US3739943A - Infusion system - Google Patents

Abstract

A portable infusion system uses a disposable piston-type syringe and a disposable two-way valve as a positive displacement pump. The syringe piston is reciprocally driven by a bidirectional DC motor under control of a battery powered circuit. Different selectable rates of pumping are maintained by controlling the width of bidirectional DC pulses coupled to the DC motor and by monitoring the motor back EMF during the off time of the pulses. Safety circuits protect against deleterious conditions such as the passage of an air bubble, an over-pressure condition, or an excess pumping rate as could be caused by a component failure.

Description

United States Patent 1191 Wilhelmson et al.

[ June 19, 1973 1 INFUSION SYSTEM [75] Inventors: Jack L. Wilhelmson, Fenton;

Theodore E. Weichselbaum, St. Louis; Vernon F. Braun, Berkely, all

[21] Appl. No.: 112,691

Related US. Application Data [63] Continuation-impart of Ser. No. 81,926, Oct. 19,

[56] References Cited UNITED STATES PATENTS 12/1960 Hyde 222/76 5/1966 Corbin... 222/76 12/1968 .lewett 222/76 10/1971 McGuire 417/326 3,648,694 3/1972 Mogos l28/D1G. 13 3,655,095 4/1972 Kienitz......... 222/76 2,693,114 11/1954 Tapp et a1 417/417 2,925,814 2/1960 Vibber et a1.... 417/417 3,118,383 1/1964 Woodward... 417/417 X 3,461,806 8/1969 Barthalon 417/418 Primary Examiner-William L. Freeh Assistant Examiner-John T. Winburn Attorney-Stanley N. Garber and Hofgren, Wegner, Allen, Stellman & McCord [57] ABSTRACT A portable infusion system uses a disposable pistontype syringe and a disposable two-way valve as a posi tive displacement pump. The syringe piston is reciprocally driven by a bidirectional DC motor under control of a battery powered circuit. Different selectable rates of pumping are maintained by controlling the width of bidirectional DC pulses coupled to the DC motor and by monitoring the motor back EMF during the off time of the pulses. Safety circuits protect against deleterious conditions such as the passage of an air bubble, an over-pressure condition, or an excess pumping rate as could be caused by a component failure.

14 Claims, 9 Drawing Figures PAIENIEDJUN 1 9 I973 suaznora' I INVENTORS JACK L. HILHELHSON THEODORE E. WIECHSELBAUH VERNON F. BRAUN 1 Mr'ronums PAIENIEUJUN 1 9ms 3. 739.943

sum 2 or 4 PAH-1min JUN! 9 ma sumac INFUSION SYSTEM RELATED APPLICATION This application is a continuation-in-part of our copending application, Ser. No. 81,926, filed Oct. 19, 1970, entitled Infusion System, and assigned to the assignee of this application.

This invention relates to an improved pumping system and an improved control and safety circuit, particularly adapted for use in an infusion system.

During typical blood transfusions and intravenous injections, a solution bottle is usually hung about a patient to allow gravity feed of fluid through disposable venoclysis tubing to a catheter inserted in the vein of the patient. Transportation of the patient is difficult because the solution bottle must always be located above the patient, requiring an attendant to hold the solution bottle. Even when the patient is located in a hospital, periodic monitoring of the process is required, utilizing valuable personnel time. Despite periodic monitoring, certain malfunctions can occur which may go unattended for lack of a suitable indication of the malfunction. For example, during an injection, it is possible for a needle to become displaced from its position in a vein and become lodged in a muscle.

In our copending application, a novel portable positive displacement pumping system is disclosed which can replace the gravity feed system typically used for transfusions and injections. As a result, the solution bottle can be located at any reasonable height with regard to the patient. The battery powered control circuit for the pump system includes a number of safety circuits which automatically monitors for deleterious conditions, such as the passage of air bubbles or the dislodgment of the intravenous needle into a muscle.

In accordance with the present invention, a further safety circuit is provided which eliminates deleterious conditions which could otherwise result due to a failure of the control circuit itself. An electrical analog of the pump is compared with the actual operation of the pump as indicated by external sensing associated with the pump drive. When the actual pump produces a rate of pumping in excess of the pumping rate of the analog circuit, a rate monitor circuit disables the pump. The analog circuit provides a safety range of allowable pump rates for each one of the plurality of pumping rates which are selectable under control of the control circuit. Desirably, the safety circuit and external pump sensing means use many parts already existing in the system, providing an additional safety factor with little increase in cost or number of components.

One object of this invention is the provision of an infusion system having improved safety circuits for modifying the operation of a control circuit for a pump means in accordance with sensed external and internal conditions.

Further objects and features of the invention will be apparent from the following specification, and from the drawings, in which:

FIG. I is a perspective illustration of an infusion system incorporating the applicants pumping system;

FIG. 2 is an exploded view of the pumping system, with the syringe pump being illustrated for clarity as located on the opposite side of the pump housing shown in FIG. 1;

FIG. 3 is a schematic diagram of the control circuit for the pump system;

FIG. 4 is a schematic diagram of a rate monitor circuit for connection to the control circuit of FIG. 3; and

FIGS. 5A-5E are waveform diagrams illustrating waveforms generated by the circuit of FIG. 4.

While an illustrative embodiment of the invention is shown in the drawings, and will be described in detail herein, the invention is susceptible of embodiment in many different forms and it should be understood that the present disclosure is to be considered as an exempliflcation of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. Throughout the specification, values will be given for certain of the components in order to disclose a complete, operative embodiment of the invention. However, it should be understood such values are merely representative and are not critical unless specifically so stated.

GENERAL DESCRIPTION FIGS. 1-3 show applicants novel portable infusion system, as disclosed in our before identified copending application. For clarity, the operation of the apparatus and circuits of FIGS. l-3 which are necessary to an understanding of the invention herein will be explained. For a more complete description of the operation of the portable infusion system, and. for additional disclosure concerning the disposable valve assembly for use therewith, reference should be made to our before identified copending application, Ser. No. 81,926, filed Oct. 19, 1970, and incorporated by reference herein.

Turning to FIG. I, a portable infusion system is illustrated for pumping fluids such as blood from asolution bottle 20 to a catheter 21 inserted into the vein of a patient. Fluid transfer is accomplishedby a pumpingapparatus 24 held by acaddy assembly 26 mounted to arail 28 of a bed for the patient. Thecaddy 26 also removably holds thesolution bottle 20, which can be located at any reasonable altitude with respect to the patient.

Solution bottle 20 is of conventional construction, and includes acap 30 having anair valve 31 and anoutput port 32 for fluid transfer.Disposable venoclysis tubing 34 couples theport 32 to aninput port 36 in a disposable two-way valve 40 which forms a part of thepump apparatus 24.

Pump apparatus 24 uses as a pump chamber a conventionaldisposable syringe 42 having aslidable piston 44 which can be reciprocated to pump fluid within a hollow syringe barrel coupled with the two-way valve 40 which includes an outlet oroutput port 46 connected byvenoclysis tubing 50 with aconventional Y connector 52 for medication introduction. The output of theY connector 52 is coupled by additional disposable venoclysis tubing 54 to the catheter 21.

The control circuit forpump apparatus 24, seen in detail in FIGS. 3 and 4, is completely contained within the housing for the pump apparatus, and can be either externally or internally powered. During a back stroke, in which thesyringe piston 44 is driven away from thevalve 40,input port 36 admits fluid fromsolution bottle 20 into the syringe barrel. The valve inoutput port 46 is closed at this time. During a forward stroke, in whichpiston 44 is driven towards thevalve 40, theinput port 36 is closed and theoutput port 46 is opened, pumping the solution throughvenoclysis tubing 52 and 54 to the catheter 21.

Thenovel pumping apparatus 24 is seen in exploded view in FIG. 2. A sterile, positive displacement pump is economically formed by using a conventionaldisposable syringe 42 in combination with a uniquedisposable valve 40.Syringe 42 includes agasket 70 fixedly mounted to thepiston 44 for movement within a hollow barrel 72 which has a single fluid opening terminating in a needle connector 74. The syringe includes extendingfinger grip arms 76, which in the present invention are held by base means for thepump apparatus 24.

Syringe 42 andvalve 40 are removably held by housing means in order to allow disposal after use with each patient and replacement with a new presteriled syringe and valve. A lower moldedcase 90 includes a pair ofupstanding arms 92 each having aslot channel 94 which slidably receives one of theextensions 76 of the syringe.Lower case 90 also includes anupstanding post 100 having aconcave surface 102 for holding thevalve 40 when it is mated to thesyringe 42, and for making electrical contact with electrodes embedded in the valve. A pair of femaleelectrical sockets 106 insurface 102 receive air bubble detector electrodes, as will appear, and a female socket 108 (not illustrated in FIG. 2), which may be separate fromcase 90 or similarly molded in a portion thereof, receives an over-pressure detector electrode. Thesockets 106 and 108 are connected by wires to the circuit of FIG. 3 which is contained within thehollow case 90. I

The mechanical drive arrangement forpiston 44 consists of abidirectional DC motor 120 having anarmature shaft 121 with anintegral motor gear 122. Themotor gear 122 meshes with anidler gear 126 rotatable about anidler shaft 128 rigidly attached to apinion gear 130. Thepinion gear 130 meshes with adrive gear 132 which is fixedly attached to the shaft of ajackscrew 134. Asyringe cylinder carrier 140 includes agripping head 142 having an opening therein for slidably receiving thehead 45 ofpiston 44. Thecarrier 140 has an internally threaded central opening for engaging the threads of thejackscrew 134 to cause the carrier to act as a drive nut on the jackscrew.

When DC motor 120 is energized by voltage of predetermined polarity, the two-stage spur reduction gears rotatejackscrew 134 and cause thecarrier 140 and attachedcylinder 44 to be driven in a forward stroke.Carrier 140 includes aprotrusion 150 with a permanent magnet which extends downward for magnetically actuating a sealed forwardstroke limit switch 154 and a sealed reversestroke limit switch 152, mounted to acircuit board 156 which contains the circuit of FIG. 3. Thecarrier 140 is driven in a forward stroke direction untilprotrusion 150 is directly overlimit switch 154, at which time the circuit of FIG. 3 reverses the polarity of voltage toDC motor 120 in order to rotatearmature 121 in a reverse direction. Thecarrier 140 andcylinder 44 are now longitudinally moved through a back stroke until theprotrusion 150 is directly overlimit switch 152, at which time the circuit of FIG. 3 again reverses the polarity of voltage toDC motor 120. While magnet ically actuated proximity switches are preferred, a mechanical switch arrangement could alternately be used, actuated by mechanical engagement withprotrusion 150.

The limit switches 152 and 154, in combination with theprotrusion 150, also serve as a sensing means for determining the actual operation of the pump. As will appear, portions of the circuit of FIG. 3 which respond to the limit switches are connected to the rate monitor circuit of FIG. 4 in order to provide an input (at con nectors A and B) representative of the actual operation of the syringe pump.

Power for the DC motor and the control circuit including the rate monitor circuit of FIG. 4 is obtained from a self-contained DC power source, as a pair of series connectedDC batteries 160. Desirably,batteries 160 are rechargeable, sealed nickel-cadmium batteries which allow the pump apparatus to be powered either from an external AC source, or internally powered in order to allow the unit to be completely portable. If the unit is constructed for portable use only, thebatteries 160 may be conventional 1.5 volt D size. TheDC batteries 160 are housed within a battery retainer cylinder 162 molded inlower case 90. Electrical connection is made through abattery contact spring 164 and a contact on abattery retainer cap 165 which threads into the battery retainer cylinder wall to allow replacement of the batteries when necessary.

An upper case mates with thelower case 90 to enclose the drive train assembly and thebatteries 160.Case 170 includes awindow 172 through which indicia on athumbwheel knob 174 may be observed in order to allow operator selection of different rates of pumping fluid. Desirably, the indicia onwheel 174 directly indicate pump rate, such as l liter of fluid per 1, 2, 3, etc., hours. A different range of pump rates may be provided by replacingsyringe 42 with a syringe of different capacity, andknob 174 may be so marked with alternate indicia. A syringeprime switch 176 allows an operator to override the setting selected bywheel 174 in order to rapidly reciprocate thepiston 44 when first priming thesyringe 42 to eliminate air bubbles. During the time theswitch 176 is actuated, the air bubble protector circuit is disabled.

CONTROL CIRCUIT The control circuit for the pump assembly is illustrated in detail in FIG. 3. DC power is provided between a DCpotential line 248 and a source of reference potential orground 250. When external 1 15 volt AC is available, aplug 256 may be inserted into the external AC source so as to couple 115 volt AC to astepdown transformer 258. The transformer is connected through a full wave diode rectifier to aline 260 connectable through a socket withline 248. Therechargeable batteries 160 form a filter capacitor for the full wave rectified AC voltage, reducing the ripple of the voltage onDC line 248. If desired, anadditional filter capacitor 262 may be provided. The stepdown trans former 258 and full wave rectifier may be housed within theplug 256, and connected through a two-line cord to the socket receptacle on the pump assembly. When the pump assembly is to be used independent of the external AC source, the line plug is simply removed from the receptacle on the pump assembly, allowing the previously rechargedbatteries 160 to thereafter power the control circuit.

DC motor 120 is a shunt wound permanent magnet motor which rotates in a forward direction when current flows from a terminal 260 to a terminal 262, and rotates in a reverse direction when current flows fromterminal 262 toterminal 260. As will appear, the motor is driven by pulses having a less than 100 percent duty cycle. During the off-time of the pulses, themotor 120 acts as a generator or tachometer, and the back EMF across the terminals is sensed and stored in order to control the duty cycle of the drive pulses.

An electronic reversing switch, includingtransistors 265, 266, 267, 268, 269 and 270 forms a double-pole, double-throw switch.Transistors 265 and 268 are synchronously driven conductive to pass current in a forward direction throughmotor 120. Alternatively,transistors 266 and 267 may be synchronously driven conductive to complete a reverse current path formotor 120 to drive the motor through its reverse or back stroke. Whentransistors 265 and 268 are on, current passes from apositive line 275 throughtransistor 265 toterminal 260 ofmotor 120, throughmotor 120 and outterminal 262 totransistor 268, and thence toground 250. When the forward limit of travel is reached, as indicated by the permanent magnet onprotrusion 150actuating limit switch 154, a reversing switch driver, to be described, turnstransistors 265 and 268 off andtransistors 266 and 267 on. Current then protrusion 150 actuates switch 152 at the end of a back stroke, grounding the base oftransistor 282. Alternatively,transistors 282 and 281 drive each other into saturation whenmagnetic protrusion 150 actuates theswitch 154, grounding the base oftransistor 283 at the forward stroke limit of travel.

Whentransistor 281 saturates, current flows from its emitter to base and through aresistor 290 to the base oftransistor 267 to provide drive for the reversing switch. At the same time, the voltage atthe collector oftransistor 281 rises to the potential ofline 275, back biasingtransistors 269 and 265.Transistor 282 is also saturated at this time, causing current to flow through the emitterbase oftransistor 266, through aresistor 292 and via aline 293 to the collector oftransistor 282 and thence toground 250. This provides drive for the other half of the reversing switch. Since the collector voltage oftransistor 282 is at approximately ground potential, no current flows through aresistor 295 totransistor 270, nortransistor 268. When the opposite stable state of the bistable is set bymagnetic protrusion 150,transistors 280 and 283 act similar to the above described operation fortransistors 281 and 282, providing drive fortransistors 265 and 269, andtransistors 268 and 270, as will be explained with reference to the bubble detector circuit.

During the forward stroke,transistor 270 is driven on by pulses having approximately a 25 percent duty cycle. For one circuit which was constructed, the drive pulses for minimum motor speed had a 4 millisecond on-time out ofa sixteen millisecond interval, producing a hertz frequency. The duty cycle during the forward stroke is adjustable, as will appear, and is controlled by a forward stroke control.

The reverse stroke always occurs at maximum speed sincetransistors 266 and 267 are fully saturated during reverse motor movement. As the DC voltage frombatteries 160 slowly drops with age and use, lesser voltage is passed through thereverse stroke transistors 266 and 267 to theDC motor 120, resulting in a decreased speed of movement. A battery voltage variation compensation circuit is responsive to decreased battery voltage to decrease the off-time of the pulses controlled by the forward stroke control, thus increasing speed in the forward stroke in order to maintain the selected rate of pumping.

The forward stroke control includestransistors 300, 301, 302, 303, and 304, connected basically as an unsymmetrical astable multivibrator. To allow selection of different rates of pumping,thumbwheel knob 174 is connected to the wiper 310 of multi-position switches 312. Wiper 310 is connected through individual contacts, labeled 1 through 9, to any one of a plurality ofresistors 315 each having a different resistance value. A master OFFswitch 316 when actuated connects the wiper 310 toDC line 248, viaprime switch 176. When thethumbwheel 174 is rotated to cause the wiper 310 of switch 312 to contact oneparticular resistor 315, a path is formed fromDC line 248, through actuatedswitch 316 andunactuated switch 176 to wiper 310, and thence through the selectedresistor 315 to the emitter oftransistor 300. The collector oftransistor 300 is connected through acapacitor 317 and thence through the collector-emitter oftransistor 301 toground 250. The duty cycle of the pulse coupled totransistor 270 is determined by the capacitance ofcapacitor 317, the selected value ofresistor 315, and the voltage at the base oftransistor 30 0 (from the velocity feedback circuit as will appear).

The on-time of. the duty cycle is determined by thetime period transistors 301 and 303 are saturated andtransistors 302 and 304 are turned off.Transistor 300 acts as a controlled current source that dischargesca pacitor 317 during the time it holdstransistor 304 turned off. Whentransistor 301 turns on,transistor 303 is turned on by current flowing from its base and through aresistor 320 and conductingtransistor 301 toground 250.Transistor 303 drivestransistor 270 of the reversing switch driver through aresistor 322. Thus, the on-time of the duty cycle which controls the forward stroke of the motor is determined by saturation oftransistor 303.

The off-time of the duty cycle is controlled by saturation oftransistor 304, at which time transistors 30] and 303 are turned off. This off-time is determined by the capacitance value of acapacitor 325, the voltage to which thecapacitor 325 is allowed to charge during the prior on-time, and the resistance values of a pair of series connectedresistors 327 and 328. The allowable voltage to whichcapacitor 325 is allowed to charge is set by the battery voltage variation compensation circuit.

The detailed operation of the forward stroke control circuit is as follows. Assume transistor 30] has just turned on withcapacitor 317 fully charged andcapacitor 325 fully discharged. Whentransistor 301 saturates, the negative terminal ofcapacitor 317 has a negative voltage equal to the supply potential. For this example, it will be assumed that the supply potential from batteries is at maximum potential, or 3.0 volts. Current now flows from the +3.0 volt supply and throughswitches 316, 176 and 310 to the selectedresistor 315 and thence throughtransistor 300 to dischargecapacitor 317. When the negative terminal ofcapacitor 317 reaches 1.2 volts (the base-emitter drop oftransistors 302 and 304),transistors 302 and 304 are turned on, turningtransistor 301 off and rechargingcapacitor 317 to supply voltage through aresistor 330.Capacitor 325 discharges through theseries resistors 327 and 328 until the base-emitter voltage oftransistor 301 is reached, at whichtime transistor 301 turns on and the cycle is repeated.

During the forward stroke, the pulse coupled to the DC motor has an approximately 25 percent off-time at the maximum infusion rate selectable by switch 310. Due to mechanical inertia, the motor continues to turn and generates a back EMF proportional to the angular velocity of the armature. This voltage is sensed by a velocity feedback circuit and stored in order to controltransistor 300 and adjust the on-time of the pulses to compensate for variations in load. Thus, various fluids and syringes may be used without effecting to any significant extent the calibration ofthumbwheel knob 174.

During the forward stroke,transistor 265 is on, connectingterminal 260 to the supply voltage atline 275. During the off portion of the forward stroke pulse,transistor 270 is off, blockingtransistor 268 and disconnectingground 250 from themotor terminal 262. The back EMF across the motor terminal is now coupled through aresistor 335 and a pair of series connecteddiodes 336 and 337 to acapacitor 340 connected toground 250. Thecapacitor 340 charges to a potential that is the sum of the supply voltage and the voltage generated by the motor.

During the on-time of the forward stroke control,transistor 270 is driven into conduction, drivingtransistor 268 into conduction and hence connectingmotor terminal 262 to approximately ground potential, back biasing thediodes 336 and 337. The voltage charge acrosscapacitor 340 is now used to control the base drive oftransistors 300, establishing an on-time duration proportional to the voltage across the capacitor. Aresistor 342 allows the voltage acrosscapacitor 340 to slowly leak off. Since the emitter oftransistor 300 is referenced to the DC supply voltage, the current throughtransistor 300 is dependent solely on the back EMF across the DC motor, eliminating the effect of supply voltage variations.

The control circuit also includes a number of special safety circuits, described in the following sections. In addition, the control circuit includes a battery voltage variation compensation circuit, includingtransistors 370 and 371, and described in detail in the before identified copending application, to which reference should be made.

BUBBLE DETECTOR The bubble detector circuit includes the bubble detector electrodes 212 andtransistors 350 and 351. When fluids having a'conductivity equal to a salinity of 0.00] percent or greater are present between electrodes 212 which are spaced 0.25 inches apart, the resistance therebetween is on the order of 200 kilohms or lower. This causes current to flow from thesupply line 275, through the emitter-base oftransistor 350, through aresistor 352, as 10 kilohms, to one electrode 212 and thence through the fluid to the other electrode 212 to charge acapacitor 353, as 10 microfarads. Ca-

,pacitor 353 is discharged by the forward stroke control circuit through adiode 355. The time constants are chosen such thatcapacitor 353 is never charged to move than 0.1 volts unless the forward stroke control circuit fails. If the forward stroke control circuit fails in such a way that the forward stroke would be at full supply voltage across themotor 120,capacitor 353 charges to supply voltage and turnstransistor 350 off. This terminates operation. Thus, the patient is protected from excessive infusion rates which otherwise might be caused by failure of critical parts in the circuit. Additional protection is provided by the rate monitor circuit, to be described The current that chargescapacitor 353 causes a current of at least 200 times magnitude to flow from the supply, through the emitter-collector oftransistor 350, through aresistor 357 and into the base oftransistor 351. Thisforward biases transistor 351, creating a path to ground through thetransistor 351 and aresistor 358 connected to the base oftransistor 269, thereby allowing drive fortransistor 269 and 265 to flow when thetransistor 269 and 265 are turned on by the reversing switch driver circuit. When an air bubble or cavity in present between the electrodes 212, the current path is broken andtransistor 351 is biased off. Therefore, the motor stops on the forward stroke.Prime switch 176 in the forward stroke control circuit is used to override this shut-off during syringe priming.

The combination of the bubble detector circuit and the placement of theelectrodes 212 and 220 in the two-way valve assembly 40 creates a fail safe apparatus which detects air leaks caused by a defect in the pump assembly itself. For additional disclosure concerning the placement of theelectrodes 212 and 220, reference should be made to our before mentioned copending application The bubble detector control circuit serves the dual purposes of providing a safety device to prevent accidental passage of an air bubble, and also automatically shuts off the pumping apparatus when all the fluid in the solution bottle is used up. At the end of the supply of fluid, air is introduced into the solution bottle and is pumped to thevalve assembly 40. When the air reaches the point where the two sensing electrodes 212 are placed, the current path is broken and motor operation is terminated, turning off the pumping system.

OVER-PRESSURE DETECTOR This circuit is formed by integrated circuit gates 400, 401 and a transistor 372, Gates 400 and 401 are connected to form a bistable multivibrator. During normal operation (no over-pressure condition), gate 401 is on and transistor 372 is off. To insure this state, a capacitor 405 is made five times as large as acapacitor 406. When the control circuit is first energized, the capacitor 405 holds one input of gate 400 low long enough to set the bistable with gate 401 saturated and gate 400 off.

When fluid reacheselectrodes 220, indicating an overpressure condition, a circuit path is formed from one input of gate 400 to thesupply voltage line 275 viatransistor 350 and the electrode 212 connected throughresistor 352 to the base thereof, saturating gate 400 and turning gate 401 off. This turns transistor 372 on, turning offtransistor 351 which in turn opens the bias path fortransistors 269 and 265. This stops the system on the forward stroke. The over-pressure detector circuit may be reset by turning the control circuit off and back on, causing capacitor 405 to again saturate gate 401.

BUBBLE AND OVER-PRESSURE INDICATOR This circuit consists oftransistors 410 and 411 which control energization ofa visual indicator, such as a light emitting diode (LED) 413. Desirably, a light emitting diode is used rather than an incandescent lamp due to its low power consumption. When an air bubble or an over-pressure condition is detected by the circuits previously described,transistor 351 is turned off. This in turn biases offtransistor 410, ungrounding a junction formed between aresistor 415 and a diode 416 connected in series between the anode ofLED 413 and the base of transistor 411. The transistor 411 is thus forward biased, creating a current path for theLED 413 to ground through aresistor 420 and the collectoremitter junction of the conducting transistor 411. TheLED 413 is located adjacent a jewel lens mounted incase 170 in order to give a visual indication of a circuit shut-off caused by the detection of an air bubble or an over-pressure condition.

RATE MONITOR CIRCUIT This circuit, shown in FIG. 4, is connected to the circuit of FIG. 3 through corresponding numbered and lettered connections indicated within circles. The rate monitor circuit creates an electrical analog representative of the of the syringe driver, against which is compared the sensed actions of the actual syringe driver. The sensed actions are desirably determined using thelimit switches 152 and 154 activated by the permanent magnet inprotrusion 150, see FIG. 2. When, for any reason, the actual syringe driver completes its forward stroke in a predetermined amount of time less than the analog syringe driver, the rate monitor circuit terminates the forward stroke, as by activating a portion of v the existing over-pressure detector.

A number of failures might cause the actual syringe driver to have an excess pumping rate, i.e., a rate substantially in excess of the rate selected by therate knob 174. For example, certain transistors in the circuit of FIG. 3 might fail, or the rate switch 312 might opencircuit. The rate monitor circuit is designed to protect against all such occurrences, and to cause a shut-down of the syringe driver in the event that certain portions of the rate monitor circuit itself should fail.

Considering the circuit in detail, the collectors oftransistors 280 and 282 in the reversing switch driver, FIG. 3, are coupled via connector A to a 47microfarad capacitor 500, FIG. 4, and through a'3.3 kilohm resistor 502 to the base of aNPN transistor 504. Akilohm resistor 506 is connected in shunt between the base and emitter electrodes oftransistor 504. The transistor serves to discharge a 470microfarad capacitor 510 through a 10ohm resistor 512 connected in series with the collector and emitter electrodes of thetransistor 504.

Capacitor 510 is a part of a selectable time constant means which serves to generate an analog voltage which can be used to determine whether the system is operating properly. Thecapacitor 510 is charged through a constant current source consisting of aPNP transistor 516 having a collector directly connected tocapacitor 510, an emitter connected to acommon line 518, and a base connected in a voltage divider to the junction between a 220ohm resistor 520 and three series connectedsemiconductor diodes 522. The voltage divider is connected between a source of positive voltage online 248 andground 250.

The rate of charge ofcapacitor 510 depends on the position of the rate switch 312, FIG. 3. Eachcontact 1 through 9 of the rate switch is connected through acorresponding diode 530 and aresistor 532 to thecommon line 518. Eachresistor 532 has a different resistance value to produce a different time constant for the analogcircuit including capacitor 510, chosen such that the analog ramp voltage acrosscapacitor 510 will reach +1.2 volts DC at a time when the syringe driver has completed approximately percent of its forward stroke. For the infusion system which was constructed, the value of theresistors 532 corresponding to each of thecontacts 1, 2, 3, 4, 5, 6, 7, 8 and 9 was 6.2 kilohms, 20 kilohms, 33 kilohms, 47 kilohms, 62 kilohms, kilohms, 91 kilohms, I00 kilohms and kilohms, respectively.

The analog ramp voltage acrosscapacitor 510 is coupled through adiode 540 to the base of a NPN transistor 542. The emitter of the transistor 542 is directly connected toground 250, and the collector is connected through a 10kilohm resistor 544 to the +V line 248, and also to the base of aNPN transistor 550. The collector oftransistor 550 is connected via connector E with one input of the gate 401, FIG. 3. The emitter oftransistor 550 is directly connected to the collector of asecond NPN transistor 554, having its emitter directly connected toground 250. The base and emitter electrodes thereof are shunted by a 10kilohm resistor 556. To control the biasing oftransistor 554, the base is also coupled through a 10kilohm resistor 560 and via connector B to the series connected collectors oftransistors 281 and 283 in the reversing switch driver, FIG. 3.

The operation of the rate monitor circuit of FIG. 4 may be understood with reference to the waveforms shown in FIGS. SA-SE. At the termination time of the back stroke of the actual syringe driver, thesyringe cylinder carrier 140, FIG. 2, is in its rear position at which the permanent magnet on protrusion actuates the reversestroke limit switch 152. This external sensing of the actual piston position is independent of the electrical drive control, and thus provides actual positioned sensing for the rate monitor circuit. Asreverse limit switch 152 is actuated at the end of a back stroke, the

- base oftransistor 282, FIG. 3, is grounded. As previously explained, thisdrive transistors 280 and 283 into saturation, producing a positive going voltage at connector A, FIG. 5A, and a negative (or ground) voltage at connector B, FIG. 5B.

This positive voltage occurring at atime 570, FIG. 5A, drivestransistor 504 into saturation, dischargingcapacitor 510 to approximately zero volts, as seen in FIG. 5C. Since connector A is coupled to the base oftransistor 504 through acapacitor 500, thecapacitor 500 momentarily charges to the positive voltage, removing the forward bias fromtransistor 504.Capacitor 510 now charges approximately linearly at a rate determined by the particular one timeconstant resistor 532 selected by the rate switch. The values of theresistors 532 are chosen such that the analog ramp voltage, FIG.

5C, normally reaches +1.2 volts DC level, labeled 572,.

when the actual syringe driver has completed approximately 60 percent of its forward stroke. The +l .2 volts DC level forward biases thesemiconductor diode 540 and the base-emitter junction of transistor 542, thereby reducing the voltage at the base oftransistor 550 to less than 0.1 volts DC, as seen in FIG. D.

At thetermination time 580 of the actual forward stroke, as sensed by the closing ofswitch 154, the voltages at connectors A and B reverse polarity, FIGS. 5A and B. The positive voltage totransistor 554 forward biases the same. However,transistor 550 is still reverse biased by the output. FIG. SD, of transistor 542, resulting in an open circuit between connector E andground 250, as seen in FIG. 5E. At the end ofthe back stroke,switch 152 is again actuated, repeating the cycle previously described.

If for any reason the syringe driver over-speeds so that the forward stroke is completed before the ramp voltage acrosscapacitor 510 reaches the +12volt lever 572, a modified operation results. Assuming that the actual back stroke begins at atime 590 which is well in advance of the selected operation, the voltage at connector B will rise positively andforward bias transistor 554. At the same time, the voltage on the base oftransistor 550, FIG. 5D, is positive, biasingtransistor 550 into conduction. Since bothtransistors 550 and 554 are forward biased, the voltage at connector E drops to ground potential, FIG. 5E, forming a shut down or error signal. As seenin FIG. 3, the error signal, i.e., ground, at the input of the gate 401 switches the bistable multivibrator, turning gate 401 off and hence turning transistor 372 andtransistor 351 offsAs previously explained for the over-pressure detector, this opens the bias path fortransistors 269 and 265, stopping the syringe driver on the forward stroke.

By different choice of the time constant values ofresistors 532, FIG. 4, and the value ofcapacitor 510, the safety range which allows continued normal operation, herein 60% of the selected rate, can be altered as desired. This range also allows for changes in consistence of the fluid being pumped, and other factors including calibration errors.

To increase reliability, the conductors for connecting the components used in the circuits of FIGS. 3 and 4 may be doubled, as by being formed on opposite sides of a printed circuit board, and other conventional redundancy techniques may be utilized. For some applications, itmay be desirable to include less than the number of individual circuits described above, or to include various combinations thereof. Other modifications will be apparent to those skilled in the art.

We claim:

1. In a system having pump means for pumping fluid from a fluid source to an outlet, a rate monitor, comprising: control means for controlling saidpump means and for providing a control signal representative of a selected rate of flow for the fluid; sensing means for generating a monitor signal representative of the rate of flow produced by said pump means; first circuit means coupled to said control means and said sensing means for comparing said control and said monitor signals for generating an error signal when a comparison of the control signal and the monitor signal indicates that the produced rate of flow has varied by a predetermined amount from the selected rate of flow; and second circuit means coupled to said first circuit means and responsive to said error signal for disabling said pump means upon the occurrence of said error signal.

2. The rate monitor of claim I wherein said pump means includes fluid channel means interconnecting said fluid source and said outlet and including a pump chamber, and drive means including a piston slidably mounted within the pump chamber for reciprocation under control of said control means to pump fluid through said fluid channel means, said sensing means generating said monitor signal in response to a predetermined motion of said drive means.

3. In a system having pump means for pumping fluid from a fluid source to an outlet, a rate monitor, comprising: control means for controlling said pump means and for providing a control signal representative of a selected rate of flow for the fluid; sensing means for generating a monitor signal representative of the rate of flow produced by said pump means; circuit means for generating an error signal when a comparison of the control signal and the monitor signal indicates that the produced rate of flow has varied by a predetermined amount from the selected rate of flow, said pump means including fluid channel means interconnecting said fluid source and said outlet and including a pump chamber, and drive means including a piston slidably mounted within the pump chamber for reciprocation under control of said control means to pump fluid through said fluid channel means, said drive means including link means cyclically driven through a path, said sensing means generating said monitor signal in response to a predetermined motion of said drive means, said sensing means including position responsive means for sensing cyclically recurring positions of said link means whereby said monitor signal is cyclically recurring.

4. The rate monitor ofclaim 3 wherein said control means provides a fixed value control signal for a given selected rate of flow, said circuit means includes time constant means for producing a time varying signal having a value dependent on the value of said fixed control signal and the time duration thereof, and means for time comparing said time varying signal with said cyclically recurring monitor signal to detect said predetermined amount of rate variation.

5. The rate monitor ofclaim 4 wherein said time constant means includes capacitor means and a charging path therefore coupled to said fixed value control signal, and said time comparing means includes gate means for discharging said capacitor means for each occurrence of said cyclically recurring monitor signal.

6. The rate monitor ofclaim 3. wherein said sensing means comprises switch means actuated once for each repetitive cycle of said link means.

7. The rate monitor ofclaim 6 wherein said switch means comprises a magnetically actuable contact means which changes state in the presence of a magnetic field, and said link means includes magnetic field generating means carried thereby for actuating the contact means. 7

8. In a system having pump means for pumping fluid from a fluid source to an outlet, a rate monitor, comprising: control means for controlling said pump means and for providing a control signal representative of a selected rate of flow for the fluid; said control means including selector means for selecting different pumping rates, and motor means responsive to said selector means for controlling the cyclic rate of driving the pump means; sensing means for generating a monitor signal representative of the rate of flow produced by said pump means; and circuit means for generating an error signal when a comparison of the control signal and the monitor signal indicates that the produced rate of flow has varied by a predetermined amount from the selected rate of flow; said circuit means including means responsive to said selectormeans for generating a different value control signal for each selectable rate, and means for comparing the different value control signals with the monitor signal.

9. The rate monitor ofclaim 8 wherein said compar- I ing means generates the error signal when the rate of flow produced bythe motor means exceeds by a predetermined range the selected rate of flow, and safety means responsive to said error signal for disabling said motor means.

10. In an infusion system having pump means for pumping fluid from a fluid source to a patient, and control means for controlling the pump means to establish a desired pumping operation, a monitor, comprising:

sensing means associated with said pump means for providing a monitor signal representative of the actual pumping operation of the pump means;

circuit means for generating an analog waveform having a predetermined relation to the monitor signal when the actual pumping operation corresponds to the desired pumping operation;

detector means responsive to a change in the predetermined relation between the monitor signal and the analog waveform for generating an error signal; and

safety means for disabling the pump means in response tosaid error signal.

11. The monitor of claim 10 wherein said pump means comprises a positive displacement pump having a piston slidably mounted within .a pump chamber for reciprocation along a predetermined path, and .said sensing means generates a recurring monitor signal for at least each cycle of reciprocation.

12. The monitor of claim 11 wherein said circuit means generates a recurring analog waveform having a voltage level synchronized with the occurrence of the monitor signal when the actual rate of pumping corresponds to the desired rate of pumping, and said detector means is responsive to a time advance in the occurrence of the monitor signal for generating said error signal to thereby prevent an excessive pumping rate.

13. The monitor of claim 10 wherein said control means includes selector means for selecting different pumping rates for the pump means, said circuit means includes capacitor means, a plurality of circuit paths each having a different time constant, and charging means controlled by said selector means for connecting one of said circuit paths between a potential source and saidtcapacitor means to form said analog waveform across said capacitor means, said detector means includes means for time comparing the charge of the capacitor means with the occurrence of the monitor signal to detect for said predetermined relation.

14. The monitor of claim 13 wherein said detector means further includes discharge means responsive to each occurrence of the monitor signal for discharging said capacitor means.

Claims (14)

1. In a system having pump means for pumping fluid from a fluid source to an outlet, a rate monitor, comprising: control means for controlling said pump means and for providing a control signal representative of a selected rate of flow for the fluid; sensing means for generating a monitor signal representative of the rate of flow produced by said pump means; first circuit means coupled to said control means and said sensing means for comparing said control and said monitor signals for generating an error signal when a comparison of the control signal and the monitor signal indicates that the produced rate of flow has varied by a predetermined amount from the selected rate of flow; and second circuit means coupled to said first circuit means and responsive to said error signal for disabling said pump means upon the occurrence of said error signal.

2. The rate monitor of claim 1 wherein said pump means includes fluid channel means interconnecting said fluid source and said outlet and including a pump chamber, and drive means including a piston slidably mounted within the pump chamber for reciprocation under control of said control means to pump fluid through said fluid channel means, said sensing means generating said monitor signal in response to a predetermined motion of said drive meaNs.

3. In a system having pump means for pumping fluid from a fluid source to an outlet, a rate monitor, comprising: control means for controlling said pump means and for providing a control signal representative of a selected rate of flow for the fluid; sensing means for generating a monitor signal representative of the rate of flow produced by said pump means; circuit means for generating an error signal when a comparison of the control signal and the monitor signal indicates that the produced rate of flow has varied by a predetermined amount from the selected rate of flow, said pump means including fluid channel means interconnecting said fluid source and said outlet and including a pump chamber, and drive means including a piston slidably mounted within the pump chamber for reciprocation under control of said control means to pump fluid through said fluid channel means, said drive means including link means cyclically driven through a path, said sensing means generating said monitor signal in response to a predetermined motion of said drive means, said sensing means including position responsive means for sensing cyclically recurring positions of said link means whereby said monitor signal is cyclically recurring.

4. The rate monitor of claim 3 wherein said control means provides a fixed value control signal for a given selected rate of flow, said circuit means includes time constant means for producing a time varying signal having a value dependent on the value of said fixed control signal and the time duration thereof, and means for time comparing said time varying signal with said cyclically recurring monitor signal to detect said predetermined amount of rate variation.

5. The rate monitor of claim 4 wherein said time constant means includes capacitor means and a charging path therefore coupled to said fixed value control signal, and said time comparing means includes gate means for discharging said capacitor means for each occurrence of said cyclically recurring monitor signal.

6. The rate monitor of claim 3 wherein said sensing means comprises switch means actuated once for each repetitive cycle of said link means.

7. The rate monitor of claim 6 wherein said switch means comprises a magnetically actuable contact means which changes state in the presence of a magnetic field, and said link means includes magnetic field generating means carried thereby for actuating the contact means.

8. In a system having pump means for pumping fluid from a fluid source to an outlet, a rate monitor, comprising: control means for controlling said pump means and for providing a control signal representative of a selected rate of flow for the fluid; said control means including selector means for selecting different pumping rates, and motor means responsive to said selector means for controlling the cyclic rate of driving the pump means; sensing means for generating a monitor signal representative of the rate of flow produced by said pump means; and circuit means for generating an error signal when a comparison of the control signal and the monitor signal indicates that the produced rate of flow has varied by a predetermined amount from the selected rate of flow; said circuit means including means responsive to said selector means for generating a different value control signal for each selectable rate, and means for comparing the different value control signals with the monitor signal.

9. The rate monitor of claim 8 wherein said comparing means generates the error signal when the rate of flow produced by the motor means exceeds by a predetermined range the selected rate of flow, and safety means responsive to said error signal for disabling said motor means.

10. In an infusion system having pump means for pumping fluid from a fluid source to a patient, and control means for controlling the pump means to establish a desired pumping operation, a monitor, comprising: sensing means associated with said pump means for providing a monitor signal representative of The actual pumping operation of the pump means; circuit means for generating an analog waveform having a predetermined relation to the monitor signal when the actual pumping operation corresponds to the desired pumping operation; detector means responsive to a change in the predetermined relation between the monitor signal and the analog waveform for generating an error signal; and safety means for disabling the pump means in response to said error signal.

11. The monitor of claim 10 wherein said pump means comprises a positive displacement pump having a piston slidably mounted within a pump chamber for reciprocation along a predetermined path, and said sensing means generates a recurring monitor signal for at least each cycle of reciprocation.

12. The monitor of claim 11 wherein said circuit means generates a recurring analog waveform having a voltage level synchronized with the occurrence of the monitor signal when the actual rate of pumping corresponds to the desired rate of pumping, and said detector means is responsive to a time advance in the occurrence of the monitor signal for generating said error signal to thereby prevent an excessive pumping rate.

13. The monitor of claim 10 wherein said control means includes selector means for selecting different pumping rates for the pump means, said circuit means includes capacitor means, a plurality of circuit paths each having a different time constant, and charging means controlled by said selector means for connecting one of said circuit paths between a potential source and said capacitor means to form said analog waveform across said capacitor means, said detector means includes means for time comparing the charge of the capacitor means with the occurrence of the monitor signal to detect for said predetermined relation.

14. The monitor of claim 13 wherein said detector means further includes discharge means responsive to each occurrence of the monitor signal for discharging said capacitor means.

Images