Zero pulsation pump

Abstract

A positive displacement pump includes at least two pumping chambers and associated plungers. Each plunger is driven by an associated variable speed motor, such as a stepper motor, in a reciprocating motion. The stepper motor varies speed during each stroke of the plunger. A controller controls speed and direction of each stepper motor. Each stepper motor is coupled to a leadscrew having an associated guide rod mounted on the leadscrew to move along the leadscrew as the leadscrew rotates and actuate an associated plunger. The controller varies the speed, displacement and duration of the stepper motors' steps to maintain a constant outflow without pulses.

What is claimed is: 
     
         1 . A positive displacement pump, comprising:
 a plurality of pumping chambers;   a plunger associated with each pumping chamber, each of the plungers moving in a reciprocating motion;   a variable speed motor driving each plunger, the variable speed motor varying speed during each stroke; and   a controller controlling speed and direction of each variable speed motor.   
     
     
         2 . The pump according to  claim 1 , the variable speed motor being coupled to a leadscrew having a guide rod threadably mounted on the leadscrew to move along the leadscrew as the leadscrew rotates. 
     
     
         3 . The pump according to  claim 2 , wherein the guide rod is connected to the plunger. 
     
     
         4 . The pump according to  claim 3 , further comprising a position sensor in communication with the controller. 
     
     
         5 . The pump according to  claim 1 , wherein the variable speed motor comprises a stepper motor. 
     
     
         6 . The pump according to  claim 5 , wherein the stepper motors have variable rotation in one direction for a pressure stroke and in an opposite direction for the suction stroke and the controller is adapted to change speeds of each motor during the stroke so that the combined output of the plungers produce a constant flow. 
     
     
         7 . The pump according to  claim 1 , wherein the pump comprises two plungers, wherein a speed profile for a pressure stroke includes a pressure ramp portion at a beginning of the stroke and at an end of the stroke, wherein pressure builds up to a discharge pressure at a start of the stroke and decays at an end of the stroke, but no flow exits a first one of the plungers, and wherein the other one of the plungers produces full flow during periods of pressure ramping. 
     
     
         8 . The pump according to  claim 1 , further comprising a pressure input. 
     
     
         9 . The pump according to  claim 1 , further comprising a load input. 
     
     
         10 . The pump according to  claim 1 , further comprising a pressure input or a load input. 
     
     
         11 . The pump according to  claim 1 , further comprising a pressure input and a load input. 
     
     
         12 . The pump according to  claim 1 , wherein the controller is adapted to slow the motor to slow rotation speed of the leadscrew as the plunger nears top dead center and stops at top dead center first direction. 
     
     
         13 . The pump according to  claim 1 , wherein the controller is adapted to slow the motor to slow rotation speed of the leadscrew as the plunger nears bottom dead center and stops at bottom dead center second direction. 
     
     
         14 . The pump according to  claim 1 , wherein the pump comprises three plungers and wherein the guide rods have ⅓ of cycle different from each other. 
     
     
         15 . The pump according to  claim 1 , wherein the variable speed motor comprises a servo motor. 
     
     
         16 . A method for controlling a pump, the pump having a first pumping chambers and an associated first plunger, and a second pumping chamber and an associated second plunger, each plunger being driven by an associated variable speed motor, and a controller; the method comprising:
 controllably driving a first variable speed motor to vary displacement and speed of the associated first plunger;   controllably driving a second variable speed motor to vary displacement and speed of the associated second plunger;   the speed of displacement of each variable speed motor being varied as the plungers approach top dead center and bottom dead center and coordinated so that pump outflow is substantially constant.   
     
     
         17 . The method according to  claim 16 , wherein determines flow by a controller with the formula:
     dV=P*V/K      
       where:
 K and V are constants stored in the microcontroller for the pump. 
 P=the output pressure and can be entered by the operator or input from a transducer. 
 K=the combined bulk modulus of the system which includes the fluids and components that deflect during the pressure stroke. 
 V=pumping chamber volume 
 dV=the change in volume due to compression of the fluids and expansion of the pumping chamber. 
 
     
     
         18 . The method according to  claim 16 , wherein the variable speed motors comprise stepper motors.