Browse Prior Art Database

Transmissivity Tester for Flexible Magnetic Disks

IP.com Disclosure Number: IPCOM000086759D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

den Tex, K: AUTHOR [+2]

Abstract

The tester establishes a method and a standard for defining the optical transmissivity of a flexible magnetic disk 10, particularly one disposed in a protective outer envelope 24, such an assembly being disclosed, for example, in U. S. Patent 3,668,658. The tester uses an optical system 12 and beams light through registering indexing holes 24a in the opposite faces of envelope 24 and determines the amount of light transmitted. Machines using disk 10 and employing its index hole 14 for timing or sector location purposes need a specified ratio of optical transmission between the disk 1O and the index hole 14, i.e., 0.5% at 900 nanometers wavelength. The tester determines this ratio.

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Transmissivity Tester for Flexible Magnetic Disks

The tester establishes a method and a standard for defining the optical transmissivity of a flexible magnetic disk 10, particularly one disposed in a protective outer envelope 24, such an assembly being disclosed, for example, in
U. S. Patent 3,668,658. The tester uses an optical system 12 and beams light through registering indexing holes 24a in the opposite faces of envelope 24 and determines the amount of light transmitted. Machines using disk 10 and employing its index hole 14 for timing or sector location purposes need a specified ratio of optical transmission between the disk 1O and the index hole 14,
i.e., 0.5% at 900 nanometers wavelength. The tester determines this ratio.

Disk 10 is mounted rotatably about its center of rotation using disk mounting hub 16 fixed on drive shaft 18. Optical system 12 includes light-emitting (LED) light source 20 and silicon photovoltaic cell 22 disposed on the optical axis 20a of LED 20. Cell 22 has a light-transmitting aperture 22a, and openings 24a are disposed on optical axis 20a so that light is transmitted from LED 20 through disk 10 and aperture 22a to cell 22. Disk 10 has an indexing hole 14 which, during the operation of disk 10 in a disk drive, registers at times with openings 24a in cartridge 24. For the measurements of the tester, disk 10 is assumed to be rotated into positions in which hole 14 is out of register with holes 24a. The radiant energy detected by cell 22 is amplified by operational amplifier 26 and is displayed on voltmeter 28. Disk 10, during the measurements, is either stationary or is rotated slowly, but opening 14 is never allowed to register with openings 24a during the measurements.

The optical system 12 is first calibrated before measurements are done using voltmeter 28. For this purpose, a neutral density or similarly suited optical filter replaces disk 10 and envelope 24. With the neutral density filter in place between LED 20 and cell 22, meter 28 is calibrated, such as by setting it to its zero indication.

The transmissivity measurement of disk 10 is particularly determined by the magnetic coating on disk 10, since the substrate of disk 10 is generally of quite clear material. The tester provides a transmissivity test of disk 10 at a particular wavelength, and LED 20 is a monochromatic light source for this purpose. The tester, in determining the optical transmissivity of disk 10, compares the amount of light transmitted by disk 10 in comparison with that transmitted by the neutral density filter used as a standard.

More particularly, the optical transmissivity of disk 10 is the radiant energy that passes through disk 10 divided by the radiant energy applied on disk 10 from LED 20. The transmittance thus is a fraction, but is usually expressed as a percentage. The maximum allowable transmittance, so that disk 10 may be satisfactory for operation with present-day disk drives, is defined by the read...