Abstract:
Early techniques for object inspection relied on human inspectors to visually examine objects for defects. However, automated object inspection techniques were subsequently developed due to the labor intensive and subjective nature of human operated inspections. Additionally, object characteristics such as object power and object thickness need to be determined after the objects have been examined for defects. Conventionally, corresponding inspection stations are along the manufacturing lines for determining each of the object characteristics. However, the need for human intervention and time spent to move the objects from one inspection station to another adversely affect the efficiency of the object manufacturing process. An embodiment of the invention disclosed describes a high-resolution object inspection system for performing object inspection.

Description:
FIELD OF INVENTION 
     The present invention relates generally to systems for inspection of objects. More specifically, the present invention relates to a optical media or lens inspection system. 
     BACKGROUND 
     Early techniques for inspecting lenses typically relied on human inspectors to visually examine the lenses for defects (hereinafter referred to as lens defects) usually by placing the lenses under magnification or projection onto a screen whereupon the human inspectors then visually search for lens defects. However, the labour intensive and subjective nature of human operated inspections prompted interest in automating the inspection process. Numerous methods have been investigated, foremost of which are those whereby an image of a lens is acquired and the image then being electronically evaluated for lens defects. Commonly, these methods take advantage of the fact that light, under certain circumstances when encountering a lens irregularity, scatters in a manner that can be qualitatively assessed. These methods generally operate by manipulating a light beam before and/or after passing through a lens in order to extract optical information that is subsequently analysed to assess for flaws. 
     U.S. Pat. No. 5,500,732 to Ebel et at al and U.S. Pat. No. 6,134,342 to Doke et at describe a conventional system and method for lens inspection. The conventional system and method as described by Ebel and Doke transport lenses using a holder, such as a curvette. However, the conventional system and method is only suited for inspecting lenses that are dry and cannot be applied to inspect ophthalmic or contact lenses that are transported in a medium such as saline solution. Most contact lenses in the market are packaged in saline solution. This causes technical challenges for obtaining high definition images of contact lenses in saline solution for inspection thereof. 
     As demands for detecting defects of smaller dimension increases, it is necessary to use images of higher resolution to detect such defects. U.S. Pat. No. 6,301,005 to Epstein et al describes a conventional system and method for high resolution lens inspection. However, such high resolution lens inspection requires cameras that are costly and subject to availability. It is therefore difficult to obtain high definition images of the lenses without the use of the foregoing cameras. 
     Additionally, lens characteristics such as lens power and lens thickness are typically determined after the lenses have been examined for defects. Conventionally, inspection stations are along the lens manufacturing lines in which each inspection station independently measures and determines the corresponding lens characteristics. However, the time spent to transfer the lenses from one inspection station to another adversely affects the efficiency of the lens manufacturing process and hence lowers the overall yield of lens production. Moreover, the need for human intervention during the transferring of lenses from one inspection station to another potentially creates opportunities for human-related mistakes to occur. 
     Accordingly, there exists a need for a system for addressing the foregoing problems of existing lens inspection systems by minimizing the need to physically transfer the lenses between inspection stations thereby improving the overall efficiency for lens manufacturing. 
     SUMMARY 
     The present embodiments of the invention disclosed herein provide a high-resolution object inspection system for performing object inspection. 
     In accordance with a first aspect of the invention, there is disclosed an object inspection system for inspecting an object, comprising a first station, a second station and a third station. The first station captures a first image of the object in which the first image is processable to determine one of presence and absence of at least one defect on the object. The second station captures at least one second image in which the at least one second image is a magnified view of at least one portion of the object. The at least one second image is processable to determine quality of the at least one defect and the quality of the at least one defect is one of acceptable and unacceptable. The third station determines optical property such as the object power and thickness of the object upon one of absence of the at least one defect and the quality of the at least one defect being determined as acceptable from the at least one second image. 
     In accordance with a second aspect of the invention, there is disclosed an object inspection method comprising capturing a first image of an object by a first station. The first image is processable to determine one of presence and absence of at least one defect on the object. The method also comprises capturing at least one second image by a second station in which the at least one second image is a magnified view of at least one portion of the object. The at least one second image is processable to determine quality of the at least one defect and the quality of the at least one defect is one of acceptable and unacceptable. Lastly, the method comprises determining optical property such as the object power and thickness of the object by a third station upon one of absence of the at least one defect and the quality of the at least one defect being determined as acceptable from the at least one second image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are disclosed hereinafter with reference to the drawings, in which: 
         FIG. 1  shows a high-resolution lens inspection system according to an embodiment of the invention; 
         FIG. 2  shows a lens defect inspection subsystem of the high-resolution lens inspection system of  FIG. 1  in which the lens defect inspection subsystem comprises a Full Field-of-View (FOV) station and a Magnified Field-of-View (FOV) station; 
         FIG. 3  shows an FOV image of an object that can be split into nine portions (as shown on left side of the figure) and nine corresponding magnified images captured by the Magnified FOV station. The nine magnified images can be merged to obtain a total whole image of the object (as shown on right side of the figure); 
         FIG. 4  shows an image of a lens captured by the Full FOV station of  FIG. 2 ; 
         FIG. 5  shows an image of a portion of the lens captured by the Magnified FOV station of  FIG. 2  in which the portion of the lens containing the defects is identified from the image of  FIG. 4 ; 
         FIG. 6  shows a lens characteristic measurement subsystem of the high-resolution lens inspection system of  FIG. 1  in which the lens characteristic measurement subsystem comprises a lens power meter station and a lens thickness meter station; and 
         FIG. 7  shows a flowchart illustrating a lens inspection process performed by the high-resolution lens inspection system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A high-resolution lens inspection system for performing object inspection is described hereinafter for addressing the foregoing problems. 
     For purposes of brevity and clarity, the description of the invention is limited hereinafter to lens inspection, for instance, involving a lens having at least one of a convex side and a concave side (e.g., a lens corresponding or generally corresponding to a portion of a sphere). This however does not preclude various embodiments of the invention from other applications of similar nature or from applications in inspection of other types of objects. The fundamental inventive principles of the embodiments of the invention are common throughout the various embodiments. 
     Exemplary embodiments of the invention described hereinafter are in accordance with  FIGS. 1 to 7  of the drawings, in which like elements are numbered with like reference numerals. 
       FIG. 1  shows a high-resolution object inspection system  100  according to an embodiment of the invention. The high-resolution object inspection system  100  is suitable for inspecting objects such as lens, for instance, lens having a convex side and a concave side (e.g., a lens corresponding or generally corresponding to a portion of a sphere) or other manufactured products for detecting defects on the objects. The following description of the embodiments of the invention applies but is not limited to inspection of lenses. 
     The high-resolution object inspection system  100  comprises three subsystems: a lens defect inspection subsystem  102 , a lens placement subsystem  130  and a lens characteristic measurement subsystem  150 . The lens defect inspection subsystem  102  serves to assess and detect defects on lenses, such as aberration defects. The lens defect inspection subsystem  102  comprises two inspection stations: a Full Field-of-View (FOV) station  104  and a Magnified Field-of-View (FOV) station  106 . 
     At the Full FOV station  104 , an image of a lens is captured and electronically evaluated to detect any defects on the lens. Thereafter, regardless whether defects are detected by the Full FOV station  104 , high-resolution images of different portions of the lens are captured using the Magnified FOV station  106  for further inspection of the lens. The multiple high-resolution images of the lens are preferably captured using a device that comprises two mirror galvanometers for focusing different portions of the lens for allowing the high-resolution images to be captured. The mirror galvanometers are preferably variable speed mirror galvanometers. If no defects are detected, the lens is then transferred to the lens placement subsystem  130 . However, if defects have been detected, the severity and complexity of the defects determine whether the lens should be accepted or discarded. If the lens is accepted, the lens will be transferred to the lens placement subsystem  130 . 
     Preferably, the object inspection system  100  determines the severity and complexity of detected defects. Alternatively, a human inspector may be alerted to inspect the lens if the high-resolution object inspection system  100  is unable to make a judgement on whether to discard or accept the lens. The Full FOV station  104  comprises a first detection means  108  and a first illumination source  110 . Separately, the Magnified FOV station  106  comprises a second detection means  112 , a mirror galvanometer  114  and a second illumination source  116 . The first and second illumination sources  110 / 116  are, for example, laser beam emitting sources. 
     The lens placement subsystem  130  serves to transfer the lens from the lens defect inspection subsystem  102  to the lens characteristic determination subsystem  150 . As shown in  FIG. 1 , the lens placement subsystem  130  comprises a bottom pickup unit  132 , a top pickup unit  134 , a curvette  136  and actuator motors  138  and operates in association with a lens holder  152 . Both the curvette  136  and the lens holder  152  can be positioned relative to a common axis controlled by actuator motor(s)  154 . The bottom pickup unit  132  picks up the lens and flips or rotates (e.g., by 180°) and/or inverts the lens. This action results in the lens facing the top pickup unit  134  (for example, the lens becomes inverted or turned “inside out”). The bottom pickup unit  132  then transfers the lens to the top pickup unit  134  and moves away to allow the top pickup unit  134  to place the lens in the curvette  136 . The lens holder  152  then moves to the lens characteristic determination subsystem  150  (e.g., without rotation or inversion thereto). Additionally, the actuator motors  138  displace and position the bottom pickup unit  132  and top pickup unit  134  along a plane parallel to the optical axis of the lens. 
     At the lens characteristic determination subsystem  150 , the lens power and thickness of the lens are determined. Lens power essentially measures the focal length of a lens. The lens is first transferred from the curvette  136  onto a lens holder  152 . The lens holder  152  is operated by an actuator motor  154  and is movable perpendicular to the optical axis of the lens. The measurement of the lens thickness is performed using a third detection means  156  and a third illumination source  158 . Independently, the measurement of the lens power is performed using a fourth detection means  160 , a test target  602  and a fourth illumination means  162 . The fourth detection means  160  is movable along a plane parallel to the optical axis of the lens and is driven by an actuator motor  164 . 
     Additionally, the first illumination source  110 , second illumination source  116  and fourth illumination means  162  provide backlighting to illuminate the lens at the respective subsystems of the high-resolution object inspection system  100 . Further, the first illumination source  110 , second illumination source  116  and fourth illumination means  162  are preferably operable for varying the amount of illumination to thereby enable images of the lens to be selectively captured and inspected (e.g., under different lighting conditions). The first illumination source  110 , second illumination source  116  are preferably operable to emit light along an optical path that includes the lens and the detection means  108 ,  112 . The first detection means  108 , second detection means  112 , third detection means  156  and fourth detection means  160  are preferably one of complementary metal-oxide semiconductor (CMOS) sensor and a charge-coupled device (CCD) to provide lens imaging. Typically, digital cameras equipped with either the CMOS sensor or the CCD are used in the detection means. The first detection means  108 , second detection means  112 , third detection means  156  can include imaging elements in a manner understood by one of ordinary skill in the art. 
     Details with respect to the Full FOV station  104  and the Magnified FOV station  106  are as shown in  FIG. 2 . The setup at the Full FOV station  104  shows a lens  200  enclosed in a protective casing or holder  202  that is positioned on a support  204 . The holder  202  can carry a lens having a convex and/or concave portion in a manner that facilitates image capture, processing, evaluation, magnification and/or assessment. Illumination is provided by the first illumination source  110  to enable the first detection means  108  to capture a clear image of the lens  200 . The image is then digitally processed and evaluated for detecting defects on the lens. If defects are detected, the lens  200  is transferred to the Magnified FOV station  106  for further assessment in which portions of the lens  200  containing the defects are magnified by the second detection means  112 . The magnification is performed preferably by taking high-resolution images of the required portions of the lens  200 . 
     In addition, the Full FOV station  104  might not be able to detect very fine defects on the lens. Under such conditions, it is still necessary for the lens to undergo inspection at the Magnified FOV station  106  to ensure that the lens is defect-free. Hence, there are situations in which the defects are only detectable by the Magnified FOV station  106  and not by the Full FOV station  104 . 
     To selectively capture images of any portion of the lens or object  200 , usage of the mirror galvanometer  114  or a positionable or steerable mirror  206  in conjunction with the second detection means  112  is required. The mirror galvanometer  114  or positionable or steerable mirror  206  is operable for bringing a portion of the light passing through the object  200  into focus to thereby facilitate capturing images thereof. The detection means  112  captures the images of portions of the lens  200  and thereby sequence of the images of portions of the lens  200  is generated. The sequence of images can include, for instance, nine images and can be merged to get a total image of the entire lens  200  or substantially the entire lens  200  as a result. Consequently, the Magnified FOV station  106  can have a resolution as small as 2.5 μm in size. 
     The nine aforementioned portions of the object  200  are shown in  FIG. 3 . The object  200  is placed under the full FOV station to obtain image portions  304 . The magnified FOV station  106  can generate nine proper images that can be merged to get magnified image portions  306  and the magnified image  310  of the whole object  200 . 
     Although the magnified image  306  is shown in  FIG. 3  as being partitioned into nine segments, the magnified image  306  can be partitioned into any number of segments depending on the specifications of the defects to be inspected. 
       FIG. 4  shows an image  400  of a sample lens captured by the Full FOV station  104  whereas  FIG. 5  shows an image  402  of a portion of the sample object (e.g., lens) magnified by the Magnified FOV station  106 . Defects present on the portion of the sample lens were identified after digitally processing and evaluating the image  400  and image  402  to determine whether the defects are acceptable or unacceptable. 
       FIG. 6  shows the lens characteristic determination subsystem  150 , which comprises two stations for measuring the lens power and lens thickness. A first station for measuring the lens power comprises the fourth detection means  160  and the fourth illumination means  162 , motor  164 , the imaging lens  604  and the test target  602 . The imaging lens  604  in combination with a lens  600  generates an image of the test target  602 . The image is captured by detection means  160  that is movable by motor  164  along the optical axis of the imaging lens  604 . Hence, the detection means  160  adjusts the image of the test target  602  by adjusting the position of the detection means  160  by motor  164 . The lens power of a lens  600  is measured by providing a test image  602  to thereby enable the fourth detection means  160 , together with the usage of an imaging lens  604 , to capture a virtual image (not shown) of the test image  602 . Equations for determining the lens powers and magnification ratio of a lens are expressed as: 
                       1   u     +     1   v       =     1   f             (     1   ⁢   a     )               M   =     u   v             (     1   ⁢   b     )               
in which u is the distance of the virtual image from the lens, v is the distance of the object from the lens, f is the focal length of the lens and M is the magnification ratio of the lens.
 
     Equations (1a) and (1b) are known as the Thin Lens formula and the Magnification formula respectively, as well known to practitioners in the art. Hence, by adjusting the position of the fourth detection means  160  until a virtual image of the test image  602  is captured by the fourth detection means  160 , both the focal length and the magnification ratio of the lens  600  are then computable using equations (1a) and (1b). By definition, the lens power, P, is given as P=1/f. 
     A second station for determining the lens thickness comprises the third detection means  156  and the third illumination source  158 . The third illumination source  158  emits beams which are directed at an angle towards the center of the lens  600 . The beams are preferably one of laser beams and light beams. Subsequently, the beams reflected by the lens  600  are received by the third detection means  156  and further processed for obtaining a set of optical information, by which a lens thickness can be determined based upon techniques known to practitioners in the art. 
       FIG. 7  shows a flowchart illustrating a lens inspection process  700  performed by the high-resolution object inspection system  100 . Firstly in step  702 , the Full FOV station  104  captures an image of a lens under inspection. The image is then digitally processed and evaluated to detect defects on the lens. If defects are detected, the lens is then transferred to the Magnified FOV station  106 . Optionally, even if no defects are detected by the Full FOV station  104 , the lens is still transferred to the Magnified FOV station  106  for further inspection to detect defects that are not detectable by the Full FOV station  104 . 
     At the Magnified FOV station  106 , magnified images of portions of the lens containing the defects are captured in step  704 . The magnified images are then further inspected to determine whether the lens can be accepted. The lens is then transferred to the subsystem  130 . The lens can then be rotated and/or inverted by subsystem  130  in step  706 . The subsystem  130  picks up the lens and put it on the lens holder  152  in step  708 . The lens holder  152  can then be transferred to the lens characteristic determination subsystem  150 . The lens characteristic subsystem  150  measures the lens power and lens thickness in step  710 . 
     In the foregoing manner, a high-resolution inspection system for performing object inspection is described according to various embodiments of the invention for addressing the foregoing disadvantages of conventional lens inspection systems. Although a few embodiments of the invention are disclosed, it will be apparent to one skilled in the art in view of this disclosure that numerous changes and/or modifications can be made without departing from the scope and spirit of the invention.