In the periodic scheduling problems of a dual-arm wafer-residency-time-constrained (W-R-T-C) cluster tool (CT) with multivariety wafers, it is important to balance workload at each step. This work proposes a method of processing module (PM) two-layer configuration. First, one PM configuration is made for each wafer type, i.e., the suitable number of PMs is selected for processing wafers, ensuring that the natural workload is balanced at each step for a type of wafers. Then, the other PM configuration is made, i.e., adopt a virtual module method for balancing the natural workload at bottleneck processing steps of different types of wafers. Based on two-layer PM configuration, this work derives necessary and sufficient conditions for a CT’s schedulability, which are less restrictive than the current state-of-the-art ones. It proposes a polynomial-time algorithm for computing its minimum periodic schedule when it is schedulable. Several examples are given to show our algorithm’s superiority over existing ones.

With the rapid changes and diversity of market demand, fabs have to produce wafers in many varieties and small batches. This brings a great challenge to the scheduling of wafer-residency-time-constrained cluster tools that concurrently process multiple types of wafers. Existing practice tends to employ all processing modules (PMs) of a required type to process wafers, and adopt a virtual module technology to balance PM workload for different types of wafers. However, since the virtual module technology may fail to well balance the natural workload of each processing step of a type of wafers, the corresponding scheduling results can be too conservative for the cluster tools to reach their optimal productivity. Can we improve their schedulability by choosing the most appropriate number of PMs to process wafers instead of all PMs? Under what conditions, may we use fewer PMs in a cluster tool to reach the same cycle time reached by using all PMs, thus saving resources and reducing energy consumption? This work presents a PM dual-layer configuration method. The first configuration is performed to decide the proper number of PMs, and the second one is done for so-called virtual PMs that are not physically existing PMs. It derives necessary and sufficient conditions for the schedulability of a cluster tool, which are more relaxed than all the existing ones. Furthermore, this work presents a polynomial-complexity algorithm to find an optimal cyclic schedule, and its superiority over existing ones is shown via several examples.Note to Practitioners—This paper addresses the cyclic scheduling problem of wafer-residency-time-constrained single-arm cluster tools handling multiple wafer types, and gives an efficient method to configure PMs for processing wafers. Through the method, we can balance not only the PM workload for different types of wafers, but also the PM workload for each step of a type of wafers. Based on it, a cyclic scheduling approach is presented, which is readily applied to industrial wafer manufacturing. By using our method, the schedulability of the tool can be greatly improved, and some energy and resource consumption can be eliminated to make wafer fabrication greener than the existing methods.

In today’s semiconductor manufacturing industry, wafer foundries often face the challenge of producing a variety of integrated circuit chip products using a single manufacturing line. To address this, multicluster tools have become a popular choice for processing multiple wafer types simultaneously. Operating such tools involves coordinating the robots in adjacent individual tools to transport multitype wafers through a shared buffer. This study aims to develop a scheduling method for the concurrent fabrication processes of two wafer types, performed by a multicluster tool with wafer residency time constraints. The proposed approach presents a two-backward sequence, based on a backward strategy of a single wafer type, to convert a one-wafer cyclic schedule into a one-wafer-per-type cyclic schedule while revealing its temporal properties. To ensure a smooth operation of a single-arm multicluster tool system and synchronize multiple robots, several necessary and sufficient conditions are derived for the first time. Two efficient algorithms are then proposed to determine the feasibility of a periodic schedule and obtain a schedule that achieves the lower-bound cycle time under a two-backward strategy, maximizing the productivity of such a multicluster tool. Finally, numerical simulations and two practical examples are presented to demonstrate the applications and performance of the proposed approach.

The control issue of underwater robots is very challenging due to the nonlinearity, time variance, unpredictable external disturbances, such as the sea current fluctuation, and the difficulty in accurately modeling the hydrodynamic effect. Conventional linear controllers may fail in satisfying performance requirements, especially when changes in the system and environment occur during the operation since it is almost impossible to manually retune the control parameters in water. Therefore, it is highly desirable to have an underwater robot controller capable of self-adjusting control parameters when the overall performance degrades. This paper presents the theory and experimental work of the adaptive plus disturbance observer (ADOB) controller for underwater robots, which is robust with respect to external disturbance and uncertainties in the system. This control scheme consists of disturbance observer (DOB) as the inner-loop controller and a nonregressor based adaptive controller as the outer-loop controller. The effectiveness of the ADOB was experimentally investigated by implementing three controllers: PID, PID plus DOB, and ADOB on an autonomous underwater robot, ODIN III.

This paper presents the theory and experimental work of the adaptive plus disturbance observer (DOB) controller on underwater robot. This control scheme consists of DOB as an inner-loop compensator and a non-regressor based adaptive controller as an outer-loop controller. It is regressor-free, and is robust with respect to external disturbance as well as the variation of the nominal model used to construct DOB. The performance and characteristics of this controller are shown through comparison tests among four different controllers: PID controller, PID plus DOB controller, adaptive controller and adaptive plus DOB controller.

This paper presents an adaptive DOB (disturbance observer) controller for underwater robots, which consists of DOB as an inner-loop controller and a non-regressor based adaptive controller as an outer-loop controller. This control scheme does not require any parametric information, and is robust with respect to external disturbance as well as the variation of the nominal model used to construct DOB. Results of computer simulation using a hydrodynamic model of an underwater robot, ODIN, show the effectiveness of the adaptive DOB controller compared to PID, PID DOB, and adaptive controller. Experimental investigation of the presented controller is in progress on ODIN and results are also presented at IROS 2003.

Hydrodynamics of the manipulator mounted on the vehicle are poorly known and time-varying. Furthermore, its motion is disturbed by the vehicle motion and current. This paper presents a non-regressor based adaptive control scheme with a disturbance observer for tracking the trajectory of underwater mobile platform-mounted manipulators. The presented control system does not require any information about the system. The disturbance observer regards the difference between the actual output and the output of the nominal model as an equivalent disturbance applied to the nominal model. The adaptive control law then estimates control gains defined by the combinations of the bounded constants of parameter matrices of the nominal model with disturbance error. The performance of the proposed control scheme was evaluated by a computer simulation with a two-link planar manipulator mounted on a one 1-DOF mobile platform. The effect of hydrodynamic forces acting on the manipulator was also considered.