A flexible robotic arm with real-time controllable stiffness based on shape memory alloy

Abstract

This invention discloses a flexible robotic arm with real-time adjustable stiffness based on shape memory alloy, comprising a fixed plate, pneumatic actuators, and an adjustable stiffness limiting layer; multiple pneumatic actuators are connected between two fixed plates; the multiple pneumatic actuators are arranged circumferentially, and each pneumatic actuator is provided with an adjustable stiffness limiting layer; the adjustable stiffness limiting layer includes a flexible substrate and a deformation unit disposed on the flexible substrate; the deformation unit includes a fluid channel and a shape memory alloy; the fluid channel is filled with liquid metal; the shape memory alloy is connected to two fluid channels, and the shape memory alloy is in contact with the liquid metal in the two fluid channels; the flexible robotic arm is used to control the energization state of the liquid metal, and thereby control the shape memory alloy to deform and increase stiffness; this invention solves the problem of insufficient structural stiffness of soft robots or excessive contact stiffness after excessive stiffness of the structure, and realizes real-time adjustment of local stiffness.

Description

Technical Field

[0001] This invention relates to the technical field of robotic arms, and in particular to a flexible robotic arm based on shape memory alloy with real-time adjustable stiffness. Background Technology

[0002] The space station is currently a crucial arena for space technology competition among nations. In recent years, space station development has exhibited characteristics such as larger structures, more complex functions, and more diversified missions. These characteristics inevitably increase the workload for astronauts inside the space station. To assist astronauts in completing repetitive tasks and adapt to the long-term unmanned operation of the space station, intravehicular robots are widely used. Currently, most existing intravehicular robots are equipped with traditional rigid robotic arms. However, the traditional rigid design of these arms results in limited adaptability, making safe interaction with humans impossible and unable to adapt to the confined environment of the space station, hindering effective work within the space station. Flexible robotic arms with continuously deformable structures, on the other hand, demonstrate unprecedented adaptability and agility, serving the confined spaces within the space station and providing astronauts with a more comfortable living and working environment. However, due to the softness of the manufacturing materials, soft robotic arms are prone to insufficient load-bearing capacity.

[0003] To address these issues, stiffness control strategies have been proposed. For example, using dielectric elastomers to improve load capacity presents the problem of high voltage requirements for actuation, leading to susceptibility to electrical breakdown and compromised interaction safety. Combining elastic materials with low-melting-point alloys overcomes the high-voltage challenge, but the mechanical properties of the low-melting-point alloys may change due to reactions with encapsulation materials, resulting in reduced encapsulation quality and potential material infiltration. Shape memory polymers require low-voltage actuation and are difficult to leak, but prolonged exposure to the external environment can lead to fatigue and irreversible plastic deformation. Using particle blocking for stiffness control improves the structural stiffness of the robotic arm, but also increases surface stiffness, which still fails to meet the requirements for compliant interaction within the space station.

[0004] The complex environment inside a space station places more precise demands on the stiffness control of flexible robotic arms. For example, Chinese Patent Publication No. CN116038679A discloses a flexible robotic arm based on the coupling of shape memory alloy and pneumatic artificial muscle. This method can only adjust the axial stiffness using the shape memory alloy as the central rod, making it difficult to work effectively inside a space station. Therefore, to meet the operational requirements inside a space station, it is urgent to develop a flexible robotic arm that can continuously and flexibly adjust its stiffness, ensuring that the structural stiffness meets load requirements while maintaining its original compliant interaction capabilities. Summary of the Invention

[0005] The purpose of this invention is to provide a flexible robotic arm with real-time adjustable stiffness based on shape memory alloy. By solving the problems of insufficient structural stiffness of the flexible arm under specific conditions or excessive contact stiffness after the lifting structure has been over-stiffened, the invention achieves real-time local stiffness adjustment of the flexible arm, thereby improving the environmental adaptability and flexibility of the flexible arm to adapt to the working environment inside the space station.

[0006] To address the aforementioned technical problems, this invention provides a flexible robotic arm with real-time adjustable stiffness based on shape memory alloy, comprising a fixed plate, pneumatic actuators, and an adjustable stiffness limiting layer; multiple pneumatic actuators are connected between two fixed plates; the multiple pneumatic actuators are arranged circumferentially, and each of the multiple pneumatic actuators is provided with the adjustable stiffness limiting layer; the adjustable stiffness limiting layer includes a flexible substrate and a deformation unit disposed on the flexible substrate; the deformation unit includes a fluid channel and a shape memory alloy; the fluid channel is filled with liquid metal; the shape memory alloy is connected to two fluid channels, and the shape memory alloy is in contact with the liquid metal in the two fluid channels; the flexible robotic arm is used to control the energization state of the liquid metal, and thereby control the shape memory alloy to deform and increase stiffness.

[0007] In one embodiment, the shape memory alloy is arranged laterally relative to the axis of the flexible robotic arm.

[0008] In one embodiment, the shape memory alloy is arranged in the same direction as the axial direction of the flexible robotic arm.

[0009] In one embodiment, within one deformation unit, multiple shape memory alloys are arranged in parallel and separate manner, with a transverse flow channel connecting adjacent shape memory alloys. The transverse flow channel is filled with liquid metal that contacts the shape memory alloy.

[0010] In one embodiment, the shape memory alloy is in the form of a ring.

[0011] In one embodiment, the flexible substrate is provided with a plurality of deformation units, which are arranged separately along the axial direction of the flexible robotic arm.

[0012] In one embodiment, the two fluid channels of the plurality of deformation units are respectively located on both sides of the flexible substrate along its length.

[0013] In one embodiment, the fluid channel is connected to a conductive contact located at the end of the pneumatic actuator.

[0014] In one embodiment, the air inlet of the pneumatic actuator and the conductive contact are both located at the same end of the flexible robotic arm, and the flexible robotic arm has a base at this end, which is connected to the fixed plate and fixedly connected to the adjustable stiffness limiting layer.

[0015] In one embodiment, there are two or more fixing plates, and multiple pneumatic actuators are fixed to multiple fixing plates.

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

[0017] This invention is a flexible robotic arm with real-time adjustable stiffness based on shape memory alloy. By organically integrating shape memory alloy with the flexible robotic arm and designing a flexible circuit layout with adjustable stiffness limiting layer, it solves the problem of insufficient structural stiffness of soft robots under specific conditions or excessive contact stiffness after the structural stiffness is increased, and realizes real-time local stiffness control of the flexible arm. Attached Figure Description

[0018] To more clearly illustrate the technical solution of the present invention, 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.

[0019] Figure 1 This is a schematic diagram of the structure provided in the first embodiment of the present invention;

[0020] Figure 2 yes Figure 1 A schematic diagram of the fixed plate structure;

[0021] Figure 3 yes Figure 1 A schematic diagram of the structure of a pneumatic actuator;

[0022] Figure 4 yes Figure 3 A cross-sectional view of a pneumatic actuator;

[0023] Figure 5 yes Figure 3 Schematic diagram of the adjustable stiffness confinement layer structure;

[0024] Figure 6 yes Figure 1 A schematic diagram of the base structure;

[0025] Figure 7 This is a structural schematic diagram provided in the second embodiment of the present invention;

[0026] Figure 8This is a structural schematic diagram provided in the third embodiment of the present invention.

[0027] The attached figures are labeled as follows:

[0028] 10. Fixing plate; 11. Through-hole structure; 12. Locking position;

[0029] 20. Pneumatic actuator; 21. Air chamber; 22. Air passage;

[0030] 30. Adjustable stiffness limiting layer; 31. Flexible substrate; 32. Deformation unit; 321. Fluid channel; 322. Shape memory alloy; 323. Lateral flow channel; 324. Conductive contact;

[0031] 40. Base. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0033] This invention provides a flexible robotic arm with real-time adjustable stiffness based on shape memory alloy, and its implementation is as follows: Figure 1 and Figure 3 As shown, it includes a fixed plate 10, a pneumatic actuator 20, and an adjustable stiffness limiting layer 30.

[0034] Regarding the fixing plate 10, it is mainly used to install and fix various components, such as... Figure 1 and Figure 2 As shown, the fixing plate 10 in this embodiment is roughly disc-shaped. Two fixing plates 10 are respectively disposed on the upper and lower parts of the flexible robotic arm. The two fixing plates 10 are arranged opposite to each other, and multiple pneumatic actuators 20 are connected between the two fixing plates 10.

[0035] While two fixing plates 10 can be used to fix the flexible robotic arm at both ends, the support strength of the middle section of the flexible robotic arm may be insufficient when the overall length of the flexible robotic arm is long. Therefore, it is advisable to set two or more fixing plates 10 so that multiple pneumatic actuators 20 can be fixed on multiple fixing plates 10.

[0036] like Figure 1 and Figure 2 As shown, there are a total of four fixing plates 10 in this embodiment. Two fixing plates 10 are located at both ends of the flexible robotic arm, and the other two fixing plates 10 are located in the middle of the flexible robotic arm. The four fixing plates 10 are distributed at equal intervals to ensure better support and fixation effect for all parts of the flexible robotic arm.

[0037] In order to fix the pneumatic actuator 20 using the fixing plate 10, this embodiment has a large through hole structure 11 in the middle of the fixing plate 10, and a slot 12 matching the number and shape of the pneumatic actuator 20 is provided on the periphery of the through hole structure 11, so that multiple pneumatic actuators 20 can be inserted into multiple slots 12 respectively for installation and fixation.

[0038] Regarding the pneumatic actuator 20, it utilizes the filling and extraction of gas to achieve swing control of the flexible robotic arm, for example, from... Figure 1 , Figure 3 and Figure 4 As shown, this embodiment is provided with multiple pneumatic actuators 20 arranged in a circumferential manner. Each pneumatic actuator 20 is made of flexible material with multiple air chambers 21. The internal air passages 22 are connected to the multiple air chambers 21. Therefore, when the different inflation states of the multiple pneumatic actuators 20 are controlled in coordination, different swing control of the flexible robotic arm can be achieved.

[0039] The pneumatic control principle described above has been applied in existing robotic arms. However, in this embodiment, multiple pneumatic actuators 20 are provided with adjustable stiffness limiting layers 30. Since the adjustable stiffness limiting layers 30 can adjust and control the stiffness, the stiffness of the corresponding pneumatic actuator 20 can be adjusted in real time as needed to meet the usage requirements of different application scenarios.

[0040] Regarding the adjustable stiffness limiting layer 30, its function is to change the stiffness of the flexible robotic arm. Therefore, to achieve this purpose, this embodiment employs... Figure 4 and Figure 5 The structure shown here includes an adjustable stiffness limiting layer 30 comprising a flexible substrate 31 and a deformation unit 32 disposed on the flexible substrate 31. The flexible substrate 31 is generally a rectangular plate structure, and the deformation unit 32 is embedded within the flexible substrate 31. The deformation unit 32 includes a fluid channel 321 and a shape memory alloy 322. The fluid channel 321 is filled with liquid metal. The shape memory alloy 322 is connected to two fluid channels 321 and is in contact with the liquid metal in the two fluid channels 321, thereby enabling the flexible robotic arm to control the energization state of the liquid metal and thereby control the shape memory alloy 322 to deform and increase stiffness.

[0041] Different choices of the shape and arrangement of the shape memory alloy 322 will result in different stiffness adjustments; for example, in this embodiment, the extension direction of the shape memory alloy 322 is aligned with the axial direction of the flexible robotic arm. Figure 5In the direction shown, the shape memory alloy 322 is arranged in a vertically extending manner. If the flexible robotic arm is energized to the liquid metal, the shape memory alloy 322 can be triggered to deform, thereby increasing the axial bending stiffness of the flexible robotic arm.

[0042] Furthermore, to ensure consistent stiffness changes across the lateral direction of the flexible robotic arm, multiple shape memory alloys 322 can be arranged in parallel and separate within a deformation unit 32, with lateral flow channels 323 connecting adjacent shape memory alloys 322. This allows the liquid metal filled in the lateral flow channels 323 to contact the shape memory alloys 322, thereby enabling the multiple shape memory alloys 322 to change synchronously and improve the axial bending stiffness of the flexible robotic arm.

[0043] For example, in this embodiment, the following is adopted: Figure 5 In the structure shown, there are two shape memory alloys 322. The upper ends of the two shape memory alloys 322 are connected to a fluid channel 321 and are in contact with the liquid metal in the fluid channel 321. The lower ends of the two shape memory alloys 322 are also connected by a transverse flow channel 323. When the liquid metal in the transverse flow channel 323 is in contact with the lower ends of the two shape memory alloys 322, the two shape memory alloys 322 are electrically connected, ensuring that the flexible robotic arm can apply electrical excitation to the two shape memory alloys 322 at the same time, thereby increasing the stiffness of the two shape memory alloys 322.

[0044] Similarly, in order to ensure that the stiffness of the flexible robotic arm varies uniformly along its axial direction, it is also possible to provide multiple deformation units 32 on the flexible substrate 31. The multiple deformation units 32 are arranged separately along the axial direction of the flexible robotic arm. In this case, the two fluid channels 321 of the multiple deformation units 32 can be respectively located on both sides of the length direction of the flexible substrate 31.

[0045] Specifically, such as Figure 4 and Figure 5 As shown, each adjustable stiffness limiting layer 30 is provided with three deformation units 32, which are arranged at equal intervals from top to bottom. In each deformation unit 32, there are two fluid channels 321 arranged vertically on the left and right sides. The two fluid channels 321 of the middle deformation unit 32 are placed outside the two fluid channels 321 of the upper deformation unit 32, and the two fluid channels 321 of the lower deformation unit 32 are placed outside the two fluid channels 321 of the middle deformation unit 32, which are arranged in a progressive manner to make reasonable use of the space of the adjustable stiffness limiting layer 30 to realize the simultaneous setting of multiple deformation units 32.

[0046] With this setup, if you only want to increase the stiffness of the upper part of the flexible robotic arm, you can apply electrical excitation to the upper deformation unit 32. Similarly, if you want to increase the stiffness of the middle and lower parts of the flexible robotic arm, you can apply electrical excitation to the middle deformation unit 32 and the lower deformation unit 32 respectively. This makes the stiffness adjustment of the flexible robotic arm more diversified and can meet the needs of more different usage scenarios.

[0047] It should also be noted that, in order to facilitate the application of electrical excitation to the shape memory alloy 322, such as Figure 4 and Figure 5 As shown, in this embodiment, the fluid channel 321 is connected to a conductive contact 324. The conductive contact 324 is located at the end of the pneumatic actuator 20. Therefore, when an electrical excitation is applied to the conductive contact 324, the shape memory alloy 322 can be deformed to increase the stiffness.

[0048] Moreover, as Figure 1 , Figure 4 , Figure 5 and Figure 6 As shown, in this embodiment, the air inlet end of the pneumatic actuator 20 and the conductive contact 324 are both located at the same end of the flexible robotic arm, and the flexible robotic arm is provided with a base 40 at this end. The base 40 is connected to the fixed plate 10 and is connected and fixed to the adjustable stiffness limiting layer 30.

[0049] The base 40 is used to connect and fix the components, and the various corresponding interfaces are placed in a unified position. It is also convenient to use the base 40 to set the corresponding holes and interfaces for connection.

[0050] The second embodiment of the present invention is substantially the same as the first embodiment, such as... Figure 7 As shown, the difference is that the shape memory alloy 322 in this embodiment is arranged laterally relative to the axis of the flexible robotic arm. If the flexible robotic arm is energized to the liquid metal, the shape memory alloy 322 can be triggered to deform, thereby increasing the horizontal bending stiffness of the flexible robotic arm.

[0051] The third embodiment of the present invention is substantially the same as the second embodiment, such as... Figure 8 As shown, the difference is that the shape memory alloy 322 in this embodiment is ring-shaped. If the flexible robotic arm is energized to the liquid metal, the shape memory alloy 322 can be triggered to deform, thereby increasing the omnidirectional bending stiffness of the flexible robotic arm.

[0052] As can be seen from the above embodiments, there are no special restrictions on the arrangement position and shape setting of the shape memory alloy 322. Technicians can choose according to actual usage needs. It can be set with a uniform shape as in the above embodiments, or various shapes can be combined with each other, or it can be arranged obliquely, or arranged in other special positions. The specific determination can be made according to actual needs.

[0053] In summary, the flexible robotic arm of the present invention has at least the following characteristics:

[0054] 1. When customized adjustment of the local stiffness of the flexible robotic arm is required, the shape pattern of the shape memory alloy 322 in the adjustable stiffness limiting layer 30 can be changed to achieve the effect of local stiffness adjustment. For example, embedding the longitudinal shape memory alloy 322 can improve the axial bending stiffness, embedding the transverse shape memory alloy 322 can improve the horizontal bending stiffness, and embedding the circular shape memory alloy 322 can improve the omnidirectional bending stiffness. When it is necessary to increase the local stiffness, simply apply electrical excitation to the corresponding position to achieve the stiffness increase, thereby improving the local load capacity of the flexible robotic arm.

[0055] 2. When the actuator at the front end of the flexible robotic arm performs a grasping task, corresponding operations are performed for different loads on the grasped object. For low-mass grasped objects, only the pneumatic actuator 20 can be fluid-driven; for large-load grasped objects, while fluid-driven, the shape memory alloy 322 inside the adjustable stiffness limiting layer 30, which is customized or programmed according to the local stiffness control requirements, is electrically heated. The shape memory alloy 322 undergoes a phase change due to heat, thereby achieving stiffness control and improving the load-bearing capacity of the flexible robotic arm.

[0056] 3. When the flexible robotic arm performs operational tasks, especially when the fluid-driven flexible robotic arm performs tasks in an embracing posture, the stiffness can be adjusted using shape memory alloy 322 while the flexible robotic arm can maintain the original compliant interaction capability of the silicone substrate. The flexible robotic arm can adapt to the shape of the embracing object. By adjusting the stiffness to change the local curvature, the interaction characteristics of the flexible robotic arm can be improved, enabling it to have a contact area with embracing objects of any shape, increasing the friction between the flexible robotic arm and the embracing object, and improving the gripping ability of the flexible robotic arm.

[0057] 4. When the flexible robotic arm enters an irregular, narrow pipe to perform a detection task, the air drive pipe required by the subsequent flexible robotic arm can be connected through the circular through hole provided in the flexible robotic arm base 40, so as to complete the series connection of the flexible robotic arms and realize the extension of the flexible arm.

[0058] Furthermore, for irregular situations in narrow pipes, a flexible robotic arm can be driven solely by fluid at pipe bends to adapt to the pipe's curvature; while for straight pipes, the local stiffness can be adjusted to prevent bending, thus ensuring the smooth passage of the flexible arm.

[0059] Furthermore, according to the stiffness control requirements, different sections of shape memory alloy 322 are connected to different branches to ensure that the different sections of shape memory alloy 322 do not interfere with each other, so that the flexible robotic arm can better adapt to the irregular situation of narrow pipes.

[0060] 5. When the flexible robotic arm performs operations inside the space station cabin, the complex environment inside the cabin places more precise requirements on the stiffness control of the flexible robotic arm. The shape memory alloy 322 in the adjustable stiffness limiting layer 30 can be customized or programmed according to the local stiffness control requirements. Combined with the transverse, longitudinal and circular arrangement of the shape memory alloy 322, axial stiffness, horizontal stiffness and full-plane stiffness can be provided.

[0061] Furthermore, according to stiffness control requirements, multiple customized shape memory alloy 322 strands can be connected to different branches and different stiffness characteristics can be edited to achieve real-time control of local structural stiffness.

[0062] Furthermore, through diverse and modular stiffness programming local control methods, the flexible robotic arm can better adapt to the operational needs inside the space station cabin.

[0063] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A flexible robotic arm with real-time adjustable stiffness based on shape memory alloy, characterized in that, Includes a fixed plate, a pneumatic actuator, and an adjustable stiffness limiting layer; Multiple pneumatic actuators are connected between the two fixed plates; The pneumatic actuators are arranged circumferentially, and each of the pneumatic actuators is provided with an adjustable stiffness limiting layer; The adjustable stiffness limiting layer includes a flexible substrate and a deformation unit disposed on the flexible substrate; the deformation unit includes a fluid channel and a shape memory alloy; the fluid channel is filled with liquid metal; the shape memory alloy is connected to two of the fluid channels, and the shape memory alloy is in contact with the liquid metal in the two fluid channels; The flexible robotic arm is used to control the energization state of the liquid metal, and thereby control the shape memory alloy to deform and improve its stiffness.

2. The flexible robotic arm according to claim 1, characterized in that, The shape memory alloy is arranged laterally relative to the axis of the flexible robotic arm.

3. The flexible robotic arm according to claim 1, characterized in that, The shape memory alloy is arranged in the same direction as the axial direction of the flexible robotic arm.

4. The flexible robotic arm according to claim 3, characterized in that, Within one of the deformation units, multiple shape memory alloys are arranged in parallel and separate, and a transverse flow channel is connected between adjacent shape memory alloys. The transverse flow channel is filled with liquid metal that contacts the shape memory alloy.

5. The flexible robotic arm according to claim 1, characterized in that, The shape memory alloy is in the form of a ring.

6. The flexible robotic arm according to claim 1, characterized in that, The flexible substrate is provided with a plurality of deformation units, which are arranged separately along the axial direction of the flexible robotic arm.

7. The flexible robotic arm according to claim 5, characterized in that, The two fluid channels of the plurality of deformation units are respectively located on both sides of the flexible substrate along its length.

8. The flexible robotic arm according to claim 1, characterized in that, The fluid channel is connected to a conductive contact, which is located at the end of the pneumatic actuator.

9. The flexible robotic arm according to claim 8, characterized in that, The air inlet of the pneumatic actuator and the conductive contact are both located at the same end of the flexible robotic arm, and the flexible robotic arm is provided with a base at this end. The base is connected to the fixed plate and is fixedly connected to the adjustable stiffness limiting layer.

10. The flexible robotic arm according to claim 1, characterized in that, There are two or more fixed plates, and multiple pneumatic actuators are fixed on multiple fixed plates.

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