Adaptive method and apparatus for controlling machining current in electric discharge machines

An apparatus for controlling a discharge current comprising:

• (a) a circuit for applying a voltage pulse having an on time and an off time across a gap formed between an electrode and a workpiece;
• (b) a monitoring circuit for monitoring an electrical characteristic of said gap;
• (c) means, connected to said monitoring circuit, for comparing the level of said monitored electrical characteristic at least at one predetermined time with at least one predetermined reference level and thereby generating a comparison output signal;
• (d) means for classifying a condition at said gap into at least a first condition or a second condition based upon said comparison output signal;
• and
• (e) means, connected to said first circuit and to said classifying means, for increasing the off time when said gap is classified into said first condition and for decreasing said off time when said gap is classified into said second condition;
• and wherein said at least one predetermined reference level is changed in accordance with a peak current discharged across said gap.

A method for controlling a discharge current comprising the steps of:

• (a) applying a voltage pulse having an on time and an off time across a gap formed between an electrode and a workpiece using a first circuit;
• (b) monitoring a detection current passed through said gap;
• (c) comparing the level of said detection current at least at two predetermined times during said on time, with at least two predetermined reference levels and thereby generating comparison output signals;
• (d) classifying a condition at said gap into at least a first condition or a second condition based upon said comparison output signals;
• and
• (e) increasing the off time when said gap is classified into said first condition and decreasing said off time when said gap is classified into said second condition.

A method for controlling a discharge current comprising the steps of:

• (a) applying a voltage pulse having an on time and an off time across a gap formed between an electrode and a workpiece using a first circuit;
• (b) monitoring an electrical characteristic of said gap;
• (c) comparing the level of said monitored electrical characteristic at least at one predetermined time, with at least one predetermined reference level and thereby generating a comparison output signal
• (d) classifying a condition at said gap into at least a first condition or a second condition based upon said comparison output signal;
• and
• (e) increasing the off time when said gap is classified into said first condition and decreasing said off time when said gap is classified into said second condition;
• and changing said at least one predetermined reference level in accordance with a peak current discharged across said gap.