There is currently known in the prior art various types of peristaltic pumps which are typically used in medical applications for facilitating the metered intravenous infusion of a medicament into a patient. In addition to being used for infusion applications, prior art peristaltic pumps are also used for withdrawing fluids such as in a wound drainage system. These prior art pumps operate in a positive manner and are capable of generating substantial outlet pressures. The peristaltic pumps known in the prior art generally fall within one of two categories, i.e., linear peristaltic pumps and rotary peristaltic pumps. Conventional linear and rotary peristaltic pumps each typically have a section of resilient tubing positioned between a wall and a set of rollers or reciprocating pushers that progressively compress sections of the tubing to facilitate the pumping of a liquid therethrough.
More particularly, typical linear peristaltic pumps include those described in U.S. Pat. No. 2,877,714 (Sorg, et al.), U.S. Pat. No. 4,671,792 (Borsannyi), U.S. Pat. No. 4,893,991 (Heminway, et al.), and U.S. Pat. No. 4,728,265 (Canon). While generally effective, these prior art linear peristaltic pumps are large, complex and cumbersome, requiring a drive shaft parallel to a resilient tube and a plurality of cams along the drive shaft to move respective ones of a plurality of pushers toward and away from the tube.
Rotary peristaltic pumps known in the prior art generally disposed a resilient tube along a circular path, with a plurality of rollers mounted around the circumference of a circular rotor sequentially rolling along the tube to occlude the same and force liquid therethrough. Typical rotary peristaltic pumps include those described in U.S. Pat. No. 4,886,431 (Soderquist, et al.) and U.S. Pat. No. 3,172,367 (Kling). Though also generally effective, these pumps often have relatively low efficiencies and impose high shear and tension stresses on the tube, thus causing internal tube wall erosion or spallation. As a result, the tube may eventually be permanently deformed so that it becomes flattened into a more oval shape and carries less liquid, i.e., provides a decreased level of fluid flow therethrough.
In addition to the above-described linear and rotary peristaltic pumps, there is also known in the prior art another type of peristaltic pump having a tube arranged along a circular path with a cam member within the circle sequentially moving a plurality of blunt pushers or fingers outwardly to sequentially compress the tube from one end of the path to the other. These types of peristaltic pumps include those described in German Pat. No. 2,152,352 (Gonner) and in Italian Pat. No. 582,797 (Tubospir). Though these types of pumps tend to be less complex than linear peristaltic pumps, the pressure imposed by the blunt fingers typically reduces tube life, and sometimes causes internal tube wall erosion or spallation, thus resulting in particulate matter getting into the fluid stream. Additionally, tubes with different wall thicknesses cannot be accommodated by these particular prior art pumps. In this respect, with thinner than standard tubes, the fingers will not properly occlude the tube. Conversely, with thicker than standard tubes, the tube will close prematurely and be subject to excessive compression, thereby requiring higher cam drive power and causing excessive wear on the cam and tube.
In recognition of the deficiencies associated with the prior art peristaltic pumps described above, Applicant developed the curvilinear peristaltic pump disclosed in U.S. Pat. No. 5,575,631 (Jester) and U.S. Pat. No. 5,683,233 (Moubayed, et al) and PCT Application No. PCT/US97/03676 (Moubayed, et al.), the disclosures of which are incorporated herein by reference. This particular curvilinear peristaltic pump of the Applicant constituted an improvement over those known in the prior art by providing greater simplicity, small size, low drive power requirements and the ability to accommodate resilient tubes of varying wall thickness while reducing wear and internal erosion of the resilient tube. More particularly, this particular curvilinear peristaltic pump of the Applicant comprises a concave, curved platen for supporting a resilient tube, a multi-lobe cam rotatable about the center of the platen concavity, and a plurality of pump fingers which ride on the cam as cam followers and are guided to move in a radial direction toward and away from the platen. When the cam is rotated, the pump finger closest to the highest area (widest lobe) on the cam in the direction of rotation is moved outwardly in a radial direction to squeeze the tube against the platen. As the cam continues to rotate, the succeeding pump finger squeezes the tube as the preceding pump finger occludes the same, thus forcing the liquid in the tube to flow in the direction of cam rotation. As the cam rotation continues, the subsequent pump fingers sequentially squeeze the tube to push liquid and then occlude the tube, with the pump finger just behind the lobe moving away from the tube and allowing the same to expand and fill with the liquid.
Though this curvilinear peristaltic pump of the Applicant overcomes many of the deficiencies of the prior art peristaltic pumps, the design features of such pump give rise to certain inefficiencies in its operation. In particular, the motor, pulley and drive belt used to rotate the cam create a susceptibility for slight amounts of forward rotation or reverse rotation (roll back) of the cam upon the deactivation of the motor. Such slight forward or reverse rotation of the cam results in the engagement of the pump fingers to the tube in a manner causing an undesirable positive flow or backflow of liquid therewithin subsequent to the deactivation of the motor. As such, in this curvilinear peristaltic pump of the Applicant, power must be continuously supplied to the motor for purposes of preventing any unwanted rotation of the cam. As will be recognized, the need to constantly maintain power to the motor substantially increases its power consumption (e.g., reduces the life of any batteries used to supply power to the motor).
In addition to the foregoing, in Applicant's existing curvilinear peristaltic pump, a "pump cycle" occurs when the first through the last pump fingers along the tube move toward and away from the platen. During each "pump cycle", the engagement of the pump fingers against the tube in the above-described manner forces liquid therethrough. However, due to the configuration of the cam and the inability of the drive unit to selectively adjust the rotational speed thereof, there is a "dead pump phase" between the pump cycles in Applicant's existing curvilinear peristaltic pump wherein liquid is not being forced through the tube. As will be recognized, it is significantly more desirable if the liquid were to flow through the tube at a more uniform, steady rate. The operational efficiency of Applicant's existing curvilinear peristaltic pump would also be increased if it were to include structures which stabilize the length of the tube in the pump chamber and prevent a backflow of liquid within the tube upon a discontinuation of positive liquid pressure therewithin. The present invention addresses and overcomes the deficiencies of Applicant's existing curvilinear peristaltic pump, as well as the other peristaltic pumps currently known in the prior art.