Absalom: Balancing assembly lines with assignment restrictions

Assembly line balancing problems (ALBPs) arise whenever an assembly line is configured, redesigned or adjusted. An ALBP consists of distributing the total workload for manufacturing products among the work stations along the line. On the one hand, research has focussed on developing effective and fast solution methods for exactly solving the simple assembly line balancing problem (SALBP). On the other hand, a number of real-world extensions of SALBP have been introduced but solved with straightforward and simple heuristics in many cases. Therefore, there is a lack of procedures for exactly solving such generalized ALBP. In this paper, we show how to extend the well-known solution procedure SALOME (INFORMS J. Computing 9, 319-334), which is able to solve even large SALBP instances in a very effective manner, to a problem extension with different types of assignment restrictions (called AR-ALBP). The extended procedure is given the acronym ABSALOM. It consists of a favourable branching scheme, an arsenal of bounding rules and a variety of logical tests using ideas from constraint programming. Computational experiments show that ABSALOM is a very promising exact solution approach though the additional assignment restrictions complicate the problem and require some components of SALOME to be modified in a relaxing manner.