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MINIMUM-time COLLISION-FREE TRAJECTORY PLANNING FOR DUAL-ROBOT SYSTEMS

IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION 1992年第5期8卷 641-644页

作者： SHIN, KG ZHENG, Q Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

Collision-free multirobot motion planning can be achieved in two steps: path planning and trajectory planning. Path planning finds for the robots geometric paths to avoid collision with static obstacles and trajectory planning determines how fast each robot must move along its geometric path to avoid collision with other moving robots. For a dual-robot system, a simple trajectory planning strategy is to let each robot move along its path as fast as possible and delay one robot at its initial position to avoid collision with the other robot. We derive in this paper a sufficient condition under which this simple (thus easy to implement) strategy for dual-robot systems can achieve time optimality as well as collision avoidance, i.e., the two robots reach their final positions without colliding with each other in the minimum amount of time. A demonstrative example is presented, showing how this strategy can be used for loading and unloading applications.

关键词： COLLISION AVOIDANCE COLLISION REGION MINIMUM-time TRAJECTORY PLANNING MULTIROBOT SYSTEMS

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MONITORING AND DEBUGGING DISTRIBUTED real-time PROGRAMS

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software-PRACTICE & EXPERIENCE 1992年第10期22卷 863-877页

作者： DODD, PS RAVISHANKAR, CV Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science The University of Michigan Ann Arbor Michigan 48109-2122 U.S.A.

In this paper we describe the design and implementation of an integrated monitoring and debugging system for a distributed real-time computer system. The monitor provides continuous, transparent monitoring capabilities throughout a real-time system's lifecycle with bounded, minimal, predictable interference by using software support. The monitor is flexible enough to observe both high-level events that are operating system- and application-specific, as well as low-level events such as shared variable references. We present a novel approach to monitoring shared variable references that provides transparent monitoring with low overhead. The monitor is designed to support tasks such as debugging real-time applications, aiding real-time task scheduling, and measuring system performance. Since debugging distributed real-time applications is particularly difficult, we describe how the monitor can be used to debug distributed and parallel applications by deterministic execution replay.

关键词： PROGRAM MONITORING DEBUGGING real-time SYSTEMS

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real-time COMMUNICATION IN LOCAL AREA RING NETWORKS 17

REAL-TIME COMMUNICATION IN LOCAL AREA RING NETWORKS

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17TH CONF ON LOCAL COMPUTER NETWORKS

作者： ZHENG, Q SHIN, KG Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor 48109-2122 MI United States

ISBN: (纸本)0818630957

timed token protocols are almost exclusively used for medium access control in local area ring networks. We consider in this paper the feasibility of using buffered transmission which has the advantages of eliminating the token passing overhead and relieving the network interface from the complex token handling operations. By establishing real-time channels (each of which is a unidirectional virtual connection), the end- to-end delivery delay of real-time packets can also be controlled more flexibly than the timed token protocols. We first review the concept of real-time channel (RTC) and the RTC establishment procedures. Its performance is then compared with the FDDI timed token protocol. Our simulation results show that the buffered transmission in local area ring networks equipped with real-time channels enhances both the networks' throughput and the ability to support heterogeneous real-time traffic. The implementation of the network interface is also examined with an example design showing the feasibility of real-time channels in high-speed local area networks. © 1992 IEEE.

关键词： Medium access control

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DESIGN AND EVALUATION OF real-time COMMUNICATION FOR FIELDBUS BASED MANUFACTURING SYSTEMS 17

DESIGN AND EVALUATION OF REAL-TIME COMMUNICATION FOR FIELDBU...

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17TH CONF ON LOCAL COMPUTER NETWORKS

作者： SHIN, KG CHOU, CC Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor 48109-2122 MI United States

ISBN: (纸本)0818630957

It is well-known that the ability to support predictable inter-process communication is of great significance to manufacturing and process control systems. In this paper, we propose a strategy for a soon-to-be industrial standard, the SP-50 Field Bus, to support both intra-cell and inter-cell real-time communications. We first describe our strategy in detail and show that it is compatible with the current FieldBus draft proposal. Under our strategy, the capacity of each link is divided into two parts. The first part is managed by the local Link Active Scheduler (LAS) for intra-cell (intra-link) communication. The second part is managed by the global network manager for inter-cell (inter-link) communication. By dividing the link capacity in this way, our strategy can allow for fast local intra-cell connection establishment, while supporting global inter- cell connections. Numerical examples are also given for a typical manufacturing network. © 1992 IEEE.

关键词： COMPUTER COMMUNICATION NETWORKS MANUFACTURING SYSTEMS FIELDBUS real-time COMMUNICATION real-time CHANNEL

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Allocation of periodic task modules with precedence and deadline constraints in distributed real-time systems

Allocation of periodic task modules with precedence and dead...

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1992 real-time Systems Symposium, RTSS 1992

作者： Hou, Chao-Ju Shin, Kang G. Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI 48109-2122 United States

ISBN: (纸本)0818631953

This papei addresses the problem of allocating (assigning and scheduling) periodic task modules to processing nodes (PNs) in distributed real-time systems subject to task precedence and timing constraints. Using the branch-and-bound technique, a module allocation algorithm (MAA) is proposed to find an "optimal" allocation that maximizes the probability of meeting task deadlines. The task system within a planning cycle is first modeled with a task flow graph (TG) which describes computation and communication modules as well as the precedence constraints among them. To incorporate both timing and logical correctness into module allocation, the probability of meeting task deadlines is used as the objective function. The MAA is then applied to find an optimal allocation of task modules in a distributed system. The timing aspects embedded in the objective function drive the MAA not only to assign task modules to PNs, but also to use a module scheduling algorithm (MSA) (with polynomial time complexity) for scheduling all modules assigned to each PN so that all tasks may be completed in time. Several numerical examples are presented to demonstrate the effectiveness and practicality of the proposed algorithms. © 1992 IEEE.

关键词： Scheduling algorithms

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Communication-oriented assignment of task modules in hypercubic multicomputers 12

Communication-oriented assignment of task modules in hypercu...

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12th International Conference on Distributed computing Systems, ICDCS 1992

作者： Tsai, Bing-Rung Shin, Kang G. Real-Time Computing Laboratory Computer Science and Engineering Division Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109-2122 United States

ISBN: (纸本)0818628650

The problem of mapping a task that is composed of interacting modules onto a hypercube multicomputer is formulated and solved by minimizing an objective function called the communication traffic. The objective function allows module assignments to be found with the usual straightforward combinatorial optimization techniques. The problem of finding an assignment that minimizes the communication traffic is proved to be NP-hard, so a standard state-space search algorithm as well as other heuristic algorithms are used to find optimal/suboptimal solutions. The relative performances of various algorithms are evaluated using simulations. The assignments obtained from these algorithms are evaluated using an event-driven simulator to learn how they perform in real-world execution environments. © 1992 IEEE.

关键词： Heuristic algorithms

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Hard Deadlines in real-time Control Systems

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IFAC Proceedings Volumes 1992年第20期25卷 9-14页

作者： Kang G. Shin Hagbae Kim Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science The University of Michigan Ann Arbor MI 48109-2122

In a real-time control system where the control input is computed by a controller computer, the transient computer failures caused by an electromagnetic interference may seriously affect system stability. The faulty controller computer causes either a long delay in the feedback loop thus failing to update the control input for one or more sampling intervals, or control input disturbances by updating the control inputincorrectly until the fault is handled properly. If the period of this abnormal behavior exceeds a certain limit called a hard deadline, either the necessary conditions for system stability will be violated or the system willleave the allowed state space. In such a case a dynamic failure is said to occur in the system. We present a method for deriving hard deadlines for linear time-invariant control systems by examining the stability of the state difference equations resulting from the modification of the original state equations with an assumed maximum delay and several random sequences that represent the effects of stationary occurrences of the disturbances to, as well as the random delays of, the control input. Moreover, a one-shot event model, in which a single long-lasting fault causes a dynamic failure, is presented based on the state trajectory and the allowed state space.

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Allocation of periodic task modules with precedence and deadline constraints in distributed real-time systems

Allocation of periodic task modules with precedence and dead...

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real-time Systems Symposium (RTSS)

作者： C.-J. Hou K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The authors address the problem of allocating (assigning and scheduling) periodic task modules to processing nodes (PNs) in distributed real-time systems subject to task precedence and timing constraints. Using the branch-and-bound technique, a module allocation algorithm (MAA) is proposed to find an optimal allocation that maximizes the probability of meeting task deadlines. To incorporate both timing and logical correctness into module allocation, the probability of meeting task deadlines is used as the objective function. The MAA is then applied to find an optimal allocation of task modules in a distributed system. The timing aspects embedded in the objective function drive the MAA not only to assign task modules to PNs, but also to use a module scheduling algorithm for scheduling all modules assigned to each PN so that all tasks may be completed in time. Several numerical examples are presented to demonstrate the effectiveness and practicality of the proposed algorithms.< >

关键词： real time systems Timing Distributed computing Processor scheduling Laboratories Flow graphs Scheduling algorithm Polynomials Load management Hazards

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Derivation of Hard Deadlines for real-time Control Systems

Derivation of Hard Deadlines for Real-Time Control Systems

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American Control Conference (ACC)

作者： Kang G. Shin Hagbae Kim Department of Electrical Engineering and Computer Science Real-Time Computing Laboratory University of Michigan Ann Arbor MI USA

The computation-time delay in the feedback controller of a real-time control system may cause failure to update the control input during one or more sampling periods. A dynamic failure is said to occur if this delay exceeds a certain limit called a hard deadline. We present a method for calculating the hard deadlines in linear time-invariant control systems. To derive necessary conditions for (asymptotic) system stability, the state difference equation is modified based on an assumed maximum delay and the probability distribution of delays whose magnitudes are less than, or equal to, the assumed maximum delay. Moreover, the allowed state-space - which is derived from given input and state constraints - is used to calculate the hard deadline as a function of time and the system state. We also consider a one-shot delay model in which a single event causes a dynamic failure.

关键词： real time systems Control systems Delay effects Electric variables control Electromagnetic interference Computer aided instruction Linear feedback control systems Sampling methods Difference equations Probability distribution

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Fault-tolerant real-time communication in distributed computing systems

Fault-tolerant real-time communication in distributed comput...

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International Symposium on Fault-Tolerant computing (FTCS)

作者： Q. Zheng K.G. Shin Real-Time Computing Laboratory Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

An increasing number of applications require packets to be delivered reliably within prespecified delay bounds. It is shown how this can be achieved by using real-time channels that make soft reservation of network resources to ensure the timely delivery of real-time packets. Algorithms are presented for the establishment of real-time channels, and it is shown how the basic real-time channels can be enhanced to be fault tolerant using the multiple paths between a pair of communicating nodes. The contribution of the former is a tighter schedulability condition that makes more efficient use of network resources than other existing approaches, and the contribution of the latter is a significant improvement in fault tolerance over the basic real-time channel, which is inherently susceptible to component failures.< >

关键词： Fault tolerant systems real time systems Distributed computing Circuits Bandwidth Delay Fault tolerance Asynchronous transfer mode Intelligent networks Computer networks

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