Virtual prototyping and digital twin

This paper presents the historical development of methods used for the study of torsional stresses in shafts. In particular, the paper covers both analog methods, especially those based on electrical analogies proposed circa 1925, and numerical methods, especially finite difference methods (FDM), finite element methods (FEM) and boundary element methods (BEM).

This paper investigates the thermal and fluid dynamic effects of a cold air jet generated by a Ranque-Hilsch vortex tube on the cutting tool of a milling machine. A simulation model that predicts the temperature field and the displacements of the tool due to the thermal effects was developed. Such a model can help to correct machining errors and improve cutting accuracy of air-cooled milling machines. Experimental results validated the model. Eventually, the post-processing of the computational fluid dynamics (CFD) data has been conducted in virtual reality.

Keywords: CFD analysis , Dry machining , Flux simulation , FSI method , Heat transfer , Machine tool , Ranque-Hilsch vortex tube , Thermo-energetic investigation , Tool , Virtual reality post-processing

Position-controlled Servo-Systems (SeSs) may be envisaged as a key technology to keep the manufacturing industry at the leading edge. Unfortunately, based on the current state-of-the-art, these mechatronic devices are well performing but intrinsically energy intensive, thus compromising the overall system sustainability. Therefore, traditional design and optimization paradigms, previously focused on productivity and quality improvement, should be critically reviewed so as to introduce energy efficiency as an optimality criterion alongside with the global production rate. In particular, focusing on mono-actuator systems with one degree-of-freedom, among the several design factors that can influence the SeS overall performance, the end-effector motion law can be easily modified without either hardware substitution or further investments. In this context, the purpose of the present paper is twofold. On one side, an effective method for the quick set-up of an energy-predictive CAD-based virtual prototype is discussed. In parallel, an energy comparison of some commonly employed Point-To-Point motions and optimization cost functions is provided. For what concerns the trajectory interpolation scheme, a standard optimization problem based on the aforementioned virtual model is solved by means of either algebraic or trigonometric splines. For what concerns the optimality criterion, either the system energy consumption or the root-means square value of the actuator torque are taken into account. In general, torque-based approaches, which may be preferred since they do not require a full knowledge of the SeS electrical parameters, can be effectively employed only when friction effects are negligible as compared to purely inertial loads. In parallel, cubic algebraic splines outperform other types of trajectories, although losing continuity of the resulting jerk profile.

Keywords: CAD/MBD tools , Eco-Design methods , Servo-Systems , Trajectory comparison , Virtual prototyping

Industrial robotics provides high flexibility and reconfigurability supported by a user-friendly programming, but still lacks in accuracy. An effective workcell calibration reduces errors in robot manufacturing and enables robot machining applications. A novel workcell calibration method is embedded in an integrated design framework for an in-depth exploitation of CAD-based simulations and offline programming. The method is composed of two steps: first calibration of the workpiece-independent equipment in the workcell layout and final automated online calibration of workpiece-dependent equipment. The method is finally applied to a changeable robotic workcell for finishing aluminium cast housings for aerospace gear transmissions characterised by complex shapes and by close dimensional and geometrical specifications. Experimental results prove the method effectiveness in enhancing accuracy in robot machining.

Keywords: Aerospace industry , Industrial robotics , Integrated design , Workcell calibration

In this paper, an engineering method for the power flow assessment of a position-controlled servo-mechanism is outlined. The considered system is composed of a permanent magnet synchronous motor coupled to a standard power converter, and directly connected to a slider crank mechanism. After the accurate description of a consistent power flow model, a sequential identification technique is discussed, which allows to determine the dynamic parameters of linkage, electric motor and electronic driver by means of non-invasive experimental measures. The proposed model allows to accurately predict the major sources of power loss within the system.

Keywords: Design of Experiments , Power flow assessment , Servo-actuated mechanism , Virtual prototyping

Spiral Torsion Springs (STS) are generally manufactured employing medium/high-carbon steel alloys shaped as thin rods with rectangular cross section. Meanwhile, plastic materials (e.g. ABS or PLA), currently used in freeform manufacturing processes, may not be suited for several applications, owing to the low material yield strength and the rather poor fatigue life. Despite the above-mentioned limitations, the main advantages of a 3D printing process, as compared to more traditional manufacturing techniques, are the design flexibility and the possibility to directly integrate elastic components within a joint mechanism produced as a single (monolithic) part. In particular, provided that the external forces acting on the spring coils are maintained within a certain threshold and that the spring geometry is suitably optimized, a reliable 3D-printed STS alternative to traditional steel springs is actually feasible. Given these premises, the main purpose of the present paper is to propose a model-based optimization algorithm that allows to optimally size STS for user-specified torque-deflection characteristics. Optimal STS geometries are then realized in ABS via Fused Deposition Manufacturing, and subsequently tested with a purposely-designed experimental set-up. Furthermore, the behavior of each STS sample (in terms of stiffness and equivalent Von Mises stress) is evaluated by means of non-linear finite elements analysis, in order to check the correspondence with the expected behavior. Finally, numerical and experimental results are provided, which demonstrate the prediction capabilities of the proposed modeling/optimization techniques, and confirm that well-behaved STS can be conceived and produced. Envisaged applications concern the development of smart structures for robot design, such as multi-articulated compliant robotic chains that can be used as low-cost manipulators (i.e. arm) or as mini-manipulators (i.e. fingers). The proposed approach effectively simplifies the production and the assembly of the mechanism, also allowing for an easier integration of embedded sensory-actuation systems.

At the current state-of-the-art, Robotic Deburring (RD) has been successfully adopted in many industrial applications, but it still needs improvements in terms offinal quality. In fact, the effectiveness of a RD process is highly influenced by the limited accuracyof the robot motions and by the unpredictable variety of burr size/shape. Tool compliance partially solves the problem, although dedicated engineering design tools are strictly needed, in order to identify those optimized parameters and RD strategies that allow achieving the best quality and cost-effectiveness. In this context, the present paper proposes a CAD-based Virtual Prototype (VP) of a pneumatic compliant spindle, suitable to assess the process efficiency in different case scenarios. The proposed VP is created by integrating a 3D multi-body model of the spindle mechanical structure with the behavioural model of the process forces, as adapted from previous literature. Numerical simulations are provided, concerning the prediction of both cutting forces and surface finishing accuracy.

Keywords: CAD-based tools , Compliant spindle , Robotic deburring , Virtual Prototyping

Abstract: In the field of orthodontics, the use of Removable Thermoplastic Appliances (RTAs) to treat moderate malocclusion problems is progressively replacing traditional fixed brackets. Generally, these orthodontic devices are designed on the basis of individual anatomies and customised requirements. However, many elements may affect the effectiveness of a RTA-based therapy: accuracies of anatomical reference models, clinical treatment strategies, shape features and mechanical properties of the appliances. In this paper, a numerical model for customised orthodontic treatments planning is proposed by means of the finite element method. The model integrates individual patient's teeth, periodontal ligaments, bone tissue with structural and geometrical attributes of the appliances. The anatomical tissues are reconstructed by a multi-modality imaging technique, which combines 3D data obtained by an optical scanner (visible tissues) and a computerised tomography system (internal tissues). The mechanical interactions between anatomical shapes and appliance models are simulated through finite element analyses. The numerical approach allows a dental technician to predict how the RTA attributes affect tooth movements. In this work, treatments considering rotation movements for a maxillary incisor and a maxillary canine have been analysed by using multi-tooth models. Graphical Abstract: [Figure not available: see fulltext.]

Keywords: Anatomical modelling , Numerical analysis , Orthodontic tooth movement , Removable thermoplastic appliance

Introduction Moment-to-force ratios (M:F) define the type of tooth movement. Typically, the relationship between M:F and tooth movement has been analyzed in a single plane. Here, to improve the 3-dimensional tooth movement theory, we tested the hypothesis that the mathematical relationships between M:F and tooth movement are distinct, depending on force system directions. Methods A finite element model of a maxillary first premolar, scaled to average tooth dimensions, was constructed based on a cone-beam computed tomography scan. We conducted finite element analyses of the M:F and tooth movement relationships, represented by the projected axis of rotation in each plane, for 510 different loads. Results We confirmed that a hyperbolic equation relates the distance and M:F; however, the constant of proportionality ("k") varied nonlinearly with the force direction. With a force applied parallel to the tooth's long axis, "k" was 12 times higher than with a force parallel to the mesiodistal direction and 7 times higher than with a force parallel to the buccolingual direction. Conclusions The M:F influence on tooth movement depends on load directions. It is an incomplete parameter to describe the quality of an orthodontic load system if it is not associated with force and moment directions.

Functionally Graded Scaffolds (FGSs) are porous biomaterials where porosity changes in space with a specific gradient. In spite of their wide use in bone tissue engineering, possible models that relate the scaffold gradient to the mechanical and biological requirements for the regeneration of the bony tissue are currently missing. In this study we attempt to bridge the gap by developing a mechanobiology-based optimization algorithm aimed to determine the optimal graded porosity distribution in FGSs. The algorithm combines the parametric finite element model of a FGS, a computational mechano-regulation model and a numerical optimization routine. For assigned boundary and loading conditions, the algorithm builds iteratively different scaffold geometry configurations with different porosity distributions until the best microstructure geometry is reached, i.e. the geometry that allows the amount of bone formation to be maximized. We tested different porosity distribution laws, loading conditions and scaffold Young's modulus values. For each combination of these variables, the explicit equation of the porosity distribution law-i.e the law that describes the pore dimensions in function of the spatial coordinates-was determined that allows the highest amounts of bone to be generated. The results show that the loading conditions affect significantly the optimal porosity distribution. For a pure compression loading, it was found that the pore dimensions are almost constant throughout the entire scaffold and using a FGS allows the formation of amounts of bone slightly larger than those obtainable with a homogeneous porosity scaffold. For a pure shear loading, instead, FGSs allow to significantly increase the bone formation compared to a homogeneous porosity scaffolds. Although experimental data is still necessary to properly relate the mechanical/biological environment to the scaffold microstructure, this model represents an important step towards optimizing geometry of functionally graded scaffolds based on mechanobiological criteria.

The paper presents an integrated technological framework, which aims to make a step forward in contract furniture design methods and supporting web-enabling applications. The implementing platform enables the extensible and temporary cluster of companies to manage the entire contract furniture process. The main contribution regards the integration of different software modules into an overall system that exploits E-marketing Intelligence applications, 3D web-based tools and Augmented Reality techniques. Different user interfaces are implemented to accomplish the involved stakeholders needs and furniture development goals.

Keywords: Collaborative Product Development , E-marketing , Web-enabled design

The sense of smell has a great importance in our daily life. Recently, smells have been used for marketing purposes for improving the people's mood and for communicating information about products as household cleaners and food. However, the scent design discipline can be used for creating a "scent identity" of these products not traditionally associated to a specific smell, in order to communicate their features to customers. In the area of virtual reality (VR), several researches concerned the integration of smells in virtual environments. The research questions addressed in this paper concern if virtual prototypes (VP), including smell simulation, can be used for evaluating products as effectively as studies performed in real environments, and also if smells can enhance the users' sense of presence in virtual environments. For this purpose, a VR experimental framework including a prototype of a wearable olfactory display (wOD) has been set up, and experimental tests have been carried out.

The sense of smell has a great importance in our daily life. In recent years, scents have been used for marketing purposes for improving the person's mood and of communicating information about products as household cleaners and food. However, scents can be also used for any kind of products to communicate their features to customers. In the area of Virtual Reality several researches have focused on integrating scents in virtual environments. The research questions addressed in this work concern if scents can contribute to increase the users' sense of presence in the virtual environment, and also if Virtual Prototypes, including the sense of smell, can be used for evaluating products as effectively as studies performed in real environments. For this purpose, a Virtual Reality experimental framework including a prototype of a Wearable Olfactory Display has been set up, and experimental tests have been performed.

Keywords: Multisensory environment , olfactory display , product evaluation

Abstract: The product design process is based on a sequence of phases where the concept of the shape of a product is typically represented through a digital 3D model of the shape, and often also by means of a corresponding physical prototype. The digital model allows designers to perform the visual evaluation of the shape, while the physical model is used to better evaluate the aesthetic characteristics of the product, i.e. its dimension and proportions, by touching and interacting with it. Design and evaluation activities are typical cyclical, repeated as many times as needed in order to reach the optimal and desired shape. This reiteration leads to an increase of the development time and, consequently, of the overall product development cost. The aim of this research work is to develop a novel system for the simultaneous visual and tactile rendering of product shapes, thus allowing designers to both touch and see new product shapes already during the product conceptual development phase. The proposed system for visual and tactile shape rendering consists in a Tactile Display able to represent in the real environment the shape of a product, which can be explored naturally through free hand interaction. The device is designed in order to be portable, low cost, modular and high performing in terms of types of shapes that can be represented. The developed Tactile Display can be effectively used if integrated with an Augmented Reality system, which allows the rendering of the visual shape on top of the tactile haptic strip. This allows a simultaneous representation of visual and tactile properties of a shape. By using the Tactile Display in the initial conceptual phases of product design, the designers will be able to change the shape of a product according to the tactile evaluation, before the development of the physical prototype. This feature will lead to a decrease of the number of physical prototypes needed, thereby reducing, both cost and overall time of the product development process.

Keywords: augmented reality , shape rendering , Tactile display , virtual prototyping

Product designers are more and more addressing the design of product experience, in addition to the more traditional product design, where the focus of the design practice is on the interaction between the product and its users. Traditional methods and tools used so far for the design of products are not suitable to the design of experience. Among the emerging methods, experience prototyping seems effective and well addressing the new requirements of experience design. The paper describes the emerging technologies enabling experience prototyping, and provides some examples where this new methodology for experience design has been applied.

A methodology for integrating the CAD-CAE design of a chain drive system is presented by evaluating meshing angles. The methodology correlates the angles of engagement with transverse vibrations and the tensile force of the chain links, showing that the dynamic behaviour of a chain drive can be significantly improved by fine tuning the meshing angles. An objective parameter was introduced to evaluate divergence from correct meshing. Here the methodology is applied to optimize the timing chain system of a high power V12 quadruple overhead camshaft engine. The reliability of the method relies on multibody modelling all the components and accurate experimental tests. Correlating the experimental measurements provided exact modelling of the contact forces, exact evaluation of stiffness and damping values and precise dynamic modelling of the tensioners and guides. Finally, the dynamic performance of the two different primary stage chain drive layouts were compared.

Keywords: Chain stiffness , Contact force model , Meshing impact , Multibody dynamics , Tensioner , Transverse vibration

The market of the hybrid electric vehicles has been increasing for several years. Different commercial EV and PHEV solutions are available for passenger cars and light vehicles for freight deliveries. However, the market of heavy trucks still regards traditional ICE vehicles powered by diesel oil fuel. The recent interest for electric solutions have been pushing the development of the hybrid solutions, but only micro-hybrid systems are considered feasible for heavy truck applications. The proposed research aims to define a methodological approach with a virtual model in order to simulate the behavior of a hybrid heavy truck. The scope of this research is the feasibility analysis of a retrofit hybrid heavy truck. A real driving cycle has been used in order to obtain reliable results in terms of cost, energy consumption and gas emission. The layout of the hybrid system has been proposed as well as the sizing of battery and electric motor. A commercial tool has been used for the vehicle modelling and simulation. As a test case, an 18-ton truck has been analyzed with a 10-liter diesel engine. Firstly, the simulation of the diesel truck has been reproduced considering the real driving cycle data. Secondly, the simulation activity has been focused on the evaluation of the hybrid system behavior by investigating different battery sizes with the same boundary conditions related to the real driving cycle.

Nowadays in many industrial applications, i.e. electrical household appliances, it is necessary to have a robust and safe control for some variables involved in the analysis of the performances of different products. In addition, the recent ecodesign directives require products increasingly eco-friendly and eco-efficient, preserving high-performance but a low power consumption. For these reasons, the physical prototypes of products require many expensive and complex tests in term of time, resources and qualified personnel involved. To overcome these limitations, the proposed approach is focused on the use of virtual prototyping tools, which support and reduce the expensive physical experiments. The main objective of this paper is the development, implementation and testing of an innovative methodology, which could be an improvement for the sustainable design of induction hobs. Induction heating applied to the domestic cooking has significantly evolved since the first cooking hobs appeared. Different issues such as maximum power available for heating a pot, dimensional compactness of the hobs, or inverter electronics efficiency have achieved a great development. The proposed methodology provides the development of a multi-physic model which is able to estimate the efficiency of the induction hobs starting from the design data of the project. In particular, the multi-physic model is composed by an electromagnetic simulation and a thermal simulation. The electromagnetic simulation, starting from electrical values such as voltage, current and frequency, is able to simulate the eddy current induced in the bottom of the pot, and resistance leads to the Joulean heating of the material. The thermal simulation is able to measure the energy consumption during the operational phase and the temperature reached by the materials. Therefore, the thermal power obtained by the Joulean heating is, at the same time, the output of the electromagnetic simulation and the input of the thermal one. The proposed model can be applied to design product and simulate the performance considering different operating conditions such as different types of cookers, different coils and different materials. Through the use of virtual prototyping tools is possible to control the heat flux on the whole system (stove, pot, water), and to evaluate the energy efficiency during the operational phase. The proposed tool makes the productengineer more aware about decision-making strategies in order to achieve an energy saving, calculated over the whole life cycle.

In high altitude operations, the cooling system takes part to the vehicle design optimization process. An integrated design of the cooling ducts is strictly necessary. At high altitudes, the cooling air is taken from high-pressure areas into an alternate, extremely optimized, path. A diffuser reduces the airspeed and increases pressure of the cooling air. Then a group of high performance finned radiators rejects the heat from coolant, air charge and oil. The high altitude, after diffuser radiator performance is discussed in this paper. At first high performance Formula 1 radiators are introduced and discussed. Experimental data are also exposed and summarized. The pressure drop and heat rejection are expressed in function or Re and Pr numbers of cooling air. Then the radiator performance at high altitude is extrapolated from the ground test data. Finally a few suggestions on radiator and cooling ducts arrangement are introduced.

Keywords: Cooling , HALE , Meredith effect , Optimization , Radiators , UAV

Low BSFC (Brake Specific Fuel Consumption) and flat-altitude-rating make piston engines ideal choice for altitudes up to 20,000m-65,000ft. These propulsion systems are more complex than traditional applications that are normally limited to 5,000-7,000m (16,000-23,000ft). In fact, the air propulsion (propeller or fan), the air intake, the fuel system, the turbocharging, the exhaust and the cooling system take part to the design optimization process. An integrated design is strictly necessary. At high altitudes, the intake air is taken from high-pressure areas into an alternate, extremely optimized, path. In propeller systems, a diffuser is usually positioned in the lower part of the aircraft. It converts kinetic energy into pressure. In fan systems, a little amount of "high pressure" air is taken from the high-pressure area of the fan. In lower power units, automotive-derived turbochargers can achieve the required pressure ratio. However, this option is limited by the maximum amount of volumetric flow rate. Moreover, automotive turbocharger housings have to be redesigned to use low-weight inconel alloys instead of heavier cast-iron. A complete redesign of the high pressure turbocharger (the unit closer to the engine manifold) can achieve pressure ratios from 8:1 to 10:1. This expensive process increases the power to mass ratio of the propulsion system. For higher power rating over about 200 kW axial compressorturbine assemblies derived from small turboshafts can be used as a turbocharging unit. In this case the burner is substituted by the piston engine. Especially for diesel engines, the advantage lies in the efficiency (BSFC). In fact, the maximum temperature reached in the diesel combustion chamber is about 4200K and the air flow is much lower than traditional turboshafts. Hybrid and turbocompound solutions are also possible. The exhaust and the intake of the piston engine have to be redesigned. However, the requirements of low weight, high reliability and long endurance HALE (High Altitude Long Endurance) UAVs (Unmanned Aerial Vehicle) requires further work on this specific subject.

Keywords: HALE , Optimization , Propulsion , Serial cascade arrangement , Turbochargers , UAV