.

[0067] Figure 6 This is a schematic diagram showing the position of the upper electrode (C4) in the three-dimensional tactile sensor of this invention after moving the maximum distance along the positive X-axis.

[0068] Figure 7 This is a schematic diagram showing the position of the upper electrode (C4) in the three-dimensional tactile sensor of this invention after moving the maximum distance along the negative Y-axis.

[0069] Figure 8 This is a schematic diagram showing the position of the upper electrode (C4) in the three-dimensional tactile sensor of this invention after moving the maximum distance along the positive Y-axis.

[0070] Figure 9 This is a schematic diagram showing the position of the upper electrode (C4) in the three-dimensional tactile sensor according to an embodiment of the present invention after displacement Δx and Δy along the X-axis and Y-axis, respectively;

[0071] Figure 10 This is the stress-strain curve of the three-dimensional tactile sensor in this embodiment of the invention, namely the curve of normal force versus normal displacement;

[0072] Figure 11 This is a simulation diagram of the force and deformation displacement of the upper electrode in the three-dimensional tactile sensor of this invention under a pressure of 10 kPa.

[0073] Figure 12 This is a simulation diagram of the stress and deformation displacement of the dielectric layer in the three-dimensional tactile sensor of this invention under a pressure of 10 kPa.

[0074] Figure 13 This is a simulation diagram of the force and deformation displacement of the lower electrode in the three-dimensional tactile sensor of this invention under a pressure of 10 kPa.

[0075] Figure 14 This is a schematic diagram of the upper electrode displacement when it is not under force in an embodiment of the present invention;

[0076] Figure 15This is a displacement data diagram of the upper electrode under a tangential force of 10 kPa in an embodiment of the present invention.

[0077] Reference numerals: 1. Upper encapsulation layer; 2. Upper electrode; 3. Dielectric layer; 4. Lower electrode; 5. Lower encapsulation layer. Detailed Implementation

[0078] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0079] like Figure 1-4 As shown, an asymmetric three-dimensional tactile sensor includes, from top to bottom, an upper encapsulation layer, an upper electrode, a dielectric layer, a lower electrode, and a lower encapsulation layer.

[0080] The number of upper electrodes (C4) is one, which is a common electrode, and the upper electrode is a square electrode; the number of lower electrodes is three, including a first lower electrode (C1), a second lower electrode (C2), and a third lower electrode (C3); all three lower electrodes are square electrodes, and the side lengths of the three lower electrodes are equal; the side length of the upper electrode is greater than the side length of a single lower electrode; wherein, the upper electrode and the three lower electrodes are respectively connected to an outgoing copper wire;

[0081] The first lower electrode and the third lower electrode are horizontally parallel, and the second lower electrode and the third lower electrode are vertically parallel;

[0082] When the three-dimensional tactile sensor is working, the three lower electrode plates are fixed at the bottom, and the upper electrode moves after being subjected to force. Based on the electrode arrangement of the three-dimensional tactile sensor and the displacement data of the upper electrode after being subjected to force, the magnitude of the longitudinal force applied to the upper electrode, i.e., the Z-direction force, and the magnitude and direction of the tangential force applied to the upper electrode are calculated.

[0083] The electrode arrangement of the three-dimensional tactile sensor is as follows:

[0084] The initial electrode arrangement of the three-dimensional tactile sensor is as follows:

[0085] The distance between the first lower electrode and the third lower electrode and the distance between the second lower electrode and the third lower electrode are equal, each being half the side length of a single lower electrode;

[0086] The distance between the upper boundary of the third lower electrode and the first lower electrode and the upper boundary of the upper electrode is equal to half the side length of a single lower electrode; the distance between the left boundary of the third lower electrode and the second lower electrode and the left boundary of the upper electrode is equal to half the side length of a single lower electrode; the first lower electrode and the second lower electrode are respectively bisected by the right boundary and the lower boundary of the upper electrode;

[0087] The distances between the upper boundary of the upper electrode, the left boundary of the upper electrode, the right boundary of the first lower electrode, the lower boundary of the second lower electrode, and the boundary of the encapsulation layer are all equal to half the side length of a single lower electrode.

[0088] The side length of the lower electrode ranges from 3mm to 4mm; the side length of the upper electrode is 2.5 times that of the lower electrode.

[0089] The above electrode arrangement ensures that when the sensor is working, the upper electrode (common electrode) moves within the normal range to meet the required facing area.

[0090] like Figure 5-8 As shown; in this embodiment, when the three-dimensional tactile sensor is working, the upper electrode can move along the positive and negative x-axis, along the positive and negative y-axis, and along the negative z-axis after being subjected to force;

[0091] The maximum distance the upper electrode can move along the positive x-axis, negative x-axis, positive y-axis, and negative y-axis is equal to half the side length of a single lower electrode.

[0092] In this embodiment, the upper encapsulation layer, the lower encapsulation layer, and the dielectric layer are all prepared using polydimethylsiloxane (PDMS) and a crosslinking agent.

[0093] The reason for choosing PDMS (polydimethylsiloxane) as the material for the encapsulation layer is that PDMS has elasticity, low Young's modulus, excellent electrical insulation, and corrosion resistance. It is a material that can provide a good insulating environment and good sensitivity for capacitors.

[0094] Preferably, the upper encapsulation layer and the lower encapsulation layer are squares with the same side length, and the side length of the upper encapsulation layer and the lower encapsulation layer is 4 times the side length of a single lower electrode.

[0095] In this embodiment, the method for calculating the magnitude of the Z-direction force applied to the upper electrode is as follows:

[0096] Assuming that the deformation of the upper electrode is negligible in the longitudinal and tangential directions, the upper electrode, after being subjected to force, will produce a downward displacement Δd, as follows: Figure 9 As shown, it generates X-direction displacement Δx and Y-direction displacement Δy along the X-axis and Y-axis, respectively;

[0097] The capacitance between the upper electrode and the first lower electrode is defined as the first capacitor C1, the capacitance between the upper electrode and the second lower electrode is defined as the second capacitor C2, and the capacitance between the upper electrode and the third lower electrode is defined as the third capacitor C3.

[0098] The longitudinal sensitivity S(f), tangential force, and displacement response curve of the three-dimensional tactile sensor are pre-measured. Based on the change in the capacitance of the third capacitor, the magnitude of the Z-direction force F applied to the upper electrode and Δd are derived according to the following formula:

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] In the formula: C3 is the initial capacitance value of the third capacitor C3 corresponding to the initial electrode arrangement state; C3′ is the capacitance value of the third capacitor C3 after the upper electrode is subjected to force; ε is the dielectric constant corresponding to the dielectric layer; b is the side length of the lower electrode; d is the electrode plate spacing; F is the longitudinal force, i.e. the magnitude of the force in the Z direction; R(f) is the responsivity; S(f) is the pre-measured longitudinal sensitivity of the three-dimensional tactile sensor, i.e. the responsivity per unit force.

[0106] Assuming negligible deformation of the upper electrode in the longitudinal and tangential directions, the upper electrode, after being subjected to force, generates X-axis displacement Δx and Y-axis displacement Δy, respectively; Δx and Δy are derived using the following formulas:

[0107]

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] In the formula: Δx is the displacement of the upper electrode along the X-axis; Δy is the displacement of the upper electrode along the Y-axis;

[0114] C1 is the initial capacitance value of the first capacitor C1 corresponding to the initial electrode arrangement; C1′ is the capacitance value of the first capacitor C1 after the upper electrode is subjected to force; C2 is the initial capacitance value of the second capacitor C2 corresponding to the initial electrode arrangement; C2′ is the capacitance value of the second capacitor C2 after the upper electrode is subjected to force; b is the side length of the lower electrode, and a is half the side length of the lower electrode, i.e., a=0.5b;

[0115] The magnitude of the tangential force applied to the upper electrode is calculated using the pre-measured tangential force and displacement response curves corresponding to the three-dimensional tactile sensor.

[0116] The magnitude of the tangential force is then determined.

[0117] The dielectric layers prepared with different proportions of polydimethylsiloxane (PDMS) and crosslinking agents exhibit varying properties, but the measurement methods for the longitudinal sensitivity S(f), tangential force, and displacement response curves of the three-dimensional tactile sensor remain the same, as follows:

[0118] (1) Measurement method for longitudinal sensitivity:

[0119] Sensitivity is defined as: the response of a unit force, which is the sensitivity. The response is defined as: the change in capacitance ΔC.

[0120] Therefore, measuring the longitudinal sensitivity requires building a force measurement platform, continuously applying longitudinal force, recording the capacitance value, fitting it, and then differentiating to obtain the longitudinal force sensitivity.

[0121] (2) Method for plotting the response curve of tangential force versus displacement: Mark the upper encapsulation layer of the prepared sensor. The mark is the center of the left side of the upper electrode. Apply an increasing tangential force through the force measuring platform and record the displacement magnitude. Plot the response curve of tangential force versus displacement. At the same time, it can be compared with the simulation to improve the curve.

[0122] In this embodiment, the three-dimensional tactile sensor can be installed on the surface of the robot's fingers or on a large area of ​​the robot's body surface.

[0123] This invention also provides a novel embodiment of a method for fabricating a capacitive sensor, the method comprising:

[0124] Preparation of upper and lower encapsulation layers: A mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent is dropped onto a spin coater slide. The spin coating speed is adjusted according to the target thickness of the encapsulation layer. After annealing and semi-curing, the upper and lower encapsulation layers are obtained.

[0125] According to the electrode arrangement of the three-dimensional tactile sensor, the upper electrode mask and the lower electrode mask are respectively covered on the annealed and semi-cured upper and lower encapsulation layers; the electrode material is selected as nano silver or graphene-doped nano silver, the electrode material solution is sprayed, and the conductive copper wire is led out.

[0126] Remove the upper electrode mask and the lower electrode mask respectively, and anneal them to cure the upper and lower encapsulation layers.

[0127] A mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent was dropped onto the encapsulation layer on which the electrode had been sprayed. The spin coater was adjusted to a suitable speed to spin coat the dielectric layer. After spin coating was completed, the layer was annealed for semi-curing.

[0128] The lower electrode is aligned with the semi-cured dielectric layer and bonded together to complete the packaging and fabrication of the three-dimensional tactile sensor.

[0129] In this embodiment, the method for preparing the mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent is as follows:

[0130] According to the mass ratio of polydimethylsiloxane PDMS: crosslinking agent = (5-15):1, the polydimethylsiloxane PDMS and crosslinking agent were mixed and stirred using a magnetic stirrer. The mixture was then placed in a vacuum chamber and evacuated to remove air bubbles. Note that since PDMS itself cannot cure at room temperature, a crosslinking agent must be added during the PDMS preparation process.

[0131] In this embodiment, PDMS is chosen as the dielectric layer due to its excellent elasticity. A pyramid structure is photolithographically etched on the contact surface between the dielectric layer and the upper electrode to further increase the sensor's sensitivity. The pyramid structure is a microstructure; while ordinary dielectric layers are flat and smooth, photolithographically etched pyramid structures are formed on the surface of the dielectric layer using a photolithography machine to create micron-scale pyramid structures. This reduces the contact area between the dielectric and the electrode, making the electrode more sensitive to force feedback when subjected to tangential and longitudinal forces.

[0132] Finite element simulation of the three-dimensional tactile sensor described in the embodiments of the present invention was performed using Comsol:

[0133] 1) such as Figure 10 The stress-strain curve (longitudinal force strain curve) of PDMS:crosslinker (10:1) is shown. This simulation result is used to prove that the stress-strain relationship of PDMS can be treated as a linear change when the deformation does not exceed 50%.

[0134] 2) such as Figure 11-13The simulation results show the stress and deformation displacement of the three-dimensional tactile sensor under a pressure of 10 kPa. The simulation data demonstrates that under normal stress conditions, the deformation of the upper electrode is negligible; the deformation of the lower electrode is also negligible and can be treated as a rigid body. Table 3-1 shows the specific simulation data.

[0135] Table 3-1

[0136]

[0137] Simulation of the displacement and area change of the upper electrode under a tangential force of 10 kPa: (e.g.) Figure 14-15 Combined with the data in Table 3-2; Figure 14 This is the condition before the force is applied; the horizontal coordinate of the left end is 2mm, and the horizontal coordinate of the right end is 12mm, indicating no deformation. For example... Figure 15 According to Table 3-2, after being subjected to tangential force, the displacement of the left end is 3.8657 × 10⁻⁶. -3 The end displacement is 5.4666 × 10⁻⁶. -3 The deformation is 1.6 × 10⁻⁶. -3 It accounts for 0.016% of the total length.

[0138] Table 3-2 Displacement data of the upper electrode after being subjected to force

[0139]

[0140] The asymmetric three-dimensional tactile sensor provided in this embodiment can be installed on the surface of a robot's finger or on a large area of ​​the robot's body surface. When the flexible sensor interacts with external forces, it reacts to the magnitude and direction of the force through changes in capacitance. It can determine whether the sensor is sliding with the contact surface by using the force information (including magnitude and direction).

[0141] The three-dimensional tactile sensor provided in this embodiment can detect the magnitude and direction of pressure and tangential force. Therefore, when the sensor slides with the contact surface, information on the magnitude of pressure and tangential force can be obtained. The magnitude of friction on the contact surface can be determined by the curve characteristics of pressure and tangential force, and thus the material of the contact surface can be determined.

[0142] Through the above embodiments, flexible electronic skin that realizes tactile sensing function during interaction with the outside world can be applied not only to industrial intelligent manufacturing, but also to medical services, such as intelligent surgery and pathological diagnosis.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A three-dimensional tactile sensor with an asymmetric structure, characterized in that, The three-dimensional tactile sensor includes, from top to bottom, an upper encapsulation layer, an upper electrode, a dielectric layer, a lower electrode, and a lower encapsulation layer; The number of upper electrodes is one, which is a common electrode, and the upper electrode is a square electrode; the number of lower electrodes is three, including a first lower electrode, a second lower electrode, and a third lower electrode; all three lower electrodes are square electrodes, and the side lengths of the three lower electrodes are equal; the side length of the upper electrode is greater than the side length of a single lower electrode. The first lower electrode and the third lower electrode are horizontally parallel, and the second lower electrode and the third lower electrode are vertically parallel; When the three-dimensional tactile sensor is working, the three lower electrode plates are fixed at the bottom, and the upper electrode moves after being subjected to force. Based on the initial electrode arrangement of the three-dimensional tactile sensor and the displacement data of the upper electrode after being subjected to force, the magnitude of the longitudinal force applied to the upper electrode, i.e. the Z-direction force, and the magnitude and direction of the tangential force applied to the upper electrode are calculated. The capacitance between the upper electrode and the first lower electrode is defined as the first capacitor C1, the capacitance between the upper electrode and the second lower electrode is defined as the second capacitor C2, and the capacitance between the upper electrode and the third lower electrode is defined as the third capacitor C3. When the upper electrode is subjected to force, it undergoes a downward displacement. The Z-direction force applied to the upper electrode is derived using the following formula. The size of the displacement and the downward displacement. : ； ； ； ； ； ； In the formula: The initial capacitance value of the third capacitor C3 is given by the initial electrode arrangement. This is the capacitance value of the third capacitor C3 after the upper electrode is subjected to force; The dielectric constant is the dielectric constant corresponding to the dielectric layer; This is the side length of the lower electrode; The distance between the electrode plates; R(f) represents the longitudinal force, i.e., the magnitude of the force in the Z direction; R(f) represents the responsiveness; S(f) represents the pre-measured longitudinal sensitivity of the three-dimensional tactile sensor, i.e., the responsiveness per unit force.

2. The asymmetric three-dimensional tactile sensor according to claim 1, characterized in that, The initial electrode arrangement of the three-dimensional tactile sensor is as follows: The distance between the first lower electrode and the third lower electrode and the distance between the second lower electrode and the third lower electrode are equal, each being half the side length of a single lower electrode; The distance between the upper boundary of the third lower electrode and the first lower electrode and the upper boundary of the upper electrode is equal to half the side length of a single lower electrode; the distance between the left boundary of the third lower electrode and the second lower electrode and the left boundary of the upper electrode is equal to half the side length of a single lower electrode; the first lower electrode and the second lower electrode are respectively bisected by the right boundary and the lower boundary of the upper electrode; The distances between the upper boundary of the upper electrode, the left boundary of the upper electrode, the right boundary of the first lower electrode, the lower boundary of the second lower electrode, and the boundary of the encapsulation layer are all equal to half the side length of a single lower electrode. The side length of the lower electrode ranges from 3mm to 4mm; the side length of the upper electrode is 2.5 times that of the lower electrode.

3. The asymmetric three-dimensional tactile sensor according to claim 2, characterized in that, When the three-dimensional tactile sensor is working, the upper electrode can move along the positive and negative x-axis, the positive and negative y-axis, and the negative z-axis after being subjected to force. The maximum distance the upper electrode can move along the positive x-axis, negative x-axis, positive y-axis, and negative y-axis is equal to half the side length of a single lower electrode.

4. The asymmetric three-dimensional tactile sensor according to claim 1, characterized in that, The upper encapsulation layer, the lower encapsulation layer, and the dielectric layer are all prepared using polydimethylsiloxane (PDMS) and a crosslinking agent.

5. The asymmetric three-dimensional tactile sensor according to claim 1, characterized in that, The method for calculating the magnitude and direction of the tangential force applied to the upper electrode is as follows: When subjected to force, the upper electrode undergoes X-direction displacement along the X-axis and Y-axis, respectively. and Y-axis displacement Δx and Δy are derived using the following formulas: ； ； ； ； ； ； In the formula: The displacement of the upper electrode along the X-axis; The displacement of the upper electrode along the Y-axis; The initial capacitance value of the first capacitor C1 corresponding to the initial electrode arrangement state; This is the capacitance value of the first capacitor C1 after the upper electrode is subjected to force; The initial capacitance value of the second capacitor C2 corresponding to the initial electrode arrangement state; This is the capacitance value of the second capacitor C2 after the upper electrode is subjected to force; The length of the lower electrode side. It is half the side length of the lower electrode, i.e., a = 0.5b; The magnitude of the tangential force is obtained by measuring the tangential force and displacement response curves corresponding to the three-dimensional tactile sensor in advance.

6. The asymmetric three-dimensional tactile sensor according to claim 1, characterized in that, The three-dimensional tactile sensor is installed on the surface of the robot's fingers or on a large area of ​​the robot's body surface.

7. A method for fabricating a capacitive sensor, used to fabricate the three-dimensional tactile sensor according to any one of claims 1-6, characterized in that, The method includes: Preparation of upper and lower encapsulation layers: A mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent is dropped onto a spin coater slide. The spin coating speed is adjusted according to the target thickness of the encapsulation layer. After annealing and semi-curing, the upper and lower encapsulation layers are obtained. According to the initial electrode arrangement of the three-dimensional tactile sensor, the upper electrode mask and the lower electrode mask are respectively covered on the annealed and semi-cured upper and lower encapsulation layers; the electrode material is selected as nano-silver or graphene-doped nano-silver wire, the electrode material solution is sprayed, and the conductive copper wire is led out. Remove the upper electrode mask and the lower electrode mask respectively, and anneal them to cure the upper and lower encapsulation layers. A mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent was dropped onto the encapsulation layer on which the electrode had been sprayed. The spin coater was adjusted to a suitable speed to spin coat the dielectric layer. After spin coating was completed, the layer was annealed for semi-curing. The lower electrode is aligned with the semi-cured dielectric layer and bonded together to complete the packaging and fabrication of the three-dimensional tactile sensor.

8. The method for fabricating a capacitive sensor according to claim 7, characterized in that, The method for preparing the mixed solution of polydimethylsiloxane (PDMS) and crosslinking agent is as follows: According to the mass ratio of polydimethylsiloxane PDMS: crosslinking agent = (5-15):1, the polydimethylsiloxane PDMS and crosslinking agent are mixed and stirred using a magnetic stirrer. The mixed solution is placed in a vacuum chamber and vacuumed to remove air bubbles in the solution, thereby obtaining the mixed solution of polydimethylsiloxane PDMS and crosslinking agent.

9. The method for fabricating a capacitive sensor according to claim 7, characterized in that, A pyramid structure was photolithographically formed at the interface between the dielectric layer and the upper electrode.

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