WO2003027503A1

WO2003027503A1 - Piezoelectric pump

Info

Publication number: WO2003027503A1
Application number: PCT/IL2002/000756
Authority: WO
Inventors: Efron Razi; Gregory Gelman; Ilya Akselrud; Ofra Kalisky; Yehoshua Kalisky
Original assignee: Digipump Ltd.
Priority date: 2001-09-24
Filing date: 2002-09-12
Publication date: 2003-04-03
Also published as: IL145583A0

Abstract

Peristaltic pump, comprising flexible tube for dispensing liquid, a plurality of piezoelectric actuators disposed across a portion of the tube, for applying pressure on the outside surface of the tube, in order to collapse the surface. The piezoelectric actuators are sequentially activated by timing and control means, to cause sequential collapse of points along the tube surface, thereby causing liquid flow in the tube. Each piezoelectric actuator is attached to pressing element(s), for exerting pressure on the tube upon actuation of the piezoelectric actuators. Each pressing element has a cross-section of an essentially right-angle triangle, one acute angle of which directs to the desired flow direction, in order to force the liquid to flow in that desired direction. In an embodiment of the invention, pairs of pressing elements are arranged face-to-face along a portion of the tube, for simultaneously pressing the portion of the tube between the elements of each pair.

Description

PIEZOELECTRIC PUMP

Field of the Invention

The present invention relates to peristaltic pumps. More particularly, the

invention relates to an improved piezoelectric-based peristaltic pump capable of

dispensing small and precise quantities of liquid.

Background of the Invention

Whenever the term "normally closed" is used herein, it refers to a pump in which the liquid channel, or elastic tube, that is used for dispensing liquids, is blocked by

means of a diaphragm inhibiting the liquid flow as long as the pump is

inactivated.

Whenever the term "normally open" is used herein, it refers to a pump in which

the liquid channel, or elastic tube, that is used for dispensing liquids, is unblocked,

allowing liquid flow while the pump is inactivated.

Fluid pumping devices have a wide variety of applications and are designed

according to specific applications. For example, in medical diagnostic and analysis applications, fluid pumping devices are incorporated into diagnostic systems that require a supply of small and accurate quantities of fluid. The accuracy of the analysis is (strongly) dependent on the pumping device.

Other applications involve administering of drugs to patients, e.g.,

administering insulin to diabetes patients.

Various micro-pump devices are known in the art of liquid pumps.

Generally, they consist of superimposed layers of silicone and glass, as well as piezoelectric elements b'onded together. These devices suffer from

complex structures, expense and limited usage due to lack of adequate precision. Additionally, pumps of this type are capable of dispensing only

small quantities of liquids, limited to the range of micro-liters / min. . The

reason for such small quantity is the hmited elasticity of the glass capillary

tube contained in such pumps. However, as science in general, and medicine

in particular, evolves, there is an increased need for pumping devices capable of precisely dispensing liquids at larger rates. An improved pump is

capable of dispensing wide-ranging volumes of liquids, i.e. up to 650 μliter /min..

WO 00/28213 discloses a two-layer pump structure basically comprising a

plain sealing layer, an actuation layer, and pump membranes. The dispensing channel disclosed in this publication has a flowing rate smaller than 10 / /min. . This structure has several drawbacks, one of which is that

the channel's membranes may wear rather fast. Another drawback is that the channel may be blocked due to liquids' residues, which, after emptying

the channel from the liquid, tend to solidify.

US 5,927,547 discloses a pump in which the liquid is displaced by the

application of pressure around a glass capillar tube by a piezoelectric

element, and by virtue of the deformation of the glass. The structure of the

pump is very complex, and since the elasticity of the glass membrane is very

poor, i.e., its physical movement is in the range of micrometers, this type of pump is capable of dispensing liquids in the range smaller than 10 i/min. .

US 5,759,015 discloses a pump in which the liquid is displaced by the application of pressure on a diaphragm by a piezoelectric element. This

pump does not employ a simple flexible tube to displace the liquid, as is

done in the present invention. Furthermore, the liquid displacement

chamber is "normally closed". Therefore, this patent suffers from the same

drawbacks as WO 00/28213.

Other publications, such as US 4,938,742, US 5,224,843, EP 949418 and SU

1776346, disclose other pumps, in which the structure is either complex, or capable of dispensing liquids only in the micro-liter/minute range. All of the above prior art pump devices suffer from at least one of the

following drawbacks:

(1) The cross-section of the liquid channel is small, in the range of

several microns, which may result in obstruction or damage to the pump.

Furthermore, if gas bubbles are trapped within the micro-pump, the

micro-pump will not function 'at all, since the presence of the gas bubbles

causes an irregular flow;

(2) Complexity of the pump and of the technology required for its

manufacturing;

(3) Sensitivity to thermal expansion, and the potential risk of breakage,

whenever glass elements are utilized, for example, when a glass

capillary tube is used;

(4) Conventional pumps have small capacities. Normally, they are capable of dispensing only very small quantities of liquids, i.e., in the

range of pico-liter/minute or micro-liter/minute; '

(5) In conventional pumps, at least some of the actuator element(s) are

in contact with the dispensed liquid, a fact that may result in

contamination of the liquid;

(6) If a same pump is used for dispensing different kinds of liquids, the internal parts of the pump in contact with the liquids must be thoroughly washed and cleaned, before reusing it to dispense other

liquids, in order to eliminate the risk of contamination;

(7) It is practically impossible to replace broken components of these pumps. Therefore, in the event of a broken component, the entire pump

must be replaced; and

(8) Conventional pumps that include dedicated "path channel" for

dispensing liquids usually require undertaking proper measures in the

manufacturing phase, in order to guarantee adequate sealing for preventing leakage.

It is an object of the present invention to provide a pump capable of

accurately dispensing liquid.

It is another object of the present invention to provide a simple pump, the

rate of which can be easily and dynamically adjusted over a relatively wide

range.

It is still another object of the present invention to provide a pump that can be fabricated by using techniques particularly oriented towards mass- production.

It is yet another object of the present invention to provide a pump having a

simple and low-cost structure. Other objects and advantages of the invention will become apparent as the

description proceeds.

Summary of the Invention

The present invention relates to a peristaltic pump, which comprises: (a) A flexible

tube for dispensing liquids; (b) A plurality of piezoelectric actuators disposed

across a portion of the tube for applying pressure on the outside surface of the tube, when actuated, in order to collapse said surface; and (c) Timing and control

means for sequentially activating said plurality of piezoelectric actuators, to cause

sequential collapse of points along the tube surface, thereby causing liquid flow in

the tube.

Preferably, each piezoelectric actuator is attached to at least one pressing

element for exerting pressure on the tube upon actuation of the piezoelectric

actuator.

Preferably, each pressing element has a cross-section shape of essentially a right- angle triangle.

Preferably, one acute angle a_P of the cross-section triangular shape of each

pressing element directs to the desired flow direction, one orthogonal side of the triangle faces the piezoelectric actuator, and the other orthogonal side to

the direction opposite to the desired flow direction.

Preferably, pairs of pressing elements are arranged along a portion of the

tube, pressing elements of each pair being arranged face-to-face for allowing

them to simultaneously press the portion of the tube, said portion of the

tube being between the elements of each pair.

In one embodiment of the invention, two pressing elements are attached to two opposing sides of one piezoelectric actuator, to alternatively exert

pressure either by a first of said pressing element on a first portion of said

tube when said actuator is in its first state, or by a second of said pressing elements on a second portion of said tube when said actuator is in its second

state, and wherein the tube is bent so that two different portions of it being

correspondingly in contact with said two pressing elements.

In another embodiment of the invention, each piezoelectric element, when

activated, exerts pressure on a fluid in a fluid chamber, and said fluid pushes a piston, which in turn exerts pressure on a portion of the tube surface in order to collapse it and activate flow in the pump. Preferably, the timing and control means is a microprocessor-based controller.

Preferably, the pump further comprises: (a) driving circuitry, for

distributing power for energizing the actuators; and (b) one or more sensors for detecting the liquid flow rate, the information relating to the flow rate

being forwarded to said timing and control means, for optimizing the flow

rate.

Brief Description of the Drawings

The above and other characteristics and advantages of the invention will be

better understood through the following illustrative and non-limitative

detailed description of preferred embodiments thereof, with reference to the

appended drawings, wherein:

- Figs, la-lc schematically illustrate a typical structure of a pump,

according to an embodiment of the present invention;

- Figs. 2a-2c schematically illustrate a typical structure of a pump,

according to another embodiment of the present invention;

- Figs. 3 a- 3c schematically illustrate a typical structure of a pump, according to still another embodiment of the present invention; - Fig. 4 is a block diagram illustrating a system for controlling a pump,

according to an embodiment of the present invention; and

- Fig. 5 is a graph showing the relationship between the flow rate and

the operating frequency of the pump of Fig. 1.

Detailed Description of Preferred Embodiments

The invention is directed to an improved piezoelectric-based peristaltic

pump capable of dispensing precise quantities of liquid at a relatively wide

range of flowing rates, said pump preferably comprising a conventional

flexible tube, normally open, on which a wave-like pressure is applied at a plurality of points by piezoelectrically-driven pressure elements. By the

term "wave-like pressure" is meant a sequential application of pressure at a

plurality of points along the liquid dispensing tube.

Among others, the following principles are also implemented in the pump of the present invention:

1) Utilizing a dispensing tube having a relatively large inner diameter,

for dispensing drug solutions or other kinds of liquids, with minimum

risk of obstruction; and

2) Prohibiting a direct contact between the dispensed liquid and elements of the tube. Figs. 1A, IB, and 1C illustrate a structure of a piezoelectric pump, according

to one embodiment of the present invention. Fig. 1A illustrates a

longitudinal cross-section of the pump. Flexible dispensing tube 10 is placed

between a plurality of pairs of piezoelectric actuating elements 13, that are

supported by supports 11. To each piezoelectric element 13 is affixed one

surface of a pressing element 12 (best shown in detail B). Each pressing

element 12 has a cross-section of an essentially right triangle. The surface of

the pressing element 12 relating to a first side (generally the longer one) of the right angle of the cross-section triangle is the one affixed to actuating

element 13. The second surface of pressing element 12, relating to a side of

the right angle of the cross-section triangle, faces the direction of the source

of the liquid flow, and the hypotenuse surface faces the flow direction, as is

best shown in detail A. An angle of the cross-section triangle is in contact with the outer surface of dispensing tube 10, as shown in detail A. According

to the present invention, whenever each pair of parallel piezoelectric

elements 13 is actuated, i.e., by supplying to it an exciting voltage, the

corresponding pair of pressing elements 12 is driven towards the surface of dispensing tube 10, bending it inwards, thereby forcing the liquid to flow in

a direction dictated by the orientation of angle 2 * α_? (see detail A). For

example, as shown in Detail A, the two angles a_P of the two pressing

elements 12, when pressed against tube 10, form an 'expulsion angle' of

2* a_P to the right hand direction. More particularly, as shown in Fig. 1A, the angle a_P of each of the two pressing elements 12 faces the right hand

direction to keep a consistent unidirectional flow. As described before, the

size of angle _Pis determined so as to achieve an optimized liquid flow, and

the activation sequence and/or timing of each pair of piezoelectric elements

13 is determined by a microprocessor-based controller (not shown) in accordance with the pump's required flow rate. It should be noted that the

timing of the activation of each pair of pressing elements is performed in a sequential manner, in order to produce a wave-like flow.

Figure IB depicts a cross-section area of dispensing tube 10, piezoelectric

elements 13 and corresponding pressing elements 12, and Figure 1C depicts

the mechanical housing in which the major elements of the pump are contained. In one embodiment of the invention, the dimensions are, for

example, 1=107 mm and m=32 mm.

According to the present invention, a liquid is dispensed through a regular

flexible tube, such as a Tygon (or any other silicone -based tube), of which

the inner diameter is, for example, 0.5-2 mm. The dispensing tube is placed

between parallel actuator elements. A piezoelectric element is normally in the form of a disk, with a diameter of, for example, Φ = 30mm and thickness

of OΛmm . However, a piezoelectric element of almost any type/form may be

utilized as an actuator. These pairs of actuator elements are aligned essentially along a longitudinal line to render the spacing between each two

consecutive pairs essentially equal.

As said, to each piezo-electric actuating element is affixed one surface of a pressing element. The cross-section of the pressing element is essentially a

right triangle. Another part of the pressing element is pushed, upon

actuation, against an outer 'surface of the dispensing flexible tube. Each

pressing element has an angle a_P such that 0° < a_P « 90° , and a same

angle exists between the hypotenuse of the cross-section triangle and the longitudinal axis of the tube. Therefore, two face-to-face pressing elements

attached to corresponding parallel piezoelectric actuators create an angle

that is as twice that created by one pushing element, i.e. 2*a_P .

Each two piezoelectric actuator elements forming a pair are simultaneously

activated. Whenever activated, each pair of actuator elements exerts

pressure via the pressing elements on the outer face of the dispensing tube.

Since the pressing elements are driven each against the other, and the flexible tube is placed in between, the exerted pressure causes the elastic

surface of the dispensing tube to press and bend inwards.

Coordinating the activation of the actuator elements is carried out by a

controller, one task of which is to allow determining the supply rate of the pump, i.e., by allowing controlling the parameters of the pumping

'sequence 7' cycle', and another task of which is translating the total required

quantity of the dispensed liquid into the corresponding number of cycles.

The controller is capable of changing the capacity of the pump within a

rather large range of capacities (e.g. from several picoliters to hundreds of

microliters). Moreover, the capacity of the pump disclosed herein may be changed, automatically or manually, while the pump is dispensing liquid(s).

Figs. 2A, 2B, and 2C illustrate a structure of a pump, according to another

embodiment of the present invention. The pump of this embodiment is more economical with respect to the pump of Fig. 1, as it requires half the number

of piezoelectric elements; in this case, only two piezoelectric elements (21 and 24) drive four pressing elements (22, 23, 25 and 26). Fig. 2A depicts the

pump in its initialized, 'rest' state. In the rest state, the piezoelectric

elements 21 and 24 are inactivated so that pressing elements 23 and 26 act essentially as a valve in its 'close' state, thereby inhibiting liquid flow. In

order to activate the pump, a voltage is applied to piezoelectric element 21,

which causes it to bend (Fig. 2B), thereby achieving simultaneously two

effects: opening and allowing a liquid flow in the middle section 70 of tube

10 by lifting pressing element 23, and generating a pushing force on the liquid contained in dispensing tube 10 by pushing pressing element 22 against the wall 71 of tube 10. The next step of the pump is the inactivation

of piezoelectric element 21 and the activation of piezoelectric element 24, thereby causing piezoelectric element 21 to return to its initial position and

piezoelectric element 24 to bend (see 2C), thereby achieving similar effects

to those described with respect to the state of Fig. 2b. Namely, the valve is kept open (now by pressing element 26), and the liquid is pushed further by

pressing element 25. A normal operation of such a pump involves

intermittently activating piezoelectric elements 21 and 24 by supplying

voltage to each of them in turn. Referring to 2A, the dimensions of the pump

may be, for example, 1=42 mm, m=42 mm and n=27 mm.

Figs. 3A, 3B, and 3C illustrate a structure of a piezo-hydraulic pump, according to another embodiment of the present invention. The pump has

only one piezoelectric element 31, two opposing sides of which are connected

to moveable membranes, such as membranes 32 and 33. One operation cycle

of this pump involves piezoelectric element 31 being in three different

states, at three different times. In the first state the piezoelectric element is inactivated (i.e., no voltage is supplied to it), in the second state it is

supplied with a positive voltage, and in the third state it is supplied with a

negative voltage. The three pairs of piezoelectric elements (13) and

corresponding pressing elements (12) of the embodiment of Fig. 1 are replaced in the embodiment of Fig. 3 by three hydraulic tubes and three pistons (37, 38 and 39). One operating cycle of this pump essentially comprises the following steps: 1) Step one (see Fig. 3A) - no voltage is supplied to piezoelectric element

31. Consequently, it retains the initial state, in which the inlet of the

pump is blocked by piston 39, while two other pistons 37 and 38 exert no

pressure on dispensing tube 10. It should be noted that despite the fact

that the volume of each of chambers 35 and 36 is smaller now with

respect to the volume in step one (Fig. 3a), only piston 39 exerts pressure

on dispensing tube 10. The reason for this is that tube 35a has a larger

diameter than that of tube 36a. Therefore, despite the fact that

essentially the same amount of hydraulic fluid is discharged from

chambers 35 and 36, piston 39 travels a longer distance than piston 38.

2) Step two (Fig. 3B) — a positive voltage (not shown) is supplied to

piezoelectric element 31, causing it to expand. Consequently, piston 38

exerts pressure on dispensing tube 10. In this step piston 39 is still

blocking the inlet side of tube 10 and prevents liquid from flowing 'backwards'. Therefore, piston 38, by exerting pressure on tube 10,

causes the liquid to flow in the other direction, i.e., to the outlet of tube

10.

3) Step three (Fig. 3C) - a negative voltage (not shown) is supplied to

piezoelectric element 31, which causes it to be in its contracted state, wherein hydraulic liquid is pushed out from chamber 34 so as to elongate piston 37, thereby blocking the outlet of dispensing tube 10. Contraction of piezoelectric element 31 also causes chambers 35 and 36 to increase their volume, thereby causing pistons 38 and 39 to withdraw and release

any pressure from dispensing tube 10, thereby allowing it to be filled

with supplement liquid before the next cycle begins.

It should be noted that other modes for operating the pump might be

utilized. For example, one operating cycle of the latter pump might comprise

only the above-mentioned steps 2 and 3.

The present invention is therefore characterized by the following novel features: The first feature is the utilization of the dispensing tube itself as

part of the piezoelectric pump, i.e., as an integral dispensing channel. This feature stands in contrast to prior art piezoelectric pumps, wherein a

special/dedicated dispensing channel exists in the pump, in order to be

utilized as a dispensing tube/line. The second novel feature is affixing

pressing elements having a unique shape, i.e., preferably a right-angle triangle, to piezoelectric actuator elements, through which pressure is

applied to the flexible tube, thereby achieving a better fluidity of liquid.

Fig. 4 schematically illustrates a general layout and functioning of a system

for controlling the pump of Fig. 1. The piezoelectric elements (not shown) of pump 41 are connected to voltage excitation distributor 42 that transfers the voltage required for the functioning of each pair of piezoelectric

elements at the right time. Power supply 43 is the voltage source for both the voltage excitation distributor and for controller 44 (generally a

microprocessor), and it is capable of supplying positive and negative

voltages required for activating the pumps, such as depicted in Figs. 1, 2

and 3. Microprocessor-based controller 44 determines the activation timing of each piezoelectric element, as set by the pump operator/user.

Fig. 5 is a graph showing the 'relationship between the flow rate of the pump

of Fig. 1, and the operating frequency of the pump, according to a test

conducted by the inventors. The testing procedure was carried out by

utilizing a flexible dispensing tube having an inner diameter of 1mm and a

wall thickness of 0.5mm. The pump functioning was tested by dispensing

three different liquids, i.e., Water, Insulin and Oil, of which dispensing rate

q (in micro-liter per minute) versus the operating frequency of the pump (in

Hertz) has been recorded.

Some of the advantages of the present invention:

The present invention is characterized in that the pressing elements are

pushed directly against . the outer face of the flexible dispensing tube,

thereby solving many problems of the prior art devices. The structure of the micro-pump disclosed herein is very simple, since, unlike most of the prior art pumping devices, it does not contain sealing layers, glass elements, membranes or valves. Such elements are not required in the pump of the present invention, since the elasticity characteristics of portions of the

dispensing tube are utilized as membrane substitutes. This is advantageous since whenever the elasticity of the portion becomes poor, the pump can be

moved so as to press another portion of the tube.

While some embodiments of the invention have been described by way of

illustration, it will be apparent that the invention can be carried into

practice with many modifications, variations and adaptations, and with the

use of numerous equivalents or alternative solutions that are within the

scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims.

Claims

1. A peristaltic pump, comprising:

a) A flexible tube for dispensing a liquid;

b) A plurality of piezoelectric actuators disposed across a portion of the

tube for applying pressure on the outside surface of the tube, when actuated,

in order to collapse said surface; and

c) Timing and control means for sequentially activating said piezo¬

electric actuators, to cause sequential collapse of points along the tube

surface, thereby causing liquid flow in the tube.

2. A peristaltic pump according to claim 1, wherein each piezoelectric

actuator is attached to at least one pressing element.

3. A peristaltic pump according to claim 2, wherein each pressing element

has a cross-section shape of essentially a right-angle triangle.

4. A peristaltic pump according to claim 3, wherein one acute angle a_P of

the cross-section triangular shape of each pressing element directs the

' desired flow direction, one orthogonal side of the triangle faces the

piezoelectric actuator, and the other orthogonal side to the direction

opposite to the desired flow direction.

5. A peristaltic pump according . to claim 3, wherein pairs of pressing

elements are arranged along a portion of the tube, each pair of pressing elements being arranged face-to-face to allow them to simultaneously

press the portion of the tube, said portion of the tube being between said

elements of each pair.

6. A peristaltic pump according to claim 3, wherein two pressing elements are attached to two opposing sides of one piezoelectric actuator, to

alternatively exert pressure either by a first of said pressing element on

a first portion of said tube when said actuator is in its first state, or by a second of said pressing elements on a second portion of said tube when said actuator is in its second state, and wherein the tube is bent so that

two different portions of it are correspondingly in contact with said two

pressing elements.

7. A peristaltic pump according to claim 1 wherein each piezoelectric

element, when activated, exerts pressure on a fluid in a fluid chamber,

and said fluid pushes a piston, which in turn exerts pressure on a portion

of the tube surface in order to collapse it and activate flow in the pump.

8. A peristaltic pump according to claim 1, wherein the timing and control

means is a microprocessor-based controller.

9. A peristaltic pump according to claim 1, further comprising:

a) Driving circuitry, for distributing power for energizing the actuators; and b) One or more sensors for detecting the liquid flow rate, the information

relating to the flow rate ' being forwarded to said timing and control

means, for optimizing the flow rate.