Underwater multi-mode mobile robot equipped with flexible bionic gripper

Abstract

The invention discloses an underwater multi-mode mobile robot equipped with a flexible bionic gripper, which integrates three operation modes of propeller propulsion, six-foot crawling and target object grabbing, and realizes'movement-attachment-operation 'integrated collaboration. The robot main body adopts a five-thruster vector layout and has a five-degree-of-freedom motion capability; and six groups of three-degree-of-freedom mechanical feet and two groups of three-degree-of-freedom mechanical arms are arranged outside, and a cruising mode, a crawling mode or a grabbing mode can be automatically switched according to tasks. A coordination dual-network hydrogel bionic sucker and a flexible gripper are integrated at the foot end and the arm end, and controllable adsorption and desorption are achieved through a diaphragm pump. The control system generates a rhythm signal based on the central mode generator, and coordinates multi-module actions of paddles, legs and arms in combination with inverse kinematics solution. The robot is suitable for tasks such as wide water area cruising, complex terrain exploration, environment maintenance and seabed sampling, has high maneuverability and high integration degree, and provides an innovative platform for underwater fine operation.

Description

Technical Field

[0001] This invention relates to the field of underwater robot technology, specifically to an underwater multimodal mobile robot equipped with a flexible bionic gripper. Background Technology

[0002] Currently, marine development and protection have entered a new stage, and the demand for underwater robots is shifting from "observation" to "operation." Faced with the increasingly urgent tasks of marine resource exploration and development, and underwater environmental governance and protection, underwater robots with sophisticated operational capabilities have become a focus in scientific research and engineering. The key to achieving this transformation lies in developing highly autonomous, adaptable, and precise integrated operational robots capable of performing compliant grasping tasks, to meet the needs of scientific research, fisheries, and environmental protection sectors for tasks such as seabed sampling, aquaculture harvesting, and underwater waste recycling.

[0003] To date, underwater grasping robot technologies have mainly focused on two categories: one is surface-controlled systems, where the control components (such as hydraulic power sources, power units, and main control systems) are located on the water's edge or on surface vessels, extending underwater operations only through robotic arms or cable-controlled grasping mechanisms. While these systems can achieve a certain degree of grasping functionality, they still require remote operation by professionals to control the entire grasping process. Their mobility, real-time performance, and operating range are severely limited, making it difficult to achieve stable and precise operation in complex water currents or confined spaces. The other category of research focuses on optimizing the materials and performance of the grasping mechanism itself, such as bionic grippers and soft swallowing robots. Although significant progress has been made in laboratory environments, these often deviate from complete autonomous underwater vehicle (AUV) or remotely operated underwater vehicle (ROV) mobile platforms, resulting in insufficient validation of their applicability and integration in real-world underwater environments. The aforementioned research paradigm of "separation of control and execution" or "decoupling of mechanism and platform" greatly limits the application effectiveness of underwater grasping robots in real-world scenarios, which urgently requires an integrated solution that deeply integrates a high-efficiency mobile platform with agile operating mechanisms.

[0004] In complex underwater environments, existing end effectors for grasping and manipulating tasks mainly fall into two categories: traditional rigid robotic arms and purely flexible bionic grippers. Traditional rigid robotic arms are known for their high precision, large load capacity, and mature servo control. However, their inherent rigid structure makes them highly susceptible to damage or breakage of ultra-soft, fragile, or irregularly shaped underwater objects due to improper gripping force control. In contrast, purely flexible bionic grippers draw inspiration from biological structures such as octopus tentacles, developing hydrogel bionic grippers that can achieve strong adhesion and non-damaging grasping. Their inherent flexibility and continuous deformation capabilities give them unique advantages in grasping fragile objects. However, their limitations are also significant: the actuation method is usually pneumatic or tendon-driven, resulting in slow response speed and limited output force, making them unsuitable for heavy-load tasks; the end-effector positioning accuracy is relatively low, making them inadequate for operations requiring precise insertion, removal, or twisting. Therefore, a rigid-flexible robotic arm that integrates rigid mechanical joints with flexible bionic grippers to perform non-destructive and compliant gripping after accurately locating the target object has unique advantages.

[0005] The integration of underwater grasping mechanisms with underwater robots has become an important path to improve the performance of underwater grasping operations; the combination of rigid robotic arms and flexible bionic grippers provides a new method for precise and compliant underwater grasping. As underwater operations become more sophisticated and diverse, robot systems that integrate motion and grasping capabilities are receiving increasing attention. When crawling on unstructured surfaces such as bridge structures, rocks, or shipwrecks, the reliable adsorption properties of hydrogel materials provide the ability to maintain a tight grip; when grasping smooth and deformable objects, hydrogel materials fill the gap in the ability to firmly grasp and grasp without damage. This paper proposes an underwater multimodal mobile robot equipped with a flexible bionic gripper, aiming to expand the robot's operational dimensions in complex underwater scenarios through the integration of motion, attachment, and manipulation functions. Summary of the Invention

[0006] The purpose of this invention is to provide an underwater multimodal mobile robot equipped with flexible bionic grippers. For long-distance cruising missions, it is driven by a propeller. When walking on the seabed, it adopts a six-legged crawling motion. It can use its two arms to grasp targets. For irregular surfaces, it uses hydrogel bionic suction cups on the bottom of its six legs to stably attach and walk. For fishing tasks such as harvesting marine delicacies and cleaning tasks such as recycling seabed debris, it uses hydrogel bionic grippers at the ends of its two arms to grasp objects firmly without damage. This effectively improves the environmental adaptability and task completion rate of seabed grasping operations.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: an underwater multimodal mobile robot equipped with a flexible bionic gripper, comprising a robot body, an electronic sealed chamber and a sensing module inside the body, three vertical thrusters on the front sides and rear of the body, two horizontal thrusters on the rear sides of the body, two LED searchlights and a camera at the head of the body, a cable communication interface at the tail of the body, six sets of leg crawling mechanisms symmetrically distributed on the outside of the body, and two sets of arm gripping mechanisms symmetrically distributed on the upper part of the body.

[0008] The aforementioned electronic sealed cabin includes all electronic components for controlling the robot's movement. These components include a Raspberry Pi as the main controller, used to send motion commands and communicate with a host computer; a PCA9685 control board and a flight controller as slave controllers. The PCA9685 sends control commands to drive the legs and arms, driving six sets of 18 waterproof servos in the legs and diaphragm pumps in the legs to control the hydrogel bionic suction cups; it also drives two sets of six waterproof servos in the arms and diaphragm pumps in the arms to control the hydrogel bionic grippers. The flight controller sends commands to drive three vertical thrusters and two horizontal thrusters. The flight controller includes a gyroscope and accelerometer for measuring the robot's attitude and acceleration information. The electronic components also include an electronic speed controller, an LED driver board, and a power module. The electronic speed controller converts the control signals sent by the flight controller into digital signals to drive the brushless motors. The LED driver board controls the LED searchlight on the main body's head. The power module supplies power to all components of the robot.

[0009] The aforementioned pressure sensor is installed inside the robot body directly below, and is used to measure the robot's depth information in the water.

[0010] Preferably, the three vertical thrusters are fixed to the robot's outer shell by bolts and consist of a 930kV brushless motor and a propeller. The vertical thrusters achieve upward and downward motion by rotating at the same speed and in the same direction, and achieve pitching motion by rotating at the same speed and in opposite directions. The vertical thrusters achieve tumbling motion by rotating in opposite directions on both sides in front of the main body.

[0011] Preferably, the horizontal thrusters on both sides of the robot body are fixed to the robot shell by the base and are composed of a 980kV brushless motor and a propeller. The horizontal thrusters achieve forward and backward movement by rotating at the same speed and in the same direction, and the vertical thrusters achieve turning movement by rotating at the same speed and in opposite directions.

[0012] Preferably, the LED searchlight is fixed to the robot's head by bolts. The searchlight consists of 5W LED beads and a waterproof focusing lens, and is waterproofed by epoxy resin casting.

[0013] Preferably, the camera is fixed to the robot's head with bolts. The camera parameters are 1080P high-definition USB camera module, 3.6mm focal length lens, 90° field of view. The camera is placed in a small sealed chamber and waterproofed by epoxy resin casting.

[0014] Preferably, the cable communication interface is fixed to the tail of the robot by bolts. The communication interface consists of a WF16-10 core waterproof socket, and the waterproof function is achieved by sealing ring and epoxy resin casting.

[0015] Preferably, the leg crawling mechanism is symmetrically fixed to the outside of the robot body by bolts. The leg crawling mechanism consists of three joints with dimensions of 48mm, 76mm, and 147mm respectively. Each joint is driven by three standard IPX893 waterproof digital servos. A diaphragm pump is installed inside the third joint of the crawling mechanism. The diaphragm pump achieves waterproofing by epoxy resin casting. The foot end of the crawling mechanism is equipped with a hydrogel biomimetic suction cup. The hydrogel biomimetic suction cup is prepared by 3D printing of metal ion coordination hydrogel using digital light processing. The hydrogel has improved mechanical strength and anti-expansion performance through a double-network toughening strategy. An interconnecting circuit is added inside the hydrogel suction cup, and the adhesion and detachment functions of the suction cup are realized by opening and closing the diaphragm pump.

[0016] Preferably, the arm gripping mechanism is symmetrically fixed to the upper part of the robot body by bolts. The arm gripping mechanism consists of three joints with dimensions of 51mm, 83mm, and 174mm respectively. Each joint is driven by three standard IPX893 waterproof digital servos. A diaphragm pump is installed inside the third joint of the gripping mechanism. The diaphragm pump achieves waterproofing by epoxy resin casting. The end of the gripping mechanism is equipped with a hydrogel bionic gripper. The hydrogel bionic gripper is prepared by photopolymer 3D printing of supramolecular hydrogel. The hydrogel has improved mechanical strength and anti-expansion performance through a dual-network toughening strategy. An interconnecting circuit is added inside the hydrogel suction cup, and the bending function of the tentacle and the adhesion function of the suction cup are realized by dual independently controlled diaphragm pumps.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. The underwater robot disclosed in this invention has five degrees of freedom motion control capability in propeller-driven mode. The streamlined appearance of the underwater robot and the configuration and installation of the thrusters are designed based on the principle of reducing water resistance and improving space utilization. The vector combination arrangement of three vertical thrusters and two horizontal thrusters enables the robot to meet the requirements of multi-degree-of-freedom motion control such as forward, backward, rising, sinking, throbbing, pitching, rolling, and hovering. This mode is applicable to tasks such as long-distance cruising and data acquisition.

[0019] 2. The underwater robot disclosed in this invention has all-terrain adaptability in a six-legged crawling mode. The bionic joint structure of the robot's legs is designed to improve motion stability and optimize the distribution of foot-ground contact force. The six sets of mechanical legs are driven by modularization and closed-loop control to ensure stable dwelling in dynamic flow environments and complex structural surfaces, realizing omnidirectional maneuvering in open water and robust adsorption crawling in complex terrain.

[0020] 3. The underwater robot disclosed in this invention is equipped with hydrogel bionic suction cups at its feet, which have the ability to stably attach to the surface of underwater structures. The hydrogel suction cups have interconnected circuits inside, and the adhesion and detachment functions are realized by opening and closing the diaphragm pump. Combined with the gait design in the six-legged crawling mode and the synergistic cooperation of the diaphragm pump, the robot can achieve stable crawling on vertical or inverted surfaces. This mode is applicable to near-wall operations such as hull cleaning, crack detection and damage repair.

[0021] 4. The underwater robot disclosed in this invention possesses flexible grasping capabilities in complex environments during target grasping mode. The biomimetic joint structure of the robot's arm achieves a balance between rigidity and flexibility in the rigid robotic arm joint and flexible end effector. The rigid joints provide the grasping mechanism with strong mobility; the flexible end effector provides it with the ability to grasp irregular and fragile targets, enabling the robot to perform various grasping functions such as compliant grasping, precise grasping, firm grasping, and non-destructive grasping. This mode is applicable to delicate operational tasks such as underwater collection, pinpoint capture, and foreign object removal.

[0022] 5. The hydrogel bionic gripper equipped at the end of the arm of the underwater robot disclosed in this invention has the ability to stably and gently adhere to the surface of underwater target objects. The hydrogel gripper has an internal interconnection circuit, and the adhesion and detachment functions are realized by opening and closing the diaphragm pump. Combined with the motion design in the target object grasping mode and the synergistic cooperation of the diaphragm pump, the robot can achieve precise and compliant grasping of target objects. This mode is applicable to underwater grasping operations such as seafood harvesting and underwater garbage recycling. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0024] Figure 2 This is a schematic diagram of the overall structure of the present invention in both propeller propulsion and hexapod crawling modes;

[0025] Figure 3 This is a schematic diagram of the single-arm gripping mechanism of the present invention;

[0026] Figure 4 This is a schematic diagram of the hydrogel biomimetic gripper in its normal and bent states.

[0027] Figure 5 This is a schematic diagram of the single-leg structure of the present invention;

[0028] Figure 6 This is a schematic diagram of the hydrogel biomimetic suction cup structure of the present invention;

[0029] Figure 7 This is a schematic diagram of the vertical propeller propeller and the horizontal vertical propeller propeller structure of the present invention.

[0030] In the diagram: 1. Communication cable interface; 2. Robot shell; 3. Arm gripping mechanism; 4. Leg walking mechanism; 5. Camera; 6. LED light; 7. Vertical propeller thruster; 8. Horizontal propeller thruster; 91. Left arm gripping mechanism; 92. Right arm gripping mechanism; 101. Left front leg; 102. Right front leg; 103. Left middle leg; 104. Right middle leg; 105. Left hind leg; 106. Right hind leg; 111. Upper half of arm base; 112. Lower half of arm base; 12. First joint of arm; 131. Upper half of second joint of arm; 132. Second joint of arm. Lower half of the segment 132, upper half of the third joint of the arm 141, lower half of the third joint of the arm 142, first hydrogel bionic gripper buckle of the arm 151, second hydrogel bionic gripper buckle of the arm 152, first hydrogel bionic gripper of the arm 161, second hydrogel bionic gripper of the arm 162, diaphragm pump of the third joint of the arm 17, waterproof servo of the third joint of the arm 181, waterproof servo of the second joint of the arm 182, waterproof servo of the first joint of the arm 183, top base of the hydrogel bionic gripper 191, hydrogel bionic 192, base of gripper; 193, hydrogel bionic gripper foot; 194, internal connecting circuit of hydrogel bionic gripper; 201, first joint of leg; 202, connecting plate of first joint of leg; 21, second joint of leg; 221, first part of third joint of leg; 222, second part of third joint of leg; 23, hydrogel bionic suction cup of leg; 24, diaphragm pump of third joint of leg; 251, waterproof servo motor of third joint of leg; 252, waterproof servo motor of second joint of leg; 253, waterproof servo motor of first joint of leg; internal connecting circuit of hydrogel bionic suction cup. 261, Internal support pillar of hydrogel bionic suction cup; 262, Top base of hydrogel bionic suction cup; 263, Bottom base of hydrogel bionic suction cup; 264, Base of hydrogel bionic suction cup; 265, Vertical propeller base; 271, Motor rotating shaft; 272, Vertical propeller fixing shaft; 273, Vertical propeller fixing hole; 274, 930kV waterproof brushless motor; 275, Horizontal propeller fixing hole; 281, Motor rotating shaft; 282, 980kV waterproof brushless motor; 283, Horizontal propeller outer shell; 284, Thruster fixing base; 285. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that the specific embodiments described herein are only for explanation and illustration of the present invention and are not intended to limit the present invention.

[0032] Example 1: Using Figures 1 to 2 The following example illustrates the external structure of this underwater multimodal mobile robot. Figures 1 to 2 The internal electronic sealing chamber of the robot is omitted to clearly illustrate the main structural components. The underwater multimodal mobile robot includes a robot shell 2, an arm-grabbing mechanism 3, a leg-walking mechanism 4, a vertical propeller thruster 7, and a horizontal propeller thruster 8. The robot shell is fixed by internal connectors; the cable communication interface 1 is bolted to the tail of the main body, and the camera 5 and LED lights 6 are bolted to the head of the main body; the leg-walking mechanism consists of six three-degree-of-freedom crawling legs, with the left front leg 101, right front leg 102, left middle leg 103, right middle leg 104, left hind leg 105, and right hind leg 106 symmetrically distributed on the outside of the robot body; the left front vertical thruster, right front vertical thruster, and rear vertical thruster are bolted to the robot body, while the left rear horizontal thruster and right rear horizontal thruster are fixed to the robot body via a base. The vector combination of the five thrusters enables multi-degree-of-freedom motion control of the robot in swimming mode. The robot system mainly has three motion modes:

[0033] A. Propeller drive mode, suitable for mobile tasks such as large-scale waterway cruise and systematic data acquisition;

[0034] B. The six-legged crawling mode is suitable for stable positioning and anti-current maneuvering tasks during complex seabed topography exploration, equipment maintenance, and cruise approach.

[0035] C. Target object grasping mode, suitable for delicate operation scenarios such as non-destructive collection of marine biological samples, underwater waste recycling, and equipment component maintenance and replacement.

[0036] Example 2: Figure 1 and Figure 3The following example illustrates the working principle of this underwater multimodal mobile robot in target grasping mode. When the host computer selects the target grasping mode, the main controller, a Raspberry Pi, simulates biological neural rhythms through a central mode generator based on a Hopf oscillator, outputting two sets of target grasping trajectories for the arms. The two robotic arms achieve 360° full-range rotation positioning through the first joint 12. The second joints 131 and 132, along with the third joints 141 and 142, coordinate swinging to adjust the arm posture and working radius. The end effector maintains stable target orientation during movement. The robot's arm motion control adopts a centralized architecture based on inverse kinematics: the Raspberry Pi main controller calculates the target angles of the six joints in real time, converts them into PWM parameters, and then sends them to I... 2 The C-bus batch writes data to the PCA9685 controller register, driving it to output a 50Hz PWM signal in parallel to each joint servo. At the same time, it integrates the attitude feedback from the fuselage IMU to dynamically correct the joint angles to maintain balance. Finally, it achieves continuous grasping operations through rhythmic instructions generated by the central mode generator.

[0037] Example 3: Using Figure 3 and Figure 4 The following example illustrates the working principle of the hydrogel bionic gripper in the target object grasping mode of this underwater multimodal mobile robot. When the host computer selects the target object grasping mode, the main controller, a Raspberry Pi, coordinates the control of two sets of arms and the hydrogel bionic gripper to achieve the grasping process. The dual-channel independently controlled diaphragm pump 17 simultaneously provides negative pressure (vacuuming during adsorption) and positive pressure (inflating during bending). The hydrogel grippers 161 and 162 achieve surface adhesion through the negative pressure principle. The MOSFET drive module adjusts the start / stop and direction of the diaphragm pump. When the robot encounters a target object during crawling, the dual-channel independently controlled diaphragm pump is activated, allowing the hydrogel bionic gripper to bend and grasp. The main controller, a Raspberry Pi, generates the crawling gait and integrates the diaphragm pump opening / closing signals, sending them to the slave controller. The slave controller, a PCA9685, and MOSFETs drive in parallel, ensuring synchronous updates of the grasping signal and joint PWM, achieving compliant grasping of the target object.

[0038] Example 4: Figure 2 and Figure 5 The following example illustrates the working principle of this underwater multimodal mobile robot in hexapod crawling mode. When the host computer selects the hexapod crawling mode, the main controller, a Raspberry Pi, simulates biological neural rhythms through a central mode generator based on a Hopf oscillator, outputting the target trajectories of the six legs. The six legs move by swinging the first joints 201 and 202, the second joint 21 adjusts the leg lift height, and the third joints 221 and 222 maintain foot translation. The Raspberry Pi calculates the 18 joint angles of the six legs in real time through inverse kinematics and converts the joint angles into the PWM duty cycle of the PCA9685, which is then controlled via the Raspberry Pi's GPIO I / O pins. 2The C interface sends the PWM register value to the PCA9685. Based on the received duty cycle parameters, the PCA9685 outputs a 50Hz PWM signal to the corresponding servo motor. Using the PWM output, 18 joints of six legs are controlled in parallel via I / O. 2 The C-bus batch write registers reduce single communication latency. The robot's posture is detected by the built-in inertial measurement unit, the joint angle of the supporting legs is adjusted to maintain balance, and the continuous crawling is achieved by continuously generating periodic signals based on the central pattern generator.

[0039] Example 5: Figure 5 and Figure 6 The following example illustrates the working principle of the hydrogel bionic suction cup in the six-legged crawling mode of this underwater multimodal mobile robot. When the host computer selects the six-legged crawling mode, the main controller Raspberry Pi coordinates the six legs and the hydrogel bionic suction cup to achieve adhesion and detachment during the crawling process. The diaphragm pump 24 provides negative pressure (air extraction during adsorption) and positive pressure (air inflation during detachment). The hydrogel suction cup 23 achieves surface adhesion through the negative pressure principle. The MOSFET drive module adjusts the start / stop and direction of the diaphragm pump. During the robot's crawling process, before the foot enters the support phase (ground contact and weight-bearing), the diaphragm pump is activated to extract air and apply negative pressure to the suction cup for adhesion. Before the foot enters the swing phase (leg lifting and movement), the diaphragm pump is switched to inflate and the suction cup detaches. The main controller Raspberry Pi generates the crawling gait and integrates the diaphragm pump opening and closing signals and sends them to the slave controller. The slave controller PCA9685 and MOSFET drive in parallel to ensure the synchronous update of the adhesion signal and the joint PWM, achieving stable adhesion and crawling on vertical or inverted surfaces.

[0040] Example 6: Figure 2 and Figure 7 The following example illustrates the working principle of this underwater multimodal mobile robot in propeller-driven mode. When the host computer selects propeller-driven mode, the main controller Raspberry Pi generates control commands based on trajectory planning algorithms or upper-level inputs. It communicates with the flight controller via the MAVLink protocol, receives the main control commands from the flight controller, and parses them into motor speed commands. These commands are then parsed into digital signals by the electronic speed controller to control the brushless motor rotation. The brushless motor's rotating shaft is fixed with propeller blades, propelling the robot's movement. The robot adjusts its attitude and depth in real time using its built-in inertial measurement unit and depth sensor. The flight controller updates the motor speed every 20ms to dynamically adjust the robot's direction of motion. Multi-degree-of-freedom motion control is achieved through the vector combination of the five thrusters.

[0041] The above embodiments are merely illustrative of the inventive concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An underwater multi-modal mobile robot equipped with flexible biomimetic grippers, comprising a robot body, a dual-arm gripping mechanism, a six-legged crawling mechanism, a propeller propulsion system, a hydrogel biomimetic gripper, a hydrogel biomimetic suction cup, an electronic sealed cabin and a sensing module, characterized in that: the robot head is provided with a 1080P high-definition camera and a double LED searchlight, and the camera and the LED lamp are both sealed by epoxy resin pouring; the robot tail is provided with a WF16-10 core waterproof communication interface supporting cable data transmission; the upper part of the robot body is symmetrically distributed with two sets of arm gripping mechanisms, each set of arm gripping mechanism comprising a base and a mechanical arm composed of three joint drives, and the end is provided with a hydrogel biomimetic gripper; the outer part of the robot body is symmetrically distributed with six sets of leg crawling mechanisms, each set of leg crawling mechanism comprising three joint-driven mechanical legs, and the foot end is provided with a hydrogel biomimetic suction cup; the propeller system comprises three vertical propellers and two horizontal propellers, the vertical propellers are arranged on both sides in front of the robot body and at the back, and the horizontal propellers are arranged on both sides at the back of the robot body; the electronic sealed cabin is integrated with a main controller, a slave controller and a power module, the main controller is a Raspberry Pi, which is used to plan the crawling motion and gripping path of the whole robot, the slave controller includes a PCA9685 control board and a flight controller, the PCA9685 control board receives instructions from the main controller through the I2C protocol and outputs PWM signals for driving the leg servos, arm servos and diaphragm pumps, and the flight controller receives instructions from the main controller through the MAVLink protocol and analyzes them into motor speed signals, which are driven by an electronic speed regulator to drive brushless motors; the sensing module includes an inertial measurement unit, a depth sensor, a foot end contact switch and an arm end contact switch, the inertial measurement unit is used to feedback the robot posture in real time, the depth sensor is used to measure the underwater depth of the robot, the foot end contact switch is used to trigger the adsorption / desorption action, and the arm end contact switch is used to realize the bending and adhesion action; the robot has three motion states: propeller propulsion mode: through the vector combination of vertical and horizontal propeller propellers, multi-degree-of-freedom motion is realized, the robot can complete typical swimming operations such as hovering, turning and lifting in this state, which is the main way for the robot to quickly maneuver and transfer in water, in this mode, the dual arms are retracted on the upper part of the body to reduce water resistance and optimize the fluid shape, achieving efficient propulsion. Six-legged crawling mode: a periodic gait is generated by a central pattern generator to control the leg joint servos to realize crawling, the third joint of the leg is provided with a diaphragm pump, which can control the negative pressure adsorption and desorption of the hydrogel biomimetic suction cup, and cooperate with the six-legged gait to realize stable crawling on vertical or inverted surfaces, in this mode, the dual arms also maintain the retracted posture to reduce fluid resistance and posture interference during crawling. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Target object grasping state: through the driving of each mechanical arm three joints of the robot and the control of the end hydrogel bionic gripper, single-arm independent operation, double-arm cooperative operation and double-arm asynchronous operation three grasping configurations are supported, which can respectively realize the grasping tasks of single target, large target and multiple targets. During grasping, the double-path independent control diaphragm pump drives the hydrogel bionic gripper to bend and adhere at the same time to realize negative pressure grasping. In this state, the robot body is usually kept stationary, and the arm system independently completes the fine operation task.

2. The underwater multi-modal mobile robot of claim 1, wherein: The base size of the double-arm grasping mechanism is 45mm, the three joint sizes are 51mm, 83mm and 174mm in turn, and the end hydrogel bionic gripper size is 82mm. Each joint is driven by a standard IPX893 waterproof digital servo; a diaphragm pump is integrated in the third joint, and waterproof sealing is achieved through epoxy resin casting.

3. The underwater multi-modal mobile robot of claim 1, wherein: The three joint sizes of the six-legged crawling mechanism are 48mm, 76mm and 147mm in turn, and each joint is driven by an IPX893 waterproof digital servo; a diaphragm pump is integrated in the third joint, and waterproof sealing is achieved through epoxy resin casting.

4. The underwater multi-modal mobile robot of claim 1, wherein: The propeller propulsion system includes three vertical propellers and two horizontal propellers. The vertical propellers are driven by 930kv brushless motors, and through constant speed and same direction rotation, ascending / descending motion is realized, and through constant speed and opposite direction rotation, pitching / rolling motion is realized. The horizontal propellers are driven by 980kv brushless motors, and through constant speed and same direction rotation, forward / backward motion is realized, and through differential rotation, yaw motion is realized.

5. The underwater multi-modal mobile robot of claim 1, wherein: The hydrogel bionic gripper is prepared by supermolecular hydrogel of light-cured 3D printing, and the gripper structure includes a negative pressure cavity and a pneumatic cavity. The gripper is controlled by a hydraulic drive system, and through double-path independent control of the diaphragm pump, the bending of the gripper and the adsorption / desorption action of the gripper suction cup are realized. The gripper suction cup utilizes negative pressure difference to realize reversible adhesion. Negative pressure is applied during adsorption, and normal pressure is restored during desorption, so as to realize non-destructive grasping and releasing of various underwater objects.

6. The underwater multi-modal mobile robot of claim 1, wherein: The hydrogel bionic suction cup is prepared by metal ion coordination double network hydrogel of digital light processing 3D printing, and a communication loop is arranged in the suction cup. The adhesion and desorption functions are realized by the air extraction and inflation of the diaphragm pump. The diaphragm pump is controlled by a MOSFET module. The adsorption action is synchronized with the phase of the six-legged gait. The adsorption is started in the support phase, and the desorption is triggered in the swing phase.

7. The underwater multi-modal mobile robot of claim 1, wherein: The propeller propulsion system and the hydrogel bionic suction cup can provide the robot with posture adjustment capability, and improve the center of gravity drift of the robot. Through the multi-propeller vector layout and closed-loop control algorithm, the depth and spatial posture of the robot can be actively adjusted. The strong van der Waals force and capillary adsorption effect generated by the foot end hydrogel suction cup make the robot and the contact surface form a rigid connection, which significantly reduces the center of gravity drift of the body on the vertical or inclined surface. 8.A method for motion control of an underwater multi-modal mobile robot, characterized by, The underwater multi-modal mobile robot is realized based on any one of claims 1-7, comprising the following steps: Selecting a motion mode according to task requirements, generating corresponding control commands through a main controller Raspberry Pi; In the propeller propulsion mode, the flight controller assigns the speed of each propeller, which is converted into a digital signal by the electronic speed controller to drive the brushless motor to rotate, realizing multi-degree-of-freedom motion control. In the six-legged crawling mode, the central pattern generator network generates periodic gait signals, which are used to drive the servo to execute the joint angles calculated by inverse kinematics through the PCA9685 control board, while the diaphragm pump is controlled by the gait phase to realize adsorption / detachment, and the IMU attitude feedback is fused to adjust the body attitude in real time. In the target object grabbing state, the central pattern generator network generates periodic signals, which are sent to the PCA9685 control board to drive the servo to execute the joint angles calculated by inverse kinematics to grab the target object, and the diaphragm pump is started to realize the bending and adhesion of the gripper, so as to realize the grabbing of the target object.

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