Abstract:
A stage comprising a first translation platform having a first axis of motion, and a second translation platform having a second axis of motion, a first linear drive motor for driving the first translation platform in the first axis of motion, and a second linear drive motor for driving the second translation platform in the second axis of motion, wherein each linear drive motor further comprises a coil assembly enclosing a rod stator, and wherein the coil assembly is fixed and the rod stator is movable within the coil assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Application 61/252,263, filed Oct. 16, 2009, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention generally relates to a motorized stage, and more particularly to a microscopy stage, for example, that is capable of operating a high speeds and with negligible backlash compared to conventional lead screw driven microscopy stages. 
       BACKGROUND 
       [0003]    Motorized microscopy stages are typically controlled by lead screws that are driven by x-axis and y-axis motors that extend well beyond the footprint of the loading stage plates. This can be problematic in tight environments where there is not much space between a microscope and the stage plates, for example, or where it is desired to interact with and manipulate specimen plates relative to the stage. In addition, high speed microscopy stages often experience mechanical backlash from a motorized screw-driven or contact-based drive system, which delays positioning of the specimen relative to the microscope objective. 
       SUMMARY 
       [0004]    A stage comprising, in one embodiment, a base platform, a first translation platform having a first axis of motion, and a second translation platform having a second axis of motion, a first linear drive motor for driving the first translation platform in the first axis of motion, and a second linear drive motor for driving the second translation platform in the second axis of motion, wherein each linear drive motor further comprises a coil assembly enclosing a rod stator, and wherein the coil assembly is fixed and the rod stator is movable within the coil assembly. The linear drive motors enable operation of the stage platforms at high speeds and with negligible backlash compared to conventional lead screw driven microscopy stages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is an exploded view of a stage in accordance with an embodiment of the invention. 
           [0006]      FIG. 2  is an exploded view of a linear drive in accordance with an embodiment of the invention. 
           [0007]      FIG. 3  is an assembled view of the linear drive of  FIG. 2 . 
           [0008]      FIG. 4  is an elevation of the linear drive of  FIG. 3 . 
           [0009]      FIG. 5  is a cross-section taken through line  5 - 5  of  FIG. 4 . 
           [0010]      FIG. 6  is an end view of the stator of the linear drive of  FIG. 3 . 
           [0011]      FIG. 7  is a cross-section taken through line  7 - 7  of  FIG. 6 . 
           [0012]      FIG. 8  is a partially exploded view of the stage of  FIG. 1 . 
           [0013]      FIG. 9  is a close-up view of the circled area  9  in  FIG. 8 . 
           [0014]      FIG. 10  is a partially exploded view of a stage in accordance with an alternative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    This disclosure describes the best mode or modes of practicing the invention as presently contemplated. This description is not intended to be understood in a limiting sense, but provides an example of the invention presented solely for illustrative purposes by reference to the accompanying drawings to advise one of ordinary skill in the art of the advantages and construction of the invention. In the various views of the drawings, like reference characters designate like or similar parts. 
         [0016]      FIG. 1  is an exploded view of one embodiment of a motorized stage such as, for example, a microscopy oriented XY translation stage  100  that is capable of operating a high speeds and with negligible backlash compared to conventional lead screw driven microscopy stages. The stage  100  described herein can be used with, for example, an autofocus apparatus as described in U.S. Patent Application 61/252,263, filed Oct. 16, 2009, the contents of which are incorporated herein by reference. Other uses of the stage  100  are possible. As will be described below, stage  100  comprises a tightly integrated, highly compact design with minimal thickness and moving parts in the optical axis of a microscope, for example. 
         [0017]    Stage  100  further comprises a base plate layer  110 , an X translation platform layer  120  and a Y translating platform layer  130  all with central apertures  112 ,  122 ,  132  respectively that are designed to accept microscopy oriented loads (not shown). The stage  100  is designed to accept a variety of loads including, but not limited to any style well plate, microscope slide, or general mounting platform, for example. The apertures  112 ,  122 ,  132 , whether arranged perpendicular or parallel to the mounting surface of the stage  100 , are preferably unobstructed by any components of the stage. The embodiment of the X platform  120  is coupled to the base plate  110  via a low-friction cross roller bearing rail pair  114 , and the Y platform  130  is coupled to the X platform  120  via another orthogonally orientated low-friction cross roller bearing rail pair  124 . While cross roller bearing rails are shown, it will be appreciated that other types of bearings may be used, such as carriage-type (see  FIG. 10 ), linear air bearings and others. Separation gaps between the platforms  120 ,  130  of the stage  100  are kept to a minimum while still allowing the three layers  110 ,  120 ,  130  of this construction to move freely with respect to each other. All motion and position feedback components are preferably integrated tightly within cavities formed between the platforms. In addition to the low friction bearing rails  114 ,  124  in the embodiment described herein, there are preferably no other physical contact points or coupled interfaces between the three layers  110 ,  120 ,  130  of the stage  100 , which ensures a high degree of friction free motion with consequent low maintenance and high reliability. 
         [0018]    In one embodiment described herein, motion drive forces in both the X and Y directions are generated in a non contact implementation that eliminates the need for lead screws, belts drives, gear boxes or any other form of contact-based drive system. In one embodiment, the non contact drive comprises orthogonally located linear motors  140 ,  142  that are fully integrated within the structure of the stage  100 . Cavities are preferably created between the three layers of the stage  100 , one cavity  116  for the X linear motor  140  between the base plate  110  and X translation platform  120  and one cavity  126  for the Y linear motor  142  between the X translation platform  120  and the Y translation platform  130 . While the linear motors  140 ,  142  are illustrated as integrated into the stage construction, the drive/controller system could also be separate from the stage construction if desired. 
         [0019]      FIG. 2  is an exploded view of one embodiment of the linear motor  140 ,  142  of  FIG. 1 .  FIG. 3  is an assembled view,  FIG. 4  is an elevation and  FIG. 5  is a cross-section taken through line  5 - 5  of  FIG. 4  of the embodiment of the linear motor  140 ,  142 . While linear motors  140 ,  142  are, for purposes of this discussion preferably identical, for ease of explanation the linear motor of  FIGS. 2-5  will be identified as linear motor  140 . Linear motor  140  comprises a rod shaped stator  150  and an enclosing electromagnetic coil assembly  160 . The stator  150  is assembled preferably using a stainless steel stator tube  152  within which are located a series of cylindrical magnets  154  disposed between end caps  156 , the magnets  154  being arranged end face to end face and in such an orientation that the same magnetic poles are adjacent to each other as shown in  FIG. 7 , which is a cross-section taken through line  7 - 7  of the end view of the stator  150  of  FIG. 6 . The coil assembly  160  preferably comprises a stainless steel tube  162  on which a number of coil segments  164  are wound and bonded to the tube. Insulating washers  166  are located between each coil segment  164 . The stator tube  152  is dimensioned to allow the coil assembly tube  162  to slide freely over and without making contact. While certain materials are described herein in connection with the construction of certain aspects of the linear motor, it will be appreciated that other materials, alloys, material compositions or combinations of the same are also contemplated. 
         [0020]      FIG. 8  illustrates a partially exploded view of one embodiment of the stage  100  with the X translation platform  120  assembled onto the base  110  and the Y translation platform  130  positioned above the X translation platform  120  for assembly thereon.  FIG. 9  is a close-up view of circled region  9  in  FIG. 8 . The coil assembly  160  of each linear motor  140 ,  142  is tightly integrated into the stage assembly by being housed in cavities  116 ,  126  therein. For the X axis of motion, the coil assembly is held in a cavity  116  ( FIG. 1 ) within the base plate  110 . For the Y axis of travel, the coil assembly is held within a cavity  126  within the X translation platform  120 . The X axis coil assembly is fixed relative to the motion of the X translation platform  120  and the Y axis coil assembly is fixed relative to the motion of the Y translation platform  130 . The X axis stator tube is mounted to the X translation platform  120  in such a way that it passes through the center of the X axis coil assembly tube ( FIG. 1 ). Similarly, the Y axis stator tube is mounted to the Y translation platform  130  in such a way that it passes through the center of the Y axis coil assembly tube. In the embodiments illustrated herein, it is the stator tube and not the coil assembly that is in motion for each axis of travel. 
         [0021]    As shown in  FIG. 1 , position feedback is facilitated using, in one embodiment, linear encoder scales  170 ,  180  embedded in cavities  118 ,  128  respectively located within the stage construction. The X axis encoder  170  is located in cavity  118  contained within the base plate  110  and the Y axis encoder  180  is contained within a cavity  128  located within the X translation platform  120 . The associated read heads are located in the X translation platform  120  for the X axis and the Y translation platform  130  for the Y Axis. While linear encoder scales are described herein, other positioning means are contemplated. In the stage  100  of the current embodiment, the bearing rails, stator tube and linear encoder scale are preferably oriented to be parallel to each other in each axis of motion. 
         [0022]      FIG. 10  illustrates an alternative embodiment of a stage  200  further comprising a base plate layer  210 , an X translation platform layer  220 , and a Y translating platform layer  230  that is similar in design to the stage  100  of  FIGS. 1-9 . In the embodiment of  FIG. 10 , the Y platform  230  is coupled to the X platform  220  via a low-friction recirculating-type carriage bearing rail pair  224  including carriage bearings  225  that are secured to the Y platform by fasteners  226 , for example. While screw fasteners  226  are shown, other fasteners are possible. Similarly, the X platform  220  is coupled to the base plate layer  210  via another orthogonally orientated low-friction recirculating-type carriage bearing rail pair including carriage bearings (not shown). With recirculating type bearings that use a single rail  224 , for example, the performance of the stage  200  may be more reliable as such bearings are less likely to open up than the crossed rollers if the stage  200  is distorted through, preloading, pinning to an uneven mounting platform or through thermal expansion, for example. Irrespective of the type of bearings used, separation gaps between the platforms  220 ,  230  of the stage  200  are kept to a minimum while still allowing the three layers  210 ,  220 ,  230  of this construction to move freely with respect to each other. 
         [0023]    Thus, there is provided a monolithic two-axis or three-axis stage, each axis being driven by a linear induction motor comprised of a linearly displaceable magnetic rod assembly encapsulated by stationary cylindrical coils. Each axis of movement is dependent on the translation platform and the positioning of the X and Y translation platforms relative to each other and to the base platform, such that aside from the base platform of the stage, each axis is preferably not operable on its own if separated. In addition, while not shown, the concepts disclosed herein could also be expanded to a third axis of movement, such as the Z axis or along an optical axis as in microscopy applications, for example, where a similar translation along a third axis is driven by a similarly arranged linear motor assembly. 
         [0024]    The stage  100  or  200 , for example, can be used in a variety of industries for a variety of applications. One non-limiting example is for microscopy where the stage is used to either position any part of a microscope with respect to a sample, or a sample with respect to a microscope. With microscopy applications in particular, a major practical advantage is realized by incorporating plates with minimal thickness and a minimum separation therebetween, which results in a lower overall mass and less power required to accelerate the stage. Another non-limiting example includes machine vision inspection, or non contact-based dimensional inspection. Other industries and applications are contemplated. 
         [0025]    While the present invention has been described at some length and with some particularity with respect to the several described embodiments, it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment, but it is to be construed with references to the appended claims so as to provide the broadest possible interpretation of such claims in view of the prior art and, therefore, to effectively encompass the intended scope of the invention. Furthermore, the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto.