Note: Descriptions are shown in the official language in which they were submitted.
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B13CKOROL1ND OF THE IN~IENTION
Magnetic tape recording systems are widely used to
archive digital information, but have historically been
la ued b erformance and stora a
p g Y P g problems that render
their continued use for high volume information storage
unacceptable. For example, due to the relatively low
storage density c~f the magnetic recording media, a large
number of expensive tape reels or cassettes are required to
store the infor$nation. Furthermore, the mechanical devices
and parts used in providing a storage system for the reels
and cassettes of recorded media often require expensive and
time c~nsuming maintenance and/or complete replacement.
The ~agn~tic tapes must also be repacked every six months
to account for tape stretch an,d rerecorded every five to
en years in order to preserve data integrity.
pgtical' systems are now a~masoraly used in place of
magnetic systems far r~cdrdinc~ and playback of digitized
information. Ira ~ptical recorders, the data is used to
amplaaude modulate a. light la~a~ ha~~ing a predetermined
intensity nedessary to dark a light sensitive recording
media. The ~todul.ated beam i.s focused to a small spot and
~,r~c~d across the media to record the data as a fine
optical pattern coanprised oaf a number of closely spaced,
t~icrascopic dots (data marks) along a data track. To
recover the reworded data from the optical media, a low
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intensity illumination beam is scanned along the data track
and modulated by the opta:cal pattern recorded therein. The
i
modulated beam is reflected from the media to illuminate a
Light detector producing an electrical signal in accordance
~ with the beam modulation for recovery of the recorded data.
Optical recording and playback systems have proven to
prQVide enhanced performance characteristics over magnetic
systems: The microscopic optical pattern of data recorded
on the recording media by an optical system dramatically
.increases bhe data storage density over conventional
magnetic systems. Furthermore, there is a decr~~eased
susceptibility to type .stretch and ~rsar with optical
playback systems 'bee~useunlike magnetic systems,' there is
active optical tracking during tk~e reading process with no
contact between the read heaid and the media. Accordingly,
data life on the media i:s increase's to over twenfiy years.
Fina:lly,' because'significantly moredata can be-stored by
optical systems, the complexity of an archiving system (and
requa.red space) for storing recording media reels and
9,
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cassettes is significantly reduced. i
The problem with present optical recording and
v playback sys~e~n: >technology, however; is!: lew record anc3'
.
playback data rates. Currently available ~~lhigh speed's
~ptiGal recording systems provide only a three megabyte
(twenty-dour megabits) per second record nr read rate. ~t
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that rate, it would take nearly four full days to record or
playback one terabyte of digital data. For current and
future needs, record and playback rates on the order of
three megabytes per second are unacceptably slow. The
National Aeronautics and Space Administration, for example,
anticipates a data rate of 500 megabits per second by the
year 21300 for the Desp Space Network. This is far too much
data; on the order of a five terabyte per day archive rate,
~c~r conventional Qpti~al systems to handle. Accordingly, ;
there is a need f~r an improved optical data storage and
playback apparatus capable of handling data input and
o~,tput rates in excess of 400 megabits per second.
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SLTf~~ARY OF TH~ ~NVENTTON
Conventional optidal recording and playback systems
amplitude modulate a single beam of light with digital data
to record at a rate of approximately twenty-four megabits
5 per second. The optical tape recorder of the present
invention is capable of archiving and retrieving data at
rates in excess of BOO megabias per second by concurrently
writing and/or reading a plura~.ity of data tracks in each
data trace scanx~~d across the light sensitive recording
media: Each of the data tracks (channels? with a multi-
channel data trace records a different predetermined
portion of the data: Thus, the effective read or write
rite is a,ncrease~ over conventional systems by a factor
equivalent to the number of data tracks combined and
1,5 concurrently written o~ read in each mufti-channel data
Mace: Thzs multi~ch~nnel read anted write scheme pravides
enhanced data capacity performance over conventional
magnetic dnd sa.nc~le channel opt~.ca3 systems.
To ach~.eve a multiple data track ger data Mace record
and read, the optical recox°der of the present invention
utilize a mead-write ~nodul~ that outputs a mufti-beam
,allum,inat~.on beam for the data trace including: a mul~i'
channel write beam t~ x~e>~~xd multiple data tracks in each
data tracer a read beam that sans the mufti-channel data
trace to recover the multiple data tracks of recorded data;
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and an autofocus beam to assist in focusing the mufti-
channel write beam and read beam combined within the mufti-
beam illumination beam on the surface of the recording
t
media . Recording and reading multiple data tracks per data
trace reguires accurate combination of the multiple write,
read and autofocus beams into the mufti-beam illumination
beam for scanning across the media. To accomplish this
cc~mb~.nation, the read-write module includes spatial
combining optics and pointing and' translating optics to
1.0 deflect the beams together and accurately position and
orient the multiple write, read and autofocus beams with
respect to each other, thereby ensuring proper alignment
within the illumination beam. ~'he optics of the read-write
module further adjust and separate the individual write,
15 read and autofo~us beams within the illumination beam to
pxovide, accuracy arad efficiency in archiving and retrieving
data at high rates.
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a
ERIEF DE~CRIPTTOhI OF ~I~E DRAWINGS
A more complete understanding of the optical tape ,
recarder of the present invention may be had by reference
to the following Detailed Description in conjunction with
the accompanying Drawings wherein:
FIGURE l illustrates an optical tape recorder system
according to the present invention;
FIGURE 2 is a schematic diagram of the read°write
module for the aptical tape recorder of FIGU~tE 1 showing
~.C7 the spatial combination of the multiple write, read and
autofocus beams into a mufti°beam illumination beam;
FIGURE 3A is a. schematic diagram of a single
polarization embodiment of the write beam s~urce for the
read-write module shown in FIGURE 2; ,.~
1~ FIGURE 3B i~ a schematic diagram of a multi°
polarizati~n embodiment of the write beam source for the
read-wra.te module- shown in FIGURE 2
FIGURE 4 i.s a schematic diagram of the scanning
transm.issive polygon of the read~write head fox the optical
20 tape recordex shown in FIGURE 1 showing the displacement
and translation of the mufti-beam illumination beam
c~mprisad o'f the multiple reed, write and autofocus beams ;
F"IGU~tE 5A iilustra~es the lens wheel of the read-write
p~~ad shown in FTGUR~ 1.:
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FIGURE 5B is a close-up illustration of a portion of
the lens wheel as in FIGt3R.E 5A showing the synchronized
paths of movement of the translated illumination beam and
lenses on the rotating lens wheel; '
FIGT1RE 5C illustrates the field of view of one lens of
the ens wheel wherein tk~e multiple write, read ands
autofocu,s beams of the m~alti-beam illumination beam are
focused on the recording media along ~ data trace.;
FIGURE 5D illustrates the spacing between adjacent
to data tracks in the data trace and the spacing between
adjacent data marks i~ each data track;
FIGU~tE 6 is a cross ectional view of a unitary lens
wheel
FIGtJR~ 7 is a sch~anatic diagram of the recorder shown
~n FIGL?RE 1 including a pair o~ opposed beam expanders
positioned on opposite sides of the scanning transmissive
~rol~gon ' ira tie read-write head of the present a.z~ention
FIGU~ ~ ~:s a s~hemat2c diagram of the mead beam
source and x°ead' array detadtor for the read-write module
shown iri FIGU~ 2 ;
FIGURE 9 is a schematid diagraun of the autofdcus beam
s'ousce and autof~cu~ ear~r detector for the reed~w~ite
module slaowr~ in F"IGU~t7E ~
F'~G10 l.llilstX'a~Ea the astlgmatlC f~GiI,S- error
correcta.on geometry utilized by the autofocus error ~ t
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detector shown in FIGURE ~ to detect focusing errors in the
optical tape recorder shown in FIGURE 1;
FIGURE 11.~ illustrates one embodiment of the optics
for the autofocus system included in the optical tape
recorder of FIGURE 1;
FIGURE 11~ illustrates another embodiment of the
optics for the autdfocus system included in the optical
tape recorder of FTGURE 1; and
FIGURE 11C illustrates still another embodiment of the
20 optics for the autnfocus system included in the optical
tape recorder ~f FIGURE 1.
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DETAILED DESCRIPTION OF' THE D1~AWINGS
Referring now to FIGURE 1, there is shown a schematic
diagram of an optical tape recorder 100 according to the
present invention. The recorder 100 comprises a read-write
module 102 outputting an mufti-beam illumination beam 104
and a read-write head 106 for focusing the mufti-bean
illizmir~ation be~xn an a recording media 108 that is
sensitive to light: Th.e mufti-beam illumination beam 104
may include either ~r both a write beam and a read bean:
The naultz-beam iliuaiin~tion beam 104 may also include other
beams, such as an autofocus beam, combined with the'read
and Barite beaza as needed to perform the desired functions
of t3ae recorder 200. As will be discussed below, the read°
write module 102 includes light s~urces and optics (see
1S F~G~~~ 2,. 3A, 3B, 8 and 9) fir generating and combining
the included multi.~channe~. write;'r~ad and autofocus beams
into the a~ulti-beam illumination beam 104:
~'or purpases of either writing data to or reading data
from the recording media 108, the mufti-beam illumination
beam 1.f34 ~utput by the r~ad-~write module 102 is directed
t~~ra~d t3ae read-writs head 1.06 comprised of a synchronized
sc~nn~.ng transmissive.polygon 110 and rotating lens wheel'
112. The scanning transmissive polygon 110' is rotated
about ~n axis of rotation 1~:3 in the direction indicated by
arrow x.14 by a motor 116 turning a shaft 118 mounted to the °
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11 -
polygon. The lens wheel 112 is rotated about its axis of
rotation 120, in the direction indicated by arrow 122, by
a motor 124 turning a shaft 126 mounted to the lens wheel.
The polygon 110 and lens wheel 112 of the read-write head
function in combination to accurately focus and scan the
mufti-beam illumination beam 104 across the recording media
108 to provide; in a manner to be described, a multiple
data track data trace.
Conventional optical storage devices include only a
l0 single write beam that is focused and scanned across the
recording media by a read-write head to record the data as
a fine optical pattern, commonly referred to as a data
track, comprised of a single line (channel) of closely
spaced, microscopic dots (data marks). To increase the
record and read data rates significantly over the rates
provided by the conv~ntiohal sing~.e channel system, the
read--write module 102 of the present invention - outputs a
mufti-beam illumination beam 1.04 having a plurality of
write b~a~s combined together. This illumination bean 1oa
is f~cused arad scanned across the recording a~aedia 108 dy
the read~write head 1o6 to record the data in a fine
optical pattern (data trace) comprised of multiple da~.a
tracks (channel,s) of closely spaced, microscopic dots (lots
ma~,k~) a~ will be described in more detail with respect to
~S ~; gGS 5G and 5I?. ~y enabling the recorder loo of the
W~ 93122765 PCT/US93/~~~..~2 ~.
~~~~ - lz -
present invention to record multiple data tracks in each
i
data Mace scanned across the recording media, the rate for
archiving and retrieving data is significantly increased
over conventional single channel recorders (by at least a
factor of n where n equals the number data tracks recorded
in each data trace).
Referring now to ~IGUR~ 2, there is shown a schematic
di~g~"am of the read°write module 102 for the aptical
rec~~der lOt? og the present invention. The mufti-beam
Zo illumination beam 104 output by the read-write module 102
comprises a plurality of spatially combined beams,
including a plurality of coZl,ixnated write beams 128, a
dollimated read beam 130 and a collimated autofocus beam ~ .
x,32, each collimated write beam 128 is output by a write
35 beam source 134 (see FIGU~S 3A and 38) amplitude modulated
f,~ a p~edeteranzn~d p~artion of the data to be recorded. The
plurality of write ~ beau soux°ces and means 135 for
madulat~:ng the sources' in r~sp~anse t~ the predetermined
porn~n of the data to be recorded comprise a write sub-
2a ~ module 136 f~r the read--w~~ae module I~2. The collimated
re~c3 beam 1~0: arid cc~7.linated autofocus beam 132 are
;similarly ,;output froze a read beam source and! an autofocus
beam S~u~Ce (nsat showru, see F~CGLTRES 8 and 9) 'included in a
read sub~znodule 138 and autofocus sub-module 1~0,
25 respectively, for the read-write module 102.
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~~193/227~5 . . r P~ d'llJS93I03602
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The read°write module 1.02 further includes spatial
combining optics for combining the plurality of write beams
128, read beam 130 and autofocus beam 132 to form the
mufti-beam illumination beam 104 . The co7 ~ ; m~~rA~ ~,oa~,e
(128, 130 and 132) output by the write, read and autofocus
sub-modules (136, 138 and 140, respectively) are reflected
by a mufti~pane, layered reflector 142 having a plurality
of offset, layered pane mirrors 144. The beams reflected
by the layered reflector 142 are further reflected by a
single pane mirror 146. The angles of reflection for the
panes of the layered reflector 142 and the single pane
mirror 246 are chosen to deflect and spatially combine the
ref3,~cted plurality of write beams 128, read beam 130 and
autofocus beam 132 to converge at a point 148. A two lens
system 150, comprised of an objective lens 150a positioned
at the point 148 and a collimating hens 150b, pro~acts the
mufti-~aea~ illuminate~n beam 7.04, ~ comprised of the
spatially combined write beams 128, read beam 130 and
autgfocus beam Z32, from the read-write module 1.02.
2 ~ Referring noxa to FTGIJR~ 3A, there is shown a sche~aatic
diagram of a single-polarization embodiment of the y~rite
beam source 234 utilized in the write Bulb-module 136 of the
read-write moeiule 1.~2. A laser diode ~ 152 of a
redetermined
p polari~at~.on and wavelength outputs light
that is collimated b a le s
y n 154 a.nto a collimated wrote
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beam 128. The write beam 128, as output from the write
beam source 134 , is spatially combined with the write beams
output from the other write beam sources 134(n) of the
write sub--module 136, the read beam 130 and the autofocus
beam 132. The position of the write beam 128, as output
from the write beam source 134, within the multi~beam
illumination beam 104 is circularized by an anamorphic
prism pair 158, translated by an adjustable di placement
plate 156 and painted by an . adjustable risley prism pair
159 to accurately position and orient the beam with respect
to the other included beams (read, write and autofocus) to
ensure proper alignment and separation of the multiple
beams within the multi~beam illumination beam.
Referring now to FIG(TRE 3~, there is shown a schematic
da.agran~ view of a multi-polarization embodiment of the
write beam source x.34' utilized in tie write sub-module 136
~f the read~write module 102. The multi~polarization
em~odim~n~ of the write beam source 134' utilizes a
dielectric polari.zer 160 (that through transmits s.~
polara:~~d light anrl reflects p-polarized light) to combine
an s~polarized collimated wrat~ beam 162 channel with a p--
~?o~.~rized ,,c~ll~;~ated write bean 164 channel emitted by
laser diodes 152 of nearly equal wavelength ~to output a
do~:bine~ polarizati~n collimated write beam 128' . With the
polar~.zat~.on combined write beam source 134' the output '
s
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V~~ 93122765 ~ ~ ~ -~.y ~ PCT/IJS93/03602
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power of the write beam 128' is significantly increased.
Each polarization channel utilizes an anamorphic prism pair '
158 to circularize the beam, an adjustable displacement .
plate 156 for translating the beam and an adjustable risley
prism pair 159 for pointing the beam to accurately position
the s- and p-polarized laeams, 162 and 164, respectively, at
the dielectzic pola~°i~er 160. The displaceanent plate 156
and risley prism pair 159 also function to accurately
po~~a~.on and arien~t the write beam 128', as output by the
write beam source 13 4 ' , with respect to the other . write
beams 128', read beam 130 and autofocus beam 132 to ensure
p~opeg alignment and separation within the mufti-beam
a~.l~xnination beam x.04.
As h~wn in FIGUIRE 1; the mufti-beam illumination beam
1.04, including the multiple collimated write beams 128
emitted from the read=writs module 102, is directed toward
the 'scanning txansm~.ssive polygon 110 of the mead-write
head 1~6. Referring now to FIGURE 4, there is shown a
sch~ma°tic diagram of the scanning trans~i~sive polygon 110.
T.t~e ppl,yg~n 110 is c~mprised o~ a puce of optical quality
transparent ma~,erial having an even number ~f sides 166
~r~a~~ed in''oPpo~ed parallel pairs. The polygon llo is
pcasiti~ned ~o receive the mu3.t~-beam illumination beam l04
Q that the beam is transmitted through th~ polygon and
r~~~sct~d by one of tie op~aosed pairs of parallel sides
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166. The refracted beam is thus displaced without changing
the direction of (i.e., parallel to) the callimated beam
104 received by and transmitted through the polygon 110.
Rotation of the polygon 110 about axis 113 (in the
direction shown by arrow 114) causes the thraugh
transmitted and displaced mufti-beam illumination beam 104
to translate and repeatedly scan, in the direction
indicated by arxow ~16~; along a linear path: 170 (shown also
in detail as a solid line in FIGURE 5~) . The displaced
mufti-beat illumination beam 104 will scan, as the polygon
110 rotates, along path 170 from a first position,
ge~~rally indichted by the output beam'172 for the solid
link p~lygon, to a e~or~d pdsiti.on, ~enerall~ indicated by
the output beam 174 for the dashed line polyg~n.' One scan
of the beam along the path 170 occurs for each ~pposed pair
of -parallel sides x.66 refracting the through transmitted
mult,i-beam illumination beam 104 as the polygon 110
,,.
:rotates::
Re~er~a,ng again to FIGURE 1, the through transmitted
and'da.splaced scanning mufti-beam illumin~taon beam 104 is
directed toward the rotating lens wheel 112. Referring nom
' ~ to FIGURE SA, there is' shown an illustration of the lens
'
wheel 112 of the present invention. The lens
wheel 11~ has
s
a disk shape and compra,ses a plurality of individual Lenses
176 positioned with equal spacing about the circumference
~CJ~ 9/22765 P~lUS93/d~3602
- 17 -
of the disc. The individual lenses 176 successively
receive and focus the mufti-beam illumination beam 104 onto
the recording media 108. The lens wheel is preferably a
unitarily formed disk-shaped piece of optical quality
material having the plurality of lenses 176 precision
molded or diamond point turned therein. Each lens 176 array
alternat~,vely be manufactured individually, separate and
apart from the lens wheel 112; and inserted and secured
within a plurality of openings forzaed about the
c~.rcu~nference of the lens wheel disc. Separate manufacture .
and installation of indiv,idua~. lenses 176 is not preferred,
h~wever, as ~.h~ unitary lens wheel 1I2 described above more
accurately performs ane~ may be manufactured less ..
~xpensa.vely and rep~od~acecl more consistently.
~s th~,lens wheel 112 is rotated about its center 120
by the,motor 1~4 (FI~tTR~ 1), successive individual lenses
x76 about the circumference of the wheel m~mentarily
~eee~;~e and focus the mufti-beam i.lluxnination beam 104 on
'the recording meeiia 108. F~cusing of the mufti-beam
illuz~i~at3can laeam 104 by ~ dens 176 occurs only when the
lens momentara.ly moves thr~uc~h an active area 178 on the
~.~ns'wheel 112 generally correspcanding to the 1~cation of
the recording ~aedia 108 and the area where the ~nulti-beam
illu~aiz~ation beam 1.0~ illuminates the lens wheel. Rotation
of the lens wheel 112 in the direction shown by arrow 122
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causes successive individual lenses 176 to follow an
arcuate path 180 (shown in detail as a broken line in
FIG~TI~E SE) through the active area 1.78. The path 180
consists of a portion of the circumferential path within '
the active area 178 f~llowed by the center of each lens 176
as the lens wheel 112 rotates. Each lens 176 passing
through the active area 178 receives and focuses the
incident mufti-beam illumination beam 304 onto the
retarding media 108 to scan a data trace 182 across the
width of the media. With movement of the recording media
1(7g in a direction (shown by arrow 184) Perpendicular to
the direction of the- race 182 and rotation of the lens
wh~e1 112 (shown by arrow 122), successive lenses 176
bet~me active to scan out successive para17.e1 and adjacent
data traces across tlae recording media.
The linear path 170 followed '~y the scanning mufti-
~ea~ illumination beam 104 amd arcuate path 180 followed by
each ~.ens 1;76 on the routing ~.ens wheel 112 through the ,
acta:ve ~:re~ 178 are shown superimposed over each other in
FIT 5F1, mhe muftibeam illumination beam 1Q4 (shown
ill.umi~ating a circular area 1~6 ~n the lens wheel that is
lightly larger thin the diameter of a lens v1~76y.
illuminates a portion of the active area 178, while
scanning Tong pith 17C~, between the broken lines 188.
Full illu~nanation of each successive lens I76 moving along
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path 180 by the scanning of the multi-beam illumination
beam 104 along path 170 to scan successive parallel data
traces 182 first requires treat the position of the paths be
substantially aligned (as shown in FIGURE 5B). A slight
deviation between the paths as Shawn caused by the lens
path 180 being'arcuate and the scan path 170 being linear
i.s permissible due to the size of the area between lines
188 that will be illuminated.
Referring now o FIGURES 1, 4, 5A and 5E, full
l0 illumination of each successive lens 176 further requires
that the movement of each scan of the multi-beam
illumination beam 104 along path 170 be synchronized to
cgincide with the movement of each successive lens along
path x;80 through the active area 178. With
synchronizaa~.on, the circular area 186 illuminated on the
~:ens wheel 112'will fully illuminate each lens 176 as the
lens waves through the active area 17f thereby -achieving
the smallest possible bit diameter on the recording media
108 a~ p~ssible fox° each of the anultiple data tracks
reco~d~d in sash data tr~.ce 182 a~ will be described. To
achieve full illumination, the actuation of the motors 116
anc~ 124 for ; the polygon 110 and lens wheel 112,
respectively, are ~ontr~lled for synchronization, as
generally indic~t~d ~t 19a, such that one scan of the
~~ mufti--beam illumination beam 104 along linear path 1.70 will
i~V~ 93/22765 , ,
PCf/U~93J036~','t
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- 20 -
occur for and correspond with the movement of each lens 176
a.
through the active area 1.78 along arcuate path 180.
Referring now to FIGURE 5C, there is shown the field
of view 192 of the mufti-beam illumination beam 104 as
focused on the recording media 108 by a lens 176 of the
.lens wheel 112. As discussed above with respect to FIGURE
2, in order to provide the increased archive and retrieval
data rates for the optical recorder 100 of the present
invention, the mufti-beam: illumin~ti~n beam 104 includes a
mul~i-ch~.nnel write bean 128 output by the n write sources
134(n) in the wrzte sub-module 136. Thus, each data trace
x.82 on the rec~rdi.ng media 108 will be comprised of n
channe~a of rec~rded data. Each channel of data is
recorded on the recording media 108 as a data track 194
(see also FIGURE 5D) within the data trace 182. The
posita.on of each write beam 128 within the mufti-beam
i~:lmnination ~aeaan 104 is controlled by the pointing and
trans~,ati.ng optics (see FTGURES 3~ and 3B) such that the
multipi.e channels ire separated from each other to
2~ i.llu~inate separate and d:isti.x~~t write spots 195 within the
field ~f view 192 as f~cu~ed on the recording media 108.
As .oho, there arm thiY°ty-two write spots corresponding to
the n = 32 write ~ou~ces 134 and data channels in the write
s~-~~dule 136. .The permissihle number of write sources
25 134(n) inc~.~aded in the optical recorder 300 is limited by _
.. ... " ....: , :.. _._.. . .:,..,, ..:; .., :, ::: ..:::~ :::~ .. :.. v ~~
~.: .: w:.: .;::
.,
t.
...:,: .. ...,. ...-:... :v.. , :_, .;;: ;.: ;;,~; , :;. ;.~ . ,,,. ,..
. . : . .. .. . .. .. :': . . ... .. : .. ..,...,. .. . . ... . .. . .... . :
: .. ,: . . .. ;. ~. . _ .. . .. .
w~ 93rxz7ss ~crr~u~~~io~oz
v,- ~:.~..~
- 21 - ,
the chosen size of the field of view 192 and the accuracy
1
of the spatial combining optics shown in FIGURE 2.
Referring now to FIGURE 5D, there is illustrated a
k
piece of recording media 108, within a portion of a data '
track 182 as shown in FIGURE 5C, illustrating the marking
of the light sensitive media by the multiple write beams
128 of the fodused raulti-beam illumination beam 104 to
recprd the data. portions of two data tracks 194 within a
data trace 182 are shown: The spacing between the centers
Z0 of adjacent data ti°acks 194 in a data trace 182 is
~ppraximately one and a half microns with the centers of
adjacent data max°ks 196 within a data track 194 separated
bY ~~proximately one micron. Referring again to FIGURES
3~, 3~ and SG, the displacement plate 156 and risley prism .
~5 Pa~.r 158 are ~djus~ed for each write beam source 134 to .
transl~t~ and point each write beaan 128 for accurate
po~gt~;oning and arien~ation of the plurality of collimated
be~~as w~.th respect ~o each other within the multi-beam
illt~tin~tion be~a~ 104 a~ projected within the field of vie~r
20 192 can the recording media 10~. Froper translation and
pointing ensures an ~pproxi~~te one and a half micron
~p~~ing between adjacent data'tracks 194. The modulation v.
of the write sources 134 by the data to be recorded is also
~'~~Wated, i~a acc~rdance with the predetermined rotational
2 5 velocity of the lens wheel 112, to maintain proper one
W~ 93J2z7~55 PCT/~JS9310360
..f;
~~.34325
- 22 -
i
micron (approximate) spacing between adjacent data marks
7.96 in a data track 194. Adjustment of the spacing between
adj scent data tracks 194 and adj scent data marks 196 in the
manner indicated maximises data storage density while
maintaining system data recording and recovery accuracy.
Referring now to FIGURES 1-5D, to record data on the
recording media 108, the intensity of the collimated write
beams 128 output by the write sub-module 136 is adjusted
such that the beam wi3l mark the Light sensitive media.
each write beam 128 is axaplitud~ modulated (on/off)
according to the means 135 by a predetermined portion of
the data, carried by a data signal, to be recorded. The
plurality of write beams 128 are spatially combined within
the read-write m~dtale 1.02 to form the mufti-beam
illumination beam 104, translated by the scanning polygon
110 and focused on the media by the lenses 176 of the
rotating lens wheel. 112 to scan multiple data tracks 194
caathir~ ~ach,data trace 182. Translation of the media in a
direction (shown' by arraw 184) perpendicular to the
rotation of the lens wheel 112 allows a plurality of data
traces 182 to be rec~rded adjacent to each other on the
media lOS .
For e~cample, the lens wheel 112 may include twelve
lenses 176 and be rotated at 6,500 revolutions per minute.
This results ~.n a scan of 1, 300 lenses 176 across a 3/4
.. .: ". .. .. . , . . , :. . ; ; : v 'r . .; ,., . . ; . ,:
. . . .; ~ . ~ '
iN~ 13J22765 P~I'J~1S93J03502
f:;~:~
- 23 -
inch wide tape 108 every second. Assuming a one micron
spacing between adjacent marks 19~, if one channel (data
track 194) of data is written per data trace 182 (as in the
prior art conventional optical recorder), 19,000
unformatted data samples will be written across the tape
media 108 in each data track. This.is equivalent to an
unformatted twenty-four megabit per secanr3 archive rate.
With the mu3ti~channel recording capability of the optical
recorder l00 of the present invention, a thirty-two (n=32)
channel (data track 194) per data trace 282 write beam
128(n) (as shown in FIGURE 5C) is provided resulting in an
u~,~e~atted archive rite in excess of 760 megabits per
second. This a~cl~iv~ rate wily easily satisfy the design
goal of a X00 megabyte per second archive rate rec~uuired for
handling current and future data recording needs.
g~ef~rring now to F'IGU~ 6, there is shown a cross-
seed.ona.l view of the uxrita~y lens wheel 112 ~ hawing a
plurality oaf precision molded or diamond point turned
o lenses 176 p~siti~n~d abo~~ the circumference of a disk
shaped body. ~Yae preferred optical lens desi n for each
q
lens 176 in the lens wheel 112 is a piano-convex singlet
ha~rirag an aspher~:c figure on the convex side 198. The use
of a piano surface 200 in conjunction with a convex powered
surface 198 prova.des for a less complex lens design by
removing the alignment tolerances associated with centering
i~dJ 93/22765 PC,'TfU~93/~36~2
~~
.'~
- 24 -
two powered surfaces to ether
g (as in a double-convex or
concave-convex design). The piano-convex design is further
preferred because the design minimizes the wedge between
included optical surfaces in the lens and the piano surface
provides a useful reference flat. Thus, the piano-convex
design using a convex surface 198 coupled to a piano
surface 200 provides for easier, less expensive and more
efficient fabrication, testing and assembly of the lens
wheel 112.
With a lens design where one surface (the aspheric
surface 198) prov~.des the majority of the focusing power,
an optical material with a refractive index exceeding 2.25
(far example, "Gl:eartran°' zinc sulfide) is preferably used
for fabricata.ng each lens 176. In the preferred
embodiment, the ~ntir~ lens wheel 112 (as shown in FTGURE
6) , including the disc support structure and the individual
lenses, i~ un.itarily ,fabricated . from the highly refractive
~pt.ical, duality material usa:ng precision molding or diamond
ppint turning techna:ques. Precision molding of the
indiva.ciual lenses 176 with the disk substrate of the lens
wheel f~~s ~ unitary lens wheel 112 possessing the
advantages Qf ; being consistently accurate,' easily
reproducible .and interchangeable. In the alternative,
after ~:ndividual fabrication of each lens 176 from the
~5 preferred optical material, the lenses are inserted and '
. _ . . . . , ... : -: . .., . , ;. .; ..... .. ; .; .:, _ . : .: . ::--. : -
. : ~ . .; . ; . ; . . ; .
.f ". . . . : . . ,. , , .. _ . . . . . . ,
wc~ ~~rzz76~ P~ri~s93io3~oa
f
secured in one of a plurality of openings around the
c~.rcumference of the disk-shaped lens wheel 112 in
accordance with the teachings of~the prior art.
i
As mentioned above, the lens wheel 112 used in the
read-write heaa~ 106 has a disk shape unitarily formed from
an optical quality material using precision molding or
diamond point turning techniques. Tf precision molding
techniques are employed; a master lens wheel that is .
essentially a negati~re of the optacal surface desired on
the dens wheel is used to form the lens wheel. To .
fabricate the lens w~.eel la2 from. the master, a~ high
c~ual.aty optical polymer or specially formulated glass is
precision molded a.n ~cco~rdance with the shape of the
master. In the altegnative; a flat high quality optical
substrate serves as a base for deposition of a thin epoxy
layer, with the mater melding the lenses into the epoxy to
~abriaa~e the c~h~el.
I f .refractwe optics are to be used for each
individual lens 176 on the lens wheel 112, the master is
2 ~ created using ccanv~ntional diamond turning and polishing
techniques. hf di:ffractive optics are to be used, either
li~h~graphy, oz° dli~mond turning are used t~ create the
,.
master. Diffractiv~ lenses:~x°e typically modelled and
fabricht~d as e~.thez° ki.noforms rar binary lenses. A fresnel
25 lens ~:s a specific tlrpe ~~ kinoform. The smooth surfaces
... . >. .. . . ~ ; , . . .;, . , ..: ...
~.... . . . . .
!~'~ 93122765 PCT/US~310~ ~2
b~~.~43~~ w
of kinoforms are apprr~ximated using flat surfaces and step
functions (binary optics). Flat surface approximated _
kinoforms are manufactured using diamond turning
techniques. binary optics are manufactured using either
photolithography or electron beam lithography by
iteratively masking and etching a substrate. Once the lens
type (refractive or diffractivey and manufacturing method
are determined, the master is fabricated according to the
preferred method: A plurality of lens wheels are then
1p manufactured from the master using precision molding with
the resulting lens wheels being identical, interchangeable
and functional over a broad wavelength range. the lenses
wil l also have substantially identical back focal
distances, aind and aberrations due to lens design are
1.5 consistently present across all lenses on the wheel.
Fte~erring again to FIGURE 4, for several mechanical
and optical per~ox~nance optixnizati.on reasons discussed
below, the nu~;ber of opp~sed pairs of sides 165 for the
~olyg~ra 1I0 shoulr~ be maximised (as a function of resulting
20 a~ncrease~ in ~aanufacturing: complexity and cost). One
benefit obtained from increasing the number of opposed
i
sides 1,66 as , that the polygon 1.10 more closely resembles a
disk thereby ~ecreacing .~h~ effects of windage as the
polygon rotates. F'urther~ore; an increase in the number of
25 opposed sides lfi~ decreases the rotational velocity of the
.
b~'~ 93122765 PC'd'/~JS93/~D36~2
y.
27 -
polygon 110 required for a fixed rotational speed of the t
i
lens wheel 112. This is important because high rotational
velocities for the polygon 110 load the motor 116 and '
induce optical barefrangence in some optical materials
chosen for fabrication of the polygon. Finally, increasing
the number of :opposed sides 16G of the polygon 110
decreases the maximum angle s~f incidence of the multi-beam
illumination beam 1Q4: This reduces variations in fresnel
refledtion coefficien~.s and enables the use of both s- and
p-polarized light for the multi-beam illumination beam 104
to increase recorder bandwidth (see, for example, the
mult~.-polarization writs beam in FIGiJRE 3H)
Referring now to- FIGURE 7, the read-write head 106 for
the optical tape recorder 1.n0 of the present in~r~:ntion (see
FIGURE 1) is shown f~,rtlaer a.ncluding a gair of beam
expanders 202 positioned along the multi~beam iZlur~ination
beam 104 on mach side ~f the'scannir~g trans~issive polygon
x..10 s H~~m expander 202a is l.c~cated between the scanning
polygon 110 and the read-write module I02: Heam expander
2c~ 202b is ,located 'between the scanning polygon 310 and the
lens wheel x:1.2,' The use of a pair of beam expanders 202
provides a ~demaga~ifi:catiort-aaagni.fication system around the
poiyg~~ 1.1.~ that nax~ro~s the diameter of the mufti-beam
illu~inat~.on be~~ 1,~4 incident on and transmitted through
.: . ,._~. -.. : - . .. ,, ,, , - _ . ,-,..: v, ;.- ;-.v .. . ':.' : , , , ,;
.r
". ,":. , . ... ,.,. ... .:.. ... ....
.. ,... ., " ,. . .. . : ...:.. ,:. . . . . .
~V~ 93/22765 - P~T/US93/036~2 ;::.
:.
. ...
~,~~ 4~2
.. - 28 -
..,
the polygon and expands the diameter of the beam output
from the polygon.
With a smaller diameter multi-beam illumination beam ~ .:;
104 transmitted through the polygon, the size and shape of ~ ;
the polygon may be scaled as desired in accordance with
manufacturing complexity and cost concerns while realizing
the mechanical and optical performance benefits of an
increased number of sides 166 as discussed above. An
additional benefit from scaling the size of the polygon 110
is a less stringent manufacturing specification for the
parallelism of opposing sides 166 causing a corresponding
decrease ~.n polygon manufacturing costs. Furthermore, by
narrowing the diameter of the mufti-beam illumination beam
104 transmitted through the scanning polygon 110, the duty
7.5 cycle of the system is increased.
Referring now to FIGURE 8, there is shown a schematic
view of the read sub-module 138 within the read-write
~odula 102. The read sub°-module includes a read source 204
(similar to the ~rrite source 134 shown in FI~UR~ 3A) for
outputting a collimated read beam 130. The read source 204
includes an anam~rphic prism pair 158, a displacement plate
156 and risley'p~ism pair 159 for shaping, translating and
pointing the read beam 130 output by a laser diode 154 and
collimated by a lens 154. In particular, the anamorphic
prism pair 158 shapes the read beam 130 forming a ~ ,
r.. i .:~ ~'..~'~.. ~ . ~..., ...
t,,. , ~ "-~ ,,:;Y ,
;:.,:;:, 1~~ 93J~x765 PCfJ~JS93103602
~~,; ..n..f .. . y
2 ~ - i
rectangular illumination field 246 within the field of view
192 as focused on the media 1.08 (see FIGL7RE 5Cj to ~
illuminate across the multiple data tracks 184 (channels]
of a recorded data trace x.82. The pointing and translating
optics of the read source 204 also function to accurately
position and orient the read beam 23~ with respect'to the
mu3'~ipl~ write beams 128 and ~autof~cus beam 132 to ensure
proper alignment of the multiple beats within the multi-
beam illumination beam 1o4. The pblari:zation of the read
~
.
2o J
beam 1.30 is Changed by forty~five degrees by passing the
beam through a quarter-wave plate 208.
Referring again to FTGUFtES 1, 2, 5C arasi 5D, the
rectangular pattern 20f of the ~eadbeam 130 is scanned by
the rotating lens wheel 21.2 along the length of a data
trace 182 to be modulated by the data marks 156 of the
mina ipl a data trac~CS 19 ~ ( channel s j therein . The mufti--
channel -modulated read beam- 1.30 is reflected by- the media
1~8 back thxough the rotating lens wheel 112 and scanning'
transmass~.v~ polyg~n ~.~.0 of the gead-write head 106 t~ the
read: sub-module 138 of the read~write moriule '102. As shown'
in FIGURE 8,'tMe p~l~rization of the modulated read beam
l
~.1~0'is rotated an additional forty-five degrees (~~for a
total ~f ninetqr degrees and a c~a~rage, for exa~aple, from s~
to p~p~lari~ati~nj by the quarter-wave piste 208. The
m~dulated read beam 130 is then zeflected by a polarisation
~t~ 93I2z76S ~ ~ ~. PCTILJS93/03602
f
° 30 °
beam splitter 210 and imaged on a linear photodiode array
212 by a magnification system 214. The linear ph~todiode
array 27.2 preferably comprises a plurality of avalanche
photodiodes or PIN photodiodes that produce electrical '
signals in accordance with the mufti°channel modulation of
the read beam 130 to recover each channel (data track lg4)
of data scanned within each data trace 182. The multiple
charnels of data arm then reassembled in proper order to
recover the data signal.
7L0 ~2ef~rring now to FIGURE 9, there is shown a schematic
view of the autof~cus sub°module 140 within the read-~irite
module 102. The autofocus sub-module includes an autofocus
so~.rce 21.6 (sa~milar to the write source 134 shown in FIGURF
3A) for outputting,a collimated autofocus beam 132. The
autofoctas source 216 includes an anamorphic prism pair 158,
a displacement plate 1:56 and a ri~'ey prism pair 159 for
shapi.a~g; ~ransla~ing and Pointing the autofocus~ beam 132
output by a laser diode 152 and c~llimated by a lens 154.
The po.in,ting and translating optics of th.e autofocus source
216 shape the aut~focu~ beam 132 for focusing to a spot 218
see FI~U12E 5~) on ' the ~aedia 108. The painting and
~tra~slating opti;~s further function ;to accurately: position
and orient the .autofocus beam 132 with respect to the
mul.t~.ple s~gite k~eam~ 12~ and read beam 130 to ensure proper
aliment of the multiple beams within the mufti-beam '
r, . . :: , .. . .. . ,; .: . , .,: : .. . ; . , , ; ... - ,.;. . , . . . ;: ;
. ~ ::
s ..;. ::.. ;;:: :;-:. .;. : , . ~: .. , ..- ;: .: . ; " ,,, , ,: .. ; .
... . ..
W~ 93/22755 ~ ~ ~ 3: ~ ~ ~C'I'/~JS93/036df2
t, ,r~ : F
f
31 -
illumination began 104 as focused on the recording media
w~ ~3rzz°~ss ~ ~ ~ pcrius~~r~3~o2
- 32 -
i
Many autofocus techniques may be employed. For
1
example, referring to FIGURE 10, there is shown a geometry ,
utilizing the autofocus detection system shown in FIGURE 9
to detect focusing errors. The distance "D" represents the
distance between the write lens 176 of the lens wheel 112
and the astigmatic lens 228. The distance "fo" represents
the focal length ~f the lens 176 on the lens wheel 112.
The distances "~~'° and '°fz" represent the focal lengths of
the astigmatic-lens 228. The distance "d" represents the
distance between th~,astiga~atic lens 228 and the guadrant
detector 224 and is given by the following equation
d _ 2 ( ft) ( f2) ~ (ft + gz) .
If tie distance d is set according to the above ee~uation,
then the astigmatic lens 228 focuses a circular
illua~anation spot on the quadrant detector 224 for the
reflected autof~cus beam 132 when the error distance "err"
between'the re~c~rdi.ng media 108 and the focal plane of the
write ~.ens x.76 is zexo (a.e~. the autofocus beam is focused
on the'media). When the aut~f~cus beam is not focused on
he recordia~g media 108; the error distance err is non-zero
'and the astic~ati.c lens 228 focuses an elliptical
~:~:luaaina~ion spot on tY~e r~uadrant detector 224.
sacra g~a~ir~nt 2 3 0 ( a. ) -2 ~ 0 ( 4 ) of the detector 2 2 4
outputs a cnrrespending signal (~1-Q4) proportional to the
intensity og the fight from the ref3ected autofocus beam - x
. r~o ~~~zx~ss ~ ~ ~ ~ ~ ~ ~ ~c.-rms~3~o3~oz
- 33 -
132 focused thereon by the astigmatic lens 228. The
signals Q1-Q4 may be used to determine a focus error signal
(FES) indicative of whether the mufti-beam illumination
beam 104 is properly focused an the media LO8. The FES is
determined in accordance with the following equation:
FES -- [(QZ + Q3) (Q2,+ Q4)] / [Q1 + Q2 + Q3 + g4].
The F'ES is output from a signal processor 232 implementing
the above equation tca control the adjustment of the read-
wr~ae head 106 in a manner to be described to fcacus the
o mufti-bean illumination beam'on the recording media 108.
When the error distance "err" is positive (i.e., the
distance between the media 108 and the write lens 176 is
greater than fo);;the vertical~diameter of the elliptical
illumination spot across quadrants 230(2) and 230(4) is
1S greater than the horiz~ntal diameter across quadrants
230 (1) and 230 (3) . Thus, the sigr?als Q2 and Q4 will be
greater khan the signals Q1. and Q3. The FES determined by
the above stated equation will therdfore be.negative. The
opposite is rue when the distance between the media 108
2Q and the write lens I76 is less than fa. If the error
distance "err" is zero (i.e:, the mufti-beam illumination
~eam~l0h isfocused on the media lpg); 'the,illumination~
spot on the ~xadrant detector' 224 wily be eircular and the
ignals Q1°S2~ will be substantially equal to each other
ddlJ 93IxZ765 PC'Tl~J~93/036#~Z
c . . ~:.::.::Y !
~,~~~~~~ 34 w ,.
(because the vertical and horizontal diameters of the spot
are equal ) , resulting in an FES substantially equal to zero .
Reference is now made to FIGURES 11A-11C wherein there
are shown seve~ca.l embodiments for the autofocus error
correction system 234 in the read-write head 106 for the
optical recorder 100. The embodiments of FIGURES 11A and
118 illustrate lens translation methods for providing
autofocrxs error cc~~rectzon. The embodiment of FIGURE 11C
illustrates a media translate~n method for providing
autbfocus error correction. The translation of either lens
ox media for the error correction system of each embodiment
is controlled by the sign (either positive or negative) of
the focus error signal ( FES ) generated by the processor 2 3 2
accord,irag to the equation above in response to the signals
Q1°°Q4 ou~pu~ by the quadrant detector 224 (see FIGURES J
and I O ) , ~
I~, the ea~boc3ixnent for the autofocus error correcti~n
sYs~~m 234 illustrated in FIGURE 11A, a pair of autofocus
lenses 236 are posata.oned in line with the mufti-beam .
illumination bean 104, including the multiple write, read
end autofocus beams, between the read-write module 102 and
thte sc~nnin~ tra,nsma~si~r~ polygon 3:10. A' servomotor 238'
i ~ ~
adjusts (translate) the position of a first one of the
au~ofocus lenses (lens 23Ca), back and forth in the
direction indicated by the two-headed arrow 140, along the
.:..-:, ~~ 9122765 ~ ~, ~ y ~ ~ PL'I"IU~93/03602
,:-.,.. .. ;
. ,. ..
- 35 _ . .
Path of the mufti-beam illumination beam 104. The
i
translation of the autofocus lens 236a by the servomotor
238 is controlled by the sign of the focus error signal
output from the autofocus sub-module 240 of the read-write
module 102 such that the focus of the mufti-beam
illumination beam 104 occurs at the recording media 108.
One drawback experienced with this autofocus method is the
difficulty in designing the fixed autofocus lens 236b and
wxite lens 176 to correct for the varying amounts of
-10 spherical aberration produced by translation of the
autofacus lens 236a.
pn~ way to avoid the spherical aberration drawbacks
encountered w~.th the emb~diment of FIGURE 11A is to
t~°anslate each write lens 17 ~ on he rotating lens wheel
15 112; as shown in the embodiment i~.lustrated in FIGURE 118.
The se~vomot~~° 238 i~ mounted on the lens wheel 1I2 and
connected to t~°anslate each write lens 176 back and forth
in the da.r~cti~ns indicated by the two-headed arxow 240 for
focusing the mufti-~bea~ illumination beam 104 on the
20 reco~cding media 108: Trar~s~.ation ~f the write lens 176
occtars within the ~trudtux°~ of the lens wheel disk in
,response to the; sign ~f the focus error signal (FES)
recei~red fr~m the autofocus sub-module 140 'of the read-
write a~~dul.e 102. This ; technique; however, is not
2~ . P~'efe~'~'ed due to the increased compleacity of the servomotor
Y
- ~ n S ;'. . . . .:~ ~-.:. ,..: ~.,. . . ..... . ."'. .~ ,, ' .ri.
S ,
........ ." ...'..' . -. : :.; ...n ":..:. .,-....:., ~.~:.;. . . .,y.-,. .
....... ~:~ ..y.. .. ".:..., , '.:":v . ,:.:'~.,, . : '~ ,. ,'. :.:n' : , ;,:
.,.. ':. :~ ,:..v.. :. .; h,. .,.. !: ..,..,
to Y 5. ..
p .. . . I ,. .,.., . . . . . .. . ,...,
..1...".u.... .,. n .... .. . ... . .. ...... , ., . .n . .... ,.. . ... .l...
w ... ,. .. . . ,
i
w~ ~~izz'6s ~ ~~rm~g~io~soz
.,
°:~::,' ,
- 36 -
and lens wheel 212 required for translating each individual
lens in the lens wheel.
An alternate means for avoiding both the spherical
aberration servomotor actuation drawbacks described above
is to translate the recording media 108 as illustrated in
the embodiment of FIGLTFtE 1ZC. An air plate 242 is
positioned under the moving recording media 108 on the
oppesite side from the rotatang lens wheel 112. Movement
of'the recording media lg8 back and forth an the directions
indicated by the two-headed arrow 240 is effectuated by an
array of air nozzles 244 expelling air through the air
plate 242 against the underside of the media. The amount
of mo~rement for the media 208 along arrow 140 is controlled
not on;llr by the amount of air expelled by the air nozzles
244; but also by the amount of tension appl~.ed to the media
108 while p~s~ing over the air date 242. A control
circuit 2~6 responsive to the sign of the FES output by the
auto~ocus sub-module 140 adjusts the aauount of air expelled
via control. line 248 and further adjusts the tension on the
2 0 med~:a 10~ , as generally indicated at 250, to props r l y
~as~tion the ~aedi:a fir focusing the rnulti~-beam illum~.nation
beam 104: 4 - ,
Although several embodiments of the optical tape
recorder og the present invention have been described in
the foregoangf Detailed Description and illustrated in the
F
3
', . ,.'.:; ~........ .~,...,, , ... ... , ... ,.. ; . ,, . .,.... ...:~,...
... , ... '~:., ~ , ., : ,
L .'. ,..:.. ,; ....,,. : .. ,';r.'.., ' .~;: . ,~.'.. :: :.. ,~ ~ '
..:.:..._.... ;..~ ....,:., , ..., , ~.. .., ,
!'CT/US9~/03602
__ ~'~'~3/22765 '~ ~ ~ ~ '~.~ ,
i:,a::;: 1
- 37 -
accompanying Drawing, it will be understood that the
a
invention is not limited to the eaabodiments disclosed, but
is capable of numerous rearrangements, substitutions and
modifications without departing from the spirit of the
inventionv
