AN IMPROVED PERISTALTIC PUMP

TECHNICAL FIELD

The present invention relates in general to peristaltic pumps and or tube compression and or roller based pumps.

BACKGROUND Peristaltic pumps have been used for many years as a means of transferring fluid.

They are used in many different fields from medical to industrial.

A peristaltic pump is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained within a flexible tube fitted inside a circular pump casing (though linear peristaltic pumps have been made). A rotor with a number of cams such as 'rollers', 'shoes' or 'wipers' attached to its external circumference compresses the flexible tube.

As the rotor turns, the part of tube under compression closes (or 'occludes') thus forcing the fluid in the flexible tube to be pumped through the tube. Additionally, as the tube opens after the cam passes, ('restitution') fluid flow is induced to the pump. This process is called peristalsis and is used in many biological systems such as the gastrointestinal tract.

Peristaltic pumps are typically used to pump clean or sterile fluids because the pump does not contaminate the fluid, or to pump aggressive fluids because the fluid does not contaminate the pump. Some common applications include pumping aggressive chemicals, high solid slurries, and other materials where isolation of the product from the environment, and the environment from the product, are important.

Higher pressure peristaltic pumps that operate at pressures up to 16 bar typically use shoes and have casings filled with lubricant to prevent abrasion of the exterior of the pump tube and to increase heat dissipation. Lower pressure peristaltic pumps typically have dry casings and use rollers. High pressure peristaltic pumps typically use reinforced tubes often called 'hoses' and are often classified as a 'hose pump'. Lower pressure peristaltic pumps typically use non-reinforced tubing and are often classified as a 'tube pump' or 'tubing pump'.

Because the only part of the pump in contact with the fluid being pumped is the interior of the tube, the inside surfaces of the pump are easy to sterilize and clean. Furthermore, since there are no moving parts in contact with the fluid, peristaltic pumps are

inexpensive to manufacture. Peristaltic pumps lack valves, seals, and glands, which make them comparatively inexpensive to maintain compared to other pump types.

Commonly, a roller that can 'roll' along the tube is used to compress and occlude the tube, as it creates less wear, though a non-rolling compression method may be used. A number of different means exist for moving the roller as it compresses the tube. A rotary system may be used to move the rollers around a circumference, wherein the tube is compressed between a wall and a roller. A linear system may also be used to move a roller along a straight length, wherein the tube is compressed between a wall and a roller. Or a compression method may be used, which has sequential rollers or fingers to compress the tube. Before a roller has moved its designed distance and no longer occludes the tube, a second roller compresses and occludes the tube so the material does not flow back. The first roller then lifts from the tub, and the second roller pushes the material through the tube. The first, or another, roller then compresses the tube so the second roller may lift without allowing material to flow back. Any number of rollers may be used to smooth the flow of material. The speed of this squeezing action may be varied, and the tube size may also be varied. The pressure the pump generates is directly related to the strength of the seal created inside the tube. Pressing the roller against the tube with greater force is one exemplary method. The vacuum the pump generates may be related to the durometer (stiffness) of the tube and the force of compression. A greater force will not increase the vacuum beyond the point of no vacuum leak in the compressed portion of the tube.

The "squeeze" force the peristaltic pump generates is a significant operational parameter. While high squeeze force will allow stiff fluids to be pumped, it also causes tube degradation with use. The greater the squeeze force, the more severe the tube deformation, and thus the tube will tolerate fewer compression cycles due to stresses in the material and heat generated by the deformation. Advances have been made in materials used in tubes that enable them to be more resistant to wear. Springs have also been incorporated in some peristaltic pump designs to provide a more constant force between roller, tube, and compression surface. A tube that undergoes significant wear will eventually become nonfunctional and require replacement.

SUMMARY

The surface interfaces used to compress the tube of a peristaltic pump are configured to cooperatively reduce the stress on the tube edges when the tube is flattened causing an occlusion. One interface is the surface of the compression element, and the other interface is the compression surface the tube is pressed against by the compression element.

As the tube of a peristaltic pump is compressed, its non-compressed cross-section shape changes from substantially circular to substantially rectangular. When the tube is being compressed, the compressed edges where the tube walls make a 180 degree fold develop significant stress and degradation due to wall flexure. Embodiments disclosed herein shape the interface surfaces to make the folding of the tube at its compressed edges more gradual, thus reducing the stress in the tube walls.

In one embodiment, the compression surface remains flat while the engaging compression element surface is shaped to gradually recede from the tube allowing a space for the wall fold to assume a lower stress shape.

In another embodiment, the compression element surface is substantially flat and the compression surface is shaped to gradually recede from the tube allowing for the wall fold to assume a lower stress shape.

In yet another embodiment, both the compression element surface and the compression surface are shaped to gradually recede from the tube allowing the wall fold to assume a symmetrical lower stress shape on either side of the tube opening thereby further reducing stress and improving tube life.

In embodiments herein, the compression element may be a roller, a shoe, or a wiper device. If a shoe or wiper device is used as the compression element, the tube may require surface lubricant to reduce frictional wear and stress.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent to one skilled in the art from the description and drawings.

DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing an embodiment of a shaped roller and a flat wall with a compressed tube;

FIG. 2 is a drawing showing an embodiment of a shaped wall and a flat roller with a compressed tube;

FIG. 3 is a drawing showing an embodiment of a shaped roller and a shaped wall with a compressed tube; and

FIG. 4 is a side view of portions of a peristaltic pump illustrating the compression element and the mechanism for moving the compression element, in accordance with the embodiments disclosed herein.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments described herein. However, it will be obvious to those skilled in the art that the embodiments may be practiced without such specific details.

In other instances, well-known elements may be shown in block diagram form in order not to obscure the description of the embodiments in unnecessary detail. For the most part, details concerning detailed dimensions and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the embodiments and are within the skills of persons of ordinary skill in the relevant art.

In the following, the term 'roller' for the purposes of this document will be understood to mean any structure used to create a compression point in a tube compression pump. These structures include but are not limited to rolling, sliding, and/or stationary structures. The term compression surface is understood to be a structure that the roller is pressing against to create a compression point, including but not limited to, rolling, sliding, and/or stationary structure.

FIG. 1 illustrates roller 100 compressing tube 105 against support element 106 forming contours 103 according to one embodiment. Line 107 indicates the interface formed when the interior walls of tube 105 touch when sufficiently compressed. The roller 100 may be cylindrical in shape with a center section with center surface 101 at a first diameter

disposed between two edge sections with edge surfaces 108 at a second diameter. The roller 100 has a center surface 101 that may be substantially flat and formed of a suitable material (e.g., rubber, plastic, or metal). A contour 102 is designed to smoothly transition between the center surface 101 and the edge surfaces 108 to minimize stress in the edges 103 of tube 105. As the roller 100 engages and flattens tube 105 in its center area 104, the contours 102 allow the edges 109 of the compressed tube 105 to assume a low stress shape while the center of the tube opening (indicated by line 107) is flattened forming an occlusion that in turn enables fluid material in the tube 105 to be transported from an intake to an output of tube 105 (see FIG. 4). It is understood that it is within scope of the present invention to have the diameter of the edge sections assume other values after they have extended sufficiently to form surfaces 108.

Roller 100 has a shape defined by contour 102 that is a reciprocal to the assumed shape of compressed tube 105. The shape of contour 102 may be varied to optimize compression, and such variations are considered to be within the scope of the present invention. A contour shape may be achieved by various methods, such as a pliable (self- forming) layer that acquires a desired shape due to stresses from the compression and/or a rigid shape, and such variations are considered to be within the scope of the present invention.

FIG. 2 illustrates an effect of roller 200 compressing tube 105 against support element 206, which has a center surface 208 at one level and edge surfaces 205 disposed at a lower level. Contours 202 allow contours 209 in tube 105 to occur when tube 105 is compressed by roller 200 according to one embodiment. Line 207 represents when the interior tube walls touch when sufficiently compressed. The surface of roller 200 is formed of a suitable material (e.g., rubber, plastic, or metal) and may be shaped to have a flat surface 201 designed to compress tube 105. As the roller 200 engages and flattens tube 105 in its center area 204, the contours 202 allows the edges 203 of the compressed tube 105 to assume low stress shapes while the center of the tube opening (defined by line 207) is flattened forming an occlusion that in turn enables fluid material in the tube 105 to be transported from an intake to an output (see FIG. 4). It is understood that it is within scope of the present invention to have the level of the edge sections assume other values after the edge sections of the support element 206 have extended sufficiently to form surfaces 205.

Support element 206 has a shape defined by contours 202 that form contours 209 when tube 105 is compressed. The shape of contour 202 may be varied to optimize compression, and such variations are considered to be within the scope of the present invention. A contour shape may be achieved by various methods such as a pliable (self- forming) layer that acquires a desired shape due to stresses from the compression and/or a rigid shape, and such variations are considered to be within the scope of the present invention.

FIG. 3 illustrates a roller 300 compressing tube 105 against a support element 306 forming contours 309 according to embodiments herein. Roller 300 and support element 306 each have contours 302 and 303, respectively, which reduce the stress from compression in tube 105. The roller 300 may be cylindrical in shape with a center section with center surface 301 at a first diameter disposed between two edge sections with edge surfaces 308 at a second diameter. Center surface 301 may be substantially flat and formed of a suitable material (e.g., rubber, plastic, or metal). Support element 306 has a center section with a center surface 304 at one level and edge sections with edge surfaces 305 disposed at a lower level. When roller

300 compresses tube 105, both contours 302 on roller 300 and contours 303 on support element 306 allow the edges 309 of the compressed tube 105 to assume low stress shapes while the center of the tube opening 307 is flattened forming an occlusion that in turn enables fluid material in the tube 105 to be transported from an intake to an output of tube 105 (see FIG. 4).

FIG. 4 is a side view of portions of a peristaltic pump 400 suitable for practicing embodiments described herein. A length of tube 401 is supported in a circular arc configuration with inlet 403 and outlet 402. Compression elements 405 and 406 are shown engaging and compressing tube section 401 against a surface of support element 409 over segments 407 and 408. Compression elements 405, 406 may take shapes as described above with respect to any one or more of FIGS. 1-3. Support element 409 may take shapes as described above with respect to any one or more of FIGS. 1-3. As rotor 404 moves as shown by the arrow, compression element 405 will disengage from segment 407 of tube 401 and compression element 406 will engage and compress segment 408 of tube 401 such that at least compression element 406 maintains a seal in tube 401 preventing back flow of fluid.

Material in tube 401 will be moved by peristalsis in the direction of movement of the

compression elements 405 and 406 and will be delivered to outlet 402. By contouring compression elements 405 and 406 and/or surfaces of support 409 as described with respect to FIGS. 1-3, the stresses in tube 401 may be significantly reduced during the pumping process.

The contour shapes may vary to optimize compression, and such variances are considered to be within the scope of the present invention. A contour shape may be achieved by various methods such as a pliable (self-forming) layer that acquires the contour shape due to stresses in the compression or a rigid shape and such variances are considered to be within the scope of the present invention.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.