Image-based fuzzy trajectory tracking control for four-wheel steered mobile robots

A four-wheel steered mobile robot is fit for a higher power or improvement in the movement speed of a robot than a two-independent wheeled one. Since a steered mobile robot that slips very often cannot apply a popular dead-reckoning method using rotary encoders, it is desirable to use external sensors such as cameras. This paper describes a method to trace a straight line for four-wheel steered mobile robots using an image-based control method. Its controller is designed as a fuzzy controller and evaluated through some simulations and real robot.     

基于模糊自适应控制的全向移动机器人的运动控制研究

由于四轮驱动全向移动机器人轮系分布的特点,四轮之间存在耦合关系,在运行过程中,机器人整体运动的稳定性及控制精度都不佳。针对此问题,本文设计一种基于模糊自适应控制器的误差修正方法,结合模糊控制和PD控制,在线对机器人体进行误差修正,并将整体误差按轮系结构分布合理分配到单个轮子上,从而将整体的误差修正转化为单个轮子的误差修正。通过在Matlab-Simulink环境下仿真实验表明,在使用模糊自适应控制器进行误差修正后,机器人对线速度及角速度的跟随性明显提高,改善了机器人运动控制的精度。     

A Practical Iterative Learning Path‐Following Control Of An Omni‐Directional Vehicle

A new practical iterative learning control (ILC) updating law is proposed to improve the path following accuracy for an omni‐directional autonomous mobile robot. The ILC scheme is applied as a feedforward controller to the existing feedback controller. By using the local symmetrical double‐integral of the feedback control signal of the previous iteration, the ILC updating law takes a simple form with only two design parameters: the learning gain and the range of local integration. Convergence analysis is presented together with a design procedure. Simulation results on a difficult maneuver are presented to illustrate the effectiveness of the proposed simple and yet practical scheme. The simulation is based on the model of a novel robotic platform, the Utah State University (USU) Omni‐Directional Vehicle (ODV), which uses multiple “smart wheels,” whose speed and direction can be independently controlled through dedicated processors for each wheel.     

Dynamic path tracking control of a vehicle on slippery terrain

This paper deals with accuracy and reliability for the path tracking control of a four wheel mobile robot with a double-steering system when moving at high dynamics on a slippery surface. An extended kinematic model of the robot is developed considering the effects of wheel–ground skidding. This bicycle type model is augmented to form a dynamic model that considers an actuation of the four wheels. Based on the extended kinematic model, an adaptive and predictive controller for the path tracking is developed to drive the wheels front and rear steering angles. The resulting control law is combined with a stabilization algorithm of the yaw motion which modulates the actuation torque of each four wheels, on the basis of the robot dynamic model. The global control architecture is experimentally evaluated on a wet grass slippery terrain, with speeds up to 7 m/s. Experimental results demonstrate enhancement of tracking performances in terms of stability and accuracy relative to the kinematic control.     

具有MY轮的全方位移动机器人运动学研究

根据MY轮的结构特点建立了由MY轮组成的全方位移动机器人的运动学模型.分析了由于轮结构带来的运动学特性.对全方位移动机器人在运动过程中的振动、控制及误差进行了深入研究.提出了通过优化接触距离及MY轮转速来减小机器人运动误差的控制方法.为获得优化结构,比较了三轮结构和四轮结构的运动学特性.同时应用正弦控制规律来合理控制MY轮的转动,改善了机器人的运动稳定性.仿真结果充分证明了分析的正确性.     

Variable Structure Control of a Differentially Steered Wheeled Mobile Robot

This paper discusses dynamic modeling and robust control of a differentially steered mobile robot subject to wheel slip and external loads. Consideration of wheel slip and external loads is crucial for high load and/or high speed applications because they act as disturbances to the system. Furthermore, a tire model that adequately accounts for the tire/ground interaction is essential and Dugoff's pneumatic tire friction model is utilized herein in deriving the dynamic equations of motion of the mobile robot. It is shown that the dynamic equations satisfy the matching condition, and the variable structure control method is employed to design a tracking controller of the mobile robot. Numerical simulation shows the promise of the developed control algorithm.     

Multi-sensor measurement system for robotic drilling

In this paper we present a multi-sensor measurement system for robotic drilling. The system enables a robot to measure its 6D pose with respect to the work piece and to establish a reference coordinate system for drilling. The robot approaches the drill point and performs an orthogonal alignment with the work piece. Although the measurement systems are readily capable of achieving high position accuracy and low deviation to perpendicularity, experiments show that inaccuracies in the test scenario and slippage on the work piece when exerting clamping force considerably impact the results. With the current robotic drilling system an average position deviation of 0.334 mm and an average deviation to perpendicularity of 0.29° are achieved.     

基于模糊控制的全位移平衡机器人设计

设计了一种模糊控制的四轮全位移平衡机器人,通过SolidWorks改进设计了基于麦克纳姆轮的全位移平衡底盘、双轴云台等机械结构。以Altium Designer为开发平台设计了STM32F405核心板主控,外设电路设计主要包括:ICM20948传感器电路、CAN通信差分电路等。使用Simulink对算法进行仿真验证,云台控制算法使用了串级PID控制,底盘通过HI220陀螺仪传感器结合模糊控制算法实现平衡及运动。最终制作出了实体机器人并对模糊控制算法进行了验证,与传统PID算法相比,基于模糊控制的平衡机器人在响应速度、鲁棒性、稳定性等方面均有一定的提升。相比于传统四轮机器人,制作的平衡机器人能够更好地通过狭小的空间,对环境的适应性更强。     

Construction of an Omnidirectional Mobile Robot Platform Based on Active Dual-Wheel Caster Mechanisms and Development of a Control Simulator

In this paper, we describe a new type of holonomic and omnidirectional mobile robot using two driving assemblies, one of which consists of two independent driving wheel mechanisms, just like an active dual-wheel caster with an offset steered axis. Kinematic models of the wheel mechanism and a mobile robot with two driving assemblies are derived, and these models are applied to construct a feedback control system based on a resolved velocity control system for the robot. The effectiveness of the presented method is illustrated by some computer simulations. The prototype of a mobile robot platform using two driving assemblies, which can be controlled by a personal computer or a 3D joystick manipulated by human, is constructed.     

Predictive seam tracking with iteratively learned feedforward compensation for high-precision robotic laser welding

In this paper, a novel architecture for robotic seam tracking using an industrial robot and off-the-shelf sensors is proposed to compensate the residual errors that are commonly observed in high-precision robotic laser welding due to the nonlinearity of a seam and the fast path drifts along a robot path. Our experiments demonstrate that the robot system can track both linear and nonlinear long seams at a high speed of 100 mm/s with TCP offset-error within ±0.1 mm using the proposed method.     

火工品运载机器人的设计与研究

为了解决具有高度危险性的火工原料和产品生产线之间的运输完全依靠人工完成这一难题,设计了一种基于PC的轮式移动机器人;根据机器人的工作环境和特点,结构上使用四轮驱动和前后独立转向,并通过PC机将处理后的信息传输给运动控制卡控制机器人的方向和速度,采用人工势场法进行路径规划和贝叶斯方法将超声波传感器获取的信息进行融合,使机器人实现避障行进;运行实验表明,轮式移动机器人能成功地避开周围1m内的障碍物将火工品运送到目的地,运载负荷可以达到8kg,速度最快为2m/s,系统工作稳定可靠,满足火工品的运输要求。     

Development of a steerable,wheel-type,in-pipe robot and its path planning

This paper presents the development of a steerable, wheel-type, in-pipe robot and its path planning. First, we show the construction of the robot and demonstrate its locomotion inside a pipe. The robot is composed of two wheel frames and an extendable arm which links the centers of the two wheel frames. The arm presses the frames against the interior wall of a pipe to support the robot. The wheels of the frames are steered independently so that the robot can turn within a small radius of rotation. Experimental results of the locomotion show that the steering control is effective for autonomous navigation to avoid obstacles and to enter the joint spaces of L- and T-shaped pipes. Generally, autonomous navigation is difficult for wheel-type robots because the steering angles required to travel along a desired path are not easily determined. In our previous work, the relationship between the steering angles and locomotion trajectories in a pipe has already been analyzed. Using this analysis, we propose the path planning in pipes.     

An open-source multi-DOF articulated robotic educational platform for autonomous object manipulation

This research presents an autonomous robotic framework for academic, vocational and training purpose. The platform is centred on a 6 Degree Of Freedom (DOF) serial robotic arm. The kinematic and dynamic models of the robot have been derived to facilitate controller design. An on-board camera to scan the arm workspace permits autonomous applications development. The sensory system consists of position feedback from each joint of the robot and a force sensor mounted at the arm gripper. External devices can be interfaced with the platform through digital and analog I/O ports of the robot controller. To enhance the learning outcome for beginners, higher level commands have been provided. Advanced users can tailor the platform by exploiting the open-source custom-developed hardware and software architectures. The efficacy of the proposed platform has been demonstrated by implementing two experiments; autonomous sorting of objects and controller design. The proposed platform finds its potential to teach technical courses (like Robotics, Control, Electronics, Image-processing and Computer vision) and to implement and validate advanced algorithms for object manipulation and grasping, trajectory generation, path planning, etc. It can also be employed in an industrial environment to test various strategies prior to their execution on actual manipulators.     

室内机器人及其路径跟踪网络设计

近年来,室内移动机器人的研究和设计成为关注的焦点。我们采用单片机作为机器人的核心控制器,利用超声波传感器、碰撞传感器、步进电机及其控制芯片Ta8435联合制作开发了机器人实验平台。最后介绍了模糊控制、模糊神经网络,并利用模糊控制和模糊神经网络技术对室内机器人导航中的模糊控制避障和模糊神经网络路径跟踪作了MATLAB仿真研究,达到了预期的目的。     

一种球形滚动机器人的路径跟踪控制器设计

对一种球形滚动机器人的路径跟踪问题进行研究,设计一种基于自适应滑模控制策略的路径跟踪控制器。所设计的路径跟踪控制器采用鲁棒滑模自适应增益控制律,能够有效实现带有扰动和不确定性的实际球形滚动机器人的路径跟踪。推导球壳纯滚动和无自转非完整约束下球形滚动机器人的运动方程,并在此基础上设计自适应滑模路径跟踪控制器。对于给定的参考几何路径,所设计的路径跟踪控制器能够确保路径跟踪误差在有限时间内收敛至很小的零邻域内。基于Lyapunov稳定性理论证明了闭环控制系统的稳定性,数值仿真与样机实验结果进一步验证了所设计的路径跟踪控制器的有效性。     

Time-optimal tool motion planning with tool-tip kinematic constraints for robotic machining of sculptured surfaces

A time-optimal motion planning method for robotic machining of sculptured surfaces is reported in this paper. Compared with the general time-optimal robot motion planning, a surface machining process provides extra constraints such as tool-tip kinematic limits and complexity of the curved tool path that also need to be taken into account. In the proposed method, joint space and tool-tip kinematic constraints are considered. As there are high requirements for tool path following accuracy, an efficient numerical integration method based on the Pontryagin maximum principle is adopted as the solver for the time-optimal tool motion planning problem in robotic machining. Nonetheless, coupled and multi-dimensional constraints make it difficult to solve the problem by numerical integration directly. Therefore, a new method is provided to simplify the constraints in this work. The algorithm is implemented on the ROS (robot operating system) platform. The geometry tool path is generated by the CAM software firstly. And then the whole machine moving process, i.e. the feedrate of machining process, is scheduled by the proposed method. As a case study, a sculptured surface is machined by the developed method with a 6-DOF robot driven by the ROS controller. The experimental results validate the developed algorithm and reveal its advantages over other conventional motion planning algorithms for robotic machining.     

基于Mindstorms的四轮智能机器人实时控制系统设计

传统机器人控制系统是以辅助控制机器人转向为基准进行设计的,存在转向控制效果差的问题,为实现四轮智能机器人控制系统研发,以Mindstorms平台为基础,搭建由主控模块、传感器模块、无线通信模块、运动模块以及电源模块组成的四轮智能机器人结构。在运动控制模块中选用TMC236芯片作为电机驱动芯片,通过电路为桥臂上开关管提供控制电压;在底层控制模块中,采用PID控制器控制电机期望转角与实际转角之间差值,实现机器人转向角度控制。对软件控制策略研发中,利用嵌入式操作软件系统实现车道保持控制和避障控制功能,实现机器人自主换道功能。保证机器人自主充电情况下,测试转向控制功能,由测试结果可知,基于Mindstorms系统控制效果始终维持在98%以上,实现机器人转向精准控制。     

Maneuverability modeling and trajectory tracking for fish robot

This study develops a 6-DOF mathematical model for a robotic fish that considers surge, sway, heave, roll, pitch, and yaw. The model considers the conditions of a fish swimming in ocean current perturbations similar to the ocean current perturbations of the slender-body autonomous underwater vehicles. For swimming and turning behaviors, a nonlinear, dynamic, carangiform locomotion model is derived by using a planar four-link model. A 2-DOF barycenter mechanism is proposed to provide body stabilization and to serve as an actuating device for active control design. A barycenter control scheme is developed to change the center of gravity of the robot fish body by moving balancing masses along two axes. The projected torque on x and y axes propel pitch and roll angles to the desired settings. A Stabilizing controller, fish-tail mechanism, rigid body dynamics, and kinematics are incorporated to enable the fish robot to move in three dimensional space. Simulation results have demonstrated maneuverability and control system performance of the developed controller which is proposed to conduct path tracking of the robot fish as it swims under current perturbations.     

Adaptive unified motion control of mobile manipulators

This paper presents a unified motion controller for mobile manipulators which not only solves the problems of point stabilization and trajectory tracking but also the path following problem. The control problem is solved based on the kinematic model of the robot. Then, a dynamic compensation is considered based on a dynamic model with inputs being the reference velocities to the mobile platform and the manipulator joints. An adaptive controller for on-line updating the robot dynamics is also proposed. Stability and robustness of the complete control system are proved through the Lyapunov method. The performance of the proposed controller is shown through real experiments.     

基于阿克曼原理的4WID/4WIS汽车循迹控制研究

针对四轮独立驱动、独立转向汽车循迹控制精度和转向稳定性兼容问题,同时考虑减小轮胎磨损,延长轮胎使用寿命,本文基于阿克曼转向原理和RBF神经网络PID理论,提出了一种自适应的循迹控制方法.首先,设计了基于RBF神经网络PID理论的自适应转向控制器,用于控制前内轮转角,保证循迹精度;其次,后内轮以减小质心侧偏角为目标进行辅助转向,保证转向稳定性;接着,基于阿克曼转向原理,确定外轮转角,保证各轮侧偏力分配合理;最后,采用同一瞬心法,确定各车轮转速,以减小轮胎滑动率.本文搭建了CarSim和MATLAB/Simulink联合仿真平台,进行了仿真实验,结果表明：本文提出的循迹控制方法,不仅能获得较小的循迹偏差和质心侧偏角,保证了足够的循迹控制精度和转向稳定性,同时还减小了轮胎滑动率,有利于减小轮胎的磨耗.