Patent ID: 7557589

Claim:
A gap detection device for laser beam machine, for detecting a gap between a nozzle of a laser beam machine for outputting a laser beam and an object to be machined by using the laser beam, comprising: a composite admittance acquisition portion for obtaining a composite admittance which is the reciprocal of a composite impedance of gap static capacitance depending on said gap and a plasma impedance depending on plasma generated during laser beam machining on said object; a composite static capacitance acquisition portion for obtaining composite static capacitance which is the sum of said gap static capacitance and a static capacitance component included in said plasma impedance from an imaginary part of said composite admittance; a resistance component acquisition portion for obtaining a resistance component included in said plasma impedance from a real part of said composite admittance; a static capacitance component acquisition portion for obtaining said static capacitance component by using a model representing a relation between said resistance component and said static capacitance component and said resistance component obtained by said resistance component acquisition portion; a gap static capacitance acquisition portion for obtaining said gap static capacitance by subtracting said static capacitance component from said composite static capacitance; and a gap acquisition portion for obtaining said gap from said gap static capacitance obtained by said gap static capacitance acquisition portion.