Programmed path for automatic tool retraction and return responsive to degradation threshold

A method of operating a numerically controlled machine tool of the kind having an original cutting tool relatively moved with respect to a workpiece, the original cutting tool being relatively moved during normal operation along a machining path during the execution of a part program including instructions defining the machining path, said method including the steps of interrupting the relative movement of the original cutting tool along the machining path at an arbitrary departure point in response to a trigger signal generated in response to the comparison of a tool degradation signal to a predetermined threshold, and automatically moving the original cutting tool relative to the workpiece to a tool change location in such a fashion that interference between the original cutting tool and the workpiece does not occur, said step of automatically moving the original cutting tool including the steps of moving the original cutting tool along an incremental retract vector from said departure point to a retract point, automatically moving the original cutting tool from said retract point to said tool change point, changing the original cutting tool and automatically moving the changed cutting tool back to the machining path without interference between the changed cutting tool and the workpiece, and resuming machining along the machining path using the changed cutting tool,

• wherein the method further comprises,
• said step of automatically moving the changed cutting tool back to the machining path includes relatively moving the changed tool with respect to the workpiece along an entry vector beginning at an approach point displaced from the retract point and comprising a straight move along an entry path at a grazing angle terminating at the departure point, wherein said retract vector has a substantial angle with respect to the reverse direction of the machining path, and said entry vector has a smaller grazing angle with respect to the reverse direction of the machining path, so that remachining of the workpiece does not occur and a relatively smooth surface is obtained on the workpiece at the location of the departure point.

A method of operating a numerically controlled machine tool of the kind having an original cutting tool relatively moved with respect to a workpiece, the original cutting tool being relatively moved during normal operation along a machining path during the execution of a part program including instructions defining the machining path, said method including the steps of interrupting the relative movement of the original cutting tool along the machining path at an arbitrary departure point in response to a trigger signal generated in response to the comparison of a tool degradation signal to a predetermined threshold, and automatically moving the original cutting tool relative to the workpiece to a tool change location in such a fashion that interference between the original cutting tool and the workpiece does not occur, said step of automatically moving the original cutting tool including the steps of moving the original cutting tool along an incremental retract vector from said departure point to a retract point, automatically moving the original cutting tool from said retract point to said tool change point, changing the original cutting tool and automatically moving the changed cutting tool back to the machining path without interference between the changed cutting tool and the workpiece, and resuming machining along the machining path using the changed cutting tool,

• wherein the method further comprises,
• said step of interrupting the relative movement of the original cutting tool along the machining path at an arbitrary departure point in response to a trigger signal generated in response to the comparison of a tool degradation signal to a predetermined threshold is conditioned on the position of said original cutting tool for selected respective beginning and ending distances of specified machining moves through the workpiece, and wherein for a consecutive series of said machining moves, the selected beginning distance is applied only to the first cut in said series, and the selected ending distance is applied only to the last cut in said series.

A method of operating a numerically controlled machine tool of the kind having a cutting tool relatively moved with respect to a workpiece, a numerical computer and control program for executing a part program, the cutting tool being relatively moved during normal operation along a machining path during the execution of said part program including instructions defining the machining path, said method including the steps of interrupting the relative movement of the cutting tool along the machining path at an arbitrary departure point in response to a plurality of trigger signals and automatically moving the cutting tool relative to the workpiece to predefined locations in such a fashion that interference between the cutting tool and the workpiece does not occur, said step of automatically moving the cutting tool including an initial step of moving the cutting tool along an incremental retract vector from said departure point to a retract point, the retract vector being determined at least in part by signals representing predetermined values for certain parameters and the identity of the trigger signal,

• wherein the method further comprises,
• generating said trigger signals by sensing conditions at the interface between said cutting tool and workpiece during the relative movement of said cutting tool along said machining path, and operating said numerical computer to repetitively execute instructions in said control program to determine the values of a plurality of signals responsive to said sensed conditions and to compare selected ones of said values to selected threshold values to generate triggering signals for respective actions,
• wherein the signals, threshold values, and actions are selected in response to definitional function calls coded in the part program and interpreted during the execution of said part program.

A method of operating a numerically controlled machine tool of the kind having a cutting tool relatively moved with respect to a workpiece along a programmed feed vector when the cutting tool is engaged with the workpiece so that material is removed from the workpiece by the cutting tool, said method causing said cutting tool being initially disengaged from said workpiece to become engaged with said workpiece at a predetermined point and comprising the steps of:

• (a) obtaining the angle of said feed vector with respect to said machine tool at said predetermined point;
• (b) adding said predetermined angle to said angle of said feed vector with respect to said machine tool to obtain a third angle;
• (c) determining an approach point displaced from said predetermined point along an entry vector having said third angle with respect to said machine tool;
• (d) relatively moving said cutter in a straight line motion to said approach point;
• and
• (e) moving said cutter directly in a straight line motion to said predetermined point at a narrow grazing angle.