Numerical controller for corner path optimization

1. A numerical controller controlling a machine tool processing a workpiece based on a program including a plurality of blocks, the numerical controller comprising

a path conversion unit for obtaining a curved correction path passing through three points corresponding to a start point of a third block, an end point of the third block, and a shift point obtained by shifting an intermediate point of a command path based on the third block in an inward direction of a corner path within a limit of a preset allowable error amount when the corner path is formed by a series of blocks included in the program and a tangential direction of the corner path is continuous, and generating a path obtained by replacing the command path of the third block included in the corner path by the correction path, the third block commanding curvilinear movement at a larger curvature than a first curvature and a second curvature being interposed between the first block commanding rectilinear movement or curvilinear movement at the first curvature corresponding to a small curvature and the second block commanding rectilinear movement or curvilinear movement at the second curvature corresponding to a small curvature in the series of blocks.

2. The numerical controller according to claim 1 , wherein the path conversion unit calculates a first inward turning amount when a curve is inserted between the first block and the third block using a predetermined algorithm, and a second inward turning amount when a curve is inserted between the third block and the second block using a predetermined algorithm, and sets a point obtained by shifting an intermediate point of a tool path commanded by the third block in the inward direction of the corner path by a shift amount to the shift point, the shift amount being obtained by subtracting a larger inward turning amount in the first inward turning amount and the second inward turning amount from the allowable error amount.