Apparatus and method for electrical discharge machining

Apparatus for electrical discharge machining of the type in which a wire electrode (1) is guided between two guides (5) in a commanded guide path which includes a rest or reference position to cut a workpiece (6), said apparatus comprising

• at least one displacement pick-up system (7) positioned around the wire electrode between the wire guides (5) and the workpiece (6) and measuring the deflection of the wire electrode from a rest position in two mutually perpendicular coordinate directions and providing coordinate information signals indicative of the distance and direction of deflection of the wire from the guide path;
• said pick-up system comprising
• four test electrodes (9) arranged crossed about, and spaced from the wire electrode in a plane essentially perpendicular to the axial direction of the wire electrode;
• means applying an alternating voltage between the wire electrode (1) and each of the test electrodes;
• means rectifying the alternating electric current flowing between the wire electrode and the test electrodes;
• absolute value former means (14) controlled by and connected to the rectifying means to provide output signals representative of deflection of the wire with respect to the test electrodes, in coordinate form;
• means (25, 26) relatively moving the workpiece and the wire in respective coordinate directions;
• means (27) controlling the moving means to command a predetermined movement;
• and means (24, 29, 30) responsive to said output signals additionally relatively moving the wire electrode and the workpiece, in respective coordinate directions, to compensate for deflection of the wire from the commanded path.

Apparatus for electrical discharge machining of the type in which a wire electrode (1) is guided between two guides (5) in a commanded guide path which includes a rest or reference position to cut a workpiece (6), said apparatus comprising

• at least one displacement pick-up system (7) positioned around the wire electrode between the wire guides (5) and the workpiece (6) and measuring the deflection of the wire electrode from a rest position in two mutually perpendicular coordinate directions and providing coordinate information signals indicative of the degree and direction of deflection of the wire from the guide path;
• said pick-up system comprising
• a light source and two light sensors, positioned in a plane perpendicular to the axis of the wire electrode and in relative perpendicular directions with respect to each other and so located that, if the electrode is in its commanded guide path including the rest or reference position, the electrode will cast an equally wide shadow zone on both sensor halves of the double-light sensors in both relatively mutually perpendicular directions whereas, upon deflection of the electrode from said rest position in the commanded path, the shadow zone on one sensor half, in a respective direction, is enlarged to the same extent as it is reduced on the other sensor half;
• means deriving output signals from said light sensors representative of the deflection of the wire electrode from said commanded guide path, including the rest or reference position;
• means (25, 26) relatively moving the wire electrode and the workpiece in respective coordinate directions;
• means (27) controlling the moving means to command a predetermined movement;
• and means (24;
• 29, 30) responsive to the output signals additionally relatively moving the wire electrode and the workpiece, in respective coordinate directions, to compensate for deflection of the wire from the commanded guide path.

Apparatus for electrical discharge machining of the type in which a wire electrode (1) is guided between two guides (5) in a commanded guide path which includes a rest or reference position to cut a workpiece (6), said apparatus comprising

• at least one displacement pick-up system (7) positioned around the wire electrode between the wire guides (5) and the workpiece (6) and measuring the deflection of the wire electrode from a rest position in two mutually perpendicular coordinate directions and providing coordinate information signals indicative of the distance and direction of deflection of the wire from the guide path;
• analog computer means (21) connected to and receiving the coordinate information and processing signals representative of said coordinate information of positive and negative component values for each coordinate of the coordinate information derived from the displacement pick-up system (7);
• wherein the analog computer means comprises a summing circuit (18), an inverter-amplifier (19), a divider (20) and a differentiator (17) to derive deflection error signals of positive and negative value representative of positive and negative deflection of the electrode in respective Cartesian coordinate directions,
• the average value of the positive and negative component in each axial direction being calculated by said summing circuit and inverter, the differentiator subtracting the average value from the positive component of the deflection signal to derive a derived signal, said derived signal being divided in the divider by the average value of the positive and negative components.

Apparatus for electrical discharge machining of the type in which a wire electrode (1) is guided between two guides (5) in a commanded guide path which includes a rest or reference position to cut a workpiece (6), said apparatus comprising

• at least one displacement pick-up system (7) positioned around the wire electrode between the wire guides (5) and the workpiece (6) and measuring the deflection of the wire electrode from a rest position in two mutually perpendicular coordinate directions and providing coordinate information signals indicative of the distance and direction of deflection of the wire from the guide path;
• analog computer means (21) connected to and receiving the coordinate information and processing signals representative of said coordinate information of positive and negative component values for each coordinate of the coordinate information derived from the displacement pick-up system (7);
• control amplifiers for processing the position information signals as computed by said analog computers for each axial coordinate direction;
• means (25, 26) relatively positioning the wire with respect to the workpiece in respective coordinate directions;
• and auxiliary drive means (29, 30) effective in said coordinate directions and additionally relatively moving the wire electrode and the workpiece to so displace the wire electrode relative to the pick-up system (7) that errors resulting from deflection of the wire electrode from the commanded guide path will be reduced to zero or null.