US20140276569A1 - System and method for detecting presence of an infusion cartridge in an infusion pump - Google Patents

Abstract

Infusion devices, systems, and methods can detect a presence or absence of an infusion cartridge in an infusion pump. Embodiments may include a loading sequence, recording loading pulse width modulation (PWM) commands applied to an infusion pump motor during the loading sequence, setting a value of threshold PWM commands based on the commands applied during the loading sequence and comparing values of operational PWM commands applied during pumping operations to the value of the threshold PWM commands. If the value of the operational PWM commands drops below the threshold by a predetermined amount, a missing infusion cartridge warning may be generated.

Description

BACKGROUND
• There are many applications in academic, industrial, and medical fields, as well as others, that benefit from devices and methods that are capable of accurately and controllably delivering fluids, including liquids and gases that have a beneficial effect when administered in known and controlled quantities. Such devices and methods are particularly useful in the medical field where treatments for many patients include the administration of a known amount of a substance at predetermined intervals.
• Insulin-injecting pumps have been developed for the administration of insulin for those suffering from both type I and II diabetes. Continuous subcutaneous insulin injection and/or infusion therapy with portable infusion device has been adapted for the treatment of diabetes. Such therapy may include the regular and/or continuous injection or infusion of insulin into the skin of a person suffering from diabetes and offer an alternative to multiple daily injections of insulin by an insulin syringe or an insulin pen. Such pumps can be ambulatory/portable infusion pumps that are worn by the user that may use replaceable cartridges. Examples of such pumps and various features that can be associated with such pumps include those disclosed in U.S. patent application Ser. No. 13/557,363, U.S. patent application Ser. No. 12/714,299, U.S. patent application Ser. No. 12/538,018, U.S. Provisional Patent Application No. 61/655,883, U.S. Provisional Patent Application No. 61/656,967 and U.S. Pat. No. 8,287,495, each of which is incorporated herein by reference.
• There are, however, some drawbacks associated with the use of subcutaneous injection syringes and/or some currently available infusion pumps for the delivery of insulin and other medicaments. Some commercially available pumps may have an interchangeable infusion cartridge containing insulin and/or other medicaments. The correct attachment of this interchangeable infusion cartridge is important for the proper delivery of medicament. For instance, the cartridge may inadvertently become detached or may not be attached to the pump, resulting in possible inaccuracies in treatment and other issues.
• Therefore, there is a need for a system and a method for detecting the presence or absence of the infusion cartridge in the infusion pump.
SUMMARY
• Disclosed herein are systems and methods for detecting the presence of an interchangeable infusion cartridge in an infusion pump and particularly in a portable or ambulatory infusion pump. In some embodiments, the method may include installing an infusion cartridge in an infusion pump, initiating an infusion cartridge loading sequence, recording loading pulse width modulation (PWM) commands applied to an infusion pump motor, setting a value of threshold PWM commands, comparing values of operational PWM commands applied during pumping operations to the value of the threshold PWM commands, and generating a missing cartridge indication whenever the value of an operational PWM command drops below the value of the threshold PWM commands by a predetermined amount.
• In some embodiments an infusion system is provided. The infusion system may be configured for detecting a presence or absence of an infusion cartridge. The infusion system may include an infusion cartridge and an infusion pump. The infusion cartridge may include a delivery mechanism for effectuating delivery of fluid having an axial bore, a spool which may be disposed within the axial bore and axially translatable within the axial bore, and a drug delivery reservoir for storing fluid. The infusion pump may include a drive mechanism and a processor. The processor may be coupled to a memory configured for receiving input data from the memory and using input data for generating operational parameters for the infusion system. Programming may be stored in the memory for execution by a processor to control a closed-loop motor control algorithm. The closed-loop motor control algorithm may be configured for generating PWM commands that operate a motor of the drive mechanism, and to indicate an absence of the infusion cartridge if the value of the operational PWM command falls below the predetermined value the threshold PWM commands.
• Certain embodiments are described further in the following description, examples, claims, and drawings. These features of embodiments will become more apparent from the following detailed description when taken in conjunction with the accompanying exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a flowchart illustrating a method embodiment for detecting the presence of an interchangeable infusion cartridge in an infusion pump.
• FIG. 2 is an exploded view of an embodiment of an infusion cartridge and an infusion pump with the infusion cartridge removed from the infusion pump.
• FIG. 3 is a block diagram representing an embodiment of an infusion pump.
• FIG. 4 is an elevation view in partial section of a delivery mechanism embodiment of the infusion cartridge embodiment ofFIG. 2 coupled to a drive mechanism embodiment.
DETAILED DESCRIPTION
• Provided herein are systems, devices and methods for continuous or semi-continuous monitoring of the absence or presence of an interchangeable infusion cartridge in an infusion pump, and particularly in a portable or ambulatory infusion pump utilizing a replaceable cartridge containing insulin and/or other medicaments for the treatment of diabetes. Some embodiments may include advances in the internal components, the control circuitry, and improvements in a user interface of the systems and devices. The advances may allow for a safer and more accurate delivery of medicament to a patient than is currently attainable today from other devices, systems, and methods. Although embodiments described herein may be discussed in the context of the controlled delivery of insulin, delivery of other medicaments, including, for example, glucagon, pramlintide, etc., as well as other applications are also contemplated, other applications are also contemplated. Device and method embodiments discussed herein may be used for pain medication, chemotherapy, iron chelation, immunoglobulin treatment, dextrose or saline IV delivery, or any other suitable indication or application. Non-medical applications are also contemplated.
• It should be noted that labels associated with operations described herein do not necessarily represent an order in a sequence; rather, they are used only to uniquely identify each operation. The words “loaded”, “written”, and “programmed” are used interchangeably in this document when they refer to a processor or a memory device. The terms “pump” and “infusion pump” may be used interchangeably throughout the document as may be the terms “fluid” and “liquid medicament.” In addition, the terms “pulse width modulation (PWM) commands” and “PWM commands” interchangeably represent a series of electrical pulses provided to power an electric motor of the infusion pump. A value, of PWM commands generally represents a duty cycle of the series of pulses during a command sequence. For example, if the PWM is 100% with an input voltage of 3.0 volts, the output will be 3.0 volts. If the PWM command is 50%, the output voltage of the same 3.0 volt input would be 1.5 volts.
• FIG. 2 depicts an embodiment of aninfusion pump system100 with aninfusion cartridge16 detached from the full-featuredinfusion pump device12. Thepump12 can include anattachment mechanism64, positioned within thefirst receiving slot22 that corresponds to areceiving mechanism62 at an end of theinfusion cartridge16. The attachment and receiving mechanisms can be configured to removably couple to each other to provide for an interchange of cartridges within theslot22. The coupling keeps an interior of the cartridge and interior of the pump sealed from the surrounding environment such that fluid is retained within the volumes even under significant pressure. This attachment embodiment may be configured to produce a leak free detachable coupling that can withstand significant pressure. Thereceiving mechanism62 may be configured to detachably couple with theattachment mechanism64 such that theinfusion cartridge16 may be removably attached to thehousing26 of theinfusion pump12 for fluid delivery. In this embodiment, theattachment mechanism64 may include apneumatic tap66 having an O-ring or other sealing device. Thecorresponding receiving mechanism62 may include a port through which thepneumatic tap66 may be inserted. Areservoir fill port76 may be disposed on a top portion of theinfusion cartridge16. In some cases, the desired fluid may be manually dispensed from the interior volume of a syringe or other source, through the reservoir fillport76 and into the interior volume of theinfusion cartridge16.
• FIG. 3 illustrates a block diagram of some features that may be incorporated within thehousing26 of theinfusion pump12. Theinfusion pump12 may include amemory device30, a transmitter/receiver32, analarm34, aspeaker36, a clock/timer38, aninput device40, aprocessor42, a user interface such as a graphical user interface (GUI)60 having a touchsensitive screen46 with input capability, adrive mechanism48, and anestimator device52. Thememory device30 may be coupled to theprocessor42 to receive and store input data, and to communicate that data to theprocessor42. The input data may include user input data and sensor input data. The input data from thememory device30 may be used to generate operational parameters for theinfusion pump12. The GUI60 may be configured for displaying a request for the user to input data, for receiving user input, data in response to the request, and communicating that data to the memory. TheGUI60 can also be configured to display a missing infusion cartridge indication/warning as discussed herein.
• Theprocessor42 can function to control the overall operation of the pump.Processor42 may communicate with and/or otherwise control the drive mechanism, output/display, memory, transmitter/receiver, and the like.Processor42 of the infusion pump may communicate with a processor of another device, such as a continuous glucose monitor, a remote controller/commander, etc.Processor42 may include programming that can control the infusion of insulin or other medicament from the cartridge, the data, to be displayed by the display, the data to be transmitted via the transmitter, etc. Part of the programming may be configured to control anelectric motor170 depicted inFIG. 4.Processor42 may also include programming that may allow the processor to receive signals and/or other data from an input device, such as a sensor sensing pressure, temperature, and the like. Theprocessor42 may be included as a part ofinfusion pump12 or may be used in conjunction therewith.
• According to an embodiment, a motor control program may be stored in thememory30 for retrieval by theprocessor42 to operate a closed-loop motor control algorithm. The closed-loop motor control algorithm may be configured for generating PWM commands. The PWM commands may be, e.g., a series of uniform amplitude voltage pulses that are used to measure the command input into the motor. The PWM commands may be coupled, to theelectric motor170 to power adrive mechanism48. An embodiment of the motor control algorithm may be a velocity loop algorithm. Such a velocity loop algorithm can be a proportional-integral-derivative (PID) loop in which motor velocity is the controlled output. A value of the PWM commands may be proportional to a load on theelectric motor170. The load may differ greatly, depending on the presence or absence of aninfusion cartridge16. In the case where theinfusion cartridge16 is absent, a smaller load may indicate this absence.
• Theprocessor42 may also include additional programming to allow theprocessor42 to learn user preferences and/or user characteristics and/or user history data. For instance, to implement changes in use, suggestions based on detected trends, such as, weight gain or loss, and may include programming allowing the device to generate reports, such as user history, compliance, trending, and/or other such data. Additionally, infusion pump embodiments of the disclosure may include a “power off” or “suspend” function for suspending one or more functions of the device, such as, suspending a delivery protocol, and/or for powering off the device or the delivery mechanism thereof. For some embodiments, two or more processors may be used for controller functions of the infusion pumps, including a high power processor and a low power processor used to maintain programming and pumping functions in low power mode in order to, e.g., save battery life.
• Housing26 of theinfusion pump12 may be functionally associated with an interchangeable and aremovable glucose meter20 and/orinfusion cartridge16. Theinfusion cartridge16 may have anoutlet port54 that may be connected to an infusion set (not shown) via an infusion set connector18 (as shown inFIG. 2).
• Referring now toFIG. 1, a flowchart depicting a top-level view of amethod200 according to embodiments of the present disclosure is illustrated. Themethod200 includes detecting the presence or absence of an infusion cartridge in an infusion pump. In somecases method200 may include two phases, acalibration phase210 and apumping phase220.
• Method200 may start thePWM calibration phase210 at operation S211. In operation S211, an infusion cartridge may be installed in an infusion pump such as, for example, as described above. In operation S212, an infusion cartridge loading sequence may be initiated. During the loading sequence an electric infusion pump motor, propelling a chive mechanism, may engage a fluid delivery mechanism within the infusion cartridge. The engaged fluid delivery mechanism may represent a specific load on the infusion pump motor. In operation S213, PWM commands applied on the infusion pump motor during the loading sequence may be recorded into memory. For example, the PWM commands may have a percent/value ranging from 20% to 80%. In operation S214, an average value of the recorded PWM commands may be calculated. In operation S215, a value threshold of the PWM commands may be set to be the average value of the recorded PWM commands may be, for example, 52%. Because thePWM configuration procedure210 can be clone each time a cartridge is loaded, the threshold can be set at an appropriate value for each specific cartridge. This is advantageous because the load that each cartridge imparts on the motor can vary greatly.
• After a threshold value has been established for a particular cartridge, apumping phase220 can be begun. In operations S221 and S222, during thepump phase220, applied values of the operational PWM commands may be recorded and the average values of those operational PWM commands may be calculated. The PWM commands can be recorded and averaged for the duration of each distinct motor move. In operations S223 and S224, during each subsequent motor move in a pumping cycle, the average value of the operational PWM commands may be compared to the threshold value of the PWM commands. For example, the average value may be somewhere between 40% and 90%.
• If an average value of the operational PWM commands is smaller, by a predetermined amount, than the value of the threshold PWM commands, a missing infusion cartridge indication/warning may be generated inoperation225, and the pumping may be halted. In some embodiments, the average value of more than one motor move must deviate from the threshold to generate an alarm. In one embodiment, the alarm is generated if two motor moves in a row generate an average PWM value greater that deviate from the threshold by the predetermined amount. In certain embodiments, the number of motor move values that must cross the threshold to generate an alarm can be adjusted to vary the sensitivity of the alarm. If an average value of the operational PWM commands is larger, by the predetermined value, than the value of threshold PWM commands, the pumping may continue inoperation221. In one example, the predetermined amount may be 10%. Thus, in the example in which the threshold value was 52%, of the average value of the operational commands is below 42%, the alarm is generated.
• The predetermined value may be selected and set differently based on a selected pumping speed. For example, for a low pumping speed the predetermined value may be in the range of 20%-40% of the value of the threshold PWM command, for a high pumping speed the predetermined value may be in the range of 40%-60% of the value of the threshold PWM command, in one embodiment, thisloop220 can be conducted continuously in order to indicate that a cartridge is absent as soon as possible when a cartridge. Is dislodged or removed.
• FIG. 4 depicts an embodiment of portion of an infusion cartridge such asinfusion cartridge16 including thedelivery mechanism120, as well as a portion of thedrive mechanism48 of an infusion pump such as infusion pump12 with which themethod200 described above can be employed. Thedelivery mechanism120 may be configured to deliver fluid from a collapsibledrug delivery reservoir68 via a collapsible or variable volume element of aspool106. For the embodiments discussed herein, the variable volume elements may include constrained variable volume elements that are mechanically constrained to vary between a minimum volume and a maximum volume. Thedelivery mechanism120 may include a delivery mechanism body102, or housing, and anaxial bore104 disposed in the delivery mechanism body102. Theaxial bore104, may have a substantially round transverse cross section that may include adistal end144, aproximal end148 disposed towards thedrive mechanism48 of theinfusion pump system100, areservoir inlet port108, afluid outlet port114, a vent inlet port112, and avent outlet port116. Thespool106 may also have a substantially round transverse cross section, which may be slidingly disposed within theaxial bore104 and may form a constrainedvariable volume122 and a second ventedvolume154 with theaxial bore104. Thedrive mechanism48 may include a rack andpinion mechanism174 actuated by anelectric motor170 through agear box172.
• The constrainedvariable volume122 of thedelivery mechanism120 may be positionable to overlap thereservoir inlet port108 independent of an overlap of thefluid outlet port114. The constrainedvariable volume122 may be formed between afirst seal140 around thespool106, asecond seal142 around thespool106, an outer surface of the spool body between the first andsecond seal140 and142 and an interior surface of theaxial bore104 between the first andsecond seal140 and142. The first andsecond seals140 and142 are axially moveable, relative to each other so as to increase a volume of the constrainedvariable volume122 when the first andsecond seals140 and142 are moved away from each other, and decrease the constrainedvariable volume122 when the first andsecond seals140 and142 are moved closer together.
• Thesecond seal142 may be disposed on aproximal section134 of thespool106 and may move in conjunction with movement of theproximal section134 of thespool106. A proximal end of thespool136 may be coupled to aball portion178 of adrive shaft176 of thedrive mechanism48 of theinfusion pump12. Thedrive mechanism48 may include a rack andpinion mechanism174 actuated by anelectric motor170 through agear box172. As such, thesecond seal142 may move or translate axially in step with axial translation of thespool106 and driveshaft176. Thefirst seal140, however, may be disposed on adistal section128 of thespool106 which may be axially displaceable with respect to the main section190 of thespool106. Thedistal section128 of thespool106 may be coupled to the main section of the spool by anaxial extension156 that may be mechanically captured by acavity158 in themain section132 of thespool106. This configuration may impart a predetermined amount of controlled axial movement between thedistal section128 of the spool and themain section132 of thespool106 and may translate the constrainedvariable volume122 from thereservoir inlet port108 to thefluid outlet port114. This configuration may expand or contract the constrained variable volume112 of thespool106 by exerting translational axial force through a boundary section of the constrainedvariable volume122.
• For some embodiments, a volume of a “bucket” of fluid dispensed by a complete and full dispense cycle of thespool106 may be approximately equal to the cross-sectional area of theaxial bore104 multiplied by the length of displacement of the captured axial extension of the spool for thedistal section128. The complete bucket of fluid may also be dispensed in smaller sub-volumes in increments as small as a resolution of thedrive mechanism48 allows. For some embodiments, a dispense volume or bucket defined by the constrainedvariable volume122 of thedelivery mechanism120 may be divided into about 10 to about 100 sub-volumes to be delivered or dispensed. In some cases, the maximum axial displacement between thedistal section128 and main section of thespool132 may range from about 0.01 inch to about 0.04 inch; more specifically, from about 0.018 inch to about 0.022 inch.
• For some embodiments, theaxial bore104 of the delivery mechanism may have a transverse dimension or diameter ranging from about 0.04 inches to about 0.5 inches; more specifically, from about 0.08 inches to about 0.15 inches. For some embodiments, thespool106 may have a length ranging from about 10 mm to about 40 mm; more specifically, from about 15 mm to about 20 mm. Thespool106 and housing of thedelivery mechanism48 may be made from any suitable material or materials, including polymers or plastics such as polycarbonate, PEEK, thermoplastics, cyclic olefin copolymer, and the like. In some cases, the seals disposed on the spool may have an outer transverse dimension or diameter that may be slightly larger than that of thespool106. In some instances, the seals on the spool may have an axial thickness ranging from about 0.01 inches to about 0.03 inches and may be made from materials such as butyl, silicone, polyurethanes or the like having a shore hardness ranging from about 65 A. to about 75 A and, more specifically, about 70 A.
• In some instances, a second ventedvolume154 of thedelivery mechanism120 may be formed by thespool106 andaxial bore104 of thedelivery mechanism48. The second ventedvolume154 may be formed by athird seal150 disposed around thespool106 and afourth seal152 also disposed around the spool and axially separated from thethird seal150. The axial separation between the third andfourth seals150 and152 forming the second ventedvolume154 may be greater than the axial separation between the vent inlet port112 and ventoutlet port116 of theaxial bore104 in some instances. The second ventedvolume154 may be formed by an outside surface of thespool106 between the third andfourth seals150 and152 and an inside surface of theaxial bore104 between the third andfourth seals150 and152.
• The second ventedvolume154 may be axially displaceable with the movement of thespool106 and may also be positionable by such axial displacement in order to simultaneously overlap the second ventedvolume154 with the vent inlet port112 and thevent outlet port116 of theaxial bore104. Such an overlap of both the vent inlet port112 and thevent outlet port116 may put these ports in fluid communication with each other, and may allow an equilibration of pressure between the first ventedvolume80 of theinfusion cartridge16 and the environment surrounding thevent outlet port116. In most cases, thevent outlet port116 may be in communication with the atmosphere and air may pass from the environment surrounding thevent outlet port116, through the second ventedvolume154 of theaxial bore104, and into the first ventedvolume80 to replace the fluid dispensed subsequent to the last vent cycle. When the vent inlet port112 and ventoutlet port116 do not share a common volume formed by thespool106 andaxial bore104 of thedelivery mechanism120, they are typically isolated and no venting of the first ventedvolume80 may take place.
• In operation, thespool106 defines one or more volumes between thespool106, theaxial bore104 and thecircumferential seals140,142,150 and152 disposed on the spool of thedelivery mechanism120. Thespool106 is typically translated in a proximal and distal direction in order to move the volumes into and out of communication with the various ports of theaxial bore104. This axial movement in alternating proximal and distal directions of thespool106 within theaxial bore104 may be used to put the various ports in fluid communication with translatable volumes of thedelivery mechanism120. For reliable operation, it may be desirable in some circumstances for thespool106 and thecircumferential seals140,142,150 and152 disposed about thespool106 to move smoothly within theaxial bore104 of thedelivery mechanism120 while maintaining a seal between an outside surface of thespool106 and an inside surface of theaxial bore104. It may also be desirable for thecircumferential seals140,142,150 and152 disposed on thespool106 to move axially back and forth within theaxial bore104 while maintaining a seal and with a minimum of friction. Achieving these features of thespool106 may be facilitated with the use of particular seal configurations or gland configurations used to house the seals of the spool embodiments.
• Thedelivery mechanism120 may be configured to deliver fluid from thereservoir68. Thedelivery mechanism120 may include a delivery mechanism body102, or housing, and theaxial bore104 disposed in the delivery mechanism body102. Theaxial bore104 may have a substantially round transverse cross section. Thespool106 may also have a substantially round transverse cross section, and may be slidingly disposed within theaxial bore104. Thedrive mechanism48 may include a rack andpinion mechanism174 actuated by anelectric motor170 through agear box172.
• With regard to the above detailed description, like reference numerals used therein may refer to like elements that may have the same or similar dimensions, materials, and configurations. While particular forms of embodiments have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the embodiments herein. Accordingly, it is not intended that the invention be limited by the forgoing detailed description.
• The entirety of each patent, patent application, publication, and document referenced herein is hereby incorporated by reference. Citation of the above patents, patent applications. publications and documents is not an admission that any of the foregoing is pertinent prior art, nor does it constitute any admission as to the contents or date of these documents.
• Modifications may be made to the foregoing embodiments without departing from the basic aspects of the technology. Although the technology may have been described in substantial detail with reference to one or more specific embodiments, changes may be made to the embodiments specifically disclosed in this application, yet these modifications and improvements are within the scope and spirit of the technology. The technology illustratively described herein may suitably be practiced in the absence of any element(s) not specifically disclosed herein. The terms and expressions which have been employed are used as terms of description and not of limitation and use of such terms and expressions do not exclude any equivalents of the features shown and described or portions thereof and various modifications are possible within the scope of the technology claimed. Although the present technology has been specifically disclosed by representative embodiments and optional features, modification and variation of the concepts herein disclosed may be made, and such modifications and variations may be considered within the scope of this technology.

Claims (19)

What is claimed is:

1. A method for detecting a presence of an infusion cartridge in an infusion pump, comprising:

installing an infusion cartridge in an infusion pump;

initiating an infusion cartridge loading sequence;

recording loading pulse width modulation (PWM) commands applied to an infusion pump motor during the loading sequence;

setting a value of threshold PWM commands;

comparing values of operational PWM commands that are applied during pumping operations to the value of the threshold PWM commands; and

generating a missing cartridge indication if the value of the operational PWM commands drop below the value of the threshold PWM commands by a predetermined amount.

2. The method ofclaim 1 wherein the value of threshold PWM commands is an average value of the loading PWM commands.

3. The method ofclaim 1 wherein values of operational PWM commands are average values of PWM commands of each subsequent motor move during a pumping cycle.

4. The method ofclaim 1, wherein the PWM commands are uniform amplitude voltage pulses.

5. The method ofclaim 1, where the predetermined amount is based on a pumping speed of the pumping operations.

6. The method ofclaim 1 wherein the predetermined amount is between 20% and 40% of the threshold.

7. The method ofclaim 1. wherein the predetermined amount is between 40% and 60%.

8. An infusion system configured for detecting a presence of an infusion cartridge, comprising:

an infusion cartridge comprising:

a delivery mechanism for effectuating a delivery of fluid, the delivery mechanism including;

an axial bore, and

a spool disposed within the axial bore and axially translatable within the axial bore, and

a drug delivery reservoir for storing fluid; and

an infusion pump comprising:

a drive mechanism including a motor operatively coupleable to the spool and configured to impart controlled axial movements of the spool that move fluid from the infusion cartridge to an outlet port;

a processor, the processor coupled to a memory configured for receiving input data from the memory and using input data for generating operational parameters for the infusion system;

the memory adapted to receive and store input data coupled to the processor and configured for communicating that data to the processor; and

programming stored in the memory for retrieval by the processor to control a closed loop motor control algorithm, the closed loop motor control algorithm configured to generate pulse width modulation (PWM) commands to operate the motor of the drive mechanism, wherein when values of the PWM commands fall below a threshold value by a predetermined amount an absence of the infusion cartridge warning is generated.

9. The infusion system ofclaim 8, further comprising a user interface configured for displaying a request for a user to input data, wherein the display is further configured for receiving user input data in response to the request and communicating that data to the memory.

10. The infusion system ofclaim 9, wherein the user interlace is further configured to display the absence of the infusion cartridge warning.

11. The infusion system ofclaim 8, in which the closed loop motor control algorithm is a velocity loop algorithm.

12. The infusion system ofclaim 8, in which value of the PWM commands is proportional to a load on the motor of the drive mechanism.

13. The infusion system ofclaim 8, wherein the threshold value is determined based off of PWM commands applied to the pump motor during a loading sequence of an infusion cartridge.

14. The infusion system ofclaim 8, wherein the PWM commands are uniform amplitude voltage pulses.

15. The infusion system ofclaim 8, where the predetermined amount is based on a pumping speed of the pumping operations.

16. A method of calibrating an infusion pump that utilizes an infusion cartridge, comprising:

installing an infusion, cartridge in an infusion pump;

initiating an infusion cartridge loading sequence;

recording loading pulse width modulation (PWM) commands applied to an infusion pump motor during the loading sequence; and

setting a value of threshold PWM commands.

17. The method ofclaim 16, wherein the value of threshold PWM commands is an average value of the loading PWM commands.

18. The method ofclaim 16, wherein the PWM commands are uniform amplitude voltage pulses.

19. The method ofclaim 16, wherein the threshold value is variable based on a speed of subsequent pumping operations of the infusion pump.

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