4D printing rigidity variable bionic joint based on humanoid robot application

Abstract

The invention designs a 4D printing rigidity-variable bionic joint based on humanoid robot application. The 4D printing rigidity-variable bionic joint comprises a joint ball socket base, a joint upper cover, a high-elasticity hemispherical composite structure, a joint ball head structure, an electromagnetic coil and a pressure sensor. The joint ball socket base is provided with an upper flange and a lower flange, and the high-elasticity hemispherical composite structure is made of high-elasticity silica gel and a magnetic thixotropic material through a composite 4D printing technology. The 4D printing rigidity-variable bionic joint applied to the humanoid robot can be driven by artificial muscles, has the characteristic of quickly responding to joint stress, timely adjusts the rigidity of a stress part, can realize regional automatic change of the rigidity and damping of a high-elasticity composite structure, and has the advantages of simple structure, low cost and the like. The working performance and flexible connection of the robot joint are met, the damping performance of the joint is improved, and abrasion of all components in the relative movement process is avoided.

Description

Technical Field

[0001] The invention patent relates to the field of key component design of robots, and in particular to a bionic joint with variable stiffness for the field of humanoid robots. Background Art

[0002] With the continuous development of humanoid robots, their driving methods are undergoing a profound change. Traditional humanoid robots mainly rely on mechanical parts such as motors, motors and gears to achieve driving, but in the future, they will be driven by artificial muscles made of polymer materials. This artificial muscle can control its expansion and contraction through hydraulic drive, bringing more natural and smooth movement performance to the robot.

[0003] In the future, humanoid robots will need to perform more complex and delicate movements, such as free rotation of arms and flexible movement of legs. This requires that each joint of the robot must have extremely high flexibility. However, traditional robot joints can often only achieve linear or fixed axial movement, which greatly limits the flexibility and adaptability of robots in complex environments. Even some designs that use ball hinge joints have mostly rigid joints, such as the Chinese literature patent with publication number CN118952297A. For a long time, this rigid connection will lead to frequent relative rotation and extrusion of joint components, which will cause wear and deformation, seriously affecting the robot's motion accuracy and stability, shortening the service life of the joints, and increasing maintenance costs.

[0004] To avoid this problem, we designed a 4D printed bionic joint with variable stiffness for humanoid robot applications. This design is inspired by the human spherical-cup joint structure, and cleverly uses composite 4D printing technology to create a highly elastic composite structure to simulate soft materials such as cartilage between human joints. When the robot faces different working conditions, this bionic joint can achieve variable joint stiffness through the control of the built-in electromagnetic coil, thereby achieving significant effects of shock absorption and wear reduction.

[0005] In addition, the output shaft of this bionic joint can be tightly wrapped by artificial muscles in the future. When the artificial muscles stretch and contract, they can drive the joints to rotate. This design not only gives the robot joints higher flexibility, but also significantly improves its adaptability and motion accuracy in different tasks. Compared with traditional rigid joints, this bionic joint based on 4D printing and artificial muscles has undoubtedly opened up a new path for the development of humanoid robots, making robots more intelligent and flexible and better serving human society. Summary of the invention

[0006] The purpose of this invention patent is to propose a 4D printed bionic joint with variable stiffness for humanoid robot applications. The purpose of its application is that when the joint is stressed, the highly elastic composite structure wrapped with magnetic thixotropic material transmits force signals to the force sensor, and the force sensor converts the force signal into an electrical signal to control whether the corresponding electromagnetic coil below is energized, that is, whether a magnetic field is generated. When the electromagnetic coil generates a magnetic field, the corresponding position of the highly elastic hemispherical composite structure wrapped with magnetic thixotropic material will change in stiffness, which improves the joint's force bearing capacity, improves the traditional rigid collision working conditions, plays a good buffering and shock absorbing effect, and improves the service life of the joint and the motion accuracy of the robot actuator.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A 4D printed bionic joint with variable stiffness based on humanoid robot application, characterized in that it includes: a joint ball socket base, a joint upper cover, a highly elastic hemispherical composite structure, a joint ball head structure, an electromagnetic coil, and a pressure sensor; the joint ball socket base is cylindrical in shape as a whole, has an upper flange and a lower flange, and is made of non-ferromagnetic material; the threaded holes of the upper flange and the threaded holes of the lower flange are evenly distributed along the circumferential direction, the center of the circle is on the axis of the joint ball socket base, and the threaded holes are 60° apart, and are all through holes; three circles of holes are drilled on the inner side of the ball socket base, and the axes of the six holes in the outermost circle are at an angle of 60° to the vertical center axis of the ball socket, and the center points of the holes are 60° apart; the axes of the six holes in the second outer circle are The angles with the vertical axis of the ball socket are all 30°, and the center points of each hole are 60° apart; a hole is drilled at the lowest point of the ball socket, and the axis of the hole coincides with the vertical axis of the ball socket; the highly elastic hemispherical composite structure is installed in the base of the joint ball socket, and the lower surface of the composite structure is in contact with and fixed to the inner surface of the ball socket; a pressure sensor is installed on the top of each electromagnetic coil, and the pressure sensor is in contact with the lower surface of the highly elastic hemispherical composite structure to ensure timely reception of force signals; the joint ball head structure is wrapped by the highly elastic hemispherical composite structure, and relative rotation can occur between the spherical part and the highly elastic hemispherical composite structure; the joint upper cover is installed last, and is used to constrain the joint ball head structure and the highly elastic hemispherical composite structure in the ball socket so that they do not fall out.

[0009] The joint ball socket base is an overall symmetrical cylindrical structure, and the material is non-ferromagnetic aluminum alloy; the joint ball socket base is connected to other parts where the joint needs to be installed by bolts; the flange on the joint ball socket base is evenly arranged with six threaded holes along the circumferential direction, and is bolted and fixed to the joint cover. An installation position is reserved in the ball socket for the electromagnetic coil, and a total of thirteen electromagnetic coils are installed. The electromagnetic coils are evenly distributed, covering the possible force angles more comprehensively.

[0010] The joint cover is in the shape of a disk with a hole punched in the center. It is made of non-ferromagnetic aluminum alloy and has threaded through holes along the circumferential direction. The position distribution corresponds to the position of the threaded holes on the flange of the ball socket and is bolted to the joint ball socket base. The diameter of the center hole of the joint cover is smaller than the outer diameter of the highly elastic hemispherical composite structure and larger than the diameter of the spherical joint output shaft. The purpose is to constrain the joint ball head structure and the highly elastic hemispherical composite structure in the ball socket so that they do not fall out, while allowing the spherical joint to rotate flexibly.

[0011] The highly elastic hemispherical composite structure is made of highly elastic wear-resistant silica gel and magnetic thixotropic material by 4D printing; the magnetic thixotropic material is prepared by mixing magnetic particles with high coercivity, bentonite, deionized water and silicone oil; the magnetic thixotropic material itself will change its viscoelasticity when stimulated by a magnetic field, and the macroscopic manifestation is the mutual transformation between the sol state and the gel state. Under the control of the magnetic field, it can assist the highly elastic composite structure to adjust the stiffness; the hemispherical structure is installed in the ball socket, and the lower surface is in contact with the ball socket and is fixed, and no relative rotation occurs.

[0012] The joint ball head structure is the moving part of the bionic joint, which is wrapped by a high-elastic hemispherical composite structure. The joint ball head structure is in contact with the high-elastic hemispherical composite structure and can rotate relative to it. The material of the joint ball head structure is a non-ferromagnetic aluminum alloy. The output shaft part of the joint ball head structure can act as the forearm, leg and other parts of the humanoid robot, which is wrapped by artificial muscles and driven by stretching and relaxing the artificial muscles.

[0013] The electromagnetic coil is composed of a coil and an iron core. The coil is evenly wound on the central iron core. The coil material is copper wire and the iron core material is silicon steel sheet. When current is applied to the electromagnetic coil, the coil generates a magnetic field.

[0014] The pressure sensor is installed between each electromagnet coil and the highly elastic hemispherical composite structure. When the spherical joint squeezes one side, the pressure sensor converts the force signal into an electrical signal, thereby controlling the electromagnet coil to generate a magnetic field, changing the viscoelasticity of the magnetothixotropic material, thereby achieving the effect of changing the stiffness of the highly elastic hemispherical composite structure.

[0015] The working principle of the variable stiffness bionic joint is that when the joint is subjected to force, the spherical part will squeeze the high-elastic hemispherical composite structure, and the pressure will be transmitted to the pressure sensor installed on the electromagnetic coil through the high-elastic hemispherical composite structure. When the pressure sensor senses the force signal, it will convert the force signal into an electrical signal to control the electromagnetic coil to generate a magnetic field. The part where the magnetic field is generated will cause the surrounding magnetic thixotropic material to change its rheological properties, that is, the wrapped magnetic thixotropic material will change from a sol state to a gel state. The overall stiffness of the high-elastic composite structure increases rapidly, and it has the performance of absorbing and dispersing impact force, thereby reducing the force intensity of the joint and playing a shock-absorbing role.

[0016] The beneficial effects of the present invention are:

[0017] The 4D printed bionic joint with variable stiffness based on humanoid robot application transmits an electrical signal to the electromagnetic coil after sensing the force on the joint through the pressure sensor, thereby timely adjusting the viscoelasticity and stiffness of the magnetic thixotropic material, thereby changing the overall stiffness of the high elastic hemispherical composite structure to achieve the effect of shock absorption. The structure responds quickly, works reliably, is easy to operate, and has strong bionics. The 4D printed bionic joint with variable stiffness based on humanoid robot application has a simple structure, convenient installation, and low cost; based on the ball hinge, the joint is wrapped with artificial muscles on the outside, the joint output shaft is driven by artificial muscles, and the rigid parts are separated by a high elastic hemispherical composite structure inside, which can prevent the rigid parts from being directly squeezed and rubbed while also realizing the flexible rotation of the spherical joint, thereby enhancing the adaptability and flexibility of the robot. The 4D printed bionic joint with variable stiffness based on humanoid robot application can effectively absorb and disperse the impact force in time when the robot joint collides or is accidentally impacted, thereby protecting the safety of the robot and the surrounding environment. By adjusting the joint stiffness, the robot can reduce the damage caused by the impact when it collides. This property is particularly important in humanoid robots, as they need to frequently interact with humans and other objects, and ensuring safety is crucial. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a half-section view of a 4D printed bionic joint with variable stiffness for humanoid robot application as described in the patent of this invention.

[0019] Figure 2 This is a top view of a ball and socket structure in a 4D printed bionic joint with variable stiffness for humanoid robot applications as described in the patent of this invention.

[0020] Figure 3 It is a half-section view of a 4D printed bionic joint with variable stiffness for humanoid robot application as described in the patent of the present invention when it is rotated to the upper left and is acted upon by the upper left force.

[0021] Figure 4 This is a control flow chart of the on-off process of the electromagnetic coil controlled by a pressure sensor in a 4D printed bionic joint with variable stiffness for humanoid robot applications as described in the patent of this invention.

[0022] In the figure: 1-joint ball socket base, 2-joint upper cover, 3-high elastic hemispherical composite structure, 4-joint ball head structure, 5-electromagnetic coil, 6-pressure sensor, 11-threaded hole of the lower flange of the joint ball socket base, 12-threaded hole of the upper flange of the joint ball socket base, 13-hole punched in the joint ball socket base for installing the electromagnetic coil, 21-threaded hole of the joint upper cover flange, 31-upper surface of the high elastic hemispherical composite structure, 32-magnetic thixotropic material, 33-lower surface of the high elastic hemispherical composite structure, 41-spherical part of the joint ball head structure, 42-output shaft part of the joint ball head structure. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0024] like Figure 1 The figure shows a cross-sectional view of a 4D printed bionic joint with variable stiffness based on humanoid robot application described in the present invention. It includes: a joint ball socket base 1, a joint cover 2, a high elastic hemispherical composite structure 3, a joint ball head structure 4, an electromagnetic coil 5, and a pressure sensor 6; the high elastic hemispherical composite structure is installed in the joint ball socket base, and the lower surface of the high elastic hemispherical composite structure is in contact with and fixed to the inner surface of the socket; a pressure sensor is installed on the top of each electromagnetic coil, and the pressure sensor is in contact with the lower surface of the high elastic hemispherical composite structure to ensure timely reception of force signals; the joint ball head structure is wrapped by the high elastic hemispherical composite structure, and the spherical part and the high elastic hemispherical composite structure can rotate relative to each other; the joint cover is installed last to constrain the joint ball head structure and the high elastic hemispherical composite structure in the socket so as not to fall out.

[0025] like Figure 2 The figure shows a top view of a joint ball socket base 1 in a 4D printed bionic joint with variable stiffness for humanoid robot applications described in the present invention. The upper flange of the joint ball socket base 1 is evenly provided with six threaded holes 12 for bolt connection and fixing with the joint upper cover 2. An installation position 13 is reserved for the electromagnetic coil 5 at the socket. Three circles of holes 13 are punched on the inner side of the socket base. The axis of each of the six holes in the outermost circle is at an angle of 60° to the vertical center axis of the socket, and the center points of each hole are 60° apart; the axis of each of the six holes in the second outer circle is at an angle of 30° to the vertical axis of the socket, and the center points of each hole are 60° apart; a hole is punched at the lowest point of the socket, and the axis of the hole coincides with the vertical axis of the socket; the diameter of each hole is 20mm and the depth is 23mm.

[0026] like Figure 3 As shown in the figure, it is a half-section view of the joint ball head structure 4 of the 4D printed variable stiffness bionic joint for humanoid robot application described in the present invention when it is rotated to the left in the viewing plane and is acted upon by the upper left force. When the joint ball head structure is rotated to the left in the viewing plane and is acted upon by the upper left force, the joint as a whole will move a certain distance to the lower right, producing an extrusion effect on the highly elastic hemispherical composite structure 6, and the highly elastic hemispherical composite structure wrapped with magnetic thixotropic material will undergo the following Figure 3 The deformation in the electromagnetic coil 5 exerts a force on the pressure sensor 6 on the electromagnetic coil 5. The greater the force signal received by the pressure sensor 6 in the area with the largest deformation, the stronger the electrical signal to the electromagnetic coil 5 will be. The electromagnetic coil 5 will then generate a corresponding magnetic field strength. The strength of the magnetic field is Figure 3 The density of the drawn magnetic flux lines is used to represent the density of the magnetic flux lines. The denser the distribution of the magnetic flux lines, the stronger the magnetic field strength. The generated magnetic field will cause the magnetic thixotropic material to produce a corresponding degree of stiffness change. The stronger the magnetic field, the more obvious the stiffness change of the nearby magnetic thixotropic material, so that each area jointly adjusts the overall stiffness of the highly elastic hemispherical composite structure 6.

[0027] like Figure 4 As shown, it is a control flow chart of the process of the pressure sensor 6 controlling the electromagnetic coil 5 on and off based on the 4D printed bionic joint with variable stiffness for humanoid robot application described in the present invention. Before use, the system is initialized so that the force signal received by the pressure sensor 6 is at a stable initial value, and a threshold value for the pressure sensor to receive the signal is set. When the joint is working, the pressure sensor receives the force signal, first determines whether the force signal exceeds the set threshold, if it is less than the threshold, then only the elastic structure and the original shock-absorbing performance of the magnetic thixotropic material are relied on to provide the shock-absorbing and pressure-dividing effects; when the force signal is greater than the threshold, the pressure sensor transmits an electrical signal to the control system, thereby providing a current of corresponding magnitude to the electromagnetic coil 5 according to the degree of exceeding the threshold, the electromagnetic coil 5 is energized, and a magnetic field of corresponding magnitude is generated, and then the magnetic thixotropic material near the magnetic field undergoes viscoelasticity and stiffness changes. At the same time, the pressure sensor continues to receive the force signal. If the joint force decreases at this time, and the force signal received by the pressure sensor is less than the original set threshold again, the pressure sensor stops transmitting the electrical signal to the control system, and then the electromagnetic coil 5 that was originally energized is de-energized, the magnetic field during work disappears, the joint returns to its initial state, and the pressure sensor continues to receive the force signal.

[0028] The embodiments described are preferred embodiments of the present invention, but the present invention is not limited to the embodiments described above. Without departing from the essential content of the present invention, any obvious improvement, replacement or modification that can be made by a person skilled in the art shall fall within the protection scope of the present invention.

Claims

1. A 4D printed bionic joint with variable stiffness for humanoid robot applications, characterized in that: include: A joint ball socket base (1), a joint upper cover (2), a high-elasticity hemispherical composite structure (3), a joint ball head structure (4), an electromagnetic coil (5), and a pressure sensor (6); the upper flange (12) of the joint ball socket base (1) is evenly provided with six threaded holes along the circumferential direction and is connected to the joint upper cover (2) by bolts; the high-elasticity hemispherical composite structure (3) is installed in the ball socket base (1), and the lower surface (33) of the high-elasticity hemispherical composite structure (3) is in contact with and fixed to the inner surface of the ball socket base (1); a pressure sensor (6) is installed on the top of each electromagnetic coil (5), and the pressure sensor (6) is in contact with the lower surface (33) of the high-elasticity hemispherical composite structure (3); the joint ball head structure (4) is wrapped by the high-elasticity hemispherical composite structure.

2. A 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The joint ball socket base (1) is cylindrical in shape as a whole, has an upper flange and a lower flange, and is made of non-ferromagnetic material; the upper flange threaded holes (11) and the lower flange threaded holes (12) are evenly distributed along the circumferential direction, the center of the circle is on the central axis of the joint ball socket base (1), and the threaded holes are 60° apart and are all through holes; three circles of holes (13) are drilled on the inner side of the ball socket base, and the axes of the six holes in the outermost circle are at an angle of 60° to the vertical center axis of the ball socket, and the center points of the holes are 60° apart; the axes of the six holes in the second outer circle are at an angle of 30° to the vertical axis of the ball socket, and the center points of the holes are 60° apart; a hole is drilled at the lowest point of the ball socket, and the axis of the hole coincides with the vertical axis of the ball socket; the diameter of each hole is 20 mm and the depth is 23 mm.

3. The 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The joint upper cover (2) is in the shape of a disk as a whole, and the positions of the threaded holes (21) of the upper cover correspond to the positions of the threaded holes of the flange (11) on the ball socket base (1); the overall material uses non-ferromagnetic material; a through hole is provided in the joint upper cover (2) along the vertical axis direction, the axis of the through hole coincides with the vertical axis of the joint upper cover (2), and the hole diameter is smaller than the diameter of the spherical part (41) of the joint ball head structure (4) and larger than the diameter of the output shaft part (42).

4. The 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The highly elastic hemispherical composite structure (3) is made of highly elastic silicone and magnetic thixotropic material through a composite 4D printing process, and is hemispherical in shape as a whole. The upper opening of the structure has a tendency to shrink inwards. A portion of the lower surface (33) is fitted and fixed to the ball socket base, a portion is in contact with the inner surface of the joint upper cover (2), and the remaining portion is in contact with the pressure sensor (6); the upper surface (31) is in contact with the spherical portion (41) but is not fixed.

5. The 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The joint ball head structure (4) is made of non-ferromagnetic material; it is formed by a spherical part (41) and an output shaft part (42); the spherical part (41) is wrapped by a highly elastic hemispherical composite structure; the output shaft part (42) extends from the central hole of the joint upper cover (2) and does not exceed the opening range of the central hole when rotating.

6. The 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The electromagnetic coil (5) is composed of a coil and an iron core. The coil is evenly wound on the central iron core. The coil material is copper wire and the iron core material is silicon steel sheet. The electromagnetic coil (5) is installed in a hole (13) on the inner side of the joint ball socket base (1).

7. The 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The pressure sensor (6) is small in size and can detect minute stress; it is fixed between each electromagnet coil (5) and the lower surface (33) of the highly elastic hemispherical composite structure (3).

8. The 4D printed bionic joint with variable stiffness based on humanoid robot application according to claim 1, characterized in that: The magnetic thixotropic material in the highly elastic hemispherical composite structure (3) is composed of nano magnetic particles with high coercive force, deionized water, silicone oil and bentonite.

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