Stefania Pellegrinelli

Network part program approach based on the STEP-NC data structure for the machining of multiple fixture pallets

The adoption of alternative process plans, that is, process plans that include alternative ways of machining a workpiece, can improve system performance through a better management of resource availability. Unfortunately even if this opportunity is deeply analysed in literature, it is not frequently adopted in real manufacturing practice. In order to fill this gap, this article presents the network part program (NPP) approach for the machining of multiple fixture pallets. The NPP approach is based on the STEP-NC data structure which supports nonlinear sequences of operations and process flexibility. In the NPP approach, a machining system supervisor defines the machining sequences and generates the related part programs just before the execution of the pallet. This article provides an approach with high scientific value and industrial applicability based on the integration of new and existing process planning methods. A real industrial case study is considered in order to show that in real applications the final quality is unaffected by the change of the sequence of the operations due to the employment of nonlinear process plans. Since the results appear very encouraging, the proposed approach is a possible solution to accelerate the adoption of nonlinear process planning in real manufacturing practice.

Holistic Approach for Jointly Designing Dematerialized Machine Tools and Production Systems Enabling Flexibility-Oriented Business Models

Machine tools and production systems are traditionally designed in two separate stages, thus severely penalize the possibility to match customer production requirements. This work introduces the concept of dematerialization for machine tools and systems whose design principles answer to energy savings and cutting edge performance requirements across their lifecycles. The proposed approach consists of four main steps: new business total-life cycle services, design of dematerialized machine tools, process planning and configuration of production system solutions. The benefits coming from the adoption of machine and system dematerialization strategy have been addressed with reference to an industrial case study.

Human-robot shared workspace collaboration via hindsight optimization

Our human-robot collaboration research aims to improve the fluency and efficiency of interactions between humans and robots when executing a set of tasks in a shared workspace. During human-robot collaboration, a robot and a user must often complete a disjoint set of tasks that use an overlapping set of objects, without using the same object simultaneously. A key challenge is deciding what task the robot should perform next in order to facilitate fluent and efficient collaboration. Most prior work does so by first predicting the humans intended goal, and then selecting actions given that goal. However, it is often difficult, and sometimes impossible, to infer the humans exact goal in real time, and this serial predict-then-act method is not adaptive to changes in human goals. In this paper, we present a system for inferring a probability distribution over human goals, and producing assistance actions given that distribution in real time. The aim is to minimize the disruption caused by the nature of human-robot shared workspace. We extend recent work utilizing Partially Observable Markov Decision Processes (POMDPs) for shared autonomy in order to provide assistance without knowing the exact goal. We evaluate our system in a study with 28 participants, and show that our POMDP model outperforms state of the art predict-then-act models by producing fewer human-robot collisions and less human idling time.

Energy-efficient distributed part programme for highly automated production systems

Distributed part programmes (PPs) across the shop-floor resources have been identified as a possible enabler of production flexibility, while the energy assessment has been recognised as a relevant factor for the global sustainability. This article proposes a distributed PP approach, identified as network part programme (NPP), while addressing the minimisation of system energy consumption. The approach, called energy-based NPP, is based on two mathematical models. The first model generates a number of alternative pallet configurations according to the minimisation of workpiece set-ups and energy consumption. The second model grants the energy consumption threshold at system level through the selection of previously-generated and alternative workplans. The application of the approach on a real case shows a reduction of the energy consumption, the respect of the system energy consumption threshold and a substantial improvement in operational costs compared to traditional workplan design methods.

Integrated Approach for Multi-Robot Spot-Welding Cell Design and Welding-Point Allocation

The design of multi-robot cells for spot welding strictly influences the feasibility and complexity of the multi-robot motion planning. In comparison to existing literature, the proposed approach simultaneously addresses: (i) the design of multi-robot cells for spot welding; (ii) the allocation of the welding points to the robots on the basis of required cell cycle time. First, the algorithm selects one robot model and one robot fixturing structure. Second, the approach identifies free trajectories among welding points for each couple gun/position of the robot in the fixturing structure through probabilistic roadmaps (PRMs). Third, on the basis of the previous results, an innovative mathematical model selects and allocates the resources taking into account cell investment costs. Finally, the solutions that differ on robot model and robot fixturing structure are compared and the best solution is selected. A test case is provided to show the applicability of the approach.

Shared autonomy via hindsight optimization for teleoperation and teaming

In shared autonomy, a user and autonomous system work together to achieve shared goals. To collaborate effectively, the autonomous system must know the user’s goal. As such, most prior works follow a predict-then-act model, first predicting the user’s goal with high confidence, then assisting given that goal. Unfortunately, confidently predicting the user’s goal may not be possible until they have nearly achieved it, causing predict-then-act methods to provide little assistance. However, the system can often provide useful assistance even when confidence for any single goal is low (e.g. move towards multiple goals). In this work, we formalize this insight by modeling shared autonomy as a partially observable Markov decision process (POMDP), providing assistance that minimizes the expected cost-to-go with an unknown goal. As solving this POMDP optimally is intractable, we use hindsight optimization to approximate. We apply our framework to both shared-control teleoperation and human–robot teaming. Compared with predict-then-act methods, our method achieves goals faster, requires less user input, decreases user idling time, and results in fewer user–robot collisions.

An integrated framework for combined designing dematerialised machine tools and production systems enabling flexibility-oriented business models

The current work outlines an innovative production system design and management approach based on the concept of dematerialisation whose major purpose is to reduce the amount of material, energy and degrees of flexibilities of machine tools and systems to the minimum requirements based on the user needs. The successful introduction of this new generation of Dematerialised Machines and Systems relies on a structured design framework. It starts from an accurate identification of the business models driving the company strategy and the identification of specific markets where the dematerialisation principle is a winning leverage to compete. Based on the analysis of production demand and the reference market context, the framework presents a set of methodologies related to the pallet configuration and process planning, the machine tool configuration and the system configuration, all nested together. The benefits of the Dematerialisation framework will be investigated with regard to a set of benchmarks coming from the industrial practice.

Design and motion planning of body-in-white assembly cells

This paper proposes a method for the automatic and simultaneous identification of the body-in-white assembly cell design and motion plan. The method solution is based on an iterative algorithm that looks for a global optimum by iteratively identifying the optimum of three sub-problems. These sub-problems concern system layout design and motion planning for single and multi-robot systems, while collision detection is addressed. The sub-problems are handled through ad-hoc developed Mixed Integer Programming (MIP) models. The proposed solution overcomes the limitations of the current design and motion plan approaches. In fact, the design of body-in-white assembly cell and the robot motion planning are two time-expensive and interconnected activities, up to now generally managed from different human operators. The resolution of these two activities as non-interrelated could lead to an increase of the engineer-to-order time and a reduction of the solution quality. Thus, a test bed is described in order to prove the applicability of the approach.

Zero-point fixture systems as a reconfiguration enabler in flexible manufacturing systems

ABSTRACTTodays manufacturing systems need to be able to quickly adapt to customer demands, ranging from high volumes of mass production to high volumes of mass customization. Flexible Manufacturing Systems provide a high degree of flexibility to cope with these challenges. They consist of machine tools capable of executing a wide range of machining operations while the use of pallets to reference and block the parts allows the decoupling of the setup operations from the machining centers activity. This paper presents an ontology-based framework to support the design and management of flexible manufacturing systems, aimed at integrating the various involved activities including the pallet configuration and process planning, the management policies for short-term production planning and the pallet checking to verify the correct configuration of the physical pallet.