AND/OR net representation for robotic task sequence planning

The paper describes a framework for task sequence planning for a generalized robotic work cell. The AND/OR net provides a compact, distributed, domain-specific representation of geometric configurations of parts and devices in the work cell. The approach maintains a correspondence from geometric state information to task and motion plans and on-line discrete-event control that is not available in traditional action-based planners. The feasibility criteria for each AND/OR net transition guide the geometric reasoning required in the planning of feasible sequences. The resulting search space for plans is often much smaller (due to explicit representation of geometric constraints) than the state space of an action-based task planner. For purposes of analysis, the AND/OR net is mapped into a Petri net and the resulting Petri net is shown to be bounded and have guaranteed properties of liveness, safeness, and reversibility. In this form, the AND/OR net may be viewed as a Petri net synthesis tool in which the resulting Petri net representation may be used for on-line scheduling and control of the system     

Petri net modelling for robotic assembly and trajectory planning

A new approach to process modelling, task synthesis, motion control and trajectory planning for robotic assembly is presented. Assembly is modelled as a discrete event dynamic system using Petri nets, incorporating both discrete and continuous aspects of the process. A process monitor based on recognizing contact state transitions is presented. A discrete event controller is developed. The controller issues velocity commands that direct the system toward the next desired contact state, while maintaining currently desired contacts and avoiding unwanted transitions. A novel means of trajectory planning which incorporates the system's ability to both monitor and control the process is given. Experimental results are given for a dual peg-in-the-hole example. The experimental results not only demonstrate highly successful insertion along the desired trajectory, but also demonstrate the ability to detect, recognize, and recover from errors and unwanted situations     

An admittance based hierarchical control framework for dual-arm cobots

Dual-arm robotic platforms have solid arguments to match the growing need for versatility in the industry. Coupling the control of two manipulators for cooperative purposes enlarges the scope of feasible operations, while adding perception capabilities allows to navigate in dynamic environments. In this respect, we propose a complete online kinematic control framework for dual-arm robots operating in unstructured industrial settings. We base our approach on admittance control in the cooperative task space. Regulating internal and external efforts offer safe bimanual task execution and enables physical interaction. We implement a hierarchical quadratic programming architecture that applies a prioritization of tasks: most efforts are concentrated on the proper tracking of relative motions of the arms, which is the most critical for safety reasons. We demonstrate the performance of our framework through a “teaching-by-demonstration” experiment on the dual-arm mobile cobot BAZAR.     

云计算中任务分解算法的改进

云计算中任务分解是提高任务执行并行度的重要手段。针对云计算中任务分解算法在解决复杂任务分解问题时容易陷入分解粒度过大及局部最优的缺陷,提出了一种树形分解问题思想与启发式策略相结合的任务分解算法（Improve Heuristic Algorithm,IHA）。该算法首先对任务进行分解,然后将问题用形式化方法转化成可行操作集,最后使用推理机调度任务给解空间进行处理,此算法在Cloudsim中进行了仿真验证。     

一种多值Petri网及其应用

为了更好地将Petri网应用在基于多值逻辑的知识表示和推理中，以普通Petri网的基本定义为基础．结合模糊Petri网和有色Petri网各自的一些特点，将其进行必要的扩展和简化，从而提出一种多值Petri网，使托肯和变迁多值化，然后将它用于知识工程中多值产生式建模和推理中，并根据推理的需要提出了相应的算法。     

面向集成电路制造的基于Petri网的生产调度

本文提出了一个新的面向集成电路(IC)制造的调度方法,核心内容包括两方面:首先,用本文提出的扩展定时Petri 网对IC生产工艺进行描述;其次,对所得Petri 网模型的状态空间进行搜索,得到以Transition序列表示的最优或近似最优调度.该方法可以很好地描述IC制造系统中存在的多制造路径、资源共享、可变晶片组及并发等特性,通过引入测试弧增强Petri 网的建模能力,进而在调度模型上对设备维护、设备优先级以及操作优先级进行描述,而且支持多目标的评价函数,使得到的调度结果更具实用价值.文中给出试验结果表明了算法的有效性.     

A reliability analysis technique for object-oriented model using a reliability petri net

We propose a reliability analysis technique for the design specifications which are made by CRC methodology. We use a reliability Petri net as an analysis technique for CRC specification. The procedure of analyzing the system reliability is as follows: first, the collaboration graphs and message flow diagrams of CRC specification are transformed into an equivalent reliability Petri net which consists of places, transitions, input functions, output functions, failure rate of the input and output functions, and tokens. Secondly, we construct a reachability tree from a reliability Petri net, and establish the paths of all transitions for the reachability tree. These paths can be test cases. Finally, we calculate the values of reliability effect for all transitions in a reliability Petri net, select the transitions that have most effect on the system reliability, and search the messages and classes that are places of input and output fucntion in these transitions. Therefore, we can design these messages and classes very well for increasing the system reliability.     

Assessment of operation plan performance under uncertainty

A military air operations plan contains a number of sequential and/or parallel tasks. Given information about the battlefield situation (including a task status estimate) during the plan's execution, it is necessary to assess the situation impact on the plan, especially whether the entire plan would be delayed. Plan performance assessment fuses the task status estimate into the status estimate of the entire plan. The plan performance assessment assists the air operations commander in deciding the need for plan modification to assure the air operations goal. The performance assessment of the plan must deal with uncertainty in the task status estimate. This paper presents a comparative study of two information fusion techniques that infer the entire plan's status estimate from the task status estimate under uncertainty: a decomposition technique with low computational cost and a composition technique with high computational cost. The test results of these two techniques indicate their similar estimation accuracies. Due to its low computational cost, the decomposition technique is recommended. Guidelines for applying the decomposition technique to a large-scale complex task plan are also provided     

Petri-net based performance-evaluation of distributed homogeneoustask systems

TG (task graphs) are used to describe the execution of several tasks under some precedence constraints. Direct evaluation of TG provides an average completion time of the overall job, assuming no limits exist in the number of processing units and with no regard for allocation schemes. This paper presents a systematic approach for evaluating TG of jobs executed under predetermined allocation constraints. This extension of TG relies on GSPN (generalized stochastic Petri nets). A systematic mapping of a TG into a GSPN model is discussed. This GSPN model is extended to incorporate information about the static allocation of the set of tasks in the TG. An algorithm is implemented to evaluate static allocation schemes with or without task replication. However, for task replication, a homogeneous system is assumed because the execution time of those tasks does not change when allocated to various processing units. Also, under this assumption, task execution rates are modified by adding communication costs involved in sending data required by the next task, in turn, to execute. Thus, using a single model, TG are evaluated with constraints not only on where replicated and nonreplicated tasks are to be executed but on the number of processing units available, task allocation constraints, and the communication costs involved when they are remotely located     

Stochastic Petri nets: Properties, applications and tools

This paper presents a survey on stochastic Petri nets. A stochastic Petri net is first and foremost a Petri net, whose places represent resources and transitions represent operations. Random time variables attached to transitions are associated with random operation durations. The stochastic behavior must be completely defined by a set of rules associated with the choice of the next transition to be fired in a given marking, the memory properties of the time already spent for a given operation. We introduce some of the main stochastic Petri nets classes, and we give theoretical results associated with conservation properties, ergodic properties and computational methods leading to exact and approximated solutions. From a practical point of view we present the modeling example of a bus allocation and existing software tools.     

Performability of integrated software-hardware components ofreal-time parallel and distributed systems

A method for analyzing performability of the integrated software-hardware components of parallel and distributed systems is presented. The technique uses generalized stochastic Petri nets at the system level (analysis of integrated software-hardware systems). The intractable problem of evaluating a parallel software environment consisting of interacting fault-tolerant parallel tasks is addressed. This is accomplished using a decomposition technique at the task-graph level, where the task graph is decomposed into segments. Recovery blocks are effectively modeled in the interacting parallel modules as well as their supporting hardware. This method greatly facilitates the analysis of performability at the system level. However, the integrated performability model increases the size of the Markov generator matrix. This issue is addressed, and a performability decomposition technique at the task-graph level presented is illustrated by a simple example of a radar command center     

控制电路基于Petri网元件的图形化设计与仿真研究

Petri网是异步并发系统建模的重要工具,正越来越多地被应用在超大规模集成电路之中,从系统的Petri网模型直接获得相应的逻辑电路是许多学者研究的目标.文章在通用的EDA软件中,使用硬件描述语言建立Petri网元件,并给出了它们的源代码.对于Petri网中的C/E系统,变迁用组合逻辑电路实现,库所用时序逻辑电路实现;而对于P/T系统,为了减少连线,库所和它的输入、输出变迁一起组成一个元件.在对一个受控系统建立了控制器的Petri网模型后,通过调用元件库中的Petri网元件,绘制控制器的Petri网图,经编译、仿真、优化、适配、下载在CLPD或FPGA中,就可获得控制器.Petri网元件与其它电路元件可混合使用,这为控制器的设计与实现提供了一种新的有效途径.文章分别给出了C/E系统和P/T系统的实例,仿真结果表明基于Petri网元件的图形化设计方法的正确性.     

Integration of task scheduling, action planning, and control inrobotic manufacturing systems

This paper presents a novel approach for solving a challenging problem in the intelligent control of robotic manufacturing systems, i.e., the integration of low-level system sensing and control with high-level system behavior and perception. First, a newly developed event-based planning and control method will be introduced. It will then be extended to a robotic manufacturing system via a hybrid system approach. The tasks of a robotic manufacturing system usually consist of multiple segments of robotic actions, which involve both continuous and discrete types of actions. The max-plus algebra model has been proposed to model such a system. Combined with the event-based planning and control methods, both discrete and continuous actions can be planned and controlled based on the max-plus algebra model. More important, the interactions between discrete and continuous actions can be formulated analytically. A typical parts-sorting task in a robotic manufacturing system is used to illustrate the proposed approach. The experimental results clearly demonstrate the advantages of this method     

生产者-消费者系统的建模与行为分析方法研究

生产者一消费者系统是系统工程中的一个典型系统。讨论了基于Petri网的生产者一消费者系统建模．借助基于库所指标的Petri网分解方法来分析生产者一消费者的系统行为，利用Petri网语言的同步混排运算给出了生产者一消费者系统的行为描述，对基于Petri网的系统分析提供了有效的方法。     

Tutorial: Petri nets as a graphical description medium for manyreliability scenarios

One of the basic problems of dependability modeling is the adequate abstraction of real-world technological problems to the principle terms of reliability/safety scenarios. This concerns primarily the definition of components and of faults on different system levels. Given these terms the rest of any modeling needs basic logical operations, mostly AND and OR, and delays, and often some counting (of time or events). All of these basic operations are offered by a fairly simple kind of Petri net (PN), i.e., timed stochastic Petri nets, allowing also for the modeling of immediate activities and of such with a deterministic delay. In this half-tutorial paper it is shown how such Petri nets modeling, i.e., the construction of the relevant nets, works in practice. No math will be needed for that. Several typical engineering virtues are needed; primarily imagination as to how to (i) find simple solutions, since often nonelegant solutions can be correct too, (ii) compose larger PN from elementary building blocks, and (iii) the ability to model the real world by interpreting the so-called tokens of a PN intelligently in different places of one and the same PN. In the appendix it is shown how the PN can also help in the analytical analysis of nonrepairable systems. In that context they are superior to state graphs since they show state durations explicitly     

A Petri Net Control Unit for High-Speed Modular Signal Processors

This paper proposes a hierarchical representation of digital signal processing algorithms suitable for real-time implementations. Petri net models are used to demonstrate every possible operating parallelism in their graphical expression, the marked Petri graph. Moreover, a hierarchical algorithm execution control based on delayed Petri graphs is presented. A strictly modular system architecture suitable for VLSI implementation and data-driven processing is reviewed in its main components. The algorithm representation is then applied to the design of the control part of the system modules. Details at the logic level of the controllers for an array of digital signal processors are presented as an application of the proposed methodology.     

Markov chain reduction and analysis of GSPN models for task allocation in distributed systems

In this paper, we present a Markov chain (MC) reduction technique for analysis of a certain class of MCs. It requires only O(t) steps to analyze an MC having t states by this technique, as compared to O(t³) steps required by the usual matrix inversion method. We also present a generalized stochastic Petri net (GSPN) model for task allocation in distributed computer systems, where execution and inter-module communication costs are treated as random variables with exponential probability distribution. We show that the MC of this task system falls into a class to which the reduction technique is applicable. As an illustration of the reduction technique, we use a GSPN model of the task system to find the mean completion time of the system.     

Automatic design rule adaptation of leaf cell layouts

The automatic adaptation of mask layouts to new design rules is considered. A new concept is presented that is based on geometric operations and mask compaction. The geometric operation MELT is discussed in detail; the other operations OR, AND, ANDNOT, OVERSIZE and UNDERSIZE are derived from it. The mask compaction consists mainly of a design rule analysis phase and the execution of a longest path algorithm. Contrary to symbolic compaction the mask compaction is based on polygon edges rather than symbols. With the example of the buried contact it is shown that even relatively complex design rule requirements may be met. Tests with several mask layouts sometimes led to overconstrained conditions. These conditions are located with the aid of a longest path algorithm that has not been applied to compaction programs up to now. Furthermore the inconsistent constraint cycles are broken by a fast jog generation algorithm.     

A Systematic Approach to Predict Performance of Human–Automation Systems

This paper discusses an approach for predicting system performance resulting from humans and robots performing repetitive tasks in a collaborative manner. The methodology uses a systematic approach that incorporates the various effects of workload on human performance, and estimates resulting performance attributes derived between teleoperated and autonomous control of robotic systems. Performance is determined by incorporating capabilities of the human and robotic agent based on accomplishment of functional operations and effect of cognitive stress due to continuous operation by the human agent. This paper provides an overview of the prediction system and discusses its implementation on a simulated rendezvous/docking task.     

Improvement of visual perceptual capabilities by feedback structures for robotic system FRIEND

The main aim behind the design of rehabilitation robotic systems is to support disabled people in daily life situations as well as in the working environment. This requires the autonomous execution of different tasks. In order to achieve the ability of the robotic system to operate autonomously, the sensor system for the scene observation providing the necessary inputs for the manipulator control is essential. In this paper, the main emphasis is on the development and integration of the closed-loop controls at the visual sensory input level in order to increase the robustness of the vision-based system control. Moreover, the integration of additional sensors in order to support the vision system and to increase the reliability of the whole robotic system is discussed.