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A Quick and Reliable Method of Measuring Disk Pre-Written Track Center Offset on Spin Stand Spindles Disclosure Number: IPCOM000015523D
Original Publication Date: 2002-Jan-28
Included in the Prior Art Database: 2003-Jun-20

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Disclosed is a method that measures disk pre-written track center offset on spin stand spindles using the signal of the pre-written track written anywhere on the disk. It enables us to evaluate disk substrate inner hole and spin stand spindle hub specifications in an easy and reliable way. It also enables us to correlate different types of spindle analysis tools for defect analysis purpose, such as locating a pre-written information, or defects marked file return disks. When a disk with a written track is removed from and put back again on a spin stand spindle the center of the pre-written track usually offsets from the previous one. The offset is dependent on disk inner hole and spindle specifications. This makes it difficult for heads to locate the pre-written tracks often used for radius calibration and as disk surface defects marker. It is therefore important to be able to measure the offset of the disk pre-written track center in a quick and reliable way. In this invention a method for such a measurement has been development. Figure 1a shows schematically the principle of this method. First a disk is put on a spindle and a track of radius R 0 is written using a read/write head. Then the disk is removed and put back again on the spindle. Now the pre-written track center has an offset of OS. This is also the offset of the disk center . As can be seen from Fig. 1a, there are only two radii, namely R 1 and R 2 R 2 R 1 ), where the tracks defined by the head are tangential to the pre-written track. The R 1 and R 2 can be determined experimentally using the unique head read out signal (see Figs. 2 and 3 and compared with Fig. 4 which is a typical head read out signal when the head is not tangential to but intersected with the pre-written track) at these two radii using an oscilloscope. Then the offset OS can be obtained by OS R 2 R 1 )/2 (1), and it is not dependent on the R 0 . In addition, the angular position of the offset relative to linear motor moving direction (Fig. 1b) can be determined by the time the R 2 tangential signal appears on the oscilloscope (Fig. 2),