A Six Degree-of-Freedom-positioner for optical components

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.