JP3164887B2 - Automatic exposure control device for optical equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic exposure control device mounted on an optical apparatus such as a video camera, and more particularly to an automatic exposure control device for driving an exposure amount adjusting member such as an aperture blade with a stepping motor.

[0002]

2. Description of the Related Art The configuration and operation of a conventional automatic exposure control device in a video camera will be described with reference to FIG.

An image pickup light from a subject incident from the lens optical system 1 forms an image on an image pickup surface of an image pickup device 3 after an amount of light is adjusted by a diaphragm blade 2 which is an exposure amount adjustment member. The subject image formed on the image sensor 3 is photoelectrically converted here and output to the camera signal processing circuit 4 as an image signal. The camera signal processing circuit 4 performs processing such as γ (gamma) conversion, and extracts the color signal C and the luminance signal Yγ as video signals. The video signal is output from the camera unit to the outside in the form of a composite video signal or the like via a camera encoder 5 that converts the video signal into an NTSC signal.

A luminance signal Y output from the camera signal processing circuit 4 is input to a detection circuit 6 for generating a control signal for controlling the aperture blade 2 so as to obtain an appropriate exposure according to the luminance state of the screen. Then, it is taken into the camera microcomputer 7. A value integrated and detected by the camera microcomputer 7 is compared with a reference value (appropriate exposure value) by a comparator 8, and the difference is output to a driver 9. The driver 9 converts the signal from the microcomputer 7 into an appropriate voltage and outputs the signal to the actuator 10 to drive the diaphragm blade 2.

Further, the encoder 11 detects the position of the diaphragm blade 2 and is taken into the camera microcomputer 7 and the AF microcomputer.

[0006]

In the above-mentioned conventional automatic exposure control apparatus for a video camera, the actuator 10 for driving the aperture blade 2 is an analog electromagnetic motor, and the driver for controlling the electromagnetic motor is also constituted by an analog circuit. The control system of the motor is configured as a closed loop control system. In such a closed-loop control system using analog signals, unstable characteristics such as oscillation and hunting are likely to occur in the aperture blade to be controlled if the characteristics of the control elements are not matched. In order to prevent instability such as oscillation and hunting, the dynamic characteristics and frequency response of the aperture mechanism must be constant.However, the dynamic characteristics and frequency response of each aperture mechanism are slightly different for each unit. In the automatic exposure control device, unstable phenomena such as oscillation and hunting may occur in the aperture blades, particularly when the difference between the luminance signal and the luminance reference value is small (that is, as the aperture approaches the target value, ) May cause hunting and oscillation.

It is an object of the present invention to provide an automatic exposure control device which does not cause oscillation or hunting in the aperture blade.

[0008]

In order to solve the above-mentioned problems, the present invention employs a stepping motor which can be driven by a digital signal as an actuator for driving the aperture blades, and a luminance signal (detection luminance) having an appropriate exposure. value
When approaching the (target brightness) , the driving pulse signal to be applied to the stepping motor is switched from a rectangular wave to a micro step wave to perform a micro step wave drive. In addition, to drive the aperture blade slowly near an appropriate exposure value. , The period of the micro step wave is the period of the above rectangular wave
It is assumed to control to longer than.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a video camera equipped with an automatic exposure control device according to the present invention will be described in detail.

FIG. 1 is a block diagram showing a schematic configuration of a main part of a video camera having an automatic exposure control device according to the present invention.

The imaging light from the subject incident from the lens optical system 1 forms an image on the imaging surface of the imaging device 3 after the amount of light is adjusted by a diaphragm blade 2 which is an exposure adjustment mechanism (iris). The subject image formed on the image sensor 3 is photoelectrically converted here and output to the camera signal processing circuit 4 as an image signal. The camera signal processing circuit 4 performs processing such as γ (gamma) conversion, and extracts the color signal C and the luminance signal Yγ as video signals. And this video signal is NT
It is output from the camera unit to the outside in the form of a composite video signal or the like via the SC type camera encoder 5.

The luminance signal Y output from the camera signal processing circuit 4 is input to a detection circuit 6 for generating a control signal for controlling the aperture blade 2 to obtain an appropriate exposure according to the luminance state of the screen. Then, it is taken into the camera microcomputer 7. The luminance signal Y is output to the AF microcomputer to perform focusing. The luminance signal is compared with a reference value (appropriate exposure value) by a comparator 8 in the camera microcomputer 7, and a rectangular wave having a cycle corresponding to a difference from the appropriate exposure value is sent to the driver.

The driver 12 drives the stepping motor 13 at a certain speed by the input rectangular wave. Further, the camera microcomputer 7 detects from the information of the encoder 11 how far the aperture is away from the reset position by counting the number of pulses of the output rectangular wave.

FIG. 2 is a flowchart of the control operation performed in the camera microcomputer 7. This will be described below with reference to FIG.

# 1: The diaphragm blade is driven in the CLOSE direction.

[0016] # 2: Make sure came down Ri wings to reset the sensor position.

# 3: The drive stops because the diaphragm blade has reached the reset sensor position.

# 4: Counter reset # 5: The aperture blade is driven to the initial position.

# 6: Check whether the counter has reached the initial value.

# 7: Since the counter has reached the initial value, A
To start the E control, an A / D converted value of the luminance signal is input.

# 8: It is confirmed whether the absolute value of the difference between the A / D value input in # 7 and a preset reference value is 25 or more.

# 9: Since the absolute value of the difference of # 8 is 25 or more, driving is performed in the direction of the sign of the difference at time / pulse number = 10/10.

# 10: Check whether the absolute value of the difference between the A / D value input in # 7 and a preset reference value is 15 or more.

# 11: Since the absolute value of the difference of # 10 is 15 or more, microstep wave drive is performed in the direction of the sign of the difference at a time / pulse number = 6/10 .

# 12: It is checked whether the absolute value of the difference between the A / D value input in # 7 and a preset reference value is 5 or more.

# 13: Since the absolute value of the difference of # 10 is 5 or more, microstep wave driving is performed in the direction of the sign of the difference at time / pulse number = 8/10 .

# 14: Check whether the difference between the A / D value input in # 7 and a preset reference value is 0 or not.

# 15: Since the difference of # 10 is not 0, the micro step wave drive is performed in the direction of the sign of the difference with time / pulse number = 20/10 .

# 16: Since the difference between # 10 is 0, the driving is stopped.

# 17: Update the counter in the sign direction.

# 18: It is checked whether the A / D value input in # 7 is equal to the reference value.

# 19: Since A / D value = reference value, driving is stopped.

The aperture blade 2 is controlled by the stepping motor by repeating the above operation. With the above control, the brightness smoothly converges to the reference value of the luminance as shown in the graph of FIG.

<Other Embodiment> Next, another embodiment will be described.

The resolution can be substantially increased by increasing the number of divisions of the microstep wave. Therefore, in the present embodiment, when the difference between the luminance signal and the reference value falls below a certain level, the mode is switched to the micro step wave drive.

Furthermore, as the number approaches the reference value, the number of divisions of the microstep wave is increased and the driving speed is reduced, so that the reference value can be smoothly converged.
This is a particularly effective means on the small aperture side.

This will be described in detail with reference to FIG. It is assumed that the reference value is F8. At that time, the driving resolution substantially increases as the reference value is approached, and the driving speed can be further reduced to smoothly converge to the reference value.

As described above, according to the present invention, the light amount adjusting member such as the aperture blade, the driving unit for driving the light amount adjusting member, the luminance detecting unit for detecting the luminance, and the luminance detecting unit detect the luminance. An automatic exposure control device for an optical apparatus having a control unit for controlling the driving unit so that a difference between the detected luminance and the target luminance is set to 0, wherein the driving unit is a stepping motor, and the detection is performed by the luminance detecting unit. When the difference between the detected luminance and the target luminance becomes smaller than a first value, the driving of the stepping motor is switched from the rectangular wave driving to the micro step wave driving, and then the detected luminance detected by the luminance detecting means and when the difference between the target luminance is smaller than the smaller second value than the first value, the period of the micro-step wave drive the rectangular wave
Since the control is performed so as to be longer than the period of the rectangular wave at the time of movement , hunting and oscillation can be prevented, and a transitional luminance change can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a non-interchangeable lens type video camera equipped with an automatic exposure control device according to the present invention.

FIG. 2 is a flowchart of a control operation performed by a camera microcomputer 7 in the configuration shown in FIG.

FIG. 3 is a diagram showing a relationship between a driving time of an aperture blade and an aperture amount in the configuration shown in FIG. 1;

FIG. 4 is a diagram showing a relationship between a drive time of an aperture blade and an aperture amount in the configuration shown in FIG. 1;

FIG. 5 is a schematic diagram of a main part of a video camera equipped with a conventional automatic exposure control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lens optical system 2 ... Aperture blade 3 ... Imaging element 4 ... Camera signal processing circuit 5 ... Camera encoder 6 ... Detection circuit 7 ... Camera microcomputer 8 ... Comparator 9,12 ... Driver 10 ... Actuator 11 ... Encoder 13 ... Stepping motor 14: Lens microcomputer 15: Communication line

Continuation of the front page (56) References JP-A-63-131661 (JP, A) JP-A-63-61570 (JP, A) JP-A-61-273194 (JP, A) JP-A-3-86098 (JP) JP-A-2-155497 (JP, A) JP-A-2-105121 (JP, A) JP-A-4-21198 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H04N 5/222-5/257 G03B 7/095 G03B 9/02

Claims (1)

(57) [Claims] 1. A light amount adjusting member such as an aperture blade, a driving unit for driving the light amount adjusting member, a luminance detecting unit for detecting luminance, and a difference between a detected luminance detected by the luminance detecting unit and a target luminance. An automatic exposure control device for an optical device, comprising: a control unit that controls the driving unit so that the value of the driving unit is set to zero. The driving unit is a stepping motor, and the control unit detects the detection detected by the luminance detection unit. When the difference between the luminance and the target luminance becomes smaller than the first value, the driving of the stepping motor is switched from rectangular wave driving to micro step wave driving, and thereafter, the detected luminance detected by the luminance detecting means and the target luminance are compared. when the difference between the luminance is smaller than the smaller second value than the first value, the period of the micro-step wave during the rectangular wave drive rectangular
An automatic exposure control device for optical equipment, wherein the control is performed so as to be longer than the period of the shape wave .