US2730026A - Shutter blade drive linkage - Google Patents

Description

. Jan. 10, 1956 L... F. WELANETZ SHUTTER BLADE DRIVE LINKAGE 2 Sheets-Sheet 1 Filed April 22, 1952 Ludo/0h E Pile/Q0652,

INVENTOR,

BY WW Jan. 10, 1956 F. WELANETZ SHUTTER BLADE DRIVE LINKAGE 2 sheets -sheat 2 Filed April 22, 1952 Fan rofaf/all INVENTOR:

6 W m% l 4 w United States Patent SHUTTER BLADE DRIVE LINKAGE.

Ludolph' F. Welanetz, Hempstead, N. Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application April 22, 1952, Serial No. 283,695

3 Claims.- (Cl. 95-63) This inventionpertains to photographic shutter mechanisms, and particularly to an improved novel. linkage by which a-desired motion of a shutter blade may be obtained in a simple and economical manner.

In. the design of high speed shutters of themovingblade type, the requirements for increasingly high speeds of operation have raised important and difficult problems. Thus, eilorts to increase the speed of travel of the blades themselves generally require that-the moment of, inertia of the blade itselfbe reduced to a minimum, but the elimination ofmaterial to satisfy this aim usually involves a reduction in the force which can be safely be applied to the blade. At the same time, speeds of operation can also-be increased by increasing the force applied to the. blade, so that these two approaches to some extent conflict with one another.

Many efiorts have been made to control the-rate. at which force is applied to the blade, or-theblade linkage, in order to achieve the highest possible acceleration'with adequate reliability of the construction, and one very promising approach has been theuse ofv a mechanism which will cause the blade travel to be harmonically (or approximately harmonically) related .to the motion of the member which drives the blade, and various types of cam and gear mechanisms have beenproposed to this end; Byharmonically related as used herein is meant so related that the shutter blade is accelerated and de celerated at the extremes of its travel in a manner similar to that realized in simple harmonic motion; the blade velocity increases at first very slowly, then more rapidly as it rotates, and finally slows downrapidly prior to" coming to a stop. Such a velocity curve is approximately represented by a sinusoidal wave, such 'asexecuted by a particle moving in a simple harmonic motion.

It is a principal object, of the present inventionto provide a photographic shutter in which a substantially harmonic motion of the bladeor blades,-with respect to their driving mechanism, is achieved'by relatively simple linkages and without recourse toprecision cams, gears and the like.

A further object is to provide an arrangement of parts satisfying the above objects without requiring ,an excessive diameter of the outer shutter profile for a given size of exposure aperture.

An additional object of the invention isto provide a linkage of the above type whose parts canreadily be fabricated by production techniqueswithout excessive costs.

Still another object of the invention is to provide a linkage of the above type which is particularly suited for driving the individual blades of a multi-blade shutter Other'objects and advantages of thenovel construction willbeapparent from the following detailed-specification" "ice of a preferred embodiment thereof, taken in connection with the appended drawings, in which:

Fig. 1 is a view in elevation showing the principalportions of a multi-bladeshutter incorporating the novel arrangement of the invention, the shutter blades being.

Fig. 5 is a curve showing the harmonic motion of the blades.

Referring now to Figs. 1 and 2 of the drawings, the

blade and control mechanism of the shutter is shown as comprising a mechanism plate 10 having a center exposure aperture 12 adapted to be successively covered and uncovered by a set of five shutter blades 14 pivotally mounted upon plate 10 as by pivots 16 and equally spaced about exposure aperture 12. The force for moving. the plates 14 between the open and closed positions is derived from a single main operating member 18 which may be given a reciprocating motion by suitable power' mechanism which does not form a part of the present invention. This member 18 is pivotally connected to a so-called fan 20 pivoted at 22 onthe plate 10*and connected by a drag link 24 to a crank 26 also' pivotedi on the plate 10 as at point 28.

As indicated, the fan which is directly driven by member 18 is denoted by numeral 20. Three of the remaining fans are designated by numeral 20, because they ditfer' slightly in shape from fan 20 in that they are not connected to any drive member such as member 20; Counting clockwise from fan 20, the last fan of the set of five also dilfers slightly in shape, and is designated by numeral 42 as will be described below. There is a crank 26 for each fan, connected thereto as by a drag link 24, and each of the cranks transmits motion to the corresponding blade 14 by an arcuate link 30 pivoted to the crank 26 as at 32 and to the blade 14 as at point 34.

As indicated above, there is a set of elements comprising a fan, drag link, crank and arcuate link for each of the blades 14, and in the particular embodiment chosen for disclosure, the fan corresponding to each blade 14 is connected to the fan of the next blade 14 by an elongated motion-transmitting link 36. Thus, there are five elongated links 36 which, together with the five fans to which they are pivoted, form a closed motion-transmitting system extending completely aroundthe exposure aperture 12 and serving to drive the successive blades 14- substantially simultaneously. Actually, and as shown, the hole at each end of each link is slightly elongated to ensure that, regardless of the direction of motion, the links 36 are subjected to pure tension forces.

As has been stated, Fig. 1 shows the blades in their open condition, and a comparison of Figs. 1 and 3 will show that a movement of the drive member 18 in Fig. l

a counter-clockwise rotation of the fan 20, and, through link 24, a counter-clockwise rotation of the crank 26,"

and thereby a counter-clockwise rotation of each of the blades 14. Ultimately, and at the end of the motion of the drive member 18, the five blades will have assumed the "closed position illustrated in Fig. 3.

A particular shutter chosen and illustrated happens to be one in which there are two coaxial sets of five shutter blades disposed about a common optical axis at the center of the lens aperture 12, one set being normally open andthe other closed. An exposureis made by allowing one set of theblades to move froir'tcloSe'd p'o'sil atented Jan. 10, 1956' tion to open, and thereafter allowing the other set to move from open position to closed. The reverse movements of the two sets of blades, in order to prepare the shutter for another exposure, are made in such a way that the lens aperture remains covered during the interval between the successive desired high-speed eXp sures.

Since the fact that the shutter chosen for illustration is of the above described type is of no significance insofar as concerns the blade-control linkage which forms the basis of this invention, the duplication of parts necessary for the complete shutter has been omitted from the drawings.

Figs. 2 and 4 of the drawings are drawn to an enlarged scale, in order to show more clearly the necessary relationships between the elements associated with each one of the moving shutter blades. With this linkage, each fan 20 rotates through approximately 90 degrees during each cycle of movement of the shutter blades, while the blades themselves move through an angle of less than 90 degrees. In the drawings, the total rotation angle of each blade is about 60, this being conventional for a five-bladed shutter. It will be observed that if a reference line is drawn through the two fixed points which are the centers of the blade pivot 16 and the fan pivot 22, the 90 rotation of point 38 around axis 22 is distributed about equally on opposite sides of such reference line; i. e., 45 on each side. This arrangement prevents any binding or over-center action between the fan 20 and the crank 26. In order to define the geometry of the arrangement, reference number 38 has been assigned to the pivotal connection between each fan and its drag link 24, and reference number 40 has been assigned to the pivotal connection between link 24 and crank 26. The distance between two pivotal points such as 33 and 45 will be indicated by the notation 38-40. With the proportions as shown in Figs 2 and 4, the angular displacement of crank 2% will be approximately twice the angular displacement of fan 2t), and the blade motion will be approximately harmonic with respect to the motion of the fan, if the proportions of the links and the center-to-center pivotal distances are as follows:

For compactness of notation, the distance 22-28 has been given the symbol X, the distance 28-40 the symbol Y, the distance 2238 the symbol Z, and the distance 38-40 the symbol W. Thus, the equations given above can be written:

Since the angular displacement of bell crank 26 is approximately proportional to that of fan 2%, and since the angular displacement of blade 14 is approximately harmonic with respect to that of bellcrank 26, then the angular displacement of blade 14 is approximately harmonic with respect to that of fan 29, and this relation is obtained with the mechanism shown by simple linkages and without the use of gears, cams or other relatively difficult elements to manufacture.

Fig. of the drawings shows how closely the desired harmonic relationship can be achieved by the structure shown. The full line curve in this figure shows the angular relationship between a blade motion and fan motion, both expressed for example in arbitrary angular units, while the dash line curve represents a true harmonic relationship. It will be observed that the actual curve obtained is a very close approximation to the ideal.

The harmonic relationship obtained has, from the practical viewpoint, several advantages. Among these are the fact that the harmonic motion gives the blade 14 a relatively short time of traverse of the exposure opening without the necessity of excessive acceleration or jerk, and the fact that the driving linkage (here represented by member 13 and the parts which drive it) can be accelerated to an appreciable velocity before the blade moves any substantial amount. Finally, the blade can be caused to decelerate smoothly near the end of its travel without the necessity of a braking mechanism of large capacity. This decelerating action will now also be quite free from shocks.

In the above description, pivot points 32 and 40 are shown as located in spaced positions on crank 26. Theoretically, and without altering the kinematic characteristics of the mechanism, the links 24 and 30 could be pivoted to crank 26 at the same point. However, for reasons of strength and rigidity, it is preferred that points 32 and 49 be separated on crank 26, and the amount of separation shown is just sutficient to provide clearance between the profiles of the adjacent ends of links 24 and 36. It will be noted that the distance between points 32 and does not enter into the fundamental equations given above, which must be satisfied in order to achieve the desired harmonic relationship.

It will be noted that the blade pivots are adjacent the edge of exposure aperture 12, and that each fan 20 has its pivot axis outward from the pivot 16; that is, the fan is mounted at a longer radius from the center of the exposure aperture than is the blade 16. With blades of the necessary shape, this means that the fan and crank can be mounted in space which is not required to accommodate any part of the blades when they are in fully open condition, as shown in Fig. l, and permits a minimum outside diameter of the shutter mechanism.

It is also clear from a comparison of Figs. 1 and 3 that regardless of the blade position (open or closed) the connection point 34 of the blade driving link lies on the opposite side, from blade pivotal mount 16, of a line drawn from the center of the exposure aperture to the fan pivot 22.

For the larger sizes of shutters, it may be desirable to provide some additional braking action near the end of the closing movements of the parts. This may be furnished, by way of example, by a spring-loaded snubber 46 arranged to be struck by a projection 44 on the particular fan 42 which is the last fan in the series counting clockwise from the first fan 20. Equivalent bumper or snubber arrangements may obviously be substituted for this element, if and as required by the size and speed of the particular shutter.

While the proportions and relations of the parts are stated above for the case of a shutter having a certain amount of angular travel of the blades 14 and the fans, it is clear that the same principles can be applied to shutters in which these parts undergo ditterent angular travels. These and other changes and modifications can be made in the structure without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. In a photographic shutter, a support defining an exposure aperture, a plurality of blades pivotally mounted on said support at points adjacent and surrounding the edge of said aperture for movement between two extrerne angular positions with respect to said aperture, each blade being clear of said aperture in one of said extreme positions, and the blades together completely occluding said aperture in the other of their extreme positions; for each blade a fan pivoted on said support outwardly of the blade pivots, a crank pivoted on said support adjacent said fan, a first link pivotally connecting a first point on said fan with a second point on said crank, means for driving said fan to move said first point between angular positions substantially apart and lying on opposite sides of the line joining the pivotal supports of said fan and said blade, at second link pivotally connected to said crank and pivoted to said blade at a point spaced from the blade pivot and lying on the opposite side, from said blade pivot, of a line connecting the center of the exposure aperture and the fan pivot, the distance between said second point and the pivot of said crank, and the distance between the pivots of said crank and fan, both being substantially one-half the distance between said first point and the pivot of said fan, and the length of said first link being equal to the distance between the pivots of said crank and fan multiplied by the square root of two; and means interconnecting all the fans for simultaneous rotation.

2. A photographic shutter in accordance with claim 1, in which a line connecting the pivotal axes of said fan and said blade substantially bisects the angle of total travel of said first point on the fan.

3. A photographic shutter in accordance with claim 1, in which the pivot points of said second link are in alignment with the pivot mount of said crank in both of the extreme positions of said blade.

Robertson Mar. 1, 1949 Willcox Sept. 19, 1950

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