JPH05344415A - Automatic exposure controller for optical equipment - Google Patents

Abstract

PURPOSE:To eliminate the transient change or the hunting of brightness by slowing down the driving speed of a stepping motor when a difference between a luminance signal and a brightness reference value reaches a level or below and converging the brightness into its reference value smoothly. CONSTITUTION:A stepping motor 13 driven by a digital signal is adopted for an actuator driving an iris blade 2, and the iris blade 13 is moved smoothly toward an objective position (position corresponding to a brightness reference value) without causing an oscillator or a hunting by slowing down the speed of the stepping motor 13 when a difference between a luminance signal Y and a brightness reference value reaches a level or below. The control slowing down the speed of the stepping motor 13 is implemented by decreasing the number of pulses per time.

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 device such as a video camera, and more particularly to an automatic exposure control device for driving an exposure amount adjusting member such as a diaphragm blade with a stepping motor.

[0002]

2. Description of the Related Art With reference to FIG. 6, the structure and operation relating to an automatic exposure control device in a conventional video camera will be described.

The image pickup light from the subject which is incident from the lens optical system 1 is imaged on the image pickup surface of the image pickup device 3 after the light amount is adjusted by the diaphragm blade 2 which is an exposure amount adjusting member. The subject image formed on the image pickup device 3 is photoelectrically converted here and is output to the camera signal processing circuit 4 as an image pickup signal. In the camera signal processing circuit 4, processing such as γ (gamma) conversion is performed, and the color signal C and the luminance signal Yγ are extracted as video signals. Then, this video signal is output to the outside from the camera unit in the form of a composite video signal or the like through the camera encoder 5 which converts it into an NTSC signal.

The brightness signal Y output from the camera signal processing circuit 4 is input to the detection circuit 6 to generate a control signal for controlling the diaphragm blade 2 so as to obtain an appropriate exposure according to the brightness state of the screen. Then, it is taken into the camera microcomputer 7. The value integratedly detected by the camera microcomputer 7 is compared with a reference value (appropriate exposure value) by the comparator 8, and the difference is output to the driver 9. The driver 9 converts the signal from the microcomputer 7 into an appropriate voltage and outputs it 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 conventional automatic exposure control device for a video camera described above, the actuator 10 that drives the diaphragm blade 2 is an analog electromagnetic motor, and the driver that controls the electromagnetic motor is also an analog circuit. The control system for the motor is configured as a closed loop control system. In such a closed loop control system using analog signals, if the characteristics of the control elements are not matched, unstable phenomena such as oscillation and hunting are likely to occur in the aperture blades to be controlled. In order to prevent unstable phenomena such as oscillation and hunting, the dynamic characteristics and frequency response of the diaphragm mechanism must be constant, but since the dynamic characteristics and frequency response of each diaphragm mechanism differ slightly, The automatic exposure control device may cause unstable phenomena such as oscillation and hunting in the diaphragm blades, especially when the difference between the brightness signal and the brightness reference value becomes small (that is, the closer the diaphragm is to the target value, the closer ) May cause hunting or oscillation.

An object of the present invention is to provide an automatic exposure control device that does not cause oscillation or hunting in the diaphragm blade.

[0008]

In order to solve the above-mentioned problems, the present invention adopts a stepping motor which can be driven by a digital signal as an actuator for driving a diaphragm blade, and further, a difference between a luminance signal and a luminance reference value. When the level becomes lower than a certain level, the speed of the stepping motor is slowed to smoothly move the diaphragm blade toward the target position (the position corresponding to the brightness reference value) without causing oscillation or hunting. Eliminates transient changes in brightness and hunting.

The control for reducing the speed of the stepping motor is performed by decreasing the number of pulses per time.

[0010]

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

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

The image pickup light from the subject which is incident from the lens optical system 1 is formed on the image pickup surface of the image pickup device 3 after the light amount is adjusted by the diaphragm blade 2 which is an exposure amount adjusting member. The subject image formed on the image pickup device 3 is photoelectrically converted here and is output to the camera signal processing circuit 4 as an image pickup signal. In the camera signal processing circuit 4, a process such as γ (gamma) conversion is performed, and the color signal C and the luminance signal Yγ are taken out as a video signal. Then, this video signal is output from the camera unit to the outside through the NTSC type camera encoder 5 in the form of a composite video signal or the like.

The brightness signal Y output from the camera signal processing circuit 4 is input to the detection circuit 6 to generate a control signal for controlling the diaphragm blade 2 so as to obtain an appropriate exposure according to the brightness state of the screen. And is taken into the camera microcomputer 7. The brightness signal Y is output to the AF microcomputer for focusing. The brightness 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 the difference from the proper exposure value is sent to the driver 12.

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

Next, the control operation performed by the camera microcomputer 7 will be described with reference to FIG.

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

# 2: Check if the diaphragm blade has come to the reset sensor position.

# 3: Since the diaphragm blade has come to the reset sensor position, the driving is stopped.

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

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

# 7: Since the counter has reached the initial value, AE
The A / D conversion value of the luminance signal is input to start the control.

# 8: It is confirmed whether the absolute value of the difference between the A / D value input in # 7 and the preset reference value is 10 or more.

# 9: Since the absolute value of the difference of # 8 is 10 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 the preset reference value is 6 or more.

# 11: Since the absolute value of the difference between # 10 and # 10 is 6 or more, driving is performed in the direction of the sign of the difference at time / pulse number = 6/4.

# 12: Check whether the absolute value of the difference between the A / D value input in # 7 and the preset reference value is 2 or more.

# 13: Since the absolute value of the difference of # 10 is 2 or more, driving is performed at the time / pulse number = 8/4 in the direction of the sign of the difference.

# 14: Check whether the difference between the A / D value input in # 7 and the preset reference value is zero.

# 15: Since the difference between # 10 and # 10 is not 0, driving is performed at the time / pulse number = 10/2 in the direction of the sign of the difference.

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

# 17: It is confirmed whether the A / D value input in # 7 = reference value.

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

By repeating the above operation, the drive control of the diaphragm blade 2 by the stepping motor is performed.
When the diaphragm blades 2 are controlled as described above, the brightness converges smoothly with respect to the reference value of brightness, as shown in the graph of FIG.

<Other Embodiments> FIG. 4 shows another embodiment.

As in the case of FIG. 1, the luminance signal subjected to the integral detection is taken into the camera microcomputer 7 and compared with the reference value by the comparator 8 in the camera microcomputer 7. The resultant diaphragm drive information is transmitted to the lens microcomputer 14 through the communication line 15 provided between the lens microcomputer and the camera microcomputer. The lens microcomputer 14 outputs the communicated diaphragm drive information to the driver 12 as a rectangular wave having a certain period. Further, the driver 12 supplies electric power for driving the diaphragm to the stepping motor 13 to drive the diaphragm blade 2. The reset sensor confirms the reset position when the power is turned on and resets the counter.

Next, the control operation performed in the camera microcomputer 7 will be described with reference to FIG.

# 1: The luminance signal output from the camera signal processing circuit 4 is integrated by the integrating circuit 6, and the output is taken into the camera microcomputer 7.

# 2: The reference level is taken into the camera microcomputer 7.

# 3: The camera microcomputer executes the calculation (integrated value of video signal-reference level).

# 4: Wait until the input timing of Vsync (video vertical synchronizing signal).

# 5: The chip select signal is output.

# 6: Iris data is converted from parallel to serial and transmitted from the camera side to the lens side via the transmission line 9.

# 7: Reset the chip select signal.

With the above, the communication of the iris control information to the lens side is completed. This communication is repeated periodically.

Next, the operation of the lens microcomputer 14 performed based on the data transmitted from the camera side will be described.

# 8: Confirm the chip select input.

# 9: Iris data is taken into the lens microcomputer 14 by serial-parallel conversion.

# 10: The lens microcomputer 14 outputs to the driver 12 a rectangular wave having a direction and speed corresponding to the received aperture value.

The driver of # 11: 12 drives the actuator at the speed and direction corresponding to the cycle and phase of the transmitted rectangular wave.

# 13: Update the counter.

Control information is communicated between the camera unit and the lens unit by repeatedly performing the above control and flow in a predetermined cycle, and thereby various controls including iris control are executed.

[0052]

As described above, according to the exposure control device of the present invention, when the difference between the luminance signal and the reference value of the luminance becomes less than a certain level, the driving speed of the stepping motor is slowed to reduce the luminance. By smoothly converging with respect to the reference value of, it is possible to eliminate a transient change in luminance and hunting.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a non-lens interchangeable 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 the camera microcomputer 7 in the configuration shown in FIG.

FIG. 3 is a diagram showing the relationship between the driving time of the diaphragm blades and the diaphragm opening amount in the configuration shown in FIG.

FIG. 4 is a schematic view of a main part of a lens interchangeable video camera equipped with the automatic exposure control device of the present invention.

5 is a flowchart of control operations executed in the camera microcomputer and the lens microcomputer in the configuration of FIG.

FIG. 6 is a schematic view 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

Claims (1)

[Claims] 1. A light amount adjusting member such as a diaphragm blade, driving means for driving the light amount adjusting member, brightness detecting means for detecting the brightness of an object to be observed, and detected brightness and target detected by the brightness detecting means. An automatic exposure control device for an optical instrument, comprising: a control unit that controls the driving unit so that a difference from the luminance is 0. The driving unit is a stepping motor, and the control unit is configured to detect the detected luminance and An automatic exposure control device for an optical instrument, which has a function of controlling so as to slow down the driving speed of the stepping motor when the difference from the target brightness is below a certain level.