Research results regarding synthesis techniques for Petri nets are reviewed. These methods can be adopted for modeling parallel and distributed application environments such as automated manufacturing systems to provi...
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Research results regarding synthesis techniques for Petri nets are reviewed. These methods can be adopted for modeling parallel and distributed application environments such as automated manufacturing systems to provide a solution for handling complex and concurrent interactions. Significant synthesis techniques, which are basically classified into bottom-up and top-down methods, are discussed. Bottom-up techniques, consisting of merging of places and sharing of simple elementary paths, have the advantage of ease of system description since the modeled subsystems usually have real-life correspondences. Nevertheless, with existing techniques the synthesized system may not exhibit the same control properties as the subsystems. Top-down methods, including refinement of transitions and refinement of places, have the advantage of viewing the system globally, which may generate more structured designs. However, it is difficult to apply these methods to environments with highly shared resources. Automated manufacturing system examples are given to demonstrate the applications of the methods.< >
Transverse acoustoelectric voltage (TAV) of Te-doped GaAs and n-GaAs/SI GaAs samples with photon energy and bias voltage is demonstrated. GaAs electronic properties were investigated using a surface acoustic wave (SAW...
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Transverse acoustoelectric voltage (TAV) of Te-doped GaAs and n-GaAs/SI GaAs samples with photon energy and bias voltage is demonstrated. GaAs electronic properties were investigated using a surface acoustic wave (SAW) technique. The TAV was monitored across the GaAs sample by fabricating the interdigital transducer directly on the GaAs surface using electron beam lithography. In the processing, to protect the surface from contamination, the metal lift-off technique is also used. The TAV is developed due to the nonlinear interaction between the electric field accompanying SAW, and the free carriers near the GaAs surface. The TAV spectra are obtained to determining the bandgap energy and the Te-level which is observed at 300 K. It is also noticed that the TAV amplitude changes with bias voltage under the room illumination. However, when the illumination is turned off, the TAV does not change with bias voltage.< >
A colored Petri net (CPN) model of a cell controller capable of real-time control and monitoring of multiple workstations is described. The need to incorporate the ideas of both computer integrated manufacturing (CIM)...
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A colored Petri net (CPN) model of a cell controller capable of real-time control and monitoring of multiple workstations is described. The need to incorporate the ideas of both computer integrated manufacturing (CIM) and flexible manufacturing systems (FMS) is discussed, and the controller is based on these concepts. The CPN for the cell controller is presented and described. The controller in this case controls two workstations: the Cincinnati Milacron 5VC machining center and a robotic assembly workstation using an Adept robot. An analysis of the net is performed, and relevant portions are presented. A data structure for implementing this type of a CPN is given. The code for the controller is divided into application-dependent and -independent code. An execution algorithm is provided. The conclusions emphasize the advantages of CPNs in modeling and analysis for discrete-event control of manufacturing systems.< >
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