JPH08334677A - Automatic focus detector for camera - Google Patents

Abstract

PURPOSE: To improve the responsiveness by wobbling a focus lens together with a driving motor for driving the focus lens using a piezoelectric element. CONSTITUTION: A lens driving unit 20 constituted of the lens driving motor 21, a driving screw 23, etc., is housed in a recessed part 10a formed in a part of a lens barrel 10. The piezoelectric element 24 is attached to a bracket 22 supporting the driving screw 23 of the lens driving unit 20 and pressing springs 25, 26 and 28 are interposed between the lens driving motor 21 and the wall part 10d of the recessed part 10a, the piezoelectric element 24 and a wall part 10e and a cover 27 and the driving unit 20, respectively. A driving nut part 32 in the top end part of a driving arm 31a formed in a part of a lens frame 31 is screwed on the driving screw 23, to move the lens frame 31 forward and backward in an optical axial direction by the pivoting of the driving screw 23. In an initial operation of in focus operation, the lens driving unit 20 is vibrated by the piezoelectric element 24, to make wobbling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera, a video camera or the like equipped with an autofocus device for automatically focusing the focus of a photographing lens on an object, thereby improving the response of the initial operation for focusing. The present invention relates to an improved automatic focus detection device for a camera.

[0002]

2. Description of the Related Art The spread of video cameras and electronic still cameras, especially household video cameras, has made it possible for anyone to operate the camera so that the focus of the photographic lens can be reliably focused on by capturing the subject in the viewfinder. There has been a demand for improving the responsiveness of an automatic focusing device that can be adjusted, a so-called autofocus device.

An autofocus device mounted on a video camera, an electronic still camera, or the like is an autofocusing device that performs so-called hill-climbing contrast detection based on the principle that a high-frequency component of a video signal increases or decreases during a process of focusing on a subject. This is a focusing means, and is of a type in which focusing is performed by moving the focusing optical system in the optical axis direction and searching for a focusing point when defocusing. At the time of initial operation, the autofocus means performs so-called wobbling in which the focus lens is reciprocated in a minute range in the optical axis direction in order to recognize the moving direction of the focus lens.

FIG. 4 is a schematic diagram showing a conventional focus lens driving device. A lens drive motor 2 is housed in a recess 1a formed in a part of the lens barrel 1, and a drive screw 3 having a longitudinal direction parallel to the optical axis of the focus lens is provided on an output shaft of the lens drive motor 2. The driving screw 3 is connected and is rotated when the lens driving motor 2 is operated. A drive arm 4a is provided on a part of the lens frame 4 that holds the focus lens, and a drive nut portion 5 that engages with the drive screw 3 is formed at the tip of the drive arm 4a. A guide arm 4b is provided on the lens frame 4, and a tip end of the guide arm 4b is loosely inserted into a guide rod 6 supported by the lens barrel 1 in parallel with the optical axis of the focus lens. That is, when the lens driving motor 2 is actuated to rotate the driving screw 3, the lens frame 4 provided with the driving nut portion 5 screwed with the driving screw 3 moves in the optical axis direction. It will drive the focus lens.

When wobbling is performed, the lens drive motor 2 is rotated in the normal and reverse directions to reciprocate the lens frame 4 in the optical axis direction.

[0006]

However, when wobbling is performed by the above-described conventional focus lens driving device, the mechanical accuracy of the lens driving motor 2 and the processing accuracy of the driving screw 3 and the driving nut portion 5 are not correct. In some cases, the reciprocating amplitude of the lens frame 4 may not reach the designed distance. That is, the responsiveness of the wobbling operation of the focus lens to the drive signal input to the lens drive motor 2 may deteriorate.

When the responsiveness of the wobbling operation is poor, it takes a long time to focus, and a dynamic subject may not be focused. In particular, a video camera usually captures a dynamic subject, which is disadvantageous.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an automatic focus detection device for a camera, which can improve responsiveness in an initial operation and focus an object in a shortest possible time.

[0009]

As a technical means for achieving the above object, an automatic focus detection apparatus for a camera according to the present invention is an automatic focus detection apparatus for moving a focus lens forward and backward in the optical axis direction to focus on a subject. In an automatic focus detection device of a camera equipped with an automatic focus matching device that recognizes the moving direction of the focus lens by reciprocating the focus lens at a small distance in the optical axis direction during the initial operation of the focus matching device, A lens driving unit including a lens driving motor is equipped with a piezoelectric element, and the lens driving unit is vibrated by the vibration of the piezoelectric element to perform wobbling.

Further, during the initial operation of the automatic focusing device for moving the focus lens forward and backward in the optical axis direction to focus on the subject, the focus lens is reciprocated at a small distance in the optical axis direction to move the focus lens. In an automatic focus detection device for a camera provided with an automatic focus matching device for recognizing a lens, a lens drive unit including a lens drive motor for a focus lens is provided with a piezoelectric element, and the lens drive unit is supported by elastic means, The lens drive unit is vibrated by the vibration of the element and the restoring force of the elastic means to perform wobbling.

[0011]

When the subject is captured by the viewfinder of this camera and the release button is pushed slightly into the half-pressed state, the automatic focusing device operates to drive the focus lens in the optical axis direction so as to focus on the subject. Will be done. In the initial operation of this drive, wobbling is performed in order to determine whether to move the focus lens forward or backward. That is, when the piezoelectric element is placed in an electric field and vibrated, the lens driving unit to which the piezoelectric element is attached vibrates. Since the focus lens is linked to the lens drive unit, the focus lens reciprocates a small distance in the optical axis direction to perform wobbling.

Further, since the lens driving motor of the focus lens is attached to the lens driving unit, the vibration of the piezoelectric element also vibrates the lens driving motor. Therefore, the focus lens can be reciprocated without being affected by an error in the processing accuracy of the mechanism for driving the focus lens by the lens drive motor, such as screwing of the drive screw and the drive nut portion. Wobbling can be performed with the amplitude of. Therefore, the direction in which the focus lens should move can be quickly recognized.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An automatic focus detection device for a camera according to the present invention will be specifically described below based on the illustrated embodiments.

FIG. 1 is a sectional view of the lens barrel 10 taken along a plane including the optical axis of the focus lens, and FIG. 2 is a schematic perspective view of the lens barrel 10. A concave portion 10a for accommodating the lens driving unit 20 is formed in a part of the lens barrel 10, and the bottom plate of the concave portion 10a is formed.
A through hole 10c is formed in 10b in such a range that a drive arm to be described later is inserted and the movement of the drive arm is allowed.

The lens drive unit 20 has a bracket 22 having a substantially U-shaped cross section, on which a lens drive motor 21 for a focus lens is supported, and both ends of a drive screw 23 whose longitudinal direction is the optical axis direction of the focus lens. The drive screw 23 and the output shaft of the lens drive motor 21 are connected to each other and are integrally configured. The piezoelectric element is attached to one wall portion 22a of the bracket 22 of the lens driving unit 20.
24 is installed. The lens drive motor 21 is supported on the other wall 22b of the bracket 22.

Pressing springs 25 and 26 as elastic means are arranged on both sides of the lens driving unit 20. That is, a holding spring 25 is interposed between the back surface of the lens driving motor 21 and one side wall 10d of the recess 10a, and a holding spring 26 is interposed between the piezoelectric element 24 and the other side wall 10e of the recess 10a. By doing so, the lens drive unit 20 is positioned at a predetermined position in the recess 10a. Also, this recess 10
A is closed by a lid 27, and a holding spring 28 as an elastic means is interposed between the lid 27 and the lens drive unit 20. The presser springs 25, 26, 28 as elastic means
May be constituted by a spring such as a leaf spring or a coil spring, or may be constituted by a member having a cushioning property such as an elastic body such as rubber.

The focus lens is held by a lens frame 31, and a drive arm 31a and a guide arm 31b are provided to extend on a part of the outer periphery of the lens frame 31. This drive arm 31
A drive nut portion 32 is provided at the tip of a, and the drive nut portion 32 is screwed with the drive screw 23. The guide arm 31b extends in the direction opposite to that of the drive arm 31a. Then, the support projection 10 formed at the end of the lens barrel 10
The tip end of the guide arm 31b is loosely inserted into the guide rod 33 supported by the optical axes f and 10g with the optical axis direction as the longitudinal direction.

FIG. 3 is a block diagram of the control circuit of the automatic focus detection device for this camera. The release button of this camera is equipped with a two-step switch, and the first-step switch S ₁ Is turned on, and the second-stage switch is turned on when the switch is pressed to the end. Then, when the first stage switch is turned on, the autofocus means is activated, and when the second stage switch is turned on, exposure is started. A switch detection circuit 41 is connected to the first stage switch S _{1 so} that the switch detection circuit 41 detects that the first stage switch S ₁ is on. The detection signal of the switch detection circuit 41 is output to the AC voltage generation circuit 42. The AC voltage generation circuit 42 is driven by the detection signal of the switch detection circuit 41, and the AC voltage is applied to the piezoelectric element 24 and the driving direction calculation circuit 43. Therefore, the piezoelectric element 24 vibrates.

On the other hand, the subject light transmitted through the focus lens 44 held by the lens frame 31 is photoelectrically converted by the photoelectric conversion element 45.
And is photoelectrically converted, and is output to a frequency detection circuit 46 that detects a high-frequency component of the subject light and detects an amplitude. The detection signal of the frequency detection circuit 46 is output to the drive direction calculation circuit 43. This drive direction calculation circuit 43
Then, the focus lens 44 is compared by comparing the detection signal of the frequency detection circuit 46 with the AC signal of the AC voltage generation circuit 42.
The drive direction signal is calculated and the drive direction signal is sent to the motor drive circuit 47. Then, the lens drive motor 21 is driven by receiving the drive signal output from the motor drive circuit 47, and the focus lens 44 is focus-driven.

The drive direction signal output from the drive direction calculation circuit 43 is also sent to the AC voltage generation circuit 42, and the AC voltage generation circuit 42 receives the drive direction signal and outputs the AC voltage to the piezoelectric element 24. Is stopped.

The operation of the embodiment of the automatic focus detection device for a camera according to the present invention constructed as described above will be described below.

The autofocus means performs a focusing operation by so-called hill climbing contrast detection, and drives the focus lens, that is, the lens frame 31 in a direction in which the high frequency component of the video signal obtained from the subject increases. is there. When the camera is aimed at the subject and the release button is half-pressed to turn on the first-stage switch S ₁ , a focusing operation is performed, and the driving direction of the lens frame 31 is recognized as an initial operation of this focusing operation. Wobbling is performed for this purpose.

When the switch detection circuit 41 detects that the first-stage switch S ₁ is turned on, the AC voltage generation circuit 42 is driven in response to the detection signal, and the piezoelectric element 24 and the driving direction calculation circuit 43 receive an alternating current. A voltage will be applied. Therefore, the piezoelectric element 24 is placed in an electric field and vibrates, and the vibration causes the lens driving unit 20 to vibrate. The drive nut portion 32 is screwed into the drive screw 23 of the lens drive unit 20, and the drive nut portion 32 is a lens frame.
Since it is formed in a part of 31, the lens drive unit 20
The vibration of the lens frame 31 causes the lens frame 31, that is, the focus lens 44 to vibrate. Therefore, the focus lens 44 reciprocates in the optical axis direction with a predetermined amplitude, and wobbling is performed.

While the focus lens 44 reciprocates, the subject light transmitted through the focus lens 44 is incident on the photoelectric conversion element 45, and the output signal thereof is output from the frequency detection circuit 46.
When the input signal is input to, the high-frequency component contained in the subject light is detected, its amplitude is detected, and the detection signal is output to the drive direction calculation circuit 43. Since the AC voltage that is synchronized with the AC voltage applied to the piezoelectric element 24 is applied to the driving direction calculation circuit 43 by the AC voltage generation circuit 42, this AC signal and the detection signal of the frequency detection circuit 46 are Focus lens 44 to compare and focus on the subject
Is calculated.

The driving direction signal calculated by the driving direction calculation circuit 43 is output to the motor driving circuit 47 and the AC voltage generating circuit 42. The AC voltage generation circuit 42 receives the drive direction signal and stops the output of the AC voltage to the piezoelectric element 24. Therefore, the piezoelectric element 24 stops vibrating and wobbling stops. Further, the motor drive circuit 47 receives the drive direction signal and drives the lens drive motor 21 so as to move the focus lens 44 in the direction to be focused. Therefore, the focus lens 44 moves in a fixed direction along the optical axis, and the initial operation of the automatic focusing device is completed.

That is, when the lens drive motor 21 operates, the drive screw 23 connected to the output shaft rotates. A drive nut portion 32 linked to the lens frame 31 is screwed into the drive screw 23, and the lens frame 31 is prevented from rotating about the optical axis. The frame 31 moves along the drive screw 23, that is, in the optical axis direction. Then, the subject is focused while being moved to an appropriate position.

[0027]

As described above, according to the automatic focus detection device for a camera of the present invention, the wobbling at the initial operation when the focus lens is focused is driven by a piezoelectric element including a lens drive motor. Since the unit is made to vibrate, there is no influence of processing accuracy error in the drive mechanism such as the drive screw rotated by the lens drive motor and the drive nut portion screwed to the drive screw, The focus lens can be wobbled with a desired amplitude. For this reason, the direction in which the focus lens should move in order to focus can be promptly determined and can be surely recognized. Therefore, it is possible to provide an automatic focusing device with good responsiveness.

Moreover, since the piezoelectric element is used, the focus lens can be reciprocated with a desired amplitude, so that the degree of freedom in optical design and circuit design for autofocus can be increased.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a lens barrel of a camera including an automatic focus detection device according to the present invention, cut along a plane including an optical axis of a lens.

FIG. 2 is a schematic perspective view of a lens barrel suitable for including the automatic focus detection device according to the present invention.

FIG. 3 is a block diagram illustrating a control circuit of the automatic focus detection device according to the present invention.

FIG. 4 is a schematic cross-sectional view of a lens barrel of a camera equipped with a conventional automatic focus detection device, corresponding to FIG.

[Explanation of symbols]

10 Lens barrel 10a Recess 20 Lens drive unit 21 Lens drive motor 23 Drive screw 24 Piezoelectric element 25, 26 Holding spring (elastic means) 27 Lid 28 Holding screw (elastic means) 31 Lens frame 32 Drive nut S ₁ 1st stage Switch 41 Switch detection circuit 42 AC voltage generation circuit 43 Driving direction calculation circuit 44 Focus lens 45 Photoelectric conversion element 46 Frequency detection circuit 47 Motor drive circuit

Claims (2)

[Claims] 1. A moving direction of the focus lens by reciprocating the focus lens at a small distance in the optical axis direction during an initial operation of an automatic focusing device for moving a focus lens forward and backward in the optical axis direction to focus on a subject. In an automatic focus detection device for a camera equipped with an automatic focus matching device for recognizing, a lens drive unit including a lens drive motor for a focus lens is provided with a piezoelectric element, and the vibration of the piezoelectric element causes the lens drive unit to vibrate. An automatic focus detection device for a camera, which performs wobbling. 2. The moving direction of the focus lens by reciprocating the focus lens at a small distance in the optical axis direction at the initial operation of an automatic focus matching device for moving the focus lens forward and backward in the optical axis direction to focus on a subject. In an automatic focus detection device for a camera equipped with an automatic focus matching device for recognizing the above, a lens driving unit including a lens driving motor of a focus lens is equipped with a piezoelectric element, and the lens driving unit is supported by elastic means, An automatic focus detection device for a camera, wherein the lens drive unit is vibrated by the vibration of an element and the restoring force of the elastic means to perform wobbling.