基于点云的补漆机器人系统

汽车补漆机器人需要面对各种不同大小的车型,适配各种造型曲面和颜色,这种高度自适应要求使得补漆机器人在目标跟踪、路径规划、运动空间等方面的设计难度远超汽车厂的喷漆机器人.因此需要重新规划喷漆路径,首先对汽车的点云数据进行分部位切割,然后以八邻域法计算封闭曲面轮廓,最后以切片法在曲面上生成光栅轨迹,形成了每一个补漆面的关键路径.设计了八轴桁架机器人系统,用蚁群算法计算生成八轴联动时的路径规划,再通过倍福的ADS协议将路径数据和梯形曲线的加速度下发到PLC运动控制程序,完成各关节轴的联动协同补漆运动.实测表明,该系统能针对不同汽车,自动控制机器人工具轴心以法向量对准任意曲面,并以联动方式驱动八轴平稳跟踪曲面运动.该系统可广泛应用于各种曲面的机器人加工.     

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.     

基于多工业机器人的轮毂打磨工作站系统

以汽车轮毂打磨加工作业为研究对象,针对其内侧镂空打磨作业轨迹规划和自动化生产协调难度大的问题,提出一种双工业机器人协同打磨作业工作站设计方案。该方案首先根据汽车轮毂实际生产工艺流程,利用SolidWorks和RobotStudio软件设计相关模型组件并搭建工作站整体布局,然后创建并设计由Smart动态逻辑组件、传感器及I/O通讯网络构建的系统的电气控制模型,最后通过多工业机器人协同作业离线编程实现系统功能及仿真。本文提出的方案为汽车轮毂打磨自动化生产线的实现提供了设计依据和实验平台,缩短了生产线开发周期,节约了操作者时间,提高了工作效率。     

人工鱼群算法在机器人加工路径规划中的应用

针对机器人加工路径规划问题,提出了一种基于人工鱼群算法的机器人加工路径规划新方法。仿真实验表明,该算法实现简单,搜索效率高,在较短时间内能够求得最优解,可满足机器人加工的实时性要求。     

Smooth tool path generation for 5-axis machining of triangular mesh surface with nonzero genus

NC machining of a nonzero genus triangular mesh surface is being more widely confronted than before in the manufacturing field. At present, due to the complexity of geometry computation related to tool path generation, only one path pattern of iso-planar type is adopted in real machining of such surface. To improve significantly 5-axis machining of the nonzero genus mesh surface, it is necessary to develop a more efficient and robust tool path generation method. In this paper, a new method of generating spiral or contour-parallel tool path is proposed, which is inspired by the cylindrical helix or circle which are a set of parallel lines on the rectangular region obtained by unwrapping the cylinder. According to this idea, the effective data structure and algorithm are first designed to transform a nonzero genus surface into a genus-0 surface such that the conformal map method can be used to build the bidirectional mapping between the genus-0 surface and the rectangular region. In this rectangular region, the issues of spiral or contour-parallel tool path generation fall into the category of simple straight path planning. Accordingly, the formula for calculating the parameter increment for the guide line is derived by the difference scheme on the mesh surface and an accuracy improvement method is proposed based on the edge curve interpolation for determining the cutter contact (CC) point. These guarantee that the generated tool path can meet nicely the machining requirement. To improve further the kinematic and dynamic performance of 5-axis machine tool, a method for optimizing tool orientation is also preliminarily investigated. Finally, the experiments are performed to demonstrate the proposed method and show that it can generate nicely the spiral tool path or contour-parallel tool path on the nonzero genus mesh surface and also can guarantee the smooth change of tool orientation.     

An integrated framework of tool path planning in 5-axis machining of centrifugal impeller with split blades

Centrifugal impeller is a complex part commonly used in aerospace, energy, and air-conditioning industries. Its manufacture involves multi-axis free form machining, a time consuming and error-prone process. Tool path planning is considered a critical issue in the process but still lacking of systematic solutions. This paper proposes a tool path planning framework for 5-axis machining of centrifugal impeller with split blades. It provides several CAM functions that assist the users to generate collision-free cutter motions with smooth tool orientations. First, the machining process is divided into four operations and the planning tasks of each operation are standardized. Second, the hub surfaces are properly decomposed, re-grouped, and re-parameterized to facilitate calculation of quality tool path with reduced cutter retraction and plunging. Finally, geometric algorithms are developed to automatically detect tool collisions and then correct the erroneous tool orientations. An optimization scheme is applied to minimize the total amount of tool posture changes after the correction. An impeller is machined with the NC codes generated from the framework. The result shows the effectiveness of this work in automating the tool path planning in 5-axis machining of highly intricate impeller.     

Development of an automatic mold polishing system

In this study, an automatic mold polishing system (AMPS) has been successfully developed. The AMPS integrates with mold geometry process kernel, path planner, process planner, and force control robot into a system. The polishing path is generated and drawn on the three-dimensional mold surface for verification. The AMPS can also automatic process the task planning according to the polishing requirements of the mold. The task list includes all the procedures and optimal polishing parameters. The polishing tasks were then executed by a force controllable robot. The experiment shows that the resultant of surface roughness satisfies the expectation in the process planning. Note to Practitioners -In the manufacturing of molds, the most time-consuming process is on the final stage the polishing process. The polishing processes in the mold industry are almost conducted manually. The worker needs exceptional skill that can only be trained by experienced master. For mass production of molds, automatic polishing of the mold is a necessary. From the long-term research effort, we have constructed an automatic mold polishing system (AMPS). The AMPS includes a dedicated 5-axes robot to execute the polishing task; a force control mechanism to hold the tool and apply constant pressure on the mold surface; and a software system that can read the geometry of the mold surface and automatically generate the detail polishing process and the polishing path for the robot. The AMPS now can handle polishing process for planar surfaces with obstacle inside and surfaces of revolution. Research effort is now concentrated on dealing with the free-from surfaces. Besides, reading the Initial Graphics Exchange System (IGES) format from various computer-aided design systems is another important issue for the system to be more useful. In all, the AMPS is just begin to accumulate any further researches and developments that may sustain various requirements of polishing applications.     

Dynamic steering control of conventionally steered mobile robots

This article presents an algorithm for dynamically steering an autonomous mobile robot (AMR) along a collision-free path to a goal using local feedback information. A twolevel navigation algorithm is presented in which a subgoal selection algorithm (SSA) generates visible subgoals to be pursued by the steering control algorithm (SCA). An earlier article presented the SSA in detail, demonstrating how subgoals can be updated while the AMR is moving so that a continuous motion is achieved without stopping to replan the path when new sensor data become available. This study focuses on the SCA. In particular, a general feedback scheme is developed for dynamically steering an AMR to a visible goal in the local obstacle-free space identified by the SSA. We present the detailed implementation of the SCA for a conventionally steered AMR (CAMR). Simulation results are presented that demonstrate the effectiveness of the combined SSA-SCA feedback scheme. The algorithm has been successfully implemented on the NavLab at CMU.     

基于三维环境模型的启发式路径规划算法

针对多自由度机器人手臂在未知环境中实时避障的问题,提出了一种基于环境信息的连杆机器人实时路径规划方法。采用笛卡尔空间内的障碍物检测信息建立了障碍物的空间模型,并依据该模型设计一种基于启发式规则的机器人路径规划算法。该算法不断猜测和修正路径,通过模糊推理得到下一位姿点,通过曲线拟合得到到达该位姿点的路径。在Matlab下利用机器人工具箱建立了PUMA560型机器人的运动学模型,并在运动空间设置障碍物,对该算法进行仿真分析,分析结果说明所提出的路径规划算法可以在较短时间内完成避障运动,具有较好的实时性,同时运动关节的角度变化曲线比较平滑,运动中冲击力较小,这些特点使其便于在实际工程中使用。     

A Study on Error Recovery Search Strategies of Electronic Connector Mating for Robotic Fault-Tolerant Assembly

In this paper, a CAD-based trajectory planning scheme for parallel machining robots is introduced using the parametric Non-uniform rational basis spline (NURBS) curves. First, a trajectory is designed via a NURBS curve then, a motion scheduling architecture consisting of time-dependent and constant feedrate profiles is advised to generate the position commands on the represented NURBS curve as the tool path. Using the generated commands, the inverse kinematics is elaborated to obtain the joints motions of the parallel machining robot. This paper investigates the NURBS trajectory generation for a parallel robot with 4(UPS)-PU mechanism as the case study. In order to evaluate the effectiveness of the proposed method, the inverse kinematic results for the parallel machining robot of 4(UPS)-PU is compared with the simulation results obtained from the CATIA software. The results confirmed that the proposed trajectory planning scheme along with the advised motion planning architecture is not only feasible for the parallel machining robots but also yields a smooth trajectory with a satisfactory performance for all the joints.     

A robot motion position and posture control method for freeform surface laser treatment based on NURBS interpolation

Laser surface treatment, such as laser cladding, laser quenching and laser cleaning, for the freeform surface can dramatically enhance the properties of the working surface. During the laser surface treatment, the posture of the treatment tool to the surface influences the size and shape of the laser spot, which further influences the quality of the laser surface treatment. Thus, accurate posture and high synchronization between position and posture are crucial. Industrial robots have the irreplaceable advantages of high flexibility, large workspace and cost-effectiveness over the 5-axis machine tools, therefore, they have become more and more popular in freeform surface laser treatment. However, the research on industrial robot motion mainly concentrates on position control, while less attention has focused on posture control and synchronization of position and posture control. In this paper, a robot motion position and posture (P&P) control method based on the non-uniform rational B-spline (NURBS) interpolation is proposed to realize the high-order continuity and synchronization of P&P as well as the self-adaptive motion control. Firstly, simultaneously considering the position and posture, a novel path generation method based on 6-dimensional NURBS is proposed to provide smooth, continuous and collision-free P&P coordinates of the designed scanning path. Next, a self-adaptive path segmentation method is introduced to recognize the corners and divide the whole treatment path into safe and dangerous segments. Based on the kinematical characteristics of the industrial robot, the joint motion constraint is especially considered in addition to the chord error limit and the centripetal acceleration constraint, and the self-adaptive motion parameters are obtained to match with safe and dangerous segments to avoid mechanical shock and ensure the accessibility of joint servos. Moreover, a synchronized look-ahead method with a dynamically refreshed window is employed to obtain the optimal node speed between adjacent segments and relieve the heavy computational burden, after which a series of smooth, accurate and synchronized motion instructions for the freeform surface laser treatment is generated in real time. Finally, simulations and experiments of a NURBS scanning path for a turbine blade laser surface cladding are conducted. The results show the proposed method can realize the high-order continuity and synchronization of P&P as well as the self-adaptive motion control for the freeform surface laser treatment.     

非平坦地形下移动机器人安全路径规划

提出一种基于双分辨率2.5D分层栅格地图的Secure A*(SA*)路径规划方法,以解决移动机器人在非平坦地形下的安全路径规划问题.首先,设计一种双分辨率2.5D分层栅格地图,利用双分辨率栅格对环境中的障碍物信息与高程信息进行存储,以节约地图的存储空间;然后,结合移动机器人运动能力,将环境中的高程信息转化为约束因子,...     

Collision-free and smooth joint motion planning for six-axis industrial robots by redundancy optimization

Planning collision-free and smooth joint motion is crucial in robotic applications, such as welding, milling, and laser cutting. Kinematic redundancy exists when a six-axis industrial robot performs five-dimensional tasks, and there are infinite joint configurations for a six-axis industrial robot to realize a cutter location data of the tool path. The robot joint motion can be optimized by taking advantage of the kinematic redundancy, and the collision-free joint motion with minimum joint movement is determined as the optimal. However, most existing redundancy optimization methods do not fully exploit the redundancy of the six-axis industrial robots when they conduct five-dimensional tasks. In this paper, we present an optimization method to solve the problem of inverse kinematics for a six-axis industrial robot to synthesize the joint motion that follows a given tool path, while achieving smoothness and collision-free manipulation. B-spline is applied for the joint configuration interpolation, and the sum of the squares of the first, second, and third derivatives of the B-spline curves are adopted as the smoothness indicators. Besides, the oriented bounding boxes are adopted to simplify the shape of the robot joints, robot links, spindle unit, and fixtures to facilitate collision detections. Dijkstra's shortest path technique and Differential Evolution algorithm are combined to find the optimal joint motion efficiently and avoid getting into a local optimal solution. The proposed algorithm is validated by simulations on two six-axis industrial robots conducting five-axis flank milling tasks respectively.     

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.     

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.     

基于ROS的蛇形机器人基本仿生运动与自主爬台阶控制

设计了一种带正交关节和主动轮组合的蛇形机器人。该机器人不仅能够实现基本的蜿蜒运动、纵向行波运动、横向翻滚运动和横向行波运动,且针对台阶式障碍物提出了一种自主爬越台阶的控制策略。机器人通过激光测距传感器与头部关节的仰角得到台阶高度,抬起相应高度的关节将头关节搭在台阶上,控制主动轮的推进速度与关节抬起的角速度相结合的方式达到上台阶的目的,并且在运动过程中将头部俯仰关节舵机的负载反馈作为判别下台阶的条件。基于ROS （robot operating system）构建了蛇形机器人仿真模型,并通过仿真与实验验证了机器人的基本运动控制和自主爬台阶控制策略的有效性。     

Dynamic visual servo control of a 4-axis joint tool to track image trajectories during machining complex shapes

A large part of the new generation of computer numerical control systems has adopted an architecture based on robotic systems. This architecture improves the implementation of many manufacturing processes in terms of flexibility, efficiency, accuracy and velocity. This paper presents a 4-axis robot tool based on a joint structure whose primary use is to perform complex machining shapes in some non-contact processes. A new dynamic visual controller is proposed in order to control the 4-axis joint structure, where image information is used in the control loop to guide the robot tool in the machining task. In addition, this controller eliminates the chaotic joint behavior which appears during tracking of the quasi-repetitive trajectories required in machining processes. Moreover, this robot tool can be coupled to a manipulator robot in order to form a multi-robot platform for complex manufacturing tasks. Therefore, the robot tool could perform a machining task using a piece grasped from the workspace by a manipulator robot. This manipulator robot could be guided by using visual information given by the robot tool, thereby obtaining an intelligent multi-robot platform controlled by only one camera.     

融合环境信息和运动约束的改进A*算法研究

标准A*算法存在着无法考虑移动机器人运动特性及处理后的路径不利于移动机器人运动等问题。针对这一问题提出了一种新改进A*算法,通过环境信息引入障碍物权重系数来改进算法的启发函数并进行全局路径规划;优化搜索节点的选取方式和设定障碍物与路径之间的安全距离;基于对移动机器人的运动特性的考虑优化其路径,并在不同环境地图中与其他算法进行仿真实验对比分析。相关实验表明：基于新改进A*算法规划的路径始终与障碍物保持一定的安全距离;改进A*算法在时间上相比标准A*算法平均减少了80%,路径长度平均减少了2%,路径转角平均降低了82%。改进后算法相比其他算法在时间、搜索节点以及平滑度上有很大的改进,融合机器人环境信息和运动特性的规划路径算法可为移动机器人的路径规划提供一种新的方法。     

An integrated processing energy modeling and optimization of automated robotic polishing system

The automated robotic polishing system (ARPS) consisting of several robotic polishing cells (RPCs) is widely adopted in polishing industry to replace manual labor. Recently, energy-saving becomes a hotspot issue in manufacturing industry because of the increase in energy costs and requirement of environmental protection. Traditionally, robot motion planning and task scheduling are carried out separately and sequentially, which constrain the potential for energy-saving. In this paper, a task energy characteristic model is proposed as a polynomial function of the feedrate override to forecast the energy consumption of the polishing process of RPC, in which the designed parameters of the RPC and the polishing process parameters are encapsulated into the polynomial coefficients based on experimental data. Furthermore, an optimization model is proposed for an ARPS with mass tasks to minimize the energy consumption, in which the robot motion planning and the task scheduling are considered integratedly. An adaptive genetic algorithm with elite retention strategy is adopted to solve the optimization model. A case study is introduced to verify the proposed approach, which demonstrates the forecast error of task energy is less than 7%, and the proposed optimization approach can reduce the energy consumption of ARPS by more than 18% compared with the original processing scheme.     

Open-architecture of CNC system and mirror milling technology for a 5-axis hybrid robot

This paper presents an open-architecture of CNC system and mirror milling technology for a new-type 5-axis hybrid robot named TriMule. The CNC system with dual CPUs is developed first to achieve human-computer interaction and motion control. Then, three key technologies are integrated in the system for improving the control quality, including singularity avoidance, feedforward control considering joint couplings and real-time error compensation by using externally mounted encoders. Based on these control technologies for single robot system, a collaborative machining strategy on the mirror milling system that consists of two TriMule robots is proposed to control the machining wall thickness of large thin-walled structural parts. Experiments on the TriMule robot and mirror milling system verify that the acceptable machining accuracy on the NAS test part and large thin-walled structural part can be ensured by using the developed CNC system and technologies. The root mean square of wall thickness error using the collaborative machining strategy can be 41.67% lower than the case without using the strategy.