A Robust Scheduling Approach for a Single Machine to Optimize a Risk Measure

Robustness in scheduling addresses the capability of devising schedules which are not sensitive – to a certain extent – to the disruptive effects of unexpected events. The paper presents a novel approach for protecting the quality of a schedule by taking into account the rare occurrence of very unfavourable events causing heavy losses. This calls for assessing the risk associated to the different scheduling decisions. In this paper we consider a stochastic scheduling problem with a set of jobs to be sequenced on a single machine. The release dates and processing times of the jobs are generally distributed independent random variables, while the due dates are deterministic. We present a branch-and-bound approach to minimize the Value-at-Risk of the distribution of the maximum lateness and demonstrate the viability of the approach through a series of computational experiments

Switching- and hedging- point policy for preventive maintenance with degrading machines: application to a two-machine line

Maintenance and production are frequently managed as separate activities although they do interact. Disruptive events such as machine failures may find the company unready to repair the machine immediately leading to time waste. Preventive Maintenance may be carried out and maintenance time reduced to the effective task duration, in order to prevent time waste. Companies and researchers have been focusing on policies able to mitigate the impact of Preventive Maintenance on system availability, by exploiting the knowledge about degradation profiles in machines and the joint information from the machine state and the buffer level. In this work, the mathematical proof of the optimal threshold-based control policy for Preventive Maintenance with inventory cost, maintenance cost, backlog cost is provided. The control policy is defined in terms of buffer thresholds and dependency of the thresholds on the degradation condition. The optimal control policy is proved to include a combination of switching points and hedging points, where the first ones activate the Preventive Maintenance for a given condition and the latter ones control the production rate in order to minimize the surplus. An extensive experimental campaign analyzes the impact of system parameters such as the Maintenance duration on the cost function. The results show that there exists cases in which the optimal policy is dominated by the effect of the hedging points or the switching points, alternatively. Therefore, the proposed method is used to provide suggestions to the management for operative decisions, in order to choose the policy fitting best the system

De-manufacturing systems

open3noDe-Manufacturing Systems allow implementing optimized End-Of-Life strategies and are necessary to support a sustainable and competitive Manufacturing/De-Manufacturing integrated paradigm. However, available technologies, management methods and business models present several limitations that make landfill and, at a lower extent, materials recycling, the most diffused End-Of-Life practices. To overcome these limitations, this paper proposes an integrated multi-disciplinary research framework addressing single technologies improvement, system integration and business model coherency. The main challenges and research opportunities are presented that can boost the development of sustainable De-manufacturing Systems at industrial level.Colledani, Marcello; Copani, Giacomo; Tolio, TullioColledani, Marcello; Copani, Giacomo; Tolio, TULLIO ANTONIO MARI

An automated approach to reuse machining knowledge through 3D – CNN based classification of voxelized geometric features

The enhanced digitalization in the manufacturing sector is claimed to facilitate the generation or the use of the existing process data incorporating the production variations and offers a significant increase in the productivity and efficiency of a system. Moreover, manufacturing companies possess substantial knowledge while designing a product and manufacturing procedures. The primary requirement is to link and organize all the information sources related to the operation design and production. This research is concerned with the reuse of machining knowledge for existing and new parts having similarities in geometric features and operational conditions. The proposed methodology starts by extracting each machining operation's geometric information and cutting parameters using industrial part programs in the numerical control (NC) simulator VERICUT. The removed material between two consecutive operations is obtained through mesh comparison in the simulator to analyze the feature interactions. A deep learning approach based on 3D convolutional neural networks (CNN) is applied to classify similar geometries to reuse the process design knowledge by creating a library of operations. The proposed approach is implemented on actual machining data, and the results demonstrate the effectiveness of the proposed solution. The obtained knowledge clusters in the operations library assist in making propositions related to operational parameters for similar geometric features during the process planning phase reducing the planning and designing time of operations

Monitoring of long-term tolerance of European ash to Hymenoscyphus fraxineus in clonal seed orchards in Sweden

The invasive alien pathogenic fungus Hymenoscyphus fraxineus causing ash dieback (ADB) has devastated European ash (Fraxinus excelsior) populations across Europe. Breeding for resistance is the most feasible measure to reduce future losses of ash, and the presence of resistance, albeit at low level, has been demonstrated in numerous genetic trials around Europe. This study is a continuation of the inventories tracking the vitality status of different clones, which started in 2006 at two ash seed orchards in southern Sweden. A new inventory conducted in the summer of 2021 revealed that the ten clones previously identified as the most tolerant to ADB based on periodic surveys from 2006 and onwards still remain the most tolerant, while susceptible clones continued to decline and are completely disappearing from the orchards. Browsing caused mortality in some of the most tolerant clones in one of the orchards during the last assessment period. Despite the animal damage, the stable resistance observed in tolerant clones over a 15 years period forms a solid basis for the continuation of the breeding programme where good candidates are selected for further study

Standardizing the Process Information for Machining Operations Through Self-Contained Structures

A mechanical product is manufactured through multiple processes and procedures. The process information is coded in a part program, and a large amount of unstructured information comes from the shop floor. This results in the loss of logic formulated for the creation of a code. Moreover, it is impossible to track the modifications carried out during these processes. Thus, the unavailability of appropriate and standard knowledge of part processing leads to the situation where the information must be recreated every time a similar part is manufactured, hence, increasing the process planning time. One solution is to divide it into two steps: first, by fetching the information and coding it in a standardized structure; second saving it in a suitable form, facilitating in improving the efficiency and effectiveness of process design for available parts as well as anticipating the new parts. This was achieved by using the previous information related to the process combined with the one obtained from the shop floor. The proposed work concerns capturing the unstructured information from the existing part programs and regaining it using process simulation (VERICUT). Through the extraction of theoretical and graphical geometric data, the interactions between the operations were analyzed. The operational knowledge in this work includes: origin, feed-rate, rotating speed of the tool, rapid movement, cutting tool, material knowledge, and some geometric information of the process. The proposed approach based on simulations and mathematical programming logic is a way to improve flexibility at process and system level by formalizing the available operational knowledge. To illustrate the applicability of the proposed approach, a case study was carried out on a real industrial part program

Multi-robot spot-welding cells: An integrated approach to cell design and motion planning

The necessity to manage several vehicle models on the same robotized assembly cell has made the cell design and the robot off-line motion planning two fundamental activities. Industrial practice and state-of-the-art methods focus on the technical issues of each activity, but no integrated approach has been yet proposed, resulting in a lack of optimality for the final cell configuration. The paper introduces a formalization of the whole process and proposes a heuristic multi-stage method for the identification of the optimal combination of cell design choices and motion planning. The proposed architecture is depicted through a real case for welding application

Multi-robot spot-welding cell design: Problem formalization and proposed architecture

The multi-robot cell design for car-body spot welding is faced by industry as a sequence of tasks, where researches are focused on issues of the problem as a whole. In authors’ knowledge, none work in literature have suggested any formalization for the complete process. This paper tries to bridges the gap proposing coherent process formalization, and presenting a corresponding innovative architecture for the automatic optimal cell design. Specifically, the formalization involves the identification and allocation of the resources in terms of a set of decisional variables (e.g. robot model/positioning/number, welding gun models/allocation/number, welding point allocation etc.); then, the design optimization process minimizes the investment costs granting the cycle time. The multi-loop optimization architecture integrates both new algorithms and existent procedures from different fields. Test-bed showing its feasibility is reported