JP2001008094A - Diaphragm control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make switching operation of diaphragm blades stable while reducing the power consumption in a steady-state. SOLUTION: An image pickup element 14 outputs an image signal corresponding to an optical image that is made incident through a photographing lens 10 and diaphragm blades 12. The output of the image pickup element 14 is given to a process circuit 20 via a CDS/AGC circuit 16 and an A/D converter 18. The circuit 20 converts the output of the A/D converter 18 into video data such as the NTSC data. A microcomputer 32 applies a control signal, which decreases a luminance level when the luminance level of the photographing picture is too high and increases the luminance level when the luminance level of the photographing picture is too low, to an iris drive control circuit 30. The circuit 30 generates a drive control voltage to an IG meter 24 according to this control signal and a chopper circuit 32 applies pulse width modulation to the voltage signal. The output of the chopper circuit 32 controls switching of a switching element 34. When the switching element 34 is closed, a voltage is applied to the IG meter 24. An iris encoder 28 detects a rotational position of the IG meter 24 from the output of a Hall element 26 and gives the detected signal to the circuit 30 and the microcomputer 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aperture control device, and more particularly, to an aperture control device for an electronic camera.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a schematic configuration of a conventional aperture control circuit in an electronic camera. 110 is a photographing lens, 112 is an aperture blade, 114 is an image sensor, 116 is correlated double sampling of an output signal of the image sensor 114,
CDS / AGC circuit for automatically adjusting signal level, 118
Is an A / D converter for converting an analog output of the CDS / AGC circuit 116 into a digital signal, and 120 is a gamma correction, a color balance correction, and an NTSC for the output of the A / D converter 118.
A process circuit 122 performs conversion into a format and the like, and a D / A converter 122 converts a digital output of the process circuit 120 into an analog signal.

Reference numeral 124 denotes an IG meter for mechanically driving the diaphragm blades 112; 126, a Hall element for detecting the position of the IG meter 124; 128, an iris encoder for outputting a signal indicating the diaphragm position based on the output of the Hall element 126;
130 is an iris drive circuit for generating a current for driving the IG meter 124, and 132 is for controlling the aperture blade 112 to a desired value through the iris drive circuit 130 and the IG meter 124 in accordance with the luminance signal from the process circuit 120 and the output of the iris encoder 128. This is a microcomputer that moves the aperture value.

The amount of the subject light transmitted through the taking lens 110 is regulated by the aperture blades 112,
Incident on. The image sensor 114 outputs an image signal corresponding to the incident optical image. The CDS / AGC circuit 116
The output signal of the image sensor 114 is correlated double-sampled and amplified to an appropriate level. The A / D converter 118 converts the analog output of the CDS / AGC circuit 116 into a digital signal.
18 is converted to video data in a standardized format such as NTSC. The D / A converter 122 is connected to the process circuit 1
The video data output from the output terminal 20 is converted into an analog signal.

[0005] The microcomputer 132 follows a signal (for example, a luminance signal) indicating a video level in the process circuit 120, and controls the control signal such that the luminance signal becomes low when the luminance level is too high and becomes high when the luminance level is too low. Is supplied to the iris drive circuit 130. The iris drive circuit 130 drives the IG meter 124 according to the control signal. Since the IG meter 124 itself is an inductance element, a time response delay occurs with respect to the applied voltage. In order to compensate for this delay, the rotational position of the IG meter 124 is detected by the Hall element 126 and fed back to the iris drive circuit 130 and the microcomputer 132 via the iris encoder 128.

FIG. 6 is a schematic block diagram showing the configuration of the IG meter and iris drive circuit 130. The D / A converter 140 converts a digital control signal from the microcomputer 132 into an analog signal. The OP amplifier (operational amplifier) 156, the resistors 154 and 162, and the capacitors 160 and 164 form an integrating circuit. D / A converter 1
The output of 40 is input to this integration circuit via a resistor 158. The output voltage of the OP amplifier 156 is the IG meter 12
4 is applied to the drive coil 166, and a current corresponding to the applied voltage flows through the drive coil 166. Drive coil 166
The magnetic field generated by the current flowing through the IG meter 124
Is rotated to drive the aperture blade 112 in the opening or closing direction.

The Hall element 126 detects the rotational position of the magnet 168. The iris encoder 128 amplifies the output of the Hall element 126 to an appropriate level. OP
The amplifier 142, the resistors 144, 146, 148, 152 and the capacitor 150 form a differentiating circuit. This differentiating circuit differentiates the output of the iris encoder 128,
The speed component is extracted and supplied to the inverting input of the OP amplifier 156. Thereby, the speed of the IG meter 124 is controlled.

With such a circuit configuration, the aperture blades 112 are controlled so as to obtain an appropriate video level.

[0009]

In the prior art, the voltage applied to drive the IG meter 124 from the fully closed state to the fully open state with respect to the applied voltage value Vc when the aperture of the diaphragm blade 112 is kept constant. The voltage value Vo must be set to a considerably large value, and generally, the voltage must be about twice as high as Vc. Therefore, the iris drive circuit 130 must be configured to always output the Vo voltage value. That is, the power supply voltage of the iris drive circuit 130 must be equal to or higher than Vo.

In the conventional aperture driving circuit, even when the open / closed state of the iris is kept constant, the applied voltage Vc is supplied from a power supply voltage higher than Vo, so that the difference between the two voltages and the current, That is, the power is supplied to the OP amplifier 156.
It will be consumed as internal collector loss.

In a general video camera, when the shooting scene changes, the aperture is operated in the opening direction or the closing direction, and in almost all other cases, a substantially constant steady state is maintained. Therefore, in most cases, the above-described collector loss is accompanied, which means that more power is consumed than necessary. Since most home video cameras use a rechargeable battery as a power source due to their characteristics, useless power loss leads to a reduction in shooting time, which is not preferable.

The conventional example also has the following problems. FIG. 7 shows the relationship between the applied voltage of the IG meter 124 and the F value of the diaphragm blade 112 due to the rotation of the IG meter 124. The vertical axis indicates the voltage applied to the IG meter 124, and the horizontal axis indicates the F value of the aperture blade 112. As shown in FIG.
In the case of the aperture blade shape used in a general video camera, the change in the F value is greater on the small aperture side than on the open side with respect to the rotation angle of the rotor of the IG meter 124. Therefore, I
In the range where the applied voltage of the G meter 124 is small, the change in the F value with respect to the applied voltage is large, and in the range where the applied voltage is large, the change in the F value with respect to the applied voltage is small.

In general photographing, for example, when the illuminance of a subject is extremely high, the aperture mechanism of the video camera is in a small aperture state. At this time, the loop gain of the iris drive system becomes too large, and the opening / closing operation of the aperture blade 112 becomes unstable. This may cause a so-called hunting phenomenon of the aperture. When the hunting phenomenon occurs, the image level of the subject is not constant, but changes repeatedly at a certain cycle, which is not preferable in photographing.

An object of the present invention is to provide an aperture control device which has solved such a disadvantage.

An object of the present invention is to provide an aperture control device in which power consumption in a steady state is reduced.

Another object of the present invention is to provide an aperture control device in which the opening and closing operation of the aperture blade is more stable.

[0017]

According to the present invention, there is provided a diaphragm control apparatus comprising: a photographing lens; a diaphragm mechanism; and an image sensor for converting a subject image transmitted through the photographing lens and the diaphragm mechanism into an electric signal. And a process circuit for obtaining a standardized video signal from the output of the image sensor, wherein the aperture control device controls the aperture mechanism, and obtains information on the video signal level of the process circuit. ,
A logical operation unit for performing an operation for making the image level constant, an iris drive control unit for controlling an aperture mechanism of the photographing lens based on a signal from the logical operation unit, and an output of the iris drive control unit And chopper driving means for driving the aperture mechanism with a chopper.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic block diagram showing an embodiment of the present invention. 10 is a photographing lens, 12 is an aperture blade, 1
Reference numeral 4 denotes an image sensor, and 16 denotes a CDS / CCD for automatically correlating double sampling an output signal of the image sensor 14 and automatically adjusting a signal level.
An A / C converter 18 for converting an analog output of the CDS / AGC circuit 16 into a digital signal;
Is a process circuit for performing gamma correction, color balance correction, conversion to NTSC format, and the like on the output of the A / D converter 18, and 22 is a D / A converter for converting the digital output of the process circuit 20 into an analog signal.

Reference numeral 24 denotes an I for mechanically driving the diaphragm blade 12.
G meter, 26 is a Hall element that detects the position of the IG meter 24, 28 is an iris encoder that outputs a signal indicating the aperture position based on the output of the Hall element 26, 30 is an iris drive control circuit that controls driving of the IG meter 24, 32
Is a chopper circuit that performs pulse width modulation on the output of the iris drive control circuit 30; 34 is a switching element that is switched by the output of the chopper circuit 32 to supply a predetermined drive current to the IG meter 24;
The microcomputer controls the iris drive control circuit 30 to move the aperture blade 12 to a desired aperture value in accordance with the luminance signal from 0 and the output of the iris encoder 28.

The amount of light of the subject transmitted through the photographing lens 10 is regulated by the aperture blades 12 and enters the image pickup device 14. The image sensor 14 outputs an image signal corresponding to the incident optical image. The CDS / AGC circuit 16 includes the image sensor 1
4 is correlated double-sampled and amplified to an appropriate level. The A / D converter 18 is a CDS / AGC
The analog output of the circuit 16 is converted into a digital signal, and the process circuit 20 converts the output of the A / D converter 18 into an NTSC signal.
And the like into video data in a standardized format. D / A
The converter 22 converts the video data output from the process circuit 20 into an analog signal. The operation so far is the same as in the conventional example.

According to a signal (for example, a luminance signal) indicating the video level in the process circuit 20, the microcomputer 32 controls the control signal such that the luminance level becomes low when the luminance level is too high, and increases when the luminance level is too low. Is supplied to the iris drive control circuit 30. The iris drive control circuit 30 responds to this control signal and
A signal to the IG meter 24 similar to 30 (a drive signal in the conventional example, but a drive control signal in the present embodiment)
Occurs. The chopper circuit 32 performs pulse width modulation (PMW) on the output of the iris drive control circuit 30, and the output of the chopper circuit 32 controls opening and closing of the switching element 34. When the switching element 34 is closed, the IG meter 2
4 is supplied with a power supply voltage. In order to compensate for the response delay of the IG meter 24 as in the conventional example, the rotation position of the IG meter 24 is detected by the Hall element 26 and fed back to the iris drive control circuit 30 and the microcomputer 32 via the iris encoder 28. IG meter 2
4 is controlled.

FIG. 2 shows a detailed configuration of a portion including the chopper circuit 32, the switching element 34, and the IG meter 24. 40 is an oscillator, 42 is a sawtooth wave generating circuit for generating a sawtooth voltage signal according to the output of the oscillator 40, 44
Is a comparison circuit for comparing the output of the iris drive control circuit 30 and the output of the sawtooth wave generation circuit 42 to generate a PWM pulse. The IG meter 24 includes a drive coil 46 and a magnet 48 directly connected to the diaphragm blade 12 as in the conventional example. In this embodiment, a diode 50 is connected in parallel with the drive coil 46.

FIG. 3 shows an example of the waveform of the output of the iris drive control circuit 30 and the output of the chopper circuit 32 corresponding to the output. FIG. 3A shows the output of the iris drive control circuit 30 and the output waveform of the sawtooth wave generation circuit 42, and FIG.
Shows the output waveform of the chopper circuit 32. FIG. 3 (a)
Numeral 52 indicates an output waveform of the iris drive control circuit 30, and numeral 54 indicates an output waveform of the sawtooth wave generation circuit 42.

The output voltage of the iris drive control circuit 30 is input to a + (plus) input of a comparator 44 of the chopper circuit 32. The oscillator 40 oscillates at a frequency serving as a reference of the PWM waveform output from the chopper circuit 32. This frequency signal may be obtained from another frequency source oscillating inside the camera, such as the horizontal synchronization frequency, outside the chopper circuit 32. The saw-tooth wave generating circuit 42 generates a saw-tooth wave at the cycle of the frequency signal from the oscillator 40, as shown by a waveform 54 in FIG. The output of the sawtooth wave generation circuit 42 is input to the-(minus) input of the comparator 44. Comparator 4
4 compares the two inputs and outputs a PWM signal as shown in FIG.
Outputs a waveform voltage signal.

The switching element 34 is controlled to open and close by the output of the comparator 44. When the switching element 34 is closed, a predetermined voltage value is applied to the drive coil 4 of the IG meter 24.
6 is applied. Thereby, the iris drive control circuit 3
The drive current is applied to the IG meter 24 under the chopper control of the output of 0.

The drive coil 46 of the IG meter 24 is an inductance element. Therefore, even if the voltage is intermittently applied to the drive coil 46 by the switching element 34 that is opened and closed by the PWM signal, the period of the PWM waveform is sufficiently shorter than the time constant based on the inductance L of the drive coil 46 and the internal resistance r. For example, a current that is approximately proportional to the duty ratio of the PWM waveform flows through the drive coil 46 via the diode 50. That is, the same drive current as that of the conventional example shown in FIG. 5 can be applied to the drive coil 46 of the IG meter 24. At this time, the power consumed by the switching element 34 is only a very small switching loss.

As described with reference to FIG. 7, the relationship between the applied voltage of the IG meter and the aperture F value indicates that the aperture value is large.
That is, in a small aperture state, a small change in applied voltage greatly increases F
The value fluctuates and the aperture value is small, that is, in the aperture state near the opening, the change in the F value is small even with a large applied voltage change.
Therefore, in order to obtain an appropriate system loop gain according to the F value of the aperture, it is desirable to reduce the drive gain of the IG meter when the aperture is small, and to increase the gain as the aperture is closer to full aperture.

For this purpose, the waveform of the saw-tooth wave generated by the saw-tooth wave generation circuit 42 may be a waveform that rises rapidly as shown in FIG. FIG. 4 (a)
3B shows the output of the iris drive control circuit 30 and the output waveform of the sawtooth wave generation circuit 42, and FIG. 3B shows the output waveform of the chopper circuit 32. In FIG. 4A, reference numeral 56 denotes an output waveform of the iris drive control circuit 30, and reference numeral 58 denotes an output waveform of the sawtooth wave generation circuit 42.

The output waveform of the sawtooth wave generation circuit 42 is different from a general sawtooth, and its time axis is non-linear, that is,
The slope is steep in a low voltage part and is gentle in a high voltage part. As a result, as shown in FIG. 4B, when the output voltage of the iris drive control circuit 30 is small, the change in the pulse width is large, and the output voltage of the iris drive control circuit 30 is low. When it is large, the change in pulse width is small.

As a result, an output gain corresponding to the relationship between the IG applied voltage and the aperture F value shown in FIG. 7 can be obtained.
That is, regardless of the F-number of the aperture, a substantially constant loop gain can be obtained in the entire range from the small aperture to the open aperture, and hunting on the small aperture side hardly occurs.

In the above embodiment, the position of the IG meter is detected by the Hall element, and the output speed of the Hall element is fed back to control the moving speed of the IG meter. In some IG meters, a braking coil is provided together with a driving coil, and speed control is performed based on the electromotive force of the braking coil.
The present invention can also be applied to a control system using this type of braking coil.

[0033]

As can be easily understood from the above description, according to the present invention, by driving the IG meter with the chopper, the IG meter has a sufficient output capability so that the diaphragm mechanism can be changed from the fully closed state to the fully opened state. However, even when the opening / closing state of the aperture mechanism maintains a constant steady state, the power consumption can be minimized.

The time axis portion of the sawtooth wave of the sawtooth wave generation circuit included in the chopper circuit is a non-linear waveform with a steep rising side, so that the loop of the iris drive system can be operated even on the small aperture side. The gain can be kept within an appropriate range, and hunting of the aperture can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a part of a chopper circuit 32, a switching element 34, and an IG meter 24.

3 is a diagram illustrating an example of a driving waveform of a chopper circuit 32. FIG.

FIG. 4 is a diagram showing another example of a driving waveform of the chopper circuit 32.

FIG. 5 is a schematic block diagram of a conventional example.

FIG. 6 is an iris drive circuit 130 and an IG meter 1
It is a schematic block diagram of 24 parts.

FIG. 7 is a diagram showing a relationship between an applied voltage of an IG meter and an F value of a diaphragm.

[Explanation of symbols]

10: Photographing lens 12: Aperture blade 14: Image sensor 16: CDS / AGC circuit 18: A / D converter 20: Process circuit 22: D / A converter 24: IG meter 26: Hall element 28: Iris encoder 30: Iris drive control circuit 32: Chopper circuit 34: Switching element 36: Microcomputer 40: Oscillator 42: Sawtooth wave generation circuit 44: Comparison circuit 46: Drive coil 48: Magnet 50: Diode 52: Output waveform of the iris drive control circuit 30 54: Output waveform of sawtooth wave generation circuit 42 56: Output waveform of iris drive control circuit 30 58: Output waveform of sawtooth wave generation circuit 42 110: Photographing lens 112: Aperture blade 114: Image sensor 116: CDS / AGC circuit 118: A / D converter 120: Process circuit 122: D / Converter 124: IG meter 126: Hall element 128: Iris encoder 130: Iris drive circuit 132: Microcomputer 140: D / A converter 142, 156: OP amplifier (operational amplifier) 144, 146, 148, 152, 154 158,1
62: resistor 150, 160, 164: capacitor 166: drive coil 168: magnet

Claims (2)

[Claims] An imaging device for converting a subject image transmitted through the imaging lens and the aperture mechanism into an electric signal; and a video signal standardized from an output of the imaging device. An aperture control device for controlling the aperture mechanism, comprising: obtaining information on a video signal level of the process circuit and performing an operation for making the video level constant. A logical operation unit, an iris drive control unit that controls an aperture mechanism of the photographing lens based on a signal from the logical operation unit, and a chopper drive unit that drives the aperture mechanism chopper according to an output of the iris drive control unit. An aperture control device, comprising: 2. The diaphragm according to claim 1, wherein the chopper driving means includes a saw-tooth wave generating circuit, and the saw-tooth wave generated by the saw-tooth wave generating circuit has a steep nonlinear waveform in a time axis part. Control device.