JPH0628405B2 - Automatic focusing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocusing device effective for use in a television (TV) camera.

2. Description of the Related Art In recent years, in TV cameras, the autofocus function has been emphasized in terms of improving operability. As a conventional technique, a high-frequency component is detected by passing a video signal obtained from an image sensor through a bandpass filter, and the peak value of this detection signal is maximized in, for example, one field or one frame. There is a method of driving the focus matching device.

First, the conventional technique will be described with reference to FIG. Reference numeral 1 denotes a lens with a focus matching device, which is driven by a motor 14.
Reference numeral 2 is an image pickup device, 3 is a preamplifier for amplifying an output signal of the image pickup device, 4 is a process circuit for converting into a standard TV signal, 5 is a synchronizing signal generating circuit, 6 is a scanning drive circuit of the image pickup device, and 7
Is a band-pass filter (hereinafter referred to as BPF) that passes the high frequency component of the video signal output from the preamplifier 3, and 8 is a screen range (hereinafter referred to as an image) of the output of the BPF 7, which is focused when displayed on the TV receiver. A gate circuit that passes only a signal corresponding to the angle), 9 is a detection circuit that detects the peak value of the output of the gate circuit 8 in one field or one frame period, and 10 is 1 / N of the frame frequency.
A reference frequency generation circuit for generating a reference frequency (N is an integer of 1 or more), 11 is a reference frequency component detection circuit for detecting the reference frequency component from the output of the detection circuit 9, and 12 is detected by the reference frequency component detection circuit 11. The synchronous detection circuit for synchronously detecting the reference frequency component with the reference frequency signal generated by the reference frequency generation circuit 10, 13 is a motor drive circuit for driving the motor 14, and the motor 14 is finely moved to periodically focus the lens 1. The output signal of the reference frequency generation circuit 10 for making a slight change (hereinafter referred to as wobbling) and the output signal of the analog switch 17 described later are input. 15 AD converter, the controller using a microcomputer 16, 17 and the output of the synchronous detection circuit 12 for lens drive in a closed loop mode, the positive voltage + V M to drive the high speed lens in the search _mode, the negative voltage -V _M, and an analog switch for switching to one of the ground voltage G to stop is controlled by the controller 16. A lens position encoder 18 detects the lens position and sends lens position information to the controller 16.

Next, the automatic focusing operation will be briefly described. FIG. 5 is a characteristic diagram showing the output level of the detection circuit 9 when the focus position of the focus matching device for the object at the distance D ₁ is moved from the in-focus position to the short distance / long distance side. First, when the focal position is closer than D _{1, the} reference frequency component A ₂ is detected from the detection output by the wobbling A ₁ at the reference frequency, and when this is synchronously detected at the reference frequency, a positive polarity signal A ₃ is obtained. To be This positive polarity signal moves the focus position of the focus matching device in the direction of arrow A ₄ . Next, when the distance is greater than D ₁ , the wobbling B ₁ detects a reference frequency component B _{2 having a} phase opposite to that of A _2, and the negative signal B ₃ is obtained by synchronous detection. Since this has the opposite polarity to A ₃ , the focal position moves in the direction of arrow B ₄ . In other words, it moves in the direction of the in-focus position in both cases of near and far, and the reference frequency component disappears at the in-focus point, so the movement stops and the in-focus point becomes stable. In this way, a closed loop including the lens system is configured to obtain high focusing accuracy.

On the other hand, as the detection output level decreases with increasing distance from the in-focus point, the level change amount with respect to the focus movement distance decreases, and the control sensitivity due to closed-loop drive decreases significantly, and eventually control becomes impossible. It is necessary to switch from the mode to the search mode in which the lens is simply moved to the far side or the near side. This is shown in FIG. Similar to FIG. 5, FIG. 6 is a characteristic diagram showing the output level of the detection circuit 9 when the focus position of the focus matching device for the object is moved from the in-focus position to the short distance side or the long 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 less than 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 equal to or higher than the set level Vref, the analog switch 1
And a closed loop mode is switched to the output of the synchronous detection circuit 12 by 7, also when the high-frequency detector output level is less than Vref, switched to + V _M or -V _M by the analog switch 17, near side or far side of the lens Move to search mode.

In the search mode, the lens position encoder 18 always detects the lens end, the direction of movement is reversed when the lens end is reached, 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 that.

Problems to be Solved by the Invention As shown in the above-mentioned conventional example, when 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 regarded as no contrast. When the lens movement is stopped by using the
In the case of a low-contrast subject that can be discriminated from or a subject having a high contrast in the area outside the in-focus angle of view, the user feels a malfunction and the frequency is high. In actual use,
If the subject becomes non-contrast by panning, the distance of the subject is highly likely to be equal to the distance of the subject that was in focus immediately before panning, and therefore, when it is regarded as no contrast by the search mode, It is extremely useful to return the lens to the focus position at the time of switching to the search mode, and it is useful for reducing a feeling of malfunction of the user.

For this purpose, a means for detecting and storing the lens position at the time of switching from the closed loop mode to the search mode is required. However, when this is realized by a lens position encoder or the like, high accuracy is required, and this causes a problem that the scale becomes large.

The present invention solves the above-mentioned inconvenient problems in the search mode, and an object thereof is to provide an automatic focusing device capable of focusing with an extremely high probability even when it is determined that there is no contrast. is there.

Means for Solving the Problems In order to solve the problems in the search mode, the present invention is based on focusing deviation information obtained by processing the detection output of a high frequency component in an image sensor output video signal. And a search drive means for driving the focus motor so as to simply move or stop the focus lens at a short distance side or a long distance side at a constant speed. When the detection output level of the component is equal to or higher than a predetermined level, the closed-loop drive mode in which the focus motor is driven by the closed-loop drive means is set, and in the search drive mode in which the focus motor is driven by the search drive means otherwise. An automatic focus adjustment device that can be switched, and a timer that measures the focus motor drive time When the search drive mode is switched to, the time measurement by the timer means is started at the same time when the search drive is started,
The relative position with respect to the position of the focus lens at the time of starting the search drive is detected from the motor drive time and the moving direction and moving speed of the focus lens, and the high frequency component for the near-end movement of the focus lens during the search drive mode is detected. When the detection output level of 1 is not higher than a predetermined level, the focus lens is returned to the position at the time of starting the search drive and stopped, and the timing is ended.

Operation 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 closed loop drive mode to search mode, and the lens moves at a constant speed. At the same time, a timer consisting of an up-down counter starts counting up or down from zero, and when the high-frequency detection output level reaches the lens edge without reaching the specified level, the motor rotation direction and timer counter By inverting the count up / down, the timer count becomes zero when the lens returns to the original position, and when the high-frequency detection level reaches the opposite lens edge without reaching the specified level, it is regarded as a no-contrast subject. Judge and adjust the motor rotation direction again. And the up / down of the count of the timer counter are reversed, and the motor is stopped when the timer counter reaches zero. At this time, the lens has returned to its original position. Therefore, even when it is determined that the subject has no contrast, it is possible to focus with an extremely high probability.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 1 to 18 have the same functions as those of the conventional example shown in FIG. Reference numeral 19 is a timer composed of an up / down counter, which is connected to the controller 16. Whether the timer 19 counts up or down is determined according to the moving direction of the lens 1. For example, when the lens 1 moves to the short distance side, the countdown is performed, and when the lens 1 moves to the long distance side, the countup is performed. Is set to.

Next, this operation is shown in the flow charts of FIGS. 2 (A) and 2 (B) and FIG. 3 is an operation showing the relationship between the operation of the lens after switching to the search mode and the timer content linked to it. This will be described with reference to the explanatory diagram. Here, the detection of the high frequency component in the video signal, the count of the timer 19 and the detection of the lens end are performed in units of one frame, and therefore the operation of each flowchart is performed in each frame. In the operation mode, the reference frequency component is detected from the detection output of the high frequency component of the video signal focus-modulated by the wobbling at the reference frequency, and the reference frequency signal generated by the reference frequency generation circuit 10 is synchronously detected. There is a closed-loop drive mode in which the focus motor is driven by the obtained signal to move the lens to the in-focus point, and a search mode in which the lens is simply moved to the near or far distance side. It is the same as described in the conventional example that the detection output is determined by whether it is equal to or higher than a preset specified level.

First, when the focus position of the lens is largely deviated from the in-focus point of the subject, the high-frequency detection level does not reach the specified level, so the search mode is entered. When the lens moves and approaches the in-focus point in the search mode, the high frequency detection level exceeds the specified level, the mode is switched to the closed loop drive mode, and the lens moves to the in-focus point and stops.

Next, when the subject is changed from the focused state to a no-contrast object by panning 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 search mode. The focal position of the lens at this point is A ₀₁ in FIG. With timer counter in this A ₁ is reset (step 21 of FIG. 2) to zero, the motor constant speed count up or down in the rotational direction and the timer counter of the motor for moving the focusing lens is set (Step 22) To start rotating (step 23). Then, for each frame, the high-frequency detection output level is detected, the timer is counted, and the lens position encoder 18 detects the lens end (steps 24 to 30). In FIG. 3, when the mode is switched to the search mode, the lens 1 starts moving to the short distance side at a constant speed. The timer counter is reset at the time of switching from the closed loop mode to the search mode, and its value shows zero. After that, the timer counter counts down at a constant cycle in conjunction with the movement of the lens 1 to the short distance side. Since the moving speed of the lens is constant, the value indicated by the timer counter represents the relative distance from the lens position A ₁ 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 does not reach the specified level and reaches the lens end on the short distance side, the motor rotation direction and the count up / down of the timer counter are reversed (step 31), and at the same time the number of lens end detections M Count up (step 32). Further, the lens 1 is moved and the above steps are repeated. In FIG. 3, when the controller 16 reverses the lens movement direction at the short-distance end B and starts moving at a constant speed toward the long-distance side, at the same time, the timer counter is also switched from countdown to countup, and at a constant cycle. Start counting up. The content of the counter when the lens 1 reaches the short distance end B is indicated by a negative value N _B. While the lens 1 is moving toward the far side, the counter passes the position A ₀₂ at which the counter again shows zero. Since the lens 1 always moves at a constant speed, the position A ₀₂ basically coincides with the position A ₀₁ . When the lens 1 further moves and reaches the long distance end C, the lens end is detected by the lens position encoder.

If the high-frequency detection level reaches the lens end on the far distance side (that is, when the number of detections of the lens end M = 2 in FIG. 2) without reaching the specified level, it is judged as a no-contrast subject and the motor is rotated again. Reverse direction and count up / down of timer counter. In FIG. 3, the controller 16 switches the moving direction of the lens 1 from the far side to the near side again, and switches the count of the timer counter from up to down. The contents of the counter at this point are indicated by a positive value N _C. Further, the controller 16 has determined that the detection output level of the high frequency component does not exceed the specified level with respect to the movement A ₀₁ → B → C of the lens 1, so that it is determined as a no-contrast subject, and the position A where the counter shows zero. Move lens 1 to ₀₃ , and stop the motor when it reaches zero (steps 33 to 37) (step 3
8) Allow it. Since the position A ₃ basically coincides with the position A ₀₂ , the lens has returned to the position at the time of switching to the search mode.

The counting cycle of the timer counter determines the lens position detection resolution, and in FIG. 3, it is 1/1 / the distance from the near end to the far end.
| Has a resolution of | _N C -N _B. Also, since the lens basically moves at a constant speed, the maximum value N of the counter
_max and the minimum value N _min are | N _max −N _min |
≧ _{2 |} N C -N _{B |} if they meet, it is possible to detect all the lens positions.

During this period and after the motor is stopped, the high-frequency detection level is detected for each frame, and when the level exceeds the specified level (steps 39 to 41), the closed-loop drive mode is switched to.

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

On the other hand, when the timer counter temporarily exceeds the count range and overflows or underflows due to an external factor such as an external force applied to the focus ring while the lens is moving, which temporarily prevents the low-speed movement. In addition to the fact that the lens position cannot be detected, the position where the lens stops is undefined, and the lens movement becomes redundant, which may cause a malfunction. Therefore, in the present embodiment, the presence or absence of overflow or underflow of the timer counter is always detected, and if it occurs, the counter is set to 30 when the lens edge detection count M reaches 2, that is, when it is determined that there is no contrast object. Or-
It is preset to 33, and the lens is moved to the center position and stopped.

In the present embodiment, the timer 19 is configured by installing an up / down counter outside the controller 16, but it is easy to implement it in software inside the controller using a microcomputer, etc. Needless to say, it is simpler and more cost effective than the above configuration. It is also possible to use a method in which the lens stop position when it is determined as a no-contrast subject is fixed depending on conditions.

As described above, according to the present invention, a relative position of a lens can be detected with high accuracy by a timer without using a lens position detection sensor having a complicated mechanism, and a high probability is obtained even for a non-contrast subject. Therefore, it is possible to realize a practical automatic focusing device.

Needless to say, the present invention can be applied not only to the wobbling method but also to an automatic focusing method such as a hill climbing servo method.

[Brief description of drawings]

FIG. 1 is a block diagram showing an automatic focusing device according to an embodiment of the present invention, FIGS. 2 (A) and 2 (B) are operation blow charts of the automatic focusing device, and FIG. 3 is the automatic focusing device. FIG. 4 is a block diagram showing the configuration of the 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 focus matching device, 2 ... Image sensor, 5 ...
Synchronous signal generator, 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, 16 …… controller, 17 …… analog switch, 18 …… lens position encoder, 19 …… up / down count timer.

Claims (1)

[Claims] 1. Closed loop drive means for driving a focus motor based on focus deviation information obtained by processing detection output of a high frequency component in an image signal output from an image pickup device, and a focus lens simply at a short distance side. Alternatively, a search drive means for driving the focus motor so as to move or stop at a constant speed to a long distance side, and a timer means for measuring the focus motor drive time are provided, and the detection output level of the high frequency component is equal to or higher than a predetermined level. In the case of, the closed-loop drive mode in which the focus motor is driven by the closed-loop drive means is set, and when the detection output level of the high-frequency component is equal to or lower than a predetermined level, the search drive mode in which the focus motor is driven by the search-drive means This is an automatic focusing device that is switched to the Sometimes, it starts measuring time by simultaneously the timer means and the search drive start, and a moving direction and a moving speed of the motor driving time and the focus lens,
It has a function to detect the relative position with respect to the position of the focus lens at the start of search drive and move the lens for an equivalent time to return the lens to the position at the time of switching to search drive mode. When the detection output level of the high frequency component does not exceed the predetermined level with respect to the near-far movement of the focus lens, the direction of rotation of the motor and up / down of the timer means are reversed to focus An automatic focusing device, characterized in that the lens is moved to a position at the time of starting the search drive and stopped, and the timing of the timer means is ended.