Abstract:
The present invention is directed to a system and method which utilize a feedback loop arrangement to control the accurate positioning of components. The system and method may utilize the feedback loop to control a component engaging member operable to retrieve a component. The feedback loop may control the component engaging member by activating a drive subsystem operable to translate the component engaging member. Additionally, the feedback control loop may implemented by utilizing a signal source operable to emit a signal and a signal receiver operable to receive the signal emitted by the signal source. The signal source and signal receiver are fixedly attached to the device. Also, the feedback loop may involve a processor operable to control retrieval of a desired component utilizing at least in part the signal emitted by the signal source and received by the signal receiver.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates in general to the accurate positioning of components and in particular to using feedback to position a component in a media autochanger.  
         BACKGROUND  
         [0002]    Mass storage devices frequently require a number of sometimes diverse media to store a sufficient amount of data for certain applications. For example, corporate entities may create libraries of optical media and magnetic media to retain imaging files of purchase orders, invoices, and other forms for accounting purposes. To maintain such a library or other large data collections, it is frequently appropriate to utilize a media autochanger. Media autochangers provide a unitary structure to store a plurality of such diverse media, such as optical media, magnetic disks, tape cartridges, and/or the like. Media autochangers store the media in predefined locations within the unitary structure.  
           [0003]    In operation, a media autochanger typically utilizes a drive unit and an associated drive train to physically move a media engaging component to the predetermined location associated with a media storage position when retrieval of the media is desired. After being translated to the appropriate position, the media engaging component may extend from a drive position to an engage position to retrieve the media. The media engaging component then retracts. The media engaging component with the retrieved media is transported to a media drive. Again, the media engaging component extends to place the media into the media drive. Of course, the reverse of this process occurs when it is desired to replace the media to its respective predetermined position.  
           [0004]    It shall be appreciated that the steps associated with retrieving and replacing media require significant mechanical precision. Specifically, imprecise positioning may damage media or may cause the media autochanger to cease functioning. To properly position the media engaging component, media autochangers utilize a drive train feedback arrangement. In these configurations, various encoding mechanisms allow the media autochanger to determine how the drive train has been translated. By knowing the offset or translation of the drive train, the media autochanger may then estimate the position of the media engaging component. However, this approach is problematic. Specifically, physical characteristics of mechanical components frequently change with time. For example, the drive train may slip. Thus, the offset or translation of the drive train does not necessarily provide a completely accurate determination of the position of the media engaging component.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is directed to a system and method which utilize a feedback loop arrangement to control the accurate positioning of components. The system and method may utilize the feedback loop to control a component engaging member operable to retrieve a component. The feedback loop may control the component engaging member by activating a drive subsystem operable to translate the component engaging member. Additionally, the feedback control loop may implemented by utilizing a signal source operable to emit a signal and a signal receiver operable to receive the signal emitted by the signal source. The signal source and signal receiver are fixedly attached to the device. Also, the feedback loop may involve a processor operable to control retrieval of a desired component utilizing at least in part the signal emitted by the signal source and received by the signal receiver.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 depicts an exemplary media autochanger implemented according to the prior art.  
         [0007]    [0007]FIG. 2 depicts an exemplary media autochanger implemented according to the present invention.  
         [0008]    [0008]FIG. 3 depicts an exemplary ultrasonic transmitter and receiver pair implemented according to the present invention.  
         [0009]    [0009]FIG. 4 depicts an exemplary optical transmitter and receiver pair implemented according to the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0010]    [0010]FIG. 1 depicts a prior art device where components such as media disks, tapes, and/or the like must be accurately positioned. In our example, the device is a media autochanger implemented according to the prior art. Media autochanger  100  includes a chassis holding a number of elements. The chassis holds drive unit  101 , drive train  102 , media engaging component  103 , and media holders  104 .  
         [0011]    Media holders  104  are fixedly disposed in predetermined positions on one side of the chassis along the Z-axis. When a particular media is needed, media autochanger  100  causes media engaging component  103  to be translated to the respective position. Media engaging component  103  extends along the X-axis to retrieve the needed media from its media holder.  
         [0012]    Drive unit  101  provides the necessary mechanical translation to position media engaging component  103  in the desired positions associated with media holders  104 . Drive unit  101  physically translates media engaging component  103  by utilizing its motor to translate drive train  102  either in a forward direction or a backward direction. Media engaging component  103  is mechanically coupled to drive train  102 . Accordingly, translation of drive train  102  causes media engaging component  103  to be translated. Also, media autochanger  100  utilizes the offset position of drive train  102  to estimate the position of media engaging component  103 . Specifically, media autochanger  100  associates encoders with drive train  102 . The encoders may be provided in mechanical form or electronic form. The encoders allow media autochanger  100  to determine the offset position of drive train  102 . If drive train  102  is detected to be translated a distance X from a known position, the position of media engaging component  103  may be estimated to be a distance X from another known position. However, this does not necessarily provide a completely accurate estimation of the position of media engaging component  103 , since the characteristics of drive train  102  may change with time.  
         [0013]    [0013]FIG. 2 depicts an exemplary media autochanger implemented according to the present invention. Media autochanger  200  includes a chassis holding a number of elements. The chassis holds drive unit  101 , drive train  102 , media engaging component  103 , and media holders  104 . Media autochanger  200  further includes processor  203  and temperature sensor  204 . Also, transmitter and receiver pair  300  is fixedly attached to media engaging component  103 . Processor  203  communicates with transmitter and receiver pair  300 .  
         [0014]    As seen with respect to media autochanger  100  of FIG. 1, media holders  104  of media autochanger  200  are fixedly disposed in predetermined positions on one side of the chassis along the Z-axis. When a particular media is needed, media autochanger  200  causes media engaging component  103  to be translated to the respective position. Media engaging component  103  extends along the X-axis to retrieve the needed media from its media holder.  
         [0015]    Drive unit  101  provides the necessary mechanical translation to position media engaging component  103  in the desired positions associated with media holders  104 . Drive unit  101  physically translates media engaging component  103  by utilizing its motor to translate drive train  102  either in a forward direction or a backward direction. Media engaging component  103  is mechanically coupled to drive train  102 . Accordingly, translation of drive train  102  causes media engaging component  103  to be translated.  
         [0016]    Media autochanger  200  provides a substantially more accurate mechanism to determine the position of media engaging component  103 . Media autochanger  200  is implemented to utilize transmitter and receiver pair  300  to provide a feedback arrangement. In accordance with one embodiment of the present invention, the feedback arrangement may be implemented utilizing an ultrasonic signal. However, the present invention is not limited to any particular signal or waveform type. Any signal or waveform type may be utilized, so long as the signal or waveform type facilitates measurement of distance.  
         [0017]    According to an ultrasonic embodiment, processor  203  causes transmitter and receiver pair  300  to emit an ultrasonic signal. The ultrasonic signal propagates from transmitter and receiver pair  300  toward chassis ceiling  202 . Chassis ceiling  202  causes the ultrasonic signal to be reflected back toward transmitter and receiver pair  300 . Processor  203  determines when the reflected ultrasonic signal is detected by the receiver portion of transmitter and receiver pair  300 . Processor  203  is then able to calculate the propagation time for the ultrasonic signal to propagate from transmitter and receiver pair  300  to chassis ceiling  202  and back again. Processor  203  also utilizes temperature sensor  204  to detect the ambient air temperature. Processor  203  then is able to calculate the distance from transmitter and receiver pair  300  to chassis ceiling  202 . Specifically, the distance in meters approximately equals:  
         (The Measured Propagation Time in Seconds)/2*(331.5+0.6* T   c  Meters/Second)  
         [0018]    where T c  represents the ambient air temperature. The factor of 2 in the denominator reflects the fact that the propagation of the ultrasonic signal occurs to chassis ceiling  202  and back. Thus, the ultrasonic signal travels twice the offset distance before being detected by the receiver of transmitter and receiver pair  300 . Also, it shall be appreciated that T c  may be neglected if a certain amount of positioning tolerance exists or if media autochanger  200  is operated in a controlled environment.  
         [0019]    After calculating the position of transmitter and receiver pair  300 , processor  203  calculates the exact position of media engaging component  103 . The exact position of media engaging component  103  is readily calculable, since media engaging component  103  and transmitter and receiver pair  300  are fixedly attached. Moreover, this type of mechanical arrangement is unlikely to vary with time or excessive use. Thus, the position calculation utilizing the present invention will remain accurate over the useable life of media autochanger  200 .  
         [0020]    Since the exact position of the media engaging component  103  has been calculated, processor  203  compares the position to the respective predetermined position associated with the desired media. If the positions are not equal, processor  203  may control drive unit  101  to effect drive train  102  to translate media engaging component  103  as appropriate. Thus, accurate positioning has been effected utilizing a control signal feedback loop.  
         [0021]    It shall be appreciated that the present invention may be practiced with any type of media autochangers which may utilize any number of arrangements, configurations, components, and devices. Specifically, the present invention may dispose transmitter and receiver pair  300  in any number of locations. For example, transmitter and receiver pair  300  may be located on chassis ceiling  202  directly above media engaging component  103 . Additionally, an optical feedback arrangement may be employed by measuring the angle of displacement of an optical signal reflected by a mirror disposed on chassis ceiling  105 . The feedback loop may be implemented utilizing components other than a processor. For example, integrated circuitry may provide the desired feedback loop functionality. Moreover, it shall be appreciated that media autochanger  200  is merely exemplary. The present invention may be employed with any media autochanger. The present invention does not require any particular drive unit, drive train, type of media engaging components, or number of media engaging units, and/or the like. Also, the present invention may operate on any number of media types including, but not limited, to CD-ROMs, DVDs, magnetic disk media, tape media, and/or the like.  
         [0022]    [0022]FIG. 3 depicts an exemplary transmitter and receiver pair implemented according to the present invention. Transmitter and receiver pair  300  comprises transmitter  301  which is operable to emit an ultrasonic signal. For example, transmitter  301  may emit a baseband signal modulated by an ultrasonic carrier signal of approximately 40 KHz. Of course, other carrier frequencies may be utilized. Also, transmitter  301  may emit an unmodulated carrier signal if desired. Transmitter and receiver pair  300  comprises a receiver  302  which is operable to detect an ultrasonic signal. Transmitter and receiver pair  300  comprises connection  303  which facilitates communication with and control by processor  203 .  
         [0023]    [0023]FIG. 4 depicts another arrangement  400  of components according to the present invention. Feedback arrangement  400  includes light source  401  (e.g., a light emitting diode), mirror  402  which may be mounted on the ceiling, and optical detector  403 . Light source  401  emits a light signal at angle Ø. The light signal is reflected by mirror  402  toward optical detector  403  (such as a charge coupled device (CCD)). The light signal is received at point  404  on optical detector  403 . Point  404  is a distance X from light source  405 . The geometry of feedback arrangement allows the offset position to be readily determined. Specifically, the distance to the mirror equals: (distance X)*½*tan (angle ø).  
         [0024]    It shall be appreciated that an actual implementation of a media autochanger would comprise substantially more components, elements, and devices. The preceding high level description has been provided to clarify the discussion of the present invention. Discussion of other implementation details of media autochangers is not necessary for those of ordinary skill in the art to make and use the present invention. Therefore, those details have not be discussed at length. However, further details regarding implementation of other aspects of media autochangers may be founded in U.S. Pat. No. 5,682,096, entitled “METHOD AND APPARATUS FOR MONITORING OPERATING POSITIONS OF A MEDIA AUTOCHANGER.” 
         [0025]    Additionally, it shall be appreciated that the present invention provides substantial advantages over known autochangers. The precision of positioning does not deteriorate with time or with excessive use. Specifically, the present invention is not subject to variations in drive train characteristics such as slippage or material deformation. The present invention is much more reliable, since fixedly attaching the ultrasonic transmitter and receiver pair to the media engaging component is much more stable than drive train methods.