Locomotion Trajectory Generation and Dynamic Control for Bipedal Walking Robots

Ph.DDOCTOR OF PHILOSOPH

Climbing and Walking Robots

Nowadays robotics is one of the most dynamic fields of scientific researches. The shift of robotics researches from manufacturing to services applications is clear. During the last decades interest in studying climbing and walking robots has been increased. This increasing interest has been in many areas that most important ones of them are: mechanics, electronics, medical engineering, cybernetics, controls, and computers. Today’s climbing and walking robots are a combination of manipulative, perceptive, communicative, and cognitive abilities and they are capable of performing many tasks in industrial and non- industrial environments. Surveillance, planetary exploration, emergence rescue operations, reconnaissance, petrochemical applications, construction, entertainment, personal services, intervention in severe environments, transportation, medical and etc are some applications from a very diverse application fields of climbing and walking robots. By great progress in this area of robotics it is anticipated that next generation climbing and walking robots will enhance lives and will change the way the human works, thinks and makes decisions. This book presents the state of the art achievments, recent developments, applications and future challenges of climbing and walking robots. These are presented in 24 chapters by authors throughtot the world The book serves as a reference especially for the researchers who are interested in mobile robots. It also is useful for industrial engineers and graduate students in advanced study

Robotics 2010

Without a doubt, robotics has made an incredible progress over the last decades. The vision of developing, designing and creating technical systems that help humans to achieve hard and complex tasks, has intelligently led to an incredible variety of solutions. There are barely technical fields that could exhibit more interdisciplinary interconnections like robotics. This fact is generated by highly complex challenges imposed by robotic systems, especially the requirement on intelligent and autonomous operation. This book tries to give an insight into the evolutionary process that takes place in robotics. It provides articles covering a wide range of this exciting area. The progress of technical challenges and concepts may illuminate the relationship between developments that seem to be completely different at first sight. The robotics remains an exciting scientific and engineering field. The community looks optimistically ahead and also looks forward for the future challenges and new development

Generating Trajectories for Wide Ditch Crossing of Biped Robots

Ditch crossing is one of the essential capabilities required for a biped robot in disaster management and search and rescue operations. This thesis presents di�erent approaches for trajectory generation of a planar biped robot crossing a wide ditch, which is de�ned as a ditch for which the ankle to ankle stretch required to cross the ditch is equal to or more than the leg length of the biped robot. Crossing a wide ditch can be considered as an application of long step walking. It is an extreme case walking demanding more attention than normal walking. In crossing a wide ditch the di�culty lies in generating trajectories considering friction and impact. With the proposed approaches in this work trajectories are generated for crossing wide ditch considering a least friction coe�cient of 0.15 also. With the analysis carried out in this work, some of the key issues to be considered in crossing a wide ditch are identi�ed. The thesis starts with proposing an o�ine approach for �nding feasible trajectories for dynamically crossing a wide ditch in ideal conditions. Later an online approach for the same task is proposed using the concept control constraints. The e�orts have been extended further to propose a real time approach for �nding joint trajectories crossing a wide ditch with uncertainties and also to �nd optimal solutions with Genetic Algorithm (GA). In generating feasible trajectories o�ine for a biped robot to dynamically cross a wide ditch, the dynamic balance of the biped robot, friction between the robot foot and ground, impact on the foot, limitations on the joint actuator torques and angular velocities are considered. The biped robot is modeled as a seven link planar robot with the ditch crossing task consisting of two single support phases and a double support phase. An algorithm is developed to �nd the joint trajectories and the joint torques in each phase of ditch crossing by formulating the ditch crossing task as a constrained nonlinear optimization problem. In order to make the algorithm converge fast and to give feasible solutions, additional constraints called Adopted Constraints (ACs) are incorporated into the system of constraints. With time being one of the parameters, the developed algorithm adaptively adjusts the time for crossing a wide ditch. The signi�cance of ground reaction force constraints in obtaining feasible solutions for crossing the wide ditch is shown through simulations. Feasible solutions obtained from simulation results provide not only the feasible joint angle trajectories, but also the joint torques required for the selection of actuators for a biped robot crossing the wide ditch. From the results obtained it is felt that an approach for �nding faster solutions (trajectories) is essential for studying the behavior of the biped robot with various initial postures. Ful�lling the above requirement this work also proposes a multibody dynamics approach to generate online trajectories. Trajectories are generated using control constraints that depend on the horizontal distance traveled by the center of mass and are not explicitly dependent on time. Behavior of the biped robot for various initial postures is studied considering dynamic balance, friction, and impact in order to �nd the preferred initial postures considering the net energy consumption and peak power requirements at various joints. Several cases of friction, zero moment point location, and the center of mass height variation are considered in the study. Using the proposed approach, feasible trajectories for an adult sized biped robot could be generated for a wide ditch of 1.05 m width at coe�cients of friction as low as 0.2. The results obtained are useful for designing reference trajectories and actuation systems for biped robots that need to cross wide ditches or take large steps. Time needed for trajectory generation is found to be su�ciently low for online implementation. The work has been extended for generating trajectories for wide ditch crossing with uncertainties.\ud viii Wide ditch crossing with landing uncertainties by a planar biped robot demands real-time solutions, at the same time it has to ful�ll the necessary criteria mentioned before. Besides using the timeindependent control constraints, considering the impact, dynamic balance and friction, to generate real time solutions, a novel concept called the point of feasibility is introduced, for bringing the biped robot to complete rest at the end of ditch crossing. With the proposed approach real-time solutions are found for various initial postures of the biped robot at di�erent friction coe�cients to give the feasible regions for crossing a wide ditch with landing uncertainties. A study on the in uence of initial posture on landing impact and net energy consumption is presented. Through simulations, the best initial postures to e�ciently cross a wide ditch of width 1.05 m, with less impact and without singularities are found. Finally, the advantage of the proposed approach to cross a wide ditch when the surface friction is not same on both sides of the ditch is demonstrated. Using the model with control constraints an approach is proposed for �nding optimal solutions for wide ditch crossing with GA multiobjective optimization. With the proposed approach optimal solutions with GA can be obtained without any additional constraints. Finally optimal initial postures for the biped robot to cross a wide ditch are given along with the peak torque, peak rotational speed and the peak power rating of the actuators required at various joints of the biped robot

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

Generating Feasible Solutions for Dynamically Crossing a Wide Ditch by a Biped Robot

The aim of this research work is to generate feasible motion for a biped robot to dynamically cross a wide ditch which is defined as a ditch with width more than or equal to the leg length. We propose an approach to obtain feasible solutions for dynamically crossing the wide ditch considering the dynamic balance of the biped robot, friction between the robot foot and ground, impact on the foot, limitations on the joint actuator torques and angular velocities. The biped robot is modeled as a seven link planar robot with the ditch crossing task consisting of two single support phases and a double support phase. An algorithm is developed to find the joint trajectories and the joint torques in each phase of ditch crossing by formulating the ditch crossing task as a constrained nonlinear optimization problem. In order to make the algorithm converge fast and to give feasible solutions, additional constraints called Adopted Constraints (ACs) are incorporated into the system of constraints. With time being one of the parameters, the developed algorithm adaptively adjusts the time for crossing a wide ditch. The significance of ground reaction force constraints in obtaining feasible solutions for crossing the wide ditch is shown through simulations. Feasible solutions obtained from simulation results provide not only the feasible joint angle trajectories, but also the joint torques required for the selection of actuators for a biped robot crossing the wide ditch

Maritime expressions:a corpus based exploration of maritime metaphors

This study uses a purpose-built corpus to explore the linguistic legacy of Britain’s maritime history found in the form of hundreds of specialised ‘Maritime Expressions’ (MEs), such as TAKEN ABACK, ANCHOR and ALOOF, that permeate modern English. Selecting just those expressions commencing with ’A’, it analyses 61 MEs in detail and describes the processes by which these technical expressions, from a highly specialised occupational discourse community, have made their way into modern English. The Maritime Text Corpus (MTC) comprises 8.8 million words, encompassing a range of text types and registers, selected to provide a cross-section of ‘maritime’ writing. It is analysed using WordSmith analytical software (Scott, 2010), with the 100 million-word British National Corpus (BNC) as a reference corpus. Using the MTC, a list of keywords of specific salience within the maritime discourse has been compiled and, using frequency data, concordances and collocations, these MEs are described in detail and their use and form in the MTC and the BNC is compared. The study examines the transformation from ME to figurative use in the general discourse, in terms of form and metaphoricity. MEs are classified according to their metaphorical strength and their transference from maritime usage into new registers and domains such as those of business, politics, sports and reportage etc. A revised model of metaphoricity is developed and a new category of figurative expression, the ‘resonator’, is proposed. Additionally, developing the work of Lakov and Johnson, Kovesces and others on Conceptual Metaphor Theory (CMT), a number of Maritime Conceptual Metaphors are identified and their cultural significance is discussed