Electromagnetic Drive For Photographic Shutters

Abstract

An electromagnetic drive for the blades of a photographic shutter, using at least one pot-shaped magnet in fixed position. A cylindrical coil, when properly energized, moves into or out of the pot-shaped magnet. The coil is connected directly to a movable shutter blade in one embodiment, or to a blade operating member (such as a rotatable ring) in another embodiment. To obtain faster exposures, the moving parts engage a resilient stop when the shutter reaches fully open position, and this resilient stop absorbs some of the kinetic energy of the opening movement and gives it back to the moving parts in a closing direction.

Parent Case Text

This is a division of application, Ser. No. 88,849, filed Nov. 12, 1970.

Description

BACKGROUND OF THE INVENTION

Electromagnetic drives for shutters are known, broadly. The present invention provides an improvement in this broad class of drives. It has been found, according to the present invention, that better results can be obtained if, instead of the conventional electromagnetics, the drive comprises one or more magnets having thin annular gaps, such magnets being herein described as pot-shaped, in conjunction with a hollow cylindrical coil movable axially through the narrow gap or slot of each magnet, when the coil is electrically energized. The moving coil may be operatively connected to the movable shutter blade, either through intermediate operating mechanism (e.g., a blade ring for operating several pivoted shutter blades) or directly to a shutter blade without any intermediate mechanism.

The use of a pot-shaped electromagnet in stationary position with a coil operatively connected to a shutter blade, enables the shutter to have operating mechanism of relatively low mass, since the coil itself can be very light although adequately strong to perform its function. Moreover, the magnet may be so shaped that the force produced upon energizing the coil is uniform throughout the entire stroke of the coil.

An object of the invention is the provision of a generally improved and more satisfactory shutter drive of the general character above mentioned.

Another object is the provision of such a drive so designed that it is relatively inexpensive and easy to manufacture and to install in the shutter.

Still another object is the provision of a shutter drive so designed that such a drive may be used to power two or more shutter blades, or alternatively, an individual electromagnetic drive of this character may be used for each individual shutter blade.

A further object is the provision of a shutter so designed that at the end of the opening movement, the moving parts engage with one or more resilient or elastic members which absorb the kinetic energy of the opening movement and give such energy back to the parts in a closing direction creating a "bounce" effect which assists in speeding up the shutter operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a fragment of an objective shutter according to a first embodiment of the invention, with parts in elevation and parts in vertical section;

FIG. 2 is a section taken approximately on the line II--II of FIG. 1;

FIG. 3 is a schematic front view of a fragment of a different type of shutter, illustrating a second embodiment of the invention;

FIG. 4 is a schematic view, partly in elevation and partly in section, of a third embodiment of the invention, illustrating the coils of the electromagnet connected directly to the shutter blades;

FIG. 5 is a similar view of a fourth embodiment of the invention, illustrating an arrangement in which the coil of the electromagnet is directly connected to a pivoted blade; and

FIG. 6 is a view similar in general to FIG. 1, illustrating the additional feature of elastic members to assist in quick return of the shutter parts from open position to closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIGS. 1 and 2, there is shown only a fragment of an objective shutter which, except for the electromagnetic drive parts, may be of conventional construction. Thus it may include a conventional base plate 101 and an aperture plate 103, these two plates having aligned openings through them which define the exposure aperture. The plates are axially spaced from each other as usual, providing a space between them for receiving the conventional pivoted shutter blades 105 commonly found in objective shutters, there usually being about five such blades although the number may vary. The blades are mounted in the usual conventional way for swinging movement between open and closed positions, the swinging of the blades being accomplished by rotary movement of the usual blade ring 111, mounted for rotation about the optical axis as a center. In some objective shutters, the blades are mounted on pivot pins, and pins are fixed to the blade ring to engage in slots in the blades to cause swinging movement of the blades when the blade ring is rotated. In other shutters, the blades are mounted on pivots fixed to the blade ring, and the slots in the blades engage other pivots mounted on another part of the mechanism, for causing swinging of the blades when the blade ring is rotated relative to the other part on which the other pivots are mounted. For purposes of the present invention, it is entirely immaterial which of these arrangements is used for mounting the blades, or whether some other known arrangement for mounting the blades is used, since the invention (in this first embodiment thereof) relates only to the manner in which the blade ring is driven and is independent of the manner in which the blades themselves are mounted. Merely as a convenient example, FIGS. 1 and 2 illustrate a typical construction in this respect, the blades 105 being mounted on fixed pins 114 and having slots 113 (FIG. 6) for engaging the pins on the blade ring 111.

The electromagnetic drive of the present invention, which serves to drive the blade ring 111 in one direction to open the blades and in the opposite direction to close the blades, includes at least one and preferably two pot-shaped magnets mounted in stationary position. When two magnets are used, as in the preferred construction, they face each other as seen in FIG. 1. The first magnet has a cup-shaped or pot-shaped body 1 of soft iron and an inserted core 2 consisting of a permanent magnet. Between the parts 1 and 2 is an annular gap or slot 3 to accommodate the moving coil 4. At the mouth or other end (considered in an axial direction relative to the pot-shaped magnet) of the annular gap 3, it is narrowed down considerably as indicated at 5, leaving just enough space for free axial passage of the annular or hollow cylindrical core 4. This produces in the gap 5 a very intense magnetic field, so that the coil 4, over its entire length, is drawn into or extracted from the pot 1, as the case may be, with a constant or uniform force throughout the entire length of the axial movement, when the coil 4 is appropriately energized by the electric current.

Thus the electromagnetic drive is particularly suitable for a case in which constant force is desired over a certain distance. By reversing the polarity of the winding of the coil 4 (that is, reversing the direction of the direct current flowing through it) the system can be used with same effect in both directions, to produce the desired constant or uniform driving force in either axial direction throughout the entire range of movement, since the same number of turns of wire in the coil will be within the narrowed portion 5 of the gap in any position of the coil, assuming that the coil is sufficiently long in an axial direction so that it fills the full axial length of the narrow gap 5 in both of the extreme or limit positions of the coil.

In this first embodiment, illustrated in FIGS. 1 and 2, the pot magnet coil system is arranged on the tandem principle. The first magnet system having the parts, 1, 2, 3, 4, and 5 is duplicated by a second magnet and coil system arranged coaxially with the first and faced toward the first system, with a gap between the two systems. They are reverse duplicates of each other and the second system requires no further description except to say that the main body or pot of the second system is indicated at 6, and the coil thereof at 7. The adjacent ends of the two coils 4 and 7 are interconnected with each other by a connecting ring 8, which has fixed thereto an arm 8a terminating in a forked portion 9 which embraces a pin 10 on the previously mentioned blade ring or shutter drive ring 111.

If one or both of the coils 4 and 7 are electrically energized in the proper direction to move leftward in FIG. 1, in the direction of the arrow B, the fork 9 engaging the pin 10 will swing the blade ring 111 clockwise and will open the shutter blades. When one or both coils are energized by direct current in the opposite direction, so as to move rightwardly in FIG. 1, in the direction of the arrow A, then the fork 9 moves the pin 10 to the right, turning the blade ring 111 counterclockwise and closing the shutter blades.

With an arrangement like this, with two electromagnetic drives arranged in tandem relation and faced oppositely, it is possible to operate the mechanism in various ways. For example, the electrical connections (which can easily be made within the skill of the art, in the light of the present disclosure) may be such that for closing the shutter, only the coil 4 is energized in a direction to pull the coil into the magnet 1, in the direction of the arrow A, and for opening the shutter, only the coil 7 is energized, in a direction to pull this coil into its magnet 6, in the direction of the arrow B. Although this is possible, it is usually preferred to operate both magnets for operating the shutter in both directions, thereby producing greater force for quicker operation. Thus for closing the shutter, the coil 4 is preferably energized by current in a direction to pull the coil rightwardly into its magnet 1, while at the same time the coil 7 is energized in a direction to push it rightwardly out of its magnet 6. Reversely, for opening the shutter, both coils 4 and 7 are energized for movement in a leftward direction.

Since the number of coil turns or windings in the narrow gap 5 remains constant no matter what the axial position of the coil may be, it is entirely possible, when the coils are connected in opposition to each other, to produce a state of equilibrium, whatever their position may be. Thus the present drive is also suitable for use as a diaphragm regulator for exposure control devices, if permanently flowing currents are used in place of the short duration or impulse currents which would normally be employed if one desires only the quick opening and quick closing of a shutter.

Referring now to FIG. 3, there is illustrated a second embodiment of the invention in which approximately the same pot magnet drive is applied to a shutter of a different type having two blades 14 and 15 pivoted for opposite movement on the respective pivots 16 and 16a. The tandem magnet assembly is essentially the same as illustrated in FIG. 1, the main bodies of the magnets being shown in FIG. 3 by the same numerals 1 and 6 used in FIG. 1. The coils of these magnets are as before, and are connected by a connecting ring 8 as before. The extension 8b on this ring carries the pin 10' which engages appropriate slots 12 and 13 in the respective shutter blades 14 and 15. When the coils and their connecting ring 8 move to the left, the action of the pin 10' on the slots 12 and 13 swings both blades to their open positions illustrated in dotted lines, to open the exposure aperture of the shutter. When the coils and connecting ring move back in a rightward direction, both shutter blades are swung back to their closed positions illustrated in full lines.

FIG. 4 shows the application of the electromagnetic drive to a shutter which has rectilinear sliding blades rather than pivoted blades. The exposure aperture shown at 121 is open when the sliding blades 17 and 18 are pulled back away from each other as illustrated in FIG. 4, and are closed when the blades move toward each other into an overlapping relation.

In this embodiment of the invention, each blade has its own individual electromagnetic drive. The respective coils 19 and 20 are directly connected to the respective blades 17 and 18, without any intervening moving parts. These coils operate in the respective pot magnets 21 and 22, the coils and magnets being of essentially the same construction and operating in the same way as in the first embodiment described in connection with FIGS. 1 and 2. This embodiment of the invention illustrates the applicability of the invention to shutters having blades which are not pivoted, and also to shutters in which it is desired to have each blade with its own independent electromagnetic drive unit, and it also illustrates the possibility of a direct connection between the coil and the blade.

Another embodiment, illustrated in FIG. 5, shows that a shutter with pivoted blades can also make use of the present electromagnetic drive invention for each individual blade separately, and with a direct connection, without intervening moving parts. In FIG. 5, there are several pivoted shutter blades which collectively close and open the exposure aperture 123, but only one blade 23 is illustrated, pivoted for swinging movement on the pivot 26. Directly connected to this blade is the coil 24 of annular construction in cross section, but with its axis curved or bent arcuately, concentric with the shutter blade pivot 26.

The magnet 25 is formed exactly like the magnets previously described, except that its axis also is bent concentrically with the shutter blade pivot 26. When the coil 24 is electrically energized in a direction to push it out of the magnet 25, the blade 23 swings counterclockwise to its open position illustrated in FIG. 5. When the coil 24 is electrically energized in the opposite direction, to pull it into the magnet body 25, this swings the blade 23 clockwise on its pivot 26, so that this blade, in conjunction with other similar blades arranged at intervals around the exposure aperture, will cover the exposure aperture to close the shutter.

The shutter driving arrangement according to the present invention enables higher acceleration to be produced in opening and closing the shutter blades, as compared with prior electromagnetic shutters, this being due partly to the constant driving force generated through the full length of the opening stroke or closing stroke (as the case may be), and partly to the fact that the moving masses can be kept very small, because the moving coils are very light in weight. Thus the system provides not only a very short switching time or exposure time, amounting to about one-fifth of the time involved in the customary electromagnetic shutter drives of the prior art so far as known to applicant at present, but also these short times are obtained at the cost of a much more moderate expenditure of electrical power, believed to amount to about one-tenth or less then one-tenth of the power required in prior art electromagnetic shutter drives known to applicant.

The blade driving system of the present invention is usable not only for driving shutter blades between two defined limit positions (fully open and fully closed) but also for driving diaphragm blade systems or combined shutter and diaphragm blade systems of variable stroke, such as required, for example, in preselection diaphragms which have to be fully opened for viewing purposes (as in the case of a single lens mirror reflex camera) and have to be reclosed to a certain preselected aperture, before the photograph is taken. In such a system, if the shutter is prestressed or biased, e.g., mechanically, in such a way that when the electromagnetic drive is in the non-energized state the blades assume the fully open position, then it is possible, by suitably regulating the flow of current through the coil, via an exposure regulating device or manual device, to cause the electromagnetic drive to close or open the diaphragm to a certain preselectable distance.

The rapid exposures possible with the present invention have already been mentioned. Still faster exposures are possible if, according to another feature of the invention, resilient or elastic members are used, against which the moving parts of the shutter hit when the shutter reaches or closely approaches the fully open position, so that the elastic elements will produce a "bounce" effect on the moving parts, first absorbing kinetic energy from the moving parts and then returning such energy to these parts in the opposite direction, to cause quicker closing.

Merely as an example, FIG. 6 illustrates this feature of the invention as applied to a shutter of the type disclosed in FIGS. 1 and 2. It is to be understood, however, that this same feature of the invention, to produce a resilient "bounce" effect at the end of the opening movement and beginning of the closing movement, could be applied to any of the other forms of shutters such as illustrated, for example, in FIGS. 3-5.

Referring now to FIG. 6, the construction is the same as previously described in connection with FIGS. 1 and 2, except for the addition of the resilient or elastic members. The same reference numerals are used as in FIG. 1, for corresponding parts. The difference is that, just as the moving parts are about to reach the position in which the shutter blades are fully open, a flange 161 on the connecting ring 8 strikes against an elastic or resilient arm 151 which is permanently mounted on a fixed part of the mechanism by screws or rivets 153. Initially, the upper end of this elastic arm is in the position shown in broken lines. As the moving ring 18 reaches its extreme position in the shutter opening direction, it displaces the resilient arm 151 slightly from the broken line position to the full line position, so that this arm absorbs kinetic energy, helps to slow down rapidly the fast movement of the ring 8, and then gives back its absorbed kinetic energy to the ring, starting the ring rapidly back in the opposite or shutter-closing direction.

If desired, such an elastic member may be used only in conjunction with the connecting ring 8 and the associated coils 4 and 7. However, it is preferred to use a similar elastic member also in conjunction with a projection on the blade ring 111. Such a projection is illustrated at 181, and it engages the resilient or elastic arm 171 permanently mounted in fixed position by means of screws or rivets 173. The projection 181 engages the elastic arm 171 at substantially the same time that the flange 161 engages the elastic arm 151. The combined effect of both of these elastic arms is to absorb smoothly a great deal of the kinetic energy of the fast moving parts at the end of the opening stroke, and to create a substantial "bounce" effect with helps to speed the parts at the beginning of their closing stroke. Exposure times of less than 1/500th of a second can be obtained by utilizing this feature of the invention.

These buffers or elastic members must be dimensioned in such a way that the maximum storage of kinetic energy and elastic effect becomes operative when the shutter drive is moving at its maximum speed. In the case of lower opening speeds (longer exposure time) they merely act as stops which, owing to their intrinsic resilience, prevent violent impact. Of course the spring force and the driving force of the moving coils have to be adapted to the inertia forces of the shutter blades and other moving parts of the shutter mechanism. The use of this bounce feature makes it possible, without any appreciable extra expenditure of electrical energy, to obtain very short exposure times. This is particularly important from the point of view of dimensions to be adopted and space to be provided for the driving batteries of the electromagnetic drive system. The electromagnetic drive itself, according to the present invention, provides a very suitable drive which can be operated with minimum use of electric power, thus enabling small batteries to be used and enabling minimum dimensions of the casing or housing. When the further feature of the elastic "bounce" is added to the advantages also obtainable merely from the use of the electromagnetic drive, it is seen that a particularly advantageous construction is the result, with great economy of electrical power even though high shutter speeds are attained.

The elastic members 151 and 171 may be constructed of various materials. Satisfactory results have been attained by the use of spring steel, or by using phosphor bronze.

Claims

What is claimed is:

1. Electromagnetic drive for a photographic shutter blade, comprising a pot-shaped magnet having a pot-shaped outer body and a central core in position to provide an annular gap between the outer body and the core, the outer end portion of said gap being narrower than the major portion of the axial length of said gap, an electrical coil of generally cylindrical shape wound with uniformly spaced turns and mounted for axial movement through said narrower portion of said annular gap upon electric energization of said coil, and means operated by such movement of said coil for moving a shutter blade, said coil having an effective length sufficiently greater than the axial length of the narrower portion of said annular gap so that in all axial positions of said coil during its working stroke necessary for moving a shutter blade from open to closed position, the same number of turns of said coil will lie within said narrower portion of said gap.

2. A drive as defined in claim 1, characterized by the fact that there is more than one shutter blade and that each shutter blade is individually provided with its own moving coil and pot-shaped magnet.

3. A drive as defined in claim 2, characterized by the fact that the associated shutter blade is mounted to swing on a pivot, and that the axis of the moving coil and the axis of the pot-shaped magnet are curved circularly and concentrically with said pivot, and that the curved coil is rigidly connected to the shutter blade.

4. A drive as defined in claim 2, characterized by the fact that the associated shutter has an exposure aperture with two blades mounted for rectilinear movement radially with respect to the exposure aperture, and that each blade is rigidly connected to the moving coil of its individual drive.

5. A drive as defined in claim 1, characterized by the fact that said central core of said magnet is a permanent magnet.

6. A drive as defined in claim 1, characterized by the provision of two such pot-shaped magnets mounted coaxially in tandem relation to each other with a separate coil movable in each pot-shaped magnet, the two coils being connected to each other for joint movement in the same direction.

7. A drive as defined in claim 6, in which only one coil is energized to produce joint movement of the two coils in one direction to open an associated photographic shutter, and in which only the other coil is energized to produce joint movement of the two coils in the opposite direction to close the shutter.

8. A drive as defined in claim 6, in which both coils are energized to produce joint movement of the two coils in one direction to open an associated photographic shutter, and in which both coils are also energized to produce joint movement of the two coils in the opposite direction to close the shutter.

9. A drive as defined in claim 1, wherein the moving coil of the drive is directly coupled to one or more shutter blades by means of a pin and slot connection.

10. A drive as defined in claim 1, further comprising an elastic buffer member engaged by a moving part at substantially the completion of a shutter opening movement, to absorb kinetic energy from such opening movement and return the absorbed energy to such part in a reverse direction to assist a closing movement.

11. A construction as defined in claim 10, in which the part which engages said elastic buffer member is a part of said drive fixed to and rigid with the moving coil of said drive.

12. A construction as defined in claim 11, further comprising a second elastic buffer member engaged by and absorbing kinetic energy from a shutter member separate from but driven by the moving coil of said drive.

13. A drive as defined in claim 1, in combination with a photographic objective shutter of the type having a plurality of swinging blades and a rotatable blade driving ring for swinging the blades between their closed and open positions, characterized by the fact that said drive is mounted with the axis of said coil approximately tangential to said blade driving ring and is operatively coupled thereto to turn said ring from axial movement of said coil.

14. A construction as defined in claim 13, further comprising a first elastic buffer member engaged by a part of the moving coil structure at substantially the completion of a shutter opening movement, to absorb kinetic energy from such opening movement and return the absorbed energy to the coil structure in a reverse direction to assist a closing movement, and a second elastic buffer member engaged by and absorbing kinetic energy from a portion of said blade driving ring, to return the absorbed energy to the blade driving ring to assist a closing movement in a reverse direction.