A classification of stability margins for walking robots

Throughout the history of walking robots several static and dynamic stability criteria have been defined. Nevertheless, different applications may require different stability criteria and, up to the authors’ best knowledge, there is no qualitative classification of such stability measurements. Controlling a robot gait by means of using the wrong stability criterion may prevent the task from succeeding. By the other hand, if the optimum criterion is found the robot gait can also be optimized. In this work, the stability criteria that have been applied to walking robots with at least four legs are examined attending to the stability margin on different static and dynamic situations. As a result, a qualitative classification of stability criteria for walking machines is proposed so that the proper criterion can be chosen for every desired application.Peer reviewe

DYLEMA: Using walking robots for landmine detection and location

Detection and removal of antipersonnel landmines is an important worldwide concern. A huge number of landmines has been deployed over the last twenty years, and demining will take several more decades, even if no more mines were deployed in future. An adequate mineclearance rate can only be achieved by using new technologies such as improved sensors, efficient manipulators and mobile robots. This paper presents some basic ideas on the configuration of a mobile system for detecting and locating antipersonnel landmines efficiently and effectively. The paper describes the main features of the overall system, which consists of a sensor head that can detect certain landmine types, a manipulator to move the sensor head over large areas, a locating system based on a global-positioning system, a remote supervisor computer and a legged robot used as the subsystems’ carrier. The whole system has been configured to work in a semi-autonomous mode with a view also to robot mobility and energy efficiency.This work has been funded by the Spanish Ministry of Science and Technology under Grant CICYT DPI2001-1595 and DPI2004-05824.Peer reviewe

Thrust control, stabilization and energetics of a quadruped running robot

In order to achieve powered autonomous running robots it is essential to develop efficient actuator systems, especially for generating the radial thrust in the legs. In addition, the control of the radial thrust of the legs can be a simple, effective method for stabilizing the body pitch in a running gait. This paper presents the mechanical systems, models and control strategies employed to generate and control leg thrust in the KOLT quadruped running robot. An analytical model of the electro-pneumatic leg thrusting system is presented and analyzed to evaluate its performance and to facilitate the design of control strategies. Several experiments have been conducted to estimate the energy losses and determine their origins as well as to compute the energetic efficiency of the actuation system. Two thrust control methods are also proposed and tested experimentally. The closed loop method regulates thrust through the control of the hip liftoff speed, a conceptually simple control strategy that stabilizes the body pitch in pronk and trot gaits without the need for central feedback, even on irregular terrain. The open-loop control method regulates the energy added in each hop based on the model of the actuator system. The efficacy of these models and techniques is tested in several planar trot and pronk experiments, and the results are analyzed focusing on the body stabilization, the power consumption and the energetic efficiency. © SAGE Publications 2008 Los Angeles.Peer Reviewe

Continuous free-crab gaits for hexapod robots on a natural terrain with forbidden zones: An application to humanitarian demining

Autonomous robots are leaving the laboratories to master new outdoor applications, and walking robots in particular have already shown their potential advantages in these environments, especially on a natural terrain. Gait generation is the key to success in the negotiation of natural terrain with legged robots; however, most of the algorithms devised for hexapods have been tested under laboratory conditions. This paper presents the development of crab and turning gaits for hexapod robots on a natural terrain characterized by containing uneven ground and forbidden zones. The gaits we have developed rely on two empirical rules that derive three control modules that have been tested both under simulation and by experiment. The geometrical model of the SILO-6 walking robot has been used for simulation purposes, while the real SILO-6 walking robot has been used in the experiments. This robot was built as a mobile platform for a sensory system to detect and locate antipersonnel landmines in humanitarian demining missions.Funding for this paper was provided by CICYT under Grant DPI2001-1595 and DPI2004-05824.Peer reviewe

A control architecture for humanitarian-demining legged robots

The use of autonomous robots for humanitarian demining tasks is a promising solution. Among the different types of autonomous robots, walking robots exhibit significant advantages to negotiate uneven and unstructured terrain. However, the complete autonomous control of walking robots is still challenging. In this work, a hybrid reactive/deliberative control architecture is proposed for the autonomous control of a demining system composed of a hexapod walking robot and a scanning manipulator. This control architecture allows the control system to both plan global control and navigation strategies and react to unmodelled disturbances.Peer reviewe

Optimizing Leg Distribution around the Body in Walking Robots

Proceedings of the 2005 IEEE International Conference on Robotics and Automation Barcelona, Spain, April 2005Abstract: Walking-robot technology has reached an advanced stage of development, as has already been demonstrated by a number of real applications. however, further improvement is still needed if walking robots are to compete with traditional vehicles. Some potential improvements could be gained through optimization. Thus, this paper presents a method for distributing the legs around the robot's body such as to reduce the forces the legs must exert to support and propel the robot. The method finds through non-linear optimization techniques the middle leg displacement that nulls the difference between foot forces in a middle leg and a corner leg. A walking robot has been built to assess the theoretical results.This work is supported by CICYT (Spanish Ministry of Education and Science) under Grants DPI2001-1595 and DPI2004-05824.Peer reviewe

Quadrupedal locomotion : an introduction to the control of four-legged robots

xiv, 267 p.: ilWalking machines have potential advantages over traditional vehicles, and they have already succeeded in carrying out many tasks that wheeled or tracked robots cannot handle. Nevertheless, their use in industry and services is currently limited in scope. Quadrupedal Locomotion: An Introduction to the Control of Four-legged Robots brings together some of the methods and techniques in this emerging field that have recently been developed in an effort to deal with the problems that currently prevent legged robots being more widely used for real applications. Quadrupedal Locomotion: An Introduction to the Control of Four-legged Robots illustrates the appropriate algorithms and methods through a discussion of simulation and experiments that have been tested on a real machine, the SILO4 walking robot. Data from the experiments can be found on-line. This book is divided into two parts: the first part, Walking Measurements and Algorithms, introduces the historical development of quadrupeds, their advantages/disadvantages and potential uses, and the trade-off between quadrupeds and hexapods. The second part, Control Techniques, concentrates on general techniques that have been specifically applied to legged robots, including kinematic and dynamic models, soft computing techniques to increase speed, virtual sensors that help reduce the electronic burden of the machine, and software simulators to study and test certain robot properties. As the first book to focus specifically on quadrupeds, Quadrupedal Locomotion: An Introduction to the Control of Four-legged Robots will be suitable for researchers, postgraduates and senior undergraduates in the field of robotics as well as engineers working in industry.Part I Walking Measurements and Algorithms Walking Robots Stability in Walking Robots Generation of Periodic Gaits Generation on Non-periodic Gaits New Approaches to Stability Part II Control Techniques Kinematics and Dynamics Improving Leg Speed by Soft Computing Techniques Virtual Sensors for Walking Robots Human-Machine Interaction The SIL04 Walking Robot Simulation Software for Walking RobotsPeer reviewe

Location of legged robots in outdoor environments

Knowledge of a robot's position with an accuracy of within a few centimeters is required for potential applications for legged robots, such as humanitarian de-mining tasks. Individual sensors are unable to provide such accuracy. Thus information from various sources must be used to accomplish the tasks. Following this trend, this paper describes the method developed for estimating the position of legged robots in outdoor environments. The proposed method factors in the specific features of legged robots and combines dead-reckoning estimation with data provided by a Differential Global Positioning System through an extended Kalman filter algorithm. This localization system permits accurate trajectory tracking of legged robots during critical activities such as humanitarian de-mining tasks. Preliminary experiments carried out with the SILO4 system have shown adequate performance using this localization system. © 2007 Elsevier B.V. All rights reserved.Peer Reviewe

A Comparative Study of Stability Margins for Walking Machines

Several static and dynamic stability criteria have been defined in the course of walking robot history. Nevertheless, different applications may require different criteria and, to the authors' best knowledge, there is no qualitative classification of such stability measurements. Using the wring stability criterion to control a robot gait may prevent the task from succeeding. Furthermore, if the optimum criterion is found, the robot gait can also be optimized. In this paper, the stability criteria that have been applied to walking robots with at least four legs are examined in terms of their stability margins in different static and dynamic situations. As a result, a qualitative classification of stability criteria for walking machines is proposed so that the proper criterion can be chosen for every desired application.Peer reviewe

Accurate tracking of legged robots on natural terrain

Statically stable walking locomotion research has focused mainly on robot design and gait generation. However, there is a need to expand robots’ capabilities so that walking machines can accomplish the kinds of real tasks for which they are eminently suited. Many such tasks demand trajectory tracking, but researchers have traditionally ignored this subject. This article focuses on the tracking of predefined trajectories with hexapod robots walking on natural terrain with forbidden zones. The method presented herein, which relies on gait algorithms defined elsewhere, describes certain localization strategies and control techniques that have been employed to follow trajectories accurately and have been implemented in a real walking hexapod. Several experimental examples are included to assess the proposed algorithms.Funding for this work was provided by the Spanish Ministry of Science and Technology under Grants DPI2001-1595 and DPI2004-05824.Peer reviewe