JPH07162732A - Automatic focus adjusting device and video camera - Google Patents

Abstract

PURPOSE:To perform an automatic focus adjustment with high stability and high responsiveness, regarding a video camera having an automatic focus adjusting device. CONSTITUTION:This device has an AF control means 6 which is provided with a 30Hz vibration means 6a vibrating a lens 1d for focus adjustment which is the part of an image pickup lens 1 and has a focus adjusting function by a 30Hz frequency and a modulation means 6b modulating the output of focus signal detection means 5, instructs the direction and the speed that the lens 1d for focus adjustment should be driven and performs an AF control, and a lens driving means 7 driving the electromagnetic driving type voice coil type linear actuator interlocking with the lens 1d for focus adjustment by the output signal of the AF control means 6, vibrates the lens 1d for focus adjustment by 30Hz frequency and determines the driving direction and the driving speed of the lens for focus adjustment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device for automatically focusing an image of a subject to be photographed to an optimum focus position when adjusting the focus of a video camera, a still camera, etc. It was about a video camera that I had.

[0002]

2. Description of the Related Art In an image pickup system such as a video camera, several types of methods have been already proposed and implemented for an automatic focusing device (autofocus, hereinafter referred to as AF), which is an important function. Regarding one of them, a method using a video signal of a video camera (referred to as “video signal method”) is, for example, “automatic focus adjustment of a video camera by a hill climbing servo method” ([NHK Technology Research] Vol. 17). No. 1, p. 21, 1965, published by Ishida et al.). An embodiment of a video camera configured by the video signal system will be described below. FIG. 7 is a block diagram of a video camera device configured by a conventional video signal system.

In FIG. 7, reference numeral 22 denotes a zoom lens, which is composed of four lens groups. Reference numeral 22d denotes a part of the zoom lens which is a focus adjusting lens having a focus adjusting function. Although each lens group is shown as one convex lens or one concave lens for convenience, it is actually composed of a plurality of convex lenses or concave lenses, which are shown by 22a to 22d in FIG.

Reference numeral 23 is a subject to be photographed, 24 is an image pickup device such as a CCD, and 25 is a predetermined video signal (for example, NTS) obtained by subjecting an electric signal obtained from the image pickup device 24 to various signal processes.
C signal) A camera process circuit for outputting Co, 26 is a luminance signal Y output from the camera process circuit 25,
A focus signal detecting means for extracting a frequency component of a certain value or more and calculating a focus signal (hereinafter referred to as a focus voltage) corresponding to the focus state of the zoom lens 22 in a field cycle.
Reference numeral 7 denotes AF control means for obtaining AF information from the output signal of the focus signal detection means 26 to calculate the driving direction and speed of the focus adjustment lens 22d to control AF, and 28 drives the focus adjustment lens 22d. A stepping motor, 29 is a motor driving means for driving the stepping motor 28 by the output signal of the AF control means 27.

With respect to the conventional video camera device configured as described above, the AF operation method will be described below. The video signal method AF is a method of performing focus adjustment by using the amount of high frequency components (focus voltage) in the video signal. The zoom lens 22 has a characteristic of exhibiting a low-pass filter characteristic with respect to an image to be captured. When the captured image is focused, the cutoff frequency of the low-pass filter is maximized and the amount of focus voltage is also maximized. As the zoom lens defocuses, the cutoff frequency tends to shift to the low frequency side, and as a result, the amount of focus voltage tends to decrease.

FIG. 8 shows the relationship between the focus voltage and the position of the focus adjustment lens. In FIG. 8, the horizontal axis represents the position of the focus adjustment lens that represents the defocus amount of the focus adjustment lens, and the vertical axis represents the focus voltage. Here, the curve of the focus voltage drawn with respect to the position of the focus adjustment lens is called a hill climbing curve. The focus voltage shows the maximum value at the point P of the focus adjusting lens in the figure. The focus voltage monotonically increases and monotonically decreases at points Q and R before and after the focus adjustment lens position P.

In the hill-climbing AF, while moving the lens in a fixed direction, the focus voltage is obtained for each field, for example, and compared with the focus voltage of the previous field to climb the mountain to the point where the focus voltage becomes maximum. Focus adjustment is done by the thing. However, in this type of AF, when the lens is stationary, the top of the hill climbing curve, that is, the driving direction to the in-focus point is unknown, so the lens or CCD or other image sensor is vibrated at a cycle of 15 Hz in the optical axis direction ( This vibration control is called auxiliary vibration control.) The focus voltage is modulated to obtain the differential coefficient of the hill climbing curve, and the direction is determined by its positive or negative.

FIG. 9 shows an example of a vibration command for auxiliary vibration control. In FIG. 9, T1 to T8 indicate focal voltage extraction periods, each of which corresponds to a field scanning period.
Of T1 to T8, T2, T4, T6, and T8 indicate the extraction period of the focus voltage used for modulation. Generally, the phase of auxiliary vibration is set so that the extraction period of the focus voltage used when modulating is near the peak of the amplitude, and the amplitude is within the depth of focus of the imaging lens and does not exceed the limit drive speed of the lens drive motor. The size is set within the range so that a sufficient modulation output can be obtained.

Next, in the AF state at point S in FIG. 8, first, the auxiliary vibration is started to judge the driving direction of the lens. If the direction is known, then the lens is driven toward point P at once.
After the point P, the focus voltage goes in a decreasing direction, but after detecting this, the lens is driven in reverse and stopped in the vicinity of the point P, and a series of AF is performed.
The operation is completed.

Further, the above-mentioned auxiliary vibration may be applied during the hill climbing or near the point P (focus point). In addition to determining the direction of lens drive, this is because there is modulation output when the hill climbing speed is determined according to the amount of modulation output during the course of hill climbing and the mountain is flat near the in-focus point. This is because the lens is stopped and the AF control is completed at a threshold value or less. Further, if the auxiliary vibration control is always performed during the mountain climbing, the modulation component is always fed back, so that there is an advantage that focusing can be performed with extremely high accuracy.

[0011]

However, the above-described hill climbing curve has a large differential coefficient of the hill climbing curve at a position where the focus is greatly deviated and a subject with low contrast, and the amount of the modulation component is also reduced, so that the lens driving direction is changed. There were times when I made a mistake. Further, with the above conventional configuration, the focus voltage can be obtained at 1-field intervals, but since the modulation frequency is 15 Hz, which is the same as the auxiliary vibration frequency, it is necessary to have 3 fields or more to calculate the lens driving direction from the start of vibration. Become. Even in the modulation operation during the hill climbing, since the hill climbing operation is performed every three fields, time delays are accumulated in proportion to the number of modulations performed until reaching the in-focus point and the focusing speed is restricted.

The present invention solves the above-mentioned conventional problems, and provides an automatic focusing device and a video camera capable of significantly reducing the direction error of driving the focusing lens and performing AF control with high stability and responsiveness. The purpose is to do.

[0013]

In order to achieve the above object, the present invention provides an image pickup device for photoelectrically converting an optical signal of an object image obtained through an image pickup lens, and a certain signal processing is performed on the output of the image pickup device. A camera process circuit that outputs a video signal, and a focus that calculates a focus signal corresponding to the focus state of the imaging lens by extracting a frequency component of a certain value or more from the video signal generated by the camera process circuit. Based on the output of the signal detection means, the AF control means for instructing the driving direction and the driving speed of the focus adjustment lens having the focus adjustment function based on the focus signal to control the autofocus, and the output of the AF control means. Lens drive means for moving the focus adjustment lens along the optical axis of the image pickup lens, and the AF control means includes 30H.
A 30 Hz vibrating means for vibrating the focus adjustment lens in the optical axis direction at a frequency of z and a modulating means for modulating the output of the focus signal detecting means by the 30 Hz vibrating means.

[0014]

According to the present invention, by virtue of the above construction, the focus adjusting lens is vibrated in the optical axis direction at a frequency of 30 Hz and the output signal of the signal detecting means is modulated to determine the lens driving direction and the lens driving speed. It realizes stable and responsive automatic focus adjustment.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the automatic focus adjusting device of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of this embodiment.

In FIG. 1, reference numeral 1 is a zoom lens,
Four lens groups (each lens group is shown as a single convex lens or a concave lens for the sake of convenience, but actually it is composed of a plurality of convex lenses or concave lenses. Each is shown as 1a to 1d in FIG. 1) It is composed of 1d
Is a focus adjusting lens which is a part of the zoom lens and has a focus adjusting function. The subject 2 is input to the CCD 3 via the zoom lens 1. The camera process circuit 4 performs various signal processing on the electric signal obtained from the CCD 3,
A predetermined video signal (for example, NTSC signal) Co is output.

The focus signal detecting means 5 extracts a frequency component of a certain value or more from the luminance signal Y output from the camera process circuit 4, and a focus signal corresponding to the focus state of the zoom lens 1 (hereinafter referred to as focus voltage (Referred to) is calculated in the field cycle. The inside of the focus signal detection means 5 is shown in FIG.
As shown in FIG. 2, the bandpass filter 8 extracts a frequency component in a certain range, the absolute value circuit 9 takes an absolute value, and the peak detection circuit 10 detects a peak and outputs a focus voltage.

The AF control means 6 modulates the focus voltage which is the output of the focus signal detection means 5 when the focus adjusting lens 1d is provided with a 30 Hz vibrating means 6a and a 30 Hz vibrating means 6a which vibrate at 30 Hz in the optical axis direction. The modulation means 6b is provided, and AF information is obtained by obtaining information regarding focusing from the focus voltage and the output of the modulation means 6b to calculate the driving direction and speed of the focus adjustment lens 1d.
The focus adjusting lens 1d is driven by the output signal of the control means 6.

The control method of the video signal type AF performed by the AF control means 6 in the video camera device configured as described above will be described below.

FIG. 3 shows the relationship between the focus adjustment lens position and the focus voltage. Consider the AF control when the focus adjustment lens 1d is in a stationary state at a position Q deviated from the in-focus point in FIG. First, the auxiliary vibration control is started by the 30 Hz vibrating means 6a, and the direction in which the focus adjusting lens 1d should be driven is determined from the output of the modulating means 6b.

FIG. 4 shows an example of a vibration command output from the 30 Hz vibrating means. In FIG. 4, T1, T2, T3, T
Reference numerals 4 and T5 are periods for extracting the focus voltage used in the modulator 6b, which correspond to field scanning periods. The phase of the vibration command is controlled so that the peak of the vibration amplitude is located at the center of the focus voltage extraction period so that the output of the modulation means 6b is maximized.

The shape of the vibration may be as close as possible to a rectangular wave so as to suppress the decrease of the modulation means 6b. In addition, the visual characteristics of the human eye may cause some fluctuation depending on the brightness, but compared to the flickering of the moving screen due to the vibration of 15 Hz, it is 30
Utilizing the fact that the flicker due to the vibration at Hz is extremely small, the magnitude of the vibration amplitude is large enough to take a sufficient modulation component even in the case of a low contrast subject or a subject with large blurring, and the flicker on the moving screen cannot be recognized. Set to

Note that this 30 Hz corresponds to half the field frequency of the television signal currently used, and if the field frequency of the television signal changes, the vibration frequency is changed in consideration of the visual characteristics of the human eye. It goes without saying that it is only necessary to set it.

Next, if the direction to the in-focus point P can be determined,
While performing a hill climbing operation in that direction, auxiliary vibration control is continuously performed by the 30 Hz vibrating means 6a. FIG. 5 shows an example of the drive command when the auxiliary vibration control by the 30 Hz vibration means 6a is applied during the hill climbing operation. In FIG. 5, T1
T8 is a focus voltage extraction period, and each corresponds to a field scanning period.

First, the auxiliary vibration control is started by the 30 Hz vibrating means 6a, and the focus voltage output at T1 and T2 is modulated by the modulating means 6b. Since the focus voltage output at T1 is higher than the focus voltage output at T2, the output of the modulation means 6b becomes positive and the AF control means 6 drives the lens drive means 7 to drive the focus adjustment lens 1d in the hill climbing direction. Order is issued. At T3, the amount of movement for hill climbing is added to the auxiliary vibration control by the 30 Hz vibration means.

Next, the driving direction of the lens is calculated by the modulation output of the focus voltage output at T3 and the focus voltage output at T4, and the movement amount for hill climbing is added at T5. After that, the driving direction of the lens is calculated and the movement of the lens is controlled every two fields. Here, the method of switching the hill-climbing drive speed according to the amount of the modulation component may be adopted. For example, if the slope of the mountain is steep, increase the speed,
For example, the speed is set to be small in a place where the inclination is small such as near the focal point.

By the hill-climbing operation described above, the lens passes in the opposite direction so that the output of the modulation means 6b becomes negative at point R, which passes through the point P which is the in-focus point in FIG. Driven. Then, after repeating the reversing operation several times near the point P, the lens drive is stopped when the output of the modulating means 6b becomes a certain threshold value or less, and a series of AF operations are ended.

Next, details of the lens driving means 7 of FIG. 1 will be described with reference to FIG.
Shown in. In FIG. 6, reference numeral 11 denotes a voice coil type linear actuator, which includes permanent magnets 12a and 12b, a driving coil 13, and yokes 14a, 14b, 14c and 14d.
And bearings 15a and 15b. The driving coil 13 is configured to surround the yoke 14b, the yoke 14c, and the bearings 15a and 15b.
14b surrounds the permanent magnet 12a and the driving coil 13, and the yokes 14c and 14d surround the permanent magnet 12b and the driving coil 13 to form magnetic circuits.

The shaft 16a is a shaft for holding the linear actuator, and the bearing portion 15a of the linear actuator,
It is a sliding bearing system that contacts with 15b. The linear actuator 11 is configured to generate a magnetic field in the direction of the center of the shaft 16a, and when a current is passed through the driving coil 13, a thrust is generated in the direction of the shaft 16a according to Fleming's left-hand rule, and the driving coil of the linear actuator 11 is driven. Thirteen
Also, the bearings 15a and 15b move in the direction of the shaft 16a. Reference numeral 17 is a bearing portion 15 of the linear actuator 11.
Reference numeral 19 is a focus adjustment lens attached to a lens fixing frame 18 integrated with a and 15b, reference numeral 19 is a rotation stopping portion for preventing the focus adjustment lens 17 from rotating around the axis 16a, and 16b is a rotation stopper. It is a shaft provided to urge the stop portion 19.

Reference numeral 20 is a position detecting means for providing position information of the focus adjusting lens 17, and the LED 20a does not move.
Also, the moving slit 20c mounted in conjunction with the photodiode 20b and the lens fixing frame 18, and further the photodiode output signal processing means 20d and the output of the photodiode signal processing means 20d for processing the output of the photodiode 20b are interpolated and digitalized. It is composed of an interpolating means 20e for converting into position information.

Reference numeral 21 is a linear actuator position control means for controlling the position of the linear actuator 11 based on the output signals of the AF control means 6 and the position detection means 20 of FIG. Here, it is configured so as to have a servo characteristic capable of sufficiently responding to a vibration command of the 30 Hz vibrating means 6a and a hill climbing command.

As described above, according to this embodiment, 30 Hz
The focus adjustment lens 1d is vibrated in the optical axis direction at the frequency of, and the output signal of the focus signal detection means 5 is modulated to determine the lens drive direction and the lens drive speed, thereby stabilizing the stability,
A highly responsive automatic focus adjustment can be realized, and by applying the automatic focus adjustment device of this embodiment to a video camera, a high-speed and high-quality image can be easily obtained.

[0033]

As described above, according to the present invention, a linear actuator is used as a drive actuator for a focus adjustment lens to perform auxiliary vibration control at a frequency of 30 Hz, so that the focus adjustment lens can be driven stably with little error in direction. In addition, it is possible to perform focus adjustment with good responsiveness, and to exert an extremely excellent effect in the automatic focus adjustment device.

Further, by applying the above-mentioned automatic focus adjusting device to a video camera, a device capable of obtaining high-speed and high-quality images can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of an automatic focusing device according to an embodiment of the present invention.

FIG. 2 is a block diagram of focus detection means according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a focus adjustment lens position and a focus voltage and an operation according to the present embodiment.

FIG. 4 is a diagram showing an example of an auxiliary vibration command according to an embodiment of the present invention.

FIG. 5 is a diagram showing an example of a composite of an auxiliary vibration command and a hill climbing command according to an embodiment of the present invention.

FIG. 6 is a block diagram showing a detailed configuration of lens driving means according to an embodiment of the present invention.

FIG. 7 is a block diagram of a conventional automatic focusing device.

FIG. 8 is a diagram showing a relationship between a focus adjustment lens position and a focus voltage.

FIG. 9 is a diagram showing an example of a conventional auxiliary vibration command.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 zoom lens 1d focus adjustment lens 2 subject 3 CCD 4 camera process circuit 5 focus signal detection means 6 AF control means 7 lens drive means 8 bandpass filter 9 absolute value circuit 10 peak detection circuit 11 linear actuator 12 permanent magnet 13 drive coil 14 Yoke 15 Bearing part 16 Axis 17 Focus adjustment lens 18 Lens fixing frame 19 Rotation stop part 20 Position detecting means 20a LED 20b Photodiode 20c Moving slit 20d Photodiode output signal processing means 20e Interpolation means 21 Linear actuator position control means

Claims (4)

[Claims] 1. An image pickup lens for picking up an image of a subject, an image pickup device for photoelectrically converting an optical signal of a subject image obtained through the image pickup lens, and a video signal obtained by subjecting the output of the image pickup device to a certain signal processing. And a focus signal detection unit that extracts a frequency component of a certain value or more from the video signal generated by the camera process circuit and calculates a focus signal corresponding to the focus state of the imaging lens. AF control means for instructing the direction and drive speed of the focus adjustment lens, which is a part of the imaging lens and has a focus adjustment function, from the output of the focus signal detection means, and controls the autofocus, Lens driving means for moving the focus adjusting lens along the optical axis of the imaging lens based on the output of the AF controlling means. The output of the focus signal detecting means is modulated by a 30 Hz vibrating means for vibrating the focus adjusting lens in the optical axis direction at a frequency of 30 Hz to detect the direction of the focus adjusting lens to the in-focus point and the 30 Hz vibrating means. An automatic focus adjustment device comprising a modulation means. 2. The automatic focus adjustment device according to claim 1, wherein the 30 Hz vibrating means controls the phase of the vibration so that the output of the modulating means becomes maximum. 3. The automatic focus adjusting device according to claim 1, wherein the lens driving means uses an electromagnetically driven voice coil type linear actuator having a coil and a magnet which are driven in conjunction with the focus adjusting lens. . 4. A video camera comprising the automatic focusing device according to claim 1.