fig1 illustrates the overall pumping system of the present invention . nutrient flows from a reservoir 1 , either hung on an intravenous pole or worn on the patient , down a pump supply tube 2 and into a cassette 3 . preferably , cassette 3 includes a resilient bellows , but other hollow , compressible elements , such as a rubber dome or a spring encaseed in a collapsible membrane , could be used and are within the scope of the present invention . during operation , cassette 3 is secured within a chamber 4 , indicated by dotted lines , within a pump - and - control housing 5 . preferably , chamber 4 is angled about 30 ° with respect to the pump housing . if supply tube 2 contains any air bubbles , they will tend to rise by gravity and be purged . after pumping , solution flows from cassette 3 through pump outlet tube 6 into the patient . fig2 illustrates the front control panel of the pump housing 5 . it features a display window 8 , preferably comprising alarm indicators and standard seven - segment displays such as liquid crystal displays ( l . c . d ) or light - emitting diodes ( l . e . d ). a suitable lcd is hamlin model 4717315431 . a plurality of buttons 9 , preferably membrane switches , permit adjusting the numbers shown in window 8 . a novel flip - handle control dial 10 is provided for switching between the modes indicated by the legends on the drawings . a half - spherical recess 11 is provided in the face of the pump housing and permits a disk - shaped handle 12 , which is pivotally secured at two of its opposing edges , to be push - pivoted into recess 11 . handle 12 is secured in a dial housing attached to pump housing 5 . the dial housing is attached to a multi - position switch , whose six contacts are illustrated at the lower left corner of fig1 . the user can place one finger on each face of disk 12 and rotate the disk about a horizontal axis , thereby closing respective switch contacts located , for example , on a printed circuit board ( pcb ) mounted within housing 5 . when the desired setting is reached , disk 12 can be pivoted back flush with the housing surface , leaving no projecting elements to be snagged by an ambulatory patient &# 39 ; s clothing , tubing , or the like . this also reduces unauthorized manipulation of the controls . fig3 is a vertical cross - section through pump housing 5 , showing a cassette - receiving chamber 4 and other components . the cassette is releasibly secured within chamber 4 by a latch 14 , preferably spring - loaded , and released by a sliding handle 16 on the exterior side surface of housing 5 . an optical emitter 18 , disposed within the wall of a chamber 4 into which cassette 3 is inserted , emits a light beam into one side of cassette 3 and an optical decoder 19 on the opposing side of cassette 3 detects when a chamber 39 within cassette 3 is empty of fluid and causes an alarm to sound . suitable components 18 and 19 are the trw oftron # op240 sla gaa1as plastic infrared emitting diode and the trw oftron # op550 slc npn silicon photo - transistor , both operating at a wavelength of 880 nanometers . a microprocessor 20 , preferably a thomson / mostek model etc 944n - xyh or a national semiconductor model cop444cn , is shown in fig1 and is connected to all electrical elements in the pump housing , and responds to sensor input signals by generating appropriate control output signals in accordance with its program . in particular , microprocessor 20 generates control pulses for rotation of a motor 22 , which rotates a cam and thereby causes a cam follower or piston 24 to compress the bellows portion of cassette 3 . motor 22 is preferably a dc gearmotor such as model 1624e003sp42 + 16 / 5 , 262 : 1 k297 from micromo electronics . of course , an equivalent element , such as an eccentric cam , could be used in place of piston 24 , with minor modifications . microprocessor 20 controls window 8 &# 39 ; s seven - segment display driver 26 , which is preferably a national semiconductor model cop472n - 3 . microprocessor 20 also monitors switches 9 , control dial 10 , optical detector 19 , battery strength , and a pressure sensor 28 . pressure sensor 28 is preferably a piezo - electric disc transducer , such as model pzt - 5a # 6020 from the vernitron piezoelectric division , and detects the pressure between bellows 34 and piston 24 . microprocessor 20 processes the shape of the curve of the variation of pressure with time to detect whether a blockage or break in the tubing has occurred . the system can distinguish the following conditions : ( 1 ) an empty cassette - receiving chamber ; ( 2 ) an upstream blockage or occlusion in supply tube 2 ; and ( 3 ) a downstream blockage or occlusion , such as the patient kinking output tube 6 . in the case of an upstream occlusion , the typical bell curve described by the pressure signal from the transducer 28 is shifted some milliseconds later in time with respect to the motor cycle and piston movement . in the case of a downstream occlusion , the peak of the pressure curve is higher than the normal voltage signal peak of about 1 . 2 volts . electrical power is supplied by a battery 29 , preferably of the 4 - volt variety . the microprocessor &# 39 ; s memory preferably includes at least 200 bytes of ram ( random access memory ) and about 2 kilobytes of rom ( read - only memory ), preferably containing the operating program whose flow charts are shown in fig7 - 13 . fig4 is a cross - sectional view of cassette 3 . the cassette includes a generally cylindrical retainer 30 , having at one end a bowl - shaped recess 31 , and at the other end an annular chamber 32 , into which fits the single open end of a compressible element 34 , such as an axially corrugated , generally cylindrical bellows . a tubular protective shroud 35 portion of retainer 30 has a somewhat larger diameter than bellows 34 and surrounds the bellows for a portion of its length . the other end of bellows retainer 30 interfits with , and is secured to , a valve retainer 36 having a generally cylindrical exterior , a central axial passage 37 and an off - center axial passage 39 . the interfit may take the form of an annular groove and matching annular rib . plastic material is used to reduce weight , and other semi - annular recesses may be provided , as shown . a cassette cap 38 , forming apertures for receiving pump supply tube 2 and output tube 6 , is secured to the end of valve retainer 36 remote from bellows retainer 30 . the periphery of cap 38 preferably has an irregular shape , as shown in fig3 a , so that it will fit into housing 5 in only one orientation , thereby preventing erroneous mounting of cassette 3 . preferably , these elements comprise styrene acrylonitrile ( san ) or similar rigid thermoplastic , and are secured together by sonic welding at a frequency of 20 , 000 hertz or by adhesives . bellows 34 preferably comprises ethyl vinyl acetate ( eva ) and is injection blow - molded . contained between retainer 30 and valve retainer 36 is a combination valve 40 , preferably of a silicone - based material . valve 40 has a central tubular portion or stem 41 , which extends into axial passage 37 of valve retainer 36 , containing a duck - bill check valve 42 which prevents backflow of solution away from the patient toward the pump . valve 42 closes under back - pressure in pump output tube 6 thus prevents backflow , regardless of whether the pump is operating or how the pump , supply reservoir , and tubing are oriented with respect to the patient . extending from stem 41 is an umbrella valve 44 , with its outer peripheral rim 45 pointing away from bellows 34 and toward supply tube 2 . between valves 42 and 44 , stem 41 has an outwardly extending annular rib 43 , which interfits with a radially inwardly extending annular rib of valve retainer 36 . valve 44 opens under a pressure of about 85 pounds per square inch ( psi ) of water as the &# 34 ; umbrella rim &# 34 ; 45 flexes away from central portion 41 , deeper into bowl - shaped recess 31 , and permits fluid to flow from tube 2 into the cavity defined by bowl - shaped recess 31 and bellows 34 , as bellows 34 expands due to its inherent resiliency . rib 43 on stem 41 prevents valve 40 from sliding axially . thereafter , compression of bellows 34 forces a repeatable , metered volume of its contents , preferably about one - third cubic centimeter of fluid , out through central axial aperture 46 , duck - bill valve 42 and passage 37 into tube 6 . the repetition or pulse rate of these compressions is varied to obtain the desired flow rate . valves 42 and 44 are self - actuating and require no external controls , linkages , solenoids , or the like . their opening and closing is timed exactly by the fluid flow . this substantially improves accuracy , simplifies the construction , increases reliability , and reduces cost . valve 40 is press - fitted into valve retainer 36 . in searching for an appropriate design for valve 40 , i recognized that a prototype combination valve shown as model va 3836 in a catalog from vernay laboratories , inc . of yellow springs , ohio would provide the needed functionality . the basic design of this valve is set forth in u . s . pat . no . 3 , 159 , 176 . after some research and development , including adjustment of the &# 34 ; cracking pressure &# 34 ; of the valve , such a valve design was found to be satisfactory . the shape and the pre - loading of the umbrella 44 are important features . preferably , as set forth above , they are chosen so that valve 44 opens at a pressure somewhere above about 84 psi . bellows 34 simultaneously serves as a metering chamber and performs four functions : ( 4 ) opening the distal or outlet valve 42 to eject fluid . the fact that bellows 34 is self - returning means that no attachment of it to the reciprocating element is necessary , unlike prior art syringe elements , so that setting up by patients or nurses may be rendered error - free . bellows 34 is press - fit to bellows retainer 30 and may be further secured by an adhesive , preferably a cyano - acrylic such as loctite pyramid 460 cyanoacrylate , which is water - resistant . fig5 is an end view of cassette 3 , showing that supply tube 2 preferably connects into an off - center aperture to cassette cap 38 , while output tube 6 fits centrally . the periphery of cap 38 preferably has an irregular shape , such as the irregular polygon or &# 34 ; arrow &# 34 ; shape shown in fig5 so that it will fit into housing 5 in only one orientation , thereby preventing erroneous mounting of cassette 3 by a relatively unskilled patient or an inadequately trained health care employee . the cassette will not latch into the housing if improperly inserted , and the pressure sensor will cause an alarm to be generated within a predetermined number of motor cycles . fig6 is a cross - sectional view of the optical system . two wedge - shaped radial sections of element 36 are cut away or formed with recesses . emitter 18 directs a beam of light through one of these sections of cassette 3 toward detector 19 , which is adjacent the other of these recesses . if fluid is in the path of the beam , the light scatters and is attentuated below a threshold set for the detector signal ; if supply tube 2 , and thus chamber 39 , runs empty , the light is not scattered , detector 19 is triggered , and an alarm indication is generated . preferably , the word &# 34 ; empty &# 34 ; is illuminated on the lcd window 8 and a beeper sounds . fig7 is a flow chart of the overall structure of the preferred operating program for microprocessor 20 and its associated components . the function scan step detects where the rotating switch shown on fig2 is positioned . the function selection jump table transfers control to the subroutine corresponding to that one of the five functions which has been selected on the control dial . fig8 illustrates the subroutine to set rate , that is , to determine how fast the fluid will be pumped , within the preferred operating range of 5 - 300 milliliters per hour . fig9 illustrates the first part of the run subroutine , for actually starting pumping at the chosen rate . fig1 illustrates the second part of the run subroutine , for monitoring sensors to determine if any alarm indications should be generated . fig1 illustrates the hold subroutine , for preserving the data on the volume of fluid fed to the patient while deciding which function or rate to set next . fig1 illustrates the volume fed subroutine . it is noteworthy that this subroutine , as well as the hold , set rate , and clear volume subroutines , cause an audible alarm if the pump is left unattended for 5 minutes . this prevents patient neglect and preserves battery power . fig1 illustrates the clear volume subroutine , for erasing the data on the volume of fluid fed . fig1 b is sheet 1 of the circuit diagram of the pump circuit . beginning at lower left , fig1 b shows a reed switch which detects the passage of a magnet ( not shown ) which rotates with the shaft of motor 22 . this generates a cycle signal which goes into the pin 1b of the multiplexer shown in fig1 , and thereby tells the microprocessor 20 when each motor rotation occurs . just above the reed switch , the contacts for rotary switch 11 - 12 are shown . a capacitor c18 and associated resistors serve to &# 34 ; de - bounce &# 34 ; the switch contacts . above the rotary switch contacts , the charging circuit , including diode d1 , is shown . this circuit supplies v bat for powering other parts of the circuit . a signal goes through resistor r2 to pin l6 ( fig1 ) of microprocessor 20 to indicate when power is coming from the charger in a pole clamp assembly or backpack ( not shown ) rather than from the battery . downstream of diode d1 , a circuit including transistor q1 supplies voltage v &# 39 ; which supplies all of the comparators and the operational amplifier in the rest of the circuit . this voltage is typically in the range between about 3 . 65 volts and about 4 . 5 volts . further downstream , in the lower middle portion of fig1 b , a low - battery shutdown circuit , including a first comparator u1 and transistors q2 and q3 acting as switches , shuts down the circuit and latches whenever voltage v &# 39 ; goes below 3 . 65 volts . as a safety feature , the circuit cannot be restarted without turning off the pump . further to the right in the lower portion of fig1 b , a circuit including a transistor q3 supplies a voltage v + which powers microprocessor 20 , the multiplexer , the occlusion detector circuit of fig1 b , to be described below , and the pull - up resistors shown in fig1 . in the middle right portion of fig1 b , a resistor r10 connects the low - battery shutdown circuit to a motor voltage regulation circuit including transistors q6 , a second comparator u1 , and a power transistor q4 . a fuse f1 is provided at the output for safety . the output of this circuit is a motor supply voltage v m which is preferably about 1 . 5 volts . signals applied to the positive input of second comparator u1 shut down the circuit if a &# 34 ; runaway &# 34 ; condition is detected , i . e . the microprocessor cannot tell when the motor cycle is over . in the center of fig1 b , a low - battery warning circuit , including a third comparator u1 , detects when battery voltage goes below about 3 . 95 volts and provides an &# 34 ; early warning &# 34 ; signal to pin l7 ( fig1 ) of microprocessor 20 , which can then actuate an alarm before actual shutdown occurs . in the left middle of fig1 a , a downstream occlusion detector circuit , including an operational amplifier u4 and a fourth comparator u2 , determines whether the peak of the pressure transducer 28 output signal exceeds the 1 . 2 volt reference voltage . if so , this indicates that piston 24 is encountering more - than - usual resistance in compressing bellows 34 . a piezo - electric ceramic transducer 28 is mounted at the end of the drive system cam follower or piston 24 . during normal pumping , the piston remains in constant contact with the cassette bellows 34 , thus producing an electrical potential across the plates of the piezo - electric transducer 28 . this signal varies in amplitude with the change in force required to compress the bellows . the transducer signal is fed directly through a high - impedance voltage divider network and a low - pass filter . this reduces the signal level to a usable operating range and eliminates any unwanted noise caused by motion artifact . the transducer signal is fed into amplifier u4 , preferably a model tlc271 , whose gain is adjusted by a potentiometer p2 . the signal is then compared with a 1 . 2 - volt fixed reference voltage . under normal operating conditions , the transducer signal falls below the 1 . 2 - volt reference , thus causing the output of fourth comparator u2 to go high . if a downstream occlusion is present , the amount of force required to compress the bellows 34 increases . this causes the transducer output signal to increase . if the transducer level is greater than the 1 . 2 volt reference voltage , the output of comparator u2 will trigger low . an occlusion signal is supplied to pin 2b ( fig1 ) of the multiplexer for transmission to microprocessor 20 , which is preferably programmed to respond when a minimum of 2 motor cycles and / or 45 seconds have passed without relief of the blockage . above the aforementioned downstream occlusion detector circuit , fig1 a shows a combination upstream occlusion and &# 34 ; cassette not present &# 34 ; detection circuit , including fifth comparator u2 . this measures whether the transducer output bell curve exists or is later than usual with respect to the motor cycle . if so , a warning signal is provided to pin 3b ( fig1 ) of the multiplexer for transmission to microprocessor 20 . the piezo - electric ceramic transducer is used to detect the presence of an upstream occlusion . during normal pumping , the piston 24 remains in constant contact with bellows 34 . when an upstream occlusion , e . g . caused by an obstruction , fluid coagulation , or pinched tubing , occurs , the bellows fails to return to its natural state and to make contact with the piston . as the pump unit commences its next pumping cycle , there is a slight delay between the time the motor turns on and the time piston 24 makes contact with the already - compressed bellows 34 . this time delay is monitored by comparator u2 , and thence by microprocessor 20 . during normal pumping , and even when an upstream or downstream occlusion occurs , piston 24 at some point makes contact with bellows 34 , generating an output signal from transducer 28 . if there is no cassette properly latched into the cassette - receiving chamber , the transducer output signal remains at 0 volts . therefore , the output of comparator u2 remains high throughout the pumping cycle , which causes microprocessor to generate an &# 34 ; empty &# 34 ; visual and audible alarm within two pumping cycles . at top left of fig1 a , a circuit including transistors q12 , q13 , and q5 disconnects the motor terminals at the end of each cycle , as indicated by the reed switch discussed above , thereby causing a counter - electro - motive - force ( emf ) to be generated in the motor windings , braking the motor . at top right of fig1 a , a circuit including transistor q10 turns on emitter 18 to test whether there is fluid in the cassette . in order to conserve power , emitter 18 is only activated during motor braking . preferably , a gaa1as plastic infrared emitter diode and an npn phototransistor 19 are used in a through - beam configuration ( fig6 ) to detect the lack of fluid in the inlet chamber of the disposable cassette . a potentiometer , p1 , controls the collector current of phototransistor 19 . this allows for tolerances in the emitter / detector pairs 18 , 19 . a sixth comparator u2 compares the voltage drop across the phototransistor &# 39 ; s emitter resistor to a fixed 1 . 2 - volt reference voltage . the comparator &# 39 ; s output is monitored by microprocessor 20 . when there is liquid in the inlet chamber of the cassette , the output of comparator u2 is high , the normal operating condition . when the cassette is pumped dry , the output signal goes low , triggering an alarm . another circuit , including transistor q11 and a seventh comparator u2 , controls actuation and loudness of a beeper , as ordered by volume , runaway or beep signals from microprocessor 20 ( see fig1 ). fig1 is sheet 3 of the circuit diagram of the pump circuit . as previously noted , microprocessor 2 is preferably a masked thomson / mostek model with about 2 kilobytes × 8 bits internal rom and at least 128 bytes × 4 bits internal ram . the time - based counter mode is utilized with an internal divide - by - 16 counter and an external 2 - megahertz crystal to generate a clock signal for an 8 - microsecond instruction cycle . a multiplexer , preferably a cmos ( complementary metal oxide semiconductor ) version of the national semiconductor model 74hc257 2 - data selector , is used to multiplex inputs to the microprocessor . a restart circuit , comprising a resistor r16 , diode d9 , and capacitor c12 , is connected to the reset pin of the microprocessor . output pin g2 of the microprocessor actuates the turning on of a backlight which illuminates the lcd display if the pump is operating on ac power or if the lightbulb logo switch on the front panel ( fig2 ) is pressed . the remainder of fig1 will be self - explanatory to those skilled in the art . fig1 illustrates the pin - out of the liquid crystal display and its control chips , and their interconnections . fig1 is a schematic diagram of a power supply for use in operating the pump on a . c . power and in charging the internal rechargeable battery of the pump . such a power supply is preferably housed in a backpack into which the pump housing can slide sideways . this backpack ( not shown ) includes a set of contacts which fit into the left side of the pump housing for power transmission purposes . the power supply includes a primary 1 - amp slow - blow fuse , a transformer , a pair of diodes d301 and d302 , an rc network , a voltage regulator , a 2 - amp output fuse , and a pair of terminals supplying about 5 . 15 volts direct current for operating the pump or charging its battery . the backpack preferably has a vertical slot in its back into which a standard hospital pole can be clamped by turning a knob on the side of the backpack and actuating a screw - driven clamp . the power supply circuit is itself supplied with power via an ac cord running from an outlet to the backpack . those skilled in the art will appreciate that numerous variations of the cassette and pump described above are possible within the scope of the inventive concept , and that the scope of the invention is not restricted to the embodiments described , but rather is defined by the appended claims .
a readily sterilizable , disposable cassette can be used in a medical pumping system having a supply tube , an outlet tube and means , such as a motor - driven piston , for intermittently applying pressure to the cassette . the cassette features a hydraulically self - actuating inlet valve communicating with the supply tube , a hydraulically self - actuating outlet check valve communicating with , and preventing backflow from , the outlet tube , a hollow , resilient compressible member , such as a bellows , having an interior communicating with the inlet and outlet valves , and a support structure securing together the tubes , valves and bellows in operating relation . preferably , the inlet and outlet valves are a unitary element . an optical sensing system detects fluid exhaustion in the cassette . the cassette has an irregularly - shaped cap which prevents incorrect insertion into a pump .