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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23700号 / 理博第4790号 / 新制||理||1686(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 永江 知文, 准教授 銭廣 十三, 教授 中家 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

<p>As an object approaches an observer’s eye, tau, defined as the inverse relative expansion rate of the object’s image on the retina (Lee, 1976) approximates time-to-collision (TTC). Many studies have suggested that human observers use TTC information, but evidence for the use of tau remains inconclusive. Here we present two studies that investigated the use of tau in object-motion and observer-motion situations. In Study I, we dissociated several monocular variables that potentially contributed to TTC perception, and found that participants were most sensitive to TTC information when performing a relative TTC estimation task; and less sensitive to non-time variables such as distance-to-collision, speed and object size. Additionally, when we manipulated sources of information to specify conflicting time-of-arrivals, TTC specified by tau was weighted more than TTC derived from distance and speed. Thus, we concluded that even in the presence of monocular depth information, observers strongly utilize tau when estimating TTC.</p> <p>In Study II, observers estimated TTC of a looming target in the presence or absence of background expansion. Results demonstrated that participants overestimated TTC in situations where the surroundings of the target’s contours expanded at a reduced rate. Moreover, simulated self-motion was unnecessary to induce this bias, as results were comparable in situations where this relative expansion was limited to the target’s immediate surroundings. Therefore, we also concluded that a relative tau variable, based on the relative rate of expansion, is utilized whenever expansion beyond the object’s immediate boundaries is less than the target’s absolute rate of expansion.</p> / Master of Science (MSc)

In this thesis, solutions to two of the problems encountered in the design and control of human-friendly robots are investigated. The first problem is severe human injuries can occur when an accidental human-manipulator impact happens. A theoretical and experimental study on using foam coverings to reduce the severity of a human-manipulator impact and enhance human safety is presented. An improved human-manipulator impact model that incorporates the manipulator dynamics, foam covering dynamics and the coupling between the human head and torso is introduced. A method for approximating the configuration-dependent dynamics of robotics manipulators with the dynamics of a single DOF manipulator is proposed. With this model, the design parameters that significantly influence the human head acceleration are investigated. A model-based foam covering design procedure to properly select parameters of foam coverings in accordance with safety criteria and the foam thickness constraint is then proposed. The impact model and the foam covering design procedure are validated experimentally with two manipulators. The maximum error between the predicted and experimental head acceleration was less than 9%. The maximum error between the predicted and experimental foam compressed depth was less than 12%. The second problem is mobile robot navigation in the presence of humans and other motion-unpredictable obstacles. A novel navigation algorithm, based on the virtual force field (VFF) method, is proposed as a solution. It features improved functions for the repulsive and detour virtual forces, and a new stabilizing virtual force. Methods to calculate sizes of the active and critical regions for different obstacles are developed. Stability of the new VFF is proven using a novel piecewise Lyapunov function and Lyapunov's second method. Based on simulations for different obstacle configurations, the new VFF-based algorithm successfully produces collision-free paths while five well known navigation algorithms incurred collisions in one of the configurations. With the new VFF-based navigation algorithm, simulations and experiments are successfully performed with a holonomic robot and a nonholonomic robot for several configurations, including multiple moving obstacles. / Thesis / Doctor of Philosophy (PhD)

A flotation model has been proposed that is applicable in a turbulent environment. It is the first turbulent model that takes into account hydrodynamics of the flotation cell as well as all relevant surface forces (van der Waals, electrostatic, and hydrophobic) by use of the Extended DLVO theory. The model includes probabilities for attachment, detachment, and froth recovery as well as a collision frequency. A review of the effects fluids have on the flotation process has also been given. This includes collision frequencies, attachment and detachment energies, and how the energies of the turbulent system relate to them. Flotation experiments have been conducted to verify this model. Model predictions were comparable to experimental results with similar trends. Simulations were also run that show trends and values seen in industrial flotation systems. These simulations show the many uses of the model and how it can benefit the industries that use flotation. / Ph. D.

Recently there has been a growing interest in the use of Low Rate Wireless Personal Area Networks (LR-WPAN) [1] driven by the large number of emerging applications such as home automation, health-care monitoring and environmental surveillance. To fulfill the needs for these emerging applications, IEEE has created a new standard called IEEE 802.15.4 for LR-WPAN, which has been widely accepted as the de facto standard for wireless sensor networks. Unlike IEEE 802.11 [2], which was designed for Wireless Local Area Networks (WLAN), it focuses on short range wireless communications. The goal of the IEEE 802.15.4 LR-WPAN is to support low data rate connectivity among wireless sensors with low complexity, cost and power consumption [3]. It specifies two types of network topologies, which are the beacon-enabled start network and the nonbeacon-enabled peer-to-peer network. For the beacon-enabled network, it defines the Guaranteed Time Slot (GTS) to provide real-time guaranteed service for delay-sensitive applications. In the nonbeacon-enabled network the GTS is reserved time slots such that it is requested, allocated and scheduled to wireless sensors that need guaranteed service for delay-sensitive applications. Existing GTS scheduling algorithms include First-Come-First-Served (FCFS) [1], priority-based [4] and Earliest Deadline First (EDF) [5] methods. Such FCFS and priority-based scheduling methods have critical drawbacks in achieving real-time guarantees. Namely, they fail to satisfy the delay constraints of delay-sensitive transactions. Further, they lead to GTS scarcity and GTS underutilization. On the other hand, the EDF-based scheduling method provides delay guarantee while it does not support delay-sensitive applications where arrival of the first packet has a critical impact on the performance. To solve these problems, we design the optimal work-conserving GTS Allocation and Scheduling (GAS) algorithm that provides guarantee service for delay-sensitive applications in beacon-enabled networks. Not only does the GAS satisfy the delay constraints of transactions, but also it reduces GTS scarcity and GTS underutilization. Further, it supports delay-sensitive applications where arrival of the first packet has a critical impact on the performance. Through the extensive simulation results, we show that the proposed algorithm outperforms the existing scheduling methods. Our algorithm differs from the existing ones in that it is an on-line scheduling and allocation algorithm and allows transmissions of bursty and periodic transactions with delay constraints even when the network is overloaded. In the nonbeacon-enabled peer-to-peer network some operating scenarios for rate-sensitive applications arise when one considers wireless video surveillance and target detection applications for wireless sensor networks. To support such rate-sensitive applications in wireless sensor networks, we present a Multirate-based Service Differentiation (MSD) operating in the nonbeacon-enabled peer-to-peer network. Unlike existing priority-based service differentiation models, the MSD defines the independent Virtual Medium Access Controls (VMACs), each of which consists of a transmission queue and the Adaptive Backoff Window Control (ABWC). Since the VMACs serve multiple rate-sensitive flows, it is possible that more than one data frame is collided with each other when their backoff times expire simultaneously. To solve such a virtual collision in the virtual collision domain, we design the Virtual Collision Avoidance Control (VCAC). The ABWC component adjusts the backoff window to reflect the local network state in the local collision domain. The VCAC component prevents virtual collisions and preempts packets with the minimal cost in the virtual collision domain. By analyzing these algorithms, we prove that the ABWC component enables the achieved data rate to converge to the rate requirement and the VCAC component produces a virtual-collision-free schedule to avoid degradation of the achieved data rate. Through the simulation, we validate our analysis and show the MSD outperforms existing algorithms. / Ph. D.