A bidirectional stepping flexible piezoelectric cable based on inchworm effect and a control method thereof

Abstract

The application discloses a bidirectional stepping flexible piezoelectric cable based on inchworm effect and a control method thereof in the technical field of aerospace, which comprises a shell with a hollow cavity, and the middle part region is hollowed out along the thickness direction; the cable can penetrate through the hollow cavity, and an interference fit is formed between the cable and the hollow cavity in the thickness direction, and there is a gap between the cable and the hollow cavity in the width direction; two groups of piezoelectric fiber composite components are respectively installed on the two sides of the cable; the piezoelectric fiber composite comprises a piezoelectric fiber layer located at the center of the piezoelectric fiber composite, epoxy resin layers are respectively arranged on the two sides of the piezoelectric fiber layer, packaging layers are respectively arranged outside the two epoxy resin layers, and interdigital electrodes are arranged on the surfaces of the packaging layers; the bidirectional stepping movement of the cable is realized, and the application is more suitable for flexible planar thin film antennas.

Description

Technical Field

[0001] This invention belongs to the field of aerospace technology, and particularly relates to a bidirectional stepping flexible piezoelectric rope based on the inchworm effect and its control method. Background Technology

[0002] With the development of space technology, the demand for large space antennas is becoming increasingly urgent. When the antenna size exceeds the capacity of the launch vehicle fairing (or space shuttle), a deployable antenna structure must be adopted, and most deployable antennas are mesh-type deployable antennas. As the size of mesh-type deployable antennas increases, the requirements for surface accuracy also become increasingly stringent (especially in the high-frequency band). Although increasing the number of main ribs can improve the accuracy of the reflector surface to some extent, it also significantly increases the antenna mass.

[0003] Compared to traditional planar rigid antenna structures, flexible planar thin-film antennas have become an important development direction for large antennas (with an area of ​​hundreds of square meters or even larger) due to their advantages such as light weight and small folded volume. The stiffness of the thin-film array, the effective area ratio of the thin-film array, the stress on the support frame, and the dimensions of the support frame all depend on the design of the rope tensioning system.

[0004] In the published patent CN114243308A, titled "Piezoelectric Rope for Adjusting the Accuracy of the Reflector Surface of a Mesh Antenna," the piezoelectric fiber composite material at the top or bottom is elongated by applying a single-phase current, thereby clamping the rope. This clamping force originates from the increased normal pressure on the rope after the outer shell deforms. Furthermore, the rope requires the cumulative motion of multiple piezoelectric fiber composite materials in the middle to produce a single unit displacement, significantly increasing the rope's size and mass, which is detrimental to the design of flexible rope tensioning systems.

[0005] In addition, existing inchworm piezoelectric actuators, by mimicking the movement of inchworms in nature, accumulate the step displacements generated by piezoelectric elements into a bidirectional type, possessing all the advantages of piezoelectric actuators. However, existing piezoelectric inchworm actuators all use metal frames and piezoelectric stacks as basic working elements in their design, resulting in relatively large mass and high rigidity. These characteristics severely limit their application in thin-film antenna tensioning systems. Summary of the Invention

[0006] This invention provides a bidirectional stepping flexible piezoelectric rope based on the inchworm effect and its control method. By mimicking the working principle of piezoelectric stacks, it utilizes interdigitated electrodes to prepare a lightweight and flexible piezoelectric fiber composite. Using this composite as an actuator, the rope's stepping bidirectional movement is achieved through optimized rope design. This results in a smaller mass, fewer operation steps, a simple and compact structure, high positioning accuracy, good flexibility, and good dynamic characteristics, making it more suitable for flexible planar thin-film antennas. This invention solves the bottleneck problems existing in current rope tensioning systems.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a bidirectional stepping flexible piezoelectric rope based on the inchworm effect, comprising:

[0008] It has a hollow outer shell, and the middle part is hollowed out along the thickness direction;

[0009] A rope that can penetrate a hollow cavity and forms an interference fit with the hollow cavity in the thickness direction, while there is a certain gap between the rope and the hollow cavity on both sides in the width direction;

[0010] Two sets of piezoelectric fiber composite assemblies are respectively installed on both sides of the rope;

[0011] The piezoelectric fiber composite assembly includes three sheet-like piezoelectric fiber composites in each group. The top and bottom ends are horizontally bonded, and the middle sheet is vertically bonded. The top and bottom ends of the middle sheet are respectively bonded to the bottom of the top sheet and the top of the bottom sheet. The piezoelectric fiber composite includes a piezoelectric fiber layer located at the center of the piezoelectric fiber composite. Epoxy resin layers are respectively disposed on both sides of the piezoelectric fiber layer. Encapsulation layers are respectively disposed on the outer sides of the two epoxy resin layers. Interdigitated electrodes are disposed on the surface of the encapsulation layers.

[0012] In the unpowered state, due to the interference fit, the rope shell exerts compressive stress on the rope, causing the rope to be in an automatically clamped state. When the rope is powered on, the two piezoelectric fiber composites at both ends of the piezoelectric fiber composite assembly elongate horizontally. Because the left and right ends of the piezoelectric sheet are fixed to the shell, and the shell's hardness is greater than that of the polyimide film, this elongation deformation cannot extend to the left and right ends. Therefore, after the piezoelectric fiber composites elongate, they cause the polyimide film to form a bending effect with a greater curvature, thereby reducing the original interference fit effect and achieving the purpose of loosening. The piezoelectric fiber composite in the middle of the piezoelectric fiber composite assembly moves vertically.

[0013] Furthermore, the outer shell is made of polyimide or other flexible polymer materials.

[0014] Furthermore, the top surfaces on both the left and right sides of the outer casing are fixed ends.

[0015] Furthermore, the piezoelectric fiber layer is made of piezoelectric ceramic fiber, and the encapsulation layer is a polyimide film.

[0016] Furthermore, the rope is made of fiberglass sheet or other engineering plastics.

[0017] Furthermore, the left forked lead of the interdigitated electrode serves as the positive electrode, and the right forked lead of the interdigitated electrode serves as the negative electrode.

[0018] The present invention also provides a control method for the above-mentioned piezoelectric rope, wherein the piezoelectric fiber composite assembly includes three sheet-like piezoelectric fiber composites arranged in a single row, the top and bottom two sheets being horizontally stretchable transverse patches, and the middle sheet being a vertically stretchable vertical patch.

[0019] By applying pulsed current to the piezoelectric fiber composite, and changing the power supply sequence of the top and bottom plates in two modes—extension and shortening of the middle plate—controllable upward or downward feeding motion of the rope can be achieved, depending on the movement pattern of the middle plate.

[0020] Furthermore, the piezoelectric fiber composites at the top and bottom are energized in a single phase, while the piezoelectric fiber composites in the middle are energized in a two-phase phase.

[0021] Furthermore, when the movement of the intermediate plate is shortening, the rope has two movement modes. Mode one is the upward feeding movement of the rope, which specifically includes the following steps:

[0022] Step S1: Apply electricity to the piezoelectric fiber composite at the top, causing the piezoelectric sheet at the top to elongate and eliminate the clamping effect caused by the original interference fit, that is, the top loosens the rope.

[0023] Step S2: While keeping the top plate energized, energize the middle plate to make the shell move the rope upwards.

[0024] Step S3: While keeping the middle plate energized, disconnect the top plate, and the rope will be clamped again;

[0025] Step S4: Apply power to the bottom plate so that the rope is held only by the top plate;

[0026] Step S5: Disconnect the intermediate plate. The outer shell is restored to its original state without affecting the rope. One power-on cycle is completed.

[0027] Furthermore, Mode 2 is a downward feeding motion mode using a rope, specifically including the following steps:

[0028] Step A1: Apply electricity to the bottom piezoelectric fiber composite, causing the bottom piezoelectric sheet to elongate and eliminate the clamping effect caused by the original interference fit, i.e., loosen the rope;

[0029] Step A2: While keeping the bottom plate energized, energize the middle plate. While the rope is held still, move the bottom of the shell upward.

[0030] Step A3: While keeping the middle plate energized, disconnect the bottom plate; the rope will remain clamped.

[0031] Step A4: Apply power to the top plate so that the rope is held only by the bottom plate;

[0032] Step A5: Disconnect the middle plate. The outer shell returns to its original state without being affected by the top plate, that is, its bottom end moves downward, which in turn drives the rope to move downward. One power-on cycle ends.

[0033] When the movement mode of the intermediate plate is elongation, under the same power supply conditions, the effects of movement mode one and movement mode two are opposite.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] I. The piezoelectric rope employs a structure that abandons the metal frame and piezoelectric stack structure used in traditional piezoelectric inchworm actuators. It is entirely made of piezoelectric ceramics and polymer composite materials, offering advantages in flexibility and lightweight design. This allows it to be applied in systems requiring precise bidirectional adjustment but with very limited load capacity. Furthermore, compared to piezoelectric stack actuators, the piezoelectric rope designed with piezoelectric composite materials can not only be distributed but also possesses flexibility, giving it foldability within a certain space. This makes it particularly suitable for mesh antennas and thin-film antenna tensioning systems, simplifying antenna structures and facilitating the development of larger and more flexible structures.

[0036] II. The bidirectional stepping flexible piezoelectric rope based on the inchworm effect disclosed in this invention has a simple and compact structure, high positioning accuracy, good flexibility, and good dynamic characteristics.

[0037] Third, compared with the published patent "Piezoelectric Rope for Adjusting the Accuracy of Mesh Antenna Reflector Surface", the structure and operating principle of the bidirectional stepping piezoelectric rope in this invention are completely different. This patent is based on the inchworm effect principle, and the step displacement generated by the piezoelectric composite material can be accumulated. The motion mode of the structural unit is simple and easy to implement. In one power-on cycle, fewer steps are required to make the rope move in both directions. Its mass is smaller and it is more suitable for flexible planar thin film antennas. Attached Figure Description

[0038] Figure 1 This is a front view structural diagram of the present invention;

[0039] Figure 2 This is a schematic diagram of the left-side structure of the present invention;

[0040] Figure 3This is a schematic diagram of the bottom view structure of the present invention;

[0041] Figure 4 This is a schematic diagram of the shell structure in this invention;

[0042] Figure 5 This is a schematic diagram of the piezoelectric fiber composite component structure in this invention;

[0043] Figure 6 This is a schematic diagram of the piezoelectric fiber composite structure in this invention;

[0044] Figure 7 This is a simulation demonstration diagram of the upward movement of the rope in this invention;

[0045] Figure 8 This is a simulation demonstration diagram of the rope downward motion in this invention;

[0046] Figure 9 This is a simulation demonstration diagram of clamping and releasing in this invention;

[0047] Figure 10 This is a diagram simulating the effect of simultaneous energization of the upper and middle sheets of the piezoelectric fiber composite in this invention;

[0048] Figure 11 This is a simulation of the rope movement effect after the upper and middle sheets of the piezoelectric fiber composite are simultaneously energized, as shown in the diagram.

[0049] The attached diagram lists the components represented by each number as follows:

[0050] 1. Outer shell; 2. Rope; 3. Piezoelectric fiber composite assembly; 4. Piezoelectric fiber layer; 5. Epoxy resin layer; 6. Encapsulation layer. Detailed Implementation

[0051] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0052] Example 1

[0053] Please refer to the details. Figure 1-5 A bidirectional stepping flexible piezoelectric rope based on the inchworm effect, comprising:

[0054] The outer shell 1 has a hollow cavity, and the middle part is hollowed out along the thickness direction; the top end faces on the left and right sides of the outer shell 1 are fixed ends;

[0055] Rope 2 can penetrate the hollow cavity and form an interference fit with the hollow cavity in the thickness direction, while there are gaps between the rope 2 and the hollow cavity on both sides in the width direction.

[0056] Two sets of piezoelectric fiber composite components 3 are respectively installed on both sides of the rope 2;

[0057] The piezoelectric fiber composite assembly 3 includes three sheet-like piezoelectric fiber composites arranged in a single row in each group. The two sheets at the top and bottom are horizontally stretchable transverse sheets, and the middle sheet is a vertically stretchable vertical sheet.

[0058] The piezoelectric fiber composite includes a piezoelectric fiber layer 4 located at the center of the piezoelectric fiber composite, epoxy resin layers 5 respectively disposed on both sides of the piezoelectric fiber layer 4, an encapsulation layer 6 respectively disposed on the outer side of the two epoxy resin layers 5, and interdigitated electrodes disposed on the surface of the encapsulation layer 6.

[0059] Please see Figure 6 The outer shell 1 is made of polyimide, the rope 2 is made of fiberglass sheet, the piezoelectric fiber layer 4 is made of piezoelectric ceramic fiber, and the encapsulation layer 6 is made of polyimide film. The structure of the piezoelectric rope abandons the metal frame and piezoelectric stack structure used in traditional piezoelectric inchworm actuators. The whole is made of piezoelectric ceramic and polymer composite materials, which has the advantages of flexibility and lightweight.

[0060] In the unpowered state, due to the interference fit, the rope shell exerts compressive stress on the rope, causing the rope to be in an automatically clamped state. When the rope is powered on, the two piezoelectric fiber composites at both ends of the piezoelectric fiber composite assembly elongate horizontally. Because the left and right ends of the piezoelectric sheet are fixed to the shell, and the shell's hardness is greater than that of the polyimide film, this elongation deformation cannot extend to the left and right ends. Therefore, after the piezoelectric fiber composites elongate, they cause the polyimide film to form a bending effect with a greater curvature, thereby reducing the original interference fit effect and achieving the purpose of loosening. The piezoelectric fiber composite in the middle of the piezoelectric fiber composite assembly moves vertically.

[0061] Please see Figure 6 The left forked lead of the interdigitated electrode serves as the positive electrode, and the right forked lead of the interdigitated electrode serves as the negative electrode.

[0062] The piezoelectric fiber composites at the top and bottom are energized using a single phase, while the piezoelectric fiber composites in the middle are energized using a two-phase phase.

[0063] A control method for a bidirectional stepping flexible piezoelectric rope based on the inchworm effect is disclosed. The control method includes applying pulsed current to the piezoelectric fiber composite and then changing the power supply sequence of the top and bottom plates according to the different movement patterns of the middle plate, which are divided into two modes: middle plate extension and shortening.

[0064] Please see Figure 7 China AG, Figure 9When the middle piece (ab) moves in a shortening motion, rope 2 has two motion modes: mode one is the upward feeding motion of rope 2, and mode two is the downward feeding motion of rope 2. Mode one specifically includes the following steps:

[0065] Step S1: Apply electricity to the piezoelectric fiber composite at the top, causing the piezoelectric sheet at the top to elongate and eliminate the clamping effect caused by the original interference fit, i.e., the top loosens the rope 2.

[0066] Step S2: While keeping the top plate energized, energize the middle plate to make the shell move the rope 2 upward.

[0067] Step S3: While keeping the middle plate energized, disconnect the top plate, and rope 2 is clamped again;

[0068] Step S4: Apply power to the bottom plate so that the two ropes are clamped by the top plate;

[0069] Step S5: Disconnect the intermediate plate. The outer shell is restored to its original state without affecting rope 2. One power-on cycle ends.

[0070] Please see Figure 8 China AG, Figure 9 The specific steps of the AB mode 2 are as follows:

[0071] Step A1: Apply electricity to the bottom piezoelectric fiber composite, causing the bottom piezoelectric sheet to elongate and eliminate the clamping effect caused by the original interference fit, i.e., loosen rope 2;

[0072] Step A2: While keeping the bottom plate energized, energize the middle plate. While the rope 2 is held still, move the bottom of the shell upward.

[0073] Step A3: While keeping the middle plate energized, disconnect the bottom plate; rope 2 remains clamped.

[0074] Step A4: Apply power to the top plate so that the two ropes are clamped by the bottom plate;

[0075] Step A5: Disconnect the middle piece. The outer shell returns to its original state without being affected by the top piece, that is, its bottom end moves downward, which simultaneously drives the rope 2 to move downward. One power-on cycle ends.

[0076] When the intermediate plate moves in the elongation mode, under the same power supply conditions, the effects of movement mode one and movement mode two are opposite.

[0077] Example 2

[0078] Finite element simulation of piezoelectric rope

[0079] In the calculation process, the constitutive equation was introduced into the kinetic energy equation and the charge conservation equation using COMSOL Multiphysics software to calculate the piezoelectric equation. The calculation formulas are shown in (1)-(3):

[0080]

[0081]

[0082]

[0083] In this context, equation (1) represents the constitutive relation in stress-charge form, (2) and (3) are the equilibrium equation and charge conservation equation of solid mechanics, respectively, where T is stress, S is strain, E is electric field, D is electric displacement, CE is the elastic matrix represented by Voigt, e is the coupling matrix, εs is the dielectric matrix, F is the deformation gradient, S is the Piola-Kirchhoff stress tensor, FV is the main force of deformation per unit volume, ρV is the charge density, u is the displacement vector, and V is the electric potential. The working region of the piezoelectric fiber composite is considered as PZT-5A material, and its elastic matrix, electromechanical coupling matrix, and relative permittivity matrix are shown in equations (4)-(6).

[0084]

[0085]

[0086]

[0087] The non-working region of the piezoelectric fiber composite material is a polyimide film with a tensile modulus of 3.1 GPa, a Poisson's ratio of 0.34, and a density of 1300 kg / m³. 3 The shell has a tensile modulus of 4.1 GPa, a Poisson's ratio of 0.36, and a density of 1300 kg / m³. 3 The piezoelectric rope has a tensile modulus of 12 GPa, a Poisson's ratio of 0.30, and a density of 3000 kg / m³. 3 The electric field strength of the piezoelectric fiber composite material is set to 3.77 kV / mm (the maximum value under normal operating conditions).

[0088] Piezoelectric fiber composite (piezoelectric sheet) dimensions: The working area dimensions of the top and bottom four sheets are 14mm*1mm*3*0.2mm, and the overall dimensions (including the polyimide film) are 20mm*15mm*0.4mm; the working area dimensions of the middle sheet are 16mm*14mm*0.2mm, and the overall dimensions are 20mm*16mm*0.4mm.

[0089] To maintain the self-clamping effect when no power is applied, the thickness of the piezoelectric rope must be greater than the thickness of the hollow area of ​​the shell, i.e., an interference fit, with an interference of 0.1 mm. Under this interference condition, the rope can support a weight of 8 N (when no power is applied, with an 8 N weight hanging below the rope, the rope is still clamped by the shell and will not slip).

[0090] The coefficient of friction between the housing and the piezoelectric cord is set to 0.45. This simulates the effect of simultaneously energizing the upper and middle plates. When the upper plate is energized, the piezoelectric plate elongates, forming a bulge in the thickness direction, such as... Figure 10 As shown, the highest point can be raised by 0.034mm to reduce the contact area between the piezoelectric shell and the rope in that area, thus achieving a loosening effect. At this time, the lower plate clamps, the upper plate loosens, the middle plate shortens vertically, and the lower plate, holding the rope, is lifted upwards by a certain displacement. Simultaneously, the bottom of the shell moves upwards by 0.07434mm, and the rope, overcoming friction, is also lifted upwards by 0.02491mm. Figure 11 As shown.

[0091] Compared with the previous model, the displacement of the rope is about twice as large, and the stability of the new model is much higher. The previous model showed some swaying at the bottom of the rope during operation, while the displacement of the bottom of the rope in the xy plane in this model is very small, with almost no swaying, and only stable vertical up and down movement in the z direction.

[0092] In summary, this invention applies two-phase pulse energization to the piezoelectric fiber composite of the intermediate sheet, enabling the intermediate sheet to form two motion modes. By changing the energizing sequence of the top and bottom sheets in both elongation and shortening modes, the rope 2 can achieve controllable upward or downward feeding motion, i.e., the rope's step-like bidirectional motion. Furthermore, it has a smaller mass, fewer operation steps, a simple and compact structure, high positioning accuracy, good flexibility, and good dynamic characteristics, making it more suitable for flexible planar thin-film antennas and solving the bottleneck problems existing in current rope tensioning systems.

[0093] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances. In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0094] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A bidirectional stepping flexible piezoelectric rope based on the inchworm effect, characterized in that, Including: The outer shell (1) has a hollow cavity, and the middle part is hollowed out along the thickness direction; The rope (2) can penetrate the hollow cavity and form an interference fit with the hollow cavity in the thickness direction, and there are gaps between the rope (2) and the hollow cavity on both sides in the width direction. Two sets of piezoelectric fiber composite components (3) are respectively installed on both sides of the rope (2); The piezoelectric fiber composite assembly (3) includes three sheet-like piezoelectric fiber composites arranged in a single row in each group. The top and bottom two sheets are horizontally stretchable transverse sheets, and the middle sheet is a vertically stretchable vertical sheet. The piezoelectric fiber composite includes a piezoelectric fiber layer (4) located at the center of the piezoelectric fiber composite, epoxy resin layers (5) are respectively disposed on both sides of the piezoelectric fiber layer (4), and an encapsulation layer (6) is respectively disposed on the outer side of the two epoxy resin layers (5), and interdigitated electrodes are disposed on the surface of the encapsulation layer (6).

2. The bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 1, characterized in that: The outer shell (1) is made of polyimide or other flexible polymer materials, the rope (2) is made of fiberglass sheet or other engineering plastics, the piezoelectric fiber layer (4) is made of piezoelectric ceramic fiber, and the encapsulation layer (6) is made of polyimide film.

3. The bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 1, characterized in that: The top surfaces on the left and right sides of the outer shell (1) are fixed ends.

4. The bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 1, characterized in that: The left forked lead of the interdigitated electrode serves as the positive electrode, and the right forked lead serves as the negative electrode.

5. The bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 1, characterized in that: The piezoelectric fiber composites at the top and bottom are energized using a single phase, while the piezoelectric fiber composites in the middle are energized using a two-phase phase.

6. A control method for a bidirectional stepping flexible piezoelectric rope based on the inchworm effect, applied to a bidirectional stepping flexible piezoelectric rope based on the inchworm effect as described in any one of claims 1-5, wherein the control method includes, after pulse energizing the piezoelectric fiber composite, changing the energizing sequence of the top and bottom plates according to the different movement patterns of the middle plates, in two modes: elongation and shortening of the middle plates.

7. The control method for a bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 6, characterized in that: When the intermediate piece moves in a shortening manner, the rope (2) has two movement modes: mode one is the upward feeding movement of the rope (2), and mode two is the downward feeding movement of the rope (2). Mode one specifically includes the following steps: Step S1: Apply electricity to the piezoelectric fiber composite at the top, and the piezoelectric sheet at the top will elongate, eliminating the clamping effect caused by the original interference fit, that is, the rope at the top will be loosened (2); Step S2: While keeping the top plate energized, energize the middle plate to make the shell drive the rope (2) to move upward; Step S3: While keeping the middle plate energized, disconnect the top plate, and the rope (2) is clamped again; Step S4: Apply power to the bottom plate so that the rope (2) is only held by the top plate; Step S5: Disconnect the intermediate plate and restore the outer shell to its original state without affecting the rope (2). One power-on cycle ends.

8. The control method for a bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 7, characterized in that: The second mode specifically includes the following steps: Step A1: Apply electricity to the bottom piezoelectric fiber composite, and the bottom piezoelectric sheet elongates, eliminating the clamping effect caused by the original interference fit, that is, loosening the rope (2); Step A2: While keeping the bottom plate energized, energize the middle plate. While the rope (2) is held still, move the bottom of the shell upward. Step A3: While keeping the middle plate energized, disconnect the bottom plate; the rope (2) remains clamped. Step A4: Apply power to the top plate so that the rope (2) is held only by the bottom plate; Step A5: Disconnect the middle piece. The outer shell is restored to its original state without being affected by the top piece, that is, its bottom end moves downward, and at the same time, it drives the rope (2) to move downward. One power-on cycle ends.

9. The control method for a bidirectional stepping flexible piezoelectric rope based on the inchworm effect according to claim 7, characterized in that: When the intermediate plate moves in an elongation mode, under the same power supply conditions, the effects of movement mode one and movement mode two are opposite.

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