JPH0293510A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To accurately position a focusing lens at a focusing point even if the rotating speed of a lens motor varies by detecting a return quantity according to brush noises outputted by the lens motor while a focusing lens moves from a focusing point to a passage detection point and returning the focusing lens to the focusing lens according to the corrected return quantity. CONSTITUTION:The brush noises generated by the lens motor 16 from the focusing point X1 to the passage detection point X3 are counted, the counted value is corrected as specified, and the focus lens 11 is returned by the corrected counted value until the lens motor 16 generate a brush noise. The measured return quantity is therefore proportional to the rotating speed of the lens motor 16. Consequently, the rotating speed of the lens motor varies and the focus lens 11 can be positioned accurately at the focusing point.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention detects focus evaluation information indicating the in-focus state of a focus lens from an image signal of a subject in a camera or a video camera, and The present invention relates to an automatic focusing device that automatically positions a focus lens to a focused point using a mountain climbing servo based on focus evaluation information.

(Prior Art) In cameras and video cameras, generally, an automatic focusing device for automatically positioning a focus lens to an in-focus point, a so-called autofocus device (hereinafter referred to as an AF
equipment) is provided.

The AF equipment can be broadly classified into active type AF equipment and passive type AF equipment. Active type AF equipment also has infrared type and ultrasonic type AF.
There is a mounting device. In addition, the passive AF equipment is TC
There are L-type and image-detection type AF systems.

Emit infrared light, ultrasonic waves, etc. from an active AF device, video camera, etc., use the reflected light and waves from the subject to determine the distance to the subject, and adjust the focus lens according to this measurement result. This is to position the focal point.

However, in the case of this active method, the accuracy of measuring the distance to the subject is limited to a? Since it is greatly influenced by the reflectance of the subject with respect to the J distance medium, attenuation due to the traveling distance of the distance measuring medium, the state of the distance measuring space, etc., there is a high possibility that the positioning accuracy of the focus lens will be low.

On the other hand, since the focus lens is positioned at the in-focus point according to the image signal obtained from the passive AF-equipped imaging device, the positioning accuracy is not affected by the reflectance or the like.

However, in the case of this passive AF device, the positioning accuracy of the focus lens is affected by the contrast and brightness of the object, as well as the pattern.

However, this effect is being resolved with recent improvements in image processing technology. Therefore, from the standpoint of positioning accuracy of the focus lens, it is more advantageous to use a passive type AF device.

An AF device using an image detection method, which is one of the passive methods,
Information indicating the in-focus state of the focus lens (hereinafter referred to as
The focus lens is positioned at the in-focus point according to the detected output.

As methods for detecting focus evaluation values, there are, for example, a method for detecting a peak value of image contrast and a method for detecting an average value. Both methods focus on the fact that the peak value or average value of contrast increases as the image comes into focus, and the focus lens is positioned at the point where the peak value or average value is maximum, which is the focal point. be.

As a servo method for positioning the focus lens to the in-focus point according to the focus evaluation value, there is, for example, a mountain climbing servo method.

Here, a conventional AF device using a mountain-climbing servo system as a servo system will be explained using FIGS. 3 to 6.

In FIG. 3, 11 is a focus lens. 12
is an imaging unit that captures a subject image provided through the focus lens 11 and converts it into an image signal. Reference numeral 13 denotes a focus evaluation value detection circuit that detects a focus evaluation value according to the image signal output from the imaging section 12. A microprocessor 14 performs mountain climbing servo according to the focus evaluation value detected by the evaluation value detection circuit 13. 15
is a motor drive circuit that drives the lens motor 16 in accordance with control signals supplied from the microprocessor 14.

The focus evaluation value detection circuit 13 is configured as shown in FIG. 4, for example. The illustrated focus evaluation value detection circuit 13 detects, for example, an average value of contrast as the focus evaluation value.

That is, high frequency components of the image signal provided from the imaging section 12 in FIG. 3 are extracted by the high-pass filter 131. This high frequency component is converted into a digital signal by a detection circuit 132 and an analog/digital conversion circuit 133. This digital signal is supplied to a gate circuit 134, and only a portion of a predetermined focus area is gated. This focus area is set, for example, at the center of the screen. This gate output is integrated by an integrating circuit 135 and output as a focus evaluation value.

The integration circuit 135 is composed of, for example, an adder circuit and a latch circuit, and the adder circuit adds the digital signals of the focus area, latches this addition output to the latch circuit for each field, and outputs this latch output as a focus evaluation value. It is supposed to be done.

Note that 136 and 137 are a synchronous separation circuit and a gate control circuit, respectively, used to generate gate pulses for the gate circuit 134.

5 and 6 are diagrams for explaining the mountain climbing servo executed by the microprocessor 14. Here, FIG. 5 is a characteristic diagram showing changes in the focus evaluation value when the focus lens 11 is changed, and FIG. 6 is a flowchart showing the processing program of the microprocessor 14.

This mountain-climbing servo detects that the focus lens 11 has passed the in-focus point By returning the focus lens 11 by the distance between x2 (hereinafter referred to as a passing detection point) (see FIG. 5) and the focused point X1, the focus lens 11 is positioned at the focused point X1.

That is, when there is a trigger input for focus adjustment (for example, turning on the power), the microprocessor 14 performs initialization processing and then moves the focus lens 11 in a predetermined direction (step S1 in FIG. 6). (See S2). Assuming that the focus lens 11 is now at point A in FIG. 5, the microprocessor 14 moves the focus lens 11, for example, to the INF side. Next, compare the focus evaluation value before the movement with the focus evaluation value after the movement (see step S3 in FIG. 6), and if the former is larger, the focus lens 1
1 to the opposite direction (see step S4 in FIG. 6), and conversely, if the former is smaller, the moving direction of the focus lens 11 is left unchanged (see step S5 in FIG. 6). In this case, since the former is larger, the moving direction of the focus lens 11 is switched to the opposite direction.

In step S6, it is determined whether the focus evaluation value continues to increase while moving the focus lens 11, and if it continues to increase, the focus lens 11 is moved as is. On the other hand, when it changes from rising to falling, the moving direction of the focus lens 11 is switched and the in-focus point
(see step S7 in FIG. 6). This results in
The focus lens 11 will be positioned at the focal point Xl.

Thereafter, the microprocessor 14 monitors the shift of focus due to movement of the subject in step S8, and if the focus shifts, the process returns to step S2 and repeats the same operation again.

This mountain-climbing servo method is a servo method that has been tried for a long time, but it has rarely been used in the past because the dynamic range of the circuit is small and it cannot be used with a variety of subjects. However, with recent improvements in digital technology, this problem has been resolved, and the servo system is now used in many AF equipment.

By the way, in this mountain-climbing servo method, the amount of return from the passing detection point (X2 in Fig. 5) to the in-focus point is accurately measured, and the focus lens 11 is not accurately returned by the total return amount of 11111. Therefore, the focus lens 11 cannot be accurately positioned at the in-focus point X.

Conventionally, the position of the focus lens 11 is constantly monitored, the position when the in-focus point X1 is obtained is memorized, the difference between this memorized position and the A detection point X2 is determined, and the focus lens 11 is returned by that difference. It was like that.

However, in such a configuration, one of the image signals obtained by imaging
It is difficult to accurately measure the return amount due to the time delay of the vertical scanning period, the play of the focus lens 11, and the inertia and play of the lens drive mechanism, and it is also difficult to accurately return the return amount. There was a problem in that the hardware required to correct this was large-scale.

In order to solve this problem, there is a structure that uses a timer to measure the amount of return over time.

However, in this configuration, since the lens motor 17 and the timer are independent, there is a problem that if the rotational speed of the lens motor 17 fluctuates, the focus lens 11 cannot be accurately positioned at the in-focus point X1.

(Problems to be Solved by the Invention) As described above, in the conventional image detection type AP equipment that adopts the mountain climbing servo system as the servo system, in order to reduce the hardware, a timer is used to return the mountain climbing servo. However, since the timer and lens motor are completely independent, if the rotation speed of the lens motor fluctuates, the focus lens cannot be accurately positioned at the focal point. Ta.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an AF device that can accurately position a focus lens at a focal point even if the rotational speed of a lens motor varies.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention adjusts the return amount according to the brush noise output from the lens motor during the period from the in-focus point to the passage detection point. A predetermined correction is applied to the returned amount, and the focus lens that has passed through the in-focus point is returned to the in-focus point in accordance with the corrected returned amount.

(Function) According to the above configuration, the total amount of return 2 is determined by the brush noise which is proportional to the rotational speed of the lens motor, so even if the rotational speed of the lens motor changes, the focus lens can be accurately adjusted. It can be positioned to the focal point.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. In addition, in this figure 1, the same parts as in the previous figure 3,
The same reference numerals are used to omit detailed explanation.

In FIG. 1, the lens motor 16 is a brushed type motor, and the brush noise output from the motor 16 is amplified by an amplifier circuit 21 and then supplied to a monostable multivibrator 22 as a trigger input. As a result, the brush noise train is converted into a pulse train in which each brush noise corresponds to one pulse. This pulse train is supplied to the microprocessor 23. The microprocessor 23 counts this pulse train by interrupt processing, and uses this count value every time the focus evaluation value detection circuit 13 gives the focus 57 value.
It is stored in the internal memory in association with this focus evaluation value. At the same time, this microprocessor 23 executes the mountain climbing servo according to the flowchart explained in FIG. 6 above.

In this mountain climbing servo, the microprocessor 23
When it is detected that the in-focus point X1 has passed, the count value of the pulse train at this passing detection point X2 and the focus TP fit! stored in the internal memory up to that point are calculated. Among the i values, the difference from the count value corresponding to the largest one (this is taken as the focus evaluation value of the in-focus point X1) is determined. After adding a predetermined correction to the count value of this difference, the pulse train of brush noise is counted while driving the lens motor 16 in reverse. Then, while comparing this count value with the corrected cant value, the lens motor 16 is stopped when the two become equal. As a result, the focus lens 11 is positioned at the focal point.

The second process will be explained below with reference to FIG.

This FIG. 2 shows an enlarged view of the peak portion of the characteristic shown in FIG. 5 above.

In FIG. 2, the count value of the pulse train at the passing detection point X2 is ahead of the count value at the focused point Xl by (B+b10). Therefore, originally, it would be sufficient to return the focus lens 11 by this count value (a+b+c). Here, a, b, and c are the count values of the pulse train for each processing period between the focused point X1 and the passing detection point X2, that is, for each field.

However, from when the microprocessor 23 issues a start command or a stop command to the lens system 16 until the processing according to the command is completed, there actually occurs a time lag corresponding to one processing period. That is, even if the microprocessor 23 issues a command to stop the lens motor 16 at the passing detection point X2, the focus lens 11 has moved to X3 by the time the lens motor 16 stops according to the command. Therefore, the return amount of the focus lens 11 is
Added cant values from 2 to X3 (a + b + c + d)
It is necessary to

However, even with this correction, it cannot be said that the perfect return amount was necessarily obtained. That is, the focus lens 11
Considering the inertia of the drive mechanism, it is necessary to further add the count value e for one processing period. Therefore, as a return breath, the count value is (a+b+c+d+e).

By returning the focus lens 11 by this cant value, the focus lens 11 can be accurately positioned at the in-focus point.

Note that the above correction processing is also performed by the microprocessor 23.

As described above, in this embodiment, the number of occurrences of brush noise of the lens motor 16 from the in-focus point X to the passing detection point X2 is counted, a predetermined correction is made to this count value, and the corrected count value is The focus lens 11 is returned only until brush noise is generated from the lens motor 16.

According to such a configuration, since the calculated return amount is proportional to the rotational speed of the lens motor 16, the focus lens 11 can be accurately aligned even if the rotational speed of the lens motor 16 changes. Can be positioned at the focal point.

Note that the present invention is not limited to the above embodiments.

For example, in the previous embodiment, a case has been described in which the return port is determined using the number of occurrences of brush noise itself, but the return amount may be set using information corresponding to the number of occurrences.

Furthermore, in the previous embodiment, the present invention was applied to an AF device using an image detection method that detects the average value of contrast as a focus evaluation value, but this invention applies to an AF device that uses a method that detects the peak value of contrast. Needless to say, the present invention is applicable to general AF equipment that uses an image detection method and employs a mountain-climbing servo method as a servo method.

It goes without saying that the present invention can be modified in various other ways without departing from the spirit thereof.

[Effects of the Invention] As described above, according to the present invention, even if the rotational speed of the lens motor fluctuates in mountain climbing reservo, the focus lens can be accurately positioned at the in-focus point.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a characteristic diagram for explaining the operation of Figure 1, Figure 3 is a circuit diagram showing the configuration of a conventional AF equipment, and Figure 4 is a specific configuration of the focus evaluation value detection circuit shown in Figure 3. A circuit diagram showing an example, FIG. 3 is a characteristic diagram for explaining the operation of the microprocessor shown in FIG. 1, and FIG. 6 is a flowchart. 11... Focus lens, 12... Imaging unit, 13
...Focus evaluation value detection circuit, 15...Motor drive circuit, 16...Lens motor, 21...Amplification circuit, 22
...monostable multivibrator, 23...microprocessor. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 5 w & Figure 6

Claims (1)

[Claims] Focus evaluation information indicating the in-focus state of the focus lens is detected from an image signal of a subject imaged through the focus lens, and based on this detection output, the focus lens is positioned at the in-focus point by a mountain climbing servo. In an automatic focusing device, the amount of return of the focus lens is determined according to brush noise output from a motor for driving the focus lens, from when the focus lens passes through the focused point until this passage is detected. a return amount measuring means for measuring the return amount; a return amount correction means for adding a predetermined correction to the return amount measured by the return amount measurement means; An automatic focusing device comprising: lens return means for returning the focus lens to the in-focus point.