Distributed control of industrial robot systems using Petri net based multitask processing
In this paper, the methods of the modeling of the discrete event robotic manufacturing systems using Petri nets are considered, and a methodology of decomposition and coordination is presented for hierarchical and distributed control, where the cooperation of each controller is implemented so that the behavior of the overall system is the same as the centralized control system and the task specification is completely satisfied. First, a task specification is defined as a Petri net model at the conceptual level, and then transformed to the detailed Petri net representation of the subtasks. Finally, the overall Petri net is decomposed and the constituent subnets are assigned to local Petri net based controllers. The controllers are coordinated so that the decomposed transitions fire at the same time by the coordinator. System coordination algorithm through communication between the coordinator and the controllers, is presented. By the proposed method, modeling, simulation and control of large and complex manufacturing systems can be performed consistently using Petri nets.
Application of the mark flow graph to represent discrete event production systems and system control
condition systems, and several works2)•`4) have confirmed the wide modeling power of this tool. However, to model a specific system, we need to provide an interpretation, both for the MFG structural elements and the structure composed by these elements, up to an appropriate level to clearly model the features of the system. From this viewpoint, a hierarchical approach is adopted in which the system model at macro level is broken-down to a detailed level. This approach provides a systematic design procedure in which an interpreted MFG model is synthesized. With the resultant model the structural information of the whole system and the detail of each component are explicitly described. Therefore this concept is effective for representing discrete event production systems and system control. Firstly, we consider that discrete event production systems are represented by activity elements, distributing elements and the connections between these elements. After discussing the hierarchical structure of the activity elements, the production flow schema and an interpreted form of MFG are introduced as regulation and representation tools. Thereafter, several control rules are derived based on the MFG modeling method and its properties, in which problems such as resource allocation and conflict arbitration are discussed.
The Protection of the Right to Education by International Law: Including a Systematic Analysis of Article 13 of the International Covenant on Economic, Social and Cultural Rights. International Studies in Human Rights, 82.
[In view of the trend of demoting education from ”human right” to “human need” and the accompanying commercialisation of education, and the complex nature of the right to education under international law, entailing a freedom and a social aspect, this book seeks to affirm education as a “human right” and to describe the various state duties flowing from the right to education, by referring to the provisions on the right to education found in instruments of international law and by systematically analyzing article 13 of the International Covenant on Economic, Social and Cultural Rights., In view of the trend of demoting education from ”human right” to “human need” and the accompanying commercialisation of education, and the complex nature of the right to education under international law, entailing a freedom and a social aspect, this book seeks to affirm education as a “human right” and to describe the various state duties flowing from the right to education, by referring to the provisions on the right to education found in instruments of international law and by systematically analyzing article 13 of the International Covenant on Economic, Social and Cultural Rights.]