Method and device for measuring minute volume of liquid

Abstract

A method and test apparatus determines a volume of a droplet of liquid. The test apparatus deposits a drop of liquid to be measured on a surface that provides a known contact angle with the liquid under the deposition conditions used, thereby establishing one of: (i) an advancing, (ii) a receding, and (iii) an intermediate contact angle. The test apparatus images the drop. The test apparatus measures a dimension of height or diameter of the drop. In one embodiment, the test apparatus calculates a volume of the drop of liquid from the relationship of the contact angle to one or more parameters selected from the maximum height, the diameter of the contact patch, the radius of curvature, or the cross sectional area of the drop.

What is claimed is: 
     
         1 . A method of determining a volume of a droplet of liquid dispensed from a liquid dispensing apparatus, the method comprising:
 (a) depositing an assumed volume of liquid to be measured from the liquid dispensing apparatus as a drop onto a calibrating reference surface, wherein the calibrating reference surface provides for a known contact angle with the drop of liquid under the deposition conditions used;   (b) establishing a known contact angle with the drop of liquid selected from the group consisting of: (i) an advancing contact angle, (ii) a receding contact angle, and (iii) an intermediate contact angle;   (c) measuring a dimension of the drop of liquid, wherein the dimension measured is selected from the group consisting of (i) a maximum height of the drop, (ii) a diameter of the contact patch, (iii) radius of curvature, and (iv) cross sectional area; and   (d) calculating the actual volume of the drop of liquid from the relationship of the known contact angle to the measured dimension.   
     
     
         2 . The method of  claim 1 , further comprising step (e) determining the difference between the assumed volume and the calculated actual volume of the drop of liquid. 
     
     
         3 . The method of  claim 2 , further comprising step (f) correcting for the difference between the calculated actual volume of liquid dispensed by the liquid dispensing apparatus and the assumed volume. 
     
     
         4 . The method of  claim 3 , wherein the correcting for the difference between the calculated actual volume of liquid dispensed by the liquid dispensing apparatus and the assumed volume comprises adjusting the volume of actual liquid dispensed by the test apparatus to correct for the difference. 
     
     
         5 . The method of  claim 4 , wherein the adjusting the volume of actual liquid dispensed by the liquid dispensing apparatus to correct for the difference is by adjusting the time interval during which one or more valves is opened, the degree of opening of one or more valves and/or the pressure provided by the liquid dispensing apparatus to the dispensing liquid. 
     
     
         6 . The method of  claim 4 , wherein the liquid dispensing apparatus comprises is a device for measuring the wetting characteristics of a liquid on a surface of a material comprising: a liquid dispensing component, a dimension determining component and a processor component, wherein the liquid dispensing component is configured to deposit a volume of a liquid on the surface of the material; wherein the dimension determining component is configured to determine one or more dimensions of a liquid deposited on the surface wherein the processor component is configured to analyze information based on the dimension determining component about one or more geometrical features of the volume of the liquid on the surface of the material. 
     
     
         7 . The method of  claim 5 , further comprising: averaging a difference between the assumed volume and the calculated actual volume of the drop of liquid measured from a plurality of areas of the calibrating reference surface. 
     
     
         8 . The method of  claim 1 , where a calibrating reference surface comprises a substrate coated with an ink, polymer, metal or other coating that has a consistent pre-determined contact angle. 
     
     
         9 . The method of  claim 1 , wherein the liquid dispensing apparatus is a device for depositing a known volume of liquid. 
     
     
         10 . A liquid dispensing apparatus calibration system comprising: a liquid dispensing component, a dimension determining component and a processor component, wherein the liquid dispensing component is configured to deposit a volume of a liquid on the surface of a substrate; wherein the dimension determining component is configured to determine one or more dimensions of a liquid deposited on the surface wherein the processor component coupled to the dimension determining component and configured to analyze information based on the dimension determining component about one or more geometrical features of the volume of the liquid on the surface of the substrate. 
     
     
         11 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the dimension measured is selected from the group consisting of (i) a maximum height of the drop, (ii) a diameter of the contact patch, (iii) radius of curvature, and (iv) cross sectional area. 
     
     
         12 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the processor component is adapted to calculate the volume of the drop of liquid from the relationship of a known contact angle to the measured dimension. 
     
     
         13 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the processor component is adapted to determine a difference between the volume of dispensed liquid and an expected volume level. 
     
     
         14 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the processor component is adapted to transmit an adjustment signal to a nozzle valve coupled to the liquid dispensing component, the signal adjusting the one or more parameters so as to cause the nozzle to dispense a volume of liquid approximating the expected volume level. 
     
     
         15 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the processor component is adapted to controllably adjust the operation of the liquid dispensing component by adjusting one or more parameters of the system selected from the group consisting of adjusting the time interval during which one or more nozzle valves is opened, the degree of opening of one or more nozzle valves and/or the pressure provided by the liquid dispensing apparatus to the dispensing liquid. 
     
     
         16 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the processor component is adapted to auto-calibrate, for each of the liquid dispensing components, the drop volume by adjusting the time interval during which one or more nozzle valves is opened, the degree of opening of the one or more nozzle valves and/or the pressure provided by the liquid pressurizing system according to the calculated volume of a drop deposited onto a calibrating reference surface. 
     
     
         17 . The liquid dispensing apparatus calibration system of  claim 10 , wherein the processor component is adapted to calculate an average of measured liquid volumes over a plurality of areas of the one or more substrate.