A pneumatically variable stiffness soft gripper

Abstract

The present invention discloses a pneumatic variable stiffness soft gripper, comprising a gripper and a flexible wrist. The gripper has a plurality of variable stiffness fingers, each variable stiffness finger comprising a strain limiting plate, a driving airbag fixed on the outside of the strain limiting plate, and a variable stiffness airbag fixed on the inside. The variable stiffness airbag has a honeycomb-shaped support grid inside, which divides the inner cavity of the variable stiffness airbag into a plurality of cells, and the plurality of cells are connected to a second airway. Each cell is filled with spherical blocking particles. During the grasping process of the soft gripper, the driving airbag is first pressurized by the first airway, the variable stiffness finger is bent, and then negative pressure is applied to the variable stiffness airbag through the second airway, so that the blocking particles are arranged closely, the friction between the particles is increased, and adaptive variable stiffness is achieved. The flexible wrist comprises a bellows, and three third airways are evenly distributed along the circumference of the bellows, so that the flexible wrist can produce good deflection and elongation properties.

Description

Technical Field

[0001] The present invention relates to the technical field of soft grippers, and in particular to a soft gripper with pneumatic variable stiffness. Background Art

[0002] Traditional rigid grippers are mainly made of rigid materials and are installed on robotic arms to perform large-scale grasping movements. They rely on precise control to grasp objects. However, when grasping fragile objects with soft surfaces, rigid grippers are prone to damage. Soft grippers have a certain degree of active or passive adaptability to objects of various shapes, sizes, weights, and rigidities. Therefore, when grasping fragile objects with soft surfaces, they can grasp and manipulate fragile objects more safely to avoid damage. However, due to the characteristics of the flexible materials used to make soft grippers, soft grippers have problems such as low rigidity and poor grasping ability. In addition, they need to cooperate with the robotic arm when performing multi-position grasping operations, which increases the difficulty of operational control.

[0003] Chinese invention patent publication number CN111791247A discloses a variable-stiffness wire-driven flexible gripper and its variable stiffness control method. The motor rotates to drive the eyelash cord, thereby bending the fingers. An external negative pressure pump applies negative pressure to bring the top of the flexible skeleton's T-shaped block structure into contact with the inner surface of a flexible sheet, thereby controlling the gripper's stiffness. This gripper provides a secure grip and can handle fragile objects. However, the gripper's stiffness after variable stiffness depends on the stiffness of the T-shaped block structure, resulting in a narrow range of stiffness variation and a limited range of applicability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a pneumatic variable stiffness soft gripper, which can stably achieve variable stiffness gripping targets and expand the working space of the soft gripper.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A pneumatic variable stiffness soft gripper, characterized by comprising:

[0007] A gripper comprising a mounting plate, with a plurality of variable stiffness fingers circumferentially distributed below the mounting plate, each variable stiffness finger comprising a strain limiting plate, a driving airbag fixed to the outside of the strain limiting plate, the driving airbag having a first air passage therein, a row of protruding airbag fingers on the outside of the driving airbag, a telescopic cavity connected to the first air passage within the airbag fingers, a variable stiffness airbag fixed to the inside of the strain limiting plate, the variable stiffness airbag having a honeycomb-shaped support grid therein that divides the interior of the variable stiffness airbag into a plurality of cells, the plurality of cells being connected to the second air passage, each cell being filled with spherical blocking particles; and

[0008] The flexible wrist has one end fixed to the top of the mounting plate and the other end fixed to the robotic arm. The flexible wrist includes a bellows, and three third air channels are evenly distributed along the circumference of the bellows, and each third air channel is connected to an air path.

[0009] A further technical solution is that the cross section of the third air channel is fan-shaped and arches radially outward.

[0010] A further technical solution is that the flexible wrist includes two separate bellows, an upper bellows and a lower bellows.

[0011] A further technical solution is that both sides of the strain limiting plate are fixed to the driving airbag and the variable stiffness airbag by gluing.

[0012] A further technical solution is that the mounting plate has a plurality of slide grooves evenly arranged radially with the flexible wrist as the center, the number of the slide grooves matches the number of variable stiffness fingers, and the upper ends of the variable stiffness fingers slide into the slide grooves and can be locked.

[0013] A further technical solution is that the number of the variable-rigidity fingers is three.

[0014] A further technical solution is that the flexible wrist applies pressure to the third airway in steps of 10 KPa, with a maximum air pressure of 80 KPa; and the variable stiffness finger applies pressure to the first airway in steps of 1.5 KPa, with a maximum air pressure of 30 KPa.

[0015] A further technical solution is that the particle size of the blocking particles is 2 to 3 mm, and the filling amount of the blocking particles in each cell is 80% to 85%.

[0016] A further technical solution is that the strain limiting plate is a polydimethylsiloxane plate with a thickness of 2 to 3 mm.

[0017] A further technical solution is that the bellows is 126 mm long and has a radius of 35 mm; the driving airbag is 150 mm long, 60 mm wide and 25 mm high; and the variable stiffness airbag is 150 mm long, 60 mm wide and 15 mm high.

[0018] The beneficial effects of adopting the above technical solution are:

[0019] During the gripping process, the first air channel pressurizes the driving airbag, causing the variable-stiffness fingers to bend. Then, the second air channel applies negative pressure to the variable-stiffness airbag, tightly arranging the blocking particles and increasing inter-particle friction, achieving adaptive variable stiffness. Furthermore, a honeycomb grid support structure, combined with particle blocking, achieves variable stiffness while preventing particle reorganization and accumulation. The flexible support structure also wraps around the target object, enhancing the gripper's shape adaptability.

[0020] The flexible wrist adopts a bellows structure, with three third air channels evenly distributed along the circumference inside. Each third air channel is connected to an air path. The deflection and elongation of the flexible wrist are controlled by controlling the gas pressure in the third air channel. When one or two third air channels are inflated, the flexible wrist produces a deflection movement. When the three fan-shaped air cavities are inflated and the air pressure in the cavities is the same, the flexible wrist produces a stretching movement, thereby producing good deflection and elongation performance, increasing the working space and flexibility of the gripper. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1 Schematic diagram of the structure of the pneumatic variable stiffness soft gripper of the present invention;

[0023] Figure 2 Schematic diagram of the structure of the variable stiffness finger of the present invention;

[0024] Figure 3 Schematic diagram of the structure of the flexible wrist of the present invention;

[0025] Figure 4 It is a structural schematic diagram of the connector of the present invention;

[0026] Figure 5 It is a schematic diagram of the mounting plate structure of the present invention;

[0027] Figure 6 Schematic diagram of the cross-sectional structure of the variable stiffness finger of the present invention;

[0028] Figure 7 It is a schematic diagram of the honeycomb-shaped flexible support structure of the present invention;

[0029] Figure 8 Schematic diagrams of the cross-sectional shapes of four flexible wrist cavities of the present invention;

[0030] Figure 9 is a graph showing the relationship between the deflection angle of the series flexible wrist and the air pressure according to Comparative Example 1 of the present invention;

[0031] Figure 10 is a graph showing the relationship between the deflection angle and elongation of the series flexible wrist according to comparative example 2 of the present invention and the air pressure;

[0032] Figure 11 It is a schematic structural diagram of the driving airbag of the present invention;

[0033] Figure 12 is a graph showing the relationship between the deflection angle of the variable-rigidity finger and the air pressure according to Comparative Example 3 of the present invention;

[0034] Figure 13 4 is a graph showing the relationship between the deflection angle of the variable-rigidity finger and the air pressure in comparative example 4 of the present invention. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] Example 1

[0038] like Figures 1 to 7 As shown, a pneumatic variable stiffness soft gripper includes a gripper and a flexible wrist. The gripper includes a mounting plate 6, below which a plurality of variable stiffness fingers are evenly distributed circumferentially. The preferred number of variable stiffness fingers is three, providing stable gripping and simple control.

[0039] Each variable-rigidity finger includes a strain-limiting plate 13, which can be made of a 2-3mm thick polydimethylsiloxane plate, preferably 2.5mm thick. Both sides of the strain-limiting plate 13 are glued to the actuating airbag 12 and the variable-rigidity airbag 14. This serves to limit the torsional deformation of the actuating airbag 12, allowing the soft gripper to conform to the surface of an object for grasping.

[0040] Actuating airbag 12 is fixed to the outside of strain limiting plate 13. The overall length of the actuating airbag 12 is 150 mm, the width is 60 mm, and the height is 25 mm. A first air channel 10 is located within the actuating airbag 12. A row of protruding, continuous airbag fingers are located on the outside of the actuating airbag 12. Within these airbag fingers are telescopic cavities 12-1, connecting to the first air channel 10. Preferably, there are ten of these cavities 12-1, each rectangular and 15 mm high. Pressure is applied to the first air channel 10 from within the variable-stiffness fingers in 1.5 kPa increments, reaching a maximum pressure of 30 kPa.

[0041] A variable-stiffness airbag 14 is fixed to the inner side of the strain-limiting plate 13, with the other side of the variable-stiffness airbag 14 contacting the target object. The variable-stiffness airbag 14 is a rectangular parallelepiped with an overall length of 150 mm, a width of 60 mm, and a height of 15 mm. The variable-stiffness airbag 14 has a honeycomb-shaped support grid 14-1 inside. The honeycomb support grid 14-1 can be made of high-density sponge. It divides the interior of the variable-stiffness airbag 14 into multiple polygonal cells, each of which is connected to the second airway 11. Each cell is filled with spherical blocking particles 14-2, which can be made of polyoxymethylene plastic with a particle size of 2 to 3 mm. The filling rate of each cell is 80% to 85% (a 100% filling rate means that the blocking particles 14-2 completely fill the entire cell). The honeycomb-shaped support grid 14-1 has a large bending modulus and excellent mechanical properties. The blocking particles 14-2 have the advantages of light weight and high hardness. They are filled in the honeycomb-shaped gaps. All the blocking particles 14-2 have exactly the same shape and size and are evenly distributed in density, which can reduce the degree of position change during particle reorganization. Because of the honeycomb structure, the shape and position uncertainty caused by the reorganization of the blocking particles 14-2 when negative pressure is applied to the variable stiffness airbag 14 can be avoided.

[0042] A threaded hole 6-2 is provided in the center of the mounting plate 6 along the axial direction for connecting the flexible wrist. One end of the flexible wrist is fixed to the top of the mounting plate 6 by means of threads or other means, and the other end is fixed to the robotic arm by a joint structure. The flexible wrist includes a bellows 3, inside which three third air channels 3-2 are evenly distributed along the circumference. The cross-section of the third air channels 3-2 is fan-shaped and arches radially outward. Each third air channel 3-2 connects to an air path. The three third air channels 3-2 have the same shape, and the cross-sectional area of ​​a single third air channel 3-2 is 3cm 2 The deflection and elongation of the flexible wrist are controlled by controlling the pressure of the gas in the third air channel 3-2. Pressure is applied to the third air channel 3-2 in the flexible wrist in steps of 10 kPa, reaching a maximum pressure of 80 kPa. When one or two third air channels 3-2 are inflated, the flexible wrist deflects. When the three fan-shaped air cavities are inflated and the air pressure in the cavities is the same, the flexible wrist stretches, resulting in excellent deflection and elongation performance, increasing the working space and flexibility of the gripper.

[0043] In order to make the flexible wrist have good deflection and elongation performance, the flexible wrist includes two separate bellows 3 in the upper and lower sections. The two bellows 3 have the same structure, the length of the bellows 3 is 126mm, and the radius is 35mm. The two bellows 3 are fixed together by a connector 4. The connector 4 has protruding connecting columns 4-1 at both ends. The connecting column 4-1 is threadedly connected to the upper and lower bellows to seal the two bellows 3, so that the third airway 3-2 on the upper and lower bellows 3 is not connected, and they are controlled separately without affecting each other. The two sections of the flexible wrist connected in series can further increase the working space of the soft gripper.

[0044] There are a total of 6 conversion joints 1 on the flange 2 and the connector 4, which are respectively connected to the six third air channels 3-2. A conversion joint 1 is also provided at the entrance of each first air channel 10 and the second air channel 11, that is, 6 conversion joints 1 are provided on the movable gripper, and the specifications of the 12 conversion joints 1 are consistent. The other end is connected to the air pump, which can control the inflow or outflow of gas in the air circuit.

[0045] The above-mentioned driving airbag 12, variable stiffness airbag 14 and bellows 3 in the flexible wrist are all made of superelastic silicone material. Superelastic material usually has a high plasticity and shape memory effect, and can return to its original shape after being subjected to deformation such as pressure or twisting, thereby ensuring the service life and performance stability of the soft gripper.

[0046] The mounting plate 6 has multiple slots 6-1 evenly arranged radially around the flexible wrist. The number of slots 6-1 matches the number of variable-stiffness fingers. The upper ends of the variable-stiffness fingers slide into and lock into the slots 6-1. When there are three variable-stiffness fingers, the edge of the mounting plate 6 has three arms spaced 120° apart, each with a slot 6-1. A cover 8 is secured to the top of each variable-stiffness finger. The cover 8 is secured to a mounting block 7 via bolts 9. The mounting block 7 slides into the slots 6-1 and can be secured to the slots 6-1 with screws. This allows the position of the variable-stiffness fingers to be adjusted according to the size of the target object, ensuring that three identical variable-stiffness fingers are evenly distributed across the arms of the mounting plate 6.

[0047] The pneumatic variable-rigidity soft gripper utilizes two flexible wrists connected in series, each individually driven. This maximizes the gripper's degrees of freedom while expanding its workspace. By connecting the variable-rigidity fingers to a mounting plate (6), the distribution of the three variable-rigidity fingers can be adjusted based on the size of the target object. By combining a honeycomb grid support structure with particle blocking, variable stiffness is achieved while avoiding particle reorganization and accumulation. The flexible support structure also provides wrapping for the target object, enhancing the gripper's shape adaptability. The present invention offers advantages such as stable grasping, a large workspace, simple control, a wide variable-rigidity range, and the ability to achieve adaptive conformity to the object's surface.

[0048] The working principle of the pneumatic variable stiffness soft gripper is as follows:

[0049] Before use, the flange 2 of the designed soft gripper is mounted on the robotic arm. The position of the variable-rigidity finger on the mounting plate 6 is adjusted according to the target object. During use, the vacuum pump is activated, and the soft gripper is positioned appropriately by controlling the air pressure in the third air channel 3-2 of the series-connected flexible wrist. During the grasping process, the first air channel 10 first pressurizes the driving airbag 12, causing the variable-rigidity finger to bend. Then, negative pressure is applied to the variable-rigidity airbag 14 via the second air channel 11, causing the blocking particles 14-2 to be tightly arranged and increasing the friction between the particles. This achieves adaptive variable stiffness and allows the target object to be grasped. Furthermore, the honeycomb grid support structure is combined with the particle blocking to achieve variable stiffness while avoiding particle reorganization and accumulation. At the same time, the flexible support structure also wraps around the target object, enhancing the gripper's shape adaptability.

[0050] Comparative Example 1

[0051] A pneumatic variable stiffness soft gripper, such as Figure 3 As shown, it is basically the same as Example 1, except that, Figure 8 As shown in the figure, the flexible wrist has four different cavity cross-sectional shapes: circular, fan-shaped, semicircular and elliptical. These four shapes have the same cross-sectional area and the same cavity height. Figure 9 As shown in the figure, among the four structures, the flexible wrist with a fan-shaped air cavity cross-section has the best deflection performance, and the higher the air cavity pressure, the more obvious the deflection performance of the flexible wrist. The circular structure has the worst deflection performance, while the deflection angles of the semicircular and elliptical structures are similar. Because the flexible wrist needs to have a large deflection capacity, the flexible wrist with a fan-shaped air cavity is more optimal.

[0052] Comparative Example 2

[0053] A pneumatic variable stiffness soft gripper, such as Figure 3 As shown, it is basically the same as embodiment 1, except that the number of flexible wrist air cavities inflated in series is as follows. Figure 10 As shown, when the three air chambers are inflated simultaneously, the serial flexible wrist will no longer produce bending movement but only stretching movement. The deflection angle of the serial flexible wrist with double chamber pressurization is about 5° larger than that with single chamber pressurization.

[0054] Comparative Example 3

[0055] A pneumatic variable stiffness soft gripper, such as Figure 11 As shown, it is basically the same as embodiment 1, except that the number of continuous cavities in the pneumatic grid driver is n. Figure 12As shown in the figure, within a certain range, there is a positive correlation between the number of cavities n and the deflection angle of the pneumatic grid actuator. When the air pressure reaches 30 kPa and the number of cavities is 11, the deflection angle can reach 270°.

[0056] Comparative Example 4

[0057] A pneumatic variable stiffness soft gripper, such as Figure 11 As shown, it is basically the same as embodiment 1, except that the continuous cavity height h in the pneumatic grid driver is as follows. Figure 13 As shown in the figure, within a certain range, the smaller the air cavity height h, the better the bending performance of the actuator. When the air pressure reaches 30 kPa and the air cavity height is 14 mm, the deflection angle can reach 270°.

[0058] The above are only preferred embodiments of the present invention. Any simple modification, deformation and equivalent replacement made by anyone to the present invention based on the contents of the present invention shall fall within the protection scope of the present invention.

Claims

1. A pneumatic variable stiffness soft gripper, characterized in that: include: A gripper, comprising a mounting plate (6), a plurality of variable stiffness fingers circumferentially distributed below the mounting plate (6), each variable stiffness finger comprising a strain limiting plate (13), a driving airbag (12) fixed on the outside of the strain limiting plate (13), the driving airbag (12) having a first air channel (10) therein, a row of protruding airbag fingers on the outside of the driving airbag (12), a telescopic cavity (12-1) communicating with the first air channel (10) within the airbag fingers, a variable stiffness airbag (14) fixed on the inside of the strain limiting plate (13), the variable stiffness airbag (14) having a honeycomb-shaped support grid (14-1) therein, dividing the inner cavity of the variable stiffness airbag (14) into a plurality of cavities, the plurality of cavities communicating with the second air channel (11), and each cavity filled with spherical blocking particles (14-2); and The flexible wrist has one end fixed to the top of the mounting plate (6) and the other end fixed to the robotic arm. The flexible wrist includes a bellows (3). Three third air channels (3-2) are evenly distributed along the circumference of the bellows (3), and each third air channel (3-2) is connected to an air path.

2. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The cross section of the third air channel (3-2) is fan-shaped and arches radially outward.

3. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The flexible wrist comprises two separate bellows (3) in the upper and lower sections.

4. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: Both sides of the strain limiting plate (13) are fixed to the driving airbag (12) and the variable stiffness airbag (14) by gluing.

5. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The mounting plate (6) has a plurality of slide grooves (6-1) radially and evenly arranged with the flexible wrist as the center, the number of the slide grooves (6-1) matches the number of variable stiffness fingers, and the upper ends of the variable stiffness fingers are slidably connected in the slide grooves (6-1) and can be locked.

6. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The number of the variable-rigidity fingers is three.

7. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The flexible wrist applies pressure to the third airway (3-2) in steps of 10 KPa, with a maximum air pressure of 80 KPa; the variable-rigidity finger applies pressure to the first airway (10) in steps of 1.5 KPa, with a maximum air pressure of 30 KPa.

8. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The particle size of the blocking particles (14-2) is 2-3 mm, and the filling amount of the blocking particles (14-2) in each cell is 80%-85%.

9. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The strain limiting plate (13) is a polydimethylsiloxane plate with a thickness of 2 to 3 mm.

10. The pneumatic variable stiffness soft gripper according to claim 1, characterized in that: The bellows (3) has a length of 126 mm and a radius of 35 mm; The driving airbag (12) is 150 mm long, 60 mm wide and 25 mm high; The variable stiffness airbag (14) is 150 mm long, 60 mm wide and 15 mm high.

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