Abstract:
A multiple port, dual diameter piston fluid dispensing pump which includes multiple input and output ports accessed by rotating at least one of the pistons and a dual or multiple diameter piston or set of pistons that cooperate so that they follow each other. The dispensing piston is of smaller diameter than the pushing piston. This diameter difference permits a longer, controllable stroke to dispense micro-liters of fluid accurately.

Description:
This application is related to and claims priority from U.S. provisional patent application No. 60/511,566 filed Oct. 15, 2003. Application No. 60/511,566 is hereby incorporated by reference. 

   BACKGROUND 
   1. Field of the Invention 
   The present invention relates generally to fluid pumps and more particularly to multiple port, dual diameter fluid pumps. 
   2. Description of the Prior Art 
   Multiple port linear pumps have been used in the biosciences as a means to dispense different fluids from the same pump. Multiple ports also provide the capability to rinse the pump between dispensing strokes. For example, U.S. Pat. No. 6,666,666 shows such a pump. Prior art pumps however have single pistons of fixed diameter. To dispense micro-liter quantities of fluid, they require extremely tiny strokes. This leads to inaccuracy. 
   What is badly needed is a multiple port, dual or multiple diameter pump for the dispensing of fluids where micro-liters can be dispensed with a reasonably controllable length stroke. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a multiple-port, dual-diameter piston pump that has a top piston having a first diameter and a second bottom piston having a second diameter smaller than the first diameter. The first and second pistons cooperate with each other to load and dispense fluid. This cooperation can be achieved by having a spring or magnet hold the pistons together on the up-stroke with a direct contact push on the down-stroke. Any other method of cooperation or coupling between the pistons is within the scope of the present invention. The pump can have several input ports, the input ports being selected by rotation of at least one of the pistons. The pump also can have several output ports, the output ports also being selected by rotation of at least one pistons. Usually the pistons rotate together; however, this is not a requirement. The first and second pistons operate to cause fluid to be drawn into one of the input ports and dispensed from one of the output ports. The pump can have the pistons coupled with a spring, with magnets or otherwise. The lower or smaller piston can be partially contained in the upper or larger piston. 

   
     DESCRIPTION OF THE FIGURES 
       FIG. 1  shows a two diameter piston pump. 
       FIG. 2  shows a rotary positive displacement pump with two diameters with piston spring coupling. Here one piston is partially within the other. 
       FIG. 3  shows a different embodiment of a two diameter pump with spring coupling. 
       FIG. 4  shows an embodiment with magnet coupling. 
   

   Various figures and illustrations have been presented to better explain the present invention. The scope of the present invention is not limited to the figures. 
   DESCRIPTION OF THE INVENTION 
   Multiple port positive displacement pumps offer the biosciences the capability of having multiple pump capability in one pump. The use of as many as nine or more ports in one pump allows a single pump to be connected to an eight channel pipettor where each of the eight channel volumes can be individually adjusted. At least one of the multiple port pump ports can be an inlet port. The inlet port can be attached to a buffer solution used for washing any of the output channels. When a multiple port pump is designed, it is necessary to provide adequate distance between each of the pump ports in order to make an effective seal. The distance between ports is related to the fluid properties being pumped and that of the fluid internal pressure developed as the pump is used. A typical pump could have around 7 mm spacing between ports with port apertures of around 2.3 mm diameter. The piston diameter for such a pump could be around 30 mm. For this particular example, the effective surface area for the piston is around 706.5 square mm. Different ports can be accessed by simply rotating the piston. 
   When a pump with a piston of around 30 mm is used, a piston movement of around 1 mm can result. This would result in around 706 micro-liters of fluid being dispensed. The dispensing of small micro-liter volumes could require a linear piston motion of around 7 microns. It is very hard to control such a small linear motion. 
   The present invention solves this problem by using a dual or multi diameter piston and chamber on a multiple inlet/outlet pump. This greatly diminishes the piston effective area. For example, if the primary piston is around 30 mm in diameter, the face surface area is around 706.5 square mm. If the second diameter of the dual diameter piston is only around 28 mm, the surface area is around 615.1 square mm. This results in the dispensing of only around 91.1 micro-liters of fluid for each 1 mm of piston travel. The motion for a 5 micro-liter dispense would thus be around 55 microns. The difference between the two piston diameters can be further reduced to enhance small volume multiple port dispensing. Piston arrangements with more than two diameters are within the scope of the present invention. 
     FIG. 1  shows a pump with two piston diameters configured in one piston as a single piece. This pump has multiple input and output ports. A piston groove on the larger and smaller pistons is used to keep them aligned. 
     FIG. 2  shows a cross-section of a pump with two piston diameters configured in a piston-in-a-piston approach where the internal piston can be spring loaded. Here the spring is used to keep the pistons together on the up-stroke, and direct contact is used to push them together on the down-stroke. 
     FIG. 3  shows a cross-section of a pump where one of the pistons is located in line with the primary piston and is also spring loaded. This embodiment functions in a manner similar to the embodiment of  FIG. 2 . 
     FIG. 4  shows a cross-section of a pump where one of the pistons is located in line with the primary piston and is magnetically coupled to it. Here, the two pistons cooperate with each other by being held together with the two magnets. In this arrangement, it is easy to separate the two pistons for cleaning. 
   The various pump configurations shown in  FIGS. 1–4  can be fabricated out of various materials such as stainless steel, ceramic, glass or plastic. Any rigid material can be used to construct such a pump and is within the scope of the present invention. It is preferred that the material used be immune to corrosion or chemical reaction with the fluid being dispensed. 
   The secondary piston can follow the primary piston making the pump&#39;s entire stroke volume equal to the area difference between the two diameters times the stroke length. However, it is not necessary that the secondary piston follow the primary piston throughout the entire stroke. The defined movement of the secondary piston can be anywhere from very small to that of the entire stroke. Optionally, the secondary piston can have a convex curvature where it meets the primary piston thus minimizing the amount of contact area. 
   Various descriptions and illustrations have been presented to better aid in understanding the present invention. One skilled in the art will understand that many changes and variations are possible. All such changes and variations are within the scope of the present invention.