US20050191194A1 - Low power electromagnetic pump having internal compliant element - Google Patents
Low power electromagnetic pump having internal compliant element Download PDFInfo
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- US20050191194A1 US20050191194A1 US10/787,999 US78799904A US2005191194A1 US 20050191194 A1 US20050191194 A1 US 20050191194A1 US 78799904 A US78799904 A US 78799904A US 2005191194 A1 US2005191194 A1 US 2005191194A1
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- Prior art keywords
- pump
- accumulator
- armature
- low power
- pump body
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Classifications
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
- A61M5/14212—Pumping with an aspiration and an expulsion action
- A61M5/14216—Reciprocating piston type
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/16877—Adjusting flow; Devices for setting a flow rate
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B11/00—Equalisation of pulses, e.g. by use of air vessels; Counteracting cavitation
- F04B11/0008—Equalisation of pulses, e.g. by use of air vessels; Counteracting cavitation using accumulators
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B17/00—Pumps characterised by combination with, or adaptation to, specific driving engines or motors
- F04B17/03—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors
- F04B17/04—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors using solenoids
- F04B17/042—Pumps characterised by combination with, or adaptation to, specific driving engines or motors driven by electric motors using solenoids the solenoid motor being separated from the fluid flow
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
- A61M5/14244—Pressure infusion, e.g. using pumps adapted to be carried by the patient, e.g. portable on the body
- A61M5/14276—Pressure infusion, e.g. using pumps adapted to be carried by the patient, e.g. portable on the body specially adapted for implantation
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
- A61M5/145—Pressure infusion, e.g. using pumps using pressurised reservoirs, e.g. pressurised by means of pistons
- A61M5/148—Pressure infusion, e.g. using pumps using pressurised reservoirs, e.g. pressurised by means of pistons flexible, e.g. independent bags
- A61M5/152—Pressure infusion, e.g. using pumps using pressurised reservoirs, e.g. pressurised by means of pistons flexible, e.g. independent bags pressurised by contraction of elastic reservoirs
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/165—Filtering accessories, e.g. blood filters, filters for infusion liquids
Definitions
- This invention relates to the field of low power electromagnetic pumps that, for example, can be used in implantable medical device applications, and more particularly to a new improved low power electromagnetic pump having an internal compliant element.
- the inertial effects may come into play.
- the inertia of the flow through the rigid inlet and tubes can be an important factor tending to degrade the accuracy of low power electromagnetic pumps.
- One way this flow inertia is controlled is by the combination of suitable located orifices and properly chosen catheter and accumulator designs.
- a solenoid pump including a titanium aneroid accumulator element installed within a sideport assembly.
- the sideport assembly is located on an external surface of the pump housing between an exit port of the pump mechanism an a catheter.
- the compliant element being installed between the pump and the outlet tube, the flow through the outlet tube can be decoupled from the flow through the pump, thus reducing or eliminating the inertial flow.
- the outlet tube- may therefore be longer and of smaller diameter as required, thus providing the flexibility desired by the customer without degrading the pump accuracy.
- One aspect of this invention involves the benefits that are derived from an alternative approach which comprises moving the accumulator from the end of the outlet tube to the interior of the pump body.
- These benefits comprise: a more compact pump assembly; facilitated installation of the pump in implantable medical devices; decreased pump housing size; and a decrease in the number of external parts and components. Additionally, there is the added benefit that the accumulator is protected from the outside environment by the pump body.
- Another aspect of the invention involves a low porosity filter at the inlet side of the pump.
- the connecting tubing is usually short enough and of large enough diameter so that the viscous pressure drop through the tubing is not a problem, and a conventional accumulator is not required.
- this filter may be incompatible with high flow rates.
- the filter itself, or the structure which supports the filter in the pump housing are designed so that they flex during the pump stroke so that flow may be delivered rapidly to the pump inlet without passing through the filter. Flow may then pass through the filter more slowly driven by the spring constant of the deformed filter or its supporting structure during the interval between pumping strokes.
- This is a special type of accumulator in which the total internal volume of the flow system is not changed as the accumulator is emptied and refilled, but the volume change downstream exactly compensates for the volume change upstream.
- the invention encompasses a low power electromagnetic pump having an internal compliant element.
- the pump has a pump body or housing defining an interior fluid containing region comprising a inlet port and an outlet port that are in fluid communication with one another.
- Check valve means are operatively associated with the fluid containing region for allowing fluid flow in a direction from the inlet port through the outlet port and blocking fluid flow in a direction from the outlet port through the inlet port.
- An accumulator is located inside the pump body in the interior fluid containing region and is fluid communication with the inlet port and outlet port.
- the electromagnet means are carried by the pump body and located external to the interior fluid containing region defined in the pump body.
- An armature is positioned in the interior fluid containing region of the housing and comprises a pole portion for attraction to the electromagnet means.
- the armature is movably supported in the housing for movement from a rest position through a forward pumping stroke when the pole portion is attracted by the electromagnet to force fluid out the outlet port and for movement in an opposite direction through a return stroke back to the rest position.
- the accumulator may comprise a bellows-shape or a diaphragm shape.
- the inlet filter may also serve as an accumulator.
- FIG. 1 shows a longitudinal sectional view of a low power electromagnetic pump with an aneroid type (bellows-shaped) accumulator installed in the pump body in accordance with the invention.
- FIG. 2 shows a longitudinal sectional view of an embodiment of a low power electromagnetic pump according to the invention comprising a diaphragm type accumulator installed in the pump body.
- FIG. 3 shows a longitudinal sectional view of an embodiment of a low power electromagnetic pump according to the invention having an inlet filter mounted between two compliant O-rings in the pump body.
- FIG. 4 shows a longitudinal sectional view of a an embodiment of a low power electromagnetic pump according to the invention having an accumulator comprising a bellow-shaped accumulator with a dimple modification.
- FIG. 5 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element at the rest stage of pump operation.
- FIG. 6 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing another stage of the forward stroke of the pump armature.
- FIG. 7 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing a stage of the forward stroke of the pump armature.
- FIG. 8 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing the return stroke of the pump armature.
- FIG. 1 shows a longitudinal sectional view of a low power electromagnetic pump 10 having an internal compliant element 300 according to the invention.
- One of the purposes of placing the internal compliant element 300 inside the pump body 32 is to allow for rapid pumping operation of the pump 10 , and the subsequent slow delivery of the fluid pumped to the outlet port 20 .
- the outlet port 20 may be connected with an appropriate fitting so that it can be connected to a catheter (not shown).
- the pump 10 may thus be used, for example, in implantable drug delivery systems, although the principles of this invention can be variously applied.
- Following the description of the pump 10 herein are exemplary comparisons showing the pumping results obtained when the pump 10 does not have an internal compliant element, and when the pump does have the internal compliant element 300 . The comparisons show the beneficial effects of the internal compliant 300 .
- the pump 10 comprises a pump housing or pump body 32 which is generally hollow, and defines an interior fluid containing region 12 .
- An inlet ferrule 56 is affixed to the pump body 32 .
- the inlet ferrule 56 defines a fluid receiving chamber 14 , and the inlet port 18 leads to the fluid receiving chamber 14 .
- An outlet ferrule 318 is affixed to the pump body 32 .
- a fluid output chamber 16 is in fluid communication with an outlet port 20
- the internal compliant 300 is interposed in the flow path between the fluid output chamber 16 and the outlet port 20 .
- the inlet port 18 and outlet port 20 are in fluid communication with one another via pump 10 .
- Inlet port 18 is adapted to be connected to a source or supply of fluid to be pumped, and outlet port 20 is adapted to be in fluid communication with a location to which fluid is to be pumped.
- a check valve means 24 operatively associates with the fluid-containing region of pump 10 for allowing fluid flow in a direction from the inlet port 18 through the pump 10 and out through the outlet port 20 , while blocking fluid flow in a direction from the outlet port 20 through the pump 10 and out through the inlet port 18 .
- the check valve means 24 is operatively associated with a pump armature 45 . Fluid enters the inlet port 18 , is pumped through the pump 10 by the armature 45 , and exits through the outlet port 20 .
- the pump body 32 contains an accumulator recess 320 for accommodating the internal compliant element 300 therein.
- the internal compliant element 300 in FIG. 1 is embodied as a bellows-type compliant element 300 and may be embodied as an aneroid-type compliant element 300 .
- the accumulator recess 320 is in fluid communication with a outlet tube 130 located within the pump body 32 and with the fluid output chamber 16 .
- the internal compliant element 300 is positioned in the accumulator recess 320 which is located between and which is in fluid communication with both the outlet tube 130 and the pump outlet port 20 .
- the accumulator recess 320 is closed or sealed from the external environment by a plug or the like.
- the bellows type compliant element 300 When fluid is pumped, the bellows type compliant element 300 , which may be made of a resilient material such as rubber, plastics, springable titanium, and other suitable materials, flexes and controls viscous pressure drops and the inertial effects of the fluid being pumped.
- the pump body 32 defines a plurality of chambers in the pump 10 . These chambers comprise an armature shaft chamber 124 , a main spring retainer chamber 126 , a bypass chamber 136 , and the accumulator recess 320 in fluid communication with one another.
- the inlet port 18 is in fluid communication with and leads to the armature shaft chamber 124 which is sized to accommodate the pump armature 45 therein.
- the armature shaft chamber 124 leads to and is in fluid communication with the main spring retainer chamber 126 the width or cross-section dimension of which is greater than the width or cross-section dimension of the armature shaft chamber 124 .
- the main spring retainer chamber 126 is in fluid communication with and leads to output chamber 16 , the width or cross-section dimension of the output chamber 16 being greater than the width or cross-section dimension of the main spring retainer chamber 126 .
- the output chamber 16 leads to outlet tube 130 defined in the pump body 32 , and the outlet tube 130 is in fluid communication with the compliant element recess 320 defined in the pump body 32 .
- the compliant element recess 320 is sized to hold the internal compliant element 300 therein, thus allowing the internal compliant element 300 to be in fluid communication with the fluid output chamber 16 , outlet tube 130 , and outlet port 20 .
- the outlet tube 130 is short. As an illustrative example the length of the outlet tube 130 , designated L in FIG.
- the outlet tube 130 defines an outlet orifice 132 that may be, for example, between about 0.005 inches and 0.03 inches in diameter.
- FIGS. 2 and 3 show other embodiments wherein the length of the outlet tube 130 is greater than that shown in FIG. 1 .
- a passage or orifice 44 is defined in the housing 32 and leads from the armature shaft chamber 124 to a plug chamber 134 .
- the orifice 44 which may be of small diameter, provides for fluid communication between the armature shaft chamber 124 and the plug chamber 134 .
- the plug chamber 134 leads to and is in fluid communication with a bypass chamber 136 .
- the bypass chamber 136 is in fluid communication with the output chamber 16 .
- the pump armature 45 comprises a pole portion 48 joined to a plunger portion 59 by inner weld ring 75 .
- the armature 45 plunger portion 59 comprises a first shaft portion 60 , a second shaft portion 62 of slightly greater diameter than the first shaft portion 60 , a third shaft portion 64 of greater diameter than the second shaft portion 62 , and a head portion 66 comprising a diameter many time greater than the diameter of the third shaft portion 64 .
- the plunger portion 59 which might be titanium and/or its alloys and/or biocompatible materials, may machined and/or formed from a piece of plunger stock.
- the inner weld ring 75 thus joins the head portion 66 of the armature 45 with the pole portion 48 and a shell 108 .
- the shell 108 holds a magnetic body 109 , and a vacuum hole 70 is provided in armature head portion 66 .
- a vacuum is created through the vacuum hole 70 and in the shell 108 to draw the magnetic body 109 against the head portion 66 whereupon the hole is sealed by a plug 71 .
- the body 109 is thus held tightly inside the shell 108 as the armature 45 cycles.
- the pole portion 48 is thus encased to protect the body 109 against potentially corrosive effects of the fluid being pumped.
- the main check valve means 24 shown in FIG. 1 is adjacent the upstream end of the armature shaft chamber 124 and allows fluid from an upstream location, for example a reservoir, to enter the pump 10 when the pump 10 is activated.
- This is the forward stroke 148 shown FIGS. 6 and 7 which will be described presently.
- the check valve means 24 comprises a disc shaped body or seat 150 with one surface 152 contacting the inlet ferrule 56 and the opposite surface 153 contacting biasing spring 154 .
- the spring 154 biases against the seat 150 and armature 45 .
- the check valve means 24 opens allowing fluid from an upstream location to enter the pump 10 .
- An electromagnet means 100 is isolated from the fluid being pumped by a plate or diaphragm 110 .
- the plate 110 serves as a barrier to prevent the fluids being pumped from contacting the electromagnet 100 and its parts and components.
- the electromagnet means 100 is activated cyclically to generate an electromagnetic field to pull the armature 45 towards which draws fluid into the pump 10 .
- the electromagnet means 100 is deactivated, the armature 45 is returned to its at rest state ( FIG. 5 ) by spring 90 in a manner which will be described, and the check valve means 24 closes.
- a retainer element 52 having an annular body 54 and a lip portion 55 is provided for the main spring 90 to act against.
- the first and second shaft portions 60 , 62 of the armature 45 are fitted through the bore of the retainer element 52 , until the retainer element 52 contacts a shoulder 68 formed on the armature 45 .
- the retainer element 52 is joined to the second shaft portion 62 by welding/laser welding and/or friction fitting.
- a retainer plate 80 is provided, having a bypass fluid chamber opening 82 , an outlet opening 84 , and a central opening 86 .
- the central opening 86 is sized to receive the third plunger shaft portion 64 therein, as shown in FIG. 1 .
- the retainer plate 80 also comprises an annular flange 88 surrounding the central opening 86 .
- An outer weld ring 94 comprises an annular support protrusion or lip 95 .
- the retainer plate 80 is positioned between the pump body 32 and the support protrusion 95 , and becomes trapped therebetween upon welding the outer weld ring 94 . This prevents the movement of the retainer plate 80 as the pump 10 cycles.
- the electromagnet means 100 is carried by the pump body 32 and is external to the fluid containing region of the pump body 32 .
- the electromagnet 100 may comprise a core wrapped in a coil and is capable of rapidly energizing and de-energizing to create a magnetic field. This magnetic field then attracts the pole portion 48 of the armature 45 . When the pole portion 48 is attracted, the armature 45 compresses the main spring 90 as it moves towards the electromagnet 100 . At substantially the same time fluid is drawn into the pump 10 . When the electromagnet 100 de-energizes the main spring 90 expands and applies force on the retainer element 52 which moves the armature 45 back to its at rest position in the pump 10 ( FIG. 1 ).
- a means for bypass check valving 74 (bypass check valve means) 74 is positioned internal to the pump body 32 , between the orifice 44 and a bypass chamber 136 .
- Spring 76 is located between check valve element 78 and a plug 42 mounted to the housing 32 in a plug chamber 134 .
- the bypass check valve means 74 controls fluid communication between the orifice 44 and bypass fluid chamber 136 .
- the bypass check valve means 74 opens. Fluid from the armature shaft chamber 124 flows through the orifice 44 and forces element 78 to open the bypass check valve means 74 . The fluid then flows into the bypass chamber 136 .
- the first shaft portion 60 , second shaft portion 62 , and third shaft portion 64 are moved through the central opening 86 in the spring retainer plate 80 and through the main spring 90 . Then, the first and second shaft portions 60 , 62 , respectively, are moved through the retainer element 52 until the retainer element 52 contacts shoulder 68 . The retainer element 52 is joined, welded/laser welded, or pressure fitted and welded/laser welded to the second shaft portion 62 . The armature 45 is then inserted into the armature shaft chamber 124 .
- the outer weld ring 94 is moved into the pump body 32 around the retainer plate 80 , until the outer weld ring 94 support protrusion 95 and retainer plate 80 contact.
- the outer weld ring 94 is welded/laser welded to the pump body 32 , trapping the retainer plate 80 between the pump body 32 and the support protrusion 95 .
- FIGS. 5-8 show the cycling of the pump 10 :
- the above-described pumping cycle can be repeated at predetermined intervals. It is noted that the closed check valve 24 during the return stroke 149 prevents fluid from exiting the inlet port 18 . Also, the following structure for the pump is for illustrative purposes, and the installation of the internal compliant 300 will work with pumps embodied with different internal structure.
- Compliance may be related to how a fluid path, as defined by the structural body forming the path or part of the path, expands, contracts or deflects under an environmental input, such as, for example, a pressure load from a pump mechanism that is intended to deliver an amount of fluid to an output component, for example a catheter.
- One of the purposes of the internal compliant element 300 is to allow for rapid pumping of the pump 10 , and the subsequent slow delivery of the fluid pumped to the outlet port 20 , and then to, for example, a catheter.
- Another of the purposes of the internal compliant element 300 is to reduce inertial effects of the fluid being pumped, as such inertial effects can interfere with the smooth operation of the pump 10 and may cause delivery problems.
- the 3.46 inch effective length outlet tube used in this calculation is intended to represent an actual outlet tube 2.57 inches long terminated by an outlet fitting. Since the outlet fitting is assumed to be of smaller inner diameter than the outlet tube, the inertial effective length of the outlet tube is increased by the fitting by an amount greater than the physical length of the outlet fitting.
- Table 1 shows the calculated results for a representative configuration of a low power electromagnetic pump with an external accumulator similar to that shown in U.S. Pat. No. 5,9979,733. Although values for leakage through the armature pump body clearance and for the inertial flow were calculated they are omitted from the tabulated results.
- results shown incorporate the calculated magnetic force on the armature, the drag of the pole button as it moves through the pump body and approaches the diaphragm face, the inertia of the plunger, the inertia of the flow upstream of the pump and downstream of the pump outlet, pressure drops in the main flow, bypass circuit and outlet tube caused by check valves, viscosity and orifice restrictions, leakage of fluid through the between the pump body and armature, the increase in pressure in the accumulator during the pumping pulse.
- the outlet tube has a length of 2.6 inches.
- the effective outlet tube length with outlet fitting is 3.46 inches.
- Table 1 shows the calculated results for an external accumulator with the effective length of outlet tube being 3.46 inches. It is noted that in the table the phrase “pounds per square inch” has been abbreviated to PSI in the tables.
- the results for the 0.03 ⁇ L/psi accumulator and the 0.005 inch outlet orifice correspond to a pump of the type shown in U.S. Pat. No. 5,797,733 if it is driven by the lower excitation normally used to drive a pump shown in U.S. Pat. No. 6,264,439.
- the results indicate that under these conditions the armature 45 is not drawn in fully against 10 psi before the capacitor is discharged and the pulse volume against 10 psi is 10% lower than the pulse volume with no pressure increase across the pump 10 , a value just meeting the specified performance of the pump.
- the pulse volume ratio (pulse volume against 10.0 psi divided by the pulse volume against 0 psi) can be improved to 0.956 by increasing the accumulator compliance to 0.1 ⁇ L/psi or to 0.937 by increasing the diameter of the outlet orifice to 0.009 inches. If both changes are made the pulse volume ratio is degraded to 0.91 by increased inertial flow.
- the third value of compliance listed represents the compliance which would exist if a 50 ⁇ L bubble occupied the volume of the pump body 32 . It is assumed that there is no air in the pump chamber (between the check valve means 24 and armature 45 ), because even a small bubble could cause a reduction in pump volume and a decrease in pump accuracy.
- the use of the 0.03 orifice in this calculation reflects the fact that there is no satisfactory location for an orifice between the armature 45 and the accumulator (bubble) and therefore the effective orifice is large.
- Table 1 also shows that pulse volume is reduced from that calculated for the 0.1 ⁇ L/psi example. This occurs because the inertia of the fluid in the long outlet tube no longer affects the flow during the pumping pulse.
- the calculated PV ratio at 10 psi of 0.952 is well above the specified lower limit of 0.9. However, the PV ratio is less meaningful than the ratio of the fluid delivered with the bubble present to the delivery with the bubble in normal operation with no bubble.
- the pump 10 would deliver greater volume with the bubble within the pump body 32 than it would with no bubble present.
- Table 2 shows the results of calculations in which the accumulator 300 is assumed to be internal to the pump body 32 . This placement of the accumulator 300 shortens the effective length of the outlet tube and reduces the inertial effect. If necessary an orifice can also be accommodated within the pump body 32 upstream of the accumulator. Results are therefore shown for all three orifice sizes. Since the outlet orifice serves to control the inertia effects of both the inlet and outlet tubes, there may be a benefit from including an orifice even though there is effectively no outlet tube.
- Table 2 shows the results of locating a bellows-type accumulator 304 internal to the pump body 32 , between the outlet tube 130 and pump outlet port 20 , as shown in FIG. 1 .
- the internal accumulator 304 has an effective outlet tube 130 length of 0.1 inches, and the outlet orifice 132 diameter is any of the following: 0.005 inches; 0.009 inches; and 0.03 inches. The results are presented in Table 2.
- the effect of a bubble in the body of the pump 10 on the volume delivered against 10 psi is less when the accumulator is internal.
- An advantage of placing the accumulator (compliant element) within the pump body 32 is that it reduces or eliminates the effect of the inertial flow and orifice 132 in the outlet tube 130 on the delivered pulse volume, thereby improving the accuracy of the pump 10 . If a bubble (not shown) should be trapped within the pump body 32 it also acts as an internal compliant element and changes (while the bubble is present) the delivered volume. Placing the compliant element 300 within the pump body 32 has the effect of reducing the magnitude of the change due to the bubble and assists in maintaining the accuracy of the low power electromagnetic pump 10 . Other advantages of placing the compliant internal to the pump body include a more compact pump.
- the pump 10 comprises a diaphragm-type accumulator 306 mounted therein.
- the diaphragm-type accumulator 306 functions in substantially the same way as the bellow-shaped accumulator 304 , in that it allows for rapid pumping of the pump 10 , and the subsequent slow delivery of the fluid pumped to the outlet port 20 and from there to, for example, a catheter.
- the diaphragm type internal compliant 306 also reduces inertial effects of the fluid being pumped, that can interfere with the smooth operation of the pump 10 and that may cause delivery problems.
- the diameters of the orifice 132 presented in the Table 2 are not the only sized orifices available for use in the present invention.
- the orifice diameter of the outlet tube 130 may be in the range of 0.004 inches to 0.04 inches, and the present invention encompasses all outlet orifices sized in this range.
- the length of the outlet tube 130 may be about 0.1 inches.
- FIG. 3 a combination of a diaphragm-type accumulator 306 and a flexible filter accumulator 308 is shown.
- the flexible filter accumulator 308 comprises a filter 98 supported in the ferrule 56 by means for support 305 .
- the means for support 305 shown in FIGS. 3 and 4 include O-rings 310 , but the means for support 305 may be otherwise embodied.
- the flexible filter accumulator 308 shown in FIG. 3 is suitable for use in combination with a low porosity filter 98 , because it permits slow flow through the filter 98 with rapid with rapid flow through the pump 10 .
- FIG. 4 Another embodiment of the low power electromagnetic pump with internal compliant element 10 is shown in FIG. 4 .
- a bellows-type accumulator 304 is used in combination with a flexible filter accumulator 308 .
- the bellows-type accumulator 304 is provided with dimples 307 on the outer surface of the bellows. These dimples 307 ensure proper communication with the pressure source and the mated surfaces of the outer pillows 309 and center pillow 311 of the accumulator 304 .
- the dimples 307 may, in other embodiments, be replace with plus-shaped spacer (not shown) placed above and below each pillow 309 , 311 , with the two center spacers shared by adjacent pillows.
- Other embodiments include a split ring (not shown) that supports the outer edge of each assembly, with its thickness determined by the desired spacing between the pillows.
- the internal compliant element 300 may be variously embodied, all of these within the scope of the present low power electromagnetic pump having an internal compliant element. Also, the performance benefits obtainable by installing an accumulator within the pump body 32 of a low power electromagnetic pump 10 rather than at the end of an external outlet tubing have been calculated, and suitable configurations of the accumulator are shown and described. In addition, an accumulator which does not cause a change in the volume of the flow path has been shown and described. This accumulator is particularly suitable for use in combination with a low porosity filter, since it permits slow flow through the filter and rapid flow through the electromagnetic pump.
- the low power electromagnetic pump having an internal compliant element has been described in connection with particular embodiments and examples, the low power electromagnetic pump having an internal compliant element is not necessarily so limited and that other examples, uses, modifications, and departures from the embodiments, examples, and uses may be made without departing from the low power electromagnetic pump having an internal compliant element. All these embodiments are intended to be within the scope and spirit of the appended claims.
Abstract
Description
- This invention relates to the field of low power electromagnetic pumps that, for example, can be used in implantable medical device applications, and more particularly to a new improved low power electromagnetic pump having an internal compliant element.
- An example of a low power electromagnetic pump provided with an accumulator is found in U.S. Pat. No. 5,797,733 issued Aug. 25, 1988, the disclosure of which is hereby incorporated by reference. This patent shows an outlet tube extending from the pump, with an accumulator attached to the outlet tube and a catheter extending from the accumulator. It has been found to be desirable to incorporate an accumulator in the flow path of a low power electromagnetic pump for several reasons. Such placement of the accumulator allows for both the rapid actuation of the pump and the relative slow delivery of the pumped fluid.
- The need for an accumulator in a pump flow system arise out of two somewhat different causes, namely, viscous pressure drops which may severely limit flow, and inertial effects which may cause the flow to continue after the pump stroke is complete. The design of a low power electromagnetic pump of the type shown in U.S. Pat. No. 5,797,733 is such that the pump operates more and more efficiently as the rate of the plunger strokes increases. The magnetic force required to move the plunger needs to be maintained for a short time and the electrical energy required to energize the electromagnetic coil can be minimized. However, it is usually not possible to move fluid rapidly through the entire flow path, that is, from the fluid reservoir to the outlet of the flow system. In implantable drug delivery systems it is generally required that the drug be delivered through a small diameter catheter. High flow rates through a small diameter catheter lead to high viscous pressure drops and impose significant performance limitations on the pumping device. This problem is typically alleviated by installing an accumulator at some point between the pump outlet and the catheter to accept the rapid pump outflow and deliver it slowly to the catheter.
- If the catheter or the associated tubing are of larger diameter so that the viscous pressure or orifice drops no longer predominate, then the inertial effects may come into play. The inertia of the flow through the rigid inlet and tubes can be an important factor tending to degrade the accuracy of low power electromagnetic pumps. One way this flow inertia is controlled is by the combination of suitable located orifices and properly chosen catheter and accumulator designs.
- The inertial flow problem is aggravated in a pump of the type shown in U.S. Pat. No. 5,797,733, due to the long length of the rigid outlet tube located between the pump and the accumulator. The length of this outlet tube was determined not by the performance requirements of the flow system, but rather by the need to bend the tubing as it was being installed in a particular device. Reducing the diameter of the particular tubing would have allowed the bending requirement to be met with a shorter length of tubing, but this would have been at the expense of increased inertial and perhaps viscous effects degrading the pump accuracy.
- The benefits of reduction of inertial flow and rapid pull-in can be retained even with a long outlet tube of small inner diameter (for flexibility) if the accumulator can be placed between the pump and the outlet tube. This normally requires that the accumulator be hermetically isolated from the environment. Most accumulator designs used in hydraulic systems meet that requirement or can be modified to do so. However, simple accumulators used for testing the pump, for example a short length of silicone rubber tubing between the rigid outlet tube and catheter, do not satisfy the hermetic requirement.
- Published International Patent Application PCT/US99/13902 discloses a solenoid pump including a titanium aneroid accumulator element installed within a sideport assembly. The sideport assembly is located on an external surface of the pump housing between an exit port of the pump mechanism an a catheter. With the compliant element being installed between the pump and the outlet tube, the flow through the outlet tube can be decoupled from the flow through the pump, thus reducing or eliminating the inertial flow. The outlet tube-may therefore be longer and of smaller diameter as required, thus providing the flexibility desired by the customer without degrading the pump accuracy.
- One aspect of this invention involves the benefits that are derived from an alternative approach which comprises moving the accumulator from the end of the outlet tube to the interior of the pump body. These benefits comprise: a more compact pump assembly; facilitated installation of the pump in implantable medical devices; decreased pump housing size; and a decrease in the number of external parts and components. Additionally, there is the added benefit that the accumulator is protected from the outside environment by the pump body.
- Another aspect of the invention involves a low porosity filter at the inlet side of the pump. In particular, on the inlet side of the pump the connecting tubing is usually short enough and of large enough diameter so that the viscous pressure drop through the tubing is not a problem, and a conventional accumulator is not required. However, in some applications it may be desirable to install a low porosity filter on the inlet side, but this filter may be incompatible with high flow rates. In such cases the filter itself, or the structure which supports the filter in the pump housing, are designed so that they flex during the pump stroke so that flow may be delivered rapidly to the pump inlet without passing through the filter. Flow may then pass through the filter more slowly driven by the spring constant of the deformed filter or its supporting structure during the interval between pumping strokes. This is a special type of accumulator in which the total internal volume of the flow system is not changed as the accumulator is emptied and refilled, but the volume change downstream exactly compensates for the volume change upstream.
- Thus, the invention encompasses a low power electromagnetic pump having an internal compliant element. The pump has a pump body or housing defining an interior fluid containing region comprising a inlet port and an outlet port that are in fluid communication with one another. Check valve means are operatively associated with the fluid containing region for allowing fluid flow in a direction from the inlet port through the outlet port and blocking fluid flow in a direction from the outlet port through the inlet port. An accumulator is located inside the pump body in the interior fluid containing region and is fluid communication with the inlet port and outlet port. The electromagnet means are carried by the pump body and located external to the interior fluid containing region defined in the pump body. An armature is positioned in the interior fluid containing region of the housing and comprises a pole portion for attraction to the electromagnet means. The armature is movably supported in the housing for movement from a rest position through a forward pumping stroke when the pole portion is attracted by the electromagnet to force fluid out the outlet port and for movement in an opposite direction through a return stroke back to the rest position. There are means defining a magnetic circuit including the electromagnet means and the armature and a gap between the pole portion of the armature and the electromagnet means for moving the armature toward the electromagnet means to close the gap in response to electrical energization of the electromagnet means. The accumulator may comprise a bellows-shape or a diaphragm shape. The inlet filter may also serve as an accumulator.
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FIG. 1 shows a longitudinal sectional view of a low power electromagnetic pump with an aneroid type (bellows-shaped) accumulator installed in the pump body in accordance with the invention. -
FIG. 2 shows a longitudinal sectional view of an embodiment of a low power electromagnetic pump according to the invention comprising a diaphragm type accumulator installed in the pump body. -
FIG. 3 shows a longitudinal sectional view of an embodiment of a low power electromagnetic pump according to the invention having an inlet filter mounted between two compliant O-rings in the pump body. -
FIG. 4 shows a longitudinal sectional view of a an embodiment of a low power electromagnetic pump according to the invention having an accumulator comprising a bellow-shaped accumulator with a dimple modification. -
FIG. 5 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element at the rest stage of pump operation. -
FIG. 6 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing another stage of the forward stroke of the pump armature. -
FIG. 7 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing a stage of the forward stroke of the pump armature. -
FIG. 8 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing the return stroke of the pump armature. -
FIG. 1 shows a longitudinal sectional view of a low powerelectromagnetic pump 10 having an internalcompliant element 300 according to the invention. One of the purposes of placing the internalcompliant element 300 inside thepump body 32 is to allow for rapid pumping operation of thepump 10, and the subsequent slow delivery of the fluid pumped to theoutlet port 20. Theoutlet port 20 may be connected with an appropriate fitting so that it can be connected to a catheter (not shown). Thepump 10 may thus be used, for example, in implantable drug delivery systems, although the principles of this invention can be variously applied. Following the description of thepump 10 herein are exemplary comparisons showing the pumping results obtained when thepump 10 does not have an internal compliant element, and when the pump does have the internalcompliant element 300. The comparisons show the beneficial effects of the internal compliant 300. - As shown in
FIG. 1 , thepump 10 comprises a pump housing or pumpbody 32 which is generally hollow, and defines an interior fluid containing region 12. Aninlet ferrule 56 is affixed to thepump body 32. Theinlet ferrule 56 defines afluid receiving chamber 14, and theinlet port 18 leads to thefluid receiving chamber 14. Anoutlet ferrule 318 is affixed to thepump body 32. Afluid output chamber 16 is in fluid communication with anoutlet port 20, and the internal compliant 300 is interposed in the flow path between thefluid output chamber 16 and theoutlet port 20. Theinlet port 18 andoutlet port 20 are in fluid communication with one another viapump 10.Inlet port 18 is adapted to be connected to a source or supply of fluid to be pumped, andoutlet port 20 is adapted to be in fluid communication with a location to which fluid is to be pumped. A check valve means 24 operatively associates with the fluid-containing region ofpump 10 for allowing fluid flow in a direction from theinlet port 18 through thepump 10 and out through theoutlet port 20, while blocking fluid flow in a direction from theoutlet port 20 through thepump 10 and out through theinlet port 18. The check valve means 24 is operatively associated with apump armature 45. Fluid enters theinlet port 18, is pumped through thepump 10 by thearmature 45, and exits through theoutlet port 20. - As shown in
FIG. 1 , thepump body 32 contains anaccumulator recess 320 for accommodating the internalcompliant element 300 therein. The internalcompliant element 300 inFIG. 1 is embodied as a bellows-typecompliant element 300 and may be embodied as an aneroid-typecompliant element 300. Theaccumulator recess 320 is in fluid communication with aoutlet tube 130 located within thepump body 32 and with thefluid output chamber 16. The internalcompliant element 300 is positioned in theaccumulator recess 320 which is located between and which is in fluid communication with both theoutlet tube 130 and thepump outlet port 20. Theaccumulator recess 320 is closed or sealed from the external environment by a plug or the like. When fluid is pumped, the bellows typecompliant element 300, which may be made of a resilient material such as rubber, plastics, springable titanium, and other suitable materials, flexes and controls viscous pressure drops and the inertial effects of the fluid being pumped. - The
pump body 32 defines a plurality of chambers in thepump 10. These chambers comprise anarmature shaft chamber 124, a mainspring retainer chamber 126, abypass chamber 136, and theaccumulator recess 320 in fluid communication with one another. Theinlet port 18 is in fluid communication with and leads to thearmature shaft chamber 124 which is sized to accommodate thepump armature 45 therein. Thearmature shaft chamber 124 leads to and is in fluid communication with the mainspring retainer chamber 126 the width or cross-section dimension of which is greater than the width or cross-section dimension of thearmature shaft chamber 124. The mainspring retainer chamber 126 is in fluid communication with and leads tooutput chamber 16, the width or cross-section dimension of theoutput chamber 16 being greater than the width or cross-section dimension of the mainspring retainer chamber 126. Theoutput chamber 16 leads tooutlet tube 130 defined in thepump body 32, and theoutlet tube 130 is in fluid communication with thecompliant element recess 320 defined in thepump body 32. Thecompliant element recess 320 is sized to hold the internalcompliant element 300 therein, thus allowing the internalcompliant element 300 to be in fluid communication with thefluid output chamber 16,outlet tube 130, andoutlet port 20. Theoutlet tube 130 is short. As an illustrative example the length of theoutlet tube 130, designated L inFIG. 1 , may be about 0.1 inches. Theoutlet tube 130 defines anoutlet orifice 132 that may be, for example, between about 0.005 inches and 0.03 inches in diameter.FIGS. 2 and 3 show other embodiments wherein the length of theoutlet tube 130 is greater than that shown inFIG. 1 . - A passage or
orifice 44 is defined in thehousing 32 and leads from thearmature shaft chamber 124 to aplug chamber 134. Theorifice 44, which may be of small diameter, provides for fluid communication between thearmature shaft chamber 124 and theplug chamber 134. Theplug chamber 134 leads to and is in fluid communication with abypass chamber 136. Thebypass chamber 136 is in fluid communication with theoutput chamber 16. These chambers thus provide for a bypass passage in thepump 10 - The
pump armature 45 comprises apole portion 48 joined to aplunger portion 59 byinner weld ring 75. Thearmature 45plunger portion 59 comprises afirst shaft portion 60, asecond shaft portion 62 of slightly greater diameter than thefirst shaft portion 60, athird shaft portion 64 of greater diameter than thesecond shaft portion 62, and ahead portion 66 comprising a diameter many time greater than the diameter of thethird shaft portion 64. Theplunger portion 59, which might be titanium and/or its alloys and/or biocompatible materials, may machined and/or formed from a piece of plunger stock. Theinner weld ring 75 thus joins thehead portion 66 of thearmature 45 with thepole portion 48 and ashell 108. Theshell 108 holds amagnetic body 109, and avacuum hole 70 is provided inarmature head portion 66. During assembly of the pump armature 45 a vacuum is created through thevacuum hole 70 and in theshell 108 to draw themagnetic body 109 against thehead portion 66 whereupon the hole is sealed by a plug 71. Thebody 109 is thus held tightly inside theshell 108 as thearmature 45 cycles. Thepole portion 48 is thus encased to protect thebody 109 against potentially corrosive effects of the fluid being pumped. - The main check valve means 24 shown in
FIG. 1 is adjacent the upstream end of thearmature shaft chamber 124 and allows fluid from an upstream location, for example a reservoir, to enter thepump 10 when thepump 10 is activated. This is theforward stroke 148 shownFIGS. 6 and 7 which will be described presently. The check valve means 24 comprises a disc shaped body orseat 150 with onesurface 152 contacting theinlet ferrule 56 and theopposite surface 153 contacting biasingspring 154. Thespring 154 biases against theseat 150 andarmature 45. During a forward pumping stroke 148 (FIGS. 6 and 7 ) the check valve means 24 opens allowing fluid from an upstream location to enter thepump 10. - An electromagnet means 100 is isolated from the fluid being pumped by a plate or
diaphragm 110. Theplate 110 serves as a barrier to prevent the fluids being pumped from contacting theelectromagnet 100 and its parts and components. The electromagnet means 100 is activated cyclically to generate an electromagnetic field to pull thearmature 45 towards which draws fluid into thepump 10. When the electromagnet means 100 is deactivated, thearmature 45 is returned to its at rest state (FIG. 5 ) byspring 90 in a manner which will be described, and the check valve means 24 closes. - A
retainer element 52 having anannular body 54 and alip portion 55 is provided for themain spring 90 to act against. During assembly, the first andsecond shaft portions armature 45 are fitted through the bore of theretainer element 52, until theretainer element 52 contacts ashoulder 68 formed on thearmature 45. Theretainer element 52 is joined to thesecond shaft portion 62 by welding/laser welding and/or friction fitting. - A
retainer plate 80 is provided, having a bypass fluid chamber opening 82, anoutlet opening 84, and acentral opening 86. Thecentral opening 86 is sized to receive the thirdplunger shaft portion 64 therein, as shown inFIG. 1 . Theretainer plate 80 also comprises anannular flange 88 surrounding thecentral opening 86. When the pump is assembled oneend 91 of themain spring 90 abuts thelip portion 55 of theretainer element 52, and theopposite end 92 of themain spring 90 abuts against theannular flange 88 of theretainer plate 80. - An
outer weld ring 94 comprises an annular support protrusion orlip 95. Theretainer plate 80 is positioned between thepump body 32 and thesupport protrusion 95, and becomes trapped therebetween upon welding theouter weld ring 94. This prevents the movement of theretainer plate 80 as thepump 10 cycles. - The electromagnet means 100 is carried by the
pump body 32 and is external to the fluid containing region of thepump body 32. Theelectromagnet 100 may comprise a core wrapped in a coil and is capable of rapidly energizing and de-energizing to create a magnetic field. This magnetic field then attracts thepole portion 48 of thearmature 45. When thepole portion 48 is attracted, thearmature 45 compresses themain spring 90 as it moves towards theelectromagnet 100. At substantially the same time fluid is drawn into thepump 10. When theelectromagnet 100 de-energizes themain spring 90 expands and applies force on theretainer element 52 which moves thearmature 45 back to its at rest position in the pump 10 (FIG. 1 ). - A means for bypass check valving 74 (bypass check valve means) 74 is positioned internal to the
pump body 32, between theorifice 44 and abypass chamber 136.Spring 76 is located betweencheck valve element 78 and aplug 42 mounted to thehousing 32 in aplug chamber 134. The bypass check valve means 74 controls fluid communication between theorifice 44 and bypassfluid chamber 136. During the return stroke when thearmature 45 returns to its rest position, the bypass check valve means 74 opens. Fluid from thearmature shaft chamber 124 flows through theorifice 44 andforces element 78 to open the bypass check valve means 74. The fluid then flows into thebypass chamber 136. - Assembly and Movement of the Armature
- During assembly of the armature, the
first shaft portion 60,second shaft portion 62, andthird shaft portion 64, are moved through thecentral opening 86 in thespring retainer plate 80 and through themain spring 90. Then, the first andsecond shaft portions retainer element 52 until theretainer element 52contacts shoulder 68. Theretainer element 52 is joined, welded/laser welded, or pressure fitted and welded/laser welded to thesecond shaft portion 62. Thearmature 45 is then inserted into thearmature shaft chamber 124. - The
outer weld ring 94 is moved into thepump body 32 around theretainer plate 80, until theouter weld ring 94support protrusion 95 andretainer plate 80 contact. Theouter weld ring 94 is welded/laser welded to thepump body 32, trapping theretainer plate 80 between thepump body 32 and thesupport protrusion 95. - For a further and/or more detailed description of the structure of
pump 10 and the assembly of the parts thereof, reference may be made to pending U.S. patent application Ser. No. 10/291,130 filed Nov. 8, 2002 and entitled “Low Power Electromagnetic Pump,” now U.S. patent application Publication No. 20030086799 published May 8, 2003, the disclosure of which is hereby incorporated by reference. - Reference is made to the diagrammatic views shown in
FIGS. 5-8 which show the cycling of the pump 10: -
- a) the
pump 10 at rest is shown inFIG. 1 andFIG. 5 (the electromagnet means 100 is deactivated; - b) when the
electromagnetic means 100 is activated, a magnetic circuit comprising the electromagnet means 100 and thearmature 45 separated by a gap (designated G in diagrammaticFIGS. 5-8 ) is established, and moves thearmature 45 toward the electromagnet means 100 to close the gap, this being aforward stroke 148; - c) during the
forward stroke 148 shown inFIGS. 6 and 7 , thecheck valve 24 opens and fluid enters thepump 10 as indicated by thefluid inflow arrow 138, theaccumulator 300 fills with fluid, and thearmature 45 moves to the left as shown inFIG. 6 in the direction of the arrow designated 140; - d) as the
forward stroke 148 continues, themain spring 90 compress between theretainer element 52 and theretainer plate 80 as thearmature 45 moves toward theelectromagnet 100, and theaccumulator 300 continues to amass fluid being pumped and controllably release the fluid as indicated by the fluid outflow arrow designated 142 inFIGS. 6 and 7 ; - e) when the gap designated G is substantially closed, the
electromagnet 100 is deactivated and thereturn stroke 149 follows, as shown inFIG. 8 and indicated by the arrow designated 144, themain spring 90 moves thearmature 45 back to its at rest position (FIG. 5 ), and theaccumulator 300 continues to controllably release the fluid being pumped to theoutlet port 20, and from there the fluid exits thepump 10 and may flow through a catheter or the like; and - f) as shown in
FIG. 8 , during thereturn stroke 149 thebypass check valve 74 opens because the fluid between theend 47 of thearmature 45 andcheck valve 24 becomes pressurized and forces oncheck valve element 78, and the fluid flows throughorifice 44 and then into thebypass chamber 136, as indicated by the arrow designated 146, thus allowing thearmature 45 to return to its rest position.
- a) the
- The above-described pumping cycle can be repeated at predetermined intervals. It is noted that the
closed check valve 24 during thereturn stroke 149 prevents fluid from exiting theinlet port 18. Also, the following structure for the pump is for illustrative purposes, and the installation of the internal compliant 300 will work with pumps embodied with different internal structure. - Calculated Results
- Compliance may be related to how a fluid path, as defined by the structural body forming the path or part of the path, expands, contracts or deflects under an environmental input, such as, for example, a pressure load from a pump mechanism that is intended to deliver an amount of fluid to an output component, for example a catheter.
- One of the purposes of the internal
compliant element 300 is to allow for rapid pumping of thepump 10, and the subsequent slow delivery of the fluid pumped to theoutlet port 20, and then to, for example, a catheter. Another of the purposes of the internalcompliant element 300 is to reduce inertial effects of the fluid being pumped, as such inertial effects can interfere with the smooth operation of thepump 10 and may cause delivery problems. - The following results compare the calculated fluid volume delivered by a
pump 10 having an internal compliant element with a pump where the compliant element is located external to the pump body at the end of an outlet tube. A primary basis for the comparison is the percentage reduction in the pulse volume when the back pressure is increased from 0 (zero) pounds per square inch (hereinafter psi) to 10 (ten) psi. A typical performance specification for a pump of the type shown in the above-referenced U.S. Pat. No. 5,797,733 allows for about a 10% decrease in pulse volume when the outlet pressure is increased by 10 psi. - The two basic configurations compared are:
-
- 1) a pump having an outlet tube with an effective length of 3.46 inches with an outlet orifice of 0.005 inch, 0.009 inch, or 0.03 inch diameter located upstream of the end of the outlet tube with a compliant element located at the end of the outlet tube (compliant element external to pump body and at end of outlet tube); and
- 2) a pump having an outlet tube 130 (located internally within the pump body 32) that is 0.1 inch in length with any of the same three outlet orifices (0.005 inch, 0.009 inch, or 0.03 inch in diameter), and a compliant element located at the end of the internal outlet tube and within the
pump housing 32. This second configuration is intended to represent the effect of moving the compliant element and outlet orifice to a location within thepump body 32 in accordance with the invention.
- An orifice located downstream of the compliant element would not limit the speed of the
pump armature 45 or the volume of internal flow. It is further noted that both configurations are also assumed to incorporate abypass orifice 44 to help control the inertial flow at the end of thearmature 45 stroke. - The 3.46 inch effective length outlet tube used in this calculation is intended to represent an actual outlet tube 2.57 inches long terminated by an outlet fitting. Since the outlet fitting is assumed to be of smaller inner diameter than the outlet tube, the inertial effective length of the outlet tube is increased by the fitting by an amount greater than the physical length of the outlet fitting.
- The results are believed accurate enough to provide a useful estimate of the effects.
- Table 1 shows the calculated results for a representative configuration of a low power electromagnetic pump with an external accumulator similar to that shown in U.S. Pat. No. 5,9979,733. Although values for leakage through the armature pump body clearance and for the inertial flow were calculated they are omitted from the tabulated results.
- The results shown incorporate the calculated magnetic force on the armature, the drag of the pole button as it moves through the pump body and approaches the diaphragm face, the inertia of the plunger, the inertia of the flow upstream of the pump and downstream of the pump outlet, pressure drops in the main flow, bypass circuit and outlet tube caused by check valves, viscosity and orifice restrictions, leakage of fluid through the between the pump body and armature, the increase in pressure in the accumulator during the pumping pulse.
- For the external accumulator, the outlet tube has a length of 2.6 inches. The effective outlet tube length with outlet fitting is 3.46 inches. Table 1 shows the calculated results for an external accumulator with the effective length of outlet tube being 3.46 inches. It is noted that in the table the phrase “pounds per square inch” has been abbreviated to PSI in the tables.
TABLE 1 Calculated Pulse Volumes for a Pump With An External Accumulator Accumulator Compliance 0.005 0.009 0.03 (micro inch inch inch liter)/PSI ΔP(PSI) orifice orifice orifice Pulse Volume Delivered (μL) 0.03 0.0 0.4896 0.5088 0.5515 10.0 0.4405 0.4768 0.4934 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.900 0.937 0.895 Pulse Volume Delivered (μL) 0.10 0.0 0.505 0.5541 0.5929 10.0 0.4828 0.5045 0.5397 Pulse Volume (10 PSI)/ PulseVolume (0 PSI) 0.956 0.910 0.910 Pulse Volume Delivered (μL) 2.024 0.0 0.5445 (Bubble In Pump Body) 10.0 0.5182 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.9520 - As shown in Table 1, the results for the 0.03 μL/psi accumulator and the 0.005 inch outlet orifice correspond to a pump of the type shown in U.S. Pat. No. 5,797,733 if it is driven by the lower excitation normally used to drive a pump shown in U.S. Pat. No. 6,264,439. The results indicate that under these conditions the
armature 45 is not drawn in fully against 10 psi before the capacitor is discharged and the pulse volume against 10 psi is 10% lower than the pulse volume with no pressure increase across thepump 10, a value just meeting the specified performance of the pump. The pulse volume ratio (pulse volume against 10.0 psi divided by the pulse volume against 0 psi) can be improved to 0.956 by increasing the accumulator compliance to 0.1 μL/psi or to 0.937 by increasing the diameter of the outlet orifice to 0.009 inches. If both changes are made the pulse volume ratio is degraded to 0.91 by increased inertial flow. - The third value of compliance listed represents the compliance which would exist if a 50 μL bubble occupied the volume of the
pump body 32. It is assumed that there is no air in the pump chamber (between the check valve means 24 and armature 45), because even a small bubble could cause a reduction in pump volume and a decrease in pump accuracy. The use of the 0.03 orifice in this calculation reflects the fact that there is no satisfactory location for an orifice between thearmature 45 and the accumulator (bubble) and therefore the effective orifice is large. - Table 1 also shows that pulse volume is reduced from that calculated for the 0.1 μL/psi example. This occurs because the inertia of the fluid in the long outlet tube no longer affects the flow during the pumping pulse. The calculated PV ratio at 10 psi of 0.952 is well above the specified lower limit of 0.9. However, the PV ratio is less meaningful than the ratio of the fluid delivered with the bubble present to the delivery with the bubble in normal operation with no bubble. Against 10 psi with a 0.005 orifice and a 0.1 μL/psi accumulator the ratio is 0.5182/0.4828=1.0735. Thus the
pump 10 would deliver greater volume with the bubble within thepump body 32 than it would with no bubble present. - Table 2 shows the results of calculations in which the
accumulator 300 is assumed to be internal to thepump body 32. This placement of theaccumulator 300 shortens the effective length of the outlet tube and reduces the inertial effect. If necessary an orifice can also be accommodated within thepump body 32 upstream of the accumulator. Results are therefore shown for all three orifice sizes. Since the outlet orifice serves to control the inertia effects of both the inlet and outlet tubes, there may be a benefit from including an orifice even though there is effectively no outlet tube. As in Table 1, a 0.005 inch outlet orifice would slow the armature pull-in to a point where the pull-in would be incomplete at 10 psi with a less compliant accumulator and the calculated PV ratio is an unacceptable 0.894. Increasing the orifice size to 0.03 inch improves the PV ratio at 10 psi to 0.94 with the 0.03 μL/psi accumulator. Note that all three of the orifice sizes and both the accumulator compliances meet the PV ratio accuracy criterion, except for the combination of the smallest (0.005 inch) orifice and the least compliant accumulator (0.03 μL/psi). - Table 2 shows the results of locating a bellows-
type accumulator 304 internal to thepump body 32, between theoutlet tube 130 andpump outlet port 20, as shown inFIG. 1 . For this example, theinternal accumulator 304 has aneffective outlet tube 130 length of 0.1 inches, and theoutlet orifice 132 diameter is any of the following: 0.005 inches; 0.009 inches; and 0.03 inches. The results are presented in Table 2.TABLE 2 Calculated Pulse Volumes for a Pump with an Internal Accumulator Accumulator Compliance 0.005 0.009 0.03 (micro inch inch inch liter)/PSI ΔP(PSI) orifice orifice orifice Pulse Volume Delivered (μL) 0.03 0.0 0.4895 0.5039 0.5118 10.0 0.4376 0.4651 0.4816 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.8940 0.9230 0.9410 Pulse Volume Delivered (μL) 0.10 0.0 0.5055 0.5185 0.5330 10.0 0.4822 0.5032 0.5081 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.9540 0.9710 0.9530 Pulse Volume Delivered (μL) 2.024 0.0 0.5445 (Bubble In Pump Body) 10.0 0.5183 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.9520 - There still remains some inertial effect even with an internal accumulator installed in the
pump 10. The source of this inertial effect is the inlet tube, which has not been varied in these calculations. Thus, in the example of the 0.1 μL/psi compliant element, which does not control inertial flow as well as the stiffer compliance, a 0.009 inch orifice, as compared with the 0.03 inch orifice, improves the PV ratio from 0.953 to 0.971. However, with the 0.03 μL/psi compliance thepump 10 is more accurate with the larger 0.03 inch orifice. - The effect of a bubble in the body of the
pump 10 on the volume delivered against 10 psi is less when the accumulator is internal. As shown in Table 2, the volume delivered with the bubble present is 0.5183 μL. If the accumulator compliance without the bubble is 0.1 μL/psi, then the normal delivered volume is 0.5081 μL so that the effect of the bubble in the pump body is to increase the delivered volume by the ratio 0.5183/0.5081=1.02, that is, by about two percent (2%). - An advantage of placing the accumulator (compliant element) within the
pump body 32 is that it reduces or eliminates the effect of the inertial flow andorifice 132 in theoutlet tube 130 on the delivered pulse volume, thereby improving the accuracy of thepump 10. If a bubble (not shown) should be trapped within thepump body 32 it also acts as an internal compliant element and changes (while the bubble is present) the delivered volume. Placing thecompliant element 300 within thepump body 32 has the effect of reducing the magnitude of the change due to the bubble and assists in maintaining the accuracy of the low powerelectromagnetic pump 10. Other advantages of placing the compliant internal to the pump body include a more compact pump. - In another embodiment, shown in
FIG. 2 , thepump 10 comprises a diaphragm-type accumulator 306 mounted therein. The diaphragm-type accumulator 306 functions in substantially the same way as the bellow-shapedaccumulator 304, in that it allows for rapid pumping of thepump 10, and the subsequent slow delivery of the fluid pumped to theoutlet port 20 and from there to, for example, a catheter. The diaphragm type internal compliant 306 also reduces inertial effects of the fluid being pumped, that can interfere with the smooth operation of thepump 10 and that may cause delivery problems. - Applications arise in which it is desirable to install a low porosity filter on the inlet side of the
pump 10, but such filters are incompatible with high flow rates. In such cases the filter itself or the structure which or means forsupport 305 that supports the filter in the pump housing are designed so that they flex during the pump stroke so that flow may be delivered rapidly to the pump inlet without passing through the filter. O-rings can be used as the means for support along with other suitable structures. Flow may then pass through the filter more slowly driven by the spring constant of the deformed filter or its supporting structure during the interval between pumping strokes. This is a special type of accumulator in which the total internal volume of the flow system is not changed as the accumulator is emptied and refilled, but the volume change downstream exactly compensates for the volume change upstream. - It is to be understood that the diameters of the
orifice 132 presented in the Table 2 (0.005, 0.009, and 0.03 inches) are not the only sized orifices available for use in the present invention. The orifice diameter of theoutlet tube 130 may be in the range of 0.004 inches to 0.04 inches, and the present invention encompasses all outlet orifices sized in this range. Also, the length of theoutlet tube 130 may be about 0.1 inches. - In another embodiment shown in
FIG. 3 , a combination of a diaphragm-type accumulator 306 and aflexible filter accumulator 308 is shown. Theflexible filter accumulator 308 comprises afilter 98 supported in theferrule 56 by means forsupport 305. The means forsupport 305 shown inFIGS. 3 and 4 include O-rings 310, but the means forsupport 305 may be otherwise embodied. Theflexible filter accumulator 308 shown inFIG. 3 is suitable for use in combination with alow porosity filter 98, because it permits slow flow through thefilter 98 with rapid with rapid flow through thepump 10. - Another embodiment of the low power electromagnetic pump with internal
compliant element 10 is shown inFIG. 4 . Here, a bellows-type accumulator 304 is used in combination with aflexible filter accumulator 308. The bellows-type accumulator 304 is provided withdimples 307 on the outer surface of the bellows. Thesedimples 307 ensure proper communication with the pressure source and the mated surfaces of theouter pillows 309 andcenter pillow 311 of theaccumulator 304. Thedimples 307 may, in other embodiments, be replace with plus-shaped spacer (not shown) placed above and below eachpillow - Thus, it has been shown that the internal
compliant element 300 may be variously embodied, all of these within the scope of the present low power electromagnetic pump having an internal compliant element. Also, the performance benefits obtainable by installing an accumulator within thepump body 32 of a low powerelectromagnetic pump 10 rather than at the end of an external outlet tubing have been calculated, and suitable configurations of the accumulator are shown and described. In addition, an accumulator which does not cause a change in the volume of the flow path has been shown and described. This accumulator is particularly suitable for use in combination with a low porosity filter, since it permits slow flow through the filter and rapid flow through the electromagnetic pump. - It will be appreciated by those skilled in the art that while the low power electromagnetic pump having an internal compliant element has been described in connection with particular embodiments and examples, the low power electromagnetic pump having an internal compliant element is not necessarily so limited and that other examples, uses, modifications, and departures from the embodiments, examples, and uses may be made without departing from the low power electromagnetic pump having an internal compliant element. All these embodiments are intended to be within the scope and spirit of the appended claims.
Claims (27)
Priority Applications (1)
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US10/787,999 US20050191194A1 (en) | 2004-02-26 | 2004-02-26 | Low power electromagnetic pump having internal compliant element |
Applications Claiming Priority (1)
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US10/787,999 US20050191194A1 (en) | 2004-02-26 | 2004-02-26 | Low power electromagnetic pump having internal compliant element |
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US20050191194A1 true US20050191194A1 (en) | 2005-09-01 |
Family
ID=34886903
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US10/787,999 Abandoned US20050191194A1 (en) | 2004-02-26 | 2004-02-26 | Low power electromagnetic pump having internal compliant element |
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US20070066939A1 (en) * | 2005-09-19 | 2007-03-22 | Lifescan, Inc. | Electrokinetic Infusion Pump System |
US20070106281A1 (en) * | 2005-11-09 | 2007-05-10 | Searete Llc, A Limited Liability Corporation Of The State Of Delaware | Remote controller for in situ reaction device |
EP1967223A1 (en) * | 2007-03-08 | 2008-09-10 | Jean-Denis Rochat | Enteral parenteral or perfusion nutrition pump |
US20090005727A1 (en) * | 2006-03-09 | 2009-01-01 | Searete Llc | Acoustically controlled substance delivery device |
US7699834B2 (en) | 2005-11-09 | 2010-04-20 | Searete Llc | Method and system for control of osmotic pump device |
US7942867B2 (en) | 2005-11-09 | 2011-05-17 | The Invention Science Fund I, Llc | Remotely controlled substance delivery device |
US8273071B2 (en) | 2006-01-18 | 2012-09-25 | The Invention Science Fund I, Llc | Remote controller for substance delivery system |
US8349261B2 (en) | 2006-03-09 | 2013-01-08 | The Invention Science Fund, I, LLC | Acoustically controlled reaction device |
US8529551B2 (en) | 2005-11-09 | 2013-09-10 | The Invention Science Fund I, Llc | Acoustically controlled substance delivery device |
US8906000B2 (en) | 2005-11-09 | 2014-12-09 | The Invention Science Fund I, Llc | Injectable controlled release fluid delivery system |
US9067047B2 (en) | 2005-11-09 | 2015-06-30 | The Invention Science Fund I, Llc | Injectable controlled release fluid delivery system |
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Cited By (36)
Publication number | Priority date | Publication date | Assignee | Title |
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US20070066939A1 (en) * | 2005-09-19 | 2007-03-22 | Lifescan, Inc. | Electrokinetic Infusion Pump System |
US7942867B2 (en) | 2005-11-09 | 2011-05-17 | The Invention Science Fund I, Llc | Remotely controlled substance delivery device |
US7699834B2 (en) | 2005-11-09 | 2010-04-20 | Searete Llc | Method and system for control of osmotic pump device |
US8998884B2 (en) | 2005-11-09 | 2015-04-07 | The Invention Science Fund I, Llc | Remote controlled in situ reaction method |
US8968274B2 (en) | 2005-11-09 | 2015-03-03 | The Invention Science Fund I, Llc | Acoustically controlled substance delivery device |
US8992511B2 (en) | 2005-11-09 | 2015-03-31 | The Invention Science Fund I, Llc | Acoustically controlled substance delivery device |
US9028467B2 (en) | 2005-11-09 | 2015-05-12 | The Invention Science Fund I, Llc | Osmotic pump with remotely controlled osmotic pressure generation |
US7817030B2 (en) | 2005-11-09 | 2010-10-19 | Invention Science Fund 1, Llc | Remote controller for in situ reaction device |
US7819858B2 (en) | 2005-11-09 | 2010-10-26 | The Invention Science Fund I, Llc | Remote controlled in vivo reaction method |
US20070106281A1 (en) * | 2005-11-09 | 2007-05-10 | Searete Llc, A Limited Liability Corporation Of The State Of Delaware | Remote controller for in situ reaction device |
US8568388B2 (en) | 2005-11-09 | 2013-10-29 | The Invention Science Fund I, Llc | Remote controlled in situ reaction device |
US9254256B2 (en) | 2005-11-09 | 2016-02-09 | The Invention Science Fund I, Llc | Remote controlled in vivo reaction method |
US9474712B2 (en) | 2005-11-09 | 2016-10-25 | Gearbox, Llc | In situ reaction device |
US9067047B2 (en) | 2005-11-09 | 2015-06-30 | The Invention Science Fund I, Llc | Injectable controlled release fluid delivery system |
US8114065B2 (en) | 2005-11-09 | 2012-02-14 | The Invention Science Fund I, Llc | Remote control of substance delivery system |
US8172833B2 (en) | 2005-11-09 | 2012-05-08 | The Invention Science Fund I, Llc | Remote control of substance delivery system |
US8936590B2 (en) | 2005-11-09 | 2015-01-20 | The Invention Science Fund I, Llc | Acoustically controlled reaction device |
US8906000B2 (en) | 2005-11-09 | 2014-12-09 | The Invention Science Fund I, Llc | Injectable controlled release fluid delivery system |
US8882747B2 (en) * | 2005-11-09 | 2014-11-11 | The Invention Science Fund I, Llc | Substance delivery system |
US8617141B2 (en) | 2005-11-09 | 2013-12-31 | The Invention Science Fund I, Llc | Remote controlled in situ reaction device |
US8585684B2 (en) | 2005-11-09 | 2013-11-19 | The Invention Science Fund I, Llc | Reaction device controlled by magnetic control signal |
US8529551B2 (en) | 2005-11-09 | 2013-09-10 | The Invention Science Fund I, Llc | Acoustically controlled substance delivery device |
US7896868B2 (en) | 2005-12-13 | 2011-03-01 | The Invention Science Fund I, Llc | Method and system for control of osmotic pump device |
US8109923B2 (en) | 2005-12-13 | 2012-02-07 | The Invention Science Fund I, Llc | Osmotic pump with remotely controlled osmotic pressure generation |
US8998886B2 (en) | 2005-12-13 | 2015-04-07 | The Invention Science Fund I, Llc | Remote control of osmotic pump device |
US8273075B2 (en) | 2005-12-13 | 2012-09-25 | The Invention Science Fund I, Llc | Osmotic pump with remotely controlled osmotic flow rate |
US8192390B2 (en) | 2005-12-13 | 2012-06-05 | The Invention Science Fund I, Llc | Method and system for control of osmotic pump device |
US8273071B2 (en) | 2006-01-18 | 2012-09-25 | The Invention Science Fund I, Llc | Remote controller for substance delivery system |
US8083710B2 (en) | 2006-03-09 | 2011-12-27 | The Invention Science Fund I, Llc | Acoustically controlled substance delivery device |
US8367003B2 (en) | 2006-03-09 | 2013-02-05 | The Invention Science Fund I, Llc | Acoustically controlled reaction device |
US8349261B2 (en) | 2006-03-09 | 2013-01-08 | The Invention Science Fund, I, LLC | Acoustically controlled reaction device |
US20090005727A1 (en) * | 2006-03-09 | 2009-01-01 | Searete Llc | Acoustically controlled substance delivery device |
US7981083B2 (en) * | 2007-03-08 | 2011-07-19 | Jean-Denis Rochat | Perfusion or enteral/parenteral feeding pump |
US20100114030A1 (en) * | 2007-03-08 | 2010-05-06 | Jean-Denis Rochat | Perfusion or enteral/parenteral feeding pump |
WO2008106817A1 (en) * | 2007-03-08 | 2008-09-12 | Jean-Denis Rochat | Perfusion or enteral/parenteral feeding pump |
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