Freeform manufacturing of a progressive addition lens by use of a voice coil fast tool servo

The back surface of progressive addition lens (PAL) is a non-rotationally symmetric freeform surface. The local radius varies progressively from the far zone to the near zone along the intermediate zone to give the addition power. Numerical simulation method is performed to calculate the discrete points on the freeform surface in polar coordinate and generate the data files containing the trajectory of diamond tool tip for surface machining. The fabrication of PAL is accomplished by using self-developed single-point diamond turning machine with voice coil fast tool servo. The polished freeform surface profile measured by a 3-axes coordinate measuring machine shows little deviation to the simulation result. Surface power and cylinder of the fabricated PAL is also measured for comparison with theoretical design.