Closed-Loop Tracker for Target-Oriented and Twisting Heliostats

Abstract

This thesis presents the design of a closed-loop tracker for target-oriented and twisting heliostats. To be effective twisting heliostats need a pointing accuracy of less than 0.5 milliradians on average. To achieve this goal two avenues were explored: a method of closed-loop control that utilized a fisheye lens and a method of closed-loop control that utilized a beamsplitter. The fisheye scenario included the use of LEDs on the target and a glass filter aligned with the spectral output of the LEDs to attempt to make both the LED and the sun appear not saturated in a single exposure from the fisheye camera. This method proved unwieldy. The second method utilized the beamsplitter with a cone lens camera. By utilizing the fact that the heliostat is target-oriented the beamsplitter allows for closed-loop control by keeping the disc image of the sun through the beamsplitter on the reflected image of the target. This method proved successful and closed loop tracking with errors in the x-axis of 0.36 milliradians and in the y-axis of 0.15 milliradians were achieved.