CN114422675A

CN114422675A - Multifunctional elastic sheet structure

Info

Publication number: CN114422675A
Application number: CN202210038293.7A
Authority: CN
Inventors: 王林; 卢煌杰; 王文祥
Original assignee: Chengdu Yixun Photoelectric Technology Co ltd
Current assignee: Chengdu Yixun Photoelectric Technology Co ltd
Priority date: 2022-01-13
Filing date: 2022-01-13
Publication date: 2022-04-29

Abstract

The invention belongs to the technical field of voice coil motors, and discloses a multifunctional spring plate structure which is used as an elastic part movably connected between a carrier and a support in a VCM motor. The invention adopts the elastic piece plane material which is the same as the elastic piece to replace the existing built-in metal circuit, complete PCB circuit and FPC circuit, thereby having smaller volume, and being capable of completing and simultaneously installing when manufacturing the elastic piece, thereby reducing the manufacturing difficulty and the manufacturing cost.

Description

Multifunctional elastic sheet structure

Technical Field

The invention belongs to the technical field of voice coil motors, and particularly relates to a multifunctional spring plate structure.

Background

The VCM motor is a device that converts electric energy into mechanical energy and realizes linear and limited swing angle motion. The device generates regular movement by utilizing the interaction between the magnetic field from the permanent magnetic steel and the magnetic poles in the magnetic field generated by the conductor of the electrified coil. Because the voice coil motor is a non-commutation type power device, the positioning accuracy is completely dependent on the feedback and control system, and is independent of the voice coil motor. The VCM motor changes the smart phone camera from fixed focus to automatic focusing, and simultaneously endows a small or miniature camera with an anti-shake function, and the VCM motor has the greatest effect that the camera can automatically focus and also can provide motion compensation.

The VCM of the mobile phone camera needs Driver IC to complete focusing and anti-shake, the current VCM controls the magnitude of VCM power supply current through the Driver IC to determine the moving distance of a lens carried by the VCM, and therefore the VCM is adjusted to a proper position to shoot a clear image. The VCM motor actually moves by the principle that an energized coil receives an acting force in a magnetic field, and the precise control needs to be performed by some external components, wherein an elastic sheet is further needed to elastically limit and support the sensor or the lens module, so as to provide a support fixing effect and an elastic movement state.

However, as the pixel requirements are higher and higher, the motor lens is larger and heavier, and under the requirements of small size and high pixel, the motor space layout and utilization are very tested for structural design, especially in the AF closed-loop control, the large lens can be driven by adopting a bar magnet, and the T-shaped magnet does not meet the thrust requirement, so that the space can be further compressed, the AF closed-loop control is difficult to realize by directly adopting an SMT manner, and can only be realized by adopting a conventional PCB/FPC manner, but the IC and AF conduction structure can be relatively complex to realize.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a multifunctional spring plate structure, which can simultaneously meet the elastic supporting and conducting effects through an elastic part directly assembled outside during production, so that a part or all of insert circuits are replaced, and the manufacturing cost is reduced.

The technical scheme adopted by the invention is as follows:

in a first aspect, the present invention provides a multifunctional spring structure, which is used as an elastic member movably connected between a carrier and a support in a VCM motor, and includes at least two parts, one part is a brown wire fixed on the support and used for conducting electricity, and the other part is a spring arranged between the carrier and the support and used for conducting electricity and elastically connecting.

It should be noted that the carrier and the bracket are two independent components movably connected or capable of relatively moving in the VCM motor, and can be used not only for AF (auto focus, i.e. as two parts for pushing the lens to move along its axis), but also as two moving parts of OIS (optical anti-shake, including two parts of lens anti-shake and sensor anti-shake, and also as two parts for using magnetic components to perform relative movement). An elastic body is arranged between the two parts for elastic support and limit, and the two parts are driven to act by a coil or a magnet which is respectively arranged on the two parts when the external power supply is supplied.

The cord and the spring plate are of the same or similar metal conductive structure and have elasticity, but the spring plate mainly provides an elastic connection effect between the support and the carrier and has a conductive characteristic. The cord does not play a role of elastic support, and is only used for replacing an insert circuit, an FPC circuit or a PCB circuit in the existing bracket. The support is only divided into two lines of power supply and signals, and does not have a more complicated circuit structure.

The design of the broken filament structure can be carried out according to the size of the bracket during design, materials are obtained by etching on the same or a plurality of metal plates, and the materials and the elastic sheets are placed on the bracket and the carrier together during assembly and are fixedly connected in a welding mode, a dispensing mode and the like.

In combination with the first aspect, the present invention provides a first implementation manner of the first aspect, wherein the brown threads and the elastic pieces are made of the same material by etching.

In combination with the first aspect, the present disclosure provides a second implementation manner of the first aspect, wherein the threaded wires and the elastic pieces are independent structures.

With reference to the first aspect and the first or second embodiment of the first aspect, the present invention provides a third embodiment of the first aspect, wherein the elastic member has an inner ring and an outer ring for fixed installation.

It is worth to be noted that the brown wire and the spring plate can be designed as an integrated structure, and the mutually connected parts are formed on the same metal plate by etching, and the integrated connection mode includes various modes.

The carrier and the bracket are both annular structural members, and the cord and the spring plates are also uniformly distributed on the carrier or the bracket by taking the axis of the lens module as the center of a circle. The structural design can be made in various ways during etching in order to ensure that both functional parts can be mounted together.

In the fixing mode of the inner material ring and the outer material ring, the inner material ring is connected with the inner side end of the elastic sheet, and the outer material ring is connected with the outer side end of the suspension wire and connected through a connecting body with a notch. Such a cut is a half-cut groove cut at a corresponding portion by a cutter or other tool after etching, and can be broken off by the tool directly after mounting.

Meanwhile, because the brown threads on the outer ring can form a plurality of independent parts after the material ring is removed, the brown threads are not of a complete annular structure, and a space is arranged at part of the brown threads, so that the inner material ring can extend outwards to be directly connected with the outer material ring to form an integral connection mode.

Similarly, the connection mode can also be adopted, the black silk and the spring plate are all in the same thickness overlapping range (namely on the same horizontal plane), the external material ring, the black silk, the spring plate and the internal material ring are arranged in sequence, and the connection positions of every two are provided with the breakable connecting bodies for connection. Compared with the mode, the broken part is more, and the connector between the broken wire and the elastic sheet is smaller, so that the broken part cannot be effectively removed after being broken, and the broken part is only shown as a theoretical real-time mode.

Similarly, the two independent structures of the cord and the spring plate are respectively included, and different material rings are adopted for fixing. Because the part that the broken lines and the elastic sheets are not overlapped with each other on the vertical plane is not present, the broken lines and the elastic sheets can be assembled simultaneously or in a time-sharing way as independent structures. The cord and the spring plate are in independent structures and can be formed by etching the same metal plate, so that materials are saved as much as possible, and the cost is reduced.

With reference to the first aspect and the first or second implementation manner of the first aspect, the present invention provides a fourth implementation manner of the first aspect, wherein the elastic members are fixedly installed by a single material ring arranged outside or inside, and the material ring, the brown wire and the elastic sheet are connected by a breakable connecting body.

It should be noted that, because the cord and the elastic sheet are not complete ring structures, openings are provided at partial positions for the connecting body to pass through for connection and fixation. The fixed mode of single material ring, in can being applicable to the shell fragment mysterious silk structure of integral type or split type setting equally, then connect through a plurality of connectors, and single material ring can take off after the rupture can.

With reference to the first aspect and the first or second implementation manner of the first aspect, the present invention provides a fifth implementation manner of the first aspect, wherein the cord and the elastic piece have non-overlapping height ranges in the thickness direction after being installed.

It should be noted that the non-overlapping height ranges refer to the fact that the two portions of the structure design can be connected by the same material ring in a manner of arranging two layers of connectors from top to bottom, because the two portions are not on the same horizontal plane in the axial direction of the lens module, and have a certain thickness but do not overlap.

Similarly, the suspension wires and the elastic sheets can be made of materials with different thicknesses according to use requirements, and the suspension wires and the elastic sheets are etched by adopting plates with two thicknesses to form two independent structures and then are simultaneously arranged on the carrier bracket. And because the connecting bodies are arranged on different horizontal mounting surfaces, the connecting bodies can be mutually independent and do not interfere with each other.

With reference to the first aspect and the first or second implementation manner of the first aspect, the present invention provides a sixth implementation manner of the first aspect, where the two wires and the elastic sheet have pad ends, and the pad ends are both disposed in the same region and connected to the same PCB board assembly disposed on the support in the same region.

It should be noted that the pad end is an expanded end of the corrugated wire and the elastic sheet, and the expanded end is conductively welded with the PCB assembly in a manner of increasing the thickness and the width. Because the black wire and the elastic sheet are adopted for conducting, the PCB assembly is mainly used for power supply control and signal processing, can be arranged on one side of the bracket and has smaller volume.

With reference to the sixth implementation manner of the first aspect, the present invention provides a seventh implementation manner of the first aspect, wherein the PCB board assembly is connected with a hall sensor for implementing AF closed-loop control;

the electric wire is provided with a part which is connected with the Hall sensor to provide IC signal transmission and a part which is connected with power supply.

It should be noted that the IC signal here is also an electrical signal, but an independent cord is used to connect the PCB assembly and the external circuit, and the hall sensor reading data arranged on the PCB assembly is sent out, so as to achieve the effect of performing closed-loop control by moving distance feedback.

With reference to the seventh implementation manner of the first aspect, the present invention provides an eighth implementation manner of the first aspect, wherein a conductive metal part is embedded in the bracket, the conductive metal part has a plurality of contacts on the bracket, and the brown wire has an end connected to the contacts and is connected to an external circuit through the conductive metal part.

With reference to the sixth implementation manner of the first aspect, the present invention provides a ninth implementation manner of the first aspect, wherein the carrier has a winding end for winding an end of the coil, and the elastic piece has an end portion attached to the winding end.

The invention has the beneficial effects that:

(1) the invention adopts the elastic piece plane material which is the same as the elastic piece to replace the existing built-in metal circuit, complete PCB circuit and FPC circuit, thereby having smaller volume, and being capable of completing and installing simultaneously when manufacturing the elastic piece, thereby reducing the manufacturing difficulty and the manufacturing cost;

(2) the invention can keep part of the internal circuit and reduce the space size occupied by the circuit in the whole motor as much as possible by more flexible structural design of the broken wires and the spring pieces, thereby providing support for reducing the volume of the whole camera module.

Drawings

FIG. 1 is a top view of the carrier and carrier assembly of the present invention with the entire spring assembled;

FIG. 2 is an enlarged view of portion A of FIG. 1 in accordance with the present invention;

FIG. 3 is a side view of the carrier and carrier assembly of the present invention with the spring in its entirety;

FIG. 4 is a first axial side view of the carrier and carrier assembly of the present invention with the entire spring assembled;

FIG. 5 is an enlarged view of portion B of FIG. 4 in accordance with the present invention;

FIG. 6 is a second axial side view of the carrier and carrier assembly of the present invention with the entire spring assembled;

fig. 7 is a partially enlarged view of C in fig. 6 according to the present invention.

In the figure: 1-carrier, 2-bracket, 3-spring plate, 4-brown wire, 5-built-in conductor, 6-PCB assembly, 7-magnet, 8-material ring and 9-Hall sensor.

Detailed Description

The invention is further explained below with reference to the drawings and the specific embodiments.

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

In the description of the present application, it should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which is usually placed when the product of the application is used, the description is only for convenience and simplicity, and the indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation and be operated, and thus, should not be construed as limiting the present application. Furthermore, the appearances of the terms "first," "second," and the like in the description herein are only used for distinguishing between similar elements and are not intended to be construed as indicating or implying relative importance.

Furthermore, the terms "horizontal", "vertical" and the like when used in the description of the present application do not require that the components be absolutely horizontal or overhanging, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present application, it should also be noted that, unless otherwise explicitly stated or limited, the terms "disposed," "mounted," "connected," and "connected" should be interpreted broadly, e.g., as being fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.

Example 1:

the embodiment discloses a multifunctional spring plate structure, as shown in fig. 1-7, which is a structure disposed in a voice coil motor of a miniature camera module and used for supporting two movable parts.

First, the micro camera module in this embodiment includes a lens module, a sensor, and a voice coil motor, where the voice coil motor is used to control the lens module to move relative to the sensor, and mainly performs an AF auto-focusing function.

Therein, the voice coil motor mainly comprises two relatively movable parts, namely a support 2 and a carrier 1 structure as illustrated in the figure. The two structures are annular injection-molded parts which are mutually nested, the support 2 is fixed on the shell of the voice coil motor, and the carrier 1 is matched with the support 2 through elastic parts arranged on the upper surface and the lower surface.

The existing voice coil motor is matched with an electrified coil through a magnet, a magnetic field is formed after the coil is electrified, and controllable relative motion is realized through controlling the direction and the size of current to generate a specific magnetic field and matching with the magnet.

In the present embodiment, the holder 2 is provided with one magnet in each of four directions, and the carrier 1 is provided at its outer side surface with an annular groove in which a coil is disposed. This embodiment is an embodiment adopted in the present embodiment, but the technical solution is not limited thereto.

The whole voice coil motor is provided with an FPC circuit to be connected with external equipment, and a BTB connector is generally adopted. And the external equipment supplies power to the voice coil motor and controls the voice coil motor, and the power supply circuit comprises an FPC (flexible printed circuit) arranged at the bottom and an inner built-in conductor 5 connected with the FPC and arranged in the bracket 2 in the injection molding process. The inner conductor 5 has two ends, one end extending downward and connected to the bottom FPC, and the other end extending upward to expose a contact point on the top annular surface of the holder 2. This embodiment is an embodiment adopted in the present embodiment, but the technical solution is not limited thereto.

In this embodiment, because the AF module needs to be controlled by power supply and movement, and the displacement of the carrier 1 relative to the bracket 2 needs to be detected in real time by the displacement detection module arranged inside, at least two lines, namely, a power supply line and an IC signal line, are provided.

At least four independent internal conductors 5, including two power supply lines and two IC signal lines, are provided in the support 2.

In this embodiment, the mode that the FPC circuit, the PCB circuit, and the internal conductor 5, which are simply used on the support 2 and the carrier 1 in the conventional voice coil motor, form a circuit is optimized, and the cost and the volume are reduced by replacing the circuit with an elastic body on the upper surface.

In this embodiment, a plurality of annular metal elastic members, including two types, i.e., a brown wire 4 and a spring plate 3, are disposed on the upper surfaces of the carrier 1 and the bracket 2.

As shown in fig. 1 and 2, the brown wire 4 is a strip-shaped metal material which is located on the same horizontal plane as the spring plate 3 and has the same thickness. The cord 4 is arranged at the outer ring, and the shrapnel 3 is arranged at the inner ring. The brown wire 4 is only arranged on the upper surface of the bracket 2 and is equally divided into two groups of four independent metal pieces in the axis direction, and each group of brown wires 4 comprises one long wire and two short wires. This embodiment is an embodiment adopted in the present embodiment, but the technical solution is not limited thereto.

Because the brown threads 4 are independent structures, although the structures are similar to annular structures after arrangement, openings are formed at two corners or one corner, and materials on the same horizontal plane can extend into the openings to be connected with other materials.

The elastic sheet 3 is an elastic part connected between the carrier 1 and the support 2, and has the main function of providing relative elastic limiting effect for the support 2 and the carrier 1, so that the elastic supporting effect on the carrier 1 is achieved.

Meanwhile, the elastic sheet 3 is also used as a conductor, one end of the elastic sheet is provided with an expansion end which is close to a winding post arranged on the outer wall of the carrier 1, the end part of the coil is wound on the winding post, and the elastic sheet 3 is connected with the two end parts of the coil by soldering and other modes, thereby forming a circuit for supplying power to the coil.

Optionally, in this embodiment, because the elastic element is used to replace the existing circuit structure, the elastic element itself may be directly assembled and molded by adopting an integrated structure design during installation, and the problem of high cost and weight caused by the need of arranging a large number of metal elements during injection molding is eliminated. In this embodiment, a recess is provided in a corner of one side of the bracket 2, and a vertically disposed PCB board assembly 6 is provided in the recess. The PCB assembly 6 has a plurality of contacts and a hall sensor 9 is provided on a side close to the carrier 1. A magnet 7 is arranged at a corresponding position of the carrier 1, and the position information is acquired by detecting the magnet 7 through a Hall sensor 9,

The brown wire 4 and the elastic sheet 3 are both provided with end parts located at the position of the PCB board assembly 6, and the end parts are provided with bonding pads which are connected with the PCB board assembly 6 to form a complete circuit.

As can be seen in fig. 2, the PCB assembly 6 is provided with a label corresponding to each contact, including two OUT contacts connected to the spring 3, VDD and VSS contacts for power supply, and two SDA and SCL contacts for data transmission as an I2C bus.

Wherein the SCL forms a circuit by connecting with the contacts of the position built-in conductor 5. And the other contacts are connected with the brown wire 4 or the bonding pad of the elastic sheet 3.

Optionally, in order to improve assembly efficiency and cost control in the manufacturing process, the assembly method and the form structure of the spring plate 3 structure are further defined in this embodiment. Wherein, when assembling, the whole elastic part is provided with an inner material ring 8 and an outer material ring 8 for fixed installation.

Optionally, the brown wire 4 and the spring plate 3 are designed as an integrated structure, and the mutually connected parts are formed on the same metal plate by etching, and the integrated connection mode includes multiple modes. Because the carrier 1 and the bracket 2 are both annular structural members, the cord 4 and the spring plate 3 are also uniformly distributed on the carrier 1 or the bracket 2 by taking the axis of the lens module as the center of a circle. The structural design can be made in various ways during etching in order to ensure that both functional parts can be mounted together.

In the fixing mode of the inner material ring 8 and the outer material ring 8, the inner material ring 8 is connected with the inner side end of the elastic sheet 3, and the outer material ring 8 is connected with the outer side end of the suspension wire and connected through a connecting body with a notch. Such a cut is a half-cut groove cut at a corresponding portion by a cutter or other tool after etching, and can be broken off by the tool directly after mounting. Because the brown threads 4 at the outer ring can form independent parts after the material ring 8 is removed, the brown threads are not of a complete annular structure, and spaces are formed at partial positions for the inner material ring 8 to extend outwards partially and directly connect with the outer material ring 8 to form an integral connection form.

Optionally, a sequential connection mode may also be adopted, the brown wire 4 and the elastic sheet 3 are all within the same thickness overlapping range (i.e. on the same horizontal plane), the outer material ring 8, the brown wire 4, the elastic sheet 3 and the inner material ring 8 are sequentially arranged, and the two connection positions are all provided with breakable connectors for connection. Compared with the mode, the broken part is more, and the connection body between the broken wire 4 and the elastic sheet 3 is smaller, so that the broken part cannot be effectively removed after being broken, and the mode is only shown as a theoretical real-time mode.

Optionally, the two independent structures including the brown wire 4 and the spring plate 3 are respectively adopted, and different material rings 8 are adopted for fixing. Because the part of the cord 4 and the spring plate 3 which are overlapped with each other does not exist on the vertical plane, the cord can be assembled simultaneously or in a time-sharing way as an independent structure. The cord 4 and the spring plate 3 are independent structures and can be formed by etching the same metal plate, so that materials are saved as much as possible, and the cost is reduced.

Optionally, as shown in the figure, the elastic members in this embodiment are all fixedly mounted by a single material ring 8 disposed outside, and the material ring 8 is connected with the brown wire 4 and the elastic sheet 3 by breakable connecting bodies. Because the cord 4 and the spring plate 3 are not complete ring structures, openings are formed at partial positions for the connecting body to pass through for connection and fixation. The fixed mode of single material ring 8 can be applicable to in the shell fragment 3 mysterious silk 4 structure of integral type or split type setting equally, then connects through a plurality of connectors, and single material ring 8 can be taken off after the rupture can.

Optionally, the cord 4 and the spring plate 3 have non-overlapping height ranges in the thickness direction after being mounted. The non-overlapping height range means that the cord 4 and the spring plate 3 are not on the same horizontal plane in the axial direction of the lens module, and although the cord has a certain thickness, the cord and the spring plate are not overlapped, so that the structural design can connect two parts by arranging two layers of connecting bodies from top to bottom through the same material ring 8.

Optionally, the brown wire 4 and the spring plate 3 can be arranged in different thickness modes, and the brown wire 4 does not have the force bearing requirement, so that the spring plate can be made of a thinner material. The thickness of the elastic sheet 3 can be increased as required by considering the supporting effect of the carrier 1. As the above-mentioned contents adopt the split structure design, the elastic parts with two thicknesses can be separately or simultaneously installed.

If the integrated structure design is adopted, a multilayer structure mode can be adopted, wherein the brown threads 4 are only made of a single-layer material, the elastic sheets 3 are made of double-layer or more than double-layer materials, and though the two layers are fixed by the same material ring 8, the two layers form independent bodies after being broken.

The present invention is not limited to the above-described alternative embodiments, and various other forms of products can be obtained by anyone in light of the present invention. The above detailed description should not be taken as limiting the scope of the invention, which is defined in the claims, and which the description is intended to be interpreted accordingly.

Claims

1. The utility model provides a multi-functional shell fragment structure for set up as swing joint's elastic component between carrier (1) and support (2) in the VCM motor, its characterized in that: comprises at least two parts, one part is a brown wire (4) which is fixed on the bracket (2) and is used for conducting electricity, and the other part is an elastic sheet (3) which is arranged between the carrier (1) and the bracket (2) and is used for conducting electricity and elastically connecting.

2. The multifunctional spring plate structure of claim 1, wherein: the brown thread (4) and the spring plate (3) are made of the same material by etching.

3. The multifunctional spring plate structure of claim 1, wherein: the cord (4) and the spring plate (3) are both independent structures.

4. A multifunctional spring plate structure according to any one of claims 1-3, characterized in that: the elastic part is provided with an inner material ring (8) and an outer material ring (8) for fixed installation.

5. A multifunctional spring plate structure according to any one of claims 1-3, characterized in that: the elastic pieces are fixedly installed by a single material ring (8) arranged outside or inside, and the material ring (8) is connected with the brown wire (4) and the elastic sheet (3) through a breakable connecting body.

6. A multifunctional spring plate structure according to any one of claims 1-3, characterized in that: the cord (4) and the spring plate (3) have non-overlapping height ranges in the thickness direction after being installed.

7. A multifunctional spring plate structure according to any one of claims 1-3, characterized in that: the brown wire (4) and the elastic sheet (3) are provided with welding disc ends, and the welding disc ends are arranged in the same area and are connected with the same PCB assembly (6) arranged on the support (2) in the same area.

8. The multifunctional spring plate structure of claim 7, wherein: the PCB assembly (6) is connected with a Hall sensor (9) for realizing AF closed-loop control;

the electric wire (4) is provided with a part which is connected with the Hall sensor (9) and provides IC signal transmission and a part which is connected with power supply.

9. The multifunctional spring plate structure of claim 8, wherein: the support (2) is internally provided with a conductive metal piece, the conductive metal piece is provided with a plurality of contacts on the support (2), and the cord (4) is provided with an end part connected with the contacts and is connected with an external circuit through the conductive metal piece.

10. The multifunctional spring plate structure of claim 8, wherein: the carrier (1) is provided with a winding end for winding the end part of the coil, and the elastic sheet (3) is provided with an end part attached to the winding end.