Planar soft parallel gripper and multi-mode gripping method thereof

Abstract

The invention discloses a planar soft parallel gripper and a multi-mode gripping method thereof. The planar soft parallel gripper comprises two parallel soft palms, a rigid connecting piece and a connecting screw, the soft palm comprises a sealing plate, two tubular drivers, four stretching limiting strips, a grabbing layer and a tail end limiting block. Joule heat generated by current is used for controlling phase change of the low-melting-point alloy so as to generate rigidity change, and four working modes of stretching, left bending, right bending and twisting can be generated when the tubular driver is charged with positive pressure; through air pressure and electric heating cooperative control and combination of the two parallel soft palms, an envelope grabbing mode and three hooking modes can be achieved only through bending deformation. According to the planar parallel soft gripper, point / line contact is upgraded into surface contact, friction force and supporting force are remarkably improved, and targets with large sizes, complex curved surfaces and even multiple convex-concave characteristics can be stably gripped.

Description

Technical Field

[0001] The present invention relates to the fields of soft grippers and deformable interfaces, and particularly to a planar soft parallel gripper and its multi-modal grasping method. Background Art

[0002] The applications of robots have expanded from traditional manufacturing and industrial automation to fields such as services, healthcare, and human-robot collaboration. Powerful end-effectors are required to complete complex tasks. However, rigid end-effectors composed of rigid joints and linkages face challenges in grasping objects with different sizes, shapes, and material properties. To grasp these objects, various sensors and complex algorithms are usually used to accurately calculate their positions and geometries, which greatly increases the usage cost and limits the universality of rigid grippers. In addition, such a grasping process is prone to damage the target object and the operator, and cannot safely interact with humans.

[0003] Due to its ability to undergo large-scale deformations of the surface shape under external driving to present an expected shape, the deformable interface can be applied to the end-effector to enhance its interaction ability with the grasped object. In recent years, with the development of deformable materials and the progress of driving technologies, deformable flexible interfaces and deformable bodies have more flexible deformation capabilities, providing feasibility for realizing special and novel requirements. 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 planar soft gripper with softness and compliance, so that it can increase the contact area with the surface of the target object, and thus can efficiently and stably grasp various types of irregular objects. At the same time, in the face of different objects, the gripper needs to be able to adjust the grasping mode to achieve actions such as enveloping and hooking.

[0004] Soft grippers rely on the compliance of deformable materials to adaptively conform to the target surface without the need for high-precision sensing and complex algorithms, and evenly distribute the contact pressure, so as to safely grasp objects with different shapes, sizes, and materials. Compared with traditional strip-shaped flexible fingers, planar parallel soft grippers achieve large-scale programmable deformations in a two-dimensional plane, upgrading point / line contact to surface contact, significantly enhancing the frictional force and supporting force, and can stably grasp targets with large sizes, complex curved surfaces, or even multiple convex and concave features. Its multi-chamber independent driving structure can also switch between modes such as wrapping and hooking, meeting the urgent needs of scenarios such as warehousing, healthcare, and human-robot collaboration for "multi-modal and one gripper for all". Summary of the Invention

[0005] The purpose of the present invention is to provide a planar soft parallel gripper and its multi-modal grasping method in view of the deficiencies of the prior art, aiming to solve the problems of stability and reliability in the prior art when traditional strip-shaped flexible fingers grasp objects with different shapes, sizes, and materials, and at the same time its multi-modal grasping can be applied to various scenarios.

[0006] The present invention is realized through the following technical solutions: A planar soft parallel gripper, which comprises a rigid connecting piece, connecting screws and two parallel soft palms; the rigid connecting piece is directly manufactured by 3D printing with PLA material; the soft palm is a rigid-soft mixture, including a sealing plate, two tubular drivers, four stretching limiting strips, a grasping layer and a terminal limiting block; the sealing plate is obtained by 3D printing with PLA material; the two tubular drivers, four stretching limiting strips, the grasping layer and the terminal limiting block are all obtained by casting and bonding silicones with various hardnesses; the positioning groove on the rigid connecting piece and the sealing plate positioning groove on the soft palm are connected in a matching manner by mutual inlay, and then completely positioned through the positioning hole on the rigid connecting piece and the sealing plate positioning hole, and the thread in the sealing plate positioning hole is completely fixed with the connecting screw.

[0007] Specifically, there are four air inlet channels, two positioning holes and two positioning grooves on the rigid connecting piece; air pipes are connected to the air inlet channels and connected to an external pneumatic system; the external pneumatic system adjusts the air pressure to provide controllable driving force and compliant force feedback for the tubular driver to realize the adjustment of the bending angle of the driver.

[0008] Specifically, the soft palm includes a sealing plate, a first tubular driver, a second tubular driver, a first stretching limiting strip, a second stretching limiting strip, a third stretching limiting strip, a fourth stretching limiting strip, a grasping layer and a terminal limiting 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 are aligned with the air holes on the rigid connecting piece so that the air pipes 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.

[0009] Specifically, the first tubular driver and the second tubular driver belong to fiber-reinforced drivers, which are composed of a silicone inner bladder and winding wires. The side and two ends of the silicone inner bladder are made of silicones with two different hardnesses. The winding wires are embedded in the side wall of the silicone inner bladder. When manufacturing, an inner bladder base is first cast, and after the winding wires are wound, a wrapping layer made of the same silicone as the side of the inner bladder is cast to integrate them. The diameter of the winding wires is 2-4 mm and they are in the form of a series of circles. The interval between adjacent winding wires is 5-8 mm, which is used to limit the stretching of the tubular driver in its radial direction, so that when gas is filled, the tubular driver can produce stretching in the axial direction and will not expand.

[0010] Specifically, the four stretching limit strips on the soft palm are composed of a silica gel coating layer, heating wires, and a low melting point alloy. The heating wires are spirally embedded in the silica gel coating layer, and there are hollow pipes inside for placing the low melting point alloy. After the heating wires are energized, Joule heat can be generated within 5 s. When the tubular actuator stretches, the spirally wound heating wires can be stretched simultaneously without damaging the heating wire body. The heating wires are also connected to an external electronic control system for realizing different temperature adjustments.

[0011] Furthermore, the low melting point alloy completes solid-liquid phase change at 30-65 °C. Specifically, it liquefies when heated to the phase change temperature, so that the restriction of the stretching limit strip is released. When cooled, it solidifies, instantaneously locks the posture of the stretching limit strip, and increases the modulus, thereby realizing the programmable stiffness of "soft-hard" switching. When cooling is achieved by cooperating with a cooling layer, the stretching limit strip returns to the solid state.

[0012] Specifically, the Shore hardness of the silica gel inner liner side of the tubular actuator and the silica gel coating layer of the stretching limit strip is 15A-25A, the Shore hardness of the two ends of the silica gel inner liner of the tubular actuator and the silica gel of the grasping layer is 25A-45A, and the Shore hardness of the silica gel of the end limiting block is 45A-65A.

[0013] Specifically, the grasping layer is made of silica gel with a Shore hardness of 25A-45A, so that it can be passively stretched under the active drive of the tubular actuator. In addition, the grasping layer is also the contact area with the object to be grasped, and can passively conform to and fit the surface of the object to be grasped.

[0014] Specifically, the end limiting block is made of silica gel with a Shore hardness of 45A-65A, and can hook the object to be grasped in the hooking mode and also prevent the object to be grasped from slipping in the enveloping mode.

[0015] The present invention also provides a multi-modal grasping method for a planar soft parallel gripper, which is characterized by including the following steps: (1) When a target object to be grasped is given, first enter the object positioning stage. The RGB-D image obtained by the depth camera is first subjected to object detection, and object recognition / classification is performed within the candidate box, not only determining the category, but also judging whether the target has the geometric attribute of "having large holes". (2) Then perform object segmentation at the pixel level or point cloud level to obtain a clean contour and point cloud. That is, when classifying the object, the classification results include two types: having large holes and not having large holes. At this time, after the control system of the planar soft parallel gripper receives this classification result, it judges the working mode. For objects with large holes, the hooking mode is adopted, and for objects without large holes, the enveloping mode is adopted. (3) If it is in the hooking mode, then according to the relative distance and size of the holes of the object to be grasped, three sub-modes of hooking on both sides, left hooking, and right hooking are selected; meanwhile, the segmented point cloud is sent to the object pose estimation module to output the 6D pose; according to the pose, gripper mode, and environmental collision constraints, several grasping candidates are generated and scored; (4) Finally, the optimal grasping pose is handed over to the gripper motion planning to generate the manipulator trajectory and the motion curve of the planar parallel gripper, completing the work from visual perception to grasping.

[0016] The beneficial effects of the present invention are as follows: The planar soft parallel gripper proposed by the present invention takes the tubular actuator filled with low melting point alloy as the core unit. Its actuator is flexible and can be bent greatly by relying on air pressure; and the low melting point alloy can achieve solid-liquid phase change without being heated to too high a temperature and can be simply controlled by electrothermal; at room temperature, the alloy quickly solidifies, "locking" the soft wall into a high modulus structure, instantly improving the stiffness and load capacity of the gripper, and the stiffness change range is large. Two tubular actuators are connected in parallel to form a "soft palm", and after assembling two soft palms into a parallel mechanism, it not only retains the advantage of the soft gripper's adaptive wrapping of the target, but also has a synchronous opening and closing pose similar to that of a mechanical gripper, and can be accurately inserted and centered in a narrow channel.

[0017] The advantages of the planar parallel gripper are as follows: ① Multi-modal grasping - in the flexible state, the two palms can be bent into arcs respectively to achieve large-area envelope, which is suitable for fragile objects such as fruits and medicine bottles; or only the end part can be bent locally to form a hook, and the heavy load can be hooked through holes or handles. ② High load and shape retention - after the target is positioned, the alloy is solidified, and the stiffness of the gripper is increased by dozens of times. At the same time, by using air pressure, components several times heavier than its own weight can be stably transported and the pose can be maintained unchanged during the conveying process; after the delivery is completed, it can be reheated to restore softness, and the cycle life is high. Generally speaking, the variable stiffness parallel soft gripper realizes "one gripper with multiple functions" based on the double mechanisms of "compliant adaptation + rigid locking" in tasks with limited space, diverse targets, and large load spans, providing an efficient and reliable end-effector solution for fields such as logistics sorting, assembly automation, and surgical instruments. Brief Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the planar soft parallel gripper of the present invention; Figure 2 It is the three-view drawing of the planar soft parallel gripper of the present invention; Figure 3 It is a schematic structural diagram of the rigid connecting piece of the present invention; Figure 4 It is a schematic structural diagram of the sealing plate on the soft palm of the present invention; Figure 5It is a schematic structural diagram of the soft palm and the stretching limit strip of the present invention; Figure 6 It is a control method and working mode diagram of the soft palm of the present invention; Figure 7 It is a schematic diagram of multi-modal grasping modes of the planar soft parallel gripper of the present invention; Figure 8 It is a schematic diagram of a grasping system based on the planar soft parallel gripper of the present invention; Figure 9 It is a flow chart of the grasping solution of the present invention.

[0019] Reference numerals: 1 rigid connecting piece, 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 stretching limit strip, 305 second stretching limit strip, 306 third stretching limit strip, 307 fourth stretching limit strip, 308 grasping layer, 309 end limiting block; 3011 sealing plate air inlet channel, 3012 sealing plate positioning hole, 3013 sealing plate positioning groove. Detailed implementation manners

[0020] The present invention will be described in detail below with reference to the drawings. It should be understood that the specific implementation manners described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0021] The present invention provides a planar soft parallel gripper, as shown in Figure 1 and Figure 2 which includes: a rigid connecting piece 1, a connecting screw 2, and a soft palm 3. The rigid connecting piece 1 is directly made by 3D printing with PLA material. The soft palm 3 is a rigid-soft mixture, including a sealing plate 301, two tubular drivers (the first tubular driver 302 and the second tubular driver 303), four stretching limit strips (the first stretching limit strip 304, the second stretching limit strip 305, the third stretching limit strip 306, and the fourth stretching limit strip 307), a grasping layer 308, and an end limiting block 309. The sealing plate 301 is made by 3D printing with PLA material, and the rest are all formed by pouring and bonding silicones with various hardnesses. Specifically, the Shore hardness of the silicone inner liner side of the tubular driver and the silicone coating layer of the stretching limit strip is 15A - 25A, the Shore hardness of the two ends of the silicone inner liner of the tubular driver and the silicone of the grasping layer is 25A - 45A, and the Shore hardness of the silicone of the end limiting block is 45A - 65A.

[0022] As shown in Figure 3As shown, there are four air intake channels 101, two positioning holes 102 and two positioning grooves 103 on the rigid connector 1; air pipes are connected to the air intake channels 101 and connected to an external pneumatic system. The external pneumatic system is a known technology in the field, including an air pump, a pneumatic pressure controller, etc., which is used to adjust the air pressure, provide a controllable driving force and compliant force feedback for the tubular actuator, and realize the adjustment of the bending angle of the actuator; the positioning groove 103 on the rigid connector and the sealing plate positioning groove 3013 on the soft palm can be matched by means of mutual inlay, and then completely positioned through the positioning hole 102 of the rigid connector and the sealing plate positioning hole 3012 on the sealing plate 301. The sealing plate positioning hole 3012 has an internal thread and is completely fixed after being assembled by the connecting screw 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.

[0023] As Figure 4 shown, the soft palm 3 includes a sealing plate 301, a first tubular actuator 302, a second tubular actuator 303, a first stretching limit strip 304, a second stretching limit strip 305, a third stretching limit strip 306, a fourth stretching limit strip 307, a grasping layer 308, and a terminal limit block 309; wherein the sealing plate 301 includes a sealing plate air intake channel 3011, a sealing plate positioning hole 3012, and a sealing plate positioning groove 3013, as Figure 5 shown. The air holes on the sealing plate 301 are aligned with the air holes on the rigid connector 1, so that the air pipes can smoothly enter each tubular actuator, and the top layer of each tubular actuator is bonded to the circular plates at both ends of the sealing plate.

[0024] The first tubular actuator 302 and the second tubular actuator 303 belong to fiber-reinforced actuators, which are composed of a silicone inner bladder and winding wires. The side and two ends of the silicone inner bladder are made of two different hardness silicones, namely Shore hardness 15A - 25A and 25A - 45A. The side has a small hardness for easy stretching, and the hardness of the two ends is greater than that of the side to obtain greater strength when bonding with the rest of the components. The winding wires are embedded in the side wall of the silicone inner bladder. During production, an inner bladder base is first poured, and after the winding wires are wound, a wrapping layer made of the same silicone as the side of the inner bladder is selected and poured to integrate them. The diameter of the winding wires is 2 - 4 mm, which are a series of rings, and the interval between adjacent winding wires is 5 - 8 mm, which is used to limit the stretching of the tubular actuator in its radial direction. Thus, when gas is filled, the tubular actuator can generate greater stretching in the axial direction and will not expand like a balloon.

[0025] The stretching limit strip as Figure 5As shown in the enlarged view, it is composed of a silica gel coating layer, a heating wire, and a low melting point alloy. The heating wire is spirally embedded in the silica gel coating layer, and a hollow pipe is placed inside for the low melting point alloy. The heating wire has a relatively large resistance value and can generate a large amount of Joule heat within 5 s after passing a suitable current. At the same time, the spiral winding method also increases its contact area with the low melting point alloy, thereby reducing the heating time when reaching the phase change temperature of the low melting point alloy. In addition, when the tubular actuator is stretched, the spirally wound heating wire can be stretched simultaneously without damaging the heating wire body. The heating wire is connected to an external electronic control system, which can achieve different temperature adjustments. The external electronic control system is a known technology in the field. The low melting point alloy (such as gallium-indium, gallium-tin eutectic, etc.) can quickly complete solid-liquid phase change at 30~65 °C: it can be liquefied when heated to the phase change temperature, so that the restriction of the stretching restriction bar is released, and it solidifies when cooled, instantaneously locks the posture of the stretching restriction bar and significantly increases the modulus, thereby realizing the "soft-hard" switchable programmable stiffness. In addition, with the cooperation of a cooling layer, rapid cooling can be achieved, so that the stretching restriction bar returns to the solid state.

[0026] The grasping layer is made of silica gel with a Shore hardness of 25A~45A, so that it can be passively stretched under the active drive of the tubular actuator. In addition, the grasping layer is also the main contact area with the object to be grasped and can passively conform to and fit the surface of the object to be grasped.

[0027] The end limiting block is made of silica gel with a Shore hardness of 45A~65A. In the hooking mode, it can hook the object to be grasped such as a bag, a kitchen utensil handle, etc., and in the enveloping mode, it can prevent the object to be grasped from slipping.

[0028] In addition, the present invention also provides a multi-modal grasping method. By an external pneumatic system, the magnitude of the air pressure can be adjusted to control the bending degree of the tubular actuator, and by an external circuit system, the temperature of the heating wire can be adjusted to control the solid-liquid phase change of the low melting point alloy. The cooperative control strategy of air pressure and electrothermal energy can effectively change the stiffness of the stretching restriction bar, so that the tubular actuator can achieve stretching and bending deformation.

[0029] As Figure 6As shown, the soft palm can achieve four working modes: elongation, left bending, right bending, and twisting. In this embodiment, the same positive air pressure is applied to all the tubular drivers in the four working modes. In the elongation mode, the first stretching restraint strip 304, the second stretching restraint strip 305, the third stretching restraint strip 306, and the fourth stretching restraint strip 307 are all powered, so that the low-melting-point alloy is in a liquid state and can be stretched. In the left bending mode, the first stretching restraint strip 304 and the second stretching restraint strip 305 are not powered, the low-melting-point alloy is in a solid state and cannot be stretched, the third stretching restraint strip 306 and the fourth stretching restraint strip 307 are powered, the low-melting-point alloy is in a liquid state and can be stretched. Due to the incompatibility of the stretching on the opposite side of the same tubular driver, it bends towards the side with restricted stretching. 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 drivers on the soft palm are different. For example, when the first stretching restraint strip 304 is energized and the second stretching restraint strip 305 is not energized, this tubular driver bends to the right. When the third stretching restraint strip 306 is not energized and the fourth stretching restraint strip 307 is energized, this tubular driver bends to the left. Therefore, the grasping layer connecting the two tubular drivers forms a twist. Similarly, the twist, like the bend, has two directions: clockwise and counterclockwise. Only one example is listed in this embodiment.

[0030] Since the elongation mode and the twisting mode are not very useful for the parallel soft gripper, only the bending mode is utilized during parallel grasping. As Figure 7 shown, when the two parallel soft palms bend inward simultaneously, an enveloping mode can be formed; when the two parallel soft palms bend outward simultaneously, a two-side hooking mode can be formed; when the two parallel soft palms bend left simultaneously, a left hooking mode can be formed; when the two parallel soft palms bend right simultaneously, a right hooking mode can be formed. When the target object is fragile, has an irregular surface, or requires a large-area force distribution, the enveloping mode is the safest and most reliable for the soft gripper; when the target has a built-in handle, hole, edge flange, or high structural rigidity, the gripper can use the hooking mode to achieve fast and stable grasping.

[0031] As Figure 8 shown, in addition to the planar soft parallel gripper, the grasping system in the present invention mainly includes a depth camera and a supporting robotic arm. The flow chart of the grasping scheme is as Figure 9 shown, including object positioning, object pose estimation, gripper working mode judgment, grasping estimation, and gripper motion planning. Among them, object positioning includes object detection, object recognition and classification, and object segmentation.

[0032] Specifically, when a target object to be grasped is given, it first enters the object localization stage. The system first performs object detection on the RGB-D image obtained by the depth camera to roughly find the candidate bounding boxes. Subsequently, object recognition / classification is performed within the bounding boxes to not only determine the category but also judge whether the target has the geometric property of "having large holes". Immediately afterwards, pixel-level or point-cloud-level object segmentation is carried out to obtain a clean contour and point cloud. Specifically, during object classification, the classification results include two types: having large holes and not having large holes. At this time, after receiving this classification result, the control system of the planar soft parallel gripper makes a judgment on the working mode. For objects with large holes, the hooking mode is adopted, and for objects without large holes, the enveloping mode is adopted. If it is the "hooking mode", then three sub-modes of bilateral hooking, left hooking, and right hooking are selected according to the relative distance and size of the holes of the object to be grasped. At the same time, the segmented point cloud is sent to the object pose estimation module to output the 6D pose. The pose result and the gripper working mode selected in the previous step are jointly combined into the grasping estimation: several grasping candidates are generated and scored here according to the pose, gripper mode, and environmental collision constraints. Finally, the optimal grasping pose is handed over to the gripper motion planning to generate the robotic arm trajectory and the motion curve of the planar parallel gripper, completing the closed-loop action from visual perception to execution completion.

[0033] As described above, it is only the preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the implementation process of the present invention has been described in detail above, for those familiar with the art, they can still modify the technical solutions recorded in the foregoing examples or make equivalent replacements for some of the technical features. Any modifications, equivalent replacements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A planar soft parallel gripper, characterized in that, The gripper includes a rigid connector, connecting screws, and two parallel soft palms; the rigid connector is directly fabricated by 3D printing with PLA material; the soft palm is a rigid-soft mixture, including a sealing plate, two tubular actuators, four stretching limit strips, a grasping layer, and a terminal limit block; the sealing plate is obtained by 3D printing with PLA material; the two tubular actuators, four stretching limit strips, the grasping layer, and the terminal limit block are all obtained by casting and bonding silicones with various hardnesses; the positioning groove on the rigid connector and the sealing plate positioning groove on the soft palm are connected by means of mutual inlay, and then completely positioned through the positioning holes on the rigid connector and the sealing plate positioning holes, and the threads in the sealing plate positioning holes are completely fixed with the connecting screws.

2. The planar soft parallel gripper according to claim 1, wherein There are four air intake channels, two positioning holes, and two positioning grooves on the rigid connector; air pipes are connected to the air intake channels and connected to an external pneumatic system; the external pneumatic system adjusts the air pressure to provide controllable driving force and compliant force feedback for the tubular actuators to achieve the adjustment of the bending angle of the actuators.

3. The planar soft parallel gripper according to claim 1, wherein The soft palm includes a sealing plate, a first tubular actuator, a second tubular actuator, a first stretching limit strip, a second stretching limit strip, a third stretching limit strip, a fourth stretching limit strip, a grasping layer, and a terminal limit block; wherein the sealing plate includes a sealing plate air intake channel, a sealing plate positioning hole, and a sealing plate positioning groove, and the air holes on the sealing plate are aligned with the air holes on the rigid connector so that the air pipes can smoothly enter each tubular actuator; the top layer of each tubular actuator is bonded to the circular plates at both ends of the sealing plate.

4. The planar soft parallel gripper according to claim 3, characterized in that, The first tubular actuator and the second tubular actuator belong to fiber-reinforced actuators, which are composed of a silicone inner bladder and winding wires. The side and two ends of the silicone inner bladder are made of two different hardness silicones. The winding wires are embedded in the side wall of the silicone inner bladder. When manufacturing, a bladder base is first cast, and after the winding wires are wound, a wrapping layer is cast with the same silicone as the side of the inner bladder to integrate them. The diameter of the winding wires is 2 - 4 mm, which are a series of circles, and the interval between adjacent winding wires is 5 - 8 mm, used to limit the stretching of the tubular actuator in its radial direction, so that when gas is filled, the tubular actuator can produce stretching in the axial direction and will not expand.

5. The planar soft parallel gripper according to claim 1, characterized in that The four stretching limit strips on the soft palm are composed of a silicone coating layer, heating wires, and a low melting point alloy. The heating wires are spirally embedded in the silicone coating layer, and there is a hollow pipe inside to place the low melting point alloy; the heating wires can generate Joule heat within 5 s after passing an electric current. When the tubular actuator stretches, the spirally wound heating wires can be stretched simultaneously without damaging the heating wire body; the heating wires are also connected to an external electronic control system for realizing different temperature adjustments.

6. The planar soft parallel gripper according to claim 5, wherein The low melting point alloy completes solid-liquid phase change at 30 - 65 degrees Celsius; specifically, it liquefies when heated to the phase change temperature, so that the restriction of the stretching limit strip is released, and it solidifies when cooled, instantaneously locks the posture of the stretching limit strip and increases the modulus, thus realizing the programmable stiffness of "soft-hard" switching; when cooperating with a cooling layer to achieve temperature reduction, the stretching limit strip returns to the solid state.

7. The planar soft parallel gripper according to claim 1, wherein The Shore hardness of the side of the silicone inner liner of the tubular driver and the silicone coating layer of the stretching limit strip is 15A - 25A, the Shore hardness of the two ends of the silicone inner liner of the tubular driver and the silicone of the grasping layer is 25A - 45A, and the Shore hardness of the silicone of the end limit block is 45A - 65A.

8. The planar soft parallel gripper according to claim 1, characterized in that, The grasping layer is made of silicone with a Shore hardness of 25A - 45A, so that it can be passively stretched under the active drive of the tubular driver. In addition, the grasping layer is also the contact area with the object to be grasped, and can passively conform to and fit the surface of the object to be grasped.

9. 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, and can hook the object to be grasped in the hooking mode, and can also prevent the object to be grasped from slipping in the enveloping mode.

10. A multimodal grasping method for the planar soft parallel gripper according to any one of claims 1-7, characterized in that, It includes the following steps: (1) When a target object to be grasped is given, first enter the object positioning stage. The RGB-D image obtained by the depth camera is first subjected to object detection, and object recognition / classification is performed within the candidate box, not only determining the category, but also judging whether the target has the geometric property of "having large holes". (2) Then perform object segmentation at the pixel level or point cloud level to obtain a clean contour and point cloud; that is, when classifying the object, the classification results include two types: having large holes and not having large holes. At this time, after the control system of the planar soft gripper receives this classification result, it judges the working mode. For objects with large holes, the hooking mode is adopted, and for objects without large holes, the enveloping mode is adopted. (3) If it is the hooking mode, then select three sub - modes of double - side hooking, left - hand hooking, and right - hand hooking according to the relative distance and size of the holes of the object to be grasped; at the same time, the segmented point cloud is sent to the object pose estimation module to output a 6D pose; several grasping candidates are generated and scored according to the pose, gripper mode, and environmental collision constraints. (4) Finally, hand over the optimal grasping pose to the gripper motion planning to generate the robotic arm trajectory and the motion curve of the planar parallel gripper, and complete the work from visual perception to grasping.

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