Voice coil motors, lens barrels

Abstract

To provide a voice coil motor and a lens barrel that suppress the increase in product outer diameter by improving the efficiency of arrangement and propulsion.SOLUTION: The voice coil motor has a first yoke, a second yoke, a magnet, and a coil. The first yoke is inserted into the coil, and has a polygonal shape having a convex portion. The coil moves along the first yoke when energized. The second yoke is arranged along the convex portion, and holds the magnet on the first yoke side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a voice coil motor and a lens barrel. [Background technology]

[0002] Since imaging devices such as digital cameras and interchangeable lenses are often taken outdoors, there is a strong demand for them to be smaller and lighter. There is also a strong demand for improved focusing speed.

[0003] In addition, imaging devices are now required to be able to capture not only still images but also video. In the case of video recording, the driving noise of the focus lens is also recorded as shooting noise, which is undesirable. Therefore, quieter focus driving is also required.

[0004] Therefore, a voice coil motor can be used as an actuator that is small but has a large thrust and suppresses the driving noise during focus driving.

[0005] However, in order to improve focusing speed and drive a larger focus lens group, it is necessary to increase the thrust of the voice coil motor. However, increasing the thrust of the voice coil motor requires increasing the size and weight of the components that make up the voice coil motor, such as the magnet and yoke.

[0006] Patent Document 1 discloses a voice coil motor in which the long side of the yoke that holds the magnet is elongated in the yoke that constitutes the voice coil motor. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6457701 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the voice coil motor described in Patent Document 1 has a long yoke long side on the side that holds the magnet, which poses a problem in that when this voice coil motor is housed inside a cylindrical shape, the yoke arrangement diameter must be large.

[0009] Next, as mentioned above, the longer the long side of the yoke, the more space there is between the cylinder and the long side of the yoke. This space does not contribute to thrust, so there is a problem in that it is wasted space in the structure.

[0010] When a voice coil motor having these problems is used in an interchangeable lens or the like, the outer diameter of the interchangeable lens or the like increases, resulting in a problem of increased size.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a voice coil motor and a lens barrel that suppress an increase in the product outer diameter by improving the efficiency of arrangement and propulsion. [Means for solving the problem]

[0012] In order to solve the above problems, the voice coil motor of the present invention has a first yoke, a second yoke, a magnet, and a coil, the first yoke is polygonal with a convex portion, the coil is inserted into the first yoke, the coil moves along the first yoke when current is applied, In a cross section taken along a plane perpendicular to the direction of travel of the coil, The second yoke is disposed along the protrusion and holds a magnet on the first yoke side.

[0013] Furthermore, the lens barrel of the present invention is characterized in that it has the voice coil motor, a yoke holding member that holds the second yoke, and a lens holding frame that engages with the coil, and that the lens is moved by passing current through the coil to move the lens holding frame. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a voice coil motor and a lens barrel in which the increase in the product outer diameter is suppressed by improving the efficiency of arrangement and propulsion. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing the configuration of a voice coil motor according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view of a voice coil motor according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional comparison diagram of a voice coil motor according to an embodiment of the present invention and a conventional example; [Figure 4] 10 is a cross-sectional view of a voice coil motor according to another embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0016] The best mode for carrying out the present invention will be described below with reference to the accompanying drawings, but the present invention is not limited to these embodiments.

[0017] FIG. 1 is a structural diagram showing a voice coil motor 1 according to one embodiment of the present invention. Note that FIG. 1 has been simplified to facilitate explanation of the present invention. FIG. 2 is a cross-sectional view of the voice coil motor 1 taken along the dotted line in FIG. 1 and viewed from the K side. FIG. 3 is a diagram comparing cross-sectional views of the voice coil motor 1 of the present invention shown on the left side of the central dotted line C with a conventional voice coil motor shown on the right side. FIG. 4 is a cross-sectional view of a voice coil motor 1 showing another embodiment of the present invention.

[0018] Furthermore, when the voice coil motor 1 in each drawing is placed in a lens barrel, the upper side of each drawing becomes the outer diameter side of the lens barrel, and the lower side becomes the inner diameter side, and the moving lens group (not shown) engaged with the coil 11 in the drawing is positioned on the inner diameter side of the lens.

[0019] As shown in the drawings, a voice coil motor 1 of the present invention includes a first yoke 10, a coil 11, a magnet 12, a second yoke 13, and an end yoke 14.

[0020] The first yoke 10 is made of a magnetic material. Its cross section perpendicular to the direction of travel of the coil 11 has a convex shape. The first yoke 10 shown in Fig. 1 is made by stacking rectangular iron plates that are magnetic materials.

[0021] Coil 11 is formed by repeatedly winding an electric wire member such as a copper wire around the outer periphery of first yoke 10. The cross section of coil 11 taken along a plane perpendicular to the direction of travel is a polygon with convex portions.

[0022] In the magnetic field created by the coil 11 and the magnet 12, an electromagnetic force is generated when current is applied to the coil 11. By controlling the drive, the coil 11 moves in the direction along the first yoke 10, that is, in the direction of the arrow in FIG.

[0023] The magnet 12 is fixed to the second yoke 13 on the first yoke 10 side.

[0024] The second yoke 13 is made of a magnetic material, similar to the first yoke 10. It is arranged on the convex side of the first yoke. In this embodiment, the second yoke 13 is divided into left and right halves and arranged along the convex portion of the first yoke 10.

[0025] The end yoke 14 is made of a magnetic material, just like the first yoke 10 and the second yoke 13. The first yoke 10 and the second yoke 13 are positioned parallel to each other along the direction of the arrow in FIG. 1 , and are therefore connected to each other by the end yoke 14. Specifically, the first yoke 10 and the second yoke 13 each have a protruding portion, and the end yoke 14 has a fitting portion into which the protruding portions fit. The protruding portions of the first yoke 10 and the second yoke 13 fit into the fitting portions of the end yoke 14, thereby connecting the first yoke 10 and the second yoke 13 to the end yoke 14. As a result, a magnetic circuit is formed that reduces magnetic flux leakage due to the coil 11 and the magnet 12.

[0026] Here, we will explain the coil 11. The coil 11 in this embodiment has the first yoke 10 inserted therethrough, and is formed by repeatedly winding copper wire around the outer periphery of the first yoke 10, so that it has a shape with a convex portion.

[0027] FIG. 2 is a cross-sectional view of the voice coil motor 1 including the dotted line portion of FIG. 1, which is perpendicular to the direction of movement of the coil 11.

[0028] The coil 11 will be described with reference to Figure 2. The cross-sectional shape of the coil 11 is a polygon with convex portions, and the cross-sectional shape of the coil 11 in this embodiment is a pentagon with convex portions. The convex portions are formed from the sides La and Le. Lb and Ld are the side sides, and Lc is the base. When current is applied to the coil 11, current flows in the order La → Lb → Lc → Ld → Le. It is also possible to flow in the opposite direction by controlling it.

[0029] The relationship between the direction of the current flowing through coil 11 and the generated thrust is governed by Fleming's left-hand rule, since the direction of the magnetic field is known. Therefore, the direction of the current is determined depending on the thrust that is desired to be generated in coil 11. Regardless of the direction of the current, thrust is generated from the sides La and Le that form the convex portion in response to the magnetic flux generated by magnet 12. At the same time, the current flowing through base Lc, which is located across first yoke 10 from the sides La and Le that form the convex portion, flows in the opposite direction to the aforementioned magnetic flux. Therefore, a thrust in the opposite direction is generated from base Lc.

[0030] Next, the thrust force generated in the coil 11 will be described. If the thrust generated in the coil is F (N), the current flowing through the coil is I (A), the magnetic flux density is B (T), and the length of the coil passing through the magnetic flux is L (m), the following equation holds true. F=I×B×L (1)

[0031] FIG. 3 compares the cross sections of a rectangular coil, which is a conventional coil, with that of the present invention. Because both the coil 11 used in the present embodiment and the conventional coil are symmetrical, only one side of each will be used for explanation. The dotted line C represents the axis of symmetry between the coils. The left side represents the coil 11, magnet 12, and second yoke 13 of the present invention, while the right side represents the magnet 12 and second yoke 13 positioned to match the conventional rectangular coil. Focusing on the convex portion of coil 11, the length of the overlapping portion between magnet 12 and coil 11, where thrust is generated, is L0, and similarly, the length of the overlapping portion between the conventional coil and magnet is L1. Since L0 and L1 can be expressed as a right-angled triangle with L0 as the hypotenuse and L1 as the base, the following equation holds: L0>L1 (2)

[0032] Then, when the magnetic flux density for each coil is B and the current flowing through it is I, the following equation (3) is obtained from equations (1) and (2). I×B×L0>I×B×L1 (3)

[0033] As can be seen from equation (1), the generated thrust is proportional to the length of the coil through which the magnetic flux passes. Since equation (2) also shows that this length is longer for coil 11 of the present invention than for a conventional coil, it can be confirmed from equation (3) that the thrust generated in coil 11 of the present invention is greater than that generated in a conventional coil.

[0034] Next, as described above, when current is passed through the coils to drive the voice coil motor, thrust is generated from the portions L0 and L1 in Figure 3 located on the magnet 12 and yoke side of each coil. However, as described above, both coil 11 of the present invention and the conventional coil are configured with repeatedly wound electric wire members, so current also flows in the opposite direction to the coil located on the opposite side of magnet 12 and second yoke 13. As a result, thrust in the opposite direction is generated from the portion of the coil located on the opposite side of magnet 12 and second yoke 13 in both the present invention and the conventional coil.

[0035] Here, we focus on the yokes located inside each coil. Comparing the coil 11 of the present invention with a conventional coil, it can be seen from Figure 3 that the space surrounded by the coil 11 of the present invention is larger. This means that it is possible to fit the first yoke 10, as shown in Figure 2, into the space surrounded by the coil 11 of the present invention. Therefore, the volume of the first yoke 10 is larger than that of a yoke that can be fitted into the space surrounded by a conventional coil. In other words, the voice coil motor 1 of the present invention has less magnetic flux leaking into the coil that generates thrust in the reverse direction than a voice coil motor using a conventional coil. Therefore, the magnetic flux density B at the base of the coil 11 of the present invention (corresponding to Lc in Figure 2) is smaller than that of a conventional coil.

[0036] Therefore, since the magnitude of the reverse thrust also satisfies formula (1), it can be seen that the reverse thrust generated by the coil 11 of the present invention is smaller than the reverse thrust generated by a conventional coil.

[0037] From the above, compared to a voice coil motor using a conventional coil, the voice coil motor of the present invention generates a larger thrust by increasing the length of the coil through which magnetic flux passes, and by increasing the volume of the yoke inserted into the coil, it is possible to reduce the magnetic flux leaking into the coil that generates thrust in the opposite direction, thereby reducing the thrust in the opposite direction.

[0038] The cross section of the first yoke 10 shown in FIG. 2 is polygonal with a convex portion, while the first yoke 10 of the present embodiment is configured by stacking rectangular iron plates toward the second yoke 13. Specifically, in a cross section cut along a plane perpendicular to the direction of movement of the coil 11 inserted through the first yoke 10, the width of the stacked rectangular iron plates narrows as they are stacked toward the second yoke 13, resulting in the first yoke 10 having a convex portion. Alternatively, V-shaped iron plates may be stacked to match the convex portion. The first yoke 10 may also be made of a single piece of magnetic material. Specifically, it may be a single piece machined from a block of iron.

[0039] FIG. 4 shows another embodiment of the first yoke 10 having a stacking configuration different from that of the embodiment of the present invention.

[0040] The rectangular iron plates of the first yoke 10 may be stacked in such a way that the width of the iron plates narrows from the magnet 12 side as shown in FIG.

[0041] In the present embodiment, the magnet 12 and the second yoke 13 are split into left and right halves to fit the convex portion of the first yoke 10, but there is no problem if they are one piece that is bent into a dogleg shape. However, by splitting the magnet 12 and the second yoke 13 into left and right halves as in the present embodiment, it is possible to avoid problems such as the tedious processing required to make them one piece, and the fact that the dogleg shape of the magnet weakens the magnetic force compared to splitting the magnet into left and right halves.

[0042] As shown in Figure 4, with regard to magnet 12 and second yoke 13, as mentioned above, the thrust generated in coil 11 is proportional to the length of the overlapping portion of coil 11 and magnet 12, so the length of magnet 12 is generally set to L4. However, in addition to L4, which forms the convex portion of coil 11, L5 is also affected by magnetic flux in the same way as L4, and so thrust is generated. The direction of the magnetic flux passing through L5 can be controlled depending on the settings of magnet 12 and second yoke 13.

[0043] Specifically, the lengths of magnet 12 and second yoke 13 are set so that the line connecting the end faces of second yoke 13 and magnet 12 is extended toward first yoke 10 (dotted line in FIG. 4) and includes coil 11 (dotted lines (a) and (b) in FIG. 4). In this way, the thrust generated at L5 of coil 11 is controlled to be in the same direction as the thrust generated at L4, and as a result, the thrust of voice coil motor 1 of the present invention can be increased.

[0044] The voice coil motor 1 of the present invention described above can be used in a lens barrel. Specifically, the coil 11 is engaged with a lens holding frame of a moving lens group, such as a focusing lens group or a variable magnification lens group (not shown), and the second yoke 13 is fixed to a yoke holding member. When current is applied to the coil 11, the moving lens group moves in a direction along the first yoke 10 together with the coil 11, so that the drive of the moving lens group can be controlled by controlling the current.

[0045] Furthermore, when the voice coil motor 1 of the present invention is used in a lens barrel, the moving lens group is engaged with the coil 11 as described above, so the optical axis of the moving lens group (not shown) is located below the coil 11 shown in each drawing. Therefore, when the voice coil motor of the present invention is disposed in a lens barrel, the lower side of the voice coil motor 1 in each drawing is the inner diameter side of the lens barrel, and the upper side is the outer diameter side of the lens barrel.

[0046] Because the lens barrel is cylindrical, the yoke holding member located on the outer diameter side of the lens barrel is arc-shaped. The arc R in FIG. 3 represents the yoke holding member. The second yoke 13 held by the yoke holding member is preferably arranged along the arc R for efficient placement. A conventional voice coil motor, such as the one shown on the right side of FIG. 3, has wasted space between the coil and the arc R representing the yoke holding member. In contrast, the voice coil motor 1 of the present invention, shown on the left side of FIG. 3, eliminates wasted space by arranging the second yoke 13 and magnet 12 along the arc R in FIG. 3, and increases the thrust force generated by increasing the overlap length between the conductor coil 11 and the magnet 12 that generates magnetic flux, as described above.

[0047] Furthermore, the cross section of first yoke 10 shown in each drawing is a polygonal shape with a convex portion. If it is configured by stacking thin, rectangular iron plates, a step will occur due to the difference in width of the stacked iron plates, where the width is perpendicular to the direction of movement of coil 11. Coil 11 is configured by repeatedly winding copper wire along the outer periphery of first yoke 10, but there is no problem if the shape of coil 11 is not adjusted to fit the step that occurs when first yoke 10 is configured by stacking iron plates, and the line connecting the tops of the step can be made parallel to the line. This reduces the effort required to process coil 11.

[0048] Furthermore, in the present invention, a thrust is generated by the sides that form the convex portion of coil 11. In the present embodiment, the convex portion of coil 11 is formed by two sides, and is combined with a concave portion formed by three sides located on the inner diameter side of the lens to form a pentagon. However, it is also acceptable to form the convex portion with three sides and make coil 11 hexagonal. Specifically, it is also acceptable to form the three sides of the convex portion in the shape of the upper side of a regular hexagon, and to combine the lower side with the arrangement of the side edges and base edges Lb to Ld shown in Figure 2.

[0049] Furthermore, although the interior angles of the sides and bases of the pentagonal coil 11 shown in each drawing and the hexagons Lb to Ld described above are right angles, a regular pentagon or regular hexagon may also be used.

[0050] Furthermore, the cross-sectional shape of the first yoke 10 on a plane perpendicular to the direction of movement of the coil 11 is a polygon with a convex portion. More preferably, it is a polygon in which all interior angles are smaller than two right angles, a so-called convex polygon. The same applies to the shape of the coil 11 along the outer periphery of the first yoke 10. [Explanation of symbols]

[0051] 1 voice coil motor 10 First York 11 Coil 12 Magnet 13 Second York 14 End yoke

Claims

1. In a voice coil motor having a first yoke, a second yoke, a magnet, and a coil, the first yoke is inserted through the coil and has a polygonal shape with a protrusion, The coil moves along the first yoke when energized, In a cross section taken along a plane perpendicular to the direction of travel of the coil, the second yoke is disposed along the protrusion and holds the magnet on the first yoke side. A voice coil motor characterized by:

2. 2. The voice coil motor according to claim 1, wherein the cross section of the first yoke is a convex polygon.

3. 3. The voice coil motor according to claim 1, wherein the first yoke is configured by stacking rectangular yokes.

4. 4. The voice coil motor according to claim 1, wherein the first yoke is configured by stacking the rectangular yokes in a direction perpendicular to the direction of movement of the coil, and the width of the rectangular yokes becomes narrower as they are stacked toward the second yoke.

5. 5. The voice coil motor according to claim 1, wherein the second yoke and the magnet are separated so as to face the protrusion.

6. 6. The voice coil motor according to claim 1, wherein the coil is located within a range of a straight line on the first yoke side that connects the second yoke end located at the convex portion and the magnet end.

7. A voice coil motor according to any one of claims 1 to 6; a yoke holding member that holds the second yoke; a lens holding frame that engages with the coil, The lens barrel is characterized in that the lens holding frame is moved by energizing the coil, thereby moving the lens.

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