Torquer in coaxial holographic storage system and electromagnetic structure thereof

Abstract

The utility model relates to a torquer in a coaxial holographic storage system and an electromagnetic structure thereof, the electromagnetic structure comprises a metal frame and a focusing coil, the thickness of the focusing coil is less than 2mm, and the height of the focusing coil is less than 8mm; the height of the tracking coil is less than 3mm, the width of an inner ring is less than 3mm, and the length of the inner ring is less than 8mm; the two permanent magnets are respectively arranged between the tracking coil and the focusing coil at the two ends of the metal frame; and the number of the yokes is two, and the yokes are inverted U-shaped, are respectively arranged at the two ends of the metal frame, and are respectively buckled on the focusing coil, the permanent magnet and the tracking coil at the two ends of the metal frame. It is ensured that a space magnetic field formed by the tracking coil, the focusing coil and the permanent magnet in the two yokes under interaction can generate electromagnetic force with enough strength, and meanwhile the problem that the servo tracking speed of the torquer is reduced due to the fact that the focusing coil and the tracking coil are too large is solved.

Description

Technical Field

[0001] This application relates to the field of optical technology, specifically to a torque device in a coaxial holographic storage system and the coaxial holographic storage system. Background Technology

[0002] In holographic storage, data is stored in the form of holograms in a medium (such as photopolymer organic materials). The reading and writing process requires high-precision optical head control, such as controlling the micro-displacement of the objective lens or mirror to ensure that the laser beam is accurately aligned with a specific position in the storage medium, and to compensate for minor deviations caused by medium jitter or thermal drift, maintaining stable alignment between the beam and the hologram. The torque device is the core component in the holographic storage system used to control the precise positioning of the optical head, and its performance directly affects the tracking speed, positioning accuracy, and data reading and writing reliability that the storage system can achieve.

[0003] During torque converter operation, its spatial magnetic field is mainly formed from two sources: one is the magnetic field generated by the permanent magnet, and the other is the magnetic field generated by electromagnetic waves passing through the coil. The interaction of these two magnetic fields together constitutes the spatial magnetic field of the coil and its surroundings. To increase the electromagnetic force on the focusing or tracking coil, one can consider increasing the magnetic induction intensity of the permanent magnet, increasing the volume of the coil passing through the magnetic field, and placing the coil as close to the magnet as possible. However, due to material limitations, the magnetic induction intensity of the permanent magnet cannot be increased indefinitely. Similarly, due to the response speed requirements of the torque converter, the coil volume cannot be increased indefinitely; otherwise, excessive weight will reduce its servo tracking speed. Utility Model Content

[0004] In view of the above problems, this application provides a torque generator and a coaxial holographic storage system, which solves the problem that if the torque generator and the focusing coil or tracking coil in the existing coaxial holographic storage system are too bulky, it will lead to a decrease in its servo tracking speed.

[0005] To achieve the above objectives, the inventors provide an electromagnetic structure for a torque converter in a coaxial holographic storage system, comprising:

[0006] Metal frame, and

[0007] A focusing coil, which is made of a single copper wire wound in a counter-clockwise direction, is located in the middle of a metal frame, and has a thickness of less than 2 mm and a height of less than 8 mm.

[0008] The tracking coil consists of four coils, with two coils located on one side of the metal frame and the other two coils located on the other side. The winding directions of the tracking coils on the same side are opposite, with the two coils on one side wound inward and the two coils on the other side wound outward. The height of the tracking coil is less than 3 mm, the inner circle width is less than 3 mm, and the inner circle length is less than 8 mm.

[0009] Two permanent magnets are respectively disposed between the tracking coil and the focusing coil at both ends of the metal frame;

[0010] Two yokes, each in an inverted U-shape, are respectively positioned at both ends of a metal frame and fastened to the focusing coil, permanent magnet, and tracking coil at both ends of the metal frame.

[0011] In some embodiments, the distance between the focusing coil and the tracking coil and the permanent magnet, and the distance between the focusing coil and the yoke, is greater than 0.2 mm.

[0012] In some embodiments, all four tracking coils are wound from the same copper wire.

[0013] In some embodiments, one end of the permanent magnet is embedded in the yoke, and the other end is embedded in the metal frame.

[0014] Another technical solution is also provided: a torque converter in a coaxial holographic storage system, wherein the electromagnetic structure of the torque converter includes:

[0015] Metal frame, and

[0016] A focusing coil, which is made of a single copper wire wound in a counter-clockwise direction, is located in the middle of a metal frame, and has a thickness of less than 2 mm and a height of less than 8 mm.

[0017] The tracking coil consists of four coils, with two coils located on one side of the metal frame and the other two coils located on the other side. The winding directions of the tracking coils on the same side are opposite and even. The two tracking coils on one side are wound inward, and the two tracking coils on the other side are wound outward. The height of the tracking coil is less than 3mm, the inner circle width is less than 3mm, and the inner circle length is less than 8mm.

[0018] Two permanent magnets are respectively disposed between the tracking coil and the focusing coil at both ends of the metal frame;

[0019] Two yokes, each in an inverted U-shape, are respectively positioned at both ends of a metal frame and fastened to the focusing coil, permanent magnet, and tracking coil at both ends of the metal frame.

[0020] In some embodiments, the distance between the focusing coil and the tracking coil and the permanent magnet, and the distance between the focusing coil and the yoke, is greater than 0.2 mm.

[0021] In some embodiments, all four tracking coils are wound from the same copper wire.

[0022] In some embodiments, one end of the permanent magnet is embedded in the yoke, and the other end is embedded in the metal frame.

[0023] Unlike existing technologies, the above technical solution limits the thickness of the focusing coil to less than 2mm and the height to less than 8mm, and the height of the tracking coil to less than 3mm, the inner circle width to less than 3mm, and the inner circle length to less than 8mm. This ensures that the spatial magnetic field formed by the interaction of the tracking coil, the focusing coil, and the permanent magnet in the two yokes can generate a sufficiently strong electromagnetic force, while avoiding the problem of reduced torque servo tracking speed caused by excessively large focusing and tracking coils.

[0024] The above description of the utility model is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the description and drawings, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and drawings of this application. Attached Figure Description

[0025] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of this application and other related content, and should not be considered as limitations on this application.

[0026] In the accompanying drawings of the instruction manual:

[0027] Figure 1 A schematic diagram of the electromagnetic structure of the torquer in the coaxial holographic storage system described in a specific embodiment;

[0028] Figure 2 A schematic diagram illustrating the arrangement of permanent magnets in the torque device according to a specific embodiment;

[0029] Figure 3 A schematic diagram of the position distribution of the tracking coil of the torque device described in a specific embodiment;

[0030] Figure 4 A schematic diagram illustrating the positional distribution of the focusing coil of the torque device described in a specific embodiment;

[0031] Figure 5This is a schematic diagram of the torque device described in a specific embodiment on the plane formed by the tangential direction and the tracking direction.

[0032] The reference numerals used in the above figures are explained as follows:

[0033] 110. Metal frame,

[0034] 120. Focusing coil

[0035] 130. Tracking coil

[0036] 140. Permanent magnet,

[0037] 150. Yoke. Detailed Implementation

[0038] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended only as examples, not as limiting the scope of protection of this application.

[0039] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0040] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0041] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0042] In this application, 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 actual quantity, hierarchy or order between these entities or operations.

[0043] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0044] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0045] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0046] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0047] Please see Figure 1 This embodiment provides an electromagnetic structure for a torque converter in a coaxial holographic storage system, comprising:

[0048] Metal frame 110, and

[0049] A focusing coil 120 is made of a single copper wire wound in a counter-clockwise direction. The focusing coil 120 is located in the middle of the metal frame 110. The thickness of the focusing coil 120 is less than 2 mm and the height is less than 8 mm.

[0050] Tracking coil 130, there are four tracking coils 130, two tracking coils 130 are arranged on one side of the metal frame 110, and the other two tracking coils 130 are arranged on the other side of the metal frame. The winding directions of the tracking coils 130 on the same side are opposite, but the two tracking coils 130 on one side are wound inward and the two tracking coils 130 on the other side are wound outward. The height of the tracking coil 130 is less than 3mm, the inner circle width is less than 3mm, and the inner circle length is less than 8mm.

[0051] Permanent magnet 140, there are two permanent magnets, which are respectively disposed between the tracking coil 130 and the focusing coil 120 at both ends of the metal frame 110;

[0052] Two yokes 150 are provided. The yokes 150 are in the shape of an inverted U and are respectively set at both ends of the metal frame 110 and respectively fastened to the focusing coil 120, the permanent magnet 140 and the tracking coil 130 at both ends of the metal frame 110.

[0053] like Figure 2 The torque generator shown has the permanent magnets 140 positioned as follows: A, B, C, and D are the magnetization surfaces of the two magnets, respectively. According to the theory of medium magnetization and the molecular current theory, when the permanent magnets are uniformly magnetized, the surface magnetic charge only appears at the interface of the magnetic medium. The formula for its surface magnetic charge density is: σ m =B d -μ0H d Wherein, the free permeability is represented by μ0, and at the operating point of the permanent magnet 140, the magnetic induction and magnetic field strength are represented by B, respectively. d With H d express.

[0054] With the center of mass of the movable part of the torque converter as the origin, denoted as O(0,0,0), the tracking direction as the Y-axis and the focusing direction as the Z-axis, a spatial rectangular coordinate system XOYZ is established. The geometric centers of the permanent magnet 140, the tracking coil 130, and the focusing coil 120 are respectively denoted as O... m (x m ,y m ,z m ), O t (x t ,y t ,z t ) and O f (x f ,yf ,z f According to the equivalent magnetic charge method, P in plane B B (x B ,y B ,z B The magnetic flux density produced by the element magnetic charge at point P(x,y,z) at any point P(x,y,z) in space can be expressed by the following formula:

[0055]

[0056] in Because magnetic fields can be superimposed, the entire B-plane will generate a magnetic field distribution in space, as expressed by the following formula:

[0057]

[0058] Where b1 = y m -H m / 2, b2=y m +H m / 2, c1 = z m -W m / 2, c2=z m +W m / 2.

[0059] The total magnetic field generated by permanent magnet 140 can be represented by summing the magnetic induction intensity produced in space by all its surface magnetic charges, as shown in the formula:

[0060] Let the area be divided Surface differential dA B =dy B dz B The subscript B denotes the integral and differential over surface B, which can be replaced by A, C, and D, to obtain the following equation:

[0061]

[0062] Where, x A =x m -L m / 2-T m x B =x m -L m / 2,x C =x m +L m / 2,x D =x m +L m / 2+T m .

[0063] According to the Biot-Savart-Laplace law, a current element JdV with current density J has a distance of [missing information]. The magnetic field generated at any point in space can be expressed by the formula:

[0064] like Figure 3 The torque converter's tracking coils 130 are shown in the diagram. The four tracking coils 130, labeled 1, 2, 3, and 4, have a total of 4 × n positions. t The number of turns is d, and the diameter of the wire is d. t The current magnitude is I t If the tracking coil 130 is equivalent to a uniform and dense circuit, the equivalent current density can be expressed as J t =4I t / πd t 2 The equivalent thickness is T. t =πn t d t 2 / 4H t Each tracking coil 130 is positioned according to the current direction as follows: Figure 3 The right side is divided into four parts: A, B, C, and D. The current distribution in each part is uniform. Taking part A of coil 2 as an example, the magnetic field generated by any current element on it can be expressed by the formula:

[0065]

[0066] Based on this, the expression for the rest can be written:

[0067]

[0068] like Figure 4 The schematic diagram shown is of the focusing coil 120 of the torque generator, with a wire diameter of d. f , revolving together n f Turns, current is I f If it can be equivalently represented as a uniform and dense loop, then the equivalent current density can be written as J f =4I f / πd f 2 The equivalent thickness can be written as T. f =πn f d f 2 / 4H f Dividing the coil into four regions, A, B, C, and D, according to the current direction, with uniform current distribution in each region, similar to the principle of tracking coil 130, the spatial magnetic field distribution of focusing coil 120 can be obtained as follows:

[0069]

[0070] Given the superposition property of magnetic fields, the distribution of the above three magnetic fields at any point P(x,y,z) in space can be expressed by the following formula:

[0071]

[0072] The force on a current element in a coil within a magnetic field can be expressed by the following formula:

[0073]

[0074] in It is the current density vector of the current element. It is the spatial magnetic flux density vector of the current element.

[0075] Based on the aforementioned spatial magnetic field distribution of the focusing coil 120 and the tracking coil 130, the magnetic forces they experience can be expressed as follows: and This can be expressed by the formula:

[0076]

[0077] in Let i be the i-th current density vector of the focusing coil 120. Let i be the i-th current density vector of the tracking coil 130. is the spatial magnetic induction intensity vector. and All include equivalent force components in the x, y, and z directions.

[0078] Therefore, once the maximum current that the coil wire can withstand is determined, if the electromagnetic force on the focusing or tracking coil 130 is to be increased, it can be done by: 1. increasing the magnetic induction intensity of the permanent magnet 140; 2. increasing the volume of the coil passing through the magnetic field; and 3. bringing the coil as close to the magnet as possible. The reverse is also true.

[0079] However, due to material limitations, the magnetic induction intensity of the permanent magnet 140 cannot be increased indefinitely; due to the response speed requirements of the torque converter, the coil volume cannot be increased indefinitely, otherwise it will be too bulky and reduce its servo tracking speed; due to mechanical assembly precision issues, a certain gap must be left between the coil and the magnet, so the coil cannot get infinitely close to the magnet.

[0080] Therefore, by limiting the thickness of the focusing coil 120 to less than 2mm and the height to less than 8mm, and limiting the height of the tracking coil 130 to less than 3mm, the inner circle width to less than 3mm, and the inner circle length to less than 8mm, it is ensured that the spatial magnetic field formed by the interaction of the tracking coil 130, the focusing coil 120, and the permanent magnet 140 in the two yokes 150 can generate a sufficiently strong electromagnetic force. At the same time, it avoids the problem of the torque servo tracking speed being reduced due to the focusing coil 120 and the tracking coil 130 being too large, and also avoids the problem of the torque servo being unable to move normally due to the friction caused by the focusing coil and the tracking coil 130 being too large.

[0081] In some embodiments, the distance between the focusing coil 120 and the tracking coil 130 and the permanent magnet 140 and the distance between them and the yoke 150 is greater than 0.2 mm.

[0082] By setting the distance between the focusing coil 120 and the tracking coil 130 and the permanent magnet 140 and the yoke 150 to be greater than 0.2mm, the focusing coil 120 and the tracking coil 130 have a certain gap, so that the torque device is not limited by the mechanical assembly precision problem.

[0083] In some embodiments, all four tracking coils 130 are wound from the same copper wire. By using the same copper wire for all four tracking coils 130, it is ensured that the four tracking coils 130 generate magnetic fields of the same strength. In other embodiments, the four tracking coils 130 may be wound from four separate copper wires, or two tracking coils 130 on the same side may be wound from the same copper wire.

[0084] In some embodiments, one end of the permanent magnet 140 is embedded in the yoke 150, and the other end is embedded in the metal frame 110. By embedding the permanent magnet in the yoke 150 and the metal frame 110, the stability of the permanent magnet 140 is ensured, and the magnetic field generated by the permanent magnet 140 is more uniformly distributed.

[0085] like Figure 1 The torque generator shown includes four tracking coils 130, one focusing coil 120, two yokes 150, two permanent magnets 140, and a metal frame 110. The four tracking coils 130 are wound with a single copper wire, and the focusing coil 120 is wound with a separate copper wire. Figure 5 The diagram shows a torque generator on the plane formed by the tangential and tracking directions, where the focusing coil 120 is wound counter-clockwise. The two tracking coils 130 on the left are wound to the sides, and the two tracking coils 130 on the right are wound towards the center. The dots and crosses indicate whether the ends of the coils are perpendicular to the paper and facing outwards or inwards. The north poles of the two permanent magnets 140 on the left and right are placed facing each other. Figure 5Taking the left side of the plan view as an example, a magnetic field is formed between the left side of the yoke 150, the metal frame 110, and the permanent magnet 140. This magnetic field interacts with the magnetic force generated by the tracking coil 130, driving the tracking coil 130. A magnetic field is also formed between the right side of the yoke 150, the metal frame 110, and the permanent magnet 140. This magnetic field interacts with the magnetic force generated by the focusing coil 120, driving the focusing coil 120.

[0086] Another technical solution is also provided: an electromagnetic structure for a torque converter in a coaxial holographic storage system, such as... Figure 1 As shown, the electromagnetic structure of the torque generator includes:

[0087] Metal frame 110, and

[0088] A focusing coil 120 is made of a single copper wire wound in a counter-clockwise direction. The focusing coil 120 is located in the middle of the metal frame 110. The thickness of the focusing coil 120 is less than 2 mm and the height is less than 8 mm.

[0089] Tracking coil 130, there are four tracking coils 130, two tracking coils 130 are arranged on one side of the metal frame 110, and the other two tracking coils 130 are arranged on the other side of the metal frame. The winding directions of the tracking coils 130 on the same side are opposite, but the two tracking coils on one side are wound inward and the two tracking coils on the other side are wound outward. The height of the tracking coil 130 is less than 3mm, the inner circle width is less than 3mm, and the inner circle length is less than 8mm.

[0090] Permanent magnet 140, there are two permanent magnets, which are respectively disposed between the tracking coil 130 and the focusing coil 120 at both ends of the metal frame 110;

[0091] Two yokes 150 are provided. The yokes 150 are in the shape of an inverted U and are respectively set at both ends of the metal frame 110 and respectively fastened to the focusing coil 120, the permanent magnet 140 and the tracking coil 130 at both ends of the metal frame 110.

[0092] By limiting the thickness of the focusing coil 120 to less than 2 mm and the height to less than 8 mm, and limiting the height of the tracking coil 130 to less than 3 mm, the inner circle width to less than 3 mm, and the inner circle length to less than 8 mm, it is ensured that the spatial magnetic field formed by the interaction of the tracking coil 130, the focusing coil 120, and the permanent magnet 140 within the two yokes 150 can generate a sufficiently strong electromagnetic force. At the same time, it avoids the problem of reduced torque servo tracking speed caused by the focusing coil 120 and the tracking coil 130 being too large, and also avoids the problem of the torque servo being unable to move normally due to the friction caused by the focusing coil and the tracking coil 130 being too large.

[0093] In some embodiments, the distance between the focusing coil 120 and the tracking coil 130 and the permanent magnet 140 and the distance between them and the yoke 150 is greater than 0.2 mm.

[0094] By setting the distance between the focusing coil 120 and the tracking coil 130 and the permanent magnet 140 and the yoke 150 to be greater than 0.2mm, the focusing coil 120 and the tracking coil 130 have a certain gap, so that the torque device is not limited by the mechanical assembly precision problem.

[0095] In some embodiments, all four tracking coils 130 are wound from the same copper wire. By using the same copper wire for all four tracking coils 130, it is ensured that the four tracking coils 130 generate magnetic fields of the same strength. In other embodiments, the four tracking coils 130 may be wound from four separate copper wires, or two tracking coils 130 on the same side may be wound from the same copper wire.

[0096] In some embodiments, one end of the permanent magnet 140 is embedded in the yoke 150, and the other end is embedded in the metal frame 110. By embedding the permanent magnet in the yoke 150 and the metal frame 110, the stability of the permanent magnet 140 is ensured, and the magnetic field generated by the permanent magnet 140 is more uniformly distributed.

[0097] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. An electromagnetic structure for a torque converter in a coaxial holographic storage system, characterized in that, include: Metal frame, and A focusing coil, which is made of a single copper wire wound in a counter-clockwise direction, is located in the middle of a metal frame, and has a thickness of less than 2 mm and a height of less than 8 mm. The tracking coil consists of four coils, with two coils located on one side of the metal frame and the other two coils located on the other side. The winding directions of the tracking coils on the same side are opposite, with the two coils on one side wound inward and the two coils on the other side wound outward. The height of the tracking coil is less than 3 mm, the inner circle width is less than 3 mm, and the inner circle length is less than 8 mm. Two permanent magnets are respectively disposed between the tracking coil and the focusing coil at both ends of the metal frame; Two yokes, each in an inverted U-shape, are respectively positioned at both ends of a metal frame and fastened to the focusing coil, permanent magnet, and tracking coil at both ends of the metal frame.

2. The electromagnetic structure of the torque generator in the coaxial holographic storage system according to claim 1, characterized in that, The distance between the focusing coil and the tracking coil and the permanent magnet, and the distance between them and the yoke, is greater than 0.2 mm.

3. The electromagnetic structure of the torque generator in the coaxial holographic storage system according to claim 1, characterized in that, All four tracking coils are wound from the same copper wire.

4. The electromagnetic structure of the torque generator in the coaxial holographic storage system according to claim 1, characterized in that, One end of the permanent magnet is embedded in the yoke, and the other end is embedded in the metal frame.

5. A torque converter in a coaxial holographic storage system, characterized in that, The electromagnetic structure of the torque generator includes: Metal frame, and A focusing coil, which is made of a single copper wire wound in a counter-clockwise direction, is located in the middle of a metal frame, and has a thickness of less than 2 mm and a height of less than 8 mm. The tracking coil consists of four coils, with two coils located on one side of the metal frame and the other two coils located on the other side. The winding directions of the tracking coils on the same side are opposite, with the two coils on one side wound inward and the two coils on the other side wound outward. The height of the tracking coil is less than 3 mm, the inner circle width is less than 3 mm, and the inner circle length is less than 8 mm. Two permanent magnets are respectively disposed between the tracking coil and the focusing coil at both ends of the metal frame; Two yokes, each in an inverted U-shape, are respectively positioned at both ends of a metal frame and fastened to the focusing coil, permanent magnet, and tracking coil at both ends of the metal frame.

6. The torque device in the coaxial holographic storage system according to claim 5, characterized in that, The distance between the focusing coil and the tracking coil and the permanent magnet, and the distance between them and the yoke, is greater than 0.2 mm.

7. The torque device in the coaxial holographic storage system according to claim 5, characterized in that, All four tracking coils are wound from the same copper wire.

8. The torque device in the coaxial holographic storage system according to claim 5, characterized in that, One end of the permanent magnet is embedded in the yoke, and the other end is embedded in the metal frame.

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