Freeform active mirror designed for additive manufacturing

A possible answer to the challenge brought by the construction of the next generation 40 m-class telescopes was the case study of FAME (Freeform Active Mirror Experiment). As the new instruments typically increased in both volume and complexity, the use of highly aspherical freeform surfaces could be a great solution as these systems are built up from fewer parts and can achieve higher performance. The idea of FAME was to create a thin face sheet which is then deformed to the nominal shape utilizing actuators mounted on the back of the mirror and acting parallel to the optical surface. The test phase of the FAME prototype revealed the complexity of the design and its sensitivity to manufacturing and assembly processes. As part of the characterization it was very difficult to predict correctly how the system behaves which is due to the several interfaces between the actuators and the face sheet. These experiences led to the development of a new structure that eliminates the strict tolerance chain obtained from a variety of components mounted on one another. It also means that the design for conventional manufacturing technologies should be left behind, and additive manufacturing must be introduced. This paper gives a brief overview how the lessons learned from the previous development is matched with the new design approach of the same component using topology optimization, additive manufacturing of metals and post processing of 3D printed parts. This work is funded under the OPTICON H2020 INFRAIA-2016-2017/H2020-INFRAIA-2016-1 Grant Agreement 730890.