Method of and means for spacing control of plasma arc cutting torch including vector velocity compensation
AssigneeCaterpillar Tractor Co.
InventorRonald D. Brown
Life of this patent
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Abstract
A method of automatically maintaining a selected spacing for a plasma arc cutting torch form a workpiece is disclosed which takes advantage of the fact that at any given setting of a plasma arc power supply the current in the arc varies inversely and the voltage across the arc varies directly in relation to the spacing of the plasma arc torch from the workpiece when new material in the workpiece is presented to the plasma arc at an essentially constant rate and which includes the step of automatically compensating for variations in the rate at which new material is presented to the arc.
Claims11
In a method of automatic control by means of a control signal of the spacing of a plasma arc cutting torch from a workpiece during movement of said torch through a path in a plane substantially parallel to the surface of said workpiece at vector velocities equal to and less than a given maximum vector velocity with respect to said workpiece, the improvement comprising the steps of generating a signal representative of the vector velocity of said torch and generating comparable signals representative of the plasma arc current and plasma are voltage, properly polarizing all of said signals with respect to each other and summing all of said signals with each other and with a selected offset signal to produce a zero control signal at a selected spacing and said given maximum vector velocity between said torch and said workpiece and changing said signal representative of vector velocity in response to a decrease in said vector velocity in inverse sense to changes which occur in the sum of said signals representative of arc current and arc voltage when said vector velocity decreases, whereby said zero control signal will tend to be maintained unless a change occurs in said spacing of said torch from the surface of said workpiece.
The method of automatically maintaining a selected spacing of a plasma arc torch from the work surface of a workpiece during movement of said torch along said work surface at velocities equal to and less than a given velocity comprising the steps of:
- (a) establishing a plasma arc between said surface and said plasma arc torch at said selected spacing by means of a plasma arc torch power supply;
- (b) electrically sensing the voltage present between said workpiece and said plasma arc torch and generating a first electrical signal representative thereof;
- (c) electrically sensing the current flow between said workpiece and said plasma arc torch and generating a second electrical signal representative thereof comparable to said first electrical signal;
- (d) electrically inverting one of said first and second electrical signals with respect to the other;
- (e) electrically sensing the vector velocity of said movement of said plasma arc torch along said work surface and generating a third electrical signal representative thereof comparable to said first and second electrical signals and electrically summing said first, second and third electrical signals to produce a composite signal;
- (f) electrically generating a fourth electrical signal equal in magnitude and opposite in sign to said composite signal at said selected spacing and said given velocity and summing said fourth electrical signal with said composite signal to produce an electrical control signal representative of both the sense and the amount of any change in said composite signal;
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- (g) applying said electrical control signal to electromechanical means coupled to said plasma arc torch for moving said plasma arc torch toward said selected spacing from said work surface in response to said control signal.
Apparatus for automatically maintaining a selected spacing between a plasma arc torch and the work surface of a workpiece during movement of said torch along said work surface at vector velocities equal to and less than a given vector velocity comprising:
- (a) mechanical means for simultaneously moving said plasma arc torch in X and Y directions perpendicular to each other along the work surface of the workpiece at controllable velocities to establish vector velocities of movement of said torch along said work surface equal to and less than a given vector velocity;
- (b) means establishing a plasma arc between said torch and said work surface of said workpiece including a DC power supply;
- (c) means sensing the output voltage of said DC power supply and producing a first electrical signal representative thereof;
- (d) means sensing the output current of said DC power supply and producing a second electrical signal representative thereof comparable to said first electrical signal;
- (e) means inverting one of said first and second electrical signals with respect to the other;
- (f) means for generating a third electrical signal representative of the vector velocity of movement of said plasma arc torch along said work surface of said workpiece;
- (g) means for generating a fourth electrical signal equal in magnitude and opposite in sign to the sum of said first, second and third electrical signals at said selected spacing and given vector velocity between said plasma arc torch and said work surface of said workpiece;
- (h) means summing said first, second, third and fourth electrical signals to produce an electrical control signal representative of the sum thereof;
- (i) electromechanical means coupled to said plasma arc torch for moving said plasma arc torch toward and away from said work surface of said workpiece;
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- (j) means applying said electrical control signal to said electromechanical means.
Dependencies are inferred from the claim text.