Fault-tolerant Gait Research Articles

Design, motions, capabilities, and applications of quadruped robots: a comprehensive review

Robots are becoming integral to society and industries due to their enormous advantages. Among the various categories of mobile robots, including wheeled robot, tracked robot, and legged robots, the latter stands out as a better choice for most field applications due to their adaptability across various terrains. The purpose of this review is to study the locomotion capabilities of quadruped robots and judge their suitability for climbing applications as most unexplored applications of automation and robotics are required to climb. This review explores the locomotion capabilities of quadruped robots. It covers different aspects of quadruped robots like types of legs, leg design, gait patterns, and their mathematical formulations, and types of motions like omnidirectional motion and body sway motion. It also emphasizes its fault-tolerant gait, adaptability, and reliability. The paper also focuses on slope and stair climbing, outlining design requirements and applications. The study includes an examination of the applicability of various gaits under different conditions and the methods for increasing stability without compromising speed. Overall, the review serves as a valuable resource for future research in this field.

Fault-tolerant motion planning for a hexapod robot with single-leg failure using a foot force control method

Hexapod robots are widely used for resource exploration, post-disaster rescue, and military equipment. They typically travel on rugged and complex roads. The robot itself has a high probability of failure owing to mechanical failure, driving motor failure, or external environmental interference. To improve the adaptability of the robot to a complex environment, a motion control method for fault-tolerant gait was designed. The trajectory generator based on zero-moment point information can generate a smooth desired trajectory for the body’s center of mass, thereby improving the robot’s zero-moment point trajectory tracking effect and motion stability. The force-distribution algorithm based on torque optimization selects the minimum square sum of the driving force as the objective function and reduces the number of constraint equations through QR decomposition to increase the speed at which the expected contact force at the foot is calculated. A CoppeliaSim and MATLAB/Gurobi joint simulation platform were built to simulate and verify the fault-tolerant motion planning of the hexapod robot and foot contact force control algorithm. The feasibility and effectiveness of the fault-tolerant motion planning and foot force control algorithm applied to a hexapod robot with a single-foot failure are verified.

Fault-tolerant gait design for quadruped robots with one locked leg using the GF set theory

The fault-tolerant gait plays an important role in improving the reliability and prolonging the service life of legged robots. However, few fault-tolerant gaits are available for quadruped robots and the static stability margin in some gaits cannot avoid being zero. This paper designs a novel fault-tolerant gait for quadruped robots with one locked leg using the GF set theory. First, a quadruped robot with serial-parallel leg mechanism and its typical static gait are introduced. Then, the mobility of the robot with one locked leg in different stages is addressed using the GF set theory. The fault-tolerant gait pattern is developed by taking full advantage of the mobility. Further, the performances of the fault-tolerant gaits are analyzed to demonstrate its capability. Finally, simulations are conducted to validate the fault-tolerant gait and its performance. The results show that the fault-tolerant gait has the capability of omnidirectional walking and adapting to rough terrains while maintaining a nonzero static stability margin.

Instability Adjustment and Fault-tolerant Gait Design for Hexapod Robot Single Leg Failure

Instability Adjustment and Fault-tolerant Gait Design for Hexapod Robot Single Leg Failure

Hexapod robot fault tolerant gait on slope and simulation verification

Currently, hexapod robot has been widely used in the field of outdoor detection and nuclear power disaster relief because of its adaptability to terrain, excellent movement performance and redundant fault tolerance. In this paper, fault-tolerant gait and motion planning method on the slope are researched. Firstly, the kinematics model of the robot on the slope is established, and the Jacobian matrix mapping the foot end velocity and joint velocity is derived, which is the basis of the robot movement. Then the phase sequence of the robot with one leg fault is planned to solve the problem of leg phase coordination. After then, the adjustment strategy of the centre of gravity on the slope is planned, which can effectively improve the stability of the robot. Finally, a simulation is demonstrated to verify the research.

Fault tolerance properties and motion planning of a six-legged robot with multiple faults

SUMMARYThe six-legged robot Octopus is designed for nuclear disaster relief missions. When the robot suffers from failures, its performance can be significantly affected. Thus, fault tolerance is essential for walking and operating in environments inaccessible to humans. The current fault-tolerant gaits for legged robots usually either initially lock the entire broken leg or just abandon the broken leg, but then fail to take full advantage of the normal actuators on the broken leg and add extra constraints. As the number of broken legs increases, the robot will no longer be able to walk using the existing fault-tolerant gaits. To solve this problem, screw theory is used for analyzing the remaining mobility after failure. Based on the analysis, a method of motion planning through fault-tolerant Jacobian matrices, which are linear, is presented. This method can enable the robot to accomplish desired movement using broken legs along with other certain concomitant motions as compensation. Finally, experiments and simulations of multiple faults demonstrate the real effects on the Octopus robot.

Kinematic analysis and motion planning of a quadruped robot with partially faulty actuators

Actuator failure is a serious problem for legged robots working in remote or complicated environments. Having a fault-tolerant gait is essential to keep the robot walking when actuator failures occur. This paper proposes an algorithm for the fault-tolerant gait to overcome the failure of more than one actuator. The idea is that the degrees of freedom (DOFs) of the robot body are divided into two parts: the major DOFs which are critical to maintain walking and the secondary DOFs. By finding an appropriate kinematic resolution of the motions of the secondary DOFs the motions of the major DOFs can be realized. In this process, a repeatable control problem is also solved by minimizing the actuator displacement function. This method can make full use of the remaining actuators of the robot. The performance of the fault-tolerant gait is demonstrated through a series of simulations and experiments on a hydraulic quadruped robot.

Gait planning for a quadruped robot with one faulty actuator

Fault tolerance is essential for quadruped robots when they work in remote areas or hazardous environments. Many fault-tolerant gaits planning method proposed in the past decade constrained more degrees of freedom(DOFs) of a robot than necessary. Thus a novel method to realize the fault-tolerant walking is proposed. The mobility of the robot is analyzed first by using the screw theory. The result shows that the translation of the center of body(CoB) can be kept with one faulty actuator if the rotations of the body are controlled. Thus the DOFs of the robot body are divided into two parts: the translation of the CoB and the rotation of the body. The kinematic model of the whole robot is built, the algorithm is developed to actively control the body orientations at the velocity level so that the planned CoB trajectory can be realized in spite of the constraint of the faulty actuator. This gait has a similar generation sequence with the normal gait and can be applied to the robot at any position. Simulations and experiments of the fault-tolerant gait with one faulty actuator are carried out. The CoB errors and the body rotation angles are measured. Comparing to the traditional fault-tolerant gait they can be reduced by at least 50%. A fault-tolerant gait planning algorithm is presented, which not only realizes the walking of a quadruped robot with a faulty actuator, but also efficiently improves the walking performances by taking full advantage of the remaining operational actuators according to the results of the simulations and experiments.

Modeling and Analysis of Fault Tolerant Gait of a Multi-legged Robot Moving on an Inclined Plane

Abstract This paper proposes the fault tolerant gait to be used in locomotion of hexapod robot on inclined plane. Comparison between various possible gaits has been made. Out of these, the described gait is selected for slow walking of hexapod. A general fault tolerant algorithm is developed depending on the leg failed. In case there occurs a sudden fault event in one of the legs, turning motion is used to rotate the robot body to desired position to avoid permanent damage of failed leg. The condition under which turning motion takes place is analyzed theoretically.

평판 발을 가지는 사족 보행 로봇의 내고장성 걸음새

This paper proposes fault tolerant gaits of a quadruped robot with feet of flat shape. Fault tolerant gaits make it possible for a legged robot to continue static walking against a leg failure. In the previous researches, it was assumed that a legged robot had feet that have point contact with the surface. When the robot is endowed with feet having flat shape, fault tolerant gaits can show better performance compared with the former gaits, especially in terms of the stride length and gait stability. In this paper, fault tolerant gaits of a quadruped robot against a locked joint failure are addressed in straight-line motion and crab walking, respectively.

Improving the Navigability of a Hexapod Robot Using a Fault-Tolerant Adaptive Gait

This paper encompasses a study on the development of a walking gait for fault tolerant locomotion in unstructured environments. The fault tolerant gait for adaptive locomotion fulfills stability conditions in opposition to a fault (locked joints or sensor failure) event preventing a robot to realize stable locomotion over uneven terrains. To accomplish this feat, a fault tolerant gait based on force-position control is proposed in this paper for a hexapod robot to enable stable walking with a joint failure. Furthermore, we extend our proposed fault detection and diagnosis (FDD) method to deal with the critical failure of the angular rate sensors responsible for the attitude control of the robot over uneven terrains. A performance analysis of straight-line walking is carried out which shows that the proposed FDD-based gait is capable of generating an adaptive walking pattern during joint or sensor failures. The performance of the proposed control is established using dynamic simulations and real-world experiments on a prototype hexapod robot.

고장이 존재하는 육족 보행 로봇을 위한 대수적 힘 분배

본 논문에서는 육족 보행 로봇의 새로운 힘 분배 알고리듬을 제안한다. 본 논문에서 고려하는 육족 보행 로봇은 다리 하나에 관절고착고장이 발생하여 내고장성 정적 세다리 걸음새로 보행한다. 제안되는 힘 분배 알고리듬의 핵심은 내고장성 걸음새가 가지는 안정여유도를 결정하는 지지 다리의 미끄러짐을 최소화시키는 것이다. 불연속적으로 움직이는 내고장성 세다리 걸음새는 정상 걸음새보다 안정도가 떨어진다는 약점이 있다. 본 논문에서 제안하는 힘 분배 알고리듬은 이러한 약점을 고려하여 내고장성 걸음새의 지지 다리가 세 개라는 성질과 Zero-Interaction Force 원리를 이용하여 최적화 기법을 쓰지 않고 대수적으로 모든 다리의 힘 성분을 구한다. 컴퓨터 시뮬레이션 사례 연구를 통해서 제안된 힘 분배 알고리듬과 기존 방법의 비교 분석을 실시하고 제안된 방법의 효용성을 입증한다. In this paper, a novel foot force distribution algorithm for hexapod walking robots is presented. The considered hexapod robot has fault-tolerant tripod gaits with a failed leg in locked-joint failure. The principle of the proposed algorithm is to minimize the slippage of the leg that determines the stability margin of the fault-tolerant gaits. The fault-tolerant tripod gait has a drawback that it has less stability margin than normal gaits. Considering this drawback, we use the feature that there are always three supporting legs, and by incorporating the theory of Zero-Interaction Force, we calculate the foot forces analytically without resort to any optimization technique. In a case study, the proposed algorithm is compared with a conventional foot force distribution method and its applicability is demonstrated.

Fault-Tolerant Gait Planning for a Hexapod Robot Walking over Rough Terrain

Multi-legged robots need fault-tolerant gaits if one of attached legs suffers from a failure and cannot have normal operation. Moreover, when the robots with a failed leg are walking over rough terrain, fault-tolerance should be combined with adaptive gait planning for successful locomotion. In this paper, a strategy of fault-tolerant gaits is proposed which enables a hexapod robot with a locked joint failure to traverse two-dimensional rough terrain. This strategy applies a Follow-The-Leader (FTL) gait in post-failure walking, having the advantages of both fault-tolerance and terrain adaptability. The proposed FTL gait can produce the maximum stride length for a given foot position of a failed leg and better ditch-crossing ability than the previous fault-tolerant gaits. The applicability of the proposed FTL gait is verified using computer graphics simulations.

Two-phase discontinuous gaits for quadruped walking machines with a failed leg

A fault-tolerant gait of multi-legged robots with static walking is a gait which can maintain gait stability and continue its walking against an occurrence of a leg failure. This paper proposes two-phase discontinuous gaits as a new fault-tolerant gait for quadruped robots suffering from a locked joint failure, which prevents a joint of a leg from moving and makes it locked in a known place. By comparing with previously developed one-phase discontinuous gaits, it is shown that the proposed gait has great advantages in gait performance such as the stride length and terrain adaptability. As an application of the proposed gait, the gait algorithm for ditch crossing and avoidance of quadruped robots with a failed leg is presented and illustrated by simulated figures.

Omnidirectional walking of legged robots with a failed leg

This paper studies omnidirectional walking of a hexapod robot with a locked joint failure by proposing crab gaits and turning gaits. Due to the reduced workspace of a failed leg, fault-tolerant gaits have limitations in their mobility. As for crab gaits, an accessible range of the crab angle is derived for a given configuration of the failed leg. As for turning gaits, the conditions on turning trajectories guaranteeing fault tolerance are derived for spinning gaits and circling gaits. Based on the principles of fault-tolerant gait planning, periodic crab gaits and turning gaits are proposed in which a hexapod robot realizes tripod walking after a locked joint failure, having a reasonable stride length and stability margin. The proposed fault-tolerant gaits are then applied to an obstacle avoidance problem of a hexapod robot with a locked joint failure. The kinematic constraints of fault-tolerant gaits should be considered in planning the robot trajectory.

Kinematic Constraints on Fault-Tolerant Gaits for a Locked Joint Failure

Fault-tolerant gaits in legged locomotion are defined as gaits with which legged robots can continue their walking after a failure event has occurred to a leg of the robot. For planning an efficient fault-tolerant gait, kinematic constraints and remaining mobility of the failed leg should be closely examined with each other. This paper addresses the problem of kinematic constraints on fault-tolerant gaits. The considered failure is a locked joint failure which prevents a joint of a leg from moving and makes it locked in a known place. It is shown that for the existence of the conventional fault-tolerant gait for forward walking on even terrain, the configuration of the failed leg must be within a range of kinematic constraints. Then, for coping with failure situations where the existence condition is not satisfied, the conventional fault-tolerant gait is adopted by including the adjustment of the foot trajectory of the failed leg. The foot trajectory adjustment procedure is analytically derived to show that it can help the fault-tolerant gait avoid dead-lock resulting from the kinematic constraint. To demonstrate its effectiveness, the proposed method is applied to the fault-tolerant gait generation for a quadruped robot walking with the wave-crab gait before a locked joint failure.

Gait synthesis for hexapod robots with a locked joint failure

This paper presents a strategy for generating fault-tolerant gaits of hexapod walking robots. A multi-legged robot is considered to be fault-tolerant with respect to a given failure if it is capable of continuing its walking after the occurrence of a failure, maintaining its static stability. The failure concerned in this paper is a locked joint failure for which a joint in a leg cannot move and is locked in place. The kinematic condition for the existence of fault-tolerant gaits is derived for straight-line walking of a hexapod robot on even terrain. An algorithm for generating fault-tolerant gaits is described and, especially, periodic gaits are presented for forward walking of a hexapod robot with a locked joint failure. The leg sequence and the stride length formula are analytically driven based on gait study and robot kinematics. A case study on post-failure walking of a hexapod robot with the wave gait is shown to demonstrate the applicability of the proposed method.

Fault-tolerant crab gaits and turning gaits for a hexapod robot

This paper studies crab gaits and turning gaits of a hexapod robot with a locked joint failure. Due to the reduced workspace of a failed leg, fault-tolerant gaits have limitations in their mobility. Based on the principles of fault-tolerant gait planning, periodic crab gaits and turning gaits are proposed in which a hexapod robot carries out tripod walking after a locked joint failure, having a reasonable stride length and stability margin.

Tripod gaits for fault tolerance of hexapod walking machines with a locked joint failure

Fault tolerance is an important design criterion for robotic systems operating in hazardous or remote environments. This paper addresses the issue of tolerating a locked joint failure in gait planning for hexapod walking machines which have symmetric structures and legs in the form of an articulated arm with three revolute joints. A locked joint failure is one for which a joint cannot move and is locked in place. If a failed joint is locked, the workspace of the resulting leg is constrained, but hexapod walking machines have the ability to continue static walking. A strategy of fault tolerant tripod gait is proposed and, as a specific form, a periodic gait is presented in which hexapod walking machines have the maximum stride length after a locked failure. The adjustment procedure from a normal gait to the proposed fault tolerant gait is shown to demonstrate the applicability of the proposed scheme.

자율 보행 로봇을 위한 내고장성 제어

A strategy for fault-tolerant gaits of autonomous legged robots is proposed. A legged robot is considered to be fault tolerant with respect to a given failure if it is guaranteed to be capable of walking maintaining its static stability after the occurrence of the failure. The failure concerned in this paper is a locked joint failure for which a joint in a leg cannot move and is locked in place. If a failed joint is locked, the workspace of the resulting leg is constrained, but legged robots have fault tolerance capability to continue static walking. An algorithm for generating fault-tolerant gaits is described and, especially, periodic gaits are presented for forward walking of a hexapod robot with a locked joint failure. The leg sequence and the formula of the stride length are analytically driven based on gait study and robot kinematics. The transition procedure from a normal gait to the proposed fault-tolerant gait is shown to demonstrate the applicability of the proposed scheme.