Paolo Paoletti

University of Liverpool | UoL · School of Engineering

This paper aims to elucidate the application of feedback linearization in systems having nonsmooth nonlinearities. With the aid of analytical expressions originating from classical feedback linearization theory, it is demonstrated that for a subset of nonsmooth systems, ubiquitous in the structural dynamics and vibrations community, the theory hold...

The interaction of a robotic manipulatorwith unknown soft objects represents a significant challenge for traditional robotic platforms because of the difficulty in controlling the grasping force between a soft object and a stiff manipulator. Soft robotic actuators inspired by elephant trunks, octopus limbs and muscular hydrostats are suggestive of...

While Laser powder bed fusion (L-PBF) machines have greatly improved in recent years, the L-PBF process is still susceptible to several types of defect formation. Among the monitoring methods that have been explored to detect these defects, camera-based systems are the most prevalent. However, using only photodiode measurements to monitor the build...

Most current works in Sim2Real learning for robotic manipulation tasks leverage camera vision that may be significantly occluded by robot hands during the manipulation. Tactile sensing offers complementary information to vision and can compensate for the information loss caused by the occlusion. However, the use of tactile sensing is restricted in...

A microcantilever is a suspended micro-scale beam structure supported at one end which can bend and/or vibrate when subjected to a load. Microcantilevers are one of the most fundamental miniaturized devices used in microelectromechanical systems and are ubiquitous in sensing, imaging, time reference, and biological/ biomedical applications. They ar...

Sleep posture and movements offer insights into neurophysiological health and correlate with overall well-being and quality of life. Clinical practices utilise polysomnography for sleep assessment, which is intrusive, performed in unfamiliar environments, and requires trained personnel. While sensor technologies such as actigraphy are less invasive...

Autonomous path planning along riverbanks is crucial for unmanned surface vehicles (USVs) to execute specific tasks such as levee safety detection and underwater pipe inspections, which are vital for riverbank safety and water environment protection. Given the intricate shapes of riverbanks, the dynamic nature of tidal influences, and constraints i...

In the nuclear industry, the need for improved reliability in current and future technology hinders the deployment of autonomous robotic systems. The following research aims to develop a method of reliably mapping a large environment and abstracting the map into a sparse node graph to create a more efficient data form. The proposed data form allows...

Recent studies in additive manufacturing (AM) monitoring techniques have focussed on the identification of defects using in situ monitoring sensor systems, with the aim of improving overall AM part quality. Much work has focussed on the use of of camera-based monitoring systems; however, limitations such as the slow response rates of the sensors (1...

Recently, several morphologies, each with its advantages, have been proposed for the \textit{GelSight} high-resolution tactile sensors. However, existing simulation methods are limited to flat-surface sensors, which prevents their usage with the newer sensors of non-flat morphologies in Sim2Real experiments. In this paper, we extend a previously pr...

Sensors based on self-excitation of microcantilevers have been proposed as effective devices for the measurement of rheological properties of the fluid where they are immersed. However, embedding microcantilevers in a feedback loop causes complex phenomena that need to be investigated. Specifically, a variable delay in the loop originates jumps in...

This work describes a new platform for sensing mass or rheological properties of gases with unprecedented responsivity and limits of detection. The system consists of a microcantilever working in a Phase-Locked Loop with an imposed phase between its excitation and deflection signals. The optically detected cantilever deflection is demodulated again...

Dynamically substructured systems (DSS) are a typical technique to achieve real-time numerical simulations combined with physically tested components. However, the rigorous feasibility analysis before the implementation is missing. This paper is aimed to fill this gap by establishing rigorous conditions for when DSS is suitable for dynamic testing....

We investigate the response of a digitally controlled and parametrically pumped microcantilever used for sensing in a Phase-Locked Loop (PLL). We develop an analytical model for its dynamical response and obtain an explicit dependence on the rheological parameters of the surrounding viscous medium. Linearization of this model allows to find improve...

Sleep behaviour and in-bed movements contain rich information on the neurophysiological health of people, and have a direct link to the general well-being and quality of life. Standard clinical practices rely on polysomnography for sleep assessment; however, it is intrusive, performed in unfamiliar environments and requires trained personnel. Progr...

Sleep posture is linked to several health conditions such as nocturnal cramps and more serious musculoskeletal issues. However, in-clinic sleep assessments are often limited to vital signs (e.g. brain waves). Wearable sensors with embedded inertial measurement units are used for sleep posture classification; nonetheless, existing works consider onl...

This work presents a feedback closed-loop platform to be used for viscosity or viscoelasticity sensing of Newtonian or non-Newtonian fluids. The system consists of a photothermally excited microcantilever working in a digital Phase-Locked Loop, in which the phase between the excitation signal to the cantilever and the reference demodulating signals...

OrigamiSats, a new concept in solar sailing, are origami spacecraft with reflective panels which, when flat, operate as a conventional solar sail. Shape reconfiguration, i.e. "folding" of the origami design, allows the OrigamiSat to change operational modes, performing different functions as per mission requirements. For example, a flat OrigamiSat...

Path-keeping requires unmanned surface vehicles (USVs) to follow a planned path in autonomous navigation. It is essential for USVs to carry out autonomous tasks such as collecting various data of water quality and surrounding terrain for exploration and protection of water environments. However, due to obstacle avoidance and other factors such as w...

Prestrained elastic networks arise in a number of biological and technological systems ranging from the cytoskeleton of cells to tensegrity structures. Motivated by this observation, we here consider a minimal model in one dimension to set the stage for understanding the response of such networks as a function of the prestrain. To this end we consi...

Sleep posture is linked to several health conditions such as nocturnal cramps and more serious musculoskeletal issues. However, in-clinic sleep assessments are often limited to vital signs (e.g. brain waves). Wearable sensors with embedded inertial measurement units have been used for sleep posture classification; nonetheless, previous works consid...

In this article, a self-reconfiguring OrigamiSat concept is presented. The reconfiguration of the proposed OrigamiSat is triggered by combining the effect of 4D material (i.e. origami’s edges) and changes in the local surface optical properties (i.e., origami’s facets) to harness the solar radiation pressure acceleration. The proposed OrigamiSat us...

Prestrained elastic networks arise in a number of biological and technological systems ranging from the cytoskeleton of cells to tensegrity structures. To understand the response of such a network as a function of the prestrain, we consider a minimal model in one dimension. We do this by considering a chain (1D network) of elastic springs upon whic...

The human foot is uniquely adapted to bipedal locomotion and has a deformable arch of variable stiffness. Intrinsic foot muscles regulate arch deformation, making them important for foot function. In this study we explore the hypothesis that normal daily activity in minimal footwear, which provides little or no support, increases foot muscle streng...

A self-oscillating microcantilever in a feedback loop comprised of a gain, a saturator, and an adjustable phase-shifter is used to measure the viscosity of Newtonian fluids. Shifting the signal of the loop with the adjustable phase-shifter causes sudden jumps in the oscillation frequency of the cantilever. The exact position of these jumps depends...

Most current works in Sim2Real learning for robotic manipulation tasks leverage camera vision that may be significantly occluded by robot hands during the manipulation. Tactile sensing offers complementary information to vision and can compensate for the information loss caused by the occlusion. However, the use of tactile sensing is restricted in...

Recent studies on sleep reveal its impact on the well-being of humans. Monitoring of in-bed body postures can provide clinicians with early indicators of a wide range of musculoskeletal disorders. Current work on sleep pose classification is directed at non-wearable technologies, with issues associated to limited body observability and concerns ove...

This paper presents the design of an end-effector for handling of supplies commonly found in chemistry labs. The system uses a cable loop capable of providing an effective grasp of any prismatic or cylindrical object, making it ideal for handling vials and other containers commonly used in laboratories. When compared to the more common parallel jaw...

A simplified model for predicting behaviour of soft actuators and support the development of an automatic design tool is proposed in this paper. In particular, the model aims to predict curvature and tip force of inflated soft pneumatic actuators (SPAs) using computationally inexpensive models. Experimental validation shows that the proposed models...

Dynamic substructuring is a popular hybrid testing technique that mixes physical testing with numerical simulations. Research in this domain has mainly focused so far on structures and decomposition strategies that result in asymptotically stable systems. However, several cases fall outside this family, with either the physical or the numerical par...

This paper presents the design of an end-effector for handling of supplies commonly found in chemistry labs. The system uses a cable loop capable of providing an effective grasp of any prismatic or cylindrical object, making it ideal for handling vials and other containers commonly used in laboratories. When compared to the more common parallel jaw...

This study evaluates whether a combination of photodiode sensor measurements, taken during laser powder bed fusion (L-PBF) builds, can be used to predict the resulting build quality via a purely data-based approach. We analyse the relationship between build density and features that are extracted from sensor data collected from three different photo...

This paper presents a low-cost localisation system based on ultrasonic sensing and time of flight measurements. A compact ultrasound emitter has been designed to generate omnidirectional trains of ultrasound pulses which are then picked up by several fixed receivers measuring time difference of arrival. A least squares approach is used to analytica...

One of the most difficult challenges faced by ground robots operating in the aftermath of a disaster is the presence of uneven and unstable terrains; in these environments traditional locomotive systems struggle. In this work, a Polyurethane Foam depositing system is proposed to enable ground robots to overcome obstacles and navigate challenging su...

One of the most difficult challenges for terrestrial robotic platforms in disaster scenarios is their inability to traverse highly irregular terrain. Many different robotic architectures have been proposed over recent years, each with benefits and shortfalls. In this work, we propose a Polyurethane Foam depositing system, which can be applied to an...

Risk-averse areas such as the medical, aerospace and energy sectors have been somewhat slow towards accepting and applying Additive Manufacturing (AM) in many of their value chains. This is partly because there are still significant uncertainties concerning the quality of AM builds. This paper introduces a machine learning algorithm for the automat...

Using the atomic force microscopy- (AFM-) PeakForce quantitative nanomechanical mapping (QNM) technique, we have previously shown that the adventitia of the human internal mammary artery (IMA), tested under dehydrated conditions, is altered in patients with a high degree of arterial stiffening. In this study, we explored the nanoscale elastic modul...

Risk-averse areas such as the medical, aerospace and energy sectors have been somewhat slow towards accepting and applying Additive Manufacturing (AM) in many of their value chains. This is partly because there are still significant uncertainties concerning the quality of AM builds. This paper introduces a machine learning algorithm for the automat...

A versatile mass-sensing platform based on the nonlinear dynamical response of a microcantilever embedded in a self-excitation feedback loop is proposed. It is experimentally shown that the delay imposed in the feedback loop by an adjustable phase-shifter can be used to finely tune this system to work in three different modalities, according to the...

Statement of significance: Arterial stiffening occurs as part of the natural aging process and is strongly linked to cardiovascular risk. Although arterial stiffening is routinely measured in vivo, little is known about how localised changes in artery structure and biomechanics contributes to in vivo arterial stiffening. This study focusses on the...

A viscosity sensor based on the nonlinear behaviour of a microcantilever embedded in a self-excitation loop with an adjustable phase-shifter is proposed. The self-sustained oscillation frequencies of the cantilever are experimentally and theoretically investigated as functions of the fluid viscosity and of the imposed phase shift of the signal alon...

Arterial stiffening is well-established as a powerful predictor of cardiovascular diseases. However, arterial stiffening is rarely associated with extracellular matrix changes in arterial tissue. In this study, we present localized nanomechanical properties in the human internal mammary artery (IMA) along with collagen fibril morphology in patients...

Microcantilevers are increasingly being used to create sensitive sensors for rheology and mass sensing at the micro- and nano-scale. When operating in viscous liquids, the low quality factor of such resonant structures, translating to poor signal-to-noise ratio, is often manipulated by exploiting feedback strategies. However, the presence of feedba...

Aeroelastic instabilities due to the interaction between airflow and wings have long constrained the flight envelope of many types of aircrafts. A typical example of these phenomena is fluttering, a self-sustained oscillation in pitch, plunge or flap angle. Control systems and accurate models are then required to describe and suppress this undesire...

Large networks of interacting dynamical systems are well-known for the complex behaviours they are able to display, even when each node features a quite simple dynamics. Despite examples of such networks being widespread both in nature and in technological applications, the interplay between the local and the macroscopic behaviour, through the inte...

Control of nonlinear systems with uncertain information about the nonlinearity poses significant challenges, as any mismatch between the true nonlinearity and the one assumed for controller design can result in performance degradation or even instability. In this paper we merge optimal nonlinearity approximations with controller dissipativity prope...

The paper introduces a novel platooning model for vehicles subject to nonlinear drag. A linear parametric controller, taking into account both the actual position and the relative displacement with respect to neighbors, is applied to each vehicle and, then, its effects are investigated via a semi-analytical approach based on partial differential eq...

When dealing with linear systems feedback interconnected with memoryless nonlinearities, a natural control strategy is making the overall dynamics linear at first and then designing a linear controller for the remaining linear dynamics. By canceling the original nonlinearity via a first feedback loop, global linearization can be achieved. However,...

Systems composed by a linear dynamical part feedback interconnected with a static nonlinearity are traditionally controlled by canceling the nonlinearity through a first feedback loop, and then designing a linear controller for the remaining linear dynamics. However, this procedure may provide unsatisfactory performance, and even lead to instabilit...

The locomotion of many soft-bodied animals is driven by the propagation of rhythmic waves of contraction and extension along the body. These waves are classically attributed to globally synchronized periodic patterns in the nervous system embodied in a central pattern generator (CPG). However, in many primitive organisms such as earthworms and inse...

Feedback linearisation is a well-known technique in the controls community but has not been widely taken up in the vibrations community. It has the advantage of linearising nonlinear system models, thereby enabling the avoidance of the complicated mathematics associated with nonlinear problems. A particular and common class of problems is considere...

A natural way of controlling linear systems feedback interconnected with memoryless nonlinearities is canceling this latter with a first feedback loop, and then designing a linear controller for the remaining linear dynamics. Nevertheless, this procedure may provide unsatisfactory performance, and even lead to instability, when the nonlinearity can...

Birds, fish and other animals routinely use unsteady effects to save energy by alternating between phases of active propulsio and passive coasting. Here, we construct a minimal model for such behaviour that can be couched as an optimal control proble via an analogy to travelling with a rechargeable battery. An analytical solution of the optimal con...

We apply the PeakForce Quantitative Nanomechanical Property Mapping (PFQNM) atomic force microscopy mode for the investigation of regional variations in the nanomechanical properties of porcine sclera. We examine variations in the collagen fibril diameter, adhesion, elastic modulus and dissipation in the posterior, equatorial and anterior regions o...

Networks of dynamical systems are widespread both in nature and in technology applications, but the interplay between the node dynamics, their interconnections and the macroscopic behavior is still not completely understood. In fact, the intrinsically large dimension of the phase space of such networks represents the main obstacle for their analysi...

Dynamic mode atomic force microscopy provides high resolution in imaging biological samples, but it features a reduced scanning velocity. In this paper we investigate a recent scheme in which the cantilever gets excited by a feedback loop containing a saturation function. The proposed modality is then analyzed via Floquet theory and compared to the...