Numerical Control Device

A numerical control device for, in a machine tool including a spindle holding a tool, and feed axes corresponding to reference axes:

• a Z-axis extending along an axis of the spindle, and an X-axis and a Y-axis orthogonal to the Z-axis and orthogonal to each other, numerically controlling the feed axes, the numerical control device comprising:
• an error data storage storing therein error data including components regarding angular errors Eax, Eay, Eaz around the X-axis in the feed axes, angular errors Ebx, Eby, Ebz around the Y-axis in the feed axes, and angular errors Ecx, Ecy, Ecz around the Z-axis in the feed axes;
• and
• a position compensator compensating for commanded positions Ix, Iy, Iz for the feed axes with compensation amounts Cx, Cy, Cz corresponding to the commanded positions Ix, Iy, Iz, wherein
• the position compensator is further configured to calculate modification amounts Mx, My, Mz for the compensation amounts Cx, Cy, Cz for the feed axes in accordance with equations below, the commanded positions Ix, Iy, Iz for the feed axes, the error data stored in the error data storage, and data on a tool length of a tool to be used for machining, and modify the compensation amounts Cx, Cy, Cz with the calculated modification amounts Mx, My, Mz, the modification amounts Mx, My, Mz varying in accordance with the tool length:
• Mx=−(Ecx+Ecy+Ecz)−Ly+(Ebx+Eby+Ebz)−Lz;
• My=−(Eax+Eay+Eaz)−Lz+(Ecx+Ecy+Ecz)−Lx;
• and
• Mz=−(Ebx+Eby+Ebz)−Lx+(Eax+Eay+Eaz)−Ly,
• where Lx, Ly, and Lz are deviations from a predetermined reference position of a tip position of a tool attached to the spindle of the machine tool, Lx being a deviation in a direction of the X-axis, Ly being a deviation in a direction of the Y-axis, and Lz being a deviation in a direction of the Z-axis.