In robotics, Learning from Demonstration (LfD) aims to transfer skills to robots by using multiple demonstrations of the same task. These demonstrations are recorded and processed to extract a consistent skill representation. This process typically requires temporal alignment through techniques such as Dynamic Time Warping (DTW). In this pa per, we consider a novel algorithm, named Spatial Sampling (SS), specifically designed for robot trajectories, that enables time-independent alignment of the trajectories by providing an arc-length parametrization of the signals. This approach eliminates the need for temporal alignment, enhancing the accuracy and robustness of skill representation, especially when recorded movements are subject to intermittent motions or extremely variable speeds, a common characteristic of operations based on kinesthetic teaching, where the operator may encounter difficulties in guiding the end-effector smoothly. To prove this, we built a custom publicly available dataset of robot recordings to test real-world movements, where the user tracks the same geometric path multiple times, with motion laws that vary greatly and are subject to starting and stopping. The SS demonstrates better performances against state-of-the-art algorithms in terms of (i) trajectory synchronization and (ii) quality of the extracted skill.

The interest in Physical Human-Robot Interaction (pHRI) has significantly increased over the last two decades, thanks to the availability of collaborative robots that ensure user safety during force exchanges. For this reason, stability concerns remain a key issue in the literature whenever new control schemes for pHRI applications are proposed. Due to the nonlinear nature of robots, stability analyses generally rely on passivity concepts and consider ideal models of robot manipulators. Therefore, the first objective of this paper is to conduct a detailed analysis of the sources of instability in proxy-based constrained admittance controllers for pHRI applications, taking into account parasitic effects such as transmission elasticity, motor velocity saturation, and actuation delay. The second objective of this paper is to perform a sensitivity analysis, supported by experimental results, to identify how the control parameters affect the stability of the overall system. Finally, the third objective is to propose an adaptation technique for the proxy parameters, with the goal of maximizing transparency in pHRI. The proposed adaptation method is validated through simulations and experimental tests.

Modular Multilevel Converters (MMCs) are one of the most interesting multilevel converter categories. In this paper, further results based on a model-based cascade MMC control architecture from our previous work, based on the concept of having time-varying average capacitor voltages in the converter arms, are presented. This architecture employs the circulating current control to enable the reduction of both the load current tracking error and harmonic content.

In this paper, the Power-Oriented Graphs (POG) technique is used to model a Hybrid Propulsion System for driving an agricultural tool. The main elements present in the system are: an ICE (Internal Combustion Engine), two PMSMs (Permanent Magnet Synchronous Electric Motors) equipped with two inverters in order to be properly driven, a planetary gear, an energy storage device and an agricultural tool. Based on the system dynamic model, a dedicated control strategy has been developed allowing to efficiently control the system by reducing the ICE specific consumption as much as possible. Simulation results showing the operation of the control strategy are finally reported and commented in detail.

In this paper, a study of the bidirectional efficiency of linear and nonlinear physical systems is performed. The methodology to compute the bidirectional efficiency map of the system is described, highlighting which is the power flow orientation giving the maximum system efficiency. The designer can therefore easily evaluate whether a physical system, such as for instance an electric machine, is more suitable for being used in forward motor mode rather than in reverse generator mode or viceversa. Three different types of physical systems are modeled and simulated in Matlab/Simulink, and the different characteristics they exhibit in terms of efficiency are highlighted. Finally, the properties that the efficiency maps exhibit if the linear system is affected by symmetric or nonsymmetric nonlinearities are studied and commented in detail.