A two-degree of freedom control system that is most frequently encountered in practice is the so-called Internal Model Control (IMC) structure. However, the design procedure of such a structure does not present an easy task, which implies a limited utility of IMC. In this paper two alternative solutions are proposed that may be lumped together as Model-Following Control (MFC). These are two-loop control systems being easy to implement and offering interesting properties. Theoretical assumptions have been verified experimentally on a two-joint robot manipulator. Both qualitative and quantitative results yielded by experiments are presented and discussed.
Most nonlinear control concepts used in robotics are based on a more or less accurate inverse model of the robot. In contrast to this, the design and properties of a general $n$-loop control structure based on a divided forward model of the robot, the so-called multi-loop Model Following Control Structure ($n$-MFC), is presented in this paper. Its theoretical basics and its concept are explained. The stability and robustness of the proposed control structure is analyzed. The theoretical assumptions are verified in many experiments with a two-joint robot manipulator. Qualitative as well as quantitative results of the experiments are presented and discussed.
Although numerous sophisticated nonlinear control algorithms exist in literature, it is still state of the art to use simple linear joint controllers in industrial robotic systems. Most nonlinear concepts are based on a more or less accurate inverse model of the robot. In this paper a forward-model-based control system, the so-called Model Following Control (MFC), for robot manipulators is presented. Its theoretical basics and its
concept are explained. The quality and the applicability of the MFC control concept has been analyzed in many experiments. The MFC system is compared with classical linear controllers and nonlinear feedforward controllers with respect to robustness. Qualitative as well as
quantitative results are presented and discussed.
SUMMARYThe paper deals with three robust control systems that may be regarded as a part of the model-following control (MFC) family. The systems are easy-to-synthesize control structures, thus offering an alternative to the low-robust single-loop PID system, to the relatively difficult-to-synthesize internal-model control structures, or to complex adaptive systems. A basic comparative theoretical and computational analysis of properties exhibited by the presented control structures is given. Also, recommendations as to practical implementation are provided. The solutions presented in the paper have found some application, e.g. in force/position control for an industrial robotic manipulator, temperature control of electro-heated furnaces with highly varying parameters, and oxide content control in a steam boiler. Owing to the interesting robustness properties displayed by MFC strict requirements on quality of controlled processes that are both strongly nonlinear and time variant have been met.
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