Abstract:
A peristaltic pump uses a length of elastic tube with an inlet at one end and an outlet at the second end for delivering fluid material an outlet pressure greater than the inlet pressure. A support element disposed along the length of elastic tube is in contact with the elastic tube. A mechanism moves a compression element into engagement with a segment of the elastic tube thereby forming a compressed segment with a tube center section and two folded tube edges wherein at least one surface engaging the folded tube edges has a contours that reduce stresses in the elastic tube walls at the folded tube edges increasing pump performance and/or life of the elastic tube.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates in general to peristaltic pumps and or tube compression and or roller based pumps. 
       BACKGROUND 
       [0002]    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. 
         [0003]    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. 
         [0004]    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 solids slurries and other materials where isolation of the product from the environment, and the environment from the product, are critical. 
         [0005]    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’. 
         [0006]    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 makes them comparatively inexpensive to maintain compared to other pump types. 
         [0007]    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 could be used that has sequential rollers or fingers to compress the tube. Before a roller has moved its design 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 tube 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. 
         [0008]    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 non-functional and require replacement. 
         [0009]    There is, therefore a need for a device and method to improve the usable life of the tube used in peristaltic pumps. Further, there is a need for a device and method to improve the performance of a peristaltic pump. 
       SUMMARY 
       [0010]    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. 
         [0011]    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 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. 
         [0012]    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. 
         [0013]    In another embodiment, the compression element surface is substantially flat and the compression surface is shaped to gradually recede from the tube again allowing for the wall fold to assume a lower stress shape. 
         [0014]    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. 
         [0015]    In the 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 most likely would require surface lubricant to reduce frictional wear and stress. 
         [0016]    The 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 
         [0017]      FIG. 1  is a drawing showing an embodiment of a shaped roller and a flat wall with a compressed tube; 
           [0018]      FIG. 2  is a drawing showing an embodiment of a shaped wall and a flat roller with a compressed tube; 
           [0019]      FIG. 3  is a drawing showing an embodiment of a shaped roller and a shaped wall with a compressed tube; and 
           [0020]      FIG. 4  is a side view of portions of a peristaltic pump illustrating the compression element and the mechanism for moving the compression element. 
       
    
    
       [0021]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0022]    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. 
         [0023]    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. 
         [0024]    Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
         [0025]      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 touch when sufficiently compressed. The roller  100  is 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 is substantially flat and is 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 . 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 . 
         [0026]    Roller  100  has a shape defined by contour  102  that is a reciprocal to the assumed shape of a 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. 
         [0027]      FIG. 2  illustrates the 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 is 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 (defined by line  207 ) opening is flattened forming an occlusion that in turn enables fluid material in the tube  105  to be transported from an intake to an output. 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 . 
         [0028]    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. 
         [0029]      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 ) which reduce the stress from compression in tube  105 . The roller  300  is 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  is substantially flat and is 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 . 
         [0030]      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  406  and  405  are shown engaging and compressing tube section  401  against a surface of support element  409  over segments  407  and  408 . 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 , the stresses in tube  401  may be significantly reduced during the pumping process. 
         [0031]    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. 
         [0032]    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.