Special and innovative aspects of the GTC M2 drive mechanism

The paper presents some special, innovative and technological aspects of the secondary mirror mechanism for the GTC 10.8-m telescope, such as: The dual control loop of the hexapod actuators, which provides the GTC M2 alignment system with an absolute accuracy better than a few microns, and a resolution as low as 200 nm. The particular design of the hexapod flexure joints, which ensures frictionless joints without backlash, while effectively limiting the travel of the hexapod to the desired range only. The locking devices, based on an original rotating cam principle, which ensure the safe locking of the M2 support to the hexapod lower plate when the chopper function is not utilized. CuBe flexure parts have been manufactured by Electrodischarge Machining (EDM), and heat treated for maximum strength and fatigue load. A systematic approach to the Reliability, Maintainability and Safety aspects, aimed at ensuring the operational feasibility of the mechanism along its life cycle.