JPH02118506A - automatic focus device - Google Patents

Abstract

PURPOSE:To reduce the size and weight of the automatic focusing device and to obtain the high moving accuracy thereof by providing a lead screw part to the output shaft of a pulse motor, meshing a master lens moving frame therewith and providing a member for energizing the screw part. CONSTITUTION:The lead screw part 23 is provided to the output shaft of the pulse motor 26 of a master lens driving mechanism and the master lens moving frame 20 is meshed with this screw part 23. The elastic member 25 which energizes the screw part of the master lens moving frame 20 is provided to the lead screw part 23. The pulse motor 26 is slightly rotated forward and backward and is then largely turned unidirectinoally at the time of a focusing action with this constitution. The focus detection is executed by oscillating and moving the holding frame of the master lens in this way and, therefore, the formation of the zoom lens to the smaller size and lighter weight is possible. The clatter generated in the screw part is suppressed and the moving accuracy is improved by providing the elastic member 25.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a focusing lens moving mechanism for video cameras, electronic still cameras, etc. Regarding a focusing device.

[Conventional technology]

In conventional automatic focusing devices, it has been common practice to move the front lens in the optical axis direction using a helicoid screw. In this focusing device using the front lens, the amount of movement of the front lens to focus on a subject from close range to infinity is converted to the amount of rotation of the distance ring, which sets the distance adjustment, using a helicoid screw. . This amount of rotation is set to several tens of degrees, and is expanded with respect to the amount of movement. For this reason, the movement accuracy of the front lens can be considered by replacing the accuracy of the rotation amount of the distance ring with 0, that is, the feed accuracy of the helicoid, which determines the movement accuracy of the front lens, making it easier to achieve movement accuracy. . However, the front lens is heavy, and the motor to drive it requires a large torque. If this motor is used in a device that automatically focuses on the subject at all times, a large motor is required, and the lens itself It also has the disadvantage that the shape of the

In order to overcome this drawback, a method has been proposed in which focusing is performed using a lens other than the front lens. For example, this method focuses on an object by moving a master lens in a zoom lens system. At this time, the amount of movement of the master lens to focus on the subject from close range to infinity varies depending on the lens aperture and zoom magnification, but usually 2
It is about ~5 rhymes and requires high transposition accuracy.

An example of an automatic focusing device using a moving master lens is disclosed in Japanese Patent Application Laid-Open No. 65-49717, which describes that the master lens is driven by a pulse motor. In this example, a focusing lens and a lens for detecting focus are separated, and the focusing lens is driven by a step motor. Further, the lens for focus detection is vibrated by a vibrating means. As described above, since the focusing lens movement mechanism and the lens vibration mechanism for focus detection are provided separately, these mechanisms increase the size and weight of the lens itself.

In addition, as a master lens moving means,
As disclosed in Japanese Patent No. 827, a method has been proposed in which a linear step motor is incorporated into a lens barrel.

[Problem to be solved by the invention]

In an example in which the motor of the above-mentioned prior art is incorporated into a lens barrel, a moving element and a stator made of soft magnetic material are fixed to a focusing lens holding frame and an outer frame that includes this holding frame, and the stator Alternatively, one of the movers has a structure in which a plurality of coil windings are provided. Further, the focusing lens holding frame and the outer frame are engaged with each other via a bearing or the like.

In this structure, the lens barrel incorporates a linear motor and a bearing part for receiving the focusing lens holding frame.
The outer diameter of the lens barrel itself in the mask part is thick (this makes it thick. Therefore, when used in a zoom lens installed in a video camera, etc., the mechanism part that performs the power zoom operation and the automatic aperture operation that the zoom lens itself has) Interfering with the mechanical parts that cause

In order to avoid this interference, it is necessary to provide the mechanism section at a distance from the outer diameter of the lens barrel of the mask section, which increases the size of the zoom lens itself.

Further, there are problems such as restrictions on the design of the mechanism due to the distance.

Furthermore, since the lens barrel itself (including the motor) is incorporated, the number of assembly steps increases.

In addition, the above-mentioned useless lens and focus detection lens are separated,
In an automatic focusing device having a mechanism for driving a focusing lens and a mechanism for vibrating a focus detection lens, a volume occupied by each mechanical section is required, and the size of the lens itself becomes large. Further, there are problems such as the need for separate members to hold these mechanisms, which increases the weight.

SUMMARY OF THE INVENTION An object of the present invention is to provide a master lens drive mechanism that is small, lightweight, and capable of ensuring movement accuracy, suitable for an automatic focusing device for a zoom lens that performs a focusing operation using a master lens.

[Means to solve the problem]

In order to achieve the above object, the master lens drive mechanism was configured as follows.

The motor was a pulse motor, and the output shaft of this motor was provided with a lead threaded portion, and a master lens moving frame was provided with a threaded portion that engaged with the lead threaded portion. The pulse motor is slightly rotated forward and backward to detect focus by slightly vibrating the master lens, and based on the result of the focus detection in parentheses, the master lens is moved to the position where the pulse motor is rotated to focus on the subject. I tried to let him do it.

Then, play is suppressed between the lead screw portion and the master lens moving frame screw portion that meshes with the lead screw portion, and the master lens moving frame, which is moved by rotation of the lead screw portion, is moved parallel to the optical axis. In addition, the structure allows the lead screw part to be adjusted in two directions.

[Effect]

Focusing is achieved by vibrating and moving the master lens using a lead screw. To vibrate and move the master lens, one pulse motor and a lead screw are used, and the pulse motor is slightly rotated in forward and reverse directions, and then rotated largely in one direction. This causes the holding frame that holds the master lens to vibrate and move. Therefore, the conventional mechanism for independently driving the vibrating lens and the movable lens can be integrated into one, and the zoom lens can be made smaller and lighter.

Furthermore, ensuring the accuracy of the moving mechanism is achieved by the following steps. In other words, a member that biases the threaded portion of the master lens moving frame is applied to the lead screw portion so that the biasing force suppresses the looseness that occurs between the two, thereby ensuring movement accuracy. A mechanism for adjusting in two directions in a plane perpendicular to the optical axis is provided, and this mechanism moves the lead screw part so that it becomes parallel to the optical axis.

Thereby, the master lens can be moved parallel to the optical axis, and performance deterioration due to the movement of the master lens does not occur.

That is, resolution degradation due to the collapse of the master lens due to twisting of the optical axis does not occur.

Further, the master lens holding frame can be smoothly moved without any increase or decrease in the driving force of the master lens holding frame due to twisting of the member that guides and moves the master lens parallel to the optical axis.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a schematic configuration diagram showing an embodiment of an automatic focusing device according to the present invention. In the figure f, 1 is a front lens group consisting of three lenses, 2 is a variator lens group that performs a variable power function, 3 is a compensator lens that corrects aberrations caused by the variable power function, and 4 is a master lens. The front group 5 is a master lens, and the rear group 1 or more constitutes a lens system.

Next, the structure of the lens barrel that holds these lens systems will be described.

6 is a variator frame that holds a variator lens group; 7 is a convencator frame that holds a convencator lens; 8
9 is a cam ring that moves the variator frame and compensator frame to predetermined positions in the optical axis direction during zoom operation; 9 is a cam follower that fits into a cam groove (not shown) provided in this cam ring;
ID is a guide tube that guides the variator frame and convencator frame in the optical axis direction; 11 is a fixed tube that contains the variator frame that acts as a zoom, the convencator frame, a cam ring, etc., and holds the front lens group; 12 is a fixed tube and a mask; 15 is a zoom ring driven by the drive gear 15 of the zoom motor 14, which is engaged with the cam ring (
(not shown). 16 is a zoom position detector that meshes with the gear part of the zoom ring and detects the zoom position; 17 is an aperture that changes brightness; 18 is an iris motor that rotates and places the aperture; 19 is an aperture that detects the aperture value. Detector, 20
21 is a moving frame that holds the master lens rear group and moves in the optical axis direction, and 21 is a master cylinder that slides and guides this moving frame and holds the master lens front group.

Next, the configuration of a mechanism for moving the moving frame in the optical axis direction will be described. 22 is an engagement member that engages the moving frame and the lead screw 25; 24 is a pulse motor that fixes this retaining portion and drives the engagement member; 27 is a movable member to which this pulse motor is attached and that moves in a plane perpendicular to the optical axis. The plate 28 is a mounting plate that moves with respect to the movable plate in a plane perpendicular to the optical axis direction and is attached to the master tube.

Next, the circuit structure of this embodiment will be described. 29 is an image sensor, 50 is a preamplifier circuit that amplifies the signal from the image sensor, 31 is a high frequency component extraction circuit that extracts high frequency components from the video signal, and 52 is a composite signal based on the output from the high frequency component extraction circuit. 55 is an autofocus circuit (hereinafter referred to as AF circuit) that drives and controls a focusing pulse motor; this AF circuit also inputs zoom position information output from a zoom position detector; be done.

Next, the structure of a mechanism for moving the moving frame in the optical axis direction will be further explained using FIG. FIG. 2 is an exploded view of this mechanism.

The pulse motor 26 is fixed to a movable plate 27. This is possible
A rotation shaft 27a is attached to the D plate. The rotating shaft 27a is fitted into the receiving plate 28b of the mounting plate 28, and rotates about the rotating shaft 27aj) relative to the mounting plate 28J. The movable plate and the mounting plate are placed in tension with each other by springs 55 between spring mounting portions 27c and 28c provided respectively. The screw 37 pushes the spring attachment part 27c through the screw hole of the spring attachment part 28c. Next, the mounting plate 28 is bent so that a rotating shaft 28a provided on the mounting plate fits into a receiving hole provided on the master stud 21. Collar part 2 provided on the master
1a is provided with a mounting portion for the spring 56 and a screw hole for the screw 38 (not shown). This spring mounting part (!: A spring 56 is interposed between the spring mounting part 28d of the mounting plate. Screw 5
8 is designed to abut against the spring mounting portion 28c of the mounting plate. When the screw 3B is rotated, the structure is such that the screw 3B rotates about the rotating shaft 28a. Also, master (
A lead screw receiving portion 21c is provided here, and a notch groove for attaching an engaging member is provided.

This is the above configuration (a configuration in which the lead screw can be adjusted in two directions in a plane perpendicular to the optical axis).

Next, the focusing operation will be explained.

The AF circuit sends a periodic signal to the step motor 26 to cause the rear group of the master lens to slightly vibrate in the optical axis direction. At this time, a high-frequency component is extracted from the video signal obtained from the image pickup device 29 to determine the in-focus state, and a step motor drive circuit outputs a signal to move the master lens rear group to the in-focus point. This signal causes the motor shaft of the step motor to rotate. The lead screw that is integrated with the motor shaft rotates.

Therefore, the engaging member 22 that meshes with this is moved in the optical axis direction by the lead screw. Since the engaging member is attached to the moving frame of the master lens rear group, the moving frame also moves in the optical axis direction, and as a result, the master lens rear group moves in the optical axis direction to perform a focusing operation.

Next, a method for absorbing play in the lead screw and the engaging member during this focusing operation will be explained.

Fig. 5 (This is a drawing showing the main parts of the backlash absorption part.6
Reference numeral 9 denotes a hole through which the fixing member is slid relative to the engaging member in the optical axis direction, and 40 is a set screw that holds the fixing member through this hole. The elastic member 25 is inserted between the fixing member and the engaging member so that an elastic force acts between them. Therefore, the fixing member is inserted in the direction of arrow A, and the engaging member is inserted in the direction of arrow B. Therefore, the play between the lead screw and the engaging member is absorbed.Also, the biasing force can be kept constant regardless of the movement of the movable frame.

Note that in this example t, the fixing member 24 may be a member that deforms in the direction of arrow A from the elastic member 254.

FIG. 4 shows an example of a configuration in which the holding frame of the master lens rear group is guided in the optical axis direction without rotation due to the rotation of the lead screw.

Numeral 41 is a groove provided in the master, and 42 is a bottle into which the serial numbers are fitted and which prevents rotation of the moving frame. The bottle is fixed with four screws inserted into the bottle positioning part 4fa of the moving frame.

Reference numerals 20a and 20b are sliding fitting parts between the master stud and the moving frame, which guide and restrict movement of the moving frame in the optical axis direction.

FIG. 5 is an example in which the moving frame guide and the lead screw portion are attached to the same member.

Reference numeral 20' denotes a movable frame which, unlike the movable frame, does not have a sliding fitting portion with the master studs. 45 is a rod provided in place of this sliding fitting portion to guide the movement of the moving frame in the optical axis direction, 22' is an engagement member, and 45 is a holder for holding the rod and lead screw and for attaching a step motor. A member 44 is a fitting portion provided on the holding member for positioning the pulse motor and the lead screw portion. Reference numeral 46 denotes a rod positioning fitting hole provided in the holding part.)0 By providing the lead screw receiving part positioning hole and the rod positioning part hole in the holding member so that the lead screw and the rond are parallel to each other in this way, , performance can be achieved as a step motor assembly. Work efficiency is improved because adjustments do not need to be made after the lens barrel is assembled.

The step motor assembly described above is attached to a mounting portion 21e provided on a master stud.

〔Effect of the invention〕

According to the present invention, the lead screw portion and the engaging member of the moving frame of the master lens rear group can be held together without any play, so it is possible to eliminate errors in the position of the master lens rear group caused by play, This has the effect of improving positional accuracy.

In addition, the noise caused by the engagement member and the lead screw portion coming into contact or not coming into contact with each other can also be eliminated.

Further, according to the present invention, since a mechanism is provided for adjusting the lead screw portion in parallel with the optical axis, the movement position of the moving frame that has been caused by twisting of the lead screw with respect to the optical axis is reduced. There is no torque unevenness when driving the moving frame. Therefore, stable movement of the moving frame is possible.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 2 is an exploded view of the main parts of the invention, Fig. 3 is a partial view showing the lead screw engagement part, and Fig. 4 shows the main parts of the moving frame. FIG. 5 is a partial view of the main part showing another embodiment. 20...Moving frame 21...Master tube 22.
...Engagement member 23...Lead screw 24...
Fixed member 25...Elastic member 26...Pulse motor 27...Movable plate 28...Mounting plate
27a, 28a...rotating shaft 28b...receiver
27c, 28c...Spring mounting part 67...Screw 35...Spring gate 1 figure 45 figure 4 figure 102 figure

Claims (1)

[Claims] 1. A zoom lens that forms an image of a subject on an image sensor (29), which focuses the subject image on a part (5) or all of the master lens (5).
4, 5) in the optical axis direction while causing minute vibrations, the image sensor (22, 23, 26) is moved.
29) means (1, 2, 5, 4, 5) for forming an image on the image sensor; means (54) for extracting a high frequency component from the video signal obtained from the image sensor (29); means (32) for detecting the focused state of the subject image from the signal from the component extracting means (34); and the moving means (22, 23, means (55) for controlling (26)
, 34), and means (21) for aligning the moving direction of the master lens (5) by the moving means (22, 23, 26) with the optical axis direction.
, 27, 28, 35, 36, 37, 38). 2. The moving means (22, 25, 26) includes a pulse motor (26), a lead screw (25), a moving frame (20) that holds the focusing master lens (5), and the lead screw (23). an engaging member (22) that meshes with the lead screw (23), and biasing means (24, 25) that biases the engaging member (22) in one direction with respect to the lead screw (23).
2. The automatic focusing device according to claim 1, wherein said portion (23) is rotatably driven by said pulse motor (26) to linearly move said engagement frame (22).