Precision Fluid Dispensing Using Peristaltic Roller Control

Abstract

A precision fluid dispensing system that can be effectively used for accurate fluid dispensing in peristaltic pumps if roller control is used. A peristaltic pump driven by a primary motor with a first encoder can be combined with pinch valves allowing a dispense tube to be open while a source tube is blocked. Controlled roller movement is used to move the next roller to the same starting position as the previous roller was on the previous dispense, the dispense pinch valve is closed and the source valve is opened. The system uses roller positioning where the each roller is properly positioned so that each dispense cycle starts in the same position. The precision and accuracy is better than 0.3% total. Tubing can be pre-stretched using a second motor and second encoder. Tube wear and stretch during use can be monitored by the second encoder.

We claim: 
     
         1 . A precision fluid dispensing system comprising:
 a peristaltic pump with N rollers on a rotor, where N is a positive integer;   a primary motor driving the rotor;   a first encoder cooperating with the rotor, the first encoder adapted to determine a rotational position of the rotor;   a deformable tube passing through the peristaltic pump connected at a first end to a fluid source and connected at a second end to a dispense point;   the deformable tube passing through a first pinch valve located between the fluid source and the peristaltic pump;   the deformable tube also passing through a second pinch valve located between the peristaltic pump and the dispense point;   the system constructed to make a precision fluid dispense by a) opening the first pinch valve, closing the second pinch valve, and rotating the rotor to draw fluid into the deformable tube; b) closing both the first and second pinch valves and rotating the rotor to a predetermined relative dispense starting angular position determined by the first encoder; c) closing the first pinch valve, opening the second pinch valve, and rotating the rotor a predetermined number of degrees determined by the first encoder to dispense a predetermined amount of fluid; d) moving the rotor a predetermined amount in an opposite direction to prevent a drip;   wherein, the system is constructed to perform subsequent dispenses by executing steps a), b), c) and d) in order always bringing the rotor to the same predetermined relative angular dispense position determined by the first encoder in step b), and   wherein the predetermined relative angular dispense position is reached by moving the rotor until one of the N rollers is at a predetermined angle with respect to a vertical direction.   
     
     
         2 . The precision fluid dispensing system of  claim 1  wherein the sequence of single dispenses, along with an optional partial dispense, results in a total dispense of a predetermined quantity of fluid. 
     
     
         3 . The precision fluid dispensing system of  claim 1  further including a scale that determines weight of a dispensing volume of fluid in a single dispense. 
     
     
         4 . The precision fluid dispensing system of  claim 3  wherein the scale determines the weight of each dispense. 
     
     
         5 . The precision fluid dispensing system of  claim 1  wherein the primary motor is a stepper motor that has a fixed number of micro-steps per revolution; the peristaltic pump has a fixed number of rollers on the driven rotor, and the number of micro-steps in a single dispense equals the number of micro-steps per revolution divided by the number of rollers. 
     
     
         6 . The precision fluid dispensing system of  claim 1  further comprising a secondary motor with a second encoder attached to the deformable tube constructed to pre-stretch deformable tube before dispensing begins. 
     
     
         7 . The precision fluid dispensing system of  claim 6  wherein said pre-stretch is repeated through a plurality of dispense cycles until the second encoder indicates that stretching has reached a minimum or a predetermined amount. 
     
     
         8 . The precision fluid dispensing system of  claim 4  wherein the predetermined angular start position has a small angular adjustment to achieve a small volume adjustment to keep the dispensing volume to a predetermined amount. 
     
     
         9 . The precision fluid dispensing system of claim wherein a total dispense includes a plurality of single dispenses; the primary motor being a stepper motor having a fixed number of micro-steps per revolution, and the peristaltic pump having a fixed number of rollers; and wherein, the number of micro-steps per revolution divided by the number of rollers is not an integer, the number of micro-steps in each single dispense is the number of micro-steps per revolution divided by the number of rollers truncated to the next lower integer for each single dispense, except for a last single dispense, with the last single dispense containing a number of micro-steps needed to bring a total number of micro-steps in the total dispense to the fixed number of micro-steps per revolution. 
     
     
         10 . A method of making a precision fluid dispense with a peristaltic pump system, the peristaltic pump system having peristaltic pump with a primary motor driving a rotor with N rollers, where N is a positive integer, a first encoder on the rotor; a deformable tube running from a fluid source, passing through the peristaltic pump, and running to a dispense point, the method comprising:
 a) drawing fluid into the deformable tube by rotating the rotor;   b) rotating the rotor so that the nth roller is at a predetermined dispense starting angle determined by the encoder, where n is a positive integer greater than or equal to 1 and less than or equal to N   c) making a partial dispense by rotating the rotor through a dispense angle determined by the encoder causing only the nth roller to pinch the deformable tube;   d) closing a pinch valve on the deformable tube located between the peristaltic pump and the dispense point;   e) rotating the rotor so that the n+1 roller is at the predetermined dispense starting angle determined by the encoder, where n+1 is a positive integer greater than or equal to 1 and less than or equal to N, and is n+1 is greater than n by one unless n=N, wherein if n=N, n+1=1;   f) opening the pinch valve;   g) letting n become n+1;   h) repeating steps b) through g) until a predetermined total dispense of fluid has taken place.   
     
     
         11 . The method of  claim 10  wherein a second motor with a second encoder pre-stretches the deformable tube before dispensing starts.