José Soeiro Ferreira

Algorithms for Nesting Problems

The Nesting Problem naturally appears in the context of several production processes, as in the textile, wood or steel industries, whenever is necessary to cut pieces with irregular (non-rectangular) shapes from larger plates. This problem belongs to the more generic class of Cutting and Packing problems.

A simulation analysis of sequencing rules in a flexible flowline

Abstract The paper concerns a flexible flowline scheduling problem, which arises in the footwear industry. Flexibility of the line allows for manufacturing simultaneously more products in lower quantities, but it also increases the complexity of the task of balancing the line, specially because the mix of products changes everyday. A simulation model to deal with the flexible line is developed and several job sequencing rules and different part input criteria are implemented. The impact of each rule on the quality of the schedules is measured, namely, according to makespan, productivity and average machine utilisation. Computational results concerning a real application are also presented. SIMPLE++ is the simulation language used.

A New Upper Bound for the Cylinder Packing Problem

This paper introduces a new upper bound to the problem of fitting identical circles into a rectangle. This problem is usually referred to as the ‘cylinder packing problem’ or ‘cylinder palletization’. In practice, it arises when it is desired to maximize the number of cylindrical items packed in an upright position onto a rectangle/pallet. The upper bound developed consists in determining the reduced pallet area by deducting a lower bound for the unused pallet area from the total area of the pallet. The upper bound for the number of identical circles to pack into the pallet is computed by the ratio reduced pallet area/circle area. The results obtained for five distinct sets of problems are analyzed and compared with previous bounds found in the published literature.

Lot sizing algorithms with applications to engineering and economics

This paper presents two new solution procedures for a deterministic lot size problem, a matrix algorithm and a heuristic matrix method. The algorithm is based on the dual of a linear programming model formulation of the lot size problem, and it provides optimal solutions even in the general case of time-varying parameters. A comparison of the efficiency of the new solution procedures with well-known methods is developed. New applications of the techniques described within the fields of engineering (optimal design of a pump-pipe system) and economics (a model for import-planning) are referred to.

Optimization of a pump-pipe system by dynamic programming

In this paper the problem of minimizing the total cost of a pump-pipe system in series is considered. The route of the pipeline and the number of pumping stations are known. The optimization will then consist in determining the control variables, diameter and thickness of the pipe and the size of the pumps. A general mathematical model is formulated and Dynamic Programming is used to find an optimal solution. Practical reasons, derived from the techniques engineers generally use to cope with such problems, and special characteristics of the mathematical structure of the model justified the consideration of particular cases of the system. This analysis, based on Dynamic Programming, enabled us to elaborate a simple heuristic method, condensing those techniques, and supplied sufficient conditions for the heuristic to operate as an optimal procedure. The solution of a realistic example confirms the viability of the conditions developed and tests the formulation (also presented) of the optimization problem by...

Waste collection routing-limited multiple landfills and heterogeneous fleet

This article deals with a real-life waste collection routing problem. To efficiently plan waste collection, large municipalities may be partitioned into convenient sectors and only then can routing problems be solved in each sector. Three diverse situations are described, resulting in three different new models. In the first situation, there is a single point of waste disposal from where the vehicles depart and to where they return. The vehicle fleet comprises three types of collection vehicles. In the second, the garage does not match any of the points of disposal. The vehicle is unique and the points of disposal landfills or transfer stations may have limitations in terms of the number of visits per day. In the third situation, disposal points are multiple they do not coincide with the garage, they are limited in the number of visits, and the fleet is composed of two types of vehicles. Computational results based not only on instances adapted from the literature but also on real cases are presented and analyzed. In particular, the results also show the effectiveness of combining sectorization and routing to solve waste collection problems.

Measures in Sectorization Problems

Sectorization means dividing a whole into parts (sectors), a procedure that occurs in many contexts and applications, usually to achieve some goal or to facilitate an activity. The objective may be a better organization or simplification of a large problem into smaller sub-problems. Examples of applications are political districting and sales territory division. When designing/comparing sectors some characteristics such as contiguity, equilibrium and compactness are usually considered. This paper presents and describes new generic measures and proposes a new measure, desirability, connected with the idea of preference.

FAFNER-accelerating nesting problems with FPGAs

The nesting problem consists of defining the cutting plan of a piece of raw material in smaller irregular shapes, and has applications in the apparel and footwear industries. Due to its NP-hard nature, the optimal solution can only be guaranteed by exhaustively trying all possible solutions and choosing the best one. Because this is impractical in real-life industrial problems, automatic approaches are based on optimization meta-heuristics that search for sub-optimal but good enough solutions. These optimization techniques rely on the construction and evaluation of several solutions, thus requiring heavy geometric manipulation of the irregular polygons that constitute the problem data. Efficient processing of this geometric information is thus necessary to make effective fully automatic approaches to nesting problems in industrial environments. This paper describes FAFNER, an FPGA-based custom computing machine that is used to accelerate the geometric operations, that are in the core of heuristic solutions to the nesting problem. The system is used as an auxiliary processor attached to a low cost personal computer, and combines a custom programmable processor with an array of custom circuits for the processing of irregular polygons.

Flexible hardware acceleration for nesting problems

The nesting (or placement) problem is an NP-hard combinatorial problem with important industrial applications, e.g. in apparel or footwear industry. This paper describes a hardware infrastructure to accelerate the processing of the underlying geometric information. The system consists of an FPGA-based reconfigurable platform enhanced by an ASIC for the processing of irregular polygons. The paper discusses the need for such a platform, establishes the main design guidelines and describes the architecture and modes of operation of both the reconfigurable infrastructure and the dedicated IC.

Balancing mixed-model assembly systems in the footwear industry with a variable neighbourhood descent method

Abstract This paper addresses new Mixed-model Assembly Line Balancing Problems (MALBP) in a real industrial context, the stitching systems of a footwear company. The work is part of large ongoing projects with this industry, and the main purposes are minimising the number of required workstations and smoothing the operators’ workload. The company has invested in new flexible automated assembly systems, which accommodate dozens of workstations and many moving boxes. Footwear components are inside boxes (with various quantities) which can move from the warehouses to a convenient workstation or between any workstations (in any order). This is a significant and distinct feature of the MALBP, together with the fact that the assignment of different skilled operators and machines is achieved simultaneously. An optimisation model is developed, in part to facilitate the understanding of the situation and to solve small-size instances. Due to the complexity of the problems, we had to devise an approximate method, based on the Variable Neighbourhood Descent (VND) metaheuristic and integrating an adaptation of the Ranked Positional Weighted (RPW) method. The adapted RPW method is used to create initial feasible solutions, while preassigning special operators and machines. After choosing good initial solutions, VND is applied to improve their quality. The new contributed method, named as RPW-VNDbal, is tested with medium and large instances, in two distinct stitching systems. A Lower Bound of the objective function and Simulation contribute to evaluate the solutions and their practicability. The results implemented by the project team, show that the RPW-VNDbal method is fast enough and offers better solutions than those implemented by the experienced operation managers of the company.