http://hdl.handle.net/1721.1/7896 Search the Channel search http://dspace.mit.edu/simple-search http://hdl.handle.net/1721.1/37271 Title: Estimation of ground reaction force and zero moment point on a powered ankle-foot prosthesis <br/> <br/>Authors: Martinez Villalpando, Ernesto Carlos <br/> <br/>Abstract: Commercially available ankle-foot prostheses are passive when in contact with the ground surface, and thus, their mechanical properties remain fixed across different terrains and walking speeds. The passive nature of these prostheses causes many problems for lower extremity amputees, such as a lack of adequate balance control during standing and walking. The ground reaction force (GRF) and the zero moment point (ZMP) are known to be basic parameters in bipedal balance control. This thesis focuses on the estimation of these parameters using two prostheses, a powered ankle-foot prototype and an instrumented, mechanically-passive prosthesis worn by a transtibial amputee. The main goal of this research is to determine the feasibility of estimating the GRF and ZMP primarily using sensory information from a force/torque transducer positioned proximal to the ankle joint. The location of this sensor is ideal because it allows the use of a compliant artificial foot to be in contact with the ground, in contrast to rigid foot structures employed by walking robots. Both, the active and passive, instrumented prostheses were monitored with a wearable computing system designed to serve as a portable control unit for the active prototype and as an ambulatory gait analysis tool.; (cont.) A set of experiments were conducted at MIT's gait laboratory whereby a below-knee amputee subject, using the prosthetic devices, was asked to perform single-leg standing tests and slow-walking trials. For each experiment, the GRF and ZMP were computed by combining the kinetic and kinematic information recorded from a force platform and a 3D motion capture system. These values were statistically compared to the GRF and ZMP estimated from the data collected by the embedded prosthetic sensory system and portable computing unit. The average RMS error and correlation factor were calculated for all experimental sessions. Using a static analysis procedure, the estimation of the vertical component of GRF had an averaged correlation coefficient higher than 0.96. The estimated ZMP location had a distance error of less than 1 cm, equal to 4% of the anterior-posterior foot length or 12% of the mediolateral foot width. These results suggest that it is possible to estimate the GRF between the ground and a compliant artificial prosthesis with a sensor positioned between the knee and the ankle joint.; (cont.) Moreover, this sensory information is sufficient to closely estimate the ZMP location during the single support phase of slow walking and while standing on one leg. This research contributes to the development of fully integrated artificial extremities that mimic the behavior of the human ankle-foot complex, especially to help improve the postural stability of lower extremity amputees. <br/> <br/>Description: Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2006.; Includes bibliographical references (leaves 89-97). Sat, 29 Oct 2005 22:58:59 GMT http://hdl.handle.net/1721.1/33884 Title: The affordance-based concept <br/> <br/>Authors: Gorniak, Peter John <br/> <br/>Abstract: Natural language use relies on situational context. The meaning of words and utterances depend on the physical environment and the goals and plans of communication partners. These facts should be central to theories of language and automatic language understanding systems. Instead, they are often ignored, leading to partial theories and systems that cannot fully interpret linguistic meaning. I introduce a new computational theory of conceptual structure that has as its core claim that concepts are neither internal nor external to the language user, but instead span the objective-subjective boundary. This theory proposes interaction and prediction as a central theme, rather than solely emphasizing deducing, sensing or acting. To capture the possible interactions between subject and object, the theory relies on the notion of perceived affordances: structured units of interaction that can be used for prediction at certain levels of abstraction. By using perceived affordances as a basis for language understanding, the theory accounts for many aspects of the situated nature of human language use. It provides a unified solution to a number of other demands on a theory of language understanding including conceptual combination, prototypicality effects, and the generative nature of lexical items.; (cont.) To support the theory, I describe an implementation that relies on probabilistic hierarchical plan recognition to predict possible interactions. The elements of a recognized plan provide an instance of perceived affordances which are used by a linguistic parser to ground the meaning of words and grammatical constituents. Evaluations performed in a multiuser role playing game environment show that this implementation captures the meaning of free-form spontaneous directive speech acts that cannot be understood without taking into account the intentional and physical situation of speaker and listener. <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.; Includes bibliographical references (p. 89-95). Fri, 29 Oct 2004 22:58:59 GMT http://hdl.handle.net/1721.1/33876 Title: Intelligent antenna sharing in cooperative diversity wireless networks <br/> <br/>Authors: Bletsas, Aggelos Anastasiou, 1975- <br/> <br/>Abstract: Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require simultaneous relay transmissions at the same frequency bands, using distributed space-time coding algorithms. Careful design of distributed space-time coding for the relay channel is usually based on global knowledge of some network parameters or is usually left for future investigation, if there is more than one cooperative relay. We propose a novel scheme that eliminates the need for space-time coding and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and the destination. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing gain tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M relay nodes is required. Additionally, the proposed scheme increases the outage and ergodic capacity, compared to non-cooperative communication with increasing number of participating relays, at the low SNR regime and under a total transmission power constraint.; (cont.) Coordination among the participating relays is based on a novel timing protocol that exploits local measurements of the instantaneous channel conditions. The method is distributed and allows for fast selection of the best relay as compared to the channel coherence time. In addition, a methodology to evaluate relay selection performance for any kind of wireless channel statistics is provided. Other methods of network coordination, inspired by natural phenomena of decentralized time synchronization, are analyzed in theory and implemented in practice. It was possible to implement the proposed, virtual antenna formation technique in a custom network of single antenna, half-duplex radios. <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.; Includes bibliographical references (p. 143-152). Fri, 29 Oct 2004 22:58:59 GMT http://hdl.handle.net/1721.1/33875 Title: Choreographing the extended agent : performance graphics for dance theater <br/> <br/>Authors: Downie, Marc (Marc Norman), 1977- <br/> <br/>Abstract: The marriage of dance and interactive image has been a persistent dream over the past decades, but reality has fallen far short of potential for both technical and conceptual reasons. This thesis proposes a new approach to the problem and lays out the theoretical, technical and aesthetic framework for the innovative art form of digitally augmented human movement. I will use as example works a series of installations, digital projections and compositions each of which contains a choreographic component - either through collaboration with a choreographer directly or by the creation of artworks that automatically organize and understand purely virtual movement. These works lead up to two unprecedented collaborations with two of the greatest choreographers working today; new pieces that combine dance and interactive projected light using real-time motion capture live on stage. The existing field of"dance technology" is one with many problems. This is a domain with many practitioners, few techniques and almost no theory; a field that is generating "experimental" productions with every passing week, has literally hundreds of citable pieces and no canonical works; a field that is oddly disconnected from modern dance's history, pulled between the practical realities of the body and those of computer art, and has no influence on the prevailing digital art paradigms that it consumes.; (cont.) This thesis will seek to address each of these problems: by providing techniques and a basis for "practical theory"; by building artworks with resources and people that have never previously been brought together, in theaters and in front of audiences previously inaccessible to the field; and by proving through demonstration that a profitable and important dialogue between digital art and the pioneers of modern dance can in fact occur. The methodological perspective of this thesis is that of biologically inspired, agent-based artificial intelligence, taken to a high degree of technical depth. The representations, algorithms and techniques behind such agent architectures are extended and pushed into new territory for both interactive art and artificial intelligence. In particular, this thesis ill focus on the control structures and the rendering of the extended agents' bodies, the tools for creating complex agent-based artworks in intense collaborative situations, and the creation of agent structures that can span live image and interactive sound production. Each of these parts becomes an element of what it means to "choreograph" an extended agent for live performance. <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.; Includes bibliographical references (v. 2, leaves 448-458). Fri, 29 Oct 2004 22:58:59 GMT