Fingertip-imitated multi-stage flexible sensor

Abstract

The invention discloses a fingertip-imitating multi-stage flexible sensor which can accurately measure the surface curvature, shape, hardness and multi-dimensional force of an object to be measured through a skin-imitating layer, a muscle-imitating layer and a skeleton-imitating layer from outside to inside and a simple structure.

Description

Technical Field

[0001] The present invention belongs to the field of flexible tactile sensors, and particularly relates to a multi-level flexible sensor imitating a fingertip. Background Art

[0002] The dexterous fingertip of a robot is the core component for the robot to achieve precise environmental perception and task execution. It integrates multiple sensing units such as pressure sensors, tactile sensors, and strain sensors to simulate the tactile function of a human fingertip and real-time collect multi-dimensional tactile information such as the magnitude of the contact force, the surface texture of an object, and the geometric shape. After these data are analyzed and processed by algorithms, they help the robot accurately judge the characteristics of the object such as hardness, roughness, and center of gravity distribution. Based on the perception of the object characteristics, the robot can dynamically adjust the grasping strategy, such as adaptively adjusting the finger grip force, bending angle, and contact position, to achieve stable grasping of objects with different shapes and materials. Whether it is the assembly of precision parts in an industrial scenario, the sorting of irregular packages in the logistics field, or the operation of minimally invasive surgery in the medical field, the dexterous fingertip can help the robot complete complex tasks, significantly improve its environmental interaction ability and operation accuracy, and promote the robot to advance in a more flexible and intelligent direction in the fields of intelligent service, intelligent manufacturing, etc., becoming the key link connecting the physical world and intelligent control.

[0003] The literature "DIGIT: A Novel Design for a Low-Cost Compact High-Resolution Tactile Sensor With Application to In-Hand Manipulation" discloses a visual tactile sensor, whose main components include a high-resolution camera, a flexible tactile surface, and an LED light source. The sensor captures the minute deformation that occurs on the tactile surface when it comes into contact with an object through the high-resolution camera and generates an image to provide precise visual data; the flexible tactile surface transmits tactile information through the deformation of the material, ensuring that the sensor can sense subtle contact forces; the LED light source evenly illuminates the tactile surface to enhance the image clarity. After obtaining the tactile image through the sensor, the image data is transmitted to the processing unit, and the processing unit analyzes the image using algorithms to analyze various tactile information such as material and hardness. Finally, the sensor transmits the processed data to the robot or other devices for performing corresponding tasks. However, the sensor disclosed in the above literature has a very weak ability to extract and decouple tactile signals. The front-end sensor only responsible for obtaining the tactile image, and the processing and analysis of signal features mainly rely on the algorithms at the back-end, which will result in a large computational cost and hardware overhead.

[0004] The multi-dimensional tactile sensor PX-6AX GEN2 developed by domestic sensor company Pacini Sensing Technology Co., Ltd. (related website: https: / / paxini.com / ax / gen2). The flexible tactile sensing device used in this product is a high-density flexible electromagnetic pressure sensing array. Through the Hall effect of the electromagnetic sensor, the magnetic field changes around each sensing point are measured to measure signals such as the force and torque it receives, and then through the high-density sensing array, signals such as the surface stress distribution, three-dimensional force, and three-dimensional torque of the sensor are obtained. Finally, the measured signals are transmitted to the backend and combined with algorithms such as machine learning to analyze the tactile information. The disadvantage of this product is that the high-density sensing array often brings complex wiring, extremely high signal crosstalk, and high-difficulty manufacturing processes. After the high design and manufacturing costs, the tactile signals that the front-end sensor can actually output are only "surface stress distribution (three-axis array, unit MPa), three-dimensional force and three-dimensional torque (N / Nm)" (from the Pacini official website). Its measurement output results are single, the efficiency of front-end signal extraction is low, and most feature recognition still requires a large amount of computing costs.

[0005] The products disclosed in the above prior art and most of the similar products on the market at present are difficult to achieve a good balance among low cost, structural simplicity, and rich functionality, and they all have a strong dependence on the backend algorithms, which is undoubtedly a serious burden for robots that themselves have a large demand for computing power. Summary of the Invention

[0006] The present invention provides a fingertip-like multi-stage flexible sensor, which has a simple structure, can achieve low-cost measurement of the curvature, soft hardness, and multi-dimensional force of the object to be measured, and has strong tactile feature signal extraction ability.

[0007] The present invention provides a fingertip-like multi-stage flexible sensor, comprising:

[0008] A skin-like layer, which is attached to the surface of the object to be measured. The hardness of the skin-like layer is <Shore10A. The skin-like layer includes a resistive strain sensing layer, and through the resistive strain sensing layer, the shape and curvature of the surface of the object to be measured, the total displacement generated by the elastic deformation of the object to be measured and the fingertip-like multi-stage flexible sensor, and whether the soft hardness of the object to be measured is within the measurable range are measured.

[0009] The muscle-like layer is located below the skin-like layer. The hardness of the muscle-like layer is Shore 30A - Shore 70A, and it is convex. The muscle-like layer includes a capacitive sensing film. The pressing force applied to the object to be measured is measured through the capacitive sensing film. When the soft hardness of the object to be measured is within the measurable range, based on the elastic coefficients of the skin-like layer and the muscle-like layer, as well as the measured total displacement and pressing force, the elastic coefficient of the object to be measured is obtained through Hooke's law;

[0010] The bone-like layer is located below the muscle-like layer. The hardness of the bone-like layer is > Shore 60D, and it is convex. The bone-like layer includes capacitive sensing films distributed at an angle. Based on the capacitive sensing films distributed at an angle, multiple normal forces are obtained. Based on the multiple normal forces and the pressing force, the magnitude and direction of the multi-dimensional force received by the multi-level flexible fingertip sensor are obtained through finite element analysis.

[0011] Preferably, the muscle-like layer further includes a muscle-like encapsulation layer. The muscle-like encapsulation layer is convex. The capacitive sensing film is located at the convex part. The muscle-like encapsulation layer is an elastic material with a hardness of Shore30A - Shore 70A;

[0012] The material of the muscle-like encapsulation layer is liquid PDMS, or TPU with a hardness > Shore 30A, or liquid silicone rubber.

[0013] Preferably, the capacitive sensing film includes a first dielectric layer and two electrode parts sandwiching the first dielectric layer:

[0014] The first dielectric layer includes a first support module and a first pressure-sensing module inserted into the first support module. The first pressure-sensing module is an elastomer filled with conductive fillers inside. The hardness of the first support module and the first pressure-sensing module is different;

[0015] The electrode part includes a substrate on the outside and a T-shaped electrode on the inside. The contour edge of the convex part of the T-shaped electrode extends inward to form an induction functional area. The T-shaped electrodes of the two electrode parts are arranged in the opposite direction, and the projections of the two induction functional areas overlap. The first induction module is located within the two induction functional areas.

[0016] Preferably, the material of the first support module is a rigid elastomer material, and the material of the elastomer of the first pressure-sensing module is a soft elastomer material, or the material of the first support module is a soft elastomer material, and the material of the elastomer of the first pressure-sensing module is a rigid elastomer material. Among them, the rigid elastomer material is PDMS, or TPU with a Shore hardness greater than 30A or liquid silicone rubber, and the soft elastomer material is Ecoflex, PVA hydrogel, or TPU with a Shore hardness less than 30A or liquid silicone rubber;

[0017] The conductive filler is [EMIM][TFSI], H3PO4, PEG, Nafion or CNT;

[0018] The material of the T-shaped electrode is Ag, Cu, Ti, PEDOT:PSS or ITO;

[0019] The substrate is PET, PI, PDMS or TPU.

[0020] Preferably, the bone-like layer further includes a bone-like encapsulation layer, the bone-like encapsulation layer is in a convex shape, and the capacitively sensing film distributed at an angle is located at the convex part of the bone-like encapsulation layer;

[0021] The Young's modulus of the bone-like encapsulation layer is at the GPa level, and the material of the bone-like encapsulation layer is TPU, resin-based material or silicone rubber.

[0022] Preferably, the capacitively sensing film distributed at an angle includes a second dielectric layer, and an upper electrode part and a plurality of lower electrode parts sandwiching the second dielectric layer;

[0023] The second dielectric layer includes a second support module and a plurality of second pressure-sensing modules. The second support module is in a radial shape and includes a plurality of strip-shaped support modules. The ends of the plurality of strip-shaped support modules are connected at the center point, and the starting ends radiate outwards. The plurality of second pressure-sensing modules are respectively inserted into the starting ends of the corresponding strip-shaped support modules;

[0024] The upper electrode part includes an outer upper substrate and a plurality of T-shaped upper electrodes located inside. The upper substrate includes a plurality of strip-shaped upper substrates and is in a radial shape. The ends of the plurality of strip-shaped upper substrates are connected at the center point, and the starting ends radiate outwards. Each T-shaped upper electrode is located at the starting end of the corresponding strip-shaped upper substrate. The contour edge of the convex part of the T-shaped upper electrode extends inwards to form an upper electrode sensing functional area;

[0025] Each lower electrode part is located at the bottom of the starting end part of the corresponding strip-shaped support module. Each lower electrode part includes a lower substrate located on the outer side and a T-shaped lower electrode located on the inner side. The contour edge of the protruding part of the T-shaped lower electrode extends inwards to form a lower electrode induction functional area. The T-shaped lower electrode and the T-shaped upper electrode are arranged in opposite directions, and the projection of the upper electrode induction functional area overlaps with that of the lower electrode induction functional area. The second induction module is located within the upper electrode induction functional area and the lower electrode induction functional area.

[0026] Preferably, in the horizontal plane projection, in the circumferential direction, the included angle between every two adjacent strip-shaped support modules is α, and the included angle between every two adjacent strip-shaped upper substrates is β, and α = β.

[0027] Preferably, the skin-like layer further includes a skin-like encapsulation layer, and the resistive strain gauge is cured above the skin-like encapsulation layer;

[0028] The material of the skin-like encapsulation layer is liquid silicone rubber, Ecoflex or PVA hydrogel.

[0029] Preferably, the resistive strain sensing layer includes a bidirectional resistive strain gauge. When the skin-like layer contacts the object to be measured and the object does not contact the muscle-like layer, based on the shape of the object to be measured, the shape of the bidirectional resistive strain gauge changes correspondingly, and a corresponding resistance change rate is generated through the change of the shape. The surface curvature and shape of the contacting object are judged through the relationship between the bending strain and the resistance change rate;

[0030] When the object contacts the muscle-like layer, the resistance signal of the resistive strain gauge continues to change, then it is judged that the soft hardness of the object to be measured is within the measurable range.

[0031] Preferably, the material of the resistive strain gauge is a metal material or a semiconductor, and the metal material is constantan, platinum, tungsten or nickel.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention utilizes the relatively soft skin-like layer and the resistive strain sensing layer. When the object to be measured presses down on the skin-like layer, the resistive strain sensing layer deforms correspondingly, and then a corresponding resistance value change is generated. Based on the corresponding relationship between the resistance value change and the bending curvature, the curvature and shape of the surface of the object to be measured are obtained.

[0034] Since the muscle-like layer has a high hardness and is convex, it can be regarded as a hardness meter. When the object to be measured contacts the muscle-like layer, the resistance value of the resistive strain sensing layer changes, which indicates that the soft hardness of the object to be measured can be measured. Then, based on the elastic modulus of the skin-like layer and the muscle-like layer, as well as the measured total displacement and pressing force, the elastic modulus of the object to be measured is obtained through Hooke's law, and the soft hardness of the object to be measured is obtained through the elastic modulus of the object to be measured.

[0035] Since the hardness of the bone-mimicking layer provided by the present invention is relatively high, it can increase the pressure measurement range of the capacitive sensing film to measure the force condition more accurately, and perform finite element analysis on the normal force and pressing force measured on the bone-mimicking layer and the muscle-mimicking layer to obtain the magnitude and direction of the multi-dimensional force received by the fingertip multi-flexible sensor.

[0036] In summary, the present invention can use a relatively simple structure and a method with low dependence on algorithms to simultaneously measure the surface curvature, softness and hardness, and the multi-dimensional force received by an object. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the structure of the fingertip multi-flexible sensor provided by a specific embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the capacitive sensing film structure of the muscle-mimicking layer provided by a specific embodiment of the present invention;

[0039] Figure 3 Schematic diagram of the capacitive sensing film structure with an angular distribution of the bone-mimicking layer provided by a specific embodiment of the present invention;

[0040] Figure 4 Classification scale diagram of the object softness measurement interval provided by a specific embodiment of the present invention;

[0041] Figure 5 Schematic diagram of the sensor softness measurement principle provided by a specific embodiment of the present invention;

[0042] Figure 6 Schematic diagram of the sensor multi-dimensional force measurement provided by a specific embodiment of the present invention.

[0043] Wherein, the skin-mimicking layer 1, the resistive strain sensing layer 11, the skin-mimicking encapsulation layer 12, the muscle-mimicking layer 2, the capacitive sensing film 21, the first dielectric layer 211, the first support module 211a, the first pressure sensing module 211b, the first electrode part 212, the substrate 212a, the T-shaped electrode 212b, the induction functional area 212c, the second electrode part 213, the substrate 213a, the T-shaped electrode 213b, the induction functional area 21c, the muscle-mimicking encapsulation layer 22, the bone-mimicking layer 3, the capacitive sensing film 31 with an angular distribution, the second dielectric layer 311, the second support module 3111, the strip-shaped support module 3111a, the second pressure sensing module 3112, the upper electrode part 312, the upper substrate 3121, the strip-shaped upper substrate 3121a, the T-shaped upper electrode 3122, the lower electrode part 313, the lower substrate 3131, the T-shaped lower electrode 3132, the bone-mimicking encapsulation layer 32. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] To deepen the understanding of the present invention, the following will give a detailed description of this embodiment in conjunction with the accompanying drawings.

[0045] In order to accurately measure the surface curvature, shape, softness and hardness of an object to be measured, as well as the multi-dimensional forces applied thereto, with a relatively simple structure, a specific embodiment of the present invention provides a fingertip-mimicking multi-stage flexible sensor, as shown in a and b of Figure 1 which successively includes a skin-mimicking layer, a muscle-mimicking layer and a bone-mimicking layer from outside to inside.

[0046] The skin-mimicking layer 1 provided by a specific embodiment of the present invention includes a skin-mimicking encapsulation layer 12 and a resistive strain sensing layer 11 fixed on the skin-mimicking encapsulation layer. The resistive strain sensing layer 11 is composed of bidirectional resistive strain gauges. The skin-mimicking encapsulation layer 12 provided by a specific embodiment of the present invention is relatively soft, with a hardness of <Shore 10A, and the bidirectional resistive strain gauge can achieve bidirectional detection, that is, the resistance increases when bending towards one side and decreases when bending towards the other side. Thus, when the object to be measured contacts the skin-mimicking layer, it will cause the bidirectional resistive strain to deform, resulting in a change in resistivity. Based on the relationship between the bending strain of the strain gauge and the resistance change rate, the curvature and shape of the object to be measured can be obtained.

[0047] The resistive strain sensing layer 12 provided by a specific embodiment of the present invention can also be used to determine whether the softness and hardness of the object to be measured are within the measurable range. When the object to be measured continues to press down and contacts the muscle-mimicking layer with a higher hardness, if the hardness of the object to be measured is lower than that of the muscle-mimicking layer, the resistive strain sensing layer will continue to generate different resistance changes, indicating that the hardness of the object to be measured is within the measurable range.

[0048] In a specific embodiment, the skin-mimicking encapsulation layer 11 provided in this embodiment is obtained by curing liquid silicone rubber, Ecoflex or PVA hydrogel.

[0049] In a specific embodiment, the material of the bidirectional resistive strain gauge provided in this embodiment is a metal material or a semiconductor, and the metal material is constantan, platinum, tungsten or nickel.

[0050] In a specific embodiment, the bidirectional resistive strain gauge provided in this embodiment is cured and flatly encapsulated on the top of the skin-mimicking encapsulation layer 11 by liquid silicone rubber, and is composed of two cross-arranged constantan (or platinum, tungsten, nickel, semiconductor) bidirectional resistive strain gauges.

[0051] In a specific embodiment of the present invention, the top of the muscle-like layer 2 is adhesively attached to the bottom of the skin-like encapsulation layer 12. The muscle-like layer 2 includes a muscle-like encapsulation layer 22 and a capacitive sensing film 21 located on the muscle-like encapsulation layer. The muscle-like encapsulation layer 22 is convex. In one embodiment, the muscle-like encapsulation layer 22 is frustum-shaped. The capacitive sensing film is located at the convex portion. Since the hardness of the muscle-like encapsulation layer 22 is relatively hard, with a hardness of Shore 30A - Shore 70A, and the capacitive sensing film 21 is located at the convex portion, the capacitive sensing film 21 has a relatively high pressure measurement range. When the object to be measured is pressed down onto the muscle-like layer 22, the pressing force applied to the object to be measured can be measured more accurately. When the hardness of the object to be measured is within the measurable range, based on the elastic coefficients of the skin-like layer 1 and the muscle-like layer 2, as well as the measured total displacement and pressing force, the elastic coefficient of the object to be measured is obtained through Hooke's law, and its soft hardness is obtained based on the elastic coefficient of the object to be measured.

[0052] In a specific embodiment, the muscle-like encapsulation layer 22 provided in this embodiment is convex. The muscle-like encapsulation layer 22 is made of an elastic material with a hardness of Shore 30A - Shore 70A, providing strong support for the capacitive sensing film 21 and increasing the pressure range of the capacitive sensing film 21. The material of the muscle-like encapsulation layer 22 is liquid PDMS, or TPU with a hardness greater than Shore 30A or liquid silicone rubber.

[0053] In a specific embodiment, as Figure 2 shown in a and b of, the capacitive sensing film 21 provided in this embodiment includes a first dielectric layer 211 and two electrode portions 212 and 213 sandwiching the first dielectric layer. The first dielectric layer 211 includes a first support module 211a and a first pressure-sensing module 211b inserted into the first support module 211a. The first pressure-sensing module 211b is an elastomer with a high dielectric constant filled with conductive fillers inside, which mainly functions to sense pressure. Through this design, a wide pressure-sensing range and high sensitivity can be achieved simultaneously. The hardness of the first support module 211a and the first pressure-sensing module 211b is different. Hard in the middle and soft around, or soft in the middle and hard around can have different sensing characteristics, but both can promote the sensing performance of the sensing layer;

[0054] The material of the first support module provided by the specific embodiment of the present invention is a rigid elastomer material, and the material of the elastomer of the first pressure-sensing module is a soft elastomer material, or the material of the first support module is a soft elastomer material, and the material of the elastomer of the first pressure-sensing module is a rigid elastomer material. Among them, the rigid elastomer material is PDMS, or TPU or liquid silicone rubber with a Shore hardness of 30A, and the soft elastomer material is Ecoflex, PVA hydrogel, or TPU or liquid silicone rubber with a Shore hardness of less than 30A.

[0055] The conductive filler provided by the specific embodiment of the present invention is [EMIM][TFSI], H3PO4, PEG, Nafion or CNT.

[0056] The material of the T-shaped electrode provided by the specific embodiment of the present invention is Ag, Cu, Ti, PEDOT:PSS or ITO.

[0057] The substrate provided by the specific embodiment of the present invention is PET, PI, PDMS or TPU.

[0058] The first electrode portion 212 provided by the specific embodiment of the present invention includes a substrate 212a located on the outside and a T-shaped electrode 212b located on the inside. The contour edge of the protruding portion of the T-shaped electrode extends inward to form an induction function area 21a.

[0059] The second electrode portion 213 provided by the specific embodiment of the present invention includes a substrate 213a located on the outside and a T-shaped electrode 213b located on the inside. The contour edge of the protruding portion of the T-shaped electrode extends inward to form an induction function area 21b. The areas of the induction function areas formed by the corresponding first electrode portion 212 and the second electrode portion 213 overlap.

[0060] The T-shaped electrodes 213b and 212b of the two electrode portions provided by the specific embodiment of the present invention are arranged in opposite directions, and the projections of the two induction function areas 212c and 213c overlap, that is, the inner edge lines of the long strip portions of the two T-shaped electrodes coincide. The first induction module 211b is located within the two induction function areas.

[0061] By arranging the first induction module 211b within the two induction function areas with overlapping projections in the specific embodiment of the present invention, when the two electrode portions are subjected to shear stress, even if they are misaligned, the overlapping area of the two electrodes remains the same, thereby avoiding the influence of the tangential force on the change of the pressure signal, and further enabling the accurate acquisition of the pressing force applied to the object to be measured.

[0062] As Figure 2 shown in b of, in one embodiment, the length of the induction function area 21c is 3 mm, the width is 3 mm, and the area of the overlapping region is 9 mm 2, when subjected to a tangential force, the two electrode portions are offset by 1 mm, but the overlapping area is 2×3 + 1×1.5 + 1×1.5 = 9 mm 2 , and the overlapping area remains the same.

[0063] In a specific embodiment of the present invention, the bone-like layer 3 includes a bone-like encapsulation layer 32 and a capacitively sensing film 31 arranged at an angle and fixed on the bone-like encapsulation layer. Since the hardness of the bone-like encapsulation layer 32 is at the GPa level, the pressure measurement range of the capacitively sensing film arranged at an angle is improved. Based on the capacitively sensing film 31 arranged at an angle, a plurality of normal forces are obtained, and based on the plurality of normal forces and the pressing force, the magnitude and direction of the multi-dimensional force received by the fingertip-like multi-flexible sensor are obtained through finite element analysis.

[0064] The material of the bone-like encapsulation layer 32 provided in the specific embodiment of the present invention is a high-hardness TPU, resin-based material, or silicone rubber with extremely high Young's modulus, almost no deformation, and good bonding with the first two layers. This material selection and structural design can improve the pressure measurement range of the sensing layer while ensuring that the three sensing points in the sensing layer are arranged at an angle in three-dimensional space, so as to better measure the force received by the sensor.

[0065] As Figure 3 shown, the capacitively sensing film 31 arranged at an angle provided in the specific embodiment of the present invention includes a second dielectric layer 311 and an upper electrode portion 312 and a plurality of lower electrode portions 313 sandwiching the second dielectric layer.

[0066] The second dielectric layer 311 provided in this embodiment includes a second support module 3111 and a plurality of second pressure-sensing modules 3112. The second support module 3111 is radially arranged and includes a plurality of strip-shaped support modules 3111a. The ends of the plurality of strip-shaped support modules 3111a are connected at the center point, and the starting ends radiate outward. The plurality of second pressure-sensing modules 3112 are respectively inserted into the starting ends of the corresponding strip-shaped support modules.

[0067] The upper electrode portion 312 provided in this embodiment includes an outer upper substrate 3121 and a plurality of T-shaped upper electrodes 3122 located inside. The upper substrate 3121 includes a plurality of strip-shaped upper substrates 3121a and is radially arranged. The ends of the plurality of strip-shaped upper substrates 3121a are connected at the center point, and the starting ends radiate outward. Each T-shaped upper electrode 3122 is located at the starting end of the corresponding strip-shaped upper substrate 3121a. The contour edge of the protruding portion of the T-shaped upper electrode 3122 extends inward to form an upper electrode sensing functional area 312a.

[0068] In each embodiment, each lower electrode portion 313 is located at the bottom of the starting end of the corresponding strip-shaped support module 3111a. Each lower electrode portion 313 includes a lower substrate 3131 on the outer side and a T-shaped lower electrode 3132 on the inner side. The contour edge of the protruding portion of the T-shaped lower electrode 3132 extends inward to form a lower electrode induction functional area 312b. The T-shaped lower electrode 3132 and the T-shaped upper electrode 3122 are arranged in opposite directions, and the upper electrode induction functional area 312a and the lower electrode induction functional area 312b are projected to overlap. The second induction module 3112 is located within the upper electrode induction functional area 312a and the lower electrode induction functional area 312b.

[0069] In this embodiment, the materials of the second support module and the second pressure sensing module in the bone-like layer can be distributed the same as those of the first support module and the second pressure sensing module, and the materials of the substrate and the electrode in the bone-like layer can also be the same as those of the substrate and the electrode in the muscle-like layer.

[0070] In a specific embodiment, in the horizontal plane projection, in the circumferential direction, the angle between every two adjacent strip-shaped support modules is α, and the angle between every two adjacent strip-shaped upper substrates is β, and α = β. In one embodiment, α = β = 120°.

[0071] In a specific embodiment, this embodiment is mainly aimed at the application scenario of a robot adaptively grasping an object. Therefore, in this example, the objects to be grasped are classified according to softness and hardness in combination with the actual grasping situation in reality, mainly as follows Figure 4 It can be divided into three major categories.

[0072] Among them, the first category is the object to be measured that is softer than the encapsulation material of the skin-like layer. Since such objects are too fragile and prone to deformation or damage, it is also very difficult to directly grasp them by hand in daily life. The dexterous fingertip provided in this embodiment cannot completely ensure damage-free grasping. Therefore, in the subsequent grasping work, this embodiment will mainly discuss the measurement and pre-grasping processes of the latter two major categories of objects.

[0073] The second major category is the object whose softness and hardness are between the skin-like encapsulation layer and the muscle-like encapsulation layer. Such objects can be normally grasped during actual operation, but there are certain requirements for the magnitude of the grasping force during grasping. If the grasping force is too small, the object will slip, and if the grasping force is too large, the object is prone to deformation or damage. Objects with softness and hardness in this range can be accurately measured for softness and hardness through the present invention, so as to provide guidance for the magnitude of the applied grasping force.

[0074] The third category is the object to be measured with a hardness greater than that of the muscle - like encapsulation layer. Such objects to be measured are often difficult to deform and break, and are even close to being rigid. Therefore, when grasping such objects to be measured, the selection of the grasping force magnitude can be relatively less strict. This embodiment can distinguish the latter two major categories of objects to be measured through the present invention and adopt different strategies for different objects when applying the grasping force. Of course, in order to expand the accurately measurable range of hardness and match the grasping scenarios in reality, the hardness of each layer of encapsulation material will be carefully compared and screened.

[0075] The measurement of the curvature of the object to be measured (grasping surface) provided in this embodiment is completed through the skin - like layer. During the measurement and grasping process, first, the resistive strain sensing layer is arranged at the fingertip of the manipulator. The manipulator is controlled to gently touch the object to be measured with a relatively small pressure. Here, the gentle touch means that the object to be measured comes into contact with the skin - like layer but is hardly affected by the muscle - like layer. Considering that the size of the resistive strain sensing layer is such that the relative displacement after the object contacts the surface of the skin - like layer is within 5 mm. Within this range, when the surface of the object to be measured contacts the resistive strain sensor, it will first cause the soft skin - like layer to deform. The resistive strain gauge will deform to conform to the surface of the object along with the skin - like encapsulation layer. Since the strain gauge used in this embodiment has a bidirectional resistance change (i.e., the resistance increases when the strain gauge bends to one side and decreases when it bends to the other side), this embodiment can judge whether the basic shape of the grasping surface of the object is a plane, a concave surface, or a convex surface according to the trend of the resistance signal change.

[0076] As shown in Table 1, during the gentle - touch stage, if the grasping surface is a plane, then the strain gauge of the skin - like layer sensing layer hardly deforms, so the resistance signal hardly changes; if the grasping surface is a convex surface, then the center of the strain gauge will be squeezed by the object and protrude inward, and the resistance of the bidirectional resistive strain gauge will increase; if the grasping surface is a concave surface, then both sides of the bidirectional resistive strain gauge will be squeezed first and the whole will protrude outward, and the resistance of the bidirectional resistive strain gauge will decrease. By the trend of the signal change during the gentle - touch stage, the shape of the grasping surface can be judged, and then the specific curvature size of the grasping surface can be calibrated and measured by the magnitude of the resistance change of the bidirectional resistive strain gauge, thus completing the complete acquisition of the shape information of the grasping surface.

[0077] The measurement of the softness and hardness of the object (grasping surface) provided in this embodiment is completed through the cooperation of the skin-like layer and the muscle-like layer. After the curvature of the grasping surface is measured, the multi-stage flexible fingertip sensor provided in this embodiment continues to increase the contact pressure, reaching the pressing stage of the resistive strain sensing layer (that is, when the relative displacement after the object contacts the surface of the skin-like layer exceeds 5 mm, the muscle-like layer begins to affect the surface of the object). At this time, the hemispherical protrusion structure of the harder muscle-like layer contacts the surface of the object. As shown in Table 1, after entering the pressing stage, through the change trend of the signal, this embodiment can first distinguish whether the softness and hardness of the object grasping surface belong to the second category or the third category, that is, whether it is greater than the hardness of the elastomer encapsulated by the muscle-like layer: If the softness and hardness of the grasping surface are greater than the softness and hardness of the muscle layer, the muscle layer will be squeezed and deformed by the grasping surface, then the bi-phase resistive strain gauge will continue to maintain the original shape that fits the grasping surface, and the resistance signal will not change significantly; If the softness and hardness of the grasping surface are less than the softness and hardness of the muscle-like encapsulation layer, the grasping surface will be squeezed and deformed by the muscle-like layer, thus continuing to generate a signal change different from that in the light-touch stage, and thus it can be judged whether the softness and hardness of the grasping surface of the object to be measured are within the measurable range.

[0078] When the skin-like layer exactly fits the surface of the object, this state is the boundary between the light-touch stage and the pressing stage. Denote the signals of the strain gauge of the skin-like layer and the sensing film of the muscle layer at this time as T1 and T2 respectively. If the surface hardness of the object is less than the hardness of the muscle layer (that is, the softness and hardness of the object to be measured are within the measurable range), then during the pressing process, T1 will generate a signal change with different characteristics from that in the light-touch stage. Without damaging the surface of the object, press the total displacement Δx in the direction towards the inside of the object. The signal of the strain gauge of the skin-like layer becomes T1', and T1' - T1 = ΔT1. The mapping relationship between Δx and ΔT1 can be obtained through calibration. Similarly, at this time, the signal of the sensing film of the muscle layer becomes T2', and T2' - T2 = ΔT2. The mapping relationship between ΔF and ΔT2 can also be obtained through calibration, so as to measure the total displacement and pressing force generated by the elastic deformation of the object to be measured and the multi-stage flexible fingertip sensor.

[0079] If the softness and hardness of the object grasping surface are within the measurable range, then as Figure 5As described above, by combining the relevant formula derivation of Hooke's law, it can be found that to calculate the elastic coefficient of the object to be measured, k2 and k3 are the basic properties of the elastomer material and can also be obtained through prior measurement, so they are known quantities. The remaining unknowns F and Δx can be measured by the sensing layers of the muscle layer and the skin-like layer respectively. Thus, the elastic coefficient k1 of the object to be measured can be obtained to achieve accurate measurement of the hardness of the object. This softness and hardness measurement strategy adopts full-flexible contact, and the displacement and the applied pressure can be accurately controlled, so it is almost non-destructive. At the same time, this method measures two parameters, pressure and displacement, so it does not require other parts of the robot to provide additional measurement data. And this strategy can also consider the shape of the object grasping surface and add corresponding correction parameters during calculation, so it has high versatility.

[0080] Table 1 Signal change situation table of the skin-like layer sensing layer after the sensor contacts objects with different shapes and softness and hardness

[0081] (divided into two stages: light touch and pressing)

[0082]

[0083] Figure 5 In it, F represents the pressing force applied by the manipulator; k1, k2, k3, and k respectively represent the elastic coefficients of the object to be measured, the encapsulation material of the skin-like layer, the encapsulation material of the muscle-like layer, and the entire system that undergoes elastic deformation including the above items; x1, x2, x3, and Δx respectively represent the displacements generated by the deformations of the object to be measured, the skin layer, the muscle layer, and the entire system that undergoes elastic deformation including the above items; ΔT1 and ΔT2 respectively represent the signal changes that occur in the sensing layers of the skin layer and the muscle layer.

[0084] The measurement of the multi-dimensional force received by the sensor provided in this embodiment is completed through the cooperation of the muscle-like layer and the bone-like layer. As Figure 6 shown, the three sensing points of the bone-like layer that are angularly distributed in three-dimensional space can measure the magnitude of the normal force perpendicular to it, so as to obtain three force vectors that are not in the same plane. If the entire sensor is regarded as a mass point, then the magnitude and direction of the overall force received by the multi-level flexible sensor of the finger tip can be obtained through these three vector forces. However, the multi-level flexible sensor of the finger tip is not a mass point. Therefore, by introducing the force parameters measured by the capacitive sensing film of the muscle-like layer and combining finite element analysis with software such as ABAQUS and COMSOL, the overall force distribution of the sensor can be obtained, and finally the specific situation of the multi-dimensional force received by the sensor can be obtained, where is an external force vector with an arbitrary magnitude and direction received by the entire sensor, They are respectively the vectors of the normal forces received by three angled sensing points of the bone layer, and are the normal force vectors measured by the muscle layer sensors.

Claims

1. A multi-level flexible sensor imitating a fingertip, characterized in that, Comprising: A skin-like layer that fits onto the surface of the object to be measured. The hardness of the skin-like layer is <Shore 10A. The skin-like layer includes a resistive strain sensing layer. Through the resistive strain sensing layer, the shape and curvature of the surface of the object to be measured are measured, as well as the total displacement generated by the elastic deformation of the object to be measured and the multi-stage flexible sensor of the fingertip-like structure, and it is determined whether the softness or hardness of the object to be measured is within the measurable range; A muscle-like layer that is located below the skin-like layer. The hardness of the muscle-like layer is Shore 30A - Shore 70A and it is convex. The muscle-like layer includes a capacitive sensing film. Through the capacitive sensing film, the pressing force applied to the object to be measured is measured. When the softness or hardness of the object to be measured is within the measurable range, based on the elastic coefficients of the skin-like layer and the muscle-like layer, as well as the measured total displacement and pressing force, the elastic coefficient of the object to be measured is obtained through Hooke's law; A bone-like layer that is located below the muscle-like layer. The hardness of the bone-like layer is >Shore 60D and it is convex. The bone-like layer includes capacitive sensing films distributed at an angle. Based on the capacitive sensing films distributed at an angle, multiple normal forces are obtained. Based on the multiple normal forces and the pressing force, the magnitude and direction of the multi-dimensional force received by the multi-stage flexible sensor of the fingertip-like structure are obtained through finite element analysis.

2. The multi-stage flexible sensor imitating a fingertip according to claim 1, characterized in that The muscle-like layer further includes a muscle-like encapsulation layer that is convex. The capacitive sensing film is located at the convex part. The muscle-like encapsulation layer is made of an elastic material with a hardness of Shore 30A - Shore 70A; The material of the muscle-like encapsulation layer is liquid PDMS, or TPU with a hardness >Shore 30A, or liquid silicone rubber.

3. The multi-stage flexible sensor imitating a fingertip according to claim 1 or 2, characterized in that The capacitive sensing film includes a first dielectric layer and two electrode parts sandwiching the first dielectric layer: The first dielectric layer includes a first support module and a first pressure sensing module inserted into the first support module. The first pressure sensing module is an elastomer filled with conductive filler inside, and the hardness of the first support module and the first pressure sensing module is different; The electrode part includes a substrate on the outside and a T-shaped electrode on the inside. The contour edge of the convex part of the T-shaped electrode extends inward to form an induction functional area. The T-shaped electrodes of the two electrode parts are arranged in reverse, and the projections of the two induction functional areas overlap. The first induction module is located within the two induction functional areas.

4. The multi-level flexible sensor imitating a fingertip according to claim 3, wherein, The material of the first support module is a rigid elastomer material, and the elastomer material of the first pressure sensing module is a soft elastomer material, or the material of the first support module is a soft elastomer material, and the elastomer material of the first pressure sensing module is a rigid elastomer material. Among them, the rigid elastomer material is PDMS, or TPU with a hardness >Shore 30A, or liquid silicone rubber, and the soft elastomer material is Ecoflex, PVA hydrogel, or TPU with a hardness <Shore 30A, or liquid silicone rubber; The conductive filler is [EMIM][TFSI], H3PO4, PEG, Nafion, or CNT; The material of the T-shaped electrode is Ag, Cu, Ti, PEDOT:PSS or ITO; The substrate is PET, PI, PDMS or TPU.

5. The multi-level flexible sensor imitating a fingertip according to claim 1, characterized in that, The bone-like layer further includes a bone-like encapsulation layer, which is convex, and the capacitively sensing film distributed at an angle is located at the convex part of the bone-like encapsulation layer; The Young's modulus of the bone-like encapsulation layer is at the GPa level, and the material of the bone-like encapsulation layer is TPU, resin-based material or silicone rubber.

6. The multi-level flexible sensor imitating a fingertip according to claim 1 or 5, wherein, The capacitively sensing film distributed at an angle includes a second dielectric layer, an upper electrode part and a plurality of lower electrode parts sandwiching the second dielectric layer; The second dielectric layer includes a second support module and a plurality of second pressure-sensing modules. The second support module is radially arranged and includes a plurality of strip-shaped support modules. The ends of the plurality of strip-shaped support modules are connected at the center point, and the starting ends radiate outwards. The plurality of second pressure-sensing modules are respectively inserted into the starting ends of the corresponding strip-shaped support modules; The upper electrode part includes an upper substrate located on the outer side and a plurality of T-shaped upper electrodes located on the inner side. The upper substrate includes a plurality of strip-shaped upper substrates and is radially arranged. The ends of the plurality of strip-shaped upper substrates are connected at the center point, and the starting ends radiate outwards. Each T-shaped upper electrode is located at the starting end of the corresponding strip-shaped upper substrate. The contour edge of the convex part of the T-shaped upper electrode extends inwards to form an upper electrode sensing functional area; Each lower electrode part is located at the bottom of the starting end of the corresponding strip-shaped support module. Each lower electrode part includes a lower substrate located on the outer side and a T-shaped lower electrode located on the inner side. The contour edge of the convex part of the T-shaped lower electrode extends inwards to form a lower electrode sensing functional area. The T-shaped lower electrode and the T-shaped upper electrode are arranged in reverse, and the projections of the upper electrode sensing functional area and the lower electrode sensing functional area overlap. The second sensing module is located in the upper electrode sensing functional area and the lower electrode sensing functional area.

7. The fingertip-mimicking multi-stage flexible sensor according to claim 6, characterized in that, In the horizontal plane projection, in the circumferential direction, the angle between every two adjacent strip-shaped support modules is α, and the angle between every two adjacent strip-shaped upper substrates is β, and α = β.

8. The multi-level flexible fingertip-like sensor according to claim 1, wherein The skin-like layer further includes a skin-like encapsulation layer, and the resistive strain gauge is cured above the skin-like encapsulation layer; The material of the skin-like encapsulation layer is liquid silicone rubber, Ecoflex or PVA hydrogel.

9. The multi-stage flexible fingertip-mimicking sensor according to claim 1 or 8, wherein The resistive strain sensing layer includes a bidirectional resistive strain gauge. When the skin-like layer contacts the object to be measured and the object does not contact the muscle-like layer, based on the shape of the object to be measured, the shape of the bidirectional resistive strain gauge changes correspondingly, and a corresponding resistance change rate is generated through the change of the shape. The surface curvature and shape of the contacting object are judged through the relationship between the bending strain and the resistance change rate; When the object contacts the muscle-like layer, the resistance signal of the resistive strain gauge continues to change, then it is judged that the soft hardness of the object to be measured is within the measurable range.

10. The multi-stage flexible sensor imitating a fingertip according to claim 9, characterized in that, The material of the resistive strain gauge is a metal material or a semiconductor, and the metal material is constantan, platinum, tungsten or nickel.

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