Mechanism for controlling position of optical element

An optical element position control mechanism includes an optical element holding member which holds an optical element of a photographing system; an advancing/retracting movement guide member which guides the optical element holding member in an optical axis direction of the photographing system to be movable in the optical axis direction; and a biasing device including an arm, the arm being swingable about a swing axis which is substantially orthogonal to the optical axis and being engaged with the optical element holding member. The biasing device simultaneously exerts via the arm both a biasing force in a direction of movement of the optical element holding member that is guided by the advancing/retracting movement guide member and a biasing force in a direction orthogonal to the direction of movement of the optical element holding member on the optical element holding member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mechanism for controlling the position of an optical element which is moved in an optical axis direction in an optical apparatus.

2. Description of the Related Art

In optical apparatuses such as cameras, a mechanism in which a guide shaft is inserted into a guide hole to be freely slidable relative to the guide hole with the lengthwise direction of the guide shaft being parallel to an optical axis, and another mechanism wherein a guide projection is engaged in a guide groove to be freely slidable relative to the guide groove with the lengthwise direction of the guide groove being parallel to an optical axis, are known in the art as an advancing/retracting movement guide mechanism for moving an optical element holding member which supports an optical element such as a lens group in an optical axis direction. The former type of guide mechanism which includes the guide shaft and the guide hole is disclosed in, e.g., Japanese Unexamined Patent Publication 2000-206391.

In aforementioned type of guide mechanisms, at each of the slidable portions between the guide hole and the guide shaft and between the guide groove and the guide projection, a predetermined clearance is created to make relative sliding movement possible. Furthermore, measures are taken to eliminate backlash to prevent rattle and noise which may be caused by the clearance and to make stable position-control possible.

SUMMARY OF THE INVENTION

The present invention provides an optical element position control mechanism which can easily eliminate backlash in the advancing/retracting movement guide mechanism for the optical element holding member in a space-saving manner.

According to an aspect of the present invention, an optical element position control mechanism is provided, including an optical element holding member which holds an optical element of a photographing system; an advancing/retracting movement guide member which guides the optical element holding member in an optical axis direction of the photographing system to be movable in the optical axis direction; and a biasing device including an arm, the arm being swingable about a swing axis which is substantially orthogonal to the optical axis and being engaged with the optical element holding member. The biasing device simultaneously exerts via the arm both a biasing force in a direction of movement of the optical element holding member that is guided by the advancing/retracting movement guide member and a biasing force in a direction orthogonal to the direction of movement of the optical element holding member on the optical element holding member.

It is desirable for the biasing device to be a torsion spring including a coiled portion supported by a support member provided separately from the optical element holding member, a central axis of the coiled portion being substantially coincident with the swing axis; a first arm portion which constitutes the arm and extends radially outwards from the coiled portion to be engaged with the optical element holding member; and a second arm portion which extends radially outward from the coiled portion to be engaged with the support member. The torsion spring varies an amount of resilient deformation thereof in a direction of rotation about the swing axis in accordance with movement of the optical element holding member. The first arm portion extends along a swing plane defined by a swing motion thereof about the swing axis, in a force-applied state of the biasing device in which the first arm is engaged with the optical element holding member. The first arm portion is positioned outside the swing plane in a free state of the biasing device in which the first arm is disengaged from the optical element holding member. The first arm portion is resiliently deformed in a direction so as to coincide with the swing plane when the biasing device is brought into the force-applied state from the free state.

It is desirable for the arm of the biasing device to include a lever pivoted at one end thereof on a support member, that is provided separately from the optical element holding member, the other end of the lever being engaged with the optical element holding member. The biasing device includes a lever biasing member for biasing the lever in one of forward and reverse rotational directions about the swing axis. The lever extends along a swing plane defined by swing motion thereof about the swing axis, in a force-applied state of the biasing device in which the lever is engaged with the optical element holding member. The lever is positioned outside the swing plane in a free state of the biasing device in which the lever is disengaged from the optical element holding member. The lever is resiliently deformed in a direction to approach the swing plane when the biasing device is brought into the force-applied state from the free state.

It is desirable for the advancing/retracting movement guide member to include a guide shaft, an axis of which extends in the optical axis direction. The optical element holding member includes a guide hole into which the guide shaft is inserted to be slidable. The arm of the biasing device is in contact with a contacting portion in a close vicinity of the guide hole and presses the optical element holding member in a manner to cause an inner wall surface of the guide hole to press against the guide shaft.

It is desirable for the optical element holding member to include a projection which projects from the contacting portion and is positioned within a swinging range of the arm of the biasing device to receive the biasing force in the direction of movement of the optical element holding member.

It is desirable for the optical element position control mechanism to include a pressing device which presses the biasing device in a direction orthogonal to the direction of movement of the optical element holding member when the biasing device is in a force-applied state in which the arm is engaged with the optical element holding member.

It is desirable for the pressing device to include a stationary wall member positioned at least one of inside and outside the biasing device. The arm of the biasing device is in contact with the stationary wall member to be pressed in the direction orthogonal to the direction of movement of the optical element holding member.

It is desirable for the stationary wall member to include an outer wall member which is positioned outside the arm of the biasing device and presses the biasing device in a direction to approach the optical axis.

It is desirable for the stationary wall member to include an inner wall portion positioned on the inner side of the biasing spring, the inner wall portion pressing the arm of the biasing device in a direction away from the optical axis.

It is desirable for the stationary wall member to include a pressing projection which is in pressing contact with the arm of the biasing device.

It is desirable for the arm of the biasing device to be formed to bulge toward the stationary wall member so that a bent portion of the biasing device comes in contact with the stationary wall member.

It is desirable for the arm of the biasing device to include a first extending portion which extends to the bent portion toward the stationary wall member and a second extending portion which extends from the bent portion away from the stationary wall member.

It is desirable for the optical element position control mechanism to include an inner cylindrical member positioned outside the optical element holding member; and an outer wall member positioned outside the optical element holding member so as to face the outer surface of the cylindrical member. The biasing device is held between the inner cylindrical member and the outer wall member and the arm of the biasing device is in pressing contact with one of the inner cylindrical member and the outer wall member to be pressed in a direction orthogonal to the direction of movement of the optical element holding member.

It is desirable for the optical element holding member to be guided linearly without rotating about the optical axis.

It is desirable for the optical element position control mechanism to be incorporated in a photographing lens unit, the support member constituting a stationary member of the photographing lens unit.

According to the present invention, backlash in the advancing/retracting movement guide portion can be eliminated by a simple and space-saving structure made of a small number of elements because the biasing device, which biases the holding member in the optical axis direction of the optical element to move the holding member in this direction, also biases the holding member in a direction orthogonal to the direction of movement of the holding member. In addition, a greater effect on the prevention of backlash in the advancing/retracting movement guide portion can be obtained by providing the optical element position control mechanism with a device for pressing the biasing device in the force-applied state in a direction orthogonal to the direction of movement of the holding member.

The present disclosure relates to subject matter contained in Japanese Patent Application No. 2007-291657 (filed on Nov. 9, 2007) and Japanese Patent Applications No. 2008-175178 (filed on Jul. 4, 2008) which are expressly incorporated herein by reference in their entireties.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, the overall structure of a zoom lens barrel1to which an optical element position control mechanism according to the present invention is applied will be hereinafter discussed with reference mainly toFIGS. 1 through 7.FIGS. 1 and 2each show a cross sectional view of the zoom lens barrel1,FIG. 1shows a state where the zoom lens barrel1is in a lens barrel accommodated state, in which no pictures are taken, an upper half of the cross sectional view inFIG. 2shows the zoom lens barrel1set at the wide-angle extremity, and a lower half of the cross sectional view inFIG. 2shows the zoom lens barrel1set at the telephoto extremity. FIGS.3and4are perspective views of the zoom lens barrel1in the lens barrel accommodated state, andFIGS. 5 and 6are perspective views of the zoom lens barrel1in a ready-to-photograph state.

The zoom lens barrel1is provided with a photographing optical system which includes a first lens group LG1, a second lens group LG2, a set of shutter blades (mechanical shutter) S that also serves as a diaphragm, a third lens group LG3, a low-pass filter (optical filter) LPF and an image-pickup device (image sensor)24such as CCD or CMOS, in that order from the object side. This photographing optical system is configured as a zoom optical system. A focal-length varying operation (zooming operation) is performed by moving the first lens group LG1and the second lens group LG2along an optical axis O of the photographing optical system in a predetermined moving manner, and a focusing operation is carried out by moving the third lens group LG3along the optical axis O. In the following descriptions, the expression “optical axis direction” includes the direction parallel to the optical axis O of the photographing optical system.

The zoom lens barrel1is provided with a housing (support member)22which supports the optical system from the first lens group LG1to the third lens group LG3inside the housing22to allow these lens groups to move in the optical axis direction. The zoom lens barrel1is provided with an image-pickup device holder23which is fixed to the back of the housing22. An opening is formed in a central portion of the image-pickup device holder23, and the image-pickup device24is held in the opening via an image-pickup device frame62. A filter frame21which is fixed to the front of the image-pickup device holding frame62holds the low-pass filter LPF. A packing (sealing member)61for dust prevention is tightly held between the low-pass filter LPF and the image-pickup device24. The image-pickup device frame62is supported by the image-pickup device holder23to make a tilt adjustment of the image-pickup device frame62relative to the image-pickup device holder23possible.

The housing22is provided around a cylindrical portion22athereof with a zoom motor support portion22b,an AF mechanism mounting portion22cand a front wall portion22d.The cylindrical portion22asurrounds the optical axis O, the zoom motor support portion22bsupports a zoom motor32, the AF mechanism mounting portion22csupports an AF motor30, and the front wall portion22dis positioned in front of the AF mechanism mounting portion22c.The cylindrical portion22asupports the aforementioned optical elements such as each lens group inside the cylindrical portion22aand forms a substantial outer-shape of the zoom lens barrel1. The zoom motor support portion22b,the AF mechanism mounting portion22cand the front wall portion22dare positioned radially outside the cylindrical portion22aabout the optical axis O. As shown inFIGS. 3 through 7, the AF mechanism mounting portion22cis formed in the vicinity of the rear end portion of the cylindrical portion22a,and the rear surface portion of the AF mechanism mounting portion22cis closed by the image-pickup device holder23. The front wall portion22dis formed on the housing22at a position forwardly away from the AF mechanism mounting portion22cin the optical axis direction to face the AF mechanism mounting portion22c.

The zoom lens barrel1is provided with a third lens group frame (optical element holding member)51which holds the third lens group LG3. The third lens group frame51is provided with a pair of guide arm portions51band51cwhich are formed to extend from a central lens holding portion51aof the third lens group frame51in substantially opposite radial directions symmetrical with respect to the optical axis O. The guide arm portion51bis provided in the vicinity of the radially outer end thereof with a pair of guide holes (front and rear guide holes which align in the optical axis direction)51dinto which a third lens group guide shaft (advancing/retracting movement guide member)52is inserted to be freely slidable relative to the pair of guide holes51d.The third lens group guide shaft52is fixed at the front and rear ends thereof to the housing22and the image-pickup device holder23, respectively. As shown inFIGS. 6 and 10, the third lens group guide shaft52is positioned outside the cylindrical portion22aof the housing22, and the front end portion of the third lens group guide shaft52is supported by the front wall portion22d.The rear end portion of the third lens group guide shaft52passes below the AF mechanism mounting portion22cand is engaged in a shaft support hole formed in the image-pickup device holder23. In order to be guided by the third lens group guide shaft52, the guide arm portion51bof third lens group frame51is formed so that a portion of the guide arm portion51bin the vicinity of the radially outer end thereof projects outwardly from the cylindrical portion22aof the housing22, and the cylindrical portion22ais provided with an opening22e(seeFIG. 7) which allows the guide arm portion51bfrom projecting outwardly from the cylindrical portion22a.The third lens group frame51is provided at the radially outer end of the other guide arm portion51cwith an anti-rotation projection51e,and the housing22is provided on an inner peripheral surface thereof with a linear guide groove22felongated in the optical axis direction in which the anti-rotation projection51eis engaged to be freely slidable. The axis of the third lens group guide shaft52and the lengthwise direction of the linear guide groove22fare parallel to the optical axis O, and the third lens group frame51is guided linearly in a direction parallel to the optical axis O to be movable in the same direction with the guide hole51dand the anti-rotation projection51ebeing guided by the third lens group guide shaft52and the linear guide groove22f,respectively. In addition, the third lens group frame51can be moved forward and rearward along the optical axis O by the AF motor30. The drive mechanism for the third lens group frame51will be discussed later.

The zoom lens barrel1is provided inside the zoom motor support portion22bof the housing22with a reduction gear train which transfers the driving force of the zoom motor32to a zoom gear31(seeFIGS. 6 and 7). The cam ring11that is supported inside the cylindrical portion22aof the housing22is provided at the rear end thereof with an annular gear11awhich is in mesh with the zoom gear31. The cam ring11is driven to rotate by the zoom motor32via the engagement of the annular gear11awith the zoom gear31. The cam ring11is provided on the annular gear11awith guide projections11b,and the housing22is provided on an inner peripheral surface of the cylindrical portion22awith cam ring control grooves22gin which guide projections11bare slidably engaged, respectively. Each cam ring control groove22gis composed of a lead groove portion and a circumferential groove portion, wherein the lead groove portion is inclined with respect to the direction of the optical axis O and the circumferential groove portion is made solely of a circumferential component about the optical axis O. When the zoom lens barrel1is in between the accommodated (fully retracted) state shown in FIG.1and the wide-angle extremity state shown by an upper half ofFIG. 2, by applying torque onto the cam ring11via the zoom motor32causes the cam ring11to move in the optical axis direction while rotating, with the guide projections11bbeing respectively guided by the aforementioned lead groove portions of the cam ring control grooves22g.More specifically, the cam ring11advances (toward the object side) in the optical axis direction while rotating when the zoom lens barrel1moves into the wide-angle extremity state (ready-to-photograph state) from the lens barrel accommodated state. Conversely, when the zoom lens barrel1moves into the lens barrel accommodated state from the wide-angle extremity state (ready-to-photograph state), the cam ring11retracts in the optical axis direction while rotating. On the other hand, when the zoom lens barrel1is in a ready-to-photograph state (in the zoom range) between the wide-angle extremity state and the telephoto extremity state, the guide projections11bof the cam ring11are positioned in the aforementioned circumferential groove portions of the cam ring control grooves22gso that the cam ring11rotates at a fixed position in the optical axis direction, i.e., without moving in the optical axis direction.

The zoom lens barrel1is provided inside the cylindrical portion22aof the housing22with a first advancing barrel13and a linear guide ring10which are supported inside the cylindrical portion22awith the cam ring11being positioned between the first advancing barrel13and the linear guide ring10. The first advancing barrel13is guided linearly in the optical axis direction by the engagement of linear guide projections13awhich project radially outwards from the first advancing barrel13with linear guide grooves22hwhich are formed on an inner peripheral surface of the cylindrical portion22a,respectively, and the linear guide ring10is guided linearly in the optical axis direction by the engagements of linear guide projections10awhich project radially outwards from the linear guide ring10with linear guide grooves22iwhich are formed on an inner peripheral surface of the cylindrical portion22a,respectively. Each of the first advancing barrel13and the linear guide ring10is coupled to the cam ring11to be rotatable relative to the cam ring11and to move with the cam ring11in the optical axis direction.

The linear guide ring10guides a second lens group moving frame8linearly in the optical axis direction by linear guide keys10b(seeFIG. 2) of the linear guide ring10which are positioned inside the cam ring11. The zoom lens barrel1is provided inside the second lens group moving frame8with a second lens holding frame6which holds the second lens group LG2. The second lens holding frame6is integral with the second lens group moving frame8. In addition, the first advancing barrel13is provided on an inner peripheral surface thereof with linear guide grooves13bextending parallel to the optical axis O, and the second advancing barrel12is provided with linear guide projections12awhich project radially outwards to be slidably engaged in the linear guide grooves13b,so that the second advancing barrel12is also guided linearly in the optical axis direction. The zoom lens barrel1is provided inside the second advancing barrel12with a first lens group holding frame4which holds the first lens group LG1.

The cam ring11is provided on an inner peripheral surface thereof with second-lens-group control cam grooves11c, and the second lens group moving frame8is provided on an outer peripheral surface thereof with cam followers8a, for moving the second lens group LG2, which are slidably engaged in the second-lens-group control cam grooves11c, respectively. Since the second lens group moving frame8is guided linearly in the optical axis direction via the linear guide ring10, a rotation of the cam ring11causes the second lens group moving frame8(the second lens group LG2) to move in the optical axis direction in a predetermined moving manner in accordance with the contours of the second-lens-group control cam grooves11c.

The second advancing barrel12is provided with cam followers12b,for moving the first lens group LG1, which project radially inwards, and the cam ring11is provided on an outer peripheral surface thereof with first-lens-group control cam grooves11din which the cam followers12bare slidably engaged, respectively. Since the second advancing barrel12is guided linearly in the optical axis direction via the first advancing barrel13, a rotation of the cam ring11causes the second advancing barrel12(the first lens group LG1) to move in the optical axis direction in a predetermined moving manner in accordance with the contours of the first-lens-group control cam grooves11d.

The second lens group moving frame8and the second advancing barrel12are biased in opposite directions away from each other by an inter-lens-group biasing spring27to improve the degree of precision of the engagement between each cam follower8aand the associated second-lens-control cam groove11cand the degree of precision of the engagement between each cam follower12band the associated first-lens-group control cam groove11d.

The zoom lens barrel1is provided inside the second lens group moving frame8with a shutter unit15including the set of shutter blades S which are supported by the second lens group moving frame8. The zoom lens barrel1is provided behind the second lens group moving frame8with a rear-mounted limit member5, and the second lens group moving frame8and the rear-mounted limit member5are provided with a guide projection8band a guide projection5aas a pair of projections which project in directions toward each other along a direction parallel to the optical axis O. The shutter unit15is supported by the two guide projections8band5ato be slidable thereon in the optical axis direction.

A decorative plate16having a photographing aperture16ais fixed to the front end of the second advancing barrel12, and the zoom lens barrel1is provided immediately behind the decorative plate16with a set of protective barrier blades17which opens and shuts the photographing aperture16athat is positioned in front of the first lens group LG1.

Operations of the zoom lens barrel1that has the above described structure will be discussed hereinafter. In the lens barrel accommodated state shown inFIGS. 1,3and4, the length of the optical system in the optical axis direction (the distance from the front surface (object-side surface) of the first lens group LG1to the imaging surface of the image-pickup device24) is shorter than that in a ready-to-photograph state shown inFIGS. 2,5and6. In the lens barrel accommodated state, upon a state transitional signal for transition from the lens barrel accommodated state to a ready-to-photograph state (e.g., turning ON a main switch of the camera to which the zoom lens barrel1is mounted) is turned ON, the zoom motor32is driven in the lens barrel advancing direction. This causes the zoom gear31to rotate, thus causing the cam ring11to move forward in the optical axis direction while rotating with the guide projections11bbeing guided by the lead groove portions of the cam ring control grooves22g,respectively. The linear guide ring10and the first advancing barrel13linearly move forward with the cam ring11. This rotation of the cam ring11causes the second lens group moving frame8to move in the optical axis direction in a predetermined moving manner due to the engagements between the cam followers8aand the second-lens-group control cam grooves11c.In addition, the rotation of the cam ring11causes the second advancing barrel12, which is guided linearly in the optical axis direction via the first advancing barrel13, to move in the optical axis direction in a predetermined moving manner due to the engagements between the cam followers12band the first-lens-group control cam grooves11d.

Namely, the amount of advancement of the first lens group LG1from the lens barrel accommodated state is determined by the sum of the amount of forward movement of the cam ring11relative to the housing22and the amount of advancement of the second advancing barrel12relative to the cam ring11, and the amount of advancement of the second lens group LG2from the lens barrel accommodated state is determined by the sum of the amount of forward movement of the cam ring11relative to the housing22and the amount of advancement of the second lens group moving frame8relative to the cam ring11. A zooming operation is carried out by moving the first lens group LG1and the second lens group LG2on the optical axis O while changing the air distance between the first lens group LG1and the second lens group LG2. Driving the zoom motor32in a barrel-advancing direction so as to advance the zoom lens barrel from the lens barrel accommodated state shown inFIG. 1firstly causes the zoom lens barrel1to move to the wide-angle extremity shown in the upper half of the cross sectional view inFIG. 2, and further driving the zoom motor32in the same direction causes the zoom lens barrel1to move to the telephoto extremity shown in the lower half of the cross sectional view inFIG. 2. In the zooming range between the telephoto extremity and the wide-angle extremity, the cam ring11only performs the above described fixed-position rotating operation while the guide projections11bare engaged in the cam ring control grooves22gof the housing22, respectively, thus not moving either forward or rearward in the optical axis direction. Upon the main switch being turned OFF, the zoom motor32is driven in the lens barrel retracting direction, which causes the zoom lens barrel1to perform a lens barrel retracting operation reverse to the above described lens barrel advancing operation, thus returning the zoom lens barrel1back to the lens barrel accommodated state shown inFIG. 1.

The set of shutter blades S are positioned behind the second lens group LG2when the zoom lens barrel1is in a ready-to-photograph state as shown inFIG. 2. When the zoom lens barrel1moves from a ready-to-photograph state to the lens barrel accommodated state that is shown inFIG. 1, the shutter unit15is moved forward relative to the second lens group moving frame8, inside the second lens group moving frame8, in the optical axis direction so that a part of the second lens group LG2and the set of shutter blades S lie in a plane orthogonal to the optical axis O. In addition, the set of protective barrier blades17are closed when the zoom lens barrel1is in the lens barrel accommodated state. The set of protective barrier blades17are opened in accordance with the advancing operation of the zoom lens barrel1, in which the zoom lens barrel1is extended into a ready-to-photograph state.

The third lens group frame51that supports the third lens group LG3can be moved forward and rearward in the optical axis direction by the AF motor30independently of the above described driving operations of the first lens group LG1and the second lens group LG2that are performed by the zoom motor32. In addition, when the zoom lens barrel1is in a ready-to-photograph state at any focal length from the wide-angle extremity to the telephoto extremity, the third lens group frame51that supports the third lens group LG3is moved along the optical axis direction to perform a focusing operation by driving the AF motor30in accordance with object distance information obtained by a distance measuring device (not shown) provided in, e.g., the camera to which the zoom lens barrel1is mounted.

The details of the position control mechanism for controlling the position of the third lens group frame51will be discussed hereinafter. As described above, the AF mechanism mounting portion22cis formed on the housing22so as to be positioned outside the cylindrical portion22a,and the front wall portion22dis formed on the housing so as to be positioned in front of the AF mechanism mounting portion22cto face thereto. The AF motor30is fixed to the front of the AF mechanism mounting portion22cby a set screw33so that a pinion30afixed on the rotary shaft of the AF motor30projects rearward from the back surface of the AF mechanism mounting portion22c(seeFIG. 6). An intermediate gear34which is engaged with the pinion30aand a driven gear35which is engaged with the intermediate gear34are rotatably supported on a back surface of the AF mechanism mounting portion22c.The driven gear35is fixed to the rear end of a lead screw (screw shaft)36. Rotation of the rotary shaft of the AF motor30is transferred to the lead screw36, via the pinion30a,the intermediate gear34and the driven gear35which constitute a reduction gear train of AF drive mechanism. The front and rear ends of the lead screw36are fitted in a front shaft hole and a rear shaft hole which are formed in the front wall portion22dof the housing22and the image-pickup device holder23to be rotatably supported thereby, respectively, so that the lead screw36can freely rotate on an axis of rotation substantially parallel to the optical axis O.

The third lens group frame51is provided at the radially outer end of the guide arm portion51bwith a nut abutting portion51f.A through hole into which the lead screw36is inserted is formed through the nut abutting portion51f.An AF nut37which is screw-engaged with the lead screw36is installed in front of the nut abutting portion51f.The AF nut37is prevented from rotating by the engagement of an anti-rotation recess37a(seeFIG. 7) of the AF nut37with an anti-rotation projection51g(seeFIG. 8) of the third lens group frame51and the engagement of an anti-rotation projection37bof the AF nut37with an anti-rotation recess (not shown) formed in the housing22. Rotating the lead screw36forward and reverse causes the AF nut37to move forward and rearward in a direction parallel to the optical axis O without rotating with the lead screw36. The third lens group frame51is provided, in the vicinity of the radially outer end of the guide arm portion51bbetween the pair of guide holes51d,with an upright wall portion (contacting portion)51kwhich is formed in a flat shape substantially parallel to the optical axis O. The third lens group frame51is provided on the upright wall portion51kwith a spring hook51hwhich projects laterally from the upright wall portion51k.The spring hook51his formed in an L-shaped projection which is bent so that the front end faces rearwardly in the optical axis direction. The third lens group frame51is provided, behind the spring hook51hon a side of the upright wall portion51k,with a semicircular-cross-sectional portion51m.

The zoom lens barrel1is provided therein with a torsion spring38serving as a biasing device which gives the third lens group frame51a biasing force in a direction to move the third lens group frame51along the optical axis O. The torsion spring38has a coiled portion38a.The coiled portion38ais supported by a spring support projection22jformed on the housing22. The spring support projection22jis shaped into a cylindrical projection and formed on an outer surface of the cylindrical portion22awith the axis of the spring support projection22jextending in a direction substantially orthogonal to a vertical plane P1(seeFIG. 10) parallel to the optical axis O (the vertical plane P1includes the optical axis O). The coiled portion38aof the torsion spring38is held onto the cylindrical outer surface of the spring support projection22jwhile being prevented from slipping off the spring support projection22jby screwing a set screw39in a screw hole formed through the center of the spring support projection22j.The central axis of the coiled portion38aheld to the spring support projection22jis substantially coincident with the central axis of the spring support projection22j.

The torsion spring38is provided with a short support arm portion (second arm portion)38band a long biasing arm portion (arm/first arm portion)38c,each of which projects radially outward from the coiled portion38a.The short support arm portion38bis hooked onto a spring hook (projection)22k(seeFIG. 12) which is formed on the housing22in the vicinity of the spring support projection22j.On the other hand, the free end of the biasing arm portion38cis hooked onto the spring hook51hof the third lens group frame51. The upright wall portion51kand the semicircular-cross-sectional portion51mof the third lens group frame51also have a function to prevent the biasing arm portion38cfrom coming in contact with any nearby parts other than the spring hook51hupon the biasing arm portion38cbeing brought into engagement with the spring hook51h.The biasing arm portion38cserves as a swingable force-applied portion capable of swinging about a swing axis38x(fulcrum) substantially coincident with the axis of the coiled portion38a(i.e., capable of swinging in a swing plane substantially parallel to the vertical plane P1). In other words, the biasing arm portion38cis swingable about the swing axis38xwhich is substantially orthogonal to the optical axis O.

When in a free state where the biasing arm portion38cis not hooked on the spring hook51h,the biasing arm portion38cextends vertically downward from the coiled portion38awith respect toFIG. 12as shown by a two-dot chain line designated by a reference numeral38c(F) inFIG. 12. From this state, rotating the biasing arm portion38cby a substantially half rotation counterclockwise with respect to38c(F) ofFIG. 12and hooking a portion of the biasing arm portion38cat the free end thereof onto the rear surface of the spring hook51hin the optical axis direction, the amount of resilient deformation (twist) of the torsion spring38increases, and the resilience of the torsion spring38acts as a load on the spring hook51hwhich makes the biasing arm portion38cpress against the spring hook51hin a direction toward the front of the optical axis direction. Namely, the torsion spring38comes into a force-applied state in which a biasing force of the torsion spring38toward the front in the optical axis direction is applied to the third lens group frame51via the biasing arm portion38c.

In this manner, the third lens group frame51, to which a biasing force toward the front in the optical axis direction is applied by the torsion spring38, is prevented from moving forward by the abutment of the nut abutting portion51fagainst the AF nut37. Namely, as shown inFIGS. 8,9and12, the third lens group frame51is held with the nut abutting portion51fbeing in contact with the AF nut37by the biasing force of the torsion spring38, and the position of the third lens group frame51in the optical axis direction is determined according to the AF nut37. Since the AF nut37is moved forward and rearward in a direction parallel to the optical axis O via the lead screw36by rotating the pinion30aof the AF motor30forward and reverse, the position of the third lens group frame51in the optical axis direction is controlled in accordance with the driving direction and the driving amount of the AF motor30. For instance, if the AF nut37is moved forward by the AF motor30, the third lens group frame51follows the forward movement of the AF nut37via the biasing force of the torsion spring38to move forward by the amount of the forward movement of the AF nut37. Conversely, if the AF nut37is moved rearward from the forward moved position thereof, the AF nut37presses the nut abutting portion51frearward, so that the third lens group frame51is moved rearward against the biasing force of the torsion spring38.

An origin position sensor40for detecting the limit of rearward movement of the third lens group frame51in the optical axis direction that is moved by the AF motor30is installed in the housing22. The origin position sensor40is constructed from a photo-interrupter which includes a body having a U-shaped cross section with a light emitter and a light receiver which are provided thereon so as to face each other with a predetermined distance therebetween, and it is detected that the third lens group frame51is positioned at the limit of rearward movement thereof when a sensor interrupt plate51iformed integral with the third lens group frame51passes between the light emitter and the light receiver. The AF motor30is a stepping motor. The amount of movement of the third lens group LG3when a focusing operation is performed is calculated as the number of steps for driving the AF motor30with the limit of rearward movement being taken as the point of origin.

The limit of rearward movement of the third lens group frame51in the range of movement thereof that is controlled by the AF motor30is shown by a solid line inFIG. 12, and the limit of forward movement of the third lens group frame51in the same range of movement thereof is shown by a two-dot chain line inFIG. 12.FIG. 14Ashows variations in load of the torsion spring38in accordance with positional variations of the third lens group frame51in the optical axis direction. The degree of the swing angle of the biasing arm portion38cof the torsion spring38from the position in a free state thereof when the third lens group frame51is at the limit of rearward movement is represented by θmax, and the degree of the swing angle of the biasing arm portion38cof the torsion spring38from the position in a free state thereof when the third lens group frame51is at the limit of forward movement is represented by θmin (seeFIG. 12). In addition, the loads of the torsion spring38which correspond to the swing angles θmin and θmax are represented by Fmin and Fmax, respectively. As can be seen fromFIG. 12, the amount of angular displacement θv between the minimum swing angle θmin and the maximum swing angle θmax when the torsion spring38is in the aforementioned force-applied state is far smaller than the minimum swing angle θmin that ranges from a free state of the torsion spring38until when the torsion spring38comes into the force-applied state. Therefore, the variation from the minimum load Fmin to the maximum load Fmax in the range of movement of the third lens group frame51can be reduced to a minimum.

FIG. 13shows a comparative example in which the torsion spring38is replaced by an extension spring38′ which expands and contracts in a direction parallel to the optical axis O. One end of the extension spring38′ is hooked onto a spring hook51h′ of a third lens group frame51′ (which corresponds to the third lens group frame51) and the other end of the extension spring38′ is hooked onto a spring hook22j′ of a housing22′ (which corresponds to the housing22). The third lens group frame51′ is movable forward and rearward in the optical axis direction along a third lens group guide shaft52′ (which corresponds to the third lens group guide shaft52), and the limit of rearward movement and the limit of the forward movement of the third lens group frame51′ in the range of movement thereof that is controlled by an AF motor30′ (which corresponds to the AF motor30) are represented by a solid line and a two-dot chain line, respectively. In addition, inFIG. 13, the length of the extension spring38′ with the position of engagement with the spring hook22j′ of the housing22′ as a reference position when the third lens group frame51is at the limit of forward movement thereof is represented by Lmin, and the length of the extension spring38′ with the position of engagement with the spring hook22j′ of the housing22′ as a reference position when the third lens group frame51is at the limit of rearward movement thereof is represented by Lmax. Since the spring hook22j′, the position of which is fixed, is positioned at the front of the optical element position control mechanism, the extension spring38′ becomes longest (Lmax) when the third lens group frame51′ is positioned at the limit of rearward movement thereof. Lf shown inFIG. 13designates the length of the extension spring38′ when it is in a free state.

FIG. 14Bshows variations in load of the extension spring38′ in the comparative example shown inFIG. 13. Fmin′ inFIG. 14Brepresents the spring load when the length of the extension spring38′ is Lmin, and Fmax′ inFIG. 14Brepresents the spring load when the length of the extension spring38′ is Lmax. As can be understood fromFIG. 13, the displacement Lv2between the minimum length Lmin and the maximum length Lmax (in a force-applied state where a biasing force of the extension spring38′ toward the front in the optical axis direction is applied to the third lens group frame51′) is far greater than the displacement Lv1from the length Lf (the length when the extension spring38′ is in a free state) until when the extension spring38′ comes into the force-applied state. Since the magnitude of the load of the extension spring38′ varies in proportion to the variation in length of the extension spring38′, the difference between the load Fmin′ when the length of the extension spring38′ is the minimum length Lmin and the load Fmax′ when the length of the extension spring38′ is the maximum length Lmax becomes extremely large in the extension spring38′. In addition, the AF motor30′ needs to be a high-power motor in order to cope with the maximum load Fmax′.

To reduce the load variation, namely, to reduce the difference in length of the extension spring38′ between the maximum length Lmax and the minimum length Lmin, it is conceivable that an extension spring having a longer length in a free state will be adopted as the extension spring38′. However, if such a long extension spring is adopted as the extension spring38′, a corresponding larger space will be necessary, which runs counter to the demand for miniaturization of the zoom lens barrel. The comparative example shown inFIG. 13is substantially identical in structure of the embodiment shown inFIG. 12except for the extension spring38′. If an extension spring having a longer length is adopted as the extension spring38′, the spring hook22j′ has to be provided in front (on the right-hand side with respect toFIG. 13) of the position of the front end of the zoom lens barrel (which substantially corresponds to the position of the front end of the housing22′) in the accommodated state. Namely, adopting an extension spring having a longer length as the extension spring38′ causes an increase in length of the zoom lens barrel in the accommodated state. In this respect, a maximum length which is structurally possible in the zoom lens barrel has been given to the extension spring38′ in the comparative example shown inFIG. 13, and accordingly, it is difficult to reduce the load variation to a small degree more than the degree shown inFIG. 14Bwhile maintaining the current size of the zoom lens barrel in the accommodated state, so that it is impossible to satisfy both the demand for miniaturization of the zoom lens barrel and the demand for a reduction of the load variation simultaneously.

If the range of movement of the third lens group frame51′ is reduced (if the limit of rearward movement of the third lens group frame51′ is set in front of that shown by a solid line inFIG. 13), it is possible to reduce the maximum load of the extension spring38′ with no need to lengthen the length of the extension spring38′ in a free state; however, such a reduction of the range of movement of the third lens group frame51′ inevitably limits the range of movement of the third lens group LG3, so that a required optical performance may not be obtained. Accordingly, it is not practical to reduce the range of movement of the third lens group frame51′.

Although the extension spring38′ is used in the comparative example shown inFIG. 13, the same problem arises even if the extension spring38′ is replaced by a compression spring. Namely, regardless of as to whether the spring member for biasing the third lens group frame51′ is an extension spring or a compression spring, it is difficult to achieve a balance between miniaturization of the zoom lens barrel and a reduction of the load variation of the spring member in the particular biasing structure in which the spring member which expands and contracts in the direction of forward/rearward movement of the third lens group frame51′ is directly connected between the third lens group frame51′ and a stationary member (the housing22′).

In contrast, in the above described embodiment of the optical element position control mechanism that uses the torsion spring38as a biasing device for biasing the third lens group frame51, the load variation of the torsion spring38is far smaller than that in the comparative example and also the maximum load of the spring is smaller than that in the comparative example even though the torsion spring38is a biasing device installed in an installation space which is equal in size to that in the comparative example, as can be understood by the comparison between the graphs inFIGS. 14A and 14B. As a result, the energy required for driving the third lens group frame51is averaged at a low level, which makes it possible to reduce the power consumption of the AF motor30. In other words, a power-saving type of AF motor can be adopted as the AF motor30. In addition, since the load variation in accordance with movement of the third lens group frame51is small, the third lens group frame51can be driven smoothly over the entire range of movement thereof; moreover, noise does not easily occur from the drive mechanism for transmitting a driving force from the AF motor30to the third lens group frame51.

As described above, in the torsion spring38, the amount of angular displacement (θv) of the biasing arm portion38cin the force-applied state between the limit of forward movement and the limit of rearward movement of the third lens group frame51is smaller than the minimum swing angle (θmin) of the biasing arm portion38c,which ranges from a free state thereof until when the torsion spring38comes into the force-applied state, and a conditional expression “θv/θmin<1” is satisfied, which minimizes the load variation in the force-applied state. Although the degree of the minimum swing angle θmin is set to substantially a half rotation in the embodiment shown inFIG. 12, the amount of angular displacement (θv) of the biasing arm portion38cin the working section in the force-applied state can be made relatively small by increasing the value of the minimum swing angle θmin that serves as a denominator of the aforementioned conditional expression (the amount of angular displacement θv is constant since the maximum swing angle θmax increases as the minimum swing angle θmin increases), which makes it possible to achieve a further reduction of the difference between the maximum load and the minimum load of the torsion spring38. Although the load variation is effectively suppressed by satisfying the conditional expression “θv/θmin<1”, a better effect is obtained if a conditional expression “θv/θmin<0.5” is satisfied. As a practical technique to increase the value of the minimum swing angle θmin, the biasing arm portion38ccan be hooked on the spring hook51hafter being twisted through 360-degree or more about the coiled portion38a(about the swing axis38x) from a free state of the biasing arm portion38c.Since the torsion spring38does not substantially change the size thereof even if the amount of resilient deformation of the torsion spring38in a rotation direction about the axis of the coiled portion38a(the swing axis38x) is increased, the space for the installation of the torsion spring38does not have to be increased, unlike the above described case in the comparative example where an extension spring or a compression spring which has a longer length in a free state is adopted. If conditions such as the thickness of the steel wire of the spring are the same, the load of the torsion spring38averagely increases if the amount of resilient deformation of the torsion spring38which ranges from a free state thereof until when the torsion spring38comes into the force-applied state is increased, so that the amount of resilient deformation of the torsion spring38is set within a range in which the maximum load thereof does not become excessively great.

Also, one of the factors which have minimized the load variation of the torsion spring38is the length of the biasing arm portion38cfrom the coiled portion38a,about which the biasing arm portion38cswings, to the force application point (working point) on the third lens group frame51. The greater the length of the biasing arm portion38from the swing axis38xto the force application point, i.e., the greater the radius of rotation of the swing operation of the torsion spring38in the vicinity of the free end thereof, the smaller the displacement angle (θv) of the biasing arm portion38cper unit of displacement of the third lens group frame51, thereby making it possible to curb variations in the spring load. Assuming a horizontal plane P2which is substantially parallel to the swing axis38xof the torsion spring38and includes the optical axis O, the spring hook51hat which the biasing arm portion38cis hooked onto the third lens group frame51is positioned in the area above the horizontal plane P2as shown inFIG. 10. On the other hand, the spring support projection22jof the housing22, which supports the coiled portion38athat serves as the swing axis of the torsion spring38, is positioned in the area below the horizontal plane P2. Therefore, the biasing arm portion38cof the torsion spring38is elongated in the vertical direction across the horizontal plane P2. Since the torsion spring38is installed radially outside the cam ring11that is a rotatable member in the zoom lens barrel1, it is possible for such a long length be given to the biasing arm portion38cwithout the biasing arm portion38cinterfering with any movable members associated with the first lens group LG1or the second lens group LG2that is driven by the cam ring11.

In addition, also in regard to the shape of the front projection view of the zoom lens barrel1, the position control mechanism for controlling the position of the third lens group frame51that includes the torsion spring38has been installed in the zoom lens barrel1in a space saving manner. As shown inFIG. 10, elements of the zoom lens barrel1such as the third lens group guide shaft52(which is an element of a guide mechanism for the third lens group frame51), the AF nut37, the AF motor30and the lead screw36(which are elements of the drive mechanism for the third lens group frame51) are installed in a substantially triangular space formed above the horizontal plane P2along an outer peripheral surface of the cylindrical portion22aof the housing22. The coiled portion38aof the torsion spring38is supported in another substantially triangular space formed below the horizontal plane P2, wherein the two substantially triangular spaces that are respectively formed above and below the horizontal plane P2are substantially symmetrically positioned with respect to the horizontal plane P2. Although the shapes of front projectional views of optical devices such as a camera to which the zoom lens barrel1is mounted are often based on a rectangular shape (e.g., having a rectangular housing), such a configuration makes it possible to accommodate the position control mechanism for controlling the position of the third lens group frame51effectively in a dead space created between a rectangular housing portion of the camera and an outer peripheral surface of the cylinder-shaped housing portion22a.In addition, as can be seen fromFIG. 10, the biasing arm portion38cof the torsion spring38is elongated in close vicinity of the cylindrical portion22a,extending toward the upper triangular space from the lower triangular space in a manner such that the biasing arm portion38cof the torsion spring38is substantially tangent to an outer peripheral surface of the cylindrical portion22a.Therefore, the installation of the torsion spring38outside the cylindrical portion22ahas little effect on the lateral width of the zoom lens barrel1.

As described above, the mechanism for biasing the third lens group frame51by the torsion spring38in the above described embodiment of the optical element position control mechanism can reduce load on the AF motor30to thereby achieve a reduction in power consumption of the AF motor30while contributing to miniaturization of the zoom lens barrel1, especially to a reduction of the length of the zoom lens barrel1in the accommodated state.

A second embodiment of the optical element position control mechanism according to the present invention will be hereinafter discussed with reference toFIGS. 15 and 16. Movements of the third lens group frame51are controlled by the lead screw36and the AF nut37in the first embodiment of the optical element position control mechanism. However, in the second embodiment of the optical element position control mechanism, instead of a lead screw, a lead cam shaft136is used as an element of a drive mechanism for driving a lens frame (optical element holding member)151which holds a lens group LG. The lens frame151is guided linearly in a direction parallel to the optical axis O by a guide shaft (advancing/retracting movement guide member)152and an anti-rotation shaft153which extend parallel to the optical axis O. The guide shaft152is slidably inserted into a guide hole formed through a cylindrical portion151aof the lens frame151, and the anti-rotation shaft153is slidably engaged in an anti-rotation groove151dformed on a portion of the lens frame151on the opposite side of the lens frame151from the cylindrical portion151a,wherein the anti-rotation groove151dand the cylindrical portion151aare substantially symmetrically positioned with respect to the optical axis O. A guide pin151bprojects from the cylindrical portion151athat is guided by the guide shaft152. The guide pin151bis engaged in a lead groove136aformed on a peripheral surface of the lead cam shaft136. The lead groove136aincludes a pair of axially opposed guide surfaces which are inclined with respect to the direction of the optical axis O, and a predetermined clearance is created between the guide pin151band the pair of axially opposed guide surfaces to allow the guide pin151bto slide thereon. The lead cam shaft136is provided at one end thereof with a gear135. By applying a torque to the lead cam shaft136via the gear135by a motor130causes the lead cam shaft136to rotate about an axis of rotation parallel to the optical axis O. Thereupon, the guide pin151bis guided while sliding on the pair of axially opposed guide surfaces of the lead groove136a,which causes the lens frame151to move in the optical axis direction.

A torsion spring (biasing device)138is supported by an outer peripheral surface of a cylinder-shaped spring support projection122jwith a coiled portion138aof the torsion spring138being fitted on the spring support projection122jand with the axis of the coiled portion138aextending in a direction orthogonal to the optical axis O. The position of the spring support projection122jis fixed. The torsion spring138includes a support arm portion (second arm portion)138band a biasing arm portion (arm/first arm portion)138cboth of which project radially outwards from the coiled portion138a,and the support arm portion138bis engaged with a fixed projection122kwhile the free end of the biasing arm portion138cis engaged with a spring hook (projection)151cof the lens frame151. In this spring-engaged state, the biasing arm portion138cof the torsion spring138can swing about a swing axis138xwhich is substantially orthogonal to the optical axis o and substantially coincident with the axis of the coiled portion138athat is supported by the spring support projection122j,and biases the lens frame151forward in the optical axis direction (leftward direction with respect toFIG. 15). This biasing force causes the guide pin151bto be pressed against one of the pair of axially opposed guide surfaces of the lead groove136awhich is closer to the front in the optical axis direction to eliminate backlash between the guide pin151band the lead groove136a.Since the spring hook151cis formed at substantially a center of the cylindrical portion151ain the lengthwise direction thereof, a tilting moment acting on the cylindrical portion151ato tilt the cylindrical portion151arelative to the guide shaft152does not easily occur upon the spring hook151creceiving the load of the torsion spring138, which ensures smooth movement of the lens frame151in the optical axis direction.

According to the torsion spring138, in a similar manner to the torsion spring38of the first embodiment, variations of the spring load in the force-applied state can be reduced and loads on the motor130can be reduced when the lens frame151is moved forward and rearward in the optical axis direction via the motor130and the lead cam shaft136. In addition, similar to the position control mechanism for controlling the position of the third lens group frame51that includes the torsion spring38, the space for the installation of the torsion spring138does not increase even if the amount of rotation of the biasing arm portion138cis changed when the torsion spring138is brought to come into the force-applied state from a free state, hence, the position control mechanism for controlling the position of the lens frame151that includes the torsion spring138is installed in a space saving manner. Additionally, as can be understood from the second embodiment shown inFIGS. 15 and 16, the application of the biasing device to an optical element holding member in the present invention is not limited to the application like that in the first embodiment which is directly concerned in the driving operation of a forward/rearward moving member, and the biasing device can also be used to eliminate backlash, just like the torsion spring138. As a drive mechanism for driving a holding member such as the lens frame151, the present invention is not limited solely to the above described particular structure using a combination of a groove and a projection like a combination of the lead groove136and the guide pin151b;for instance, a structure using a face cam (end-face cam) or the like is possible. In short, the present invention is widely applicable so long as the drive mechanism is of a type that is required to eliminate backlash between a guide surface and a follower which is in sliding contact with the guide surface.

The torsion spring38that is made of a single torsion spring in the above described first embodiment is the biasing device which biases the third lens group frame51, and the torsion spring138that is made of a single torsion spring in the above described second embodiment is the biasing device which biases the lens frame151. However, the biasing device is not limited to such a single torsion spring if the biasing device satisfies the requirement that the biasing device gives a biasing force to an optical element holding member (51or151) via a swingable force-applied portion (arm) capable of swinging about the swing axis which is substantially orthogonal to the optical axis of the optical element held by the optical element holding member.

Third through fifth embodiments of the optical element position control mechanism that use different biasing devices will be hereinafter discussed with reference toFIGS. 17 through 21. Each embodiment which will be discussed below is similar in structure to the first embodiment except for the biasing device and the structure associated therewith, and elements which are similar to those of the first embodiment of the optical element position control mechanism are designated by the same reference numerals and given the same member names.

In the third embodiment shown inFIGS. 17 through 19, the biasing device for biasing the third lens group frame51is composed of a combination of swing lever (arm/lever)70and a torsion spring (lever biasing member)238. The housing22is provided with a swing support projection22mwhich projects laterally from the housing22(so that the axis of the swing support projection22mextends in a direction substantially orthogonal to the vertical plane P1), and the swing lever70is provided at one end thereof with a shaft hole70ainto which the swing support projection22mis inserted so that the swing lever70is freely rotatable about the swing support projection22mand swingable about a swing axis70x(fulcrum) which is substantially orthogonal to the optical axis O and substantially coincident with the axis of the swing support projection22m.The other end (free end) of the swing lever70engages with a lever engaging projection51jformed on the third lens group frame51. The coiled portion238aof the torsion spring238is fitted on the swing support projection22mto be supported by the outer peripheral surface of the swing support projection22m.The torsion spring238biases the swing lever70clockwise with respect toFIG. 19with a support arm portion238band a biasing arm portion238cbeing hooked onto a fixed projection22nof the housing22and a portion of the swing lever70in the vicinity of the swing support projection22m,respectively, wherein each of the support arm portion238band the biasing arm portion238cextends radially outwards from the coiled portion238a.The biasing force of the torsion spring238on the swing lever70is exerted in a manner so as to press the third lens group frame51forward in the optical axis direction via the lever engaging projection51j.

The swing lever70itself has no resiliency in the swinging direction thereof. However, with a biasing force given to the swing lever70from the torsion spring238, a combination of the biasing arm portion238cof the torsion spring238and the swing lever70substantially function as a swingable force-applied portion, similar to the biasing arm portion38cof the torsion spring38in the first embodiment of the optical element position control mechanism or the biasing arm portion138cof the biasing spring138in the second embodiment of the optical element position control mechanism. Therefore, just like the biasing devices of the previous (first and second) embodiments, the load on the AF motor30can be reduced by reducing the load variation in the force-applied state to the third lens group frame51even through the biasing device can be arranged in a space-saving manner in the optical axis direction. Unlike the third embodiment, it is possible to make the coiled portion238aof the torsion spring238supported by a support portion different from the swing support projection22mof the swing lever70.

A fourth embodiment shown inFIG. 20is similar to the third embodiment shown inFIGS. 17 through 19except that the torsion spring238is replaced by an extension spring (lever biasing member)338as a biasing member for biasing the swing lever70that is adopted in the third embodiment. The swing lever70is provided with a main arm70bwhich extends from the pivoted portion (shaft hole70a) of the swing lever70in a direction to engage with the lever engaging projection51jof the third lens group frame51, and is further provided with a spring-hooked arm70cwhich extends from the pivoted portion (shaft hole70a) of the swing lever70in a direction substantially opposite to the direction of extension of the main arm70b.The extension spring338is installed so that the axis thereof extends substantially parallel to the optical axis O with one and the other ends of the extension spring338being hooked on the spring-hooked arm70cand a spring hook22p formed on the housing22, respectively. In the swing lever70, a distance D1from the swing axis70xto an engaging portion El of the swing lever70which engages with the lever engaging projection51jis greater than a distance D2from the swing axis70xto an engaging portion E2of the swing lever70which engages with the extension spring338; namely, D1>D2. Due to the ratio (lever ratio) between the length of the main arm70band the spring-hooked arm70c,the amount of movement of the engaging portion E1on the main arm70b(the amount of rotation of the engaging portion E1about the swing axis70x) per unit of movement of the third lens group frame51in the optical axis direction is greater than the amount of movement the engaging portion E2on the spring-hooked arm70c(the amount of rotation of the engaging portion E2about the swing axis70x) per unit of movement of the third lens group frame51in the optical axis direction. Consequently, as can be understood upon comparison betweenFIG. 13andFIG. 20, a displacement Lv3between the minimum length Lmin and the maximum length Lmax of the extension spring338in a force-applied state to the third lens group frame51is smaller than the displacement Lv2of the comparative example shown inFIG. 13, so that the load variation can be reduced to a smaller degree than the case of using a single extension spring as a biasing device for biasing the third lens group frame51, which makes it possible to lighten the load on the AF motor30by reducing the maximum load.

A fifth embodiment shown inFIG. 21is similar to the fourth embodiment shown inFIG. 20except that the extension spring338of the fourth embodiment is replaced by an extension spring (lever biasing member)438which is different in tensile direction from the extension spring338. The swing lever70is provided with a spring-hooked arm70dwhich projects from the pivoted portion (shaft hole70a) of the swing lever70in a direction substantially orthogonal to the direction of extension of the main arm70b,i.e., at a substantially right angle relative to the main arm70b.The extension spring438is installed so that the axis thereof extends substantially in the vertical direction of the zoom lens barrel, that corresponds to the direction of elongation of the main arm70b,with one end of the extension spring438being hooked onto the spring-hooked arm70dand the other end of the extension spring438being hooked onto a spring hook22qformed on the housing22. In the swing lever70, the distance D1from the swing axis70xto an engaging portion E1of the swing lever70which engages with the lever engaging projection51jis greater than a distance D3from the swing axis70xto an engaging portion E3of the swing lever70which engages with the extension spring438, namely, D1>D3. Accordingly, when the third lens group frame51moves forward and rearward in the optical axis direction, the amount of movement of the engaging portion E1on the main arm70b(the amount of rotation of the engaging portion E1about the swing axis70x) is greater than the amount of movement the engaging portion E3on the spring-hooked arm70d(the amount of rotation of the engaging portion E3about the swing axis70x). Consequently, the displacement Lv4between the minimum length Lmin and the maximum length Lmax of the extension spring438in a force-applied state to the third lens group frame51is small (smaller than the displacement Lv2of the comparative example shown inFIG. 13), so that the load variation can be reduced to a smaller degree than the case of using a single extension spring as a biasing device for biasing the third lens group frame51, which makes it possible to lighten the load on the AF motor30by reducing the maximum load.

In the fourth embodiment, it is desirable that the ratio between the length of the main arm70bof the swing lever70(D1) and the length of the spring-hooked arm70c(D2) satisfy the following conditional expression: D2<D1/2. Likewise, in the fifth embodiment, it is desirable that the ratio between the length of the main arm70bof the swing lever70(D1) and the length of the spring-hooked arm70d(D3) satisfy the following conditional expression: D3<D1/2.

As can be understood from the fourth and fifth embodiments, with the swing lever70provided as a biasing device for biasing the third lens group frame51, the load variation of the biasing device can be reduced by a structure which is designed compact in the optical axis direction even if an extension spring which expands and contracts in the axial direction thereof is adopted instead of a torsion spring. From this point of view, a similar effect is obtained even if the extension spring338or438in the fourth or fifth embodiment is replaced by a biasing device composed of a combination of a compression spring and a swing lever.

In addition, in each of the above described embodiments, the biasing device which biases the third lens group frame51or the lens frame151in a direction along the optical axis o to move the frame51or151in the same direction also imposes a load in a direction orthogonal to the moving direction of the frame51or151on the frame51or151, which eliminates backlash of the frame51or151in the advancing/retracting movement guide mechanism.

The biasing arm portion38cof the torsion spring38in the first embodiment extends along a swing plane (defined by the swinging movement of the biasing arm portion38cshown by a solid line inFIGS. 10 and 11) orthogonal to the swing axis38x,and swings in the swing plane as described above when the third lens group frame51moves along the optical axis O in the force-applied state, in which the biasing arm portion38cof the torsion spring38is engaged with the spring hook51h.Note that the spring hook51his positioned within a swinging range of the biasing arm portion38cdefined by the radial length of the biasing arm portion38c.When the biasing arm portion38cof the torsion spring38is in a free state, in which the biasing arm portion38cis not engaged with the spring hook51h,the biasing arm portion38cis inclined with respect to the swing plane (i.e., is positioned outside the swing plane) and has a shape inclined toward the optical axis O as shown by a two-dot chain line inFIGS. 10 and 11. When the biasing arm portion38cis brought into the force-applied state, in which the biasing arm portion38cof the torsion spring38is engaged with the spring hook51h,the biasing arm portion38cis resiliently deformed by being rotated counterclockwise with respect toFIGS. 10 and 11until coming into contact with the upright wall portion51kformed on the third lens group frame51(so that the biasing arm portion38ccoincides with the above described swing plane) to be prevented from returning to a free state. The upright wall portion51kis formed in a flat shape substantially parallel to the swing plane of the biasing arm portion38c,and the third lens group frame51is provided on the upright wall portion51kwith the semicircular-cross-sectional portion51mwhich comes in contact with the biasing arm portion38c.The spring hook51h,which is formed on the third lens group frame51to project therefrom, is positioned in front of the semicircular-cross-sectional portion51m.

Upon the biasing arm portion38cbeing brought into contact with the upright wall portion51k(the semicircular-cross-sectional portion51m) while being resiliently deformed from a free state, the upright wall portion51kof the third lens group frame51is biased rightward with respect toFIGS. 10 and 11by the resiliency of the biasing arm portion38c.The upright wall portion51kis formed immediately below the pair of guide holes51dthat are formed in the vicinity of the radially outer end of the guide arm portion51b,and the load on the upright wall portion51kfrom the biasing arm portion38cacts as a pressing force which urges the pair of guide holes51drightward with respect toFIGS. 10 and 11. As a result, the inner wall surfaces of the pair of guide holes51dare pressed against the third lens group guide shaft52to thereby eliminate play between the third lens group guide shaft52and the pair of guide holes51din a direction orthogonal to the direction of movement of the third lens group frame51(direction along the optical axis O). In addition, a moment of force acts on the anti-rotation projection51eand the linear guide groove22fthat are symmetrically positioned on the opposite side of the optical axis O from the pair of guide holes51dand the third lens group guide shaft52so that the anti-rotation projection51eis pressed against one of the opposed guide surfaces in the linear guide grooves22fto eliminate backlash between the anti-rotation projection51eand the linear guide groove22f.Accordingly, the third lens group frame51is held with stability with no variations in position which may be caused by the clearance created in the advancing/retracting movement guide mechanism. This stable holding state is maintained even if the third lens group frame51is moved to any position since the biasing force imposed on the upright wall portion51kfrom the biasing arm portion38cis continuously imposed on the upright wall portion51kas long as the torsion spring38remains in the force-applied state. This makes it possible to move the third lens group frame51smoothly with no backlash or noise being produced. Additionally, the positional accuracy of the third lens group frame51in a plane orthogonal to the optical axis O in a state where the third lens group frame51is stopped is improved. It should be noted that the upright wall portion51kand the semicircular-cross-sectional portion51mof the third lens group frame51also have a function to prevent the biasing arm portion38cfrom coming in contact with any nearby parts other than the spring hook51hupon the biasing arm portion38cis brought into engagement with the spring hook51h.

Since the torsion spring38(the biasing arm portion38c) that biases the third lens group frame51in a direction along the optical axis O also serves as a biasing device which applies a biasing force to the upright wall portion51kin a direction orthogonal to the direction of movement of the third lens group frame51, backlash between the third lens group frame51and the elements for guiding the third lens group frame51in the optical axis direction such as the third lens group guide shaft52and the linear guide groove22fcan be eliminated by a simple and space-saving structure made of a small number of elements with no need to provide an independent biasing member used exclusively for eliminating the backlash.

Similar to the biasing arm portion38cof the torsion spring38in the first embodiment, the biasing arm portion138cof the torsion spring138in a free state (where the biasing arm portion138cis not hooked onto the spring hook151c) in the second embodiment also has a shape inclined toward the optical axis O with respect to the position of the biasing arm portion138cin the swing plane (in the force-applied state shown by a solid line inFIG. 16) as shown by a two-dot chain line inFIG. 16. In addition, when the biasing arm portion138cis brought into the force-applied state, in which the biasing arm portion138cis hooked onto the spring hook151c,the biasing arm portion138cis resiliently deformed clockwise with respect toFIG. 16, and the resiliency of the biasing arm portion138ccauses the biasing arm portion138cto press an outer surface portion (contacting portion) of the cylindrical portion151aof the lens frame151leftward with respect toFIG. 16. This pressing force prevents the lens frame151from rattling relative to the guide shaft152and stabilizes the position of the lens group LG in a plane orthogonal to the optical axis O. Namely, the torsion spring138has the following two functions: the function of biasing the lens frame151in the direction of movement thereof and the function of biasing the lens frame151in a direction orthogonal to the direction of movement thereof, thus making it possible to hold the lens frame151with stability by a simple and space-saving structure constructed from a small number of elements.

The swing lever70in each of the third through fifth embodiments is also configured to impose a load on the third lens group frame51in a direction orthogonal to the direction of movement of the third lens group frame51. Taking the swing lever70in the third embodiment as a representative of the swing lever in each of the third through fifth embodiments, the swing lever70is resiliently deformable in a direction orthogonal to the optical axis O, and the swing lever70in a free state (where the swing lever70is not hooked on the spring hook51h) has a shape inclined toward the optical axis O with respect to the position of the swing lever70in the swing plane in the force-applied state (shown by a solid line inFIGS. 17 and 18) as shown by a two-dot chain line inFIGS. 17 and 18. In addition, when the swing lever70is brought into the force-applied state, in which the swing lever70is hooked onto the spring hook51h, the swing lever70is resiliently deformed counterclockwise with respect toFIGS. 17 and 18to be brought into contact with the upright wall portion51k(the semicircular-cross-sectional portion51m) of the third lens group frame51, and the swing lever70presses the upright wall portion51krightward with respect toFIGS. 17 and 18by the resiliency of the swing lever70. This pressing force prevents the third lens group frame51from rattling relative to the third lens group guide shaft52and the linear guide groove22fand stabilizes the position of the third lens group LG3in a plane orthogonal to the optical axis O. Namely, the swing lever70has the following two functions: the function of biasing the third lens group frame51in the direction of movement thereof by the biasing force of the torsion spring238and the function of biasing the third lens group frame51in a direction orthogonal to the direction of movement thereof, thus making it possible to hold the third lens group frame51with stability by a simple and space-saving structure made of a small number of elements. Although the details will not be discussed in the following descriptions, the swing lever70in each of the fourth and fifth embodiments also has the multiple function of biasing the third lens group frame51in two different directions.

FIGS. 22 through 26show modified embodiments, each of which is structured to be capable of giving a biasing force to a holding member which holds an optical element in a direction orthogonal to the direction of movement of the holding member in a more effective manner. These modified embodiments are substantially identical to the above described first embodiment except several portions are different in structure from those of the first embodiment, and the descriptions of elements which are similar to those of the first embodiment are omitted from the following descriptions.

FIGS. 22 and 23show a first modified embodiment. In this embodiment, the image-pickup device holder23is provided with a main body portion23aand a protective wall portion (pressing device/stationary wall member/outer wall member)23b.The main body portion23aholds the image-pickup device24and closes the back of the cylindrical portion (pressing device/stationary wall member/inner wall member/inner cylindrical member)22aof the housing22, and the protective wall portion23bextends forward in the optical axis direction from the main body portion23a.The protective wall portion23bfaces an outer peripheral surface of the cylindrical portion22ato form an accommodation space Q between the protective wall portion23band the outer peripheral surface of the cylindrical portion22a.The torsion spring38is held in the accommodation space Q. As described above, the biasing arm portion38cof the torsion spring38in a free state has a shape inclined toward the optical axis O as shown by a two-dot chain line inFIG. 23, and is resiliently deformed as shown by a solid line inFIG. 23when in the force-applied state, in which the biasing arm portion38cis engaged with the spring hook51h.A spring pressing portion (pressing projection)23cwhich is in pressing contact with the biasing arm portion38cin the force-applied state is formed on the protective wall portion23bof the back wall23. As shown inFIG. 22, the spring pressing portion23cis formed on a surface of the protective wall portion23bfacing the accommodation space Q (i.e., facing a surface of the projective wall portion23bwhich faces an outer peripheral surface of the cylindrical portion22a) to have the shape of a rib-like projection elongated in the optical axis direction. The spring pressing portion23cremains in contact with the biasing arm portion38cwherever the third lens group frame51is positioned within the range of movement thereof.

The amount of projection of the spring pressing portion23cis determined so that the spring pressing portion23cpresses the biasing arm portion38cin a direction toward the upright wall portion51k(the semicircular-cross-sectional portion51m) when the biasing arm portion38cis hooked onto the spring hook51h. Therefore, it is possible to cause the biasing force of the torsion spring38, in a direction orthogonal to the direction of movement of the third lens group frame51, to reliably act on the third lens group frame51and to satisfactorily eliminate backlash between the third lens group guide shaft52(which serves as an advancing/retracting movement guide member of the third lens group frame51) and the guide hole51d.

FIG. 24shows a second modified embodiment. This modified embodiment is similar to the first modified embodiment in that a pressing force by the spring pressing portion23cthat is formed on the protective wall portion23bof the image-pickup device holder23is imposed on the biasing arm portion38cof the torsion spring38in the force-applied state shown by a slid line shown inFIG. 24. However, the second modified embodiment is different from the first modified embodiment in that a cylindrical portion22a′ of the housing22in the second modified embodiment is not a complete cylindrical body, i.e., the cylindrical portion22a′ is an incomplete cylindrical body in which a portion thereof, corresponding to a portion of the cylindrical portion22athat faces the protective wall portion23b, is missing. Due to this modification, the coiled portion38aof the torsion spring38is fitted on a spring hook23dformed on the protective wall portion23b,not on the cylindrical portion22a′, to be supported by the spring hook23d,and a spring fixing screw39′ is screwed in the spring hook23dto prevent the coiled portion38afrom coming off the spring hook23d.In this manner, the tubular member (the cylindrical portion22a′) positioned on an inner side with respect to the biasing device (the torsion spring38) (i.e., positioned farther from the protective wall portion23bthan the biasing device) does not necessarily have to be completely cylindrical in shape; in this case, it is effective to form a pressing portion on an outer wall member (the protective wall portion23b) for pressing the biasing device (torsion spring38).

FIG. 25shows a third modified embodiment. The third modified embodiment is similar to each of the above described first and second modified embodiments in that the biasing arm portion38cof the torsion spring38is pressed against the protective wall portion23bof the image-pickup device holder23to make a biasing force in a direction orthogonal to the direction of movement of the third lens group frame51securely act on the third lens group frame51; however, the third modified embodiment is different from each of the first and second modified embodiments in that a similar biasing force is securely made to act on the third lens group frame51by utilizing the particular shape of the biasing arm portion38cin the third modified embodiment without utilizing a spring pressing portion23c.Specifically, the biasing arm portion38cof the torsion spring38in the third modified embodiment is provided with an outwardly extending portion (first extending portion)38c-1, a bent portion38c-2and an inwardly extending portion (second extending portion)38c-3which are formed to bulge toward the protective wall portion23bat the bent portion38c-2. The outwardly extending portion38c-1extends obliquely toward the protective wall portion23bfrom the coiled portion38a(in a direction away from the cylindrical portion22a), the bent portion38c-2is continuously formed

FIG. 26shows a fourth modified embodiment. In this modified embodiment, a pressing portion which presses against the biasing arm portion38cof the torsion spring38is formed on the cylindrical portion22aof the housing22, not on the protective wall portion23bof the image-pickup device holder23, contrary to the first through third modified embodiments. In the fourth modified embodiment, the biasing direction of the biasing arm portion38cto an advancing/retracting movement guide portion (the third lens group guide shaft52and the guide hole51d) of the third lens group frame51is the reverse to that in the case shown inFIGS. 23 through 25. When the biasing arm portion38cis resiliently deformed to come into the force-applied state shown by a solid line inFIG. 26from a free state shown by a two-dot chain line inFIG. 26, the biasing arm portion38cpresses an upright wall portion51k′ (a semicircular-cross-sectional portion51m′) formed at an end of the spring hook51hin a direction away from the optical axis O. The cylindrical portion22ais provided on an outer peripheral surface thereof with a spring pressing portion (pressing projection)22rwhich projects into the accommodation space Q (in a direction to approach the protective wall portion23b), and the spring pressing portion22rpresses the protective wall portion23bin the force-applied state in a direction to approach the upright wall portion51k′ (the semicircular -cross-sectional portion51m′). Accordingly, in this fourth modified embodiment, a biasing force in a direction orthogonal to the direction of the movement of the third lens group frame51can also be made to reliably act on the third lens group frame51by the biasing arm portion38cof the torsion spring38.

In an embodiment in which the biasing arm portion38cis pressed by the cylindrical portion22a,the biasing arm portion38ccan be formed to have a bent portion like the biasing arm portion38cof the torsion spring38of the third modified embodiment. Namely, although the biasing arm portion38cis bent to bulge toward the protective wall portion23bin the embodiment shown inFIG. 25, it is possible that the biasing arm portion38cbe bent to bulge toward the cylindrical portion22ato make the bent portion press against the cylindrical portion22a.However, it is desirable that a specific pressing portion like the spring pressing portion22rbe formed on an outer peripheral surface of the cylindrical portion22ato secure stability when the bent portion of the biasing arm portion38cis pressed against the cylindrical portion22a.

Although each of the first through fourth modified embodiments has been applied to the biasing arm portion38cof the torsion spring38of the first embodiment, each of the first through fourth modified embodiments can also be applied to the biasing arm portion138cof the torsion spring138of the second embodiment and the swing levers70of the third through fifth embodiments. In the force-applied state of the biasing arm portion138cor the swing lever70, a greater effect on the prevention of backlash of the advancing/retracting movement guide member is obtained by pressing the biasing arm portion138cor the swing lever70in a direction orthogonal to the direction of movement of the holding member (51or151) that is guided by the advancing/retracting movement guide member (the third lens group guide shaft52/the guide shaft152).

Although the above described embodiments according to the present invention have been discussed with reference to the accompanied drawings, the present invention is not limited solely to these particular embodiments. For instance, although an optical element moved forward and rearward in the optical axis direction is provided as a lens group for focusing in the above illustrated embodiments, the present invention is applicable to a position control mechanism for controlling the position of an optical element other than a lens group for focusing.

Although the support arm portion38bof the torsion spring38in the first embodiment, the support arm portion238bof the torsion spring238in the third embodiment, and one end of each of the extension springs338and438of the fourth and fifth embodiments are each engaged with a projection formed on the housing22, the member on which this projection is formed is not limited to a stationary member such as the housing22and can be a movable member as long as the member on which the projection is formed is movable relative to at least the holding member corresponding to the third lens group frame51. Likewise, the support member which pivots the lever70in the third through fifth embodiments is not limited to a stationary member such as the housing and can be a movable member as long as it is movable relative to at least the holding member corresponding to the third lens group frame51.

In addition, in each of the above described embodiments, the biasing arm portion38cof the torsion spring38, the biasing arm portion138cof the torsion spring138and the swing lever70all have a linear shape, and the biasing arm portion38cof the torsion spring38, the biasing arm portion138cof the torsion spring138and the swing lever70are made to swing about the swing axes38x,138xand70xin a fixed swing plane, respectively, in the force-applied state, in which the biasing arm portion38cor138cor the swing lever70is engaged with the third lens group frame51or the lens frame151. However, in the present invention, the swingable force-applied portion (swingable portion) is not limited to such a linear-shaped member. For instance, like the bent-shaped biasing arm portion38cshown inFIG. 25, the swingable force-applied portion can be formed into various shapes. If the swingable force-applied portion is not formed into a simple linear-shaped portion or is formed to be inclined to a direction orthogonal to the swing axis even in the force-applied state, the traveling path of the swingable force-applied portion will not simply lie in a plane. However, if attention is focused on a specific portion of the swingable force-applied portion, the swingable force-applied portion can be assumed to be moved in a fixed plane about the swing axis. In the present invention, a plane orthogonal to the swing axis in which the traveling path of this specific portion lies is defined as a swing plane.