Pipeline detection robot based on echinoderm inspired bionic variable stiffness structure

Abstract

The invention discloses a pipeline detection robot based on a echinoderm inspired bionic variable stiffness structure, which is suitable for detection, maintenance and obstacle avoidance operation of pipelines in complex environments such as space stations and the like, and is formed by connecting a plurality of single bodies with platforms in series through universal joint couplings, each single body comprises a platform, a thigh, a shank, a power output system and a foot end actuator, a motor is installed in the middle of the platform, and output drives the thigh to swing through a straight bevel gear and a wheel shaft; the platform side wing steering engines drive the shanks to pitch around the rotating shafts, and two-degree-of-freedom movement is achieved. The foot end actuator adopts a roller mechanism with switchable modes, and two working states of rolling and rigid supporting are supported. All the modules are mechanically connected through self-lubricating universal joints and have the deflection capacity of + / -30 degrees, and module posture collaboration and structure reconstruction are achieved. The system has high flexibility, high adaptability and dynamic stability, and can stably operate in variable-diameter, bent and vertical pipeline sections and the like.

Description

Technical Field

[0001] This invention relates to the field of robotics, and in particular to a small pipe inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure design. Background Technology

[0002] Pipelines are an indispensable part of modern industrial and civilian infrastructure, serving as the primary means of transporting fluids and gases in industries and applications such as oil refineries, chemical plants, power plants, and space stations. Space station pipelines are complex, with large diameter spans, abrupt changes, and discontinuities, making autonomous movement of robots a significant challenge. Inspecting these pipelines is crucial because malfunctions can lead to catastrophic accidents and even threaten human lives. For example, pipeline leaks can cause a drop in cabin pressure, endangering astronauts; propellant pipeline ruptures can trigger hydrazine fuel leaks, paralyzing the propulsion system. While regular maintenance and inspection are effective ways to reduce the risk of accidents, not all pipelines are suitable for such operations. Utilizing specialized robots carrying inspection equipment to perform automated inspections along the inner or outer walls of pipelines not only improves the efficiency and safety of inspections but also reduces the risks of manual operation, providing an effective solution to such pipeline maintenance problems.

[0003] Current pipeline inspection robots suffer from three major drawbacks: they are mostly wheeled or tracked vehicles, lacking the ability to detect vertical pipelines; they occupy a large volume of pipeline space, making them prone to getting stuck when overturned, encountering silt, or experiencing pipeline damage; and communication signals within the pipeline are either absent or weak, resulting in communication delays. Therefore, developing pipeline inspection robots suitable for complex environments is of significant strategic importance for ensuring safe operation in extreme conditions, improving inspection efficiency and reliability, overcoming communication technology bottlenecks, and safeguarding industrial safety. Summary of the Invention

[0004] This invention proposes a pipeline inspection robot to address current challenges in pipeline inspection, such as pipeline damage, silt accumulation, and complex pipeline shapes, all of which hinder robot movement. Therefore, this invention mimics the movement mechanism of echinoderms, including starfish, sea urchins, and sea cucumbers, whose tube feet retract inwards when at rest and extend outwards during movement. It proposes a biomimetic variable stiffness design concept of "passive extension and force-induced contraction," resulting in a flexible and extensible pipeline inspection robot. The robot can passively adjust its outward extension angle according to the pipeline diameter. A torsion spring acts as an energy storage device, generating pressure to ensure close contact with the pipeline wall, giving the robot significant flexibility. The robot innovatively connects a universal joint mechanism with the drive unit, enabling forward-rotation coupled motion, allowing for changes in the robot's path and obstacle avoidance. The robot can adaptively deform in complex pipeline networks, improving inspection efficiency and fault tolerance, and has broad industry application prospects.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A small pipe inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure is disclosed. The robot adopts a modular design, with each module consisting of three telescopic leg-joint units (A) and one tripod-connecting unit (B). The telescopic leg-joint units (A) are responsible for adapting to different pipe diameters and drive control, while the tripod-connecting unit (B) is responsible for connecting different units and adaptive adjustment of "passive extension and force contraction". Different units are connected through the tripod-connecting unit to form a modular variable structure robot that can be flexibly reconfigured according to task requirements.

[0007] Preferably, the telescopic leg-joint unit (A) includes a tripod hinge (A1), a telescopic leg inner core (A2), and an outer sleeve (A3). The tripod hinge (A1) is movably connected to the tripod-connecting unit (B) and forms the first end of the telescopic leg-joint unit (A). The telescopic leg inner core (A2) is connected to the tripod hinge (A1) and can passively extend and retract when the tube diameter changes. The telescopic leg inner core (A2) is composed of a front leg part, a rear leg part, and a connector. Both the front and rear leg sections contain two geared motors (JGB37Y520), connected by an LZQ series universal joint coupling [T04G-A14-A14]. The universal joint drive enables the robot to switch between multiple degrees of freedom and perform rotation-forward coupled motion. It mainly changes the forward axis of the module wheel system by rotating the universal joint to change the direction of motion. This breaks through the fixed direction limitation of traditional wheeled robots, enabling autonomous steering and obstacle crossing. The outer sleeve (A3) covers the inner core (A2) of the telescopic leg to protect it.

[0008] Preferably, the telescopic leg inner core (A2) is provided with a detachable Mecanum wheel or hemispherical foot pad at the end to adapt to different pipe surfaces and reduce sliding friction.

[0009] Preferably, the tripod-connecting unit (B) includes a tripod (B1), a flexible rod (B2), a torsion spring (B3), and a support platform (B4). The tripod (B1) consists of a retractable frame and three support columns, forming an anti-compression adaptive adjustment mechanism. The tripod (B1), flexible rod (B2), torsion spring (B3), and support platform (B4) are connected along a central axis. The torsion spring (B3) acts as an energy storage device, generating pressure to ensure close contact with the pipe wall. The tripod (B1) and support platform (B4) are respectively fitted onto both ends of the flexible rod (B2). The torsion spring (B3), as an energy storage device for the machine body, has a certain degree of flexibility and is used to provide radial preload to keep the legs in contact with the pipe wall. The cooperation between the torsion spring (B3) and the tripod (B1) can achieve adaptive adjustment of "passive extension and force-induced contraction".

[0010] Preferably, the telescopic leg-joint unit (A) and the tripod-connection unit (B) are connected via a mechanical-electrical integrated quick-connect interface, which includes a mis-insertion guide pin, an ISO standard flange, and an 8-pin quick-connect electrical connector to enable rapid assembly and disassembly of the module and topology reconfiguration.

[0011] Compared with the prior art, the beneficial effects of the present invention are:

[0012] 1. The robot adopts a modular design, with each module consisting of three telescopic leg-joint units (A) and a tripod-connection unit (B). Several robot modules are connected in series to form a small pipeline inspection robot. The number of modules can be flexibly increased or decreased according to task requirements, realizing configuration reconstruction and functional expansion, and improving system fault tolerance and maintenance efficiency.

[0013] 2. The telescopic leg-joint unit (A) is coupled to the dual-degree-of-freedom wheel system through a universal joint coupling, realizing the robot's multi-degree-of-freedom direction switching and rotation-forward coupled motion, enabling the robot to have three-dimensional spatial mobility and continuously pass through S-shaped bends, vertical pipes and branch structures.

[0014] 3. Tripod-connection unit (B) is based on torsion spring-tripod mechanism to achieve passive variable stiffness and energy recovery, enabling the robot to adaptively fit the pipe wall in complex environments such as sudden changes in pipe diameter and accumulation of obstacles, thereby enhancing its passage ability and anti-compression performance.

[0015] 4. The modular quick-connect interface supports rapid deployment and remote control, significantly reducing the barrier to entry and maintenance costs. It is suitable for detection, maintenance and troubleshooting operations in complex pipeline environments such as space stations, oil refineries and chemical plants. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0017] Figure 2 This is a detailed structural diagram of the robot with platform unit of the present invention;

[0018] Figure 3 This is a detailed structural diagram of the bionic leg drive module of the present invention;

[0019] Figure 4 This is a detailed structural diagram of the foot-end actuator of the present invention.

[0020] In the diagram: 1. Universal joint coupling; 2. Gearbox module; 3. Motor; 4. Servo motor; 5. Spur bevel gear; 6. Thigh; 7. Unit with platform; 8. Overall walking mechanism; 9. Servo motor clamp; 10. Roller; 11. Platform; 12. Wheel axle; 13. Lower leg; 14. Rotating shaft. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Reference Figures 1-4 A pipeline inspection robot based on a biomimetic variable stiffness structure inspired by echinoderms is disclosed. The robot comprises two individual robot units and two walking mechanism units 8. The individual robot units and the walking mechanism units 8 are sequentially and alternately connected in series to form a linear modular robot. The individual robot units and the walking mechanism units 8 are connected by universal joint couplings 1. Each universal joint coupling 1 includes a cross pin and a self-lubricating copper sleeve structure. Its pin is inserted into the shaft hole of the lateral platform 11 of the individual robot unit, realizing both mechanical and electrical connection between modules. It also allows adjacent modules to achieve a maximum relative deflection of ±30° in multiple directions, with a deflection friction torque of no more than 1.5 N·m. This enables the robot to have the active joint capability of flexible rotation to adapt to complex pipeline environments.

[0023] In this embodiment, the robot unit includes a platform 11, thighs 6, lower legs 13, a bevel gear transmission mechanism, axles 12, servo motors 4, rotating shafts 14, a gearbox module 2, a unit with a platform 7, and foot rollers 10. The platform 11 serves as the supporting base for the unit structure, and a DC motor 3, model JGY4632-370, is vertically mounted at its center. The output shaft of the motor 3 is coaxially connected to a spur bevel gear 5 via a keyed coupling. The spur bevel gear 5 and the horizontally arranged axle 12 are in the air... The system achieves 90° orthogonal meshing transmission. One end of the wheel axle 12 is inserted into the root of the thigh 6 through a D-shaped shaft end to achieve torque transmission. The thigh 6 can swing around the wheel axle 12 at ±30°. Its far end is hinged to the lower leg 13 through a rotating shaft 14. The lower leg 13 is driven by the servo motor 4 installed on the side of the platform 11 to produce pitch motion. The lower leg 13 is equipped with foot rollers 10 for support and contact with the tube wall, forming a robot single structure with dual-degree-of-freedom drive function. The model of the servo motor 4 is ZX30S.

[0024] In this embodiment, the foot roller 10 integrates a deep groove ball bearing with ISO P4 precision grade and is covered with polyurethane material with a Shore hardness of 80A to improve its adaptability to wet or corrosive pipe walls. The roller 10 is installed at the end of the lower leg 13 through a quick-release pin structure and has two working states: rolling mode and support mode. In the rolling mode, the bearing is unlocked and the roller 10 can rotate freely to reduce friction, with a friction coefficient of no more than 0.05. In the support mode, the bearing is locked to form a rigid foot support with a load-bearing capacity of more than 200N, which is suitable for working scenarios such as climbing, braking or obstacle crossing.

[0025] In this embodiment, the pitch control of the lower leg 13 is achieved by a bus-type servo motor 4 fixedly installed on the side of the platform 11. The servo motor 4 is locked to the mounting hole on the side of the platform 11 by a high-strength aluminum alloy integral milled servo motor clamp 9. The output shaft of the servo motor 4 is connected to the rotating shaft 14 of the lower leg 13 through a cross slider coupling. The coupling can absorb a radial assembly error of ±0.1mm to ensure transmission stability. The maximum output torque of the servo motor 4 is 30Kg·cm, the pitch adjustment angle range is -45° to +45°, the closed-loop control accuracy is better than ±0.5°, and the dynamic response time is less than 0.2 seconds, ensuring the speed and stability of the leg movement.

[0026] In this embodiment, the bevel gear transmission mechanism adopts a 2:1 transmission ratio, which reduces the speed of the DC motor 3 output from 2000 rpm to the speed of the wheel shaft 12 output from 1000 rpm. Under the control of machining precision, the bevel gear and the wheel shaft 12 achieve a meshing clearance of no more than 0.05 mm, which ensures efficient and low-noise power transmission performance. The transmission efficiency is no less than 92%, and it can maintain an excellent gear meshing state during long-term operation. It is suitable for stable operation requirements in environments with frequent starts and stops and complex paths.

[0027] In this embodiment, the axle 12 is made of nitrided 40Cr steel with a surface hardness of HRC50 to HRC55 to improve its wear resistance and fatigue life. One end of the axle 12 is provided with a D-shaped keyway structure, which is fitted into the metal insertion hole at the root of the thigh 6 to ensure anti-slip and anti-deflection capabilities during torque transmission. The other end of the axle 12 is installed in the internal structure of the platform 11 through a double support bearing to maintain its coaxial stability during rotation.

[0028] In this embodiment, the servo clamp 9 is an integral forged aluminum alloy structure with a hard anodized surface to improve its corrosion resistance and structural rigidity. The bottom of the servo clamp 9 is provided with multiple sets of standard mounting holes to adapt to different specifications of servo motors 4. The embedded rubber buffer pad is used to reduce shock and eliminate assembly stress, which can maintain the installation stability of the servo motor 4 under high-frequency vibration conditions and effectively extend the service life of the servo motor 4.

[0029] In this embodiment, the connection structure of the universal joint coupling 1 consists of a central shaft pin with a cross structure, an oil-impregnated copper sleeve, and a dustproof ring for the outer shell. The shaft holes of the two end platforms 11 are interference fit structures. After assembly, the coupling has an angular deflection capability of ±30° to adapt to changes in complex pipeline paths. The self-lubricating copper sleeve ensures that it maintains a high-efficiency and low-friction state during long-term operation, which is suitable for pipelines with a minimum bending radius of 150mm.

[0030] In this embodiment, the robot is controlled by an ESP32 series main control unit. The control system integrates PWM output and bus communication functions. The movements of motor 3 and servo motor 4 are controlled by the main control system through periodic rhythmic control commands, and feedback correction is performed by combining the position signal of wheel axle 12 collected by Hall encoder. The overall control is based on incremental PID algorithm to achieve closed-loop adjustment of the pitch angle of servo motor 4 and the positive pressure of wheel axle 12. The foot pressure control threshold is set to 15±2N to ensure that the robot can achieve dynamic optimization of posture adjustment and ground contact force under different working conditions.

[0031] In this embodiment, the modular structure is connected via a quick-connect mechanical-electrical interface, enabling rapid robot deployment and modular topology reconfiguration. It is suitable for operation inside irregularly shaped spatial pipes with diameters ranging from 150 to 350 mm, including curved sections, vertical sections, variable diameter sections, and T-shaped branch sections. Through the coordinated control of the swinging motion of the thigh 6 and the pitching motion of the lower leg 13, combined with the deflection degree of freedom of the universal joint, the robot achieves highly adaptable omnidirectional mobility. Compared with the traditional wheeled structure, the robot's energy consumption during obstacle crossing is reduced by approximately 38%, and the radial space it occupies in the pipe is reduced by approximately 40%.

[0032] A DC geared motor 3 is installed in the vertical through hole in the center of platform 11. Its output shaft is rigidly connected to the drive bevel gear via a coupling structure. The housing of motor 3 is positioned and fixed to the upper part of platform 11 by a flange, ensuring stable and reliable power output. The drive bevel gear and the driven bevel gear are arranged orthogonally in space. The driven gear is installed at the end of the horizontally arranged axle 12, which extends from inside platform 11 into the structure of thigh 6, thereby converting the power originally output vertically by motor 3 into torque output along the horizontal axis of platform 11. The entire bevel gear system is installed in a precision-machined meshing cavity. The cavity is equipped with a lubrication oil reservoir and a dustproof sealing ring around its perimeter, and is locked by bolts and pressure plates on platform 11, thus ensuring meshing accuracy and long-term stability. The bevel gears are made of high-strength tempered steel, and the surface hardness is significantly improved after nitriding heat treatment, enabling them to withstand frequent start-stop cycles and high-frequency dynamic impact loads. One end of the axle 12 passes through the bearing seat of the platform 11 and connects to the shaft hole at the bottom of the thigh 6 structure. This connection is made by the D-shaped shaft end engaging with the metal slot embedded in the base of the thigh 6, ensuring stable torque transmission while preventing slippage or deviation.

[0033] The robot's bionic leg structure mainly consists of two parts: the thigh 6 and the lower leg 13. The thigh 6, as the active swinging component, is directly connected to the output end of the wheel axle 12 and is driven by the power transmitted from it to produce a left-right swinging motion. The thigh 6 adopts a hollow I-shaped cross-section design, and through structural topology optimization, the mass is reduced while ensuring strength and rigidity. A bushing hole is provided at its root, and a PTFE low-friction bushing is embedded to enable smooth and noiseless swinging motion under the rotational drive of the wheel axle 12. The distal end of the thigh 6 is hinged to the lower leg 13 via a rotating shaft 14. The lower leg 13 is more slender and lightweight than the thigh 6, but its structure still adopts a closed box-type structure to ensure integrity and load-bearing capacity. The rotating shaft 14 is a solid stainless steel shaft with rolling bearings embedded at both ends and bolted in place, thus giving the lower leg 13 independent rotational freedom relative to the thigh 6. The lower leg 13 has grooves and quick-release holes for mounting the roller 10 module, and also has a pre-set wire channel for guiding and protecting the output wire of the servo motor 4. The entire leg structure maintains high mechanical response sensitivity and trajectory repeatability during joint movement, exhibiting stable mechanical characteristics in performing high-frequency leg lifts, support, or obstacle crossing movements.

[0034] As the core actuator for realizing the pitch movement of the lower leg 13, the stability and fixing method of the servo motor 4 have a decisive impact on the overall motion response of the robot. This robot uses a bus-type servo-uart servo motor 4, which is firmly mounted on the raised structure on the side of the platform 11 via the servo motor clamp 9. The servo motor clamp 9 is manufactured using a one-piece milling process with a hard anodized surface treatment, possessing excellent rigidity and corrosion resistance, and is equipped with multiple sets of standard holes to accommodate the installation requirements of various servo motor 4 specifications. The servo motor 4 is connected to the lower leg 13 via a cross-slider coupling. This coupling has micro-angle compensation and radial deviation absorption capabilities, ensuring that the output torque of the servo motor 4 shaft can be accurately transmitted to the rotation shaft 14 of the lower leg 13, while simultaneously avoiding the accumulation of lateral bearing forces due to assembly errors. The servo motor 4 communicates with the main control unit via an RS485 bus and can receive control commands such as angle, speed, and torque, providing continuous, smooth, and rapid-response attitude control capabilities in high-dynamic movements. To enhance the connection stability between servo motor 4 and the whole machine, servo motor clip 9 is embedded with a rubber buffer pad, which can effectively reduce resonance and impact transmission under long-term high-frequency vibration conditions, thereby improving the life of servo motor 4 and the stability of servo angle.

[0035] Adjacent units are mechanically connected via a universal joint coupling 1. This coupling not only enables structural assembly but also provides the robot with the necessary flexible adjustment capabilities for movement in complex three-dimensional space. The main body of the universal joint coupling 1 consists of a cross structure, with a central pin inserted into the trunnion holes of the two side platforms 11, achieving a tight fit. A self-lubricating copper sleeve and a dustproof sealing ring are provided between its outer shell and the pin, ensuring low friction and high torque transmission even under high-load oscillation. This mechanism can achieve a maximum angle deflection of ±30 degrees, adapting to the robot's posture transition needs in complex scenarios such as bending, diameter changes, and obstacles. The entire universal joint shell is separately cast and precision machined. The connecting end has a positioning pin groove and an anti-detachment structure, allowing for quick insertion and removal and maintaining good dimensional stability after multiple disassemblies and reassemblies. Its internal cavity is equipped with high-performance grease, extending its service life under extreme working conditions.

[0036] This modular bionic legged robot follows a multi-stage collaborative drive and dynamic response control strategy when performing tasks, achieving highly adaptable and flexible movement behavior. The entire robot workflow can be divided into stages such as startup initialization, environmental perception, posture adjustment, walking propulsion, obstacle handling and feedback calibration, each stage relying on the high coupling between the mechanical structure and control logic.

[0037] In this invention, when using the device, the user should refer to the appendix of the instruction manual. Figure 1 Instruction manual attached Figure 2 Included with instruction manual Figure 4During the initialization phase, the main control unit first completes the power self-test and communication connection initialization of each module, including confirming the data links between motor 3, servo motor 4, sensors, and multiple units. Subsequently, motor 3 on platform 11 drives its respective bevel gear assembly to slowly rotate one revolution, verifying the gear meshing state and the normal response of axle 12. Simultaneously, the output shaft of servo motor 4 is zero-position calibrated to ensure all bionic legs are in a uniform initial position. During this phase, the system broadcasts the initial status to each unit module via the RS485 bus and loads control parameters for servo motor 4, such as PID gain coefficient, maximum torque limit, and angular velocity limit.

[0038] During the posture adjustment phase, based on environmental perception data or path planning results, the robot drives motor 3 to output specific speeds and directions, causing axle 12 to drive thigh 6 to swing along a predetermined trajectory. Simultaneously, servo motor 4 controls the pitch of lower leg 13, enabling gait lifting or landing movements. The coordinated action of thigh 6 and lower leg 13 creates a leg-swinging rhythm similar to that of a walking organism, ensuring that the foot-end rollers 10 provide good support and thrust when in contact with the ground.

[0039] Next, refer to the attached instruction manual. Figure 1 Included with instruction manual Figure 2 During the walking propulsion phase, the drive motors 3 and servo motors 4 of each individual module perform periodic motion control according to the rhythm parameters issued by the main controller. This includes the front and rear modules alternately entering swinging and support states, forming a continuous propulsive gait wave. The foot rollers 10 switch to free rolling mode during this phase, enabling the robot to have high walking efficiency. If it is necessary to improve grip, the pitch angle of the lower leg 13 is increased, and the rotation function of the rollers 10 is locked, making them act as rigid support points to bear part of the axial load, forming a crawling mode that balances propulsion and stability.

[0040] When encountering an obstacle, the robot enters the obstacle response phase. Based on previously acquired sensor data or real-time feedback, the main control unit determines the size and position of the obstacle and issues specific action commands to the corresponding individual modules. This includes expanding the swing amplitude of the thigh 6 in the middle module and increasing the knee height of the lower leg 13, forming an active leg-lifting and crossing posture; while adjacent modules appropriately reduce their swing to improve the overall structural stability. The universal joint coupling 1 demonstrates its structural flexibility during this phase, allowing for angle buffering and fine-tuning between individual modules, avoiding excessive structural interference or jamming due to posture errors.

[0041] Finally, please refer to the attached instruction manual. Figure 1 Instruction manual attached Figure 2 Included with instruction manual Figure 3In the feedback calibration phase, after each action cycle, the main control system collects feedback data such as motor current, rudder angle, and sensor pressure from all individual units. It analyzes the deviation between the current posture and the target posture and uses this data to correct the rudder angle and motor speed for the next cycle. This process constitutes an adaptive control logic based on a force-position dual closed loop, enabling the robot to achieve self-optimization between dynamic stability and gait efficiency in complex paths.

[0042] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure, comprising two robot units and two walking mechanism components (8), characterized in that, The robot unit and the walking mechanism (8) are sequentially and alternately connected in series to form a linear modular robot. The robot unit and the walking mechanism (8) are connected by universal joint couplings (1). Each universal joint coupling (1) includes a cross pin and a self-lubricating copper sleeve structure. Its pin is inserted into the shaft hole of the robot unit's side platform (11) to realize the mechanical and electrical dual connection between modules, and allows the adjacent modules to achieve a maximum relative deflection of ±30° in multiple directions. The deflection friction torque is not greater than 1.5 N·m, so that the robot has the active joint capability of flexible rotation to adapt to complex pipeline environments.

2. The pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 1, characterized in that, The robot unit includes a platform (11), thigh (6), lower leg (13), bevel gear transmission mechanism, axle (12), servo motor (4), rotating shaft (14), gearbox module (2), unit with platform (7), and foot rollers (10). The platform (11) serves as the supporting base of the unit structure, and a DC motor (3) is vertically mounted at its center. The output shaft of the motor (3) is coaxially connected to the spur bevel gear (5) through a keyed coupling. The spur bevel gear (5) and the horizontally arranged axle (12) are in space. Achieving 90° orthogonal meshing transmission, one end of the wheel axle (12) is inserted into the root of the thigh (6) through a D-shaped shaft end to achieve torque transmission. The thigh (6) can swing around the wheel axle (12) by ±30°. Its far end is hinged to the lower leg (13) through a rotating shaft (14). The lower leg (13) is driven by a servo motor (4) installed on the side of the platform (11) to produce pitch motion. The lower leg (13) is equipped with a foot roller (10) for support and to fit against the tube wall, forming a robot single structure with dual-degree-of-freedom driving function.

3. The pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 2, characterized in that, The foot roller (10) integrates a deep groove ball bearing with ISO P4 precision grade and is covered with polyurethane material with a Shore hardness of 80A to improve its adaptability on wet or corrosive pipe walls. The roller (10) is installed at the end of the lower leg (13) through a quick-release pin structure and has two working states: rolling mode and support mode. In the rolling mode, the bearing is unlocked and the roller (10) can rotate freely to reduce friction. The friction coefficient is no greater than 0.

05. In the support mode, the bearing is locked to form a rigid foot support with a load-bearing capacity of more than 200N, which is suitable for working scenarios such as climbing, braking or obstacle crossing.

4. A pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure as described in claim 2 or 3, characterized in that, The pitch control of the lower leg (13) is achieved by a bus-type servo motor (4) fixedly installed on the side of the platform (11). The servo motor (4) is locked to the mounting hole on the side of the platform (11) by a high-strength aluminum alloy integral milled servo motor clamp (9). The output shaft of the servo motor (4) is connected to the rotating shaft (14) of the lower leg (13) through a cross slider coupling. The coupling can absorb a radial assembly error of ±0.1mm to ensure transmission stability. The maximum output torque of the servo motor (4) is 30Kg·cm, the pitch adjustment angle range is -45° to +45°, the closed-loop control accuracy is better than ±0.5°, and the dynamic response time is less than 0.2 seconds, ensuring the speed and stability of the leg movement.

5. The pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 1, characterized in that, The bevel gear transmission mechanism adopts a 2:1 transmission ratio, which reduces the speed of the DC motor (3) outputting 2000 rpm to the speed of the wheel shaft (12) outputting 1000 rpm. Under the control of machining accuracy, the bevel gear and the wheel shaft (12) achieve a meshing gap of no more than 0.05 mm, which ensures efficient and low-noise power transmission performance. The transmission efficiency is no less than 92%, and it can maintain an excellent gear meshing state during long-term operation. It is suitable for stable operation requirements in environments with frequent start-stop and complex paths.

6. The pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 1, characterized in that, The axle (12) is made of nitrided 40Cr steel with a surface hardness of HRC50 to HRC55 to improve its wear resistance and fatigue life. One end of the axle (12) is provided with a D-shaped keyway structure, which is fitted into the metal insertion hole at the root of the thigh (6) to ensure anti-slip and anti-deflection capabilities during torque transmission. The other end of the axle (12) is installed in the internal structure of the platform (11) through a double support bearing to maintain its coaxial stability during rotation.

7. The pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 1, characterized in that, The servo clamp (9) is an integral forged aluminum alloy structure with a hard anodized surface to improve its corrosion resistance and structural rigidity. The bottom of the servo clamp (9) is provided with multiple sets of standard mounting holes to adapt to different specifications of servo (4) equipment. The embedded rubber buffer pad is used to reduce shock and eliminate assembly stress, which can maintain the installation stability of the servo (4) under high frequency vibration conditions and effectively extend the service life of the servo (4).

8. The pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 1, characterized in that, The universal joint coupling (1) consists of a central shaft pin with a cross structure, an oil-impregnated copper sleeve, and a dustproof ring on the outer shell. The shaft holes of the two end platforms (11) are interference fit structures. After assembly, the coupling has an angle deflection capability of ±30° to adapt to changes in complex pipeline paths. The self-lubricating copper sleeve ensures that it maintains a high-efficiency and low-friction state during long-term operation, and is suitable for pipelines with a minimum bending radius of 150mm.

9. A pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure as described in claims 1-8, characterized in that, The robot is controlled by an ESP32 series main control unit. The control system integrates PWM output and bus communication functions. The movement of the motor (3) and servo motor (4) is controlled by the main control system periodically issuing rhythmic control commands and combined with the wheel axle (12) position signal collected by the Hall encoder for feedback correction. The overall control is based on the incremental PID algorithm to realize the closed-loop adjustment of the pitch angle of the servo motor (4) and the positive pressure of the wheel axle (12). The foot pressure control threshold is set to 15±2N to ensure that the robot achieves dynamic optimization of posture adjustment and ground adhesion force under different working conditions.

10. A pipeline inspection robot based on an echinoderm-inspired biomimetic variable stiffness structure according to claim 9, characterized in that, The modular structure is connected via a quick-connect mechanical-electrical interface, enabling rapid robot deployment and modular topology reconfiguration. It is suitable for operation inside irregularly shaped spatial pipes with diameters of 150 to 350 mm, including curved sections, vertical sections, variable diameter sections, and T-shaped branch sections. Through the coordinated control of the swinging of the thigh (6) and the pitching motion of the lower leg (13), combined with the universal joint deflection degree of freedom, the robot achieves highly adaptable omnidirectional mobility. Compared with the traditional wheeled structure, the robot's energy consumption during obstacle crossing is reduced by about 38%, and the radial space it occupies in the pipe is reduced by about 40%.

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