Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-08-16
2004-06-22
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S071000, C360S130210
Reexamination Certificate
active
06754033
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to tape drive systems for moving a tape, such as a recording tape for storing information, longitudinally across a head where the tape is subject to lateral movement, and, more particularly to tape having tracks extending in the longitudinal direction, where the tape head has a track following servo system for moving the head in the lateral direction for track following the lateral movement of the longitudinal tracks.
BACKGROUND OF THE INVENTION
Typically, tape drive systems provide tape guides for controlling the lateral movement of the tape as the tape is moved along a tape path in a longitudinal direction across a tape head. The tape may have a plurality of data tracks extending in the longitudinal direction, and the tape drive system may provide a track following servo system for moving the tape head in a lateral direction for following lateral movement of the longitudinal tracks as the tape is moved in the longitudinal direction. The track following servo system may employ servo tracks on the tape which are parallel to the data tracks, and employ servo read heads to read the servo tracks to detect position error and thereby position the tape head at the data tracks and follow the data tracks. This allows the data tracks to be placed closely together and increase the number of data tracks.
The tape is typically contained in a cartridge of one or two reels, and the tape is moved between a supply reel and a take up reel. The reels typically have runout causing the tape to move laterally as the tape is moved longitudinally. Tape guides provide the conventional means for limiting at least the amplitude of the lateral movement of the tape so that it does not exceed the lateral movement capability of the track following servo system.
In functions other than tape guiding, such as a tension roller (U.S. Pat. No. 4,310,863), an inertia roller (U.S. Pat. No. 4,633,347), or a tape timer roller (U.S. Pat. No. 3,037,290), where only longitudinal motion of the tape is concerned, high friction rollers that are in the tape path and displaced a considerable distance from the tape head, insure that the tape does not slip longitudinally with respect to the roller.
Typical tape guides may comprise stationary buttons or edges, or flanges at the side of tape guide rollers, positioned against the edges of the tape to control the amplitude of the lateral movement of the tape. In order to increase the total capacity of a tape, the tape is increasingly made thinner to allow more wraps of tape to fit on a given tape reel. As a result, the tape is very weak in the lateral direction, and can easily be damaged at the edge from the tape guide. Thus, the tape guides are typically positioned at a bearing where the tape assumes a cylindrical shape, thus increasing the tape edge ability to support a load. The bearing is also typically designed to have low friction. This arrangement minimizes the potential to distort the edge of the tape as the guides push against the edges of the tape to move the tape to the center of the bearing to reduce the amplitude of lateral displacement of the tape. One example is illustrated in U.S. Pat. No. 5,447,279, which employs an air bearing to reduce the friction of the bearing for stationary tape guides. Roller bearings may also be utilized for reducing the friction of the bearing while the flanges of the roller bearings push against the edges of the tape. One example of a roller bearing or fixed pin with flanges arranged to have low friction is U.S. Pat. No. 4,427,166. Fixed surfaces may also be arranged to have low friction. One example is described in U.S. Pat. No. 4,466,582, where a synthetic resin or metal coated tape guide bearing has a reduced contact area for the tape to lower the friction between the guide surface and the running tape and allow the flanges to stabilize the tape.
However, when wound on a reel, tape is typically subjected to stack shifts or stagger wraps, in which one wrap of the tape is substantially offset with respect to an adjacent wrap. Thus, as the tape is unwound from the reel, there is a rapid lateral transient shift of the tape. Other common sources of rapid lateral transient shifts include 1) a buckled tape edge in which the tape crawls against a tape guide flange and suddenly shifts laterally back down onto the bearing, 2) a damaged edge of the tape which causes the tape to jump laterally when contacting a tape guide, and 3) when the take up reel or supply reel runout is so significant that the reel flange hits the edge of the tape.
Because of the low friction of the bearing and the low mass of the tape, any rapid lateral transient shift of the tape at any point of the tape path is not slowed by the typical tape guide and is transmitted along the tape path to the tape head.
A tape head track following servo system may comprise a single actuator, or a compound, multiple element actuator.
The transient response of the tape head track following “servo system typically comprises a high bandwidth for a very limited lateral movement, called “fine” track following, for allowing the tape head to accurately follow small displacements of the tape. Larger movement of the tape head is typically conducted as coarse” track following, which is also employed to shift the tape head from one set of tracks to another set, and is conducted at a slow rate. The occurrence of a lateral transient shift, however, is so rapid that neither the fine track follower nor the coarse track follower is able to respond, with the result that the tracking error becomes so large that writing must be stopped to prevent overwriting an adjacent track and to insure that the tracking error on read back is not so large as to cause a readback error.
One approach has been to make the tape guide edges or flanges closer together to maintain a pressure on both edges of the tape. However, this tends to stress and damage the edges of the tape, reducing its durability. An attempt at reducing the stress comprises spring loaded tape guides, such as the above-mentioned '279 patent. However, although the amplitude of the tape shift may be reduced somewhat by this approach, the speed of the shift is typically not reduced, and the track following servo error still occurs, reducing the performance of the tape drive.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce the rate of the lateral transient movement of the tape so that the track following system may continue to track follow the longitudinal tracks of the tape.
A tape movement constraint is provided for a tape drive system. The tape drive system moves a tape along a tape path in a longitudinal direction across a tape head, the tape having tracks extending in the longitudinal direction, the tape head having a track following servo system for moving the head in a lateral direction for following lateral movement of the longitudinal tracks, where the tape is subject to lateral transient movement.
The tape movement constraint comprises at least one tape roller bearing for positioning along the tape path closely adjacent the tape head, having a cylindrical peripheral surface parallel to the lateral direction of the tape and extending a length greater than the width of the tape, for contacting a surface of the tape. The tape roller bearing is rotatable about a central axis parallel to the cylindrical peripheral surface, allowing the tape freedom of movement in the longitudinal direction.
The cylindrical peripheral surface comprises a frictional surface for contacting and engaging the surface of the tape, allowing the tape to move freely with the tape roller bearing cylindrical peripheral surface in a direction perpendicular to the central axis, and constraining movement of the tape in the lateral direction. The frictional surface limits slip in the lateral direction, thereby reducing the rate of the lateral transient movement of the tape to allow the track following servo system to follow the reduced rate lateral transient movement of the longitudinal tracks.
Thus, the tape
Argumedo Armando Jesus
Biskeborn Robert Glenn
Childers Edwin Ralph
Eaton James Howard
Holcombe John H.
International Business Machines - Corporation
Sniezek Andrew L.
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