A continuous robot joint reversible locking device and method of use thereof

Abstract

A continuous robot joint reversible locking device and a method for using the same belong to the technical field of robots, and the locking device comprises a hollow connecting rod, a variable stiffness joint and an air pipe. The variable stiffness joint comprises a universal joint, a bellows inner wall, a flexible heating layer and a variable stiffness layer. The two hollow connecting rods are connected through the universal joint, the bellows inner wall is connected to the side surface of the hollow connecting rod at the two ends of the universal joint and wraps the universal joint, and the flexible heating layer and the variable stiffness layer are used for layer-by-layer wrapping of the bellows inner wall. The invention inflates the gap between the bellows inner wall and the flexible heating layer, so that the flexible heating layer and the variable stiffness layer expand at the same time to generate local support on the surrounding environment; by controlling the temperature of the flexible heating layer, the phase change material in the variable stiffness layer is changed into a solid state to realize the locking of the joint; the coupling of inflation control and phase change control realizes the control of the stiffness of the continuous robot. The invention can solve the problem of insufficient variable stiffness capability of the continuous robot.

Description

Technical Field

[0001] This invention belongs to the field of robotics technology and relates to a reversible locking device for continuous robot joints and its usage method. Background Technology

[0002] In the fields of high-end equipment manufacturing and maintenance, such as aerospace, nuclear power plant repair, and medical surgery, there are numerous confined spaces with narrow openings, deep cavities, and convoluted geometries, such as fuel lines in aircraft engines, fuel tanks in aircraft, and the interiors of pipelines in nuclear power plants. High-precision manufacturing, inspection, and maintenance tasks within these spaces are extremely challenging. Traditional rigid robots, limited by their structural dimensions and degrees of freedom, struggle to enter and operate stably, while manual operation suffers from low precision, high risk, and poor efficiency. Continuous robots, with their high degrees of freedom, flexible configuration, and remote reachability, have become one of the effective solutions for tasks involving confined spaces and deep cavities.

[0003] Continuous robots possess good dexterity and accessibility; however, they often employ a serial open-chain structure. When performing high-precision, high-load tasks at the end effector, the lack of effective support results in low overall stiffness, severely limiting their application in high-end manufacturing. Variable stiffness technology can improve the stiffness capability of continuous robots while maintaining their flexibility, thus meeting engineering application requirements and possessing crucial technical significance. In recent years, numerous institutions have conducted research on variable stiffness technology for continuous robots. For example, in 2025, Northwestern Polytechnical University disclosed a "Variable Stiffness Rigid-Flexible Coupled Ultra-Redundant Continuous Robot" in Chinese Invention Patent CN119748418A. This robot achieves variable stiffness by using damping springs connected to the sides of each segment. When the robot bends and deforms, the resistance of the springs is "activated," thereby increasing the stiffness of the entire structure. However, this method is a passive variable stiffness mechanism, lacking the ability to actively control the variable stiffness, and the overall structure is complex with high assembly costs.

[0004] While existing variable stiffness techniques can improve the stiffness of continuous robots to some extent, these methods mainly include blocking methods, force-resistance methods, form-locking methods, and phase change material methods. For example, stiffness can be improved through particle blocking, fiber entanglement, or interlayer friction; or by using low-melting-point alloys, magnetorheological fluids, and other materials to undergo phase changes under external field excitation to achieve stiffness switching. However, these methods are often structurally complex, have redundant mass, and limited stiffness ratios. Moreover, they mostly focus on adjusting the stiffness of the robot's own structure and do not fully consider active interaction with the environment, making it difficult to achieve high-stiffness support while ensuring motion flexibility. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a reversible locking device for continuous robot joints and its usage method. By using the high stiffness of the joint after cooling of the phase change material and the expansion support of the joint, it can solve the problem of insufficient variable stiffness capability of continuous robots, and improve the situation of existing robot variable stiffness technology with complex structure, redundant mass, limited stiffness ratio and inability to adapt well to narrow and deep cavity environments.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A reversible locking device for a continuous robot joint includes hollow connecting rods, a variable stiffness joint, and an air tube. The variable stiffness joint includes a universal joint, a bellows inner wall, a flexible heating layer, and a variable stiffness layer. Two hollow connecting rods are connected to the variable stiffness joint via the universal joint. The bellows inner wall is located on the outer periphery of the universal joint and fixed to the ends of the two hollow connecting rods. The bellows inner wall is connected to a solenoid valve, a positive pressure regulating valve, and an air compressor via the air tube to control the air path. The flexible heating layer is located on the outer periphery of the bellows inner wall, providing heat to the variable stiffness layer, heating the phase change material within the variable stiffness layer to achieve a phase change. The variable stiffness layer is located on the outer periphery of the flexible heating layer. The air tube inflates the gap between the bellows inner wall and the flexible heating layer, causing rapid expansion of both the flexible heating layer and the variable stiffness layer. This creates localized support force on the surface of the deep cavity environment of the target, thereby increasing the stiffness of the continuous robot. Specifically:

[0008] Furthermore, two hollow connecting rods are orthogonally connected to a universal joint with end forks, achieving pitch and yaw motion of the variable stiffness joint through rotation. The universal joint includes an intermediate body, four rotating shafts, and four internal hexagonal cone-shaped set screws. Specifically, the intermediate body is a hollow, ring-like structure with eight symmetrically machined surfaces on its outer surface. Cylindrical through holes for the rotating shafts are machined at intervals on the machined surfaces. The axis of the cylindrical through holes is perpendicular to the axis of the intermediate body. The rotating shafts connect to the cylindrical through holes of the end forks of the hollow connecting rods, thereby enabling the hollow connecting rods to rotate around the axis. The upper and lower surfaces of the intermediate body are machined with threaded through holes for installing the internal hexagonal cone-shaped set screws. The rotating shafts are secured by pressing them against the inner side of the cylindrical through holes of the intermediate body using the internal hexagonal cone-shaped set screws.

[0009] Furthermore, the inner wall of the corrugated tube is an axially expandable, corrugated tubular structure that wraps around the outer periphery of the universal joint's middle body. Connecting holes are machined on both sides, and an air pipe interface is machined on the bottom. It is installed at the ends of two hollow connecting rods via screws through the connecting holes and connected to an air pipe through the air pipe interface to form an air passage. The other end of the air pipe is sequentially connected to a solenoid valve, a positive pressure regulating valve, and an air compressor. Specifically, the air compressor's outlet is connected to the positive pressure regulating valve's inlet via an air pipe; the positive pressure regulating valve's outlet is connected to the solenoid valve's inlet via another air pipe; and the solenoid valve's outlet is connected to the air pipe interface via an air pipe. When the air passage is open, the gap between the corrugated tube's inner wall and the flexible heating layer begins to fill with air, causing the flexible heating layer and the degree-adjustment layer to rapidly expand and extend under positive pressure. When the air passage is closed, the gap between the corrugated tube's inner wall and the flexible heating layer begins to release air, causing the flexible heating layer and the degree-adjustment layer to contract back to their natural state.

[0010] Furthermore, the flexible heating layer has a circular ring structure, sleeved on the outer periphery of the inner wall of the corrugated pipe; the flexible heating layer includes a first silicone encapsulation layer, a flexible circuit channel, and heating electrodes, with the first silicone encapsulation layer being the main structure; the flexible circuit channel is located on the outer periphery of the first silicone encapsulation layer, and the heating electrodes are connected to both ends of the flexible circuit channel for connecting to an external power source to realize the switching of the circuit. When the flexible heating layer is energized, the flexible circuit channel generates heat, causing the temperature of the entire flexible heating layer to rise, heating the temperature change layer; when the flexible heating layer is de-energized, the flexible circuit channel dissipates heat, causing the temperature of the entire flexible heating layer to drop, cooling the temperature change layer.

[0011] Furthermore, the variable stiffness layer is a ring structure, fitted around the outer periphery of the flexible heating layer. The variable stiffness layer includes a second silicone encapsulation layer and a phase change material channel. The main structure is the second silicone encapsulation layer, and the phase change material channel is a key structure located on the outer periphery of the second silicone encapsulation layer. The phase change material channel contains patterned phase change material, which can receive heat generated by the flexible heating layer through the thermal conduction of the first and second silicone encapsulation layers. The solidification of the phase change material after solidification locks the variable stiffness joints, thereby increasing the stiffness of the continuous robot. When the variable stiffness layer is heated, the phase change material in the phase change material channel melts into a liquid state, making the entire variable stiffness layer flexible, allowing the encapsulated variable stiffness joints to move freely. When the variable stiffness layer is cooled, the phase change material in the phase change material channel solidifies into a solid state, making the entire variable stiffness layer rigid, firmly locking the encapsulated variable stiffness joints.

[0012] Furthermore, a temperature sensor is provided between the first silicone encapsulation layer and the second silicone encapsulation layer to indirectly determine the melting state of the phase change material in the phase change material channel.

[0013] A method for using a reversible locking device for a continuous robot joint includes the following steps:

[0014] Step 1: Check the gas and heat status of the reversible locking device to ensure that the gas path is closed and that the flexible heating layer and the variable degree layer are in a contracted state; at the same time, connect the heating electrode to the adjustable DC constant current power supply through the wire, start the power supply, set the constant current output, and set the current to a reasonable value. At this time, the flexible circuit channel forms a closed loop and starts to work, so that the flexible heating layer is in a heating state.

[0015] Step 2: Observe the temperature sensor reading to indirectly determine the melting state of the phase change material in the phase change material channel. If the temperature rises too slowly, and the temperature sensor reading does not reach the melting point of the phase change material within a few minutes, adjust the current appropriately. After heating to the melting point of the phase change material, adjust the current to avoid the temperature rising too quickly and too high, which could damage the silicone structure of the first and second silicone encapsulation layers.

[0016] Step 3: After the phase change material in the phase change material channel has completely melted, the stiffness joint is changed to a flexible state. By controlling the movement of the hollow connecting rod and universal joint, the continuous robot is freely and flexibly extended into the deep cavity environment of the target until the end tool of the continuous robot reaches the designated working position.

[0017] Step 4: Turn on the air compressor, adjust the positive pressure regulating valve to set a stable positive pressure value, and open the solenoid valve. The air path enters the air pipe interface through the air pipe and begins to inflate the gap between the inner wall of the bellows and the flexible heating layer. Since the inner wall of the bellows is connected to the hollow connecting rod through the connecting hole and wraps around the universal joint, the variable stiffness layer will expand until it can provide local support with the surface of the deep cavity environment, thus initially improving the stiffness of the variable stiffness joint of the continuous robot.

[0018] Step 5: Turn off the adjustable DC power supply to allow the phase change material to solidify. The entire variable stiffness layer becomes rigid. Since the shaft is fixed to the intermediate body by the internal hexagonal cone end set screw, the rigid wrapping of the variable stiffness layer restricts the rotation of the hollow connecting rod around the shaft, thereby locking the entire variable stiffness joint and further improving the stiffness of the variable stiffness joint of the continuous robot. At this time, the continuous robot can start to perform high-precision operations.

[0019] Step 6: After the continuous robot finishes its operation, turn on the adjustable DC power supply. Based on steps 1 and 2, after the phase change material has completely melted, the variable stiffness joint changes to a flexible state. At the same time, close the air path to release the air from the gap between the inner wall of the bellows and the flexible heating layer. The variable stiffness layer contracts, releasing the local support effect on the surface of the deep cavity environment. At this time, the overall stiffness of the continuous robot decreases, and it can be manipulated to freely and flexibly exit the deep cavity environment.

[0020] The beneficial effects of this invention are as follows:

[0021] The flexible heating layer and variable stiffness layer of the reversible locking device designed in this invention expand rapidly under positive pressure, providing local support to the deep cavity environment. Simultaneously, the phase change material solidifies with high stiffness, providing excellent reversible locking for continuous robot joints and improving their variable stiffness capability. This reversible locking device has a simple structure, high lightweight design, and significant variable stiffness effect. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of a reversible locking device for a continuous robot joint provided by the present invention;

[0023] Figure 2 This is an internal sectional view of the variable stiffness joint structure in this invention;

[0024] Figure 3 This is a schematic diagram of the universal joint structure in this invention;

[0025] Figure 4 This is a schematic diagram of the connection between the hollow connecting rod and the universal joint in this invention;

[0026] Figure 5 This is a schematic diagram of the corrugated pipe structure in this invention;

[0027] Figure 6 This is a cross-sectional view of the flexible heating layer structure in this invention;

[0028] Figure 7 This is a cross-sectional view of the variable stiffness layer structure in this invention;

[0029] Figure 8 This is a schematic diagram of the expansion support of the reversible locking device in this invention;

[0030] In the diagram: 1. Hollow connecting rod; 2. Variable stiffness joint; 3. Trachea; 4. Deep cavity environment surface;

[0031] 21 Universal joint; 22 Corrugated inner wall; 23 Flexible heating layer; 24 Variable stiffness layer;

[0032] 211 Intermediate body; 212 Shaft; 213 Hexagonal tapered set screw; 221 Connecting hole; 222 Air pipe interface; 231 First silicone encapsulation layer; 232 Flexible circuit channel; 233 Heating electrode; 241 Second silicone encapsulation layer; 242 Phase change material channel. Detailed Implementation

[0033] The following is a detailed description of a reversible locking device for a continuous robot joint provided by the present invention, with reference to the accompanying drawings;

[0034] like Figure 1As shown, the continuous robot joint reversible locking device provided in this embodiment mainly consists of a hollow connecting rod 1, a variable stiffness joint 2, and an air tube 3.

[0035] like Figure 2 As shown, the variable stiffness joint 2 includes a universal joint 21, a bellows inner wall 22, a flexible heating layer 23, and a variable stiffness layer 24.

[0036] like Figure 3 As shown, the universal joint 21 includes one intermediate body 211, four rotating shafts 212, and four hexagonal tapered set screws 213; as Figure 4 As shown, there are two hollow connecting rods 1 connected by universal joints 21. The forks at the ends of the hollow connecting rods 1 are connected to the rotating shaft 212. The two hollow connecting rods 1 are arranged orthogonally with their end forks. By rotating, the pitch and yaw motion of the variable stiffness joint 2 can be realized. Specifically, the intermediate body 211 is a hollow ring-like structure with eight machined surfaces symmetrically arranged on its outer surface. Cylindrical through holes for passing through the rotating shaft 212 are machined at intervals. The axis of the through holes is perpendicular to the axis of the intermediate body 211. The cylindrical through holes of the end forks of the hollow connecting rods 1 are connected to the rotating shaft 212 to realize the rotational motion of the hollow connecting rods 1 around the axis. The upper and lower surfaces of the intermediate body 211 are machined with threaded through holes for installing hexagonal set screws 213. The rotating shaft 212 is fastened by pressing the rotating shaft 212 against the inner side of the cylindrical through holes of the intermediate body 211 with hexagonal set screws 213.

[0037] like Figure 5 As shown, the inner wall 22 of the corrugated pipe is an axially expandable, corrugated tubular structure that wraps around the outer periphery of the middle body 211 of the universal joint 21. Connecting holes 221 are machined on both sides of the pipe, and an air pipe interface 222 is machined on the bottom. The pipe is installed at the ends of the two hollow connecting rods 1 by screws through the connecting holes 221 and connected to the air pipe 3 through the air pipe interface 222. The other end of the air pipe 3 is connected to the solenoid valve, the positive pressure regulating valve and the air compressor in sequence. Specifically, the air outlet of the air compressor is connected to the air inlet of the positive pressure regulating valve through an air pipe, the air outlet of the positive pressure regulating valve is connected to the air inlet of the solenoid valve through another air pipe, and the air outlet of the solenoid valve is connected to the air pipe interface 222 through the air pipe 3. When the air passage is opened, the gap between the inner wall 22 of the bellows and the flexible heating layer 23 begins to fill with air, causing the flexible heating layer 23 and the variable stiffness layer 24 to expand rapidly under positive pressure; when the air passage is closed, the gap between the inner wall 22 of the bellows and the flexible heating layer 23 begins to release air, causing the flexible heating layer 23 and the variable stiffness layer 24 to contract back to their natural state.

[0038] like Figure 6As shown, the flexible heating layer 23 has a circular ring structure and is fitted around the outer periphery of the inner wall 22 of the corrugated pipe. The flexible heating layer 23 includes a first silicone encapsulation layer 231, a flexible circuit channel 232, and a heating electrode 233. Its main structure is the first silicone encapsulation layer 231. The flexible circuit channel 232 is disposed on the outer periphery of the first silicone encapsulation layer 231, and the two ends of the flexible circuit channel 232 are connected to the heating electrode 233 for connecting to an external power source to realize the switching on and off of the circuit. When the flexible heating layer 23 is powered on, the flexible circuit channel 232 generates heat, causing the temperature of the entire flexible heating layer 23 to rise and heating the variable stiffness layer 24. When the flexible heating layer 23 is de-powered, the flexible circuit channel 232 dissipates heat, causing the temperature of the entire flexible heating layer 23 to drop and cooling the variable stiffness layer 24.

[0039] In this embodiment, the flexible circuit channel 232 contains a patterned liquid metal circuit in a micro-oxidized state.

[0040] In this embodiment, the heating electrode 233 is a copper electrode;

[0041] like Figure 7 As shown, the variable stiffness layer 24 is a ring structure, sleeved on the outer periphery of the flexible heating layer 23. The variable stiffness layer 24 includes a second silicone encapsulation layer 241 and a phase change material channel 242. Its main structure is the second silicone encapsulation layer 241, and the phase change material channel 242 is a key structure, located on the outer periphery of the second silicone encapsulation layer 241. The phase change material channel 242 contains patterned phase change material, which can receive heat generated from the flexible heating layer 23 through the thermal conduction of the first silicone encapsulation layer 231 and the second silicone encapsulation layer 241. The solidification effect of the phase change material after solidification can be used to lock the variable stiffness joint 2, thereby increasing the stiffness of the continuous robot. When the variable stiffness layer 24 is heated, the phase change material in the phase change material channel 242 melts into a liquid state, making the entire variable stiffness layer 24 flexible and the variable stiffness joint 2 encased therein free to move; when the variable stiffness layer 24 is cooled, the phase change material in the phase change material channel 242 solidifies into a solid state, making the entire variable stiffness layer 24 rigid and the variable stiffness joint 2 encased therein firmly locked.

[0042] In this embodiment, the phase change material is a low-melting-point polymer, which has a high stiffness-to-weight ratio before and after the phase change.

[0043] In this embodiment, the flexible heating layer 23 and the variable stiffness layer 24 are fixed to the two ends of the inner wall 22 of the bellows by cable ties, and a small amount of silicone is applied at the connection to ensure the airtightness of the internal structure.

[0044] An embodiment provides a method for using a reversible locking device for a continuous robot joint, comprising the following steps:

[0045] Step 1: Check the gas and heat status of the reversible locking device to ensure that the gas path is closed, so that the flexible heating layer 23 and the variable stiffness layer 24 are in a contracted state; at the same time, connect the heating electrode 233 to the adjustable DC constant current power supply through the wire, start the power supply, set the constant current output, and set the current value to 1A. At this time, the flexible circuit channel 232 forms a closed loop and starts to work, so that the flexible heating layer 23 is in a heating state.

[0046] Step 2: Observe the temperature sensor reading to indirectly determine the melting state of the phase change material in the phase change material channel 242. If the temperature sensor reading does not reach the melting point of the phase change material within 3 minutes, the current can be appropriately increased. After heating to the melting point of the phase change material, the current can be reduced to prevent the temperature from rising too quickly and too high, which could damage the silicone structure of the first silicone encapsulation layer 231 and the second silicone encapsulation layer 241. The temperature sensor is located between the first silicone encapsulation layer 231 and the second silicone encapsulation layer 241.

[0047] Step 3: After the phase change material in the phase change material channel 242 has completely melted, the stiffness joint 2 is changed to a flexible state. By controlling the movement of the hollow connecting rod 1 and the universal joint 21, the continuous robot is freely and flexibly slowly extended into the target deep cavity environment until the end tool of the continuous robot reaches the designated working position.

[0048] Step 4: Turn on the air compressor, adjust the positive pressure regulating valve to set a stable positive pressure value, and open the solenoid valve. Air enters through the air pipe 3 and enters the air pipe interface 222 to begin inflating the gap between the inner wall 22 of the bellows and the flexible heating layer 23. Since the inner wall 22 of the bellows is connected to the hollow connecting rod 1 through the connecting hole 221 and wraps around the universal joint 21, air continues until the variable stiffness layer 24 expands to provide local support to the surface 4 of the deep cavity environment. Figure 8 As shown, the stiffness of the variable stiffness joint 2 of the continuous robot is initially improved;

[0049] Step 5: Turn off the adjustable DC power supply to allow the phase change material to solidify. The entire variable stiffness layer 24 becomes rigid. Since the rotating shaft 212 is fixed to the intermediate body 211 by the internal hexagonal cone end set screw 213, the rigid wrapping of the variable stiffness layer 24 restricts the rotational movement of the hollow connecting rod 1 around the rotating shaft 212, thereby locking the entire variable stiffness joint 2 and further improving the stiffness of the variable stiffness joint 2 of the continuous robot. At this time, the continuous robot can start to perform high-precision operations.

[0050] Step 6: After the continuous robot finishes its operation, turn on the adjustable DC power supply. Based on steps 1 and 2, after the phase change material has completely melted, the variable stiffness joint 2 changes to a flexible state. At the same time, close the air path to release the air from the gap between the inner wall 22 of the bellows and the flexible heating layer 23. The variable stiffness layer 24 contracts, releasing the local support effect on the surface 4 of the deep cavity environment. At this time, the overall stiffness of the continuous robot decreases, and it can be manipulated to freely and flexibly exit the deep cavity environment.

[0051] The above description only focuses on the design of a reversible locking device for the joints between two links in a continuous robot. In practical applications, this device can be added between multiple links according to specific needs. The coupling of the cooling and solidification effect and the expansion support effect of the low-melting-point polymer between multiple joints can greatly improve the variable stiffness capability of the continuous robot in narrow and deep cavity environments.

[0052] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A reversible locking device for continuous robot joints, characterized in that, The reversible locking device includes a hollow connecting rod (1), a variable stiffness joint (2), and an air pipe (3); the variable stiffness joint (2) includes a universal joint (21), a bellows inner wall (22), a flexible heating layer (23), and a variable stiffness layer (24); there are two hollow connecting rods (1), which are connected to the variable stiffness joint (2) through the universal joint (21); the bellows inner wall (22) is located on the outer periphery of the universal joint (21) and fixed to the ends of the two hollow connecting rods (1), and the bellows inner wall (22) is connected to a solenoid valve, a positive pressure regulating valve, and an air compressor in sequence through the air pipe (3) to realize the control of the air path; the flexible heating layer (23) is located on the outer periphery of the bellows inner wall (22) to provide heat to the variable stiffness layer (24), heating the phase change material in the variable stiffness layer (24) to realize the phase change; the variable stiffness layer (24) is located on the outer periphery of the flexible heating layer (23); The air tube (3) is used to inflate the gap between the inner wall (22) of the bellows and the flexible heating layer (23), thereby enabling the flexible heating layer (23) and the variable stiffness layer (24) to expand rapidly, generating local support force on the surface (4) of the deep cavity environment of the target, and increasing the stiffness of the continuous robot.

2. The reversible locking device for a continuous robot joint according to claim 1, characterized in that, Two hollow connecting rods (1) are orthogonally connected to the universal joint (21) with end forks, and the pitch and yaw motion of the variable stiffness joint (2) is realized by rotation.

3. The reversible locking device for a continuous robot joint according to claim 2, characterized in that, The universal joint (21) includes an intermediate body (211), four pivots (212) and four internal hexagonal set screws (213); The intermediate body (211) is a hollow ring-like structure with eight symmetrically machined surfaces on its outer surface. Cylindrical through holes for passing through the rotating shaft (212) are machined at intervals on the machined surfaces. The axial direction of the cylindrical through holes is perpendicular to the axial direction of the intermediate body (211). The cylindrical through holes of the end fork of the hollow connecting rod (1) are connected through the rotating shaft (212), thereby realizing the rotational movement of the hollow connecting rod (1) around the axis. The upper and lower surfaces of the intermediate body (211) are machined with threaded through holes for installing hexagonal set screws (213). The rotating shaft (212) is fastened by pressing the rotating shaft (212) against the inner side of the cylindrical through hole of the intermediate body (211) through the hexagonal set screws (213).

4. The reversible locking device for a continuous robot joint according to claim 3, characterized in that, The inner wall (22) of the corrugated pipe is a corrugated tubular structure that can expand and contract axially. It is wrapped around the outer periphery of the middle body (211) of the universal joint (21). Connection holes (221) are machined on both sides of the pipe and air pipe interface (222) is machined on the bottom. The pipe is installed at the ends of the two hollow connecting rods (1) by screws through the connection holes (221) and connected to the air pipe (3) through the air pipe interface (222) to form an air passage. The other end of the air pipe (3) is connected to the solenoid valve, the positive pressure regulating valve and the air compressor in sequence. When the air passage is opened, the gap between the inner wall (22) of the bellows and the flexible heating layer (23) begins to fill with air, causing the flexible heating layer (23) and the variable stiffness layer (24) to expand rapidly under positive pressure; when the air passage is closed, the gap between the inner wall (22) of the bellows and the flexible heating layer (23) begins to release air, causing the flexible heating layer (23) and the variable stiffness layer (24) to contract back to their natural state.

5. The reversible locking device for a continuous robot joint according to claim 4, characterized in that, The specific connection method of the air pipe (3) to the solenoid valve, the positive pressure regulating valve and the air compressor is as follows: the air outlet of the air compressor is connected to the air inlet of the positive pressure regulating valve, the air outlet of the positive pressure regulating valve is connected to the air inlet of the solenoid valve, and the air outlet of the solenoid valve is connected to the air pipe interface (222) through the air pipe (3).

6. The reversible locking device for a continuous robot joint according to claim 5, characterized in that, The flexible heating layer (23) is a ring structure and is sleeved on the outer periphery of the inner wall (22) of the corrugated pipe. The flexible heating layer (23) includes a first silicone encapsulation layer (231), a flexible circuit channel (232), and a heating electrode (233). The flexible circuit channel (232) is located on the outer periphery of the first silicone encapsulation layer (231), and the two ends of the flexible circuit channel (232) are connected to the heating electrode (233) for connecting to an external power source to realize the switching on and off of the circuit. When the flexible heating layer (23) is powered on, the flexible circuit channel (232) generates heat, which raises the temperature of the flexible heating layer (23) and heats the variable stiffness layer (24). When the flexible heating layer (23) is de-powered, the flexible circuit channel (232) dissipates heat, which lowers the temperature of the flexible heating layer (23) and cools the variable stiffness layer (24).

7. The reversible locking device for a continuous robot joint according to claim 6, characterized in that, The variable stiffness layer (24) is a ring structure and is sleeved on the outer periphery of the flexible heating layer (23). The variable stiffness layer (24) includes a second silicone encapsulation layer (241) and a phase change material channel (242). The phase change material channel (242) contains patterned phase change material, which can receive heat generated from the flexible heating layer (23) through the heat conduction of the first silicone encapsulation layer (231) and the second silicone encapsulation layer (241). The solidification effect of the phase change material after solidification is used to lock the variable stiffness joint (2) and increase the stiffness of the robot. When the variable stiffness layer (24) is heated, the phase change material melts, and the variable stiffness layer (24) becomes flexible, allowing the variable stiffness joint (2) to move freely. When the variable stiffness layer (24) is cooled, the phase change material solidifies, and the variable stiffness layer (24) becomes rigid, firmly locking the variable stiffness joint (2) to be enclosed.

8. The reversible locking device for a continuous robot joint according to claim 7, characterized in that, A temperature sensor is provided between the first silicone encapsulation layer (231) and the second silicone encapsulation layer (241) to indirectly determine the melting state of the phase change material in the phase change material channel (242).

9. A method of using the reversible locking device for a continuous robot joint as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Check the gas and heat status of the reversible locking device to ensure that the gas path is closed, so that the flexible heating layer (23) and the variable stiffness layer (24) are in a contracted state; at the same time, connect the heating electrode (233) to the DC constant current power supply, start the power supply, set the constant current output, and at this time the flexible circuit channel (232) forms a closed loop and starts to work, so that the flexible heating layer (23) is in a heating state. Step 2: Observe the reading of the temperature sensor to indirectly determine the melting state of the phase change material in the phase change material channel (242); Step 3: After the phase change material in the phase change material channel (242) has completely melted, the stiffness joint (2) is in a flexible state. By controlling the movement of the hollow link (1) and the universal joint (21), the continuous robot is extended into the deep cavity environment of the target until the end tool of the continuous robot reaches the designated working position. Step 4: Turn on the air compressor, adjust the positive pressure regulating valve, set a stable positive pressure value, and open the solenoid valve. The air path enters the air pipe interface (222) through the air pipe (3) and begins to fill the gap between the inner wall (22) of the bellows and the flexible heating layer (23) until the variable stiffness layer (24) expands to be able to generate local support with the surface (4) of the deep cavity environment, thus initially improving the stiffness of the variable stiffness joint (2). Step 5: Turn off the adjustable DC power supply to solidify the phase change material. The entire variable stiffness layer (24) is in a rigid state, which locks the entire variable stiffness joint (2) and further improves the stiffness of the variable stiffness joint (2). At this time, the continuous robot starts to work. Step 6: After the operation is completed, turn on the adjustable DC power supply. Based on Step 1 and Step 2, after the phase change material is completely melted, the variable stiffness joint (2) is transformed into a flexible state. At the same time, the air path is closed, so that the gap between the inner wall (22) of the bellows and the flexible heating layer (23) is released, the variable stiffness layer (24) contracts, and the local support effect on the surface (4) of the deep cavity environment is released, and the continuous robot exits the deep cavity environment.

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