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This paper presents a new interpolation method suitable for increasing the measurement resolution obtainable from quadrature encoder signals. Based on the existing sinusoidal signals, high-order sinusoids can be derived, from which binary pulses can be generated, which can be decoded using only standard servo controllers for position information. A look-up table, constructed off-line, serves as the inferencing engine for the proposed method. Imperfections in the encoder signals can be directly compensated for in the look-up table, including mean and phase offsets, amplitude difference, and waveform distortion. Simulation and experimental results are provided in this paper.

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An enhanced automatic tuning procedure developed for process control of PI and PID controllers addresses several potential problems present in current standard autotuners. The proposed enhanced autotuner uses a novel technique based on relay feedback to estimate the process frequency response at two specified phase lags on the Nyquist curve automatically. An iterative procedure then uses these two points to obtain a transfer--function model of the process. Based on this model and a controller-selection scheme, an appropriate controller (PI or PID) is applied to the process automatically. The controller is tuned so that the Nyquist curve of the compensated system is appropriately shaped to satisfy a combined gain and phase-margin type of specGcation. The effectiveness of this enhanced autotuner is demonstrated both in simulations and in real-time experiments for level control of a coupled-tanks system. frequency can be identified. When the critical point, that is, the ultimate gain and frequency, is known, it is straightforward to apply the classic Ziegler-Nichols tuning rules (1943)

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