An underactuated variable stiffness continuum robot based on multi-layer interference spherical joints

Abstract

The application discloses a kind of underactuated variable stiffness continuum robots based on multilayer interference spherical joint.The robot includes series continuum arm, drive box and system linear feed slide.The multilayer interference spherical joint structure proposed in the application integrates robot joint movement and variable stiffness function, greatly improves the variable stiffness range of continuum robot, both guarantees structural flexibility and takes into account high bearing stable operation.In addition, the underactuated control strategy proposed effectively overcomes the dependence of traditional wire-driven continuum robot on redundant driving elements and complex decoupling algorithm, only four driving wires are needed to autonomously reproduce complex three-dimensional motion of multi-section, while significantly improving the flexibility of operation in narrow unstructured environment such as deep cavity, the integration complexity of system hardware and the congestion problem of control cable are significantly reduced.The application is supported by national key research and development plan (2025YFB4711800).

Description

Technical Field

[0001] This invention relates to the field of robotics, and in particular to an underactuated variable stiffness continuum robot based on a multi-layered perturbation ball joint. Background Technology

[0002] In complex, unstructured environments such as nuclear facility maintenance, aircraft engine inspection, and disaster search and rescue, continuum robots, with their inherent structural compliance and environmental adaptability, exhibit superior performance compared to traditional rigid linkage robots. However, the flexible structural design of continuum robots often faces the challenge of insufficient stiffness, and their structures are prone to buckling deformation when suspended or subjected to external loads, affecting positioning accuracy. Therefore, introducing an efficient variable stiffness adjustment mechanism is of paramount technical significance for significantly improving the motion controllability, payload capacity, and adaptability to complex spaces of continuum robots. Simultaneously, to avoid structural bulkiness caused by excessive drive components, simplifying control at the robot structure level, reducing the redundancy of the drive system, and decreasing the coupling of continuous joints are crucial for ensuring the miniaturization and high reliability of continuum robots. However, existing variable stiffness continuum robots still have significant limitations in spatial accessibility, variable stiffness levels, and control strategies, making it difficult to simultaneously meet the multiple requirements of large compliant deformation, high-load operation, and simplified system control.

[0003] The following problems were mainly exposed:

[0004] 1. Among the existing methods for variable stiffness of continuum robots, the layer interference method based on vacuum negative pressure is widely used because of its fast response and compact structure. However, it is limited by the negative pressure limit of one atmosphere, resulting in a significant lack of stiffness control range for continuum robots.

[0005] 2. Regarding the drive system, the existing multi-segment continuous robot drive system is seriously redundant. Each segment usually requires 3 to 4 drive rods to be laid out independently, and the number of actuators increases dramatically with the number of robot segments, which greatly increases the structural complexity and overall weight of the control terminal.

[0006] 3. During the driving process, the driving channel of the far end section of the continuum robot will inevitably generate physical friction and multi-degree-of-freedom motion coupling effect when passing through the near end section, which poses a great challenge to the precise decoupling control of the continuum robot. Summary of the Invention

[0007] This invention provides an underactuated variable stiffness continuum robot based on multi-layered perturbation spherical joints. The proposed positive pressure driven multi-layered nested spherical continuum joint structure has a significant effect on greatly expanding the range of variable stiffness. Moreover, the continuum robot adopts an underactuated control logic of "unlock-drive-lock", which can realize complex three-dimensional motion control of multiple continuum segments with only four drive wires. The number of drive wires does not increase with the number of continuum segments. It simplifies control at the robot body level, physically eliminates multi-segment motion coupling, and effectively reduces system hardware redundancy and control cable congestion.

[0008] The specific technical solution adopted in this invention is as follows:

[0009] An underactuated variable stiffness continuum robot based on a multi-layered perturbation ball joint is disclosed. The robot mainly includes a series continuum arm, a drive box, and a system linear feed slide.

[0010] (a) Series continuous arms

[0011] This section elaborates on the detailed structure of the proposed continuum arm, the principle of variable stiffness, and the underactuated control strategy adapted to it.

[0012] This series continuous arm consists of several multi-layered interference spherical joint units, an airbag actuator, and four nickel-titanium alloy flexible drive wires. The overall structure is cylindrical, with adjacent bending joints connected by hinges. In this embodiment, four spherical units form a variable stiffness group, with four groups connected in series. This structure can be continuously connected as needed for practical applications, achieving flexible customization. The main body of the spherical joint component consists of an upper interference layer and a lower interference layer: the upper interference layer contains two friction layers, and the lower interference layer has three friction layers. The upper and lower interference layers are complementary and nested, allowing for dual-axis rotational freedom after hinge. The multi-layered interference friction layer design can generate a larger contact area within a limited volume, thereby increasing friction and raising the overall variable stiffness limit. The bending hinge area adopts a constant curvature arc design, ensuring flexibility in bending motion while enhancing connection stability through geometric constraints. The connection layer between the upper and lower interference layers is equipped with component mounting holes, a central through-hole, and a pre-drilled hole for the airbag inlet pipe, used for installing the airbag actuator and for closing and fixing the outer shells of the left and right unit components. The spherical bending unit has a pre-reserved spherical cavity, providing ample space for the integration of the airbag actuator. To achieve the stiffness adjustment function of the continuum robot, a suitable segmented spherical inflatable airbag actuator structure is designed in this structure. The airbag mainly consists of four spherical driving cavities connected in series, corresponding to the four spherical basic units of the continuum segment. Adjacent spherical airbags are connected by small-diameter non-expandable cylindrical cavities. The airbag is made of silicone casting, which has high air pressure resistance. When air pressure is injected into the driving cavity, the airbag expands and compresses the adjacent friction interference layer, achieving constraint reinforcement through interlayer friction, thereby improving the overall stiffness. Moreover, during the pressurization and stiffness change process, because the airbag is tightly covered by the interference layer, the airbag can trigger interlayer friction locking with very low expansion deformation, effectively improving the stiffness change sensitivity. Secondly, thanks to the constraint effect of the interference layer structure on the airbag, the deformation of the airbag during the pressurization and driving process is effectively limited, which is then converted into a uniform normal support force acting on the surface of the interference layer, greatly improving the service life of the airbag. All of the above structures use Figure 4 The identical spherical shell parts shown are inlaid and connected end to end. After a spherical airbag is placed inside, they are assembled from the left and right sides using the same parts. The spherical parts are only slightly different in structure at the top of the continuum and the base. The top shell part only retains the 4-3 three-layer interference layer, while the 4-1 double-layer interference layer is removed and flattened. The base spherical part is provided with a bottom disc connecting seat in order to connect and fix it to the drive box.

[0013] To achieve bending control of the continuous arm, four nickel-titanium alloy drive wires are arranged in a ring around the arm's axial direction. These drive wires run the entire length of the continuous arm, with their ends fixed to the top of the continuous arm and the drive housing behind the base via small couplings, providing structural support and smooth bending deformation capability. In traditional rod / rope driven multi-DOF continuous robot designs, the number of drive wires increases linearly with the number of continuous segments: for a robot composed of n continuous segments, N=4n drive wires are required (e.g., 16 drive wires for a four-segment structure). As the number of continuous segments increases, the dense drive wire layout severely occupies the internal space of the slender body, restricting the robot's degree of freedom expansion and length extension. To address this drive redundancy problem and the design requirement of reducing the number of drive wires, this invention proposes an underactuated strategy based on segmented variable stiffness. Specifically, when a segment of the continuum enters a flexible state through depressurization, the drive wire is pulled to cause bending deformation in that segment. The remaining segments, due to internal pressurization, maintain a high stiffness state and remain unchanged, thus achieving bending control of specific segments of the continuum. By pre-setting the drive sequence, each segment switches between "unlock-bending-locking" states. Utilizing the variable stiffness characteristic, the coupled motion of multiple segments is decoupled into independent bending of a single segment. The coordinated action of multiple segments is achieved through the alternation of states of specific segments. With this strategy, the proposed continuum structure can achieve complex three-dimensional motion control using only four flexible drive wires. Furthermore, increasing the number of segments does not affect the number of drive wires, effectively solving the problem of the linear increase in the number of drive wires in traditional wire-driven robots as the number of controlled segments increases, significantly reducing system complexity and integration redundancy.

[0014] (ii) Drive box

[0015] The proposed continuum robot system consists of two main parts: the aforementioned serial continuum arm and the drive box. The drive box includes core components such as drive motors, drive wires, and optical axis guides. As the power source for the continuum arm's motion, the overall configuration design of the drive box directly affects its spatial dimensions. Thanks to the segmented variable stiffness underactuated actuation strategy proposed in this invention, the continuum arm can complete the robot's motion control using only four drive wires. Therefore, the drive box is equipped with only four sets of drive motor modules, evenly distributed parallel to each other along the continuum axis. Each drive wire is independently controlled by a drive mechanism to retract and extend. This invention allows for adjustments to the number of drive wires based on actual application requirements. Regarding the choice of drive transmission scheme, two common schemes are circular and linear. Circular transmission schemes often employ wire drive, where the drive wire is connected to the spool via a guide wheel. The motor drives the spool in both forward and reverse directions to retract and extend the drive wire. However, this type of transmission scheme is prone to wire slippage, and when the spool winds the wire, the drive wire tends to spirally coil and stack on the outer circumference of the spool, affecting the accuracy of wire length control. To address the above issues, this invention employs a wire-driven linear transmission scheme. The drive wire is connected to the connecting plate via a miniature coupling, and a helical screw passes through the connecting plate and is connected to the drive motor. The screw mechanism converts the motor's rotational motion into linear motion, completing the winding and unwinding of the drive wire. To improve the linear accuracy of the connecting plate during movement and the overall structural robustness, four optical axis guide rails are installed inside the drive box, each connected in series with the connecting plate. Experiments have shown that this transmission system is stable and reliable, and offers high precision in controlling the length of the drive wire. This allows for precise control of the bending posture of the continuous segment through changes in the drive wire length, providing a reliable guarantee for the stable operation of the robot.

[0016] (III) System linear feed slide

[0017] To achieve overall displacement of the aforementioned continuous robot system, enabling it to deeply penetrate unstructured environments for exploration and other tasks, this invention incorporates a linear feed slide at the bottom of the robot system to drive its forward and backward movements. Structurally, this base assembly primarily comprises a support slide, a main lead screw, a coupling, bearing housings, linear guides, and a drive motor. The output shaft of the drive motor is connected to the main lead screw via the coupling, and the main lead screw is rotatably supported on the base frame via bearing housings. The bottom of the support slide has a nut structure adapted to the main lead screw, and its two sides slide and engage with parallel linear guides. An aluminum profile is mounted on the bottom of the drive box of the continuous robot system, fixed to the support slide via angle bracket connectors. During operation, the forward and reverse rotation of the drive motor drives the main lead screw to rotate, thereby converting the motor's rotational motion into the translational motion of the support slide along the linear guides. The linear motion of the base as a whole, combined with the independent bending deformation of each pneumatic segment of the continuous arm, enables the robot to flexibly adjust its overall posture in a confined and complex environment, thereby efficiently completing complex tasks such as traversing narrow passages, three-dimensional obstacle avoidance, and target grasping.

[0018] Compared with the prior art, the beneficial effects of the present invention after adopting the above technical solution are as follows:

[0019] 1. The continuous joint adopts a multi-layered interference spherical nested structure driven by positive pressure, which breaks through the stiffness control limit of traditional negative pressure variable stiffness technology and greatly improves the variable stiffness adjustment range and system load performance.

[0020] 2. By utilizing a variable stiffness mechanism to achieve multi-section motion decoupling, the full drive is transformed into underactuated control of single-section independent bending, which greatly reduces the number of system drive components and wiring complexity.

[0021] 3. It enables rapid switching and physical locking of joint stiffness and flexibility, maintaining a stable posture without the need for continuous torque compensation from the motor, thus improving motion stability and reducing energy consumption.

[0022] 4. It enhances the obstacle avoidance, maneuvering, and dexterous operation capabilities of continuum robots in narrow, complex, three-dimensional unstructured environments. Attached Figure Description

[0023] Figure 1 This is a three-dimensional front view of the overall structure of the continuum robot system of the present invention in its initial state;

[0024] Figure 2 This is a side-rear perspective view of the overall structure of the continuum robot system of the present invention;

[0025] Figure 3 This is a partially enlarged schematic diagram of the series continuum arm of the present invention;

[0026] Figure 4 This is a front and back schematic diagram of the multi-layer interference spherical joint shell component structure in the serial continuum arm of the present invention;

[0027] Figure 5 This is a schematic diagram of the structure of the positive pressure airbag actuator provided in an embodiment of the present invention;

[0028] Figure 6 This is an internal assembly diagram of the variable stiffness section of the continuous arm base of the present invention;

[0029] Figure 7 This is a partially enlarged schematic diagram of the front fixing plate of the drive box and its connecting components in an embodiment of the present invention;

[0030] Figure 8 This is a schematic diagram of the structure of the drive box drive wire push-pull connection plate in an embodiment of the present invention;

[0031] Figure 9 This is a partially enlarged schematic diagram of the rear support plate and its connecting components in the drive box according to an embodiment of the present invention;

[0032] Figure 10 This is a partially enlarged schematic diagram of the motor mounting plate at the rear end of the drive box and its drive components in an embodiment of the present invention;

[0033] Figure 11 This is a side view of the overall drive module assembly structure of the drive box in an embodiment of the present invention;

[0034] Figure 12 A three-dimensional structural diagram of the bottom system linear feed slide provided in an embodiment of the present invention;

[0035] The attached diagram lists the components represented by each number as follows:

[0036] 1. Drive wire, 2. Airbag actuator, 2-1 Unit spherical airbag, 2-2 Airway transfer tube, 2-3 Inlet pipe, 3. Drive wire coupling, 4. Multi-layer interference spherical joint unit housing, 4-1 Upper interference layer, 4-2 Part mounting hole, 4-3 Lower interference layer, 4-4 Center through hole, 4-5 Airbag inlet pipe reserved hole, 4-6 Drive wire through hole, 5. Multi-layer interference spherical joint base, 6. Drive box front end fixing plate, 6-1 Optical axis fixing seat, 6-2 Diamond screw bearing base, 6-3 Continuous body base connection hole, 6-4 Optical axis, 6-5 Drive screw, 6-6 Angle bracket, 6-7 Aluminum profile, 7. Drive wire connecting plate, 7-1 Optical axis linear bearing, 7-2 Drive screw nut, 8. Drive box middle fixing plate, 8-1 Drive screw clearance hole, 8-2 8-3 Connecting column fastening hole; 9 Drive box rear motor mounting plate; 9-1 Rear plate support column fastening hole; 9-2 Optical shaft fixing hole; 9-3 Drive screw coupling; 9-4 Motor connecting hole; 9-5 Drive motor; 9-6 Motor fastening hole; 10 System linear feed slide; 10-1 Bearing platform; 10-2 Slide screw; 10-3 Slide screw coupling; 10-4 Slide screw support seat; 10-5 Slide linear guide rail; 10-6 Slide drive motor. Detailed Implementation

[0037] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0038] To achieve the above objectives, the present invention provides the following specific embodiments: Figure 1 , Figure 2 As shown, the underactuated variable stiffness continuum robot based on multi-layer interference spherical joints mainly includes a series continuum arm, a drive box, and a system linear feed slide 10. The series continuum arm is fixedly mounted on the base connection hole 6-3 of the front fixing plate of the drive box via a joint base 5. The front fixing plate 6 and the middle fixing plate 8 of the drive box are uniformly fixedly mounted on the bottom aluminum profile 6-7 via angle brackets 6-6. At the same time, the aluminum profile is fixedly mounted on the bearing platform 10-1 of the system linear feed slide 10. Through the bottom system linear feed slide 10, the forward and backward movement of the entire continuum robot system can be realized to adapt to the overall position movement requirements of confined unstructured spaces such as deep cavities.

[0039] Furthermore, such as Figure 3 , Figure 4 , Figure 5 and Figure 6As shown, the series continuous arm is composed of at least one (four in this embodiment) variable stiffness continuous segments connected in series. Each continuous segment includes four multi-layer interference spherical joint units, a built-in silicone airbag actuator 2, and four nickel-titanium alloy drive wires 1 distributed around the entire body along the axial direction of the continuous. The outer shell 4 of the multi-layer interference spherical joint unit includes an upper interference layer 4-1 and a lower interference layer 4-3. The upper and lower interference layers of adjacent joints are complementarily nested and hinged to achieve dual-axis rotational freedom. The center of the outer shell 4 is provided with a central through hole 4-4 and an airbag inlet pipe reserved hole 4-5, and drive wire through holes 4-6 are uniformly provided around the periphery in the circumferential direction. The airbag actuator 2 includes four series-connected unit spherical airbags 2-1, which are connected by airway transmission pipes 2-2. The first end is provided with an air inlet pipe 2-3, and the whole is nested in the spherical cavity inside the spherical joint unit. The central through-hole 4-4 provides space for the airway transfer tube 2-2. The air inlet tube 2-3 inserts into the pre-drilled hole 4-5 in the airbag inlet tube and extends outwards to connect with the pneumatic equipment. The drive wire 1 passes through the drive wire through-holes 4-6 of each joint, with one end fixed to the top of the continuous arm and secured by the drive wire coupling. The other end passes through the multi-layer interference ball joint base 5 and enters the drive box. The assembly structure of a single variable stiffness section is as follows... Figure 6 As shown, based on Figure 6 The assembly is completed when the two shells are mirror-symmetrically joined together and bolted together through the mounting holes 4-2.

[0040] like Figures 7 to 11As shown, the drive box is used to control the independent retraction and extension of the four drive wires 1. The main frame of the drive box consists of a front fixing plate 6, a middle fixing plate 8, and a rear motor mounting plate 9 from front to back. The middle fixing plate 8 and the rear motor mounting plate 9 are connected by a support connecting column 8-3. The front fixing plate 6 and the middle fixing plate 8 are fixed to the aluminum profile 6-7 at the bottom by angle brackets 6-6 on one side. In terms of the specific internal structure and assembly sequence, the four drive wires 1 pass through the continuous arm base and enter the front end of the drive box, and are inserted into the rear through the continuous base connection hole 6-3. The front fixing plate 6 has optical axis fixing seats 6-1 and diamond-shaped screw bearing bases 6-2 installed on its four edges, which are used to support the front ends of the four sets of optical axes 6-4 and drive screws 6-5 arranged in parallel inside. Within the movable space between the front fixing plate 6 and the middle fixing plate 8, each set of optical shafts and screws is fitted with a drive wire connecting plate 7. A linear bearing 7-1, which slides with the optical shaft 6-4, and a drive screw nut 7-2, adapted to the drive screw, are mounted on this plate. The end of each drive wire 1 is fixed to the corresponding drive wire connecting plate 7 via a drive wire coupling 3. Each connecting plate 7 can slide independently back and forth. Continuing rearward, the drive screw 6-5 passes through the drive screw clearance hole 8-1 pre-drilled on the middle fixing plate 8, until it reaches the rear motor mounting plate 9 at the very end. The end of the optical shaft 6-4 is fixed within the optical shaft fixing hole 9-2 of the middle fixing plate 8. On the outside of the rear motor mounting plate 9, four drive motors 9-5 are mounted through motor fastening holes 9-6. The output shaft of each motor passes through the motor connecting hole 9-4 and is poweredly connected to the corresponding drive screw 6-5 via a drive screw coupling 9-3. In actual operation, the forward and reverse rotation of the drive motor 9-5 drives the drive screw 6-5 to rotate. The lead screw transmission mechanism converts this rotational motion into linear motion of the drive wire connecting plate 7 sliding smoothly along the optical axis 6-4, thereby achieving high-precision push-pull and retraction control of the drive wire 1. The overall assembly side view of the drive box is shown below. Figure 11 As shown.

[0041] like Figure 12 As shown, the linear feed slide 10 of the system includes a support platform 10-1, a slide screw 10-2, a slide screw coupling 10-3, a slide screw support 10-4, a linear guide rail 10-5, and a slide drive motor 10-6. The slide drive motor 10-6 drives the slide screw 10-2 to rotate through the slide screw coupling 10-3, thereby driving the support platform 10-1 to perform linear feed motion along the linear guide rail 10-5.

[0042] Working Principle and Practical Application: This invention employs a positive pressure variable stiffness mechanism and an underactuated control strategy of "unlock-drive-lock," effectively solving the problems of small variable stiffness range, redundant drive system, and multi-segment motion coupling in continuous robots. During variable stiffness operation, positive pressure gas is injected into the air inlet pipe 2-3 of the airbag actuator 2 of a specific continuous segment. The unit spherical airbag 2-1 expands radially and compresses the adjacent upper interference layer 4-1 and lower interference layer 4-3. The nested, interconnected layer interference units achieve rigid joint locking through the enormous normal friction force generated between the layers, resulting in a high-stiffness structure. Conversely, by deflating the airbags, the interlayer friction force is significantly reduced, and the joint returns to flexibility (unlocked state). In attitude and trajectory control, when a bending motion is required on a specific variable stiffness segment of the continuous arm, the target motion segment is first "unlocked" into a compliant state by deflating the airbags, while the remaining segments remain inflated and "locked" to act as a high-stiffness base. Subsequently, the drive motor 9-5 inside the drive box operates, driving the corresponding drive wire connecting plate 7 to translate, thereby pushing and pulling the four drive wires 1. Since only the target segment has compliant deformation capability, the traction force generated by the drive wires will be precisely converted into the bending deformation of that single segment, while the remaining segments maintain their original posture. After the posture is adjusted to the correct position, the target segment is re-inflated and pressurized to make it rigidly locked. Through the alternating switching of the rigid and flexible states of each continuous segment, the system only needs four fixed drive wires to complete the large curvature coordinated deformation of the entire arm in space. At the physical level, multi-segment coupling interference is eliminated. Secondly, the entire continuous robot system is translated and controlled by the linear feed slide of the system. This invention greatly improves the flexibility and reliability of the continuous system in performing obstacle avoidance, insertion, and detection and maintenance tasks in narrow and complex spaces such as deep cavities.

[0043] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An underactuated variable stiffness continuum robot based on a multi-layered perturbation ball joint, characterized in that: Includes a series continuous arm, a drive box, and a system linear feed slide (10). The serial continuous arm is composed of several multi-layered interference ball joint unit shells (4), airbag actuators (2), and a drive wire (1) running through the whole; The base of the serial continuous arm is fixedly installed on the drive box, and the drive box is equipped with a drive module for independently controlling the extension and retraction of each drive wire (1). The drive box is fixedly installed on the linear feed slide (10) of the system and is used to drive the robot system to perform overall linear translational motion; The airbag actuator (2) is configured to change the stiffness of the multi-layer interference ball joint unit by inflating and deflating the air, and combined with the traction of the drive wire (1) by the drive box, to realize segmented independent bending control of a specific segment of the serial continuous arm.

2. The underactuated variable stiffness continuum robot based on a multi-layered perturbation spherical joint according to claim 1, characterized in that: The basic frame of the serial continuous arm is composed of several multi-layer interference spherical joint unit shells (4) connected in series. The main body of the shell part (4) includes an upper interference layer (4-1), a part mounting hole (4-2), a lower interference layer (4-3), a central through hole (4-4), a pre-reserved hole for the airbag inlet pipe (4-5), and a drive wire through hole (4-6). The upper and lower interference layers are in a complementary nested relationship. After hinge, dual-axis rotational freedom can be realized. The complete unit joint is obtained by closing and fixing the left and right identical shells (4) through the part mounting hole (4-2).

3. The underactuated variable stiffness continuum robot based on a multi-layered perturbation spherical joint according to claim 1, characterized in that: The airbag actuator (2) features: a unit spherical airbag (2-1), an airway delivery tube (2-2), and an air inlet tube (2-3); the multi-layer interference spherical joint unit has a reserved spherical cavity inside, and the segmented airbag actuator (2) is nested in the spherical cavity; the airway delivery tube (2-2) is installed inside the central through hole (4-4), and the air inlet tube (2-3) is inserted into the reserved hole (4-5) of the airbag air inlet tube and then extends out to connect to an external air source device; When the airbag actuator (2) is filled with positive pressure gas and expands, it squeezes the upper interference layer (4-1) and lower interference layer (4-3) nested around it. The rigid locking of the joint segment is achieved through interlayer friction. In this embodiment of the invention, four spherical units are used as a variable stiffness group, and four groups are connected in series. This structure can be continuously connected as needed according to actual application to achieve flexible customization.

4. The underactuated variable stiffness continuum robot based on a multi-layered perturbation spherical joint according to claim 1, characterized in that: The drive wire (1) is arranged in a ring around the axial direction of the continuous arm and runs through the entire body. It is inserted into the drive wire through holes (4-6) of each ball joint and the end is fixed by the drive wire coupling (3). During bending control, the target continuous segment enters a flexible state by depressurizing, while the other continuous segments maintain a high-stiffness locked state by internal pressurization. The drive box pulls a specific drive wire (1) to cause the target continuous segment in the flexible state to bend and deform, thereby achieving underactuated control. By using a preset drive sequence, the "unlock-bend-lock" state is switched for each segment. The variable stiffness characteristic is used to decouple the coupled motion of multiple segments into independent bending of a single segment, thereby realizing the complex bending action of the multi-segment coordinated by the continuous robot.

5. The underactuated variable stiffness continuum robot based on a multi-layered perturbation spherical joint according to claim 1, characterized in that: The main frame of the drive box includes a front fixing plate (6), a middle fixing plate (8) and a rear motor mounting plate (9), which are used to fix the position of the overall drive module. The drive box contains four sets of drive motors (9-5), drive screws (6-5), optical shafts (6-4), and drive wire connecting plates (7). The end of the drive wire (1) is fixed on the corresponding drive wire connecting plate (7). The drive screw (6-5) converts the rotational motion of the drive motor (9-5) into the linear motion of the drive wire connecting plate (7) along the optical axis (6-4), thereby completing the independent winding and unwinding of the drive wire (1).

6. The underactuated variable stiffness continuum robot based on a multi-layered perturbation spherical joint according to claim 1, characterized in that: The linear feed slide (10) of the system includes a support platform (10-1), a slide screw (10-2), a linear guide rail (10-5), and a slide drive motor (10-6); the slide drive motor (10-6) drives the slide screw (10-2) to rotate, thereby causing the support platform (10-1) to make linear feed movements along the linear guide rail (10-5), and the drive box is fixedly installed on the support platform (10-1).

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