Methods, apparatus and program products for determining off-track time shift estimates to be used in writing timing patterns on a storage medium

#This invention relates, in general, to writing timing information on storage media and, in particular, to determining off-track time shift estimates used in the writing of the timing information.

#There is a continuing desire to increase the amount of information that can be stored on various forms of storage media, including floppy and hard disks. One way of increasing the capacity of the storage media is by providing higher track densities. Higher track densities have been made possible by the advent of voice-coil and other types of servo positioners, as well as by the ability to read and write narrower tracks by using, for example, magnetoresistive (MR) head technology.

#As technology advances to provide the increased track densities and smaller disk drives, there is an ever-increasing need for more accurately positioned timing information. It is this timing information that is used when writing product servo-patterns on the storage media.

#The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

#FIG. 1 illustrates a shifting of the centers of a trigger pattern demonstrating a problem addressed by the present invention;

#FIG. 2a depicts one example of a self-servowrite apparatus incorporating and using the capabilities of the present invention;

#In accordance with the principles of the present invention, off-track time shift estimates are determined, which are used in writing timing information (e.g., trigger patterns) on a storage medium. In particular, the off-track time shift estimates are used in order to adjust for trigger pattern slew when shifting from one propagation pitch to another. Off-track time shifts are considered a type of systematic error. Systematic errors have the characteristic of being constant in the sectors of a storage medium.

#An off-track time shift occurs, for example, when there is read to write non-parallelism (i.e., the read element is perpendicular to a track direction, but the trigger pattern it is reading is not perpendicular to the track direction) or with misaligned head mounts. In particular, the time shift is a result of a shift in the geometric centers of a trigger pattern, when a trigger pattern is read at two different radial locations. For example, when a read element 100a (FIG. 1) is located at a ¼ track position, it detects the center of Trigger Pattern A (TPA) at 102. (Note that TPA is non-parallel to read element 100a.) However, when the read element is moved to a ½ track position (read element 100b), it detects the center of Trigger Pattern A at 104. Thus, there is a shift in the center of the trigger pattern, which results in a pattern rotation.

#Such a shift cannot be determined by taking a time measurement between two trigger patterns, TPA and TPB, because the centers of both trigger patterns shift equally. Thus, measurement T1, taken when read element 100a is at the ¼ track position, is equal to time T2, taken when read element 100b is at the ½ track position. Therefore, there is no detection of an off-track time shift.