Browse Prior Art Database

Optical Tape Path with Liquid Crystal Prism

IP.com Disclosure Number: IPCOM000123327D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 4 page(s) / 109K

Publishing Venue

IBM

Related People

Finkelstein, B: AUTHOR [+2]

Abstract

This invention uses a liquid crystal prism to read data from and write data to optical tape.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Optical Tape Path with Liquid Crystal Prism

   This invention uses a liquid crystal prism to read data
from and write data to optical tape.

   As shown in Figure 1, optical tape drive 100, supply reel
120, and takeup reel 121.  Reels 120 and 121 may be in a dual reel
cassette.  Alternately, reel 120 may be in a single reel cartridge
and reel 121 is resident in drive 100.

   The supply reel is rotated by motor 130.  Digital
tachometer 140 measures the rotation of motor 130.  Similarly,
takeup reel 121 is rotated by motor 131.  Digital tachometer 140 is a
multi-line tachometer encoder.  However, digital encoder 141 may be
either a single-line tachometer as in the IBM 3480 tape drive family
or a multi-line tachometer.

   Microprocessor 150 gathers the digital signals from
tachometers 140 and 141 and uses that information to calculate the
instantaneous radius of tape one each of reels 120 and 121.  The
angular velocity of the motor is calculated by dividing the
equiangular distance between fine-line tachometer encoder pulses from
tachometer 140 by the time spacing between those pulses.  Then, the
linear velocity of the optical tape is calculated from the product of
the instantaneous radius of tape on reel 120 times the angular
velocity of reel 120.

   Microprocessor 150 controls the linear tape velocity and
keeps the optical tape from going slack by sending low level signals
to power amplifier 160.  Power amplifier 160 then sends high level
power to motors 130 and 131 to effect tape motion across optical
recording head 200.

   In Figure 1, the linear tape motion is in the  X
direction.  The reels 120 and 121 as well as motors 130 and 131
rotate about the Y axis.  The Z axis is perpendicular to the tape as
the tape passes over the optical recording head 200.

   Figure 2 illustrates a detailed schematic diagram of the
optical recording head 200.  Optical head 200 includes a laser diode
201.  The primary light beam is first diffracted by grating 202 to
produce two secondary beams for tracking, in addition to the primary
data beam, and then collimated by lens 203.  The resulting
three-component beam 204 then passes to a beam splitter 205.  A
portion of beam 204 is reflected by beam splitter 205 to a lens 206
and an optical detector 207.  Via detector 207, microprocessor 150
monitors the power of laser 201 and its beam 204.  That portion of
beam 204 not reflected by beam...