In-Flight Collision Avoidance Controller Based Only on OS4 Embedded Sensors

The major goal of this research was the development and implementation of a control system able to avoid collisions during the flight for a mini-quadrotor helicopter, based only on its embedded sensors without changing the environment. However, it is important to highlight that the design aspects must be seriously considered in order to overcome hardware limitations and achieve control simplification. The controllers of a UAV (Unmanned Aerial Vehicle) robot deal with highly unstable dynamics and strong axes coupling. Furthermore, any additional embedded sensor increases the robot total weight and therefore, decreases its operating time. The best balance between embedded electronics and robot operating time is desired. This paper focuses not only on the development and implementation of a collision avoidance controller for a mini-robotic helicopter using only its embedded sensors, but also on the mathematical model that was essential for the controller developing phases. Based on this model we carried out the development of a simulation tool based on MatLab/Simulink that was fundamental for setting the controllers' parameters. This tool allowed us to simulate and improve the OS4 controllers in different modeled environments and test different approaches. After that, the controllers were embedded in the real robot and the results proved to be very robust and feasible. In addition to this, the controller has the advantage of being compatible with future path planners that we are developing.

Motion capture and reinforcement learning of dynamically stable humanoid movement primitives

Tadej Petric

Direct transfer of human motion trajectories to humanoid robots does not result in dynamically stable robot movements due to the differences in human and humanoid robot kinematics and dynamics. We developed a system that converts human movements captured by a low-cost RGB-D camera into dynamically stable humanoid movements. The transfer of human movements occurs in real-time. As need arises, the developed system can smoothly transition between unconstrained movement imitation and imitation with balance control, where movement reproduction occurs in the null space of the balance controller. The developed balance controller is based on an approximate model of the robot dynamics, which is sufficient to stabilize the robot during on-line imitation. However, the resulting movements cannot be guaranteed to be optimal because the model of the robot dynamics is not exact. The initially acquired movement is therefore subsequently improved by model-free reinforcement learning, both with respect to the accuracy of reproduction and balance control. We present experimental results in simulation and on a real humanoid robot.

IEEE2013

Optimization of the treatment of hydrocephalus by the non-invasive measurement of the intra-cranial pressure

Alec Ginggen

This thesis work aims to optimize the treatment of hydrocephalus. It consists of two distinct objectives: the optimization of the diagnosis of patients implanted with a shunt system for the derivation of cerebro-spinal fluid (CSF) and the optimization of the treatment by a better understanding of the fluidic characteristics of shunts. The diagnosis optimization was addressed by a pressure sensor allowing for the measurement of the intra-cranial pressure (ICP). It has been characterized experimentally in vitro and in vivo in animals. The pressure sensor is integrated along a shunt system for the derivation of CSF and it can be interrogated by telemetry. The non-invasive access to the ICP will allow the physician to verify that the implantation of a shunt system has successfully restored a physiological ICP level. It will also provide a method to verify that the shunt is not blocked and fully functional. Simple mathematical models of the hydrodynamics of shunt systems used clinically are presented to address the second objective. These simple models are verified experimentally by characterizing the shunts on a setup developed for that purpose. This setup allows the characterization of non-bijective flow-pressure characteristics. The integration of mathematical models of shunt systems in a broader model describing the circulation of CSF in a patient implanted with a shunt will permit to predict the dynamics of the CSF circulation. It will also be a useful tool for shunt manufacturers to identify shunt characteristics critical to successfully restore a physiological condition after implantation. The results of this thesis work are presented in the form of an introduction, three scientific publications and a short conclusion. The motivations for the thesis work are presented in the introduction chapter along with background information about hydrocephalus and its treatment. A mathematical model describing the circulation of CSF is described in the same chapter. This model illustrates the interactions between the fluidic constituents of the cranial vault that lead to a physiological CSF circulation and ICP level. This model has been adapted to account for the implantation of a shunt system. The key technical characteristics of the pressure sensor are exposed in the subsequent section along with the experimental techniques and a short summary of the publications and patents. The pressure sensor is described in the first publication with a focus on the pressure transducer, the original sensor encapsulation technique, the electronics embedded in the sensor and the telemetry technique. A capacitive pressure transducer, which provides an accurate measurement of the absolute pressure, has been developed. The transducer technology guarantees a minimal drift of its characteristics with time. The design and the key manufacturing steps of the transducer are exposed. A hermetically closed capsule protects the sensor electronics. The effect of the packaging components and the assembly techniques on the sensor characteristics are analyzed. An analysis of the water diffusion through the walls of the capsule is presented since resistance to water permeation is a critical characteristics of the packaging. Minimal drift with time can only be achieved if the atmosphere in the capsule is extremely stable. The packaging provides a barrier to water diffusion in order to keep a constant low humidity level in the sensor. The telemetric link between the sensor and the external reading unit is provided by an inductive coupling between two loop antennas. The coupling allows the simultaneous transmission of power to the sensor and of the pressure data to the external unit. The fundamental characteristics of the telemetric link are described. The interfacing electronic components are integrated in an ASIC that consumes a minimal amount of energy. Lastly, the experimental characterization of the accuracy of the sensor and its thermal stability are presented. The second publication is focused on the in vivo characterization of the pressure sensor in animals. An animal model of hydrocephalus has been developed in order to characterize the correlation between the pressure measured by the sensor integrated into a shunt system and a reference provided by a direct measurement of the ICP in the ventricles of the brain. Hydrocephalus was induced in dogs by injection of kaolin and glue in the cisterna magna. The time course of hydrocephalus induction was followed by the measurement of the size of the ventricles by an ultrasonic imaging technique. Approximately 50 days after the injection of kaolin and glue, a shunt system integrating a pressure sensor was implanted between the brain ventricles and the peritoneum. A reference pressure sensor was also implanted in the ventricles. The pressure was then measured for up to 48 hours. The correlation between the pressure in the shunt and the intra-ventricular pressure is documented in the publication. The advantages associated with the measurement of the pressure in the shunt versus an intra-ventricular measurement technique are discussed and the pressure sensor is compared with other published sensors. The third publication describes three commonly used shunt systems by simple hydrodynamic mathematical models. A setup allowing the characterization of shunt systems having a non-bijective pressure-flow characteristics is presented. The experimental characteristics of the three shunt systems is compared to the theoretical models. The "pressure-controlled" and "flow-controlled" terminologies, which are frequently used in the clinical field, are discussed in the context of the hydrodynamic characteristics of shunts. Four patent applications have been submitted in the course of this thesis work. The three first applications have been granted, and the last one is filed. The first patent protects the pressure sensor encapsulation technique. The second patent protects the concept of a shunt system allowing the non-invasive adjustment of the resistance of the shunt valve. This concept has been developed as a result of the analysis of the critical parameters to successfully restore a physiological ICP level by the mathematical model of the CSF circulation. The third patent protects the use of the pressure sensor packaging technique for a flow sensor integrated in the shunt system. The last application protects the mechanism that regulates the power of the radio-frequency wave emitted by the external reading unit on the basis of the voltage induced in the sensor. The last chapter, entitled "Conclusion and Perspectives" summarizes the outcome of this thesis work in reference to the optimization of the treatment of hydrocephalus. This work laid the foundation for the use of the sensor in humans through a clinical study. The ICP data gathered during such a study would then allow the validation of the mathematical model of CSF circulation presented in this thesis.

EPFL2007

Distributed intelligent algorithms for robotic sensor networks monitoring discontinuous anisotropic environmental fields

Christopher Cianci

Robotic sensor networks, at the junction between distributed robotics and wireless sensor networks, represent a strategic convergence between mobile and networked systems. In this thesis, we have begun to explore this crossover, and where possible, to bring tools, experience, and insight from the field of robotics to bear in the field of sensor networks. We present here a formal and general framework for the classification and construction of distributed intelligent controllers to facilitate implementation, understanding, and analysis, including a complete parameterized system description, and its corresponding generalized performance metrics. The methods shown are capable of uniquely and unambiguously describing any mechanism for distributed control of a robotic sensor network engaged in a monitoring task. A variety of simple distributed intelligent algorithms are illustrated within this framework, which introduce methods for activity control in time, space, and mobility. Appropriate tools, equipment, and controlled testing environments for systematic experimentation have been designed and built, both for a physical system and for corresponding experimentally validated simulations. The general methods presented are intended neither as an exhaustive collection of possible controllers, nor as a replacement for application-specific solutions, but as a flexible, reusable roadmap for system design allowing a user to make educated design choices systematically and rigorously while encoding available information into the provided template, adapting the control model to the constraints of any given specific scenario, accounting for issues of data quality, measurement, communication, mobility, or any combination of the above.

EPFL2009

Optimization of the treatment of hydrocephalus by the non-invasive measurement of the intra-cranial pressure

Alec Ginggen

EPFL2007