Tool trajectory display device having function for displaying inversion position of servo axis

A tool trajectory display device for displaying a trajectory of a tool center point of a machine tool with a plurality of servo axes including at least one rotation axis controlled by a numerical controller, the tool trajectory display device comprising:

• a position information obtaining part which obtains position information of at least one of the servo axes;
• a velocity information obtaining part which obtains velocity information of the servo axis;
• a tool coordinate calculating part which calculates a coordinate value of the tool center point based on the position information of the servo axis and information of a mechanical constitution of the machine tool;
• an inversion position calculating part which calculates an inversion position where a polarity of a velocity of at least one servo axis is changed, based on the velocity information of the servo axis and the coordinate value of the tool center point;
• and
• a displaying part which displays a trajectory of the tool center point based on the coordinate value of the tool center point, and displays the inversion position of the servo axis on the trajectory of the tool center point.