Abstract:
A data tape drive senses the ambient temperature and the relative humidity of the environment in which the tape drive is operating. The tension exerted on the data tape by the tape drive is then adjusted as a function of the temperature and/or humidity. When the tape is more rigid at low temperature/humidity, the tension is increased. At nominal temperature/humidity, a nominal tape tension is used. However, under elevated conditions a lower tension is utilized to avoid damaging the tape. The sensors also may be used to completely prohibit drive and tape operation when the tape drive is in an extreme environment that is beyond an acceptable design range. Tape acceleration profiles due to atmospheric conditions are changed based on the propensity of the tape to stick to the head.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates in general to an improved means for enhancing the performance of a data recording device, and in particular to an improved means for adapting a data recording device to changes in environmental conditions. Still more particularly, the present invention relates to an improved apparatus and method for adapting a data tape drive to changes in ambient temperature and humidity.  
           [0003]    2. Description of the Related Art  
           [0004]    Data recording devices, such as data tape drives, record information to or read information from a data storage device, such as the data tape of a tape cartridge. As data tapes have become increasingly thinner, they have become more susceptible to damage during operation at elevated temperatures and relative humidity levels. Although the tapes and tape drives are typically designed to operate in such conditions, a majority of users never operate their equipment in extreme environments. However, testing has repeatedly shown that the mechanical properties of thin tapes change dramatically (in terms of tape handling) at elevated temperature and humidity.  
           [0005]    For example, the tension used to reliably manipulate tape at relatively cool temperatures can damage the same tape if the ambient temperature and/or relative humidity of the environment surrounding the tape drive increases. Because of the extremely thin dimensions of modern data tapes, mechanical-only solutions that alter the mechanical properties of the materials can no longer compensate for the entire range of operational environments. Thus, an improved apparatus and method for adapting a data recording device to changes in environmental conditions in order to reduce the risk of damage to the storage media is needed.  
         SUMMARY OF THE INVENTION  
         [0006]    One embodiment of a media or data tape drive uses the spare inputs on the analog to digital converter to sense the ambient temperature and the relative humidity of the environment in which the tape drive is operating. The tension exerted on the data tape by the tape drive is then adjusted as a function of the temperature and/or humidity. When the tape is more rigid at low temperature/humidity, the tension may be increased to provide a good read/write interface to the head. At nominal temperature/humidity, a nominal tape tension is used. However, at elevated temperature/humidity, a lower tension is utilized to avoid damaging the tape. The sensors also may be used to completely prohibit drive and tape operation when the tape drive is in an extreme environmental condition that is beyond an acceptable design range. The tape acceleration/deceleration profiles are altered due to changes in atmospheric conditions based on the propensity of the tape to stick to the head. Thus, in hostile environments, the performance of the tape drive is lowered to reduce the risk of tape damage.  
           [0007]    The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.  
         [0009]    [0009]FIG. 1 is an exploded isometric view of a magnetic tape drive constructed in accordance with the invention.  
         [0010]    [0010]FIG. 2 is an exploded isometric view of the tape drive of FIG. 1 and a chassis having shock mounts for isolating the tape drive.  
         [0011]    [0011]FIG. 3 is an isometric view of a head guide assembly of the tape drive of FIG. 1 having a head actuator assembly mounted therein.  
         [0012]    [0012]FIG. 4 is a logical schematic diagram showing the tape drive of FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    Referring to FIG. 1, a magnetic tape drive  11  in which the present invention may be incorporated is shown. Although a magnetic tape drive is illustrated, one skilled in the art will recognize that air bearing sliders on the magnetic heads used in disk drives with removable media, an optical media drive, such as a CD-ROM device, a Near Field Recording device that combines magnetic and optical recording, or other devices having transducer heads for processing information with media, such as reading information from and/or writing information to media, also may employ the present invention.  
         [0014]    Drive  11  includes a base unit  13  to which are mounted a power supply  15 , various electronic circuit cards  17 ,  19  (such as motion control and data control), a deck assembly  21 , a pneumatic assembly  23  that provides pressurized air, and tape tension transducer  201  that measures the tension in the data tape and feeds back that information to cards  17 ,  19 . Mounted to the deck assembly  21  are a loader mechanism  27 , drive motors (not shown), a pantocam assembly  29 , and a head guide assembly  31 . A head actuator assembly  33  is mounted to the head guide assembly  31 . Drive  11  can operate in stand alone and automated tape loader environments interconnected with a host computer and also can be incorporated into a multi-drive automated data storage and retrieval system or library.  
         [0015]    As shown in FIG. 2, shock mounts  35  are supported by the base unit  13  for isolating the deck assembly  21  from shock. Shock mounts  35  are stud-mounted-type shock mounts for assembly ease. Four shock mounts  35  (only two are shown) are positioned approximately equidistant from the center of gravity of deck assembly  21 .  
         [0016]    Referring now to FIG. 3, actuator assembly  33  of head guide assembly  31  is secured to a base member  41 . Base member  41  is coupled to a head guide support  43 . Various brackets and screws secure the elements of the actuator assembly  33  together. Various cables, including ribbon cables  45  for the transducer or input/output recording head  47 , interconnect the head and the coil with the circuit cards of drive  11 . To reduce mechanical interference by ribbon cables  45  with proper motion of a beam member, ribbon cables  45  are preferably guided upwards along the sides of the beam member and outwardly from the base member  41  by winged surfaces inside the beam member. Head  47  may comprise a device that is read only, write-once, or one that can perform both read and write functions.  
         [0017]    An arcuate tape guide  40  is located immediately adjacent to each side of head  47  for precisely conveying data tape toward and away from head  47 . In the embodiment shown, an alumina ceramic, flat plate-like tape guide  40  is supported from above by D-bearings  42  and from below by lower support members  44  that are spaced apart from each other to provide a slot for tape guide  40 . Tape guide  40  has a row of teeth  46  that define the arcuate guide path for the data tape, locating pin slots or holes (not shown), mounting bolt holes, and an air vent for hydrostatic air delivered to the head guide assembly  31 . A more detailed disclosure of drive  11  is shown and described in U.S. Pat. Nos. 5,508,865, and 5,377,052, which are incorporated herein by reference.  
         [0018]    During operation of drive  11 , a removable tape cartridge  37  (FIG. 1) having a supply reel wound with magnetic tape is inserted through a slot  39  in a front face of base unit  13 , and into loader assembly  27 . A warning indicator  38  is located adjacent to slot  39  and will be described in further detail below. Loader assembly  27  draws the tape cartridge  37  in and lowers it onto the deck assembly  21 . The pantocam assembly  29  engages the tape leader block attached to a free end of the magnetic tape and pulls the magnetic tape around the head guide assembly  31  such that the magnetic tape winds through the tape path defined by tape guide  40 , and across the magnetic tape head  47  mounted to the head actuator assembly  33 . The leader block is then engaged by a take-up reel  200  on the deck assembly  21  and drive  11  is then ready to record information to or read information from the magnetic tape. While drive  11  includes a take-up reel and accepts tape cartridges containing only the supply reel, the present invention is not limited to use with such a drive or cartridge combination, but also could be incorporated in other drive or cartridge combinations, such as those in which the tape cartridge contains both supply and take-up reels. A two-reel tape cartridge is also called a dual-reel cassette.  
         [0019]    Referring again to FIG. 3, a solenoid  101  controls the flow of pressurized air through a hose  102  to head  47 . Head  47  has an orifice  103  that is typically located between or to the sides of columns of I/O elements  104 ,  105 . The data tape normally flies over I/O elements  104 ,  105  via, for example, a hydrodynamic air film or rollers. A hydrodynamic air film is preferred for a good head, because hydrodynamic air films are very thin. A thin hydrodynamic air film allows the data tape to fly very close to I/O elements  104 ,  105 , which allows the transfer of data between the tape and the I/O elements of head  47 . The thickness of a hydrodynamic air film is a few microinches.  
         [0020]    The tape also flies over D-bearings  42  via a very thick hydrostatic air film. Hydrostatic air films are typically orders of magnitude thicker than hydrodynamic air films (in the range of the thickness of the tape), which is a few thousandths of an inch rather than mere microinches. Since the tape should not physically contact D-bearings  42 , and since D-bearings  42  only facilitate the guiding of the tape over head  47 , a thick layer of hydrostatic air between the tape and D-bearings  42  is desirable.  
         [0021]    Referring now to the schematic diagram of FIG. 4, the preferred version of tape drive  11  includes a pair of reels  111 ,  117 , each driven by a bi-directional motor  116 ,  121 , respectively. Mounted to the drive shaft of each of the motors  116  and  121 , is a fine-line tachometer  112 ,  118 , with an outer circular array of fine tachometer lines  114 ,  119 , and an index line  115 ,  120  displayed radially inward on a respective coding wheel from the fine-line array. A tape  122  is wound to the reels  111 ,  117  and the motors  116 ,  121  are controlled to move the tape  122  for recording and playback in either of the two directions indicated by the arrow  123 .  
         [0022]    Each of the tachometers  112 ,  118 , functions as a tape motion sensor; each emits a single pulse in response to an index mark to signify completion of a relatively large preselected angle, preferably 360°, that is, once per revolution of the reels  111 ,  117 . In addition, each of the tachometers  112 ,  118  generates a two-phase fine tachometer signal comprising two phase-displaced pulse streams. The fine-line tachometer arrays on the tachometers  112 ,  118  are identical, each emitting N pulses during each revolution of respective reels  111 ,  117 .  
         [0023]    Assume that the tape  122  is being advanced from the reel  111  to the reel  117  for recording data through a magnetic write/read record head  124  positioned between the reels  111  and  117  in engagement with a recording surface of the tape  122 . Relatedly, the reel  111  is the “supply” reel while the reel  117  is the “take-up” reel. Also assume that a complete longitudinal track of data has been written on the tape  122  while the tape is being fed from the reel  111  to the reel  117 . In order to continue recording without rewinding the tape, the direction of the tape motion is reversed while recording continues, that is data is written while the tape is advanced from the reel  117  (which now becomes the supply reel) to the reel  111  (now the take-up reel). Another complete longitudinal track of data, parallel to the first data track is written on the tape, and the tape motion is once again reversed, and so on.  
         [0024]    During advancement of the tape  122 , various parameters, such as a tape motion, position, tension, are monitored in order to derive motor currents having the polarity and magnitude necessary to operate the motors  116 ,  121  while recording data on the tape  122 . These currents are derived by the algorithm of U.S. Pat. No. 4,125,881 (incorporated herein as the &#39;881 patent) in response to fine tachometer line and tachometer index signals which are fed to a tape motion control unit  126 . The tape motion control unit  126  processes the fine tachometer and index pulses, generating currents for the motors  116  and  121  on respective current lines  127  and  128 . The signals on the current lines  127  and  128  are amplified at  129  and  130 , respectively, and amplified motor currents are conducted to the motors  116 ,  121  on the outputs  132 ,  133 .  
         [0025]    Under normal operating conditions, the tape motion control unit  126  operates to maintain the motors  116  and  121  at constant nominal velocities for recording, reading, and searching. In addition, unit  126  controls the motors  116  and  121  to perform the back hitch operation described above in response to a signal indicating the last data record on signal line  134 , which is provided by a recording channel control unit  135 . Recording channel control unit  135  provides a record signal for driving the magnetic write/read head  124  and also generates signals for synchronizing recording operations with tape motion, one of the signals indicating the writing of a last data record. A clock unit  136  provides clock pulses to the tape motion control unit  126  and the recording channel control unit  135  for synchronization of their operations.  
         [0026]    During a back hitch operation, when the recording is interrupted, the motion of the tape  122  must be stopped to await the next record operation. When signal line  134  is activated, indicating that the last data record has been written, the control unit  126  operates the motors  116  and  121  to decelerate and stop the motion of the tape  122  and to move the tape in the reverse direction to a pont where the tape is stopped to await the next record operation.  
         [0027]    As described in the &#39;881 patent, clock pulses are counted from the beginning of the IBG until the first fine-line tachometer pulse occurs in the IBG, which produces a timing reference between the end of the last data record and the fine-line tachometer pulse occurring in the IBG. This timing reference is employed to determine the end of the IBG by subtracting from the nominal IBG transit time. The result is the time from the fine-line tachometer pulse in the IBG to the end of the IBG, and it is used to generate the end of IBG signal  148 , which resynchronizes the recording channel unit,  135 , to the data previously recorded on tape. The tachometer pulse occurring in the IBG is referred to as the “position reference pulse” and it initiates counting of fine-line pulses during the repositioning of tape until tape has been stopped to await the next data record.  
         [0028]    When the next data record is ready for recording, tape motion is started by provision of the start signal on  137  by the control unit  135 . In response to the start signal, the control unit  126  provides motor drive currents to accelerate the tape  122  from its stopped position back through the IBG. When the end of the IBG is traversed, the control unit  126  provides a resynchronization signal to the control unit  135 , which causes recording to start. The control unit  126  determines the location of the IBG during tape acceleration by counting down a fine-line tachometer pulse count which was accumulated from the location of the position reference pulse to the point where the tape was stopped and then timing by clock pulse count from the occurrence of the position reference pulse to the end of the IBG.  
         [0029]    The relationship between fine-line tachometer pulse generation and tape position must be unchanging during the back hitch operation. Otherwise, the fine-line pulse countdown and clock pulse timeout to the end of the IBG will be incorrect. The relationship between tape position and tachometer fine-line pulse count is changed when entrained air bleeds out from between the outermost layers of the tape on the take-up reel. In this regard, the take-up reel is that reel to which tape is advanced during a write operation, the designation remaining unchanged even during the back hitch operation. The invention is based upon the realization that the fine-line tachometer pulses can be obtained from the supply reel in a bi-directional reel-to-reel operation by multiplexing between the fine-line tachometer outputs in response to a signal indicating the direction in which the tape has advanced for recording. This is hereinafter referred to as the “write direction.” This signal is produced by the tape motion control unit  126  and provided to the multiplexer  140 . The multiplexer  140  receives the fine-line tachometer outputs from the tachometers  112 ,  118  on signal lines  141 ,  142 , and selects a fine-line tachometer pulse stream in response to a write direction signal produced by the tape motion control unit  126  on the signal line  144 . The multiplexer  140  provides the control unit  126  the fine-line tachometer signal produced by the tachometer on the supply reel as indicated by the write direction signal.  
         [0030]    Each of the tachometers  112  and  118  is constructed and operated to provide both a fine-line and an index pulse output during revolution of the reels  111  and  117 . For the aspect of the invention illustrated in FIG. 4, the provision of an index pulse on a tachometer is a convenience which eliminates the requirement to derive an index pulse for gating fine-line tachometer pulses by means of a second tachometer assembly for each of the reels  111  and  117 . Accordingly, the tape motion control apparatus in the tape drive of FIG. 4 accommodates this convenience by a second multiplexer  145  which receives the index pulse outputs of the tachometers  112  and  118  on signal lines  146  and  147 . The control mechanization of the multiplexer  145  is complementary to that of the multiplexer  140  in that the index pulse output is selected from the take-up reel as indicated by the write direction signal. A fine-line tachometer pulse stream and an index pulse sequence are provided on signal lines  143  and  148  to the tape motion control unit  126 , which employs them to operate the motors  116  and  121  as described in the incorporated &#39;881 patent.  
         [0031]    Again referring to FIG. 4, drive  11  is also provided with means for sensing and measuring the ambient environmental conditions, such as temperature and relative humidity, in order to handle tape  122  in a different manner. In the embodiment shown, temperature sensing means  151  and humidity sensing means  153  are utilized to detect the surrounding temperature and relative humidity, respectively, of drive  11  and provide such information to tape motion control  126 . For example, means  151 ,  153  may comprise solid state temperature and humidity sensors, respectively. In one type of tape drive, spare inputs on the analog to digital converter are used to input the information from means  151 ,  153 .  
         [0032]    As the ambient temperature and/or humidity rise, the media tape becomes weaker and less rigid. The strength of media tape is especially sensitive to elevated temperatures. As a result of sensing the increase in the environmental conditions, the tape is not handled in a manner that is suitable for a normal range of operating temperature and relative humidity. This is particularly true during the starting and stopping sequences of the tape, which subject the tape to its maximum operational stress. Thus, the acceleration and/or deceleration of the tape is limited by tape motion control  126  during start/stop operations to avoid damage to the weakened tape. Ideally, tension on the tape is a function of temperature and humidity. When the tape is more rigid at lower temperature and/or humidity, the tension is increased to provide a good read/write interface to the head. At nominal temperature and/or humidity, a nominal tape tension is provided. At elevated temperature and/or humidity, a lower tape tension is provided to avoid damaging the tape.  
         [0033]    Altering the handling of the tape in response to elevated temperature and/or humidity may change the overall performance of drive  11 . Moreover, if the temperature and/or humidity rises to such extreme levels that any operations risk damage to the tape (i.e., the temperature and/or humidity exceeds an acceptable level, such as during an air conditioning failure), drive  11  may temporarily cease operations and/or refuse to load the tape until the risk of damage to the tape subsides.  
         [0034]    The present invention has several advantages. The tape drive is provided with means for adjusting the tension exerted on the data tape as a function of the temperature and/or humidity in which the tape drive is operating. Alternatively, the tape drive may be temporarily disabled when the tape drive is in extreme environmental conditions. Thus, in more hostile environments, the performance of the tape drive is lowered to reduce the risk of damage to the media.  
         [0035]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, the present invention also applies to optical tape.