Peristaltic pump with accommodating rollers
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of U.S. application Ser. No. 616,642, filed Sept. 25, 1975, entitled &#34;Peristaltic Pump with Forgiving Rollers&#34;, now abandoned. 
    
    
     BRIEF SUMMARY OF INVENTION 
     In order to squeeze and strip the flexible tubing of a peristaltic pump with optimum pressure a novel &#34;forgiving&#34; pump roller is utilized. The roller comprises a hard surface, such as steel, having a smooth low friction surface, such as a sintered polytetrafluroethylene coating or a polished and lubricated porous chromium electroplating. Such a hard surface will squeeze and strip the tubing with minimum generation of frictional heat. The roller is made to bear against the tubing with a pressure which is largely independent of minor variations in tubing diameter by mounting the hard roller on internal elastomer bushings, which in turn are mounted on bearings which support the roller and drive it along the tubing in yielding rolling contact. The elastometer bushings permit the hard roller to deflect and yieldingly ride over tubing irregularities, without creation of excessive squeezing pressure and without generation of appreciable noise. Thus, the peristaltic pump is suitable for use in a setting where quiet is desirable. More important, the peristaltic pump is especially suitable for pumping blood, because there is less hemolysis of the living blood when the squeezing pressure is correct than when it is either too small or too large. 
     Because of the forgiving characteristics of the pump roller, it is feasible to utilize one set of rollers to squeeze and strip a pair of side by side peristaltic pump tubings. This arrangement ensures that the two tubings pump substantially equal amounts of fluid and this arrangement is therefor suited for pumping the input and output fluids of certain processes in which the volume of fluid processed must not substantially change. 
    
    
     BRIEF DESCRIPTION OF VIEWS OF DRAWING 
     FIG. 1 is a perspective view of the peristaltic pump; 
     FIG. 2 is a partly exploded end-on view of the peristaltic pump, showing how the roller occlusion distance can be changed by adjustment and by deflection; 
     FIG. 3 is a cross sectional view of the roller, in use with two peristaltic tubings of slightly different diameter. 
     FIG. 4 is a cross sectional view, similar to FIG. 3, of an alternative construction for the roller; and 
     FIG. 5 is a cross sectional view, similar to FIGS. 3 and 4, showing yet another alternative construction for the roller. 
    
    
     BACKGROUND OF THE INVENTION 
     Peristaltic pumps, in which rollers sweep tangentially along the inner race of a cylindrical housing and thereby squeeze and strip compliant tubing which lies along the inner race, are widely used to pump chemical and biological fluids. The instant invention was developed in connection with the pumping of blood, which is a living organism which must be handled gently. 
     An important feature of the inventive peristaltic pump is the setting of the occlusion distance between the roller of the pump and the race of the pump. The occlusion distance is critical for several reasons in biological systems. Firstly, blood is hemolyzed when the occlusion distance is either too great or too little. Secondly, when the occlusion distance is too great, resulting in a non-occluded tubing state, inefficient pumping will occur and the pump will not provide a reliable output of fluid for each revolution. If the occlusion distance is too small, in addition to harmful effects on the blood, the tubing has an extremely shortened life. The requirement to pump blood without hemolyzing it is essential to the health of the blood undergoing pumping and the patient to whom the pump may be connected or the patient to whom blood may be transfused. 
     The occlusion distance must be adjusted for each piece of tubing which is put into the pump. Tubing sizes will vary from lot to lot and dimension-variations will occur within a few inches of the length. Extremely close mechanical tolerances are required in order to build a peristaltic pump in which the roller will track around the race and maintain the occlusion distance within a tolerance of 0.003 inch. Because of the problems associated with either under or over occluded tubing, occlusion distance is, of course, critical. Since pumps equipped with rollers of the new design have the ability to accept tubing of various sizes without changes to the occlusion setting, thereby forgiving the operator from maladjustment problems, the rollers are called forgiving rollers. 
     But occlusion need not be caused by confining tubing between two rigid objects of precisely set separation; actually, occlusion can be caused by exerting enough force between two rigid objects to cause the tube to be flattened. The elastomeric inserts of the rollers of the invention permit the tubing to be flattened by the force exerted by the compression of the elastomer working over a small but variable distance. The responsibility for proper occlusion is thereby removed from uncertain dimensional setting and placed on the predictable elastomeric property of the rubber or like material. 
     DETAILED DESCRIPTION 
     In the perspective view of FIG. 1, 10 is a pump casing having a race 11, along which lies, in a semicircular loop, a bight of peristaltic tubing 12 made of a suitable elastomer, such as vinyl chloride polymer or silicone rubber. A rotary shaft 13 carries two adjustable sweep arms 14, which are clamped to the rotary shaft 13 by means of cap screws 15 and washers 16. Each of the sweep arms 14 carries a roller 17, supported on the sweep arm by a respective spindle 18 which is pinned to the sweep arm by a taper pin 19 (FIG. 3). 
     The adjustment of the sweep arm 14 on rotary shaft 13 is such that the rollers 17 squeeze shut, or occlude, the peristaltic tubing 12. Thus, as rotary shaft 13 rotates, the rollers sweep along the semicircular bight of the peristaltic tubing 12, thereby stripping the tubing and propelling the liquid in the tubing along its length. 
     In order to ease the transition of the rollers between the straight run and the bight of the peristaltic tubing 12, transistor ramps 20 are provided at each end of the race 11. 
     In order to keep the peristaltic tubing 12 from creeping around the race in the direction of the sweep of the rollers 17, the peristaltic tubing is anchored by clamps 25. The left clamp 25 is shown closed while the right clamp 25 is shown open. 
     Each clamp 25 consists of a pivoted member 26 having a semicircular cut-out 27, in which sits a moveable clamping jaw 28, retained by screw 29. In the stationary part of each clamp 25, there is a similar semicircular cut-out in casing 10, in which semicircular cut-out a respective field clamping jaw 29 is similarly fastened. 
     The moveable clamping jaw 28 has two gripping faces, each in the form of a toothed semicylinder. The &#34;lower&#34; gripping face 28L cooperates with a similar gripping face in fixed clamping jaw 29 to anchor securely the peristaltic tubing 12 in the lower of two possible positions. The peristaltic tubing is shown securely gripped in the lower position of the left clamp 25, while the bore formed by the upper gripping surfaces of the left moveable and the left fixed clamping jaws 28 and 29 is shown empty, without any peristaltic tubing. Indeed, the illustrated pump can be operated with either one or two peristaltic tubings, and is especially designed for use with two tubings, but the upper one is omitted in the drawing in order to better illustrate the construction. At the right side the peristaltic tubing 12 can be seen seated in the lower gripping face of fixed clamping jaw 29, while the semicircular upper gripping face thereof, corresponding to upper gripping face 28U, is empty. 
     The pivoted members 26 are held in clamping position by toggle levers 30. The left toggle lever is shown in latched position, while the right one is disengaged. Each toggle lever 30 has a pin 31 which engages a lip 32 on the pivoted member 26, to draw the pivoted member up into the closed and locked position. 
     The rotary shaft 13 carries four guiding rollers 40, supported on sweep arms 41. Guiding rollers 40, which are mounted just ahead of the rollers 17, keep the peristaltic tubing 12 from wandering away from the appropriate portions of the rollers 17. 
     As depicted in FIG. 1, the semicircular bight of peristaltic tubing 12 does not lie against the race 11. This permits a better view of the race, but in use, it is advisable for the peristaltic tubing to lie close to the race, in order to prevent undue wear. This is achieved by merely pushing the excess tubing at the right into the casing and then closing the right clamp 25. 
     In order to load the peristaltic pump with new peristaltic tubing, it is necessary to clamp two lengths of fresh tubing in the left clamp 25 and then to rotate the rotary shaft 13. The rotary shaft 13 can conveniently be turned, for this purpose, with a hand crank having a socket which engages the upwardly protruding end of rotary shaft 13, which has a drive flat 35. When the rotary shaft 13 is rotated counterclockwise, the guiding rollers 40 will, with slight manual assistance of the operator, gather the two lengths of new peristaltic tubing, and lay them against the race 11 just ahead of the first roller 17 which makes a sweep of the semicircular race 11. The two peristaltic tubings, 12 are thusly formed into semicircular bights and their free ends can then be clamped in the right clamp 25. 
     FIG. 2 illustrates how the occlusion distance, between roller 17 and race 11 is set. The adjustable sweep arm 14 is fastened to a machined seating on shaft 13 by means of cap screw 15 and washer 16. The hole 45, through which the shank of cap screw 15 is threaded, is oversize, permitting the adjustable sweep arm to be moved in its machined seating, as indicated by double-headed arrow A. The adjustment indicated by A controls the distance B, which would be the fixed occlusion distance if the roller 17 were rigidly mounted with respect to spindle 18. However, the internal construction of the hard surfaced roller 17 is such that the roller 17 can deflect, as shown by C, while the spindle 18 does not deflect. Thus, the total occlusion distance, with deflection, is the sum of B and C. 
     As pointed out above, the occlusion distance is fairly critical for satisfactory pumping of blood without damage to the blood, as blood must be handled gently. 
     Accordingly, the ability of roller 17 to deflect a distance C forgives an error in the set-up of the adjustment A, and forgives the inevitable slight variations of perstaltic tubing dimensions along the length thereof and forgives any slight eccentricity between the axis of rotary shaft 13 and the axis of the race 11. 
     One of the numerous possible embodiments for achieving a yielding hard surface roller 17 on an unyielding spindle 18 is illustrated in FIG. 3. 
     The spindle 18 is pinned into fixed relationship with sweep arm 14 by means of a taper pin 19. Two self-aligning ball bearing 50 on spindle 18 support the two outer race housings 51, which in turn support the hollow roller arbor 54 between them. The self-aligning ball bearings 50, outer race housings 51 and hollow arbor 54 are locked up into a rigid assembly because the parts fit properly and because they are subjected to an axial compression between spacer 52 and cup washer 53. The amount of this axial compression is adjusted by choice of the thickness of spacer 52, and should be such as would give the self-aligning bearings 50 a suitable pre-load. 
     Supported on hollow roller arbor 54, on either side of collar 58, are two elastomeric bushings 60 and 61, made of a material, such as rubber, of suitable hardness. The roller 17 is mounted on the outer edges of elastomeric bushings 60 and 61. 
     The roller 17 is shown as occluding two peristaltic tubings 12 between its outer surface and the race 11. Although the two peristaltic tubings are of the same nominal diameter, at the particular cross section shown, the left one has thinner walls and the right one has thicker walls. In FIG. 3, the effect of these different thicknesses is apparent -- the roller 17 is riding over the two peristaltic tubings 12 on a sidewise slant, even though the spindle 18 is still parallel to the axis of the race 11. The roller 17 is skewed while the spindle 18 is not because the bushings 60 and 61 permit deflection of roller 17 by virtue of the lesser distortion in bushing 60 and the greater distortion in bushing 61. 
     In order to assemble the roller 17 of FIG. 3, the following procedure is used: elastomeric bushing 60 is forced over ramp 56 until it seats against land 55 and elastomeric bushing 61 is similarly forced over ramp 57 against land 55. Then a suitable close fitting hollow fid, having an outer diameter equal to that of collar 58, is united with hollow roller arbor 54 and the union is forced through the holes in elastomeric bushings 60 and 61 until collar 58 is seated against one elastomeric bushing, whereupon the fid is pulled out, permitting collar 58 to seat against the other elastomeric bushing. 
     It is preferable for the elastomeric bushings to be cemented or vulcanized to the metal parts in order to increase lifetime. If this is done, the outer race housings 51 are added to the assembly, without the self-aligning ball bearings 50, and the assembly is suitably clamped up tight in a jig before the curing processing. 
     Rollers constructed in accordance with this invention have undergone extensive testing and have performed well as judged by their ability to pump liquids through tubings of slightly differing dimensions without requiring mechanical adjustment of the assembly. They have also proved to be remarkably durable. 
     The preferred embodiment utilizes a low-friction coating on the exterior of the roller, but the use of high-friction coating on the annular race to prevent the peristaltic tubing from wandering has not proved to be necessary. 
     In actual operation, a peristaltic pump in accord with the teachings herein is remarkably quiet. The lack of sudden shock loads which is the result of using forgiving rollers necessarily reduces the noise level, prolongs life of the peristaltic tubing and other pump components and reduces destructive turbulence in the blood being pumped. 
     While the above described embodiment is preferred, the invention should not be limited to single spindled rollers or rollers wherein the outer casing revolves relative to a single fixed spindle 18. 
     For example, the construction shown in FIG. 4 may be employed wherein a pair of short spindles 18A and 18B, held by pins 19A, 19B perform the same function as the single spindle 18. 
     Another alternative embodiment is shown in FIG. 5, wherein the spindle 18&#39; is fixably connected to the washers 60 and 61, but journaled in bearings 50&#39; to rotate with the roller. 
     It could also be noted that the elastomeric bushings 60, 61 need not necessarily be in the form of a washer, as shown, but also could be in the form of a spider having radial arms, or in other forms. 
     It is understood that the above description is exemplary and not limiting. More particularly, the improved rollers of this invention can be used equally well with one or two peristaltic tubes. 
     Further, the cylindrical race 11 can, by the exercise of ordinary skill in the art, be replaced by a conical or flat race, with which cooperate rollers of conical or cylindrical shape. 
     Other mechanical expedients will be obvious to those skilled in the art. For example, the spindle 18, which spans both ball bearings 50, could be replaced by two stub shafts, each individual to one bearing (in which case the arbor 54 need not be hollow). In the embodiment disclosed, the outer races of ball bearings 50 rotate, while the inner races are fixed to the sweep arm 14. However, the outer races of ball bearings 50 could be fixed to the sweep arm 14 and the inner races could rotate with and support the roller 17.