JP3199590B2 - Electromagnetic braking mechanism for autofocus camera with moving film surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera having an interchangeable photographic lens, and more particularly to an electromagnetic braking mechanism for adjusting the focus of a back focus control type auto focus camera.

[0002]

2. Description of the Related Art Generally, when a single-lens reflex camera is made into an AF system, a method of automating an operation of focusing a subject by adjusting a distance ring of a lens is adopted. As the driving method, there are a method using a motor in a body and a method using a motor in a lens, and these methods have been put to practical use. In each case, the lens becomes an AF-only lens, and it has not been possible to convert a conventional lens to AF.

[0003]

A conventional MF lens based on a lens mount that can be mounted and exchanged with a conventional lens is A
In order to enable the F operation, the present inventor has already proposed a so-called back focus control method in which the camera body is divided into front and rear portions and the position of a rear film surface is controlled. In this back focus control, the movable unit, which is a movable unit, has a photographing function including a film chamber and includes many of the functions of the camera, and therefore has a considerable weight and volume. In order to perform AF, the movable unit must be controlled at high speed and precisely. To solve this problem, the present inventor uses an ABF (Automa).
TicBack Focusing), a product concept that adheres to this concept, even if the movable range of the flange back of the lens is 5 mm or less, when considering the popular model with priority on the small size and light weight of the whole camera within the range that does not impair the concept of ticback focusing. (Japanese Patent Application No. 6-243448).

Therefore, when considering only a model in which the movable range of the flange back is not so large, the film cartridges disposed on the left and right sides of the camera main body and the film chamber of the take-up spool are installed on the fixed side of the camera main body. A mirror box mechanism having an AF sensor module and a finder mechanism on the side, a shutter, a film opening, and an optical axis unit having an optical axis photographing function including a film pressure plate are moved parallel to the optical axis while holding the film, and the back is moved. A method of adjusting the focus was proposed. With this proposal, the weight of the movable section can be further reduced, and high-speed control of the back focus has become possible as compared with the case where the film chamber is provided on the movable side. Further, by adopting a voice coil type linear motor instead of the method of converting the rotation output of the rotary motor into linear drive, higher speed control can be realized. This is an unprecedented high-speed operation comparable to the focusing operation of the human eyeball.

However, for controlling the focus position, a CPU is required.
, It was necessary to execute a complicated control program. In particular, when the movable distance is long and acceleration is applied, overshoot or oscillation is likely to occur.
In addition, after being positioned at the focal position, it is necessary to continue energizing and maintain the control operation in order to maintain the position,
At the time of non-operation, there is a problem that the BF easily moves to the maximum position or the minimum position of the BF due to the gravity of the movable portion due to a difference in attitude of the camera. An object of the present invention is to solve the above-mentioned problem, and to make it possible to swing two positions around a swing axis and apply a positive / negative pulse near a target BF position.
Provided is an electromagnetic braking mechanism for a film surface moving type autofocus camera that controls braking of a movable part by repeating braking that stops F movement and release of braking, and that can reliably maintain the position of the movable part even when power is cut off. Is to do.

[0006]

In order to achieve the above object, an electromagnetic braking mechanism of a film surface moving type autofocus camera according to the present invention comprises a lens mount for a photographing lens,
A film chamber on the film winding side and a film chamber on the rewinding side are arranged on the left and right sides, and a camera external part having a film feeding mechanism part to be passed therethrough and a back lid for taking in and out the film, and passing through a lens. An optical axis unit having a finder mechanism, a distance measuring mechanism, an exposure mechanism, and a film opening installed at the center of the optical axis, and being movable by a predetermined distance in the optical axis direction with respect to the external appearance of the camera. In the camera mechanism, in order to move the opening of the optical axis unit to a focus position in accordance with the distance of the subject, a distance detection signal from a movement amount reading unit capable of directly reading the movement amount of the optical axis unit is provided. Receiving side of the optical axis unit
Provided with a hollow coil and a yoke.
Giving a linear driving force to the coil by passing a current,
The coil and the optical axis unit are connected by arm means
Thereby directly driving the optical axis unit,
Each time the positive and negative currents are applied and shut off, two stable states are formed.
An electromagnetic braking unit that applies a braking force to the optical axis unit by forming one stable state is provided, and the electromagnetic braking unit applies braking from near the in-focus position to reach the in-focus position. Later, the optical axis unit is locked with the current interrupted.
It is configured for Kusuru.

Further, according to the present invention, in the above-described structure, when the positioning of the focus position is finely adjusted, a short positive / negative repetitive pulse drive current is applied from near the focus position.
The shaft unit is configured to step brake .

[0008]

According to the above construction, the movable portion is unlocked by the negative pulse current before starting the BF drive by the voice coil type linear motor, and at the same time, near the desired BF position by the drive current of the voice coil type linear motor. At this point, by applying one or more positive and negative pulses, deceleration braking is applied with a characteristic such that the speed of the movable portion becomes asymptotic, and the BF position can be accurately positioned. After the positioning, the locked state is maintained even after the power is cut off by the final positive pulse current.
The BF position does not move carelessly.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a cross-sectional plan view showing a basic configuration of a film surface moving type autofocus camera according to the present invention, showing a state of movement of an optical axis unit serving as a movable portion.
This figure shows a state in which the focus can be adjusted only by moving the optical axis unit B having a photographing function. The movable amount of the flange back is reduced, and the patrone 1 and the spool disposed on both sides of the aperture are shown. 3 is provided in the camera exterior part A. Optical axis unit B is 2
It is a portion surrounded by a chain line and includes a mirror 4, a mirror box mechanism, a shutter mechanism, a pressure plate 5, and the like as photographing functions. In this example, fitting portions 6a, 6b, 7 are attached to the side surfaces of the optical axis unit B, and the optical axis unit B is guided in the optical axis direction by guiding the optical axis unit B with guide rods 8, 9 whose ends are fixed to the camera exterior portion A. Move in a state of being held parallel to.

FIG. 1A shows a state where the optical axis unit B has moved to the film winding position, that is, the maximum movable position, and FIG. 1B shows that the optical axis unit B is brought to the minimum movable position for focusing. It shows the state that is being done. By employing such a configuration, the weight of the movable portion is extremely reduced, and focusing control is facilitated. Assuming that the optical axis unit is used, by using a voice coil type linear motor as a method of controlling the driving of the optical axis unit, the control speed can be dramatically improved. However, it is very difficult to apply a braking technique after the drive starts, and there is an irrationality that the braking must be applied from the beginning and the drive speed itself must be reduced in order to prevent overshoot and oscillation during focus positioning. The present invention solves this,
It operates electromagnetically and mechanically brakes the drive system itself to effectively prevent movement.

FIG. 2 is a perspective view showing an embodiment of an electromagnetic braking mechanism of the film plane moving type autofocus camera according to the present invention, and shows in detail a back focus driving mechanism and an electromagnetic braking mechanism using a voice coil type linear motor. It is. A ground plate 43 is fixed to the mount base 21 of the camera external part A with screws 46. Bent portion 4 below base plate 43
The cross lever 33 is rotatably coupled to the upper lever 3a by a pin 34, and is inserted into the long groove 43c of the upper bent portion 43b.
A pin 44 fixed to the second end is slidably connected. The cross levers 32 and 33 are crossed in an X shape, and the cross point is rotatably connected by a pin 35. On the other hand, the main plate 45 is fixed to the side surface of the movable mirror box, and the lower end of the cross lever 32 is rotatably mounted below the main plate 45 by the pin 31. Further, a pin 29 fixed to the upper end of the cross lever 33 is slidably coupled to the long groove 45a above the main plate 45. The cross lever mechanism is similarly installed on the opposite side (invisible portion) of the mirror box, and the optical axis unit B is held so as to be movable in parallel with the optical axis.

In the voice coil type linear motor, U-shaped yokes 38 and 40 are arranged side by side, magnets 39 and 41 are adhered and fixed to the inside of the U-shape, and a rectangular hollow coil (moving coil) is mounted on the central yoke. 37 is inserted. When a current is applied to the coil 37, a force acts on the coil 37 in a direction along the center yoke. The U-shaped yokes 38 and 40 are the base plate 4 fixed to the mount base 21.
3, and the central yokes of the yokes 38 and 40 are bonded to each other to form a two-ply configuration. As described above, the coil 37 can be inserted into and retracted from the yoke at the center of the two-layered structure.
The coil 37 is fixed between the arms 30a and 30b of the holding member 30. Since the holding member 30 is fixed to the base plate 45 of the mirror box, if an electric current is applied to the coil 37, the optical axis unit B can be moved in parallel to the optical axis by a force acting on the coil.

Photointerrupters 27 and 28 for detecting the movement amount and position of the optical axis unit B are installed at the upper right position of the camera body fixing portion A. Slits 24, 25
Is fixed to the optical axis unit B, and the slits 24 and 25 are configured to move in the photointerrupters 27 and 28 via the masks 22 and 23. The encoder plate 26 moves together with the optical axis unit B, and the movement position of the optical axis unit B can be measured. A braking rod 12 is fixed to the optical axis unit B,
During FB driving, the brake rod 12 also moves integrally. On the other hand, on the mount base 21 side of the camera body fixing part A, the electromagnetic braking part 11 composed of a rotor and a stator is incorporated. The rotor has a brake 14 and can swing left and right about a shaft 15. A stop friction plate 17 is attached to the brake element 14. When the brake element 14 is tilted counterclockwise and pressed against the brake rod 12 of the optical axis unit B, the optical axis unit B
Is held and the movement is locked. The state of FIG.
Reference numeral 4 denotes a state in which the BF is fixed (locked).

When the clockwise rotation about the shaft 15 is performed, the stop friction plate 17 pressed against the brake rod 12 is released, and the stopping of the optical axis unit B is released. A magnet 13 is fixed to the lower side of the brake element 14, and yokes 16 and 18 having arc-shaped end faces centered on the shaft 15 are fixed to both pole ends. The rotor comprises a shaft 15, a brake 14, a stopping friction plate 1
7 and yokes 16 and 18. An electromagnet serving as a stator in which a coil 20 is wound around a central core 19a of the E-shaped core 19 is disposed below the rotor with a small gap therebetween. By applying a positive pulse current to the coil 20 to rotate the rotor to the braking side and supplying a negative pulse current to the releasing side to rotate, the braking and locking operation of the optical axis unit B can be performed.

FIG. 3 is a diagram for explaining the basic principle of the operation of the electromagnetic braking unit. (A) shows a state in which the rotor is rotated clockwise, abuts against the stopper pin 14a and is stationary. This state corresponds to the state of the brake rod 12 of the optical axis unit B.
Is separated from the stop friction plate 17 of the brake element 14, and the optical axis unit B is in a free state. In the state where the current to the coil 20 is cut off at this position, the yoke 16 on the N pole side of the rotor is located between the yoke 16 and the central core 19 a of the E-shaped core 19,
The yoke 18 on the pole side generates magnetic lines of force (indicated by a dashed line) so that an attractive force acts between the yoke 18 and the left core portion 19c of the E-shaped core 19, and the yoke 18 around the shaft 15 in a direction to further reduce the magnetic resistance. Power works. That is, the clockwise rotational moment is acting, but is stopped by the stopper pin 14a,
This state is maintained.

Now, when a positive current is applied to the coil 20 from the state of (a), as shown in (b), the center core 19a of the E-shaped core 20 has the N pole, and the cores 19b and 19c on both sides have the S pole. Is generated. Therefore, the yoke 16 on the N pole side of the rotor receives a repulsive force from the N pole of the central core portion 19a and a suction force on the S pole of the right core portion 19b. On the other hand, the yoke 18 on the S pole side of the rotor receives a repulsive force from the S pole of the left core portion 19c of the E-shaped core 19 and a suction force on the N pole of the central core portion 19a, so that the rotor generates a counterclockwise rotational force. Then, it falls to the state of FIG. The stopping friction plate 17 of the brake element 14 is
2, the frictional force between the stop friction plate 17 and the brake rod 12 prevents the movement of the optical axis unit B. In the state (b), even when the current is cut off, a further counterclockwise couple acts due to the positional relationship between the magnetic poles of the rotor and the respective cores of the E-shaped core 19, so that the stopping friction plate 17
Maintain the pressure contact state with 2.

The release of the locked state is performed by applying a negative current to the coil 20. The magnetic poles generated in the E-shaped core 19 are opposite to those shown in (b), and a clockwise rotating torque is generated around the shaft 15 in the rotor,
The stopper pin 14a falls down to the position of the stopper pin 14a, the stop friction plate 17 is separated from the brake rod 12, the lock of the optical axis unit B is released, and the state of FIG. In the above two stable states, only positive and negative pulse currents need to be supplied during conversion.
It can be understood that there is no need to continue energization to maintain the respective stable states. The electromagnetic braking unit 11 can be said to be an ideal operation for a camera using a battery as an energy source whose energy capacity cannot be increased due to the size of the outer shape.

FIG. 4 is a circuit block diagram showing an embodiment of a control circuit of the electromagnetic braking mechanism according to the present invention. AFCPU
52 is an encoder plate 26 and photointerrupters 27 and 2
8, the current position of the optical axis unit B can be known from the FB position detection signal from the linear encoder 55. Also, an AF signal is output from the AF sensor 56 of the distance measuring mechanism.
It is sent to the CPU 52. Upon receiving the release signal, the camera operation CPU 53 sends an instruction signal for the AF operation to the AF CPU 52. AFCPU 52 is a camera operation CPU
BF drive driver 5 which receives a command signal from 53 and drives voice coil type linear motor 57 including hollow coil 37, yokes 38 and 40, magnets 39 and 41, etc.
0 and an electromagnetic brake driver 51 for operating the electromagnetic brake unit 11 are controlled.

Next, the braking operation during the actual BF control operation will be described with reference to the timing chart of FIG. FIG.
FIG. 4 is a waveform diagram illustrating a relationship between a current flowing when performing braking and locking at the time of focus positioning and a braking operation. Now, position or BF position of the optical axis unit B before operation is in BF _1, A
And needs to be moved to the position of the BF ₂ is caused by the F signal. When a positive current is applied to the coil 20 of the electromagnetic braking unit 11, the brake element 14 falls to the braking side, and falls to the release side with the negative current, so that the locking and releasing operations are performed. First, A
The FCPU 52 controls the electromagnetic braking driver 51 before driving the BF.
Is controlled to flow the negative current i ₀ of the braking operation for the time T ₀ , the state is switched from the locked state to the released state. At this time, when the BF driving current _id is supplied to the voice coil type linear motor 57 by controlling the BF driving driver 50, the braking rod 1
Since 2 is free, the optical axis unit B starts moving from the point a as shown in the figure.

During movement, the AF CPU 52 receives a position detection signal from the linear encoder 55 and reads the movement position. When approaching the target BF ₂ position and moving to point b, B
Cut off the drive current i _d of F driver 50, the flow a positive current i _S of the braking operation than solenoid brake driver 51, following the brake shoe 14 is switched to the brake-side. This switching time is T _S , during which the voice coil linear motor 57
Even if the drive current to the motor is interrupted, the point moves from point b to point c due to inertia. In consideration of this inertia, a stop operation is applied at the point c, but since it has not yet reached the BF ₂ position,
Only short time t _1, again, passing a negative current for canceling an electromagnetic brake driver 51. If a drive current is passed through the voice coil linear motor 57 again during this time when the stop friction plate 17 is slightly lifted from the brake rod 12 by flowing the negative current, the stop friction plate 17 approaches the BF ₂ side by a minute distance.

Further, when the current is switched to the positive current for the braking for only a short time t _{2 and} the driving current of the voice coil type linear motor 57 is cut off, the braking is applied and stopped. Then, again, a negative current is passed by t ₃ for release, and a drive current is passed, thereby bringing the current closer to the target BF side. Also flowing positive current for braking by t _4, finally floated t ₅ only stopped the friction plate 17, and the fine movement be allowed to flow a drive current to the voice coil type linear motor 57, BF ₂ reached the final point d purposes Secure position. Be allowed to flow braking operation current by t ₆ in BF ₂ position is at this final point, in order to hold the locked state even when cut off the current becomes locked, until the next BF movement command from the camera operating CPU 53 BF ₂ Never move.

The latter part of the waveform diagram of FIG. 5 shows an example of the voice coil type linear motor 57 flowing negative drive current to move the BF position to the position of the return BF ₃ to the initial BF ₁ position side However, the braking operation for this positioning is the same as that described above. In other words, only the driving current of the voice coil type linear motor 57 is composed of a positive to a negative current, others Similarly, before the start of driving to perform the unlocking operation to the electromagnetic brake 11, from the vicinity of the BF ₃ purposes The braking operation current is repeatedly braked and released by a positive / negative alternating pulse current, during which the driving pulse current gradually approaches the point g of the target position, and the BF
Reach position ₃ . The feature of this electromagnetic braking mechanism is that the inconvenience that the optical axis unit, which is a movable part, is always fixed except when the BF is moved, is inadvertently moved depending on the posture of the camera is solved. The focus positioning operation in FIG. 5 shows an example in which the position of the BF ₂ is gradually approached by 3 pulses and the position of the BF ₃ is gradually approached by 2 pulses. The numbers are different. In such a case, a faster and more accurate BF control can be performed by creating a program suitable for the above and performing asymptotic control by a braking operation corresponding to each program.

[0023]

As described above, according to the present invention, the film chamber is provided in the camera external part which is the fixed part, the weight of the optical axis unit which is the movable part is reduced as much as possible, and the optical axis unit is directly driven by the linear motor. This is a BF control type film surface moving camera, which is provided with an electromagnetic braking unit that applies braking immediately before positioning at the focal point and locks the optical axis unit after reaching the focal point. Therefore, in the BF drive by the voice coil type linear motor, deceleration braking is applied with characteristics such that the speed of the movable portion becomes asymptotic, and the BF can be accurately positioned at a predetermined BF position. After the positioning, the locked state is maintained even after the power is cut off by the final positive pulse current, and there is an effect that the BF position does not accidentally move due to a difference in the posture of the camera or an external impact.

[Brief description of the drawings]

FIG. 1 is a cross-sectional plan view showing a basic configuration of a film surface moving type autofocus camera according to the present invention, showing a state of movement of an optical axis unit serving as a movable portion.

FIG. 2 is a perspective view showing an embodiment of an electromagnetic braking mechanism of the film surface moving type autofocus camera according to the present invention, showing in detail a back focus driving mechanism and an electromagnetic braking mechanism using a voice coil type linear motor.

FIG. 3 is a diagram for explaining a basic principle of an electromagnetic braking unit.

FIG. 4 is a circuit block diagram showing an embodiment of a control circuit of the electromagnetic braking mechanism according to the present invention.

FIG. 5 is a waveform diagram showing a relationship between a current flowing when performing braking and locking at the time of focus positioning and a braking operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Patrone 2 ... Interchangeable lens 3 ... Spool 4 ... Mirror 5 ... Pressure plate 6a, 6b, 7 ... Fitting part 8, 9 ... Guide rod 10 ... Film 11 ... Electromagnetic braking part 12 ... Brake rod 13 ... Magnet 14 ... Braking element 15 ... Shaft 16, 18 ... Yoke 17 ... Stop friction plate 19 ... E-shaped core 20 ... Coil 21 ... Mount base 22,23 ... Mask 24,25 ... Slit 26 ... Encoder plate 27,28 ... Photo interrupter 29,31,34 , 35, 44 ... pin 30 ... holding member 32, 33 ... cross lever 37 ... hollow coil 38, 40 ... U-shaped yoke 39, 41 ... magnet 43, 45 ... ground plate 46 ... screw 50 ... BF drive driver 51 ... electromagnetic braking Driver 52: AFCPU 53: Camera operation CPU

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03B 17/14 G02B 7/28 G03B 3/04 G03B 13/32 G03B 17/28

Claims (2)

(57) [Claims] 1. A lens mount for a photographic lens, a film chamber on a film winding side and a film chamber on a rewinding side are arranged on the left and right sides, and a film feeding mechanism for passing the film chamber and a back side for taking in and out the film. A camera external part having a lid,
A finder mechanism installed at the center of the optical axis passing through the lens,
An optical axis unit having a distance measuring mechanism, an exposure mechanism, and a film opening, and being movable by a predetermined distance in an optical axis direction with respect to the camera exterior part, a film plane moving type camera mechanism, comprising: In order to move the opening of the optical axis unit to the in-focus position in accordance with the distance, a distance detection signal is received from a moving amount reading unit capable of directly reading the moving amount of the optical axis unit, and the side of the optical axis unit is The hollow coil and
And a yoke, and applying a current to the hollow coil.
To give a linear driving force to the coil,
The optical axis unit is directly driven by connecting the axis units by arm means , and a bi-stable state is formed each time a positive current and a negative current are applied and cut off.
And providing an electromagnetic braking unit that applies a braking force to the optical axis unit by forming one of the stable states.The electromagnetic braking unit applies braking from near the focus position and reaches the focus position. Later, the optical axis unit is interrupted by current.
An electromagnetic braking mechanism for a film surface moving type autofocus camera, which is locked when disconnected . 2. The electromagnetic braking unit according to claim 1, wherein, when performing fine adjustment of a focus position, the optical axis unit is applied with a short positive and negative repetitive pulse drive current from near the focus position.
2. The electromagnetic braking mechanism according to claim 1, wherein step braking is performed .