Abstract:
Devices for using optical filters in a filter holder that enable optical filters to be simply, conveniently, and flexibly interchanged.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a related application of the following patent applications, each of which is incorporated herein by reference: U.S. patent application Ser. No. 09/062,472, filed Apr. 17, 1998 U.S. Pat. No. 6,071,768; and PCT patent application Ser. No. PCT/0398/14575, filed Jul. 15, 1998, 
     This application is based upon and claims benefit under 35 U.S.C. §119 of the following U.S. Provisional Patent Applications, each of which is incorporated herein by reference: Ser. No. 60/052,876, filed Jul. 16, 1997; Ser. No. 60/059,639, filed Sep. 20, 1997; Ser. No. 60/063,811, filed Oct. 31, 1997; Ser. No. 60/072,499, filed Jan. 26, 1998; Ser. No. 60/072,780, filed Jan. 27, 1998; Ser. No. 60/075,414, filed Feb. 20, 1998; Ser. No. 60/075,806, filed Feb. 24, 1998; Ser. No. 60/082,253, filed Apr. 17, 1998; Ser. No. 60/084,167, filed May 4, 1998; Ser. No. 60/085,335, filed May 13, 1998; Ser. No. 60/085,500, filed May 14, 1998; and Ser. No. 60,089,848, filed Jun. 19, 1998. 
     This application incorporates by reference the following U.S. patent applications: Ser. No. 09/118,341 filed Jul. 16, 1998 now U.S. Pat. No. 6,025,985, and Ser. No. 09/118,310 filed Jul. 16, 1998, now U.S. Pat. No. 6,033,600. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to optical filters. More particularly, the invention relates to devices for using optical filters in a filter holder that enable optical filters to be simply, conveniently, and flexibly interchanged. 
     BACKGROUND OF THE INVENTION 
     Optical systems typically include many components, which interact to generate, transmit, modify, and detect light. Light may be generated by light sources, transmitted by optical relay structures, and detected by detectors. Light may be modified by optical filters positioned in an optical path in one or both of the light source and detector ends of the instrument. 
     Optical filters modify the intensity, spectrum, polarization, and other properties of light. “Intensity filters” modify the intensity of light, where intensity is the amount of light per unit area per unit time. Intensity filters may absorb light, dissipating the absorbed energy as heat, or they may reflect or scatter light. “Spectral filters” modify the spectrum of light, where spectrum is the wavelength composition of light. Spectral filters may selectively transmit light of preselected wavelengths and selectively absorb, reflect, or scatter light of other wavelengths. A spectral filter may convert light of many colors into light of one or only a few colors. “Polarization filters” modify the polarization of light, where polarization is the direction of the electric field associated with light. 
     Different applications or conditions may require different optical filters. For this reason, filter holders have been developed that allow one of a plurality of optical filters to be selected and placed in an optical path. Examples include filter wheels and filter slides. Unfortunately, these filter holders have a number of shortcomings. In particular, the number of optical filters required even for a single application often exceeds the filter-holding capacity of a given filter holder. Therefore, it sometimes is necessary to replace the optical filters within a given filter holder. 
     Replacing optical filters may be difficult and time-consuming. If individual optical filters are affixed permanently to the filter holder, the entire filter holder may need to be replaced. If individual optical filters are affixed to removable filter cartridges within the filter holder, the filter holder still must be opened, individual filter cartridges removed and replaced, and the filter holder closed again. In known filter holders, filter cartridges must be replaced with the filter holder attached to an associated instrument. Working space may be minimal, and filter cartridges and other components may be dropped into the instrument, where they may cause damage and be difficult to retrieve. 
     Replacing optical filters within filter cartridges also may be difficult and time-consuming. Many or most optical filters are permanently affixed to any associated filter cartridge, and may not be replaced at all. Other optical filters may be removably affixed to an associated filter cartridge, but replaceable only with a limited selection or number of filters. Filter cartridges with removable optical filters may employ a retaining ring that fits into a groove on the inside of the filter cartridge to hold the optical filter. The groove establishes a predetermined position for the retaining ring, and may limit the thickness or number of replacement filters. Optical filters that are thicker than the provided space will not fit, and optical filters that are thinner than the provided space may require spacers. Filter cartridges with removable optical filters also may employ a threaded retention member that can be screwed into the filter cartridge until a point where it holds the optical filter. This approach may require extra tools and be time-consuming. This approach also may force the retaining ring into a plane that is slightly skewed relative to the filter, misaligning the optical filter. 
     SUMMARY OF THE INVENTION 
     The present invention addresses these and other shortcomings by providing filter cartridges and filter holders that enable optical filters to be simply, conveniently, and flexibly interchanged. 
     In one embodiment, the invention provides a device for holding an optical filter that includes a filter barrel having an inner wall and a stop structure, a removable annular friction member inside the filter barrel, and at least one optical filter sandwiched between the stop structure and the friction member. In this embodiment, the friction member is held in place relative to the inner wall by static friction, without any thread, groove, or adhesive. The filter barrel and friction member may take a variety of forms and may hold optical filters of various sizes and numbers. The friction member may hold the optical filter snugly in place during routine use, while also permitting easy removal when replacing optical filters. 
     In another embodiment, the invention provides a tool device for loading an optical filter into a holder. The device includes a funnel structure having a top end and a lower edge configured to rest on top of a filter holder. The funnel structure includes an inner diameter that enlarges gradually in a direction from the lower edge toward the top end. The device also may include a slug for applying pressure to a friction member when loading the optical filter. 
     In yet another embodiment, the invention provides an optical filter holder system that includes a holder having a plurality of apertures, and two sets of filter cartridges configured to fit in the apertures. The first set of filter cartridges includes an optical filter permanently fixed in the filter cartridge. The second set of filter cartridges includes a mechanism that permits easy replacement of different optical filters in the same filter cartridge. The filter holder may include a filter wheel, and the mechanism that permits easy replacement my include a filter barrel and friction member. 
     In yet another embodiment, the invention provides an optical filter wheel module including an optical filter wheel that is rotatable around a hub structure, and a wheel case having a static portion and a removable portion and at least one set of windows for transmitting light through the wheel case and through a selected optical filter contained in the optical filter wheel. The hub structure is built into the removable portion of the wheel case. The wheel case may be light tight and include more that one set of windows. 
     In yet another embodiment, the invention provides a device for holding an optical filter comprising a base having a hub structure, and an elongate filter cartridge having a filter end and a pivot end, the filter end configured to hold at least one optical filter, the pivot end configured turnably to attach to the hub structure, so that an optical filter can be turned between two positions about the hub structure. 
     The invention will be understood more readily after consideration of the drawings and the detailed description of the invention that follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially exploded perspective view of an optical filter wheel assembly constructed in accordance with the invention. 
     FIG. 2 is a partially exploded perspective view of a portion of an optical filter wheel assembly like that shown in FIG. 1, showing a mechanism by which short filter cartridges may be removed. 
     FIG. 3 is a partially exploded perspective view of the portion of the optical filter wheel assembly shown in FIG. 2, showing a mechanism by which tall filter cartridges may removed. 
     FIG. 4 is a perspective view showing a mechanism by which optical filters may be placed in a tall filter cartridge. 
     FIG. 5 is a perspective view showing a mechanism by which a friction member may be pressed into place using a funnel and slug. 
     FIG. 6 is a top view of a short filter cartridge constructed in accordance with the invention. 
     FIG. 7 is a cross-sectional view of the short filter cartridge, taken generally along the line  7 — 7  in FIG.  6 . 
     FIG. 8 is a top view of a tall filter cartridge constructed in accordance with the invention. 
     FIG. 9 is a cross-sectional view of the tall filter cartridge, take generally along the line  9 — 9  in FIG.  8 . 
     FIG. 10 is a top view of a funnel structure constructed in accordance with the invention. 
     FIG. 11 is a cross-sectional view of the funnel structure, taken generally along the line  11 — 11  in FIG.  10 . 
     FIG. 12 is a partial perspective view of an alternative filter holder assembly constructed in accordance with the invention. 
     FIG. 13 is a schematic, partial perspective view of an exemplary light detection system incorporating optical filter wheel assemblies. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a partially exploded perspective view of an optical filter wheel assembly  20  constructed in accordance with the present invention. Optical filter wheel assembly  20  includes a filter wheel  22  that is rotatable about a hub structure  24 , and a wheel case having a static base portion  26  and a removable lid portion  28 . Hub structure  24  is built into removable lid portion  28 . 
     Filter wheel  22  holds filter cartridges  30 . Filter wheel  22  is substantially circular and includes a plurality of apertures  32  disposed symmetrically about its outer perimeter  34 . Apertures  32  are used for mounting filter cartridges  30  and may hold the filter cartridges via friction, threads, or other means. Filter wheel  22  may have a variety of shapes, and apertures  32  may be disposed in a variety of configurations, although a symmetric embodiment is preferred for balance and ease of rotation about hub structure  24 . 
     Removable lid portion  28  holds filter wheel  22 . Removable lid portion  28  is substantially rectangular, with an enclosed top  36  and sides  38   a-d  and an open bottom  40  for receiving filter wheel  22 . Opposed flanges  42  extend downward from one pair of opposed sides  38   b,d  of removable lid portion  28  to support hub structure  24 . Filter wheel  22  is rotatably mounted through its center on hub structure  24 . 
     Static base portion  26  holds removable lid portion  28  and filter wheel  22 . Static base portion  26  is substantially rectangular, with an enclosed bottom  44  and sides  46   a-d  and an open top  48  for receiving filter wheel  22 . Opposed slots  50  extend downward into one pair of opposed sides  46   b,d  of static base portion  26  to receive opposed flanges  42 . Opposed posts  52  extend upward from the other pair of opposed sides  46   a,c  of static base portion  26  to be received by opposed holes  54  in opposed sides  38   a,c  of removable lid portion  28 . Flanges  42  and slots  50 , and posts  52  and holes  54 , individually and collectively form a post-to-hole mating structure that aligns static base portion  26  and removable lid portion  28  when the two portions are mated together to form the wheel case. Captive screws  56  situated in holes  54  and accessible from top  36  may be threaded into posts  52  to hold together removable lid portion  28  and static base portion  26 . Static base portion  26  further may be fixed to an instrument platform to form a portion of a light source module, detector module, or other optical assembly, among other applications. 
     The assembled wheel case is substantially light-tight, except for light that is transmitted through two sets of opposed windows  58  included in static base portion  26 . Windows  58  are used for transmitting light through the wheel case and through a selected optical filter contained in a filter cartridge  30  in filter wheel  22 . Windows  58  are located on opposite sides of hub structure  24 , so that any given optical filter in filter wheel  22  can be rotated into alignment with either set of windows. In turn, light sources, detectors, and other optical components can be aligned with either or both sets of filters. Generally, the wheel case includes at least one set of windows, which may be located on the static portion, removable portion, or other portion of the wheel case. 
     Filter wheel  22  may be rotated by a drive motor  60 , which is attached to removable lid portion  28  in optical filter wheel assembly  20 . Drive motor  60  or other drive mechanisms also may be operatively connected to optical filter wheel assembly  20  at other points and in other manners. 
     FIG. 1 also shows a mechanism by which optical filter wheel assembly  20  may be disassembled and reassembled. Optical filter wheel assembly  20  is disassembled as follows. First, any associated instrument is powered down and unplugged. Second, any secondary housing enclosing optical filter wheel assembly  20  is removed. Third, drive motor  60  is unplugged at its inline connector  62 . Fourth, captive screws  56  are loosened. Finally, removable lid portion  28  and filter wheel  22  are pulled out of static base portion  26 . 
     Optical filter wheel assembly  20  may be reassembled as follows. First, filter cartridges  30  are checked to verify that they are properly seated in filter wheel  22 , and filter wheel  22  is checked to verify that it rotates smoothly about hub structure  24  when moved by hand. Second, removable lid portion  28  and filter wheel  22  are inserted into static base portion  26 , aligning flanges  42  with slots  50 , and posts  52  with holes  54 . Third, captive screws  56  are tightened. Fourth, drive motor  60  is plugged back in at inline connector  62 . Fifth, any secondary housing is replaced. Finally, any associated instrument is plugged back in and powered up, if desired. 
     FIG. 2 shows a partially exploded perspective view of a removable portion  80  of an optical filter wheel assembly, including a filter wheel  82 , removable lid portion  84 , and drive motor  86 . Filter wheel  82  includes a set of “short” filter cartridges  88  and a set of “tall” filter cartridges  90 . Filter wheel  82  may hold a variety of filter cartridges, so long as the filter cartridges are configured to fit in apertures  92  in the filter wheel. Generally, opposed apertures in filter wheel  82  should contain matching filter cartridges or a suitable slug to balance the filter wheel and to prevent unfiltered radiation from reaching a detector. 
     FIG. 2 also shows a mechanism by which short filter cartridges  88  may be removed and replaced. Generally, short filter cartridges  88  include an optical filter  94  permanently affixed by suitable means, such as glue, to a short filter barrel  96  having a low profile. Optical filter  94  may include an intensity filter, a spectral filter, or a polarization filter, among others. Short filter cartridges  88  are removed from filter wheel  82  as follows. First, with the filter wheel removed as described above, the desired short filter cartridge is located by sight or by location. (Filter cartridge locations within the filter wheel may be marked on the filter wheel or elsewhere for reference.) Second, the short filter cartridge is removed by turning it counter-clockwise, which unscrews it. The short filter cartridge may be turned by hand or by a special tool, such as a spanner wrench  98  having prongs  100  that engage grooves  102  in the sides of the short filter cartridge  104 . Finally, filter changes are noted on the filter wheel or elsewhere and in any associated instrument software. Short filter cartridges  88  may be replaced in filter wheel  82  by reversing the process, turning the short filter cartridge clockwise. 
     FIG. 3 shows a partially exploded perspective view of a removable portion  120  of an optical filter wheel assembly, as shown in FIG.  2 . FIG. 3 also shows a mechanism by which tall filter cartridges  122  may be removed and replaced. Generally, tall filter cartridges  122  include an optical filter  124  affixed by a removable friction member  126  to a tall filter barrel  128 . Optical filter  124  may include an intensity filter, a spectral filter, or a polarization filter, among others. Friction member  126  and tall filter barrel  128  may be substantially annular. Tall filter cartridges  122  may be removed from and replaced in filter wheel  130  much like short filter cartridges  88 ; however, tall filter cartridges  122  generally are turned by hand rather than by a tool. 
     FIGS. 4 and 5 show a perspective view of a mechanism by which optical filters may be replaced in the tall filter cartridges. First, as shown in FIG. 4, the optical filter  150  is placed in the tall filter barrel  152 . Optical filter  150  should be oriented properly if one side is different than the other. Additional optical filters  150  can be placed in tall filter barrel  152 , if desired. Second, as shown in FIG. 5, a funnel structure  154  is placed on top of tall filter barrel  152 . Third, an annular friction member  156  is placed in funnel structure  154 , followed by a slug  158 . Slug  158  and optical filter  150  have approximately equivalent peripheral dimensions, including radii. Fourth, slug  158  is pushed down through funnel structure  154  to compress friction member  156 , which should fit snugly against optical filter  150 . Finally, slug  158  and funnel structure  154  are removed. The completed tall filter cartridge then can be installed in a filter wheel, as described above. 
     Optical filter  150  also may be replaced by other techniques. Generally, the tall filter cartridges incorporate a mechanism that permits easy replacement of different optical filters in the same cartridge, enhancing the flexibility of the tall cartridges. 
     Optical filter  150  may be removed from the tall filter cartridge as follows. First, a lint-free cloth is placed on a work surface. Second, the installed optical filter  150  (or slug  158 ) is pushed gently near its center with a gloved finger or thumb, which will cause the optical filter  150  and friction member  156  to drop out of tall filter barrel  152 . Removed optical filter  150  should be stored so that it will not become dirty or scratched. 
     FIGS. 6 and 7 show detailed views of a short filter cartridge  180 , which includes a short filter barrel  182  and optical filter  184 . Short filter barrel  182  is substantially annular, with a threaded lower portion  186  that screws into an aperture in a filter wheel, and a graspable upper portion  188  having a knurled rim  190  that may be turned by hand. Optical filter  184  is supported by upper portion  188 , and mounts adjacent a stop structure  192  and inner wall  194  on short filter barrel  182 , so that it is substantially centered relative to short filter barrel  182 . Stop structure  192  includes an edge  196  oriented substantially perpendicular to a principal plane of optical filter  184  and to inner wall  194 . 
     FIGS. 8 and 9 show detailed views of a tall filter cartridge  210 , which includes a tall filter barrel  212  and optical filter  214 . Tall filter cartridge  210  resembles short filter cartridge  180  in many respects. Tall filter barrel  212  is substantially annular, with a threaded lower portion  216  that screws into an aperture in a filter wheel, and a graspable upper portion  218  having a knurled rim  220  that may be turned by hand. Optical filter  214  is supported by upper portion  218 , and mounts adjacent a stop structure  222  and inner wall  224 . Stop structure  222  includes an edge  226  oriented substantially perpendicular to a principal plane of optical filter  214  and to inner wall  224 . Inner wall  224  may be substantially perpendicular to the optical filter, as here, or it may have a funnel portion that graduates in diameter in a direction toward the stop structure, among other configurations. Lower portion  186  of short filter barrel  182  is substantially identical to lower portion  216  of tall filter barrel  212 . However, upper portion  188  of short filter barrel  182  is shorter than upper portion  218  of tall filter barrel  212 , giving it a lower profile. In addition, optical filter  184  of short filter barrel  182  is permanently affixed to upper portion  188 , whereas optical filter  214  of tall filter barrel  212  is removably sandwiched in upper portion  218  between stop structure  222  and a friction member  228 . Friction member  228  holds optical filter  214  in place relative to inner wall  224  in tall filter cartridge  210  by static friction, without any thread, groove, or adhesive. For this reason, among others, optical filters of various numbers and sizes may be secured. 
     Friction member  228  may take a variety of forms, including a compressible ring having an uncompressed outer diameter greater than the inner diameter of inner wall  224 . The compressible ring may exert a force on the inner wall that provides sufficient static friction to hold an optical filter snugly in place during routine use, while also permitting easy removal when replacing optical filters. 
     FIGS. 10 and 11 show detailed views of a funnel structure  240 , which is used for loading an optical filter into a tall filter cartridge or other holder as described above. Funnel structure  240  is substantially annular and includes inner and outer walls  242 ,  244  and a top end  246  and lower edge  248 . Lower edge  248  includes a groove  250  adjacent inner wall  242  configured to rest on top of a filter cartridge or other holder. The inner diameter of funnel structure  240  measured between inner walls  242  enlarges gradually in a direction from lower edge  248  to top end  246 . 
     FIG. 12 shows a partial perspective view of an alternative filter holder assembly  270 . Filter holder assembly  270  includes an elongate filter cartridge  272  and a base  274 . Elongate filter cartridge  272  includes a filter end  276  and a pivot end  278 . Filter end  278  is configured to hold optical filters, and includes two filter slots  280   a,b  in which optical filters  281  may be glued or otherwise attached. Generally, the filter end may hold one or more optical filters, using slots, apertures, short or tall filter cartridges, or other mechanisms. Filter slots may be left open to allow light to pass unfiltered, include filters to filter light, or include slugs or other opaque structures to block light. Pivot end  278  is configured turnably to attach to a hub structure, and includes an aperture  282  for receiving a drive axle or other pivot structure. Generally, the pivot end may attach through any means to any suitable drive mechanism. Elongate filter cartridge  278  is fan shaped, filter end  276  being wider than pivot end  272 , although other shapes also are possible. 
     Base  274  generally supports elongate filter cartridge  272 . Base  274  includes a hub structure  284  and major and walls  286 ,  287  that substantially surround elongate filter cartridge  272  on all but one side. Elongate filter cartridge  272  is turnably attached at its pivot end  278  to hub structure  284  through a drive axle  288 , about which it may turn. Base  274  also includes a window  289  in major wall  286 . 
     Elongate filter cartridge  272  may be used for moving an optical filter in and out of an optical path, much like a filter wheel or filter slide, by turning elongate filter cartridge  272  about hub structure  284 . Because elongate filter cartridge  272  may move one or a few filters in and out of an optical path by turning through a limited angle, it may be configured to require less space than a filter wheel of comparable radius. A drive mechanism  290  may be controlled or base  274  may be configured to limit the angle through which elongate filter cartridge  272  may turn. For example, in filter holder assembly  270 , a position  292  on minor wall  287  forms a stop structure that physically limits movement if drive mechanism  290  attempts to turn elongate filter cartridge  272  past the wall. 
     FIG. 13 is a partial perspective view of an exemplary light detection system  300  that incorporates optical filter wheel assemblies in accordance with the invention. The light detection system includes a light source  310 , an excitation optical filter wheel assembly  320 , an excitation optical relay structure  330   a,b  an examination site  10 , an emission optical relay structure  350   a,b , an emission optical filter wheel assembly  360 , and a detector  370 . These components may be used in photoluminescence and chemiluminescence applications. For example, in photoluminescence applications, excitation light is directed from light source  310  through excitation optical filter wheel assembly  320  to select its wavelength, through at least a portion of excitation optical relay structure  330   a,b , and onto a sample positioned in a sample holder  380  at examination site  10 . Emission light from the sample is directed through at least a portion of emission optical relay structure  350   a,b , through emission optical filter wheel assembly  360  to select its wavelength, and onto detector  370 . 
     Accordingly, while the invention has been disclosed in preferred forms, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense, because numerous variations are possible and no single feature, function, or property of the preferred embodiments are essential. The invention is to be defined only by the scope of the issued claims.