Gerrit Hartmut Färber

Performance evaluation of hybrid-CLP vs. GA: non-permutation flowshop with constrained resequencing buffers

This paper is located in the area of mixed model non-permutation flowshop production lines where jobs of more than one model are being processed on the same production line in an arbitrary sequence. Nevertheless, the majority of publications in this area are limited to solutions which determine the job sequence before the jobs enters the line and maintains it without interchanging jobs until the end of the production line, which is known as permutation flowshop. The present work considers a non-permutation flowshop. Resequencing is permitted where stations have access to intermediate or centralised resequencing buffers. The access to the buffers is restricted by the number of available buffer places and the physical size of the products. The primary objective is the minimisation of the make span, but also setup-cost and setup-time is contemplated. A hybrid approach, using constraint logic programming (CLP), is presented and compared to a genetic algorithm (GA). These solution methods are conceptually different and recommendations for their applicability are presented.

Semi-dynamic Demand in a Non-permutation Flowshop with Constrained Resequencing Buffers

This work presents the performance comparison of two conceptually different approaches for a mixed model non-permutation flowshop production line. The demand is a semi-dynamic demand with a fixed job sequence for the first station. Resequencing is permitted where stations have access to intermediate or centralized resequencing buffers. The access to the buffers is restricted by the number of available buffer places and the physical size of the products. An exact approach, using Constraint Logic Programming (CLP), and a heuristic approach, a Genetic Algorithm (GA), were applied.

Performance study of a genetic algorithm for sequencing in mixed model non-permutation flowshops using constrained buffers

This paper presents the performance study of a Genetic Algorithm applied to a mixed model non-permutation flowshop production line. Resequencing is permitted where stations have access to intermittent or centralized resequencing buffers. The access to the buffers is restricted by the number of available buffer places and the physical size of the products. Characteristics such as the difference between the intermittent and the centralized case, the number of buffer places and the distribution of the buffer places are analyzed. Improvements that come with the introduction of constrained resequencing buffers are highlighted.

Wrist-position parameterization for fast on-line determination of grasp configurations

Abstract Determining the grasp optimal configuration of a mechanical hand is a computational hard work, mainly due to the large number of degrees of freedom (fingers and wrist) and possible solutions, and to the constraints imposed by the object. The paper presents an approach to reduce this problem under certain conditions. The configurations of the hand to grasp rectangular parallelepipeds of different sizes are determined off-line using an optimality criterion. The wrist positions of these configurations are approximated with functions of the size of the object “inside” the hand. These functions are stored to be used for a fast on-line computation of a real grasp configuration. The approach has been implemented and numerical examples are presented.