Cyclic hoist scheduling in large real-life electroplating lines

IEEE Transactions on Automation Science and Engineering, 2000

In this paper, we study the no-wait multihoist cyclic scheduling problem, in which the processing times in the tanks and the transfer times between tanks are constant parameters, and develop a polynomial optimal solution to minimize the production cycle length. We first analyze the problem with a fixed cycle length and identify a group of hoist assignment constraints based on the positions of and the relationships among the part moves in the cycle. We show that the feasibility of the hoist scheduling problem with fixed cycle length is consistent with the feasibility of this group of constraints which can be solved efficiently. We then identify all of the special values of the cycle length at which the feasibility property of the problem may change. Finally, the whole problem is solved optimally by considering the fixed-cycle-length problems at these special values.

International Journal of Flexible Manufacturing Systems, 2003

Electroplating lines are totally automated manufacturing systems that are used to cover parts with a coat of metal. They consist of a set of tanks between which the parts to be treated are transported by one or several hoists. Scheduling the movements of these hoists is commonly called a hoist scheduling problem (HSP) in the literature. But the assumptions and constraints that must be taken into account greatly depend on the production environment (physical system, manufacturing specifications, and management policies). Consequently, there exist several classes of HSPs. The systematic frameworks usually used to classify deterministic scheduling problems do not allow distinguishing between these various kinds of HSPs. Therefore, identifying the scope of each published work and comparing the various proposed scheduling methods turn out to be difficult. Thus, this article presents notation for scheduling problems in electroplating systems, to make the specification of problem types and the identification of studied problem instances easier. An associated typology gives a survey of the literature and demonstrates the usefulness of the proposed classification scheme.

Computers & Operations Research, 2016

In this paper, we study the Hoist Scheduling Problem. The latter is often encountered in electroplating processes where a variety of jobs have to be processed in small quantities and in a very short amount of time. Basically, the problem consists in scheduling the hoist's movements in order to achieve two main objectives: Higher productivity and better product quality. In order to achieve these two goals, we first formulate the problem as a mixed integer linear programming model. Then, due to the problem complexity, we develop an efficient heuristic procedure to obtain the hoist's job processing sequence. Extensive numerical experiments show that the heuristic performs extremely well compared to a lower bound obtained through the mixed linear programming model and gives the optimal makespan for a large number of problem instances. Furthermore, comparison with the best available heuristic in the literature, shows that ODEST always outperforms the heuristic and achieves an improvement (i.e., reduction) of the makespan (hence the throughput of the line) of up to 43%.

Computers & Industrial Engineering, 2013

In automated electroplating lines, computer-controlled hoists are used to transfer parts from a processing resource to another one. Products are mounted into carriers and immersed sequentially in a series of tanks following a given sequence. The aim of this study is to propose an algorithm to solve the two-hoist cyclic scheduling problem. This problem consists in finding a repetitive sequence of hoists' moves, while avoiding collision between the hoists which share a common track. The objective is to minimize the period of this repetitive cycle. First, a set of sequences is generated. After that, for each sequence, an algorithm is applied to assign moves to hoists. Finally, a mixed integer linear programming model is formulated by taking into account the two sequences of hoists moves. Then it is solved to give the starting times of moves.

Operations Research, 2004

In the manufacture of circuit boards, panels are immersed sequentially in a series of tanks, with upper and lower bounds on the processing time within each tank. The panels are mounted on carriers that are lowered into and raised from the tanks, and transported from tank to tank by programmable hoists. The sequence of hoist moves does not have to follow the sequence of processing stages for the circuit boards. By optimising the sequence of hoist moves, we can maximise the production throughput.

Proceedings 1995 INRIA/IEEE Symposium on Emerging Technologies and Factory Automation. ETFA'95, 1995

Lecture Notes in Control and Information Sciences, 1994

Mathematical Problems in Engineering, 2008

Modern automated production lines usually use one or multiple computer-controlled robots or hoists for material handling between workstations. A typical application of such lines is an automated electroplating line for processing printed circuit boards PCBs . In these systems, cyclic production policy is widely used due to large lot size and simplicity of implementation. This paper addresses cyclic scheduling of a multihoist electroplating line with constant processing times. The objective is to minimize the cycle time, or equivalently to maximize the production throughput, for a given number of hoists. We propose a mathematical model and a polynomial algorithm for this scheduling problem. Computational results on randomly generated instances are reported.

IFAC Proceedings Volumes, 2011

The aim of this paper is to present a new heuristic for the resolution of the Cyclic Hoist Scheduling Problem (CHSP). It consists in determining a repetitive sequence of hoist moves that minimizes the duration time (called the cycle time). The obtained cyclic scheduling respects material as well as resource handling constraints. In this approach, time windows are maintained for all soaking operations and overlapping cycles are allowed in order to be as close as possible to optimality. Computational results, including comparison with existing algorithms are presented to show the efficiency of the proposed heuristic. To reduce the cycle time, we integrate in the general heuristic an algorithm with a set of Minimum Part Set (MPS) configurations'. This one allows us to find the best order in which jobs should be introduced into the line.

Operations Research Letters, 2006

We consider no-wait production processes, where identical products are processed sequentially on n machines and transported by programmable hoists. We present an O(n 5 ) algorithm that determines the minimum number of hoists required for all possible cycle-times; given the number of hoists, it also finds the minimum-time cyclic hoist-schedule.

On surface treatment lines, the products are transferred in successive tanks by a hoist. Moreover, each processing time is nested between a minimal and a maximal duration. This constraint is called the processing window constraint. An interesting problem is to find the hoist moves which maximise productivity. This paper deals with the production of identical parts in a balanced three-tank line. We prove that for zero-width or unbounded processing windows, production cycles of one or two parts are optimal.

IFAC Proceedings Volumes, 1997

In automated plating processes, hoists ensure the transfer of products between workstations. Scheduling their movements is known as the Hoisl Scheduling Problem (HSP). It belongs to the class of strongly NP•hard problems (Lei and Wang. 1989b). Many studies, dealing with different complexity levels of the problem have been published, and the following cl~sification should give the reader quite a large overview of them.

International Journal of Production Economics, 1994

Scheduling of automated material handling equipment is a commonly encountered problem in advanced manufacturing environments. It occurs whenever there is a choice as to the order in which robots can be dispatched to deliver jobs to various locations. In this paper, the manufacturing environment of interest is an automated electroplating system where hoists (robots) are used to move printed circuit boards (jobs) between tanks for treatment. Previous studies were restricted to the unidirectional transfer of jobs between tanks. However, when the manufacturing environment is constrained by floor space (a common situation in Hong Kong), hoists must be allowed to transfer jobs bidirectionally to minimize the number of identical tanks in the system. A visual simulation model was developed to assess the performance of three popular dispatching rules for the bidirectional multi-hoist production scheduling system. These three dispatching rules are (I) nearest robot first (NRF), (2) average robot assignment (ARA), and (3) boundary shift by job location (BSJL).

WIT Transactions on Information and Communication Technologies, 1970

The Hoist Scheduling Problem in electroplating facilities is known as an NP-Hard and strongly constrained problem. Up to now, the Operational Research approach appeared to be limited to the resolution of specific kinds of lines. We have proposed a new approach using the Constraint Logic Programming. In this paper we give a model for simple lines, aiming at providing the optimal solution for the 1-periodic problem, and that can easily be extended. Then we compare the performances of two kinds of solvers: PROLOG in that uses rational variables, and CHIP that uses finite domains. We finally give results for a benchmark example.

2019

Electroplating facilities often face the Cyclic Hoist Scheduling Problem when a repetitive sequence of moves is searched for the hoists. This paper addresses this optimization problem extended to the design of the workshop, where we aim to minimize both the cycle time and the number of hoists used. For this goal, we propose a genetic meta-heuristic approach which introduces a novel solution encoding to enlarge the solutions’ search space. Our encoding procedure is based on hoists’ empty moves, and includes separator characters. With the latter, we obtain solutions that were not reachable by previous approaches. Each solution obtained thanks to the genetic operators is evaluated by using a Mixed Integer Linear Program. This one checks the constraints of the problem (such as capacity constraints and soaking time bounds) and computes the smallest cycle time for a given moving sequence and its associated number of hoists. Some results are presented using benchmark instances for which ou...