Kinematic analysis and simulation of active-caster robotic drive with ball transmission (ACROBAT-S)

In this study, a new type of active-caster with a single ball transmission (ACROBAT-S) was proposed. The proposed ball transmission involved a novel mechanism that realized to control the active-caster for propelling robotic platforms. The combined power from two motors rotated a single ball in two dimensions. Additionally, the combined power was simultaneously decomposed to the wheel shaft and steering shaft of an active-caster in an appropriate ratio. The transmission design enabled an omnidirectional robot with three active-casters to control its 3D motion by three motors with no redundancy. The new concept of ACROBAT-S offers several advantages as compared to the previous ACROBAT design as the number of balls was reduced from two to one, and therefore the number of friction drives between a ball and rollers or a ball and another ball was also reduced from five to three. These features could contribute to simplifying the mechanism design and to reduce transmission slippages and energy losses. The design concept was verified by deriving and analyzing the kinematics of a single ball transmission mechanism and a three-wheeled omnidirectional mobile robot. Furthermore, the motions of ACROBAT-S and that of an omnidirectional robot were verified using computer simulations. The results confirmed that the proposed single ball transmission could be applied to an omnidirectional wheel mechanism to realize non-redundant omnidirectional motions.     

Design,Development, and Mobility Evaluation of an Omnidirectional Mobile Robot for Rough Terrain

Omnidirectional vehicles have been widely applied in several areas, but most of them are designed for the case of motion on flat, smooth terrain, and are not feasible for outdoor usage. This paper presents the design and development of an omnidirectional mobile robot that possesses high mobility in rough terrain. The omnidirectional robot consists of a main body with four sets of mobility modules, called an active split offset caster (ASOC). The ASOC module has independently driven dual wheels that produce arbitrary planar translational velocity, enabling the robot to achieve its omnidirectional motion. Each module is connected to the main body via a parallel link with shock absorbers, allowing the robot to conform to uneven terrain. In this paper, the design and development of the ASOC‐driven omnidirectional mobile robot for rough terrain are described. A control scheme that considers the kinematics of the omnidirectional mobile robot is presented. The mobility of the robot is also evaluated experimentally based on a metric called the ASOC mobility index. The mobility evaluation test clarifies a design tradeoff between terrain adaptability and omnidirectional mobility due to the shock absorbers. In addition, an odometry improvement technique that can reduce position estimation error due to wheel slippage is proposed. Experimental odometry tests confirmed that the proposed technique is able to improve the odometry accuracy for sharp‐turning maneuvers.     

Design and Control of a Four‐Wheeled Omnidirectional Mobile Robot with Steerable Omnidirectional Wheels

Omnidirectional mobile robots are capable of arbitrary motion in an arbitrary direction without changing the direction of wheels, because they can perform 3 degree‐of‐freedom (DOF) motion on a two‐dimensional plane. In this research, a new class of omnidirectional mobile robot is proposed. Since it has synchronously steerable omnidirectional wheels, it is called an omnidirectional mobile robot with steerable omnidirectional wheels (OMR‐SOW). It has 3 DOFs in motion and one DOF in steering. One steering DOF can function as a continuously variable transmission (CVT). CVT of the OMR‐SOW increases the range of velocity ratio from the wheel velocities to robot velocity, which may improve performance of the mobile robot. The OMR‐SOW with four omnidirectional wheels has been developed in this research. Kinematics and dynamics of this robot will be analyzed in detail. Various tests have been conducted to demonstrate the validity and feasibility of the proposed mechanism and control algorithm. © 2004 Wiley Periodicals, Inc.     

基于关联规则挖掘的全向轮移动机器人目标跟踪控制系统设计

为保证全向轮机器人在移动过程中所捕获到的目标对象能够完全符合理想目标设定条件,准确追踪目标节点的运动行为,设计基于关联规则挖掘的全向轮移动机器人目标跟踪控制系统;根据CAN主控框架的部署形式,按需连接核心管控电路与I/O跟踪模块;分别以转向控制器、速度控制器为例,完善全向轮控制结构的物理作用能力,实现机器人目标跟踪控制系统的硬件设计;在此基础上,定义频繁项集合,按照具体的关联规则特征描述结果,确定挖掘程序指令的执行能力,得到准确的关联离散度指标计算结果,实现控制系统的关联规则挖掘,再联合相关硬件设备结构,完成基于关联规则挖掘的全向轮移动机器人目标跟踪控制系统设计;分析对比实验结果可知,随着关联规则挖掘控制系统的应用,全向轮机器人在移动过程中所捕获到的目标对象能够将理想目标完全包含在内,机器人目标跟踪结果准确,可以辅助全向轮移动机器人更加准确地追踪目标节点的运动行为,符合实际应用需求。     

Adaptive Polar-Space Motion Control for Embedded Omnidirectional Mobile Robots with Parameter Variations and Uncertainties

This paper presents an adaptive polar-space motion controller for trajectory tracking and stabilization of a three-wheeled, embedded omnidirectional mobile robot with parameter variations and uncertainties caused by friction, slip and payloads. With the derived dynamic model in polar coordinates, an adaptive motion controller is synthesized via the adaptive backstepping approach. This proposed polar-space robust adaptive motion controller was implemented into an embedded processor using a field-programmable gate array (FPGA) chip. Furthermore, the embedded adaptive motion controller works with a reusable user IP (Intellectual Property) core library and an embedded real-time operating system (RTOS) in the same chip to steer the mobile robot to track the desired trajectory by using hardware/software co-design technique and SoPC (system-on-a-programmable-chip) technology. Simulation results are conducted to show the merit of the proposed polar-space control method in comparison with a conventional proportional-integral (PI) feedback controller and a non-adaptive polar-space kinematic controller. Finally, the effectiveness and performance of the proposed embedded adaptive motion controller are exemplified by conducting several experiments on steering an embedded omnidirectional mobile robot.     

Switched Modeling and Task–Priority Motion Planning of Wheeled Mobile Robots Subject to Slipping

This study is devoted to the modelling and control of Wheeled Mobile Robots moving with longitudinal and lateral slips of all wheels. Due to wheel slippage we have to deal with systems with changing dynamics. Wheeled Mobile Robots can be thus modeled as switched systems with both autonomous switches (due to wheel slippage) and smooth controls (due to control algorithm). It is assumed that the slipping is counteracted by the slip reaction forces acting at contact points of the wheels with the ground. A model of these reaction forces, borrowed from the theory of automotive systems, has been adopted and included into the Lagrangian dynamic equations of the robot. A framework for designing motion planning schemes devoid of chattering effects for systems with changing dynamics is presented. A task–priority motion planning problem for wheeled mobile robots subject to slipping is addressed and solved by means of Jacobian motion planning algorithm based on the Endogenous Configuration Space Approach. Performance of the algorithm is presented in simulations of the Pioneer 2DX mobile platform. The robot dynamics equations are derived and 4 variants of motion are distinguished. The motion planning problem is composed of two sub-tasks: robot has to reach a desired point in the task space (proper motion planning) and the motion should minimize either the control energy expendinture or the wheel slippage. Performance of the motion planning algorithm is illustrated by a sort of the parking maneuver problem.     

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.     

轮子打滑状态下全向移动机器人轨迹跟踪控制

针对全向移动机器人轨迹跟踪控制中存在未知轮子打滑干扰问题,设计自抗扰反步控制器.首先,建立存在轮子打滑扰动的全向移动机器人的运动学模型;然后,融合自抗扰控制技术与反步控制技术,设计基于全向移动机器人运动学模型的轨迹跟踪控制器,该控制器分别从纵向控制、横向控制及姿态控制上对打滑干扰进行实时估计与补偿;最后,利用Lyapunov定理分析闭环系统的稳定性并通过仿真实验验证了所提出控制算法的有效性和鲁棒性.     

Keeping smart, omnidirectional eyes on you [adaptive panoramic stereovision]

An adaptive panoramic stereo approach for two cooperative mobile platform is presented. There are four key features in the approach: 1) omnidirectional stereovision with an appropriate vertical FOV, and a simple camera calibration method; 2) cooperative mobile platforms for mutual dynamic calibration and best view planning; 3) 3D matching after meaningful object (human subject) extraction; and 4) real-time performance. The integration of omnidirectional vision with mutual awareness and dynamic calibration strategies allows intelligent cooperation between visual agents. This provides an effective way to solve the problems of limited resources, view planning, occlusion, and motion detection of movable robotic platforms. Experiments have shown that this approach is quite promising.     

Walking-support robot system for walking rehabilitation: design and control

An intelligent walking-assistance robot system has been developed to help the elderly or the disabled in rehabilitation programs. From the design viewpoint, several different mechanisms to satisfy the strict requirements for use in a rehabilitation program were considered and studied. A two-wheel mobile mechanism was developed to provide motions to follow the patient's walking trajectory, and also to make the patient follow a specified trajectory. Equations of motion were derived for the unloading control, and a force control algorithm was developed. For motion control of the mobile base, virtual trajectory planning by the B-spline method and PID control were used. Sensing the motion of the patient is performed by a linear potentiometer and a rotating encoder attached to the robot manipulator. The system was tested on patients in hospital and the experimental results are reported.     

Kinematic modeling of wheeled mobile robots

We formulate the kinematic equations of motion of wheeled mobile robots incorporating conventional, omnidirectional, and ball wheels.¹ We extend the kinematic modeling of stationary manipulators to accommodate such special characteristics of wheeled mobile robots as multiple closed-link chains, higher-pair contact points between a wheel and a surface, and unactuated and unsensed wheel degrees of freedom. We apply the Sheth-Uicker convention to assign coordinate axes and develop a matrix coordinate transformation algebra to derive the equations of motion. We introduce a wheel Jacobian matrix to relate the motions of each wheel to the motions of the robot. We then combine the individual wheel equations to obtain the composite robot equation of motion. We interpret the properties of the composite robot equation to characterize the mobility of a wheeled mobile robot according to a mobility characterization tree. Similarly, we apply actuation and sensing characterization trees to delineate the robot motions producible by the wheel actuators and discernible by the wheel sensors, respectively. We calculate the sensed forward and actuated inverse solutions and interpret the physical conditions which guarantee their existence. To illustrate the development, we formulate and interpret the kinematic equations of motion of Uranus, a wheeled mobile robot being constructed in the CMU Mobile Robot Laboratory.     

基于视觉图像的全向移动机器人轨迹跟踪控制研究

机器人轨迹节点跟踪比较难,导致机器人实际轨迹偏离期望轨迹,所以设计基于视觉图像的全向移动机器人轨迹跟踪控制方法;构建全向移动机器人的运动学数学模型,以此确定机器人移动轨迹数学模型;以移动轨迹数学模型为基础,按照视觉图像划分标准对全向移动机器人运动图像的分割,通过分离目标节点的方式提取运动学特征参量,完成机器人轨迹节点跟踪处理;结合节点跟踪处理结果,将运动学不等式与误差向量作为机器人轨迹跟踪控制的约束条件,利用滑模变结构搭建轨迹跟踪控制模型,实现全向移动机器人轨迹跟踪控制;对比实验结果表明,所设计的方法应用后,全向移动机器人角速度曲线、线速度曲线与期望运动轨迹曲线之间的贴合程度均超过90%,满足全向移动机器人轨迹跟踪控制要求。     

Design and construction of continuous alternate wheels for an omnidirectional mobile robot

Many types of omnidirectional wheels with passive rollers have gaps between rollers. Since these gaps cause a wheel to make discontinuous contact with the ground, they lead to vertical and/or horizontal vibrations during wheel operation. In addition, the radii of passive rollers are related to the height of a bump an omnidirectional wheel can surmount. In this research a new design of the alternate wheel is proposed. Because this wheel makes continuous contact with the ground and has alternating large and small rollers around the wheel, it is termed a continuous alternate wheel (CAW). In this paper a design procedure is also presented to determine the optimum number of rollers, the radii of rollers and the inside inclination angle of an outer roller for given design specifications. The CAW based on this design is compared to the existing alternate wheels in terms of design. Finally, an actual continuous alternate wheel is constructed to verify validity of the design guidelines. © 2003 Wiley Periodicals, Inc.     

Waypoint Following for Differentially Driven Wheeled Robots with Limited Velocity Perturbations

In this paper a unified motion control strategy dedicated for the waypoint following task realized by a differentially driven robot is presented. It is assumed that the vehicle moves with limited velocities and accelerations in order to reduce excessive slip and skid effects. In order to include operational constraints, a motion planner is combined with a universal stabilizer taking advantage of transverse functions. To improve tracking precision translated transverse functions are deployed and a new adaptive technique for the controller tuning is proposed. During the motion planning stage an auxiliary trajectory connecting points in the configuration space and satisfying assumed phase constraints is generated. The resulting motion execution system has been implemented on a laboratory-scale skid-steering mobile robot, which served as platform for experimental validation of presented algorithms.     

Control of wheel system under uncertainty

Consideration was given to the nonholonomic mechanical systems with rolling or the wheel systems such as mobile robot, car, or wheeled tractor. Analysis was confined to the kinematic models with regard for the dynamics of the controlling drives. Control of system motion along a given trajectory (planar smooth curve) was studied. The designed control law stabilizes this motion in large in the basic variables. The main result lies in solution of the problem of control under uncertainty when only sufficiently general dynamic characteristics of the wheel system drive are known.     

INTELLIGENT MOTION CONTROL FOR OMNIDIRECTIONAL MOBILE ROBOTS USING ANT COLONY OPTIMIZATION

This article presents an intelligent system-on-a-programmable-chip-based (SoPC) ant colony optimization (ACO) motion controller for embedded omnidirectional mobile robots with three independent driving wheels equally spaced at 120 degrees from one another. Both ACO parameter autotuner and kinematic motion controller are integrated in one field-programmable gate array (FPGA) chip to efficiently construct an experimental mobile robot. The optimal parameters of the motion controller are obtained by minimizing the performance index using the proposed SoPC-based ACO computing method. These optimal parameters are then employed in the ACO-based embedded kinematic controller in order to obtain better performance for omnidirectional mobile robots to achieve trajectory tracking and stabilization. Experimental results are conducted to show the effectiveness and merit of the proposed intelligent ACO-based embedded controller for omnidirectional mobile robots. These results indicate that the proposed ACO-based embedded optimal controller outperforms the nonoptimal controllers and the conventional genetic algorithm (GA) optimal controllers.     

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。     

Kinematic modeling of wheeled mobile robots with slip

This work presents a kinematic modeling method for wheeled mobile robots with slip based on physical principles. First, we present the kinematic modeling of a mobile robot with no-slip considering four types of wheels: fixed, centered orientable, off-centered orientable (castor) and Swedish (also called Mecanum, Ilon or universal). Then, the dynamics of a wheeled mobile robot based on Lagrange formulation are derived and discussed. Next, a quasi-static motion is considered to obtain the kinematic conditions that provide the slip modeling equations. Several types of traction models for the slip between the wheel and the floor are indicated. In particular, for a frictional force linearly dependent on the sliding velocity, the no-slip kinematic equation of the wheeled mobile robot is related, through the weighted least-squares algorithm, with the slip modeling equations. To illustrate the applications of the proposed approach a tricycle vehicle is considered in a real situation. The experimental results obtained for the slip kinematic model are compared with the ones obtained for the well-known Kalman filter.     

轮式移动机器人在圆形管道中的运动学建模与分析

为解决圆形管道中轮式移动机器人的运动控制问题,分析了轮式移动机器人在圆形管道中的运动学特性．借助接触点的切平面,单个轮子在平面上的位置和运动描述方法被应用在圆管的柱面上．推导了单个轮子在柱面上纯滚动时轮心的轨迹和速度．运用刚体运动瞬时螺旋理论,对由两个固定轮和一个舵轮组成的(1,1)型三轮机器人在圆形管道中的运动进行了建模分析,并对此运动学模型进行了仿真．     

Robust tube-based predictive control for mobile robots in off-road conditions

This paper focuses on the design of a tube-based Model Predictive Control law for the control of constrained mobile robots in off-road conditions with longitudinal slip while ensuring robustness and stability. A time-varying trajectory tracking error model is used, where uncertainties are assumed to be bounded and additive. The robust tube-based MPC is compared with other motion control techniques through simulation and physical experiments. These tests show the satisfactory behavior of the presented control strategy.