Bionic tactile sensor based on PVDF piezoelectric film and manipulator

Abstract

This invention discloses a biomimetic tactile sensor and robotic arm based on a PVDF piezoelectric film, belonging to the field of robotic tactile sensing technology. The sensor includes a silicone rubber arched elastic substrate, a PVDF piezoelectric film, upper and lower copper foil electrode layers, and an outer encapsulation layer. Hemispherical bumps are provided on the inner surface of the substrate, and the upper and lower electrodes have a special wavy double-bump arched structure with a bump alignment error of no more than 50 μm. This structure enables the sensor to generate concentrated strain in the upper bump area under normal pressure to simulate tactile perception, and asymmetrical strain in the lower bump area under tangential force to simulate slip perception. Combining the piezoelectric and pyroelectric effects of PVDF, and through signal processing circuitry to separate DC and AC signals and analyze the low-frequency and high-frequency components in the AC signal, it can simultaneously sense pressure, slip, texture, and temperature changes. This invention has the advantages of high sensitivity, multi-information sensing integration, and a good signal-to-noise ratio, making it suitable for precise operation of biomimetic robotic arms.

Description

Technical Field

[0001] This utility model belongs to the field of robot tactile sensing technology, specifically relating to a biomimetic tactile sensor and robotic arm based on PVDF piezoelectric film. Background Technology

[0002] Currently, immersive perception technology in human-computer interaction (HCI) has gradually become a research hotspot. It is essentially a multi-sensor, multi-information fusion HCI technology, integrating gesture recognition, tactile perception, and other information fusion technologies. The implementation of HCI technology can replace humans in dangerous environments, such as fire rescue and large-scale disinfection in viral infection environments. These working environments require corresponding HCI technologies.

[0003] The human body obtains information about the external environment through five basic sensory functions: sight, hearing, smell, taste, and touch. In a broad sense, when the human body comes into contact with an object, its tactile receptors receive external mechanical stimuli, prompting the human body to produce a comprehensive sensation called touch. Compared with other sensory functions, in a narrow sense, touch enables the human body to perceive the specific attributes of the object it is in contact with, so as to perform subsequent operations on the object.

[0004] Starting with tactile perception, people can obtain information about the characteristics of external objects. For example, traditional Chinese medicine practitioners can diagnose patients by taking their pulse, and blind people can perceive the world. At the same time, touch also conveys emotional information in interpersonal communication, such as a warm handshake and a friendly hug. Through various tactile sensory information, people can systematically communicate and interact with the outside world. Therefore, integrating tactile information is of positive and important significance for people to understand matter and perceive the world.

[0005] Tactile receptors are distributed throughout the human body. Skin, as the largest organ, contains various types of receptors at different locations on its surface and at different depths. A defining characteristic of human skin is its excellent mechanical properties, allowing it to stretch and extend without causing physical damage. Skin can transmit the physical properties of objects we interact with to receptors buried beneath the protective epidermis. Therefore, in the development of artificial skin, the materials chosen for its manufacture should reflect the flexibility and stretchability of natural human skin. Equally important is the self-healing ability of human skin; artificial skin should also possess this quality to enable its long-term use. Therefore, the choice of materials is crucial.

[0006] Furthermore, tactile receptors internally sense pain, itching, and temperature, while externally they perceive stimuli such as humidity, temperature, and pressure. The fingertips, in particular, have a greater number and variety of receptors, making their tactile perception capabilities exceptionally sharp. In summary, human skin's tactile perception is intricate. While tactile receptors can qualitatively distinguish different external stimuli, they cannot quantitatively differentiate the physical quantities representing the intensity of the stimulus. To address this, tactile sensors, based on the mechanism of human tactile perception, utilize sensitive materials and special structures to effectively mimic human skin's tactile perception. They can sense changes in the physical quantities produced by external stimuli and quickly convert them into signal data according to corresponding rules. In other words, tactile sensors can present the perception of different external stimuli such as hardness, temperature, and pressure, helping biomimetic mechanical devices and intelligent instrument systems acquire tactile perception capabilities.

[0007] Existing robot tactile sensors mostly adopt capacitive and piezoresistive structures. Capacitive sensors are not sensitive to shear force, piezoresistive sensors have slow dynamic response, and most sensors are difficult to decouple multiple information in a single structure. Especially in simulating multi-dimensional tactile perception of human skin, existing technologies are unable to simultaneously achieve multi-information perception of touch, slip, and heat. Utility Model Content

[0008] The purpose of this invention is to solve the above-mentioned technical problems and provide a biomimetic tactile sensor and robotic arm based on PVDF piezoelectric film.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0010] A biomimetic tactile sensor based on PVDF piezoelectric thin film, including

[0011] An arched elastic substrate made of silicone rubber, wherein the inner surface of the arched elastic substrate has at least two hemispherical protrusions arranged side by side;

[0012] A PVDF piezoelectric film covering the arched elastic substrate;

[0013] A copper foil lower electrode layer and an upper electrode layer are covered on the upper and lower surfaces of the PVDF piezoelectric film. Both the lower electrode layer and the upper electrode layer are wavy double-convex arch structures adapted to the shape of the arched elastic substrate. The positions of the upper convex points and the lower convex points of the two electrode layers are aligned with each other, and the alignment error of their center points is no greater than 50 μm. The wavy double-convex arch structure is configured such that: when subjected to normal pressure, the upper convex point area generates concentrated strain, simulating the function of Meissner bodies in human skin, for sensing static touch; when subjected to tangential force, the lower convex point area generates asymmetric strain, simulating the function of ring-like bodies in human skin, for sensing dynamic slip.

[0014] And the outermost transparent rubber encapsulation layer;

[0015] The sensor is attached to the curved surface of the mechanical fingertip through a rubber encapsulation layer, with its arched opening facing away from the direction in which the fingertip contacts the object.

[0016] Furthermore, the diameter of the hemispherical protrusion is 0.8-1.2 mm, the height is 0.3-0.5 mm, and the center distance between two adjacent protrusions is 1.5-2.0 mm.

[0017] Furthermore, the inner diameter of the arched elastic base is 4-6mm, and the curvature is similar to that of the tip of a human index finger.

[0018] Furthermore, the PVDF piezoelectric film exhibits both piezoelectric and pyroelectric effects, and the sensor can simultaneously sense pressure, slippage, texture, and temperature changes by analyzing the frequency characteristics and DC component changes of the output signal.

[0019] Furthermore, the thickness of the encapsulation layer is 0.2-0.4 mm, and its Shore A hardness is 10-20, so as to ensure effective force transmission while protecting the internal structure.

[0020] A bionic robotic hand, comprising:

[0021] As described above, the bionic tactile sensor;

[0022] The robotic hand has a sensor that is attached to the curved surface of the fingertip through its encapsulation layer, and the arched opening of the sensor faces away from the direction in which the fingertip contacts the object.

[0023] A signal conditioning circuit board is electrically connected to the electrode layer of the sensor. The signal conditioning circuit board integrates a pre-charge amplifier circuit, a bandpass filter circuit, and a signal separation circuit. The passband frequency range of the bandpass filter circuit is configured to match the frequency response characteristics of the bionic tactile sensor to effectively extract tactile and tactile signals.

[0024] The microcontroller module is used to sample and convert the conditioned analog signal to digital.

[0025] The wireless communication module is used to transmit digital signals to the host computer system.

[0026] Furthermore, the pre-charge amplifier circuit uses a JFET input type ultra-low bias current operational amplifier chip, with a feedback capacitor Cf of 100pF and a feedback resistor Rf of 100MΩ.

[0027] Furthermore, the signal separation circuit includes a voltage follower for acquiring the low-frequency voltage signal generated by the pyroelectric effect to sense temperature, and a passband filter circuit for acquiring the mid-to-high frequency AC signal generated by the piezoelectric effect to sense pressure and vibration.

[0028] Furthermore, each segment of the mechanical finger is driven by a DC servo motor, and all servos are coordinated and controlled by a main controller configured to receive instructions from a wearable data glove or a host computer and to perform adaptive gripping force control based on the tactile and slip signals fed back by the bionic tactile sensor.

[0029] Compared with the prior art, the beneficial effects of this utility model are:

[0030] 1. This utility model significantly improves the sensitivity and signal-to-noise ratio to micro-pressure, texture, sliding and temperature changes through a biomimetic "double convex point + arch" composite structure design and optimized signal conditioning circuit, realizing the effective perception of multi-dimensional tactile information by a single sensor.

[0031] 2. The unique double-convex structure of this utility model can respond to normal force and tangential force respectively, mimicking the Meissner bodies and cycloid bodies under human skin. Combined with the piezoelectric and pyroelectric effects of PVDF, a single sensor can simultaneously acquire pressure, sliding, texture roughness and temperature information, achieving high sensitivity and multi-information perception.

[0032] 3. The arched structure of this utility model enhances the mode strain of the PVDF film, and the charge output can be increased by more than 30% compared with the planar structure. The specially designed 0.1Hz-100Hz bandpass filter circuit effectively suppresses low-frequency drift and high-frequency noise, greatly improving the signal-to-noise ratio.

[0033] 4. The internal arched base of this utility model provides stable support, and the external ultra-soft silicone encapsulation layer with a Shore A hardness of 10-20 not only ensures sensitive force transmission, but also protects the fragile internal film and circuit, thereby improving the sensor's durability and environmental adaptability.

[0034] 5. The sensor of this utility model fits perfectly with the curved surface of the mechanical fingertip. Combined with the wireless communication module, it realizes the integration of information perception, signal processing and wireless transmission, providing a hardware foundation for the real-time and precise control of the bionic robotic hand.

[0035] 6. This utility model achieves the differentiation of strain distribution under normal force and tangential force through a unique wave-shaped double-convex electrode design, thereby realizing the initial decoupling of tactile and slip information on a single sensor. Attached Figure Description

[0036] Figure 1This is a schematic diagram of the arched structure layer of this utility model;

[0037] Figure 2 This is a schematic diagram of the electrode layer structure of this utility model;

[0038] Figure 3 This is a schematic cross-sectional view of the electrode layer structure of this utility model;

[0039] Figure 4 This is a schematic diagram of the sensor of this utility model installed on a robotic arm;

[0040] Figure 5 This is a schematic diagram of the control logic flow of this utility model;

[0041] Figure 6 This is a schematic diagram of the signal conditioning circuit of this utility model;

[0042] In the figure: 1-elastic substrate; 2-lower electrode layer; 3-PVDF piezoelectric film; 4-upper electrode layer; 5-encapsulation layer; 6-bump; 7-upper bump; 8-lower bump; 9-robotic arm. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0044] A biomimetic tactile sensor based on PVDF piezoelectric thin film, including

[0045] An arched elastic base 1 made of silicone rubber, the inner diameter of the arched elastic base 1 is 4-6mm, the curvature is similar to the curvature of the tip of the human index finger, and the inner surface of the arched top of the arched elastic base 1 is provided with at least two hemispherical protrusions 6 arranged side by side, the diameter of the hemispherical protrusions 6 is 0.8-1.2mm, the height is 0.3-0.5mm, and the center distance between two adjacent protrusions is 1.5-2.0mm;

[0046] A PVDF piezoelectric film 3 is covered on the arched elastic substrate 1. The PVDF piezoelectric film 3 has both piezoelectric and pyroelectric effects. The sensor can simultaneously sense pressure, sliding, texture and temperature changes by analyzing the frequency characteristics and DC component changes of the output signal.

[0047] The copper foil lower electrode layer 2 and upper electrode layer 4 cover the upper and lower surfaces of the PVDF piezoelectric film 3. Both the lower electrode layer 2 and upper electrode layer 4 are wavy double-convex arch structures adapted to the shape of the arched elastic substrate 1. The upper and lower electrode layers are processed by photolithography etching to ensure that the alignment error of the center position of the upper and lower convex points in the wavy structure is controlled within 50μm, so as to ensure the synergistic and decoupling effect of the strain field under the action of normal force and tangential force. The wavy double-convex arch structure is configured such that: when subjected to normal pressure, the upper convex point 7 region generates concentrated strain, simulating the function of Meissner bodies in human skin, for sensing static touch; when subjected to tangential force, the lower convex point 8 region generates asymmetric strain, simulating the function of ring-like bodies in human skin, for sensing dynamic slip.

[0048] The wave-shaped double-convex arch structure preferably has a sinusoidal waveform, and its period matches the distribution of hemispherical protrusions 6 on the arch elastic substrate 1. The curvature radius of the upper protrusion 7 and the lower protrusion 8 is in the range of 0.4-0.6 mm. This specific structure ensures that when under stress, the strain of the PVDF film is mainly concentrated in the protrusion area, rather than the entire plane, thereby significantly improving the charge output efficiency and signal-to-noise ratio.

[0049] And a transparent rubber encapsulation layer 5 wrapped around the outermost layer, the thickness of which is 0.2-0.4mm and its Shore A hardness is 10-20, so as to ensure effective force transmission while protecting the internal structure;

[0050] The sensor is attached to the arc-shaped surface of the fingertip of the robotic arm 9 by a rubber encapsulation layer 5, with its arched opening facing away from the direction in which the fingertip contacts the object.

[0051] A bionic robotic hand, comprising:

[0052] As described above, the bionic tactile sensor;

[0053] The robot arm 9 has a sensor that is attached and fixed to the arc-shaped surface of the fingertip of the robot arm 9 through its encapsulation layer 5, and the arched opening of the sensor faces away from the direction in which the fingertip contacts the object.

[0054] A signal conditioning circuit board is electrically connected to the electrode layer of the sensor. The circuit board integrates a pre-charge amplifier circuit, a bandpass filter circuit, and a signal separation circuit. The passband frequency range of the bandpass filter circuit is configured to match the frequency response characteristics of the bionic tactile sensor to effectively extract tactile and slip signals. The pre-charge amplifier circuit uses a JFET-input type ultra-low bias current operational amplifier chip with a feedback capacitor Cf of 100pF and a feedback resistor Rf of 100MΩ. The signal separation circuit includes a voltage follower for acquiring the low-frequency voltage signal generated by the pyroelectric effect to sense temperature, and the aforementioned passband filter circuit for... The system collects mid-to-high frequency AC signals generated by the piezoelectric effect. For tactile information, pressure is sensed by analyzing the amplitude of the AC signal. For dynamic slip and texture information, the system utilizes the frequency domain differences between the low-frequency envelope signal (usually below 10Hz) generated during sliding and the high-frequency vibration signal (usually above 50Hz) induced by texture friction. These differences are then distinguished and identified by subsequent signal processing (such as time-frequency analysis) by a microcontroller. The signal separation circuit utilizes the different frequency characteristics of piezoelectric (AC) and pyroelectric (DC) signals, processing them through different paths. Finally, the signals are acquired by the microcontroller's ADC, achieving synchronous acquisition and decoupling of temperature and force information.

[0055] The microcontroller module is used to sample and convert the conditioned analog signal to digital.

[0056] The wireless communication module is used to transmit digital signals to the host computer system.

[0057] Each segment of the mechanical finger is driven by a DC servo motor, and all servos are coordinated and controlled by a master controller configured to receive instructions from a wearable data glove or a host computer and to perform adaptive gripping force control based on the tactile and slip signals fed back by the bionic tactile sensors.

[0058] Example 1

[0059] The arched elastic base is cast from silicone rubber with a Shore A hardness of 20. Two protrusions on the base have a diameter of 1.0 mm, a height of 0.4 mm, and a center-to-center distance of 1.8 mm. The PVDF film thickness is 50 μm. The charge amplification circuit uses an AD549 chip. The bandpass filter circuit is implemented by cascading a first-order high-pass cutoff frequency of 0.1 Hz and a second-order low-pass cutoff frequency of 100 Hz. The robotic arm communicates with the host computer via a Bluetooth 5.0 module. The bandpass filter circuit is implemented by cascading a first-order high-pass filter (cutoff frequency 0.1 Hz) and a second-order low-pass filter (cutoff frequency 100 Hz). This passband range (0.1 Hz - 100 Hz) has been experimentally verified and can optimally extract the characteristic electrical signals generated by the biomimetic sensor structure described in this invention during contact, pressing, and sliding processes. Simultaneously, it effectively suppresses pyroelectric signal drift below 0.1 Hz and environmental electromagnetic noise above 100 Hz, thereby achieving the highest signal-to-noise ratio.

[0060] Test results: The sensor can clearly distinguish between different materials such as sandpaper with different grit (e.g., 200 grit and 800 grit), smooth glass, soft felt, and cold metal. Especially in the sliding test, it can not only output a low-frequency envelope signal (slip feel characteristic) related to the sliding frequency, but also analyze the unique vibration modes induced by different roughness surfaces (e.g., a finely milled surface with Ra=3.2μm and a ground surface with Ra=0.8μm) from the high-frequency components of the signal, thereby realizing the discrimination of texture.

[0061] Example 2

[0062] The arched elastic substrate is cast from silicone rubber with a Shore A hardness of 15. The two bumps on the substrate have a diameter of 1.0 mm, a height of 0.4 mm, and a center-to-center distance of 1.8 mm. The PVDF film is 50 μm thick, and the copper foil of the upper and lower electrode layers is 18 μm thick. The wavy double-bump structure is precisely fabricated using photolithography etching to ensure that the alignment error of the upper and lower bumps is less than 50 μm.

[0063] Comparative test cases

[0064] Sensitivity test: Using a spherical probe with a diameter of 5mm, under a normal force of 0.5N, the average output charge of the arched double-convex point sensor of this invention is 45pC, while the average output charge of the planar structure sensor with the same PVDF film is 32pC, and the charge output is increased by about 40.6%.

[0065] Slip perception test: The sensor is pressed against a metal surface with a roughness Ra=3.2μm by a normal force of 2N and slides at a speed of 50mm / s. In the output signal of the sensor of this utility model, a high-frequency vibration signal above 100Hz corresponding to the surface texture and a low-frequency envelope signal caused by sliding can be clearly observed. Under the sliding test conditions, the signal-to-noise ratio (SNR) of the output signal is significantly improved compared with the planar electrode sensor without protrusions, which is better than 20dB.

[0066] Multi-information sensing test: When the sensor is in contact with the surface of an object at 25°C and 40°C, the basic voltage level of the output signal is significantly shifted due to the pyroelectric effect of PVDF. At the same time, it can generate an AC signal response when pressure is applied. Through subsequent signal processing circuits, temperature change information and pressure vibration information can be successfully separated.

[0067] Working principle of this utility model

[0068] When performing a grasping task, the robotic arm 9 uses fingertip sensors to detect pressure, micro-slippage, and temperature information between itself and the object. This information is amplified, filtered, and separated by a signal conditioning circuit, and then converted into digital signals. The main controller transmits this information to a host computer via a wireless communication module for display or recording. Simultaneously, based on a preset adaptive algorithm, it adjusts the output torque of the servo motors in real time according to the slippage signal to prevent object slippage or excessive grasping force that could cause damage, thus achieving stable and smooth grasping.

Claims

1. A biomimetic tactile sensor based on a PVDF piezoelectric thin film, characterized in that: include An arched elastic base (1) made of silicone rubber, wherein the inner surface of the arched elastic base (1) is provided with at least two hemispherical protrusions (6) arranged side by side. A PVDF piezoelectric film (3) is covered on the arched elastic substrate (1). The copper foil lower electrode layer (2) and upper electrode layer (4) covering the upper and lower surfaces of the PVDF piezoelectric film (3) are both wavy double-convex arch structures adapted to the shape of the arched elastic substrate (1). The positions of the upper convex point (7) and the lower convex point (8) of the two electrode layers are aligned with each other, and the alignment error of their center points is no more than 50 μm. The wavy double-convex arch structure is configured such that: when subjected to normal pressure, the upper convex point (7) region generates concentrated strain, simulating the function of the Meissner body in human skin, for sensing static touch; when subjected to tangential force, the lower convex point (8) region generates asymmetric strain, simulating the function of the human ring-layer body, for sensing dynamic slip. And the outermost transparent rubber encapsulation layer (5); The sensor is attached to the arc-shaped surface of the fingertip of the robotic arm (9) through a rubber encapsulation layer (5), with its arched opening facing away from the direction in which the fingertip contacts the object.

2. The biomimetic tactile sensor based on a PVDF piezoelectric thin film according to claim 1, characterized in that, The diameter of the hemispherical protrusion (6) is 0.8-1.2 mm, the height is 0.3-0.5 mm, and the center distance between two adjacent protrusions is 1.5-2.0 mm.

3. A biomimetic tactile sensor based on a PVDF piezoelectric thin film according to claim 1, characterized in that, The inner diameter of the arched elastic base (1) is 4-6 mm, and the curvature is similar to that of the fingertip of the human index finger.

4. A biomimetic tactile sensor based on a PVDF piezoelectric thin film according to claim 1, characterized in that, The PVDF piezoelectric film (3) has both piezoelectric and pyroelectric effects. The sensor can simultaneously sense pressure, sliding, texture and temperature changes by analyzing the frequency characteristics and DC component changes of the output signal.

5. A biomimetic tactile sensor based on a PVDF piezoelectric thin film according to claim 1, characterized in that, The encapsulation layer (5) has a thickness of 0.2-0.4 mm and a Shore A hardness of 10-20, so as to ensure effective force transmission while protecting the internal structure.

6. A biomimetic robotic hand based on PVDF piezoelectric thin film, characterized in that, include: The biomimetic tactile sensor as described in any one of claims 1 to 5; The sensor is attached to the arc-shaped surface of the fingertip of the robotic arm (9) through its encapsulation layer (5), and the arched opening of the sensor faces away from the direction of the fingertip contacting the object. A signal conditioning circuit board is electrically connected to the electrode layer of the sensor. The signal conditioning circuit board integrates a pre-charge amplifier circuit, a bandpass filter circuit, and a signal separation circuit. The passband frequency range of the bandpass filter circuit is configured to match the frequency response characteristics of the bionic tactile sensor to effectively extract tactile and tactile signals. The microcontroller module is used to sample and convert the conditioned analog signal to digital. The wireless communication module is used to transmit digital signals to the host computer system.

7. The robotic arm according to claim 6, characterized in that, The pre-charge amplifier circuit uses a JFET input type ultra-low bias current operational amplifier chip, with a feedback capacitor Cf of 100pF and a feedback resistor Rf of 100MΩ.

8. The robotic arm according to claim 6, characterized in that, The signal separation circuit includes a voltage follower for acquiring low-frequency voltage signals generated by the pyroelectric effect to sense temperature, and a passband filter circuit for acquiring medium- and high-frequency AC signals generated by the piezoelectric effect to sense pressure and vibration.

9. The robotic arm according to claim 6, characterized in that, Each phalanx of the robotic hand is driven by a DC servo motor, and all servos are coordinated and controlled by a main controller configured to receive instructions from a wearable data glove or a host computer and to perform adaptive grasping force control based on the tactile and slip signals fed back by the bionic tactile sensors.

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