SWheg: A Wheel-Leg Transformable Robot With Minimalist Actuator Realization

This article presents the design, implementation, and performance evaluation of SWheg, a novel modular wheel-leg transformable robot family with minimalist actuator realization. SWheg takes advantage of both wheeled and legged locomotion by seamlessly integrating them on a single platform. In contrast to other designs that use multiple actuators, SWheg uses only one actuator to drive the transformation of all the wheel-leg modules in sync. This means an N-legged SWheg robot requires only N+1 actuators, which can significantly reduce the cost and malfunction rate of the platform. The tendon-driven wheel-leg transformation mechanism based on a four-bar linkage can perform fast morphology transitions between wheels and legs. We validated the design principle with two SWheg robots with four and six wheel-leg modules separately, namely Quadrupedal SWheg and Hexapod SWheg. The design process, mechatronics infrastructure, and the gait behavioral development of both platforms were discussed. The performance of the robot was evaluated in various scenarios, including driving and turning in wheeled mode, step crossing, irregular terrain passing, and stair climbing in legged mode. The comparison between these two platforms was also discussed

A literature review on the optimization of legged robots

Over the last two decades the research and development of legged locomotion robots has grown steadily. Legged systems present major advantages when compared with ‘traditional’ vehicles, because they allow locomotion in inaccessible terrain to vehicles with wheels and tracks. However, the robustness of legged robots, and especially their energy consumption, among other aspects, still lag behind mechanisms that use wheels and tracks. Therefore, in the present state of development, there are several aspects that need to be improved and optimized. Keeping these ideas in mind, this paper presents the review of the literature of different methods adopted for the optimization of the structure and locomotion gaits of walking robots. Among the distinct possible strategies often used for these tasks are referred approaches such as the mimicking of biological animals, the use of evolutionary schemes to find the optimal parameters and structures, the adoption of sound mechanical design rules, and the optimization of power-based indexes

DEPUSH HexCrawler Improvement Project

DEPUSH Technologies purchased the rights to an older six-legged walking robot design and sought help from WPI and HUST students to improve its functionality to better meet the needs of the secondary education market in mainland China. To accomplish this goal, both the mechanical walking system and control system were improved. The mechanical structure was redesigned for three degree of freedom legs and a more robust chassis, while an entirely new control system was utilized to implement full inverse body and walking kinematics. The result was a cutting-edge hexapod, the HexCrawler 2.0, a versatile platform with potential applications in a variety of robotics-related projects and solid foundation for future research on high-level control

DEPUSH HexCrawler: Mechanical and Control System Improvement

The DEPUSH HexCrawler robot has a dated control system and walking mechanism making it unstable and clumsy. DEPUSH asked our team to update the HexCrawler in conjunction with HUST students from Wuhan, China. The team redesigned the robot\u27s chassis and legs to increase mobility and stability, and implemented a powerful control system capable of precisely manipulating the robot\u27s limbs. The resulting product is a 6 Degree-of-Freedom hexapod and accompanying computer interface with applications in a variety of robotics research areas

DESIGN OF A MINIATURISED HEXAPOD ROVER FOR MARTIAN EXPLORATION

Lo scopo di questo lavoro è la progettazione preliminare di un robot esapode miniaturizzato bio-insipired per l'esplorazione dei tubi lavici marziani, ovvero i condotti sotterranei formati dall'attività lavica di vulcani non esplosivi. A tal fine, è stata scelta una suite di sensori per la caratterizzazione di questi ambienti. Con l'obiettivo di mappare le grotte, l'esapode è stato equipaggiato con una telecamera e sono stati individuati anche una serie di sensori per misurare la presenza di perclorato, la dose di radiazioni che passa lo strato basaltico, la temperatura e l'umidità relativa all'interno dei tubi di lavici. In questo lavoro vengono spiegate anche le ragioni della scelta di questo tipo di analisi e gli strumenti individuati. La scelta dei sensori da ospitare nell'esapode ha portato ad avere le dimensioni preliminari del robot, in modo da poterne decidere la configurazione. La configurazione scelta consiste in un corpo centrale rettangolare con le sei zampe disposte simmetricamente lungo il lato più lungo; le zampe sono state progettate basandosi su quelle degli insetti. Essendo un dimensionamento iniziale, è stata utilizzata la configurazione più semplice per verificare i componenti e la possibile realizzazione. Il robot è stato riprodotto con Solidworks e poi importato in Simulink. Il capitolo principale è incentrato sulla simulazione del robot e del suo movimento attraverso l'ambiente MATLAB&Simulink, in modo da verificare la possibilità di utilizzare i servi più piccoli presenti sul mercato, attraverso il rilevamento delle coppie richieste dal rover. Il metodo della cinematica inversa è stato utilizzato per imporre una traiettoria semiellittica alle gambe attraverso script e funzioni dedicate che creano i vettori dei profili di posizione, di velocità e infine i vettori dei profili di accelerazione che sono stati impostati trapezoidali per evitare problemi dovuti a discontinuità. Sono stati testati tre tipi di andature: metacronale, ondulata e tripode, corrispondenti a tre velocità del robot. È stato possibile verificare l'uso dei servi attraverso la modellazione, in quanto sono stati rispettati i limiti imposti da questi ultimi.The purpose of this work is the preliminary design of a miniaturized bio-insipired hexapod robot for the exploration of Martian lava tubes, i.e. the underground conduits formed through the lava activity of non-explosive volcanoes. For this purpose, a suite of sensor was chosen for the characterization of these environments. With the aim of mapping the caves, the hexapod has been equipped with a camera and a series of sensors were also identified to measure the presence of perchlorate, the dose of radiation that passes the basaltic layer, the temperature and the relative humidity inside the lava tubes. In this work, the reasons for choosing this type of analysis are also explained, along with the identified instruments. The choice of sensors to accommodate in the hexapod led to have the preliminary dimensions of the robot, so that a decision could be made on the configuration. The configuration chosen consists of a rectangular central body with the six legs arranged symmetrically along the longest side, the legs were designed based on those of insects. Being an initial design, it was used the simplest configuration to verify the components and the possible realisation of it. The robot was reproduced using Solidworks and then imported in Simulink. The main chapter is focused on the simulation of the robot and its motion through the MATLAB&Simulink environment so that the possibility of using the smallest servos found on the market can be verified, through the sensing of the torques required by the rover. The inverse kinematics method was used to impose a semi-elliptical trajectory on the legs through dedicated scripts and functions that create the vectors of the position profiles, the velocity profiles and, finally, the vectors of the acceleration profiles that have been set trapezoidal to avoid problems due to discontinuities. Three types of gaits were tested: metachronal, ripple and tripod gait, corresponding to three speeds of the robot. It was possible to verify the use of servos through modelling, as the limits imposed by them were respected

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

Multistable Phase Regulation for Robust Steady and Transitional Legged Gaits

We develop robust methods that allow specification, control, and transition of a multi-legged robot’s stepping pattern—its gait—during active locomotion over natural terrain. Resulting gaits emerge through the introduction of controllers that impose appropriately-placed repellors within the space of gaits, the torus of relative leg phases, thereby mitigating against dangerous patterns of leg timing. Moreover, these repellors are organized with respect to a natural cellular decomposition of gait space and result in limit cycles with associated basins that are well characterized by these cells, thus conferring a symbolic character upon the overall behavioral repertoire. These ideas are particularly applicable to four- and six-legged robots, for which a large variety of interesting and useful (and, in many cases, familiar) gaits exist, and whose tradeoffs between speed and reliability motivate the desire for transitioning between them during active locomotion. We provide an empirical instance of this gait regulation scheme by application to a climbing hexapod, whose “physical layer” sensor-feedback control requires adequate grasp of a climbing surface but whose closed loop control perturbs the robot from its desired gait. We document how the regulation scheme secures the desired gait and permits operator selection of different gaits as required during active climbing on challenging surfaces

Locomotion and pose estimation in compliant, torque-controlled hexapedal robots

Several scenarios, such as disaster response or terrestrial and extra-terrestrial exploration, comprise environments that are dangerous or even inaccessible for humans. In those cases, autonomous robots pose a promising alternative to render such endeavours possible. While most of today’s robotic explorers are wheeled or tracked vehicles, legged systems gained increased attention in recent years. With their unique combination of omnidirectional mobility and intrinsic manipulation capabilities, they are envisioned to serve as the rough terrain specialists in scouting or sample and return missions. Especially, small to mid-size hexapods are of great interest for those scenarios. Providing static stability across a wide range of walking speeds, they offer an attractive trade-off between versatility and complexity. Another important advantage is their redundancy, allowing them to tolerate the loss of single legs. However, due to their small size, the computational on-board resources are limited. Thus, the use of smart and efficient algorithms is of utmost importance in order to enable autonomous operation within a priori unknown rough environments. Working towards such autonomous robotic scouts, this thesis contributes with the development, implementation, and test of a self-contained walking layer as well as a 6 degrees of freedom (DOF) leg odometry for compliant, torque-controlled, hexapedal robots. Herein, the important property of all presented algorithms is the sole use of proprioceptive measurements provided by the legs, i. e. joint angles and joint torques. Especially the joint torque sensors improve the walking process by enabling the use of sensitive compliance controllers and distributed collision detection. Comprising a set of algorithms, the walking layer organises and structures the walking process in order to generate robust, adaptive, and leg loss tolerant locomotion in uneven terrain. Furthermore, it encapsulates the walking process, and thus hides its complexity from higher-level algorithms such as navigation. Its three main functional components are a flexible, biologically-inspired gait coordination algorithm, single leg reflexes, and active joint compliance control. Thereof, the gait coordination algorithm realises temporal adaptation of the step sequence while reflexes adjust the leg trajectories to the local terrain. The joint compliance control reduces internal forces and allows for situation dependent stiffness adjustments. An algorithmic extensions to the basic gait coordination enables the immediate adaptation to leg loss. In combination with stiffness and pose adjustments, this allows the hexapod to retain stable locomotion on five legs. In order to account for the emerging gait, the leg odometry algorithm employs an optimisation approach to obtain a kinematics-based pose estimate from joint angle measurements. Fusing the resulting pitch and roll angle estimates with joint-torque-measurement-based attitude data, reduces the associated drift, and thus stabilises the overall pose estimate. Various simulations and experiments with the six-legged, torque-controlled DLR Crawler demonstrate the effectiveness of the proposed walking layer as well as the 6-DOF leg odometry.Für die planetare Exploration sowie den Einsatz in Katastrophengebieten sind autonome Laufroboter zunehmend von Interesse. In diesen Szenarien sollen sie den Menschen an gefährlichen oder schwer zugänglichen Orten ersetzen und dort Erkundungseinsätze sowie Probenahmen in schwierigem Gelände durchführen. Unter der Vielzahl an möglichen Systemen bieten im Besonderen kleinere Sechsbeiner einen sehr guten Kompromiss zwischen Stabilität, hoher Beweglichkeit, Vielseitigkeit und einer vertretbaren Komplexität der Regelung. Ein weiterer Vorteil ist ihre Redundanz, die es ihnen erlaubt, den Ausfall einzelner Beine mit geringem Aufwand zu kompensieren. Dementgegen ist die beschränkte Rechenkapazität ein Nachteil der reduzierten Größe. Um diesen auszugleichen und das autonome Agieren in einer unbekannten Umgebung zu ermöglichen, werden daher einfache und effiziente Algorithmen benötigt, die im Zusammenspiel jedoch ein komplexes Verhalten erzeugen. Auf dem Weg zum autonom explorierenden Laufroboter entwickelt diese Arbeit einen robusten, adaptiven und fehlertoleranten Laufalgorithmus sowie eine 6D Eigenbewegungsschätzung für nachgiebige, drehmomentgeregelte Sechsbeiner. Besonders herauszustellen ist, dass alle in der Arbeit vorgestellten Algorithmen ausschließlich die propriozeptive Sensorik der Beine verwenden. Durch diesen Ansatz kann der Laufprozess von anderen Prozessen, wie der Navigation, getrennt und somit der Datenaustausch effizient gestaltet werden. Für die Fortbewegung in unebenem Gelände kombiniert der vorgestellte Laufalgorithmus eine flexible, biologisch inspirierte Gangkoordination mit verschiedenen Einzelbeinreflexen und einer nachgiebigen Gelenkregelung. Hierbei übernimmt die Gangkoordination die zeitliche Steuerung der Schrittfolge, während die Einzelbeinreflexe für eine räumliche Variation der Fußtrajektorien zuständig sind. Die nachgiebige Gelenkregelung reduziert interne Kräfte und erlaubt eine Anpassung der Gelenksteifigkeiten an die lokalen Umgebungsbedingungen sowie den aktuellen Zustand des Roboters. Eine wichtige Eigenschaft des Laufalgorithmus ist seine Fähigkeit, den Ausfall einzelner Beine zu kompensieren. In diesem Fall erfolgt eine Adaption der Gangkoordination über die Erneuerung der Nachbarschaftsbeziehungen der Beine. Zusätzlich verbessern eine Veränderung der Pose und eine Erhöhung der Gelenksteifigkeiten die Stabilität des durch den Beinverlust beeinträchtigten Roboters. Gleich dem Laufalgorithmus verwendet die 6D Eigenbewegungsschätzung nur die Messungen der propriozeptiven Sensoren der Beine. Hierbei arbeitet der Algorithmus in einem dreistufigen Verfahren. Zuerst berechnet er mit Hilfe der Beinkinematik und einer Optimierung die Pose des Roboters. Nachfolgend bestimmt er aus den Gelenkmomentmessungen den Gravitationsvektor und berechnet daraus die Neigungswinkel des Systems. Eine Fusion dieser Werte mit den Nick- und Rollwinkeln der ersten Stufe stabilisiert daraufhin die gesamte Odometrie und reduziert deren Drift. Alle in dieser Arbeit entwickelten Algorithmen wurden mit Hilfe von Simulationen sowie Experimenten mit dem drehmomentgeregelten DLR Krabbler erfolgreich validiert