Here PI uses its technological knowledge and long-term experience in micro- and nanopositioning technology.
To keep the optical path at its optimum, the subreflectors even out external impacts on the mechanical system. Deviations can occur, for example, with antenna tracking that compensates for global rotation, with bending of telescope components due to gravitation, or through thermal effects or wind load.
The hexapod systems with six degrees of freedom in motion are installed behind the subreflectors and allow for 6-D positioning with resolution in the submicrometer and arcsecond range. The positioning system's parallel kinematics structure is considerably more compact and stiffer than serially stacked multi-axis systems and leads to a very high resonant frequency. Since only a single platform is actuated, the moved mass is significantly smaller. This results in improved dynamics with considerably faster response.
For the hexapods in the ALMA antennas, PI developed and manufactured highly stiff and robust joints, suited for operation also in extreme ambient conditions. These hexapods can, therefore, adjust the position of the subreflectors within a travel range of several millimeters with a precision in the micrometer range.