Universal Mountable High Precision Rotary Head for Micro Degree Metrology

Abstract

Micro Angular measurement tools having the resolution in the range of 10-2 arc-second or better is required to calibrate gratings and mirrors at grazing angles (<1o). Such types of mirrors/ gratings are used for laser and synchrotron beam related experiments. With the evolvement of micro machining technique angular positioning tools in the range of 10-2 arc-second are also required. The basic tool required to measure such a high accuracy is a rotary table over which other metrological elements can be mounted i.e. laser source or target. Achieving such a high order of resolution is a challenging task. An ultra high precision universally mounted rotary mechanism, with a resolution of 0.02 arc second has been indigenously designed and developed. The total range of movement is +13o. In this design required resolution has been achieved by indirect drive. This rotary table has two stages of drive. The second stage table is rotated with respect to the rough table. The course stage is directly driven by stepper motor and gives the resolution of 26 arc-second. The fine stage is indirectly driven by a set of lower and higher pair combinations. Both the stages are motorized with feedback arrangement and controlled with a common P.C. based control console. Apart from rotary mechanism, mounting arrangements for laser source or target are also very important and should be of the same order of accuracy. Special type of mounts based on flexural design has also been developed which has four D.O.F. movements. Range of angular adjustment is +2o with a resolution of 10 arc sec. Laser source or target can be mounted on such a mount for its precise alignment with respect to the axis of rotation of rotary table. All the D.O.F. movements are manually operated.