JP2761280B2 - Lens drive for autofocus camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a lens driving device for an auto-focus camera, and more specifically, detects a shift amount of a subject from a focal plane expected to form an image, and focuses on the basis of the shift amount. The present invention relates to a lens driving device for an auto-focus camera that drives a lens.

[Prior Art] Conventionally, as a lens driving device of an auto-focus camera, a defocus amount between a position on an optical axis of an image plane on which a subject is formed and a position on an optical axis of a film surface is detected. Many devices have been provided which convert a defocus amount into a drive amount of a focus adjustment lens and drive the focus adjustment lens by the drive amount.

[Problems to be Solved by the Invention] In the above-described conventional lens driving device for an autofocus camera, when an attempt is made to improve the accuracy of focus adjustment,
As one method, a method of improving the positioning accuracy of the focusing lens by increasing the detection resolution of an encoder that monitors the driving amount of the focusing lens can be considered.
In this case, the detection capability of the encoder itself can be increased,
Although the detection resolution of the encoder was improved by detecting the amount of linear movement of the focus adjustment lens after expanding it with the speed increasing transmission system, such a method required fine processing technology, Since mechanical play cannot be ignored, there is naturally a limit in improving accuracy.

Another method is to reduce the image plane movement of the photographing lens with respect to a change of two images (change of defocus value) on an AF (autofocus) sensor, that is, to reduce the image plane movement amount with respect to the lens drive amount. A method for improving the detection resolution of the sensor is considered. But in this case
Another problem arises in that the focus detectable range of the AF sensor is narrowed, so that the entire range of the photographing lens cannot be covered, and a high-speed focus adjustment operation cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a lens driving device for an auto-focus camera capable of adjusting the focus quickly and accurately over a wide defocus range.

[Means for Solving the Problems] A lens driving device for an autofocus camera according to the present invention includes a first lens having a relatively large change in focal position with respect to a driving amount of a lens, A second lens whose change amount of the focal position is smaller than that of the first lens, first driving means for driving the first lens, second driving means for driving the second lens, Focus detecting means for detecting a shift amount of the focal position of the lens with respect to a predetermined focal plane position of the camera; comparing means for comparing the shift amount with a predetermined amount; and the first means according to a result of the comparing means.
And a selecting means for selectively driving the second lens and the second lens.

[Operation] At the lens drive position of this autofocus camera, the first lens whose change amount of the focal position is relatively large with respect to the drive amount of the lens, and the change amount of the focus position which is relatively large with respect to the drive amount of the lens. A second lens smaller than the first lens is prepared. Then, first, after roughly focusing by driving the first lens, the second lens is driven to accurately focus. Further, when the defocus amount is larger than a predetermined value in accordance with the value of the defocus amount by the focus detection means, the focus is first roughly detected by driving the first lens, and then the second lens is used for accurate focusing. . On the other hand, when the defocus amount is smaller than the predetermined value, focusing is performed only by the second lens.

Hereinafter, the present invention will be described with reference to the illustrated embodiments. First,
Prior to describing the embodiment of the present invention, the configuration of a general focus detection optical system in an autofocus camera will be briefly described with reference to FIG. In the figure, a condenser lens 36 is provided at or behind a predicted focal plane 37 behind the taking lens 21, and separator lenses 234a and 34b are further provided behind the condenser lens 36, respectively. Line sensors 35a and 35b having, for example, a CCD or the like as a light receiving element are provided on the image forming surface of each of the separator lenses 34a and 34b. The images on the line sensors 35a and 35b are closer to the optical axis O in the case of a so-called front focus, in which the image of the object to be focused is formed ahead of the predetermined focal plane 37, and conversely, in the case of the rear focus. It gets far from the axis. When focus is achieved, the distance between two corresponding points of the two images is a specific distance determined from the configuration of the optical system. Therefore, the focus state can be known by converting the light distribution patterns of the two images on the line sensors 35a and 35b into electrical signals and determining their relative positional relationship. The line sensors 35a and 35b are collectively referred to as a sensor 35 hereinafter.

The above is an outline of the configuration of a general focus detection optical system. Next, an embodiment of a lens driving device for an autofocus camera according to the present invention will be described with reference to the flowcharts of FIGS. 10 and 11. Before that, the hardware configuration will be described with reference to FIG. 1 and FIGS.
This will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an autofocus camera. In the figure, the photographing lens group 21 has a relatively large change amount of the focal position with respect to the driving amount of the lens, that is, a first lens 42R for roughly adjusting the focal length, and a focal position with respect to the driving amount of the lens. The amount of change is smaller than that of the first lens 42R, that is, the second lens 42F for fine-adjusting the focal length, but these first and second lenses 42R and 42F
Is actually formed by combining a large number of lenses as described in FIGS. 3 and 4 below, and is a linear type ultrasonic motor (hereinafter abbreviated as LUM) described in FIGS. ), The lens is driven by a first driving unit 23 and a second driving unit 22, respectively, so as to move to a focusing position.

The subject light condensed by the photographing lens group 21 is partially reflected by the beam splitter 25, and the focus glass 26,
The light is guided to a finder optical system including a condenser lens 27, a pentaprism 28, and an eyepiece lens 29. The rest of the subject light is transmitted through the beam splitter 25, reflected by the sub-mirror 31, and guided to the AF module 30 provided at the lower part of the camera body and measuring the shift of the focal position of the taking lens 21 with respect to the film surface 32. I will This AF module 30
It includes the focus detection optical system described with reference to FIG. 2 and serves as focus detection means for detecting the amount of deviation of the lens focal position from the expected focal plane position of the camera. 33 is a focal plane shutter.

FIG. 3 is an optical arrangement diagram showing an example of the lens configuration of the taking lens group 21 shown in FIG. In this example, a positive power first group lens 41 and a positive power second group lens 41 are shown.
42, and a third lens unit 43 having a negative power. The first lens unit 41 and the third lens unit 43 move to the object side, and
A three-group zoom in which the magnification is changed from wide to tele when the group lens 42 moves toward the object side while widening the distance between the first lens group 41 and reducing the distance between the third lens group 43. Lens. The second lens group 42 is
A second lens 42F having a negative power and a first lens 42R having a positive power, and the first lens 42R is used for coarse adjustment of a focus having a large focus movement amount with respect to movement of the lens in the optical axis direction; The second lens 42F is for fine focus adjustment where the amount of focus movement with respect to the movement in the optical axis direction is small. Accordingly, high-speed focusing can be performed by the first lens 42R, and high-precision focusing can be performed by the second lens 42F.

The first to third group lenses 41, 42, and 43 are moved out of the focal plane with different movement amounts by zooming. Furthermore, during wide, standard, and tele focusing, the amount of focusing to be extended differs depending on the focal length of the second lens group 42 that is extended from infinity to a close distance.

FIG. 4 is a sectional view of a lens barrel in which the lens group shown in FIG. 3 is incorporated in a lens frame. In the figure, a first group lens 41, a second lens 42F in the second group lens, a first lens 42R in the second group lens, and a third group lens 43 are respectively a first group frame 2, a 2F group frame 52F, 2R. The group 52R and the third group frame 53 are fixed and held respectively. 2F group frame 52F, 2R group frame
The 52R, 3rd group frame 53 is arranged on the inner peripheral portion of the 1st group frame 2 so that it can be moved only in the optical axis direction by a linear type LUM inside the hollow frame portion extending to the body side of the 1st group frame 2. Are guided by supports 60, 61, and 62 formed of bearing balls. Then, they are pressed toward the support by the LUM vibrators 56, 57, 58 disposed on the first group frame 2 at positions substantially symmetric with respect to the optical axis O with respect to each support. Therefore, 2F
The group frames 52F, 2R, the group frame 52R, and the third group frame 53 are arranged with respect to the position in the optical axis direction and the center of the optical axis with respect to the first group frame 2 by the respective supports 60, 61, 62 and the respective vibrators 56, 57, 58. Positioning is performed without any displacement and without play.

The first group frame 2 is disposed on the inner peripheral side of the fixed frame 1, and is supported on the fixed frame 1 so as to be movable only in the optical axis direction.
And is pressed in the direction of the support 13 by the vibrating body 12 arranged on the fixed frame 1 at a position facing the support 13 with respect to the optical axis. Therefore, the first group frame 2 is also positioned with respect to the fixed frame 1 without play. In addition, 54 is a cover. Next, the details of the mounting portion of the vibrator and the operation of the linear ultrasonic motor will be described. In this embodiment, 4
Although the number of LUMs is used, their attachment and operation are the same, and the LUM used for the first group frame 2 as a representative will be described below with reference to FIGS.

In FIG. 5, a first group frame 2, which is a moving member also formed of a hollow cylindrical body, has a fixed gap inside a fixed frame 1, which is a fixed member formed of a hollow cylindrical body, and has a certain gap in the center axis direction. It is arranged so that it can move. The upper part of the gap between the fixed frame 1 and the first group frame 2 (in FIG. 5)
A slide plate 3 extending in the center axis direction of the first group frame 2 is fixed on the first group frame 2, and a middle portion of the fixed frame 1 facing the slide plate 3 is long in the front-rear direction in the center axis direction. A rectangular notch 1d (see FIG. 6) is formed.
The cutout hole 1d is a hole for disposing a vibrating body described later.

On the other hand, a support guide mechanism for the first group frame 2 is provided in a gap opposite to the gap where the slide plate 3 is arranged. In the present embodiment, the support and guide mechanism includes three guide grooves and a support made up of a plurality of bearing balls disposed in each of the grooves. That is, the slide plate 3
A straight groove 2b formed of a partially arcuate concave portion is formed in the outer peripheral surface of the first group frame 2 in the direction of the central axis of the moving frame at an opposing position with respect to the center axis 0, and the inner peripheral surface of the fixed frame 1 is formed. In the middle of the position facing the straight groove 2b, a straight groove 1b composed of a partially arcuate concave portion is provided in the center axis direction of the fixed frame, and furthermore, a circumferential groove on both sides of the two straight grooves 1b, 2b is provided. Straight grooves 1a, 2a, 1c and 2c, which are also formed as partial arc-shaped concave portions, are formed at equal distances in the outer peripheral surface of the fixed frame 1 and the inner peripheral surface of the first group frame 2 in the direction of the central axis 0, respectively. Have been. And, each of the straight grooves 1a, 2
In a, 1b, 2b and 1c, 2c, supports 13a, 13b, and 13c composed of a plurality of bearing balls are provided, respectively.

In this support mechanism, when a vibrating body 12 (described later) disposed at a position facing the support 13b of the first group frame 2 is pressed in the direction of the central axis 0 via the slide plate 3, the linear groove A centripetal action is effected by 1a-1c and 2a-2c and the supports 13a-13c, and the first group frame 2 is accurately and precisely arranged so that the central axis coincides with the fixed frame 1. In addition, since the support bodies 13a to 13c have a plurality of bearing balls arranged in the direction of the center axis of the fixed frame 1, the first group frame 2 is supported without any deviation of the center axis. Further, the first group frame 2 is supported by a support 13
Since the moving frame 2 and the fixed frame 1 are processed only with the linear grooves 1a to 1c and 2a to 2c with high precision, the first group frame 2 is moved to the fixed frame 1 Positioning can be performed with high accuracy.

As shown in FIG. 7, the cutout hole 1d is formed at a position in the middle of the upper portion of the fixed frame 1 so as to face the slide plate 3.
That is, a flat portion is formed by cutting out the middle of the upper peripheral surface of the fixed frame 1 in a direction orthogonal to the central axis 0, and a cutout hole formed of a rectangular through hole long in the axial direction at the center of the flat portion. 1d is drilled. Therefore, both sides in the axial direction of the notch hole 1d is planar portion 1d ₀ is formed, the flat portion 1d ₀ has a mounting portion of the holder 8 supporting the vibrator 12.

The vibrating body is formed by a vibrating body 12 including a bending vibrator 11 and a vertical vibrator 4. The bending vibrator 11 has a relatively thick rectangular elastic body 5 having a sufficient size to be arranged in the notch hole 1d and a rectangular piezoelectric body having a shorter length and a thinner thickness than the elastic body 5. The piezoelectric body 6 is fixed to the upper surface of the elastic body 5 with an epoxy-based adhesive. A high-frequency voltage for driving is applied to the piezoelectric body 6 of the bending oscillator 11 in the thickness direction thereof, and in the case of the present embodiment, a first-order bending resonance is generated. It has become. On the lower surface of the elastic body to which the piezoelectric body 6 is not fixed at the two nodes of the bending vibration, a vertical vibrator 4 formed of a laminated piezoelectric body in a rectangular column shape and vertically vibrating in the thickness direction of the laminated plate is bent. The element 11 is fixed so as to vibrate longitudinally in the plate thickness direction.

The column vibrator 11 has four columnar support pins 7 extending outwardly in the plate width direction of the bending vibrator at the nodes thereof, which are fixed to the elastic body 5. In the middle of the pin 7, a holder mounting groove 7a is provided in the circumferential direction.

The vibrating body 12 thus configured is housed and held from below by a holder 8 formed in a shape having a channel-shaped cross section and covering the vibrating body 12 from above. That is, the holder 8 is formed by bending an elastic thin film, and at the positions corresponding to the support pins 7 on both hanging walls thereof, there is provided a circular hole-shaped receiving portion 8a whose lower part is opened. , Receiving part 8a
Is formed by a notch having a width slightly smaller than the diameter of the holder mounting groove 7a. In the middle of both hanging walls of the holder 8, there are provided mounting fixing portions 8b which are bent outward and extend horizontally, respectively.
An opening 8c through which the fixing screw 10 penetrates is formed in the mounting fixing portion 8b.

The vibrating body 12 is stored in the holder 8 so that it can vibrate freely by loosely fitting the holder mounting groove 7a of the support pin 7 into the receiving portion 8a. by screwed into screw holes 1e of the same screws 10 and the fixing screw 10 is penetrated through the dish spring 9 in the opening 8c is screwed to the flat portion 1d ₀ of the fixed frame 1, the vibrating body 12 Is disposed in the notch hole 1d of the fixed frame 1. The arranged vibrating body 12 has the lower end face of the vertical vibrator 4 pressed against the upper flat surface of the slide plate 3 fixed to the first group frame 2.

The operating principle of the ultrasonic motor of the present embodiment thus configured is the same as that of Japanese Patent Application No. 1-195767 previously proposed by the present applicant, and the phase difference between the bending vibration and the longitudinal vibration is 90 °. Thus, the first group frame 2 generates an elliptical vibration on the end face of the vertical vibrator 4 so as to move forward and backward in the direction of the center axis. Since the two vertical vibrators 4 are configured to vibrate with a vibration phase different by 180 °, only one-directional operation of the pendulum vibration around the node due to the bending vibration acts on the slide plate 3 of the first group frame 2. . Accordingly, this causes the first group frame 2 to move forward and backward in the central axis direction.

An encoder is provided to monitor the amount of movement when the first group frame 2 moves in the center axis direction.
That is, in this encoder, as shown in FIG. 5, the magnetic head 14 and the magnetic scale 15 are fixed frame 1 and group frame 2 respectively.
The block configuration is known and shown in FIG. 8, and is a typical digital type called a magnetic linear encoder.

That is, a ferromagnetic material is applied or plated on the substrate surface of each lens frame (see FIG. 4) in parallel with the central axis to form a thin magnetic film, which is then magnetized at regular intervals to form the magnetic scale 15. create. For reading the magnetism of the scale 15, a magnetic flux responsive magnetic head 14 formed by winding an excitation winding 73 and a signal winding 72 on a saturable iron core 71 is used. Make it readable.

Next, the reading circuit will be described. The number of pulses of the signal output extracted via the bandpass filter 74 is detected by utilizing the phenomenon that when the magnetic head 14 excited at a high frequency is brought close to the magnetic scale 15, the vibration of the head changes. Therefore, this method cannot detect the absolute position of the lens. In order to detect the absolute position of the lens, it is detected that the lens has reached the end, and the position is calculated back from the position by the number of pulses.

Next, a lens driving circuit in the automatic focusing camera configured as shown in FIGS. 1 and 3 to 8 will be described below with reference to FIG. 9 showing a block configuration thereof. The two images passing through the different optical paths of the taking lens in the lens barrel are formed on the light receiving surface of a sensor 35 (see FIG. 2) in the camera body. The electric signal photoelectrically converted by the sensor 35 is controlled by the sensor control circuit 83 for the integration time, the output timing of each pixel of the sensor, etc., and the obtained analog signal of each pixel of the sensor is converted by the A / D converter 82. It is converted to a digital signal. The digital signal is arithmetically processed by the CPU 84 to determine the amount of deviation between the two images, the amount of lens drive, and the like.

On the other hand, since the ROM 85R storing the lens-specific data such as the focal length and the open F-number is stored in the lens barrel, the CPU 84 determines the correct lens drive amount and the exposure value based on these data. can do. And LUM85L which drives each lens group independently in the lens barrel
(See FIGS. 5 to 7), and an encoder 85E (see FIG. 8) for measuring the amount of lens drive is also mounted. The lens driving circuit 86 is a circuit for driving the LUM85L, and is usually provided on the camera body side, but may be provided on the lens barrel side. The display circuit 87 is focused
This is a circuit for displaying the out-of-focus state. The start switch 88 is a switch that starts a focus detection operation when the switch is turned on.

The operation of the first embodiment of the lens driving device for an auto-focus camera according to the present invention thus configured will be described below with reference to the flowchart of FIG. By closing the start switch 88 shown in FIG. 9, the focus detection operation of this flow is started. And AF sensor 35
(Refer to FIGS. 2 and 9) A defocus amount Δ is calculated from the above two image interval (step S1). Now, when delta is less than a predetermined value delta ₁ previously determined (step S2), and if the lens with high accuracy by driving only the second lens 42F is a fine adjustment lens unit (see the third and fourth figures) Drive to focus position (step
S3). Next, it is checked whether or not a release signal (not shown) has been input (step S4). If no release signal has been input, the routine of steps S1 to S4 is repeatedly executed. On the other hand, if the release signal has been input, the AF operation ends.

Delta ≧ delta ₁ returns to step _S2, that is de when defocus amount delta is larger than the predetermined value delta ₁ drives the first lens 42R is coarse lens group (see the third and fourth figure) (step S5), roughly adjust the focus. In parallel with this, the second lens 42F for fine adjustment is moved to an intermediate position of the entire drive range in steps S6 to S8. That is, as described above,
Since the absolute position of the lens is not known by the encoder 85E (see FIGS. 8 and 9), it is first detected whether or not the lens has reached the end (step S7). This end detection is performed by, for example, means for judging the end if the number of pulses of the encoder does not change within a predetermined time even if a drive current is supplied to the excitation winding 73 of the encoder shown in FIG. Next, the second lens 42F can be moved to the intermediate position by moving the second lens 42F by a predetermined drive amount with reference to this end position (step S8). Then, the process returns to step S1 to calculate the defocus amount again. Then, as long as the subject does not change, delta <delta ₁ a is because (step S2), the turn drives the second lens 42F proceeds to step S3, thereby ultimately can be carried out with high accuracy focusing Becomes

As described above, according to the first embodiment, when the defocus amount is large, first drive the first lens for coarse adjustment (step S5), and then move the second lens for fine adjustment. Since the focusing is performed by driving (step S3), the focusing can be quickly and accurately performed even for a large defocus amount. At this time, since the second lens for fine adjustment is set at an intermediate position of the driving range during driving of the first lens for coarse adjustment (steps S6 to S8),
High-precision focusing by the second lens for fine adjustment can be quickly performed on both the front and rear pins.

Next, a second embodiment of the present invention will be described with reference to FIG.
The second embodiment differs from the first embodiment in that the first lens group for coarse adjustment and the second lens group for fine adjustment are set in advance to an intermediate position of the entire drive range after the release is completed. The same reference numerals are given to the same routines as in the first embodiment.

When AF is started, first, a defocus amount Δ is calculated. Then, by driving the second lens is a fine adjustment lens unit if delta <delta _1, drives the accuracy lens once the in-focus position. On the other hand, if delta ≧ delta _1, that is, Defookasu amount is greater than a predetermined value delta _1, after adjusting the rough focus by driving the first lens is a coarse lens group, calculates a defocus amount again . This time, if the subject is the same, Δ <
The fine-tuning by driving the second lens is a delta ₁ because fine adjustment lens group. Next, it is detected whether or not the shutter has been released. If the shutter has not been released, the above operation is repeatedly executed. The operations in steps S1 to S5 are the same as the operations in FIG.
If it has been released in S4, the process proceeds to the next step S11 and subsequent steps. That is, in steps S11 to S16, the second lens and the first lens
The lens is set to the middle position of the entire drive range, and the AF operation ends.

According to the second embodiment, since the second lens and the first lens are set at an intermediate position of the entire drive range after the release, the AF operation is stochastically accelerated. Further, as in the first embodiment shown in FIG. 10, the control is simplified since it is not necessary to drive the second lens to the intermediate position while driving the first lens.

As described above, according to the above-described embodiments, when the defocus amount is large, the first lens for coarse adjustment having a wide defocus range is driven first, and then the fine adjustment of the defocus range is relatively narrow. Since the focusing is performed by driving the second lens, focusing can be performed at high speed and with high accuracy even for a large defocus amount. In addition, since the lens is driven after the lens is set at an intermediate position of the entire driving range, it is possible to perform focusing quickly, reliably, and accurately with probability.

[Effects of the Invention] As described above, according to the present invention, a remarkable effect that high-speed and accurate focus adjustment can be performed in a wide defocus range is exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an autofocus camera to which the present invention is applied, FIG. 2 is an optical arrangement diagram of a focus detection optical system in the autofocus camera, and FIG. 3 is a photographing lens in FIG. FIG. 4 is a longitudinal sectional view of a lens barrel incorporating the lens group shown in FIG. 3, FIG. 5 is a sectional view taken along line AA in FIG. 4, and FIG. 4 is a sectional view of a main part in FIG. 4, FIG. 7 is an exploded perspective view showing the mounting structure of the vibrating body in FIG. 5 and FIG. 6, FIG. 8 is a block configuration diagram of the encoder in FIG. FIG. 9 is a block diagram of a lens driving circuit, FIG. 10 is a flowchart of a lens driving device for an autofocus camera showing a first embodiment of the present invention, and FIG. 11 is a second embodiment of the present invention. It is a flowchart of the lens drive device of the automatic focus camera shown. 22 second driving means 23 first driving means 30 AF module (focus detecting means) 42R first lens 42F second lens 84 CPU (comparing means, selecting means) )

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shinichi Kodama 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (56) References JP-A-2-54209 (JP, A) JP 63-125910 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 7/11 G02B 7/08

Claims (1)

(57) [Claims] 1. A first lens having a relatively large change in focal position with respect to a driving amount of a lens, and a first lens having a small change in focal position with respect to the driving amount of the lens as compared with the first lens. A second lens, a first driver for driving the first lens, a second driver for driving the second lens, and detecting a shift amount of a focal position of the lens with respect to a predetermined focal plane position of the camera. Focus detecting means, comparing means for comparing the shift amount with a predetermined amount, selecting means for selectively driving the first lens and the second lens according to the result of the comparing means, A lens driving device for an auto-focus camera, comprising: