Mozafar Saadat

Industrial applications of automatic manipulation of flexible materials

Flexible materials are used extensively in a wide range of industrial applications including the manufacture and assembly of garment and footwear products, the packaging industry and aircraft manufacturing. These applications are often extremely labour intensive requiring fast and accurate manipulation of materials by skilled human operators. This has resulted in numerous international research and development efforts to automate certain handling and manipulation processes involving flexible materials. Much of the research has been inspired by real industrial problems, and thus has been mainly sponsored by industry. A variety of innovative techniques and methods have emerged either addressing specific industrial problems, or suggesting a number of generic solutions. This paper closely examines the international research effort of automatic manipulation of flexible materials through a classification of workpieces in terms of their broad geometric shape, industrial applications, and individual processes.

Dimensional variations during Airbus wing assembly

The introduction of automation for the assembly of aircraft wing box structures will require individual components to conform closely to the CAD design specification with regard to shape geometry and dimensional tolerances. Often, due to a variety of previous manufacturing processes, the 3D shape of these large components lose the accuracy of their designed dimensional specifications. Under these circumstances part‐to‐part assembly becomes tedious and it would be impossible to rely on robots to achieve precise assembly in an automated system. For this reason, variations need to be accurately quantified in order to provide a reliable prediction model in aid of any future automated assembly. This paper describes the measurement method used to record the possible variations occurring during the assembly process. The measurements were made using a laser tracker where the results are expected to offer some explanations as to the causes of the variation. The suitability of a laser tracker in a large assembly jig environment is then assessed. This study is based on the work that was carried out at BAE Systems UK, where the Airbus commercial aircraft wings are manufactured.

Prediction of geometrical variations in Airbus wingbox assembly

Purpose – This paper aims to present a method for predicting dimensional variation in assembly processes of a wingbox structure concentrating on the assembly of skin panels to rib feet.Design/methodology/approach – Finite element modelling and experimental tests are conducted on the rib structure based on the site measurement gathered from the Airbus assembly factory.Findings – The results have shown that the simulated model has the capability of predicting to an acceptable degree of accuracy the overall geometrical variations of the ribs and skin panels, as well as the positional variations of each individual rib foot.Originality/value – The authors believe that no previous research has offered a similar prediction method for large aerostructures.

A New Agents-Based Model for Dynamic Job Allocation in Manufacturing Shopfloors

Market-based mechanisms such as the contract net protocol (CNP) are very popular for dynamic job allocation in distributed manufacturing control and scheduling. The CNP can be deployed with different configurations of the system elements. Every configuration corresponds to a basic or a hybrid topology. The subject of topology is generally discussed in the field of “distributed systems.” Inspired from the notion of topology in the distributed systems, this paper proposes a ring-like model as a competitor for the web-like CNP-based job allocation within the concept of holonic manufacturing systems. Details of the algorithm for scheduling and assignment of jobs to resources in the ring structure is presented and its performance is compared with both CNP-based distributed model, and the centralized conventional scheduling of a real manufacturing case study involving a major turbine production plant. Comparison of performance indicators such as time and cost of operations shows that the distributed models clearly outperform the conventional practice with meaningful impact on the production economy. As a possible implementation strategy, a hybrid switching model, composed of both competing models, is proposed.

ANALYSIS OF THE DISC DRESSING EFFECTS ON GRINDING PERFORMANCE-PART 1. SIMULATION OF THE DISC DRESSED WHEEL SURFACE

This article is in two parts describing the analysis and simulation of the disc dressing process and its effect on grinding performance. This part is concerned with the generation of the wheel surface by a diamond disc dresser. A new stochastic model of the prediction of wheel topography by diamond disc dresser is developed. It predicts the number of active grains per unit area and average slope of grains of the alumina grinding wheel. This model is based on the fracture of grits and it considers the kinematical influences of the disc dressing process on wheel surface. It is possible to analyze the effects of changing dressing parameters on the wheel topography. The topography that is generated from this model provides a basis for further prediction of the grinding performance.

Management of sustainable manufacturing systems-a review on mathematical problems

The ever-growing awareness of environmental protection has significantly influenced the method of manufacturing products. Due to the introduction of new processes, the management of sustainable manufacturing shows different characteristics to those of traditional systems. Sustainable manufacturing systems have attracted a great deal of attention in the past 20 years as an emerging manufacturing approach. Particularly in the last 10 years, the number of papers focusing on the topic of sustainable manufacturing systems’ management has increased rapidly. More and more practical factors have been considered and integrated into this area which makes it more complex, but closer to reality. This paper aims to classify the mathematical problems dealing with the management of sustainable manufacturing systems. More than 100 related papers mainly from 1994 to 2015 have been selected and reviewed and divided into three categories according to the main elements in a manufacturing system: production planning and control, inventory management and control and manufacturing network design. The development of each category is summarised and the corresponding mathematical problems are discussed to provide a general overview of the relevant research fields and identify future research directions.

Agent-Based Interaction Protocols and Topologies for Manufacturing Task Allocation

This paper focuses on interaction protocols and topologies of multiagent systems (MASs) for task allocation, particularly in manufacturing application. Resource agents in manufacturing are members of a network whose possible logical topologies and governing interaction protocol influence the scheduling and control in the MAS. Four models are presented in this paper, each having specific rules and characteristics for scheduling and task allocation. Two models out of the four use a well-known standard interaction method [contract-net protocol (CNP)], while the others are proposed in this paper. The newly proposed models are based on ring topology and algorithms developed in the research. A Java-based MAS was also developed to simulate different scenarios of task allocation and to compare the four models in terms of some scheduling performance indicators, using cases from manufacturing. The results produced meaningful differences between the four models, including their strengths and weaknesses. Two models, namely, modified ring and CNP-based peer-to-peer, gave superior performance compared with the others. Furthermore, the proposed modified ring exhibits significant potential in handling manufacturing task allocation applications.

Hysteresis-observer based robust tracking control of piezoelectric actuators

In this paper, a robust control approach using a novel hysteresis observer is developed for precise tracking control of piezoelectric actuators (PEAs). The proposed control methodology considers the problems of unknown or uncertain system parameters, hysteresis nonlinearity and external load disturbances. For representing the behavior of a PEA, Bouc-Wen hysteresis model is integrated with a second-order linear dynamics. It is shown that the nonlinear response of the model due to the hysteresis effect, acts as a bounded disturbance. Based on this fact a hysteresis observer is proposed to estimate the hysteresis effect. Then for real-time compensation of the observer error, parametric uncertainties and external disturbances, the sliding mode control strategy with a perturbation estimation function is utilized. By using the proposed control approach the asymptotical stability in displacement tracking and robustness to the dynamic load disturbances can be provided. Finally, experimental results are illustrated to verify the efficiency of the proposed method for practical applications.

ANALYSIS OF THE DISC DRESSING EFFECTS ON GRINDING PERFORMANCE—PART 2: EFFECTS OF THE WHEEL TOPOGRAPHICAL PARAMETERS ON THE SPECIFIC ENERGY AND WORKPIECE SURFACE ROUGHNESS

This article is the second of two parts which analyze and simulate the disc dressing process and its effect on grinding performance. In the first part a new stochastic model of the prediction of wheel topography by diamond disc dresser was developed. It predicted the number of active cutting points per unit area and average slope of the asperities on an alumina grinding wheel. In the second part the effects of a disc dressing parameter which affect the wheel topography, specific energy, and workpiece surface roughness are evaluated. An upper bound analysis of a pyramidal indenter which moves on the workpiece is used for evaluation of the specific energy and modification of the grain tip. Modified grain tip was then used to predict the surface roughness of the ground workpiece. Dressing conditions with various speed ratios, cross feed rates and depths of dressing were investigated. In each case, the grinding forces and the surface roughness were experimentally measured, and then the effect of changing dressing parameters on the grinding performance was analyzed.

Path planning of the hybrid parallel robot for ankle rehabilitation

This paper presents a new configuration for ankle rehabilitation using a 9-DOF (degree of freedom) hybrid parallel robot. The robot contains nine linear actuators serially connecting two movable platforms and one stationary platform. The optimization is based on the singularity and dynamic analysis of the robot. The obtained data of the ankle motions from a series of experiments were applied to the model in order to investigate the motion of the end-effector and the force required for each actuator in a particular path. The end-effector tracking simulation results validated the proposed theoretical analysis of the required rehabilitation path of the foot.