Patent ID: 7106528

Claim:
A method of manufacturing a large double-sided curved Fresnel lens, comprising; a machining step (A) of performing ultra-precise three-dimensional machining on a first material to make an upper mold having an upper transfer surface that engages an upper surface of a thermoplastic resin plate, and performing ultra-precise three-dimensional machining on a second material to make a lower mold having a lower transfer surface that engages a lower surface of the thermoplastic resin plate; and a hot press molding step (B) of pressing the thermoplastic resin plate between the upper and lower molds by a predetermined pressure with the resin plate being held at a temperature higher than a softening temperature thereof and lower than a melting temperature thereof so that the thermoplastic resin plate is curved, and both lens surfaces for the double-sided Fresnel lens are respectively transferred to the upper surface and the lower surface of the thermoplastic resin plate, wherein in the machining step (A), each of the materials for the upper and lower molds is rotated around a rotational axis parallel to an optical axis of the large double-sided curved Fresnel lens at a high speed, and a position of a machining tool for the material is numerically controlled in first and sec.on.d directions orthogonal to the rotational axis and in a third direction parallel to the rotational axis so as to form the upper transfer surface and the lower transfer surfaces.