JP2013257486A - Optical device, image capturing device, and method of controlling optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of driving means of an optical member.SOLUTION: An image capturing device has a focusing unit 204 for focus adjustment and a focus drive control unit 212 for controlling driving of the focusing unit 204. A control unit 213 controls the focusing unit 204 by controlling driving of an actuator via the focus drive control unit 212. The focus drive control unit 212 has an LC filter for smoothing current that flows through the actuator, and pulse-width-modulation-controls position of a focusing lens by feeding a drive signal to the actuator. When drive control is performed with a drive frequency higher than a resonance frequency, the control unit 213 provides control such that the drive frequency that is set when actuator drive control accuracy is not required is higher compared with the drive frequency that is set when the actuator drive control accuracy is required.

Description

  The present invention relates to a technique for controlling driving means of an optical member.

In the case of photographing a subject using an imaging device, a method is known in which a lens is driven by controlling an actuator such as a motor in order to automatically perform angle adjustment and focus adjustment. In the control of the actuator, there is a drive system using a pulse width modulation (hereinafter abbreviated as PWM) circuit (see Patent Document 1). In this case, in order to reduce the influence on the image sensor due to the magnetic field generated by the actuator that drives the optical member, processing for smoothing the drive current of the actuator is performed. At that time, the power consumption of the imaging device increases with the power consumed by the smoothing circuit.
On the other hand, in recent years, the size and thickness of image pickup apparatuses have been reduced, and the battery has also been downsized. Therefore, reduction in power consumption of the image pickup apparatus is required.

Japanese Patent Application No. 9-365247

The prior art disclosed in Patent Document 1 has a problem that unnecessary power is consumed when driving an actuator for focus adjustment control. That is, there is a demand for measures for further reducing power consumption.
An object of the present invention is to reduce the power consumption of the driving means of the optical member.

  In order to solve the above problems, an apparatus according to the present invention is an optical apparatus including an optical member constituting an optical system and a driving unit thereof, and controls the driving of the optical member by controlling the driving unit. And a smoothing means for smoothing a current flowing through the driving means, wherein the control means sets a driving frequency of the driving means higher than a resonance frequency of the smoothing means and the driving means. Control to reduce the drive current is performed.

  According to the present invention, the power consumption of the optical member driving means can be reduced by controlling the driving frequency.

FIG. 5 is a flowchart for explaining an example of a drive frequency changing process in order to explain the first embodiment of the present invention in conjunction with FIG. 2 to FIG. 4. It is a block diagram which shows the structural example (A) of the whole imaging device, and the structural example (B) of a focus drive control part. It is a figure explaining the drive part of a focus motor. It is a flowchart explaining the flow of imaging | photography process. It is a flowchart explaining the process example which concerns on 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. As an example of an optical device including an optical member constituting the optical system and a driving unit thereof, an imaging device including a pulse width modulation control unit related to a focus adjustment lens drive actuator (motor in this example) is taken as an example. explain.

[First Embodiment]
A first embodiment of the present invention will be described with reference to FIGS.
FIG. 2A is a block diagram illustrating a configuration example of the entire imaging apparatus. The zoom unit 201 constituting the imaging optical system is a first group lens including a zoom lens. The zoom drive control unit 209 performs zooming operation by driving and controlling the zoom unit 201. The aperture / shutter unit 202 includes an aperture device that adjusts the amount of light and a shutter device, and is driven and controlled by an aperture / shutter drive control unit 210. The correction lens unit 203 includes a correction lens (also referred to as a shift lens) as an optical member that can change a position in a plane perpendicular to the optical axis of the imaging optical system. The correction lens unit 203 includes a second lens unit that constitutes an image blur correction optical system, and corrects image blur due to vibration such as camera shake. The correction lens drive control unit 211 controls driving of the correction lens. In the present embodiment, the correction lens unit 203 is used to reduce the blurring of the subject image formed on the imaging surface of the imaging device by the imaging optical system, but the imaging device is a plane perpendicular to the optical axis. The image blur may be reduced by changing the position at. The focus unit 204 that performs focus adjustment includes a third lens group, and includes a focus lens that can change its position in the optical axis direction. The focus drive control unit 212 controls the drive of the focus unit 204. Each of these drive control units controls the drive of the movable member in charge of each according to a control command from the control unit 213 described later.

The imaging unit 205 uses an imaging element to convert an optical image formed through each lens group into an electrical signal by photoelectric conversion. The imaging signal processing unit 206 converts the output signal of the imaging unit 205 into a video signal. The video signal processing unit 207 performs image processing in order to process the output signal of the imaging signal processing unit 206 according to the application. The display unit 208 receives the output signal of the video signal processing unit 207 and displays an image. The imaging unit 205, the imaging signal processing unit 206, the video signal processing unit 207, and the display unit 208 are controlled by control signals from the control unit 213.
The control unit 213 that controls the entire system includes a processing device such as a CPU (central processing unit), and performs a process described later by executing a program read from the storage unit 217. The operation unit 214 used when the user operates the camera includes various operation members and switches. FIG. 2A illustrates a zoom switch 214z and a shutter release switch 214s. The zoom switch 214z is used for operating the zoom lens, and the shutter release switch 214s is used for shooting operation. These switch operation signals are output to the control unit 213.
The external input / output terminal unit 215 is used for input / output processing of signals and video signals communicated with external devices. The shake detection unit 216 includes a gyro sensor that detects an angular velocity as detection means for detecting shake of the imaging apparatus, and outputs a detection signal to the correction lens drive control unit 211. The storage unit 217 stores various data such as video information and control information. The power supply unit 218 supplies a power supply voltage corresponding to the application to each unit constituting the camera system.

Next, the operation of the imaging apparatus having the above configuration will be described.
The shutter release switch 214s is a two-stage switch in which a first switch (hereinafter abbreviated as SW1) and a second switch (hereinafter abbreviated as SW2) are sequentially turned on in accordance with the pressing amount of a shutter release button (not shown). Has a type switch. The first switch SW1 is turned on by the first stroke (half press) of the shutter release button, and the second switch SW2 is turned on by the second stroke (full press). When the first switch SW1 is turned on, the control unit 213 instructs the focus drive control unit 212 to perform control, and drives the focus unit 204 to perform focus adjustment. This realizes an autofocus (hereinafter referred to as AF) function. Along with the AF control, the control unit 213 sends a control instruction to the aperture / shutter drive control unit 210 and drives the aperture / shutter unit 202 to set the exposure amount to an appropriate value. Thereby, an automatic exposure (hereinafter referred to as AE) function is realized.

Thereafter, when the second switch SW2 is turned on, the control unit 213 causes the storage unit 217 to store image data obtained from the light image exposed on the imaging element of the imaging unit 205. That is, the electrical signal obtained from the light image exposed to the image sensor is converted into an image signal by the imaging signal processing unit 206 and further subjected to image processing by the video signal processing unit 207, and then stored in the storage unit 217. .
When the user operates the zoom switch 214z, the control unit 213 sends a control instruction to the zoom drive control unit 209 according to the operation instruction. Upon receiving this control instruction, the zoom drive control unit 209 drives the zoom unit 201 and moves the zoom lens to the instructed zoom position.

FIG. 2B is a block diagram illustrating a configuration example of the focus drive control unit 212 illustrated in FIG.
A focus motor (hereinafter simply referred to as a motor) 219 uses a stepping motor or the like, and performs an AF operation by moving the focus lens of the focus unit 204. The focus motor drive circuit 220 is a circuit that drives the motor 219. The reset position detector 221 detects the reset position of the focus lens. The encoder 222 is used to detect the position of the focus lens. The focus position detection unit 223 detects the position of the focus lens based on the pulse information acquired from the encoder 222 and outputs a detection signal to the focus control unit 224.
The focus control unit 224 generates a pulse width modulation (PWM) signal having a predetermined frequency. The focus control unit 224 performs focus movement control by determining the duty ratio of the PWM signal according to the detection signal of the focus position detection unit 223. The control signal of the focus control unit 224 is sent to the focus motor drive circuit 220, and the focus unit 204 is driven by the rotation control of the motor 219. Further, the focus control unit 224 obtains a detection signal from the reset position detection unit 221 and determines a reference position for focus control.

The PWM control method is a pulse control method in which the amplitude of a drive voltage is made constant and the time width of a pulse that changes in a rectangular waveform is changed within a fixed period. When the PWM circuit is used, the power supply is repeatedly turned on and off, so that the current flowing through the motor has a large ripple component. When a current is passed through the motor, a magnetic field is generated around the motor by electromagnetic induction. The strength of the magnetic field (denoted as H) can be obtained by the following equation.
[Equation 1]
H = (N / 2r) · I [A / m] (1)
In the formula (1), N represents the number of turns of the coil, r represents the radius of the coil, and I represents the current. As can be seen from Equation (1), the magnetic field strength H is proportional to the current I. For this reason, the magnetic field generated around the motor always changes according to the change in the current value as if noise is superimposed (hereinafter referred to as magnetic field noise). For example, in the case of an imaging device, when the imaging element is affected by magnetic field noise, there is a possibility that a noise component is superimposed on the signal of the captured image. In order to prevent noise, there is a method in which a low-pass filter (hereinafter referred to as LPF) is connected to the motor 219.

FIG. 3A shows a schematic configuration of the photographic lens unit on the upper side, and shows an electrical configuration diagram of the focus motor driving circuit 220 and its output unit on the lower side. An LC filter using an inductor 301 and a capacitor 302 is illustrated. That is, the inductor 301 and the capacitor 302 constitute a smoothing circuit. One end of the inductor 301 is connected to one output terminal of the focus motor drive circuit 220, and the other end of the inductor 301 is connected to the capacitor 302 and the motor 219. The capacitor 302 is connected in parallel to the motor 219. Since a current path is also formed in the capacitor 302, the corresponding current becomes a loss regardless of the driving of the motor 219.
FIG. 3B illustrates frequency characteristics of a circuit portion including an inductor 301, a capacitor 302, and a drive coil (not shown) of the motor 219. The horizontal axis indicates the frequency, and the vertical axis indicates the current gain. The resonance frequency has a value corresponding to the inductance of the inductor 301 or the drive coil and the capacitance of the capacitor 302. In a band where the frequency is higher than the resonance frequency, the current value attenuates as the frequency increases. That is, the power consumption can be reduced as the driving frequency of the motor 219 is set higher than the resonance frequency.

Next, processing for determining the frequency of the PWM signal (hereinafter referred to as PWM frequency) by the drive control of the motor 219 will be described.
As described above, the high-frequency component of the drive current can be reduced by the LPF configured by the inductor 301 and the capacitor 302. As the LPF characteristics, the higher the frequency, the more the drive current can be suppressed, but the PWM frequency is determined by hardware. For example, when the carrier frequency is constant, the PWM frequency is determined by how much resolution the duty ratio is set. In an example in which the carrier frequency is constant at 1 MHz, the PWM frequency for providing a resolution of 500 is 2 kHz. At a resolution of 1000, the PWM frequency is 1 kHz. Since the duty ratio can be set in more detail at the PWM frequency of 1 kHz, the control accuracy is improved. On the other hand, since the PWM frequency is 2 kHz higher than 1 kHz, the current is further attenuated by the LPF, and the current consumption is reduced.

FIG. 4A is a flowchart for explaining a processing example of the imaging apparatus according to the present embodiment. FIG. 4B is a flowchart illustrating an example of AF control in FIG. 4A, and includes a PWM frequency determination process related to focus lens drive control. An example of PWM frequency determination processing will be described later with reference to FIG. “YES” shown in each flowchart indicates a positive determination result, and “NO” indicates a negative determination result.
First, when the control unit 213 shown in FIG. 2 confirms that the shooting mode is set according to the user's operation input, the control unit 213 starts driving of the image sensor (S401). In S402, the control unit 213 determines whether or not the first switch SW1 of the shutter release switch 214s is turned on. When SW1 is turned on, the process proceeds to S403, and when SW1 is turned off, the determination process of S402 is repeated. In step S403, the control unit 213 performs AE control. In this AE control, subject luminance is calculated from the output signal of the image sensor, and parameters relating to exposure control such as aperture value and shutter speed are determined according to the calculation result. In subsequent S404, the control unit 213 performs AF control. Details thereof will be described later with reference to FIG.
In S405, the control unit 213 determines whether or not the second switch SW2 of the shutter release switch 214s has been turned on. When SW2 is turned on, the process proceeds to S406, and when SW2 is turned off, the process returns to S402. Shooting (image sensor exposure processing, so-called still image shooting main exposure processing) is performed in S406, and in S407, image recording processing for storing image data in the storage unit 217 is performed, and then the imaging operation ends. .

Next, an AF control example shown in S404 of FIG. 4A will be described with reference to the flowchart of FIG. In the AF control, a process for determining the PWM frequency is performed before the focus lens is driven. Details of this processing will be described later with reference to FIG.
First, after the determination process of the PWM frequency is performed in S408, the focus lens is moved to the scan start position in S409. The scan range of the focus lens that moves along the optical axis of the imaging optical system is determined by the scan start position and the scan end position of the focusable range. In this example, a description will be given assuming that the scan start position is the infinity end of the focusable range and the scan end position is the closest end. On the contrary, the scan start position may be the closest end of the focusable range, and the scan end position may be the infinity end.
In step S410, the control unit 213 calculates a focus evaluation value from the high-frequency component of the subject luminance signal, and stores this in the memory together with the position data of the focus lens. The focus evaluation value is information used for focus adjustment control. In the case of the contrast AF method, a process for calculating a focus evaluation value is performed using a signal read from the image sensor, and a focus position is detected using the focus evaluation value. In the phase difference detection method, information indicating the focus adjustment state is acquired from a detection signal using the focus state detection device.

In this embodiment, a stepping motor is used as the focus lens motor 219. In this case, the position of the focus lens is detected as a relative position from the initial position detected by the reset position detector 221 (see FIG. 2B). When a DC (direct current) motor is used as the motor 219, the encoder 222 is used to obtain the absolute value of the position of the focus lens.
In step S411, the control unit 213 determines whether or not the position of the focus lens is at the scan end position. The scan end position is the closest end of the focusable range. If it is determined that the position of the focus lens is at the scan end position, the process proceeds to S412. If it is determined that the position of the focus lens is not the scan end position, the process proceeds to S415.

In S415, the determination process of the PWM frequency related to the drive control of the focus lens is executed, and in S416, the focus lens moves by a drive amount for a predetermined pulse. And it returns to S410 again. That is, the data storage process of the focus lens position and the focus evaluation value is repeatedly executed until the focus lens position reaches the scan end position.
When the position of the focus lens reaches the scan end position (YES in S411), the process proceeds to S412. In step S <b> 412, the control unit 213 searches for the maximum value from the plurality of focus evaluation values stored in the memory, and extracts focus lens position data in which the focus evaluation value indicates the maximum value. In step S413, a PWM frequency determination process related to focus lens drive control is executed. In step S414, the control unit 213 performs control to move the focus lens to the in-focus position according to the position data of the focus lens extracted in step S412.

Next, an example of PWM frequency determination processing shown in S408, S413, and S415 of FIG. 4B will be described with reference to the flowchart of FIG. Here, two PWM frequencies A and B used for focus lens drive control are defined. The PWM frequency B is less than A (B <A). As described above, it is necessary to suppress noise superimposed on the imaging signal during energization of the focus lens motor 219. Since the noise is suppressed by the LPF as the frequency is higher, the influence on the image sensor is smaller when driven at the PWM frequency A. However, since the PWM frequency is changed under the condition that the sampling frequency is constant, the resolution of the drive control of the motor 219 is higher at the PWM frequency B.
PWM frequency size: PWM frequency B <PWM frequency A
Power saving effect: (For PWM frequency B) <(For PWM frequency A)
Effect on image sensor: (in the case of PWM frequency A) <(in the case of PWM frequency B)
Resolution of drive control of motor 219: (in the case of PWM frequency A) <(in the case of PWM frequency B).
First, in S101, the control unit 213 compares the target position of the focus lens with the reference position, and determines whether the target position is on the image sensor side or the subject side with respect to the reference position. The noise to the image sensor generated by the drive control of the motor 219 depends on the distance. For this reason, if the target position of the focus lens is at a certain distance from the image sensor, the possibility of noise being superimposed on the image signal is sufficiently low. This position, that is, the position where noise is not superimposed is set as the reference position. If it is determined that the target position is closer to the image sensor than the reference position (YES in S101), the process proceeds to S103. In S103, the control unit 213 sets the PWM frequency A. The drive signal generated by the focus drive control unit 212 is supplied to the motor 219 via the LC filter of FIG. Thereby, the noise superimposed on an imaging signal is suppressed. On the other hand, if it is determined in S103 that the target position is closer to the subject than the reference position (NO in S101), the process proceeds to S102.

  In S102, the control unit 213 determines whether one position (1 pos), which is a unit movement amount of the focus lens when driven at the PWM frequency A when the focus lens is at the target position, is within one depth (depth of focus). Determine whether or not. This determination condition and threshold value also depend on the imaging magnification and focal length. When it is determined that one position is smaller than one depth (YES in S102), the control unit 213 determines that the AF control can be performed without any trouble with the resolution when the PWM frequency A is set, and the process proceeds to S103. In S103, the PWM frequency A is set. On the other hand, when it is determined that one position is one depth or more (NO in S102), the control unit 213 determines that the resolution when the PWM frequency A is set is not sufficient for AF control, and proceeds to S104. In S104, a PWM frequency B that can obtain higher resolution is set. The generated drive signal is supplied to the motor 219 via the LC filter of FIG. After S103 and S104, the process exits from this process and returns to the original process.

  In the present embodiment, two examples of changing processing of the PWM frequencies A and B have been described. However, the PWM frequency may be continuously changed according to the target position of the focus lens. In this case, a process is performed in which the PWM frequency is set higher as the target position of the focus lens is closer to the image sensor than the reference position, and the PWM frequency is set lower as the target position is closer to the subject than the reference position. This can reduce the influence of magnetic field noise on the image sensor. In S102 of FIG. 1, the determination criterion is whether one position is one depth or less, but the determination criterion may be changed according to the AF control accuracy. Further, since the movement of the focus lens shown in S408 and S415 in FIG. 4B is not driving at the time of photographing, the drive control may be performed with the frequency always set to the PWM frequency A.

In FIG. 1, the PWM frequency setting change control has been described on the assumption that the imaging operation is performed. This corresponds to a first state in which the control accuracy of the actuator is required. On the other hand, as an example of the second state where the control accuracy of the actuator is not required, when the imaging operation is not performed, the control unit 213 sets the PWM frequency to a high value and performs power saving control. That is, the PWM frequency set when the imaging operation is not performed is set to a higher value than the PWM frequency set when the imaging operation is performed. Note that the control unit 213 determines whether or not the imaging operation is being performed based on the setting state of the camera mode such as the shooting mode and the reproduction mode and the tilt detection information using the correction lens unit 203.
According to the first embodiment, an effect of reducing power consumption can be obtained by setting the drive frequency of the actuator higher than the resonance frequency. In addition, the influence of magnetic field noise on the image sensor can be suppressed.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Note that the configuration of the imaging apparatus according to the second embodiment is the same as that of the first embodiment, and differences will be described using the symbols already used for the respective components.
In the second embodiment, processing for determining a PWM frequency related to drive control of the focus lens according to a camera mode such as a shooting mode or a playback mode is performed. When a stepping motor is used as the motor 219, if the energization is not always performed, the position of the focus lens is shifted. Therefore, the energization method may be used (hereinafter referred to as focus holding energization). Therefore, a current always flows through the motor 219 even when shooting is not actually performed, for example, even during image reproduction. However, since AF control is not performed during image reproduction, it is not necessary to increase the control resolution of the motor 219. Further, in the comparison between the case where moving image shooting is performed and the case where still image shooting is performed in the shooting mode, the image quality standard required for moving image shooting is lower. For this reason, during moving image shooting, the PWM frequency can be set higher than during still image shooting, and the control resolution of the motor 219 can be set lower to reduce power consumption.

Hereinafter, a process for determining the PWM frequency according to the determination result of whether or not the camera mode is the shooting mode will be described.
FIG. 5 is a flowchart illustrating a processing example of the operation of the imaging apparatus according to the present embodiment.
First, when the power of the imaging apparatus is turned on by the power supply unit 218 (see FIG. 2), the process starts. In step S501, the control unit 213 determines whether the imaging apparatus is in a shooting mode or a mode other than the shooting mode (for example, a playback mode). If it is determined that the current mode is not the shooting mode (NO in S501), the process proceeds to S502. If it is determined that the current mode is the shooting mode (YES in S501), the process proceeds to S504. .
In S502, the control unit 213 determines that it is not necessary to increase the control resolution of the motor 219, sets the PWM frequency A, and obtains a power saving effect by setting it higher than the PWM frequency (B) in the shooting mode. . In step S503, focus holding energization is started. Then, the process returns to S501.

In step S504, the control unit 213 sets the PWM frequency to B so that the drive control of the motor 219 can be performed with a higher resolution, and is lower than the PWM frequency A in modes other than the shooting mode. Driving is started (S401). Since the processing from S401 to S407 is the same as the processing shown in FIG. 4A, their detailed description is omitted. When the process of S407 ends, the process returns to S501.
According to the second embodiment, it is determined whether the camera mode of the imaging apparatus is a shooting mode or a mode other than the shooting mode (for example, a playback mode), and the PWM frequency is changed according to the determination result. In modes other than the shooting mode, it is not necessary to increase the control resolution of the motor 219, so that the power consumption can be reduced by increasing the PWM frequency.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to drive control of a focus adjustment lens, but can be applied to drive control of optical members such as a zoom lens and an image blur correction lens.

204 Focus unit 212 Focus drive control unit 213 Control unit 219 Motor

Claims (8)

An optical device comprising an optical member constituting the optical system and its driving means,
Control means for controlling the driving of the optical member by controlling the driving means;
Smoothing means for smoothing the current flowing through the driving means;
The optical device according to claim 1, wherein the control unit performs control to reduce a drive current by setting a drive frequency of the drive unit to be higher than a resonance frequency of the smoothing unit and the drive unit.   When the control means calculates the drive amount of the optical member and controls the drive means by pulse width modulation control, compared with the drive frequency set in the first state where control accuracy of the drive means is required, The optical apparatus according to claim 1, wherein a drive frequency set in a second state where control accuracy of the drive unit is not required is increased. As the optical member, a focus adjustment lens constituting an imaging optical system;
Comprising an imaging device for imaging a subject via the imaging optical system;
The control means determines whether or not to perform an imaging operation with the imaging optical system and the imaging element, and is set when the imaging operation is not performed compared to the drive frequency of the driving means that is set when the imaging operation is performed. The optical apparatus according to claim 2, wherein a driving frequency of the driving unit is increased.   When the control means changes the drive frequency to control the drive means, the position of the focus adjustment lens is compared to the drive frequency set when the position of the focus adjustment lens is on the subject side. The optical apparatus according to claim 3, wherein the drive frequency set when the image pickup device side is set is increased.   The control means increases the driving frequency set when the moving amount of the focus adjustment lens is smaller than the threshold, compared to the driving frequency set when the moving amount of the focus adjusting lens is larger than the threshold. The optical device according to claim 3, wherein the optical device is an optical device.   When the control means controls the driving means by changing the driving frequency, the control means sets the driving frequency to be set for moving image shooting higher than the driving frequency to be set for still image shooting. The optical device according to claim 3, wherein:   An imaging apparatus comprising the optical apparatus according to claim 1. A control method executed by an optical device comprising an optical member constituting the optical system and its driving means, and a smoothing means for smoothing a current flowing through the driving means,
Setting the drive frequency of the drive means to be higher than the resonance frequency of the smoothing means and the drive means and performing control to reduce the drive current;
A method for controlling an optical device, comprising: generating a signal of the driving frequency set in the step and outputting the signal to the driving unit via the smoothing unit.

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