CA1268528A - Quantitative dispenser for a liquid - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A quantitative dispenser for a liquid includes a pipette having a downwardly directed nozzle which serves to pick up and deliver a predetermined quantity of a liquid and a mechanism for moving the pipette downwardly to dip the lower end of the pipette into the liquid supply. A detector is provided for detecting reflection of light which is projected downwardly to the surface of the liquid while the pipette is moved downwardly to approach the surface. A control circuit is connected to the detector to determine the stop point for the downwardly moving pipette with the aid of information received from the detector.
The detector is provided with a spot type reflection sensor having a light convergent optical element having a focal point at a certain distance below the detector whereby the stop point of the downwardly moving pipette is determined so as to corre-spond to a point of maximum intensity of the incoming reflected light.

Description

~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 ~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.

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 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 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.

Claims (6)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A quantitative dispenser for a liquid, comprising; pipette means having a downwardly directed nozzle adapted to pick up and deliver a predetermined quantity of a liquid, drive means for moving said pipette means downwardly to immerse the lower end of said nozzle in a liquid supply, and liquid supply level sensing means for determining the stopping point for the downward movement of said pipette means, said liquid supply level sensing means being comprised of housing means, lens means mounted in said housing means and having a focal point outside of said housing means, light source means mounted in said housing means for directing a beam of light through said lens means onto the surface of said liquid supply, photosensor means mounted in said housing means for receiving light reflected from said surface of said liquid supply through said lens means, and control means operatively connected to said photosensor means and said drive means for controlling the operation of said drive means so as to stop the downward movement of said pipette means when the maximum intensity of reflected light is detected by said photosensor means;
wherein said lens means comprises two convex lens portions so that said beam of light from said light source means is directed through a first one of said two convex lens portions and said light reflected from said surface passes through a second one of said two convex lens portions which has a focal point on said photosensor means.

2. A quantitative dispenser for a liquid as claimed in claim 1 further comprising means connecting said pipette means and said detector means together for simultaneous downward movement toward said liquid supply.

3. A quantitative dispenser for a liquid as claimed in claim 1 further comprising mounting means for said detector means and means for moving said mounting means vertically independent of said means for moving said pipette means.

4. A dispenser for a liquid, comprising:
pipette means having a downwardly directed nozzle;
drive means for moving said pipette means downwardly to immerse a lower end of said nozzle in a liquid supply;
liquid supply level sensing means for determining a stopping point for the downward movement of said pipette means;
said liquid supply level sensing means comprising:
housing means;
lens means mounted in said housing means and having a focal point below and outside of said housing means;
light source means mounted in said housing means for directing a beam of light through said lens means onto the surface of said liquid supply;
photosensor means mounted in said housing means for receiving light reflected from said surface of said liquid supply through said lens means;
control means operating in response to said photosensor means for controlling the operation of said drive means so as to stop the downward movement of said pipette means when said lens means has been lowered to a position above said surface of said liquid by a distance approximating a focal length of said lens means; and wherein said lens means comprises two convex lens portions so that said beam of light from said light source means is directed through a first one of said two convex lens portions and said light reflected from said surface passes through a second one of said two convex lens portions which has a focal point on said photosensor means.

5. A quantitative dispenser for a liquid comprising:
pipette means having a downwardly directed nozzle for immersion in a liquid sample, drive means for controlling the downward movement of said pipette means to immerse the lower end of said nozzle in said liquid;
liquid level sensing means arranged above said lower end of said nozzle, said liquid level.
sensing means including a light source, lens means for projecting light from said light source onto the surface of said liquid, photosensor means for detecting light reflected from said liquid surface through said lens means, and peak detecting means for determining when the intensity of said reflected light at said photosensor means reaches a maximum value, said peak detecting means controlling said drive means so as to stop the downward movement of said pipette means and said liquid level sensing means upon detection of said maximum intensity level, wherein said lens means has a predetermined focal length, and wherein said maximum intensity of said reflected light occurs when said lens means is spaced above the surface of said liquid by a distance equal to said focal length; and wherein said lens means comprises two convex lens portions so that said beam of light from said light source means is directed through a first one of said two convex lens portions and said light reflected from said surface passes through a second one of said two convex lens portions which has a focal point on said photosensor means.

6. A quantitative dispenser for a liquid, comprising:
pipette means having a downwardly directed nozzle;
drive means for moving said pipette means downwardly to immerse a lower end of said nozzle in a liquid supply;
liquid supply level sensing means for determining a stopping point for the downward movement of said pipette means;
said liquid supply level sensing means comprising:
housing means;
lens means mounted in said housing means and having a focal point below and outside of said housing means;
means for moving said lens means toward and away from the surface of said liquid supply;
light source means mounted in said housing means for directing a beam of light through said lens means onto the surface of said liquid supply;

photosensor means mounted in said housing for receiving that part of the light reflected from the surface of said liquid supply which passes through said lens means;
control means receiving the output of said photosensor means and controlling downward movement of said lens means such that said lens means is lowered to a position above said surface of said liquid by a distance approximating a focal length of said lens means, said control means subsequently controlling the operation of said drive means so as to stop the downward movement of said pipette means at a position determined in accordance with the extent of said downward movement of said lens means;
and wherein said lens means comprises two convex lens portions so that said beam of light from said light source means is directed through a first one of said two convex lens portions and said light reflected from said surface passes through a second one of said two convex lens portions, which has a focal point on said photosensor means.