A variable stiffness soft gripper and a working method thereof

Abstract

This invention discloses a variable stiffness soft gripper and its working method, belonging to the field of soft manipulator technology. The invention includes a driving layer and a base layer arranged vertically. A cooling cavity is formed within the base layer, and a flexible covering layer is provided within the cooling cavity. A composite endoskeleton and a heating component are provided within the flexible covering layer, and the endoskeleton is filled with a phase change material. The composite endoskeleton includes a connecting component and several bone segments spaced apart along the extension direction of the connecting component. Filling spaces are formed between adjacent bone segments. This invention employs a flexible, segmented composite endoskeleton, allowing the phase change material to preferentially flow into and fill the filling spaces between the bone segments after the gripper bends. After cooling, a segmented locking structure is formed, thereby transforming the gripping load from a bending and torsional load borne entirely by the phase change material into a force form mainly based on compression and limiting between segments, which can more effectively improve the gripper's stiffness retention and load-bearing stability.

Description

Technical Field

[0001] This invention belongs to the field of soft robotic arm technology, and more specifically, relates to a variable stiffness soft gripper and its working method. Background Technology

[0002] With the development of flexible robots and bionic end effectors, soft grippers, due to their excellent flexibility, adaptability, and safety, have become an important research direction in the field of soft robotics, capable of handling fragile, soft, and irregularly shaped objects. Compared to traditional rigid grippers, soft grippers have significant advantages in contact safety and enveloping grasping ability. However, because soft grippers typically have low stiffness, they are difficult to maintain a fixed posture for a long time after completing a close grasp, and their ability to stably grasp and transport heavier objects remains insufficient.

[0003] To address these issues, existing technologies have proposed various solutions, including particle blocking, layered blocking, origami-style variable stiffness structures, and articulated endoskeletons. However, particles in particle blocking structures are prone to displacement; layered blocking structures are prone to creases after repeated bending, affecting grasping stability and stiffness adjustment; and solutions that rely solely on endoskeletons to enhance stiffness have limited active shaping capabilities after grasping, making it difficult to achieve rapid and reversible switching between compliant and high-stiffness states. Therefore, designing a soft gripper capable of rapid and reversible switching between compliant and high-stiffness states has significant practical implications for production.

[0004] A search revealed that patent CN121492122A discloses a flexible actuator integrating driving, sensing, and variable stiffness, as well as its fabrication and driving method. Patent CN108527411A discloses a flexible manipulator with variable stiffness; Patent CN118219308A discloses a variable stiffness joint structure for an underwater flexible mechanical finger; Patent CN115091490A discloses a soft robotic arm that mimics plant growth and can decouple stiffness and steering.

[0005] While the above solutions can achieve a certain degree of stiffness adjustment in different scenarios, there is still room for optimization. For example, in existing layered composite or external variable stiffness structures, locking is mostly achieved by relying on the overall material layer or external deformable components. When subjected to gripping forces, the variable stiffness material body often still needs to directly bear a large overall bending moment or torque, making it difficult to achieve optimal shape retention and load-bearing stability. Summary of the Invention

[0006] The problem to be solved To address at least some of the problems existing in the prior art, this invention proposes a variable stiffness soft gripper and its working method. The purpose is to solve the problem that in existing variable stiffness soft grippers, the variable stiffness material body often has to directly bear a large overall bending moment or torque when gripping, resulting in the inability to achieve optimal shape retention and load-bearing stability.

[0007] Technical solution To solve the above problems, the technical solution adopted by the present invention is as follows: The present invention provides a variable stiffness soft gripper, comprising a driving layer and a base layer arranged vertically, wherein the driving layer is used to drive the base layer to bend in a predetermined direction; A cooling cavity is formed within the substrate layer, and a flexible covering layer is provided within the cooling cavity; An assembly space is formed within the flexible covering layer. The assembly space is equipped with a composite internal skeleton and a heating component, and is filled with a phase change material. The composite endoskeleton includes a connecting component and a plurality of bone segments spaced apart along the extending direction of the connecting component; a filling space communicating with the assembly space is formed between adjacent bone segments. The phase change material solidifies within the filling space, which can limit the movement of bone segments.

[0008] In some embodiments, the drive layer is provided with a drive air chamber, and the drive air chamber is connected to an air intake pipe.

[0009] In some embodiments, multiple driving air chambers are spaced apart along the length of the driving layer, and a curved transition zone is formed between adjacent driving air chambers. Multiple drive air chambers are interconnected and connected to an air intake pipe.

[0010] In some embodiments, the filling space is an arc-shaped structure with the opening away from the driving layer.

[0011] In some embodiments, at least a portion of the heating element is located within the filling space.

[0012] In some embodiments, the heating element includes a first portion and a second portion connected to each other; wherein, The first part is a straight line segment extending along the length of the cooling cavity; The second part includes straight segments and bent segments arranged at intervals, with the bent segments located within the corresponding filling space.

[0013] In some embodiments, the bone segment is provided with a connecting groove extending along the width direction of the connecting component, and the connecting groove is in communication with the assembly space.

[0014] In some embodiments, the phase change material is a shape memory polymer, a low-melting-point metal, or paraffin wax; the connecting component is a graphene thermally conductive sheet.

[0015] In some embodiments, the variable stiffness soft gripper is a single-finger structure, or multiple single-finger structures are mounted on the same palm base to form a multi-finger gripper.

[0016] The working method of a variable stiffness soft gripper, as described above, includes the following steps. S1. When the heating element is powered on, the phase change material melts, releasing the joint lock on the composite endoskeleton. At this time, the soft gripper is in a low-stiffness and compliant state. S2. Compressed gas is introduced into the driving air chamber, causing the driving layer to expand and deform and driving the base layer to bend in a predetermined direction. At this time, the connecting parts of the composite endoskeleton bend accordingly, which increases the filling space between adjacent bone segments. Molten phase change material flows into the filling space, thereby allowing the phase change material to be redistributed under the target grasping posture. S3. When the soft gripper reaches the predetermined gripping angle and adheres to the target object, a cooling medium is introduced into the cooling chamber to rapidly solidify the molten phase change material. The solidified phase change material fills the filling space, restricting the relative movement between adjacent bone segments, thereby improving the overall stiffness of the soft gripper and maintaining the current gripping posture; S4. When releasing the target object, power is applied to the heating component again to remelt the phase change material. At the same time, the pressure in the driving air chamber is released, and the soft gripper returns to its initial state in preparation for the next gripping operation.

[0017] Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a variable stiffness soft gripper that utilizes phase change material as a reversible variable stiffness medium, enabling flexible switching between low and high stiffness. Simultaneously, a bendable segmented composite internal skeleton is employed, allowing the phase change material to preferentially flow into and fill the spaces between the skeleton segments after the gripper bends. Upon cooling, a segmented locking structure is formed, thereby transforming the gripping load from the bending and torsional load borne by the pure phase change material as a whole into a force form primarily based on compression and limiting between segments. This more effectively improves the gripper's stiffness retention and load-bearing stability.

[0018] (2) The variable stiffness soft gripper of the present invention has an overall arc-shaped structure for filling the space. After the composite endoskeleton is bent and locked, the arc transition structure can effectively reduce the stress concentration in the joint area and reduce the sudden change in local force, thereby further improving the stiffness retention and structural reliability of the composite endoskeleton under gripping force.

[0019] (3) In a variable stiffness soft gripper of the present invention, the bending section of the heating component is located in the corresponding filling space, which can preferentially heat the phase change material in the filling space; at the same time, by setting the connecting groove, the contact area between the phase change material and the bone segment can be increased while ensuring the load-bearing capacity of the bone segment, thereby improving the heat transfer efficiency between the bone segment and the phase change material, and thus improving the melting and solidification response speed of the phase change material. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a variable stiffness soft gripper according to the present invention; Figure 2 This is a schematic diagram of the internal structure of a variable stiffness soft gripper according to the present invention; Figure 3 for Figure 2 A magnified view of a portion of point A in the middle; Figure 4 This is a schematic diagram of the composite endoskeleton in this invention; Figure 5 This is a schematic diagram of the heating component in this invention.

[0021] In the picture: 100. Driver layer; 110. Drive air chamber; 120. Intake pipe; 200. Matrix layer; 210 Cooling chamber; 220 Flexible covering layer; 221 Assembly space; 231 Liquid inlet pipe; 232 Liquid outlet pipe; 300. Composite endoskeleton; 310. Connecting component; 320. Skeletal segment; 321. Connecting groove; 330. Filling space; 400. Heating components; 410. Part One; 420. Part Two. Detailed Implementation

[0022] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings.

[0023] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] The present invention will be further described below with reference to specific embodiments.

[0025] like Figure 1 As shown, a variable stiffness soft gripper according to this embodiment includes a driving layer 100 and a base layer 200 arranged vertically. The driving layer 100 can drive the base layer 200 to bend in a predetermined direction to achieve gripping of a target object.

[0026] Specifically, refer to Figure 2 As shown, the drive layer 100 is provided with a drive air chamber 110, and the drive air chamber 110 is connected to an air intake pipe 120.

[0027] Furthermore, multiple driving air chambers 110 are spaced apart along the length of the driving layer 100, and a gap is left between adjacent driving air chambers 110. This gap forms a bending transition zone so that the driving layer 100 bends and deforms in a predetermined direction when compressed gas is introduced, thereby driving the base layer 200 to bend.

[0028] In some embodiments, multiple drive air chambers 110 are interconnected and connected to an air intake pipe 120. Alternatively, each drive air chamber 110 may be independently configured, and each drive air chamber 110 may be connected to its own air intake pipe 120.

[0029] Preferably, the driving layer 100 may be made of silicone rubber, polyurethane elastomer or other elastic polymer materials with good flexibility to ensure stable bending deformation under inflation.

[0030] like Figure 2 , Figure 3 As shown, in some embodiments, a cooling cavity 210 is formed within the substrate layer 200, and a flexible covering layer 220 is provided within the cooling cavity 210. A sealed assembly space 221 is formed within the flexible covering layer 220, and a composite internal skeleton 300 and a heating component 400 are provided within the assembly space 221, which is filled with a phase change material.

[0031] The phase change material can be a shape memory polymer, a low-melting-point metal, or paraffin wax, etc. The flexible coating layer 220 can be made of silicone rubber film, thermoplastic polyurethane elastic film, or other heat-resistant and flexible sealing materials to ensure the sealing stability of the phase change material during multiple melt-solidification cycles. Specifically, in this embodiment, phase change paraffin wax is selected as the phase change material.

[0032] In other embodiments, the composite endoskeleton 300 includes a connecting member 310 and a plurality of bone segments 320 spaced apart along the extending direction of the connecting member 310; a filling space 330 communicating with the assembly space 221 is formed between adjacent bone segments 320.

[0033] Preferably, the connecting component 310 is a graphene thermally conductive sheet to accelerate heat transfer within the overall structure of the composite endoskeleton 300, ensuring the uniformity of temperature change and the rapidity of temperature transfer during heating and cooling of the phase change material. The skeletal segment 300 can be made of graphene-reinforced resin-based composite material, graphene-reinforced polymer composite material, or a composite skeleton with a graphene thermally conductive layer on its surface, thus possessing both good thermal conductivity and load-bearing capacity.

[0034] The heating component 400 may use a resistance heating wire, such as a nickel-chromium wire, to heat the phase change material in the assembly space 221, causing the phase change material to melt, thereby relieving the bending restriction on the composite inner skeleton 300, so that the composite inner skeleton 300 is in a bendable state under the drive of the drive layer 100, so as to complete the clamping action of the target object.

[0035] The cooling chamber 210 is circulated with the cooling source through the liquid inlet pipe 231 and the liquid outlet pipe 232. It is used to introduce cooling medium after the soft gripper reaches the target grasping posture to achieve rapid cooling and solidification of the internal phase change material, thereby restricting the bent composite internal skeleton 300 and keeping it in a stable grasping state of the target object. The cooling medium can be water, ethylene glycol coolant, or other fluids suitable for circulating heat exchange, and is not specifically limited here.

[0036] During operation, the heating component 400 is first energized to melt the phase change paraffin, releasing the joint lock on the composite endoskeleton 300. At this time, the soft gripper is in a low-rigidity and compliant state. Subsequently, compressed gas is introduced into the driving air chamber 110 of the driving layer 100 through the air intake pipe 120, causing the driving layer 100 to expand and deform and the base layer 200 to bend in a predetermined direction to grasp the target object. At the same time, the connecting part 310 of the composite endoskeleton 300 bends, which increases the filling space 330 between adjacent bone segments. Molten phase change paraffin flows into the increased filling space 330, thereby allowing the phase change material to be redistributed under the target grasping posture. Once the soft gripper reaches the predetermined gripping angle and conforms to the target object, a cooling medium is introduced into the cooling chamber 210 through the liquid inlet pipe 231 and discharged through the liquid outlet pipe 232. Utilizing the thermal conductivity of the graphene thermally conductive sheet and the heat exchange effect of the cooling medium, the molten phase change paraffin wax is rapidly solidified. The solidified phase change paraffin wax fills and locks in the joint area between the bone segments 320, restricting the relative movement between adjacent bone segments, thereby improving the overall rigidity of the soft gripper and maintaining the current gripping posture. When the target object is released, the heating component 400 is energized again to remelt the phase change paraffin. At the same time, the pressure in the driving layer cavity is released, and the soft gripper returns to its initial state under the action of the elastic matrix restoring force.

[0037] This embodiment of a variable stiffness soft gripper utilizes a phase change material as a reversible variable stiffness medium, enabling flexible switching between low and high stiffness. Simultaneously, a flexible, segmented composite internal skeleton is employed, allowing the phase change material to preferentially flow into and fill the space 330 between the skeleton segments after the gripper bends. Upon cooling, this forms a segmented locking structure, thereby transforming the gripping load from a bending and torsional load borne entirely by the phase change material into a force form primarily based on compression and limiting between segments. This more effectively improves the gripper's stiffness retention and load-bearing stability.

[0038] like Figure 4 As shown, in some embodiments, the filling space 330 is an arc-shaped structure with an opening away from the driving layer 100.

[0039] It is worth mentioning that the arc-shaped structure here refers only to the overall appearance of the filling space 330. In reality, the filling space 330 is formed by the opposing sidewalls of two bone segments 320 and the connecting component 310, with a certain gap between the tops of the two bone segments 320. Because the opposing sidewalls of the two bone segments 320 are concave arc-shaped structures, the filling space 330 presents a semi-circular shape.

[0040] In this embodiment, by designing the filling space 330 as a semi-circular arc structure, a relatively continuous arc transition boundary can be formed between adjacent bone segments 320 after the composite endoskeleton 300 is bent, thereby avoiding local stress concentration caused by sharp corners or abrupt edges, so that the joint area has a more uniform force distribution under compression and locking conditions, which is beneficial to improving the overall stiffness of the composite endoskeleton 300.

[0041] Furthermore, the skeletal segment 320 is provided with a connecting groove 321 extending along the width direction of the connecting member 310, and the connecting groove 321 is interconnected with the assembly space 221.

[0042] The advantage of this design is that it increases the contact area between the bone segment 320 and the phase change paraffin, allowing the heat transferred by the heating element 400 and the connecting element 310 (graphene thermally conductive sheet) to act more efficiently on the phase change paraffin. It also facilitates the rapid transfer of heat from the phase change paraffin to the composite endoskeleton 300 and the cooling chamber 210 during the cooling stage, thereby improving the melting and solidification efficiency of the phase change paraffin.

[0043] In other embodiments, at least a portion of the heating element 400 is located within the filling space 330 to preferentially heat the phase change material within the filling space 330.

[0044] Specifically, refer to Figure 5 As shown, the heating component 400 includes a first part 410 and a second part 420 connected to each other; wherein, the first part 410 is a straight segment extending along the length direction of the cooling cavity 210; the second part 420 includes straight segments and bent segments arranged at intervals, the bent segments being located within the corresponding filling space 330.

[0045] This embodiment also provides a method for operating a variable stiffness soft gripper, which includes the following steps: S1. When the heating component 400 is energized, the phase change material melts, releasing the joint lock on the composite endoskeleton 300. At this time, the soft gripper is in a low-rigidity and compliant state. S2. Compressed gas is introduced into the driving air chamber 110, causing the driving layer 100 to expand and deform and drive the base layer 200 to bend in a predetermined direction; at this time, the connecting part 310 of the composite endoskeleton 300 bends accordingly, which increases the filling space 330 between adjacent bone segments 320, and the molten phase change material flows into the filling space 330, thereby allowing the phase change material to be redistributed under the target grasping posture. S3. When the soft gripper reaches the predetermined gripping angle and adheres to the target object, a cooling medium is introduced into the cooling chamber 210 to rapidly solidify the molten phase change material. The solidified phase change material fills the filling space 330, restricting the relative movement between adjacent bone segments 320, thereby improving the overall stiffness of the soft gripper and maintaining the current gripping posture. S4. When releasing the target object, power is applied to the heating component 400 again to remelt the phase change material. At the same time, the pressure in the driving air chamber 110 is released, and the soft gripper returns to its initial state in preparation for the next gripping operation.

[0046] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A variable stiffness soft gripper, comprising a drive layer (100) and a base layer (200) arranged vertically, wherein, The driving layer (100) is used to drive the base layer (200) to bend in a predetermined direction; The feature is that a cooling cavity (210) is formed in the substrate layer (200), and a flexible covering layer (220) is provided in the cooling cavity (210). An assembly space (221) is formed within the flexible covering layer (220), and a composite internal skeleton (300) and a heating component (400) are provided within the assembly space (221), and the assembly space (221) is filled with a phase change material; The composite endoskeleton (300) includes a connecting component (310) and a plurality of bone segments (320) spaced apart along the extending direction of the connecting component (310); a filling space (330) is formed between adjacent bone segments (320) and communicates with the assembly space (221). The phase change material solidifies within the filling space (330), which can limit the movement of the skeletal segment (320).

2. The variable stiffness soft gripper according to claim 1, characterized in that: The drive layer (100) is provided with a drive air chamber (110), and the drive air chamber (110) is connected to an air intake pipe (120).

3. A variable stiffness soft gripper according to claim 2, characterized in that: The driving air chambers (110) are provided at multiple intervals along the length direction of the driving layer (100), and a curved transition zone is formed between adjacent driving air chambers (110). Multiple drive air chambers (110) are interconnected and connected to an air intake pipe (120).

4. A variable stiffness soft gripper according to any one of claims 1-3, characterized in that: The filling space (330) is an arc-shaped structure with an opening away from the driving layer (100).

5. A variable stiffness soft gripper according to claim 4, characterized in that: At least a portion of the heating element (400) is located within the filling space (330).

6. A variable stiffness soft gripper according to claim 5, characterized in that: The heating component (400) includes a first part (410) and a second part (420) connected to each other; wherein, The first part (410) is a straight segment extending along the length of the cooling cavity (210); The second part (420) includes straight segments and bent segments arranged at intervals, the bent segments being located within the corresponding filling space (330).

7. A variable stiffness soft gripper according to claim 1, characterized in that: The bone segment (320) is provided with a connecting groove (321) extending along the width direction of the connecting component (310), and the connecting groove (321) is connected to the assembly space (221).

8. A variable stiffness soft gripper according to claim 1, characterized in that: The phase change material is a shape memory polymer, a low melting point metal, or paraffin; the connecting component (310) is a graphene thermally conductive sheet.

9. A variable stiffness soft gripper according to claim 1, characterized in that: The variable stiffness soft gripper is a single-finger structure, or a multi-finger gripper formed by multiple single-finger structures mounted on the same palm base.

10. The working method of a variable stiffness soft gripper as described in any one of claims 2-9, characterized in that: Includes the following steps, S1. The heating component (400) is energized, causing the phase change material to melt and releasing the joint lock on the composite endoskeleton (300). At this time, the soft gripper is in a low-stiffness and compliant state. S2. Compressed gas is introduced into the driving air chamber (110) to cause the driving layer (100) to expand and deform and drive the base layer (200) to bend in a predetermined direction. At this time, the connecting parts (310) of the composite endoskeleton (300) bend accordingly, which increases the filling space (330) between adjacent bone segments (320). Molten phase change material flows into the filling space (330), thereby allowing the phase change material to be redistributed under the target grasping posture. S3. When the soft gripper reaches the predetermined gripping angle and fits the target object, a cooling medium is introduced into the cooling chamber (210) to rapidly solidify the molten phase change material. The solidified phase change material fills the filling space (330), restricting the relative movement between adjacent bone segments (320), thereby improving the overall stiffness of the soft gripper and maintaining the current gripping posture; S4. When releasing the target object, the heating component (400) is energized again to remelt the phase change material. At the same time, the driving air chamber (110) is depressurized, and the soft gripper returns to its initial state in preparation for the next gripping operation.

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