| 摘要 |
PURPOSE:To prevent a tool from breakage in the unattended running of a NC machine tool by reducing the feed speed as a cutting load is increased and then reducing controllably feed-in when the cutting load exceeds a reference value continuously for a predetermined time. CONSTITUTION:During cutting a workpiece 18 with a tool 22, when a cutting load 36 detected by a current detecting sensor 26 exceeds a reference value, first as first step control, the feed speed of a feed motor 42 is reduced by a comparation calculator 28 through a machine controller 30, NC device 32 and servo unit 40 to control the cutting load 36 within the reference value. Howeber, when the cutting load 36 exceeds the reference value continuously for a predetermined time even if the feed speed of feed motor 42 is reduced to the minimum allowable limit, as the second step control, a command is given from the servo unit 40 to a feed-in feeding motor 44 to carry out the feed-in control for making the tool 22 escape from the workpiece 18 by a constant amount at a time. Thus, the tool is not broken with the variation of cutting allowance of workpiece and continuous unattended running can be efficiently carried out.
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