Patent Publication Number: US-2005129545-A1

Title: Peristaltic pumping mechanism with geared occlusion rollers

Description:
FIELD OF THE INVENTION  
      This invention relates generally to peristaltic pumps and, more particularly, to a peristaltic pumping mechanism having a compression mechanism comprised of interchangeable geared occlusion rollers.  
     BACKGROUND  
      A typical peristaltic pump includes a compressible tube for carrying a fluid. The tube generally has an upstream inlet, a downstream outlet and a curved portion oriented in a horseshoe-like or circular path. The curved portion is typically supported on its outermost surface against a curved stationary surface such as the interior wall of an enclosure for the pump. Near the upstream inlet, a rotor-mounted (or cage-mounted) roller engages and progressively squeezes the tube against the surface. The squeezing force is of sufficient magnitude to at least partially compress and generally occlude the internal passage of the tube. This occlusion is carried around the curved portion by the roller, forcing fluid ahead of the occlusion toward the downstream outlet portion of the tube. As fluid ahead of the occlusion is discharged through the downstream outlet, the expansion or restitution of the tube in the wake of the occlusion creates a suction that draws in more fluid through the upstream inlet, and the cycle repeats.  
      The unique pumping properties of peristaltic pumps make them ideally suited for certain applications. For example, peristaltic pumps are widely used in applications where constant metering of fluids at relatively low flow rates is desired; applications requiring the fluids being pumped to remain free of contamination; applications requiring the fluid path to remain clean or sterile; and applications where corrosive, caustic or hazardous fluids must be pumped without the fluid directly contacting any components of the pump mechanism other than the tubing.  
      Despite these advantages, conventional peristaltic pumps suffer drawbacks, one being complexity of the pumping mechanisms. Such mechanisms often include an intricate arrangement of many small components comprised of various materials, which complicates manufacturing and maintenance and results in relatively high costs. Such complexity also creates serious quality control issues, as it provides increased opportunity for defects and failures.  
      Another shortcoming is the inability to conveniently alter the rate of the pumping mechanism. Thus far, solutions generally entail adjusting the speed of the motor that drives the pumping mechanism or adjusting gear ratios of a gear train that links the motor to the pumping mechanism. While motor speed may be adjusted by replacing the motor or using electrical components to control the speed, each of these approaches increases overall cost and complexity. Additionally, as most drive train assemblies do not readily accommodate additional or replacement gears, the entire gear train would have to be replaced at considerable effort and cost.  
      Yet another shortcoming is that conventional pumping mechanisms do not drive (i.e., provide rotational power to) the occlusion rollers. Instead a cage drags the rollers over the tube. This conventional approach is believed to be inefficient, requiring a more powerful motor and consuming more electrical power than would otherwise be required if the rollers were each rotationally driven allowing them to ride over the tubes. Additionally, this conventional approach is conducive to premature wear and tear on the tube, especially if a roller fails to freely rotate.  
      Thus, a peristaltic pumping mechanism is needed that simplifies manufacturing and maintenance, reduces cost, facilitates mechanically altering the pumping rate, and/or avoids premature abrasive wear of the tube.  
     SUMMARY  
      The invention solves the problems and/or overcomes the drawbacks and disadvantages of the prior art by providing a pumping mechanism that includes a first rotatable geared occlusion roller having a first roller portion and a first geared portion. The first roller portion of the first geared occlusion roller is configured to compress the flexible tube of a peristaltic pump upon contact therewith. The pumping mechanism also includes a rotatable drive gear having a geared portion configured to operably engage the first geared portion of the first rotatable geared occlusion roller. The rotatable drive gear is configured to rotate and cause the first rotatable geared occlusion roller to rotate.  
      In another aspect of the present invention, the peristaltic pumping mechanism includes a plurality of rotatable geared occlusion rollers, each having a first roller portion and a first geared portion. The first roller portions are configured to compress the flexible tube of a peristaltic pump upon contract therewith. The mechanism also includes a rotatable drive gear having a first driving geared portion configured to operably engage the first geared portion of each rotatable geared occlusion roller. Rotation of the drive gear causes each rotatable geared occlusion roller to rotate. A spacer plate having an axle shaft for rotatably engaging each rotatable geared occlusion roller is also provided. The spacer plate has a drive shaft opening for receiving a rotatable drive shaft to engage and rotate the drive gear.  
      In yet another aspect of the present invention, a peristaltic pump is provided that incorporates a pumping mechanism according to the principles of the invention. The pump includes a housing and a flexible curved tube within the housing. The flexible curved tube has an inlet end and an outlet end. The housing also has an inlet and an outlet, to which the tube inlet and outlet are fluidly connected. A rotatable drive shaft is provided for engaging a drive gear of the pumping mechanism.  
      The pumping mechanism includes a plurality of rotatable geared occlusion rollers, each having a first roller portion and a first geared portion. The first roller portions are configured to compress the flexible tube upon contract therewith. The mechanism also includes a drive gear having a first driving geared portion configured to operably engage the first geared portion of each rotatable geared occlusion roller.  
      A spacer plate having an axle shaft for rotatably engaging each rotatable geared occlusion roller is also provided. The spacer plate has a drive shaft opening for receiving a rotatable drive shaft to engage and rotate the drive gear.  
      An end of the drive shaft passes through an opening in the spacer plate. The drive gear engages the end. Rotation of the drive gear causes each rotatable geared occlusion roller to rotate.  
      At least one of the rotatable geared occlusion rollers frictionally engages and compresses the flexible tube at all times during operation. As a geared occlusion roller in contact with the flexible hose rotates, it rides or migrates along the length of the flexible tube, causing the spacer plate to rotate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and other objects, features and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where:  
       FIG. 1  conceptually depicts an exemplary pumping mechanism in a peristaltic pump housing in accordance with a preferred implementation of the present invention;  
       FIG. 2  conceptually depicts a front perspective of a pumping mechanism in accordance with a preferred implementation of the present invention;  
       FIGS. 3A and 3B  show front and side views of a spacer plate in accordance with a preferred implementation of the present invention;  
       FIG. 4  shows a perspective view of a geared occlusion roller in accordance with a preferred implementation of the present invention; and  
       FIG. 5  shows front, side and back views of a geared occlusion roller in accordance with an implementation of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Referring now to  FIG. 1 , a peristaltic pumping mechanism in accordance with an exemplary embodiment of the present invention includes a housing  100 , a flexible tube  105 , a drive gear  150 , a spacer plate  160  (not shown), and a plurality of geared occlusion rollers  135 - 145 . A rotatable drive shaft  155  engages the drive gear  150 . The drive gear  150  is fixedly mounted at its center on the drive shaft  155 . The drive shaft  155  may be operably coupled to a motor and/or drive train (not shown) to provide rotational motion. Each geared occlusion roller  135 - 145  meshes with the drive gear  150 . Rotation of the drive shaft  155  causes the drive gear  150  to rotate, which causes the geared occlusion rollers  135 - 145  to rotate in an opposite direction about their central axes. The exemplary pumping mechanism also includes an inlet  110  and outlet  115  fluidly coupled to the flexible tube  105  for fluid flow. A plurality of threaded mounting holes  120 - 130  for receiving screws are also provided to attach a cover (not shown) to the housing  100 .  
      Referring now to  FIG. 2 , an exemplary spacer plate  160 , with a drive gear  150  and geared occlusion rollers  135 - 145  is shown. The spacer plate  160  defines the position of the drive gear  150  and the position of each occlusion roller  135 - 145  relative to the drive gear. While a circular plate is depicted, the plate may have other shapes and accommodate more or fewer occlusion rollers without departing from the scope of the present invention.  
      Referring now to  FIGS. 3A and 3B , front and side views of an exemplary spacer plate  160  are provided. Occlusion rollers  135 - 145  are rotatably mounted to axle shafts  305 - 315 . The axle shafts  305 - 315  may be non-rotatable shafts on which the occlusion rollers rotate, or rotatable shafts which rotate with the occlusion rollers. Furthermore, the axle shafts  305 - 315  may be an integral part of the spacer plate  160  or separate shaft components attached to the spacer plate  160 . As the axle shafts accommodate the occlusion rollers, the height and diameter of the shafts should enable the axle shafts  305 - 315  to operably engage occlusion rollers and allow the occlusion rollers to freely rotate on the axle shaft, without substantial play.  
      A drive shaft opening  320  in the spacer plate  160 , enables a drive shaft to protrude through the spacer plate. The opening accommodates the drive shaft  155 . In a preferred implementation, the spacer plate  160  is free floating, thereby allowing the drive shaft  155  to rotate at a different RPM from the spacer plate. Thus, the drive shaft  155  may freely rotate through the opening  320 . When the drive gear  150  is placed on the drive shaft  155 , rotation of the drive shaft  155  will cause the drive gear  150  to rotate, which will cause the engaged occlusion rollers  135 - 145  to rotate about their corresponding axle shafts  305 - 315 . The invention thus uses a planetary gear approach to drive occlusion rollers  135 - 145 . Frictional engagement of the rotating occlusion rollers  135 - 145  with the tube  105 , will cause the occlusion rollers  135 - 145  to revolve around the drive gear, thus causing the spacer plate  160  to rotate.  
      The spacer plate  160  is preferably comprised of a durable plastic or polymeric material, such as polyvinyl chloride (PVC), polyethylene, polypropylene, polystyrene, acrylics, cellulosics, acrylonitrile-butadiene-styrene terpolymers, urethanes, thermo-plastic resins, thermo-plastic elastomers (TPE), acetal resins, polyamides, polycarbonates, nylons or polyesters. Many other materials may be used alone or in combination with the aforementioned materials and/or other materials, without departing from the scope of the present invention. Preferably the material is relatively inexpensive, exhibits acceptable physical properties including durability, and is easy to use in conventional manufacturing operations. The material may further include formulations and/or additives to provide desired properties such as transparency or desired colors, structural enhancement, and lubricity.  
      The spacer plate  160  may be produced using any suitable manufacturing techniques known in the art for the chosen material, such as (for example) injection or compression molding or casting. Preferably the manufacturing technique is suitable for mass production at a relatively low cost per unit, and results in an acceptable product with a consistent quality.  
      Referring now to  FIG. 4 , an exemplary geared occlusion roller  400  is shown. The generally cylindrically shaped gear occlusion roller  400  includes a roller portion  415  for engaging and occluding the flexible tube  105 . Preferably the roller portion  415  is relatively smooth, so as to not abrade or otherwise prematurely damage the tube  105 . In a preferred implementation, each geared occlusion roller  400  further includes two sets of gears, each having the same number of gear teeth and pitch diameter. One set of gears, i.e., the protruding gears  410 , has teeth extending outwardly beyond the roller portion  415  diameter. The other set of gears, i.e., the recessed gears  420 , has teeth that match the diameter of the roller portion  415 . A bore  510  extends axially through the center of the geared occlusion roller  400 . A portion of the bore  505  may be circular and have a diameter suitable for engaging an axle shaft  305 - 315 . For example, referring to  FIG. 5 , the bored portion starting at the end with recessed gears  420  and extending to the center of the roller portion  415 , may be circular  505  in cross section. The remaining portion  405  of the bore  510  may be keyed, e.g., non-circular in shape, to securely engage the drive shaft  155 . For example, the keyed portion  405  of the bore  510  may include a flat surface to engage a drive shaft  155  also having a flat surface. Thus, rotation of the drive shaft  155  will compel rotation of the geared occlusion roller  400 , without slippage.  
      Advantageously, such a geared occlusion roller may function as either an occlusion roller  135 - 145  or as a drive gear  150 , effectively reducing the number of different types of parts required. As a drive gear  150 , it could be mounted such that the keyed end  405  engages the keyed drive shaft  155 . As an occlusion roller, it could be mounted such that the circular portion  505  of the bore  510  engages the axle shaft  305 . Each geared occlusion roller  135 - 145  is therefore interchangeable with the drive gear  150 , and vice versa.  
      Illustratively, referring to  FIG. 6 , a geared occlusion roller assembly with four geared occlusion rollers is shown. One geared occlusion roller serves as drive gear  150 . The keyed end  405  is adjacent to the spacer plate  160 . The remaining geared occlusion rollers serve as occlusion rollers  135 - 145 . Each occlusion roller has a circular end  505  adjacent to the spacer plate to rotatably engage an axle shaft  305 - 315 . Recessed gear portion  420  of the drive gear  150  engages protruding gear portion  410  of each occlusion roller  135 - 145 . Protruding gear portion  420  of each occlusion roller  135 - 145  engages recessed gear portion  410  of the drive gear  150 . Thus, the drive gear “oppositely engages” the occlusion rollers, and vice versa.  
      The distance from the center of the drive gear  150  to the outer smooth roller surface of each geared occlusion roller  135 - 145  is preferably approximately the same as the distance from the center of the housing to an occluded tube  105  within the housing. Thus, the roller portion of the geared occlusion rollers  135 - 145  frictionally engage and compress the flexible tube  105  and cause rotation of the spacer plate  160 .  
      In operation, a motor causes the drive gear  150  to rotate, preferably, either directly by causing the shaft  155  to rotate or indirectly via a conventional drive train that may include various gears and/or belts and pulleys arranged to drive the shaft  155 . Rotation of the drive gear  150  causes the geared occlusion rollers  135 - 145  to rotate around their central axes. In a preferred implementation, at least one geared occlusion roller will contact the tube  105  at all times. Rotation of a geared occlusion roller in frictional contact with the tube will cause that geared occlusion roller to drive or migrate along the tubing  105 . Concomitantly, such driving or migration will cause or assist rotation of the spacer plate  160 .  
      The rotation and revolution speeds of the geared occlusion rollers  135 - 145  (ω r ) may generally be determined as a function of the rotational speed of the drive gear  150  (ω d ) and the pitch diameters of the gears, as is well known in the art.  
         ω   r     =       ω   d     ⁢       D   d       D   r             
          where:     ω r  is the rotational velocity of the geared occlusion rollers;     ω d  is the rotational velocity of the drive gear;     D d  is the pitch diameter of the drive gear; and     D r  is the pitch diameter of the geared occlusion rollers.        

      Pumping speed of a peristaltic pump may readily be influenced/controlled by the geometries (e.g., pitch diameters) of the gears.  
      Those skilled in the art will appreciate that the drive gear  150  and occlusion rollers  135 - 145  may be different sizes to achieve a different pumping rate and force transmission. For example, the drive gear may have a diameter (i.e., gear pitch diameter) that is approximately half of the diameter of the occlusion rollers. Such a configuration would reduce the pumping rate, as compared to the pumping rate achieved with equally sized gears, by about 50%. Conversely, a drive gear with a diameter twice that of the occlusion rollers will increase the pumping rate by approximately 100%, in comparison to the rate achieved with equally sized gears. Of course, in either case, the gears of the drive gear and the gears of the occlusion rollers must properly mesh. Additionally, the drive gear and occlusion rollers must be sized to fit the spacer plate and pump housing and effectuate a desired occlusion in the tube.  
      The driving or migration of the geared occlusion rollers  135 - 145  cause a propagating compression in the flexible tube  105  in contact with the roller surface of the geared occlusion rollers  135 - 145 . Preferably, the compression is of sufficient magnitude to generally occlude the internal passage of the tube  105 . This occlusion migrates around the curved portion of the flexible tube  105  as the occlusion rollers  135 - 145  revolve around the drive gear  150 , forcing fluid ahead of the occlusion toward the downstream outlet portion of the tube  105 . As fluid ahead of the occlusion is discharged through the downstream outlet, the expansion or restitution of the tube  105  in the wake of the occlusion creates a suction that draws in more fluid through the upstream inlet, and the cycle repeats.  
      In a preferred implementation, the flexible tube  105  includes an upstream inlet  110 , a downstream outlet  115  and a curved path between the outlet and inlet. The curved path is preferably circular or semicircular, but may have other configurations such as a horseshoe shape. A stationary surface, such as a portion of the housing for the pumping mechanism, preferably supports the circular path on its outermost side. The diameter of the flexible tube  105  along the circular path portion is preferably sufficient to accommodate the geared occlusion rollers  135 - 145 , while being substantially compressed or occluded at the portion of the tube  105  in contact with the geared occlusion rollers  135 - 145 .  
      In a preferred implementation of the present invention, a check valve means, such as a one-way valve, may be fluidly connected to the upstream inlet  110 . The valve may allow fluid to enter the upstream inlet  110 , but not escape through it.  
      In a preferred implementation, drive gear  150  and geared occlusion rollers  135 - 145  are comprised of plastic and are manufactured according to industry standards for plastic gears. The resins, additives and manufacturing process used should preferably produce gears that exhibit acceptable strength, fatigue life, temperature resistance, moisture resistance and dimensional stability. Additives such as glass and/or carbon may be included to impart desired structural characteristics. Lubricant additives such as polytetrafluoroethylene (PTFE), silicone or graphite may be compounded into the resin to reduce coefficients of friction. Examples of resins typically used for plastic gears include nylon, acetal copolymer, crystalline resins and linear polyphenylene sulfide.  
      In an alternative embodiment, a cover for the housing may include an internal gear track for engaging the protruding gear portions of the geared occlusion rollers when the cover is placed on the housing. The internal gear track may be a circular track. Rotation of the geared occlusion rollers will thus cause them to travel around the track. Such traveling will cause the spacer plate to rotate. This embodiment reduces the risk of slippage due to low friction between the flexible tube and roller portion of the geared occlusion rollers.  
      An advantage of the present invention is that the pumping mechanism may be comprised of a relatively small number of parts, as described above. A pumping mechanism in accordance with an exemplary embodiment of the present invention includes three key components—a drive gear  105 , plurality of geared occlusion rollers  135 - 145  and a spacer plate  160 . If the geared occlusion rollers and the drive gear are the same size, then two different types of parts comprise the pumping mechanism. In comparison, a pumping mechanism of a conventional peristaltic pump may include an intricate arrangement of dozens of components. Having fewer components reduces costs, simplifies manufacturing and maintenance and enhances reliability.  
      Another advantage of the present invention is that the speed of the pumping mechanism can readily be altered by replacing the drive gear  105  and geared occlusion rollers  135 - 145  with those having different pitch diameters. Of course, the drive gear  105  and geared occlusion rollers  135 - 145  must be of sufficient size to mesh properly and for the roller surface to occlude the flexible tube of a peristaltic pump. Within that constraint, for a given rotation speed of the drive shaft  155 , a wide range of revolution speeds of the geared occlusion rollers  135 - 145 , and thus a wide range of rates of progression of an occlusion in the flexible tube  105 , may be achieved by altering the ratio of pitch diameters of the drive gear  105  and geared occlusion rollers  135 - 145 . Furthermore, the process for changing the gears can be sufficiently straightforward for a mechanically unsophisticated end-user to implement.  
      A further advantage of a pumping mechanism in accordance with an exemplary embodiment of the present invention is that it may be utilized with commercially available pumping motors and drive trains. This reduces engineering and manufacturing costs.  
      Yet a further advantage of a pumping mechanism in accordance with an exemplary embodiment of the present invention is that the compression means may be changed to alter pump output volumes. The amount of compression, which is defined in part by the magnitude of the occlusion, may be altered by substituting geared occlusion rollers having a larger or smaller roller diameter. This allows use of flexible tubes having various diameters in the same pump housing.  
      Additionally, the pumping mechanism reduces risks of a jammed (i.e., non-rotating) roller. Motor power is transferred to the occlusion rollers via the engaged drive gear, causing the occlusion rollers to rotate. Such rotation reduces abrasive wear on the tube.  
      Moreover, the pumping mechanism efficiently distributes power. It is believed that the use of driven rollers reduces the power required from the motor. This may translate into increased motor life, less power consumption and reduced size and weight.  
      While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the foregoing detailed description. Such alternative embodiments and implementations are intended to come within the scope of the present invention.