Terrain Adaptability Research Articles

Development of a Load‐Bearing, Terrain‐Adaptive Hexapod Robot With Chebyshev‐Linkage Legs

ABSTRACTThis study introduces an exploratory design for a hexapod load‐carrying robot, aiming to address challenges commonly associated with quadruped robots, including limited load capacity and high control complexity. By leveraging a Chebyshev linkage‐based overconstrained leg‐foot architecture that combines high rigidity and low friction, along with a multi‐drive system for lateral movement, we propose a robot with improved adaptability to diverse terrains, such as snow, sand, puddles, ice, and deserts. This versatility suggests potential applications in areas such as factory inspection, field reconnaissance and transport, and desert exploration. Using static and dynamic analyses, we evaluated the leg structure's stress distribution and motion requirements, employing simulations in Workbench and Adams to cross‐validate our theoretical calculations. The development of a prototype and its subsequent testing under various environmental conditions aimed to demonstrate the design's practicality and the robot's operational capabilities in real‐world settings. Although the findings indicate progress toward enhancing load‐bearing capabilities and terrain adaptability with reduced control complexity, further research and development are necessary to fully realize the potential of such robotic systems in practical applications.

A linkage-type self-adaptive deformable tracked mechanism based on the six-bar mechanism

Abstract. In order to design a self-adaptive tracked mechanism that can passively adjust according to the height of different obstacles to improve its obstacle-crossing performance, this paper proposes a linkage-type self-adaptive deformable tracked mechanism. The mechanism based on the planar six-bar mechanism is proposed, and its motion modes and obstacle-crossing capabilities are analyzed. Firstly, based on the characteristics of self-adaptive deformation and the planar six-bar mechanism, a deformable single-degree-of-freedom (DOF) multi-loop mechanism is designed by limiting the DOF and adjusting the link lengths, and subsequently, a linkage-type self-adaptive deformable tracked mechanism module is designed according to the multi-loop mechanism. Secondly, the movement characteristics of the deformable tracked mechanism module are analyzed, and it is obtained that the tracked mechanism has two modes of movement: forward and reverse. These modes include deformable tracked-type obstacle crossing and rocker-arm-type obstacle crossing, respectively. Additionally, it is also obtained that this mechanism is capable of climbing up and descending down slopes. Finally, a prototype model is designed for experimental verification to verify the correctness of the theoretical analysis of the linkage-type self-adaptive deformable tracked mechanism and the feasibility of the obstacle-crossing modes. The results indicate that the linkage-type self-adaptive deformable tracked mechanism is capable of various obstacle-crossing modes, including both forward and reverse movements. These modes encompass the traditional tracked type, the deformable tracked type, and the rocker-arm type, as well as the ability to climb up and descend down slopes. This type of mechanism demonstrates excellent terrain adaptability and is capable of overcoming obstacles, allowing it to traverse some soft and rugged terrain. Consequently, it holds certain application potential.

Three-dimensional modeling of 500 kV transmission lines by airborne LiDAR

This study aims to enhance the accuracy of three-dimensional (3D) modeling in the planning, design, operation management, and risk assessment of 500 kV transmission lines. Addressing the limitations of traditional two-dimensional (2D) or low-precision 3D models, a new method based on airborne Light Detection and Ranging (LiDAR) technology is proposed. Initially, high-density, high-precision 3D point cloud data are collected using airborne LiDAR technology. This data is then processed using specialized software for noise removal, terrain classification extraction, and Geographic Information System (GIS) data integration. Subsequently, a Convolutional Neural Network (CNN) is employed to classify the 3D point cloud data to enhance the accuracy of complex structure recognition. Lastly, the point cloud data are converted into linear and planar entities using Computer-Aided Design (CAD) technology, achieving high-precision 3D reconstruction of the 500 kV transmission lines and their complex terrain environment. Experimental results show that the spatial resolution of the constructed model reaches 0.1 m per pixel, with overall geometric accuracy within ±5 cm. Compared to traditional aerial imagery and ground survey methods, the model based on airborne LiDAR technology achieves improvements of 30 % in detail richness and 35 % in terrain adaptability, with a 45 % increase in decision-making efficiency. These improvements significantly enhance the accuracy of line operations, safety assessments, and environmental impact analyses, providing solid data support for the modernization and intelligent development of the power industry.

A composite motion control method for quadruped robots in trot gait

This work aims to address the issues of instability in trot gait walking and poor terrain adaptability in rugged environments under conventional control strategies for quadruped robots by proposing a novel composite control strategy. During the support phase, a separated force-position mixing control method is employed, utilizing gravity-compensated PD (Proportional Derivative) control at the lateral swing and knee joints while employing position control at the hip joint. During the swing phase, VMC (Virtual Model Control) is used to construct three sets of virtual spring-damper components, guiding the foot to move along a predetermined trajectory and converting virtual forces into joint torques for the swinging leg. At the body, IMU (Inertial Measurement Unit) feedback data combined with PI (Proportional Integral) control is used to adjust leg length and maintain the robot’s posture stability. Finally, the proposed separated force-position hybrid control method is theoretically validated using the Lyapunov stability criterion, and simulation tests on flat and rugged terrains under the quadruped robot’s composite control method are conducted using MATLAB/Simulink, comparing it with the VMC and position control methods. The findings indicate that the composite control strategy leads to smaller changes in the attitude angles and reduced impact forces at the feet during the quadruped robot’s walk on flat ground while also demonstrating strong adaptability to rugged terrains.

Stiffness optimization design of wheeled-legged rover integrating active and passive compliance capabilities

Compliance capability is one of the most important properties of suspension systems for rough-terrain robots. This imposes specific requirements on system stiffness design, which directly determines the platform's performance in response to external stimuli. To address the challenge of stiffness optimization design in active and passive compliant systems, this paper proposes a novel and practical method for optimizing stiffness for a terrain-adaptive wheel-legged rover. Firstly, the kinematic model of this multi-degree-of-freedom platform is established. Secondly, the deformation capability coefficient, load capacity coefficient, energy efficiency coefficient, and dynamic stability coefficient are derived as performance indices to assess the behavior of the system. By establishing the relationship between joint configuration variation and system stiffness, stiffness parameters could be evaluated through these performance indices. Ultimately, the global optimum stiffness parameters are selected from the refined intersection of the individual performance optimal domains. Thirdly, the optimum parameters are calculated and applicability verified numerically. The designed parameters are verified experimentally on a wheeled-legged rover. The experimental results demonstrate that the proposed algorithm can find the parameter combination that achieves optimal system performance, thereby enhancing the system's terrain adaptability.

Unearthing the history with A‐RHex: Leveraging articulated hexapod robots for archeological pre‐exploration

AbstractThis paper aims to develop a miniature mobile robot suitable to assist archeologists in their first exploration of unknown underground tombs. Due to the rather complex and irregular terrains in the tombs and inspired by the classic RHex design, we have developed a two‐segment articulated robot (A‐RHex) with two RHex design units. The robot is compact and lightweight, with dimensions of 25 cm long, 6.5 cm wide, 7 cm high, and weighs 283 g. To assist the robot in entering the tomb, we have also designed a deployment platform that can take the robots underground through a 10‐cm exploration hole. We introduce the overall design, control, and communication methods of A‐RHex, and theoretically analyze how the articulated design can improve the stability of the robot on slopes. Laboratory experiments and field testings at two real archeological excavation sites in China have validated A‐RHex's mechanical design, control strategies, communications, and capabilities for pre‐exploration of open and closed tombs. We believe that this kind of robot with high terrain adaptability and a small profile may become an important tool for field archeology in the future.

Design of a bipedal robot for water running based on a six-linkage mechanism inspired by basilisk lizards

Legged robots have received widespread attention in academia and engineering owing to their excellent terrain adaptability. However, most legged robots can only adapt to high-hardness environments instead of flexible environments. Expanding the motion range of legged robots to water is a promising but challenging work. Inspired by basilisk lizards which can run on water surfaces by feet, this paper proposes a bipedal robot for water running by hydrodynamics instead of buoyancy. According to the motion parameters of the basilisk lizard during water running, a single-degree of freedom bipedal mechanism is proposed to reproduce the motion trajectory of the feet of the basilisk lizard. Scale optimization is conducted by a particle swarm optimization algorithm to determine the geometrical parameters of the mechanism. The effects of motion frequency and foot area on mechanism performance are studied and the optimal solutions are determined by the maximum single-cycle lift impulse through numerical calculations. A bipedal water running robot prototype was fabricated, and the experimental results show that the prototype can generate enough support for the robot running on the water by providing a maximum lift of 2.4 times its weight (160 g) and reaching a horizontal forward speed range of 0.3-0.8 m s-1, compared with the basilisk lizard weighs 2-200 g, generates a lift impulse that is 111%-225% of its body weight, and moves at a speed of 1.3 ± 0.1 m s-1.

HTEC foot: A novel foot structure for humanoid robots combining static stability and dynamic adaptability

Passive bionic feet, known for their human-like compliance, have garnered attention for their potential to achieve notable environmental adaptability. In this paper, a method was proposed to unifying passive bionic feet static supporting stability and dynamic terrain adaptability through the utilization of the Rigid-Elastic Hybrid (REH) dynamics model. First, a bionic foot model, named the Hinge Tension Elastic Complex (HTEC) model, was developed by extracting key features from human feet. Furthermore, the kinematics and REH dynamics of the HTEC model were established. Based on the foot dynamics, a nonlinear optimization method for stiffness matching (NOSM) was designed. Finally, the HTEC-based foot was constructed and applied onto BHR-B2 humanoid robot. The foot static stability is achieved. The enhanced adaptability is observed as the robot traverses square steel, lawn, and cobblestone terrains. Through proposed design method and structure, the mobility of the humanoid robot is improved.

Improving Terrain Adaptability and Compliance in Closed-Chain Leg: Design, Control, and Testing

Abstract This study investigates a novel design of a reconfigurable closed-chain leg for hexapod robot with enhanced terrain adaptability. A length adjustable hydraulic cylinder is incorporated into the Theo Jansen linkage in the proposed reconfigurable closed-chain leg, allowing for flexible trajectory by adjusting the length of the hydraulic cylinder. Kinematic model and system dynamics are analyzed considering the multi-body dynamics of the proposed system. To actively adapt to different terrains with flexible footprints, a variable-domain sliding mode control strategy to adjust the length of hydraulic cylinder is investigated and compared with other control strategies. Meanwhile, an active compliant control strategy of the driving motor is analyzed and deployed to improve the stability and compliance during walking. A prototype was fabricated and tested under various configurations. Results demonstrate that the variable-domain sliding mode control algorithm exhibits fast convergence, robustness, and smooth signals for hydraulic cylinder. In addition, the proposed active compliant control strategy of the driving motor can reduce the impact force and ensure stable equilibrium during walking. Therefore, the proposed reconfigurable closed-chain leg can enhance the terrain adaptability and enrich the applications of closed-chain legged robots.

Robust control algorithm designed for robotic legs of lunar-based equipment: Modeling and experiment

In lunar exploration, lunar-based equipment assumes the responsibility of mobility and transportation during the construction of unmanned lunar base. Legged robots are an important form of the lunar-based equipment due to their mobility and terrain adaptability. However, the influence of lunar terrain and lunar soil cannot be ignored when it comes to studying the mobile stability of lunar-based equipment. Utilizing the dynamic model of the robotic leg, this study proposes a new robust control algorithm, MBC (Model-Based with Continuous expression) algorithm, for lunar-based equipment’s robotic leg, and its effectiveness is established through experimentation and theoretical validation with the Lyapunov second method. In the design and verification, the contact force of lunar soil and the lunar environment with low gravity are considered, indicating the applicability of the proposed MBC method in special lunar scenarios. Compared to the conventional PD (Proportional-Differential) and MPD (Model-Based Proportional-Differential) techniques, MBC robust algorithm ultimately demonstrates superior stability and rapidity with a smaller steady state error.

COMPARISON OF MECHANICAL DESIGN AND FLOW ANALYSIS OF QUADRUPED ROBOTS

In recent years, there has been a trend of developing innovative technologies inspired by living creatures in nature. Quadruped robots, in particular, have emerged as walking mobile systems with articulated leg structures that can skilfully perform dynamic movements that wheeled systems are limited to. These robots offer advantages in technical criteria such as manoeuvrability, cross-capability, controllability, terrain adaptability and stability. It is important to note that this evaluation is based on objective technical criteria rather than subjective opinions. This study compares the advantages and disadvantages of quadruped robots to wheeled systems. It highlights that quadruped robots outperform wheeled systems in manoeuvrability, obstacle overcoming, and speed, particularly in rough terrains. The study also suggests that designers of quadruped robots should consider aerodynamic factors, which are often overlooked. Flow analysis using the finite element method is crucial in robot design to enhance aerodynamic performance. This paper aims to comprehensively analyse the flow structure around quadruped robots using Computational Fluid Dynamics and investigate passive flow control methods to reduce the drag coefficient (Cd). The study examines four different robots, and the resulting Cd average percentage calculations are presented. The aerodynamic efficiency of Robot 4 compared to Robot 2 was found to be 95%. Similarly, the aerodynamic efficiency of Robot 3 was determined to be 28% compared to Robot 2. Additionally, it was determined that the aerodynamic efficiency of Robot 2 was 76% compared to Robot 1. These results provide an important comparison to understand the energy efficiency, differences in aerodynamic performance and relative effectiveness of quadruped robots.

Four-bar linkage reconfigurable robotic wheel: Design, kinematic analysis, and experimental validation for adaptive size modification

Abstract This article presents the development of a robot capable of modifying its size through a wheel reconfiguration strategy. The reconfigurable wheel design is based on a four-bar retractable mechanism that achieves variation of the effective radius of the wheel. A reconfiguration index is introduced based on the number of retractable mechanisms that predicts the radius of configuration according to the number of mechanisms implemented in the wheel. The kinematics of the retractable mechanism is studied to determine the theoretical reconfiguration radius during the transformation process, it is also evaluated numerically with the help of the GeoGebra software, and it is validated experimentally by image analysis using the Tracker software. The transformation process of the robot is investigated through an analysis of forces that consider the wheel in contact with the obstacle, the calculation of the wheel torque and the height of the obstacle to be overcome are presented. On the other hand, the experimental validation of the robot reconfiguration process is presented through the percentage of success shown by the robot to overcome obstacles of 50, 75, 100 and 125 mm. In addition, measurements of energy consumption during the transformation process are reported. Reconfigurable wheels, capable of adapting their size, offer innovative solutions to various challenges across different applications such as robotic exploration and search and rescue missions to industrial settings. Some key issues that these wheels can address include terrain adaptability enhancing a robot’s mobility over uneven surfaces, or obstacles; enhanced robotic design; cost-effective design; space efficiency; and versatility in applications.

Design and experiment of multi-locomotion tensegrity mobile robot

Multi-locomotion tensegrity mobile robots have garnered significant attention in recent research due to their strong terrain adaptability and high stiffness-to-mass ratio. However, the lack of effective design method limits the application range of these robots. In this article, a mechanism design method for the multi-locomotion tensegrity mobile robot is proposed. Firstly, based on the characteristics of worms, mechanism design objectives for the tensegrity robot are put forward from three perspectives, namely bionics, motion law and tensegrity characteristics. Accordingly, the mechanism design process is conducted from two sections in terms of the design of multi-locomotion tensegrity units and the splicing of the identical units. In the mechanism design for the tensegrity units, the rod distribution is firstly determined on compliance with the proposed design objectives, followed by the determination of cable distribution with force-balance analysis method. On this basis, two identical multi-locomotion tensegrity units are axially spliced, and a series of multi-locomotion tensegrity robotic mechanisms can be acquired naturally. Finally, examples are provided, and simulations and experiments are conducted to demonstrate the effectiveness of the proposed mechanism design method.

Numerical Simulation of Motion Test of Bionic Amphibious Quadruped Robot

Bionic amphibious quadruped robots are a huge leap in robotics, with the ability to navigate various terrains with agility and efficiency. In this study, the researchers utilized numerical simulations of motion tests to assess the locomotion skills of these extraordinary robotic systems. They learned a lot about their functioning and problems by rigorously analyzing performance parameters across various terrains and conditions, such as terrain adaptability, traversal speed, energy efficiency, stability, and manoeuvrability. The results they obtained highlighted the importance of adaptive control algorithms and mechanical designs in maximizing traversal speed and energy economy, especially while negotiating difficult terrains. In addition, the study demonstrated the interdisciplinary character of research in bionic amphibious quadruped robots, drawing on insights from biomechanics, control theory, robotics, and computational modelling. By combining previous research and utilizing computational simulation approaches, they opened the road for the creation of versatile and durable robotic systems capable of navigating difficult terrains and surroundings with precision and efficiency. Future research efforts could focus on improving design and control, investigating novel propulsion mechanisms, adaptive locomotion tactics, and biomimetic control algorithms to improve performance and adaptability. Addressing the challenges identified in the research and seizing opportunities for innovation will drive the development of robotic systems that push the limits of locomotion capabilities and open up new possibilities for applications in exploration, search and rescue, environmental monitoring, and beyond.

A toe-inspired rigid-flexible coupling wheel design method for improving the terrain adaptability of a sewer robot.

The human toe, characterized by its rigid-flexible structure comprising hard bones and flexible joints, facilitates adaptive and stable movement across varied terrains. In this paper, we utilized a motion capture system to study the adaptive adjustments of toe joints when encountering obstacles. Inspired by the mechanics of toe joints, we proposed a novel design method for a rigid-flexible coupled wheel. The wheel comprises multiple elements: a rigid skeleton, supporting toes, connecting shafts, torsion springs, soft tendons, and damping pads. The torsion springs connect the rigid frame to the supporting toes, enabling them to adapt to uneven terrains and pipes with different diameters. The design was validated through kinematic and dynamic modeling, rigid-flexible coupled dynamics simulation, and stress analysis. Different stiffness coefficients of torsion springs were compared for optimal wheel design. Then, the wheel was applied to a sewer robot, and its performance was evaluated and compared with a pneumatic rubber tire in various experiments, including movement on flat surfaces, overcoming small obstacles, adaptability tests in different terrains, and active driving force tests in dry and wet pipelines. The results prove that the designed wheel showed better stability and anti-slip properties than conventional tires, making it suitable for diverse applications such as pipeline robots, desert vehicles, and lunar rovers.

Design and multimodal locomotion plan of a hexapod robot with improved knee joints

AbstractHexapod robots represent complex and highly redundant robotic systems capable of handling various tasks in extreme environments, such as planetary exploration and disaster response. To enhance the terrain adaptability and maneuverability of hexapod robots, we present a novel multimodal hexapod robot in this research. Our multimodal hexapod robot design incorporates knee joints with an improved multiparallel quadrilateral transmission mechanism, addressing singularity issues commonly encountered in legged robots. This enhancement not only improves the mechanical transmission characteristics of the knee joints but also increases the workspace of a single leg to achieve leg‐arm reuse functionality. In the presence of flat and structured terrain, the robot seamlessly switches to a wheeled locomotion mode, enabling swift traversal. Conversely, when faced with rough and unstructured terrain, it transitions into a legged mode, employing adaptive gait stability to navigate effectively. A novel operational mode in which the hexapod robot utilizes four legs for body support, while the remaining two legs are repurposed as arms is proposed. This innovative approach empowers the hexapod robot to perform dual‐arm manipulation without the need for additional degrees of freedom for the manipulator. To validate the effectiveness of our designed hexapod robot and multimodal motion planning algorithm, comprehensive experimental testing has been conducted, demonstrating the practicality and versatility of our system.

Gait Learning for Hexapod Robot Facing Rough Terrain Based on Dueling-DQN Algorithm

In the handling of dangerous goods in explosive environments, robots are increasingly being used instead of human operators. Robots designed for operation in explosive environments are mostly equipped with tracked structures, which, due to their limited terrain adaptability, struggle to movement rugged landscapes. Hexapod robots, with their excellent maneuverability and adaptability, possess advantages in completing hazardous material handling tasks in such rugged terrains. One current challenge lies in enabling hexapod robots to autonomously adjust their gaits to cope with rugged terrain. This paper proposes a gait learning method based on the Dueling Deep Q-Network (Dueling-DQN) algorithm to address the gait adjustment problem of hexapod robots in sloped, terraced, and rugged terrain. The method combines lidar data and reinforcement learning to extract features from the lidar data to determine terrain types and foot coordinates. Finally, the Dueling-DQN algorithm and redundant phase strategy are employed to facilitate the motion of hexapod robots in these three types of rugged terrain. Simulation and prototype experiments are conducted to evaluate the Dueling-DQN algorithm's performance in terms of rewards and stability margins for the three types of terrain. During algorithm training on sloped, terraced, and rugged terrain, stable rewards and positive stability margins are achieved after approximately 490 iterations. The effectiveness and feasibility of the proposed method are further validated through Gazebo simulation and prototype experiments. In the context of movement in rugged terrain within explosive environments, the gait learning method based on the Dueling-DQN algorithm offers valuable insights into the control of hexapod robots.

Design and obstacle-crossing analysis of a four-link rocker-suspension planetary exploration robot

Abstract. At present, there are still many meteorite craters and boulders on the surface of Mars and the Moon that cannot be accessed by existing planetary exploration robots. To provide a solution to this issue, this paper proposes a four-link rocker-suspension planetary exploration robot that combines both the reliability and low complexity of wheeled rovers with competent terrain adaptability and obstacle-crossing performance. Relying on its special differential pitch device, the robot can adapt to fluctuations in terrain by using both active and passive modes. Moreover, the four-link rocker suspensions on both sides of the robot can increase the instantaneous rotation radius of the rockers when the robot climbs over obstacles. In this paper, using modelling and simulations, we demonstrate that the four-link rocker suspension can improve the robot's obstacle-crossing capability. The geometric and static conditions required for the robot to cross obstacles are derived and discussed, and numerical simulations are conducted to identify the maximum obstacle-crossing heights that satisfy different conditions. Finally, a physical prototype of the robot is developed.

An Amphibious Fully-Soft Centimeter-Scale Miniature Crawling Robot Powered by Electrohydraulic Fluid Kinetic Energy.

Miniature locomotion robots with the ability to navigate confined environments show great promise for a wide range of tasks, including search and rescue operations. Soft miniature locomotion robots, as a burgeoning field, have attracted significant research interest due to their exceptional terrain adaptability and safety features. Here, a fully-soft centimeter-scale miniature crawling robot directly powered by fluid kinetic energy generated by an electrohydraulic actuator is introduced. Through optimization of the operating voltage and design parameters, the average crawling velocity of the robot is dramatically enhanced, reaching 16mm s-1. The optimized robot weighs 6.3g and measures 5cm in length, 5cm in width, and 6mm in height. By combining two robots in parallel, the robot can achieve a turning rate of ≈3° s-1. Additionally, by reconfiguring the distribution of electrodes in the electrohydraulic actuator, the robot can achieve 2 degrees-of-freedom translational motion, improving its maneuverability in narrow spaces. Finally, the use of a soft water-proof skin is demonstrated for underwater locomotion and actuation. In comparison with other soft miniature crawling robots, this robot with full softness can achieve relatively high crawling velocity as well as increased robustness and recovery.

Low-Friction Soft Robots for Targeted Bacterial Infection Treatment in Gastrointestinal Tract.

Untethered and self-transformable miniature robots are capable of performing reconfigurable deformation and on-demand locomotion, which aid the traversal toward various lumens, and bring revolutionary changes for targeted delivery in gastrointestinal (GI) tract. However, the viscous non-Newtonian liquid environment and plicae gastricae obstacles severely hamper high-precision actuation and payload delivery. Here, we developed a low-friction soft robot by assembly of densely arranged cone structures and grafting of hydrophobic monolayers. The magnetic orientation encoded robot can move in multiple modes, with a substantially reduced drag, terrain adaptability, and improved motion velocity across the non-Newtonian liquids. Notably, the robot stiffness can be reversibly controlled with magnetically induced hardening, enabling on-site scratching and destruction of antibiotic-ineradicable polymeric matrix in biofilms with a low-frequency magnetic field. Furthermore, the magnetocaloric effect can be utilized to eradicate the bacteria by magnetocaloric effect under high-frequency alternating field. To verify the potential applications inside the body, the clinical imaging-guided actuation platforms were developed for vision-based control and delivery of the robots. The developed low-friction robots and clinical imaging-guided actuation platforms show their high potential to perform bacterial infection therapy in various lumens inside the body.