A six-degree-of-freedom tactile sensor

Abstract

The application discloses a six-degree-of-freedom tactile sensor and relates to the technical field of sensors.The application is based on the principle of a capacitive sensor and comprises, from top to bottom, an upper layer circuit board, a tangential dielectric layer, a middle layer circuit board, a normal dielectric layer and a lower layer circuit board; by arranging multi-dimensional force detection in different detection layers, the difficulty of decoupling between multi-dimensional forces is reduced; based on a plurality of pairs of interdigitated electrode structures, by newly designing the shapes and distribution of electrode plates, high-sensitivity measurement of multi-dimensional force / torque and efficient decoupling between dimensions can be realized; based on the structural arrangement, the application can realize high-sensitivity measurement of six-axis force by the sensor, and has the characteristics of a large sensing area and good decoupling effect.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a six-degree-of-freedom tactile sensor. Background Technology

[0002] With the development of robotics technology, robots have been widely used in factory production, and more and more simple, tedious, and dangerous tasks can be assigned to robots or assisted by humans. To enable robots to adapt to different environments, they must be able to sample and process certain parameters of their surroundings, such as vision and touch. Currently, robot vision is maturely applied to robot localization and terrain recognition. However, vision is easily affected by light occlusion and low light conditions. Therefore, the perception of tactile force shows a significant advantage in environments where visual sensing is difficult to apply. Thus, tactile sensors are crucial for the interaction between robot systems and their external environment.

[0003] The function of a contact force sensor is to measure the contact force it experiences. In robotics, this measurement allows the robot to assess the contact between its end effector and a target object, providing feedback to the robot. The robot then adjusts its posture to adapt the end effector to different surfaces. Common tactile sensing methods include optical, piezoresistive, piezoelectric, and capacitive sensors. Piezoresistive and piezoelectric sensors mostly only measure single-dimensional forces. While optical array sensors can infer three-dimensional force distribution from visual information, their measurement accuracy is low and they are often bulky. Capacitive tactile sensing methods, due to their ability to measure multi-degree-of-freedom forces, fast response speed, and simple device structure, hold promise as a sensing approach for mapping the motion state of adhered interfaces through touch.

[0004] Chu Zhongyi et al. from Beijing University of Aeronautics and Astronautics proposed a machine decoupling design method for a six-degree-of-freedom tactile sensor. By adding a torque sensing electrode to the tangential force detection layer, the torque can be detected and decoupled from other axial forces. However, it still has drawbacks such as small sensing area and low utilization of the facing area. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a six-degree-of-freedom tactile sensor with a novel decoupling method.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A six-degree-of-freedom tactile sensor comprises, from top to bottom: an upper circuit board (1), a tangential dielectric layer (3), an intermediate circuit board (5), a normal dielectric layer (7), and a lower circuit board (9);

[0008] The upper circuit board (1) is a four-layer board, of which the bottom layer of the upper circuit board (1) is the upper electrode plate (2) for tangential force / torque detection; in the other three layers of the upper circuit board (1), the top layer is grounded by copper, and the remaining two layers are used for signal traces;

[0009] The intermediate layer circuit board (5) is a six-layer board. Its top layer is the lower electrode plate (4) for tangential force / torque detection, and its bottom layer is the upper electrode plate (6) for normal force / torque detection. The upper electrode plate (6) for normal force / torque detection consists of four exposed electrodes. The other four layers in the intermediate layer circuit board (5) are used for internal signal routing and grounding shielding.

[0010] The lower circuit board (9) is a two-layer board, wherein the top layer is the lower electrode plate (8) for normal force / torque detection, and the bottom layer is a full-layer copper-plated ground shield;

[0011] The upper electrode plate (2) and lower electrode plate (4) for tangential force / torque detection are each provided with eight sensing areas. Each area of ​​the upper electrode plate (2) for tangential force / torque detection is composed of an array of multiple pairs of interdigitated electrodes formed by alternating square wave excitation sources and active shielding. Each area of ​​the lower electrode plate (4) for tangential force / torque detection has two intersecting finger electrodes that connect different detection channels. The four triangular areas at the four corners of the lower electrode plate (4) for tangential force / torque detection are centrally symmetrical about the geometric center of the sensor. The four diamond-shaped areas are two pairs of horizontally intersecting finger electrodes and two pairs of vertically intersecting finger electrodes, and each pair of finger electrodes is axially symmetrical. By performing differential calculations on the capacitance values ​​detected by each channel, hardware decoupling between tangential forces and between tangential forces and torques can be achieved.

[0012] The upper electrode plate (6) for normal force / torque detection consists of four bare electrodes, each of which is a detection channel. The lower electrode plate (8) for normal force / torque detection consists of a whole bare electrode connected to square wave excitation. The capacitance values ​​collected by the four bare electrodes are calculated to achieve hardware decoupling between torques and between torque and normal force.

[0013] Optionally, the tangential medium layer (3) is a rectangular sheet of silicone material with a shear modulus that meets the set modulus requirement and a thickness that meets the set thickness requirement.

[0014] Optionally, the normal dielectric layer (7) is a layer of sparse elastic silicone; the sparse elastic silicone meets the set requirements.

[0015] Optionally, the intermediate layer circuit board (5) is further provided with a CDC conversion chip, and the square wave excitation, active shielding and grounding shielding signals of the upper layer circuit board (1) and the lower layer circuit board (9) are all provided by the CDC conversion chip.

[0016] Optionally, the normal dielectric layer (7) is disposed on the lower circuit board (9); the intermediate circuit board (5) is disposed on the normal dielectric layer (7); the tangential dielectric layer (3) is disposed on the intermediate circuit board (5); and the upper circuit board (1) is disposed on the tangential dielectric layer (3).

[0017] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0018] 1) Six degrees of freedom detection: This invention can simultaneously detect contact forces in six degrees of freedom, including the perception of tactile information such as normal force, tangential force, torque and torque.

[0019] 2) High sensitivity detection: This invention improves the resolution of the sensor through differential capacitor circuit design. At the same time, by designing a linear mesh structure in the normal dielectric layer and a rectangular solid-filled structure in the tangential dielectric layer, the sensitivity of the sensor to tangential force, normal force, torque and torque can be greatly improved.

[0020] 3) Hardware Decoupling: This invention designs a six-axis force detection channel layout, placing the torque and shear force detection electrodes on the same detection layer. The torque detection area and channel distribution are centrally symmetrical about the sensor center, and the tangential force detection area is axially symmetrical about the sensor's axis of symmetry, thereby achieving interdimensional decoupling between tangential forces and between tangential forces and torque. The torque and normal force detection electrodes are placed on the same detection layer, and the square wave excitation electrode completely covers the four channel areas. By performing different calculations on the four channels, decoupling between torques and between torques and normal forces is achieved. By designing different dielectric layers, the coupling force between the two layers is reduced.

[0021] 4) Strong anti-interference capability: The present invention uses a square wave excitation source and an active shielded signal, which can greatly improve the anti-interference capability of the sensor, reduce the impact of parasitic capacitance caused by integration and miniaturization, and improve the signal-to-noise ratio. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of the six-degree-of-freedom tactile sensor provided by the present invention;

[0024] Figure 2 The distribution diagram of each channel of the electrode plate for tangential force / torque detection provided by this invention;

[0025] Figure 3 The distribution diagram of square wave excitation and active shielding of the upper electrode plate for tangential force / torque detection provided by the present invention;

[0026] Figure 4 The present invention provides a distribution diagram of the normal force and torque detection electrode channels, square wave excitation, and active shielding; wherein, Figure 4 (a) shows the electrode channels and square wave excitation distribution of the upper (left) and lower (right) electrodes for normal force / torque detection. Figure 4 (b) is the distribution diagram of active shielding;

[0027] Figure 5 This is a schematic diagram illustrating the working mechanism of the six-degree-of-freedom tactile sensor provided by the present invention; wherein, Figure 5 (a) is a schematic diagram of the detection electrode. Figure 5 (b) is a diagram illustrating the working mechanism of a six-degree-of-freedom sensor when subjected to tangential forces Fx / Fy. Figure 5 (c) is a diagram illustrating the working mechanism of a six-degree-of-freedom sensor under torque Tz. Figure 5 (d) is a schematic diagram of the structure of the four electrode plates. Figure 5 (e) is a diagram illustrating the working mechanism of a six-degree-of-freedom sensor under normal pressure Fz. Figure 5 (f) is a diagram illustrating the working mechanism of a six-degree-of-freedom sensor when subjected to torque Mx or My.

[0028] Symbol explanation:

[0029] 1 is the upper circuit board, 2 is the upper electrode plate for tangential force / torque detection, 3 is the tangential dielectric layer, 4 is the lower electrode plate for tangential force / torque detection, 5 is the middle circuit board, 6 is the upper electrode plate for normal force / torque detection, 7 is the normal dielectric layer, 8 is the lower electrode plate for normal force / torque detection, and 9 is the lower circuit board. Detailed Implementation

[0030] 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, and 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.

[0031] The purpose of this invention is to provide a six-degree-of-freedom tactile sensor with a novel decoupling method, which can measure six-axis forces while having a large sensing area and good decoupling effect.

[0032] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] The six - degree - of - freedom tactile sensor provided by the present invention consists of a capacitive electrode circuit module and a chip peripheral circuit module. The capacitive electrode circuit includes, from top to bottom, an upper circuit board, a tangential dielectric layer, a middle circuit board, a normal dielectric layer, and a lower circuit board. The chip peripheral circuit module includes components such as a CDC (capacitance - to - digital converter) chip, a voltage - stabilizing module, and capacitive resistors.

[0034] As Figure 1 shown, the upper circuit board is a four - layer circuit board, which includes an upper - layer PCB board 1 and an upper - layer electrode plate 2. Among them, the upper - layer PCB board 1 only includes internal traces and does not include electrodes. It includes three layers: the top layer is entirely copper - plated and connected to an active shield, and the inner two layers are used for routing. The upper - layer electrode plate 2 is used for measuring the tangential force and torque of the sensor. Its bottom layer is divided into six regions, and the six regions can form a "rice" - shaped structure as a whole. Each region consists of an array of multiple pairs of interdigital electrodes formed by alternating square - wave excitation sources and active shields; the tangential dielectric layer 3 is a rectangular thin sheet made of elastic silica gel material with a relatively large shear modulus (i.e., meeting the set modulus requirements), which can improve the tangential sensitivity of the sensor, and both the modulus requirements and the thickness of the tangential dielectric layer can be set according to actual detection needs; the middle circuit board is a six - layer circuit board, which includes a lower - layer electrode plate 4, a middle - layer PCB board 5, and an upper - layer electrode plate 6. Among them, the lower - layer electrode plate 4 is a top - layer exposed electrode plate, which is mainly used for measuring the tangential force and torque of the sensor, and the electrodes in each region of the lower - layer electrode plate 4 and the bottom - layer electrode plate (i.e., the upper - layer electrode plate 2) of the upper circuit board together form the tangential - force detection electrode plate and the torque - detection electrode plate; the middle - layer PCB board 5 is a multi - layer structure, which only includes internal traces and does not include electrodes. Moreover, the middle - layer PCB board 5 serves as the second to fifth - layer structure of the middle - layer circuit board. The second and fifth layers serve as shielding layers, mainly used to isolate the internal traces and the signals of the bottom and top layers, reducing the coupling capacitance in the circuit; the third and fourth layers are used for internal signal routing and connect each channel of the sensor; the bottom - most layer (i.e., the upper - layer electrode plate 6) consists of four exposed electrodes, which together with the top layer (i.e., the lower - layer electrode plate 8) of the lower circuit board form the normal - force detection electrode plate or the torque - detection electrode plate, which is mainly used for detecting the normal force and torque of the sensor. The normal dielectric layer 7 is a sparse mesh - shaped thin sheet made of silica gel material. Among them, the sparsity of the mesh structure and the thickness of the normal dielectric layer can be determined according to actual detection requirements. Moreover, the purpose of making it a sparse mesh shape is mainly to increase the elastic coefficient of the dielectric layer, thereby improving the sensitivity of the sensor for normal - force detection. The lower circuit board is a two - layer circuit board. Its top layer is the lower - layer electrode plate 8 used for normal - force or torque detection, which is connected to a square - wave excitation, and its bottom layer is a ground shielding layer 9, which is used to shield external interference.

[0035] This invention uses a programmable CDC converter chip. The various detection channel traces led out from the CDC converter chip are isolated by active shielding, thereby reducing the generation of coupling capacitance between the lines. The CDC converter chip, linear regulator chip, decoupling capacitor and other components, as well as the various detection channels of the sensor, are distributed on the middle layer circuit board of the six-degree-of-freedom tactile sensor. The electrodes of the upper and lower circuit boards are connected to the square wave excitation and active shielding of the CDC converter chip.

[0036] like Figure 1 As shown, the upper electrode plate 2 in the upper circuit board and the lower electrode plate 4 in the middle circuit board together form the tangential force detection electrode plate and the torque detection electrode plate. Figure 2 and Figure 3 To detect the distribution of tangential force Fx / Fy and torque Tz in each channel, such as Figure 2 and Figure 3 As shown, both the tangential force detection electrode and the torque detection electrode consist of eight regions. Each region has two intersecting finger electrodes, and the four triangular regions near the four corners surround the center point of the six-degree-of-freedom tactile sensor (i.e., Figure 2 or Figure 3 The geometric center of the first diamond-shaped region is centrally symmetric; the remaining four diamond-shaped regions consist of two pairs of laterally intersecting finger electrodes and two pairs of longitudinally intersecting finger electrodes, and each pair of electrodes is axially symmetric (the axis of symmetry is...). Figure 2 or Figure 3 (The diagram shows the axis of symmetry). When the sensor is subjected to forces Fx and Fy, due to the central symmetry of the right-angled triangular regions at the four corners, the capacitance change in the 2 / 4 region is 1 / 2ΔC. Tz The change is positive in the 1 / 4 region and negative in the 2 / 4 region, so the total capacitance for detecting torque does not change. Since the two regions for detecting tangential force Fx are axially symmetrical, when the sensor is subjected to torque Fz, the increase in capacitance in the two regions also cancels out. The same applies to tangential force Fy. In this way, the measurement and hardware decoupling between tangential forces and between tangential force and torque are achieved.

[0037] exist Figure 1 In this circuit, the lower layer (i.e., the upper electrode plate 6) of the intermediate circuit board and the lower circuit board together form the normal force detection substrate and the torque detection substrate. For example... Figure 4 As shown in (a), the normal force detection plate and torque detection plate of the six-degree-of-freedom tactile sensor are both composed of four electrodes, as follows: Figure 4 As shown in (b), the lower electrode 8 (also known as the square wave excitation layer) is a single electrode, while the upper electrode 6 is connected to the four channels of the CDC conversion chip. The four channels are surrounded by active shielding to reduce stray capacitance interference. The lower electrode 8 is connected to the square wave excitation of the CDC conversion chip, which enables the measurement of normal and bending moment and hardware decoupling.

[0038] Cn is the capacitance value of channel n measured by the CDC conversion chip. During operation, the middle circuit board is a fixed electrode, while the upper and lower circuit boards are movable electrodes. When the sensor is subjected to external force, the sensor's capacitance output changes. By using the CDC conversion chip to detect these capacitance changes, the relationship between capacitance and force is found, thereby outputting the normal force Fx, tangential force Fx / Fy, and torque Fx / Fy / Fz. The working principle diagram is shown below. Figure 5 As shown.

[0039] When a six-degree-of-freedom tactile sensor is subjected to a force along the x-axis, the two channels used to detect the force along the x-axis are channel 1 and channel 2. The change in capacitance after being subjected to the force along the x-axis is ΔC. Fx =Δ(C1-C2), the two channels used to detect the force along the x-axis are channel 3 and channel 4. When subjected to a force along the y-axis, the change in capacitance is ΔC. Fy =Δ(C3-C4), the two channels used to detect the z-axis torque are channel 5 and channel 6. When the sensor is subjected to z-axis torque, the capacitance change is ΔC. Tz =Δ(C5-C6).

[0040] For example, based on Figure 5 The local structure shown in (a) illustrates how, when a six-degree-of-freedom sensor is subjected to tangential forces Fx / Fy, as... Figure 5 As shown in (b), the upper circuit board will have a tangential displacement ΔL relative to the middle circuit board, resulting in Figure 2 When the area of ​​the square wave excitation between the middle channel 1 / channel 2 or channel 3 / channel 4 and the upper electrode changes, ΔC changes when the sensor is subjected to a force in the x-axis direction. Fx =Δ(C1-C2), when the sensor is subjected to a force in the y-axis direction, ΔC Fy =Δ(ΔC3-C4).

[0041] When a six-degree-of-freedom sensor is subjected to torque Tz, such as Figure 5 As shown in (c), the upper and lower plates will rotate relative to each other by an angle of Δα. At this time, in Figure 2 The area of ​​the square wave excitation between the middle channel 5 / channel 6 and the upper electrode changes, thus changing the interpolation of the capacitance between the two channels. The change in the capacitance difference detected by channel 5 and channel 6 is ΔC. Tz =Δ(C5-C6).

[0042] based on Figure 5 The local structure shown in (d) is as follows: Figure 5 As shown in (e), when subjected to normal force Fz, the normal medium layer undergoes elastic deformation, and the distance between the two plates 6 and 8 changes by Δd. Figure 5In (e), when the sensor is subjected to a force along the x-axis, the sum of the capacitance changes of the four electrode detection channels is given by [formula missing]. When the six-degree-of-freedom tactile sensor is subjected to a force along the z-axis, the capacitance change is ΔC. Fz =Δ(C7+C8+C9+C10), in Figure 5 In (f), when the sensor is subjected to x-axis torque, the capacitance changes by ΔC. Mx =Δ(C7-C9+C8-C10), when the sensor is subjected to a y-axis torque, the sensor capacitance changes by ΔC. My =Δ(C7-C8+C9-C10).

[0043] Based on the above description, by performing different calculations on different channels, the decoupling of normal force Fz from torque Mx / My, torque Mx and My is achieved.

[0044] Similarly, in the tangential force / torque detection electrode, such as Figure 2 As shown, the triangular region is used to measure torque in the z-axis direction, and the diamond-shaped region is used to measure tangential forces in the x and y directions. After the thickness and material (i.e., elastic modulus) of the intermediate layer circuit board are selected when designing the sensor, the sensitivity of torque and x and y tangential force measurement can be adjusted by changing the area of ​​the triangular region and the diamond-shaped region. This will not be elaborated further here.

[0045] Based on the above-mentioned decoupling mechanism and working principle, compared with the prior art, the present invention also has the following advantages:

[0046] 1) Six degrees of freedom detection: This invention can simultaneously detect contact forces of six degrees of freedom, including the perception of tactile information such as normal force, tangential force, torque and torque.

[0047] 2) High sensitivity detection: The high-sensitivity six-degree-of-freedom tactile sensor of the present invention can improve the resolution of the sensor through differential capacitor circuit design. At the same time, by designing the linear mesh structure of the normal dielectric layer and the rectangular solid filling structure of the tangential dielectric layer, the sensitivity of the sensor to tangential force, normal force, torque and torque can be greatly improved.

[0048] 3) Hardware decoupling: By designing the regional layout of the six-axis force detection channels, the torque and tangential force detection electrodes are placed on the same detection layer. The torque detection area and channel distribution are centrally symmetrical with respect to the sensor center, and the tangential force detection area is axially symmetrical with respect to the sensor's axis of symmetry, thereby achieving interdimensional decoupling between tangential forces and between tangential forces and torque. The torque and normal force detection electrodes are placed on the same detection layer, and the square wave excitation electrode completely covers the four channel areas. By performing different calculations on the four channels, decoupling between torques and between torques and normal forces is achieved. By designing different dielectric layers, the coupling force between the two layers is reduced.

[0049] 4) Strong anti-interference capability: The use of square wave excitation source and active shielded signal can greatly improve the anti-interference capability of the sensor, reduce the impact of parasitic capacitance caused by integration and miniaturization, and improve the signal-to-noise ratio.

[0050] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0051] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A six-degree-of-freedom tactile sensor, characterized in that, From top to bottom, the layers are: upper circuit board (1), tangential dielectric layer (3), middle circuit board (5), normal dielectric layer (7) and lower circuit board (9). The upper circuit board (1) is a four-layer board, wherein the bottom layer of the upper circuit board (1) is the upper electrode plate (2) for tangential force / torque detection; in the other three layers of the upper circuit board (1), the top layer is grounded by copper plating, and the remaining two layers are used for signal traces; The intermediate layer circuit board (5) is a six-layer board. Its top layer is the lower electrode plate (4) for tangential force / torque detection, and its bottom layer is the upper electrode plate (6) for normal force / torque detection. The upper electrode plate (6) for normal force / torque detection consists of four exposed electrodes. The other four layers in the intermediate layer circuit board (5) are used for internal signal routing and grounding shielding. The lower circuit board (9) is a two-layer board, wherein the top layer is the lower electrode plate (8) for normal force / torque detection, and the bottom layer is a full-layer copper-plated ground shield; The upper electrode plate (2) and lower electrode plate (4) for tangential force / torque detection are each provided with eight sensing areas. Each area of ​​the upper electrode plate (2) for tangential force / torque detection is composed of an array of multiple pairs of interdigitated electrodes formed by alternating square wave excitation sources and active shielding. Each area of ​​the lower electrode plate (4) for tangential force / torque detection has two intersecting finger electrodes that connect different detection channels. The four triangular areas at the four corners of the lower electrode plate (4) for tangential force / torque detection are centrally symmetrical around the geometric center of the sensor. The four "diamond" shaped areas are two pairs of horizontally intersecting finger electrodes and two pairs of vertically intersecting finger electrodes, and each pair of finger electrodes is axially symmetrical. By performing differential calculations on the capacitance values ​​detected by each channel, hardware decoupling between tangential forces and between tangential forces and torques can be achieved. The upper electrode plate (6) for normal force / torque detection consists of four bare electrodes, each of which is a detection channel. The lower electrode plate (8) for normal force / torque detection consists of a whole bare electrode connected to square wave excitation. The capacitance values ​​collected by the four bare electrodes are calculated to achieve hardware decoupling between torques and between torque and normal force.

2. The six-degree-of-freedom tactile sensor according to claim 1, characterized in that, The tangential medium layer (3) is a rectangular sheet of silicone material with a shear modulus that meets the set modulus requirement and a thickness that meets the set thickness requirement.

3. The six-degree-of-freedom tactile sensor according to claim 2, characterized in that, The normal dielectric layer (7) is a layer of sparse elastic silicone; the sparse elastic silicone meets the set requirements.

4. The six-degree-of-freedom tactile sensor according to claim 3, characterized in that, The intermediate circuit board (5) is also provided with a CDC conversion chip. The square wave excitation, active shielding and ground shielding signals of the upper circuit board (1) and the lower circuit board (9) are all provided by the CDC conversion chip.

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