Automatic precision non-contact open-loop fluid dispensing

Abstract

A rugged, all-electronic fluid dispensing system for use with pipettes or in other contexts indirectly measures fluid flow by using a non-linear system model to correlate vacuum existing at the top of a column of suspended fluid. Non-contact operation is provided to eliminate the need for contact-type closed-loop fluid flow sensing and associated potential cross-contamination risks. In one particular exemplary non-limiting illustrative implementation, an electronic controller within a gun-shaped, cordless self-contained pipetter housing dynamically calculates valve opening time based on a non-linear equation. Calibration is used to derive equation constants, and column vacuum pressure before the valve is opened is used as the independent variable to derive a valve opening time that will result in accurate dispensing of a desired programmed fluid quantity. Repetitive automatic dispensing with accuracies greater than 1% are possible within the context of a relatively inexpensive portable pipette or device without the need for mechanically-complex positive displacement arrangements.

1 . A method of automatically dispensing liquid from a pipette comprising:
 restricting gas flow into said pipette to thereby substantially retain a column of liquid there within;   computing a timing parameter based at least in part on (i) height of said liquid column within said pipette, and (ii) a desired quantity of said liquid to dispense; and   automatically controlling gas flow into said pipette in accordance with said timing parameter to thereby dispense substantially said desired quantity of liquid from said pipette.   
     
     
         2 . The method of  claim 1  wherein said restricting includes maintaining a valve closed, and said controlling includes opening said valve for a time period based at least in part on said timing parameter. 
     
     
         3 . The method of  claim 1  wherein said computing includes accessing a stored mathematical model. 
     
     
         4 . The method of  claim 3  wherein said computing further includes calculating said timing parameter. 
     
     
         5 . The method of  claim 3  wherein said computing further includes looking up said timing parameter from a stored table of empirical values. 
     
     
         6 . The method of  claim 1  wherein said controlling includes actuating a pump. 
     
     
         7 . The method of  claim 1  further including measuring negative pressure at the top of said column, and ascertaining liquid column height based at least in part on said measured negative pressure. 
     
     
         8 . The method of  claim 1  further including contacting said liquid only with said pipette during said aforementioned steps. 
     
     
         9 . The method of  claim 1  wherein said controlling includes using an open-loop control mechanism. 
     
     
         10 . The method of  claim 1  wherein said controlling controls said dispensing without using feedback. 
     
     
         11 . The method of  claim 1  further including decoupling said pipette from a handheld fixture and disposing of said pipette after use. 
     
     
         12 . The method of  claim 1  further including repeating said computing and controlling to repetitively dispense said desired quantity. 
     
     
         13 . The method of  claim 12  wherein said repeating is performed in response to user actuation. 
     
     
         14 . A non-contacting, open loop automatic fluid dispensing method comprising:
 programming an amount of fluid to be dispensed from a reservoir;   using a mathematical model to generate a time parameter; and   controlling dispensing of said fluid based at least in part on said time parameter,   wherein said method accurately dispenses said desired quantities over different column heights within said reservoir.   
     
     
         15 . The method of automatically dispensing fluid from a fluid reservoir comprising:
 programming an electronic controller with a desired quantity of fluid to be dispensed;   measuring a pressure associated with the fluid reservoir;   deriving at least one open-loop control output parameter from said measured pressure and said programmed desired quantity; and   applying a signal corresponding to said derived open-loop control parameter to at least one fluid flow control element coupled to said fluid reservoir,   wherein said applying causes substantially said desired fluid quantity to be automatically dispensed.   
     
     
         16 . The method of  claim 15  wherein said reservoir comprises a pipette. 
     
     
         17 . The method of  claim 15  wherein said flow control element includes an electric valve and said control output parameter comprises opening time of said valve. 
     
     
         18 . The method of  claim 15  further including powering an electric pump. 
     
     
         19 . The method of  claim 15  wherein said reservoir provides a suspended fluid column and said measuring includes measuring the vacuum at the top of the suspended fluid column. 
     
     
         20 . The method of  claim 15  further including issuing a control output causing said reservoir to be at least partially refilled with fluid. 
     
     
         21 . The method of  claim 15  wherein said deriving includes calculating at least one non-linear equation. 
     
     
         22 . The method of  claim 15  further including a look-up table. 
     
     
         23 . A system for automatically dispensing quantities of fluid from a reservoir, comprising:
 a storage medium that stores a parameter relating to a desired quantity of fluid to be dispensed;   a pressure transducer that measures a pressure associated with the reservoir;   at least one fluid flow control element coupled to said reservoir; and   a processor coupled to said storage medium, said processor deriving at least one open-loop control output parameter from said measured pressure and said stored quantity parameter; and applying an open-loop control signal corresponding to said derived open-loop control parameter to said fluid flow control element to control substantially said desired fluid quantity to be dispensed.   
     
     
         24 . The system of  claim 23  wherein said reservoir comprises a pipette. 
     
     
         25 . The system of  claim 23  wherein said flow control element includes an electric valve. 
     
     
         26 . The system of  claim 23  wherein said flow control element includes an electric pump. 
     
     
         27 . The method of  claim 23  wherein said transducer measures the vacuum at the top of a suspended fluid column. 
     
     
         28 . The method of  claim 23  further including means for issuing a control output causing said reservoir to be at least partially refilled with fluid.