JPH05344416A - Automatic exposure controller for optical equipment - Google Patents

Abstract

PURPOSE:To eliminate the transient change or the hunting of brightness by selecting microstep wave driving for the driving of a stepping motor when a difference between a luminance signal and a brightness reference value reaches a certain level or below. CONSTITUTION:A stepping motor 13 driven by a digital signal is adopted for an actuator driving an iris blade 2. When a luminance signal (brightness detection value) is close to a brightness reference value, the number of driving pulse signals per time imparted to the stepping motor 13 is increased to apply microstep driving having a smaller step width than that of the usual driving to the stepping motor 13. Thus, the iris blade 2 close to a proper exposure is slowly approached to an objective position.

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 The structure and operation of a conventional automatic exposure control device in a video camera will be described with reference to FIG.

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 luminance signal (luminance detection value) is a luminance signal. When the value is close to the reference value (appropriate exposure value), the number of drive pulse signals given to the stepping motor per time is increased to cause the stepping motor to carry out microstep driving smaller than the normal step amount. In the vicinity of the appropriate exposure value, the diaphragm blades are slowly moved closer to the target position.

[0009]

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 amount of light is adjusted by a diaphragm blade 2 which is an exposure adjusting mechanism (iris). 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. And this video signal is NT
It is output to the outside from the camera unit in the form of a composite video signal through the SC type camera encoder 5.

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 proper 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.

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.

FIG. 2 is a flow chart 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.

# 2: It is confirmed whether or not a blade for squeezing comes 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 whether the counter has reached the initial value.

# 7: Since the counter has reached the initial value, A
To start the E control, the A / D conversion 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 the 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 the preset reference value is 15 or more.

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

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

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

# 14: It is confirmed whether or not 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, the micro step wave is driven in the direction of the sign of the difference at the time / pulse number = 5/10.

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

# 17: The counter is updated in the sign direction.

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

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

By repeating the above operation, the stepping motor controls the diaphragm blade 2. When the control is performed as described above, the brightness smoothly converges to the reference value of the brightness as shown in the graph of FIG.

<Other Embodiments> Next, other embodiments will be described.

Substantial resolution can be improved 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 becomes equal to or lower than a certain level, the driving is switched to the micro step wave driving.

Further, as the number of divisions of the micro-step wave is increased and the driving speed is decreased as the value approaches the reference value, it is possible to smoothly converge to the reference value.
This is a particularly effective means on the small aperture side.

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

[0038]

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 is below a certain level, the stepping motor is driven by the micro step wave drive. By switching and further slowing down the speed and allowing the brightness to converge smoothly with respect to the reference value, hunting and oscillation can be prevented and a transient brightness change can be prevented.

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

FIG. 5 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 ... Image sensor 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

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[Procedure amendment]

[Submission date] February 1, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

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

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction content]

# 11: Since the absolute value of the difference of # 10 is 15 or more, the micro step wave is driven in the direction of the sign of the difference at the time / pulse number = 6/10 .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

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

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

# 15: Since the difference between # 10 and # 10 is not 0, the micro step wave is driven in the direction of the sign of the difference at time / pulse number = 20/10 .

[Procedure Amendment 5]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

[Procedure Amendment 6]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

Claims (1)

[Claims] 1. A light quantity adjusting member such as a diaphragm blade, a driving means for driving the light quantity adjusting member, a brightness detecting means for detecting the brightness of an object to be observed, and a detected brightness detected by the brightness detecting means and a target. An automatic exposure control device for an optical device, comprising: a control unit that controls the drive unit so that a difference from the brightness is 0. The drive unit is a stepping motor, and the control unit controls the detected brightness When the value becomes close to the target brightness, the stepping motor drive has a function of switching from rectangular wave drive to microstep wave drive speed and performing control to lengthen the cycle of the microstep wave. The automatic exposure control device for optical equipment.