Underwater rigidity-variable flexible mechanical arm

Abstract

The invention relates to an underwater variable-rigidity flexible mechanical arm which comprises a base, a plurality of linear actuators and tensioning devices located at the far ends of the linear actuators. Each mechanical arm section is columnar, a plurality of section linear through holes penetrating through the length direction of the mechanical arm section are formed near the circumferential edge of the mechanical arm section in the circumferential direction of the mechanical arm section, and the mechanical arm section closest to the tensioning device is fixed to the tensioning device; each universal joint is movably connected with any two adjacent mechanical arm sections, and a plurality of joint linear through holes penetrating through the axial direction of the universal joint are formed near the circumferential edge of the universal joint in the circumferential direction of the universal joint; a number of wire elements, the proximal end of each wire element being connected to a respective linear actuator and each wire element extending to, one by one, pass through the corresponding segment linear through-hole of each robot segment and the corresponding joint linear through-hole of each universal joint until the distal end thereof is connected to the robot segment farthest from the tensioning device.

Description

Technical Field

[0001] The present invention relates to the technical field of robots, and particularly to an underwater variable-stiffness flexible manipulator. Background Art

[0002] Currently, there are mainly the following three types of technical solutions for traditional flexible underwater manipulators: (1) a pure flexible manipulator without a rigid support, which is based on flexible materials such as silica gel and shape memory alloy, and realizes bending through pneumatic, hydraulic or rope drive. For example, the "soft manipulator + fluid-filled flow channel" design disclosed in Chinese Patent Application CN117359628A, and typical applications include soft manipulators (such as bionic octopus tentacles); (2) a traditional cable-driven flexible manipulator with only a single-mode stiffness, which uses a wire drive (such as a steel wire rope) in series with joints to provide rigidity through a pre-tightening force, such as Chinese Patent Application CN113305827A; (3) an electromagnetic-driven flexible manipulator, which directly drives joints through an internal motor and solenoid valve, and typical applications include electric grippers and rotary joints.

[0003] The above-mentioned existing technologies have the following defects: insufficient deep-water compressive capacity, the pure flexible structure is prone to joint deformation due to water pressure in a 20m water depth environment, losing motion accuracy. Moreover, this type of design uses a combination of static seal + dynamic seal, and the dynamic seal may have a leakage risk during long-term use in a deep-water high-pressure environment; poor stiffness adjustment ability, the pure flexible manipulator cannot resist external loads (such as structural collapse when grasping heavy objects), and is only suitable for low-load scenarios (load < 0.5kg). The traditional cable-driven flexible manipulator only relies on passive springs or fixed pre-tightening forces and cannot actively switch stiffness according to the water flow intensity, resulting in the manipulator swaying under strong water flow; limited drive control accuracy, the pure flexible manipulator relies on material deformation feedback, lacks a rigid reference, and the omnidirectional bending error > 15°. The high-order degree-of-freedom model leads to a large amount of calculation and great difficulty in real-time control. The traditional cable drive or link drive method lacks a real-time feedback mechanism and is difficult to achieve precise control of omnidirectional bending. The traditional hydraulic system has a high response delay (>500ms), and the end positioning error is large under turbulent disturbances (±5cm or more); insufficient drive symmetry, the traditional four-cable or double-cable drive layout is prone to joint eccentric loading (such as unilateral rope relaxation during diagonal drive), affecting the smoothness of motion; high risk of sealing and electromagnetic interference, the traditional cable drive unit and the working module are not separated, there is a risk of electromagnetic interference, electromagnetic components such as motors need to be waterproof encapsulated, the dynamic seal is prone to aging and leakage, and at the same time, the electromagnetic components are exposed to the working environment and may interfere with underwater sensors (such as sonar and magnetic detection equipment). Therefore, there is an urgent need for an underwater flexible manipulator with a rigid-flexible coupling structure, six-cable symmetric drive and dual-mode stiffness adjustment. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides an underwater variable-stiffness flexible manipulator, which includes:

[0005] A base, comprising a plurality of linear actuators and a tensioning device located at its distal end;

[0006] A plurality of robotic arm segments, each robotic arm segment is formed as a column, and a plurality of segment linear through-holes penetrating its own length direction are provided near its circumferential periphery, wherein the robotic arm segment closest to the tensioning device is fixed to the tensioning device;

[0007] A plurality of universal joints, each universal joint is movably connected to any two adjacent robotic arm segments, and a plurality of joint linear through-holes penetrating its own axial direction are provided near its circumferential periphery;

[0008] A plurality of wire elements, the proximal end of each wire element is connected to a corresponding linear actuator, and each wire element extends to successively pass through the corresponding segment linear through-holes of each robotic arm segment and the corresponding joint linear through-holes of each universal joint until its distal end is connected to the robotic arm segment farthest from the tensioning device.

[0009] In one embodiment, each linear actuator includes a first motor, a coupling, a lead screw, a lead screw support seat and a slider. The first motor is rotationally connected to the lead screw through the coupling. The distal end of the lead screw is supported by the lead screw support seat. The slider is sleeved on the lead screw, so that the slider can slide along the lead screw by means of cooperation with the lead screw.

[0010] In another embodiment, the proximal end of each wire element is fixedly connected to the slider.

[0011] In still another embodiment, each universal joint includes a first joint disc, a second joint disc, and a universal connecting member. The first joint disc is fixed to the robotic arm segment at the proximal end, and the universal connecting member movably connects the first joint disc and the second joint disc.

[0012] In still another embodiment, each second joint disc is provided with an elastic element on its surface facing away from the first joint disc, and the elastic element is connected to the robotic arm segment at the distal end.

[0013] In still another embodiment, in the initial state of the underwater variable stiffness flexible robotic arm, the elastic element is in a compressed state, thereby exerting a repulsive force on the second joint disc and the robotic arm segment at the distal end.

[0014] In still another embodiment, the tensioning device includes a plurality of pulley mechanisms. The plurality of pulley mechanisms are in one-to-one correspondence with the plurality of wire elements. Each pulley mechanism includes a pair of clamping plates and a pulley group clamped between the pair of clamping plates, and the corresponding wire element bypasses the pulley group.

[0015] In still another embodiment, the distance between the pair of clamping plates is adjustable, and the rotational resistance of the pulley group is inversely proportional to the distance between the pair of clamping plates.

[0016] In yet another embodiment, the base further includes a second motor, a guide rail, and a moving platform. The second motor is fixed to the guide rail, the moving platform is displaceably connected to the guide rail, and the moving platform is displaced along the guide rail under the drive of the second motor. A plurality of linear actuators and tensioning devices are fixed to the moving platform.

[0017] In yet another embodiment, it further includes a pneumatic gripper, a second wire element, and a solenoid valve. The solenoid valve is arranged on the base, the pneumatic gripper is mounted to the robotic arm segment at the outermost end, and the second wire element connects the solenoid valve and the pneumatic gripper.

[0018] Compared with the prior art, the underwater variable stiffness flexible robotic arm provided by the present invention has the following advantages: By adopting a composite coupling structure of "rigid skeleton + flexible shell", a self-made high-strength universal joint (allowing ±45° double-degree-of-freedom rotation) is arranged inside each joint unit, and a high-performance waterproof silicone molded shell is coated on the outside, and a spring is embedded inside the joint to form an active elastic structure, which improves the structural compressive resistance and can achieve a high stability with a structural deformation amount <2% in a 20-meter water depth environment, realizes the omnidirectional bending ability of a single joint module of 90°, takes into account flexibility and controllability, and the universal joint and spring structure effectively improve the initial dynamic response ability of the system, enhance the bending control accuracy and system robustness. On the other hand, in view of the large change in the underwater disturbance intensity, the present application designs a tension pulley group + adjustable splint mechanism, which can automatically switch to a high stiffness mode according to the external disturbance intensity on the basis of ensuring the conventional operation mode of low stiffness and high flexibility. By controlling the distance between the splint and the pre-tensioning front plate, continuous adjustment of the rope tension in the range of 0-50N is realized, and a "stiffness state switching" closed-loop response is achieved in cooperation with the spring loading of the universal joint. Under normal conditions, a low pre-tightening force is maintained, the system response is flexible and the movement is natural. In strong water flow or high-load operations, the system stiffness can be quickly increased to ensure structural stability and end attitude maintenance, the switching delay is less than 200ms, the system has good dynamic adaptability, and ensures that the operation error under strong disturbance is <5%. Description of the Drawings

[0019] The following further describes in detail the specific embodiments of the present invention with reference to the drawings, where:

[0020] Figure 1 A perspective view of an underwater variable stiffness flexible robotic arm according to an embodiment of the present invention is shown.

[0021] Figure 2 Shows Figure 1 A combined perspective view of the robotic arm segment and the universal joint shown.

[0022] Figure 3 Shows Figure 1 An exploded view of the base shown.

[0023] Figure 4 shows Figure 2 an exploded view of the universal joint shown.

[0024] Figure 5 shows a perspective view of a linear actuator according to another embodiment of the present invention.

[0025] Figure 6 shows an exploded view of a tensioning device according to still another embodiment of the present invention. Detailed Embodiment

[0026] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0027] As Figure 1 shown, the underwater variable stiffness flexible robotic arm of the present invention includes a base, a plurality of robotic arm segments 2, a plurality of universal joints 1, and a plurality of wire elements (not shown). The base includes a plurality of linear actuators 6 and a tensioning device 5 at its distal end.

[0028] As Figure 2 shown and in combination with Figure 1 , each robotic arm segment 2 is formed in a columnar shape. Each robotic arm segment 2 is provided with a plurality of segment linear through holes 4 penetrating in its own length direction near its circumferential periphery. The robotic arm segment 2 closest to the tensioning device 5 is fixed to the tensioning device 5, and then the subsequent robotic arm segments 2 are connected in series in sequence, thereby forming a flexible robotic arm segment extending towards the distal end. Each universal joint 1 is movably connected to any two adjacent robotic arm segments 2. Each universal joint 1 is provided with a plurality of joint linear through holes penetrating in its own axial direction near its circumferential periphery. In the axial direction (from the proximal end to the distal end) of the flexible robotic arm segment, a plurality of segment linear through holes 4 and a plurality of joint linear through holes are in one-to-one correspondence. The proximal end of each wire element is connected to the corresponding linear actuator 6, and extends to sequentially pass through the corresponding segment linear through holes 4 of each robotic arm segment 2 and the corresponding joint linear through holes of each universal joint 1 until its distal end is connected to the robotic arm segment 2 farthest from the tensioning device 5.

[0029] As Figure 5As shown, each linear actuator 6 includes a first motor g, a coupling h, a lead screw i, a lead screw support j, and a slider. The first motor g is rotationally connected to the lead screw i through the coupling h. Thus, the first motor g drives the lead screw i to rotate. The distal end of the lead screw i is supported by the lead screw support j. In particular, the lead screw support j is internally provided with deep groove ball bearings, allowing the lead screw i to rotate at high speed. The slider is sleeved on the lead screw i, such that the slider can slide along the lead screw i by virtue of its cooperation with the lead screw i. As described above, the proximal end of each wire element is connected to the corresponding linear actuator 6. Specifically, the proximal end of each wire element is fixed to (e.g., bonded to) the slider of the corresponding linear actuator 6.

[0030] As Figure 4 shown, each universal joint 1 includes a first joint disc f, a second joint disc b, and a universal joint member a. The first joint disc f is fixed to a single robotic arm segment 2 at the proximal end. The universal joint member a is movably connected to the first joint disc f and the second joint disc b. Specifically, the universal joint member a is provided with a number of flange bearings d, enabling the universal joint member a to swing relatively between the first joint disc f and the second joint disc b in two dimensions. In particular, the swing amplitude in both dimensions reaches ±45°. Preferably, in order for a number of wire elements to pass through the corresponding joint linear through-holes unobstructed, especially to avoid the wire elements being scratched by the joint linear through-holes when moving relative to the joint linear through-holes, each joint linear through-hole is provided with a self-lubricating bushing e for the wire elements to pass through, and it is not easily scratched and broken during relative movement.

[0031] Furthermore, the second joint disc b is provided with an elastic element 3 (e.g., an embedded spring) on its surface facing away from the first joint disc f. The elastic element 3 is connected to a single robotic arm segment 2 at the distal end. In the initial state of the underwater variable stiffness flexible robotic arm, the elastic element 3 is in a compressed state, thereby exerting a repulsive force on the second joint disc b and the single robotic arm segment 2 at the distal end. In other words, between every two adjacent robotic arm segments 2, the elastic element 3 therebetween exerts a repulsive force on them. Thus, at the scale of the entire flexible robotic arm segment, a number of wire elements are tensioned by a number of elastic elements 3 in the above manner.

[0032] As Figure 6As shown, the tensioning device 5 includes a plurality of pulley mechanisms, and the plurality of pulley mechanisms and the plurality of wire elements also have a one-to-one correspondence. Among them, each pulley mechanism includes a pair of clamping plates l and a pulley group m clamped between the pair of clamping plates l, and the corresponding wire element bypasses the pulley group m. The pair of clamping plates l is fixed to the end plate k of the tensioning device 5 (for example, by bolts). Moreover, the distance between the pair of clamping plates l is adjustable (for example, by a threaded connection), and the clamping degree of the pair of clamping plates l on the pulley group m is adjusted in sequence, thereby adjusting the rotational resistance of the pulley group m, that is, the rotational resistance of the pulley group m is inversely proportional to the distance between the pair of clamping plates l. In this way, adjusting the above distance can change the axle distance of the pulley group m, thereby adjusting the initial pre-tension of the wire element.

[0033] As Figure 3 shown, the base further includes a second motor, a guide rail 7 and a moving platform. The second motor is fixed to the guide rail 7, the moving platform is displaceably connected to the guide rail 7, and the moving platform is displaced along the guide rail 7 under the drive of the second motor. A plurality of linear actuators 6 and a tensioning device 5 are fixed to the moving platform. Thus, the plurality of linear actuators 6 and the tensioning device 5 move together with the moving platform, realizing the movement of the underwater variable stiffness flexible robotic arm in the dimension where the guide rail 7 is located. Even further, the base is an outer shell (not shown), adopting a fully static sealing structure and applying a seal made of nitrile rubber, and the second motor, solenoid valve and associated electronic control components are integrated inside the base. The advantage of such a configuration is that there is no electromagnetic radiation source in the working space, which is suitable for high-sensitivity operation scenarios such as undersea acoustic equipment and magnetic detection instruments. The power transmission path adopts a fully flexible transmission, without a complex electro-pneumatic sealing structure, significantly reducing the failure rate. The design of electrical separation improves the overall protection level of the entire system and extends the deep-water operation life.

[0034] Further, the underwater variable stiffness flexible robotic arm of the present application further includes a pneumatic gripper, a second wire element and a solenoid valve. The solenoid valve is arranged on the base, the pneumatic gripper is installed on the robotic arm segment 2 at the farthest end, and the second wire element connects the solenoid valve and the pneumatic gripper. The pneumatic gripper controls its air pressure through the solenoid valve in the base, thereby realizing the opening and closing of the gripper. The transmission system between the solenoid valve and the pneumatic gripper is the second wire element, avoiding the electromagnetic exposure problem of the traditional electric gripper and ensuring the stability of long-distance transmission.

[0035] In this embodiment, both the wire element and the second wire element can adopt traction ropes. The self-lubricating bushings e of the segment linear through holes 4 and the joint linear through holes, their inner diameters are 0.5 mm larger than the diameter of the traction rope, allowing the rope to slide freely, and at the same time avoiding wear through chamfering the hole edge (R0.2 mm).

[0036] During the operation of the underwater variable stiffness flexible robotic arm of the present application, several linear actuators 6 operate independently of each other. Taking any one of the linear actuators 6 as an example, the lead screw i is driven by the first motor g to rotate, thereby driving the slider to move linearly. The wire element fixed to the slider, under the tension of the (multiple) elastic elements 3 and the drive of the slider, pulls the robotic arm segment 2 located at the farthest segment. In this embodiment, the underwater variable stiffness flexible robotic arm includes six linear actuators 6 and corresponding wire elements, and these wire elements are distributed at equal intervals along the circumferential direction of the robotic arm segment 2. Thus, different actions of each linear actuator 6 cause the corresponding wire elements to be in different extended states, thereby realizing the bending direction and bending degree of the underwater variable stiffness flexible robotic arm. The six linear actuators 6 and the corresponding wire elements achieve fine-segment drive control, support high-precision attitude adjustment in any direction for a single joint (control error < 3°), improve the smoothness of joint movement and the balance of driving force, effectively avoid the "off-load sway" problem of the traditional cable drive structure, and enable the entire system to have good redundancy and robustness. Even if there is a slight deviation in the tension of some ropes, the overall movement trajectory can still be maintained stable. Of course, in other embodiments, other numbers of linear actuators 6 and corresponding wire elements are also feasible.

[0037] In addition, during the operation of the underwater variable stiffness flexible robotic arm of the present application, each corresponding pulley mechanism can operate in different modes, including a normal mode and a strong disturbance mode. Among them, the normal mode is applicable in a low-speed water flow environment, and the pulley block m maintains a low pre-tightening force, and relies on the real-time tension of the towing rope to control the bending of each universal joint 1 to achieve high flexibility; while the strong disturbance mode is applicable in a high-speed water flow environment, the clamping plate pair l clamps the pulley block m, increases the pre-tightening force and locks the compression amount of the elastic element 3, and improves the overall stiffness to resist the water flow impact.

[0038] The technical solutions provided by the embodiments of the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the embodiments of the present invention. The descriptions of the above embodiments are only applicable to help understand the principles of the embodiments of the present invention; at the same time, for those of ordinary skill in the art, based on the embodiments of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An underwater variable stiffness flexible robotic arm, characterized in that, Comprising: A base, including a number of linear actuators and a tensioning device at its distal end; A number of robotic arm segments, each of the robotic arm segments being formed in a columnar shape and having a number of segment linear through-holes penetrating its own length direction near its circumferential periphery, wherein the robotic arm segment closest to the tensioning device is fixed to the tensioning device; A number of universal joints, each of the universal joints being movably connected to any two adjacent robotic arm segments and having a number of joint linear through-holes penetrating its own axial direction near its circumferential periphery; A number of wire elements, the proximal end of each wire element being connected to the corresponding linear actuator, and each wire element extending to sequentially pass through the corresponding segment linear through-hole of each robotic arm segment and the corresponding joint linear through-hole of each universal joint until its distal end is connected to the robotic arm segment furthest from the tensioning device.

2. The underwater variable stiffness flexible robotic arm according to claim 1, wherein Each linear actuator includes a first motor, a coupling, a lead screw, a lead screw support seat, and a slider, the first motor being rotationally connected to the lead screw through the coupling, the distal end of the lead screw being supported by the lead screw support seat, and the slider being sleeved on the lead screw such that the slider can slide along the lead screw by means of cooperation with the lead screw.

3. The underwater variable stiffness flexible robotic arm according to claim 2, characterized in that, The proximal end of each wire element is fixedly connected to the slider.

4. The underwater variable stiffness flexible robotic arm according to claim 1, characterized in that Each universal joint includes a first joint disc, a second joint disc, and a universal connecting member, the first joint disc being fixed to the robotic arm segment at the proximal end, and the universal connecting member being movably connected to the first joint disc and the second joint disc.

5. The underwater variable stiffness flexible robotic arm according to claim 4, wherein, Each second joint disc is provided with an elastic element on its surface facing away from the first joint disc, and the elastic element is connected to the robotic arm segment at the distal end.

6. The underwater variable stiffness flexible robotic arm according to claim 5, wherein, In the initial state of the underwater variable stiffness flexible robotic arm, the elastic element is in a compressed state, thereby exerting a repulsive force on the second joint disc and the robotic arm segment at the distal end.

7. The underwater variable stiffness flexible robotic arm according to claim 1, characterized in that The tensioning device includes a number of pulley mechanisms, the number of pulley mechanisms corresponding one-to-one with the number of wire elements, each pulley mechanism including a pair of clamping plates and a pulley group clamped between the pair of clamping plates, and the corresponding wire element bypassing the pulley group.

8. The underwater variable stiffness flexible robotic arm according to claim 7, wherein, The distance between the pair of clamping plates is adjustable, and the rotational resistance of the pulley group is inversely proportional to the distance between the pair of clamping plates.

9. The underwater variable stiffness flexible robotic arm according to claim 1, wherein The base further includes a second motor, a guide rail, and a moving platform, the second motor being fixed to the guide rail, the moving platform being displaceably connected to the guide rail, the moving platform being displaced along the guide rail under the drive of the second motor, and the number of linear actuators and the tensioning device being fixed to the moving platform.

10. The underwater variable stiffness flexible robotic arm according to claim 1, characterized in that, Also included are a pneumatic gripper, a second wire element, and a solenoid valve, the solenoid valve being arranged on the base, the pneumatic gripper being mounted to the robotic arm segment at the most distal end, and the second wire element connecting the solenoid valve and the pneumatic gripper.

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