António Ferrolho

Single Machine Total Weighted Tardiness Problem with Genetic Algorithms

Genetic algorithms can provide good solutions for scheduling problems. In this paper we present a genetic algorithm to solve the single machine total weighted tardiness problem, a scheduling problem which is known to be NP-hard. First, we present a new concept of genetic operators for scheduling problems. Then, we present a developed software tool, called HybFlexGA, to examine the performance of various crossover and mutation operators by computing simulations of scheduling problems. Finally, the best genetic operators obtained from our computational tests are applied in the HybFlexGA. The computational results obtained with 40, 50 and 100 jobs show the good performance and the efficiency of the developed HybFlexGA.

Control and Scheduling in Flexible Manufacturing Cells

In this paper, we present a work on control and scheduling in flexible manufacturing cells (FMC). We developed an FMC with industrial characteristics, with the objective of studying the control and scheduling problems in these types of manufacturing systems. First, we developed several software and hardware to control the equipments used in the FMC. Second, we developed a software tool, called HybFlexGA, to study scheduling problems, with genetic algorithms (GA), in the FMC. Finally, we applied the HybFlexGA to solve scheduling problems in the FMC.

A Sensor Classification Strategy for Robotic Manipulators

In practice the robotic manipulators present some degree of unwanted vibrations. The advent of lightweight arm manipulators, mainly in the aerospace industry, where weight is an important issue, leads to the problem of intense vibrations. On the other hand, robots interacting with the environment often generate impacts that propagate through the mechanical structure and produce also vibrations. In order to analyze these phenomena a robot signal acquisition system was developed. The manipulator motion produces vibrations, either from the structural modes or from endeffector impacts. The instrumentation system acquires signals from several sensors that capture the joint positions, mass accelerations, forces and moments, and electrical currents in the motors. Afterwards, an analysis package, running off-line, reads the data recorded by the acquisition system and extracts the signal characteristics. Due to the multiplicity of sensors, the data obtained can be redundant because the same type of information may be seen by two or more sensors. Because of the price of the sensors, this aspect can be considered in order to reduce the cost of the system. On the other hand, the placement of the sensors is an important issue in order to obtain the suitable signals of the vibration phenomenon. Moreover, the study of these issues can help in the design optimization of the acquisition system. In this line of thought a sensor classification scheme is presented. Several authors have addressed the subject of the sensor classification scheme. White (White, 1987) presents a flexible and comprehensive categorizing scheme that is useful for describing and comparing sensors. The author organizes the sensors according to several aspects: measurands, technological aspects, detection means, conversion phenomena, sensor materials and fields of application. Michahelles and Schiele (Michahelles & Schiele, 2003) systematize the use of sensor technology. They identified several dimensions of sensing that represent the sensing goals for physical interaction. A conceptual framework is introduced that allows categorizing existing sensors and evaluates their utility in various applications. This framework not only guides application designers for choosing meaningful sensor 17

Flexible software for industrial robots

This paper describes flexible software for industrial robots. WinRS232ROBOTcontrol and winEthernetROBOTcontrol software were developed to be used in industrial robots. With this software, industrial robots can be integrated in modern production systems, in an easy and efficient way. A Robotic Bar and a Flexible Manufacturing Cell (FMC) were developed with the objective of showing the potentialities of the developed software.

Job shop scheduling problems with Genetic Algorithms

The Job-Shop Scheduling Problem (JSSP) is an extremely difficult problem because it requires very large combinational search space and the precedence constraint between machines. A software tool called Hybrid and Flexible Genetic Algorithm (HybFlexGA) was developed for solving the JSSP. Computational results demonstrate that the proposed HybFlexGA is very efficient and potentially useful in solving the JSSP. The results obtained with standard JSSP benchmark demonstrate its efficiency.

A Hybrid and Flexible Genetic Algorithm for the Job-Shop Scheduling Problem

A hybrid and flexible genetic algorithm (HybFlexGA) is presented for the job-shop scheduling problem (JSSP). The JSSP is one of the most difficult production scheduling problems in industry because it requires very large combinational search space and the precedence constraint between machines. The computational results on the well-known benchmark instances show the proposed HybFlexGA is very effective and competitive with other methods presented in the literature.