## 2 Special Issue  
This Special Issue collects papers in open-access format on a broad number of aspects of robotics and vibration mechanics introduced above. The call for the Special Issue _Robotics and Vibration Mechanics_ was open from 8 May 2020 to 27 November 2021, and received 13 manuscript, 9 of which were accepted for publication, with a 69% approval rate. In most of the papers, numerical simulations are corroborated by experimental results. These articles are described in the following in order of publication.  
The paper in [18] analyzes the flexible multibody dynamics of a non-symmetric planar parallel manipulator with three degrees of freedom using the Floating Frame of Reference formulation. Numerical simulations are carried out to compare the Rayleigh-Ritz and the finite element approximations, and a sensitivity analysis is performed to investigate how to better increase the rigidity of the links.  
The authors of [19] present a multi-criteria motion planning optimization strategy for combining smoothness and speed in collaborative robotics. Thanks to the variational formalism, optimal trajectories are tested with simulations and experiments, by keeping safety requirements for human-robot collaboration into account.  
In [20], a vision-based model predictive control for a Schunk PowerCube serial robot is designed with a structured step-by-step procedure. The proposed control allows the robot to sense the environment and to be controlled with visual feedback in real-time. This approach can be suitable for multi-link flexible multibody systems, where joint angles are not sufficient to describe the state of the system due to the elasticity of the links.  
The work in [21] investigates the influence of the approach direction on the repeatability of a real industrial robot, namely an ABB IRB 1200. High-speed cameras are used to measure the range of directional deviations and determine the repeatability of the robot end-effector.  
The authors of [22] analyze the effects of end-effector compliance on impacts and collisions in robotic teleoperation. An elastic system based on a bi-stable mechanism is proposed to decouple the inertia of the tool from the inertia of the robot and mitigate the effects of potential impacts. Numerical simulations show the effectiveness of the proposed approach.  
A non-linear control strategy for flexible-link mechanisms is illustrated in [23]. The described controller is model-free and, therefore, does not require the measurement of the elastic deformation of the mechanism. The closed-loop stability of the control approach is evaluated with the Lyapunov theory, and its performance is shown with numerical simulations on a four-bar flexible robotic system.  
The paper in [24] reports the design, modelling and experimental evaluation of an amphibious robot that can move both on land and water thanks to a vibration-based mechanism, composed of a micro-DC motor with eccentric mass. Different excitation frequencies are tested on the prototype of the robot, and a good agreement between the numerical model and experimental results is found.  
In [25], the authors present a mathematical model for a Formula Student car to investigate the performance of a hydraulically interconnected suspension system with respect to a traditional one. The motion response of the vehicle is tested in simulation using a dynamic model with seven degrees of freedom for each of the two suspension architectures.  
The authors of the paper [26] analyze the performance of a reconfigurable spherical parallel mechanism dedicated to craniotomy surgery. Motion capture and force experiments are performed by a neurosurgeon to analyze the kinematic and force interaction between the robot tool and the cranium in surgery with highly real conditions.