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Estimation and Prediction of Pitch and Skew Error

IP.com Disclosure Number: IPCOM000087290D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 27K

IBM

Related People

Mantey, JP: AUTHOR

Abstract

Described is a procedure whereby pitch and skew errors are estimated or predicted from samples of the servo error in a rotating-head tape transport system.

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Estimation and Prediction of Pitch and Skew Error

Described is a procedure whereby pitch and skew errors are estimated or predicted from samples of the servo error in a rotating-head tape transport system.

Fig. 1 depicts intervals of interest in a sampled data system. In this system S(1), S(2) are the servo error samples. M(1), M(2), M(3), M(4) are the motor update voltages.

The following events are listed in ascending time sequence:

(Image Omitted)

The above sequence is repeated for each rotor revolution.

In the above example, the control system is assumed to have about the same rate of error correction on X(e) and DeltaX(e). Assume this correction is essentially represented by a single exponential transient with time constant T(e). Assume that the time between motor updates is uniform and equal to t(o), that the time from S(1) to M(1) is t(1), and that the time from S(2) to M(3) is t(2). Then

(Image Omitted)

Therefore, a(1) S(1) is the expected value of the servo error on servo stripe one if it were read at time M(1), and it is based upon what was actually read at time S(1). Similarly, a(0) a(1) S(1) is the expected value of the servo error on servo stripe one if it were read at time M(2). This prediction process is continued until a new actual sample of S(1) is obtained. If a servo sample is not valid when read, the old value is extrapolated for another rotor revolution.

The above process can be expanded to handle the situation where the transient response of...