Numerical control device

A numerical control device of a machine tool capable of controlling a spindle rotating speed of the machine tool, the numerical control device comprising:

• a program analyzing unit that
• reads ahead a machining program by one block or more and analyzes a command for the machine tool,
• determines whether the command is compatible with being executed concurrently with a spindle control command that causes a change in the spindle rotating speed, and
• calculates a first time period, a second time period, and a third time period, wherein
• the first time period is from when the spindle control command starts to when the spindle rotating speed reaches a designated rotating speed, which is a spindle acceleration or deceleration time,
• the second time period is an accumulated execution time period from a start of a second command, which is the command compatible with being executed concurrently with the spindle control command, to a start of a first command which is not compatible with being executed concurrently with the spindle control command, and
• the third time period is a time period which is an accumulated execution time period of the second command between a start of the second command to a start of the spindle control command, and
• calculates an output timing of the spindle control command by using the first time period, the second time period, and the third time period;
• and
• a command determining unit that outputs the spindle control command earlier than a timing designated by the machining program within a range of the spindle control command output timing,
• wherein the numerical control device controls the spindle rotating speed of the machine tool based on the spindle control command output by the command determining unit.