The complex variables and parameters with respect to the design of cooling channels in nonrectang... more The complex variables and parameters with respect to the design of cooling channels in nonrectangular plastic flat injection mold are investigated. Vector and simple mathematical calculations were used to solve problems related the deployment of cooling channels caused by different geometric dimensions of molded products. Furthermore, the basic geometry characteristic surface symbols and database were established. Next, the basic geometry characteristic surface was used to compose and present the shapes of molded product on the basis of a rectangular plastic flat. The conversion concept of equivalent area was also introduced to simplify the selection of model and deployment of cooling channels for nonrectangular plastic flat containing milder changes in shape. The optimization of cooling time in the first stage is based on the energy balance. A concise formula was used with empirical algorithm as the constraint of optimization design, to locate the optimal cooling time and the required optimal geometric factor constraints. Then, the optimization of channel deployment was derived to achieve the requirement of fast and uniform cooling of the mold. The method proposed in this paper is capable of handling a nonrectangular plastic flat product through the conversion to an equivalent rectangular area. This method simplifies the channel deployment problem of a molded product caused by nonuniform distribution of heat source and reduces the instances of trial and error. Furthermore, the method proposed for the system framework is capable of completing the optimization faster than conventional finite difference method, which saves the time spent in designing the cooling channels and achieves fast and uniform cooling of finished products.
Proceedings 2000 ICRA. Millennium Conference. IEEE International Conference on Robotics and Automation. Symposia Proceedings (Cat. No.00CH37065), 2000
Based on resource-oriented Petri net models of automated manufacturing systems (AMS), and Wu&... more Based on resource-oriented Petri net models of automated manufacturing systems (AMS), and Wu's previous work (1999) on a necessary and sufficient condition for deadlock-free operation, this paper proposes a new control policy such that deadlock is completely avoided, starvation and blocking situations are reduced and sometimes eliminated. It attempts to release an appropriate number of jobs into the system and control the order of resource usage based on state information in the net model. The theoretical results for the correctness of this policy are presented. A simple AMS is used to demonstrate its great potential to high utilization and productivity
2010 IEEE International Conference on Automation Science and Engineering, 2010
In the context of automated manufacturing systems (AMS), Petri nets are widely adopted to solve t... more In the context of automated manufacturing systems (AMS), Petri nets are widely adopted to solve the modeling, analysis, and control problems. So far, nearly all wellknown Petri net approaches study AMS with either flexible routes or assembly operations, whereas few work investigates their combination. In this paper, we propose a novel class of nets, which can well deal with both features. We also derive a supervisory controller for on-line ratio enforcement among all processes. Using structural analysis, we show that liveness of such systems can be attributed to the absence of undermarked siphons. We also reveal the design separability between ratioenforcing and liveness-enforcing supervisors.
2011 IEEE International Conference on Robotics and Automation, 2011
There are wafer fabrication processes in cluster tools that require revisiting. It is shown that ... more There are wafer fabrication processes in cluster tools that require revisiting. It is shown that swapping is efficient in operating a dual-arm cluster tool. For dual-arm cluster tools with wafer revisiting, if a swap strategy is applied, it forms a three wafer periodical process with three wafers completed in each period. Such a period contains three cycles in a revisiting process and another three cycles in non-revisiting process. Hence, analysis and scheduling of dual-arm cluster tools with wafer revisiting become very complicated. In this work, a Petri net model is developed to describe the operations of such tools. Based on it, it is found that if a swap strategy is applied to a dual-arm cluster tool with wafer revisiting, it is always in a transient state. A systematic method is presented to analyze its performance.
2006 IEEE International Conference on Automation Science and Engineering, 2006
Because of residency time constraints for cluster tools, it is very difficult to schedule them. T... more Because of residency time constraints for cluster tools, it is very difficult to schedule them. This paper addresses their scheduling issues and conducts their schedulability analysis. A Petri net (PN) model, called resource-oriented PN (ROPN) is developed to model them. Based on it, for the first time, necessary and sufficient conditions under which the system is schedulable are presented. Meanwhile,
Most existing prevention methods tackle the deadlock issue arising in flexible manufacturing syst... more Most existing prevention methods tackle the deadlock issue arising in flexible manufacturing systems modeled with Petri nets by adding monitors and arcs. Instead, this paper presents a new one based on a characteristic structure of WS 3 PR, an extension of System of Simple Sequential Processes with Resources (S 3 PR) with weighted arcs. The numerical relationships among weights, and between weights and initial markings are investigated based on simple circuits of resource places, which are the simplest structure of circular wait, rather than siphons. A WS 3 PR satisfying a proposed restriction is inherently deadlock-free and live by configuring its initial markings. A set of polynomial algorithms are developed to implement the proposed method. Several examples are used to illustrate them.
2006 IEEE International Conference on Systems, Man and Cybernetics, 2006
An automated manufacturing system (AMS) contains a number of versatile machines (or workstations)... more An automated manufacturing system (AMS) contains a number of versatile machines (or workstations), buffers, and an automated material handling system (MHS). The MHS can be an automated guide vehicle system, and/or a system that consists of multiple robots. The issue of deadlock resolution in AMS is very important in the operation of AMS and extensively studied. Usually, robots are seen
2003 IEEE International Conference on Robotics and Automation (Cat. No.03CH37422), 2003
Automated guided vehicles (AGV) systems are important for material handling in automated manufact... more Automated guided vehicles (AGV) systems are important for material handling in automated manufacturing systems (AMS). However, it is a great challenge to effectively manage them due to some of their features, e.g., the number of AGVs being fixed., prior unknown requests, and changing AGV initial positions. This paper aims to find the shortest time routing while both deadlock and blocking in them are avoided. We first find the shortest routing based on a layout of an AGV system, and then perform rerouting whenever necessary to avoid deadlock and blocking according to a deadlock avoidance policy previously developed by the authors. The algorithms are presented and illustrated through examples.
2007 IEEE International Conference on Networking, Sensing and Control, 2007
Since the 1980's, Petri nets (PN) have been widely used to model automated manufacturing... more Since the 1980's, Petri nets (PN) have been widely used to model automated manufacturing systems (AMS) for analysis, performance evaluation, simulation, and control. They are mostly based on process-oriented modeling methods and thus termed as process-oriented PN (POPN) in this paper. The recent study of deadlock avoidance problems in AMS led to another type of PN called resource-oriented PN (ROPN). This paper, for the first time, compares these two modeling methods and resultant models. POPN models the part production processes straightforwardly, while ROPN is more compact. The relations between these two models are investigated. Several AMS examples are used to illustrate them.
In this research, a series of 4-(1,2,3-triazol-1-yl)coumarin conjugates were synthesized and thei... more In this research, a series of 4-(1,2,3-triazol-1-yl)coumarin conjugates were synthesized and their anticancer activities were evaluated in vitro against three human cancer cell lines, including human breast carcinoma MCF-7 cell, colon carcinoma SW480 cell and lung carcinoma A549 cell. To increase the biological potency, structural optimization campaign was conducted focusing on the C-4 position of 1,2,3-triazole and the C-6, C-7 positions of coumarin. In addition, to further evaluate the role of 1,2,3-triazole and coumarin for antiproliferative activity, 9 compounds possessing 4-(piperazin-1-yl)coumarin framework and 3 derivatives baring quinoline core were also synthesized. By MTT assay in vitro, most of the compounds display attractive antitumor activities, especially 23. Further flow cytometry assays demonstrate that compound 23 exerts the antiproliferative role through arresting G2/M cell-cycle and inducing apoptosis.
In operating a multi-cluster tool, it needs to coordinate the activities of multiple robots. Thus... more In operating a multi-cluster tool, it needs to coordinate the activities of multiple robots. Thus, it is very challenging to schedule it. This paper conducts a study on one-wafer cyclic scheduling for multi-cluster tools whose bottleneck cluster tool is process-bound. The system is modeled by a Petri net. With this model, conditions under which a one-wafer cyclic schedule exists are developed. Based on them, it is shown that, for any multi-cluster tool whose bottleneck cluster tool is process-bound, there is always a one-wafer cyclic schedule. Then, a method is presented to find the minimal cycle time and the optimal onewafer cyclic schedule. It is computationally efficient. Illustrative examples are used to show the applications and effectiveness of the proposed method.
ABSTRACT This paper proposes a hybrid liveness-enforcing method for a class of Petri nets, which ... more ABSTRACT This paper proposes a hybrid liveness-enforcing method for a class of Petri nets, which can well model many flexible manufacturing systems. The proposed method combines elementary siphons with a characteristic structure-based method to prevent deadlocks and enforce liveness to the net class under consideration. The characteristic structure-based method is further advanced in this work. It unveils and takes a full advantage of an intrinsically live structure of generalized Petri nets, which hides behind the arc weights, to achieve the liveness enforcement without any external control agent such as monitors. This hybrid method can identify and remove redundant monitors from a liveness-enforcing supervisor designed according to existing policies, improve the permissiveness, reduce the structural complexity of a controlled system, and consequently save the control implementation cost. Several examples are used to illustrate this method.
Siphons are special structures of a Petri net. Their number grows exponentially with the net size... more Siphons are special structures of a Petri net. Their number grows exponentially with the net size. Hence, the traditional siphon-based deadlock control policies have two problems, that is, generating very structurally complex supervisory controllers and requiring intractable computation efforts. This paper intends to use the newly proposed concept, elementary siphons, and a mixed integer programming (MIP) method to design structurally simple supervisory controllers and reduce the computational burden. This method is applicable to a class of Petri nets, System of Simple Sequential Processes with Resources that can well model a wide class of discrete manufacturing systems. Siphons are divided into elementary and dependent ones. The proposed policy consists of three stages: siphon control, control-induced siphon control, and the elimination of control-redundant monitors. First, a monitor (control place) is added for each elementary siphon such that it is invariant-controlled. Because of the addition of monitors to the plant model, control-induced siphons are possibly generated in the augmented net. Next, monitors are added to make control-induced siphons in the augmented net always marked sufficiently without generating new problematic siphons. A MIP technique is used to guarantee that no siphon is insufficiently marked. Finally, we systematically remove control-redundant monitors. Compared with previous work in the literature, the deadlock prevention policy developed in this paper can lead to a structurally simple liveness-enforcing Petri net supervisor with more permissive behaviour by adding only a small number of monitors and arcs. Moreover, complete siphon enumeration is avoided. A manufacturing system example is utilised to illustrate the proposed methods.
A novel deadlock control policy is developed for modeling the concurrent execution of manufacturi... more A novel deadlock control policy is developed for modeling the concurrent execution of manufacturing processes with limited shared resources through a class of nets, ES 3 PR. A relevant property of the system behavior is that it is deadlock-free. Recent work has shown that deadlock situations in a plant system can be easily characterized by the structural analysis of the system, particularly, in terms of unmarked or insufficiently marked siphons in its Petri net model. The strict minimal siphons in a plant ES 3 PR net model are divided into elementary and dependent ones. The proposed deadlock prevention policy is to make all siphons satisfy maximal cs-property when the elementary siphons in the plant Petri net model are properly supervised via explicitly adding monitors for them with appropriate initial markings. Compared with the existing approaches in the literature, the advantage of the policy is that a much smaller number of supervisory places (monitors) are added and unnecessary iterative processes are avoided. Finally, its application is illustrated by a flexible manufacturing example.
Short-term scheduling for crude oil operations is a combinatorial problem and involves extreme de... more Short-term scheduling for crude oil operations is a combinatorial problem and involves extreme detail. Thus, it is very complicated and, up to now, there is no efficient technique and software tool for it. To search for efficient techniques, a twolayer hierarchical solution is proposed for it. At the upper level, one finds a realizable refining schedule to optimize some objectives. At the lower level, a detailed schedule is obtained to realize it. A methodology has been presented to solve the lower level problem from a control perspective by the authors of this paper. In this paper, the upper level problem for finding optimal refining schedules is addressed, and a novel method is proposed based on the results obtained at the lower level. This method solves a linear programming problem to determine the maximal production rate and a transportation problem to optimally assign crude oil types and volume to the distillers. This way, the method is computationally very efficient. An industrial case study is presented to show the application of the proposed method.
For short-term scheduling of crude oil operations, oil residency time and high fusion crude oil t... more For short-term scheduling of crude oil operations, oil residency time and high fusion crude oil transportation constraints are difficult to model. With high setup cost for high fusion point oil transportation, it is desired that the volume of such oil should be transported as much as possible by a single setup. To do so and obtain a feasible schedule, charging
The complex variables and parameters with respect to the design of cooling channels in nonrectang... more The complex variables and parameters with respect to the design of cooling channels in nonrectangular plastic flat injection mold are investigated. Vector and simple mathematical calculations were used to solve problems related the deployment of cooling channels caused by different geometric dimensions of molded products. Furthermore, the basic geometry characteristic surface symbols and database were established. Next, the basic geometry characteristic surface was used to compose and present the shapes of molded product on the basis of a rectangular plastic flat. The conversion concept of equivalent area was also introduced to simplify the selection of model and deployment of cooling channels for nonrectangular plastic flat containing milder changes in shape. The optimization of cooling time in the first stage is based on the energy balance. A concise formula was used with empirical algorithm as the constraint of optimization design, to locate the optimal cooling time and the required optimal geometric factor constraints. Then, the optimization of channel deployment was derived to achieve the requirement of fast and uniform cooling of the mold. The method proposed in this paper is capable of handling a nonrectangular plastic flat product through the conversion to an equivalent rectangular area. This method simplifies the channel deployment problem of a molded product caused by nonuniform distribution of heat source and reduces the instances of trial and error. Furthermore, the method proposed for the system framework is capable of completing the optimization faster than conventional finite difference method, which saves the time spent in designing the cooling channels and achieves fast and uniform cooling of finished products.
Proceedings 2000 ICRA. Millennium Conference. IEEE International Conference on Robotics and Automation. Symposia Proceedings (Cat. No.00CH37065), 2000
Based on resource-oriented Petri net models of automated manufacturing systems (AMS), and Wu&... more Based on resource-oriented Petri net models of automated manufacturing systems (AMS), and Wu's previous work (1999) on a necessary and sufficient condition for deadlock-free operation, this paper proposes a new control policy such that deadlock is completely avoided, starvation and blocking situations are reduced and sometimes eliminated. It attempts to release an appropriate number of jobs into the system and control the order of resource usage based on state information in the net model. The theoretical results for the correctness of this policy are presented. A simple AMS is used to demonstrate its great potential to high utilization and productivity
2010 IEEE International Conference on Automation Science and Engineering, 2010
In the context of automated manufacturing systems (AMS), Petri nets are widely adopted to solve t... more In the context of automated manufacturing systems (AMS), Petri nets are widely adopted to solve the modeling, analysis, and control problems. So far, nearly all wellknown Petri net approaches study AMS with either flexible routes or assembly operations, whereas few work investigates their combination. In this paper, we propose a novel class of nets, which can well deal with both features. We also derive a supervisory controller for on-line ratio enforcement among all processes. Using structural analysis, we show that liveness of such systems can be attributed to the absence of undermarked siphons. We also reveal the design separability between ratioenforcing and liveness-enforcing supervisors.
2011 IEEE International Conference on Robotics and Automation, 2011
There are wafer fabrication processes in cluster tools that require revisiting. It is shown that ... more There are wafer fabrication processes in cluster tools that require revisiting. It is shown that swapping is efficient in operating a dual-arm cluster tool. For dual-arm cluster tools with wafer revisiting, if a swap strategy is applied, it forms a three wafer periodical process with three wafers completed in each period. Such a period contains three cycles in a revisiting process and another three cycles in non-revisiting process. Hence, analysis and scheduling of dual-arm cluster tools with wafer revisiting become very complicated. In this work, a Petri net model is developed to describe the operations of such tools. Based on it, it is found that if a swap strategy is applied to a dual-arm cluster tool with wafer revisiting, it is always in a transient state. A systematic method is presented to analyze its performance.
2006 IEEE International Conference on Automation Science and Engineering, 2006
Because of residency time constraints for cluster tools, it is very difficult to schedule them. T... more Because of residency time constraints for cluster tools, it is very difficult to schedule them. This paper addresses their scheduling issues and conducts their schedulability analysis. A Petri net (PN) model, called resource-oriented PN (ROPN) is developed to model them. Based on it, for the first time, necessary and sufficient conditions under which the system is schedulable are presented. Meanwhile,
Most existing prevention methods tackle the deadlock issue arising in flexible manufacturing syst... more Most existing prevention methods tackle the deadlock issue arising in flexible manufacturing systems modeled with Petri nets by adding monitors and arcs. Instead, this paper presents a new one based on a characteristic structure of WS 3 PR, an extension of System of Simple Sequential Processes with Resources (S 3 PR) with weighted arcs. The numerical relationships among weights, and between weights and initial markings are investigated based on simple circuits of resource places, which are the simplest structure of circular wait, rather than siphons. A WS 3 PR satisfying a proposed restriction is inherently deadlock-free and live by configuring its initial markings. A set of polynomial algorithms are developed to implement the proposed method. Several examples are used to illustrate them.
2006 IEEE International Conference on Systems, Man and Cybernetics, 2006
An automated manufacturing system (AMS) contains a number of versatile machines (or workstations)... more An automated manufacturing system (AMS) contains a number of versatile machines (or workstations), buffers, and an automated material handling system (MHS). The MHS can be an automated guide vehicle system, and/or a system that consists of multiple robots. The issue of deadlock resolution in AMS is very important in the operation of AMS and extensively studied. Usually, robots are seen
2003 IEEE International Conference on Robotics and Automation (Cat. No.03CH37422), 2003
Automated guided vehicles (AGV) systems are important for material handling in automated manufact... more Automated guided vehicles (AGV) systems are important for material handling in automated manufacturing systems (AMS). However, it is a great challenge to effectively manage them due to some of their features, e.g., the number of AGVs being fixed., prior unknown requests, and changing AGV initial positions. This paper aims to find the shortest time routing while both deadlock and blocking in them are avoided. We first find the shortest routing based on a layout of an AGV system, and then perform rerouting whenever necessary to avoid deadlock and blocking according to a deadlock avoidance policy previously developed by the authors. The algorithms are presented and illustrated through examples.
2007 IEEE International Conference on Networking, Sensing and Control, 2007
Since the 1980's, Petri nets (PN) have been widely used to model automated manufacturing... more Since the 1980's, Petri nets (PN) have been widely used to model automated manufacturing systems (AMS) for analysis, performance evaluation, simulation, and control. They are mostly based on process-oriented modeling methods and thus termed as process-oriented PN (POPN) in this paper. The recent study of deadlock avoidance problems in AMS led to another type of PN called resource-oriented PN (ROPN). This paper, for the first time, compares these two modeling methods and resultant models. POPN models the part production processes straightforwardly, while ROPN is more compact. The relations between these two models are investigated. Several AMS examples are used to illustrate them.
In this research, a series of 4-(1,2,3-triazol-1-yl)coumarin conjugates were synthesized and thei... more In this research, a series of 4-(1,2,3-triazol-1-yl)coumarin conjugates were synthesized and their anticancer activities were evaluated in vitro against three human cancer cell lines, including human breast carcinoma MCF-7 cell, colon carcinoma SW480 cell and lung carcinoma A549 cell. To increase the biological potency, structural optimization campaign was conducted focusing on the C-4 position of 1,2,3-triazole and the C-6, C-7 positions of coumarin. In addition, to further evaluate the role of 1,2,3-triazole and coumarin for antiproliferative activity, 9 compounds possessing 4-(piperazin-1-yl)coumarin framework and 3 derivatives baring quinoline core were also synthesized. By MTT assay in vitro, most of the compounds display attractive antitumor activities, especially 23. Further flow cytometry assays demonstrate that compound 23 exerts the antiproliferative role through arresting G2/M cell-cycle and inducing apoptosis.
In operating a multi-cluster tool, it needs to coordinate the activities of multiple robots. Thus... more In operating a multi-cluster tool, it needs to coordinate the activities of multiple robots. Thus, it is very challenging to schedule it. This paper conducts a study on one-wafer cyclic scheduling for multi-cluster tools whose bottleneck cluster tool is process-bound. The system is modeled by a Petri net. With this model, conditions under which a one-wafer cyclic schedule exists are developed. Based on them, it is shown that, for any multi-cluster tool whose bottleneck cluster tool is process-bound, there is always a one-wafer cyclic schedule. Then, a method is presented to find the minimal cycle time and the optimal onewafer cyclic schedule. It is computationally efficient. Illustrative examples are used to show the applications and effectiveness of the proposed method.
ABSTRACT This paper proposes a hybrid liveness-enforcing method for a class of Petri nets, which ... more ABSTRACT This paper proposes a hybrid liveness-enforcing method for a class of Petri nets, which can well model many flexible manufacturing systems. The proposed method combines elementary siphons with a characteristic structure-based method to prevent deadlocks and enforce liveness to the net class under consideration. The characteristic structure-based method is further advanced in this work. It unveils and takes a full advantage of an intrinsically live structure of generalized Petri nets, which hides behind the arc weights, to achieve the liveness enforcement without any external control agent such as monitors. This hybrid method can identify and remove redundant monitors from a liveness-enforcing supervisor designed according to existing policies, improve the permissiveness, reduce the structural complexity of a controlled system, and consequently save the control implementation cost. Several examples are used to illustrate this method.
Siphons are special structures of a Petri net. Their number grows exponentially with the net size... more Siphons are special structures of a Petri net. Their number grows exponentially with the net size. Hence, the traditional siphon-based deadlock control policies have two problems, that is, generating very structurally complex supervisory controllers and requiring intractable computation efforts. This paper intends to use the newly proposed concept, elementary siphons, and a mixed integer programming (MIP) method to design structurally simple supervisory controllers and reduce the computational burden. This method is applicable to a class of Petri nets, System of Simple Sequential Processes with Resources that can well model a wide class of discrete manufacturing systems. Siphons are divided into elementary and dependent ones. The proposed policy consists of three stages: siphon control, control-induced siphon control, and the elimination of control-redundant monitors. First, a monitor (control place) is added for each elementary siphon such that it is invariant-controlled. Because of the addition of monitors to the plant model, control-induced siphons are possibly generated in the augmented net. Next, monitors are added to make control-induced siphons in the augmented net always marked sufficiently without generating new problematic siphons. A MIP technique is used to guarantee that no siphon is insufficiently marked. Finally, we systematically remove control-redundant monitors. Compared with previous work in the literature, the deadlock prevention policy developed in this paper can lead to a structurally simple liveness-enforcing Petri net supervisor with more permissive behaviour by adding only a small number of monitors and arcs. Moreover, complete siphon enumeration is avoided. A manufacturing system example is utilised to illustrate the proposed methods.
A novel deadlock control policy is developed for modeling the concurrent execution of manufacturi... more A novel deadlock control policy is developed for modeling the concurrent execution of manufacturing processes with limited shared resources through a class of nets, ES 3 PR. A relevant property of the system behavior is that it is deadlock-free. Recent work has shown that deadlock situations in a plant system can be easily characterized by the structural analysis of the system, particularly, in terms of unmarked or insufficiently marked siphons in its Petri net model. The strict minimal siphons in a plant ES 3 PR net model are divided into elementary and dependent ones. The proposed deadlock prevention policy is to make all siphons satisfy maximal cs-property when the elementary siphons in the plant Petri net model are properly supervised via explicitly adding monitors for them with appropriate initial markings. Compared with the existing approaches in the literature, the advantage of the policy is that a much smaller number of supervisory places (monitors) are added and unnecessary iterative processes are avoided. Finally, its application is illustrated by a flexible manufacturing example.
Short-term scheduling for crude oil operations is a combinatorial problem and involves extreme de... more Short-term scheduling for crude oil operations is a combinatorial problem and involves extreme detail. Thus, it is very complicated and, up to now, there is no efficient technique and software tool for it. To search for efficient techniques, a twolayer hierarchical solution is proposed for it. At the upper level, one finds a realizable refining schedule to optimize some objectives. At the lower level, a detailed schedule is obtained to realize it. A methodology has been presented to solve the lower level problem from a control perspective by the authors of this paper. In this paper, the upper level problem for finding optimal refining schedules is addressed, and a novel method is proposed based on the results obtained at the lower level. This method solves a linear programming problem to determine the maximal production rate and a transportation problem to optimally assign crude oil types and volume to the distillers. This way, the method is computationally very efficient. An industrial case study is presented to show the application of the proposed method.
For short-term scheduling of crude oil operations, oil residency time and high fusion crude oil t... more For short-term scheduling of crude oil operations, oil residency time and high fusion crude oil transportation constraints are difficult to model. With high setup cost for high fusion point oil transportation, it is desired that the volume of such oil should be transported as much as possible by a single setup. To do so and obtain a feasible schedule, charging
Uploads
Papers by Mengchu Zhou