Underwater manipulator and grasping method based on multi-modal tactile perception

Abstract

The application discloses an underwater manipulator and a grabbing method based on multi-modal tactile perception, comprising a base, a driving unit and a plurality of mechanical fingers; the mechanical fingers are hingedly connected in sequence by proximal phalanges, middle phalanges and distal phalanges, reset torsional springs are arranged at each joint, the driving unit drives the finger bending through a first traction cable and a second traction cable; a flexible composite tactile sensing module is embedded in the inner side of the distal phalange end, the module is composed of a bionic microtexture packaging layer, a triboelectric dielectric layer, a liquid metal common electrode layer, a piezoelectric sensing layer and a shielding substrate layer, and passive self-powered sensing is realized by using triboelectric and piezoelectric effects; the application adopts a mechanical-electric separation dynamic sealing structure, realizes reliable sealing and lightweight design, combines multi-modal tactile perception and adaptive grabbing control, solves the problems that a traditional underwater manipulator is easy to leak, lacks sensitive sliding feedback and causes target damage or sliding, and is suitable for complex operation scenes such as fine sampling of deep-sea biological samples.

Description

Technical Field

[0001] This invention relates to the field of underwater robots and marine engineering equipment, specifically to an underwater manipulator and grasping method based on multimodal tactile perception. Background Technology

[0002] As the core actuator for deep-sea resource exploration and scientific research, underwater manipulators still face significant limitations in structural design and sensing capabilities with current technology, making it difficult to meet the demands of precise operations in complex deep-sea environments. Regarding drive arrangement and sealing, most existing underwater manipulators employ an electromechanical integrated structure with "joint-embedded motors." While this design offers high integration, it results in a large end-effector mass and high inertia, and each joint requires an independent dynamic sealing structure, making it highly susceptible to leakage and short circuits under the high pressure of deep water, leading to extremely high maintenance costs. Although some cable-driven manipulators achieve electromechanical separation by placing the motor within a base or pressure chamber, their internal cable guiding structure lacks optimization, causing severe cable wear and sluggish movement within the channels, affecting control accuracy.

[0003] Meanwhile, in terms of tactile sensing systems, traditional underwater tactile sensors are mostly active devices, requiring complex external power supply circuits and signal transmission cables. This not only increases the difficulty of wiring in the narrow space of the fingertips, but also makes the power supply interface a high-risk area for underwater insulation failure. Currently, the industry lacks an integrated sensing solution that can utilize its own material properties (such as piezoelectric and triboelectric effects) to achieve self-powered operation while simultaneously detecting contact pressure and slip vibration. As a result, underwater manipulators often cause damage or slippage of targets when grasping fragile biological samples due to a lack of sensitive slip feedback.

[0004] In summary, developing an adaptive underwater manipulator that is lightweight, reliably sealed, and integrates passive multimodal sensing capabilities is a pressing technical challenge that needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide an underwater manipulator and grasping method based on multimodal tactile perception, in order to solve the problem of the lack of adaptive underwater manipulator technology in the prior art that is lightweight, reliably sealed, and integrates passive multimodal perception capabilities.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an underwater manipulator based on multimodal tactile perception, mainly composed of a base, a drive unit, and several mechanical fingers; wherein, the mechanical fingers are composed of proximal phalanges, middle phalanges, and distal phalanges connected in sequence, and each phalanx is hinged to the other by a joint pin with a double-ended threaded locking nut, and a return torsion spring is provided at the joint; the drive unit is connected to each phalanx through a first traction cable and a second traction cable, and the traction cable extends to the outside through a dynamic sealing assembly provided on the base, thereby realizing the physical isolation of the drive motor from the underwater environment.

[0007] Furthermore, in terms of sensing and perception structure, a flexible composite tactile sensing module is embedded on the inner side of the distal phalanx. This module, from the outside to the inside, includes: a biomimetic microtexture encapsulation layer, a triboelectric layer, a liquid metal common electrode layer, a piezoelectric sensing layer, and a shielding substrate layer. The surface of the biomimetic microtexture encapsulation layer is uniformly covered with a micron-level protrusion array to enhance friction and serve as a contact electrification surface. The liquid metal common electrode layer is located in the middle of the module and serves as a common signal output terminal for triboelectric generation and piezoelectric sensing. The above structures work together to output a composite electrical signal generated by contact pressure and slippage using the triboelectric effect and the piezoelectric effect, realizing self-powered sensing of the fingertip.

[0008] Furthermore, in terms of fluid shape and guidance optimization, the side edges of the proximal phalanx, middle phalanx, and distal phalanx are all provided with streamlined rounded transition structures. The radius of curvature of the rounded structure is optimized to reduce sudden changes in local pressure gradients during underwater movement and suppress boundary layer separation, thereby reducing pressure drag and fluid noise. In addition, the phalanx is provided with an arc-shaped guide channel, along which the traction cable passes to reduce cable wear and motion lag.

[0009] Furthermore, a grasping method for an underwater robotic arm based on multimodal tactile perception includes the following steps:

[0010] Step 1 (Envelope Grasping): The controller drives the motor to tighten several first and second traction cables, causing the robotic arm's mechanical fingers to bend and envelop the target object.

[0011] Step 2 (Signal Acquisition): The composite electrical signal output from the liquid metal common electrode layer in the flexible composite tactile sensing module is acquired in real time and amplified and filtered.

[0012] Step 3 (feature extraction and discrimination): Perform Fast Fourier Transform (FFT) on the acquired signal. Due to the microtexture effect of the biomimetic microtexture encapsulation layer, when an object undergoes a tiny slip that is invisible to the naked eye, it will induce characteristic high-frequency vibrations in the frequency range of 50Hz-500Hz. If the amplitude of the extracted signal in this frequency band exceeds the preset slip threshold, the system determines that "slippage is occurring".

[0013] Step 4 (Closed-loop compensation): Once slippage is detected, the controller immediately controls the drive unit to increase the tension of several first and second traction cables (force amplification compensation) until the high-frequency slippage characteristic signal disappears; if no slippage signal is detected, the current tension of several first and second traction cables is maintained.

[0014] Compared with existing technologies, this invention provides an underwater robotic arm and grasping method based on multimodal tactile perception:

[0015] (1) In terms of structural design and sealing reliability, the present invention adopts an electromechanical separation structure that combines rope drive and base dynamic sealing. The drive unit is placed in the pressure-resistant sealing cavity. The finger movement is driven by the traction cable passing through the dynamic sealing assembly, which completely avoids the problems of easy leakage and high maintenance cost of traditional joint built-in motor solution in deep water high pressure environment. At the same time, the finger joint adopts a two-way fixing method with double-end thread, locking nut and anti-loosening screw, which effectively prevents the connection from loosening due to underwater vibration. Automatic reset is achieved with the reset torsion spring. In terms of sensing capabilities, this invention innovatively integrates a five-layer flexible composite tactile sensing module. Utilizing the synergistic effect of triboelectric and piezoelectric effects, it can achieve self-powered sensing of contact pressure and slip vibration without external power supply. The liquid metal common electrode layer serves as both the sensing electrode for triboelectric generation and the upper electrode plate for piezoelectric sensing. Combined with the mechanical amplification effect of the biomimetic microtexture encapsulation layer on high-frequency slip vibration, it significantly improves the detection sensitivity of minute slip (characteristic frequency of 50Hz-500Hz), solving the technical problems of insulation failure in underwater power supply and difficulty in wiring in confined spaces in traditional active sensors.

[0016] (2) In terms of fluid dynamics performance and adaptive control, this invention sets a streamlined rounded corner transition structure on the side edge of the finger bone. By optimizing the radius of curvature, it suppresses boundary layer separation and wake generation, significantly reducing pressure drag and fluid turbulence noise during underwater movement, creating a low-interference signal acquisition environment for the tactile sensor. At the same time, the arc-shaped guide channel inside the finger bone reduces the wear of the traction cable and transmission hysteresis, improving control accuracy. In terms of the grasping method, this invention realizes closed-loop adaptive compensation control based on slip characteristic signals: by real-time acquisition of composite electrical signals and FFT transformation, when the high-frequency vibration amplitude induced by micro-texture is detected to exceed the slip threshold, the controller immediately increases the tension of the traction cable until the slip signal disappears, thereby achieving the most stable grasping without crushing fragile samples, effectively solving the industry pain point that open-loop force control is prone to target damage or slippage;

[0017] In summary, this invention combines the advantages of lightweight and sealed structure, passive multimodal sensing, low resistance and low noise, and adaptive grasping, making it particularly suitable for complex operational scenarios such as fine sampling of deep-sea biological samples. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0020] Figure 2 This is a diagram of the mechanical finger joint connection structure of the present invention;

[0021] Figure 3 A three-dimensional structural diagram of the distal phalanx;

[0022] Figure 4 A three-dimensional structural diagram of the middle phalanx;

[0023] Figure 5 A schematic diagram of the three-dimensional structure of the proximal phalanx;

[0024] Figure 6 This is a schematic diagram of the hierarchical structure of the flexible composite tactile sensing module in this invention;

[0025] Figure 7 The flowchart is for the adaptive grasping control method.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Distal phalanx; 2. Middle phalanx; 3. Proximal phalanx; 4. Flexible composite tactile sensing module; 5. Locking nut; 6. Joint pin; 7. Reset torsion spring; 8. Screw; 9. First traction cable; 10. Second traction cable; 11. Base; 41. Bionic microtextured encapsulation layer; 42. Triboelectric layer; 43. Liquid metal common electrode layer; 44. Piezoelectric sensing layer; 45. Shielding base layer. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] As attached Figure 1 To be continued Figure 7 As shown:

[0030] Example 1:

[0031] refer to Figures 1-5 An underwater robotic hand based on multimodal tactile perception includes a base 11, a drive unit (not shown in the figure), and several mechanical fingers arranged in a circular pattern.

[0032] To adapt to the high-pressure environment of the deep sea, this device adopts a mechanical-electrical separation design, in which the drive unit (including but not limited to the servo motor) is placed inside the pressure-resistant sealed cavity of the base 11 or in a separate pressure-resistant chamber; such as Figure 1 As shown, the base 11 is provided with several guide holes for several first traction cables 9 and second traction cables 10 to pass through. A dynamic sealing assembly is integrated at the hole, and the first traction cables 9 and second traction cables 10 are provided to extend to the external water environment through the sealing assembly, thereby achieving physical isolation between the vulnerable electronic components and the corrosive seawater.

[0033] Meanwhile, in the joint design of the mechanical finger, such as Figure 2 As shown, the mechanical finger is composed of a proximal phalanx 3, a middle phalanx 2, and a distal phalanx 1 connected in series, with each phalanx hinged together by a joint pin 6. To address the issue of screws loosening due to vibrations during underwater operations, the joint pin 6 is threaded at both ends and secured bidirectionally with a locking nut 5 and a screw 8. In addition, a return torsion spring 7 is fitted at each joint. When the first traction cable 9 and the second traction cable 10 are relaxed, the elastic potential energy of the return torsion spring 7 allows the finger to automatically return to its initial straightened state.

[0034] Secondly, in order to reduce underwater motion resistance, such as Figure 3 , Figure 4 and Figure 5 As shown, this embodiment optimizes the shape of the phalanges using hydrodynamics. The back and side edges of the middle phalanx 2 and distal phalanx 1 do not employ conventional right-angle designs, but instead feature streamlined rounded transition structures. The radius of curvature of these rounded transition structures reduces sudden changes in local pressure gradients during underwater movement. This rounded design effectively suppresses boundary layer separation during rapid opening and closing of the fingers in water, preventing the formation of high-pressure differential vortices behind the phalanges, thus significantly reducing pressure differential drag and fluid noise, creating a quiet detection environment for the sensor. Furthermore, arc-shaped guide channels are provided inside the middle phalanx 2 and proximal phalanx 3 for the passage of the first traction cable 9 and the second traction cable 10. This reduces the friction between the first and second traction cables 9 and 10 and the inner walls of the middle and proximal phalanges 2 and 3. The inner walls of the guide channels are polished, transforming the friction between the traction cables and the channel walls from "shear friction" to "smooth sliding friction," thereby reducing transmission lag.

[0035] Example 2:

[0036] refer to Figure 1 and Figure 6An underwater robotic hand based on multimodal tactile perception has a flexible composite tactile sensing module 4 embedded in the inner end of the distal phalanx 1. This module achieves self-sensing without the need for external power supply. Its main body adopts a five-layer composite structure, which consists of a biomimetic microtexture encapsulation layer 41, a triboelectric layer 42, a liquid metal common electrode layer 43, a piezoelectric sensing layer 44, and a shielding base layer 45, from the outside to the inside (i.e. from the surface in contact with the object to the finger mounting surface).

[0037] Bionic microtextured encapsulation layer 41: Located on the outermost layer, it is made of flexible PDMS or silicone material, and the surface is molded with a micron-level protrusion array or ridge array. The micron-level protrusion array or ridge array is used to enhance the friction coefficient in underwater wet and slippery environments and mechanically amplify the high-frequency slip vibration during the contact process. This layer has a dual function: first, it acts as an "anti-slip layer" to increase the gripping friction coefficient; second, it acts as a "charge-generating layer" for triboelectric nano-power generation, generating surface static charge when in contact with an object or when micro-slip occurs.

[0038] Triboelectric layer 42: Located in the second layer, it is made of a highly electronegative thin film (such as PTFE or FEP) to enhance the electrostatic induction effect and transmit minute mechanical slip vibrations to the interior;

[0039] Liquid metal common electrode layer 43: Located in the third layer, it has microchannels inside and is injected with eutectic gallium indium alloy (EGaIn); it is the common signal output terminal of the sensor, serving as the sensing electrode of the triboelectric power generation circuit upward to collect sliding signals, and as the upper electrode of the piezoelectric sensing circuit downward to collect pressure signals. Its liquid properties ensure that the electrode will not break when the finger is bent.

[0040] Piezoelectric sensing layer 44: Located in the fourth layer, it is a polarized PVDF piezoelectric film. When the robotic arm clamps an object, this layer is compressed and generates polarized charges, outputting a voltage signal proportional to the normal force.

[0041] Shielding substrate layer 45: Located at the bottom layer, it is grounded or connected to the shielding circuit; on the one hand, it serves as the lower electrode plate of the piezoelectric layer to form a circuit, and on the other hand, it effectively isolates electromagnetic interference from the internal motor of the robot or the external environment, ensuring a high signal-to-noise ratio of the output signal.

[0042] Example 3:

[0043] refer to Figure 7 A grasping method for an underwater robotic arm based on multimodal tactile perception, employing an underwater robotic arm based on multimodal tactile perception as described in Embodiments 1 and 2 above, includes the following steps:

[0044] Step 1 (Envelope Grabbing): The controller drives the motor to tighten several first traction cables 9 and second traction cables 10, causing several mechanical fingers to bend and envelop the target object.

[0045] Step 2 (Signal Acquisition): The composite electrical signal output from the liquid metal common electrode layer 43 in the flexible composite tactile sensing module 4 is acquired in real time and amplified and filtered.

[0046] Step 3 (feature extraction and discrimination): The acquired signal is subjected to Fast Fourier Transform (FFT). Due to the micro-texture effect of the biomimetic micro-texture encapsulation layer 41, when the object undergoes a tiny slip that is invisible to the naked eye, it will induce characteristic high-frequency vibrations in the frequency range of 50Hz-500Hz. If the amplitude of the extracted signal in this frequency band exceeds the preset slip threshold, the system determines that "slippage is occurring".

[0047] Step 4 (Closed-loop compensation): Once slippage is detected, the controller immediately controls the drive unit to increase the tension of several first traction cables 9 and second traction cables 10 to compensate until the high-frequency slippage characteristic signal disappears; if no slippage signal is detected, the current tension of several first traction cables 9 and second traction cables 10 is maintained, thereby achieving the most stable gripping without damaging the target.

[0048] Working principle: First, the base 11 is fixed to the end of the underwater robot's robotic arm, and the pressure-resistant sealed cavity containing the internal drive unit (such as a servo motor) is physically isolated from the external water environment through a dynamic sealing component on the base 11, ensuring the safety of the electrical system. Then, the controller issues a grasping command, and the drive unit begins to tighten the first traction cable 9 and the second traction cable 10, which are threaded through the arc-shaped guide channels inside each phalanx. These traction cables respectively drive the distal phalanx 1, middle phalanx 2, and proximal phalanx 3 to bend around the joint pin 6, overcoming the elastic force of the return torsion spring 7, causing several robotic fingers to gradually envelop the target object from their initial straightened state. During the finger bending process, because each phalanx (such as the middle phalanx 2 and distal phalanx 1) has a streamlined rounded corner transition structure on its side edges, the pressure drag and fluid noise during underwater movement can be effectively reduced, creating a low-interference environment for subsequent signal acquisition. When the robotic arm comes into contact with the target object, the flexible composite tactile sensing module 4, embedded on the inner side of the distal phalanx 1, begins to operate. This module, from the outside in, consists of a biomimetic microtexture encapsulation layer 41, a triboelectric layer 42, a liquid metal common electrode layer 43, a piezoelectric sensing layer 44, and a shielding substrate layer 45. The liquid metal common electrode layer 43 serves as a common signal output terminal, utilizing the synergistic effect of triboelectric and piezoelectric effects to output a composite electrical signal containing contact pressure and slip vibration in real time without external power supply. The controller continuously acquires this composite signal and amplifies, filters, and performs fast Fourier transform processing on it. Because the micron-level protrusion array or ridge texture evenly distributed on the surface of the biomimetic microtexture encapsulation layer 41 can induce characteristic high-frequency vibrations of 50Hz-500Hz when minute slip occurs, the system determines whether the target object is slipping by analyzing whether the amplitude of this frequency band signal exceeds a preset slip threshold. Once a slippage is detected, the controller immediately increases the tension of the first traction cable 9 and the second traction cable 10, performing force compensation until the high-frequency slippage characteristic signal completely disappears. If no slippage signal is detected, the current traction cable tension remains unchanged, thus achieving closed-loop adaptive gripping. After the gripping task is completed, the controller releases the first traction cable 9 and the second traction cable 10, and the reset torsion springs 7 at each joint drive the fingers to automatically return to their initial straightened state, awaiting the next operation command. Throughout the process, the joint fixing method using double-ended threads with locking nuts 5 and screws 8 effectively prevents connection loosening caused by underwater vibration, while the flexible nature of the liquid metal common electrode layer 43 ensures the reliability of the electrodes when the fingers are repeatedly bent, thereby achieving stable and sensitive adaptive gripping without damaging the sample.

[0049] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An underwater robotic hand based on multimodal tactile perception, comprising a base (11), a drive unit, and several robotic fingers; The mechanical finger is composed of a proximal phalanx (3), a middle phalanx (2), and a distal phalanx (1) connected in sequence; its characteristic is that: The phalanges of the mechanical finger are hinged together by double-ended threads, locking nuts (5) and screws (8) and joint pins (6), and each phalange joint is provided with a reset torsion spring (7). The drive unit is connected to each finger bone via a first traction cable (9) and a second traction cable (10); A flexible composite tactile sensing module (4) is embedded on the inner side of the distal phalanx (1) to collect the charge signal when the robotic arm grasps.

2. The underwater robotic arm based on multimodal tactile perception according to claim 1, characterized in that, The base (11) is also provided with several guide holes for several first traction cables (9) and second traction cables (10) to pass through; A dynamic sealing assembly is also provided at the guide hole to isolate the external water environment from the internal drive unit, thereby achieving electromechanical separation drive.

3. The underwater robotic arm based on multimodal tactile perception according to claim 1, characterized in that, The flexible composite tactile sensing module (4) is provided with a biomimetic microtexture encapsulation layer (41), a triboelectric layer (42), a liquid metal common electrode layer (43), a piezoelectric sensing layer (44), and a shielding substrate layer (45) from the outside to the inside. The liquid metal common electrode layer (43) serves as the common signal output terminal for triboelectric power generation and piezoelectric sensing.

4. The underwater robotic arm based on multimodal tactile perception according to claim 1, characterized in that, Both the distal phalanx (1) and the middle phalanx (2) are provided with arc-shaped guide channels inside; Furthermore, both the first traction cable (9) and the second traction cable (10) pass through the interior of the distal phalanx (1) and the middle phalanx (2) along the arc-shaped guide channel.

5. An underwater robotic arm based on multimodal tactile perception according to claim 1, characterized in that, The middle phalanx (2) and the distal phalanx (1) are both provided with streamlined rounded corner transition structures on their side edges.

6. An underwater robotic arm based on multimodal tactile perception according to claim 3, characterized in that, The piezoelectric sensing layer (44) is made of PVDF (polyvinylidene fluoride) piezoelectric film or PZT (lead zirconate titanate) piezoelectric ceramic composite material; The liquid metal common electrode layer (43) is made of gallium indium tin alloy and is encapsulated in a flexible substrate by microchannel injection or screen printing process.

7. An underwater robotic arm based on multimodal tactile perception according to claim 3, characterized in that, Several of the biomimetic microtexture encapsulation layers (41) have micron-sized arrays of protrusions or ridge-like textures evenly distributed on their surfaces.

8. A grasping method for an underwater robotic arm based on multimodal tactile perception, wherein the method employs an underwater robotic arm based on multimodal tactile perception as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1 (Envelope Grasping): The controller drives the motor to tighten several first traction cables (9) and second traction cables (10), causing the robotic fingers of the robot arm to bend and envelop the target object. Step 2 (Signal Acquisition): The composite electrical signal output from the liquid metal common electrode layer (43) in the flexible composite tactile sensing module (4) is acquired in real time and amplified and filtered. Step 3 (feature extraction and discrimination): The collected signal is subjected to Fast Fourier Transform (FFT). Due to the micro-texture effect of the biomimetic micro-texture encapsulation layer (41), when the object undergoes a small slip that is invisible to the naked eye, it will induce characteristic high-frequency vibrations in the frequency range of 50Hz-500Hz. If the amplitude of the extracted signal in this frequency band exceeds the preset slip threshold, the system determines that "slippage is occurring". Step 4 (closed-loop compensation): Once slippage is detected, the controller immediately controls the drive unit to increase the tension of several first traction cables (9) and second traction cables (10) (force amplification compensation) until the high-frequency slippage characteristic signal disappears; if no slippage signal is detected, the current tension of several first traction cables (9) and second traction cables (10) is maintained.

9. The grasping method of an underwater robotic arm based on multimodal tactile perception according to claim 8, characterized in that, The acquired composite signal is subjected to Fast Fourier Transform (FFT) or Wavelet Transform to filter out low-frequency drive noise with a frequency below 50Hz and retain the slip characteristic signal with a frequency range of 50Hz-500Hz.

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