WO1997042412A1

WO1997042412A1 - Pseudo static peristaltic pump

Info

Publication number: WO1997042412A1
Application number: PCT/AU1997/000273
Authority: WO
Inventors: Joseph Bertony
Original assignee: Pumping Systems Technologies Pty. Limited
Priority date: 1996-05-06
Filing date: 1997-05-06
Publication date: 1997-11-13
Also published as: AUPN970096A0

Abstract

A peristaltic pump comprises a flexible fluid conduit (2). A series of mutually opposed pairs of compression elements (10) are disposed externally along the length of the conduit (2). Progressive electrical stimulation of the pairs of elements, which may be flexible cells filled with polymer gel having piezoelectric properties, induces peristaltic compression (13) along the conduit. Radial expansion means in the form of a spiral tube (6) filled with a gas or a suitable polymer gel are operable to selectively expand the conduit (2) after passage of a compression wave. The spiral tube is divided, e.g., every four turns, into segments to optimise expansion characteristics. The conduit (2) has an elliptical cross section when in a relaxed state and this corresponds to the configuration of the conduit midway through a compression phase.

Description

TITLE: PSEUDO STATIC PERISTALTIC PUMP

FIELD OF THE INVENTION

The present invention relates generally to pumps, and more particularly to peristaltic

type pumps.

5 The invention has been developed primarily for use in medical applications, and will

therefore be described primarily with reference to this application. It will be appreciated,

however, that the invention is not limited to this particular field of use, but may also be

used in numerous other applications, a notable example being mineral slurry transportation.

I o BACKGROUND OF THE INVENTION

In the past, various attempts have been made to transport slurries over relatively long

distances as a means, for example, of efficiently transporting coal, sand, cement and

minerals. In most cases, however, conventional pumping technology has been found to be

inadequate, particularly where longer distances are involved, because of the unusual fluid

15 flow characteristics and other properties which many slurries typically exhibit.

For example, positive displacement type pumps incoφorating various arrangements

of pistons are often used to pump liquids. However, the vibrational pulses imparted by

pumps of this type can cause blockages in hydraulic transport lines. Also, the valve

characteristics inherent in piston type pumps typically render them inadequate for handling

0 larger particles. This is due primarily to the susceptibility of the valves and valve seats to

mechanical damage and rapid abrasive wear, as well as to the inability of the valves to pass

larger particles.

Centrifugal pumps are also known and these tend to produce less vibration and accommodate a larger range of particle size. However, because of the rotary nature of such pumps, rapid wear remains a common problem, particularly in shafts, bearings, seals and

the like which translate into high capital and maintenance costs.

Peristaltic pumps are also known. These typically comprise compression elements

such as pressure rollers which are passed in succession along the length of a flexible tube

to induce fluid flow through the tube. In the past, however, such pumps have typically

been unable to generate sufficient pressure or flow rate to be effective in large scale commercial operations. One problem is that if the tube is formed from a material

sufficiently strong to withstand high internal pressures, it is then resistant to the required

external compression from the pressure rollers, without relatively high energy inputs and

consequential inefficiency and rapid mechanical wear. On the other hand, when more

flexible tubes are used, these have a lower pressure capacity and a tendency to collapse,

particularly on the suction side, thereby substantially diminishing the performance and

efficiency of the pump. For these reasons, peristaltic pumps have hitherto been generally

confined to low pressure or flow rate applications, such as in the medical field.

For example, numerous attempts have been made to produce a pump suitable for use

in artificial hearts. In most cases, however, conventional pump technology has been found

to be inadequate. Typical problems encountered with positive displacement pumps include

mechanical failures due to the small size and intricate nature of the componentry,

inadequate reliability due to excessive complexity or rapid wear, blockages caused by

inadequate valve clearances, damage to blood cells due to the interaction of valve

mechanisms, excessive power consumption due to electrical or mechanical inefficiency, and excessive bulk due to the basic limitations inherent in conventional pump technology.

Peristaltic pumps have been found to overcome several of these problems and are

therefore used in some medical applications. In the past, however, these too have typically been unable to provide the required combination of characteristics in terms of performance, efficiency, reliability and longevity for use in artificial hearts and other specialised

applications. A particular problem again relates to the tendency of the primary tube to

collapse over time, progressively diminishing the performance and efficiency of the pump,

as well as requiring frequent replacement.

It is an object of the present invention to provide an improved pump which

overcomes or substantially ameliorates at least some of these disadvantages of the prior art.

DISCLOSURE OF THE INVENTION

Accordingly, the invention as presently contemplated provides a peristaltic type

pump comprising a primary flexible fluid conduit, a fluid inlet and a fluid outlet disposed

at opposite ends of the conduit, compression means disposed along a length of the conduit,

and actuation means adapted progressively to actuate the compression means in

predetermined sequence so as to induce peristaltic compression along the length of the

conduit and thereby move fluid from the inlet to the outlet of the pump.

Preferably, the compression means comprise a plurality of compression elements

arranged as a series of discrete mutually opposed pairs. The compression elements of each

pair are preferably movable alternately and in unison between an expanded configuration

and a contracted configuration. The pairs are preferably actuated sequentially to induce

peristaltic compression along the length of the primary conduit.

Each compression element preferably comprises a flexible cell containing a

compression medium adapted to move between an expanded configuration corresponding

to an activated state and a contracted configuration corresponding to a deactivated state in

response to control stimuli from the actuation means. The compression medium is preferably a polymer based piezoelectric gel and the control stimuli are preferably applied

electric currents or voltages.

In the preferred embodiment, the pump further includes expansion means adapted to

effect radial expansion of the primary conduit behind or upstream of each peristaltic

compression wave. The expansion means preferably include a flexible jacket surrounding

the primary conduit. The jacket preferably contains an expansion medium adapted

selectively for localised pressurisation or expansion so as to increase hoop stresses and thereby to induce a circular cross-sectional profile in the primary conduit, immediately

upstream of each compression wave.

In the preferred embodiment, the jacket includes a flexible secondary conduit or tube

extending spirally around the outer periphery of the primary conduit to form a composite

tube. The secondary conduit is preferably divided into discrete longitudinal expansion

segments, each of which is filled with a polymer based piezoelectric gel. The expansion

segments are preferably activated in predetermined phase relationship behind the

compression elements, by electrical control stimuli from the actuation means.

In one particularly preferred embodiment, the spiral secondary conduit is formed

within the side wall of the primary conduit, in which case the primary conduit, the

secondary conduit and the outer jacket are effectively integral.

According to a second aspect, the invention provides a flexible primary tube for use

with a peristaltic type pump as defined above, said tube being initially formed with an

elliptical profile in a relaxed condition, as manufactured.

Preferably, the elliptical profile of the primary tube is defined by a minor axis X and

a major axis Y, determined by the relationships: o s

X = D_ ; and Y = X x 7 where D is the nominal internal diameter of the primary tube when fully expanded to a

circular cross-sectional profile.

In this way, the inner circumference of the primary tube does not substantially

change, despite variations in the cross-sectional profile during the compression cycles. Advantageously also, the elliptical profile reduces the extent of maximum deformation

during each compression phase by effectively dividing the operational flexure into two

opposite phases of bending, about a median position corresponding to the relaxed

configuration of the tube, rather than a single bending phase of twice the magnitude.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of example

only, with reference to the accompanying drawings in which:-

Figure 1 is a longitudinal cross-section showing a peristaltic pump according to a

first embodiment of the invention;

Figure 2 is a transverse cross-sectional view taken along line 2-2 of Figure 1 ; Figure 3 is a transverse cross-sectional view taken along line 3-3 of Figure 1 ;

Figure 4 is a longitudinal cross section showing a peristaltic pump according to a

second embodiment of the invention;

Figure 5 is a transverse cross-sectional view taken along line 5-5 of Figure 4;

Figure 6 is a longitudinal cross section showing the electrical control inputs to the secondary spiral tube;

Figure 7 is a transverse cross-sectional view taken along line 7-7 of Figure 6; Figure 8 is a longitudinal cross section showing a peristaltic pump according to a

third embodiment of the invention;

Figure 9 is a transverse cross-sectional view taken along line 9-9 of Figure 8;

Figure 10 is a transverse cross-sectional view taken along line 10-10 of Figure 8;

Figure 1 1 is a transverse cross-section showing the elliptical profile of the composite

tube, in a relaxed configuration as manufactured;

Figure 12 is a transverse section showing the composite tube of Figure 11 in a compressed configuration; and

Figure 13 is a transverse section showing the composite tube of Figure 1 1 in an

expanded configuration.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring to Figures 1 to 3, wherein corresponding features are denoted by

corresponding reference numerals, the invention, according to a first embodiment, provides

a peristaltic type pump 1 comprising a flexible primary fluid conduit 2 having a fluid inlet

3 and a fluid outlet 4. The primary conduit 2 is surrounded by radial expansion means in

the form of a flexible jacket 5. The jacket 5 contains a secondary flexible tube 6 extending

spirally around the outside of the primary tube. Alternatively, a composite tube may be

provided with an internal spiral passage, in which case the primary conduit is defined by

the inner surface of the composite tube, the surrounding jacket is defined by the outer

surface of the composite tube and the secondary spiral conduit is defined within the

sidewall of the tube, and all three are thus effectively integral. In another embodiment, the

jacket 5 may simply be formed by a separate spiral tube, wound around and secured to the

outer surface of the primary conduit, again to form a composite tube. The pump further includes compression means in the form of a series of compression

elements 10 arranged in corresponding mutually opposed pairs along the length of the

primary tube, external to the secondary spiral tube 6. The compression elements are

housed within a surrounding tubular casing 1 1 and annular end caps 12 which enable the

assembly within the casing to be sealed and pressurised if required. The casing may also

be flexible such that a degree of flexibility is afforded to the entire pump assembly.

The compression elements 10 take the form of flexible cells containing a

compression medium adapted to move alternately between an expanded or active state and

a contracted or inactive state in response to control stimuli from an actuation mechanism

(not shown) which may include a microprocessor based controller. The compression

medium is preferably a polymer based gel having piezoelectric characteristics, and as such

expands in response to stimuli in the form of applied electric currents or voltages. It will

be appreciated, however, that the compression elements may be solid, liquid or gaseous,

and as such may take a variety of other forms. Also, it will be appreciated that any suitable

number of compression elements may be used in a variety of configurations to provide the required flow characteristics.

The secondary spiral tube 6 also contains an expansion medium, preferably the same

piezoelectric polymer gel as in the compression elements, adapted for controlled expansion

so as selectively to increase the hoop stresses in, and thereby to effect radial expansion of,

the primary conduit. The spiral tube is divided longitudinally into discrete segments, to

provide optimum localised expansion characteristics. Each segment is approximately 4

turns in length, in a spiral defining a helix angle of between 1° and 20°, ideally around 5°.

In the second embodiment of the invention, as shown in Figures 4 to 7, the spiral segments are activated sequentially by control voltages applied where indicated to provide localised control over the radial expansion mechanism, as described more fully below. In

alternative arrangements a pump may be used to alternately pressurise and depressurise the segments to effect the desired radial expansion.

In a third embodiment of the invention, as shown in Figures 8 to 10, the spiral

5 segments are only approximately two turns in length, and the compression elements are

correspondingly sized to provide more precise shape control over the peristaltic

compression waves during each pumping cycle.

Turning now to describe the operation of the pump in more detail, the actuator or

controller (not shown) progressively activates the opposing piezoelectric compression

l o elements 10 of each pair simultaneously, and the pairs in linear sequence, so as to induce a peristaltic compression wave 13 along the length of the primary conduit, thereby displacing

fluid from the inlet 3 to the outlet 4 of the pump. At the same time, the controller activates

the piezoelectric gel (or alternatively pressurises a fluid ) contained in the surrounding

spiral conduit 6. In the case of a longitudinally segmented spiral tube, the segments A, B,

15 C, etc are progressively activated in linear succession immediately behind or upstream of

the activated compression cells. This increases the hoop stresses in the primary conduit,

and thereby tends to induce a circular cross-sectional profile in the primary conduit, following each compression wave. In other words, the control voltages applied to the

compression cells are coordinated with the control voltages applied to the corresponding

20 segments of the outer spiral tube, such that the peristaltic compression and subsequent

positive expansion of the composite tube are appropriately synchronised. Advantageously,

this enhances the negative pressure on the suction side of the pump and thereby improves

the overall pumping efficiency. It also prevents the primary tube from permanently de¬

forming or collapsing into a flattened configuration over time in response to prolonged compression cycles, as typically occurs in prior art pumps. This arrangement also obviates

the need for moving parts and thereby offers significant benefits in terms of maintenance,

reliability, size and cost. As such, it is particularly advantageous in medical applications.

It will be appreciated that by appropriate simultaneous or sequential activation of the

compression elements, the pump may be configured to move fluid in either direction, as

well as to act as a valve by blocking fluid flow altogether. In addition, it will be

appreciated that surplus or redundant compression elements may be included as a safety

feature. These would not normally be activated, but would remain in a standby mode, to be triggered by the actuator in the event of failure of active elements in the system.

Figures 1 1 to 13 show the shape and configuration of composite tube in more detail.

Referring firstly to Figure 11, the tube is initially formed with an elliptical profile in the

relaxed condition as manufactured, so as to reduce the extent of maximum deformation during each compression phase. In terms of the pumping cycle, the elliptical profile of the

conduit in the relaxed condition as shown in Figure 1 1 corresponds to the configuration of

the conduit mid-way through a compression phase. In this way, it will be appreciated that

the elliptical shape effectively divides the operational flexure into two opposite phases of bending, as shown in Figures 12 and 13 respectively, rather than a single phase of twice the

magnitude. This in effect halves the maximum extent of deformation from the relaxed or

equilibrium condition.

Most preferably, the composite tube is formed on an elliptical mandrel having a

minor axis X and a major axis Y, as shown. If the internal diameter of the primary conduit

in the fully expanded circular condition is D, then the following relationships are applied:-

X = D ; and Y = X x 7° ⁵

2 The significance of these mathematical relationships is that the inner circumference

of the primary inner tube does not substantially change, despite variations in the cross-

sectional profile during the compression cycles, which minimises internal stress and

fatigue. However, the mean diameter of the spiral defined by the secondary tube is

necessarily larger than the inner diameter of the primary tube and hence the mathematical

identity no longer applies. Consequently, pressurisation of the secondary tube still induces the desired change from elliptical to circular profile on the suction side of each

compression element, as described above. This arrangement thus optimises the service life

of the composite tube, and enables the use of higher pressure capacity materials and

designs which might otherwise lack the required degree of flexibility.

The present invention thus provides a peristaltic pump which is compact in size,

flexible in configuration and operation, extremely reliable due to the absence of moving

parts, gentle to blood cells due to the absence of harsh mechanical valve interactions, and

efficient in terms of power consumption. This makes the invention, optionally in a twin

lobe configuration, ideal for use in medical applications and in particular for use in

artificial hearts.

The present invention is also applicable to a wide variety of fluids and slurries with

abrasive, corrosive or generally contaminate characteristics. It further has the capacity to

be set up to generate a reasonable flow with only minimal compression in a dynamic

pseudo wave action simply by reducing the control voltage to the compression elements. It

may therefore accommodate relatively large particle size and may even be used to transfer

live specimens, such as fish, between storage tanks. The invention is also particularly well

adapted to pump relatively high viscosity liquids which in prior art pumps would cause the

peristaltic tube on the suction side to collapse under atmospheric pressure. In all these respects, the invention represents a commercially significant improvement over the prior

art.

Although the invention has been described with reference to specific examples, it

will be appreciated by those skilled in the art that the invention may be embodied in many

other forms.

Claims

CLAIMS:-

1. A peristaltic type pump comprising a primary flexible fluid conduit, a fluid inlet and

a fluid outlet disposed at opposite ends of the conduit, compression means disposed along a

length of the conduit, and actuation means adapted progressively to actuate the

compression means in predetermined sequence to induce peristaltic compression along the

length of the conduit and thereby to move fluid from the inlet to the outlet of the pump.

2. A pump according to claim 1 , wherein the compression means comprise a plurality

of compression elements arranged as a series along the primary conduit and adapted for

sequential actuation.

3. A pump according to claim 2, wherein said compression elements are arranged as a

longitudinal series of discrete mutually opposed cooperating pairs.

4. A pump according to claim 3, wherein the compression elements of each pair are

actuable in unison for alternate movement between an expanded configuration and a

contracted configuration, and wherein the respective pairs are actuable sequentially to

induce peristaltic compression along the primary conduit.

5. A pump according to claim 4, wherein each compression element comprises a

flexible cell containing a compressive medium adapted to move between the expanded

configuration corresponding to an activated state and the contracted configuration

corresponding to a deactivated state, in response to control stimuli from said actuation

means.

6. A pump according to claim 5, wherein said compressive medium is a polymer based

gel formed from a piezoelectric material and wherein the control stimuli are electric

currents or voltages applied by the actuation means.

7. A pump according to any one of the preceding claims, further including radial

expansion means operable selectively to expand the primary conduit immediately upstream

of each peristaltic compression wave.

8. A pump according to claim 7, wherein said expansion means include a jacket

disposed around the primary conduit and containing an expansion medium adapted

selectively for pressurisation or expansion, to increase the hoop stress and thereby to

induce a substantially circular cross-sectional profile in the primary conduit immediately

behind each compression wave.

9. A pump according to claim 8, wherein the jacket includes a flexible secondary

conduit or tube extending spirally around the outer periphery of the primary conduit.

10. A pump according to claim 9, wherein the secondary spiral tube defines a helix angle

of between 1 ° and around 20°.

1 1. A pump according to claim 10, wherein the secondary spiral tube defines a helix

angle of approximately 5°.

12. A pump according to any one of claims 9 to 11 , wherein the secondary tube is

divided into discrete longitudinal segments.

13. A pump according to claim 12, wherein each of said segments is between 1 and

around 10 turns in length.

14. A pump according to claim 13, wherein each of said segments is approximately 5

turns in length.

15. A pump according to claim 12, wherein each of said segments of the secondary spiral

tube is filled with an expansion medium, and is thereby adapted for selective pressurisation

or expansion in predetermined phase relationship with respect to the compression means,

by the actuation means.

16. A pump according to claim 15, wherein the expansion medium comprises a polymer based piezoelectric gel.

17. A pump according to any one of claims 9 to 16, wherein the secondary spiral conduit

is formed within a side wall of the primary conduit, such that the primary conduit, the

secondary conduit, and the outer jacket are integrally formed as a unitary composite tube.

18. A pump according to claim 17, wherein the composite tube is manufactured in

discrete longitudinal segments adapted for sealable connection in axially aligned

relationship such that at least the primary conduit is effectively continuous across the

segments.

19. A pump according to any one of claims 9 to 18, wherein the spiral conduit is wound

around the outer periphery of the primary conduit and secured thereto, such that the jacket

is integrally defined by the secondary tube.

20. A pump according to any one of the preceding claims, wherein the compression

means and the primary conduit are disposed within an elongate generally tubular outer

casing.

21. A pump according to claim 20, when dependent upon any one of claims 7 to 20,

wherein said compression means are disposed within an annular clearance defined between

the outer casing and the primary conduit, and around the radial expansion means.

22. A pump according to claim 21 , wherein the outer casing is adapted to be

pressurised with a liquid to reduce friction between moving parts and to enable the pump to

accommodate relatively higher internal pressures.

23. A pump according to any one of claims 7 to 22, wherein the actuation means include a microprocessor based controller adapted to apply control voltages in predetermined sequence and phase relationship to the compression means and to the expansion means

respectively.

24. A pump according to any one of the preceding claims, wherein at least the primary

conduit is initially formed with an elliptical internal cross-sectional profile in a relaxed

condition as manufactured, so as to reduce the extent of maximum deformation during each

compression phase.

25. A pump according to any one of claims 9 to 24, wherein a composite tube

including the primary tube and the secondary spiral tube is initially formed with an

elliptical internal cross-sectional profile in a relaxed condition, as manufactured.

26. A pump according to claim 24 or claim 25, wherein the elliptical profile of the

primary tube is defined by a minor axis X and a major axis Y, determined by the

relationships:

X = D. ; and Y = X x 7° ⁵

2

where D is the nominal internal diameter of the primary tube when fully expanded to a

circular cross-sectional profile.

27. A pump according to any one of claims 24 to 26, wherein the elliptical profile of

the primary tube is determined such that the inner circumference does not substantially

alter despite variations in cross-sectional profile during peristaltic compression cycles.

28. A flexible tube adapted for use with a peristaltic type pump as defined in any one

of the preceding claims, said tube being formed with an elliptical internal cross sectional

profile in a relaxed condition, as manufactured.

29. A flexible tube according to claim 28, wherein the elliptical internal profile of the

primary tube is defined by a minor axis X and a major axis Y, determined by the

relationships:

X = D ; and Y = X x 7° ⁵ 2

where D is the nominal internal diameter of the tube when fully expanded to a circular cross-sectional profile.

30. A flexible tube according to claim 28 or claim 29, wherein the elliptical internal

profile of the primary tube is determined such that the inner circumference does not

substantially alter despite variations in cross-sectional profile during peristaltic

compression cycles.

31. A composite tube for use in a pump as defined in any one of claims 1 to 30, said

composite tube comprising a primary inner tube to contain a primary fluid to be pumped,

and an outer jacket adapted to contain a secondary expansion medium in one or more

segments defined between the primary inner tube and the outer jacket.

32. A composite tube according to claim 31 , further including one or more secondary

flexible tube segments spirally formed around the outside of the primary tube.

33. A composite tube according to claim 32, wherein the primary inner tube, the outer

jacket, and the intermediate spiral tube segments are formed from separate components.

34. A composite tube according to claim 32, wherein the primary inner tube, the outer

jacket and the intermediate spiral tube segments are effectively integral.

35. A composite tube according to claim 34, wherein the secondary tube is formed as

a spiral cavity in the side wall of a unitary tube such that the inner surface of the unitary

tube defines the primary conduit, the outer surface of the unitary tube forms the outer jacket, and the spiral cavity within the side wall of the tube forms at least a segment of the

secondary conduit.

36. A peristaltic type pump substantially as hereinbefore described, with reference to

the accompanying drawings.

37. A flexible tube for use with a peristaltic type pump, said flexible tube being

substantially as hereinbefore described, with reference to the accompanying drawings.

38. A composite tube for use with a peristaltic type pump, said composite tube being