National Astronomical Observatory of Japan (NAOJ) has had the responsibility for the Telescope Structure System (STR) of Thirty Meter Telescope (TMT) and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary/final design and pre-production work since 2012. TMT defines that STR shall be designed to withstand earthquakes up to the levels of the 1000-years annual return period as keeping accelerations at the mirror/instrumental interface points below the specified thresholds. In this paper, we present the Seismic Isolation System (SIS) of TMT STR, as focusing on (1) the design to achieve compatibility of two conflicting performances that are the rigid connection to the ground during normal observations and flexible movement during seismic to suppress the seismic energy, (2) prototype results of the seismic isolation system, and (3) compliance status of the seismic requirements which is evaluated by time history analysis using the Finite Element Method (FEM) model of TMT STR.
For the Thirty Meter Telescope (TMT) that aims high-resolution and high-sensitivity observations for optical-infrared astronomy, detailed design is underway for Telescope Structure System (STR) including the mount control system and the segment handling system. The technical requirements for the STR system are very challenging on its performance and interface condition with telescope-mounted optics and observation instruments. The major challenging technical requirements include low flexure of mirror support structure and low optical path length variation due to gravitational deformation, high seismic performance against large earthquake, very accurate mount drive control for high tracking and guiding performance, and fast, safe and labor-saving segment exchange. To meet these technical requirements, Mitsubishi Electric Corporation (MELCO) has made a detailed design and technology development. In this paper, overview of major key technologies is introduced that is adopted for the TMT telescope structure in the detailed design and technology development.
SHS (Segment Handling System) is the subsystem implemented on the telescope. One of the key technologies of SHS is our force control technology applied to Segment Mirror Exchange Robot, which makes it possible to achieve safe and reliable mirror segment exchange as shown in Video 1.
Segment Handling System (SHS) is the subsystem that is planned to be permanently implemented on Thirty Meter Telescope (TMT) telescope structure that enables fast, efficient, semi-automatic exchange of M1 segments. TMT plans challenging segment exchange (10 segments per 10 hours a day). To achieve these, MELCO develops innovative SHS by accommodating Factory Automation (FA) technology such as force control system and machine vision system into the system. Force control system used for install operation, achieves soft handling by detecting force exerted to mirror segment and automatically compensating the position error between handling segments and primary mirror. Machine vision system used for removal operation, achieves semi-automatic positioning between SHS and mirror segments to be handled. Prototype experience proves soft (extraneous force ~300N) and fast (~3 minutes) segment handling. The SHS will provide upcoming segmented large telescopes for cost-efficient, effortless, and safe segment exchange operation.
KEYWORDS: Telescopes, Optical instrument design, Computer aided design, Mirrors, Electroluminescence, Control systems design, Control systems, Earthquakes, Safety, Thirty Meter Telescope
We present an overview of the preliminary design of the Telescope Structure System (STR) of Thirty Meter Telescope (TMT). NAOJ was given responsibility for the TMT STR in early 2012 and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary design work. MELCO performed a comprehensive preliminary design study in 2012 and 2013 and the design successfully passed its Preliminary Design Review (PDR) in November 2013 and April 2014. Design optimizations were pursued to better meet the design requirements and improvements were made in the designs of many of the telescope subsystems as follows: 1. 6-legged Top End configuration to support secondary mirror (M2) in order to reduce deformation of the Top End and to keep the same 4% blockage of the full aperture as the previous STR design. 2. “Double Lower Tube” of the elevation (EL) structure to reduce the required stroke of the primary mirror (M1) actuators to compensate the primary mirror cell (M1 Cell) deformation caused during the EL angle change in accordance with the requirements. 3. M1 Segment Handling System (SHS) to be able to make removing and installing 10 Mirror Segment Assemblies per day safely and with ease over M1 area where access of personnel is extremely difficult. This requires semi-automatic sequence operation and a robotic Segment Lifting Fixture (SLF) designed based on the Compliance Control System, developed for controlling industrial robots, with a mechanism to enable precise control within the six degrees of freedom of position control. 4. CO2 snow cleaning system to clean M1 every few weeks that is similar to the mechanical system that has been used at Subaru Telescope. 5. Seismic isolation and restraint systems with respect to safety; the maximum acceleration allowed for M1, M2, tertiary mirror (M3), LGSF, and science instruments in 1,000 year return period earthquakes are defined in the requirements. The Seismic requirements apply to any EL angle, regardless of the operational status of Hydro Static Bearing (HSB) system and stow lock pins. In order to find a practical solution, design optimization study for seismic risk mitigation was carried out extensively, including the performing of dynamic response analyses of the STR system under the time dependent acceleration profile of seven major earthquakes. The work is now moving to the final design phase from April 2014 for two years.
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