A variable stiffness actuator based on magnetorheological elastic body

Abstract

This invention discloses a variable stiffness actuator based on a magnetorheological elastomer, comprising an input linkage, a lever arm, an output linkage, and a variable stiffness mechanism. The input linkage forms the actuator's outer frame, providing space and position for the installation of other components, and houses a drive motor. One end of the lever arm is fixedly connected to the drive motor, serving as a bridge for changing the equilibrium position and arranging the variable stiffness mechanism. One end of the output linkage is mounted on the input linkage coaxially with the drive motor via a revolute joint. The variable stiffness mechanism consists of a spring-like mechanism and a push rod motor. It changes the stiffness of the magnetorheological elastomer by altering the applied magnetic field, and achieves joint stiffness variation by pre-tensioning the spring-like mechanism through the push rod motor. Compared to traditional actuators that achieve variable stiffness using pre-tensioned springs, this invention offers a wider range of stiffness variations, more variation methods, and faster variation speeds, facilitating the application of variable stiffness actuators in scenarios such as bipedal robots.

Description

Technical Field

[0001] This invention relates to the field of variable stiffness actuator technology, and in particular to a variable stiffness actuator based on a magnetorheological elastomer. Background Technology

[0002] With the increasing application of robotics technology, higher demands are being placed on the safety, motion stability, and energy efficiency of robots. When bipedal robots walk dynamically, the contact between their feet and the ground can generate significant impacts. Traditional rigid robots cannot effectively absorb these impacts, leading to damage to their mechanisms and actuators, and resulting in low energy efficiency. Therefore, effectively reducing the impact of the external environment on robots is of great significance for bipedal robots. Flexibility plays a crucial role in human adaptation to changes in the external environment and achieving stable gait. Currently, more and more researchers are focusing on incorporating flexibility into actuators, designing variable stiffness actuators based on different principles, and applying them to bipedal robots. The flexible elements in variable stiffness actuators can deform upon external impact, absorbing the impact and vibration and storing energy within the elements. This stored energy is then released during subsequent movement, thus giving variable stiffness actuators strong impact resistance and high energy efficiency.

[0003] Flexible elements are an important component of variable stiffness actuators. Nowadays, most variable stiffness actuators use springs, leaf springs, torsion springs, etc. as flexible elements. These elements are good flexible units that can absorb external impacts and store and release energy. However, due to their fixed stiffness, the range of variable stiffness of the actuators achieved by pre-tensioning and other methods is limited, and the speed of stiffness change is slow, making it difficult to use in tasks that require high-frequency variable stiffness. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a variable stiffness actuator based on a magnetorheological elastomer. It achieves the effect of changing joint stiffness by altering both the external preload of the magnetorheological elastomer and the influence of an external magnetic field on the elastomer's own stiffness, thereby expanding the range of variable stiffness. It utilizes millisecond-level magnetorheological effects to achieve rapid stiffness change response. Furthermore, it employs a high-torque servo motor to drive the lever arm, improving control accuracy and driving speed.

[0005] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0006] A variable stiffness actuator based on a magnetorheological elastic body includes:

[0007] The input linkage has a drive motor mounted on its upper part;

[0008] The output link has its support plates on both sides mounted on the support plates on both sides of the input link frame via a rotary joint.

[0009] The lever arm is mounted at one end on the output end of the drive motor and at the other end on the output connecting rod via a rotary joint;

[0010] The variable stiffness mechanism includes a spring-like mechanism and a push rod motor. The spring-like mechanism is composed of a layered magnetorheological elastomer located between the upper and lower end covers of the magnetic circuit. A coil frame is installed on the lower end cover of the magnetic circuit, and an electromagnetic coil is wound around the outside of the coil frame. One end of a double-ended stud is connected to the push rod head of the push rod motor. The other end of the double-ended stud passes through the middle through hole of the lower end cover of the magnetic circuit and the layered magnetorheological elastomer and then connects to the upper end cover of the magnetic circuit. The push rod motor is mounted on the input linkage frame. The lower end cover of the magnetic circuit also fixes one end of a steel rope through a connecting plate. The other end of the steel rope passes through two sets of U-shaped bearings of the lever arm and is connected to the output linkage.

[0011] In the above technical solution, the lever arm includes:

[0012] The left-side irregular-shaped shaft is mounted on the output flange of the drive motor;

[0013] The right-side irregular shaft is mounted on a small-diameter rolling bearing located on the support plate on the right side of the output connecting rod;

[0014] There are four connecting shafts, which are installed in the four corresponding mounting holes in the middle of the left and right irregular shafts;

[0015] There are four U-shaped bearings, which are installed on four connecting shafts and located between the left and right irregular shafts.

[0016] In the above technical solution, the lower end of the magnetic circuit cover is connected to two connecting plates on both sides. The top of the two connecting plates is connected to the upper connecting plate. A tension sensor is installed on the upper connecting plate. A steel rope fixing head is connected to the tension sensor. The steel rope fixing head is used to fix one end of the steel rope.

[0017] In the above technical solution, the layered magnetorheological elastomer is a hollow cylindrical structure formed by sequentially stacking a layer of annular magnetorheological elastomer and a layer of silicon steel sheets of the same shape and size.

[0018] In the above technical solution, the output linkage includes:

[0019] The upper connecting plate of the output link connects the left support plate and the right support plate of the output link together. The output link steel rope fixing plate is installed between the left support plate and the right support plate of the output link for connecting the other end of the steel rope.

[0020] A small-diameter rolling bearing is installed inside the support plate on the right side of the output connecting rod.

[0021] In the above technical solution, the input linkage frame is formed by connecting the left support plate, the front connecting plate, the bottom support plate and the right support plate together to form the external frame of the driver, and the drive motor is mounted on the left support plate.

[0022] In the above technical solution, the shaft center of the drive motor is defined as the rotation center of the variable stiffness drive.

[0023] In the above technical solution, rolling bearing A is installed on the left support plate and rolling bearing B is installed on the right support plate. Both rolling bearing A and rolling bearing B are concentrically arranged with the rotation center.

[0024] In the above technical solution, the left support plate and the right support plate of the output link are concentrically mounted on the rolling bearing A and the rolling bearing B, respectively.

[0025] In the above technical solution, the joint stiffness of the variable stiffness actuator changes in two ways:

[0026] Adjusting the magnitude of the current I flowing through the electromagnetic coil changes the strength of the magnetic field generated by the electromagnetic coil.

[0027] By retracting the push rod via the push rod motor, the layered magnetorheological elastomer is pre-tightened to varying degrees, thereby changing the amount of compression.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) Since magnetorheological elastomers have variable stiffness, using magnetorheological elastomers instead of springs in variable stiffness actuators can further expand the range of stiffness variation while retaining the advantages and characteristics of the original variable stiffness actuators, so as to meet the stiffness requirements of more tasks.

[0030] (2) Due to the millisecond-level stiffness response speed of the magnetorheological elastomer, the stiffness response speed of the variable stiffness actuator based on the magnetorheological elastomer of this invention is faster, and it can be applied to tasks that require high-frequency stiffness changes.

[0031] (3) Compared with traditional actuators that achieve variable stiffness only through preload springs, the present invention introduces magnetorheological elastomers to expand the variable stiffness methods, adopt different variable stiffness strategies when facing different task requirements, reduce energy loss, improve energy efficiency, and at the same time reduce the requirement for the maximum output force of stiffness motors.

[0032] (4) The present invention uses a motor to directly drive the lever arm to change the balance position. Compared with the traditional method of using a push rod motor, it improves the driving speed and can be applied to more task scenarios. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall structure of the variable stiffness actuator based on magnetorheological elastomer described in this invention.

[0035] Figure 2 This is a partial cross-sectional schematic diagram of the input linkage frame described in this invention;

[0036] Figure 3 This is a partial cross-sectional schematic diagram of the output linkage described in this invention;

[0037] Figure 4 This is a partial cross-sectional schematic diagram of the lever arm described in this invention;

[0038] Figure 5 This is a partial cross-sectional schematic diagram of the variable stiffness component described in this invention;

[0039] Figure 6 This is a schematic diagram illustrating the working principle of the variable stiffness actuator based on magnetorheological elastic body described in this invention.

[0040] Figure 7(a) is a schematic diagram of the state of the variable stiffness actuator based on magnetorheological elastic body described in this invention when the equilibrium position is changed;

[0041] Figure 7(b) is a schematic diagram of the second state of the variable stiffness actuator based on magnetorheological elastic body described in this invention when the equilibrium position is changed;

[0042] Figure 7(c) is a schematic diagram of the three states of the variable stiffness actuator based on magnetorheological elastic body described in this invention when the equilibrium position is changed;

[0043] Figure 8 This is a schematic diagram illustrating the principles of two variable stiffness actuators based on magnetorheological elastic bodies as described in this invention.

[0044] In the diagram: 1-Input linkage frame; 2-Lever arm; 3-Output linkage; 4-Variable stiffness assembly; 5-Rolling bearing A; 6-Drive motor; 7-Left side support plate; 8-Front connecting plate; 9-Bottom support plate; 10-Plug bolt; 11-Right side support plate; 12-Rolling bearing B; 13-Bearing pressure plate; 14-Drive motor output flange; 15-Upper connecting plate of output linkage; 16-Output linkage steel rope fixing plate; 17-Left side support plate of output linkage; 18-Rolling bearing pressure plate; 19-Small diameter rolling bearing pressure plate; 20 21-Small diameter rolling bearing; 22-Right side support plate of output connecting rod; 23-Left irregular shaft; 24-U-shaped bearing; 25-Right irregular shaft; 26-Right irregular shaft bearing clamping ring; 27-Connecting small shaft; 28-Steel rope; 29-Steel rope fixing head; 30-Tension sensor; 31-Upper connecting plate; 32-Both side connecting plates; 33-Lower end cover of magnetic circuit; 34-Double-headed stud; 35-Push rod motor; 36-Electromagnetic coil; 37-Layered magnetorheological elastomer; 38-Coil skeleton pressure plate; 39-Upper end cover of magnetic circuit. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] like Figure 1 As shown, this embodiment of the invention discloses a variable stiffness actuator based on a magnetorheological elastomer, including an input linkage frame 1, a lever arm 2, an output linkage 3, and a variable stiffness mechanism 4. The left support plate 17 and the right support plate 21 of the output linkage are concentrically mounted on rolling bearings A5 and B12 on the input linkage frame 1, respectively. The left irregular shaft 22 of the lever arm 2 is mounted on the output flange 14 of the drive motor, and the right irregular shaft 24 is concentrically mounted on a small-diameter rolling bearing 20. The push rod motor 34 of the variable stiffness mechanism 4 is mounted on a stop bolt 10, which is mounted on a bottom support plate 9. The steel rope 27 passes through the gap between the two sets of U-shaped bearings 23 of the lever arm 2 and is connected to the steel rope fixing plate 16 of the output linkage.

[0047] Specifically, the input linkage 1 includes:

[0048] Left support plate 7, front connecting plate 8, bottom support plate 9, right support plate 11, as follows Figure 2 The drive's outer frame is formed by screws connecting the components together.

[0049] Drive motor 6 is mounted on the left connecting plate 7, and the axis of drive motor 6 is defined as the rotation center of the variable stiffness actuator.

[0050] Drive motor output flange 14 is installed at the output end of drive motor 6;

[0051] Rolling bearing A5 is installed on the left support plate 7, concentric with the rotation center; rolling bearing B12 is installed on the right support plate 11, concentric with the rotation center, and is fixed by bearing pressure plate 13.

[0052] For details, see Figure 3 The output linkage 3 includes:

[0053] The upper connecting plate 15 of the output link connects the left support plate 17 and the right support plate 21 of the output link together.

[0054] The output connecting rod steel rope fixing plate 16 is installed between the left support plate 17 and the right support plate 21 of the output connecting rod.

[0055] The small-diameter rolling bearing 20 is installed inside the support plate 21 on the right side of the output connecting rod and is fixed by the small-diameter rolling bearing pressure plate 19.

[0056] The rolling bearing pressure plate 18 is installed on the outside of the right support plate 21 of the output connecting rod and is used to press the rolling bearing B12 located on the right support plate 11 of the input connecting rod frame 1.

[0057] For details, see Figure 4 Lever arm 2 includes:

[0058] The left profiled shaft 22 and the right profiled shaft 24 are connected together by four connecting small shafts 26. Four U-shaped bearings 23 are respectively installed on the four connecting small shafts 26, located between the left profiled shaft 22 and the right profiled shaft 24. The right profiled shaft bearing clamping ring 25 is installed on the right profiled shaft 24 to clamp the small-diameter rolling bearing 20 located on the output connecting rod 3. The left profiled shaft 22 is installed on the drive motor output flange 14, and the right profiled shaft 24 is installed on the small-diameter rolling bearing 20 located on the support plate 21 on the right side of the output connecting rod.

[0059] Specifically, the variable stiffness mechanism 4 includes:

[0060] One end of the steel rope 27 is fixed to the steel rope fixing head 28, and the other end passes through the two sets of U-shaped bearings 23 of the lever arm 2 and is connected to the output connecting rod steel rope fixing plate 16; the steel rope fixing head 28 is connected to the tension sensor 29 by a thread;

[0061] The upper connecting plate 30 and the two side connecting plates 31 are as follows Figure 5As shown in the diagram, the lower ends of the connecting plates 31 on both sides are connected to the lower end of the magnetic circuit lower cover 32. A tension sensor 29 is installed on the upper connecting plate 30. The tension sensor 29 is used to measure the tension F generated by the layered magnetorheological elastomer 37 under compression. s ;

[0062] The upper magnetic circuit cover 39, the lower magnetic circuit cover 32, and the layered magnetorheological elastomer 37 are arranged as follows: Figure 5 As shown, the layered magnetorheological elastomer 37 is located between the upper cover 39 and the lower cover 32 of the magnetic circuit, forming a spring-like mechanism; the coil frame 35 is installed on the lower cover 32 of the magnetic circuit, and an electromagnetic coil 36 is wound around it and fixed by the coil frame pressure plate 38; one end of the double-ended stud 33 passes through the middle through hole of the lower cover 32 of the magnetic circuit and the layered magnetorheological elastomer 37, and is connected to the threaded hole of the upper cover 39 of the magnetic circuit, and the other end is connected to the push rod head of the push rod motor 34.

[0063] The layered magnetorheological elastomer 37 is a hollow cylindrical structure formed by sequentially stacking a 1mm thick annular magnetorheological elastomer layer and a 1mm thick silicon steel sheet of the same shape and size. The magnetorheological elastomer is a smart material made by mixing and curing micron-sized carbonyl iron powder as ferromagnetic particles with silicone as the matrix. The ferromagnetic particles in the magnetorheological elastomer form an ordered chain or columnar structure. Under the influence of a magnetic field, the material undergoes a magnetorheological effect, increasing its stiffness along the magnetic field direction. When the magnetic field is removed, the material's stiffness properties return to their state without a magnetic field. The magnetorheological elastomer has the advantages of fast response speed and good reversibility.

[0064] like Figure 6 As shown, the variable stiffness actuator based on a magnetorheological elastic body of the present invention includes two motors: a drive motor 6 for changing the equilibrium position of the actuator and a push rod motor 34 for adjusting the stiffness of the actuator. A lever arm 2 exists between the input linkage 1 and the output linkage 3, serving as a bridge between the equilibrium position change and the variable stiffness mechanism. The angle α between the lever arm 2 and the output linkage 3 is called the deviation angle. The effective length of the output linkage 3 is D, the effective length of the lever arm 2 is B, the stiffness of the spring-like mechanism is k, and the compression of the spring-like mechanism is p(t).

[0065] The principle of changing the equilibrium position is:

[0066] As shown in Figure 7(a), the drive motor 6 drives the lever arm 2 through the drive motor output flange 14. Figure 7(b) corresponds to... Figure 6 As shown, when the drive motor 6 drives the lever arm 2 to rotate, the lever arm 2 and the output connecting rod 3 are no longer aligned. This is because at this time, there is a tension F in the steel rope 27 caused by the compression of the lamellar magnetorheological elastic body 37 in the variable stiffness mechanism 4. sThis torque acts on the output link 3, causing the output link 3 to generate a torque T about the center of rotation, as shown in the following equation:

[0067]

[0068] in: A represents the distance from the outer end of the output linkage to the outer end of the lever arm, f s F represents s The component perpendicular to the direction of the output link;

[0069] This allows the output link 3 to realign with the lever arm 2, as shown in Figure 7(c).

[0070] The principle of changing stiffness is as follows:

[0071] The equivalent joint stiffness is the partial derivative of the output joint torque with respect to the deviation angle α, and is a function of the deviation angle and the amount of compression, as shown in the following equation:

[0072]

[0073] As can be seen from the formula for joint stiffness, stiffness can be varied in two ways: by changing the compression amount p(t) of the pre-tensioned spring mechanism and by changing the magnitude of the current I flowing through the electromagnetic coil 36 to affect the stiffness k of the spring mechanism.

[0074] like Figure 8 As shown, the variable stiffness actuator based on magnetorheological elastomer can, on the one hand, change the magnitude of the current I flowing through the electromagnetic coil 36, thereby changing the magnetic field strength generated by the electromagnetic coil 36 and affecting the stiffness properties of the magnetorheological elastomer itself, thus causing a change in the joint stiffness of the actuator; on the other hand, the push rod motor 34 can retract the push rod, causing the layered magnetorheological elastomer 37 to be pre-tightened to different degrees, thereby changing the compression amount p(t), thus causing a change in the joint stiffness of the actuator.

[0075] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A variable stiffness actuator based on a magnetorheological elastic body, characterized in that, include: Input linkage (1), with a drive motor (6) mounted on the upper part; The output link (3) has its two support plates mounted on the two support plates of the input link frame (1) via a rotary joint. The lever arm (2) is mounted at one end on the output end of the drive motor (6) and at the other end on the output link (3) via a rotary joint; The variable stiffness mechanism (4) includes a spring-like mechanism and a push rod motor (34). The spring-like mechanism is composed of a layered magnetorheological elastic body (37) located between the upper end cover (39) and the lower end cover (32) of the magnetic circuit. A coil frame (35) is installed on the lower end cover (32), and an electromagnetic coil (36) is wound around the outside of the coil frame (35). One end of a double-ended stud (33) is connected to the push rod head of the push rod motor (34). The other end of the double-ended stud (33) passes through the middle through hole of the lower end cover (32) of the magnetic circuit and the layered magnetorheological elastomer (37) and is connected to the upper end cover (39) of the magnetic circuit; the push rod motor (34) is mounted on the input linkage frame (1); the lower end cover (32) of the magnetic circuit also fixes one end of the steel rope (27) through the connecting plate, and the other end of the steel rope (27) passes through the two sets of U-shaped bearings (23) of the lever arm (2) and is connected to the output linkage (3).

2. The variable stiffness actuator based on a magnetorheological elastic body according to claim 1, characterized in that, The lever arm (2) includes: The left irregular shaft (22) is mounted on the output flange of the drive motor; The right-side profiled shaft (24) is mounted on a small-diameter rolling bearing (20) located on the support plate on the right side of the output connecting rod; There are four connecting shafts, which are installed in the four corresponding mounting holes in the middle of the left and right irregular shafts; There are four U-shaped bearings, which are installed on four connecting shafts and located between the left and right irregular shafts.

3. The variable stiffness actuator based on a magnetorheological elastic body according to claim 1, characterized in that, The lower end of the magnetic circuit lower end cover (32) is connected to two side connecting plates (31), the top of the two side connecting plates (31) is connected to the upper connecting plate (30), and a tension sensor (29) is installed on the upper connecting plate (30). A steel rope fixing head (28) is connected to the tension sensor (29), and the steel rope fixing head (28) is used to fix one end of the steel rope (27).

4. The variable stiffness actuator based on a magnetorheological elastic body according to claim 1, characterized in that, The layered magnetorheological elastomer (37) is a hollow cylindrical structure formed by stacking a layer of annular magnetorheological elastomer and a layer of silicon steel sheets of the same shape and size.

5. The variable stiffness actuator based on a magnetorheological elastic body according to claim 1, characterized in that, The output link (3) includes: The upper connecting plate (15) of the output link connects the left support plate (17) and the right support plate (21) of the output link together. The steel rope fixing plate (16) of the output link is installed between the left support plate (17) and the right support plate (21) of the output link for connecting the other end of the steel rope (27). A small-diameter rolling bearing (20) is installed inside the support plate (21) on the right side of the output connecting rod.

6. The variable stiffness actuator based on a magnetorheological elastic body according to claim 5, characterized in that, The input linkage frame (1) is formed by connecting the left support plate (7), the front connecting plate (8), the bottom support plate (9) and the right support plate (11) together to form the external frame of the driver. The drive motor (6) is mounted on the left support plate (7).

7. The variable stiffness actuator based on a magnetorheological elastic body according to claim 6, characterized in that, The shaft of the drive motor (6) is defined as the rotation center of the variable stiffness drive.

8. The variable stiffness actuator based on a magnetorheological elastic body according to claim 7, characterized in that, Rolling bearing A (5) is installed on the left support plate (7), and rolling bearing B (12) is installed on the right support plate (11). Both rolling bearing A (5) and rolling bearing B (12) are concentrically set with the rotation center.

9. The variable stiffness actuator based on a magnetorheological elastic body according to claim 8, characterized in that, The left support plate (17) and the right support plate (21) of the output link are concentrically mounted on the rolling bearing A (5) and the rolling bearing B (12), respectively.

10. The variable stiffness actuator based on a magnetorheological elastic body according to claim 9, characterized in that, The joint stiffness of the variable stiffness actuator changes in two ways: Adjust the magnitude of the current I flowing through the electromagnetic coil (36), thereby changing the magnetic field strength generated by the electromagnetic coil (36); By retracting the push rod through the push rod motor (34), the layered magnetorheological elastomer (37) is pre-tightened to different degrees, thereby changing the amount of compression.

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