Development of the hexapod for the secondary mirror of the YNAO 2-m Ring Solar Telescope

The 2-m Ring Solar Telescope (RST) of the Yunnan Astronomical Observatory (YAO) is a new-generation solar telescope that will provide high-resolution solar observations. The RST is now under commissioning on the YAO campus. The secondary mirror of the RST is a 0.6-m diameter convex mirror that is supported by a hexapod system which is to provide precise and stable positioning and alignment of the secondary mirror. We present the development of the hexapod system, including its technical requirement, workspace, actuator and joint design. The classic Stewart type configuration is adopted for the hexapod design and the stepmotor-ballscrew concept for the actuator design. The one-part 2D flexure concept is used to manufacture the Hooke’s joints and also used for 3D rotary joint design. We also describe the performance tests of the hexapod system in laboratory. The hexapod is able to cover a sphere of sf7 mm. The translational displacement resolution is down to 0.1 um, and repeatability <0.1 um RMS, the rotational displacement resolution is down to 0.5 arcsec with repeatability <0.1 arcsec RMS. Besides, the hexapod exhibits high stiffness over 60 Hz with a payload of 70 kg.