Abstract:
The pressure rollers of a peristaltic tube positive displacement pump are incorporated as an element of a reduction system connecting a drive shaft to the rollers.

Description:
[0001]    Priority claim: This application claims the benefit of U.S. Provisional Application No. 60/234,739, filed Sep. 22, 2000 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field  
           [0003]    This invention relates to fluid transfer by means of flexible tube displacement pumps. It is particularly directed to an improved positive displacement peristaltic pump, especially useful for medical applications.  
           [0004]    2. State of the Art  
           [0005]    Positive displacement pumps of various types are well known. Among such devices is a category known as “flexible tube pumps.” Such pumps rely upon one or more traveling pressure elements, typically rollers or shoes, pressing against a flexible tube to displace its fluid contents. The traveling elements are carried by a rotor which is powered by an external transmission.  
           [0006]    Flexible tube, positive displacement peristaltic pumps have been utilized for low volume fluid transport. In a typical construction, the pressure rollers of such pumps are mounted to revolve within a pump housing at the distal ends of rotor arms. The rollers are mounted on axes transverse the plane on which they revolve, and press against a flexible tube, thereby urging fluid in the tube to move in the direction of roller travel. Positive displacement pumps typically run at low speeds. Accordingly, the rollers are not directly powered; rather, the rotor arms are powered by a drive mechanism external the pump housing. The drive mechanism incorporates a significant gear reduction or a mechanically equivalent speed reducing arrangement.  
           [0007]    A positive displacement pump is typically primed by connecting its inlet to a fluid supply, and then running the pump to displace any entrapped air. This process takes time, which is often inconvenient, and in some medical applications, may be life threatening..  
           [0008]    The fluid transfer rate of a positive displacement pump is proportional to the speed of rotation of the rotor carrying the traveling pressure elements. Various mechanisms have been utilized to detect this speed. If the pump is operated in pulse mode; i.e., with the pump operating during spaced intervals, the number of rotations during each pulse is of specific importance. Mechanical counters are generally useful for this purpose, but have certain disadvantages. They are irritatingly noisy in medical applications, and they introduce some frictional resistence, which can be problematic in low energy pump applications, generally.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    This invention comprises a positive displacement peristaltic pump which incorporates a gear reduction system, or the equivalent, within the pump housing. Moreover, the pressure roller (or rollers) within the housing is driven, and thereby constitutes an element of the reduction system. This arrangement reduces the parts count, cost and space requirements of the pump assembly.  
           [0010]    Practical constructions combine one or more eccentric gears from a planetary gear system with a roller arranged to press against a peristaltic tubing, thereby causing pumping action to occur. This arrangement combines eccentric gear reduction and pumping into a single compact cassette, thereby reducing part count and cost. The tubing-to-roller junction also contributes to gear reduction, which increases torque within the system.  
           [0011]    The overall gear reduction of the assembly may be divided between components positioned within and outside the housing, depending upon the requirements of a particular application. In any case, incorporating the pressure rollers of the system as a portion of the reduction system constitutes a significant improvement. While pump assemblies constructed in accordance with this invention offer advantages for many applications, one embodiment of particular interest currently is structured as an ambulatory infusion pump for pain management. This structure can readily be adapted to other medical applications requiring the administration of medicaments at low dosage rates on a continuous (including steady, but intermittent) basis.  
           [0012]    It is economically practical to construct pumps in accordance with this invention for single use (disposable) applications. While medical applications are emphasized in this disclosure, the avoidance of contamination is desirable in other commercial or laboratory settings, and pumps constructed in harmony with the teachings of this disclosure are suitable for many such applications. It is generally advantageous for these pumps to be capable of rapid priming. The pump may thus be provided as an assembly, structured and arranged to hold the pressure rollers substantially out of contact with the flexible tubing comprising the pump chamber until deliberate force is applied to move those components into normal pumping association. The original such assembled condition permits unimpeded fluid flow through the tube, thereby enabling almost instantaneous priming of the pump. The second condition places the pump in pumping mode. Moving the rollers into the second assembled condition may be regarded as the final step in assembling the pump, and may be deferred until the pump is put into service.  
           [0013]    The improvement of this invention may thus be regarded as a new arrangement of components for a peristaltic pump system in which rotating pressure elements are driven by a reduction system and are structured and arranged to revolve through a chamber in contact with a flexible tube. According to this invention, the pressure elements are incorporated into the reduction system. The pressure elements will usually comprise rotating pressure rollers driven by a gear reduction system. The pressure rollers are structured and arranged to revolve through a chamber with the outer surfaces of the rollers constituting pressure surfaces in contact with a flexible tube adjacent a reaction surface. Travel of the rollers causes positive displacement pumping action through the tube. The rollers are preferably mounted in roller assemblies in association with follower gears. The follower gears may be arranged to receive rotational force from a drive gear, which in turn receives power through a driven shaft element.  
           [0014]    The pump system may include a first assembly comprising the driven shaft element; a second assembly comprising the pressure rollers; and a coupling mechanism associated with the reduction system constructed and arranged to transfer power from the driven shaft element to the pressure elements. The second assembly desirably includes a pair of structural members, the first of which includes a reaction surface. The flexible tube pumping chamber may then be mounted adjacent this reaction surface. The second structural member may carries the pressure rollers. Connection means associated with the first and second structural members are constructed and arranged to provide a first, priming, position of the rollers with respect to the reaction surface and a second, pumping, position of the rollers with respect to the reaction surface.  
           [0015]    Ideally, the reaction surface is formed as a generally conical segment with a cone axis congruent with the axis of the driven shaft, and the rollers include generally frusto conical segments, and are mounted to turn on respective roller axes, each of which is approximately parallel the cone axis. The connection means may then be operable to adjust the spacing between the reaction surface and the pressure surfaces of the rollers such that the spacing (which captures the flexible tube) is relatively larger in the priming position and relatively smaller in the pumping position. A preferred arrangement of the connection means positions the first and second structural members in the priming position by holding the rollers in a first axial location with respect to the reaction surface. The connection means further accommodates relative axial movement of the first and second structural members into the pumping position, thereby moving the rollers into a second axial location with respect to the reaction surface. The first structural member may comprise a cassette body element and the second structural member may comprises a portion of a cassette housing. The first and second structural members may then be cooperatively adapted to couple together temporarily into the priming position during an assembly operation, and to be pressed permanently into the pumping position following priming of the flexible tube. This second positioning (into the pumping position) is conveniently accomplished in the field, such as in a clinical setting.  
           [0016]    A typical dosage rate for pump assemblies applied to medical applications is less than about 50 μl (micro liters) per pump rotor revolution, and such pumps are ordinarily operated to deliver outputs of less than about 100 ml (milliliters) per hour. A typical pump speed for such applications is about 60 rpm (revolutions per minute), with 600 rpm being about the maximum practical speed for pump assemblies of this scale. Of course, these scale and operating parameters are not critical to the operability of the pump assembly. More significantly, it is practical to construct assemblies within these parameters, in accordance with this invention, at low cost and within a relatively small volume, or envelope.  
           [0017]    The pumps of this invention generally operate at a constant speed when in the “on” condition. Throughput is thus controlled as a function of “on”/“off” pulsed operation. Pulses are relied upon to distribute a specified dose over a prescribed time; typically a 24-hour period.. Certain preferred embodiments of this invention incorporate an optical sensing arrangement constructed and arranged to count the number of rotations of the rotor arms during each pulse of operation. The data accumulated in this fashion can be processed, electronically or otherwise, to maintain a precisely controlled fluid delivery rate through the pump. An electronic control system associated with the drive motor for the pump may be programmed in conventional fashion to maintain a prescribed steady or variable delivery rate as desired. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]    In the drawings, which illustrate what is currently regarded as the best mode for carrying out the invention:  
         [0019]    [0019]FIG. 1 is a schematic illustration of a first embodiment of the invention;  
         [0020]    [0020]FIG. 2 is a schematic illustration of a second, generally preferred embodiment of the invention;  
         [0021]    [0021]FIG. 3 is an exploded pictorial illustration of a pump assembly including a cassette subassembly incorporating the improvement of this invention;  
         [0022]    [0022]FIG. 4 is an exploded pictorial view of the cassette subassembly of FIG. 3 , rendered at an enlarged scale;  
         [0023]    [0023]FIG. 5 is a cross sectional view of a portion of the cassette subassembly of FIG. 4, rendered at a further enlarged scale, showing the internal components in pump priming condition;  
         [0024]    [0024]FIG. 6 is a view similar to FIG. 5 showing the internal components in pumping condition;  
         [0025]    [0025]FIG. 7 is a cross sectional view similar to FIG. 5 as viewed at a different reference plane; and  
         [0026]    [0026]FIG. 8 is a view similar to FIG. 6, as viewed at the reference plane of FIG. 7. 
     
    
       [0027]    The reference numerals on the drawings refer, respectively, to the following features:  
         [0028]    [0028] 11  fixed flexible peristaltic tube pump chamber  
         [0029]    [0029] 13  roller component  
         [0030]    [0030] 15  follower assembly  
         [0031]    [0031] 17  gear component  
         [0032]    [0032] 19  drive gear  
         [0033]    [0033] 21  drive shaft  
         [0034]    [0034] 23  idler  
         [0035]    [0035] 25  first follower assembly  
         [0036]    [0036] 27  second follower assembly  
         [0037]    [0037] 30  ambulatory infusion pump assembly  
         [0038]    [0038] 31  drive section  
         [0039]    [0039] 32  top cover portion  
         [0040]    [0040] 33  bottom cover portion  
         [0041]    [0041] 34  gear motor  
         [0042]    [0042] 34 A motor shaft  
         [0043]    [0043] 36  batteries  
         [0044]    [0044] 40  cassette subassembly  
         [0045]    [0045] 41  run/pause control button  
         [0046]    [0046] 42  bolus control button  
         [0047]    [0047] 43  first PC board contacts  
         [0048]    [0048] 44  second PC board contacts  
         [0049]    [0049] 45  PC board  
         [0050]    [0050] 46  Spring battery contacts  
         [0051]    [0051] 47  LED display  
         [0052]    [0052] 48  display cover  
         [0053]    [0053] 49  pressure sensor contact  
         [0054]    [0054] 50  pressure sensor adjustor  
         [0055]    [0055] 51  pressure sensor button  
         [0056]    [0056] 52  pressure adjustment screw  
         [0057]    [0057] 52 A speaker  
         [0058]    [0058] 53  pinion gear  
         [0059]    [0059] 54  spur gear  
         [0060]    [0060] 55  first molded fittings  
         [0061]    [0061] 56 . second molded fittings  
         [0062]    [0062] 58  battery cap  
         [0063]    [0063] 59  battery cap contact  
         [0064]    [0064] 62  cassette body  
         [0065]    [0065] 66  cassette cap  
         [0066]    [0066] 66  cassette bottom  
         [0067]    [0067] 70  roller gears  
         [0068]    [0068] 70 A roller gear pressure segment  
         [0069]    [0069] 70 B roller gear tooth segment  
         [0070]    [0070] 72  gear link assembly  
         [0071]    [0071] 72 A first gear link assembly half  
         [0072]    [0072] 72 B second gear link assembly half  
         [0073]    [0073] 74  tube roller  
         [0074]    [0074] 74 A tube roller ridge  
         [0075]    [0075] 74 B tube roller support surface  
         [0076]    [0076] 76  hole in the cassette bottom  
         [0077]    [0077] 78  cassette cover tab  
         [0078]    [0078] 78 A latching surface  
         [0079]    [0079] 80  drive section housing socket  
         [0080]    [0080] 82  optical sensor reflector  
         [0081]    [0081] 84  snap tab  
         [0082]    [0082] 85  receiver  
         [0083]    [0083] 86  first latch surface  
         [0084]    [0084] 87  second latch surface  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0085]    [0085]FIG. 1 illustrates the basic components of the invention. A fixed, peristaltic tube  11  (pump chamber) is contacted and pinched by a roller component  13  of a follower assembly  15 . The assembly  15  also includes a gear component  17 , which is driven by a drive gear  19  which receives power from a drive shaft  21 . A currently preferred arrangement is illustrated by FIG. 2. In that instance, the drive gear  19  is associated with an idler  23  positioned generally as the rotor arm of a conventional peristaltic flexible tube pump. As illustrated, however, the drive gear  19  transmits rotational force to a pair of follower assemblies  25 ,  27 , imparting a speed reduction. That is, each follower assembly crawls along the tube  11 , rather than being pushed along the tube  11  in conventional fashion.  
         [0086]    Referring to FIGS. 3 and 4, an ambulatory infusion pump assembly, generally  30 , includes a drive section, generally  31 , enclosed within a top cover portion  32  and a bottom cover portion  33 . The drive section  31  includes a small gear motor  34 , a power supply (batteries  36 ) and other “non-disposable” components of the assembly  30 . Of course, the entire assembly  30  may be either disposable or reusable. The preferred embodiment illustrated, however, contemplates reuse of the components of the drive section  31  and discard of the components contained within an associated cassette assembly, generally  40  (See FIG. 4).  
         [0087]    A run/pause control button  41  and a bolus control button  42  are associated with the top cover segment  32 , as shown. These control buttons function by being pressed against contacts  43 ,  44  on the upper surface of PC board  45 . Other components associated with the drive section  31  and its contained PC board  45 , include spring battery contacts  46 , an LED display  47  and its cover  48 , a pressure sensor contact  49 , a pressure sensor adjustor  50 , a pressure sensor button  51  and a pressure adjustment screw  52 . A speaker  52 A, and other circuit components are mounted on the PC board  45  in conventional fashion, as required to implement the pumping protocols, monitoring functions, warning signals, etc. required for any particular application.  
         [0088]    The motor  34  carries a motor pinion gear  53  on its shaft  34 A. A significant gear reduction is effected through the linkage of the pinion gear  53  to the cassette shaft  21  through the spur gear  54 .  
         [0089]    The top  32  and bottom  33  portions of the drive housing are connected together by molded fittings  55 ,  56 . A battery cap  58 , which also houses a battery cap contact  59 , is mounted on one end of the assembled housing. This cap adds integrity to the assembly, and also functions as an on/off switch for the drive section  31 . The cap  58  may be structured for occasional removal for battery replacement.  
         [0090]    As best shown by FIG. 4, the cassette assembly  40 , which comprises the improvements of most significance to this invention, includes a cassette body  62 , a cassette cap  64  and a cassette bottom  66 , which together house and support other components of the system. As illustrated, a pair of roller gears  70 , each of which has a conical pressure surface  70 A and a gear tooth segment  70 B, are mounted within a gear link assembly,  72  comprising mutually opposed halves  72 A,  72 B. A pair of tube rollers  74  is similarly mounted within the gear link assembly  72 . Each roller  74  has an annular ridge  74 A and an adjacent support segment  74 B. With the cassette assembled, as shown by FIGS.  5 - 8 , the cassette shaft  21  extends through the hole  76  in the cassette bottom  66 . With the pump assembly  30  in fully assembled condition, the cassette  40  is held in removable association with the drive assembly  30  by means of tabs  78  carried by the cassette cover  64  registering with sockets  80  formed by the connection of the upper  32  and lower  33  cover portions of the drive assembly  31   
         [0091]    Four spindles  82  within the gear link assembly  72  serve as axles for the gears  70  and rollers  72 , which are mounted on alternate such spindles. A peristaltic tube pump chamber  11  (See also FIGS. 1 and 2) is positioned within the cassette body  62  adjacent the reaction surface  62 A, which is tapered (as a conical segment) and extends somewhat more that  180  degrees. With the cassette assembled as shown by FIGS.  5 - 8 , the tube  11  is positioned between this reaction surface  62 A and the pressure surfaces  70 A of the roller gears  70 . These surfaces  70 A are also tapered, defining a frusto conical roller segment, and are approximately parallel the reaction surface  62 A at their respective contacts with the tube  11 . When the pressure segments  70 A of roller gears  70  are positioned as shown by FIGS. 5 and 7, in priming condition, fluid may flow freely through the tube, facilitating rapid priming. The rotating drive gear  19  engages the tooth segments  70 B of roller gears  70 . When the pressure segments  70 A of roller gears  70  are positioned as shown by FIGS. 6 and 8, in pumping contact with the tube  11 , the roller gears crawl along the tube  11 , displacing fluid in the direction of travel. The gear link  72  is thereby caused to rotate within the cassette body  62 , carrying the tube rollers  74  in procession between the roller gears  70 . The ridges  74 A of the rollers  74  hold the tube  11  in proper position as the pressure surface  70 A of a leading roller gear  70  leaves contact with the tube  11  and prior to contact of the tube  11  by a trailing roller gear  70 .  
         [0092]    An optical sensor reflector  82  carried by gear link segment  72 A constitutes means for detecting each rotations of the gear link. This data may be processed by conventional optical detector circuitry within the drive assembly  31 . The dosage rate may be displayed in any selected format or protocol by the LED display  47 .  
         [0093]    [0093]FIG. 5 illustrates the assembled cassette  40 , with its bottom  66  in a first axial (priming) position along the cone axis Al. The “cone axis” A 1  is a feature of the inclined conical reaction surface  62 A. The roller gears  70  are mounted to rotate around respective roller axes A 2 , A 3 , which are approximately parallel the cone axis A 1 . In priming position, the pressure surfaces  70 A are held sufficiently spaced from the reaction surface  62 A to permit free flow of liquid through the tube  11 . In usual practice, the tube will be “primed” prior to advancing the cassette bottom  66  to its second axial (pumping) position along the cone axis Al, as illustrated by FIG. 6. The cassette subassembly  40  will then be mounted to the drive subassembly  31  by plugging the tabs  78  into the sockets  80  (FIG. 3). As a consequence, the cassette shaft  21  will register with the spur gear  54 . Operation of the motor  34  will then cause the roller gears to revolve around the cone axis Al while rotating around their respective roller gear axes A 2 , A 3  in pinching relationship with the tube  11 .  
         [0094]    [0094]FIGS. 7 and 8 illustrate the internal components of the cassette subassembly  40  in the same relative positions illustrated by FIGS. 5 and 6, respectively. The cross section is rotated, however, to illustrate one mechanism for mounting the cassette bottom  66  in its priming (FIG. 7) and pumping (FIG. 8) positions. As illustrated, the cassette bottom  66  carries a plurality of resilient tabs  84  positioned to register with receivers  85 . Partial insertion of the tabs  84  effects a locking engagement with a first latch surface  86  corresponding to the priming position. Prior to mounting the cassette subassembly  40  to the drive subassembly  31 , the cassette bottom  66  is urged axially to the pumping position illustrated by FIG. 8. If the pumping chamber (tube  11 ) has been primed, pumping can commence immediately. If not, priming can be done by introducing fluid to the inlet end of the tube  11  while operating the motor, eventually displacing entrapped air from the tube  11 .  
         [0095]    For most medical, and certain other, applications, the cassette subassembly  40  is removed from the drive subassembly  31  following use. The tabs  78  are resilient, and may be pressed to disengage the latching surfaces  78 A from the sockets  80 . The drive subassembly  31  may then be reused indefinitely with replacement cassette subassemblies  40 .  
         [0096]    Reference in this disclosure to the details of preferred or illustrated embodiments in not intended to limit the scope of the invention defined by the appended claims, which themselves recite those features regarded as significant to the invention.