JPH0424625A - Device for keeping film surface flat - Google Patents

Abstract

PURPOSE:To obtain the effect of strong attraction irrespective of a small capacity by forming a magnetic circuit of a movable coil and a flat type ring magnet which is magnetized in the thickness direction. CONSTITUTION:When an attraction starting signal is outputted by a camera controller CPU 21 in a camera main body, transistors 24 and 25 are made to be in a conductive state by driving circuits 22 and 23. Instantaneous currents i1-i2 as driving currents and holding current i2 as the driving current are respectively supplied to a coil 9 by the transistors 24 and 25. The driving current i1 flows in the movable coil 9 by actuating a current driving circuit in such a way, and the magnetic circuit is formed between a permanent magnet, a yoke and a case. Then, the movable coil 9 is attracted in a right direction according to Fleming's rule on a left hand, a coil plate is made to abut on the side surface of the yoke, and attracted so as to be held. Thus, the effect of the strong attraction can be obtained irrespective of the small capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a film flatness holding device that suction-holds the back surface of a film so that the film surface becomes flat during photographing.

(Prior Art and Problems to be Solved) A film holding mechanism of a conventional camera called a tunnel type is shown in FIGS. 7 and 8.

FIG. 7 is a sectional view including the optical axis of a conventional single-lens reflex camera, and FIG. 8 is an enlarged view showing the relationship between a film, a film aperture portion, and a pressure plate.

The pressure plate 54 is in pressure contact with a pressure plate rail 53 on the body side, and the upper and lower ends of the film 55 are pressed against the film rail 52 to ensure the flatness of the film.

Since this conventional holding mechanism restricts only the upper and lower ends of the film, it is a structure in which the vicinity of the center of the film tends to lift up and a gap of ΔL is inevitably generated.

This gap of ΔL may not be ignored depending on the environmental conditions such as temperature and humidity or the material of the film, and it cannot be ignored even when photographing with a shallow depth of focus is performed using a high-performance lens.

Therefore, the inventors of the present invention have already proposed an apparatus for suctioning and holding a film on a pressure plate to maintain its flatness, which should solve the above-mentioned problem.

This film suction/holding device has a large number of small through-holes in the pressure plate to form a variable sealed space on the back side of the pressure plate, and uses an electromagnetic drive device to fill this variable sealed space with suction to bring the center of the film into close contact with the pressure plate. This is to ensure flatness.

This film suction/holding device is applied to a camera, and in particular, the electromagnetic drive device described above must have a small capacity and a strong driving force.

In general, electromagnetic drive devices can be thought of as those that obtain driving force using a moving coil and a fixed coil, or those that obtain driving force using a coil and a permanent magnet.

As a result of various experiments, the inventor of the present invention found that in order to obtain the specified driving force with the former, the coil is larger than with the latter, and that it is not suitable for application to cameras, and that a combination of a coil and a permanent magnet is required. was found to be desirable. The coil is wound in a ring shape, and in order to make effective use of the lines of magnetic force generated from the coil, a ring shape is best for the permanent magnet, and in order to reduce the number of parts, it is better to use a single ring magnet rather than multiple magnets. It is desirable to provide a Furthermore, it is much more advantageous in manufacturing a ring magnet to be magnetized in the thickness direction than in the radial direction.

(Means for Solving the Problems) In view of the above-mentioned circumstances, the present invention provides a fixed container having a ventilation hole communicating with the through hole in the pressure plate of a camera having a small through hole, and the above-mentioned a variable container forming a variable sealed space with an opening leading to a ventilation hole; a movable coil that applies electromagnetic force in a direction to expand the volume of the variable container;
It is composed of a flat ring magnet fixedly disposed opposite to the movable coil and magnetized in the thickness direction, and a spring that constantly applies an urging force to the variable container in a direction to reduce its volume.

(Example> Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing an embodiment of a mechanism section of a film flatness holding device according to the present invention. In this figure, the state before film suction is shown above the center line, and the state during film suction is shown below.

A pressure plate 4 attached to the back cover of a camera (not shown) has rails 3 above and below the surface where the film aperture is provided.
It is pushed to 3.

The upper and lower ends of the film 16 are regulated by a rail 2.2 and a pressure plate 4 provided inside the rails 3, 3.

A large number of through holes 4a of the film suction reservoir are provided near the center of the pressure plate 4.

The outer periphery of the suction rubber 6 that forms the variable sealed space is airtightly fixed to the stepped portion 15b of the shield plate 15 together with the case 11, and the shield plate 15 and the case 11 form an integrated fixed container that is airtightly attached to the back side of the pressure plate. Fixed in condition.

At the center of the shield panel 15 is a ventilation hole 1 that communicates with the through hole 4a.
5a is opened, and a suction action plate 5 is fixed in an airtight manner to the center of the suction rubber 6. Therefore, air enters and exits through the through hole 4a and the ventilation hole 15a.

A bolt-like thread is carved on the outer periphery of the bearing portion 5a of the suction action plate 5, and the coil plate 8 is attached to the suction action plate 5 by a nut 7.
is attached to. The bearing portion 5a is provided with a hole 5c through which a shaft 11a protruding from the case 11 is inserted, and the suction plate 5 is provided so as to be movable left and right using the shaft 11a as a guide.

A moving coil 9 is provided on the coil plate 8, and a ring-shaped permanent magnet 13 that exerts a magnetic effect with the moving coil 9 is fixed to the inside of the case 11. Furthermore, a ring-shaped yoke 12 is mounted on the permanent magnet 13. It is fixed. This flat ring magnet 13 is a rare earth magnet with a thickness of 2 mm, an inner diameter of 10 mm, and an outer diameter of 20 mm.

A spring 17 is provided between the nut 7 and the inner surface of the case 11, and this spring 17 causes the suction action plate 5, the suction rubber 6,
The movable coil 9 is always biased toward the left.

The magnetic circuit forming section includes a ring-shaped permanent magnet 13 attached to a case 11, an annular yoke 12, and a moving coil 9.

Although not shown, a ventilation hole communicating with the outside air is opened inside the case 11 .

With this structure, each member takes the position shown in the upper part of the first column before film suction, and when current flows through the movable coil 9, takes the position shown in the lower part.

FIG. 2 is a circuit diagram showing an embodiment of the current drive circuit of the film flatness holding device according to the present invention, and FIG. 3 is a diagram showing the switching shape of the drive current flowing through the coil.

The current drive circuit is a circuit that applies an attractive force only during film exposure. Contacts 42a, 42 from the camera body side
Vcc power is supplied to the back cover side through the terminals b, 43a, and 43b. Control signals are provided by contacts 27a, 27b, 28a
, and 28b. When the camera control CPU 21 of the camera body outputs a suction start signal, the drive circuits 22 and 23 turn on the transistors 24 and 25. The transistors 24 and 25 supply the coil 9 with an instantaneous current (il - i2 ) that is a drive current and a holding current 12 that is a drive current, respectively.

Due to the operation of the current drive circuit, the i1 drive current flows through the moving coil 9, and a magnetic circuit is formed between the permanent magnet 13, the yoke 12, and the case 11. According to Fleming's left hand rule, the moving coil 9 is attracted to the right in FIG. 1, and the coil plate 8 comes into contact with the side surface of the yoke 12,
It will be held under suction.

The value of the drive current 11 is a current value that can generate a force capable of attracting the coil 8 to the surface of the yoke 12 against the spring 17 according to Fleming's left-hand rule.

When time t1 has elapsed, the CPU 21 turns off the transistor 24 and cuts off the drive current <il-i2>.

After this, the drive current 1 supplied from the transistor 25 is
Only 2 flows into the coil 9 and continues to attract and hold the film.

The drive current 12 is the current flowing through the transistor 25 through the resistor R.
This is a small current created by limiting the current to the drive current 11, and is the minimum current required to attract and hold the coil 8.

When the exposure of the shutter is completed, the CPU 21 turns off the transistor 25 and cuts off the drive current I2 of the coil 9.

By cutting off the drive current 12, the magnetic circuit disappears, the coil plate 8 is released from the attraction restraint, and the spring 17 returns it to its original position.

As can be seen from FIG. 3, the drive current 11 for the attraction effect is made large, its pulse width is made very short, and the holding current j2 after the coil plate 8 is attracted is made small.

Since the structure is as described above, if the film is suctioned with a strong force, depending on the quality of the film, it will be sucked into the suction hole, and the film that was in the position shown in Figure 6 (a) will be moved to the position shown in Figure 6 (b). As shown in Figure 6(c), the holes are dented, which impairs the flatness of the pressure plate surface after suction, but since the film is suctioned and held with a weak force after suction, as shown in Figure 6(c).
Good flatness can be maintained as shown in FIG.

FIG. 4 is a circuit block diagram showing another embodiment of the current drive circuit.

Generally, the power supply voltage of a camera decreases with use. Therefore, the drive current ix for initial attraction becomes smaller as the power supply voltage decreases, making it impossible to obtain sufficient attraction energy.

In this embodiment, taking this point into consideration, the pulse width of the drive current for suction is changed so that the suction energy is always constant.

A short pulse drive current is supplied to the coil while the power supply voltage is high, and a long pulse drive current is supplied to the coil when the voltage drops.

The difference between this embodiment and the embodiment shown in FIG. 2 is that a bleeder resistor 30 is inserted between the power supply voltage and the ground,
detects the power supply voltage and sends the detected voltage signal to the CPU3.
2, and the pulse width of the drive current for suction is calculated by the CPU 32 so that the suction energy is always constant. Further, a constant flow path 36 is connected to the control terminal of the transistor 39 through which the holding current flows, so that a constant drive current IC for the attraction and holding action is always caused to flow regardless of voltage fluctuations.

The bleeder resistor 35 is a resistor for determining the current value of the constant current circuit 36.

Other configurations are the same as in FIG.

FIG. 5 shows an example in which the pulse width of the drive current for the attraction effect is varied as the power supply voltage decreases. When the power supply voltage is high, the drive current ix is large, so its pulse width tx is shortened, and as the power supply voltage decreases, the drive current is decreased stepwise and the pulse width is increased.

(Effects) As explained above, the film flatness holding device according to the present invention forms a magnetic circuit with a moving coil and a flat ring magnet that is magnetized in the thickness direction, so it can achieve a strong attraction effect with a small capacity. I can give it to you.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the mechanical part of the film flatness holding device according to the present invention, FIG. 2 is a circuit block diagram showing an embodiment of the current drive circuit of the film flatness holding device according to the present invention, and FIG. is a diagram showing an example of the drive current characteristics in FIG. 2, FIG. 4 is a circuit block diagram showing another embodiment of the current drive circuit, and FIG. 5 is a diagram showing an example of the drive current characteristics in FIG. 4. , FIG. 6 is a partial cross-sectional view of the pressure plate portion for comparing the film flatness of the present invention and a conventional example, FIG. 7 is a cross-sectional view including the optical axis of a conventional single-lens reflex camera, and FIG. The relationship between the film aperture section and the pressure plate [Figure 9 is an enlarged view of the system, and is a diagram showing the relationship between the suction force and the distance of the film to the pressure plate6 21° 22° 24゜52... Film rail 53... Pressure plate rail 54... Pressure plate, 5... Suction action type/suction rubber, 7... Nut/coil plate, 9... Moving coil... case, 12...・Yoke permanent magnet, 15 ・Shield block 55 ・Film 32 ・CPU (control unit) 23.37・Drive circuit 25.38.39.・Transistor, voltage detection part, constant current circuit patent applicant Kyoseji Co., Ltd. Fig. Fig. Fig. 1 (Initially, use a strong force - be careful) (b) (C) (!! Strong force τ suction wound I7 (In the case of entanglement with a weak force) Fig.

Claims (1)

[Scope of Claims] A camera pressure plate having a small through hole; a fixed container disposed on the back side of the pressure plate and having a ventilation hole communicating with the through hole; and a fixed container provided in the fixed container through the ventilation hole. a variable container forming a variable sealed space; a movable coil provided in the fixed container and applying an electromagnetic force in a direction to expand the volume of the variable container; A film flatness holding device comprising a magnetized flat ring magnet and a spring that constantly applies an urging force to the variable container in a direction to reduce its volume.