SIMULATION OF A ROBOTIC ARM FOR MULTI-DIRECTIONAL 3D PRINTING

The need to investigate new solutions and novel 3D building strategies not only requires the development of new slicing algorithms and the exploitation of machines with more than 3 Dofs, but also a safe and reliable test-bench to optimize all the phases of the process. The following article describes the assessment by simulation of suitable control architectures for the realization of a Fused Deposition Modeling printer based on a 6 Dofs serial manipulator. The focus is put on the obtained position and speed profiles for unidirectional and multi-directional 3D printing to determine the week points associated with each control strategy

An innovative machine for Fused Deposition Modeling of metals and advanced ceramics

The design of a new additive manufacturing (AM) system based on extrusion and 3D deposition of a mixture of metal (or advanced ceramic) powder and polymeric binder is described in this paper. The proposed system is totally innovative in terms of combination of deposited work material, extrusion system (head and nozzle), and deposition work table, which is based on a 5-axes parallel kinematics machine (PKM). The extrusion head and nozzle have been designed in order to be able to extrude high viscosity mixtures with low polymeric content. The 5-axes PKM is aimed at obtaining a good surface quality of the deposited work and reducing the need for supports during deposition. After the deposition, the material is de-binded and sintered to nearly the density of the solid material as-cast. The design and kinematics of the machine and especially the PKM table is described in this paper, the main design issues are discussed and some preliminary extrusion and sintering results are presented

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

DESIGN AND CONTROL OF AN ACTIVE HUMANOID LEG FOR TESTING LOWER-LIMB PROSTHESES

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A 6DOF/Hil setup for wind tunnel hybrid tests on a 1/75 scale model of a 10 MW floating wind turbine

This paper deals with the design of a 6 degrees-of-freedom (DoF) robot for Hardware-In-The-Loop wind tunnel tests of floating offshore wind turbines (FOWT) and its experimental implementation. This setup allow to perform wind tunnel tests with a physical scale model of a wind turbine and to provide the motion at the base of the tower thanks to a 6-DoF Hexaslide robot with parallel kinematics. The motion is given consistently with real time combination of measurements (aerodynamic forces) and computations (hydrodynamic forces). The paper presents an overview of the design process of the robot as well as a description of the corresponding integrated numerical model based on MSC-Adams/Adwimo/MATLAB-Simulink co-simulation environment to account for the complete dynamic system (robot, wind turbine, control, HIL algorithm). The structural model of the wind turbine has been verified against the experimental modal analysis on the scale model. The complete model has been validated against a reduced order experimental setup (2-DoF), in terms of the aerodynamic forces computed in dynamic conditions (imposed motion tests) as well as HIL methodology effectively implemented for various conditions (free decay in still water and air, irregular sea state with wind). The main results of such a validation are reported showing promising extension outputs considering the ongoing extension to 6-DoF, making this tool valuable of numerical benchmark and wind tunnel design of experiments (DoE)

A Moving 3D Laser Scanner for Automated Underbridge Inspection

Recent researches have proven that the underbridge geometry can be reconstructed by mounting a 3D laser scanner on a motorized cart travelling on a walkway located under the bridge. The walkway is moved by a truck and the accuracy of the bridge model depends on the accuracy of the trajectory of the scanning head with respect to a fixed reference system. In this paper, we describe a vision-based measurement system that can be used to identify the relative motion of the cart that moves the 3D laser scanner with respect to the walkway. The orientation of the walkway with respect to the bridge is determined using inclinometers and a camera that detect the position of a laser spot, while the position of the truck with respect to the bridge is measured using a conventional odometer. The accuracy of the proposed system was initially evaluated by numerical simulations and successively verified by experiments in laboratory conditions. The complete system has then been tested by comparing the geometry of buildings reconstructed using the proposed system with the geometry obtained with a static scan. Results showed that the error is less than 6 mm; given the satisfying quality of the point clouds obtained, it is also possible to detect small defects on the surface

Rapid production of hollow SS316 profiles by extrusion based additive manufacturing

Complex shaped stainless steel tubes are often required for special purpose biomedical equipment. Nevertheless, traditional manufacturing technologies, such as extrusion, lack the ability to compete in a market of customized complex components because of associated expenses towards tooling and extrusion presses. To rapid manufacture few of such components with low cost and high precision, a new Extrusion based Additive Manufacturing (EAM) process, is proposed in this paper, and as an example, short stainless steel 316L complex shaped and sectioned tubes were prepared by EAM. Several sample parts were produced using this process; the dimensional stability, surface roughness and chemical composition of sintered samples were investigated to prove process competence. The results indicate that feedstock with a 316L particle content of 92.5 wt. % can be prepared with a sigma blade mixing, whose rheological behavior is fit for EAM. The green samples have sufficient strength to handle them for subsequent treatments. The sintered samples considerably shrunk to designed dimensions and have a homogeneous microstructure to impart mechanical strength. Whereas, maintaining comparable dimensional accuracy and chemical composition which are required for biomedical equipment still need iterations, a kinematic correction and modification in debinding cycle was proposed