A flexible actuator based on nickel-titanium alloy and a preparation method thereof

Abstract

The application discloses a flexible actuator based on nickel-titanium alloy and a preparation method, and relates to the technical field of fruit picking flexible actuators. The application comprises a nickel-titanium alloy braided framework, the nickel-titanium alloy braided framework adopts at least one nickel-titanium alloy wire to be braided to form a tubular structure, and the outer side of the nickel-titanium alloy braided framework is covered with a covering layer; the lower side of the nickel-titanium alloy braided framework is sequentially provided with an upper end ring and a lower end ring from top to bottom, the nickel-titanium alloy braided framework is fixedly connected with the upper end ring, and the upper end ring and the lower end ring are fixed through a plurality of hollow columns. The axial stretching amount of the pull cable is accurately controlled through the motor driving mechanism, the braiding angle of the nickel-titanium alloy braided framework is actively changed, the radial stiffness of the tubular structure is continuously adjusted, the conformal envelope of the object to be grabbed can be realized through radial contraction, different sizes and shapes of objects can be adaptively gripped, the stiffness control range is wider, and the control precision is higher.

Description

Technical Field

[0001] This invention relates to the field of flexible actuators for fruit harvesting, specifically a flexible actuator based on nickel-titanium alloy and its preparation method. Background Technology

[0002] Existing flexible actuators mostly employ silicone airbags or rigid joint mechanisms, which have limited compliance and stiffness adjustment capabilities. Nickel-titanium alloys, due to their shape memory and superelasticity properties, can maintain structural stability over a large deformation range. Traditional nickel-titanium supports or mesh tubes only have passive recovery capabilities and cannot actively adjust stiffness. How to achieve variable stiffness while maintaining lightweight and flexibility is a key challenge in current research on flexible robot end effectors. To address this, this invention proposes a flexible actuator based on nickel-titanium alloy and its fabrication method. Summary of the Invention

[0003] The purpose of this invention is to provide a flexible actuator based on nickel-titanium alloy and its preparation method. By changing the weaving angle and axial stretching, the radial contraction and expansion of the structure can be achieved, thereby actively enveloping and grasping objects.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a flexible actuator based on nickel-titanium alloy, applied to fruit picking, comprising a nickel-titanium alloy woven skeleton, wherein the nickel-titanium alloy woven skeleton is woven from at least one nickel-titanium alloy wire to form a tubular structure, and the outer side of the nickel-titanium alloy woven skeleton is covered with a coating layer. The nickel-titanium alloy braided skeleton has an upper ring and a lower ring arranged from top to bottom. The nickel-titanium alloy braided skeleton is fixedly connected to the upper ring. The upper ring and the lower ring are fixed by multiple hollow columns. The nickel-titanium alloy braided skeleton, the upper ring, and the lower ring are all coaxially arranged. A drive mechanism is installed at the bottom of the lower ring. The drive mechanism is fixedly connected to the top of the nickel-titanium alloy braided skeleton through a cable. When the drive mechanism tightens the cable, the nickel-titanium alloy braided skeleton changes the braiding angle by compression, thereby achieving axial compression and radial expansion.

[0005] Furthermore, the diameter of the nickel-titanium alloy wire is 0.3mm to 1.0mm, and the braiding angle α is 25° to 65°. When the cable is tightened, the braiding angle α increases, and the nickel-titanium alloy braided skeleton expands radially.

[0006] Furthermore, the coating layer is made of silicone, TPU or medical-grade polyurethane material, and the coating layer thickness is 0.5mm to 3mm.

[0007] Furthermore, an inner convex ring and an outer convex ring are fixedly connected to the inner and outer edges of the top plane of the upper ring, respectively, and an installation groove is formed between the inner convex ring and the outer convex ring, and the nickel-titanium alloy braided skeleton is fixed in the installation groove.

[0008] Furthermore, a round hole is provided in the middle of both the upper and lower rings, and a flexible hose is fixedly connected between the upper and lower rings. The flexible hose communicates with the nickel-titanium alloy braided skeleton, the round hole on the upper and lower rings, and the round hole on the upper and lower rings.

[0009] Furthermore, the number of hollow columns is at least four, the top of the hollow columns is fixed to the lower side of the upper ring, and the hollow columns penetrate the lower ring and are flush with the bottom surface of the lower ring.

[0010] Furthermore, the flexible hose is configured as a corrugated tube and is made of PVC material.

[0011] Furthermore, the drive mechanism includes a support column fixed to the bottom of the lower ring, a base fixedly connected to the bottom end of the support column, a drive motor fixedly installed on the top of the base, a cable drum fixedly installed at the output end of the drive motor, a cable winding cable wrapped around the outside of the cable drum, and the free end of the cable being pressed and fixed to the top of the nickel-titanium alloy braided skeleton through a steel wire rope aluminum sleeve.

[0012] According to a second aspect of the present invention, the present invention provides a fruit-harvesting robot, including a flexible actuator based on a nickel-titanium alloy as described in the first aspect.

[0013] According to a third aspect of the present invention, the present invention provides a method for preparing a flexible actuator based on a nickel-titanium alloy, for preparing the flexible actuator based on a nickel-titanium alloy described in the first aspect, comprising the following steps: S1. Select nickel-titanium alloy wire with a diameter of 0.3mm to 1.0mm and clean it; S2. A tubular braided skeleton is formed on the mold using a cross-weaving method, with a weaving angle α of 25° to 65°; S3. Heat set the woven skeleton together with the mold at 450℃~550℃ for 30min~60min; S4. After cooling, remove the material and cover it with a silicone or polyurethane coating to form a nickel-titanium alloy braided skeleton; S5. Fix the nickel-titanium alloy braided skeleton in the mounting groove of the upper ring, and install the flexible hose between the upper and lower rings to complete the assembly of the support structure; S6. Fix the cable on the winding drum in the drive mechanism to the nickel-titanium alloy braided skeleton to complete the assembly of the drive mechanism. When the cable is tightened, the nickel-titanium alloy braided skeleton changes the braiding angle by compression, realizing axial compression and radial expansion. When the cable is loosened, the nickel-titanium alloy braided skeleton elongates axially and contracts radially, restoring its original shape by utilizing its own structural elasticity.

[0014] This invention has at least the following beneficial effects: 1. This invention precisely controls the axial tension of the cable through a motor-driven mechanism, actively changing the weaving angle of the nickel-titanium alloy braided skeleton, thereby continuously adjusting the radial stiffness of the tubular structure. When the weaving angle decreases, the radial contraction stiffness of the structure increases significantly, generating a stable holding force; when the weaving angle increases, the structural flexibility improves, achieving flexible envelopment. This invention has a wider stiffness control range and higher control precision, effectively solving the technical contradiction of difficulty in balancing flexibility and load-bearing capacity.

[0015] 2. The tubular braided structure of the present invention can achieve a conformal envelope of the object to be grasped through radial contraction, adapting to objects of different sizes and shapes (spherical, ellipsoidal, irregular). The flexible material properties of the covering layer and the variable stiffness capability of the braided skeleton work together to form a grasping process of "first compliant envelope, then stiffness locking". The grasping pressure is evenly distributed, and the damage rate to fragile fruits (such as tomatoes, strawberries, etc.) is low.

[0016] 3. By incorporating a flexible hose, this invention creatively integrates the gripping function with the material conveying channel. The gripped object can be directly conveyed through the internal channel, achieving a seamless connection between the "grip-transfer-release" process. This greatly simplifies the system structure of the robot's end effector, improves operational efficiency, and is particularly suitable for scenarios requiring continuous operation, such as fruit picking, avoiding potential damage caused by secondary handling.

[0017] 4. The entire structure of this invention is mainly composed of nickel-titanium alloy wire and flexible materials, which has a natural advantage in terms of lightweight.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0019] Figure 1 This is a three-dimensional schematic diagram of the overall structure of the present invention; Figure 2 This is a three-dimensional schematic diagram of the nickel-titanium alloy braided skeleton structure of the present invention; Figure 3 This is a three-dimensional schematic diagram of the flexible hose structure of the present invention.

[0020] Figure label: 1. Nickel-titanium alloy braided frame; 2. Covering layer; 3. Upper ring; 4. Lower ring; 5. Hollow column; 6. Drive mechanism; 61. Base; 62. Drive motor; 63. Cable drum; 7. Cable; 8. Mounting groove; 9. Round hole; 10. Flexible hose; 11. Support column. Detailed Implementation

[0021] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0022] Example 1: Please see Figures 1-3 The present invention provides a technical solution: a flexible actuator based on nickel-titanium alloy, applied to fruit picking, including a nickel-titanium alloy woven skeleton 1, which is woven from at least one nickel-titanium alloy wire to form a tubular structure, and the nickel-titanium alloy woven skeleton 1 is covered with a covering layer 2 on the outside. The nickel-titanium alloy braided skeleton 1 is provided with an upper ring 3 and a lower ring 4 from top to bottom. The nickel-titanium alloy braided skeleton 1 is fixedly connected to the upper ring 3. The upper ring 3 and the lower ring 4 are fixed by multiple hollow columns 5. The nickel-titanium alloy braided skeleton 1, the upper ring 3, and the lower ring 4 are all coaxially arranged. A drive mechanism 6 is installed at the bottom of the lower ring. The drive mechanism 6 is fixedly connected to the top of the nickel-titanium alloy braided skeleton 1 via a cable 7. When the drive mechanism tightens the cable 7, the nickel-titanium alloy braided skeleton 1 changes the braiding angle by compression, thereby achieving axial compression and radial expansion.

[0023] Regarding the technical solution of this embodiment, the diameter of the nickel-titanium alloy wire is 0.3mm to 1.0mm, and the weaving angle α is 25° to 65°. When the cable 7 is tightened, the weaving angle α increases, and the nickel-titanium alloy weaving skeleton 1 expands radially. During the fruit harvesting process, the expansion state increases the opening diameter of the nickel-titanium alloy weaving skeleton 1, which can enclose objects larger than the initial diameter of the structure, such as fruits of different sizes. When the cable 7 is loosened, the nickel-titanium alloy weaving skeleton 1 elongates axially and contracts radially, restoring its original shape using its own structural elasticity. At this time, the nickel-titanium alloy weaving skeleton 1 can completely wrap and fix the fruit, thereby enabling harvesting.

[0024] Regarding the technical solution of this embodiment, the covering layer 2 is made of silicone, TPU or medical-grade polyurethane material, and the thickness of the covering layer 2 is 0.5mm to 3mm. The flexible covering layer 2 can undergo elastic deformation when it shrinks radially, increasing the contact area. The nickel-titanium alloy wires are prone to fatigue fracture due to mutual friction during repeated deformation. The covering layer 2 with a thickness of more than 0.5mm can effectively isolate the wires and extend the structural life. At the same time, the covering layer 2 can also increase the friction between the nickel-titanium alloy woven skeleton 1 and the fruit.

[0025] In this embodiment, an inner convex ring and an outer convex ring are fixedly connected to the inner and outer edges of the top plane of the upper ring 3, respectively. An installation groove 8 is formed between the inner and outer convex rings. The nickel-titanium alloy braided skeleton 1 is fixed in the installation groove 8. By setting a special installation groove 8, a clear and stable mechanical fitting position is provided for the nickel-titanium alloy braided skeleton 1. The installation groove 8 structure formed by the inner and outer convex rings can clamp and constrain the end of the braided skeleton. When the drive mechanism 6 applies axial tension through the cable 7, the stress acting on the skeleton can be more smoothly transferred to the overall support structure through the installation groove 8, avoiding excessive stress concentration at the connection point between the skeleton and the upper ring 3. This optimized stress transfer path helps to reduce material fatigue damage, thereby extending the service life of the flexible gripping structure.

[0026] Regarding the technical solution of this embodiment, a round hole 9 is provided in the middle of the upper ring 3 and the lower ring 4. A flexible hose 10 is fixedly connected between the upper ring 3 and the lower ring 4. The flexible hose 10 is interconnected with the nickel-titanium alloy braided frame 1 and the round hole 9 on the upper ring 3 and the lower ring 4. By opening a dedicated round hole 9 in the middle of the upper and lower rings 4 and fixing the flexible hose 10 thereto, it is ensured that the transmission channel from the gripping end to the bottom of the support structure is always independent and complete. After the fruit is picked, the nickel-titanium alloy braided frame 1 is expanded by tightening the cable 7 to release the fruit. The fruit can then fall through the flexible hose 10 and be transported to the storage box, realizing a rapid picking operation. In addition, the flexible hose 10 can also protect the fruit during the falling process to avoid damage to the outer skin.

[0027] Regarding the technical solution of this embodiment, the number of hollow columns 5 is at least four. The top of the hollow column 5 is fixed to the lower side of the upper ring 3, and the hollow column 5 passes through the lower ring 4 and is flush with the bottom surface of the lower ring 4. This design greatly enhances the rigidity and integrity of the overall support structure. It forms a sturdy "cage" structure that can effectively resist the torsional moment and lateral load generated when grabbing irregular objects or being subjected to external collisions, and avoids the skeleton from tilting or jamming on one side due to uneven support.

[0028] In this embodiment, the flexible hose 10 is configured as a corrugated tube and is made of PVC material.

[0029] Regarding the technical solution of this embodiment, the drive mechanism 6 includes a support column 11 fixed to the bottom of the lower ring 4. A base 61 is fixedly connected to the bottom end of the support column 11. A drive motor 62 is fixedly installed on the top of the base 61. A winding drum 63 is fixedly installed at the output end of the drive motor 62. A cable 7 is wound around the outside of the winding drum 63. The free end of the cable 7 is connected to the top of the nickel-titanium alloy braided skeleton 1. When the drive motor 62 is started, the winding drum 63 is rotated. The rotation angle of the winding drum 63 can be directly and linearly controlled, thereby precisely controlling the length of the cable 7. When the cable 7 is tightened, the nickel-titanium alloy braided skeleton 1 changes the braiding angle by compression, realizing axial compression and radial expansion. When the cable 7 is loosened, the nickel-titanium alloy braided skeleton 1 elongates axially and contracts radially, restoring its original shape by utilizing its own structural elasticity.

[0030] It should be further explained that the support column 11 is not aligned with the hollow column 5. The lower end of the cable 7 is led out from the cable drum 63 of the drive motor 62, passes through the tension sensor (used to detect changes in tension in real time), and then the cable 7 is divided into four strands using the rabbit ear knot braiding method. The four strands of cable 7 pass through the lower ring 4, the upper hollow column 5 and the upper ring 3 respectively, and are connected to the upper end of the nickel-titanium alloy braided skeleton 1 to achieve uniform driving and contraction control of the skeleton.

[0031] In summary, this invention precisely controls the axial tension of the cable through a motor-driven mechanism, actively changing the weaving angle of the nickel-titanium alloy braided skeleton 1, thereby continuously adjusting the radial stiffness of the tubular structure. When the weaving angle decreases, the radial contraction stiffness of the structure increases significantly, generating a stable gripping force; when the weaving angle increases, the structural flexibility improves, achieving flexible envelopment. This invention has a wider stiffness control range and higher control precision, effectively solving the technical contradiction of difficulty in balancing flexibility and load-bearing capacity.

[0032] Example 2: This embodiment provides a fruit-harvesting robot, including a flexible actuator based on nickel-titanium alloy as described in Embodiment 1.

[0033] Example 3: This embodiment provides a method for fabricating a flexible actuator based on a nickel-titanium alloy, used to fabricate the flexible actuator based on a nickel-titanium alloy described in Embodiment 1, including the following steps: S1. Select nickel-titanium alloy wire with a diameter of 0.3mm to 1.0mm and clean it; S2. A tubular braided skeleton is formed on the mold using a cross-weaving method, with a weaving angle α of 25° to 65°; S3. Heat set the woven skeleton together with the mold at 450℃~550℃ for 30min~60min; S4. After cooling, remove the material and cover it with a silicone or polyurethane coating layer 2 to form a nickel-titanium alloy braided skeleton 1; S5. Fix the nickel-titanium alloy braided skeleton 1 in the mounting groove 8 of the upper ring 3, and install the flexible hose 10 between the upper ring 3 and the lower ring 4 to complete the assembly of the support structure; S6. Fix the cable 7 on the winding drum 63 in the drive mechanism 6 to the nickel-titanium alloy braided skeleton 1 to complete the assembly of the drive mechanism 6. When the cable 7 is tightened, the nickel-titanium alloy braided skeleton 1 changes the braiding angle by compression, realizing axial compression and radial expansion. When the cable 7 is loosened, the nickel-titanium alloy braided skeleton 1 elongates axially and contracts radially, restoring its original shape by utilizing its own structural elasticity.

[0034] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0035] For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on," "mounted on," "fixed to," or "set on" another element, it may be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0037] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A flexible actuator based on nickel-titanium alloy, used in fruit harvesting, characterized in that, It includes a nickel-titanium alloy braided skeleton (1), which is formed by braiding at least one nickel-titanium alloy wire into a tubular structure, and the nickel-titanium alloy braided skeleton (1) is covered with a coating layer (2) on the outside. The nickel-titanium alloy braided skeleton (1) has an upper ring (3) and a lower ring (4) arranged from top to bottom. The nickel-titanium alloy braided skeleton (1) is fixedly connected to the upper ring (3). The upper ring (3) and the lower ring (4) are fixed by multiple hollow columns (5). The nickel-titanium alloy braided skeleton (1) is coaxially arranged with the upper ring (3) and the lower ring (4). The bottom of the lower ring (4) is equipped with a drive mechanism (6). The drive mechanism (6) is fixedly connected to the top of the nickel-titanium alloy braided skeleton (1) through a cable (7). When the drive structure tightens the cable (7), the nickel-titanium alloy braided skeleton (1) changes the braiding angle by compression, thereby achieving axial compression and radial expansion. The diameter of the nickel-titanium alloy wire is 0.3mm to 1.0mm, and the braiding angle α is 25° to 65°. When the cable (7) is tightened, the braiding angle α increases and the nickel-titanium alloy braided skeleton (1) expands radially. The coating layer (2) is made of silicone, TPU or medical-grade polyurethane material, and the thickness of the coating layer (2) is 0.5mm to 3mm; The inner and outer edges of the top plane of the upper ring (3) are respectively fixedly connected with an inner convex ring and an outer convex ring, and an installation groove (8) is formed between the inner convex ring and the outer convex ring. The nickel-titanium alloy braided skeleton (1) is fixed in the installation groove (8). Both the upper ring (3) and the lower ring (4) have a round hole (9) in the middle. A flexible hose (10) is fixedly connected between the upper ring (3) and the lower ring (4). The flexible hose (10) is interconnected with the nickel-titanium alloy braided skeleton (1), the round hole (9) on the upper ring (3) and the lower ring (4). The number of hollow columns (5) is at least four. The top of the hollow column (5) is fixed to the lower side of the upper ring (3), and the hollow column (5) passes through the lower ring (4) and is flush with the bottom surface of the lower ring (4). The flexible hose (10) is corrugated and made of PVC material.

2. The flexible actuator based on nickel-titanium alloy according to claim 1, characterized in that: The drive mechanism (6) includes a support column (11) fixed to the bottom of the lower ring (4). The bottom end of the support column (11) is fixedly connected to a base (61). The top of the base (61) is fixedly installed with a drive motor (62). The output end of the drive motor (62) is fixedly installed with a cable drum (63). A cable (7) is wound around the outside of the cable drum (63). The free end of the cable (7) is pressed and fixed to the top of the nickel-titanium alloy braided skeleton (1) through a steel wire rope aluminum sleeve.

3. A fruit-harvesting robot, characterized in that, Includes a flexible actuator based on a nickel-titanium alloy according to any one of claims 1 to 2.

4. A method for preparing a flexible actuator based on a nickel-titanium alloy, used to prepare the flexible actuator based on a nickel-titanium alloy as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Select nickel-titanium alloy wire with a diameter of 0.3mm to 1.0mm and clean it; S2. A tubular braided skeleton is formed on the mold using a cross-weaving method, with a weaving angle α of 25° to 65°; S3. Heat set the woven skeleton together with the mold at 450℃~550℃ for 30min~60min; S4. After cooling, remove and cover with silicone or polyurethane coating (2) to form a nickel-titanium alloy braided skeleton (1); S5. Fix the nickel-titanium alloy braided skeleton (1) in the mounting groove (8) of the upper ring (3), and install the flexible hose (10) between the upper ring (3) and the lower ring (4) to complete the assembly of the support structure; S6. Fix the cable (7) on the winding drum (63) in the drive mechanism (6) to the nickel-titanium alloy braided skeleton (1) to complete the assembly of the drive mechanism (6). When the cable (7) is tightened, the nickel-titanium alloy braided skeleton (1) changes the braiding angle by compression, thereby achieving axial compression and radial expansion. When the cable (7) is loosened, the nickel-titanium alloy braided skeleton (1) elongates axially and contracts radially, restoring its original shape by utilizing its own structural elasticity.

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