Multi-curvature flexible manipulator based on segmented variable stiffness structure and preparation method thereof

Abstract

The present application relates to the technical field of soft robot, and discloses a multi-curvature flexible manipulator based on segmented variable stiffness structure, which comprises a pneumatic driving layer for realizing bending deformation and a variable stiffness unit for realizing stiffness adjustment, the variable stiffness unit is located at the lower part of the pneumatic driving layer, the pneumatic driving layer comprises an air pipe and a pneumatic grid actuator, the pneumatic grid actuator comprises a deformation layer and a bottom constraint layer, the deformation layer is provided with cavities, one end of the air pipe is communicated with the cavities, and the other end is communicated with an air pump; the variable stiffness layer comprises two variable stiffness units and a vacuum pipe, the variable stiffness unit comprises an upper layer of silica gel film, a group of scale elements, a group of connecting rods, a bottom plate and a lower layer of silica gel sheet, a group of supports are arranged on the surface of the rubber bottom plate, every two supports are connected with the scale elements through the connecting rods to form the main body structure of the variable stiffness unit, the variable stiffness unit is arranged in the upper layer of silica gel film and is packaged with the lower layer of silica gel sheet, one end of the vacuum pipe is communicated with the variable stiffness unit, and the other end is connected with a vacuum pump. The multi-curvature flexible manipulator designed in the present application adopts segmented variable stiffness units instead of traditional whole-layer variable stiffness structure, and the soft gripper is endowed with bending shape control ability, so that the multi-curvature flexible manipulator has good environmental interaction ability.

Description

Technical Field

[0001] This invention relates to the field of soft robot technology, specifically to a multi-curvature flexible manipulator based on a segmented variable stiffness structure and its fabrication method. Background Technology

[0002] While traditional rigid grippers offer superior performance in terms of precision and rigidity, precisely controlling and maintaining high stiffness, making them suitable for scenarios requiring precise manipulation, they lag behind in terms of operational complexity and environmental interaction, particularly in unstructured environments, where this becomes a significant disadvantage. To overcome these limitations, especially from the perspectives of adaptability and safety, soft robots have been rapidly developed. Through their unique soft structures, they offer more flexible and safer operational solutions in various fields, such as medical, military, and industrial applications. In particular, soft robots excel in grasping and manipulating tasks. By employing soft grippers, they can non-invasively and tightly grasp fragile objects or those with complex curved surfaces. This approach not only improves operational flexibility and safety but also demonstrates a high degree of interactivity with the manipulated object.

[0003] While soft robotics technology has made significant progress in recent years, particularly in flexible manipulation and interaction, existing pneumatic soft grippers still face some limitations in practical applications. Specifically, most of these grippers are designed primarily based on the ability to bend at a single curvature. This design limitation often makes it difficult to achieve ideal fit and conformation when attempting to precisely and safely grip objects of different sizes and shapes. Therefore, to be effective in a wider range of applications, additional technological support is necessary, such as the ability to achieve multi-curvature configurations. Multi-curvature configuration technology refers to the ability of a soft gripper to flexibly adapt to the specific shape and size of a target object through its segmented and controllable bending characteristics. This capability is crucial for improving the application range and performance of soft robots in the field of fine manipulation. Through this technology, the gripper can independently achieve different degrees of bending in different parts, thus achieving perfect conformation with objects of various shapes, significantly improving the flexibility and efficiency of grasping and manipulation.

[0004] In nature, numerous organisms demonstrate an astonishing ability to adjust the stiffness of their body structures to adapt to environmental changes and survival challenges. For example, a chameleon's tongue can rapidly increase stiffness and extend to precisely capture prey at the moment of attack; starfish can achieve stable attachment and efficient movement in changing environments by finely adjusting the stiffness of their tube feet; and spiders secrete silk with different stiffness properties to build webs that can withstand various environmental challenges. These are all vivid examples of variable stiffness structures in nature. Therefore, by studying the shape and mechanism of organisms in nature and designing biomimetic variable stiffness units, we can further broaden the types of variable stiffness technology, which has significant application value and scientific research significance. Summary of the Invention

[0005] To address the problems existing in the prior art, the main objective of this invention is to provide a multi-curvature flexible manipulator based on a segmented variable stiffness structure and its fabrication method. By combining a pneumatic actuator with a variable stiffness unit, the flexible manipulator possesses advantages such as adjustable local stiffness, strong environmental interactivity, and high load-bearing capacity.

[0006] The technical solution of the present invention is as follows:

[0007] A multi-curvature flexible manipulator based on a segmented variable stiffness structure includes a pneumatic drive layer for achieving bending deformation and a variable stiffness unit for achieving stiffness adjustment. The variable stiffness unit is located at the bottom of the pneumatic drive layer. The pneumatic drive layer includes an air tube and a pneumatic mesh actuator. The pneumatic mesh actuator includes a deformation layer and a bottom constraint layer. A cavity is provided on the deformation layer. One end of the air tube is connected to the cavity, and the other end is connected to an air pump. The variable stiffness layer includes two variable stiffness units and a vacuum tube. The variable stiffness unit includes an upper silicone film, a set of scale elements, a set of connecting rods, a base plate, and a lower silicone sheet. A set of supports is provided on the surface of the rubber base plate. Every two supports are connected to the scale elements through connecting rods to form the main structure of the variable stiffness unit, which is placed in the upper silicone film and encapsulated with the lower silicone sheet. One end of the vacuum tube is connected to the variable stiffness unit, and the other end is connected to the vacuum pump.

[0008] Furthermore, the cavity includes a main cavity and a wedge-shaped cavity disposed on top of the main cavity and connected to the main cavity. Adjacent cavities are connected by a transition wall, the wall thickness of which is greater than the wall thickness of the wedge-shaped cavity, and the wall thickness of the wedge-shaped cavity is greater than the wall thickness of the main cavity. The cavities are arranged in parallel at equal intervals along the length of the actuator. When the air pump inflates the pneumatic mesh actuator through the air pipe, the gas pressurizes the inner wall of the cavity of the pneumatic mesh actuator, and the cavity expands, causing the pneumatic mesh actuator to bend and deform.

[0009] Furthermore, the bottom of the inner cavity of the deformable layer does not contact the constraint layer to form an air passage.

[0010] Furthermore, the scale element is a black scale-shaped nylon element, the connecting rod is a white resin cylindrical slender rod, and the base plate is a black rectangular rubber part with multiple supports. When the closed cavity of the silicone film is not evacuated, the scales do not interact with each other, resulting in low stiffness. When the closed cavity of the silicone film is evacuated, the front teeth and rear grooves of the scales interact with each other to form a jamming structure, thereby achieving the transition between high and low stiffness.

[0011] Furthermore, the pneumatic drive layer is combined with two variable stiffness units. By selectively adjusting the stiffness state of the variable stiffness units, the local structural stiffness can be changed, giving the gripper multi-curvature characteristics.

[0012] The fabrication method of a multi-curvature flexible manipulator based on a segmented variable stiffness structure includes the following steps:

[0013] S1. According to the preset dimensions, use 3D printing technology to process mold 1 for preparing the deformable layer, mold 2 for preparing the bottom constraint layer, mold 3 for preparing the upper silicone mold, and mold 4 for preparing the lower silicone sheet.

[0014] S2. According to the preset dimensions, use 3D printing technology to process a set of scale elements, a set of connecting rods, a set of supports, and several rubber base plates to form the main structure of the variable stiffness unit.

[0015] S3. Pour the two silica gel solutions into a beaker, stir thoroughly with a glass rod, and then place it in a vacuum drying oven for vacuum treatment until no more bubbles emerge from the beaker. Then, slowly pour the solution into the molds 1, 2, 3 and 4 prepared in steps S1 and S2, up to the top of the molds. Place all the molds on a flat table for room temperature curing. After curing, remove the above products from the molds for later use.

[0016] S4. Apply silicone solution to the connection between the deformation layer and the bottom constraint layer for bonding to prepare the pneumatic mesh actuator. After application, cure the pneumatic actuator at room temperature.

[0017] S5. Assemble the scale elements with the supports on the rubber base plate using connecting rods to form the main structure of the variable stiffness unit. The scale elements can maintain relative rotation with the base plate. Place the main structure inside the upper silicone film and encapsulate it with the lower silicone sheet to form the variable stiffness unit.

[0018] S6. Perform an airtightness test on the pneumatic actuators and variable stiffness units that have been cured in S4 and S5. If there is a gas leak, use a glass rod to apply a small amount of silicone solution to the leak point for repair.

[0019] S7. Apply silicone solution to the connection between the pneumatic actuator and the variable stiffness unit for bonding. After curing at room temperature, the multi-curvature flexible manipulator to be prepared can be obtained.

[0020] Furthermore, in step S1, mold one and mold three are detachable molds, with rectangular teeth around them for assembly and disassembly to facilitate demolding. All molds are made of white photosensitive resin.

[0021] Furthermore, the silicone preparation process in step S2 is as follows:

[0022] Smooth-On's Slow A and B component silicone rubber has a volume ratio of 1:1; the thoroughly stirred silicone solution is placed under a negative pressure of -0.2MPa for 5 minutes until no more bubbles emerge from the beaker; the room temperature curing time is 8 hours.

[0023] Furthermore, the thickness of the upper silicone film and the lower silicone sheet in step S5 should not exceed 2mm; otherwise, when the variable stiffness unit enters the high stiffness state, it will generate initial curvature, affecting the gripper's ability to maintain a segmented, non-curvature state.

[0024] Furthermore, in step S5, the front teeth of the scale element are slightly larger than the rear groove to prevent jamming.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1) In this invention, the pneumatic drive layer is driven by a pneumatic mesh actuator with varying wall thickness. Compared with traditional rectangular pneumatic actuators with uniform wall thickness, it can achieve a larger bending angle and tip output force; at the same time, it has better negative curvature characteristics.

[0027] 2) Inspired by the variable stiffness structure of organisms, a snake scale-like variable stiffness unit was designed. The high and low stiffness states of the unit can be adjusted in real time by vacuuming, thus broadening the types of variable stiffness technology.

[0028] 3) The multi-curvature flexible manipulator designed in this invention adopts a segmented variable stiffness unit instead of the traditional whole-layer variable stiffness structure, which gives the soft gripper the ability to control the bending shape, thus giving it better environmental interaction capabilities. Attached Figure Description

[0029] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0030] Figure 2 This is a three-dimensional cross-sectional view of the pneumatic mesh actuator of the present invention;

[0031] Figure 3 This is a cross-sectional view of the cavity of the present invention;

[0032] Figure 4 This is a schematic diagram of the variable stiffness main structure of the present invention;

[0033] Figure 5This is a schematic diagram of the internal structure of the present invention;

[0034] In the diagram: 1. Pneumatic drive layer; 2. Variable stiffness unit; 3. Air tube; 4. Vacuum tube; 5. Bottom constraint layer; 6. Deformation layer; 7. Rubber base plate; 8. Connecting rod; 9. Scale element; 10. Pneumatic mesh actuator; 11. Upper silicone film; 12. Lower silicone sheet. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the scope described.

[0036] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. To provide the public with a better understanding of the invention, certain specific details are described in detail below.

[0037] Please see Figure 1-3 The multi-curvature flexible manipulator based on a segmented variable stiffness structure includes a pneumatic drive layer 1 and a variable stiffness unit 2. The pneumatic drive layer 1 is located on the upper layer and is used to achieve bending deformation, while the variable stiffness unit 2 is located on the lower layer and is used to adjust the stiffness of the local structure.

[0038] Specifically, the pneumatic drive layer 1 includes an air tube 3 and a pneumatic mesh actuator 10. The pneumatic mesh actuator 10 includes a deformable layer 6 and a bottom constraint layer 5. The deformable layer 6 is located above the bottom constraint layer 5 and has a set of cavities 601. There is a non-contact air passage 602 between the two. One end of the air tube 3 is connected to the cavity 601 through the air passage, and the other end is connected to the air pump.

[0039] The cavities 601 are arranged in parallel at equal intervals along the length of the deformable layer 6. Each cavity 601 includes a main cavity 605 and a wedge-shaped cavity 603 located on top of and connected to the main cavity 605. Adjacent cavities 601 are connected by a transition wall 604, which has the thickest wall, followed by the wedge-shaped cavity 603, and the thinnest wall of the main cavity 605. The wedge-shaped cavity 603 has a wedge-shaped cross-section. When the air pump inflates the pneumatic mesh actuator 10 through the air pipe 3, the gas applies pressure to the inner wall of the cavity 601, thereby causing bending deformation. Thanks to the unique cross-sectional cavity and non-contact air passage, the pneumatic mesh actuator can provide a large bending angle and tip output force, effectively improving the load-bearing capacity of the soft gripper.

[0040] Specifically, the overall length of the variable stiffness unit 2 is less than half the length of the pneumatic mesh actuator 10. It includes an upper silicone film 11, a scale element 9, a connecting rod 8, a base plate 7, and a lower silicone sheet 12. The upper silicone film 11 has a rectangular cross-sectional shape. The main variable stiffness structure consisting of the scale element 9, the connecting rod 8, and the base plate 7 is placed inside the silicone film and encapsulated by the lower silicone sheet 12. The vacuum pump removes the air inside the variable stiffness unit 2 through the vacuum tube 4 to achieve a vacuum state.

[0041] Specifically, the scale element 9 is made of black scale-shaped nylon, the connecting rod 8 is made of white cylindrical photosensitive resin, and the base plate 7 is made of black rectangular rubber with multiple supports. When the variable stiffness unit 2 is not evacuated, the scales do not interact with each other and the stiffness is low. When the closed cavity of the silicone film is evacuated, the front teeth and rear grooves between the scales 9 interact to form a jamming structure, thereby realizing the conversion between high and low stiffness.

[0042] The process of a multi-curvature flexible robotic arm based on a piecewise variable stiffness structure grasping an object involves two steps:

[0043] The first step is to selectively apply negative pressure to the variable stiffness element:

[0044] When the variable stiffness unit 2 is evacuated, the upper silicone film 11 contracts and interacts with the scale element 9, causing the front teeth and rear groove to mesh with each other. The variable stiffness unit enters a high stiffness state, thereby changing the local structural stiffness and laying the foundation for achieving different curvature configurations.

[0045] The second step is positive pressure bending deformation:

[0046] When the pneumatic drive layer 1 is inflated, the cavity 601 of the pneumatic mesh actuator 10 expands under pressure and undergoes bending deformation. At this time, the variable stiffness unit 2 enters a high stiffness state. The local structure at its location has high stiffness and is not easy to bend, so it can present a unique curvature to adapt to the unique outer surface of the object.

[0047] The fabrication method of a multi-curvature flexible manipulator based on a piecewise variable stiffness structure includes the following methods:

[0048] The pneumatic mesh actuator 10 has a cavity wedge angle (wedge-shaped cavity) of 75° and dimensions of 142mm × 38mm × 37.76mm. The thickness of the upper cavity wall (wedge-shaped cavity wall thickness) and the side cavity wall (main cavity wall thickness) are 3.3mm and 1.5mm respectively, and the thickness of the transition wall 604 between cavities is 4mm. The variable stiffness unit 2 has dimensions of 54mm × 38mm × 20.5mm, and the thickness of the upper silicone film 8 and the lower silicone sheet 9 is 1mm.

[0049] S1. According to the preset dimensions, use 3D printing technology to process mold 1 for preparing the deformable layer, mold 2 for preparing the bottom constraint layer, mold 3 for preparing the upper silicone mold, and mold 4 for preparing the lower silicone sheet.

[0050] S2. According to the preset dimensions, use 3D printing technology to process a set of scale elements, a set of connecting rods and several base plates to form the main structure of the variable stiffness unit.

[0051] S3. Pour the two components of Smooth-On's Slow A and B silicone rubber into a beaker at a volume ratio of 1:1. Stir thoroughly with a glass rod and place under a negative pressure of -0.2MPa for 5 minutes until no more bubbles emerge from the beaker. Then, slowly pour the solution into the molds 1, 2, 3 and 4 prepared in steps S1 and S2 until the top of the molds are reached. Place all the molds on a flat table and cure at room temperature for 8 hours. After curing, remove the above products from the molds for later use.

[0052] S4. Use a glass rod to dip a small amount of silicone solution and apply it evenly to the connection between the deformable layer 6 and the bottom constraint layer 5 to bond them together, thus preparing the pneumatic mesh actuator 10. After the application is completed, place the pneumatic mesh actuator 10 on a flat table and cure it at room temperature for 8 hours.

[0053] S5. Assemble the scale element 9 with the support on the rubber base plate 7 using a connecting rod 8 with a diameter of 1mm to form the main structure of the variable stiffness unit. The scale element 9 can rotate relative to the base plate 7. The length, width and height of the base plate 7 are 50.7mm × 30mm × 2mm, respectively. Place the main structure into the upper silicone film 11 and encapsulate it with the lower silicone sheet 12 to form the variable stiffness unit 2.

[0054] S6. Perform an airtightness test on the pneumatic actuator 10 and variable stiffness unit 2 that have been cured by S4 and S5. If there is a gas leak, use a glass rod to apply a small amount of silicone solution to repair the leak at a specific point.

[0055] S7. Apply silicone solution to the connection between the pneumatic actuator 10 and the variable stiffness unit 2 for bonding. After curing at room temperature, the multi-curvature flexible manipulator to be prepared can be obtained.

[0056] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the technical solutions of the present invention. Any technical solution that can be implemented based on the above embodiments without creative effort should be considered to fall within the scope of protection of the patent of the present invention.

Claims

1. A multi-curvature flexible manipulator based on a segmented variable stiffness structure, characterized in that... It includes a pneumatic drive layer (1) for achieving bending deformation and a variable stiffness unit (2) disposed at the lower part of the pneumatic drive layer (1) for achieving stiffness adjustment. The pneumatic drive layer (1) includes an air tube (3) and a pneumatic mesh actuator (10). The pneumatic mesh actuator (10) includes a deformable layer (6) and a bottom constraint layer (5). A set of cavities (601) is provided on the deformable layer (6). One end of the air tube (3) is connected to the cavity (601), and the other end is connected to the air pump. A ventilation gap is provided between the bottom of the inner cavity of the deformable layer (6) and the bottom constraint layer (5) to form an air passage (602) for communication between the cavities (601). The variable stiffness unit (2) includes a rubber base plate (7), an upper silicone film (11), a lower silicone sheet (12), a set of scale elements (9), a set of connecting rods (8), and a vacuum tube (4). A set of supports (701) is provided on the surface of the rubber base plate (7). Each pair of opposite supports (701) are connected to the scale elements (9) through the connecting rods (8) to form the main structure of the variable stiffness unit. It is placed in the upper silicone film (11) and encapsulated with the lower silicone sheet (12). One end of the vacuum tube (4) is connected to the variable stiffness unit (2), and the other end is connected to the vacuum pump. The cavity (601) includes a main cavity (605) and a wedge-shaped cavity (603) disposed on the top of the main cavity (605) and connected to the main cavity (605). Adjacent cavities (601) are connected by a transition wall (604). The wall thickness of the transition wall (604) is greater than the wall thickness of the wedge-shaped cavity (603), and the wall thickness of the wedge-shaped cavity (603) is greater than the wall thickness of the main cavity (605). The cavities (601) are arranged in parallel at equal intervals along the length of the actuator. When the air pump pressurizes the pneumatic mesh actuator (10) through the air pipe (3), the gas pressurizes the inner wall of the cavity (601) of the pneumatic mesh actuator (10), and the cavity (601) expands, causing the pneumatic mesh actuator (10) to bend and deform. The scale element (9) has a front tooth (901) at the front and a rear groove (902) at the rear. The front tooth (901) and the rear groove (902) between adjacent scale elements (9) correspond to each other. The closed cavity of the silicone film formed by the upper silicone film (11) and the lower silicone sheet (12) is not evacuated. When the scales do not interact with each other, the stiffness is low. When the vacuum is evacuated, the upper silicone film (11) shrinks, and the front tooth (901) and the rear groove (902) between the scale elements (9) interact to form a jamming structure with higher stiffness, thereby realizing the transformation between high and low stiffness.

2. The multi-curvature flexible manipulator based on a segmented variable stiffness structure according to claim 1, characterized in that, Two variable stiffness units (2) are provided, and the two variable stiffness units (2) are respectively located on both sides of the bottom of the pneumatic drive layer (1).

3. The multi-curvature flexible manipulator based on a segmented variable stiffness structure according to claim 2, characterized in that, The pneumatic drive layer (1) is combined with two variable stiffness units (2). By adjusting the stiffness state of the variable stiffness units, the local structural stiffness is changed, so that the gripper has multi-curvature characteristics.

4. A method for fabricating a multi-curvature flexible manipulator based on a segmented variable stiffness structure, characterized in that... Includes the following steps: S1. According to the preset size, use 3D printing technology to process mold 1 for preparing the deformable layer (6), mold 2 for preparing the bottom constraint layer (5), mold 3 for preparing the upper silicone film (11) and mold 4 for preparing the lower silicone sheet (12). S2. According to the preset dimensions, a set of scale elements (9), a set of connecting rods (8), a set of supports and a rubber base plate (7) are processed using 3D printing technology to form the main structure of the variable stiffness unit. S3. Pour the two-component silica gel solution into a beaker, stir thoroughly with a glass rod, and then place it in a vacuum drying oven for vacuum treatment until no more bubbles emerge from the beaker. Then, slowly pour the solution into the molds prepared in steps S1 and S2, including mold 1, mold 2, mold 3, and mold 4, until the top of the molds are reached. Place all the molds on a flat table for room temperature curing. After curing, remove the product from the mold for later use. S4. Apply silicone solution to the connection between the deformable layer (6) and the bottom constraint layer (5) to bond them together and prepare the pneumatic mesh actuator (10). After the application is completed, the pneumatic actuator (10) is cured at room temperature. S5. Assemble the scale element (9) with the support (701) on the rubber base plate (7) using the connecting rod (8) to form the main structure of the variable stiffness unit. The scale element (9) can maintain relative rotation with the rubber base plate (7). Place the main structure into the upper silicone film (11) and encapsulate it with the lower silicone sheet (12) to form the variable stiffness unit (2). S6. Apply silicone solution to the connection between the pneumatic actuator (10) and the variable stiffness unit (2) for bonding. After curing at room temperature, the multi-curvature flexible manipulator to be prepared can be obtained.

5. The method for fabricating the multi-curvature flexible manipulator based on a segmented variable stiffness structure according to claim 4, characterized in that, In step S1, mold one and mold three are detachable molds, with rectangular teeth around them for easy demolding; all molds are made of white photosensitive resin.

6. The method for fabricating the multi-curvature flexible manipulator based on a segmented variable stiffness structure according to claim 4, characterized in that, The silicone preparation process in step S3 is as follows: The volume ratio of components A and B of the silicone rubber is 1:1; the thoroughly stirred silicone solution is placed under a negative pressure of -0.2MPa for 5 minutes until no more bubbles emerge from the beaker; the curing time at room temperature is 8 hours.

7. The method for fabricating the multi-curvature flexible manipulator based on a segmented variable stiffness structure according to claim 4, characterized in that, The thickness of the upper silicone film (11) and the lower silicone sheet (12) in step S5 is no more than 2 mm, so as to prevent the variable stiffness unit from generating initial curvature when it enters the high stiffness state.

8. The method for fabricating the multi-curvature flexible manipulator based on a segmented variable stiffness structure according to claim 4, characterized in that, In step S5, the size of the front tooth (901) of the scale element (9) is larger than the size of the rear groove (902) to prevent jamming.

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