Numerical control apparatus

A numerical control apparatus for controlling an operation of a machine tool according to a command program, wherein

• the machine tool comprises a first linear moving axis, a second linear moving axis orthogonal to the first linear moving axis, a pivot axis for rotating a pivot member about the first linear moving axis or a axis parallel to the first linear moving axis, and a tool arranged at the distal end of the pivot member, and
• an operation route of the tool in a three-dimensional orthogonal coordinate system is commanded in the command program, and
• the numerical control apparatus comprises:
• means for interpolating the operation route of the tool in the three-dimensional orthogonal coordinate system commanded by the command program in a predetermined cycle and calculating an amount of movement of the tool between interpolation points as interpolation components on the three-dimensional orthogonal coordinate system;
• means for calculating an amount of rotation of the tool about the pivot axis required for moving the tool by an interpolation component for a third axis orthogonal to the first and second linear moving axes;
• and
• means for calculating an amount of movement of the tool in the direction of the second linear moving axis, caused by the rotation of the tool by the calculated amount of rotation, as an amount of correction, wherein
• an amount of movement of an interpolation component of the first linear moving axis is outputted to the first linear moving axis, an amount of movement corrected by the amount of correction is outputted to the second linear moving axis, and the amount of rotation is outputted to the pivot axis, in a predetermined cycle, respectively.