Automated dimensional synthesis of a portable sky scanner for measuring light pollution

Light pollution is often measured by a photometric sensor network distributed in the area of interest. However, photometric sensors usually have a narrow view angle, making difficult to perform measurements at low elevation angles. Furthermore, short-term variations are not significant; hence, a low-cost solution is to displace a portable device, able to scan the sky in a range of azimuth and zenith angles, to different locations of interest. The device should be designed with the aim of characterizing the emission function from ground based light sources, which is decreasing in intensity with respect to the zenith. In this manuscript, we propose to find the dimensions of a fourbar linkage mechanism that best fits the scanning task via an optimization problem, solved with an estimation of distribution algorithm. The optimization algorithm proposes configurations with different lengths and reference positions of four-bar linkage mechanisms; then, it measures the distance between points in the actual path and points in the desired path for each configuration. The objective function value is the sum of such distances; thus, the optimal design produces the minimum distance to the desired path. This proposal for automated design reduces the working time and experience requirements of a human designer, and trial-and-error design intends, by determining adequate dimensions for the mechatronic system. A CAD model and a simulation demonstrate the design feasibility and the high accuracy of the resulting device.