JPH1114888A - Lens driving mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lens driving mechanism correcting the reference position of a fine adjustment optical means. SOLUTION: This mechanism provided with a lens group 22 finely moving so as to detect a focusing state, a stepping motor 26 driving the lens group 22, a photosensor 27 detecting the reference position of the lens group 22 and a control circuit 28 controlling the stepping motor 26; and the control circuit 28 controls the stepping motor 26 based on the origin signal of a disk cam 25 detected by the photosensor 27 while finely moving the lens group 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens drive mechanism used for a photographing lens or the like having an automatic focusing device and for finely moving a lens group in an optical axis direction to detect a focused state.

[0002]

2. Description of the Related Art In general, a focusing system called a hill-climbing system is employed in an automatic focusing device for a photographing lens. In this hill-climbing system, an imaging means converts a light image from a subject into an electric signal, After passing the electric signal through the high-pass filter, the signal processing means performs detection integration over one field, and detects the in-focus state of the imaging screen, that is, the definition, from the high-frequency components. Then, the control means controls, for example, the position of the focusing lens group so as to maximize the definition of the imaging screen based on the signal from the signal processing means. At this time, the fact that the higher the frequency component is, the lower the definition is, and the higher the frequency component is, the higher the definition is used.

A photographing lens provided with such an automatic focusing device is disclosed in, for example, Japanese Patent Application No. 7-194990 for finely moving some lens groups in the optical axis direction during focusing. Such a lens driving mechanism is required. In this lens driving mechanism, as shown in FIG. 6, a light image from a subject incident on an outer cylinder 1 of a taking lens is converted into a focusing optical unit 2, a variable magnification optical unit 3, an exposure adjusting aperture 4, a fine movement optical system. The light passes through the means 5 and the image forming optical means 6, enters the image pickup means 7, becomes an electric signal, and is input to the signal processing means 8.

At the time of automatic focusing, a control means 9 rotationally drives a disc cam (not shown) via a driving means 10, and the disc cam finely moves the fine movement optical means 5 in the optical axis direction. As a result, the multiplication factor of the light image incident on the imaging means 7 changes little with only a slight change in the focal position, and the signal input to the signal processing means 8 changes. The signal processing means 8 calculates the moving direction of the focal point and the amount of blur, and outputs these signals to the control means 9. Then, the control unit 9 outputs a signal corresponding to the moving direction and the amount of blur of the focal point to the driving unit 11, and the driving unit 11 drives the focusing optical unit 2 to automatically focus.

[0005]

However, in the above-mentioned prior art, the inertia force varies depending on the mass of the disk cam and the magnitude of the rotation speed, so that the disk cam stops after passing the reference position or is located just before the reference position. And may stop. For this reason, a step out of the disc cam and a displacement of the fine movement optical unit 5 occur, and there is a problem that the function of the automatic focusing device is impaired.

An object of the present invention is to solve the above-mentioned problems and to provide a lens driving mechanism capable of correcting the reference position of the fine movement optical means.

[0007]

To achieve the above object, a lens driving mechanism according to the present invention comprises a focusing optical unit which moves for focusing and a fine movement which finely moves to detect a focused state. A lens drive mechanism comprising: an optical unit; a position detection unit that detects a reference position of the fine movement optical unit; a drive unit that drives the fine movement optical unit; and a control unit that controls the drive unit. Controlling the driving means based on a reference position signal of the fine movement optical means detected by the position detection means while finely moving the fine movement optical means to detect a focus state. .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a partial cross-sectional view of a photographing lens using a lens driving mechanism according to an embodiment,
An inner cylinder 23 holding a lens group 22 is fitted via a compression spring 24 movably in the optical axis direction to a large diameter portion 21a in the outer cylinder 21 of the taking lens. A disc cam 25 is in contact with the end surface of the inner cylinder 23, and the disc cam 25 is connected to an output shaft 26 a of a forward / reverse rotatable stepping motor 26 fixed to the outer surface of the outer cylinder 21 and a hole 21 b of the outer cylinder 21. Is supported through. Thus, the inner cylinder 23 and the disc cam 25 are constantly pressed against each other by the urging force of the compression spring 24. On the inner surface of the outer cylinder 21 near the disk cam 25, a reflection type photo sensor 27 for detecting the rotational position of the disk cam 25 is attached. The stepping motor 26 is controlled by a control circuit 28, and the output of the photo sensor 27 is connected to the control circuit 28.

As shown in the partial perspective view of FIG. 2, the disc cam 25 has a center hole 25a fitted and fixed to an output shaft 26a of a stepping motor 26, and a cam surface 25b abutting on the inner cylinder 23. A reflection part 25c is formed on a part of the cam surface 25b as a reference for the initial position of the disk cam 25, that is, the origin. The photo sensor 27 is a disc cam 2
5, the light is emitted toward the cam surface 25b, and the light reflected by the reflector 25c is received to detect the reflector 25c.

As shown in the partial plan view of FIG. 3, the origin of the disk cam 25 is a position when the rotation angle θ is zero.
Further, as shown in the graph of FIG. 4, when the rotation angle θ of the rotating cam 25 increases in the positive direction, the radius r of the center hole 25a and the cam surface 25b increases, and the rotation angle θ increases in the negative direction. It is formed so that the radius r sometimes decreases. Accordingly, when the stepping motor 26 repeatedly rotates in the forward and reverse directions, the rotation angle θ of the disk cam 25 decreases after returning to 0 after increasing in the forward direction, and decreases again after increasing in the negative direction. Return to Thus, the inner cylinder 23 pressed against the disk cam 25 wobbles or finely moves in the optical axis direction following the cam surface 25b of the disk cam 25, and the lens group 22 finely moves in the optical axis direction.

Here, as shown in the flowchart of FIG. 5, the control circuit 28 operates as follows.

(1) In step S1, a light image transmitted from a subject through the lens group 22 and incident is converted into an electric signal,
The direction and amount of rotation of the stepping motor 26 are determined according to the high frequency component of this signal.

(2) In step S2, the stepping motor 26 is operated based on the value determined in step S1.
At this time, when the disc cam 25 departs from the origin and passes through the origin, a first origin signal is input from the photo sensor 27, and when the disc cam 25 passes through the origin and returns to the origin again, A second origin signal is input from the photo sensor 27.

(3) In step S3, the photo sensor 2
It is determined whether the first origin signal has been input from step 7. If the first origin signal has not been input, step S3 is repeated. If the first origin signal has been input, the process proceeds to step S4.

(4) In step S4, the theoretical rotation amount from the time when the stepping motor 26 is operated to the origin is calculated, and the substantial rotation amount of the stepping motor 26, that is, the disk cam 25 is measured. It is determined whether the theoretical rotation amount is substantially equal to the actual rotation amount. When the rotation amounts are not equal, the process proceeds to step S5, and when the rotation amounts are equal, the process proceeds to step S6.

(5) In step S5, the amount of rotation from the origin is calculated and reset, and the flow advances to step S6.

(6) In step S6, the photo sensor 2
It is determined whether the origin signal has been input for the second time since the seventh time. If the second origin signal is not input, step S6 is repeated, and if the second origin signal is input, the process proceeds to step S7.

(7) In step S7, the operation of the stepping motor 26 is stopped. As described above, in the embodiment, at the time of automatic focusing, the control circuit 28 moves the disc cam 25 detected by the photo sensor 27 while the lens group 22 is finely moved.
Since the stepping motor 26 is controlled based on the two origin signals, even if the disk cam 25 loses synchronism and the lens group 22 is displaced, each time the disk cam 25 passes through the origin, the disk cam 25 The origin of 25 can be corrected, and the step-out of the disk cam 25 and the displacement of the lens group 22 can be corrected.

In the embodiment, the reflection type photo sensor 2 is used.
Although 7 is used, a transmission type photo sensor or another positioning sensor can be used. A means for determining the direction and amount of rotation of the stepping motor 26 in accordance with the high frequency component of the signal; a means for calculating the theoretical amount of rotation from the time the stepping motor 26 is operated to the origin; Means for determining whether the rotation amount is substantially equal to the rotation amount may be provided separately from the control unit 28.

[0020]

As described above, in the lens driving mechanism according to the present invention, while the control means finely moves the fine movement optical means for detecting the in-focus state, the fine movement optical means detected by the position detection means is controlled. Since the driving means is controlled based on the reference position signal, the reference position of the fine movement optical means can be corrected even if the reference position of the fine movement optical means is shifted.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a taking lens using a lens driving mechanism according to an embodiment.

FIG. 2 is a perspective view of a disc cam and a photo sensor.

FIG. 3 is a partial plan view of an inner cylinder and a disk cam.

FIG. 4 is a graph showing a rotation angle and a radius of a disk cam;

FIG. 5 is a flowchart of a control circuit.

FIG. 6 is a configuration diagram of a conventional example.

[Explanation of symbols]

 22 lens group 25 disk cam 26 stepping motor 27 photo sensor 28 control circuit

Claims (2)

[Claims] A focusing optical unit that moves for focusing; a fine movement optical unit that finely moves to detect a focus state; a position detection unit that detects a reference position of the fine movement optical unit; In a lens driving mechanism including a driving unit for driving the fine movement optical unit and a control unit for controlling the driving unit, the control unit finely moves the fine movement optical unit to detect a focus state. A lens drive mechanism for controlling the drive unit based on a reference position signal of the fine movement optical unit detected by the position detection unit. 2. The control means, when obtaining the reference position signal, compares the reference position of the fine movement optical means which should be present with the actual reference position, and controls the drive means based on the comparison value. The lens driving mechanism according to claim 1.