Method of compensating for changes in the flow characteristics of a dispensed fluid to maintain the volume of dispensed fluid at a setpoint

Abstract

Changes in the flow characteristics of a fluid being dispensed from a nozzle under .[.then.]. .Iadd.the .Iaddend.control of a metering valve are compensated for in order to maintain the volume of fluid dispensed over a predetermined time interval substantially equal to a selected setpoint. The volume of fluid delivered to the metering valve during a predetermined interval is measured and a correction factor based on the difference between the measured volume and the setpoint is calculated. The correction factor is used to generate a driving signal from which a control signal applied to the metering valve is generated.

What is claimed is: 
     
       1. A method of compensating for changes in the flow characteristics of a fluid being dispensed from a nozzle under the control of a metering valve in order to maintain the volume of fluid dispensed over a predetermined time interval at a desired setpoint, said method comprising the steps of: (a) measuring the volume of fluid delivered to the metering valve during at least one said interval;   (b) calculating a correction factor correlated to the difference between said measured volume and said setpoint,   (c) multiplying a signal by said factor to generate a driving signal, and   (d) controlling said valve in accordance with at least said driving signal to maintain the volume of fluid dispensed at said desired setpoint.   
     
     
       2. The method of claim 1 wherein said controlling step includes the step of applying a signal correlated to said driving signal to a closed-loop feedback system coupled to said metering valve. 
     
     
       3. The method of claim 1 wherein said correction factor comprises a quotient whose dividend is said setpoint and whose divisor is said measured volume of fluid. 
     
     
       4. A method for compensating for changes in the flow characteristics of a fluid being dispensed from a nozzle, said method comprising the steps of: (a) delivering the fluid under pressure to a metering valve located upstream of the nozzle, said metering valve being operable to modulate the flow of fluid to the nozzle in response to a control signal;   (b) measuring the volume of fluid delivered to said metering valve over an interval of time and generating a corresponding measurement signal, and   (c) adjusting the control signal in accordance with the difference between said measurement signal and a setpoint representing a desired volume of fluid to be dispensed during said interval so that said valve maintains the volume of fluid dispensed at said setpoint.   
     
     
       5. The method of claim 4 wherein said adjusting step comprises the steps of: calculating a correction factor correlated to the difference between said measurement signal and said setpoint;   multiplying a driving signal by said correction factor, and   generating Said control signal from at least said driving signal.   
     
     
       6. The method of claim 5 wherein said generating step comprises the step of algebraically combining the difference between said driving signal with a signal correlated to the flow rate of the fluid dispensed from the nozzle. 
     
     
       7. The method of claim 6 further comprising the step of: generating said driving signal in accordance with at least a toolspeed signal of a robot for effecting relative movement between the nozzle and a workpiece.   
     
     
       8. The step of claim 7 wherein said signal correlated to the flow rate of the fluid dispensed from the nozzle comprises a signal representing the pressure drop across said nozzle. 
     
     
       9. The method of claim 4 wherein said interval is a job cycle. 
     
     
       10. The method of claim 4 further comprising the steps of: locating said valve and said nozzle in sufficiently close proximity to one another that very little fluid pressure drop occurs between said valve and said nozzle;   sensing, at a location between said valve and said nozzle, a parameter correlated to the rate of flow of the fluid discharged from the nozzle and generating a corresponding flow rate signal, and   generating said control signal from at least said flow rate signal and a driving signal.   
     
     
       11. The method of claim 10 further comprising the steps of: calculating a correction factor correlated to the difference between said measurement signal and said setpoint;   multiplying a driving signal by said correction factor, and   generating said control signal from at least said driving signal. .Iadd.   
     
     
       12.  A method of compensating for dynamic flow characteristics of a non-newtonian fluid being dispensed from a nozzle onto a workpiece, the nozzle being in fluid communication with a metering valve responsive to a control signal, and the dynamic flow characteristics representing flow non-linearities introduced by the non-newtonian fluid, said method comprising the steps of: generating the control signal to produce a desired flow of the fluid through the nozzle, said control signal being correlated to at least a flow rate of the non-newtonian fluid; and   linearizing said control signal to reduce the flow non-linearities introduced by the non-newtonian fluid. .Iaddend. .Iadd.   
     
     
       13.  The method of claim 12 wherein said step of linearizing said control signal further comprises the steps of: determining flow linearizing factors based on known flows of the non-newtonian fluid from the nozzle as a function of the control signal for a given set of conditions;   selecting a first flow linearizing factor;   altering said control signal as a function of said first flow linearizing factor. .Iaddend. .Iadd.14. The method of claim 13 wherein the step of determining said flow linearizing factors further comprises the step of determining a series of flow linearizing factors based on known flows of the non-newtonian fluid from the nozzle as a function of said control   
     
     
        signal for given sets of conditions. .Iaddend. .Iadd.15.  The method of claim 14 wherein said step of generating said control signal further comprises the steps of: providing a tool speed signal correlated to relative motion between the nozzle and the workpiece;   selecting said first flow linearizing factor as a function of the tool speed signal; and   multiplying said tool speed signal by said first flow linearizing factor to produce a linearized tool speed value. .Iaddend. .Iadd.16. The method of claim 15 wherein the step of generating said control signal further comprises the steps of:   producing a feedback signal representing a fluid pressure correlated to a flow rate of the non-newtonian fluid; and   producing said control signal as a function of said feedback signal and said linearized tool speed value, thereby compensating said control signal as a function of the flow non-linearities introduced by the non-newtonian fluid and causing the metering valve to dispense the desired flow of the   
     
     
        non-newtonian fluid. .Iaddend. .Iadd.17.  A method of compensating for dynamic flow characteristics and intrinsic viscosity changes of a fluid being dispensed from a nozzle onto a workpiece, the nozzle being in fluid communication with a metering valve responsive to a control signal, and wherein the intrinsic viscosity changes are caused by phenomena other than shear effects, and the dynamic flow characteristics representing pressure flow non-linearities introduced by non-newtonian viscosity characteristics in the fluid, the method comprising the steps of: generating the control signal to provide a desired flow of the fluid through the nozzle, said control signal being correlated to at least a flow rate of the fluid; and   modifying said control signal to reduce the pressure flow non-linearities introduced by the dynamic flow characteristics and to compensate for the   
     
     
        intrinsic viscosity changes of the fluid. .Iaddend. .Iadd.18.  The method of claim 17 wherein the step of modifying said control signal further comprises the steps of: providing a tool speed signal correlated to relative motion between the nozzle and the workpiece;   altering said tool speed signal as a function of the dynamic flow characteristics of the fluid to produce a linearized tool speed value; and   adjusting said linearized tool speed value as a function of the intrinsic viscosity changes of the fluid to produce a driving signal. .Iaddend. .Iadd.19. The method of claim 18 wherein said step of generating the control signal further comprises the steps of:   producing a feedback signal representing a fluid pressure correlated to a flow rate of the fluid; and   producing said control signal as a function of said feedback signal, said driving signal and effects of the dynamic flow characteristics and the intrinsic viscosity changes thereby causing the metering valve to dispense   
     
     
        the desired flow of fluid. .Iaddend. .Iadd.20.  The method of claim 18 wherein said step of adjusting said tool speed signal further comprises the steps of: selecting a flow linearizing factor based on a known flow of fluid from the nozzle as a function of said control signal for a given set of conditions.; and   multiplying said tool speed signal by said flow linearizing factor to produce said linearized tool speed value. .Iaddend. .Iadd.21. The method of claim 20 wherein said step of adjusting said linearized tool speed value further comprises the steps of:   measuring a first volume of fluid delivered to the metering valve during an interval of time;   calculating a flow compensation factor as a function of a difference between the first volume of fluid and a reference; and   multiplying said linearized tool speed value by said flow compensation   
     
     
        factor to produce said driving signal. .Iaddend. .Iadd.22.  A method of compensating for intrinsic viscosity changes of a fluid being dispensed from a nozzle onto a workpiece, the nozzle in fluid communication with a metering valve responsive to a control signal, and wherein the intrinsic viscosity changes are caused by phenomena other than shear effects, said method comprising the steps of: supplying the fluid under a pressure to the metering valve;   providing a tool speed signal representing a varying relative speed between the nozzle and the workpiece;   adjusting said tool speed signal as a function of the intrinsic viscosity changes of the fluid to produce a driving signal;   producing a feedback signal representing a fluid pressure correlated to a flow rate of the fluid; and   producing the control signal as a function of said feedback signal and said driving signal to cause the metering valve to dispense a desired flow of   
     
     
        fluid. .Iaddend. .Iadd.23.  The method of claim 22 wherein said step of adjusting the tool speed signal further comprises the steps of: measuring a first volume of fluid delivered to the metering valve during an interval of time;   calculating a flow compensation factor as a function of a difference between the first volume of fluid and a reference; and   adjusting said tool speed signal as a function of said flow compensation factor. .Iaddend. .Iadd.24. The method of claim 23 wherein said step of adjusting the tool speed signal further comprises the step of multiplying said tool speed signal by said flow compensation factor. .Iaddend.   
     
     
        .Iadd.  .  A method of compensating for effects of pressure flow non-linearities of a fluid being dispensed from a nozzle onto a workpiece, the nozzle in fluid communication with a metering valve responsive to a control signal, said method comprising the steps of: supplying the fluid under a pressure to the metering valve;   providing a tool speed signal representing a relative speed between the nozzle and the workpiece;   determining a flow factor as a function of the effects of the pressure flow non-linearities of the fluid;   adjusting said tool speed signal as a function of the flow factor to produce a driving signal;   producing a feedback signal representing a fluid pressure correlated to a flow rate of the fluid; and   producing the control signal as a function of said feedback signal and said driving signal to cause the metering valve to dispense a desired flow of fluid. .Iaddend.