## 2 Special Issue Topics
A Bode plot-based tuning method for the PII\({}^{1/2}\)DD\({}^{1/2}\) controller is proposed and then applied to the position control of a mechatronic axis, both in simulation and experimentally. The results show that the use of the proposed scheme results in a remarkable reduction in the position error with respect to the PID, with similar control effort and maximum torque. As in [22], papers [23; 24] also discuss fractional-order (FO) controllers. The work in [23] focusses on the use of FO controllers for a two-DOF flexible manipulator, and undertakes simulations with noise and square wave input. Results show that the FO controllers fit better with the system properties than integer-order controllers. Paper [24] shows an example of a combination of different control techniques; it proposes a fast FO terminal sliding mode control (FFOTSMC) for a seven-degree-of-freedom manipulator with tracking control. The new controller applies the FO derivative on both the sliding surface design and the sliding control/reaching law. Stability analysis is analysed using Lyapunov functions for FO systems. The controller performance is evaluated by simulation on a single-input single-output system model in MATLAB Simulink, and by experiments on a robot manipulator. The topics of papers [25; 26; 27] are miscellaneous. Paper [25] proposes a novel analysis and design methodology of miniaturized inductive sensors with a large measuring range and nanoscale resolution. Firstly, an accurate leakage inductance model is established. Secondly, a design rule for the armature size is proposed by considering the fringing effect. Then, the error terms introduced by the measurement circuit of differential inductive sensors are analysed, and corresponding error suppression methods are described. Paper [26] deals with clinical analyses to evaluate balance control performance, and in particular with experimental protocols and devices that can provide reliable information about the ability of a subject to maintain balance. A test bench, supported by model simulations, was developed to test the proposed perturbation device. The performance of the control logic has been optimized by iterative tuning of the controller parameters, and the resulting behaviour of the automatic perturbator is discussed. Paper [27] illustrates a method to prove the stability of a generic neural network a posteriori and its application in a state-of-the-art recurrent neural network architecture. The proposed method relies on identifying the poles associated with the designed network starting from the input/output data. Providing a framework to guarantee the stability of any neural network architecture, combined with their generalizability and applicability in different fields, can significantly expand their use in dynamic system modelling and control. Overall, the accepted papers illustrate a wide variety of alternative approaches and methods for improving the performance of mechatronic and robotic systems, with possible additional applications in related emerging fields, such as biomechanics. The Guest Editor expects and hopes that the articles published in this Special Issue will contribute significantly to forming the backbone of systematic developments in this research field. The Guest Editor acknowledges the high quality of the received contributions and thanks the authors for their efforts in preparing papers. Furthermore, he thanks the reviewers for their valuable contribution to maintain the high-quality standard of this journal. The authors declare no conflict of interest.