Patent ID: 7584015

Claim:
A method for designing a mold, comprising: preparing a mold of which a molding surface is formed to be a design curved surface of a molded product; measuring a curved surface shape of a molded product which is molded from the mold, and specifying a curved surface of the molded product by approximating a measured value by an equation of an aspherical surface; comparing the specified curved surface of the molded product and the design curved surface of the molded product to obtain an error of both the curved surfaces; and correcting the molded surface of the mold by using information corresponding to the error as correction information to design the molded surface, wherein said correction information includes entire shape correction information correcting an entire shape of the molding surface of the mold to cope with an error of a spherical shape component in the curved surface of the molded product, and local shape correction information correcting a local shape of the above-described molding surface of the mold to cope with an error of a component other than the spherical shape in the curved surface of the molded product, said entire shape correction information and said local shape correction information are independently calculated, the shape of said molded surface of said mold is corrected by using said entire shape correction information and said local shape correction information, and the equation of the aspherical surface is the following equation: Z = C ⁢ ⁢ ρ 2 1 + 1 - ( 1 + K ) ⁢ C 2 ⁢ ρ 2 + ∑ i = 2 m ⁢ A 2 ⁢ i ⁢ ρ 2 ⁢ i ( 1 ) where Z is a distance measured from a vertex of the molded product in an axial direction of the molded product, p satisfies p 2 =X 2 +Y 2 when X and Y are distances measured in a perpendicular direction to the above-described axis from the above-described vertex, a vertex curvature C satisfies C=1/R when R is set as a radius of curvature at the vertex, K is a conic coefficient, and A 21 is an aspherical coefficient (i is an integer).