JP3288506B2 - Drive mechanism of autofocus single-lens reflex camera with flange back control - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-lens reflex camera with interchangeable photographic lenses, and more particularly, to a focusing drive mechanism in a single-lens reflex camera of a back focus control type.

[0002]

2. Description of the Related Art Generally, when a single-lens reflex camera is converted to AF, the focusing operation is automated by automatically adjusting a distance ring of a lens based on distance information to a subject. In such a case, a driving method using a motor in the body and a driving method using a motor in the lens have been put into practical use.
Both use a dedicated AF lens and use a conventional interchangeable lens
It was impossible to transform. In addition, in the focusing operation, a rotary encoder is installed in the middle of the drive mechanism connected to the motor, and the focusing control is performed by converting the amount of lens extension by this encoder signal. I have.

[0003]

SUMMARY OF THE INVENTION The present inventor has developed a back focus control type single-lens reflex camera to enable AF operation with a conventional MF lens based on a conventional lens mount on which a lens can be mounted and exchanged. It has been proposed (Japanese Patent Application No. 4-226556, etc.). In this back focus control type single-lens reflex camera, the camera body is divided into a front portion and a rear portion, and focusing is performed by controlling the position of the rear film surface. In this back focus drive control, since the rear movable part includes an opening, a distance measuring mechanism, a finder mechanism, and the like, depending on the design configuration, it is inevitable that the weight and volume become considerable. Therefore, it is an important subject to drive the rear movable portion at high speed and precisely.

In the conventional AF drive control, the power of the drive motor is given a margin, and it is moved to a focus position while counting the movement amount of a minute unit from the initial stage of the drive. When the distance from the position to the focal point is large, there is a disadvantage that it takes time to drive the focus.
The present invention solves the above-described problems, and an object of the present invention is to provide an AF single-lens reflex camera of a back focus control system,
It is an object of the present invention to provide a driving mechanism that can bring a rear movable portion to a focus position at high speed and precisely.

[0005]

In order to achieve the above object, a driving mechanism of a back focus control type autofocus single lens reflex camera according to the present invention comprises a camera body front block including at least a photographing lens and a lens mount for the photographing lens. A camera body rear block including at least a film opening, a front-rear block connecting portion for connecting the distance between the camera body front block and the camera body rear block so that the distance can be adjusted, and AF information. An auto-focus single-lens reflex camera, which comprises a lens mount of the front block of the camera body and an AF drive mechanism for adjusting a distance between an opening of the rear block and adjusts a flange back of the photographing lens to perform focusing. And the optical axis parallel movable range of the rear block of the camera body is p , And further divides each of the p divided parts into q pieces, and controls the driving of each of the p divided parts, and each of the q subdivided parts. and a fine driving unit for driving and controlling the provided pre
The coarse drive or precision drive includes a lead screw.
By rotating the lead screw,
The rear block of the camera body can be moved in the optical axis direction, and the rough drive unit and the precision drive unit are simultaneously operated according to the movement amount obtained by converting the predicted calculation value to the focal point obtained by the distance measurement sensor signal by the displacement amount conversion. It is configured to drive to control the focus position.

[0006]

According to the above arrangement, for example, when the size of a large divided portion divided into p pieces is s, and the size of a minute divided portion divided into q pieces is Δs, the defocus amount (based on the measurement signal) By calculating the focus shift amount, it is predicted that the distance to the in-focus position is m (a natural number smaller than p) times the size s of the large divided portion and n (natural number smaller than q) times the size Δs of the minute divided portion. Since the coarse drive unit and the precision drive unit are driven simultaneously, focusing control can be performed at high speed and precisely. If the optical axis parallel movable range is L, it can be expressed by the following relational expression. L = p · s s = q · Δs…

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment of an autofocus single-lens reflex camera according to the present invention. The camera body front fixed block includes a grip having an interchangeable lens 9, a lens mount 1, a part of the AF drive mechanism 7, and a release button 31. The rear movable block of the camera body includes an up-down mirror 13, a finder mechanism 5, an aperture 10, an exposure mechanism, a film feeding mechanism, and a distance measuring mechanism 3.

Light from a subject (not shown) passes through the interchangeable lens 9, is guided upward by the up-down mirror 13, and enters the finder mechanism 5. Penta prism 5a
The light becomes parallel to the main optical axis and reaches the eyepiece 5b. Part of the subject light that has passed through the interchangeable lens 9 also enters the AF auxiliary mirror 3a of the distance measuring mechanism 3, is guided to the lower part, and
The light reaches the AF sensor 3c via the F lens 3b. The AF driving mechanism 7 includes a coarse back motor (hereinafter referred to as "FB") rough driving motor 7a, a encoder 7 and a gear 7e fixed to the drive shaft of the motor 7a and a lead screw 7d fixed to the gear 7f. It comprises a drive unit and a precision drive unit comprising an FB precision drive motor 7b, a gear 7g fixed to the drive shaft of the motor 7b, and a precision drive gear 7c. The gear portion on the outer peripheral portion of the precision drive gear 7c meshes with the gear 7g, and the female screw portion at the center is screwed with a lead screw 7d.

The FB coarse drive motor 7a of the fine drive unit is mounted on the front fixed block side.
Are fixed to the rear movable block side, respectively. FB
The rotational output of the coarse drive motor 7a is transmitted to the lead screw 7d at a reduced speed via gears 7e and 7f, and the rotational speed is measured by the encoder 6 to control the coarse drive amount. At the same time, the rotation output of the FB precision drive motor 7b is also transmitted to the precision drive gear 7c via the gear 7g, and the drive amount is precisely controlled. That is, while the coarse driving unit is driven at high speed, the fine driving unit is driven while the coarse driving unit is being driven, and fine front and rear driving within the divided range portion is also performed before reaching the target divided range portion. When it reaches the division range portion, it is controlled so that the reached position becomes the focal point. As a result, the rear movable block is quickly and precisely brought to the in-focus position with respect to the front fixed block of the camera body. FB coarse drive motor 7a
A DC motor is used for the precision motor 7b, and a DC motor or a step motor having an encoder is used for the precision drive motor 7b.

Information indicating the positional relationship between the front fixed block and the rear movable block can be detected by the position detection switch 8. The code pattern substrate 8a constituting the position detection switch 8 is fixed to the base of the front fixing block,
The ends of the contacts 8b are respectively fixed to the bases of the rear movable blocks. When the distance between the front fixed block and the rear movable block changes, the code on the code pattern substrate 8a changes accordingly, and an FB position detection signal can be obtained. As the position detection switch 8, another method such as one that detects the sliding resistance may be used.

The connecting structure between the front fixed block and the rear movable block includes, for example, a rail provided on the front fixed block and a roller provided on the rear movable block. The rail is provided when the AF driving mechanism 7 operates. The configuration in which the rollers roll on the top makes it possible to smoothly change the distance between the two blocks so that a load is not applied as much as possible. Further, a guide rod is provided on the front fixed block and a hole for guiding the guide rod is provided on the rear movable block, so that the optical axis does not shift and the aperture surface and the lens mount surface are kept parallel. Can be moved.

FIG. 2 is a schematic view showing another embodiment of the driving mechanism according to the present invention. In this embodiment, a pulse motor is used for the coarse drive motor and the precision drive motor, and the components other than the drive mechanism are omitted. Fixed part A 'and movable part B'
Are blocks respectively corresponding to the front fixed block and the rear movable block in FIG. Coarse drive pulse motor 17
Is disposed on the fixed portion A ', and one end of a ball screw 24 for coarse movement is directly connected to the drive shaft 17a. Coarse movement board
The other end of the screw 24 is rotatably attached to the support 27. A screw portion 26a below the nut portion 26 is screwed into the coarse movement ball screw 24, and the nut portion 26 moves linearly by rotation of the ball screw.

A slider 23 is attached to a lower surface of the nut portion 26. The slider 23 is provided on the coarse drive position detecting code pattern board 22 provided on the fixed portion A '.
The moving position can be checked by sliding on the pattern. FIG. 3 is a divided view of the movable range for explaining the operation principle. Now, assuming that the movable distance of the movable portion B 'is L, the distance L is divided into p, and the slider 23 of the position detection switch of the coarse drive portion is rotated by 1 for one step rotation of the coarse drive motor.
Move by unit s. Specifically, the position detection code is 4
In the case of a bit gray code, p becomes 16, and
One unit s is a unit obtained by dividing the movable distance L into 16 units. The position detection switch detects which of the 16 divided 1 units s has been moved.

On the other hand, the precision driving pulse motor 18 is provided on the movable portion B ', and a fine moving lead screw 21 is fixed to its driving shaft. The lead screw 21 for fine movement is screwed with the screw portion 26b on the upper portion of the nut portion 26. A slider 20 is mounted on the upper surface of the nut portion 26. The slider 20 is a code pattern of the precision drive position detection code pattern board 19 provided on the movable portion B '. The fine position can be confirmed by sliding on the top. In FIG. 3, one unit s of coarse drive is divided by q, and the slider 20 of the position detection switch of the precision drive unit is a minute unit Δs for one step rotation of the precision drive pulse motor 18.
Just move.

Considering the actual driving condition, the current position a
When moving from the position to the in-focus position b, the position of the point a is detected by the position detection switches of the coarse drive unit and the precision drive unit.
This position is a distance from the reference position (0 position). Assuming that the distance at point a is A and the distance at point b is B, the distance between a and b is (BA). Here, the + sign indicates b for point a.
The point is on the right side (the focus position is closer to the current position),
The sign indicates that the point b is on the left side (far side). This defocus amount Δf is analyzed and calculated, and if Δf is obtained by adding m times 1 unit s and n times minute unit Δs, ± Δf is expressed as ± Δf = ± (m × s ± n × Δs). Note that the + sign at the time of the minute movement is insufficient at m times the coarse movement, and requires a further minute movement, and the-sign is over at m times the coarse movement and means returning by the minute movement. .

FIG. 4 is a schematic diagram showing an embodiment of a control circuit of the drive mechanism of FIG. An FB position detection signal based on a code signal is output from the code pattern substrate, an encoder signal is output from the encoder 6, and a distance measurement signal (A) is output from the AF sensor 3c.
F information) is output. The AF control circuit 29
The FB position detection signal, the encoder signal, and the distance measurement signal are input, the current FB position is confirmed, and the defocus amount is calculated. When the release button 31 is half-pressed, the first release switch 32 is turned on, and the release check signal is set to A.
The signal is sent to the F control circuit 29, and the FB drive motor drive circuit 28 simultaneously drives each of the coarse drive unit and the precision drive unit. Thus, a focusing operation is performed. Further, when the release button 31 is depressed, the second switch 33 of the next stage is turned on, a camera operation start signal is input to the camera operation CPU 30, the mirror up and shutter mechanisms are operated, and photographing is performed. Then, operations such as film winding are performed, and the camera photographing operation is completed.

FIG. 5 is a flowchart for explaining the operation of the driving mechanism according to the present invention. When the power of the camera is turned on (S501) and the AF control circuit 29 and the like of the camera are set to the standby state, the AF control circuit 29 detects the current FB position based on the FB position detection signal (S502). This is the position recognition of the point a in FIG. Next, a signal from the AF sensor is taken in (S503), and a defocus amount ± Δf is calculated (S504). Thereby, the number of coarse movement steps m
And the number n of precision movement steps are calculated (S505, S5).
06). Next, when the release button 31 is half-pressed to perform a release check (S507), the AF control circuit 29
The FB drive motor drive circuit 28 is controlled to control the coarse drive mode.
And the precision drive motor are driven simultaneously (S508, S5
09). That is, the coarse drive motor rotates m steps,
The precision drive motor rotates n steps. Then, after confirming the position of the focal point (point b) (S510), focus determination based on the AF signal is performed (S510). If the focus is determined, A
The F operation ends. If the drive amount based on the predicted defocus value has a slight deviation in the focus determination of the final confirmation, the error correction is repeated again to the calculation of the defocus amount.

[0018]

As described above, according to the present invention,
In the back focus control type autofocus single-lens reflex camera, there is an effect that focusing control can be performed by moving the rear movable block having a considerable weight and capacity at high speed and precisely.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing an embodiment of an autofocus single-lens reflex camera according to the present invention.

FIG. 2 is a schematic view showing another embodiment of the driving mechanism according to the present invention.

FIG. 3 is a diagram for explaining an operation principle according to the present invention.

FIG. 4 is a schematic diagram showing an embodiment of a control circuit of a drive mechanism according to the present invention.

FIG. 5 is a flowchart for explaining the operation of the driving mechanism.
It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Lens mount 2 ... Film surface 3 ... Distance measuring mechanism 5 ... Finder mechanism 6 ... Encoder 7 ... AF drive mechanism 8 ... Position detection switch 9 ... Interchangeable lens 10 ... Aperture 11 ... Pressure plate 13 ... Up / down mirror 15 ... Linear guide bar 16 Linear guide 17 Coarse drive pulse motor 18 Precision drive pulse motor 19 Position detection code pattern board for precision drive 20, 23 Slider 21 Lead screw for fine movement 22 Coarse drive position detection code pattern board 24 ... Coarse movement ball screw 25 ... Ball 26 ... Nut part 27 ... Support part 28 ... FB drive motor drive circuit 29 ... AF control circuit 30 ... Camera operation CPU 31 ... release button 32, 33 ... switch

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B ⁷ /02-7/09 G03B 13/36

Claims (2)

(57) [Claims] 1. A camera body front block including at least a photographing lens and a lens mount for the photographing lens, a camera body rear block including at least a film opening, a camera body front block, and the camera body rear block. The front and rear blocks are connected so that the distance can be adjusted, and an AF drive mechanism that adjusts the distance between the lens mount of the front block of the camera body and the opening of the rear block based on AF information. An autofocus single-lens reflex camera that performs focusing by adjusting a flange back of the photographing lens, wherein a movable range of an optical axis parallel of a rear block of the camera body is divided into p, and further divided into p. A coarse drive unit that subdivides each part into q parts and drives and controls each of the p divided parts; Provided a precision drive unit for driving and controlling among moieties subdivided into the q number, the coarse driving unit or the precision drive unit including a lead screw
By rotating the lead screw,
The rear block of the camera body can be moved in the optical axis direction, and the rough drive unit and the precision drive unit are simultaneously operated according to the movement amount obtained by converting the predicted calculation value to the focal point obtained by the distance measurement sensor signal by the displacement amount conversion. A driving mechanism for a flange-back control type auto-focus single-lens reflex camera, wherein the driving mechanism is configured to be driven to control a focus position. 2. The driving mechanism of a flange-back control type autofocus single lens reflex camera according to claim 1, wherein independent stepping motors having different characteristics are used for the coarse drive unit and the fine drive unit.