JP2009169010A - Imaging device, portable terminal and af control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To focus a lens of a movable section of an imaging optical system on a desired position in a short time during lens position control without causing an increase in the size of an arrangement or in power consumption. <P>SOLUTION: When the movable section including the lens of the imaging optical system and an elastic body for supporting the lens is moved to a desired control position during lens position control in AF control, first control for driving the movable section and second control for controlling the vibration of the movable section are performed. In the first control, a driving current value I1 smaller than a driving current value corresponding to the desired control position is supplied to start driving of the movable section. In the second control, after execution of the first control, a driving current value I2 corresponding to the desired control position is supplied at the timing of a time interval τ (e.g., τ≈T/2) that is not greater than the period T of natural vibration of the movable section, so as to control the vibration of the movable section in such a manner as to cancel the vibration. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging device having an autofocus (AF) function, a portable terminal, and an AF control method.

  A camera that captures a subject and obtains image information is usually provided with an AF function that adjusts the focal position of the imaging optical system and focuses the subject image on an imaging surface on which an imaging element or the like is arranged. For this AF function, an AF mechanism having a drive unit that drives the lens of the imaging optical system and a control unit that controls the drive unit is provided. There are various types of driving units for the AF mechanism. For example, a voice coil motor (hereinafter referred to as VCM) is used in a camera unit mounted on a portable terminal such as a cellular phone device. Here, an AF control operation will be described by taking an AF mechanism by a drive unit using a VCM as an example.

  In the driving unit of the AF mechanism, the lens unit of the imaging lens serving as a movable unit that is displaced in the optical axis direction has a coil of VCM, and is supported by an elastic body with respect to the frame on which the magnet is fixed. The elastic body and the electromagnet of the VCM composed of a coil and a magnet constitute an AF mechanism actuator. When performing AF control, the lens unit moves in the optical axis direction to a position corresponding to the drive current value by applying a predetermined drive current (power) to the coil of the VCM from the control unit. At this time, the in-focus state is determined based on the contrast of the obtained captured image, and the control of applying the drive current according to the in-focus state of the captured image is repeated so that the imaging optical system is focused. The

During the AF control as described above, since the lens unit of the imaging lens is supported by the frame by the elastic body, vibration is generated in the process of being displaced according to the drive current. If it takes time for the lens vibration to settle, a weight is applied for each control, and the time until AF control is completed becomes longer. The vibration characteristics (natural vibration) of the lens are determined by the mass of the lens unit, the elastic coefficient of the elastic body, and the like.
JP 2007-155801 A JP-A-6-202190

  FIG. 6 is a diagram for explaining lens vibration of the imaging lens during AF control operation in a conventional imaging apparatus, and shows the relationship between the drive current and the position of the imaging lens. In FIG. 6, (a) shows a case where the driving current is step-input in accordance with the control amount, and (b) shows a case where the lens position is temporally changed when a capacitor is added to the input portion of the driving current to smooth the input waveform. Each of them shows how it vibrates. As shown in FIG. 6A, when the drive current value corresponding to the target lens position (control target position) is step-input as it is from the non-energized state, a large vibration occurs in the imaging lens.

  As a method for suppressing such lens vibration, (1) the elastic coefficient (spring constant) of the elastic body supporting the imaging lens is increased (the spring is hardened), or (2) the input waveform of the drive current by the capacitor. Is effective. However, when the elastic coefficient of the elastic body is increased as in (1) above, the required drive current value increases, which causes a problem of increased power consumption. When the input waveform is smoothed by adding a capacitor to the drive current input section as in (2) above, the amplitude of the lens vibration is suppressed as shown in FIG. Since the rise of S is slow, the effect of shortening the settling time cannot be obtained. In this case, a capacitor having a large capacity is required, and in order to obtain a sufficient effect, the time for the drive current to reach the target value becomes long, and there is a problem that the settling time cannot be shortened.

  The present invention has been made in view of the above circumstances, and converges the lens of the movable part of the imaging optical system to the target position in a short time during lens position control without causing an increase in configuration size or power consumption. It is an object to provide an imaging device, a portable terminal, and an AF control method that can be used.

An image pickup apparatus of the present invention includes a lens constituting an image pickup optical system, an image pickup element that picks up a subject image formed by the image pickup optical system, an elastic body that supports the lens so as to be displaceable in an optical axis direction, A frame for fixing the imaging element and the elastic body; a driving section for driving a movable section including the lens and the elastic body; and a first section for driving the movable section when controlling the position of the lens. And a control unit that performs the first control and the second control for suppressing the vibration of the movable part.
As a result, it is possible to suppress the vibration peak generated when the movable part is driven with a simple configuration, and to cancel the generated vibration, so that the lens can be mounted in a short time without increasing the size of the configuration and increasing the power consumption. It becomes possible to converge to the target position.

Moreover, this invention is said imaging device, Comprising: The said 2nd control by the said control part is 1/2 or more and less than 1 of the period of the natural vibration of the said movable part after execution of the said 1st control. Includes things that run at timing.
Thereby, the vibration of a movable part can be suppressed more effectively.

Moreover, this invention is said imaging device, Comprising: The control amount in the said 1st control by the said control part contains what is larger than the control amount in the said 2nd control.
Thereby, the lens can be moved to the control target position of the lens in a shorter time, and the vibration of the movable part can be suppressed, and the time until the lens is settled to the control target position can be shortened.

The present invention is the above imaging device, wherein the control unit sets a value of driving power for driving the movable unit according to a control target position of the lens, and performs the first control and the first control. In the second control, the driving power having a set value is supplied to the movable part.
Thereby, it is possible to converge the control target position in a short time while suppressing the vibration of the movable part.

  Moreover, this invention provides a portable terminal provided with the imaging device in any one of the said.

An AF control method of the present invention includes a lens that constitutes an image optical system, an imaging element that captures a subject image formed by the imaging optical system, and an elastic body that supports the lens so as to be displaceable in the optical axis direction. , An AF control method in an imaging apparatus comprising: a frame that fixes the imaging element and the elastic body; and a drive unit that drives a movable part including the lens and the elastic body. When performing lens position control, the method includes a step of executing a first control for driving the movable portion and a step of executing a second control for suppressing vibration of the movable portion. is there.
As a result, the peak of vibration generated when the movable part is driven in the AF control can be suppressed, and the generated vibration can be canceled out, and the lens can be targeted in a short time without increasing the size of the structure and increasing the power consumption. It is possible to converge to the position.

  According to the present invention, an imaging apparatus capable of converging the lens of the movable part of the imaging optical system to a target position in a short time during lens position control without causing an increase in configuration size or an increase in power consumption. A terminal and an AF control method can be provided.

  In the present embodiment, as an example of the AF mechanism provided in the imaging apparatus, a configuration example by a drive unit using a voice coil motor (VCM) is shown. It can be similarly applied to a drive unit using means other than the VCM.

  FIG. 1 is a diagram illustrating a configuration of an AF mechanism in a camera module of an imaging apparatus according to an embodiment of the present invention. The AF mechanism according to this embodiment is a configuration example of an AF mechanism using a VCM. Of the imaging lenses constituting the imaging optical system, the lens 11 corresponding to the lens unit of the movable part is supported by a leaf spring 13 which is an example of an elastic body, and is attached to the frame 14 via the leaf spring 13. In the example of FIG. 1, the lens 11 is suspended so as to be displaceable with respect to the frame 14 by parallel links by a plurality of leaf springs 13 on both sides of the front end portion and rear end portion.

  The lens 11 is integrally provided with a coil 16 on the outer peripheral portion thereof, and this coil 16 is disposed to face the magnet 15 fixed to the frame 14. The coil 16 and the magnet 15 constitute a moving coil type VCM. An imaging element 17 such as a CCD or CMOS type sensor is disposed on the focal plane of the imaging optical system including the lens 11.

  The AF mechanism using the VCM shown in FIG. 1 can drive the lens 11 to a predetermined position by applying a drive current to the coil 16 and energizing it. At this time, the lens 11 moves in the direction of the optical axis 12 to a point (actually influenced by gravity or the like) that balances with the elastic force of the leaf spring 13 by the electromagnetic force generated between the coil 16 and the magnet 15. Here, the element including the lens 11 and the coil 16 becomes a movable part, and the VCM by the coil 16 and the magnet 15 and the leaf spring 13 become a driving part.

  FIG. 2 is a diagram illustrating a block configuration of the imaging apparatus according to the embodiment of the present invention. The imaging device of this embodiment is provided in a mobile terminal such as a mobile phone device as a camera unit, for example. In a portable terminal, a VCM is often used for the driving unit of the AF mechanism.

  A camera module 21 including the lens 11 of the imaging optical system is provided with a VCM 22 having a coil 16 and a magnet 15 as a drive unit. A constant current driver 25 that applies a drive current is connected to the VCM 22, and a control unit 26 that controls the drive current value is connected to the constant current driver 25. The camera module 21 is provided with an image sensor 17, an image processor 24 is connected to the image sensor 17, and an output of the image processor 24 is connected to the controller 26. Further, a display unit 27 including a liquid crystal display panel that displays a captured image output from the image processing unit 24, and a recording unit 28 including a memory that records image data of the captured image are provided.

  In the VCM 22 of the camera module 21, the coil 16 is displaced in proportion to the drive current input from the constant current driver 25, and drives the lens 11 configured integrally with the coil 16. The constant current driver 25 is also called an AF driver, and outputs a constant current as a drive current for the VCM 22 in accordance with a control signal from the control unit 26. The imaging element 17 photoelectrically converts the subject image formed by the imaging optical system of the camera module 21 to generate an electrical signal, and outputs the electrical signal to the image processing unit 24. The image processing unit 24 performs various processes on the output signal of the image sensor 17 to generate and output an image signal obtained by imaging the subject. The control unit 26 is configured by a processor such as a microcomputer, operates based on a predetermined program, and executes processing related to AF control. When the imaging apparatus is mounted on a portable terminal, the function of the control unit 26 is realized by a CPU of the portable terminal. The control unit 26 determines the in-focus state based on the imaging signal output from the image processing unit 24 according to a predetermined control specification based on the contrast of the obtained captured image, and the blur of the captured image is minimized. As described above, a control signal for controlling the drive current of the VCM 22 is output to the constant current driver 25.

  FIG. 3 is a diagram for explaining the AF control operation of the imaging apparatus according to the present embodiment. FIG. 3 shows the relationship between the drive current and the position of the imaging lens during the AF control operation, and shows the state of lens vibration of the imaging lens with respect to the drive current.

  In the present embodiment, in the AF control, control is performed such that the drive current is applied stepwise from the non-energized state to the drive current value corresponding to the target lens position (control target position). At this time, first, the movable part including the lens 11 is driven by the first control. In the first control, a drive current having a value smaller than the drive current value corresponding to the control target position is applied. Then, the vibration of the driven movable part is suppressed by the second control. In the second control, a drive current value corresponding to the control target position is applied, and the lens 11 is set to the control target position.

  For example, when the control is started from the initial lens position, first, as the first control, the drive current value I is applied from the current value 0 state as the current value I1. Here, the current value I1 is set to a value smaller than the drive current value corresponding to the control target position. Thereby, the lens 11 moves toward the control target position. Then, after the elapse of time τ, as the second control, the drive current value I is applied as the current value I2 from the state of the current value I1. Here, the current value I2 is a drive current value corresponding to the control target position. With this second control drive current, the first vibration peak is suppressed and the generated vibration is canceled with respect to the vibration of the lens 11.

  In FIG. 3, the alternate long and short dash line shows a comparative example, and shows lens vibration when the drive current value I2 corresponding to the control target position is applied at once. On the other hand, in the present embodiment, as indicated by a broken line, the lens vibration P is suppressed by the first control and the second control, and the lens 11 converges in a short time with respect to the control target position. become.

  The time interval τ indicating the timing for executing the second control is set to be equal to or shorter than the period T, where T is the period of the natural vibration of the movable part. Considering the effect of suppressing lens vibration, for example, it is more preferable to set τ≈T / 2. The natural frequency of the movable part is determined by the mass of the movable part including the lens, the elastic coefficient of the elastic body to be supported, and the like. In addition, the control amount of each of the first control and the second control is such that the control amount (current value I1-0) in the first control is larger than the control amount (current value I2-I1) in the second control. It is preferable to do this. By setting the control amount in this way, the movable portion can be quickly moved to the control target position and the lens vibration can be suppressed. Therefore, the stabilization time from the start of driving the lens to the stabilization. Can be shortened.

  4A and 4B are diagrams showing the operating state of the AF mechanism of the imaging apparatus according to the embodiment of the present invention, where FIG. 4A shows an initial state before the start of AF control, and FIG. 4B shows a static state after the completion of AF control. Show.

  As shown in FIGS. 1 and 4, in the AF mechanism using the VCM, the magnet 15 is fixed to the substantially cylindrical inner peripheral surface of the frame 14, and the coil 16 is connected to the lens 11 so as to face the magnet 15. The lens unit is integrally fixed to the outer peripheral surface of the lens unit. When a current flows through the coil 16, stress is generated by electromagnetic force, and the lens 11 of the movable part supported by the leaf spring 13 is displaced. In the illustrated configuration example, stress is generated in the upward direction in the drawing, and the lens 11 moves in a direction away from the image sensor 17 along the optical axis direction. Here, by adjusting the drive current value flowing through the coil 16 in accordance with the distance to the subject, the focus adjustment can be performed by changing the position of the lens 11. At this time, the moving distance of the lens 11 increases as the driving current value I increases.

  FIG. 4A shows an initial state in which AF control is not performed. In the initial state, it is assumed that the far side is in focus. In this initial state, the lens position is set to a predetermined initial position. In FIG. 4, the lens position is indicated by a distance L <b> 1 between the last surface of the lens 11 and the imaging surface of the image sensor 17. AF control is executed from this initial state, and when focusing on the foreground side, the necessary drive current value I is supplied according to the subject distance, and the position of the lens 11 is adjusted.

  FIG. 4B shows a static state where the lens 11 has settled at the target control position after one control in the AF control is completed. When AF control is started, the lens 11 is displaced upward in the figure by the application of the drive current value I1 by the first control, and then the lens vibration is caused by the application of the drive current value I2 by the second control. It is suppressed and moved to the target control position (distance L2 between the last surface of the lens 11 and the imaging surface of the image sensor 17). By repeating the control of the lens position, the position of the lens 11 is controlled to the focus position where the in-focus state is achieved.

  FIG. 5 is a flowchart showing the processing procedure of the AF control operation in the imaging apparatus according to the present embodiment. In the initial state before the start of the AF control operation (FIG. 4A), the drive current value I is 0, and the lens 11 is at a predetermined initial position (step S11). In this state, an AF control operation is started by an instruction from the control unit 26, and the control unit 26 determines a control target position for AF adjustment based on the contrast of the captured image obtained from the image processing unit 24 (step S12). .

  In the AF control, first control is first performed according to an instruction from the control unit 26 (step S13). In the first first control, the constant current driver 25 supplies the VCM 22 with a drive current value I1 smaller than the current value corresponding to the control target position, and drives the lens 11 to start moving. And 2nd control is performed by the instruction | indication of the control part 26 (step S14). The second control is executed at the timing when a time interval τ shorter than the natural vibration period T of the movable part including the lens 11 has elapsed since the execution of the first control. In the second control performed stepwise after the first control, the constant current driver 25 supplies the drive current value I2 corresponding to the control target position to the VCM 22 to drive the lens 11 to the control target position.

  By this second control, the first vibration peak of the lens 11 generated by the first control is suppressed, and the lens 11 is moved to the control target position while reducing the vibration so as to cancel the generated lens vibration. Thereby, position control can be performed so that the lens 11 converges and settles at the control target position in a short time. When the lens 11 is in a static state (FIG. 4B), the drive current value I2 is held. By repeating the drive control of the lens 11 to the control target position as described above in a short time, the lens position gradually converges to the focus position where the in-focus state is achieved, and the AF control is completed.

  When the AF control is completed, the lens 11 is held at the focus position. In this state, the subject is imaged according to the user's shutter operation input. When the AF control operation is turned off, the lens 11 returns to the initial position.

  According to the present embodiment described above, lens vibration during AF control can be suppressed with a simple configuration, and the time until the lens settles can be shortened. In this case, the lens vibration can be suppressed without using means such as increasing the elastic coefficient of the elastic body that supports the imaging lens, adding a capacitor to the input portion of the drive current, or implementing complicated control. Is obtained. Therefore, the lens of the movable part of the imaging optical system can be converged to the target position in a short time during AF control without increasing the size of the configuration or increasing the power consumption, and the time required for the AF control operation (AF control) Time to completion).

  In the above-described embodiment, the configuration example using the VCM as the driving unit of the AF mechanism has been described, but the present invention can be similarly applied to other driving units. As the drive unit, for example, a piezoelectric body, an ultrasonic motor, a stepping motor, a shape memory alloy, an ion conductive resin, or the like is also used.

  It should be noted that the present invention is not limited to those shown in the above-described embodiments, and those skilled in the art can also make changes and applications based on the description in the specification and well-known techniques. Yes, included in the scope of protection.

  The present invention has the effect of allowing the lens of the movable part of the imaging optical system to converge to the target position in a short time during lens position control without incurring an increase in configuration size or power consumption. It is useful as an imaging device having an AF function, a portable terminal including the imaging device, and an AF control method thereof.

The figure which shows the structure of AF mechanism in the camera module of the imaging device which concerns on embodiment of this invention. The figure which shows the block configuration of the imaging device which concerns on embodiment of this invention. The figure explaining AF control operation of the imaging device in this embodiment The figure which shows the operation state of AF mechanism of the imaging device which concerns on embodiment of this invention A flowchart showing a processing procedure of an AF control operation in the imaging apparatus according to the present embodiment. The figure explaining the lens vibration of the imaging lens at the time of AF control operation in the conventional imaging device

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Lens 12 Optical axis 13 Leaf spring 14 Frame 15 Magnet 16 Coil 17 Image sensor 21 Camera module 22 VCM
24 Image processing unit 25 Constant current driver 26 Control unit 27 Display unit 28 Recording unit

Claims (6)

A lens constituting the imaging optical system;
An image sensor that captures a subject image formed by the imaging optical system;
An elastic body that supports the lens so as to be displaceable in the optical axis direction;
A frame for fixing the imaging element and the elastic body;
A drive unit for driving a movable unit including the lens and the elastic body;
A control unit that performs a first control for driving the movable unit and a second control for suppressing vibration of the movable unit when performing position control of the lens;
An imaging apparatus comprising: The imaging apparatus according to claim 1,
The second control by the control unit is an imaging apparatus that is executed at a timing of ½ or more and less than 1 of the period of the natural vibration of the movable unit after the execution of the first control. The imaging apparatus according to claim 1,
An imaging apparatus in which a control amount in the first control by the control unit is larger than a control amount in the second control. The imaging apparatus according to claim 1,
The control unit sets a value of driving power for driving the movable unit according to a control target position of the lens, and sets the driving power of the value set in the first control and the second control, respectively, to the movable unit. Imaging device supplied to the unit.   A portable terminal provided with the imaging device according to claim 1. A lens constituting an imaging optical system, an imaging element that captures a subject image formed by the imaging optical system, an elastic body that supports the lens so as to be displaceable in an optical axis direction, the imaging element, and the elastic body An AF control method in an imaging apparatus, comprising: a frame that fixes the lens; and a drive unit that drives a movable unit including the lens and the elastic body,
When performing control of the position of the lens by the control unit in AF control, a step of executing a first control for driving the movable unit and a second control for suppressing vibration of the movable unit are performed. An AF control method.

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