GB2095852A - Aperture setting - Google Patents

Abstract

The aperture of a shutter diaphragm is set up by means of ram 12, leaf spring 14 and non-elastic ribbon 19 which connects leaf spring 14 and tension spring 34 and which passes between braking means comprising magnetic poles 17/18 and armature plate 22 and through hole 35 in swivel lever 29 biased by spring 30, the biased movement of lever 29 being controlled by cam 31. Spring 34 is connected at one end to lever 29 near spring 30 and rests at the other end against lever heel 29', ribbon 19 being connected to spring 34 at an intermediate resilient area thereof. <IMAGE>

Description

SPECIFICATION Camera shutter mechanism The invention relates to a mechanism for the control of a shutter in a photographic camera.

The invention is an improvement upon that disclosed and claimed in German Patent Specification No. 2939770. This in turn was based on prior art such as that described in German Offenlegungsschrift No.

2257608. In the latter, the stopping element for the shutter drive takes the form of a brake disc offer- romagnetic material which is mounted on a flexible shaft and on the circumference of which the magnetic poles of an electromagnet are arranged with a narrow gap distance. Connected with the brake disc is a pinion meshing with a toothed rack which in turn is arranged on the drive member shaped as an axially movable switching rod. The electromagnet is controlled by the light metering facility and receives an excitation current pulse when the shutter has reached the position corresponding to the prevailing brightness of the object, i.e. when the light falling through the aperture remaining will give accurate illumination of the photographic picture. The magnetic field forming at the magnetic poles when the magnet is excited closes over the brake disc.Due to the flexible shaftthe brake disc is attracted and brought to a halt mechanically at the pole surfaces of the electromagnet. The rotating brake disc thus represents the armature of the electromagnet and is part of the magnetic circuit.

With a stopping device ofthis kind considerable shutter setting errors occur, the actual shutter setting deviating from the required setting which it occupied at the moment at which the stopping signal was supplied to the electromagnet. The cause for these setting errors lies above all in the great mass of the brake disc which cannot be stopped instantlyas required - but only with a certain delay. On the other hand the mass of the brake disc can be restricted only to a limited extent, since the magnetic flux of the electromagnet closing over the brake disc requires the brake disc to be of an adequate thickness. Tolerances between the rack and the pinion driving the brake disc are another case of delay leading to setting errors.

In the device described in German Patent Specification No. 2939770, the braking member has a minimal mass with correspondingly small inertia without adversely affecting the magnet core of the electromagnet. The braking element may be halted instantly and without delay. Overswinging of the braking element as can be observed with the known brake disc does not occur. Due to the direct and rigid connection of the stopping element with the drive member, even drive members with a relatively large mass can be stopped quickly and instantly. Any overrunning of the shutter beyond the required aperture is thus safely prevented. Since the distance of the armature plate from the pole surfaces is exclusively determined by the very thin braking element, the electromagnet has practically no working distance and therefore an extremely short reaction time.

On the one hand the tension spring ensures that the low mass stopping tape is always taut, and on the other hand the mass of the tension spring can in no way affect the stopping process.

The retarding mechanism has the advantage that a certain aperture characteristic conditional upon the design of the lenses, in the particular the variety of interchangeable lenses, can be maintained. Tests with inter changeable lenses of different types and makes on which the aperture is set by means of an aperture ram axially movable in the lens have shown that on each lens the function of opening the shutter as a function of the ram path follows a different line.

It became for example evident that the shutter ram must not be driven at random speed but that the motion - time - function of the shutter ram must follow a certain characteristic line; failing this shutter opening and shutter ram path will no longer exactly coincide with each other so that for example the shutter opening might have a small lead over the shutter ram path. In this case the braking device would for example stop the drive member and thus the shutter ram instantly when the required aperture has been reached. But since the diaphragm leaves forming the aperture did not make accurate contact with the shutter ram, but due to their speed had a certain lead over it, these fall back when the shutter ram is halted and the aperture would vary from the required aperture, i.e. it would be too largeortoo small. Setting errors in reverse direction occur.By a corresponding design of the retarding mechanism according to the invention, a certain ideal speed control of the drive member and thus of the shutter ram is possible for all interchangeable lenses, which advantageously is initially very great after a start-up phase and then decreases as the displacement path of the shutter ram increases. Due to the retarding mechanism acting upon the tensioning element of the braking element at a point beyond the electromagnet, any influence from the retarding mechanism, usually carrying great mass, upon the stopping procedure of the drive member is prevented. The stopping and driving mechanism according to the invention for the lens shutter is thus not affected in its advantageous operation by the introduction of the retarding mechanism.

In the invention described in German Patent Specification No. 2939770, the tension spring for the braking element takes the form of a leaf spring which at one end is attached to that side of the swivel lever which faces away from the drive member, and at the other free end flexes away from it. The braking element passes through an opening in the swivel lever and is fastened to the free end of the leaf spring. The swivel lever is in contact with a control cam of the holding mechanism controlling the drive member, whereby the control cam is shaped as a driven cam disc. Furthermore a swivel lever spring is provided acting upon the swivel lever in drive direction.

At the start of the aperture setting procedure the control cam of the holding mechanism will initially rotate. The drive spring which is connected with the swivel lever by means of the braking element will swing in drive direction of the shutter ram due to its initial tension. This causes the shutter ram to move in drive direction, and the shutter of the interchangeable lens will gradually close. The drive speed of the drive spring at the shutter ram is controlled by the control cam of the retarding mechanism via the stopping tape and the swivel lever. As soon as the required aperture setting has reached, which is calculated by a so-called automatic aperture system from the given exposure, the set sensitivity of the film and the prevailing brightness of the object, the automatic aperture system will supply the electromagnet with a stopping signal.The excitation coils of the electromagnet carry a direct current; the electromagnet attracts the armature plate with a relatively strong force, and the braking element is pushed by the armature plate against the pole surfaces of the magnetic poles. The braking element is arrested instantly and without delay and acts as an instant brake upon the drive spring. The movement of the shutter ram and thus the opening or closing of the shutter is thus terminated at the same moment at which the automatic aperture system generates the stopping signal. The control cam ofthe retarding mechanism will continue to rotate despite the fact that the braking element has been arrested. Due to the swivel lever spring the swivel lever follows the movement of the control cam and continues to swivel, although at a reduced rate.Due to the tension spring provided on the swivel lever the section of the braking element between electromagnet and tension spring is kept taut despite swivelling of the swivel lever.

This device according to German Patent Specification No. 2939770 leads to enormous advantages as compared to previously known embodiments, but thorough tests have revealed one disadvantage: the braking element acts upon the free end of the tension spring; this free end is, however, flexed away from the swivel lever, so that the point of action in relation to the swivel lever does not have a clearly defined position. As a result varying aperture settings may be obtained due to variations in the resisting force of the shutter ram.

The invention provides a mechanism for the control of a shutter in a photographic camera, the mechanism comprising a drive spring pre-tensioned in the drive direction; a braking device for arresting the motion of the drive spring, the braking device comprising an electromagnet, an armature plate arranged to be attracted to the poles of the electromagnet when the latter is excited and a nonelastic ribbon having ferromagnetic properties, the ribbon being attached at one end to the drive spring and passing between the poles of the electromagnet and the armature plate; a swivel lever under the control of a retarding device; and a tension spring, one end of which is attached to the side of the swivel lever remote from the drive spring and the other end of which rests against a heel of the swivel lever, whereby there is à resilient area between the ends of the tension spring, the ribbon passing through an opening in the swivel lever and being fastened to the resilient area of the tension spring. The ribbon no longer acts upon the free end of the tension spring but upon its central area. When the shutter ram is operated, the free end of the spring is always in contact with the heel of the swivel lever so that the tension spring occupies an accurately defined position in relation to the swivel lever. The free running function is maintained.As the ribbon acts upon the resilient area ofthetension spring, it is ensured that the coupling of the stopping tape to the swivel lever remains elastic and does not become rigid. Aperture setting errors are further reduced as compared to the device according to German Patent Specification No.

2939770.

The invention also provides a mechanism for the control of a shutter in a photographic camera, the mechanism comprising a drive spring pre-tensioned in the drive direction; a braking device for arresting the motion ofthe drive spring, the braking device comprising an electromagnet, an armature plate arranged to be attracted to the poles of the electromagnet when the latter is excited, and a brake leaf having one end free and the other end attached to a camera ram acted upon by the drive spring, the camera ram acting on a shutter ram, the brake leaf passing between the poles of the electromagnet and the armature plate; and a swivel lever acted upon by the drive spring and under the control of a retarding device. The braking element is unsupported on one side and attached to the camera ram without an additional tensioning facility.Tests have confirmed that the brake leaf may be sufficiently thin and yet have sufficient resistance to mechanical buckling.

This alternative solution has the additional enormous advantage that the tensioning facility necessary forthe stopping device may be altogether omitted so that the swivel lever may now be arranged directly between braking device and shutter ram, i.e. in the front of the camera housing directly behind the lens. The space requirement for this device is therefore considerably reduced.

The drive spring could again take the form of a leaf spring, but is preferably a leg spring wound around the pivot of the swivel lever, the free end of which is pushed loosely th rough a recess in the camera ram..

The camera ram and with it the brake leaf attached to it may thus be arranged in a straight line, whereas in the first alternative solution the ribbon moves in a slightly bow-shaped line due to the swivel movement of the drive spring and the swivel lever. Since the brake leaf follows an exactly straight line, it may be arranged directly parallel to and at a short distrance from the pole surfaces of the electromagnet.

The drive spring is not attached to the swivel lever, but is arranged between stopping device and swivel.

lever, with its free end in flexible contact with a heel coupled with the swivel lever and forming a resilient area between its two ends which is acted upon by the brake leaf of the camera ram. The swivel lever is also acted upon in drive direction by a swivel lever spring and may be arrested in its original position by means of a liftable stop latch.

When the latch is lifted, the swivel lever is released and moves in drive direction towards the lens because it is under the influence of the tensioned drive spring in contact with the said heel. The drive spring following the swivel movement takes the camera ram with it in the direction of the shutter ram, which in turn sets the lens shutter in motion. At the moment of excitation of the electromagnet the stop leaf and thus the camera ram are stopped. At the same moment the camera ram is stopped the drive spring is also stopped. Since the swivel lever continues to move underthe influence from the swivel lever spring, the heel of the swivel lever becomes detached from the drive spring. However, due to the resilient area between camera ram and heel, the drive spring does not become detached instantly, but gradually.The electromagnet is therefore not required to use all of its braking power immediately, but has sufficient time to fully build up the magnetic field.

The resilient area of the drive spring described above does not only have the advantage of allowing the electromagnet to build up its power, but also of advantageously cushioning the impact when the camera ram lands on the aperture ram and of being capable of substantial adaptation to the intrinsic dynamics of the lens mechanism.

In a convenient embodiment the heel provided on the swivel lever may be adjustable in its height and/or its distance from the pivot of the swivel lever.

In this way an optimal compromise may be reached between ideal path requirement (where the retarding mechanism is rigidly connected to the swivel lever) and the ideal power supply (the drive spring is extremely long and flexible) without having to giveup the advantages of a free running function.

In a preferred embodiment the retarding mechanism is an electromagnetic brake timing the movement of the swivel lever. Advantageously this consists of a brake leaf with ferromagnetic properties attached on one side to the swivel lever, which moves past magnetic poles of an electromagnet and may be locked by magnetic excitation by means of an armature plate which is arranged directly opposite the magnetic poles on the side of the brake leaf facing away from the magnetic poles. The electromagnetic brake thus essentially corresponds to the construction of the stopping device. In addition, however, a sensor picking up the movement of the brake leaf has been conveniently provided to control the excitation of the magnet by means of a controller.The sensor in this case may take the form of an opto-electronic photocell and pick up the motion time - function from a special contour of the brake leaf. This contour may have an advantageous influence upon the dynamics of the shutter movement.

Advantageously the brake leaf is arranged in the swivel plane of the swivel lever so that the brake leaf is guided absolutely parallel to the pole surfaces of the electromagnet.

In an advantageous further development the heel provided on the swivel lever is part of the working shutter lever which is pivotable about the pivot of the swivel lever, may be coupled with the swivel lever by means of a coupling element and may be removed from the working path of the drive spring by operating a working shutter button to disconnect the coupling. With this arrangement it is advantageous if the coupling element is a coupling spring which is attached to the swivel lever and which pushes the working shutter lever contrary to the drive direction into its coupling position with a force which is slightly larger than that of the drive spring.

Due to the additional force applied to the end of the lever when operating the working shutter button, the initial tension of the coupling spring is overcome; the drive spring is able of moving together with the camera ram in the direction of the lens. During this movement the swivel lever may remain in its locked position behind the latch.

The invention is illustrated by the drawings of which: Figure 1 is a schematic side elevation of a camera shutter mechanism according to the invention; Figure 2 is a schematic side elevation of a further embodiment of 9 camera shutter mechanism according to the invention; and Figure 3 is a schematic side elevation of an arrangement for a working shutter button incorporable in the mechanism of Figure 2.

With reference to Figure 1 of the drawings, an interchangeable lens assembly 11 is screwed onto a camera housing 10 in the known manner. The interchangeable lens assembly 11 contains an axially movable shutter ram 12 by means of which the diaphragm leaves (not shown) ofthe interchange- able lens assembly 11 may be operated to change from the shutter-open to the shutter-closed condition and vice versa. The displacement path of the shutter ram 12 and the diameter of the aperture have a fixed relationship which is governed by the lens construction.

The drive mechanism for the shutter ram 12 comprises a drive member 13 which takes the form of a drive spring 14 pre-tensioned in the drive direction (arrow A) of the shutter ram 12. When the interchangeable lens assembly 11 is attached, the drive spring 14, which in this embodiment is a leaf spring, is in direct contact with the free end of the shutter ram 12 when in its original position, with the shutter in the open position.

The drive member 13 is acted upon by a braking device 15 which comprises an electromagnet 16 with magnetic poles 17 and 18, a braking element 19 coupled with the drive member 13, and an armature plate 22. In this embodiment the braking element 19 takes the form of a non-elastic ribbon 26. This moves past the surfaces 24 and 25 of the magnetic poles 17 and respectively 18 and may be halted by excitation of the excitation coils 20 and 21. The armature plate 22 is movably arranged directly opposite the magnetic poles 17 and 18, and rests under tension against the side of the stopping element 19 facing away from the magnetic poles 17 and 18. With this arrangement the armature plate 22 may be attached in a simple way to a stationary leaf spring 23.The latter is designed such that the initial stressing force for the armature plate 22 is very small, so that the friction force between armature plate 22 and the braking element 19 on the one hand and the magnetic poles 17 and 18 and the braking element 19 on the other hand are also very small when the electromagnet 16 is not excited. The braking element 19 is directly and firmly connected with the drive element 13 and designed such that its thickness (the dimension at right angles to the armature plate surface) is very small, preferably as small as is compatible with requisite mechanical strangth.

As shown in Figure 1 the ribbon 26 is acted upon at its lower end by a tension spring 34 which keeps it taut. The spring tension spring 34 is smaller than and opposed to the initial stressing force of the drive spring 14. The tension spring 34 is arranged on a swivel lever 29 tensioned in the drive direction of the drive spring 14. The swivel lever 29, under pressure from a swivel lever spring 30 acting in the drive direction of the drive spring 14, rests against the control cam 31 of a mechanical retarding mechanism 32.

The latter controls the speed of the automatically operating drive member 13 according to a pre-set function which produces a corresponding shutter ram speed as required by the shutter mechanism of the interchangeable lens assembly 11. Normally the shutter ram characteristic is not linear so that the shutter ram 12, after a start-up phase, is initially driven with great speed which must progressively decrease as the aperture becomes smaller. Such a motion-time characteristic of the drive member 13 can be achieved with the control cam 31 of the retarding mechanism 32, which control cam rotates about an eccentrically arranged axis 33.

At one of its ends the tension spring 34 is fixed to that side of the swivel lever 29 which faces away from the drive member 13, whilst the other, free, end 34" of the tension spring 34, under the influence from the drive spring 14, rests against a heel 29' of the swivel lever 29. Between its two ends the tension spring 34 has a resilient area 34' which is acted upon bythe ribbon 26 which passes through an opening 35 in the swivel lever 29.

Immediatley prior to the aperture setting procedure, the drive mechanism and the stopping device 15 occupy the positions shown in Figure 1.

Figure 2 shows a second embodiment of the invention. The stopping element 19 takes the form of a leaf 60 of which one end is free and the other is attached to a camera ram 12' which acts upon the shutter ram 12 and is itself acted upon by the drive spring 14. The latter passes loosely through a recess 12" in the camera ram 12' and is stressed with its free end 14" against a heel 29' of the swivel lever 29.

The drive spring 14 has a resilient area 14' between its free end 14" and the point which is acted upon by the camera ram 12'.

The swivel lever 29 in this embodiment is arranged between the stopping device 15 and the shutter ram 12, whiist the drive spring 14 lies between the stopping device 15 and the swivel lever 29.

In the drive direction A the swivel lever 29 is acted upon by a swivel lever spring 30 and is locked in its original position by a iiftable latch 69. Furthermore a resetting facility 68 is provided for the return of the swivel lever 29 to its original position.

In contrast to the embodiment of Figure 1, the retarding mechanism 32 is an electromagnetic brake timing the movement of the swivel lever 29. The electromagnetic brake comprises a brake leaf 61 with ferromagnetic properties attached on one side to the swivel lever 29 and extending past the magnetic poles 63 and 64 of an electromagnet 62 and which may be stopped by magnetic excitation via a movable armature plate covered in the drawing by the brake leaf 61 and therefore not illustrated. The armature plate lies directly opposite the magnetic poles on that side of the brake leaf 61 facing away from the magnetic poles 63 and 64.

The movement of the brake leaf 61 is picked up by a motion or speed sensor 65 which controls the electromagnet 62 via a controller 66. The sensor 65 takes the form of an opto-electronic photocell which picks up the motion-time function from a special contour 67 of the brake leaf 61. Figure 2 shows that the brake leaf 61 lies in the swivel lever plane of the swivel 29.

Figure 3 shows a proposal for the function of a working shutter button. The heel 29' provided on the swivel lever 29 is designed here as part of a working shutter lever 40 which is pivotable about the pivot 29" of the swivel lever 29 and of which a stopping edge 40" is brought into contact with the swivel lever 29 by a coupling element 41 in the form of a coupling spring and is coupled with it in this way.

The coupling is ensured by the fact that the initial stressing force of the coupling spring 41 is larger than the initial stressing force of the drive spring 14.

Figure 3 shows that the lever 40 is shaped as an angle lever. If the smaller angle arm 40' is then acted upon by an additional force by operating a working shutter button in the direction of arrow A, the initial stressing force of the coupling spring 41 is overcome; the drive spring 14 together with the camera ram 12' is able to move in the direction of the lens and to operate the lens shutter Whilst this movement is carried out the swivel lever 29 may remain locked behind the latch 69.

Claims (19)

1. A mechanism for the control of a shutter in a photographic camera, the mechanism comprising a drive spring pre-tensioned in the drive direction; a braking device for arresting the motion of the drive spring, the braking device comprising an electromagnet, an armature plate arranged to be attracted to the poles of the electromagnet when the latter is excited and a non-elastic ribbon having ferromagnetic properties, the ribbon being attached at one end to the drive spring and passing between the poles of the electromagnet and the armature plate; a swivel lever under the control of a retarding device; and a tension spring, one end of which is attached to the side of the swivel lever remote from the drive spring and the other end of which rests against a heel of the swivel lever, whereby there is a resilient area between the ends of the tension spring, the ribbon passing through an opening in the swivel lever and being fastened to the resilient area of the tension spring.

2. A mechanism according to claim 1 in which the swivel lever rests against a control cam of the retarding mechanism.

3. A mechanism for the control of a shutter in a photographic camera, the mechanism comprising a drive spring pre-tensioned in the drive direction; a braking device for arresting the motion of the drive spring, the braking device comprising an electromagnet, an armature plate arranged to be attracted to the poles of the electromagnet when the latter is excited, and a brake leaf having one end free and the other end attached to a camera ram acted upon by the drive spring, the camera ram acting in a shutter ram, the brake leaf passing between the poles of the electromagnet and the armature plate; and a swivel lever acted upon by the drive spring and under the control of a retarding device.

4. A mechanism according to claim 3 in which the swivel lever is arranged between the braking device and the shutter ram.

5. A mechanism according to claim 3 or claim 4 in which the drive spring is arranged between the braking device and the swivel lever and at its free end flexibly contacts a heel ofthe swivel lever whereby the area between its ends which is acted upon by the brake leaf through the camera ram is resilient.

6. A mechanism according to claim 5 in which the drive spring passes loosely through a recess in the camera ram.

7. A mechanism according to any of claims 1,2,5 or 6 in which the heel provided on the swivel lever is adjustable in the height by which it extends from the swivel lever and/or in its distance from the pivot of the swivel lever.

8. A mechanism according to any of the preceding claims in which a swivel lever spring acts upon the swivel lever in the drive direction.

9. A mechanism according to any preceding claim further comprising a latch for locking the swivel lever.

10. A mechanism according to any of claims 3 to 9 in which the retarding mechanism is an electromagnetic brake timing the movement of the swivel lever.

11. A mechanism according to claim 10 in which the electromagnetic brake comprises an electromagnet, an armature plate arranged to be attracted to the poles of the electromagnet when the latter is excited and a brake leaf having ferromagnetic properties, which brake leaf is attached at one end to the swivel lever and extends between the armature plate and the poles of the electromagnet.

12. A mechanism according to claim 10 or claim 11 in which the excitation of the electromagnet is controlled in response to a sensor provided to sense the movement of the brake leaf.

13. A mechanism according to claim 12 in which the sensor is an opto-electronic photocell and senses the motion-time function from a special contour of the brake leaf.

14. A mechanism according to any of claims 11 to 13 in which the brake leaf lies in the swivel plane of the swivel lever.

15. A mechanism according to any preceding claim further comprising a resetting facility for returning the swivel lever to its original position.

16. A mechanism according to any preceding claim in which the heel provided on the swivel lever is part of a working shutter lever which is pivotable about the pivot of the swivel lever, is couplable by a coupling element with the swivel lever and is steerable out of the drive path of the drive spring by operating a working shutter button to disconnect the coupling.

17. A mechanism according to claim 16 in which the coupling element is a coupling spring attached to the swivel lever and pushing the working shutter lever contrary to the drive direction into its coupling position with a force which is slightly larger than that of the drive spring.

18. A mechanism forthe control of a shutter in a photographic camera, the mechanism being substantially as described herein with reference to Figure 1 of the drawings.

19. A mechanism for the control of a shutter in a photographic camera, the mechanism being substantially as described herein with reference to Figure 2 of the drawings.