JPH10276363A - Exposure controller, camera using it, feedback controller and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the exposure controller in which the exposure is surely converged to a convergence object value even when a loop gain of a control loop is changed, to provide the camera employing the controller, the feedback controller and its control method. SOLUTION: The exposure controller 17 uses a shutter speed of a CCD image pickup element 11 to automatically control lightness of a pickup screen and controls the exposure in response to loop gain information of its control loop given externally. A dead band calculation processing section 19 calculates a dead band based on the externally given loop gain information and the dead band of the control loop set by an Automatic Exposure(AE) processing section 18 is decided depending on the dead band information, that is, the loop gain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exposure control device, a camera using the same, a feedback control device, and a control method therefor.

[0002]

2. Description of the Related Art In general, a camera using a solid-state imaging device such as a CCD (Charge Coupled Device) as an imaging device generally uses a signal charge accumulated in each pixel (photoelectric conversion element) in the CCD imaging device. A so-called electronic shutter function for sweeping the semiconductor substrate side by applying a shutter pulse, for example, is provided, and the charge accumulation time in the field period, that is, the exposure time, is controlled by changing the shutter pulse application interval, that is, the shutter speed. can do. This is an automatic exposure (AE) control device using a shutter speed.

In this automatic exposure control device, for example, luminance information in a video signal output from a CCD image pickup device is fetched as screen luminance information, and a difference between the luminance information and an AE convergence target value is obtained. Exposure (exposure) control is performed by a control loop that sets shutter speed information according to the difference and controls the timing of generating a shutter pulse to be applied to the CCD image sensor based on the shutter speed information.

A shutter pulse is generated by a timing generator, but the timing generator cannot set a continuous shutter speed, but takes a discrete shutter speed. Therefore, the obtained exposure time also takes a discrete value. As a result, when converging to the AE convergence target value, an oscillation state (hunting) occurs near the target value. In order to prevent this, in the AE control process, the AE convergence target value in the AE control has a width. Hereinafter, this is called a dead zone.

[0005] This dead zone is controlled by an object to be controlled (for AE control,
It is desirable to determine according to the control accuracy of the timing generator. Therefore, there is known an exposure control device in which the convergence accuracy to the AE convergence target value is improved by setting an appropriate dead zone width in each case according to the shutter speed (see JP-A-6-62323). However, the dead zone need not be variable but may be fixed.

When the dead zone is fixed, a dead zone at which the control accuracy of the control object becomes the worst is set. AE
In the control loop, since the dead zone is related to the shutter speed, conventionally, generally, the change rate of the exposure time when the shutter speed is changed, that is, ｛(previous exposure time−current exposure time) / previous time The dead band width is set to be wider based on the maximum exposure time 基準, so that no oscillation state occurs regardless of the shutter speed.

[0007]

By the way, there is a demand that the response of the AE control can be arbitrarily set by making the loop gain of the AE control loop variable. By increasing the loop gain, the response becomes faster, and by decreasing the loop gain, the response becomes slow. However, when the loop gain is reduced, the responsiveness of the AE control becomes slow, and the AE control enters the dead zone slowly toward the convergence target value. If it is set to be too wide, there is a concern that the control will end at the point of entering the dead zone and converge to a position far from the AE convergence target value.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an exposure control capable of reliably converging to a convergence target value even when a loop gain of a control loop is changed. It is an object of the present invention to provide a device, a camera including the same, a feedback control device, and a control method thereof.

[0009]

SUMMARY OF THE INVENTION An exposure control apparatus according to the present invention automatically controls the brightness of an image pickup screen by using a shutter speed of a solid-state image pickup device and has a variable control loop gain. A control device, comprising: difference detection means for detecting a difference from a target value of luminance information given from the solid-state imaging device; and setting a dead zone for the difference information detected by the difference detection means, according to a loop gain. And a shutter speed setting means for setting a shutter speed based on the difference information passed through the dead zone setting means.

In the exposure control device having the above-described structure, the difference detecting means fetches luminance information from the solid-state image sensor and compares the luminance information with a target value to detect a difference. This difference information is basically the value to be controlled,
The dead zone setting means is provided to prevent oscillation near the target value.
A dead zone is provided for the difference information, and the dead zone width is set according to the loop gain. Therefore,
The dead zone setting means outputs difference information outside the dead zone width. The shutter speed setting means controls the shutter speed according to the difference information outside the dead zone width to set the exposure time.

[0011] The feedback control device according to the present invention comprises:
A loop gain of the feedback control loop is variable, a deviation detecting means for detecting a deviation of the controlled variable of the controlled object from the target value, and a dead zone is set for the deviation information detected by the deviation detecting means. And a control means for controlling a control target based on the deviation information passed through the dead zone setting means.

In the feedback control device having the above configuration, the deviation detecting means detects the deviation by taking in the control amount of the control object and comparing the control amount with the target value. This deviation information is basically the value to be controlled,
The dead zone setting means is provided to prevent oscillation near the target value.
A dead zone is provided for the deviation information, and the width of the dead zone is set according to the loop gain. Therefore,
The dead zone setting means outputs deviation information outside the dead zone width. The control means controls the control target according to the deviation information outside the dead zone width.

[0013] The feedback control method according to the present invention comprises:
In a feedback control device in which a loop gain of a feedback control loop is variable, a deviation of a control amount of a control target from a target value is detected, and a dead zone width according to the loop gain is set for the detected deviation information,
The control target is controlled based on the deviation information outside the dead zone width.

In this feedback control method,
The deviation is detected by comparing the control amount of the control target with the target value. This deviation information is basically a value to be controlled. To prevent oscillation near the target value, a dead band is provided for this deviation information, and the dead band width is set according to the loop gain. Then, the control target is controlled according to the deviation information outside the dead zone width.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a basic configuration diagram showing an entire camera system to which the present invention is applied.

In FIG. 1, a solid-state imaging device, for example, CC
Image light from a subject (not shown) is incident on the imaging surface of the D imaging element 11 via an optical system including a lens 12 and the like. The CCD image pickup device 11 controls the exposure time (shutter speed), signal charge readout, vertical transfer, horizontal transfer, and the like by various timing signals generated from a timing generator (TG) 13, thereby controlling incident light. It is converted into an electric signal in pixel units and output as a video signal.

The video signal output from the CCD image sensor 11 is supplied to a preamplifier 14 where the signal component is sampled and held, and a gain control (AGC) is performed to adjust the signal component to an appropriate level. The video signal that has passed through the preamplifier 14 is converted from an analog signal to a digital signal by an A / D converter 15, and is converted into a DSP (Digit) signal.
al Signal Processor (digital signal processing) circuit 16 and various processings are performed by the DSP circuit 16 and then output as video signals.

The electronic shutter function provided in the CCD image pickup device 11 is utilized, and the CCD image pickup device 11
Is provided with an exposure control device 17 for performing automatic exposure (AE) control by changing the interval of shutter pulses applied to the AE, that is, changing the shutter speed.

The exposure control device 17 includes a DSP circuit 16
The shutter speed information is obtained based on the luminance information given from the CPU, the timing of the shutter pulse output from the timing generator 13 is controlled based on the shutter speed information, and the AE control loop is controlled according to the loop gain information given from the outside. AE control processing unit 18 having a variable loop gain, and a dead band width calculation processing unit 19 which calculates a dead band width based on loop gain information given from the outside and sets a dead band width of the AE control loop. .

FIG. 2 shows an example of a circuit configuration in the case where the AE control processing section 18 is constituted by, for example, hardware. The AE control processing unit 18 includes a target value setting circuit 21 for setting an AE convergence target value, a difference detection circuit 22 for detecting a difference of the luminance information provided from the DSP circuit 16 in FIG. Comparison circuits 23 and 24 for comparing the difference output of the difference detection circuit 22 with reference voltages V1 and V2 (V1> V2), and shutter speed setting for setting shutter speed information based on each comparison result of these comparison circuits 23 and 24 And a circuit 25.

In the AE control processing section 18, a difference detection circuit 22, comparison circuits 23 and 24, and a shutter speed setting circuit 25 are present in an AE control loop, and each gain of these circuits determines a loop gain. Then, this loop gain is set by the loop gain setting circuit 26 based on loop gain information given from the outside. That is, the loop gain of the AE control loop is variable according to loop gain information provided from the outside.

The comparison circuit 23 includes a difference detection circuit 22.
When the difference output of the difference detection circuit 22 is lower than the reference voltage V2, the comparison circuit 24 outputs the comparison result of the "H" level (high level). Output the comparison result. The shutter speed setting circuit 25 outputs the shutter speed information for decreasing the shutter speed when the comparison circuit 23 outputs the “H” level comparison result, and outputs the “H” level comparison result from the comparison circuit 24. At this time, shutter speed information for increasing the shutter speed is output. This shutter speed information is supplied to the timing generator 13 in FIG.

The shutter speed setting circuit 25
When both of the comparison circuits 23 and 24 output the comparison result at the “L” level (low level), no shutter speed information for controlling the shutter speed is output. That is,
The reference voltage V1 of the comparison circuit 23 corresponds to the upper limit of the dead zone, and the reference voltage V2 of the comparison circuit 24 corresponds to the lower limit of the dead zone.

The upper and lower limits of the dead zone, that is, the reference voltages V1 and V2 in the comparison circuits 23 and 24 are shown in FIG.
Is set by the dead zone width setting circuit 27 based on the dead zone information given from the dead zone calculation processing section 19. The dead zone calculation processing section 19 calculates dead zone information based on loop gain information supplied from outside, so that the dead zone width of the AE control loop is variable according to loop gain information supplied from outside. .

FIG. 3 shows an example of the configuration of the dead zone width calculation processing section 19. The dead zone width calculation processing unit 19 has, for example, dead zone data as a table, and the AE control processing unit 18
Dead band data conversion processing unit 31 that outputs dead band data corresponding to shutter speed information given from, a coefficient setting unit 32 that sets a multiplication coefficient according to externally supplied loop gain information, and a dead band data conversion processing unit 31
And a multiplier 33 that multiplies the dead zone data output from the multiplication factor by the multiplication coefficient set by the coefficient setting unit 32, and supplies the multiplied output of the multiplier 33 to the AE control processing unit 18 as dead zone information.

The dead band width calculation processing section 19 according to the present embodiment.
In the above, the case where the dead zone width is variable according to the shutter speed information is taken as an example, but it is not necessarily required to be variable.
It may be fixed. However, the variable case has an advantage that the convergence accuracy to the AE convergence target value can be improved because an appropriate dead zone width can be set each time according to the shutter speed. When the dead band is fixed, for example, the dead band width may be set based on the maximum change rate of the exposure time, and the fixed dead band data may be supplied to the multiplier 33.

FIG. 4 shows an example of the relationship between the dead zone width that changes according to the loop gain and the AE convergence target value. In FIG. 4, (a) shows a dead zone width preset according to or fixed to the shutter speed, (b) shows a dead zone width when loop gain = 0.5, and (c) shows a loop gain. (D) shows the dead zone width when the loop gain is 0.125, and (d) shows the dead zone width when the loop gain is 0.125.

As is apparent from FIG. 4, when the loop gain is small, the dead band width is set narrow, and when the loop gain is large, the dead band width is set wide. When the loop gain is small, the response of the AE control is slow.
It gradually converges to the E convergence target value over time. Therefore, since the correction amount in one control process is small, the dead zone width for the loop gain is set to be narrow, so that the AE convergence target value can be surely converged.

On the other hand, when the loop gain is large, AE
Since the response of the control is fast, the AE convergence target value converges quickly without taking much time. Therefore, since the amount of correction in one control process is large, the dead zone width for the loop gain is set wide, so that the oscillation does not fall into the vicinity of the AE convergence target value and the convergence can be ensured in the vicinity of the AE convergence target value. it can.

As described above, in the exposure control device for controlling the exposure time of the CCD image sensor 11 using the shutter speed, the dead zone width is automatically set according to the loop gain of the AE control loop. Accordingly, it is not necessary to reset the dead zone width in accordance with the loop gain, and even if the response of the AE control changes in a slow direction or a fast direction in accordance with the loop gain, the AE is not affected. Convergence can be ensured near the convergence target value.

Therefore, if the minimum required dead zone width is set, the optimum dead zone width according to the response of the AE control loop is automatically set even if the loop gain is changed. The response of the AE control can be arbitrarily set by changing the loop gain without worrying that the system may be in an oscillation state, and the usability is improved.

In the above embodiment, the case where the AE control processing unit 18 is constituted by hardware has been described. However, the same function can be provided by software. The operation and effect can be obtained. Here, the AE control processing unit 18
An example of the procedure of the AE control when is configured by software will be described with reference to the flowchart of FIG. It is assumed that the processing of this routine is repeatedly executed in a predetermined cycle.

First, the loop gain and dead zone of the AE control loop are set to predetermined values (widths) by initial setting (step S11). Next, it is determined whether or not there is a change in the loop gain based on the loop gain information provided from the outside (step S12). If there is a change, the loop gain according to the loop gain information provided from the outside is set. (Step S13) Subsequently, the dead zone width information calculated based on the loop gain information given from the outside in the dead zone width calculation processing unit 19 is taken in, and the dead zone width is changed accordingly (step S14).

Next, luminance information is fetched from the DSP circuit 16 (step S15), and A of the fetched luminance information is read.
A difference from the E convergence target value is obtained (step S16),
It is determined whether this difference is within the dead zone width set in step S14 (step S17). If it is within the dead zone width, it means that it has converged to the vicinity of the AE convergence target value, and thus a series of processing ends.

If not within the dead zone width, it is determined whether or not the difference of the luminance information from the AE convergence target value is equal to or greater than the upper limit of the dead zone (step S18). Shutter speed information for (faster) is output (step S19), and a series of processing ends. On the other hand, if it is not equal to or higher than the upper limit, it is subsequently determined whether or not it is equal to or lower than the lower limit of the dead zone (step S).
20) If it is equal to or lower than the lower limit, shutter speed information for lowering (slowing) the shutter speed is output (step S21), and a series of processing ends.

In the embodiment described above, the case where the present invention is applied to an exposure control device in a camera system has been described. However, the present invention is not limited to the application to an exposure control device, and automatically focuses an object. The present invention can be similarly applied to an automatic focus (AF) controller that keeps adjusting the focus, an automatic white balance (AWB) controller that automatically adjusts the color tone, and the like.

The present invention is not limited to application to a camera system, but can also be applied to a general feedback control device such as motor speed control. Hereinafter, a case where the present invention is applied to a general feedback control device will be described.

FIG. 6 is a block diagram showing an example of a basic configuration of a feedback control device to which a dead zone is added. In FIG. 6, a control target 41 is a controlled device, which corresponds to a machine, a process, or the like. Control unit 42
Amplifies the deviation signal supplied via the dead zone setting unit 43, and performs control such as phase compensation. The dead zone setting unit 43 sets a dead zone for the deviation signal in order to prevent oscillation near the convergence target value. The detection unit 44 is a type of sensor that detects a control variable (amount). Comparison section 45
Subtracts the main feedback amount from the set value (target value) and outputs this as a deviation signal.

Here, the gain of the feedback control loop is controlled by the control target 41, the control unit 42, and the dead zone setting unit 4.
3 and is variable according to loop gain information provided from the outside. This loop gain information is also provided to the dead zone width calculation processing section 46. The dead band calculation processing section 46 calculates a dead band width based on loop gain information provided from the outside, and controls the dead band width of the dead band setting section 43. FIG.
FIG. 5 shows the relationship between input and output when the dead band width is changed by the loop gain.

Next, a procedure of a control method in the feedback control device having the above configuration will be described with reference to a flowchart of FIG.

First, the loop gain and the dead zone are set to predetermined values (widths) by initial setting (step S3).
1). Next, it is determined whether or not there is a change in the loop gain based on the loop gain information provided from the outside (step S32). If there is a change, the loop gain is set according to the loop gain information provided from the outside. (Step S33) Subsequently, the dead zone width information calculated by the dead zone width calculation processing section 46 based on the loop gain information given from the outside is taken in, and the dead zone width is changed accordingly (step S34).

Subsequently, a deviation of the control variable (control amount) from the set value (target value) is determined (step S35), and control using a dead zone is performed based on the deviation signal (step S36). In the control using the dead band, it is determined whether or not the deviation signal is within the dead band width.
Since it converges to the vicinity of the set value, the control target 4
No control for 1 is performed. On the other hand, if it is not within the dead zone width, it is determined whether it is not less than the upper limit value of the dead zone or not more than the lower limit value.

As described above, in the feedback control device to which the dead zone is added, the dead zone width is automatically set according to the loop gain of the control loop, so that the dead zone width is reset according to the loop gain. It is not necessary, and even if the response of the control changes according to the loop gain, it is possible to reliably converge to the vicinity of the set value without being affected by the change.

Therefore, by setting the minimum required dead zone width, even if the loop gain is changed, the optimum dead zone width according to the response of the control loop is automatically set. The control response can be arbitrarily set by changing the loop gain without worrying that the oscillator will be in an oscillation state, and the usability is improved.

[0045]

As described above, according to the present invention,
In the exposure control device where the loop gain of the control loop is variable, the dead band width is set according to the loop gain, so that it is not necessary to reset the dead band width according to the loop gain, AE
Even if the control responsiveness changes, it is possible to reliably converge to the vicinity of the AE convergence target value without being affected by the change.

Further, according to the present invention, in the feedback control device in which the loop gain is variable, the dead band width is set according to the loop gain, so that the dead band width needs to be reset according to the loop gain. And even if the response of the control changes according to the loop gain, it is possible to reliably converge to the vicinity of the convergence target value without being affected by the change.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram showing an entire camera system to which the present invention is applied.

FIG. 2 is a block diagram illustrating an example of a configuration of an AE control processing unit.

FIG. 3 is a block diagram illustrating an example of a configuration of a dead zone width calculation processing unit.

FIG. 4 shows the dead band width and AE that change according to the loop gain.
It is a relation diagram of a convergence target value.

FIG. 5 is a flowchart illustrating a procedure of AE control.

FIG. 6 is a block diagram illustrating an example of a basic configuration of a feedback control device to which a dead zone is added.

FIG. 7 is an input / output characteristic diagram when a dead zone width is changed by a loop gain.

FIG. 8 is a flowchart showing a procedure of a feedback control method according to the present invention.

[Explanation of symbols]

Reference Signs List 11 CCD image pickup device 13 Timing generator 16 DSP (digital signal processing) circuit 17 Exposure control device 18 AE control processing unit 19, 46 Dead band width calculation processing unit 21 Target value setting circuit 22 Difference detection circuit 2
3, 24 Comparison circuit 25 Shutter speed setting circuit 26 Loop gain setting circuit 27 Dead band width setting circuit 31 Dead band data conversion processing unit 33 Multiplier 41 Control target 42 Control unit 43 Dead band setting unit 44 Detecting unit

Claims (5)

[Claims] 1. An exposure control apparatus which automatically controls the brightness of an imaging screen using a shutter speed of a solid-state imaging device and has a variable loop gain of a control loop thereof. Difference detecting means for detecting a difference from a target value of the luminance information to be obtained, and a dead band setting means for setting a dead band for the difference information detected by the difference detecting means, wherein a dead band width is variable according to the loop gain. And a shutter speed setting means for setting the shutter speed based on the difference information passed through the dead zone setting means. 2. An exposure control apparatus according to claim 1, wherein said dead zone setting means sets a dead zone width corresponding to said shutter speed. 3. A solid-state imaging device that converts incident light into an electric signal and outputs the electric signal, an optical system that guides incident light from a subject on an imaging surface of the solid-state imaging device, and a shutter speed of the solid-state imaging device. A camera that automatically controls the brightness of the imaging screen by controlling the brightness of the imaging screen, and the exposure control device having a variable loop gain of the control loop. Difference detection means for detecting a difference with respect to the target value of the above, and a dead zone setting means for setting a dead zone for the difference information detected by the difference detection device, wherein the dead zone width is variable according to the loop gain, A shutter speed setting means for setting the shutter speed based on the difference information passed through the setting means. 4. A feedback control device wherein a loop gain of a feedback control loop is variable, wherein a deviation detecting means for detecting a deviation of a controlled variable of a controlled object from a target value, and a deviation information detected by the deviation detecting means is provided. A dead zone setting unit that sets a dead zone in response to the loop gain, and a control unit that controls the control target based on the deviation information passed through the dead zone setting unit. Characteristic feedback control device. 5. A feedback control device in which a loop gain of a feedback control loop is variable, wherein a deviation of a controlled variable of a controlled object from a target value is detected, and a dead zone width corresponding to the detected loop information is provided according to the loop gain. Wherein the control target is controlled based on the deviation information outside the dead zone width.