Review on fast tool servo machining of optical freeform surfaces

Fast tool servo (FTS) in ultra-precision machining (UPM) is an enabling and efficient technology for fabricating optical freeform surfaces or microstructures with submicrometric form accuracy and nanometric surface finish. There are many kinds of FTS in the different driving principle to present their various performances currently. Their kernel technologies influence the machining ability and accuracy of freeform surfaces, consequently receiving much research attention and interest. These technologies are generally summarized as the development of FTS structure, the advanced control algorithms, tool path planning, machining condition monitoring, and surface measurement and error compensation. This paper aims to survey the current state of the art in machining freeform optics by FTS. An analysis of the principle, performance, and application of FTS machining with regard to freeform optics is presented. And the key machining technologies for optical freeform surfaces by FTS are then introduced in detail. The challenges and opportunities for further studies are concluded according to the FTS machining difficult of optical freeform surfaces finally.