JP3140730B2 - Autofocus device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device in a camera, for example, and more particularly to an automatic focusing device that enables real-time focus adjustment even for a moving subject.

[0002]

2. Description of the Related Art Conventionally, in a camera provided with an automatic focusing (AF) device, an output of a light-receiving element for focus detection is first integrated.
Obtain data corresponding to the focus state. This data is A /
After the D conversion, the data is input to a microcomputer, and the microcomputer calculates a defocus amount for the subject. Then, the photographing lens is driven in such a direction as to cancel the defocus amount, thereby achieving focusing.

However, since there is a time delay from the start of the AF operation to the end of driving of the photographing lens, if there is a temporal change in the defocus amount due to the movement of the subject,
At the end of driving the lens, the subject is not always focused. Therefore, in order to keep the subject in focus, it is necessary to repeatedly detect the defocus amount and drive the lens to follow the change in the defocus amount. Such an AF control method is disclosed, for example, in Japanese Patent Application Laid-Open No. 60-214325.
It is described in.

Further, Japanese Patent Application Laid-Open Nos. 63-2010 and 63-148218
Describes a control method in which a temporal change rate of the defocus amount is obtained from two defocus amount detection operations separated by time, and this change rate is also taken into consideration.

[0005]

The above-mentioned prior art is almost completed AF in consideration of the responsiveness of the currently used AF sensor and lens driving motor.
Control method. However, considering that the objective of AF is to always adjust the optical system to a focused state with respect to the subject, it can be said that the control method is still insufficient. Ideally, the focus state is detected in real time, and the result is fed back to the lens driving actuator.

At present, control of the AF sensor and the motor for driving the lens is mainly performed by a microcomputer. However, when the performance of the AF sensor is improved in the future and the detection of the focus state can be performed faster than before, or when the focus state can be detected in real time by the emergence of a new element, In a control method using a microcomputer, the ability of the AF sensor cannot be fully utilized due to a control speed problem.

[0007] Regarding the lens driving actuator, a microcomputer is sufficient for controlling a DC motor which is currently mainstream. However, when an ultrasonic motor or the like that has been put into practical use recently is used as an actuator, the response is remarkably improved as compared with the DC motor, and the control has nonlinearity.
It is difficult to make full use of the ability by the control method by the microcomputer. In particular, when the control target has nonlinearity, the nonlinearity is approximately calculated by an equation. However, if accurate control is performed, the calculation becomes extremely complicated, and the control by the microcomputer is performed. In this case, the control speed is reduced.

The present invention has been made in view of such a problem, and an object thereof is to generate a control signal for driving a photographing lens at a high speed, so that a moving subject can be generated in real time. It is an object of the present invention to provide an automatic focusing device that enables high-speed and accurate focus adjustment.

[0009]

In order to achieve the above object, an automatic focusing apparatus according to the present invention includes, as focus information on a subject, information on a distance to the subject or a photographing level.
A defocus amount of lens, and focus information detecting means for outputting a differential value thereof, for driving the photographing lens, ultrasonic
A motor and lens driving means including a driving circuit for the ultrasonic motor, and fuzzy inference from the output of the focus information detecting means.
And the control signal of the lens driving means
Fuzzy inference means for obtaining an amount to change the drive speed of the ultrasonic motor, and a control signal obtained from the fuzzy inference means converted into a voltage value, and a voltage applied to the ultrasonic motor is set.
It includes a constant drive control means.

[0010]

[0011]

[0012]

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, before describing the embodiment of the present invention, an outline of fuzzy inference will be described with reference to FIG. Fuzzy inference is a fuzzy expression that is expressed in obscure words used by humans in everyday life.
Inference using rules (fuzzy inference rules). The fuzzy rule is "if A = BIG and B = NO
RMALthen X = SMALL ".

In FIG. 12, A and B are input variables, and X is an output variable. "A = BIG and B = NORMAL" which is the part where the condition for the rule to be satisfied is written
Is referred to as the antecedent, and the conclusion, "X = SMALL", is referred to as the consequent. In the fuzzy inference, each input variable is converted into a value of 0 to 1 for calculation, and this conversion is defined by a membership function (antecedent membership function).

Propositions handled by fuzzy rules (BIG, NORMAL, SMALL, etc.)
Each is defined. The degree to which the input variable satisfies each proposition is calculated with reference to the membership function. If there are multiple propositions in the antecedent, find the minimum value. This is called a minimum value (MIN) operation. Next, the membership values for each rule are combined. This is done by comparing the consequents of each rule, taking the maximum value, and creating a new membership function. This is the maximum value (MAX)
It is called operation. The center of gravity value of the combined membership function becomes the inference result (output value), and the subsequent control is performed based on the result.

Although FIG. 12 shows a typical example of the fuzzy inference method, various other fuzzy inference methods have been proposed. FIG. 1 is a block diagram showing a configuration of an automatic focusing apparatus to which the first invention is applied. As shown in FIG. 1, an automatic focusing device according to a first aspect of the present invention includes a defocus amount detecting unit 2 for detecting a defocus amount of a photographing lens 1 and a defocus amount detected by the defocus amount detecting unit. Differentiating means 3 for differentiating and obtaining the differential value, and lens driving for driving the photographing lens 1 based on the defocus amount detected by the defocus amount detecting means 2 and the differential value output from the differentiating means 3 Fuzzy inference means 5 for obtaining a control signal of the actuator 4 for fuzzy as a fuzzy amount, and drive control means 6 for driving and controlling the lens driving actuator 4 based on the control signal obtained from the fuzzy inference means 5. .

FIG. 2 is a block diagram showing a configuration of an automatic focusing apparatus to which the second invention is applied. As shown in FIG. 2, the automatic focusing apparatus according to the second invention has a defocus amount detecting means 2 for detecting a defocus amount of the photographing lens 1, and a defocus amount detected by the defocus amount detecting means 2. From the defocus amount detected by the defocus amount detecting means 2 and the differential value output from the differentiating means 3 to determine the moving speed of the photographic lens 1. Fuzzy inference means 7 for obtaining the amount of change as a fuzzy amount; initial speed calculation means 8 for calculating the initial speed of the photographing lens 1; and the output of the fuzzy inference means 7 and the initial speed obtained by the initial speed calculation means 8, A speed calculating means for calculating a moving speed of the photographing lens; and a lens drive controlling means for driving and controlling the photographing lens based on an output of the speed calculating means. That.

FIG. 3 shows a first embodiment of the present invention. This embodiment shows a case where a generally used exit pupil division type focus detection method is used in a TTL AF camera, for example. That is, the pupil division optical system 14 receives light from the subject 11 via the photographing lens 12 and the half mirror 13 to divide the light beam of the exit pupil of the photographing lens 12 and to form an image based on each light beam into the first light beam. guided to the line sensor 15 ₁ and the second line sensor 15 _2.

The data from the line sensors 15 ₁ and 15 ₂ are sent to the defocus amount calculating means 16 respectively. The defocus amount calculating means 16 is provided for each line sensor 1
5 _1, 15 based on the data from the _2, by calculating the image of the first line sensor 15 on _a relative displacement between the second line sensor 15 and _second image, the defocus amount of the photographing lens 12 (D ) Is output. This defocus amount calculation method is described in detail in, for example, Japanese Patent Application Laid-Open No. 59-12517, so please refer to it.

In order to obtain the advantages of the present invention, it is necessary to output the defocus amount in real time or at a speed that can be regarded as substantially equivalent thereto. However, since the line sensor currently used for AF is a charge accumulation type sensor such as a CCD, there is an integration time,
Cannot retrieve data in real time. Also,
Since the correlation calculation for calculating the defocus amount from the extracted data is sequentially performed by the microprocessor, the defocus amount cannot be obtained in real time.

Therefore, the line sensor includes the SPD
It is desirable that a photoelectric conversion element such as a (silicon photodiode) is arranged and data can be read out in real time. However, when attempting to read in real time using an SPD or the like, it is necessary to increase the area of the element in order to increase the sensitivity, and there is a problem that the resolution is smaller than a line sensor such as a CCD.

When a CCD or the like has to be used due to the problem of resolution, it is necessary to improve the sensitivity by minimizing the resolution and to make the optical system brighter, and to make it closer to real time. is there.

In calculating the defocus amount,
Use dedicated hardware to read data in parallel and perform batch processing to shorten the operation time, or use a dedicated high-speed processor when a microprocessor must be used. is necessary.

If possible, it would be desirable for the sensor and the arithmetic means to be an analog circuit capable of real-time processing instead of digital processing. In addition, the above-described consideration is necessary for the differentiating means 17 for differentiating the defocus amount with respect to time.

Hereinafter, the defocus amount D and its differential value dD
The explanation will be continued on the assumption that / dt is obtained at a sufficiently high speed. The fuzzy inference means 18 drives the photographing lens 12 by performing fuzzy inference using the output D of the defocus amount detection means 16 and the output dD / dt of the differentiation means 17 for obtaining a differential value thereof as inputs to the antecedent part. The change amount and the driving direction of the driving speed (moving speed of the photographing lens 12) of the motor (lens driving actuator) are calculated. The fuzzy inference means 18 will be described later in detail, and an example in which an ultrasonic motor (hereinafter abbreviated as USM) is controlled based on the output of the fuzzy inference means 18 will be described below.

The speed change signal Δv of the digital value output from the fuzzy inference means 18 is sent to the speed calculation means 19. The speed calculating means 19 adds the change amount Δv to the current moving speed v of the photographing lens 12 to newly calculate v
= V + Δv to the D / A converter 31. D / A
The converter 31 converts the output of the speed calculating means 19 into an analog voltage and inputs the analog voltage to one input terminal of the differential amplifier 32.

On the other hand, the rotation speed of the USM 33 as a lens driving actuator for driving the photographing lens 12 is detected by an encoder 34, and the output thereof is converted into an analog voltage by an f / v converter (frequency / voltage converter) 35. Then, the signal is input to the other input terminal of the differential amplifier 32. The differential amplifier 32 compares the difference between the output of the D / A converter 31 and the output of the f / v converter 35, that is, the speed error signal with a comparator 36.
To supply.

The comparator 36 generates a PWM (Pulse Width Modulation) signal by comparing the error signal from the differential amplifier 32 with the output of the triangular wave oscillator 37 as a determination level, and activates the transistor 38 with the PWM signal. On / off control. Then, the battery power supply 3 passes through the transistor 38.
9 is applied to the primary coils of the transformers 43 and 44 as a voltage proportional to the on / off ratio of the transistor 38 through a smoothing circuit including a diode 40, a choke coil 41, and a capacitor 42.

The transformers 43 and 44 boost the voltage of the battery power supply 39 to a voltage required for the USM 33, and the control is performed by a pre-driver 45 and transistors 46 to 49. The pre-driver 45 distributes the pulse supplied from the voltage controlled oscillator 51 to the transistors 46 to 49 so that an alternating current having a phase shifted by 90 ° is generated, and also converts the pulse into the direction signal CCW / CW output from the fuzzy inference means 18. The phase relationship is reversed accordingly.

Then, the AC whose phase has been shifted by 90 °, which has been boosted by the transformers 43 and 44,
When supplied to the third electrodes 33 ₁ and 33 ₂ , the USM 33 rotates at its resonance frequency. USM33 resonant state of being monitored by the electrodes 33 _3, the monitoring signal is supplied to the frequency tracking circuit 50. The frequency tracking circuit 50 controls the oscillation frequency of the voltage controlled oscillator 51 to be appropriate.

Therefore, the USM 33 rotates at a speed corresponding to the calculation result of the fuzzy inference means 18 by the feedback loop. The rotational movement of the USM 33 is converted into a reciprocating movement on the optical axis of the taking lens 12 by a mechanism not shown.

In order to realize the above-described real-time AF, high-speed control of a detection system, a calculation system, and a drive system is required. In addition, high speed is required in order to follow a sudden change of the subject because of real time.
In the control based on the conventional binary theory, the control rule must be reduced to increase the speed. However, if the number of control rules is reduced, smooth control operations cannot be performed, and control becomes impossible. Such contradictions exist in conventional methods.

A feature of the control based on the fuzzy theory is a simple control rule. When the fuzzy theory makes a certain amount of judgment, the judgment criteria have a distribution and the different judgments overlap each other, so that the interpolation of the ruleless part can be performed, so that the control rule can be simplified. . In addition, as described in the automatic train operation by fuzzy control which has recently appeared, the fuzzy control operation shows a smooth behavior with human feeling.

As described above, the speed of the fuzzy control can be increased due to the simplicity of the control rules, and smooth control can be performed. For these reasons, fuzzy control is suitable for an arithmetic control system of real-time AF.

In the present embodiment, the defocus amount from the defocus amount detecting means 16 and the time differential value of the defocus amount from the differentiating means 17 are taken as inputs to the fuzzy inference means 18 and, after calculation, the motor drive is started. The change amount of the speed and the rotation direction are output.

FIG. 4 shows the membership function and its rules in the present embodiment. When the rule shown in FIG. 4 is converted into a linguistic expression “if (consequent part) then (consequent part)”, the following is obtained. Rule (1): If if D is positively large and dD / dt is close to zero, then the speed change is positively increased. Rule (2): if D is slightly larger and dD / dt
Is positively large, then the speed change is positively increased. Rule (3): if D is slightly larger and dD / dt
When is large negatively, then the speed change is made slightly large negatively. Rule (4): if D is slightly larger than negative, dD / dt
When is large negatively, then the speed change is made large negatively. Rule (5): if D is slightly larger negatively, dD / dt
Is very large, then the speed change is made slightly larger. Rule (6): When if D is close to zero and dD / dt is close to zero, then the speed change is made close to zero. Rule (7): If if D is large negatively and dD / dt is close to zero, then the speed change is made large negatively.

The operation from the antecedent part to the consequent part in FIG. 4 is called a minimum value operation, and the smaller of the respective grades for the inputs D and dD / dt is taken. According to the value, the membership function of the consequent part is truncated as shown in FIG. 4, and the area indicated by the oblique line is obtained. Do this for each rule. Next, the sum of the areas of the consequent part membership functions obtained for each rule, which is called a maximum value calculation, is calculated. Finally, an operation called defuzzification is performed to find the center of gravity of the area obtained from the result of the maximum value operation. The value of the center of gravity is output as the speed change amount of the motor rotation. In addition,
FIG. 5 shows a flow of a series of calculations.

As means for executing the fuzzy inference described above, for example, a digital fuzzy circuit disclosed in Japanese Patent Application No. 63-278797 can be used. In this case, if the outputs of the defocus amount calculating means and the differentiating means are input as digital quantities to the fuzzy circuit, and the membership function definition parameters are also input as digital quantities from the microcomputer which controls the fuzzy circuit, an inference result can be obtained.
The membership function definition parameters do not necessarily have to be fixed. If the camera is of an interchangeable lens type, parameters unique to the lens are stored for each lens, and the stored values are read out and input as parameters. May be. In the case of a zoom lens, the parameter may be changed according to a change in the focal length.

Further, a combination of a DSP (digital signal processor) and a microcomputer may be used as a substitute for a digital fuzzy circuit. FIG. 6 shows a second embodiment of the present invention. This embodiment shows a case where an active type distance detection method using a semiconductor position detecting element (hereinafter abbreviated as PSD) and a light projecting element is used in a non-TTL AF camera, for example. That is, in the distance detecting means 21, the light output from the light projecting element 22 is condensed by the light projecting lens 23 and
1 and the reflected light is
An image is formed on the light receiving surface of SD25. The PSD 25 is disposed so as to be centered on the optical axis of the light receiving lens 24. The center of gravity of the imaging point due to the reflected light from the subject of infinity (∞) and P
When the center of the SD 25 coincides with the center, if the base line length is H, the deviation of the imaging point from the optical axis is X, the focal length of the light receiving lens 24 is f _J , and the distance to the subject is L ₀ ,

[0040]

(Equation 1) Becomes Also, the total photocurrent of PSD 25 is I ₀ , PSD 2
5 is 2t, the photocurrents I ₁ and I ₂ due to the reflected light from the subject 11 are

[0041]

(Equation 2) Becomes

From the above equation, the distance information 1 is added to the photocurrents I ₁ and I _2.
/ L ₀ is included. Therefore, the distance calculating means 26 calculates the distance L ₀ from the photocurrents I ₁ and I ₂ to the subject.
Is calculated. Calculation method of the distance L ₀ to the object, for example because the described in detail in Japanese Patent Application Sho 62-310689, see it.

The distance L ₀ and the lens position signal L ₁ calculated by the distance calculating means 26 are input to a subtracter 27, and a difference signal L between them is output. The lens position signal L ₁ is a signal output by the lens position detecting means 28 in accordance with the position of the taking lens 12. Further, the difference signal L output from the subtractor 27 indicates the amount of deviation of the taking lens 12 from the in-focus position. Therefore, the photographing lens 12 may be driven so that the difference signal L becomes zero.

The difference signal L output from the subtractor 27
Is input to the fuzzy inference means 30 and the differentiation means 29. The differentiating means 29 differentiates the input difference signal L with respect to time, and sends the output dL / dt to the fuzzy inference means 30. The fuzzy inference means 30 outputs two input signals L
And dL / dt are input to the antecedent part to perform fuzzy inference to calculate the drive speed and drive direction of the USM 33 that drives the taking lens 12. On the other hand, USM33
Drives the taking lens 12 according to the driving speed and driving direction signal. Note that the control blocks of the USM 33 are the same as those shown in the first embodiment, and a description thereof will be omitted.

In addition to the AF method described above, a method of measuring the distance from the reflection time of the ultrasonic wave, a double image matching method, or the like may be used. Next, a method of calculating the defocus amount of the TTL AF at a high speed will be described. To calculate the image of the first line sensor 15 on _a relative displacement between the image on the second line sensor 15 ₂ is generally the following two expressions are employed.

[0046]

(Equation 3)

However, it is not possible to accurately determine the deviation only with this evaluation formula. Therefore, the relationship between the suffixes of the equations (1) and (2) is shifted one by one to obtain F, and as a function F (S) of the shift amount S, F (S) in the equation (1)
Then, the shift amount S is calculated by finding S that satisfies = 0 and S that satisfies F (S) = minimum value in equation (2). here,
For S, interpolation calculation is performed to find the decimal point, and the error is reduced as much as possible. In this case, if N = 24 and S =
Assuming 1 to 24, the calculations in parentheses in the above equations (1) and (2) must be performed (24-1) × 24 times (in the case of equation (1)). This is the reason why the operation time by the microprocessor becomes longer.

Here, looking at the relationship between F and defocus in equation (1), it has a certain width as shown by the hatched portion in FIG. The cause is that it is affected by the contrast and the spatial frequency of the subject, and when the defocus is large, that is, when the image is largely blurred, the contrast of the image on the line sensor becomes small. Therefore, by normalizing this F with the total contrast, for example, the sum C of the differences between adjacent sensors, the width becomes considerably small and approaches a straight line. Even by this, the defocus amount cannot be accurately obtained from the numerical value F / C.

By the way, in the fuzzy inference, if a certain amount of signal is obtained as described above, the feedback is eventually reduced to a constant value, so that not so much accuracy is required. Therefore, when fuzzy inference is used, F / C is sufficient. In this case, the number of calculations does not need to be S, so that it becomes “(24 + 1) + total contrast amount”. The formula for calculating the total contrast is

[0050]

(Equation 4) Then, since the basic configuration is the same as the equation (1),
The number of operations converted into the expression (1) is (24 × 1) × 2, which is 1/12 as compared with the above example. Further, since it is not necessary to shake S, the sensor may be only a so-called reference unit,
It is easier to configure the arithmetic unit with hardware for parallel processing. FIG. 8 shows an example of a block diagram in that case.

According to the configuration described above, high-speed and accurate AF control can be performed in response to the movement of the subject. By the way, considering the change from the initial state, for example, both the subject and the photographing lens are stopped and the state of defocusing to focusing, the moving speed of the photographing lens is as shown in FIG.
A solid line shown in FIG. 9A is obtained, and a displacement amount of the photographing lens becomes a solid line shown in FIG. 9B. In the case of a still camera, the focusing time from the initial state is also important. Therefore, it is desired to give an appropriate initial speed to make it as shown by the dotted line in FIG.

FIG. 10 shows a third embodiment in consideration of the above points. The difference of this embodiment from the first embodiment is that the fuzzy inference means 18 for outputting the speed change amount Δv
The first and fuzzy inference means 18 _1, new, second fuzzy inference means for calculating the initial velocity v ₀ from the defocus amount and the differential value 18 ₂ that was provided, and the speed calculating means 19, first as an initial velocity The output f ₀ of the two-fuzzy inference means 18 ₂ is changed to the current speed v, and the first fuzzy inference means 18 ₁
That is, a speed obtained by adding the output Δv, that is, v = v + Δv is output.

The operation of the second fuzzy inference means 18 ₂ may be the same as that of the first fuzzy inference means 18 _1, and its output may be v ₀ instead of Δv. However, the scale is different. Therefore, it may be the initial speed v ₀ is multiplied by a coefficient to the output of the first fuzzy inference means 18 _1.

[0054] The input of the second fuzzy inference means 18 ₂ is not the defocus amount and the differential value, it is also conceivable to defocus amount and the object speed. In this case, the subject speed is calculated from the speed of the motor (USM33) and the differential value of the defocus amount.

Here, the initial speed is not strict.
It may be added to the current speed at a very early stage. Further, in the initial state, the case where the differential value of the defocus amount is equal to 0 can be considered depending on the sequence. In this case, regardless of the initial speed fuzzy inference, as in the fourth embodiment shown in FIG. It is also possible to provide an initial speed calculating means 20 for calculating the initial speed v ₀ only from the above, and to input the output to the speed calculating means 19. In this case, the calculation method may be to make the speed proportional to the defocus amount.

According to the above-described third embodiment (fourth embodiment), an initial speed corresponding to the defocus amount can be given at the start of driving of the photographing lens, as compared with the first embodiment and the second embodiment. In addition, the rising characteristics at the start of driving of the taking lens can be remarkably improved.

[0057]

As described above in detail, according to the present invention, a control signal for driving a photographing lens can be generated at high speed, and therefore, high-speed and accurate focus adjustment can be performed on a moving subject in real time. It is possible to provide an autofocus device that can be used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an automatic focusing device to which the first invention is applied.

FIG. 2 is a block diagram showing a configuration of an automatic focusing device to which the second invention is applied.

FIG. 3 is a configuration diagram illustrating a first embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a membership function used for fuzzy inference.

FIG. 5 is a flowchart illustrating a calculation procedure of fuzzy inference means.

FIG. 6 is a configuration diagram illustrating a second embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between relative displacement of images on two sensors and defocus.

FIG. 8 is a block diagram showing an example of a hardware configuration for calculating a defocus amount at high speed.

FIG. 9 is a diagram illustrating a change state of a moving speed and a displacement amount at the start of driving of a photographing lens.

FIG. 10 is a configuration diagram illustrating a third embodiment of the present invention.

FIG. 11 is a configuration diagram illustrating a fourth embodiment of the present invention.

FIG. 12 is a diagram illustrating an outline of fuzzy inference.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photography lens, 2 ... Defocus amount detection means, 3 ... Differentiation means, 4 ... Lens drive actuator, 5, 7 ... Fuzzy inference means, 6 ... Drive control means, 8 ... Initial speed calculation Means 9, speed calculation means 10, lens drive control means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-118133 (JP, A) JP-A-62-139512 (JP, A) JP-A-62-253107 (JP, A) JP-A 63-118107 2010 (JP, A) JP-A-63-148218 (JP, A) JP-A-63-265309 (JP, A) JP-A-58-192407 (JP, A) JP-A-60-218290 (JP, A) JP-A-64-42712 (JP, A) JP-A-64-4563 (JP, A) JP-A-63-246546 (JP, A) JP-A-1-276106 (JP, A) JP-A-2-207229 (JP, A) JP-A-2-149811 (JP, A) JP-A-2-149810 (JP, A) JP-A-1-285907 (JP, A) JP-A-1-287514 (JP, A) ( 58) Surveyed field (Int.Cl. ⁷ , DB name) G02B 7/28 G02B 7/08 G03B 13/36

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the focus information on the subject is
Information on the distance to the object or the defocus amount of the taking lens,
A focus information detecting means for outputting a differential value thereof, for driving the photographing lens, an ultrasonic motor and
Lens driving means including a driving circuit of the ultrasonic motor, and fuzzy inference from the output of the focus information detecting means ,
The ultrasonic motor as a control signal of the lens driving means
Fuzzy inference means for obtaining the amount of change in the driving speed of the motor, and the control signal obtained from the fuzzy inference means is converted to a voltage value.
And a drive control means for converting and setting an applied voltage of the ultrasonic motor .