The Six Degree-of-Freedom (6DOF) positioner was developed to position the four off-axis conic mirrors in Altair (Gemini** North's facility adaptive optics system). This positioner takes a unique approach to 6DOF positioning by combining two 3DOF parallel mechanisms in series to create a hybrid mechanism. The mechanism design provides a number of benefits including small size, simple adjustment, position locking, relatively simple kinematics and repeatable removal and replacement of optical components.
The 6DOF positioner is capable of positioning optics at the micron level in translation and at the arcsecond level in rotation. It also maintains the position of the optics to a few microns with changing gravity vector. The position of an attached optical component can be adjusted using a computer program to provide precision adjustment about an arbitrary coordinate system. However, the arrangement of the adjustments are such that any desired motion can be made with a single actuator or with a sensible combination of actuators. This is unlike other 6DOF positioning solutions like a Stewart Platform in which all 6DOF are completely coupled making it impossible to move the platform in any desired direction without moving all six actuators.
This paper will present the design of the positioner, a kinematic analysis of the mechanism and a discussion about the effectiveness of the positioner in the optical alignment of Altair.
Mechanically Actuated Reconfigurable Slits (MARS) provide a remote means of creating and reconfiguring multi-object spectrograph slits. The MARS design provides 99 individually positionable variable-width slits over a 180 mm square telescope focal plane. It offers fast, remote configurable, suitable for optical and IR ground and space based multi- object spectrographs. The slit apertures are arranged in three columns, to optimize the placement of the spectra on the detector. Two distinct MARS designs are presented, mechanically actuated strips and mechanically actuated rolls. The methods configure the slits by translating thin strips of material across the telescope focal pane. Slits are formed either by an aperture cut in the strip or by bringing two separate strips together head-to-head.
Altair is the facility adaptive optics system for the Gemini-North 8-meter Telescope. This paper gives an overview of the key mechanical systems and feature of Altair including the optical bench assembly mechanics and opto- mechanics, the instrument structure, and the electronics enclosure.
The Convex Camera Structure (CCS) is a welded Invar structure that supports of the final two optical elements in the Altair science path. The CCS assembly holds the large camera mirror, a 295 mm diameter off-axis conic, in close relation with the smaller convex mirror, a 146 mm diameter off-axis conic. The image quality requirement imposed stringent spatial tolerance between the two mirrors: +/- 45 micrometers in axial separation, +/- 70 micrometers in decenter and +/- 30 arcsecond in allowable tilt. These tolerances include contributions from initial alignment error, geometrical and dimensional changes due to gravity and temperature. This paper gives an overview of the CCS and its associated components. Flexures are integral part of the CCS assembly, they are utilized to connect the CCS to the aluminum main optical bench, the mirror to the six degree- of-freedom mount, and the 6DOF mount to the CCS end plate. The design considerations and engineering analyses of the CCS assembly are outlined.