EP0830510A1

EP0830510A1 - Microfabricated, tube located gear pump system

Info

Publication number: EP0830510A1
Application number: EP96918363A
Authority: EP
Inventors: Darren C. Ritter; Andrew S. Dewa; Christophe J. P. Sevrain; Keren Deng
Original assignee: Concis LLC
Current assignee: Concis LLC
Priority date: 1995-06-07
Filing date: 1996-06-06
Publication date: 1998-03-25
Also published as: WO1996041080A1

Abstract

A gear-type pump is placed in line with the conduit or tube (14) through which flows the fluid to be pumped. The pump body (12) is preferably manufactured using microfabrication techniques and is secured within the tube. The mechanism (24) for driving the pump body to pump fluid is mounted completely outside of the tube.

Description

MICRQFABRICATED, TUBE LOCATED GEAR PUMP SYSTEM

Field of the Invention The present invention relates to a pump that is contained within a conduit through which flows the fluid to be pumped. The mechanism for driving the pump is located outside of the conduit.

Background and Summary of the Invention Certain pumping applications, such as intravenous drug delivery, biomedical instrumentation, clinical analyzers, and chemical instrumentation, require that the pumped fluid not be contaminated by the pumping mechanism. Moreover, it is critical that the flow rate of the fluid be precisely controlled.

In the past, peristaltic-type pumps have been used in conjunction with a deformable conduit for the purpose of pumping the fluid without having the fluid contact any parts of the pump. Such peristaltic pumps, however, are inadequate inasmuch that it is difficult to control the flow rate of fluid, especially where very low flow rates are desired.

Pumps that contact the fluid to be pumped are acceptable only if it is possible to effectively clean or sterilize the pump between uses, thereby to avoid the contamination problem mentioned above. The process for cleaning or sterilizing a pump between uses greatly increases the complexity and material requirements of a pump since, for example, autoclaving or gamma ray 96/41080 PCI7US96/096

sterilization greatly stress the electronic components, magnetic materials, bearings, etc., which comprise the drive mechanism of the pump.

A preferred embodiment of this invention is directed to a pump of the gear-type that is placed in line with the conduit or tube through which flows the fluid to be pumped. In a preferred embodiment, the pump body is secured within the tube and the mechanism for driving the pump body to pump the fluid is mounted completely outside of the tube. As one aspect of the invention, the tube with internal pump body may be discarded, and the drive mechanism reused to operate another pump body inside of another tube.

As another aspect of the invention, the pump body is constructed using microfabrication techniques, thereby availing the pump body for use in tubes having very small internal diameters, and for pumping very low flow rates.

As another aspect of this invention, the pump construction generates sufficient suction to be self- priming.

As another aspect of this invention, a substantially constant torque is delivered by the pump, even though, in one embodiment, the gear that is driven by the drive mechanism is eccentrically located. This provides steady operation of the pump.

As yet another aspect of this invention, the need for including seals between the pump and the fluid conduit is eliminated by the arrangement whereby the pump body is contained within the conduit and driven (magnetically) by a mechanism outside the conduit. The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a cross section view of an in-line gear pump system in accordance with the present invention.

Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. 1.

Fig. 3 is an exploded pictorial view of the pump body portion of the present system.

Fig. 4a illustrates one of the steps in fabricating a driving gear of the pump of the present invention, whereby a magnetic bar is centered in the gear. Fig. 4b is a diagram of another step employed in fabricating the driving gear, whereby the teeth of the gear are formed.

Fig. 5 is a cross-sectional view of the system showing a preferred motor arrangement for operating the pump.

Fig. 6 is a cross section view of an alternative motor arrangement for driving the pump.

Fig. 7 is a cross-sectional view taken along line 7-7 of Fig. 6. Figs. 8a-8c are end views of three components that comprise an alternative embodiment of a pump body portion.

Fig. 9 is an exploded pictorial view of an alternative embodiment of the pump body portion.

Figs. lOa-c are end views of three components that comprise another alternative embodiment of a pump body portion.

Fig. 11 is an exploded pictorial view of another alternative embodiment of the pump body.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to Figs. 1-3, the pump system 10 of the present invention generally comprises a pump body 12 that is mounted within a tube 14. Fluid within the tube enters an inlet aperture 16 (Fig. 3), which is in fluid communication with an inlet part 28 of a cavity 18 that is defined in the center of the pump body. A drive gear 20 and engaged driven gear 22 are rotatably mounted within the cavity 18. The drive gear 20 is driven by an actuator 24, described more fully below, for rotating both gears 20, 22, thereby to move fluid received in the inlet part 28 of the cavity 18 to an outlet part 26 of the cavity 18, from which outlet part fluid exits the pump via an outlet aperture 30 formed in the pump body.

Turning to the particulars of a pump system constructed in accordance with the present invention, the pump body 12 is preferably formed using microfabrication techniques. In particular, the pump body 12 includes a central disc 32 (Fig. 3) that is generally cylindrical, and has defined within it the cavity 18. The disc 32 is fabricated using a sacrificial

LIGA process (SLIGA) , which has been demonstrated by Prof. H. Guckel, at the University of Wisconsin, and which is an extension of the LIGA process, a known, deep x-ray lithography process originating with Prof. W. Ehrefeld of the German National Laboratory, KfK, in Karlsruhe, Germany.

In a preferred embodiment, the disc 32 is constructed by first growing on a silicon wafer a 700 nm silicon dioxide film for dielectric isolation. Next, a sacrificial layer of a polyimide film, such as is available from Brewer Science of Rolla, Missouri and designated as PiRL(III), is spun onto the silicon dioxide film. Preferably, the sacrificial layer thickness is about 1-2 μm . The sacrificial layer is heated to about 240 degrees for about one minute to partially cure the layer for mechanical and thermal stability.

Next, a film of polymethyl methacrylate (PMMA) photoresist such as that available from OCG Microelectronic Materials, Inc. of West Patterson, New Jersey, and designated as KTI 496K, is spun-coated over the sacrificial layer to form a film approximately 2 μm thick. Next a commercially available PMMA sheet, approximately 1 mm thick, is solvent bonded to the just- described substrate. A precision mill with a diamond fly cutter, such as manufactured by Leica, A.G., of Heiberg, Switzerland is used to thin the sheet to the desired thickness of the disc. In a preferred embodiment, the finished thickness of the disc 32 is 0.250 mm.

Next, the photoresist assembly is exposed to x-rays through a mask. The mask defines the shape of the cavity 18, which cavity extends completely through the thickness of the released disc 32. In a preferred embodiment, the cavity shape results from the formation of two pair of intersecting, circular holes. One pair of relatively larger holes, having diameters of

1.508 mm, have their diameters aligned with a diameter of the disc 32. The centers of the larger holes are 1.392 mm apart; hence, these holes overlap about the center line 40 of the pump body 12 (see Fig. 3) . The cavity shape also includes all of the space between the two, parallel tangent lines that are common to both of the larger holes.

One of the larger holes rotatably houses the drive gear 20, the outer diameter of which drive gear is slightly less than 1.508 mm, preferably about 1.507 mm. The other of the relatively large holes contains the driven gear 22, which has the same diameter as the drive gear 20. The other pair of relatively smaller holes, having diameters of 0.696 mm are centered on a diameter of the disc 32 that is perpendicular to the diameter with which the larger holes are aligned. The smaller holes are spaced 1.508 mm apart, symmetrically about the center of the disc.

As seen in Fig. 3, one of the smaller holes defines the cavity inlet part 28, and the other defines the cavity outlet part 26. Upon completion of the exposure to x-rays and subsequent development, the disc 32 is released by dissolving the sacrificial layer in a weak aqueous base, such as ammonium hydroxide.

A cylindrical inlet plate 42 and cylindrical outlet plate 44 are constructed using the SLIGA process just defined. Each such plate is preferably 0.250 mm thick, having a 3.175 mm outside diameter. The inlet aperture 16 in the inlet plate 42 and the outlet aperture 30 in the outlet plate 44 are preferably formed to be 0.696 mm in diameter.

The driven gear 22 is also formed in accordance with the SLIGA process described above and shaped so that its outer diameter is slightly less than 1.508 mm, preferably about 1.507 mm. In a preferred embodiment, the driven gear 22 has twenty-four teeth, and a pitch diameter of 1.392 mm.

The drive gear 20 includes a PMMA base 46, in which is embedded a 78/22 Ni/Fe permalloy bar 48. The bar may be any suitable magnetic material, such as nickel. The drive gear base 46, including its magnetic bar 48, are preferably slightly less than 0.250 mm thick and constructed as described next.

First, a 700 nm silicon dioxide film (not shown) is grown on a silicon wafer 50 (see Fig. 4a) .

Next, a sacrificial layer of a polyimide film, such as is available from Brewer Science of Rolla, Missouri and designated PiRL (III) , is spun onto the silicon dioxide film. Preferably, the sacrificial layer thickness is about 1 μm. The sacrificial layer is heated to about 240 degrees for about one minute to partially cure the layer.

Next, a multi-layer metallic film is sputtered onto the release layer to provide an electroplating base. The thickness of each of the three films is 20 nm. Preferably, the films are applied so that a layer of copper is sandwiched between two layers of titanium. After the sputtering, a film of PMMA (KTI 496) is spun onto the sacrificial layer 52 to a thickness of about 2 μm. A 1 mm thick PMMA sheet is then solvent bonded to the substrate and milled to a thickness of about 150 percent of that of the final, 0.250 mm thickness.

A first x-ray mask (not shown) , which defines the area into which will be deposited the magnetic bar 48 (in addition to marks pn the periphery of the PMMA layer used for alignment of a second mask described below) , is positioned between the PMMA and an x-ray source so that the magnetic bar volume and alignment marks are exposed and developed.

In one preferred embodiment, the magnetic bar 48 may be slightly less than 0.25 mm deep, and 0.3 mm wide, and 1.0 mm long. The bar may be manufactured to that shape and then press-fit into a correspondingly shaped volume defined in the PMMA by the process just mentioned.

Alternatively, the bar 48 is produced by electroplating the permalloy to fill the volume in the PMMA layer 54. In this regard, the permalloy is overplated by about 150 percent of the finished thickness of the drive gear.

The PMMA 54 with bar 48 in place is then polished to the desired thickness (Fig. 4a) . Next, as shown in Fig. 4a, a second x-ray mask 55 that defines the area 1 shape (teeth, etc.) of the drive gear 20 is aligned with the PMMA layer 54 for exposing and developing the layer. Afterward, the drive gear is released from the silicon by dissolving the sacrificial layer in the aqueous base.

As shown in Fig. 3, the driven gear 22 and drive gear 20 are fit within the cavity 18 so that their teeth engage or mesh in the space between the cavity inlet part 28 and outlet part 26. The facing, peripheral edges of the inlet plate 42 and outlet plate 44 are solvent bonded to the radially peripheral facing edges 56 of the disc 32, ensuring that the solvent does not reach the movable gears 20, 22, so that those gears remain free to rotate.

It is noteworthy that the rotational center 60 of the drive gear 20 is eccentric to the centerline 40 of the pump body by about 0.696 mm. As explained below, however, this eccentricity has little effect on the ability of the pump to provide a substantially uniform torque when actuated.

The assembled pump body 20 is inserted into a tube 14, which may be a glass, or a flexible, surgical- grade polyethylene tube having a 3.175 mm inside diameter and a 4.763 mm outside diameter. A glass tube may have a relatively short length, and be connectable at each end to flexible tubing. The curved peripheral side of the pump body is attached to the interior wall 64 of the tube 14 (Fig. 2) by any suitable adhesive selected to be nonreactive with the fluid that is to be pumped through the tube 14.

With particular reference to Figs. 1 and 2, the actuator 24 includes a magnetic coupling 70, comprising two diametrically opposed permanent magnets 72, bonded to internal flats defined on a ring 76 of magnetically- permeable material, such as carbon steel. One magnet 72 is bonded to ring 76 with its magnetic north pole adjacent to the ring, while the other magnet 72 is bonded with its south pole adjacent to the ring 76. The drive magnet 72 may be, for example, NdFeB32. One side edge of the steel ring 76 is fixed to a flanged bearing 78, through the center of which bearing extends -li¬

the tube 14. The bearing preferably is removably clamped to the tube 14.

It will be appreciated by one of ordinary skill in the art that by merely unclamping or otherwise removing the actuator from the tube with its internal pump may be discarded after use and a new tube with internal pump mechanism may then be used with the same actuator.

In a preferred embodiment, the drive magnets 72 are spaced about 0.794 mm from the exterior surface of the tube 14. Nevertheless, the magnetic bar 48 embedded within the drive gear 20 is magnetically coupled to those magnets 72 so that rotation of the coupling 70 (hence, an attendant change in the magnetic field between those drive magnets 72) generates a torque in the magnetic bar 48, thereby rotating the drive gear 20 and engaged driven gear 22. As best shown in Fig. 3, counterclockwise rotation of the drive gear 20 and associated clockwise rotation of the driven gear 22 urges fluid in the inlet part 28 of the cavity to the outlet part 26 of the cavity and out of the pump through the outlet aperture 30.

The minute amount of clearance between the drive and driven gears and the holes within which those gears reside permits the volumetric displacement of air or gas in the inlet part 28 as the gears are rotated. As a result, a suction (about 44 mm of water) is created for drawing liquid into the cavity part 28, thereby priming the pump in the absence of the other priming mechanisms. This self-priming feature occurs, for example, when the drive gear 20 is rotated at about 3500 rpm. The attendant liquid flow rate is about 70 μl/min.

The construction and materials described above permit a substantially uniform magnetic field throughout the pump body, so that the torque developed in the drive gear is generally invariable with respect to the position of the coupling 70 relative to the drive gear 20 in the tube for a given angle between the magnetic field and the magnetic bar 48. Put another way, since the permanent magnets of the coupling provide a constant magnetic flux across the rotating, high- permeability bar 48, a nearly constant torque is applied to the driving gear. The uniform magnetic field attributable to the above-described orientation of the drive magnets 72 is augmented by shaping the magnet surfaces 73 that face the pump body to have a generally concave configuration.

It is noteworthy that the minute, micromachined pump body is actuated by a relatively large coupling, so that a relatively large gap is present between the coupling and the drive gear. Such a gap is substantially larger than that found in conventional micromachined devices. In the preferred embodiment, the large gap accommodates the wall thickness of the tube within which the pump body is located.

It will be appreciated by someone skilled in the art that the utility of this coupling is not limited to pumps, but can benefit any other micromachined devices that can be driven by rotary motion including, but not limited to, fluid mixers, optical scanners, optical shutters, micro-robots, micromachined tools, micromanipulators, etc. It will be further appreciated by someone skilled in the art that the rotational motion can be coupled into linear motion by linkages, cams, and other mechanical devices.

The above-described coupling mechanism can be applied to any rotary pumping mechanism. The pumping mechanism need not be limited to those having eccentrically located drive members. Such pumps include, but are not limited to, three-gear pumps, internal gear pumps, rotary vane pumps, lobe pumps and centrifugal pumps. Such pumping mechanisms may be constructed, such as by microfabrication, to be small enough to fit within a tube as described above.

For example, an extension of the two-gear pump described above would lead to a three-gear pump as depicted in Fig. 8. In the three-gear embodiment, the inlet plate 132 (Fig. 8a) and the outlet plate 133 (Fig. 8c) have two apertures for the fluid to pass through. The cavity plate 134 (Fig. 8b) is modified to accommodate three pump gears. The outer two gears 135 are the driven gears 135, and the center one is the drive gear 136. Note that the cavity shape is such to span at least two gear teeth on the top and bottom of the drive gear 136. The drive gear is fabricated in the same manner as the drive gear in the two-gear pump embodiment. The pump is built up and assembled in the same manner as the two-gear pump. Due to the coupled rotation of the three gears, it should be noted that there is one inlet aperture and one outlet aperture on each side of the gears. The three-gear pump can be driven with the same drive mechanism as the two-gear pump, the flow rate through the pump, however, is double that of the two-gear pump.

Another example of a pump embodiment using the principles of this invention is a vane pump, which is depicted in Figs. 9 and 10. The vane pump is built up in generally the same manner as the gear pump. A shaft 140 extends through the center of all three plates, inlet plate 141 (Fig. 10a) , outlet plate 142 (Fig. 10b) , cavity disc 143 (Fig. 10b) and the rotor 144 (Fig. 10b) . The rotor 144 has vanes 145 assembled into it. To maintain pressure between the vanes and the cavity walls, the vanes are loaded with springs 149. The springs 149 can be fabricated as part of the vane or as separate pieces that are assembled along with the vanes 145 into the rotor 144.

The inlet aperture 146 in the inlet plate 141 is aligned with the region of maximum expansion between the rotor 144 and the cavity disc walls 146. The outlet aperture 147 in the outlet plate 142 is aligned with the region of maximum compression between the rotor 144 and the cavity disc walls.

A magnetic bar 148 is fabricated in the rotor so that the vane pump can be driven in the same manner as the two-gear pump. The rotor is magnetically driven in the same manner as the gear pump, except that the rotational center of the magnetic bar in the rotor may be aligned with the rotation center of the magnetic coupling. It will be appreciated by one of ordinary skill that any of a multitude of mechanisms can be employed for rotating the magnetic coupling 70, thereby actuating the pump. For example, the coupling may be connected with any rotating mechanism through gears, belts or chains. The coupling rotation may be imparted by an electric, pneumatic or hydraulic motor. Fig. 5 depicts in cross-section one preferred embodiment of an electric motor 80 for rotating the coupling 70. Such a motor 80 includes an internal stator 82. The external rotor 84 of the motor is connected to a T-flanged bearing 86.

The bearing is constructed of electrically insulating, non-magnetic material, thereby to magnetically and electrically shield the magnetic field established by the drive magnets 72 from the magnetic field of the electric motor.

Figs. 6 and 7 depict an alternative embodiment of an actuator 94 whereby an electric motor having an external stator 96 and internal rotor 98 is mounted to the tube 14 to substantially surround the coupling 70. The coupling 70 fits within a central recess in an annular spacer 100 that surrounds the coupling and is made of electrically insulating non-magnetic material for providing the shielding mentioned above. It is contemplated that an actuator having an external stator could be modified to extend the stator to surround the drive gear and, therefore, provide a magnetic field sufficient to drive the pump without the need for a separate coupling.

It is also contemplated that a series of pump body components could be stacked together to increase the pump capacity of the single-cavity plate embodiments discussed above. The stacked version of the pump (Fig. 11) would comprise an inlet plate 242, a cavity disc 232, an outlet plate 244, another cavity disc 332, an inlet plate 342, etc. The drive gears 220 in each disc are simultaneously rotated by a coupling that has a depth (as measured along the length of the tube) sufficiently large to span all of the connected cavity discs. The cavity discs would be assembled so that the relative positions of the drive and driven gears 222 are alternated in each successive cavity disc, thereby to alternate the rotational direction of the gears in each successive cavity disc for moving the pumped fluid through the entire stack of components.

In view of the wide variety of embodiments to which the principles of the invention can be applied, it should be apparent that the detailed embodiments are illustrative only and should not be taken as limiting the scope of the invention. For example, a preferred embodiment of the invention need not be constructed by microfabrication techniques. Standard or macrofabrication may also be employed. Also, the entire drive gear could be made from magnetic material.

It is also contemplated that an induetion-type stator could be arranged to actuate the drive gear, hence obviating the need for moving parts in the actuator. The stator, with its associated windings, could be assembled to surround the pump body so that the field induced by the stator generates the torque in the magnetic gear or other rotary member in the pump body. Accordingly, the claimed invention should include all such modifications as come within the scope and spirit of the following claims and equivalents thereto.

Claims

CLAIMS ;

1. A pump system comprising: a tube; a pump body inside the tube and in which is formed a cavity and an inlet aperture and an outlet aperture; a drive member rotatably mounted within the cavity between the inlet aperture and the outlet aperture; and an actuator rotatably mounted outside the tube, the actuator being magnetically coupled to the drive member.

2. The system of claim 1 wherein the drive member is a drive gear and further comprising a driven gear rotatably mounted within the cavity between the inlet aperture and the outlet aperture and engaging the drive gear.

3. The system of claim 2 wherein the actuator rotates about an axis and wherein the drive gear is mounted eccentric to the axis.

4. The system of claim 3 wherein the drive gear is substantially circular shaped and has a diameter that is about 1/3 the size of the outside diameter of the tube.

5. The system of claim 4 wherein the tube has an inside diameter that is about twice as large as the diameter of the drive gear.

6. The system of claim 1 wherein the drive member includes a permanent magnet part.

7. The system of claim 1 wherein the actuator incudes a permanent magnet attached thereto.

8. The system of claim 1 wherein the drive member is substantially circular shaped and has a diameter that is substantially the same as the wall thickness of the tube.

9. The system of claim 1 wherein the pump body comprises a disc attached to the tube and having the cavity formed therein in fluid communication with the inlet aperture and the outlet aperture.

10. The system of claim 9 wherein the pump body further comprises an inlet plate and an outlet plate, each plate attached to the disc thereby defining a substantially cylindrical pump body.

11. The system of claim 10 wherein the inlet aperture is formed in the inlet plate and wherein the outlet aperture is formed in the outlet plate.

12. A method of manufacturing a pump system, comprising the steps of: providing a pump body in which is formed a cavity and an inlet aperture and an outlet aperture; rotatably mounting a drive member within the cavity between the inlet aperture and the outlet aperture; rotatably mounting a driven member within the cavity and engaged with the drive member; positioning the pump body inside of a tube; mounting outside the tube an actuator having a coupling member rotatably mounted to the actuator outside the tube; and magnetically coupling the coupling member and drive member.

13. The method of claim 12 further comprising the steps of constructing the drive member to have a permanent magnet embedded therein.

14. The method of claim 12 wherein the step of rotatably mounting the drive member comprises locating the drive member eccentrically with respect to the center of the coupling member.

15. A pump mechanism adapted for placement inside of a tube, comprising: a first pump body in which is formed a cavity and an inlet aperture and an outlet aperture; and a first rotary member rotatably mounted within the cavity between the inlet aperture and the outlet aperture, the rotary member having a magnetic part.

16. The mechanism of claim 15, wherein the pump body includes a disc having the cavity formed therein in fluid communication with the inlet aperture and the outlet aperture.

17. The mechanism of claim 16 wherein the pump body further comprises an inlet plate and an outlet plate, each plate attached to the disc thereby defining a substantially cylindrical pump body.

18. The pump mechanism of claim 15, wherein the pump body is configured in part by a SLIGA fabrication process.

19. The mechanism of claim 15, further comprising a second pump body disposed adjacent to the first pump body and having a cavity in fluid communication with the outlet of the first pump body and having an outlet aperture; and a second rotary member rotatably mounted within the cavity of the second pump member, the rotary member having a magnetic part.

20. A method of coupling rotational motion from a rotating actuator to a rotary element, comprising the steps of: locating the rotary element eccentric to the rotational axis of the actuator; and providing a uniform rotating magnetic field across the rotary actuator so that a substantially uniform torque is coupled to the rotary element.