Smart Gait:A Gait Optimization Framework for Hexapod Robots

The current gait planning for legged robots is mostly based on human presets,which cannot match the flexible characteristics of natural mammals.This paper proposes a gait optimization framework for hexapod robots called Smart Gait.Smart Gait contains three modules:swing leg trajectory optimization,gait period&duty optimization,and gait sequence optimization.The full dynamics of a single leg,and the centroid dynamics of the overall robot are considered in the respective modules.The Smart Gait not only helps the robot to decrease the energy consumption when in locomotion,mostly,it enables the hexapod robot to determine its gait pattern transitions based on its current state,instead of repeating the formalistic clock-set step cycles.Our Smart Gait framework allows the hexapod robot to behave nimbly as a living animal when in 3D movements for the first time.The Smart Gait framework combines offline and online optimizations without any fussy data-driven training procedures,and it can run efficiently on board in real-time after deployment.Various experiments are carried out on the hexapod robot LittleStrong.The results show that the energy consumption is reduced by 15.9%when in locomotion.Adaptive gait patterns can be generated spontaneously both in regular and challenge environments,and when facing external interferences.

Gait Analysis of a Radial Symmetrical Hexapod Robot Based on Parallel Mechanisms

Most gait studies of multi-legged robots in past neglected the dexterity of robot body and the relationship between stride length and body height.This paper investigates the performance of a radial symmetrical hexapod robot based on the dexterity of parallel mechanism.Assuming the constraints between the supporting feet and the ground with hinges,the supporting legs and the hexapod body are taken as a parallel mechanism,and each swing leg is regarded as a serial manipulator.The hexapod robot can be considered as a series of hybrid serial-parallel mechanisms while walking on the ground.Locomotion performance can be got by analyzing these equivalent mechanisms.The kinematics of the whole robotic system is established,and the influence of foothold position on the workspace of robot body is analyzed.A new method to calculate the stride length of multi-legged robots is proposed by analyzing the relationship between the workspaces of two adjacent equivalent parallel mechanisms in one gait cycle.Referring to service region and service sphere,weight service sphere and weight service region are put forward to evaluate the dexterity of robot body.The dexterity of single point in workspace and the dexterity distribution in vertical and horizontal projection plane are demonstrated.Simulation shows when the foothold offset goes up to 174 mm,the dexterity of robot body achieves its maximum value 0.164 4 in mixed gait.The proposed methods based on parallel mechanisms can be used to calculate the stride length and the dexterity of multi-legged robot,and provide new approach to determine the stride length,body height,footholds in gait planning of multi-legged robot.

Wheel-legged Hexapod Robots:a Multifunctional Mobile Manipulating Platform

Robots are widely used to replace people in some burdensome or hamaful areas. Not only the moving ability but also the manipulating ability is needed in the missions of complex multitasking requirements. In the last decades, wheel-legged hexapod robots are extensively studied to ineet this condition.

Research on Biologically Inspired Hexapod Robot's Gait and Path Planning

Realistically there are many robot joints in the biologically inspired hexapod robot, so they will generate many complexities in the calculations of the gait and the path planning and the control variables. The software Solidworks and MSC. ADAMS are adopted to simulate and analyze the prototype model of the robot. By the simulations used in our design, the applicability of the tripod gait is validated, and the scheme which uses cubic spline curve as the endpoint of foot＇s path is feasible. The principles, methods, and processes of the simulation of hexapod robot are illustrated. A methodology is proposed to get the robot inverse solution in ADAMS, and to simplify the theoretical calculation, and further more to improve the efficiency of the design.

Leg compliance control of a hexapod robot based on improved adaptive control in different environments

Considering the compliance control problem of a hexapod robot under different environments, a control strategy based on the improved adaptive control algorithm is proposed. The model of robot structure and impedance control is established. Then, the indirect adaptive control algorithm is derived. Through the analysis of its parameters, it can be noticed that the algorithm does not meet the requirements of the robot compliance control in a complex environment. Therefore, the fuzzy control algorithm is used to adjust the adaptive control parameters. The satisfied system response can be obtained based on the adjustment in real time according to the error between input and output. Comparative experiments and analysis of traditional adaptive control and the improved adaptive control algorithm are presented. It can be verified that not only desired contact force can be reached quickly in different environments, but also smaller contact impact and sliding avoidance are guaranteed, which means that the control strategy has great significance to enhance the adaptability of the hexapod robot.

Biomimetic Experimental Research on Hexapod Robot's Locomotion Planning

To provide hexapod robots with strategies of locomotion planning, observation experiments were operated on a kind of ant with the use of high speed digital photography and computer assistant analysis. Through digitalization of original analog video, locomotion characters of ants were obtained, the biomimetic foundation was laid for polynomial trajectory planning of multi-legged robots, which was deduced with mathematics method. In addition, five rules were concluded, which apply to hexapod robots marching locomotion planning. The first one is the fundamental strategy of multi-legged robots＇ leg trajectory planning. The second one helps to enhance the static and dynamic stability of multi-legged robots. The third one can improve the validity and feasibility of legs＇ falling points. The last two give criterions of multi-legged robots＇ toe trajectory figures and practical recommendatory constraints. These five rules give a good method for marching locomotion planning of multi-legged robots, and can be expended to turning planning and any other special locomotion.

The HITCR-I:Evaluation on a free gait generation method for the hexapod robot on irregular terrain

The purpose of this paper is to present and evaluate a method of free gait generation for HITCRI,a hexapod walking robot.The HITCR-I is designed as a modularized structure of legs that is based upon a four-bar linkage mechanism and with force sensors in the tip of legs,distributed hardware structure and a modular software structure of the control system.Based on a set of local rules between adjacent legs,finite state machine(FSM) model is built to control the coordination of legs.An automatic smooth transition of gait pattern is achieved through deriving the mathematical relation between gait pattern and locomotion parameters.The disordered inter-leg phase sequence is adjusted to a regular state smoothly and quickly by the local rules based FSM,and the gait pattern can transform automatically adapting to irregular terrain.The experiment on HITCR-I has demonstrated that it can walk through irregular terrain reliably and expeditiously with the free gait controller designed in this paper.

A control structure for the autonomous locomotion on rough terrain with a hexapod robot

A motion control structure used for autonomous walking on uneven terrain with a hexapod biomimetic robot is proposed based on function-behavior-integration. In the gait planning level, a set of local rules operating between adjacent legs were put forward and the theory of finite state machine was employed to model them; further, a distributed network of local rules was constructed to adaptively adjust the fluctuation of inter-leg phase sequence. While in the leg-end trajectory planning level, combined polynomial curve was adopted to generate foot trajectory, which could realize real-time control of robot posture and accommodation to terrain conditions. In the simulation experiments, adaptive regulation of inter-leg phase sequence, omnidirectional locomotion and ground accommodation were realized, moreover, statically stable free gait was obtained simultaneously, which provided hexapod robot with the capability of walking on slightly irregular terrain reliably and expeditiously.

Development of a Bionic Hexapod Robot for Walking on Unstructured Terrain

This paper reports the design methodology and control strategy in the development of a novel hexapod robot HITCR-II that is suitable for walking on unstructured terrain. First, the entire sensor system is designed to equip the robot with the perception of external environment and its internal states. The structure parameters are optimized for improving the dexterity of the robot. Second, a foot-force distribution model and a compensation model are built to achieve posture control. The two models are capable of effectively improving the stability of hexapod walking on unstructured terrain. Finally, the Posture Control strategy based on Force Distribution and Compensation （PCFDC） is applied to the HITCR-II hexapod robot. The experimental results show that the robot can effectively restrain the vibration of trunk and keep stable while walking and crossing over the un- structured terrains.

Terrain classification and adaptive locomotion for a hexapod robot Qingzhui

Legged robots have potential advantages in mobility compared with wheeled robots in outdoor environments. The knowledge of various ground properties and adaptive locomotion based on different surface materials plays an important role in improving the stability of legged robots. A terrain classification and adaptive locomotion method for a hexapod robot named Qingzhui is proposed in this paper. First, a force-based terrain classification method is suggested. Ground contact force is calculated by collecting joint torques and inertial measurement unit information. Ground substrates are classified with the feature vector extracted from the collected data using the support vector machine algorithm. Then, an adaptive locomotion on different ground properties is proposed. The dynamic alternating tripod trotting gait is developed to control the robot, and the parameters of active compliance control change with the terrain. Finally, the method is integrated on a hexapod robot and tested by real experiments. Our method is shown effective for the hexapod robot to walk on concrete, wood, grass, and foam. The strategies and experimental results can be a valuable reference for other legged robots applied in outdoor environments.

Different manipulation mode analysis of a radial symmetrical hexapod robot with leg-arm integration

With the widespread application of legged robot in various fields,the demand for a robot with high locomotion and manipulation ability is increasing.Adding an extra arm is a useful but general method for a legged robot to obtain manipulation ability.Hence,this paper proposes a novel hexapod robot with two integrated leg–arm limbs that obtain dexterous manipulation functions besides locomotion ability without adding an extra arm.The manipulation modes can be divided into coordinated manipulation condition and single-limb manipulation condition.The former condition mainly includes fixed coordinated clamping case and fixed coordinated shearing case.For the fixed coordinated clamping case,the degrees of freedom(DOFs)analysis of equivalent parallel mechanism by using screw theory and the constraint equation of two integrated limbs are established.For the fixed coordinated shearing case,the coordinated working space is determined,and an ideal coordinated manipulation ball is presented to guide the coordinated shearing task.In addition,the constraint analysis of two adjacent integrated limbs is performed.Then,mobile manipulation with one integrated leg–arm limb while using pentapod gait is discussed as the single-limb manipulation condition,including gait switching analysis between hexapod gait and pentapod gait,different pentapod gaits analysis,and a complex six-DOF manipulation while walking.Corresponding experiments are implemented,including clamping tasks with two integrated limbs,coordinated shearing task by using two integrated limbs,and mobile manipulation with pentapod gait.This robot provides a new approach to building a multifunctional locomotion platform.

Obstacle avoidance for a hexapod robot in unknown environment

Obstacle avoidance is quite an important issue in the field of legged robotic applications, such as rescuing and detecting in complicated environment. Most related researchers focused on the legged robot’s gait generation after ssuming that obstacles have been detected and the walking path has been given. In this paper we propose and validate a novel obstacle avoidance framework for a six-legged walking robot Hexapod-III in unknown environment. Throughout the paper we highlight three themes: (1) The terrain map modeling and the obstacle detection; (2) the obstacle avoidance path planning method; (3) motion planning for the legged robot. Concretely, a novel geometric feature grid map (GFGM) is proposed to describe the terrain. Based on the GFGM, the obstacle detection algorithm is presented. Then the concepts of virtual obstacles and safe conversion pose are introduced. Virtual obstacles restrict the robot to walk on the detection terrain. A safe path based on Bezier curves, passing through safe conversion poses, is obtained by minimizing a penalty function taking into account the path length subjected to obstacle avoidance. Thirdly, motion planning for the legged robot to walk along the generated path is discussed in detail. At last, we apply the proposed framework to the Hexapod-III robot. The experimental result shows that our methodology allows the robot to walk safely without encountering with any obstacles in unknown environment.

A gait planning method applied to hexapod biomimetic robot locomotion

In order to fulfill the goal of autonomous walking on rough terrain,a distributed gait planningmethod applied to hexapod biomimetic robot locomotion is proposed based on the research effort of gait co-ordination mechanism of stick insect.The mathematical relation of walking velocity and gait pattern wasdepicted,a set of local rules operating between adjacent legs were put forward,and a distributed networkof local rules for gait control was constructed.With the interaction of adjacent legs,adaptive adjustmentof phase sequence fluctuation of walking legs resulting from change of terrain conditions or variety of walk-ing speed was implemented to generate statically stable gait.In the simulation experiments,adaptive ad-justment of inter-leg phase sequence and smooth transition of velocity and gait pattern were realized,andstatic stableness was ensured simultaneously,which provided the hexapod robot with the capability ofwalking on rough terrain stably and expeditiously.

Research on Miniature Hexapod Bio-robot

This paper described the structure and control of a new kind of miniature hexap od bio-robot, analyzed the moving principle of the robot. The robot is based on the principle of bionics, its structure is simple, design novel, unique. It can mov e forwards and backwards. The external dimensions of bio-robot is: length 30 mm , width 40 mm, height 20 mm, weight 6.3 g. Some tests about the model robot were made. The experimental results show that the robot has good mobility.

仿生六足折纸机器人结构设计与运动分析

针对现有折纸机器人组成结构单一,运动不够灵活的问题,将折纸结构与多足机器人设计相结合,耦合三浦折纸和六折痕折纸,提出新型的仿螃蟹六足折纸机器人设计方案,扩展了折纸机器人的运动构型,提升了折纸机器人的运动灵活性.在面对称假设下,该机器人单足具有2个自由度,此时将机器人腿部顶点等效为关节,轴线折痕等效为连杆,建立机器人腿部的平面连杆等效模型,并以折面夹角为运动变量,通过仿真计算得出机器人足端的理论运动范围.利用楔形面板技术对折面增厚并避免相邻折面发生物理干涉,建模得到折纸仿螃蟹六足机器人的三维模型.基于平面连杆的等效模型,分析折面夹角与足端运动之间的联系,设计确定机器人的足端运动轨迹与运动步态.利用3D打印技术设计并制作折纸仿生六足机器人试验样机,基于STM32单片机控制实现了机器人三横向角步态运动.结果表明,该折纸仿生机器人可以实现平面构型到仿螃蟹构型的转换,在6条腿的协同运动下,机器人可以平稳地左右横向移动.

金属矿山井下采场六足机器人运动分析及步态规划

六足机器人因其结构特殊带来的良好越障能力成为仿生机器人研究的热点,然而,金属矿山井下采场矿石堆积、崎岖不平的特点,给这类机器人的行走稳定性、越障性带来更多的挑战。因此,为使六足机器人在井下具有更好的通过性,对其运动能力和步态规划进行了相关研究。首先仿照自然界六足生物,设计六足机器人结构,对其腿部进行运动学分析;然后规划了用于采场的直行步态,结合采场路面环境设计了一种直线—摆线复合轨迹提升越障性,同时分析了机器人爬坡稳定性,对爬坡步态进行了优选;最后对规划步态进行仿真和现场模拟试验。仿真和试验结果表明,所规划的足端轨迹能跨越抬腿高度85%的障碍物,并且对矿石堆积形成的采场路面有更好的避障能力;三角步态爬坡时在坡底和坡顶过渡阶段容易打滑,而横向步态可以实现平滑的过渡,爬坡性能更佳。

基于分布式深度强化学习的六足机器人步态学习与控制

针对六足机器人系统结构与决策的复杂导致步态规划与控制困难的问题,提出了一种基于分布式强化学习的六足机器人步态学习与控制框架。该框架采用大规模并行学习的方式获取训练数据,通过强化学习的方法对网络进行数据驱动训练,得到最优控制策略,并在IsaacGym平台下构建仿真环境评估和验证六足机器人步态学习与控制的性能。结果表明,训练的六足机器人步态在奖励值、速度跟踪和稳定性都有良好的表现,验证了所提方法的有效性。

基于数字孪生的六足机器人高性能交互系统设计

针对当前多足机器人在封闭且复杂的环境下作业时存在的遥操作实时监控困难、人机交互(HCI)友好性差等问题,提出基于数字孪生的高性能HCI系统。首先,着重对六足机器人在狭窄环境中运动的步态进行了研究;其次,使用CoppeliaSim构建多维多时空尺度的虚拟模型;最后,通过C++/Qt开发服务层软件来实现数据的双向实时映射和驱动,达到虚实同步的效果,提升交互的性能。实验结果表明:该系统可以显著提升机器人的控制效率和HCI友好性,为狭窄环境机器人的HCI设计提供了坚实基础。

基于Hopf振荡器的Spiking-CPG六足机器人步态运动控制

中枢模式发生器(central pattern generator,CPG)在六足机器人的运动步态控制中起着至关重要的作用。为能够更高效、更低能耗地控制六足机器人的步态运动,提出了一种Spiking-CPG(SCPG)神经网络作为六足机器人的仿生控制系统,其结合Hopf振荡器与以时疏的spiking信号传递信息的仿生神经元LIF(leaky integrate-and-fire),采用环型拓扑结构,使用六组各2000个LIF神经元组成的集合相互连接而成。该SCPG控制系统能够生成六足机器人常见的波动步态、四足步态、三足步态,通过调节相位差参数实现快速、顺滑、稳定的切换运动步态,实时调整所需的频率、振幅,在面对外界干扰时能够在很短的时间内恢复原状,具有很好的鲁棒性。在Webots平台上搭建了一个三维的六足机器人模型,将SCPG的信号输出并经过关节映射函数变换后,来控制六足机器人的运动,验证了所设计六足机器人的运动稳定性和SCPG控制方案的可行性与有效性。最后,在Intel的Loihi芯片上移植了SCPG神经网络控制器,结果表明,其具备高效的执行速度和更低的能耗,在六足机器人的运动控制中具备良好的应用前景。

基于DRL和自由步态的六足机器人运动规划研究

为提高六足机器人在非结构环境下的通过率和运动性能,提出一种基于DRL和自由步态规划器的多接触运动规划算法。自由步态规划器获取目标状态下可达落足点从而输出最优步态序列;利用DRL训练得到六足机器人在随机生成的梅花桩环境中的质心运动策略。为了保证机器人在运动过程中相邻状态之间的可达性,利用状态转移可行性模型对状态转移可行性进行判定,实现六足机器人在不同宽度沟壑梅花桩环境下的落脚点规划。仿真与样机实验表明:多接触运动规划算法能够让机器人快速平稳地从起点到达目标区域,并自动调整步态模式以应对不同环境下随机分布的梅花桩。