Study and application of motion measurement methods by means of opto-electronics systems - Studio e applicazione di metodi di misura del moto mediante sistemi opto-elettronici

This thesis addresses the problem of localizing a vehicle in unstructured environments through on-board instrumentation that does not require infrastructure modifications. Two widely used opto-electronic systems which allow for non-contact measurements have been chosen: camera and laser range finder. Particular attention is paid to the definition of a set of procedures for processing the environment information acquired with the instruments in order to provide both accuracy and robustness to measurement noise. An important contribute of this work is the development of a robust and reliable algorithm for associating data that has been integrated in a graph based SLAM framework also taking into account uncertainty thus leading to an optimal vehicle motion estimation. Moreover, the localization of the vehicle can be achieved in a generic environment since the developed global localization solution does not necessarily require the identification of landmarks in the environment, neither natural nor artificial. Part of the work is dedicated to a thorough comparative analysis of the state-of-the-art scan matching methods in order to choose the best one to be employed in the solution pipeline. In particular this investigation has highlighted that a dense scan matching approach can ensure good performances in many typical environments. Several experiments in different environments, also with large scales, denote the effectiveness of the global localization system developed. While the laser range data have been exploited for the global localization, a robust visual odometry has been investigated. The results suggest that the use of camera can overcome the situations in which the solution achieved by the laser scanner has a low accuracy. In particular the global localization framework can be applied also to the camera sensor, in order to perform a sensor fusion between two complementary instrumentations and so obtain a more reliable localization system. The algorithms have been tested for 2D indoor environments, nevertheless it is expected that they are well suited also for 3D and outdoors

On the Feedback Control of Hitch Angle through Torque-Vectoring

This paper describes a torque-vectoring (TV) algorithm for the control of the hitch angle of an articulated vehicle. The hitch angle control function prevents trailer oscillations and instability during extreme cornering maneuvers. The proposed control variable is a weighted combination of terms accounting for the yaw rate, sideslip angle and hitch angle of the articulated vehicle. The novel control variable formulation results in a single-input single-output (SISO) feedback controller. In the specific application a simple proportional integral (PI) controller with gain scheduling on vehicle velocity is developed. The TV system is implemented and experimentally tested on a fully electric vehicle with four on-board drivetrains, towing a single-axle passive trailer. Sinusoidal steer test results show that the proposed algorithm significantly improves the behavior of the articulated vehicle, and justify further research on the topic of hitch angle control through TV

Study and application of motion measurement methods by means of opto-electronics systems - Studio e applicazione di metodi di misura del moto mediante sistemi opto-elettronici

This thesis addresses the problem of localizing a vehicle in unstructured environments through on-board instrumentation that does not require infrastructure modifications. Two widely used opto-electronic systems which allow for non-contact measurements have been chosen: camera and laser range finder. Particular attention is paid to the definition of a set of procedures for processing the environment information acquired with the instruments in order to provide both accuracy and robustness to measurement noise. An important contribute of this work is the development of a robust and reliable algorithm for associating data that has been integrated in a graph based SLAM framework also taking into account uncertainty thus leading to an optimal vehicle motion estimation. Moreover, the localization of the vehicle can be achieved in a generic environment since the developed global localization solution does not necessarily require the identification of landmarks in the environment, neither natural nor artificial. Part of the work is dedicated to a thorough comparative analysis of the state-of-the-art scan matching methods in order to choose the best one to be employed in the solution pipeline. In particular this investigation has highlighted that a dense scan matching approach can ensure good performances in many typical environments. Several experiments in different environments, also with large scales, denote the effectiveness of the global localization system developed. While the laser range data have been exploited for the global localization, a robust visual odometry has been investigated. The results suggest that the use of camera can overcome the situations in which the solution achieved by the laser scanner has a low accuracy. In particular the global localization framework can be applied also to the camera sensor, in order to perform a sensor fusion between two complementary instrumentations and so obtain a more reliable localization system. The algorithms have been tested for 2D indoor environments, nevertheless it is expected that they are well suited also for 3D and outdoors.La tesi affronta il problema della localizzazione di veicoli in ambienti non strutturati mediante sistemi di misura che, montati a bordo del veicolo, non richiedono modifiche dell'ambiente di navigazione. La scelta è ricaduta su due strumenti opto-elettronici largamente utilizzati, camera e Laser Range Finder (LRF), i quali consentono di effettuare misure senza contatto e quindi non intervenire sull'ambiente. Particolare attenzione è stata posta alla definizione di una serie di procedure per l'elaborazione dei dati acquisiti da questa strumentazione al fine di ottenere delle informazioni affidabili e robuste alle sorgenti di rumore ambientali. Un importante contributo di questo lavoro è lo sviluppo di un procedura di associazione robusta ed affidabile che consente di tener conto di tutti gli aspetti probabilistici in maniera tale da poter essere utilizzata in un algoritmo di localizzazione globale SLAM basato sulla teoria dei grafi e fornire una stima ottimale del moto del veicolo. Inoltre, la localizzazione del veicolo può essere eseguita in un ambiente generico dato che questo metodo di localizzazione globale non richiede l'identificazione di caratteristiche particolari nell'ambiente. Parte del lavoro è stata dedicata ad un'analisi esaustiva dei metodi di stima del moto fra scansioni laser, allo scopo di identificare il metodo con prestazioni migliori da impiegare nel metodo di localizzazione. Questo ha consentito di evidenziare come un metodo di comparazione denso permetta di ottenere buone prestazioni in diverse tipologie di ambiente. L'efficacia del metodo di localizzazione globale implementato è supportata da una serie di valutazioni sperimentali in diversi ambienti, anche di elevati dimensioni. Riguardo alla camera, è stato sviluppato un metodo robusto di visual odometry, il quale ha evidenziato come tale strumento permetta di affrontare delle situazioni nelle quali le informazioni del laser non sono sufficienti per stimare la posa del veicolo. In particolare, data la generalità del metodo di localizzazione globale, questo può essere facilmente applicato anche alla camera, al fine di ottenere la fusione di informazioni fra due strumentazioni complementari e quindi ottenere un sistema di localizzazione più affidabile. Gli algoritmi sono stati testati in un ambiente indoor bidimensionale, ma si prevede che possano essere utilizzati anche in ambienti tridimensionali e outdoor

A unified framework for uncertainty, compatibility analysis, and data fusion for multi-stereo 3-D shape estimation

This paper describes the uncertainty analysis performed for the reconstruction of a 3-D shape. Multiple stereo systems are employed to measure a 3-D surface with superimposed colored markers. The procedure comprised a detailed uncertainty analysis of all measurement phases, and the uncertainties evaluated were employed to perform a compatibility analysis of points acquired by different stereo pairs. The compatible acquired markers were statistically merged in order to obtain the measurement of a 3-D shape and an evaluation of the associated uncertainty. Both the compatibility analysis and the measurement merging are based on the evaluated uncertainty

Garment-based motion capture (GaMoCap): high-density capture of human shape in motion

This paper presents a new motion capture (MoCap) system, the garment-based motion capture system-GaMoCap. The key feature is the use of an easily wearable garment printed with colour-coded pattern and a generic multicamera setup with standard video cameras. The coded pattern allows a high-density distribution of markers per unit of surface (about 40 markers per 100 cm), avoiding markers-swap errors. The high density of markers reconstructed makes possible a simultaneous reconstruction of shape and motion, which gives several concurrent advantages with respect to the state of the art and providing performances comparable with previous marker-based systems. In particular, we provide effective solutions to counter the soft-tissue artefact which is a common problem for garment-based techniques. This effect is reduced using Point Cluster Technique to filter out the points strongly affected by non-rigid motion. Uncertainty of motion estimation has been experimentally quantified by comparing with a state-of-the-art commercial system and numerically predicted by means of a Monte Carlo Method procedure. The experimental evaluation was performed on three different articulated motions: shoulder, knee and hip flexion-extension. The results shows that for the three motion angles estimated with GaMoCap, the system provides comparable accuracies against a commercial VICON system

On the design of yaw rate control via variable front-to-total anti-roll moment distribution

In vehicle dynamics, yaw rate control is used to improve the cornering response in steady-state and transient conditions. This can be achieved through an appropriate anti-roll moment distribution between the front and rear axles of a vehicle with controllable suspension actuators. Such control action alters the load transfer distribution, which in turn provokes a lateral tire force variation. With respect to the extensive set of papers from the literature discussing yaw rate tracking through active suspension control, this study presents: i) A detailed analysis of the effect of the load transfer on the lateral axle force and cornering stiffness; ii) A novel linearized single-track vehicle model formulation for control system design, based on the results in i); and iii) An optimization-based routine for the design of the non-linear feedforward contribution of the control action. The resulting feedforward-feedback controller is assessed through: a) Simulations with an experimentally validated model of a vehicle with active anti-roll bars (case study 1); and b) Experimental tests on a vehicle prototype with an active suspension system (case study 2)

Trailer control through vehicle yaw moment control: Theoretical analysis and experimental assessment

This paper investigates a torque-vectoring formulation for the combined control of the yaw rate and hitch angle of an articulated vehicle through a direct yaw moment generated on the towing car. The formulation is based on a single-input single-output feedback control structure, in which the reference yaw rate for the car is modified when the incipient instability of the trailer is detected with a hitch angle sensor. The design of the hitch angle controller is described, including the gain scheduling as a function of vehicle speed. The controller performance is assessed by means of frequency domain and phase plane analyses, and compared with that of an industrial trailer sway mitigation algorithm. In addition, the novel control strategy is implemented in a high-fidelity articulated vehicle model for robustness assessment, and experimentally tested on an electric vehicle demonstrator with four on-board drivetrains, towing two different conventional single-axle trailers. The results show that: (i) the torque-vectoring controller based only on the yaw rate of the car is not sufficient to mitigate trailer instability in extreme conditions; and (ii) the proposed controller provides safe trailer behaviour during the comprehensive set of manoeuvres, thus justifying the additional hardware complexity associated with the hitch angle measurement