Design and Characterization of Tri-axis Soft Inductive Tactile Sensors

Tactile sensors are essential for robotic systems to safely and effectively interact with the environment and humans. In particular, tri-axis tactile sensors are crucial for dexterous robotic manipulations by providing shear force, slip or contact angle information. The Soft Inductive Tactile Sensor (SITS) is a new type of tactile sensor that measures inductance variations caused by eddy-current effect. In this paper, we present a soft tri-axis tactile sensor using the configuration of four planar coils and a single conductive film with hyperelastic material in between them. The working principle is explained and design methods are outlined. A 3D finite element model was developed to characterize the tri-axis SITS and to optimize the target design through parameter study. Prototypes were fabricated, characterized and calibrated, and a force measurement resolution of 0.3 mN is achieved in each axis. Demonstrations show that the sensor can clearly measure light touch (a few mN normal force) and shear force pulses (10 to 30 mN) produced by a serrated leaf when it is moved across the sensor surface. The presented sensor is low cost, high performance, robust, durable, and easily customizable for a variety of robotic and healthcare applications

Wearable sensors for respiration monitoring: a review

This paper provides an overview of flexible and wearable respiration sensors with emphasis on their significance in healthcare applications. The paper classifies these sensors based on their operating frequency distinguishing between high-frequency sensors, which operate above 10 MHz, and low-frequency sensors, which operate below this level. The operating principles of breathing sensors as well as the materials and fabrication techniques employed in their design are addressed. The existing research highlights the need for robust and flexible materials to enable the development of reliable and comfortable sensors. Finally, the paper presents potential research directions and proposes research challenges in the field of flexible and wearable respiration sensors. By identifying emerging trends and gaps in knowledge, this review can encourage further advancements and innovation in the rapidly evolving domain of flexible and wearable sensors.This work was supported by the Spanish Government (MICINN) under Projects TED2021-131209B-I00 and PID2021-124288OB-I00.Peer ReviewedPostprint (published version

Robust and High-Performance Soft Inductive Tactile Sensors based on the Eddy-Current Effect

Tactile sensors are essential for robotic systems to interact safely and effectively with the external world, they also play a vital role in some smart healthcare systems. Despite advances in areas including materials/composites, electronics and fabrication techniques, it remains challenging to develop low cost, high performance, durable, robust, soft tactile sensors for real-world applications. This paper presents the first Soft Inductive Tactile Sensor (SITS) which exploits an inductance-transducer mechanism based on the eddy-current effect. SITSs measure the inductance variation caused by changes in AC magnetic field coupling between coils and conductive films. Design methodologies for SITSs are discussed by drawing on the underlying physics and computational models, which are used to develop a range of SITS prototypes. An exemplar prototype achieves a state-of-the-art resolution of 0.82 mN with a measurement range over 15 N. Further tests demonstrate that SITSs have low hysteresis, good repeatability, wide bandwidth, and an ability to operate in harsh environments. Moreover, they can be readily fabricated in a durable form and their design is inherently extensible as highlighted by a 4x4 SITS array prototype. These outcomes show the potential of SITS systems to further advance tactile sensing solutions for integration into demanding real-world applications

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

Eddy current angular position sensor for automotive

Programa doutoral em Líderes para Indústrias TecnológicasOs sensores angulares usados em aplicações automóveis, requerem uma boa resolução, fiabilidade, baixa manutenção, baixo custo de produção e capacidade de trabalhar sob condições adversas. Devido a estes requisitos, os sensores mais utilizados são os magnéticos, indutivos e magneto-indutivos. Outro fator crítico é a dimensão do sensor, quanto mais reduzido e compacto, maior é o número de aplicações em que pode ser aplicado. No caso dos sensores magneto-indutivos e indutivos, uma forma de reduzir o seu tamanho é através do uso de a bobines planares impressas em placas de circuito impresso (PCB). Estas, para além de mais compactas, conseguem também reduzir os custos de produção, otimizar a repetibilidade e assemblagem, e permitir que o seu desenho seja facilmente adaptado às suas aplicações. No desenvolvimento de sensores indutivos, obter a indutância das bobinas, que funcionam como elemento transdutor, é essencial e desafiador no caso de bobinas planas. Atualmente, há duas abordagens no estado da arte: fórmulas de aproximação (para geometrias regulares), e simulações de modelos de elementos finitos (FEM). As simulações são demoradas e recorrem a ferramentas de software dispendiosas e que exigem muitos recursos computacionais. Esta tese tem como objetivo desenvolver uma ferramenta de cálculo analítico para obter a indutância de bobinas planas genéricas, reduzindo o tempo de desenvolvimento. A ferramenta possibilita ainda o cálculo da interferência que um alvo planar condutivo tem na indutância da bobine, tornando assim possível obter a resposta de um sensor indutivo baseado em eddy currents durante a sua fase de desenvolvimento. Esta tese, além de detalhar o desenvolvimento da ferramenta mencionada, também descreve todos os processos de validação implementados, através de simulações FEM e testes experimentais. A metodologia proposta foi aplicada com sucesso no desenvolvimento de um sensor de posição angular automotivo baseado em eddy currrents. Foi possível comprovar que a precisão da ferramenta desenvolvida está de acordo com as metodologias usualmente utilizadas, com a vantagem de ser mais rápida e económica.Angular sensors used in automotive applications require good precision, reliability, low maintenance, low production costs and the ability to work in harsh conditions. Due to these requirements, magnetic, inductive and magneto-inductive sensors are preferred and are used in current generations of automotive angular position sensors. The size of the sensors is another relevant factor in the development of new solutions. The smaller and more compact, the larger the number of applications in which they can be applied. In the case of magneto-inductive and inductive sensors, one way to reduce their size is to use planar coils printed on printed circuit boards (PCBs). These, in addition to occupy a smaller volume when compared to solenoids, also reduce production costs and optimize repeatability and simplify assembly. When developing inductive sensors, knowing the required inductance value of its coils is essential and this task can be challenging in the case of planar coils. Currently, two approaches are used to calculate the inductances of planar coils. When the coils have regular geometry approximation formulas are used, configuring some parameters. When they have irregular geometry or a more accurate result is desired, simulations using finite element methods (FEM) are chosen. These simulations have the disadvantage of being time-consuming, requiring expensive software applications and a huge computing resources. In view of the budget and the reduction of development time, this thesis provides an analytical calculation tool for the inductance of generic multi-layer planar coils. In this way, it is possible to develop dedicated applications in reduced time. The tool also allows to calculate the interference that a planar conductive target, of arbitrary geometry, can have on the coil inductance. Thus, it is possible to obtain the response of an inductive sensor based on eddy currents during its development phase. This thesis, in addition to detailing the development of the aforementioned tool, also describes all the validation processes implemented using FEM simulations and experimental tests. The proposed methodology was successfully applied in the development of an automotive angular position sensor based on eddy currents. It was possible to prove that the precision of the developed analytical tool is in concordance with the methodologies usually used, with the advantage of being faster and open source.Fundação para a Ciência e a Tecnologia (FCT) - bolsa de doutoramento PD/BD/128142/201

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

Design, control and error analysis of a fast tool positioning system for ultra-precision machining of freeform surfaces

This thesis was previously held under moratorium from 03/12/19 to 03/12/21Freeform surfaces are widely found in advanced imaging and illumination systems, orthopaedic implants, high-power beam shaping applications, and other high-end scientific instruments. They give the designers greater ability to cope with the performance limitations commonly encountered in simple-shape designs. However, the stringent requirements for surface roughness and form accuracy of freeform components pose significant challenges for current machining techniques—especially in the optical and display market where large surfaces with tens of thousands of micro features are to be machined. Such highly wavy surfaces require the machine tool cutter to move rapidly while keeping following errors small. Manufacturing efficiency has been a bottleneck in these applications. The rapidly changing cutting forces and inertial forces also contribute a great deal to the machining errors. The difficulty in maintaining good surface quality under conditions of high operational frequency suggests the need for an error analysis approach that can predict the dynamic errors. The machining requirements also impose great challenges on machine tool design and the control process. There has been a knowledge gap on how the mechanical structural design affects the achievable positioning stability. The goal of this study was to develop a tool positioning system capable of delivering fast motion with the required positioning accuracy and stiffness for ultra-precision freeform manufacturing. This goal is achieved through deterministic structural design, detailed error analysis, and novel control algorithms. Firstly, a novel stiff-support design was proposed to eliminate the structural and bearing compliances in the structural loop. To implement the concept, a fast positioning device was developed based on a new-type flat voice coil motor. Flexure bearing, magnet track, and motor coil parameters were designed and calculated in detail. A high-performance digital controller and a power amplifier were also built to meet the servo rate requirement of the closed-loop system. A thorough understanding was established of how signals propagated within the control system, which is fundamentally important in determining the loop performance of high-speed control. A systematic error analysis approach based on a detailed model of the system was proposed and verified for the first time that could reveal how disturbances contribute to the tool positioning errors. Each source of disturbance was treated as a stochastic process, and these disturbances were synthesised in the frequency domain. The differences between following error and real positioning error were discussed and clarified. The predicted spectrum of following errors agreed with the measured spectrum across the frequency range. It is found that the following errors read from the control software underestimated the real positioning errors at low frequencies and overestimated them at high frequencies. The error analysis approach thus successfully revealed the real tool positioning errors that are mingled with sensor noise. Approaches to suppress disturbances were discussed from the perspectives of both system design and control. A deterministic controller design approach was developed to preclude the uncertainty associated with controller tuning, resulting in a control law that can minimize positioning errors. The influences of mechanical parameters such as mass, damping, and stiffness were investigated within the closed-loop framework. Under a given disturbance condition, the optimal bearing stiffness and optimal damping coefficients were found. Experimental positioning tests showed that a larger moving mass helped to combat all disturbances but sensor noise. Because of power limits, the inertia of the fast tool positioning system could not be high. A control algorithm with an additional acceleration-feedback loop was then studied to enhance the dynamic stiffness of the cutting system without any need for large inertia. An analytical model of the dynamic stiffness of the system with acceleration feedback was established. The dynamic stiffness was tested by frequency response tests as well as by intermittent diamond-turning experiments. The following errors and the form errors of the machined surfaces were compared with the estimates provided by the model. It is found that the dynamic stiffness within the acceleration sensor bandwidth was proportionally improved. The additional acceleration sensor brought a new error source into the loop, and its contribution of errors increased with a larger acceleration gain. At a certain point, the error caused by the increased acceleration gain surpassed other disturbances and started to dominate, representing the practical upper limit of the acceleration gain. Finally, the developed positioning system was used to cut some typical freeform surfaces. A surface roughness of 1.2 nm (Ra) was achieved on a NiP alloy substrate in flat cutting experiments. Freeform surfaces—including beam integrator surface, sinusoidal surface, and arbitrary freeform surface—were successfully machined with optical-grade quality. Ideas for future improvements were proposed in the end of this thesis.Freeform surfaces are widely found in advanced imaging and illumination systems, orthopaedic implants, high-power beam shaping applications, and other high-end scientific instruments. They give the designers greater ability to cope with the performance limitations commonly encountered in simple-shape designs. However, the stringent requirements for surface roughness and form accuracy of freeform components pose significant challenges for current machining techniques—especially in the optical and display market where large surfaces with tens of thousands of micro features are to be machined. Such highly wavy surfaces require the machine tool cutter to move rapidly while keeping following errors small. Manufacturing efficiency has been a bottleneck in these applications. The rapidly changing cutting forces and inertial forces also contribute a great deal to the machining errors. The difficulty in maintaining good surface quality under conditions of high operational frequency suggests the need for an error analysis approach that can predict the dynamic errors. The machining requirements also impose great challenges on machine tool design and the control process. There has been a knowledge gap on how the mechanical structural design affects the achievable positioning stability. The goal of this study was to develop a tool positioning system capable of delivering fast motion with the required positioning accuracy and stiffness for ultra-precision freeform manufacturing. This goal is achieved through deterministic structural design, detailed error analysis, and novel control algorithms. Firstly, a novel stiff-support design was proposed to eliminate the structural and bearing compliances in the structural loop. To implement the concept, a fast positioning device was developed based on a new-type flat voice coil motor. Flexure bearing, magnet track, and motor coil parameters were designed and calculated in detail. A high-performance digital controller and a power amplifier were also built to meet the servo rate requirement of the closed-loop system. A thorough understanding was established of how signals propagated within the control system, which is fundamentally important in determining the loop performance of high-speed control. A systematic error analysis approach based on a detailed model of the system was proposed and verified for the first time that could reveal how disturbances contribute to the tool positioning errors. Each source of disturbance was treated as a stochastic process, and these disturbances were synthesised in the frequency domain. The differences between following error and real positioning error were discussed and clarified. The predicted spectrum of following errors agreed with the measured spectrum across the frequency range. It is found that the following errors read from the control software underestimated the real positioning errors at low frequencies and overestimated them at high frequencies. The error analysis approach thus successfully revealed the real tool positioning errors that are mingled with sensor noise. Approaches to suppress disturbances were discussed from the perspectives of both system design and control. A deterministic controller design approach was developed to preclude the uncertainty associated with controller tuning, resulting in a control law that can minimize positioning errors. The influences of mechanical parameters such as mass, damping, and stiffness were investigated within the closed-loop framework. Under a given disturbance condition, the optimal bearing stiffness and optimal damping coefficients were found. Experimental positioning tests showed that a larger moving mass helped to combat all disturbances but sensor noise. Because of power limits, the inertia of the fast tool positioning system could not be high. A control algorithm with an additional acceleration-feedback loop was then studied to enhance the dynamic stiffness of the cutting system without any need for large inertia. An analytical model of the dynamic stiffness of the system with acceleration feedback was established. The dynamic stiffness was tested by frequency response tests as well as by intermittent diamond-turning experiments. The following errors and the form errors of the machined surfaces were compared with the estimates provided by the model. It is found that the dynamic stiffness within the acceleration sensor bandwidth was proportionally improved. The additional acceleration sensor brought a new error source into the loop, and its contribution of errors increased with a larger acceleration gain. At a certain point, the error caused by the increased acceleration gain surpassed other disturbances and started to dominate, representing the practical upper limit of the acceleration gain. Finally, the developed positioning system was used to cut some typical freeform surfaces. A surface roughness of 1.2 nm (Ra) was achieved on a NiP alloy substrate in flat cutting experiments. Freeform surfaces—including beam integrator surface, sinusoidal surface, and arbitrary freeform surface—were successfully machined with optical-grade quality. Ideas for future improvements were proposed in the end of this thesis