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High Track Density PES System With Larger Gain Range

IP.com Disclosure Number: IPCOM000041394D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Liu, CC: AUTHOR

Abstract

As track densities of magnetic recording systems increase, track widths correspondingly decrease. Also, average head moving time specifications keep decreasing. Thus, the need for a position error signal (PES) system with a larger gain range becomes more acute. As the linear gain range increases, a more accurate and more effective head positioning and accessing servo system is required. However, in prior-art PES systems, the linear gain range is restricted to + 1/2 track-width or a total of one track-width. Disclosed here is a unique magnetic recording system structure such that the linear gain range can be increased 100% to _ 1 track-width or a total of two track-widths. In addition, a higher track density PES system can be realized with a servo head with a wider core width element.

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High Track Density PES System With Larger Gain Range

As track densities of magnetic recording systems increase, track widths correspondingly decrease. Also, average head moving time specifications keep decreasing. Thus, the need for a position error signal (PES) system with a larger gain range becomes more acute. As the linear gain range increases, a more accurate and more effective head positioning and accessing servo system is required. However, in prior-art PES systems, the linear gain range is restricted to + 1/2 track-width or a total of one track-width.

Disclosed here is a unique magnetic recording system structure such that the linear gain range can be increased 100% to _ 1 track-width or a total of two track-widths. In addition, a higher track density PES system can be realized with a servo head with a wider core width element. The basic embodiment consists of a Tetra-Orthogonal servo encodement, a unique servo head transducer, a preamplifier, a filter, and a linear synchronous PES detector. Fig. 1. shows such a PES system. The ratio [R] can be defined as the ratio of the magnetic width of the servo head to system track pitch, R = Wh / Wd (1) where Wh is the magnetic width of the servo head element, and Wd is the data track pitch of the system. It can be shown that there exists a certain ratio [R], such that the PES linear gain range is maximum. A plot of the PES linear gain range (in units of track-width) vs. the ratio [R] is shown in Fig. 2. Clearly, it is a periodic function with a period of 4. This results from the nature of the Tetra-Orthogonal servo encodement used. The first optimum ratio for the maximum PES linear gain range is 2, the second is 6, and so on. The corresponding maximum PES linear gain range is two track-widths. A Tetra-Orthogonal servo encodement is shown in Fig. 3. Servo tracks are offset a half track pitch from the associated data tracks. The servo track pitch [Ws] and the data track pitch [Wd] are equal. The ratio of the magnetic width of the servo element to the data track pitch is exactly 2. The servo sinusoidal signals are of a single frequency with phases cyclically revolving through 0OE, 90OE, 180OE, 270OE, and repeating themselves every 4 tracks. They have the following expressions: a = A(x) sin (wt + 0OE) ~ A(x) , signal for track 'a' (2) b = B(x) sin (wt + 90 ) ~ iB(x) , signal for track 'b' c = C(x) sin (wt + 180 ) ~ -C(x) , signal for track 'c' d = D(x) sin (wt + 270 ) ~ -iD(x) , signal for track 'd' where the in...