Layer interference based variable stiffness gripper and gripping method thereof

Abstract

This invention discloses a variable stiffness gripper and its gripping method based on layer interference, belonging to the field of mechanical gripper technology. The gripper includes a drive assembly, a base, and multiple flexible fingers. The drive assembly includes a stepper motor and a movable part, capable of driving the movable part to linear displacement; the base is connected to the motor body; the flexible fingers are mounted on the base to form a gripping space and are connected to the movable part via finger linkages to achieve grasping and release. Each flexible finger consists of a finger base, a first beam, a second beam, a through beam, and multiple crossbeams, forming a trapezoidal shape and multiple hollow structures to enhance passive deformation capability and enveloping properties. The first beam and the through beam each have a first and second sealed cavity, filled with a paper filling layer composed of multiple layers of flexible paper with gaps. Friction is generated between the paper layers by negative pressure compression, achieving rapid stiffness adjustment. This invention combines excellent enveloping properties, high load-bearing capacity, and rapid stiffness response; it is easy to operate and suitable for flexible gripping operations.

Description

Technical Field

[0001] This invention relates to the field of mechanical gripper technology, and in particular to a variable stiffness gripper based on layer interference and its gripping method. Background Technology

[0002] Traditional grippers mostly adopt rigid structures. As application scenarios continue to expand, their poor adaptability and low safety make them increasingly difficult to meet industrial needs.

[0003] In comparison, soft grippers made of soft materials offer superior compliance and safety, enabling them to cope more effectively with complex and changing industrial environments. However, due to the low stiffness of the material, soft grippers have insufficient inherent structural strength and are prone to overall buckling or local instability under heavy loads. This significantly limits their gripping stiffness, positioning accuracy, and load-bearing capacity, making them unsuitable for applications requiring high gripping posture maintenance and load capacity.

[0004] To address the issue of insufficient stiffness in soft grippers, existing technologies have proposed various variable stiffness improvement schemes. One type of scheme employs variable stiffness smart materials, such as shape memory alloys, shape memory polymers, or electro / magnetorheological elastomers, to dynamically adjust the gripper stiffness by controlling the material modulus through external excitations (such as temperature, electric fields, or magnetic fields). However, this type of method generally suffers from problems such as slow response speed, stringent excitation conditions, short fatigue life, and complex control models, making it difficult to meet the requirements of fast and frequent industrial gripping cycles.

[0005] Another widely used variable stiffness strategy is the interference mechanism. Particle interference technology, in particular, increases structural stiffness by filling a flexible cavity with microparticles and using vacuum negative pressure to create a frictional locking effect between the particles. However, this method has significant drawbacks: firstly, the particles are prone to irreversible accumulation and hardening failure during repeated compression, affecting reusability; secondly, to ensure effective interference, a large structural volume is required, limiting the miniaturization design and confined space operation capabilities of the gripper. Summary of the Invention

[0006] The present invention aims to at least improve one of the technical problems existing in the prior art. To this end, the present invention proposes a variable stiffness gripper based on layer interference and a gripping method thereof.

[0007] The technical solution of the present invention is as follows: A variable stiffness gripper based on layer interference, mounted on a robotic arm via a mounting flange, comprising: A drive assembly is connected to the mounting flange. The drive assembly includes a stepper motor and a movable part, which is driven by the driving force of the stepper motor to move the movable part in a linear direction. The base is connected to the outer body of the stepper motor; Multiple flexible fingers are mounted on the base to form a clamping space. The flexible fingers are connected to the movable part through finger linkages, and the movable part moves to drive the flexible fingers to perform grasping and releasing actions. In one possible technical solution, each flexible finger further comprises: Finger base; The first beam and the second beam are respectively installed at both ends of the finger base, and the other ends away from the finger base extend in a direction that approaches each other. The first beam is offset from the clamping space and has a first sealing cavity inside. A through beam is installed in the middle of the finger base, and the other end is connected to the first beam and the second beam to form a trapezoidal hollow structure, wherein the through beam has a second sealing cavity; Multiple crossbeams, one end of which is connected to the through beam and the other end of which is connected to the first beam or the second beam to form multiple hollow units, have good passive deformation ability and envelopment when clamping items, while improving the rigidity of the flexible finger clamping surface and enhancing the load capacity. The first and second sealing cavities are both connected to an external air source but are not interconnected, and can be used to independently achieve negative pressure regulation.

[0008] In one possible technical solution, the first beam and the second beam are symmetrical about the position of the through beam, and the wall thickness of the first beam is greater than that of the second beam.

[0009] In one possible technical solution, the flexible finger further includes: A paper filling layer is filled in the first and second sealed cavities. The paper filling layer is composed of multiple layers of flexible paper, with gaps between each layer of flexible paper, which are used to generate interlayer friction through negative pressure compression to achieve stiffness adjustment.

[0010] In one possible technical solution, the paper filling layers are further coated with an anti-slip coating, the number of paper filling layers is 15-30 layers, and the thickness of each paper layer is 0.1-0.3mm, which enhances the interlayer friction coefficient and improves the stiffness adjustment effect.

[0011] In one possible technical solution, the movable part is further defined as a central connecting rod, hinged to one end of the finger connecting rod, with the end of the finger connecting rod away from the central connecting rod connected to the flexible finger; the central connecting rod is fitted with a T-shaped nut, and the drive assembly further includes: The lead screw is connected to the output shaft of the stepper motor via a coupling, and the lead screw is threadedly engaged with the T-nut. The I-beam connecting rod, hinged between the base and the finger connecting rod, is used to convert the rotational motion of the lead screw into the swinging opening and closing action of the flexible finger.

[0012] In one possible technical solution, both the first sealing cavity and the second sealing cavity are provided with air holes. The air holes are opened at one end of the finger base, and the sealing cavity is sealed to the air pipe through the air holes. The other end of the air pipe is sealed to an external vacuum pump.

[0013] In one possible technical solution, the finger base, first beam, second beam, through beam, and crossbeam are integrally formed, resulting in a compact structure with controllable flexibility.

[0014] In one possible technical solution, the finger base is further provided with a through hole, through which the flexible finger is connected to the finger connecting rod bolt.

[0015] A method for clamping a variable stiffness gripper based on layer interference, wherein the variable stiffness gripper described above is used for clamping, and includes the following steps: S1: Initial state settings, specifically including: At the beginning of the clamping operation, the vacuum pump is controlled to be turned off, so that the internal air pressure of the first sealing chamber and the second sealing chamber is maintained at standard atmospheric pressure, and the flexible fingers are in a natural flexible state. At the same time, the stepper motor is controlled to start running in the forward direction. The output shaft of the stepper motor drives the lead screw to rotate synchronously in the forward direction through the coupling, which drives the flexible fingers to swing outward synchronously around their respective hinge axes, so as to realize the finger opening action. S2: Clamping posture adjustment and flexible envelope positioning, specifically including: An external robotic arm carries the gripper to a preset position above the target object. Based on the target object's dimensions and spatial orientation, the gripper's overall position is adjusted so that a pair of flexible fingers are positioned on opposite sides of the target object, with the inner envelope of the two fingers facing the outer contour of the target object, ensuring that the flexible fingers have sufficient envelope travel. Subsequently, the stepper motor is controlled to start running in reverse, causing the lead screw to rotate in the opposite direction, which in turn causes the two flexible fingers to slowly close at a constant closing speed. S3: Vacuum negative pressure excitation and layer interference variable stiffness locking, specifically including: After the flexible finger completes the enveloping adhesion to the target object, the vacuum pump is started and the vacuum pump's negative pressure value is set to -80 kPa. The first and second sealing chambers are evacuated through the sealed air tubes, so that the air pressure in the two sealing chambers gradually decreases from normal pressure to the set negative pressure steady state. As the negative pressure is formed in the chambers, the paper filling layers set in each sealing chamber are tightly squeezed by the uniform gas pressure difference. The contact positive pressure between the layers of paper increases, and the interlayer static friction is significantly increased, thereby producing a layer interference locking effect. S4: Negative pressure maintenance and target object handling, specifically including: After the target object is grasped and locked, the vacuum pump continues to run to maintain continuous negative pressure on the first and second sealed chambers, so that the vacuum degree in the two chambers is precisely stabilized at the preset working pressure. This ensures that the interlayer clamping force and friction locking state of the paper filling layer do not decrease due to leakage or pressure fluctuations throughout the entire handling process, thereby maintaining the high rigidity characteristics of the flexible fingers. In this state, the external robotic arm drives the gripper and the grasped target object to move together along a predetermined trajectory, transporting the target object from the grasping position to the target placement position, completing the spatial transfer operation. S5: Negative pressure release, flexible recovery, and object release, specifically including: After the target object reaches the designated placement position, the vacuum pump is turned off, allowing the air pressure inside the first and second sealed chambers to slowly return to standard atmospheric pressure. As the negative pressure inside the chambers disappears, the pressure on the paper filling layer is released, and the interlayer friction locking effect disappears accordingly. The stiffness of the flexible fingers returns from a high-stiffness locked state to its initial natural flexible state. Subsequently, the stepper motor is controlled to start running in the forward direction again, driving the two flexible fingers to open synchronously through the lead screw drive, so that the inner wall of the fingers detaches from the surface of the target object, completely releasing the target object. This completes one full clamping cycle operation and prepares for the next work cycle.

[0016] The variable stiffness clamp based on layer interference according to the present invention has the following advantages compared with the prior art: 1. Excellent enveloping properties and high safety. The flexible finger of this invention is composed of an integrally molded finger base, a first beam, a second beam, a through beam, and a crossbeam, and is made of flexible materials such as silicone or polyurethane, giving it excellent deformability and enveloping characteristics, thereby effectively improving the safety of the gripper.

[0017] 2. High rigidity, strong load-bearing capacity, and excellent stability under negative pressure. A vacuum is applied to the first and second sealed cavities through an air tube, creating negative pressure within the cavities. The paper filling layer is compressed under this negative pressure, generating friction between the layers. This significantly improves the overall rigidity of the flexible finger, enhances the load-bearing capacity of the gripper, and improves its resistance to external interference, ensuring stability during the gripping process.

[0018] 3. Rapid stiffness adjustment and simple clamping operation. By simply applying negative pressure to the first and second sealing cavities using a vacuum pump, the stiffness of the flexible finger can reach its maximum value within 0.5 seconds; and the time required for the first and second sealing cavities to return to normal pressure is also no more than 0.5 seconds. The entire clamping process does not rely on a complex control system, making the operation simple and efficient.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments 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.

[0021] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the structure of the flexible finger of the present invention; Figure 3 This is a cross-sectional view of the flexible finger of the present invention; Figure 4 This is a schematic diagram of the mounting flange of the present invention; Figure 5 This is a schematic diagram of the structure of the base of the present invention; Figure 6 This is a schematic diagram of the structure of the I-beam connecting rod of the present invention; Figure 7 This is a schematic diagram of the structure of the finger linkage of the present invention; Figure 8 This is a schematic diagram of the structure of the intermediate connecting rod of the present invention; Figure 9 This is a demonstration diagram of the grasping process of the present invention; Figure 10 This is a diagram illustrating the load-bearing test results of the present invention; Figure 11 This is a comparison diagram of the grasping experiments of the present invention and existing technologies; Figure 12 This is a comparison chart of the stiffness experimental data of the present invention and the prior art.

[0022] Figure label: Mounting flange 10, first mounting hole 101, second mounting hole 102, fourth mounting hole 104; Stepper motor 11, intermediate connecting rod 12, tenth mounting hole 1210, eleventh mounting hole 1211, lead screw 13, T-nut 131, coupling 14, I-beam connecting rod 15, fifth mounting hole 151, connecting screw 16; Base 2, third mounting hole 201, sixth mounting hole 202; Flexible finger 3, finger base 31, through hole 311, first beam 32, second beam 33, first sealing cavity 321, through beam 34, second sealing cavity 341, crossbeam 35, air hole 36, paper filling layer 37; Finger link 4, eighth mounting hole 401, eighth mounting hole 402, ninth mounting hole 403. Detailed Implementation

[0023] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0024] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] The terms "first," "second," "third," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects and not to describe a particular order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, it may include a series of steps or units, or optionally, steps or units not listed, or other steps or units inherent to these processes, methods, products, or devices.

[0027] The accompanying drawings show only the portions relevant to this application, not all of them. Before discussing exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe operations (or steps) as sequential processes, many of these operations may be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations may be rearranged. The process may be terminated when its operation is completed, but may also have additional steps not included in the drawings. The process may correspond to a method, function, procedure, subroutine, subprogram, etc.

[0028] The terms “component,” “module,” “system,” “unit,” etc., used in this specification are used to refer to computer-related entities, hardware, firmware, combinations of hardware and software, software, or software in execution. For example, a unit can be, but is not limited to, a process running on a processor, a processor, an object, an executable file, a thread of execution, a program, and / or distributed between two or more computers. Furthermore, these units can be executed from various computer-readable media on which various data structures are stored. Units can communicate, for example, via local and / or remote processes based on signals having one or more data packets (e.g., data from a second unit interacting with another unit between a local system, a distributed system, and / or a network; for example, the Internet interacting with other systems via signals).

[0029] Example 1 like Figures 1 to 12 As shown, this embodiment provides a variable stiffness gripper based on layer interference, which is mounted on a robotic arm via a mounting flange 10, and includes: A drive assembly is connected to the mounting flange 10. The drive assembly includes a stepper motor 11 and a movable part. Under the driving force of the stepper motor 11, the movable part is driven to move in a straight line. The base 2 is connected to the outer body of the stepper motor 11; Multiple flexible fingers 3 are mounted on the base 2 to form a clamping space. The flexible fingers 3 are connected to the movable part via finger connecting rods 4. When the movable part moves, it drives the flexible fingers 3 to perform grasping and releasing actions. Each flexible finger 3 includes: The finger base 31 is provided with a through hole 311, through which the flexible finger 3 is bolted to the finger connecting rod 4; The first beam 32 and the second beam 33 are respectively installed at both ends of the finger base 31, and the other ends away from the finger base 31 extend in a direction that approaches each other. The first beam 32 is offset from the clamping space and has a first sealing cavity 321 inside. Both the first sealing cavity 321 and the second sealing cavity 341 are provided with air holes 36. The air holes 36 are opened at one end of the finger base 31. The sealing cavity is sealed to the air pipe through the air holes 36, and the other end of the air pipe is sealed to the external vacuum pump. A through beam 34 is installed in the middle of the finger base 31, and the other end is connected to the first beam 32 and the second beam 33 to form a trapezoidal hollow structure. The through beam 34 has a second sealing cavity 341. Multiple crossbeams 35, one end of which is connected to the through beam 34, and the other end of which is connected to the first beam 32 or the second beam 33 to form multiple hollow units, have good passive deformation ability and envelopment when clamping items, while improving the rigidity of the flexible finger clamping surface and enhancing the load capacity. The first sealing cavity 321 and the second sealing cavity 341 are both connected to an external air source but are not interconnected, and can be used to independently achieve negative pressure regulation; A paper filling layer 37 is filled in the first sealing cavity 321 and the second sealing cavity 341. The paper filling layer 37 is composed of multiple layers of flexible paper, with gaps between each layer of flexible paper to generate interlayer friction through negative pressure compression, thereby achieving stiffness adjustment. The interlayers of the paper filling layer 37 are coated with an anti-slip coating. The number of layers in the paper filling layer 37 is 15-30, and the thickness of each layer is 0.1-0.3mm, which enhances the interlayer friction coefficient and improves the stiffness adjustment effect.

[0030] It should be noted that in this embodiment, the first beam 32 and the second beam 33 are symmetrical about the through beam 34, and the wall thickness of the first beam 32 is greater than the wall thickness of the second beam 33.

[0031] It should be noted that, in this embodiment, the movable part is an intermediate connecting rod 12, which is hinged to one end of the finger connecting rod 4, and the end of the finger connecting rod 4 away from the intermediate connecting rod 12 is connected to the flexible finger 3; the intermediate connecting rod 12 is equipped with a T-shaped nut 131, and the driving assembly further includes: The lead screw 13 is connected to the output shaft of the stepper motor 11 via a coupling 14, and the lead screw 13 is threadedly engaged with the T-nut 131; The I-beam connecting rod 15 is hinged between the base 2 and the finger connecting rod 4, and is used to convert the rotational motion of the lead screw 13 into the swinging opening and closing action of the flexible finger 3. In this embodiment, the stepper motor 11 is a 57 stepper motor, and its output shaft is coaxially and fixedly connected to the lead screw 13 through a coupling 14. The coupling 14 is an HBFP rigid coupling.

[0032] It should be noted that in this embodiment, the flexible finger 3 is made of a flexible material, such as silicone or polyurethane. The finger base 31, the first beam 32, the second beam 33, the through beam 34, and the crossbeam 35 are integrally formed, resulting in a compact structure with controllable flexibility.

[0033] This embodiment also provides the following specific implementation examples: 1. Install flange and base: The mounting flange 10 is made of R4600 resin and has a circular flange structure. It has a first mounting hole 101 and a second mounting hole 102 evenly distributed on it. The first mounting hole 101 is connected to the end of the FAIRINO-FR5 robotic arm via bolts for overall installation and positioning. The second mounting hole 102 is a threaded hole used for threaded connection between the connecting screw 16 and the threaded hole on the stepper motor 11. The connecting screw 16 is an M5 type to ensure a secure connection. The base 2 is also made of R4600 resin and has a rectangular block structure with a flat mounting surface at the bottom for fixing to the stepper motor 11. A fourth mounting hole 104 is provided on the base 2 corresponding to the through hole of the stepper motor 11. The base 2 is then threadedly connected to the stepper motor 11 via the fourth mounting hole 104.

[0034] 2. Driver components: The intermediate connecting rod 12 is made of R4600 resin, and the T-nut 131 is made of copper. The lead screw 13 is a T10 trapezoidal threaded lead screw with a pitch of 2mm and is made of 304 stainless steel.

[0035] The intermediate connecting rod 12 is provided with a tenth mounting hole 1210 and an eleventh mounting hole 1211. The intermediate connecting rod 12 is fixedly connected to the T-nut 131 through the eleventh mounting hole 1211 by a set screw to ensure linkage synchronization.

[0036] One end of the finger link 4 has a ninth mounting hole 403, which is hinged to the finger base 3 by means of a bolt passing through the tenth mounting hole 1210 on the intermediate link 12. The other end of the finger link 4 has an eighth mounting hole 401, which is hinged to the finger base 31 of the flexible finger 3 by means of a bolt passing through the through hole 311 on the finger base 31. The finger link 4 also has an eighth mounting hole 402, which is hinged to the finger link 4 by means of a bolt passing through the eighth mounting hole 402. One end of the I-beam link 15 has a fifth mounting hole 151, which is hinged to the finger base 2 by means of a bolt passing through the third mounting hole 201 on the base 2. The other end has a sixth mounting hole 202, which is hinged to the finger link 4 at the eighth mounting hole 402 by means of a bolt. Together with the lead screw 13, the T-nut 131, and the intermediate link 12, the flexible finger 3 can open and close smoothly.

[0037] 3. Flexible fingers: The flexible finger 3 body is made of E630 silicone material. It is formed by mixing AB glue and pouring it into a mold. The outer contour is a trapezoid with a narrow top and a wide bottom. The overall height is 100mm, the bottom base 31 is 52mm wide, the top base is 7mm wide, and the thickness is 20mm.

[0038] The first beam 32, the second beam 33, and the through beam 34 all have rectangular cross sections and a thickness of 2mm. Four horizontal beams 35 are arranged in parallel at intervals, with a spacing of 16mm between adjacent horizontal beams 35. The horizontal beams 35 are connected to the first beam 32, the second beam 33, and the through beam 34, together forming 10 triangular or trapezoidal hollow units with progressively increasing dimensions along the finger height direction. These units are used to enhance the flexible deformation capability of the flexible finger 3, making it easier to fit and enclose target objects of different shapes.

[0039] The finger base 31 is a rectangular block structure with a length of 52mm, a height of 20mm, and a thickness of 20mm. It has two through holes 311 with a diameter of 3mm, which are bolted to the eighth mounting hole 401 on the finger connecting rod 4. Anti-loosening washers are provided between the bolts and the through holes 311 to prevent loosening during clamping and ensure connection stability.

[0040] 4. Sealed cavity and paper filling layer: Both the first sealing cavity 321 and the second sealing cavity 341 are rectangular cavities with cross-sectional dimensions of 3mm×2mm and 2.5×2mm, respectively. The first sealing cavity 321 extends along the length of the first beam 32 with a length of 105mm, and the second sealing cavity 341 extends along the length of the through beam 34 with a length of 98mm. The two are not connected to each other and can be connected to a vacuum pump through independent air pipes to achieve independent negative pressure adjustment, thereby improving the flexibility of stiffness adjustment. The negative pressure of one or both sealing cavities can be flexibly adjusted according to the weight of the target object.

[0041] Both the first sealing cavity 321 and the second sealing cavity 341 are filled with paper filling layers 37. The paper filling layers 37 are made of 20 layers and 15 layers of flexible A4 paper in the first sealing cavity 321 and the second sealing cavity 341, respectively. The thickness of each paper layer is 0.1 mm. A thin silicon-based anti-slip coating with a thickness of 0.01 mm is uniformly applied between the layers to enhance the interlayer friction coefficient and ensure that stable interlayer friction can be generated when the negative pressure is squeezed, thereby realizing the stiffness adjustment of the flexible finger 3.

[0042] 5. Negative pressure connection structure: The diameter of the air hole 36 is 2mm. A copper air nozzle is embedded in the air hole 36. The air nozzle is sealed to the air pipe. The air pipe is a PU flexible tube with a diameter of 4mm. The other end of the air pipe is sealed to the external vacuum pump with a vacuum adjustment range of 0 kPa to -80 kPa. A sealing ring is provided at the connection between the air nozzle and the air pipe to prevent negative pressure leakage and ensure the stability and reliability of the stiffness adjustment.

[0043] This embodiment also provides a method for clamping a variable stiffness gripper based on layer interference, wherein the variable stiffness gripper described above is used for clamping, and the method includes the following steps: S1: Initial state settings, specifically including: At the beginning of the clamping operation, the vacuum pump is kept off to maintain the internal air pressure of the first and second sealed chambers at standard atmospheric pressure, and the flexible fingers are in a natural flexible state. At the same time, the stepper motor is started to run in the forward direction. The output shaft of the stepper motor drives the lead screw to rotate synchronously in the forward direction through the coupling. The T-shaped nut on the lead screw is fed linearly away from the stepper motor along the lead screw axis under the action of thread transmission. The T-shaped nut drives a pair of symmetrically arranged flexible fingers to swing outward synchronously around their respective hinge axes through the linkage transmission mechanism consisting of the intermediate connecting rod, the finger connecting rod and the I-shaped connecting rod, so as to realize the finger opening action. The opening angle is controlled at 30° so that the target object can be placed into the clamping space between the two fingers. S2: Clamping posture adjustment and flexible envelope positioning, specifically including: An external robotic arm carries the gripper to a preset position above the target object. Based on the target object's dimensions and spatial orientation, the gripper's overall position is adjusted so that a pair of flexible fingers are positioned on opposite sides of the target object, with the inner envelope of the fingers facing the outer contour of the object, ensuring sufficient envelope travel. Subsequently, the stepper motor is controlled to start in reverse, causing the lead screw to rotate in the opposite direction. The T-nut retracts linearly along the lead screw towards the stepper motor, simultaneously causing the two flexible fingers to slowly close at a constant closing speed, preferably controlled at 5 mm / s. During the closing process, the flexible fingers, due to their flexibility, gradually conform to the outer surface of the target object until the inner walls of the fingers completely cover at least a portion of the target object's outer contour, and the contact force is evenly distributed. Immediately after this, the stepper motor stops operating to prevent excessive compression that could damage the target object. S3: Vacuum negative pressure excitation and layer interference variable stiffness locking, specifically including: After the flexible fingers have successfully enveloped and adhered to the target object, the vacuum pump is activated and its negative pressure is set to -80 kPa. Vacuum treatment is then performed on the first and second sealed chambers via sealed air tubes, gradually reducing the air pressure within both chambers from atmospheric pressure to the set negative pressure steady state. As the negative pressure forms within the chambers, the paper filling layers inside each sealed chamber are compressed tightly under the uniform gas pressure difference, increasing the contact positive pressure between the paper layers and significantly enhancing the interlayer static friction, thus generating a layer interference locking effect. This layer interference effect abruptly increases the overall bending stiffness of the flexible fingers from its initial natural compliant state to a preset high stiffness holding state, enabling the flexible fingers to form a stable and reliable rigid clamp on the target object with sufficient gripping force, preventing deformation or slippage due to insufficient stiffness during subsequent handling. S4: Negative pressure maintenance and target object handling, specifically including: After the target object is grasped and locked, the vacuum pump continues to run to maintain continuous negative pressure in the first and second sealing chambers, so that the vacuum degree in the two chambers is precisely stabilized at the preset working pressure of -80 kPa. This ensures that the interlayer clamping force and friction locking state of the paper filling layer do not decrease due to leakage or pressure fluctuations throughout the entire handling process, thereby maintaining the high rigidity characteristics of the flexible fingers. In this state, the external robotic arm drives the gripper and the grasped target object to move together along a predetermined trajectory, transporting the target object from the grasping position to the target placement position, completing the spatial transfer operation. S5: Negative pressure release, flexible recovery, and object release, specifically including: After the target object reaches the designated placement position, the vacuum pump is turned off, allowing the air pressure inside the first and second sealed chambers to slowly return to standard atmospheric pressure. As the negative pressure inside the chambers disappears, the pressure on the paper filling layer is released, and the interlayer friction locking effect disappears accordingly. The stiffness of the flexible fingers returns from a high-stiffness locked state to its initial natural flexible state. Subsequently, the stepper motor is controlled to start running in the forward direction again, driving the two flexible fingers to open synchronously through the lead screw drive, so that the inner wall of the fingers detaches from the surface of the target object, completely releasing the target object. This completes one full clamping cycle operation and prepares for the next work cycle.

[0044] To verify the beneficial effects of the present invention, the variable stiffness gripper based on layer interference and its gripping method of the present invention were subjected to the following experiments: I. Load-bearing experiment: like Figure 9 and Figure 10 As shown, the angles of the second beam 33 on the flexible finger 3 of the gripper with the vertical direction were changed to 0°, 15°, and 30° to study the maximum load force of the gripper when grasping cylindrical target objects with different diameters of Φ50, Φ50, and Φ70 at 0 kPa and -80 kPa. The results are shown in the figure. The experimental results indicate that at -80 kPa, the maximum gripping force of the gripper is increased by 203.45%–833.33% compared to 0 kPa. Specifically, at an angle of 30° and a target object diameter of Φ50, the gripping force reaches 10.5 N.

[0045] II. Clamping Experiment: The present invention and the comparative example were used to conduct clamping experiments on different items, and the results are as follows: Figure 11 As shown, The comparative example is a traditional structure without a through beam; As can be seen, while the existing technology can successfully grasp strawberries, it fails to grasp heavier items such as apples and dragon fruit. This invention offers a wider grasping range compared to existing technologies.

[0046] III. Comparative Stiffness Experiment: The stiffness of the present invention and the comparative example were tested, and the results are as follows: Figure 12 As shown, The comparative example is a structure with only one chamber.

[0047] Experimental results show that, in both the front (perpendicular to the front beam) and side (parallel to the front beam) directions, when both the first beam and the sealing cavity of the through beam are under negative pressure, the stiffness provided is significantly higher than when only a single beam is under negative pressure. Particularly in the front direction, with a contact depth (D) of 30 mm between the finger's front beam and the target object, the finger stiffness increases by 54.92% and 31.42% respectively when only the first or second sealing cavity works alone; while when both cavities work together, the finger stiffness increases by a remarkable 137.43%.

[0048] The variable stiffness clamp based on layer interference according to the present invention has the following advantages compared with the prior art: 1. Excellent enveloping properties and high safety. The flexible finger of this invention is composed of an integrally molded finger base, a first beam, a second beam, a through beam, and a crossbeam, and is made of flexible materials such as silicone or polyurethane, giving it excellent deformability and enveloping characteristics, thereby effectively improving the safety of the gripper.

[0049] 2. High rigidity, strong load-bearing capacity, and excellent stability under negative pressure. A vacuum is applied to the first and second sealed cavities through an air tube, creating negative pressure within the cavities. The paper filling layer is compressed under this negative pressure, generating friction between the layers. This significantly improves the overall rigidity of the flexible finger, enhances the load-bearing capacity of the gripper, and improves its resistance to external interference, ensuring stability during the gripping process.

[0050] 3. Rapid stiffness adjustment and simple clamping operation. By simply applying negative pressure to the first and second sealing cavities using a vacuum pump, the stiffness of the flexible finger can reach its maximum value within 0.5 seconds; and the time required for the first and second sealing cavities to return to normal pressure is also no more than 0.5 seconds. The entire clamping process does not rely on a complex control system, making the operation simple and efficient.

[0051] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" 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 this invention and 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.

[0052] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0053] Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The reference to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily indicate the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0054] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A variable stiffness gripper based on layer interference, mounted on a robotic arm via a mounting flange (10), characterized in that, include: A drive assembly is connected to the mounting flange (10). The drive assembly includes a stepper motor (11) and a movable part. Under the driving force of the stepper motor (11), the movable part is driven to move in a straight line. The base (2) is connected to the outer body of the stepper motor (11); Multiple flexible fingers (3) are mounted on the base (2) to form a clamping space. The flexible fingers (3) are connected to the movable part through the finger link (4). When the movable part moves, it drives the flexible fingers (3) to perform grasping and releasing actions.

2. The variable stiffness clamp based on layer interference according to claim 1, characterized in that, Each flexible finger (3) includes: Finger base (31); The first beam (32) and the second beam (33) are respectively installed at both ends of the finger base (31), and the other ends away from the finger base (31) extend in a direction that approaches each other. The first beam (32) is offset from the clamping space and has a first sealing cavity (321) inside. A through beam (34) is installed in the middle of the finger base (31), and the other end is connected to the first beam (32) and the second beam (33) to form a trapezoidal hollow structure, wherein the through beam (34) has a second sealing cavity (341). Multiple crossbeams (35) are connected at one end to the through beam (34) and at the other end to the first beam (32) or the second beam (33) to form multiple hollow units. When clamping items, they have good passive deformation ability and envelopment, while improving the stiffness of the flexible finger clamping surface and enhancing the load capacity. The first sealing cavity (321) and the second sealing cavity (341) are both connected to an external air source but are not interconnected.

3. The variable stiffness clamp based on layer interference according to claim 2, characterized in that, The first beam (32) and the second beam (33) are symmetrical about the through beam (34), and the wall thickness of the first beam (32) is greater than that of the second beam (33).

4. The variable stiffness gripper based on layer interference according to claim 2, characterized in that, The flexible finger (3) also includes: A paper filling layer (37) is filled in the first sealing cavity (321) and the second sealing cavity (341). The paper filling layer (37) is composed of multiple layers of flexible paper, with gaps between each layer of flexible paper.

5. The variable stiffness gripper based on layer interference according to claim 4, characterized in that, The paper filling layer (37) is coated with an anti-slip coating between its layers. The number of layers in the paper filling layer (37) is 15-30, and the thickness of each layer is 0.1-0.3 mm, which enhances the interlayer friction coefficient and improves the stiffness adjustment effect.

6. The variable stiffness gripper based on layer interference according to claim 1, characterized in that, The movable part is a middle connecting rod (12), which is hinged to one end of the finger connecting rod (4), and the end of the finger connecting rod (4) away from the middle connecting rod (12) is connected to the flexible finger (3); the middle connecting rod (12) is equipped with a T-nut (131), and the drive assembly also includes: The lead screw (13) is connected to the output shaft of the stepper motor (11) via a coupling (14), and the lead screw (13) is threadedly engaged with the T-nut (131); The I-beam connecting rod (15) is hinged between the base (2) and the finger connecting rod (4) to convert the rotational motion of the lead screw (13) into the swinging opening and closing action of the flexible finger (3).

7. The variable stiffness clamp based on layer interference according to claim 2, characterized in that, Both the first sealing cavity (321) and the second sealing cavity (341) are provided with air holes (36). The air holes (36) are opened at one end of the finger base (31). The sealing cavity is sealed to the air pipe through the air holes (36), and the other end of the air pipe is sealed to the external vacuum pump.

8. The variable stiffness gripper based on layer interference according to claim 2, characterized in that, The finger base (31), the first beam (32), the second beam (33), the through beam (34), and the crossbeam (35) are integrally formed, with a compact structure and controllable flexibility.

9. The variable stiffness gripper based on layer interference according to claim 2, characterized in that, The finger base (31) is provided with a through hole (311), and the flexible finger (3) is bolted to the finger link (4) through the through hole (311).

10. A method for clamping a variable stiffness gripper based on layer interference, characterized in that, The clamping process using the variable stiffness clamp as described in any one of claims 1 to 9 includes the following steps: S1: Initial state settings, specifically including: At the beginning of the clamping operation, the vacuum pump is controlled to be turned off, so that the internal air pressure of the first sealing chamber and the second sealing chamber is maintained at standard atmospheric pressure, and the flexible fingers are in a natural flexible state. At the same time, the stepper motor is controlled to start running in the forward direction. The output shaft of the stepper motor drives the lead screw to rotate synchronously in the forward direction through the coupling, which drives the flexible fingers to swing outward synchronously around their respective hinge axes, so as to realize the finger opening action. S2: Clamping posture adjustment and flexible envelope positioning, specifically including: An external robotic arm carries the gripper to a preset position above the target object. Based on the target object's dimensions and spatial orientation, the gripper's overall position is adjusted so that a pair of flexible fingers are positioned on opposite sides of the target object, with the inner envelope of the two fingers facing the outer contour of the target object, ensuring that the flexible fingers have sufficient envelope travel. Subsequently, the stepper motor is controlled to start running in reverse, causing the lead screw to rotate in the opposite direction, which in turn causes the two flexible fingers to slowly close at a constant closing speed. S3: Vacuum negative pressure excitation and layer interference variable stiffness locking, specifically including: After the flexible finger completes the enveloping adhesion to the target object, the vacuum pump is started and the vacuum pump's negative pressure value is set to -80 kPa. The first and second sealing chambers are evacuated through the sealed air tubes, so that the air pressure in the two sealing chambers gradually decreases from normal pressure to the set negative pressure steady state. As the negative pressure is formed in the chambers, the paper filling layers set in each sealing chamber are tightly squeezed by the uniform gas pressure difference. The contact positive pressure between the layers of paper increases, and the interlayer static friction is significantly increased, thereby producing a layer interference locking effect. S4: Negative pressure maintenance and target object handling, specifically including: After the target object is grasped and locked, the vacuum pump continues to run to maintain continuous negative pressure on the first and second sealed chambers, so that the vacuum degree in the two chambers is precisely stabilized at the preset working pressure. This ensures that the interlayer clamping force and friction locking state of the paper filling layer do not decrease due to leakage or pressure fluctuations throughout the entire handling process, thereby maintaining the high rigidity characteristics of the flexible fingers. In this state, the external robotic arm drives the gripper and the grasped target object to move together along a predetermined trajectory, transporting the target object from the grasping position to the target placement position, completing the spatial transfer operation. S5: Negative pressure release, flexible recovery, and object release, specifically including: After the target object reaches the designated placement position, the vacuum pump is turned off, allowing the air pressure inside the first and second sealed chambers to slowly return to standard atmospheric pressure. As the negative pressure inside the chambers disappears, the pressure on the paper filling layer is released, and the interlayer friction locking effect disappears accordingly. The stiffness of the flexible fingers returns from a high-stiffness locked state to its initial natural flexible state. Subsequently, the stepper motor is controlled to start running in the forward direction again, driving the two flexible fingers to open synchronously through the lead screw drive, so that the inner wall of the fingers detaches from the surface of the target object, completely releasing the target object. This completes one full clamping cycle operation and prepares for the next work cycle.

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