it is important to eliminate the variations from one pump to the next ( of the same design ) that are a result of manufacturing limitations . the present invention can be used to minimize the effects of these variations and results in accurate delivery in any type of liquid pump . as discussed in the background , there is one type of liquid pump with which the present invention is particularly advantageous , the miniature piston type pump . the piston diaphragm assembly of a miniature pump requires extremely high manufacturing tolerances in order to generate a reproducible dose volume from one pump to the next . even with high precision manufacturing , a not insignificant variation from one pump to the next of a given design may be present . this is less than ideal , especially in applications of the pump involving drug delivery or other medicinal applications . the present invention provides a simple , inexpensive and reliable mechanism and method for minimizing , or “ zeroing out ” the differences from pump to pump . one aspect involves a logic or processor controlled routine that may be thought of as an automatic calibration of the device . in a most general sense , this involves measuring the volume of a dosage produced by a given pump , comparing that dosage to a nominal dosage volume expected for that particular type of pump design , and then adjusting the pump output accordingly . this can also be accomplished by measuring the flow rate and then adjusting accordingly . both volume and flow rate measurement comprise usage of one or more sensors that indicate the presence of liquid at a given point or points . although there are many ways of adjusting the output of the pump , the preferred way of doing this is by calculating a ratio of a measured versus expected volume and calibrating the delivery based upon the ratio . although the present invention can be used with the delivery of any fluid in any environment , in the medical environment where the present invention is particularly suitable , the types of liquids that can be delivered include , but are not limited to : insulin , antibiotics , anesthetics , nutritional fluids , analgesics , hormones or related drugs , gene therapy drugs , anticoagulants , cardiovascular medications , hiv treatments , cancer treatments , etc . these can be delivered transcutaneously , through a type of patch on the skin , or the liquid may be evaporated and inhaled . the present invention is not limited to the delivery of these liquids or by the means of ingress into the patient &# 39 ; s system , and these are only examples , not an exhaustive list . again , one application where the present invention may be particularly useful is in the delivery of insulin . specifically , it may be useful in delivery of small quantities of insulin regularly with what is known as a miniature or micro pump . as the name implies , a miniature or micro pump delivers relatively small quantities . in the preferred embodiments described , which are tailored to insulin delivery , each actuation or dose of such a micro or miniature pump is on the order of approximately 0 . 5 to 5 . 0 microliters , with a potential total delivery of around 1000 microliters per day . delivery volumes for other liquids ( in the medical arena , that is ) may be as high as around 5000 microliters or 5 cc &# 39 ; s per day . fig1 a is a flow chart describing operation according to an embodiment of the present invention seen in the schematic diagram of fig1 b . the process depicted in fig1 a can be performed at any time . it may also be done in conjunction with priming of the pump . in fig1 b there are two sensors , up - stream sensor 144 , and down stream sensor 146 , with a known volume between the two sensors . in this embodiment the known volume , or calibration region 154 , has a cylindrical shape , but any geometric ( regular or irregular ) shape may be employed , so long as the volume is known or can be ascertained . the geometry of the calibration region should be such that it can be manufactured with sufficiently high reproducibility , and the volume of the calibration region is preferably much greater than the volume of an individual dose of insulin solution . this ensures good resolution and accuracy in the measurement . the sensors are connected to control unit 150 , which is also connected to pump 200 . control unit 150 comprises drive circuitry 250 and logic unit 152 , which is preferably in the form of a microprocessor . each sensor comprises a pair of conductive electrodes , and when current passes between the electrodes of the pair , it indicates the presence of a liquid by the establishment of electrical continuity between the pair of electrodes . as long as the liquid has some measure of electrical conductivity , the presence of the liquid can be measured . as is appreciated in the art , the material of the electrodes may be tailored for the particular application . in the case of insulin , gold electrodes work well . as mentioned previously , pump 200 may be any type of liquid pump . in applications where cost is a driving factor , it is often preferable to utilize a pump that is driven by a shape memory actuator . this is particularly the case in the medical field , where devices are disposed of and replaced relatively frequently for various reasons . the control unit 150 controls operation of the pump 200 and of the fluid delivery device generally , which may also comprise a user interface ( not shown ) for setting various operating parameters such as the delivery rate and for starting and stopping the device . the control unit also initiates and controls calibration of the device . for more information on the construction and operation of such a device , please refer to u . s . application ser . no . 10 / 683 , 659 filed on oct . 9 , 2003 , published as u . s . patent application publication no . 2004 / 0115067 a1 , and hereby incorporated by this reference in its entirety . returning to the flowchart of fig1 a , in step 105 the control unit initiates liquid flow . then , in step 110 , the control unit detects the arrival of the liquid at point a , which is a first point . this corresponds to up - stream sensor 144 in fig1 b . this can be done either when the liquid first advances or by placing an interruption in the flow stream before it reaches up - stream sensor 144 . for instance , one way of interrupting the flow is to interject a gas bubble into the flow stream . in step 120 , the control unit detects the arrival of the advancing liquid at point b , which corresponds to down - stream sensor 146 in fig1 b . in the case of a cylindrical calibration region 154 with a known diameter , the volume of the region is known if the distance between the two sensors is known . in step 130 , control unit 150 measures the time it takes for the liquid to travel from point a to point b . the volumetric flow rate is also calculated in step 135 based upon the time measured and the known volume between the points . this information is then used to adjust the delivery of the pump , as is seen in step 140 . this process can take place at any time . it can be used initially to calibrate the pump , or during any time during operation of the device . even if a discrete break is not inserted into the flow stream , the sensors may also indicate the flow rate of the device . the signal produced by the electrodes will increase as the rate of conduction of the liquid increases . thus , given that the liquid is uniformly mixed , the signal will increase as the flow rate increases . for a given electrode / liquid combination , a profile of the output versus flow rate can be determined for given concentrations . the controller can then reference this data stored in memory to determine the flow rate . for more information on this , please refer to a co - pending u . s . application ser . no . 11 / 106 , 256 of benjamin m . rush , entitled “ methods for use in assessing a flow condition of a fluid ,” which is hereby incorporated by this reference in its entirety . fig2 a and 2b illustrate pump 200 , an embodiment of one type of pump particularly suited for use in the present invention . this pump is driven by a shape memory element 206 and employs feedback including that from switch 209 , switch 210 , and linear feedback system 211 , all of which indicate the position of piston 204 . pump 200 is shown in the inactive state in fig2 a , and the active state in fig1 b . switch 209 indicates that the plunger or pump is in the open position , and switch 210 indicates it is in the closed position . the pump body comprises a case 201 , a top cap 202 , and a plunger cap 203 . within the pump is a plunger 204 that is normally ( in the inactive state ) held against the plunger cap 203 by a plunger bias spring 205 . the plunger 204 is connected to shape memory element 206 which contracts when heated by a pulse or pulses of current flowing from the v + 207 contact to the v − 208 contact through the shape memory element 206 ( where the v − 208 contact may be the system ground reference ). the power in each pulse is determined by the voltage applied to the shaped memory element through the contacts . it is worth noting that the case is made of an insulating material while the plunger is either made of a conductive material ( e . g . metal ) or is coated with an appropriately conductive material . fig2 a depicts the pump in the inactive state where the shape memory element 206 is not contracted , and the plunger 204 is held against the plunger cap 203 by the plunger bias spring 205 . this is the state to which the pump returns after each activation or pumping cycle . fig2 b shows the pump in the active state where the shaped memory element 206 has contracted enough to pull the plunger 204 up against a stop built into the case 201 . fig2 c illustrates drive circuit 250 , an embodiment of a circuit that may be used with pump 200 . drive circuit 250 includes input and feedback to / from logic unit 152 , which preferably comprises a microprocessor , as mentioned previously . for more information on this and other aspects of a shape memory actuated pump , please refer to co - pending u . s . application ser . no . 11 / 106 , 155 of benjamin m . rush et al ., entitled “ variable volume , shape memory actuated insulin dispensing pump ,” which is hereby incorporated by this reference in its entirety . fig3 is a flowchart depicting operation according to one embodiment of the present invention . in step 310 , the control unit measures the flow rate , as discussed earlier . next in step 320 , the system determines the desired dosage volume . this may be done automatically or may be entered by the user . in step 330 , the system determines the calibration factor based upon the measured flow rate . the calibration factor preferably comprises a ratio of the expected volume of a dose versus the actual volume of a dose . in the case of the piston type pump earlier described , the calibration factor comprises a ratio of the nominal volume of the cylinder versus the actual volume of the cylinder . the nominal volume is either the value of the volume expected from the design specifications or the value expected based upon the nominal value of a large sample of production pieces . once it has been determined , the calibration factor is applied in step 340 and will be applied to subsequent operation of the system , including when a desired dosage is delivered in step 350 . fig4 is a flowchart depicting operation according to another embodiment of the present invention . in step 410 , the volume delivered in one pump stroke is determined . in step 420 , the system determines the desired dosage volume , which may be done automatically or entered by the user . next in step 430 the system determines the number of required strokes corresponding to a desired dosage volume . because of the linear feedback of the present invention , the system may deliver fractions of a stroke , and the number of strokes may include any number and fraction of strokes . next , in step 440 , the system delivers the desired dosage volume by moving the piston the proper number of strokes . fig5 is a flowchart depicting usage of two embodiments of the system . one embodiment comprises two units , a disposable unit and a re - usable unit , whereas the other embodiment incorporates all the components into one disposable unit . some or all of the parts of the system shown in fig1 b may be reusable , but in the case where there exists a reusable component , it comprises control unit 150 . the term disposable refers to the ordinary meaning of the word , and is involves intended usage on the order of days to months . the term reusable also refers to the ordinary meaning and describes a durable component with an intended usage on the order of months to years . in step 510 , the user unpackages the disposable component that has a selected liquid or drug in a reservoir . next , in step 520 , the user mates the disposable component with the re - usable component . alternatively , the user simply unpackages the system ( pre - loaded with the liquid in the reservoir ), which is entirely disposable , in step 525 . thereafter , the controller initiates priming and calibration of the pump in step 530 . in step 540 , the pump then drives the liquid from the reservoir through the internal volume of the pump , including through calibration region 154 . next in step 550 , calibration parameters , such as the calibration factor are determined . thereafter , in step 560 , the controller modifies the subsequent pump timing based upon the calibration parameters . for instance , if the calibration parameters indicate the measured volume of a particular pump is less than the expected nominal volume of production units , the dosage frequency will be increased . in step 570 , the user installs the disposable component ( including the controller in one embodiment ) and programs the desired delivery rate through the controller user interface . step 560 may occur before or after step 570 , and there is no particular order of the steps unless explicitly stated . an embodiment of the present invention was tested in three trials . the dose volume was determined with the embodiment and compared to a gravimetric determination of the dose volume . the results confirm the accuracy of measurements made with the embodiment . the results of three measurements are shown below . a functional model of the calibration device of the present invention was constructed of a length of tubing with an outer diameter of 0 . 125 inches and an inner diameter of 0 . 0625 inches . the sensors were pairs of copper wire and electrical continuity between the two wires of a given pair was measured as an indication of wetting by insulin . a small voltage was applied between each of the sensor electrode pairs . at the point at which the leading edge of the advancing insulin contacted either of the sensor electrode pairs , a circuit was completed resulting in the flow of current through the circuit . this current flow was detected by monitoring the voltage across a current sensing resistor placed in each sensor circuit . the time required for the leading edge of the advancing insulin to traverse the distance between the two sensors was monitored with a timing device . as can be seen below , three trial measurements were consistent to within 1 % and agreed with the two gravimetric measurements to within 1 %. the two gravimetric measurements agreed to within 2 %. the measurement made with the functional model is approximately the average of the two gravimetric measurements . this confirms the accuracy of the present invention . although the various aspects of the present invention have been described with respect to exemplary embodiments thereof , it will be understood that the present invention is entitled to protection within the full scope of the appended claims .
a micro fluid delivery device is particularly useful in medical applications . the device may be worn or carried by the user and may deliver drugs or other medicaments to the user or patient . the device has a control system that accepts input from the user and controls all aspects of operation of the device . the control system measures the output of the pump and adjusts the output of the pump to achieve the desired dosage rate and size . this eliminates differences from pump to pump that result from inevitable variations in the manufacturing of such small scale affordable devices .