|||||l|||||||||l|||l|||||||||l|||||l|||||||||l||||ll||l||llllllllllllllllll
`US005322422A
`_
`[11] Patent Number:
`5,322,422
`Ulllted States Patent
`[45] Date of Patent:
`Jun. 21, 1994
`Natwick et al.
`-
`________,_______________,____________________________________
`
`[19]
`
`2
`
`[54] VOLUMETRIC PUMP TUBE RESHAPER
`AND METHOD
`
`Attorney, Agent, or Firm-—-Christensen, O’Connor,
`Johnson & Kindness
`
`[75]
`
`Inventors: Vernon R. Natwick, Los Altos;
`Michael W. Lawless, Boulder Creek,
`both of Calm
`
`[73] Assignee: Abbott Laboratories, Abbott Park,
`111;
`[211 APPL N°-= 11391
`[22] Filed,
`Feb_ 1, 1993
`
`[62]
`
`Related U_s_ Application Data
`_
`_
`_
`Division of Ser. No. 916,426, Jul. 17, 1992, Pat. No.
`5,219,279, which is a division of Ser. No. 742,623, Aug.
`3, 1991, Pat. No. 5,153,437, which is a division of Ser.
`No. 494,210, Mar. 15, 1990, Pat. No. 5,055,001.
`Int. Cl.5 .............................................. F04]! 43/08
`................ .. 417/474
`[58] Field of Search ................................ 417/474-478;
`604/153
`
`[51]
`
`C“ d
`R f
`e
`e erences
`U.S. PATENT DOCUMENTS
`4,302,164 ll/1981 Manella ............................... 417/474
`4,515,539
`5/1935
`__ 417/477
`4,550,471
`3/1937
`_, 417/474
`4,653,987
`3/1987
`417/474
`4,906,168
`3/1990
`.. 417/476
`419361760 6/1990
`-- 417/478
`g-33:33
`------
`9/1992 Danby et al.
`5,151,019
`....................... 417/474
`Primary Examz'ner—Richard A. Bertsch
`Assistant Examiner—Peter Korytnyk
`
`[57]
`
`ABSTRACI
`_
`-
`1
`-
`'
`-
`A volumetric pump and method for disp acing a prede
`terinined quantity of fluid at a predefined cracking pres-
`sure. independent of supply and output PT¢5S“1'95- The
`volumetric pump (30) includes an inlet cracking valve
`(46), an outlet cracking valve (52), and a plunger (48)for
`displacing fluid from a pumping portion (3412) offlexible
`tubing (34) that extends throughthe volumetricpuinp.
`The pumping portion of the flexible tube fills with liq-
`uid when the inlet cracking valve is fully opened and is
`urged to expand by jaws (236) on pivotally-mounted
`31-ms (234), The arms are forced to pivot, as tubing
`'
`1
`reshape’ '°u°’5 um)’ dlspmed °“ the P unger’ mu
`;1:I:Ig)b:}‘c:_‘:;;::u:‘1?;$‘i°:n (S2:g21)n‘f_’tft°c:‘f°}t‘h“:"1:‘l'lIrl;‘i‘n“g“%y‘f
`cle, the inlet cracking valve applies a cracking force to
`the flexible tubing, while the plunger compresses the
`pumping portion of the flexible tubing sufficiently to
`develop a cracking pressure that displaces excess fluid
`back through the inlet cracking valve toward a con-
`tainer (32). After the excess fluid has been forced from
`the pumping portion of the flexible tubing, a pumping
`Segmem °f the °Y°1° begins’ ‘”h°"°i“ ‘,h°i"1e‘°"’°ki,“g
`valve closes fully and the outlet cracking valve applies
`a cracking force to compress the flexible tubing. Fluid is
`then forced by the plunger from the pumping portion of
`the flexible tubing into a distal portion (34c). The volu-
`metric pump compensates for variations in elasticity of
`the flexible tubing that would otherwise cause varia-
`::§gS5;’;_th° cmklng pressure’ "mg balance bl°°kS (22
`
`15 Claims, 17 Drawing Sheets
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`June 21,1994
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`June 21, 1994
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`U.S. Patent
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`June 21, 1994
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`
`1
`
`5,322,422
`
`VOLUMETRIC PUMP TUBE RES]-IAPER AND
`METHOD
`
`This is a divisional of the prior application Ser. No.
`07/916,426, filed on Jul. 17, 1992, now U.S. Pat. No.
`5,219,279 which is a divisional of application Ser. No.
`07/742,623 filed on Aug. 8, 1991, now U.S. Pat. No.
`5,158,437, which in turn is a divisional of U.S. Pat. No.
`5,055,001, issued Oct. 8, 1992, Ser. No. 07/494,210, filed
`on Mar. 15, l990, the benefit of the filing dates of which
`are hereby claimed under 35 U.S.C. § 120.
`TECHNICAL FIELD
`
`5
`
`10
`
`This invention generally pertains to a positive dis-
`placement volumetric pump, and specifically, to a volu-
`metric pump in which a plunger acts on a flexible mem-
`ber to displace fluid from a chamber.
`
`BACKGROUND OF THE INVENTION
`
`20
`
`30
`
`35
`
`Intravenous infusion of medicinal liquids has tradi-
`tionally been accomplished using drip regulated, grav-
`ity flow systems. However, it is generally recognized
`that a more precisely regulated flow of drug to the
`patient can be administered with a pump. Because of 25
`their simplicity and ease of use, peristaltic pumps are
`often used for this purpose. A gravity flow system is
`readily converted to a peristaltic pump infusion system
`by threading the drug delivery or intravenous (IV) line,
`which is attached to the drug container, through the
`peristaltic pump. The pump then controls the rate at
`which the drug is delivered to the patient.
`A peristaltic pump displaces liquid by repetitively
`compressing a section of the flexible tube comprising
`the IV line. This line is threaded through a channel
`formed in the pump and extends unbroken, from the
`drug container to the patient. In one type of peristaltic
`pump, the channel is curved around a central axis. A
`rotating arm with rollers fixed on each end compresses
`the section of tubing disposed within the channel, ad-
`vancing the rollers along the longitudinal axis of the
`tubing as the arm rotates about the central axis. Liquid
`within the tubing is thus forced ahead of the advancing
`roller along the internal passage in the line.
`Another type of peristaltic pump has a linear channel
`in which the IV line is threaded and is thus referred to
`as a linear (or traveling wave) peristaltic pump. The
`linear peristaltic pump includes a plurality of finger-like
`plungers
`that are sequentially actuated by cams
`mounted along a motor driven shaft. Liquid within the
`section of tubing that extends along the linear channel is
`advanced along the tubing’s longitudinal axis by the
`advancing wave-like compression of the fingers. An
`example of such a pump is disclosed in U.S. Pat. No.
`4,479,797.
`
`40
`
`50
`
`Inlet and outlet valves and a single liquid displace-
`ment plunger are used in another type of peristaltic
`pump. Each pumping cycle in this type of pump begins
`with the outlet valve closed and the ‘inlet valve open.
`Fluid flows from the source container into a short sec-
`tion of tubing that is disposed between the inlet and
`outlet valve. After this section of tubing has filled with
`liquid, the inlet valve closes and the outlet valve opens.
`The plunger then compresses the short section of tubing
`between the valves, displacing the liquid contained
`therein, and forcing it from the pump. U.S. Pat. No.
`4,559,038 discloses a peristaltic pump of this type.
`
`2
`Cassette pumps are also frequently used in adminis-
`tering medicinal fluids to a patient and normally pro-
`vide a more accurate rate of fluid flow than a peristaltic
`pump. In a cassette pump, a cassette comprising a plas-
`tic housing that includes a pumping chamber and inlet
`and outlet valves, is connected via a disposable tube set
`to a drug container. The cassette is inserted into an
`appropriate device designed to drive the cassette and
`administer fluid at a controlled rate. The pumping de-
`vice includes an inlet valve actuator, an outlet valve
`actuator, and a pumping plunger. Inside the cassette,
`passages connect the inlet valve and the outlet valve to
`the pumping chamber; a flexible membrane, which is
`sealed between two halves of the plastic housing, inter-
`rupts fluid flow through inlet and outlet valve openings
`formed in the housing when the membrane is deformed
`by the inlet and outlet valve actuators. The plunger acts
`on the flexible membrane covering the pumping cham-
`ber in the cassette to force liquid past the open outlet
`valve and through an outlet port of the cassette. An
`example of a cassette pump is disclosed in commonly
`assigned U.S. Pat. No. 4,818,186.
`The rate at which fluid is delivered by each type of
`positive displacement pump discussed above is nor-
`mally controlled by the rate at which the pump oper-
`ates, e.g., the rotational rate of the rotating arm in that
`type of peristaltic pump. Furthermore, the accuracy
`with which a given rate or volume of fluid flow can be
`achieved by these pumps is dependent upon the pres-
`sure of the fluid at the input of the pump and the back
`pressure at its output. Since both the flexible tubing (in
`the peristaltic pumps) and the flexible membrane (in the
`cassette) define a compliant pumping chamber, the vol-
`ume of fluid that fills the pumping chamber is affected
`by the head pressure of the fluid from the drug con-
`tainer. Similarly, the volume of fluid delivered at the
`output of the pump depends on the back pressure of the
`fiuid downstream of the outlet. The cassette pump and
`the single plunger type of peristaltic pump, both of
`which have positive closure inlet and outlet valves, are
`particularly sensitive to head and back pressures be-
`cause the volume of the pumping chamber disposed
`between the valves and the amount of fluid that fills the
`chamber generally must be constant to provide an accu-
`rate and consistent rate of flow from the pump.
`Several other parameters can affect the accuracy of
`fluid flow delivered by specific types of positive dis-
`placement pumps. For example, when the compression
`force is removed from the tubing in a peristaltic pump,
`the tubing must recover to a defined and consistent
`internal diameter to insure that the same volume of fluid
`is delivered in each pump cycle. If the volume of the
`passage defining the pumping chamber changes over
`time, for example, due to changes in the tubing elastic-
`ity, the pump’s flow rate will also change. Inexpensive
`polyvinyl chloride (PVC) tubing, commonly used for
`disposable tube sets in medical IV applications,
`is
`known to experience changes in elasticity over time and
`with repetitive compression of the tubing, thereby af-
`fecting the extent to which the tubing recovers when a
`compression force is removed.
`In the single plunger type of peristaltic pump, the
`plunger should compress the tubing uniformly and con-
`sistently with each pumping stroke to provide an accu-
`rate and consistent rate of fluid flow from the pump.
`The plunger mounting assembly must permit
`the
`plunger to move freely back and forth along a recipro-
`cation axis, yet should prevent it from twisting or mov-
`
`ACTA EX. 1025-019
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`ACTA Ex. 1025-019
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`
`3
`ing laterally away from this axis, because such move-
`ment can change the compression stroke volumetric
`displacement. Since the plunger is typically driven by a
`rotating cam, the mounting assembly should also pro-
`vide a biasing force to maintain the plunger in contact
`with the cam surface, preferably without introducing
`sliding friction or using helical springs. Most prior art
`plunger mounting assemblies do not address all of these
`concerns.
`
`Due to the potential safety concerns involved in ad-
`ministering medicinal fluids intravenously to a patient,
`an infusion pump should include an air-in-line sensor to
`detect large air bubbles within the pump and stop the
`pump before such bubbles are infused into the patient‘s
`circulatory system. Provision should also be made to
`detect when a drug container becomes empty or a sup-
`ply line connected to the container occluded. If the
`flow of fluid from the pump is interrupted for any rea-
`son, the pump should be shut off and an alarm sounded
`to alert medical personnel.
`Ideally,
`these functions
`should be integrated into the pump, and are in some
`prior art pumps. However, virtually none of the avail-
`able peristaltic pumps currently provide both of these
`safety-related features.
`In consideration of these problems that exist with the
`prior art pumps, it is an object of the present invention
`to provide a positive displacement pump in which the
`volume and rate of delivery of fluid from the pump is
`substantially unaffected by variations in the pressure of
`fluid supplied to the pump. Another object of this in-
`vention is to provide a pump in which the volume and
`the rate fluid is delivered from the pump is substantially
`unaffected by variations in fluid pressure downstream
`of the pump. Yet a further object is to provide a positive
`displacement fluid pump that delivers fluid to an output
`port of the pump at a predefined pressure. Still a further
`object of the invention is to provide a spring-biased
`support for a plunger enabling it to reciprocate freely
`along a reciprocation axis without sliding friction, while
`preventing it from twisting or moving laterally away
`from the reciprocation axis. These and other objects
`and advantages of the present invention will be appar-
`ent from the attached drawings and the Description of
`the Preferred Embodiments that follows.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the claimed invention, a volumet-
`ric pump is adapted to pump a fluid through a set that
`includes a flexible member, by deforming different por-
`tions of the flexible member in a predefined pumping
`cycle. The portions of the flexible member respectively
`define a chamber, an inlet passage, and an outlet pas-
`sage. Deformation of the portion of the flexible member
`defining the chamber reduces the volume of the cham-
`ber and displaces fluid from it. The volumetric pump
`includes a chassis on which an inlet valve is disposed
`adjacent to the inlet passage. The inlet valve is posi-
`tioned to act on an inlet portion of the flexible member
`to control fluid flow through the inlet passage and ex-
`erts a first and a second sealing force on the inlet portion
`of the flexible member during the pumping cycle. The
`first sealing force is substantially less than the second
`sealing force and allows fluid to flow through the inlet
`passage from the chamber as fluid in the chamber is
`initially pressurized beyond a predefined level. The
`second sealing force subsequently interrupts fluid flow
`through the inlet passage from the chamber, enabling
`
`5
`
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`
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`
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`
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`
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`
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`
`5,322,422
`
`4
`fluid pressurized in the chamber to be forced through
`the outlet passage.
`A plunger disposed on the chassis adjacent the cham-
`ber is operative to deform a pumping portion of the
`flexible member to displace fluid from within the cham-
`ber. An outlet valve is disposed on the chassis adjacent
`the outlet passage and is thus positioned to act on an
`outlet portion of the flexible member to control fluid
`flow through the outlet passage. The outlet valve exerts
`a forward-flow sealing force and a back-flow sealing
`force on the outlet portion of the flexible member dur-
`ing the pumping cycle. The forward-flow sealing force
`is substantially less than the back-flow sealing force and
`allows fluid to flow through the outlet passage from the
`chamber; however, the back-flow sealing force com-
`pletely interrupts fluid flow past the outlet valve. Means
`are also provided for actuating the inlet valve, the outlet
`valve, and the plunger to deform the portions of the
`flexible member during the pumping cycle, thereby
`forcing fluid through the outlet passage at a predeter-
`mined rate of fluid delivery.
`The means for actuating the valves and plunger com-
`prise a motor, an inlet valve cam, an outlet valve cam,
`and a pumping cam. A profile on the pumping cam
`sequentially defines a filling segment, a pumpback-
`pressurization segment, and a pumping segment. After
`the chamber is filled with fluid, the inlet valve exerts the
`first sealing force and the outlet valve blocks fluid flow
`from the chamber into the outlet passage, enabling fluid
`pressurized in the chamber to be forced through the
`inlet passage. The motor rotates the pumping cam from
`a start position and the pumping cam actuates the
`plunger to pressurize fluid in the chamber to the prede-
`fined level, thus forcing excess fluid in the chamber to
`backflow through the inlet passage until the pumping
`cam reaches a rotational position corresponding to the
`start of a pumping stroke. During the pumping stroke,
`fluid is again displaced from the chamber by the plunger
`and forced to flow through the outlet passage as the
`inlet valve cam causes the inlet valve to close with the
`second sealing force, thereby preventing fluid flow
`through the inlet passage. After the pumping stroke is
`completed, the inlet valve cam causes the inlet valve to
`open fully, enabling fluid to flow from a source through
`the inlet passage, again filling the chamber.
`At all times, even when the volumetric pump is not
`pumping fluid, at least one of the inlet and outlet valves
`blocks fluid flow through the inlet and outlet passages,
`respectively. The rate at which the motor rotates the
`inlet, the outlet, and the pumping cams, at least in part,
`controls the rate at which the fluid is delivered through
`the outlet passage. To further reduce the rate of fluid
`delivery’, the motor stops rotating the pumping cam for
`an interval of time at least once during the pumping
`stroke.
`«
`
`In one embodiment of the volumetric pump, the flexi-
`ble member comprises a tube and the pumping chamber
`comprises a portion of the tube disposed between the
`inlet and the outlet valves. In this embodiment, the
`plunger partially compresses the tube when the pump-
`ing chamber is filled with fluid at the start position of
`the pumping cam. The volumetric pump further com-
`prises tube-shaping means that are disposed where the
`plunger compresses the tube and are operative to bias
`the tube to more completely fill with fluid.
`In another embodiment of the volumetric pump, the
`flexible member comprises a generally planar, elasto-
`meric membrane disposed in a housing. The inletvalve,
`
`ACTA EX. 1025-020
`
`ACTA Ex. 1025-020
`
`

`
`5
`and the outlet valve comprise spring-biased members
`that act on the membrane to control fluid flow through
`passages in the housing.
`The volumetric pump may include means for deter-
`mining if fluid is flowing through the outlet valve as the
`plunger compresses the flexible member. It may also
`include means for sensing a fluid pressure upstream of
`the inlet valve and/or downstream of the outlet valve.
`Due to the compressibility of a gaseous fluid, if the
`chamber is substantially filled with such a fluid, the
`pressure developed in the chamber during the pumping
`cycle is insufficient to force the gaseous fluid past the
`outlet valve.
`
`A method for preventing variations in a supply pres-
`sure from affecting a fluid delivery rate from a pump
`that includes an inlet valve and an outlet valve, and
`which displaces fluid from a pumping chamber defined
`by a flexible member is another aspect of the present
`invention. The method comprises steps generally con-
`sistent with the functions implemented by the elements
`of the volumetric pump, as described above.
`Yet a further aspect of this invention is an apparatus
`for supporting a reciprocating plunger in a positive
`displacement pump. The apparatus includes a frame
`having two spaced-apart members disposed on opposite
`sides of the plunger. A plurality of pairs of flexures
`extend between the two spaced-apart members and the
`plunger, each flexure having a longitudinal axis. The
`flexures comprising each pair of flexures are aligned
`substantially parallel to each other. Due to the dispo-
`sition and spacing of the flexures, the plunger is sup-
`ported so that it can reciprocate along a reciprocation
`axis that is generally normal to the longitudinal axes of
`each pair of flexures, but is constrained by the pairs of
`flexures so that it does not move transversely in respect
`to the reciprocation axis.
`The flexures are each attached to the spaced-apart
`members and to the plunger and apply a biasing force to
`the plunger that is directed along the reciprocation axis.
`A first pair of the flexures are attached to the plunger at
`a first level along the reciprocation axis, and a second
`pair are attached to the plunger at a second level. The
`first pair of the flexures are spaced apart a first distance,
`while the second pair are spaced apart a second distance
`that is substantially different than the first. The flexures
`bias the plunger along the reciprocation axis against a
`drive force that displaces the plunger along the recipro-
`cation axis. One pair of the flexures is preferably spaced
`apart from the other pair so as to prevent rotation of the
`plunger about a rotation axis that is normal to the recip-
`rocation axis. Each flexure preferably comprises an
`elongate flat metal spring.
`A method of constraining a plunger to move only
`along a reciprocation axis, preventing it from twisting
`or moving laterally away from the reciprocation axis, is
`yet another aspect of the present invention. The method
`includes steps generally consistent with the functions of
`the elements of the apparatus for supporting a plunger,
`as described above.
`
`’
`
`Still another aspect of the present invention is appara-
`tus for compressing and shaping a flexible tube. This
`apparatus includes plunger means, mounted to move
`bidirectionally along a reciprocation axis. The plunger
`means periodically compress the flexible tube to dis-
`,place a fluid from an interior passage disposed within
`the flexible tube and then allow the flexible tube to
`expand to at least a partially uncompressed condition.
`Drive means are included for periodically driving the
`
`5
`
`20
`
`25
`
`30
`
`35
`
`45
`
`55
`
`60
`
`65
`
`5,322,422
`
`6
`plunger means to move along the reciprocation axis.
`Tube shaper means are actuated by the motion of the
`plunger means and are operative to apply a reshaping
`force against the flexible tube that tends to expand the
`interior passage to a maximum desired volume.
`The tube shaper means comprise a pair of arms that
`are pivotally mounted on opposite sides of the plunger
`means. Jaws are disposed on these arms, at each side of
`a segment of the flexible tube compressed by the
`plunger means. Also disposed on opposite sides of the
`plunger means are a pair of rollers that transmit the
`reshaping force from the plunger means to the pivotal-
`ly-mounted arms. Thus, the interior passage is expanded
`by the jaws in synchronization with the plunger means
`retracting from a position of maximum compression of
`the flexible tube.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic block diagram of a volumetric
`pump in accordance with the present invention;
`FIG. 2 is an isometric view of the volumetric pump,
`showing an access door that is closed and latched in
`place;
`FIG. 3 is an isometric view, similar to that shown in
`FIG. 2, but with the access door shown in an open
`position, disclosing the path followed by a flexible tube
`through the volumetric pump;
`FIG. 4 is a longitudinal cross section of the pump
`assembly shown in FIGS. 2 and 3;
`FIG. 5 is a schematic transverse cross section of the
`volumetric pump, illustrating compression of the flexi-
`ble tube to pump fluid;
`FIG. 6 is a schematic cross section of the volumetric -
`pump, illustrating reshaping of the flexible tube to facili-
`tate its filling with fluid;
`FIG. 7 is a plan view illustrating the calibration of
`one of the tube reshaping arms to achieve a desired
`angular deflection;
`FIG. 8 is an isometric view of an inlet cracking valve
`used in the volumetric pump and a transverse section of
`a cam assembly that is used to actuate the cracking
`valve;
`FIG. 9 is an analogous view to that of FIG. 8, isomet-
`rically showing an outlet cracking valve used in the
`volumetric pump and a transverse section of the cam
`assembly that is used to actuate the outlet cracking
`valve; FIGS. 10A—10C are cutaway, longitudinal cross
`sections of the volumetric pump respectively illustrat-
`ing a fill segment, a pumpback-pressurization segment,
`and a pumping segment of the pumping cycle;
`FIG. 11 illustrates a profile of the inlet cracking valve
`cam track;
`FIG. 12 illustrates a profile of the outlet cracking
`valve cam track;
`FIG. 13 illustrates a profile of the plunger cam track;
`FIG. 14 is an isometric view of a portion of the cam
`assembly, illustrating a torque compensation track, a
`torque compensation follower and roller, and a cam
`assembly position sensor;
`FIG. 15 is an exploded view isometrically illustrating
`one of the tube reshapers, the plunger and support flex-
`ures, and pressure sensors used in the volumetric pump;
`FIG. 16 is an isometric view of a cassette used with a
`different embodiment of the volumetric pump;
`FIG. 17 is a plan view of the cassette with a front
`panel and a flexible membrane removed to illustrate a
`fluid path through the cassette;
`
`ACTA EX. 1025-021
`
`ACTA Ex. 1025-021
`
`

`
`5,322,422
`
`7
`FIG. 18 is a cross-sectional view of the cassette, taken
`generally along section line 18-18 in FIG. 17, but
`showing the front panel and the flexible membrane;
`FIG. 19 is a partial cross-sectional view of the inlet
`cracking valve in the cassette, taken generally along
`section line 19-19 in FIG. 17, and showing the front
`panel and the flexible membrane;
`FIG. 20 is a longitudinal cross-sectional view sche-
`matically illustrating a volumetric pump drive mecha-
`nism for the cassette;
`FIG. 21 is a plan view of the volumetric pump drive
`mechanism shown in FIG. 20;
`FIG. 22 is a timing chart indicating the timing motor
`shaft revolutions and rpm for low flow ranges of the
`volumetric pump; and
`FIG. 23 is a schematic block diagram illustrating a
`volumetric pump controller.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The term “volumetric pump” is applied to the present
`invention because it appropriately emphasizes one of
`the invention’s more important advantages. Specifi-
`cally, during each pumping stroke,
`the volumetric
`pump consistently and repeatedly displaces a defined
`volume of fluid at a defined pressure, thereby ensuring
`that a desired rate of fluid flow is accurately provided
`by the pump.
`In FIG. 1, a volumetric pump in accordance with the
`present invention is generally illustrated in block dia-
`gram at reference numeral 30. Volumetric pump 30
`comprises a number of components that are serially
`arranged along a fluid path through the pump. A liquid
`31 that is administered by volumetric pump 30 is sup-
`plied from a container 32 through flexible tubing 34.
`Liquid 31 enters volumetric pump 30 through a proxi-
`mal portion 34a of the flexible tubing. The fluid path
`continues through a pumping portion 34b and exits the
`pump through a distal portion 34c of the flexible tubing.
`Distal portion 34c of the flexible tubing is connected to 40
`a needle/catheter 36 that is used to introduce liquid 31
`output from the pump intravenously into a patient. Of
`course, volumetric pump 30 may also be used in other
`applications wherein distal portion 34c of the flexible
`tubing is connected to some other apparatus disposed 45
`downstream of volumetric pump 30.
`Flexible tubing 34 is continuous, but for purposes of
`this disclosure, is referred to as divided into the proxi-
`mal, pumping, and distal portions 34a, 34b, and 34c,
`respectively; preferably, it comprises a polyvinyl chlo-
`ride (PVC) disposable tube set, such as is customarily
`used to administer fluids intravenously to a patient. The
`tubing may have a 0.137" 0.D. and 0.100” I.D.
`In this application of the volumetric pump, it is desir-
`able to prevent free flow of liquid 31 from container 32
`into the patient. For this reason, volumetric pump 30
`includes a free flow latch 38, which clamps proximal
`portion 340 of the flexible tubing to prevent liquid 31
`from container 32 flowing freely into a patient, due to
`head pressure. Free flow latch 38 does not restrict fluid
`flow during the normal pumping operation of volumet-
`ric pump 30, _but is configured to automatically clamp
`proximal portion 340 of the flexible tubing when a door
`78 (shown in FIGS. 2 and 3) on volumetric pump 30 is
`opened. While door 78 is closed, free fluid flow through
`volumetric pump 30 is otherwise precluded by volumet-
`ric pump 30, as explained below. The position of door
`78 is sensed by a door position detector 62, producing a
`
`8
`signal that prevents operation of volumetric pump 30
`when door 78 is open. Similarly, a tubing detector 40 is
`interconnected to free flow latch 38, and produces a
`signal indicative of the presence of flexible tubing 34
`within free flow latch 38; operation of volumetric pump
`30 is inhibited if the signal indicates that the flexible
`tubing is not in place.
`A balance block 42 rests against proximal portion 34a
`of flexible tubing 34 and serves to compensate for varia-
`tions or changes in the elasticity of flexible tubing 34.
`The function and operation of balance block 42 are
`more fully explained below.
`_
`Next in the serial arrangement of components along
`the fluid path within volumetric pump 30 is a proximal
`pressure sensor 44, which operates to sense the pressure
`of fluid within proximal portion 34a of the flexible tub-
`ing. Proximal pressure sensor 44 produces a signal in-
`dicative of fluid pressure in this portion of flexible tub-
`ing 34 for use in monitoring the operation of the pump
`and to determine if proximal portion 3-‘la has become
`occluded.
`A key element in the operation of volumetric pump
`30 is an inlet cracking valve 46, disposed immediately
`downstream of proximal pressure sensor 44. Inlet crack-
`ing valve 46 functions in cooperation with a plunger 48
`and an outlet cracking valve 52, which are disposed
`sequentially downstream of the inlet cracking valve, to
`provide the displacement of a volumetric quantity of
`fluid from pumping portion 34b of the flexible tubing by
`volumetric pump 30 and to generally isolate the volu-
`metric pump from variations in proximal and distal fluid
`pressure, due, for example, to variations in the elevation
`of container