Lens driving device

Abstract

[Problem] To provide a lens driving device that is compact and can suppress deteriorations in optical performance and video performance. [Solution] This lens driving device comprises: at least one lens; a lens barrel that holds the lens; and N (N is an integer greater than or equal to 2) linear motors each composed of a first coil and a second coil that generate driving force in a direction parallel to the optical axis of the lens and a magnet assembly that form a Halbach array, in the lens barrel. At least one of the first coil and the second coil is provided with a bent part. The linear motors are disposed at intervals of 360 / N degrees along a circumferential direction around the optical axis of the lens.

Description

Lens drive unit

[0001] The present invention relates to a lens driving device that drives a lens with a linear motor.

[0002] Patent Document 1 discloses a linear motor that is composed of multiple magnets and multiple coils and drives a lens barrel that holds an optical system for changing the focal length and adjusting the focus of an interchangeable lens for a camera.

[0003] Furthermore, Patent Document 2 discloses a linear motor that is driven by arranging Halbach array magnet assemblies on both sides of a plurality of coils.

[0004] International Publication No. WO 2019 / 234980 International Publication No. WO 2017 / 169908

[0005] In order to drive a lens barrel with a large mass using the linear motor of Patent Document 1, it is necessary to make the magnets and yokes larger, which may result in an increase in the size of the interchangeable lens.

[0006] Furthermore, when driving a lens barrel using the linear motor of Patent Document 2, a method is conceivable in which the lens barrel holds a coil and magnet assemblies are arranged on both sides. However, this method results in an increase in the radial size of the interchangeable lens. Here, as shown in FIG. 14( a), a case is described in which two-phase coils 1010 and 1011 are fixed to the lens barrel 1003 and a Halbach-array magnet assembly 1012 is arranged on one side. In this case, as shown in FIG. 14( b), a Lorentz force is generated in a direction perpendicular to the optical axis O (in the direction of the arrow) due to the magnetic flux in the driving direction created by the sub-magnets 1012s of the magnet assembly 1012 and the current flowing through the coils 1010 and 1011 (in the direction of the page). As a result, a moment acts on the lens barrel 1003, causing the lens barrel 1003 to tilt, which may degrade optical performance. Furthermore, when using such a linear motor, the amplitude of the current flowing through the coils 1010 and 1011 periodically increases and decreases, and the magnitude of the Lorentz force also periodically changes. As a result, the lens barrel 1003 may vibrate, generating noise and degrading video performance.

[0007] An object of the present invention is to provide a lens driving device that is small and capable of suppressing deterioration of optical performance and video performance.

[0008] A lens driving device according to one aspect of the present invention comprises at least one lens, a lens barrel that holds the lens, and N (N is an integer of 2 or more) linear motors, each of which is composed of a first coil and a second coil that generate a driving force in the lens barrel in a direction parallel to the optical axis of the lens, and a magnet assembly that forms a Halbach array, wherein at least one of the first coil and the second coil has a bent portion, and the linear motors are arranged at intervals of 360 / N degrees along a circumferential direction centered on the optical axis of the lens.

[0009] According to the present invention, it is possible to provide a small lens driving device that can suppress deterioration of optical performance and video performance.

[0010] 1 is a schematic diagram of an imaging device equipped with an interchangeable lens according to an embodiment of the present invention. FIG. 1 is an exploded perspective view of a focus unit according to Example 1. FIG. 2 is an X-Z cross-sectional view of the focus unit according to Example 1. FIG. 3 is an X-Y cross-sectional view of the focus unit according to Example 1. FIG. 4 is an explanatory diagram of an A-phase coil according to Example 1. FIG. 5 is a perspective view of a lens barrel and peripheral components according to Example 1. FIG. 6 is a side view of a magnet assembly and a magnet holding plate according to Example 1. FIG. 7 is an X-Y cross-sectional view of a linear motor according to Example 1. FIG. 8 is a diagram showing temporal changes in current flowing through the A-phase coil and the B-phase coil according to Example 1. FIG. 9 is an X-Y cross-sectional view showing main components of the focus unit according to Example 1. FIG. 10 is a perspective view showing only some components of the focus unit according to Example 2. FIG. 11 is a front view of the focus unit according to Example 2 as viewed from the negative X-axis direction. FIG. 12 is a perspective view of the A-phase coil according to Example 2. FIG. 13 is a diagram showing a case where a configuration of a conventional example is applied to a lens driving device.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, identical components are designated by the same reference numerals, and redundant descriptions will be omitted. [General Configuration of Interchangeable Lens] FIG. 1 is a schematic diagram of an imaging device equipped with an interchangeable lens 100 according to an embodiment of the present invention. The interchangeable lens 100 is mechanically and electrically connected to a camera body 200 via a mount (not shown). The interchangeable lens 100 includes a focus unit 1 for adjusting focus, a drive circuit 300 for driving a linear motor 500 (described below), and a lens control unit 400 for controlling the drive of the linear motor 500 and other components within the interchangeable lens 100. The interchangeable lens 100 also includes a zoom optical system, an aperture device for adjusting light intensity, and operating members, but these will not be described for simplicity. In this embodiment, a focus unit 1 for adjusting focus will be described as an example of a lens drive device, but it may also be a unit for driving a lens that changes the focal length.

[0012] [Configuration of Focus Unit] Fig. 2 is an exploded perspective view of the focus unit 1. In this embodiment, as shown in Fig. 2, the optical axis O is the X-axis, and axes perpendicular to the X-axis are the Y-axis and Z-axis. Fig. 3 is a cross-sectional view of the focus unit 1 cut along the X-Z plane, viewed from the negative Y-axis direction. Fig. 4 is a cross-sectional view of the focus unit 1 cut along the X-Y plane, viewed from the positive Z-axis direction.

[0013] The focus lens 2 is an optical system made of a single piece of glass for adjusting focus. However, the focus lens 2 may be made of multiple pieces of glass. The focus lens 2 may also be made of a plastic lens made of resin.

[0014] The lens barrel 3 is made of a resin material or a metal material. The focus lens 2 is adhesively fixed to the lens barrel 3. The lens barrel 3 is formed with round holes 3a and 3b through which the main guide shaft 8 is inserted, and an elongated hole 3c through which the sub-guide shaft 9 is inserted.

[0015] The position detection scale 4 is a rectangular reflective scale with a reflective pattern formed on its surface, and constitutes an optical position detection encoder together with the sensor head 5. The position detection scale 4 is adhesively fixed to the lens barrel 3.

[0016] The sensor head 5, together with the position detection scale 4, constitutes an optical position detection encoder, and detects the position of the lens barrel 3 in the X-axis direction (a direction parallel to the optical axis O). The sensor head 5 is fixed to the fixed barrel 6 via a sensor holder (not shown). The sensor head 5 is electrically connected to the lens control unit 400 via a flexible printed circuit board (not shown). The lens control unit 400 controls the linear motor 500 using the position information detected by the sensor head 5. Note that the position of the lens barrel 3 may also be detected using other means, such as a magnetic position detection encoder consisting of a magnetic sensor (MR sensor) and a magnetic scale.

[0017] The fixed barrel 6 is made of a resin material or a metal material and has a substantially cylindrical shape. The fixed barrel 6 is fixed to a fixed portion (not shown) of the interchangeable lens 100. The fixed barrel 6 includes bearing portions 6m and 6s into which the main guide shaft 8 and the sub-guide shaft 9 are press-fitted. The bearing portions 6m and 6s may be formed separately from the fixed barrel 6.

[0018] The cover member 7 is made of a resin material or a metal material and has a generally annular shape. The cover member 7 is fixed to the fixed cylinder 6 with screws (not shown). The cover member 7 has bearing portions 7m and 7s into which the main guide shaft 8 and the sub-guide shaft 9 are press-fitted. The bearing portions 7m and 7s may be formed separately from the cover member 7.

[0019] The main guide shaft 8 and sub-guide shaft 9 are made of a metal material and have a cylindrical shape. The main guide shaft 8 is press-fitted and fixed into the bearing portion 6m of the fixed barrel 6 and the bearing portion 7m of the cover member 7 so that it is parallel to the optical axis O. The sub-guide shaft 9 is press-fitted and fixed into the bearing portion 6s of the fixed barrel 6 and the bearing portion 7s of the cover member 7 so that it is parallel to the optical axis O. The main guide shaft 8 is inserted through the round holes 3a and 3b of the lens barrel 3. The sub-guide shaft 9 is inserted through the elongated hole 3c of the lens barrel 3. With the above configuration, the lens barrel 3 is configured to move linearly along the optical axis O.

[0020] The linear motor 500 is composed of an A-phase coil 10, a B-phase coil 11, and a magnet assembly 12. By passing a current through the A-phase coil 10 and the B-phase coil 11, the linear motor 500 generates a driving force for moving the lens barrel 3 linearly along the optical axis O. Two linear motors 500 are arranged at positions 180 degrees apart across the optical axis O. The number of linear motors is not limited to two. When N (N is an integer greater than or equal to 2) linear motors 500 are arranged, they may be arranged at equal intervals of 360 / N degrees in the circumferential direction centered on the optical axis O. However, to achieve stable driving and a simple configuration, the number of linear motors is preferably two or three.

[0021] The A-phase coil 10 and the B-phase coil 11 are formed by further bending a substantially rectangular air-core coil formed by winding a surface-insulated copper wire a predetermined number of times. The A-phase coil 10 and the B-phase coil 11 are adhesively fixed to the lens barrel 3 and electrically connected to the drive circuit 300 via a flexible printed circuit board (not shown). The A-phase coil 10 and the B-phase coil 11 are positioned opposite the magnet assembly 12 with an appropriate air gap maintained. The A-phase coil 10 and the B-phase coil 11 have surfaces parallel to the optical axis O, and these surfaces parallel to the optical axis O are positioned closer to the optical axis O than the surface of the magnet assembly 12 on which the magnetic flux is concentrated.

[0022] The magnet assembly 12 is an assembly of multiple magnets in a Halbach array structure. The surface of the magnet assembly 12 opposite to the side where the magnetic field is concentrated by the Halbach array structure is adhesively fixed to the magnet holding plate 13.

[0023] The magnet holding plate 13 is made of a resin or metal material and has a generally U-shape. The magnet holding plate 13 is fixed to the fixed barrel 6 with screws (not shown). The shape of the magnet holding plate 13 may be a simple flat plate or a rectangular box with one side open. Furthermore, forming the magnet holding plate 13 from a magnetic material can improve the driving force of the linear motor 500. Furthermore, the magnet assembly 12 may be adhesively fixed directly to the fixed barrel 6 without providing the magnet holding plate 13. [Coil Shape and Arrangement] The shape of the A-phase coil 10 and the arrangement of the A-phase coil 10 and the B-phase coil 11 will now be described. FIG. 5( a) is a perspective view of the A-phase coil 10. FIG. 5( b) is a front view of the A-phase coil 10 as viewed from the X-axis direction. FIG. 6 is a perspective view of the lens barrel 3 and peripheral components held by the lens barrel 3.

[0024] The A-phase coil 10 has driving force generating sides 10a and 10b that generate a driving force parallel to the Z-axis. The A-phase coil 10 also has connecting sides 10c and 10d that are parallel to the X-axis and generate almost no driving force. The A-phase coil 10 is a coil with a bent portion. Specifically, as shown in FIG. 5B , the angle θ between a plane tangent to the driving force generating sides 10a and 10b and a plane tangent to the connecting side 10c or 10d is greater than 0 degrees and less than 90 degrees. In other words, the plane tangent to the driving force generating sides 10a and 10b intersects with the plane tangent to the connecting side 10c or 10d. That is, the A-phase coil 10 has a plane parallel to the optical axis O and a plane inclined with respect to the parallel plane. The B-phase coil 11 has the same shape as the A-phase coil 10, so a description thereof will be omitted.

[0025] The driving force generating side 10b of the A-phase coil 10 is inserted into the air-core portion of the B-phase coil 11. The driving force generating side 11b of the B-phase coil 11 is inserted into the air-core portion of the A-phase coil 10. In this manner, the driving force generating sides 10a, 10b of the A-phase coil 10 and the driving force generating sides 11a, 11b of the B-phase coil 11 are alternately arranged along the X-axis direction. This arrangement allows the interchangeable lens 100 to be made smaller in size in the X-axis direction. Furthermore, by bending the A-phase coil 10 and the B-phase coil 11, the two coils can be arranged so that the connecting side 10c of the A-phase coil 10 does not interfere with the connecting side 11d of the B-phase coil, and the connecting side 10d of the A-phase coil 10 does not interfere with the connecting side 11c of the B-phase coil. [Configuration of the Magnet Assembly] FIG. 7 is a side view of the magnet assembly 12 and the magnet holding plate 13. "N" and "S" represent the poles of the magnets.

[0026] The magnet assembly 12 is formed by adhesively bonding a plurality of main magnets 12m and sub-magnets 12s. The main magnets 12m and sub-magnets 12s are arranged alternately along the drive direction. The main magnets 12m and sub-magnets 12s are identical magnets, and are arranged with their magnetization directions facing in opposite directions to form a Halbach array structure. Note that it is not essential that the main magnets 12m and sub-magnets 12s have the same shape. Furthermore, the number of main magnets 12m and sub-magnets 12s is not limited as long as they form a Halbach array structure.

[0027] The main magnet 12m and the sub-magnet 12s are formed by sintering a magnetic material containing rare earth elements, and have a substantially rectangular parallelepiped shape. [Linear Motor Driving Method and Operation] The basic driving method and operation of the linear motor 500 will be described. Figures 8(a) to 8(c) are X-Y cross-sectional views of the linear motor 500 when times T are t0, t1, and t2, respectively. Figure 9 is a diagram showing the time changes in the current flowing through the A-phase coil 10 and the B-phase coil 11.

[0028] When time T is t0, A-phase coil 10 is in the phase of sub-magnet 12s, and B-phase coil 11 is in the phase of main magnet 12m. At this time, the current in A-phase coil 10 is set to 0, and the current in B-phase coil 11 is set to a predetermined value Q. As a result, a driving force in the negative X-axis direction (indicated by the arrow in the figure) is generated in B-phase coil 11, and lens barrel 3 moves in the negative X-axis direction.

[0029] When time T is t1, the A-phase coil 10 and the B-phase coil 11 are in the intermediate phase between the main magnet 12m and the sub-magnet 12s. At this time, the current in the A-phase coil 10 is set to approximately 0.7Q, and the current in the B-phase coil 11 is set to approximately 0.7Q. As a result, a driving force in the negative X-axis direction is generated in the A-phase coil 10 and the B-phase coil 11, and the lens barrel 3 moves in the negative X-axis direction.

[0030] When time T is t2, A-phase coil 10 is in the phase of main magnet 12m, and B-phase coil 11 is in the phase of sub-magnet 12s. At this time, the current in A-phase coil 10 is set to Q, and the current in B-phase coil 11 is set to 0. As a result, a driving force in the negative X-axis direction is generated in A-phase coil 10, and lens barrel 3 moves in the negative X-axis direction.

[0031] The direction of the current flowing through each coil should be set so that each coil receives a Lorentz force from the magnet in the negative X-axis direction.When driving in the positive X-axis direction, the direction should be set so that each coil receives a Lorentz force from the magnet in the positive X-axis direction.

[0032] By passing current through the A-phase coil 10 and the B-phase coil 11 as described above, the driving force for moving the lens barrel 3 can be made constant.

[0033] In actual control of the interchangeable lens 100, more complex position feedback control and velocity feedback control are performed using the above basic driving method, but since this is different from the essence of the present invention, a description thereof will be omitted. [Operation] The operation of the present invention will be described with reference to Figure 10. Figure 10 is an X-Y cross-sectional view showing the main components of the focus unit 1 when time T in Figure 9 is t1.

[0034] In the linear motor 500, a Lorentz force is generated in a direction perpendicular to the optical axis O (direction of the arrow) due to the magnetic flux in the driving direction created by the sub-magnet 12s and the current flowing through the A-phase coil 10 and the B-phase coil 11 (direction of the paper).

[0035] In this embodiment, two linear motors 500 are arranged at positions facing each other at 180 degrees across the optical axis O. Therefore, the Lorentz force in the direction perpendicular to the optical axis O, which is generated by the magnetic flux created by the sub-magnets 12s, is generated symmetrically with respect to the optical axis O in the linear motor 500 on the upper side of the paper and the linear motor 500 on the lower side of the paper. As a result, the Lorentz forces in the direction perpendicular to the optical axis O cancel each other out.

[0036] Therefore, no moment acts on the lens barrel 3, and tilting of the lens barrel 3 can be suppressed. As a result, deterioration of the optical performance of the interchangeable lens 100 can be suppressed. Furthermore, periodically occurring Lorentz forces can be canceled out, and vibration noise of the lens barrel 3 can be suppressed. As a result, deterioration of video performance can be suppressed.

[0037] In this embodiment, the A-phase coil 110 and the B-phase coil 11 have different shapes. In this embodiment, the shape of the A-phase coil 110 is different from that of the first embodiment. Specifically, the B-phase coil 11 has a shape (second shape) that includes a bent portion, similar to the first embodiment, while the A-phase coil 110 has a shape (first shape) that does not include a bent portion. The other components and their arrangement are the same as those of the first embodiment, and therefore description thereof will be omitted. [Configuration of the Focus Unit] FIG. 11 is a perspective view showing only some components of the focus unit 1 of this embodiment. FIG. 12 is a front view of the focus unit 1 of this embodiment as viewed from the negative X-axis direction. FIG. 13 is a perspective view of the A-phase coil 110 of this embodiment.

[0038] Unlike the A-phase coil 10 of Example 1, the A-phase coil 110 is a flat coil without any bends. That is, in the A-phase coil 110, the angle θ formed between a plane tangent to the drive force generating sides 110a and 110b and a plane tangent to the connecting side 110c or 110d is 0 degrees. In other words, the plane tangent to the drive force generating sides 110a and 110b does not intersect with the plane tangent to the connecting side 110c or 110d. As a result, the A-phase coil 110 is positioned so as not to intersect with a plane including the surface 12a of the magnet assembly 12 on which magnetic flux concentrates (i.e., is positioned closer to the optical axis O than the surface 12a of the magnet assembly 12 on which magnetic flux concentrates). Note that the B-phase coil 11 is a coil with bends, so the A-phase coil 110 and the B-phase coil 11 can be positioned without interfering with each other. Like the A-phase coil 110, the B-phase coil 11 is arranged so as not to intersect with a plane including the surface 12a of the magnet assembly 12 on which the magnetic flux concentrates (i.e., closer to the optical axis O than the surface 12a of the magnet assembly 12 on which the magnetic flux concentrates). [Operation] The reason for the above-described shape of the A-phase coil 110 will be explained. A significant magnetic field is generated on the side surfaces 12r and 12l (planes perpendicular to the Z-axis) of the magnet assembly 12 in the Halbach array. Therefore, as with the A-phase coil 10 of Example 1, when a current flows through the connecting edges 10c and 10d of the A-phase coil 10, a Lorentz force is generated by the magnetic fields of the side surfaces 12r and 12l. On the other hand, since the B-phase coil 11 is far from the side surfaces 12r and 12l, almost no Lorentz force is generated by the magnetic fields of the side surfaces 12r and 12l of the magnet assembly 12. As a result, a difference occurs between the driving force generated in the A-phase coil 10 and the driving force generated in the B-phase coil 11.

[0039] In this embodiment, by arranging the A-phase coil 110 away from the side surfaces 12r and 12l, the A-phase coil 110 is hardly affected by the magnetic field of the side surfaces 12r and 12l. In other words, it is possible to reduce the Lorentz force caused by the magnetic field of the side surfaces 12r and 12l that is generated in the A-phase coil 110. Therefore, it is possible to make the driving forces of the A-phase coil 110 and the B-phase coil 111 approximately the same, enabling stable control of the interchangeable lens 100.

[0040] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

Claims

1. A lens driving device comprising: at least one lens; a lens barrel that holds the lens; and N (N is an integer of 2 or more) linear motors, each of which is composed of a first coil and a second coil that generate a driving force in the lens barrel in a direction parallel to the optical axis of the lens, and a magnet assembly in a Halbach array, wherein at least one of the first coil and the second coil has a bent portion, and the linear motors are arranged at intervals of 360 / N degrees along a circumferential direction centered on the optical axis of the lens.

2. The lens driving device according to claim 1, wherein the first coil and the second coil have different shapes.

3. A lens driving device as described in claim 1 or 2, characterized in that the first coil has a first shape that does not have a bent portion, and the second coil has a second shape that has a bent portion.

4. The lens driving device according to claim 3, wherein the first coil and the second coil are arranged on the optical axis side of the face of the magnet assembly on which magnetic flux is concentrated.

5. A lens driving device as described in claim 1 or 2, characterized in that at least one of the first coil and the second coil has a surface parallel to the optical axis and a surface inclined with respect to the parallel surface.

6. A lens driving device as described in any one of claims 1 to 5, characterized in that the first coil and the second coil have a surface parallel to the optical axis, and the parallel surface is located on the side of the optical axis rather than the surface on which the magnetic flux of the magnet assembly is concentrated.

7. The lens driving device according to any one of claims 1 to 6, characterized in that the number of said linear motors is two.

8. The lens driving device according to any one of claims 1 to 6, characterized in that the number of said linear motors is three.

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