DESIGN OF MECHATRONIC SYSTEMS WITH ALIASED PLANT MODES

When digital components are combined with analog systems, frequency co mponents in the analog system which are above one-half the sampling fr equency are excited by the output of digital-to-analog (D/A) converter s and aliased to lower frequencies in analog-to-digital (A/D) conversi on. Since low-frequency components in a digital signal excite only hig her frequencies during D/A conversion which are aliased to the same lo wer frequencies during A/D conversion, the D/A converter, analog plant , and A/D converter can be modeled by an aliased frequency response fu nction (AFRF) which includes these aliased frequency effects. System i dentification using digital excitation and acquisition can identify th e AFRF directly, or it can be developed from the frequency response fu nction of the analog plant, Using this AFRF, controller design can pro ceed using conventional methods, and issues of stability, controllabil ity of aliased modes, etc., are automatically taken into account in th e design process.