25 research outputs found
Accurate sound synthesis of 3D object collisions in interactive virtual scenarios
Questa tesi affronta lo studio di algoritmi efficienti per
la sintesi di suoni risultanti dalla collisione di oggetti
generici, partendo da una descrizione fisica del problema.
L'obiettivo della ricerca e' lo sviluppo di strumenti in grado
di aumentare l'accuratezza del feedback uditivo in ambienti
di realta' virtuale attraverso un approccio basato sulla fisica,
senza il bisogno quindi di far riferimento a suoni pre-registrati.
Data la loro versatilita' nel trattare geometrie complesse, i metodi
agli elementi finiti (FEM) sono stati scelti per la discretizzazione
spaziale di generici risonatori tridimensionali. Le risultanti equazioni
discrete sono riarrangiate in modo da disaccoppiare i modi normali del
sistema tramite l'utilizzo di tecniche di Analisi e Sintesi Modale.
Queste tecniche, infatti, portano convenientemente ad algoritmi computazionalmente
efficienti per la sintesi del suono. Implementazioni di esempio di tali algoritmi
sono state sviluppate facendo uso solo di software open-source: questo
materiale a corredo della tesi permette una migliore riproducibilita' dei
risultati di questa tesi da parte di ricercatori aventi una preparazione
nel campo della sintesi audio.
I risultati originali presenti in questo lavoro includono:
i tecniche efficienti basate sulla fisica che aiutano l'implementazione
in tempo reale di algoritmi di sintesi del suono su hardware comune;
ii un metodo per la gestione efficiente dei dati provenienti da analisi
FEM che, assieme ad un modello espressivo per la dissipazione, permette
di calcolare l'informazione caratterizzante un oggetto risonante e salvarla
in una struttura dati compatta
iii una trasformazione nel dominio discreto del tempo su due diverse
rappresentazioni nello spazio degli stati di filtri digitali del secondo
ordine, che permette il calcolo esatto di variabili derivate come la velocita'
e l'energia di un risonatore anche quando semplici realizzazioni a soli poli
sono impiegate
i un'efficiente realizzazione multirate di un banco parallelo di risonatori,
derivata usando una suddivisione con Quadrature-Mirror-Filters (QMF). Confrontata
con lavori simili presenti in letteratura, questa realizzazione permette l'uso
di eccitazione nonlineare in feedback per un banco di risonatori in multirate:
l'idea chiave consiste nello svolgere un cambio di stato adattivo nel banco
di risonatori, muovendo i risonatori dalla frequenza di campionamento elevata,
usata per il processamento della fase transiente, ad un insieme di sottofrequenze
ridotte usate durante l'evoluzione in stato libero del sistema.This thesis investigates efficient algorithms for the synthesis of sounds
produced by colliding objects, starting from a physical description of the
problem. The objective of this investigation is to provide tools capable
of increasing the accuracy of the synthetic auditory feedback in virtual
environments through a physics-based approach, hence without the need
of pre-recorded sounds.
Due to their versatility in dealing with complex geometries, Finite Element
Methods (FEM) are chosen for the space-domain discretization of
generic three-dimensional resonators. The resulting state-space representations
are rearranged so as to decouple the normal modes in the corresponding
equations, through the use of Modal Analysis/Synthesis techniques.
Such techniques, in fact, conveniently lead to computationally efficient
sound synthesis algorithms. The whole mathematical treatment develops
until deriving such algorithms. Finally, implementation examples are provided
which rely only on open-source software: this companion material
guarantees the reproducibility of the results, and can be handled without
much effort by most researchers having a background in sound processing.
The original results presented in this work include:
i efficient physics-based techniques that help implement real-time sound
synthesis algorithms on common hardware;
ii a method for the efficient management of FEM data which, by working
together with an expressive damping model, allows to pre-compute the
information characterizing a resonating object and then to store it in
a compact data structure;
iii a time-domain transformation of the state-space representation of
second-order digital filters, allowing for the exact computation of dependent
variables such as resonator velocity and energy, even when
simple all-pole realizations are used;
iv an efficient multirate realization of a parallel bank of resonators, which
is derived using a Quadrature-Mirror-Filters (QMF) subdivision. Compared
to similar works previously proposed in the literature, this realization
allows for the nonlinear feedback excitation of a multirate
filter bank: the key idea is to perform an adaptive state change in the
resonator bank, by switching the sampling rate of the resonators from
a common highest value, used while processing the initial transient of
the signals at full bandwidth, to a set of lower values in ways to enable
a multirate realization of the same bank during the steady state
evolution of the signals
Wave impedance selection for passivity-based bilateral teleoperation
When a task must be executed in a remote or dangerous environment, teleoperation systems may be employed to extend the influence of the human operator. In the case of manipulation tasks, haptic feedback of the forces experienced by the remote (slave) system is often highly useful in improving an operator's ability to perform effectively. In many of these cases (especially teleoperation over the internet and ground-to-space teleoperation), substantial communication latency exists in the control loop and has the strong tendency to cause instability of the system. The first viable solution to this problem in the literature was based on a scattering/wave transformation from transmission line theory. This wave transformation requires the designer to select a wave impedance parameter appropriate to the teleoperation system. It is widely recognized that a small value of wave impedance is well suited to free motion and a large value is preferable for contact tasks. Beyond this basic observation, however, very little guidance exists in the literature regarding the selection of an appropriate value. Moreover, prior research on impedance selection generally fails to account for the fact that in any realistic contact task there will simultaneously exist contact considerations (perpendicular to the surface of contact) and quasi-free-motion considerations (parallel to the surface of contact). The primary contribution of the present work is to introduce an approximate linearized optimum for the choice of wave impedance and to apply this quasi-optimal choice to the Cartesian reality of such a contact task, in which it cannot be expected that a given joint will be either perfectly normal to or perfectly parallel to the motion constraint.
The proposed scheme selects a wave impedance matrix that is appropriate to the conditions encountered by the manipulator. This choice may be implemented as a static wave impedance value or as a time-varying choice updated according to the instantaneous conditions encountered. A Lyapunov-like analysis is presented demonstrating that time variation in wave impedance will not violate the passivity of the system. Experimental trials, both in simulation and on a haptic feedback device, are presented validating the technique. Consideration is also given to the case of an uncertain environment, in which an a priori impedance choice may not be possible
Surface Geometry and the Haptic Rendering of Rigid Point Contacts
This thesis examines the haptic rendering of rigid point contacts in virtual simulations. The haptic renderers generate force feedback so that the operator can interact with the virtual scenes in a realistic way. They must be able to recreate the physical phenomena experienced in the real world without displaying any haptic artifacts. The existing renderers are decomposed into a projection function and a regulation scheme. It is shown that the pop-through artifact, whereby the virtual tool instantaneously jumps between two distant surface points, is caused whenever the operator encounters a singularity within the renderer's projection function. This was well known for the minimum distance based renderers, but it is shown here that such singularities arise with the constraint based renderers as well.
A new projection function is designed to minimize the existence of singularities within the model. When paired with an appropriate regulation scheme, this forms the proposed mapping renderer. The new projection is calculated by mapping the model onto a canonical shape where the haptic problem is trivial, e.g. a circle in the case of a 2D model of genus zero, which avoids pop-through on smooth models. The haptic problem is then recast as a virtual constraint problem, where the traditional regulation schemes, designed originally for planar surfaces, are shown to introduce a velocity dependent error on curved surfaces that can distort the model's rendering and to couple the regulation towards and dynamics along the constraint. Set stabilization control, based on feedback linearizing the haptic device with respect to a virtual output consisting of coordinates transversal and tangential to the model surface, is proposed as an alternative. It is shown to be able to decouple the system into transversal and tangential subsystems that can then be made asymptotically stable and assigned arbitrary dynamics, respectively
Haptics Rendering and Applications
There has been significant progress in haptic technologies but the incorporation of haptics into virtual environments is still in its infancy. A wide range of the new society's human activities including communication, education, art, entertainment, commerce and science would forever change if we learned how to capture, manipulate and reproduce haptic sensory stimuli that are nearly indistinguishable from reality. For the field to move forward, many commercial and technological barriers need to be overcome. By rendering how objects feel through haptic technology, we communicate information that might reflect a desire to speak a physically- based language that has never been explored before. Due to constant improvement in haptics technology and increasing levels of research into and development of haptics-related algorithms, protocols and devices, there is a belief that haptics technology has a promising future
Combining Sensors and Multibody Models for Applications in Vehicles, Machines, Robots and Humans
The combination of physical sensors and computational models to provide additional information about system states, inputs and/or parameters, in what is known as virtual sensing, is becoming increasingly popular in many sectors, such as the automotive, aeronautics, aerospatial, railway, machinery, robotics and human biomechanics sectors. While, in many cases, control-oriented models, which are generally simple, are the best choice, multibody models, which can be much more detailed, may be better suited to some applications, such as during the design stage of a new product
Proceedings of the 7th Sound and Music Computing Conference
Proceedings of the SMC2010 - 7th Sound and Music Computing Conference, July 21st - July 24th 2010