AN EVALUATION OF SEVERAL CONTROLLER SYNTHESIS METHODOLOGIES USING A ROTATING FLEXIBLE BEAM AS A TEST-BED

The objective of this study is to assess the effectiveness of a number of control system synthesis methodologies as practical design tools. The effectiveness is measured by the extent to which a controller obta ined by a specific methodology has to be tuned for it to work in a rea l implementation For this purpose we consider as a test bed a highly f lexible beam attached to a d.c. motor driven rigid hub. Included in th e study are five synthesis methodologies. They are (i) classical PD co ntrol, (ii) the LQR technique, (iii) robust servomechanism theory, (iv ) the Lyapunov method, and (v) Quantitative Feedback Theory (QFT). Use d are Extensive computer simulations and actual experiments with each of the controllers synthesized using these methodologies. Each of the compensators performed satisfactorily in simulations In actual impleme ntation, however, some of the controllers did not. work as predicted b y simulations. The higher the d.c. gain and the bandwidth of the synth esized controller it is less likely to work in reality. This was clear ly observed with the LQR controller, the servo controller and the Lyap unov based controllers. The QFT controller is the only one that accoun ted for the bandwidth limit at the synthesis stage. The other controll ers require much fine tuning by trial and error for satisfying actual physical limits including the bandwidth. It is established that contro llers designed using methodologies which incorporate real practical co nsiderations such as modeling uncertainties, bandwidth limitations and input saturations need very little toning whereas the others yield co ntrollers which after tuning are quite different from the synthesized ones.