Controlled force fluid delivery system

Abstract

A controlled force fluid delivery system which provides fluid delivery with continuity over a wide range of flow rate. The system sets the force provided by an energy storage device, e.g. a spring and the opening of system outlet valve in response to a low volume due command. Specifically at a low flow rate, the controlled force is decreased and/or the outlet valve of the system closes before the fluid flow reaches stable velocity whereas at a high flow rate the controlled force is increased and/or the outlet valve does not close until the fluid stops flowing. The system also reduces fluid flow rate variation in part by adjusting the timing and the level of opening and closing the outlet valve, and the speed of pumping the fluid out of system central cassette chamber.

What is claimed is:  
     
         1 . A fluid delivery system comprising: 
 a central chamber with an inlet valve and an outlet valve;    a piston assembly moving in and out of the central chamber;    a force source connected to the piston assembly, wherein the force source generates a force to move the assembly in and out of the central chamber thereby moving fluid out of and into the central chamber;    a position sensor connected to the piston assembly, wherein the position sensor determines a position change of the piston assembly; and    a processor connected to the position sensor, and the force source, wherein the processor receives the position change of the piston assembly, modifies the amount and duration of force generated by the force source, and controls the opening of the outlet valve.    
     
     
         2 . The system of  claim 1 , wherein the force source comprises a motor which generates a negative pressure in the central chamber and pumps fluid into the central chamber via the piston assembly, and an energy storage device which receives energy from the motor and employs the stored energy to generate a positive pressure in the central chamber and pump fluid out of the central chamber via the piston assembly, wherein the processor controls the amount of energy stored in the energy storage device.  
     
     
         3 . The system of  claim 2 , wherein the energy storage device is a spring.  
     
     
         4 . The system of  claim 2 , wherein the motor simultaneously generates the negative pressure and stores energy in the energy storage device.  
     
     
         5 . The system of  claim 4 , wherein the processor determines a flow rate and directs the motor to generate a negative pressure based on the flow rate.  
     
     
         6 . The system of  claim 2 , wherein the energy storage device generates a positive pressure when it is disconnected from the motor.  
     
     
         7 . The system of  claim 2 , wherein the motor opens the outlet valve.  
     
     
         8 . The system of  claim 2 , wherein the motor opens the outlet valve in a pulsed mode.  
     
     
         9 . The system of  claim 2 , wherein the processor directs the motor to open the outlet valve in a pulsed mode in response to a low volume due command.  
     
     
         10 . The system of  claim 9 , wherein the low volume due command is less than 40 μl.  
     
     
         11 . The system of  claim 1 , wherein the processor causes the outlet valve to open in a pulse mode in response to a low volume due command.  
     
     
         12 . The system of  claim 11 , wherein the low volume due command is less than 40 μl.  
     
     
         13 . The system of  claim 1 , wherein the processor causes the outlet valve to close before the fluid finishes acceleration to a stable velocity.  
     
     
         14 . The system of  claim 13 , wherein the processor causes the outlet valve to close before the fluid finishes acceleration to a stable velocity in response to a low volume due command.  
     
     
         15 . The system of  claim 1 , wherein the processor causes the outlet valve to close after the fluid stops flowing.  
     
     
         16 . The system of  claim 1 , wherein the processor causes the outlet valve to open when the assembly is moved into the central chamber.  
     
     
         17 . The system of  claim 1 , wherein the processor causes the outlet valve to open in a nudge mode in response to a low volume due command.  
     
     
         18 . The system of  claim 2 , wherein the processor directs the motor to open the outlet valve in a nudge mode in response to a low volume due command.  
     
     
         19 . The system of  claim 1 , wherein the processor causes the outlet valve to open in a period of time in response to a low volume due command.  
     
     
         20 . The system of  claim 19 , wherein the processor causes the outlet valve to open in a period of time in response to a predetermined speed of the piston assembly.  
     
     
         21 . The system of  claim 1 , wherein the processor causes the outlet valve to close in response to a position change of the piston assembly.  
     
     
         22 . The system of  claim 21 , wherein the processor causes the outlet valve to close in response to a predetermined position change of the piston assembly.  
     
     
         23 . The system of  claim 1 , wherein the processor causes the outlet valve to close in a period of time.  
     
     
         24 . The system of  claim 23 , wherein the processor causes the outlet valve to close in a period of time in response to a detected speed of the piston assembly.  
     
     
         25 . The system of  claim 2 , wherein the processor directs the motor to close the outlet valve in a period of time in response to a predetermined position change of the piston assembly.  
     
     
         26 . The system of  claim 2 , wherein the processor directs the motor to close the outlet valve in a period of time in response to a detected speed of the piston assembly.  
     
     
         27 . The system of  claim 1 , wherein the outlet valve is opened by an amount in response to a low volume due command.  
     
     
         28 . The system of  claim 1 , wherein the outlet valve is opened by an amount determined by a detected speed of the piston assembly.