Variable stiffness and damping transmission device based on magnetorheological fluid and its design method

Abstract

The present invention provides a variable stiffness and damping transmission device based on magnetorheological fluid and a design method thereof. The designed transmission device utilizes the characteristics of different forces on permanent magnets in non-uniform magnetic fields and the characteristics of different shear stresses of magnetorheological fluids in changing magnetic fields to achieve variable stiffness and damping of the mechanism. The designed variable stiffness and damping transmission device based on magnetorheological fluid consists of an outer wall, a large linear bearing, an inner wall, an end cover, a first coil, a shaft, a magnetorheological fluid, a first spring, an inner end cover, a permanent magnet PM, a second coil, a second spring, a permanent magnet PM fixing part, a bottom cover and a linear bearing; the stiffness and damping can be independently controlled, and can be applied to many different human-centered occasions, such as rehabilitation robots, intelligent prostheses and humanoid robots, etc., and can imitate the variable damping and variable stiffness functions of human muscles, and improve the flexibility of the mechanism and the adaptability to the environment in these application occasions.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical design and mechanical transmission, and in particular to a variable stiffness and damping transmission device based on magnetorheological fluid and a design method thereof. Background Art

[0002] When patients wear traditional rigid wearable ankle rehabilitation robots and move in complex environments, due to the lack of flexibility of the robot, it is very likely to produce mechanical posture errors, resulting in motion interference between humans and machines. Not only can the rehabilitation effect not be achieved, but it will also cause secondary injuries to patients to a large extent. Muscles, as the power source of the human movement system, can actively change the movement speed and muscle stiffness and damping according to changes in environmental factors and interactive task objects, thereby adapting to changes in the external environment. Therefore, in the face of the challenge of insufficient flexibility of traditional rehabilitation robots, domestic and foreign scholars are committed to applying flexible mechanisms such as variable stiffness or variable damping mechanisms to rehabilitation robots by imitating human muscles, realizing the flexibility of robot mechanisms and achieving natural human-robot interaction.

[0003] At present, variable stiffness compliance mechanisms mainly include variable stiffness structures composed of flexible materials, springs and motors or cams, artificial muscles, etc. These structures are more used in power-assisted exoskeleton robots, power orthotics, etc., and have limited application in rehabilitation robots. The existing variable stiffness structures are diverse in form and performance characteristics, but they are relatively complex, large in size and heavy, which is not conducive to application in wearable rehabilitation robots. At present, the variable damping mechanism of rehabilitation robots is mainly realized by two typical intelligent materials with variable damping characteristics, electrorheological fluid (ERF) and magnetorheological fluid. The principles of the two are similar. Due to the advantages of magnetorheological fluid such as greater yield stress, better stability and lower working voltage than electrorheological fluid, it has been more widely used in rehabilitation robots in recent years. Under the action of an external magnetic field, magnetorheological fluid will undergo a magnetorheological effect of mutual conversion between liquid and solid states within milliseconds, and the shear stress of the magnetorheological fluid can also be changed by changing the intensity of the external magnetic field.

[0004] The Chinese invention patent application with publication number CN109822615A discloses a magnetorheological shock-absorbing joint device with controllable damping and stiffness. This scheme is to change the shear stress of the magnetorheological fluid by changing the strength of the external magnetic field, so that it has the characteristics of variable stiffness and damping, and can control stiffness or damping alone, but it is mainly used in rotating application scenarios to achieve shock absorption. However, it changes stiffness through magnetorheological fluid, and the stiffness change is nonlinear, making it difficult to achieve precise control effects. It is mainly used in orthotics and prostheses, and is rarely used in lower limb rehabilitation robots.

[0005] Variable stiffness or variable damping mechanisms have improved the natural adaptability of human-computer interaction in rehabilitation to a certain extent, but the human ankle neuromuscular system will adjust different levels of joint impedance (i.e., stiffness and damping) according to different stages of the gait cycle. Therefore, only variable stiffness or only variable damping in rehabilitation robots cannot fully meet the requirements. Although some scholars have begun to study variable stiffness damping joints, they are more used in humanoid robots rather than rehabilitation robots. Since rehabilitation robots face more complex human-computer interaction situations, variable stiffness damping mechanisms are more needed to achieve compliance. Designing a variable stiffness damping structure that meets the needs of rehabilitation robots is an urgent problem to achieve structural compliance of rehabilitation robots. Summary of the invention

[0006] The purpose of the present invention is to solve the technical defects of existing variable stiffness or variable damping structures that do not meet the requirements of rehabilitation robots, and to provide a variable stiffness and damping transmission device based on magnetorheological fluid and a design method thereof.

[0007] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0008] A variable stiffness and damping transmission device based on magnetorheological fluid comprises an outer wall, a large linear bearing, an inner wall, an end cover, a first coil, a shaft, a magnetorheological fluid, a first spring, an inner end cover, a permanent magnet PM, a second coil, a second spring, a permanent magnet fixing part, a bottom cover and a linear bearing; wherein:

[0009] The outer wall is composed of two parts with the same structure and size, and the large linear bearing and the second coil are embedded in the middle;

[0010] The inner wall is mounted on the linear large bearing, one end of which is covered by the end cover, and the other end is connected to one end of the inner end cover; the permanent magnet PM is inserted into the middle of the inner end cover, and the other end is fixedly connected to the permanent magnet fixing member;

[0011] The inner wall cavity is filled with the magnetorheological fluid;

[0012] One end of the first spring contacts the large linear bearing, and the other end contacts the permanent magnet PM, and is sleeved on the inner end cover;

[0013] The second spring is sleeved on the permanent magnet fixing member, one end of the second spring is in contact with the permanent magnet PM, and the other end is in contact with the bottom cover;

[0014] The shaft is wound with the first coil and installed in the cavity of the inner wall, with the linear bearing installed in the middle to cooperate with the internal end cover; the other end of the shaft is fixedly installed on the bottom cover.

[0015] In the above scheme, the characteristic that permanent magnets are subjected to different forces in non-uniform magnetic fields is utilized to achieve variable stiffness through permanent magnets, coils and springs, and the characteristic that the shear force of magnetorheological fluid changes in the magnetic field is then utilized to achieve variable damping through magnetorheological fluid and coils, and they are combined and designed to achieve variable stiffness and damping transmission; in this way, it can be applied to rehabilitation robots or intelligent prostheses, and can independently control stiffness and damping. It can be used in many different human-centered occasions, can imitate the variable damping and variable stiffness functions of human muscles, and improve the flexibility of the mechanism and the environmental adaptability of these applications.

[0016] In the above scheme, the variable stiffness and damping transmission device based on magnetorheological fluid designed in this scheme can be well applied to the application scenarios of linear movement. It realizes the linear change of stiffness through permanent magnets, simplifies the internal calculation and processing process of the device, makes the control effect more precise, and improves the smoothness and practicality of the transmission device.

[0017] Wherein, the transmission device also includes a coil bracket; the second coil is installed on the coil bracket and embedded in the semi-cylindrical structure of the outer wall through the coil bracket.

[0018] Wherein, the transmission device also includes a sealing ring; the sealing ring is arranged on the connecting surface between the inner wall and the inner end cover.

[0019] In the above scheme, the connection surface between the inner wall and the inner end cover is sealed by a sealing ring, which improves the sealing performance of the device and prevents the magnetorheological fluid contained in the inner wall cavity from leaking out of the device and affecting the adjustment accuracy of the performance of the device.

[0020] Wherein, the cross section of one end of the shaft is I-shaped, and the first coil is arranged at the I-shaped portion.

[0021] Wherein, the inner wall and the inner end cover are connected by threaded connection; the inner end cover is connected to the permanent magnet fixing member by thread; and the shaft is mounted on the bottom cover by screws.

[0022] In the above solution, the threaded connection arrangement facilitates the assembly of the entire device. When the device needs to be cleaned or some parts need to be replaced, the threaded connection solution makes it easy for operators to disassemble and install the device.

[0023] Wherein, the outer wall is composed of two semi-cylindrical structures.

[0024] This scheme provides a design method for a variable stiffness and damping transmission device based on magnetorheological fluid, by constructing a variable stiffness part and a variable damping part, and combining these two parts through an outer wall, a large linear bearing, an end cover, an inner end cover, a bottom cover and a linear bearing, to form a variable stiffness and damping transmission device; wherein:

[0025] The variable stiffness part is composed of a permanent magnet PM, a second coil, a first spring and a second spring;

[0026] The variable damping part is composed of a shaft, a magnetorheological fluid, a first coil and an inner wall.

[0027] Among them, in the variable stiffness part, the characteristic that the permanent magnet is subjected to different forces in a non-uniform magnetic field is utilized, and the force on the permanent magnet PM is changed by adjusting the current in the second coil to change the magnetic field size formed by the energized coil, so as to realize the change of the stiffness value, wherein the calculation formula of the stiffness is:

[0028]

[0029] Among them, B r is the residual magnetic induction of the permanent magnet PM, S is the end surface area of ​​the permanent magnet, N is the number of coil turns, l is the coil length, R1 is the inner diameter of the coil, R2 is the outer diameter of the coil, I1 is the coil current, C1 is the corresponding parameter, which is related to the position of the permanent magnet PM in the coil.

[0030] Wherein, in the variable damping part, the shear stress of the magnetorheological fluid is changed by changing the current of the first coil on the inner wall by utilizing the shear force change characteristic of the magnetorheological fluid in the magnetic field, thereby realizing variable damping, wherein the calculation formula of the variable damping is:

[0031]

[0032] Where η is the zero magnetic field viscosity coefficient of the magnetorheological fluid; L is the effective length of the damping channel; D m is the inner diameter of the magnetorheological fluid cylinder; h is the gap between the piston and the cylinder; τ z The shear yield strength of magnetorheological fluid changes with the change of current; A p The effective area of ​​the magnetorheological fluid piston.

[0033] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0034] The present invention proposes a variable stiffness and damping transmission device based on magnetorheological fluid and a design method thereof, which utilizes the characteristics of different forces on permanent magnets in non-uniform magnetic fields to achieve variable stiffness through permanent magnets, coils and springs, and then utilizes the characteristics of shear force changes of magnetorheological fluid in a magnetic field to achieve variable damping through magnetorheological fluid and coils, and combines them in a design to achieve variable stiffness and damping transmission; in this way, it is applied to rehabilitation robots or intelligent prostheses to achieve better human-computer interaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1A schematic longitudinal cross-sectional view of the device of the present invention through the center line;

[0036] Among them: 1. Outer wall; 2. Large linear bearing; 3. Inner wall; 4. End cover; 5. First coil; 6. Shaft; 7. Magnetorheological fluid; 8. Sealing ring; 9. First spring; 10. Inner end cover; 11. Permanent magnet PM; 12. Second coil; 13. Coil bracket; 14. Second spring; 15. Permanent magnet fixing part; 16. Bottom cover; 17. Linear bearing. DETAILED DESCRIPTION

[0037] The drawings are for illustrative purposes only and should not be construed as limiting the present patent;

[0038] In order to better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product;

[0039] It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0040] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0041] Example 1

[0042] like Figure 1 As shown, the variable stiffness and damping transmission device based on magnetorheological fluid comprises an outer wall 1, a large linear bearing 2, an inner wall 3, an end cover 4, a first coil 5, a shaft 6, a magnetorheological fluid 7, a first spring 9, an inner end cover 10, a permanent magnet PM11, a second coil 12, a second spring 14, a permanent magnet fixing part 15, a bottom cover 16 and a linear bearing 17; wherein: the outer wall 1 is composed of two components of the same structure and size, and the large linear bearing 2 and the second coil 12 are embedded in the middle;

[0043] The inner wall 3 is mounted on the linear large bearing 2, one end of which is covered by the end cover 4, and the other end is connected to one end of the inner end cover 10; the inner end cover 10 is inserted into the middle of the permanent magnet PM11, and the other end is fixedly connected to the permanent magnet fixing part 15;

[0044] The cavity of the inner wall 3 is filled with the magnetorheological fluid 7;

[0045] One end of the first spring 9 contacts the large linear bearing 2, and the other end contacts the permanent magnet PM11, and is sleeved on the internal end cover 10;

[0046] The second spring 14 is sleeved on the permanent magnet fixing member 15, one end of the second spring 14 is in contact with the permanent magnet PM11, and the other end of the second spring 14 is in contact with the bottom cover 16;

[0047] The shaft 6 is wound with the first coil 5 and is installed in the cavity of the inner wall 3 , with the linear bearing 17 installed in the middle to cooperate with the inner end cover 10 ; the other end of the shaft 6 is fixedly mounted on the bottom cover 16 .

[0048] In the specific implementation process, the first coil 5 is wound on the shaft 6, and the number of turns of the first coil 5 is determined by the required variable damping size, and is inserted into the inner wall 3 filled with magnetorheological fluid 7. One end of the inner wall is closed by an end cap 4, and the shaft 6 can move in the inner wall 3, thereby forming a piston-type variable damping part. As the current of the first coil 5 changes, the size of the magnetic field formed also changes, which leads to an increase in the shear stress of the magnetorheological fluid 7 immersed in the magnetic field, and the force required for the movement of the shaft 6 on the inner wall 3 also increases accordingly, thereby achieving variable damping.

[0049] In the specific implementation process, the entire piston variable damper is installed in the linear large bearing 2, the inner wall 3 is in contact with the linear large bearing 2, and the first spring 1, the permanent magnet PM11, the permanent magnet PM fixing part 15, and the second spring 14 are installed in sequence. One end of the first spring 9 is in contact with the end face of the linear large bearing 2. The permanent magnet PM fixing part 15 is fixed to the internal end cover 10 by the internal thread and the external thread of the internal end cover 10. The second spring 14 is sleeved on the permanent magnet PM fixing part 15, one end is in contact with the permanent magnet PM11, and the other end is in contact with the bottom cover 16. The second coil 12 is installed on the coil support 13 and is sleeved in the piston variable damper part, so that the permanent magnet is located in the middle position of the cylindrical coil. The other end of the shaft 6 in the entire piston variable damper is fixed to the bottom cover 16 by screws. The outer wall 1 is composed of two semi-cylinders, the linear large bearing 2 and the second coil 12 with the coil support 13 are installed in a fixed position on the outer wall 1, and the two halves of the outer wall 1 are closed by bolts.

[0050] In the specific implementation process, the characteristic of different forces on permanent magnets in non-uniform magnetic fields is utilized to achieve variable stiffness through permanent magnet PM11, coils and springs, and then the characteristic of shear force change of magnetorheological fluid 7 in the magnetic field is utilized to achieve variable damping through magnetorheological fluid 7 and coils, and they are combined and designed to achieve variable stiffness and damping transmission; in this way, it can be applied to rehabilitation robots or intelligent prostheses, and can independently control stiffness and damping. It can be used in many different human-centered occasions, can imitate the variable damping and variable stiffness functions of human muscles, and improve the flexibility of the mechanism and the environmental adaptability of these applications.

[0051] In the specific implementation process, the variable stiffness and damping transmission device based on magnetorheological fluid 7 designed in this scheme can be well applied to the application scenarios of linear movement. It realizes the linear change of stiffness through permanent magnets, simplifies the internal calculation and processing process of the device, makes the control effect more precise, and improves the flexibility and practicality of the transmission device.

[0052] More specifically, the transmission device further comprises a coil support 13 ; the second coil 12 is mounted on the coil support 13 and is embedded in the semi-cylindrical structure of the outer wall 1 through the coil support 13 .

[0053] More specifically, the transmission device further includes a sealing ring 8 ; the sealing ring 8 is arranged on the connecting surface between the inner wall 3 and the inner end cover 10 .

[0054] In the specific implementation process, the connection surface between the inner wall 3 and the internal end cover 10 is sealed by a sealing ring 8, which improves the sealing performance of the device and prevents the magnetorheological fluid 7 installed in the cavity of the inner wall 3 from leaking out of the device and affecting the adjustment accuracy of the performance of the device.

[0055] More specifically, the cross-section of one end of the shaft 6 is I-shaped, and the first coil 5 is arranged at the I-shaped portion.

[0056] More specifically, the inner wall 3 and the inner end cover 10 are connected by threaded connection.

[0057] More specifically, the inner end cover 10 is connected to the permanent magnet fixing member 15 via threads.

[0058] More specifically, the shaft 6 is mounted on the bottom cover 16 by screws.

[0059] In the specific implementation process, the threaded connection setting method facilitates the assembly method of the entire device. When the device needs to be cleaned or some parts need to be replaced, the threaded connection solution makes it easy for operators to disassemble and install the device.

[0060] Example 2

[0061] More specifically, based on Example 1, a design method for a variable stiffness and damping transmission device based on magnetorheological fluid is provided, by constructing a variable stiffness part and a variable damping part, and combining these two parts through an outer wall 1, a large linear bearing 2, an end cover 4, an inner end cover 10, a bottom cover 16 and a linear bearing 17 to form a variable stiffness and damping transmission device; wherein:

[0062] The variable stiffness part is composed of a permanent magnet PM11, a second coil 12, a first spring 9 and a second spring 14;

[0063] The variable damping part is composed of a shaft 6 , a magnetorheological fluid 7 , a first coil 5 and an inner wall 3 .

[0064] More specifically, in the variable stiffness part, the characteristic that the permanent magnet is subjected to different forces in a non-uniform magnetic field is utilized, and the force on the permanent magnet PM11 is changed by adjusting the current in the second coil 12 to change the magnetic field formed by the energized coil, thereby realizing the change of the stiffness value, wherein the calculation formula of the stiffness is:

[0065]

[0066] Among them, B r is the residual magnetic induction of the permanent magnet PM, S is the end surface area of ​​the permanent magnet, N is the number of coil turns, l is the coil length, R1 is the inner diameter of the coil, R2 is the outer diameter of the coil, I1 is the coil current, C1 is the corresponding parameter, which is related to the position of the permanent magnet PM in the coil.

[0067] More specifically, in the variable damping part, the shear stress of the magnetorheological fluid 7 is changed by changing the current of the first coil 5 on the inner wall 3 by utilizing the shear force change characteristic of the magnetorheological fluid 7 in the magnetic field, thereby realizing variable damping, wherein the calculation formula of the variable damping is:

[0068]

[0069] Where η is the zero magnetic field viscosity coefficient of the magnetorheological fluid; L is the effective length of the damping channel; D m is the inner diameter of the magnetorheological fluid cylinder; h is the gap between the piston and the cylinder; τ z The shear yield strength of magnetorheological fluid changes with the change of current; A p The effective area of ​​the magnetorheological fluid piston.

[0070] In the specific implementation process, the variable stiffness and damping transmission device designed by this design method utilizes the different forces of permanent magnets in non-uniform magnetic fields and the different shear stresses of magnetorheological fluids in changing magnetic fields to achieve variable stiffness and damping of the mechanism. It can be used in many different human-centered occasions, such as rehabilitation robots, intelligent prostheses, and humanoid robots, and can improve the flexibility of the mechanism and the environmental adaptability of these applications.

[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A variable stiffness and damping transmission device based on magnetorheological fluid, characterized in that: It comprises an outer wall (1), a large linear bearing (2), an inner wall (3), an end cover (4), a first coil (5), a shaft (6), a magnetorheological fluid (7), a first spring (9), an inner end cover (10), a permanent magnet PM (11), a second coil (12), a second spring (14), a permanent magnet fixing part (15), a bottom cover (16) and a linear bearing (17); wherein: The outer wall (1) is composed of two components of identical structure and size, with the large linear bearing (2) and the second coil (12) embedded in the middle; The inner wall (3) is mounted on the large linear bearing (2), one end of which is covered by the end cover (4), and the other end of which is connected to one end of the inner end cover (10); the inner end cover (10) is inserted with the permanent magnet PM (11) in the middle, and the other end of which is fixedly connected to the permanent magnet fixing member (15); The cavity of the inner wall (3) is filled with the magnetorheological fluid (7); One end of the first spring (9) contacts the large linear bearing (2), and the other end contacts the permanent magnet PM (11), and is sleeved on the inner end cover (10); The second spring (14) is sleeved on the permanent magnet fixing member (15), one end of the second spring is in contact with the permanent magnet PM (11), and the other end of the second spring is in contact with the bottom cover (16); The shaft (6) is wound with the first coil (5) and is installed in the cavity of the inner wall (3), with the linear bearing (17) installed in the middle to cooperate with the inner end cover (10); the other end of the shaft (6) is fixedly mounted on the bottom cover (16); The device further comprises a coil support (13); the second coil (12) is mounted on the coil support (13) and is embedded in the semi-cylindrical structure of the outer wall (1) through the coil support (13); The device further comprises a sealing ring (8); the sealing ring (8) is arranged on the connection surface between the inner wall (3) and the inner end cover (10); The cross section of one end of the shaft (6) is I-shaped, and the first coil (5) is arranged at the I-shaped portion.

2. The variable stiffness and damping transmission device based on magnetorheological fluid according to claim 1, characterized in that: The inner wall (3) and the inner end cover (10) are connected in a threaded manner; the inner end cover (10) is connected to the permanent magnet fixing member (15) via threads.

3. The variable stiffness and damping transmission device based on magnetorheological fluid according to claim 1, characterized in that: The shaft (6) is mounted on the bottom cover (16) by means of screws.

4. The variable stiffness and damping transmission device based on magnetorheological fluid according to claim 1, characterized in that: The outer wall (1) consists of two semi-cylinders.

5. A design method for a variable stiffness and damping transmission device based on magnetorheological fluid, characterized in that: A variable stiffness and damping transmission device is formed by constructing a variable stiffness part and a variable damping part, and combining the two parts through an outer wall (1), a large linear bearing (2), an end cover (4), an inner end cover (10), a bottom cover (16) and a linear bearing (17); wherein: The variable stiffness part is composed of a permanent magnet PM (11), a second coil (12), a first spring (9) and a second spring (14); The variable damping part is composed of a shaft (6), a magnetorheological fluid (7), a first coil (5) and an inner wall (3); In the variable stiffness part, the characteristic that the permanent magnet is subjected to different forces in a non-uniform magnetic field is utilized, and the force on the permanent magnet PM (11) is changed by adjusting the current in the second coil (12) to change the magnetic field formed by the energized coil, thereby changing the force on the permanent magnet PM (11) to achieve a change in the stiffness value, wherein the calculation formula of the stiffness is: Among them, B r is the residual magnetic induction of the permanent magnet PM, S is the end surface area of ​​the permanent magnet, N is the number of coil turns, l is the coil length, R1 is the inner diameter of the coil, R2 is the outer diameter of the coil, I1 is the coil current, and C1 is the corresponding parameter, which is related to the position of the permanent magnet PM in the coil; In the variable damping part, the shear stress of the magnetorheological fluid (7) is changed by utilizing the characteristic of the shear force change of the magnetorheological fluid (7) in the magnetic field to change the current of the first coil (5) on the inner wall (3), thereby realizing variable damping, wherein the calculation formula of the variable damping is: Where η is the zero magnetic field viscosity coefficient of the magnetorheological fluid; L is the effective length of the damping channel; D m is the inner diameter of the magnetorheological fluid cylinder; h is the gap between the piston and the cylinder; τ z The shear yield strength of magnetorheological fluid changes with the change of current; A p is the effective area of ​​the magnetorheological fluid piston.

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