A large-angle, variable-stiffness flexible joint

Abstract

The application discloses a large-angle variable stiffness flexible joint, which is composed of a plurality of flexible joint modules stacked together; the flexible joint module comprises a lower chassis, a spiral winding type driver, an elastic main bone and an upper chassis, one end of the elastic main bone is connected with the upper chassis, and the other end is connected with the lower chassis; N spiral winding type drivers are connected between the upper chassis and the lower chassis, and N is greater than or equal to 3; the lower chassis is provided with a buckle mounting groove; the upper chassis is provided with a buckle; the spiral winding type driver is provided with a metal wire; the metal wire is connected with a control system; the elastic main bone is of a space groove type structure; the space groove type structure is provided with one or more symmetrical notches on the elastic main bone; and the stiffness of the elastic main bone is adjusted by adjusting three parameters of a groove height H, a groove inner diameter D and a groove spacing AH. The application adopts modular design and the elastic main bone is adjustable, and large-angle bending and variable stiffness of the flexible joint are realized.

Description

Technical Field

[0001] This invention relates to the field of soft robots, and more particularly to a flexible joint with large angle and variable stiffness. Background Technology

[0002] With the development of soft robotics technology, various types of soft actuators have emerged, including pneumatic / hydraulic artificial muscles, shape memory alloys (SMA), dielectric elastomers (DE), and helical winding actuators, each with its own advantages. As a flexible actuator, artificial muscles can contract, rotate, bend, twist, and combine these movements under different external conditions such as pressure, heat, light, electricity, magnetism, pH, and electrochemical stimulation, producing power output similar to biological muscles and capable of withstanding large loads and deformations. Due to their simple structure, high flexibility, light weight, and low cost, artificial muscles have seen increasingly widespread applications in recent years, including medical devices, rescue equipment, and auxiliary devices.

[0003] Among different types of artificial muscles, helical winding actuators have the advantages of high energy density (the force output is 100 times that of animal muscles under the same mass) and extremely light weight. At the same time, compared with pneumatic and hydraulic artificial muscles, helical winding actuators can be driven by electric current heating, making it easier to package helical winding actuators into different fields.

[0004] Helical wound actuators are a relatively superior type of flexible actuator in recent years. They are simple in composition, consisting of nylon wire and metal wire wound and twisted together. When an electric current is applied to the metal wire, it heats up, and due to the coefficient of thermal expansion of the materials, the helical nylon wire contracts, generating a contractile force. Since the helical wound actuator's motion is affected by temperature, precise control of the actuator can be achieved by controlling the temperature. Some studies in the literature have shown a certain relationship between the temperature and input power of the helical wound actuator. Therefore, a simple way to control the temperature is to control the input power of the metal wire, thus achieving precise control of the helical wound actuator.

[0005] Compared with current research on flexible joints, the flexible joint of this invention has the advantages of large bending angle, accurate control, modularity, low manufacturing cost, and wide application range. First, the main bone material of this invention is made of elastic metamaterial, which has high elasticity, enabling rapid recovery after deformation. Second, the main bone structure of this invention mainly bears pressure during deformation, experiencing significant compressive stress and deformation. Therefore, based on the elastic metamaterial, topology optimization design is performed, adding a groove structure. While ensuring the main bone's support / load-bearing capacity, the impact of compressive stress on the material is reduced, achieving continuous and uniform deformation of the flexible joint, increasing its service life, and simultaneously achieving variable stiffness. Third, the flexible joint of this invention can be accurately controlled, allowing for stopping at any angle, increasing the joint's application range. Finally, this invention has a modular interface, allowing for rapid installation of identical modules to form a spatial flexible robotic arm. By controlling the actuators of different modules through a control system, complex spatial movements can be achieved, making it applicable in fields such as seabed exploration, rescue, and medical assistance. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of flexible joint technology in soft robots by providing a flexible joint that achieves uniform deformation, variable stiffness, and large-angle bending. This flexible joint is driven by a helical winding actuator, with 3-6 helical winding actuators arranged on the module, each with a contraction rate of 33%-40%. This enables large-angle deformation of the flexible joint, with a single module achieving a bending deformation of 50°-65°.

[0007] The flexible joint main bone proposed in this invention is made of elastic metamaterial. By adjusting the structural parameters of the main bone, variable stiffness characteristics are achieved under support / load-bearing conditions. This prevents the flexible joint from experiencing excessive bending stress during movement, enabling continuous and uniform deformation of the flexible joint, reducing shear stress on the main bone, and increasing the service life of the flexible joint.

[0008] The flexible joint of this invention adopts a modular design. By combining multiple modules to form a mechanical arm or mechanical structure, it can achieve complex spatial movements, from simple bending movements to complex S-shaped movements in space. This increases the application space of the mechanical structure and can be used in fields such as pipeline inspection, rescue, and seabed exploration.

[0009] The flexible joint control system of the present invention is simple and low in cost. It uses existing microcontrollers and their expansion interfaces. By controlling its power output, precise control of the actuator can be achieved, thereby realizing the complex movement of the robotic arm or mechanical structure.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: a large-angle, variable-stiffness flexible joint, wherein the flexible joint is composed of one or more stacked flexible joint modules; each flexible joint module includes a lower base, a helical winding actuator, an elastic main bone, and an upper base; one end of the elastic main bone is connected to the upper base, and the other end is connected to the lower base; N helical winding actuators are connected between the upper base and the lower base, where N is greater than or equal to 3; the lower base is provided with a snap-fit ​​mounting groove; the upper base is provided with a snap-fit; the helical winding actuators are provided with metal wires; and the metal wires are connected to a control system;

[0011] The elastic main frame is a spatial groove structure; the spatial groove structure has one or more symmetrical grooves on the elastic main frame; the stiffness of the elastic main frame is adjusted by regulating the groove height H, the groove inner diameter D, and the groove spacing. ΔH These three parameters are used for adjustment.

[0012] Furthermore, the control system is composed of a microcontroller, relays, and a boost module connected in sequence.

[0013] Furthermore, both the lower and upper chassis are provided with bolt connection holes; the flexible joint modules are connected to each other by snap-fits and bolts.

[0014] Furthermore, the metal wire is wound around a spiral-wound driver, with its two ends exposed.

[0015] Furthermore, each helical winding driver can be driven independently, or multiple helical winding drivers can be driven simultaneously.

[0016] Furthermore, the N spiral winding type drivers are evenly distributed at equal angles.

[0017] Furthermore, the flexible joint modules are installed in an alternating manner.

[0018] Furthermore, the staggered installation consists of helical winding actuators of two adjacent flexible joint modules interlocking.

[0019] Furthermore, the elastic main bone is made of an elastic metamaterial.

[0020] The advantages and beneficial effects of this invention are:

[0021] 1. This invention has a wide range of applications. The robotic arm / mechanism composed of multiple flexible joints can be used in fields such as pipeline inspection, rescue, and seabed exploration. For example, the flexible robotic arm composed of this invention can be used for seabed exploration, enabling functions such as grasping seabed plant and animal samples and detecting / collecting marine information.

[0022] 2. The elastic main bone of the present invention is composed of elastic metamaterials, which increases the elastic recovery ability of the flexible joint;

[0023] 3. The elastic main bone of the present invention adopts a variable stiffness structure during preparation, which achieves continuous and uniform deformation of the flexible joint while ensuring the main bone supports / bears the load, reduces the shear stress of the main bone, and increases the service life of the flexible joint.

[0024] 4. The spiral-wound actuator used in this invention has low manufacturing cost and high control precision. The actuator's shrinkage rate can reach 33%-40%, which translates to a bending angle of 50°-65° on the module. Depending on the input power, the bending-recovery process of the flexible joint is within the range of 15-40 seconds, and rapid joint movement can be achieved under high power input.

[0025] 5. This invention adopts a modular design, with snap-fit ​​installation between modules for rapid installation and positioning. Bolts can also be used to reinforce the connection between modules. Furthermore, by combining multiple modules to form a mechanical wall / mechanical structure, complex spatial movements can be achieved, ranging from simple bending movements to complex S-shaped movements.

[0026] 6. The control system of this invention is simple. It uses a simple microcontroller to control the power of the output driver to achieve precise control of the module. Attached Figure Description

[0027] Figure 1 is a schematic diagram of the flexible joint module structure of the present invention;

[0028] Figure 2 is a schematic diagram of the module bending in one direction according to the present invention;

[0029] Figure 3 is a schematic diagram of the elastic main bone of the present invention;

[0030] Figure 4 is a schematic diagram of the module connection of the present invention;

[0031] Figure 5 is a schematic diagram of the robotic arm composed of the present invention, wherein Figure (a) shows the robotic arm in a non-working state; Figure (b) shows a movement with a bending angle exceeding 180 degrees; and Figure (c) shows the robotic arm completing a complex S-shaped movement in space.

[0032] Figure 6 is a schematic diagram of the control system for a single module of the present invention;

[0033] The components include: lower chassis 1, buckle mounting slot 1-1, spiral winding type driver 2, metal wire 2-1, elastic main frame 3, upper chassis 4, buckle 4-1, bolt connection hole 5, microcontroller 6, relay 7, and boost module 8. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 The diagram shows the structure of the flexible joint module of the present invention. The flexible joint module includes a lower base plate 1, a spiral wound actuator 2, an elastic main bone 3, and an upper base plate 4. One end of the elastic main bone 3 is connected to the upper base plate 4, and the other end is connected to the lower base plate 1. N spiral wound actuators 2 are connected between the upper base plate 4 and the lower base plate 1, where N is greater than or equal to 3. The lower base plate 1 is provided with a snap-fit ​​mounting groove 1-1. The upper base plate 4 is provided with a snap-fit. The spiral wound actuator 2 is provided with a metal wire 2-1. The metal wire 2-1 is connected to a control system. The snap-fit ​​mounting groove 1-1 and the snap-fit ​​4-1 are the installation interfaces between modules, facilitating quick interchange and installation between modules. The preferred number of actuators installed in the module is 3-6, installed evenly at equal angles, resulting in uniform force distribution and a simple structure. The more actuators installed, the higher the bending force and control accuracy of the module, but the corresponding number of control modules also increases.

[0036] Taking a module with three spiral winding actuators 2 installed, and the movement direction being a rightward bending motion as an example, the metal wire used is nickel-chromium wire, such as... Figure 2 As shown. When the nichrome wire on the right is energized, it heats up, which in turn heats the spiral-wound actuator 2. When the spiral-wound actuator 2 reaches a certain temperature, it contracts, causing the elastic main bone 3 to bend and deform, thus achieving the rightward bending deformation of the flexible joint. When the energization of the nichrome wire is stopped, the temperature of the spiral-wound actuator 2 decreases, the contraction force reduces, and under the influence of the elastic force of the main bone material, the flexible joint begins to recover until it returns to its initial state or near its initial state. Depending on the input power, the bending-recovery process of the flexible joint is within the range of 15-40 seconds. Simultaneously, due to the characteristics of the 2-spiral-wound actuator, within the bending angle range, by adjusting the output power of the control system, precise control of the flexible joint to any angle can be achieved, with reliable and accurate control precision.

[0037] like Figure 2 The diagram shows a unidirectional bending schematic of the module of this invention. This module is equipped with three 2-helical winding actuators with a contraction rate of 33%, achieving a maximum bending angle of 50° for the joint. Using the same combination of two modules, a robotic arm with a bending angle ≥90° can be obtained. The same four modules enable bending motion of the robotic arm with a bending angle ≥180°. In this way, flexible joints can be constructed for applications in various fields.

[0038] The elastic main bone 3 is made of elastic metamaterials (such as rubber-like materials, Ecoflex00-50, etc.). The main bone structure of the flexible joint is a complex spatial groove structure, realizing a function similar to a flexible hinge. Even when using a helical winding actuator 2 with a contraction rate of 50% and bending the module to 90°, the elastic main bone 3, made of elastic metamaterials, can autonomously return to its initial state by relying on the recovery properties of the elastic material.

[0039] like Figure 3 As shown, since the elastic main bone 3 has a complex spatial groove structure, the basic parameters of the main bone, such as groove height H, groove inner diameter D, and groove spacing, can be determined. ΔH Adjusting these three parameters allows for mechanical programming of the main bone, resulting in a main bone with variable stiffness. This not only maintains the supporting function of the main bone but also exhibits characteristics of superelasticity, continuous and uniform deformation, and variable stiffness, thereby improving the bending angle of the flexible joint, reducing shear stress in the main bone, and increasing the service life of the flexible joint.

[0040] like Figure 4 The diagram shown is a schematic of the module connection of the present invention. The quick interchange and installation between modules are achieved through the snap-fit ​​mounting slot 1-1 and the upper chassis snap-fit ​​4-1, ensuring modular performance. When bolts are used to strengthen the connection between modules, the snap-fit ​​also has a positioning function after installation.

[0041] like Figure 5 The diagram shows a schematic of the robotic arm constructed according to the present invention, which consists of four modules. Each module is equipped with three helical winding actuators 2 with a contraction rate of 33%. Each joint has a maximum bending angle of 50°, and the robotic arm can achieve a maximum bending angle of 200°. Using seven identical modules, near 360° deformation can be achieved. Figure 5 The modules are installed in an alternating manner, which is equivalent to installing 6 spiral winding type actuators 2 in one module. Figure (a) shows the robotic arm in a non-working state; Figure (b) shows the movement with a bending angle of more than 180 degrees; Figure (c) shows the robotic arm completing a complex S-shaped movement in space. Adding different modules can improve the spatial movement performance of the robotic arm, realize diverse movements, and increase the application range.

[0042] like Figure 6 The diagram shown illustrates the control system for a single module of this invention. Relay 7 is a four-channel relay. The overall control system is simple and low-cost. Each part of the control system utilizes existing mature microcontrollers and their expansion interfaces. This system can control the output power of the control system to simultaneously control the movement of one or more helical winding drivers 2, achieving high control precision.

Claims

1. A large-angle, variable-stiffness flexible joint, characterized in that, The flexible joint is composed of one or more flexible joint modules stacked together; the flexible joint module includes a lower base plate (1), a spiral winding actuator (2), an elastic main bone (3), and an upper base plate (4). One end of the elastic main bone (3) is connected to the upper base plate (4), and the other end is connected to the lower base plate (1); N spiral winding actuators (2) are connected between the upper base plate (4) and the lower base plate (1), where N is greater than or equal to 3; the lower base plate (1) is provided with a snap-fit ​​mounting groove (1-1); the upper base plate (4) is provided with a snap-fit ​​(4-1); the spiral winding actuator (2) is provided with a metal wire (2-1); the metal wire (2-1) is connected to a control system; The elastic main bone (3) is a spatial groove structure; the spatial groove structure has one or more symmetrical grooves on the elastic main bone (3); the stiffness of the elastic main bone (3) is adjusted by adjusting the groove height H, the groove inner diameter D and the groove spacing of the elastic main bone (3). ΔH These three parameters are used for adjustment; The flexible joint modules are installed in an alternating manner; the alternating installation is the staggered docking of the spiral winding type actuators (2) of two adjacent flexible joint modules.

2. The large-angle, variable-stiffness flexible joint according to claim 1, characterized in that, The control system is composed of a microcontroller (6), a relay (7) and a boost module (8) connected in sequence.

3. The large-angle, variable-stiffness flexible joint according to claim 1, characterized in that, Both the lower chassis (1) and the upper chassis (4) are provided with bolt connection holes (5); the flexible joint modules are connected to each other by buckles and bolts.

4. The large-angle, variable-stiffness flexible joint according to claim 1, characterized in that, The metal wire (2-1) is wrapped around the spiral winding driver (2) and exposed at both ends.

5. A large-angle, variable-stiffness flexible joint according to claim 1, characterized in that, Each spiral winding type driver (2) can be driven independently, or multiple spiral winding type drivers (2) can be driven simultaneously.

6. A large-angle, variable-stiffness flexible joint according to claim 1, characterized in that, The N spiral winding type actuators (2) are evenly distributed at equal angles.

7. A large-angle, variable-stiffness flexible joint according to claim 1, characterized in that, The elastic main bone (3) is an elastic metamaterial component.

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