Numerical control machine tool with an emergency origin returning function

A numerical control (NC) machine tool comprising:

• a frame;
• a spindle head rotatably carrying a tool spindle;
• a spindle drive motor drivingly connected to said tool spindle;
• a work table for mounting a workpiece thereon;
• an NC drive axis for effecting relative movement between said spindle head and said work table in an axial direction of said tool spindle;
• a tool magazine for storing a plurality of tools;
• a tool changer for selectively attaching said tools to said tool spindle;
• command means manually operable for generating a command signal instructing the returning of said NC drive axis to a machine origin;
• an origin detector for generating an origin signal when said NC drive axis is returned to said machine origin;
• a return inhibiting zone detector operable by the relative movement between said spindle head and said work table in the axial direction of said tool spindle for generating a return inhibiting signal when said NC drive axis is within a return inhibiting zone which is defined in the vicinity of said machine origin;
• and
• a numerical controller connected to said spindle drive motor, said NC drive axis, said tool changer, said command means, said origin detector and said return inhibiting zone detector and operable for controlling said NC drive axis and said tool changer in accordance with a numerical control program so as to perform a series of machinings on said workpiece, said numerical controller including,
• memory means for registering a tool being presently used on said tool spindle,
• origin returning control means responsive to said command signal from said command means for controlling said NC drive axis to discontinue advance movement and then to effect origin returning movement until said origin signal is output from said origin detector, wherein said origin returning movement is performed in such a manner that when said NC drive axis is within said return inhibiting zone upon the manual operation of said command means, said NC drive axis is moved first out of said return inhibiting zone in an opposite direction away from the machine origin and then is reversed toward said machine origin,
• direction decision means for determining the direction in which said tool spindle is to be rotated durig said origin returning movement of said NC drive axis under the control of said origin returning control means, by reference to said tool being registered in said memory means, and
• rotation control means for controlling said spindle drive motor to rotate said tool spindle in said direction determined by said direction means during said origin returning movement of said NC drive axis under the control of said origin returning control means.