JPH0698240A - Automatic focusing device for video camera - Google Patents

Abstract

PURPOSE:To always exactly catch the absolute position of a lens for focusing by recognizing that position without using any lens position detection circuit in the case of using a pulse motor for driving the lens. CONSTITUTION:A pulse motor 10 drives the focusing mechanism of a lens 1. A rubbing circuit 12 detects a signal impressed to a terminal 13 when the operation of the automatic focusing device is started, the pulse motor 10 is driven through a pulse motor drive control circuit 14 to the prescribed direction just for the prescribed number of pulses enough for moving all the strokes of the lens moving mechanism of the lens 1, and the content of a lens position memory 11 is set to a prescribed initial value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device, and more particularly to an autofocus device suitable for a video camera.

[0002]

2. Description of the Related Art Conventionally, a so-called hill-climbing system for detecting the definition of a photographic screen from a high frequency component in a video signal and controlling a lens position so that the definition is maximized as an autofocus device for a video camera. It has been known. This system is disclosed, for example, in Japanese Patent Application Laid-Open No. 56-
This method is described in detail in Japanese Patent Publication No. 51164, etc., but this method will be briefly described below with reference to FIG. In the figure,
1 is a lens, 2 is a camera circuit, 3 is a focus amount detection circuit, 4
Is a difference detection circuit, 5 is a DC motor drive control circuit, and 6 is D
A C motor, 7 is a focal length detection circuit for the lens 1, 8 is a lens movement range calculation circuit, and 9 is a lens position detection circuit.

Light from a subject entering the lens 1 is converted into an electric signal by the camera circuit 2. The high frequency component of this electric signal is small if the focus state of the lens 1 is weak,
By utilizing the fact that the more the focus is achieved, the focus amount detection circuit 3 forms one screen after passing the output signal of the camera circuit 2 through the high-pass filter, that is, one field period (television system). In the case of 1/60 second), the detection and integration are performed, and a higher voltage (hereinafter, this voltage is referred to as a focus voltage) is output as the focus is better.

Therefore, in this type of autofocus apparatus, the DC motor 6 drives the focus portion of the lens 1, and the lens position detection circuit 9 drives the lens 1 at that time.
While memorizing and confirming the position of, the difference detection circuit 4 detects an increase or decrease of the focus voltage which is the output of the focus amount detection circuit 3, and the DC motor drive control circuit 5 is operated while the focus voltage is increasing. By keeping the rotation direction of the DC motor 6 as it is, the focus of the lens 1 is controlled more and more, and finally when the output of the difference detection circuit 4 is detected to decrease beyond the just focus point, DC is detected. The motor drive control circuit 5 reverses the motor 6 and moves the position of the lens 1 to the position where the highest focus voltage is obtained in the process up to that point, that is, the just focus point, while referring to the output signal of the lens position detection circuit 9. return.

Here, the focal length detection circuit 7 and the lens movement range calculation circuit 8 are installed in order to secure a predetermined focusable distance range, for example, a close range of 1.5 m to infinity (∞). That is, the necessary moving range of the lens 1 depends on the focal length of the lens 1, and when the zoom magnification of the lens 1 is low, the range may be narrow because the depth of field is deep, and the zoom magnification of the lens 1 is high. By taking advantage of the fact that it becomes wider as it gets closer, the time required for the focusing operation of the autofocus device can be shortened, and the increase in the establishment of out-of-focus due to malfunction or the like can be prevented. The lens position detection circuit 9 is also used to confirm that the position of the lens 1 is within the range instructed by the lens movement range calculation circuit 8 described above, and is of a contact type or a non-contact type that is linked to the focusing mechanism of the lens 1. A potentiometer or the like is used. The above is the operation of the hill-climbing autofocus device.

As a motor used in this apparatus, instead of using a normal DC motor, it is possible to use a pulse motor having a contactless structure itself (see, for example, Japanese Patent Laid-Open No. 56-147132). If possible, there is an advantage that the life of the device can be extended. Further, since the position of the lens 1 can be known by counting the number of pulses for driving the pulse motor, the lens position detection circuit 9 can be eliminated at the same time to reduce the cost. However, there are various problems in applying this idea as it is.

[0007]

The first problem is that the focus voltage is obtained from the image pickup signal of the video camera. That is, in the television system, since one image is completed at a constant time period of 1/60 seconds, the focus voltage used for focusing can be obtained only at a constant cycle. Therefore, the difference detection is 1/60 second. Every time, or every integer multiple of the time. When the position drive of the lens 1 is continuously performed at a constant speed by the DC motor, the amount of movement of the lens 1 that occurs in the difference detection cycle is constant, so this intermittent operation of every 1/60 seconds causes no problem. However, when the position drive of the lens 1 is performed stepwise by the pulse motor in a cycle different from the difference detection cycle, the amount of movement of the lens 1 generated during the difference detection cycle of 1/60 seconds is different. Since a variation of ± 1 pulse drive is generated between the difference detection cycles, the value does not always become a constant value, and thus unevenness occurs in the generated difference voltage, which easily causes a malfunction. This is easy to understand if it is considered that the drive speed of the DC motor is not constant in each difference cycle. This phenomenon is not a problem when the drive cycle of the pulse motor is a sufficiently small value with respect to 1/60 seconds, but it is obvious that it becomes a major obstacle as the drive cycle of the pulse motor approaches 1/60 seconds.

The second problem is related to the position detection of the lens 1. When a pulse motor is used, the relative position movement of the lens 1 can be detected by counting the number of pulses described above, but the absolute position of the lens 1 required by the autofocus device can be known. Can not. That is, unless the initial state of operation of the autofocus device, for example, the absolute position of the lens 1 when the device is powered on, is known, the detected position of the lens 1 obtained by counting the number of pulses and the actual lens position. Since the position of 1 has a parallel shift, the position of the lens 1 cannot be limited to the absolute position range defined by the lens movement range calculation circuit 8.

Further, even if the initial position of the lens 1 is known and the number of pulses is counted with reference to the position, it cannot be said that the detected position of the lens 1 correctly grasps the position of the lens 1. . The reason is that the mechanism for connecting the pulse motor and the focus moving structure of the lens 1 has a substantial backlash, so that an idle feed error due to this backlash accumulates during a long-term operation, and the error cannot be ignored. It depends.

The object of the present invention is to solve the above-mentioned conventional problems, particularly the second problem, and to achieve focusing without using a lens position detection circuit when a pulse motor is used to drive the lens. An object of the present invention is to provide an autofocus device which can know the absolute position of a lens for use and can always grasp the position correctly.

[0011]

To achieve the above object, in the present invention, in an autofocus device, an optical lens including a variable zoom magnification lens and a focusing lens, and a pulse for moving the focusing lens. A focus condition is detected from a motor and a camera circuit that converts an optical image formed through the optical lens into an electric signal and outputs the electric signal as a video signal, and a high frequency component of the video signal output from the camera circuit. Focus amount detecting means, lens moving range determining means for determining a necessary moving range of the focusing lens according to a change in zoom magnification by the zoom magnification variable lens, detection results by the focus amount detecting means, and Based on the result determined by the lens moving range determining means, the pulse mode is moved so as to move the focusing lens to a position where the subject is focused. A pulse motor drive control means for controlling the drive of the focusing lens, and the pulse motor drive control means has a predetermined origin for temporarily initializing the focusing lens within a predetermined period immediately after power-on of the apparatus. To position
After that, the drive of the pulse motor is controlled so as to move to a position where the subject is in focus.

Further, a lens position memory for storing position information of the focusing lens is provided, and when the focusing lens is moved to the origin position for initial setting, the position stored in the lens position memory Initialize the information, then
The number of drive pulses supplied from the pulse motor drive control means to the pulse motor is counted, the position information stored in the lens position memory is updated based on the count result, and the pulse motor drive control means The drive of the pulse motor is controlled based on the detection result of the focus amount detection means and the determination result of the lens movement range determination means, as well as the position information stored in the lens position memory.

[0013]

In the autofocus device according to the present invention, no matter which position the focusing lens is at the time of initial operation of the autofocus device, the focusing lens is moved to a predetermined origin position of the lens driving mechanism, for example, infinity. The absolute value of the lens position is detected by driving the pulse motor for a time longer than the time enough to reach the position, or by driving the pulse motor for the number of pulses, and at the same time setting the lens position memory to the initial value and then shifting to the auto focus operation. .

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In the figure, 1, 2, 3, 4, 7, and 8 are lenses,
A camera circuit, a focus amount detection circuit, a difference detection circuit, a focal length detection circuit, and a lens movement range calculation circuit, which have the same numbers and functions as those of the conventional autofocus device described with reference to FIG. Have. 10 is the lens 1
Pulse motor for driving the focusing mechanism of No. 11, lens position memory, 12 rubbing circuit, 13 terminal,
Reference numeral 14 is a pulse motor drive control circuit. The pulse motor drive control circuit 14 generates a drive timing pulse for the pulse motor 10 in synchronization with the timing at which the focus voltage is updated. This point will be described in detail later.

The function of the rubbing circuit 12 is to perform initial alignment for matching the position (lens position) of the focusing mechanism of the lens 1 driven by the pulse motor 10 with the contents of the lens position memory 11, which is described below. It consists of two actions.

(Operation 1) Initial alignment: The rubbing circuit 12 at the start of the operation of the autofocus device, for example, immediately after the power of the video camera equipped with this device is turned on.
Detects that a signal is applied to the terminal 13 and moves the pulse motor 10 through the pulse motor drive control circuit 14 in a predetermined direction, for example, in the infinity direction, over the entire stroke of the lens moving mechanism of the lens 1. While driving for a sufficient predetermined number of pulses, the content of the lens position memory 11 is set to a predetermined initial value, for example, zero.

With this arrangement, at the start of the operation of the autofocus device, whatever the position of the lens 1 is, the position of the lens 1 moves in the infinity direction as the pulse motor 10 is driven. Hits a mechanical stopper at the infinity position, and then the pulse motor 10 idles and stays at the infinity position. Therefore, the lens position is at the infinity position immediately after all the predetermined number of pulses have been sent from the pulse motor drive control circuit 14, and the contents of the lens position memory 11 also have values corresponding to that position.
The above is the first operation.

In the subsequent autofocus operation, the lens position and the content of the lens position memory 11 are absolute by increasing or decreasing the content of the lens position memory 11 according to the number of pulses sent by the pulse motor drive control circuit 14. Since the values are the same, it can be easily inferred that the autofocus operation by the hill climbing method similar to that described with reference to FIG. 2 is performed also in this configuration unless there is rattling described later.

(Operation 2) Lens Position Correction During Mountain Climbing Operation: The contents of the lens position and the lens position memory 11 after the initial positioning by the above operation 1 are the pulse motor drive control circuit 14 in the subsequent autofocus operation.
The number of forward or reverse rotation pulses sent by the pulse motor 10,
If the contents of the lens position memory 11 are increased or decreased in correspondence with each other, it seems that no deviation will occur. However, in the normal method of connecting the focus adjusting mechanism of the pulse motor 10 and the lens 1 with or without deceleration by a gear or a structure similar thereto, there is a slight play in this connecting section, and the pulse motor 10 is driven. An error occurs between the lens position and the content of the lens position memory 11 due to this play each time the lens is stopped or reversed, and the error is accumulated during a long-time operation, resulting in an unacceptable value.

Therefore, when the content of the lens position memory 11 is close to the predetermined initial value set in (Operation 1), which is earlier than the predetermined value, during the normal autofocus operation, The rubbing circuit 12 drives the pulse motor drive control circuit 14 with priority over the output of the difference detection circuit 4 to drive the pulse motor 10 once in a predetermined direction same as (operation 1), for example, a predetermined pulse in the infinity direction. In addition to sending only the number, the content of the lens position memory 11 is reset to a predetermined initial value, for example, zero, and then the pulse motor 10 is driven again in the opposite direction. Return to 4.

In this way, the accumulated error during the autofocus operation up to that point is corrected. In this case, it is obvious that the number of feed pulses may be smaller than that of (Operation 1), and normally several pulses are enough, so that the original operation of the autofocus device by (Operation 2) is hardly damaged. The above is (Operation 2).

FIG. 3 shows an example in which the rubbing circuit 12 is implemented as a microcomputer program. In the figure, when the power-on or the like is detected by the signal applied to the terminal 13 in FIG. 1, the prepared lens feed counter has a number larger than the mechanically movable range of the lens (for example, 1
28) is set and the lens is sent in a predetermined direction (infinity direction), and at the same time, the content of the lens feed counter is decremented until it becomes zero (or negative), and at the end of this, the lens position memory 11 The operation (1) of the rubbing circuit 12 is performed by clearing the content to the initial value.

Also, (operation 2) of the rubbing circuit 12 is included in the program for the autofocus operation,
If the content of the lens position memory 11 becomes a predetermined number C (for example, 5) or less during the autofocus operation, the content of the lens feed counter described above is set to a predetermined number C.
Use a larger number of lenses (eg 10) (operation 1)
Then, the lens position memory 11 is cleared to the initial value, the lens is driven in the closest direction, and the autofocus operation is performed.

In the figure, the detection and control circuits such as the pulse motor drive control circuit 14, the difference detection circuit 4, the lens position memory 11, and the lens movement range calculation circuit 8 can be housed in the same microcomputer. Can be easily configured using, for example, a one-chip 4-bit microcomputer HMCS44, HMCS45 manufactured by Hitachi, Ltd.

In the above description, the lens 1 when the contents of the lens position memory 11 are reset to a predetermined initial value.
Is the position where the lens 1 abuts on the mechanical stopper, that is, the position of the end of the lens drive mechanism. However, in the present invention, the origin position is not limited to this position, and the lens movement is It may be at any position within the range. Further, when the position in the middle of the lens movement range is set as the origin position, whether the lens 1 has reached the origin position can be easily detected by a simple electric detection means.

Next, a method for synchronizing the drive of the pulse motor 10 with the difference detection circuit 4 will be described. In FIG. 1, the line guided from the camera circuit 2 to the pulse motor drive control circuit 14 indicates a vertical synchronizing signal of a television signal or a signal line similar to it, and the pulse motor drive control circuit 14 instructs the difference detection circuit 4 to operate. Accordingly, the pulse motor 10 is driven in synchronization with this signal to rotate the pulse motor 10 forward or backward. Therefore, the pulse motor 10 moves the lens position of the lens 1 by an amount corresponding to a predetermined number of pulses, for example, one pulse in each vertical synchronizing signal period in a phase synchronized with the vertical synchronizing signal of the television signal. .

In this way, since the period at which the focus voltage generated by the focus amount detecting circuit 3 is updated matches the vertical synchronizing signal, the difference between adjacent focus voltages, that is, the difference detecting circuit 4 increases the difference. Alternatively, since it means that the lens position movement amount of the lens 1 that contributes to the voltage that is determined to be reduced is constant, unevenness in the differential voltage does not occur,
No malfunction occurs.

Next, a case where the operation of synchronizing the driving of the pulse motor 10 described above with the difference detection circuit 4 is carried out by a microcomputer will be described. 4 is a block diagram showing the difference detection circuit 4, the pulse motor drive control circuit 14, the lens movement range calculation circuit 8, the lens position memory 11, and the rubbing circuit 12 in the configuration of the embodiment of the present invention shown in FIG. The configuration and the operation and function thereof are the same as the operation and function of each configuration of FIG. 101 is an RO for storing the program
M, 102 are CPUs, 103 is memory used as R
AM, 104 is an input / output terminal group, 105 is a timer,
Each is built in the microcomputer 100. In FIG. 4, it is obvious that the lens movement range calculation circuit 8, the lens position memory 11, and the rubbing circuit 12 can be configured by the microcomputer 100, and the description thereof will be omitted.

FIG. 5 shows a microcomputer 10 for synchronizing the driving of the pulse motor 10 with the focus voltage difference detection operation.
FIG. 6 is a waveform chart of a program for explaining the operation of 0. In FIG. 4, the vertical synchronizing signal (shown in FIG. 6a) corresponding to the captured video signal is input from the camera circuit 2 to the terminal 107. Since the interrupt input terminal of the microcomputer 100 is connected to the terminal 107, when the vertical synchronizing signal is applied to this terminal 107, the program shown in FIG.
5 starts. In this case, since the operating time of the timer 105 is selected to be about 1/2 of the vertical synchronizing signal period, the timer 105 synchronizes with the vertical synchronizing signal as shown in FIG. It operates, and the other half is stopped. Therefore, as shown in FIG. 6h, if the pulse motor 10 is driven each time the timer 105 is started and stopped, the pulse motor 10 operates in synchronization with the vertical synchronization signal supplied from the camera circuit 2, The position of the lens 1 will be moved.

On the other hand, in the camera circuit 2, as the photographed video signal is output in synchronization with the vertical synchronizing signal as shown in FIG. 6b, the focus voltage is also generated in synchronization with this. In the focus amount detection circuit 3, the focus voltage waveform (c in the figure) increases in the middle of the vertical synchronizing signal cycle and is cleared to zero potential at the rising time of the vertical synchronizing signal.
Only the video signal corresponding to the vicinity of the center of the shooting screen is passed, then the high frequency components are detected and integrated to obtain an integrated voltage, and the integrated voltage is prevented from being mixed with the integrated voltage corresponding to the next image signal. This is because the focus voltage is obtained by clearing the integrated voltage at the rising edge of the vertical synchronizing signal for the purpose of

The generated focus voltage is converted into a digital amount by the A / D converter 31 by generating the timing pulse shown in FIG. 6d at the terminal 106 in FIG. 4 and input to the microcomputer 100, and then stored in the RAM 103. Store in the reserved focus voltage memory. Therefore, the focus voltage recognized by the microcomputer 100 has a value synchronized with the vertical synchronizing signal, as schematically shown in FIG. 6e. The microcomputer 100 calculates the difference between the stored value of the focus voltage and the previously stored value of the focus voltage similarly to the CPU 10.
The difference is detected by calculating in 2. This difference detection is performed in synchronization with the vertical sync signal at the timing shown in FIG. 6g because the focus voltage corresponding to the captured image is input to the microcomputer 100 at the vertical sync signal cycle.

As described above, the microcomputer 100 performs both the difference detection operation and the drive timing of the pulse motor 10 in synchronization with the vertical synchronizing signal. It will be understood that the forward rotation, the reverse rotation, and the stop of the pulse motor 10 can be performed depending on the result of the difference detection or the result of the movement range calculation. Therefore, the configuration of FIG. 4 is the same as the configuration shown in FIG. Has the same operation and function.

Although the vertical synchronizing signal is used as the interrupt signal input of the microcomputer 100 in the above description, if the signal input is not the vertical synchronizing signal itself, but is a signal synchronized with this, The same function can be realized by changing the operating time of the timer in the flowchart of 5 or changing the order of the program blocks described in the flowchart. Also, FIG.
Although the A / D converter 31 is used in the configuration shown in FIG.
It is easy to incorporate the function of the / D converter into the microcomputer 100. Further, in the above description, the focus adjusting mechanism of the lens 1 was not particularly touched, but any mechanism may be used, but the efficiency of the pulse motor is lower than that of the DC motor of the same shape. It is also possible to move all or part of the rear ball or a small and light part such as a convensor part.

[0034]

As described above, when the pulse motor is used to drive the lens, the absolute position of the focusing lens can be known without using the lens position detection circuit, and the position is always correct. Can be captured. In addition, by using a pulse motor for driving the lens, the autofocus device according to the present invention is
It is highly reliable for a device using a C motor and is inexpensive because it does not require a lens position detection circuit using a contact type or non-contact type potentiometer or the like. In addition,
In the description of the embodiment of the present invention, the difference detection circuit performs the increase / decrease detection operation at every focal voltage generation period, that is, every 1/60 seconds. However, the basis of the increase / decrease detection operation is the blurring between different lens positions. Considering that the difference is to be detected, it is obvious that the difference detection operation may be performed every time the motor drive circuit outputs a predetermined number of pulses. In this case, the lens position memory 11 stores the predetermined difference. It is only necessary to insert a command circuit for instructing the difference detection operation into the difference detection circuit 4 at the same time as it is reset every time the number of is counted.

In the above description, the focus adjusting mechanism of the lens 1 is not particularly mentioned, but any mechanism may be used, but the efficiency of the pulse motor D is the same.
Since it is lower than that of the C motor, it is particularly suitable for a system in which the whole or a part of the rear lens of the lens and a small and light part such as a convenator part are moved.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an autofocus device using a pulse motor according to the present invention.

FIG. 2 is a configuration block diagram showing a conventional hill-climbing autofocus device using a DC motor.

FIG. 3 is a flowchart when a part of the configuration of FIG. 1 is implemented by a microcomputer.

FIG. 4 is a configuration block diagram showing a configuration of another embodiment of the present invention.

FIG. 5 is a flowchart for explaining the operation of the configuration of FIG.

FIG. 6 is a waveform conceptual diagram.

[Explanation of symbols]

1 ... Lens, 2 ... Camera circuit, 3 ... Focus amount detection circuit, 4
... difference detection circuit, 7 ... focal length detection circuit, 8 ... lens movement range calculation circuit, 10 ... pulse motor, 11 ... lens position memory, 12 ... rubbing circuit, 13 ... terminal, 14 ...
Pulse motor drive control circuit, 31 ... A / D converter, 10
1 ... ROM, 102 ... CPU, 103 ... RAM, 104
Input / output terminal group, 105 ... Timer, 100 ... Microcomputer, 107 ... Interrupt input terminal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Todaka 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture

Claims (6)

[Claims] 1. An optical lens including a variable zoom magnification lens and a focusing lens, a pulse motor for moving the focusing lens, an optical image formed through the optical lens, converted into an electric signal, and a video signal. Output from the camera circuit, focus amount detection means for detecting the degree of focus from the high frequency component of the video signal output from the camera circuit, and the zoom magnification according to the change of the zoom magnification by the zoom magnification variable lens. Based on the lens movement range determining means for determining a necessary movement range of the focusing lens, the detection result by the focus amount detecting means, and the determination result by the lens movement range determining means, the focusing lens with respect to the subject. Pulse motor drive control means for controlling the drive of the pulse motor so as to move to a focused position. Means to move the focusing lens once to a predetermined origin position for initial setting within a predetermined period immediately after power-on of the apparatus, and then to move to a position where the subject is focused. An autofocus device for a video camera, which controls driving of a motor. 2. The autofocus device according to claim 1, wherein the pulse motor drive control means moves to a predetermined origin position to initialize the focusing lens so as to initialize the focusing lens. An autofocus device for a video camera, characterized in that the drive pulse of (1) is supplied to the pulse motor. 3. The autofocus device according to claim 1, further comprising a lens position memory that stores position information of the focusing lens, and moves the focusing lens to the origin position to initialize the focusing lens. Then, the position information stored in the lens position memory is initialized, and then,
The pulse motor drive control means counts the number of drive pulses supplied to the pulse motor, updates the position information stored in the lens position memory based on the count result, and the pulse motor drive control means A video which controls the drive of the pulse motor based on the detection result by the focus amount detection means and the determination result by the lens movement range determination means, as well as the position information stored in the lens position memory. Camera autofocus device. 4. The autofocus device according to claim 3, wherein the focus amount detection means, the lens movement range determination means, the pulse motor drive control means, and the lens position memory are all configured by a microcomputer. Characteristic video camera autofocus device. 5. The autofocus device according to claim 1, 2, 3 or 4, wherein the origin position is a position where an object at infinity is in focus. 6. The autofocus device according to claim 1, 2, 3, 4 or 5, wherein the focusing lens is a rear lens or a compensator lens.