IL27712A - Self-adjusting optical slit mechanism - Google Patents

Description

SBLF-AJDSTIHG OPTICAL SLIT MECHANISM This invention relates to slit mechanisms having a variable slit width, of the type frequently utilized in optical instruments .

In various instruments in which radiant energy is measured, there is a need to restrict the radiant beam to a particular well-defined cross-sectional area. In certain types of these instruments (for example, members of the spectrometer family, including monochromators) , the desired shape is a relatively narrow rectangle. Where, as is often the case, it is desired to be able to vary the width (i.e., the narrow dimension) of this rectangular slit, difficulty in maintaining the correct adjustment is encountered, both in manufacture and more often in use. One reason for these problems is that the slit should always be defined by slit jaws which bear specific relationships to each other, in particular such slit jaws should be co-planar, their edges should remain exactly parallel, and each edge should remain an equal distance from a fixed center line (namely, the line along which the two edges would meet when the variable slit mechanism is completely closed) , at all variable slit width settings. The problem of maintaining the correct relationships between a pair of movable slit jaws defining a single variable width slit becomes compounded by the fact that a pair of such variable slits is often required (for example, in spectrometers), and there is the additional requirement that each of the variable slit mechanisms "track" so as to maintain a certain desirable relationship (which is often merely equality) at all slit width settings . To meet all of slit mechanisms (and especially those which are synchronously paired) have required extreme precision in manufacture, assembly, and alignment, and have for this reason been relatively expensive and difficult to maintain.

The . invention provides a synchronously operated pair of variable slits, having all of the above desired attributes, which is relatively inexpensive to manufacture and requires no tedious alignment and adjustment procedures whatsoever. As will appear more specifically hereafter, the slit mechanisms of the invention are inherently self-adjusting. In particular the individual slit jaws defining each of the two slits are inherently co-planar, since a single jaw and its reflection in a plane mirror define each of the slits . The edge of each slit jaw is maintained parallel to the mirror surface by semiautomatic or self-regulating adjustment relative thereto, thereby assuring that the slit has parallel edges at all variable width settings. Additionally a semi-automatic or self-adjusting operation assures that the movable slit jaw is (during use) at a known standard position relative to the means for varying the slit width.

The invention additionally assures not only that each of the individual slits are so adjusted, but also self-regulates the position of the movable jaws of both slits to the same desired known standard position relative to the variable slit width driving means. This insures that both variable slits will be in synchronous tracking adjustment relative to each other. The invention allows this multiple self-adjustment to instrument) without any expenditure of time or energy of the operator. Despite the advantages of self-adjustment of substantially all of the positional relationships of the movable slit jaws just mentioned, slit mechanisms according to the invention may be relatively inexpensively manufactured and assembled because very few of the parts require high precision in either their making or assembly.

The object of the invention is the provision of a variable width slit mechanism, particularly of the double slit type, which maintains to a high degree of precision the desired relationships and attributes mentioned above, but which is relatively inexpensive to manufacture, simple to assemble, and requires no tedious readjustment during use.

Other objects and advantages of the invention will become obvious to one skilled in the art from the exemplary embodiment, hereinafter described in detail and shown in the accompanying drawing, in which: Fig. 1 is a plan view of one example of the entire variable-width, double-slit mechanism; and Fig. 2 is a front elevational view of the same system, looking in the direction indicated at 2-2 in Fig. 1.

As may be seen in Fig. 1, the device comprises the slit mechanism proper mounted on a mechanism plate 10 and a cam 12 for varying the width of the slits in a manner which will be described hereinafter. Rigidly mounted on plate 10 is a prism 14 having flat reflecting outer surf ces at 16 and 17. In Fi . 2, rism 14 is shown as attached to the u er end of a suitable manner to the mechanism plate 10. Each of the flat reflecting surfaces 16 and 17 of this prism are adjacent to and cooperate with a different movable mounted slit jaw 18 and 19 respectively. These slit jaw elements are preferably in the form of thin plates, each having a relatively sharp straight edge (at 20 and 21, respectively) closely adjacent to the respective reflecting surfaces 16 and 17. It has been found that commercially available razor blades may be used as the slit jaw elements .

Since the elements immediately supporting each of the slit jaws are related to each other in the same manner as are left and right hands, only one set will be described (namely, those associated with slit jaw 18); in fact, since some of these elements (including the slit jaws themselves) are also symmetrical end for end, a few are actually identical and therefore interchangeable. Slit jaw 18 is ultimately supported by bracket 22, which comprises a horizontal portion 24 and an integral or at least rigidly connected vertical portion 26.

This right-angle support bracket 22 is mounted for pivotal movement about a vertical axis by being loosely secured (near one end of horizontal portion 24) by a screw 40 in a manner which will be subsequently described. A pin 28 rigidly extends from near the center of the surface of vertically extending portion 26 toward the slit jaw 18. A magnetized plate 30, apertured to allow passage of pin 28, is positioned between the adjacent surfaces of vertical portion 26 and slit jaw element 18. As may best be seen in Fig. 2, slit jaw 18 has an is illustrated as a horizontally extending central slot, since certain types of commercially available razor blades' are so apertured. However, the aperture may be of any shape which will loosely engage pin 28, since only the right-hand internal edge of the aperture 32 (as seen in Fig. 2) need be precisely located relative to pin 28, as will be subsequently explained. By utilizing ferrous materials for both the slit jaw element 18 (as is true of commercially available razor blades) and the support bracket 22 (or at least vertical portion 26 thereof) , magnetic plate 30 will be attracted to the latter and will in turn magnetically hold the former. For this reason slit jaw 18 is securely held against the adjacent face of magnetic plate 30, which in turn is held securely to the confronting surface of vertical portion 26. Nevertheless slit jaw 18 need overcome only a moderate amount of frictional resistance to move in any direction in its own plane, including angular motions therein (i.e., about a horizontal axis'). The pin (28) and slot(32) connection restrains the possible movement of slit jaw 18 to a very small vertical movement and a moderate horizontal move-ment, but does not restrict any pivotal motion thereof in its own vertical plane .

Support bracket 22 is pivotally mounted o mechanism plate 10 by means of screw 40 and washer 42 of very low coefficient of friction material (which may be, for example, "Teflon") . Mounted for similar pivotal motion about screw 40 and below support bracket 22 is a long actuating arm 44, carr in at its other end a cam-followin roller 46 bearing on which supports one end of tension spring 50, the other end of which is attached to pin 52 rigidly mounted on mechanism plate 10. As may best be seen in Fig. 1, tension spring 50 therefore biases arm 44 in a counterclockwise direction about a pivot defined by screw 40 so as to cause cam follower 46 to press against cam 12. The contour edge of cam 12 at 54 therefore determines the amount of clockwise pivotal motion of arm 44 about screw 40. A second washer 56 (which may be identical to washer 42) is positioned on screw 40 between the lower surface of long arm 44 and the mechanism plate 10. This second washer 56 is also of a material having an extremely low coefficient of friction relative to the material (any conventional structural metal) of arm 44, so that the frictional drag is substantially below the tension force supplied by spring 50; in fact the second washer 56 acts as a moderately low friction bearing surface. Although washers 42 and 56 may be somewhat different, it is entirely practical to make them both of the same material as long as the total frictional drag of both washers combined is substantially less than the torque supplied by spring 50.

Relatively high friction is maintained between the upper surface of long arm 44 and the facing lower surface of the horizontal plate portion 24 of the slit support bracket 22. Although the illustrated embodiment utilizes a thin friction or clutch plate 58 for this purpose, the same results may be accomplished by roughening the confronting surfaces of elements 24 and 44. In either case, the frictional drag between these angular position) is substantially greater than the friction provided by washers 42 and 56 (which tend to keep each of these elements stationary) . For this reason any pivoting of the arm 44 by cam 12 will cause support bracket 22 (and therefore the rest of the movable parts of the slit mechanism) to pivot in exactly the same way, despite the slight frictional drag provided by upper washer 42.

Movement of support bracket 22 in the clockwise direction is ultimately inhibited, however, by a stop or limit pin 60, which is abutted by an edge 24' of the horizontal portion 24 of support bracket 22 (as may best be seen from Fig. 1). Rotation of the slit support bracket 22 in the opposite (counterclockwise) direction is ultimately limited by the leading edge 20 of slit jaw 18 abutting against upper and lower very small stops or spacers (which may comprise shim stock) 62 and 64, attached to the upper and lower edges of that part of prism surface 16 directly opposite the edge 20 of slit jaw 18 (see Fig. 2) . Sufficient counterclockwise rotation (as seen in Fig. 1) of slit bracket 22 and its supported elements will cause this abutment, so as to move slit jaw 18 to the left in Fig. 2 until the right-hand end of slot 32 abuts against pin 28. Once this has occurred any further counterclockwise pivoting of bracket 22 is prevented, so that any further movement of arm 44 in this direction will cause slippage at the relatively high friction point (at 58) between this arm and the support bracket 22. Similar (but opposite direction) slippage will obviously occur when long arm 44 is Operation of the variable width slit involving the parts already described is as follows. Before use, the rotational position of the support bracket 22 relative to the long control arm 44 is first "overset" and then set to a standard or adjusted position. The first overset condition is obtained by moving arm 44 in a clockwise direction (in Fig. 1) sufficiently to assure that edge portion 24' of the support bracket 22 not only meets limit pin 60 but is arrested thereby before rotational movement of arm 44 ceases. This assures that arm 44 is more advanced clockwise (relative to support bracket 22) than a certain standard relationship desired to be obtained.

Subsequent movement of arm 44 in the opposite, counterclockwise direction will cause support bracket 22 to immediately start rotation in the same direction, thereby moving slit jaw 18 toward the adjacent surface 16 of prism 14 until the leading edge 20 of the slit jaw meets and then presses against the upper and lower limiting spacers 62 and 64. It should be noted that this not only stops the motion of support bracket 22 and the associated elements (assuming that the right-hand edge of slot 32 in slit jaw element 18 is already pressing against pin 28) , but also causes the slit jaw edge 20 to be made exactly parallel to the adjacent surface 16 of the prism 14 (as long as upper and lower spacers 62 and 64 are identical in size) . Specifically, if the slit jaw 20 is originally tilted, one corner will contact one of the spacers (62 or 64) before the other leading corner. This will pivot the jaw about pin 28 to the desired parallel relationship Arm 44 is now moved at least somewhat farther (in the counterclockwise direction) to a particular standard position. Since slit jaw 18 and its support bracket 22 are being rigidly held in a particular known position during this time, a standard relationship between the position of support bracket 22 and that of arm 44 is established. Such position will hereinafter be referred to as the "standard", "correct", or "adjusted" position of these two members.

Subsequent to this adjustment rotation of arm 44 in a clockwise direction will of course cause the support bracket 22 and therefore slit jaw 18 to follow, while maintaining this standard or correctly adjusted relative position. Obviously the arm 44 should not be rotated in a clockwise direction sufficiently to cause edge 24' of the support bracket horizontal portion to abut limit pin 60 during normal usage of the variable width slit. Therefore limit or "overset" pin 60 is at a position beyond the normal range of use of the variable slit.

Although the "oversetting" or the adjustment or both may be readily accomplished by manual movement of, say, arm 44, the above described setting of the standard or adjusted position may be readily incorporated in the otherwise conventional means for automatically programming the width of slits, as is used in various optical instruments (and especially in mono-chromators as . incorporated in various spectrometers) . Since a rotating edge cam is commonly used to program the width of the variable slits in such optical instruments, the exemplary means shown is of this type; however other means may be used instead. clockwise direction about axis 13 in synchronism with, say, the wavelength drive of a monochromator of a programmed spectrometer. In such instruments it is often desired to change the width of the slits in a programmed manner with the wavelength drive (so as to compensate for the varying efficiency of the radiant energy source emissivity in certain ranges of wavelength, the reduction of sensitivity of the detector at certain wavelength regions, and the like). Accordingly the edge 54 of cam 12 has a slit width programming curve extending over the major portion of this edge between points 70 and 72 (counterclockwise in Fig. 1) . A typical slit width program is indicated on this portion of the edge of the cam. Specifically the starting portion 70 is somewhat higher than a low point 74 so that the wavelength scan is initiated with the slit jaws open somewhat beyond their minimal setting. The cam edge then recedes somewhat between points 70 and 74 so as to cause gradual closing of the slits to their minimal opening. After maintaining this minimal radius for some time, the cam edge then constantly increases this distance from the center of rotation of the cam, thereby causing the slits to open more and more. The highest point 72 of this gradual increasing radius portion of the cam is at the end of the normal scan program.

The smaller, more steeply curved part of the cam between points 72 and 70 (in the counterclockwise direction in Fig. 1) are used for the oversetting operation (namely between points 72 and 76) and the adjustment to the standard or correct position o eration between oints 76 and 78 described above. points 72 and 76 will drive the long arm 44 beyond its normal maximum setting so as to cause the edge portion 24' of the support bracket 22 to abut against the pin 60, thereby "oversetting" bracket 22 relative to arm 44 as previously described. After the highest point on the cam has caused this extreme clockwise motion of arm 44, the cam will allow the arm 44 to return relatively rapidly in a counterclockwise direction (under the pull of spring 50) until the arm has reached the standard position (cam point 78) , and bracket 72 has been forced into a correctly adjusted position relative thereto as previously described. It is again pointed out that since the support bracket 22 was "overset" (i.e., forced to a more counterclockwise position than the correct adjustment position relative to arm 44) by the high part of the cam between points 72 and 76, slit jaw edge 20 will abut against spacers 62 and 64 somewhat before the low point (78) of the cam has been reached. This assures that support bracket 22 and arm- 44 are forced into the correctly adjusted standard position when this low point (78) is finally reached. As previously noted, any canting of the slit jaw element 18 about pin 28 will also be corrected by this adjustment. Thus all parts are now in the desired standard adjusted position.

The short cam edge portion between points 78 and 70 is merely to move all of the slit elements (44 and 18-30) slightly clockwise, so that at the starting point 70 of actual programming of the slits, slit jaw 18 will provide somewhat more than the minimal slit width (which is assumed to be the desired standard position of the parts relative to each other has been insured by that part of the cam cycle between points 72, 76 and 78, any desired program may be provided on the remaining parts of the cam edge (i.e., extending from point 78 counterclockwise to point 72) .

A somewhat different contour of the cam edge (in the vicinity of point 78) is shown in dotted line at 80. As noted above, the use of spacers 62 and 64 is considered optional. If they are not used, the edge 20 of slit jaw 18 will obviously abut directly on prism surface 16 during the adjustment phase. This will obviously cause the standard or correctly adjusted relationship between the arm 44 and the rest of the slit mechanism to occur at a zero width opening (i.e., edge 20 completely tight against prism surface 16) . Since it is obviously undesirable to allow the slit to ever close during an optical measurement, the optional cam edge contour 80 would be provided if spacers 62 and 64 are not used. Optional' contour 80 contains portions more recessed than any other part of cam edge 54, to insure that no other part of the cam program will cause the slits to completely close. In other words, if no spacers 62, 64 are utilized, the adjustment to the correct standard position will occur at a position corresponding to zero width adjustment; and the optional deeper recessed portion 80 insures that the slits will not close at any other part of the controlled cycle. In general the standard or correctly adjusted position will be set with the slits at least as much troublesome (involving the greatest percentage error in actual slit width, the greatest error contribution because of lack of parallelism of the slit jaws, etc.)/ it is an advantage that the semi-automatic adjustments to the correct standard position are obtained at or near this ideal (narrow) slit width condition.

Although until now only one of the slits has been fully described, the other slit mechanism is substantially identical in every respect, except for two differences. First, all of the elements thereof are related to the elements of the already described slit in the same manner as a right hand is related to a left hand, and therefore operate in exactly the opposite angular directions . All of these elements (numbered between 19 and 65) are otherwise identical to the corresponding elements numbered one lower, already described. The second exception is that there are no elements exactly corresponding to long arm 44, cam follower 46 or cam 12 (or any of its parts 54 and 70-80) . Instead of long actuating arm 44, the second slit mechanism has a relatively short actuating plate 144 which fractionally engages the lower part of horizontal portion 25 of support bracket 23 in essentially the same manner as long arm 44 engages the corresponding horizontal plate portion 24 of the already-described first slit mechanism. A follower portion 146 of actuating plate 144 extends toward the adjacent portion of long arm 44, and is engaged by a driving nose portion 112 of arm 44, as may best be seen in Fig. 1. Spring with driving finger 112 at all times . Thus elements 112 and 146 operate at least somewhat analogously to elements 12 and 46, while actuating plate 144 is even more closely comparable to actuating arm 44. Thus except for the difference in the manner in which actuating plate 144 is indirectly driven by cam 12 through long arm 44, and the exact shape of this actuating plate, all of the elements of the second (i.e., right-hand in Fig. 2) slit mechanism are both structurally and functionally the same (except for being mirror images and rotating in the opposite direction) to the corresponding parts already fully described of the left-hand slit.

Thus all of the description concerning the first slit mechanism (elements 16-42 and 48-64, with the exception of cam contour 54) apply also to the other slit elements numbered one higher. Since counterclockwise motion of arm 44 is converted to clockwise motion of actuating, plate 144, both slit mechanisms open and close in synchronism. Further, since both are set to the same standard or correctly adjusted position at the same time, both slits inherently have the same minimum standard opening, as long as spacers 62 and 64 are identical to spacers 63 and 65.

It might be noted that even errors in the position or shape of prism 14 do not in general adversely affect the desired standard relationship between the slit jaws and their various actuating mechanisms, since each slit jaw element (18 and 19) is positively set by the structure of its opposing nd 1 ectivel and plate 144) are in their standard position. For this reason almost none of the parts need be manufactured to a high precision, and wear of most parts does not affect the precision of either slit individually or the synchronism of the two slits collectively. For example, wearing of the surface in an even manner of cam 12 or follower 46 causes no misadjustment of the slits in any position of their program. This is true since the entire mechanism automatically adjusts so that both slit jaws are in their standard (minimal) position at the lowest point of the cam (i.e., at 78), and are opened to wider settings according to the relative distance of the various portions of · the cam edge 54 from its center. Extreme wear will of course cause the oversetting portion (between points 72 and 76) of the cam contour eventually to be insufficient to cause the two support brackets 22 and 23 to be overset against their respective limit pins 60 and 61; however, since the amount of overset is not critical, the overset portion of the cam may be made more than sufficient to compensate for substantial wear. Wear between the abutting parts of driving and driven fingers 112 and 146 is also not critical, as long as their respective effective lever arms remain reasonably constant relative to their respective pivots (a one-to-one ratio in such lever arm length being used in the illustrated embodiment) . This is so because each movable slit jaw (18, 19) is adjusted to the correct standard position relative to its own actuating member (44 and 144 respectively) .

As previously noted, the exact position of the "overset" that is necessary is that they be far enough from the center of the double slit so as not to engage the adjacent portions of the support brackets 22 and 23 at any (i.e., the widest) slit width actually used in the slit program, but are sufficiently close to the center line to assure that these adjacent portions (24', 25') press against these pins when the highest point of cam 12 (or other means) pushes the arm 44 to its most clockwise position.

The only parts that require high precision are the edges 20, 21 of the slit jaw element (18, 19), the cooperating parts of the reflecting surfaces 16 and 17 of prism 14, and the spacers or shims (if used) 62, 64 and 63, 65. As previously noted slit jaws 18 and 19 may be razor blades, thus providing extremely precise edges 20, 21 at very low cost. The spacers 62-65 may comprise readily available inexpensive shim stock. All of these elements may therefore be replaced from time to time at minimal expense. Prism 14 need not be of optical glass or other expensive material, only its reflecting surfaces 16 and 17 being used. Thus all of the elements requiring a high degree of precision may be obtained at low expense. The use of magnetic plates at 30, 31 makes the replacement of worn or nicked slit jaws (razor blades) 18, 19 an extremely simple matter. Although the spacers 62-65 have been described as fixed to the reflective surfaces 16 and 17, they may instead be attached to the adjacent portions of the edges 20, 21 of the slit jaws themselves.

Since in the illustrated embodiment (see Fig. 2) the reflecting surfaces are the limiting factor in the height of the usable slit, elongating these surfaces will obviously increase the usable slit length (the spacers 62-65, if used, being positioned near the ends of whatever is the limiting element of the slit length) . Normally the upper and lower edges of the slit will be defined by the upper and lower edges of an auxiliary element, for example, an opaque mask having a rectangular opening; and the spacers 62-65 would be just obscured by such a mask.

An exemplary light path is indicated in Fig. 1. The incoming light beam will follow ray 9Q so as to be reflected off the surface 17 of prism 14 along the direction indicated by ray 92. Edge 21 of slit jaw 19 and its reflection in mirror 17 will therefore define a variable width entrance slit (of narrow rectangular shape) to, say, the monochromator of a spectroscopic optical instrument. The beam represented by ray 92 will then pass through the, say, monochromator (which will disperse the radiant energy according to its wavelength) . At least some of the radiation (in this case a particular wavelength thereof) will return from the monochromator along ray path 94 to the second slit defined by edge 20 of slit jaw 18 and its reflection in mirror surface 16. After passing through this exit slit, the beam will be traveling along ray path 96, ultimately to fall upon, say, a radiation detector.

Although the slits are particularly useful when utilized in pairs as indicated in the exemplary embodiment, a single surface (16) may be utilized to form a single variable width optical slit, if only one such slit is required. The particular illustrated embodiment achieves not only a precise, reproducibly tracking variable slit, but additionally provides a pair of such slits that inherently maintain synchronous width adjustment, so that it is particularly applicable to such double slit requirements . Although the specific exemplary embodiment accomplishes the "oversetting" and final adjustment of the slits by automatic means (incorporated in mechanically driven parts) , other embodiments of the invention may effect either or both of these functions by semi-automatic (e.g., a push button) or purely manual means .

The invention thus provides precise variable-width optical slits having all the desirable relationships previously mentioned between the variable effective slit jaws, that are self-adjusting and relatively inexpensive to manufacture and assemble. The invention is not limited to any of the details of the specific illustrated embodiment, but rather is defined by the scope of the appended claims .

Claims (1)

1. 27712/2 HA.T IS CLAIMED ISt 1» A self-adjusting optical silt mechanism of variable width* comprising. means defining a variable position slit jaw; actuating means for moving said slit jaw means* including a slippable connection having substantial drag between said slit Ja and said actuating means; means for limiting movement of said slit jaw in a relatively opon extreme} standard position means for limiting movement of said slit jaw in a relatively closed extreme$ amovi g means for moving said actuating means and for forcing said actuating means to move relative to said slit jaw through said slippable connection when the movement of said slit jaw reaches the open or closed extreme) whereby said slit jaw means and said actuating means are caused to assume a known standard position relative to each other* so that subsequent movement of said actuating means will cause movement of said variable position slit jaw means in a precisely known tracking manner. 2· An optical slit mehhanism according to claim 1# in which! a second slit jaw is in confronting relationship with said variable position slit jaw means; so that a variable width slit is defined between said second sli jaw and said variable position slit jaw means* 3* An optical mechanism according to claim 2, in whicht said second slit jaw comprises a fixed mirror surface, causing a reflected image of said variable position s it jaw means to act as an effective second confronting variable slit jaw; whereby a slit having a fixed longitudinal center line is defined between said second effective slit jaw Image and said variable position slit jaw means* regardless of the position of the latter. An optical slit mechanism according to claim 1, in whlbhf said moving means comprises in part* first and second portions of a single cam; whereby motion of said cam causes automatic adjustment of said variable position slit jaw means to said standard position relative to said actuating means· 5* An optical slit mechanism according to claim ht in which I said single cam comprises a third portion for causing a programmed variation <in the position of said slit jaw means; whereby continuous movement of said cam causes resetting* adjustment* and then slit width programming of said variable position slit jaw means. 6. A self-adjusting optical slit mechanism for forming a pair of slits of variable width* comprising! a pair of adjustable slit jaw means; 27712/2 -ψ an actuating: means fo movi g each of said slit jaw means, including a slippable connection having substantial drag between each said slit Jaw and its corresponding actuating means} means for limiting movement of each of said slit jaws in a relatively open extreme} standard position means for limiting movement of each of said slit jaws in a relatively closed extreme) moving means for moving said actuating means and for forcin said, actuating means to move relative to each of said slit jaws through said slippable Connections when the movement of each of said slit jaws reaches the open or closed extreme; whereby each said slit jaw means and its said actuating means are caused to assume a known standard position relative to each other* so that subsequent movement of each of said actuating means will cause movement of its corresponding slit j w means in a precisely known tracking manner* 7* A self-adjusting slit mechanism according to claim 6f in whic t coupling means connect each of said actuating meanst whereby each of said variable position slit jaw means is moved by its actuating means in a similar manner; thus assuring sjtochronous tracking of both said slit jaw means. COHEN ZEDEK & SPISBACH P l Av