A variable stiffness rotary joint

Abstract

This invention discloses a variable stiffness rotary joint, relating to the field of robot joint technology. It includes two joint units and a connecting rod for connecting the two joint units. Each joint unit includes a fixed base and several pole plates fixed at intervals on the fixed base. The pole plates in both joint units are electrically connected to a power supply device, and the pole plates in the two joint units have opposite polarities and are staggered and stacked. The gaps between adjacent staggered pole plates are filled with a giant electrorheological fluid. The connecting rod is distributed on the sides of the pole plates and is arranged crosswise. The two ends of the connecting rod are respectively hinged to the fixed bases in the two joint units. This invention combines a reverse four-bar linkage rotation mechanism with a giant electrorheological fluid shear mode variable stiffness mechanism to form a unique rotational structure. The rotational stiffness is adjustable by adjusting the voltage at both ends of the giant electrorheological fluid, eliminating the need for other driving devices. The structure is simpler, making it easier to reduce the size of the rotary joint and facilitating miniaturization and lightweight design.

Description

Technical Field

[0001] This invention relates to the field of robot joint technology, and in particular to a variable stiffness rotary joint. Background Technology

[0002] With the development of robotics technology, robots are increasingly entering industrial production and daily life. Currently, the vast majority of robots have rigid structures. The advantages of such robots are their precise models, convenient control, and large load capacity, making them suitable for performing labor-intensive and repetitive tasks in structured environments. However, in the aerospace and medical fields, due to the emphasis on environmental adaptability and user-friendliness, the design and development of soft robots are gradually gaining attention.

[0003] As an important component of flexible robots, the design of flexible variable stiffness joints is currently mainly based on mechanical variable stiffness principles. For example, based on the lever principle, the joint stiffness is adjusted by changing the transmission ratio between the joint output and the joint's built-in elastic unit, or by adjusting the preload of the joint's built-in spring. This mechanical variable stiffness method often requires a dedicated motor to adjust the stiffness, further increasing the overall size and manufacturing cost of the joint.

[0004] Giant electrorheological fluids (GEMs), as a novel smart material, offer adjustable mechanical properties and fast response speeds, providing new insights into the design of variable stiffness joints. Compared to mechanical variable stiffness, GEMs, as a novel liquid material, occupy a smaller volume and have a simpler design structure, which is beneficial for the miniaturization of variable stiffness joints. Furthermore, since the shear yield stress of GEMs can achieve changes of more than two orders of magnitude under field strength control, this variable stiffness method holds great potential.

[0005] Magnetorheological fluids are also a type of controllable smart fluid material. Unlike giant electrorheological fluids, magnetorheological fluids require a magnetic field to achieve their rheological effects. Invention patent CN109015739B discloses a "variable stiffness flexible joint for a rehabilitation robot," comprising a transmission sleeve, coil frame, active spacer ring, driven disc, driven spacer ring, active disc, large spacer ring, coil baffle, two magnetic end plates, bearing end cap, and input shaft. This invention employs a traditional clutch-type rotary mechanism design. The torque of the active disc is transmitted to the driven disc via the magnetorheological fluid. By adjusting the magnetic field, the mechanical properties of the magnetorheological fluid are altered, thereby changing the torque transmission efficiency and achieving variations in output rotational stiffness. Since this flexible joint still relies on a rotating shaft for drive, a motor is generally the only viable power source, limiting its application scenarios. Furthermore, the presence of coils and related components increases the joint's size and manufacturing costs. Summary of the Invention

[0006] The purpose of this invention is to provide a variable stiffness rotary joint to solve the problems existing in the prior art. The rotary stiffness can be adjusted by adjusting the voltage at both ends of the giant current rheostat, without the need for other driving devices. The structure is simpler and it is easier to reduce the volume of the rotary joint, which is beneficial for miniaturization and lightweight design.

[0007] To achieve the above objectives, the present invention provides the following solution: The present invention provides a variable stiffness rotary joint, comprising two joint units and a connecting rod for connecting the two joint units. Each joint unit includes a fixed base and a plurality of electrode plates fixed at intervals on the fixed base. The electrode plates in both joint units are electrically connected to a power supply device, and the electrode plates in the two joint units have opposite polarities and are staggered and stacked. The gaps between adjacent electrode plates staggered and stacked are filled with a giant electrorheological fluid. The connecting rod is distributed on the sides of the electrode plates and is arranged crosswise. The two ends of the connecting rod are respectively hinged to the fixed bases in the two joint units.

[0008] Preferably, the electrode plate is further covered with an insulating PI film.

[0009] Preferably, the fixing base is provided with a fixing clamping piece and a sliding clamping piece, the electrode plate is disposed between the fixing clamping piece and the sliding clamping piece, and the fixing clamping piece, the sliding clamping piece and the electrode plate are each provided with at least two through holes, and the connector passes through the through holes to fix the three together.

[0010] Preferably, a gasket is provided between adjacent electrode plates in the joint unit, and the gasket has the through hole.

[0011] Preferably, the connector is a female rivet.

[0012] Preferably, the fixing base is further fixed to the fixing base, the fixing clamping piece is fixed to the end of the base, the base is provided with a T-shaped part, the sliding clamping piece has a T-shaped opening adapted to the T-shaped part, and the sliding clamping piece is slidably disposed on the T-shaped part.

[0013] Preferably, the fixed base is provided with hinge holes at intervals, and the hinge pin passes through the hinge holes to hinge the end of the connecting rod; in the direction of the line connecting the ends of the two connecting rods, a plurality of hinge holes are provided at intervals.

[0014] Preferably, the end face of the fixing base is also provided with a plurality of connecting holes for connecting other components.

[0015] The present invention achieves the following technical effects compared to the prior art:

[0016] This invention combines a reverse four-bar rotating mechanism with a giant electrorheological fluid shear mode variable stiffness mechanism to form a unique rotating structure; and the rotational stiffness is adjustable by adjusting the voltage across the giant electrorheological fluid. Furthermore, the variable stiffness rotating joint in this invention only requires applying voltage across the giant electrorheological fluid, eliminating the need for other driving devices, resulting in a simpler structure, easier reduction of the rotating joint's size, and facilitating miniaturization and lightweight design. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the overall structure of the rotating joint in this invention;

[0019] Figure 2 for Figure 1 Side view;

[0020] Figure 3 for Figure 1 The main view;

[0021] Figure 4 This is a schematic diagram of the base structure;

[0022] Figure 5 This is a schematic diagram of the structure of the fixed clamping piece;

[0023] Figure 6 This is a schematic diagram of the sliding clamping piece.

[0024] Figure 7 This is a schematic diagram of a two-degree-of-freedom variable stiffness rotary joint;

[0025] Among them, 1. connecting rod; 2. fixed seat; 3. pole plate; 4. base; 5. fixed clamping plate; 6. sliding clamping plate; 7. T-shaped part; 8. T-shaped opening; 9. hinge hole; 10. hinge pin; 11. washer. Detailed Implementation

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] The purpose of this invention is to provide a variable stiffness rotary joint to solve the problems existing in the prior art. The rotary stiffness can be adjusted by adjusting the voltage at both ends of the giant current rheostat, without the need for other driving devices. The structure is simpler and it is easier to reduce the volume of the rotary joint, which is beneficial for miniaturization and lightweight design.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] like Figures 1 to 7 As shown, this embodiment provides a variable stiffness rotary joint, including two identical joint units and four connecting rods 1 for connecting the two joint units. Each joint unit includes a fixed base 2 with a circular end face and several electrode plates 3 fixed at intervals on the fixed base 2. The electrode plates 3 in both joint units are electrically connected to a power supply device, and the electrode polarities of the electrode plates 3 in the two joint units are opposite. Specifically, the electrode plate 3 in one joint unit is connected to a positive DC current terminal, and the electrode plate 3 in the other joint unit is connected to a negative DC current terminal. The electrode plate 3 connected to the positive electrode and the electrode plate 3 connected to the negative electrode are staggered and stacked, and the gaps between adjacent staggered electrode plates 3 are filled with a giant electrorheological fluid. The four connecting rods 1 are arranged in pairs, crossing each other on the sides of the electrode plates 3, and the two ends of the connecting rods 1 are respectively hinged to the fixed bases 2 in the two joint units.

[0030] When a voltage is applied across the ends of the mega-electroractic fluid, it transforms into a solid-like state due to rheological effects, increasing the shear force on plate 3. This increases the joint's rotational resistance and stiffness, with the increase becoming more pronounced as the voltage increases. Therefore, adjusting the applied voltage can alter the joint's rotational stiffness.

[0031] Therefore, this embodiment combines the reverse four-bar linkage rotation mechanism with the giant electrorheological fluid shear mode variable stiffness mechanism to form a special rotation structure; and the rotation stiffness is adjustable by adjusting the voltage at both ends of the giant electrorheological fluid. In addition, the variable stiffness rotation joint in this embodiment only requires applying voltage to both ends of the giant electrorheological fluid, without the need for other driving devices, making the structure simpler and easier to reduce the size of the rotation joint, which is beneficial for miniaturization and lightweight design.

[0032] It should be noted that giant electrorheological fluid is a high-viscosity fluid. If the purpose is only a short-term experiment with variable stiffness, then only a layer of giant electrorheological fluid needs to be applied to the surface of the electrode 3. Because the gap between adjacent electrode 3 is very small, the adhesion force of the giant electrorheological fluid on both sides of the electrode 3 can offset most of the gravity, so it can remain in the gap between the electrode 3 for a relatively long time. If it is used in a practical engineering structure, in order to prevent leakage of the giant electrorheological fluid, a sleeve made of soft materials such as silicone or rubber can be used to cover the entire variable stiffness joint and fill it with giant electrorheological fluid.

[0033] Furthermore, the electrode plate 3 is also covered with a negligible thickness of insulating PI film to prevent short circuits caused by contact between dissimilar electrode plates 3. The electrode plates 3 within the same joint unit are separated by spacers 11. In this embodiment, the thickness of the electrode plate 3 is 0.1 mm, the thickness of the spacer 11 is 0.9 mm, and the gap between adjacent dissimilar electrode plates 3 is 0.4 mm. Within a controllable voltage range, the stiffness variation range of the variable stiffness rotary joint is jointly determined by the number of electrode plate 3 stacks, the overlapping area of ​​the electrode plates 3, and the size of the gap between adjacent dissimilar electrode plates 3. The more electrode plate 3 stacks, the larger the overlapping area of ​​the electrode plates 3, and the smaller the gap between adjacent dissimilar electrode plates 3, the larger the range of joint stiffness variation. In other words, changing the number of electrode plates 3, the overlapping area, or the gap can also change the stiffness of the rotary joint and directly affect the upper limit of its variation range.

[0034] The joint unit has a base 4, a fixed clamping plate 5, and a sliding clamping plate 6 mounted on a fixed base 2. The base 4 is detachably fixed to the fixed base 2 with bolts, and the fixed clamping plate 5 is detachably fixed to the end of the base 4 with bolts. The base 4 also has a T-shaped portion 7, and the sliding clamping plate 6 has a T-shaped opening 8 that matches the T-shaped portion 7. The sliding clamping plate 6 is slidably mounted on the T-shaped portion 7. The pole plate 3 is positioned between the fixed clamping plate 5 and the sliding clamping plate 6. The fixed clamping plate 5, the gasket 11, the sliding clamping plate 6, and the pole plate 3 are each provided with at least two through holes, and rivets pass through the through holes to fix the four components together. By loosening the sliding clamping plate 6, its position can be moved to change the number of stacked pole plates 3, thereby adjusting the upper limit of the rotational joint stiffness variation. Before using the sliding clamping piece 6 and the fixed clamping piece 5 to clamp the gasket 11 and the electrode plate 3, the base of the gasket 11 and the electrode plate 3 can be tied together with exposed thin copper wire and a section can be led out to connect to the power supply to achieve electrical connection.

[0035] The fixed base 2 has hinge holes 9 spaced apart. Hinge pins 10 pass through the hinge holes 9 to hinge the ends of the connecting rods 1. Several hinge holes 9 are spaced apart along the line connecting the ends of the two connecting rods 1. When the connecting rod 1 is connected to the innermost hinge hole 9, the height of the variable stiffness rotary joint is at its highest. Besides this height adjustment method, the joint height can also be changed by altering the length of the connecting rod 1. Of course, there is a minimum length for the connecting rod 1; if the connecting rod 1 is very short, the rotation range of the variable stiffness rotary joint will be very small or even impossible to rotate.

[0036] The end face of the fixed base 2 is also provided with several connecting holes for connecting other components. Connecting two rotary joints in series can improve the efficiency of connecting a single-degree-of-freedom rotary joint to another single-degree-of-freedom variable stiffness rotary joint by offsetting one single-degree-of-freedom rotary joint by 90 degrees around the z-axis (i.e., the vertical axis) of the Cartesian coordinate system and then connecting it in series with another single-degree-of-freedom variable stiffness rotary joint through bolts and connecting holes, thus forming a two-degree-of-freedom variable stiffness rotary joint, further expanding the application scenarios of the variable stiffness rotary joint provided in this embodiment.

[0037] In this embodiment, apart from the connecting rod 1 being made of high-strength carbon fiber and the electrode plate 3 being made of highly flexible spring steel, the base 4, the fixed clamping plate 5, and the sliding clamping plate 6 are all made of insulating ABS material using photopolymerization 3D printing to prevent the dissimilar electrodes from conducting through the joint support structure. The other unmentioned parts are all made of easily machinable aluminum.

[0038] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0039] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A variable stiffness rotary joint, characterized in that, The device includes two joint units and a connecting rod for connecting the two joint units. Each joint unit includes a fixed base and several electrode plates fixed at intervals on the fixed base. The electrode plates in both joint units are electrically connected to a power supply device, and the electrode plates in the two joint units have opposite polarities and are staggered and stacked. The gaps between the staggered and stacked adjacent electrode plates are filled with giant electrorheological fluid. The connecting rod is distributed on the side of the electrode plates and is arranged crosswise. The two ends of the connecting rod are respectively hinged to the fixed bases in the two joint units. The fixed base is provided with a fixed clamping plate and a sliding clamping plate. The electrode plate is disposed between the fixed clamping plate and the sliding clamping plate. The fixed clamping plate, the sliding clamping plate and the electrode plate are each provided with at least two through holes. The connector passes through the through holes to fix the three together. A gasket is provided between adjacent electrode plates in the joint unit, and the gasket has the through hole.

2. The variable stiffness rotary joint according to claim 1, characterized in that, The electrode plate is also covered with an insulating PI film.

3. The variable stiffness rotary joint according to claim 1, characterized in that, The connector is a female rivet.

4. The variable stiffness rotary joint according to claim 1, characterized in that, The fixed base is also fixed to the base, the fixed clamping piece is fixed to the end of the base, the base is provided with a T-shaped part, the sliding clamping piece has a T-shaped opening adapted to the T-shaped part, and the sliding clamping piece is slidably disposed on the T-shaped part.

5. The variable stiffness rotary joint according to any one of claims 1 to 4, characterized in that, The fixed base is provided with hinge holes at intervals, and the hinge pin passes through the hinge holes to hinge the end of the connecting rod; in the direction of the line connecting the ends of the two connecting rods, there are a number of hinge holes at intervals.

6. The variable stiffness rotary joint according to claim 5, characterized in that, The end face of the fixing base is also provided with several connection holes for connecting other components.

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