WO1982003427A1

WO1982003427A1 - A roller pump,preferably for implantation

Info

Publication number: WO1982003427A1
Application number: PCT/DK1982/000029
Authority: WO
Inventors: Centralen Elektronik
Original assignee: Kristensen Hans Saustrup; Ejlersen Henning Munk
Priority date: 1981-04-07
Filing date: 1982-04-07
Publication date: 1982-10-14
Also published as: DK146303B; DK156681A; DK146303C

Abstract

Implanted roller pumps must under no circumstances go to pieces during their stipulated service life. Therefore, they are provided with means for ensuring that the tubing (8) of the roller pumps are not either sujected to a displacing force or, that such a force is maintained on an absolute minimum. This can be done by chosing the radii (R) of the presser rollers (4, 4') almost as long as the radius (r) of the circle (C) defining the movement of the presser roller centres, by which feature the longitudinally displacing forces to which the tubing is subjected, are reduced as much as possible.

Description

A roller pump, preferably for implantation.

Technical Field.

The invention relates to a roller pump, preferably of the kind disposed to be implanted and comprising a pump housing having a substantially circular cylindrical back pressure surface or roller path for supporting a resiliently compressible or squeezeable tubing for carrying liquids, a rotor member having at least two presser rollers pivotally mounted thereon, the centres of which during the revolving of the roύor member follow a circle, the presser rollers further being so mounted on the rotor member that at least one of them at a time squeezes the tube against said roller path to full occlusion.

Background Art.

In connection with roller pumps of this kind it has been found difficult to achieve a sufficiently long and impeccabl service life. This situation is mainly due to the wear on the resiliently compressible tube. Chiefly, this wear results from the action of the presser rollers as they, during their frictional engagement with the tube, not only slide and roll on it but also subject the tube to longitudinal displacement forces so that the tube tends to travel or creep. This has the effect that the tube is stretched and slackened a great number of times not only in a transversal direction but also in a longitudinal one. An obvious way to prolong the service life of the tube would be to seek to employ a more wear-resisting material for the tube or increase the wall thickness of the tube; however, in connection with implantable pumps of the kind described above it is very important to seek solutions which demand as little power as ever possible because implanted units of th: kind usually are powered by small batteries or cells.

A method of reducing the tube's tendency travel or creep is known from the specification of the Swedish Patent Ho. 325.201. The presser rollers described therein are so designed that a part of their rolling surface is in engagement with the tube, whereas the remaining part of the rolling surface is in engagment with the backing or bearing surface. This is obtained by placing the tube in a recess in the backing surface combined with a corresponding increase of the diameter of the presser rollers in the parts confronting the recess. By suitable dimensioning it is then possible to subject the tube with a rearwardly directed frictional force which can neutralize the forwardly directed displacing force originating in the rolling resistance. This is not a practicable method in connection with implantable equipment because the need for power increases when providing an extra force to neutralize the effect from another force.

Disclosure of Invention.

According to this invention a roller pump of the kind described in the opening paragraph is characterized in that the radius of each of the presser rollers are approximately equal. to the radius of the circle along which the centres of the presser rollers travel to minimize the longitudinal forces exerted on the tube. Thereby it is achieved in a particularly simple manner to optimize the rolling conditions at the spots in which the rollers engage the .tube so that the άisplacing forces on the tube are reduced as much as possible, and it is simultaneously achieved that the influence on the tube in a radial direction becomes as lenient as possible thereby further reducing the wear.

Brief Description of Drawings. The invention is described in greater detail in the followin having reference to the accompanying drawings, wherein: Fig. 1 shows a geometrical figure, by means of which the condition for reducing the displacing force can be read, and Fig. 2 is an embodiment of a roller pump of the invention.

3est Mode for Carrying Out the Invention.

In Fig. 1 the capital letter C denotes a part of a circle having its centre 0 in the point (0,0) of a system of coordinates X,Y and a radius r. This circle intersects the X-axis in a point a . This point a is the centre of a circle C' having a radius R and intersecting the X-axis in a point p. If the circle C' having a radius R represents a presser roller the centre of which follows the circle C then this roller will be situated at a later moment with its centre at the point b and its periphery be represented by the circle C" which intersects the extension of the radius 0-b at a point q . The point of the periphery of the roller which in the first position is denoted p will in its next shown position have been transferred to the point p'. The rolling path forms a circle B having its centre in 0 and a radius equal to (r + R). The angle between the radii from 0 to p and from 0 to q is denoted θ. That angle the roller has turned relative to the line Oq during the transition of its centre from the point a. to the point b is denoted (θ + φ ).

Now, we wish to express, that the arc pq of the circle 3 due to the rolling action equals the arc p'q of the circle C".

pq = (r + R)θ = p'q = R(θ + φ) which implies rθ + Rθ = Rθ + Rφ giving φ = θ(r/R).

The rectangular co-ordinates of the point b referred to the signs indicated by arrows are (r·cosθ, r·sinθ) and of the point p' (r·cosθ + R·cosφ, r·sinθ - R-sinφ) which, when employing the above is (r·cosθ + R·cos(θ·r/R), r·sinθ - R · s in( θ ·r/R)) In the above expression r can be replaced by R · r/R and then we can write (dx/dθ, dy/dθ) for the point p' as (-r·sinθ -R·r/R·sin(θ·r/R), (r·cosθ - R · r/R-cos ( θ ·r/R).

Then, the track of the point p' can be characterized by

From this it can be deduced that if r = R the numerator of the last fraction becomes zero implying that the point p' will be situated on the X-axis. This is, however, a condition that a resiliently flexible tube engaging the bearing surface B, as it appears from Fig. 2, shall not be subjected to a displacement in its own longitudinal direction.

The result of this recognition is utilized in the design of the roller pump illustrated in Fig. 2. Here, numeral 1 refers to a pump housing comprising a rotor member 2, which is mounted with its rotational axis in 0 corresponding to the point 0 in Fig. 1. The rotor member 2 carries two presser rollers 4 and 4', respectively, having equal radii R and jour nalled in smooth-running bearings 3 and 3', respectively. The pump housing 1 is provided with a roller path 7 which accommodate a tubing 8 having walls 8'. The tubing is shown in section. The centre a. of the presser roller 4 is placed in a distance r from the centre 0 of the rotor member 2 and of the roller path 7. The total of the radii r. and R and two wall thicknesses of the tubing 8 is a small amount lar- ger than the radius of the roller path 7 in order to ensure full occlusion of the tubing 3 under the presser roller 4. thereby applying some elastical deformation of the tube walls 8'.

If it was possible to make the radius R of a presser roller just as long as the radius r of the circular track of the centre a, then, according to the above derivation, the point p on the periphery of the presser roller would, during the continued rolling action, follow the straight line p0 having the effect that any longitudinal displacement of the tubing be prevented. It is, however, not possible to make the radius r exactly equal to the radius R of the presser rollers, because the two presser rollers 4 and 4 ' on the rotor member 2 then would touch each other and prevent their smooth-running action. Therefore, it is necessary to make the radius r a bit larger than the radius R so that these two presser rollers do not engage mutually.

Further, as indicated for the embodiment shown in Fig. 2, the rotor member 2 may in a known manner be provided with supporting rollers 12 and 12', the envelopping circle 13 of which has a diameter just that shorter than the diameter of the envelopping circle for the presser rollers 4 and 4 ' that these supporting rollers only touch the tubing. This has the effect that the supporting rollers 12 and 12' can contribute in preventing the tubing 8 from lifting itself from the roller path 7.

Claims

Patent Claim.

A roller pump preferably of the kind disposed to be implanted and comprising a pump housing (1) having a substantially circular cylindrical back pressure surface or roller path (7) for supporting a resiliently compressible or squeezeable tube (8) for carrying liquids, a rotor member (2) having at least two presser rollers (4,4') pivotally mounted thereon, the centres of which during the revolving of the rotor member follow a circle (C), and the presser rollers further being so mounted on the rotor member that at least one of them at a time squeezes the tube against said roller path (7), c h a r a c t e r i z e d in that the radius of each of the presser rollers ( 4 , 4 ' ) being approximately equal to the radius (r) of said circle (C) along which the centres of the presser rollers are travelling to minimize the longitudinal forces exerted on the tube.