Linear motor, lens barrel, and drive mechanism

Abstract

To provide a linear motor which can improve power efficiency while suppressing an increase in its external size, and to provide a lens barrel and a driving device.SOLUTION: A linear motor 230 is a VCM with a finite track, having a main magnet and two sub-magnets arranged in a Halbach application array. The two sub-magnets are arranged in a posture in which main magnetization directions are arranged to be tilted at approximately 90° from a side facing a back yoke 233b toward a main axis direction 230c with respect to the main magnetization direction of the main magnet, the main magnet is inclined to an inner side of the main magnet in a side in which a part or the whole of a face substantially adjacent to each of the two sub-magnets faces the back yoke 233b in the main magnetization direction of the main magnet, and the two sub-magnets are inclined to the inner sides of the two sub-magnets in a side in which a part or the whole of a face substantially adjacent to the main magnet faces a center yoke 233a in the main magnetization direction of the main magnet.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a linear motor, a lens barrel, and a driving device.

Background Art

[0002] A linear motor is mainly a motor that generates force in one direction, and has been put into practical use in various forms, from small micro devices such as MEMS to large driving mechanisms such as linear motor cars, and is utilized in a wide range of industrial fields. A linear motor is often used exclusively in applications that drive linearly, and is often used in combination with a linear guide mechanism.

[0003] [[ID=I5]] When classified by the principle of thrust generation, linear motors are classified into electromagnetic, pressure, friction, tension / extrusion types, etc. When classified by the driving range, they are classified into finite orbit, infinite orbit, etc. Also, a device that converts the thrust of a normal rotary motor into a linear thrust using mechanisms such as so-called rack and pinion or tires is sometimes classified as a linear motor (linear actuator) in a broad sense.

[0004] An example of the use of a linear motor is a focus mechanism in a lens barrel. In a lens barrel, in order to focus on a subject at a desired position during shooting, a focus operation is performed to move the focus lens group inside it back and forth on the optical axis orthogonal to the camera's imaging element. A linear motor is used for the movement adjustment of this focus lens group.

[0005] The requirements for a linear motor used in the focusing mechanism within a lens barrel include being small enough to fit inside the lens barrel, having sufficient maximum thrust output and resolution to move and adjust the focusing lens group, and being quiet. To meet these requirements, among the above classifications, finite-track electromagnetic linear motors, in particular, those that generate a Lorentz force using a combination of permanent magnets and coils, commonly known as voice coil motors (VCMs), are sometimes used.

[0006] Since VCMs do not generate thrust when unpowered, when using a VCM as the focusing mechanism within a lens barrel, it is necessary to keep the VCM powered at all times during use to maintain the focus lens group. Therefore, depending on the shooting scene, using a VCM may consume more power and drain the camera battery faster compared to using other friction-type ultrasonic motors in the focusing mechanism within the lens barrel. Thus, when using a VCM as the focusing mechanism within a lens barrel, improvements in the power efficiency of the VCM are required.

[0007] To improve the power efficiency of a finite-track VCM without increasing its external size, the key lies in increasing the efficiency of the magnetic circuit composed of permanent magnets and yokes (hereinafter simply referred to as magnetic efficiency), that is, the density of magnetic flux that contributes to the generation of thrust in the coil region of the VCM. Here, the magnetic circuit is an expression that likens the flow of magnetic flux in space to the flow of current in a circuit, and it indicates the direction and magnitude of the magnetic flux density at each point, but it also refers to the combination of permanent magnets and yokes themselves. Furthermore, in a typical finite-track VCM, it is known that the magnetic efficiency decreases relatively at both ends compared to the central part of the drive stroke, and suppressing this is also an important point in practical terms (see, for example, Patent Document 1).

[0008] As an example of a configuration to improve the magnetic efficiency of a finite-trajectory VCM, a configuration is known in which the stroke amount and other factors differ significantly from the configuration used in the focusing mechanism inside the lens barrel, but the magnets are arranged in a way that applies the concept of a Halbach arrangement (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-175244 [Patent Document 2] Japanese Patent Publication No. 2020-185503 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, the VCM in Patent Document 1 suffers from the problem that the overall power efficiency is poor because the magnetic efficiency in the central part of the drive stroke is reduced in order to equalize the magnetic efficiency in the drive stroke. In addition, the configuration in Patent Document 2 has the problem that the external size of the linear motor tends to be large because a separate fixing means is required to fix the magnet.

[0011] Therefore, the present invention aims to provide a linear motor, a lens barrel, and a drive device that can improve power efficiency while suppressing an increase in external size. [Means for solving the problem]

[0012] To solve the above problems, the linear motor according to claim 1 of the present invention is a linear motor that generates thrust in the direction of the main axis, comprising: a coil portion arranged with its winding core direction substantially aligned with the direction of the main axis; a center yoke portion arranged in the region inside the coil portion so as to extend in the direction of the main axis; a main magnet arranged in the region outside the coil portion at a position substantially opposite to the center yoke portion, with its main magnetization direction oriented perpendicular to the direction of the main axis; a back yoke portion arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke portion; and a main magnet substantially adjacent to the main magnet in the direction of the main axis, with respect to the main magnetization direction of the main magnet, on the side facing the back yoke portion. Furthermore, the device comprises two sub-magnets positioned in a orientation aligned in a direction tilted greater than 0° but within 90° in the direction of the main axis, and two side yoke portions, each positioned substantially adjacent to the center yoke portion and the back yoke portion at front to and behind the magnet group consisting of the main magnet and the two sub-magnets in the direction of the main axis, wherein part or all of the surfaces substantially adjacent to each of the two sub-magnets of the main magnet are inclined inward of the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet, and at least part of the surfaces substantially adjacent to the main magnet of the two sub-magnets are inclined inward of each of the two sub-magnets on the side facing the center yoke portion in the main magnetization direction of the main magnet. In the direction of the main axis, the length of the surface of each of the two sub-magnets substantially adjacent to the back yoke portion is shorter than the length of the surface of the main magnet substantially adjacent to the back yoke portion. [Effects of the Invention]

[0013] According to the present invention, it is possible to improve power efficiency while suppressing an increase in external size. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a camera system, which is a combination of a lens barrel according to Example 1 and a camera to which it is attached. [Figure 2]An exploded perspective view of a focus mechanism provided with a linear motor according to Example 1, which is inside a lens barrel. [Figure 3] A front view of the focus mechanism of FIG. 2 as viewed from the subject side on the optical axis. [Figure 4] A schematic diagram of a linear motor according to Example 1. [Figure 5] A schematic diagram of a linear motor according to a conventional example. [Figure 6] An explanatory diagram showing the principle of thrust generation in a linear motor. [Figure 7] A graph showing the thrust characteristics of a linear motor according to a conventional example and the thrust characteristics of a linear motor according to Example 1. [Figure 8] An explanatory diagram showing the forces acting on each magnet in the linear motor according to Example 1. [Figure 9] A schematic diagram showing a first example of the magnet arrangement in a linear motor according to Example 2. [Figure 10] A schematic diagram showing a second example of the magnet arrangement in a linear motor according to Example 2. [Figure 11] A schematic diagram showing a third example of the magnet arrangement in a linear motor according to Example 2. [Figure 12] A schematic diagram showing a fourth example of the magnet arrangement in a linear motor according to Example 2. [Figure 13] An explanatory diagram of a method for fixing a magnet group in a linear motor according to Example 2. [Figure 14] A schematic diagram showing an auxiliary fixing configuration of a magnet group of a linear motor according to Example 2. [Figure 15] A schematic diagram showing an example of fixing a magnet group of a linear motor according to Example 2 with an offset. [Figure 16] A schematic diagram showing the configuration of a linear motor according to Example 3.

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be illustrated and described.

[0016] (Example 1) Figure 1 is a schematic diagram of a camera system 10, which is a combination of a lens barrel 200 and a camera 100 to which it is mounted, according to this embodiment.

[0017] In Figure 1, the camera system 10 comprises a camera 100 and a lens barrel 200. Figure 1 also shows the optical axis 11 of the camera system 10, the image sensor 110 in the camera 100, the lens group 210 in the lens barrel 200 (details not shown), and the focusing lens group 211 in the lens group 210.

[0018] In the camera system 10, the imaging plane of the image sensor 110 is approximately perpendicular to the optical axis 11 of the camera system 10 near its center. Furthermore, when the lens barrel 200 is attached to the camera 100, the optical axis of the lens group 210 approximately coincides with the optical axis 11 of the camera system 10.

[0019] In this state, when the focusing lens group 211 moves back and forth in a direction parallel to the optical axis 11 (hereinafter simply referred to as the optical axis 11 direction), the focus of the lens group 210 on the subject (not shown) is brought to approximately coincide with the imaging surface of the image sensor 110. As a result, the image of the subject is formed on the imaging surface of the image sensor 110, and a clear image can be captured. The operation of moving the focusing lens group 211 to adjust the focus in order to obtain such a clear image is generally called focusing.

[0020] In recent camera systems, not only manual focus, where the photographer repeatedly checks and manually inputs the focus, but also autofocus (AF), where the focus is automatically controlled electronically, is common. In camera system 10, as a mechanism for performing this AF, a focus mechanism is provided inside the lens barrel 200, which has a motor for moving the focus lens group 211 in the direction of the optical axis 11.

[0021] To enable photographers to comfortably focus and shoot using autofocus, the motor in the focusing mechanism needs to have sufficiently high thrust and resolution to move the focus lens group 211 precisely and quickly using electronic control. Furthermore, to avoid impacting the photographer's experience and video recording, the motor in the focusing mechanism needs to be quiet. In addition, to avoid unnecessarily increasing the size of the lens barrel 200, it is desirable that the motor in the focusing mechanism be as small as possible.

[0022] In addition to improving the performance of the motor in the focusing mechanism as described above, another method to improve AF performance is to make the driven components, the focusing lens group 211, smaller and lighter. However, the latter method imposes constraints on the optical design, so the demand for the former method remains high.

[0023] In this embodiment, the lens barrel 200 is equipped with a focusing mechanism that includes a linear motor to meet the above requirements. Next, the detailed configuration of this focusing mechanism will be described.

[0024] Figure 2 is an exploded perspective view of the focusing mechanism 220, which is located inside the lens barrel 200 and includes the linear motors 230 and 240 according to this embodiment.

[0025] In Figure 2, the focusing mechanism 220 includes a lens holder 221, a fixing cylinder 222, a cover part 223, linear motors 230 and 240, guide bars 224a and 224b, and guide parts groups 225a and 225b.

[0026] The lens holder 221 is a movable part of the focusing mechanism that holds the focusing lens group 211 so that it can move back and forth in the direction of the optical axis 11.

[0027] The fixed cylinder 222 and the cover part 223 are lens barrel components that make up the lens barrel 200 itself, and are the fixed parts of the focusing mechanism.

[0028] Linear motors 230 and 240 are each composed of a coil section 230a and 240a, which are relative driven parts, and a magnetic circuit section 230b and 240b, which are relative driving parts.

[0029] In this embodiment, a configuration is illustrated in which one focus lens group 211, one focus mechanism 220 that drives it, and two linear motors 230 and 240 provided on the focus mechanism 220 are arranged inside the lens barrel 200. However, the linear motor of the present invention can also be applied to configurations with two or more focus lens groups (so-called floating focus configurations) or configurations with one or three or more linear motors for each focus mechanism.

[0030] There are two main reasons why the focusing mechanism 220 in this embodiment is equipped with two linear motors 230 and 240. One is to obtain greater thrust by driving the linear motors 230 and 240 simultaneously. The other is to reduce the generation of unnecessary forces in other directions while the lens holder 221, which is a moving body, is moving in the direction of the optical axis 11, by distributing the point of application of force approximately symmetrically with respect to the center of gravity of the lens holder 221 that holds the focusing lens group 211.

[0031] The guide component groups 225a and 225b engage with their respective guide bars (224a and 224b) and roll or slide on the cylindrical surface of the guide bars (224a and 224b) in the direction of the cylindrical axis. These components include a bearing train and biasing members, not shown in detail.

[0032] In the focusing mechanism 220 of this embodiment, guide bars 224a and 224b are fixed to the fixing cylinder 222 and cover part 223 in a position substantially parallel to the optical axis 11 and spaced apart from each other. In addition, two groups of guide parts 225a and 225b are fixed to the lens holder 221 while engaged with the two guide bars 224a and 224b. This constitutes a linear guide mechanism that holds the lens holder 221 so that it can move in only one direction substantially parallel to the optical axis 11. Note that the details of the individual guide engagement parts are not essential to the present invention, and therefore detailed illustrations and descriptions are omitted in this invention.

[0033] Linear motors 230 and 240 are each composed of a combination of a coil section, a group of permanent magnets, and a group of yokes. In other words, linear motors 230 and 240 are finite-track, electromagnetic voice coil motors (VCMs) that generate and utilize the Lorentz force through a combination of permanent magnets and coils.

[0034] In the linear motors 230 and 240, the magnetic circuit sections 230b and 240b, which are relative driving parts, are formed by a combination of permanent magnet groups and yoke groups, and the coil sections 230a and 240a, which are relative driven parts, are arranged to move relative to these. In the focusing mechanism 220, the coil sections 230a and 240a, which are the main thrust-generating parts of the linear motors 230 and 240, are fixed to the lens holder 221, which is the moving body of the focusing mechanism 220, in a position where their relative movement direction aligns with the optical axis 11 direction. Furthermore, the magnetic circuit sections 230b and 240b are fixed to either or both of the fixing cylinder 222 or the cover part 223, which are the fixing parts of the focusing mechanism 220. As a result, in the focusing mechanism 220, the focusing lens group 211 is driven in the direction of the optical axis 11 by the linear motors 230 and 240.

[0035] Furthermore, the focusing mechanism 220 employs a so-called moving coil system, in which the magnetic circuit sections 230b and 240b of the linear motors 230 and 240 are fixed and the coil sections 230a and 240a are movable, but it is not limited to this. For example, the linear motors of the focusing mechanism 220 may employ the opposite moving magnet system.

[0036] Furthermore, the focusing mechanism 220 has various other components to perform its function. For example, the focusing mechanism 220 further includes a position detection mechanism (not shown) that detects the position of the lens holder 221, which corresponds to the moving body, and performs feedback control to move the focusing lens group 211 to the desired position. The focusing mechanism 220 also further includes coil power supply wiring (not shown) used to supply power to the coil sections 230a and 240a of the linear motors 230 and 240, and this coil power supply wiring supplies power to the moving coil sections 230a and 240a. However, since these components are not essential parts in this invention, detailed illustration and description are omitted.

[0037] Figure 3 is a front view of the focusing mechanism 220 as seen from the subject side on the optical axis 11.

[0038] As shown in Figures 1 and 3(a), the cross-sectional shape of the focusing mechanism 220 inside the lens barrel 200, which generally has a cylindrical shape, is also close to a circle. Furthermore, the central region is occupied by the focus lens group 211 and lens holder 221, which are the objects to be driven. Therefore, in the focusing mechanism 220, the linear motors 230, 240, linear guide mechanism, position detection mechanism (not shown), and coil power supply wiring (not shown), etc., must be arranged within a limited area inside and outside these radial directions.

[0039] The linear motors 230 and 240 in this embodiment have a shape that allows for efficient placement in the above-mentioned area. Specifically, the conventional VCM shown in Figure 3(c) has a shape in which two magnets positioned on either side of the central main axis face each other at an angle of approximately 180°, a so-called horizontally opposed shape. In contrast, as shown in Figure 3(b), the linear motors 230 and 240 have a shape in which the angle between the two magnets positioned on either side of the main axis is offset to one side, so as to conform to the circumferential shape of the focus mechanism 220, a so-called V-shape. This allows the linear motors 230 and 240 to be efficiently housed within the focus mechanism 220 without unnecessarily miniaturizing them and reducing efficiency.

[0040] However, the shapes of the linear motors 230 and 240 shown in Figure 3(b) are not essential to the present invention, and they may have the shape shown in Figure 3(c). In the following description, for the convenience of illustration, the case in which the linear motors 230 and 240 according to this embodiment have the horizontally opposed shape shown in Figure 3(c) will be illustrated and described in detail.

[0041] Linear motors 230 and 240 improve magnetic efficiency by having a magnetic circuit configuration consisting of a combination of permanent magnet groups and yoke groups. Their detailed configuration will be described below. In the following description, only one linear motor 230 will be illustrated and described as a representative example of this embodiment; however, the configuration of the other linear motor 240 is the same.

[0042] Figure 4 is a schematic diagram of the linear motor 230 according to this embodiment.

[0043] Figure 4(c) is a view of the linear motor 230 from the radially outer side of the focusing mechanism 220 (side cross-sectional view). Figure 4(a) is a view of the linear motor 230 shown in Figure 4(c) from above using the third-angle projection method (top view), and Figure 4(b) is a view of the linear motor 230 shown in Figure 4(c) from the left side using the third-angle projection method (front view).

[0044] Figure 5 is a schematic diagram (a three-view drawing similar to Figure 4) of a conventional linear motor 330, which is used as a comparison for the linear motor 230.

[0045] The conventional linear motor 330 has a similar configuration to the linear motor 230 of this embodiment, is size-compatible, and can be used interchangeably with the focus mechanism 220 of this embodiment. For the sake of convenience in the following explanation, the part numbers of the corresponding components between the linear motor 230 of this embodiment and the conventional linear motor 330 will have the same last two digits.

[0046] First, the configuration of a conventional linear motor 330 will be explained using Figure 5. Unless otherwise specified, this explanation also applies to the configuration of the linear motor 230 in this embodiment.

[0047] In Figure 5, the conventional linear motor 330 comprises a coil section 330a, main magnets 332a, 332d, center yoke 333a, back yokes 333b, 333c, and side yokes 333d, 333e.

[0048] The coil section 330a is the relative driven part of the linear motor 330, and the part of the linear motor 330 excluding the coil section 330a is the relative driving part of the linear motor 330, forming a magnetic circuit section mainly consisting of a magnet group and a yoke group.

[0049] The main magnets 332a and 332d are groups of permanent magnets in the magnetic circuit section, respectively. The main magnets 332a and 332d are magnetized and polarized into a north pole and a south pole, respectively. In Figure 5, the most important polarization among these symbols is indicated, and the direction from the south pole to the north pole in the figure is defined as the principal magnetization direction for each magnet.

[0050] The center yoke 333a, back yokes 333b and 333c, and side yokes 333d and 333e are yoke members (yoke groups) made of soft magnetic material or the like that constitute the yoke group in the magnetic circuit section. The main axis direction 330c indicates the direction of the main axis of the linear motor 330. The center yoke 333a is the yoke corresponding to the center yoke section of the yoke group of the linear motor 330. Furthermore, the back yokes 333b and 333c are yokes corresponding to the back yoke sections of the main magnets 332a and 332d, respectively, in the yoke group of the linear motor 330. Also, the side yokes 333d and 333e are yokes corresponding to the side yoke sections of the yoke group of the linear motor 330.

[0051] In the linear motor 330, the main axis direction 330c is the direction in which the main thrust is generated, and the coil section 330a is positioned so as to be able to move relative to the magnetic circuit section, which consists of a group of permanent magnets and a group of yokes, with the winding core direction substantially aligned with this direction.

[0052] The center yoke 333a serves as the main axis of the linear motor 330 and is positioned to extend in the direction of the main axis 330c within the region inside the coil section 330a. In this configuration, the coil section 330a and the center yoke 333a are fitted together with a clearance, allowing for relative movement without contact between them. In the linear motor 330, the magnetic circuit is formed by assembling other yoke groups and magnet groups to the center yoke 333a. Therefore, in the focusing mechanism 220, it is sufficient to fix the center yoke 333a in a position where its axial direction is approximately aligned with the optical axis 11.

[0053] The main magnets 332a and 332d are positioned in the region outside the coil section 330a, with their main magnetization direction perpendicular to the main axis direction 330c and approximately opposite the center yoke 333a. The magnetic pole surface approximately opposite the center yoke 333a can be either a north pole or a south pole, but the type of magnetic pole must be the same for both main magnets 332a and 332d. These magnets primarily play a role in forming a magnetic field that contributes to the generation of the Lorentz force.

[0054] The back yokes 333b and 333c are positioned so as to be approximately adjacent to the magnetization surface opposite to the magnetization surface on the side that is approximately opposite to the center yoke 333a in their main magnetization direction, relative to the main magnets 332a and 332d. The back yokes 333b and 333c play a role in increasing the magnetic flux density in the coil direction and improving magnetic efficiency by suppressing magnetic flux leakage in the opposite direction to the coil section 330a.

[0055] The back yokes 333b and 333c are each set to have a length in the direction of the main axis 330c that is longer than that of the main magnets 332a and 332d. Furthermore, both ends of the back yokes 333b and 333c in the direction of the main axis 330c are provided with interlocking joint shapes with protrusions and recesses that engage with the side yokes 333d and 333e, which will be described later.

[0056] The side yokes 333d and 333e each have fitting holes corresponding to the shafts of the mounting parts at both ends of the center yoke 333a, and are inserted into the center yoke 333a from both sides in the direction of the main axis 330c. They then engage with the back yokes 333b and 333c at a total of four points through a joint shape of interlocking grooves. In this state, the back yokes 333b and 333c and the side yokes 333d and 333e are all subjected to a force directed toward the center yoke 333a by the magnetic force of the main magnets 332a and 332d. Therefore, the engaging parts interlock tightly and the shape is stable, so the magnetic circuit section of the linear motor 330 can be constructed without the need for additional screws or other fasteners.

[0057] Next, the principle of thrust generation in the linear motor 330 will be explained using Figure 6.

[0058] Figure 6 is a side cross-sectional view showing the linear motor 330 and the direction of its magnetic field and Lorentz force.

[0059] In the magnetic field extending from the main magnets 332a and 332d (indicated by the arrows in Figure 6, with the sign omitted) toward the center yoke 333a (or vice versa), when a current flows circumferentially through the coil section 330a, a Lorentz force is generated in the direction indicated by arrow 633, which becomes the thrust. This thrust is proportional to the current flowing through the coil section 330a. The proportionality constant is a thrust constant proportional to the strength of the magnetic field in the region through which the current flows. Therefore, to increase the power efficiency of the linear motor 330, it is necessary to increase the magnetic field in the coil section 330a shown in Figure 6, i.e., the effective magnetic field strength, which corresponds to increasing the magnetic efficiency.

[0060] In contrast to the conventional linear motor 330 described above, the linear motor 230 of this embodiment has a group of magnets in which sub-magnets 232b, 232c, 232e, and 232f are added adjacent to the main magnets 232a and 232d in the direction of the main axis 230c. Furthermore, the main magnetization direction of each of the sub-magnets 232b, 232c, 232e, and 232f substantially coincides with the direction of the main axis 230c, and in particular, the magnetic poles of the faces adjacent to the main magnets 232a and 232d coincide with the magnetic poles of the face of the main magnet facing the center yoke 233a. Furthermore, the adjacent faces of the two sub-magnets corresponding to the main magnet in this embodiment are inclined inward from the main magnet on the back yoke 233b and 233c side with respect to the main magnetization direction of the main magnet. The effects of these will be explained next.

[0061] In the linear motor 230 of the present invention, the sub-magnets 232b, 232c, 232e, and 232f are each adjacent to one of the main magnets 232a and 232d, partially reproducing the Halbach arrangement of permanent magnets. In other words, the linear motor 230 of the present invention is characterized by a magnet arrangement that applies the concept of the Halbach arrangement (hereinafter referred to as the Halbach applied arrangement).

[0062] It is known that when the magnet arrangement is a Halbach arrangement, the magnetic field on the surface of the magnet arrangement (the surface opposite to the back surface when the back side is the back side) is stronger compared to other magnet arrangements. A simple explanation for this is that the sub-magnets promote the return of the magnetic flux from the front to the back surface of the main magnets, thereby reducing magnetic flux leakage to the surroundings, and the resulting magnetic flux appears as an additional amount on the front side. A more detailed explanation of the principle is omitted in this invention. By adopting a Halbach application arrangement that partially reproduces such a Halbach arrangement, the effective magnetic field strength of the linear motor 230 in this embodiment becomes stronger than the effective magnetic field strength of the conventional linear motor 330 shown in Figure 6, thus improving the thrust constant.

[0063] Figure 7 is a graph showing the thrust characteristics 730 of a conventional linear motor 330 and the thrust characteristics 720 of a linear motor 230 according to this embodiment. The vertical axis represents the thrust constant, and the horizontal axis represents the absolute values ​​of the positive and negative stroke amounts when the stroke center of the linear motors 230 and 330 is set to 0. In general, in a finite track VCM, the magnetic efficiency at the stroke ends is lower than that at the center, so the thrust constant at the stroke ends decreases, as shown in the thrust characteristics 730 of the conventional linear motor 330. In contrast, the thrust characteristics 720 of the linear motor 230 in this embodiment show a relatively higher thrust constant at the stroke ends. As a result, power efficiency is improved.

[0064] Improving power efficiency at the stroke ends in this way raises the minimum performance level of the linear motor and is therefore useful from a practical standpoint. In particular, in the case of the linear motor 230 used in the focusing mechanism of the camera system 10 as in this embodiment, the stroke ends are used for shooting subjects at an infinity equivalent distance and for shooting subjects at close range, respectively, so power efficiency is greatly improved in these shooting scenes. Examples of the former shooting scenes include those where the camera system is held in an upward-facing position for a long time, such as in astrophotography. Examples of the latter shooting scenes include those where the camera system is held in an overhead-facing position for a long time, such as in product photography. The power efficiency of the linear motor 230 in these shooting scenes is improved compared to conventional models, meaning that the power consumption of the camera system 10 is reduced, allowing the photographer to concentrate on shooting without worrying as much about battery level or heat generation.

[0065] Here, if a general rectangular magnet is used in the same Halbach arrangement as in this embodiment, as shown in Figure 8(b), the magnets will repel each other, causing them to rotate as shown in Figure 8(c). To prevent such rotation, a separate means for fixing the magnets is required, which leads to an increase in the size of the magnetic circuit and thus the linear motor. The linear motor 230 of the present invention solves this problem by changing the shape of each magnet in the Halbach arrangement to the shape shown in Figure 8(a). The following describes this problem and its solution in detail.

[0066] Figure 8 is a schematic diagram illustrating the main forces acting on the magnet arrangement in the linear motor 230 of this embodiment and the magnet arrangement of a comparative example thereof.

[0067] The shapes of the main magnet 432a and sub-magnets 432b, 432c of the comparative example, shown in Figure 8(b), differ from the shapes of the main magnet 232a and sub-magnets 232b, 232c of this embodiment, shown in Figure 8(a). In both cases, the adjacent surfaces are not inclined and they have a general rectangular parallelepiped shape.

[0068] Furthermore, the comparative linear motor 430, like the conventional linear motor 330, has a similar configuration to the linear motor 230 of this embodiment and is size-compatible, with the same last two digits numbering corresponding to the parts. In addition, both the linear motor 230 of the present invention and the comparative linear motor 430 have a symmetrical structure with respect to the central plane including their main axis directions (230c, 430c), so for simplicity, only one side (the upper half of the side view) is shown here. Similarly, subsequent illustrations in this embodiment also show only one side of the symmetrical structure.

[0069] Figure 8(a) shows the linear motor 230 of this embodiment, and Figure 8(b) shows the linear motor 430 of a comparative example. Figure 8(c) shows the state of the linear motor 430 immediately after the state shown in Figure 8(b). In Figures 8(a) to (c), only the forces acting on each magnet that are relevant to the essential parts of the present invention are indicated by arrows.

[0070] In the Halbach application array, as shown in the rotational forces 843b1 and 843c1 in Figure 8(b), a resultant force (hereinafter simply referred to as rotational force for convenience of explanation) acting exclusively on the sub-magnets 432b and 432c is a rotational force, which is a force received from the main magnet 432a. That is, the like poles of the magnets repel each other, and the opposite poles attract each other, resulting in this rotational force. Therefore, in a magnet array like the one in Figure 8(b), if the sub-magnets 432b and 432c are not fixed by methods such as pressing or bonding, they will immediately rotate, pushing and spreading the side yokes 433d and 433e, as shown in Figure 8(c). As a result, they will eventually end up adjacent to the main magnet 432a with opposite poles facing each other. In other words, if the sub-magnets 432b and 432c are not fixed, the Halbach application arrangement will quickly collapse, further pushing out the side yokes 433d and 433e and destroying the structure of the magnetic circuit.

[0071] In contrast, when each magnet in the Halbach application array is shaped as shown in Figure 8(a), the rotational forces 823b1 and 823c1 on the sub-magnets 232b and 232c are reduced compared to the rotational forces 843b1 and 843c1 in Figure 8(b). Furthermore, attractive forces 823b2 and 823c2 are generated between the adjacent surfaces of the sub-magnets 232b and 232c and the main magnet 232a. This is because the adjacent surfaces 823ab and 823ac, which correspond to the sides of the main magnet 232a in the main magnetization direction, are shaped with the back yoke 233b side inclined inward with respect to the main magnetization direction, causing these surfaces to become slightly magnetic pole surfaces (N poles in the figure).

[0072] As a supplement, in an example of actual magnet creation, if the main magnet 232a is created in the shape shown in the figure before magnetization, and then magnetized in the main magnetization direction, the adjacent surfaces 823ab and 823ac will become some magnetic pole surfaces. Since the magnetic poles of the main magnet 232a on these surfaces are opposite to the magnetic poles on the opposing surfaces of the sub-magnets 232b and 232c, an attractive force is generated between the main magnet 232a and the sub-magnets 232b and 232c. The same applies to the sub-magnets 232b and 232c. A more intuitive explanation is that a portion of the attractive force of the main magnet 232a to the back yoke 233b is converted into an attractive force between it and the sub-magnets 232b and 232c. Furthermore, it can be said that a portion of the rotational force applied to the sub-magnets 432b and 432c in the comparative example is converted into an attractive force between it and the sub-magnets 232b and 232c of the present invention. Therefore, the rotational force acting on the sub-magnets 232b and 232c is weaker compared to the rotational force 843b1 and 843c1 in the comparative example (Figure 8(b)). In this state, although the rotational force 823b1 and 823c1 remains on the sub-magnets 232b and 232c, they are attracted to the main magnet 232a, and the shape of the main magnet 232a acts as a wedge-like retainer. For this reason, the sub-magnets 232b and 232c are stable and do not rotate even without separate fixing.

[0073] Here, the sub-magnets 232b and 232c are each subjected to a force moving away from the main magnet 232a, as indicated by arrows 823b3 and 823c3. This force is the reaction force that the sub-magnets 232b and 232c receive from the side yokes 233d and 233e as a reaction to the force that attracts them. This force acts to move the sub-magnets 232b and 232c away from the main magnet 232a, but on the other hand, the sub-magnets 232b and 232c are subjected to an attractive force 823b2 and 823c2 from the main magnet 232a, and this attractive force is set to be stronger. Therefore, the sub-magnets 232b and 232c will not move away from the main magnet 232a. To achieve this setting, a certain clearance should be provided between the sub-magnets 232b and 232c and the side yokes 233d and 233e.

[0074] Furthermore, at this time, the main magnet 232a is also attracted to the side yokes 233d and 233e on both sides via the sub-magnets 232b and 232c. However, the main magnet 232a is strongly attracted to the back yoke 233b, which is opposite in the main magnetization direction, and is held in place by a strong static friction force. Therefore, the main magnet 232a will not easily move to either the side yoke 233d or 233e along with one of the sub-magnets 232b or 232c. To address this, it would be preferable to provide an auxiliary fixing measure that holds the magnet group (main magnet 232a and sub-magnets 232b and 232c) on the back yoke 233b, but the configuration of such a measure will be explained in a later embodiment.

[0075] Furthermore, since the side yokes 233d and 233e are attracted by the sub-magnets 232b and 232c, the structure of the magnetic circuit section with the aforementioned joint structure becomes more stable. In other words, the stability of the magnetic circuit section is not compromised by the configuration of the present invention, and therefore, the present invention can be applied to the conventional magnetic circuit configuration shown in Figure 5 by essentially just replacing the magnet group without requiring any major modifications.

[0076] As described above, in the linear motor 230 of the present invention, by using a Halbach-applied arrangement of magnets, magnetic efficiency can be improved, and thus power efficiency can be improved. Furthermore, the shape of each magnet constituting the linear motor 230 of the present invention is not a general rectangular parallelepiped shape but a shape having an inclined surface. This eliminates the need to add separate fixing means to eliminate the repulsion between magnets in the Halbach-applied arrangement. Therefore, the power efficiency of the linear motor 230 can be improved without changing its external size compared to the conventional linear motor 330. Accordingly, the present invention can provide a linear motor 230 with higher power efficiency than conventional models while maintaining a size suitable for, for example, the focusing mechanism of a lens barrel 200.

[0077] (Example 2) While Example 1 showed a simplified embodiment of the linear motor of the present invention, here we will list and describe more practically preferable embodiments. In this embodiment as well, the same components as in the linear motor 230 of Example 1 will be denoted by the same reference numerals. Also, similar to the linear motor 230 of Example 1 shown in Figure 8(a), only one side of the symmetrical structure of the linear motor in this embodiment will be shown and described.

[0078] Figure 9 is a schematic diagram showing a first example of the magnet arrangement in the linear motor 230 according to this embodiment. In Embodiment 1, the main magnetization direction of the sub-magnets 232b and 232c was set to a direction in which the main magnetization direction of the main magnet 232a was tilted at an angle of approximately 90° in the direction of the main axis direction 230c from the side facing the back yoke 233b. However, the tilt angle of the main magnetization direction of the sub-magnets 232b and 232c is not limited to this, as long as it is greater than 0° and within 90°. Therefore, the tilt angle of the main magnetization direction of the sub-magnets 232b and 232c in this embodiment is set to a range greater than 0° and less than 90°, as shown in Figure 9.

[0079] Thus, by changing the tilt angle of the sub-magnets 232b and 232c, the role of the sub-magnets 232b and 232c (the role of promoting the recirculation of the magnetic flux of the main magnet 232a in the magnetic circuit) partially shifts to a role of creating a magnetic field that contributes to the generation of the Lorentz force. Even in this case, the arrangement of the magnets can be considered a Halbach application arrangement, and the benefit of improved power efficiency can be obtained. By adjusting these balances, the optimal magnet arrangement for each linear motor can be designed.

[0080] Figure 10 is a schematic diagram showing a second example of the magnet arrangement in the linear motor 230 according to this embodiment. In Embodiment 1, the surfaces of the main magnet 232a and the sub-magnets 232b and 232c that are substantially adjacent to each other were all inclined inward toward each magnet. However, as shown in Figure 10, only a portion of these surfaces may be inclined. That is, the main magnet 232a may retain the non-inclined surfaces 1023ab and 1023ac shown in Figure 10, while the sub-magnets 232b and 232c may retain the non-inclined surfaces 1023b and 1023c. In the example in Figure 10, the main magnet 232a and the sub-magnets 232b and 232c are configured to retain non-inclined surfaces, but it is also possible to have a configuration where only one of the main magnet 232a or the sub-magnets 232b and 232c retains a non-inclined surface.

[0081] While this configuration reduces the efficiency improvement somewhat due to the decrease in magnet volume, it eliminates the sharp edges of the magnets, thus preventing damage to the magnets and improving demagnetization resistance. Furthermore, it eliminates areas of undefined magnetization, reducing individual variations during mass production. These are some of the practical advantages that can be obtained.

[0082] Figure 11 is a schematic diagram showing a third example of the magnet arrangement in the linear motor 230 of this embodiment. Figure 12 is a schematic diagram showing a fourth example of the magnet arrangement in the linear motor 230 of this embodiment, with a top view at the top and a front view at the bottom.

[0083] As shown in Figure 11, the heights of the sub-magnets 232b and 232c in the height direction parallel to the main magnetization direction of the main magnet 232a (direction of the double arrow 1100) should be lower than those of the main magnet 232a.

[0084] This configuration increases the distance at which the magnetized surfaces of the same pole (in this embodiment, the magnetized surfaces of the south pole) are close together at their ends between the main magnet 232a and the sub-magnets 232b and 232c. As a result, the rotational force corresponding to the repulsive force between the main magnet 232a and the sub-magnets 232b and 232c can be further reduced, and the magnets can be made more stable. In addition, the strength of the demagnetizing field acting between nearly adjacent magnets can be reduced, thereby further improving the demagnetization resistance.

[0085] Furthermore, Figure 12 shows a schematic diagram of the linear motor 230, specifically a combination of one magnet group and the back yoke 233b, with the main magnet 232a viewed from the center yoke 233a. As shown in Figure 12, the width of the sub-magnets 232b and 232c in the width direction (direction of the double arrow 1200) perpendicular to the two directions of the main axis direction 230c and the main magnetization direction of the main magnet 232a should be smaller than that of the main magnet 232a.

[0086] With this configuration, the sub-magnets 232b and 232c receive a convergent attractive force in the width direction, which holds them in the center due to the main magnet 232a, thus making the magnets more stable.

[0087] As mentioned above, in the linear motor 230 of the present invention, the magnet group in the magnetic circuit is stable because it attracts each other even in a Halbach applied arrangement, so it is possible to eliminate the need for fixing means for the magnet group. However, in order to further improve the practical strength of the linear motor 230 of the present invention and prevent the magnet group from shifting due to impact, for example, the magnet group may be fixed by separately provided fixing means.

[0088] Figure 13 is a schematic diagram showing a method for fixing the magnet group in the linear motor 230 of this embodiment, with a top view at the top and a front view at the bottom. As a method for fixing the magnet group, for example, adhesive can be applied to the region reference numerals 1323ab and 1323ac shown in Figure 13, and the main magnet 232a, sub-magnets 232b and 232c, and back yoke 233b can be fixed to each other. In this case, as shown in Figures 11 and 12, if the height and width of the sub-magnets 232b and 232c are made lower (smaller) than the main magnet 232a, the adhesive can be applied in the resulting empty space. This allows the adhesive to be applied without protruding from the outer shape of the linear motor 230. Therefore, the magnet group can be fixed without increasing the outer size of the linear motor 230.

[0089] Figure 14 is a schematic diagram showing the auxiliary fixing configuration of the magnet group of the linear motor 230.

[0090] As shown in Figure 8 of Example 1, the magnet group of the linear motor 230 receives an attractive force from the side yokes 233d and 233e as a reaction to the force that attracts them. The main magnet 232a of the magnet group is held on the back yoke 233b by a strong static friction force. For this reason, it will not easily move due to this force even without any additional means, but the impact resistance of the linear motor 230 can be improved by providing an auxiliary fixing means to hold the magnet group more firmly.

[0091] For example, in Figure 14(a), compression support members 1423bd and 1423ce are provided between the side yokes 233d and 233e on both sides and the sub-magnets 232b and 232c as an auxiliary fixing configuration for the magnet group. The restoring force of these compression support members 1423bd and 1423ce supports the magnet group. Here, the side yokes 233d and 233e are components of the magnetic circuit section 230b of the linear motor 230 and are strongly magnetically attracted to the main magnet 232a. Therefore, the restoring force of these compression support members 1423bd and 1423ce does not cause the magnetic circuit section to break, and the stability of the magnetic circuit section is maintained.

[0092] Alternatively, as shown in Figure 14(b), compression support members 1423ab and 1423ac may be provided between the main magnet 232a and the sub-magnets 232b and 232c. In this case, the sub-magnets 232b and 232c are attracted to the side yokes 233d and 233e, respectively, and rotate to exert an attractive force on the main magnet 232a. However, because the compression support members 1423ab and 1423ac hold down the main magnet 232a, the main magnet 232a will not move, due to the static friction force it exerts on the back yoke 233b. Note that the fixing configurations shown in Figures 14(a) and 14(b) may be used in combination.

[0093] Figure 15 is a schematic diagram showing an example of offsetting and fixing the magnet group of the linear motor 230.

[0094] As shown in Figure 15(a), the magnet group of the linear motor 230 may be pre-positioned to one side of either the side yoke 233d or 233e, that is, fixed offset from the center in the main axis direction 230c. In this case as well, it is advisable to provide a compression support member in the gap between the magnet group of the linear motor 230 and the side yokes 233d and 233e. In Figure 15(a), a compression support member 1523ce is provided between the sub-magnet 232c and the side yoke 233e. In this case, since the magnet group is positioned towards the side yoke 233d, the magnet group can be supported with high rigidity by pre-attaching it to the side yoke 233d as shown in Figure 15(a). Alternatively, even if a small clearance remains due to assembly requirements, for example, this clearance can be filled with a thin compression support member with a high Young's modulus, making it easier to increase the rigidity when supporting the magnet group compared to when a clearance remains.

[0095] Here, as shown in Figure 2 of Example 1, the coil portion 230a of the linear motor 230 is generally supported and fixed at one end in the direction of the main axis to the moving body to which it is fixed (lens holder 221 in Example 1). Therefore, in the linear motor 230, the support portion for the moving body occupies a certain amount of space in the direction of the main axis 230c, which corresponds to the stroke direction. As a result, at one end of the stroke, there is often a relative unused area where the coil portion 230a is not located compared to the other end. Conversely, at the other end, there is a relative usable area where the coil portion 230a can be positioned further towards the end.

[0096] Therefore, when offsetting the arrangement of the magnet group, it is preferable to offset the magnet group to the side where the usable area of ​​the coil section 230a is generated (the other end of the coil section 230a in the main axis direction 230c). For example, as shown in Figure 15(b), suppose that the support part 1521 of the moving body is fixed to the right end of the coil section 230a in the drawing. In this case, the area 1521e at the right end of the stroke in the drawing becomes the unused area, and the area 1521d at the left end of the stroke in the drawing becomes the usable area. By adopting such an arrangement, the magnetic efficiency in the usable area 1521d can be optimized, thereby minimizing the efficiency reduction at the stroke end of the linear motor 230.

[0097] With the configuration described above, the present invention can provide a linear motor that is also practically preferable.

[0098] (Example 3) The configuration of the present invention is not limited to the forms shown in Examples 1 and 2, but can also be applied to other forms of linear motors. Here, we show an example in which the linear motor 530 of this embodiment is used in the lens barrel 200 instead of the linear motor 230.

[0099] For the sake of convenience in the following explanation, the part numbers of the corresponding components in the linear motor 530 of this embodiment and the linear motor 230 of Embodiment 1 will have the same last two digits.

[0100] Figure 16 is a schematic diagram showing the configuration of the linear motor 530 according to this embodiment.

[0101] Figure 16(c) is a view of the linear motor 530 from the radially outer side of the focus mechanism 220 (side cross-sectional view). Figure 16(a) is a view of the linear motor 530 shown in Figure 16(c) from above using the third-angle projection method (top view), and Figure 16(b) is a view of the linear motor 530 shown in Figure 16(c) from the left side using the third-angle projection method (front view).

[0102] In Figure 16, the linear motor 530 comprises a main axis direction 530c, a coil section 530a, a main magnet 532a, sub-magnets 532b and 532c, a U-shaped yoke (hereinafter referred to as the U-shaped yoke) 533a, and a side yoke 533d.

[0103] A key feature of the linear motor 530 in this embodiment is that the U-shaped yoke 533a is an integrated yoke that performs the same function as the yoke group (center yoke, back yoke, and side yoke) of the linear motor 230 in Embodiments 1 and 2. In Figure 16, the center yoke portion 533aa, back yoke portion 533ab, and side yoke portion 533ae, which perform the functions of these yoke groups, are roughly separated by dotted lines. Even with this configuration, as shown in Figure 16, by having the magnet group have the shape of the present invention and adopting a Halbach application arrangement, it is possible to increase the magnetic efficiency and thus the power efficiency of the linear motor 530.

[0104] Furthermore, the linear motor of the present invention is not limited to a configuration in which multiple main magnets (232a, 232d) face the center yoke 233a from multiple directions, as shown in Example 1. For example, as shown in Figure 16, a configuration may be taken in which only one main magnet 532a faces the center yoke portion 533aa from one direction. In addition, the coil portion of the linear motor of the present invention is not limited to a solenoid coil with a circular cross-section, such as the coil portion 230a shown in Example 1, but can also be a coil portion with a cross-sectional shape as illustrated in Figure 16, or a coil portion with various other cross-sectional shapes.

[0105] Furthermore, the U-shaped yoke 533a in this embodiment is constructed by laminating and joining a large number of thin electromagnetic steel sheets in the width direction perpendicular to the main axis direction 530c and the main magnetization direction of the main magnet 532a. Such a yoke configuration is widely used in the motor field and has the advantage of excellent electromagnetic high-frequency characteristics as well as a high degree of freedom in the shape of the laminated steel sheets in the surface direction. Therefore, taking advantage of this feature, for example as shown in Figure 16, the height of the main magnet 532a in the main magnetization direction may be reduced in the region near the center of the back yoke portion 533ab, rather than the stroke end in the main axis direction 530c. That is, as shown in Figure 16(c), the region near the center of the main magnet 532a in the main axis direction 530c may be partially embedded in the back yoke portion 533ab (hereinafter referred to as the embedded shape). Here, the shape of the main magnet in which the side surface of the main magnet according to the present invention is inclined inward matches well with such an embedded shape. In other words, as shown in Figure 16, the height change of the back yoke portion 533ab can be made into a continuous slope shape rather than a discontinuous step shape, making it easier to increase magnetic efficiency. Furthermore, by adopting this configuration, the height of the main magnet 532a of the linear motor 530 in the main magnetization direction can be reduced, allowing for further miniaturization.

[0106] Here, the effect of reducing the height of the central region of the back yoke portion 533ab is small because this region has a relatively low magnetic flux density within the magnetic circuit. Therefore, the linear motor 530 can be miniaturized without significant impact. Alternatively, taking the opposite approach, without increasing the size of the linear motor 530, the magnetic efficiency can be further improved by increasing the height of the back yoke portion 533ab in the region near the stroke end where the magnetic flux density is relatively high within the magnetic circuit.

[0107] As described above, the configuration of the linear motor according to the present invention can be modified and applied in various ways within the scope of its gist. For example, in the above embodiment, an example in which the linear motor according to the present invention is used as a motor for a focusing mechanism was described, but it may also be used as a motor for other lens drive mechanisms, such as the motor for the zoom mechanism of a lens barrel. Furthermore, the linear motor according to the present invention can be applied to any drive device that moves a driven object in a straight line, and the applicable devices are not limited to optical equipment such as lens barrels and imaging devices. [Explanation of Symbols]

[0108] 10 Camera Systems 11 Optical axis 100 Cameras 200 Lens barrel 211 Focusing lens group 220 Focusing mechanism 221 Lens Holder 222 Fixed tube 223 Lid parts 224a, 224b Guide Bars 225a, 225b Guide component group 230,240 Linear Motor 230a, 240a coil section 230b, 240b Magnetic Circuit Section 232a Main Magnet 232b, 232c Sub-magnets 233a Center York 233b Back Yoke 233d, 233e Side yoke

Claims

1. A linear motor that generates thrust in the direction of the main axis, A coil section arranged such that the winding direction substantially coincides with the direction of the main axis, In the region inside the coil portion, a center yoke portion is arranged to extend in the direction of the main axis, A main magnet is positioned in the region outside the coil portion, substantially opposite the center yoke portion, with its main magnetization direction perpendicular to the main axis direction, A back yoke portion is arranged with respect to the main magnet so as to be substantially adjacent to the magnetization surface opposite to the magnetization surface on the side that is substantially opposite to the center yoke portion in the main magnetization direction of the main magnet, Two sub-magnets are positioned substantially adjacent to the main magnet in the main axis direction, and their respective main magnetization directions are aligned with the main magnetization direction of the main magnet, tilted by more than 0° and no more than 90° toward the main axis direction from the side facing the back yoke portion, Each comprises two side yoke sections positioned substantially adjacent to the center yoke section and the back yoke section at front to and behind the magnet group consisting of the main magnet and the two sub-magnets in the direction of the main axis, The main magnet has a portion or all of the surfaces substantially adjacent to each of the two sub-magnets inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. A linear motor characterized in that, in the direction of the main axis, the length of the surface of each of the two sub-magnets substantially adjacent to the back yoke portion is shorter than the length of the surface of the main magnet substantially adjacent to the back yoke portion.

2. The linear motor according to Claim 1, characterized in that, in the direction of the main axis, the sum of the lengths of the surfaces substantially adjacent to the back yoke portion of each of the two sub-magnets is shorter than the length of the surface substantially adjacent to the back yoke portion of the main magnet.

3. A linear motor that generates thrust in the direction of the main axis, A coil section arranged such that the winding direction substantially coincides with the direction of the main axis, In the region inside the coil portion, a center yoke portion is arranged to extend in the direction of the main axis, A main magnet is positioned in the region outside the coil portion, substantially opposite the center yoke portion, with its main magnetization direction perpendicular to the main axis direction, A back yoke portion is arranged with respect to the main magnet so as to be substantially adjacent to the magnetization surface opposite to the magnetization surface on the side that is substantially opposite to the center yoke portion in the main magnetization direction of the main magnet, Two sub-magnets are positioned substantially adjacent to the main magnet in the main axis direction, and their respective main magnetization directions are aligned with the main magnetization direction of the main magnet, tilted by more than 0° and no more than 90° toward the main axis direction from the side facing the back yoke portion, Each comprises two side yoke sections positioned substantially adjacent to the center yoke section and the back yoke section at front to and behind the magnet group consisting of the main magnet and the two sub-magnets in the direction of the main axis, The main magnet has a portion or all of the surfaces substantially adjacent to each of the two sub-magnets inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, and the height of each of the two sub-magnets in the height direction corresponding to the main magnetization direction of the main magnet is lower than the height of the main magnet. A linear motor characterized in that, in the height direction, the two sub-magnets, the main magnet, and the back yoke portion are bonded and fixed to each other in the empty space resulting from the height difference between the two sub-magnets and the main magnet.

4. A linear motor that generates thrust in the direction of the main axis, A coil section arranged such that the winding direction substantially coincides with the direction of the main axis, In the region inside the coil portion, a center yoke portion is arranged to extend in the direction of the main axis, A main magnet is positioned in the region outside the coil portion, substantially opposite the center yoke portion, with its main magnetization direction perpendicular to the main axis direction, A back yoke portion is arranged with respect to the main magnet so as to be substantially adjacent to the magnetization surface opposite to the magnetization surface on the side that is substantially opposite to the center yoke portion in the main magnetization direction of the main magnet, Two sub-magnets are positioned substantially adjacent to the main magnet in the main axis direction, and their respective main magnetization directions are aligned with the main magnetization direction of the main magnet, tilted by more than 0° and no more than 90° toward the main axis direction from the side facing the back yoke portion, Each comprises two side yoke sections positioned substantially adjacent to the center yoke section and the back yoke section at front to and behind the magnet group consisting of the main magnet and the two sub-magnets in the direction of the main axis, The main magnet has a portion or all of the surfaces substantially adjacent to each of the two sub-magnets inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The linear motor is characterized in that at least a portion of the surfaces of the two sub-magnets substantially adjacent to the main magnet are inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, and the magnet group consisting of the main magnet and the two sub-magnets is offset from one of the two side yoke portions located in front of and behind the main axis.

5. The linear motor according to any one of claims 1 to 3, characterized in that the length of the back yoke portion in the direction of the main axis is longer than that of the main magnet.

6. The linear motor according to any one of claims 1 to 5, characterized in that the width of each of the two sub-magnets in the width direction perpendicular to the main axis direction and the main magnetization direction of the main magnet is smaller than the width of the main magnet.

7. The linear motor according to claim 6, characterized in that the two sub-magnets, the main magnet, and the back yoke portion are bonded and fixed to each other in the space remaining after the width of the two sub-magnets has become smaller than the width of the main magnet in the width direction.

8. The linear motor according to any one of claims 1 to 7, characterized in that it has a compression support member disposed between each of the two sub-magnets and the two side yoke portions.

9. A linear motor according to any one of claims 1 to 8, characterized in that it has a compression support member disposed between the main magnet and the two sub-magnets.

10. The movable body is the object to which the coil portion is fixed, The coil portion further comprises a support portion for the movable body fixed to one end of the coil portion in the main axis direction, The linear motor according to claim 4, characterized in that the magnet group is offset to the other end of the coil portion in the direction of the main axis.

11. The linear motor according to any one of claims 1 to 10, characterized in that the coil portion is arranged to be movable relative to the magnet group consisting of the main magnet and the two sub-magnets, and the yoke group consisting of the center yoke portion, the back yoke portion, and the side yoke portion.

12. The linear motor according to any one of claims 1 to 11, characterized in that, in the back yoke portion, the height in the height direction corresponding to the main magnetization direction of the main magnet is lower in the region near the center in the main axis direction than in the regions at both ends.

13. The linear motor according to any one of claims 1 to 12, characterized in that the main magnetization direction of each of the two sub-magnets is in a direction that is greater than 0° and less than 90°.

14. Lens and, A lens holder that holds the lens and is movable in the optical axis direction of the lens, A fixing part that movably supports the aforementioned lens holder, The system further comprises a linear motor that generates thrust in the optical axis direction to drive the lens holder, The linear motor comprises: a coil section arranged with its winding direction substantially aligned with the optical axis direction; a center yoke section arranged in the inner region of the coil section so as to extend in the optical axis direction; a main magnet arranged in the outer region of the coil section at a position substantially opposite to the center yoke section, with its principal magnetization direction perpendicular to the optical axis direction; a back yoke section arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke section; two sub-magnets arranged substantially adjacent to the main magnet in the optical axis direction, with their respective principal magnetization directions aligned in a direction greater than 0° and within 90° in the optical axis direction, from the side facing the back yoke section with respect to the principal magnetization direction of the main magnet; and two side yoke sections, each positioned in front of and behind the magnet group consisting of the main magnet and the two sub-magnets, substantially adjacent to the center yoke section and the back yoke section in the optical axis direction. The main magnet has at least a portion of the surfaces substantially adjacent to each of the two sub-magnets that are inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. One of the magnetic circuit section and the coil section, consisting of the main magnet, the two sub-magnets, the center yoke section, the back yoke section, and the side yoke section, is fixed to the fixing section, and the other of the magnetic circuit section and the coil section is fixed to the lens holder. A lens barrel characterized in that, in the optical axis direction, the length of the surface of each of the two sub-magnets substantially adjacent to the back yoke portion is shorter than the length of the surface of the main magnet substantially adjacent to the back yoke portion.

15. A lens and, A lens holder that holds the lens and is movable in the optical axis direction of the lens, A fixing part that movably supports the aforementioned lens holder, The system further comprises a linear motor that generates thrust in the optical axis direction to drive the lens holder, The linear motor comprises: a coil section arranged with its winding direction substantially aligned with the optical axis direction; a center yoke section arranged in the inner region of the coil section so as to extend in the optical axis direction; a main magnet arranged in the outer region of the coil section at a position substantially opposite to the center yoke section, with its principal magnetization direction perpendicular to the optical axis direction; a back yoke section arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke section; two sub-magnets arranged substantially adjacent to the main magnet in the optical axis direction, with their respective principal magnetization directions aligned in a direction greater than 0° and within 90° in the optical axis direction, from the side facing the back yoke section with respect to the principal magnetization direction of the main magnet; and two side yoke sections, each positioned in front of and behind the magnet group consisting of the main magnet and the two sub-magnets, substantially adjacent to the center yoke section and the back yoke section in the optical axis direction. The main magnet has at least a portion of the surfaces substantially adjacent to each of the two sub-magnets that are inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. One of the magnetic circuit section and the coil section, consisting of the main magnet, the two sub-magnets, the center yoke section, the back yoke section, and the side yoke section, is fixed to the fixing section, and the other of the magnetic circuit section and the coil section is fixed to the lens holder. In the height direction corresponding to the main magnetization direction of the main magnet, the heights of the two sub-magnets are lower than the height of the main magnet. A lens barrel characterized in that, in the aforementioned height direction, the two sub-magnets, the main magnet, and the back yoke portion are bonded and fixed to each other in the empty space resulting from the height difference between the two sub-magnets and the main magnet.

16. A lens and, A lens holder that holds the lens and is movable in the optical axis direction of the lens, A fixing part that movably supports the aforementioned lens holder, The system further comprises a linear motor that generates thrust in the optical axis direction to drive the lens holder, The linear motor comprises: a coil section arranged with its winding direction substantially aligned with the optical axis direction; a center yoke section arranged in the inner region of the coil section so as to extend in the optical axis direction; a main magnet arranged in the outer region of the coil section at a position substantially opposite to the center yoke section, with its principal magnetization direction perpendicular to the optical axis direction; a back yoke section arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke section; two sub-magnets arranged substantially adjacent to the main magnet in the optical axis direction, with their respective principal magnetization directions aligned in a direction greater than 0° and within 90° in the optical axis direction, from the side facing the back yoke section with respect to the principal magnetization direction of the main magnet; and two side yoke sections, each positioned in front of and behind the magnet group consisting of the main magnet and the two sub-magnets, substantially adjacent to the center yoke section and the back yoke section in the optical axis direction. The main magnet has at least a portion of the surfaces substantially adjacent to each of the two sub-magnets that are inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. One of the magnetic circuit section and the coil section, consisting of the main magnet, the two sub-magnets, the center yoke section, the back yoke section, and the side yoke section, is fixed to the fixing section, and the other of the magnetic circuit section and the coil section is fixed to the lens holder. A lens barrel characterized in that the magnet group consisting of the main magnet and the two sub-magnets is offset to one of the two side yoke portions located in front of and behind the optical axis.

17. Mobile and A fixing part that supports the movable body so that it can move in a predetermined direction, The system includes a linear motor that generates thrust in the predetermined direction to drive the moving body, The linear motor comprises: a coil section arranged with its winding core direction substantially aligned with the predetermined direction; a center yoke section arranged in the region inside the coil section so as to extend in the predetermined direction; a main magnet arranged in the region outside the coil section at a position substantially opposite to the center yoke section, with its main magnetization direction perpendicular to the predetermined direction; a back yoke section arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke section; two sub-magnets arranged substantially adjacent to the main magnet in the predetermined direction, with their respective main magnetization directions aligned in a direction greater than 0° and within 90° relative to the main magnetization direction of the main magnet, from the side facing the back yoke section toward the predetermined direction; and two side yoke sections, each positioned in front of and behind the magnet group consisting of the main magnet and the two sub-magnets, substantially adjacent to the center yoke section and the back yoke section in the predetermined direction. The main magnet has at least a portion of the surfaces substantially adjacent to each of the two sub-magnets that are inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. The main magnet, the two sub-magnets, the magnetic circuit section consisting of the center yoke section, the back yoke section, and the side yoke section, and one of the coil sections are fixed to the moving body, and the magnetic circuit section, the coil section, and the other are fixed to the fixed section. The drive device is characterized in that, in the predetermined direction, the length of the surface of each of the two sub-magnets substantially adjacent to the back yoke portion is shorter than the length of the surface of the main magnet substantially adjacent to the back yoke portion.

18. A mobile body and A fixing part that supports the movable body so that it can move in a predetermined direction, The system includes a linear motor that generates thrust in the predetermined direction to drive the moving body, The linear motor comprises: a coil section arranged with its winding core direction substantially aligned with the predetermined direction; a center yoke section arranged in the region inside the coil section so as to extend in the predetermined direction; a main magnet arranged in the region outside the coil section at a position substantially opposite to the center yoke section, with its main magnetization direction perpendicular to the predetermined direction; a back yoke section arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke section; two sub-magnets arranged substantially adjacent to the main magnet in the predetermined direction, with their respective main magnetization directions aligned in a direction greater than 0° and within 90° relative to the main magnetization direction of the main magnet, from the side facing the back yoke section toward the predetermined direction; and two side yoke sections, each positioned in front of and behind the magnet group consisting of the main magnet and the two sub-magnets, substantially adjacent to the center yoke section and the back yoke section in the predetermined direction. The main magnet has at least a portion of the surfaces substantially adjacent to each of the two sub-magnets that are inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. The main magnet, the two sub-magnets, the magnetic circuit section consisting of the center yoke section, the back yoke section, and the side yoke section, and one of the coil sections are fixed to the moving body, and the magnetic circuit section, the coil section, and the other are fixed to the fixed section. In the height direction corresponding to the main magnetization direction of the main magnet, the heights of the two sub-magnets are lower than the height of the main magnet. A drive device characterized in that, in the aforementioned height direction, the two sub-magnets, the main magnet, and the back yoke portion are bonded and fixed to each other in the empty space resulting from the height difference between the two sub-magnets and the main magnet.

19. A mobile body and A fixing part that supports the movable body so that it can move in a predetermined direction, The system includes a linear motor that generates thrust in the predetermined direction to drive the moving body, The linear motor comprises: a coil section arranged with its winding core direction substantially aligned with the predetermined direction; a center yoke section arranged in the region inside the coil section so as to extend in the predetermined direction; a main magnet arranged in the region outside the coil section at a position substantially opposite to the center yoke section, with its main magnetization direction perpendicular to the predetermined direction; a back yoke section arranged substantially adjacent to the main magnet so as to the magnetization surface opposite to the magnetization surface on the side of the main magnetization direction of the main magnet that substantially faces the center yoke section; two sub-magnets arranged substantially adjacent to the main magnet in the predetermined direction, with their respective main magnetization directions aligned in a direction greater than 0° and within 90° relative to the main magnetization direction of the main magnet, from the side facing the back yoke section toward the predetermined direction; and two side yoke sections, each positioned in front of and behind the magnet group consisting of the main magnet and the two sub-magnets, substantially adjacent to the center yoke section and the back yoke section in the predetermined direction. The main magnet has at least a portion of the surfaces substantially adjacent to each of the two sub-magnets that are inclined inward toward the main magnet on the side facing the back yoke portion in the main magnetization direction of the main magnet. The two sub-magnets are such that at least a portion of the surface substantially adjacent to the main magnet is inclined inward on the side facing the center yoke portion in the main magnetization direction of the main magnet, respectively. The main magnet, the two sub-magnets, the magnetic circuit section consisting of the center yoke section, the back yoke section, and the side yoke section, and one of the coil sections are fixed to the moving body, and the magnetic circuit section, the coil section, and the other are fixed to the fixed section. A drive device characterized in that the magnet group consisting of the main magnet and the two sub-magnets is offset to one of the two side yoke portions located in front of and behind in the predetermined direction.

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