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Measuring Tangential Tilt of a Rotating Disk

IP.com Disclosure Number: IPCOM000038668D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Hancock, RA: AUTHOR

Abstract

Tilt of a rotating disk is an important parameter to know for rotating signal-storing disks. The use of a laser vibrometer (VM), (a machine that generates a voltage n(z) proportional to the velocity of a vibrating surface normal to the laser beam) allows one to measure tangential tilt of the disk during its rotation by capturing the axial runout signal from the VM and displaying it on a digital oscilloscope. One can determine the tangential tilt profile by multiplying the VM output waveform by an appropriate value. Given an axial runout signal shown in the figure, the tilt angle, r, is a function of the slope of the waveform ZS by the following relations: (Image Omitted) where z is axial displacement and s is angular displacement.

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Measuring Tangential Tilt of a Rotating Disk

Tilt of a rotating disk is an important parameter to know for rotating signal-storing disks. The use of a laser vibrometer (VM), (a machine that generates a voltage n(z) proportional to the velocity of a vibrating surface normal to the laser beam) allows one to measure tangential tilt of the disk during its rotation by capturing the axial runout signal from the VM and displaying it on a digital oscilloscope. One can determine the tangential tilt profile by multiplying the VM output waveform by an appropriate value. Given an axial runout signal shown in the figure, the tilt angle, r, is a function of the slope of the waveform ZS by the following relations:

(Image Omitted)

where z is axial displacement and s is angular displacement.

(Image Omitted)

where r is the radius of the disk where the VM laser beam is incident, and l is the rotational speed of the disk.

(Image Omitted)

The axial velocity, in the z direction combining 3 and 4 into z, results in:

(Image Omitted)

Then, substituting 5 into 1 results in:

(Image Omitted)

Now for small angles of tilt (less than 2 degrees).

(Image Omitted)

So that:

(Image Omitted)

which is the velocity signal multiplied by the constant _1 . rw Choosing appropriate units, the tilt angle, r, can be determined in degrees by using the above-described computations.

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