System and method for adjusting the speed of tape

A cartridge tape drive for use with a tape cartridge includes a temperature sensor for determining the temperature of the tape cartridge and a control device responsive to the temperature sensor for automatically adjusting the speed of the tape when a temperature threshold value is realized. The cartridge tape drive includes a housing including an opening dimensioned to receive the cartridge and a device for supporting the cartridge within the housing, a magnetic head within the housing, a driver for moving the cartridge in operative engagement with the magnetic head, a temperature sensor for determining the temperature of the cartridge when the cartridge is in operative engagement with the magnetic head, and a control device responsive to the temperature sensor for automatically adjusting the speed of the tape when a temperature threshold value is realized.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates generally to cartridge tape drives, and more
 particularly to adjusting the speed of tape to optimize operation of
 cartridge tape drives.
 2. Description of the Prior Art
 Magnetic tape storage devices are commonly used for the storage of large
 amounts of digital data because they provide an economical and reliable
 means for temporary and permanent storage. Because magnetic tape systems
 inherently rely on sequential recording, access times are substantially
 longer than other modern storage devices, but at the same time the danger
 of catastrophic failure is virtually absent. Thus it has become common
 practice to utilize tape systems as data backup for floppy disk and hard
 disk files, typically by reading out the entire contents of a random
 access memory system at the end of the day or other operating period, and
 retaining this data in storage until the next backup date or time. Where
 the volume of data is limited, one tape system and tape reel or cartridge
 may suffice, but where the data base is much larger, many reels or
 cartridges may be needed.
 Tape drive systems have evolved over the past with technical improvements
 that have resulted in substantial increases in capacity accompanied by
 significant decreases in size. The cartridge (also called a cassette) used
 for these applications is very small, the standard cassette being 3.25"
 inches by 2.5" inches by 0.5" inches, with a nominal tape width of 0.25"
 inch. Both the data capacity and transfer rate for tape cartridges has
 increased over the years. For example, the Travan minicartridge, model
 TR-4, manufactured by Imation Corporation of St. Paul, Minn., has a data
 storage capacity of 4.0 gigabytes (GB)(uncompressed data) at a sustained
 transfer rate of 783 kilobytes-per-second (Kbps) when the tape is run at
 120 inches per second (ips). Tape cartridges are expected to store 15 or
 more GB of uncompressed data in the near future.
 Despite the technical improvements in tape drive systems including data
 cartridges, the data transfer rate is limited by the amount of heat which
 is generated by the cartridge when the tape is operated at its maximum
 speed of 120 ips. In particular, when the cartridge tape is operated at a
 relatively high speed for a period of time, such as at 120 ips for half an
 hour, a substantial amount of heat, due to friction between the components
 within the cartridge, is developed. After a period of time, such as when
 the cartridge is run at 120 ips for half an hour, the tape exceeds its
 safe operating temperature range. The heat must be dissipated to preclude
 malfunction of the cartridge tape and prevent degradation of the data
 being transferred.
 In an attempt to overcome the above problem, the cartridge tape is commonly
 run at a slower speed than the specified maximum speed of 120 ips. In many
 cases, the tape is run at a speed of 90 ips or less. At this lower speed,
 overheating problems caused by the rubbing of individual components in the
 tape cartridge, such as the rollers, are minimized.
 The obvious drawback to this approach, however, is that the data transfer
 rate of the tape is compromised. For example, to utilize a tape backup
 system efficiently, it is preferred to record the backup data at a high
 data transfer rate during what would normally be down time for the system,
 e.g. the time between the close of business one evening and the start of
 business the next morning.
 What is needed therefore is an apparatus and method for minimizing the heat
 generated by the frictional components within the cartridge while
 optimizing the data transfer rate.
 SUMMARY OF THE INVENTION
 The preceding and other shortcomings are overcome by the present invention
 which provides a cartridge tape drive for use with a tape cartridge which
 includes a temperature sensor for determining the temperature of the tape
 cartridge and a control device responsive to the temperature sensor for
 automatically adjusting the speed of the tape when a temperature threshold
 value is realized. The cartridge tape drive includes a housing including
 an opening dimensioned to receive the cartridge and a system for
 supporting the cartridge within the housing, a magnetic head within the
 housing, a cartridge moveable in operative engagement with the magnetic
 head, a temperature sensor for determining the temperature of the
 cartridge when the cartridge is in operative engagement with the magnetic
 head, and a control device responsive to the temperature sensor for
 automatically adjusting the speed of the tape when a temperature threshold
 value is realized.
 In another aspect, the present invention provides a method for adjusting
 the speed of a tape cartridge disposed in a cartridge tape drive,
 including the steps of receiving the cartridge in a housing of the
 cartridge tape drive, a method for supporting the cartridge disposed
 within the cartridge tape drive, moving the cartridge in operative
 engagement with the magnetic head, determining the temperature of the
 cartridge with a temperature sensor when the cartridge is in operative
 engagement with the magnetic head, and adjusting the speed of the tape in
 response to the temperature sensor when at least one temperature threshold
 value is realized.
 The foregoing and additional features and advantages of this invention will
 become apparent from the detailed description and accompanying drawing
 figures that follow. In the figures and written description, numerals
 indicate the various features of the invention, like numerals referring to
 like features throughout for both the drawing figures and the written
 description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
 As is illustrated in FIG. 1, the present invention provides a cartridge
 tape drive assembly 10 for use with a tape cartridge 12 which includes a
 temperature sensor for determining the temperature of the tape cartridge
 12 and a controller 14 (FIG. 3) responsive to a temperature sensor 16
 (FIG. 2) for automatically adjusting the speed of the tape 18 when one or
 more temperature threshold values are realized. The cartridge tape drive
 assembly 10 includes a housing 20 including an opening or access door 22
 dimensioned to receive the cartridge 12 and a system for supporting the
 cartridge 12 within the housing 20, a magnetic head 26 within the housing
 20, a mechanism or other means (not shown) for moving the cartridge 12 in
 operative engagement with the magnetic head 26, a temperature sensor 16
 (FIG. 2) for determining the temperature of the cartridge 12 when the
 cartridge 12 is in operative engagement with the magnetic head 26, and a
 controller 14 (FIG. 3) responsive to the temperature sensor 16 for
 automatically adjusting the speed of the tape 18 when a temperature
 threshold value is realized.
 It should be noted that this invention is directed mainly to adjusting the
 speed of the tape 18 in response to the detected temperature of the
 cartridge 12.
 There is no detailed description of the function and operation of the
 cartridge tape drive assembly 10. Similarly, although the magnetic head 26
 is mounted in the tape drive assembly in such a manner as to allow the
 head 26 to be moved between various tracks on the tape 18, there is no
 detailed description of the mounting or track adjusting mechanism.
 Moreover, the mechanism(s) which open the access door 22 and move the
 cartridge 12 laterally within the housing 20 into operative engagement
 with the magnetic head 26 is not described in detail. This is because
 these elements may vary depending on the desired function of any given
 drive embodying the present invention. One skilled in the art will thus
 recognize that the tape drive assembly 10 and tape cartridge 12
 illustrated and described herein is not limited to the particular
 embodiments presented herein.
 Moreover, the present invention is not limited to minimizing the heat
 buildup in a particular cartridge 12. Rather, the present invention may be
 adapted to minimize heat buildup in any cartridge 12, including those in
 development. For illustrative purposes, however, the present invention is
 illustrated with the Travan minicartridge, model TR-4, manufactured by
 Imation Corporation of St. Paul, Minn. As seen in FIG. 1, the cartridge 12
 has a metal base plate 28, a metal top cover 30, two end walls 3234, a
 rear side wall 36, and a front side wall 38. The end walls 3234 are inset
 slightly from the end edge of the base plate 28 and the top cover 30. The
 front and rear ends 4042 of the base plate 28 are each provided with an
 indexing notch 4446, respectively, which extends from the edge of the base
 plate 28 inward to the end wall 3234. In operational use, the cartridge 12
 is supported within the housing 20 of the cartridge tape drive assembly
 10.
 A pair of spools are rotatably mounted within the cartridge 12. A magnetic
 tape 18 is wrapped around the spools 4850 with a portion extending between
 the spools 4850. The tape path between the spools 4850 is defined by idler
 rollers 522554 such that a portion of the tape 18 between the spools 4850
 extends lengthwise within the cartridge 12 slightly behind the front side
 wall 38. Posts 565860 provide guidance for the tape 18. A capstan 62,
 which is accessible through a cut away portion of the cartridge 12, drives
 a drive belt (not shown) which rotates the spools 4850 to move the tape 18
 from one spool 48 to the other 50.
 During operation of the cartridge 12, friction is generated at numerous
 areas on the cartridge 12 including at the spools 4850, idler rollers 5254
 and posts 565860. Consequently, the frictional interaction between the
 drive belt (not shown), tape 18 and the spools 4850, rollers 5254 and
 posts 565860, which are mounted on the base plate 28, causes the base
 plate 28 to heat up. For example, when the drive operates the tape 18 at
 120 ips for some time, typically half an hour, of continuous running, the
 cartridge 12 heats up to a critical temperature where data can become lost
 or compromised and heat generated by the cartridge 12 can adversely affect
 adjacent components inside the cartridge tape drive assembly 10.
 Generally, the critical temperature is approximately 57.degree. Celsius
 (C). One skilled in the art will recognize that the critical temperature
 will depend on variables such as the number of frictional points on a
 particular cartridge 12, the size of the cartridge 12, the width of the
 tape 18, tape speed, ambient temperature, and so forth.
 Referring to FIG. 2, in accordance with an advantage of the present Eh
 invention, a temperature sensor 16 depending downwardly from a circuit
 board 17 (which not only supports the electronic controller components of
 FIG. 3, but also forms the rear portion of a top cover of the cartridge
 tape drive assembly 10 of FIG. 1) senses the temperature of the metal
 components (base plate 28 and top cover 30) of the cartridge 12, where
 most of the heat is transferred, and automatically adjusts the speed of
 the tape 18 when one or more critical temperature values are realized. In
 particular, when the cartridge 12 is inserted into its operational
 position through door 21, the temperature sensor 16 is mounted just in
 front of the front surface of the cartridge 12. The temperature sensor 16
 is thus mounted to circuit board 17 such that it is in close proximity to
 the front edge of the base plate 28 of the cartridge 12 when it has been
 moved into position for engagement with the magnetic head 26.
 Referring to FIG. 3, speed control is achieved by closed loop control which
 requires temperature feedback information. The temperature information is
 conveniently provided by the temperature sensor 16 monitoring the
 temperature of the base plate 28 of the cartridge 12. The temperature
 sensor 16 is preferably a thermocouple type temperature sensor, such as
 Model # LM56BIM manufactured by National Semiconductor of Arlington, Tex.
 One skilled in the art will recognize that the temperature sensor 16 is
 not limited to the above model, but may be any conventional digital or
 analog temperature sensor 16 which can adequately provide feedback
 information to a controller 14 for adjusting the speed of the tape drive
 assembly 10.
 Referring to FIG. 3, in the cartridge tape drive assembly 10, temperature
 feedback is provided to the controller 14 which compares the temperature
 detected by the temperature sensor 16 with one or more predetermined
 temperature limit values. The controller 14 generates a speed adjustment
 signal when the measured temperature falls outside of the established
 acceptable temperature range. The speed adjustment signal is applied to
 the capstan controller 68, which controls the capstan drive motor 70 which
 in turn drives the capstan 62. The capstan 62, which is accessible through
 a cut away portion of the cartridge 12, rotates the spools 4850 to move
 the tape 18 from one spool 48 to the other 50. The capstan drive motor 70
 drives the capstan 62 at a motor shaft speed .omega.. A speed adjustment
 signal is thus applied over control line 72 to capstan drive motor 70 to
 adjust the motor shaft speed .omega. thereby adjusting the tape speed in
 accordance with the temperature of the cartridge 12.
 In accordance with a primary advantage of the present invention, when the
 temperature of the cartridge 12 exceeds a predetermined high temperature
 threshold value, the controller 14 sends a speed adjustment signal to the
 capstan controller 68 to decrease the speed of the tape 18, which in turn
 causes the temperature over time to decrease. When the temperature of the
 cartridge 12 drops below a predetermined low temperature threshold value,
 the controller 14 sends a speed adjustment signal to the capstan
 controller 68 to increase the speed of the tape 18 until the high
 temperature threshold value is realized or exceeded. The cartridge speed
 may be continuously adjusted in accordance with the predetermined
 threshold values, resulting in optimal operation of the tape drive
 assembly 10. Since the high and low temperature threshold values are
 adjustable, the speed adjustment can be carefully coordinated with the
 known characteristics of the cartridge 12 and the tape drive assembly 10.
 The measured temperature of the cartridge 12 is compared with the threshold
 values at specific intervals. In accordance with the present invention,
 the specific intervals may be adjusted. When the sampling interval is
 decreased, less time is allowed between each determination of the high or
 low threshold temperature.
 In operation, at an initial time t.sub.0, the capstan drive motor 70 is at
 rest and the tape 18 consequently is not in motion. The temperature sensed
 is the temperature of the base plate 28 at rest. At startup, at time
 t.sub.1 the drive may operate the tape 18 at 120 ips, the maximum speed
 for the tape 18. During this time, the temperature of the base plate 28 on
 the cartridge 12 is continuously monitored and compared to the
 predetermined threshold values. As long as the temperature of the base
 plate 28 does not exceed the high temperature threshold value, the drive
 may continue to operate the tape 18 at 120 ips. At time t.sub.2, after a
 period of continuous running, the friction generated by the constant
 interaction between the drive belt, tape 18 and the spools 4850, rollers
 5254 and posts 565860, all of which are connected to the base plate 28 of
 the cartridge 12, causes the base plate 28 to heat up. At this point, if
 the detected temperature meets or exceeds the high temperature threshold
 value, the controller 14 sends a signal to the capstan controller 68 to
 slow the capstan motor 70 down. If at any time the temperature of the base
 plate 28 falls below a predetermined low temperature threshold, the
 controller 14 sends a signal to the capstan controller 68 to speed up the
 capstan motor 70 such that the tape drive assembly 10 can operate at an
 optimal speed for data transfer. The present invention thus continuously
 monitors the temperature and adjusts the speed of the cartridge 12 such
 than optimal data transfer is achieved.
 FIG. 4 is a flow chart of an algorithm 100 for adjusting the speed of the
 tape 18 in the cartridge tape drive assembly 10 of FIG. 4. The algorithm
 100 is implemented on a digital microcomputer which uses an input port to
 sample the temperature of the base plate 28 and an output port for
 producing a temperature adjustment signal which is applied to the capstan
 controller 68. As shown in FIG. 5, the procedure begins with sensing the
 temperature of the cartridge base plate 28 (step 102). As shown in FIG. 4,
 the capstan drive motor 70 drives the capstan 62 at a motor shaft speed
 .omega.. In step 104, a limit check is performed on the temperature
 determined in step 102. If the temperature does not fall between the
 minimum and maximum temperature threshold values, a signal is generated
 and sent to the capstan controller 68 (step 106) to adjust the speed of
 the capstan motor 70. When the temperature is less than the minimum
 temperature threshold value, a signal to speed up the capstan motor 70 is
 sent to the capstan controller 68 (step 108). When the temperature is
 greater than the maximum temperature threshold value, a signal to slow
 down the capstan motor 70 is sent to the capstan controller 68 (step 110).
 If the temperature falls within the minimum and maximum temperature
 threshold values, no adjustment signal is generated and the speed of the
 tape 18 is not adjusted (step 112).
 It will be appreciated by persons skilled in the art that the present
 invention is not limited to what has been shown and described hereinabove,
 nor the dimensions of sizes of the physical implementation described
 immediately above. For example, the present invention may be used with
 tape drive assemblies and cartridges currently available or in
 development. The scope of the invention is limited solely by the claims
 which follow.