Robot design for leak detection in water-pipe systems

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 113-116).Leaks are major problem that occur in the water pipelines all around the world. Several reports indicate loss of around 20 to 30 percent of water in the distribution of water through water pipe systems. Such loss of water represents critical waste of valuable resources, especially in countries such as Saudi Arabia where water is scarce. Moreover, leaks provide pathways for outside contaminants to enter into water pipe system which can deteriorate the quality of water and pose health risks to those drink from it. Considering these negatives, the importance of detecting where the leaks occur within vast network of water pipe system cannot be overemphasized. Further, for accurate and effective detection of the leaks, an in-pipe approach is taken which differs from previous detection methods. This thesis is on the design of mobile robotic platform that carries the necessary sensor and travels inside the water pipe systems. To begin with, experiments were carried out to investigate the suitability of using acoustic sensor to detect the leaks and favorable results were obtained. Then design specification of the mobile robotic platform that will carry the sensor is discussed with brief description of each components of the robot given. As components for the mobile robotic platform, a rigid-flexible robotic joint is developed that enables the robot to travel through bends and turns. Further, a novel braking mechanism using permanent magnet is presented. The mechanism results in a friction controllable leg that can be used to slow down and control the speed of robot in the presence of water flow. Finally, possible candidates for propulsion unit are discussed and evaluated with guidance for future work to be progressed.by Changrak Choi.S.M

Robot motion planning with contact from global pseudo-inverse map

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 101-108).In the robot motion planning problems, environment and its objects are often treated as obstacles to be avoided. However, there are situations where contacting with the environment is not costly. Moreover, in many cases, making contact can actually help a robot to maneuver around to reach a goal state which would not have been possible otherwise. This thesis presents a framework for motion planner that utilizes multiple contacts with the environment and its objects. The planner is targeted to autonomously generate motion, where robot has to make multiple contact with different part of its body in order to achieve a task objective. It is motivated by and has significance in developing a robust humanoid planner that is capable of recovering from a fall down. The recent DRC has been marked with compilation of humanoid robots falling down, but only one robot managed to recover to a standing up position. In a real disaster scenario, the inability to stand up would mean end of the rescue mission for what is extremely expensive machinery. A robust planner capable of recovery is must and this work contributes towards it. The developed planner autonomously generates standing up motion from fall down in the presence of torque limits. The proposed multi-contact motion planner leverages upon following two key components. Existing multi-contact planners require good initial seeds to successfully generate a motion. These are hard to find and often manually encoded. Here, we utilize pre-computed global pseudo-inverse map (inverse kinematic map for each contact-state that has property of global resolution, connected by connectivity functions) to generate multi-contact motion from current configuration to the goal without need for an initial seed. Nevertheless, constructing the global pseudo-inverse map is computationally expensive. In an effort to facilitate the construction, we utilize singular configurations as a heuristic to reduce the search space and justify its use based on the physical analysis. Although computationally expensive, once pre-computed, the global map can be used to generate plans fast online in a multi-query manner.by Changrak Choi.Ph. D

Coordinated Motion Planning for On-Orbit Satellite Inspection using a Swarm of Small-Spacecraft

This paper addresses the problem of how to plan optimal motion for a swarm of on-orbit servicing (OOS) small-spacecraft remotely inspecting a non-cooperative client spacecraft in Earth orbit. With the goal being to maximize the information gathered from the coordinated inspection, we present an integrated motion planning methodology that is a) fuel-efficient to ensure extended operation time and b) computationally-tractable to make possible on-board re-planning for improved exploration. Our method is decoupled into first offline selection of optimal orbits, followed by online coordinated attitude planning. In the orbit selection stage, we numerically evaluate the upper and lower bounds of the information gain for a discretized set of passive relative orbits (PRO). The algorithm then sequentially assigns orbits to each spacecraft using greedy heuristics. For the attitude planning stage, we propose a dynamic programming (DP) based attitude planner capable of addressing vehicle and sensor constraints such as attitude control system specifications, sensor field of view, sensing duration, and sensing angle. Finally, we validate the performance of the proposed algorithms through simulation of a design reference mission involving 3U CubeSats inspecting a satellite in low Earth orbit

Characterization of In-Pipe Acoustic Wave for Water Leak Detection

This paper presents experimental observations on the characteristics of the acoustic signal propagation and attenuation inside water-filled pipes. An acoustic source (exciter) is mounted on the internal pipe wall, at a fixed location, and produces a tonal sound to simulate a leak noise with controlled frequency and amplitude, under different flow conditions. A hydrophone is aligned with the pipe centerline and can be re-positioned to capture the acoustic signal at different locations. Results showed that the wave attenuation depends on the source frequency and the line pressure. High frequency signals get attenuated more with increasing distance from the source. The optimum location to place the hydrophone for capturing the acoustic signal is not at the vicinity of source location. The optimum location also depends on the frequency and line pressure. It was also observed that the attenuation of the acoustic waves is higher in more flexible pipes like PVC ones.Center for Clean Water and Clean Energy at MIT and KFUP

CaRT: Certified Safety and Robust Tracking in Learning-based Motion Planning for Multi-Agent Systems

The key innovation of our analytical method, CaRT, lies in establishing a new hierarchical, distributed architecture to guarantee the safety and robustness of a given learning-based motion planning policy. First, in a nominal setting, the analytical form of our CaRT safety filter formally ensures safe maneuvers of nonlinear multi-agent systems, optimally with minimal deviation from the learning-based policy. Second, in off-nominal settings, the analytical form of our CaRT robust filter optimally tracks the certified safe trajectory, generated by the previous layer in the hierarchy, the CaRT safety filter. We show using contraction theory that CaRT guarantees safety and the exponential boundedness of the trajectory tracking error, even under the presence of deterministic and stochastic disturbance. Also, the hierarchical nature of CaRT enables enhancing its robustness for safety just by its superior tracking to the certified safe trajectory, thereby making it suitable for off-nominal scenarios with large disturbances. This is a major distinction from conventional safety function-driven approaches, where the robustness originates from the stability of a safe set, which could pull the system over-conservatively to the interior of the safe set. Our log-barrier formulation in CaRT allows for its distributed implementation in multi-agent settings. We demonstrate the effectiveness of CaRT in several examples of nonlinear motion planning and control problems, including optimal, multi-spacecraft reconfiguration.Comment: IEEE Conference on Decision and Control (CDC), Preprint Version, Accepted July, 202

Coordinated Motion Planning for On-Orbit Satellite Inspection using a Swarm of Small-Spacecraft

This paper addresses the problem of how to plan optimal motion for a swarm of on-orbit servicing (OOS) small-spacecraft remotely inspecting a non-cooperative client spacecraft in Earth orbit. With the goal being to maximize the information gathered from the coordinated inspection, we present an integrated motion planning methodology that is a) fuel-efficient to ensure extended operation time and b) computationally-tractable to make possible on-board re-planning for improved exploration. Our method is decoupled into first offline selection of optimal orbits, followed by online coordinated attitude planning. In the orbit selection stage, we numerically evaluate the upper and lower bounds of the information gain for a discretized set of passive relative orbits (PRO). The algorithm then sequentially assigns orbits to each spacecraft using greedy heuristics. For the attitude planning stage, we propose a dynamic programming (DP) based attitude planner capable of addressing vehicle and sensor constraints such as attitude control system specifications, sensor field of view, sensing duration, and sensing angle. Finally, we validate the performance of the proposed algorithms through simulation of a design reference mission involving 3U CubeSats inspecting a satellite in low Earth orbit

Information-Based Guidance and Control Architecture for Multi-Spacecraft On-Orbit Inspection

We present an architecture for inspection or mapping of a target spacecraft, referred to as chief, in an orbit around Earth using multiple spacecraft, referred to as deputies (or) observers, in stable Passive Relative Orbits (PROs). We use an information gain approach to directly consider the trade-off between gathered data and fuel/energy cost. The four components of our architecture are: 1) information estimation, 2) state estimation, 3) motion planning for relative orbit initialization and reconfiguration, and 4) relative orbit control. The information estimation quantifies the information gain during inspection of a spacecraft, given past and potential future poses of all spacecraft. The estimated information gain is a crucial input to the motion planner, which computes PROs and reconfiguration strategies for each of the observers to maximize the information gain from distributed observations of the target spacecraft. The resulting motion trajectories jointly consider observational coverage of the target spacecraft and fuel/energy cost. For the PRO trajectories, we design a fuel optimal attitude trajectory that minimizes rest-to-rest energy for each observer to inspect the target spacecraft. We validate our architecture in a mission simulation to visually inspect the target spacecraft