System and method for repetitive, high performance, low volume, non-contact liquid dispensing

Abstract

An apparatus and method for delivering repetitive, precision, low volume liquid dispensing from a dispensing orifice of a non-contact liquid dispensing apparatus. An elongated communication passageway of the dispensing apparatus is defined by interior walls having one end in fluid communication with a system fluid reservoir and an opposite end terminating at the dispensing orifice. A system fluid is placed in the communication passageway extending substantially continuously from the system fluid reservoir to the dispensing orifice. The system fluid reservoir is pressurized at a substantially constant back pressure, with a pressurizing gas, preferably helium, that suppresses in-gassing, and that is substantially insoluble to the system liquid. A dispensing liquid is aspirated through the dispensing orifice and into the communication passageway substantially to an interface region with the system fluid contained in the communication passageway. To effect dispensing, a rapid pressure pulse with a predetermined pulse width is applied to the system fluid, enabling substantially accurate, relatively small volume, non-contact liquid dispensing of the dispensing liquid from the dispensing orifice.

1 . A method for delivering repetitive, precision, low volume liquid dispensing from a dispensing orifice of a non-contact liquid dispensing apparatus having an elongated communication passageway with one end in fluid communication with a system reservoir of system liquid and an opposite end terminating at the dispensing orifice, said method comprising: 
 pressurizing the system liquid in system reservoir, at a substantially constant back pressure, with a pressurizing gas that suppresses in-gassing, and that is substantially insoluble to the system liquid;    placing the system liquid in the communication passageway extending substantially continuously from the system liquid reservoir to the dispensing orifice;    aspirating a dispensing liquid in the communication passageway in a manner extending from the dispensing orifice substantially to an interface region with the system fluid contained in the communication passageway; and    applying a rapid pressure pulse with a predetermined pulse width to the pressurized system liquid causing substantially accurate, relatively small volume, non-contact liquid dispensing of the dispensing liquid from the dispensing orifice.    
     
     
         2 . The method according to  claim 1 , wherein 
 said pressurizing gas is comprised of helium.    
     
     
         3 . The method according to  claim 2 , wherein 
 said back pressure is in the range of about 2.0 psi to about 15.0 psi.    
     
     
         4 . The method according to  claim 3 , wherein 
 said back pressure is about 8.0 psi.    
     
     
         5 . The method according to  claim 2 , wherein 
 said applying a rapid pressure pulse includes actuating a rapid actuation dispensing valve in fluid communication with said communication passageway, downstream from the system liquid reservoir and upstream from said air gap, between a closed condition and an opened condition, providing fluid communication between the communication passageway and the system liquid reservoir.    
     
     
         6 . The method according to  claim 5 , further including: 
 before aspirating a dispensing liquid, aspirating a relatively small volume of gaseous fluid through the dispensing orifice and into the communication passageway in a manner such that said gaseous fluid extends substantially continuously across the transverse cross-sectional dimension of the communication passageway such that, at the interface region, the relatively small volume of aspirated gaseous fluid forms a minute, unitary air gap fully enclosed between interior walls defining the communication passageway and a liquid interface between the system liquid and the dispensing liquid contained in the communication passageway to substantially prevent dispersion and dilution therebetween at said liquid interface.    
     
     
         7 . The method according to  claim 6 , further including: 
 maintaining the air gap greater than about 1.0 inch to about 3.0 inches from said dispensing valve.    
     
     
         8 . The method according to  claim 6 , wherein 
 said actuating a rapid actuation dispensing valve includes maintaining the dispensing valve in the opened condition for a predetermined duration correlating to said predetermined pressure pulse.    
     
     
         9 . The method according to  claim 6 , wherein 
 aspirating said relatively small volume of gaseous fluid includes actuating a metered analytical aspiration device, fluidly coupled to the communication passageway, a metered amount to aspirate said gaseous fluid.    
     
     
         10 . The method according to  claim 9 , wherein 
 said actuating the metered analytical device is performed by stepping a metered analytical syringe.    
     
     
         11 . The method according to  claim 10 , wherein 
 said actuating an analytical aspiration device includes aspirating said relatively small volume of gaseous fluid in the range of about 150 nl to about 5 μl.    
     
     
         12 . The method according to  claim 11 , wherein 
 said actuating an analytical aspiration device includes aspirating said relatively small volume of gaseous fluid in the range of about 250 nl to about 2 μl.    
     
     
         13 . The method according to  claim 1 , further including: 
 after the aspirating a dispensing liquid and before the applying a rapid pressure pulse to the system liquid, switching the communication passageway from an aspiration source to a dispensing source.    
     
     
         14 . The method according to  claim 13 , wherein 
 said switching the communication passageway is performed by positioning a switching valve device from an aspiration condition, fluidly coupling the aspiration source to the communication passageway, to a dispensing position, fluidly coupling a dispensing source to the communication passageway and fluidly decoupling the aspiration source from the communication passageway.    
     
     
         15 . The method according to  claim 14 , wherein 
 said switching valve device is provided by a shear valve having a rotor face and a stator face, and    said switching the valve device to one of the aspiration condition and the dispensing condition includes slideably and rotatably engaging a rotor face of the valve device against the stator face about a longitudinal axis of said rotor face at a stator-rotor interface, to fluidly couple the aspiration actuator to the communication passageway and fluidly couple the dispensing actuator to the communication passageway, respectively.    
     
     
         16 . The method according to  claim 2 , wherein 
 said placing the system liquid in the communication passageway includes flowing the system liquid contained in the communication passageway toward the dispensing orifice until expulsion or near expulsion of the system liquid from the dispensing orifice.    
     
     
         17 . The method according to  claim 16 , wherein 
 said flowing the system liquid contained in the communication passageway is performed by actuating a dispensing valve from the closed condition to the opened condition.    
     
     
         18 . The method according to  claim 5 , further including: 
 before the aspirating a dispensing liquid, purging trapped gas contained in the dispensing valve.    
     
     
         19 . The method according to  claim 18 , wherein 
 said purging trapped gas includes rapidly actuating the dispensing valve between the closed condition and the opened condition to purge trapped gases from the dispensing valve.    
     
     
         20 . The method according to  claim 19 , wherein 
 said rapidly actuating the dispensing valve is performed by actuating the dispensing valve at a discrete frequency for a predetermined period of time.    
     
     
         21 . The method according to  claim 20 , wherein 
 said rapidly actuating a dispensing valve is performed by varying the actuation frequency of the dispensing valve from said discrete frequency.    
     
     
         22 . The method according to  claim 21 , wherein 
 said varying the actuation frequency of the dispensing valve is performed at a plurality of set discrete frequencies, each actuation at one of the discrete frequencies being for a respective predetermined period of time.    
     
     
         23 . The method according to  claim 22 , wherein 
 said plurality of discrete frequencies are in the range of about 1 Hz to about 1750 Hz.    
     
     
         24 . The method according to  claim 21 , wherein 
 said varying the actuation frequency is performed by a ramped frequency sweep, incrementally changing the actuation frequency at said discrete frequencies.    
     
     
         25 . The method according to  claim 24 , wherein 
 said incrementally increasing the actuation frequency is performed in the range from about 10 Hz to about 420 Hz.    
     
     
         26 . The method according to  claim 2 , further including: 
 providing substantially smooth diametric transitions in said communication passageway from the dispensing valve to the dispensing orifice to facilitate the integrity of said minute air gap moving through the communication passageway during the applying a rapid pressure pulse.