Patent Publication Number: US-7907796-B2

Title: Alignment of tape cartridge accessor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a division of U.S. application Ser. No. 09/957,948, filed Sep. 20, 2001, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to automated tape library systems, and more particularly to an image based bar code reading and robotic registration apparatus and method for use in automated tape library systems. 
     2. Description of Related Art 
     Magnetic tape has long been used as a storage media for audio, video and computer information. Tape cartridges have been used extensively because they provide a convenient way to house and support a length of magnetic tape for engagement by a transducer in a tape drive while protecting the tape upon removal of the cartridge. 
     Storage libraries provide large capacity secondary storage to modern computing requirements. Such storage libraries typically employ robotic control mechanisms used by a host computer to physically manage tape media cartridges. A plurality of tape cartridges are stored within a storage library. Each tape cartridge is in a particular slot in the storage library. Each slot is identifiable by its physical position in the storage library. Each tape cartridge is typically uniquely identified by a machine readable label. The storage library maintains inventory information to associate a particular tape cartridge with a particular slot in the storage library. Responsive to a host computer request, a robotic mechanism or picker physically retrieves an appropriate tape cartridge from its associated slot in the storage library, moves the tape cartridge to an appropriate read/write device for processing, and inserts the tape cartridge into the device. 
     The robotic mechanism typically includes a hand or gripper mechanism positioned on a movable arm. To retrieve a tape cartridge, the arm moves to position the gripper near the slot holding the desired tape cartridge. The gripper then extends and grips the tape cartridge and retracts to take the tape cartridge out of the slot. The arm with the hand gripping the tape cartridge moves to the device and the hand then extends and inserts the tape cartridge into the device. Conversely, when the use of the tape cartridge is complete, the robotic mechanism retrieves the tape cartridge from the read/write device, moves the tape cartridge adjacent its associated slot according to the inventory maintained by the storage library, and inserts the tape cartridge into the storage slot of the storage library ready for future use in response to another host computer request. 
     A problem with prior automated storage libraries designs which contributed to their relatively higher complexity and resultant higher costs relates to the multiplicity and complexity of various sensing mechanisms used to sense several parameters of the operating storage library. Picker registration has proven to be a problem, resulting in occasional dropped cartridges and decreased system performance. Past registration techniques made of a “flying spot” paradigm, using an LED retroreflective sensor to locate the position of a few fiducial marks and then calculate the theoretical position of every cartridge cell in robot coordinates to initialize its position table. In practice this method has been less than perfect, with some systems suffering jams or drops. Other techniques have used a dedicated vision processor and bulky CCD camera with incandescent lighting. However, the production cost of such a system is high. 
     Such excessive cost has been addressed by using a laser-based scanner for the barcodes, and a “flying spot” sensor for registration. However, registration accuracy has proven to be a problem because the environment is dynamic and the robot accessor (picker) begins to drift over time. Recalibration with the sensor requires complete control of the robot, halting all other operations. Other camera-based vision systems in tape libraries have been used that depend on special fiducial markings for registration. Accordingly, a cost-effective imaging system for aligning a picker in an automated tape library system has not been developed. 
     It can be seen that there is a need for an image-based bar-code reading and robotic registration apparatus and method for use in automated tape library systems. 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses an image based bar-code reading and robotic registration apparatus and method for use in automated tape library systems. 
     The present invention solves the above-described problems by positioning an imager on picker assembly with its own illumination source and appropriate optics to filter out ambient light. The imager connects to a microprocessor in its immediate vicinity. All image acquisition and processing are done by these components. To ensure operation independent of illumination variations, the image processing code developed for this invention automatically adapts to dynamic lighting situations. 
     A system in accordance with the principles of the present invention includes a picker assembly, an imager disposed on the front of the picker assembly, illumination sources disposed at the front of the picker assembly and a processor, coupled to the imager and illumination sources, for processing image data obtained from the imager and for controlling the illumination sources. 
     Other embodiments of a system in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the system further includes optics selected to filter out ambient light. 
     Another aspect of the present invention is that the processor performs image processing on the image data to automatically adapt to dynamic lighting situations. 
     Another aspect of the present invention is that the system further includes an external bus interface for coupling the processor to an external communications bus. 
     Another aspect of the present invention is that the imager further comprises a camera and lens assembly. 
     Another aspect of the present invention is that the imager further comprises an IR filter coupled to the lens assembly. 
     Another aspect of the present invention is that the illumination source comprises IR LED lighting assemblies. 
     Another aspect of the present invention is that the system further includes LED drivers disposed between the processor and the IR LED lighting assemblies, the LED drivers receiving control signals from the controller and providing drive signals to the IR LED lighting assemblies. 
     Another aspect of the present invention is that the processor comprises a microcontroller. 
     Another aspect of the present invention is that the imager receives specular reflection off of the tape cartridge cells during calibration operations to allow tape cartridge registration without fiducial markings. 
     Another aspect of the present invention is that the imager uses the tape cartridge cells as fiducials to allow tape cartridge registration without fiducial markings. 
     Another aspect of the present invention is that the use of the tape cartridge cells as fiducials maximizes storage capability. 
     Another aspect of the present invention is that the imager detects bar codes on the tape cartridges to identify the tape cartridges. 
     Another aspect of the present invention is that the processor operates in two states to provide tape cartridge position registration and to provide bar code resolution. 
     Another aspect of the present invention is that the processor outputs the values of bar-codes when the processor is configured to provide bar code resolution 
     Another aspect of the present invention is that the processor outputs an offset value of some detected image feature from its nominal location in the x, y plane when the processor is configured to provide tape cartridge position registration. 
     Another aspect of the present invention is that the processor continuously visually verifies the position of the picker to eliminate the need for time-consuming recalibration. 
     In another embodiment of the present invention, a method for aligning a tape cartridge accessor with cartridges in cells of a tape cartridge magazine is provided. The method includes applying IR illumination to an object expected to include a desired physical feature, receiving specular reflections from the illuminated object to create an image of the object, applying dynamic image thresholding to the image to select an optimum gray scale level of the image expected to include the desired physical feature and using bounding boxes to identify the location of the desired physical feature in the thresholded image. 
     Another aspect of the method of the present invention is that the desired physical feature comprises a corner of a cell in a tape cartridge magazine. 
     Another aspect of the method of the present invention is that the applying dynamic image thresholding enhances relevant portions of the image and suppresses irrelevant portions of the image. 
     Another aspect of the method of the present invention is that the tape cartridge cells are used as fiducials to allow tape cartridge registration without fiducial markings. 
     Another aspect of the method of the present invention is that the use of the tape cartridge cells as fiducials maximizes storage capability. 
     In another embodiment of the present invention, an article of manufacture comprising a program storage medium readable by a computer is disclosed. The medium tangibly embodies one or more programs of instructions executable by the computer to perform a method for aligning a tape cartridge accessor with cartridges in cells of a tape cartridge magazine, wherein the method includes applying IR illumination to an object expected to include a desired physical feature, receiving specular reflections from the illuminated object to create an image of the object, applying dynamic image thresholding to the image to select an optimum gray scale level of the image expected to include the desired physical feature and using bounding boxes to identify the location of the desired physical feature in the thresholded image. 
     Another aspect of the article of manufacture of the present invention is that the desired physical feature comprises a corner of a cell in a tape cartridge magazine. 
     Another aspect of the article of manufacture of the present invention is that the applying dynamic image thresholding enhances relevant portions of the image and suppresses irrelevant portions of the image. 
     Another aspect of the article of manufacture of the present invention is that the tape cartridge cells are used as fiducials to allow tape cartridge registration without fiducial markings. 
     Another aspect of the article of manufacture of the present invention is that the use of the tape cartridge cells as fiducials maximizes storage capability. 
     In another embodiment of the present invention, a picker system for use in aligning a tape cartridge accessor with cartridges in cells of a tape cartridge magazine is provided. The picker system includes a picker assembly, illumination means disposed at the picker assembly for illuminating an object, imaging means disposed on the picker assembly for gathering image data of the object and processing means, coupled to the imager and illumination sources, for processing the image data obtained from the imaging means and for controlling the illuminating means. 
     These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
         FIG. 1  illustrates an automatic tape library in accordance with the present invention; 
         FIG. 2  illustrates an image based bar-code reading and robotic registration apparatus for use in automated tape library systems according to the present invention; 
         FIG. 3  illustrates a block diagram of the an image based bar-code reading and robotic registration apparatus for use in automated tape library systems according to the present invention; 
         FIG. 4  illustrates a flow chart of the image based bar-code reading and robotic registration method for use in automated tape library systems according to the present invention; and 
         FIG. 5  illustrates the two modes of operation  500  of the image processing system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description of the exemplary embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration the specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized as structural changes may be made without departing from the scope of the present invention. 
     The present invention provides an image-based bar-code reading and robotic registration apparatus and method for use in automated tape library systems. The present invention positions an imager on a picker assembly with its own illumination source and appropriate optics to filter out ambient light. The imager connects to a microprocessor in its immediate vicinity. All image acquisition and processing are done by these components. To ensure operation independent of illumination variations, the image processing code developed for this invention automatically adapts to dynamic lighting situations. 
       FIG. 1  illustrates an automatic tape library system  100  in accordance with the present invention. As shown in  FIG. 1 , the tape library includes a dual gripper assembly  110  coupled to a gripper/picot assembly  112 . The gripper assembly  110  moves in the y-axis along the y-axis assembly  120  and in the x-axis along the x-axis assembly  130 . 
       FIG. 2  illustrates an image-based bar-code reading and robotic registration apparatus  200  for use in automated tape library systems according to the present invention. In  FIG. 2 , a picker assembly  210  is disposed along the outside of a cartridge magazine  212 . The cartridge magazine  212  includes cartridges  214  in the cartridge cells  216 . The picker  210  includes an imager  220 , such as a camera (CCD, CMOS, etc.), positioned on the front of the picker assembly  210 . The imager  220  includes appropriate optics  222  selected to filter out ambient light. Illumination  230  sources are disposed on the picker  210 . The imager  220  connects to a microprocessor or microcontroller  240  that may be disposed in the immediate vicinity of the imager  220 . All image acquisition and processing are done by the imager  220  and microcontroller  240 . 
     To ensure operation independent of illumination variations, the image processing automatically adapts to dynamic lighting situations. Output format is dependent upon the host system, for example, a serial or Controller Area Network (CAN) bus. The imager  220  provides an inexpensive self-contained image processing system to visually verify the alignment of the picker  210  with the cartridges  214 . The tape cartridge cells  216  are used as fiducials to allow tape cartridge registration without fiducial markings. The use of the tape cartridge cells  216  as fiducials maximizes storage capability. Registration can be checked with every pick, greatly increasing reliability. 
       FIG. 3  illustrates a block diagram  300  of an image based bar-code reading and robotic registration system for use in automated tape library systems according to the present invention. An external bus interface  310  is coupled to an external communications bus  312 . The external communications bus  312  may communicate with any type of host processor  314 . The external bus interface  310  is connected to a microcontroller  320 . The microcontroller  320  controls both the imager  330  and the lighting assemblies  340 . The microcontroller  320  provides the control signals to, for example, the camera  332  and lens assembly  334 . An IR filter  336  may be provided at the lens of the imager  330 . 
     The microcontroller  320  also drives LED drivers  350 . The LED drivers  350  provide signals to the IR LED lighting assemblies  340 . As discussed above, during operation, the lighting  340  mounted to the picker provides specular reflection off of the cartridge cells during calibration operations to allow cartridge registration. 
     The system  300  may also double as a bar-code reader thereby eliminating the need for a costly laser-based scanner. The image processing system  300  will operate with two possible modes of operation. It can be operate as either a bar-code reader to provide bar code resolution or as a registration sensor. The state of the system  300  determines the type of output it provides. As a bar-code reader, the system  300  outputs the values of bar-codes to the external bus interface  310 . As a registration sensor, the system  300  outputs an offset value of some detected image feature from its nominal location in the x, y plane to the external bus interface  310 . 
     The system  300  uses imaging techniques by combining imagers  330  and inexpensive, yet powerful, microcontrollers  320 . The entire system  300  is mounted on the picker assembly and is therefore completely self-contained. Calibration could be verified on every single pick operation, and a need for a separate bar-code scanner is eliminated, thereby reducing system cost. The present invention also increases product reliability because it continuously visually verifies the position of the picker, eliminating the need for time consuming recalibration. During operation, the lighting  340  mounted to the picker provides specular reflection off of the cartridge cells during calibration operations. More diffuse lighting may be selected for bar-code reading. 
       FIG. 4  illustrates a flow chart  400  of the image based bar-code reading and robotic registration method for use during the registration mode in automated tape library systems according to the present invention. First, IR illumination is applied to an object expected to include a desired physical feature  410 , e.g., a corner of a cell for holding a tape cartridge. Specular reflections are received from the illuminated object to create an image of the object  420 . Dynamic image thresholding is applied to the image to select an optimum gray scale level of the image expected to include the desired physical feature  430 . The dynamic image threshold enhances relevant portions of the image and suppresses irrelevant portions of the image. Bounding boxes are used to identify the location of the desired physical feature in the thresholded image  440 . 
       FIG. 5  illustrates the two modes of operation  500  of the image processing system according to the present invention. As can be seen in  FIG. 5 , the image processing system may operate in a registration mode  510 . The registration mode  510  is the mode of operation described above with reference to  FIG. 4 . The image processing system may also operate in a bar code reader mode  520 . 
     Referring again to  FIG. 3 , an image based bar-code reading and robotic registration system  300  according to the present invention is shown, wherein the process illustrated with reference to  FIG. 4  may be tangibly embodied in a computer-readable medium or carrier, e.g. one or more of the fixed and/or removable data storage devices  368  illustrated in  FIG. 3 , or other data storage or data communications devices. A computer program  390  expressing the processes embodied on the removable data storage devices  368  may be loaded into the microcontroller  320  or into a processor  314  coupled to the external communications bus  312  to configure the microcontroller  320  or host processor  314  of  FIG. 3 , for execution. The computer program  390  comprise instructions which, when read and executed by the microcontroller  320  or host processor  314  of  FIG. 3 , causes the microcontroller  320  or host processor  314  to perform the steps necessary to execute the steps or elements of the present invention. 
     The foregoing description of the exemplary embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.