CN111805528A - Variable-rigidity three-degree-of-freedom pneumatic flexible driver and preparation method thereof - Google Patents

Abstract

A variable-rigidity three-degree-of-freedom pneumatic flexible driver and a preparation method thereof aim to solve the technical problems that in the prior art, a pneumatic flexible driver cannot be attached to a bionic design to realize variable rigidity adjustment, the bearing capacity of the driver is poor, and the response rate in the rigidity adjustment process is low. The variable-rigidity air pipe type air-cooled driver comprises a driver body, wherein one end of the driver body is provided with a mounting groove arranged along the length direction of the driver body, a variable-rigidity module is embedded in the mounting groove and comprises liquid metal, a protective shell and a heating element, the liquid metal is packaged in the protective shell, a plurality of air cavities are formed in the driver body and arranged along the length direction of the driver body, one end of an air pipe inserted in the driver body is communicated with the air cavities, and the other end of the air pipe extends to the outside of the driver body.

Description

Variable-rigidity three-degree-of-freedom pneumatic flexible driver and preparation method thereof

Technical Field

The invention relates to the technical field of flexible robots or bionic robots, in particular to a three-degree-of-freedom pneumatic flexible driver with variable rigidity and a preparation method thereof.

Background

With the continuous progress and development of human production and life, and the continuous progress of robot technology and automatic control technology, the robot is widely applied to various aspects of human society, and particularly provides great convenience for human beings in extreme and dangerous engineering environments where human beings are not suitable to be involved. From the type of robot driver, early mechanical arms were hydraulically driven, which was characterized by relatively simple control and high power/weight ratio, but had the problems of oil leakage, high cost, poor safety, etc., and required a pressurized oil supply system; the appearance of the motor provides a new driving mode for the robot, and a hydraulic driving mode is gradually replaced, the motor driving has the advantages of simple control, cleanness, low noise and relatively low cost, and the defects of small power/volume-weight ratio and potential safety hazards in certain (such as inflammable and explosive) occasions. The traditional rigid robot assembled by components such as a motor, a piston, a joint, a hinge and the like has the advantages of large bearable external load, high operation accuracy, sufficient power, large power, mature performance and the like, but along with the expansion of the application of the robot from the industrial field to the fields of social service, environmental survey and the like, the operation environment of the robot is changed from a simple, fixed and predictable structural environment to a complex, dynamic and uncertain unstructured environment, and the robot needs to develop to intellectualization, flexibility and collaboration. Based on the fact that the traditional rigid robot cannot meet the requirements in the fields of high-end manufacturing, medical rehabilitation, national defense safety and the like, researchers in recent years try to apply the relevant biological principles of molluscs to the research and design of a robot system, and the concept of a flexible robot is provided.

Compared with the traditional rigid robot, the flexible robot has many advantages, can better adapt to various environments, and can complete complex tasks in the environment with narrow space and non-structure. At present, the research flexible robot has multiple degrees of freedom and continuous transformation capability, and can randomly change the shape and the size of the robot in a large range. The technical difficulty of research is that the flexible robot has multiple degrees of freedom and continuous transformation capability, both benefit from the driver, the design of the flexible robot needs a large number of flexible drivers, and the traditional hydraulic driving and motor driving modes can not meet the requirements; based on this, researchers turned their eyes to some new driving techniques, such as: micro-motors, piezoelectric actuators, shape memory alloy actuators, polymeric artificial muscle actuators, magnetostrictive actuators, and pneumatic flexible actuators.

Chinese patent with application number CN201410406261.3 discloses a rigidity-variable module of a bionic soft robot, wherein the rigidity-variable module comprises an elastic base body, a vent pipe, a central driving cavity and a side driving cavity, the cross section of the elastic base body is circular, the middle part of the elastic base body is provided with the central driving cavity, at least three side driving cavities are arranged on a circle of the elastic base body outside the central driving cavity at equal intervals, the two ends of the central driving cavity and the side driving cavities are both sealed, and the central driving cavity and the side driving cavities are both communicated with the vent pipe; mounting a central restraint piece on the inner wall and the outer wall of the central driving cavity, and mounting a side restraint piece on the inner wall and the outer wall of the side driving cavity; the central restraint piece comprises a central restraint spring and a central restraint ring, the central restraint spring is installed on the inner wall of the central driving cavity, the central restraint ring is installed on the outer wall of the central driving cavity, the side restraint piece comprises a side restraint spring and a side restraint ring, the side restraint spring is installed on the inner wall of the side driving cavity, and the side restraint ring is installed on the outer wall of the side driving cavity.

The variable stiffness modules of the bionic soft robot provided by the patent can be combined into various optimal configurations according to the requirements of work tasks, and the soft robot can control and change the stiffness of the soft robot in real time and keep stable grabbing action; the variable stiffness module is characterized in that compressed gas with different pressures is injected into the central cavity to realize variable stiffness adjustment, when the required stiffness is larger, high-pressure compressed gas needs to be injected, the required gas amount is larger, in the gas injection and pressurization process, on one hand, a certain time is required for gas injection, and a certain transition time is required for changing the variable stiffness module from low stiffness to high stiffness, namely, the stiffness module cannot realize quick response of stiffness change, on the other hand, safety risk exists when the gas pressure is too large, and on the basis of the consideration of use safety, the upper limit of stiffness adjustment of the variable stiffness module in the practical application process is smaller, so that the application range of the variable stiffness module is narrower.

Chinese patent application No. CN201811236251.4 discloses a variable stiffness robot, which includes a variable stiffness device, a sealing device and a fluid filling device, wherein the variable stiffness device includes an outer tube, an inner tube, an elastic filler and an expansion bag, the outer tube is sleeved outside the inner tube, and a filling cavity is formed between the outer tube and the inner tube, the sealing device includes a first sealing device and a second sealing device, the first sealing device connects one end of the outer tube and one end of the inner tube and closes one end of the filling cavity, the second sealing device connects the other end of the outer tube and the other end of the inner tube and closes the other end of the filling cavity; the filling cavity is filled with the elastic filling body, and the expansion bag body is embedded in the elastic filling body; the output end of the fluid filling device penetrates through the first sealing device or the second sealing device and is communicated with the expansion bag body so as to fill pressure fluid into the expansion bag body.

Compared with a variable stiffness adjusting mode of single air pressure adjustment in the last comparative patent, the comparison document expands the stiffness adjusting range, and the variable stiffness device in the patent has no three-degree-of-freedom motion capability and cannot meet the requirements of bionic design when applied to a flexible robot.

Disclosure of Invention

The invention provides a variable-rigidity three-degree-of-freedom pneumatic flexible driver and a preparation method thereof, aiming at overcoming the technical problems that a pneumatic flexible driver in the prior art cannot be attached to a bionic design to realize variable adjustment of rigidity, the bearing capacity of the driver is poor, and the response rate in the rigidity adjustment process is low.

In order to achieve the above object, the present invention adopts the following technical solutions.

The utility model provides a pneumatic flexible drive of variable rigidity three degrees of freedom, includes the driver body, the one end of driver body is equipped with the mounting groove of arranging along its length direction, inlays in the mounting groove and is equipped with the variable rigidity module, and the variable rigidity module includes liquid metal, protecting crust and heating member, and the liquid metal encapsulation is inside the protecting crust, and a plurality of air cavity has been seted up to driver body inside, and the air cavity is arranged along the length direction of driver body, insert establish tracheal one end on the driver body with the air cavity intercommunication, tracheal other end extends to the driver body outside. When the driver works, the liquid metal is heated by the heating element, the liquid metal is transited from a solid state to a liquid state after absorbing heat, when the liquid metal is liquefied, the rigidity of the driver can be approximate to the rigidity of the driver, at the moment, the driver can be driven by compressed gas, the compressed gas is injected into the air cavity through the air pipe and acts on the front end of the silica gel body of the flexible simulation finger, the air cavity expands radially along with the rise of the gas pressure in the air cavity, the arrangement of the surface tension springs can limit the expansion trend of the air cavity on one hand, the phenomenon that the deformation of the air cavity exceeds the elastic recovery upper limit of the material to cause the scrapping of the driver is avoided, and on the other hand, the tension springs which are subjected to axial tension can realize the conversion of the radial expansion force of the air cavity towards the axial tension force, the extension amount control of different air cavities is realized, so that the flexible driver can do bending, deflection or extension movement, specifically, when two air cavities are introduced with the same air pressure and the other air cavity is introduced with an air source with different pressure, the flexible driver is forced to do pure bending movement towards one side of the cavity with small relative extension amount (the air pressure of the air cavities is low) due to the length difference and constraint of the air cavities, taking the number of the air cavities as three as an example; when the three air cavities are introduced with air sources with different pressures, the flexible driver can generate deflection and bending movement and deflect around one side of the air cavity with small relative elongation (low air pressure of the inner cavity); the invention reduces the resistance of the air cavity for assisting the posture adjustment by liquefying the liquid metal, can ensure the posture of the robot to be quickly adjusted in place when being applied to the flexible robot, has three-degree-of-freedom motion capability and meets the requirement of bionic design; further, when the driver reaches a working point, the heating element is powered off and stopped, the driver body is made of a mixed material of platinum catalytic silicone rubber and graphene, the graphene is excellent in heat conductivity, and the liquid metal can quickly dissipate heat, so that the liquid metal can realize quick phase change from liquid to solid, the rigidity of the driver is the rigidity superposition of the driver body and the liquid metal, and the rigidity of the cured liquid metal is far greater than that of a plastic material, so that the quick response of the driver from small rigidity to large rigidity can be realized, and the quick adjustment of the rigidity upwards can be realized according to environmental requirements while larger bearing capacity is provided for the driver.

Preferably, the axis of the mounting groove is obliquely arranged with the axis of the driver body, the center of the opening end of the mounting groove is on the axis of the driver body, a mounting cavity used for filling liquid metal is arranged inside the protective shell, and the contour of the mounting cavity is scaled by the contour of the mounting groove. When the liquid metal is changed from the solid state to the liquid state, the volume of the liquid metal is increased, if the mounting cavity is arranged on the axis of the driver body during the initial arrangement, in the phase change process of the liquid metal from the solid state to the liquid state, the containment vessel may be subjected to unbalanced loads from the installation cavity due to volumetric expansion of the liquid metal, in order to avoid the phenomenon that the variable stiffness module deviates from the axis of the driver body under the driving of the unbalanced load, the invention leaves a certain offset allowance during the initial arrangement of the installation cavity, namely, the center of the opening end of the mounting groove is positioned on the axis of the driver body, the axis of the mounting groove is obliquely arranged with the axis of the driver body, when the liquid metal is changed from the solid state to the liquid state, along with the increase of the volume of the liquid metal, the axis of the mounting cavity gradually draws close to the axis of the driver body, so that the uniform load bearing of each position of the three-degree-of-freedom time-varying rigidity adjusting module can be ensured.

Preferably, the driver body comprises a packaging part and a first packaging layer, a tension spring is wound on the outer peripheral surface of the columnar packaging part and positioned between the packaging part and the annular columnar first packaging layer, and the variable stiffness module, the air cavity and the air pipe are all arranged on the packaging part. According to the invention, the arrangement of the tension springs on the surface of the packaging part can limit the expansion trend of the air cavity, so that the condition that the deformation of the air cavity exceeds the elastic recovery upper limit of the material to cause the driver to be scrapped is avoided, and the tension springs allowing axial stretching can realize the conversion of the radial expansion force of the air cavity towards the axial stretching force, so that the three-degree-of-freedom motion capability is realized in an auxiliary.

Preferably, the heating member is a resistance wire, the resistance wire is wound on the circumferential surface of the mounting cavity in a spiral mode, the resistance wire is embedded in the protective shell, and the resistance wire is connected with a power supply arranged outside the driver body through a lead.

Preferably, the number of the air cavities is three, the air cavities are arranged along the circumferential direction of the mounting groove at equal included angles, the number of the air pipes is equal to that of the air cavities, and the air pipes are communicated with the air cavities one by one correspondingly. When the two air cavities are introduced with the same air pressure and the other air cavity is introduced with an air source with different pressure, the flexible driver is forced to do pure bending motion towards one side of the cavity with small relative elongation (the air pressure of the air cavities is low) due to the length difference and the constraint of the air cavities; when air sources with different pressures are introduced into the three air chambers, the flexible driver can generate deflection and bending movement and deflect around one side of the air chamber with small relative elongation (low air pressure of the inner chamber).

Preferably, the driver body is cast and molded by a mixed material of platinum-catalyzed silicone rubber and graphene. The pouring silica gel of the driver body is mixed with graphene, so that the heat conduction function is enhanced, the rigidity-variable module can dissipate heat more quickly, and the quick response of liquid metal liquid-solid phase change is realized.

Preferably, the tension spring is made of 304 stainless steel.

Preferably, the air pipe is made of a PU pipe, and a silica gel adhesive for sealing is filled between the air pipe and the driver body.

Preferably, the protective shell is made of platinum catalyzed silicone rubber. The platinum-catalyzed silicone rubber is very soft after being cured, has good tensile tearing resistance, good elasticity and elongation, can be stretched by multiple times without tearing, and can rebound to the original size without deformation, and the platinum-catalyzed silicone rubber can ensure that the protective shell can still reset to the original shape after being deformed for multiple times, so that the durability of the protective shell is improved, and the service life of the protective shell is prolonged; in addition, the platinum-catalyzed hyperelastic silica gel is adopted to reduce the driving air pressure and improve the utilization rate of energy.

A preparation method of the three-degree-of-freedom pneumatic flexible driver with variable rigidity comprises the following steps:

(1) preparing a variable stiffness module: spirally winding a resistance wire on the surface of solid liquid metal, connecting one end of the resistance wire with one end of a lead, putting the liquid metal wound with the resistance wire into a mold, extending the other end of the lead to the outside of the mold, performing surface pouring and packaging on the liquid metal by using platinum catalytic silicone rubber, and standing and cooling a poured and molded variable-stiffness module;

(2) preparing a packaging piece: placing the cooled variable stiffness module in a mold, pouring the packaging part by using a graphene and platinum catalytic silicone rubber mixed material, ensuring that the three air cavities are arranged at equal included angles along the circumferential direction of the variable stiffness module in the pouring process, and standing and cooling the poured packaging part;

(3) preparing a driver body: the surface of the cooled packaging part is wound with a tension spring, the packaging part wound with the tension spring is subjected to secondary pouring by using a graphene and platinum catalytic silicone rubber mixed material, after the first packaging layer is cooled and fixedly connected with the packaging part, one end of an air pipe is inserted into the packaging part, the air pipe and the air cavity are ensured to be correspondingly communicated one by one, the other end of the air pipe extends to the outside of the packaging part, and then a silicone adhesive is filled between the air pipe and the packaging part for sealing.

In conclusion, the invention has the following beneficial effects: (1) the driver can realize the rigidity change of the driver according to the environmental condition, and the rigidity change can realize quick response; (2) the driver has three-degree-of-freedom movement capability, meets the requirements of bionic design, and can provide effective driver guarantee for the development of a subsequent flexible robot; (3) the rigidity change control of the driver is realized through the solid-liquid phase change characteristic of the liquid metal, and the rigidity of the pneumatic flexible driver is greatly improved; (4) the graphene is mixed with the pouring silica gel of the driver body, so that the heat conduction function is enhanced, the rigidity-variable module can dissipate heat more quickly, and liquid-solid phase change is realized; (5) the flexible driver adopts platinum-catalyzed hyperelastic silica gel to reduce the driving air pressure, thereby improving the utilization rate of energy.

Drawings

Fig. 1 is an isometric view of the present invention.

Fig. 2 is a cross-sectional view of the present invention.

Fig. 3 is a cross-sectional view of a variable stiffness module of the present invention.

In the figure:

the device comprises a mounting groove 1, a variable stiffness module 2, liquid metal 3, a protective shell 4, a heating element 5, an air cavity 6, an air pipe 7, a mounting cavity 8, a packaging part 9, a first packaging layer 10, a tension spring 11 and a lead 12.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience of description and for simplicity of description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Example (b):

as shown in fig. 1 to 3, a variable-rigidity three-degree-of-freedom pneumatic flexible driver comprises a driver body, wherein one end of the driver body is provided with a mounting groove 1 arranged along the length direction of the driver body, a variable-rigidity module 2 is embedded in the mounting groove and comprises liquid metal 3, a protective shell 4 and a heating element 5, the liquid metal is packaged in the protective shell, a plurality of air cavities 6 are formed in the driver body and arranged along the length direction of the driver body, one end of an air pipe 7 inserted in the driver body is communicated with the air cavities, and the other end of the air pipe extends to the outside of the driver body; the axis of the mounting groove and the axis of the driver body are obliquely arranged, the center of the opening end of the mounting groove is positioned on the axis of the driver body, a mounting cavity 8 for filling liquid metal is arranged in the protective shell, and the contour of the mounting cavity is formed by scaling the contour of the mounting groove; the driver body comprises a packaging part 9 and a first packaging layer 10, a tension spring 11 is wound on the outer peripheral surface of the columnar packaging part and is positioned between the packaging part and the annular columnar first packaging layer, and the variable stiffness module, the air cavity and the air pipe are all arranged on the packaging part; the heating element is a resistance wire, the resistance wire is spirally wound on the circumferential surface of the mounting cavity, the resistance wire is embedded in the protective shell, and the resistance wire is connected with a power supply arranged outside the driver body through a lead 12; the number of the air cavities is three, the air cavities are arranged along the circumferential direction of the mounting groove at equal included angles, the number of the air pipes is equal to that of the air cavities, and the air pipes are communicated with the air cavities one by one correspondingly; the driver body is formed by casting a mixed material of platinum catalytic silicone rubber and graphene; the tension spring is made of 304 stainless steel; the air pipe is made of a PU pipe, and a silica gel adhesive used for sealing is filled between the air pipe and the driver body; the protective shell is made of platinum-catalyzed silicone rubber.

A three-degree-of-freedom flexible driver with variable rigidity comprises a variable rigidity module and a driver body, wherein the variable rigidity module comprises liquid metal, platinum-catalyzed silicon rubber, a resistance wire and a lead, the liquid metal is arranged in a cavity made of the platinum-catalyzed silicon rubber, the resistance wire is wound on the surface of the cavity in a spiral mode, the resistance wire is electrified through the lead, the resistance wire is subjected to surface pouring and packaging through the platinum-catalyzed silicon rubber after being wound, the cavity made of the liquid metal is sealed, three air cavities are formed in the driver body and are uniformly distributed at 120 degrees, the driver body pouring material adopts the platinum-catalyzed silicon rubber mixed with graphene, pouring is divided into two times, the variable rigidity module is placed in a central area during first pouring and is manufactured together with the three air cavities, and during second pouring, firstly, a tension spring is wound on the surface of a silica gel body which is poured for the first time, then pouring is carried out, and finally, an air pipe is inserted and sealed and fixed by using a silica gel adhesive. The variable stiffness module has the main task of realizing the stiffness change of the driver in the motion process so as to improve the bearing capacity of the driver, and has the principle that liquid metal is solid under the condition of normal temperature, when the driver needs to move, a resistance wire wound on the surface of a liquid metal cavity is electrified through a lead to heat a resistor, so that the temperature inside the liquid metal cavity is higher than the normal temperature, the liquid metal can be converted into liquid, the driver can be driven by compressed gas, the extension, bending and torsion of the driver can be realized by controlling the air pressure in three air cavities and impelling the air cavities to axially deform by means of the radial constraint of a tension spring, when the driver reaches a target position and needs to bear the load, the power supply of the resistance wire can be immediately cut off to cool the driver, and because the graphene is mixed in silica gel poured on the driver body, the heat conduction speed is greatly improved compared with common silica gel, thereby promoting the liquid metal to solidify more quickly and improving the rigidity of the driver.

As shown in fig. 2, a first packaging layer is arranged outside the dotted line, a packaging part is arranged inside the dotted line, the first packaging layer is obtained by secondary pouring molding on the basis of the packaging part, a tension spring is arranged between the first packaging layer and the packaging part, the packaging part is columnar, a mounting groove is formed in the right end surface of the packaging part, the mounting groove is arranged from right to left, the mounting groove is arranged in a left-low-right-high manner, the axis of the mounting groove is inclined with the axis of the packaging part, a variable stiffness module is embedded in the mounting groove and comprises a protective shell with the outline consistent with the inner outline of the mounting groove, a mounting cavity for filling liquid metal is arranged inside the protective shell, the outline of the mounting cavity is formed by scaling the outline of the mounting groove, a resistance wire spirally wound along the length direction of the liquid metal is arranged inside the protective shell, the right end of the resistance wire is connected with, in this embodiment, the inside three air cavities that are equipped with of packaging part, the direction of arranging of air cavity is parallel with the axis of packaging part, and the air cavity passes through the trachea with external environment and communicates, and the trachea is horizontal pegs graft in the packaging part, and tracheal left end communicates with the air cavity, and tracheal right-hand member extends to the outside of packaging part, and three air cavities are laid along the equal contained angles of the circumference of variable stiffness module, and the contained angle between two adjacent air cavities is 120.

The preparation process of the three-degree-of-freedom pneumatic flexible driver with variable rigidity comprises the following steps:

(1) preparing a variable stiffness module: firstly, injecting a certain amount of platinum catalytic silicone rubber into a mold, pouring a solid part at the left end of the protective shell in the figure 3, spirally winding a resistance wire on the surface of liquid metal in a solid state, connecting one end of the resistance wire with one end of a lead, after the solid part of the protective shell in the mold is cooled, putting the liquid metal wound with the resistance wire into the mold, extending the other end of the lead to the outside of the mold, performing surface pouring and packaging on the liquid metal by using the platinum catalytic silicone rubber, standing and cooling a poured variable-stiffness module, and demolding after cooling to obtain the variable-stiffness module;

(2) preparing a packaging piece: pouring a certain amount of graphene and platinum catalytic silicone rubber mixed material into a mold, pouring a solid part at the left end of the package in the graph 2, after the solid part of the package in the mold is cooled, obliquely placing the variable stiffness module obtained in the step (1) into the mold, ensuring that the upper end of the variable stiffness module is concentric with the open end of the mold, deviating the lower end of the variable stiffness module from the axis of the mold, arranging a mold core for preparing an air cavity in the circumferential direction of the variable stiffness module at equal included angles, heating the preparation material of the mold core to be in a liquid state, wherein the melting point of the mold core is far lower than that of the preparation material of the package, performing secondary pouring on the package by using the graphene and platinum catalytic silicone rubber mixed material, after the package is cooled, inserting one end of an air pipe into the package to ensure that the air pipe is communicated with the air cavity one by one correspondingly, extending the other end of, after the liquefied core is led out, a silica gel adhesive is filled between the air pipe and the packaging part for sealing, and then the packaging part is demoulded;

(3) preparing a driver body: and winding a tension spring on the surface of the packaging part, placing the packaging part wound with the tension spring into a mold, pouring the packaging part wound with the tension spring by using a graphene and platinum catalytic silicone rubber mixed material, and demolding after the first packaging layer is cooled and fixedly connected with the packaging part.

Claims (10)

1. The utility model provides a pneumatic flexible drive of variable rigidity three degrees of freedom, includes the driver body, its characterized in that, the one end of driver body is equipped with the mounting groove of arranging along its length direction, inlays in the mounting groove and is equipped with the variable rigidity module, and the variable rigidity module includes liquid metal, protecting crust and heating member, and the liquid metal encapsulation is inside the protecting crust, and a plurality of air cavity has been seted up to driver body inside, and the air cavity is arranged along the length direction of driver body, insert the tracheal one end of establishing on the driver body with the air cavity intercommunication, the tracheal other end extends to the driver body outside.

2. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 1 is characterized in that the axis of the mounting groove is obliquely arranged with the axis of the driver body, the center of the opening end of the mounting groove is on the axis of the driver body, a mounting cavity for filling liquid metal is arranged inside the protective shell, and the contour of the mounting cavity is scaled by the contour of the mounting groove.

3. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 1 is characterized in that the driver body comprises a packaging part and a first packaging layer, a tension spring is wound on the outer peripheral surface of the columnar packaging part and positioned between the packaging part and the annular columnar first packaging layer, and the variable rigidity module, the air cavity and the air pipe are all arranged on the packaging part.

4. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 2 is characterized in that the heating element is a resistance wire, the resistance wire is spirally wound on the peripheral surface of the mounting cavity, the resistance wire is embedded in the protective shell, and the resistance wire is connected with a power supply arranged outside the driver body through a lead.

5. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 1 is characterized in that the number of the air chambers is three, the air chambers are arranged along the circumferential direction of the mounting groove at equal included angles, the number of the air pipes is equal to that of the air chambers, and the air pipes are communicated with the air chambers one by one correspondingly.

6. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 1 is characterized in that the driver body is formed by casting a mixed material of platinum-catalyzed silicone rubber and graphene.

7. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 3 is characterized in that the tension spring is made of 304 stainless steel.

8. The three-degree-of-freedom pneumatic flexible driver with variable rigidity according to claim 1 is characterized in that the air pipe is made of a PU pipe, and a silica gel adhesive for sealing is filled between the air pipe and the driver body.

9. The three-degree-of-freedom pneumatic flexible actuator with variable rigidity according to claim 1, wherein the protective shell is made of platinum-catalyzed silicone rubber.

10. A method for preparing a variable-rigidity three-degree-of-freedom pneumatic flexible actuator by using any one of claims 1 to 9, which is characterized by comprising the following steps of:

(1) preparing a variable stiffness module: spirally winding a resistance wire on the surface of solid liquid metal, connecting one end of the resistance wire with one end of a lead, putting the liquid metal wound with the resistance wire into a mold, extending the other end of the lead to the outside of the mold, performing surface pouring and packaging on the liquid metal by using platinum catalytic silicone rubber, and standing and cooling a poured and molded variable-stiffness module;

(2) preparing a packaging piece: placing the cooled variable stiffness module in a mold, pouring the packaging part by using a graphene and platinum catalytic silicone rubber mixed material, ensuring that the three air cavities are arranged at equal included angles along the circumferential direction of the variable stiffness module in the pouring process, and standing and cooling the poured packaging part;

(3) preparing a driver body: the surface of the cooled packaging part is wound with a tension spring, the packaging part wound with the tension spring is subjected to secondary pouring by using a graphene and platinum catalytic silicone rubber mixed material, after the first packaging layer is cooled and fixedly connected with the packaging part, one end of an air pipe is inserted into the packaging part, the air pipe and the air cavity are ensured to be correspondingly communicated one by one, the other end of the air pipe extends to the outside of the packaging part, and then a silicone adhesive is filled between the air pipe and the packaging part for sealing.

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