Abstract-A Stewart platform is a kind of parallel robot which can be used for a wide variety of technological and industrial applications. In this paper, a Stewart platform designed and assembled at the Universitat Politècnica de Catalunya (UPC) by our research group is presented. The main objective is to overcome the enormous difficulties that arise when a realtime vision-based control of a fast moving object placed on these mechanisms is required. In addition, a description of its geometric characteristics, the calibration process, together with an illustrative experiment to demonstrate the good behavior of the platform is given.

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We present an advanced design methodology for pulse-width-modulated (PWM) DC-AC signal generation. Using design methods based on the Walsh transform, AC sinusoidal signals can be approximated by suitable PWM signals. For different AC amplitudes, the switching instants of the PWM signals can be efficiently computed by using appropriate systems of explicit linear equations. However, the equation systems provided by conventional implementations of this approach are typically only valid for a restricted interval of AC amplitudes and, in general, a supervised implementation of several equation systems is necessary to cover the full AC amplitude range. Additionally, obtaining suitable equation systems for designs with a large number of switching instants requires solving a complex optimization problem. In defining the constitutive pulses of a PWM signal, a suitable partition of the time interval is used as a reference system. In the new methodology, pulses are chosen to be symmetric with respect to the partition points, and the switching times are specified by means of switching ratios with respect to the endpoint subintervals. This approach leads to particularly simple Walsh series representations, introduces a remarkable computational simplification, and achieves excellent results in reducing the harmonic distortion.

The use of the Walsh transform in DC-AC PWM waveform generation allows the calculation of the switching angles by means of linear equations dependent on the fundamental amplitude. After the description of the mathematical method used to find the solutions, it is presented a method to reduce the computation time needed to find all the switching intervals that give a useful range variation of the fundamental amplitude.