Wheel-legged Robot Research Articles

Vision-based dynamic modeling of wheeled-legged robot considering slippage using Gibbs–Appell formulation

Vision-based dynamic modeling of wheeled-legged robot considering slippage using Gibbs–Appell formulation

Dynamic modeling of wheeled biped robot and controller design for reducing chassis tilt angle

Abstract The wheeled-legged robot combines the advantages of wheeled and legged robots, making it easier to assist people in completing repetitive and time-consuming tasks in their daily lives. This paper presents a study on the kinematic and dynamic modeling, as well as the controller design, of a wheeled biped robot with a parallel five-bar linkage mechanism as its leg module. During the motion of the robot, the robot relies on the tilt angle of the inverted pendulum, and this angle often results in the tilting of the chassis of the robot, presenting challenges for the installation of upper-body payloads and sensor systems. The controller proposed in this paper, which is developed by decoupling the primary motions of the robot and designing a multi-objective, multilevel controller, addresses this issue. This controller employs the pendulum pitch angle of the equivalent inverted pendulum model as the control variable and compensates for the chassis tilt angle (CTA). This control method can effectively reduce the CTA of such robots and eliminate the need for additional counterweights. It also provides a more spacious structural design for accommodating upper-body devices. The effectiveness of this control framework is verified through variable height control, walking on flat ground, and carrying loads over rough terrain and slopes.

Light weight design and integrated method for manufacturing hydraulic wheel-legged robots

Light weight design and integrated method for manufacturing hydraulic wheel-legged robots

Overview of structure and drive for wheel-legged robots

Wheel-legged robots are a type of mobile robot that combines the advantages of wheeled robots, such as fast and stable movement and high efficiency, with the adaptability of legged robots to complex and unstructured environments. Therefore, wheel-legged robots have great potential for application in fields such as deep space exploration, disaster relief, and wilderness exploration. This paper categorizes and summarizes the structural forms and driving modes of wheel-legged robots, dividing them into three categories: wheel-legged hybrid robots, wheel-legged separation robots, and wheel-legged transformation robots based on their structural characteristics. Finally, this paper summarizes the structure and driving aspects of wheel-legged robots and provides an outlook on their development in these two areas. The research results presented in this paper help researchers understand the development process of wheel-legged robots and serve as a valuable reference for future research.

Research on Foot Contact State Detection Technology of Wheel-Legged Robot.

The accurate perception of external environment information through the robot foot is crucial for the mobile robot to evaluate its ability to traverse terrain. Adequate foot-end contact signals can provide robust support for robot motion control and decision-making processes. The shape and uncertain rotation of the wheel-legged robot foot end represent a significant challenge to sensing the robot foot-end contact state, which current foot-end sensing schemes cannot solve. This paper presents a sensing method for the tire stress field of wheel-legged robots. A finite element analysis was conducted to study the deformation characteristics of the foot-end tire under force. Based on this analysis, a heuristic contact position estimator was designed that utilizes symmetrical deformation characteristics. Strain sensors, arranged in an array, extract the deformation information on the inner surface of the tire at a frequency of 200 Hz. The contact position estimator reduces the dimensionality of the data and fits the eigenvalues to the estimated contact position. Using support vector regression, the force estimator utilizes the estimated contact position and sensor signal to estimate the normal reaction force, designated as FZ. The sensing system is capable of detecting the contact position on the wheel circumference (with a root mean square error of 1.150°), as well as the normal force of 160 N on the Z axis (with a root mean square error of 6.04%). To validate the efficacy of the sensor detection method, a series of randomized and repeated experiments were conducted on a self-constructed test platform. This novel approach offers a promising avenue for perceiving contact states in wheel-legged robots.

W-Leg Jumping Robot: Mechanical Design, Dynamical Analysis and Simulation of Jumping Dual Wheel-Leg Hybrid Robot

This study primarily focuses on design, mathematically model and simulate a novel two wheel-legged hybrid robot called W-Leg Jumping robot, which has a unique ability to overcome step-like obstacles efficiently. In general, in transformable wheel-leg robot studies, the leg and wheel structure perform their movements in an interdependent manner. However, in this study, it is aimed to design a robot in which the leg and wheel structure can move independently of each other and to develop a robot that can easily overcome obstacles on flat surfaces with the wheel mode and with the leg mode. The robot can fold its legs hidden within the wheels and deploy its two degree of freedom (DoF) legs when it detects step-like obstacles. This mechanism allows the robot to overcome an obstacle with a height of twice the radius of the robot's open/close mechanism of the legs, along with the two-dimensional kinematic and dynamic analyzes of the legs, are presented in detail within the scope of this study proportional-integral-derivative (PID) controller is designed to control the joint angles of the legs. The reference angle values to be followed according to the height of the obstacle are determined using artificial neural network (ANN). Additionally, motion simulations of the robot are conducted for four different obstacle heights (20, 30, 40, and 50 cm). As a result of the PID controller, when exceeding the highest obstacle of 50 cm, the average absolute joint angular tracking error is max. 1.8829°, average tracking error max. 0.265 s and max.

Learning robust autonomous navigation and locomotion for wheeled-legged robots.

Autonomous wheeled-legged robots have the potential to transform logistics systems, improving operational efficiency and adaptability in urban environments. Navigating urban environments, however, poses unique challenges for robots, necessitating innovative solutions for locomotion and navigation. These challenges include the need for adaptive locomotion across varied terrains and the ability to navigate efficiently around complex dynamic obstacles. This work introduces a fully integrated system comprising adaptive locomotion control, mobility-aware local navigation planning, and large-scale path planning within the city. Using model-free reinforcement learning (RL) techniques and privileged learning, we developed a versatile locomotion controller. This controller achieves efficient and robust locomotion over various rough terrains, facilitated by smooth transitions between walking and driving modes. It is tightly integrated with a learned navigation controller through a hierarchical RL framework, enabling effective navigation through challenging terrain and various obstacles at high speed. Our controllers are integrated into a large-scale urban navigation system and validated by autonomous, kilometer-scale navigation missions conducted in Zurich, Switzerland, and Seville, Spain. These missions demonstrate the system's robustness and adaptability, underscoring the importance of integrated control systems in achieving seamless navigation in complex environments. Our findings support the feasibility of wheeled-legged robots and hierarchical RL for autonomous navigation, with implications for last-mile delivery and beyond.

Design and research of deformable wheel-legged robot based on origami mechanisms

This study presents a novel deformable wheeled robot based on an origami mechanism, designed to address the limited environmental adaptability of traditional wheeled robots. The research begins by rigorously establishing the fundamental parameters of the origami unit through an in-depth analysis of the Miura origami motion principle and a comprehensive study of the correlation between geometric parameters. Leveraging the theory of origami thickening, the origami unit is thickened and integrated into the design of the deformable Wheel-Legged mechanism. Controlled by a single motor, four Wheel-Legged structures enable seamless transformation between wheeled and legged forms. The paper provides a comprehensive analysis of the robot’s deformation, obstacle crossing, and other motion processes. Furthermore, it thoroughly investigates the effects of various gaits on the stability of the robot’s movement, followed by rigorous simulation and experimental verification. The experimental results unequivocally demonstrate the robot’s capability in deformation, steering, and obstacle avoidance.

Obstacle detection and obstacle-surmounting planning for a wheel-legged robot based on Lidar

PurposeThis paper aims to investigate an autonomous obstacle-surmounting method based on a hybrid gait for the problem of crossing low-height obstacles autonomously by a six wheel-legged robot. The autonomy of obstacle-surmounting is reflected in obstacle recognition based on multi-frame point cloud fusion.Design/methodology/approachIn this paper, first, for the problem that the lidar on the robot cannot scan the point cloud of low-height obstacles, the lidar is driven to rotate by a 2D turntable to obtain the point cloud of low-height obstacles under the robot. Tightly-coupled Lidar Inertial Odometry via Smoothing and Mapping algorithm, fast ground segmentation algorithm and Euclidean clustering algorithm are used to recognize the point cloud of low-height obstacles and obtain low-height obstacle in-formation. Then, combined with the structural characteristics of the robot, the obstacle-surmounting action planning is carried out for two types of obstacle scenes. A segmented approach is used for action planning. Gait units are designed to describe each segment of the action. A gait matrix is used to describe the overall action. The paper also analyzes the stability and surmounting capability of the robot’s key pose and determines the robot’s surmounting capability and the value scheme of the surmounting control variables.FindingsThe experimental verification is carried out on the robot laboratory platform (BIT-6NAZA). The obstacle recognition method can accurately detect low-height obstacles. The robot can maintain a smooth posture to cross low-height obstacles, which verifies the feasibility of the adaptive obstacle-surmounting method.Originality/valueThe study can provide the theory and engineering foundation for the environmental perception of the unmanned platform. It provides environmental information to support follow-up work, for example, on the planning of obstacles and obstacles.

Research on the energy transfer and efficiency performance of an electro-hydrostatic actuator for wheel-legged robot joint

Intelligence and electrification stimulate the development of wheel-legged robots (WLRs), providing excellent environmental adaptability and mobility. This paper investigates a novel electro-hydrostatic actuator (EHA) with a four-quadrant working principle, two models of electro-hydraulic drive and energy recovery integrated into WLR joints. The range and stability of WLRs will be dramatically improved by utilizing highly efficient EHAs with a high force-to-weight ratio. Mathematical models depending on the force and velocity characteristics are developed and analyzed to explore the energy conversion mechanism. Furthermore, experiments and parameter identification are performed to verify the feasibility and obtain unknown parameters, including torque, leakage, and damping coefficients. The analysis results indicate that the presented EHA is highly efficient, achieving a drive efficiency of up to 87 % and an energy recovery efficiency of up to 88 %. The primary concentration of loss is pressure reduction within the hydraulic circuit. Practical solutions to promote the work and the average efficiency are given in the last. The research will provide theoretical guidance, aiding further structural optimization and control strategies.

Mechanism design and dynamic switching modal control of the wheel-legged separation quadruped robot

AbstractCurrently, most wheel-legged robots need to complete the switching of the wheel-and-leg modal in a stationary state, and the existing algorithms of statically switching the wheel-leg modal cannot meet the control requirements of multimodal switching dynamically for robots. In this paper, to achieve efficient switching of the wheel-and-leg modal for a quadruped robot, the novel transformable mechanism is designed. Then, a multimodal coordination operation control framework based on multiple algorithms is presented, incorporating the minimum foot force distribution method (algorithm No.1), the minimum joint torque distribution method (algorithm No.2), and the method of combining the single rigid body dynamic model with quadratic programming (algorithm No.3). In the process of switching wheel-leg modal dynamically, the existing algorithm No.3 is prone to produce the wrong optimal force due to the change of the whole-body rotational inertia. Therefore, an improved algorithm No.1 and algorithm No.2 are proposed, which do not consider the change in the body’s inertia. The control effects of the three algorithms are compared and analyzed by simulation. The results show that algorithm No.3 can maintain a small error in attitude angle and speed tracking regardless of whether the robot is under multilegged support or omnidirectional walking compared to the other two algorithms. However, proposed algorithms No.1 and No.2 can more accurately track the target speed when the robot is walking with wheels raising and falling. Finally, a multi-algorithm combination control scheme formulated based on the above control effects has been demonstrated to be effective for the dynamic switching of the wheel-and-leg modal.

Design of A Novel Wheel-Legged Robot with Rim Shape Changeable Wheels

The wheel-legged hybrid structure has been utilized by ground mobile platforms in recent years to achieve good mobility on both flat surfaces and rough terrain. However, most of the wheel-legged robots only have one-directional obstacle-crossing ability. During the motion, most of the wheel-legged robots’ centroid fluctuates violently, which damages the stability of the load. What’s more, many designs of the obstacle-crossing part and transformation-driving part of this structure are highly coupled, which limits its optimal performance in both aspects. This paper presents a novel wheel-legged robot with a rim-shaped changeable wheel, which has a bi-directional and smooth obstacle-crossing ability. Based on the kinematic model, the geometric parameters of the wheel structure and the design variables of the driving four-bar mechanism are optimized separately. The kinetostatics model of the mobile platform when climbing stairs is established to determine the body length and angular velocity of the driving wheels. A prototype is made according to the optimal parameters. Experiments show that the prototype installed with the novel transformable wheels can overcome steps with a height of 1.52 times of its wheel radius with less fluctuation of its centroid and performs good locomotion capabilities in different environments.

Distributed MPC-based posture control for knee-wheeled wheel-legged robots with multi-actuation

Wheel-legged robots (WLRs) with knee-wheel placement can switch motion mode into wheeled motion and legged motion depending on the road condition. However, in wheeled motion mode, robots are energy-efficiency and high maneuverability but struggle to handle rough terrain. To address this challenge, we propose a quarter-car model predictive controller (MPC) that utilizes both thigh and calf leg actuation to track sprung mass displacement and regulate tire force during unknown road disturbances. To overcome the high computational demands of whole-body MPC-based posture control for the entire robot, we propose a distributed MPC-based framework with inverse kinematics. Simulations, including quarter-car wheel-legged system simulation, posture tracking, braking, and steering with load transfer, were conducted to evaluate the effectiveness of our proposed control framework and the promising performance of multi-actuation involving the calf leg. The results of this paper demonstrate that our proposed approach is effective in improving the posture control and stability of knee-wheeled WLRs, particularly in rough terrain conditions.

Development and research of the model of a wheel-legged robot

BACKGROUND: The development of robots capable of moving in both walking and wheeled modes and distinguishing with a simple design from the already developed robots is a relevant task for some recent years. In order for such a robot to have scientific and commercial success, it is necessary for it to be as structurally complex, smooth, reliable and inexpensive as its wheeled equivalent and, in addition, to be able to move stably and quickly over terrain that is impassable for wheeled robots. The robot dynamics is modeled with the Universal Mechanism and the MATLAB/Simulink software packages. The results of virtual tests of the robot in main motion modes (straight-line motion, turning, step climbing) are given in the paper.
 AIM: Increasing the mobility of a wheel-legged robot, equipped with the pseudo-walking propulsion system, using reasonable control laws.
 METHODS: In order to evaluate ride performance of the studied robot, methods of numerical simulation of its motion based on the multibody dynamics software packages are used.
 RESULTS: The maximal velocity of stable straight-line motion, the turning velocity and the height of the largest climbed step were obtained for the robot with given power of engines.
 CONCLUSION: The model of the new mobile robot equipped with the simple-designed propulsion system has been developed. This model demonstrated high cross-country abilities and other mobility indicators according to the results of virtual tests.

Safe Trajectory Generation for Wheel-Leg Hybrid Mechanism Using Discrete Mechanics and Optimal Control

Abstract The wheel-legged robot inherits the merit of both the wheeled robot and the legged robot, which can not only adapt to the complex terrain but also maintain the driving efficiency on the flat road. This article presents an optimization-based approach that leverage ideas from computational geometric mechanics to generate safe and high-quality wheel-leg hybrid motions among obstacles. The formulation of the proposed motion optimization problem incorporates the Lagrange–d’Alembert principle as the robot’s dynamic constraints and an efficient closed-form formulation of collision-free constraints. By discretizing the variational mechanics principle directly, rather than its corresponding forced Euler–Lagrange equation, the continuous trajectory optimization problem is transformed into a nonlinear programming (NLP) problem. Numerical simulations and several real-world experiments are conducted on a wheel-legged robot to demonstrate the effectiveness of the proposed trajectory generation approach.

Evolution, Design, and Future Trajectories on Bipedal Wheel-legged Robot: A Comprehensive Review

This comprehensive review delves into the realm of bipedal wheel-legged robots, focusing on their design, control, and applications in assistive technology and disaster mitigation. Drawing insights from various fields such as robotics, computer science, and biomechanics, it offers a holistic understanding of these robots' stability, adaptability, and efficiency. The analysis encompasses optimization techniques, sensor integration, machine learning, and adaptive control methods, evaluating their impact on robot capabilities. Emphasizing the need for adaptable, terrain-aware control algorithms, the review explores the untapped potential of machine learning and soft robotics in enhancing performance across diverse operational scenarios. It highlights the advantages of hybrid models combining legged and wheeled mobility while stressing the importance of refining control frameworks, trajectory planning, and human-robot interactions. The concept of integrating soft and compliant mechanisms for improved adaptability and resilience is introduced. Identifying gaps in current research, the review suggests future directions for investigation in the fields of robotics and control engineering, addressing the evolution and terrain adaptability of bipedal wheel-legged robots, control, stability, and locomotion, as well as integrated sensory and perception systems, microcontrollers, cutting-edge technology, and future design and control directions.

Autonomous Navigation With Online Replanning and Recovery Behaviors for Wheeled-Legged Robots Using Behavior Trees

Autonomous Navigation With Online Replanning and Recovery Behaviors for Wheeled-Legged Robots Using Behavior Trees

Design and Control of a Novel Hydraulic-Driven Humanoid Hand

The robots with humanoid hands can take the place of humans in carrying objects and using tools efficiently in different situations. This paper presents a novel hydraulic-driven robotic hand named the WLRH-II (the second-generation wheel-legged robot humanoid hand) which bears heavy load and has strong robustness. This paper focuses on the design of humanoid hand driving and transmission mechanisms, kinematic and static analyses. First, the linkage mechanism is proposed according to the particle swarm optimization algorithm. Then, the kinematics and the statics of WLRH-II are analyzed in grasp state. In addition, the hydraulic servo control method is used to control the position of a hand through angle feedback. Finally, position tracking and load experiments are completed to verify the reasonableness and effectiveness of the control. The robotic hand can grasp objects of 30[Formula: see text]kg with 2.85-kg self-weight. The WLRH-II has a high load/self-weight ratio of 10.55 in this paper, which is rare in similar humanoid robotic hands.

Hierarchical jumping optimization for hydraulic biped wheel-legged robots

This paper addresses the challenging task of implementing dynamic jumping motions for biped wheel-legged robots, a motion mode that significantly enhances their mobility and adaptability to complex terrains. However, due to the under-actuation and dynamic instability nature of this type of robots, executing high-dynamic motions remains difficult. To tackle this issue, this paper proposes a novel Hierarchical Jumping Optimization (HJO) framework specifically designed for hydraulic biped wheel-legged robots. The framework involves an upper layer center of mass (CoM) trajectory optimization based on the dynamic properties of a dual-mass spring loaded inverted pendulum (DM-SLIP) model, along with the CoM dynamic coupling relationship introduced by the under-actuated nature of two-wheel self-balancing robots. This leads to a reduction in the dimensionality of optimization variables, facilitating effective CoM trajectory generation. Subsequently, the CoM motions of the robot in the Cartesian space are mapped into the joint space in real-time by using the middle layer hierarchical operational space control (HOSC). By incorporating centroid angular momentum as a task objective, the stability of the robot in highly dynamic motions can be enhanced. Finally, the proposed HJO framework is experimentally validated through jumping experiments on an actual robot. The experimental results demonstrate that the framework optimally utilizes the robot’s under-actuated characteristics, significantly reducing computational costs associated with planning and tracking, while simultaneously preserving motion accuracy and robust.

Research on wheel-legged robot based on LQR and ADRC

The traditional two-wheeled self-balancing robot can travel quickly in a flat road environment, and it is easy to destabilize and capsize when passing through a bumpy road. To improve the passing ability of a two-wheeled robot, a new wheel-legged two-wheeled robot is developed. A seven-link leg structure is proposed through the comprehensive design of mechanism configuration, which decouples the balanced motion and leg motion of the robot. Based on the Euler–Lagrange method, the dynamic model of the system is obtained by applying the nonholonomic dynamic Routh equation in the generalized coordinate system. The robot’s state space is divided according to the robot’s height, and the Riccati equation is solved in real-time by the linear quadratic regulator (LQR) method to complete the balance and motion control of the robot. The robot leg motion control is achieved based on the active disturbance rejection control (ADRC) way. A robot simulation model is built on Recurdyn to verify the algorithm’s feasibility, and then an experimental prototype is built to demonstrate the algorithm’s effectiveness. The experimental results show that the control method based on LQR and ADRC can make the robot pass through the bumpy road.