Linear actuator, control method, and computer program

Abstract

We provide linear actuators that enable high-precision and highly efficient control. [Solution] A linear actuator comprises a multipole magnet formed by arranging a plurality of magnets in series, a coil body formed by bundling two or more coils that can move relative to each other in the direction of the arrangement of the multipole magnet, a sensor for detecting the position of the coil body with respect to the direction of the arrangement of the multipole magnet, and a current control means for controlling the current supplied to each coil based on the position of the coil body detected by the sensor, wherein the current control means controls the phase difference between the magnetic phase of the multipole magnet and the potential supplied to the coil body within a predetermined range.

Description

Technical Field

[0001] The present invention relates to a linear actuator, a control method, a computer program, and the like.

Background Art

[0002] An electromagnetic linear motor can have a non-contact linear configuration, and can achieve excellent characteristics in terms of quietness, durability, and fine feeding compared to other combinations of rotary motors and power conversion mechanisms and linear drive devices by friction, so it is used in various fields.

[0003] An electromagnetic linear motor can be classified into a synchronous type that uses the mutual acting force between magnetic poles and an induction type and a DC type that use the Lorentz force according to its driving principle. Among these, a DC linear motor (LDM) uses the Lorentz force generated substantially proportional to the current flowing through the coil as a direct driving force.

[0004] Therefore, it is generally possible to perform delicate force control, and it has characteristics suitable for precise positioning. For this reason, LDM is used in, for example, lens drive units in optical devices such as cameras, read head drive units of HDDs, industrial transport devices, and the like. LDM is also called a linear actuator due to its driving principle and applications.

[0005] A linear actuator can be further classified into a single-pole type and a multi-pole type according to the configuration of the field magnet part. This is the difference in whether the direction of the magnetic field acting on the same part of the coil in the stroke range of the linear actuator is constant or periodically changes. The latter multi-pole type is generally configured by arranging a plurality of magnets such as permanent magnets alternately.

[0006] Generally, unipolar linear actuators have advantages such as a simple configuration and, in principle, the absence of thrust ripple. On the other hand, they have the disadvantage of having a narrow stroke range in which they can generate large thrusts due to limitations such as the permeance of the magnets and the magnetization saturation of the yoke.

[0007] In contrast, multi-pole linear actuators tend to have a more complex configuration and are prone to thrust ripple. However, they have the advantage of being able to easily avoid the effects of magnet permeance and yoke magnetization saturation, and allowing for a wider stroke range. Therefore, these linear actuators are used selectively depending on the application.

[0008] One example of the use of linear actuators is in cameras, where these linear actuators are used as lens drive devices to implement functions such as autofocus and image stabilization.

[0009] In this case, the range of movement of the required lens group is limited, so conventionally, unipolar linear actuators were relatively often used. However, in recent years, there has been an increase in scenes where it is necessary to expand this range of movement, and multipolar linear actuators are also being used.

[0010] In cameras, disturbances such as changes in the camera's attitude by the user or the movement of components like the shutter occur during static positioning and operation of the linear actuator, negatively affecting static position accuracy and constant speed operation. Therefore, a robust control system that is resistant to disturbances is required even when driving multi-pole linear actuators.

[0011] Patent Document 1 discloses a multi-pole linear actuator in which magnets with like poles facing each other are surrounded by a coil, which is a movable part. Patent Document 2 discloses a configuration in which a multi-pole magnet with alternating S poles and N poles is combined with a movable coil body formed by arranging multiple unit coils. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Patent No. 7347548 [Patent Document 2] Patent No. 5515310 [Overview of the project] [Problems that the invention aims to solve]

[0013] However, the technology disclosed in Patent Document 1 only considers the magnitude of thrust during linear motion, and has the problem that it cannot efficiently maintain a static position with high precision or drive at a constant speed when disturbances occur.

[0014] Furthermore, the technology disclosed in Patent Document 2 allows for holding by applying current in the same direction to all coils, and can maintain a statically fixed position with high precision even when disturbances occur. However, it has the problem that it does not address the issue of constant-speed driving.

[0015] Therefore, one of the objectives of the present invention is to provide a linear actuator that enables high-precision and high-efficiency control. [Means for solving the problem]

[0016] To achieve the above objective, the linear actuator of the embodiment of the present invention is A multi-pole magnet, which consists of multiple magnets arranged in series, A coil body formed by bundling two or more coils that are relatively movable in the direction of the arrangement of the multipole magnets, A sensor for detecting the position of the multi-pole magnets of the coil body with respect to the arrangement direction, The system includes a current control means that controls the current supplied to each coil based on the position of the coil body detected by the sensor, The current control means is characterized by controlling the phase difference between the magnetic phase of the multipole magnet and the potential-entraining phase to the coil body within a predetermined range. [Effects of the Invention]

[0017] According to the present invention, a linear actuator capable of high-precision and high-efficiency control can be provided.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 12 is a perspective view showing an example of a camera system using an interchangeable lens including a linear actuator according to Embodiment 1 of the present invention. [Figure 2] FIG. 15 is an exploded perspective view of an interchangeable lens 20 including a linear actuator according to Embodiment 1. [Figure 3] (A) to (C) are schematic diagrams for explaining the configuration of a linear actuator 100 according to Embodiment 1. [Figure 4] FIG. 21 is a diagram for explaining the magnetic flux in the field magnet portion 120 of the linear actuator 100 according to Embodiment 1. [Figure 5] FIG. 24 is a diagram showing an example of a coil energization control method for the driving force of the linear actuator 100. [Figure 6] FIG. 27 is a diagram for explaining a coil energization control method for generating a holding force acting in a direction orthogonal to the optical axis 1a in the linear actuator 100 according to Embodiment 1. [Figure 7] FIG. 30 is a diagram for explaining the generation ratio of the driving force and the holding force generated by the energization phase of the coil in the control method of the linear actuator according to Embodiment 1. [Figure 8] FIG. 33 is a diagram for explaining an example of the time-series transition of the energization phase of the coil for position holding according to Embodiment 1.

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. In each figure, the same members or elements are denoted by the same reference numerals, and overlapping explanations are omitted or simplified.

[0020] <Embodiment 1> Figure 1 is a perspective view showing an example of a camera system 1 using an interchangeable lens equipped with a linear actuator according to Embodiment 1 of the present invention. In Figure 1, 10 represents the camera body and 20 represents the interchangeable lens.

[0021] Furthermore, 1a represents the optical axis of the camera system 1, 11 represents the image sensor, 12 represents the mount component on the camera body 10 side, 21 represents a part of the lens group, 21a represents a part of the focus lens group within the lens group 21, and 22 represents the mount component on the interchangeable lens 20 side.

[0022] Camera system 1 is a device for taking still images and videos, and mainly consists of a combination of a camera body 10 and an interchangeable lens 20. The camera body 10 is equipped with an image sensor 11 and the like, which has an imaging function, and the interchangeable lens 20 is equipped with a lens group 21 and the like, which has a light-gathering function.

[0023] The camera body 10 and the interchangeable lens 20 are securely joined and fixed together, while still being easy to attach and detach, by the engagement of their respective mount parts 12 and 22 using a bayonet or similar mechanism.

[0024] In this state, the image sensor 11 in the camera body 10 is positioned and oriented so that its shooting surface is approximately perpendicular to the optical axis 1a of the camera system 1 near its center. Furthermore, the lens group 21 in the interchangeable lens 20 is positioned and oriented so that its optical axis approximately coincides with the optical axis 1a of the camera system 1.

[0025] In camera system 1, a beam of light from the subject passes through the interchangeable lens 20, is collected via the lens group 21, and is formed as an image on the shooting surface of the image sensor 11 of the camera body 10.

[0026] In the image sensor 11, photoelectric conversion is performed, and information about the subject's light beam is converted into an electrical signal. Various processing is performed on this electrical signal within the camera body 10 to acquire still images and video image data, and this image data is stored in a non-volatile memory means within the camera body 10.

[0027] Here, the exposure time in the camera system 1 is controlled by opening and closing a shutter mechanism (not shown) provided in the camera body 10 or interchangeable lens 20, or by controlling the accumulation time in the image sensor 11.

[0028] This allows for the capture of images with appropriate brightness (exposure) for subjects of varying brightness levels. Similarly, exposure can also be adjusted by controlling the opening and closing of an aperture mechanism (not shown) in the interchangeable lens 20 and by controlling the sensitivity (ISO sensitivity, gain) of the photoelectric conversion in the image sensor 11.

[0029] The camera system 1 includes a focus lens group 21a with a focus adjustment function within the lens group 21 in order to photograph subjects at a wide range of distances, from very close to infinity.

[0030] The camera system 1 detects subject distance information using a subject distance detection means (not shown), and controls the movement of the focus lens group 21a in the direction of the optical axis 1a accordingly, thereby focusing on the subject and taking a picture.

[0031] Alternatively, the photographer can observe the subject through a viewfinder (not shown) to estimate the distance and, accordingly, move the optical axis 1a of the focus lens group 21a to focus on the subject and take a photograph.

[0032] In this embodiment, the linear actuator of this embodiment is provided within the interchangeable lens 20 and used as a driving means for controlling and operating the movement of the focus lens group 21a. Although this embodiment shows a camera system 1 consisting of a camera body 10 and an interchangeable lens 20, the linear actuator of this embodiment can also be applied to camera systems with other configurations.

[0033] For example, the linear actuator of this embodiment can be applied to cameras with an integrated body and lens, or to camera modules with a modular configuration for various information and communication devices. Furthermore, the linear actuator of this embodiment is not limited to autofocus functionality; for example, it can be used to drive a zoom lens group.

[0034] Figure 2 is an exploded perspective view of an interchangeable lens 20 equipped with a linear actuator according to Embodiment 1. In Figure 1, the external shape of the interchangeable lens 20 was shown as an external component (partially an internal cross-sectional view), but this is omitted in Figure 2 and subsequent figures, and only the internal functional components are illustrated and explained. Furthermore, an example of applying the linear actuator of this embodiment to a focus unit will be described.

[0035] In Figure 2, 100 and 200 are linear actuators of this embodiment. Each linear actuator is positioned so that its driving direction, the principal axis, is substantially aligned with the optical axis 1a direction, and comprises a coil, a group of permanent magnets, and a field section consisting of a yoke group, etc.

[0036] In Figure 2, 23 represents the focus unit case, 24 the lens holder, 25 the focus unit cover, and 26a and 26b the guide bars. The focus unit case 23 includes a position detection sensor (not shown) and a flexible printed circuit board for detecting the amount of movement of the focus lens group 21a.

[0037] The focus unit case 23 is directly or indirectly fixed to the mount component 22 and holds other unit components. Furthermore, the focus unit case 23 in this embodiment has an external shape that conforms to the inside of the cylindrical interchangeable lens 20, and thus has a cylindrical shape.

[0038] Furthermore, the focus unit case 23 is made of a material that offers an excellent balance of lightness and strength, such as fiber-reinforced resin or die-cast alloy. Two metal guide bars 26a and 26b are positioned in the focus unit case 23 at a predetermined distance from each other, both in a position approximately parallel to the optical axis 1a, and their respective ends are fitted together and fixed.

[0039] The fixing method in this case may be various methods such as press-fitting or bonding. The role of these guide bars 26a and 26b is to support the lens holder 24 that holds the focus lens group 21a so that it can move linearly (degree of freedom 1) along the direction of the optical axis 1a. In other words, they restrict translation in the direction perpendicular to the optical axis 1a, as well as unwanted movements such as pitch, yaw, and roll.

[0040] A focus unit cover 25 is attached to the focus unit case 23, and the other ends of the two guide bars 26a and 26b are fitted into and fixed to the focus unit cover 25. As a result, both guide bars 26a and 26b become double-supported guide bars, allowing the focus lens group 21a to be held rigidly and driven with high precision.

[0041] The lens holder 24 is a component that holds the focus lens group 21a and has two fitting parts that correspond to the two guide bars 26a and 26b.

[0042] These fitting parts are configured as sliding parts, sliding bearings, and rolling parts, and have minimal play in directions other than the linear motion relative to the guide bars 26a and 26b, and are configured to reduce resistance such as wear. The lens holder 24 is made of, for example, fiber-reinforced resin.

[0043] The lens holder 24 further includes coil holding sections 24a and 24b (24b is invisible). The coils of the linear actuators 100 and 200 are fixed to the coil holding sections 24a and 24b, for example, by adhesive. As a result, the lens holder 24 and the focus lens group 21a, which are driven parts, are driven by the output of the linear actuators 100 and 200.

[0044] The other field section of the linear actuators 100 and 200 is fixed to the focus unit case 23 by a locking member such as a screw. As a result, the linear actuators 100 and 200 transmit driving force from the fixed part including the focus unit case 23 and the mount part 22 to the lens holder 24, thereby driving the focus lens group 21a.

[0045] Thus, the linear actuators 100 and 200 of this embodiment employ a so-called moving coil system, where the field element is fixed and the coil is movable. This is because the coil is lighter than the field element in a linear actuator, making it easier to improve motion performance and power efficiency by reducing the mass of the moving part.

[0046] However, the moving magnet method has advantages such as easier reliability improvement because, for example, the wiring section is not a moving part, and the linear actuator of this embodiment can be applied to either method.

[0047] Furthermore, the linear actuators 100 and 200 in this embodiment are DC-type linear DC motors (LDMs), which are a type of electromagnetic linear motor. LDMs have the characteristic of being able to perform fine force control regardless of position or speed, and are suitable as driving means for various positioning applications, including the focusing mechanism in this embodiment.

[0048] The interchangeable lens 20 in this embodiment is equipped with two linear actuators for driving the focus lens group 21a. Since the coils of these actuators are fixed to the same lens holder 24, the outputs of the two linear actuators act in parallel.

[0049] This enables the driving of the high-mass focusing lens group 21a. Furthermore, reducing the constraints on the mass of the focusing lens group 21a leads to a relaxation of constraints on the optical configuration of the lens group 21, resulting in further improvements in performance such as higher precision and miniaturization of the interchangeable lens 20. For this reason, it is desirable to use two or more linear actuators in the interchangeable lenses of a camera system.

[0050] Next, we will describe the more detailed configurations of the linear actuators 100 and 200. However, in this embodiment, the linear actuators 100 and 200 have the same configuration, so only the linear actuator 100 will be illustrated and described as a representative example.

[0051] Figures 3(A) to 3(C) are schematic diagrams illustrating the configuration of the linear actuator 100 according to Embodiment 1. Figure 3(A) is an isometric projection view showing a portion of the actuator in cross-section, Figure 3(B) is a front view, and Figure 3(C) is a side cross-sectional view.

[0052] In Figure 3, 101 represents the main shaft, 111a and 111b represent the coils, and 120 represents the field section other than the coils. The field section 120 is composed of multiple permanent magnets, a yoke component made of magnetic material, and a skewer mainly made of non-magnetic material. As shown in Figure 3(A), this embodiment uses a multipole magnet in which multiple magnets are arranged in series.

[0053] 121a, 121b, and 122a represent thrust monopole magnetized ring magnets, 123aa and 123ab represent inner ring yokes corresponding to the inner yoke, 124a and 124b represent outer yokes, and 125 represents cover yokes. Additionally, 126a and 126b together represent skewer 126.

[0054] The thrust ring magnets 121a, 121b, and 122a are ring-shaped, unipolar permanent magnets (thrust unipolar magnetized ring magnets) magnetized in the direction of the central axis. Thrust ring magnets are manufactured, for example, by sintering and pressing a magnetic material in a magnetic field, or by removing a sintered base material.

[0055] The reasons for using this ring-shaped magnet include its ease of manufacture, ease of creating the coils to be combined with it, and ease of laying out these combinations. However, the linear actuator in this embodiment may use magnets of other shapes.

[0056] The various yoke components, 123aa, 123ab, 124a, 124b, and 125, play a crucial role in allowing a large amount of magnetic flux to pass through the field section of the linear actuator. Therefore, they are constructed from highly permeable pure iron-based steel or magnetic stainless steel.

[0057] The skewer 126 passes through the inner diameter openings corresponding to the internal opening regions of the thrust ring magnets 121a, 122a, 121b and the inner ring yokes 123aa, 123ab, and supports them. This makes it easier to bundle and fix them in the field section 120.

[0058] Of the skewer 126, 126a is the main shaft portion, and 126b is the end component at one end. The shaft 126a and the end component 126b are firmly fixed to each other, for example by press-fitting, to constitute the skewer 126.

[0059] In this case, in order to prevent a decrease in efficiency due to magnetic flux leakage on the inner diameter side of the thrust ring magnets 121a, 122a, and 121b, the shaft 126a that passes through them is made of a non-magnetic material, such as a copper-based or aluminum-based material. On the other hand, the end part 126b of the skewer 126 is made of a magnetic material.

[0060] Next, we will explain the details of each component. First, the main shaft 101 is shown such that the direction at each stroke position coincides with the direction of thrust, and for convenience, that position is taken as an arbitrary reference position.

[0061] For example, in the linear actuator 100 of this embodiment, the main shaft 101 is positioned on the central axis of the coil core position, or on the central axis of the thrust ring magnets 121a, 121b, 122a and inner ring yokes 123aa, 123ab which are coaxial with it.

[0062] Since the direction of thrust in the linear actuator 100 is basically constant and independent of the stroke position, the main shaft 101 is basically straight. Note that the configuration of this embodiment may also be applied to a linear actuator having a gently curved main shaft.

[0063] In the linear actuator 100 of this embodiment, the main shaft 101 is considered to be an ideal straight reference axis. The central axes of the winding cores of the coils 111a and 111b, the thrust ring magnets 121a, 121b, and 122a, and the inner ring yokes 123aa and 123ab are aligned with the main shaft 101.

[0064] For example, the flux linkage density distribution for generating the Lorentz force corresponding to the thrust in coils 111a and 111b is uniform, or distributed symmetrically around the winding core. In that case, the point of application of the thrust in each stroke of the linear actuator 100 theoretically coincides with the main shaft 101 taken at the winding core position of coil 111.

[0065] On the other hand, if the flux linkage density distribution is not uniform or symmetrical, it will deviate from the main shaft 101, but the amount of deviation is generally small. Therefore, when using the linear actuator 100, the layout can be designed by considering the main shaft 101 as the practical thrust application position.

[0066] Coils 111a and 111b are formed by winding an insulated conductor wire, such as enameled wire, around a core and hardening it with an adhesive, and are particularly air-core coils with an opening in the core.

[0067] Furthermore, coils 111a and 111b have a circular solenoid coil shape (cross-sectional shape relative to the winding core). Coils of this shape are easy to manufacture and have the advantage of being easy to improve the precision of the inner diameter shape. However, the linear actuator of this embodiment may also use coils with other winding shapes, such as rectangular or elliptical shapes.

[0068] In this embodiment, the linear actuator has a multi-pole magnetic field, and therefore the linear actuator 100 has two coils to ensure that stable thrust can be obtained at any stroke position.

[0069] The two coils move as a single integrated coil body, formed by bonding or other means. That is, the coil body in this embodiment has a configuration in which two or more coils, each capable of relative movement in the direction of the multi-pole magnet arrangement, are bundled together. Furthermore, control is performed to change the current supply ratio to each coil according to the magnetic field acting on each coil at each stroke position. Details of this control will be explained later.

[0070] The thrust ring magnets 121a, 121b, and 122a are arranged periodically in the direction of the main axis 101 within the internal opening regions of coils 111a and 111b. That is, the thrust ring magnets 121a and 122a are arranged in that order, followed by the thrust ring magnet 121b again.

[0071] In this embodiment, an example of a magnet array configuration for 1 and 1 / 4 periods has been shown, but the number of ring magnet groups can be increased to extend the period. Doing so will extend the stroke of the linear actuator.

[0072] The thrust ring magnets 121a, 121b, and 122a all have substantially the same external shape in the direction perpendicular to the main shaft 101. That is, their ring-shaped outer diameters are almost equal. Their outer diameters are slightly smaller than the inner diameters of the coils 111a and 111b, and they have a predetermined clearance from the coils 111a and 111b. Therefore, the coil bodies can move relative to each other in the direction of the ring magnet group's arrangement without contact.

[0073] Furthermore, the thrust ring magnets 121a, 121b and thrust ring magnet 122a each have principal magnetization directions that are opposite to each other in the direction of the principal axis 101. In addition, inner ring yokes 123aa and 123ab are added to the periodic arrangement of these ring magnet groups.

[0074] Furthermore, the thrust ring magnets 121a, 121b, 122a and the inner ring yokes 123aa, 123ab generate a flux linkage, which is the effective flux for generating the Lorentz force of coils 111a, 111b, corresponding to the thrust in the linear actuator 100. As described above, in this embodiment, the multipole magnet is constructed by directly or indirectly connecting multiple magnets, and also has a yoke arranged between the multiple magnets.

[0075] Next, we will explain the control for changing the current supply ratio to the coil using Figures 4 and 5. Figure 4 is a diagram illustrating the magnetic flux in the field section 120 of the linear actuator 100 according to this embodiment.

[0076] Figure 4 shows an enlarged portion of the side cross-sectional view of the field section 120, specifically showing the peripheral areas of the thrust ring magnet 121a, inner ring yoke 123aa, and thrust ring magnet 122a.

[0077] Furthermore, in Figure 4, the sign for the magnetic flux is represented by a leader line only for the magnetic flux in the upper half of the cross-section, but the same applies to the magnetic flux in the lower half (both are in the same region on the cylindrical surface). Also, for ease of illustration, the diagonal lines in the cross-section of the permanent magnet and inner yoke are omitted in Figure 4.

[0078] The flux linkage of coils 111a and 111b, which constitute the effective magnetic flux in the linear actuator 100, is in the direction of 411aa0. That is, it corresponds to the radial direction in a cylindrical coordinate system with the principal axis 101 as the reference.

[0079] In contrast, because the thrust ring magnets 121a and 122a are arranged so that their poles (N poles in the figure) face each other in the direction of the main axis 101, the magnetic flux between them becomes as shown in 425aa1 and 411aa1.

[0080] First, the flux emitted in the direction of the main shaft 101 repels each other and bends in a direction perpendicular to the main shaft 101, resulting in a larger component in the flux linkage direction 411aa0, which is then released to the outer coil portion.

[0081] Furthermore, the linear actuator 100 of this embodiment is equipped with a shaft 126a as a skewer that penetrates and bundles the ring magnet group and the inner ring yoke group, but it is preferable that this shaft be made of a non-magnetic material.

[0082] This is to minimize the ineffective magnetic flux emitted into the interior of the magnet, as shown in 428aa. In other words, this ineffective magnetic flux arises because the permanent magnet has a ring shape with an opening inside, and it can be reduced by decreasing the permeability of this part.

[0083] Furthermore, since reducing the opening shape is also effective, the inner diameters of the ring magnet group and inner ring yoke group, and the outer diameter of the skewer should be made as small as possible while still meeting the required strength of the skewer.

[0084] The linear actuator of this embodiment can be constructed using only the arrangement of the ring magnet group and inner ring yoke group described above. However, the linear actuator 100 of this embodiment is further equipped with outer yokes 124a and 124b and a cover yoke 125 to further improve efficiency.

[0085] These are configured to cover all or part of the ring magnet group and inner ring yoke group on the outside of the coils 111a and 111b in a direction perpendicular to the main shaft 101. Therefore, the outer yokes 124a and 124b and the cover yoke 125 appear to attract the magnetic fluxes 425aa1 and 411aa1 of the ring magnet group shown in Figure 4 in the direction of the linked flux 411aa0, thereby strengthening the component in this direction.

[0086] The outer yoke 124a is a flat plate component formed, for example, by press-punching a pure iron-based steel sheet. The outer yoke 124a includes screw holes for fixing to the focus unit case 23, a fitting hole for pivotally supporting the skewer 126 that bundles the ring magnet group and the inner ring yoke group, and a fitting portion that engages with the outer yoke 124b. The outer yoke 124a also serves as a fixed reference part in the linear actuator 100.

[0087] The outer yoke 124b is a component made by, for example, pressing and bending a pure iron-based steel sheet. The outer yoke 124b has a fitting portion that engages with the outer yoke 124a, and a fitting hole for pivotally supporting the skewer 126. The outer yoke 124b, together with the outer yoke 124a, stably supports the skewer 126 from both sides.

[0088] As explained earlier, the skewer 126 is used to improve convenience in the assembly and integration of linear actuators by passing through and bundling the ring magnet group and the inner yoke group.

[0089] In other words, the linear actuator can be assembled by sequentially passing the ring magnet group and the inner yoke group onto the skewer 126. Furthermore, since the skewer secures these parts, the process of fixing these parts by means of adhesive, for example, can be omitted.

[0090] Furthermore, when the linear actuator is incorporated into equipment, the skewer protrudes from the outer shape, and the end of the protruding skewer can be used as a boss for introduction or positioning, allowing for simple and highly accurate positioning.

[0091] Of the skewers 126, the shaft 126a is made of a non-magnetic material as described above, but the end component 126b at one end is made of a magnetic material. This is to ensure that the field section 120 of the linear actuator 100 is stably configured solely by its own magnetic force.

[0092] In this embodiment, since magnets with like poles are connected to a yoke, the stroke can be significantly extended by increasing the number of connections. Furthermore, thrust reduction at the end of the stroke is less likely to occur, and a long stroke can be achieved, making it suitable for lenses with long focus or zoom strokes.

[0093] Figure 5 shows an example of a coil energization control method for the thrust of a linear actuator 100. Figure 5 shows an example of energization distribution between two coils 111a and 111b to ensure that the linear actuator 100 has as constant a thrust efficiency as possible regardless of the stroke position.

[0094] The horizontal axis of the graph in Figure 5 represents the position on the field section 120 in the direction of the main axis 101, or the stroke position of the combination of the two coils 111a and 111b (hereinafter referred to as the coil body).

[0095] The center positions of the field section and the coil body in the schematic diagram of the linear actuator 100 shown at the bottom of Figure 5 are taken as the zero position as a reference. The vertical axis (left) in Figure 5 represents the average effective magnetic flux density with respect to the position on the field section, and represents the magnetic phase with respect to the position in the direction of the main axis 101 on the field section 120. The vertical axis (right) represents the current distribution to coils 111a and 111b with respect to the stroke position of the coil body.

[0096] In the linear actuator 100 of this embodiment, the stroke position of the coil body is detected by a position detection sensor for drive control (not shown). That is, this embodiment has a position detection sensor that detects the position of the coil body with respect to the arrangement direction of the multipole magnets.

[0097] Furthermore, it has a current control means that controls the current supplied to each coil based on the position of the coil body detected by the position detection sensor. That is, according to the sign and relative magnitude of the average effective magnetic flux density at the position of each coil, a current control circuit (current control means) (not shown) changes and controls the current distribution between each coil.

[0098] For example, when the stroke position of the coil body is at the zero position, the average effective magnetic flux densities in coils 111a and 111b are in opposite directions and approximately equal in magnitude (absolute value B0 [T] in Figure 5). Therefore, the current distribution between the coils is also made to have opposite signs and approximately equal in magnitude (absolute value P0 [%] in the figure).

[0099] On the other hand, for example, when the stroke position of the coil is at position A, the average effective magnetic flux density is at its maximum in coil 111a (absolute value Bmax[T] in the figure). Also, since the average effective magnetic flux density is almost zero in coil 111b, current is supplied only to coil 111a at a rate that is at its maximum, corresponding to the sign of the average effective magnetic flux density.

[0100] The ratio in this case is such that, for example, the power consumed by coil 111a is approximately equal to the sum of the power consumed by the two coils when the stroke position of the coil body is at the zero position (absolute value 100[%] in the figure).

[0101] Furthermore, when the stroke position of the coil body is at position B, the average effective magnetic flux densities in coils 111a and 111b are in the same direction and are approximately equal in magnitude (absolute value B0[T] in the figure). Therefore, the current distribution between the coils is also made to have the same sign and be approximately equal in magnitude. The ratio in this case is approximately equal to the ratio when the stroke position of the coil body is at the zero position (absolute value P0[%] in the figure).

[0102] Furthermore, the above example shows the current distribution between coils so that approximately the same thrust direction and magnitude can be obtained with approximately the same power at any stroke position, assuming that the winding directions of coils 111a and 111b are the same. In addition, the average effective magnetic flux density at each coil position takes into account the value at the center of gravity of the coil in the direction of the main axis 101.

[0103] As explained above, by applying current, the linear actuator can generate thrust in the direction along the optical axis 1a. Next, we will explain how to generate a holding force acting in the direction perpendicular to the optical axis 1a.

[0104] Figure 6 is a diagram illustrating a coil energization control method for generating a holding force acting in a direction perpendicular to the optical axis 1a in the linear actuator 100 according to Embodiment 1. Figure 6 shows an example of energization distribution between two coils 111a and 111b so that the linear actuator 100 can maintain a constant holding force regardless of the stroke position.

[0105] The graph in Figure 6, like the graph in Figure 5, shows the position on the horizontal axis of the graph in the direction of the main axis 101 on the field section 120, or the stroke position of the coil body, which is a combination of two coils 111a and 111b. The center position of the field section and the center position of the coil body in the schematic diagram of the linear actuator 100 shown at the bottom of the figure are used as the reference zero position.

[0106] In the linear actuator 100, the stroke position of the coil body is detected by a position detection sensor for drive control (not shown). Then, according to the sign and relative magnitude of the average effective magnetic flux density at the position of each coil, the current distribution between each coil is changed and controlled by the current control circuit. This makes it possible to generate a holding force acting in a direction perpendicular to the optical axis 1a without generating a thrust force in the direction along the optical axis 1a of the coil body.

[0107] For example, when the stroke position of the coil body is at the zero position, the average effective magnetic flux densities in coils 111a and 111b are in opposite directions and approximately equal in magnitude (absolute value B0 [T] in the figure). Therefore, the current distribution between the coils should be such that the signs are the same and the magnitudes are approximately equal (absolute value P0 [%] in the figure).

[0108] With this current distribution, the only effective Lorentz force component is the one that pulls the stroke to the zero position, i.e., the coercive force. On the other hand, for example, when the stroke position of the coil is at position A, the average effective magnetic flux density is at its maximum in coil 111b (absolute value Bmax[T] in the figure), while the average effective magnetic flux density is almost zero in coil 111a.

[0109] Therefore, current is supplied only to coil 111b at a maximum rate corresponding to the sign of the average effective magnetic flux density. The rate at this time is set to a value such that, for example, the power consumed by coil 111b is approximately equal to the sum of the power consumed by the two coils when the stroke position of the coil body is at the zero position (absolute value 100[%] in the figure).

[0110] Furthermore, when the stroke position of the coil body is at position B, the average effective magnetic flux densities in coils 111a and 111b are in opposite directions and approximately equal in magnitude (absolute value B0[T] in the figure). Therefore, the current distribution between the coils should be such that the signs are opposite and the magnitudes are approximately equal. The ratio in this case is approximately equal to the ratio when the stroke position of the coil body is at the zero position (absolute value P0[%] in the figure).

[0111] The above example shows the current distribution between coils so that holding force can be obtained with approximately the same power at any stroke position, assuming that the winding direction of coils 111a and 111b is the same. Furthermore, the average effective magnetic flux density at each coil position takes into account the value at the center of gravity of the coil in the direction of the main axis 101.

[0112] Figures 5 and 6 show that the linear actuator 100 of this embodiment controls the potential flow phase to coils 111a and 111b with respect to the magnetic phase of the field section (stroke position of the coil body). This demonstrates that the ratio of the thrust force in the direction along the optical axis 1a to the holding force in the direction perpendicular to the optical axis 1a can be controlled.

[0113] Figure 7 is a diagram illustrating the ratio of thrust force and holding force generated by the potential-entraining phase to the coils in the control method of a linear actuator according to Embodiment 1. Specifically, Figure 7 shows the ratio of thrust force and holding force generated by the potential-entraining phase to each coil with respect to the magnetic phase of the field section (stroke position of the coil body) in the linear actuator 100. The horizontal axis (X axis) represents the holding force ratio, and the vertical axis (Y axis) represents the thrust force ratio.

[0114] For example, point 721 in Figure 7 represents the angle θ with the X-axis and the vector length H. This point 721 indicates a state in which the energizing phase is delayed by θ and the amplitude is multiplied by H relative to the energizing phase (energy distribution in Figure 6, point 722 in Figure 7) relative to the magnetic phase where the coercivity ratio is 1 and the thrust ratio is 0, and the energizing phase is energized by H. When this energizing is performed, a coercivity ratio A and a thrust ratio B are generated in the moving part.

[0115] On the other hand, when coils 111a and 111b are energized with respect to the magnetic phase of the linear actuator 100 using the energization distribution and potential phase shown in Figure 6, the energization will be performed at the ratio indicated by point 722 in Figure 7. This is an energization with a propulsion ratio of 0 and a holding force ratio of 1, which does not generate thrust in the direction along the optical axis 1a, but generates holding force in the direction perpendicular to the optical axis 1a. However, this state is power inefficient.

[0116] On the other hand, when coils 111a and 111b are energized with respect to the magnetic phase of the linear actuator 100 using the energization distribution and potential-enhancing phase shown in Figure 5, the energization will occur as indicated by point 723 in Figure 7. This is an energization where the thrust ratio is 1 and the holding force ratio is 0.

[0117] In this case, if the current is applied to the coil body with the potential phase delayed by, for example, 90°, from the current application with a thrust ratio of 0 and a holding force ratio of 1 as shown in Figure 6, and thrust force is generated in the direction along the optical axis 1a, then no holding force is generated in the direction perpendicular to the optical axis 1a.

[0118] This embodiment is characterized by its ability to maintain the stroke position of the coil body in a power-efficient manner by controlling the potential phase between the two coils 111a and 111b with respect to the magnetic phase within the exemplary range 724 shown by the shaded area in Figure 7.

[0119] In other words, in the linear actuator of this embodiment, the current control circuit controls the phase difference between the magnetic phase of the multipole magnet and the potential-entraining phase to the coil body within a predetermined range. The exemplary range 724 is the range in Figure 7 in which the holding force ratio is less than 1 and below a certain value.

[0120] This controls the ratio between the thrust force, which is the force in the direction of the arrangement of the relative-movable coil bodies, and the holding force, which is the force perpendicular to the direction of arrangement. The energization control circuit (energy control means), not shown in this embodiment, incorporates a CPU as a computer. Furthermore, the system is configured so that each means of the linear actuator can be controlled by the computer by the CPU executing a computer program stored in memory as a storage medium.

[0121] By using such a range, the stroke position of the coil body can be maintained while reducing power consumption compared to conventional control. Specifically, the exemplary range 724 in this embodiment is the range where the holding force ratio is less than 1 and the thrust force ratio is 1.

[0122] Conventionally, in LDMs, in order to maintain the stroke position of the coil body, the stroke position was constantly sensed and the direction and magnitude of the thrust force in the driving direction were controlled according to the detected position. In the linear actuator 100 of this embodiment, this corresponds to energizing coils 111a and 111b with the current distribution shown in Figure 5, which is the energized phase at point 723 in Figure 7.

[0123] In other words, Figure 5 illustrates the current distribution between coils 111a and 111b so that approximately the same power and thrust of the same direction and magnitude can be obtained at any stroke position, when the winding direction of coils 111a and 111b are the same.

[0124] Therefore, conventionally, in practice, the stroke position is maintained by using the energization ratio shown in Figure 5, as well as the energization phase between coils to obtain thrust in the opposite direction along the optical axis 1a. However, when such control is implemented, there is a problem in that a lot of power is consumed because energization is always performed at a point on the circumference 720 shown in Figure 7.

[0125] On the other hand, since the linear actuator 100 of this embodiment can generate a holding force as shown in Figure 6, it is not necessary to control the thrust force in the driving direction as in the conventional method when it is desired to maintain the stroke position.

[0126] For example, coils 111a and 111b can be energized in the potential-passing phase on the X-axis within the example range 724, and since the energization is performed in a region inside the circumference 720, high-efficiency driving with reduced power consumption can be achieved. Alternatively, instead of energizing only one point on the X-axis within the example range 724, several points within the example range 724 may be energized in a time-series manner depending on the situation in which the linear actuator 100 is positioned.

[0127] Figure 8 is a diagram illustrating an example of the time-series transition of the potential-passing phase to the coil for position holding according to Embodiment 1, and shows an example of transitioning several points within the example range 724 in time series. That is, it assumes a case where it is desired to keep the moving part of the linear actuator 100 in a certain position.

[0128] First, power is supplied to point 821 in the potential phase. Point 821 has no thrusting force, only holding force. However, because point 821 has little holding force, although the power consumption is small, it may not be able to maintain the position of the moving part.

[0129] Therefore, the system transitions to the potential-passing phase at point 822 and uses thrust to maintain its position. However, when using thrust to some extent, as at point 822, the position can be maintained by appropriately controlling the direction of the thrust, so the power used for holding the position is wasted. Therefore, the system ultimately transitions to point 823 and maintains its position using only thrust.

[0130] By transitioning the potential-passing phase within the example range 724 over time, the position can be held with less power consumption and with higher efficiency than if the position were held using only point 723 in Figure 7.

[0131] Therefore, even if vibrations generated when a mechanical shutter mechanism or the like mounted on the camera body 10 is driven are transmitted to the linear actuator 100 through the mount parts 12 and 22, the predetermined stroke position can be maintained efficiently with low power consumption.

[0132] Furthermore, the example range 724 in Figures 7 and 8 is an example of a range for controlling the potential-carrying phase, and is not limited to the size or shape of the example range 724 shown in Figures 7 and 8, but is a predetermined range in which the ratio of thrust force to holding force can be arbitrarily changed.

[0133] Furthermore, this embodiment is also useful for constant-speed driving. In the driving method that drives the linear actuator 100 with the current distribution shown in Figure 5, the force generated in the linear actuator 100 is only the thrust force along the optical axis 1a.

[0134] Therefore, when driving at a constant speed, it is necessary to carefully control the magnitude and direction of the thrust force, and it is particularly difficult to maintain constant speed accuracy when driving at low speeds in an environment where the attitude of the linear actuator 100 changes moment by moment.

[0135] In contrast, this embodiment utilizes a holding force in a direction perpendicular to the optical axis 1a in addition to the thrust force, and allows for arbitrary changes in their ratio. Therefore, even in environments where the attitude of the linear actuator 100 fluctuates, the position fluctuates less, and constant-speed driving can be performed with higher precision. Furthermore, in order to generate both holding force and thrust force simultaneously, the example range 724 in Figure 7 is set to a range where the holding force ratio is below a certain value.

[0136] In the above embodiment, the permanent magnet was described as having a ring shape, but other shapes are also acceptable. Furthermore, the permanent magnets may not be single permanent magnets, but rather a combination of multiple permanent magnets.

[0137] Furthermore, the field section 120 is not limited to a configuration in which a ring magnet group and an inner ring yoke are arranged between them, but may be composed only of a magnet group. Also, the multi-pole field section may be configured, for example, in the shape of a flat plate. In that case, a small field section can be configured perpendicular to the optical axis 1a, but it is more preferable not to configure a yoke in the direction of the magnet arrangement, as this reduces the thrust ripple.

[0138] Furthermore, in this embodiment, a multi-pole magnet (group of ring magnets) is configured as the stator and a coil body as the movable element, but it is also possible to configure the multi-pole magnet (group of ring magnets) as the movable element and the coil body as the stator.

[0139] Furthermore, the ratio of thrust to holding force may be changed only at times when disturbances are expected to occur. This prevents a shortage of thrust when needed, which could prevent the target drive from being achieved.

[0140] Examples of times when disturbances are expected include the moment the mechanical shutter mechanism is activated, the moment the mechanical aperture mechanism is activated, and when the camera's orientation changes due to camera shake or other factors.

[0141] <Embodiment 2> Next, the linear actuator of Embodiment 2 will be described. In Embodiment 2, the camera system 1 is equipped with a handheld determination unit (determination means). The handheld determination unit is mounted on the camera body 10, for example, and determines whether the camera system 1 is being held by hand or fixed to a fixed object such as a tripod based on signals from acceleration sensors such as a gyro sensor on the camera body 10.

[0142] Furthermore, the determination means may be one that determines whether the shaking of the camera body or other electronic device exceeds a predetermined value. Alternatively, it may be one that determines whether the mechanical mechanism within the camera body or other electronic device is being driven.

[0143] If the handheld detection unit determines that camera system 1 is being held by hand and not fixed to a fixed object, or if it determines that there is significant shaking, it is possible that the change in posture may affect the constant speed drive, so the ratio control of thrust and holding force is implemented.

[0144] On the other hand, if the handheld detection unit determines that the camera system 1 is fixed to a fixed object or that there is a large amount of shaking, the ratio control of thrust and holding force is not performed, and the coils 111a and 111b are driven by supplying power with the current distribution shown at point 723 in Figure 7.

[0145] By controlling the ratio of thrust to holding force only when the camera's posture may fluctuate or when there is significant camera shake, it is possible to allocate power to holding force without unnecessarily reducing thrust, resulting in more efficient operation.

[0146] For example, the gyro sensor may be mounted on the camera body 10 or on the interchangeable lens 20. Furthermore, the signals used for handheld detection and shake detection may include at least one of the following: the gyro sensor mounted on the camera body 10, the gyro sensor mounted on the interchangeable lens 20, or shake detection from the image captured by the camera system 1.

[0147] Furthermore, the handheld detection unit only needs to determine if the camera's orientation is likely to change or if there is significant camera shake. For example, if the camera is mounted on a moving object such as a drone, the camera's orientation is likely to change, so it can be determined to be handheld.

[0148] Thus, in this embodiment, the handheld determination unit functions as a determination means for determining the state of disturbances to the coil body. Furthermore, when the determination means predicts or detects the occurrence of a disturbance, the energization control means controls the phase difference between the magnetic phase of the multipole magnet and the phase of potential supply to the coil body within a predetermined range.

[0149] Furthermore, if the occurrence of a disturbance is predicted or detected by the determination means, it is sufficient if it includes at least one of the following: when an electronic device such as a camera equipped with a multipole magnet and coil body is not fixed; when the vibration of the electronic device exceeds a predetermined level; or when the mechanical mechanism of the electronic device is being driven.

[0150] Furthermore, electronic equipment includes imaging devices such as cameras, and mechanical mechanisms include mechanical shutter mechanisms or mechanical aperture mechanisms. However, electronic equipment is not limited to imaging devices such as cameras; it may also include, for example, mobile devices equipped with linear actuators or machine tools.

[0151] Furthermore, if the camera's orientation may change or if the camera shake is significant, for example, the width in the X-axis direction within the example range 724 may be increased. Also, if the camera's orientation may change or if the camera shake is significant, the number of transition points when transitioning between multiple points within the example range 724 over time may be increased.

[0152] Previously, driving the shutter while the camera was stationary introduced a high-frequency shutter shock as a disturbance, potentially causing the camera to move from its target position. Furthermore, even when driving at a constant speed, user changes in posture could cause speed inconsistencies, a problem particularly with zoom cameras where posture changes during operation are frequent. Additionally, increasing power to suppress these adverse effects reduces power efficiency.

[0153] However, according to this embodiment, even in the presence of disturbances, it is possible to drive while maintaining a constant holding force, thereby achieving highly accurate and efficient position control and constant-speed driving while suppressing power consumption.

[0154] Although the present invention has been described in detail above based on its preferred embodiments, the present invention is not limited to the above embodiments, and various modifications and combinations of the above embodiments are possible in accordance with the spirit of the present invention, and these are not excluded from the scope of the present invention. Furthermore, some of the above embodiments may be combined as appropriate. The present invention includes the following combinations.

[0155] (Configuration 1) A linear actuator comprising: a multipole magnet in which a plurality of magnets are arranged in series; a coil body in which two or more coils that can move relative to each other in the direction of arrangement of the multipole magnet are bundled together; a sensor for detecting the position of the coil body with respect to the direction of arrangement of the multipole magnet; and a current supply control means for controlling the current supplied to each coil based on the position of the coil body detected by the sensor, wherein the current supply control means controls the phase difference between the magnetic phase of the multipole magnet and the potential supply phase to the coil body within a predetermined range.

[0156] (Configuration 2) The linear actuator according to Configuration 1, characterized in that the current control means controls the ratio of the thrust force, which is a force in the direction of arrangement of the relatively movable coil body, to the holding force, which is a force perpendicular to the direction of arrangement, by controlling the phase difference between the magnetic phase of the multipole magnet and the potential-applying phase to the coil body.

[0157] (Configuration 3) A linear actuator according to Configuration 1 or 2, comprising a determination means for determining the state of disturbance with respect to the coil body, wherein when the occurrence of the disturbance is predicted or detected by the determination means, the current control means controls the phase difference between the magnetic phase of the multipole magnet and the potential-supplying phase to the coil body within the predetermined range.

[0158] (Configuration 4) The linear actuator according to Configuration 3, characterized in that when the occurrence of the disturbance is predicted or detected by the determination means, at least one of the following conditions is met: the electronic device equipped with the multipole magnet and the coil body is not fixed; the vibration of the electronic device is greater than a predetermined value; or the mechanical mechanism of the electronic device is being driven.

[0159] (Configuration 5) The linear actuator according to Configuration 4, characterized in that the electronic equipment includes an imaging device and the mechanical mechanism includes a mechanical shutter mechanism or a mechanical aperture mechanism.

[0160] (Configuration 6) The linear actuator according to any one of Configurations 1 to 5, characterized in that the multipole magnet is composed of multiple magnets connected together.

[0161] (Configuration 7) The linear actuator according to any one of Configurations 1 to 6, characterized in that the multipole magnet has a yoke arranged between a plurality of magnets.

[0162] (Configuration 8) A linear actuator according to any one of Configurations 1 to 7, characterized in that the multipole magnet is used as the stator and the coil body is used as the movable element.

[0163] (Configuration 9) A linear actuator according to any one of Configurations 1 to 8, characterized in that the multipole magnet is used as a movable element and the coil body is used as a stator.

[0164] (Method) A control method for controlling a linear actuator comprising: a multipole magnet formed by arranging a plurality of magnets in series; a coil body formed by bundling two or more coils that can move relative to each other in the direction of arrangement of the multipole magnet; a sensor for detecting the position of the coil body with respect to the direction of arrangement of the multipole magnet; and a current supply control means for controlling the current supplied to each coil based on the position of the coil body detected by the sensor, characterized in that the phase difference between the magnetic phase of the multipole magnet and the potential supply phase to the coil body is controlled within a predetermined range.

[0165] (Program) A computer program for controlling each means of a linear actuator described in any one of configurations 1 to 8 by a computer. [Explanation of Symbols]

[0166] 1: Camera system (camera system) 1a: Optical axis 10: Camera body 11: Image sensor 20: Interchangeable lenses 21: Lens group 21a: Focusing lens group 100, 200: Linear actuator 101: Main shaft 111a, 111b: Coil 120: Field section 121a, 121b, 122a: Thrust monopole magnetized ring magnet 123aa, 123ab: Inner ring yoke 124: Outer Yoke 125: Cover yoke 126: Skewer

Claims

1. A multi-pole magnet, which consists of multiple magnets arranged in series, A coil body formed by bundling two or more coils that are relatively movable in the direction of the arrangement of the multipole magnets, A sensor for detecting the position of the multi-pole magnets of the coil body with respect to the arrangement direction, The system includes a current control means that controls the current supplied to each coil based on the position of the coil body detected by the sensor, The linear actuator is characterized in that the current control means controls the phase difference between the magnetic phase of the multipole magnet and the potential-entraining phase to the coil body within a predetermined range.

2. The linear actuator according to claim 1, characterized in that the current control means controls the phase difference between the magnetic phase of the multipole magnet and the potential-applying phase to the coil body, thereby controlling the ratio of the thrust force, which is a force in the direction of arrangement of the relatively movable coil body, and the holding force, which is a force perpendicular to the direction of arrangement.

3. The linear actuator according to claim 1, further comprising determination means for determining the state of disturbances with respect to the coil body, wherein when the occurrence of the disturbance is predicted or detected by the determination means, the energization control means controls the phase difference between the magnetic phase of the multipole magnet and the potential-supplying phase to the coil body within the predetermined range.

4. The linear actuator according to claim 3, characterized in that the determination means predicts or detects the occurrence of the disturbance if at least one of the following conditions is met: the electronic device equipped with the multipole magnet and the coil body is not fixed; the vibration of the electronic device exceeds a predetermined level; or the mechanical mechanism of the electronic device is being driven.

5. The linear actuator according to claim 4, characterized in that the electronic device includes an imaging device, and the mechanical mechanism includes a mechanical shutter mechanism or a mechanical aperture mechanism.

6. The linear actuator according to claim 1, characterized in that the multipole magnet is formed by connecting a plurality of magnets.

7. The linear actuator according to claim 1, characterized in that the multipole magnet has a yoke arranged between a plurality of magnets.

8. The linear actuator according to claim 1, characterized in that the multipole magnet is used as the stator and the coil body is used as the movable element.

9. The linear actuator according to claim 1, characterized in that the multipole magnet is used as a movable element and the coil body is used as a stator.

10. A multi-pole magnet, which consists of multiple magnets arranged in series, A coil body formed by bundling two or more coils that are relatively movable in the direction of the arrangement of the multipole magnets, A sensor for detecting the position of the multi-pole magnets of the coil body with respect to the arrangement direction, A control method for controlling a linear actuator comprising: energization control means for controlling the current supplied to each coil based on the position of the coil body detected by the sensor, A control method characterized by controlling the phase difference between the magnetic phase of the multipole magnet and the potential-passing phase to the coil body within a predetermined range.

11. A computer program for controlling each means of a linear actuator according to any one of claims 1 to 8 by computer.

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