Abstract:
In order to minimize potential damage to a rewritable storage media, and to consequently extend the life of the media, the laser power is carefully controlled in order to avoide sharp power transitions. Rather than simply turning the laser power on to its full power level, the power utilized during writing dedicated sections of data sectors is transitioned from 0 to its full power level over a desired period of time. In this way, the thermal shock caused by repeated rewriting in these areas can be minimized, thus extending the life of the rewritable media.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to storage devices which use rewritable optical storage media. More specifically, the present invention involves a system and method for extending the life of the rewritable optical media used in such storage systems, thus also extending the operable life of the storage device itself. Furthermore, the present invention necessarily also increases the life of a library which utilizes these storage devices.  
           [0002]    As is clearly recognized by virtually all members of society, the use and storage of data for multiple applications is a critical component of day-to-day activities. The various applications that are using data continue to become more and more complex, thus utilizing larger amounts of data. Naturally, the storage and retrivability of this data is a critical function which must meet the capacity and speed needs of the related system or application. As is continuously seen in many areas of technology, there is a continued desire/demand for bigger and faster storage devices.  
           [0003]    In recent years, optical storage devices have become increasingly well accepted for many storage needs This acceptance is due primarily to the speed and capacity that can be achieved using optical storage devices. Further, some optical storage devices are rewritable, thus making them even more versatile and powerful data storage options. With a rewritable optical storage device, the media itself is capable of existing in two different phases. Consequently, by configuring this media in a predetermined phase at desired locations, meaningful data can thus be stored. Due to the ability to reset the state of material, the storage device thus becomes rewritable and reusable.  
           [0004]    As is recognized, the repeated writing in the same physical area to these rewritable optical disks can be detrimental. As with many physical devices, the localized changing of states in a very repetitive manner can cause thermal damage, thus making it ineffective. In operation, each writing step involves the heating of the media surface, and controlled cooling in order to achieve the desired state. This localized repeated heating and cooling is obviously harmful as it can cause damage to the media surface itself. At some point, the media becomes so damaged that it cannot be utilized for its intended purpose. In order to meet desired performance standards, storage device makers want to have increased life and high cyclability of the media. The current industry target is to obtain a storage system that will continue operating even after 1 million rewrites of data.  
           [0005]    The most damage to the media surface is caused by the thermal shock created when write operations are initiated. Obviously, the sudden turn-on of a laser can cause severe damage to those locations. This is especially problematic if the same data is rewritten in the same location on the media. Specific areas of the data format are prone to this due to the repetitive nature of the recording (e.g. preambles and postambles). Protecting preambles and synchronization fields at the beginning of each sector from over-write damage is especially critical, because they are essential for PLL-capture and sector synchronization. A damaged preamble and synchronization field may lead to loss of a large chunk of data in the sector In the past, efforts have been made to minimize this damage by altering the start location for write operations. Specifically, some approaches have involved a random starting point, within a predetermined range or predetermined write area. This is recognized as the SPS approach (Start Position Shift) that is well known by those in the industry. Versions of this approach are shown in U.S. Pat. Nos. 6,091,698 and 6,128,260. Other approaches have involved the reconfiguration or recoding of data in order to alter patterns and rewrite only those portions of data which have actually changed.  
           [0006]    While these approaches certainly have some benefit, they simply prolong the ultimate damage. Consequently, additional measures are desired to increase the useable life of an optical storage device.  
         SUMMARY OF THE INVENTION  
         [0007]    In order to extend the life of the rewriteable media, the present invention implements a method to minimize the thermal shock provided during writing operations. Specifically, the shock is minimized by tapering the write power during the initial portions of a write operation. Most often, this will involve the tapering of write power during a designated portion of the data sector immediately preceding the preamble. Additionally, the same tapering can be accomplished at the end of the data sectors (i.e., immediately following the postamble). In order to avoid interference with the various functions of the preamble and the postamble, separate guard fields are used for this power tapering function. Using these transitions will allow write power to be stable at its nominal value during writing of the preamble and postamble sections. Additional measures can also be taken to extend life such as SPS, and the international writing of marks on existing space and visa-versa.  
           [0008]    In order to accomplish the desired power tapering, the power level must be appropriately controlled while writing to these guard fields. The actual power taper can have various characteristics and can be controlled to form many different wave forms, all in an effort to minimize this thermal shock. Obviously a straight line power taper, over a predetermined period of time, is the most straightforward and easiest to implement. Such a straight line taper does achieve the benefits of minimizing thermal shock.  
           [0009]    In addition to the obvious benefits of the variable power approach, the methodology of the present invention can easily be implemented to complement other methodologies directed toward extending the life of the media. For example, the above-mentioned SPS approach could also be implemented along with the tapered power concept of the present invention.  
           [0010]    Extending the life of the media also has a beneficial effect on related components and systems. For example, storage libraries utilize multiple storage devices, media, and appropriate media handling mechanisms to provide high capacity storage solutions. By extending media life, the related life of the library is also extended—media replacement and re-writing is necessarily minimized. Over time, this also has a beneficial effect on the storage media itself.  
           [0011]    It is an object of the present invention to extend the life of the data media by minimizing the damage caused by continuous rewriting of repetitive data. It is a further object of the present invention to increase the potential rewriting cycles for the media, without compromising any data storage capabilities. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The above-mentioned objects and advantages can be further seen by reading the following detailed description in conjunction with the drawings in which:  
         [0013]    [0013]FIG. 1 is a block diagram illustrating the basic components of an example data storage system;  
         [0014]    [0014]FIG. 2 is a conceptual drawing illustrating the format of one data storage sector;  
         [0015]    [0015]FIG. 3 is a graphical illustration of the power level used by the present invention; and  
         [0016]    [0016]FIG. 4 is a block diagram of the actual data writing systems. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]    Referring now to FIG. 1, there is shown a schematic diagram of an exemplary disk storage system  10 . The core component of storage system  10  is a rewritable optical media  12 . Optical media  12  may include any well known rewritable optical disk, however, it may also be any type of rewritable media that may be damaged by continuous rewriting. Disk storage system  10 , necessarily has a read/write system  14  incorporated therein for writing data to the optical media  12 , and reading data therefrom. Storage system  10  further includes drive electronics  16  for operating the functions of the drive. Associated is a drive controller  20  which includes a memory or RAM  24 . Interacting with the output from read/write head  14  is a read/write channel  26  which necessarily includes an internal decoder (now shown). Read/write channel  26  is capable of producing either decoded or non-decoded data and providing this data to controller  20 . Controller  20  also communicates with a host system (not shown) to respond to its data storage and retrieval needs.  
         [0018]    It will be understood that the system depicted in FIG. 1 is simply an example of hardware often found in data storage systems. Many variations could be incorporated into this component hardware and are all contemplated as being part of the present invention. Also, many additional functions may be undertaken by controller  20  or may be controlled by other components.  
         [0019]    Read/write head  14  includes various components that are necessary for its operation. Specifically, a radial actuator  30  is included for accommodating radial motion for read/write system  14 . Also, a vertical actuator  32  is included to move appropriate components closer to the surface of optical media  12  when necessary. For example, appropriate vertical motion (z axis) would be required for appropriate focusing. Vertical actuator  32  may also be referred to as a focus motor as it typically moves a focusing lens  34  into its optimum position. Lastly, read/write system  14  includes a laser and detector  36  for appropriately producing optical signals for use in either writing or reading to the optical media. Additionally, this laser and detector  36  cooperates with the light signals produced to detect data which has already been written to optical media  12 .  
         [0020]    Referring now to FIG. 2, there is shown a graphical representation of a single data sector  50 . The data sector itself includes a preamble region  52 , a data storage area  54 , and a postamble  56 . As mentioned, this is one illustration of a typical data storage sector. It is understood that many variations could occur. As is well known by those skilled in the art, this sector is often incorporated into a larger data storage scheme which may include error correction provisions, etc. One such example is the standard data storage format for a DVD, or a CD ROM.  
         [0021]    In order to extend the life of rewritable media, the present invention minimizes the thermal shock typically encountered by the data storage media. In typical data storage operations, using the format shown in FIG. 2, the preamble for a particular sector will often remain constant, while the actual information in data region  54  is more likely to change. Consequently, when rewriting this sector, the same information or data patterns are rewritten in preamble  52 . Because the same areas are simply rewritten again and again, this causes the undesired stress on the media.  
         [0022]    In order to minimize this stress, the systems within the data storage device of the present invention will incorporate a tapered power-on operation. One example of the power curve used by the present invention is shown in FIG. 3. This power curve illustrates the various power levels throughout the initial operation of the storage device. Obviously, laser power is kept at 0 until a writing operation is initiated. At a start time (t S ) the writing operation will start, causing the write power to begin tapering or ramping up to a full power level. At a predetermined time (t fp ) the laser is established or has reached its full power level. Consequently, the tapering will take place over a predetermined time period (t ramp ). From that time on, the laser is operated at its full power level.  
         [0023]    The storage device of the present invention is coordinated so that this ramp or transition time period (t ramp ) operates during the writing of the guard field  58 . Consequently, because the media is not being immediately “hit” with full power, the stress on the storage media is re-distributed. More specifically, a dedicated area or guard field  58  is utilized to taper write power. Guard field  58  is shown in FIG. 2 as a portion of the data sector immediately preceding preamble  52 . Similarly, an ending guard field  60  is included immediately following postamble  56 .  
         [0024]    Referring now to FIG. 4, there is a shown a block diagram illustrating the functional components of the data storage system. In this embodiment, data is received on an input  82 . In this case the data writing system  80  of the present invention includes a preamble/postamble identification device  84  along with a power controller  86 , both of which are functionally attached to a laser  90 . As is well known by those skilled in the art, laser  90  is appropriately positioned adjacent to a storage media  12  in order to appropriately write and read data. In this data writing system  80 , the preamble/postamble identification system  84  identifies which region of the data sector is currently being written. Appropriate signals are then provided to power controller  86  along with the actual data, in order to appropriately actuate and control laser  90 . Within power controller  86 , the system will appropriately control the power level so that the above referenced tapering or ramping will occur during the preamble and postamble writing operations.  
         [0025]    Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. In that the foregoing description of the present invention discloses only exemplary embodiments thereof, it is to be understood that other variations are contemplated as being within the scope of the present invention. Accordingly, the present invention is not limited in the particular embodiments which have been described in detail therein. Rather, reference should be made to the appended claims as indicative of the scope and content of the present invention.