JP2004070013A - Lens drive mechanism and imaging unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely hold a lens so as not to become out of a predetermined alignment position when an impact is applied. <P>SOLUTION: A lens drive mechanism is provided with a lead screw 6a which rotates by the drive of a stepping motor 6, a rack 5 engaged in the state of holding the lead screw 6a, a lens holding frame 2 holding a lens 1 and being connected to the rack 5, and a means for increasing holding force which increases the force holding the lead screw 6a of the rack 5 when the force along in the axial direction of the lead screw 6a is applied from the lens holding frame 2 to the rack 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lens driving mechanism that drives a lens by moving a rack in parallel by rotation of a screw by a motor, and an imaging apparatus.
[0002]
[Prior art]
In recent years, in imaging devices such as digital still cameras and digital video cameras, portability and ease of use have been demanded, and the size of the entire device has been reduced. Miniaturization of lenses is also being promoted. On the other hand, there is a strong demand for higher image quality and higher pixels, and even though the lens, which is a component of the optical system, is large, there is a demand for downsizing as an optical system barrel by downsizing the drive mechanism. In some cases.
[0003]
A lens driving device in an optical system barrel of an imaging device such as a digital still camera and a digital video camera is described in Japanese Utility Model Laid-Open No. 2-71155, and Japanese Patent Publication No. 2725491 is an extension of the technology. Proposed.
[0004]
That is, a motor having a lead screw parallel to the optical axis direction is arranged near the lens holding frame that is the driven member, and the rack gear of the rack provided on the lens holding frame that is the driven member meshes with this lead screw. At the same time, a spring member that opposes the rack gear and applies a predetermined pressure to the lead screw is disposed.
[0005]
This allows the rack to be rotatable in the direction orthogonal to the lens holding frame in the optical axis direction and to rotate in the direction perpendicular to the lens holding frame, to function to engage the rack with the lead screw, and to attach the rack to the lens holding frame without play. With one coil spring having a function, the number of parts is reduced, the assembly is facilitated, and the cost is reduced.
[0006]
[Problems to be solved by the invention]
In a lens driving mechanism constituted by such a conventional technique, when a large shock or acceleration is applied to an imaging device (such as when a camera is hit during photographing), a load acting on a rack in an axial direction is instantaneously applied. As a result, the torque for rotating the output shaft of the stepping motor increases, and the lead screw of the stepping motor rotates, which causes a problem that the lens cannot be held at a predetermined position.
[0007]
Further, when the lens is displaced from a predetermined position, it is necessary to perform the initialization operation by the reset sensor again, so that a time loss is forced when the user uses the camera, and there is a problem that a photographing timing is missed. .
[0008]
Also, by providing a sensor system for position detection to avoid re-initialization operation, a feedback circuit can be configured, but the number of components increases, the configuration becomes complicated and large, and assembly becomes complicated, resulting in cost reduction. There is a problem of being high.
[0009]
Further, there is a problem in that the lens, the lens holding frame, the driving mechanism, and the like come into contact with other lens barrel constituent members due to the above-mentioned positional shift and are physically destroyed. Here, in order to prevent the displacement, it is conceivable to always apply a large voltage assuming a large impact, load, and acceleration to the stepping motor. Contrary to the demand for low power consumption for continuous shooting time), there is a problem that it is very difficult to stamina an imaging device such as a digital still camera and a digital video camera.
[0010]
[Means for Solving the Problems]
The present invention has been made to solve such a problem. That is, the present invention provides a screw that rotates by driving a motor, a rack that is meshed with the screw being sandwiched, a lens holding frame that holds the lens and is connected to the rack, and a lens holding frame to the rack. A lens driving mechanism comprising: a pinching force increasing unit that increases a pinching force of the screw of the rack when a force along an axial direction of the screw is applied. It is also an imaging device having this lens drive mechanism.
[0011]
In the present invention, when a force is applied from the lens holding frame to the rack in the axial direction of the screw, the force for pinching the screw of the rack is increased by the holding force increasing means, so that only when an impact is applied. The rack can be strongly sandwiched between the screws, and the displacement during impact application can be accurately prevented without hindering the movement of the rack during normal operation.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating the overall configuration of the lens driving mechanism according to the present embodiment, FIG. 2 is a perspective view illustrating the overall configuration of the lens driving mechanism according to the present embodiment, and FIG. FIG. 3 is an exploded perspective view illustrating an overall configuration of the lens driving mechanism. That is, the lens driving mechanism of the present embodiment is mainly applied to an imaging device such as a digital still camera or a digital video camera, and the lens holding frame 2 holding the lens 1 is moved in the optical axis direction by the guide shafts 3 and 4. It is held so that it can be driven.
[0013]
The rack 5 is attached to the lens holding frame 2 and meshes with a lead screw 6a that rotates using a stepping motor 6 as a power source. The lens holding frame 2 drives the stepping motor 6 under a predetermined control by converting the power of the stepping motor 6 which is the power source for rotating the driving into the driving force in the optical axis direction by the rack 5 meshing with the lead screw 6a. , Is driven with a minute resolution in the optical axis direction.
[0014]
The lens holding frame 2 has a lens chamber 2a in which the lens 1 is positioned and fixed, a sleeve portion 2b for fitting and positioning with the guide shaft 3, a U-groove 2c for engaging with the guide shaft 4 and positioning (stopping rotation), and a rack. The supporting arms 2d and 2e for mounting the rack 5, the hole 2f of the supporting arm against which the conical portion 5c of the rack is pressed, and the thin portion 5e of the rack are deformed by the extension restoring force of the coil spring 7, thereby deforming the conical portion of the rack. The portion 5d is provided with a hole 2g of the support arm to be pressed.
[0015]
The rack 5 has a rack gear portion 5a meshing with the lead screw 6a, a clamp portion 5b opposed to the rack gear portion 5a by a coil spring 7, meshing the lead screw 6a with a predetermined pressure, and a conical portion pressed by the hole 2f of the lens holding frame. 5c, a conical portion 5d pressed by the hole 2g of the lens holding frame, a thin portion 5e deformed by the extension and restoring force of the coil spring 7, and a hook portion 5f serving as a fulcrum of the coil spring 7 in the clamping direction.
[0016]
In this configuration, since the conical portions 5c and 5d are pressed by the holes 2f and 2g of the lens holding frame by the extension restoring force of the coil spring 7, the rack 5 is attached to the lens holding frame 2 without play, and the lead is provided. Even if the screw 6a is tilted, the rack 5 can be slightly rotated with respect to the lens holding frame 2, and the engagement between the rack 5 and the lead screw 6a can be kept good.
[0017]
Here, the axial runout of the lead screw 6a caused by the structural characteristics of the stepping motor 6 can be absorbed by the above-mentioned minute rotation. However, the conical portions 5c and 5d receive the extension restoring force of the coil spring 7 and the hole portions 2f and When the force pressed by 2 g (that is, the thrust force of the fitting portion) is strong, the above-mentioned minute rotation cannot be performed, and the shaft vibration of the lead screw 6 a is transmitted to the lens holding frame 2, causing image shaking. I will.
[0018]
Therefore, assuming that the thrust force PS of the fitting portion is the load PW acting on the rack 5 from the lens holding frame 2 held by the rack 5 and the fitting portion thrust force PZ in the case where the image swing occurs.
PW ≦ PS <PZ
If it is not within the range, the performance requirement that the lens holding frame can be driven and the above-mentioned image shake does not occur cannot be satisfied.
[0019]
The load PW causes the rack gear 5a to apply an axial load P1 to the lead screw 6a, the load P1 causes a tangential force Q1 acting on the effective diameter of the lead screw 6a, the lead angle β of the lead screw 6a, the lead screw 6a and the rack gear 5a. , The frictional angle ρ1 of the surface of the lead screw 6a, the effective radius r1 of the lead screw 6a, and the torque T1 acting on the output shaft of the stepping motor 6 by the load P1.
μ1 = tanρ1
Q1 = tan (β + ρ1) × P1
T1 = Q1 × r1 = tan (β + ρ1) × P1 × r1
Holds, the torque T1 is determined by the load P1 if the friction coefficient μ1 is almost constant.
[0020]
Furthermore, the load P2 in the orthogonal direction applied by the coil spring 7 to the lead screw 6a by the clamp part 5b of the rack, the coefficient of friction μ2 between the lead screw 6a and the clamp part 5b, the outer radius r2 of the lead screw 6a, and the load P2 When the torque T2 acting on the lead screw 6a, that is, the output shaft of the stepping motor 6, is given by
T2 = μ2 × P2 × r2
Holds, the torque T2 is determined by the load P2 assuming that the friction coefficient μ2 is substantially constant.
[0021]
Here, the torque T1 is a torque for rotating the lead screw 6a, but the torque T2 acts in a direction for stopping the rotation of the lead screw 6a, so that the output of the lead screw 6a, that is, the output of the stepping motor 6 is controlled by the load P1 and the load P2. The torque T acting on the shaft is
T = T1-T2
Holds.
[0022]
Here, when the load P2 is large, the torque T2 becomes large, and it is necessary to generate a large torque on the output shaft of the stepping motor 6 when driving the lens, and it is necessary to apply a large voltage to the stepping motor 6, thereby reducing power consumption. It is not suitable for
[0023]
The stepping motor 6 has a holding torque of the torque T0 with respect to its output shaft, that is, the lead screw 6a when no power is supplied, and has a holding torque of the TV when only a certain voltage V is applied.
[0024]
Normally, a certain voltage V is applied to the lens driving device, that is, the stepping motor 6. However, when an external impact is applied to an imaging device such as a digital still camera or a digital video camera, the lens holding frame 2 is accelerated. Then, apparently, the load PW increases and the load P1 increases, so that the torque T increases. Therefore, if the torque at this time is TG,
TV <TG
As a result, the lead screw 6a rotates, and the lens holding frame 2 cannot be held at a predetermined position in some cases.
[0025]
If the lens holding frame 2 is displaced from the predetermined position as described above, the system for calculating the lens position by the pulse counting by the stepping motor 6 breaks down.
[0026]
For example, it is necessary to redo the initialization operation by the reset sensor, which imposes a time loss at the time of user use and misses the photographing timing. Here, a feedback circuit can be configured by providing a sensor system for position detection in order to avoid a re-initialization operation. However, the number of parts increases, the configuration becomes complicated and large, and assembly becomes complicated. High cost.
There is a problem.
[0027]
In addition, there is a problem that the lens holding frame 2 comes into contact with another lens barrel constituent member due to the above-mentioned positional shift and is physically destroyed.
[0028]
In order to prevent the above positional deviation, it is conceivable to always apply a large voltage to the stepping motor 6 assuming a large impact, load, and acceleration. Contrary to the demand for lower power consumption for), there is a problem that it is very difficult to stamina an imaging device such as a digital still camera and a digital video camera.
[0029]
In the present embodiment, when the load P1 increases due to the above-described impact / acceleration, the load P2 is simultaneously increased.
T = T1-T2
Than,
TG <TV
The present invention is characterized in that the range of impact / acceleration is widened, and even if a large impact load is applied with a small applied voltage, the lens is prevented from being displaced by the torque generated by the axial load.
[0030]
As a result, the voltage applied to the stepping motor 6 can be constantly reduced, and stamina of an imaging device such as a digital still camera and a digital video camera can be achieved.
[0031]
As described above, in the present embodiment, increasing the load P2 at the moment when the load P1 increases is a means for solving the problem, and a configuration for realizing this will be shown in comparison with a conventional example. FIG. 4A shows a conventional rack, and FIG. 4B shows the rack of the present embodiment.
[0032]
As a premise, the load P2 is determined by the displacement of the coil spring 7 in the clamping direction (the coil spring may be considered to be determined by the amount of torsion). At the moment when the load P1 increases, the thin portion 5e and the coil spring 7 are deformed and compressed so as to bend in the direction indicated by the arrow A in the figure. At this time, the coil spring 7 is supported by a point B which is hooked on the hook 5f. The arm C is turned by the compression of the coil spring 7 and falls down.
[0033]
In the conventional rack, the arm C falls down in the direction of arrow A in the figure, so that the displacement of the coil spring 7 in the clamping direction does not change, and the load P2 remains constant.
[0034]
Here, as in the present embodiment shown in FIG. 4B, a clamping force increasing means is formed by providing a slope (taper) 5g on the rack, and the arm C is displaced along the slope in the direction of arrow D in the figure. By doing so, when the load P1 increases, the load P2 can be increased.
[0035]
By forming the slope 5g, when the load P1 is small, the load P2 can be small, and when the load P1 is large, the load P2 can be large. When no impact load or acceleration is applied, the lens can be smoothly moved without image shaking. When a shock load, acceleration, or the like is received, the rack 5 and the lens can be accurately held at predetermined positions.
[0036]
In the present embodiment, when the load P1 increases, the load P2 is changed only in the increasing direction. However, in another embodiment shown in FIG. 5, a slope 5i in which the direction of the slope changes at a certain position is further provided. When the load P1 increases within a range where the rack thin portion 5e is not broken, the arm P is displaced in the direction of arrow E in the figure to increase the load P2 and increase the torque T2, thereby increasing the lens of the rack 5. Improve position holding ability.
[0037]
When the load P1 increases to a range where the rack thin portion 5e is broken, the load P2 is reduced by displacing the arm C in the direction of the arrow D in the drawing, and the torque T2 is reduced to reduce the state of TV <TG. Then, the lead screw 6a can be rotated to prevent the rack thin portion 5e and the rack gear portion 5a from being broken.
[0038]
In the drawings of the present embodiment, the slope is formed by a straight line, but the "changing the load P2" proposed in the present invention can be realized even if the slope is formed by a curve. Further, in the present embodiment, the slope is shown as a method of changing the load P2 when the load P1 increases. However, as long as the above-described formula is satisfied, the component configuration and method are not limited. Further, the coil spring 7 is used as a means for biasing the rack 5 between the lead screw 6a, but the rack 5 is clamped between the lead screw 6a by another biasing means not using the coil spring 7. The same applies to the case where the load P2 can be changed by increasing the load P1.
[0039]
【The invention's effect】
As described above, the present invention has the following effects. In other words, when a large shock or acceleration is applied to the imaging device (such as when the camera is hit at the time of shooting), the load acting on the rack in the axial direction increases instantaneously, and the output shaft of the stepping motor is rotated. In contrast to the increased torque, the instantaneous increase of the load in the clamping direction increases the torque that tries to control the rotation of the output shaft of the stepping motor, thereby preventing the lens from shifting. Become.
[0040]
In addition, since the above-described positional deviation can be prevented, it is not necessary to perform the initialization operation by the reset sensor again, so that there is no need to impose a time loss at the time of using the user, and it is possible to solve the problem that the photographing timing is missed. .
[0041]
Furthermore, since the number of parts and the configuration do not change, the above-mentioned positional deviation can be prevented while the assembling is easy and the cost is maintained, there is no need to provide a sensor system for position detection to avoid the re-initialization operation. .
[0042]
In addition, since the above-described positional deviation can be prevented, there is no problem that the lens, the lens holding frame, the driving mechanism, and the like come into contact with other lens barrel constituent members and are physically destroyed.
[0043]
Further, since the above-described displacement can be prevented, it is not necessary to constantly apply a large voltage to the stepping motor assuming a large impact, load, and acceleration, and a relatively small voltage may be applied relatively constantly. Therefore, it is possible to satisfy the demand for low power consumption for long use (long continuous shooting time / long continuous shooting time) and realize stamina of imaging devices such as digital still cameras and digital video cameras. Become.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an overall configuration of a lens driving mechanism according to an embodiment.
FIG. 2 is a perspective view illustrating an overall configuration of a lens driving mechanism according to the embodiment.
FIG. 3 is an exploded perspective view illustrating an overall configuration of a lens driving mechanism according to the embodiment.
FIG. 4 is a perspective view illustrating a main part of the embodiment.
FIG. 5 is a perspective view illustrating another example of the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Lens, 2 ... Lens holding frame, 3 ... Guide shaft, 4 ... Guide shaft, 5 ... Rack, 6 ... Stepping motor, 6a ... Lead screw, 7 ... Coil spring

Claims (4)

A screw rotating by driving a motor,
A rack that is meshed with the screw sandwiched therebetween,
A lens holding frame that holds a lens and is connected to the rack;
A lens driving mechanism comprising: a clamping force increasing unit configured to increase a force for clamping the screw of the rack when a force along the axial direction of the screw is applied to the rack from the lens holding frame. . A spring is provided for urging the rack to pinch the screw,
2. The lens driving device according to claim 1, wherein the holding force increasing unit increases the urging force of the spring when a force along the axial direction of the screw is applied to the rack from the lens holding frame. 3. mechanism. A coil spring is provided to bias the rack against the screw.
The gripping force increasing means is configured such that, when a force along the axial direction of the screw is applied to the rack from the lens holding frame, the spring is moved along a tapered portion provided at a portion that abuts one end of the coil spring. 2. The lens driving mechanism according to claim 1, wherein the urging force of the coil spring is increased by moving one end of the lens driving mechanism. A screw rotating by driving a motor,
A rack that is meshed with the screw sandwiched therebetween,
A lens holding frame that holds a lens and is connected to the rack;
A lens driving mechanism comprising: a pinching force increasing unit configured to increase a pinching force of the screw of the rack when a force along the axial direction of the screw is applied to the rack from the lens holding frame. Imaging device.

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