Patent Publication Number: US-7905859-B2

Title: Pump with venting

Description:
REFERENCE TO CO-PENDING APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 11/152,880, filed Jun. 15, 2005, now U.S. Pat. No. 7,510,544, issued Mar. 31, 2009, which is a divisional application of U.S. patent application Ser. No. 10/086,646, filed Feb. 28, 2002, now U.S. Pat. No. 7,033,338, issued Apr. 25, 2006, both of which are hereby incorporated herein in their entireties. 
     This application is also related to the following six commonly assigned patent applications, which were all filed on Feb. 28, 2002: “Syringe Pump Control Systems and Methods” U.S. application Ser. No. 10/086,994, now U.S. Pat. No. 7,041,082 issued May 9, 2006, “Child Safety Cap for Syringe Pump” U.S. application Ser. No. 10/086,993, now abandoned, “Insulin Pump Having Missed Meal Bolus Alarm” U.S. application Ser. No. 10/087,460, now U.S. Pat. No. 6,744,350 issued Jun. 1, 2004, “Programmable Medical Infusion Pump Displaying a Banner” U.S. application Ser. No. 10/087,205, “Programmable Insulin Pump” U.S. application Ser. No. 10/086,641, now U.S. Pat. No. 6,852,104 issued Feb. 8, 2005, and “Programmable Medical Infusion Pump” U.S. application Ser. No. 10/087,449. The disclosures of these six patent applications are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a medication pump and a cartridge for use in a medication pump, and methods for using the same. More particularly, the present invention is particularly useful in the context of portable medication pumps that automatically discharge medication from a medication cartridge. 
     Various ambulatory or portable medical devices are known for treating patients at a remote site away from the caregiver or clinician office. One example of an ambulatory medical device is a drug delivery device, such as a drug pump, for providing periodic or continuous drug delivery to the patient when the patient is away from the caregiver&#39;s office. Ambulatory drug pumps are shown for example in U.S. Pat. Nos. 4,559,038, 4,731,058, 5,531,697, 5,389,078 and 5,695,473, the disclosures of which are hereby incorporated by reference. Drug pumps may be used to deliver insulin and many other medications. 
     Medication pumps are known that use a piston-like arrangement to push medication out of a cylindrical medication reservoir. The cylindrical medication reservoir may be provided within a cylindrical barrel, where a plunger pushes medication out of the reservoir, and may be called a syringe or cartridge. Drug pumps typically have a delivery conduit for connecting to the patient&#39;s body for delivery of the drug. An infusion set typically includes the delivery conduit, an access device for attaching the delivery conduit to the patient&#39;s body and an attachment device for attaching the delivery conduit to a medication cartridge. Improved structures and methods are needed for filling medication cartridges, loading medication cartridges, and sensing conditions within medication pumps. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a medication pump, a cartridge for use in a medication pump, a pump cap for use with a medication pump, components of the cartridge and methods of use of these devices. 
     A cartridge for use in a medication pump includes a cylindrical barrel and a plunger slidably received within the barrel, where the plunger includes a first tab projecting inwardly from an interior wall face. Preferably the cartridge also includes a removable cartridge rod including a shaft and an interface cylinder at one end of the shaft, where the interface cylinder defines a first channel for receiving and retaining the first tab of the plunger. The first channel of the interface cylinder preferably includes an axial portion disposed parallel to an axis of the shaft and a locking portion disposed in a circumferential direction around an outer surface of the interface cylinder. The cartridge may also include axial guides at a closed end. 
     A cartridge barrel for use in a medication pump includes a cylindrical barrel wall with an open end and a closed end, where the closed end defines an orifice. The cartridge barrel also includes a cylindrical end wall projecting from the closed end of the cylindrical barrel wall and surrounding the orifice, where the end wall includes an interior face, an exterior face, and axial guides on the exterior face. 
     A plunger for use within a medication cartridge in a medication pump includes a cylindrical plunger wall having an interior cylindrical wall face and a first tab projecting inwardly from the interior wall face. Preferably, the plunger also includes a second tab projecting inwardly from the interior wall face positioned opposite the first tab. 
     A removable cartridge rod for use with a medical cartridge in a medical pump includes a shaft and an interface cylinder at the one end defining a first channel. The first channel includes an axial portion disposed parallel to an axis of the shaft and a locking portion disposed in a circumferential direction around an outer surface of the interface cylinder. Preferably, the interface cylinder also defines a second channel for receiving and retaining a portion of a plunger. The second channel also includes an axial portion disposed parallel to the axis of the shaft and a locking portion disposed in a circumferential direction around the outer surface of the interface cylinder. 
     Another medication cartridge for use in a medication pump includes a cartridge barrel comprising an open end and a closed end, wherein the closed end defines an orifice. The cartridge barrel also includes a cylindrical end wall projecting from the closed end and surrounding the orifice, the end wall having an interior face, an exterior face, and axial guides on the exterior face. A plunger is slidably received within the barrel. A medication pump includes a motor, a cartridge chamber for receiving a medication cartridge, and a drive rod extending into the cartridge chamber through the drive rod opening, where the drive rod is configured to be axially moved by the motor. The drive rod includes an interface structure at one end, where the interface structure defines a first channel. The first channel includes an axial portion disposed parallel to an axis of the drive rod and a locking portion disposed in a circumferential direction around an outer surface of the interface structure. This pump may be used with a medication cartridge that has a plunger including a first tab projecting inwardly from an interior wall face, and the first tab may be received in the first channel to lock the plunger to the drive rod. Preferably, the interface structure also defines a second channel comprising an axial portion disposed parallel to the axis of the drive rod and a locking portion disposed in a circumferential direction around the outer surface of the interface structure. This second channel can receive a second tab on the plunger, in a preferred configuration. The interface structure of the drive rod may include a visual indicator, wherein when the interface structure is coupled to a plunger, the visual indicator is positioned within the plunger. The pump may include a window in its outer housing that allows a view into the cartridge chamber. 
     The medication pump may include a pump cap configured to rotationally attach to an open end of the cartridge chamber to close the cartridge chamber, where the pump cap has an interior surface including guides that engage axial guides at a closed end of the medication cartridge. When the pump cap is rotated into engagement with the open end of the cartridge chamber, the cartridge is rotated in a first direction to move the tab into the locking portion of the channel on the drive rod interface structure. 
     The present invention also includes a medication pump having a motor, a cartridge chamber for receiving a medication cartridge, and a drive rod having an interface structure at one end that extends into the cartridge chamber through an end of the cartridge housing. The drive rod is configured to be axially moved by the motor. The interface structure includes a visual indicator, so that when the interface structure is coupled to a plunger of a medication cartridge, the visual indicator is positioned within the plunger. The pump also includes an outer housing having a window into the cartridge chamber that allows a view of the visual indicator. 
     A method of filling a medication cartridge with fluid includes a attaching fill rod to a plunger by inserting an interface end of the rod into an interior cylinder of the plunger axially and rotating the rod in a first direction so that a tab of the plunger is moved into a locking portion of a channel of the interface end of the rod. Then the plunger is retracted within the barrel by pulling on the rod to draw fluid into the barrel. Then the rod is detached from the plunger by rotating the rod in a second direction opposite the first direction and withdrawing the rod from the interior cylinder of the plunger. 
     Another method according to the present invention is a method of locking a medication cartridge into a pump involving inserting the cartridge axially into a cartridge chamber so that a tab of a plunger travels along an axial portion of the channel of the drive rod. Then the cartridge is rotated in a first direction so that the tab travels along a locking portion of the channel in the drive rod. 
     Another medication pump system according to the present invention includes a pump cap for rotationally attaching to an open end of a cartridge chamber to close the cartridge chamber, where the pump cap comprising guides located on an interior surface. These guides engage axial guides at a closed end of a medication cartridge, so that when the pump cap is rotated into engagement with the open end of the cartridge chamber, the cartridge is rotated into engagement with an interface structure of a drive rod. 
     The present invention also involves a method of locking a medication cartridge into a pump, where the cartridge is axially inserted into the cartridge chamber and a pump cap is rotated into engagement with an open end of a cartridge chamber. The rotation of the pump cap causes guides on an interior surface of the pump cap to interact with axial guides on the cartridge so that the cartridge is rotated, whereby the plunger is rotated into engagement with the drive rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood by considering the detailed description of various embodiments of the invention which follows in connection with the accompanying drawings. 
         FIG. 1  is a back, left perspective view of a syringe pump according to one embodiment of the present invention. 
         FIG. 2  is a front, left perspective view of a housing of the pump of  FIG. 1  with the bolus button, battery cap and pump cap removed, with the front cover separated from the housing. 
         FIG. 3  is a front view of the pump of  FIG. 1  showing the keypad and display screen, where the pump is attached to an administration set. 
         FIG. 4  is a front view of the drive assembly components within the pump housing for the pump of  FIG. 1 . 
         FIG. 5  is a front view of the drive assembly components within the pump housing for the pump of  FIG. 1  where the drive rod is partially advanced into the cartridge chamber. 
         FIG. 6  is a cross-sectional view of the components of  FIG. 5  along line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the components of  FIG. 5  along line  7 - 7  of  FIG. 5 . 
         FIG. 8  is a front, right view of a drive rod of the pump of  FIG. 1 . 
         FIG. 9  is a front view of the drive assembly components within the pump housing for the pump of  FIG. 1  where the cartridge chamber is not present and a plunger is attached to the end of the drive rod. 
         FIG. 10  is a top view of the removable cartridge rod, plunger, and cartridge barrel of a cartridge for use in a syringe pump of one embodiment of the present invention. 
         FIG. 11  is a top view showing the components of  FIG. 10  where the cartridge rod is attached to the plunger and the plunger is positioned within the cartridge barrel. 
         FIG. 12  is a perspective end view of the removable cartridge rod of  FIG. 10 . 
         FIG. 13  is a top perspective view of the removable cartridge rod of  FIG. 10 . 
         FIG. 14  is a rear perspective view of the plunger of  FIG. 10 . 
         FIG. 15  is a front end perspective view of the cartridge barrel of  FIG. 10 . 
         FIG. 16  is a back end perspective view of the cartridge barrel of  FIG. 10 . 
         FIG. 17  is a top perspective view of a pump cap according to one embodiment of the present invention. 
         FIG. 18  is a bottom perspective view of the pump cap of  FIG. 17 . 
         FIG. 19  is a top view of the pump cap of  FIG. 17 . 
         FIG. 20  is a cross-sectional view of the pump cap of  FIG. 17  taken along line  20 - 20  of  FIG. 19 . 
         FIG. 21  is a front view of the pump of  FIG. 1  where a medication cartridge is loaded in the cartridge chamber. 
         FIG. 22  is a cross-sectional view of the pump of  FIG. 21  along line  22 - 22  of  FIG. 21 . 
         FIG. 23  is an enlarged view of the pump components of  FIG. 1  within the pump housing. 
         FIG. 24  is a front perspective view of an idler gear having a magnetic flag according to one embodiment of the present invention. 
         FIG. 25  is a front perspective view of an idler gear circuit board according to one embodiment of the present invention. 
         FIG. 26  is a side view of a bushing used to space the idler gear from the idler gear sensor according to one embodiment of the present invention. 
         FIG. 27  is a front view of a drive assembly chassis of the present invention. 
         FIG. 28  is a right view of the drive assembly chassis of  FIG. 27 . 
         FIG. 29  is a front perspective view of the drive assembly of the pump of  FIG. 1 . 
         FIG. 30  is a block diagram of the components of the pump of  FIG. 1 . 
         FIG. 31  is a flowchart of the cartridge loading method of one embodiment of the present invention. 
         FIG. 32  is a flowchart of further cartridge loading steps of one embodiment of the invention. 
         FIG. 33  is a flowchart of additional cartridge loading steps of one embodiment of the present invention. 
         FIG. 34  is a right perspective view of the drive rod of  FIG. 8 . 
         FIG. 35  is a left front perspective view of a pump housing for the pump of  FIG. 1  without drive assembly components, where two circuit boards are shown separated from the pump housing. 
         FIG. 36  is a front perspective view of one embodiment of a pump clip for attachment to the pump of  FIG. 1 , according to the present invention. 
         FIG. 37  is a rear perspective view of the pump clip of  FIG. 36 . 
         FIG. 38  is a bottom perspective view of a child safety pump cap cover according to one embodiment of the present invention. 
         FIG. 39  is a bottom view of the child safety pump cap cover of  FIG. 38 . 
         FIG. 40  is a side view of the child safety pump cap cover of  FIG. 38 . 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS 
     The present invention is believed to be applicable to a variety of devices, systems and methods for delivering medication using a syringe or cartridge and a pump. The invention has been found to be particularly advantageous in application environments where a cartridge is axially loaded into a pump. While the present invention is not so limited, an appreciation of various aspects of the invention is best gained through a discussion of various application examples operating in such an environment. 
     Various embodiments of the present invention will be described in detail with reference to the drawings, where like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention. 
       FIG. 1  illustrates one particular embodiment of a syringe pump where a syringe or cartridge is axially loaded. The terms syringe and cartridge will be used interchangeably to refer to a device having a hollow barrel fitted with a plunger. The pump  10  of  FIG. 1  includes an outer pump housing  14 . A pump cap  16  covers an opening into a cartridge chamber  80  (shown in  FIG. 4 ) that receives a syringe or cartridge. The pump outer housing  14  also includes a viewing window  20  into the cartridge chamber. The pump  10  also includes a battery cover  24 . 
     Now referring to  FIG. 2 , the pump  10  is shown without the pump cap  16 , revealing the opening  28  to the chamber  80 . In addition, the battery cap  24  is removed in the view shown in  FIG. 2 , revealing the battery chamber opening  32 . A front panel  38  is shown removed from the remainder of the pump housing  14 , allowing a view into the interior of the pump housing  14 . The drive assembly components and circuit boards of the pump  10  are removed from the pump housing  14  in the view shown in  FIG. 2 . A cylindrical chamber wall  82  surrounds the cartridge chamber  80 . The battery chamber  114  is positioned adjacent to the battery opening  32 . 
     The front panel  38  defines a depression  39  for receiving a lens and an opening  43  for a display screen. The front panel  38  also defines a depression  41  for receiving a keypad and an opening  42  for facilitating an electrical connection to the keypad. 
     A vent  36  is visible in  FIG. 2  on the right end of the pump outer housing  14 . The vent  36  preferably incorporates a water barrier that is air permeable so that moisture is not allowed into the interior of the pump, but pressure equalization is possible between the interior and exterior of the pump. The use of a water barrier in vent  36  allows pressure equalization of a sealed environment within the pump housing  14 . The water barrier may be attached to an interior surface of the pump housing  14  using a pressure sensitive adhesive. Adhesive capable of a water tight seal may be provided along perimeter  35  of pump housing  14  to bond the pump housing  14  to the front panel  38  so that the pump  10  can be exposed to water without allowing water into the pump interior. 
     Now referring to  FIG. 3 , the front panel  38  of the pump  10  is shown including a keypad  40  with individual buttons  45 - 48  for allowing a user to input information and make menu choices. The front panel  38  also includes a display  44  present behind a lens  49 , within the opening  43 . In  FIG. 3 , an administration set is shown emerging from the pump cap  16 . The administration set includes tubing  52  for delivering medication to the body of a patient or user. The administration  50  also includes a connector  54  for attaching the tubing to a medication cartridge within the pump. Often, a luer-lock connection is used between the administration set  50  and the medication cartridge. 
     Now referring to  FIG. 4 , a front view of some of the components of the pump  10  within the pump housing  14  is shown, where the front panel  38  has been removed. The cartridge opening  28  opens into the cartridge chamber  80 .  FIG. 4  shows a top view of the exterior wall  82  of the cartridge chamber  80 . The cartridge chamber is where cartridges or syringes of medication are placed for delivery to the patient. A drive rod  88  is configured to move axially to dispense medication from a cartridge in the cartridge chamber  80 . The drive rod has a first end  92  and a second end  94 . At the second end  94  of the drive rod  88  an interface cylinder  98  is defined for coupling to a plunger of a medication cartridge. A drive rod flange  100  is present at the second or distal end  94  of the drive rod  88 , and adjacent to the interface cylinder. 
     The cartridge chamber  80  includes an open end at the cartridge opening  28  and a closed end  102  opposite the cartridge opening  28 . The closed end  102  of the cartridge chamber  80  defines an opening for allowing the drive rod  88  to enter the cartridge chamber. The cartridge chamber also includes a vent  108 . The vent includes openings  110  to allow for the passage of gas between the cartridge chamber  80  and the interior of the pump housing. The vent  108  may also include a gas permeable water barrier that covers the openings  110 , similar to vent  36 . Preferably, the vent  108  allows for pressure equalization between the chamber  80  and the pump interior but prevents the passage of fluid. A watertight vent between the cartridge chamber  80  and the interior of the pump is valuable because the pump components will not be exposed to any fluid in the cartridge chamber, for example, if fluid leaks from a medication cartridge. 
     The pump  10  also includes a battery chamber  114  having an open end at the battery opening  32  that is closeable using the battery cover  24 . A battery within the battery chamber  114  is electrically connected to a motor  118 . The motor rotates a motor gear  122 . An idler gear  126  is in turn rotated by the motion of the motor gear  122 . The idler gear interacts with a drive rod gear  128  causing the drive rod gear to rotate when the idler gear  126  is rotated. The pump may also include a vibratory motor  129  with a protruding structure  130  that is moved by the motor  129 . The vibratory motor  129  can be used to call the user&#39;s attention to the device. An audible signal may also be used to attract the user&#39;s attention, alone or in combination with a vibration. A bracket  131  holds the driving motor  118  and the vibratory motor  129  in place in the pump housing. A mount structure  132  for the vibratory motor is shown in  FIG. 2 . 
     In  FIG. 4 , the drive rod  88  is fully retracted, so that its first end  92  is as close to the drive rod gear  128  as possible. In this fully retracted position, the interface cylinder is as close as possible to the interior face of closed end  102  of the cartridge chamber. Preferably, the flange  100  is contacting the chamber&#39;s closed end  102  when the drive rod  88  is in the fully retracted position. 
     The interior face  134  of the closed end  102  is shown in  FIG. 6 . The closed end  102  defines a cavity  135  for holding an elastomeric sealing member (not shown) to seal the opening in the closed end through which the drive rod passes. The drive rod flange  100  will preferably contact the sealing member within the cavity  135  in the closed end  102  of the cartridge chamber  80 . 
       FIG. 5  shows a front view of the components of the pump  10  similar to  FIG. 4  but where the drive rod is at a different position. In  FIG. 5 , the drive rod  88  is partially extended into the cartridge chamber  80 . 
     When the motor  118  operates, the drive rod gear  128  is rotated and the drive rod  88  is axially moved. A lead screw  136  is connected to the drive rod gear  128  and is rotated when the drive rod gear  128  is rotated. The lead screw  136  includes threads  138  on its outer surface. As can be seen in  FIGS. 6-7  and  34 , the first end  92  of the drive rod  88  includes an opening  144  for receiving the lead screw  136 . The lead screw  136  is received within the drive rod opening  144  and extends within an interior  146  of the drive rod  88 . The drive rod  88  includes a cylindrical shaft  148  and defines a cylindrical interior chamber  146 . At the first end  92  of the drive rod  88 , threads  149  are defined on the interior surface of the drive rod  88  for interacting with the threads  138  of the lead screw  136 . 
     The drive rod  88  does not rotate as it is axially moved. Preventing the drive rod from rotating as it is axially moved is important because if the drive rotates, it will not be axially moved by the rotation of the lead screw. The drive rod  88  is held in a fixed orientation by a clip  154  that interacts with the outer housing  14 . The drive rod  88  includes a recessed portion  152  at the first end  92 . The clip  154  attaches to the drive rod  88  at the recessed portion  152 . The clip  154  prevents the drive rod  88  from rotating when the lead screw  136  is rotated. As best seen in  FIG. 7 , the clip  154  includes a U-shaped portion  158  that fits around the recessed portion  152  of the drive rod  88 . The clip  154  also includes a downward extension  160  that rides on a rib  164 . The rib  164  is a part of the pump housing  14  and extends along the length of the drive rod and lead screw from the drive rod gear  128  to the closed end  102  of the cartridge chamber  80 . When the lead screw  136  rotates, the threads  149  at the opening  144  at the first end  92  of the drive rod  88  ride along the threads  138  of the lead screw  136 , causing the drive rod  88  to be axially moved. 
     Preferably, the interior chamber  146  of the drive rod  88  does not extend all the way through the drive rod  88  from the first end  92  to the second end  94 . As seen in  FIG. 6 , preferably a closure  166  is present within the interior  146 . The closure  166  may be molded into the structure of the drive rod  88  when the drive rod is manufactured. Alternatively, a plug structure may be inserted into the interior  146  to provide the closure  166 . The closure  166  prevents any moisture or fluid from traveling from the cartridge chamber  80  to the interior of the pump housing. The closure  166  could be a plug structure made of a gas-permeable water barrier, which would provide a path for pressure equalization between the chamber  80  and the pump interior. 
     Medication Cartridge and Cartridge Interface with Drive Rod 
     Now referring to  FIGS. 10-16 , a medication cartridge is shown that may be used with the pump  10  shown in  FIGS. 1-7  and  9 . The medication cartridge  200  may include a cartridge barrel  202 , a plunger  204  and a cartridge rod  206 . The cartridge barrel  202  is cylindrically shaped and includes a closed end  210  and an open end  212 . The closed end  210  defines an orifice  216  through which medication can be delivered. As seen in  FIG. 11 , the interior of the cylindrical cartridge barrel  202  defines a medication reservoir  220  bounded by a barrel interior wall  222 . The cartridge barrel  202  may also include a cylinder  224  protruding from the closed end  210 . The cylinder  224  includes an exterior wall face  226  and an interior wall face  228  shown in  FIG. 15 . Now referring to  FIGS. 10 ,  11  and  15 , the protruding end cylinder  224  surrounds a protruding tip  232 . The tip  232  protrudes beyond the cylinder  224  and is in fluid communication with the orifice  216  of the cartridge barrel. On the exterior wall  226  of the end cylinder  224 , axial guides  234  are defined. The axial guides  234  may be ridges molded into the structure of the protruding cylinder  224 . Alternatively, the axial guides may be depressions or grooves molded into the cylinder  224 . The axial guides  234  interact with the pump cap  16 , as will be further described. Thread structures  236  are defined on the interior wall  228  of the protruding cylinder  224 . The thread structures  236  are useful for securing an administration set  50 , as illustrated in  FIG. 3 , to the medication cartridge  200 . 
     In a preferred embodiment, the outer diameter of the cartridge barrel is about a half inch, or about 540 thousandths of an inch, while the inner diameter of the cartridge barrel is about 475 thousandths of an inch. The entire cylindrical barrel including the protruding cylinder and tip may preferably be about 3 inches or less, more preferably about 2 inches or less. Preferably, the maximum travel distance of the plunger from the fill line to the closed end is about an inch or less. 
     Now referring to  FIGS. 9 ,  10 , and  14 , the plunger  204  includes a cylindrical wall  250 , a closed end  254 , an open end  256 , and a conical face  258  at the closed end  254 . The cylindrical plunger wall  250  includes an exterior wall face  262  defining grooves  264  ( FIG. 9 ) into which O-rings  266 ,  267  ( FIG. 10 ) are seated. The O-rings  266 ,  267 , seal against the interior barrel wall  222  of the medication cartridge barrel  202 . Now referring to  FIG. 14 , the cylindrical plunger wall  250  also includes an interior wall face  268 . A first tab  270  protrudes inwardly from the interior face  268  of the plunger cylinder wall  250 . In a preferred embodiment of the plunger of the present invention, a second tab  272  also protrudes from the interior wall  268  of the plunger. Preferably, the first and second tabs are positioned opposite each other on the cylindrical interior wall face  268 . 
     The tabs  270 ,  272  are designed for mating with another structure that is used to move the plunger, such as a removable cartridge rod  206  for filling or a drive rod  88  of a pump  10  for pumping. Many different numbers and configurations of tabs, or other protruding structures, may be provided on the interior wall  268  of the plunger  204  to allow for mating with another structure. For example, one, two, three, four, five, six or more tabs may be provided on the interior wall  268 . Two or more tabs are preferred to one tab, and it is preferred that the tabs are evenly spaced around the interior wall face  268 , so that force can be evenly applied to withdraw the plunger in the cartridge. The plunger  204  is sized to be slidably received within the medication reservoir  220  of the cartridge barrel  202 . The O-rings  266 ,  267  provide a sealing engagement with the barrel interior wall  222  so that the plunger can be used to push medication out of the medication reservoir  220 . 
     Now referring to  FIG. 16 , the cartridge barrel  202  may include a fill line ridge  280  projecting from the interior barrel wall  222  near the open end  212 . The fill line ridge  280  provides a tactile indication of the fully retracted position for the plunger  204 . As a user pulls the plunger away from the closed end  210 , for example when filling the medication reservoir  220  with fluid, the rearmost O-ring  266  will come into contact with the fill line ridge  280 . When the O-ring  266  contacts the fill line ridge  280 , an increased force will be necessary to further withdraw the plunger past the fill line ridge  280 . As the O-ring  266  passes over the fill line ridge  280 , a tactile bump will be felt by the user. This indicates that the plunger should not be withdrawn further in the medication reservoir. Optionally, the portion  282  of the cylindrical barrel  202  that extends from the ridge fill line  280  to the open end  212  may be shaded or textured. This shading or texturing may provide the user with a visual indication of the fill line. In addition, the shaded or textured portion  282  may be useful in conjunction with a cartridge sensor that will be further discussed herein. Shading or texturing may be provided on either the interior or the exterior of the barrel  202  at the shaded or textured portion  282 .  FIGS. 10-11  and  15  illustrate a shaded portion  282  on the exterior surface of the barrel.  FIG. 16  illustrates a shaded portion  282  on an interior surface of the barrel. Alternatively, the shading or texturing could be incorporated into the material of the barrel  202 . 
     The cartridge fill rod  206  shown in  FIGS. 10-13  may be removably coupled to the plunger  204  and may be used to move the plunger  204  axially within the cartridge barrel  202 . The cartridge fill rod  206  may be especially useful for filling the medication cartridge before inserting it into a pump. The cartridge fill rod  206  may be attached to the plunger  204  and then used to pull the plunger back in the medication reservoir, thereby drawing in fluid. Then, the cartridge fill rod  206  may be detached from the plunger  204  and the cartridge barrel  202  and plunger  204  may be inserted into a chamber of a pump. 
     The cartridge fill rod  206  includes a shaft  290  extending between an interface end  294  and a handle end  298 . A handle flange  302  at the handle end  298  is useful for grasping and pulling or pushing the cartridge fill rod  206 . The cartridge fill rod may also include an interface flange  303  at the interface end  294 . An interface cylinder  304  may extend from the interface end  294  of the fill rod  206 . The interface cylinder defines a first channel  308  for receiving and retaining a tab of the plunger  204 . The first channel  308  may include two portions for receiving and retaining the portion of a plunger. The first channel  308  may include a first axial portion  312  that is disposed parallel to an axis of the cartridge fill rod  206 . The first channel  308  may also include a first locking portion  314  that is disposed in a circumferential direction around the interface cylinder  304 . Preferably, the junction of the first locking portion and the first axial portion forms a right angle. A portion of a plunger, such as a tab  270 , is first received in an axial portion  308  of the channel  312  as the fill rod is moved axially toward the plunger. Then, the cartridge rod  206  is rotated so that the tab travels along a circumferential locking portion  314  of the channel  308 . Preferably, within the locking portion  314  of the first channel  308 , a ridge  318  is defined. The cartridge rod  206  is rotated so that the tab passes over the ridge  318  and is thereby more securely retained within the first channel  308 . The interface cylinder  304  may also include a ramp portion  320  associated with and adjacent to the first channel  304  for guiding a portion of the plunger into the first channel  308 . 
     As best seen in  FIG. 13 , preferably, the interface cylinder  304  also defines a second channel  322  for receiving a second portion of a plunger, such as a tab  272 . The second channel  322  may include a second axial portion  324  disposed parallel to an axis of the cartridge rod  206 . The second channel  322  may also include a second locking portion  326  disposed in a circumferential direction around the interface cylinder. The locking portion  326  may also include a ridge  328  over which the tab  272  may be pushed as it is rotated into the locking portion  326  of the second channel  322 . Preferably, the axial and locking portions of the second channel also form a right angle. A second ramp portion  330  may be associated with the second channel  322  to guide a portion of the plunger into the second channel  322 . The interface cylinder  304  of the fill rod could also include additional channels for receiving additional portions of a plunger. 
     The ridges  318  and  328  within the locking portions of the channels  312  and  322  may be sized so that they will contact the tabs of the plunger and configured so that they deform after the tabs of the plungers pass over them. This deformation allows the tab to move farther into the locking portion of the channel and provides the user with a tactile indication that the tabs are positioned in the locking portions of the channels. The interface cylinder  304  may include a hollow portion  336  at its interface end  294 , seen in  FIGS. 12-13 , which is useful in facilitating the molding process if the fill rod is molded. 
     Cartridge Interface on Pump 
     Now referring to  FIGS. 4 and 8 , the interface cylinder  98  of the drive rod  88  includes a structure for coupling the drive rod  88  to a plunger of a medication cartridge, such as the plunger  204  shown in  FIGS. 9 ,  10 - 11  and  14 . The interface cylinder  98  of the drive rod  88  may include a first channel  350  for receiving a tab of the plunger. The channel may include a first axial portion  354  extending from the second end  94  of the drive rod in a direction parallel to the axis of the drive rod. The first channel  350  may also include a first locking portion  356  extending circumferentially around the surface of the interface cylinder  98 . The first channel  350  may also have a first ramp  358  associated with it to guide a tab into the first channel. The interface cylinder  98  may also include a second channel  362  opposite from the first channel on the interface cylinder  98 . The second channel  362  may also include a second axial portion  366  that extends in a direction parallel to an axis of the drive rod. The second channel  362  may also include a second locking portion  368  extending circumferentially around the interface cylinder  98 . The second channel  362  may also include a ramp portion  370  for guiding a tab into the second channel  362 , similar to the ramp  358  associated with the first channel. The interface cylinder  98  could also include third, fourth or additional channels for receiving a portion of the plunger. 
     When a medication cartridge is loaded into the cartridge chamber  80 , the user first removes the cartridge rod  206  from the medication cartridge  200 . Then, the user inserts the medication cartridge  200  axially into the cartridge chamber  80  through the cartridge opening  28 . The medication cartridge  200  is inserted axially until the plunger comes into contact with the interface cylinder  98  of the drive rod  88 . If the tabs  270 ,  272  of the plunger  204  are aligned with the channels of the interface cylinder when the medication cartridge  200  is inserted, then the tabs will be received in the axial portions  354 ,  366  of the channels  350 ,  362  as the cartridge is further axially inserted into the cartridge chamber  80 . If the tabs of the plunger  204  are not aligned with the channels of the interface cylinder when the plunger contacts the interface cylinder, the tabs will be guided into the axial portions  354 ,  362  of the channels  350 ,  352  by the ramps  358 ,  370  as the medication cartridge  200  is rotated. If the pump is positioned with the cartridge chamber opening facing upward, then the cartridge is dropped into the chamber, and possibly with some rotation of the cartridge, the tabs  270 ,  272  drop into the axial portions  354 ,  362  of the channels  350 ,  362  on the interface cylinder  98  of the drive rod  88 . Once the tabs  270 ,  272  are positioned at the ends of the axial portions of the channels  350 ,  362 , the cartridge is rotated so that the tabs are positioned within the locking portions  356 ,  368  of the two channels. Preferably, the pump is positioned with the cartridge chamber opening  28  facing up during loading so that the action of gravity may be used to help engage the tabs of the plunger with the channels on the interface cylinder  98 . 
     Pump Cap 
     After the medication cartridge is inserted into the cartridge chamber  80 , the pump cap  16  may be reattached to the cartridge chamber opening  28 . The pump cap  16  is illustrated in  FIGS. 1 ,  3 , and  17 - 20 . The pump cap includes a pump or attachment end  410  closest to the pump and a delivery end  412 . At the pump end  410  of the pump cap  16 , an interior cylindrical surface  413  is defined. Protruding from the interior cylindrical surface at the attachment end are two opposing tabs  414 . These tabs are used to attach the pump cap to a mating structure  416  at the cartridge chamber opening  28 , shown in  FIGS. 4-5 . In  FIG. 1 , the pump cap  16  is shown attached to the pump housing  14 . The tip  232  of the medication cartridge  200  is shown within the delivery end  412  of the pump cap. 
     Now referring back to  FIGS. 17-20 , another interior cylindrical surface  418  is defined at the delivery end  412  of the pump cap  16 . Axial guides  420  are defined in the interior cylindrical surface  418  at the delivery end  412  of the pump cap  16 . These axial guides may interact with axial guides  234  at the closed end  210  of the cartridge barrel  202 . In one embodiment, the axial guides  234  on the cartridge barrel are protruding ridges while the axial guides on the interior wall  418  of the pump cap are grooves, as illustrated. However, these structures could be reversed so that grooves would be defined on the protruding cylinder  224  of the cartridge barrel  202  and protruding ribs would be defined on the interior surface  418  of the pump cap  16 . Alternatively, cooperating ridges may be formed on both the pump cap and the cartridge barrel end. The cooperating guides  234 ,  420  help ensure that the drive rod of the pump is securely attached to the plunger. When the pump cap  16  is rotated into attachment with the cartridge chamber opening  28 , the axial guides  420  on the pump cap cooperate with the axial guides  234  on the medication cartridge to rotate the medication cartridge and plunger in a direction to secure the tabs of the plunger within the channels of the interface cylinder. 
     If the plunger is already attached to the drive rod when the pump cap is rotated onto the pump cap opening, then the interacting guides  234  and  420  will cause the cartridge barrel to rotate around the plunger, while the plunger remains fixed to the drive rod. Once the drive rod is attached to the plunger, the rotation of the pump cap does not cause any axial movement of the plunger relative to the barrel, so no fluid is caused to be ejected from the barrel and no air is drawn into the barrel. 
     When the pump cap  16  is removed from the pump housing  14 , the cooperating guides  234 ,  420  cause the medication cartridge  200  to rotate also. This rotation moves the tabs out of the locking portion of the channels on the drive rod interface structure  98 , thereby facilitating removal of the medication cartridge from the cartridge chamber. 
     On the exterior surface of the pump cap  16 , gripping members  422  are defined. The gripping members  422  may provide the user with structure to grasp when removing or attaching the pump cap. The gripping structures  422  may also interact with a cap cover as further described herein. In a preferred embodiment, the gripping structures  422  are made of an elastomeric material. The pump cap  16  may include two materials such as a molded polymeric material and a molded elastomeric material. The exterior wall surface extending between the pump end  410  and the delivery end  412  is made of the molded polymeric material and defines openings  425  that surround the gripping structures  422 . The molded polymeric portion  424  is shown in  FIG. 20 . An elastomeric portion  426  may be formed within the polymeric portion  424 , so that the elastomeric gripping structures  422  protrude from the openings  425 . As seen in the cross-sectional view of  FIG. 20 , the polymeric portions  424  surround the elastomeric portions  426 . A lower portion of the elastomeric portion  426  may form a seal area  428  for interacting with the cartridge chamber opening  28  and with the closed end  210  of the medication cartridge  202 . 
     Visual Indicator of Drive Rod Attachment to Cartridge 
     Now referring to  FIG. 4 , at least a portion of the interface cylinder  98  may include a visual indicator to assist the user with confirming that the interface cylinder is properly attached to the plunger  204 . A viewing window  20 , shown in  FIG. 1 , provides a view into the cartridge chamber  80 . Preferably, the cartridge chamber  80  is made of a fairly transparent material so that a user can view the interface cylinder  98  within the chamber. When the plunger is not attached to the interface cylinder, the visual indicator on the interface cylinder  98  will be visible to the user through the window  20 . However, when the interface cylinder  98  is properly attached to the plunger  204 , the visual indicator will be hidden within the wall  250  of the plunger  204 .  FIG. 9  shows a view of the pump drive assembly where the plunger  204  is properly attached to the drive rod  88 . As a result, the interface cylinder  98  is not visible. In  FIG. 9 , the cartridge chamber  80  is not shown so that the attachment to the plunger may be more clearly illustrated. 
     The visual indicator on the interface cylinder may take a variety of forms. For example, a portion of or the entire surface of the interface cylinder  98  may include a dark color, a pattern, a bright color, or other readily observable markings. In the embodiment shown in  FIG. 4 , the entire drive rod is a dark color, such as brown or black. Alternatively, at least the end of the drive rod may be bright pink. In another alternative, a black and white pattern is present on the interface cylinder. 
     Cartridge Sensor 
     A pump according to the present invention may be provided with a cartridge sensor  440  configured to confirm whether or not a cartridge is present in the cartridge chamber  80 . In one embodiment of the invention, a cartridge sensor assembly  440  includes a light emitter  442  located opposite a light detector  444  across the cartridge chamber  80  at the closed end  102  of the cartridge chamber  80 , as shown in  FIGS. 4-5 ,  21 - 22  and  29 .  FIGS. 21 and 22  illustrate a pump housing  14  including the drive assembly components, circuit boards  450  and  452 , and a medication cartridge  200  positioned within the cartridge chamber  80 . The closed end  210  of the medication cartridge  200  protrudes from the chamber cartridge opening  28  in  FIG. 21 .  FIG. 22  is a cross-sectional view along line  22 - 22  of  FIG. 21 , through the emitter  442  and the detector  444 . A line  454  connecting the emitter  442  with the detector  444  draws a chord across a top portion of the cylindrical barrel  202  within the cartridge chamber  80 . The chord  454  is provided in  FIG. 22  for illustration purposes only, to show the path of light between the emitter  442  and the detector  444 , and is not part of the pump. The chord  454  does not pass through the drive rod  88  or the plunger  204 . 
     The sensor  440  is preferably positioned on the outside of the cartridge chamber  80 . The detector  444  detects light from the emitter  442  through the partially transparent cartridge chamber wall when the cartridge chamber is empty. By positioning the sensor  440  outside of the cartridge chamber wall  82 , the sensor  440  is less likely to be in contact with fluid or dirt which could affect its operation. As shown in  FIG. 2 , a support  445  and a detent  446  are used to mount and position emitter  442 . Similar structures can be provided to mount the detector  444 . 
     When a medication cartridge  200  is present in the cartridge chamber  80 , the open end  212  of the cylindrical barrel  202  will be adjacent to the closed end  102  of the cartridge chamber  80 . Accordingly, the end of the cartridge barrel  202  will interrupt the light transmission between the emitter  442  and the detector  444 . The sensor  440  may therefore be used to indicate whether a cartridge is present in the cartridge chamber  80 . 
     Typically, a barrel  202  of a medication cartridge  200  is at least partially transparent so that the level of fluid within the reservoir  220  can be viewed. However, at least an end portion of the barrel is preferably sufficiently opaque that it interrupts light transmission between the two sensors. An end portion  282  of the cartridge barrel  202  may be textured or shaded in order to ensure that light transmission is interrupted between the emitter  442  and the detector  444 . The texturing or shading on the cylindrical barrel  202  of the medication cartridge may be provided on an inside surface of the barrel  202 , an exterior surface of the barrel  202 , or throughout the material of the barrel wall. It is also possible for the sensor  440  to be able to detect the cartridge barrel  202  without any texturing or shading present at the end of the cartridge barrel. Preferably, most of the barrel is sufficiently transparent to allow viewing of the medication level, while at least the end portion of the barrel is sufficiently opaque to interrupt light transmission between the emitter  442  and the detector  444 . 
     Idler Gear Sensor 
     The idler gear  126  is intermediate between the motor gear  122  and the drive gear  128  as shown in  FIG. 23 . According to one embodiment of the present invention, a sensor may be provided to determine whether or not a gear in the pump, such as the idler gear  126 , is rotating as a confirmation that the pump is operating normally. Components of an idler gear sensor are described with respect to  FIGS. 23-29 . A magnetic flag  460  may be provided on a front face  461  of the idler gear  126  as shown in  FIG. 24 . The magnetic flag  460  may include a plurality of legs  462  extending from the center of the idler gear to near an outer perimeter of the idler gear. To determine whether or not the idler gear  126  is rotating, a magnetic sensor  468  may be provided within the pump interior near the magnetic flag  460 , as shown in  FIG. 23 . The magnetic sensor  468 , for example, a Hall Effect sensor, can determine the magnetic field at a point near the idler gear  126 . Therefore, as the magnetic field at a point near the idler gear fluctuates because of the rotation of the magnetic flag  460 , the sensor  468  measures the magnetic field. 
     Preferably, the sensor  468  is spaced away from a point on the idler gear that is near the outer diameter of the idler gear. In one embodiment, the magnetic sensor and magnet is configured so that the sensor detects a magnetic field when one of the legs  462  is directly in front of the sensor and detects no field when one of the spaces between the legs  462  is directly in front of the idler gear. As the idler gear rotates, the sensor outputs information indicating the magnetic field. In this configuration, the sensor output is approximately a square wave indicating when the magnetic field is detected and when it is not detected. This information can be used by a processor to confirm that the pump is operating properly, and to signal an alarm or appropriate message if desirable. The processor may also have an input from the motor  118  indicating the number of motor cycles, or encoder counts, occurring over time. Based on the number of times a magnetic field is sensed at the magnetic sensor, the number of encoder counts, and the gear ratios, the processor can confirm that operation is normal. 
     The magnetic sensor  468  is preferably positioned on a circuit board  470 . In order to provide accurate determinations of the magnetic field and consequently the rotation of the idler gear, the magnetic sensor  468  is maintained at a specific distance from the magnetic flag  460  on the idler gear  126 . A bushing  476  may be used to provide a fixed distance between the magnetic flag  460  and the circuit board  470 . The bushing, illustrated in  FIGS. 23 and 26 , includes a hollow cylindrical portion  477  for receiving a shaft end  475  of the idler gear  126 . The hollow portion  477  is defined adjacent to a first end  482  of the bushing  476 . A second end  484  of the bushing  476  is situated opposite from the first end  482 . The second end  484  fits within the opening  488  in the circuit board  470 . Therefore the circuit board is spaced from the magnetic flag  460  by the width W of the widest portion of the bushing  476 . 
     Additional stability for the circuit board  470  may be provided by a drive mechanism chassis, shown in  FIGS. 23 ,  27  and  28 , that supports the three gears of the pump. The drive mechanism chassis includes an opening  492  for a shaft of the motor gear  122 , an opening  493  for a shaft of the idler gear  126 , and an opening  494  for a shaft of the drive gear  128 . In addition, the drive mechanism chassis  490  includes a number of pins that are used to support the circuit board  470 . First pin  496 , second pin  497  and third pin  498  protrude from a front surface  500  of the drive mechanism chassis  490 . The pins protruding from the drive mechanism chassis  490  may be received within openings in the circuit board  470 . In a preferred embodiment, a first pin  496  is received in a first hole  501  on the circuit board. The second pin  497  and the third pin  498  are received in the second hole  502  and the third hole  503 , respectively, of the circuit board  470 . The drive mechanism chassis  490  may be secured to the pump housing by screws through openings  512  and  513  on the chassis, corresponding to openings  515  and  516  on the rear of the pump housing, shown in  FIG. 1 . 
     In the embodiment show in  FIG. 27 , the pins  496 ,  497 , and  498  have a uniform outer diameter slightly less than the diameter of the openings  501 ,  502 , and  503  on the circuit board  470 , so that the pins fit within the openings. In an alternative embodiment, the pins  496 ,  497 , and  498  each have a smaller diameter end portion and a larger diameter base portion. The end portion of each pin fits into the openings  501 ,  502  and  503 . The larger diameter base portion provides a hard stop against which the circuit board  470  can rest. This configuration helps provide the correct spacing between the circuit board and the drive mechanism chassis. 
     Additional stability may be provided to the circuit board  470  by providing a bracket  508  behind the circuit board  470 . A resilient foam layer  506  may also be provided between the circuit board  470  and the bracket  508  to push the circuit board  470  toward the bushing  476 . 
     Pressure Sensor 
     Now referring to  FIGS. 5-6 , in a preferred embodiment of a pump of the present invention, a pressure sensor  550  is also included in the pump  10 . The pressure sensor  550  may be positioned behind the end  554  of the lead screw  136  that interfaces with the drive gear  128 . If the drive rod  88  encounters resistance as it advances into the cartridge chamber  80 , then the lead screw  136  will be pushed back toward the drive gear  128 . As shown in  FIG. 6 , the end  554  of the lead screw  136  contacts a strain element  552  of the pressure sensor. The strain element  552  deflects as a result of pressure from the lead screw. Preferably, the pressure sensor  550  registers even very small deflections caused in the strain element  552 . For example, the pressure sensor  550  could be configured to allow the strain element to deflect about 20 mils or less, more preferably 10 mils or less, and most preferably about 5 mils before sending a signal to the pump&#39;s processor. 
     One reason the drive rod  88  might encounter greater than normal resistance as it advances in a cartridge is an occlusion in tubing connected to a cartridge within the chamber. A blockage in a cannula inserted into a user or at the users infusion site could also be detected by the pressure sensor. Preferably, the processor connected to the pressure sensor alerts the user to a possible occlusion when the strain element deflects. 
     As seen in  FIG. 6 , a portion of the lead screw  136  near end  554  is supported by the drive chassis mechanism  490 . The lead screw  136  is positioned within an opening  494  in the drive mechanism chassis  490 . Within the opening  494 , a Teflon support  556  surrounds the lead screw  136 . The Teflon support provides a low friction interface between the lead screw  136  and its support in the drive mechanism chassis  490  so that the lead screw can more easily rotate and move axially toward the pressure sensor  550  when the drive rod encounters resistance. A top bracket  558  helps maintain the pressure sensor  550  in its proper position. The top bracket  558  includes an opening  560  that is aligned with an opening  512  on the drive mechanism chassis. Bracket opening  560 , chassis opening  512  and pump housing opening  515  may receive a screw or other structure for holding the top bracket  558  and the drive mechanism chassis  490  in a stable position with respect to the pump housing  14 . 
     In one embodiment, the pressure sensor  550  is configured to detect a negative pressure in the system that would pull the plunger and drive rod toward the open end of the cartridge chamber. A negative pressure might occur if a vacuum was drawn on the cartridge or tubing, if the medication freely flowed from the cartridge, or if the cartridge was removed from the cartridge chamber. The strain element  552  is spring-loaded so that it could deflect toward the lead screw if the drive rod was pulled toward the open end of the chamber. A deflection of the strain element toward the open end of the cartridge is communicated to the processor, and this information may cause an alarm or may be taken into account in pump operations, such as the cartridge loading process. 
     Pump System 
       FIG. 30  is a functional block diagram illustrating one of many possible embodiments of a medication pump, generally identified as  600 . A microprocessor  602  is in electrical communication with and controls a pump motor  118 , a display  44 , an audio alarm  608 , and a vibratory alarm  129 . The pump motor  118  causes the actuation of the drive rod or drive mechanism  88  that pushes the plunger  204 . 
     Other embodiments can use a microcomputer, or any other type of programmable circuit, in place of the microprocessor. Further possible functions of the processor and other pump components are described and illustrated in the following four commonly assigned co-pending United States patent applications, which were previously incorporated by reference: “Insulin Pump Having Missed Meal Bolus Alarm” U.S. application Ser. No. 10/087,460, now U.S. Pat. No. 6,744,350, “Programmable Medical Infusion Pump Displaying a Banner” U.S. application Ser. No. 10/087,205, “Programmable Insulin Pump” U.S. application Ser. No. 10/086,641, now U.S. Pat. No. 6,852,104 and “Programmable Medical Infusion Pump” U.S. application Ser. No. 10/087,449. 
     The display  44  can have many different configurations such as an LCD display. The display  44  displays various items of information that are useful to a patient or caregiver. The audio alarm  608  may be a beeper. Similar to other portable electronic devices such as a cellular telephone, the vibratory alarm  129  provides an alarm when an audible beep would be disruptive. A user can selectively enable or disable the audio  608  and vibratory  129  alarms. In one possible embodiment, however, both the audio  608  and vibratory  129  alarms cannot be disabled at the same time. 
     The microprocessor  602  is in electrical communication with both a random access memory (RAM)  616  and a read only memory (ROM)  618 . The RAM  616  is a static RAM that stores data that can change over time such as pump settings and a historical log of events experienced by the pump  600 . The ROM  618  stores code for the operating system and the application programs. The ROM  618  can be any type of programmable ROM such as an EPROM. In one possible embodiment, the RAM  616  has about 500 kilobytes of memory capacity and the ROM  618  has about 2 megabytes of memory capacity. 
     An infrared (IR) port  620  is in electrical communication with the microprocessor. The IR port  620  may provide data communication with an external device such as a computer for programming an application program, programming pump settings, and downloading historical data logs. The pump  600  can include other types of communication ports in place or in addition to the IR port  620 . Examples of other possible communication ports include a radio frequency (RF) port or a port that provides a hard-wired data communication link such as an RS-232 port. The IR port  620  may be located within the pump housing as shown in  FIG. 29  and includes an IR emitter and an IR detector. The IR port  620  may be positioned adjacent to two openings  624  and  626  in the pump housing  14 , as seen in  FIGS. 1 and 4 , for allowing communication with the IR emitter and IR detector. 
     Again referring to  FIG. 30 , a real-time clock  622  provides a clock signal to the microprocessor  602 . An advantage of having a real-time clock  622  is that it provides the program with the actual time in real-time so that the application program can track and control the actual time of day that insulin delivery and other events occur. 
     A keypad  40  also provides input to the microprocessor  602 . Although other possible types of keypads are possible, one type of keypad has four buttons and is a membrane-type of keypad, which provides resistance to water and other environmental conditions. As explained in more detail below, the keypad  40  contains soft keys in that the function of the keys can change as a user executes different menu selections and commands. 
     Other inputs into the microprocessor  602  include the pressure sensor  550 , which is sensitive to the pressure within a reservoir of medication, the cartridge sensor  440  which is sensitive to the presence of a medication cartridge within the medication chamber, and the motion detector or idler gear sensor  468 , which detects motion of a gear. 
     The pump may also include a bolus button  25  for allowing the user to administer a dose of medication. The depression of the bolus button  25  may provide feedback to the user, such as a beep, a tone, or vibration of the pump. The bolus button  25  communicates with the processor  602  to instruct the processor to activate the pump motor  118  so that the drive rod  88  is moved a specified distance, thereby providing the user with a specified dose of medication. The bolus button  25  can be seen within the pump housing  14  in  FIG. 1 . The bolus button  25  fits within a bolus button cavity  37 , best seen in  FIG. 2 . 
     Many elements of the pump  600  may be positioned within one or more circuit boards within the pump housing  14 . For example, the microprocessor  602 , the RAM  616 , ROM  618 , real-time clock  622 , and a driver for the display  44  may be positioned on a circuit board. In a preferred embodiment, a top circuit board  450  is positioned above a bottom circuit board  452  within the pump housing  14 , as seen in the cross-sectional view of  FIG. 22  and the exploded view of  FIG. 35 . Now referring to  FIG. 35 , the top circuit board  450  may include an opening  454  and the bottom circuit board  452  may include a corresponding opening  455 . The openings  454  and  455  may receive a screw or other connecting structure to allow the circuit boards  450 ,  452  to be secured to the pump housing  14  via opening  515  in the pump housing  14  ( FIG. 1 ). Preferably, top circuit board  450  is electrically connected to bottom circuit board  452  using a flexible electrical connector. The electrical connector may emerge from the bottom circuit board  452  at the connection location  456  and then attach to the top circuit board  450  at a location above the connect location  456 . 
     Cartridge Detection and Loading Process 
     The cartridge sensor  440  at the rear most part of the cartridge chamber  80  senses whether the rear edge of the cartridge is positioned at the rear edge of the chamber  80 . This information may be used to ensure proper operation of the pump. For example, if the cartridge is removed while the pump is running, an alarm will sound to protect against non-delivery or a free flow of medication. If a cartridge is present in the chamber, but the pump is not programmed to deliver medication, an alarm may be programmed to sound to notify the user that the pump is not running. If no cartridge is present in the cartridge chamber, the user can be notified. 
     Information from the cartridge sensor  440  may also facilitate the cartridge loading process. An auto-loading process may be programmed into the pump microprocessor  602  and assist the user in loading the cartridge. Information from the pressure sensor  500  or idler gear sensor  126  may also be used in the cartridge loading process.  FIGS. 31-33  are flowcharts illustrating one cartridge loading process. In order to load a new cartridge, first a user fills a new cartridge at step  650  and removes the pump cap  16  at step  654 . Any old cartridge already within the chamber  80  is removed at step  658 , and the user selects the load cartridge menu at step  702 . 
     Alternatively, the pump may detect when a cartridge is removed as shown in step  659  and automatically enter the new cartridge menu as a result. There are situations where a user will want to remove the cartridge briefly and then put it back in. For example, the user may want to look for air bubbles in the cartridge. In this situation, it may not be necessary to enter the load cartridge menu. The pump may be alert for this situation and not enter the load cartridge menu if a user is removing the cartridge only to check it, not to change it. For example, if the cartridge is more full than a certain threshold level, the pump may assume that the user is checking the cartridge when the cartridge is removed. However, to ensure the user is not unknowingly without medication, the pump may alternatively warn the user and ask the user if she is checking the cartridge or changing the cartridge at step  700 . If the user responds that she is checking the cartridge, the pump may maintain the drive rod in the same position, or may slightly extend the drive rod so that it is easy for the user to reattach the drive rod to the cartridge. If the user does not respond or responds that she is changing the cartridge, then the pump may automatically enter the new cartridge menu at step  701 . However, to ensure that the cartridge is properly attached to the drive rod after a cartridge is checked, the pump may be programmed to automatically enter the new cartridge menu whenever the cartridge is removed, as shown in  FIG. 31 . In this case, the pump may query the user at step  703  whether she is checking or changing the cartridge, and may use the answer to that question later in the loading process to determine the best initial loading position for the drive rod. 
     Once the load cartridge menu is initiated, the pump checks the cartridge sensor  440  to determine if the rear portion of a cartridge is detected at the rear of the chamber at step  704 . Typically, no cartridge will be detected at step  704  because the pump has not retracted the new cartridge and the old cartridge has already been removed by the user. 
     If no cartridge is detected, the motor may be activated to move the drive rod to an initial loading position at step  706 . The initial loading position may be fully extended, fully retracted, or somewhere in between, depending on the typical initial plunger position within the cartridge. One preferred initial loading position is between the starting point and the ending point of the distance that the drive rod traveled during delivery of the medication in the previous cartridge. Preferably, the initial loading position is approximately halfway between the starting point and ending point for delivery during the previous cartridge. For example, if the drive rod traveled about 1 inch during delivery of the previous cartridge, the drive rod will be retracted about 0.5 inch at step  706 . The automatic retraction of the drive rod to an initial loading position is designed to save the user&#39;s time when loading the cartridge. The pump is typically designed to deliver fairly small doses of medication over a long period of time. The full retraction and advancement of the drive rod can therefore take a relatively long period of time. By retracting the drive rod partially, the pump gets a head start on the retraction of the cartridge all the way into the pump. 
     It is also possible, though not preferred, for the pump to retract fully to the rear of the chamber before the cartridge is loaded. Full retraction is not necessary unless the new cartridge is completely full. If the new cartridge is not completely full, and the drive rod has been fully retracted, the drive rod will have to be advanced in order for the plunger to be attached to the drive rod. Therefore, it is preferable to underestimate the amount that the drive rod will need to be retracted in order to pull the cartridge to the rear of the chamber. In addition, the pump system can take advantage of the fact that most users will fill new cartridges to approximately the level of the previous cartridge. By retracting the drive rod half of this distance, the drive rod is unlikely to be retracted an unnecessary distance. 
     In determining the initial loading position in step  706 , the pump may take into account whether the user removed the previous cartridge in order to install a new cartridge or merely to check the existing cartridge for some reason, such as checking for air bubbles. If the user previously responded at step  703  that they were removing the cartridge to check it, then the initial loading position in step  706  may be the same position or slightly extended from the position it was in when the cartridge was removed. 
     If a cartridge was detected at step  704 , then the user is reminded to make sure that the old cartridge has been removed. If the old cartridge was not already removed, the user does so at step  710 . The user attaches the new cartridge to the drive rod interface structure  98  at step  710 . The process used to attach a cartridge to the drive rod was previously described. Then the user selects a load cartridge command using the display  44  and keypad  40  at step  714 . The cartridge sensor  440  is checked to determine if a cartridge is present at the rear of the chamber at step  718 . The pump does not expect a cartridge to be present at the rear of the chamber because the retraction process has not yet been initiated. If no, the steps illustrated in  FIG. 32  are followed. If yes, the steps illustrated in  FIG. 33  are followed. 
     If a cartridge is detected at the rear of the chamber in step  718 , before the drive rod has retracted beyond the initial loading position, this indicates that possibly the old cartridge was never removed or the cartridge is less full than a minimum amount. Detection of a cartridge at step  718  could also indicate that the new cartridge is considerably less full than the old cartridge, such as less than about half of the previous cartridge. In this situation, the cartridge might have been fully inserted into the chamber without having the plunger engaged with the interface structure  98 . For example, if the previously delivered cartridge was initially completely full and all of the medication was delivered, the drive rod traveled the full distance of the cartridge chamber during delivery of that cartridge. The initial loading position of the drive rod for the next cartridge would be halfway extended. However, if the next cartridge was only one-eighth full, the cartridge could be inserted fully in the chamber without contacting the plunger, resulting in detection of a cartridge although the plunger has not yet been attached to the drive rod. 
     If a cartridge is detected at the rear of the chamber in step  718 , the user is prompted to remove the cartridge at step  724 . The user then removes the cartridge and acknowledges the removal at step  728 . The cartridge sensor  440  is again checked to see if the cartridge has been removed at step  732 . If not, the process returns to step  724  where the user is again instructed to remove the cartridge. If the cartridge has been removed, the pump displays a message indicating that the user needs to wait at step  734  while the pump fully advances the drive rod at step  738 . By fully advancing the drive rod, the pump ensures that the interface cylinder can be attached to the plunger regardless of the fullness of the cartridge. While the drive rod is fully advanced, the processor recalibrates the fully extended drive rod position to ensure accuracy of future position calculations. The processor also recalibrates the drive rod position when it is fully retracted. After the drive rod is fully advanced at step  738 , the user is prompted to attach the new cartridge at step  710  and then selects a load cartridge option at step  714 . 
     The pump may be calibrated to know when the drive rod is at full extension and full retraction. By observing the encoder counts from the motor  118 , the intermediate positions of the drive rod may also be calculated. The pump may calculate the beginning position of the drive rod when a cartridge is initially loaded. By knowing the starting position and the intervening encoder counts, the amount of medication expelled from the cartridge may be tracked by the pump. 
     If a cartridge is not detected at step  718 , then the process illustrated in  FIG. 32  is followed. The pump retracts the drive rod at step  742 , which should now be attached to the plunger of the cartridge, until the rear of the cartridge is detected by the cartridge sensor  440 , the motor stalls, or the drive rod is fully retracted. The pump may also use the pressure sensor  550  to determine when the drive rod is fully retracted where the pressure sensor is pre-loaded to detect negative pressures on the drive rod. If the cartridge is detected, the pump calculates the cartridge volume based on how far the drive rod was retracted before a cartridge was detected at step  750 . The pump begins a priming program, and prompts the user to attach the pump cap  16  and an infusion set to the delivery end of the cartridge at step  754 . Once the cap and an infusion set are attached at step  758 , the user initiates the priming process at step  762 . 
     If at step  746 , the motor stalled or the drive rod was determined to be fully retracted through other detection methods before a cartridge was detected, then the pump displays an install cartridge alert at step  764 . If this occurs, two possible causes would be that the user never inserted a new medication pump or the cartridge sensor is not functioning properly. The cartridge sensor is again checked at step  766 . If a cartridge is detected, the user is instructed to remove the cartridge at step  768  to confirm that the cartridge sensor is working properly. The pump checks for a state change at the cartridge sensor at step  770  to confirm that the cartridge was removed. If the cartridge was removed, the pump fully advances the drive rod and recalibrates the drive rod position when it is fully extended at step  772 . Because of the preceding cartridge sensor checks, the system ensures that there is no cartridge sensor in the chamber when the drive rod is fully advanced. The process then returns to step  710  on  FIG. 31  where the user is prompted to attach a new cartridge. 
     Child Safety Cap 
     It may be desirable to configure the pump cap  16  to require some dexterity and strength to operate, so that it is difficult for a young child to open the cap. Now referring to  FIGS. 38-40 , in one embodiment, a safety cap cover  800  may be configured to snap over the standard pump cap  16 . The pump cap  16  is illustrated in FIGS.  1  and  17 - 20 . The cap cover  800  may have a first pump end  802  and a second delivery end  804 . At both ends, the cap cover  800  preferably defines openings to allow passage of an infusion set for attachment to the user. At the attachment end  802 , a lip  808  may be included that can fit around the pump end  410  of the pump cap  16 . The lip  808  may be discontinuous, as illustrated in  FIG. 38 , to facilitate snapping the cap cover  800  over the pump cap  16  and removing it when it is no longer desired. A wall  809  extends between the pump end  802  and the second delivery end  804 , including a first portion  810  of the wall that has a truncated cone shape. The wall of the first portion  810  is preferably sufficiently flexible so that an adult of normal strength can squeeze the first portion  810  of the cap cover to apply torque to the pump cap  16 . When the wall of the first portion  810  is squeezed, the cap cover  800  moves between a first shape or state and a second shape or state. In the first state, the cover  800  rotates freely around the pump cap  16 . In the second state, the safety cap cover contacts the exterior surface of the pump cap so that the cap cover  800  does not rotate freely. In the second state or position, the user may apply torque to the pump cap  16  through the cap cover  800 . Alternatively, the pump cap may be configured so that the user can press down on the cap cover  800  while turning the cap cover  800  to apply torque to the pump cap  16 . 
     Structures on the pump cap  16  or the cap cover  800  can facilitate the rotation of the pump cap  16 . For example, the gripping structures  422  on the exterior surface of the pump cap  16  shown in  FIG. 17  may make it easier for the user to grip the pump cap surface through the cap cover  800 . Preferably, the gripping structures  422  are constructed of an elastomeric material. Alternatively, or in combination with the gripping structures  422 , mating gripping structures  812  may be included on an internal surface  814  of the first portion  810  of the wall  809  of the cap cover, as shown in  FIG. 38 . The inclusion of gripping structures on the cap cover, pump cap, or both, prevent the cap cover from slipping as it is pressed against the pump cap. 
     In an alternative embodiment of a pump cap that is difficult for children to open, an outer shell similar to the cap cover  800  is integral with the pump cap  16 . The outer shell may rotate freely on the pump cap unless the outer shell is squeezed or pressed down while it is turned. 
     Belt Clip Attachment 
     An attachment device may be provided and used with the pump  10  that is useful for attaching the pump to a belt clip or another holding device. One example of a belt clip attachment device  850  is shown in  FIGS. 36-37 . The attachment device  850  includes a first protrusion  852  and a second protrusion  854 . The first protrusion  852  is configured to be inserted into a first slot  856  on the top of the pump housing  14 , as shown in  FIG. 1 . The second protrusion  854  is configured to be inserted into a second slot  858  on the bottom portion of the housing  14  as shown in  FIG. 29 . A main body portion  860  of the attachment device  850  rests against the back side of the pump housing  14 , opposite the display area. The attachment device  850  may also include a third protrusion  862  that can be used to further support the pump  14  within the attachment  850 . The device  850  may also include a pivot point  864 . The pivot point may be the point of attachment between the attachment device  850  and another structure, such as a belt clip. The pivot point  864  may allow the body  860  of the attachment device  850  to rotate with respect to the other device to which it is attached. This rotation allows for maximum comfort of the pump user. For example, if the pump  10  is attached to a belt clip using the clip attachment device  850 , then the pump may be rotated to the optimal position when the user is seated. The pivot point may be positionable between several discrete positions. Belt clips that can receive a pivot point similar to pivot point  864  are well known. 
     Alternatively, the pump may be positionable in one of several orientations in the belt clip, but may not be allowed to rotate freely between those positions. Free rotation of the pump may cause kinking of the tube. In this scenario, the user would remove the attachment device from the belt clip in order to move the pump to a different orientation relative to the belt clip. 
     The various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. Those skilled in the art will readily recognize various modifications and changes which may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein and without departing from the true spirit and scope of the present invention which is set forth in the following claims.