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Flexible Disk Sensing Apparatus

IP.com Disclosure Number: IPCOM000086757D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 76K

Publishing Venue

IBM

Related People

Taylor, NB: AUTHOR

Abstract

In the scanning system shown in Fig. 1, a white light from a source 10 is projected through a disk pack 11. Since the scanning assembly can see only a few disks from any single location, the assembly is mounted on a positioning device (not shown) which allows positioning at different axial locations along the disk pack. The edges of the disks are imaged onto a photocell 12 after being reflected from an oscillating mirror 13. Although a greater angle is shown for purposes of illustration, mirror 13 oscillates in practice through an angle not in excess of six degrees. The photocell is masked by an aperture 14 which is the same size as a disk image. The mirror is caused to oscillate about an axis parallel to the plane of the media which results in a photocell output, as indicated in trace B.

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Flexible Disk Sensing Apparatus

In the scanning system shown in Fig. 1, a white light from a source 10 is projected through a disk pack 11. Since the scanning assembly can see only a few disks from any single location, the assembly is mounted on a positioning device (not shown) which allows positioning at different axial locations along the disk pack. The edges of the disks are imaged onto a photocell 12 after being reflected from an oscillating mirror 13. Although a greater angle is shown for purposes of illustration, mirror 13 oscillates in practice through an angle not in excess of six degrees. The photocell is masked by an aperture 14 which is the same size as a disk image. The mirror is caused to oscillate about an axis parallel to the plane of the media which results in a photocell output, as indicated in trace B. Each negative-going signal represents a disk-edge image passing the photocell aperture. The negative peak is detected by using the second differential of such signal, as shown in trace C of Fig. 2.

To derive an analog signal from the second derivative pulses, the times at which the pulses occur relative to the mirror scan start time (position a) are used. A timer is started at the beginning of the mirror scan. After approximately 45 electrical degrees of the mirror cycle (a-b of Fig. 2), two electronic circuits are set (traces D and E of Fig. 2). The first disk detected thereafter resets one circuit to provide the disk #1 signal, and the second disk resets the other of the circuits to provide the disk #2 signal. The length of time that these two circuits are on is a representation of the instantaneous disk locations with reference to the scanner assembly. The output from these circuits operates two electric switches which gate the velocity profile of the mirror scan derived from a sense coil on the mirror drive (trace A) into two low-pass filters. By gating the velocity of the mirror into the low-pass filters, compensation is achieved for the sinusoidal scan characteristic of the mirror. By using the low-pass filters with each of the two outputs, two analog signals are derived representing the hanging position of two adjacent disk edges.

The above decoded signals are used to derive two aspects of disk axial location. One is peak-to-peak runout, the total axial distance occupied by the disk during rotation. The other is the 100% window, the axial space between adjacent disks present throughout 360 degrees of disk rotation.

Average peak-to-peak runout of the disks is determined by the circuit of Fig.
3. The ch...