Abstract:
Disclosed is a low cost, disposable, infusion pump. The infusion pump can include an integrated occlusion detector that detects both upstream and downstream occlusions in an infusion tube. In addition, the infusion pump can easily monitor flow rates through the infusion tube, and be quickly set to infuse at a pre-determined rate. An armature within the infusion pump works in concert with a pair of tubing pinchers to precisely control the movement of fluid within the tubing. Sensors mounted within the device detect the position of the armature and can determine if an occlusion has occurred in the tubing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a medication infusion device for administering fluid to patients and more particularly to an improved infusion pump with integral flow monitor that is small, inexpensive to manufacture, disposable, and very power efficient. 
     2. Description of the Related Art 
     Infusion Devices 
     Current generation infusion pumps are costly to use. They are difficult to program and require significant resources to properly train medical personnel in their use. The infusion pumps usually require devices that allow the loading and unloading of the cassette and connection to a source of AC power. The pumps require high front-end capital equipment costs and expensive routine maintenance. They typically become obsolete in a few years and must be replaced by newer technology pumps. Pump replacement not only results in high capital equipment costs but also typically requires costly retraining of medical personnel in their use. Investment in these high front-end capital equipment and training costs also forces an unearned “loyalty” to the particular infusion pump provider that further increases the user&#39;s costs by a stifling competition and restricting the adoption of newer, better, or less expensive infusion pump technologies. Additionally, the disposable cassettes require costly features to precisely interface with the pump and to prevent uncontrolled free flow of fluid to the patient when incorrectly loaded or unloaded. Further, the size and weight of current generation pumps make mobile care difficult and expensive, especially in military applications when they must be transported long distances or in battlefield environments. 
     As a result of the ongoing need for improved health care, there is a continuous effort to reduce the cost of and to improve the administration of intravenous fluids from infusion devices. As is well known, medication dispensers and infusion devices are used for infusion of predetermined amounts of medication into the body of a patient. Various types of medication dispensers employing different techniques for a variety of applications are known to exist. 
     Primary types of prior art infusion devices are commonly known as controllers, pumps, disposable elastomeric pumps, and mechanical pumps. 
     Controllers are infusion devices that control the rate of flow of a gravity infusion. They are limited in use because they are unable to generate positive pressure over and above that provided by gravity. Many infusions require the generation of pressure to overcome pressure losses due to filters or other devices in the fluid path to the patient. Arterial infusions can also require positive pressure to overcome the high blood pressures involved. 
     Infusion pumps are able to generate positive pressure over and above that provided by gravity and are typically a preferred infusion device. Prior art devices demonstrate a complexity of design in order to sense the presence of tubing, sense the disposable cassette loading operation, control the motor, gear down or reduce the speed of the pumping mechanism, sense upstream and downstream occlusions, and sense the proper operation of the motor. They typically require a complex pumping mechanism with a platen, cams, cam followers, gears or belts, and pressure sensors. The motor drives typically require a costly encoder wheel to sense the position of the motor or cam. 
     Disposable elastomeric pumps utilize an elastic membrane to form a reservoir to contain and then “squeeze” the medication therefrom. A precision orifice usually controls the rate of infusion. As the elastomeric container empties, the pressure inside can vary significantly which can change the infusion rate. The infusion rate can also vary depending on the viscosity of the infused medication. These devices are typically disposable and utilized for a single infusion. 
     Mechanical pumps can utilize a spring mechanism in combination with a precision orifice to control the infusion rate. A disposable medication container is loaded into the device. The spring mechanism then squeezes the medication out of the container and through the controlling orifice to the patient. Although mechanical pumps are able to generate positive pressure, they typically cannot detect actual fluid flow nor can they adjust flow rate based on the presence of restrictions in the fluid path. The disposable medication container is used once and discarded after use. Since the infusion rate is dependent on the forces exerted by the spring mechanism, complex mechanisms are required to generate an infusion rate that is accurate from the beginning of the infusion when the reservoir is full to the end of the infusion when the reservoir is empty. 
     An example of a controller is shown in U.S. Pat. No. 4,626,241 to Campbell et al. The controlling mechanism in this reference can only control the rate of the gravity infusion by repetitively opening and closing a control valve. This device not only has the disadvantages inherent in a controller but also has several other problems in its implementation. The device has limited ability to accurately monitor the volume or rate of the infusion. It uses a drop sensor to count the number of drops infused. It is well known that drop size varies wildly with not only drip chamber canulla size and the rate of infusion, but also with the type of medication being infused. 
     Another example of a controller mechanism is demonstrated in U.S. Pat. Nos. 4,121,584 and 4,261,356 to Turner et al. This device is further improved in U.S. Pat. No. 4,185,759 to Zissimopoulos, U.S. Pat. No. 4,262,668 to Schmidt, U.S. Pat. No. 4,262,824 to Hrynewycz, and U.S. Pat. No. 4,266,697 to Zissimopoulus. The improved design uses a combination of gravity pressure, a permanent magnet, and an electromagnet to alternately open and close two valves to sequentially fill and empty a fluid chamber. This controller design also operates with gravity flow and has no capability to generate positive fluid pressure as is required in many clinical applications. This design requires a very complex cassette and has no capability to monitor the presence or absence of flow. The presence of an occlusion or empty reservoir cannot be detected by the mechanism. A low head height or low fluid reservoir results in a reduction of the rate of infusion. This type of undetected under-infusion can be hazardous to patient safety. 
     The implementations of this design in U.S. Pat. No. 4,262,824 to Hrynewycz utilizes the combination of permanent magnets and electromagnets to provide a bistable rocker arm motion to sequentially open and close cassette valves. The permanent magnet(s) are utilized to force one or the other of the two valves to a closed position when power is interrupted, thereby stopping potentially hazardous free flow of fluid to the patient. 
     The implementation of the design in U.S. Pat. No. 4,266,697 to Zissimopoulos provides a plunger means for the valve members. The design utilizes a very complex combination of magnets, a leaf spring, coil springs, and plungers to implement a bistable valving function that reduces the wear on the valve membrane. 
     The ability of an infusion pump to generate positive pressure greatly increases its clinical acceptability. Prior art devices, however, demonstrated greatly increased complexity of design. An example of such an infusion pump is in U.S. Pat. No. 6,371,732 to Moubayed et al. The invention includes a variable speed motor with a complex motor speed control, a worm and worm gear, a complex cam and cam follower with roller members and pinch members and pinch fingers and biasing springs. The invention also requires an optical sensor, two pressure sensors with beams and strain gages, a platen sensor, and a tubing sensor. The invention also requires a shut-off valve and an encoder wheel. 
     An example of a disposable elastomeric pump is shown in U.S. Pat. No. 5,398,851 to Sancoff et al. It can be seen that the shape of the device is bulky and inconvenient for a patient to wear unobtrusively. The device requires an expensive elastomeric membrane to contain the medication and force it through the controlling orifice to the patient. It is disposable and typically filled only once for a single infusion then discarded. 
     An example of a mechanical pump is shown in U.S. Pat. No. 7,337,922 to Rake et al. It can be seen that the spring mechanism of a preferred embodiment includes two lateral springs and a complex mechanism. Complexity is added to the mechanism to provide a low profile package that is less bulky for the patient to wear. Although large forces are not required to load the infusion reservoir, large forces can be required to force the spring mechanism closed around the reservoir. Additional complexity is added to the mechanism to help reduce the resulting forces and the larger the medication bag, the larger the forces involved. This typically limits the usage of this type of device to fluid reservoirs of a few hundred milliliters or less while many commercially available fluid reservoir bags are one liter in size. 
     Occlusion Detection Devices 
     In many cases it is of critical importance to provide an infusion pump that can effectively detect fluid path occlusions either upstream (from the supply reservoir) or downstream (to the patient) in a timely manner. These needs are only partially fulfilled by prior art infusion pumps. Specifically, the occurrence of an occlusion in the pump&#39;s medication supply tube or output tube may endanger the patient without warning. If, for example, the supply reservoir is empty, or the supply tube becomes kinked, pinched, or otherwise blocked, the supply of medication to the patient will cease. As the continued supply of some medications is necessary to sustain the patient or remedy the patient&#39;s condition, cessation of supply may even be life threatening. Yet, with some infusion devices, such an occlusion would either go unnoticed or require an excessive amount of time to be detected. Some prior art devices such as that described in U.S. Pat. No. 4,398,542 to Cunningham et al. utilize a pressure transducer and membrane to monitor fluid pressure as an indicator of an occlusion. 
     Still other prior art devices such as that described in U.S. Pat. No. 6,371,732 to Moubayed et al. use strain gages to measure changes in the diameter of tubing as a means of detecting occlusions. 
     Still other prior art devices as described in U.S. Pat. No. 6,110,153 to Davis et al., utilize a complex optical system to detect changes in the diameter of tubing resulting from upstream occlusions. These devices require costly optical components, expend significant amounts of power to excite the elements, and require precise alignment to operate properly. 
     Programming Devices 
     Programming devices for infusion pumps are well known. Devices such as shown in U.S. Design Pat. No. 282,002 to Manno et al. utilize an array of push button switches to select a program value and an electronic display to display the selected value. Devices such as that shown in U.S. Pat. No. 4,037,598 to Georgi utilize switches that can both select the program value and display the selected value on a printed switch assembly. These devices cannot be programmed remotely nor can they be attached or made part of the fluid reservoir. 
     U.S. Pat. No. 4,943,279 to Samiotes et al. discloses an infusion device that uses an attached magnetic label. The label includes a display of the drug name and concentration with a set of parameter scales that surround the manual controls on the pump when the label is attached. Magnets in the label are sensed by the infusion pump so that it knows the scales and drug information. This device still requires patient specific programming that must be performed at the infusion pump. 
     The infusion device of U.S. Pat. No. 5,256,157 to Samiotes et al. describes an infusion device that uses replaceable memory modules to configure non-patient specific parameters such as patient controlled analgesia, patient controlled analgesia with a continuous infusion, et cetera. The patient specific programming must then be performed by the user. These replaceable modules do not display either the non-patient specific parameters or the patient specific parameters. Displaying these parameters electronically on the infusion pump requires an increase in cost in the pump and complexity to the operator. 
     SUMMARY OF THE INVENTION 
     An infusion pump configured to pump fluid through a flexible tubing having an upstream end and a downstream end is provided. The infusion pump includes an armature configured to compress the tubing when in a first position and uncompress the tubing when in a second position; and an occlusion detector configured to detect the position of the armature and identify upstream or downstream occlusions in the flexible tubing. In some embodiments, the infusion pump also includes a flow monitor configured to detect the armature moving from the second position to the first position. 
     A method of detecting an occlusion in an infusion tube is also provided. The method includes providing an infusion pump having an armature configured to compress the infusion tube when in a first position and uncompress the infusion tube when in a second position; instructing the armature to compress and uncompress the infusion tube to move fluid through the infusion tube; and sensing an error when the armature does not move as instructed, where the error indicates an occlusion in the infusion tube. 
     Also provided is an infusion pump including an armature configured to compress an infusion tube when in a first position and uncompress the infusion tube when in a second position; means for instructing the armature to compress and uncompress the infusion tube; and means for sensing an error when the armature does not move as instructed, where the error indicates an occlusion in the infusion tube. In one embodiment, the means for instructing includes a control module. In another embodiment, the means for sensing includes an occlusion sensor configured to detect the position of the armature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of an embodiment of a pump in operation. 
         FIG. 2  is an enlarged view of the pump of  FIG. 1 . 
         FIG. 3  is a view of an embodiment of a programming device. 
         FIG. 4  is a perspective view of another embodiment of a pump. 
         FIG. 4A  is a sectional view of the pump of  FIG. 4  taken along line  4 A- 4 A. 
         FIG. 5  is a top view of another embodiment of a pump. 
         FIG. 6  is an enlarged sectional view of a flow sensing mechanism of the pump of  FIG. 5 . 
         FIG. 7A  is a side view of the pump of  FIG. 5  at the completion of the fill stroke. 
         FIG. 7B  is a side view of the pump of  FIG. 5  at the completion of the pump stroke. 
         FIG. 8  is a sectional view of the pump of  FIG. 5  showing pinchers during the fill stroke. 
         FIG. 9  is a sectional view of the pump of  FIG. 5  showing pinchers during the pump stroke. 
         FIG. 10  is a flow chart of one programming process of the pump of  FIG. 5  using a resistive programming device. 
         FIG. 11  is a flow chart of another programming process of the pump of  FIG. 5  using a memory based programming device. 
         FIG. 12  is a flow chart of a fill stroke process of the pump of  FIG. 5 . 
         FIG. 13  is a flow chart of a pump stroke process of the pump of  FIG. 5 . 
         FIG. 14  is an enlarged view of the pump of  FIG. 1  with a roller clamp. 
         FIG. 15  is a flow chart of a rate setting process of the pump of  FIG. 14 . 
         FIG. 16A  is a graph of forces present in the fill stroke of the pump shown in  FIG. 7A . 
         FIG. 16B  is a graph of forces present in the pump stroke of the pump shown in  FIG. 7B . 
     
    
    
     DETAILED DESCRIPTION 
     Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this description, and the knowledge of one skilled in the art. In addition, any feature or combination of features may be specifically excluded from any embodiment of the present invention. For purposes of summarizing the present invention, certain aspects, advantages and novel features of the present invention are described herein. Of course, it is to be understood that not necessarily all such aspects, advantages or features will be embodied in any particular embodiment of the present invention. 
     In reference to the disclosure herein, for purposes of convenience and clarity only, directional terms, such as top, bottom, left, right, up, down, upper, lower, over, above, below, beneath, rear, and front, may be used. Such directional terms should not be construed to limit the scope of the invention in any manner. It is to be understood that embodiments presented herein are by way of example and not by way of limitation. The intent of the following detailed description, although discussing exemplary embodiments, is to be construed to cover all modifications, alternatives, and equivalents of the embodiments as may fall within the spirit and scope of the invention. 
     Pumping System 
     Embodiments of the invention provide an energy efficient pumping mechanism. In one embodiment, a magnet arrangement reduces the required pumping forces and stores energy for later use by the mechanism. 
     As will be described in more detail below, in one embodiment an electromagnet is used to compress tubing which leads to movement of liquid within the tubing. By actuating the electromagnets, an armature compresses the tubing. In one embodiment, other electromagnets control closing the tubing downstream and upstream of the armature so that the flow of fluid into a particular direction can be controlled. In addition, in another embodiment, the compression force exerted by the electromagnets is stored in the tubing and then recovered as the tubing returns to its original state. In one embodiment the tubing is part of an infusion system for delivering medicine to a patient and the electromagnet is part of an infusion pump. 
     In another embodiment, magnets mounted on a rocker arm and on the armature force an upstream “pincher” and the armature closed when their associated electromagnets are de-energized. When power is lost to the device, the electromagnets lose magnetic energy which results in the armature and pincher preventing fluid flow through the tubing. This results in a default safe condition in the event that power to the system is interrupted. In representative embodiments, the closed pincher and armature protect against free flow of fluid to the patient. 
     In yet another embodiment, the device comprises a pivoting armature arrangement that is configured to reduce the magnetic force required to compress the tubing. In this embodiment, the compressing force that is necessary to compress the tubing is shared between a pivoting hinge and the magnet. This reduction in the required magnet force results in a reduction in force that need be supplied by the armature electromagnet. 
     Occlusion Detection and Flow Monitoring System 
     Implementations of the present invention also include a pump that comprises a mechanism for detecting occlusions in the tubing. In one embodiment, the pump itself is part of the upstream and downstream occlusion detection system. The pump tubing may be used to help push open the armature during the tubing opening fill stroke. If an upstream occlusion occurs during the fill cycle, then the resulting negative pressure in the tubing will reduce the tubing force on the armature and not allow the armature to complete its opening stroke. A sensor may be provided to sense the armature has not completed its opening stroke. An occlusion control module that is linked to the sensor and monitors the position of the armature may then activate, indicating an upstream occlusion. 
     In the pumping stroke, the armature closes the tubing. In the event that a downstream occlusion occurs, the resulting increased pressure in the tubing may increase the tubing force on the armature and prevent the armature from compressing the tubing in a predetermined time period. In that case, the armature will not properly complete its delivery stroke. A sensor may be supplied to sense the armature has not completed its delivery stroke, and an occlusion control module linked to the sensor may output an alarm signal, indicating a downstream occlusion. 
     In a representative embodiment of the invention, the force on the pump tubing is minimized. Larger forces on the tubing result in less tubing life and can lead to permanent deformation of the tubing or, more seriously, to the introduction of particulate pieces of the tubing into the medicament which can be infused into the patient. The magnet configuration can result in a force that constrains the tubing to a specific gap. The armature may actually be limited by the dimension of the magnet itself. This insures that the optimum magnetic force is applied when the gap is zero. 
     In another representative embodiment of the invention, the occlusion control module not only indicates the presence of upstream and downstream occlusions, but also functions as a fluid flow monitor. The absence of transitions of the armature from open to closed states can indicate improper fluid flow. The presence of transitions from open to closed states can indicate that a specific amount of fluid (one stroke volume amount) has been infused. Accordingly, the system can determine whether or not fluid is flowing though the tube by monitoring the transition states of the armature that is compressing the tubing. In addition, by storing and analyzing the transition states over time, the system can determine how much liquid is flowing through the tubing by knowing the fluid flow per stroke and multiplying that number by the number of strokes of the armature. 
     In a representative embodiment, the magnetic flux developed by the electromagnet does not travel through the other magnets. Including the other magnets in the flux path of the electromagnet may reduce the amount of flux available to develop the force required to move the armature to the open position, and result in an increase in the cost and size of the electromagnet. Finally, the flux generated by the electromagnet may be configured to travel only through a single gap in an exemplary embodiment of the present invention. 
     Representative Features of an Infusion Pump 
     A representative embodiment of the present invention will now be described with reference to  FIG. 1 , illustrating an embodiment of a pump in operation. A fluid reservoir  4  is shown containing a medicament to be infused into the arm  2  of a patient  3 . Infusion pump  17  is shown attached to reservoir  4 . Medicament flows into the pump  17 , then out of the pump, past an optional flow clamp  110  and through exit tubing  109  to the patient  3 . The infusion pump can be accompanied by a programming device  6  to monitor and control the flow of medicament to the patient. In some embodiments, the programming device is a programming module. 
     Illustrating the pump of  FIG. 1  in greater detail,  FIG. 2  shows infusion pump  17  attached to fluid reservoir  4  through its reservoir spike  103  through which medicament may flow into pump  17 . Programming device  6  may be attached to the infusion pump through programming connector  8  which provides an electrical connection between the infusion pump  17  and the programming device  6 . To minimize infusion errors, the programming device may also be attached to reservoir  4  through a locking tamper evident tie  10 . In alternate embodiments, the programming device may be made part of the fluid reservoir or wired directly to and made part of the infusion pump. In one embodiment where the programming device is made part of the fluid reservoir, a fluid reservoir such as but not limited to an intravenous (IV) bag contains a programming module which can be linked to infusion pump  17  through an electronic connection. The programming module can include, for example, an electronic chip that is attached to the IV bag and contains dosing parameters. The programming module can contain any suitable programming parameter, such as but not limited to infusion rate and duration. In another embodiment, a user can insert the electronic chip into infusion pump  17  to program pump  17 . 
     Programming device  6  may be configured to control pump programming information such as, but not limited to, infusion rate, volume to be infused, and keep vein open rate. The programming device  6  displays programming information for the user of the device. Such programming information could include, for example, limits on time of infusion to ensure that time sensitive infusions would not be delivered late or at inappropriate times. The programming device may optionally contain status or history information retrieved from the pump, such as infusion complete, volume infused amount, alarm history, et cetera that may later be downloaded for user access. The device may have a tamper resistant lock for patient safety. 
     Attaching the programming device  6  to the pump  17  can cause the pump to be automatically programmed to the desired infusion parameters or may cause the pump to automatically prime the fluid path with a specific volume of fluid to remove air in the tubing. Alternatively, the pump  17  may have tamper resistant switches that allow the user to prime the fluid path. The pump exit tubing  109  may include the clamp  110  to allow the user to start and stop the infusion. Closing the clamp could stop the infusion and cause a downstream occlusion alarm and display. Reopening the clamp could cause the infusion to resume. The infusion pump is configured in one embodiment to measure the time required to infuse an increment of fluid at a given infusion rate and produce a display of information that allows a user to observe how much resistance the fluid is encountering and take steps necessary to accommodate the restriction. For example, the user may raise or lower the fluid reservoir  4  to increase or decrease the fluid pressure or replace a partially obstructed catheter on the patient. A control module, a measurement module, or any other suitable electronic device can measure the time required to infuse the increment of fluid. 
     A display  15  on the infusion pump can indicate the amount of volume infused or any alarm conditions present. For example, a display  26  resembling a fluid drop can be programmed to flash at a rate proportional to the actual infusion rate to emulate a standard infusion set drip chamber. The flashing display  26  could change in color or size or brightness depending on the fluid resistance encountered. 
     The infusion pump may have the ability to purge air that has entered the pump tubing by collapsing the tubing while the downstream pincher is closed, thereby forcing the air back into the fluid reservoir. Reopening the tubing with the same pincher closed could refill the tubing with fluid absent of air. 
     In another embodiment, the programming device can include a memory device such as an EEPROM (Electrically Erasable Programmable Read-Only Memory). The device could be programmed with the desired programming information and include a check sum or CRC (Cyclic Redundancy Code) that could be compared to a value calculated by representative embodiments of the invention after downloading the programming parameters. Methods to calculate these codes are well known in the industry. 
     Other arrangements may also be desirable such as locating a power source or control module on the programming device. The volume infused indicator may also be optionally located on the programming device. Alternatively, the programming device or parts of it may be incorporated into representative embodiments of the invention. Additionally, the device may have a rechargeable power system that could be recharged from a wall outlet or other power source. 
     As illustrated with continued reference to  FIG. 2 , a representative programming device  6  includes infusion parameter display  12 , infusion parameter recall device  14 , infusion parameter testing device  16 , and optional programming device connector  18 . In some embodiments, these devices enable infusion pump  17  to test and recall infusion parameters. 
     Infusion pump  17  optionally includes enclosure  5 , display  15 , speaker  32 , and priming switches  20 . The display may include indicators, such as air alarm indicator  7 , up occlusion indicator  9 , down occlusion indicator  22 , replace me indicator  24 , flow indicator  26 , Keep Vein Open (KVO) indicator  42 , and optional volume infused indicator  30 . The KVO indicator  42  indicates that the infusion is complete and the device is pumping at a minimal rate to keep the vein open. 
       FIG. 3  shows another embodiment of a programming device  6  that allows users to select and display programming parameters. The programming device may include such features as an infusion parameter selector  11 , a tamper resistant infusion parameter selector lock  13 , infusion parameter display  12 , infusion parameter testing device  16 , and programming device connector  18 . 
     Another embodiment of the present invention will now be described with reference to  FIGS. 4 and 4A .  FIG. 4 , a perspective view of infusion pump  17 , shows tubing  25  on pump frame  21  and passing under armature  23 . The direction of fluid flow from a fluid reservoir  4  (not shown), through the pump, and to the patient is indicated by arrow  15 .  FIG. 4A , a cross-section of pump  17  taken along line  4 A in  FIG. 4 , illustrates downstream pincher  61 A and upstream pincher  61 B provided under tubing  25 . In representative embodiments, downstream pincher  61 A and upstream pincher  61 B push tubing  25  against downstream detent  65 A and upstream detent  65 B. Through the application or removal of magnetic forces provided in one embodiment, downstream pincher  61 A pushes tubing  25  against detent  65 A, while upstream pincher  61 B does not push tubing  25  against detent  65 B. Referring again to  FIG. 4 , armature  23  is next rotated by the application of magnetic force supplied by armature electromagnet  47 , such that armature  23  is raised up, thereby uncompressing and/or releasing tubing  25 . In this state, fluid flows through tubing  25  up to the area of tubing pinched by the downstream pincher  61 A. 
     Again through the application or removal of magnetic forces, upstream pincher  61 B then pushes tubing  25  against detent  65 B and downstream pincher  61 A releases from the tubing  25  to allow fluid to flow in a downstream direction. Armature  23  is next brought down on tubing  25  by magnetic force supplied by magnets (not shown) provided on pump frame  21 . With this step, the volume of fluid in tubing  25  in the areas between the upstream and downstream pinchers is forced in the direction indicated by arrow  15 , to be infused into the patient. To begin another infusion cycle, magnetic forces are again applied or removed to downstream and upstream pinchers  61 A,  61 B to allow fluid to flow through tubing  25  up to the area of tubing pinched by downstream pincher  61 A. The steps described above are repeated with each infusion cycle. 
     The representative embodiment of the invention illustrated in  FIG. 4  can administer fluid at a precise rate. Pump  17  may be extremely small, lightweight, and power efficient. In a representative embodiment of the invention, the infusion pump is a disposable device intended for a single use or perhaps for a single patient use. The invention, however, is not limited to a disposable device and other embodiments may allow parts of the device to be disposable and replaceable and other parts to be used multiple times. 
     Features of a representative embodiment of the invention will now be described with reference to  FIG. 5 , which illustrates a top view of infusion pump  17 . As shown, tubing  25  rests on pump frame  21 . Armature  23  is shown pivoting on pump frame  21  and in contact with pump tubing  25 . Magnets  43 A and  43 B are also located on pump frame  21 . A magnet cover  27  may optionally be provided to hold magnets  43 A and  43 B in place on pump frame  21 . Flow sensor post  31  of a flow sensor, discussed in more detail with reference to  FIG. 6  below, is attached to pump frame  21 . 
     Pump tubing  25  passes under both upstream pincher detent  65 B and downstream pincher detent  65 A. The upstream end of pump tubing  25  is attached to air detector  99 . Air detector  99  is attached to medication reservoir piercing spike  103  which is attached to pump frame  21 . The downstream end of pump tubing  25  is attached to optional flow controlling orifice  107 . Flow controlling orifice  107  is connected to exit tubing  109 . 
     Pump frame  21  is made of any suitable material, such as formed cold rolled steel. Upstream pincher detent  65 B is formed on pump frame  21  adjacent pincher slots  67 C and  67 D. Downstream pincher detent  65 A is also formed on pump frame  21  adjacent pincher slots  67 A and  67 B and rocker pivot slots  91 A and  91 B. 
     Armature sensor arm  73  extends from armature  23 . Armature  23  may be made of any suitable material such as cold rolled steel. Upstream armature pivot arm  71 B extends from the right side of armature  23  and downstream armature pivot arm  71 A extends from the left side of armature  23 . Magnet cover  27  is attached to frame  21  by magnet cover screws  41 A and  41 B. Magnet cover  27  may be made of any suitable material, such as cold rolled steel, while magnet cover screws may be made of brass, for example. Tubing full contactor  29  is disposed on flow sensor post  31  and retained by tubing full contactor upper nut  33 . 
     A partial exploded view of a flow sensor of one embodiment of the present invention is described with reference to  FIG. 6 . In some embodiments, the flow sensor is an occlusion detector. Flow sensor post  31  extends through frame  21  and is retained by flow sensor post lock nut  38 . Tubing empty contactor  35  is disposed on flow sensor post  31  and retained by tubing empty contactor lower nut  39  and tubing empty contactor upper nut  37 . Tubing empty contactor contact  36  is attached to the upper side of tubing empty contactor  35 . Tubing full contactor  29  is disposed on flow sensor post  31  and retained by tubing full contactor lower nut  34  and tubing full contactor upper nut  33 . Tubing full contactor contact  28  is attached to the lower side of tubing full contactor  29 . Armature sensor arm tubing full contact  75  is attached to the upper side of armature sensor arm  73 . Armature sensor arm tubing empty contact  77  is attached to the lower side of armature sensor arm  73 . 
       FIG. 7A  is a cross-sectional end view of a representative embodiment of the present invention. Magnet cover screw  41 A, magnet cover  27 , and upstream magnet  43 A are formed on frame  21 . Flow sensor post lock nut  38  is also provided on frame  21 . Armature  23  is shown in the tubing full position, with armature  23  in contact with armature magnet core  87 . Armature sensor arm tubing full contact  75  is formed on armature sensor arm  73 . Armature sensor arm tubing full contact  75  is shown contacting tubing full contactor contact  28 . A cross-section of tubing  25  in the “full” state is shown resting on tubing shim  45 . Armature electromagnet  47  is attached to pump frame  21  at armature magnet mounting slot  95  (not shown) by armature magnet core  87 . Armature magnet coil  85  is shown surrounding armature magnet core  87 . Armature magnet core  87  may be made of any suitable material, such as cold rolled steel. 
     Downstream armature pivot slot  69 A (not shown) is formed on downstream pincher detent  65 A (not shown). Similarly, upstream armature pivot slot  69 B is formed on upstream pincher detent  65 B. Downstream armature pivot arm  71 A (not shown) may be disposed in downstream armature pivot slot  69 A (not shown) and upstream armature pivot arm  71 B may be disposed in upstream armature pivot slot  69 B. 
       FIG. 7B  is a cross-sectional view of an embodiment of the present invention. Armature  23  is shown in the tubing empty position, with a cross-section of tubing  25  illustrated in the “empty” state. Armature sensor arm tubing empty contact  77  is shown contacting tubing empty contactor contact  36 . 
       FIG. 8  is a cross-sectional side view of a representative embodiment of infusion pump  17  during the fill stroke. Cross-sections of armature  23 , pump frame  21 , and rocker support  51  are shown. Pincher electromagnet  49  is attached to pump frame  21  at pincher magnet mounting slot  97  (not shown) by pincher magnet core  81 . Pincher magnet coil  79  is shown surrounding pincher magnet core  81 . Rocker support  51  is shown contacting pincher magnet core  81 . Pincher magnet core  81  may be made of any suitable material, such as cold rolled steel. Rocker  55  is attached to rocker leaf spring  57  and rocker support  51  by rocker support screw  53 . Rocker support pivot arms  93 A and  93 B (not shown) are formed from the rocker support  51  and pivot, respectively, in the rocker pivot slots  91 A and  91 B (not shown) on frame  21 . Downstream leaf spring pre-load screw  63 A and upstream leaf spring pre-load screw  63 B are attached to rocker  55 . An upstream sensor, upstream contact switch  64 A, is attached to rocker leaf spring  57  and fits between leaf spring  57  and the upstream leaf spring pre-load screw  63 B. A downstream sensor, downstream contact switch  64 B, is attached to rocker leaf spring  57  and fits between leaf spring  57  and the downstream leaf spring pre-load screw  63 A. Rocker magnet  62  is attached to rocker  55 . It will be understood by persons of skill in the art that rocker magnet  62  can be positioned in various locations, and is not limited to a location on the rocker. 
     With continued reference to  FIG. 8 , downstream pincher  61 A is attached to leaf spring  57  by downstream pincher retention screw  59 A and contacts tubing  25 . Upstream pincher  61 B is attached to leaf spring  57  by upstream pincher retention screw  59 B and contacts tubing  25 . Leaf spring  57  may be made of any suitable material, such as spring steel. Power source  105  and control module  101  are optionally attached to pump frame  21 . 
       FIG. 9  is another cross-sectional side view of a representative embodiment of infusion pump  17 , illustrating the position of downstream pincher  61 A and upstream pincher  61 B during the pump stage. Rocker support  51  is shown not contacting pincher magnet core  81 . 
     Operation of an Infusion Pump 
     The programming flow chart of  FIG. 10  shows a programming process  400  that could be used with a resistive type programming device, such as programming device  6 . Plugging the programming device into the infusion pump starts the programming process at state  402 . At state  405 , the infusion parameter rate resistor  14  is measured. The measured value is then tested at decision state  410  for the appropriate tolerance. If the value is out of tolerance, then the process moves to a state  415  wherein an alarm is generated. If the resistance is determined to be within tolerance, then the process  400  moves to state  420  wherein a test resistor is measured. The infusion parameter test resistor  16  is then tested at decision state  425  for the appropriate tolerance. If the test resistor is out of tolerance, then the process  400  moves to state  430 , wherein an out of tolerance condition results in an alarm being generated. The sum of the values read from the two resistors  14  and  16  is then calculated at state  431 , and compared with the fixed known value resistance. If the calculated sum resistance is determined to be out of tolerance at a decision state  432 , an alarm is generated at a state  434 . If the calculated sum is within tolerance, the process  400  moves to state  435  and the infusion rate is calculated. At state  440 , the cycle time is then calculated from the infusion rate and the amount of fluid that is infused in each pump cycle, also known as the stroke volume. The stroke volume can be previously determined during manufacturing. The maximum pump time can then be calculated at state  445 , by subtracting the previously determined fill time and pincher switching times from the cycle time. The infusion cycle can then begin at state  450 , and the programming process terminates at an end state  455 . If an alarm is generated at state  434 , the programming process terminates at end state  455 . 
     Methods of measuring resistance are well known. A common method is to charge a capacitor through a known resistance and measure the charge time between two voltage points. The capacitor is then discharged and the same capacitor and voltage trip points are used to measure the charge time through the unknown resistance. The unknown resistor value can then be determined by multiplying the ratio of the charge times by the value of the known resistor. Embodiments of the invention could use this technique or others to accurately measure the value of resistances in the programming device. 
     One embodiment of a programming device may include two resistors for each programming parameter. One of the resistors could vary directly with the programmed parameter such as 1000 ohms for each ml/hr of infusion rate while the other could decrease 1000 ohms for each ml/hr of infusion rate. The sum of the resistances of the two resistors could be made fixed for all rates at, for example, 500,000 ohms. Each of the resistances of the resistors could be measured by representative embodiments of the infusion pump. The pump could then calculate the sum and verify that it is the fixed value. This would provide the ability to detect a single point failure in either resistor or in the connector and signal an alarm. 
     An alternate programming process  500  is described with reference to the programming flow chart shown in  FIG. 11 . In this example a memory device such as an EEPROM is used to recall programming parameters. Again, plugging the programming device into the infusion pump starts the programming process at state  502 . The rate value is then downloaded from the memory device at state  505 . At state  510 , the rate check value is downloaded. The infusion pump next calculates what the rate check value should be from the downloaded rate value at state  515 . The calculated and downloaded rate check values are then compared at decision state  520 . If the values are not equal, an alarm is generated at state  525 . If the values are equal, the cycle time is then calculated at step  530  from the rate value and the known stroke volume. As described above with reference to programming process  400 , the maximum pump time is then calculated at state  535  from the previously determined fill time and pincher switching times. The infusion cycle can then begin again at state  540 , and the programming process is complete at end state  545 . If an alarm is generated at state  525 , the programming process terminates at end state  545 . 
     An alternative programming device could use switches to select the desired programming parameters. Still another embodiment could use the voltages or currents developed by applying a voltage or current to a network of parameter setting resistors to select the appropriate parameters. 
     Referring now to  FIGS. 5 and 8 , the infusion pump  17  can include an optional reservoir spike  103  to pierce a fluid reservoir  4  containing medicament to be infused and an air detector  99  to detect the presence of air bubbles in the fluid path. The pump may also include a flow controlling orifice  107 , which functions to both limit the peak infusion rate and to provide an additional measure of safety by providing a more precise time interval during which the pump tubing  25  empties its fluid and discharges the fluid through the controlling orifice  107 . That time interval is measurable by the control module  101  using the pump stroke process  700  described in greater detail below with reference to  FIG. 13 . Should an out-of-range time interval be encountered, the appropriate safety measures of shutting down the infusion and/or providing the appropriate warning to the user can be taken. 
       FIG. 12  describes the fill stroke process  600 , which is also described with reference to  FIG. 8 . The start of the infusion cycle starts at state  603  with the air detector  99 , the armature electromagnet  47 , and the pincher electromagnet  49  de-energized. Forces from right magnet  43 A and left magnet  43 B (not shown) draw the armature  23  in contact with their surfaces, in opposition to the opening forces that are generated by the collapsed pump tubing  25 . Force from rocker magnet  62  pivots the rocker  55  counterclockwise so as to pivot upstream pincher  61 B in order to prevent fluid flow in the tubing. Upstream pincher  61 B, attached to the rocker leaf spring  57  by the upstream pincher retention screw  59 B, is forced against pump tubing  25  (thereby stopping fluid flow through the tubing) by rocker leaf spring  57 . Rocker leaf spring  57  has separated from upstream leaf spring preload screw  63 B, since in this position the pump tubing  25  force on the pincher exceeds the opposite rocker leaf spring  57  preload force on the upstream leaf spring preload screw  63 B. This opens upstream contact switch  64 A and sends a signal to the control module. Thus, when an occlusion occurs, an error in the flow is sensed and an error signal is generated and sent to the control module. 
     Downstream pincher  61 A, which is attached to rocker leaf spring  57  by downstream pincher retention screw  59 A, is drawn slightly away from pump tubing  25  (thereby allowing fluid to flow through the tubing) by the counterclockwise pivoting of the rocker  55 . Rocker leaf spring  57  is in contact with downstream leaf spring pre-load screw  63 A because the force exerted on the downstream pincher  61 A by the pump tubing  25  is less than the force exerted on the downstream leaf spring pre-load screw  63 A by the rocker leaf spring  57 . This closes downstream contact switch  64 B and sends a signal to the control module. The control module distinguishes the combination of an open upstream contact switch and a closed downstream contact switch as an indication that the pinchers  61 A and  61 B are in the pump position. 
     This state in the infusion cycle is further described with reference to  FIG. 7B . Armature sensor arm  73  is in its lowest position since the pump tubing  25  is completely collapsed and the armature is resting against the right magnet  43 A and the left magnet  43 B. In this position armature sensor arm tubing empty contact  77  is forced against tubing empty contactor contact  36 . As shown in  FIG. 6 , tubing empty contactor contact  36  is connected, such as by welding, to tubing empty contactor  35 , which is held in place on flow sensor post  31  by tubing empty contactor upper nut  37  and tubing empty contactor lower nut  39 . This contact sends a tubing empty signal to the control module  101  (not shown). 
     Referring again to the fill stroke process  600  shown in  FIG. 12 , the control module  101 , programmed to wait for an appropriate time interval from the last activation of the pincher electromagnet  49  to accurately deliver fluid at the prescribed rate, now tests if the infusion pump is priming at decision state  605 . If the infusion pump is not priming, the air detector is turned on at state  610 . If the infusion pump is priming, the air detector remains off. The pincher electromagnet  49  is then activated at state  615 . This state in the infusion cycle is further described with reference to  FIG. 8 . Magnetic flux generated in the pincher magnet core  81  from current flowing in the pincher magnet coil  79  attracts the rocker support  51  toward the core  81 . This attractive force causes the rocker  55  to pivot clockwise on pivot arms  69 A and  69 B in rocker pivot slots  91 A and  91 B. 
     This clockwise motion forces rocker leaf spring  57  to push downstream pincher  61 A against pump tubing  25  (thereby stopping fluid flow through the tubing). Rocker leaf spring  57  has separated from downstream leaf spring pre-load screw  63 A, since in this position the pump tubing  25  force on the pincher  61 A exceeds the opposite rocker leaf spring  57  pre-load force on the downstream leaf spring preload screw  63 A. This opens the downstream contact switch and sends a signal to the control module. 
     Upstream pincher  61 B is drawn slightly away from pump tubing  25  (thereby allowing fluid to flow through the tubing) by the clockwise pivoting of the rocker  55 . Rocker leaf spring  57  is in contact with upstream leaf spring pre-load screw  63 B because the force exerted on the upstream pincher  61 B by the pump tubing  25  is less than the force exerted on the upstream leaf spring pre-load screw  63 B by the rocker leaf spring  57 . This closes the upstream contact switch  64 A and sends a signal to the control module. This opening of the pump tubing  25  adjacent the upstream pincher  61 B does not occur until the pump tubing  25  adjacent the downstream pincher  61 A has closed, thereby stopping backflow of fluid during the transition. 
     As illustrated with reference to  FIG. 8 , this position of the rocker  55  is referred to as the “fill” stroke, because the fluid path to the fluid source at reservoir spike  103  has been opened and the fluid path downstream to the optional flow controlling orifice  107  has been closed. The control module distinguishes this position by the signals sent by the closed upstream contact switch  64 A and the open downstream contact switch  64 B. 
     At decision state  620 , the control module tests for the fill position signals until the maximum pincher switching time has elapsed at decision state  625 . If the fill position has not been achieved by this time, a pincher failure alarm occurs at state  630 . 
     The control module  101  now activates the armature electromagnet  47  at state  635 . With reference to  FIG. 7B , magnetic flux generated in the armature magnet core  87  from current flowing in the armature magnet coil  85  attracts the armature  23  toward armature magnet core  87 . This force counteracts the tubing closing forces generated by the right and left magnets and contributes to the pump tubing opening force generated by the tubing itself. If the upstream fluid path is open and no upstream occlusions or vacuums are present, the armature pivots counterclockwise at the upstream armature pivot arm  71 B and the downstream armature pivot arm  71 A in the downstream armature pivot slot  69 A and the upstream armature pivot slot  69 B, respectively. 
       FIG. 7A  illustrates the rotated position of the armature. At this point in the pump cycle, armature sensor arm  73  is now raised and fluid has entered the section of pump tubing  25  from the reservoir spike. Pump tubing  25  is shown in its open state filled with one stroke volume of fluid which will be dispensed to the flow controlling orifice during the next pump stroke, described below. 
     Now referring to  FIG. 6 , the armature sensor arm  73  is now raised and the armature sensor arm tubing full contact  75  is pressed against the tubing full contactor contact  28 . Tubing full contactor contact  28  is connected, such as by welding, to the tubing full contactor  29 , which in turn is attached to the flow sensor post  31  by tubing full contactor upper nut  33  and tubing full contactor lower nut  34 . This contact sends a tubing full signal to the control module  101  (not shown). The switching arrangement described herein is certainly not the only possible embodiment that can detect the opening or closing of the pump tubing segment, and any suitable arrangement may be employed. For example, an optical arrangement or even a flux measuring arrangement could be implemented to detect the shown positions. 
     Referring again to the fill stroke process shown in  FIG. 12 , after turning on the armature electromagnet at state  635 , the control module waits for the tubing full signal at decision state  650 , until the maximum fill time has been exceeded. If the maximum fill time is exceeded at decision state  655  before the tubing full signal is received, an upstream occlusion alarm is generated at state  660 . During this time the control module also tests for an air signal from the air detector  99  at state  640 . If an air signal is detected, an air alarm is generated at state  645 . No air signal will be generated if the air detector is off. 
     Having successfully completed the fill stroke without the detection of air, the control module  101  may now power down the air detector  99  at state  665  to conserve power. This is the completion of the fill stroke of the infusion cycle. At process  700 , the infusion pump starts the pump stroke process, described below with reference to  FIGS. 13 and 9 . If the pincher failure, air, or upstream occlusion alarm is generated, the fill stroke process terminates at end state  670 . 
     Turning now to the pump stroke process  700  illustrated in  FIG. 13 , the control module de-energizes the pincher electromagnet  49  at state  703 . As shown in  FIG. 9 , the force from the rocker magnet  62  causes the rocker  55  to pivot counter clockwise forcing rocker leaf spring  57  to push upstream pincher  61 A against pump tubing  25  (thereby stopping fluid flow through the tubing). Rocker leaf spring  57  has separated from upstream leaf spring pre-load screw  63   b . This opens upstream contact switch  64 A and sends a signal to the control module. This counterclockwise motion also causes downstream pincher  61 A to be drawn slightly away from pump tubing  25  (thereby allowing fluid flow through the tubing). Rocker leaf spring  57  is in contact with downstream leaf spring pre-load screw  63 A because the force exerted on the downstream pincher  61 A by the pump tubing  25  is less than the force exerted on the downstream leaf spring pre-load screw  63 A by rocker leaf spring  57 . This closes the downstream contact switch  64 B and sends a signal to the control module. The opening of the pump tubing  25  adjacent the downstream pincher  61 A does not occur until the pump tubing  25  adjacent the upstream pincher  61 B has closed, thereby stopping backflow during the transition. 
     The above-described pincher transition from the fill position to the pump position is monitored by the control module at decision state  705 . If the pump position is not attained by the pinchers before the maximum pincher switching time is exceeded at decision state  710 , then a pincher failure alarm is generated at state  715 . If the pump position is attained before the maximum pincher time has elapsed, the armature electromagnet  47  is then turned off at state  720 . 
     Without the attractive force on the armature  23  by the armature magnet core  87 , the force generated by the right and left magnets  43 A and  43 B (not shown in  FIG. 9 ), in opposition to the natural opening force of the pump tubing, will attempt to pivot the armature, collapse the tubing, and infuse the tubing contents downstream to the optional flow controlling orifice  107 . 
     In the event that the downstream fluid path is not restricted and the downstream fluid pressure is not at an unacceptably high pressure, the armature  23  will pivot clockwise, collapse the tubing, and infuse the fluid to the optional flow controlling orifice  107 . This pump sequence is referred to as the pump stroke. At the end of this pump stroke, the armature is resting flat against the right and left magnets. For example,  FIG. 7B  shows the position of the armature sensor arm  73  with the armature sensor arm tubing empty contact  77  pressing against the tubing empty contactor contact  36 , signaling to the control module  101  (not shown) that the pump tubing is empty, and the stroke infusion volume has been infused. 
     After turning off the armature electromagnet, the control module waits for the reception of the tubing empty signal at decision state  725 . In the event that the downstream fluid path is restricted or at an unacceptably high pressure, the right and left magnets  43 A and  43 B will be unable to collapse the tubing and infuse the fluid before the maximum pumping time has elapsed at decision state  730 . In that case, the armature sensor arm  73  will not move to the appropriate position to send the tubing empty signal to the control module  101 . The control module  101  may then take the appropriate action to warn the user of the occlusion at state  735 . Alternatively, if the occlusion is transitory or short lasting, the control module  101  may compensate for the reduced flow rate by reducing the infusion time interval on successive infusion strokes to make up for the transitory reduction in flow rate. 
     If the tubing empty signal is received before the maximum pumping time elapses, the ratio of the actual elapsed pumping time to the maximum allowable pumping time is displayed in an appropriate manner for the user at state  740 . The volume infused is then increased by one stroke volume amount at state  745 . The new volume infused amount is then compared with the programmed volume to be infused value at decision state  750 . If the volume has been infused, then the infusion is complete and this information is displayed to the user at state  755 . If the volume to be infused has not yet been infused and the infusion pump is not priming or in the set rate mode (described in greater detail below with reference to  FIGS. 14-15 ), then the control module waits until the required infusion cycle time has elapsed, as illustrated in decision state  760 . If the infusion pump is priming at decision state  765 , then the infusion cycle is immediately terminated to start the next infusion cycle. If the infusion pump is in the set rate mode at decision state  768 , then the elapsed cycle time is saved at state  769  and then the infusion cycle is terminated to start the next infusion cycle. If the infusion pump is neither priming nor in the set rate mode, then the infusion cycle is complete only after the required infusion cycle time has elapsed at state  770 . If the pincher failure or downstream occlusion alarm is generated, the pump stroke process terminates at end state  775 . 
     Operation of an Infusion Pump with Roller Clamp 
     An alternative embodiment of an infusion pump according to the present invention is illustrated in  FIG. 14 . This embodiment utilizes a conventional roller clamp  111  to establish an initial infusion rate, without the use of a programming device. Pump  17  is shown with conventional roller clamp  11 , set rate switches  112 , and infusion rate display  113 . 
     The controlled infusion rate of the pump can be set according to the rate setting process  800  illustrated in  FIG. 15 . The infusion pump starts in the set rate mode at state  802 . The pump starts and completes the fill cycle as previously described with reference to fill stroke process  600  illustrated in  FIG. 12 . Upon completion of the fill stroke, the pump executes the pump stroke process  700  as illustrated in  FIG. 13 . Since the pump is in the set rate mode, it saves the elapsed cycle time at state  769  at the end of the infusion cycle before it starts the next infusion cycle (illustrated at state  603  in  FIG. 12 ). 
     Referring again to  FIG. 15 , the above-described saved elapsed cycle time at state  769  is recalled at state  805 . The infusion rate is then calculated at state  810  by dividing the stroke volume by the elapsed cycle time. The infusion rate can be calculated by any suitable device, including but not limited to a control module, a measurement module, and an electronic device. As an example, the stroke volume might be 0.05 ml and the elapsed cycle time might be 1.44 seconds. In such a case, the calculated rate would be 125 ml/hr. The calculated rate of 125 ml/hr would then be displayed at state  815  on the infusion rate display  113 , as illustrated in  FIG. 14 . If the displayed rate is not the rate desired by the user, the user would not depress the rate selection switches at decision state  820 , and the next cycle time would be recalled at state  805 . If the user desired a higher rate, the user would open the roller clamp further. The resulting new rate would then be displayed on rate display  113 . If the user desired a lower rate, the user would close the roller clamp further. The resulting new rate would then be displayed on rate display  113 . When the desired infusion rate is displayed, the user could then, at decision state  820 , activate a control input that sets the infusion rate to the desired rate, such as, for example, by depressing the set rate switches  112 . Upon depression of the switches, the infusion pump control rate is set to the display rate at state  825  and, at state  830 , the cycle time is set to the previously recalled elapsed cycle time from state  805 . Activating the set rate switches  112 , or in some embodiments, a second control input, terminates the set rate mode and activates the infusion pump to pump at the selected rate. The infusion pump then continues as though the infusion rate had been obtained from a programming device. The user may then fully open the roller clamp and the selected infusion rate will be maintained automatically by the infusion pump. 
     It will be understood by persons of skill in the art that the above-described magnet arrangements are not limited to positions and locations described herein. Magnets may be advantageously positioned to move pump components and safely infuse medicament to a patient. For example, in one embodiment of the present invention, magnet arrangements on a rocker arm and on an armature force an upstream pincher and the armature closed when their respective electromagnets are de-energized. This results in a default safe condition in the event that power to the system is interrupted. In representative embodiments, the closed pincher and armature protect against free flow of fluid to the patient. In another embodiment of the present invention, all electromagnets are energized or “on” during the fill stroke and deenergized or “off” during the pumping stroke. This arrangement can again result in a default safe condition in the event that power to the system is interrupted. 
     Persons of skill in the art will understand that the invention is not limited to electromagnet arrangements to move various components. Other devices may be advantageously provided to move the armature and the pinchers. For example, in one embodiment of the present invention, a solenoid moves the armature during the fill and pump strokes. The operation of the solenoid may be controlled by the control module. Similarly, the various magnet arrangements described herein are not limited to a particular type of magnet, as permanent magnets, electromagnets, or both can be advantageously provided. In addition, persons of skill in the art will understand that the above-described detent arrangements are not limited to the mechanisms described herein. In one embodiment, for example, pinchers and anvils are used to constrain the tubing, instead of pinchers and detents. The anvils can be made of any suitable material, such as but not limited to, plastic. 
     It will also be understood by persons of skill in the art that all or various components of the present invention may be disposable. Embodiments of the present invention may include disposable single-use pumps that infuse medicament to a single patient over a lifespan of three to four days, for instance. In some embodiments, the tubing mechanism and air detector may be disposable, single-use components, while the flow sensor mechanism may be a permanent pump component for use on successive patients. 
     Finally, it will be understood by persons of skill in the art that the present invention is not limited in the type or size of magnet, type or size of tubing, or type or viscosity of medicament. 
     Experimental Results 
     The results of one experiment are shown in  FIG. 16A . The force (designated “Tubing Filling Force at 0 Pressure”) exerted by a representative section of tubing filled with fluid at 0 psi pressure was shown to vary from about 5 ounces at a tubing gap of 0.035 inches to about 13.5 ounces when flattened at a tubing gap of 0 inches. The shape of the force curve over this range was nonlinear in nature. In the same experiment, a magnetic force (designated “Magnetic Force Applied to Tubing”) was applied to the tubing. The shape of the applied force resembled the shape of the force curve of the tubing. The size of the applied force was about 8.1 ounces at a tubing gap of 0.035 inches and about 18.5 ounces at a flattened tubing gap of 0 inches. This force is slightly larger than the force required to compress the tubing when pressurized at maximum pressure and is the same magnet force applied to the tubing during the pump stroke, as described above with reference to pump stroke process  700  illustrated in  FIG. 13 . As shown in  FIG. 16A , the difference between these two forces (designated net force) is somewhat more linear in shape and varies from about −4 ounces (the minus sign indicates that the direction of the force is in the direction of compressing the tubing) at a tubing gap of 0.035 inches and about −5 ounces at a collapsed tubing gap of 0 inches. 
     In order to open and fill the above collapsed tubing, an external force with a magnitude slightly greater than the designated net force must be applied to the tubing in the direction of opening the tubing. In an embodiment of the invention illustrated in  FIG. 7A , this force is supplied by the armature electromagnet as it pivots the armature to open the tubing. As the tubing opens from a collapsed gap of 0 inches to a gap of 0.035 inches, energy is transferred from the elastic energy in the tubing walls and the armature electromagnetic field to the field of the magnet. It was found that increasing the pressure in the tubing during this fill stroke did not result in a failure of the tubing to open when the armature electromagnetic field was applied. However, decreasing the pressure in the tubing slightly did cause the tubing to fail to fully open and thereby fail to “fill” with fluid. Embodiments of the present invention, such as that shown in  FIG. 7A , could detect this failure to “fill” and generate an upstream occlusion alarm. 
     Further results of the experiment are shown in  FIG. 16B . The force (designated “Tubing Force at Maximum Fluid Pressure”) required to collapse a representative section of pressurized tubing is shown to vary from about 8 ounces at a tubing gap of 0.035 inches to about 18.5 ounces when flattened at a tubing gap of 0 inches. The shape of the force curve over this range was nonlinear in nature. In the same experiment, a magnetic force (designated “Magnetic Force Applied to Tubing”) was applied to the tubing. The shape of the curve of the applied force resembled the shape of the force curve of the tubing. The size of the applied force was only slightly larger than the force exerted by the pressurized tubing so that the applied force caused the tubing to be compressed. It was found that reducing the pressure in the tubing did not result in a failure of the magnet to collapse the tubing and thereby fail to “pump” the fluid out of the tubing. However, increasing the pressure in the tubing slightly did cause the magnet to fail to collapse the tubing, and therefore the fluid failed to “pump” out of the tubing. Embodiments of the present invention, such as those shown in  FIG. 7B , could detect this failure to collapse the tubing and generate a downstream occlusion alarm. 
     Again referring to  FIG. 16B , because the applied magnet collapsing force is greater than the tubing force at maximum pressure, no additional forces need be applied to collapse the tubing. Energy is transferred from the field of the magnet to elastic energy in the tubing walls as the tubing transitions from an open to collapsed state. 
     In summary, it was found in this experiment that no force was required to open the tubing under 0 pressure when the magnet force was not present. An applied force from about −5 ounces to about −4 ounces was required to open the tubing when the magnetic force was present. It was also found that the force required to collapse the tubing under maximum pressure without the magnetic force present varied from about 18.5 ounces to about 8.1 ounces. The addition of the magnetic force caused the tubing to collapse entirely without any additional force applied. In this experiment, the addition of a magnetic collapsing force to the tubing resulted in a reduction of peak force from about 18.5 ounces to about 5 ounces, thereby significantly reducing both the size and the power requirements required to evacuate and fill the tubing. 
     The above-described embodiments have been provided by way of example, and the present invention is not limited to these examples. Multiple variations and modifications to the disclosed embodiments will occur, to the extent not mutually exclusive, to those skilled in the art upon consideration of the foregoing description. Additionally, other combinations, omissions, substitutions and modifications will be apparent to the skilled artisan in view of the disclosure herein. Accordingly, the present invention is not intended to be limited by the disclosed embodiments.