Real time precise position control of Linear Scan Mechanism for the VELC Payload operation of the Aditya-L1 Mission

Aditya-L1 is the first Indian mission to study the solar corona and solar atmosphere. Visible Emission Line Coronagraph (VELC) onboard Aditya-L1 is a coronagraph designed to monitor the solar corona. The observation is carried out by precise movement of Linear Scan Mechanism (LSM) in linear step intervals that helps in generating the raster scan images of the solar corona to help in understanding various physical parameters of the coronal features. The coronal image quality and information of heliocentric distance depend on how precisely LSM is moved from one location to another location with high degree of repeatability even though LSM system may have backlash. In this paper, we present the design, realization challenges and its operational techniques of Linear Scan Mechanism to achieve micron level accuracy are discussed. Precision control electronics using FPGA is designed to move LSM from -1 mm to +1 mm in steps of integral multiples of $10 \mu \mathrm{~m}$ with an accuracy of $\pm 2 \mu \mathrm{~m}$.