Abstract:
Devices and methods for protecting components of imaging devices are provided. In the illustrative embodiment, a plano-concave protective cover is provided which is bonded to an imager window by applying a thick, quick-setting adhesive to the exterior of the cover and of the imager window.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    None.  
           [0002]    1. Field of the Invention  
           [0003]    The invention relates generally to protective covers for imaging devices.  
           [0004]    2. Background of the Invention  
           [0005]    Electronic-type imaging devices of the type used, for example, in microscopes, telescopes, camcorders, thermal imagers, digital cameras, and especially with digital inspection systems (e.g., borescopes, and endoscopes), often are subjected to harsh physical operating conditions, and must embody a degree of survivability, in terms of mechanical durability, temperature tolerance, etc., which exceeds that required for similar electronics designed to operate in more benign environments, such as in clean rooms and climate-controlled office environments. In addition, these “hearty” imaging devices must be protected against environmental debris, such as dirt, dust, chemicals, and corrosive fluids, which might damage the optical elements (typically located in a tip of the imaging device) associated with the imaging devices introduced into hostile environments. “Optical elements” include well-known components used in imaging devices, such as miniature electronic image sensors (of the type, for example, used in CCD-type or CMOS-type imagers), mirrors, light sources (such as LEDs and laser diodes), and lenses.  
           [0006]    In the past, windows, lenses, CHL assemblies, or other imaging portals leading to the optical elements of an imager (hereinafter, “imager window”) located in a tip of an imaging device have been afforded a modicum of protection by affixing a flat, optically transmissive element onto the imager window, such as a flat glass disk or plate. The flat element typically is bonded to the imager window using a UV adhesive, i.e., an adhesive cured under ultraviolet light during manufacturing. UV adhesives typically are used because of their generally quick cure times which, in turn, allow for a relatively short manufacturing step associated with the bonding.  
           [0007]    This method of protecting the imager window, however, creates certain disadvantages with regard to the operation of the imaging device. For example, the use of a flat optical element bonded to an imager window, with UV adhesive interposed between the optical element and the imager window, gives rise to Newton&#39;s rings, a phenomenon observed when two materials with differing refractive indices are in close contact with each other. In practice, the presence of these rings (which typically are a series of concentric rings surrounding a central dark spot) reduces the image quality produced by the imaging device. Furthermore, the UV adhesives used to bond the flat optical element to the imager window, when stressed mechanically or thermally, tend to fail and crack, creating unwanted distortions and artifacts in the image produced by the imaging device. The failure of these adhesives also allows the flat optical element to disengage from the imager window, losing any protective benefit conferred by the presence of the flat optical element.  
           [0008]    One prior art approach to addressing these problems has been to interpose bonding pads between the optical element and the imager window, and then to bond the optical element to the bonding pad in such a manner as to create a seal between the bonding pad and the optical element. That approach, however, is disadvantageous in that it requires additional materials and time-consuming alignment and bonding steps with regard to the bonding pads.  
           [0009]    Another prior art approach has been to interpose adhesive, in the form of strips of preformed thermoplastic or thermosetting adhesives, between the optical element and the imager window at the edges where the optical element and imager window contact each other. However, this approach also is flawed in that the preformed adhesive strips cannot be tightly controlled when melted under heat, allowing the adhesive to “run” into the viewing area of the imager window.  
         SUMMARY OF THE INVENTION  
         [0010]    It is the object of this invention to provide a cover for an imager window assembly which overcomes the disadvantages of prior art methods of protecting the imager window.  
           [0011]    In one aspect of the invention, an imager window cover assembly is provided including an optically transmissive cover element mounted to an imager window by means of a mounting element applied to the exterior of the imager window cover and the imager window so that light traveling toward an imager window does not pass through the mounting element.  
           [0012]    In another aspect of the invention, an imager window cover assembly is provided which eliminates image distortion attributable to Newton&#39;s rings.  
           [0013]    In another aspect of the invention, an imager window cover assembly is provided which does not create visual distortion upon failure of an adhesive.  
           [0014]    In a further aspect of the invention, an imager window cover assembly is provided which is less likely than prior art imager window covers to disengage from the imager window.  
           [0015]    In yet another aspect of the invention, an imaging device is provided with an imager window cover element which protects optical elements of the imaging device from adverse environmental conditions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is an imaging device according to the invention;  
         [0017]    [0017]FIG. 2 is an enlarged view of a distal end of the imaging device of FIG. 1;  
         [0018]    [0018]FIG. 2A is an enlarged view of the distal end of FIG. 2; and  
         [0019]    [0019]FIG. 3 is a side perspective view of an imager window cover element according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    It is to be understood that the invention is not limited in its application to the details of construction and arrangements of components set forth herein in the detailed description of the preferred embodiment or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways.  
         [0021]    Referring to FIG. 1, a typical imaging device  100  (a boroscope in the illustrative embodiment) according to the invention is illustrated, such as is sold by Everest VIT® of Flanders, N.J. Such a device could include, as shown in the illustrative embodiment, a portable shipping/operating case  110 , that includes a power supply  120  for the device and a light source, such as a metal halide arc lamp (not shown). The shipping/operating case  100  is shown in operative communication with a handpiece  140  by means of a cable  130 . The handpiece  140  can include, by way of example, an LCD monitor  150  (which displays images seen by the imaging device), a joystick control  145  (for articulating a distal end  170  of the imaging device  100 ), and a button set  143  (for accessing measurement, digital, and measurement controls associated with the imaging device  100 ). The handpiece  140  also is connected to an insertion tube  160 , which terminates in a distal end  170 . As used herein, the term “distal” shall mean “in the direction of the tip of the boroscope, furthest from the handpiece  140 .” The insertion tube  160  can be sized according to the desired application, by varying a diameter and a length of the insertion tube  160 . The insertion tube  160  can include, for example, a durable tungsten braid overlaying a stainless steel monocoil for crush resistance, and one or more layers of a polyurethane sealant for protection from liquids and vapors. The interior of the insertion tube  160  (not shown) can include standard imager lines and communication/control means, such as fiber-optic cables and articulation wires.  
         [0022]    An enlarged view of the distal end  170  of the imaging device  100  described herein is illustrated in FIG. 2. The distal end  170  includes a camera housing  210  surrounding a camera assembly comprising, in the illustrative embodiment, an objective window  250 , an aperature  240 , an acromat  230 , a light baffle  220 , and an imaging assembly  225 . Such camera assemblies (without the inventive cover assembly) are well-known, and commercially available from the Semiconductor Business Division of Sony Electronics Inc.  
         [0023]    An enlarged view of the imaging assembly  225  is shown in FIG. 2A. The imaging assembly generally includes an imager cover element  270  (described in greater detail in relation to FIG. 3) and a CHL assembly  260 . As used herein, “CHL” is an acronym for “Chip Hybrid Lead”, which refers generally to a imager (“chip”), the electronics which amplify the signal from the imager (“hybrid”), and a harness which carries the imager signal back to an imaging device (“lead”). The cover element  270  is fitted to the CHL assembly  260  by a mounting element  280 . In the illustrative embodiment, the mounting element  280  is shown as an adhesive portion deposited in a bead-like pattern on a peripheral, exterior edge of imager cover element  270  and an exterior edge of CHL assembly  260  in the illustrative embodiment of FIG. 2A. One of ordinary skill will appreciate, however, that the mounting element could comprise, instead of adhesive, tapes (such as MYLAR® tape), shrink tubes, and mechanical mountings. In the illustrative embodiment, the mounting element  280  (which shall be referred to as an “adhesive portion” in connection with the illustrative embodiment) preferably is a thick adhesive, to prevent the adhesive from being interposed between (or “running” into) the space between the imager cover element  270  and the CHL assembly  260  during manufacture. By “thick” what is meant is an adhesive having a viscosity of between about 100,000 centipoise and about 1,000,000 centipoise. The prevention of, and lack of, adhesive (or any other desired mounting element) between the imager cover element  270  and the CHL assembly  260  is an important feature of the invention, as adhesive between the two might crack (leading to degraded image quality) or fail (leading to loss of the imager cover element  270 ).  
         [0024]    The imager cover element  270 , as illustrated in FIG. 2A and FIG. 3, is shaped to create an air gap  275  between the imager cover element  270  and the CHL assembly  260 . This air gap provides a sufficient distance so that the imager cover element  270  and the CHL assembly  260  are not close enough for any differences in their respective refractive indices to give rise to Newton&#39;s rings.  
         [0025]    The adhesive portion  280  also preferably is a quick-cure adhesive, so that the application of the adhesive portion  280  does not become a time-consuming step during the manufacture of the imaging assembly  225 . By “quick” what is meant is an adhesive that is cured within about 15 minutes of application. Generally, epoxy adhesives, and in particular HYSOL®  608 , offered by Loctite Corporation, have been found to be a well-suited for the purposes of bonding the imager cover element  270  to the CHL assembly  260 .  
         [0026]    Referring to FIG. 3, the imager cover element  270  is shown, in the illustrative embodiment, to have a plano-concave shape, though the invention equally may be practiced using other shapes, such as convex-concave or concave-concave. In the illustrative embodiment, the imager cover element  270  has a distal, non-imager facing side  320 , which is shown as being planar, and a proximal, imager facing side  310 , which is shown having a concave indentation  315 . The concave indentation  315 , when paired with the CHL assembly  260 , creates the tight fit as well as the air gap  275  defined between the imager cover element  270  and the CHL assembly  260 , as shown in FIG. 2A. The concave indentation  315  prevents the formation of Newton&#39;s rings by preventing a surface to surface orientation between the imager cover element  270  and the viewable area of the CHL assembly  260 , as is seen in (prior art) cover assemblies employing a flat cover element. The concave indentation  315  also serves to prevent the externally applied adhesive portion from being drawn into the air gap  275  by means of capillary action. In the illustrative embodiment, the indentation  315  can be described by a radius of curvature  330  which is about equal to the focal length of the imaging device  100  (which in the case of the illustrative boroscope is about 3.00 mm+/−0.03 mm). The radius of curvature, however, is not a vital feature of the present invention, and any radius of curvature between the focal length of the device and infinite could be used, so long as enough of the air gap  275  is maintained to prevent the formation of Newton&#39;s rings.  
         [0027]    The imager cover element  270  is achromatic in the illustrative embodiment, though the imager cover element could be pigmented or otherwise treated to filter out certain wavelengths of light if desired. If desired, the imager cover element  270  also could be machined to provide an additional, optical modification of light coming entering the CHL assembly  260 , i.e., the imager cover element  270  could act as a lens. The imager cover element  270  could be fabricated from any desired, optically-transmissive material, such as glass, plastic, crystal, or composites suitable for optical uses. Notably, the short distance between the imager cover element  270  and the CHL assembly  260  ensures that any environmental debris that is deposited on the distal end  320  of the imager cover element  270  remains out of focus, and does not materially alter any image that is subsequently generated by the CHL assembly  260 .  
         [0028]    The imager cover element  270  is shaped so that the edges of the cover element sealingly engage the edges of the CHL assembly  260  to form a tight fit. By “tight,” what is meant is that the edges are shaped in a manner so that when the adhesive portion  280  (or other selected mounting element) is applied to the exterior of cover element  270  and the CHL assembly  260 , as shown in FIG. 2A, the adhesive portion  280  (or other selected mounting element) is unable to enter the air gap  275 . After the adhesive portion  280  sets, a seal is formed comprising the adhesive portion  280 , and the tight fit between the edges of the imager cover element  270  and the CHL assembly  260 , preventing environmental debris from entering the air gap  275  and affecting the CHL assembly  260 .  
         [0029]    While the invention has been described in conjunction with a preferred embodiment, it is evident that numerous alternatives, variations, and modifications will be apparent to those skilled in the art in light of the foregoing description. Thus, it is understood that the invention is not to be limited by the foregoing illustrative details.  
       Equivalents  
       [0030]    While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.