Remote Angular Measurement of Flat Targets
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This report presents a method for the remote measurement of angular position of flat surfaces, especially focussing on improving the accuracy of the measured angle. The technique is based on obtaining the temporal signature of non-linear, reflecting image patterns that are printed on to the surface of the target. The system uses a laser scanning system for reading a bar pattern, which can be represented by a pulse position modulation scheme. Angular orientation can be measured upto the distance of one meter. The complete angle measurement system comprises of a laser scanning section and a photodiode receiver which provides the raw signal which is processed by a 32-bit microcontroller using an analog to digital converter and a time base counter. The recovered digital signal from the analog to digital converter is processed to recover the rotational angle of a flat surface at a distance of 1 meter from the scanning mirror. The system has a measured angular resolution which is better than +/-0.005 degree over a 2 degree span when the printed bars are having the initial orientation from the vertical axis greater than 80° with respect to horizontal scanning axis. The angular resolution is +/- 0.05 degree for an absolute angle measurement in the range of -85 degree to +85 degree.