A dual-mode sensing self-decoupling fingertip three-dimensional force sensor and its preparation method

Abstract

The present invention discloses a dual-mode induction self-decoupling fingertip three-dimensional force sensor and a preparation method thereof. The sensor includes a PCB circuit board with a Hall element and an FPC circuit board fixed on the upper surface, and a pneumatic element, a capacitive element and a resistive element fixed on the lower surface; a signal source component, including a contact, a contact base and a permanent magnet; an elastic layer for wrapping the signal source component; a support component, including an upper support layer and a bottom base; the upper support layer for carrying the signal source component and the elastic layer, and the bottom base for carrying the PCB circuit board and cooperating with the upper support layer; a protective shell for wrapping the support component; and a rubber sealing layer for wrapping the signal source component to keep the internal air pressure of the sensor relatively independent and cooperate with the protective shell for overall sealing. The sensor of the present invention has stable output performance, good decoupling of three-dimensional force signals and a small size.

Description

Technical Field

[0001] The present invention relates to the technical field of robot sensing, and particularly to a self-decoupling fingertip three-dimensional force sensor with dual-mode sensing and a preparation method thereof. Background Art

[0002] Three-dimensional force sensors are often installed on the end effectors of robots or other systems to detect the contact force between the end and the environment in real time. These force feedback signals can be used for closed-loop control to precisely control the force application and movement of the end effector, realizing safer and more flexible human-machine interaction or material handling. Currently, researchers have developed various types of three-dimensional force sensors based on different physical principles and design schemes. These new three-dimensional force sensors utilize various advanced physical mechanisms to provide more accurate and rich force feedback information for intelligent systems.

[0003] Although three-dimensional force sensors are widely used in many fields, there are still some limitations and challenges. Chinese Patent with application number CN202323455363.8 discloses a robot fingertip force sensor, which measures force by attaching two strain gauges to both the inner top wall and the inner bottom wall of its square perforations. It has a small appearance and is suitable for most robot hand application scenarios; however, this device is limited by the natural frequency of its core sensing element, i.e., the strain gauge, which will affect the dynamic measurement ability of the sensor.

[0004] In addition, existing sensors also face the problem of decoupling three-dimensional forces. When the sensor is subjected to forces in different directions, there is a certain coupling relationship in the response signals of the sensor, and complex signal processing algorithms or means such as experiments and simulations are required to establish a three-dimensional force calibration model. These all increase the computational burden and reduce the real-time performance and reliability of the system. And the existing three-dimensional force sensors are relatively large and heavy in structure, which may affect the dynamic characteristics of the measured object and limit their application in some small or lightweight systems. Summary of the Invention

[0005] In order to overcome the technical problems such as non-linear response, coupling of three-dimensional force output signals, and large external dimensions of three-dimensional force tactile sensors in existing robot sensing technologies, which limit the flexibility of the manipulator, the purpose of the present invention is to provide a self-decoupling fingertip three-dimensional force sensor with dual-mode sensing and a preparation method thereof.

[0006] To achieve the above purpose, the present invention adopts the following technical solution: A self-decoupling fingertip three-dimensional force sensor with dual-mode sensing, the sensor includes:

[0007] The PCB circuit board adopts a double-layer board layout. A Hall element and an FPC circuit board are fixed on the upper surface of the PCB circuit board, and a pneumatic element, a capacitor element and a resistor element are fixed on the lower surface. The PCB circuit board is provided with ventilation holes to ensure the consistency of the internal air pressure of the sensor.

[0008] The signal source component, the signal source component includes a contact, a contact base and a permanent magnet. The contact is a regular cavity hemisphere, and the air pressure in the cavity realizes the conversion of the total external force. The bottom of the contact is stepped to bear the external force applied. The upper part of the contact base is reverse stepped and fixedly matched with the bottom of the contact. The inside of the contact base is hollow, and four flow holes are circumferentially arranged on the hollow cylindrical wall to realize the connection between the internal gas of the sensor and the gas in the contact cavity. A groove is provided at the bottom of the contact base for placing the permanent magnet. The permanent magnet is only affected by the tangential force and moves on the upper support layer surface to realize the decomposition of the force.

[0009] The elastic layer is used to wrap the signal source component. When the tangential component force causes the signal source component to move, the detection range of the tangential force is increased. When the acting force is removed, the signal source component is reset to the initial position.

[0010] The support component includes an upper support layer and a bottom base. The upper support layer is used to carry the signal source component and the elastic layer, and the bottom base is used to carry the PCB circuit board and cooperate with the upper support layer.

[0011] The protective shell is used to wrap the support component.

[0012] The rubber sealing layer is used to wrap the signal source component to keep the internal air pressure of the sensor relatively independent and cooperate with the protective shell for overall sealing.

[0013] Further, the contact is made of 40-degree silica gel, and the contact base is made of epoxy resin.

[0014] Further, the permanent magnet adopts an axially magnetized neodymium iron boron permanent magnet.

[0015] Further, the model of the Hall element is SS49E, and the model of the pneumatic element is MS5611-01BA03.

[0016] Further, the upper support layer and the bottom base are processed and manufactured by 3D printing, and the material is epoxy resin.

[0017] Further, the material of the elastic layer is Ecoflex0030.

[0018] Further, the material of the rubber sealing layer is nitrile rubber.

[0019] Further, the protective shell material is epoxy resin.

[0020] The present invention also provides a preparation method of a dual-mode induction self-decoupling fingertip three-dimensional force sensor, comprising the following steps:

[0021] Step 1: Cut the nitrile rubber film into appropriate sizes for subsequent use, and use 3D printing technology to print the required parts and molds, including the contact base;

[0022] Step 2: Thoroughly mix AB silicone in a ratio of 1:1, remove air bubbles by vacuum treatment, then pour it into the molding mold, and place the mold in an oven at 60-70°C for drying to accelerate the curing of the silicone. After casting, the contact is obtained;

[0023] Step 3: Thoroughly mix two components of Ecoflex0030 in a ratio of 1:1, remove air bubbles by vacuum treatment, then pour it into the molding mold, and place the mold in an oven at 60-70°C for drying to accelerate the curing of the silicone. After casting, the elastic layer is obtained;

[0024] Step 4: After embedding the permanent magnet into the contact base printed in Step 1, fix the contact to the contact base and let it stand to obtain the signal source component;

[0025] Step 5: By measuring and classifying the initial analog voltages of the sensor, select three Hall sensors with relatively small differences in initial analog voltages to manufacture Hall elements; weld the selected three Hall elements and the FPC circuit board to the corresponding pads on the PCB circuit board respectively;

[0026] Step 6: Flip the PCB circuit board welded in Step 5, and weld the pneumatic component, capacitor and resistor to the corresponding pads on the PCB circuit board respectively;

[0027] Step 7: Fit the PCB circuit board welded in Step 6 with the bottom base, and use sealant to fill the contact gap between the PCB circuit board and the bottom base;

[0028] Step 8: After applying sealant to the installation opening on the upper part of the base assembled in Step 7, immediately fit it with the upper support seat and pre-tighten it with a fastening table, and wait for it to cure;

[0029] Step 9: Fit the elastic layer made in Step 3 with the signal source component made in Step 4, rotate the signal source component so that the vent hole of the contact base is on the sensor axis, apply adhesive on the outer surface of the elastic layer and then embed it into the upper support layer;

[0030] Step 10: Apply sealant on the upper part of the upper support layer, and use a stretching platform to unfold the nitrile rubber film prepared in Step 1. Then, cover the rubber film on the upper surface of the sensor with a protective shell. Finally, wait for two hours for the sealant to cure to obtain the sensor.

[0031] The present invention has the following beneficial effects:

[0032] The sensor can detect the magnitude of the acting force based on the air pressure in the inner cavity, and can detect the tangential force based on the output change of the Hall element caused by the horizontal offset of the magnet.

[0033] Through the layered design scheme, the independence of the total force and tangential force detection sources is realized, thereby effectively decoupling the three-dimensional force output signal.

[0034] By combining a commercial Hall element with a pneumatic element and through appropriate structural design, stable high-dynamic response detection can be achieved, without being limited by the quality of the sensing material characteristics.

[0035] The outer dimensions of the sensor refer to the three-dimensional data of a human fingertip, making it closer to a human fingertip in appearance and laying a certain hardware foundation for the anthropomorphic dexterous operation of the manipulator.

[0036] The sensing performance of the sensor can be adjusted by using elastic layers and contacts with different elastic moduli.

[0037] The cost of manufacturing the sensor is low and the process is simple, enabling large-scale commercial use. Description of the Drawings

[0038] Figure 1 is the external view of the three-dimensional force sensor in the present invention;

[0039] Figure 2 The PCB layout diagram of the three-dimensional force sensor in the present invention;

[0040] Figure 3 The structural schematic diagram of the three-dimensional force sensor in the present invention;

[0041] Figure 4 The cross-sectional view of the right view of the three-dimensional force sensor in the present invention;

[0042] Figure 5 The pneumatic detection airway diagram of the three-dimensional force sensor in the present invention;

[0043] Figure 6 The linearity of the three-dimensional force sensor in the present invention under the action of the total force;

[0044] Figure 7 The calculation of the magnetic field strength of the permanent magnet at any point in the three-dimensional force sensor in the present invention;

[0045] Figure 8 Output variation diagram of Hall element under the action of tangential force in the three-dimensional force sensor of the present invention;

[0046] Figure 9 Schematic diagram for solving tangential force of three-dimensional force sensor in the present invention;

[0047] In the figure: rubber sealing layer 1, FPC circuit board 2, upper support layer 3, bottom base 4, protective shell 5, permanent magnet 6, signal source component 7, elastic layer 8, contact base 9, contact 10, Hall element 11, ventilation hole 12, capacitive element 13, resistive element 14, pneumatic element 15, PCB circuit board 16. Specific embodiments

[0048] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0049] As Figure 1 shown, an embodiment of the present invention provides a dual-mode induction self-decoupling fingertip three-dimensional force sensor. The sensor is designed according to the three-dimensional data of a real human fingertip. The pneumatic cavity for detecting the total force and the permanent magnet 6 for detecting the tangential force adopt a laminated design scheme. The sensor includes: a PCB circuit board 16, which adopts a double-layer board layout. As Figure 2 shown, a Hall element 11 and an FPC circuit board 2 are fixed on the upper surface of the PCB circuit board 16, adopting a triple rotational symmetry arrangement, which reduces the difficulty of signal analysis. Capacitive element 13, resistive element 14 and pneumatic element 15 are fixed on the lower surface; the PCB circuit board is provided with ventilation holes 12 to ensure the consistency of the internal air pressure of the sensor.

[0050] A signal source component 7, the signal source component 7 includes a contact 10, a contact base 9 and a permanent magnet 6; the contact 10 is a regular hollow hemisphere, and the air pressure in the cavity realizes the conversion of the external total force. The bottom of the contact 10 is stepped for bearing the external applied force; the upper part of the contact base 9 is anti-stepped and is fixedly matched with the bottom of the contact 10. The inside of the contact base 9 is hollow, and four flow holes are circumferentially arranged on the inner wall of the hollow cylinder for realizing the connection between the internal gas of the sensor and the gas in the cavity of the contact 10. A groove is provided at the bottom of the contact base 9 for placing the permanent magnet 6; the permanent magnet 6 only moves translationally on the surface of the upper support layer 3 under the action of the tangential force, so as to realize the decomposition of the force.

[0051] The elastic layer 8 is used to wrap the signal source component 7; when a tangential component force causes the signal source component 7 to move, it increases the tangential force detection range, and when the acting force is removed, it resets the signal source component 7 to its initial position.

[0052] The support component includes an upper support layer 3 and a bottom base 4; the upper support layer 3 is used to carry the signal source component 7 and the elastic layer 8, and the bottom base 4 is used to carry the PCB circuit board and cooperate with the upper support layer 3 with a gap for filling sealant.

[0053] The protective shell 5 is used to wrap the support component.

[0054] The rubber sealing layer 1 is used to wrap the signal source component 7 to keep the internal air pressure of the sensor relatively independent and cooperate with the protective shell 5 for overall sealing. The shapes and mating relationships of the above components are as Figure 3 and Figure 4 shown.

[0055] The force acting on the surface of the elastic body is defined as the total force. In the XYZ coordinate system, the force in the plane formed by the X-axis and the Y-axis is defined as the tangential component of the total force, and the force along the Z-axis direction is defined as the normal component of the total force. The three-dimensional force sensor based on the above structure can be used to decouple and sense three-dimensional forces and contact positions.

[0056] Total force detection principle: As Figure 5 shown, when an acting force acts on the top of the contact 10, the relationship between the internal air pressure value and the change in the internal volume can be deduced:

[0057] P0V0 = P1V1;

[0058] where P0 is the internal air pressure value before the change, V0 is the internal volume value before the change, P1 is the internal air pressure value after the change, and V1 is the internal volume value after the change.

[0059] Therefore, the external force causes the internal cavity of the contact 10 to deform, resulting in an increase in the air pressure value in the cavity. It should be noted that the gas in the internal cavity of the contact 10 enters the internal cavity of the sensor through the groove reserved in the middle of the contact base 9 and the gap between the contact base 9 and the elastic layer 8, and is connected to the pressure element 15 through the vent hole 12 reserved on the PCB circuit board 16. The path is as Figure 5 shown. A linear mapping relationship can be established between the value output by the pressure element and the external force applied to the sensor:

[0060]

[0061] Among them, p1 is the air pressure value after the applied force, p0 is the initial air pressure value, α and β are determined through experiments respectively. α represents the change rate, and β is the automatic correction coefficient to ensure that the initial air pressure value is constant each time the air pressure component is used.

[0062] When a force acts on the contact 10, the magnitude of the external force is determined through this linear relationship; when the force is removed from the contact 10, due to the self-elastic restoring force of the contact 10, the shape of the contact 10 returns to its original shape, and the air pressure value inside the sensor also returns to the initial value, as Figure 6 shown, which is the change in the air pressure value inside the sensor when it is subjected to an external force.

[0063] Tangential force detection principle: The equivalent current model of the cylindrical axial magnet can be considered that the external magnetic field of the permanent magnet 6 is generated by the bound surface current on the side surface of the permanent magnet 6. The bound surface current density is:

[0064]

[0065] Among them, J s represents the bound surface current density; B r represents the remanent magnetization; μ0 is the vacuum permeability.

[0066] According to the axial symmetry of the current loop, the magnitude of the magnetic field generated at point P is only related to the relative distance between the current loop and point P. Therefore, to simplify the calculation process, point P can be taken on the XOZ plane, as Figure 7 shown.

[0067] According to the Biot-Savart law, the magnetic induction intensity of the current element at Q at P(x0, 0, z0) is:

[0068]

[0069] Among them, dB is the magnetic induction intensity microelement, dz represents the height of the intercepted current loop, dl represents the current element selected on the current loop, and R is the distance between the current element at Q and point P.

[0070] Integrate the magnetic induction intensity generated by the current element along the current direction in the current loop, and at the same time use the magnetic field superposition law to integrate along the z-axis direction, then the magnetic induction intensity generated by the cylindrical permanent magnet at point P can be obtained:

[0071]

[0072] Among them, B x 、B y 、B z are the magnetic induction intensity components in different axis directions at point P, h0 is the height of the permanent magnet, r0 is the radius of the permanent magnet, is the angle between the current element and the x-axis.

[0073] In this application, the normal direction of the detection chip inside the Hall element 11 is parallel to the z-axis, so the Hall element 11 is z The intensity is measured and a Hall voltage V is generated. H , and its calculation formula is:

[0074]

[0075] Among them, I is the current passing through the Hall element; n is the carrier concentration; d is the thickness of the Hall element. And z0 is known in the design, so the distance x0 between the normal line of a single Hall element and the axis of the permanent magnet can be calculated by combining the two equations.

[0076] like Figure 8 As shown, the signal source component 7 is acted upon by the tangential force, causing the permanent magnet 6 to move, causing the output voltages of the three Hall elements 11 to change. The center distances of the three Hall elements 11 from the permanent magnet 6 can be calculated by the above formula, and then a circle with the distance from each Hall element 11 to the permanent magnet 6 as the radius can be drawn to uniquely determine the position of the permanent magnet 6, thereby determining the magnitude and direction of the tangential force, as shown in FIG. Figure 9 When the tangential component force is removed, the permanent magnet 6 embedded in the contact base 3 will be reset under the action of the elastic layer 4, thereby ensuring that the output signals of the three Hall elements 11 are restored to their original values.

[0077] Total force self-decoupling principle: According to the above total force detection principle and tangential force detection principle, the magnitude of the force, the magnitude and direction of the tangential component of the force can be obtained, and then the corresponding normal component force can be obtained according to the orthogonal decomposition principle of the force, that is, And the angle between the total force and the XY plane can be expressed by the formula have to.

[0078] The embodiment of the present invention also provides a method for preparing a dual-mode sensing self-decoupling fingertip three-dimensional force sensor, the method comprising the following steps:

[0079] Step (1), using scissors to cut the nitrile rubber film into suitable sizes for subsequent use, and using 3D printing technology to print the required parts and molds, including the contact base 9.

[0080] Step (2), fully mix AB silicone in a ratio of 1:1, then evacuate in a vacuum barrel to remove bubbles, then pour into a molding mold, put the mold into an oven at 60-70°C for one hour to accelerate the curing of the silicone, and finally reverse the mold to manufacture the contact 10.

[0081] Step (3), the two components of Ecoflex0030 are fully mixed in a ratio of 1:1, and then vacuumed in a vacuum barrel to remove bubbles, and then poured into a molding mold, and the mold is placed in an oven at 60-70°C for one hour to accelerate the curing of the silicone, and finally reversed to produce an elastic layer 8.

[0082] Step (4), embed the permanent magnet 6 into the contact base 9, then fix the contact 10 and the contact base 9 with Sil-Poxy adhesive, and let it stand for one hour to obtain the final signal source component 7.

[0083] Step (5), by measuring and classifying the initial analog voltages of the sensors, three Hall sensors with smaller initial analog voltage differences are selected to manufacture the Hall element 11. The selected three Hall elements 11 and the FPC circuit board 2 are respectively soldered to the corresponding pads of the PCB circuit board 16.

[0084] Step (6), flip over the PCB circuit board 16 soldered in step (5), and solder the air pressure element 15, the capacitor element 13 and the resistor element 14 to the corresponding pads of the PCB circuit board 16 respectively.

[0085] Step (7), match the PCB circuit board 16 welded in step (6) with the bottom base 4. In order to ensure the safety of the pneumatic element 15, the inside of the base is designed to be stepped to ensure that the bottom surface element of the PCB circuit board 16 is suspended. Finally, use sealing glue to fill the contact gap between the PCB circuit board 16 and the bottom base 4. Pay attention to ensure that the vent hole 12 on the PCB circuit board 16 is not blocked.

[0086] Step (8), after applying sealant to the installation opening on the upper part of the base assembled in step (7), immediately mate with the upper support layer 3, and pre-tighten it using a fastening table, and wait for two hours for it to solidify.

[0087] Step (9), match the elastic layer 8 made in step (3) with the signal source component 7 made in step (4), and rotate the signal source component 7 so that the vent hole of its contact base 9 is located on the sensor axis, then apply Sil-Poxy adhesive on the outer ring surface of the elastic layer 8 and embed it into the upper support layer 3.

[0088] Step (10), finally, apply sealant on the upper support layer 3, and use the stretching platform to unfold the nitrile rubber film prepared in step (1) as the rubber sealing layer 1, and then use the protective shell 5 to cover the rubber sealing layer 1 on the upper surface of the sensor. Finally, wait for two hours for the sealant to solidify, and the sensor is now complete.

[0089] Other embodiments of the present application will be readily apparent to those skilled in the art upon consideration of the specification and practice of the disclosure herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include known common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and examples are only to be considered as exemplary.

[0090] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor, characterized in that, The sensor includes: A PCB circuit board with a double-layer layout. On the upper surface of the PCB circuit board, three Hall elements and an FPC circuit board are fixed. On the lower surface, a pressure element, a capacitance element, and a resistance element are fixed. The PCB circuit board is provided with ventilation holes to ensure the consistency of the internal air pressure of the sensor; A signal source component, which includes a contact, a contact base, and a permanent magnet. The contact is a regular hollow hemisphere, and the air pressure in the cavity realizes the conversion of the external total force. The bottom of the contact is stepped to bear the external applied force. The upper part of the contact base is anti-stepped and is fixedly matched with the bottom of the contact. The inside of the contact base is hollow, and four through holes are circumferentially arranged on the inner wall of the hollow cylinder to realize the connection between the internal gas of the sensor and the gas in the contact cavity. A groove is provided at the bottom of the contact base for placing the permanent magnet. The permanent magnet is only affected by the tangential force and moves on the surface of the upper support layer, so as to realize the decomposition of the force; An elastic layer for wrapping the signal source component; when the tangential component force causes the signal source component to move, it increases the detection range of the tangential force. When the applied force is removed, the signal source component is reset to the initial position; A support component, including an upper support layer and a bottom base; the upper support layer is used to carry the signal source component and the elastic layer, and the bottom base is used to carry the PCB circuit board and cooperate with the upper support layer; A protective shell for wrapping the support component; A rubber sealing layer for wrapping the signal source component to keep the internal air pressure of the sensor relatively independent and cooperate with the protective shell for overall sealing; Among them, after the signal source component is affected by the tangential force, the permanent magnet moves, causing the output voltages of the three Hall elements to change. After calculating the central distances of the three Hall elements from the permanent magnet, circles are drawn with the Hall elements as the centers and the distances from the permanent magnet as the radii to determine the position of the permanent magnet, so as to determine the magnitude and direction of the tangential force. When the tangential component force is removed, the permanent magnet embedded in the contact base is reset under the action of the elastic layer to ensure that the output signals of the three Hall elements return to the original values.

2. The self - decoupling fingertip three - dimensional force sensor with dual - mode induction according to claim 1, wherein, The contact is made of 40-degree silica gel, and the contact base is made of epoxy resin.

3. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor according to claim 1, characterized in that, The permanent magnet uses an axially magnetized neodymium iron boron permanent magnet.

4. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor according to claim 1, characterized in that, The model of the Hall element is SS49E, and the model of the pressure element is MS5611-01BA03.

5. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor according to claim 1, characterized in that, The upper support layer and the bottom base are processed and manufactured by 3D printing, and the material is epoxy resin.

6. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor according to claim 1, wherein, The material of the elastic layer is Ecoflex0030.

7. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor according to claim 1, characterized in that, The material of the rubber sealing layer is nitrile rubber.

8. A dual-mode sensing self-decoupling fingertip three-dimensional force sensor according to claim 1, characterized in that, The material of the protective shell is epoxy resin.

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