CN113340479B - Three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle - Google Patents

Abstract

The invention relates to a three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectricity. ; The top surface of the quadrangular pyramid is composed of a thin metal layer; the bottom surface of the quadrangular pyramid is composed of a flexible substrate; the excitation coil is a plane spiral structure and is located directly below the metal thin layer; the excitation coil inputs a sinusoidal alternating current, Output impedance signal. The invention utilizes the advantages of the large dynamic response range of the eddy current tactile sensing and the high sensitivity of the piezoelectric tactile sensing, and is processed and manufactured by the micromachining technology, so as to achieve the purpose of simple structure, light and small size, and detection of contact force, and can be used in Applications in bionic manipulators, artificial limbs and other fields.

Description

Three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle

technical field

The invention belongs to the field of tactile sensing, and relates to a three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle.

Background technique

Tactile sense is an important sense when an organism is in contact with the outside world. Humans can use this sense to feel the shape, texture, quality and temperature of objects. Since intelligence is an important direction for the development of robots in the future, robots need reliable tactile sensing capabilities. In order to accurately and properly manipulate objects in unstructured and complex environments, the development and application of tactile sensing technology is an important part of the development of intelligent robots, which are widely used in medical rehabilitation, health detection, mechanical grasping and safety. measurement and many other fields. At present, the working principles of tactile sensors mainly include capacitive, piezoelectric, eddy current and resistive. Among them, piezoelectric and eddy current are widely used. Piezoelectric tactile sensors have high sensitivity and good stability, and eddy current tactile sensors have the advantages of large dynamic response range and linear output.

For tactile sensors, large response range and high sensitivity are two important metrics, and the relationship between the two is trade-offs. Most of the current tactile sensors are based on one of these principles, which makes the sensor unable to take into account both a large response range and high sensitivity, which limits the practical application of tactile sensors. And for tactile sensing used in bionic manipulators, artificial limbs and other fields, it not only needs to have a large response range and high sensitivity, but also needs to have the characteristics of small size, simple structure and bendability.

Therefore, it is of great significance to design a tactile sensor that meets the above characteristics.

SUMMARY OF THE INVENTION

In order to meet the requirements of large response range, high sensitivity and small size of the tactile sensor, the present invention provides a three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle.

For achieving the above object, the scheme that the present invention adopts is as follows:

A three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principles, including a quadrangular pyramid-shaped body with a hollow structure and a single excitation coil located in the body; the sides of the quadrangular pyramid are surrounded by PVDF films; The top surface is composed of a thin metal layer; the bottom surface of the quadrangular pyramid is composed of a flexible substrate; the excitation coil is a plane spiral structure and is located directly under the thin metal layer; the PVDF film can be deformed under the action of pressure; the excitation coil The coil inputs sinusoidal alternating current and outputs impedance signal.

After the PVDF film is deformed by force, charges are generated on the surface, which changes the internal magnetic field of the sensor. The impedance signal of the excitation coil is directly connected to the signal processing circuit, and the induced voltage is output after the circuit processing. The size of the tactile sensor needs to be small and thin. According to the principle of eddy current, when an eddy current is generated on the thin metal layer, there will be a skin layer depth. Through the simulation experiment and the application requirements of the sensor, the initial distance between the coil and the thin metal layer is set. is 500 microns. When a contact force is applied to the sensor, the distance between the excitation coil and the thin metal layer becomes smaller, and the PVDF film deforms.

As the preferred technical solution:

For the above-mentioned three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectricity, a single excitation coil is bonded to the upper surface of the flexible substrate with liquid silica gel (the other side of the carrier where the copper coil is located is bonded to the flexible substrate). The metal thin layer and the side surrounded by the PVDF film are bonded with liquid silica gel.

As mentioned above, the three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, the thin metal layer can deform under the action of pressure.

In the above-mentioned three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectricity, the metal thin layer is a layered structure with a certain thickness, the top view of the layered structure is rectangular, and the upper and lower surfaces are corrugated. The papillary lines and Minas corpuscles in human skin are imitated, which increases the maximum static friction between the sensor and the surface of the contacting object, and improves the sensitivity and response speed of the sensor.

As mentioned above, the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, the thin metal layer is made by mixing copper powder or aluminum powder with liquid silica gel at a mixing ratio of 10:1, pouring it into the mold, and pouring it into the mold at room temperature. Set aside for 3 hours to solidify. This ratio can not only make the metal thin layer have metallic properties, but also can make the metal thin layer flexible and able to bend and deform.

The three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectricity as mentioned above has a thickness of 100-300 microns; the ratio of the projected area of the metal thin layer on the plane where the excitation coil is located to the projected area of the excitation coil on the plane 1:1. It has been verified that the area ratio greater than 1 or less than 1 has no great influence on the performance of the flexible tactile sensing unit based on the eddy current principle. For the convenience of manufacture, experiment and calculation, the area ratio is set to 1.

The above-mentioned three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, when no deformation occurs, the four sides of the quadrangular pyramid have the same shape.

In the above-mentioned three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectricity, the excitation coil is composed of a flexible carrier and a copper coil with a planar spiral structure on it.

For the above-mentioned three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, the excitation coil is formed by using magnetron sputtering process to plate copper on a polyimide film (flexible carrier). Using the magnetron sputtering process in the micromachining process, the formed metal film has better density and is more closely combined with the flexible substrate.

For the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectricity as described above, the thickness of the flexible substrate is 200 microns and is made of silica gel. Silica gel is selected, which is as flexible as human skin, deformable and elastic, easy and fast to process, low material cost, cheap price, higher tensile strength and impact resistance than other flexible films, and is used in bionic manipulators, artificial Prosthetics, etc. can be bent at will, which is very suitable for curved surfaces.

In the above-mentioned three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, the deformation ability of the PVDF film satisfies 0.083P+0.021=w; wherein, P is the vertical pressure, and w is the deformation amount.

The working principle of the present invention is described as follows:

A three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, when the tactile sensor is subjected to external force, the PVDF film is compressed and deformed, the distance between the metal thin layer and the excitation coil changes, and the function generator moves toward the excitation The sinusoidal alternating current I ₁ is input to the coil, and an alternating magnetic field H ₁ is generated around the excitation coil, and at the same time, the excitation coil outputs an impedance signal. The impedance signal is directly connected to the signal processing circuit, and the induced voltage is output after the circuit processing. According to Faraday's law of electromagnetic induction, An eddy current I ₂ is generated on the surface of the thin metal layer, and the eddy current I ₂ will generate an induced magnetic field H ₂ opposite to the direction of the alternating magnetic field. The alternating magnetic field changes, and the impedance and induced voltage of the excitation coil change accordingly; at this time, deformation occurs The surface of the PVDF film generates electric charge, which changes the internal magnetic field of the tactile sensor, and further changes the impedance and induced voltage of the excitation coil.

The invention utilizes the advantages of the large dynamic response range of the eddy current tactile sensing and the high sensitivity of the piezoelectric tactile sensing, and applies the two principles to the tactile sensor at the same time, so that the tactile sensor can take into account the large response range and high sensitivity at the same time. ;Using micro-processing technology to make the overall size of the tactile sensor small; the selected material is flexible, light in weight, can be applied on complex curved surfaces, and the output signal is an alternating voltage signal, which can be directly connected to the signal processing circuit, The detection system of the tactile sensor is simplified. Only a single coil is printed on the flexible substrate to avoid complicated wiring and signal crosstalk. The excitation coil adopts a plane spiral structure, which can obtain high inductance and low resistance, and improve the sensitivity and resolution of the tactile sensor. The direction of the external force on the PVDF film is different, and the amount of charge generated on the surface of the film is also different, which can realize three-dimensional force detection; the structure is simple, the surface where the contact force is applied is not connected by any wires, and the damaged surface is easy to replace.

Beneficial effects:

(1) The three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle of the present invention utilizes the advantages of large dynamic range response of eddy current tactile sensing and high sensitivity of piezoelectric tactile sensing. The principles are combined together to ensure high sensitivity while achieving a large dynamic range response;

(2) The three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principle of the present invention, by designing PVDF film to enclose the side of the three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, to the tactile When the sensor applies external force in different directions, the PVDF film deforms differently, the internal magnetic field of the tactile sensor changes, and the induced voltage output by the excitation coil changes accordingly, thereby realizing three-dimensional force detection;

(3) The three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle of the present invention, the tactile sensor has a simple structure and manufacturing process, and selects suitable flexible materials, so that the sensing unit has flexibility, simple structure and high flexibility. The advantages of light and small size can be applied in fields such as bionic manipulators and artificial prostheses.

Description of drawings

Fig. 1 is the three-dimensional structure schematic diagram of the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle of the present invention;

2 is a cross-sectional view of a three-dimensional force-flexible tactile sensor based on the coupling of eddy current and piezoelectric principles of the present invention;

Fig. 3 is the plane structure schematic diagram of the excitation coil of the present invention;

Fig. 4 is the three-dimensional structure diagram of the metal thin layer of the present invention;

Fig. 5 is the top view of the metal thin layer of the present invention;

Fig. 6 is the longitudinal sectional view of the metal thin layer of the present invention;

Fig. 7 is the working principle diagram of the present invention;

8 is a schematic structural diagram of the three-dimensional force-flexible tactile sensor of the present invention installed on a robot bionic finger;

Figure 9 is a schematic diagram of the direction of the vertical force 1;

Figure 10 is the test result diagram corresponding to the vertical force 1;

Figure 11 is a schematic diagram of the direction of the sliding force 1;

Fig. 12 is the test result graph corresponding to sliding force 1;

Figure 13 is a schematic diagram of the directions of sliding force 2 and vertical force 2;

Fig. 14 is the test result graph corresponding to sliding force 2 and vertical force 2;

Among them, 1-metal thin layer, 2-PVDF film, 3-excitation coil, 4-flexible substrate, 5-three-dimensional force flexible tactile sensor, 6-robot bionic finger.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

The three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, as shown in Figures 1 to 3, includes a quadrangular pyramid-shaped body with a hollow structure and a single excitation coil 3 located in the body; the sides of the quadrangular pyramid are made of PVDF The film 2 is enclosed and formed; the top surface of the quadrangular platform is composed of a metal thin layer 1; the bottom surface of the quadrangular platform is composed of a flexible substrate 4; the PVDF film can be deformed under the action of pressure. When no deformation occurs, the four sides of the quadrangular pyramid have the same shape.

The excitation coil is a plane spiral structure and is located directly under the thin metal layer; the excitation coil inputs a sinusoidal alternating current and outputs an impedance signal. After the PVDF film is deformed by force, charges are generated on the surface, which changes the internal magnetic field of the sensor. The impedance signal of the excitation coil is directly connected to the signal processing circuit, and the induced voltage is output after the circuit processing.

The single excitation coil is bonded to the upper surface of the flexible substrate with liquid silica gel (the other side of the carrier where the copper coil is located is bonded to the flexible substrate). The metal thin layer and the side surrounded by the PVDF film are bonded with liquid silica gel.

The thin metal layer is prepared by mixing copper powder or aluminum powder with liquid silica gel at a mixing ratio of 10:1, pouring it into a mold, and standing at room temperature for 3 hours to solidify. This ratio can not only make the metal thin layer have metallic properties, but also can make the metal thin layer flexible and able to bend and deform. The metal thin layer is a layered structure with a certain thickness (100-300 microns), the top view of the layered structure is rectangular, and the upper and lower surfaces are corrugated. The papillary lines and Minas corpuscles in human skin are imitated, which increases the maximum static friction between the sensor and the surface of the contacting object, and improves the sensitivity and response speed of the sensor. The ratio of the projected area of the thin metal layer on the plane where the excitation coil is located to the projected area of the excitation coil on the plane is 1:1. It has been verified that the area ratio greater than 1 or less than 1 has no great influence on the performance of the flexible tactile sensing unit based on the eddy current principle. For the convenience of manufacture, experiment and calculation, the area ratio is set to 1. Thin metal layers can deform under pressure.

The excitation coil is composed of a flexible carrier and a copper coil in a spiral structure on it. The excitation coil is formed by plating copper on polyimide using a magnetron sputtering process. Using the magnetron sputtering process in the micromachining process, the formed metal film has better density and is more closely combined with the flexible substrate.

The flexible substrate is a layered structure made of silicone. Silica gel is selected, which is as flexible as human skin, deformable and elastic, easy and fast to process, low material cost, cheap price, higher tensile strength and impact resistance than other flexible films, and is used in bionic manipulators, artificial Prosthetics, etc. can be bent at will, which is very suitable for curved surfaces.

A three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principles, the tactile sensor formed by multiple arrays has the ability to detect the distribution of contact force.

The working principle of the present invention is described as follows:

As shown in Figure 7, a three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, when the tactile sensor is subjected to external force, the PVDF film is compressed and deformed, and the distance between the metal thin layer and the excitation coil changes. , the function generator inputs a sinusoidal alternating current I ₁ to the excitation coil, then an alternating magnetic field H ₁ is generated around the excitation coil, and at the same time, the excitation coil outputs an impedance signal, which is directly connected to the signal processing circuit, and the induced voltage is output after the circuit processing, According to Faraday's law of electromagnetic induction, an eddy current I ₂ is generated on the surface of the thin metal layer, and the eddy current I ₂ will generate an induced magnetic field H ₂ opposite to the direction of the alternating magnetic field. The alternating magnetic field changes, and the impedance and induced voltage of the excitation coil follow change; at this time, the deformed PVDF film surface generates electric charge, which changes the internal magnetic field of the tactile sensor, and further changes the impedance and induced voltage of the excitation coil.

In order to verify the technical effect of the present invention, the specific dimensions of the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle manufactured by the present invention are:

As shown in Figures 4 to 6, the thickness of the metal thin layer is 200 microns (that is, m shown in Figure 6), the top view is square, and the side length is 4000 microns; The distance between the points is 100 microns (i.e., l in Figure 6); the ratio of the projected area of the thin metal layer on the plane where the excitation coil is located to the projected area of the excitation coil on this plane is 1:1. The thickness of the PVDF film is 200 microns, and the angle between the four sides of the quadrangular pyramid and the flexible substrate is 45°. The top view of the flexible substrate is a square with a side length of 5000 microns and a thickness of 200 microns. The size of the three-dimensional force-flexible tactile sensor prepared in the experiment in the present invention is 700 microns in thickness and 25 mm ² in area.

The specific use process is as follows: as shown in FIG. 8, the three-dimensional force flexible tactile sensor 5 is installed on the robot bionic finger 6, and the excitation coil 3 of the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle is connected to the sinusoidal When the robot bionic finger 6 touches an object, the surface of the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle is subjected to external force, and the side of the three-dimensional force flexible tactile sensor surrounded by PVDF film 2 is compressed and deformed , the distance between the thin metal layer 1 and the excitation coil 3 changes at this time. According to the working principle of the three-dimensional force flexible tactile sensor based on the coupling of eddy current and piezoelectric principle, the application of external force can be obtained by detecting the impedance and induced voltage on the excitation coil 3, so as to further control the operation state of the robot bionic finger 6.

The specific test process is as follows:

As shown in Figures 9-10, a vertical force 1 of 10 N is applied to the metal thin layer of the sensor, and the detected output voltage curve is shown in Figure 10. The maximum output signal amplitude is 4.97 volts. After 2.2 seconds, the 10N force disappeared and the PVDF film began to release charges, with a minimum output signal amplitude of -5.58 volts.

Next, as shown in Figures 11 to 12, a sliding force 1 of 10 N is applied to the sensor. When the sliding force is applied, the projected area of the thin metal layer on the excitation coil decreases, causing changes in the magnetic field inside the sensor. Compared with Figure 10, the frequency of output voltage changes is higher, but the voltage value is smaller. The maximum amplitude at 1.9s is 0.397V. Therefore, the form and value of the haptic signal can be distinguished by the change of the output voltage waveform.

Next, as shown in Figures 13 to 14, a sliding force 2 of 10N is applied to the sensor, and then a vertical force 2 of 3N is applied from the moment of 1.6s, and the cycle period is 5s. When the vertical force 2 is applied, the output voltage value and the curve fluctuation range increase, and the maximum amplitude of the output voltage reaches 1.92V. When the vertical force 2 is removed, the output voltage value and curve fluctuation range return to the original output state.

By analyzing the above simulation results, it can be seen that when the magnitude and direction of the force change, the deformation of the PVDF is different, the distance between the metal thin layer and the excitation coil decreases, and the projected area also decreases, resulting in a significant difference in the output curve of the output voltage. Haptic signals can be distinguished based on output voltage amplitude and curve fluctuations. Therefore, tactile sensors can detect vertical and sliding forces.

Claims (10)

1. Three-dimensional flexible tactile sensor of power based on electric vortex and piezoelectricity principle coupling, its characterized in that: the excitation coil comprises a quadrangular frustum pyramid-shaped body with a hollow structure and a single excitation coil positioned in the body; the side surface of the quadrangular frustum is surrounded by a PVDF film; the top surface of the quadrangular frustum is formed by a metal thin layer; the bottom surface of the quadrangular frustum is formed by a flexible substrate; the excitation coil is of a planar spiral structure and is positioned right below the metal thin layer; the PVDF film can deform under the action of pressure; the exciting coil inputs sine alternating current and outputs an impedance signal.

2. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling according to claim 1, wherein the single excitation coil is bonded with the upper surface of the flexible substrate by liquid silicone.

3. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling according to claim 1, wherein the thin metal layer can be deformed under pressure.

4. The three-dimensional flexible force tactile sensor based on eddy current and piezoelectric principle coupling according to claim 1, wherein the metal thin layer is a layered structure with a certain thickness, the top view of the layered structure is rectangular, and the upper surface and the lower surface are corrugated.

5. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling of claim 1, wherein the metal thin layer is prepared by mixing copper powder or aluminum powder and liquid silica gel in a mixing ratio of 10:1, pouring into a mold, and standing at normal temperature for solidification.

6. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling of claim 1, wherein the four sides of the quadrangular frustum are the same shape when no deformation is generated.

7. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling of claim 1, wherein the excitation coil is composed of a flexible carrier and a copper coil with a planar spiral structure thereon.

8. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling of claim 7, wherein the excitation coil is formed by plating copper on polyimide by magnetron sputtering process.

9. The three-dimensional force flexible touch sensor based on eddy current and piezoelectric principle coupling according to claim 1, wherein the flexible substrate is made of silicon gel.

10. The eddy current and piezoelectric principle coupled based three-dimensional force flexible touch sensor according to claim 1, wherein the PVDF film has a deformation capability of 0.083P +0.021 ═ w; where P is the vertical pressure and w is the amount of deformation.

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