Digital Speed Control

Contemporary motion control systems comprise discrete-time speed and position controllers. This chapter restates the basic concepts of discretetime control, and provides the means to analyze, design, implement, and evaluate discrete-time speed controllers. The sampling process is reviewed and explained. The system dynamics are described in terms of difference equations. The z-transform is introduced as the means of converting the difference equation into an algebraic form, thus simplifying the analysis, design, and performance prediction of discrete-time controllers. The ztransform definition and properties are restated. Before discussing and designing the structure of discrete-time speed controllers, the signal flow between the discrete-time controller and continuous-time control object is explained and detailed. The optimization rule is devised and the parameter setting procedure proposed. In closing sections of the chapter, the large step response is analyzed, explaining the system limits and the wind-up phenomenon. The speed controller structure is enhanced in order to preserve the response character and avoid overshoots and oscillations with large input and load disturbances.