State estimation and traversability map construction method of a quadruped robot on soft uneven terrain

Quadruped robots show excellent application prospects in complex environment detection and rescue. At present, scholars mainly focus on quadruped walking in rigid environments. However, quadruped robots often need to pass through uneven and soft unconstructed terrains, prone to slip and impact. The mismatch between the planned foothold position and the real one resulting from environmental uncertainties makes the robot unstable. In this paper, the state estimation and traversability map construction methods are proposed for quadruped robots to achieve stable walking in an unstructured environment, especially on soft terrains. First, the Error-state Kalman Filter (ErKF) is extended by optimizing the leg odometry information to get an accurate robot state, especially in soft, uneven terrain. The ErKF method fuses the sensor data from the inertial measurement unit, laser, camera, and leg odometry. The leg odometry is optimized by considering the foot slippage, which easily occurs in soft uneven terrains. Then, the unstructured environment is parameterized and modeled by the terrain inclination, roughness, height, and stiffness. A traversability map, which is essential for robot path and foothold planning in autonomous movement, is constructed with the above parameters. Finally, the proposed method is verified by simulation and experiments. The results show that the quadruped robot can walk stably on different soft and uneven terrains.     

基于扩展雅可比矩阵的冗余液压驱动四足机器人运动控制

针对冗余液压驱动四足机器人运动学逆解问题,提出一种基于扩展雅可比矩阵的冗余液压驱动四足机器人运动控制方法.该方法既能解决冗余自由度带来的逆解多解问题,还能使机器人足端入地角度满足摩擦锥要求避免足端滑动.首先,规划机器人足端轨迹得到机器人足端速度,在分析机器人足端入地角度对机器人运动性能影响的基础上,结合机器人腿部结构几...     

Novel Energy Transfer Mechanism in a Running Quadruped Robot with One Actuator per Leg

In this work we develop a novel method, or mechanism, of energy transfer in a quadruped running robot. The robot possesses only one actuator per leg, for lower weight and greater power autonomy. The developed mechanism ensures correct dispersion of energy to the actuated and the unactuated degrees of freedom of the robot for stable running. In the mechanism design, we address the added problem of running on inclined ground. In conjunction with a pitch control method, the energy transfer mechanism forms a complete control algorithm. Due to the novel dynamics-based design of the mechanism, it allows the arbitrary setting of the motion forward speed and apex height. Further, it may be applied for different robot physical parameters and ground inclines, without extensive controller tuning. This has not been previously possible using only one actuator per leg. Simulations of a detailed three-dimensional model of the robot demonstrate the mechanism on two different robots. The simulations take into account many real-world characteristics, including realistic leg models, energy loss due to feet collisions, foot–ground friction and energy losses in the joints. Results demonstrate that inclines of up to 20° are properly negotiated.     

基于高阶多项式的爬游机器人足端轨迹规划

针对深海爬游机器人足端轨迹规划问题,采用高阶多项式拟合的方法对其进行研究;首先,介绍了爬游机器人整体结构并对其进行运动学建模,结合爬游机器人运动学模型提出了一种直线与曲线相结合的机器人足端轨迹;其次,利用四阶多项式和六阶多项式分别对机器人足端轨迹进行拟合,比较两种拟合结果可知,六阶多项式拟合方法对机器人足端速度、加速度的规划效果更佳;利用六阶多项式轨迹拟合方法对多段轨迹连接点处的速度问题进行了分析,解决了机器人在运动过程中腿部抖动问题,使机械腿具有良好的控制柔顺性;最后,根据D-H法则建立机器人单腿仿真模型,通过仿真验证了算法的可行性,进一步在水池中利用机器人实物样机验证了算法的有效性.     

Power Consumption Optimization for a Hexapod Walking Robot

Power consumption is one of the main operational restrictions on autonomous walking robots. In this paper, an energy efficiency analysis is performed for a hexapod walking robot to reduce these energy costs. To meet the power-saving demands of legged robots, the torque distribution algorithm required to minimize the system’s energy costs was established with an energy-consumption model formulated. In contrast to the force distribution method, where the objective function is related to the tip-point force components, the torque distribution scheme is based on minimization of the mechanical energy cost and heat loss power. The simulation results show that this scheme could reduce the system energy costs with use of the appropriate walking velocities and duty factors for the robot. The paper also discusses the effects of the gait patterns and the mechanical structure on the system energy costs. For this purpose, the prescribed periodic walking gait of the robot is described in terms of several parameters, including the duty factor, the stride length, the body height, and the foot trajectory lateral offset. The numerical results indicate some analogies between the characteristics of the simulated walking robot and those of animals in nature. The optimized parameters derived here are intended for robot platform development applications.     

Development of snake-like robot ACM-R8 with large and mono-tread wheel

One of the important advantages of an active wheeled snake-like robots is that it can access narrow spaces which are inaccessible to other types of robot (such as crawlers, walking robots), since snake-like robots have an elongated, narrow body. Additionally, in areas with rubble, snake-like robots can traverse rough terrain and large obstacles since its body can conform to the terrain’s contours. ‘ACM-R8’ is a new snake-like robot which can climb stairs and reach doorknobs in addition to the features explained above. To fulfill these functions, the design of this robot incorporates several key features: joints with parallel link mechanism, mono-tread wheels with internal structure, force sensors and ‘swing-grousers’ which were developed to improve step climbability. In this paper, the design and control methods are described. Experiments confirmed high mobility on stairs and steps, with the robot succeeding in overcoming a step height of 600 mm, despite the height of the robot being just 300 mm.     

基于Klann连杆的球腿复合机器人的设计与研究

结合球形和四足机器人两者优势,创新性地提出一种能适应多重作业环境的球腿复合移动机器人．在滚动模式下,对其进行直线滚动和侧滚转向分析,验证机器人转向的可行性．在四足模式下,以复数矢量法求得机器人足端坐标,并用Matlab绘制的足端轨迹曲线与Adams仿真曲线对比,验证了理论的正确性．以抬腿高度作为目标函数,由非线性规划算法求得足端轨迹最优解．采用质心投影法分析了机器人四足行走时的稳定性．建立仿真模型对机器人的四足直行、四足转向、四足爬坡和球体侧滚等运动模式进行仿真试验．同时,制作一台样机,验证了该机器人方案设计及各运动模式的可行性．     

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.     

足式机器人SLIP模型向上跳跃台阶的运动控制

由于存在地势起伏,台阶对足式机器人运动稳定性会带来较大挑战.弹簧负载倒立摆模型(SLIP)作为研究足式机器人的优良模板,能否完成向上跳跃台阶的动作与其腿部摆角,起跳位置和跳跃高度都有密切的关系.由于调整模型腿部摆角规律容易引发运动失效,故本文在算法中引入虚拟弹簧腿,根据虚拟弹簧腿的运行规律确定合理起跳位置,根据起跳位置来控制系统跳跃高度进而完成跳跃台阶的动作.最后利用仿真软件进行多组仿真,结果表明本文算法对起跳区间划分合理,对起跳高度控制精准,能够实现SLIP模型跳跃台阶前后的稳定运动.     

Neural networks IC controlled multi-legged walking MEMS robot with independent leg mechanism

In this paper, we will compare the walking behavior of quadruped and hexapod walking MEMS robots. These robots are fabricated by connecting same modules, which are composed of a couple of independent leg mechanisms. Independent leg mechanisms can actuate the single leg by a single artificial muscle wire. The neural networks IC that mimics real living organisms controls the mechanical systems. The length and weight of the quadruped MEMS robot were 7.2 mm and 95.8 mg, respectively. The quadruped robot showed the walking speed of 24.6 mm/min. The robot tended to lose its balance and the weight balance is quite important for the moving quadruped. On the other hand, the length and weight of the hexapod MEMS robot were 9.0 mm and 162 mg, respectively. The hexapod robot showed stable walking. The speed was 27.0 mm/min.     

Design and Development of the Lifting and Propulsion Mechanism for a Biologically Inspired Water Runner Robot

This paper describes the design and development of a novel robot, which attempts to emulate the basilisk lizard's ability to run on the surface of water. Previous studies of the lizards themselves have characterized their means of staying afloat. The design of a biomimetic robot utilizing similar principles is discussed, modeled, and prototyped. Functionally, the robot uses a pair of identical four bar mechanisms, with a 180 ^deg phase shift to achieve locomotion on the water's surface. Simulations for determining robot lift and power requirements are presented. Through simulation and experimentation, parameters are varied with the focus being a maximization of the ratio of lift to power. Four legged robots were more easily stabilized, and had a higher lift-to-power ratio than two legged robots. Decreases in characteristic length and running speed, and increases in foot diameter and foot penetration depth all cause a higher lift to power ratio. Experimental lift approached 80 gr, and experimental performance exceeded 12 gr/W for four legged robots with circular feet. This work opens the door for legged robots to become ambulatory over both land and water, and represents a first step toward robots which run on the water instead of floating or swimming.     

Optimal fault tolerant gait sequence of the hexapod robot withoverlapping reachable areas and crab walking

This paper extends the authors' previous results on fault tolerant locomotion of the hexapod robot on even terrain by relaxing nonoverlap of redefined reachable cells of legs and considering crab walking. It is shown that in fault tolerant locomotion two adjacent legs of the hexapod robot can have overlapping redefined reachable cells with each other and consequently the stride length of the gaits is increased. Also, the optimal fault tolerant periodic gaits for hexapod robots to have the maximum stride length in one cycle in crab walking on even terrain are derived with distinct reachable cells. The derived sequence for crab walking has different orders of leg swing according to the relative values of the crab angle and some design parameters of the robot     

Improving the Motion of Walking Machines by Autonomous Kinematic Calibration

Legged machines designed to walk on flat or irregular terrain do not need to possess great foot positioning accuracy in order to perform stable motion. However, the propulsion of the body—which normally follows a straight line—, requires feet to follow perfect straight lines—in the body's reference frame—, which must be parallel to each other; otherwise internal foot forces will arise. When this occurs, mainly due to mechanical imperfections and kinematic inaccuracies, foot slippage and changes in the attitude/altitude of the vehicle appear. In the case of legged robots that need to move on rigid structures to achieve stable locomotion, precise foot positioning is required to reduce the foot force interaction. Examples of such robots are legged robots that move by grasping structures or climbing robots that clasp their feet to a wall. Kinematic calibration is a traditional method of improving the accuracy of robot manipulators. These techniques, especially those based on kinematic closed chains, can also be applied to legged robots. This article introduces a method for calibrating legged machines autonomously. The theory has been developed to control a special four-legged robot, and for calibrating purposes each leg has been considered as a 2-DOF leg. Nevertheless, the theory can be easily extended to 3-DOF-leg machines as well as to six-legged machines. The method is of particular interest for industrial machines that walk on rigid structures so that the feet clasp firmly and cannot slip. The method is evaluated through simulation and tested in an industrial four-legged machine developed to walk in a double bottom cell of a ship's hull. Some experiments have been conducted using the calibrated kinematic model to validate the usefulness of the calibration method.     

The ASURA I harvestman-like hexapod walking robot: compact body and long leg design

This paper reports the design of a new hexapod walking robot, ASURA I, inspired by the physical features of a harvestman’s behavior. ASURA I has a special mobile form with one compact body and much longer legs than conventional hexapod walking robots. This form enhances the walking performance of the robot on rocky or uneven terrain. Here, we present the design and analysis of the leg mechanism, body structure design, gait planning, and prototype development. The long legs (relative to the body) are managed by special parallel link mechanisms, which powerfully and effectively drive the leg joints. The leg mechanism is analyzed by its kinematics, singularity, and static characteristics. The leg length and weight of ASURA I is 1.3 m and 27 kg, respectively. The alternating tripod and wave gaits of ASURA I are successfully demonstrated in a series of walking experiments.     

Evolving gaits for hexapod robots using cyclic genetic algorithms

A major facet of multi-legged robot control is locomotion. Each leg must move in such a manner that it efficiently produces thrust and provides maximum support. The motion of all the legs must be coordinated so that they are working together to provide constant stability while propelling the robot forward. In this paper, we discuss the use of a cyclic genetic algorithm (CGA) to evolve control programs that produce gaits for actual hexapod robots. Tests done in simulation and verified on the actual robot show that the CGA successfully produces gaits for both fully capable and disabled robots.     

连续电驱动四足机器人腿部机构设计与分析

提出了一种四足机器人腿部的连续电驱动（即电机整周转动驱动腿部实现摆转跨步动作）方案,设计了一种具有由切比雪夫机构、五杆机构组成的2自由度双曲柄复合连杆机构的机器人腿部结构．分析了动物的足端轨迹特性,采用轨迹圆滑、无突变、导数连续的椭圆曲线规划了机器人足端运动轨迹．以规划的足端轨迹再现为优化目标,采用遗传算法与fmincon函数内点法计算得到了腿部机构杆长的最佳尺寸．在此基础上,建立了机器人仿真模型,通过Adams仿真分析了机器人腿部机构的足端运动特性,并研制了腿部结构性能测试平台．完成了单腿足端运动轨迹跟踪实验,验证了腿部结构设计方案的可行性．     

Design and control of tensegrity robots for locomotion

The static properties of tensegrity structures have been widely appreciated in civil engineering as the basis of extremely lightweight yet strong mechanical structures. However, the dynamic properties and their potential utility in the design of robots have been relatively unexplored. This paper introduces robots based on tensegrity structures, which demonstrate that the dynamics of such structures can be utilized for locomotion. Two tensegrity robots are presented: TR3, based on a triangular tensegrity prism with three struts, and TR4, based on a quadrilateral tensegrity prism with four struts. For each of these robots, simulation models are designed, and automatic design of controllers for forward locomotion are performed in simulation using evolutionary algorithms. The evolved controllers are shown to be able to produce static and dynamic gaits in both robots. A real-world tensegrity robot is then developed based on one of the simulation models as a proof of concept. The results demonstrate that tensegrity structures can provide the basis for lightweight, strong, and fault-tolerant robots with a potential for a variety of locomotor gaits.     

Analysing and solving body misplacement problems in walking robots with round rigid feet

Round rigid feet for multi-legged robots offer a number of advantages over flat feet, and even over flat feet with articulated ankles. The main benefits are low cost, low complexity and robustness. A round rigid foot of small radius works well on hard terrain; however, it is prone to sink into soft terrain. Sinking can be avoided by increasing the radius of the foot, but in that case a round foot will roll during the leg-support phase, causing the hip to become misplaced and the robot to assume an incorrect attitude. This paper analyses this problem and provides a hip-control algorithm for restoring leg coordination. The algorithm is implemented in a real leg with a large-radius ball foot in order to evaluate how the algorithm would perform if applied to a real robot.     

带主动腰关节的四足机器人平稳运动控制

针对四足机器人在对角小跑运动时出现的后腿“拖地”、机体振荡的现象,提出了一种基于偏航方向上主动腰关节摆动的解决方法。通过D-H法对机器人各关节进行运动学建模,获得其运动学方程,并采用Kuramoto振荡器模型作为扩展的CPG耦合网络振子,实现对腰、腿关节的统一控制。仿真实验表明,经过腰关节控制优化后的机器人在对角小跑时,相对于刚体躯干的机器人,姿态角变化幅度显著减小,抬腿高度明显增加,有效地提高了机器人的运动稳定性,证明了方法的可行性。