~6~35i~8
QUANTITATIVE DXSPENSER FOR A LIQUID
. . . _
BAC~GROUND OF THE INVEN~ION
The present invention is directed to a quantitative
dispenser for small amounts of liquid samples or reagents and
more specifica~ly ~o a quantitative dispenser using an opt~cal
sensing device for controlling the amounts of liquid to be
dispensed~
In the f~elds of biology and medicine, various meth~ds of
a~alysis have been proposed for detecting trace substances in
body li~uids and, in corxelation with ~he analyses, vario~s
systems and devlces have been proposed for automatic qualita-
tive and ~uantitative analyses. One of ~he common requlsites
arising in these systems ~nd devices is the strict contr~l of
the amount of liquid samples and reagen~s to be added to the
reactio~ chamber and the prevention o~ contamination of the
samples ~rom each ~ther. For this reason, pipettes, such as
tho~e called micropipet~es, are usually employed which are
manufactured with a high deg~ee of precision and contain a dis-
posable tip. In employing these micropipettes, the disposable
tips are disposed of after each sample to a~oid contamination
o~ the samples ~rom each other. The sample is usually sucked
into the pipette ~y means of a negative air pressure.
As mentioned above, the strict control of the amount of
the liquid samples in reagents is necessary for minimizing
variationS in the amounts of the samples and for obtaining
reliable results, particularly in an immunological estimation
~6~352~
~n the o~er hand, ~he use o~ disposable tlps is also desi
to avoid con~amination of the samples from each other since ~h~
concentrat~on ratio of minute components can sometLmes reach up
to 1~ ~ 10~ depending on samples ln the immunolosical mea-
sur~ments of the biological materials~ Even when micr~pipettes
havina disposable tips are used Lt ~s st~ll absolutely essen-
tial that ~he mlnut~ a~o~nts ~f l~quld to be d~spensed must be
determ1ned w~th a h~gh degree o prec~s~on and that contr~ls
axe necess~ry ~r position~ng the ~icroplpetteS relative to ~he
reservoir fro~ which the l~quld samples or reagents are taken.
More par~C~larly~ if a ~eg~e pressure is utilized ~or
~ak~ng up the ~ample solut~n, the ~gat~Ye pressure c~ he
~rlc~ly controllefl when the p~pet~e ls lnserted ~n a sample
~esselO The ~epth to w~lch the ~o~le ~ the plpe~e
~er~ed ~ the ~mple ~olut~o~ ~ kely t~ ~ry dependin~ ~
th~ ~ze <of ~h~ ple. The ~ri~t~on may ~e r~se to an
errar ~ ~he q~n~it~ti~e d~peQs~n~ wh1ch c~nn~t ~e ~g~red.
~he ~ame pr~blcm ol~ ~r1~es when th~ surf~ce o~ ~he s~mple
solutlon ~s canc~ due to the ~a~m~tlon of a ~eniscus ~r ~he
~essel 1tsel ~5 i~ a ~l~nt pos~t1on and ~he d~a~eter of ~he
vessel ~s small.
~ n ~he past 1~ h~s been praposed ~o install detcctors to
~ense the level o~ ~he l~quld surface ln A d~spensing dev~ce.
~owever, ~n elec~rode type c~ detcctor ln~olves c~ntam~natlon
~nd ~ n~n.C~ntact type aptical deteCtor ln general is n~t suf-
f~Cl~tL~ precise with ~oler~nces o~ several milllmeters and
fu~rthermore cannat accur~telY operate with t~rbld solutionS or
slanted surfaces~ rn ~act an error o~ se~eral mllllme~erS ln
~ 5~ 8
immersion may introduce, for example, up to ten percent of dis-
persion when 5~1 of solution is taken with a pipette of 200~1
capacity.
SU~RY OF THE INVENTION
The present invention provides a new and improved quanti-
tative dispenser for a liguid which is capable of dispensing a
precisely controlled amount of liquid when a minute amoun~ of
liquid is to be taken up.
The present invention provides a new and improved quanti-
tative dispenser for a liquid which is favorably applicable to
an automatic analyser, particularly to the portion of an auto-
matic analyser for estimating immunological reactions.
The quantitative dispenser for a liquid accordin~ to the
present invention is comprised of a pipette having a downwardly
directed nozzle which serves to pick up and deliver a liquid, a
mechanism for moving the pipette downwardly to immerse the
lower end of the pipette in the liquid and a detector for
detecting reflection of light which ls projected downwardly to
the surface of the liquid while the pipette is being moved
downwardly to approach the surface and means for determining
the stop point of the downwardly moving pipette with the aid of
information from the detector, said detector being provided
with a spot type reflection sensor having a light convergent
optical element with a focal point at a certain distance below
the optical element whereby the stop point of the downwardly
moving pipette is determined so as to correspond to a point of
maximum intensity of the incoming reflected light.
~ ~ 6~
Tha mechanism for moving the pipette downwardly may be
comprised of a support frame on which the indication device oE
the pipette is supported for movement in the vertical direction
and means for moving the frame up and down such as a pulse
motor operating through an intexmediate cam mechanism. The
spot type reflection sensor to be used in the present invention
may be comprised of a light emitting portion and a light
receiving portion in which the light from the light source and
reflected light are transmitted through a convergent optical
element such as a convex lens. The portions may be either
assembled in a unitary body or arranged separately in appro-
priate positions relative to each other. The maximum intensity
point of the reflected light detected by the reflection t~pe
sensor can be detected by converting the reflected light into
an electrical signal and by detecting the high peak of the
electrical signal.
When such a sensor is used, the maximum intensity of the
incoming reflected light occurs when the surface of the liquid
coincides with the focus point of the light irrespective of a
slanted surace or the turbidity of the liquid. The stop point
of the downwardly moving pipette as determined by the maximum
intensity makes it possible to precisely control the depth to
which the nozæle of the pipette is immersed in the liquid.
Generally the present invention is favorably applied to
those devices for analysis and measurement in which the quanti-
tative ~ispensing of 1000 ~1 or less of a liquid is required.
More particularly the dispenser according to the present inven-
tion is favorably used in carrying out estimations in
-- 4 --
~un~loglcal and biochemical reactions where~ a very small
amount o a li~uid on the ~rder c~f 1~0 IJl or less is <Iuan~i-
tatively dispensed. The li<auid dispensed may be a sample or a
reagent .
The mechanism for lowering the sensor to approach the
sur~ace may be ~nstall ed on the support :~rarne supporting t~e
pipette lowering mechanisr~ or installed on a separate supEort
frame inclependently from the pipette supporting r~me~. It is
preferr~d that the point at which ~he sensor detects the ~ s~rfaoe is hori -
zontally as close as p~ssible 1:o the point where the lower eQd of
the nozzle is partially im~ersed in the ll~uid to obtain a high
degree of precision in the d~spensing of the liquid.
The foregoing and other objects, features and advantages
o~ the i~ention will be apparent ~ro~ ~he following more par-
t~cular descrip~lo~ o~ a p~e~er~ed e~bodime~t o~ the ~vent~on
as lllustrated i~ the acco~pa~y~g draw~ngs~
~RIEF DESCRIPTIO~ OF THE DRAWINGS
Figure 1(a~ is a schema~c diagram showing a ~irst embo-
d~ment of a quantitative l~quid dispenser according to the
present invention with the pipette disposed above the liquid
reservoir.
Figure l(b) is a partial view of the dispenser sh~wn in
Figure l(a) wi~h the tip of ~he pipet~e immersed ln a liquid.
Figure 2~a) is a graph showing light intensity curves.
~L2~8~
Figure 2(b) is a schematic diagram showing
the relationship o an optical sensor accordirlg to the
present invention relative to various points on a light
intensity curve where the liquid is level.
Figure 2(c) is a view similar to Figure 2(b)
showing the relationship of the optical sensor relative
to a slanted surface.
Figure 3 is a partial perspective view of the
apparatus for moveably supporting a pipette and optical
sensor for movement relative to a liquid reservoir.
Figure 4(a) is a detailed sectional view of
an optical detector according to the present invention,
and Figure 4(b) is a slant and partially cross-sectional
view of the op~ical element in Figure 4(a).
Figure 5 is a schematic circuit diagram or
detecting the maximum light intensity detected by the
optical sensor.
Figure S is a flow chart for a process carried
out with the apparatus according to the present invention.
Figure 7 is a partial perspective view of a
further embodiment of the apparatus for moveably support-
ing a pipette and optical sensor separate from each other.
Figure 8 is a flow chart showing the operational
sequence for the apparatus shown in Figure 7.
-- 6 --
DETAILED DES~RIPTION OF THE INVENTION
. _ . . .., ., _
The quan~itative liquid dispenser as shown in Figure 1 is
comprised of a pipette 3 hav~ng a disposable tip 4 which is
adapted to be moved into and o~t of a llguid sample contained
in a sample vessel 1. The pipette 3 is carried by a supporting
rod or frame 6 which in turn is moved vertically by means of a
dxive mechanism 5 including a pulse motor under the control of
a drive control circuit 9. A spot type reflection sensor 10 is
also firmly supported by the support rod or frame 6 for move-
ment with the pipette. The sensor 10 is disposed slightly
higher than the lowex end of the disposable tip 4 and an elec-
trical signal from the sens~r 10 is supplied to the control
circuit 9 ~or c~ntrolling the drive mechanism S. When the
pipette 3 is positioned over ~he liquid sample 2 the pipette 3
may be lowered from the pos~tion shown in Figure l(a) to the
positiun shown in Flgure 1(b~ wherein the lower end of the
disposable tip 4 is Lmmersed in the liquid to a degree deter-
mined by the optical sensor 10. WLth the lower end of the dis-
posable tip 4 Lmmersed in the li~uid 2 as shown in Flgure 1(b~
a predetermined amount of liquid is drawn up into the pipette
by means of a negative pressure applied to the plpette 3
through a tube 8 under.the control of a liquid volume con-
troller 7. The pipe~te 3 is then raised to the position shown
in Fioure 1 (a) and t~.e liquid ~Y~eLn may be subsequently dispensed by
appllcation of a positive air pressure through the tube 8 to
the pipette 3 under the control of the liquid volume
controller 7.
The sensor 10 can be constructed, or example with an
optical reflective sensor HEDS-1000 (Yokokawa Hewlett Packard
Corp.). Such a spot type reflection sensor 10 emits light to
the surface of ~he liquid 2 in the sample vessel 1 in which the
lower end of the nozzle tube 4 is to be immersed and receives
light reflacted from the surface of the liquidO The intensity
of the reflected light reaches a maximum when the sensor 10
reaches a point above the surface equal to the focal distance
of the lens within the detector, the focal distance being
preset by selecting an appropriate convex lens such as that
shown in Figure4(b). me plot diagram of s-everal light intensity
curves shown in Figure 2(a) showing the relationship of the
light intens-ity relative to the distance 1 of the detector
above the surface of the liquid. The dista~ce 11 from the
sur~ace of the liquid where the maximum intensity is o~tained
is constant as shown in Figure 2(a) regardless of the reflec-
tivit~ of the liquid surface or the degree of concavity or
slanting of the surface. Thus the depth of i~mersion of the
noz21e tip into the li~uid can be controlled with a high degree
of accuracy. The maximum intensity of the light can be detected
by using a high-peak detecting circuit such as that shown in
Figure 5 so that the downward movement o~ the pipette is stop-
ped when the maximum value is detected or when the pipette
moves a vary short distance past the point of maximum
intensity.
Figure 2(b) shows three representative positions of a
light detector relative to a flat liquid surface with respect
to three different portions of a liyht intensity curve such as
that shown in Figure 2(a). The focal point of the lens~in the
s~
middle posi~ion is coincident with th~ surface of the li~uid
and the light intensity is at a maximum. Figure 2(c) shows a
similar illustration but with the surface of the li~uid concave
or slanted. The overall intensity of the reflected light will
be less in such a situation than with flat surface as in
Fi~ure 2(b) but the light intensity will still be at a maximum
when the focal point of the lens is coincident with the surface
of the liquid. When the maximum or peak value of the light
intensity is expressed as 100, the light intensity detected
with 0.2 mm deviation from the focal length representing the
maximum or peak value may be lowered about ten percent.
Figure 3 shows one embodiment of an apparatus suitable
for carrying out the present invention which corresponds to the
schematic arrangement shown in Figure 1. In Figure 3 the
numerical references 1, 3, 4, 8, and 10, represent the same
elements as shown in Figure 1. For moving the pipette up and
down the rotating shaft 5b is rotated by means of a pulse
motor 5a to rotate the cam 5c in an amount corresponding to the
amount of rotation of the pulse motor so that the frame 11 sup-
porting the pipette 3 is moved downwardly. In this way the
disposable nozzle 4 detachably connected to the lower end of
the pipette 3 moves downwardly a corresponding amount and
enters the liquid within the sample vessel. The point at which
the downwardly moving nozzle stops is determined by detectin~
the maximum value of the intensity of the reflected light by
the sensor 10 which is mo~nted on the same support frame 11 as
the pipette 3. The detector 10 is connected to the detecting
circuit and a source of power by means of the cable 14. The
s~ppor~: fra~e 11 is move~ble h<: rizontally al<: ng guide rods 13
carried by a main frasne 12 so as to allc~w the plpet~e t:o be
moved sel~c~;ively be~ween various vessels and reaction cham~
~rs. q~he suppor~ rame 11 may be moved along th~ guide
rails 13 by any suitable means which have alot ~}een sho~n slnce
such sneans 3.re cc~nventior~al in ~he art.
~ he ph~t<:~sensar 10 ~s shown in detall in Flgt~e 4(~) and
lrlcludes ~n LED l~gh~ so~ce 10~ ~nd a phc)t<~di od~ lOb mo~ted
ln sLde by $~de rel~.t~.an~. ~he liqht ~r~ the LED light s~urce
~s pro~ec~ce<l ~utwar~ly o~ tb.e: glass window ~c through t:he <::an-
vex le~s lOb having ~ts oc:al pc~ t at lOe. The light
re~Elected ~ra~ liquid sur~Eace p~sses ~rough the convex
lects lac a~<l ~rs ~:he photo~ d~ sign2l1 input and
o ~e ~e~gr 10 ~e ca~sect~ 'cc~ t~e dr~ve cort'crol
~ 9 ~s ~hc~ is~ Flgure 1 thrt~ugh ~:he cable 14 ~ t~t
the ~ ~u~ c~f t~e ~te~ the l~ght inc~de~t a~ the
. . p~lot~d~2te ~s det:ected. The con~rex lens el~nt shown ln Figure
4(h~ f:s p~p~ced by ~old~ng plastic ~aterlal as o~e body w~1:h a
sk~t porti<:~n and a cc~llar portiosl in such a shape a~; isE two
convex lenses are c~mbined.
Fig~ S sh<~ws a blclck circui~ diagxa~n for the de~cection
o~ the maxi~m intensit~ ol~ the incident light in which an
C~sc~ll~tc~r I S supp~Les a signaL to ~he detector 10 to ac~i~rate
the LED llgh~ sc~urce l~a. The s~.gnal ~om the photod~ode lOd
is passed thr~ugh an ~mpli~er 16, a wave de~ec~or 17 and an
A~ converter prior ~ being supplied to a mlcrocomputer 19- A
desired high peak detec~r can be constructed using the abo~
companeA~s b~ a persc)n havlng c)rd~ nary skill ih the electriCal
arts. When the maximum val~e or peak of light intensity is
-- 10 --
8.
detec~ed ~y ~se mlcrocompu~er 19, such ~n~c~rmatlQn is t~nsml~-
te~ to tlhe pulse motor Sa to stop the downward movemerlt n~ ~he
pipette 3.
Fi~lre 6 is a f low . h~rt show~ng the operational s~uence~
~or the embodiIr~ents desc:rlbed a~ove:. Although t!he suppor~
ra~&e 11 moYeS ~orl~ont~ly as descr~bed above the o~eratior~al
se~uer~ nlted to ~e up ar~d dc~wn mc~veme~t o t:he p~pette
wh~ch ~; c~rle~-by t~ ~pp~ rasne 11. ~t the ~ c:~
operalt~on ~he ~ g he~d rao~r~s ~6mwardly ~d ~ l~gh~c
~s ~upplie~l 1by th~ p~ sens~r as ~e i~ght ~rona t:he pho~ e
~s reflec~ rc~ th~ ç:urace ~f ~e ll~uld below the ~a~l~
he~d. ~5 ~he input value c~ s rom a~ cre~se ~co de~::rease
e dow~r~ ve~ t cl~ ~the ~ pL~ng ~ead 1~;3;topped~8 ~ ple
w~h~rawn ~ra~ ~he 1~9U~d reservo~r ~d th~ ~a~pl~ Ræ~
~ubsequently rl~es to comple~e the operational cycle. Th~
osal lenath of ~he ~ensor 10 ls 4.3 mm, and the distance
: .
from the lower end of t~.e sensor to the lower en~ of the
nozzle t~p ls 7.3 mm. In this example the nozzle and
sensor were ~lxed ~o the s~ne control mechani~m as shown
in Flgures 1 nnd 3. Figure 7 shows a fuxther embodiment
of the present inven~,lo~ wheréi.n the pipette 3 ~nd the
sensor 10 are mounted ~epax~t~ly ~rom each other on separate
6uppor~ mechanisms. A detector 10 is carried by a support-
ina frame 21 whlch ls mounted in a mechanlsm 22 for movi.ng
the same up and down. The pipette 3 is mounted for movement
by ~eans of a mechanism simllar to that described above with
respect to Flgure 3 and the detail~ of such movement need
not be repeated. As in the prevlous embodlment, a downward
2~3
movement of the sensor i~ detected and when the maxlmum
value of re~lected light intenslty ls detected the pulse
motor ox movina the pipette ls controlled to limit the
lmmersion of the ~p of the plpette in the ll~uid. In
the embod~ment of Figure 7 ~he s~mple vessels are shown
as be~n~ mounted in a rack 20 and sultable means may be
provlded ~or moving the pipette and detector and the rack
relative to each other ~o alian the pipette with dif~erent
samples, In this embodiment,for determin~ the posi~ion
at which the downward moving nozzle ls stopped, the volume
of sample in ~ne vessel ls measured and once memorized ln
a m~mory ln the control mechanls~, and then when the s~mple
vessel comes just ~elow ~he n~zzle the position at which
the ~ozzle ls stopped is dete~mined on the basls of the
memorlzed ~ample volume meas~rement of the vessel. F1~ure
8 ~ a flow chart showin~ the ~peratlonai sequence of the
de~tce of Fl~ure 7~ As an example, when t~e sample vessel
1 has a dia~eter of 11 ~m ~nd ~ plp~tte havlna a capacity
of 200-~ is used, a llauid volume of 5 ~l ls plcked up
wLth the lower end of the nozzle tlp belng immersed to a
depth of 3 mm below the surace of the liquid. It was
noted th~t the dl~perslon with respect to the depth of
lmmerslon of the nozzle ~lp was 1 ~m or less and wlth re~pect
to the volume o~ llquld picke~ up was two percent or les~.
~ O~g ~ ~e prese~ ~en~ n ~e q~t~
disp~g ~ ~ ~t~ ~raL~e ~ l.f.~d c:~ be ~orra~i wl~h
extrc~c~y high deyree ~ precL~ As a result the ~r1G~S
~t~ and gual~t~t~vc ~o~lyses can be acc~ra~ely and
-- 12
precisely ~.trol3ed~ It is ob~rious that the device accc~rdlnc3
to t:he pre~ .n~ren~ian car~ be applied to a nurQb~r o~ ~tc~ma-
c a~al~c~l sys~ems and ana~s~rs ~
W~le t~e inveQtion has beerl par~ic:ularly shown and
descri~d wi~h re~erence ~o preerred em~odi merlts ~chereof ~t
will ~e u~derstood by those ~n the art that the foreg~ and
other changes in form and details may ~e made there~ n wlthout
departing from the spirit and scope of the invention.
- 13 -
