ABSTRACT
The “heart” of the controller is the digital computer. The A/D converter converts a continuous-time signal into a discrete-time signal at times specified by a clock. The D/A converter, in contrast, convert the discrete-time signal output of the computer to a continuous-time signal to be fed to the plant. Digital controllers have certain disadvantages compared with analog controllers. The most significant disadvantage is due to the error introduced during sampling of the analog signals, as well as during the quantization of the discrete-time signals. The term discrete-time systems cover systems which operate directly with discrete-time signals. With regard to the maximum principle, an analogous treatment leads to the discrete-time Hamiltonian function, and from there to the discrete-time canonical Hamiltonian equations. Using this discrete-time mathematical background, one may then solve the discrete-time regulator and servomechanism problems along the same lines as those used for the case of continuous-time systems.
