Abstract:
A cylindrical array of tightly spaced optical discs is arranged such that all optical discs in the array share the same axis of symmetry. An optical system is aligned with the optical disc array. The optical system includes a light source, such as a diffuse reflector, and a photo detector, such as a photo detector. The photo detector is aligned to receive either light transmitted through the optical disc array or light reflected off the optical disc array. Illumination directed at the optical disc array results in a pattern of alternating light and dark illuminations, or bands. The photo detector focusing on the cylinder surfaces of the optical discs detects the light/dark transitions and thus enables counting of discrete optical discs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 U.S.C. §119(e) of the U.S. Provisional Patent Application Ser. No. 62/066,752, filed Oct. 21, 2014 and titled, “OPTICAL METHODS FOR DETERMINING POSITIONS OF OPTICAL DISCS IN TIGHTLY PACKED CYLINDRICAL ARRAYS,” which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of optical disc storage and access. More specifically, the present invention relates to a system and method of determining positions of optical discs in tightly packed cylindrical arrays. 
     BACKGROUND OF THE INVENTION 
     Optical discs provide a reliable long term storage medium available for digital information. In order to automate archived optical disc storage in a cost effective manner, optical discs are shelved for occasional automated retrieval. It is desired to minimize the amount of space that the optical discs themselves occupy so as to maximize optical disc storage density. As such, optical discs are stacked as closely together as possible. A problem with closely stacking optical discs is the subsequent process of accessing a specific optical disc within a tightly spaced optical disc stack. One technique of accessing a specific optical disc within an optical disc stack is to use a robotic gripper. The specific optical disc is accessed by moving the robotic gripper a determined distance within the optical disc stack based on an anticipated average thickness of each optical disc. However, variances in manufacturing tolerances for optical disc thicknesses results in inaccurate determination of a specific optical disc position within an optical disc stack. 
     SUMMARY OF THE INVENTION 
     A cylindrical array of tightly spaced optical discs is arranged such that all optical discs in the array share the same axis of symmetry. An optical system is aligned with the optical disc array. The optical system includes a light source, such as a diffuse reflector, and a photo detector, such as a photo detector. The photo detector is aligned to receive either light transmitted through the optical disc array or light reflected off the optical disc array. Illumination directed at the optical disc array results in a pattern of alternating light and dark illuminations, or bands. The photo detector focusing on the cylinder surfaces of the optical discs detects the light/dark transitions and thus enables counting of discrete optical discs. 
     In an aspect, an optical disc retrieval system is disclosed. The system includes an array of optical discs, a light source, a photo detector and a processor. The array of optical discs has a central axis. The light source is configured to direct light toward the array of optical discs. The photo detector is aligned with the light source to detect light having impinged the array of optical discs and to output a corresponding detected signal. The light source and the photo detector are configured to move together parallel to the central axis while directing light toward the array of optical discs and detecting light such that the detected signal comprises a series of alternating high intensity value bands and low intensity value bands. Each high intensity value band corresponds to a location of an optical disc in the array and each low intensity value band corresponds to a gap between adjacent optical discs in the array. The processor is coupled to the photo detector to receive the detected signal. The processor is configured to count the high intensity value bands to determine a location of a specific optical disc within the array of optical discs. In some embodiments, the system also includes a movement mechanism coupled to both the light source and the photo detector, wherein the movement mechanism is configured to move the together in tandem. In some embodiments, the system also includes one or more optical elements positioned between the light source and the array of optical discs, wherein the one or more optical elements are configured to focus light output from the light source onto the array of optical discs. In some embodiments, the system also includes one or more optical elements positioned between the array of optical discs and the photo detector, wherein the one or more optical elements are configured to focus light having impinged the array of optical discs onto the photo detector. In some embodiments, the one or more optical elements comprise a slit aperture. In some embodiments, the photo detector is positioned relative to the light source such that at least a portion of the array of optical discs is positioned between the light source and the photo detector. In some embodiments, the light directed toward the array of optical discs is transmitted through the array of optical discs and the transmitted light is detected by the photo detector. In some embodiments, transmitted light that passes through an optical disc in the array is detected as the high intensity value band, and transmitted light that passes through a gap between adjacent optical discs in the array is detected as the low intensity value band. In some embodiments, the photo detector is positioned relative to the light source and the array of optical discs such that reflected light resulting from light directed toward the array of optical discs impinging the optical discs in the array is detected by the photo detector. In some embodiments, reflected light that reflects off an optical disc in the array is detected as the high intensity value band, and light directed toward the array of optical discs that passes through a gap in adjacent optical discs in the array is not reflected and is indicated as the low intensity value band detected by the photo detector. In some embodiments, the light source comprises an axis of symmetry, further wherein the photo detector is aligned with the axis of symmetry of the light source. In some embodiments, the light source comprises an axis of symmetry, further wherein the photo detector is aligned off the axis of symmetry of the light source. In some embodiments, the system also includes a tray configured to store the array of optical discs, wherein the array of optical disc are stored in the tray on edge such that the central axis of the array forms a horizontal axis. In some embodiments, the system also includes a compression mechanism coupled to the tray, wherein the compression mechanism is configured to compress the array of optical discs stored in the tray. In some embodiments, the system also includes a robotic gripper configured to selectively grab the specific optical disc. 
     In another aspect, a method of retrieving specific optical disc within an array of optical discs is disclosed. The method includes directing a light from a light source toward the array of optical discs and scanning the light along a length of the array of optical discs. The method also includes detecting light having impinged the array of optical discs and generating a corresponding signal. The signal comprises a series of alternating high intensity value bands and low intensity value bands, each high intensity value band corresponding to a location of an optical disc in the array and each low intensity value band corresponding to a gap between adjacent optical discs in the array. The method also includes counting the high intensity value bands to determine a location of the specific optical disc within the array of optical discs. In some embodiments, the scanned light is transmitted through the array of optical discs, and transmitted light that passes through an optical disc in the array is detected as the high intensity value band and transmitted light that passes through a gap between adjacent optical discs in the array is detected as the low intensity value band. In some embodiments, a portion of the scanned light is reflected off the optical discs in the array, and reflected light off an optical disc in the array is detected as the high intensity value band and scanned light directed toward the array of optical discs that passes through a gap in adjacent optical discs in the array is not reflected and is indicated as the low intensity value band detected. 
     Other features and advantages of the present invention will become apparent after reviewing the detailed description of the embodiments set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Several example embodiments are described with reference to the drawings, wherein like components are provided with like reference numerals. The example embodiments are intended to illustrate, but not to limit, the invention. The drawings include the following figures: 
         FIG. 1  illustrates a conceptual diagram of a system using a transmission option for determining positions of optical discs in an optical disc array according to some embodiments. 
         FIG. 2  illustrates a conceptual diagram of a system using a reflective option for determining positions of optical discs in an optical disc array according to some embodiments. 
         FIG. 3  illustrates an exemplary configuration of the light source and photo detector for both the transmission option and the reflective option. 
         FIG. 4  illustrates an enlarged view of the detector side for the transmission option shown in  FIG. 3 . 
         FIG. 5  illustrates an enlarged view of the detector side for the reflective option shown in  FIG. 3 . 
         FIG. 6  illustrates a top down view of a functional system for storing an optical disc array and retrieving a specific optical disc from within the optical disc array according to some embodiments. 
         FIG. 7  illustrates a functional block diagram of a control system for controlling storage of an optical disc array and retrieval of a specific optical disc from within the optical disc array according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present application are directed to a method and system for determining positions of optical discs in tightly packed cylindrical arrays. Those of ordinary skill in the art will realize that the following detailed description of the method and system is illustrative only and is not intended to be in any way limiting. Other embodiments of the method and system will readily suggest themselves to such skilled persons having the benefit of this disclosure. 
     Reference will now be made in detail to implementations of the method and system as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application and business related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
     Automated retrieval of a specific individual optical disc within a tightly spaced array of optical discs requires distinguishing individual optical discs in the optical disc array. Embodiments are directed to systems and methods for determining positions of individual optical discs for retrieval. In some embodiments, the optical discs in the optical disc array are tightly spaced, yet a small gap is still present at the perimeter between each adjacent optical disc in the optical disc array. Such a configuration is common for those types of optical discs that are configured with a center portion having a larger thickness than a perimeter portion. When such optical discs are stacked together, the center portions of adjacent optical discs contact each other, but the thinner perimeter portions remain slightly separated. Light is scanned onto the optical disc array and a photo detector detects high and low intensity signals and their corresponding locations. The high intensity signals correspond to the thickness of an individual optical disc while the low intensity signals correspond to the gap between individual optical discs. The light source and corresponding photo detector pair detect reflections (or transmissions) off (or through) the cylindrical array of optical discs or the absence thereof. A threshold detector determines when the amplitude of the reflected (or transmitted) signal indicates the presence or absence of an optical disc in the light path between the light source and the photo detector. The threshold detector and a counter enable an optical scan to locate an exact position of a specific optical disc in the array of tightly spaced optical discs. 
     In another embodiment, the optical discs in the cylindrical array are tightly spaced, and there is substantially no space between adjacent optical discs in the optical disc array. The light source illuminates the compressed array of optical discs and the photo detector detects the outer surface of the compressed, or touching, cylindrical optical disc array. Individual interfaces between optical discs are less efficient at transmitting the diffused light than the internal region of individual optical discs. The photo detector detects high and low intensity signals and their corresponding locations, where the high intensity signals correspond to the thickness of an individual optical disc and the low intensity signals correspond to the boundary between individual optical discs. The threshold detector and the counter enable determination of the transitions between low and high intensity signal regions to determine the transition from one optical disc to the next and thus determine a specific optical disc location in an array of optical discs compressed together. 
     Optical scanning along the length of the optical disc array results in a detected pattern of alternating light and dark bands representing the high intensity signals and low intensity signals, respectively. The light and dark bands can be observed using a reflective option or a transmission option. In the transmission option, the photo detector is aligned with the light source but with a portion of the optical disc array positioned between the two. The light emitted by the light source is transmitted through the optical disc array arriving at the photo detector.  FIG. 1  illustrates a conceptual diagram of a system using a transmission option for determining positions of optical discs in an optical disc array according to some embodiments. The system includes a light source  12 , source-side optics  14 , an optical disc array  2 , detector-side optics  16  and a photo detector  18 . In some embodiments, the light source  12  is an LED light source. In other embodiments, the light source  12  is a laser light source. It is understood that other types of light sources can be used. The optical disc array  2  includes a plurality of optical discs  4  stacked along a cylindrical axis  10 . In some embodiments, the optical discs  4  are each configured with a center portion  8  that is slightly thicker than a perimeter portion  7 . In such a case, when the optical discs  4  are tightly stacked or compressed together, the center portions  8  of adjacent optical discs  4  contact each other, but a gap  6  remains between adjacent optical discs  4  due to the smaller thickness of the perimeter portions  7 . 
     The light source  12  emits light  20  which is received by the source-side optics  14  and directed as light  22  onto the optical disc array  2 . In some embodiments, the source-side optics  14  focus the received light  20  as focused light  22 , such as a narrow line of light that is parallel to a diameter of each optical disc  4 . In other embodiments, the light from the light source does not need to be focused, there can be broad illumination of the optical disc array. Although source-side optics  14  are shown in  FIG. 1  as a single component, it is understood that the source-side optics  14  can include multiple optical components. As described in greater detail below in regard to  FIG. 6 , the light source  12  and the source-side optics  14  are configured to move parallel to the cylindrical axis  10  thereby scanning the light  22  along a length of the optical disc array  2 . The light  22  impinges either an optical disc  4  or a gap  6  depending on the scanning location as the light source  12  and source-side optics  14  are moved. The impinging light  22  is transmitted through a width of the optical disc array  2  toward the detector-side optics  16  and the photo detector  18 . 
     The photo detector  18  and the detector-side optics  16  are aligned to receive the transmitted light  24  leaving the optical disc array  2 . The detector-side optics  16  focus the received light  24  as focused light  26  and directs the focused light  26  to the photo detector  18 . Although detector-side optics  16  are shown in  FIG. 1  as a single component, it is understood that the detector-side optics  16  can include multiple optical components. In some embodiments, the optical train includes a slit aperture for limiting light impinging the photo detector  18 . In this case, the optical elements focus the light directed from the light source to the optical disc array as a focused line, and an orientation of the slit in the slit detector is aligned to match an angle of the focused line. In particular, the focused line is oriented to be parallel to the faces of the optical discs and the slit in the slit detector is also oriented to be parallel to the faces of the optical discs. In this manner, the slit aperture allows differentiation of narrow low and wide high irradiance regions thereby maximizing sensitivity to the narrow dark bands in the pattern corresponding to gaps between optical discs. 
     In some embodiments, the light emitted from the light source  12  is focused onto the optical disc array  2  and scanned across the length of the optical disc array (parallel to the cylindrical axis  10 ) by simultaneously moving the light source  12 /photo detector  18  pair, along with the corresponding optics  14 ,  16 , parallel to the cylindrical axis  10 . In some embodiments, the light source  12 , the source-side optics  14 , the detector-side optics  16  and photo detector  18  are aligned along an optical axis  11 . The optical axis  11  is perpendicular to the cylindrical axis  10  of the optical disc array  2 . However, the optical axis  11  is offset from the cylindrical axis such that the optical axis does not intersect the cylindrical axis  10 . In this manner, the light transmitted through the optical disc array  2  does not pass through the center portions  8  of the optical discs  4 . Such a configuration is illustrated in  FIG. 3 . 
     Each optical disc  4  functions as a waveguide for impinging light. In the case where there are gaps between adjacent optical discs in the array, the gaps between adjacent optical discs also function as waveguides. Total internal reflection within the body of the optical disc accounts for more efficient transmission of visible light through the optical discs relative to transmission of visible light in the air gap between the optical discs. This results in a pattern of light and dark bands of light detected by the photo detector, where each light band of the pattern corresponds to an optical disc and each dark band of the pattern corresponds to an air gap between optical discs. In tightly spaced arrays, the dark band of the pattern is narrower than the light band of the pattern, since a distance at the perimeter between adjacent optical discs in the optical disc array is smaller than a thickness of the optical discs. 
     In other embodiments, the optical discs are configured to have substantially constant thickness such that a center portion thickness and a perimeter portion thickness are substantially the same. In such a case, adjacent optical discs in a stacked array substantially contact each other over their entire flat surfaces. Similar to the configuration with gaps between adjacent optical discs, the contacting surfaces of adjacent optical discs also function as a waveguide, but again with less efficient transmission of visible light than that of visible light transmitted through the optical disc itself. This again manifests itself as a pattern of light and dark bands detected by the photo detector. 
     In some applications, writing on the surface of the optical discs may lead to unintended effects on the transmitted light. The reflective option alleviates this effect. In the reflective option, the photo detector is positioned at an angle to the optical disc array so as to receive reflected light resulting from the light emitted by the light source impinging the optical disc array and reflecting.  FIG. 2  illustrates a conceptual diagram of a system using a reflective option for determining positions of optical discs in an optical disc array according to some embodiments. The system includes a light source  32 , source-side optics  34 , the optical disc array  2 , detector-side optics  36  and a photo detector  38 . In some embodiments, the light source  32  is an LED light source. In other embodiments, the light source  32  is a laser light source. It is understood that other types of light sources can be used. 
     In the reflective option, the light  40  emitted from the light source  32  is focused onto the optical disc array  2  and scanned across the length of the optical disc array (parallel to the cylindrical axis  10 ) by moving the light source/photo detector pair parallel to the cylindrical axis  10  as described above. In this case, the photo detector  38  is positioned at a reflection angle relative to the edge of the optical discs  4  and the light source  32 . The optimal reflection angle is a function of the curvature of the optical disc  4  and the angle of incidence of the light  42  impinging the edge of the optical disc  4 . The light source  32  emits light  40  which is received by the source-side optics  34  and directed as light  42  onto the optical disc array  2 . In some embodiments, the source-side optics  34  focus the received light  40  as focused light  42 , such as a narrow line of light that is parallel to a diameter of each optical disc  4 . Although source-side optics  34  are shown in  FIG. 2  as a single component, it is understood that the source-side optics  34  can include multiple optical components. As described in greater detail below in regard to  FIG. 6 , the light source  32  and the source-side optics  34  are configured to move parallel to the cylindrical axis  10  thereby scanning the light  42  along a length of the optical disc array  2 . The light  42  impinges either the optical disc  4  or the gap  6  depending on the scanning location as the light source  32  and source-side optics  34  are moved. The light  42  is reflected as reflected light  44  when impinging the optical disc  4 , and transmitted through a width of the optical disc array when impinging the gap  6 . In practice, there is some amount of reflected light even when the light  42  impinges a gap  6  in the optical disc array  2 . The photo detector  38  and the detector-side optics  36  are aligned to receive the reflected light  44  reflected off the optical disc array  2 . The detector-side optics  36  focus the reflected light  44  as focused light  46  and directs the focused light  46  to the photo detector  38 . 
     The photo detector  38  detects the reflected light from the impinging area on the optical disc array  2 . Reflected light detected as having a high intensity, such as a light band in the pattern, is determined to correspond to an optical disc position, and reflected light detected having a low intensity, such as a dark band in the pattern, is determined to correspond to a space between adjacent optical discs. 
       FIG. 3  illustrates an exemplary configuration of the light source and photo detector for both the transmission option and the reflective option. As shown in  FIG. 3 , the photo detector  18  and the detector-side optics  16  used in the transmission option are offset from the cylindrical axis  10  of the optical disc array  2 . As also shown in  FIG. 3 , the photo detector  38  and the detector-side optics  36  used int the reflective option are positioned at an exemplary reflective angle of 90 degrees, which corresponds to the Z-axis. 
       FIG. 3  also shows an exemplary conceptual representations of a light and dark pattern corresponding to a scanned distance d along the optical disc array  2 . The beam of light impinging the optical disc array  4  represents the light  22 ,  42  integrated over the distance d. For the transmission option, the corresponding beam of transmitted light received by the detector-side optics  16  and the photo detector  18  represents the light  24  integrated over the distance d. For the reflective option, the corresponding beam of reflected light received by the detector-side optics  36  and the photo detector  38  represents the reflected light  44  integrated over the distance d. It is understood that the beam shapes shown in  FIG. 3  are for illustrative purposes only and that in practice, the transmitted light  24  and the reflected light  44  are diverging in nature, not collimated as shown, and the transmitted light and reflected light need to be re-imaged to form the band patterns.  FIG. 3  is illustrative of the conceptual light and dark band patterns formed. 
       FIG. 4  illustrates an enlarged view of the detector side for the transmission option shown in  FIG. 3 . As shown in  FIG. 4 , integration of the transmitted light  24  over scanning distance d results in an alternating pattern of light bands  50  and dark bands  48 . The light bands  50  correspond to light that traveled through the thickness of the optical discs  4 , and the dark bands  48  correspond to light that traveled between adjacent optical discs  4  in the gaps  6 . The area between the optical discs has lower irradiance and the area occupied by the optical discs has higher irradiance, as detected by the photo detector. 
       FIG. 5  illustrates an enlarged view of the detector side for the reflective option shown in  FIG. 3 . As shown in  FIG. 5 , integration of the reflected light  44  over scanning distance d results in an alternating pattern of light bands  54  and dark bands  52 . The light bands  54  correspond to light that reflected off the optical discs  4 , and the dark bands  52  correspond to light that reflected from between adjacent optical discs  4  in the gaps  6 . The area between the optical discs has lower irradiance as most of the impinging light is transmitted through the gaps, and the area occupied by the optical discs has higher irradiance, as detected by the photo detector. 
     The light source, the source-side optics, the detector-side optics and the photo detector are connected to a common frame and movement mechanism that moves each of these components in unison so as to optically scan the optical disc array.  FIG. 6  illustrates a top down view of a functional system for storing an optical disc array and retrieving a specific optical disc from within the optical disc array according to some embodiments. An optical disc array  70  is stored in a tray  60  and the optical discs of the optical disc array  70  are compressed together within the tray  60  using compression mechanisms  72  and  74 . In some embodiments, the compression mechanism  72  and  74  are spring loaded. A light source/source-side optics  62  is connected to a frame and movement mechanism  66 , and a photo detector/detector-side optics  64  are also connected to the frame and movement mechanism  66 . To retrieve a specific optical disc in the optical disc array  70 , the light source/source-side optics  62  and photo detector/detector-side optics  64  pair is moved by the frame and movement mechanism  66  in the Y direction to scan the length of the optical disc array  70 . The light source/source-side optics  62  and photo detector/detector-side optics  64  pair starts at one end of the optical disc array  70  and the resulting light and/or dark bands are counted while moving toward the opposite end of the optical disc array  70  to determine the exact position of each optical disc and to find the specific optical disc according to the count. The relative position of each individual optical disc in the optical disc array  70  is previously known, for example optical disc A is known to be in the fifth position of a twenty disc array. Once the specific optical disc is located within the optical disc array  70  according to the count, the corresponding Y coordinate along the cylindrical axis  82  is noted and a robotic gripper grabs the specific optical disc using the determined Y coordinate. 
     In many applications, robotic grippers are not able to grab a single optical disc from within a tightly spaced, or compressed, array. In such cases, an optical disc separating means is used whereby the compression mechanism compressing the optical discs in the optical disc array is released and the optical discs are separated so as to enable a robotic gripper to grab the specific optical disc. In some embodiments, the robotic gripper is configured to perform at least three functions. A first function is to push along the positive Y direction to separate an adjacent optical disc on a first side of the specific optical disc to be retrieved. A second function is to push along the negative Y direction to separate an adjacent optical disc on a second side of the specific optical disc. A third function is to grab the specific optical disc after the adjacent optical discs have been pushed away from both sides. Once the specific optical disc is retrieved and removed from the optical disc array, the robotic gripper mechanism that pushed away the adjacent optical discs is removed and the spring loaded tray compresses the remaining optical discs. The relative positions of each remaining optical disc in the optical disc array are updated in memory. 
     In some embodiments, the system for storing an optical disc array and retrieving a specific optical disc from within the optical disc array is automated.  FIG. 7  illustrates a functional block diagram of a control system for controlling storage of an optical disc array and retrieval of a specific optical disc from within the optical disc array according to some embodiments. The control system is configured to control the functionality previously described. As applied to the exemplary system of  FIG. 6 , controller and processing circuitry  80  is coupled to a robotic gripper  76 , the frame and movement mechanism  66 , the light source/source-side optics  62  and the photo detector/detector-side optics  64 . The controller and processing circuitry  80  provides control signaling. The controller and processing circuitry  80  also includes memory, the threshold detector and the counter described above. In some embodiments, the robotic gripper  76  is of the type described above in which the robotic gripper  76  is configured to separate a specific optical disc from adjacent optical discs and to grab the specific optical disc after the adjacent optical discs have been pushed away from both sides. It is understood that the robotic gripper  76  is generally representative of a robotic mechanism for retrieving a determined specific optical disc from an optical disc array. 
     The present application has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the method and system. Many of the components shown and described in the various figures can be interchanged to achieve the results necessary, and this description should be read to encompass such interchange as well. As such, references herein to specific embodiments and details thereof are not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications can be made to the embodiments chosen for illustration without departing from the spirit and scope of the application.