Numerical controller for multi-axis machine tool

A numerical controller for a multi-axis machine tool having a mechanism including at least three linear axes and at least three rotating axes for machining a workpiece attached to a table by rotating the table or a tool head, the numerical controller being adapted to instruct a tool center point position by linear axis positions on a command program coordinate system and giving a tool direction command to the multi-axis machine tool, the numerical controller comprising:

• rotating-axis multiple solutions computing means for obtaining an interpolated tool direction vector by interpolating the tool direction command for every interpolation period and computing multiple solutions for the three rotating axes, as a first rotating axis fixed solution assuming that a first rotating axis is fixed, a second rotating axis fixed solution assuming that a second rotating axis is fixed, and a third rotating axis fixed solution assuming that a third rotating axis is fixed, from the interpolated tool direction vector;
• rotating axis position computing means for computing three rotating axis positions by calculating evaluation values for highly evaluating smaller motion amounts in the multiple solutions, respectively, and synthesizing products of the motion amounts obtained respectively by the multiple solutions and the evaluation values, wherein smaller motion amounts are motion amounts that are less than a small amount threshold;
• and
• linear axis position computing means for obtaining an interpolated tool center point position by interpolating the tool center point position instructed for every interpolation period and then computing three linear axis positions on a machine coordinate system from the interpolated tool center point position, a tool length compensation amount and the positions of the rotating axes, wherein
• the numerical controller is operable to move the three rotating axes to the rotating axis positions determined by the rotating axis position computing means and to move the three linear axes to the linear axis positions determined by the linear axis position computing means.