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PIETRO BILANCIA

Ricercatore Legge 240/10 - t.det.
Dipartimento di Scienze e Metodi dell'Ingegneria
Docente in convenzione
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - A method for the assessment and compensation of positioning errors in industrial robots [Articolo su rivista]
Ferrarini, S.; Bilancia, P.; Raffaeli, R.; Peruzzini, M.; Pellicciari, M.
abstract

Industrial Robots (IR) are currently employed in several production areas as they enable flexible automation and high productivity on a wide range of operations. The IR low positioning performance, however, has limited their use in high precision applications, namely where positioning errors assume importance for the process and directly affect the quality of the final products. Common approaches to increase the IR accuracy rely on empirical relations which are valid for a single IR model. Also, existing works show no uniformity regarding the experimental procedures followed during the IR performance assessment and identification phases. With the aim to overcome these restrictions and further extend the IR usability, this paper presents a general method for the evaluation of IR pose and path accuracy, primarily focusing on instrumentation and testing procedures. After a detailed description of the experimental campaign carried out on a KUKA KR210 R2700 Prime robot under different operating conditions (speed, payload and temperature state), a novel online compensation approach is presented and validated. The position corrections are processed with an industrial PC by means of a purposely developed application which receives as input the position feedback from a laser tracker. Experiments conducted on straight paths confirmed the validity of the proposed approach, which allows remarkable reductions (in the order of 90%) of the orthogonal deviations and in-line errors during the robot movements.

2024 - Empirical Characterization of Track Dimensions for CMT-Based WAAM Processes [Relazione in Atti di Convegno]
Lettori, J.; Raffaeli, R.; Bilancia, P.; Borsato, M.; Peruzzini, M.; Pellicciari, M.
abstract

Wire Arc Additive Manufacturing is based on a welding torch usually attached to a robotic arm with multiple degrees of freedom. Robot-based additive manufacturing allows non-planar and non-uniform thickness layers to be deposited where the slices have non-constant thickness. Thus, in addition to the motion settings, fine regulations of the welding parameters become necessary to obtain variable bead heights in the same slice. This paper aims to evaluate the user-accessible welding parameters’ influence on the deposited material’s dimensions during continuous Cold Metal Transfer (CMT) and its variant named CMT Cycle Step. In particular, the height and width of beads are investigated by varying the travel speed and the wire-feed rate (continuous CMT), as well as the size of the droplets by varying the number of CMT cycles and the wire-feed rate (CMT Cycle Step). In particular, the characterization of the material deposited during the CMT Cycle Step is not deeply studied in the literature. The experimental specimens are measured and the obtained values are numerically processed to yield empirical formulas that link the dimensions of the deposited material with the selected process parameters. The results show that CMT Cycle Step is more stable than continuous CMT, which confirms its higher suitability for accurate manufacturing.

2024 - Preliminary Design of an Automatic Palletizing System During the Pre-sales Stage [Relazione in Atti di Convegno]
Guidetti, E.; Bilancia, P.; Raffaeli, R.; Pellicciari, M.
abstract

2023 - An Overview of Industrial Robots Control and Programming Approaches [Articolo su rivista]
Bilancia, Pietro; Schmidt, Juliana; Raffaeli, Roberto; Peruzzini, Margherita; Pellicciari, Marcello
abstract

Nowadays, manufacturing plants are required to be flexible to respond quickly to customer demands, adapting production and processes without affecting their efficiency. In this context, Industrial Robots (IRs) are a primary resource for modern factories due to their versatility which allows the execution of flexible, reconfigurable, and zero-defect manufacturing tasks. Even so, the control and programming of the commercially available IRs are limiting factors for their effective implementation, especially for dynamic production environments or when complex applications are required. These issues have stimulated the development of new technologies that support more efficient methods for robot control and programming. The goal of this research is to identify and evaluate the main approaches proposed in scientific papers and by the robotics industry in the last decades. After a critical review of the standard IR control schematic, the paper discusses the available control alternatives and summarizes their characteristics, range of applications, and remaining limitations.

2023 - Exploring the Adoption of UX-Driven Approaches to Design Industrial PLC User Interfaces [Relazione in Atti di Convegno]
Peruzzini, M.; Valentini, L.; Tutarini, A.; Bilancia, P.; Raffaeli, R.
abstract

Modern automated production systems (e.g., automatic machines, assembly lines, robotic cells) are typically governed by dedicated industrial controllers, such as Programmable Logic Controllers (PLCs), which supervise and coordinate the process by exchanging I/O data, sequencing tasks or triggering actions with the involved automation modules. Different solutions have been developed to offer an intuitive Human-Machine Interface (HMI) programming to the user, based on PLC HMI editors, according to vendor-specific programming languages. However, in the current industrial practice, user interfaces (UIs) are usually generated by software specialists and far from adopting any user-centered approach. As a result, the generated UIs are poorly usable and hard to understand for end users (e.g., operators), diverging from Industry 5.0 ideas that put humans at the center of the modern factory design. In this context, the present paper aims at exploring how the adoption of User eXperience (UX) driven approaches can benefit the design of industrial PLC UIs, reflecting on advantages and limits, and transdisciplinary perspectives. A case study utilizing Beckhoff TwinCAT as PLC environment and Adobe XD as UX design tool is examined and discussed.

2023 - Path Approximation Strategies for Robot Manufacturing: A Preliminary Experimental Evaluation [Relazione in Atti di Convegno]
Bigliardi, Matteo; Bilancia, Pietro; Raffaeli, Roberto; Peruzzini, Margherita; Berselli, Giovanni; Pellicciari, Marcello
abstract

Industrial Robots (IRs) are increasingly adopted for material subtraction or deposition functions owing to their advantages over machine tools, like cost-effectiveness and versatility. Unfortunately, the development of efficient robot manufacturing processes still faces unsolved issues related to the IRs poor positioning accuracy and to the tool path generation process. Novel engineering methods and tools are needed for CAD based programming of accurate paths and continuous robot motions to obtain the required manufacturing quality and tolerances. Within this context, to achieve smoothness along the tool path formed by linear G-code segments, the IR controllers’ approximation strategies, summarily reported in the manufacturer’s manuals, must be considered. The aim of this paper is to present the preliminary work carried out to identify the approximation algorithms of a Kuka IR when executing linear moves. An experimental study is conducted by varying the controller settings and the maximum translational velocity. The robot behavior has been acquired thanks to the controller tracing function and then processed to yield relations readily employable for the interpretation of G-Code commands and the subsequent generation of proper robot motion instructions. The obtained formulas allow to accurately predict the robot geometric path and kinematics within the corner transition between two linear segments.

2022 - A review of geometry representation and processing methods for cartesian and multiaxial robot-based additive manufacturing [Articolo su rivista]
Lettori, J.; Raffaeli, R.; Bilancia, P.; Peruzzini, M.; Pellicciari, M.
abstract

Nowadays, robot-based additive manufacturing (RBAM) is emerging as a potential solution to increase manufacturing flexibility. Such technology allows to change the orientation of the material deposition unit during printing, making it possible to fabricate complex parts with optimized material distribution. In this context, the representation of parts geometries and their subsequent processing become aspects of primary importance. In particular, part orientation, multiaxial deposition, slicing, and infill strategies must be properly evaluated so as to obtain satisfactory outputs and avoid printing failures. Some advanced features can be found in commercial slicing software (e.g., adaptive slicing, advanced path strategies, and non-planar slicing), although the procedure may result excessively constrained due to the limited number of available options. Several approaches and algorithms have been proposed for each phase and their combination must be determined accurately to achieve the best results. This paper reviews the state-of-the-art works addressing the primary methods for the representation of geometries and the subsequent geometry processing for RBAM. For each category, tools and software found in the literature and commercially available are discussed. Comparison tables are then reported to assist in the selection of the most appropriate approaches. The presented review can be helpful for designers, researchers and practitioners to identify possible future directions and open issues.

2022 - Accurate transmission performance evaluation of servo-mechanisms for robots [Articolo su rivista]
Bilancia, Pietro; Monari, Luca; Raffaeli, Roberto; Peruzzini, Margherita; Pellicciari, Marcello
abstract

2022 - Analysis and Preliminary Design of a Passive Upper Limb Exoskeleton [Articolo su rivista]
Vazzoler, Greta; Bilancia, Pietro; Berselli, Giovanni; Fontana, Marco; Frisoli, Antonio
abstract

2022 - Engineering Method and Tool for the Complete Virtual Commissioning of Robotic Cells [Articolo su rivista]
Raffaeli, Roberto; Bilancia, Pietro; Neri, Federico; Peruzzini, Margherita; Pellicciari, Marcello
abstract

Intelligent robotic manufacturing cells must adapt to ever-varying operating conditions, developing autonomously optimal manufacturing strategies to achieve the best quality and overall productivity. Intelligent and cognitive behaviors are realized by using distributed controllers, in which complex control logics must interact and process a wide variety of input/output signals. In particular, programmable logic controllers (PLCs) and robot controllers must be coordinated and integrated. Then, there is the need to simulate the robotic cells’ behavior for performance verification and optimization by evaluating the effects of both PLC and robot control codes. In this context, this work proposes a method, and its implementation into an integrated tool, to exploit the potential of ABB RobotStudio software as a virtual prototyping platform for robotic cells, in which real robots control codes are executed on a virtual controller and integrated with Beckhoff PLC environment. For this purpose, a PLC Smart Component was conceived as an extension of RobotStudio functionalities to exchange signals with a TwinCAT instance. The new module allows the virtual commissioning of a complete robotic cell to be performed, assessing the control logics effects on the overall productivity. The solution is demonstrated on a robotic assembly cell, showing its feasibility and effectiveness in optimizing the final performance.

2021 - A variable section beams based Bi-BCM formulation for the kinetostatic analysis of cross-axis flexural pivots [Articolo su rivista]
Bilancia, P.; Baggetta, M.; Hao, G.; Berselli, G.
abstract

The Cross-Axis Flexural Pivot (CAFP) is a well-established compliant rotational joint characterized by a highly configurable behavior. Its classic form, consisting of two uniform beams that cross at an arbitrary angle, has been thoroughly examined via either theoretical approaches or Finite Element Analysis (FEA). Conversely, the effects of utilizing variable section beams have had minor consideration, possibly due to the more complex modeling phase. The present paper addresses the analysis of CAFPs incorporating beams whose width and thickness are assumed to vary along the axis with either linear or parabolic functions. The CAFP planar behavior is studied resorting to the Beam-Constraint Model (BCM) for different load cases, namely with an ideal rotation applied to one rigid link or a more practicable cable-driven actuation. To extend the use of BCM to large deflections, each CAFP's beam is modeled as a chain of two BCM elements, named Bi-BCM. A preliminary study has been carried out to establish empirical equations that provide the BCM characteristic coefficients for every considered beam shape. Next, these have been used to perform the pivot behavioral analysis and to generate, as an output of the sensitivity studies, the performance maps of stiffness, maximum stress and center shift. These results have been verified with FEA, which confirmed the Bi-BCM accuracy for any tested configuration. Finally, direct comparisons between predicted behaviors of the CAFP actuated via the flexible cable and experimental data obtained with 3D printed specimens further validated the proposed Bi-BCM model.

2021 - An Integrated Approach for Motion Law Optimization in Partially Compliant Slider-Crank Mechanisms [Relazione in Atti di Convegno]
Baggetta, Mario; Bilancia, Pietro; Pellicciari, Marcello; Berselli, Giovanni
abstract

Servo-Actuated Mechanisms (SAM) are capable of improving the flexibility and reconfigurability of modern automatic machines. On one hand, as compared to fully mechanical drives, SAM may suffer from non-negligible positioning inaccuracies, whose effect can become unacceptable in case of undesired part deformations during high dynamic motions. On the other hand, it may be the case that parts of the system are purposely designed to provide an highly compliant behaviour, so as to potentially increase the device safety in case of interaction with humans. In both cases, practical strategies to reduce the SAM positioning errors are necessary. As a possible solution to such issue, in this paper, an integrated approach to improve the accuracy of a partially compliant SAM in position-controlled tasks is described. The method exploits a multi-software framework comprising Matlab and RecurDyn, namely a commercial Computer-Aided Engineering (CAE) tool that can be used to simulate the motion of systems comprising both rigid and flexible bodies. Starting from an initial, sub-optimal, motion law of the input link, a trajectory optimizer iteratively runs the CAE solver and automatically computes an optimal, compensated, position profile. The obtained results show that the method may represent a useful tool for analyzing/designing partially compliant SAM, whenever analytical models are either too complex or not readily available.

2021 - An Overview of Procedures and Tools for Designing Nonstandard Beam-Based Compliant Mechanisms [Articolo su rivista]
Bilancia, P.; Berselli, G.
abstract

Beam-based Compliant Mechanisms (CMs) are increasingly studied and implemented in precision engineering. Straight beams with uniform cross section are the basic modules in several design concepts, which can be deemed as standard CMs. Their behavioral analysis can be addressed with a large variety of techniques, including the Euler–Bernoulli beam theory, the Pseudo-Rigid Body (PRB) method, the beam constraint model and the discretization-based methods. This variety is unquestionably reduced when considering nonstandard CMs, namely design problems involving special geometries, such as curve/spline beams, variable section beams, nontrivial shapes and contact pairs. The 3D Finite Element Analysis (FEA) provides accurate results but its high computational cost makes it inappropriate for optimization purposes. This work compares the potentialities of computationally efficient modeling techniques (1D FEA, PRB method and chained-beam constraint model), focusing on their applicability in nonstandard planar problems. The cross-axis flexural pivot is used as a benchmark in this research due to its high configurable behavior and wide range of applications. In parallel, as an attempt to provide an easy-to-use environment for CM analysis and design, a multi-purpose tool comprising Matlab and a set of modern Computer-Aided Design/Engineering packages is presented. The framework can implement different solvers depending on the adopted behavioral models. Summary tables are reported to guide the designers in the selection of the most appropriate technique and software framework. Lastly, efficient design procedures that allow to configure nonstandard beam-based CMs with prescribed behavior are examined with two design examples.

2021 - Conceptual design and virtual prototyping of a wearable upper limb exoskeleton for assisted operations [Articolo su rivista]
Bilancia, P.; Berselli, G.
abstract

This paper introduces a novel upper limb robotic exoskeleton designed to assist industrial operators in a wide range of manual repetitive tasks, such as tool handling and lifting/moving of heavy items. Due to its reduced size and high maneuverability, the proposed portable device may also be employed for rehabilitation purposes (e.g. as an aid for people with permanent neuromuscular diseases or post-stroke patients). Its primary function is to compensate the gravity loads acting on the human shoulder by means of a hybrid system consisting of four electric motors and three passive springs. The paper focuses on the exoskeleton mechanical design and virtual prototyping. After a preliminary review of the existent architectures and procedures aimed at defining the exoskeleton functional requirements, a detailed behavioral analysis is conducted using analytical and numerical approaches. The developed interactive model allows to simulate both kinematics and statics of the exoskeleton for every possible movement within the design workspace. To validate the model, the results have been compared with the ones achieved with a commercial multibody software for three different operator’s movements.

2021 - Design of a Test Rig for Tuning and Optimization of High Dynamics Servo-Mechanisms Employed in Manufacturing Automation [Articolo su rivista]
Belloni, Mattia; Bilancia, Pietro; Raffaeli, Roberto; Peruzzini, Margherita; Pellicciari, Marcello
abstract

The Industry 4.0 framework is pushing the manufacturing systems towards a zero-defect production based on robot technologies. The increasing level of automation in the production lines is raising new challenges for designers that must face the latest requirements in terms of product quality and power consumption. Among the multitude of components of the industrial plants, Servo-Mechanisms (SMs) play a crucial role and govern important performance indices of both robots and automatic machines. During the execution of high dynamics tasks, the SMs performance is influenced by many factors, including motion law, acting load, temperature and degradation. The development of accurate models aiming at predicting and optimizing the SMs behavior may not be practicable without extensive experimental activities. Owing to these considerations, this work introduces a novel test rig for the accurate characterization of industrial SMs. The rig is designed by combining the advantages of the existing prototypes. It is equipped with high precision sensors and an active loading system that enable to test the SM in various working conditions. Also, the rig modularity facilitates the installation of newly commissioned components and the execution of static and dynamic experiments. The paper mainly focuses on the rig mechanical design and components selection criteria.

2021 - Design of a bio-inspired contact-aided compliant wrist [Articolo su rivista]
Bilancia, P.; Baggetta, M.; Berselli, G.; Bruzzone, L.; Fanghella, P.
abstract

This paper reports about the design of a bio-inspired compliant wrist, whose mobility (i.e. ulnar-radial deviation and flexion-extension) has been realized by employing two pairs of contact-aided Cross-Axis Flexural Pivots (CAFPs), actuated via remotely-placed servo-motors and tendon transmissions. The human wrist behaves differently when deflecting in clockwise or anticlockwise direction, both in terms of maximum angular deflection and passive stiffness. The device proposed hereafter aims at mimicking such natural asymmetry, while withstanding unexpected external loads. In order to fulfill these requirements, two contacts are included: (i) a pure rolling contact (named passive contact), achieved via a cam mechanism guiding the CAFP deflection and ensuring the wrist resistance to compressive loads; (ii) a purposely shaped contact pair (named active contact), acting on one beam of the CAFP so as to increase its stiffness. The design procedures and tools specifically developed for the wrist optimization are described. In the first step, a CAFP shape optimization is performed, followed by the synthesis of the active contact pair. In the second step, the centrodes are computed and then used to generate the passive contact profiles. At last, the third step focuses on the definition of the tendons routing. To prove the validity of the numerical models, a physical prototype of the wrist is produced and tested. Direct comparisons between simulations and experiments confirm the efficacy of the proposed design method.

2021 - Functional design of a hybrid leg-wheel-track ground mobile robot [Articolo su rivista]
Bruzzone, L.; Baggetta, M.; Nodehi, S. E.; Bilancia, P.; Fanghella, P.
abstract

This paper presents the conceptual and functional design of a novel hybrid leg-wheel-track ground mobile robot for surveillance and inspection, named WheTLHLoc (Wheel-Track-Leg Hybrid Locomotion). The aim of the work is the development of a general-purpose platform capable of combining tracked locomotion on irregular and yielding terrains, wheeled locomotion with high energy efficiency on flat and compact grounds, and stair climbing/descent ability. The architecture of the hybrid locomotion system is firstly outlined, then the validation of its stair climbing maneuver capabilities by means of multibody simulation is presented. The embodiment design and the internal mechanical layout are then discussed.

2021 - Hinges and curved lamina emergent torsional joints in cylindrical developable mechanisms [Articolo su rivista]
Seymour, K.; Bilancia, P.; Magleby, S.; Howell, L.
abstract

Cylindrical developable mechanisms are devices that conform to and emerge from a cylindrical surface. These mechanisms can be formed or cut from the cylinder wall itself. This paper presents a study on adapting traditional hinge options to achieve revolute motion in these mechanisms. A brief overview of options is given, including classical pin hinges, small-length flexural pivots, initially curved beams, and an adaptation of the membrane thickness-accommodation technique. Curved lamina emergent torsional (LET) joints are then evaluated in detail, and a thin-walled modeling assumption is checked analytically and empirically. A small-scale cylindrical developable mechanism is then evaluated with Nitinol curved LET joints

2021 - Preliminary Analysis and Design of a Passive Upper Limb Exoskeleton [Relazione in Atti di Convegno]
Vazzoler, Greta; Bilancia, Pietro; Berselli, Giovanni; Fontana, Marco; Frisoli, Antonio
abstract

This article reports the preliminary analysis and design of a novel 6 degrees of freedom, passive, upper limb exoskeleton for industrial applications. The aim is to conceive a wearable device to support workers in a vast range of repetitive tasks, offering an effective strategy to reduce the risk of injuries in production lines. The exoskeleton primary purpose is to compensate for the gravity loads acting on the human upper limb via the action of five springs. By reaching the static balancing through the use of passive elements only, several advantages in terms of reduced weight and cost can be provided. In this scenario, a detailed analytical approach has been developed to study the exoskeleton statics and synthesize the springs within the human upper limb workspace. In particular, a 3R balancer is designed for the exoskeleton shoulder joint and a set of computationally efficient optimization studies are carried out to determine the optimal coefficients and positions of the springs. The obtained results have been validated with a commercial multibody tool.

2020 - Design and testing of a monolithic compliant constant force mechanism [Articolo su rivista]
Bilancia, P.; Berselli, G.
abstract

This paper reports the design of a monolithic long-stroke constant force compliant mechanism (CM). The device is suitable for applications requiring a predefined force magnitude at the contact interface, such as manipulation systems. Starting from a compliant slider-crank mechanism providing a constant force within a rather limited deflection range, the paper describes the shape optimization carried out with the aim of extending the CM available stroke. In the first design step, the pseudo-rigid body (PRB) method is used to synthesize a sub-optimal lumped compliance solution. Secondly, two improved beam-based alternatives are evaluated by means of an integrated software framework, comprising Matlab and ANSYS. These new embodiments make use of a variable thickness beam, whose shape and dimensions have been optimized so as to provide a constant reaction force in an extended range. In particular, straight and spline segments are respectively used for the first and second prototype. With reference to the lumped compliance configuration, the available stroke has been increased of amounts equalling to 467% in the straight segments version (namely, from 3 mm to 14 mm) and to 833% in the spline segments version (namely, from 3 mm to 25 mm). All the predicted behaviors have been validated via physical experiments on 3D printed specimens. The proposed multi-step design flow may also be applied to a large variety of CMs, starting from their PRB model.

2020 - Hinges and curved lamina emergent torsional joints in cylindrical developable mechanisms [Relazione in Atti di Convegno]
Seymour, K.; Bilancia, P.; Magleby, S.; Howell, L.
abstract

Cylindrical developable mechanisms are devices that conform to and emerge from a cylindrical surface. These mechanisms can be formed or cut from the cylinder wall itself. This paper presents a study on adapting traditional hinge options to achieve revolute motion in these mechanisms. A brief overview of options is given, including classical pin hinges, small-length flexural pivots, initially curved beams, and an adaptation of the membrane thickness-accommodation technique. Curved Lamina Emergent Torsional (LET) joints are then evaluated in detail, and a thin-walled modeling assumption is checked analytically and empirically. A small-scale cylindrical developable mechanism is then evaluated with Nitinol curved LET joints.

2020 - Load-displacement characterization in three degrees-of-freedom for general lamina emergent torsion arrays [Articolo su rivista]
Pehrson, N. A.; Bilancia, P.; Magleby, S.; Howell, L.
abstract

Lamina emergent torsion (LET) joints for use in origami-based applications enables folding of panels. Placing LET joints in series and parallel (formulating LET arrays) opens the design space to provide for tunable stiffness characteristics in other directions while maintaining the ability to fold. Analytical equations characterizing the elastic load-displacement for general serial-parallel formulations of LET arrays for three degrees-of-freedom are presented: rotation about the desired axis, in-plane rotation, and extension/compression. These equations enable the design of LET arrays for a variety of applications, including origami-based mechanisms. These general equations are verified using finite element analysis, and to show variability of the LET array design space, several verification plots over a range of parameters are provided.

2020 - ON THE DESIGN OF A LONG-STROKE BEAM-BASED COMPLIANT MECHANISM PROVIDING QUASI-CONSTANT FORCE [Relazione in Atti di Convegno]
Bilancia, P; Geraci, A; Berselli, G
abstract

In this paper the design of a linear long-stroke quasi constant force compliant mechanism (CM) is presented and discussed. Starting from a flexure-based slider-crank mechanism, providing the required constant force within a rather limited deflection range, the paper reports about the shape optimization carried out with the specific aim of extending the available CM operative range. The proposed device is suitable in several precision manipulation systems, which require to maintain a constant-force at their contact interface with the manipulated object. Force regulation is generally achieved by means of complex control algorithms and related sensory apparatus, resulting in a flexible behavior but also in high costs. A valid alternative may be the use of a purposely designed CM, namely a purely mechanical system whose shape and dimensions are optimized so as to provide a force-deflection behavior characterized by zero stiffness. In the first design step, the Pseudo-Rigid Body (PRB) method is exploited to synthesize the sub-optimal compliant configuration, i.e. the one characterized by lumped compliance. Secondly, an improved design alternative is evaluated resorting to an integrated software framework, comprising Matlab and ANSYS APDL, and capable of performing non-linear structural optimizations. The new embodiment makes use of a variable thickness beam, whose shape and dimensions have been optimized so as to provide a constant reaction force in an extended range. Finally, a physical prototype of the beam-based configuration is produced and tested, experimentally validating the proposed design method.

2020 - On the modeling of a contact-aided cross-axis flexural pivot [Articolo su rivista]
Bilancia, P.; Berselli, G.; Magleby, S.; Howell, L.
abstract

This paper reports the study of a planar Cross-Axis Flexural Pivot (CAFP) comprising an additional contact pair. The proposed device may be useful for applications requiring a revolute joint that behaves differently when deflecting clockwise/anti-clockwise. The presence of the contact pair reduces the free length of one flexures, resulting in a considerable increment of the overall joint stiffness. The pivot behaviour is investigated, for different load cases, via the Chained-Beam-Constraint Model (CBCM), namely an accurate method to be applied in large deflection problems. A framework comprising Matlab and ANSYS is developed for testing the CAFP performances in terms of rotational stiffness, parasitic shift and maximum stress, with different combinations of geometrical aspect ratios and contact extensions. Results achieved via CBCM for a pure rotation applied to the CAFP's output link are then verified through Finite Element Analysis. The resulting performance maps show good agreement between the numerical results. Furthermore, the CBCM shows an improved computational efficiency, which is a crucial aspect for preliminary design steps. At last, direct comparison between simulations and experiments, developed by means of two custom test rigs, confirms the efficacy of the proposed design method for the modeling of contacts in large deflection problems.

2020 - Project-based learning of advanced CAD/CAE tools in engineering education [Articolo su rivista]
Berselli, G.; Bilancia, P.; Luzi, L.
abstract

The use of integrated Computer Aided Design/Engineering (CAD/CAE) software capable of analyzing mechanical devices in a single parametric environment is becoming an industrial standard. Potential advantages over traditional enduring multi-software design routines can be outlined into time/cost reduction and easier modeling procedures. To meet industrial requirements, the engineering education is constantly revising the courses programs to include the training of modern advanced virtual prototyping technologies. Within this scenario, the present work describes the CAD/CAE project-based learning (PjBL) activity developed at the University of Genova as a part of course named Design of Automatic Machines, taught at the second level degree in mechanical engineering. The PjBL activity provides a detailed overview of an integrated design environment (i.e. PTC Creo). The students, divided into small work groups, interactively gain experience with the tool via the solution of an industrial design problem, provided by an engineer from industry. The considered case study consists of an automatic pushing device implemented in a commercial machine. Starting from a sub-optimal solution, the students, supervised by the lecturers, solve a series of sequential design steps involving both motion and structural analysis. The paper describes each design phase and summarizes the numerical outputs. At last, the results of the PjBL activity are presented and commented by considering the opinions of all the parties involved.

2020 - Virtual and physical prototyping of a beam-based variable stiffness actuator for safe human-machine interaction [Articolo su rivista]
Bilancia, P.; Berselli, G.; Palli, G.
abstract

This paper reports about the virtual and physical prototyping of an antagonistic Variable Stiffness Actuator (VSA) to be used on robotic arms specifically realized for physical human-robot interaction. Such antagonistic actuation system, which comprises purposely conceived Compliant Transmission Elements (CTEs) characterized by a nonlinear relation between the deflection and the applied torque, allows to simultaneously control both the joint's position and stiffness. The CTE's beams geometry, namely slender spline beams, has been defined by means of an automatic routine leveraging on Matlab and ANSYS and allowing for the shape optimization of complex flexures. The synthesized springs are characterized by a predefined quadratic torque-deflection characteristic, which is shown to guarantee a precise stiffness modulation while avoiding the need for a joint's position sensor. After shape optimization, the CTE is fabricated via additive manufacturing and subsequently tested. The acquired data show a very good consistency with the numerical results, although highlighting a non-negligible hysteresis due to material damping. Therefore, in order to cope with such unavoidable effect along with other parameter uncertainties and unmodeled effects (e.g. static friction), a robust feedback controller is proposed, allowing for the simultaneous and decoupled regulation of joint position and stiffness. Finally, a VSA prototype is produced and tested. Experimental results confirm that the VSA behaves as expected.

2020 - Zero torque compliant mechanisms employing pre-buckled beams [Articolo su rivista]
Bilancia, P.; Smith, S. P.; Berselli, G.; Magleby, S. P.; Howell, L. L.
abstract

The concept of a statically balanced mechanism with a single rotational degree-of-freedom is presented. The proposed device achieves static balancing by combining positive stiffness elements and negative stiffness elements within an annular domain. Two designs are discussed. The first is composed of an Archimedean spiral and two pinned-pinned pre-buckled beams. The overall mechanism is modeled via an analytical approach and the element dimensions are optimized. The optimal configuration is then tested through finite element analysis (FEA). A second approach replaces the spiral beam with elastic custom-shaped spline beams. A FEA optimization is performed to determine the shape and size of such spline beams. The behavior of the negators is used as reference for the optimization so as to achieve a complete balancing. A physical prototype of each configuration is machined and tested. The comparison between predicted and acquired data confirmed the efficacy of the design methods.

2019 - A CAD/CAE integration framework for analyzing and designing spatial compliant mechanisms via pseudo-rigid-body methods [Articolo su rivista]
Bilancia, P.; Berselli, G.; Bruzzone, L.; Fanghella, P.
abstract

Compliant Mechanisms (CMs) are currently employed in several engineering applications requiring high precision and reduced number of parts. For a given mechanism topology, CM analysis and synthesis may be developed resorting to the Pseudo–Rigid Body (PRB) method, in which the behavior of flexible members is approximated via a series of rigid links connected by spring-loaded kinematic pairs. From a CM analysis standpoint, the applicability of a generic PRB model requires the determination of the kinematic pairs’ location and the stiffness of a set of generalized springs. In parallel, from a design standpoint, a PRB model representing the kinetostatic behavior of a flexible system should allow to compute the flexures’ characteristics providing the desired compliance. In light of these considerations, this paper describes a Computer-Aided Design/Engineering (CAD/CAE) framework for the automatic derivation of accurate PRB model parameters, on one hand, and for the shape optimization of complex-shape flexures comprising out-of-plane displacements and distributed compliance. The method leverages on the modelling and simulation capabilities of a parametric CAD (i.e. PTC Creo) seamlessly connected to a CAE tool (i.e. RecurDyn), which provides built-in functions for modelling the motion of flexible members. The method is initially validated on an elementary case study taken from the literature. Then, an industrial case study, which consists of a spatial crank mechanism connected to a fully-compliant four-bar linkage is discussed. At first, an initial sub-optimal design is considered and its PRB representation is automatically determined. Secondly, on the basis of the PRB model, several improved design alternatives are simulated. Finally, the most promising design solution is selected and the dimensions of a flexure with non-trivial shape (i.e. hybrid flexure) is computed. This technique, which combines reliable numerical results to the visual insight of CAD/CAE tools, may be particularly useful for analyzing/designing spatial CMs composed of complex flexure topologies.

2019 - Additive manufacturing-oriented redesign of Mantis 3.0 hybrid robot [Relazione in Atti di Convegno]
Bruzzone, L.; Fanghella, P.; Berselli, G.; Bilancia, P.
abstract

The paper presents the third version of the hybrid leg-wheel ground mobile robot Mantis, a small-scale platform designed for inspection and surveillance tasks. The locomotion system is based on the cooperating action of a couple of actuated front legs and wheels, along with a passive rear carriage. The system performs wheeled locomotion on even grounds and hybrid locomotion in case of terrain irregularities or obstacles. This architecture combines high speed, energy efficiency, maneuverability and stable camera vision on flat terrains with good motion capabilities in unstructured environments. In the embodiment design presented hereafter, referred to as Mantis 3.0, the rear carriage has been equipped with four passive wheels, instead of two as in the previous versions, in order to improve the stability during steep stair climbing maneuvers; moreover, the legs, the main body and the rear carriage have been significantly redesigned in order to be realized by additive manufacturing techniques, with the final aim of obtaining a low-cost device suitable for Open Source distribution.

2019 - Design Issues for Tracked Boat Transporter Vehicles [Relazione in Atti di Convegno]
Bruzzone, L.; Berselli, G.; Bilancia, P.; Fanghella, P.
abstract

Elloboat is a tracked vehicle for launching and beaching of small boats and watercrafts, capable of operating in a wide range of operative conditions, here including rescue applications. This paper presents the vehicle architecture and discusses the main design issues. The effects of track dimensions on terrain compaction, bulldozing resistances and, consequently, on track sinkage are analyzed by means of the Bekker model. Obviously, track dimensions also influence the vehicle mass and size, leading to a complex engineering problem. Since vehicle speed and acceleration are limited, stability during locomotion can be assessed using a quasi-static approach, computing the longitudinal and lateral tipping angles for a given vehicle configuration and payload position, and imposing a proper limit to their minimum. Stability analysis can be exploited not only in the design phase, but also for the real-time evaluation of the actual margin of stability, so as to help the operator in the vehicle path/speed planning.

2019 - Project-based learning of CAD/CAE tools for the integrated design of automatic machines [Relazione in Atti di Convegno]
Berselli, G.; Bilancia, P.; Razzoli, R.
abstract

This paper reports about project-based learning activities carried out within the course of Design of Automatic Machines at the University of Genova. This didactic experience, provided to the students enrolled in the second-level degree in Mechanical Engineering, aims at providing the knowledge of those methods and tools required to optimally design functional parts of automatic machines, here including the mechanical architecture and the actuation subsystem. Lecture hours are equally devoted to the introduction of theoretical concepts and to lab exercises, which leverage on the extensive and advanced use of dedicated CAD/CAE software tools (i.e. PTC Creo). In particular, the projects are related to the in-depth study of automated packaging systems, initial (sub-optimal) design solutions being provided by an industrial partner with years of practice in the sector. After a description of the educational goals, the presentation discusses the phases of the activity and the main methodological aspects. In addition, the adopted tools for the design and simulation of the developed systems are discussed in detail.

2019 - Re-design of a packaging machine employing linear servomotors: A description of modelling methods and engineering tools [Articolo su rivista]
Berselli, G.; Bilancia, P.; Bruzzone, L.; Fanghella, P.
abstract

Position-controlled servo-systems mostly make use of electric rotary motors and gearboxes and, if necessary, a transmission mechanism to convert rotary into linear motion. Even so, especially in the field of automatic machines for packaging, it should be highlighted that most of the required movements are usually linear, so that Linear Electric Motors (LEM) should somehow represent a more convenient solution for designers. LEM can directly generate the required trajectory avoiding any intermediate mechanism, thus potentially minimizing the number of linkages/mechanical parts and, therefore, the undesired backlash and compliance that come along. On the other hand, particularly within small-medium enterprises, LEM may be rarely employed despite obvious advantages, mostly due to their high-cost as compared to rotary actuators and the lack of knowledge of the achievable performance. In light of these considerations, the present paper reports an industrial case study where an automatic machine for packaging, comprising distributed actuation and several tasks requiring a linear motion, has been completely redesigned employing different kind of LEM (i.e. iron-core and iron-less). Such machine architecture is compared to a “traditional” design where brushless gearmotors are coupled to linkage systems. The paper mainly focuses on the selection criteria for the LEM system and on the engineering tools employed during the different design stages. Qualitative and quantitative conclusions are finally drawn, which may provide useful hints for designers that are willing to actually employ LEM-based solutions in an industrial scenario.

2018 - DESIGN OF A BEAM-BASED VARIABLE STIFFNESS ACTUATOR VIA SHAPE OPTIMIZATION IN A CAD/CAE ENVIRONMENT [Relazione in Atti di Convegno]
Bilancia, P; Berselli, G; Scarcia, U; Palli, G
abstract

Industrial robots are commonly designed to be very fast and stiff in order to achieve extremely precise position control capabilities. Nonetheless, high speeds and power do not allow for a safe physical interaction between robots and humans. With the exception of the latest generation lightweight arms, purposely design for human-robot collaborative tasks, safety devices shall be employed when workers enter the robots workspace, in order to reduce the chances of injuries. In this context, Variable Stiffness Actuators (VSA) potentially represent an effective solution for increasing robot safety. In light of this consideration, the present paper describes the design optimization of a VSA architecture previously proposed by the authors. In this novel embodiment, the VSA can achieve stiffness modulation via the use of a pair of compliant mechanisms with distributed compliance, which act as nonlinear springs with proper torque-deflection characteristic. Such elastic elements are composed of slender beams whose neutral axis is described by a spline curve with non-trivial shape. The beam geometry is determined by leveraging on a CAD/CAE framework allowing for the shape optimization of complex flexures. The design method makes use of the modeling and simulation capabilities of a parametric CAD software seamlessly connected to a FEM tool (i.e. Ansys Workbench). For validation purposes, proof-concept 3D printed prototypes of both non-linear elastic element and overall VSA are finally produced and tested. Experimental results fully confirm that the compliant mechanism behaves as expected.

2017 - A Practical Method for Determining the Pseudo-rigid-body Parameters of Spatial Compliant Mechanisms via CAE Tools [Articolo su rivista]
Bilancia, P.; Berselli, G.; Bruzzone, L.; Fanghella, P.
abstract

Compliant Mechanisms (CMs) are employed in several applications requiring high precision and reduced number of parts. For a given topology, CM analysis and synthesis may be developed resorting to the Pseudo-Rigid Body (PRB) approximation, where flexible members are modelled via a series of spring-loaded revolute joints, thus reducing computational costs during CM simulation. Owing to these considerations, this paper reports about a practical method to determine accurate PRB models of CMs comprising out-of-plane displacements and distributed compliance. The method leverages on the optimization capabilities of modern CAE tools, which provide built-in functions for modelling the motion of flexible members. After the validation of the method on an elementary case study, an industrial CM consisting of a crank mechanism connected to a fully-compliant four-bar linkage is considered. The resulting PRB model, which comprises four spherical joints with generalized springs mounted in parallel, shows performance comparable with the deformable system.

2017 - Quasi-static models of a four-bar quick-release hook [Articolo su rivista]
Bruzzone, L.; Berselli, G.; Bilancia, P.; Fanghella, P.
abstract

Quick-Release Hooks (QRHs) are connection devices for chains or metal ropes, which can be unfastened under full-load conditions by using a limited opening force. Despite their widespread use, the scientific literature about the mechanical behaviour of QRHs is rather limited. This paper deals with the kinematic and quasi-static analysis of a class of QRHs, based on a spring-loaded four-bar mechanism operating in the proximity of a singularity configuration. The quasi-static analysis allows to estimate the opening force as a function of the mechanism geometry and of the safety spring's features. At last, a multibody model of the system is developed, in order to validate the analytical model and to evaluate the influence of friction in revolute joints.

2017 - Virtual Prototyping of a Flexure-based RCC Device for Automated Assembly [Articolo su rivista]
Vaschieri, V.; Gadaleta, M.; Bilancia, P.; Berselli, G.; Razzoli, R.
abstract

The actual use of Industrial Robots (IR) for assembly systems requires the exertion of suitable strategies allowing to overcome shortcomings about IR poor precision and repeatability. In this paper, the practical issues that emerge during common “peg-in-hole” assembly procedures are discussed. In particular, the use of passive Remote Center of Compliance (RCC) devices, capable of compensating the IR non-optimal performance in terms of repeatability, is investigated. The focus of the paper is the design and simulation of a flexure-based RCC that allows the prevention of jamming, due to possible positioning inaccuracies during peg insertion. The proposed RCC architecture comprises a set of flexural hinges, whose behavior is simulated via a CAE tool that provides built-in functions for modelling the motion of compliant members. For given friction coefficients of the contact surfaces, these numerical simulations allow to determine the maximum lateral and angular misalignments effectively manageable by the RCC device.