JPH0821945A - Lens driving mechanism - Google Patents

Abstract

PURPOSE:To obtain a highly accurate driving result with a simple constitution and to prevent lens driving force amount from being unnecessarily increased by setting an elastic member in a state where it presses a lens frame in one direction within only a first extending area. CONSTITUTION:The lens frame 1 is driven to a focusing position by a transmitting member 6 connected to a driving pin 5. The extending amount of the lens frame 1 is made small in the case where the distance to an object is long. At this time, a spring 4 is brought into contact with the spring receiving part 7 of the lens frame 1, and presses the lens frame 1 to the extending direction of a helicoid on an optical axis. Consequently, since the spring 4 eliminates clearance effect exerted by the helicoid, focusing accuracy of the lens barrel is improved. On the other hand, if the distance to the object is short, the lens frame 1 is extended, and the extended amount is larger than that in long distance photographing. At this time, the length of the spring 4 is a natural length, and is brought into non-contact with the spring receiving part 7 of the lens frame 1. Consequently, the lens is not required to resist the pressing fore of a pressing member, so that the driving amount of the lens can be minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens driving mechanism.

[0002]

2. Description of the Related Art As a conventional photographing lens driving mechanism in a camera with an autofocus mechanism, as shown in FIG. 8, a feeding helicoid screw provided on the main body side,
A lens frame having a portion that holds the photographing lens and moves back and forth while engaging with the feeding helicoid screw,
It is generally composed of an elastic member that presses the lens frame in one direction.

However, in recent cameras, the photographing lens is zoomed and the magnification thereof is also increased. Alternatively, since the photographic range is wide, the amount of extension of the photographic lens is increasing. As the amount of extension of the lens increases, the amount of force of the elastic member pressing the lens frame in one direction also increases, and accordingly, the load for driving the lens frame also naturally increases. Such an increase in driving force causes the driving force source to increase in size, which is contrary to the demand for miniaturization of the camera.

As a method of suppressing an increase in driving load, as disclosed in Japanese Utility Model Publication No. 6-3371, a lens frame holding a taking lens is provided with a first cam for feeding a lens and a first cam. A second cam having a shape similar to that of the first cam, and an elastic member that abuts and presses the second cam on the fixed side, and a convex portion that abuts the first cam and cooperates with the pressing action of the elastic member. Has been devised to keep the displacement amount of the elastic member constant.

[0005]

Since the conventional structure requires the biasing of the elastic member over the entire extension range of the lens frame holding the photographing lens, the force of the elastic member increases. There is a problem in that the structure becomes complicated in order to increase the amount of lens driving force or to keep the biasing force of the elastic member constant.

Therefore, the present invention provides a lens driving mechanism that can obtain a highly accurate driving result with a simple structure and that does not unnecessarily increase the lens driving force amount.

[0007]

In order to solve the above-mentioned problems, in a lens driving mechanism for a camera of the present invention, a lens frame which is supported so as to be able to move forward and backward in the optical axis direction and which holds a photographing lens, and the lens frame. In a camera with a lens driving mechanism including an elastic member that presses in one direction, the elastic member has a first extending region and a second extending region set within the extending range of the photographing lens. The first
The lens frame is set to be pressed in one direction only in the feeding area.

[0008]

The elastic member for absorbing the helicoid clearance of the photographing lens is biased in the optical axis direction only in a certain section near the retracted position, and is not biased in other areas.

[0009]

1 is a block diagram of the system. The arithmetic circuit 10 controls the entire system as a whole. When the release switch 11 is pressed by the photographer, photographing is performed through the distance measuring operation and lens driving described below. The distance measuring circuit 20 is an active distance measuring device.
Upon receiving a distance measurement start command from the light emitting element 21, the light projecting element 21 is driven to project the signal light toward the subject. The light receiving element 22 receives the light reflected by the subject and returned in the signal light, and the distance measuring circuit 20 converts this into distance information and outputs it to the arithmetic circuit 10. Usually, in order to avoid the influence of noise or the like, the distance measuring operation is performed plural times, and the average value of each distance measuring result is used as the distance information. The magnitude of the variation in the value of each distance measurement result at this time will be simply referred to as "distance measurement variation" hereinafter. Arithmetic circuit 1
0 controls the motor 3 based on the distance information output from the distance measuring circuit 20, moves the lens frame 1 along the helicoid screw 2, and drives the lens barrel 31. A spring 4 is provided at the operation end of the lens frame 1. Then, the shutter 40 is controlled to perform the exposure operation.

FIG. 2 is a cross-sectional view of the lens barrel 31, showing a known photographing lens in a retracted position, that is, in a long-distance photographing region. The lens frame 1 is provided on the outer circumference of the taking lens and holds the taking lens. The lens driving device 30 is fixed to a camera body having a screw portion that engages with the helicoid screw 2. The spring 4 is fixed to the lens driving device 30 and urges the lens 4 in the lens extension direction (upward in the drawing) when it comes into contact with the lens frame 1. Drive pin 5
Outputs the driving force from the lens driving device 30 as a rotational movement. The transmission member 6 connects the drive pin 5 and the lens frame 1.

FIG. 3 is a front view and, like FIG. 2, shows a state in the long-distance photographing region. The drive pin 5 rotates right until it reaches a rotation angle determined by the arithmetic circuit 10 based on the distance measurement result, drives the photographing lens to the in-focus position, and photographs. After shooting, it rotates counterclockwise and drives the shooting lens to the standby position.

FIG. 4 is a cross-sectional view showing the above embodiment, showing a state in which the photographing lens is in the extended position, that is, the photographing lens is in the short-distance photographing region.

Next, the operation of this embodiment will be described.
The arithmetic circuit 10 controls the lens driving device 30 based on the distance measurement result, and the lens driving device 30 rotates the driving pin 5 to the right. At this time, the lens frame 1 is driven to the in-focus position by the transmission member 6 connected to the drive pin 5.

Here, if the distance to the subject is long, the amount of extension of the lens frame 1 is small as shown in FIG. In the long-distance photographing area shown in FIG. 2, the spring 4 is within the urging range (long-distance photographing area). At this time, the spring 4 is attached to the lens frame 1.
The lens frame 1 is in contact with the spring receiving portion 7 and urges the lens frame 1 on the optical axis in the payout direction of the helicoid. Therefore, the clearances of the helicoids provided in the lens frame 1 and the lens driving device 30 are shifted in one direction. Since the influence of the clearance of the helicoid is removed by the spring 4, the focusing accuracy of the lens barrel 31 becomes high.

On the contrary, if the distance to the subject is short, the lens frame 1 is extended by the rotating operation of the drive pin 5 (right in the drawing), and the extension amount is larger than that in the case of long-distance photographing as shown in FIG. large. At this time, the spring 4 has a natural length and is not in contact with the spring receiving portion 7 of the lens frame 1.
Therefore, the extension amount of the lens frame 1 with respect to the rotation angle of the drive pin 5 allows the influence of the clearance of the helicoid, but on the other hand, it is not necessary to resist the urging force of the urging member, and the lens driving force amount is It can be small.

FIG. 5 is an explanatory diagram concerning the distance measuring accuracy of the active type autofocus device. The light projecting means projects light onto the subject, and the reflected light is received by the light receiving means,
In an active autofocus device that performs trigonometric distance measurement by the light receiving angle, the reflected photocurrent decreases in proportion to the reciprocal of the distance, while the amount of external infrared light received is constant. That is, when the subject is at a short distance, the reflected photocurrent is large and the signal-to-noise ratio (hereinafter referred to as the S / N ratio) is large, and the variation in distance measurement is sufficiently small with respect to the permissible circle of confusion. On the contrary, the farther the subject is, the smaller the S / N ratio becomes, and the variation in distance measurement may not fall within the permissible circle of confusion. In this case, by performing the urging shown in this embodiment, the clearance can be removed and the focusing accuracy of the lens can be improved.

According to the present embodiment, the taking lens is extended with a simple construction in which the spring 4 which operates only in the region where the detection accuracy of the active distance measuring device is deteriorated (predetermined long-distance region) is provided. The position accuracy can be obtained with substantially constant accuracy that does not deteriorate depending on the shooting distance, and the lens driving force amount can be reduced.

Although a known active type distance measuring device is used in the above embodiment, a known passive type distance measuring device may also be used.

In the above embodiment, the elastic member is a leaf spring, but a coil spring as shown in FIGS. 6 and 7,
Alternatively, rubber or the like can be used and is not necessarily limited to the embodiment. Further, the elastic member does not necessarily have to be fixed to the camera body, but may be fixed to the helicoid screw 2 side.

Further, in the embodiment, the supporting structure of the lens frame 1 is a helicoid, but if it can be moved in the optical axis direction, it may be composed of a guide shaft and a rotating shaft, and within the scope of the present invention. It can be freely transformed.

[0021]

According to the structure of the present invention, particularly when the urging member is added, the moving-out position of the photographing lens in the long-distance region where the distance measuring accuracy of the active type distance measuring device is deteriorated is highly accurate. Can be kept at

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the lens driving device of the camera according to the exemplary embodiment of the present invention when the lens driving device is retracted.

FIG. 3 is a front view of the lens driving device of the camera according to the exemplary embodiment of the present invention when the lens driving device is retracted.

FIG. 4 is a sectional view of the lens driving device of the camera according to the exemplary embodiment of the present invention when the lens driving device is extended.

FIG. 5 is a diagram for explaining distance measurement accuracy of an active distance measuring device.

FIG. 6 is a sectional view of a lens driving device for a camera according to another embodiment of the present invention when it is extended.

FIG. 7 is a front view of a lens driving device of a camera according to another embodiment of the present invention when it is extended.

FIG. 8 is a cross-sectional view of a conventional lens driving device of a camera when it is extended.

[Explanation of symbols]

Claims (1)

[Claims] 1. A camera with a lens drive mechanism, comprising: a lens frame that is supported so as to be movable back and forth in the optical axis direction and that holds a taking lens; and an elastic member that presses the lens frame in one direction. Has a first payout area and a second payout area set within the payout range, and the elastic member is configured to press the lens frame in one direction only with the first payout area. Characteristic lens drive mechanism.