Drive system for an infusion pump

A pump system for an infusion system includes a linear drive (36, 36′) which minimizes the space occupied by the pump components in a portable housing (10, 10′). A motor (34) and a motor drive shaft (42) are arranged in parallel with, and adjacent to a syringe (14, 14′) and lead screw (94, 94′). A gear box (54) connects the drive shaft and lead screw to transfer rotational movements between them. A piston driving member, such as a cone (116) or drive nut (116′) converts the rotational movement of the lead screw into linear motion of a syringe piston (24). Sensors (150, 152) detect when the piston or cone is in a “home” position and in an “end” position, respectively. Optionally, a proximity sensor (170) is used to ensure that the cone and the piston (24) are abutting during dispensing. Alternatively, a clamping member (350) selectively clamps the lead screw (94′) against linear motion in at least a dispensing direction.

BACKGROUND OF THE INVENTION

The present invention relates to a portable pump for delivery of a medicament, such as insulin, from a syringe, and will be described with particular reference thereto. It should be appreciated, however, that the invention also has application in the miniaturization of pumps for delivery of other liquid substances.

Insulin pump systems which use a piston-operated cartridge for delivery of a medicament, such as insulin, allow patients to administer safely doses of an intravenous or subcutaneous medication at will, without the need for constant supervision by medical staff. These devices often include a housing, which is small enough to fit in a patient's pocket, that houses the cartridge, a motor, and a drive system. A power supply, such as a battery, is also included for supplying power to the motor. The outside of the housing provides key pad entry for allowing the patient to program the rate of insulin delivery and to modify the delivery rate according to the patient's expected or actual carbohydrate intake. To increase the portability of the infusion pump, a smaller housing is desirable. However, current designs for infusion pumps limit the overall minimum length of the housing.

The present invention provides for a new and improved pump system, which overcomes the above-referenced problems, and others.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a liquid delivery system is provided. The system includes a housing which accommodates a syringe containing the liquid. A motor is carried by the housing. A drive system, operatively connected with the motor, advances a piston of the syringe to expel liquid from a barrel of the syringe. The drive system includes a threaded rotatable shaft and a piston drive member, which linearly advances the piston, the drive member defining a threaded portion which engage threads of the shaft, the piston drive member advancing linearly as the shaft rotates.

In accordance with another aspect of the present invention, an infusion system is provided. The infusion system includes a housing for supporting a cartridge. The cartridge includes a chamber which holds a medicament and a means for expelling the medicament from the chamber. A means is provided for linearly advancing the means for expelling the medicament. A sensor means detects at least one of an abutting relationship and a lack of an abutting relationship between the advancing means and the expelling means.

In accordance with another aspect of the present invention, an infusion system is provided. The system includes a housing which receives a cartridge, the housing defining an opening for receiving the cartridge therethrough. A threaded shaft is selectively drivingly coupled with a piston of the cartridge, the threaded shaft linearly advancing the piston as the shaft rotates to expel a liquid from a barrel of the cartridge. A clamping member is selectively actuated to engage the shaft and thereby inhibit linear advancement of the shaft, relative to the barrel.

In accordance with another aspect of the present invention, a method of dispensing a liquid from a barrel of a cassette having a piston is provided. The method includes bringing a piston drive member and the piston into an abutting relationship. The piston drive member is advanced to advance the piston to dispense the fluid from the barrel. In the event that a change in ambient pressure causes the piston to separate from the piston drive member, the method includes detecting that the separation has occurred, and alerting a user of the cassette that a condition associated with the separation has occurred.

In accordance with another aspect of the present invention, a method of dispensing a medicament from a cartridge including a barrel and a piston is provided. The method includes bringing a piston drive member and the piston into an abutting relationship in a first position, sensing that the piston drive member is in the first position and sending a signal to a controller. The piston drive member is advanced incrementally under the control of the controller to advance the piston to dispense the fluid from the barrel until the piston drive member is in a second position linearly spaced from the first position. Further, the method includes sensing that the piston drive member is in the second position and sending a signal to a controller.

In accordance with another aspect of the present invention, a method of dispensing a liquid from a barrel of a cassette having a piston is provided. The method includes coupling a piston drive member to the piston, the piston drive member carrying a rotatable shaft. A clamping means is actuated which clamps the shaft against linear motion in a dispensing direction. The clamped shaft is rotated to advance the piston drive member and the piston to dispense the fluid from the barrel.

One advantage of at least one embodiment of the present invention is that it reduces the size of an infusion pump for improved portability.

Another advantage of at least one embodiment of the present invention is that occlusions in an infusion line are detected.

Yet another advantage of at least one embodiment of the present invention is that the end of travel of the drive mechanism is detected.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1, a portable pump system for use in an ambulatory injection system, such as an insulin injection system, is shown. The system includes a housing10, which is designed to fit conveniently in the pocket of a user or to be attached to a belt clip. A cassette14, such as a disposable or reusable syringe, is selectively received within the housing10. The syringe14holds a supply of a medicament, such as insulin, for injection into a diabetic person, or other user in need of the medicament. The syringe14includes a barrel16, which defines an internal chamber18for holding the medicament, a dispensing outlet20connected with one end of the barrel16, and an opening22at an opposite end of the barrel16. A plunger or piston24is received within the barrel16via the opening22for reciprocal motion within the barrel16for ejecting the medicament from the barrel. The piston24includes a head portion or cap26, which seals the opening22, and a longitudinally extending cylindrical or frustoconical portion28, extending from the head portion, which defines an internal piston chamber30with an open end32furthest from the barrel16.

With reference also toFIG. 2, mounted within the housing10, are a motor34and a drive system36for incrementally advancing the piston24to eject aliquots of the medicament according to a preprogrammed injection schedule. The motor34is under the control of a microprocessor-controller38, which is preferably housed within the housing10. Power for the motor and other operative components of the pump system is supplied by a battery40, or other source of power. The motor34is preferably a stepper motor, which rotates in finite, small increments or steps. The drive system36includes a drive shaft42, which is coupled to the motor so that it rotates a small portion of a revolution with each step of the motor. For example, the motor34may advance twenty steps to turn the drive shaft42one complete revolution. As shown inFIG. 1, the drive shaft42is aligned generally in parallel with the longitudinal axis x of the syringe barrel16and piston24and rotates generally perpendicular thereto about an axis parallel with the x axis.

An encoder50is attached to an armature of the motor34to detect when the steps are occurring. For example, a two-phase encoder alternatively registers a “zero” or a “one” output with each successive step. The microprocessor-controller38is equipped with processing software or hardware to detect the change in output of the encoder and thereby determine whether the motor34is advancing as instructed. The motor shaft42in turn drives a gearbox54comprising a series of gears56,58,60, as shown in greater detail in FIG.2. The number and size of the gears will depend on the desired ratio of drive shaft rotation to output rotation.

As shown inFIGS. 2 and 3, the gearbox54, by way of example has three gears56,58, and60. Gears56, and58are cluster gears, which each have a larger spur portion and a smaller pinion portion connected thereto. As shown inFIG. 2, the drive shaft42has a toothed-portion70at its distal end, having, for example 9 teeth, which drives a spur72of the gear56(having, for example 38 teeth), thereby turning an associated pinion74(having, for example 10 teeth). The pinion74in turn engages a spur78(having, for example 37 teeth) of the second gear58, which in turn turns the pinion80(having, for example ten teeth) of the second gear. The pinion80engages teeth on the third gear60, which forms a part of a universal yoke element90.

As shown inFIG. 4, the yoke element90is selectively connectable with a first portion, or driven end92of a threaded, rotatable shaft or lead screw94. Thus, the rotations of the motor shaft42are transferred to the lead screw via the gear box54at a selected ratio, for example a ratio of about 60:1 (60 rotations of the motor shaft for each rotation of the lead screw). A second, or distal end96(FIG. 1) of the lead screw94drives the piston24towards the chamber, so that the medicament is expelled. Specifically, the lead screw94is received longitudinally within the piston chamber30and extends generally parallel to the drive shaft42. As shown inFIG. 4, the driven end92may comprise a ball and pin member98, which is received in a slotted opening100in the yoke element90. Other engagement methods which transfer the rotation of the yoke member to the lead screw are also contemplated, such as a fitting comprising a hexagonal pin102on the driven end92, which is received in a corresponding hexagonal socket104in the universal joint90, as shown in FIG.5. Alternatively, the yoke90and lead screw94may be formed as a single component.

The lead screw94is exteriorly threaded along at least a portion of its length. The threads110engage corresponding threads112on an interior surface of a piston drive member116generally in the form of a cone. The pitch on the threads110,112is such that as the lead screw rotates, the cone116moves towards the barrel chamber, carrying the piston24with it. In particular, as the lead screw94is rotated in a driving direction, the cone116converts the rotational movement of the lead screw into a linear advancement of the cone116in a fluid expelling direction.

As best shown inFIGS. 6-8, the cone116includes a longitudinally extending conical body118, which is generally frustoconical in shape and which is received within the internal piston chamber30. The body118is narrowest at an end120, closest to the head portion26of the syringe14. A flange124extends outwardly from an opposite end126of the conical body118. The end126of the conical body118fits snugly in the open end32of the piston chamber30, such that lateral movement of the piston24relative to the cone116is substantially or entirely eliminated. The conical body defines a longitudinal interior bore or passageway128which is threaded along at least a portion of its length, for receiving the lead screw94therethrough. It will be readily appreciated that the exact shape of the cone116is not limited to a conical shape as illustrated in FIGS.1and6-8, but may be of any convenient shape to fit within the interior chamber30of the piston24and to provide guidance to the lead screw94so that the piston24moves longitudinally without excessive lateral wobbling. This ensures accurate and smooth dispensing of the medicament from the barrel chamber18.

As shown inFIG. 1, the lead screw94may engage threads on the cone116at two, or more, spaced positions, one position130, on the flange124, adjacent the open end of the cone116, the other131, being adjacent the head end26of the piston24, or the conical portion may be interiorly threaded along its entire length. Or, the distal end96of the lead screw may pass through a narrowed circular opening132in the cone tip120and be received in the end of the piston chamber adjacent the barrel chamber18.

As best shown inFIG. 6-8, the cone116is a separate element from the piston24and slides into and out of the piston without any form of engagement therewith (other than touching contact). The tip120slidably contacts the cylindrical wall of the piston24, or is slightly spaced therefrom. The cone116is thus configured for one-way guiding of the piston24, i.e., the cone pushes the piston in a fluid expelling direction only. Retraction of the cone116(e.g., by rotation of the drive shaft94in an opposite direction to the driving direction) does not withdraw the piston24from the barrel16.

In another embodiment, shown inFIG. 1, the narrow tip120of the cone116is externally threaded at134to engage corresponding threads136on the internal piston chamber30. In this embodiment, the cone is configured for two-way driving of the piston24. Retraction of the cone (e.g., by rotation of the drive shaft94in an opposite direction to the driving direction) withdraws the piston24from the barrel16.

As best seen inFIGS. 9-10, the flange124includes a first portion138, which is wider than the piston open end and a second portion139, which is square shaped or otherwise defines an engagement surface. The first portion138provides a stop or abutting surface for abutting the piston24. The second portion139of the flange124is guided by a longitudinally extending guide element140, which extends generally parallel to the piston24and direction of travel of the cone116. The guide element140contacts at least one of several flat peripheral surfaces144(four in the embodiment ofFIG. 9) of the flange124and inhibits rotation of the flange and attached conical body118. In the embodiment ofFIGS. 9 and 10, the guide element140defines an interior bore145having a square cross section which snugly receives the corresponding square cross sectioned second portion139. As the cone116is advanced, the piston24is driven into the barrel16of the syringe14and the medicament is expelled. Seals146, such as o-rings, seal the gap between the piston24and the barrel16.

In an alternative embodiment, shown inFIG. 6, the entire flange124has a uniform, square cross section. In yet another embodiment, shown inFIGS. 11 and 12, the guide element140′ is in the form of a plate which extends parallel to the direction of travel of the cone116. The guide element140,140′ is mounted to the housing10or to another rigid support within the housing.

The travel of the cone116or piston24is preferably sensed by sensors150,152, which will be referred to herein as position sensors. For example, a first position sensor150detects when the cone116or piston24is in the “home” position (adjacent the driven end of the lead screw), as shown in FIG.1. The sensor150may be an optical sensor, such as infra-red sensor, mounted adjacent the home position of the flange124(or other suitable portion of the cone116or piston24). The sensor150includes a transmitter (not shown), such as an infra-red transmitter, and a receiver (not shown) such as an infra-red receiver. When the flange124is adjacent the sensor150, for example, within about one millimeter of the sensor, the infra-red radiation from the transmitter strikes a reflective portion156of the flange124, such as a piece of reflective metal, and is returned to the receiver. The sensor150detects when the signal is received and transmits a signal to the microprocessor controller to indicate that the cone116is in the “home” position. In an alternative embodiment, the head26or other part of the piston24includes the reflective portion.

A second position sensor152, analogous to the first sensor150, is positioned close to, or adjacent to the “end” or “barrel empty” position157. The “end” position is the position that the reflective portion156is in when the piston head engages a dispensing end158of the barrel, i.e., where the flange124ends up when the piston24is depressed to the full extent of its travel. Preferably, the sensor152's position is just before the end position157(i.e., slightly to the right of the end position, in the arrangement of FIG.1). The second sensor152signals the microprocessor-controller38when the reflective portion156is adjacent to the sensor152, and the microprocessor portion of the microprocessor-controller thereby recognizes that the cone116and piston24are approaching the end position. The controller portion of the microprocessor-controller instructs the motor34to cease advancing the shaft42and the piston24comes to a stop. In this way, the advancement of the piston24can be arrested before it hits a dispensing end158of the barrel16, thereby avoiding potential damage to the drive system36or to the motor. This allows a “software” stop for the piston24, rather than a “hard” stop. Alternatively, or additionally, the microprocessor may determine the position of the piston24from the signals received from the encoder50and by a calculation therefrom of the number of revolutions of the shaft42. The microprocessor may use this determination as a check on the signals received from the second sensor152, or to override the signal received from the second sensor when the two sets of signals are in conflict over the position of the piston24. The microprocessor-controller38may signal an alarm, such as an audible alarm160, a vibration alarm162, and/or send a message to an LCD or other visual display164(seeFIG. 1) to indicate to the user or care provider that the syringe14is empty and needs to be refilled or replaced. The housing10may also include a window168for providing a visual indication to the user of the quantity of medicament still present.

With reference once more toFIGS. 6-8, a third sensor or proximity sensor170detects when the cone116is properly seated in the piston24. During dispensing, the cone116is properly seated when it is in an abutting position, shown inFIG. 8, in which the cone flange124touches, or is closely adjacent to, a corresponding radially extending flange or lip172at the end of the piston body118. In the event that a sudden change in ambient pressure, such as when the user travels by airplane, occurs, the piston24may separate from the cone116, and move towards the spaced position shown in FIG.7. The sensor170is electrically connected with the microprocessor-controller38. The sensor170detects when such a separation occurs and a signal (or lack of signal) is sent to the microprocessor-controller38. The microprocessor-controller38activates the audible alarm160, the vibration alarm162, and/or sends an appropriate message to the LCD or other visual display164. The user is advised to open the housing10and ensure correct positioning of the piston24. In one embodiment, illustrated inFIGS. 6-8, the sensor170includes a contact switch173(shown in greater detail in FIG.6A), which is mounted to a surface of the cone flange124facing the piston flange172. The contact switch173detects a pressure exerted by the piston flange172on the switch when the two flanges172,124are closely adjacent or touching (FIG.8). If the two flanges172,124move apart, the switch173signals the resulting lack of pressure or reduced pressure to the microprocessor-controller38. Alternatively, the sensor170sends a signal when the two flanges are abutting and a lack of signal is indicative of lack of abutment. It will also be appreciated that the contact switch173may alternatively be located on the piston flange172.

In another embodiment, shown inFIGS. 13 and 13Athe sensor170includes a first conductive portion, such as a conductive ring174, mounted to the piston flange172, and a second conductive portion, such as two conductive half rings176,178mounted to the cone flange124, in facing relationship to the conductive ring174. The two conductive half rings176,178are electrically isolated from each other. The conductive ring174and a disk enscribed by the half rings176,178have generally the same internal and external diameters such that when the flanges172,124are positioned in abutting relationship, as inFIG. 8, an electrical circuit is formed. Specifically, electrical current supplied to one of the conductive half rings176flows to the conductive ring174and thence to the other of the conductive half rings178. When the circuit is broken, as in when the piston24separates from the cone116, a signal (or lack of signal) is sent to the microprocessor-controller38. It will be appreciated that the positions of the ring174and half rings176,178may alternatively be switched.

While the third sensor170has been described as sensing contact, or lack thereof, between the flanges172,124, it is to be appreciated that the sensor170may alternatively detect contact or lack of contact between other abutting surfaces of the cone116and the piston24. For example, the sensor could sense an abutting relationship between the tip120of the cone and the head portion26of the piston24. Electrical connections (not shown) connect the sensor170or one or more conductive portions thereof, with the microprocessor controller38. Or, the sensor may be an optical sensor which detects when the piston24and cone116are within a prescribed distance range of one another.

With reference once more toFIG. 1, and reference also toFIGS. 14-17, an external cap190optionally secures the syringe14to the housing10and inhibits rotation of the syringe relative to the housing. In a preferred embodiment, best shown inFIG. 14, the cap includes a top192. A first annular skirt194extends from a periphery of the top and is exteriorly threaded to engage corresponding interior threads on an annular engagement portion196, which extends from the housing10. The annular skirt includes a radial shelf198. An O-ring200or other sealing member encircling the skirt. The radial shelf198holds the O-ring200in sealing engagement with a portion202of the housing10, which is radially outward of the engagement portion. The O-ring inhibits the migration of water into the housing10. The housing portions196and202are concentric and are joined together to define a circular opening204which is wide enough to receive the syringe14therethrough.

The cap190defines a second annular skirt210, which depends from the top192and is spaced radially inward of the first skirt194. The outlet20of the syringe14fits snugly within a first interior passage212defined by the second annular skirt210. The second skirt210is exteriorly threaded and threadably engages a corresponding annular threaded portion214of the syringe14. Specifically, the threaded portion214is a luer fitting, which extends from the syringe14in parallel with the outlet20and is radially spaced therefrom.

A second luer fitting220selectively connects the top192of the cap with an infusion line222. The second luer fitting defines a second interior passage224which extends at right angles from the first interior passage212.

After a syringe14is filled with a medical solution, such as insulin, the syringe is screwed on to the first luer fitting212of the syringe cap190. Alternatively, the user may use prefilled, single use ampules. The piston24is depressed to purge air bubbles from the cap and infusion line. The syringe14is inserted into the housing10through the opening204and the cap190, with the infusion line222attached, is rotated clockwise to lock the cap to the housing.

The piston24slides over the conical sides of the cone116(which is already retracted to its home position), and is thereby guided into its correct position in the housing. When the piston24is fully inserted, i.e., with the lip172of the piston24engaging or adjacent to the cone flange124, the user programs the microprocessor-controller by way of a user-microprocessor interface230, such as a keypad, touch screen, or other suitable interface (see FIG.16). The user may select, for example, from a range of preprogrammed injection schemes or enter information, such as blood glucose levels, expected or actual carbohydrate intake, etc. in order for the microprocessor to calculate an appropriate infusion regimen. Or, the user may enter the amount of insulin to be infused in a selected time period. The infusion line222may be connected with an infusion set (not shown) or other suitable infusion device for supplying the medication to the user's body.

In the embodiment ofFIG. 1where the cone116is exteriorly threaded, the piston24is rotated a few turns (e.g., by grasping the syringe14adjacent the connector portion20and turning it) to engage the internal piston threads136with the corresponding threads134of the cone, thereby locking the piston24to the cone116.

The motor34rotates the drive shaft and the lead screw rotates, as described above. The interior threads on the cone116cause the lead screw and cone to begin to separate, pushing the cone and piston24in the dispensing direction.

Prior to making a connection between the infusion line222and an infusion set (not shown), the user preferably instructs the pump microprocessor-controller38to conduct a purge phase to clear the infusion line222of air by passing a quantity of the medicament through the line. The user visually observes when the line is filled with the medicament and instructs the microprocessor38to halt the purge phase. The microprocessor detects that the cone flange124is no longer against the first sensor150and also determines the quantity of medicament expelled during the purge phase from the signals from the two-phase encoder50.

The microprocessor-controller38then controls the operation of the pump through the selected cycle. Using the information from the two-phase encoder50, the microprocessor keeps a check of the amount of medicament dispensed and provides a visual display to the user on the LCD display164. This may be a numerical display of the amount of insulin and/or in the form of a bar which decreases in size or in number of elements (similar to the indicator of battery level on a cellular phone) or other visual indication of decreasing medicament supplies. The controller uses this value as a second check as to when the medicament supply is about to run out. When the second sensor detects that the cone flange124is in the “empty” position, it signals the microprocessor-controller, which in turn stops the advancement of the motor. By way of the LCD display164, the microprocessor-controller instructs the user to remove the syringe14. Once the user has removed the syringe14, the user signals the microprocessor that the syringe has been removed by making a suitable entry on the interface230. The controller then reverses the direction of advancement of the motor34and the motor backs the cone116up to the “home” position. When the cone “home” position is detected by the sensor150, the microprocessor instructs the user, by way of the LCD display164, to insert a fresh syringe and the process is repeated.

In the event that an occlusion blocks the line222and reduces the flow of medicament to the user, an occlusion sensor system240detects the occlusion and signals an alarm to indicate to the user that the medicament is not being administered at the appropriate rate. As shown inFIG. 1, the occlusion sensor240is integral with the microprocessor-controller38, although a separate occlusion sensor is also contemplated. The alarm can be the visual alarm, such as on the LCD display164, the audible alarm160, or the vibration alarm162. In the device ofFIG. 1, each of these alarms is employed. The vibration alarm162preferably takes the form of a vibrating motor, which is connected with the microprocessor. The user may select which of the alarm functions is to be in operation, for example, by switching off the audible alarm160and activating the vibration alarm162.

In one preferred embodiment, the occlusion sensor system240operates by detecting stalling of the motor34. If an occlusion in the line occurs, the pressure build up in the line inhibits advancement of the piston, which, in turn, reduces or prevents rotation of the lead screw, gears and motor shaft, and causes the motor to stop or reduce its advancement. For example, the microprocessor-controller38detects if the signals from the two-phase encoder50indicate that the motor is not advancing or is advancing too slowly. For example, in this embodiment of the occlusion sensor, the microprocessor-controller counts how many signals are received from the encoder in a preselected time period and determines whether the number of signals is less than expected. Or, the microprocessor-controller detects an absence of any encoder signals in a preselected time period.

In an alternative embodiment of an occlusion sensor240, shown inFIG. 4, a pressure transducer250or micro switch may be attached to a shaft portion252of the universal joint90to detect build-up of pressure in the lead screw94caused by the piston24being unable to traverse. The transducer signals the microprocessor-controller38, which, if the pressure is above a preselected minimum pressure, signals the alarm, as with the other embodiment.

As can be seen, the arrangement of the motor34and drive shaft42in parallel with and adjacent to the syringe14and lead screw94makes good use of the space within the housing10and minimizes the overall length of the housing. Additionally, since neither the lead screw nor the drive shaft advances longitudinally in the housing10(both simply rotate), the housing10does not have to be enlarged to accommodate for longitudinal movement of these components. For example, a convenient size for the housing10is about 75 mm in length and about 45 mm in width.

FIGS. 18to23show an alternative embodiment of a portable pump system where analogous components will be indicated by a prime (′) and new components are given new numbers. The system includes a housing10′, motor (not shown), drive shaft (not shown), and gear box analogous to the housing10, drive shaft42, and gear box54of FIG.1. In this embodiment, however, a lead screw94′ has a fitting102′, such as a pin, at a rearward end or driven end92′ thereof, which is configured for receipt by a correspondingly-shaped cavity302in the final gear60′ of the gear box. In this embodiment, the universal joint is omitted, although it is also contemplated that a universal joint98similar to that shown inFIG. 4may alternatively be used to couple the lead screw to the gear box. As shown inFIG. 21, the fitting102′ preferably has an angled cross section, such as a hexagonal cross section as shown, or square cross section, so that the rotational movements of the gear60′ are transferred to the lead screw94′. Exterior surfaces303of the fitting engage corresponding abutting surfaces303′ of the cavity302. It should also be appreciated that the shapes of the fitting102′ and gear may be reversed, i.e., with the fitting defining a hexagonal or similar cavity shaped to receive a corresponding pin or protrusion on the gear.

Alternatively, the lead screw94′ may be threadably or otherwise releasably connected with the gear60′ of the gear box.

As with prior embodiments, rotation of the lead screw94′ is converted to linear motion of a piston drive member116′. In this embodiment, the piston drive member116′ is threadably connected to the piston24′. Specifically, the drive nut116′ includes a threaded portion304, which is externally threaded and is configured for threadable connection to an internally threaded rearward end306of the piston. As is shown inFIG. 19, the rearward end306of the piston24′ is preferably widened, relative to the head26′ of the piston, and defines a flange172′ which abuts a corresponding flange124′ on the drive nut116′ when the two parts are coupled together. As shown inFIG. 19, the widened end has a tapered portion308, which abuts a corresponding tapered portion310of the drive nut116′. In this embodiment, the piston drive member116′ extends only a short distance into the piston24′ and the abutment of the tapered portions308,310and flanges172′,124′ and engagement of the threads assist in maintaining the axial alignment of the drive nut116′ and piston24′ during advancement of the piston. As will be appreciated, the drive nut116′ of this embodiment is configured for two-way guidance of the piston, i.e., the drive nut optionally drives the piston24′ linearly, both in the advancement (dispensing) stage and in a subsequent piston withdrawal stage, although it is also contemplated that the piston is not withdrawn by the drive nut, as will be described in greater detail below.

As with the embodiments ofFIGS. 9-12a guiding member (not shown) analogous to guiding member140preferably guides the flange124′ of the drive nut116′ to ensure that the drive nut and piston24′ advance linearly towards the syringe barrel16′ as the lead screw94′ rotates.

The drive nut116′ defines an opening or axial bore132′, which is internally threaded to receive a forward or distal end96′ of the threaded lead screw94′ therethrough. In this embodiment, the bore132′ is threaded along its entire length and the lead screw94′ extends into the interior chamber30′ of the piston24′, at least during the initial period of dispensing.

In this embodiment, the cap190ofFIGS. 1-17is optionally replaced by a mounting member320, which is integral with the syringe barrel16′. The mounting member serves the same functions as the cap190, i.e., releasably mounting the syringe14′ to the housing10′ and providing a means for attachment of an infusion line222′. In this embodiment, the syringe has a luer connection214′ adjacent the dispensing outlet24′ analogous to that shown inFIG. 14, but in this embodiment, the luer connection214′ attaches directly to the infusion line222′, rather than to a portion of a cap. Specifically, as shown inFIGS. 18 and 19, the outlet20′ has a tapered exterior surface322, which slidingly engages a corresponding tapered surface324of the infusion line or a fitting thereon. An annular cylindrical portion326extends forward from the syringe barrel16′, and is spaced radially outward of the outlet20′. The cylindrical portion326is interiorly threaded at328to engage corresponding exterior threads330on the infusion line or fitting connected therewith.

Exterior threads340on the forward end158′ of the syringe barrel16′ are configured for threadable connection with corresponding interior threads342around the housing opening204′. As best shown inFIG. 22, a pair of gripping flanges344,346extend radially outward of the cylindrical portion for ease of gripping by a user. To attach the syringe14′ to the housing10′, the user inserts the syringe through the housing opening204′ into the housing and grips the griping flanges in one hand while holding the housing in the other. The user then rotates the syringe to threadably attach the threads340,342and thus lock the syringe to the housing.

As shown inFIG. 23, the drive nut116′ and lead screw94′ are preferably connected with the prefilled syringe14′ outside the housing, i.e., prior to inserting the syringe into the housing. Specifically, the drive nut116′, with the lead screw94′ already attached, is first threadably connected to the syringe by rotating the syringe or drive nut to threadably couple the two components. Prior to or after coupling the drive nut116′ to the piston24′, the lead screw94′ is correctly axially positioned relative to the drive nut and piston, such that when the syringe is positioned into in the housing, the fitting102′ is received in the cavity302and the threads340of the syringe are positioned for engagement of the threads342. Preferably, the positioning of the lead screw94′ is carried out by the controller38′, after the medicament has been dispensed. The controller instructs the drive system (not shown) to rotate the lead screw so that it moves forward, relative to the drive nut,116′ to its home position, ready to begin dispensing again.

With particular reference toFIGS. 19-21, a clamping member or clip350serves to selectively lock the rearward portion92′ of the lead screw so that the lead screw fitting102′ remains engaged with the gear60′ during advancement of the piston24′. The clamping member350is carried by the housing10′ and includes a post352, which is received through an opening354in the housing. An interior end356of the post defines a slotted portion358, which defines a slot360(FIG. 21) configured for receiving the rearward portion92′ of the leadscrew therein. The post is biased to an engaged position (FIGS. 18 and 20) by a spring362, which is held under compression between the slotted portion358and an adjacent interior surface364of the housing10′.

A projection, such as a gasket370, is preferably formed from rubber or other suitable resiliently compressible material. The gasket is mounted to the leadscrew94′ in a fixed position, adjacent the rearward portion92′. The gasket is spaced from the fitting102′ by a distance just sufficient to receive the slotted portion358therebetween such that when the clamping member350is in the engaged position, the lead screw94′ is prevented or inhibited from moving, in either direction along axis x, relative to the gear60′ and housing. Most preferably, the gasket370and fitting102′ act as projections whose facing surfaces372,374abut corresponding opposing sides surfaces376,378of the slotted portion358. Since the gasket370is formed from a resiliently compressible material, such as rubber, the slotted portion is gripped between the gasket and the fitting. The lead screw is still able to rotate, however, when the clamping member is in the engaged position, and thereby advance the piston drive member and piston. As shown inFIG. 20, the surface372is preferably tapered to provide a camming surface which assists in guiding the slotted portion358during movement between the disengaged and engaged positions.

The clamping member350, in cooperation with the fitting102′, prevents linear movement of the lead screw94′ in a dispensing direction, thereby preventing unintended dispensing of the medicament from the syringe. For example, in the event of a sudden drop in ambient pressure, the suction forces created tend to try to draw the piston24′ into the syringe barrel16′ and dispense additional medicament. The clamping member350holds the shaft94′ in a fixed linear position, relative to the syringe barrel and housing and since the shaft94′, drive nut116′ and piston are all coupled together, the piston is inhibited from advancing. Additionally, the gasket370in cooperation with the clamping member prevents the leadscrew94′ from moving in a piston retracting direction (i.e., opposite to the advancing direction) in the event that a sudden increase in ambient pressure or other reason tends to move the syringe piston24′ in a retracting direction. In this way, the amount of each bolus of medicament dispensed is correctly metered by the controller38′.

An upper end380of the post352, which is positioned outside of the housing10′, defines a flange382or other engagement member. The clamping member350is held in a disengaged position (FIG. 19) by a stop384, such as a movable or releasable member. The stop384engages the engagement member382during the period of insertion of the syringe14′ into the housing10′. When the syringe14′ is correctly positioned in and attached to the housing, the stop384is rotated, depressed, or otherwise actuated by the user (or by the controller38′) to release the flange382and post352. The post352, under the biasing action of the spring362, then moves from the disengaged position ofFIG. 19to the engaged position of FIG.20.

As with prior embodiments, position sensors150′,152′ detect the linear position of the piston. In this embodiment, the reflective portion156′ is shown on the piston head, although it is also contemplated that the reflective portion156′ may be positioned elsewhere on the piston24′ or drive nut116′. Optionally, additional position sensors390,392are positioned at spaced distances apart between the two position sensors150′ and152′ for use in determining or providing a check on the incremental amounts of liquid dispensed. While two additional position sensors390,292are shown inFIG. 19, it is to be appreciated that fewer or more additional position sensors may be employed.

As will readily be appreciated, the infusion pump and drive system of the present invention has applications outside the medical field and is not limited to use in an infusion system.