Precision point design of a cam indexing mechanism

This work regards on the design of a cylindrical cam indexing mechanism with a motion law that passes through a positional precision point. A numerical algorithm is proposed to solve this problem and, particularly, a genetic algorithm. The algorithm and the encoding of the problem are described

A general design method of cam profile based on cubic splines and dynamic model : case study of a gravity-driven tricycle

This paper proposes a general design method for cams based on the kinematics and dynamics of a mechanical system. According to the actuator’s trajectory, the cam profile is generated in reverse based on the kinematic model of the system. Firstly, the cam design’s optimising problem is converted into the execution trajectory’s optimisation to obtain the optimum operation trajectory according to the actuator’s requirements. Secondly, the relationship between the cam profile and the actuation trajectory is modelled based on the kinematics and dynamics of the mechanical system. Then, applying the cubic spline interpolation method, the cam profile is generated, and the error compensation methods are illustrated through numerical analysis. Finally, the validity of the presented design method is verified through experiments, which demonstrate the reliability of this method

Aspects of the design of a circular warp knitting machine

The warp knitting machine market has long been dominated by large-scale flat models, which have been steadily developed. Tubular fabrics are generally made in a special version of flat warp knitting machines containing two needle bars, one for each side of the tube, joined on the sides by yarns knitting alternatively on each bar. Warp knitting technology has failed to enter the circular knitting industry, dominated by weft knitting, due to its complexity in achieving warp knit structures in circular form. This thesis presents the design, synthesis, manufacture and test of an innovative method of producing tubular warp knitting fabrics, using a circular format rather than flat needle bars. This novel concept opens up many industrial applications from medical textiles to fruit packaging. [Continues.

Multiscale modelling of woven and knitted fabric membranes

Light-weight fabric membranes have gained increasing popularity over the past years due to their tailorable structural and material performances. These tailorable properties include stretch forming and deep drawing formability that exhibits excellent stretchability and drapeability properties of textiles and textile composites. Since the inception of computerised numerical control for three-dimensional textile-manufacturing machines, technical textiles paved their way to numerous applications, certainly not limited to; aerospace, biomedical, civil engineering, defence, marine and medical industries. Digital interlooping and digital interlacing technology in additive manufacturing greatly advanced the manufacturing processes of textiles. In this work, we consider two branches of technical fabrics, namely plain-woven and weft-knitted. Multiscale modelling is the tool of choice for homogenising periodic structures and has been used extensively to model and analyse the mechanical behaviour of woven and knitted fabrics. But there is a plethora of literature discussing the demerits of such conventional multiscale modelling. These demerits include higher computational costs, rigid numerical models, ineffcient algorithmic computations and inability to incorporate geometric nonlinearities. We propose a data-driven nonlinear multiscale modelling technique to analyse the complex mechanical behaviour of plain-woven and weft-knitted fabrics with a neat extension to fabric material designing. We show how the integration of statistical learning techniques mitigates the weaknesses of conventional multiscale modelling. Moreover, we discuss the avenues that will open in many potential fields with regard to material modelling, structural engineering and textile industries. In the proposed data-driven nonlinear computational homogenisation technique, we effi ciently integrate the microscale and macroscale using Gaussian Process Regression (GPR) statistical learning technique. In the microscale, representative volume elements (RVEs) are modelled using nite deformable isogeometric spatial rods and deformation is homogenised using periodic boundary conditions. This nite deformable rod is profi cient in handling large deformations, rod-to-rod contacts, arbitrary cross-section de finitions and follower loads. Respecting the principle of separation of scales, we construct response databases by applying different homogenised strain states to the RVEs and recording the respective incremental volume-averaged energy values. We use GPR to learn a model using a 5-fold cross-validation technique by optimising the log marginal likelihood. In the macroscale, textiles are modelled as nonlinear orthotropic membranes for which the stresses and material constitutive relations are predicted by the trained GPR model. This coupling between GPR and membrane models is achieved through a systematic and seamless nite element integration using C++ and Python environments. A neat extension to material designing is also discussed with potentials to extend the work into other related fi elds.Cambridge trust and Trinity Hall scholarshi

Computational Tools and Experimental Methods for the Development of Passive Prosthetic Feet

Modern prosthetic foot designs are incredibly diverse in comparison to what was o↵ered to amputees at the turn of the millennium. Powered ankles can supply natural levels of joint torque, whilst passive feet continue to optimise for kinematic goals. However, most passive feet still do not solve the issue of unhealthy loads, and an argument can be made that optimisation methods have neglected the less active and elderly amputee. This thesis creates a framework for a novel approach to prosthetic foot optimisation by focusing on the transitionary motor tasks of gait initiation and termination.An advanced FEA model has been created in ANSYS® using boundary con-ditions derived from an ISO testing standard that replicates stance phase loading. This model can output standard results found in the literature and goes beyond by parameterising the roll-over shape within the software using custom APDL code. Extensive contact exploration and an experimental study have ensured the robustness of the model. Subject force and kinematic data can be used for specific boundary conditions, which would allow for easy adaptation to the transitionary motor tasks.This FEA model has been used in the development of prosthetic experiment tool, which can exchange helical springs to assess e↵ects of small changes in sti↵-ness on gait metrics. A rigorous design methodology was employed for all compo-nents, including parametric design studies, response surface optimisation, and ISO level calculations. The design has been manufactured into a working prototype and is ready for clinical trials to determine its efficacy.The conclusion of this framework is in the development of an experimental method to collect subject data for use in the models. A pilot study uncovered reliable protocols, which were then verified with ANOVA statistics. Proportional ratios were defined as additions to metric peak analyses already found in the liter-ature. These tools are ready for deployment in full clinical trials with amputees, so that a new prosthetic optimisation pathway can be discovered for the benefit of less active or elderly amputees

Utilization of the geared five-bar slider-crank mechanism for positive displacement machines.

The conventional slider-crank mechanism which is often employed to drive reciprocating positive displacement machines is not adequate when it is necessary to produce non-uniform reciprocations in order to improve machine performance. Instead, this thesis dicusses the utilisation of the geared five-bar slider-crank mechanism to drive these machines." -- Introduction.Doctor of Philosph

Aerial Vehicles

This book contains 35 chapters written by experts in developing techniques for making aerial vehicles more intelligent, more reliable, more flexible in use, and safer in operation.It will also serve as an inspiration for further improvement of the design and application of aeral vehicles. The advanced techniques and research described here may also be applicable to other high-tech areas such as robotics, avionics, vetronics, and space

Study and development of a holdingchamber for inhalation

Tese de Doutoramento em Engenharia MecânicaAsthma is a respiratory disease that causes chronic airway inflammation. Affecting more than 300 million individuals worldwide, it is a growing public health hazard. Inhalation therapy is the preferred strategy for medication delivery. This therapy is executed through specific delivery devices, whereas the pressurized Metered-Dose Inhaler (pMDI) is one of the most preferred. However, the pMDI efficiency is highly dependent on a correctly executed inhalation procedure. For children under 5 years old (or elderly individuals), it is advisable to use the pMDI coupled with an add-on device (i.e. spacer). Within the spacers, the Valved Holding Chamber (VHC) is the mostly used, due to its good capacity to reduce the pMDI spray coarse fraction and the oral-pharyngeal deposition ( 80%). Additionally, the VHC’s one-way valve allows the patient to maintain his tidal breathing during treatment. The VHC typically delivers a Fine Particle Mass (FPM) that is 20% of the labelled dose. Several design characteristics dictate the VHC performance, such as, the dimensions and the materials. The study herein focus on the assessment of eight commercial VHCs, through experimental and numerical methods. An experimental setup was developed, allowing the evaluation of the devices at constant flow rate (30 L/min and 60 L/min) and at variable flow (sine breath pattern). The waveform was obtained through a breathing simulator specially developed for this purpose, based in a cam-follower mechanism. The salbutamol sulphate (i.e. Ventolin) was collected using a cascade impactor (i.e. MSLI), and assessed by UV-Vis spectrophotometry analysis. Several metrics, regarding VHC performance, were calculated. Results have shown that the VHC capacity reduce the oral-pharyngeal deposition (64% - 94%), which is deeply related with the VHC valve design. It was observed that the VHC reduces the plume coarse fraction ( 70%), keeping the FPM bioequivalent to the pMDI solo. A correlation between the fine particle fraction and the volume of air passing through the VHC was proposed. Patient relevant metrics were suggested to classify the VHC devices upon quantitative and qualitative characteristics. A Computational Fluid Dynamics (CFD) model was developed where the air flow (i.e. 60 L/min)) was calculated along with the pMDI spray modelling as a discrete phase. The spray particle-wall interaction was modelled using different approaches and compared against literature and experimental data. This study, shed some light upon the spray evaporation process inside the VHC, showing that the efficiency of evaporation process is related with the VHC volume. A new VHC design, based in CFD dimensional optimisation of the VHC body is proposed, which shows an improvement of the FPM delivered.A asma é uma doença respiratória que causa a inflamação crónica das vias aéreas. Mundialmente, afeta mais de 300 milhões de indivíduos e é um problema crescente de saúde publica. A terapia de inalação é a estratégia preferida para administrar a medicação de controlo ou de alívio. Esta terapia é executada através de dispositivos específicos, entre os quais o Inalador Pressurizado com Válvula Doseadora (IPVD) é o mais usual. Contudo, a eficiência do IPVD é dependente de uma técnica de inalação correta. Para crianças com menos de 5 anos (ou idosos), é recomendável o uso do IPVD acoplado a um espaçador. Entre os espaçadores, a Câmara Expansora (CE) é a mais utilizada, devido à sua boa capacidade de redução das partículas grandes do aerossol do IPVD, e da redução da deposição orofaringeal ( 80%). Adicionalmente, a válvula de sentido único da CE, permite que o paciente mantenha a sua respiração normal durante o tratamento. A CE emite, tipicamente, uma massa de partículas finas (MPF) que é 20% da dose calibrada do IPVD. Este estudo foca-se na avaliação de oito CEs, através de uma metodologia experimental e numérica. Uma instalação experimental foi projetada para a avaliação dos dispositivos a fluxo constante (30 L/min e 60 L/min) e variável (um padrão respiratório sinusoidal). A onda foi obtida através de um simulador respiratório especialmente desenvolvido para este propósito, o qual foi baseado num mecanismo cam-seguidor. O sulfato de salbutamol (Ventilan HFA) foi recolhido utilizando um impactor em cascata em vários estágios (Aparelho C da Farmacopeia Portuguesa), e quantificado por espetrofotometria UV-Visivel. Foram calculadas várias métricas sobre o desempenho das CEs. Os resultados demonstram a capacidade da CE para reduzir a deposição orofaringeal (64% - 94%), a qual está intrinsecamente relacionada com o design da válvula do dispositivo. Foi observado que a CE reduz a fração de partículas grandes na pluma ( 70%), mantendo a MPF bioequivalente à emitida pelo IPVD. Foi proposta uma correlação entre a fração de partículas finas e o volume de ar que atravessa a CE. Foram também sugeridas métricas com relevância para o paciente, que classificam as CEs de forma quantitativa e qualitativa. Foi desenvolvido um modelo de Dinâmica Computacional de Fluidos (DCF), onde o fluxo de ar (a 60 L/min) foi calculado juntamente com o aerossol do IPVD, tendo sido este modelado como uma fase discreta. A interação entre partícula e parede foi modelada utilizando diferentes aproximações matemáticas, sendo posteriormente comparadas com a literatura e dados experimentais. Este estudo contribui com um melhor conhecimento do processo de evaporação das gotas do aerossol dentro da CE, onde se verificou que este processo está relacionado com o volume da CE. Foi proposto em novo design para CE, baseado numa otimização das dimensões do corpo da CE, que demonstra melhoria da MPF emitida