A parallel gripper for planar soft objects and its multimodal grasping method

Abstract

The present invention discloses a planar soft parallel gripper and a multimodal grasping method thereof, wherein the planar soft parallel gripper comprises two parallel soft palms, a rigid connector, and connecting screws; the soft palms comprise a sealing plate, two tubular actuators, four stretch-limiting bars, a grasping layer, and an end stop block; the Joule heat generated by electric current is used to control the phase transformation of a low-melting-point alloy, thereby producing a change in stiffness; when the tubular actuator is charged with positive pressure, four working modes can be generated: elongation, left bending, right bending, and twisting; through the coordinated control of air pressure and electric heat and the combination of two parallel soft palms, only using bending deformation, one envelope grasping mode and three hooking modes can be achieved. The planar parallel soft gripper upgrades point / line contact to surface contact, significantly improving friction and support force, and can firmly grasp targets of large size, complex curved surfaces, and even multiple convex and concave features.

Description

Technical Field

[0001] The present invention relates to the field of soft grippers and deformation interfaces, and in particular to a planar soft parallel gripper and a multi-modal gripping method thereof. Background Art

[0002] The application of robots has expanded from traditional manufacturing and industrial automation to fields such as services, medical care, and human-robot collaboration, requiring powerful end-effectors to complete complex tasks. However, rigid end-effectors composed of rigid joints and links face challenges in grasping objects of different sizes, shapes, and material properties. In order to grasp these objects, various sensors and complex algorithms are usually used to accurately calculate their position and geometry, which greatly increases the cost of use and limits the universality of rigid grippers. In addition, such a grasping process can easily cause damage to the target object and the operator, making it impossible to interact safely with humans.

[0003] Deformable interfaces can undergo a large range of surface deformation under external drive to present the expected shape. When used on end effectors, they can enhance their ability to interact with the grasped object. In recent years, with the development of deformable materials and the advancement of driving technology, deformable flexible interfaces and deformable bodies have more flexible deformation capabilities, which provides feasibility for meeting special and novel needs. Traditional strip-shaped soft grippers lack stability and robustness when grasping target objects with irregular surfaces. Therefore, in this context, there is an urgent need to develop a surface-shaped soft gripper with softness and compliance, so that it can increase the contact area with the surface of the target object, so that it can grasp various types of irregular objects efficiently and stably. At the same time, facing different objects, the gripper needs to be able to adjust the grasping mode to achieve actions such as enveloping and hooking.

[0004] Leveraging the flexibility of deformable materials, soft grippers can adaptively conform to target surfaces without the need for high-precision sensing and complex algorithms, evenly distributing contact pressure and thus safely grasping objects of varying shapes, sizes, and materials. Compared to traditional strip-shaped soft fingers, planar parallel soft grippers achieve significant programmable deformation within a two-dimensional plane, upgrading point / line contact to surface contact, significantly improving friction and support, enabling secure grasping of large, complex curved surfaces, and even targets with multiple convex and concave features. Its multi-cavity independent drive structure can also switch between wrapping and hooking modes, meeting the urgent need for "multimodal, universal gripper" in scenarios such as warehousing, medical care, and human-machine collaboration. Summary of the Invention

[0005] The purpose of the present invention is to address the shortcomings of the existing technology and provide a planar soft parallel gripper and its multimodal grasping method, aiming to solve the problems of stability and reliability of traditional strip-shaped soft fingers in existing research when grasping objects of different shapes, sizes and materials. At the same time, its multimodal grasping can be applied in a variety of scenarios.

[0006] The present invention is achieved through the following technical solutions:

[0007] A planar soft parallel gripper, comprising a rigid connector, connecting screws and two parallel soft palms; the rigid connector is directly made of PLA material through 3D printing; the soft palms are a rigid-soft mixture, comprising a sealing plate, two tubular drivers, four stretch-limiting strips, a gripping layer and an end limit block; the sealing plate is made of PLA material through 3D printing; the two tubular drivers, four stretch-limiting strips, the gripping layer and the end limit block are all made by casting and bonding silicone of various hardnesses; the positioning groove on the rigid connector and the sealing plate positioning groove on the soft palm are matched and connected by mutual inlaying, and then completely positioned by the positioning hole of the rigid connector and the positioning hole of the sealing plate, and the threads in the positioning hole of the sealing plate are completely fixed with the connecting screws.

[0008] Specifically, the rigid connector has four air inlet channels, two positioning holes and two positioning slots; the air inlet channels are connected to an air pipe and an external pneumatic system; the external pneumatic system adjusts the air pressure to provide controllable driving force and compliance force feedback for the tubular actuator, thereby achieving adjustment of the actuator bending angle.

[0009] Specifically, the soft palm includes a sealing plate, a first tubular driver, a second tubular driver, a first stretch limiting strip, a second stretch limiting strip, a third stretch limiting strip, a fourth stretch limiting strip, a gripping layer and an end limit block; wherein the sealing plate includes a sealing plate air inlet channel, a sealing plate positioning hole and a sealing plate positioning groove, and the air holes on the sealing plate and the air holes on the rigid connecting part are aligned, so that the air pipe can smoothly enter each tubular driver; the top layer of each tubular driver is bonded to the circular plates at both ends of the sealing plate.

[0010] Specifically, the first and second tubular actuators are fiber-reinforced actuators, consisting of a silicone liner and a winding wire. The side and two ends of the silicone liner are made of two types of silicone with different hardness. The winding wire is embedded in the side wall of the silicone liner. During the production process, an inner liner base is first cast. After the winding wire is wound, a wrapping layer is cast using the same silicone as the inner liner side to integrate them. The winding wire has a diameter of 2-4 mm and is a circle of rings. The interval between two adjacent winding wires is 5-8 mm, which is used to limit the stretching of the tubular actuator in its radial direction, so that when gas is filled, the tubular actuator can be stretched in the axial direction without expanding.

[0011] Specifically, the four stretch-limiting strips on the soft palm are composed of a silicone coating, a heating wire, and a low-melting-point alloy. The heating wire is spirally embedded in the silicone coating, and there is a hollow tube inside to place the low-melting-point alloy. The heating wire can generate Joule heat within 5 seconds after current is passed through it. When the tubular driver is stretched, the spirally wound heating wire can be stretched at the same time without damaging the heating wire body. The heating wire is also connected to an external electronic control system to achieve different temperature adjustments.

[0012] Furthermore, the low-melting-point alloy completes a solid-liquid phase transition at 30 to 65 degrees Celsius. Specifically, it liquefies when heated to the phase transition temperature, thereby releasing the restriction of the tensile limit strip. When cooled, it solidifies, instantly locking the posture of the tensile limit strip and increasing the modulus, thereby achieving programmable stiffness of "soft-hard" switching. When the temperature is lowered in conjunction with the cooling layer, the tensile limit strip returns to a solid state.

[0013] Specifically, the Shore hardness of the silicone inner liner side of the tubular driver and the silicone coating of the tensile limit strip is 15A~25A, the Shore hardness of the silicone inner liner of the tubular driver and the gripping layer silicone is 25A~45A, and the Shore hardness of the silicone of the end limit block is 45A~65A.

[0014] Specifically, the gripping layer is made of silicone with a Shore hardness of 25A to 45A, so that it can achieve passive stretching under the active drive of the tubular actuator. In addition, the gripping layer is also the contact area with the grasped object and can passively conform to and fit the surface of the grasped object.

[0015] Specifically, the end limiting block is made of silicone with a Shore hardness of 45A to 65A, which can hook the grasped object in the hook mode and prevent the grasped object from slipping in the envelope mode.

[0016] The present invention also provides a multi-modal grasping method of a planar soft parallel gripper, which is characterized by comprising the following steps:

[0017] (1) When a target is grasped, the object localization phase begins. The RGB-D image acquired by the depth camera is first used for object detection, and object recognition / classification is performed within the candidate box. This not only determines the category, but also determines whether the target has a large hole, a geometric property.

[0018] (2) Then, the object is segmented at the pixel level or point cloud level to obtain a clean outline and point cloud. That is, when the object is classified, the classification results include two types: objects with large holes and objects without large holes. At this time, the control system of the planar soft parallel gripper receives the classification results and determines the working mode. The objects with large holes adopt the hook mode, and the objects without large holes adopt the envelope mode.

[0019] (3) If it is a hook mode, then the three sub-modes of hooking on both sides, hooking on the left, and hooking on the right are selected according to the relative distance and size of the holes of the grasped object; at the same time, the segmented point cloud is sent to the object pose estimation module to output the 6D pose; several grasping candidates are generated and scored according to the pose, gripper mode, and environmental collision constraints;

[0020] (4) Finally, the optimal grasping posture is handed over to the gripper motion planning to generate the robot arm trajectory and the motion curve of the planar parallel gripper, completing the work from visual perception to completion of grasping.

[0021] The beneficial effects of the present invention are as follows:

[0022] The proposed parallel soft gripper is based on a flexible tubular actuator filled with a low-melting-point alloy, capable of significant bending under pressure. The low-melting-point alloy undergoes a solid-liquid phase transition without requiring high temperatures, allowing for simple electrical control. At room temperature, the alloy rapidly solidifies, locking the soft wall into a high-modulus structure and instantly increasing the gripper's stiffness and load capacity. The gripper's stiffness can be varied over a wide range. Two tubular actuators connected in parallel form a "soft hand." Assembling these two soft hands into a parallel mechanism retains the adaptive wrapping capabilities of a soft gripper while offering the synchronized opening and closing properties of a mechanical gripper, enabling precise insertion and centering within narrow channels.

[0023] The advantages of the surface parallel gripper are: ① Multimodal grasping - in a flexible state, the two palms can be bent into arcs to achieve a large-area envelope, which is suitable for fragile objects such as fruits and medicine bottles; the end can also be partially bent to form a hook, which can be used to hook heavy loads through holes or handles. ② High load and shape retention - after the target is positioned, the alloy is solidified, and the gripper's stiffness is increased by dozens of times. At the same time, using air pressure, it can stably carry parts that are several times its own weight and maintain its posture during the transmission process; after the delivery is completed, it can be reheated to restore its softness and has a high cycle life. In summary, the variable stiffness parallel soft gripper uses the dual mechanism of "flexible adaptation + rigid locking" to achieve "one claw with multiple functions" in tasks with limited space, diverse targets, and large load spans, providing efficient and reliable end-to-end execution solutions for logistics sorting, assembly automation, surgical instruments and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of the planar soft parallel gripper of the present invention;

[0025] Figure 2 3-D views of the planar soft parallel gripper of the present invention;

[0026] Figure 3 It is a structural schematic diagram of the rigid connector of the present invention;

[0027] Figure 4 It is a schematic structural diagram of the sealing plate on the soft palm of the present invention;

[0028] Figure 5 It is a structural schematic diagram of the soft palm and the stretch limiting strip of the present invention;

[0029] Figure 6 This is a diagram of the control method and working mode of the soft palm of the present invention;

[0030] Figure 7 Schematic diagram of the multi-modal grasping mode of the planar soft parallel gripper of the present invention;

[0031] Figure 8 Schematic diagram of a gripping system based on a planar soft parallel gripper of the present invention;

[0032] Figure 9 It is a flowchart of the crawling scheme of the present invention.

[0033] Figure numerals: 1 rigid connector, 2 connecting screw, 3 soft palm; 101 air inlet channel, 102 positioning hole, 103 positioning groove; 301 sealing plate, 302 first tubular driver, 303 second tubular driver, 304 first stretch limiting strip, 305 second stretch limiting strip, 306 third stretch limiting strip, 307 fourth stretch limiting strip, 308 gripping layer, 309 end limit block; 3011 sealing plate air inlet channel, 3012 sealing plate positioning hole, 3013 sealing plate positioning groove. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0035] The present invention provides a planar soft parallel gripper, such as Figure 1 and Figure 2As shown, the device comprises a rigid connector 1, connecting screws 2, and a soft palm 3. The rigid connector 1 is directly fabricated from PLA material via 3D printing. The soft palm 3 is a rigid-soft hybrid and includes a sealing plate 301, two tubular actuators (a first tubular actuator 302 and a second tubular actuator 303), four stretch-limiting bars (a first stretch-limiting bar 304, a second stretch-limiting bar 305, a third stretch-limiting bar 306, and a fourth stretch-limiting bar 307), a gripping layer 308, and an end stopper 309. The sealing plate 301 is 3D printed from PLA, while the remaining components are cast and bonded using silicone of various hardnesses. Specifically, the Shore hardness of the silicone liner on the sides of the tubular actuators and the silicone coating of the stretch-limiting bars ranges from 15A to 25A. The Shore hardness of the silicone at the ends of the tubular actuators and the gripping layer ranges from 25A to 45A. The Shore hardness of the silicone at the end stopper ranges from 45A to 65A.

[0036] like Figure 3 As shown, the rigid connector 1 has four air inlet channels 101, two positioning holes 102 and two positioning slots 103; the air inlet channel 101 is connected to an air pipe and an external pneumatic system. The external pneumatic system is a known technology in the field, including an air pump and an air pressure controller, etc., which are used to adjust the air pressure, provide controllable driving force and flexible force feedback for the tubular actuator, and realize the adjustment of the actuator bending angle; the positioning slots 103 on the rigid connector and the sealing plate positioning slots 3013 on the soft palm can be matched by mutual inlaying, and then completely positioned by the positioning holes 102 of the rigid connector and the sealing plate positioning holes 3012 on the sealing plate 301. The sealing plate positioning holes 3012 have internal threads and are completely fixed after assembly by the connecting screws 2. The rigid connector provided in the present invention is a fixed connector. If a slider structure is provided to adjust the relative position between the two positioning holes, the relative distance between the two parallel soft palms 3 can be adjusted.

[0037] like Figure 4 As shown, the soft palm 3 includes a sealing plate 301, a first tubular driver 302, a second tubular driver 303, a first stretch limiting strip 304, a second stretch limiting strip 305, a third stretch limiting strip 306, a fourth stretch limiting strip 307, a gripping layer 308, and an end stopper 309; wherein the sealing plate 301 includes a sealing plate air inlet channel 3011, a sealing plate positioning hole 3012, and a sealing plate positioning groove 3013, as shown in FIG. Figure 5 The air holes on the sealing plate 301 and the air holes on the rigid connector 1 are aligned, so that the air pipe can smoothly enter each tubular driver, and the top layer of each tubular driver is bonded to the circular plates at both ends of the sealing plate.

[0038] The first and second tubular actuators 302 and 303 are fiber-reinforced actuators, consisting of a silicone liner and a winding wire. The sides and ends of the silicone liner are made of two different hardnesses of silicone: 15A-25A and 25A-45A Shore A hardness, respectively. The sides are less hard to facilitate stretching, while the ends are harder than the sides to provide greater strength when bonded to the remaining components. The winding wire is embedded in the sidewalls of the silicone liner. During fabrication, a base is first cast. After the winding wire is wrapped, a wrapping layer is cast using the same silicone as the liner sides to integrate them. The winding wire has a diameter of 2-4 mm and is arranged in a series of circular loops. The spacing between adjacent winding wires is 5-8 mm, which serves to limit radial stretch of the tubular actuator. This allows for greater axial stretching when inflated with gas, without expanding like a balloon.

[0039] The stretch limiting strip is as follows Figure 5 As shown in the enlarged image, the device consists of a silicone sheath, a heating wire, and a low-melting-point alloy. The heating wire is spirally embedded in the silicone sheath, with a hollow tube containing the low-melting-point alloy. The heating wire has a high resistance and generates significant Joule heating within 5 seconds when a suitable current is applied. The spiral winding also increases the contact area between the heating wire and the low-melting-point alloy, reducing the heating time when the low-melting-point alloy reaches its phase transition temperature. Furthermore, the spirally wound heating wire allows for simultaneous stretching during tubular actuator extension without damaging the heating wire itself. The heating wire is connected to an external electronic control system for variable temperature regulation. This external control system is well known in the art. Low-melting-point alloys (such as gallium-indium and gallium-tin eutectics) undergo a rapid solid-liquid phase transition between 30 and 65 degrees Celsius. Upon heating to the phase transition temperature, they liquefy, releasing the restraint of the tensile restraint bar. Upon cooling, they solidify, instantly locking the restraint bar in place and significantly increasing the modulus, thereby achieving programmable stiffness that can be switched from "soft" to "hard." In addition, the cooling layer can be used to achieve rapid cooling, allowing the stretch-limiting strip to return to a solid state.

[0040] The gripping layer is made of silicone with a Shore hardness of 25A to 45A, so that it can achieve passive stretching under the active drive of the tubular actuator. In addition, the gripping layer is also the main contact area with the grasped object and can passively conform to and fit the surface of the grasped object.

[0041] The end limit block is made of silicone with a Shore hardness of 45A~65A. In the hook mode, it can hook the grasped object such as a bag, kitchen utensil handle, etc., and in the envelope mode, it can prevent the grasped object from slipping.

[0042] The present invention also provides a multimodal grasping method. An external pneumatic system adjusts air pressure to control the bending degree of the tubular actuator, while an external circuit system adjusts the temperature of the heating wire to control the solid-liquid phase transition of the low-melting-point alloy. This coordinated control strategy of air pressure and electric heating effectively changes the stiffness of the stretch-limiting strip, enabling the tubular actuator to achieve both stretching and bending deformation.

[0043] like Figure 6 As shown, the soft palm can realize four working modes: extension, left bending, right bending and twisting; in this embodiment, all tubular actuators in the four working modes are fed with the same positive air pressure; in the extension mode, the first stretching limit bar 304, the second stretching limit bar 305, the third stretching limit bar 306 and the fourth stretching limit bar 307 are all powered, so that the low-melting-point alloy is in liquid state and can be stretched; in the left bending mode, the first stretching limit bar 304 and the second stretching limit bar 305 are not powered, the low-melting-point alloy is in solid state and cannot be stretched, and the third stretching limit bar 306 and the fourth stretching limit bar 307 are powered, so that the low-melting-point alloy is in liquid state. , it can be stretched, but due to the incompatibility of stretching on the opposite side of the same tubular actuator, it bends toward the side where stretching is limited; the control strategy in the right bending mode is opposite to that in the left bending mode; in the twisting mode, the bending directions of the two tubular actuators on the soft palm are different. For example, when the first stretch limiting bar 304 is energized and the second stretch limiting bar 305 is not energized, the tubular actuator bends to the right; when the third stretch limiting bar 306 is not energized and the fourth stretch limiting bar 307 is energized, the tubular actuator bends to the left, so that the gripping layer connecting the two tubular actuators is twisted. The same twisting has two directions, clockwise and counterclockwise, just like bending, and only one is listed in this embodiment.

[0044] Since the extension mode and twisting mode are not very useful for parallel soft grippers, only the bending mode is used for parallel grasping. Figure 7 As shown, two parallel soft palms simultaneously bending inward form an enveloping mode; two parallel soft palms simultaneously bending outward form a double-sided hooking mode; two parallel soft palms simultaneously bending to the left form a left-hooking mode; and two parallel soft palms simultaneously bending to the right form a right-hooking mode. When the target object is fragile, has an irregular surface, or requires force distribution over a large area, the soft gripper employs an enveloping mode for the safest and most reliable results. When the target has handles, holes, flanges, or a rigid structure, the gripper can utilize a hooking mode for fast and secure grasping.

[0045] like Figure 8 As shown in FIG, the grasping system of the present invention mainly includes a depth camera and a matching robotic arm in addition to the planar soft parallel grasper. Figure 9As shown, it includes object positioning, object pose estimation, gripper working mode judgment, grasping estimation and gripper motion planning, among which object positioning includes object detection, object recognition and classification, and object segmentation.

[0046] Specifically, given a target object to be grasped, the system first enters the object localization phase. The system performs object detection on the RGB-D image captured by the depth camera, roughly identifying candidate boxes. Object recognition / classification then occurs within the box, determining not only the category but also whether the object possesses the geometric property of "large holes." This is followed by pixel-level or point cloud-level object segmentation, resulting in clean contours and point clouds. Specifically, object classification results include either "with large holes" or "without large holes." Upon receiving this classification result, the control system of the planar soft parallel gripper determines the operating mode: objects with large holes adopt the hook mode, while objects without large holes adopt the envelope mode. If the "hook mode" is selected, three sub-modes are selected: two-side hook, left hook, or right hook, based on the relative distance and size of the holes in the grasped object. Simultaneously, the segmented point cloud is fed into the object pose estimation module, which outputs a 6D pose. The pose results, along with the gripper operating mode selected in the previous step, are combined into a grasp estimation process. Here, several grasp candidates are generated and scored based on the pose, gripper mode, and environmental collision constraints. Finally, the optimal grasp pose is submitted to the gripper motion planner, which generates the robot arm trajectory and the motion curve for the planar parallel gripper, completing the closed-loop process from visual perception to execution.

[0047] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the implementation process of the present invention is described in detail above, it is still possible for those familiar with the art to modify the technical solutions described in the above examples or to replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A planar soft parallel gripper, characterized in that: The gripper includes a rigid connector, a connecting screw and two parallel soft palms; the rigid connector is directly made of PLA material through 3D printing; the soft palm is a rigid-soft mixture, including a sealing plate, two tubular drivers, four stretch limiting strips, a gripping layer and an end limit block; the sealing plate is made of PLA material through 3D printing; the two tubular drivers, four stretch limiting strips, the gripping layer and the end limit block are all made by casting and bonding silicone with various hardness; the positioning groove on the rigid connector and the sealing plate positioning groove on the soft palm are matched and connected by mutual inlaying, and then completely positioned by the positioning hole of the rigid connector and the positioning hole of the sealing plate, and the threads in the positioning hole of the sealing plate are completely fixed with the connecting screws; the soft palm includes a sealing plate, The first tubular driver, the second tubular driver, the first stretch limiting strip, the second stretch limiting strip, the third stretch limiting strip, the fourth stretch limiting strip, the gripping layer and the end limit block; wherein the sealing plate includes a sealing plate air inlet channel, a sealing plate positioning hole and a sealing plate positioning groove, and the air holes on the sealing plate and the air holes on the rigid connector are aligned so that the air pipe can smoothly enter each tubular driver; the top layer of each tubular driver is bonded to the circular plates at both ends of the sealing plate; the four stretch limiting strips on the soft palm are composed of a silicone coating layer, a heating wire and a low melting point alloy, and the heating wire is spirally embedded in the silicone coating layer, and there is a hollow tube inside. A low-melting-point alloy is placed in the channel; the heating wire can generate Joule heat within 5 seconds after the current is passed through, and when the tubular driver is stretched, the spirally wound heating wire can be stretched at the same time without damaging the heating wire body; the heating wire is also connected to an external electronic control system to achieve different temperature adjustments; the low-melting-point alloy completes a solid-liquid phase transition at 30-65 degrees Celsius; specifically, it liquefies when heated to the phase transition temperature, so that the restriction of the stretch limit strip is released, and solidifies when cooled, instantly locking the posture of the stretch limit strip and increasing the modulus, thereby achieving programmable stiffness of "soft-hard" switching; when the cooling layer is used to achieve cooling, the stretch limit strip returns to a solid state.

2. The planar soft parallel gripper according to claim 1, characterized in that: The rigid connector has four air inlet channels, two positioning holes, and two positioning slots; an air pipe is connected to the air inlet channel and is connected to an external pneumatic system; the external pneumatic system adjusts the air pressure to provide controllable driving force and compliance force feedback for the tubular actuator, thereby achieving adjustment of the actuator bending angle.

3. The planar soft parallel gripper according to claim 1, characterized in that: The first and second tubular actuators are fiber-reinforced actuators, consisting of a silicone liner and a winding wire. The side and two ends of the silicone liner are made of two types of silicone with different hardness. The winding wire is embedded in the side wall of the silicone liner. During production, an inner liner base is first cast. After the winding wire is wound, a wrapping layer is cast using the same silicone as the inner liner side to integrate them. The winding wire has a diameter of 2-4mm and is a circle of rings. The interval between two adjacent winding wires is 5-8mm, which is used to limit the stretching of the tubular actuator in its radial direction. Therefore, when gas is filled, the tubular actuator can be stretched in the axial direction without expanding.

4. The planar soft parallel gripper according to claim 1, characterized in that: The Shore hardness of the silicone inner liner side of the tubular driver and the silicone coating of the tensile limit strip is 15A~25A, the Shore hardness of the silicone inner liner of the tubular driver and the gripping layer silicone is 25A~45A, and the Shore hardness of the silicone of the end limit block is 45A~65A.

5. The planar soft parallel gripper according to claim 1, characterized in that: The gripping layer is made of silicone with a Shore hardness of 25A to 45A, so that it can achieve passive stretching under the active drive of the tubular actuator. In addition, the gripping layer is also the contact area with the grasped object and can passively conform to and fit the surface of the grasped object.

6. The planar soft parallel gripper according to claim 1, characterized in that: The end limit block is made of silicone with a Shore hardness of 45A~65A. It can hook the grasped object in the hook mode and prevent the grasped object from slipping in the envelope mode.

7. A multi-modal grasping method of a planar soft parallel gripper according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) When a target is grasped, the object localization phase begins. The RGB-D image acquired by the depth camera is first used for object detection, and object recognition / classification is performed within the candidate box. This not only determines the category, but also determines whether the target has a large hole, a geometric property. (2) Then, the object is segmented at the pixel level or point cloud level to obtain a clean outline and point cloud. That is, when the object is classified, the classification results include two types: objects with large holes and objects without large holes. At this time, the control system of the planar soft parallel gripper receives the classification results and determines the working mode. The objects with large holes adopt the hook mode, and the objects without large holes adopt the envelope mode. (3) If it is a hook mode, then the three sub-modes of hooking on both sides, hooking on the left, and hooking on the right are selected according to the relative distance and size of the holes of the grasped object; at the same time, the segmented point cloud is sent to the object pose estimation module to output the 6D pose; several grasping candidates are generated and scored according to the pose, gripper mode, and environmental collision constraints; (4) Finally, the optimal grasping posture is handed over to the gripper motion planning to generate the robot arm trajectory and the motion curve of the planar parallel gripper, completing the work from visual perception to completion of grasping.

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