Lens barrel

A lens barrel with improved precision is obtained by reducing fitting play of a lens barrel. A coil and a magnetic member are fixed on a lens holding member, and a magnet and a yoke are fixed on an outer barrel. When energizing the coil, the lens holding member moves in the optical axis direction along guide bars by magnetic fluxes from the magnet. The magnetic member receives a magnetic attraction force toward the magnet by leakage fluxes. In the lens holding member, a bearing sleeve is biased by the attraction force perpendicularly to the axis of the guide bar, and the resultant force of the attraction force and a gravitational force exerted on the lens holding member removes play. A resultant force of a force toward the guide bar exerted on the bearing and the gravitational force thereon removes fitting play between the bearing and the guide bar.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel that drives a lens moving portion using a voice coil motor for use in an optical apparatus such as a digital camera or digital video camera.

2. Description of the Related Art

In recent years, the image quality of digital cameras and video cameras has been improved, their prices have been lowered and their sizes have been made smaller. Lens barrels built in cameras are also required to be manufactured with higher precision to improve optical performance and achieve high image quality at lower cost and to be made small.

In lens barrels of optical apparatuses such as digital cameras, a voice coil motor is used as an actuator that drives a lens holding member during zooming or focusing.

FIG. 6shows the basic structure of a voice coil motor, which includes a magnet1, yoke2and a coil3. The yoke2has a looped shape inside which a magnet1is provided. A part of the yoke2is passing inside the coil3having an annular shape. Magnetic fluxes of the magnet1are perpendicular to the axial direction of the coil3, and the yoke2forms a closed magnetic circuit through which magnetic fluxes flow. When a current flows in the coil3, a Lorentz force associated with the magnetic fluxes of the magnet1is generated, and the coil3is subjected to a force in the axial direction.

FIG. 7is a perspective view of a lens holding member that is driven by this voice coil motor. The coil3is provided on a lens holding member5that holds a lens4, and the magnetic circuit element including the magnet1and the yoke2is provided on a fixed member such as an outer barrel that is not shown in the drawings. When the coil3is energized, a Lorentz force associated with the magnetic fluxes of the magnet1acts in the optical axis direction, so that the lens holding member5is subjected to a force in the optical axis direction.

In the lens holding member5, a sleeve5ais supported on a guide bar6ahaving an axis parallel to the optical axis, and a bearing5bis supported on a guide bar6b. The direction of movement of the lens holding member5is restricted to the forward and backward directions along the optical axis. Thus, when the lens holding member5is subjected to a force in the optical axis direction, the lens holding member5moves relative to the outer barrel on which the magnetic circuit element is mounted, so that the lens4held by the lens holding member5is moved.

Since the direction of the Lorentz force can be switched between the forward and backward directions of the optical axis by changing the direction of the current supplied to the coil3, the lens holding member5can be moved in the forward and backward directions along the optical axis. With the above structure, the lens barrel controls driving of the lens holding member5in zooming and focusing operations of the optical system.

In the above described bearing-sleeve-and-bar structure constituted by the lens holding member5and the guide bar6a, if fitting play that deteriorates operation performance occurs, the precision of operation of the lens holding member5deteriorates. However, to ensure operation of the lens holding member5while taking into account temperature conditions as well, the fitting play should not be eliminated completely. The play will cause displacement of the lens4held by the lens holding member5in a plane perpendicular to the optical axis and tilt of the lens relative to the optical axis. To avoid such deterioration of performance as much as possible, it is necessary to reduce the fitting play as much as possible or to separately provide a conventional mechanism for removing the play.

Japanese Utility Model Application Laid-Open No. H05-90418 discloses such a mechanism for removing the play.FIG. 8is a perspective view of this mechanism, in which a lens holding member12that holds a lens11is supported by a basic guide bar13and a rotation regulation guide bar14. The lens holding member12is adapted to be capable of sliding in the optical axis direction. The basic guide bar13made of a magnetic material is passing through guide holes12b(one of which is not shown inFIG. 8) formed on a bearing portion12aprovided in the lens holding portion12. Magnet members15a,15bare embedded above the guide holes12b. The lens holding member12is always biased in a direction transverse to the basic guide bar13by attraction force of the magnet members15a,15b. Thus, the play between the lens holding member12and the basic guide bar13is removed.

However, providing an additional mechanism like the conventional art shown inFIG. 8to remove the play leads to an increase in the number of parts and complexity of the structure and assembly, which makes the cost higher and prevents downsizing of the lens barrel due to an increase in the space required to accommodate the parts.

An object of the present invention is to eliminate the above described problems and to provide a lens barrel in which the fitting play that hampers precision of the lens barrel is removed by using a small number of parts.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a lens barrel comprising a lens holding member that holds a lens and a voice coil motor that drives the lens holding member along a guide member, wherein a magnetic member is fixedly attached on the lens holding member, and the lens holding member is shifted in one direction relative to the guide member by means of a magnetic attraction force acting between the magnetic member and a magnet of the voice coil motor.

According to a further aspect of the invention, in the lens barrel, a coil of the voice coil motor is fixedly attached on the lens holding member and a magnetic circuit element formed by a yoke of the voice coil motor and the magnet is fixedly attached on a fixed portion that holds the lens holding member.

According to a further aspect of the invention, in the lens barrel, the magnetic attraction force is generated utilizing a leakage flux from the yoke.

According to a further aspect of the invention, in the lens barrel, the lens holding member is shifted in one direction relative to all guide members by a resultant force of the magnetic attraction force and a gravitational force generated by the self weight of the lens holding member.

According to a further aspect of the invention, in the lens barrel, the guide member is a guide bar, and the lens holding member is supported by a sleeve provided on the lens holding member and the guide bar in such a way that the lens holding member can slide in the axial direction of the guide bar.

According to a further aspect of the invention, in the lens barrel, the entire length of the magnetic member with respect to the optical axis direction is in the range of the entire length of the magnet with respect to the optical axis direction all over the operation range of the lens holding member with respect to the optical axis direction.

According to the lens barrel of the present invention, the play between the lens holding member and the guide bar can be removed, and precise positioning and driving of the lens can be achieved.

DESCRIPTION OF THE EMBODIMENTS

The present invention will be described in detail based on an embodiment shown inFIGS. 1 to 5C.

FIG. 1is a side view of a voice coil motor as seen from a direction perpendicular to the optical axis of a lens barrel according to the embodiment, andFIG. 2is a front view thereof as seen from the direction of the optical axis. A magnet21is connected to a yoke22, which is composed of an upper yoke22a, a front yoke22b, a lower yoke22cand a rear yoke22dthat are connected in a loop shape. The lower yoke22cis inserted through a coil23. A magnetic member24is disposed in the vicinity of the magnet21of the voice coil motor. Magnet fluxes from the magnet21run in a closed magnetic circuit along the loop of the yoke22, and a part of the fluxes leaks from the closed magnetic circuit to planes perpendicular to the optical axis, whereby a magnetic path of a leakage flux φ is formed.

In this embodiment, use is made of a magnetic attraction force that the above mentioned leakage flux φ exerts on the magnetic member24. The magnitude of this magnetic attraction force can be adjusted by controlling the magnetic permeability of the magnetic member24, its shape and its distance from the magnet21.

FIG. 3is a perspective view of a lens holding member, andFIG. 4is a front view thereof. The coil23and the magnetic member24of the voice coil motor are fixedly attached on the lens holding member26that holds a lens25, and the magnetic circuit element including the magnet21and the yoke22is fixedly attached on an outer barrel of a lens barrel. A cylindrical bearing sleeve26aserving as a sliding shaft portion provided on the lens holding member26is supported by a guide bar27ain a slidable manner in a bearing-sleeve-and-bar mechanism. A bearing26bfor preventing rotation is supported by a guide bar27bwith its opening facing outside.

When the coil23is energized, a Lorentz force associated with magnetic fluxes of the magnet21is generated, whereby the lens holding member26is moved forward or backward in the direction of optical axis O along the guide bars27aand27bthat are inserted through the bearing sleeve26aand the bearing26brespectively. Due to the presence of leakage magnetic fluxes φ in planes perpendicular to the optical axis O, the magnetic member24is subjected to a magnetic attraction force M in such a direction that the bearing sleeve26is biased in a direction perpendicular to the axis of the guide bar27aand made closer to the magnet21, as shown by an arrow inFIG. 4. Accordingly, the bearing sleeve26ais shifted in one direction relative to the guide bar27a.

In the lens holding member26in which the magnetic member24is provided, the resultant force Fa of the aforementioned magnetic attraction force M and the gravitational force G by the self weight of the lens holding member26acts to remove the play. In addition, between the bearing26band the guide bar27balso, a force in a direction in which bearing26bis made closer to the guide bar27bacts on the bearing26b. The resultant force Fb of this force and the gravitational force G by the self weight acts to remove the play between the bearing26band the guide bar27b.

As shown inFIG. 5A, the movable range S of the magnetic member24along the optical axis is always within the range of the entire length L of the magnet21along the optical axis throughout the operation range of the lens holding member26in the optical axis direction. In other words, even in the state in which the lens holding member26is at its frontmost position with respect to the optical axis direction as shown inFIG. 5B, the front end of the magnetic member24with respect to the optical axis direction is rearward of the front end of the magnet21with respect to the optical axis direction.

In addition, even in the state in which the lens holding member26is at its rearmost position with respect to the optical axis direction as shown inFIG. 5C, the rear end of the magnetic member24with respect to the optical axis direction is forward of the rear end of the magnet21with respect to the optical axis direction.

Accordingly, the magnitude of the leakage flux φ from the yoke22is substantially uniform all over the entire length of the magnet21in the optical axis direction. Therefore, the magnetic attraction force of the magnet21acting on the magnetic member24is constant irrespective of where the lens holding member26is located in its operation range, and the biasing force for removing the play can be exerted stably on the lens holding member26.

As per the above, a voice coil motor is used as an actuator for driving the lens holding member26, and leakage fluxes φ from the closed magnetic circuit of the yoke22among the magnetic fluxes generated by the magnet21exert a magnetic attraction force M on the magnetic member24. Accordingly, the lens holding member26on which the magnetic member24is provided is subjected to the magnetic attraction force M in the direction toward the magnet21, and the magnetic attraction force M acts in a composite manner with the gravity G generated by the self weight of the lens holding member26. The resultant force biases the lens holding member26toward the guide bars27a,27b.

In other words, the lens holding member26is shifted in one direction relative to the guide bars27a,27b, whereby the play is removed. Consequently, displacement or tilt of the lens25due to fitting play is prevented, and high precision in lens drive control is achieved. Thus, the optical performance of the lens is enhanced.

As per the above, by providing a magnetic member24on a lens holding member26in a lens barrel equipped with a voice coil motor, play between the lens holding member26and a guide member can be removed. In this structure, an increase in the cost and an enlargement of the space required to accommodate parts involved by an increase in the number of parts and/or complexity of the structure and assembly can be made small as compared to conventional structures for removing play, and improvement in the optical performance of the lens barrel can be achieved at a low cost while saving space.

This application claims the benefit of Japanese Patent Application No. 2006-339482, filed Dec. 18, 2006, which is hereby incorporated by reference herein in its entirety.