Abstract:
A microscope stage providing improved optical performance. A carriage for supporting an object has a transparent portion for receiving the object and permitting trans-illumination thereof. A base supports the carriage, at least a portion of the base comprising a transparent material to permit illumination of the specimen there through. Bearings disposed between the base and the carriage support the carriage on the base and permit relative movement thereof. The base has a dovetail cross sectional shape with bearings between the top of the carriage and the base and between the sidewalls of the carriage and the base. A cover is coupled to the carriage so as to transfer force thereto without imparting a significant movement thereto. A mechanism connected to the cover for moving the carriage relative to the base is disposed at a position offset from the axis of lateral symmetry of the carriage and base.

Description:
FIELD OF THE INVENTION 
   This invention relates to microscope stages, particularly to stages for scanning microscopes. 
   BACKGROUND OF THE INVENTION 
   To produce a high-resolution image, a microscope requires a numerical aperture in excess of about 0.6. To form a sharp image of an object over its full lateral extent, the features of the object that are of interest must be within the depth of focus of the microscope. To try to maintain the full lateral extent of an important feature of an object within the depth of focus of a microscope, high-grade mechanical stages are typically used to achieve sufficient flatness and repeatability of travel. In a scanning microscope the problem of maintaining the feature within the depth of focus can be remedied in part by detection of the best focal plane for the feature and adjusting the position of the optical system along its optical axis relative to the stage to compensate for any changes in flatness as the feature is moved laterally with respect to the optical system. This solution can only be successfully implemented to the extent the stage can repeatably position the object along the optical axis. In any case, a numerical aperture of 0.6 or more can reduce the depth of focus to the sub-micrometer level, which challenges the capability of known mechanical stages. 
   Another problem encountered with high numerical aperture microscopes is that, since the numerical aperture of the illumination system should match the numerical aperture of the observation optics to maximize the optical resolution of the image, a high numerical aperture requires a relatively large space for the mechanical components of the stage. This is because of the need to accommodate the components of a high numerical aperture illumination system. 
   These problems become particularly acute in a recent innovation in microscopy known as a miniature microscope array (“MMA”) or, when applied to a common object, as an “array microscope”. In miniaturized microscope arrays, a plurality of imaging lens systems are provided having respective optical axes that are spaced apart from one another. Each imaging lens system images a respective portion of the object. 
   In an array microscope, a linear array of imaging elements is preferably provided for imaging across a first dimension of the object, and the object is translated past the fields of view of the individual imaging elements in the array, so that the array is caused to scan the object across a second dimension to image the entire object. The relatively large individual imaging elements of the imaging array are staggered in the direction of scanning so that their relatively small fields of view are contiguous over the first dimension. The provision of the linear detector arrays eliminates the requirement for mechanical scanning along the first dimension, providing a highly advantageous increase in imaging speed. 
   The MMA concept invites the corresponding concept of providing each imaging element with a corresponding trans-illumination element. For optimal effect, the numerical aperture of the illumination lens systems needs to be matched to the numerical aperture of their corresponding imaging elements. That is, if the illumination system transmits light to the object at angles greater than the acceptance angle of the imaging system, some of the light may be wasted, which reduces system efficiency. On the other hand, if the illumination system transmits light over a narrower angular range, that is, one that does not extend to the acceptance angle, the imaging system cannot take full advantage of its resolving power. 
   In a high numerical aperture array microscope it is desirable to pack the imaging elements of the array close together so as to acquire image data for contiguous parts of the object in the minimum scan time. However, a trans-illumination system places a limit on how close the corresponding illumination lens system can be packed and still provide the desired matching of numerical apertures. This is because the object must be supported by a slide or other transparent member that must be sufficiently thick to provide mechanical stability. Where the illumination system must project light through a glass substrate 1 to 1.5 mm thick, the working distance cannot be greater than that amount. To have a sufficiently long illumination system working distance, while maintaining the same numerical aperture as the imaging system, the diameter of the lens of the illumination system must be larger than the diameter of the lens of the imaging element. This means that providing each imaging element with its own illumination element requires either that sub optimal imaging element packing or sub optimal numerical aperture matching must be employed. However, in a related patent application Ser. No. 10/191,874, entitled SINGLE AXIS ILLUMINATION FOR MULTI-AXIS IMAGING SYSTEM, it has been disclosed that in a multi-axis imaging system such as an array microscope, a single axis trans-illumination system permits maximum packing of the imaging elements and optimum matching of the numerical aperture of the illumination system with the numerical aperture of the imaging elements, while providing a practical working distance for the illumination system. Thus, a single axis optical system may be provided for illumination, preferably having the same numerical aperture as the individual imaging elements and an exit pupil large enough to fill the collective contiguous fields of view of the imaging array. 
   Since an object of using an MMA ordinarily is to achieve a high-resolution image, the afore-mentioned problem of maintaining focus with a scanning, high numerical aperture microscope array is typically encountered. Also, due to the wide lateral dimensions of the array, a relatively large stage is required to accommodate the illumination system whether it is a single axis or multi-axis illumination system. 
   Accordingly, there is a need for a microscope stage that maintain high flatness and repeatability during lateral movement for scanning, and that provides room for relatively large trans-illumination optics. 
   SUMMARY OF THE INVENTION 
   The present invention fulfills the need identified above by providing a microscope stage comprising a carriage for supporting an object to be viewed by a microscope, the carriage having a transparent portion for receiving the specimen and permitting trans-illumination thereof, a base for supporting the carriage, at least a portion of the base comprising a transparent material to permit illumination of the specimen there through, and bearings disposed between the base and the carriage for supporting the carriage on the base and permitting relative movement thereof. Preferably, the transparent portion of the base comprises glass and the transparent portion of the carriage comprises an aperture through the carriage. Also preferably, the base has a dovetail cross sectional shape, the bearings including one or more bearings between the top of the carriage and the base, and one or more bearings between the sidewalls of the carriage and the base. In a preferred embodiment, a movable cover is disposed over the base, the cover having an aperture for receiving the carriage. The cover is slidably supported on one side by a rail and supported on the other side by a lead screw drive mechanism, both of which are mounted on a support member that also supports the glass base. The carriage, base and cover define an axis of lateral symmetry in the direction of movement of the carriage, and the drive mechanism which moves the cover relative to the base, is disposed at a position offset from the axis of lateral symmetry. The cover is coupled to the carriage so that movement of the cover along the axis of lateral symmetry will also move the carriage, but will not impart a significant movement to the carriage. 
   Therefore, it is a principle object of the present invention to provide a novel and improved microscope stage. 
   It is another object of the present invention to provide a microscope stage that has improved flatness and straightness of travel characteristics. 
   It is a further object of the present invention to provide a microscope stage that permits trans-illumination of an object as well as mechanical stability. 
   The foregoing and other objects, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration of a first exemplary embodiment of a scanning microscope array. 
       FIG. 2  is an illustration of a second exemplary embodiment of a scanning microscope array. 
       FIG. 3  is a schematic diagram of an end view of a first microscope stage configuration according to the present invention. 
       FIG. 4  is a schematic diagram of the effect of placing a glass base between an illumination source and an object to be viewed by a microscope according to the present invention. 
       FIG. 5  is a schematic diagram of an end view of a second microscope stage configuration according to the present invention. 
       FIG. 6  is a schematic diagram of an end view of a third microscope stage configuration according to the present invention. 
       FIG. 7A  is a top view of a preferred embodiment of a microscope stage according to the present invention. 
       FIG. 7B  is a side section of the microscope stage of  FIG. 7A  taken along line  7 B— 7 B thereof. 
       FIG. 7C  is a side section of the microscope stage of  FIG. 7A , taken along line  7 C— 7 C thereof. 
       FIG. 7D  is an end section of the microscope stage of  FIG. 7A , taken along line  7 D— 7 D thereof. 
       FIG. 7E  is an end section of the microscope stage of  FIG. 7A , taken along line  7 E— 7 E thereof. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention comprises a microscope stage, including a microscope stage together with a microscope array, and particularly an array microscope. While the microscope stage is especially advantageous when combined with an array microscope, it may also be used advantageously with other types of microscopes and the invention is not limited by the specific configurations or embodiments disclosed herein. 
   1. Microscope Arrays 
   A first exemplary microscope array  10  is shown in  FIG. 1 . The microscope array  10  comprises an imaging lens system  12  having a plurality of individual imaging elements  14 . Each imaging element  14  may comprise a number of optical elements, such as the elements  16 ,  18 ,  20  and  22 . In this example, the elements  16 ,  18  and  20  are lenses and the element  22  is a detector, such as a CCD array. More or fewer optical elements may be employed. The optical elements are typically mounted on a vertical support  24  so that each imaging element  14  defines an optical imaging axis  26  for that imaging element. 
   The microscope array  10  is typically provided with a detector interface  28  for connecting the microscope to a data processor or computer  30  which stores the image data produced by the detectors  22  of the imaging elements  14 . An object is placed on a carriage or stage  22  which may be moved beneath the microscope array so that the object is scanned by the array. The array would typically be equipped with an actuator  34  for moving the imaging elements axially to achieve focus. The microscope array  10  would also include an illumination lens system, as explained hereafter. 
   A second exemplary embodiment of a microscope array  36  is shown in  FIG. 2 . In the imaging lens system, a plurality of lenses  38  corresponding to individual imaging elements are disposed on respective lens plates  40 ,  42  and  44 , which are stacked along respective optical axes  46  of the imaging elements. Detectors  48  are disposed above the lens plate  44 . As in the case of the microscope array  10 , the microscope array  36  may be employed to scan an object on a stage  50  as the stage is moved with respect to the array or vice versa. 
   Microscope arrays wherein the imaging elements are arranged to image respective contiguous portions of a common object in one dimension while scanning the object line-by-line in the other dimension are also known as an array microscope. Array microscopes may be used, for example, to scan and image entire tissue or fluid samples for use by pathologists. Individual imaging elements of array microscopes are closely packed and have a high numerical aperture, which enables the capture of high-resolution microscopic images of the entire specimen in a short period of time by scanning the specimen with the array microscope. 
   The detectors of array microscopes preferably are linear arrays of detector elements distributed in a direction perpendicular to the scan direction. As the imaging elements produce respective images that are magnified, each successive row of elements is offset in the direction perpendicular to the scan direction. This permits each imaging element to have a field of view that is contiguous with the fields of view of other appropriately positioned optical systems such that collectively they cover the entire width of the scanned object. The present invention is particularly suited for array microscopes; however, the present invention may be employed in other types of microscope arrays and multi-axis of imaging systems having a plurality of elements for imaging respective locations in space  2 . 
   2. Microscope Stage 
   The schematic illustration of a first configuration  52  of a microscope stage according to the present invention is shown in  FIG. 3 . This stage comprises a movable carriage  54  for supporting a microscope slide  56  and is supported by low friction bearings  58  on a base  60 . Preferably, the base has a dovetail shape; that is, its cross section is a quadrangle having two parallel sides  62  and  64 , side  62  being wider than side  64 , and having reflection symmetry about an axis  66 , thereby forming two conjugate sloped sides  68  and  70 . The carriage  54  includes downwardly extending sidewalls  72  and  74  whose interior surfaces  76  and  78  are substantially parallel to the respective sloped sides  68  and  70  of the base  60 , and are separated there from by bearings  80  and  82 , respectively. It should be understood that while a dovetail is the preferred shape for the base, other shapes, such as a rectangle, may be used without departing from the principles of the invention. 
   A window  84  is provided in a top portion  86  of the carriage  54  to permit trans-illumination of an object to be viewed by a microscope. Preferably, the window is an aperture through the top portion  86  of the carriage; however, it may also be a solid window of material, or a liquid cell, transparent over the wavelength band of interest. The base  60  comprises a transparent material, preferably glass, also to permit trans-illumination of the object. An appropriate illumination system  88 , as is understood in the art, is provided for propagating illumination light through the base  60  and the window  84  to the object. Axis  66 , which is the axis of symmetry of the base  60 , preferably serves also as the optical axis for the illumination and observation optical systems. 
   The transparent base  60  simultaneously provides mechanical support for the stage  54  and optical transparency over the wavelength band of interest for trans-illumination. Moreover, the dovetail shape provides a particularly stable mechanical configuration and the transparent material enables the carriage to move with high flatness and repeatability. One or the other of the bearings  82  and  80  may be preloaded to ensure constant contact with the surfaces of the base  60  and carriage  54 , thereby providing straightness of travel. The dovetail shape resists both lateral and vertical movement of the carriage with respect to the base. The base is preferably made of glass so that the surfaces adjacent to bearings  58 ,  80  and  82  may be polished to high flatness. The bearings are preferably made of Teflon® or another suitable material which provides a low friction contact. Alternatively, air bearings of a type commonly understood in the art could be employed. 
   Glass can be machined to very tight tolerances, for example, one quarter of the wavelength of visible light at 630 nanometers, that is, a tolerance of 150 nanometers. Using a BK7 glass dovetail with an included angle, 2θ, of 30°, it has been found that the flatness of travel of 0.03 microns and a straightness of travel of 0.2 microns can be achieved. It should be understood that while glass is the preferred medium for the base  60 , other materials having similar properties may be used without departing from principles of the invention. 
   Turning now to  FIG. 4 , in addition to providing for trans-illumination and polished bearing surfaces, the transparent base  60  provides the additional advantage of increasing the space available for the illumination system. When a plate  90  of refractive material having a refractive index n is placed in a focused beam  92  propagating through air, the optical path length of the beam is increased so that the original focal point  94  moves a distance d to new focal point  96 . The distance d is found as follows:
 
 d=t−t/n 
 
where t is the thickness of the refractive plate. Consequently, the base  60  actually extends the working distance of the illumination system  88  which provides more space for the stage and illumination system.
 
   A second configuration  98  of a microscope stage according to the present invention is shown in  FIG. 5 . The difference between configuration  98  and configuration  52  is in the structure of the base. In the case of the second configuration  98 , the base comprises two rails  100  and  102  which can be understood as what is left over from base  60  when a rectangular prism is removed from the center of base  60 , as shown by dotted lines  104  in  FIG. 3 . In this case, the transparency of the base is achieved by leaving the space between the two rails  100  and  102  empty. While this does not provide an increase in the working distance of the illumination system, it does provide the mechanical advantages of the dovetail base design, including the flatness and straightness of movement of the carriage. Preferably the rails  100  and  102  are made of glass with polished surfaces adjoining the bearings, though other materials with similar properties may be used, even if they do not have the property of transparency over the required wavelength range of the illumination light. 
   As shown in a third configuration  106  of a microscope stage according to the present invention, the base  108  of a microscope stage according to the present invention may incorporate or support additional optical elements of the illumination system. Thus, for example, an array of lenses  110  may be disposed on the top surface  112  of the base  108  to shorten the focal length of the illumination system and thereby increase its numerical aperture. In this case, a transparent base  108  is used, as explained with respect to the base  60  in configuration  52  of  FIG. 3 . However, it is to be understood that different types of optical elements, including diffractive elements as well as refractive elements, may be incorporated in or supported by the base  108 , depending upon the purpose they are to serve without departing from the principles of the invention. 
   3. Preferred Embodiment 
   A preferred embodiment  114  of a microscope stage according to the present invention is shown in  FIGS. 7A–7E . This embodiment is based on configuration  52  of  FIG. 3 . Accordingly, it comprises a glass base  116  having a dovetail cross section, a carriage  118  supported by bearings 120  on the glass base and having side bearings  122  for separating the side elements  124  of the carriage from the side walls  126  of the base. Preferably, bearings  120  and  122  are made of a low-friction material such as Teflon®, but air bearings could also be used as mentioned above. A cover  130  is also provided for engaging and moving the carriage. The cover  130  has an aperture  132  there through for receiving the stage  118 . The cover portion is supported at one side by slides  121 , which ride on rail  123  and at the other side by a bracket  125  which is supported by an anti-backlash nut  146  that engages a lead screw  142 . Thus, both the carriage and the cover have freedom to move longitudinally substantially along parallel but independent axis  134  and  135 , respectively, of the microscope stage. 
   The stage  118  is anti-backlash coupled to the cover  130  by a bearing or contact button  136  on the carriage which is disposed against a pawl  137  on the cover, and by a spring  138  held in place by a tab  139  on the cover so as to push against the carriage. Consequently, while the cover can impart force on the carriage portion to produce longitudinal movement of the stage portion, the carriage is not subjected to moment loading. This permits translational force to be applied to the cover long one side  140  thereof, without imparting significant rotational torque to the carriage, which ensure symmetric alignment with the base. Thus, for example, the lead screw  142  operating against a retainer block  144  and engaging the anti-backlash nut  146  and mounting block  148  can be disposed at side  140  so as to impart longitudinal motion to the cover while keeping to a minimum the eccentricity of loading of the carriage portion due to an induced moment thereon. The lead screw is preferably rotated by a motor  150 . However, other mechanisms for imparting force to the cover portion for producing longitudinal motion, such as a linear motor, may be used without departing from the principles of the invention. The glass base  116 , rail  123 , retainer block  144 , mounting block  148  and motor  150  are supported by a support member  156 . 
   As described with respect to  FIG. 3 , the preferred embodiment described in  FIGS. 7A–7E , includes an aperture  152  in the carriage portion for receiving a microscope slide  154  while permitting trans-illumination of the object to be observed by the microscope through the glass base  116 . 
   The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.