A method for designing high-rigidity joints for robotic arms operating in confined spaces

Abstract

This invention relates to a high-rigidity joint design method for a robotic arm operating in confined spaces, belonging to the field of robot design and manufacturing. The method controls the lengths of three ropes distributed at 120° intervals to achieve movement of two degrees of freedom of the joint. At the same pose, the joint stiffness is controlled by optimizing the rope force; the stiffness is significantly improved by controlling the suction cup's adhesion to the environment and the phase state and combination of the phase change material within the phase change holding module. The high-rigidity joint consists of two sleeves, two hollow arm rods, a hollow connecting ring assembly, a phase change conformal holding module, and driving ropes. This invention improves joint stiffness and stability by controlling the vacuum suction cup's adhesion to the environment, rope force, and the phase state and combination of the phase change material within the phase change holding module. The high-rigidity joint adopts a symmetrical upper and lower structure, which is simple in structure and easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of robot design and manufacturing, and relates to a high-rigidity joint design method for a robotic arm used in confined spaces. Background Technology

[0002] In the fields of aerospace, energy, and nuclear power, there exists a large category of deep-cavity manufacturing tasks characterized by confined spaces, complex structures, and harsh environments. Examples include aircraft air intake maintenance, aircraft fuel tank foreign object detection and removal, and nuclear power pipeline cutting and replacement. These tasks must be completed within extremely demanding, irregularly shaped, and complex deep-cavity operating spaces, making operation exceptionally difficult. On the one hand, manual operation in these tasks suffers from high labor intensity, poor manufacturing quality consistency, and low efficiency, making human intervention impractical. On the other hand, traditional industrial robots and machine tools, due to their large size and structure, are unsuitable for operations in such irregularly shaped and complex deep-cavity spaces. Rope-driven, ultra-redundant robotic arms, a type of robotic arm with rear-mounted electromechanical drive, numerous redundant joints, a slender structure, and flexible obstacle avoidance capabilities, offer a feasible solution to these complex deep-cavity manufacturing tasks due to their high aspect ratio and flexible motion capabilities.

[0003] Currently, numerous institutions have conducted research on hyper-redundant robotic arms. In 2015, Xu Wenfu et al. from Harbin Institute of Technology disclosed "a rope-driven two-degree-of-freedom robotic arm joint" in invention patent CN105150241A. Their subsequent invention patents CN108908318A and CN105150219A both disclosed two rope-driven hyper-redundant flexible robotic arms that adopted this two-degree-of-freedom cross-axis joint form. In 2021, Wang Yongqing et al. from Dalian University of Technology disclosed "a decoupled variable stiffness joint suitable for hyper-redundant robotic arms" in invention patent CN113386166A, which achieves changes in the joint's two degrees of freedom of motion and stiffness through the flow and phase state of liquid metal inside three hollow bellows. In 2022, Guo Yaxing et al. from the Beijing Institute of Precision Electromechanical Control Equipment disclosed a "Joint Module for an Ultra-Redundant Robotic Arm" in invention patent CN115416046A. This joint module has two degrees of freedom and uses an intermediate connecting plate to achieve the phenomenon of interference between the drive rope and the joint. The above-mentioned changes in joint stiffness applicable to ultra-redundant robotic arms can only be achieved by controlling the force of the drive rope or the liquid metal phase. The range of stiffness variation is limited, and as the number of joints (degrees of freedom) of the robotic arm increases, the superposition and transmission of joint flexibility will further deteriorate the end-effector stiffness, making it unable to adapt to tasks with high loads and high stiffness. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a high-rigidity joint design method for robotic arms operating in confined spaces. The high-rigidity joint designed using this method adopts a symmetrical upper and lower structure, resulting in a simple structure and convenient operation. By controlling the lengths of three ropes distributed at 120° intervals, the movement of two degrees of freedom of the joint is achieved. Controlling the suction cup's adhesion to the environment and the phase state and combination of the phase change material within the phase change holding module significantly improves the joint's stiffness. This also helps to improve the end-effector stiffness of ultra-redundant robotic arms, expanding their application range in complex deep cavity environments.

[0005] The technical solution adopted in this invention is a high-rigidity joint design method for robotic arms operating in confined spaces. This method achieves the movement of two degrees of freedom of the joint by controlling the lengths of three ropes distributed at 120° intervals. At the same pose, the joint's rigidity is significantly improved by optimizing rope forces, controlling the suction cup's adhesion to the environment, and utilizing the phase changes and combinations of phase change materials within the phase change holding module. The specific details of the design method are as follows:

[0006] A) The high-rigidity joint design adopts a symmetrical layout of upper and lower structures, which is simple in structure and easy to operate;

[0007] The high-rigidity joint consists of two sleeves 1, two hollow arms 5, a hollow connecting ring assembly 2, a phase-change conformal holding module 3, and a drive rope 4. Each of the upper and lower hollow arms 5 is fitted with a sleeve 1, and the sleeve 1 is connected to a connecting key installed on the keyway 5.4 of the hollow arm 5. Each end of the hollow arm 5 is machined with a boss 5.2 and an integrated universal joint fork 5.3. A series of evenly distributed rope through holes 5.1 are machined on both end faces of the hollow arm 5. Three ropes 4 are passed through the rope through holes 5.1 of the two hollow arm 5 at 120° angles. One end of the rope 4 passes through the rope through hole and is fixed to the end face of the hollow arm, while the other end can be connected to a motor-driven slider. By controlling the length of the three ropes, movement in two degrees of freedom of the joint can be achieved. At the same pose, the joint stiffness is controlled by optimizing the rope force.

[0008] B) In the designed hollow connecting ring assembly, the hollow connecting ring 2.5 is installed in the middle of the universal joint fork 5.3, which is assembled with the upper and lower hollow arms 5 at one end. Four rotating shafts 2.2 are used to connect the universal joint fork 5.3 and the hollow connecting ring 2.5 through the four shaft holes 2.4 on the hollow connecting ring 2.5 respectively. Four fastening screws 2.3 are used to fix the four rotating shafts 2.2 to the hollow connecting ring 2.5 respectively.

[0009] C) Design a phase change conformal holding module. Control the temperature with a heating wire to realize the transformation between the solid and liquid phases of the phase change material in the phase change conformal holding module, thereby changing the joint stiffness and improving the overall stiffness of the robotic arm composed of joints.

[0010] The phase change conformal holding module 3 consists of an inner silicone rubber layer 3.4, an outer silicone rubber layer 3.1, an integrated 3D-printed vacuum suction cup 3.2 on the outer silicone rubber layer 3.1, an insulating heating wire 3.3, a heating wire electrode 3.5, and a phase change material 3.6; wherein, the inner silicone rubber layer 3.4, the outer silicone rubber layer 3.1, and the vacuum suction cup 3.2 are integrally formed with the outer silicone rubber layer 3.1 using a 3D printing method;

[0011] First, the inner silicone rubber layer 3.4 is fixed to the inside of the protrusions 5.2 of the two hollow arm rods 5 using an adhesive sealing method. Then, the insulating heating wire 3.3 is wound in a double spiral along the groove on the outer surface of the inner silicone rubber layer 3.4, and the two heating electrodes 3.5 are led out through the two electrode holes, which are then sealed. Next, the outer silicone rubber layer 3.1 is sealed to the outside of the protrusions 5.2 of the two hollow arm rods 5 in the same way. Finally, liquid phase change material is injected into the inner silicone rubber layer through the injection hole 3.7. After the phase change material is filled into the cavity formed by the outer layer 3.4 and the outer layer 3.1, the injection hole 3.7 is sealed by adhesive sealing. The temperature is controlled by the heating wire 3.3 to realize the solid-liquid two-phase transformation of the phase change material 3.6 in the phase change conformal holding module 3, thereby changing the joint stiffness and improving the overall stiffness of the robotic arm composed of the joint. At the same time, the vacuum suction cup 3.2 on the outside of the phase change conformal holding module 3 is used to contact the environment for adsorption and support, thereby changing the stress on the joint and improving the stiffness of the robotic arm.

[0012] D) There are 7 ways to improve the stiffness of a high-stiffness joint in the same pose:

[0013] ① Under the same posture, the rope force and phase change material are kept unchanged. The joint is held in place by adsorption and fixation with the environment through vacuum suction cup 3.2, so that the environment supports the joint, thereby changing the stress state of the joint and improving the joint stiffness and stability.

[0014] ② Under the same posture, keep the rope force constant and control the temperature of the insulating heating wire 3.3 to make the phase change material 3.6 in the phase change conformal holding module change from liquid to solid, thereby increasing the stiffness at the joint and thus increasing the stiffness at the end of the joint.

[0015] ③ The stiffness can be improved by optimizing the rope force, that is, by increasing the force of the three drive ropes 4 under the same posture, the end stiffness of the joint can be improved.

[0016] Methods ④, ⑤, ⑥, and ⑦ are achieved by combining two of the above three methods or by having all three methods work simultaneously.

[0017] The beneficial effects of this invention are that the high-rigidity joint design adopts a symmetrical arrangement of upper and lower structures, resulting in a simple structure and convenient operation. By varying the rope force, specifically controlling the lengths of three ropes distributed at 120° intervals, the movement of the two degrees of freedom of the joint is achieved. By controlling the suction cup's adhesion to the environment and the phase state and combination of the phase change material within the phase change holding module, the joint's stiffness is significantly improved. Furthermore, joint stiffness can be enhanced through various methods, which is beneficial for improving the end effector stiffness of ultra-redundant robotic arms and expanding their application range in complex deep cavity environments. Attached Figure Description

[0018] Figure 1 - Schematic diagram of the overall structure of the high-rigidity joint. 1-Sleeve, 2-Hollow connecting ring assembly, 3-Phase change conformal holding module, 4-Drive rope, 5-Hollow boom.

[0019] Figure 2 - Schematic diagram of hollow connecting ring assembly 2. Wherein, 2.1-fastening screw hole, 2.2-rotating shaft, 2.3-fastening screw, 2.4-shaft hole, 2.5-hollow connecting ring.

[0020] Figure 3 - Schematic diagram of the phase change conformal holding module 3. Wherein, 3.1-outer layer of silicone rubber, 3.2-vacuum chuck, 3.3-insulating heating wire, 3.4-inner layer of silicone rubber, 3.5-heating electrode, 3.6-phase change material, 3.7-injection hole.

[0021] Figure 4 - Schematic diagram of the hollow boom 5 structure. Among them, 5.1-rope passage, 5.2-boss, 5.3-universal joint fork, 5.4-keyway. Detailed Implementation

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] Appendix Figure 1 This is a schematic diagram of the overall structure of a high-rigidity joint for operating a robotic arm in a confined space, as proposed in this invention. The high-rigidity joint consists of a sleeve 1, a hollow connecting ring 2, a phase change conformal holding module 3, a drive rope 4, and a hollow arm 5.

[0024] This design method controls the length of three ropes distributed at 120° intervals to achieve movement of the joint in two degrees of freedom. At the same pose, the joint stiffness is controlled by optimizing the rope forces; the stiffness is significantly improved by controlling the suction cup's adhesion to the environment and the phase state and combination of the phase change material within the phase change holding module. The specific details of the design method are as follows: A) The high-stiffness joint design adopts a symmetrical layout of upper and lower structures, resulting in a simple structure and convenient operation.

[0025] The high-rigidity joint consists of two sleeves 1, two hollow arms 5, a hollow connecting ring assembly 2, a phase-change conformal holding module 3, and a drive rope 4. Each of the upper and lower hollow arms 5 is fitted with a sleeve 1, and the sleeve 1 is connected to a connecting key installed on the keyway 5.4 of the hollow arm 5. Each end of the hollow arm 5 is machined with a boss 5.2 and an integrated universal joint fork 5.3. A series of evenly distributed rope through holes 5.1 are machined on both end faces of the hollow arm 5. Three ropes 4 are passed through the rope through holes 5.1 of the two hollow arm 5 at 120° angles. One end of the rope 4 is fixed to the end face of the hollow arm after passing through the rope through hole, and the other end can be connected to a motor-driven slider. By controlling the length of the three ropes, the joint can move in two degrees of freedom. At the same pose, the joint stiffness is controlled by optimizing the rope force. See [link to relevant documentation]. Figure 1 , Figure 4 .

[0026] B) In the designed hollow connecting ring assembly, the hollow connecting ring 2.5 is installed in the middle of the universal joint forks 5.3, which are cross-assembled at one end of the upper and lower hollow arms 5. Four rotating shafts 2.2 are used to connect the universal joint forks 5.3 and the hollow connecting ring 2.5 through four shaft holes 2.4 on the hollow connecting ring 2.5. Four fastening screws 2.3 are used to fix the four rotating shafts 2.2 to the hollow connecting ring 2.5. (See...) Figure 2 , Figure 3 , Figure 4 .

[0027] C) Design a phase change conformal holding module. Control the temperature with a heating wire to realize the transformation between the solid and liquid phases of the phase change material in the phase change conformal holding module, thereby changing the joint stiffness and improving the overall stiffness of the robotic arm composed of joints.

[0028] Figure 3 This is a schematic diagram of the phase change conformal holding module 3. The phase change conformal holding module 3 consists of an inner silicone rubber layer 3.4, an outer silicone rubber layer 3.1, an integrated 3D-printed vacuum suction cup 3.2 on the outer silicone rubber layer 3.1, an insulating heating wire 3.3, a heating wire electrode 3.5, and a phase change material 3.6. Among them, the inner silicone rubber layer 3.4, the outer silicone rubber layer 3.1, and the vacuum suction cup 3.2 are integrally formed with the outer silicone rubber layer 3.1 using a 3D printing method.

[0029] First, the inner silicone rubber layer 3.4 is fixed to the inside of the protrusions 5.2 of the two hollow arm rods 5 using an adhesive sealing method. Then, the insulating heating wire 3.3 is wound in a double spiral along the groove on the outer surface of the inner silicone rubber layer 3.4, and the two heating electrodes 3.5 are led out through the two electrode holes, which are then sealed. Next, the outer silicone rubber layer 3.1 is sealed to the outside of the protrusions 5.2 of the two hollow arm rods 5 in the same way. Finally, liquid phase change material is injected into the inner silicone rubber layer through the injection hole 3.7. After the phase change material is filled into the cavity formed by the outer layer 3.4 and the outer layer 3.1, the injection hole 3.7 is sealed by adhesive sealing. The temperature is controlled by the heating wire 3.3 to realize the solid-liquid two-phase transformation of the phase change material 3.6 in the phase change conformal holding module 3, thereby changing the joint stiffness and improving the overall stiffness of the robotic arm composed of the joint. At the same time, the vacuum suction cup 3.2 on the outside of the phase change conformal holding module 3 is used to contact the environment for adsorption and support, thereby changing the stress on the joint and improving the stiffness of the robotic arm.

[0030] D) There are 7 ways to improve the stiffness of a high-stiffness joint in the same pose:

[0031] ① Under the same posture, the rope force and phase change material are kept unchanged. The joint is held in place by adsorption and fixation with the environment through vacuum suction cup 3.2, so that the environment supports the joint, thereby changing the stress state of the joint and improving the joint stiffness and stability.

[0032] ② Under the same posture, keep the rope force and the adsorption state of the vacuum suction cup 3.2 unchanged, control the temperature of the insulating heating wire 3.3, so that the phase change material 3.6 in the phase change conformal holding module changes from liquid to solid, thereby increasing the stiffness at the joint and thus increasing the stiffness at the end of the joint;

[0033] ③ Under the same posture, the stiffness is improved by optimizing the driving rope force, that is, by controlling the adsorption state of the vacuum suction cup 3.2 and the phase state of the phase change material 3.6 to remain unchanged, the force of the three driving ropes 4 is increased under the same posture, thereby improving the end stiffness of the joint.

[0034] Methods ④, ⑤, ⑥, and ⑦ are achieved by combining two of the above three methods or by having all three methods work simultaneously.

[0035] Example 1 provides an example of improving joint stiffness by combining methods ② and ③:

[0036] ②③ The specific process for enhancing stiffness through combination is as follows: First, by controlling the lengths of the three drive ropes at 120° angles, the joint end reaches a given position. Then, by maintaining the adsorption state of the vacuum suction cup 3.2, the tension of the three drive ropes 4 is optimized and enhanced. Finally, the power supply to the insulating heating wire 3.3 is disconnected, thereby reducing the internal temperature of the phase change conformal holding module 3, causing the phase change material 3.6 to change from a liquid to a solid state, thus completing the enhancement of joint stiffness.

[0037] Example 2 illustrates the specific process for improving joint stiffness using a combination of methods ①②③: First, control the lengths of the three drive ropes at 120° angles to bring the joint ends to a given position. Then, control the vacuum suction cup 3.2 to allow the joint to adhere to the environmental surface via negative pressure, forming effective support. Next, optimize and increase the tension of the three drive ropes 4; disconnect the power supply to the insulating heating wire 3.3 to lower the internal temperature of the phase change conformal holding module 3, causing the phase change material 3.6 to change from a liquid to a solid state. Through effective support between the joint and the environment, the combined effect of increasing the tension of the drive ropes 4 and improving the stiffness of the phase change conformal holding module 3 enhances the joint's stiffness.

[0038] The high-rigidity joint design of this invention adopts a symmetrical layout with upper and lower structures, resulting in a simple structure and convenient operation. Movement in two degrees of freedom is achieved by controlling the lengths of three drive ropes distributed at 120° intervals. The designed phase-change conformal holding module uses heating wires to control the temperature. When the joint is in free movement, the phase-change material in the module continues to be heated and remains in a liquid phase. The highly elastic silicone rubber inner and outer layers flexibly deform to ensure the flexibility of the joint module's movement. When the joint reaches a designated pose, the phase-change material cools and transitions to a solid phase, realizing the solid-liquid phase transition within the phase-change conformal holding module. Simultaneously, a vacuum suction cup stably adheres to and holds the joint within the deep cavity environment, providing rigid support and ensuring the stability of the joint module, thus improving the overall rigidity of the robotic arm composed of the joint.

Claims

1. A high-rigidity joint design method for a robotic arm operating in confined spaces, characterized in that, This design method controls the length of three ropes distributed at 120° intervals to achieve movement in two degrees of freedom of the joint; at the same pose, the joint stiffness is controlled by optimizing the rope forces; the suction cups are controlled to adhere to the environment for support, and the phase state and combination of the phase change material within the phase change conformal holding module are used to significantly improve the joint stiffness; the specific details of the design method are as follows: A) The high-rigidity joint design adopts a symmetrical layout of upper and lower structures; The high-rigidity joint consists of two sleeves (1), two hollow booms (5), a hollow connecting ring assembly (2), a phase change conformal holding module (3), and a drive rope (4); each of the upper and lower hollow booms (5) is fitted with a sleeve (1), and the sleeve (1) is connected to the connecting key installed on the keyway (5.4) of the hollow boom (5); a boss (5.2) and an integral universal joint fork (5.3) are respectively machined at both ends of the hollow boom (5); a series of evenly distributed rope through holes (5.1) are machined on the two end faces of the hollow boom (5), through which three ropes (4) pass at 120° through the rope through holes of the two hollow booms (5). 5.1), one end of which is fixed to the end face of the hollow arm after passing through the rope hole, and the other end can be connected to the motor-driven slider; by controlling the length of the three ropes, the movement in two degrees of freedom of the joint can be realized; at the same pose, the joint stiffness can be controlled by optimizing the rope force; B) In the designed hollow connecting ring assembly, the hollow connecting ring (2.5) is installed in the middle of the universal joint fork (5.3) that is cross-assembled at one end of the upper and lower hollow arms (5). Four rotating shafts (2.2) are used to connect the universal joint fork (5.3) and the hollow connecting ring (2.5) through the four shaft holes (2.4) on the hollow connecting ring (2.5). Four fastening screws (2.3) are used to fix the four rotating shafts (2.2) to the hollow connecting ring (2.5). C) Design a phase change conformal holding module. Control the temperature with a heating wire to realize the transformation between the solid and liquid phases of the phase change material in the phase change conformal holding module, thereby changing the joint stiffness and improving the overall stiffness of the robotic arm composed of joints. The phase change conformal holding module (3) consists of an inner silicone rubber layer (3.4), an outer silicone rubber layer (3.1), a vacuum chuck (3.2), an insulating heating wire (3.3), a heating wire electrode (3.5), and a phase change material (3.6). The vacuum chuck (3.2) is located on the outer silicone rubber layer (3.1). The inner silicone rubber layer (3.4), outer silicone rubber layer (3.1), and vacuum suction cup (3.2) are integrally molded using 3D printing. First, the inner silicone rubber layer (3.4) is fixed to the inside of the bosses (5.2) of the two hollow arms (5) using adhesive sealing. Then, the insulating heating wire (3.3) is wound in a double spiral along the groove on the outer surface of the inner silicone rubber layer (3.4), and the two heating wire electrodes (3.5) are led out through the two electrode holes, while the electrode holes are sealed. In the same way, the outer silicone rubber layer (3.1) is sealed to the outside of the bosses (5.2) of the two hollow arms (5). Finally... Liquid phase change material is injected into the cavity formed by the inner layer (3.4) and outer layer (3.1) of silicone rubber through the injection hole (3.7). After the phase change material is filled, the injection hole (3.7) is sealed by adhesive sealing. The temperature is controlled by the heating wire (3.3) to realize the transformation between the solid and liquid phases of the phase change material (3.6) in the phase change conformal holding module (3), thereby changing the joint stiffness and improving the overall stiffness of the robotic arm composed of joints. At the same time, the vacuum suction cup (3.2) on the outside of the phase change conformal holding module (3) is used to contact the environment for adsorption support, changing the force on the joint and improving the stiffness of the robotic arm. D) There are 7 ways to improve the stiffness of a high-stiffness joint in the same pose: ① Under the same posture, the rope force and phase change material are kept unchanged. The joint is held in place by adsorption and fixation with the environment through vacuum suction cup (3.2), thereby achieving environmental support for the joint and changing the stress state of the joint to improve the joint stiffness and stability. ② Under the same posture, keep the rope force and the vacuum suction cup (3.2) adsorption state unchanged, control the temperature of the insulating heating wire (3.3) so that the phase change material (3.6) in the phase change conformal holding module changes from liquid to solid, thereby increasing the stiffness at the joint and thus increasing the stiffness at the end of the joint; ③ Under the same posture, the stiffness is improved by optimizing the driving rope force, that is, the adsorption state of the vacuum suction cup (3.2) and the phase state of the phase change material (3.6) are kept unchanged, and the force of the three driving ropes (4) is increased under the same posture, thereby improving the end stiffness of the joint. Methods ④, ⑤, ⑥, and ⑦ are achieved by combining two of the above three methods or by having all three methods work simultaneously.

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