The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Mengchu Zhou - One of the best experts on this subject based on the ideXlab platform.
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Optimal One-Wafer Cyclic Scheduling of Hybrid Multirobot Cluster Tools With Tree Topology
IEEE Transactions on Systems Man and Cybernetics: Systems, 2018Co-Authors: Fajun Yang, Yan Qiao, Mengchu ZhouAbstract:A hybrid multirobot cluster tool is composed of both single and dual-arm robotic cluster tools. Since the behavior of different individual tools is different, it is very challenging to coordinate their activities in such a tool and to Schedule it optimally. To find a one-wafer Cyclic Schedule to reach the shortest cycle time for a treelike hybrid multirobot cluster tool whose bottleneck tool is process-bound, this paper extends resource-oriented Petri nets to model it such that a Schedule can be parameterized by its robots’ waiting time. Based on the model, this paper then establishes the conditions under which there is a one-wafer Cyclic Schedule such that the shortest cycle time can be obtained. An efficient algorithm is also given to test the existence of such a Schedule and to find it if existing. At last, examples are used to illustrate the proposed approaches.
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optimal one wafer Cyclic scheduling and buffer space configuration for single arm multicluster tools with linear topology
Systems Man and Cybernetics, 2016Co-Authors: Liping Bai, Mengchu ZhouAbstract:This work studies the scheduling problem of a single-arm multicluster tool with a linear topology and process-bound bottleneck individual tool. The objective is to find a one-wafer Cyclic Schedule such that the lower bound of cycle time is reached by optimally configuring spaces in buffering modules that link individual cluster tools. A Petri net (PN) model is developed to describe the dynamic behavior of the system by extending resource-oriented PNs such that a Schedule can be parameterized by robots’ waiting time. Based on this model, conditions are presented under which a one-wafer Cyclic Schedule with the lower bound of cycle time can be found. With the derived conditions, an algorithm is developed to find such a Schedule and optimally configure buffer spaces. The algorithm requires only simple calculation to set the robots’ waiting time and buffer size. Illustrative examples are presented to demonstrate the proposed method.
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How to Respond to Process Module Failure in Residency Time-Constrained Single-Arm Cluster Tools
IEEE Transactions on Semiconductor Manufacturing, 2014Co-Authors: Yan Qiao, Chunrong Pan, Mengchu ZhouAbstract:Cyclic scheduling and operation of a residency time- constrained single-arm cluster tool with failure-prone process modules are highly challenging. In some cases, when a fail- ure occurs, there still exists a feasible Cyclic Schedule for the performance-degraded tool. In other cases, such a Schedule no longer exists. For the latter, it is highly desired to respond to a process module failure properly such that the tool can continue working and the wafers in the tool can be completed in a feasi- ble way. This work is the first one to study this important issue. The idea is to apply Petri nets to describe the dynamic behav- ior of a single-arm cluster tool. With the developed Petri net model, this paper formulates failure response policies to control the cluster tool such that it can keep working without violat- ing any residency time constraint. The failure response policies are implemented via efficient real-time control laws. Illustrative examples are presented to show their usage. Index Terms—Wafer fabrication, Cluster tools, Petri net, Scheduling, Failure response.
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Petri Net-Based Scheduling of Single-Arm Cluster Tools with Reentrant Atomic Layer Deposition Processes
IEEE Transactions on Automation Science and Engineering, 2011Co-Authors: Feng Chu, Chengbin Chu, Mengchu ZhouAbstract:For some wafer fabrication processes in cluster tools, e.g., atomic layer deposition (ALD), wafer revisiting is required. Typically, in such processes, wafers need to visit two consecutive processing steps several times. Such a revisiting process can be denoted as (mi, mi + 1)h, where i means the ith-step and mi and mi + 1 mean the corresponding quantity of the processing modules in i and (i+1)th steps, and h the number of visiting times. This paper conducts a study for scheduling single-arm cluster tools with such a wafer revisiting process. The system is modeled by Petri nets (PNs) to guarantee the feasibility of robot activities. Based on the model, a deadlock avoidance policy is presented. With the control policy, cycle time analysis for the revisiting process is made. With the fact that wafer processing times are much longer than robot movement times in cluster tools, it is shown that, when mi = mi + 1 = 1, i.e., each step has only one processing module, the optimal one-wafer Cyclic Schedule is deterministic and unique, and the minimal cycle time can be calculated by an analytical expression. It is also shown that, when mi = 1 and mi + 1 = 2 or mi = 2 and mi + 1 = 1, the optimal one-wafer Cyclic Schedule can be obtained by finding h deterministic Schedules and the one with the least cycle time. A novel analytical method is finally presented to Schedule the overall system containing such reentrant wafer flow. This represents a significant advance in single-arm cluster equipment automation.
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a closed form solution for schedulability and optimal scheduling of dual arm cluster tools with wafer residency time constraint based on steady Schedule analysis
IEEE Transactions on Automation Science and Engineering, 2010Co-Authors: Mengchu ZhouAbstract:Because of wafer residency time constraints for cluster tools, it is very difficult to Schedule them. This paper addresses their scheduling issues and conducts their schedulability and scheduling analysis. A Petri net (PN) model is developed to model them. With this model, to Schedule a dual-arm cluster tool with wafer residency time constraints is to determine when and how long the robot should wait for. Based on the model, necessary and sufficient conditions under which the system is schedulable are presented. The conditions can be checked analytically. Meanwhile, an algorithm is developed for the optimal scheduling of dual-arm cluster tools. The algorithm finds an optimal periodic Schedule with closed form expressions if it is schedulable. A method is also presented for the implementation of the obtained Cyclic Schedule by appropriately controlling the initial transient process. Examples are presented to show the application and power of the theory and algorithm.
Taeeog Lee - One of the best experts on this subject based on the ideXlab platform.
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k Cyclic Schedules and the worst case wafer delay in a dual armed cluster tool
IEEE Transactions on Semiconductor Manufacturing, 2019Co-Authors: Donghyun Roh, Taegyung Lee, Taeeog LeeAbstract:In a cluster tool for semiconductor manufacturing, a wafer waits within a chamber after processing until it is unloaded by the robot. Such wafer delays degrade wafer quality due to residual gases and heat, even cause quality failures. A cluster tool mostly operates in a ${K}$ -Cyclic Schedule, where an identical timing pattern repeats for each ${K}$ cycles, because of sporadic disruptions in process times or robot task times and the closed-architecture of the tool Scheduler. In addition, it is hard to predict the ${K}$ -Cyclic Schedule that the tool will reach. Such a ${K}$ -Cyclic Schedule makes wafer delays at each chamber repeat ${K}$ different values. Therefore, such variability of wafer delays increases the risk of quality failure. Therefore, we examine the maximum wafer delay among all possible ${K}$ -Cyclic Schedules called the worst-case wafer delay in this paper. We first characterize the maximum Cyclicity ${K}$ of tool Schedules. We then develop closed-form formulas for most frequently used wafer flow patterns and an optimization model that computes the worst-case wafer delay. We also identify factors that affect the worst-case wafer delay and their influences by experiments. Finally, we suggest tool operation guidelines for lowering the worst-case wafer delay.
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${K}$ -Cyclic Schedules and the Worst-Case Wafer Delay in a Dual-Armed Cluster Tool
IEEE Transactions on Semiconductor Manufacturing, 2019Co-Authors: Donghyun Roh, Taegyung Lee, Taeeog LeeAbstract:In a cluster tool for semiconductor manufacturing, a wafer waits within a chamber after processing until it is unloaded by the robot. Such wafer delays degrade wafer quality due to residual gases and heat, even cause quality failures. A cluster tool mostly operates in a ${K}$ -Cyclic Schedule, where an identical timing pattern repeats for each ${K}$ cycles, because of sporadic disruptions in process times or robot task times and the closed-architecture of the tool Scheduler. In addition, it is hard to predict the ${K}$ -Cyclic Schedule that the tool will reach. Such a ${K}$ -Cyclic Schedule makes wafer delays at each chamber repeat ${K}$ different values. Therefore, such variability of wafer delays increases the risk of quality failure. Therefore, we examine the maximum wafer delay among all possible ${K}$ -Cyclic Schedules called the worst-case wafer delay in this paper. We first characterize the maximum Cyclicity ${K}$ of tool Schedules. We then develop closed-form formulas for most frequently used wafer flow patterns and an optimization model that computes the worst-case wafer delay. We also identify factors that affect the worst-case wafer delay and their influences by experiments. Finally, we suggest tool operation guidelines for lowering the worst-case wafer delay.
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characterizing the worst case wafer delay in a cluster tool operated in a k Cyclic Schedule
Conference on Automation Science and Engineering, 2018Co-Authors: Donghyun Roh, Taeeog LeeAbstract:Cluster tools are widely used manufacturing equipment in semiconductor manufacturing systems and consist of several process chambers, loadlock modules, and a wafer transport robot. The operation of the cluster tool relies on decision making about the robot operations. Generally, a robot iteratively determines its next task according to a given task sequence. This tool Schedule is called a Cyclic Schedule. If the same timing pattern repeats every $K$ work cycles in a Cyclic Schedule, the Schedule is called a $K$ -Cyclic Schedule. In a cluster tool with a $K$ -Cyclic Schedule, wafer delay, which is the time that a processed wafer is stored in the process chamber, becomes an important issue. In this study, we identify the worst-case wafer delay, which is the maximum value of wafer delay among all the $K$ -Cyclic Schedules a cluster tool can have. To do this, we present timed event graph models for dual-armed and single-armed cluster tools and briefly explain the previous research on closed-form formulae of token delays in timed event graphs with K-Cyclic Schedules suggested by Lee et al. [1]. Finally, we propose a method for deriving a closed-form formula for the worst-case wafer delay in a cluster tool, which can be applied to arbitrary wafer flow patterns and time parameters.
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Characterizing Token Delays of Timed Event Graphs for K-Cyclic Schedules
IEEE Transactions on Automatic Control, 2017Co-Authors: Taeeog Lee, Donghyun Roh, Hyun-jung Kim, Ramavarapu S. SreenivasAbstract:A timed discrete event system, which repeats identical work cycles, has task delays due to synchronization between work cycles. Real such systems tend to operate mostly in a K-Cyclic timing regime, where a sequence of identical timing patterns is repeated for every K cycles. Therefore, the task delays fluctuate and repeat a sequence of K different values, and hence have higher risk of violating an upper limit. Task delays correspond to token delays at the system's timed event graph model. We therefore examine token delays in K-Cyclic Schedules of a timed event graph, an essential class of Petri nets. We first identify all possible K-Cyclic Schedules and define their initial phases. We then develop a closed-formula on the token delays on a path for a K-Cyclic Schedule, which can be computed by the longest path lengths between the nodes in an associated directed graph. We also present a formula for 1-Cyclic Schedules. The formulae can be used for computing statistics on K-different token delays, maximizing or minimizing the token delays with regard to all possible initial phases, and verifying task delay constraints, if any.
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analysis and control of wafer delays in a dual armed cluster tool for a k Cyclic Schedule
Systems Man and Cybernetics, 2016Co-Authors: Donghyun Roh, Taeeog LeeAbstract:We examine wafer delays, particularly the worst-case delay, of a dual-armed cluster tool for a K-Cyclic Schedule. We propose two useful concepts related to robot operations for the analyses, which are the time difference σ and the robot delay R. By using these concepts, we formulate a mixed-integer linear programming for computing the worst-case wafer delay. An upper bound for the worst-case wafer delay and experimental results are suggested. We also suggest an improved wafer delay regulation method by exploiting workload balancing. We introduce the effects of workload balancing and the strategies for achieving workload balancing. Explanations related to the configuration of the tool also are suggested.
Yan Qiao - One of the best experts on this subject based on the ideXlab platform.
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Optimal One-Wafer Cyclic Scheduling of Hybrid Multirobot Cluster Tools With Tree Topology
IEEE Transactions on Systems Man and Cybernetics: Systems, 2018Co-Authors: Fajun Yang, Yan Qiao, Mengchu ZhouAbstract:A hybrid multirobot cluster tool is composed of both single and dual-arm robotic cluster tools. Since the behavior of different individual tools is different, it is very challenging to coordinate their activities in such a tool and to Schedule it optimally. To find a one-wafer Cyclic Schedule to reach the shortest cycle time for a treelike hybrid multirobot cluster tool whose bottleneck tool is process-bound, this paper extends resource-oriented Petri nets to model it such that a Schedule can be parameterized by its robots’ waiting time. Based on the model, this paper then establishes the conditions under which there is a one-wafer Cyclic Schedule such that the shortest cycle time can be obtained. An efficient algorithm is also given to test the existence of such a Schedule and to find it if existing. At last, examples are used to illustrate the proposed approaches.
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Polynomial approach to optimal one-wafer Cyclic scheduling of treelike hybrid multi-cluster tools via Petri nets
IEEE CAA Journal of Automatica Sinica, 2018Co-Authors: Fajun Yang, Yan QiaoAbstract:A treelike hybrid multi-cluster tool is composed of both single-arm and dual-arm cluster tools with a treelike topology. Scheduling such a tool is challenging. For a hybrid treelike multi-cluster tool whose bottleneck individual tool is process-bound, this work aims at finding its optimal one-wafer Cyclic Schedule. It is modeled with Petri nets such that a onewafer Cyclic Schedule is parameterized as its robots’ waiting time. Based on the model, this work proves the existence of its onewafer Cyclic Schedule that features with the ease of industrial implementation. Then, computationally efficient algorithms are proposed to find the minimal cycle time and optimal onewafer Cyclic Schedule. Multi-cluster tool examples are given to illustrate the proposed approach. The use of the found Schedules enables industrial multi-cluster tools to operate with their highest productivity.
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How to Respond to Process Module Failure in Residency Time-Constrained Single-Arm Cluster Tools
IEEE Transactions on Semiconductor Manufacturing, 2014Co-Authors: Yan Qiao, Chunrong Pan, Mengchu ZhouAbstract:Cyclic scheduling and operation of a residency time- constrained single-arm cluster tool with failure-prone process modules are highly challenging. In some cases, when a fail- ure occurs, there still exists a feasible Cyclic Schedule for the performance-degraded tool. In other cases, such a Schedule no longer exists. For the latter, it is highly desired to respond to a process module failure properly such that the tool can continue working and the wafers in the tool can be completed in a feasi- ble way. This work is the first one to study this important issue. The idea is to apply Petri nets to describe the dynamic behav- ior of a single-arm cluster tool. With the developed Petri net model, this paper formulates failure response policies to control the cluster tool such that it can keep working without violat- ing any residency time constraint. The failure response policies are implemented via efficient real-time control laws. Illustrative examples are presented to show their usage. Index Terms—Wafer fabrication, Cluster tools, Petri net, Scheduling, Failure response.
Joris Van De Klundert - One of the best experts on this subject based on the ideXlab platform.
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Cyclic Scheduling of Identical Parts in a Robotic Cell
Operations Research, 1997Co-Authors: Yves Crama, Joris Van De KlundertAbstract:We consider a robotic flowshop in which one type of product is to be repeatedly produced, and where transportation of the parts between the machines is performed by a robot. The identical parts Cyclic scheduling problem is then to find a shortest Cyclic Schedule for the robot; i.e., a sequence of robot moves that can be infinitely repeated and that has minimum cycle time. This problem has been solved by Sethi et al. (Sethi, S. P., C. Sriskandarajah, G. Sorger, J. Blazewicz, W. Kubiak. 1992. Sequencing of parts and robot moves in a robotic cell. Internat. J. Flexible Manufacturing Systems 4 331–358.) when m ≤ 3. In this paper, we generalize their results by proving that the identical parts Cyclic scheduling problem can be solved in time polynomial in m, where m denotes the number of machines in the shop. In particular, we present a dynamic programming approach that allows us to solve the problem in O(m3) time. Our analysis relies heavily on the concept of pyramidal permutation, a concept previously investi...
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The 1-part m-machine Cyclic scheduling problem in robotic cells
Operations Research ’93, 1994Co-Authors: Yves Crama, Joris Van De KlundertAbstract:We consider a flow shop consisting of m machines, an input device and an output device, in which one type of product is to be produced. There are no buffers in the flow shop and the transportation of items between machines is taken care of by a robot. The 1-part Cyclic scheduling problem consists in finding the shortest Cyclic Schedule for the robot, i.e. a Schedule that outputs one part in each cycle, can be repeated infinitely many times and has maximum throughput rate. The problem has been solved by Sethi et al. (1992) in the case where m ≤ 3. We present an algorithm solving the 1-part Cyclic scheduling problem in polynomial time for arbitrary values of m. Our approach is based on dynamic programming techniques.
Donghyun Roh - One of the best experts on this subject based on the ideXlab platform.
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k Cyclic Schedules and the worst case wafer delay in a dual armed cluster tool
IEEE Transactions on Semiconductor Manufacturing, 2019Co-Authors: Donghyun Roh, Taegyung Lee, Taeeog LeeAbstract:In a cluster tool for semiconductor manufacturing, a wafer waits within a chamber after processing until it is unloaded by the robot. Such wafer delays degrade wafer quality due to residual gases and heat, even cause quality failures. A cluster tool mostly operates in a ${K}$ -Cyclic Schedule, where an identical timing pattern repeats for each ${K}$ cycles, because of sporadic disruptions in process times or robot task times and the closed-architecture of the tool Scheduler. In addition, it is hard to predict the ${K}$ -Cyclic Schedule that the tool will reach. Such a ${K}$ -Cyclic Schedule makes wafer delays at each chamber repeat ${K}$ different values. Therefore, such variability of wafer delays increases the risk of quality failure. Therefore, we examine the maximum wafer delay among all possible ${K}$ -Cyclic Schedules called the worst-case wafer delay in this paper. We first characterize the maximum Cyclicity ${K}$ of tool Schedules. We then develop closed-form formulas for most frequently used wafer flow patterns and an optimization model that computes the worst-case wafer delay. We also identify factors that affect the worst-case wafer delay and their influences by experiments. Finally, we suggest tool operation guidelines for lowering the worst-case wafer delay.
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${K}$ -Cyclic Schedules and the Worst-Case Wafer Delay in a Dual-Armed Cluster Tool
IEEE Transactions on Semiconductor Manufacturing, 2019Co-Authors: Donghyun Roh, Taegyung Lee, Taeeog LeeAbstract:In a cluster tool for semiconductor manufacturing, a wafer waits within a chamber after processing until it is unloaded by the robot. Such wafer delays degrade wafer quality due to residual gases and heat, even cause quality failures. A cluster tool mostly operates in a ${K}$ -Cyclic Schedule, where an identical timing pattern repeats for each ${K}$ cycles, because of sporadic disruptions in process times or robot task times and the closed-architecture of the tool Scheduler. In addition, it is hard to predict the ${K}$ -Cyclic Schedule that the tool will reach. Such a ${K}$ -Cyclic Schedule makes wafer delays at each chamber repeat ${K}$ different values. Therefore, such variability of wafer delays increases the risk of quality failure. Therefore, we examine the maximum wafer delay among all possible ${K}$ -Cyclic Schedules called the worst-case wafer delay in this paper. We first characterize the maximum Cyclicity ${K}$ of tool Schedules. We then develop closed-form formulas for most frequently used wafer flow patterns and an optimization model that computes the worst-case wafer delay. We also identify factors that affect the worst-case wafer delay and their influences by experiments. Finally, we suggest tool operation guidelines for lowering the worst-case wafer delay.
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characterizing the worst case wafer delay in a cluster tool operated in a k Cyclic Schedule
Conference on Automation Science and Engineering, 2018Co-Authors: Donghyun Roh, Taeeog LeeAbstract:Cluster tools are widely used manufacturing equipment in semiconductor manufacturing systems and consist of several process chambers, loadlock modules, and a wafer transport robot. The operation of the cluster tool relies on decision making about the robot operations. Generally, a robot iteratively determines its next task according to a given task sequence. This tool Schedule is called a Cyclic Schedule. If the same timing pattern repeats every $K$ work cycles in a Cyclic Schedule, the Schedule is called a $K$ -Cyclic Schedule. In a cluster tool with a $K$ -Cyclic Schedule, wafer delay, which is the time that a processed wafer is stored in the process chamber, becomes an important issue. In this study, we identify the worst-case wafer delay, which is the maximum value of wafer delay among all the $K$ -Cyclic Schedules a cluster tool can have. To do this, we present timed event graph models for dual-armed and single-armed cluster tools and briefly explain the previous research on closed-form formulae of token delays in timed event graphs with K-Cyclic Schedules suggested by Lee et al. [1]. Finally, we propose a method for deriving a closed-form formula for the worst-case wafer delay in a cluster tool, which can be applied to arbitrary wafer flow patterns and time parameters.
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Characterizing Token Delays of Timed Event Graphs for K-Cyclic Schedules
IEEE Transactions on Automatic Control, 2017Co-Authors: Taeeog Lee, Donghyun Roh, Hyun-jung Kim, Ramavarapu S. SreenivasAbstract:A timed discrete event system, which repeats identical work cycles, has task delays due to synchronization between work cycles. Real such systems tend to operate mostly in a K-Cyclic timing regime, where a sequence of identical timing patterns is repeated for every K cycles. Therefore, the task delays fluctuate and repeat a sequence of K different values, and hence have higher risk of violating an upper limit. Task delays correspond to token delays at the system's timed event graph model. We therefore examine token delays in K-Cyclic Schedules of a timed event graph, an essential class of Petri nets. We first identify all possible K-Cyclic Schedules and define their initial phases. We then develop a closed-formula on the token delays on a path for a K-Cyclic Schedule, which can be computed by the longest path lengths between the nodes in an associated directed graph. We also present a formula for 1-Cyclic Schedules. The formulae can be used for computing statistics on K-different token delays, maximizing or minimizing the token delays with regard to all possible initial phases, and verifying task delay constraints, if any.
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analysis and control of wafer delays in a dual armed cluster tool for a k Cyclic Schedule
Systems Man and Cybernetics, 2016Co-Authors: Donghyun Roh, Taeeog LeeAbstract:We examine wafer delays, particularly the worst-case delay, of a dual-armed cluster tool for a K-Cyclic Schedule. We propose two useful concepts related to robot operations for the analyses, which are the time difference σ and the robot delay R. By using these concepts, we formulate a mixed-integer linear programming for computing the worst-case wafer delay. An upper bound for the worst-case wafer delay and experimental results are suggested. We also suggest an improved wafer delay regulation method by exploiting workload balancing. We introduce the effects of workload balancing and the strategies for achieving workload balancing. Explanations related to the configuration of the tool also are suggested.
