JPS63281576A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To obtain a practical device capable of focussing at an object having no contrast with a high probability by returning a lens to the position at the start time of a search driving mode by the action of a timer, and fixing the lens at the position. CONSTITUTION:When a higher-band detection level does not reach a determined level, a controller 16 switches the operation mode to the search mode. With the focus point position of a lens at this time, an updown count timer 19 is reset to zero, and at the same time, a motor driving circuit 13 drives a motor 14 to move the lens 1 closer toward the object. Simultaneously, the timer 19 starts counting corresponding to the position of the lens 1, and the lens 1 moves the extreme of close distance. At the moment, the moving is reversed, and when the higher-band detection level does not satisfy the determined value even when the lens 1 reaches the extreme of the far distance, the object is judged to be an object of no contrast, hence the lens 1 is returned to the position at the time of starting the search mode (counting of the timer 19 is '0') and fixed there. As a result, the lens 1 can be focussed with a high probability.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an automatic focusing device useful for use in television (TV) cameras.

BACKGROUND OF THE INVENTION In recent years, an automatic focus function has become important in TV cameras in terms of improving operability. As a conventional technique, a video signal obtained from a layered image element is passed through a bandpass filter to detect high frequency components, and the lens is adjusted so that the peak value of this detected signal is maximized, for example, within one field or one frame. There is a method for driving the focusing device.

First, the prior art will be explained using FIG. 4. Reference numeral 1 denotes a lens with focus matching vtWl, which is driven by a motor 14. 2 is a layered image element, 3 is a preamplifier that amplifies the image sensor output signal, 4 is a process circuit that converts it into a standard TV signal, 5 is a synchronization signal generation circuit, 6 is a driving circuit for scanning the layered image element, and 7 is a preamplifier. Band pass filter (hereinafter referred to as BPF) that passes the high frequency components of the video signal output from 3.
8 is a gate circuit that passes only the signal corresponding to the screen range to be focused (hereinafter referred to as the angle of view) when displayed on a TV receiver out of the output of the BPF 7, and 9 is the output of the gate circuit 8. 10 is a reference frequency generation circuit that generates a reference frequency of 1/N (N: an integer of 1 or more) of the frame frequency; 11 is a detection circuit; a reference frequency component detection circuit that detects the reference frequency component from 9 outputs;
12 is a synchronous detection circuit that synchronously detects the reference frequency component detected by the reference frequency component detection circuit 11 with a reference frequency signal generated from the reference frequency generation circuit 10; 13 is a motor drive circuit that drives the motor 14; The focus of lens 1 is periodically slightly changed by slightly moving the
Reference frequency generation circuit 1 for (hereinafter referred to as wobbling)
An output signal of 0 and an output signal of an analog switch 17, which will be described later, are input. 15 is an AD converter, 16 is a controller using a microcomputer, etc., and 17 is a synchronous detection circuit 12 for driving the lens in closed loop mode.
This is an analog switch that switches between the output of , positive voltage +VIIN to drive the lens at high speed in search mode, negative voltage -Vn, and ground voltage G to stop the lens, and is controlled by the controller 16 as ff, IJW. . A lens position encoder 18 detects the lens position and sends lens position information to the controller 16.

Next, automatic focusing operation will be briefly explained.

FIG. 5 is a characteristic diagram showing the output level of the detection circuit 9 when the focal position of the focus matching device for an object at a distance D1 is moved from the in-focus position to the near-distance and far-distance sides. First, when the focus position is closer than 01, a reference frequency component A2 is detected from the detection output by wobbling A1 using the reference frequency, and when this is synchronously detected using the reference frequency, A3
A positive polarity signal is obtained. This positive polarity signal causes the focal position of the focusing device to move in the direction of arrow A4. Next, when the distance is farther than 01, a reference frequency component 82 having an opposite phase to A2 is detected by wobbling B1, and a negative polarity signal B3 is removed by synchronous detection. Since this has the opposite polarity to A3, the focal point moves in the direction of arrow B4.

In other words, in both the far and near directions, the object moves in the direction of the in-focus position, and since the reference frequency component disappears at the in-focus point, it stops moving and stabilizes at the in-focus point. In this way, an open loop including the lens system is constructed, achieving high focusing accuracy.

On the other hand, as you move away from the focal point and the level of the detection output decreases, the amount of change in level with respect to the distance traveled by the focal point becomes smaller, and the sensitivity of the control 11 by closed-loop drive becomes significantly lower, and eventually control becomes impossible. It is necessary to switch from the drive mode to the search mode in which the lens is purely moved to the long distance side or the short distance side. This situation is shown in FIG. Similarly to FIG. 5, FIG. 6 is a characteristic diagram showing the output level of the detection circuit 9 when the focal position of the focus matching device relative to the object is moved from the in-focus position to the near-distance side or to the far-distance side. At this time, when the detection level is higher than the specified level, the closed loop drive mode is selected, and when it is below the specified level, the search mode is selected. That is, the output of the detection circuit 9 is constantly read by the controller 16 via the AD converter 15, and when the high frequency detection output level is above the set level VrefJX, it is switched to the output of the synchronous detection circuit 12 by the analog switch 17. When the closed-loop mode is set and the high-frequency detection output level is less than rof, the analog switch 17 is switched to +VM or -Vn, and the search mode is set to move the lens to the short distance side or the long distance side.

In search mode, the lens end is always detected by the lens position encoder 18, and when the lens end is reached, the direction of movement is reversed, and when the lens end is reciprocated M times or more, it is regarded as no contrast, and the analog switch 17 is switched to G. It is stopped by this.

Problems to be Solved by the Invention As shown in the conventional example above, if the high frequency detection output does not exceed the specified level even if the lens end is reciprocated M times or more in the search mode, it is considered as no contrast. When you stop the lens movement, the TV receiver actually produces a “blur” effect.
In the case of low-contrast objects that can be distinguished, or objects that have high contrast in areas outside the in-focus angle of view, the user feels a sense of malfunction, and this occurs frequently. In actual use,
When the subject becomes no contrast due to panning, there is a high probability that the distance of the subject is equal to the distance of the subject that was in focus just before panning. Returning the lens to the focal position at the time of switching to search mode is extremely useful and helps reduce the user's sense of malfunction.

For this purpose, a means for detecting and storing the lens position at the time of switching from closed loop mode to search mode is required. However, if this is achieved using the lens position encoder 18, a high viscosity is required, resulting in an increase in scale.

The present invention solves the above-mentioned problems that are inconvenient in the search mode, and aims to provide an automatic focusing device that is capable of focusing with extremely high probability even when the size FJi is determined to be no contrast. It is.

Means for Solving the Problems In order to solve the above-mentioned problems in the search mode, the present invention provides a search drive means for moving the lens toward the near side or the far side at a constant speed, and measures the motor drive time. When in search mode, approximately 2 timers are linked to measure the motor drive time from the start of the search drive, and the lens movement amount obtained is determined from the lens position at the time the switch to search mode is made. By detecting the relative distance and moving the lens by an equivalent amount of time, it has a function to return the lens to the position it was in when switching to search mode. It is designed to return to the position at the start of the search drive mode and fix it.

Effect With the above configuration, when the subject changes due to panning etc. and the detection output level of the high frequency component of the video signal falls below the specified level, the controller switches the operation mode from leap loop drive mode to search mode, and the lens remains constant. At the same time, a timer consisting of, for example, a map-down counter starts counting up and down from zero, and when the high-frequency detection output level reaches the end of the lens without reaching the specified level, the motor rotation direction and the timer counter are The up/down of the count is reversed, and the timer count becomes zero when the lens returns to its original position. Furthermore, if the high frequency detection level reaches the opposite end of the lens without reaching the specified level, no-contrast subject is detected. The motor rotation direction and the up/down count of the timer counter are reversed again, and the motor is stopped when the timer counter reaches zero. At this time, the lens has returned to its original position. Therefore, even if the subject is determined to have no contrast, it is possible to focus with an extremely high probability.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, elements 1 to 18 have the same functions as the elements shown in FIG. 4 of the conventional example, so they are numbered the same. 19
is a timer composed of an up/down counter, and is connected to the controller 16. Whether the timer 19 counts up or counts down is determined in accordance with the moving direction of the lens 1. For example, when the lens 1 moves toward the near distance side, it counts down, and when it moves toward the far distance side, it counts up. is set to.

Next, this operation is shown in the flowcharts shown in FIGS. 2(A) and (B), and the operation shown in FIG. This will be explained using an explanatory diagram. Here, the video @
Detection of high frequency components in 0, counting of the timer 19, and detection of the lens edge are performed on a frame-by-frame basis.
Therefore, the operations in each flowchart are performed for each frame. In addition, in the operation mode, a reference frequency component is detected from the detection output of a high frequency component of a video signal focus-modulated by wobbling at the reference frequency, and synchronized with a reference frequency signal generated by the reference frequency generation circuit 10. There is a closed-loop drive mode in which the focus motor is driven by the g signal and the lens is moved to the in-focus point, and a search mode in which the lens is moved to the near or far distance side. , the switching between the two modes is performed by determining whether the detected output of the high frequency component is above a predetermined level, which is the same as described in the conventional example.

First, if the focal point of the lens is significantly deviated from the focal point of the subject, the high frequency detection level is less than the specified level and the camera enters search mode. When the lens moves in the +J-na mode and approaches the focal point, the high frequency detection level exceeds the specified level, the mode is switched to the closed loop drive mode, and the lens stops after reaching the focal point.

Next, when the in-focus state changes to a no-contrast subject due to vanning or the like, the high-frequency detection level becomes less than the specified level, and the controller 16 switches the operation mode from the closed-loop drive mode to the ψ-chi mode. Let the focal position of the lens at this point be AOl in FIG. At A1, the timer counter is reset to zero (step 21 in FIG. 2), and the rotational direction of the motor that moves the focus lens and the count up or down of the timer counter are set (step 22).
) and the motor starts rotating at a constant speed (step 23).
. Detecting the high frequency detection output level for each frame,
The timer counts and the lens end is detected by the lens position encoder 18 (steps 24 to 30). In FIG. 3, when switching to the search mode, the lens 1 begins to move toward the short distance side at a constant speed. The timer counter is reset to zero when the closed loop mode is switched to the search mode, and then counts down at a constant cycle in conjunction with the movement of the lens 1 toward the short distance side. Since the moving speed of the lens is constant, the value indicated by the timer counter represents the relative distance to the lens position A1 at the time of switching to the search mode. When the lens 1 moves to the short distance end B, the lens position encoder 18 detects the lens end.

When the high-frequency detection output level reaches the end of the lens on the near-distance side while it is still below the specified level, the motor rotation direction and the up/down count of the timer counter are reversed (
Step 31) and at the same time count up the number of times M of lens end detection (Step 32). Furthermore, lens 1
Move and repeat the above steps. In Figure 3,
When the direction of lens movement is reversed by the controller 16 at the near distance end B and the lens starts moving at a constant speed toward the far distance side, the timer counter is also switched from countdown to countup at the same time and starts counting up at a constant cycle. do. The contents of the counter at the time when the lens 1 reaches the near end B are indicated by a negative value N@. While the lens 1 is moving toward the far side, it passes through a position AO2 where the counter again indicates zero. Since the lens 1 is always moving at a constant speed, the position [Ao 2 basically coincides with the position Aot. When the lens 1 moves further and reaches the far distance end C, the lens position encoder detects the lens end.

If the high-frequency detection level reaches the far end of the lens without reaching the specified level (that is, when the number of lens end detections reaches M = 2 in Figure 2), it is determined that the object has no contrast, and the motor rotates again. Reverses the direction and up/down of the timer counter count. In FIG. 3, the controller 16 again switches the moving direction of the lens 1 from the long distance side to the near distance side, and changes the count of the timer counter from up to down. The contents of the counter at this point are indicated by a positive value Nc. Furthermore, since the detection output level of the high frequency component did not exceed the specified level for the movement of the lens 1 Ao1→B→C, the controller 16 determined that the subject was a no-contrast object, and the counter indicated zero! The lens 1 is moved to ffAo 3, and when it reaches zero (steps 33 to 37), the motor is stopped (step 38). Position A3 is basically position @Ao
2, the lens has returned to the position at the time of switching to the search mode.

The count period of the timer counter determines the lens position detection resolution, and in Figure 3, it is 1/1 of the distance from the near end to the far end.
It has a resolution of l Nc-Net I.

Also, since the lens basically moves at a constant speed, the maximum value Nwax and minimum value Nm1n of the counter are lN
If 11ax −Nmin l≧21Nc Net is satisfied, detection of all lens positions is possible.

During this time and after the motor stops, the high frequency detection level is detected every frame, and when it reaches a specified level or higher (steps 39 to 41), the mode is switched to the closed loop drive mode.

In this embodiment, the moving speed of the lens 1 in the search mode is set to move between the near end and the far end in about 2 seconds, so the lens position detection resolution by the timer 19 is This is 1/60 of the distance, and the timer counter can count from -64 to 63.

On the other hand, if the low-speed movement is temporarily interrupted while the lens is moving due to an external factor such as an external force being applied to the focus ring, causing the timer counter to overflow or underflow, the lens position cannot be detected. Not only this, but the position where the lens stops becomes unstable and the movement of the lens becomes redundant, which may cause malfunctions.

Therefore, in this embodiment, the presence or absence of overflow or under-70 of the timer counter is constantly detected, and if this occurs, the counter is activated when the number of times M of lens edge detection reaches 2, that is, when it is determined that the subject has no contrast. The lens is preset to 30 or -33, and the lens is moved to the center position and stopped.

In this embodiment, the timer 19 is configured by installing a 7-updown counter outside the controller 16, but it can be easily implemented as software inside a controller using a microcomputer or the like. Needless to say, this is easier and more cost-effective than configuring hardware. It is also possible to use this method in combination with a method in which the lens stop position is set to a fixed position depending on conditions when the subject is determined to have no contrast.

Effects of the Invention As described above, according to the present invention, it is possible to detect the relative position of the lens with high accuracy using a timer without using a lens position detection sensor with a complicated mechanism, and it is possible to detect the relative position of the lens with high accuracy even for subjects with no contrast. This enables a practical automatic focusing device to be realized.

It goes without saying that the present invention can be applied not only to the wobbling method but also to an automatic focusing method such as a rising servo method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an automatic focusing device according to an embodiment of the present invention, FIGS. 2(A) and (B) are operation flowcharts of the automatic focusing device, and FIG. 3 is a block diagram showing an automatic focusing device according to an embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of a conventional example, and FIGS. 5 and 6 are high frequency detection output characteristic diagrams for explaining the operation of the conventional example. 1... Lens with focusing device, 2... Image pickup element, 5
...Synchronization signal generation circuit, 7...Band pass filter, 8...Gate circuit, 9...Detection circuit, 10...
Reference frequency generation circuit, 11... Reference frequency component detection circuit, 12... Synchronous detection circuit, 13... Motor drive circuit, 14... Motor, 15... AD converter, 1
6... Controller, 17... Analog switch,
18... Lens position encoder, 19... Up/down count timer. Agent Rehiro Morimoto Figure 3 7x - Focus on Caslace! , pull 12 Fig. 4 Internal existence of Kuimer counter

Claims (1)

[Claims] 1. Closed-loop drive means that drives the focus motor based on defocus information obtained by processing the detection output of high-frequency components in the image sensor output video signal, and a closed-loop drive means that simply moves the lens to the near or far side. It has a search drive means that moves the lens at a constant speed, and a timer that measures the motor drive time, and when in the search drive mode, the relative position of the lens is detected from the motor drive time measured by interlocking the timer, and the relative position of the lens is detected. An automatic focusing device that returns and fixes the lens to a position at the start of a search drive mode when the level of the high frequency component does not exceed a predetermined level with respect to far and near limit movement.