Patent Grant
8699174
Linear tape drive systems provide for high-density recording on multiple tracks of a magnetic storage tape. In certain arrangements, parallel tracks extend along a longitudinal direction of the tape. During recording or playback, the read/write elements of the head should be aligned with the desired track as the tape moves in a longitudinal direction across the head. Closed loop positioners are often used in tape systems having higher track densities. In high-density tape systems, the tape may wander in the lateral direction (perpendicular to the longitudinal direction) as it moves in the longitudinal direction across the head, which can result in a positioning error or offset between the head and a center line of the desired track. Moreover, if the positioning error or offset is sufficiently large, it can further result in a track misregistration (TMR) error.
To avoid these types of problems, tape cartridges for high-density tape drives are preformatted with what is known as servo information, which is used to maintain the correct lateral position of the tape with respect to the read/write head. Servo information provides the system with feedback that is used to continuously position the head relative to the tape. Analysis of the servo signals such as a position error signal (“PES”) allows for a determination of an offset and the distance of the offset between the track and the head. Based on the PES, the head is moved by a positioner in the lateral direction to the center line of the track so that write/read operations can occur properly.
Linear Tape Open (“LTO”) is a computer storage magnetic tape format that employs a servo-based, closed loop control mechanism. The LTO roadmap calls for successive increases in capacity and speed, requiring increased track densities. As track densities increase with each new generation of LTO tape cartridges, the ability to precisely control the read/write head relative to the magnetic tape becomes increasingly important and more difficult. External vibrations (also sometimes referred to herein as “system disturbances”) degrade the performance of LTO drives by causing a misalignment of the head that increases the PES, thus degrading the ability of the head to follow the desired track. If the tracking performance degrades too far then a TMR error can occur causing the drive to stop reading or writing.
Because external vibrations are present in most non-sterile conditions (due to fans, hard drives, and other rotating systems), it is imperative to compensate for such external vibrations to decrease the likelihood and/or extent of TMR. Previous technology uses an additional sensor such as an accelerometer to measure the external vibrations and feed forward the signal, possibly through a filter, to control the position of the head. Unfortunately, such technology has certain limitations. A critical element of this previous technology is the ability to measure the external vibrations ahead (in time) of when they affect the position of the head. Due to imperfections in the sensor, additional filtering is required in order to increase accuracy. As a result, incorporating a sensor into the system can increase the overall complexity of the drive.
The present invention is directed toward a tape drive that receives a tape cartridge having a tape. In certain embodiments, the tape drive comprises a tape head and a control system. The tape head transfers data between the tape drive and the tape. The control system utilizes linear parameterization to control the position of the tape head relative to the tape.
In some embodiments, the control system includes a compensator and a filter. The compensator can be a combination of the information contained in a nominal control system and the information contained in a model of the servo system. Additionally, the model of the servo system estimates system disturbances that affect the tracking ability of the control system. Further, the filter filters the estimated system disturbances to generate a filtered system disturbance signal. The filtered system disturbance signal is then used to adjust the output of the compensator. Moreover, in certain embodiments, the filter can be updated to improve the performance of the compensator. For example, in one such embodiment, the filter is updated utilizing one of least mean squares filtering and recursive least squares filtering.
Additionally, in one embodiment, the control system utilizes Youla-Kucera parameterization to control the position of the tape head relative to the tape.
Further, in one embodiment, the control system controls the position of the tape head relative to the tape without the use of a feed-forward sensor.
The present invention is further directed toward a media library including a library housing, and the tape drive, as described above, positioned within the library housing.
Additionally, the present invention is further directed toward a combination including a tape cartridge and the tape drive, as described above, that receives the tape cartridge.
Further, the present invention is also directed toward a method for compensating for system disturbances in a tape drive.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Reference will now be made in detail to various embodiments of the subject matter, examples of which are illustrated in the accompanying drawings. While the subject matter discussed herein will be described in conjunction with various embodiments, it will be understood that they are not intended to limit the described subject matter to these embodiments. On the contrary, the presented embodiments of the invention are intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the various embodiments as defined by the appended claims. Furthermore, in the following description of embodiments, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the subject matter. However, embodiments may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the described embodiments.
In one embodiment, the media library 10 includes a library housing 12 (also sometimes referred to herein simply as a “housing”), a power supply 14, a storage media loader controller slot 16, a library controller slot 18, a plurality of data transfer assembly slots 20, one or more storage media retainer slots 22, and a storage media mover assembly 24 (also sometimes referred to herein simply as a “mover assembly”).
The housing 12 may be substantially rectangular or square in cross section. Alternatively, the housing 12 can have another suitable shape or configuration. For example, the housing 12 can have a substantially circular cross-sectional shape. Additionally, the housing 12 may be constructed of any number of conventional materials such as, for example, those utilized in industry standard rack mount cabinets.
The power supply 14 provides electrical power in a well known manner to the storage media loader controller slot 16, the library controller slot 18, the plurality of data transfer assembly slots 20, and the storage media mover assembly 24. The power supply 14 is interfaced with these components as well as with an external power source in a well known manner using industry standard cabling and connections.
The storage media loader controller slot 16 receives a storage media loader controller 26. Additionally, the library controller slot 18 receives a library controller 28. The storage media loader controller 26 and the library controller 28 can have any suitable design, many of which are well known in the industry.
In alternative embodiments, the media library 10 can have any suitable number of data transfer assembly slots 20, which may differ from that shown in
Each data transfer device 32 includes a storage media slot 34 and a corresponding storage media sensor 36 positioned within the storage media slot 34 which generates a storage media presence signal.
In alternative embodiments, the media library 10 can have any suitable number of storage media retainer slots 22, which may differ from that shown in
It is recognized that many different types of mover assemblies 24 can be used in the media library 10. For example, the mover assembly 24 can include a rack and pinion system, a pulley or belt system, or some other suitable type of mover assembly 24.
As shown in
In the embodiment illustrated in
During use, upon receiving a signal from the storage media loader controller 26 and/or the library controller 28 to access a certain storage media cartridge 42, the mover motor 50 drives the storage media mover 46 so that it moves translationally along the mover rack 48 to the appropriate position to access the requested storage media cartridge 42.
The design, size and shape of the storage media cartridge 42 can be varied. For example, in one non-exclusive embodiment, the storage media cartridge 42 can be a tape cartridge, such as an LTO tape cartridge. In the embodiment illustrated in
The design of the tape drive 232 can vary. In one embodiment, the tape drive 232 includes a drive housing 260, a cartridge receiver 262 (illustrated with dashed lines), a take-up reel 264, a guide assembly 266, a head assembly 268, and a control system 270. In certain embodiments, the tape drive 232 may further include a cover, but the cover has not been included in
The drive housing 260 retains the various components of the tape drive 232. The drive housing 260 generally houses and/or surrounds the components within the tape drive 232.
The cartridge receiver 262 receives the cartridge 42. In particular, during use, a robotic picker mechanism or a human operator inserts the cartridge 42 into the cartridge receiver 262 of the tape drive 232. Upon insertion of the cartridge 42 into the tape drive 232, the tape 256 moves along a tape path 272 (as illustrated by arrow) between the cartridge reel 254 of the cartridge 42 and the take-up reel 264 of the tape drive 232, and past the head assembly 268.
The tape 256 includes a first side 274 and an opposing second side 276. In one embodiment, one of the sides 274, 276 stores the data. In the embodiment illustrated in
The guide assembly 266 guides the tape 256 along the tape path 272 past the head assembly 268 and onto the take-up reel 264. The guide assembly 266 can inhibit lateral tape motion during operation of the tape drive 232. In one embodiment, all or some of the guide assembly 266 is coupled or directly secured to the drive housing 260.
In one embodiment, the guide assembly 266 includes one or more tape rollers 278 (sometimes referred to herein as “rollers”) that guide the tape 256 between the cartridge reel 254 and the take-up reel 264 and past the head assembly 268. In the embodiment illustrated in
The head assembly 268 is coupled or directly secured to the drive housing 260. In one embodiment, the head assembly 268 includes (i) a tape head 280 that reads data from and writes data to the tape 256; and (ii) a mover assembly 282 that moves the tape head 280 in a direction that is approximately perpendicular to the direction of movement of the tape 256 along the tape path 272, i.e. in and out of the page in
The mover assembly 282 positions the tape head 280 relative to the tape 256. The design of the mover assembly 282 can be varied to suit the design requirements of the tape drive 232. In one embodiment, the mover assembly 282 can include a first mover (not illustrated) that provides coarse positioning of the tape head 280 and a second mover (not illustrated) that provides fine positioning of the tape head 280. Alternatively, the mover assembly 282 can have a different design which may include a different number and type of movers.
The control system 270 controls movement of the mover assembly 282, and thus, the positioning of the tape head 280. In one embodiment, the control system 270 can control movement of the tape head 280 based on a positioning signal received from the tape head 280. This positioning signal is generated by the tape head 280 based on servo information located on the storage tape 256. For example, the tape head 280 can include one or more sensors (not illustrated) that sense the actual position of the tape head 280 relative to the tape 256 versus the desired position of the tape head 280 relative to the tape 256 based on servo information located on the storage tape 256. The tape head 280 transmits the positioning signal to the control system 270. Based on the positioning signal, the control system 270 controls movement of the tape head 280, e.g., through use of the mover assembly 282, to maintain and/or adjust, as necessary, the lateral position of the tape head 280 with respect to the storage tape 256. This type of closed-loop system provides continuous feedback to the control system 270 to determine and/or correct the position of the tape head 280 relative to the storage tape 256.
In addition to utilizing the positioning signal to control movement of the tape head 280, the control system 270 further utilizes linear parameterization, e.g., Youla-Kucera parameterization (sometimes referred to as “Q-parameterization”), to compensate for vibrations and other disturbances that may otherwise cause the tape head 280 to be improperly positioned relative to the tape 256. As utilized herein, vibrations and other disturbances can be referred to collectively as “system disturbances”. With this design, the present invention does not require an additional sensor, i.e. a feed-forward sensor, as has been utilized in previous attempts to address the issue of such system disturbances potentially causing TMR errors, and thus, does not require feed-forward-based control. Through use of linear parameterization, such as Youla-Kucera parameterization, as discussed in greater detail below, the present invention is able to adjust the control system 270, and thus the control of the position of the tape head 280, automatically (adaptively) to improve the performance of the tape drive 232 during vibration or while other disturbances may be present. System disturbances may be caused by the mover assembly 282, the tape roller 278, or various other features included within the tape drive 232, the media library 10 (illustrated in
The precise design of the control system 270 can be varied. As illustrated in
The compensator J compensates for position error that is due to the normal operation of the tape drive 232 (illustrated in
Additionally, in alternative embodiments, the compensator J can replace an existing control system, e.g., a control system that simply utilizes a nominal controller, or can be simply added onto and/or used in combination with the existing (nominal) control system.
As utilized herein, the nominal controller 370A, which is designed to achieve proper tracking performance and stability when external disturbances are not present, can be represented by Cx; wherein Cx=NcDc−1. In this equation, both Nc and Dc are right coprime. Additionally, the model of the servo system 370B, which is used to estimate the system disturbances that affect the tracking ability of the control system 270, can be represented by Gx; wherein Gx=NxDx−1. In this equation, both Nx and Dx are also right coprime.
Thus, the function of the compensator J can be described by the following equation:
When used as an add-on to an existing nominal controller, then Cx=0 and Gx is a model of the whole tracking system that is comprised of the mover assembly 282 and the existing nominal controller.
Referring back to
During use, the filter Q is adjusted to improve the performance of the compensator J, and thus the control system 270 as a whole. When Q=0, the overall adaptive compensator, as illustrated in
Thus, the new control system 270 can be represented by the following equation:
CQ=(Nc+DxQ)(Dc−NxQ)−1, (Equation 2)
which is known as the Youla-Kucera parametrization or Q-parametrization from control theory. Subsequently, the output of the control system, as shown in
Thus, the filter Q can be updated online or adaptively to remove external disturbances, and as a result no feed-forward sensor is needed to compensate for system disturbances in the tape drive 232. The Q-parameter is updated by searching for a filter that improves PES performance. This filter improves the PES signal which in turn will decrease the number and/or extent of TMRs. Moreover, by property of the Q-parameterization, the filter Q will always produce a controller that stabilizes the feedback system.
In different embodiments, various methods can be used to update the filter Q. For example, the filter Q can be updated through use of least mean squares filtering, recursive least squares filtering, or any other method that drives the error signal towards zero. Additionally, bounding and filtering the parameters of the filter Q can be shown to be beneficial in the presence of modeling errors by increasing the likelihood that the parameters do not get too large and change relatively slowly with time.
The control system 270 and method, as described herein, functions as a robust, reliable, and effective technique to decrease the effect of, cancel, or otherwise account for system disturbances to the tape drive 232 and thus to improve the overall tracking performance of the tape drive 232.
While a number of exemplary aspects and embodiments of a media library 10, data transfer device 32 and various methods have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4031369 | Heaman et al. | Jun 1977 | A |
| 4935827 | Oldershaw et al. | Jun 1990 | A |
| 5212388 | Izraelev | May 1993 | A |
| 5293565 | Jaquette et al. | Mar 1994 | A |
| 5357421 | Tautz et al. | Oct 1994 | A |
| 5610843 | Chou | Mar 1997 | A |
| 6553337 | Lounsbery | Apr 2003 | B1 |
| 6574065 | Sri-Jayantha et al. | Jun 2003 | B1 |
| 7529054 | Pang et al. | May 2009 | B2 |
| 20020131195 | Dehnert | Sep 2002 | A1 |
| 20040120069 | Kitazaki et al. | Jun 2004 | A1 |
| 20050075740 | Gao et al. | Apr 2005 | A1 |
| 20070041115 | Lee | Feb 2007 | A1 |
| 20090206190 | Bui et al. | Aug 2009 | A1 |
| 20100226039 | Bui et al. | Sep 2010 | A1 |
| 20110043945 | Cherubini et al. | Feb 2011 | A1 |
| 20130050868 | Kinney et al. | Feb 2013 | A1 |
| 20130100554 | Biskeborn et al. | Apr 2013 | A1 |
| Entry |
|---|
| I.D. Landau, A. Constantinescu, and D. Rey. Adaptive narrowband disturbance rejection applied to an active suspension—an internal model principle approach. Automatica, 41(4):563-574, Jan. 2005. |
| T. Tay, I. Mareels, and J.B. Moore. High Performance Control. Birkh{umlaut over ( )}auser, Boston, 1998. |
| Number | Date | Country | |
|---|---|---|---|
| 20130050868 A1 | Feb 2013 | US |
