Note: Descriptions are shown in the official language in which they were submitted.
l~Z~481
Backqround of the Invention
One of the main problems with electrophotographic
copiers arises from thc desire for speed in copy production.
After a photoconductor has been charged, the energy required
to produce a latent image in light and shade of the oriqinal
of sufficient contrast to produce an acceptable copy is a
~unction of the quantum of light falling upon the photo-
conductor and the light sensitivity of the photoconductor.
Ideally, the illumination of the photoconductor should be
such that the brightest part of the image will be fully
discharged while the darke~t part of the imag~a will leave
the photoconductor fully charged. In practice, th~s ls
never achieved, owing to the limits of the light response
of known photoconductors. In the current state of the art
lS of photocopying machlnes, when the speed of producing copies
exceeds about 30 copies per minute, the energy required to
operate the copier approaches 1500 watts. Since the ordinary
potential in office and house wiring is 110 volts, the power
from a given outlet is limited to 1500 watts. Accordinqly,
to produce satisfactory coples at a higher rate, a ~peclal
electrical installatlon will be required. This mean~ that
the copying machine cannot be decentralized, but mu~t be
located in the region of the hlgher voltage outlet. Purther-
more, the high energy will produce thermal pro~lems, both ln
respect of the photoconductor and in the environment, aslda
from the expense of energy consumption. Becau~e of the~e
.
ilZ~
problems, many effort~ are being made to increa~o the
light sensit~vity of photoconductor~.
Field of the Invention
My invention relstes to a novel method of
increasing the effective sensitivity of photoconductors,
thus enabling me to increase the speed of electrophoto-
graphic reproduction of documents.
Description of the Prior Art
The following art is of interest in respect of
or i8 referred to in this specification:
Steinhilper ......... Patent 2,756,676
Schaefer et al ...... Patent 3,892,481
Hayashi et al ....... Patent 3,907,423
BrooXe .............. Patent 3,912,3~7
Brooke .......... ~... Patent 3,994,723
Steinhilper, which will be discus~ed more fully
hereinafter, propose~ to maXe multiple copie~ of an image
produced from a 3ingle light exposuro of an original. He
recharges the photoconductor after each transor of n de-
veloped image and cnhances the recharged image by sub~ectlng
it to illumination. There is no teaching o lncreasing the
speed o the xerographic reproduction proces~. The appa-
ratus shown by Steinhilper has only one development ~tatlon.
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1129481
rl~he.re is no o~tica:l maskinc~ station. There is no sho~7illc~
of a biasc~cl toncr app:licator at ~ toni.nc3 station where
optical shie:ld.in(l is achievc(~.
Schaefer et al show an aut:omatic control system
for bias:incJ a deve,~opment elec-trode. 'l'his system can be
used both for the mask-formirlg step, which is a salient
feature of my inventi.on, and for the development step as
taught by Schaefer et al.
}~ayashi _ al show a revcrse roller desicJIled to
remove excess liqui,d from thc pho-tocollcluctor after the
latent image has been developed. I employ a roller oE
this type, insulatcd from ground arld biased to a voltage
of the same po:l.arity as -the charcJe on the ph(-tc)conductc)r,
bu-t: at a potentill hiCJtlC`l- than the backc3roul~cl potential,
in order to ellsure -that no -toner is deposited on the bc~ck-
q~ound areas oE the i.mac~e when the mat;k~fol-millcl st.ep is
performecl.
]3rooke Patent 3,9:L2,387 ancl i.ts cl:ivisional pclterlt
3,99~,72~ show det:c~c-t,:intJ l~ackcJround al-etls wh:i.cil arc~, un(lc~-
cxposccl an('l discli~ ;.tl~l t:llcrll b~ :I.iclht: bcro~-c dc~vel.opmellt
o~ the :L~LcnL elc~cl:rost,at:i.c imat~e~.
Sulnmary o:l~ t:lle Illvc3nl i.OII
. _ .. ... . , _ _ .. .. _ .... .... .
13.r:o~ld:l~ ~;E)(~(I}~ CJ tllc~ r~ t;(~ lvc~n~ l rc~tlt,~!C; to
met:llocl oE elocctro~)llol:ocll-al~lly W]IC.l-C.ill a ~.at,ellt, c~loc~trost:ati.c
,im~ e oE a clocurncrlt: havinc~ l;.qht ancl slladc ~.ll'CclS :iS .fOrlllC'd Orl
a photoconcluctor alld thc laterlt :ima~Jc i.s developed to produce
a vlsible :ilna~Je. In accordclnce with the metllod of -the inven-
tion the ~atellt elcctr.ostatic isll.lc~e it.; toned so as to for.m an
.. - . i .
~ pCJ/"; - 5 -
llZ9481
Optical sl~i~ld over -the shacle ar~as o:E t,he e]ectl-osta-tic
image. ~l~he pl~otoconc~uctor i.s then ~ubject,ccl to lic~ht -Lo
dischar-Je tlle l:ic3ht al^~as o:E the imac~e on the phoL()(.onductor
b~Eore practicincJ ~he d~velopi.nc~ step~
The appara-tus ~or practicing the above Inethod
includes a photoconductor, a station for el.ectrostatically
charc3illy tlle photoconduc-tor, an ~xposin~ s-ta-tion for sub-
jectinc3 -the charge~ photoconductor to a lic3ht and shade
image o:E the document to b~ copied -to ~orm a lat~nt
electrostclt.ic imacJ~ on the pllot.ocon~uc-tor and a develop-
ing station to ma]{~ the laterl-t ima~ optically visible.
Betwe~n the charging stati.on and th~ dev~lopinc~ station
i.s a s-tcltion Eor optica],]y maskirlcJ -the Sllc-l~tO are(ls oE thc
latent elc~ctrostcat:i.c i.macJe anc~ a Stclt:iOIl :Eor l.icJht-dischclrc3-
ing the unlllasked ar~as o:E tllc pl-lotocoIlcluctor. In addition,
means are providcd ~or e:EI-ecti~ re:lat:ivc movemellt oF thC!
photoconcluctox Wi.tll L~Sp(~Ct: to all. o.E l-he c~bc)~o-lllentic)ned
~tation~.
Otll~r c-lIId :~ur~.ll~l~ c-l<.l~(lcl:~; o~ i.nv~ t.ion w~ b~
~l~p~ nt C~ tll~.~ f~ t~ c~ c~ i.ol~.
Br.ie:E l)esc~ .?ti.on o:E the ]~ lWi n(;JS
_ _ ___ . .. .......... . . . __. . .. .. . .. . .. ~ . .. ..... .Ill t~ ccol~l}?~ yil)(~ ill(J~; ~ wh-i.(.~ .toJ-m l~cl.rl: c)I'
the i.n~tallt sE)cc~l'.:i.cat:i.on and Wll;.C]I CnIe t.o b-` reC~ j.n COn~
junctioll thcrew:i.l~
FIGUR13 ]. is a :E.~ow cliacJJ-clm showi.ncJ tllc~ steps oE
my improved method o-E el.ectrophotc)(~raplly, in which the
P~/ - 6 -
1129481
full-line arrows indicate necessary steps and the broken-
line arrows indicate optional steps of my process.
FIGURE 2 is a diagrammatic view showing apparatus
capable of carrying out my invention.
FIGURE 3 is an idealized curve in which tho
ordinates are logarithmic and the abscis~ae are linear,
showing the potential on the surface of the photoconductor
plotted against quantum of light in foot-candle second~
to which the photoconductor has been exposed.
FIGURE 4 i9 a chart plotted with logarithmic
ordinates, showing the voltages on the surface of the
photoconductor, charged as shown in FIGURE 3, after an
exposure of 0.25 foot-candle seconds.
FIGURE S i9 a view similar to FIGURE 4, showing
the voltages on the photoconductor after the image areas oS
FIGURE 4 have been masked and the non-image or background
areas have been discharged by light in accordance with my
invention.
~ Descri~tion of_the Preferred Embodiment
In general, my invention contemplntes charging a
photoconductor in the dark. The charged photoconductor i-
then exposed to a light and shade image of the originnl.
This will form a latent electrostatic image on the photo-
conductor. The oriqinal exposure is only a fraction, such
1129481
as 5% or 10~, of the quantum of light normally required to
produce a sati~factory image -- that i~, one having 3uffi-
cient contrast so the image areas are dark and the back-
ground areas are white. The latent image thus form~d has
sufficient contrast, however, 80 that it can be toned --
that i~, developed -- with any appropriate toner such a~
resinous powder or, more preferably, by a toner di~persed
in an insulating liquid, as i3 well known to the art. This
masking step produces a shield substantially OpaquQ to
light over the image areas of the original being copied.
A critical feature of the masking step is that a shield
will be produced only over the image areas, and not over
any of the background areas. This is accomplished by en-
suring that the development electrode, or means for applying
the toner, during the masking ~tep is biased to a potential
above that existing on the background area~ and below that
present on the image areas of the latent electrostatic image.
I then expose the photoconductor to a blankot of
light. The electrostatic charge of the masked image on the
photoconductor will decay marglnally or not at all, while
the electrostatic charge of thc background areas will bo
discharged to a very low voltage, such as 50 volts or thQ
like. This has the effect of enhancing the charge of tho
latent electrostatic image by a very largo percentage with
the requirement of about one-tenth of the energy which would
normally be neces~ary to produce a latent image having tho
1129~B~
strong contrast now achieved by my method. The cnhanced
electro~tatic image can then be developed in any appro-
priate manner known to the art and, if de~ired, readily
transferred to a carrier sheet.
More particularly, referring now to FIGURE 2 in
which apparatus for carrying out my invention i9 ~hown, a
metal drum 10 carries a photoconductive layer 12 which may
be selenium. The metal drum 10 is supp~rted by apertured
di~s 14 which are mounted or. a shaft 16 and keyed theroto
for rotation therewith. The shaft 16, which may be grounded,
i9 driven by any appropriate means Xnown to the art to ro-
tate the drum 10 in the direction of the arrow. A charging
corona 18 is adapted to charge the 3urface of the selenium
photoconductor 12 to a voltage of between 800 and 1000 volts.
To accomplish this, the charging corona is energized to a
positive potential of 5000 or 6000 volts. The element~ of
the corona discharge unit cause ionization of the circum-
ambient atmosphere and place a uniform positive chnrge over
the surface of the selenium. If my proccss were belng
practiced with a zinc oxide-coated paper, the corona would
be powered to produce a negative charge, a9 will be readily
understood by those skilled in the art. ~he photoconductor
12 is then carried past the exposure station indicntod
generally by the reference numeral 20. Projection optic~,
indicated diagrammntically by the lenu 22, pro~ect an imnge
of the original to be copied upon the photoconductor 12.
llZ9481
In my method, the exposure time i8 extremely ~hort. I have
made copies with an expo~ure of a~ little as 5X of normal
and have been able to achieve completely satisfactory
copie~ of the originals.
A selenium photoconductor will generally discharge
to about one-fifth of its original charge in about three
foot-candle second3. This can be readily seen by reference
to FIGURE 3, which shows a surface potential on a selenium
photoconductor of 800 volts b~ing discharged to 160 volts
in between two to thrce foot-candle seconds. Normally,
sufficient energy is employed in the light source of photo-
copying machine~ so that the bacXground areas of the photo-
conductor will be discharged to about 50 or 60 volts. Thi~
will require about five foot-candle seconds. Five percent
of this quantum of light is about 0.25 foot-candle second~.
By referring to FIGU~ES 3 and 4, it will be noted that,
after this short exposure, the background area~ (B) will
have dropped in voltage about 100 volts from the 1mage
areas ~I). If this image were toned, a very low-contrast
image would be achieved. If thi~ imago, after boing toned,
were to be transferred onto papor from the drum, thc density
of the toned image would be so small that a poor transfer
or a failure to transfer would re~ult and only a faint image
would appear. The low-contrast image, however, when de-
veloped, has sufficient optical density so that it provides
a ma~k or shield for the latent electrostatic image which is
sufficiently dense for the practice of my proce~.
--10--
~lZ948~
Referring again to FIGURE 2, I show apparatu~ for
providing a mask or shield for the latent electrostatlc
image. It comprises a tank 24, from which a developlng
liquid 26 containing dispersed toner particles, whlch may be
S charged, is drawn through pipe 28 and pumped by pump 30
through pipe 32 to nozzle 34, adapted to discharge the de-
veloper between the photoconductor and a reverse roller 36.
If the toner particles are conductive, they may acquire a
charge by induction, owing to their passage ad~acent the
latent image under the action of its electric field. In this
case, the clectrostatic charge pattern serves first to charge
the particles and then to trap them. In the case of a liquid-
carried toner particle, the continuous phase is an insulating
liq~id -- such as a hydrocarbon liquid, a fluorinated hydro-
carbon liquid, or the li~e -- having low vapor pressures at
room temperature, and the disperse phase is composed of the
minute particles of toner adapted to make the latent electro-
static image visible. As iB known in the art, the polarity
of the charged particles may be controlled by materlals
added to the developing liquid. Thcse act by adsorption
onto the surface of the particlcs and alter the magnitude
and polarity of the charge acquircd by the particles, de-
pending on the environment of the particles at the tlmc of
their formation and tho method of their preparatlon. Tho
toner particles must bc applicd by a dcvelopment electrode
biased to a potential of the same polarity a~ that of the
latent electrostatic image and to a potentlal greater thnn
--11--
l~Z9481
that o~ the background areas and below that of the image
are~. Preferably, I employ a reverse ro~ler a~ the de-
velopment electrode when a liquid developer i~ used. Thlo
reverse roller i~ made of metal and is mounted on ~haft 38
for rotation in a direction oppoRite to the rotation of
the photoconductor. The reverse roller i8 insulated from
ground and is positioned closely adjacent the ~urface of
the photoconductor to provide a gap ranging from 0.05 to
0.1 millimeter. The reverse roller is driven by a prime
mover and is controlled in speed so as to remove excess
developing fluid from the photoconductor. The biasing of
the development electrode i~ critical to my process, ~ince
there can be no masking of the background areas in my
process, as will be pointed out more fully hereinafter.
It will be appreciated that the close proximity of the
insulated metal reverse roller to the ~urface of the charged
photoconductor is such that it will float to a~sumo tha
average potential of the photoconductor and thus be auto-
biased. Since the average potential on the rever~e
applicator roller 36 will be above the background potentlal
on the photoconductor, toner particles will migrate to the
applicator roller in~tead of to the background area~ on the
photoconductor. If desired, in~tead of pcrmitting the
reverse applicator or metering roller 36 to float electrl-
cally, it may be biased to a potential from any appropriate
D.C. voltage ~ource to above the potential of tho bac~ground
areas but below the potcntial of the image areas. The ~ia~
- -12-
112948~
on the toner applicator roller will substantially elimlnate
the deposition of ma~king toner on the background areas of
the photoconductor. In the usual developing liquid, how-
ever, the carrier liquid has a low boiling point, ~o that
it is easily vaporized to ensure that the developed image,
when transferred to a carrier sheet such as paper, will pro-
duce a copy dry to the touch. In the maskinq step, however,
a hydrocarbon carrier liquid having a higher boiling point
which will not vaporize may be employed. Thi~, of cour~e,
will reduce the danger of atmospheric pollution during the
masking step. If desired, instead of a liquid-carried toner,
dry toner may be used for the masking step. Such dry toners
are well known to the art. One example of a reverse roller
which can be u3ed in my invention is shown in Hayashi et al
Patent 3,907,423. The excess toner from the masking step
will be caught in the tank 24 for recycling. A wiper blade
40 keeps the metal reverse roller clean.
After the optical shield is produced in any
appropriate manner such as described, the photoconductor i~
subjected to a blanket of light. This may be accompli~hod
by an elongated incandescent lamp 42 placcd adjacent the
photoconductor bearing the masked image and extending thore-
across. In an office copier, a ~uartz-halogen lnmp h~ving
an output of about 500 watts i3 u3ually employed. In my
process, a much lower-energy exposurQ lamp to project the
image may be employed. Furthermore, the illuminAtion of
-13-
l~Z9481 'I
the background areas to discharge them to n re~ldual v~ltago
of about 50 volts requires comparatively ~mall energy. A8
will be readily appreciated by those skilled ~n the nrt, the
exposure step subject~ the photoconductor to an image of the
original by reflected light. The illuminated original i~
focused by the optical system upon the charged photoconductor.
Since the light gathered by the optical system i9 a small
fraction of the light which illuminates the original, a
bright illumination of the original is required. In the
background discharging step, after the optical 3hield is in
place, the illumination of the photoconductor i8 by direct
light, which accounts for the small energy required to
discharge the background areas. The image areas ~I) will
not be discharged owing to the mask or shield which I have
lS provided by my proces~ as jUQt described. The effect of
discharging the potential of the background areas (~) whilQ
leaving the image areas (I) substantially undischarged t~
shown in FIGURE 5.
It will be seen that my process has achieved a
contrast of substantially 750 volts between the bacXground
areas and the image areas and accomplishod tha creation of
this strong field nt approximately a tenfold reduction of
the energy required to expose thc original. This mean~, as
will be readily apparent, that a photocopying machine which
prosently uses a 500-watt lamp of the quartz-halogen typo
with a tungsten filament could use a 50-watt lamp or,
-14-
~2948~
alternatively, employ a fluore~cent light. It will aloo be
appreciated that, where a photocopying machine presently i8
able to make only about 25 copies per minute, theoretically,
I can easily make a photocopying machine capable of pro-
ducing 150 copie~ per minute. A~ a practical matter,
however, owing to the inertia of the parts of the photo-
copying machine and in order to avoid marginal operation
to provide a factor of safety, a photocopying machine which
will produce 75 to 100 copies per minute can be made embody-
ing my invention. Furthermore, this can be done without
having to increase the energy expended significantly, since
the only additional energy required will be that employed
in the first developing or masking step and that in the
light discharging of the photoconductor after the image
areas have been masked. It will be further understood that,
instead of an incandescent lamp, I may u~e any appropriata
light source adapted to flood the photoconductor.
The use of a floodlight to enhance a faint latent
image on a photoconductor i8 not new in and of it~elf.
Steinhilper Patent 2,756,676 dcscribes a method of making a
plurality of xcrographic reproductions from a single expo-
sure of an origin~l. In Stcinhilper, however, the effective
speed of the photoconductor is not increased, owing to the
fact that Steinhilper must go through a first development
step which produce3 a fully-toned image. There i9 no m~king
step a~ described in my process. After the first image i~
-15-
l~Z9481
developed, it is transferred to a carrier sheet ~uch as
paper. The faint image which is left on the photoconductor
is of a potential too low to be enhanced by light or to be
redeveloped. Steinhilper does not erase this image on the
- 5 photoconductor, but recharges the photoconductor. He then
discharges the background areas by light. Since the faint
image does produce a shield, an enhanced latent image will
be produccd. The salient feature of my proces~, however, is
absent from Steinhilper. He does not form a lcw-contrast
latent e1ectrostatic image in such a manner a~ to leave the
bacXground areas free of developer, owing to the fact that
his development electrode is never biased but always at
ground. Steinhilper must carry out his proce~s to form the
residual image from the first transfer of the developed
image at the normal ~low rate. Thus the unobv~ou~ re~ult
which I achieve -- namely, the increasing of the effective
sensitivity of the photoconductor -- is not taught, nor can
it be achieved, by Steinhilper.
Owing to the tremendous range through which I am
enabled to obtain sufficient optical density to produce a
mask, I can employ a single exposure and a biased ~etting in
the developer system and obtain a sharp, clear copy from any
orlginal, whether the bacXground is ultra white or dingy gray.
It will be readily apparent to tho~e ~killed in
the art that, with the contra~t potential shown in FIGURB 5,
-16-
,
~lZ9~81
there is no problem in obtaining a ~harp, clear im~ge.
After the background potential has been di~chargod by tho
lamp 42, the optical shield may be wiped from the enhanced
latent image thus formed by a cleaning roller 44 made of
sponge rubber or the like, if desired. This wiping action
can take place with either a liquid-toned mask or a dry
developer-toned ma~k. The enhanced latent electro~tatic
image may then be toned by any usual method known to the art.
In FIGURE 2, I have shown the toning system
described in Schaefer et al Patent 3,892,481, employing a
tank 46 from which a liquid toner 48 circulates from pipe 50
to a toner supply tank ~not shown) and back through pipe 52
to the tank 46. A development electrode 54 i9 controlled
to bias any residual voltage left on the background of the
photoconductor. It will be readily appreciated, however,
that since I have discharged the background potential by my
method, I can use a fixed bia~ slightly nbove the average
residual bias of the background. This will produce a cluar
white background and enable me to eliminate, if deaired,
the sensing and biasing method shown in the Shaefer et al
patent.
After development with a liquid-carried toner, a
rever~e roller 56, sucll ag shown in ~}ayashi et al Patent
3,907,~23, i9 positioned to remove excess developer from the
developed image, The reverse roller 56 i8 provided with a
-17-
... .
1129481
wiper 5~. The reverse roller 56 i9 positioned and rotate~
at ~peeds as described in the llayashi et al patent.
The image is now ready to be transferred to a
carrier sheet such as plain paper. A plain paper sheet 60
i9 fed by rollers 62 to a roller 64, past a transfer-
charging corona 66. It will be recalled that the toned
image still comprises a visible image over a high positive
charge on the surface of the selenium drum in the image
areas which haye not been discharged by light or by the
bia~ applied to remove the residual background potential.
To transfer the developed image from the drum to the paper
carrier sheet, a high positive charge is applied to the back
of the copy paper. As a result of the application of the
high positive charge to the sheet, the toner particles are
pulled from the drum surface onto the paper. A pic~-off 68
ensures that the paper leaves the drum, and the end of the
paper 70, now carrying the image, may be dried and passed
to a receiving tray tnot shown). A cleaning roller 72 wipes
the drum clean of any particle~ of toner which have not been
removed from the drum, and a wiper blade 74 complates the
drum-cleaning operation.
It will be understood, of course, that lf my
process i9 applied to a ~inc oxide-coated paper, the im~ge
will remain on the coated paper. It will al80 be under-
stood that a dry toner, made of fusible resinous powder nnd
fixed by heat, may be employed, as i9 well known to the art.
-18-
~129481
It will be understood by thos~ sXllled in the art
that, since the photoconductor now bears an enhanced latent
electrostatic image having a strong field, it may be de-
veloped in any appropriate manner known to the art.
A selenium photoconductor i8 very ~ensitlve to
blue light and, accordingly, photocopylng machine~ using a
qelenium photoconductor do not produce copies from blue-
colored originals with high contra~t. That ls to ~ay, a
selenium photoconductor "sees" blue light as almost white.
My method will reproduce bluo originals as if they were
black. A yellow original is very light in color and re-
flects considerable light, 80 that it appears faint in the
copie~ made by photocopying machines. My method of ~mage-
enhancing reproduces yellow effectively. Furthermore,
gradations in density -- that is, a gray scale -- are also
achieved with my method.
Owing to the wide latitude of effective photo-
conductive sensitivity which my process provides, when uslng
the automatic bias of Schaefer et al Patent 3,892,4al, I can
adjust the illumination in the step whlch forms the low-
contrast image prior to thc mask-forming step to produco a
satisfactory reproduction with the brlghtest background --
that is, a purc white background -- in the original document.
Thia will produce an image of contrast too low to be effec-
tively developed to a aatisfactory copy, but such that the
--19--
1~29481
mask-forming ~tep can be easily performed. The bla~
potential applied to the applicator roller will be well
above that required to eliminate background potential of
the latent electrostatic image completely, but will be
S below the potential of the image areas. This permits the
image areas to be optically masked by toner during the
optical shield-forming step. The illumination of the
image-forming step may be readily controlled by varying
the intensity of the light source or by a shutter in the
optical path of the image-projection system.
It will be further under~tood by those skilled
in the art that, while I have shown and described the
toning of an image and then its tranqfer to n carrier sheet,
my image-enhancing process can be used in any method of
electrophotography. For example, the enhanced latent
electrostatic image can be transferred to a dielectric
sheet and then toned or developed into a visible im~ge on
the dielectric sheet, a~ is well known in the art.
It will be qeen that I have accomplished the
objects of my invention. I havo increased tho effective
sensitivity of photoconductors. I have provided an improved
method of electrophotography which will qreatly incroaJe the
speed of COpyillg operations. My method achieveJ thiD ln-
crease in speed with a reduction of the quantum of energy
required. I am enabled to copy originals having poor
-20-
llZ9481
contrast which will produce copies having surprisingly
increased contrast a~ compared with the originalJ. I am
enabled to copy originals formed in colors to wh$ch the
photoconductor has great sensitivity and which, accord-
ingly, do not ordinarily produce copies having the desired
contrast. I have provided a novel appAratUs for carrying
out my improved method.
It will be understood that certain features and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. ~his is
contemplated by and is within the scope of my claims. It
i9 further obvious that various change~ may be made in de-
tails within the scope of my claim~ without departing from
the spirit of my invenition. It is, therefore, to be under-
stood that my invention is not to be limited to the specific
details shown and described.
Having this described my invention, what I claim
