Lens driving apparatus and optical apparatus having the same

An apparatus includes a driver configured to rotate a lead screw, a rack unit including a mated portion mated with the lead screw, the rack unit being coupled with the holder and configured to move along the lead screw as the lead screw is rotated by the driver, a first elastic member configured to force the mated portion against the lead screw with a first force F1, an opposed cog arranged opposite to the mated portion with respect to the lead screw and displaceable relative to the mated portion, and a second elastic unit configured force the opposed cog unit with a second force F2 toward the lead screw. F1<F2<F3 is satisfied where a force containing F3 is a component that opposes to F2, at least one of the mated portion and the lead screw getting damaged when F3 is applied between the mated portion and the lead screw.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens driving apparatus and an optical apparatus having the same.

2. Description of the Related Art

One conventionally known driving unit for a focusing or zooming lens holding frame includes a motor having a lead screw, and a rack unit that is coupled with the lens holding frame, mated with the lead screw, and configured to move along the lead screw as the motor rotates.

Japanese Patent Laid-Open No. (“JP”) 4-240609 discloses a configuration of a rack unit that includes two sub-units and is forced against a lead screw by a spring member.

JP 9-258087 discloses a rack unit that includes a mated portion, a forcing portion, and an opposed cog. The mated portion is arranged on one side of the lead screw, and the forcing portion is arranged on the other side. The mated portion is mated with the lead screw, and the fixed opposed cog is arranged on the opposite side of the mated portion and is offset in the optical-axis direction from the mated portion so as to prevent a cog skip (positional shift) upon impact. In addition, at an end of a movable range of the rack unit, an opposed cog is located at a non-threaded area of the lead screw so as to prevent cogging of the rack unit at the end of the movable range of the lens holding frame.

In the structure disclosed in JP 4-240609, the spring member must apply a considerable force in order to prevent a positional shift between the rack unit and the lead screw upon impact. Then, a load of the motor increases, a large and high-torque motor is required, and a larger size and an increased cost of the apparatus become problematic.

In the structure disclosed in JP 9-258087, a strong impact at the position other than the end of the movable range of the lens holding frame would cause a plastic deformation (cogging) between the mated portion and the lead screw, and at least one of the mated portion and the lead screw get damaged and become inoperable.

SUMMARY OF THE INVENTION

The present invention provides a lens driving apparatus and an optical apparatus having the same, which can prevent a positional shift and cogging between the rack unit and a lead screw.

The lens driving apparatus according to the present invention is configured to drive a holder configured to hold a lens, and includes a driver configured to rotate a lead screw, a rack unit including a mated portion mated with the lead screw, the rack unit being coupled with the holder and configured to move along the lead screw as the lead screw is rotated by the driver, a first elastic member configured to force the mated portion against the lead screw with a first force, an opposed cog arranged opposite to the mated portion with respect to the lead screw and displaceable relative to the mated portion, and a second elastic unit configured force the opposed cog unit with a second force toward the lead screw. The following conditional expression is satisfied F1<F2<F3, where F1is the first force, F2is the second force, and a force containing F3is a component that opposes to F2, at least one of the mated portion and the lead screw getting damaged when F3is applied between the mated portion and the lead screw.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a block diagram of an image pickup apparatus (optical apparatus) according to this embodiment, such as a video camera and a digital still camera.

InFIG. 1, L1is a first lens unit having a positive refractive power which is fixed during zooming. L2is a second lens unit having a negative refractive power which serves as a zooming lens unit configured to move in an optical-axis direction during zooming. L3is a third lens unit having a positive refractive power which is fixed. L4is a fourth lens unit having a positive refractive power and configured to move in the optical-axis direction during focusing. The first lens unit L1to the fourth lens unit L4constitute an image pickup optical system configured to form an optical image of an object.

Reference numeral1denotes a front barrel configured to hold the first lens unit L1. Reference numeral2denotes a first holder (lens holding frame) configured to hold the second lens unit L2. Reference numeral3denotes a fixed unit configured to hold the third lens unit L3. Reference numeral4denotes a second holder (lens holding frame) configured to hold the fourth lens unit L4. The first holder2and the second holder4are supported so that they can move in the optical-axis direction of the image pickup optical system.

Reference numeral5denotes a diaphragm unit configured to change an aperture diameter of the optical system. This diaphragm unit5is a guillotine type diaphragm configured to change an aperture diameter by moving two diaphragm blades in opposite directions utilizing a driver6.

An image pickup unit30includes, such as, an image pickup element (such as a CCD and a CMOS), a low-pass filter, and an infrared cutting filter, and is fixed in a back barrel (not illustrated). The image pickup unit30outputs an image pickup signal to a camera signal processor31.

The camera signal processor31amplifies and gamma-corrects an output of the image pickup unit30. A signal amplified and gamma-corrected by the camera signal processor31is output to the microcomputer32.

The microcomputer32receives a multiplicity of signals, processes them, outputs a multiplicity of signals in accordance with an input signal, and controls the optical apparatus. Reference numeral33is a recording unit configured to record an image signal processed by the microcomputer32, and a recording condition.

Reference numeral34denotes a diaphragm detector circuit configured to detect a rotating position of a driving magnet of the driver6utilizing a Hall element. The microcomputer32outputs a diaphragm driving signal to a diaphragm driving circuit so as to adjust the light quantity in accordance with an input signal, such as a rotating amount of the driver6from the diaphragm detector circuit34and an input signal from the camera signal processor31.

Reference numeral50denotes a zoom switch configured to instruct zooming. Reference numeral51denotes a focus switch configured to instruct manual focusing (in-focus operation) made by a photographer. Reference numeral52denotes a power switch.

The first holder (lens holding frame)2is moved in the optical-axis direction by the lens driving apparatus.FIGS. 2A to 2Care perspective views of the lens driving apparatus configured to drive the first holder (lens holding frame)2viewed with different angles.FIG. 3is a partially enlarged plane view of the lens driving apparatus.

FIG. 4Ais a partially exploded perspective view of the lens driving apparatus, where the lead screw8ais omitted.FIG. 4Bis a schematic partially sectional view of the lens driving apparatus.FIG. 5Ais a partially plane view of the lens driving apparatus, viewed with a different angle from that of each ofFIGS. 5B and 5C, where the lead screw8ais omitted.

As illustrated inFIG. 2A, the first holder2is supported by a pair of guide bars101,102that extend parallel to the optical-axis direction so that the first holder2can be moved in the optical-axis direction of the image pickup optical system. In addition, the first holder2includes, as illustrated inFIGS. 2A to 2Cand5A, a sleeve unit2a, a rotation-stop recess2b, a pair of engagement hole members2c,2d, and a stopper2e.

The lens driving apparatus includes a rack unit7, a zoom motor8, a lead screw8a, an opposed cog unit40, a torsion coil spring (first elastic member)46, a spring member (second elastic member)47.

The rack unit7is coupled, as illustrated inFIG. 1, with the first holder2, and includes a main cog (mated portion)71, a stopper72, an shaft73, a spring holder74, an shaft75, a tapered portion76, an engagement portion77, a stopping hole78, a rotation stopper79.

As illustrated inFIGS. 3 and 4A, the main cog serves as a mated portion that can be mated or engaged with the threaded portion of the lead screw8a.

The stopper72is recessed and engaged with one end46aof the torsion coil spring46at the bottom of the recess, and the torsion coil spring46applies the force F1as illustrated inFIG. 4B. As a result, the force F1normally presses the main cog71of the rack unit7against the lead screw8a. The first elastic member is not limited to the torsion coil spring.

The zoom motor8is an actuator (driver) configured to move the second lens unit L2in the optical-axis direction for zooming, and is driven by a driving signal from the zoom driving circuit35.

The lead screw8ais mated with the rack unit7, and the first holder2is moved in the optical-axis direction as the zoom motor8rotates. The lead screw8ais concentric with a rotor of the zoom motor8, and rotated by the zoom motor8. The lead screw8ais arranged so that its longitudinal direction is parallel to the optical axis of the image pickup optical system (or second lens unit L2). As illustrated inFIG. 3, D1denotes the outermost diameter of the lead screw8(which is a diameter of a thread tip), and D3is the innermost diameter (which is a diameter of the deepest point (bottom) in the groove).

The shaft73is engaged rotatably with the opposed cog unit40, and serves as a rotating shaft of the opposed cog unit40. The shaft73has a sectional shape that combines a rectangle and a partially projecting semicircle.

The opposed cog unit40includes an opposed cog41configured to prevent cog skip upon disturbance impact, such as a drop, and a pair of engagement hole members42engaged rotatably with the shaft73.

As illustrated inFIGS. 3 and 4B, the main cog71and the opposed cog41are opposite to each other with respect to the lead screw8a. As described later, since the main cog unit40is attached rotatably to the rack unit7, an interval between the main cog71and the opposed cog41is made variable.

As schematically illustrated inFIG. 4B, the ridges of the main cog71and the opposed cog41are parallel to each other. As illustrated inFIGS. 3 and 4B, the main cog71normally contacts the lead screw8awhereas the opposed cog does not normally contact or is separated from the lead screw8a(or there is a gap as illustrated inFIG. 3). The opposed cog41is configured to contact the thread of the lead screw8aonly when the main cog71goes across the thread.

When a load applies upon impact of a fall, etc. to the rack unit7in the optical-axis direction so as to separate the main cog71from the lead screw8a, the opposed cog41becomes mated with the lead screw8aand prevents a positional shift caused by the cog skip.

Herein, D2denotes a distance between a thread tip of the main cog71and a thread tip of the opposed cog41. At this time, the following conditional expression is satisfied. The expression 1 can prevent a positional shift between the main cog71and the lead screw8awith a simple structure:
D3≦D2<D1  (1)

A pair of engagement hole members42are provided at both sides of the opposed cog41, have U-shaped sections, and are engaged with the shaft73so that the engagement hole members42can be rotated around a centerline of the shaft73or an X1-X1axis approximately parallel to the optical axis illustrated inFIG. 4A.

Where the shaft73of the rack unit7is fixed, as illustrated in the right side ofFIG. 4A, a stopper73aof the shaft73prevents the opposed cog unit40having the engagement hole members42from rotating in a counterclockwise direction C2, and the opposed cog unit40is allowed to rotate only in the clockwise direction C1. Since the stopper73ais planar, its structure is simple. On the right side ofFIG. 4A, the stopper73ais perpendicular to the end surface of the engagement hole member42on the rack unit side, but the stopper73amay be upwardly inclined in the clockwise direction C1.

Thus, the stopper73aprevents the opposed cog41from displacing in a direction approaching to the lead screw8a(and the main cog71), and permits the opposed cog41to displace in a direction separating from the lead screw8a(and the main cog71). As a result, the distance D2is normally maintained constant.

In addition, a recessed stopper73bof the shaft73contacts the engagement hole members42and prevents the opposed cog unit40from rotating by larger than a predetermined angle in the clockwise direction C1.

The spring holder74is a projection that is inserted into a hollow46cof the torsion coil spring so as to hold the torsion coil spring46, and configured to project in the optical-axis direction from an end surface74aof the rack unit7. The one end46aof the torsion coil spring46is engaged with the stopper72, and the other end46bis engaged with a stopper2eof the first holder2. As a result, the torsion coil spring46applies the force F1as illustrated inFIG. 5B.

The spring portion of the torsion coil spring into which the spring holder74is inserted also serves as a compression spring. As illustrated inFIG. 5A, this spring portion is engaged with the end surface74aof the rack unit7at one end thereof and with the end2d1in the engagement hole member2dof the first holder2(on the side of the rack unit7) at the other end thereof. As a result, as illustrated inFIG. 5B, the torsion coil spring46includes a spring portion that applies a force F4between the rack unit7and the first holder2. The torsion coil spring46applying two forces F1and F4achieves multiple functions, and realizes the miniaturization and the cost reduction in comparison with providing two springs that apply these forces separately.

A pair of shafts75are cylindrical projections engaged rotatably with the engagement hole members2c,2dof the first holder2, and thereby the rack unit7is coupled with the first holder2. The centerline of the shaft75is an X2-X2axis that is parallel to the X1-X1axis, and located on the other side of the main cog71with respect to the X1-X1axis. One of the pair of shafts75is provided on the end of the spring holder74.

The shaft75located on the opposite side of the spring holder74has the tapered portion76. As illustrated inFIG. 5B, the force F4of the torsion coil spring46forces the tapered portion76against the engagement hole member2cin the optical-axis direction, and enables the first holder2to stably move with the rack unit7in the optical-axis direction.

In addition, the opposed cog unit40is engaged with a spring member47that serves as a flat spring having a J-shaped section. The spring member47includes an engagement groove47a, a forcing portion47b, and a stopping portion47c. The spring member47may be another elastic member, such as a wire spring or a torsion spring.

An engagement unit77is a projection that is provided under the shaft73illustrated inFIG. 4A(on the opposite side of the main cog71), and projects to the inside (or towards the opposed cog unit40). The bottom illustrated inFIG. 4Aof the engagement member is arranged in the engagement groove47aof the spring member47, and the stopping portion47cis inserted into and fixed in the engagement hole78. The forcing portion47bcontacts the back surface of the opposed cog41as illustrated inFIGS. 5B and 5C, and applies a (second) force F2to the opposed cog41towards the lead screw8a.

The (second) force F2of the spring member47forces the opposed cog41to the side of the lead screw8a(in the counterclockwise direction C2on the right side ofFIG. 4A), but its rotation is prohibited by the stopper73a. In other words, the opposed cog41is forced against the stopper73aby the force F2. As described above, the opposed cog41is normally spaced from the lead screw8a.

Herein, the following expression 2 is a conditional expression to prevent a positional shift and cogging between the main cog71of the rack unit7and the lead screw8a. Since the second force F2applied by the second elastic member is larger than the first force F1applied by the first elastic member to the main cog71, the cog skip (positional shift) can be prevented upon strong impact. In addition, the second force F2is set smaller than a force F3. The force F3is a component that opposes to the force F2and a force containing F3causes at least one of the main cog71and the lead screw8ato get damaged when the force F3is applied between the main cog71and the lead screw8a. As a result, the opposed cog unit40rotates in a direction separating from the rack unit7(or the opposed cog41displaces in a direction separating from the main cog71), and can prevent cogging of the rack unit7.
0<F1<F2<F3  (2)

The rotation stopper79has a thin rectangular plate shape, and is provided to the end opposite to the main cog71as illustrated inFIGS. 2B,4A, and5A, so that it can contact the stopper2eof the first holder2.

In the provisional assembly of the first holder2, the rack unit7is forced around the X2-X2axis by the force F1of the torsion coil spring46, and the rotation stopper79of the rack unit7is brought into contact with the stopper2e.

When the zoom motor8is incorporated, the main cog71is mated with the lead screw8a, the rotation stopper79of the rack unit7is separated from the stopper2e, and the main cog71is forced against the lead screw8aby the force F1.

Due to the strong impact force of a fall, when a force F3that occurs in a direction separating the opposed cog41from the lead screw8aexceeds the force F2as illustrated inFIG. 3, the opposed cog unit40is separated from the lead screw8aaround the X1-X1axis. Thereby, damages and cogging of the opposed cog41and the main cog71are prevented.

Reference numeral9denotes a photo-interrupter as a zoom initial-position detector. The photo-interrupter9electrically detects switching between shielding and transmitting of the light as a light shield (not illustrated) formed on the first holder2moves in the optical-axis direction, and detects a reference position of the first holder2in the optical-axis direction.

When the power switch52is turned on, the zoom motor8receives the driving signal from the zoom driving circuit35in accordance with the signal from the microcomputer32, the photo-interrupter9detects the initial position of the first holder2, and the first holder2moves to the predetermined initial position and stands by there. The zoom motor8is driven from the initial position by the number of steps corresponding to a manipulation of the zoom switch50. In other words, when the zoom switch50is manipulated, the microcomputer32determines a moving direction designated by the manipulation, and performs zooming.

Reference numeral11denotes an actuator (driver) configured to move the fourth lens unit L4in the optical-axis direction for focusing. The focus motor11is driven by the driving signal from the focus driving circuit36.

The second holder4is also supported by the pair of guide bars101,102that extend parallel to the optical-axis direction so that the second holder4can be moved in the optical-axis direction of the image pickup optical system. The second holder4is configured similar to the first holder2, and the second holder4is also moved in the optical-axis direction by a lens driving apparatus that is similar to that for the first holder2.

The lead screw11ais mated with a rack unit10that is provided to the second holder4that can be moved and guided in the optical-axis direction. As the focus motor11rotates, the second holder4moves in the optical-axis direction. The lead screw11ais arranged concentric to a rotor of the focus motor11and parallel to the optical axis of the image pickup optical system (or the fourth lens unit L4).

Reference numeral12denotes a photo-interrupter as a focus initial-position detector. The photo-interrupter12electrically detects switching between shielding and transmitting of the light as a light shield (not illustrated) formed on the second holder4moves in the optical-axis direction, and detects a reference position of the second holder4in the optical-axis direction.

When the power switch52is turned on, the focus motor11receives the driving signal from the focus driving circuit36in accordance with the signal from the microcomputer32, the photo-interrupter12detects the initial position of the second holder4, and the second holder4moves to the predetermined initial position and stands by there. The focus motor11is driven from the initial position by the number of steps corresponding to manipulations of the zoom switch50and the focus switch51. In autofocusing, the focus driving circuit36electrifies the focus motor11in accordance with the input signal from the microcomputer32and drives the fourth lens unit L4in the optical-axis direction.

In this embodiment, the rack unit7and the opposed cog unit40are separate units, and the opposed cog unit40is attached to the rack unit7so that the opposed cog unit40can rotate around the shaft73. Alternatively, the rack unit7and the opposed cog unit may be integrated with each other and have a U-shaped section as a whole, and a part corresponding to the opposed cog unit40may be displace relative to a part corresponding to the rack unit7through an elastic deformation.

This embodiment can prevent a positional shift (cog skip) between the main cog71and the lead screw8asince the second force F2is larger than the first force F1. In addition, since the second force F2is smaller than the force F3, cogging between the main cog71and the lead screw8acan be prevented and damages at least one of the main cog71and the lead screw8acan be prevented.

The lens driving apparatus of this embodiment can be used to move a lens holding frame or a holder other than the zooming lens holding frame and the focusing lens holding frame. The optical apparatus of this embodiment can be a portable digital camera, etc. which is likely to receive an impact of a fall, and thus a configuration of this embodiment is effective. However, a non-portable electronic apparatus is also subject to an impact by an earthquake, etc. Therefore, the optical apparatus of this embodiment is not limited to the portable electronic apparatus, and is broadly applicable to a driving (or moving) apparatus of an object.

This application claims the benefit of Japanese Patent Application No. 2011-126894, filed Jun. 7, 2011, which is hereby incorporated by reference herein in its entirety.