Adhesive gripper with cross-scale structure mimicking gecko toes

Abstract

The present invention discloses an adhesive gripper with a cross-scale structure that mimics the toes of a gecko. The gripper comprises a clamp bracket connecting mechanism, a steering gear connected to the clamp bracket connecting mechanism, a crank slider mechanism connected to the steering gear, the crank slider mechanism connected to two foot mounting seat connecting mechanisms, and the foot mounting seat and the gecko-like fold cross-scale controllable dry adhesive structure integrally cast. During gripping, the gripper uses the elastic force provided by the tension spring to cause the two symmetrically arranged gecko-like fold cross-scale controllable dry adhesive structures to obtain tangential displacement, causing them to undergo elastic deformation, thereby increasing the contact area between the dry adhesive material and the clamped object, thereby obtaining adhesion. During desorption, the interaction force between the slot pins provides shear displacement along the desorption direction, causing the dry adhesive material to gradually break away from contact with the clamped object, thereby eliminating the adhesion force. The gripper controls the adhesion state by changing the shear distance and shear direction, thereby achieving the conversion between adhesion and desorption of planar objects.

Description

Technical Field

[0001] The invention belongs to the technical field of bionics and mechanical design and manufacturing, and relates to an adhesive claw that imitates the cross-scale structure of a gecko's toe. Background Art

[0002] In various application scenarios, grippers often need to pick up or grasp objects of various shapes. This involves how to design precise motion strategies based on the properties of the object, such as softness, hardness, texture, and shape, to ensure that the object does not fall off, slide, or be damaged during the gripping process. Currently, robot end effectors mainly manipulate objects in two ways: one is to imitate the mechanism of the human hand, which uses multiple joints and degrees of freedom to achieve complex grasping movements; the other is to use a gripper to perform gripping movements, using a motor or hydraulic pneumatic mechanism to control the opening and closing of the claws. However, both types of grippers have certain limitations in grasping flat objects.

[0003] Specifically, while mechanisms that mimic the human hand possess high flexibility and adaptability, enabling grasping of objects of various shapes and sizes to a certain extent, they remain deficient in grasping flat objects. Because flat objects cannot be grasped simply by restricting their external structure, mechanisms that mimic the human hand have certain limitations in this regard, making it difficult to effectively grasp flat objects.

[0004] Regarding the gripper structure, although the gripper can be opened and closed by a motor or hydraulic and pneumatic mechanism, this gripping method often fails to provide sufficient adhesion for flat objects, resulting in unstable or even impossible gripping. In addition, the design of this gripper also makes the gripper prone to slipping during the grasping process, further affecting the accuracy of the grasping. In summary, existing grippers cannot achieve strong adsorption and efficient desorption for flat objects. Summary of the Invention

[0005] The purpose of the present invention is to provide an adhesive gripper with a cross-scale structure that mimics the gecko toe. The gripper regulates the adhesion state by changing the shear distance and shear direction, thereby realizing the conversion of adhesion and detachment of planar objects.

[0006] The technical solution adopted by the present invention is an adhesive gripper that imitates the cross-scale structure of a gecko toe, including a clamper bracket connection mechanism, a servo connected to the clamper bracket connection mechanism, a crank slider mechanism connected to the servo, and the crank slider mechanism connected to two foot mounting seat connection mechanisms.

[0007] The present invention is also characterized in that:

[0008] The clamp bracket connection mechanism includes a clamp bracket, and guide rods are respectively provided on opposite sides of the clamp bracket. The servo is fixed to the clamp bracket by fixing the servo self-tapping screws.

[0009] The crank slider mechanism includes a rudder arm, which is connected to the clamp bracket through a rudder arm connecting screw. The two ends of the rudder arm are respectively connected to one end of the connecting rod through a connecting rod short pin. The other end of the connecting rod is provided with a guide groove. A revolving pair is formed between the rudder arm and the connecting rod through the connecting rod short pin. The rudder arm is also connected to the output end of the servo.

[0010] The foot mounting seat connection mechanism includes a foot mounting seat, the bottom of the foot mounting seat is provided with a gecko-like fold cross-scale controllable dry adhesion structure, the bottom of the gecko-like fold cross-scale controllable dry adhesion structure is bonded with dry adhesive material, the foot mounting seat is connected to a connecting rod pin, and the connecting rod pin is embedded in the guide groove.

[0011] Two opposite sides of the top ends of the foot mounting seat are respectively provided with guide holes, that is, there are four guide holes on each foot mounting seat.

[0012] Two foot mounting seats are provided below the clamp bracket, and two guide rods are respectively connected to the two foot mounting seats through corresponding guide holes, so that a moving pair is formed between the foot mounting seats and the guide rods.

[0013] The two symmetrically arranged foot mounting seats are connected by a tension spring. The two ends of the same side of each foot mounting seat are respectively provided with a spring connecting seat. The two ends of the same tension spring connecting the two foot mounting seats are respectively connected to the two spring connecting seats located on the same side of the two foot mounting seats.

[0014] The foot mount adopts a double-layer mesh structure design, and the foot mount and the gecko-like fold cross-scale controllable dry adhesion structure are integrally cast.

[0015] During grasping, the cross-scale controllable dry adhesion structure of the gecko-like wrinkles undergoes elastic deformation under the action of tangential displacement along the adhesion direction, thereby increasing the contact area between the dry adhesion material and the clamped object to obtain strong adhesion force; during desorption, the cross-scale controllable dry adhesion structure of the gecko-like wrinkles undergoes elastic recovery under the action of shear displacement along the desorption direction, so that the dry adhesion material gradually breaks away from contact with the clamped object, thereby eliminating the adhesion force and realizing the easy desorption function.

[0016] The beneficial effects of the present invention are as follows:

[0017] (1) The macrostructure of the foot mimics the wrinkles of a gecko's toes. Under the same loading conditions, the deformation of the wrinkle-like structure is larger, allowing it to adhere more compliantly to the contact surface.

[0018] (2) The foot mounting seat adopts a double-layer hole mesh structure design and is integrally cast with the cross-scale controllable dry adhesion structure. This can reduce the process steps of integrating the slider mechanism and the cross-scale controllable dry adhesion structure, and prevent the cross-scale controllable dry adhesion structure from being subjected to excessive force and the slider mechanism from being detached, thereby improving the reliability of the clamp;

[0019] (3) When the soles of the feet touch the surface of the clamped object, the servo drives the connecting rod, and the slot pin pair makes the two feet not follow the movement of the connecting rod. Since the surface state of the clamped object is uncertain, the distance required for the two feet to move to grasp is not unique. The tangential force is provided by the tension spring, which improves the adaptability of the clamp. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 3. It is a schematic structural diagram of the initial state of the adhesive claw of the present invention imitating the cross-scale structure of the gecko toe;

[0021] Figure 2 Schematic diagram of the groove-pin pair connection structure of the adhesive claw of the gecko toe-mimicking cross-scale structure of the present invention;

[0022] Figure 3 Schematic diagram of the bottom connecting rod structure of the adhesive claw imitating the gecko toe cross-scale structure of the present invention;

[0023] Figure 4 Schematic diagram of the foot mounting seat connection mechanism structure of the adhesive claw of the gecko toe-mimicking cross-scale structure of the present invention;

[0024] Figure 5 2. This is a schematic structural diagram of the gecko toe-mimicking adhesive claw of the present invention in a grasping state;

[0025] Figure 6 Schematic diagram of the foot mounting structure of the adhesive claw that mimics the gecko toe spanning structure of the present invention;

[0026] Figure 7 Schematic diagram of the cross-scale controllable dry adhesion structure of the gecko-like folds of the adhesive claw of the gecko-like toe cross-scale structure of the present invention;

[0027] Figure 8(a) to Figure 8(h) Schematic diagram of the process of picking up, transferring and releasing a target object by the adhesive gripper of the present invention imitating the cross-scale structure of a gecko toe;

[0028] Figure 9(a) to Figure 9(b) It is a schematic diagram of the elastic deformation process of the gecko-like wrinkle cross-scale controllable dry adhesion structure of the gecko toe cross-scale structure of the present invention during the adhesion process.

[0029] In the figure, 1. servo;

[0030] 2. Crank slider mechanism, 2-1. Connecting rod short pin, 2-2. Connecting rod, 2-3. Rudder arm, 2-4. Rudder arm connecting screw, 2-5. Guide groove;

[0031] 3. Clamp bracket connection mechanism, 3-1. Clamp bracket, 3-2. Guide rod, 3-3. Self-tapping screw for fixing the servo;

[0032] 4. Foot mounting seat connection mechanism, 4-1. Foot mounting seat, 4-2. Gecko-like fold cross-scale controllable dry adhesion structure, 4-3. Connecting rod pin, 4-4. Dry adhesion material, 4-5. Tension spring, 4-6. Guide hole, 4-7. Spring connecting seat;

[0033] 5. The object being clamped, 6. The ground. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] The adhesive claw of the invention imitating the cross-scale structure of the gecko toe is as follows: Figure 1 As shown, it includes a clamper bracket connecting mechanism 3, a servo 1 is fixedly connected to the clamper bracket connecting mechanism 3, the servo 1 is connected to the crank slider mechanism 2, the crank slider mechanism 2 is connected to two foot mounting seat connecting mechanisms 4, and the servo 1 drives the crank slider mechanism 2 to realize the opening of the two foot mounting seat connecting mechanisms 4.

[0037] Example 2

[0038] like Figure 2 As shown, the clamp bracket connection mechanism 3 includes a clamp bracket 3-1, a guide rod 3-2, and a self-tapping screw 3-3 for fixing the servo;

[0039] like Figure 3 As shown, the crank slider mechanism 2 includes a connecting rod short pin 2-1, a connecting rod 2-2, a rudder arm 2-3, and a rudder arm connecting screw 2-4; the two ends of the servo 1 are respectively fixed to the clamp bracket 3-1 by fixing the servo self-tapping screws 3-3, and the output end of the servo 1 is fixed to the rudder arm 2-3.

[0040] The rudder arm 2-3 is connected to the clamp bracket 3-1 through the rudder arm connecting screw 2-4. The two ends of the rudder arm 2-3 are respectively connected to one end of the connecting rod 2-2 through the connecting rod short pin 2-1. The other end of the connecting rod 2-2 is provided with a guide groove 2-5. A revolute pair is formed between the rudder arm 2-3 and the connecting rod 2-2 through the connecting rod short pin 2-1.

[0041] Example 3

[0042] like Figure 4As shown, the foot mounting seat connection mechanism 4 includes a foot mounting seat 4-1, a gecko-like fold cross-scale controllable dry adhesion structure 4-2, a dry adhesion material 4-4, a connecting rod pin 4-3, and a tension spring 4-5;

[0043] The dry adhesive material 4-4 is an adhesive material made by imitating the structure of the gecko's toe bristles. When the dry adhesive material 4-4 contacts an object, an intermolecular force, namely, a van der Waals force, is generated, enabling it to generate stable adhesion on various materials.

[0044] like Figure 5 As shown, the bottom of the foot mounting seat 4-1 is provided with a gecko-like fold cross-scale controllable dry adhesion structure 4-2, the bottom of the gecko-like fold cross-scale controllable dry adhesion structure 4-2 is glued with a dry adhesive material 4-4, and the foot mounting seat 4-1 is connected to a connecting rod pin 4-3, and the connecting rod pin 4-3 is embedded in the guide groove 2-5; Figure 6 As shown, guide holes 4 - 6 are respectively provided at both ends and two opposite sides of the top of the foot mounting seat 4 - 1 , that is, there are four guide holes 4 - 6 on each foot mounting seat 4 - 1 .

[0045] Guide rods 3-2 are arranged in parallel on both sides of the bottom of the clamp bracket 3-1. Two foot mounting seats 4-1 are provided below the clamp bracket 3-1. The two guide rods 3-2 pass through the corresponding guide holes 4-6 and are connected to the two foot mounting seats 4-1, thereby forming a moving pair between the foot mounting seat 4-1 and the guide rods 3-2; the guide rods 3-2 act as guide rails.

[0046] The two symmetrically arranged foot mounting seats 4-1 are connected by a tension spring 4-5. A spring connecting seat 4-7 is provided at both ends of the same side of each foot mounting seat 4-1. The two ends of the same tension spring 4-5 connecting the two foot mounting seats 4-1 are respectively connected to the two spring connecting seats 4-7 located on the same side of the two foot mounting seats 4-1.

[0047] The movement of the connecting rod 2-2 is controlled by the servo 1 to realize the opening of the foot mounting seat 4-1. The groove pin pair connection makes the tangential force of the two feet not provided by the servo 1, but by the tension spring 4-5, thereby providing adhesion.

[0048] like Figure 6 As shown, the foot mounting seat 4-1 adopts a double-layer mesh structure design, and the foot mounting seat 4-1 and the gecko-like fold cross-scale controllable dry adhesion structure 4-2 are integrally cast. On the one hand, it can reduce the process steps of integrating the slider mechanism and the cross-scale controllable dry adhesion structure. On the other hand, it can prevent the cross-scale controllable dry adhesion structure from being subjected to excessive force and the foot mounting seat 4-1 from being detached.

[0049] In the foot mount connection mechanism 4, foot mount 4-1 is connected to guide rod 3-2 to form a slider mechanism. Connecting rod pin 4-3 fits into the slot at the end of connecting rod 2-2, forming a slot-pin pair. The servo 1 controls the movement of connecting rod 2-2 to open foot mount 4-1. After the dry adhesive material 4-4 contacts the clamped object 5, the slot-pin pair ensures that the tangential force is not provided by the servo 1, but by the tension spring 4-5, which applies tangential force to the two symmetrically arranged gecko-like fold-like cross-scale controllable dry adhesive structures 4-2, thereby providing adhesion. During the detachment process, the servo 1 drives the crank slider mechanism 2 to open again, leveraging the interaction between the slot and pin to quickly detach the foot, thus completing the object placement.

[0050] The structure of the cross-scale controllable dry adhesion structure 4-2 imitating the gecko wrinkle is as follows Figure 7 As shown, the height h of a single wrinkle-like structure is 9 mm, the height f of the wrinkle-like structure at its root is 2-3 mm, the width s of its base is 5-6 mm, the angle α between the left tilt and the normal is 40-45°, the angle β between the right tilt and the normal is 20-25°, the angle θ at the top is 30°, the angle γ between the contact surface and the tangent is 10°, and the fillet radius R is 0.5-0.6 mm. To avoid the adverse effects of contact between wrinkle-like structures and maximize the contact area of ​​the cross-scale controllable dry adhesion structure, the distance e between each wrinkle-like structure is 5-6 mm.

[0051] The working process of the adhesive claw of the gecko toe-like cross-scale structure of the present invention is as follows: the adhesive claw of the gecko toe-like cross-scale structure is divided into two states: grasping and detaching;

[0052] Figure 8(a) is a state diagram of the starting position of the gecko-like dry adhesive gripper before grasping, Figure 8(b) is a state diagram of the steering engine 1 rotating forward, driving the two symmetrically arranged foot mounting seat connection mechanisms 4 to separate through the crank slider mechanism, and reaching the state diagram of the pre-grasping preparation stage position, Figure 8(c) is a state diagram of the gecko-like toe cross-scale structure of the adhesive claw moving downward to make it initially contact with the clamped object 5, Figure 8(d) is a state diagram of the steering engine 1 rotating reversely to relax the tension spring, so that the gecko-like fold cross-scale controllable dry adhesive structure 4-2 undergoes elastic deformation under the action of the tangential force, increasing the contact area between the dry adhesive material 4-4 and the clamped object 5, Figure 8(e) is a state diagram of the gecko-like fold cross-scale structure of the gecko under the continuous action of the tangential force. The wrinkle-span-scale controllable dry adhesive structure 4-2 continues to deform until the dry adhesive material 4-4 is in complete contact with the clamped object 5. Figure 8(f) shows the state diagram of the adhesive claw of the gecko toe-like span-scale structure moving upward, so that the clamper and the clamped object 5 leave the ground 6, completing the grasping state diagram; Figure 8(g) shows the state diagram of the adhesive claw of the gecko toe-like span-scale structure moving downward, so that the clamper and the clamped object 5 are placed flat on the ground 6. Figure 8(h) shows the servo 1 rotating forward, driving the two symmetrically arranged foot mounting seat connection mechanisms 4 to separate through the crank slider mechanism to obtain a reverse tangential force, so that the dry adhesive material 4-4 gradually breaks away from contact with the clamped object 5, completing the desorption state diagram.

[0053] After the gecko-like dry adhesion gripper reaches the starting position before grasping, as shown in Figure 8(a), the servo 1 rotates in the positive direction, driving the connecting rod 2-2 to move by rotating the rudder arm 2-3. During the straightening process of the connecting rod 2-2, the elastic force of the tension spring 4-5 is overcome, causing the two symmetrically arranged foot mounting seat connection mechanisms 4 to move toward each other and reach the pre-grasping preparation stage position, as shown in Figure 8(b).

[0054] During grasping, the gecko-like wrinkle-cross-scale controllable dry adhesion structure 4-2 approaches the clamped object 5 until the dry adhesion material 4-4 contacts the clamped object 5, and initial adhesion force is generated as shown in Figure 8(c). The servo 1 rotates the driving connecting rod 2-2 in the opposite direction, and the slot pin pair at the end of the connecting rod 2-2 makes the foot mounting seat connection mechanism 4 not follow the movement of the connecting rod, so that the tension spring 4-5 is relaxed. The relaxed tension spring 4-5 generates tension, thereby providing tangential force to the gecko-like wrinkle-cross-scale controllable dry adhesion structure 4-2. The tangential force causes the gecko-like wrinkle-cross-scale controllable dry adhesion structure 4-2 to undergo elastic deformation, so that the dry adhesion material 4-4 gradually adheres to the clamped object 5 and generates van der Waals force, as shown in Figures 8(d) and 8(e). At the same time, the position of the gecko-like dry adhesion clamp is raised to make it leave the ground 6 and complete grasping, as shown in Figure 8(f).

[0055] As shown in Figure 9(a), the gecko-like wrinkle cross-scale controllable dry adhesive structure 4-2 approaches the clamped object 5 until the dry adhesive material 4-4 contacts the clamped object 5, initially generating adhesion. Subsequently, due to the tangential force, the tangential displacement causes the gecko-like wrinkle cross-scale controllable dry adhesive structure 4-2 to elastically deform, increasing the contact area between the dry adhesive material 4-4 and the clamped object 5 and generating strong adhesion.

[0056] During desorption, the steering gear 1 rotates in the positive direction again, and drives the connecting rod 2-2 to move by rotating the rudder arm 2-3 until the groove in the connecting rod 2-2 contacts the connecting rod pin 4-3 in the foot mounting seat connection mechanism 4, so that the two symmetrically arranged foot mounting seat connection mechanisms 4 are separated again, providing a reverse tangential force, so that the dry adhesive material 4-4 gradually breaks away from contact with the clamping object 5, as shown in Figure 8(g), completing the forced desorption.

[0057] As shown in FIG9( b ), under the action of the reverse tangential force, the dry adhesive material 4 - 4 on the gecko-like wrinkle cross-scale controllable dry adhesive structure 4 - 2 gradually breaks away from contact with the clamp 5 , and finally realizes the desorption process.

[0058] The present invention utilizes a specially designed cross-scale controllable dry-adhesion structure, which achieves controllable adhesion properties by combining micron-scale dry-adhesion materials with millimeter-scale controllable structures. On the one hand, the adhesion function is achieved through the micron-scale dry-adhesion material, and the controllable properties are achieved through the millimeter-scale gecko-like wrinkled cross-scale controllable dry-adhesion structure. The two are combined to achieve controllable adhesion. On the other hand, the hierarchical structural design can reduce the elastic modulus of the entire adhesion system, improve the adaptability of the cross-scale controllable dry-adhesion structure to surface contours, and enhance the adhesion performance of the adhesion system. This structure can produce microscopic elastic deformation when contacting a surface. By increasing the actual contact area, van der Waals forces are generated between the gecko-like dry-adhesion material and the grasped object, thereby providing adhesion. The core of this process lies in precisely controlling the deformation and recovery of the structure to ensure both secure grasping and rapid release of the object.

[0059] To achieve this precise control, a crank-slider mechanism with a slotted pin pair is employed. The key to this mechanism's design lies in the fact that during the grasping process, the servo controls the movement of the connecting rod, thereby expanding the foot mounting bracket. Once the dry adhesive material contacts the grasped object, the slotted pin pair connects, ensuring that the tangential force on the two feet is provided by a tension spring, not the servo. This results in a tangential displacement in the adhesion direction, causing the wrinkle-like structure to begin to deform, increasing the contact area with the clamped object and thereby enhancing adhesion. When the dry adhesive material and the clamped object are in contact, the actual contact area is maximized, and the gecko-like cross-scale structure of the adhesive gripper is in a strong adhesion state, providing adhesion. During the detachment process, the servo again drives the crank-slider mechanism to expand, leveraging the interaction between the slot and the pin to provide shear displacement in the detachment direction. This initiates shearing in the detachment direction, gradually separating the dry adhesive material from the clamped object, eliminating adhesion and ultimately completing object placement. The adhesive gripper, which mimics the cross-scale structure of gecko toes, provides an efficient and controllable grasping and detaching mechanism, demonstrating the great potential of bionics in modern engineering.

Claims

1. An adhesive gripper with a cross-scale structure imitating a gecko's toe, characterized by: The invention comprises a clamp bracket connecting mechanism (3), the clamp bracket connecting mechanism (3) is connected to a steering gear (1), the steering gear (1) is connected to a crank slider mechanism (2), and the crank slider mechanism (2) is connected to two foot mounting seat connecting mechanisms (4); The clamp bracket connection mechanism (3) comprises a clamp bracket (3-1), guide rods (3-2) are respectively provided on opposite sides of the clamp bracket (3-1), and the servo (1) is fixed to the clamp bracket (3-1) by fixing the servo self-tapping screws (3-3); The crank slider mechanism (2) includes a rudder arm (2-3), the rudder arm (2-3) is connected to the clamp bracket (3-1) through a rudder arm connecting screw (2-4), the two ends of the rudder arm (2-3) are respectively connected to one end of the connecting rod (2-2) through a connecting rod short pin (2-1), the other end of the connecting rod (2-2) is provided with a strip-shaped guide groove (2-5), a rotation pair is formed between the rudder arm (2-3) and the connecting rod (2-2) through the connecting rod short pin (2-1), and the rudder arm (2-3) is also connected to the output end of the steering gear (1); The foot mounting seat connection mechanism (4) comprises a foot mounting seat (4-1), a gecko-like fold cross-scale controllable dry adhesion structure (4-2) is provided at the bottom of the foot mounting seat (4-1), a dry adhesion material (4-4) is bonded to the bottom of the gecko-like fold cross-scale controllable dry adhesion structure (4-2), and a connecting rod pin (4-3) is connected to the foot mounting seat (4-1), and the connecting rod pin (4-3) is embedded in the guide groove (2-5); Guide holes (4-6) are respectively provided on opposite sides of the top ends of the foot mounting seat (4-1), that is, there are four guide holes (4-6) on each foot mounting seat (4-1); Two foot mounting seats (4-1) are provided below the clamping bracket (3-1), and two guide rods (3-2) pass through corresponding guide holes (4-6) and are connected to the two foot mounting seats (4-1), thereby forming a moving pair between the foot mounting seats (4-1) and the guide rods (3-2); The two symmetrically arranged foot mounting seats (4-1) are connected via a tension spring (4-5), and spring connecting seats (4-7) are respectively provided at both ends of the same side of each foot mounting seat (4-1), and both ends of the same tension spring (4-5) connecting the two foot mounting seats (4-1) are respectively connected to the two spring connecting seats (4-7) located on the same side of the two foot mounting seats (4-1).

2. The adhesive gripper imitating the gecko toe cross-scale structure according to claim 1 is characterized in that: The foot mounting seat (4-1) adopts a double-layer mesh structure design, and the foot mounting seat (4-1) and the gecko-like fold cross-scale controllable dry adhesion structure (4-2) are integrally cast.

3. The adhesive gripper imitating the gecko toe cross-scale structure according to claim 1, characterized in that: During attachment, the gecko-like wrinkle cross-scale controllable dry adhesive structure (4-2) undergoes elastic deformation under the action of tangential displacement along the adhesion direction, thereby increasing the contact area between the dry adhesive material (4-4) and the clamped object (5) to obtain strong adhesion; during desorption, the gecko-like wrinkle cross-scale controllable dry adhesive structure (4-2) undergoes elastic recovery under the action of shear displacement along the desorption direction, so that the dry adhesive material (4-4) and the clamped object (5) gradually break away from contact, thereby eliminating the adhesion force and achieving the easy desorption function.

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