Low power electromagnetic pump

Abstract

An electromagnetic pump comprising an armature comprising a pole portion and plunger portion, the plunger portion sized to be received in a cylindrical passage formed in the housing and which guides the armature. The pump further comprises an electromagnet operatively associated with the armature, and the pump is driven during a forward pumping stroke by the partial discharge of a capacitor into the electromagnet. The case of the electromagnet is sized such that a ratio of the case diameter to the core diameter and a ratio of the case length to the case diameter provide for improved electromagnetic efficiency.

1 . In an electromagnetic pump for delivering an infusion medium to a patient, wherein the pump includes an inlet, an outlet, an electromagnet, and an armature positioned for magnetic attraction by said electromagnet to cause movement of said armature to force fluid from said inlet out through said outlet, the electromagnet comprising:
 a) a core of magnetic material in said electromagnet, said core having a core diameter,   b) a coil surrounding said core,   c) a case of magnetic material surrounding said coil and said core, said case being spaced in insulated relation to said coil, said case having a case diameter and a case length, and   d) a ratio of said case diameter to said core diameter being in a range from about 2.5 to about 7.   
   
   
       2 . The electromagnetic pump of  claim 1 , further including a ratio of said case length to said case diameter being in a range from about 1.3 to about 2.3. 
   
   
       3 . The electromagnetic pump of  claim 1  wherein said diameter of said case is less than about 0.28 inches so that said pump can be installed in an implantable drug delivery system. 
   
   
       4 . The electromagnetic pump of  claim 1  wherein said coil has a length of about 0.35 inches, said core has a diameter of about 0.08 inches, and said coil case has a thickness of about 0.013 inches. 
   
   
       5 . The electromagnetic pump of  claim 1  wherein said electromagnet is energized by partial discharge of a capacitor into said coil, and wherein said capacitor is a low leakage high energy density capacitor. 
   
   
       6 . The electromagnetic pump of  claim 5  wherein said capacitor is a solid tantalum capacitor. 
   
   
       7 . The electromagnetic pump of  claim 1  wherein a voltage supplied to said coil ranges between about 1.5 volts to about 6.0 volts. 
   
   
       8 . The electromagnetic pump of  claim 1  wherein a voltage supplied to said coil is terminated at time intervals ranging between about 1 millisecond to about 6 milliseconds. 
   
   
       9 . The electromagnetic pump of  claim 1 , wherein the armature has a pole portion of chrome-molybdenum-iron alloy. 
   
   
       10 . An electromagnetic pump for delivering an infusion medium to a patient, the electromagnetic pump comprising:
 a) a housing having an interior fluid containing region including a fluid receiving chamber and a fluid output chamber in fluid communication therewith, an inlet in fluid communication with said receiving chamber and an outlet in fluid communication with said output chamber,   b) an electromagnet joined to said housing and located external to said fluid containing region,   c) an armature positioned in said fluid containing region of said housing having a pole portion located for magnetic attraction by said electromagnet and having a plunger portion extending from said pole portion, said armature being movably supported in said housing for movement from a rest position through a forward pumping stroke when attracted by said electromagnet to force fluid from said output chamber through said outlet and for movement in an opposite direction through a return stroke back to said rest position, said armature having a stroke volume comprising the cross-sectional area of said armature pole portion times the total displacement of said armature plunger portion during the forward pumping stroke,   d) a magnetic circuit including said electromagnet and said armature and a gap between said pole portion of said armature and said electromagnet for moving said armature toward said electromagnet to close said gap in response to electrical energization of said electromagnet, and   e) said armature comprising said pole portion and said plunger portion being of fixed length and having a structural relationship to said housing and/or components of said pump in said housing to provide a delivered armature stroke volume less than about 0.4 microliters.   
   
   
       11 . The electromagnetic pump of  claim 10  further comprising a check valve operatively associated with said fluid containing region for allowing fluid flow in a direction from said inlet through said outlet and blocking fluid flow in a direction from said outlet through said inlet, said check valve having an element which contacts said armature plunger portion when said armature is in said rest position so as to determine the location of said rest position thereby affecting extent of armature axial movement. 
   
   
       12 . The electromagnetic pump of  claim 10  wherein said housing comprises a pair of components having at least one shim located therebetween so as to allow adjustment of the delivered armature stroke volume. 
   
   
       13 . The electromagnetic pump of  claim 10  wherein said armature pole portion is of chrome-molybdenum-iron alloy. 
   
   
       14 . An electromagnetic pump for delivering an infusion medium to a patient, said electromagnetic pump comprising:
 a) a housing having an interior fluid containing region including a fluid receiving chamber and a fluid output chamber in fluid communication therewith, an inlet in fluid communication with said receiving chamber and an outlet in fluid communication with said output chamber,   b) a check valve operatively associated with said fluid containing region for allowing fluid flow in a direction from said inlet through said outlet and blocking fluid flow in a direction from said outlet through said inlet,   c) an electromagnet carried by said housing and located external to said fluid containing region,   d) an armature positioned in said fluid containing region of said housing having a pole portion located for magnetic attraction by said electromagnet and said armature having a plunger portion extending from said pole portion, said plunger portion having an axial end face facing said check valve, said armature being movably supported in said housing for movement from a rest position through a forward pumping stroke when attracted by said electromagnet to force fluid from said output chamber through said outlet and for movement in an opposite direction through a return stroke back to said rest position, there being a clearance between said armature plunger portion and a surface of said housing, said armature having a stroke volume comprising the cross-sectional area of said armature pole portion times the total displacement of said armature plunger portion during the forward pumping stroke,   e) a bypass check valve for allowing fluid to flow around said armature during said return stroke,   f) a magnetic circuit including said electromagnet and said armature and a gap between said pole portion of said armature and said electromagnet for moving said armature toward said electromagnetic to close said gap in response to electrical energization of said electromagnetic,   g) a pump chamber having a volume defined by a region within said housing surface bounded by said check valve, said axial end face of said plunger, and said bypass check valve, and   h) wherein a ratio of said volume of said pump chamber to a stroke volume being less than about 0.9 so as to enable said pump to move a liquid containing gas bubbles.   
   
   
       15 . The electromagnetic pump of  claim 14  wherein said ratio enables said pump to move said liquid containing said gas bubbles having a volume up to about 300 microliters against a pressure increase of at least five pounds per square inch. 
   
   
       16 . The electromagnetic pump of  claim 14  further comprising a cylinder formed in said housing and a bypass circuit including said bypass check valve formed around said plunger portion for allowing the passage of air through said pump without breaking down a liquid seal formed between said plunger portion and said cylinder. 
   
   
       17 . The electromagnetic pump of  claim 16  wherein said bypass circuit allows rapid return of said plunger portion to said rest position after a pumping stroke. 
   
   
       18 . The electromagnetic pump of  claim 14 , wherein said armature pole portion is of chrome-molybdenum-iron alloy. 
   
   
       19 . An electromagnetic pump for delivering an infusion medium to a patient, said electromagnetic pump comprising:
 a) a housing having an interior fluid containing region including a fluid receiving chamber and a fluid output chamber in fluid communication therewith, an inlet in fluid communication with said receiving chamber and an outlet in fluid communication with said output chamber,   b) a check valve operatively associated with said fluid containing region for allowing fluid flow in a direction from said inlet through said outlet and blocking fluid flow in a direction from said outlet through said inlet,   c) an electromagnet carried by said housing and located external to said fluid containing region,   d) an armature positioned in said fluid containing region of said housing having a pole portion located for magnetic attraction by said electromagnet and said armature having a plunger portion extending from said pole portion, said plunger portion having an axial end face facing said check valve, said armature being movably supported in said housing for initial movement from a rest position through a forward pumping stroke when attracted by said electromagnet to force fluid from said output chamber through said outlet and for movement in an opposite direction through a return stroke back to said rest position, there being a clearance between said armature plunger portion and a surface of said housing,   e) a magnetic circuit including said electromagnet and said armature and a gap between said pole portion of said armature and said electromagnet for moving said armature toward said electromagnetic to close said gap in response to electrical energization of said electromagnetic, and   f) a ratio of the sealing diameter of the check valve to the diameter of the armature axial end face being greater than about 0.6 to reduce inhibiting the initial movement of the armature.   
   
   
       20 . The electromagnetic pump of  claim 19 , wherein said armature pole portion is of chrome-molybdenum alloy. 
   
   
       21 . In an electromagnetic pump for delivering an infusion medium to a patient, wherein said pump includes a housing having an interior fluid containing region, an inlet and an outlet in fluid communication with said region, an electromagnet carried by said housing and located external to said fluid containing region of said housing, an armature positioned in said fluid containing region of said housing and having a pole portion, a magnetic circuit including said electromagnet, said armature pole portion and a gap in said fluid containing region of said housing between said armature pole portion and said electromagnet, said armature pole portion being located for magnetic attraction by said electromagnetic causing movement of said armature to force fluid out of said region through said outlet:
 a) an electrical circuit including a battery, a capacitor, and a battery recharge component wherein the pump is driven by the partial discharge of said capacitor into said electromagnet; and   b) said capacitor having a capacitance greater than about 1.2 times the minimum value of said capacitor required to drive the pump.   
   
   
       22 . The electromagnetic pump according to  claim 21  wherein said capacitor has low leakage and wherein capacitor energy retained at the end of a pulse driving said armature is not lost between pulses. 
   
   
       23 . The electromagnetic pump according to  claim 21  wherein said capacitor is in electronic communication with said battery having a battery voltage and said capacitor has a voltage at a start of a recharge that is closely below said battery voltage in order that energy lost by a moving charge from said battery voltage to said capacitor voltage is small. 
   
   
       24 . The electromagnetic pump according to  claim 21  wherein a voltage supplied to said electromagnet ranges between about 1.5 volts to about 6.0 volts. 
   
   
       25 . The electromagnetic pump of  claim 21  further wherein a voltage supplied to said electromagnet is terminated at time intervals ranging between about 1 millisecond to about 6 milliseconds. 
   
   
       26 . In an electromagnetic pump for delivering an infusion medium to a patient, wherein said pump includes a housing having an interior fluid containing region, an inlet and an outlet in fluid communication with said region, an electromagnet carried by said housing and located external to said fluid containing region of said housing, an armature positioned in said fluid containing region of said housing and having a pole portion, a magnetic circuit including said electromagnet, said armature pole portion and a gap in said fluid containing region of said housing between said armature pole portion and said electromagnet, said armature pole portion being located for magnetic attraction by said electromagnetic causing movement of said armature to force fluid out of said region through said outlet:
 a) an electrical circuit including a battery, a capacitor, and a battery recharge component wherein the pump is driven by the partial discharge of the capacitor into the electromagnet; and   b) wherein the minimum value of the capacitor required to drive the pump is Cmin=2×Ep/Vb 2  where Ep is the energy required to drive the pump and Vb is the voltage of said battery and wherein the energy required to be supplied by said battery to recharge the capacitor is Erecharge/Ep=2C/Cmin(1−Cmin/c) 1/2 .   
   
   
       27 . The electromagnetic pump according to  claim 26 , wherein the capacitor is a low leakage capacitor. 
   
   
       28 . The electromagnetic pump according to  claim 26 , wherein the capacitor has a value greater than the minimum value of the capacitor required to drive the pump. 
   
   
       29 . The electromagnetic pump according to  claim 26 , wherein the capacitor has a high energy density. 
   
   
       30 . The electromagnetic pump according to  claim 26 , wherein the capacitor is a solid tantalum capacitor. 
   
   
       31 . An electromagnetic pump for delivering an infusion medium to a patient, said electromagnetic pump comprising:
 a) a housing having an interior fluid containing region including a fluid receiving chamber and a fluid output chamber in fluid communication therewith, an inlet in fluid communication with said receiving chamber and an outlet in fluid communication with said output chamber,   b) a check valve operatively associated with said fluid containing region for allowing fluid flow in a direction from said inlet through said outlet and blocking fluid flow in a direction from said outlet through said inlet,   c) an electromagnet carried by said housing and located external to said fluid containing region,   d) an armature positioned in said fluid containing region of said housing having a pole portion located for magnetic attraction by said electromagnet and said armature having a plunger portion extending from said pole portion, said plunger portion having an outer surface and having an axial end face facing said check valve, said armature being movably supported in said housing for initial movement from a rest position through a forward pumping stroke when attracted by said electromagnet to force fluid from said output chamber through said outlet and for movement in an opposite direction through a return stroke back to said rest position, there being a clearance between said outer surface of said armature plunger portion and a surface of said housing,   e) a magnetic circuit including said electromagnet and said armature and a gap between said pole portion of said armature and said electromagnet for moving said armature toward said electromagnetic to close said gap in response to electrical energization of said electromagnetic, and   f) at least one of said outer surface of said armature plunger portion and said surface of said housing being hydrophilic in nature.   
   
   
       32 . The electromagnetic pump according to  claim 31 , wherein at least one of said outer surface of said armature plunger portion and said surface of said housing is of hydrophilic material. 
   
   
       33 . The electromagnetic pump according to  claim 31 , wherein at least one of said outer surface of said armature plunger portion and said surface of said housing is coated with hydrophilic material. 
   
   
       34 . The electromagnetic pump according to  claim 31 , wherein both of said outer surface of said armature plunger portion and said surface of said housing are hydrophilic in nature. 
   
   
       35 . The electromagnetic pump according to  claim 34 , wherein both of said outer surface of said armature plunger portion and said surface of said housing are of hydrophilic material. 
   
   
       36 . The electromagnetic pump according to  claim 34 , wherein both of said outer surface of said armature plunger portion and said surface of said housing are coated with hydrophilic material. 
   
   
       37 . A method for making an electromagnet for an electromagnetic pump to deliver an infusion medium to a patient, the electromagnetic pump comprising an inlet, an outlet, an electromagnet, and an armature positioned for magnetic attraction by said electromagnetic to cause movement of said armature to force fluid out from said inlet through said outlet, said method comprising
 providing said electromagnet with a core of magnetic material, said core having a core diameter,   providing said electromagnet with a coil surrounding said core,   providing said electromagnet with a case of magnetic material surrounding said coil and said core, said case having a case diameter and a case length, and   establishing a ratio of said case diameter to said core diameter being in a range from about 2.5 to about 7.   
   
   
       38 . The method of  claim 37  further including establishing a ratio of said case length to said case diameter in a range from about 1.3 to about 2.3. 
   
   
       39 . The method of  claim 37  further including selecting said diameter of said case to be less than about 0.28 inches so that said pump can be installed in an implantable drug delivery system. 
   
   
       40 . The method of  claim 37  further including selecting said coil length to be about 0.35 inches, selecting said core diameter to be about 0.08 inches, and selecting said coil case thickness to be of about 0.013 inches. 
   
   
       41 . The method of  claim 37  further comprising providing a cylinder formed in said housing and forming a bypass circuit around said plunger portion for allowing the passage of air through said pump without breaking down a liquid seal formed between said plunger portion and said cylinder. 
   
   
       42 . The method of  claim 37  further comprising supplying a voltage to said coil that ranges between about 1.5 volts to about 6.0 volts. 
   
   
       43 . The method of  claim 37  further comprising supplying a voltage to said coil and terminating said voltage at time intervals ranging between about 1 millisecond to about 6 milliseconds. 
   
   
       44 . The method of  claim 37 , wherein said armature is formed to have a pole portion of chrome-molybdenum-iron alloy. 
   
   
       45 . A method of making an electromagnetic pump for delivering an infusion medium to a patient comprising:
 a) providing a housing having an interior fluid containing region including a fluid receiving chamber and a fluid output chamber in fluid communication therewith, an inlet in fluid communication with said receiving chamber and an outlet in fluid communication with said output chamber,   b) providing an electromagnet joined to said housing and located external to said fluid containing region,   c) providing an armature positioned in said fluid containing region of said housing having a pole portion located for magnetic attraction by said electromagnet and having a plunger portion extending from said pole portion, said armature being movable supported in said housing for movement from a rest position through a forward pumping stroke when attracted by said electromagnet to force fluid from said output chamber through said outlet and for movement in an opposite direction through a return stroke back to said rest position, said armature having stroke volume comprising the cross-sectional area of said armature pole portion times the total displacement of said armature plunger portion during the forward pumping stroke,   d) defining a magnetic circuit including said electromagnet and said armature and a gap between said pole portion of said armature and said electromagnet for moving said armature toward said electromagnet to close said gap in response to electrical energization of said electromagnet, and   e) providing said armature comprising said pole portion and said plunger portion of fixed length and having a structural relationship to said housing and/or components of said pump in said housing to provide a delivered armature stroke volume less than about 0.4 microliters.   
   
   
       46 . The method of  claim 45  comprising providing a check valve operatively associated with said fluid containing region for allowing fluid flow in a direction from said inlet through said outlet and blocking fluid flow in a direction from said outlet through said inlet, said check valve being provided with an element which contacts said armature plunger portion when said armature is in said rest position so as to determine the location of said rest position and thereby affect extent of armature axial movement. 
   
   
       47 . The method of  claim 45  comprising providing said housing with a pair of components having at least one shim located therebetween so as to allow adjustment of the delivered armature stroke volume. 
   
   
       48 . The method of  claim 45  wherein said armature pole portion is formed of chrome-molybdenum-iron alloy. 
   
   
       49 . A method of making an electromagnetic pump for delivering an infusion medium to a patient comprising:
 a) providing a housing having an interior fluid containing region including a fluid receiving chamber and a fluid output chamber in fluid communication therewith, an inlet in fluid communication with said receiving chamber and an outlet in fluid communication with said output chamber,   b) providing a check valve operatively associated with said fluid containing region for allowing fluid flow in a direction from said inlet through said outlet and blocking fluid flow in a direction from said outlet through said inlet,   c) providing an electromagnet carried by said housing and located external to said fluid containing region,   d) providing an armature positioned in said fluid containing region of said housing having a pole portion located for magnetic attraction by said electromagnet and said armature having a plunger portion extending from said pole portion, said plunger portion having an axial end face facing said check valve, said armature being movably supported in said housing for movement from a rest position through a forward pumping stroke when attracted by said electromagnet to force fluid from said output chamber through said outlet and for movement in an opposite direction through a return stroke back to said rest position, there being a clearance between said armature plunger portion and a surface of said housing, said armature having a stroke volume comprising the cross-sectional area of said armature pole portion times the total displacement of said armature plunger portion during the forward pumping stroke,   e) providing a bypass check valve for allowing fluid to flow around said armature during said return stroke,   f) defining a magnetic circuit including said electromagnet and said armature and a gap between said pole portion of said armature and said electromagnet for moving said armature toward said electromagnetic to close said gap in response to electrical energization of said electromagnetic,   g) said pump having a pump chamber having a volume defined by a region within said housing surface bounded by said check valve, said axial end face of said plunger, and said bypass check valve, and   h) selecting the stroke volume and the volume of said pump chamber so that a ratio of the volume of said pump chamber to the stroke volume is less than about 0.9 so as to enable said pump to move a liquid containing gas bubbles.   
   
   
       50 . The method of  claim 49  further comprising selecting said ratio so as to enable said pump to move said liquid containing said gas bubbles having a volume up to about 300 microliters against a pressure increase of at least five pounds per square inch. 
   
   
       51 . The method of  claim 49  further comprising forming a cylinder in said housing and forming a bypass circuit including said bypass check valve around said plunger portion for allowing the passage of air through said pump without breaking down a liquid seal formed between said plunger portion and said cylinder. 
   
   
       52 . The method of  claim 49  wherein said armature pole portion is formed of chrome-molybdenum-iron alloy. 
   
   
       53 . In a method for operating an electromagnetic pump for delivering an infusion medium to a patient, wherein said pump includes a housing having an interior fluid containing region, an inlet and an outlet in fluid communication with said region, an electromagnet carried by said housing and located external to said fluid containing region of said housing, an armature positioned in said fluid containing region of said housing and having a pole portion, a magnetic circuit including said electromagnet, said armature pole portion and a gap in said fluid containing region of said housing between said armature pole portion and said electromagnet, said armature pole portion being located for magnetic attraction by said electromagnetic causing movement of said armature to force fluid out of said region through said outlet, and an electrical circuit including a battery, a capacitor and a battery recharge component for energizing said electromagnet, the method comprising:
 a) causing said capacitor to have low leakage and retaining capacitor energy at the end of a pulse driving said armature so that said capacitor energy is not lost between pulses, and   b) causing said capacitor to be in electronic communication with said battery having a battery voltage and causing said capacitor to have a voltage at a start of a recharge that is closely below said battery voltage in order that energy lost by a moving charge from said battery voltage to said capacitor voltage is small.   
   
   
       54 . The method of operating an electromagnetic pump according to  claim 53  including supplying a voltage to said electromagnet that ranges between about 1.5 volts to about 6.0 volts. 
   
   
       55 . The method of operating an electromagnetic pump according to  claim 53  wherein a voltage is supplied to said electromagnet and is terminated at time intervals ranging from between about 1 millisecond to about 6 milliseconds.