GB2210414A

GB2210414A - A pumping device

Info

Publication number: GB2210414A
Application number: GB8723075A
Authority: GB
Inventors: Alastair Sibbald
Original assignee: Thorn EMI PLC
Current assignee: Thorn EMI PLC
Priority date: 1987-10-01
Filing date: 1987-10-01
Publication date: 1989-06-07
Also published as: GB8723075D0

Abstract

A pumping device 10 (40, Fig. 4) for fluids comprises a duct 12 (41) along which fluid can flow; a resiliently flexible arm 14 (56) having an upstream end and a downstream end, the arm being free to oscillate transversely with respect to the flow; and magnetic means 20 (59) effective on the arm intermediate said upstream and downstream ends for enabling said transverse oscillation. The downstream end of the arm is free to move transversely with respect to the flow and the upstream end of the arm is so constrained as to be prevented from undergoing transverse movement with respect to the flow. Because of this, the transverse oscillation due to the magnetic means imparts a flagellating action in the arm causing a flow of fluid along the duct. <IMAGE>

Description

PUMPING DEVICE This invention relates to a pumping device suitable for transporting small quantities of fluids, especially liquids.

This invention particularly relates to a pumping device in which the motion of the fluid to be transported is caused by the magnetically induced oscillation of a flexible plate or fin.

There are many occasions when it is required that small quantities of fluids, especially liquids, are transported through conduit systems. One example is in the chemical analysis of liquids by automated analyzers which generally requires pumping systems having small flow rates (e.g. 0.5 to 5 ml mien 1). As small quantities of fluid are involved, the pump should be small, with the individual components requiring little space.

In many cases, the ergonomics of the system are very important, in that the fluid media are corrosive or otherwise aggressive (e.g. blood, which tends to clot and precipitate protein on to all contacting surfaces), and it is necessary to replace all of the ducts, conduits, tubing etc. which have been in contact with the fluid. Replacement of fluid-management components might also be necessary for reasons of hygiene and it is desirable that this operation is simple and can be carried out by non-skilled personnel. Furthermore, it is important that the cost of the items to be replaced is small.

It is known to use peristaltic pumps to transport small quantities of fluid. A peristaltic pump comprises a length of pliable (silicone rubber) tubing stretched and fixed around a group of rotating rollers, such that rotary peristalsis occurs.

However, even the smallest of peristaltic pumps tend to be relatively bulky and expensive, and replacement of the pump tubing is not straightforward as the correct tube tension must be maintained. In addition, the operator is exposed to residual stagnant fluid in the tubing, which is undesirable for hygiene reasons. A further disadvantage when transporting blood is that the compressive forces encountered in peristaltic pumps tend to cause cell disruption and haemolysis, thus changing significantly the fluid composition.

Another method of transporting fluids, in which little compressive force is produced, is by the magnetically induced oscillation of a fleaible plale onfin. Stumping devices.

incorporating such flexible plates or fins are disclosed in GB 2041447A (Tetra Werke) and GB 2121111A (Cox).

GB 2041447A discloses a pump having an oscillating armature provided with a resiliently flexible plate for executing the pumping movement. The armature is mounted on a plate spring which is secured to the pump housing. The plate spring is substantially 'U' or Omega-shaped, 80 that it takes up less space than an elongated flat plate spring, and also provides a favourable transition between the active oscillating end of the spring plate and the static end of the spring plate secured to the housing. A disadvantage of this type of pump is the number of components - the plate spring, the armature and the flexible plate - which are arranged to come into contact with the fluid even though only the flexible plate executes the pumping movement.The combination of the plate spring, the armature rod and the flexible plate takes up an undesirable amount of space in the cavity through which the fluid flows, and it is conplicated to manufacture, to insert and to replace in the pump housing.

GB 2121111A discloses a pump comprising a duct containing a magnet which can pivot about a fixed axis transverse to the duct, the magnet being attached on the upstream side of the pivot to a flexible fin member extending downstream in the duct with respect to the pivot point. At least one electromagnet is arranged to cause oscillation of the magnet and hence the fin to provide the pumping movement. The disadvantages of this pump are that the requirement for attachment of a magnet and pivot arrangement prevents low cost fabrication and the transverse mounting arrangement makes for considerable intricacy of manufacture and large fluid dead space.

It is an object of the present invention to provide a pumping device for pumping small quantities of fluid which at least alleviates the disadvantages of known pumping arrangements described hereinbefore.

According to the present invention, there is provided a pumping device for fluids comprising a duct along which fluid can flow; a resiliently flexible arm having an upstream end and a downstream end, the arm being free to oscillate transversely with respect to the flow; and magnetic means effective on the arm intermediate said upstream and downstream ends for enabling said transverse oscillation, wherein said downstream end of the arm is free to move transversely with respect to the flow and said upstream end of the arm is so constrained as to be prevented from undergoing transverse movement with respect to the flow whereby said transverse oscillation due to said magnetic means imparts a flagellating action in the arm causing a flow of fluid along the duct.

Advantages of such a pumping device include its compactness, ease and low cost of fabrication and ease of replacement in a system through which the fluid is being transported.

Preferably the magnetic means comprises a magnetic pad mounted on one surface of the arm which is caused to oscillate by the influence of a changing magnetic field. Alternatively, the magnetic means may comprise magnetic particles incorporated within the arm.

Preferably the arm is laminar.

Preferably the arm comprises a resiliently flexible tail which executes the flagellating action and a locating section at said upstream end which locates said upstream end in the duct.

The locating section may be integral with the tail and of the same resiliently flexible material, or alternatively the locating section may be of a rigid material.

Preferably, the duct includes only one input port and only one output port.

In one preferred embodiment, the duct is of annular cross-section and the tail comprises a rectangular strip.

In a second preferred embodiment, the duct is of varying rectangular cross-section and the locating section is preferably a hinge attaching the tail to the base of the duct.

The present invention will be described further, by way of example, with reference to the accompanying drawings in which: Figure 1 is a cutaway perspective view of a first embodiment of a pumping device in accordance with the present invention.

Figure 2 is a plan view of an arm used to execute the pumping motion in the pumping device of Figure 1.

Figure 3 is a perspective view of an alternative form of arm used to execute the pumping motion in the pumping device of Figure 1.

Figure 4 is a perspective view (cover slip not shown) of a second embodiment of a pumping device in accordance with the present invention.

Figure 5 is a plan view of the pumping device of Figure 4.

Referring to Figure 1, a pumping device 10 for pumping small quantities of fluid, i.e. liquid or gas, comprises a length of silicone rubber tubing 12 of suitable dimensions which can be inserted into a system (not shown) through which the fluid is being transported. The fluid is pumped in the direction indicated by the arrow A by an arm 14 (shown in greater detail in Figure 2). The arm 14 is a 'T'-shaped strip of resiliently flexible material which can be considered as having an upper crossbar 16 and a tail 18. A pad 20 of ferromagnetic material is attached to the tail 18 of the arm 14 near the 'T'-junction. The arm 14 is located in the tubing 12 by the upper crossbar 16 which remains substantially stationary relative to the tubing 12 when the pumping device is in action.

Two magnetic actuators 22, 24 (shown symbolically in Figure 1) are placed diametrically across the tubing 12 from each other.

Alternate activation of these magnetic actuators 22, 24 causes the pad 20 of the arm 14 to oscillate imparting a flagellating motion to the tail 18 which pumps fluid through the tubing 12 in the direction A.

In one example, the arm 14 is made of a thin, i.e. 0.1 mm thick, inert, polymeric material such as polyimide having tail dimensions of 25 x 1 mm. The ferromagnetic pad 20 of dimensions 3 x 1 mm is produced from nickel foil.

Figure 3 shows an alternative form of arm 26 which can be used with the pumping device of Figure 1. In this arm 26, the oscillating tail 28 is made of a resiliently flexible material such as polyimide to which is attached a ferromagnetic pad 30.

The arm 26 is however located in the tubing 12 by a rigid locating head 32 made of e.g. metal.

Such arms 14, 26 can be fabricated very easily in large quantities at very low cost by means of flexible printed circuit board technology (flexi-PCB). The ferromagnetic pads 20, 30 can be manufactured by the screen-printing of metal-loaded inks or by electroplating. It is to be noted that the pumping device 10 is readily engineered in a form which is a 'use and dispose' item and can be fitted to equipment merely by clipping in place between the magnetic actuators 22, 24.

Several factors influence the efficiency of the pumping device 10, including the choice of optimal dimensions (width, length and bore of the tubing 12), the rigidity/flexibility of the tail 18 and its mass, the viscosity of the fluid to be transported and the frequency of the alternating magnetic field. The mass/flexibility ratio of the arm can be increased, if necessary, by the use of a reticulated tail.

A pumping device 40 having an enhanced efficiency is shown in Figures 4 and 5 (magnetic actuators not shown). The fluid flows through a conduit 41 having a cavity 42 of rectangular cross-section with an inlet port 44 and an outlet port 46, and walls 48, 50 and a base 52 formed in a substrate 54. The fourth side is bounded by a cover slip (not shown). The arm 56 is formed of a tail 58 of resiliently flexible matersal and a hinge 60 attaching the tail 58 to the base 52. The pumping action is produced by the alternate activation of the magnetic actuators (not shown) causing the pad to oscillate, imparting a flagellating action to the tail 58. The enhanced efficiency is achieved by the tail 58 having a wider dimension (i.e. lower aspect ratio) and by the arm 56 being deployed in the cavity 42 of rectangular cross-section.

The conduit 41 can be fabricated using a combination of liquid crystal display and flexi-PCB technologies. The pumping device 40 can be built integrally into a micro-or mini-conduit system using a flexi-PCB base element.

Advantageously, the pumping device provides a reverse pressure valve action to reduce reverse flow as the tail 18, 26, 58 would tend to crumple up and block the tubing 12 or conduit 41 if fluid flowed in the reverse direction.

Turbulence will be automatically introduced into the fluid being pumped, breaking down the zero-velocity boundary layer at the- internal surfaces, and so promoting efficient flushing of the system and, in an analytical instrument, a more rapid response in downstream sensors (e.g. electrochemical or optical).

An indirect measurement of the viscosity of the fluid being pumped, and hence the prescence of (unwanted) entrained air bubbles, may be made by the measurement of the reluctance of the magnetic actuators.

It is envisaged that the magnetic material incorporated in the tail may be a pad of permanent magnetic material rather than of ferromagnetic material or alternatively the magnetic material could be incorporated in the tail in the form of ferromagnetic or permanently magnetic particles suspended within the material of the tail.

Claims

1. A pumping device for fluids comprising a duct along which fluid can flow; a resiliently flexible arm having an upstream end and a downstream end, the arm being free to oscillate transversely with respect to the flow; and magnetic means effective on the arm intermediate said upstream and downstream ends for enabling said transverse oscillation, wherein said downstream end of the arm is free to move transversely with respect to the flow and said upstream end of the arm is so constrained as to be prevented from undergoing transverse movement with respect to the flow whereby said transverse oscillation due to said magnetic means imparts a flagellating action in the arm causing a flow of fluid along the duct.

2. A pumping device according to Claim 1 wherein the magnetic means comprises a magnetic pad mounted on one surface of the arm which is caused to oscillate by the influence of a changing magnetic field.

3. A pumping device according to Claim 1 wherein the magnetic means comprises magnetic particles incorporated within the arm.

4. A pumping device according to any one of the preceding claims wherein the arm is laminar.

5. A pumping device according to any one of the preceding claims wherein the arm comprises a resiliently flexible tail which executes the flagellating action and a locating section at said upstream end which locates said upstream end in the duct.

6. A pumping device according to Claim 5 wherein the locating section is integral with the tail and of the same resiliently flexible material.

7. A pumping device according to Claim 5 wherein the locating section is of a rigid material.

8. A pumping device according to any one of the preceding claims wherein the duct includes only one input port and only one output port.

9. A pumping device according to any one of Claims 5 to 8 wherein the duct is of annular cross-section and the tail comprises a rectangular strip.

10. A pumping device according to any one of Claims 5 to 8 wherein the duct is of varying rectangular cross-section.

11. A pumping device according to Claim 10 wherein the locating section is a hinge attaching the tail to the base of the duct.

12. A pumping device for fluids substantially as hereinbefore described with respect to, and as illustrated in, Figure 1 and one of Figures 2 and 3 of the accompanying drawings.

13. A pumping device for fluids substantially as hereinbefore described with respect to, and as illustrated in, Figures 4 and 5 of the accompanying drawings.