Enrico Fiore

On the functional design of the DTU10 MW wind turbine scale model of LIFES50+ project

This paper illustrates the mechatronic design of the wind tunnel scale model of the DTU 10MW reference wind turbine, for the LIFES50+ H2020 European project. This model was designed with the final goal of controlling the angle of attack of each blade by means of miniaturized servomotors, for implementing advanced individual pitch control (IPC) laws on a Floating Offshore Wind Turbine (FOWT) 1/75 scale model. Many design constraints were to be respected: among others, the rotor-nacelle overall mass due to aero-elastic scaling, the limited space of the nacelle, where to put three miniaturized servomotors and the main shaft one, with their own inverters/controllers, the slip rings for electrical rotary contacts, the highest stiffness as possible for the nacelle support and the blade-rotor connections, for ensuring the proper kinematic constraint, considering the first flapwise blade natural frequency, the performance of the servomotors to guarantee the wide frequency band due to frequency scale factors, etc. The design and technical solutions are herein presented and discussed, along with an overview of the building and verification process. Also a discussion about the goals achieved and constraints respected for the rigid wind turbine scale model (LIFES50+ deliverable D.3.1) and the further possible improvements for the IPC-aero-elastic scale model, which is being finalized at the time of this paper.

Dynamics Modeling and Accuracy Evaluation of a 6-DoF Hexaslide Robot

Parallel Robots are commonly preferred in place of Serial Robots for tasks in which the working volume is limited, compared to the overall extension of the machine, but where the accuracy requirements are very high. In fact, since the errors do not sum together in series, the positive effect of the closed-loop linkages arrangement is a lower overall sensitivity of the end-effector positioning to the various sources of error. The precision depends on many factors among which the flexibility of the components plays a fundamental role. This paper investigates the contribution of belt-driven and screw-ball-driven linear transmission systems to the overall flexibility of the HexaSlide parallel architecture, using an ADAMSⓇmodel. The six Degrees-of-Freedom (DoF) of its mobile platform are provided through the actuation of the same number of Linear Transmission Units (LTUs), fixed to the base, while its links have fixed length. The LTUs are integrated together in the robot. The first eigenfrequencies are mapped in a systematic manner over the whole workspace, using a discretized grid of poses.

Error Analysis and Adaptive-Robust Control of a 6-DoF Parallel Robot with Ball-Screw Drive Actuators

Parallel kinematic machines PKMs are commonly used for tasks that require high precision and stiffness. In this sense, the rigidity of the drive system of the robot, which is composed of actuators and transmissions, plays a fundamental role. In this paper, ball-screw drive actuators are considered and a 6-degree of freedom DoF parallel robot with prismatic actuated joints is used as application case. A mathematical model of the ball-screw drive is proposed considering the most influencing sources of nonlinearity: sliding-dependent flexibility, backlash, and friction. Using this model, the most critical poses of the robot with respect to the kinematic mapping of the error from the joint- to the task-space are systematically investigated to obtain the workspace positional and rotational resolution, apart from control issues. Finally, a nonlinear adaptive-robust control algorithm for trajectory tracking, based on the minimization of the tracking error, is described and simulated.

Workspace Limiting Strategy for 6 DOF Force Controlled PKMs Manipulating High Inertia Objects

This article describes an efficient and effective strategy for limiting the workspace of a six degrees of freedom parallel manipulator, with challenging motion smoothness requirements due to both the high inertia objects carried by the end effector and the pose references coming from a force feedback loop. Firstly, a suitable formulation of the workspace is studied, distinguishing between different conventions and procedures. Thereafter a discrete and analytical formulation of the workspace is obtained and developed in order to suit this application. Having obtained the limits, a methodology to evaluate the robot pose is discussed, taking into account the reference pose buffering technique and the real time pose estimation through the numeric solution of the nonlinear forward kinematics equations. The safety algorithm designed checks the actual robot pose and future poses to be commanded, and takes control of the reference pose generation process, if an exit of the safety workspace is detected. The result obtained is a soft compliant surface within which the robot is free to move, but outside of which a “force field” pushes the robot end-effector to return smoothly. To reach this objective, the control deflects the end effector trajectory safely and smoothly and moves it back to within the workspace limits. Nevertheless, this preserves the continuity of the velocity and controls the acceleration, to avoid dangerous vibrations and shocks. Simulation and experimental result tests are conducted to verify the algorithm effectiveness and the efficient implementation.

Dimensional synthesis of a 5-DOF parallel kinematic manipulator for a 3d printer

Additive manufacturing is a growing method for the industrial production. New methods have been developed and in particularly methods for the production of metal parts to a minimum cost. Innovative approach is the use of a MIM technique for 3D printing which requires a suitable kinematics for its movements. The main purpose of this article is the kinematic optimization of a 5Dofs PKM robot for additive manufacturing. Its been studied the kinematics of the robot and used a genetic algorithm to optimize the parameters of the machine in order to cover a specified workspace, furthermore design of the robot and outline of the control system are given.

An Innovative Method for Sizing Actuating Systems of Manipulators with Generic Tasks

This paper describes an innovative method for the design of the driving system for manipulators whose task is a generic handling within a workspace, in particular robotic simulators. For those mechanisms the choice of an actuating system of the correct size is particularly arduous. As a matter of fact, tipically the requirements for the machine are described in the workspace, but the intrinsically complex kinematics make difficult to understand which is the case that requires the highest dynamic performances. Analyzing all the possible combinations of the parameters that characterize the motion of the end-effector would require an incredible computational burden, and that’s the reason why a statistical method is taken into account: in particular the sizing process described in this paper relies on the Monte Carlo Method. In order to show the its effectiveness, its implementation in a particular application is presented.

The "robot mechanics" course experience at Politecnico di Milano

This paper is aimed at describing the authors experience on developing a practical robotic course for students of the last year of Master of Science in Mechanical Engineering at Politecnico di Milano. The course is born from the will to satisfy the request of a course where students are able to put into practice all concepts acquired during theoretical lessons. The aim of the course is to design a 3-DoF robot with a given architecture. The subject is intrinsically interdisciplinary, so students, organized in groups, are require to focus their attention on different aspects related to the design of a robotic device, from the modeling of structural components using CAD programs, to the dynamic analyses of the system and to the development of the control software.

Multibody/FEM Numerical Tool for HIL Scaled Offshore Wind Turbine

Nowadays the study of the renewable sources of energy is one of the most important lines of research. For this reason the wind tunnel researchers of Politecnico di Milano want to apply new hardware in the loop approach to study floating offshore wind turbines scale models by reproducing at the same time both the aerodynamic and hydrodynamic phenomena involved. These experiments allow to have a better understanding of the operating conditions of these structures and to properly set the control algorithm for the blades pitch in order to have a better exploitation of the wind stream. In addition the results of the experimental phase could be used to validate the numerical codes. While it is possible to physically reproduce the wind profile with a good approximation, the sea waves effect has to be simulated by means of a 6-DoF parallel kinematic machine. The result is a coupled system in which two flexible structures, the turbine and the robot, cannot be regarded as two separate entities. The aim of this paper is to provide a multibody model to perform dynamic analysis of this coupled system and to study how the pose of the manipulator and the wind profile affect the results.