Robustness analysis of Petri nets for assembly/disassembly processes with unreliable resources

In most application of Petri nets, resources are modeled as tokens. Unreliable resources pose challenges as existing Petri net theory is deficient in analyzing the impacts of the perturbation due to resource failures. One strategy to analyze a perturbed system is to study its robustness with respect to uncertainties. In this paper, we study the robustness of a class of controlled Petri nets called controlled assembly/disassembly Petri net (CADPN) for assembly/disassembly processes with unreliable resources. The number of tokens in CADPN is not conservative to capture the effects of resource failures. Based on the CADPN model, we characterize different types of tolerable resource failures allowed for a nominal marking of a live CADPN. We show that liveness of a CADPN can still be preserved under tolerable resource failures.     

可移动机器人的运动学模型与控制原理

本文首先对可移动机器人的运动学进行了分析,建立了运动学模型与控制结构图,然后采用时域分析法对此系统进行了校正,最后通过对此系统的仿真与时测实验,对各校正环节的参数进行了整定.     

Coloured Petri nets and graphical simulation for the validation of a robotic cell in aircraft industry

This paper proposes a mixed validation approach based on coloured Petri nets and 3D graphic simulation for the design of supervisory systems in manufacturing cells with multiple robots. The coloured Petri net is used to model the cell behaviour at a high level of abstraction. It models the activities of each cell component and its coordination by a supervisory system. The graphical simulation is used to analyse and validate the cell behaviour in a 3D environment, allowing the detection of collisions and the calculation of process times. The motivation for this work comes from the aeronautic industry. The automation of a fuselage assembly process requires the integration of robots with other cell components such as metrological or vision systems. In this cell, the robot trajectories are defined by the supervisory system and results from the coordination of the cell components. The paper presents the application of the approach for an aircraft assembly cell under integration in Brazil. This case study shows the feasibility of the approach and supports the discussion of its main advantages and limits.     

受非完整约束移动机器人的跟踪控制

讨论受非完整约束移动机器人运动学模型和动力学模型的跟踪控制问题.通过把它们化成统一的标准型,提出了新的动态跟踪控制器.这些控制器具有维数低和没有奇异点的优点.仿真结果表明了所提出控制方法的有效性.     

立体分层Petri网的对象化专家系统实现

Ｐｅｔｒｉ网是描述分布式系统的强有力工具,立体分层Ｐｅｔｒｉ网是从系统的监控、行为和运行三个侧面分析实时分布式多智能体系的建模和分析工具。将立分层Ｐｅｔｒ８网转化为对象化的高级Ｐｅｔｒｉ网,利用和ＲＥＴＥ算泊结构相似性改善其软件实现方法,提高系统运行效率。     

Virtual prototyping of automated manufacturing systems with Geometry-driven Petri nets

The design process of automated manufacturing systems typically involves physical prototypes to validate the interactions between hardware and software components. However, physical prototyping is expensive and time consuming, which often leads to insufficient opportunities for testing early during the development cycle. Our objective is to improve this situation by providing a method to develop realistic prototypes using virtual reality technology that can be applied during earlier development stages. Our approach combines a virtual reality engine capable of enacting the laws of rigid body physics with a new hybrid software modelling language to control the simulated hardware using virtual sensors and actuators as they would be present in a physical prototype. The new modelling language is called Geometry-driven Petri nets (GPN) and combines a class of timed, high-level Petri nets with data structures used in state-of-the-art VR environments. This article describes the new GPN approach, applies it to a case study of an automated manufacturing line, and compares it with related approaches.     

一种全方位移动机械手的体系结构设计与分析

首先介绍了我们设计和开发的一种全方位移动机械手系统的硬件体系结构,然后根据硬件平台、应用环境和任务,设计了全方位移动机械手系统的基于行为的混合式软件体系结构,并通过两个实例进一步分析说明所设计的体系结构的合理性和可行性,同时指出了下一步研究的方向.􀁱     

Contact identification for assembly–disassembly simulation with a haptic device

Assembly/Disassembly (A/D) simulations using haptic devices are facing difficulties while simulating insertion/extraction operations, such as removing cylinders from holes. In order to address this configuration as well as others, an approach based on contact identification between components is presented in this paper. This approach can efficiently contribute either to a new A/D simulation preparation process relying on two types of shape representations (mesh and CAD NURBS models), or directly to the real time simulation process when it is performed with 6D haptic devices. The model processing pipeline is described and illustrated to show how information can be propagated and used for contact detection. Then, the contact identification process is introduced and illustrated through an example.

轮式移动机器人预见预测运动控制

针对移动机器人的运动控制问题,该文采用预见预测控制方法加以解决。利用三阶Bezier曲线作为路径生成器生成目标轨迹,并据此设计了最优预见控制器作为系统的前馈补偿;使用扩展卡尔曼滤波器作为预测模型,基于广义预测控制(GPC)实现了PPC运动控制器的设计。仿真实验结果证明了该方法的有效性。     

基于神经网络的不确定移动机器人鲁棒自适应跟踪控制

针对含运动学未知参数以及动力学模型不确定的非完整轮式移动机器人轨迹跟踪问题,基于Radical Basis Function(径向基函数)神经网络,提出了一种鲁棒自适应控制器.首先,考虑移动机器人运动学参数未知的情况,提出了一种含自适应参数的运动学控制器,用以补偿参数不确定性导致的系统误差;其次,利用神经网络控制技术,对于机器人在移动中动力学模型不确定问题,提出了一种具有鲁棒性的动力学控制器,使得移动机器人可以在不知道具体动力学模型的情况下跟踪到目标轨迹;最后利用Lyapunov稳定性理论证明了整个系统的稳定性.通过数值仿真验证了所设计的控制器的可行性.     

Firing sequences backward algorithm for simple assembly line balancing problem of type 1

The objective of simple assembly line balancing problem type-1 (SALBP-1) is to minimize the number of workstations on an assembly line for a given cycle time. Since SALBP-1 is NP-hard, many iterative backtracking heuristics based on branch and bound procedure, tabu search, and genetic algorithms were developed to solve SALBP-1. In this study, a new heuristic algorithm based on Petri net approach is presented to solve the problem. The presented algorithm makes an order of firing sequence of transitions from Petri net model of precedence diagram. Task is assigned to a workstation using this order and backward procedure. The algorithm is coded in MATLAB, and its efficiency is tested on Talbot’s and Hoffmann’s benchmark datasets according to some performance measures and classifications. Computational study validates its effectiveness on the benchmark problems. Also comparison results show that the algorithm is efficiency to solve SALBP-1.     

带滚动约束轮移式机器人动态规划的研究

根据轮移式机器人的运动学模型,研究受到滚动约束轮移式机器人在动态环境中的运动规划问题.将快速随机搜索树算法与优化方法相结合,实现了一种新的算法,规划出既可避障又可满足机器人滚动约束的运动.将该算法运用到动态环境下机器人的运动规划中,并通过仿真表明该算法能较好地引导机器人在动态环境中实现满足滚动约束的避障路径.     

Navigation of Mobile Robots Using a Fuzzy Logic Controller

This paper describes a mobile robot navigation control system based on fuzzy logic. Fuzzy rules embedded in the controller of a mobile robot enable it to avoid obstacles in a cluttered environment that includes other mobile robots. So that the robots do not collide against one another, each robot also incorporates a set of collision prevention rules implemented as a Petri Net model within its controller. The navigation control system has been tested in simulation and on actual mobile robots. The paper presents the results of the tests to demonstrate that the system enables multiple robots to roam freely searching for and successfully finding targets in an unknown environment containing obstacles without hitting the obstacles or one another.     

基于时延Petri网的移动电子支付协议模型

时延Petri网是在一般Petri网的基础上,在变迁上引入相应的时间函数,使其具有很强的描述能力与性能分析能力。针对移动电子支付中愈加严重的交易安全问题,通过对电子支付系统和移动电子支付流程的分析,发现移动电子商务SET协议存在漏洞,建立基于时延Petri网移动电子支付协议时延Petri网模型,为安全电子交易过程提供进一步的安全保障。