Control Engineering Practice 10 (2002) 847–855 A servo control system design using dynamic inversion $ Corrado Guarino Lo Bianco*, Aurelio Piazzi Dip. di Ingegneria dell’Informazione, University of Parma, Parco Area delle Scienze, 181/A, 43100 Parma, Italy Received 6 August 2001; accepted 18 January 2002 Abstract Thispaperpresentsaninversion-basedapproachtothedesignofadcmotor-positionservosystem.Specifically,usingtherecently developed transition polynomials, a dynamic inversion procedure is established to determine a feedforward command signal to achieve high-performance position transfers. It is shown how to improve a traditional proportional and derivative controller feedback scheme and how a coordinated feedforward/feedback design using the new approach further improves the servo performances. Moreover, the methodology can easily comply with a voltage saturation avoidance constraint. Experimental results on a standard test bench highlight the effectiveness of the dynamic inversion idea. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Servo design; Dynamic inversion; Saturation avoidance control; Transition polynomials; Optimal set-point transfers; dc motors; PD controller 1. Introduction Dynamic inversion is a feedforward methodology designed to achieve high performances in the control or regulation of dynamic systems. An ideal or desired output trajectory planning is set out and then, using the inverse system, the command input that will cause the desired output can be determined. Historically, dynamic inversion was first developed in the aerospace field where possible difficulties in implementing the designed command signals were overcome due to the great technological assets of the aerospace industry (Enns, Bugajski, Hendrick, & Stein, 1994; Meyer, Hunt, & Su, 1995). Nowadays, the widespread availability of cheap microprocessors and related digital control technology makes dynamic inversion a methodology that can be profitably applied and developed for a great variety of control applications, starting from the very basic control problem of linear scalar set-point regulation. This line of control research has been recently initiated in Piazzi and Visioli (2000, 2001a-c). For multivariable plants, the first result on set-point output transitions achieved with optimal inversion- based techniques is described in Perez and Devasia (2001). In this paper, we develop a dynamic inversion approach to the design of a position servo system using a dc motor. Instrumental to this control design is the parameterized family of transition polynomials devel- oped in Piazzi and Visioli (2001b) to shape ‘‘ideal’’ position transfers. An intrinsic advantage of the proposed method is the ease with which amplitude or rate limitations on the (voltage) manipulative input can be satisfied. Moreover, the minimum-phase prop- erty of the dc motor as a system plant makes the synthesis of the command signal a straightforward operation. This paper is organized as follows. Section 2 shows how to improve an existing or classic servo control systemusingtransitionpolynomialsandinversion-based feedforward.Section3furtherimprovestheservodesign by means of a combined feedforward/feedback design procedure. Experimental results are presented in Section 4 using standard laboratory equipments. An analysis of the performances against an artificially perturbed plant is also included. Section 5 reports concluding remarks. $ This work was partially supported by MURST scientific research funds under the framework of a COFIN 2000 project. *Corresponding author. Tel.: +39-0521-905752; fax: +39-0521- 905723. E-mail address: guarino@ce.unipr.it (C. Guarino Lo Bianco). 0967-0661/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0967-0661(02)00036-9