GB2416810A

GB2416810A - Peristaltic pump and rotor

Info

Publication number: GB2416810A
Application number: GB0417530A
Authority: GB
Inventors: James Kitchen
Original assignee: VERDER Ltd
Current assignee: VERDER Ltd
Priority date: 2004-08-06
Filing date: 2004-08-06
Publication date: 2006-02-08
Anticipated expiration: 2024-08-06
Also published as: WO2006013316A1; GB0417530D0; GB2416810B

Abstract

A peristaltic pump comprising: a compressible conduit 8; an arcuate support surface 71 arranged to support the compressible conduit, the arcuate support surface following a substantially circular path around an axis R and the conduit being arranged to extend around the arcuate support surface; and a rotor 1 arranged to rotate about the axis. The rotor comprises at least one lobe 2a,2b arranged to periodically compress the conduit against the support surface to form a constriction and to sweep the constriction along the conduit as the rotor rotates. The rotor has a profile in a plane perpendicular to the axis of rotation, that profile being described by a function r( r ) in polar coordinates where r is the radial distance of a point on the profile from the axis of rotation and r is the angular position of the point relative to a reference position. The lobe portion comprising a curved portion of the rotor profile in which r increases smoothly, with no discontinuity in dr/d r , from a value r1 at an angle r 1 to a second value r2 at an angle r 2, and dr/d r = 0 at r 1 and at r 2. The rotor may therefore take the form of an ellipse or oval.

Description

PERISTALTIC PUMP AND ROTOR

Field of the Invention

The present invention relates to peristaltic pumps.

Background to the Invention

Peristaltic pumps are well known, and one general type comprises a mechanical rotor arranged to rotate inside a housing so as to periodically compress a hose or tube against an inner wall of the housing, thereby occluding the hose and sweeping the occlusion axially along the hose as the rotor rotates. If the hose contains a fluid, this action pushes fluid ahead of the occlusion, and the natural resilience of the hose draws in fluid behind the occlusion. Peristaltic pumps offer advantages and fmd use in a number of applications, such as the pumping of abrasive media, corrosive media, sterile media, and live or shear- sensitive media.

A known peristaltic pump is illustrated schematically in figure 1. The pump comprises a housing H inside which a compressible hose C is arranged to follow a generally U-shaped path from an inlet IN to an outlet OU. The housing includes an inner surface I which follows a circular path, centred on an axis R. against which the hose C is periodically compressed by lobes L of a rotor RT as the rotor rotates about the axis R. Compression of the hose forms an occlusion O which is axially swept along the hose as the rotor rotates. In this known design, the rotor is a single, solid component, having a base radius rl. The outer tip of each lobe has a relatively small radius of curvature rc which is approximately (l/4.rl. Each lobe also comprises straight lead-in and lead-out surfaces LI, LO which are tangential to the curved tips and the portion of the rotor having the base radius rl. A problem with the pump shown in figure 1, however, is that when the rotor is driven at constant speed the pump produces a pulsating discharge. Pulsation can be regarded as the repeated acceleration and deceleration of the pumped media, and is undesirable in some circumstances. For example, uneven flow throughout each cycle makes metering difficult.

Peristaltic pumps with other forms of rotors arc also known. For example, rotors are known in which the hose-compressing members are rollers, of relatively small diameter compared with the overall rotor diameter, mounted on suitable supports or arms. Also known are rotors in which curved "shoes" are attached to a rotor body having a basic radius, the shoes extending radially outwards from the body to provide hosecompressing structures. The curved hose-compressing surfaces of these shoes typically have a constant radius of curvature (the surfaces have profiles which follow circular paths), that radius of curvature being substantially smaller than the basic radius of the rotor body. However, a problem with pumps employing these roller- and shoe-type rotors is again that they produce pulsations.

GB 2 290 582 A describes an attempted solution to the pulsation problem.

That document discloses a peristaltic pump having a rotor comprising two diametrically opposed rollers arranged to periodically compress a flexible pipe against internal support walls. These support walls comprise a substantially semi-circular wall of constant radius, centred on the rotor axis, joined to walls of larger radius having centres offset from the rotor axis. One of these walls of larger radius supports the flexible pipe on the lead in to the semi-circular section, providing gradual closure of the pipe, and the other supports the flexible pipe on the lead out from the semi- circular section, providing gradual opening of the pipe. Although reducing pulsations, a disadvantage of the disclosed device is that it requires a particular support wall configuration, and so is not applicable to pumps in which the housing has already been manufactured to provide a typical semi-circular, part-circular, or U-shaped support surface.

An important factor associated with the use of peristaltic pumps is hose life.

Hose life has previously been regarded as a quantity which could simply be expressed in terms of a number of compressions to which the hose could be subjected. Thus, doubling rotor speed or changing from a two-lobe rotor to a four-lobe rotor, keeping rotor speed constant, would result in the hose life expiring in half the time.

However, the present inventor has determined that this "rule of thumb" for hose life represents an oversimplification; rather than the lifetime of a hose simply being determined by the number of times it can be compressed, the inventor has determined that the shape (i.e. profile) of the peristaltic pump rotor, and in particular the shape of its lobes, has a major effect on hose life, pumping performance, and other pumping characteristics. Observations and analysis of known rotor profiles have led to the inventor determining that on contact with, and on decompression of the hose, prior art rotors have created acceleration spikes, resulting in large cyclic pressure changes in the hose. The fluid in the hose transmits these pressure fluctuations, which are absorbed by the hose at the point where the rotor leaves the hose after compression. This is typically the only area where the hose is both under discharge pressure and unconstrained by the housing and rotor. Hence the hose is free to stretch like a balloon, which it does, causing fatigue and eventually resulting in failure.

With regard to the pump shown in figure 1, the inventor has determined that the curved tips of the lobes, with small radii, in particular result in the hose wall experiencing relatively high accelerations as the rotor lobes strike and then leave the hose. The high transient pressures generated in the pumped fluid can make hose life very short, and may cause pipe work to rupture With regard to peristaltic pumps comprising the roller- and shoe-type rotors described above, the inventor has determined that when one considers the dynamics of how the rotor compresses the hose, there is a sharp increase in velocity of the hose wall, and hence it experiences a large acceleration, as the rotor both strikes and leaves the hose. Thus, the hose is subjected to a large force, and there is also a rapid change in fluid velocity inside the hose (which is manifested as a pressure pulsation). Both of these components contribute to hose fatigue, and can ultimately lead to premature failure.

These problems will be better appreciated from a consideration of figures 2-5.

Figure 2 is a highly schematic representation of a known rotor, in which two shoes S are attached to a rotor body B of basic radius rl. The shoes extend the rotor to a peak radius of r2 (i.e. the shoes provide a lift h, where h = r2 - rl). Each shoe has an outer surface which has a generally semi-circular profile, of radius rc. Looking at just one quadrant of the overall profile of the rotor, which in polar coordinates can be expressed as a function r(0), we see that r is constant at r = rl for 0 < 0 < x, but then as we enter the portion of the profile corresponding to the shoe there is an abrupt transition to increasing r; there is a discontinuity in dr/d0 at x. As a result, the second derivative of r with respect to 0, which is proportional to the acceleration experienced by a flexible hose being displaced by the rotating rotor, includes a large spike at x.

It is therefore an object of embodiments of the present invention to provide peristaltic pumps and peristaltic pump rotors which overcome, at least partially, one or more of the above-described problems associated with the prior art. Particular embodiments aim to reduce hose (i.e. conduit) fatigue and reduce pressure pulsations (previously caused by rapid hose compression). Embodiments also aim to provide increased hose life and/or enable the pump to be operated at higher rotor speeds.

Summary of the Invention

According to a first aspect of the present invention, there is provided a peristaltic pump comprising: a compressible conduit; an arcuate support surface arranged to support the compressible conduit, the arcuate support surface following a substantially circular path around an axis and the conduit being arranged to extend around the arcuate support surface; and a rotor arranged to rotate about said axis and comprising at least one lobe arranged to periodically compress the conduit against the support surface to form a constriction and to sweep the constriction along the conduit as the rotor rotates, the rotor having a profile in a plane perpendicular to the axis of rotation, the profile being described by a function r() in polar coordinates where r is the radial distance of a point on the profile from the axis of rotation and is the angular position of the point relative to a reference position, wherein the rotor profile comprises a lobe portion corresponding to the lobe and determining the compression of the conduit as the rotor rotates, the lobe portion comprising a curved portion of the rotor profile in which r increases smoothly, with no discontinuity in dr/dO, from a value rl at an angle (31 to a second value r2 at an angle (32, and dr/dO = 0 at 01 and at 02.

Employing a rotor of the defined profile provides the advantage that pressure pulsations in pump output are reduced compared with the prior art, and the accelerations experienced by the conduit material are reduced, thereby increasing conduit life for a given rotor speed, or enabling increased rotor speed to be used for the same conduit life.

In certain preferred embodiments the arcuate support surface is concave, although the invention also finds application in peristaltic pumps where the rotor compresses a conduit radially inwards against a convex support surface.

It will be appreciated that the description of the support surface following a circular path is not intended to require that the surface extends around a complete circle. Instead, it merely indicates that the surface follows a circular path for an arc of at least a few degrees. In certain embodiments, the extent of the support surface may be approximately 180 degrees, such that the surface has semicircular profile, but in other embodiments the extent may be less or more than 180 degrees.

It will also be appreciated that the profile of the rotor is to be understood as an overall shape or outline of the rotor on a macroscopic scale related to the size and flexibility of the conduit. Features on the rotor surface which are small enough to have no substantial influence on the deformation of the conduit by the rotor are not to be regarded as part of the rotor profile. Similarly, the support surface follows a generally circular path, and small deviations from a perfect circular path, having no substantial effect on the pump operation, are to be disregarded.

Preferably, the lobe portion further comprises a curved portion of the rotor profile in which r decreases smoothly, with no discontinuity in dr/dO, from value r2 at angle 03 to value rl at an angle 04, where 04>03> 02>01 and dr/dO = 0 at 03 and at 04. Thus, in addition to providing reduced conduit acceleration on compression, embodiments may also provide reduced acceleration as the conduit is released.

In certain embodiments (04 - 03) = (02 - 01), such that the rise and fall intervals are the same. The rise and fall portions may furthermore be symmetrical.

In certain embodiments, 03 = 02, such that there is no dwell at maximum radius (i.e. at maximum lift).

The lobe portion may have a radius of curvature rc2 at 02, where rc2>(1/3) rl, and even more preferably rc2 may be equal to r2.

In alternative embodiments, 03>02 and the lobe portion comprises a curved portion of the rotor profile in which r is substantially constant at value r2 from 02 to 03. In other words, the profile may include a dwell at maximum lift, which provides the advantage that a higher pressure seal may be achieved. A low dwell will increase the slug size of the pump, and a high dwell will improve the sealing of the hose and its ability to develop high pressure without over compression.

In addition, or alternatively, the rotor profile may comprise a portion of constant radius rl immediately adjacent the lobe portion on one side of the lobe portion (e.g. preceding the lobe portion, relative to the direction of rotation of the rotor in normal use). The rotor profile may also comprise a second portion of constant radius rl immediately adjacent the lobe portion and on the opposite side of the lobe portion (e.g. following the lobe portion). Thus, the rotor may comprise dwells at base radius rl before and/or after the or each lobe.

In certain preferred embodiments, the curved portion of the profile in which r increases smoothly is described by the relation r = rl + ((r2 rl)/2).(1 - cos (IT (O - (31)/( 02 - 01))) for 01 < < 02. Similarly, the curved portion of the profile in which r decreases smoothly may be described by the relation r = rl + ((r2 - rl)/2).(1 - cos(n (04 - 0)/(04 03))) for 03 < 0 <04.

Preferably, the pump rotor comprises two lobes, the rotor profile comprising two lobe portions each corresponding to a respective one of the two lobes. The two lobes may be diametrically opposed on the rotor, and/or may be separated by portions of the rotor profile having constant radius rl (i.e. dwells).

The pump rotor may comprise a plurality of lobes, the rotor profile comprising a plurality of lobe portions each corresponding to a respective one of the plurality of lobes, and the plurality of lobes may be evenly spaced around the rotor. Each adjacent pair of lobe portions may be separated by a respective dwell.

In certain preferred embodiments the rotor profile is elliptical.

In alternative preferred embodiments the rotor profile is given by: r=rl for (-a)<<a and (7c - a) < < (7+ a); r = rl + (h/2).[1 - cos (7r (O - a) 10)] for a<<(a+,B) and(+a)< 0<(7+a+); r=rl +h for(a+)<H<7r -(a+) and(7+a+, B)<O< 27-(a+p); and r = rl + (h/2).[1 - cos (a (O + a - a) / p)] for (am) <0 < n-a Andre -(a+)<3<2-a where rl = a base circle radius, h = a radial lift provided by each lobe = r2 -rl' a = an angle, per quadrant (i. e. per 90 degree, or /2 radian section), over which the rotor profile has a radius equal to the base circle radius, p= a rise angle, over which the radius of each lobe portion smoothly increases from rl to r2, and a fall angle over which the radius of each lobe portion smoothly decreases from r2 to rl.

Although embodiments of the invention may utilise flexible conduits of various forms, in certain preferred embodiments the conduit is a flexible hose.

The circular path followed by the arcuate support surface may have a radius r3, and r3 - rl may correspond to a radial thickness of the conduit in an uncompressed state. The quantity r3 - r2 may then correspond to a radial thickness of the conduit in a compressed state in which the conduit is fully occluded.

A second aspect of the invention provides a pump rotor for a peristaltic pump of the type comprising a compressible conduit and an arcuate support surface arranged to support the compressible conduit, the arcuate support surface following a substantially circular path around an axis and the conduit being arranged to extend around the arcuate support surface, the rotor having a rotational axis about which the rotor, in use, is arranged to rotate, and which, in use, is arranged so as to coincide with the axis of the circular path followed by the support surface, the rotor comprising at least one lobe for periodically compressing the conduit against the support surface to form a constriction and sweeping the constriction along the conduit as the rotor rotates, the rotor having a profile in a plane perpendicular to the axis of rotation, the profile being described by a function r(H) in polar coordinates where r is the radial distance of a point on the profile from the axis of rotation and theta is the angular position of the point relative to a reference position, wherein the rotor profile comprises a lobe portion corresponding to the lobe and determining the compression of the conduit as the rotor rotates, the lobe portion comprising a curved portion of the rotor profile in which r increases smoothly, with no discontinuity in dr/dO, from a value rl at an angle 01 to a second value r2 at an angle 02, and dr/dO = 0 at (31 and at 02.

It will be appreciated that a pump rotor embodying the second aspect of the invention may comprise any of the rotor features described above in relation to the first aspect, with corresponding advantage.

Brief description of the Figures

Embodiments of the invention will now be described with reference to the accompanying drawings of which: Figure I is a schematic representation of a peristaltic pump according to the

prior art;

Figure 2 is a schematic representation of a peristaltic pump rotor according to

the prior art;

Figures 3, 4 & 5 illustrate the radius of the rotor of figure 2 as a function of angular position around the axis R. and its first and second derivates respectively; Figure 6 illustrates the profile of a rotor embodying the invention, together with the profile of a rotor in accordance with the prior art, for comparison; Figure 7 is a plot of the radius of the rotor of figure 6 as a function of an angular position, together with the equivalent plot for a rotor according to the prior art; Figure 8 is a plot indicative of the radial velocity of the surface of the rotor of figure 6 as a function of angular position on the rotor profile, again including a corresponding plot for a rotor in accordance with the prior art; Figure 9 is a plot indicative of the radial acceleration at the surface of the rotor of figure 6 as a function of angular position on the rotor profile, again with a corresponding plot for a rotor in accordance with the prior art; Figure 10 illustrates the profile of another peristaltic pump rotor embodying the invention; Figure 11 illustrates the variation of radius as a function of angular position for the rotor profile shown in figure 10; Figure 12 is a plot illustrating the variation of radial velocity with angular position for the rotor of figure 10; Figure 13 is a plot illustrating the variation of radial acceleration as a function of angular position for the rotor of figure 10; Figure 14 is a plot indicative of the jerk expcricnccd by a hose or other conduit in contact with the surface of the rotor shown in figure 10, as a function of angular position with respect to the rotor, as the rotor rotates; Figures 15, 16 &17 are front, rear and isometric views respectively of a peristaltic pump rotor embodying the invention; Figure 18 is a schematic representation of a peristaltic pump embodying the invention; Figure 19 is a schematic representation of yet another peristaltic pump rotor embodying the invention; Figure 20 is a schematic representation of a further pump rotor embodying the invention; and Figure 21 is a schematic representation of part of another peristaltic pump embodying the invention.

Detailed description of Preferred Embodiments

Referring now to figure 6, a first peristaltic pump rotor 1 embodying the invention comprises a core portion 10 of base radius b, and two diametrically opposed lobes 2a and 2b. Each lobe provides a lift, h. The profile of the rotor comprises a first lobe portion 3a and a second lobe portion 3b. Lobe portion 3a comprises a curved portion of the rotor profile P in which the radius r increases smoothly, with no discontinuity in dr/dO, from value b at 0 to (b + h) at 90 . Furthermore, dr/dO equals zero at 0 and at 90 . Similarly the first lobe portion comprises another curved portion of the rotor profile from 90 to l 80 , in which r decreases smoothly from (h + b) to b. The second lobe has the same shape as the first. Also shown in figure 6 is a broken line indicating the profile of a rotor in accordance with the prior art. In this prior art rotor, rather than comprising only curved portions of the rotor profile, the lobes have lead in and lead out surfaces which are straight in profile. These straight sections connect the portion of the prior art rotor having the base radius to the lobe tips, which are curved sections with relatively small radii of curvature. Figure 7 shows the variation of the rotor profile radius as a function of angle for the rotor embodying the invention in figure 6 in the first quadrant (i.e. from 0 to 90 ) and also shows the corresponding plot, as a broken line, for the prior art rotor depicted in figure 6. Figure 8 is a corresponding velocity plot, which corresponds to the first derivative of the relationships shown in figure 7. Figure 9 is a corresponding plot of radial acceleration, which corresponds to the second derivative of the relationship shown in figure 7. It will be seen, from figure 9 in particular, that the prior art rotor, in use, would result in the adjacent compressible hose or other conduit experiencing a high acceleration spike, and hence a high force. In contrast, when using the pump rotor embodying the invention, illustrated in figure 6, the acceleration experienced by the pump conduit is considerably reduced.

Referring now to figure 10, a further peristaltic pump rotor embodying the invention comprises two lobes 2a, 2b diametrically opposed about the rotor axis of rotation R. The rotor profile is symmetrical. The profile may be divided into segments, of which just five sl-s5 are labelled on the figure. The first lobe portion of the profile, which corresponds to the first lobe 2a, consists of segments s2, s3, and s4.

In segments sl and sS the rotor profile has constant radius, equal to the base radius b.

Segment s2, a rise segment, is a curved portion of the profile in which r increases smoothly, with no discontinuity in dr/dO, from b at an angle a to (b + h) at an angle (a + ,B), and dr/dO = 0 at 0 =a and at =(a + O. The first lobe portion then comprises segment s3, from (a + ,0) to (180 - (a + ,B)), over which radius r remains constant at (b + h). Finally, the first lobe portion comprises segment s4, a fall segment, which is a curved portion of the profile in which r decreases smoothly, with no discontinuity in dr/dO, from (b + h) at an angle (180 - (a + ,8)) to b at an angle (180 - a) and dr/dO = O at 0 =(180 - (a + ,3)) and at = (180 - a) The second lobe 2b has the same shape as the first lobe 2a. Segments sl and s5, in which radius is constant may be described as base radius dwells. Similarly, segment s3, and the corresponding unlabelled segment of the second lobe profile, may be described as maximum lift dwells. The incorporation of maximum lift dwells provides the advantage that the rotor can produce an extended seal (occlusion) along the hose, which is able to withstand higher pressures without necessitating overcompression of the hose material. By avoiding overcompression, hose life can be greatly extended. Thus, by incorporating a rotor as shown in figure 10, one can provide a pump with high pressure capabilities and with long hose life.

The profile of the rotor of figure 10 can be described as follows: Segments 1 and 5 - constant base radius dwell s=b where(l80-a)<O<a Segment 2 - rise s = b + (h/2)[ 1 - cos (7(0 - a)lp)] where a <O< (a+) Segment 3 constant max lift dwell s = b + h where (a + ,3) < 0 < (180 - (a + p)) Segments- fall s = b + (h/2)[1 - cos ((0 + a - 1 80)/,B)] where(180-(a+))<O< (180-a) where: s = radius of profile (or, equivalently, displacement) b = base circle radius h = radial lift 0 = angle a = angle of constant base circle radius per 90 degree section B = rise / fall angle.

The rise segment may be referred to as a sinusoidal rise, from b to (b + h), and the fall segment may similarly be referred to as a sinusoidal fall. The overall algorithm may be referred to as a sinusoidal displacement algorithm, with dwells.

In embodiments of the invention these parameters may be selected in the following ways: Base circle radius b is the amount of displacement required to produce zero compression on the hose (or other form of conduit).

Radial lift h is the extra amount required when added to the base circle radius to go from zero hose compression to a fully sealed state. This figure will usually be a little larger than the hose bore.

The angle of constant base circle radius, a, is used to increase the volume per slug. However, increasing this value also increases the peak velocity and acceleration on the hose, so a should be selected to obtain a suitable compromise.

The rise and fall angles should ideally be as long as possible in order to minimise peak velocity and accelerations and to help prevent inversions (i.e. negative curvatures in Cartesian space).

The angle of constant lift (providing the dwells at maximum radius) is used to provide an extended contact and extended seal along the hose, rather than a point contact. This angle is represented by the quantity (90 - (a + A)) in figure 10. This enables high pressure to be developed without the need for shims and over compression which would have a detrimental effect on hose life. However, it should be noted that increasing the extent of the dwells at maximum radius decreases the volume per slug of pump output.

It should be noted that the above algorithm is valid only for (a,8) < 90 degrees. The rise algorithms are designed to work in the range O degrees and the fall algorithms in the range 90 -- 180 degrees, and produce a two-lobe rotor.

Figure 11 is a plot of lift versus rotor angle over the five segments sls5 for the rotor of figure 10 (and hence corresponds to a plot of rotor profile radius, r, as a function of 0, the angle from the nominal zero degree reference position on the profile). Figure 12 is a corresponding "velocity" plot, which may also be regarded as a plot of dr/dO as a function of theta. Figure 13 is the corresponding "acceleration" plot, which may also be regarded as a plot of d2r/dO2 as a function of (3. Figure 14 illustrates the corresponding "jerk", which corresponds to d3r/dO3.

From figures 11 to 14 it will be appreciated that the above-mentioned sinusoidal displacement algorithm, with dwells, produces non-zero acceleration at the ends of each section. However, the peak accelerations are very small compared with those produced by prior art rotor profiles, and the rotor enables substantially reduced pulsation and increased hose life to be achieved.

Thus, the rotor of figure 10 is designed to smooth the pressure peaks in a pumped fluid by controlling velocity and acceleration of the hose walls. It does, however, reduce flow per revolution (and hence flow rate for a given rpm) to approximately 75% of that achievable with an equivalent rotor having the shape illustrated in figure 1, and so requires an increase of approximately 33% to achieve an equivalent flow rate. However, even with this speed increase, the peak acceleration is much reduced using the rotor of figure 10.

Referring now to figures 15-17, another peristaltic pump rotor 1 embodying the invention is a one-piece component comprising a central hub, with an array of attachment holes, and two lobes 2a, 2b. In this embodiment the hub and lobes have been machined from a single piece of suitable material, although in alternative embodiments the rotor may be an assembly of separate components. The rotor profile P consists of a first lobe portion 3a and a second lobe portion 3b, and in this embodiment has no dwells. The lobes provide a smooth, continuously curving, hose- engaging surface 6 for engaging (directly or indirectly) a pump hose so as to produce periodic compression. The rotor profile is giver) by the relation: r = rl + (r2 rl)/2.[1 - cos (2.)] for 0 < 0 < 360 degrees Moving on to figure 18, this shows a peristaltic pump embodying the invention. The peristaltic pump comprises a compressible conduit in the form of a hose 8, having an inlet and an outlet, and arranged to follow a substantially U-shaped path within a pump housing 7. The housing 7 provides a concave arcuate support surface 71 which is arranged to support the compressible conduit 8. The arcuate support surface follows a substantially circular path of radius r3 around an axis R (in this example the support surface is part-cylindrical, with a semicircular profile) and the conduit is arranged to extend axially aroundthe arcuate support surface. The housing 7 also provides straight sections of support surface 72 adjacent the straight portions of the U-shaped conduit. A rotor l is arranged inside the housing 7 to rotate about the axis R and has an elliptical profile, having a minor radius rl and a major radius r2. The elliptical rotor thus provides two lobes which periodically compress the conduit 8 against the support surface 71 to form a constriction 82 and sweep the constriction along the conduit as the rotor rotates. It will be appreciated that the elliptical profile may be described by a function r() in polar coordinates where r is the radial distance of a point on the profile from the axis of rotation R and theta is the angular position of the point relative to a reference position. The rotor profile comprises two lobe portions, which determine the compression of the conduit as the rotor rotates, each lobe portion comprising a respective curved portion of the rotor profile in which r increases smoothly, with no discontinuity in dr/dO, from a value rl at a respective first angle to a second value r2 at a respective second angle, and dr/dO = 0 at the respective first and second angles. In figure 18, the quantity r3 -rl corresponds to the thickness t of the conduit 8 in an uncompressed state, and r3 - r2 corresponds to the radial thickness of the conduit in a compressed state in which the conduit is fully occluded.

Moving on to figure 19, another pump rotor embodying the invention comprises three lobes 2a, 2b, 2c providing a radial lift (r2 -rl) from a body portion 10. The lobes are evenly spaced around the rotational axis R. and between each pair of adjacent lobes there is a respective dwell portion of constant radius rl. All three lobes have the same shape. Considering just the first lobe 2a, between angles al and a2 its profile is curved and r increases smoothly, with no discontinuity in dr/dO, from a value rl at angle al to r2 at angle a2, and dr/dO = 0 at al and at a2. Similarly, between angles a2 and as its profile is curved and r decreases smoothly, with no discontinuity in dr/dO, from r2 to rl, and dr/dO = 0 at a2 and at a3. The curved rise portion between al and a2 may be a sinusoidal rise as described above, or may have a different curved shape.

Similarly, the fall portion between a2 and a3 may be sinusoidal or a different smooth, curved shape. The rotor of figure 19 with long base radius dwells can produce long slugs and reduced hose accelerations, to prolong hose life.

Figure 20 is a highly schematic representation of a fabricated rotor, having a body portion 10 with a rectangular profile, and two lobes 2a, 2b attached to the body to provide lift displacement from rl to r2. Although the overall rotor profile includes flats, the lobe portions of the profile are curved, and satisfy the relation that dr/dO equals zero at the beginning and end of each rise and fall portion.

Figure 21 is a highly schematic representation of part of another pump embodying the invention. Here, the support surface 71 is convex, and the rotor 1 is arranged to rotate around the outside of the support surface. Thus, rather than the rotor having lobes projecting radially outwards, in this example the two lobes 2a and 2b project radially inwards, so as to compress a hose arranged between the rotor and the convex support surface. The lobes have the same shape, and considering just the first lobe 2a, it has a curved profile between angle 01 and angle 02 in which r smoothly increases, and dr/dO is zero at both 01 and 02.

It will be appreciated that pumps embodying the present invention are able to offer reduced pulsation compared with the prior art. Rotor profiles in embodiments of the invention are shaped so as lo reduce, and even minimise, the rate of change of hose internal volume, and hence reduce, or minimise, the rate of change of flow of the pumped medium (i.e. accelerations and decelerations are reduced). Thus, embodiments of the invention are able to increase hose life (by a factor of ten or more, increase pumphead reliability, increase overall system reliability (as there is a lower risk of pipework rupture with reduced pressure pulses), increase pump efficiency, provide a pumping mechanism suitable for materials with even greater shear sensitivity, and provide an improved metering capability (metering is facilitated as pulsations are reduced).

By selecting a rotor profile to control the dynamics of the rotor on the hose, embodiments of the invention are able to reduce peak velocity and acceleration, offering a substantial improvement over prior art pumps in which the rotors created large acceleration spikes in their actions on the hose.

Embodiments of the invention are able to reduce fatigue on the pump hose by controlling the fluctuations of pressure in the hose, and hence pump flow may be increased by increasing rotor speed, whilst retaining the same, or similar, hose life as

in prior art pumps operating at reduced speed.

Claims

CLAIMS: 1. A peristaltic pump comprising: a compressible conduit; an

arcuate support surface arranged to support the compressible conduit, the arcuate support surface following a substantially circular path around an axis and the conduit being arranged to extend around the arcuate support surface; and a rotor arranged to rotate about said axis and comprising at least one lobe arranged to periodically compress the conduit against the support surface to form a constriction and to sweep the constriction along the conduit as the rotor rotates, the rotor having a profile in a plane perpendicular to the axis of rotation, the profile being described by a function r() in polar coordinates where r is the radial distance of a point on the profile from the axis of rotation and O is the angular position of the point relative to a reference position, wherein the rotor profile comprises a lobe portion corresponding to the lobe and determining the compression of the conduit as the rotor rotates, the lobe portion comprising a curved portion of the rotor profile in which r increases smoothly, with no discontinuity in dr/dO, from a value rl at an angle (31 to a second value r2 at an angle 02, and dr/dO = 0 at Of and at 02.
2. A pump in accordance with claim 1, wherein the arcuate support surface is concave.
3. A pump in accordance with any preceding claim, wherein the lobe portion further comprises a curved portion of the rotor profile in which r decreases smoothly, with no discontinuity in dr/dO, from value r2 at angle H3 to value rl at an angle 04, where 04>03>02>01 and dr/dO = 0 at 83 and at 04.
4. A pump in accordance with claim 3, wherein (04 - 03) = (02 - 01).
5. A pump in accordance with claim 3 or claim 4, wherein 03 = (32.
6. A pump in accordance with any preceding claim, wherein the lobe portion has a radius of curvature rc2 at (32, where rc2>(1/3)rl.
7. A pump in accordance with claim 6, wherein rc2 = r2.
8. A pump in accordance with claim 3 or claim 4, wherein 03>02 and the lobe portion comprises a curved portion of the rotor profile in which r is substantially constant at value r2 from 02 to 03.
9. A pump in accordance with any preceding claim, wherein the rotor profile comprises a portion of constant radius r] immediately adjacent the lobe portion on one side of the lobe portion.
10. A pump in accordance with claim 9, wherein the rotor profile comprises a second portion of constant radius rl immediately adjacent the lobe portion and on the opposite side of the lobe portion.
11. A pump in accordance with any preceding claim wherein said curved portion of the profile in which r increases smoothly is described by the relation r = rl + ((r2 - rl)/2) (1 - cos (71(0 - 01)/(02 - O))) for 01 < < 02.
12. A pump in accordance with claim 3, or any one of claims 4 to 11 as dependent on claim 3, wherein said curved portion of the profile in which r decreases smoothly is described by the relation r = rl + ((r2 - rl)/2). (1 - cos((04 - O)/(04 - 03))) for 03 < O<04.
13. A pump in accordance with any preceding claim, comprising two said lobes, the rotor profile comprising two said lobe portions each corresponding to a respective one of the two lobes.
14. A pump in accordance with claim 13, wherein the two said lobes are diametrically opposed on the rotor.
15. A pump in accordance with claim 13 or claim 14 wherein said two lobe portion are separated by portions of the rotor profile having constant radius rl.
16. A pump in accordance with any one of claims 1 to 12, comprising a plurality of said lobes, the rotor profile comprising a plurality of said lobe portions each corresponding to a respective one of the plurality of lobes.
17. A pump in accordance with claim 16, wherein the plurality of lobes are evenly spaced around the rotor.
18. A pump in accordance with claim 16 or claim 17 wherein each adjacent pair of lobe portions are separated by a respective portions of the rotor profile having constant radius rl.
19. A pump in accordance with any one of claims 1 to 6, wherein the rotor profile is elliptical.
20. A pump in accordance with any one of claims 1 to 4, wherein the rotor profile Is given by: r=rl for (-a)<O<a and(-a)<<(7+a); r=rl +(h/2).[1cos(7(-a)/p)] for a < 0 < (a + ,B) and(7+a)<0<(7+a+); r=rl+h for(a+)<Q< 71-(+) and(+a+,B)<< 27T-(a+);and r = rl + (h/2).[1 - cos (7: ( 0 +a- 7) / ,B)] for 7-(a+,6)<<7-a and2-(a+,B)<0<2-a where rl = a base circle radius, h = a radial lift provided by each lobe = r2 -rl, = an angle, per quadrant, over which the rotor profile has a radius equal to the base circle radius, p= a rise angle, over which the radius of each lobe portion smoothly increases from rl to r2, and a fall angle over which the radius of each lobe portion smoothly decreases from r2 to rl.
21. A pump in accordance with any preceding claim, wherein the conduit is a flexible hose.
22. A pump in accordance with any preceding claim, wherein the circular path followed by the arcuate support surface has a radius r3, and r3 - rl corresponds to a radial thickness of the conduit in an uncompressed state.
23. A pump in accordance with claim 22, wherein r3 - r2 corresponds to a radial thickness of the conduit in a compressed state in which the conduit is fully occluded.
24. A pump rotor for a peristaltic pump of the type comprising a compressible conduit and an arcuate support surface arranged to support the compressible conduit, the arcuate support surface following a substantially circular path around an axis and the conduit being arranged to extend around the arcuate support surface, the rotor having a rotational axis about which the rotor, in use, is arranged to rotate, and which, in use, is arranged so as to coincide with the axis of the circular path followed by the support surface, the rotor comprising at least one lobe for periodically compressing the conduit against the support surface to form a constriction and sweeping the constriction along the conduit as the rotor rotates, the rotor having a profile in a plane perpendicular to the axis of rotation, the profile being described by a function r() in polar coordinates where r is the radial distance of a point on the profile from the axis of rotation and is the angular position of the point relative to a reference position, wherein the rotor profile comprises a lobe portion corresponding to the lobe and determining the compression of the conduit as the rotor rotates, the lobe portion comprising a curved portion of the rotor profile in which r increases smoothly, with no discontinuity in dr/dO, from a value rl at an angle 01 to a second value r2 at an angle 02, and dr/dO = 0 at O1 and at 02.
25. A rotor in accordance with claim 24, wherein the lobe extends radially outwards from the rotor.
26. A rotor in accordance with any one of claims 24 or 25, wherein the lobe portion further comprises a curved portion of the rotor profile in which r decreases smoothly, with no discontinuity in dr/dO, from value r2 at angle 03 to value rl at an angle 04, where 04>03>02>01 and dr/dD = 0 at 03 and at 84.
27. A rotor in accordance with claim 26, wherein (04 - 03) = (02 - 01).
28. A rotor in accordance with claim 26 or claim 27, wherein 03 = 02.
29. A rotor in accordance with any one of claims 24 to 28, wherein the lobe portion has a radius of curvature rc2 at 02, where rc2>(1/3)rl.
30. A rotor in accordance with claim 29, wherein rc2 = r2.
31. A rotor in accordance with claim 26 or claim 27, wherein 03>02 and the lobe portion comprises a curved portion of the rotor profile in which r is substantially constant at value r2 from 02 to 03.
32. A rotor in accordance with any one of claims 24 to 31, wherein the rotor profile comprises a portion of constant radius rl immediately adjacent the lobe portion on one side of the lobe portion.
33. A rotor in accordance with claim 32, wherein the rotor profile comprises a second portion of constant radius rl immediately adjacent the lobe portion and on the opposite side of the lobe portion.
34. A rotor in accordance with any one of claims 24 to 33, wherein said curved portion of the profile in which r increases smoothly is described by the relation r = rl + ((r2 - rl)/2).(1 - cos (7r (O - 01)/(02 - 01))) for 01 < O< 02
35. A rotor in accordance with claim 26, or any one of claims 27 to 34 as dependent on claim 26, wherein said curved portion of the profile in which r decreases smoothly is described by the relation r = rl + ((r2 - rl)/2).(1 - Cos(T(04 - 0)/(04 - 03))) for 03 < <04.
36. A rotor in accordance with any one of claims 24 to 35, comprising two said lobes, the rotor profile comprising two said lobe portions each corresponding to a respective one of the two lobes.
37. A rotor in accordance with claim 36, wherein the two said lobes are diametrically opposed on the rotor.
38. A rotor in accordance with claim 36 or claim 37 wherein said two lobe portion are separated by portions of the rotor profile having constant radius rl.
39. A rotor in accordance with any one of claims 24 to 35, comprising a plurality of said lobes, the rotor profile comprising a plurality of said lobe portions each corresponding to a respective one of the plurality of lobes.
40. A rotor in accordance with claim 39, wherein the plurality of lobes are evenly spaced around the rotor.
41. A rotor in accordance with claim 39 or claim 40 wherein each adjacent pair of lobe portions are separated by a respective portions of the rotor profile having constant radius rl.
42. A rotor in accordance with any one of claims 24 to 29, wherein the rotor profile is elliptical.
43. A rotor in accordance with any one of claims 24 to 27, wherein the rotor profile is given by: r=rl for (-a)<O<a and(7-a)<Q<(+); r = rl + (h/2).[1 - cos (7r ( O - a) / ,0)] fora<O<(a+) and(7+a)<0<(7+a+); r=rl+h fork 7-(a+) and(7+a+,B)< 2-(a+);and r=rl +(h/2).[1 -cos((+a-7)/,B)] for (a+)'O'-a and 2 - (am) 2,T - a where rl = a base circle radius, h = a radial lift provided by each lobe = r2 -rl, a = an angle, per quadrant, over which the rotor profile has a radius equal to the base circle radius, = a rise angle, over which the radius of each lobe portion smoothly increases from rl to r2, and a fall angle over which the radius of each lobe portion smoothly decreases from r2 to rl.
44. A peristaltic pump substantially as hereinbefore described with reference to figures 6 to 21 ofthe accompanying drawings.
45. A peristaltic pump rotor substantially as shown in figures 6 to 21 of the accompanying drawings.

45. A peristaltic pump substantially as shown in figures 6 to 21 of the accompanying drawings.

46. A peristaltic pump rotor substantially as hereinbefore described with reference to figuecs 6 to 21 ofthe accompanying drawings.