Method of electrically cutting materials with a wire-shaped electrode and apparatus for practicing the same

An apparatus for electrically cutting a work piece with a wire-shaped electrode in which electric current is applied to said wire-shaped electrode and said work piece through a working liquid applied to the working gap formed between said wire-shaped electrode and said work piece to electrically cut said work piece, and in correspondence to said cutting operation, said wire-shaped electrode and said work piece are relatively moved in a predetermined manner to cut said work piece into a desired configuration, in which the improvement comprises a power supply unit for applying said electric current to said wire-shaped electrode and said work piece, said power supply unit comprising:

• digital setting means for setting digital values corresponding to a pulse width, pulse interval and peak current, respectively, of said electric current applied to said wire-shaped electrode and said work piece;
• a first presettable counter receiving on preset inputs thereof said digital value representing said pulse width;
• a second presettable counter receiving on preset inputs thereof said digital value representing said pulse interval;
• a toggle-type flip-flop;
• an oscillator for producing clock pulses;
• a first AND gate having a first input coupled to receive said clock pulses, a second input coupled to a Q output of said flip-flop and an output coupled to a clock input of said first presettable counter;
• a second AND gate having a first input coupled to receive said clock pulses, a second input coupled to a Q output of said flip-flop, and an output coupled to a clock input of said second presettable counter;
• an OR gate having a first input coupled to a predetermined count output of said first presettable counter, a second input coupled to a predetermined count output of said second presettable counter, and an output coupled to reset inputs of said first and second presettable counters and a clock input of said flip-flop;
• a plurality of third AND gates, each of said third AND gates having a first input coupled to said Q output of said flip-flop and said third AND gates having second inputs coupled to receive said value representing said peak current;
• a plurality of current limiting resistors, one of said current limiting resistors being provided for each of said third AND gates;
• a plurality of switching means, one of said switching means being provided for each of said third AND gates, each of said switching means having a control input coupled to an output of a corresponding one of said third AND gates and a first current-carrying terminal coupled through a corresponding one of said current limiting resistors to a first of said wire-shaped electrode and said work piece;
• and a DC power source having a first terminal coupled to a second of said wire-shaped electrode and said work piece and a second terminal coupled to a second current-carrying terminal of each of said switching means.