Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-12-07
2004-08-10
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06775092
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to digital tape drive storage devices, and in particular, to a lateral tape motion sensor that detects and responds to lateral movement of multitrack tape media.
PROBLEM
It is a problem in the field of tape drives to maintain alignment of the tape drive head assembly and the track as data is being transferred to or from the magnetic tape media as the magnetic tape media is wound between the supply reel located with the tape cartridge and the take-up reel located within the tape drive while providing a plurality of narrow tracks on one length of tape media. Providing a plurality of narrow tracks on one length of tape media for recording data increases tape storage densities. To maximize capacity, tracks are recorded as closely as possible to adjacent tracks. It is a problem in the field of tape drives to prevent overwriting data previously written on an adjacent track when the magnetic tape media moves laterally.
Lateral tape motion (commonly referred to as LTM) is movement of the tape media in a direction perpendicular to the tracks. Lateral tape motion is the tendency of tape media to move laterally due to poor quality tape media, excessive usage of a tape cartridge, excessive vibration or movement of the tape drive during operation, wobbling of the supply or take-up reel, or by imperfect tape guides. It is common practice in the industry to discard tapes after a plurality of uses to prevent inadvertent erasure of data on adjacent tracks due to LTM.
Apparatus are known for adjusting the position of the tape head in response to lateral movement of the tape media and for maintaining the alignment of the tape media as data is transferred to and from the tape media. These devices include apparatus to prevent overwriting data on an adjacent track by detecting lateral tape motion and quickly moving the tape head in the same direction to compensate for the movement. However, precise measurement of the tape motion and a fast mechanical response is required, making such systems complex and therefore costly solutions to a common problem.
Read After Write System:
Miller, (U.S. Pat. No. 4,414,593) discloses a serpentine tape drive apparatus for writing and reading data on a magnetic tape. Using a write-read magnetic head, information is written onto the tape and subsequently read and checked in a continuous manner to assure the correctness of the data written onto the tape. In a serpentine tape drive, the tape moves past the head in a first direction, and when the end of the tape is reached, the head is adjusted to a new track and the tape travels past the head in an opposite direction as the write-read operation continues. Writing and reading as the tape moves in opposite directions provides adjacent serpentine tracks. Reading the data immediately after a write verifies that the data written is correct. The read after write system described in the Miller patent does not check adjacent tracks as data is being written to prevent the tape head from writing over data on an adjacent track.
Track Following Systems:
Apparatus are known for adjusting the magnetic head while reading and writing to maintain alignment between the head and the edge of the tape. The track following servo apparatus disclosed by Saliba, (U.S. Pat. No. 5,371,638) reduces cross talk and the effects of lateral tape motion by adjusting the position of the magnetic head during read and write operations. The apparatus includes a magnetic head with longitudinally placed read and write head gaps and a servomotor for adjusting the head. The read gaps are laterally offset from the write gaps and data is read immediately after a write to check for errors. If the read does not correspond to the write, the data is rewritten. The recorded data includes both low frequency servo blocks and higher frequency data. As a track is written, the adjacent tracks are monitored for low frequency servo data. When servo data is encountered, the write is temporarily suspended. The servo data is compared with predetermined reference data to determine a corresponding head adjustment. The reference data may be last recorded head positional information. The tape head is adjusted corresponding to the servo data in relation to the predetermined reference data. If the tape head is adjusted, a new positional reference is created and stored. The embedded blocks of servo data are also used during reading.
While this system, referred to in the industry as a track following servo system, reduces the risk of overwriting data on adjacent tracks, it requires a costly, precise mechanism capable of moving the tape head as quickly as the tape media moves. Providing a complex apparatus with an additional read/write head that quickly responds to lateral tape motion is expensive and not suitable for use with slower responding tape head designs. The positioning apparatus for adjusting the magnetic head during reading and writing disclosed by Fasen, (U.S. Pat. No. 5,999,359) uses a light source that moves with the head to monitor the distance between the head and the edges of the tape media. The light source illuminates the light detector that generates a motor drive signal for adjusting the position of the tape head as necessary.
This system measures the distance between the head and the edge of the tape to obtain and maintain alignment. When the distance between the head and the edge of the tape varies, the tape head is adjusted. The head adjustment is in reference to the lateral edge of the tape without taking into consideration the adjacent tracks. The apparatus disclosed by Fasen employs an expensive tape head design that can move fast enough to follow the signal from the light source. While the apparatus adjusts the tape head to compensate for lateral tape motion, like the track following servo apparatus previously described, the apparatus is complex and therefore expensive.
Another track following apparatus utilizing a light source for positioning the tape head is disclosed by Iwamatsu, (U.S. Pat. No. 5,196,969) and includes a feedback control apparatus for precisely positioning the head. The feedback control comprises a light emitting source located on one side of the magnetic tape and a plurality of light receiving devices located on the opposite side of the tape and directly across from the light emitting device. The light receiving devices are positioned relative to tracks and with respect to each other to provide tape position feedback. The plurality of light receiving devices has a predetermined relation that governs the feedback control when the magnetic head is moved to a predetermined track position. When the feedback from the plurality of light receiving devices varies from the predetermined track position, the head is adjusted correspondingly.
As the tape head moves widthwise to an adjacent track, the light receiving device corresponding to that track should be illuminated by the light emitting device. Similarly, as the head is reading or writing data, the system monitors the light received by the plurality of light receiving devices to determine the alignment of the head with respect to the tape. Data received from the light receiving devices is compared to the predetermined data, and if a misalignment is encountered, the tape head is adjusted accordingly.
The track following apparatus described above provide an apparatus and method for responding to lateral tape motion, however, the apparatus must have the capability of moving fast enough to follow the vertical tape motion because the tape is so light that it can move very quickly. Apparatus that monitor the lateral position of the tape media and quickly adjust the tape head to compensate for the movement are therefore complex, expensive and are known to be prone to error. The described track following apparatus are not suitable for less expensive, slower responding tape heads.
Tape Aligning:
Another method for aligning tape media with the tape head disclosed in Cope, (Pat. App. No. 20010002158) comprises a series of guide rollers to maintain the alignme
Turner Philip John
Zweighaft James
Hudspeth David
Patton & Boggs LLP
Slavitt Mitchell
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