Numerical control apparatus

A numerical control apparatus that controls a machine tool including a plurality of linear axes and a first rotation axis and a second rotation axis and controls a relative tool posture of a tool with respect to work placed on a table, the numerical control apparatus comprising:

• a program reading unit that sequentially reads, from a machining program including a plurality of blocks described by a command code to the machine tool, for each of the blocks, a tool posture of the tool with respect to the work;
• a determining unit that determines whether or not the read tool posture is within a predetermined tool posture range;
• a tool-posture control unit that determines control content of the tool posture according to a result of the determination by the determining unit;
• and
• an interpolation/acceleration and deceleration processing unit that controls the plurality of linear axes and the two or more rotation axes according to the determined control content of the tool posture, wherein:
• the predetermined tool posture range includes a peculiar posture in which a principal plane of the table and a center axis of a tool cross perpendicularly to each other, and which corresponds to an angle of the first rotation axis,
• when, for each of the read blocks, an angle of the first rotation axis at a start point of the read block is within the predetermined tool posture range and an angle of the first rotation axis at an end point of the read block is within the predetermined tool posture range, the determining unit determines that the read tool posture is within the predetermined tool posture range, and
• when the read tool posture is within the predetermined tool posture range, the tool-posture control unit determines a rotation axis angle of the second rotation axis such that a change of an angle of the second rotation axis from a last angle of the second rotation axis is limited to a certain value and when the read tool posture is outside of the predetermined tool posture range, the tool-posture control unit determines the rotation axis angle of the second rotation axis such that the change of the angle of the second rotation axis angle is permitted to exceed the certain value.