Demonstration of High Resolution Absolute Optical Encoder by Piecewise Linear Approximation

This paper discusses the design, realization and demonstration of high resolution absolute optical encoder based on a piecewise linear estimate of the sinusoidal signals. Opto-mechanical elements are realized using maskless laser lithography technique for minimum feature size with high accuracy. The code design is done such a way that coarse bits are generated using optical resolution and fine bits are generated by electronics resolution using sin/cos tracks. One electrical cycle of sinusoidal signal is segmented as octants. In each of the octants, linear segment from sin or cos signal is alternatively used to obtain the phase information. From the phase information, high resolution position information is derived. This scheme with the optical resolution gives accurate higher resolution absolute position information. The presented method has many merits compared to the conventional resolution improvement methods like more accurate, simple to implement, easily scalable and amenable with less computational overheads. The design features, hardware realization, test strategy, experimental evaluation and test results along with the error handling are discussed in detail.