265 research outputs found
Model-Based Stability Analysis for Mobile Manipulators
Analisi della stabilità del movimento di un sistema composto da piattaforma mobile, sulla quale è stato montato un robot a 6 assi rotazionali. Per questo si sono calcolate le reazioni vincolari alla base del manipolatore attraverso l'implementazione dell'algoritmo di Newton-Euler, ed è stato fatto un lavoro di parameter estimation per stimare i parametri dinamici del manipolatore. Successivamente è stato applicato l'algoritmo Moment-Height Stability Measur
Optimization-based methods for real-time generation of safe motions in mobile robots
Having robots operating in unstructured and dynamically changing environments is a challenging task that requires advanced motion generation approaches that are able to perform in real-time while maintaining the robot and environment safety.
The progress in the field of numerical optimization, as well as the development of tailored algorithms, made Nonlinear Model Predictive Control (NMPC) an appealing candidate for real-time motion generation. By considering the robot model as prediction model and through appropriate constraints on the robot states and control inputs, NMPC can enforce safety to the resulting motion in a straightforward way.
This thesis addresses the problem of real-time generation of safe motions for mobile robots and mobile manipulators. The different structure of the considered robots introduces different safety risks during the robot motion and so the motion generation problem for each robot is addressed in separate parts of this thesis.
In the first part, the problem of motion generation for mobile robots navigating in environments populated by static and/or moving obstacles is considered. For the generation of the desired motion, real-time NMPC is used. We argue that, in order to tackle the risk of collision with the environment, traditional distance-based approaches are incapable of maintaining the robot safety when the NMPC uses relatively short prediction horizons. Instead, we propose two NMPC approaches that employ two alternative collision avoidance constraints. The first proposed NMPC approach is applied to a scenario of safe robot navigation in a human crowd. The NMPC serves as a motion generation module in a safe motion generation framework, complete with a crowd prediction module. The considered collision avoidance constraint is built upon an appropriate Control Barrier Function (CBF). The second NMPC approach is applied to a scenario of robot navigation among moving obstacles, where the dynamics of the considered robot are significant. The proposed collision avoidance constraint is built upon the notion of avoidable collision state, which considers not only the robot-obstacle distance but also their velocity as well as the robot actuation capabilities. The simulation results indicate that both methods are effective and able to maintain the robot safety even in cases where their purely distance-based counterparts fail.
The second part of the thesis addresses the problem of safe motion generation for mobile manipulators, called to execute tasks that may require aggressive motions. Here, in addition to the risk of collision with its environment, the robot, consisting of multiple articulated bodies, is also susceptible to self-collisions. Moreover, fast motions can always result to loss of balance. To solve the problem, we propose a real-time NMPC scheme that uses the robot full dynamics, in order to enforce kinodynamic feasibility, while it also considers appropriate collision and self-collision avoidance constraints. To maintain the robot balance we enforce a constraint that restricts the feasible set of robot motions to those generating non-negative moments around the edges of the support polygon. This balance constraint, inherently nonlinear, is linearized using the NMPC solution of the previous iteration. In this way, we facilitate the solution of the NMPC in real-time, without compromising the robot safety.
Although the proposed NMPC is effective when applied to MM with low degrees of freedom, when the robot becomes more complex the use of its full dynamic model as a prediction model in an NMPC can lead to unacceptably large computational times that are not compatible with the real-time requirement. However, the use of a simplified model of the robot in an NMPC can compromise the robot safety. For this reason, we propose an optimization-based controller equipped with balance constraints as well as CBF-based collision avoidance constraints. The proposed controller can serve as an intermediate between a motion generation module that does not consider the robot full dynamics and the robot itself in order to ensure that the resulting motion will be at least safe. Simulation results indicate the effectiveness of the proposed method
Energy-saver mobile manipulator based on numerical methods
The work presents the kinematic and dynamic control of a mobile robotic manipulator
system based on numerical methods. The proposal also presents the curvature analysis of a path
not parameterized in time, for the optimization of energy consumption. The energy optimization
considers two aspects: the velocity of execution in curves and the amount of movements generated
by the robotic system. When a curve occurs on the predefined path, the execution velocity is
analyzed throughout the system in a unified method to prevent skid e ects from a ecting the mobile
manipulator, while the number of movements is limited by the redundancy presented by the robotic
system to optimize energy use. The experimental results are shown to validate the mechanical and
electronic construction of the system, the proposed controllers, and the saving of energy consumptionThis research was funded by Corporación Ecuatoriana para el Desarrollo de la Investigación y Academia–CEDI
Autonomous navigation of a wheeled mobile robot in farm settings
This research is mainly about autonomously navigation of an agricultural wheeled mobile robot in an unstructured outdoor setting. This project has four distinct phases defined as: (i) Navigation and control of a wheeled mobile robot for a point-to-point motion. (ii) Navigation and control of a wheeled mobile robot in following a given path (path following problem). (iii) Navigation and control of a mobile robot, keeping a constant proximity distance with the given paths or plant rows (proximity-following). (iv) Navigation of the mobile robot in rut following in farm fields. A rut is a long deep track formed by the repeated passage of wheeled vehicles in soft terrains such as mud, sand, and snow.
To develop reliable navigation approaches to fulfill each part of this project, three main steps are accomplished: literature review, modeling and computer simulation of wheeled mobile robots, and actual experimental tests in outdoor settings. First, point-to-point motion planning of a mobile robot is studied; a fuzzy-logic based (FLB) approach is proposed for real-time autonomous path planning of the robot in unstructured environment. Simulation and experimental evaluations shows that FLB approach is able to cope with different dynamic and unforeseen situations by tuning a safety margin. Comparison of FLB results with vector field histogram (VFH) and preference-based fuzzy (PBF) approaches, reveals that FLB approach produces shorter and smoother paths toward the goal in almost all of the test cases examined. Then, a novel human-inspired method (HIM) is introduced. HIM is inspired by human behavior in navigation from one point to a specified goal point. A human-like reasoning ability about the situations to reach a predefined goal point while avoiding any static, moving and unforeseen obstacles are given to the robot by HIM. Comparison of HIM results with FLB suggests that HIM is more efficient and effective than FLB.
Afterward, navigation strategies are built up for path following, rut following, and proximity-following control of a wheeled mobile robot in outdoor (farm) settings and off-road terrains. The proposed system is composed of different modules which are: sensor data analysis, obstacle detection, obstacle avoidance, goal seeking, and path tracking. The capabilities of the proposed navigation strategies are evaluated in variety of field experiments; the results show that the proposed approach is able to detect and follow rows of bushes robustly. This action is used for spraying plant rows in farm field.
Finally, obstacle detection and obstacle avoidance modules are developed in navigation system. These modules enables the robot to detect holes or ground depressions (negative obstacles), that are inherent parts of farm settings, and also over ground level obstacles (positive obstacles) in real-time at a safe distance from the robot. Experimental tests are carried out on two mobile robots (PowerBot and Grizzly) in outdoor and real farm fields. Grizzly utilizes a 3D-laser range-finder to detect objects and perceive the environment, and a RTK-DGPS unit for localization. PowerBot uses sonar sensors and a laser range-finder for obstacle detection. The experiments demonstrate the capability of the proposed technique in successfully detecting and avoiding different types of obstacles both positive and negative in variety of scenarios
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Synthesis of continuous whole-body motion in hexapod robot for humanitarian demining
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonIn the context of control, the motion of a legged robot is very challenging compared
with traditional fixed manipulator. Recently, many researches have been conducted
to control the motion of legged robot with different techniques. On the other hand,
manipulation tasks have been addressed in many applications. These researches solved
either the mobility or the manipulation problems, but integrating both properties
in one system is still not available. In this thesis, a control algorithm is presented
to control both locomotion and manipulation in a six legged robot. Landmines
detection process is considered as a case study of this project to accelerate the mine
detection operation by performing both walking and scanning simultaneously. In
order to qualify the robot to perform more tasks in addition to the walking task,
the joint redundancy of the robot is exploited optimally. The tasks are arranged
according to their importance to high level of priority and low level of priority. A new
task priority redundancy resolution technique is developed to overcome the effect
of the algorithmic singularities and the kinematic singularity. The computational
aspects of the solution are also considered in view of a real-time implementation.
Due to the dynamic changes in the size of the robot motion space, the algorithm
has the ability to make a trade-off between the number of achieved tasks and the
imposed constraints. Furthermore, an appropriate hierarchy is imposed in order
to ensure an accurate decoupling between the executed tasks. The dynamic effect
of the arm on the overall performance of the robot is attenuated by reducing the
optimisation variables. The effectiveness of the method is evaluated on a Computer
Aided Design (CAD) model and the simulations of the whole operation are conducted
using MATLAB and SimMechanics.Iraqi ministry of Higher Education and Scientific Researc
Modeling and control of a robot manipulator
Includes bibliographical references.This thesis presents work completed on the design of the modelling and path planning components for a robot manipulator mounted on a mobile platform. This platform is for use in the mining safety inspections of the mine roof, i.e., the hanging wall. Currently this process is done by mine workers and it places them at risk of falling of unstable rocks from the roof. A geometric based inverse kinematics algorithm for a 5 DOF redundant manipulator is proposed and implemented on a Packbot510i used as a test platform. Three versions of the Rapidly-exploring Random Trees planning algorithm namely, basic RRT, RRT Ball and RRT_ are compared. Results obtained show that RRT_ is more suitable than RRT and RRT Ball in terms of the length and the consistency of the trajectories produced. A Force Angle stability measure is used to guide the robot arm into trajectories that prevent the robotic system from tipping over. Results show that the Force Angle stable measure is more cautious, i.e., it classifies trajectories close to the instability of the system as unstable. Simulation results provided show that this system is capable of carrying out the safety inspections of the roof in the mining environment. Experimental results show that a few modifications are required for the system to be used practically on the test platform due to issues experienced with the hardware
Advanced Strategies for Robot Manipulators
Amongst the robotic systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. Modern manipulators are designed complicatedly and need to do more precise, crucial and critical tasks. So, the simple traditional control methods cannot be efficient, and advanced control strategies with considering special constraints are needed to establish. In spite of the fact that groundbreaking researches have been carried out in this realm until now, there are still many novel aspects which have to be explored
Climbing and Walking Robots
With the advancement of technology, new exciting approaches enable us to render mobile robotic systems more versatile, robust and cost-efficient. Some researchers combine climbing and walking techniques with a modular approach, a reconfigurable approach, or a swarm approach to realize novel prototypes as flexible mobile robotic platforms featuring all necessary locomotion capabilities. The purpose of this book is to provide an overview of the latest wide-range achievements in climbing and walking robotic technology to researchers, scientists, and engineers throughout the world. Different aspects including control simulation, locomotion realization, methodology, and system integration are presented from the scientific and from the technical point of view. This book consists of two main parts, one dealing with walking robots, the second with climbing robots. The content is also grouped by theoretical research and applicative realization. Every chapter offers a considerable amount of interesting and useful information
Contemporary Robotics
This book book is a collection of 18 chapters written by internationally recognized experts and well-known professionals of the field. Chapters contribute to diverse facets of contemporary robotics and autonomous systems. The volume is organized in four thematic parts according to the main subjects, regarding the recent advances in the contemporary robotics. The first thematic topics of the book are devoted to the theoretical issues. This includes development of algorithms for automatic trajectory generation using redudancy resolution scheme, intelligent algorithms for robotic grasping, modelling approach for reactive mode handling of flexible manufacturing and design of an advanced controller for robot manipulators. The second part of the book deals with different aspects of robot calibration and sensing. This includes a geometric and treshold calibration of a multiple robotic line-vision system, robot-based inline 2D/3D quality monitoring using picture-giving and laser triangulation, and a study on prospective polymer composite materials for flexible tactile sensors. The third part addresses issues of mobile robots and multi-agent systems, including SLAM of mobile robots based on fusion of odometry and visual data, configuration of a localization system by a team of mobile robots, development of generic real-time motion controller for differential mobile robots, control of fuel cells of mobile robots, modelling of omni-directional wheeled-based robots, building of hunter- hybrid tracking environment, as well as design of a cooperative control in distributed population-based multi-agent approach. The fourth part presents recent approaches and results in humanoid and bioinspirative robotics. It deals with design of adaptive control of anthropomorphic biped gait, building of dynamic-based simulation for humanoid robot walking, building controller for perceptual motor control dynamics of humans and biomimetic approach to control mechatronic structure using smart materials
Design and Real Time Control of a Versatile Scansorial Robot
This thesis presents investigations into the development of a versatile scansorial mobile robot and real-time realisation of a control system for different configurations of the robot namely climbing mode, walking mode and steering mode. The mobile robot comprises of a hybrid leg and wheel mechanism with innovative design that
enables it to interchange its configuration to perform the specific tasks of pole climbing in climbing mode, walking and step climbing in walking mode, and skid steering and inclined slope climbing in steering mode. The motivation of this research is due to the surrounding environment which is not always structured for exploration or navigation missions, and thus poses significant difficulty for the robot to manoeuvre and accomplish the intended task. Hence, the development of versatile scansorial robot with a flexible and interchangeable configuration can provide a broad
range of applications and locomotion system and to achieve the mission objective successfully.
The robot design consists of four arms/legs with wheel attached at each end-effector and has two link manipulation capability. In climbing mode, the arms are configured as grippers to grip the pole and wheels accelerate to ascend or descend. The climbing
angle is monitored to retain the level of the robot while climbing. However, in walking mode, the arms are configured as legs and the wheels are disabled. By implementing a periodic walking gait, the robot is capable of performing stable walking and step climbing. In steering mode, the arms are configured as suspension and the wheels are used for manoeuvring. In this mode, the skid steering system is used to enable the robot perform the turn.
The versatile scansorial robot’s configurations and locomotion capabilities are assessed experimentally in real time implementation using the physical prototype. The experiments provided demonstrate the versatility of the robot and successfully fulfill the aims and objectives of the research
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