CA1127003A - Metering apparatus for a fluid infusion system with flow control station - Google Patents

Abstract

Abstract of the Disclosure A system for infusing fluids into the human body includes a peristaltic-type metering apparatus which con-trols the flow of fluid through a disposable administra-tion set. The metering apparatus includes a control system which allows the volume and rate of flow of the fluid to be infused to be accurately preset by the operator. The control system provides an alarm function in the event of malfunction of the pump or occlusion of the tubing of the administration set, and a minimum pumping rate for maintaining fluid flow through a system after the desired volume of fluid has been infused. Novel power supply circuitry within the control system renders the system immune to power line transients, and a novel bubble detector circuit provides for more reliable detection of air bubbles in the tubing. A mechanical linkage between the pressure plate and downline flow restriction plunger of the metering apparatus provides for convenient loading of the administration set and for automatic closure of the plunger prior to use.

Description

~ ~ r ~ 'he pres~nt invention relates generally -to fluid infusion sys~ems, and more particularly to an improved flow me-tering apparatus for such systems.
The infusion of fluids into the human body is usually ~ccompli.shed by means of an admin:Ls-kration set in conjunction with metering apparakus which contr~1~ the rate of flow oE fluid through the set. Peristaltia type pumps, which funetion by repetiti.vel~ compressing and e~panding a sec-tion of tubing, have proven particularly attractive for use in metering apparatus si.nce they do not introduee the possibility of leakage or eontamination into the system, while p.roviding positive control of fluid flow through the system.
One form of peristaltic type pump whieh is particularly well adapted :Eor infusion applieations is deseribed in applicant's issued Canadian Patent 1,088,835 of Thurman S.
Jess, issued November 4, 1980. Basically, this pump construction ineludes individually spring-biased rollers in the pump rotor whieh provide a uniform co~pression foree, and a spring-biased plunger which restricts the lumen of the administration set downline o:E the pump rotor to provide a back pressure against which the pump must work. This prevents tm/ ~
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the release of dissolved gas in the tubing section, assists in restoring the tubing to its original shape 0110~1ing corn-pression by the p~p, and prevents uncontrolled gravit~ ~lo~
in the event of pump Eailure.
S In many applications, such as where ~edicatior. is being administered, it is necessary that the operation of the peristaltic pump be precisely controlled to infuse only a predetermined volume of fluid at a predetermined xate. Thus, the need has developed for a control system for peristaltic type infusion pumps which enables the operator to preset a quantity and rate of infusion, and which continuously monitvrs the performance of the pump to insure compliance with the pre-set parameters by interrupting operation and alerting the - operator in the event of a malfunction~ Furthermore, it is desirable that the system be fall-safe, and substar,tially unaffected in opera ion or accuracy by power line interruptions or transients. The metering apparatus of the present invention provides these features in an integrated unit which is simple and convenient to use.
Accordingly, it is a general object of the present invention to provide a new and improved system for infusing fluids into the human body.
It is a more specific object of the present inven-tion to provide a new and improved metering appara~us for use in con3unction with an administration set for infusing fluids :into the human ~ody.
According to the present invention -there is provided a fluid metering apparatus for controlllng the flow of fluid thxouyh -the tubing of a fluid administra-tion se-t, the apparatus having ahousi.ny with a rotor mounted on the housing Eor xota-tion about a flxed axis, the rotor including a plural.ity of pressure rollers disposed about the circumEerence thereof. Means is prov:ided, includiny a pressure plate disposed adjacen-t the circumference of the rotor so that a segment of the tubiny is positioned in compressive engagement with the pressure rollers and fluid is caused to flow through the tubing with rotation of the rotor. Flow restriction means is provided which includes a slidably mounted plunger spring-biased agains-t the tubing for occluding the tubing at a predetermined location downline of the tubing segment to increase the pressure of the fluid in the tubing segment. A platen assembly is provided which is slidably mounted to the housing,and the pressure plate has an open position displaced from the circumference of the rotor so -that the tubing can tm/,~/t............................ ~3 ! t ~ n ~
be insertec1 therebetween and a closed position adjclccnt th~
rotor circumference so tha-t a segment of the -tubing is positioned in the compressive engagement w:ith the pressure rollers. The plunger has an open posi-tion rer~oved from -the tubing and an operatincJ posi-tion cornpressively enyacJincJ
-the tubincJ. Means is carried on the hous:iny ~or bias:Lng the plunger to the operating position even if the p:Laten assembly is accidently moved to its open po~ition.
user-actuable latchiny means is op~rable only when the platen assembly :is in the open position for latchiny the p]unyer in the open position. The latching means automatically releases the plunger to allow the plunger to move to the operating position upon actuation oE the pressure plate to the closed position.
BRIEF DESCRIPTION OF THE DRAWINGS
-The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
Figure 1 is a perspective view of an infusion me-tering apparatus constructed in accordance with the invention.
Figure 2 is an exploded perspective view showing the principal components of the metering apparatus housing.
Figure 2a is a cross-sectional view of the meteriny apparatus taken along line 2a~2a of Figure 1.
Figurc 3 is an enlarged front elevational view of the peristaltic pump utilized in the metering apparatus of Figure 1 broken away to show the rotor and downline occlusion tm/~

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statio~s thereof.
F'igures 3a and 3b show th~ do~nlir~e occlusion station of the pump as seen in Figure 3 in altexnate pcsitior,s.
Pigure 4 is a cross sectional view of the pump ta~:er:
alon~ line 4-4 of Figure 3.
~igures 4a and 4b sho~^7 the latch member of the do~n-line occlusion station as shown in Figure 4 in alternate positions.
Figure 5 is an enlarged exploded perspective vie~
of the principal components of the fluid metering station of the metering apparatus.
Figure 6 is a simplified functional block diagram of the control system incorporated in the metering apparatus of the invention.
Figure 7 is a functional block diagram partially in schematic form of the control system.
Figure 8 is a simplified schematic diagram of the bubble detector utilized in the fluid metering apparatus of the invention.
Figure 9 is a simplified schematic diagram of the power supplies utilized in the fluid metering apparatus of the invention.
escription of the Prel~r-.d Er~aiMc:~=
Referring to the Figures, and particularly to Figure 1, a peristaltic-type flow metering system 10 for use in con-~, g ~ '5~

junction with an administration set for controlling the flo-"~
of fluid into a vein or ,artery includes a generally xeckanyular housing 12 having a handle 13 at one end thereof for ccnw venient carrying. The front surface of the housing includes a control panel 1~ which allows the operator to control anc monitor the operation of the metering apparatus, and a peri~
staltic-type flow metering head 15 for compressin~ a section of tubiny 16 of the administration set to effect control of fluid flow therein. A channel 17 is provided above the 10 metering head 15 for maintaining a portion of the tubing segmer.t in a convenient view of the operator whereby flow irregularities can be more readily observed.
The administration set, of which tubing segment 16 is a part, and which may be conventional in design and con-15 struction, is preferably formed of a plastic material such as vinyl and packaged in a sterile and non-pyrogenic condition.
To avoid the danger of contamination, the administratior. set is normally utilized for one application only, and is disposed of after use.
The operating mode of the metering apparatus is controlled by means of a push button STOP switch 20, a push button START switch 21, and a push button power ON-OFF switch 22~ Each of these push button switches includes an internal indicator lamp which provides a positive indication of the 25 operating mode of the apparatus~

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Various abnormal operating conditions are annunciated by means of indicator lights 23~27 contained on the control panel to the left (as vie~1ed in Fiyure 1) c,f the mode control pusll buttons. The operation of these indicator lights will be explained in conjunction with the operation of their respective systems within the metering apparatus.
Control panel 14 further includes a digital dis-play 30 of volume infused, a digital display 31 of volume to be infused, and a digital display 32 of the fluid flcw rate. The volume displayed by display 30 is the volume of fluid actually infused, and can be reset to 0 by the operator by means of a push button RES~T switch 33. Ihe volume to be infused by display 31 is preset by the operator by means of a set of push button switches 34 to indicate a desired volume of fluid to be infused. Similarly, the infusion rate display 32 is preset by the operator by means of a second set o ~ush button switches 35 to indicate the rate at which infusion is to take place.
As shown in Figures 2 and 2a, to provide an aes-thetically pleasing front panel surface free of openings which might harbor contaminants, the front panel 14 is preferably constructed from a single seamless panel 36 having necessary transparent sections 37 for viewing readouts 30, 31 and 32.
The push button switches 33 35 ~ssociated with these displays '7~.k~

are preferably pressure-sensitive s~itches, which respond to very s~all deformations of the front panel brouyhk about by finger pressure from the operator to actuate their re-spective circuits. The pressure-sensitive s~itches are mounted on one side of a printed wiring board 38 behin~
panel 36, with connections from the board e~tending through apertures in the housing to a printed wiring board 28 within the housing. Additional individual system wiring boards 29 are plugged into soc~ets contained on this board. ~. plurality of metallic screen panels 39 may be provided between board 38 and housing 12 for the purpose of providing radio fre-quency interference (RPI) shielding for the electronic circuitry of the metering apparatus.
Referring to Figure 3~ the peristaltic metering head 15 includes a rotor 40 having foux pressure roilers 41 disposed in equi-spaced relation about its circumference.
The rollers are each mounted on a shaft 42 for free rotation thereon, and the shafts are carried on carriages 43 and con-strained to radial movement by respective radial slots 44.
Each carriage 43 is mounted for reciprocation within a radially aligned recess 45 and spring loaded in a radially outward direction by a helical spring 46 disposed within the recess.
The pump also includes a pressure plate 50 having an arcuate working surface 51 which substantially corres-~ ,7J;~

ponds in shape to the circumference of the pump rotor and is positioned to bring the tubing segment 16 into co~pres sive engagernent with rollers 41 around at least a portior.
of the rotor circumference extending bet~Jeen adjacent rollers. The pressure plate may be reciprocated to~ard and a~ay from rotor 40 to facilitate installation and re-moval of tu~ing segment 16 by rotation of an eccentric cam 52, ~ihich is constraine~ to operate within a vertical slot 53 provided on the pressure plate. Rotation of the cam is accomplishe~ by a shaft 54 and user-actuable lever 55 operatively connected to the car.. ~hen the lever 55 is in its bottom position, as shown in Figure 3, the pressure plate is moved sufficiently close to the rotor circumference to cause tubing seg~ent 16 to be completely occluded by the rollers. Since each of rollers 41 is individually biased into engagement with the tubing segment, the pressure applied by each roller is independent of the number of rollers engaging the tubing segment.
After passing through the peristaltic metering ~0 station, tubing segment 16 extends between a light source 60 and a photodetector 61, which together comprise a ~ubble detector station 62. As will be seen presently, it is the function of this station to discontinue operation and alert the operator upon formation of a bubble in the tubing segment.
Referring to Figures 3-5, the tubing next passes _g_ ~ ~ ~ 7 ~

through a flow restriction sta~ion 63 This stat.ion in-cludes a pressure block 66 and a slidably mounted flo~ re-striction plunger 67 biased against the sidewall of tu~iny segment 16. The end of plunger 67 ~hich engages khe tubirc~
segment includes a generally L-shaped head portion 6~.
having a wedge-shaped working surface 7C and a generally flat control surface 71. Plunger 67 includes a central body portion which is slidably received within a stationary mounting bl~ck 73, and which extends through the center of a helical compression spring 74 provided for biasing head 68 into engagement with tubing segment 16.
The working surface 70 of head portion 68 bears against the sidewall of tubing segment 16 substantially perpendicular to the direction of fluid flow within the tubing as the tubing is held in position against pressure block 66. As a result, the lumen of the tubing segment is occluded at the point of engagement, and a downline conduit segment is defined between the point of engagement of the rollers 41 and the point of engagement of the wedge-shaped working surface 70. ~s previously developed, the occlusion of the tubing in this way increases the pressure of the fluid in the tubing segment and prevents separ-ation of dissolved gases therein.
The control surace 71 of plunger 67 exte~ds substantially parallel to the direction of fluid flow ,r~ ,r' '~

anZ is substantially greater an are~ than the working surface 70. The relatively large area of the control surface 71 renders the plunger more sensitive to pres sures in the tublng lumen when the pump is operative so that higher pressures can be exerted by spring 74 tG
more positively close off the tuhing when the pump is not in operation, without detriment to its ability to open at lower operating pressures.
Plunger 67 may be opened to facilitate load-10 ing or unloading of tubing segment 16 by means of a user-actuated lever 76 mounted for reciprocation with plunger 67. The plunger is constrained to reciprocation along a defined operating path by the stationary mounting block 73 which is mounted to the apparatus housing 14. The 15 helical compression spring bears against this mounting block at one end and against the head of the plunger at its other end, causing the desired bias of the plunger asainst the tubing segment.
Automatic release of the plunger is obtained 20 by means of a latch member 77 which is pivotably mounted at 78 to pressure plate 50 and biased by a helical spring 79 for operation within a plane perpendicular to the plunger. The plunger includes a slot 80 in which the latch m~mber 77 is received when the plunger is moved to its 5 full open position, as shown in Figure 3b. The end 81 of the plunger may be tapered to facilitate displacement o the latch member prior to seating in slot 80. On~e the latch member has been received in the slot, the plunger i5 locked open and the tubiny segment 1~ can be readily removed.
To insure that plunger 67 will be released when pressure plate 50 is subsequently closed, mounting block 73 is provided with an actuator pin 82. As shown in Figures 3 and 4, this actuator pin has a tapered end surface 83 which serves to displace the pivotably mounted latch m~.mber 77 from slot 80 when the pressure plate is returned to its closed position by rotation of knob 55. In this way, the plunger is automatically released so as to again become spring-biased against the adminis-tration set tubing segment 16 as the metering station is closed. This prevents inadvertent operation of the system without the back pressure and gravity flow pro-tection provi.ded by the plunger. Also, when the pres-sure plate is open, the displacement of latching mel~er 77 prevents the plunger from being latched open. A gate member 84 adjacent the control surface 71 of plunger 67 prevents the tubing segment from being inadvertently pulled free of the compression plunger during operation.
By reason of the tubing segment 16 being held in a highly visible vertical position within ~ ~ ~;7'~ 3 channel 17 the flow of fluid therethrough can be readily monitored. Furthermore, this channel obviates the need for add1tional tubing clam~s at the inlet and outlet portions of metering head 15 while a~ the sarne time providing an aesthetically pleasing structure on the pum~, housing.
~eferring now to Figure 6, the contrcl system for metering apparatus 12 is seen to include a stepper motor 100 which is rotatably coupled to rotor 40 so as to drive the rotor one increment for each step command applied to the motor. To sup~ly the multi-phase signals required for operation of the stepper motor the metering apparatus includes multi-phase motor drive circuits 101 which respond to an applied control pulse to generate a multi-phase output signal which steps the motor one increment.
The control pulses are generated by a variakle rate di-vide.r 102 which produces an output signal after a pre-determined number of input pulses have been received from a continuously running clock 103. The divider, which may be conventional in design and construction, is preset by the user to a desired division rate which is displayed by an associated display device 104. In this way, by setting different division factors into the variable rate diviser 102, the stepper motor can be operated over a wide range of rotational speeds.
To provide a display indicative of the total volume of fluid infused a register 105 responsive to the output pulses from divider 102 is provided, The counting state of register 105, and hence the volume infused, is displayed by a display device 106. The output pulses from divider 102 are also applied to a register 107 having an associated display device 108O This register is a bi-directional register, which prior to use of the metering apparatus is counted up to a counting state corresponding to the quantity of fluid to be infused, and then during use is counted down with infusion of the fluid until a zero counting _ state is reached. At this time the register generates an output signal which disables a gate 109 to inter-rupt application of control pulses to motor drive circuits 101.
The control system of the flow metering ap-paratus 10 is shown in greater detail in Figure 7. HPre the division factor of variable divider 102, and hence the fluid infusion rate, is seen to depend on the counting state of a register 110. This counting state can be con-veniently set by the user by means of the xate setting switches 35 which ena~le respective NOR gates 112 to supply pulses to the register from a pulse source 113.

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In practice, several MOR gates and rate settiny switches are provided to allow each digit of the register to ~e independently set. The counting state of register 110 is displayed by display device 104 as an inclication of the metering or infusion rate of the apparatus.
The output of register 110 is applied to a compari-son circuit 114 wherein the register counting state is com-pared with a predetermined fixed minimum rate, typically 5 ml. per hour, to determine whether the infusion rate es~
tablished by divider 102 is greater than or less than the minimum rate. In the event that the desired rate is greater than the minimum rate, comparison circuit 114 produces an out-put signal which enables NAND gate 115 to provide for establish-ment of a minimum "keep open" rate after the desired quantity of fluid has been infused. To this end, the output of clock 103 is applied to a fixed divider 116 which provides output pulses at a fixed minimum "keep open" rate. These pulses are applied to a NOR gate 117 and, depending on the state of this gate, to an OR gate 118 for application to the motor drive circuits 101. The "keep open" mode is operative only after the desired quantity of fluid has been infused, as signaled by the bi-directional register 107 reaching a zero counting state.
The output signal generated by register 107 upon reaching a zero counting state is applied to the remaining ~15~

3 r~ ~q~JJ3 input of NAND gate 115 and to one input of a 130P~ gate 119. As a result, NOR gate 119 is inhibited and the application oE
pulses from variable divider 102 is interrupted. Should N~.~'D
gate 115 be enabled as a result of the variable rate being greater than the predetermined minimum flow rate,the zero state output signal from register 107 is applied through an in-verter 120 to a keep open indicator 2~ and to an input of ~OR gate 117, wherein it serves as an enabling signal. This gate, when enabled, allows the fixed rate pulses from the fixed rate divider 116 to be applied to OR gate 118, and hence to motor drive circ~ s 101. In this way, a minimum flow rate is maintained even after the desired quantity has been infused.
To provide start-stop control over stepper motor 100 the remaining inputs of NOR gates 117 and 119 are con-nected to the ou~put of a start-stop flip-flop 121. This flip-flop may be conditioned to a start state by actuation of the push button START switch 21, or to a stop state by actuation of the push button STOP switch 20, or by occurrence of any one of a number of abnormal conditions, including interruption of power, detection of a bubble in the adminis-tration set, detection of an occlusion in the administration set, or the opening of the metering head pressure plate while the metering apparatus is in operation.
To provide an accurate indication of the volume of fluid actually infused, the output of OR gate 118 is 'iI,a~f'~t~

applied to a fixed divider stage 122 wherein a constant division factor is applied to generate one output pulse for each milliliter of fluid infused. In practice, where stepper motor 100 is re~uired to s~ep 2,352 tirnes to pump 1 milliliter through tubing segment 16, divider 122 may be set to divide by 2,352 to obtain the desired volume-indicative output signal.
This output signal is applied to register 105 wherein it advances the counting state of the register so that the in-stantaneous counting state thereof indicates the volume of fluid actually infused. As previously stated, this volume is displayed by display device 106.
The volume-indicative output pulses from divider 122 are also applied through an OR gate 123 to the stepping input of bi-directional register 107 wherein they cause that register to count down one step toward zero with each milli-liter passing thro~gh the system. As stated previously, the counting state of register 107, and hence the volume of fluid to be infused, is dispiayed by display device 108.
Prior to use of the infusion metering apparatus, the counting state of register 107 is prese~ by the user by momentarily applying pulses to the register from pulse source 113. This is accomplished through ~ NO~ gate 124 which is enabled by the operator by actuation of the SET VOLUME switch 34. In practice, one such switch and NO~ gate are provided for each d~cade of the counterO The remaining input of NOR

gate 124 is connected to the output of the start-stop flip-flop 121 to prevent the volurne display from being changed ~hile the metering apparatus is in opexation.
Registex 107 is capable of counting either u~ or down depending on an applied mode control signal. This signal is developed from the output of start~stop flip-flop 121 by means of an inverter 125 so as to condition register 107 to count up with application of set pulses from source 113 ~hen the apparatus is stopped, and to count down with application of volume-indicative pulses from divider 122 when the metering apparatus is in operation.
Prior to initial operation of the metering apparatus register 105 is reset by the operator by actuation of push button RESET switch 33. This switch is connected to one ln-put of an AND gate 126, the other input of which is connected to the output of the start-stop flip-flop 121 to render the reset switch 33 non-functional while the metering apparatus is in operation. The output of AND gate 126 is applied through an OR gate 127 to the reset inputs of register 106 and divider 122. In this way, the divider and register are simultaneously reset to a zero counti~g state prior to initial operation of the apparatus.
An auto reset state 130 responsive to initial applica-tion of power to the apparatus is provided to automatically establish .,hrD3 an initial counting state in registers 10~, 107 an~ 110. lhe output of tlle auto reset stage i5 applie~ to the remaining input of o~ oate 127 so as to establish a zero counting stat~
in xegister 105 and divider 122, anc7 to the reset input Gf xegister 110 through A~D gate 131. Should the operator atte~ t to set the most significant digit of register 110 above 4, a reset circuit coupled to the remaining input of AND gate 131 also resets the register. In this way the setting of infusion rates in excess of ~55 ml. per hour is prevente~.
The output of the auto reset stage is also applied. to register 107, wherein it establishes a ~.inimum counting state of 1 ml.
to prevent initiation of the "keep open" mode before the metering apparatus has been placed in ope.ration.
Operation of the infusion metering apparatus is interrupted upon occurrence of an occlusion within the ad-ministration set, as detected by a switch 132 associated with plunger 67 (Figures 3 and 5). This switch, which may be a pressure switch similar to switches 33-35, or a magnet-ically-actuated Hall-effect switch, is actuated by an actuator lever attached to the plunger when the plunger is allowed to close against the tubing as a result of an occlusion with-in the administration set. The switch provides an output signal which actuates a latch circuit to condition start-stop flip-flop 121 to a STOP state and illuminate occlusion indi-cator lamp 25.

7'9~h~/3 Operation of the apparatus is also interruptec' in the event of a bubbl~ being detected at bubkle detector 6~. In this event, an output signal is generated by the ~ubble detector which actuates a latch circuit to conditior the start~stop flip-fl.op 121 to interrupt operation of the meterir,y apparatus. At the same time, B~T~L~ indicator lamp 23 is illuminated to alert the operator.
Operating po~er for the fluid metering apparatus is supplied by means of t~o unidire~tional current supplies 135 and 136 which receive operating power from the AC line through ON-OFF switch 22. A battery 138 is provide~ as an additional source of operating power in the event of failure of the AC line. ~he battery is connected through s~itch 22 across the output of power supply 135.
Normally, battery 138 is maintained charged by power supply 135 and the various control circuits of the infusion metering apparatus are powered by this combineZ
source, while the stepper motor 100 is powered by the power supply 136. To guard against interruption of AC line voltage the output of the power supply 135 is continuously monitored by a voltage comparator 140. ~pon occurrence of a line voltage interruption an output signal is produced by comparator 140 which simultaneously illuminates a BA~TERY ON indicator 26 and actuates a relay 141.
Operation o ~he metering apparatus is i.nterrupted ~ '7'~

whenever the battery voltage falls below a predeterminFd minimum level for a predetermined period of ti~e. To this end, the battery volt~ge is continuously monitored by a voltage comparator stage 133. I,pon occurrence of a lo~
S voltage condition, an output signal is produced which ac-tivates a latch circuit to illuminate the BP~TEP~Y LOI~, la~p 27 and initiate operation of a timing counter 134. This counter counts the "keep open" output pulses developed by fixed divider 116 to obtain a 10 minute time delay. If the low voltage condition persists beyond this delay period an output signal is developed by timing counter 134 which causes the BATTERY LO~ lamp to flash and conditions start-stop flip-flop 121 to interrupt operation of the metering apparatus.
It should be noted that the operation of comparator 133 is entirely independent of comparator 140, and serves as a check on syste~ voltage whether supplied by power supply l35 or battery 138.
Stepper motor 100 is powered by power supply 136 through transfer contacts on relay 141. The purpose of these contacts is to substitute battery 138 as a source of power for the stepper motor in the event of an AC line failure as detected by comparator 140. The various phase windings of motor 100 are individually supplied from power supply 136 by means of switching transistors 142-145 connected in series with the windings.

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In accordance with another featwre of the apparatu.~, isolation is obtained between stepper motor 100 ancl the pulse-sensitive control circuits of the ~eteri.ny apparatus by means of individual optical isolators 146-14q associated with re-spective ones of the switching transistors. Each of the optical isolators includes a licht detecting ele~.ent connected between the motor current source and a respective one of the switching transistors, and a light emitting diode (LED) element connected to the output of a respective one of inverting a~.-plifiers 150-153. These amplifiers receive phase control signals fror~ motor drive circuits 101 through respective NOR gates 154-157 which serve as a safety shutoff control means for the ~etering apparatus.
The NOR gates 154-157 are disabled when the start-stop flip-flop 121 is conditioned to a stop mode by means of an OR gate 158 having an output connected to one input of each of the I~OR gates~ Also, these NOR gates can be dls-abled by outputs from bubble detector 62 and occlusion switch 132 through an additional OR gate 159 which provides an additional input to OR gate 158. Thus, occurrence of an ooclusion, detection of a bubble, or conditioning of the start-stop flip-flop to a stop state for any reason causes the interruption of control signals to optical isolators :L46-149 and interruption of drive power to stepper motor 100.
In operation, the user initially sets an infusion rate by actuating switch 35 to apply a requisite num~er of pulses to register 110. The counting state of this r~gister sets the variable divider 102 such that control pulses are developed at the output thereof with a repetition rate co~~
mensurate with the desired infucion rate. These control pulses are applied through NOR gate 119 to the motor drive circuits 101 wherein they are utilized to generate multiple phase control signals suitable for controlling the operation of the multi-phase stepper motor 100. Each of the phase signals developed by drive circuits 101 is applied through a respective one of NOR gates 154-157 and inverter amplifiers 150-153 to a respective one of optical isolators 146-149.
These isolators in turn control conduction in respective - ones of drive transistors 142-145 to apply current from power supply 136 to stepper motor 100. In this way, the stepper motor turns the peristaltic rotor 40 at a ra~e es-tablished by the operatorO
To provide a continuous readout of fluid volume infused the drive pulses applied to the drive circuits 101 are also applied to divider 122 to develop pulses indicative of the number of compl2te milliliters infused. These pulses are counted by register 105 to provide a display in device 106 indicative of the actual quantity of fluid infused.
Prior to initial operation of the apparatus an

2~ .initial coun ing state is established in register 107 by momentary application o pulses from pulse ~ource 113 t~rough NOR gate 12~ and OR gate 123 to esta~lish an i~itlal countir~g state indicative of the total volu~le of fluid to be infused.
Register 108 is conditioned to count up at this time by start-stop flip-flop 121 through inverter 125.
Once this volume is set, operation is started by actuation of switch 21 and register 107 is conditioned tG
count down by flip-flop 121. Pulses from divider 122 indi~
cative of actual volume infused are now applied through CP~
gate 123 to count register 107 down toward 2ero. When the register reaches a zero counting state, indicating that the desired volume of 1uid has been infused, an output signal from register 107 inhibits NOR gate 119 and prevents further operation of stepping motor 100 by pulses from the variable divider 102. However, should the rate established by vari-able divider 102 be greater than a predetermined minimum infusion rate, comparison circuit 114 provides an enabling signal to NAND gate 115 which allo~s the output signal from register 107 to enable NOR gate 117 through inverter 120.
This es~ablishes a "keep open" mode of operation wherein pulses from fixed divider 116 provide motor dri~e circuits 101 with stepping command signals at a frequency which maintains a desired minimum flow rate through the system.
Registers 106, 107 and 110 are automatically xeset upon initial operation of the system by the auto reset cir~

cuit 130. Register 105 may alsc) be manually reset ~y switch 33 when the start~stop flip-flop 121 is conditione~
to a sto~ state.
Protection against ccclusion in the administration set is pro~ided by switch 132, which conditions flip-flGI
121 to a stop state and inhibits AND gates 15~-157. Cimilarly, protection against the formation of bubbles within the ad-ministration set is provided by bubble detector 62, which also conditions flip-flop 121 to a stop state and inhibits AND gates 154-157. Protection against AC line failure is provide~ by voltase comparator 140 which actuates relay 141 to switch stepper motor 100 to battery 138~ and by voltage comparator 133 which interrupts operation of the apparatus upon occurrence of a low voltage condition for a predetermined period of time.
Upon occurrence of any one of the above alarm functions, or upon infusion of the desired fluid volume, an aural alarm 160 is actuated to alert the operator that attention to the apparatus is required. A switch associated with the pressure plate of the pump head locks out the alarm when the pump head is opened.
Referring to Figure 8, the bubble detector 62 of the infusio~ apparatus includes an AC-powered detection circuit which offers improved detection sensitivity and stability.
Basically, the detection circuit, as shown in Figure 8, comprises a multi-vibrator 161 consistiny of three N~.~J~
gates 162, 163 and 164. A capacitor 165 connected to the output of gate 163 and a potentiometer 166 connected to the output of gate 16~ provide an RC time constant which determine the frequency of the multi-vibrator output signal in a manner well ~nown to the art. A diode 167 is connected between the arm of potentiometer 166 and khe outpu~ of gate 164 to vary the duty cycle of the oscillator output signal.
A fixed impedance 168 connected in series with the body of potentiometer 166 provides a desired adjustment range.
The AC signal generated by multi-vibrator 161 is applied through an impedance 169 to the base of a transistor 170. The emitter of transistor 170 is connected to groun~
and the collector is connected to the cathode of a light emitting diode (LED) which comprises the light source 60 disposed on one side of the administration set tubing seg~
ment 16. The anode of the LED is connected to a source of positive unidirectional current through a resistor 171. As a result, the AC signal developed by multi-vibrator 161 is amplified by transistor 170 and utilized to drive the LED, causing the LED to produce a light output which ~aries at a rate dependent on the output frequency of the multi-vibrator.
The alternating light developed by the LED is detected by photodetector 172 and associated amplifier ~5 transistor 173 r which together comprise the light detector ?~

61 adjacent tubing segment 16. The collectors of photo-dete~tor 172 and transistor 173 are connected to the positive unidirectional current source of the apparatus, and the emitter of detector 172 is connected to the base of transistor 173. The emitter of transistor 173 is connected to ground through a resistor 174 and through respective diodes 175-177 to respective inputs of a dual Schmitt trigger 178. The cathodes of diodes 175-177 are connected to ground by respective ones of capacitors 180-182 and re-sistors 183-185 in parallel circuit configuration. These elements serve in conjunction with the diodes a signal de-tector, generating a DC signal at the inputs of trigger 178 dependent on the amplitude o~ the AC signal produce~ by de-tector 61. Trigger 178, which may be a commercially avail-able component such as a type MC14583B marketed by Motorola, produces an output upon reduction below a predetermined threshold level of the DC signal developed at either of the inputs associated with diodes 176 and 177. The input associated ~lith diode 175 functions as ~n enabling input for both triggers. The output of Schmitt trigger 178 is applied to cne input of an OR gate 179~
The emitter of transistor 173 is also connected to ground through series-connected resistors 186 and 187.
The signal developed at the junction of the two resistors is filtered by a series-connected resistor 188 and a capacitor 189 and parallel-connected resistor connected to ground and applied to the remaining input of O~ gate 179.
In this way OR gate 179 is provided with the output siynal developed by the two Schmitt triggers 178 and a DC control signal developed across capacitor 189, either of which can result in a bubble-indicative output from the gate in the ev~nt of a bubble occurring in tubing segment 16. The out-put of Schmitt triggers 178 and the output of OR gate 179 are also connected to the positive unidirectional current source of the system by respective resistors.
Since the output of OR gate 179 is dependent on both the amplitude of the AC signal as rectified and applied to the parallel-connected Schmitt triggers 178/ and on the DC signal developed across capacitor 189, the bubble de-tector utilized in the metering apparatus provides two in-dependent control channels. The first channel, which utili2es Schmitt triggers 178, establishes a highly precise threshold below which an alarm output is produced. The second channel, which depends only on the input characteristic of ~ate 179 and is less precise, serves as a backup in the event of fallure of the Schmitt triggers in an active mode.
In order for bubble detector 62 to not provide an output, it is necessary that the DC signals applied to the Schmitt triggers as a xesult of rectification by diodes 176 and 177 be above a predetermined minimum level, which ,7~

is possible only when there is fluid ~ithin tubiny segrerlt 16 which acts ~s a lens to direct ligh~ frorn light source 60 to detector 172. In the event of failure o the light source or the detector, or any other component of the system, the DC signal applle~ to the Sc~itt triggers is remove~ ar.d an alarm output is generated. In the event of failure of the Sc~itt triggers, an alarm output will be developed by OR gate 179 upon loss of the DC signal from capacitor 189.
The use of an AC signal eliminates drift in the circuitry as a factor affecting the threshold level of the Schmitt triggers, thereby allowing the threshold to be set closer to the normal operating level of the system for greater detection efficiency.
Transient spikes on the AC line, which are parti-cularly prevalent in institutions such as hospitals where electrical machinery is in operation, introauce the potential of spurious counts in the digital registers and gates utilized in the control circuits of the metering apparatus~
For this reason, it is imperative that the greatest possible isolation be provided by power supplies 135 and 136 between the control circuits and the AC line, particularly in view of the possibly critical life-determining nature of the metering apparatus.
To this end, separate power supplies each incor-porating special transient protection features are provided in the metering apparatus. Referring to Figure 9, it is seen that the two po~er supplies 135 and 136 share a co~or, power t.ransformer 190 which includes individual secondary windings 191 and 192 each electrostatically shielded from the line. The output of secon~ary winding 191 is connected across a b.rldge rectifier 193 within power supply 136. Ihe positive polarity output of bridge recti~ier 1~3 is connected to the positive polarity input terminal 194 of a first four-terminal filter capacitor 195. The negative input terminal 196 of this capacitor is connected to the negative polarity output of the bridge rectifier.
Filter capacitor 195 is an electrolytic type capacitor which includes four terminals; a first pair of terminals associated with respective ends of the positive plate of the capaci~or, and a second pair of terminals associated with respective ends of the negative or foil side of the capacitor.
The output terminals 17 and 198 of capacitor 195 are connected to a conventional voltage regulator circuit which includes a series-connected regulator transistor 200.
In a manner well known to the art, the conduction state of transistor 2~0 is varied in response to the voltage level existing at the output of power supply 136 so as to maintain the voltage level constant. To this end, a zen~r diode 201 and resistor 202 are connected across the output electrodes ~5 of the capacitor to develop a reference voltage. This r~a~ hf~

reference voltage is compared within a comparator ampliier 203 ~ith a portion of the output voltaye of the power supply as developed by a potentiometer 204 connected across the output terminals of the supply. The output of compara-tor 203, representing the deviation of the output voltage from a reference level, is applied to a transistor 205 which serves to amplify the error signal prior to applica-tion to the base of transistor 200. Additional regulation to compensate for changes in current load is provided by a series-connected resistor 206 at the emitter of transistor 20C. This register develops an additional error signal which is applied through three series-connected voltage dropping diodes 207 to the base of the error amplifier transistor 205~ Protection against transient spikes is provided by reverse-biased diodes 208 and 209 connected across the input and output leads of the voltage regulator, respectively.
Power supply 135, which is virtually identical to power supply 136, includes a bridge rectifier 210 con-nected across secondary winding 192, and a four terminal filter capacitor 211 having input terminals 212 and 213 connected across the output of the bridge rectifier. The output terminals 214 and 215 of the capacltor are connected to a series regulator circuit similar to that contained in power supply 136, including a series regulator transistor I X ~ ~

216, a voltage reference zener diode 217 and a diferential amplifier 218 with similax functions. ~ ilter capacitor 220 is connected across the output of the power supply to provid~ additional filtering.
~he described po~er supply arrangement has the ad-vantage of providing a high degree of filtering between the AC line and the respective power supply busses of the meter-ing apparatus. The four-terminal filter capacitors are particularly effective in this respect, in that any transient 10 currents attempting to enter or leave the respective power supplies must pass through the electrodes of the capacitor, since these electrodes are relied upon to complete the metallic circuit. As a result, the filtering action of the capacitors ls not reduced with transients of higher frequencies, 15 as in conventional filter capacitors.
The use of separate power supplies, each utilizing the four-terminal filter capacitor component, provides a very high degree of isolation between the stepper motor circuit and the digital control circuitry of the metering apparatus.
20 This is desirable because of the relatively high switching transients inherent in the operation of a stepper motor, and the possibility of these transients affecting the critical digital control circuitry.
Thus/ the invention provldes a flow metering appar-~5 atus for flu.id infusion systems which allows the operator to -32~

directly select fluid ~low rate and volume without the need for calculations. The apparatus is convenient to install and does not require particulax skills or, the part of the operator for its operation. Protection is provided within the apparatus against malfunctions in the administratior set and with the apparatus itself, in the event of which the operator is signaled and operation of the apparatus is terminated. The apparatus is portable and of a construction which lends itself to convenient use in a hospital environ-ment.
While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to coYer all such changes and modifications as fall within the txue spirit and scope of the invention.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Fluid metering apparatus for controlling the flow of fluid through the tubing of a fluid administration set, comprising:
a housing;
a rotor mounted on said housing for rotation about a fixed axis, said rotor including a plurality of pressure rollers disposed about the circumference thereof;
a platen assembly slidably mounted to said housing and having a pressure plate having an open position displaced from the circumference of said rotor whereby said tubing can be inserted therebetween, and having a closed position adjacent said rotor circumference whereby a segment of said tubing is positioned in compressive engagement with said pressure rollers and fluid is caused to flow along the tubing with rotation of said rotor;
flow restriction means including a plunger slidably mounted on said housing for occluding said tubing at a predetermined location downline of said tubing segment for increasing the pressure of said fluid in said tubing segment, said plunger having an open position removed from said tubing and an operating position compressively engaging said tubing;
means carried on said housing for biasing said plunger to said operating position even if said platen assembly is accidently moved to said open position; and user-actuable latching means operable only when said platen assembly is in said open position for latching said plunger in said open position, said latching means automatically releasing said plunger to allow said plunger to move to said operating position upon actuation of said pressure plate to said closed position.

2. Fluid metering apparatus as defined in claim 1 wherein a portion of said latching means is carried on said slidably mounted platen assembly.

3. Fluid metering apparatus as defined in claim 1 wherein said latching means include a lever pivotally mounted to said platen assembly, detent means on said plunger for engaging said lever to lock said plunger for movement with said platen assembly, and actuator means on said housing for displacing said lever for said detent means upon closure of said platen assembly whereby said plunger is returned to said operating position by said biasing means.

4. Fluid metering apparatus as defined in claim 3 wherein said lever is mounted for movement in a plane generally perpendicular to said plunger, said detent means comprise a notch in said plunger dimensioned to receive said lever, and wherein means are provided for biasing said lever against said plunger whereby said lever is received in said notch when said plunger is locked in said open position.

5. Fluid metering apparatus as defined in claim 4 wherein said actuator means comprise a tapered actuator pin extending from said housing in generally parallel-spaced relationship to said plunger for displacing said lever from said notch upon closure of said platen assembly.