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Plants are usually considered static organisms, but they can perform a wide range of movements that can be a source of inspiration for robots. The roots’ growing motion is the most noteworthy since they are excellent diggers that can move in unstructured environments and navigate past barriers. Furthermore, root growth has a high energy efficiency since it penetrates the soil at its tip, adding new material without displacing the already grown portion, minimizing the energy dissipation due to friction and lowering the inertia. A robot inspired by the growth of roots could be used in search and rescue or environmental monitoring. The design of a soft robot inspired by root growth is presented in this article. The robot body consists of a cylindrical plastic membrane folded inside itself. The robot body is inflated, and its tip is everted, expanding its length as air is blown from the base. Velcro straps are placed on the membrane’s exterior surface to keep it folded. The head is positioned inside the tip, which houses the mechanism that controls the growth direction. It consists of housing for two balloons that are selectively inflated, and their expansion applies pressure on the exterior surface, opening the Velcro straps and determining the growth direction. The robot was constructed, and a kinematic model of its motion in the plane was created and compared with experimental data. The error in predicting the turning angle is only 5%, and the resulting predicted position differs on average by 55 mm on a total length of 850 mm.

Structural health monitoring of civil infrastructure, such as bridges and buildings, has become a trending topic in the last few years. The key factor is the technological push given by new technologies that permit the acquisition, storage, processing and visualisation of data in real time, thus assessing a structure’s health condition. However, data related to anomaly conditions are difficult to retrieve, and, by the time those conditions are met, in general, it is too late. For this reason, the problem becomes unsupervised, since no labelled data are available, and anomaly detection algorithms are usually adopted in this context. This research proposes a novel algorithm that transforms the intrinsically unsupervised problem into a supervised one for condition monitoring purposes. Considering a bridge equipped with N sensors, which measure static structural quantities (rotations of the piers) and environmental parameters, exploiting the relationships between different physical variables and determining how these relationships change over time can indicate the bridge’s health status. In particular, this algorithm involves the training of N models, each of them able to estimate the quantity measured via a sensor by using the others’ N−1 measurements. Hence, the system can be represented by the ensemble of the N models. In this way, for each sensor, it is possible to compare the real measurement with the predicted one and evaluate the residual between the two; this difference can be addressed as a symptom of changes in the structure with respect to the condition regarded as nominal. This approach is applied to a real test case, i.e., Candia Bridge in Italy, and it is compared with a state-of-the-art anomaly detector (namely an autoencoder) in order to validate its robustness.

This paper shows the design of an underwater autonomous robot. The challenges of this activity are mainly linked to motion design and to energy efficiency. Therefore, a bioinspired approach has been used. Batoid fishes swim moving their pectoral fins, they produce a wave travelling in the direction opposite to their motion, pushing water backwards and gaining thrust as a consequence of momentum conservation. The motion of the fin has been studied and reproduced with a series of articulated mechanisms. In this work the optimization of the mechanism’s geometry is described and the experimental results on the reconstructed fin are presented., https://youtu.be/72AKxWktQBI

Wireless power transfer (WPT) devices represent one of the most efficient and increasingly used technologies for the transfer of data and power in the near-field range. This work analyzes and describes a new type of device: a ferrite-cored, variable gap, high-frequency power and data transfer system. The classic theoretical models existing in the literature for near-field communication (NFC) and WPT devices have foreseen a lumped-parameters characterization based on the representation of an equivalent circuit model (ECM). The strict interdependence between the different physical domains has clearly increased the difficulty in predicting the behavior of the device, due to the unwanted continuous and chaotic variation of the parameters. The proposed paper aims to provide a general and reliable multi-physics model based on the co-simulation of a Spice®-based ECM analysis and the ESRF Radia®-based 3D finite volume methodology (3DFVM), placing particular emphasis on the intrinsic sensitivity with respect to variables that cannot be directly controlled, such as the variation of the air gap between the coupled coils interfaces. Furthermore, this work outlines a detailed and effective experimental methodology for the estimation of static and dynamic electro-magnetic parameters and the validation of the numerical models in both the time and frequency domain, through the analysis of a real coupled WPT device.

This article presents the design and the experimental tests of a bioinspired robot mimicking the cownose ray. These fish swim by moving their large and flat pectoral fins, creating a wave that pushes backward the surrounding water so that the fish is propelled forward due to momentum conservation. The robot inspired by these animals has a rigid central body, housing motors, batteries, and electronics, and flexible pectoral fins made of silicone rubber. Each of them is actuated by a servomotor driving a link inside the leading edge, and the traveling wave is reproduced thanks to the flexibility of the fin itself. In addition to the pectoral fins, two small rigid caudal fins are present to improve the robot’s maneuverability. The robot has been designed, built, and tested underwater, and the experiments have shown that the locomotion principle is valid and that the robot is able to swim forward, perform left and right turns, and do floating or diving maneuvers.

The study of fish swimming is of great interest for engineers and researchers because the investigation of novel propulsion mechanisms is functional to the development of autonomous underwater vehicles. Among the different locomotion strategies adopted by fish species, the one characterizing the cownose ray is known to be very efficient. These fishes move their large pectoral fins and create a wave travelling in a direction opposite to the swimming direction. Thus, thanks to momentum conservation, the fish receives a propulsive thrust. This mechanism has been reproduced in a bioinspired robot mimicking a cownose ray, which has been designed and built. Before testing the robot underwater, some preliminary experiments in a small wind tunnel have been performed on a single fin. These tests are aimed at assessing the fluid dynamics of the fin shape and at verifying the effectiveness of this propulsive strategy. The fluid dynamic forces acting on the profile are measured with the fin still; the velocity of the incoming air is such that the Reynolds number is the same as for the fish swimming in water. Then, the propulsive strategy is tested with the fin in motion; the velocity of the incoming air is the same as the relative velocity of water for the fish during forward swimming, and several experiments were carried out with different frequencies and wavelengths of fin motion. Finally, having the fluids different densities, the measured forces and moments are scaled. These tests have confirmed that the cownose ray swimming strategy is effective and a relation between the measured forces with frequency and wavelength of fin motion has been found.

Among all aquatic species, mantas and rays swim by oscillating their pectoral fins; this motion is similar to other fishes in term of efficiency, but it gives better agility in turning with respect to fishes moving their caudal fin. The fin motion is featured by a travelling wave going opposite to the forward motion, producing a force thanks to momentum conservation. Another contribution to the generation of thrust is given by the generation of a vortex in correspondence of the leading edge of the fin, which pulls the fish forward thanks to the lower pressure in its centre. In literature these contributions have been highlighted, but it remains to understand which one of these two mechanisms is prevailing according to different conditions of swimming, how they affect each other and what is the influence of the two on energetical efficiency. The object of this activity is to investigate how thrust generation is influenced by geometrical characteristics of the fin, such as size, geometry and flexibility and by parameters of motion, such as speed, amplitude and frequency of fin oscillation and velocity of the travelling wave. A CFD model of the fish has been implemented in OpenFOAM, not only confirming that both upstroke and downstroke contribute positively to the forward movement according to the momentum conservation principle, but also highlighting the formation of a leading-edge vortex enhancing thrust generation. The description of how thrust generation is linked to motion parameters is simulated also coupling the CFD with a multibody to simulate the whole motion in its complexity.

The increasing availability of small size and low cost sensors is orienting the world of smart structures towards a deep integration of a large number of these devices. This makes possible a more accurate knowledge of the dynamics of the structure, even if it requires the ability to manage an increasing number of information, potentially not consistent. In applications of vibration suppression, this circumstance must be avoided as measurements are used as a feedback in the control loop and therefore they can potentially capable of altering the stability of the controlled system and, in any case, to limit its performance. This work proposes a new algorithm for the automatic identification of inconsistent measurements due to sensors malfunctions, noise, wrong calibrations, etc. The approach is based on an innovative sliding mode observer that has been designed to seek faults and to avoid false positive results. The algorithm has been numerically and experimentally tested on a composite smart structure with 15 Fiber Bragg grating sensors embedded. Tests have been carried out considering different faults. Results confirm the effectiveness of the approach and allows to always identify faulty sensors.

A huge problem in cruise ships is related to undesired noise and vibrations generated by engines and exhaust stacks. Reduction or suppression of ship noise has traditionally been implemented by passive means, such as by the use of vibration isolation mounts, flexible pipe-work, and interior acoustic absorbing materials. However. while passive devices are effective mostly for attenuating high-frequency noise, they are generally ineffective to suppress low-frequency vibrations. The paper deals with the design of an active standalone device to suppress vibrations on cruise ships funnels. The device can work independently and, matched with others through a decentralized control, can dissipate most of the kinetic energy of the system, thus limiting the propagation of vibration and improving comfort on surroundings.

Professional players claim that stringed musical instruments exhibit better acoustic behaviour if they are frequently played. Although in literature there is no clear relationship between these phenomena, this work aims to develop a device capable of “making a violin sound” autonomously, so that it can always be kept in optimal conditions. The paper shows the design aspects of the magnetostrictive actuator, its operating principle, the prototype development and the experimental characterization. The prototype is then mounted on a new violin, simulating its continuous use for a week. During the test the acoustic measurements showed a large change in the acoustic response of the instrument, thus demonstrating the effectiveness of the magnetostrictive actuator in the training of a stringed instrument.

Operators of construction trucks (such as wheel loaders, excavators, etc.) are often exposed to severe whole body vibrations induced by road/soil unevenness. Most of construction trucks are not equipped with any cabin suspensions unless seat and tires. Especially these latter are of paramount importance since they also govern the natural frequencies and the modes of vibration of the vehicle. Specific care has thus been paid to tires during the years and different technologies were adopted for their construction.

Wind turbine blades are being bigger and bigger, thus requiring lightweight structures that are more flexible and thus more sensitive to dynamic excitations and to vibration problems. This paper investigates a preliminary architecture of large wind turbine blades, embedding thin sheets of SMA to passively improve their total damping. A phenomenological material model is used for simulation of strain-dependent damping in SMA materials and an user defined material model was developed for this purpose. The response of different architectures of SMA embedded blades have been investigated in the time domain to find an optimal solution in which the less amount of SMA is used while the damping of the system is maximized

Deep drawing is a practical process to create shell metal parts. In this process punch draw sheet metal into die cavity. Punch and die must be changed for part with new geometry leading to high costs and time waste. To overcome this problem, in the last years the use of rubber die has become more and more widespread. This technique requires the use of ultrasonic vibration that helps to reduce friction between punch and die and then the risk of thinning. In this paper a numerical study, based on finite element method, of the deep drawing process of circular sections with rubber die assisted by ultrasonic vibration is presented. An in depth analysis on the effects of amplitude and frequency of ultrasonic vibration is carried out. Results show that by increasing amplitude and frequency of ultrasonic vibration, limits on the forming force can be profitably increased, ensuring a better execution of the process.

Dynamic measurements on carbon nanotube (CNT) multiscale glass fiber reinforced polymers (GFRPs) were performed to assess the usage of self-sensing composite structures in vibration environment. To achieve that purpose, a composite cantilever beam was tested in static and dynamic conditions. Applied strain was measured by means of strain gauges mounted on the tested specimen. Static measurements were performed to investigate linearity and repeatability of the CNT sample response. The dynamic behavior was evaluated with step sine excitation at different forcing frequencies. Preliminary results finally proved the validity and the applicability of carbon nanotubes composites to measure dynamic forcing and vibration.

Electrical measurements of carbon nanotube multiscale GFRPs have been carried out for the monitoring of low velocity impact dynamics. To achieve that purpose, several plates have been fed by a power supply and a high frequency acquisition system has been used. Electrical measurements show that there is an initial decrease of electrical resistance due to plate compression, followed by an increase due to tunneling effect of carbon nanotubes. Finally, the effect of mechanical rebound is correlated to drop rise cycles of the electrical resistance. The sensitivity of the measured signals is also correlated with the impact energy and the electrodes disposition. Thus, the proposed method proves the validity and applicability of carbon nanotubes to characterize the low-velocity impact dynamics of a composite laminate.

The design of an automatic system requires a synergistic collaboration between several disciplinary areas, involving know-how and expertise in mechanical, electrical and technical fields. A robot is a complex automatic system, which carries on more than the common features of a simple machine, since it is usually designed to accomplish tasks which are not known during the design phase. This paper deepens the design of a five-bar parallel manipulator with two degrees of freedom highlighting the multidisciplinary approach used in its development. Starting from the machine requirements, the process of kinematic optimization, the structural design phase, the dynamic analysis and the sizing of the driving systems are deeply described. Finally the designed PKM is realized and tested, comparing experimental results with those obtained from numerical analysis.

The paper deals with the design of a device for sound reproduction to be fixed to a supporting surface. The device is made up of two different types of acoustic actuators based on different technologies. This allows to reproduce sound in the range of frequencies from 20 Hz to 20 kHz. The generation of sound at high frequencies is demanded to a magnetostrictive actuator, while a more traditional magnetodynamics actuator is used to generate sound at low frequencies. The coupling between these two actuators leads to a device having small overall dimensions and high performance.

Resonance transducers have been widely developed and studied, as they can be profitably used in many application such as liquid atomizing and sonar technology. The active element of these devices can be a giant magnetostrictive material (GMM) that is known to have significant energy density and good performance at high frequencies. The paper introduces an analytical model of GMM transducers to describe their dynamics in different working conditions and to predict any change in their performance. The knowledge of the transducer behavior, especially in operating conditions different from the ideal ones, is helpful in the design and fabrication of highly efficient devices. This transducer is design to properly work in its second mode of vibration and its working frequency is around 8000 Hz. Most interesting parameters of the device, such as quality factor, bandwidth and output strain are obtained from theoretical analysis.

Liquid atomization has many applications such as car fuel injector, heat dissipation, coating, medical use, etc. The most common way in atomization is to exploit high frequency and high vibration amplitudes of piezoelectric devices. This paper investigates the effectiveness of a giant magnetostrictive transducer for atomizing liquids. Effect of vibration amplitudes on output parameters such as atomization size and output Dubai have been investigated so as the frequency response of the transducer when plunged into the water. Droplet size particles have been measured through high speed camera. Results show that using giant magnetostrictive transducer leads to uniformity that is considered a key factor in many applications. Results demonstrates that sonic transducers based on giant magnetostrictive material can be profitably used as liquid atomizers.

The aim of active vibration control is to enhance the performance of a system (eg. comfort, fatigue life, etc.) by limiting vibrations. One of the most effective technique to reach this goal is to increase the equivalent damping of the system and then the dissipation of the kinetic energy (the so called skyhook damping technique). Application of active vibration control often require a complex setup. When large structures are considered, it is often necessary to have a high number of sensors and actuators, suitably cabled, in addition to all the devices necessary to condition and amplify the signals of measurement and control and to execute in real time the control algorithms synthesized. This work arises from the need to simplify this situation, developing a standalone device that is able of carrying out operations of vibration control in an autonomous way, thus containing in itself an actuator, the sensors needed to evaluate the vibratory state of the structure, and a micro-controller embedding different control algorithm. The design of the smart damper covers many aspects and requires a strong integration of different disciplines. A prototype has been realized and tested on a vibrating structure. The experimental results show good performance in suppress vibration.

Magnetostrictive inertial actuators are profitably used in applications of vibration control. However their use is limited to high frequencies because of problems related to control stability and to small exertable forces. This paper presents the design of an innovative low-frequency magnetostrictive inertial actuator. With respect to traditional magnetostrictive actuators it is able to significantly multiply the amplitude of the elongation of the magnetostrictive bar and to extend its functioning well below the working frequencies of traditional devices. The design of the actuator has been optimized through both an analytical model and a finite element model taking into account all the design parameters. The optimized low-frequency magnetostrictive inertial actuator has then been produced and its frequency response compared to that of a traditional magnetostrictive actuator made up of the same components (except for the supporting structure).

One of the most frequent applications of magnetostrictive actuator technology is the active structural vibration control (AVC). Magnetostrictive actuators (MAs) can deliver high-output forces and can be driven at high frequencies. These characteristics make them suitable for a variety of vibration control applications. The use of this technology, however, requires an accurate knowledge of the dynamics of such actuators. Several models are available in the literature. However, their use in control applications, characterized by high dynamics, is often limited by nonlinearities and complexity of the model. To overcome this difficulty, the paper introduces a linear model of magnetostrictive actuators that is valid in a range of frequencies below 2 kHz. The assumptions supporting the linearity of the system are discussed and the theoretical model is presented. Finally the model is validated through experimental tests carried out on two different magnetostrictive actuators.

As well known, the kinetostatic performances (repeatability, stiffness, maximum force or velocity) of serial and parallel manipulators depend strongly on the kinematic structure and on the manipulator configuration inside its working space. The manipulator performances are often analyzed using the manipulability ellipsoids which depend on the manipulator Jacobian. This paper investigates the significance of the classical definition of manipulability ellipsoid highlighting its lack of significance in some circumstances and proposes a new extended definition which takes into account the different performances of each actuator. This definition is particularly useful for manipulators with different kinematic chains and various types of actuated joints (e.g. revolute and prismatic). Then the paper reviews the concept of isotropy and its properties: a manipulator exhibits an isotropic behaviour when it has the same performances along all the directions of the working-space. Then, the authors introduce the new concept of Point of Isotropy both for serial and parallel manipulators, showing how in some circumstances a non-isotropic manipulator may be transformed into an isotropic one simply changing the location of its TCP (Tool Center Point). This concept may be used to design new manipulators or to make isotropic already existing manipulators just modifying the shape or dimension of the last link. The theoretical investigation of this new concept is supported by its application to the design of an isotropic Stewart–Gough platform.

Traditional aeroelastic models rely only on good mechanical design and accurate crafting in order to match the required structural properties. This paper proposes an active regulation of their structural parameters in order to improve accuracy and reliability of wind tunnel tests. Following the design process steps typical of a smart structure, a damping tuning technique allowing to control a specific set of vibration modes is developed and applied on the aeroelastic model of a long-span suspended bridge. Depending on the testing conditions, the structural damping value can be adjusted in a fast, precise and repeatable way in order to highlight the effects of the aerodynamic phenomena of interest. In particular, vortex-induced vibration are taken into consideration, and the response of a bridge section to vortex shedding is assessed. The active parameter regulation allows to widen the pattern of operating conditions in which the model can be tested. The paper discusses the choice of both sensors and actuators to be embedded in the structure and their positioning, as the control algorithm to obtain the desired damping. Experimental results are shown and results are discussed to evaluate the performance of the smart structure in wind dunnel tests.

Terfenol-D resonance transducer has high energy-density and high vibration amplitude. These features make them good selection for using in different applications such as liquid atomizers and sonar transducers. Operating mode of the Terfenol- D transducer plays an important role in efficiency of it. It can also change some parameters of the transducer such as quality factor. In this paper, experimental comparative study between first and second longitudinal modes of vibration in the Terfenol-D transducer is presented. It contains the mechanical quality factor, band with frequency and also effect of changing Young modulus in resonance frequency and mode shape. For this purpose, a resonance transducer for working in 3 kHz in first mode and 8.25 kHz in second mode has been designed and fabricated. In design procedure, preload mechanism location is considered as nodes. Quality factor and bandwidth is calculated experimentally and resonance frequency and mode shape has been calculated both with analytical method and ANSYS12 FEM commercial software. Results show that higher quality factor in the second mode shape and this mode shows lower sensitivity with Young modulus .

In the manufacturing field it happens that products are processed by high-speed production lines. They pass through different machines in order to be processed, according to a pre-established order, resting on moving supports. Usually they do not stop during this process: rather, the machines are able to track and handle them while they are moving.

The paper deals with a project aimed to improve the reliability of a condition monitoring system applied on gearboxes installed on rolling mills. In this context, to properly set up the algorithm, it is necessary to have measurements associated both to standard operating conditions and to malfunctioning. The latter, not being able to be experimentally generated, can be simulated by developing numerical models of the machine under varying conditions. The outputs generated, corresponding to different fault conditions associated with the main common failures of the elements that constitute the transmission, will provide a useful data base to tune the algorithm of condition monitoring.

The paper discusses the opportunity to use piezoelectric actuators (PZT) and Fiber Bragg Grating sensors (FBGs) to realize a smart structure including in itself both the sensing and the actuating devices. Different control strategies have been implemented on a test rig consisting on a plate made of carbon fiber using two chains with 15 FBG sensors each and 6 PZT actuators. Control forces are designed to increase the damping of the structures, allowing to increase of damping of the first modes of vibration of about 10 times.

Embedding FBG sensors in carbon fiber structures is a very attractive solution, due to the small fiber diameter, and the possibility to manufacture arrays of many gratings into a single optical fiber. These embedding is particularly useful for the manufacturing of smart structures, able to improve their characteristics thanks to embedded sensors and actuators. In this work a carbon fiber beam of 3 m length, with an array of 30 FBG sensors and 3 piezoelectric actuators, is described. The focus of the work is on the evaluation of the good operation of embedded FBG sensors, that is not easy due to the microstructure of woven carbon fiber layers, producing non-homogeneous strain field, a well known problem for the reliability of FBG strain measurements. The proposed technique looks at the standard deviation of the full width at -6 dB of the spectra of each FBG sensors, during a quasi-static motion producing quasi-static strains. 37% of the 30 FBG sensors have been found to produce measurements corrupted by a small error. At the end, vibration control of the described structure is shown.

Fiber Bragg Gratings (FBG) sensors have a great potential in active vibration control of smart structures thanks to their small transversal size and the possibility to make an array of many sensors. The paper deals with the opportunity to reduce vibration in structures by using distributed sensors embedded in carbon fiber structures through the so called sensors-averaging technique. This method provides a properly weighted average of the outputs of a distributed array of sensors generating spatial filters on a broad range of undesired resonance modes without adversely affecting phase and amplitude. This approach combines the positive sides of decentralized control techniques as the control forces applied to the system are independent of one another, while, as for the centralized controls it has the possibility to exploit the information from all the sensors. The ability to easily manage this information allows to synthesize an efficient modal controller. Furthermore it enables to evaluate the stability of the control, the effects of spillover and the consequent effectiveness in reducing vibration. Theoretical aspects are supported by experimental applications on a large flexible system composed of a thin cantilever beam with 30 longitudinal FBG sensors and 6 piezoelectric actuators (PZT).

The large use of lightweight structures has emphasized the need to reduce undesired vibrations which can compromise the integrity and the safety of flexible structures. The advancements in materials technology have made available a new generation of materials regarded as smart. Thanks to the results obtained in this field, many research are focusing on the study of intelligent structures, able to modify their mechanical properties. Composite materials are interesting in the construction of smart structures, thanks to their high mechanical properties which allow to obtain lightweight structures with high resistance and due to the possibility of embedding sensors and actuators inside the structure. Among all, optical fiber sensors are widely used in the development of smart structures. However, while they are usually considered for structural health monitoring, this paper proposes their use in active control application. A structure made of carbon fiber with Fiber Bragg Grating (FBG) sensors and piezoelectric actuators is able to self-sense its state of vibration and to provide control forces to reduce it. The peculiarity of this structure is represented by the possibility to monitor a large number of sensors (to approximate distributed measurements), suitable for physical feedback or modal control. The experimental tests carried out allow to investigate the effectiveness of these setup in the active vibration control and to evaluate the limits of this technology.

Flexible-link robots are an important class of manipulators which uses lightweight arms for assembly, civil infrastructure, bridge/vehicle systems and large-scale space structures. The wide spread of these systems in various application areas has ensured that the modeling of flexible elements and the control of vibration have received a great deal of attention in recent years. In this work it is analyzed a two DOF parallel robot with two flexible links used for pick and place operations, developing a control strategy based on piezoelectric actuators and strain gauges or accelerometers embedded in the links. The analysis of the robot behaviour and the development of the controller, have been carried out on an electromechanical model built in Matlab® and co-simulated with the multibody flexible model built in Adams®. Results show positive confirmation of the study and encourage future tests on the real manipulator to validate the multibody model and the control strategy.