CA1058997A - Syringe pump valving control system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates generally to improvements in an improved valve control system for syringe pumps. Prior art syringe pumps are often overly complex and unstable or inaccurate in their valving and motor control systems. The present invention overcomes these deficiencies by providing apparatus which repetitively and sequentially opens and closes a pair of intake and output I.V. tubes communicating with a syringe, the tubes alternating between opened and closed states, one tube always being open while the other is closed, by means of a pair of L-shaped pivotal tube pinchers, one pincher controlling each I.V. tube. The tube pinchers are alter-nately pivoted to a non-clamping, tube-open position by a spring biased, intermittent motion, reciprocating slide bar under the con-trol of a reversible, rotating cam, the cam being driven by a syringe drive motor which is also used to drive the syringe through fill and pump strokes. A sensor may be provided to determine whether the syringe pump performs a fill stroke or a pump stroke. Control of the intake I.V. tube and the output I.V. tube is aided by a pincher spring secured at one end to the intake tube pincher and at the other end to the output tube pincher, the pincher spring extending there between and biasing the pinchers toward the clamp-off position. The tube pinchers, under control of the rotary cam, are adapted for snap action positioning, so that only one tube is open and only one tube is closed at any time.

Description

-1~5~197 Thl~ invention relates generally to improvement~
in ~yringe pumps and, more partlcularly, to a new and lm-: proved valve ¢ontrol ~ystem ~or ~uch pump~ whlch reliably and pra¢isely open~ and clo es the lntake and output I.V, ~ubes ~or a ~yrlnge at appropriate points in the pumping cycle and also g2nerates a control signal ~or e~tabli~hin~
dlrection o~ motor rotakion.
The usual mediGal procedure for the gradual par-~nt~ral adminl~tration of llqulds into the human body, ~uch as llquid nutrlent~, blood or pla~ma, makes use o~ appara- .
tus whl~h i~ commonly re~erred to in the medical arts as an intraYenous admlnistration ~et. The l~travenous ~et U8U~
ally ¢ompri~e~ a bottle o~ uid, normally 3upported ln .
an lnverted po~itlon, an intravenou~ ~eeding tube, typl- :
~ally o~ ~lear pla~tlc, and a suitable valve me¢hani~m, ~uch as a roll clamp, whlch allow~ the liquld to drip out ~ ~`
Or the bottle at a selectively ad~u~table rate into a t:ran~parent drlp chamber below the bottle. ~he drip cham-ber serve~ th~ dual func~lon o~ allowln~ a nur~e or other 20 attendant to observe the rate at which the llquld drlps out of th~ bottle, am3 al~o creates a re~ervolr rOr the llqu~d at the lower end o~ the drip chamber to inaure that no alr :, .
ent~rs the main ~eeding tube leading to the patien~. ~
While ob~ervation o~ the rate of drop ~low via ~:
the drip ohamber i a ~lmple way of controlling the amount - o~ liquid ~ed to a patlent over a perlod o~ tlme, it~ ultl-. .
mat~ eP~`ectivenes~ requiree that a relatlvely con~tant v~gii be malntained on the drop ~low, le3t lt cease en-t~rely due to exhau~tîon o~ the llquld supplled or be¢ome 30 a continuou~ ~tream and perhap~ lncrease the rate o~ llquld introduction to the patient 1;o dangerous level~
- By way o~ example, lt has been the general prac tl¢e in ho~pital~ to have nurse~ periodically monltor drop . ~ .

9 9 ~

~low rate at ea~h intravenous feecling or parenteral in-rus~on ~tation. Such monitorlng of drop ~low is a tedlou~, and time consumin~ proces~, prone to error and associated, po~slbly serLous consequences, and re3ulting ln a substan-tlal reductlon of the available tlme o~ quali~ied medical per~onnel ~or other lmportant duties. Typlcally, the nurs~
~onitoring drop ~low rate will use a watch to tlme the numb~r o~ drops ~lowing ln an interval of one or mors :~
minutes, and ~he wiLl then mentally perform the mathe matic3 neces~ary to convert the ob~erved data to an appro-prlate rluld f~ow rate, e.g., in drops per minute. I~
the calculated ~low rate i~ sub~tantially dlf~er2nt than the pre~ribed rateJ the nurse must manually adJust the roll clamp for a new rate, count drop~ again, and reaalcu-late to measure the new ~low rate.
. Obviou~ly, each o~ the a~or~described measurement~
¢al¢ulations and ~low rate ad~u~tmenks usually take ~ever~
al mlnute~ time wh~ch, when multip:Lied by the number of ~tations being monitored and the mlmber of times each ~tation ~hould be monitored per day, can re~ult in a ~ub-. .
stantial percentage o~ ~otal personnel tlme available. Inadd1tion, under the pres~ure of a heavy s~hedule~ the ob-~ervati~n~ and calculatlons performed by a harrled nurse ln measuring and ad~usting flow rate may not always prove ~ to be reliable and, hence, errors do occur re~ultlng ln ::: undeslred, po ~ibly dangerous lnfRsion ~low rate~
In addition to the a~oredescrlbed dif~lculties, - the parenteral admini~tration of medlcal liquid~ by gravity induced hydro~tatic pres~ure in~usion o~ the llquld from a bottle or other container su~pended above the patlent, 1 very su~ceptible to ~luld flow rate variatlon due to change~ ln the liquid level in the bottlç, changes in tem~
-perature, changes in the venou~ or arterlal pressure of :

-2 " , ~ ~ S~ 9 7 the patient, ~atlent mDvementJ and drirt ln the e~fectlve setting Or the roll clamp or other valve mechanism pin¢hing the feedlng tube. Moreover, ~he:re are a number o~ sltu-ations, such a~ ln intenslve care J cardlac and pediatrlc patients, or where rather potent drug~ are bein~ admin-l~tered, where the de~ired drop flow rate must be c~pable o~ very prec1~e ~election.
It wlll be apparent~ there~ore, that some o~ the ;~
mo~t crltlcal problems confrontlng ho~pital per~onnel fac~d 10 w~th an overwh~lming duty ~hedule and llm~ted tlme avall~
~blllty are khe problems Or quickly, easlly, rellably and accurate~y monitor1ng and regulatlng ~low rates ln the ~`
; parenteral admlnlstration Or medlcal liquld~.
In recent years, a number Or electrlcal monitor- .
lng ~ystems, drop rlow controllers and lnfuslon pumps have be~n developed to acc~mpli3h the various ta~k~ o~ senslng and regulatlng drop ~low rates. EIowever, whlle such mon~
toring and drop rate con~rol devioe~ have general~ y served ~ -their purpose, they have not alwa~t~ proven entlrely ~atis- ` -~actury ~rom the standpolnt o~ co~t, complexlty, stabllity, rellability, accuracy, or preclslon oP adJust~ent ov~r a wlde range Or selected rlow rates. In additlon, su~h system~ ~ave 80metimeS been subJect to drlrt and ~ubstan~
t~al ~low rate varlatlons due to change3 ln temperature, feeding tube crimp~, vartatlons in venous or arterlal pre9-~ure Or th~ patient, or variatlon~ in the height of the bottle or solution level wlthln the bottle. Substantial dl~cultiea have al~o ~een experlenced particularly in :
connectlon wlth e~tablish1ng and mRlntaining accurate rlow a~ very low flow ra~es.
Po~ltive pressure pump~ o~ the clo~ed-l~op .~ p~ristalt~c type hav~ been provide~ whlch overcome some o~
..
the a~orementioned dl~rl~ultle3 with regard to dri~t, and

-3-~s . . . ........................... . . .
,. . . . .

accurate rlow at low flow rates. However, even such closed-loop positive pressure systems only serve to maintaln ac~
curacy of flow in terms o~ stabilizlng to a preselected drop ~low rate, rather than deliverlng a precise pre-~elected volume of ~luld, e.g.~ ln cubic centim2ters per hour. The reason for thl~ is that the accuracy o~ ~uch a ~y~tem i3 llmited lnherently to the accuracy o~ the ~ize ~:
Or the drops produced by an intravenou~ administration -~
8Gt, and the actual drop~ produced by the latter apparatus can vary rather substantially ~rom its deslgnated drop : 3izeJ e.g., due to drlp chamber structural variatlon~, by as much as thlrty percent.
More recently, positlve pre~sure lnfu~lon pumps -~:
of the syrlnge type have slso been provided, wherein a `:
~yrlnge havlng a very preclse displacement volume is re~
peatedly ~illed and emptied on alternate ~yringe pls~on ~trokes durlng a combined 'l~ill" and "pump" operational :
: cycle, so that control of the rate at whlch the syringe ls lled and emptied provide~ an accurate means for preclse ~lUld volume deliver~ over a prescribed period o~ time.
5uch ~yringe pumps are essentially independent of drop flow lnaccuraoie~ lntroduced by I.V. admlnl~tration sets ~ :
and appear to provlde the best overall ~olutlon to accur~
. : ~
at~ and ~table ~luid volume delivery over long perlod~ o~ :
.t~m~, at both hlgh and low flow rates. However~ since a . . .
portion of each opera~ing cycle wlth such eyrlnge pumps t8 concerned with filling the syringe, rather than de- ~
livering ~luld to the patient in a pumping mode, there ls . i:
a heed ~or extremely precise control over the lntake and 30 output syringe valvlng and the directlon o~ rotation o~ ~
the motor drlving the syringe. Such valve control must :: :
not only be very po~itlve in lts actlon and extremely accurate ln lts timlng, but must also be ln precise : ~4- :

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synchronlsm wlth the control over motor direction.
In addltlon, ~yringe pumps of the prior art pri-marlly depend on valving embodied directly wlthin the ~yrlnge itsel~. Thi~ not only increases the cost and complexity of the syringe, particularly where d~sposable syrlnges are employed, but usually also results ln reduced rellabillty of operation.
~; Hence, those concerned with the development and u~e of parenteral fluid administration system s, and par-ticularly those concerned with the de~ign o~ syrlnge pumps, have long recognized the n~ed for improved, rela- -tively simple, economlcal, reliable, stable and aocurate valvlng and mokor control sy~tems ~or ~uch syringe pumps.
The present inventlon clearly ful~ills this need.
Brie~ly, and in general terms, the present inven-tlon provldes a new and improved system for accurately controlling ~luid ~low ln the parlenteral adminlstration of medical liquids, wherein the repetitive opening and clos-ing of a pair of lntake and output I.V tubes communicating 20 with a syrlnge is automatically accomplished durlng suc-- cesslve fi~l and pump perlods by means of cam control of a .;
palr o~ pivotal tube pinchers which alternately pinch off and open the intake and output tubes in proper sequence. ;~
` In addition, the phy~ical po~ition of one of the tube . pi~ohers is monltored and controls the dlrectlon of rota-tlon of the pump motor and, hence, determine~ the fill or pump mode of operatlon o~ the syrlnge. Such valving and motor direction control is accompllshed with no lost motion or delay~ ln that the valvlng actlon and motor direction 30 ¢hanges are automat~cally malntained in precise synchron-ism. Moreover, valvlng ls provlded without the need for providlng relatively complex, expenslve and sometimes un-rellable valve structure~ in the ~yringe lt~el~.

w5_ . .

l~S~ 97 More particularly, the present lnvention provldes a new and lmproved syrlnge pump embodylng a rever~ible, rotary cam controlled reclprocating slide ~ar for alter-nately movlng each of a pair o~ tube pincher~ to su¢ces-~ively clamp of~ and open the lntake and output I.V tubes o~ the syringe to fluid ~low, and, further, controlling motor direction ln synchronlsm with the sequential open and ~losed stateA of the I.V. tubes, to properly enable per~ormance of succes~lve cycles Or ~ill and pump strokes.
~he rotary cam lncludes an arcuate ridge ad~acent lt~ outer perlphery def`lning semi-circular inner and outer : -camming sur~aces against which a cam follower is b~ased, the cam follower belng held again~t one camming sur~ace : :
during performance of a pump ~trolce and again3t the other ~ ;
camming sur~ace during per~ormance o~ a flll strokeJ the ~ :
~am follower typicall~ belng in the form o~ a pln secured to and pro~ecting ~rom one slde o~ a slide bar whlch re-clprocates intermittently back and forth ln a guide block, along a linear path~ Each movement o~ the sllde bar ~olncides ~ith a change ~rom a flll stroke ,o a pump stroke, or ~rom a pump ~troke to a fill stro~eJ in the `~ :
overal} operatlonal cycle of th~ syrlnge pump.
~ oth tube pinchers are pivotally mounted and ~prlng biased towards each other and towards the tube clamping state. The slide bar is power driven by an ex~
tension spring. During performance o~ each ~yringe strokeJ
the cam sur~ace engaging the sllde bar pln holds the ~llde `~
bar asalnst the approprlate tube plncher to pivot the latter and hold it in ~he tube-open posi~ionJ thereby relievlng the slide bar spring of the task of overcomlng ;:
the pincher spring durlng performance of each syringe stroke. In addition, during the tran~ition perlod between syrlnge strokes, the slide bar ~prlng i~ lnitlally -6- .

' 1~5~3~'97 as~lsted in its movement by the pincher spring, the slide bar ~pring only having to work again~t the plncher spring in the latter portlon o~ the sllde bar stroke when the ;~
~lide bar has already acquired some momentum.
The slide bar center i~ offset rrom the center o~
rotation o~ the cam, at the end o~ each slide bar ~troke reposltloning the pinchers. In thi~ regard, one end of the ~; slide bar ~pring 1~ secured to the center o~ the slide bar, whlle the other end ls secured to a point along the outer periphery of the rotary cam. Therefore, a~ the cam rotates, wikh the sllde bar held ~tationary (slnce the ~lide bar pln biased agalnst either the inner or outer arcuate cam- ~
ming surface), the ~lide bar spring 1~ tensloned and sud- ~ -denly relea~ed, to shift the sllde bar longltudlnally and ;:
reposltion the tube pinchers, onl~ when the slide bar pln cam follower comes to the end of the arcuate camming sur~
~ace and drop~ o~ to move either from the inner camming sur~ace to the outer cammlng sur~ace, or ~rom the outer ~ur~ace to the lnner ~ur~ace o~ the cam, depending upon 20 the partlcular ~yringe skroke Just completed. Then the - cam beglns to turn in the oppo~ite direction, aBain trap-plng the ~llde bar cam ~ollower pin to maintain the slide bar in a fixed po~ltion while stretching and rotatlng the slide bar extension sprlng. When the latter ~pring has -been ~ully ~tretched and rotated 1&Q to cock the ~llde bar mechanls~, the other end of the arcuate rldge on the cam goe~ pa~t the ~llde bar pln, allowing the slide bar to ~nap over to it~ alternate po~itlon and begin the entire `
c~cle over again.
A ~xed light source and photoelectric ~ensor ; arrangement provldes a re~erence light beam whlch is ... ~
selectively interrupted by an opaque ~lag carried on one :. o~ the tube plnchers. ~he flag is reposltloned each time . -.. .. . . . . .

~S13997 . .

the tube pincher on which it is mounted is move~, so that a control signal is developed indicative of the syringe stroke about to be performed, the control signal being used to ~ I
establish the proper direction of rotation of the motor.
The new and improved syringe pump valving and motor direction control system of the present invention is extremely accurate and reliable. The system provides valve control ~ithout the need for separate valves in the syringe itself and provides precise motor direction con- `
trol in perfect synchronism with the opeming and closing ~-o~ the syringe intake and output lines.
In one aspect o~ this invention there is provided - ,:
apparatus for use in a syringe pump. The apparatus comprises:
a housing; an intake I.V. tube and output I.V. tube; an in-; take tube pincher`within said housing for alternately clamping off and opening said intake I.V. tube; and output tube pincher ., `1 within said housing for alternately clamping off and ope~ing ~ ?~

~ said output I.V. tube; a pincher spring secured at one end I
~ to said intake tube pincher and at the oth~r end to said ~
'!~
ou~,put tube pincher; a tu~e pincher control means within ~ `; I
i s-aid housing for alternately and eequentially moving one of ;~ said tube pinchers and then the other of said tube pinchers ~`~
, to the tube open posltion. The tube pinchers are movably ~ ~;
j mounted with respect ~o one another. The pincher spring ex~
i tends between said tube pinchers and biases sa~d tube pinchers towards the tube clamping off posi~tion. The tube pincher, control means includes a single common member for substan- --tially simultaneous s~ap action positioning both of said tube I
pinchers so that said positioning maintains a one tube always ., . ; : ~
open and one tube always closed relationship.

The apparatus may further comprises a reversible -~ -8 .. ...
':' ' , :' ~ g~5~g97 .~
rotary cam; a single cam follower coupled to said pincher control means and engaging said cam; and reversible, electri-cal motor means for rotating said rotary cam in either of two directions~
Th~ above a~d other objects, aspects and advantages of the present inventlon will become apparent from the following more detailed description, when taken in conjunc-tion with the accompanying drawings of an illustrative embodiments.
~IGURE 1 is a perspective view showing the in-terior st~ucture of a:syringe pump embodying the present invention, the outer pump housing being shown in dashed -~-lines;
FIGURE 2 is an e~larged, plan view, of the syringe : -~
p.ump of FIGURE ~ with the top plate removed, and illus~
t~ates the-~ap~a~atuscldnr.~n~iapp~mpsst~r.o~e,ss~qi~eh.ti~
positions of the apparatus being shown in phantom;
~IGURE 3 is a fragmentary sectional view, taken '~ .. along tRe llne 3-3 in FIGU~E ~
2Q~ U~E 4 i~ a fragmentary sectional view,:taken alon~ the line 4~4 in FIGURE 2;
FIGURE 5 is a.plani view similar to FIQURE 2, .1 and illustrates the state of the apparatus during per~
:1 i -- formance of a fill stroke; and -. FIGURE 6 is a combined elevational and sec~ional ~ .
. view~ taken along ~he line 6-6 in FIGURE
i Referring now to the drawings, there is sh~n.Ja ~

~ 30 ~ ;
:: .. ~ 8a ,, ,.
' ..

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1~58~7 syrlnge pump system for fluld flow control, embodying the ~eatures o~ the present lnvention. In the ensuing descrlp-tlon, while re~erence ls made to the term "I.V.", normally connoting lntravenous administration, it is to be understood that this ls by way of example only, and the system of the present inventlon is suitable for other forms of parenteral admini~tration as well as lntravenous adminl~tratlon.
The system shown in FIGURE 1 depicts a syringe pump embodylng a syringe 10 which preferably i5 in the form 10 0~ a dlsposable cartridge, but lt will become apparent that all ~ the ~eatures of the present inventlon may be prac-ticed lndependently of wheth~r or not the syringe 10 is dispo~able. The syringe 10 essentially includes a molded ~ -cylinder lOa in which a plston lOb is slfdably received and adapted to be reciprocated back and forth along the axis of the cylinder by an lntegral piston rod lOc which is re-m~vably mounted at one end in a coupling shoe 11 carrled by a lead ~crew 12 which is advanced and retracted by a sult-able drive system. The drive system lncludes a rever~lble, . i . , .
`'20 d.c. stepping motor 13 and approprlate gearing 14, to drive ~
.j .
~the lead ~crew 12 which 1~, in turn, coupled to the plston ;~d lOc o~ the ~yringe 10. The motor 13 is energlzed by a pulse train of motor drive pulses generated by an appro~
priate electrical control ~ystem 15.
The syringe 10 includes an inlet port lOd and an ;
outlet port lOe. The lnlet port lOd communlcate~ through a . .
suitable intake I.V. tube 16 wlth any appropriate llquid source (not shown), usually an f.V. bottle containing appro~
prlate drug~ ~nd~or nutrients ln fluid form. Typical~y~
30 the lntake f.V. tube 16 ls part of an I.V. admlnstration set -~
whlch include~ a transparent drip chamber ln the line be~
tween the syrlnge 10 and the llquld source.
A similar output I.V tube 17 is conneoted at ~;
.

.... . . . . . .
, .. . ~ .. ~. .; . , . . ~ . . . . . .
... . ., . . . , . . , ~ . ...

l~S8997 one end to the outlet port lOe o~ the syringe lO and conveys ~luld ~rom the syringe to a patient .
A palr of syringe pump valves 18, l9, external to the syrlnge 10, are of the tube pincher type, and are selec-tlvely opened and closed at appropriate times ln the overall pumping cycle, under the control o~ a sultable valve control ~y~tem 20. The valve 18 controls the inlet port lOd and i~
~pen dur~ng the ~111 stroke to enable fluid to be drawn from the liquid source, through the intake line 16, lnto the syringe lO, the valve 18 being closed during the pump stroke to prevent fluld ~rom exiting the ~yringe through the inlet ~ ~
port~ The valve l9 controls the outlet port lOe and is~ -open during the pump stroke to enable fluid del~very ~rom the syrlnge lO to the patient through the output line 17, the valve l9 being closed ~urlng the fill ~troke.
The valve control system 20 is al30 driven, through the gearing 14, by the same drive motor 13 as ls used to operate the syrlnge lO. The valve control system 20 also ..
prov~des ln~ormatlon to the electrical oontrol system 15 ~:
controlllng the motor 13, lndicatlng that the ~yrlnge 10 i~ either in the fill stroke or the pump stroke, and this - :~
in~ormatlon, in turn~ enable~ the electrlcal control ~ystem to establish the proper direction of rotation of the motor.
The electrical control system 15 may be o~ conventional .
design for electrically energlzlng the motor 13 and con~
trolling lts direction o~ rotation.
The motor 13 drives, through the gearing 14 and an output camshaft 21, a reversible~ semi-clrcular rotary cam ;~
;.
: 22 which controls the opened and closed posltions o~ the 30 ~yringe pump valves 18, l9. ~
~he gear ratio o~ the gearing 14 is speciflcally .~ -8elected so that the rotary cam 22 rotates through an angle of approximately 180 during a pump stroke of the syringe ;-~

:
, . . . . .
:,; ~ ., ~S~997 10, and then reverses and rotate~ through another 180 ln the opposite dlrection during an intake stroke. Hence, the rotary ~am 22 is essentially a half-turn cam. The camsha~t 21 rotates the cam 22 which blases a slide bar 23 to alter nately hold one Ryringe pump valve open and then the other, ln proper cyclical sequence.
The ~yrlnge pump valves 18J 19 con~l~t of a pair o~ pivotal tube pinchers 24, 25 whlch alternatlvely pinch o~ and open the intake and output tubes 16, 17 respectively, ?
10 ~ the ~yringe 10. The tube p~nchers 24, 25 are spring bla~ed to the tube shut-off position and are po~ltively . . .
drlven open by the valve control system 20, thus allowing ~11 tube clo~ure regardless of normal varlation3 ln I.V, .:
, ; tubing dlameter and wall thickness, : As best ob~erved in FIGS. 2 5, each of the tube : pinchers 24, 25, ls o~ ~ubstantlally L-shape and lncludes a ;: ;
`. long arm 24a, 25a, re~pectively, and a short arm 24b, 25b, :. -; respectively. One face o~ the short arm 24b is 3haped to ~ ~ -de~ine a pincher blade 24c adapted to oooperate with the 20 con~rontin~ face of a shoulder 26 de~lned on the interior ~:~
, s~e of a syringe pump access door 27 to the syr~nge com-partment. Similarly, a pincher blade 25c 1~ defined by the : short arm 25b o~ the output tube plncher 25. Together, th~
plncher blades 24c, 25c and the access door shoulder 26 : - , de~ine a pair of clamping ~urfaces between whlch the intake and output I.V tubes 16, 17 pass. The access door 27 ls held ~hut, after the syr~nge has been installed, by any .
~uitable latch 27a.
. .~. .
The intake tube pincher 24, is plvotally mounted 30 by means o~ a plvot pin and bu~hlng at 28. Simllarly, the .; output pincher is plvotally mounted at 29. Both tube : pinchers are ~pring-blased to the tube clamplng shut-o~
state by a coll sprlng 30 extendlng between the plncher~

;. ~11--. - . ,. . - . . ~, . ,~, , , ~ 9 9 7 and approprlately secured at each end to one o~ the plnchers, as by anchor pins 24d, 25d, respectively.
The syringe pump valves 18, l9 are selectively opened in proper cycllcal sequence by pivoting the tube pinchers 24, 25, one at a tlme, vla contact wlth the re-ciprocatingJ intermlttent motion slide bar 23 whlch i~ power driven by a slide bar extension spring 32. The slide bar 23 i8 slidably mounted withln a guide block 31 and contacts the tube pinchers 24, 25 by bumper pads 33 mounted at each ~nd of the slide bar. In order ~or the slide bar spring 32 ~ to drlve the slide bar 23 ln both directlons, one end of -:
; the ~llde bar spring ls secured to the ~llde bar at itB
¢enter, by an anchor pin 32a, whlle the other end Q~ the~.
... .
~lide bar spring i9 secured to the :rotary cam 22 near its ~-outer periphery by an anchor pin 32b. In either o~ its ~wo positions at the end o~ a slide bar stroke, the center o~
the slide bar 23 along its longitud:lnal axis is of~set from ~ the center o~ rotation o~ the cam 22.
The slide bar 23 moves only up~n completion o~ a ~; 20 syrlnge stroke~ either a ~111 stroke or a pump strDke. The llde bar 23 is maintained in a ~ixed posltion during per- -formance of any syrlnge stroke by an arcuate, semi-circular ~-ridge 22a on the cam 22 defining inner and outer camming sur~aces 22b, 22c, respectlvely, ad~acent the outer per-lphery of the camJ each of the~e camming surfaces alter-nately abutting a sllde bar pin 23a secured to and pro~ect-ing ~rom one face of the ~lide bar at the end of the slide bar.
The slide bar pln 23a is a cam ~ollower which is 30 held against one of the camming surfaces 22b, 22c during performance o~ each syringe stroke and swltche~ positions :
-- ~rom one o~ these camming sur~aces to the other camming sur~ace at the end of each ~troke. As the cam 22 rotates, .

~ 7 the ~,lide bar spring 32 is tensloned to cock the slide bar mechanlsm. Since the center of the sllde bar 23 does not coinclde wlth the center of the cam 22 in elther of the two posltions of the slide bar, rotation of the cam causes the ~llde bar spring 32 to stretch because the sllde bar center is always repo~itioned to the oppo~lte side of the cam center when the cam rotates through a 180 cycle. -~
HenceJ the slide bar spring 32 is tensioned by turning the cam 22 and yet the cam holds the slide bar 23 ln the same - 10 positlon throughout the 180 rotary cycle.
-` AR bes,t observed ln FIGS. 2 and 5, wherein mid-cycle positions of the rotary cam 22 are shown in phantom, when the end of the ridge 22a on the cam 22 is rotated pa~t ,~
'~ the slide bar pin 23a, the slide bar spring 32 snaps the ~ el~de bar 23 over from one of it~, ~wo position~ to the other ;i position in per~ormance of a slide bar stroke, causing the tube plnchers 24, 25 to change po~ition. The tube pincher that was px-evlously open, now closes, while the tube pin~
cher that was previou~ly closed now opens. Then the cam 22 ~ -begln~ to turn in the reverse direction, again trapping the ~lide bar pin 23a agains~ one of the camming surfaces 22b, 22c, to maintain the slide bar 23 in a ~ixed position while ;~
ten~ioning and rotating the sllde bar spring 32. When the ~lide bar spring 32 has been ~ully tensloned and rotated 180, again cocklng the slide bar mechani3m, the other end ` ~ -~
~ Or the ~emi-circular ridge 22a on the cam 22 goes past the ~-;~ ~,lide bar pin 23a, allowing the slide bar 23 to briskly ~nap over to lts alternate position and begln the entire v syringe pump oycle again. The re~ult is extremely precise, 30 positlve action valvlng.
In the embodiment of the invention illustrated, the ~llde bar pin 23a rides on the outer surface 22c of the oam 22 during the pump stroke (FIG. 2) and rldes on the , . . .

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1~5~3~97 lnner surface 22b of the cam durlng the fill stroke (FI~.5).
As the sllde bar 23 moves from one position to the other, lt pushes one or the other of the tube pincher~ 24, 25 open.
The tube pincher spring 30 is what actually provide~ the tube closure ~orce, l.e.~ the ~orce necessary to clo~e on the I.V tubes 16, 17. The ~llde bar extension spring 32 merely provlde3 a ~orce to drive the slide bar 23 thrDugh a ~llde bar stroke.
One advantage of the valve control system 20 re-10 sldes in the manner in whlch the tube plncher spring 30 always holds one of the tube pinchers 24, 25 against the I.V. tublng. As a result, the slide bar sprlng 32 can move :
the slide bar 23 and both tube pinchers 24, 25 without hav-~ ing to overcome the tube pincher sprlng 30 during the ; entire ~llda bar stroke. ~he tube pincher sprlng 30 is -; stretched between the palr of tube pinchers 24, 25 and, i~
the I.V. tubing were not present, it would cause both tube pin¢hers to rest against both of the bumper pads 31 o~ the ~llde bar 23. However, when the I.V. tubing ls ln place, -. .
20 lt causes the closed tube pincher to be spaced a small dis-tance away from the end of the slide bar 23, as at 34 ln ;~
FIG. 2 and at 35 ln FIG. 5. Because o~ thls gap, when the ~llde bar 23 ~irst starts tomove at the end of a syringe ~ -~ill or pump stroke, the tube plncher spring 30 a~tually aids the slide bar spring 32 in initially drlvlng the s}ide bar. Only near the end of the slide bar stroke, when the slide bar 23 has already bu~lt up cons~derable momentum, does the tube pincher sprlng 30 exert any force tendlng to retard the motion of the slide bar. ;~
The position o~ the tube pinchers 24~ 25 is sensed . .
by a combined light source and photoelectrlc sensor assem~
- bly 37, which controls the directlon of rotatlon o~ the motQr 13. In this regard, the pincher position sensor , , . . : , , ~. . , ,: . .

~ 5~gj~7 assembly 37 is mounted on the underside of the cover plate (FIG. 6~ o~ the pump housing and is thereby supported ln a fixed position. An opaque flag 39 is carrled by the output tube pincher 25.
As shown in FIGURE 2, when the flag 39 interrupts the re~erence light beam between the light source and photo-electric sensor, an electrical signal is generated indica-~ng that the system ls elther about to inltlate or is al-: ready performlng a pump stroke, l.e., the output tube 17 ls 10 ~en. In contrast, as observed in FIGURE 5, when the flag 39 i3 retracted by the tube plncher 25, an electrlcal signal is generated indicating that the system is either about to -lnitiate or is in the per~ormance of a fiIl stroke, l.e., the intake tubing 16 is open. The motor directlon control a~orded b~ such an arrangement is in precise synchronism with the intake and output tube valving and the pump can never cause ~luid to be taken in through the syrlnge output tube ~7, or be pumped through the s~yrlnge intake tube 16. ~-Moreover, the motor 13 never reverses until the tube -~ 2n pinchers 24, 25 have been actuated. This results ln a very ~;~
!,. . ` . ' precise volume displacement for each syringe stroke.
In ~ummary, when the slide bar pin 23a arrives at .
the end o~ the inner camming ~r~ace 22b at the completion -~o~ a ~ill stroke, the slide bar pin will drop Ofr the cam 22 because o~ the ~orce exerted by the tensioned slide bar ~pring 32, and the pin will then move to the outer camming -.. ~ .- .
~ aurface 22c for perPormance of a pump stroke (FIG. 2).
.. : .
Thls will reposition the tube pinchers 24, 25 to close the -intake tube 16, open the output tube 17, and generate a - 30 control signal via the posltion sensor 37 to reverse the motor 13. Then khe cam 22 will reverse, because the motor -13 is reversed~ and the cam will rotate while capturing the slide bar pin 23a on its outer camming surface 23c. The :~
.' , :', . ., -. .. . . - .: :
: ~ ,: . . : -, . ~:
.. ..

~S~'g7 cam 22 will go through another 180 cycle in the reverse direction while a~ain stretching the sllde bar sprlng 32, thls time because the sllde bar center ls on the other slde of the cam center. At the end of the 180 cycle, the slide bar pln 23a will again drop off the outer camming sur~ace 22c, and move to the inner camming surface 22b where it started (FIG. 5). In this way, the sllde bar 23 03cillates ~ntermittently between its two extreme posltlons to pivot the tube pinchers 24, 25 and open and close the lntake and -: ~
10 output I.V. tubes 16, 17, preclsely and positively at appro-priate times in the operational cycle of the syringe pump.
The syringe pump valvlng and motor direction con-trol system of the present invent~on satisfles a long ~xlsting need for improved, relatlvely ælmple, economical, rellable, stable and accurate valving and motor control `~ ~ystems for such syringe pumps. The system provides ~, extremely precise valve control wlthout the need for separ- ~;
ate valves in the syringe itsel~ and provides preciæe motor dlrect~on control in per~ect synchronism with the opening 20 and olo~ing of the syringe intake and output tubes It wlll be apparent from the foregolng tha~, whllo particular forms of the lnventlon have been lllustrated and described, various modif~cations can be made wlthout departing ~rom the sp~rit and scope of the invention.
Accordingly, it ls not lntended that the inventlon be . . , ~ l~mlted, except as by the appended claims.
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Claims (2)

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

1. Apparatus for use in a syringe pump, said apparatus comprising: a housing; an intake I.V. tube and output I.V tube;
an intake tube pincher within said housing for alternately clamping off and opening said intake I.V. tub; an output tube pincher within said housing for alternately clamping off and opening said output I.V.
tube; said tube pinchers being movably mounted with respect to one another; a pincher spring secured at one end to said intake tube pincher and at the other end to said output tube pincher, said pin-cher spring extending between said tube pinchers and biasing said tube pinchers towards the tube clamping off position; a tube pincher control means within said housing for alternately and sequentially moving one of said tube pinchers and then the other of said tube pinchers to the tube open position, said tube pincher control means including a single common member for substantially simultaneous snap action positioning both of said tube pinchers so that said position-ing maintains a one tube always open and one tube always closed relationship.

2. Apparatus as claimed in Claim 1, and further comprising:
a reversible rotary cam; a single cam follower coupled to said pincher control means and engaging said cam; and reversible, electrical motor means for rotating said rotary cam in either of two directions.