Design,development, and control of a tough electrohydraulic hexapod robot for subsea operations

Abstract

In this paper, the design, the development, and the control for an 18 degree-of-freedom electrohydraulic hexapod robot for subsea operations are presented. The hexapod, called HexaTerra, can be equipped with a trenching machine, and move over obstacles and on sloped terrain. Optimization techniques are employed to size the robot legs. Rigid body equations of motion and hydraulic dynamics are developed. Compact electrohydraulic components are sized and selected taking into account the leg kinematics and system dynamic analysis. A model-based control system design is implemented in a real-time environment, able to produce the overall functionality and performance. Experimental results obtained from preliminary tests with the developed electrohydraulic hexapod show good controlled performance and demonstrate excellent system stability over obstacles.     

圆周对称分布六腿机器人三种典型行走步态步长及稳定性分析

针对现有圆周对称分布六腿步行机器人步长研究中存在的缺点和不足,提出了并联机构支链工作空间相交法,将由机器人本体、支撑腿和地面组成的并联机构分割成不同的分支,利用各分支工作空间求交,从而确定机器人在某一本体高度上的步长和稳定裕度.该方法可在已知机器人立足点和本体高度的情况下求得机器人的最大可行步长和稳定裕度,也可以求得机器人在某一本体高度上的极限可行步长和在这种情况下的立足点的位置,还可以根据已知步长和机器人本体高度来确定最大稳定裕度和最大稳定裕度下的立足点的位置.这种方法为圆周对称分布六腿机器人采用不同步态行走过程中立足点、本体高度和步长的选取提供重要参考.     

六足仿生机器人机构与控制系统设计

由于六足仿生机器人的足数较多,控制其稳定行走较为复杂,针对控制六足机器人稳定行走的要求,该六足机器人的腿部是参照蚂蚁的腿部结构进行设计,并对其进行建模分析.整个系统在硬件上选取了Arduino、无线模块、显示模块、舵机控制板等;软件上选用Qt Creator在上位机上编程,用于远程遥控六足机器人及观察其行走状态变化;在步态控制上采用了三角步态控制算法.通过设计机械结构、建模分析以及硬件、软件和算法的结合,实现了六足仿生机器人的稳定行走.     

六足机器人不规则地形下的运动规划算法研究

以六足类昆虫典型代表——蚂蚁爬越障碍柱和障碍柱堆的两种运动过程及其特点为分析对象,总结了蚂蚁在应对不规则地形时的运动策略,建立了更为合理的六足机器人的运动学数学模型;并仿照蚂蚁在应对不规则地形时的运动策略,提出在进行仿生六足机器人运动规划时,可将地形划分为浅度不平地形和深度不平地形两种情况,进而针对两种地形情况提出了六足机器人在不规则地形条件下的运动规划算法。最后通过样机试验验证所提算法的有效性。     

Foot Force Based Reactive Stability of Multi-Legged Robots to External Perturbations

Many environments and scenarios contain rough and irregular terrain and are inaccessible or hazardous for humans. Robotic automation is preferred in lieu of placing humans at risk. Legged locomotion is more advantageous in traversing complex terrain but requires constant monitoring and correction to maintain system stability. This paper presents a multi-legged reactive stability control method for maintaining system stability under external perturbations. Assuming tumbling instability and sufficient friction to prevent slippage, the reactive stability control method is based solely on the measured foot forces normal to the contact surface, reducing computation time and sensor information. Under external perturbations, the reactive stability control method opts to either displace the CG or the foot contacts of the robot based on the measured foot force distribution. Details describing the reactive stability control method are discussed including algorithms and an implementation example. An experimental demonstration of the reactive stability control method is presented. The experiment was conducted on a hexapod robot platform retrofitted with a tiny computer and force sensitive resistors to measure the foot forces. The experimental results show that the presented reactive stability control strategy prevents the robot from tipping over under external perturbation.     

控制六足仿生机器人三角步态的研究

基于仿生学原理,在分析六足昆虫运动机理的基础上,对六足仿生机器人的三角步态运动原理进行了分析.论文涉及六腿机器人步态研究的一些基本参数的描述,讨论了用相对运动的原理研究步态的方法,结合慧鱼机器人组合包中的构件拼出六足仿生机器人.该机器人模型结构简单,设计独特,能前进和后退,且能避开小型障碍物.基于三角步态运动原理对其进行了反复实验,实验结果表明六足仿生机器人具有较好的机动性和稳定性.     

基于ARM的六足仿生机器人野外定位系统

为了更好地控制六足仿生机器人适应野外作业环境,针对机器人野外定位问题,提出了一种六足仿生减灾救援机器人无线野外定位系统解决方案,方案以三星S3C2440为硬件平台,以嵌入式linux系统为软件平台,设计了六足仿生机器人野外定位系统。通过GPS全球定位系统进行六足仿生机器人的定位,利用GPRS实现网络通信,并将定位信息传输到终端设备,终端设备通过发送命令的方式控制六足仿生机器人实现相应的动作。实验证明：该系统的稳定性好,可靠性较高,能较好的满足六足仿生减灾救援机器人野外定位的需求。     

Safe Collaborative Assembly on a Continuously Moving Line with Large Industrial Robots

Robot safety standards defines Collaborative Operation as a state in which purposely designed robots work in direct cooperation with a human within a defined workspace. That is, an operator and an industrial robot complete assembly tasks at the collaborative workspace. A prerequisite to ensuring safety during all phases of operation is an understanding of the nature of hazards pertinent to collaborative systems. An automotive assembly station, where plastic panels are assembled on a continuously moving line, formed the basis for research operations meant to understand safety issues when a large industrial robot aids an operator in assembly tasks. This led to the development of a laboratory demonstrator whose design and functioning will be presented in this article. Additionally, the hazards identified during risk assessment along with measures to mitigate the associated risks will be presented in order to highlight the nature of hazards pertinent to collaborative systems.     

一种六足仿生巡检机器人的设计与实现

六足仿生机器人因其灵活度好、可靠性高、适应性强等特点而得到广泛应用;针对六足仿生巡检机器人,从结构设计、步态规划、系统仿真和实物构建等方面,探索一般意义上系统设计和实现方法;首先设计了六足仿生机器人的多关节机械结构,并给出了此类系统的量化建模方法;然后采用了重心随动的三角步态规划方法,对系统稳定性和典型步态规划进行了量化分析;在此基础上基于标准D-H参数法建立了机器人的运动学模型,并且通过仿真实现了六足机器人向前纵向行走和向右横向行走的直线平稳运动;最后通过六足仿生巡检机器人实物测试,验证了所设计的结构和步态规划方法的可行性和有效性。     

An integrated approach for simulation of mechatronic systems applied to a hexapod robot

Mechatronics is the integration of mechanism, electronics and computer control to produce a functional system. The design process involves application of many engineering areas and various approaches are possible. Computer programs are available in different engineering areas. Engineers define systems and inputs, and user-friendly programs establish mathematical models, solve them and give simulation outputs. In this study, SolidWorks is used for solid modeling and assembly, CosmosMotion is used for rigid body dynamics, CosmosWorks is used for finite element vibration and strength analyses, and Adlink module is used for actuator control. The integration of the design process is achieved with a main program developed in Visual Basic, which uses the application programming interface (API) capabilities. The procedure is applied to a hexapod robot. The robot has been produced to develop and test the procedure. CosmosMotion results are verified by the analytical results obtained from the dynamic equations of the hexapod. Besides known kinematic workspace definition of robots, kinetic and rigidity workspace concepts are introduced. Mechatronic systems can be designed and evaluated easily and effectively by using the design process developed in this work.     

Projection operator-based robust adaptive control of an aerial robot with a manipulator

This paper describes a quadcopter manipulator system, an aerial robot with an extended workspace, its controller design, and experimental validation. The aerial robot is based on a quadcopter with a three degree of freedom robotic arm connected to the base of the vehicle. The work aims to create a stable airborne robot with a robotic arm that can work above and below the airframe, regardless of where the arm is attached. Integrating a robotic arm into an underactuated, unstable system like a quadcopter can enhance the vehicle's functionality while increasing instability. To execute a mission with accuracy and reliability during a real-time task, the system must overcome the inter-coupling effects and external disturbances. This work presents a novel design for a robust adaptive feedback linearization controller with a model reference adaptive controller and hardware implementation of the quadcopter manipulator system with plant uncertainties. The closed-loop stability of the aerial robot and the tracking error convergence with the robust controller is analyzed using Lyapunov stability analysis. The quadcopter manipulator system is custom developed in the lab with an off-the-shelf quadcopter and a 3D-printed robotic arm. The robotic system architecture is implemented using a Jetson Nano companion computer for autonomous onboard flight. Experiments were conducted on quadcopter manipulator system to evaluate the autonomous aerial robot's stability and trajectory tracking with the proposed controller.     

A new seam-tracking algorithm through characteristic-point detection for a portable welding robot

The welding task in double-hulled structures in shipyards and in steel-frame structures is hazardous and difficult due to the toxic gas and limited workspace. Therefore, many efforts have been undertaken for automation. The main challenge for automation is the development of a simple and robust seam-tracking algorithm that can be applied to a portable welding robot that operates under irregular and diverse task conditions in the workspace. We developed a seam-tracking algorithm for weaving weld path planning using a laser displacement sensor. The goal of the proposed algorithm is to detect the seam of single-butt welding with manually tack-welded non-zero gaps. The focus is on keeping the algorithm simple and affordable so that it can be applied to portable robots that operate in hazardous fields. The algorithm consists of four steps: scanning, filtering, generation of the reference points, and path planning. In the scanning process, the depth data of a cross-section of the seam profile is obtained. Next, a Gaussian filter is used to remove noise from the raw data. A differential characteristic-point detection algorithm is applied to the filtered data to detect the reference points that represent the shape and location of the gap to be welded. Finally, path planning for single-V butt multi-pass welding is done based on the detected reference points. A portable four-axis welding robot is built using the developed algorithm. The algorithm is validated through welding experiments regarding a single-V butt welding task with a manually tack-welded non-zero gap.     

面向双操作者的六足机器人共享遥操作

随着六足机器人遥操作系统研究工作的日趋深入,针对其操控系统的开发也将面临诸多挑战.为了实现双人操控条件下各操作者的控制权重实时分配,设计一种基于透明性及控制状态(TCS)的六足机器人双用户控制权重分配方法.其双主端与单从端采取位置-速度的交互模式,通过分析系统实时透明性与当前控制状态,构建三边遥操作控制律,实时计算共享因子,采用速度跟踪模式设计基于触觉力反馈的系统控制架构,并利用三端口绝对稳定定理确定控制律参数的稳定范围.最后,搭建半物理仿真实验平台并验证所设计的三边共享遥操作方法能够在兼顾系统安全性与透明性的同时以较高的效率与安全性实现六足机器人的双用户操控,并能充分考虑双用户的控制意图.     

Multi-Criteria Optimization of a Hexapod Machine

Alternative designs of a hexapod machine are proposed and investigated with the aims to reduce flexibility and to eliminate singular kinematic configurations that appear in the workspace for the current design of the machine. The hexapod is modeled as a rigid multibody system. Articular coordinates associated with desired tool trajectories are computed by inverse kinematics. Hence, dynamic forces and torques are not considered and, as there is no closed-loop control realized in the model, the actual rotational and translational position of the tool deviates from the desired position due to machining loads. These deviations serve as objective functions during a multi-criteria optimization in order to determine the best design regarding stiffness/flexibility of the machine. Further, a general approach for evaluating flexibility behavior of the machine in the complete workspace is introduced and the results from the optimization are verified. Besides flexibility, a crucial point for machining tools is the size of the feasible workspace. Therefore, the influence of the design modification on the workspace is also taken into account.     

Adaptive calibration and control of 2D monocular visual servo systems

For most visual servo systems, accurate camera/robot calibration is essential for precision tasks, such as tracking time-varying end-effector trajectories in the image plane of a remote (or fixed) camera. This paper presents details of control-theoretic approaches to the calibration and control of monocular visual servo systems in the case of a planar robot with a workspace perpendicular to the optical axis of the imaging system. An on-line adaptive calibration and control scheme is developed, along with an associated stability and convergence theorem. A redundancy-based refinement of this scheme is proposed and demonstrated via simulation.     

A geometric approach to solving the stable workspace of quadruped bionic robot with hand–foot-integrated function

This paper discusses stable workspace of a hand–foot-integrated quadruped walking robot, which is an important issue for stable operation of the robot. This robot was provided with combined structure of parallel and serial mechanisms, whose stable workspace was the subspace of the workspace in which the system was considered stable. The reachable region was formed under structural conditions, while the stable space was formed by the overall conditions of stability which changed with the robot's pose and the mass of grabbed object. In this paper, based on the robot's main structure, the key issues in solving the robot's workspace are discussed in detail, including searching steady conditions of operation of the robot. To research the robot's workspace, working leg's motion curve needed to be solved by kinematics analysis. Due to the redundant drive, it was problematic to deal analytically with the kinematics of the quadruped walking robot. A geometric method of kinematic analysis was proposed as well. Based on the geometric method, the workspace of the robot under varying postures was analyzed by the method of grid partition and in combination with Matlab, VB and Solidworks software programs. An automated computational system of the stable workspace was developed and an example was given to illustrate the whole process in detail. The theory and analysis procedures were also verified by simulation of the robot and its actual grabbing of an object.     

Conceptual design and analysis of the 2T1R mechanism for a cooking robot

This paper deals with the design and analysis of a two-translation and one-rotation (2T1R) mechanism for a novel cooking robot. Firstly the motions involved in stir-fry, the most representative operation in the cooking processes used in Chinese cuisine, are analyzed in details. Then the featured motions are decomposed into four main movements that are used as a design base for a wok motion mechanism. Several three-degrees-of-freedom (DOF) parallel manipulators are considered. From these, a 2T1R mechanism is selected as an ideal candidate. A 4-DOF (2T1R+1T) cooking robot is constructed by combining the 2T1R parallel manipulator with a 1-DOF linear feed mechanism. It is shown that the combined 4-DOF robot can perform the required cooking operations, particularly the stir-fry. The analysis conducted on the proposed 2T1R parallel manipulator includes inverse kinematics, forward kinematics, the velocity analysis, the constant orientation workspace, and the total orientation workspace. A prototype of the cooking robot is developed. The experiments verify that the proposed cooking robot is suitable for performing the required operations.     

基于CPG的六足机器人运动步态控制方法

中枢模式发生器（CPG）在六足机器人的运动步态控制中起着至关重要的作用。为了研究六足机器人的运动控制方法,首先基于仿生学原理设计了六足机器人的机械结构,并在虚拟样机软件ADAMS中搭建其三维模型;其次选择Hopf振荡器作为CPG单元,并改进了振荡器模型;然后设计了六足机器人的CPG网络拓扑结构,包含单腿关节映射函数方案和腿间CPG环形耦合网络方案,并对其进行了改进;最后通过ADAMS和MATLAB联合仿真实验,验证了所设计六足机器人的运动稳定性和CPG控制方案的可行性与有效性。仿真结果表明,该方法能够满足六足机器人不同运动步态的控制需求,对六足机器人的运动控制具有一定的实际应用价值。     

A singularity-free motion control algorithm for robot manipulators—a hybrid system approach

This paper presents the design and implementation of a singularity-free tracking algorithm for robot manipulators using a hybrid system approach. A hybrid robot motion controller is designed to ensure feasible robot motion in the neighborhood of kinematic singularities. The hybrid control system has a two-layered hierarchical structure, a discrete layer and a continuous layer. The robot workspace is partitioned into subspaces based on the singular configurations of the robot. Switching between continuous controllers is involved when the robot travels across the subspaces. With the hybrid controller, the robot can work at the vicinity of singular configurations, but also can go through and stay at the singular configurations. The stability of the hybrid system is investigated using multiple Lyapunov function theory. Experimental results have demonstrated the advantages of the hybrid robot motion control method.     

六边形对称分布六腿机器人的典型步态及其运动性能分析

为了便于在不同地理条件下合理地选择较优的步态,实现稳定高效的智能行走,本文针对一种六边形 对称分布的六腿机器人研究其不同步态的优劣．主要从行走能力、稳定性和能耗3 个角度对六边形对称结构的六腿 机器人在同样占空比下的3 种静态稳定周期步态进行了比较研究,此外还简要分析了其越障能力和穿越窄道的能 力．研究分析结果表明3 种步态（横向昆虫式摆动步态、哺乳动物式踢腿步态和混合步态）在不同条件下各有优劣： 横向昆虫式摆动步态在能耗和越障能力方面较其他两种步态有优势;而混合步态在稳定性上最具优势,其它能力处 于中间;哺乳动物式踢腿步态则可穿越窄道,步长上较昆虫摆动步态略好．本文的研究工作为六边形对称结构的六 腿机器人在未知复杂地貌环境下的智能行走提供了重要参考．