Patent ID: 7411152

Claim:
A plasma detector of a laser beam machine, said laser beam machine having a torch for radiating a laser beam on a workpiece, said plasma detector for detecting whether or not plasma generates between said torch and said workpiece, said plasma detector comprising: a trace control means for holding a gap length between said torch and said workpiece, said trace control means having: a nozzle at a top end of said torch for introducing said laser beam to said workpiece, said nozzle being an electrode; a trace voltage detecting means for detecting voltage of said nozzle as trace voltage; and a gap length control means for controlling said gap length between said torch and said workpiece based on said trace voltage of said nozzle which has been detected by said trace voltage detecting means; a voltage fluctuating section detecting means for detecting a voltage fluctuating section where said trace voltage fluctuates as detected by said trace voltage detecting means; a voltage fluctuating time integrating means for integrating voltage fluctuating time corresponding to said voltage fluctuating section detected by said voltage fluctuating section detecting means as voltage fluctuating integrated time; a voltage fluctuation occurrence rate computing means for computing a rate of occurrence of voltage fluctuation for time based on said voltage fluctuation integrated time integrated by said voltage fluctuating time integrating means; and a plasma detection determining means for determining whether or not said plasma was detected based on said rate of occurrence of voltage fluctuation computed by said voltage fluctuation occurrence rate computing means, and for outputting a determination result; whereby said plasma detector determines whether or not plasma generates between said torch and said workpiece based on said trace voltage detected by said trace control means.