Abstract:
A spring mounted tube pressing member for peristaltic pumps allows loading and unloading of an elastic tube section between the tube pressing member and a continuously revolving rotor assembly by selectively moving between a locked position for fluid transfer and an open position for unhindered mounting and demounting of the tube section or a replaceable tube cassette. Not only is the pressure on the tube pressing member adjustable by the spring used, its dynamic pressure distribution on the tube section also prolongs the tube flex life and reduces fluid back mixing and pulsation in the tube.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to the field of peristaltic pumps. More particularly, the present invention relates to a tube loading assembly comprising a tube pressing member riding on one arm of a two-arm torsion spring. 
         [0003]    2. Description of the Related Art 
         [0004]    A peristaltic pump moves and meters liquid through tubing of a dispensing circuit free of ambient contaminants. The dispensing circuit is releasably mounted to the pump and the tubing of the dispensing circuit is loaded in the pump. The rotating pump drives liquids through the tubing of the dispensing circuit. In a hospital or lab setting, the liquid transferred are body fluids, intravenous solutions, extracorporeal bloods, reagent solutions, nutrient culture media, etc. 
         [0005]    A peristaltic pump assembly usually includes a base, a motor, a rotor assembly with circulating tube occluding rollers, and a tube pressing member with a tube track or raceway. In such arrangement, the space between rollers on the rotor and the pressing member is less than the diameter of the tubing and the tubing must be squeezed in. How one loads the tubing decides further variations of the assembly. 
         [0006]    Early peristaltic pumps rely on hand-feeding for tube loading. Its benefit in structural simplicity is compromised because both hands are needed at the same time. Retractable mechanisms to move either the sliding rollers or the pressing member away from one another during tube loading are less cumbersome but add parts and cost, e.g., in both U.S. Pat. No. 4,256,442 to Lamadrid &amp; Cullis and U.S. Pat. No. 4,599,055 to Dykstra, a movable pressing member is pivotally mounted on the base and allows single-handed tube loading. Further improvements allow automatic loading of the tubing loop to pump through progressively tightened space between rollers on a rotor and the housing of the modified pressing member (e.g. U.S. Pat. No. 4,861,242 to Finsterwald), or through a rotor with tube guiding grooves and notch to lower the tubing into the raceway (as in U.S. Pat. No. 5,387,088 to Knapp et al.), or through a further simplified self-loading version (as in U.S. Pat. No. 7,018,182 to O&#39;Mahony &amp; Behan). These improvements also aid loading of a disposable tube section into the pump between a pressing raceway and a rotor before use. Also available is a disposable tube cassette and the likes for use in a peristaltic pump as in U.S. Pat. No. D264,134 to Xanthopoulos. Methods for its quick loading and unloading are also desirable. 
         [0007]    To accommodate a collapsible and resilient tube of different materials, sizes and degrees of compressibility, the tube pressing member and the opposing sliding rollers must be urged toward and occlude the tube section for fluid transfer. This tube compression force must not be so tight as to damage the tube or so loose as to lose pressure for flow. To prolong tube flex life, U.S. Pat. No. 4,559,040 to Horres &amp; Moers has a removable pumping chamber portion so the tubing may be stored in the pump head without being pinched by the eccentric rotor. The device in U.S. Pat Pub 2006/0083644 (Zumbrum &amp; Coates III) uses location of flanged ends of tubing section to absorb part of the tubing tension thereby extending its flex life. Further improvements employ means for dynamic compression force which gradually closes in or increases upon fluid entry and gradually opens up or decreases before exit. They are represented in U.S. Pat. No. 5,110,270 to Morrick using spring-loaded sliding rollers and in U.S. Pat. No. 5,230,614 to Zanger et al., in which a specific arcuate surface on one pressing pump head to move a fluid through the tube in one direction without creating undue fluid back pressure in an opposite direction. Reduced fluid pulsation or back mixing is a feature important for steady and precision dosing by a peristaltic pump. 
         [0008]    Besides tube loading, tube caring and dynamic compression mechanisms tend to be mechanically complex, they are also difficult to make and use. Accordingly, the main objective of the present invention is a peristaltic pump that is simple to make, easy to load, unload and store, especially with a disposable tube section, not prone to finger pinching and does not aggravate the tubing flex or the inherent fluid pressure pulsation issue. 
       SUMMARY OF THE INVENTION 
       [0009]    In summary, the present invention simplifies the mechanical design for tube loading and provides easy operation at the same time. When unloading, the tube pressing member swings wide open and exposes the pumping head for tube mounting and demounting without risk of finger pinching. This releasable and retractable tube pressing member simply swings back to a locked position for pump action and fluid flow. 
         [0010]    A spring mounted tube pressing member is employed to simplify the make and use of a peristaltic pump. It loads and unloads an elastic tubing piece between a continuously circulating tube occluding rollers and a tube pressing member by selectively installing the spring and the accompanying tube pressing member in a locked loading position for fluid transfer, and in an open unloading position from the circulating tube occluding roller assembly for unhindered mounting and demounting of an elastic tube section as well as easy gravity or air back-pressure flushing of the system. Preferably, a pivotally mounted two-arm helical torsion spring meets the above need with a retractable tube pressing member mounted on one arm, and a pressuring device, which adjusts pressure on the tube pressing member, on the other arm. 
         [0011]    Further benefit of the invention is the dynamic and decreasing pressure distribution on the tube pressing member in the direction of the fluid flow. This decreasing dynamic pressure not only aids the flex life of the tube section but also enables the occluded fluid to move through the tube in one direction while minimizing undue fluid back pressure in the opposite direction. 
         [0012]    Additional objective in easy tube mounting and demounting is to provide quick and straightforward replacement of either stand-alone disposable tube cassette, or a disposable tube section attached to the tube pressing member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of an assembled peristaltic pump in accordance with the present invention, when the torsion spring mounted retractable tube pressing member opens wide for tube mounting or tube pressing member replacement 
           [0014]      FIG. 2  is a perspective view of an assembled peristaltic pump in accordance with the present invention, when the torsion spring mounted retractable tube pressing member centers itself on the spring&#39;s tube locking arm and locks on the tube section and the tube occluding rotors by force from the spring&#39;s tube locking arm. 
           [0015]      FIG. 3  is a schematic description of the torsion spring mounted tube pressing member corresponding to  FIG. 2  in accordance with the present invention, when the tube pressing member and the tube section are pressed by the dynamic compression force from the spring&#39;s tube locking arm. 
           [0016]      FIG. 4  is a cross-sectional view of the torsion spring mounted retractable tube pressing member with its tube track and rotor-guiding groove and track guard in accordance with the present invention. 
           [0017]      FIG. 5  is a perspective exploded view of the peristaltic pump shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    As shown in  FIGS. 1 and 2 , a peristaltic pump assembly in accordance with the present invention includes a base plate  5 , a motor  4 , a rotor assembly  2  with a plurality of circulating rollers  21 , and a tube pressing member  3  with an arcuate side  30  forming a tube track  31 . In such arrangement, the space between the rollers  21  on the rotor assembly  2  and the pressing member  3  is less than the diameter of the tube  1  and the tube  1  must be squeezed in between. The pump assembly of the present invention in an open (or unlocked) position with a tube section in place is shown in  FIG. 1 . An elastic tube section  1  is installed between a plurality of freely rotating rollers  21  installed on a rotor assembly  2  circulating about an axis  20  and a tube track  31  formed on a tube pressing member  3 . The tube pressing member  3  is pressed and locked in the proximity of the circular orbit of the rollers  21  by force from a two-arm helical torsion spring  35  pivotally mounted on a bolt  39  fixed to the base plate  5 . While the rotor assembly  2  circulates about the axis  20 , the circular motion of the rollers  21  causes fluid transfer in the tube section  1  (as indicated by the arrows) by squeezing the tube section  1  against the tube track  31 . The circular motion of the rollers  21  is driven by a motor  4 . In this case, the tube pressing member  3  is releasably installed on the two-arm ( 36  and  37 ) helical torsion spring  35  at the working or locked position p 2  and r 2  (see  FIG. 2 ) for carrying out fluid transfer, or at the retracted or open position p 1  and r 1  for loading or unloading the tube section  1  or replacing the tube pressing member  3 . With the straight tube locking arm  36  of the torsion spring  35  inserted through its longitudinal through hole  38 , the tube pressing member  3  rides along the straight tube locking arm  36  and can be removed or loaded in directions of  36   a.  When a disposable tube cassette is used as in U.S. Pat. No. D264,134 in place of the tube pressing member, the same retractable and arm sliding mechanism may be applied for quick change of the pumping tube. 
         [0019]      FIG. 2  shows the pump assembly of the present invention in the locked position with a tube section  1  and fluid flow  10  in place. The arcuate side  30  of the tube pressing member  3  centers itself through sliding in the directions  36   b  on the tube locking arm  36  when locked against the circulating rollers  21  on the rotor assembly  2 . The pressure on the pumping tube section  1  comes from the force F 2  exerted by the tube locking arm  36  of the two-arm helical torsion spring  35 , which in turn comes from the bending force or stress F 1  exerted on the spring locking arm  37  when set inside any of the spring locking slots  51 ,  52 ,  53  located on the extended base plate  50 . The bending force F 1 , and therefore the force F 2  increases as the spring locking arm  37  moves from the spring locking slot  51  to  52 , and from  52  to  53 . 
         [0020]    A tube anchoring clamp  6  is provided to withhold the friction pull on the tube from the rollers  21  and the tube pressing member  3 , as shown in  FIGS. 1 and 2 . The tube anchoring clamp  6  comprises two matching halves—one anchoring half  66  fixed to the base plate  5  and one removable half  67 . The anchoring half  66  and the removable half  67  are connected by a tubing clamp anchoring bolt  68  (see  FIG. 5 ) and clamped down together by a wing nut  65 . Holes of assorted sizes  60 - 64  are centered at the interface of the two matching halves for selected tube sizes. Holes  60 / 61 / 62  are slightly smaller than the tubes they serve, hence can hold the inlet portion  11  of the tube section  1  firmly when clamped down tight by the wing nut  65 . At the outlet end  12 , the holes  63 / 64  are slightly larger than the tubes they serve, therefore, allow excess tube slack fed by the circulating rollers  21  to tunnel out the pump head area through the holes  63 / 64 . 
         [0021]    The dynamic and decreasing pressure distribution on the tube locking arm  36  and the tube pressing member  3  along the direction of the fluid flow in this invention prolongs the tubing flex life and reduces fluid back mixing and pulsation in the tube. The physics of the mechanical assembly in  FIG. 2  is shown schematically in  FIG. 3 . The pressure on the wall of the tube section  1  is the force of the tube pressing member  3  applied against the circulating rollers  21  on the rotor assembly  2 , which is driven by the motor  4  to rotate about the rotation axis  20  in the direction  22 . The force F 2  on the tube pressing member  3  comes from the tube locking arm  36  of the two-arm helical torsion spring  35 , which is pivotally mounted on the top of the base plate  5 . The spring locking arm  37  of the torsion spring  35  can move parallel to the top plane of the base plate  5  between a locked position r 2  and an open or unlocked position r 1  (see  FIGS. 2 and 1  respectively). While in the locked position r 2 , the tension force F 1  of the torsion spring  35  is transmitted from the spring locking arm  37  at one of the spring locking slots  51 - 53 . The spring tension force F 1  must be strong enough to overcome the sum of the back pressure at fluid destination, the gravitational force of the fluid or the so called liquid head in the dispensing circuit and the resistance of the resilient tube wall material against the rollers  21  and the tube pressing member  3  in the fluid pumping position p 2 . The forces F 1  and F 2  from the helical torsion spring  35  exerted on the tube locking arm  36  follows the principle of leverage which states that the amount of torque exerted by a spring arm or lever is the product of force and distance on the arm or lever from the fulcrum. Hence the forces F 2  along the longitudinal or tube-axial direction of the tube pressing member  3  decreases with the flow  10  or in the pumping direction  22 . In addition to occluding the fluid to move through the tube in a pressure-decreasing direction, hence minimizing undue fluid back pressure in the opposite direction, this decreasing dynamic force F 2  pressed on the pumping tube section  1  in the direction of pumping  22  also prolongs the flex life of the tube section  1 . 
         [0022]    One design of the pump head with corresponding tube pressing member  3  is further disclosed by taking a cross-sectional view defined by planes i and i perpendicular to the base plate  5  in  FIG. 3 . This is shown in  FIG. 4 . The pumping head includes a rotating rotor disc  23 , a roller  21  with a circulating roller core with attached self-lubricating bearings  26  and an end cap  25 , and the tube pressing member  3  under spring bending stress or pressure F 2 . The tube section  1 , embedded at the arcuate side  30  of the tube pressing member  3  in the tube track  31  and the pumping chamber  13 , is protected and guided at the outside by a track guard  33  and at the inside by the rotor disc  23  itself. The circulating rotor assembly  2  is mounted onto a motor drive  40  at its center column  24  and the motor is mounted to the base plate  5 . Critical dimension of the tube pumping chamber  13  is further defined by the width of the tube track  31  and the depth of rotor-guiding groove  32  at the topside of the rotor disc  23 . The former dictates the circumference of the tube used, while the latter the minimum chamber clearance in the radial direction of the rotor assembly  2 , hence the tube wall thickness, for tubing protection from excessive spring pressure. Hugging the rim of the rotor assembly  2 , the track locking guide  34  next to the underside of the arcuate side  30  of the pressing member  3  is to fit in the gap between the rotating rotor disc  23  and the base plate  5  under spring tension F 2  to assure longitudinal or tube-axial direction stability of the tube pressing member  3  in the direction of flow. The longitudinal through hole  38  of the pressing member  3  and the tube locking arm  36  are conveniently center placed relative to the tube track  31  for full compression on the tube section  1 . 
         [0023]    A full exploded view of the peristaltic pump described above without the pumping tube is shown in  FIG. 5 . Tube track area  31   a,  torsion spring pivot axis  39   a,  spring mounting screw  39   b,  roller mounting screws  27 , motor mounting screws  42 , motor drive penetration port  41 , tubing clamp anchoring bolt  68  and port  68   a,  and a pair of tubing clamp guiding posts  69  and ports  69   a  are further revealed as one practice example.