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For discrete automation systems, certain human operations may violate desired safety requirements and result in catastrophic failure. For such humanin-the-loop systems, this paper proposes a systematic approach to developing supervisory agents which guarantee that manual operations meet required safety specifications. In the present approach, Petri nets (PN) are applied to construct a system model and synthesize a desired supervisor. Applications to 1) a rapid thermal process (RTP) in semiconductor manufacturing controlled over the Internet (Lee and Hsu, 2003) and 2) a two-robot remote surveillance system (Lee et al., 2005) are provided to demonstrate the practicability of the developed supervisory control approach. The technique developed in this paper is significant in industrial applications. 1.1 General Review Basically, an automated process is inhe rently a discrete event system (DES). The Petri net (PN) has been developed as a powerful tool for modelling, analysis, simulation, and control of DES. PN was named after Carl A. Petri (1962), who created a net-like mathematical tool for describing relations between the conditions and the events. PN was further developed to meet the need in specifying process synchronization, asynchronous events, concurrent operations, and conflicts or resource sharing for a variety of industrial automated systems at the discrete-event level. Starting in the late of 1970’s, researchers investigated possible industrial applications of PN in discrete-event systems as in the survey/tutorial papers of Murata (1989), Zurawski and Zhou (1994), David and Alla (1994), and Zhou and Jeng (1998).

ZigBee is an emerging standard specifically designed for wireless personal area networks (WPANs) with a focus on enabling the wireless sensor networks (WSNs). It attempts to provide a low-data rate, low-power, and low-cost wireless networking on the device-level communication. In this paper, we have established a realistic indoor environment for the performance evaluation of a 51-node ZigBee wireless network. Several sets of practical experiments have been conducted to study its various features, including the (1) node connectivity, (2) packet loss rate, and (3) transmission throughput. The results show that our developed ZigBee platforms could work well under multihop transmission over an extended period of time.

This paper presents a preliminary development of the smart shopping cart (SSC) that can be integrated into the smart mall system. The SSC can provide customers with the efficient user interface so that the shopping service can be effectively promoted. In the current design, with the function of face recognition on the user interface, the SSC can recognize the customer and further provide the associated assistive shopping information based on the purchase history. With the use of radio-frequency identification (RFID) tags, the SSC can automatically detect the various products which are being added in the cart and show the related information on the user interface. Through the searching function of SSC, the purchasing efficiency and navigation aid in the mall can be effectively supplied. Finally, the automatic billing service can be done by the SSC and the stored shopping data will be transmitted to the cloud server of shopping mall. The experimental demonstration shows the effectiveness of the proposed SSC which interacts with the customer and provides efficient shopping service.

Control design plays a key role in electric-assist bikes. This paper has established dynamic models of electrically assisted biking systems, and then, designed proportion-assisted power controllers (PAPC) in accordance with Taiwan government rules. In the PAPC controllers, current bike speed and pedal torque are used as inputs to determine the assisted torque generated from a motor. On the other hand, a fuzzy logic controller (FLC) has been also designed, using the current bike speed and pedal frequency as inputs to determine the assisted torque. In order to compare these two controllers, simulations of riding bikes on a flat ground and different slopes have been performed. Simulation results show that the FLC outperforms PAPC in a more stable bike speed.

This paper was motivated by the requirement of remote coordination for flexible manufacturing systems (FMS), in which certain requested commands may lead to undesired states. For such discrete event systems (DES), this paper applies a command filtering scheme for modeling and synthesis of filters using Petri nets so as to guarantee that the closed coordinated manufacturing system satisfies the requirements. Moreover, a systematic algorithm for the design and integration of modular command filters is proposed in order to cope with the complexity and realization issues in large-scale FMS. To show the practicability of the developed method, an application to an FMS with three product types is provided. The proposed approach contributes a promising tool for preventing undesirable actions from occurring in FMS which may be also applied to other types of DES if appropriately modified.

In semiautonomous mobile sensor networks (MSNs), since human operators may be involved in the control loop, particular improper actions may cause accidents and result in catastrophes. For such systems, this paper proposes a command filtering framework to accept or reject the human-issued commands so that undesirable executions are never performed. In the present approach, Petri nets are used to model the operated behaviors and to synthesize the command filters for supervision. An application to a mobile wireless surveillance system is provided to show the feasibility of the developed approach. It is believed that the technique presented in this paper could be further applied to large-scale wireless MSNs.

In a semiconductor manufacturing system, particular human operations may violate desired requirements and lead to destructive failure. For such human-in-the-loop systems, this paper proposes a supervisory framework which guarantees that manual operations meet required specifications so as to prevent human errors in operation using Petri nets. Moreover, a modular technique with an intersection mechanism is proposed in order to cope with the state-space explosion problem of large-scale systems. A rapid thermal process in semiconductor manufacturing systems is provided to show the practicability of the proposed approach. Note to Practitioners - This work was motivated by the requirement of remote monitoring and supervision of semiconductor manufacturing systems. In such human-in-the-loop and large-scale systems, certain human operations may violate desired safety requirements and result in catastrophic failure. Moreover, the overall complexity of most existing Petri net modeling and analysis approaches significantly increases with the size of the considered systems. This paper suggests a modular supervisory scheme for modeling and synthesis of supervisory agents using Petri nets. The proposed method contributes a promising tool for preventing abnormal operations from being carried out to semiconductor manufacturing systems which, if appropriately modified, may be also applied to other types of discrete event systems.

In a distributed robotic system, both human-controlled (semi-autonomous) and computer-controlled (fully autonomous) robots may simultaneously exist. From the global system's point of view, supervisory control for the interactions between the human and computer are important and necessary. For such human-computer interactive systems, this paper proposes a supervisory framework to guarantee that both human and computer commands meet collision-free and deadlock-free requirements. In the presented approach, Petri nets are applied to construct a system model and synthesize a desired supervisor. An application to a two-robot remote surveillance system is provided to demonstrate the practicability of the developed supervisory control approach. It is believed that the technique developed in this paper is significant in the industrial practice.

This paper presents a systematic approach for the design and implementation of the sequence controller in manufacturing systems. By employing the IDEF0, we construct the simplified Petri net controller (SPNC) through the material flow diagram and the information flow diagram. Then, the ladder logic diagram (LLD) can be transformed from the SPNC through the token passing logic (TPL). The proposed approach, including the IDEF0, SPNC, and TPL tools, leads to the standard IEC1131-3 LLD for PLC implementation. Finally, an application of a stamping process is provided to illustrate the design procedure of the developed approach .

Due to the rapid development of the Internet, research on networked control system (NCS) has attracted much attention. However, when the control is over the network, the communication time delay will reduce the stability and performance of the entire system. This paper presents a comparative study of time delay compensation methods based on a communication disturbance observer (CDOB) architecture. Also, applications of fuzzy control theory and neural network modeling to the CDOB are presented. Simulation results show that the presented approach can be effectively applied to the NCS with time delays.

Modeling and control plays an important role in the automated manufacturing applications. Remote operation provides the capability to perform monitoring and control over a great distance. In this paper, behavior modeling and remote control of an industrial conveyor system has been presented. In the present approach, colored Petri nets (CPNs) are used to model the operated behaviors so as to result in a more compact structure. A prototype of a seven-position conveyor system is designed and implemented to show the feasibility of the developed approach. It is believed that the technique presented in this paper could be further applied to large-scale industrial conveyor systems.

In wireless sensor networks (WSN), a binding is an association between a sensor and an actuator. The binding mechanism defined in the ZigBee specification is restricted within a personal area network (PAN). For a complex WSN application, it is desired to have an inter-PAN binding mechanism to combine sensors and actuators from different PANs, respectively. In this paper, we have proposed a gateway-based inter-PAN binding mechanism for global event detection and action invocation. By collecting device capabilities from each intra-PAN gateway, an inter-PAN gateway is used to create a binding specification. Once all events defined in the binding specification are received from related intra-PAN gateways, the inter-PAN gateway would initiate corresponding actions on all associated intra-PAN gateways. To demonstrate the practicality, an inter-PAN binding system for ZigBee sensors and actuators has been implemented based on the universal plug and play (UPnP) and representational state transfer (REST) Web services for intra-PAN gateway discovery and device capability collection. Also, a Web-based wizard has been provided to create binding specification. It is believed that the technique presented in this paper would enable the interaction between ZigBee PANs to perform wide-ranging WSN applications.

For complicated pharmaceutical manufacturing processes, using real devices for system integration and testing not only increases the cost but also takes a longer time. In this paper, a systematic approach to the model construction for system integration in pharmaceutical manufacturing processes is proposed. In the present approach, the integration definition language zero (IDEF0) for function modeling and Petri net (PN) are applied to perform the functional and behavior analyses of the processes, and a verified PN model can be then obtained for the implementation of system integration. An application of a monomer synthesis process in pharmaceutical manufacturing systems is provided to illustrate the design procedure of the developed approach.

In remotely operated weapon systems (ROWS), since the human soldier is involved in the control loop, particular improper operations may cause accidents and result in catastrophes. For such systems, this paper has used a command-filter-based framework to accept or reject the human-issued commands so that undesirable executions would never be performed. In the present approach, Petri nets (PN) are used to model the operated behaviors and to synthesize the command filter for supervision. An application to missile loading and launching processes is provided to show the feasibility of the developed approach. It is believed that the technique presented in this paper could be further applied to large-scale military weapon systems.

For the improvement of the reliability and safety of industrial processes, a fault detection and tracing approach has been proposed. In this paper, the P-invariant of Petri Nets (PN) is applied to discover sequence faults, while both sensor faults and actuator faults are detected using exclusive logic functions. For industrial applications, the proposed fault detector has been implemented within a programmable logic controller (PLC) by converting the fault detection logic functions into ladder logic diagrams (LLD). Moreover, a fault tracer has been modeled by an AND/OR tree and a tracing procedure is provided to locate the faults. A mark stamping process is demonstrated as an example to illustrate the proposed diagnostic approach.

Inside a wireless sensor network comprising both static sensors and mobile robots, as human commands are issued within the control loop, particular improper actions may cause accidents and result in disasters. For such systems, this paper has proposed a command filtering framework to accept or reject the human-issued commands so that undesirable executions are never performed. In the present approach, Petri nets (PN) are used to model the operated behaviors and to synthesize the command filters for supervision. An application to a mobile wireless surveillance system is provided to show the practicability of the developed approach. It is believed that the technique presented in this paper could be further applied to large-scale wireless mobile sensor networks.

Bluetooth (over IEEE 802.15.1), ultra-wideband (UWB, over IEEE 802.15.3), ZigBee (over IEEE 802.15.4), and Wi-Fi (over IEEE 802.11) are four protocol standards for short- range wireless communications with low power consumption. From an application point of view, bluetooth is intended for a cordless mouse, keyboard, and hands-free headset, UWB is oriented to high-bandwidth multimedia links, ZigBee is designed for reliable wirelessly networked monitoring and control networks, while Wi-Fi is directed at computer-to-computer connections as an extension or substitution of cabled networks. In this paper, we provide a study of these popular wireless communication standards, evaluating their main features and behaviors in terms of various metrics, including the transmission time, data coding efficiency, complexity, and power consumption. It is believed that the comparison presented in this paper would benefit application engineers in selecting an appropriate protocol.

IEEE 802.15.4 is an emerging standard specifically designed for low-rate wireless personal area networks (LR-WPAN) with a focus on enabling the wireless sensor networks. It attempts to provide a low data rate, low power, and low cost wireless networking on the device-level communication. In this paper, we have established a realistic environment for the preliminary performance evaluation of the IEEE 802.15.4 wireless networks. Several sets of practical experiments are conducted to study its various features, including the effects of I) the direct and indirect data transmissions, 2) CSMA-CA mechanism, 3) data payload size, and 4) beacon-enabled mode. The data throughput, delivery ratio, and received signal strength indication (RSSI) are investigated as the performance metrics

Sequence controller designs play a key role in advanced manufacturing systems. Traditionally, the ladder logic diagram (LLD) has been widely applied to programmable logic controllers (PLC), while recently the Petri net (PN) has emerged as an alternative tool for the sequence control of complex systems. The evaluation of both approaches has become crucial and has thus attracted attention. The “basic element” approach was developed to evaluate the complexity and flexibility for LLD and PN design approaches [1, 2, 3, 4]. However, the basic elements of these two designs are inherently different and hence that approach may lead to unreliable results. Since sequence control here naturally implies the use of logic rules, a rule-based approach is proposed in this paper to provide unified measures for both LLD and PN designs. To illustrate the proposed approach, it is applied to five control sequences with increasing complexity for a stamping process. Results indicate that the proposed approach is more suitable for real applications and, furthermore, PN is increasingly superior to LLD as the control sequence becomes more complex.

Recently, methods have been proposed for obtaining the ladder logic diagram (LLD) based on the Petri net (PN). However, those resulting LLD are usually not in compact forms. Moreover, forming the PN structures to model manufacturing processes is not straightforward. In this paper, we propose a simplified Petri net controller (SPNC) by introducing sensor states into the PN. A compact LLD can be then obtained through the token passing logic (TPL). By employing the integration definition language 0 (IDEF0) technique, we obtain the SPNC structure sequentially through material flow diagrams and information flow diagrams. The result of an integrated IPTL (IDEF0/SPNC/TPL/LLD) algorithm, including the IDEF0, SPNC, and TPL tools, leads to the standard IEC1131-3 LLD for PLC implementation. An example of a mark stamping system is provided to illustrate the developed design approach.