## 2 Modelling and Control of Mechatronic and Robotic Systems  
This Special Issue of the journal Applied Sciences encompasses the kinematic and dynamic modelling, analysis, design, and control of mechatronic and robotic systems, with the scope of improving their performance, as well as simulating and testing novel devices and control architectures. A broad range of disciplines are included, such as robotic manipulation, mobile systems, cable-driven robots, wearable and rehabilitation devices, variable stiffness safety-oriented mechanisms, optimization of robot performance, and energy-saving systems. Several papers deal with control problems, applied to both robotic systems and mechanical vibrations. In paper [7], a novel sliding mode control algorithm is presented and applied for the trajectory tracking on a robotic manipulator with 3 degrees of freedom (DOF). The proposed controller runs without a precise dynamic model in the presence of uncertainties and enhances the response, fast convergence time, and accuracy of the tracking position. The main goal of paper [8] is the design, simulation, and experimental verification of an adaptive feed-forward motion control for a hydraulic differential cylinder. The proposed solution is implemented on a hydraulic loader crane. Experimental results show the advantage of the proposed controller in reducing the cylinder position error and the adaptation to model uncertainties. The authors in [9] present the modelling and control of a cable-suspended sling-like parallel robot for throwing a mass at a suitable time. The mass is carried at the end-effector by a gripper, which releases the mass so that it can reach a given target point. Mathematicalmodels, which also account for the effect of cable elasticity, provide guidelines for planning the trajectory. In [10], a 8-DOF integrated model of a semi-active seat suspension with a human model over a quarter is presented. A fuzzy logic-based self-tuning PID controller allows to regulate the controlled force on the basis of sprung mass velocity error and its derivative as input. Simulation results show that the semi-active seat suspension improves the ride comfort significantly by reducing the head acceleration compared to passive seat suspensions. Moreover, in [11], the authors investigate the control of the over-critical vibration of a transmission shaft system with a device named Smart Spring, an active vibration control mechanism based on piezoelectric material. Simulation results based on a model implemented in ADAMS and MATLAB show the feasibility of the approach in reducing the vibration of the shaft system. Papers [12; 13] deal respectively with trajectory optimization and with a novel kinematic directional index for industrial manipulators. In particular, in [12] a \"chip-lashing\" method is proposed to optimize the trajectory in order to increase the velocity of individual robot parts, thereby minimizing motion cycle times and exploiting the torque of the joints more effectively. The efficiency of the method is confirmed by simulation results on a 5-DOF RV-2 AJ manipulator. In [13], a novel method is proposed for evaluating the maximum speed that a serial robot can reach with respect to both the position of the robot and its direction of motion. This approach, called Kinematic Directional Index, is experimentally applied to a SCARA robot and to an articulated robot with 6-DOF to outline their performances. Paper [14] presents an energy-saving system based on a prefill system and a buffer system to improve the energy efficiency and the processing performance of hydraulic presses. Experimental results demonstrate that the proposed system could reduce the installed power and pressure shock, increase energy efficiency, and provide the same processing characteristics as the traditional hydraulic press. Several papers in this Special Issue are focused on the design, modelling, and control of mobile robots and systems.