Multi-Attribute Task Sequencing Optimisation with Neighbourhoods for Robotic Systems

Modern manufacturing processes have to be continuously updated to catch up with fast-evolving requirements, as dictated my competitive and dynamic markets, which demand high product variety. Indeed, in the era of smart factories and cyber-physical production systems (CPPS) we are experiencing a fast transition from mass production to mass customisation. Key Enabling Technologies (KETs) are then necessary to hinge business and market needs on digital solutions which enable the rapid delivery of new and innovative products. If on one side mass customisation imposes high level of product variety, on the other hand customers wish to receive high quality products, which reflect the need for near-zero defects manufacturing systems. Therefore, the combination of macro-level changes (product variety) and micro-level variety (product defects) leads to the concept of self-evolving production systems, one of the KETs to enable CPPS. In this context, industrial robots play a key role to deploy automation and fast responsiveness. Currently, robots are programmed following off-line methods. Tough those methods are still a premium solution to model and simulate production systems, they suffer the capability to incorporate dynamic changes. Therefore, it is crucial to introduce the new concept of dynamic robot programming which enables real-time robot adjustments. Robot programming usually consists of four steps: (1) task planning; (2) task sequencing; (3) path planning and (4) motion planning. These steps are strictly coupled although robot trajectory is mainly affected by defined tasks. In literature, task sequencing is modelled as Travelling Salesman Problem with Neighbourhoods (TSPN). There exist several methods for solving TSPN, but no one enables the dynamic programming. This thesis aims to develop robot tasks sequencing methodology with the ultimate goal of finding the near-optimum task sequence, by minimising computational time to enable dynamic robot programming in the case of multiple and coupled tasks’ attributes. The thesis introduces two methodologies: (1) “Enhanced Heuristic with Hierarchical Clustering” (EH2C); and, (2) “Augmented-EH2C” (A-EH2C). EH2C is a general framework to solve TSPN-like problems. The method uses a novel approach which hinges on the key idea of pre-computed feasible robot poses based on analytical formulation of Euclidian weighted functions. Results and benchmarking studies have showed that this approach allows to reach a faster convergence rate, when compared to the top-1method available in the public domain. The EH2C methods has been then deployed to solve robotic task sequencing problem, with multiple attributes. This has led to the A-EH2C method, which introduces the concept of multi-attribute task sequencing, as a paradigm to solve coupled and hierarchical robotic task sequencing and path planning problems. The thesis poses the following contributions: (1) enhanced heuristic approach based on Euclidian distance to define the initial guess points for constructing tour in TSPN; (2) multi-attribute approach to find the optimised task sequencing via candidate poses solving inverse kinematics in T-space; (3) break-through paradigm shift from static robot path planning to dynamic robot path to enable on-the-fly robot re-programming to facilitate product and process adjustments. The proposed solutions have been tested in the context of automotive body assembly systems. However, results could impact a wider area, from navigation systems, game and graph theory, to autonomous systems

A graph-based approach and an interactive tool for preliminary digital prototyping

AbstractDesign process is usually based on past experiences and best practises which compose the company know-how. The challenge is to identify common patterns in the design solutions generated for different design problems. The present paper focuses on the identification of product patterns by using a graph-based approach. It deals with the designing of automotive gearboxes and with the development of an approach and a software tool aimed to support preliminary design and CAD modelling activities in gearbox designing. The approach is applied to two different architectures of manual transverse gearboxes characterized by two and three shafts. It aims at the identification of common design features through the detection of the directed graphs matching. A Matlab software tool for gearbox preliminary design is implemented according to the detected common features. The proposed approach and the developed software tool provide an effective way to keep and re-use company know-how, especially in the context of large automotive companies

A sensor data fusion-based locating method for large-scale metrology

The measurement of geometric and dimensional variations in the context of large-sized products is a complex operation. One of the most efficient ways to identify deviations is by comparing the nominal object with a digitalisation of the real object through a reverse engineering process. The accurate digitalisation of large geometric models usually requires multiple acquisitions from different acquiring locations; the acquired point clouds must then be correctly aligned in the 3D digital environment. The identification of the exact scanning location is crucial to correctly realign point clouds and generate an accurate 3D CAD model. To achieve this, an acquisition method based on the use of a handling device is proposed that enhances reverse engineering scanning systems and is able to self-locate. The present paper tackles the device’s locating problem by using sensor data fusion based on a Kalman filter. The method was firstsimulated in a MatLAB environment; a prototype was then designed and developed using low-cost hardware. Tests on the sensor data fusion have shown a locating accuracy better than that of each individual sensor. Despite the low-cost hardware, the results are encouraging and open to future improvements

A graph-based method and a software tool for interactive tolerance specification

Abstract The paper deals with the problem of tolerance specification and, in particular, proposes a graph-based method and a preliminary software tool: (i) to accomplish the tolerance specification for a mechanical assembly; (ii) to verify the consistency of the specification and, (iii) to allow the tracing of relationships among parts and features of the assembly. The method adopts Minimum Reference Geometric Elements (MRGE), directed graphs (di-graphs) and a set of dedicated algorithms to tackle the problems of consistency that occur during an interactive tolerance specification activity. Finally, an application illustrates the proposed method and its actual implementation

A knowledge-based approach to the layout optimization of human–robot collaborative workplace

AbstractHuman–robot collaboration (HRC) solutions are replacing classic industrial robot due to the possibility of realizing more flexible production systems. Collaborative robot systems, named cobot, can work side by side with humans combining their strengths. However, obtaining an efficient HRC is not trivial; indeed, the potential advantages of the collaborative robotics increase as complexity increases. In this context, the main challenge is to design the layout of collaborative workplaces facing the facility layout problem and ensuring the safety of the human being. To move through the high number of safety standards could be very tiring and unproductive. Therefore, in this work a list of key elements, linked to reference norms and production needs, characterizing the collaborative workplace has been identified. Then, a graph-based approach has been used in order to organize and easily manage this information. The management by means graphs has facilitated the implementation of the acquired knowledge in a code, developed in Matlab environment. This code aims to help the designer in the layout organization of human–robot collaborative workplaces in standards compliance. The paper presents the optimization code, named Smart Positioner, and the operation is explained through a workflow diagram

A Functional Classification of Text Annotations for Engineering Design

Describing and supplementing geometric shapes (parts) and layouts (assemblies) with relevant information is key for successful product design communication. 3D annotation tools are widely available in commercial systems, but they are generally used in the same manner as 2D annotations in traditional engineering drawings. The gap between technology and practices is particularly evident in plain text annotations. In this paper, we introduce a functional classification of text annotations to provide an information framework for shifting traditional annotation practices towards the Model-Based Definition (MBD) paradigm. In our view, the current classification of dimensions, tolerances, symbols, notes, and text does not stress the inherent properties of two broader categories: symbols and text. Symbol-based annotations use a symbolic language (mostly standardized) such as Geometric Dimensioning and Tolerancing (GD&T) to provide precise information about the implications of geometric imperfections in manufacturing, whereas notes and text are based on non-standardized and unstructured plain text, and can be used to convey design information. We advocate that text annotations can be characterized in four different functional types (objectives, requirements, rationale, and intent), which should be classified as such when annotations are added to a model. The identification and definition of a formalized structure and syntax can enable the management of the annotations as separate entities, thus leveraging their individual features, or as a group to gain a global and collective view of the design problem. The proposed classification was tested with a group of users in a redesign task that involved a series of geometric changes to an annotated assembly model

Scaling behaviour of braided active channels: a Taylor’s power law approach

none9At a channel (reach) scale, braided channels are fluvial, geomorphological, complex systems that are characterized by a shift of bars during flood events. In such events water flows are channeled in multiple and mobile channels across a gravel floodplain that remain in unmodified conditions. From a geometrical point of view, braided patterns of the active hydraulic channels are characterized by multicursal nature with structures that are spatially developed by either simple- and multi-scaling behavior. Since current studies do not take into account a general procedure concerning scale measurements, the latter behavior is still not well understood. The aim of our investigation is to analyze directly, through a general procedure, the scaling behavior of hydraulically active channels per transect and per reach analyzed. Our generalized stochastic approach is based on Taylor’s law, and the theory of exponential dispersion distributions. In particular, we make use of a power law, based on the variance and mean of the active channel fluctuations. In this way we demonstrate that the number of such fluctuations with respect to the unicursal behavior of the braided rivers, follows a jump-process of Poisson and compound Poisson–Gamma distributions. Furthermore, a correlation is also provided between the scaling fractal exponents obtained by Taylor’s law and the Hurst exponents.Samuele De Bartolo, Stefano Rizzello, Ennio Ferrari, Ferdinando Frega, Gaetano Napoli, Raffaele Vitolo, Michele Scaraggi, Carmine Fallico, Gerardo SeverinoDE BARTOLO, Samuele; Rizzello, Stefano; Ferrari, Ennio; Frega, Ferdinando; Napoli, Gaetano; Vitolo, Raffaele; Scaraggi, Michele; Fallico, Carmine; Severino, Gerard

Mobile Robots and Cobots Integration: A Preliminary Design of a Mechatronic Interface by Using MBSE Approach

Enabling technologies that drive Industry 4.0 and smart factories are pushing in new equipment and system development also to prevent human workers from repetitive and non-ergonomic tasks inside manufacturing plants. One of these tasks is the order-picking which consists in collecting parts from the warehouse and distributing them among the workstations and vice-versa. That task can be completely performed by a Mobile Manipulator that is composed by an industrial manipulator assembled on a Mobile Robot. Although the Mobile Manipulators implementation brings advantages to industrial applications, they are still not widely used due to the lack of dedicated standards on control and safety. Furthermore, there are few integrated solutions and no specific or reference point allowing the safe integration of mobile robots and cobots (already owned by company). This work faces the integration of a generic mobile robot and collaborative robot selected from an identified set of both systems. The paper presents a safe and flexible mechatronic interface developed by using MBSE principles, multi-domain modeling, and adopting preliminary assumptions on the hardware and software synchronization level of both involved systems. The interface enables the re-using of owned robot systems differently from their native tasks. Furthermore, it provides an additional and redundant safety level by enabling power and force limiting both during cobot positioning and control system faulting

A Graph-based Software Tool for the CAD Modeling of Mechanical Assemblies

The challenge of reducing designing time for new mechanical assemblies, especially in the context of large companies, encourages the use of methods and tools aimed to support designing activities and to re-use the company know-how. Furthermore, the design choices must be rapidly check to avoid errors that could cause delay or expensive re-designing. In such a context, the graph theory and related algorithms could be used to define a transfer function, easily to implement, that governs a software tool able to support the designing activities. Therefore, the paper presents a designing approach, based on the graph theory, aimed to generate the geometric modeling of mechanical assemblies. The approach and the software tool are useful both for designer and companies that want to customize and improve such activities. Finally, the paper shows the case study related to the design of a transversal manual gearbox and the generation of a GUI, developed in MatLAB® environment, to validate the approach

Systems and Requirements Engineering: An Approach and a Software Tool for the Interactive and Consistent Functional Requirement Specification

Managing the complexity of modern systems is a current challenge involving all the phases of a system development process. Complex systems also mean a great number of stakeholders involved and just as many needs to satisfy. In the Systems Engineering approach for complex systems design, Requirements Engineering provides methods to collect stakeholders needs and to translate them into system requirements. Furthermore, several tools currently allow creating requirements repository and manage their properties and changes. Traceability is also implemented to verify design against requirements. Although there are several standards and guidelines which provide criteria and rules for writing requirement statements, it is still missed a process that drives the user in the correct requirement construction. The present paper faces the requirement specification process in order to provide tools that can support and drive designers in the requirements writing. In particular, the paper (i) provides a framework for writing syntactically correct requirements that can be early verified against pre-defined criteria such as clarity, singularity, conformity, and descriptiveness; (ii) presents a software tool for creating well-defined requirements statements offering the user the possibility to formulate “correct requirements by construction”. The driven definition of system requirements leads to a well-defined specification, thus allowing time and efforts reduction during the following steps of system development process