JPH0226834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to an autofocus device, and particularly to an autofocus device suitable for a video camera.

[Prior art]

Conventionally, as an autofocus device for a video camera, a so-called hill-climbing method has been known, which detects the definition of the shooting screen from high frequency components in the video signal and controls the position of the lens to maximize the definition. There is. This method is described in detail in, for example, Japanese Patent Laid-Open No. 56-51164, which was previously filed by the present applicant, but this method will be briefly explained below using FIG. 1. In the same figure, 1 is the lens 2 is the camera circuit, 3
is a focus amount detection circuit, 4 is a difference detection circuit, and 5 is a DC
6 is a DC 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 that enters a lens 1 is converted into an electrical signal by a camera circuit 2. Taking advantage of the fact that the higher the focus of the lens 1 is, the lower the high frequency component of this electric signal is, and the higher the focus is, the higher the frequency component is, the focus amount detection circuit 3 filters the output signal of the camera circuit 2 through a high frequency filter. After passing, the detection is integrated over the period to form one screen, that is, one field period (1/60 second in the case of television system), and the better the focus, the higher the voltage (hereafter this voltage is called the focal voltage). ) is output. Therefore, in this type of autofocus device, the focus portion of the lens 1 is driven by the DC motor 6,
While the lens position detection circuit 9 memorizes and confirms the position of the lens 1 at that time, the difference detection circuit 4
Detects an increase or decrease in the focus voltage, which is the output of the focus amount detection circuit 3, and while the focus voltage is increasing, the DC motor drive control circuit 5 maintains the direction of rotation of the DC motor 6 to control the lens. The DC motor drive control circuit 5 reverses the motor 6, and when the output of the difference detection circuit 4 detects a decrease in the focus point of While referring to the output signal of the lens position detection circuit 9, the lens 1 is returned to the position where the highest focal voltage was obtained in the process up to this point, that is, the just-focus point. Here, the focal length detector 7 and the lens movement range calculation circuit 8 are installed to ensure a predetermined focusable distance range, for example, a close range of 1.5 m to infinity (∞). In other words, the required range of movement of lens 1 varies depending on the focal length of lens 1, and when the zoom magnification of lens 1 is low, the depth of field is deep, so the range needs to be narrow, and when the zoom magnification of lens 1 is high, By taking advantage of the fact that the width increases as the distance increases, the time required for the focusing operation of an autofocus device is shortened, and the probability of out-of-focus due to malfunction is prevented from increasing. The lens position detection circuit 9 detects the position of the lens 1 using the lens movement range calculation circuit 8 described above.
A contact or non-contact potentiometer linked to the focusing mechanism of the lens 1 is also used to confirm that the focus is within the range indicated by the lens 1. The above is the operation of the hill-climbing autofocus device.

Now, as a motor used for this device, a normal
If instead of using a DC motor, it is possible to use a pulse motor which itself has a non-contact structure (see, for example, Japanese Unexamined Patent Publication No. 56-147132), there is an advantage that the life of the device can be extended. Furthermore, since the position of the lens 1 can be known by counting the number of pulses that drive the pulse motor, it is simple to understand that cost can be reduced by simultaneously eliminating the lens position detection circuit 9. Although this is a win, there are various problems in applying this idea as is.

The first problem arises from the fact that the focal voltage is obtained from the imaging signal of the video camera. That is,
In the television system, one image is completed at a fixed time period of 1/60 seconds, so the focal voltage used for focusing can only be obtained at fixed intervals.
Therefore, difference detection is performed every 1/60 seconds or every integral multiple thereof. When the position of the lens 1 is continuously driven by a DC motor at a constant speed, the position of the lens 1 that occurs in the difference detection period is
Since the amount of movement is constant, this intermittent operation every 1/60 seconds does not cause a problem, but if the pulse motor drives the position of lens 1 in a stepwise manner at a period different from the period of difference detection. This occurs because the amount of movement of the lens 1 that occurs during the difference detection period of 1/60 seconds varies by ±1 pulse drive in each difference detection period, so it does not necessarily remain a constant value. This causes unevenness in the differential voltage, making malfunctions more likely. This is easy to understand if you consider that it corresponds to the fact that the drive speed of the DC motor is not constant in each differential cycle. This phenomenon is not a problem if the drive cycle of the pulse motor is a sufficiently small value compared to 1/60 seconds, but it is clear that it becomes a major problem as the drive cycle of the pulse motor approaches 1/60 second. .

The second problem concerns position detection of the lens 1. When using a pulse motor, it is possible to detect the relative position movement of the lens 1 by counting the number of pulses described above, but it is not possible to know the absolute position of the lens 1 required by an autofocus device. I can't. That is,
The initial state of operation of an autofocus device, for example, unless the absolute position of lens 1 when the device is powered on is known, the detected position of lens 1 obtained by counting the number of pulses and the actual lens 1 Since the position of the lens 1 has a parallel deviation, the position of the lens 1 cannot be kept within the absolute position range determined by the movement range calculation circuit 8. Furthermore, even if the initial position of the lens 1 is known and the number of pulses is counted based on that position, it cannot be assumed that the detected position of the lens 1 accurately captures the position of the lens 1. The reason for this is that the mechanism that connects the pulse motor and the focus movement structure of lens 1 has substantial play, and during long-term operation, the idle feed error due to this play accumulates, and this error cannot be ignored. It depends.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an autofocus device having a lens drive mechanism using a pulse motor, which does not have the above-mentioned drawbacks.

[Summary of the invention]

In order to achieve the above object, the autofocus device of the present invention synchronizes the driving timing of the pulse motor with the timing at which the focal voltage is updated, thereby making the number of pulses sent in each difference cycle period the same. do. Furthermore, at the time of initial operation of the autofocus device, etc., the pulse motor is driven for a time or number of pulses sufficient to sufficiently press the end of the lens moving mechanism to the end of the lens moving mechanism, for example, the infinity position, regardless of the position of the lens. The absolute value of the lens position is detected by setting the lens position memory at that time to an initial value and then shifting to autofocus operation.

[Embodiments of the invention]

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, camera circuits, focal length detection circuits, difference detection circuits, focal length detection circuits, and movement range calculation circuits, which were explained using Fig. 1. It has the same functions and circuits as the conventional autofocus device with the same numbers. 10 is a pulse motor that drives the focusing mechanism of the lens 1, 11 is a lens position memory, 12 is a rubbing circuit, 13 is a terminal 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 focal voltage is updated. This point will be explained in detail later.

The function of the rubbing circuit 12 is that the pulse motor 1
The position (lens position) of the focusing mechanism of the lens 1 driven by the lens 1 is stored in the lens position memory 11.
The process consists of the following two operations:

(Operation 1) Initial positioning: At the start of operation of the autofocus device, for example, immediately after turning on the power of a video camera equipped with this device, the rubbing circuit 12 detects that a signal is applied to the terminal 13, The pulse motor 10 is driven via the pulse motor drive control circuit 14 in a predetermined direction, for example, toward infinity, by a predetermined number of pulses sufficient to move the entire stroke of the lens moving mechanism of the lens 1, and also controls the lens position. The contents of memory 11 are set to a predetermined initial value, for example zero. In this way, when the autofocus device starts operating,
No matter where the lens position of the lens 1 is, it will move toward infinity as the pulse motor 10 is driven, and will eventually hit a mechanical stopper at an infinity position, and after that, the pulse motor 10 will move toward the infinite distance. stays at an infinite position while idling. Therefore, immediately after all the predetermined number of pulses are sent out from the pulse motor drive control circuit 14, the lens position is at an infinite position, and the contents of the lens position memory 11 are also values corresponding to that position. The above is operation 1. The subsequent autofocus operation is
By increasing or decreasing the contents of the lens position memory 11 in accordance with the number of pulses sent out by the pulse motor drive circuit 14, the lens position and the contents of the lens position memory 11 will match as absolute values, so this configuration In this case as well, it can be easily inferred that the autofocus operation is performed using the same hill-climbing method as explained using FIG. 1 as long as there is no play as will be described later.

(Operation 2) Lens position correction during hill-climbing operation: The lens position and the contents of the lens position memory 11 after initial alignment in the above-mentioned operation 1 are changed to the pulse motor drive circuit 14 in the subsequent autofocus operation. If the number of forward or reverse rotation pulses sent by the pulse motor 10 is made to correspond to the increase or decrease in the contents of the lens position memory 11, it appears that no deviation will occur. However, in the usual method of connecting the pulse motor 10 and the focus adjustment mechanism of the lens 1 with or without deceleration using gears or similar structures, there is a slight play in this connection section, and the pulse motor 10 is driven. , stopping, and reversing, an error occurs between the lens position and the contents of the lens position memory 11 due to this backlash, and during long-term operation, this error accumulates and becomes an unacceptable value. Therefore, even during normal autofocus operation, if the contents of the lens position memory 11 become closer to the predetermined initial value set in (operation 1) earlier than the predetermined value, the rubbing circuit 12 is a pulse motor drive circuit 14;
The output of the difference detection circuit 4 is prioritized and driven, and the pulse motor 10 is driven in the same predetermined direction as the first drive (operation 1).
For example, after sending a predetermined number of pulses in the direction of infinity, resetting the contents of the lens position memory 11 to a predetermined initial value, for example zero, and driving the pulse motor in the opposite direction,
The control input of the pulse motor drive circuit 14 is returned to the difference detection circuit 4. In this way, the error accumulated during the autofocus operation up to that point is corrected. It is obvious that the number of sending pulses in this case may be smaller than that in (operation 1), and usually only a few pulses are required, so that the original operation of the autofocus device by this (operation 2) is hardly impaired. 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 is turned on, etc. is detected by the signal applied to the terminal 13 in Figure 2, a number (for example, 128) larger than the mechanically movable range of the lens is input to the lens advance counter provided. At the same time as setting the lens and sending the lens in a predetermined direction (∞ direction), the contents of the lens feed counter are subtracted in conjunction with this until it becomes zero (or negative), and when this is completed, the contents of the lens position memory 11 are initialized. By clearing it to a value, (operation 1) of the rubbing circuit 12 is performed.

Further, (operation 2) of the rubbing circuit 12 is included in the autofocus operation program, and is performed when the contents of the lens position memory 11 become less than a certain number C (for example, 5) during the autofocus operation. , the contents of the lens advance counter described above are set to a number larger than the predetermined number C (for example,
10) in the same direction as in (operation 1), then clear the contents of the lens position memory 11 to the initial value, and then drive the lens in the closest direction,
It returns with auto focus operation. In the figure, detection and control circuits such as a pulse motor drive circuit 14, a difference detection circuit 4, a lens position memory 11, a lens movement range calculation circuit 8, etc. can be housed in the same microcomputer; For example, it can be easily configured using one-chip 4-bit microcomputers HMCS44, HMCS45, etc. manufactured by Hitachi.

Next, the pulse motor 10 is driven by the differential detection circuit 4.
We will explain how to synchronize with. The line led from the camera circuit 2 to the pulse motor drive circuit 14 in FIG. Accordingly, the pulse motor 10 is driven in synchronization with this signal, and the pulse motor 10 is rotated forward or reverse. 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, 1 pulse, in each period of the vertical synchronization signal in a phase synchronized with the vertical synchronization signal of the television signal. Become. In this way, the period in which the focus voltage generated by the focus amount detection circuit 3 is updated matches the vertical synchronization signal, so that the difference between adjacent focus voltages, that is, the increase in the difference detection circuit 4,
Or the lens 1 that contributes to the voltage that is determined to be reduced
This means that the lens position movement amount is constant, so there is no unevenness in the differential voltage, and no malfunction occurs.

Next, the drive of the pulse motor 10 explained above is as follows.
A case will be described in which the operation for synchronizing with the difference detection circuit 4 is performed by a microcomputer. FIG. 4 shows the configuration of the embodiment of the present invention shown in FIG.
Difference detection circuit 4, pulse motor drive control circuit 1
4. Movement range calculation circuit 8, lens position memory 1
1. The rubbing circuit 12 is constituted by a microcomputer 100, and its operation and function are the same as those of the respective configurations shown in FIG. 101 is for storing programs
ROM, 102 is a CPU, 103 is a RAM used as memory, 104 is an input/output terminal group, and 105 is a timer, each of which is built in the microcomputer 100. In FIG. 4, it is clear that the movement range calculation circuit 8, lens position memory 11, and rubbing circuit 12 can be constructed by the microcomputer 100, and the explanation thereof will be omitted.

FIG. 5 is a flowchart of a program for explaining the operation of the microcomputer 100 for synchronizing the drive of the pulse motor 10 with the focus voltage difference detection operation, and FIG. 6 is a waveform diagram. In FIG. 4, a vertical synchronization signal (shown in FIG. 6a) corresponding to the photographed 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 a vertical synchronization signal is applied to this terminal 107, the program shown in FIG. 5 is started and the timer 105 is activated. In this case, the operating time of the timer 105 is selected to be about 1/2 of the vertical synchronizing signal period, so the timer 105 is synchronized with the vertical synchronizing signal and 1/2 of the period of the vertical synchronizing signal, as shown in FIG. 6g. 2 are working and the remaining 1/2 are stopped.
Therefore, as shown in FIG. 6h, if the pulse motor 10 is driven each time the timer 105 starts and stops, the pulse motor 10 will synchronize with the vertical synchronization signal supplied from the camera circuit 2. This will cause the lens 1 to move. On the other hand, in the camera circuit 2, since the photographed video signal is output in synchronization with the vertical synchronization signal as shown in FIG. 6b, the focal voltage is also generated in synchronization with this. Here, the focus voltage waveform (c in the same figure) increases in the middle of the vertical synchronization signal period and is cleared to zero potential at the rise time of the vertical synchronization signal because the focus voltage generation circuit 3 Vertical synchronization is used to pass only the video signal corresponding to the image signal, detect and integrate its high frequency components to obtain an integrated voltage, and to prevent the integrated voltage from mixing with the integrated voltage corresponding to the adjacent imaging signal. This is because the focal voltage is obtained by clearing the integrated voltage at the rising edge of the signal. The generated focal voltage is applied to the A/D converter 31 by generating the timing pulse shown in FIG. 6d at the terminal 106 in FIG.
is converted into a digital quantity, inputted to the microcomputer 100, and stored in the focal voltage memory secured in the RAM 103. Therefore, the focal voltage recognized by the microcomputer 100 is as shown in FIG.
As schematically shown in , the value is synchronized with the vertical synchronization signal. The microcomputer 100 performs difference detection by calculating the difference between the stored focal voltage value and the previously stored focal voltage value in the same manner using the CPU 102. This difference detection is performed in synchronization with the vertical synchronizing signal at the timing shown in FIG. 6g, since the focal voltage corresponding to the photographed image is inputted to the microcomputer 100 at the period of the vertical synchronizing signal. As explained above, the microcomputer 100 performs both the difference detection operation and the drive timing of the pulse motor 10 in synchronization with the vertical synchronization signal. Here, it is understood without explanation that the forward rotation, reverse rotation, and stop of the pulse motor 10 can be performed based on the result of difference detection or the result of movement range calculation, so the configuration of FIG. 4 is shown in FIG. 2. It has the same operation and function as the configuration.

In addition, in the above explanation, microcomputer 1
Although the vertical synchronization signal was used as the interrupt signal input for 00, even if this signal input is not the vertical synchronization signal itself, as long as it is a signal synchronized with this, the operation time of the timer in the flowchart in Figure 5 can be changed. Alternatively, the same function can be realized by changing the order of the program blocks described in the flowchart. In addition, although the A/D converter 31 is used in the configuration shown in FIG.
It is easy to incorporate the converter function into the microcomputer 100. Furthermore, in the above explanation, the focus adjustment mechanism of the lens 1 was not particularly mentioned, but this mechanism may be of any type;
Since the efficiency of a pulse motor is lower than that of a DC motor of the same shape, it is also possible to move a small and light part such as all or part of the rear lens of the lens or the compensator section.

〔Effect of the invention〕

As described above in detail using FIGS. 2 to 6, the autofocus device using a pulse motor according to the present invention has higher reliability than devices using a conventional DC motor, In addition, it is inexpensive because it does not require a lens position detection circuit using a contact or non-contact potentiometer. In addition,
In the explanation of the embodiment of the present invention, the difference detection circuit performs the increase/decrease detection operation every 1/60 second, which is the generation cycle of the focal voltage. Considering that the objective is to detect a difference, it is obvious that the difference detection operation may be performed every time the motor drive circuit sends out a predetermined number of pulses. It is only necessary to insert a command circuit which is reset every time the number of is counted and at the same time instructs the difference detection circuit 4 to perform a difference detection operation.

Also, in the above explanation, the focus adjustment mechanism of lens 1 was not specifically mentioned, but this mechanism may be of any type, but since the efficiency of a pulse motor is lower than that of a DC motor of the same shape, It is particularly suitable for a method in which small and light parts such as all or part of the rear ball or the compensator section are moved.

[Brief explanation of drawings]

Figure 1 is a configuration block diagram showing a conventional mountain-climbing autofocus device using a DC motor.
FIG. 2 is a configuration block diagram showing an embodiment of an autofocus device using a pulse motor according to the present invention, FIG. 3 is a flowchart when a part of the configuration of FIG. 4
5 is a block diagram showing the configuration of another embodiment of the present invention, FIG. 5 is a flowchart for explaining the operation of the configuration of FIG. 4, and FIG. 6 is a waveform conceptual diagram. DESCRIPTION OF SYMBOLS 1...Lens, 2...Camera circuit, 3...Focus amount detection circuit, 4...Difference detection circuit, 5...Motor drive circuit,
6...DC motor, 7...focal length detection circuit, 8...movement range calculation circuit, 9...lens position detection circuit, 10
...Pulse motor, 11...Lens position memory, 12
...Rubbing circuit, 31...A/D converter, 101
...ROM, 102...CPU, 103...RAM, 10
4...I/O terminal group, 105...Timer, 100...Microcomputer, 107...Interrupt input terminal.

Claims (1)

[Claims] 1. An optical lens including a focusing lens, a pulse motor for moving the focusing lens, and converting an optical image formed through the optical lens into an electrical signal and outputting a video signal. a camera circuit; a focus amount detection means for detecting a degree of focus accuracy from high-frequency components of a video signal output from the camera circuit; and a pulse motor drive control means for controlling the pulse motor to move to a focusing position, and the pulse motor is controlled by the pulse motor drive control means to cause the camera circuit to generate a video signal. An autofocus device characterized in that it is driven in synchronization with the cycle of the autofocus device. 2. The pulse motor drive control means drives the pulse motor so as to move the focusing lens to a focusing position of an object at infinity and perform initial setting at the time of initial operation. 1
Autofocus device as described in section. 3. The pulse motor drive control means has a lens position memory that stores position information of the focusing lens, and the pulse motor drive control means drives and controls the focusing lens while referring to the information in the lens position memory. Further, at the time of initial operation, the pulse motor drive control means moves the focusing lens to a focusing position of an object at infinity and performs initial setting by supplying a predetermined number of pulses to the pulse motor. 2. The autofocus device according to claim 1, further comprising setting the position information stored in the lens position memory as an initial value. 4. The autofocus device according to claim 1, 2, or 3, wherein the focusing lens is a rear lens. 5. The autofocus device according to claim 1, 2, or 3, wherein the focusing lens is a compensator lens.