WO2007069844A1

WO2007069844A1 - Apparatus for automatically controlling focal point of small optical lens

Info

Publication number: WO2007069844A1
Application number: PCT/KR2006/005415
Authority: WO
Inventors: Gi Tae Kweon
Original assignee: Yoosung Precision Co., Ltd.; Mobinus Co., Ltd.
Priority date: 2005-12-12
Filing date: 2006-12-12
Publication date: 2007-06-21

Abstract

The invention relates to an automatic focus control apparatus of a small optical lens employing a linear DC motor. The apparatus includes a movable unit configured to include a lens holder combined with a lens assembly therein, a spring unit required to restore the movable unit to an initial position thereof, a magnetic circuit unit configured to include a permanent magnet for continuously generating magnetic flux and a coil for moving the movable unit using internally generated magnetic force, and a housing configured to integrate the individual elements to a single body, wherein the magnetic circuit unit is configured such that a bonded permanent magnet is mounted in the movable unit and the coil is disposed to be spaced apart from an outside of the bonded permanent magnet, so that the magnetic circuit unit moves the movable unit by applying repulsive force to the bonded permanent magnet using generated magnetic force, further comprising an additional circuit unit that is disposed outside the coil of the magnetic circuit unit and generates new drag force in conjunction with the bonded permanent magnet in addition to the magnetic force of the coil.

Description

APPARATUS FOR AUTOMATICALLY CONTROLLING FOCAL POINT OF SMALL OPTICAL LENS

Technical Field

[1] The present invention relates, in general, to an apparatus for automatically controlling the focal point of a small optical lens and, more particularly, to an automatic focal point control apparatus in which the configuration of a magnetic circuit is improved, thereby reducing the size and cost of the product thereof. Background Art

[2] A digital camera capable of automatically focusing on an image requires an automatic focal point control apparatus that can vary the position of a lens. In general, in an apparatus for automatically controlling the focal point of an optical lens, which is used for a digital camera, a method of transforming the rotating movement of a stepping motor or a Direct Current (DC) motor into the rectilinear movement of a focal lens in the direction of an optical axis using a transformation device, such as gears, has been widely used.

[3] However, it is difficult to mount a rotary motor and a gear box in an apparatus for automatically controlling the focal point of a small optical lens, which is used in a limited space, as in the camera module of a mobile phone. Accordingly, a driving apparatus, such as a Linear DC Motor (LDM) shown in FIGS. 1 and 2, is used.

[4] Furthermore, although both a moving coil-type LDM, in which a coil moves, and a moving magnet-type LDM are used as such LDMs that are used in apparatuses for automatically controlling the focal point of a small optical lens, the moving coil-type LDM shown in FIG. 1 is preferred because a permanent magnet is heavier than a coil, and thus the weight of the movable unit increases.

[5] A conventional apparatus 20 for automatically controlling the focal point of a small optical lens, as shown in FIGS. 1 and 2, includes a moving unit in which a coil 9 is mounted on a lens holder 10 combined with a lens assembly 1 in a threaded manner, a magnetic circuit unit that includes two soft magnetic bodies 6 and 8 and a ring-shaped permanent magnet 7, and a stationary unit that includes upper and lower housings 3 and 13 fastened to each other using four screws 2.

[6] The rectilinear movement of the conventional automatic focal point control apparatus is achieved in such a way that the magnetic circuit unit is constructed using the two soft magnetic bodies 6 and 8 and the ring-shaped permanent magnet 7, constant magnetic flux is continuously generated through the gap between the inner plate 6a of the upper magnetic body 6 and the inner surface of the lower magnetic body 8, and rectilinear movement is generated using optical axial magnetic force (according to Fleming's left hand rule), generated when current passes through the magnetic flux, by applying current to the coil 9 located in the gap.

[7] However, in the conventional automatic focal point control apparatus described above, the inner plate 6a of the upper magnetic body is located between the lens holder 10 and the coil 9. Accordingly, the apparatus has problems in that the size of the product thereof is increased due to the thickness of the inner plate and the gap beside the inner plate, and in that interference occurs between the inner plate 6a of the upper magnetic material and the coil 9 or lens holder 10 during operation. Furthermore, there is a disadvantage in that the cost of the magnetic circuit unit is high because the upper and lower magnetic bodies and the sintered permanent magnet, which require precise processing, are used. Disclosure of Invention Technical Problem

[8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus for automatically controlling the focal point of a small optical lens, in which a magnetic circuit unit is formed of an inexpensive bonded permanent magnet and an inexpensive coil, and an additional circuit unit, made of soft magnetic material and configured to have a simple structure, is added, thereby reducing the cost of the magnetic circuit unit, and a conventional magnetic inner plate is removed and a bonded permanent magnet, which can be formed to be thin, is used, thereby significantly reducing the size of the product thereof and interference defects upon fabrication.

[9] Another object of the present invention is to provide an apparatus for automatically controlling the focal point of a small optical lens, in which an additional circuit unit made of soft magnetic material is disposed to be spaced apart from a permanent magnet so as to increase magnetic force reduced due to the use of a bonded permanent magnet, thereby increasing driving force. Technical Solution

[10] In order to accomplish the above objects, the present invention provides an apparatus for automatically controlling a focal point of a small optical lens, the apparatus comprising a movable unit configured to include a lens holder combined with a lens assembly therein; a spring unit required to restore the movable unit to an initial position thereof; a magnetic circuit unit configured to include a permanent magnet for continuously generating magnetic flux and a coil for moving the movable unit using internally generated magnetic force; and a housing configured to integrate the individual elements to a single body; wherein the magnetic circuit unit is configured such that a bonded permanent magnet is mounted in the movable unit and the coil is disposed to be spaced apart from an outside of the bonded permanent magnet, so that the magnetic circuit unit moves the movable unit by applying repulsive force to the bonded permanent magnet using generated magnetic force; further comprising an additional circuit unit that is disposed outside the coil of the magnetic circuit unit and generates new drag force in conjunction with the bonded permanent magnet in addition to the magnetic force of the coil. Brief Description of the Drawings

[11] FIG. 1 is an exploded perspective view showing a conventional apparatus for automatically controlling the focal point of a small-sized lens;

[12] FIG. 2 is a sectional view of the automatic focal point control apparatus shown in

FIG. 1;

[13] FIG. 3 is an exploded perspective view showing an apparatus for automatically controlling the focal point of a small optical lens according to the present invention;

[14] FIG. 4 is a sectional view showing an apparatus for automatically controlling the focal point of a small optical lens according to the present invention;

[15] FIG. 5 is a diagram showing the magnetic flux pattern of a magnetic circuit unit, which illustrates the drag force of a bonded permanent magnet based on the longitudinal end effect, according to the present invention;

[16] FIG. 6 is a graph showing magnetic force generated by the coil of a magnetic circuit unit according to the present invention;

[17] FIG. 7 is a graph showing drag force generated by the magnetic force of an additional circuit unit according to the present invention; and

[18] FIG. 8 is a graph showing the total driving force that moves a movable unit in the apparatus for automatically controlling the focal point of a small optical lens according to the present invention.

[19] <Description of reference numerals of principal elements>

[20] 51: lens assembly 52: upper cover

[21] 53: upper spring 54: housing

[22] 55: magnetic circuit unit 55a: coil

[23] 55b: bonded permanent magnet 56: terminal

[24] 57: additional circuit unit 59: lens holder

[25] 60: spacer 61: lower spring

[26] 62: lower cover 80: apparatus for automatically controlling the focal point of a small optical lens Best Mode for Carrying Out the Invention

[27] The construction of the present invention will be described in detail with reference to the accompanying drawings.

[28] First, as shown in FIGS. 3 and 4, the construction includes a movable unit that includes a lens holder 59 combined with a lens assembly 51 therein, upper and lower plate springs 53 and 61 that are required to restore the movable unit to its initial position, a magnetic circuit unit 55 in which a bonded permanent magnet 55b is mounted in the movable unit and a coil 55a is disposed to be spaced apart from the bonded permanent magnet 55b, thereby moving the movable unit by applying repulsive force to the bonded permanent magnet 55b using generated magnetic force, an additional circuit unit 57 that is disposed outside the coil 55a of the magnetic circuit unit 55 and that is configured to generate drag force in conjunction with the bonded permanent magnet 55b in addition to the magnetic force of the coil 55 a, a terminal 56 that supplies current to both ends of the copper wire of the coil 55, a spacer 60 that protects the lead wires of the coil and prevents the rotation of the lens, and an upper cover 52, a housing 54 and a lower cover 62 that combine the individual elements into a single body.

[29] For the purpose of increasing magnetic force by increasing the amount of magnetic flux passing through the coil 55 and also increasing the total driving force by generating drag force using the longitudinal end effects between the bonded permanent magnet 55b and the additional circuit unit 57, the additional circuit unit 57 is formed to come into contact with the outside of the coil 55a of the magnetic circuit unit 55, and is manufactured of soft magnetic material.

[30] Furthermore, it is preferred that the terminal 56 be made of Flexible Printed Circuit

Board (FPCB) material, be inserted into two bosses of the spacer 60, be fixed thereto through thermal melting, be connected to the + and - lead wires of the coil 55a, and then be supplied with current.

[31] The motor-driving method of the magnetic circuit unit uses a moving magnet- type scheme in which the coil 55 and the additional circuit unit 57 are disposed in a stationary part and the bonded permanent magnet 55b is disposed in a movable part, instead of a moving coil-type scheme, in which the upper and lower magnet materials 6 and 8 and the permanent magnet 7 are disposed in a stationary part and the coil 9 is disposed in a movable part. Through this, the conventional upper magnetic inner plate 6a is removed, so that the thickness of the inner plate and the gap beside the inner plate 6a can be eliminated, thereby reducing the size of the magnetic circuit unit 55, and interference frequently occurring in the gap between the upper magnetic inner plate 6a and the coil 9 or lens holder 10 is eliminated, thereby reducing interference defects. Furthermore, the upper and lower magnet materials 6 and 8, which are expensive because precise processing is required, are eliminated, so that the cost of the magnetic circuit unit 55 can be reduced. [32] Furthermore, in the conventional technology, one or several sintered permanent magnets 7 having strong magnetic force are generally used. However, the sintered permanent magnet 7 has problems in that the size of an adjustment device increase because it is difficult to form the sintered permanent magnet 7 to have a thin thickness, and the cost of the product thereof is high because the manufacturing cost of the sintered permanent magnet 7 is high when the sintered permanent magnet 7 has a curved shape, such as a C shape or a cylindrical shape. In particular, in the apparatus 80 for automatically controlling the focal point of a small optical lens that uses the moving magnet-type motor-driving scheme in which the magnet and the lens are moved together as in the present invention, a problem may occur at the time of moving the lens because the weight of the permanent magnet is heavy.

[33] Therefore, the present invention solves the problems using the bonded permanent magnet 55b, which is inexpensive, is lightweight and can be formed to be thin. Furthermore, the bonded permanent magnet 55b is formed to have a cylindrical ring shape by taking advantage of a characteristic in which the bonded permanent magnet 55b can be formed in various shapes, and is then inserted to come into contact with the outer circumference of the lens holder 59, so that the ability of the permanent magnet 55b to withstand shocks when dropped can be improved.

[34] However, the magnetic circuit unit 55 has a problem in that the magnetic force within the magnetic circuit unit 55 is reduced because a bonded permanent magnet 55b, having magnetic force weaker than that of a sintered permanent magnet, is used and the upper and lower magnetic materials 6 and 8 constituting the magnetic circuit unit 55 are eliminated. In order to solve the problem, it is necessary to increase magnetic force generated in the coil 55a (force that is generated according to Fleming's left hand rule when current flows through the coil in a direction crossing magnetic flux in a space in which the magnetic flux exists), and to generate drag force.

[35] In the present invention, the additional circuit unit 57 made of soft magnetic material is disposed to come into contact with the outside of the coil 55 of the magnetic circuit unit in order to increase driving force that is reduced due to a change in the configuration of the magnetic circuit unit.

[36] The effect of the additional circuit unit 57 is that soft magnetic material is added into the magnetic circuit unit 55, so that the magnetic resistance of the magnetic circuit unit 55 is decreased, thereby increasing the amount of magnetic flux, as illustrated in FIG. 5. When the amount of magnetic flux increases as described above, magnetic force generated in the coil 55a increases, as illustrated in FIG. 6. Furthermore, drag force based on the longitudinal end effect of the moving magnet type LDM shown in FIG. 5 is generated at both ends of the additional circuit unit 57. Accordingly, repulsive force is applied to the bonded permanent magnet 55b using the generated drag force shown in FIG. 7, so that the total driving force used to move the lens of the automatic focal point control apparatus can be increased, as illustrated in FIG. 8.

[37] The drag force generated at both ends of the additional circuit unit 57 increases in proportion to the amount of movement of the bonded permanent magnet 55b, regardless of the amount of current of the coil 55a. Accordingly, when the bonded permanent magnet 55b starts to move using the magnetic force of the coil 55a, which is generated by the current, drag force proportional to the amount of movement of the bonded permanent magnet 55b is additionally generated, so that sufficient driving force capable of stably moving the lens holder 59 can be obtained.

[38] The assembly and operation of the present invention constructed as described above are described below.

[39] First, the movable unit is constructed by combining the bonded permanent magnet

55b and the lens holder 59 together.

[40] Thereafter, after the housing 54 is turned upside down, the additional circuit unit 57 and the coil 55a are inserted into the housing 54 and the movable unit is inserted inside the coil 55 a.

[41] Furthermore, the spacer 60, the lower plate spring 61 and the lower cover 62 are sequentially mounted using the lower thermal melting boss of the housing 54 as a guide, and then four projected bosses are fixed through thermal melting. Thereafter, after the housing 54, with which the individual elements are combined, is turned upside down, the upper plate spring 53 and the upper cover 52 are sequentially mounted using the upper thermal melting boss of the housing as a guide, and four projected bosses are fixed through thermal melting. Finally, the lead wires of the coil, which are projected outside the product, are soldered to the terminal 56, the terminal 56 is inserted into two bosses that project through the spacer 60, and thermal melting is performed, thereby assembling the automatic focal point control apparatus.

[42] The vertical rectilinear movement of the movable unit is generated due to magnetic force (according to Fleming's left hand rule) that is generated in the coil 55a in a vertical direction when current passes through magnetic flux. At this time, since the coil 55a is fixed, the bonded permanent magnet 55b is moved according to the principle of action and reaction.

[43] At this time, when magnetic force is applied to the bonded permanent magnet 55b, the movable unit overcomes the elastic restoring force of the upper and lower plate springs 53 and 61 and starts to move. Since the elastic restoring force of the upper and lower plate springs 53 and 61 is proportional to the amount of movement of the movable unit, the displacement of the movable unit can be controlled using the magnetic force that is controlled according to the amount of current flowing through the coil 55 a. [44] Furthermore, when the movable unit moves, the magnetic force of the additional circuit unit 57 is additionally generated in proportion to the amount of movement, so that driving force, reduced due to the variation in the configuration of the magnetic circuit unit 55, is increased.

[45] When voltage applied to the coil 55a is removed after an automatic focusing operation has been terminated, the coil 55a returns to the initial position thereof due to the elastic force of the upper and lower plate springs 53 and 61 that press the movable unit.

Industrial Applicability

[46] In the apparatus for automatically controlling the focal point of a small optical lens according to the present invention, the magnetic circuit unit is formed of a bonded permanent magnet and a coil, instead of upper and lower magnetic materials and a sintered permanent magnet, which require precise processing, so that the cost of the magnetic circuit unit can be reduced. In particular, since the conventional magnetic inner plate is removed and a bonded permanent magnet, which can be formed to be thin, is used instead, both the size of the resultant product and the rate of interference defects upon fabrication can be reduced.

[47] Furthermore, the additional circuit unit made of soft magnetic material is provided, and thus generates drag force, so that the insufficient magnetic force of the bonded permanent magnet can be supplemented, thereby increasing the total driving force.

Claims

[1] An apparatus for automatically controlling a focal point of a small optical lens, the apparatus comprising a movable unit configured to include a lens holder combined with a lens assembly therein; a spring unit required to restore the movable unit to an initial position thereof; a magnetic circuit unit configured to include a permanent magnet for continuously generating magnetic flux and a coil for moving the movable unit using internally generated magnetic force; and a housing configured to integrate the individual elements to a single body; wherein the magnetic circuit unit is configured such that a bonded permanent magnet is mounted in the movable unit and the coil is disposed to be spaced apart from an outside of the bonded permanent magnet, so that the magnetic circuit unit moves the movable unit by applying repulsive force to the bonded permanent magnet using generated magnetic force; further comprising an additional circuit unit that is disposed outside the coil of the magnetic circuit unit and generates new drag force in conjunction with the bonded permanent magnet in addition to the magnetic force of the coil.

[2] The apparatus according to claim 1, wherein the additional circuit unit is made of soft magnetic material.