Abstract:
This invention provides a system and method to determine orientation/pose of a contact lens residing on the transparent bottom of a fluid-filled, typically opaque-sided cuvette. This allows the system to determine whether the subject contact lens is in a concave up or concave down orientation, and whether the lens is everted. An illuminator is aligned on a longitudinal axis of the cuvette through the contact lens at a position over the cuvette, and a vision system camera is aligned beneath the bottom of the cuvette on the axis. In alternate embodiments the axial locations of the camera and the illuminator can be varied. The camera acquires images of the contact lens. The vision system associated finds the appropriate contact lens edges and characteristics of features. These features allow each of the four poses to be distinguished and categorized for either an acceptable/good or unacceptable/bad pose within the cuvette.

Description:
FIELD OF THE INVENTION 
     This invention relates to the use of vision systems in testing manufactured products, and more particularly to the testing of contact lenses. 
     BACKGROUND OF THE INVENTION 
     The wearing of contact lenses is a popular technique for correcting a variety of vision problems. So-called “soft” contact lenses are particularly popular with wearers because they consist of a high water volume and conform closely to the wearer&#39;s eye. This significantly increases the comfort of the wearer, particularly when a contact lens is worn over a long duration. 
     Like many other medical products, contact lenses are expected to meet high standards for quality and reliability. As part of the quality assurance and quality control (QAQC) procedures in manufacturing contact lenses, specimens from some or all of the manufactured batches are subjected various test processes. This ensures generally that the manufacturing processes are sound and that a stable level of quality is maintained over time. An approach to testing a sample contact lens entails loading it manually or automatically (e.g. robotically) into a fluid-filled (e.g. saline) cuvette, and testing the contact lens. An exemplary cuvette is a glass or polymer tube with a flat transparent bottom. Notably, processes can be properly performed on the subject contact lens if the contact lens rests on the bottom of the cuvette in a concave down orientation, and is not everted (inside out). While the manual or automated loading process makes efforts to ensure the lens is in the desired non-everted, concave-down orientation, there are times when the contact lens is loaded improperly. In fact, there are four possible orientations (“poses”) for a soft contact lens resting on the bottom of a fluid-filled cuvette for any given inspection cycle. These four loaded poses are: 
     1. non-everted concave down (CCD, good) 
     2. non-everted concave up (CCU, bad) 
     3. everted concave down (ECCD, bad) 
     4. everted concave up (ECCU, bad) 
     If the contact lens has pose 1 (CCD, good), then it can be transferred to one or more further processes. If the contact lens has pose 2 (CCU, bad), it should be flipped into the correct orientation, requiring further physical action before proceeding to further processes. If the contact lens has pose 3 or 4 (ECCD or ECCU, both bad), it is typically discarded, as it has experienced possible plastic deformation that renders it imperfect. 
     While it may be possible to determine the pose of a contact lens readily based upon a side view image of it in the cuvette, the processes to which the contact lens is subjected employ a cuvette with opaque or diffusive side walls. It is therefore not practical to obtain a side view of the lens. Rather, only a top or bottom view with front or back lighting of the contact lens is attainable, i.e. a “face-on” view. It is more challenging to determine the pose of the contact lens (either manually or using a vision system application) from this view point. 
     It is therefore desirable to provide a system and method for determining the orientation/pose of a contact lens with respect to a cuvette in a face-on view, using a vision system that can distinguish between various poses based upon such direct, face-on view of the top or bottom surface of the contact lens. This system and method should allow for relatively quick categorization of the pose so that further processes (if desired) can be employed with respect to the contact lens and should enable the use of commercially available illuminators and vision system components. 
     SUMMARY OF THE INVENTION 
     This invention overcomes disadvantages of the prior art by providing a system and method that employs vision system tools to determine the orientation or pose of a contact lens residing on the transparent bottom of a fluid-filled, typically opaquesided or diffusive-sided cuvette. This allows the system to determine whether the contact lens is in a concave up or concave down orientation, and whether the lens is everted. In an illustrative embodiment, an illuminator is aligned approximately on a longitudinal axis of the cuvette through the contact lens at a position over the cuvette. A vision system camera is aligned beneath the bottom of the cuvette approximately on the axis to acquire a face-on view of the contact lens. In alternate embodiments the axial locations of the camera and the illuminator can be varied. The camera acquires one or more (typically grayscale) images of the contact lens. The vision system associated with the camera operates vision system tools to find the appropriate contact lens edges and to identify the characteristic features within the perimeter of the lens in the vicinity of the perimeter edge. These features allow each of the four poses to be distinguished and categorized. These vision system tools can determine, illustratively, subtle cues in the acquired image of the contact lens. These cues include focus gradients and dark/bright bands near the edge of the lens. Illustratively, the system and method processes the contact lens image to obtain (a) an average radial intensity profile near the edge of the contact lens and (b) a focus gradient profile measured in the radial direction from the lens center to its edge. These raw profiles (as well as features computed from these profiles) are used to classify the pose of each lens. This classification can be based upon one of a plurality of sets of image features for each pose of lens. These features can be derived from a plurality of acquired images of actual contact lenses in each pose. Typically a large number of training images for each pose can be trained and the classification of the pose of the contact lens in the runtime image is based upon conformity to the training image(s) using vision tool conventional techniques. 
     In an illustrative embodiment, the system and method can be used to classify the pose of a variety of differing contact lens types. Such types include, but are not limited to, spherical, toric, and those contact lenses with or without printed iris designs (e.g. eye-color-changing contact lenses). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention description below refers to the accompanying drawings, of which: 
         FIG. 1  is a diagram of an arrangement for determining the orientation or pose of a contact lens in a fluid-filled cuvette with a vision system, in which the camera thereof is aligned approximately along a longitudinal axis of the cuvette; 
         FIG. 2  is a diagram of four images of an exemplary spherical contact lens in the fluid-filled cuvette of  FIG. 1 , showing four discrete poses for the lens with respect to the bottom of the cuvette; 
         FIG. 3  is a diagram of four images of an exemplary spherical contact lens having a printed iris pattern in the fluid-filled cuvette of  FIG. 1 , showing four discrete poses for the lens with respect to the bottom of the cuvette; and 
         FIG. 4  is a flow diagram of a procedure for identifying and classifying a contact lens in the fluid-filled cuvette of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an arrangement  100  for use in performing the classification of contact lens poses prior to further processes either at the same location or a subsequent station (not shown). For clarity, a robotic manipulator that handles contact lenses and the underlying cuvette holder and various supporting structures have been omitted. Such devices and structures can be present and implemented in accordance with either conventional or custom designs. 
     The arrangement  100  includes an illuminator  110  of any acceptable type, which in this embodiment is aligned to direct light approximately along a longitudinal axis LA of a cuvette  120 . As described generally above the cuvette  120  defines a tube that can be circular, square or another cross-sectional shape. The cuvette  120  includes an open top  122  through which the light from the illuminator  110  passes. The sidewall(s)  124  of the cuvette  120  are shaded to indicate a generally opaque or diffuse surface—for example, a matte black surface coating, a frosted/rough surface, or the like. In this manner, light penetrates the cuvette mainly through the top and also, illustratively, through a transparent, enclosed bottom  126 . As shown by the dashed fill-line  128 , the cuvette  120  is filled with an acceptable fluid such as saline to a level that fully covers an exemplary contact lens  130  resting against the interior side of the cuvette bottom  126 . The cuvette  120  can be constructed from glass, crystal, polymer or any other material (or combination of materials) that allows for a clear, light-transmissive, and generally non-distorting bottom  126 . The longitudinal (i.e. top-to-bottom) length and cross-sectional dimension (e.g. diameter) of the cuvette is highly variable. The length is sufficient to provide full fluid coverage of the contained contact lens  130 . The cross-section of the sidewall(s) is at least large enough to provide clearance for the outer edge  132  of the contact lens  130  and the inside surface of the sidewall  124  can be located a few millimeters radially beyond the outer edge  132  of the contact lens  130 . This ensures that the contact lens has sufficient clearance within the cuvette and a good image can be acquired. 
     The image of the exemplary contact lens  130  is acquired by a vision system camera  140  that can be of conventional design. In an embodiment, the camera  140  includes a lens  142  that is adapted to acquire detailed images of an object the size of a contact lens. The lens optical axis is approximately aligned with the longitudinal axis LA of the cuvette so as to provide a straight-on view of the contact lens  130 . An appropriate image sensor (not shown) mounted orthogonally to the optical axis within the camera is used to capture the image and convert it to pixel data, typically in grayscale, but optionally in color. In an illustrative embodiment, the pixel data is transmitted by an appropriate link  144  (wired and/or wireless) to a vision system processor, which can be a standalone computer (e.g. PC  150 ) with an appropriate video acquisition peripheral  151  (e.g. a framegrabber, etc.). Alternatively, the vision system processor can comprise another type of networked data processing system (not shown), or an on-camera vision system processor  152  (shown in phantom), that carries out appropriate vision system processes and provides inspection results either via an interface and/or using an indicator assembly mounted on the camera body. The illustrative computer  150  contains conventional interface devices, such as a display  154 , mouse  156  and keyboard  158 . This is exemplary of a variety of interface arrangements (e.g. a touch screen), some of which are purpose-built for the particular vision task. For example, the computer  150  or other processor(s) can interface with a robot controller (not shown) that manipulates contact lenses, contact lens packages, cuvettes and/or other elements of the arrangement. 
     The vision system processor/process  160  resides within the computer  150  as a software process consisting of a non-transitory computer-readable medium of program instructions. The vision system process and any other processes herein can be implemented alternatively as hardware, or a combination of hardware and software. Note also, the term “process” as used herein should be taken broadly to include hardware and software based process blocks, which can be combined, in whole or in part, with other process blocks. Likewise, a given process or processor can be divided into a plurality of sub-processes or sub-processors as appropriate. The vision system process  160  includes an image acquisition and image data handling process  162  that acquires, transmits and stores image data from the camera  140  with respect to contact lenses ( 130 ). The image data is then analyzed, as described below, by one or more vision system tools  168  (which can be conventional in structure and function) to recognize and evaluate certain features in the contact lens image. Based upon the identified features and their particular characteristics, the vision system applies a classification process  166  that can be trained using stored training data  164  based on models of contact lenses in certain poses. This classification process thereby decides which pose (CCD, CCU, ECCD or ECCU, above) the contact lens exhibits. 
     Reference is now made to  FIG. 2 , which is a diagram  200  showing four discrete, exemplary images  210 ,  212 ,  214  and  216  of a spherical contact lens in accordance with the arrangement of  FIG. 1 , respectively exhibiting the poses CCD, CCU, ECCU and ECCD. At least a portion of the perimeter of the contact lens in each pose is visible (as the cuvette walls can be inwardly tapered toward its top  122 ). Each image  210 ,  212 ,  214 , and  216  includes a respective outer edge  220 ,  222 ,  224  and  226  that can be detected by an appropriate vision system tool such as a contrast or edge-detection tool. Notably, each of the contact lens images  210 ,  212 ,  214  and  216  also respectively exhibits a lighter-intensity region  230 ,  232 ,  234  and  236 , respectively, directed radially inward from the outer edge. This lighter-intensity region terminates radially at a contrasting darker-intensity annular region (band)  240 ,  242 ,  244  and  246 , respectively. The average radius R 10 , R 12 , R 14  and R 16  for the lighter-intensity region (band) for each respective image  210 ,  212 ,  214  and  216  can vary for each image and may exhibit a given relative level of brightness. Likewise, the average radius R 20 , R 22 , R 24  and R 26  for the darker-intensity region/band for each respective image  210 ,  212 ,  214  and  216  can also vary for each image. Likewise, the overall average intensity of each band can vary. For example, a small dark band  270  and  272  of differing intensity for each image  210 ,  212  exists just outside the contact lens&#39; perimeter edge. This provides another distinguishing feature. Other geometric variations between the edges of the two or more concentric contrast regions in each image can also occur and the circularity of the outer perimeter edge for everted contact lenses can exhibit a more out-of-round shape than the normal profile. 
     Thus, there exist a plurality of detectible features that distinguish between each pose for the contact lens. These features, and their relative differences, can allow the illustrative vision system to distinguish between, and classify, each pose. 
     Note that the cuvette edge  250  is visible in each image. As described below, the cuvette edge  250  can be used as part of the process of identifying and classifying features. The space in the imaged area beyond the cuvette window can be provided in a fixed, opaque shade, such as black. In this manner, the cuvette top and bottom exclusively transmit light upon which contrast differences can be determined by the vision system. 
     The contact lens images  210 ,  212 ,  214  and  216  also reveal an exemplary etched or printed mark  260 ,  262 ,  264  (not readily visible) and  266 , respectively located in the vicinity of the perimeter edge of the subject contact lens (where it does not interfere with normal vision through the pupil of the wearer&#39;s eye). The mark is typically provided on the outer surface of the contact lens, but can be embedded in the material or placed on an inside (eye-contacting surface of the lens). Each image  210 ,  212 ,  214  and  216  respectively shows the mark in a different orientation (i.e. rotated and in either a forward or reversed (e.g. mirror image) orientation. As described further below, the radial focus gradient for each mark can differ for each respective pose. This provides further information to the vision system on the orientation of the subject contact lens in the acquired image. Note that when a mark is present on a contact lens, the mark can be any character(s) and/or pictorial graphic(s) that is/are non-transparent to the illumination light, and can be effectively resolved by a camera and analyzed by a vision system. 
     The variation between features can be used to identify and classify pose in other types of contact lenses. As shown in the diagram  300  of  FIG. 3 , four discrete images  310 ,  312 ,  314  and  316  represent four respective poses CCD, CCU, ECCU and ECCD for a contact lens having an exemplary color-printed iris (i.e. an eye-color changing/enhancing contact lens) pattern  340 ,  342 ,  344  and  346 , respectively. Each imaged contact lens includes an outer perimeter edge  320 ,  322 ,  324  and  326 , respectively. Beyond this edge is a region of lighter intensity  330 ,  332 ,  334  and  336 , respectively. Notably, in each image  310 ,  312 ,  314  and  316 , the printed iris  340 ,  342 ,  344  and  346  provides a large quantity of graphic information that the vision system can use to determine the radial focus gradient and assist in differentiating between contact lens poses. Thus, for the purpose of this description, the term “mark” can be taken broadly to include such printed iris patterns. 
     The principles described above for differentiating edge features is also applicable to other contact lens types, such as toric contact lenses. Acquired images (not shown) possess similar contrasting edge features that define approximate concentric circles relative to the outer perimeter edge of the contact lens. As described below, the type of lens is specified by the user so that the appropriate set of corresponding training data (i.e. spherical, toric, etc.) is employed by the vision system. 
     An illustrative procedure  400  for identifying contact lens features, and using these features to classify the contact lens pose is shown in further detail in  FIG. 4 . Briefly, the procedure identifies subtle cues in the image of the contact lens. These cues include focus gradients and dark/bright bands near the edge of the lens. In particular, the procedure  400  processes the image to obtain (a) an average radial intensity profile near the edge of the lens and (b) a focus gradient profile measured in the radial direction from the lens center to its edge. These raw profiles (as well as features computed from these profiles) are used to classify the pose of each lens. 
     The classifiers used by the procedure are first trained on profile data and features computed from images in a training database of contact lenses with known pose. After training is complete, these same classifiers are then used to classify the pose of each lens that enters the machine. Illustratively, the classifiers can include the well known k-nearest neighbor (KNN) technique, a Bayes classifier and/or a support vector machine (SVM). 
     The procedure  400  begins with the vision system acquiring an image of the area containing the cuvette. In step  410 , the vision system then employs an appropriate tool (e.g. an edge detection tool) to locate the edge of the transparent round window at the bottom of the cuvette, hereinafter referred to as the “cuvette edge”. The cuvette should define a predictable feature in terms of size and approximate location. If the edge is not found, then most likely there is no cuvette present (decision step  412  and step  414 ). This state is indicated and the procedure returns to the beginning awaiting another image acquisition. If the cuvette edge is located (decision step  412 ), then the procedure finds a first edge of the contact lens (step  420 ). Finding of this edge feature can also be based on operation of an edge detection tool or similar vision system tool. If the first contact lens edge is not found (decision step  422 ), then the procedure  400  indicates a missing contact lens (step  424 ), and returns to await a new image. If the first contact lens edge is found (decision step  422 ), then the procedure  400  attempts to find a second contact lens edge  430 . In general, if two or more lenses are present in the cuvette, their image typically includes at least two crossing points, in the manner of interlocking rings, formed by their edges. If a second (typically crossing) edge is found, then the procedure indicates a double-inclusion of contact lenses in the cuvette (decision step  432  and step  434 ). 
     If a single lens is present in the cuvette (decision step  432 ), then the procedure  400  collects caliper tool profiles from the image (step  400 ). These profiles are respective plots of image intensity as a function of radial position crossing from the outside to the inside of the contact lens. More generally, the caliper tool includes a function that allows it to generate such one-dimensional intensity profiles from the edge information of each image. Other tools and techniques for obtaining intensity profiles of the contact lens image can be employed in alternate embodiments that should be clear to those of skill in the art. The procedure  400  receives an input of lens type ( 450 ), typically from a user interface or a programmable logic controller (PLC). In an embodiment, the lens is either spherical or toric. If the lens is toric, then decision step  452  branches to the classification process for a toric lens (step  460 ). The caliper tool&#39;s radial intensity profiles from step  440  are used in the classification process ( 460 ). The classification process uses classifiers, as described above, which operate with respect to the caliper profiles to compare these to candidate intensity profiles for training images in each of the four poses. This process can be accomplished using known techniques. In the case of a toric lens the geometry offers sufficient caliper profile detail to classify the lens. Based upon that classification, the pose of the contact lens is determined (i.e. CCD, CCU, ECCU and ECCD). If the result is good (CCD), then decision step  462  indicates a good pose to the user/system, and passes the contact lens on to other processes. If the decision step  462  determines that the pose from classification ( 460 ) is unacceptable (bad—CCU, ECCU or ECCD), then the system is notified that the contact lens is misoriented (step  466 ), and appropriate action is taken to correct the presence of a misoriented contact lens—either by flipping the contact lens in the cuvette or discarding it. 
     If the contact lens type (input  450 ) is spherical, then the decision step  452  branches to a process for classifying spherical lenses (either with or without printed iris). This process performs two concurrent steps of feature extraction of the contact lens, including extraction of the features from the radial caliper profiles in step  470 , and extraction of features from the image focus metrics in step  472 . 
     Illustratively, the features extracted from the radial intensity caliper profiles in step  470  include (a) intensity of a dark band just outside the edge of the lens (e.g.  270  in  FIG. 2 ), (b) intensity of a light band inside the lens (e.g.  230 ), and (c) blurriness of the lens edge. The features extracted from the image focus metrics in step  472  include average slope and slope error. Step  472  includes edge detection enhanced by specific morphological filters. The image is then divided into concentric rings, and the average sharpness is computed for each of the rings. A linear regression algorithm is applied to the resulting radial data to obtain the two features: the regression slope and the regression error. The set of features extracted in steps  470  and  472  is then used both to train the classifier  474  during the training phase and determining the pose of the lens during runtime operations. 
     Note that, as described generally above, focus metrics step  472  include providing a radial focus profile based upon the mark features (graphic or character mark, printed iris, etc.). Illustratively, this focus profile can be provided and processed in a procedurally similar manner as the radial intensity profile. In general, the radial focus profile will exhibit a high amplitude if the focus is good and a low amplitude if the focus is poor. For example, if the contact lens is in a good, CCU orientation, then the printed iris ( FIG. 3 ) will become more blurred radially outwardly from the center region of the contact lens. This is because the center of a CCU lens is resting on the surface of best camera focus (the bottom of the cuvette) whereas the outer edge of the lens is maximally elevated away from the surface of best camera focus. Illustratively, on non-printed spherical lenses ( FIG. 2 ), the radial focus metric relates to the contrast in the mark (e.g.  260 ), providing an indication of the relative focus quality at the small versus large radius limits of the mark. 
     This is used to determine the pose. If the decision step  476  determines that the pose is good (CCD), then the procedure  400  indicates a proper pose (step  464 ). If the decision step  476  determines that the pose is “bad” (or otherwise unacceptable) unacceptable (CCU, ECCU or ECCD), then the system indicates a misoriented (step  466 ) requiring appropriate action. 
     In an illustrative embodiment, training data for use in the procedure  400  can be generated by running the edge detection tool, caliper tool and other processes (e.g. focal metric determination) on a large number of acquired images of one or more contact lenses of each type in each of the four poses. This iterative process thereby creates a database of information for each pose. 
     It should be clear that the system and method for determining contact lens orientation/pose in a contact lens test arrangement effectively and efficiently provides accurate pose information based upon a face-on view of the contact lens within an enclosed structure, such as a cuvette, where side view information is generally unavailable. This system and method can employ conventional vision system tools and classifiers with appropriate training data. 
     The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. Each of the various embodiments described above may be combined with other described embodiments in order to provide multiple features. Furthermore, while the foregoing describes a number of separate embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. For example, the position of the camera and illuminator can be reversed with respect to the top and bottom of the cuvette. Likewise, multiple illuminators can be employed or the illuminator(s) and/or camera can be mounted at a non-aligned position, and at a non-parallel angle with respect to the cuvette&#39;s longitudinal axis. For example an off-axis illumination configuration can be provided. Moreover, the illuminator(s) and the camera can be positioned all on the same side of the cuvette, or in addition to an illuminator on the opposite side of the cuvette. Furthermore, the various vision tools and processes used to identify features and characterize the contact lens pose are illustrative of a wide variety of tools/combinations of tools that can be used to perform the general functions of the system and method described herein. Other equivalent tools and processes can be substituted in accordance with ordinary skill. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.