Pulse width modulation control of gas flow for plasma cutting and marking

Abstract

Gas flow control for a plasma arc torch is provided. More particularly, a method and apparatus to modulate the pressure and flow from a plasma arc torch is provided. Cyclic pulsing of a flow control valve between states of fully open and fully closed provides for a relatively constant flow of plasma gas to the torch at a relatively constant pressure.

What is claimed is: 
     
         1 . A plasma arc torch system, comprising
 a plasma arc torch;   a gas flow valve connected to the torch by a gas supply line and controlling the flow of plasma gas to the torch, the gas flow valve having an inlet; and   a controller connected to the gas flow valve, the controller configured to
 determine the pressure of plasma gas provided to the inlet of the gas flow valve; 
   ascertain a frequency and duty cycle at which to cycle the valve between conditions of fully opened and fully closed using the pressure of plasma gas provided to the valve inlet; and
 provide a signal to the gas flow control valve whereby the valve is cycled between conditions of fully opened and fully closed so as to maintain a substantially constant flow of gas to the plasma arch torch. 
   
     
     
         2 . A plasma arc torch system as in  claim 1 , wherein the gas flow valve is a solenoid valve. 
     
     
         3 . A plasma arc torch system as in  claim 1 , further comprising a plasma gas supply in fluid communication with the gas flow valve. 
     
     
         4 . A plasma arc torch system as in  claim 3 , further comprising a pressure regulator connected between the plasma gas supply and the gas flow valve whereby the pressure of plasma gas at the inlet of the gas flow valve may be determined. 
     
     
         5 . A plasma arc torch system as in  claim 1 , further comprising a preflow gas supply in fluid communication with the gas flow valve. 
     
     
         6 . A plasma arc torch system as in  claim 5 , further comprising a pressure regulator connected between the preflow gas supply and the gas flow valve whereby the pressure of preflow gas at the inlet of the gas flow valve may be determined.