Patent Publication Number: US-10307536-B2

Title: Operating an infusion pump system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/370,279 filed Dec. 6, 2016, which is a continuation of U.S. patent application Ser. No. 14/146,885 filed on Jan. 3, 2014, now U.S. Pat. No. 9,539,388 issued Jan. 10, 2017, which is a divisional of U.S. patent application Ser. No. 13/009,644 filed on Jan. 19, 2011, now U.S. Pat. No. 8,622,966 issued Jan. 7, 2014, which is a divisional of U.S. patent application Ser. No. 11/677,743 filed on Feb. 22, 2007, now U.S. Pat. No. 8,409,142 issued Apr. 2, 2013, the contents of these prior applications being fully incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This document relates to an infusion pump system, such as a medical infusion pump system. 
     BACKGROUND 
     Pump devices are commonly used to deliver one or more fluids to a targeted individual. For example, a medical infusion pump device may be used to deliver a medicine to a patient as part of a medical treatment. The medicine that is delivered by the infusion pump device can depend on the condition of the patient and the desired treatment plan. For example, infusion pump devices have been used to deliver insulin to the vasculature of diabetes patients so as to regulate blood-glucose levels. 
     A number of factors may affect the design of infusion pump devices. One such factor is the size of the device. The pump device may be sized to house the various pump components, yet a large device may reduce the portability for the user. Another factor that may affect the design of an infusion pump device is the reservoir that contains the medicine. For example, if the reservoir is provided in a sealed form, the seal may require penetration before the medicine is infused to the user. Yet another factor that can affect the design of the pump device is the disposability. If, for example, the pump device is to be disposed after exhaustion (e.g., after a single use or a certain number of uses, after a particular period of time, or the like), reuse of the exhausted pump device may create a safety risk to the user. 
     SUMMARY 
     Some embodiments of a medical infusion pump system include a pump device having a cap device that mates with a pump housing to retain a medicine cartridge therein. In addition to retaining the medicine cartridge in the pump housing, the cap device may perform one or more functions, such as forcing the medicine cartridge to secure to a pump drive component, piercing a sealed end of the medicine cartridge to provide a flow path for the medicine, priming the plunger in the medicine cartridge with a “break away” force, providing a flow sensor to the medicine flow path, locking the medicine cartridge in the pump housing to promote disposal of the pump device after the medicine cartridge is exhausted, preventing the dispensation of medicine if the cap device is improperly engaged with the pump housing, or a combination thereof. 
     In addition or in the alternative, some embodiments of the pump device may include a drive system that reliably advances a piston rod to dispense medicine to the patient. The drive system may employ a spring device or the like to provide the dispensing drive energy to a ratchet mechanism. Also, the drive system may include an electrically powered actuator (e.g., a reversible motor) that provides the reset energy to the ratchet mechanism yet contributes no force on the ratchet mechanism when the spring device is delivering the dispensing drive energy. In such circumstances, the pump device can reliably and accurately dispense dosages of medicine in a safe and energy efficient manner. 
     In some embodiments, an infusion pump device may include a pump housing that defines a space to receive a medicine cartridge. The infusion pump device may also include a drive system to dispense a medicine from the medicine cartridge when the medicine cartridge is received by the pump housing. The infusion pump device may further include a cap device that engages the pump housing to retain the medicine cartridge therein when the medicine cartridge is received by the pump housing. When the cap device engages the pump housing, the cap device may act upon the medicine cartridge to urge a plunger of the medicine cartridge to attach to a component of the drive system. 
     Particular embodiments include a method of operating an infusion pump device. The method may include engaging a cap device with a pump housing to retain a medicine cartridge is a space defined by the pump housing. The method may also include urging the cap device against the medicine cartridge so that a plunger of the medicine cartridge attaches a component of a pump drive system. 
     In other embodiments, an infusion pump device may include a pump housing that defines a space to receive a medicine cartridge. The infusion pump device may also include a drive system to dispense a medicine from the medicine cartridge when the medicine cartridge is received by the pump housing. The drive system may include a piston rod having a plunger engagement device that attaches to the plunger of the medicine cartridge when the medicine cartridge is received by the pump housing. 
     Some or all of the embodiments described herein may provide one or more of the following advantages. First, some embodiments of the pump device may be attached to a controller device so that a user can readily monitor infusion pump operation by simply viewing a user interface connected to the pump device. In these circumstances, the user may activate and control the pump device without the requirement of locating and operating a separate monitoring module. 
     Second, some embodiments of the infusion pump system may be configured to be portable, wearable, and (in some circumstances) concealable. For example, a user can conveniently wear the infusion pump system on the user&#39;s skin under clothing or can carry the pump device in the user&#39;s pocket (or other portable location) while receiving the medicine dispensed from the pump device. 
     Third, a number of preparatory functions can be accomplished while the user performs the relatively simple task of attaching the cap device to the pump housing. For example, attachment of the cap device can cause the medicine cartridge to be retained in a cavity of the pump housing and can provide a water-tight seal for cavity. In another example, attachment of the cap device can force the plunger of the medicine cartridge to secure to the piston rod in the pump device. In a further example, attachment of the cap device can cause a sealed end of the medicine cartridge to be pierced and thereby provide a flow path for the medicine. In another example, attachment of the cap device can provide a “break away” force to initiate movement of the plunger in the medicine cartridge. 
     Fourth, one or more of safety functions can be performed while the user performs the task of attaching the cap device to the pump housing. For example, attachment of the cap device may arrange a flow sensor in the medicine flow path to detect occlusions. In another example, attachment of the cap device may result in the medicine cartridge being locked in the pump housing. Such a configuration may be useful, for example, in circumstances in which the pump device is designed to be a “one time use” disposable unit. In a further example, if the cap device is improperly engaged with the pump housing, the dispensation of medicine can be prevented. 
     Fifth, some embodiments of the drive system of the pump device can accurately and incrementally dispense fluid from the pump device in a controlled manner. 
     Sixth, the drive system of the pump device can be controlled dispense dosages of medicine in a safe and energy efficient manner. For example, in some embodiments, the motor of the drive system can be decoupled from the ratchet mechanism during the drive step. In such a configuration, the motor is not required to draw energy from a battery over an extended period of time (e.g., during the drive step in which the piston rod is advanced to dispense medicine over a period of time). 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective exploded view of an infusion pump system in accordance with some embodiments. 
         FIG. 2  is a perspective view of the infusion pump system of  FIG. 1 . 
         FIG. 3  is an perspective exploded view of a portion of the infusion pump system of  FIG. 1 . 
         FIG. 4  is a perspective exploded view of a cap device of the infusion pump system of  FIG. 1 , in accordance with some embodiments. 
         FIG. 5  is a perspective exploded view of the cap device of  FIG. 4 . 
         FIG. 6  is a perspective exploded view of the cap device of  FIG. 4 . 
         FIGS. 7A-D  are cross-sectional views of a portion of the infusion pump system of  FIG. 1 , in accordance with some embodiments. 
         FIGS. 8A-B  are cross-sectional views of a portion of the infusion pump system of  FIG. 1 , in accordance with further embodiments. 
         FIG. 9  is an exploded perspective view of a portion of a pump device of the infusion pump system of  FIG. 1 , in accordance with some embodiments. 
         FIG. 10  is an exploded perspective view of a piston rod and a medicine cartridge plunger of the pump device of  FIG. 9 . 
         FIG. 11  is a perspective view of a plunger engagement device of the piston rod of  FIG. 10 . 
         FIG. 12  is a side view of the piston rod and the medicine cartridge plunger of  FIG. 10 . 
         FIGS. 13A-D  are perspective views of a plunger engagement device of a piston rod and a medicine cartridge plunger, in accordance with some embodiments. 
         FIGS. 14A-B  are perspective and axial views of a plunger penetration member and a medicine cartridge plunger, in accordance with some embodiments. 
         FIGS. 15A-B  are perspective and axial views of a plunger penetration member and a medicine cartridge plunger, in accordance with other embodiments. 
         FIGS. 16A-B  are perspective and axial views of a plunger penetration member and a medicine cartridge plunger, in accordance with further embodiments. 
         FIG. 17  is a side view of a plunger penetration member having a retention portion, in accordance with some embodiments. 
         FIG. 18  is a side view of a plunger penetration member having a retention portion, in accordance with some embodiments. 
         FIG. 19  is an axial view of a plunger penetration member and a medicine cartridge plunger, in accordance with particular embodiments. 
         FIG. 20  is an axial view of plunger penetration members and a medicine cartridge plunger, in accordance with other embodiments. 
         FIG. 21  is an axial view of plunger penetration members and a medicine cartridge plunger, in accordance with some embodiments. 
         FIG. 22  is an axial view of plunger penetration members and a medicine cartridge plunger, in accordance with particular embodiments. 
         FIG. 23  is an axial view of plunger penetration members and a medicine cartridge plunger, in accordance with other embodiments. 
         FIG. 24  is an axial view of plunger penetration members and a medicine cartridge plunger, in accordance with some embodiments. 
         FIG. 25  is cross-sectional side view of plunger engagement device of a piston rod and a medicine cartridge plunger, in accordance with some embodiments. 
         FIG. 26  is perspective view of an pump device, with some portions removed to view a drive system. 
         FIG. 27  is a perspective view of the drive system of the pump device of  FIG. 26 , in accordance with some embodiments. 
         FIG. 28  is another perspective view of the drive system of  FIG. 27  in a first position. 
         FIG. 29  is a perspective view of the drive system of  FIG. 27  in a second position. 
         FIG. 30  is a perspective view of the drive system of  FIG. 27  while returning to the first position. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Referring to  FIG. 1 , an infusion pump system  10  can include a pump device  100  and a controller device  200  that communicates with the pump device  100 . The pump device  100  includes a housing structure  110  that defines a cavity  116  in which a fluid cartridge  120  can be received. The pump device  100  also includes a cap device  130  to retain the fluid cartridge  120  in the cavity  116  of the housing structure  110 . The pump device  100  includes a drive system (described in more detail below) that advances a plunger  125  in the fluid cartridge  120  so as to dispense fluid therefrom. The controller device  200  communicates with the pump device  100  to control the operation of the drive system. When the controller device  200 , the pump device  100  (including the cap device  130 ), and the fluid cartridge  120  are assembled together, the user can (in some embodiments) conveniently wear the infusion pump system  10  on the user&#39;s skin under clothing or in the user&#39;s pocket while receiving the fluid dispensed from the pump device  100 . 
     The controller device  200  may be configured as a reusable component that provides electronics and a user interface to control the operation of the pump device  100 . In such circumstances, the pump device  100  can be a disposable component that is disposed of after a single use. For example, the pump device  100  can be a “one time use” component that is thrown away after the fluid cartridge  120  therein is exhausted. Thereafter, the user can removably attach a new pump device  100  to the reusable controller device  200  for the dispensation of fluid from a new fluid cartridge  120 . Accordingly, the user is permitted to reuse the controller device  200  (which may include complex or valuable electronics) while disposing of the relatively low-cost pump device  100  after each use. Such a pump system  10  can provide enhanced user safety as a new pump device  100  (and drive system therein) is employed with each new fluid cartridge  120 . 
     In use, the cap device  130  is coupled to the pump housing  110  to retain the fluid cartridge  120  in the cavity  116  of the pump device  100 , and the pump device  100  (with the fluid cartridge therein) is removably attached to the controller device  200 . The cap device  130  may be multifunctional in that it performs a number of functions for the pump device operation. For example, in some embodiments, attachment of the cap device  130  may cause one or more of the following preparatory functions: forcing the plunger  125  of the fluid cartridge  120  to secure to a piston rod (described in connection with  FIG. 7B ), piercing a septum  121  of the fluid cartridge  120  to provide a flow path for the fluid (described in connection with  FIG. 7C ), and priming the fluid cartridge  120  with a “break away” force to initiate movement of the plunger  125  in the fluid cartridge  120  (described in connection with  FIG. 7D ). In addition or in the alternative, attachment of the cap device  130  may also cause one or more of the following safety related functions: aligning a flow sensor with the fluid flow path (described in connection with  FIGS. 8A-B ), locking the fluid cartridge  120  in the pump housing  110  to thereby promote disposal of the pump device  100  after exhaustion (described in connection with  FIGS. 8A-B ), and ceasing or preventing the dispensation of fluid if the cap device  130  is improperly engaged with the pump housing  110  (described in connection with  FIGS. 8A-B ). 
     In addition, the drive system of the pump device  100  may have a design that enables the dispensing of fluid in a safe and energy efficient manner. As described in more detail below in connection with  FIGS. 26-30 , the piston rod can be advanced incrementally using pawl and ratchet techniques. For each incremental advancement of the piston rod, there is a reset step and a drive step. In the reset step, an electrically powered component forces a pawl to move in a first direction and to engage another tooth of a ratchet wheel. Then, when the pawl is engaged on the next tooth of the ratchet wheel, the drive step begins in which the electrically powered component decouples from the pawl (e.g., the electrically powered actuator assembly separates from the pawl). This allows a spring device that is attached to the pawl to move the pawl in the opposite direction, thereby causing the ratchet wheel to turn an incremental amount. A gear system translates the incremental rotation of the ratchet wheel into incremental advancement of the piston rod. Among other advantages, such embodiments of the drive system help to reduce the overall time that the electrical power is drawn from a battery, which may facilitate a reduction in battery requirements. In addition, the release of medicine from the cartridge, which occurs during the drive step, is caused only by the force applied by the spring, and thus is consistent and repeatable. Examples of such drive systems are described in more detail below in connection with  FIGS. 26-30 . 
     Still referring to  FIG. 1 , in this embodiment, the pump system  10  is a medical infusion pump system that is configured to controllably dispense a medicine from the cartridge  120 . As such, the fluid cartridge  120  may contain a medicine  126  to be infused into the tissue or vasculature of a targeted individual, such as a human or animal patient. For example, the pump device  100  can be adapted to receive a medicine cartridge  120  in the form of a carpule that is preloaded with insulin or another medicine for use in the treatment of Diabetes (e.g., Byetta®, Symlin®, or others). Such a cartridge  120  may be supplied, for example, by Eli Lilly and Co. of Indianapolis, Ind. Other examples of medicines contained in the fluid cartridge  120  include: pain relief drugs, hormone therapy, blood pressure treatments, anti-emetics, osteoporosis treatments, or other injectable medicines. The fluid cartridge  120  may have other configurations. For example, the pump housing structure  110  may include one or more walls that surround a plunger to define a reservoir in which the medicine is injected or otherwise received. 
     In some embodiments, the controller device  200  may be removably attached to the pump device  100  so that the two components are mechanically mounted to one another in a fixed relationship. Such a mechanical mounting can form an electrical connection between the removable controller device  200  and the pump device  100 . For example, the controller device  200  may be in electrical communication with a portion of a drive system (not shown in  FIG. 1 ) of the pump device  100 . As described in more detail below, the pump device  100  includes a drive system that causes controlled dispensation of the medicine or other fluid from the cartridge  120 . In some embodiments, the drive system incrementally advances a piston rod (not shown in  FIG. 1 ) longitudinally into the cartridge  120  so that the fluid is forced out of an output end  122 . A septum  121  at the output end  122  of the fluid cartridge  122  can be pierced to permit fluid outflow when the cap device  130  is connected to the pump housing structure  110  (described in more detail below). Thus, when the pump device  100  and the controller device  200  are attached and thereby electrically connected, the controller device  200  communicates electronic control signals via a hard-wire-connection (e.g., electrical contacts or the like) to the drive system or other components of the pump device  100 . In response to the electrical control signals from the controller device  200 , the drive system of the pump device  100  causes medicine to incrementally dispense from the medicine cartridge  120 . 
     Still referring to  FIG. 1 , the controller device  200  includes a controller housing structure  210  that is configured to mate with a complementary portion of the pump housing structure  110  so as to form a releasable mechanical connection. For example, the controller housing structure  210  may define a cavity  215  that mates with a portion of the pump housing structure  110  for a snap fit engagement (as shown, for example, in  FIG. 2 ). Also, the controller housing structure  210  may include a tab  212  that engages a mating surface  117  of the pump housing structure  110  when the controller device  200  is removably attached to the pump device  100 . In some embodiments, a magnetic attachment may be employed to releasably secure the pump device  100  to the controller device  200 . For example, the magnetic attachment can serve to retain the pump housing structure  110  in the cavity  215  defined by the controller housing structure  210 . In alternative embodiments, one or more releasable connector devices (e.g., mating tongues and grooves, mounting protrusions friction fit into mating cavities, or the like) can be used to further implement the releasable attachment of the controller device  200  to the pump device  100 . 
     As shown in  FIG. 1 , the pump device  100  may include one or more electrical contacts  118  (e.g., conductive pads, pins, and the like) that are exposed to the controller device  200  and that mate with complementary electrical contacts (not show in  FIG. 1 ) on the adjacent face of the controller device  200 . The electrical contacts  118  provide the electrical communication between the control circuitry (e.g., one or more circuits including a microprocessor or the like and memory) housed in the controller device  200  and at least a portion of the drive system or other components of the pump device  100 . For example, in some embodiments, the electrical contacts permit the transmission of electrical control signals to the pump device  100  and the reception of feedback signals (e.g., sensor signals) from particular components within the pump device  100 . Previously filed U.S. patent application Ser. No. 11/522,603 (incorporated herein by reference) describes further embodiments of a controller device that can be attached to and communicate with a pump device. 
     Still referring to  FIG. 1 , the controller device  200  includes a user interface  220  that permits a user to monitor the operation of the pump device  100 . In some embodiments, the user interface includes a display  222  and one or more user-selectable buttons (e.g., four buttons  224   a ,  224   b ,  224   c , and  224   d  in this embodiment). The display  222  may include an active area  223  in which numerals, text, symbols, images, or combination thereof can be displayed. For example, the display  222  may be used to communicate a number of settings or menu options for the infusion pump system  10 . In this embodiment, the user may press one or more of the buttons  224   a ,  224   b ,  224   c , and  224   d  to shuffle through a number of menus or program screens that show particular settings and data (e.g., review data that shows the medicine dispensing rate, the total amount of medicine dispensed in a given time period, the amount of medicine scheduled to be dispensed at a particular time or date, the approximate amount of medicine remaining in the cartridge  120 , or the like). In some embodiments, the user can adjust the settings or otherwise program the controller device  200  by pressing one or more buttons  224   a ,  224   b ,  224   c , and  224   d  of the user interface  220 . For example, in embodiments of the infusion pump system  10  configured to dispense insulin, the user may press one or more of the buttons  224   a ,  224   b ,  224   c , and  224   d  to change the dispensation rate of insulin or to request that a bolus of insulin be dispensed immediately or at a scheduled, later time. 
     The display  222  of the user interface  220  may be configured to display quick reference information when no buttons  224   a ,  224   b ,  224   c , and  224   d  have been pressed. In this example, the active area  223  of the display  222  can display the time and the date for a period of time after no button  224   a ,  224   b ,  224   c , and  224   d  has been actuated (e.g., five seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, or the like). Thereafter, the display  222  may enter sleep mode in which the active area  223  is blank, thereby conserving battery power. In addition or in the alternative, the active area can display particular device settings, such as the current dispensation rate or the total medicine dispensed, for a period of time after no button  224   a ,  224   b ,  224   c , or  224   d  has been actuated (e.g., five seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, or the like). Again, thereafter the display  222  may enter sleep mode to conserve battery power. In certain embodiments, the display  222  can dim after a first period of time in which no button  224   a ,  224   b ,  224   c , or  224   d  has been actuated (e.g., after 15 seconds or the like), and then the display  22  can enter sleep mode and become blank after a second period of time in which no button  224   a ,  224   b ,  224   c , or  224   d  has been actuated (e.g., after 30 seconds or the like). Thus, the dimming of the display device  222  can alert a user viewing the display device  222  when the active area  223  of the display device will soon become blank. 
     Accordingly, when the controller device  200  is connected to the pump device  100 , the user is provided with the opportunity to readily monitor infusion pump operation by simply viewing the user interface  220  connected to the pump device  100 . Such monitoring capabilities may provide comfort to a user who may have urgent questions about the current operation of the pump device  100  (e.g., the user may be unable to receive immediate answers if wearing an infusion pump device having no user interface attached thereto). 
     Also, in these embodiments, there may be no need for the user to carry and operate a separate module to monitor the operation of the infusion pump device  100 , thereby simplifying the monitoring process and reducing the number of devices that must be carried by the user. If a need arises in which the user desires to monitor the operation of the pump device  100  or to adjust settings of the pump system  10  (e.g., to request a bolus amount of medicine), the user can readily operate the user interface  220  removably attached to the pump device  100 , without the requirement of locating and operating a separate monitoring module. 
     In other embodiments, the user interface  200  is not limited to the display and buttons depicted in  FIG. 1 . For example, in some embodiments, the user interface  220  may include only one button or may include a greater numbers of buttons, such as three buttons, four buttons, five buttons, or more. In another example, the user interface  220  of the controller device  200  may include a touch screen so that a user may select buttons defined by the active area of the touch screen display. Alternatively, the user interface  220  may comprise audio inputs or outputs so that a user can monitor the operation of the pump device  100 . 
     Referring to  FIG. 2 , the infusion pump system  10  may be configured to be portable and can be wearable and concealable. For example, a user can conveniently wear the infusion pump system  10  on the user&#39;s skin (e.g., skin adhesive) underneath the user&#39;s clothing or carry the pump device  100  in the user&#39;s pocket (or other portable location) while receiving the medicine dispensed from the pump device  100 . As described below in connection with  FIGS. 26-30 , the drive system may be housed in the housing structure  110  of the pump device  100  in a compact manner so that the pump device  100  has a reduced length. For example, in the circumstances in which the medicine cartridge  120  has a length of about 6 cm to about 7 cm (about 6.4 cm in one embodiment), the overall length of the pump housing structure  110  (which contains medicine cartridge and the drive system) can be about 7 cm to about 9 cm (about 8.3 cm or less in one embodiment). In addition, the pump housing structure  110  may have an overall height of about 1.5 cm to about 4 cm (about 2.9 cm or less in one embodiment) and an overall thickness of about 8 mm to about 20 mm (about 14.5 mm or less in one embodiment). In such circumstances, the controller device  200  can be figured to mate with the pump housing  110  so that, when removably attached to one another, the components define a portable infusion pump unit that stores a relatively large quantity of medicine compared to the overall size of the unit. For example, in this embodiment, the infusion pump system  10  (including the pump device  100  attached to the removable controller device  200 ) may have an overall length of about 7 cm to about 9 cm (about 8.5 cm or less in one embodiment), an overall height of about 1.5 cm to about 4 cm (about 3.5 cm or less in one embodiment), and an overall thickness of about 8 mm to about 20 mm (about 15 mm or less in one embodiment). 
     The pump system  10  is shown in  FIG. 2  as being held in a user&#39;s hand so as to illustrate an exemplary size of the system  10 . As shown, this embodiment of the infusion pump system  10  is pocket-sized so that the pump device  100  and controller device  200  can be worn in the user&#39;s pocket or in another portion of the user&#39;s clothing. In such embodiments, the cap device  130  of the pump device  100  may be configured to mate with an infusion set  127 . In general, the infusion set  127  is tubing system that connects the infusion pump device  100  to the user (e.g., to deliver medicine into the vasculature under the user&#39;s skin). The infusion set  127  may include a connector  128  (e.g., a leur connector), a flexible tube  129  that extends from the connector  128  to a subcutaneous cannula (not shown in  FIG. 2 ), and a skin adhesive patch (not shown in  FIG. 2 ) that secures the subcutaneous cannula to the infusion site. The skin adhesive patch can retain the infusion cannula in fluid communication with the tissue or vasculature of the patient so that the medicine dispensed through the tube  129  passes through the cannula and into the user&#39;s body. The cap device  130  may provide fluid communication between the output end  122  ( FIG. 1 ) of the medicine cartridge  120  and the tube  129  of the infusion set  127 . In these embodiments, the user can carry the portable infusion pump system  10  (e.g., in the user&#39;s pocket, connected to a belt clip, adhered to the user&#39;s skin, or the like) while the tube  129  extends to the location in which the skin is penetrated for infusion. If the user desires to monitor the operation of the pump device  100  or to adjust the settings of the infusion pump system  10 , the user can readily access the user interface  220  of the controller device  200  without the need for carrying and operating a separate module. 
     In other embodiments, the infusion pump system  10  may be configured to adhere to the user&#39;s skin directly at the location in which the skin is penetrated for medicine infusion. For example, a rear surface  102  ( FIG. 1 ) of the pump device  100  may include a skin adhesive patch so that the pump device  100  is physically adhered to the skin of the user at a particular location. In these embodiments, the cap device  130  may have a configuration in which medicine passes directly from the cap device  130  into an infusion cannula that is penetrated into the user&#39;s skin. In one example, the fluid output port through the cap device  130  may include a curve or a 90° corner so that the medicine flow path extends longitudinally out of the medicine cartridge and then laterally toward the patient&#39;s skin. Again, if the user desires to monitor the operation of the pump device  100  or to adjust the settings of the infusion pump system  10 , the user can readily access the user interface  220  of the controller device  200  without the need for carrying and operating a second, separate device. For example, the user may look toward the pump device  100  to view the user interface  220  of the controller device  220  that is removably attached thereto. 
     Referring now to  FIG. 3 , the cap device  130  may include a number of components that permit the cap device  130  to mate with the pump housing  110  and to interact with the medicine cartridge  120 . For example, in this embodiment, the cap device comprises a slider component  132 , and rotator component  134 , and a fluid path component  136  that can be assembled together. The fluid path component  136  may include needle penetrator  139  (shown, for example, in  FIG. 4 ) that is advanced through the septum  121  of the cartridge  120  when the cap device  130  is received by the pump housing  110 . The needle penetrator  139  may comprise a hollow needle device that provides fluid communication with an output port  135  of the fluid path component  136 . The output port  135  is capable of directing the fluid toward the infusion set tubing  129  ( FIG. 2 ) when the infusion set connector  128  ( FIG. 2 ) is joined with the cap device  130 . In this embodiment, the infusion set connector  128  ( FIG. 2 ) is a leur connector that mates with a threaded cavity  138  of the fluid path component  136 . As such, the leur connector can be secured into the threaded cavity  138  so that the output port  135  comes into fluid communication with the infusion set tubing  129  ( FIG. 2 ). 
     Still referring to  FIG. 3 , one or more components of the cap device  130  may engage the portion of the pump housing  110  that defines the cavity  116  in which the medicine cartridge  120  is received. For example, in this embodiment, the slider component  132  includes a first set of protrusions  131  that slidably mate with longitudinal slots  111  form in the interior wall of the pump housing  110 . Likewise, the rotator component  134  includes a second set of protrusions  133  that also slidably mate with the longitudinal slots  111 . Accordingly, the cap device  130  can be advanced into the cavity  116  of the pump housing  110  when the protrusions  131  and  133  are aligned with longitudinal slots  111  of the pump housing  110 . Such a configuration provides for guidance of the cap device  130  as the cap device is advanced toward the medicine cartridge  120  received in the cavity  116 . 
     After the cap device  130  is advanced into the cavity a particular distance, the second set of protrusions  133  on the rotator component  134  may align with circumferential slots  113  that extend from the longitudinal slots  111 . For example, in this embodiment, the cap device  130  can be advanced into the cavity  116  toward the medicine cartridge  120  until a rim  144  of the rotator component  134  reaches the end face of the pump housing  110 . At this point, the protrusions  133  on the rotator component  134  align with the circumferential slots  113 , thereby permitting the rotator component  134  to rotate relative to the pump housing  110  (e.g., the protrusions  133  can slide circumferentially within the circumferential slots  113 ). Although the rotator component  134  of the cap device  130  is permitted to rotate relative to the pump housing  110 , the protrusions  131  of the slider component  132  remain engaged with the longitudinal slots  111 , thereby permitting the slider component to slide in an axial direction relative to the pump housing (but hindering rotation of the slider component  132  relative to the pump housing  110 ). 
     As described in more detail below, the relative movement of the components of the cap device  130  (e.g., rotation of the rotator component  134  and longitudinal advancement of the slider component  132 ) enables a user to perform a number of functions by merely attaching of the cap device  130  to the pump housing  110 . For example, such functions may include one or more of the following: forcing the medicine cartridge  120  to secure to a portion of a piston rod  370  (described in connection with  FIGS. 7A-D  and  10 - 25 ), piercing the septum  121  of the medicine cartridge  120  to provide a flow path for the medicine (described in connection with  FIGS. 7A-D ), priming the medicine cartridge  120  with a “break away” force to initiate movement of the plunger  125  in the medicine cartridge  120  (described in connections with  FIGS. 7A-D ), providing the a flow sensor  165  to the medicine flow path (described in connection with  FIGS. 8A-B ), locking the medicine cartridge  120  in the pump housing  110  to thereby promote disposal of the pump device  100  after exhaustion (described in connection with  FIGS. 8A-B ), and ceasing or preventing the dispensation of medicine if the cap device  130  is improperly engaged with the pump housing  110  (described in connection with  FIGS. 8A-B ). 
     Referring now to  FIGS. 4-6 , the cap device  130  can be assembled to permit relative movement of the components  132 ,  134 , and  136 . In this embodiment, the slider component  132 , the rotator component  134  and the fluid path component  136  are assembled to one another along a longitudinal axis  150 . The slider component  132  is configured to rotatably engage the rotator component  134 . For example, in this embodiment, the slider component  132  includes external cylindrical surfaces  151  that mate with an internal bore  152  of the rotator component  134 . As such, the rotator component  134  can rotate relative to the slider component  132 . 
     In addition, the slider component  132  is configured to slidably engage the fluid path component  136 . For example, in this embodiment, the slider component  132  includes opposing flat surfaces  153  that mate with complementary flat surfaces  154  of the fluid path component  136 . This configuration permits the fluid path component  136  to move longitudinally along the axis  150  toward the slider component  132 . When the shoulder surfaces  156  of the fluid path component  136  abut against the forward faces  155  of the slider component  132 , the longitudinal movement of the fluid path component  136  can cause similar movement of the slider component  132 . Also, this configuration permits the fluid path component  136  to remain rotationally fixed relative to the slider component  132 . For example, the fluid path component  136  remains rotationally stationary when the slider component  132  is retained in a rotationally stationary position (e.g., when the slider component protrusions  131  are mated with the longitudinal slots  111  of the pump housing  110  ( FIG. 3 )). As such, the slider component  132  and the fluid path component  136  can remain rotationally stationary relative to the pump housing  110  ( FIG. 3 ) while the rotator component  134  is rotated relative to the pump housing  110 . 
     Still referring to  FIGS. 4-6 , the rotator component  134  may be configured to engage the fluid path component  136  such that rotational movement of the rotator component  134  causes longitudinal movement of the fluid path component  136 . For example, in this embodiment, the rotator component  134  includes an internal thread pattern  157  that mates with an external thread pattern  158  of the fluid path component  136 . The thread patterns  157  and  158  mate together when the slider component  132  and the fluid path component  136  are arranged at least partially in the rotator component  134 . Accordingly, when the slider component  132  is retained in a rotationally stationary position (e.g., when the slider component protrusions  131  are mated with the longitudinal slots  111  of the pump housing  110  ( FIG. 3 )), the rotator component  134  can rotate relative thereto and thereby cause the longitudinal movement of the fluid path component  136 . In these circumstances, the engagement of the flat surfaces  153  with the complementary flat surfaces  154  prevents the fluid path component  136  from rotating with the rotator component  134 , so the thread engagement translates the rotator component&#39;s rotational movement to the fluid path component&#39;s longitudinal movement. 
     As previously described, the fluid path component  136  includes a needle penetrator  139  that extends longitudinally to pierce the septum  121  of the medicine cartridge  120  ( FIG. 3 ) when the cap device  130  is urged toward the medicine cartridge  120 . The needle penetrator  139  of the fluid path component  136  is configured to extend through a bore  159  ( FIGS. 4-6 ) of the slider component  132  when the cap device  130  is assembled. As such, during engagement of the cap device  130  with the pump housing  110  ( FIG. 3 ), the cap device  130  can be operated to penetrate the medicine cartridge  120  and create a fluid path to the output port  135 . As described in more detail below, the cap device  130  may also be used to perform a number of other functions when the user performs the relatively simple task of engaging the cap device  130  to the pump housing  110 . 
     Referring now to  FIGS. 7A-D  and  8 A-B, some embodiments of the cap device  130  are capable of performing multiple functions when the cap device  130  is being coupled to the pump housing  110 . Some of these functions may include preparatory functions and safety functions. For example, in some embodiments, attachment of the cap device  130  may cause one or more of the following preparatory functions: retaining the medicine cartridge  120  in the cavity  116  of the pump housing  110  (described in connection with  FIG. 7A ), forcing the plunger  125  of the medicine cartridge  120  to secure to a piston rod (described in connection with  FIG. 7B ), piercing the septum  121  of the medicine cartridge  120  to provide a flow path for the medicine (described in connection with  FIG. 7C ), and priming the medicine cartridge  120  with a “break away” force to initiate movement of the plunger  125  in the medicine cartridge  120  (described in connection with  FIG. 7D ). In addition or in the alternative, attachment of the cap device  130  may also cause one or more of the following safety related functions: aligning a flow sensor  165  with the medicine flow path (described in connection with  FIGS. 8A-B ), locking the medicine cartridge  120  in the pump housing  110  to thereby promote disposal of the pump device  100  after exhaustion (described in connection with  FIGS. 8A-B ), and ceasing or preventing the dispensation of medicine if the cap device  130  is improperly engaged with the pump housing  110  (described in connection with  FIGS. 8A-B ). 
     Referring to now  FIG. 7A , the cap device  130  can be coupled to the pump device  100  so as to retain the medicine cartridge  120  in the cavity  116  of the pump housing  110 . In this embodiment, the medicine cartridge  120  includes a cylindrical wall that fits within the cylindrical cavity  116  at least partially defined by the pump housing  110 . As shown in  FIG. 7A , the cap device  130  may approach the pump housing  110  after the medicine cartridge  120  is received in the cavity  116  so that the cap device  130  seals the cavity  116  and retains the cartridge  120  therein. For example, the rim  144  of the cap device  130  may include a seal  142  (e.g., an elastomer o-ring seal or the like) that provides a water-tight seal when the rim  144  is urged against the front face of the pump housing  110 . The cartridge may be arranged the pump housing  110  so that the septum  121  at the output end  122  faces toward the cap device  130  when the cap device  130  engages the pump housing  110 . As such, the plunger  125  of the medicine cartridge  120  is arranged in the cavity  116  to face toward a component of the pump drive system, such as a piston rod  370  (as described in more detail below, for example, in connection with  FIGS. 9-10 ). In this embodiment, the medicine cartridge  120  comprises an insulin carpule that is separate from the pump device  100 . In such circumstances, the medicine cartridge  120  may be inserted into the cavity  116  to rest against a portion of the piston rod  370  ( FIG. 10 ). 
     Referring to  FIG. 7B , during engagement of the cap device  130  to the pump housing  110 , a longitudinal force  140  may be applied to the medicine cartridge  120  so a portion of the medicine cartridge  120  becomes secured to the piston rod  370  (e.g., the plunger  125  becomes secured to a plunger engagement device  375  of the piston rod  370  as shown in  FIG. 10 ). This longitudinal force  140  may be applied to the medicine cartridge  120  when at least a portion of the cap device  130  is inserted under force from a user into the pump housing  110 . For example, in this embodiment, the slider component  132  of the cap device  130  includes the first set of protrusions  131  ( FIG. 3 ) that mate with the longitudinal slots  111  ( FIG. 7A ) of the pump housing  110  during the guided insertion of the cap device  130  into the cavity  116 . During this insertion, the slide component  132  includes a shoulder surface  137  that abuts with the medicine cartridge  120 . The insertion force applied by the user during the attachment of the cap device  130  to the pump housing  110  can be translated to a longitudinal force  140 . As described in more detail below in connection with  FIGS. 9-10 , this longitudinal force  140  can be used to secure the medicine cartridge  120  to the piston rod  370  or to another component of the drive system. For example, during the attachment of the cap device  130  to the pump housing  110 , the slider component  132  may act upon the medicine cartridge  120  to force the medicine cartridge  120  a rearward displacement  145  that drives the plunger  125  ( FIG. 10 ) toward one or more penetration members  376  of the plunger engagement device  375  of the piston rod  370 . In such circumstances, the penetration members  376  ( FIG. 10 ) penetrate into the plunger  125  of the medicine cartridge  120  and thereby secure the medicine cartridge  120  the piston rod  370  ( FIG. 10 ). A number of further embodiments for the plunger engagement device are described in more detail below in connection with  FIGS. 9-25 . 
     Referring to  FIG. 7C , when the cap device  130  is inserted longitudinally into the cavity  116  to a particular depth, the rim  144  and the seal  142  can be urged against the end face of the pump housing  110  to seal the medicine cartridge  120  in the cavity  116 . Also, as previously described in connection with  FIG. 3 , the second set of protrusions  133  on the rotator component  134  may align with the circumferential slots  113  in the pump housing  110  when the cap device  130  is inserted to this particular depth. As such, the rotator component  134  of the cap device  130  is rotatable relative to the pump housing  110  (e.g., the protrusions  133  can move circumferentially in the circumferential slots  113 ). Again, as previously described in connection with  FIG. 3 , the first protrusions  131  of the slider component  132  remain in the longitudinal slots  111  of the pump housing  110 , so the slider component  132  does not rotate with the rotator component  134 . Such relative movement between the rotator component  134  and the slider component  132  can be used to longitudinally advance the fluid path component  136  (and its needle penetrator  139 ) toward the septum  121  of the medicine cartridge  120 . 
     As shown in  FIG. 7C , the rotator component  134  of the cap device  130  can be moved in a rotational direction  146  relative to the pump housing  110  (which maintains the slider component  132  in a rotational stationary position due to the engagement of the first protrusions  131  ( FIG. 3 ) and the longitudinal slots  111  ( FIGS. 3 and 7A )). For example, a user may grasp the rim  144  of the rotator component  134  and twist it relative to the pump housing  110  so that the second protrusions  133  ( FIG. 3 ) are guided in the circumferential slots  113  ( FIG. 3 ). Such rotation of the rotator component  134  causes the interior thread pattern  157  of the rotator component  134  to engage the exterior thread pattern  158  (not shown in  FIG. 7C ; refer to  FIGS. 4-6 ) of the fluid path component  136 . Because the opposing flat surfaces  153  of the slider component  132  engage the complementary flat surfaces  154  of the fluid path component  136 , the fluid path component  136  remains in a rotationally stationary position with the slider component  132  (e.g., the rotator component  134  also rotates relative to the fluid path component  136 ). As such, the engagement between the thread patterns  157  (on the rotator component  134 ) and  158  (on the fluid path component  136 ) cause the rotational motion of the rotator component  134  to be translated into a longitudinal motion for the fluid path component  136 . As shown in  FIG. 7C , the rotation of the rotator component  134  can cause the fluid path component  136  to move a longitudinal displacement  147  toward the medicine cartridge  120 . This longitudinal displacement  147  results in the needle penetrator  139  piercing the septum  121  of the medicine cartridge  120  and thereby establishing a fluid path from the medicine cartridge  120  to the output port  135  of the fluid path component  136 . 
     In some embodiments in which the attachment of the cap device  130  provides the force  140  ( FIG. 7B ) to cause securement of the medicine cartridge  120  to the piston rod  370  ( FIG. 10 ), this force  140  may be applied before the needle penetrator  139  penetrates the septum  121  ( FIG. 7C ). Because the septum  121  is not yet pierced during the application of the force  140  ( FIG. 7B ), the force  140  can be used to urge the plunger  125  against the plunger engagement device  375  ( FIG. 10 ) without necessarily forcing some portion of the medicine out of the cartridge  120 . 
     Referring now to  FIG. 7D , attachment of the cap device  130  to the pump housing  110  can also provide a “break away” force to initiate movement of the plunger  125  in the medicine cartridge  120 . Such a “break away” force may be used prepare the plunger  125  for future incremental displacements caused by the drive system. For example, as shown in  FIG. 1 , the plunger  125  is arranged in the medicine cartridge  120  as to act upon the medicine  126  therein. The “break away” force that is required to initially move the plunger  125  for the first time may be substantially greater than the operational drive force required to advance the plunger  125  yet another increment toward the output end  122  of the medicine cartridge  120 . In this embodiment, the “break away” force can be provided during the attachment of the cap device  130  to the pump body  110 , (rather than by activating the drive system to initiate movement of the plunger  125  for the first time). Accordingly, drive system can provide the operational drive force that (during normal operation) advances the plunger  125  in subsequent increments toward the output end  122  of the medicine cartridge  120 , and the user&#39;s action (during attachment of the cap device  130 ) can provide the generally greater “break away” force to initiate movement of the plunger  125  for the first time. 
     Still referring to  FIG. 7D , the rotator component  134  of the cap device  130  can be moved in the rotational direction  146  relative to the pump housing  110 , for example, by twisting the rim  144  relative to the pump housing  110 . As previously described in connection with  FIG. 7C , such rotation of the rotator component  134  can be translated into a longitudinal motion for the fluid path component  136 . After a particular amount of longitudinal advancement of the fluid path component  136 , the shoulder surfaces  156  of the fluid path component  136  abut against the forward faces  155  of the slider component  132  (refer also to  FIGS. 4-6 ). Accordingly, the continued longitudinal movement of the fluid path component  136  (due to the rotation  146  of the rotator component  134 ) further causes a longitudinal displacement  148  of the slider component  132 . As previously described in connection with  FIG. 7B , the slider component  132  includes a shoulder surface  137  that acts upon the medicine cartridge  120 , so the longitudinal displacement  148  of the slider component  132  causes the medicine cartridge  120  to likewise move in the rearward longitudinal direction. Because the plunger  125  ( FIG. 10 ) is already engaged with the piston rod  370  ( FIG. 10 ) as previously described in connection with  FIG. 7B , the plunger  125  does not share in this rearward longitudinal movement. Instead, a break away force  149  is applied to the medicine cartridge  120  relative to the plunger  125  (which is maintained in its position due to the piston rod engagement), thereby causing the initial movement of the plunger  125  in the medicine cartridge  120  for the first time. 
     It should be understood from the description herein that this initial break away movement of the plunger  125  in the medicine cartridge  120  may cause a small amount of medicine to be dispensed. However, the infusion set connector  128  ( FIG. 2 ) can be joined with the threaded cavity  138  of the fluid path component  136  before the break away force  149  is applied and (in some embodiments) before the cap device  130  is advanced toward the medicine cartridge  120  to create the fluid output path. As such, the relatively small amount of medicine dispensed during the initial “break away” movement of the plunger  125  in the medicine cartridge  120  may be dispensed through the output port  135  and into the infusion set tubing  129  ( FIG. 2 ) to at least partially prime the tubing  129 . The pump device  100  may be controlled to perform a subsequent priming operation to fully prime the remaining portion of the infusion set tubing  129 . 
     Accordingly, a number of functions can be performed when the cap device  130  is being coupled to the pump housing  110 . Some of these functions may include initialization and preparatory functions, including but not limited to: retaining the medicine cartridge  120  in the cavity  116  of the pump housing  110  (described in connection with  FIG. 7A ), providing a water-tight seal for the cavity  116  of the pump housing  110  (described in connection with  FIGS. 7A and 7C ), forcing the plunger  125  of the medicine cartridge  120  to secure to a piston rod (described in connection with  FIG. 7B ), piercing the septum  121  of the medicine cartridge  120  to provide a flow path for the medicine (described in connection with  FIG. 7C ), and providing a “break away” force to initiate movement of the plunger  125  in the medicine cartridge  120  (described in connection with  FIG. 7D ). 
     Referring now to  FIGS. 8A-B , in some embodiments, the process of coupling the cap device  130  to the pump housing  110  may result in a number of safety related functions also being performed. For example, attachment of the cap device  130  to the pump housing can cause the medicine cartridge  120  to be “locked” in the pump housing  110 , thereby encouraging disposal of the pump device  100  after exhaustion of the medicine cartridge. As shown in  FIGS. 8A-B , a portion of the cap device  130  may include locking tabs  161  that mate with corresponding notches  162  in the pump housing  110  when the cap device  130  is received by the pump housing  110  at a particular depth. In this embodiment, the locking tabs  161  are formed as part of the slider component  132  of the device  130  so that the tabs  161  are spring biased to extend outwardly. As such, when the slider component  132  is advanced into the cavity  116  ( FIG. 3 ) of the pump housing  110 , the locking tabs  161  adjust inwardly toward the longitudinal axis of the slider component  132  (refer, for example, to  FIG. 8A ). When the locking tabs  161  reach the corresponding notches  162  in the wall of pump housing  110 , the locking tabs  161  adjust outwardly into the notches  162  (refer, for example to  FIG. 8B ). In this embodiment, the locking tabs  161  may be advanced to reach the corresponding notches  162  in when the longitudinal movement of the fluid path component  136  (due to the rotation  146  of the rotator component  134 ) further causes the longitudinal displacement  148  of the slider component  132 , as previously described in connection with  FIG. 7D . 
     Due to the engagement of the locking tabs  161  in the notches  162 , the slider component  132  of the cap device  130  is retained in the pump housing  110  in a manner that hinders removal of the medicine cartridge  120 . Accordingly, the cap device  130  can be secured to the pump housing  110  in a manner that encourages disposal of the pump device  100  after exhaustion of the medicine cartridge  120 . Such a configuration may be useful, for example, in circumstances in which the pump device  100  is designed to be a “one time use” disposable unit. Thus, the cap device  130  may facilitate a “one time use” disposable pump device, thereby reducing the likelihood of failure due to non-intended repeated use of the disposable pump device. 
     It should be understood from the description herein that, in other embodiments, the locking tabs  161  may be arranged on other components of the cap device  130 , such as the rotator component  134  or the fluid path component  136 . Also, in other embodiments, the locking mechanism may be in a form other than the locking tabs  161  and corresponding notches  162 . For example, the locking mechanism may include an adhesive engagement that prevents removal of the cap device  130  after attachment to the pump housing  110 , a unidirectional thread pattern that permits tightening but hinders loosening, or the like. 
     In another example of a safety related function, if the cap device  130  is improperly engaged with the pump housing  110 , the medicine dispensation can be shutdown. As shown in  FIGS. 8A-B , the cap device  130  may be used to close a circuit loop that indicates when the cap device is engaged with the pump housing  110  in a particular position. In this embodiment, the circuit loop includes a first conductive line  163   a  and a second conductive line  163   b  that extend along the pump housing  110  and are separated by a gap in the previously described notch  162 . The gap between the first and second conductive lines  163   a - b  creates a break in the sensor circuit that can be closed when the locking tabs  161  reach the corresponding notches  162  in the wall of pump housing  110 . In this embodiment, one of the locking tabs  161  can be used to close the circuit loop due to a conductive pad  164  disposed on the outer surface of the locking tab. When the locking tab  161  is adjusted to mate with the corresponding notch  162  (as previously described), the electrical circuit through the first line  163   a , the conductive pad  164 , and the second line  163   b  can be closed, thereby indicating that the cap device  130  is properly engaged with the pump housing  110  at a particular depth. The electrical circuit that includes the conductive lines  163   a - b  may be a part of (or communicate with) a sensor circuit arranged within the pump device  100  ( FIG. 1 ) or within the removable controller  200  ( FIG. 1 ). 
     Accordingly, if the cap device  130  is secured with the pump housing  110  in a proper manner, the controller device  200  may be operated to dispense medicine from the medicine cartridge  120 . If, however, the cap device  130  is improperly oriented or becomes dislodged relative to the pump housing  110 , the electrical circuit loop (e.g., through the first line  163   a , the conductive pad  164 , and the second line  163   b ) may become open to indicate such a misalignment to the controller device  200  ( FIG. 1 ). In response to such an indication, the controller device  200  may prevent medicine dispensation (e.g., cease activation of the drive system) and communicate an alarm to the user. Such a configuration permits the user with an opportunity to correctly attach the cap device  130  to the pump housing  110  and thereafter restart safe dispensation of the medicine. 
     It should be understood from the description herein that, in other embodiments, the electrical circuit loop (e.g., through the first line  163   a , the conductive pad  164 , and the second line  163   b ) may be arranged on other components of the cap device  130 , such as the rotator component  134  or the fluid path component  136 . Also, in some embodiments, other devices can be used to detect the proper attachment of the cap device  130  to the pump housing  110 . For example, the cap device  130  may be used to actuate a position sensor that indicates when the cap device is engaged with the pump housing  110  in a particular position. Alternatively, an optical sensor can be used in combination with a light emitted from the controller device  200  ( FIG. 1 ) to indicate when the cap device  130  is engaged with the pump housing  110  in a particular position. 
     In yet another example of a safety related function, attachment of the cap device  130  to the pump housing  110  can cause a flow sensor to be arranged along the medicine flow path to detect the flow (or nonflow) of medicine from the pump device  100 . As shown in  FIGS. 8A-B , the cap device  130  may house at least a portion of a flow sensor  165  that is configured to detect the flow of medicine through the cap device  130  or to detect an occlusion in the fluid path. In this embodiment, the flow sensor  165  may be arranged within or adjacent to a bypass fluid path  166 . A portion of the medicine that is dispensed from the medicine cartridge  120  may be redirected through the bypass fluid path  166  for detection by the flow sensor  165 . The bypass fluid path  166  has an outlet that is in communication with the output port  135  of the cap device  130 . In some embodiments, the bypass fluid path  166  may have a substantially smaller diameter than the primary fluid path between the needle penetrator  139  and the output port  135 . 
     The flow sensor  165  may be used to detect when an occlusion exists in the fluid path between the medicine cartridge  120  and the infusion site on the user&#39;s skin. Such an occlusion may occur, for example, when the infusion set tubing  129  ( FIG. 2 ) is kinked. If the medicine dispensation path to the user is occluded, the user may receive no dosage or a lower dosage of the medicine. As such, the flow sensor  165  housed in the cap device  130  can be used to indicate when the fluid is flowing or not flowing, thereby permitting the controller device  200  ( FIG. 1 ) to communicate an alarm to the user if an occlusion exist. 
     In some embodiments, the flow sensor  165  housed at least partially in the cap device  130  may include electrodes  165   a  and  165   b  that are arranged to detect fluid flow through the bypass fluid path  166 . For example, an AC current may be passed through the fluid between the electrodes  165   a - b , and the electrodes  165   a - b  can be configured to sense the electrical admittance (e.g., the inverse of the electrical impedance) through the fluid in the bypass fluid path  166 . The electrical admittance sensed using the electrodes  165   a  and  165   b  can be correlated to a fluid velocity (e.g., a change in the flow speed causes a change in the electrical admittance). In such embodiments, the controller device  200  ( FIG. 1 ) may be programmed to correlate the fluid velocity from the electrical admittance sensed using the electrodes  165   a  and  165   b . If the fluid velocity falls below a threshold value, the controller device  200  may communicate an alarm to the user that an occlusion exists in the fluid path. When the cap device  130  is attached with the pump housing  110  in a particular position, the flow sensor  165  may be in electrical communication with the controller device  200  ( FIG. 1 ) via one or more electrical lines that extend along the pump housing  110  (refer, for example, to  FIG. 8B ). 
     In an alternative embodiment, the flow sensor  165  housed at least partially in the cap device  130  may include a pressure sensor that indicates the fluid pressure in the bypass fluid path  166 . For example, a miniature pressure transducer can be arranged in the cap device  130  to detect the fluid pressure. In some cases, the miniature pressure transducer can be formed as a MEMS (Micro-ElectroMechanical System) device. The miniature pressure transducer may be output an electrical signal that can be correlated to a fluid pressure value. In such embodiments, the controller device  200  ( FIG. 1 ) may be programmed to correlate the fluid pressure from the signal output by the pressure transducer. If the fluid pressure increases above a threshold value, the controller device  200  may communicate an alarm to the user that an occlusion exists in the fluid path. The fluid passing through the cap device  130  may act directly upon the pressure transducer, or alternatively, the fluid passing through the cap device may act upon a miniature piston device or diaphragm device that in turn acts upon the pressure transducer. 
     It should be understood from the description herein that, in alternative embodiments, other types of flow sensors can operate within the cap device  130  to detect flow (or nonflow) of the medicine. For example, the flow sensor  165  may include a first probe and a second probe arranged in the cap device  130 —the first probe being used to induce a small oxygen (O 2 ) concentration into the fluid flow, and the second probe being used to detect the oxygen level in the fluid flow. If the second probe detects an oxygen concentration greater than a threshold level, the fluid flow may be occluded or partially occluded. As such, the controller device  200  may communicate an alarm to the user that an occlusion exists in the fluid path. In another example, the flow sensor  165  may include an optical sensor device arranged in a flow path (e.g., bypass flow path  166 ) of the cap device  130 . The optical sensor may respond to a laser light that is emitted from the reusable controller device  200  ( FIG. 1 ) proximate the cap device  130 . In some circumstances, the optical sensor device may deform when the fluid pressure increases above a threshold level, thereby providing a different response to the laser light (e.g., reflecting or bending the light in a different manner that indicates a fluid pressure greater than the threshold level). Such detection of an increased fluid pressure in the cap device  130  can indicate that an occlusion exists in the fluid path, and the controller device  200  the controller device  200  may communicate an alarm to the user. 
     Referring now to  FIGS. 9-10 , the pump device  100  may include a piston rod  370  that is configured to attach with the medicine cartridge  120 . For example, as previously described in connection with  FIG. 7B , a longitudinal force  140  may be applied to the medicine cartridge  120  during engagement of the cap device  130  to the pump housing  110 . This longitudinal force  140  can be used to urge a portion of the medicine cartridge  120  (e.g., the plunger  125  in this embodiment) to secure to a plunger engagement device  375  ( FIG. 10 ) of the piston rod  370 . In some embodiments, the plunger engagement device  375  may include penetration members  376  that penetrate into the plunger  125  of the medicine cartridge  120  and thereby secure the medicine cartridge  120  to the piston rod  170 . (It should be understood that  FIG. 9  depicts the piston rod  370  arranged in the pump housing  110  of the pump device  100 , and  FIG. 10  shows a similar view with the pump housing  110  and other portions removed for purposes of illustrating the piston rod  370  and medicine cartridge  120 .) 
     As shown in  FIG. 9 , the pump device  100  may include a drive system  300  that is controlled by the removable controller device  200  ( FIGS. 1-2 ). Accordingly, the drive system  105  can accurately and incrementally dispense fluid from the pump device  100  in a controlled manner. The drive system  300  may include the flexible piston rod  370  that is incrementally advanced toward the medicine cartridge  120  so as to dispense the medicine from the pump device  100 . In this embodiment, at least a portion of the drive system  300  is mounted to the pump housing  110 , and a detachable shell  112  covers at least a portion of the drive system  105 . The detachable shell  112  may include an inner curved surface against which a curved section of a piston rod  370  rests. A cover mount  113  may be assembled to the pump housing  110  to secure some components of the drive system  300  with the pump housing  110 , and the “unused” or retracted portion of the piston rod  370  may rest in a channel defined in the top of the cover mount  113 . Some embodiments of the drive system  300  may include a battery powered actuator (e.g., reversible motor  320  or the like) that resets a ratchet mechanism  330 , a spring device  350  that provides the driving force to the ratchet mechanism  330 , and a drive wheel  360  that is rotated by the ratchet mechanism  330  to advance the flexible piston rod  370  toward the medicine cartridge  120 . The operation of the drive system  300  is described in more detail below in connection with  FIGS. 26-30 . Previously filed U.S. patent application Ser. No. 11/522,560 (incorporated herein by reference) describes further drive system configurations for use in an infusion pump device. 
     Referring to  FIG. 10 , in some embodiments, the flexible piston rod  370  comprises a plurality of segments  372  serially connected by hinge portions  373  so that the flexible piston rod  370  is adjustable from a curved shape to a noncurved shape. The plurality of segments  372  and the interconnecting hinge portions  373  can be integrally formed in one piece from one or more moldable materials, including polymer materials such as Nylon or POM. In this embodiment, each of the plurality of rod segments  372  includes an exterior thread pattern  374  along at least one cylindrical surface portion. The plunger engagement device  375  can be arranged at a forward end of the piston rod  370 . As such, the plunger engagement device  375  faces toward the medicine cartridge  120  when the medicine cartridge  120  is inserted into the cavity  116 . 
     The plunger engagement device  375  is configured to attach to the plunger  125  of the medicine cartridge  120  when urged together. For example, as previously described in connection with  FIG. 7B , a longitudinal force  140  may be applied to the medicine cartridge  120  during engagement of the cap device  130  to the pump housing  110 . This longitudinal force  140  can be used to urge the medicine cartridge  120  (and the plunger  125  therein) toward the plunger engagement device  375 . In this embodiment, the plunger engagement device  375  includes a plurality of penetration members  376  that extend from a pusher disc  378  toward the plunger  125  and are configured to penetrate into the plunger  125  in response to the longitudinal force  140  ( FIGS. 7B and 10 ). Thereafter, the plunger  125  may remain secured to the piston rod  370  during operation of the pump device  100 . 
     Referring to  FIGS. 11-12 , in some embodiments, the penetration members  376  may comprise rigid blades having pointed tips to pierce into the rear face of the plunger  120  (e.g., the “dry” face of the plunger  125  opposite the “wet” face). The penetration members  376  may extend for a length that is slightly less than the axial length of the plunger  125 . In such circumstances, the penetration members  376  do not penetrate through the front face (e.g., the “wet” face) of the plunger  125 . The rigid blades may include serrations or another retention portion that enhances the engagement with the plunger  125  and hinders separation of the plunger  125  from the penetration members  376 . Also, in this embodiment, the pusher disc  378  includes a protruding spherical surface  379  that is configured to press against the rear face of the plunger  125  ( FIG. 12 ). In some circumstances, the center core of the plunger  125  may be urged forward more than the radial surfaces of the plunger  125  (due to the frictional engagement with the inner wall of the medicine cartridge  120 ). Accordingly, the protruding surface  379  of the disc  378  may promote full contact with the rear face of the plunger  125  during advancement of the plunger  125  within the cartridge  120 . 
     In some embodiments, the penetration members  376  can reduce the compliance of the plunger material and thereby increase the dosage accuracy. For example, the plunger  125  may comprise an elastomer material that exhibits flexibility and compliance when it is urged longitudinally relative to the inner wall of the medicine cartridge  120  (e.g., the center of the plunger is urged forward while the outer radial surfaces flex due to the frictional engagement with the inner wall of the medicine cartridge). Such compliance may create a level of unpredictability between the piston rod movement and the corresponding plunger movement. The penetration members  376  can pierce into the plunger  125  and thereby serve as generally rigid inserts that reduce the compliance exhibit by the plunger  125 . In some circumstances, the penetration members  376  can serve as inserts that provide greater uniformity between the piston rod movement and the corresponding plunger movement. As such, the pump device  100  may have increased accuracy for the dosage of medicine that is dispensed in response to an incremental movement of the piston rod  370 . 
     Furthermore, the penetration members  376  can reduce the likelihood of accidental medicine delivery when the pump device  100  undergoes an impact (e.g., when the pump device is dropped on the ground). The penetration members  376  secure the plunger  125  to the drive system (e.g., to the piston rod  370  in this embodiment), so the plunger  125  does not necessarily become displaced when the medicine cartridge  120  is impacted. For example, if the pump device  100  is dropped on the ground and undergoes an impact, the plunger  125  may be retained in its position relative to the wall of the cartridge due to the attachment with the piston rod  370 . As such, the likelihood of the plunger  125  moving slightly relative to the inner wall of the medicine cartridge  120  (and thereby forcing some medicine from the cartridge) in response to an impact may be reduced. 
     It should be understood from the description herein that, in some embodiments, the penetration members  376  can reduce the compliance of the plunger  125  so that the pusher disc  378  need not include a protruding spherical surface (e.g., surface  379  in  FIG. 12 ). Rather, the pusher disc  376  may include a generally flat surface that pushes against the rear face of the plunger  125  (as shown, for example, in  FIGS. 13A-D ). 
     Referring to  FIGS. 13A-D , in operation, the plunger engagement device  375  can be secured to the plunger  125  to reduce or prevent relative motion between the plunger  125  and the pusher disc  378  and to reduce the compliance of the plunger  125 . As previously described in connection with  FIG. 7B  and  FIG. 10 , a longitudinal force  140  may be applied to the medicine cartridge  120  during engagement of the cap device  130  to the pump housing  110 . This longitudinal force  140  is used to urge the medicine cartridge  120  (and the plunger  125  therein) toward the penetration members  376  of the plunger engagement device  375 . As the plunger  125  continues its motion toward the pusher disc  378  in response to the longitudinal force  140 , the penetration members  376  can pierce into the rear face of the plunger  125 . The insertion of the penetration members  376  may continue until the rear face of the plunger  125  abuts the pusher disc  378 . As shown in  FIG. 13D , the penetration members  376  do not penetrate through the front face (e.g., the “wet” face) of the plunger  125  in this embodiment. 
     In this embodiment, the plunger engagement device  375  includes three penetration members  376  that are laterally offset from the center of the pusher disc  378 . The penetration members  376  comprise rigid blades or knife-like pins that include serrations to facilitate engagement with the plunger  125 . These rigid blades may be laterally offset from the center of the pusher disc  378  so as to pierce the rear face of the plunger  125  in an outer radial portion of the plunger  125  (e.g., a portion of the plunger that might otherwise be more compliant during advancement of the plunger  125  inside the cartridge  120 ). 
     It should be understood from the description herein that, in other embodiments, the plunger engagement device  375  may have a different configuration. For example, as shown in  FIGS. 14A-B , some embodiments of the plunger engagement device  375  may include penetration members  382  in the form of pin inserts. These penetration members  382  can include a generally straight shaft and pointed tip to facilitate penetration into the rear face of the plunger  125  ( FIG. 14B ). In another example, as shown in  FIGS. 15A-B , some embodiments of the plunger engagement device  375  may include penetration members  384  in the form of radially curved blades. Such embodiments of the penetration members  384  may include generally flat blade shafts that are curved about a longitudinal axis. The radial curvature of the penetration members  384  may reflect the radial distance from the central longitudinal axis of the plunger  125  ( FIG. 15B ). In yet another example, as shown in  FIGS. 16A-B , some embodiments of the plunger engagement device  375  may include penetration members  386  in the form of generally flat blades without serrations. These penetration members  386  may include a pointed tip to facilitate insertion into the plunger  125  ( FIG. 16B ). In a further example, the plunger engagement device  375  may include an adhesive layer arranged on the pusher disc  378  so that the pusher disc  378  becomes adhered to the rear face of the plunger  125 . 
     In some embodiments in which the plunger engagement device  375  includes penetration members having serrations or other retention portions, the retention portions may be formed in a number of configurations. For example, as shown in  FIG. 17 , some embodiments of the plunger engagement device  375  may include penetration members  387  having straight-cut retention portions that hinder separation of the plunger  125  away from the plunger engagement device  375 . In another example, as shown in  FIG. 18 , some embodiments of the plunger engagement device  375  may include penetration members  388  having angled-cut retention portions. 
     Some embodiments of the plunger engagement device  375  may include one penetration member, two penetration members, three penetration members (as previously described in connection with  FIGS. 11-12 and 13A -D), four penetration members, five penetration members, or more. Moreover, the penetration members may be arranged on the plunger engagement device  375  in a number of different configurations so as to penetrate the plunger  125  at different locations. For example, as shown in  FIG. 19 , some embodiments of the plunger engagement device  375  may include only one penetration member (depicted here in the form of a pin insert penetration member  382  described in  FIGS. 14A-B ). In this embodiment, the single penetration member  382  is arranged to pierce the rear face of the plunger  125  proximate to the central axis of the plunger  125 . In another example, as shown in  FIG. 20 , some embodiments of the plunger engagement device  375  may include two penetration members (again, depicted here in the form of a pin insert penetration member  382  described in  FIGS. 14A-B ). In this embodiment, the pair of penetration members  382  are offset from the central axis of the plunger  125  and oriented approximately 180° from one another. As such, the penetration members  382  can pierce into the rear face of the plunger  125  on generally opposite sides of the central axis of the plunger  125 . In a further example, as shown in  FIG. 21 , some embodiments of the plunger engagement device  375  may include four penetration members  382  that are offset from the central axis of the plunger  125  and oriented approximately 90° from one another. In yet another example, as shown in  FIG. 21 , some embodiments of the plunger engagement device  375  may include five penetration members  382  that are offset from the central axis of the plunger  125  and oriented approximately 72° from one another. 
     Some embodiments of the plunger engagement device  375  may include penetration members that are not oriented circumferentially equidistant to one another. For example, as shown in  FIG. 23 , some embodiments of the plunger engagement device  375  may include four penetration members  382  that are spaced apart in two pairs. A first pair of the penetration members  382  are spaced apart from the second pair of penetration members  382 . As such, the first and second pairs of the penetration members  382  can pierce into the rear face of the plunger  125  on generally opposite sides of the central axis of the plunger  125 . 
     Also, some embodiments of the plunger engagement device  375  may include combinations of the previously described configurations. For example, as shown in  FIG. 24 , some embodiments of the plunger engagement device  375  may include a first penetration member  382  arranged to pierce the rear face of the plunger  125  proximate to the central axis of the plunger  125  (similar to that shown in  FIG. 19 ) and four addition penetration members  382  that are offset from the central axis of the plunger  125  and oriented approximately 90° from one another (similar to those shown in  FIG. 21 ). 
     Some embodiments of the piston rod  370  may include a plunger engagement device  380  that penetrates along the outer circumferential surface of the plunger  125 . For example, as shown in  FIG. 25 , the plunger engagement device  380  may include a cylindrical penetration member  381  that is integral with the pusher disc portion. The cylindrical penetration member  381  can penetrate along the outer circumferential surface of the plunger  125  (e.g., through the outer rings of the plunger  125  or between the outer rings and the cartridge wall) when the plunger  125  is urged toward the piston rod  370 . In this example, the cylindrical penetration member  381  bypasses the first two outer rings of the plunger  125  so that at least a portion of the load on the third ring is directly transmitted to the plunger engagement device  380 . As such, the plunger engagement device  380  can be used to retain the plunger  125  relative to the piston rod  370  and to reduce the compliance of the plunger  125  when being advanced inside the medicine cartridge  120 . 
     Referring now to  FIGS. 26-30 , the drive system  300  of the pump device can be controlled to accurately dispense fluid from the pump device  100 . As previously described in connection with  FIGS. 9-10 , the drive system  300  may include the flexible piston rod  370  that is incrementally advanced toward the medicine cartridge  120  so as to dispense the medicine from the pump device  100 . The drive system  300  may also include an electrically powered actuator (e.g., reversible motor  320  or the like) that is coupled to a guided pusher arm  325  ( FIGS. 28-30 ), which is used to adjust a ratchet mechanism  330  to a reset position. A spring device  350  ( FIGS. 28-30 ) stores potential energy when the ratchet mechanism  330  is adjusted to the reset position and thereafter drives the ratchet mechanism  330  to a forward position to advance the piston rod  370  and dispense the medicine. The motor  320  can be decoupled from the ratchet mechanism  330  during the drive step. Accordingly, the reversible motor  320  is used to shift the ratchet mechanism to a reset position, but the motor  320  does not drive the ratchet mechanism  330  to the forward position. 
     In those embodiments in which the pump device  100  is connected to a removable controller device  200  ( FIGS. 1-2 ), the controller device  200  can communicate control signals to the drive system  300  or other components of the pump device  100 . As previously described, the controller device  200  can include a controller housing structure  210  ( FIGS. 1-2 ) that is configured to mate with a complementary portion of the pump housing structure  110  so as to form a mechanical connection. In such circumstances, the pump device  100  may include on or more electrical contacts  118  ( FIG. 26 ) that are exposed to the controller device  200  and that mate with opposing electrical contacts (e.g., pads, pins, or the like) on the adjacent face of the controller device  200 . In this embodiment, the electrical contacts  118  are disposed on a connection circuit  119  ( FIG. 26 ). The connection circuit  119  may be simple and inexpensive so as to facilitate a low-cost pump device  100  that is disposable. The connection circuit  119  can be in electrical communication with one or more components housed in the pump device  100 , such as the motor  320 , the battery  305 , one or more sensor devices, or a combination thereof). The connection circuit  119  facilitates electrical communication with the removable controller device  200  ( FIGS. 1-2 ). As such, the controller device  200  is capable of transmitting electrical signals to the pump device  100  and is capable of receiving feedback signals (e.g., sensor signals) from the components in the pump device  100 . 
     As shown in  FIG. 26 , some components of the drive system  300  can be retained by the pump housing  110 . For example, the motor  320 , the pusher arm  325 , the ratchet mechanism  330 , and the spring device  350  can be assembled into the pump housing  110  and then retained by the cover mount  113  ( FIG. 9 ). Also, the drive wheel  360  and an adjacent bearing  365  (to facilitate rotation of the drive wheel  360  relative to the pump housing  110 ) can be received in annular channels of the pump housing  110 . In this embodiment, a locking pawl  342  ( FIGS. 28-30 ) is integrally formed with the pump housing  110  so as to align with a portion of the ratchet mechanism  330  when the ratchet mechanism  330  is assembled onto the pump housing  110 . When the cover mount  113  ( FIG. 9 ) is assembled to the pump housing  110 , the cover mount  113  can align and retain the ratchet mechanism  330  and other components of the drive system  300 . In such a construction, the assembled pump housing  110  can permit the desired motion of the components of the drive system  300  while reducing the likelihood of “backlash” movement or component dislodgement (which might otherwise occur, for example, when the pump device  100  is dropped to the ground). 
     Referring to  FIGS. 27-30 , in some embodiments of the drive system  300 , the reversible motor  320  is used to shift the ratchet mechanism  330  to the reset position, yet the motor  320  can be decoupled from the ratchet mechanism  330  during the drive step that causes dispensation of medicine. Briefly, the motor  320  can be used to act upon the pusher arm  325 , which is guided along a predetermined path in a guide slot  328 . In this embodiment, the guide slot  328  is integrally formed in an inner wall of the pump housing  110  (refer to  FIG. 26 ), and the pusher arm  325  includes a slider pin  326  that mates with the guide slot  328 . (It should be understood that  FIG. 26  depicts the drive system  300  mounted to the pump housing  110  of the pump device  100 , and  FIG. 27  shows a similar view with the pump housing  110  removed for purposes of illustrating components of the drive system  300 .) After the pusher arm  325  is advanced in the guide slot  328  so that the ratchet mechanism  330  is adjusted to the reset position (refer to  FIG. 29  in which the ratchet mechanism  330  is reset to engage a new tooth on the ratchet body  340 ), the motor  320  can reverse direction and promptly retract the pusher arm  325  to the first position (refer to  FIG. 30  in which the pusher arm  325  is retracted). The spring device  350  provides the energy for the drive step that advances the piston rod  370  and dispenses medicine, but the drive step may occur over a period of time that is greater than the relatively quick retraction of the pusher arm  325  to the first position. In such circumstances, the pusher arm  325  may be temporarily separated from the ratchet mechanism  330 , thereby causing the motor to be decoupled from the ratchet mechanism  330  during the drive step. Accordingly, the drive system  300  can provide an efficient process for accurately and reliably dispensing medicine in a manner that conserves battery life. Moreover, the drive system  300  may comprise few, if any, high-cost actuator components or electronics, thereby facilitating the production of a disposable and reliable pump device  100 . 
     Referring now in more detail to the components of the drive system  300  depicted in  FIGS. 27-30 , the electrically power actuator may be in the form of the motor  320  having a rotatable output shaft  321 . In this embodiment, the motor  320  is reversible in that can receive signals that cause the output shaft  321  to rotate in a first rotational direction or in a second, opposite rotational direction. One example of a suitable motor  320  is a coreless DC motor with reversible rotation capabilities, as supplied by Mabuchi Motor Co. of Japan. As previously described, the operation of the motor  320  can be controlled by a control device (e.g., removable control device  200  as described in connection with  FIGS. 1-2  or the like) via electrical signals communicated through one or more electrical contacts. 
     Still referring to  FIGS. 27-30 , a gear system  322  may be coupled to the motor  320  so that actuation by the motor  320  causes the pusher arm  325  to act upon the ratchet mechanism  330  or to decouple from the ratchet mechanism  330 . In this embodiment, the gear system  322  includes a worm gear  323  and a gear reduction assembly comprising spur gears  324   a ,  324   b , and  324   c . The pusher arm  325  can be pivotably coupled to the gear  324   c  so that partial rotation of the gear  324   c  causes the pusher arm to reciprocate within the guide slot  328 . Accordingly, rotation of the motor  320  in a first direction can be translated into an advancement force to the pusher arm  325 . The advancement force on the pusher arm  325  is applied to a pawl member  335 , which (in this embodiment) causes the pawl member  335  to pivot to a reset position (refer to  FIG. 29 ). In addition, rotation of the motor  320  in a second direction can be translated into an retraction force to the pusher arm  325 , which can cause the pusher arm  325  to be separated from the pawl member  335  during the drive step (refer to  FIG. 30 ). 
     As such, the motor  320 , the gear system  322 , and the pusher arm  325  can collectively operate as an actuator assembly that provides a reliable and consistent adjustment of the ratchet mechanism  330  during a reset step (refer to  FIG. 29 ). Moreover, this actuator assembly (e.g., the motor  320 , the gear system  322 , and the pusher arm  325 ) can be activated to separate from the pawl member  335 , thereby permitting the motor  320  to decouple from the ratchet mechanism  330  during a drive step (refer to  FIG. 30 ). 
     The motion path of the pusher arm  325  can be configured to provide an efficient mechanical advantage orientation during the desired motion of the adjustable pawl member  335 . In this embodiment, the pusher arm  325  is directed by a guide slot  328  formed in the pump housing  110  ( FIG. 26 ). In particular, the pusher arm  325  includes the slider pin  326  that is received within the guide slot  328  during assembly. The portion of the pusher arm  325  proximate the slider pin  326  can abut against the pawl member  335  when the pusher arm is advanced. As such, when a first end of the pusher arm  325  is moved by the gear  324   c , a second end of the pusher arm (proximate the slider pin  326 ) is directed by the guide slot  328 . The orientation of the pusher arm  325  relative to the guide slot  328  can be configured to provide an efficient mechanical advantage for the pushing force applied by the pusher arm  325  during the desired motion of the adjustable pawl member  335 . 
     Still referring to  FIGS. 27-30 , the ratchet mechanism  330  includes the pawl member  335  and a ratchet body  340 , which in this embodiment is a ratchet wheel having a number of teeth along its circumferential surface. In this embodiment, the ratchet wheel  340  is coupled with a worm gear  345 , and incremental rotation of the ratchet wheel  340  causes rotation of a drive wheel  360  (due to engagement with the worm gear  345 ). The pawl member  335  is adjustable between a reset position (refer to  FIG. 29 ) and a forward position (refer to  FIG. 28 ). For example, during the reset step, the motor  320  may be activated to advance the pusher arm  325  (guided by the guide slot  328 ), and the pusher arm  325  then applies a pushing force that adjusts the pawl member  335  to the reset position in which the pawl member  335  grabs a new tooth of the ratchet wheel  340  (refer to  FIG. 29 ). In this embodiment, the adjustable pawl member  335  is pivotably coupled to about the axis of an axle  332  (refer to  FIG. 26 ) that receives the ratchet wheel  340  and the worm gear  345 . 
     A spring device  350  is also coupled to the pawl member  335  so as to urge the pawl member  335  toward the forward position (refer to  FIG. 28 ). In this embodiment, the spring device  350  is in the form of a coil spring that is fixed to the pump housing  110  (not shown in  FIGS. 27-30 ) at a first end portion  352  and that is engaged with the pawl member  335  at a second end portion  354 . Thus, as shown in  FIG. 29 , when the pawl member  335  is adjusted to the reset position, the spring device  350  is in tension and stores potential energy that urges the pawl member  335  to return to the forward position (refer to  FIG. 28 ) and thereby drive the ratchet wheel  340  in a forward rotational direction. As previously described, a locking pawl  342  ( FIGS. 28-30 ) can be used to prevent the ratchet wheel  340  from reverse motion. The locking pawl  342  can flex or otherwise adjust to permit the incremental forward rotation of the ratchet wheel  340 . As such, the adjustable pawl member  335  can adjust from the forward position (refer to  FIG. 28 ) to the reset position (refer to  FIG. 29 ) to engage a new tooth of the ratchet wheel  340  while the ratchet wheel  340  remains in position due to the locking pawl  342 . 
     It should be understood that the drive system  300  can employ a set of location sensors to indicate when the pawl member  335  has reach the reset position or the forward position. For example, these sensors can be optical, magnetic, or contact-type sensors. The sensors may be capable of transmitting signals that indicate when the location of one of the gears in the gear system  322 , the pusher arm  325 , or the pawl member  335  is detected. Such sensor signals may be transmitted to the motor  330 , to the controller device  200  ( FIGS. 1-2 ), or a combination thereof. In one embodiment, the pawl member  335  may be equipped with an electrically conductive contact that engages a first contact-type sensor when moved to the reset position and that engages a second contact-type sensor when moved to the forward position. As such, the first and second contact-type sensors can electrically communicate with the motor  330 , the controller device  200 , or both when the pawl member reaches the reset and forward positions. These signals may be used to indicate when the motor  330  should cease rotation or reverse rotation. 
     Still referring to  FIGS. 27-30 , in some embodiments the ratchet wheel  340  can be integrally formed with the worm gear  345  so that the incremental rotation of the ratchet wheel  340  is translated to the worm gear  345 . Such rotation of the worm gear  345  causes rotation of the drive wheel  360 . The drive wheel  360  includes a central aperture having an internal thread pattern therein (not shown in  FIGS. 27-30 ), which mates is an external thread pattern  374  on the rod segments  372 . Thus, the incremental motion provided by the ratchet mechanism  330 , the pusher arm  325 , and the motor  320  causes the drive wheel  360  to incrementally rotate, which in turn translates to a longitudinal advancement of the flexible piston rod  370 . 
     Accordingly, in some embodiments, the piston rod  370  may undergo only forward or positive longitudinal displacement as a result of drive system  300 . For example, the drive system  300  substantially hinders the piston rod  370  from retracting or “backing up” in response to fluid pressure in the medicine cartridge  120  or other reversal forces. In such circumstances, the flexible piston rod  370  can be retracted only upon disassembly of the pump device  300  (e.g., to disengage the drive gear  360  or the ratchet mechanism  330 ). In those embodiments in which the pump device  100  is intended to be disposable, the non-retractable piston rod configuration may facilitate a “one time use” disposable pump device, thereby reducing the likelihood of failure due to non-intended repeated use of the disposable pump device  100 . 
     Still referring to  FIGS. 27-30 , the flexible piston rod  370  can comprise a plurality of rod segments  372  serially connected by hinge portions  373  so that the flexible piston rod  370  is adjustable from a curved shape to a noncurved shape. As previously described, the plurality of segments  372  and the interconnecting hinge portions can be integrally formed in one piece from one or more moldable materials, including a number of polymer materials. In this embodiment, the plurality of segments  372  comprise generally cylindrical segments that have an exterior thread pattern  374  along at least one cylindrical surface portion. As previously described, the plunger engagement device  375  can be arranged at a forward end of the piston rod  370  so that the plunger engagement device  375  faces toward the medicine cartridge  120 . 
     In some embodiments, the flexible piston rod  370  can include an anti-rotation structure that hinders the piston rod  370  from rotating with the drive wheel  360  (thereby allowing the rotation of the drive wheel  360  to translate into a longitudinal motion of the piston rod  370 ). For example, in this embodiment, the flexible piston  370  includes longitudinal flat surfaces  371  extending along each of the segments  372 . The longitudinal flat surfaces  371  can engage a complementary surface on the pump housing  110  (not shown in  FIGS. 27-30 ) proximate the drive wheel  360  so that the flexible piston rod  370  is hindered from rotating when the drive wheel  360  turns. Accordingly, the longitudinal flat surfaces  371  on each segment  372  aligns to form a keyway that receives a mating key (e.g., a complementary flat surface) on the pump housing. In other embodiments, the anti-rotation structure may include one or more longitudinal channels  173  (with each channel capable of engaging an associated protrusion that acts as a key to hinder rotation while permitting longitudinal motion) or the like. Previously filed U.S. patent application Ser. No. 11/522,836 (incorporated herein by reference) describes further piston rod configurations for use in an infusion pump device. 
     Because the flexible piston rod  370  is adjustable from a curved shape to a noncurved shape, the overall length of the pump device can be reduced in some embodiments. For example, in a typical infusion pump that houses a straight and rigid rod, the typical infusion pump requires a package or housing having a linear dimension sufficient to accommodate the length of the rigid piston rod when it is at its limit of travel in which it is fully withdrawn from the container or cylinder. The pump device  100  incorporating the flexible piston rod  370  can require less space than a similar device that houses a non-flexible, rigid rod. 
     Referring now to  FIGS. 28-30 , the incremental motion cycle of the drive system  300  may include rotation of the motor  320  so that the pusher arm  325  is advanced from a first position to act upon the pawl member  335  and then retracted back to the first position. Such movement of the pusher arm  325  can cause the pawl member  335  to adjust from the forward position (refer to  FIG. 28 ), to the reset position (refer to  FIG. 29 ), and back to the forward position (under the driving force of the spring device  350 ). The adjustment of the pawl member  352  from the reset position to the forward position drives the ratchet wheel  340  and worm gear  345 , which incrementally rotates the drive wheel  360  and thereby advances the flexible piston rod  370  a longitudinal increment distance. In one example, the drive system  300  can advance the piston rod  370  a longitudinal increment distance of about 16 microns or less (about 4 microns to about 12 microns, about 5 microns to about 9 microns, and preferably about 6 microns to about 8 microns) for each incremental motion cycle of the ratchet mechanism  330 . 
     Referring to  FIG. 28 , in this embodiment of the incremental motion cycle, the pawl member  335  begins at the forward position with the pusher arm  325  retracted in a first position (e.g., the rest position in this embodiment). The adjustable pawl member  335  can be in this forward position, for example, because the drive system  300  previously completed a drive step at an earlier time. 
     Referring to  FIG. 29 , in response to the controller device transmitting a signal to initiate the cycle, the motor  320  may begin to rotate in a first rotational direction that advances the pusher arm  325  to push against the pawl member  335 . Such movement of the pusher arm  325  causes a pushing force  327  that overcomes the bias of the spring device  350  and adjusts the pawl member  335  toward the reset position (e.g., the reset step). When the adjustable pawl member  335  reaches the reset position, as shown in  FIG. 29 , the pawl member  335  is capable of engaging a new tooth of the ratchet wheel  340 . The locking pawl  342  prevents the ratchet wheel  340  from rotating in a reverse (non-forward) rotational direction while the adjustable pawl member  335  is shifting back to the reset position. Such an adjustment of the pawl member  335  back to the reset position creates a tension force  357  in the spring device  350  (as shown in  FIG. 29 ), thereby storing potential energy to drive the adjustable pawl member  335  and ratchet wheel  340  in a forward rotational direction for the drive step. 
     Referring to  FIG. 30 , after the pawl member  335  reaches the reset position, the motor  330  stops rotating in the first rotational direction and reverses to rotate in the second, opposite rotational direction. Such rotation in the second direction by the motor  320  causes the pusher arm  325  to promptly retract to the first position (while guided by the guide slot  328 ). As such, the spring device  350  begins to urge the pawl member  335  toward the forward position. When the adjustable pawl  335  is driving the ratchet wheel  340  in the forward rotational direction, the potential energy of the spring device  350  is being translated to kinetic energy for the motion of the pawl member  335  and the ratchet wheel  340 . Such an adjustment of the pawl member  335  from the reset position to the forward position drives the ratchet wheel  340  and the integrally formed worm gear  345 . The incremental rotation of the worm gear  345  results in an incremental rotation by the drive wheel  360 , which advances the flexible piston rod  370  a longitudinal increment distance. Such an incremental advancement of the flexible piston rod  370  can cause a predetermined volume of fluid to be dispensed from the cartridge  120 . In the event of a subsequent cycle (including the reset step and the drive step), the motor  320  would begin by rotating in the first rotational direction so as to advance the pusher arm  325  yet again. This pattern of cycles may continue until the piston rod  370  has reached the limit of its longitudinal travel. 
     Still referring to  FIG. 30 , although the pusher arm  325  can be promptly retracted to the first position due to the reverse rotation of the motor  320 , the pawl member  335  is driven to the forward position ( FIG. 28 ) over a greater period of time. This period of time required for the drive step is affected by a number of factors, including the spring force from the spring device  350 , the fluid pressure inside the medicine cartridge  120 , and the like. Accordingly, the pusher arm  325  can be temporarily separated from the pawl member  335  when it is retracted to its first position, thereby causing the motor  320  to be decoupled from the ratchet mechanism  330  during the drive step. For example, the portion of the pusher arm  325  proximate the slider pin  326  can become temporarily spaced apart by a distance  329  from the pawl member  335  while the pawl member  335  is being driven from the reset position ( FIG. 29 ) to the forward position ( FIG. 28 ). Such a configuration permits the motor  320  to expend a short burst of electrical energy to reset the ratchet mechanism  330  (e.g., during advancement of the pusher arm  325 ) while contributing no energy during the drive step to drive the ratchet mechanism  330  to the forward position for dispensation of medicine. Because the motor  320  can be decoupled from the ratchet mechanism  330  during the drive step, only the spring device  350  expends energy over a period of time to drive the ratchet mechanism  330  to the forward position. Accordingly, the pump device  100  can reliably and accurately dispense dosages of medicine in a safe and energy efficient manner. In particular, the motor  320  is not required to draw energy from the battery over an extended period of time (e.g., during the drive step in which the piston rod  370  is advanced to dispense medicine over a period of time). Instead, the motor  320  may draw upon the battery power during advancement of the pusher arm  325  to quickly reset the ratchet mechanism  330  and during the brief retraction of the pusher arm  325 . 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.