A Framework to Illustrate Kinematic Behavior of Mechanisms by Haptic Feedback

The kinematic properties of mechanisms are well known by the researchers and teachers. The theory based on the study of Jacobian matrices allows us to explain, for example, the singular configuration. However, in many cases, the physical sense of such properties is difficult to explain to students. The aim of this article is to use haptic feedback to render to the user the signification of different kinematic indices. The framework uses a Phantom Omni and a serial and parallel mechanism with two degrees of freedom. The end-effector of both mechanisms can be moved either by classical mouse, or Phantom Omni with or without feedback

Study of Control Strategies for Robot Ball Catching

La tesi riguarda lo studio di un possibile scenario per la cattura di una palla con un braccio robotico usando tecnologie disponibili e considerando due problemi principali: studiare differenti strategie di controllo per il braccio robotico al fine di catturare la palla (controllo predittivo e prospettivo); implementare un simulatore in ROS che simula il robot reale, includendo un sistema di visione per riconoscere e tracciare la palla usando il sensore Microsoft Kinect, con diverse simulazion

Design and development of an Autonomous Mobile Robot (AMR) based on a ROS controller

openAn Autonomous Mobile Robot is a robot that runs and navigates by itself without human intervention. AMRs are foundamental for automating materials handling into warehouses. This thesis work ex- plains the procedure followed for designing and developing an AMR. The hardware components are chosen considering the way in which the robot will be controlled. A layered controlling approach is used. The high-level controller is a mini PC running ROS nodes. The ROS controller manages the actions that drivers have to perform and the data received from sensors. The medium-level controller translates the actions into signals that will be sent to the low-level controllers. The medium-level controller is an Arduino Mega, which sends PWM signals for controlling the speed of two BLDC motor wheels. The low-level controllers are two BLDC motor drivers that power, sense and drive the motor wheels. The Arduino implements a PI controller on the speed of rotation of each motorized wheel. Real tests are per- formed on the robot in order to evaluate the efficiency of the control- ling system. A future implementation consists in an integration of a LiDAR sensor in order to execute a SLAM algorithm, which will allow the robot to move autonomously in a space with obstacles.An Autonomous Mobile Robot is a robot that runs and navigates by itself without human intervention. AMRs are foundamental for automating materials handling into warehouses. This thesis work ex- plains the procedure followed for designing and developing an AMR. The hardware components are chosen considering the way in which the robot will be controlled. A layered controlling approach is used. The high-level controller is a mini PC running ROS nodes. The ROS controller manages the actions that drivers have to perform and the data received from sensors. The medium-level controller translates the actions into signals that will be sent to the low-level controllers. The medium-level controller is an Arduino Mega, which sends PWM signals for controlling the speed of two BLDC motor wheels. The low-level controllers are two BLDC motor drivers that power, sense and drive the motor wheels. The Arduino implements a PI controller on the speed of rotation of each motorized wheel. Real tests are per- formed on the robot in order to evaluate the efficiency of the control- ling system. A future implementation consists in an integration of a LiDAR sensor in order to execute a SLAM algorithm, which will allow the robot to move autonomously in a space with obstacles

Ball catching by a puma arm : a nonlinear dynamical systems approach

We present an attractor based dynamics that autonomously generates temporally discrete movements and movement sequences stably adapted to changing online sensory information. Autonomous differential equations are used to formulate a dynamical layer with either stable fixed points or a stable limit cycle. A neural competitive dynamics switches between these two regimes according to sensorial context and logical conditions. The corresponding movement states are then converted by simple coordinate transformations into spatial positions of a robot arm. Movement initiation and termination is entirely sensor driven. In this article, the dynamic architecture was changed in order to cope with unreliable sensor information by including this information in the vector field. We apply this architecture to generate timed trajectories for a Puma arm which must catch a moving ball before it falls over a table, and return to a reference position thereafter. Sensory information is provided by a camera mounted on the ceiling over the robot. We demonstrate that the implemented decisionmechanism is robust to noisy sensorial information. Further, a flexible behavior is achieved. Flexibility means that if the sensorial context changes such that the previously generated sequence is no longer adequate, a new sequence of behaviors, depending on the point at which the changed occurred and adequate to the current situation emerges

On Robotic Work-Space Sensing and Control

Industrial robots are fast and accurate when working with known objects at precise locations in well-structured manufacturing environments, as done in the classical automation setting. In one sense, limited use of sensors leaves robots blind and numb, unaware of what is happening in their surroundings. Whereas equipping a system with sensors has the potential to add new functionality and increase the set of uncertainties a robot can handle, it is not as simple as that. Often it is difficult to interpret the measurements and use them to draw necessary conclusions about the state of the work space. For effective sensor-based control, it is necessary to both understand the sensor data and to know how to act on it, giving the robot perception-action capabilities. This thesis presents research on how sensors and estimation techniques can be used in robot control. The suggested methods are theoretically analyzed and evaluated with a large focus on experimental verification in real-time settings. One application class treated is the ability to react fast and accurately to events detected by vision, which is demonstrated by the realization of a ball-catching robot. A new approach is proposed for performing high-speed color-based image analysis that is robust to varying illumination conditions and motion blur. Furthermore, a method for object tracking is presented along with a novel way of Kalman-filter initialization that can handle initial-state estimates with infinite variance. A second application class treated is robotic assembly using force control. A study of two assembly scenarios is presented, investigating the possibility of using force-controlled assembly in industrial robotics. Two new approaches for robotic contact-force estimation without any force sensor are presented and validated in assembly operations. The treated topics represent some of the challenges in sensor-based robot control, and it is demonstrated how they can be used to extend the functionality of industrial robots

The role of turbulence in particle-fluid interaction as induced by the outer geometry of catching-type precipitation gauges

This thesis work investigates the particle-fluid interaction of hydrometeors along the terminal part of their fall trajectories, while approaching the collector of catching-type precipitation gauges in windy conditions. Both the turbulence generated by the bluff body aerodynamics of precipitation gauges when impacted by the wind and the free-stream turbulence inherent to the natural wind are addressed to assess their role in precipitation measurements. The bluff body aerodynamics of precipitation gauges induces deviations in the trajectories of the approaching hydrometeors due to the acceleration, updraft and turbulence development upstream and above the collector of the gauge. The resulting wind-induced errors were studied in the literature using different approaches \u2013 field measurement campaigns, numerical simulations and wind tunnel experiments. In this work, the numerical approach based on Computational Fluid Dynamic (CFD) simulation, which reduces, when compared with field observations, the time and resources needed to investigate different configurations by varying the wind speed, type of precipitation and gauge geometry, is employed. A Lagrangian Particle Tracking (LPT) model provides the catch ratios as a function of the particle size and wind speed. The LPT model, already available from the literature, was adapted to simulate the trajectories of water droplets when falling through the atmosphere and approaching the gauge collector by parameterizing liquid particles with spherical shape and using suitable drag coefficient equations. The first part of the work aims to validate the numerical approach against a dedicated, innovative and robust experimental campaign obtained by means of Wind Tunnel (WT) experiments (flow velocity measurements, Particle Image Velocimetry and video tracking of water drops) conducted in the wind tunnel facilities available at DICCA and at Politecnico di Milano (within the PRIN 20154WX5NA project). The video tracking experimental setup allowed to compare observed and simulated trajectories under various wind velocity and drop size conditions, and to validate the Lagrangian Particle Tracking model, here adapted to simulate particles falling at a different vertical velocity than the terminal one. Comparison and validation of numerical simulation results against field-measured data introduce the problem of confronting this simplified approach with the natural atmospheric conditions actually affecting operational instruments in the field. Natural wind fields are indeed characterized by turbulent fluctuations, especially near to the ground where precipitation gauges are located. Dedicated CFD simulations with various turbulence generating solutions, based on imposing specific boundary conditions or inserting suitable obstacles designed to achieve the desired level of free-stream turbulence upstream of the gauge, were performed. Wind tunnel measurements were performed in the DICCA facility using, as a turbulence-generating device, a fixed solid fence with a regular square mesh inserted upstream of a calyx shaped gauge. CFD simulations were performed reproducing the same conditions and results were validated by comparison with WT measurements. The comparison between the uniform and turbulent free-stream conditions showed that the normalized updraft in the upwind part, upstream of the centre of the collector, and the downdraft in the downwind part are less accentuated in the turbulent free-stream configuration than in uniform free-stream conditions. This is ascribable to the energy dissipation induced by turbulent fluctuations. The dissipative effect of the free-stream turbulence also has a damping role on the acceleration of the flow above the collector as demonstrated by CFD results. The overall free-stream turbulence effect on the collection performance of the gauges was quantified by computing and comparing the Collection Efficiency (CE) values in uniform and turbulent free-stream conditions. Results demonstrated that the CE values are higher in turbulent free-stream conditions. The effect of the free-stream turbulence on the collection efficiency of the Hotplate\ua9 snow gauge was investigated, and the literature turbulence intensity level (from 8istad, 2015) impacting on the gauge by was obtained in the simulation by imposing a constant turbulent kinetic energy value as a boundary condition upstream of the gauge. The calculated catch ratios are larger for the free-stream turbulence condition with respect to the uniform one for all characteristic sizes of snowflakes. Consequently, the same effect was observed in the calculated CE values. In addition, in order to introduce a realistic level of turbulence at the gauge collector elevation in the simulation, wind speed measurements obtained from a 3D ultrasonic anemometer in the Nafferton Farm site (UK), recorded at high frequency (20 Hz) and at the gauge elevation, were analysed to calculate the free-stream turbulence intensity values for various wind speeds. This was used to perform a CFD simulation on a chimney shaped gauge and to calculate its effect on the collection performance. To better reproduce the decay of the turbulence intensity in space and its effect on the gauge, Large Eddy Simulations (LES) were also performed in both uniform and turbulent free-stream conditions while simulating the trajectories of solid precipitation particles, which are more sensitive than raindrops to the turbulent fluctuations. Results, in terms of the catch ratio for each characteristic size of snowflakes, show a different behaviour when compared to the uniform conditions. A larger free-stream turbulence intensity induces a more pronounced undercatch for small size particles (less than 2 mm) with respect to the uniform case, while the undercatch is reduced for larger particles. This is due to the greater aptitude of the small size particles to follow the turbulent velocity fluctuations, while larger particles are more inertial, and to the reduced velocity components that particles cross in turbulent free-stream conditions near the gauge body. The obtained CE values are higher in turbulent free-stream conditions, confirming the observations already obtained for the airflow features, where a potential overestimation of the undercatch obtained in uniform free-stream conditions was hypothesized. Based on the CFD results and on the validation provided by wind tunnel observations it is possible to conclude that accounting for the free-stream airflow turbulence in the simulation is required to avoid underestimation of the collection efficiency of precipitation gauges. A turbulent free-stream is indeed the natural atmospheric condition of the wind impacting on operational precipitation gauges in the field. This work demonstrates that numerical derivation of correction curves for use in precipitation measurements as proposed hitherto in the literature is affected by a systematic overestimation of the wind-induced error due to the simplifying assumption of uniform free-stream conditions. Finally, in order to achieve results that can be used in an operational context, suitable Collection Efficiency (CE) curves and the associated adjustment curves, which directly provide the expected undercatch as a function of the wind speed and the measured precipitation intensity, were derived for two sample measurement instruments. The first one is best suited for rainfall measurements and is characterised by the common cylindrical shape of traditional catching type gauges, therefore a numerical formulation of the CE curves as a function of rainfall intensity is proposed. The second one, the Hotplate\ua9 gauge, is best suited for snowfall measurements and is characterised by an innovative measuring principle implying a dedicated geometry of the sensor. In this case, the numerically derived CE curves are expressed as a function of snowfall intensity. For the typical cylindrical gauge, the residual dependency of the CE curves on the rainfall intensity was investigated in order to obtain a single CE expression as a function of both the rainfall intensity and wind speed. The parameters of the Particle Size Distribution (PSD) for various classes of the RI were derived by literature data from the Italian territory. Then the variation of the PSD parameters as a function of the RI was obtained, and subsequently also the parameters of the sigmoidal curves, used to fit the numerical CE values, were parametrized with the RI. As a result, easy to use adjustment curves as a function of both the measured rainfall intensity and wind speed were derived. In the case of the Hotplate\ua9 snow gauge, the shape of the CE curves differs from the typical sigmoidal one due to its complex geometry. At low wind speed, the aerodynamic response of the gauge is predominant and CE values decrease with increasing the wind speed up to a wind threshold value beyond which the geometrical effect on the collection performance starts to be relevant and the CE increases. At very high wind speeds the geometrical contribution prevails and the CE becomes even larger than one

Robotics of human movements

The construction of robotic systems that can move the way humans do, with respect to agility, stability and precision, is a necessary prerequisite for the successful integration of robotic systems in human environments. We explain human-centered views on robotics, based on the three basic ingredients (1) actuation; (2) sensing; and (3) control, and formulate detailed examples thereof