Abstract:
A system for inspecting an ophthalmic lens comprising an optical connection: an illumination source  60,  wherein the light source is arranged to project the light to wards the ophthalmic lens held in the holder; an optical lens  83,  wherein the lens is arranged to condition and project the light beam to illuminate the lens; a swivel glass plate  40,  which is arranged to move in and out of the optical axis  110;  a bright field imaging unit, wherein the bright field imaging unit is arranged to capture an image projected by the illumination source  60;  a dark field imaging unit, wherein the dark field imaging unit is arranged to capture an image projected by the illumination source  60;  and at least one camera sensor operatively coupled with the swivel glass plate, wherein the at least one camera sensor is arranged to capture an image of the light penetrating through the optical lens  83  contained at the bottom of the container  50  and the optical module  20  positioned in line with the optical axis  110.

Description:
[0001]    The present invention relates to an inspection system to automatically inspect ophthalmic lens, preferably in an automated ophthalmic lens production line. The inspection system provides an imaging unit and an inspection method using said swivel plate mechanism designed to capture multiple images and subsequently recognize defective lenses effectively and efficiently with a very high degree of accuracy and reliability. 
       TECHNICAL FIELD 
       [0002]    The present invention generally relates to an automated inspection system and more specifically to a process and method for inspecting ophthalmic lenses. 
         [0003]    Ophthalmic lens is extensively used and in high demand. It has created a need to produce very high quality lenses, both standard and cosmetic, in large quantities. It is a generally a known fact that lenses produced in an automated manufacturing line are more reliable than those manufactured by a manual system of production which suffer from unpredictable problems. It is also a widely accepted fact that inspection systems are an essential part of an automated manufacturing line to inspect the lenses and maintain a consistent and high quality inspection process to deliver premium quality product to customers. Regular tweaking of inspection parameters and generating configuration files that comprise of inspection characteristics, for various ophthalmic lens models, enables flexible adaptation of the inspection system. Ophthalmic lenses are intended for use in the human eye not just to correct the vision but also to enhance the cosmetic look of the eye by printing designs on the ophthalmic lens. Therefore great care must be taken to ensure that they are defect free and also ensure minimum handling occurs during the inspection process. These ophthalmic lenses are produced in very high volumes in an automated manufacturing line. In order to ensure that each one of the lenses is manufactured as per strict quality control standards, it is essential that the lenses are inspected just before packaging, using automated inspection methods. It is also common to implement inline inspection before packaging, so the ophthalmic lenses need not be moved away from the manufacturing line. The present invention is designed such that it may be incorporated into existing lens manufacturing lines or into standalone inspection systems. 
         [0004]    The Opthalmic lenses are usually placed in lens holders, which are transparent. Each holder holds one lens, which is generally immersed in a liquid solution. The wet lens inside the holder is inspected as the lens carrier moves along a transport system in an automated manufacturing line. In order to increase the throughput of the manufacturing line, it is essential that the lenses are inspected as quickly as possible. 
       BACKGROUND OF INVENTION 
       [0005]    Prior arts disclose different techniques of inspection of contact lenses wherein the lens holder is filled with saline solution with the contact lenses floating therein. The consistency of the inspection is a very important requirement for effective and accurate determination of defects. Inspection systems disclosed generally an optical system which is designed with a fixed depth of focus. The depth of focus is so determined in relation to the thickness of the lens as the primary guiding parameter. The objective of such an optical system is to ensure the entire lens from the edge of the lens to the bottom of the lens is in focus. In most cases the images captured by inspection system having adequate depth of focus, provide optimally enhanced images where any contamination or bubbles within the lens material is easily detected and measured to determine if it is reject or not. The problem with such inspection systems is when the size of a defect criterion falls in a region where a definitive decision cannot be made. In current systems with the production line mainly prevalent in clean rooms, the size of the defects found in lenses and the saline solution is getting smaller and smaller. A wrong decision can either lead to a faulty product being shipped to the customer or the manufacturer ending up with a lot of rejects. This excessive rejection can have a significant impact on the productivity of the manufacturing line. The issue is more pronounced if the defect to be measured varies in less than tens of microns. To overcome over rejection, many prior arts resort to extensive algorithm processing to manipulate the image, which is time consuming, thus rendering the process to become slow and low production volumes. 
         [0006]    In prior art inspection systems used to check the quality of the ophthalmic lens, the optical modules utilised, condition the illumination for a particular purpose such as for detecting foreign particle, diameter or other defects in the lens. There is no option to change the optical characteristics dynamically. Any changes that are possible is limited to illumination, if such a feature is available. While optical modules can be re-configured for a set batch of objects, they cannot be re-configured dynamically for each and every object or for objects that may need enhanced inspection as the nature of defect may be such that, it may be difficult to accurately determine the type of defect without capturing different set of images to aid further analysis. This enhancement feature in inspection is required especially if the over rejection rate needs to be reduced for better productivity. 
         [0007]    Prior art systems that acquire only a single image or multiple images by only varying illumination characteristics are susceptible to high false rejection rates, which may be due to the inability to determine whether a potential defect in the lens is actually a defect of the lens, or whether it is debris. Accordingly, these systems may have high false rejection rates (e. g., rejection of lenses that were placed in a holder with contaminated Saline solution), or may accept lenses that have small, but significant, defects within the lens. There are also no options to clean the Saline solution that is filled in the lens holder. Unclean or dirty saline solution affect the quality of inspection and increases the inspection time significantly as the software has to perform more analysis of the image in the event of foreign material contamination in the saline. 
         [0008]    Further, it has been found that in prior art systems, there is no option to capture multiple images of the same object at different focal points which makes analysis of certain types of defects difficult. Images captured at different focal points has the advantage of highlighting certain defects better than if it were captured at a single focal point. The lack of such enhanced images, results in complex algorithms being deployed to minimise over rejection or under rejection which affects productivity. It is therefore essential to obtain multiple images of the same object with different focal points to be able to accurately and effectively differentiate between an actual defect and a false alarm. 
         [0009]    Further, many prior art systems utilise multiple cameras and multiple illumination systems which suffer from maintenance issues. It is difficult to obtain consistency across all the cameras, optics and illumination systems as they have inherent product variations which add up to the inconsistencies. In addition, a breakdown or fault occurring in one optical system, results in the complete sub assembly being shut down. Using a single camera and optical system though slower, ensures good consistent performance and quick changeover to different product types when compared to multi-inspection module systems. There is therefore a need for capturing and inspecting multiple images under different optical characteristics in combination with multiple illumination wavelengths to provide an enhanced capability to detect defects that are very small, to minimise over-rejection. This is the objective of the present invention. 
       SUMMARY 
       [0010]    It is an object of the present invention to provide an automated apparatus for inspecting contact lenses. 
         [0011]    It is further an object of the present invention to provide an automated apparatus for inspecting contact lenses that are suspended in a saline solution. 
         [0012]    It is further an object of the present invention to provide an automated apparatus for inspecting contact lenses by ensuring a consistent amount of Saline solution to be dispensed in the lens holder to eliminate any captured image variations due to inconsistent Saline solution volumes. 
         [0013]    It is further an object of the present invention to provide an automated apparatus for inspecting an ophthalmic lens comprising a movable swivel glass plate consisting of at least one lens, that may be positioned in line with the optical axis  110  ( FIG. 1 ). 
         [0014]    It is further an object of the present invention to provide an automated apparatus for inspecting an ophthalmic lens comprising a swivel glass plate that consists of multiple lenses, each having a different optical characteristic. Primarily each lens of the Swivel plate acts to shift the focal point to a different location. The images acquired with and without the swivel glass would specifically aid in the inspection of small defects in the lens, which would otherwise be faded or masked in a standard image. The swivel glass plate is rotated around its centre, to position different lenses embedded in the swivel plate, in line with the optical axis  110  ( FIG. 1 ) to capture multiple images. 
         [0015]    It is an object of the present invention to provide an automated illumination apparatus consisting for different wavelength of light emitters to be incorporated into the illumination module. These illumination modules are configured to be able to dynamically select a particular wavelength followed by a single strobe signal to capture the image of the object under inspection. 
         [0016]    It is further an object of the present invention to provide a method for inspecting an ophthalmic lens comprising using a swivel glass plate. Preferably the method further comprises of capturing at least one dark field image and at least one Bright field image. Even more preferably the method allows selectively employing the swivel glass plate to capture at least one dark-field image or at least one Bright field image. 
         [0017]    It is further an object of the present invention to provide an improved method of inspecting contact lenses to differentiate between foreign matter or bubbles and actual defects on the lenses. 
         [0018]    It is further an object of the present invention to provide an improved method for inspecting contact lenses by ensuring an accurate dispensing of Saline solution to the lens holder. 
         [0019]    In still another aspect of invention, the present invention provides a device and method 
         [0000]    to capture and inspect multiple dark field and Bright field images, of the object that are printed, tinted or a simple transparent ophthalmic lenses. 
         [0020]    While the invention is described with particular reference to contact lenses, it is understood the present consolidation apparatus is equally suitable for non-hydrated lens inspection as well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The foregoing objects and advantages of the present invention for an automated apparatus and method for inspecting contact lenses may be more readily understood by one skilled in the art with reference to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like elements are designated by identical reference numerals throughout the several views. 
           [0022]    Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. 
           [0023]      FIG. 1  is an illustration of the optical and illumination system according to the present invention. 
           [0024]      FIG. 2  is a plan view of the swivel glass  30  as indicated in  FIG. 1 . 
           [0025]      FIG. 3  is an enlarged cross sectional view of the ophthalmic lens holder assembly  50  as indicated in  FIG. 1 . 
           [0026]      FIG. 4  shows Dark Field and Bright field images of ophthalmic lens, showing the de-focussing effect of the swivel glass. 
           [0027]      FIG. 5  shows a typical flow chart of the inspection process. 
       
    
    
       [0028]    Further details and advantages of the invention may be seen from the description and drawings that follow. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    According to the present invention, a preferred embodiment will be described, with reference to the drawings mentioned. 
         [0030]    The system of the present invention uses a single camera, an optical module, a lens holder and an illumination module, a accurate Saline solution volume dispenser (not, shown), suitably integrated with a Swivel glass plate comprising a multiple lenses arranged in a circular fashion, to capture high-resolution images of the object, at different focal points. The object is illuminated by a single illumination module that is designed using varied wavelengths and may also be of different polarization. 
         [0031]    References in the prior art do not refer to defocussed images that have been found to be very useful in differentiating defects which can be mistaken for contamination or otherwise. The optical mechanism in conjunction with the swivel glass plate translates very minute defects. 
         [0032]    In a preferred aspect of the invention, an imaging unit comprising a single camera, an optical module, the lens holder, the Swivel Glass plate mechanism in combination with the illumination module to capture Dark field and Bright field images provides an accurate inspection system. 
         [0033]    It may be noted that the present invention is directed towards an imaging system that uses a single imaging device and a dynamically configurable illumination system that enable a highly accurate and sharply focused image of the defects (ophthalmic lens) suitably integrated with a mechanism to capture a defocused image by the introduction of a swivel glass in the optical axis  110  ( FIG. 1 ). Only then, is the said images can be efficiently utilised to detect minute features or defects in a ophthalmic lens that includes but not limited to tears, cuts, bubbles, inclusions, ruptures, deformities, dimensional defect and foreign material contamination. 
         [0034]    In another embodiment of the invention, the illumination module  60  is strobed at different instances in the time domain and the corresponding images are captured. 
         [0035]    In another embodiment of the invention, the illumination module  60  can be programmed to selectively strobe the illumination at different intensities and the corresponding dark field or Bright field images, as captured as per the light setting. 
         [0036]    In another embodiment of the invention, a specific illumination wavelength maybe configured to inspect different features such as print quality, foreign material and edge defects. 
         [0037]    In yet another embodiment of the present invention, the illumination module containing different wavelengths of LEDs, may be selectively turned OFF/ON depending upon the type of defects to be inspected. 
         [0038]    The illumination controller (not shown) may be CPU controlled, to change the intensity and pulse duration of the strobe. The CPU may also control the timing of the trigger pulse synchronization with respect to the camera shutter to get a consistent image quality. For the purpose of clarity the strobing mechanism and the art of image capture is not discussed, as it is a well-established technology. Images are then moved or copied to different memory locations for further image processing. 
         [0039]    The present invention is preferably used in an automated manufacturing line where the specimen (ophthalmic lens) is transported along a predetermined path and positioned under the inspection station for inspection. Preferably the ophthalmic lens may be moving through the inspection system. However, the ophthalmic lens may also be inspected in a stationary position, if the inspection process requires it. 
         [0040]    In the foregoing description the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto by a skilled person in the art, without deviating from the broader spirit and scope of the invention. For eg: One such embodiment may be in the form of using a single colour or monochrome camera in conjunction with multiple illumination modules, configured to selectively capture multiple dark field and bright field images of the same object at different time domains which may include the use of a single or multiple Swivel plates. The specification and drawings are, accordingly, to be regarded as illustrative rather than a restrictive sense. 
       DETAILED DESCRIPTION OF DRAWINGS 
       [0041]    The present invention was designed for and is particularly adapted for use in contact lenses molded section of an automated production line. 
         [0042]    According to the present invention, a preferred embodiment will be described with reference to the drawings mentioned. 
         [0043]    The system of the present invention illustrated in  FIG. 1  uses a single camera  10  and an optical module  20  to capture high-resolution images of the object  81  that is illuminated using multiple wavelengths of illumination incorporated in single illumination module  60 . In addition, the optical system  20  may contain option to incorporate colour filters to reject parasitic illumination interfering into the inspection area. The system also enables capturing multiple high-resolution images of the same object under different optical characteristics by introducing a swivel glass  40  in the optical axis  110  ( FIG. 1 ).The swivel glass  40  may consist of “N” areas of different optical characteristics for focussing the illumination at different points to enable a multiple types of defects to be highlighted The swivel glass  40  illustrated in  FIG. 2  is divided into four areas of different optical focus points  71 , 72 ,  73 ,  74  and so on, which may be positioned in the path of the optical axis  110  ( FIG. 1 ) to enable capturing of different images. Depending on the illumination parameters, either Dark Field or Bright field images may be captured using the package configurations selected by the user. 
         [0044]    The lens holder setup shown in  FIG. 3  consists of a holder  80  with an outlet  84  for excess Saline solution outflow. The holder  80  has lens  83  which forms the bottom surface of the lens receiving cavity that positions the object  81  to be inspected. A accurate saline dispensation device that injects saline solution  82 , into the cavity  80  is not shown. 
         [0045]    The lens receiving cavity consists of the holder  80  and a lens  83  that is preferably made of clear glass with no coating on its bottom surface. The lens  83  enables illumination of the lens  81  from the bottom by illuminating module  60  (in  FIG. 1 ). The concave curvature of lens  83  shown in  FIG. 3  closely matches that of the convex surface of the lens  81  such that the lens  81  always moves to the centre of the lens receiving cavity. This feature helps inspection algorithm to locate the edge of the lens quickly, to ensure better throughput of the inspection system. 
         [0046]    In a preferred embodiment of the present invention an example is described.  FIG. 4  shows a dark field image  90  of an ophthalmic lens captured with the Swivel glass  40  located in position  31 . Upon further analysis of area A in image  90 , a probable defect as indicated at position  96  and  97  is shown in enlarged image  91 . In such cases whereby it is difficult to differentiate between contamination and an actual defect in the lens, the swivel glass is moved to position  30 , in line with the optical axis  110  ( FIG. 1 ). Furthermore the software determines the level of defocussing needed to enhance the defects and the appropriate lens position ( 71 , 72 , 73 , 74 ) as determined by the software program is positioned, by rotating the swivel plate  40 . Further, new image is captured by strobing the illumination module resulting in image  92 . Subsequently the same area A is shown in the enlarged image  93 . The Swivel glass produces the effect of enhancing certain types of defects. The dark spots  96  and  97  viewed in the image  91  where they appear faint, is now enhanced as shown in image  93 . The defects  96  and  97  indicated in  91  appear much larger and more pronounced as indicated by  98 ,  99  and  100 . As evident, by applying the same analysis that was applied to image  91 , to the image  93 , the software is able to accurately and consistently decide the nature of the defect and if the object under inspection is a Pass or a Reject. 
         [0047]    Let us refer to  FIG. 5 . It shows the flow chart for the process of inspection. The program begins at process step  180 . The program checks if a package type has been configured for inspection at step  182 . If a package has already been configured the program moves to step  204 . However if there is no package type selected, then the program moves to step  184  to begin the process of Package setup. The package setup may consist of selecting a previously configured package type or may involve the steps of configuring a new package type that may include all the parameters related to the ophthalmic lens which includes diameter, Pattern template, logo position, Logo type, critical areas on the lens and the grey scale value of user selected areas. For the purpose of clarity, the setup process is not discussed in detail. When the package setup is completed, the program moves to step  204 . The program checks if the Swivel Mode is disabled at step  204 . Swivel mode is a mode where the Swivel glass  40  ( FIG. 1 ) is moved from position  31  to position  30  in line with the optical axis  110  ( FIG. 1 ) before an image is captured. A person skilled in the art will realise that the swivel plate  40  is positioned around the centre of axis in the area  30  ( FIG. 2 ), if the lens used in the swivel glass plate is of a single characteristic. If the plate  40  has multiple lens embedded in it, the swivel glass is positioned around the perimeter of the circle  32  ( FIG. 2 ) which is offset from the centre of the swivel plate  40 . The image captured in the swivel glass plate mode, is to produce a shift in the focal point so an enhanced image of the object  81  is captured. The swivel glass shown in  FIG. 2  constitutes multiple areas with different lenses assembled in the rotary disk  40  shown in  FIG. 2 . For e.g. Lenses  71 ,  72 ,  73  and  74  are assembled in four different quadrants of the disk. The disk in  FIG. 2  shows four quadrants but, a person skilled in art will realise that many more lenses can be incorporated in disk  40  depending upon the inspection requirements of a package type. A person skilled in the art will recognise the fact the Swivel glass plate can also consist of one single lens. If the Swivel mode check at step  204  is found to be enabled, the program proceeds to step  205 , wherein the Swivel glass mechanism is instructed to rotationally position the plate  40  to a pre-selected area depending upon the configured parameters for the selected package type. After completion of rotation, the Swivel glass is moved from position  31  to position  30  in step  206  and subsequently proceeds to step  209 . If the Swivel mode check at step  204  is found be disabled, the program proceeds to step  209 . 
         [0048]    In step  209 , the program checks if the programmed number of images has been captured. If the said number of images is not captured, the program moves to step  207 . It may be noted here that the number of images to be captured can be either preset or determined dynamically during program execution and inspection. In step  207 , the program sets up the illumination controller  60  for parameters such as intensity and the segments that are required to be illuminated based on the configured parameters. The illumination controller  60  setup involves sending a string of instructions from the PC (not shown), either through a serial link (RS232) or via Ethernet, to the illumination controller  60  which in turn interprets the instructions and performs the necessary steps to configure the hardware. Details of configuring the hardware is not described as it falls beyond the scope of this invention. 
         [0049]    Upon completion of setup in step  207 , the program proceeds to step  208  where a trigger is sent to the illumination controller and the camera  10 , to capture an image. After capturing an image, the program stores the captured image in  230  and moves to the next step  240  where the Swivel glass is moved from position  30  to position  31 . Subsequently the program moves to step  204  and repeats the process. 
         [0050]    In step  209 , if the program checks and determines that the programmed number of images has been captured, it moves to step  210 . 
         [0051]    At step  210 , the program identifies the lens profile using edge finding algorithms. Once the edge is identified the position is logged. Referring to  FIG. 4 , the lens edge  94  is shown in image  90  by the outer dashed circle. 
         [0052]    A first method relies on the lens structure and its characteristics. In this method, a concentric area of lens as shown in  FIG. 4  from the lens edge is selected and a blob locating algorithm detects spots around an area A as shown in  FIG. 4 . The area enclosed by the box A in image  90  is shown enlarged in image  91 . The blobs which may indicate a bubble or a foreign material contaminant is shown by circles  96  and  97  in image  91 . As evident, it is not easily detectable as a defect as the size of the blob is out of focus or very small and may be measured as a very small defect. When compared with the reject or accept parameters in the software setup, the measured defect may be too small to be rejected. The program now proceeds to inspect all the images captured and logs the defects types and sizes in a table. After completing inspection of all the images, a decision as to whether the defects falls above or below the threshold limit is made. As described earlier all parameters are setup during configuring a particular package type. Defects sizes and types falling above the threshold are rejected and the rest are accepted as Pass. 
         [0053]    If the object under inspection is determined to be a defect, the step  214  is initiated along with a display shown on the monitor at step  215 , indicating the failure type and subsequently moves to step  220 , to the end of the program. However, if the defect is determined to be within the parameters set by the user in the program, the program moves to step  212 , with a display shown on the monitor at step  213 . Subsequently, the program moves to step  220 , to the end of the program. 
         [0054]    While processing method explained in the foregoing paragraph enables easy detection of foreign material or other types of contamination, a person skilled in the art will realize, the software algorithm can be configured to measure other types of inclusions at different areas of the lens. 
         [0055]    The method described above is suitable to inspect all kinds of ophthalmic lenses, preferably soft conventional hydrogel contact lens, comprising poly-HEMA homo or copolymer, a PYA homo or copolymer, or a cross linked polyethylene glycol or polysiloxane hydrogel. 
         [0056]    Although reference to preferred and exemplary embodiments of the present invention has been described, but the skilled person will understand that various modifications, additions, deletion is possible without deviating from the objective of the inspection.