A flexible three-dimensional force capacitive sensor for humanoid robot force feedback scenarios

Abstract

The application discloses a flexible three-dimensional force capacitance sensor for a humanoid robot force feedback scene, and mainly relates to a haptic sensing technology, and aims to solve the problems of low sensitivity and nonlinear output of a haptic sensor. The sensor comprises an elastic body convex point contactor on a top layer, an air cavity layer and an elastic body layer on a middle layer, a printed circuit board and a unit capacitor on a bottom layer. Through electrode layout and multi-layer elastic body design, the detection and decoupling of normal force and shear force are realized. The sensor is manufactured by using 3D printing manufacturing technology and rapid prototyping technology, has high sensitivity, low hysteresis and good repeatability, and can be applied to a robot force feedback scene.

Description

Technical Field

[0001] This invention belongs to the field of tactile sensing technology, specifically relating to a flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots, mainly applied to force feedback scenarios in humanoid robots. Background Technology

[0002] The primary function of flexible sensors is to sense external signals, mimicking the tactile sensation of skin contacting the outside world. They have wide applications in robotics, human-computer interaction, and automated equipment. The core function of flexible pressure sensors is to accurately detect force signals applied to the sensor surface, including normal and shear forces, providing reliable tactile feedback to the equipment so that the machine can make adjustments and ensure operational accuracy.

[0003] Existing multidimensional force detection tactile force sensors employ piezoelectric, piezoresistive, inductive, magnetic, and capacitive sensing mechanisms, but all have significant drawbacks: piezoelectric sensors can only detect dynamic forces and require periodic calibration; piezoresistive sensors suffer from poor output consistency and high temperature sensitivity; inductive sensors exhibit poor dynamic response and low long-term reliability; and among traditional capacitive sensors, those with overlapping area have low sensitivity. Furthermore, some high-performance sensors are costly to manufacture, hindering large-scale application. Summary of the Invention

[0004] The purpose of this invention is to provide a flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots, addressing the problems of low sensitivity, poor stability, or high cost inherent in existing sensors. This invention, through the structure and symmetrical layout of the electrode plates, enables the sensor to possess high sensitivity, three-dimensional force detection, and good stability, meeting the application requirements of practical sensing scenarios.

[0005] The technical solution adopted in this invention is as follows: A flexible three-dimensional force-capacitance sensor for force feedback in humanoid robots comprises, from top to bottom, a top layer structure, a middle layer structure, and a bottom layer structure: The top-layer structure includes an elastomer bump contact; The intermediate layer structure includes an air cavity layer and an elastomer layer, with the elastomer layer located above the air cavity layer; The underlying structure includes a printed circuit board, on which multiple unit capacitors are provided; In this system, the air cavity layer and the elastomer layer together serve as the dielectric of multiple unit capacitors. When subjected to external force, the change in the thickness of the air cavity layer leads to a change in the dielectric constant, which in turn causes a change in the capacitance of the unit capacitor. By detecting the change in capacitance, the measurement and decoupling of normal force and shear force can be achieved.

[0006] Furthermore, for the top layer structure, octagonal silicone rubber elastomer bump contacts are used. The octagonal structure design allows force to be applied evenly to the sensor surface from different directions. Moreover, the Young's modulus of the silicone rubber elastomer is higher than that of the elastomer in the middle layer, thus external force can be effectively transmitted to the elastomer, improving force transmission efficiency.

[0007] Furthermore, in the intermediate layer structure, the air cavity layer is encased in an elastomer layer. The air cavity layer and the elastomer layer together serve as the dielectric of the capacitor. Under external force, the thickness of the air cavity layer changes due to the elastic deformation of the elastomer.

[0008] Furthermore, regarding the underlying structure: the FR4 printed circuit board, multiple pairs of independent electrodes are arranged on the board, each pair including an inner excitation electrode and an outer sensing electrode. This electrode arrangement enhances the edge electric field effect of the capacitive sensor, improving its sensitivity. Under external force, the proportion of electric field lines passing through the air cavity layer and the elastomer layer changes according to the thickness of the air cavity, leading to a change in the dielectric constant, which in turn changes the capacitance. By detecting the capacitance changes of the four unit capacitors, the detection and decoupling of normal and shear forces can be achieved.

[0009] Furthermore, the overall size of the sensor is 10mm×10mm×12mm, which is relatively small and suitable for environments with limited working space. The total area of ​​each capacitor is 2.4mm×2.4mm, the area of ​​the inner sensing electrode is 1.2mm×1.2mm, the width of the outer excitation electrode is 0.5mm, and the distance between the inner and outer electrodes is 0.1mm. This size effectively reduces the space occupied by the electrodes while ensuring the sensitivity of the sensor. The height of the air cavity is 1mm, at which the sensor has a good linear output response under external force.

[0010] Furthermore, the preparation process of the silicone rubber elastomer is as follows: silicone rubber is thoroughly mixed with a curing agent at a volume ratio of 1%, stirred for 3 minutes to fully degas, and then poured into a 3D-printed mold. After curing at room temperature for 24 hours, the mold is peeled off. The preparation process of the Ecoflex elastomer is the same as that of the silicone rubber elastomer. This preparation process uses 3D printing technology for the mold and rapid prototyping technology for the elastomer, which can reduce manufacturing costs and ensure the performance stability of the elastomer.

[0011] Furthermore, the electrodes on the printed circuit board are made using traditional PCB manufacturing processes, and the various layers of the sensor are assembled and fixed using cyanoacrylate adhesive. This adhesive has high bonding strength and fast curing speed, which can ensure the stability and durability of the overall sensor structure.

[0012] Furthermore, to enhance the sensor's anti-interference capability, a grounded flexible metal coating is provided below the printed circuit board, between the Ecoflex elastomer and the bumps. This flexible metal coating is prepared using inkjet printing technology. The shielding structure effectively isolates the sensor output from the influence of the external environment, improving the sensor's operational reliability.

[0013] The nominal capacitance of a sensor can be calculated using the following formula:

[0014]

[0015] in, For nominal capacitance without considering the height of the air cavity, The nominal capacitance takes into account the height of the air cavity; The dielectric constant of air is . The dielectric constant of the elastic body; The width of the sensing electrode. The length of the sensing electrode side. The distance between the sensing electrode and the excitation electrode; This represents the ratio of electrode length to width. This characterizes the ratio of electrode spacing to length. The height of the air cavity; , and These are parameters related to geometry. , and It can be obtained by fitting experimental data and can accurately estimate the nominal capacitance under different electrode sizes and air cavity heights.

[0016] The capacitance changes of the four unit capacitors under forces acting in different directions follow a pattern. The decoupled calculation of the three-dimensional forces can be achieved using the following formula: Changes in normal force capacitance:

[0017] x-axis shear capacitance variation:

[0018] y-axis shear capacitance variation:

[0019] Changes in shear capacitance at a 45° angle:

[0020] Changes in shear capacitance at a 135° angle:

[0021] Changes in shear capacitance at 225° angle:

[0022] Changes in shear capacitance at 315° angle:

[0023] in, , , , These represent the normalized capacitance changes of the four unit capacitors. Using the above formula, normal, shear, and angular shear forces at different angles can be directly distinguished, achieving three-dimensional force detection and decoupling. Furthermore, the relationship between capacitance change and the magnitude of external force can be estimated.

[0024] Furthermore, the printed circuit board is provided with multiple independent sensing electrodes, and each sensing electrode is surrounded by an excitation electrode. One sensing electrode and its corresponding excitation electrode constitute a unit capacitor.

[0025] Furthermore, after the electrode is subjected to voltage, an edge field effect is generated between the excitation electrode and the induction electrode. According to the change in the thickness of the air cavity layer, the proportion of electric field lines passing through the air cavity layer and the elastic body layer changes, resulting in a change in the dielectric constant, which in turn changes the capacitance of the unit capacitor.

[0026] Furthermore, the multiple unit capacitors on the printed circuit board are axially and centrally symmetrically distributed.

[0027] Furthermore, the sensor is installed on the parts of the humanoid robot that require force feedback. The sensor detects changes in capacitance during the contact process and transmits the force feedback signal to the computer to adjust the force and avoid applying too much or too little force.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) Three-dimensional force detection and decoupling: The layout of multiple sensing electrodes and multiple surrounding excitation electrodes, and the structure of the elastic body layer and the air cavity layer, realize the detection and decoupling of normal force and shear force.

[0029] 2) Strong anti-interference capability: By setting up a grounded flexible metal coating shielding structure, it effectively isolates external environmental interference.

[0030] 3) Simple manufacturing: The elastomer is prepared using 3D printed molds, and the electrodes are manufactured using traditional PCB manufacturing processes.

[0031] 4) Small size and compact structure: The overall size of the sensor is small (e.g., 10mm×10mm×12mm) and the structure is compact. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic diagram illustrating the working principle of the sensor in an embodiment of the present invention; Figure 2 This is a schematic diagram of the sensor structure in an embodiment of the present invention; Figure 3 This is a schematic diagram of the sensor electrode structure in an embodiment of the present invention; Figure 4 This is a schematic cross-sectional view of the sensor structure in an embodiment of the present invention; Figure 5 This is a schematic diagram of the deformation of the sensor under normal force in an embodiment of the present invention; Figure 6 This is a schematic diagram of the deformation of the sensor under shear force in an embodiment of the present invention.

[0033] Wherein: 1 is a silicone rubber elastomer bump contact, 2 is an Ecoflex elastomer layer, 3 is an air cavity layer, 4 is a printed circuit board, 41 is a circuit board, 42 is an excitation electrode, and 43 is a sensing electrode. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] like Figure 1 As shown in the figure, this invention provides a flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots, utilizing the edge field effect of capacitance to achieve three-dimensional force detection. When a voltage is applied to the excitation electrode, an edge electric field is generated between the sensing electrode and the excitation electrode, and the electric field lines pass through the intermediate dielectric layer. Under the action of the normal force, the distribution of the intermediate dielectric layer changes, the air layer is compressed as a whole, the proportion of electric field lines passing through the elastic body increases, causing a change in the dielectric constant and a regular increase in capacitance. The direction and magnitude of the force are decoupled by detecting the difference in the changes of the four unit capacitors.

[0036] like Figures 2-4 As shown, the flexible three-dimensional force-capacitance sensor has a flexible multilayer structure, comprising, from top to bottom: The top load-bearing layer, or top structure, includes an octagonal silicone rubber elastomer protrusion contact 1 with a diameter of 5mm and a height of 2mm, used to uniformly transmit external force. The intermediate dielectric layer, or intermediate layer structure, comprises a 1mm thick Ecoflex elastomer layer 2 and an air cavity layer 3 with an initial height of 1mm. The Ecoflex elastomer layer 2 is located above the air cavity layer 3, and the Young's modulus of the silicone rubber elastomer bump contact 1 is greater than that of the Ecoflex elastomer layer 2. The difference in dielectric constant between the Ecoflex elastomer layer 2 and air is the core sensing mechanism for capacitance changes. Besides using Ecoflex elastomer, other elastic insulating materials with high dielectric constants, such as PDMS and PVDF, can also be used in other embodiments. The bottom electrode layer, or bottom structure, includes an FR4 printed circuit board. Four symmetrically distributed unit capacitors, each 0.1 mm high, are integrated on the circuit board 41 of the FR4 printed circuit board 4. The circuit board 4 has four independent square sensing electrodes 43, each surrounded by an excitation electrode 42. Each sensing electrode and its corresponding excitation electrode 42 constitutes a unit capacitor. The four unit capacitors are denoted as follows: , , , ; In the bottom electrode layer, simultaneously solving for unknown forces in three directions requires at least three independent capacitors, theoretically requiring at least three unit capacitors. The sensor employs four unit capacitors, which can accurately determine the relationship between force and unit capacitors when pure normal and pure tangential forces are applied, offering higher accuracy compared to three unit capacitors. Using more than four unit capacitors can further improve detection accuracy. In one embodiment, each of the unit capacitors includes a sensing electrode 43 located on an inner ring with a side length of 1.2 mm and an excitation electrode 42 located on an outer ring with a width of 0.5 mm, with an electrode spacing of 0.1 mm. Four unit capacitors are also included. - The distribution is both axisymmetric and centrally symmetric. The symmetric distribution inherently provides decoupling capability. For example, when a normal force is applied, all four unit capacitors increase in size simultaneously and are equal in magnitude. In this case, only the normal force signal will be read.

[0037] In one embodiment, the overall dimensions of the sensor are 10mm × 10mm × 12mm; the total area of ​​the unit capacitor is 2.4mm × 2.4mm, wherein the area of ​​the inner electrode (sensing electrode 43) is 1.2mm × 1.2mm, the width of the outer electrode (excitation electrode 42) is 0.5mm, and the distance between the outer electrode and the inner electrode is 0.1mm; the height of the air cavity layer in the initial state is 1mm.

[0038] In one embodiment, the preparation process of the silicone rubber elastomer bump contact 1 includes: mixing silicone rubber with a curing agent of 1% by volume, stirring for 3 minutes and then degassing, pouring into a 3D printed mold, curing at room temperature for 24 hours, and then peeling it off from the mold; the preparation process of the Ecoflex elastomer layer 2 is the same as that of the silicone rubber elastomer bump contact 1.

[0039] In one embodiment, the top layer structure, the intermediate layer structure, and the bottom layer structure are assembled and fixed using cyanoacrylate adhesive.

[0040] In one embodiment, a flexible metal coating is provided below the printed circuit board 4 of the sensor and between the Ecoflex elastomer layer 2 and the silicone rubber elastomer bump contact 1. The flexible metal coating is prepared using inkjet printing technology and is grounded.

[0041] In one embodiment, the nominal capacitance of the sensor is calculated using the following formula:

[0042]

[0043] in, For nominal capacitance without considering the height of the air cavity layer, The nominal capacitance takes into account the height of the air cavity layer; The dielectric constant of air is The dielectric constant of the Ecoflex elastomer layer; The width of the sensing electrode. The length of the sensing electrode, The distance between the sensing electrode and the excitation electrode; This represents the ratio of electrode length to width. This characterizes the ratio of electrode spacing to length. The height of the air cavity layer; , and These are parameters related to geometry.

[0044] The deformation and capacitance changes of the elastic body of the sensor under normal force, such as... Figure 5 As shown, when a normal force Fz is applied to the top silicone rubber elastomer bump contact 1, the silicone rubber elastomer bump contact 1 is compressed downwards, causing the Ecoflex elastomer layer 2 of the intermediate dielectric layer (intermediate layer structure) to deform, resulting in: (1) The Ecoflex elastomer layer 2 undergoes elastic deformation and is recessed towards the air cavity layer 3; (2) The height of the air cavity layer 3 decreases linearly from the initial 1 mm, about 0.7 mm when the normal force is 1 N, and about 0.4 mm when the normal force is 3 N; (3) The thickness of the air cavity layer 3 corresponding to the four unit capacitors varies in the same way.

[0045] (4) Under the action of the normal force, the volume of air passing through the edge field decreases, while the volume of the elastic body passing through increases. Therefore, the dielectric constant increases overall, and the four unit capacitors... - The capacitance values ​​all increase, and the changes are approximately equal, that is... .

[0046] The deformation and capacitance changes of the elastic body when the sensor is subjected to shear force, such as... Figure 6 As shown, when a shear force Fx or Fy is applied to the top silicone rubber elastomer bump contact 1, the silicone rubber elastomer bump contact 1 undergoes a horizontal displacement, causing the elastomer layer 2 of the intermediate dielectric layer to deform asymmetrically: (1) The side closer to the direction of the force, such as , In the corresponding area, the air cavity layer 3 is compressed, and its thickness is reduced; (2) The side away from the direction of the force, such as , In the corresponding area, the air cavity layer 3 is stretched, and its thickness increases; (3) The maximum deformation occurs at the two ends of the air cavity layer 3 that are furthest apart in the direction of force action. The thickness difference between the two air cavities is about 0.3 mm when the force is 1.5 N.

[0047] (4) Under the action of shear force Fx, the change in capacitance of different units follows a certain pattern. , The capacitance increases synchronously. , The capacitance decreases synchronously, that is , , Located in the negative direction of shear force Fx, , It is located in the positive direction of the shear force Fx.

[0048] In one embodiment, a flexible three-dimensional force-capacitance sensor for force feedback scenarios in humanoid robots is provided. The sensor is installed on the parts of the humanoid robot that require force feedback. The sensor detects the capacitance change during the contact process and transmits the force feedback signal to the computer to adjust the force and avoid excessive or insufficient force.

[0049] The above embodiments, through structural design and verification, illustrate the working mechanism of the sensor of the present invention under three-dimensional force, providing a reliable basis for its application in force feedback scenarios for humanoid robots. All equivalent modifications made within the principles and structural scope of the present invention should be included within the scope of protection.

Claims

1. A flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots, characterized in that, It includes a top-level structure, a middle-level structure, and a bottom-level structure arranged from top to bottom; The top-layer structure includes an elastomer bump contact; The intermediate layer structure includes an air cavity layer and an elastomer layer, with the elastomer layer located above the air cavity layer; The underlying structure includes a printed circuit board, on which multiple unit capacitors are provided; In this system, the air cavity layer and the elastomer layer together serve as the dielectric of multiple unit capacitors. When subjected to external force, the change in the thickness of the air cavity layer leads to a change in the dielectric constant, which in turn causes a change in the capacitance of the unit capacitor. By detecting the change in capacitance, the measurement and decoupling of normal force and shear force can be achieved.

2. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, The Young's modulus of the elastomeric bump contact is greater than that of the elastomeric layer.

3. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, The elastomeric bump contact is a silicone rubber elastomeric bump contact. The preparation process of the silicone rubber elastomeric bump contact includes: mixing silicone rubber with a curing agent of a preset volume ratio, stirring for a first preset time and then degassing, pouring into a 3D printed mold, curing at room temperature for a second preset time, and then peeling it off from the mold.

4. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, The printed circuit board is provided with multiple independent sensing electrodes, and each sensing electrode is surrounded by an excitation electrode. One sensing electrode and its corresponding excitation electrode constitute a unit capacitor.

5. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 4, characterized in that, After the electrode is subjected to voltage, an edge field effect is generated between the excitation electrode and the induction electrode. Depending on the change in the thickness of the air cavity layer, the proportion of electric field lines passing through the air cavity layer and the elastic body layer changes, resulting in a change in the dielectric constant, which in turn changes the capacitance of the unit capacitor.

6. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, Multiple unit capacitors on a printed circuit board are axially and centrally symmetrically distributed.

7. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, The top layer, middle layer, and bottom layer are assembled and fixed with glue.

8. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, A flexible metal coating is provided below the printed circuit board and between the elastomer layer and the silicone rubber elastomer bumps, and the flexible metal coating is grounded.

9. The flexible three-dimensional force-capacitive sensor for force feedback scenarios in humanoid robots according to claim 1, characterized in that, The nominal capacitance of the sensor is calculated using the following formula: in, For nominal capacitance without considering the height of the air cavity layer, The nominal capacitance takes into account the height of the air cavity layer; The dielectric constant of air is The dielectric constant of the elastomer layer; The width of the sensing electrode. The length of the sensing electrode, The distance between the sensing electrode and the excitation electrode; Characterizes the ratio of electrode length to width; Characterizes the ratio of electrode spacing to length; The height of the air cavity layer; , and These are parameters related to geometry.

10. The application of the flexible three-dimensional force-capacitance sensor for force feedback scenarios in humanoid robots as described in any one of claims 1-9, characterized in that, The sensor is installed on the part of the humanoid robot that requires force feedback. The sensor detects the change in capacitance during the contact process and transmits the force feedback signal to the computer to adjust the force and avoid excessive or insufficient force.

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