| 摘要 |
PROBLEM TO BE SOLVED: To set an initial height in a relatively short time without being influenced by fumes and sputter scattered by plasma arc cutting, also even if coating of electric insulation is applied to the surface of a workpiece and further even in a torch having a shield cap. SOLUTION: The shield cap 7 and an electrically connected signal line 25 are incorporated in the plasma torch 1. The signal line 25 is connected to a detecting circuit 29. Voltage is applied between the shield cap 7 and a workpiece 101 by the detecting circuit 29, the difference of voltage changed when those are mutually brought into contact and are electrically conducted is detected. An annular projection 33 is provided on the surface coming into contact with the workpiece 101 at the tip end of the torch 1. In setting of the initial height, the torch 1 is lowered at a relatively high speed to detect the rough position of the workpiece 101, thereafter the torch 1 is lifted by the prescribed distance to separate the torch 1 from the workpiece 101, and this time the torch 1 is lowered at a relatively low speed to detect the position of the workpiece 101.
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