RESEARCH TOWARDS THE DESIGN OF A NOVEL SMART FLUID DAMPER USING A MCKIBBEN ACTUATOR

Vibration reducing performance of many mechanical systems, decreasing the quality of manufactured products, producing noise, generating fatigue in mechanical components, and producing an uncomfortable environment for human bodies. Vibration control is categorized as: active, passive, or semi-active, based on the power consumption of the control system and feedback or feed forward based on whether sensing is used to control vibration. Semi-active vibration control is the most attractive method; one method of semi-active vibration control could be designed by using smart fluid. Smart fluids are able to modify their effective viscosity in response to an external stimulus such as a magnetic field. This unique characteristic can be utilised to build semi-active dampers for a wide variety of vibration control systems. Previous work has studied the application of smart fluids in semi-active dampers, where the kinetic energy of a vibrating structure can be dissipated in a controllable fashion. A McKibben actuator is a device that consists of a rubber tube surrounded by braided fibre material. It has different advantages over a piston/cylinder actuator such as: a high power to weight ratio, low weight and less cost. Recently McKibben actuator has appeared in some semi-active vibration control devise. This report investigates the possibility of designing a Magnetorheological MR damper that seeks to reduce the friction in the device by integrating it with a McKibben actuator. In this thesis the concept of both smart fluid and McKibben actuator have been reviewed in depth, and methods of modelling and previous applications of devices made using these materials are also presented. The experimental part of the research includes: designing and modelling a McKibben actuator (using water) under static loads, and validating the model experimentally. The research ends by presenting conclusions and future work

Haptics in Robot-Assisted Surgery: Challenges and Benefits

Robotic surgery is transforming the current surgical practice, not only by improving the conventional surgical methods but also by introducing innovative robot-enhanced approaches that broaden the capabilities of clinicians. Being mainly of man-machine collaborative type, surgical robots are seen as media that transfer pre- and intra-operative information to the operator and reproduce his/her motion, with appropriate filtering, scaling, or limitation, to physically interact with the patient. The field, however, is far from maturity and, more critically, is still a subject of controversy in medical communities. Limited or absent haptic feedback is reputed to be among reasons that impede further spread of surgical robots. In this paper objectives and challenges of deploying haptic technologies in surgical robotics is discussed and a systematic review is performed on works that have studied the effects of providing haptic information to the users in major branches of robotic surgery. It has been tried to encompass both classical works and the state of the art approaches, aiming at delivering a comprehensive and balanced survey both for researchers starting their work in this field and for the experts

Research on real-time physics-based deformation for haptic-enabled medical simulation

This study developed a multiple effective visuo-haptic surgical engine to handle a variety of surgical manipulations in real-time. Soft tissue models are based on biomechanical experiment and continuum mechanics for greater accuracy. Such models will increase the realism of future training systems and the VR/AR/MR implementations for the operating room

A Numerical Exploration of the Crystalline Lens: from Presbyopia to Cataracts and Intraocular Lenses

Esta tesis aborda, de forma numérica, la resolución de tres problemas relacionados con el cristalino. En primer lugar, se ha construido un modelo de elementos finitos del cristalino humano para abordar la simulación de la acomodación, gracias a la incorporación de la contracción muscular del músculo ciliar. El modelo se ha validado con resultados experimentales comparando con Ramasubramanian & Glasser, 2015. Con el mismo modelo, se ha estudiado como afecta el cambio de las propiedades mecánicas de los tejidos del cristalino en la pérdida de amplitud de la acomodación con la edad para entender si la rigidización de los tejidos juega un papel importante en la presbicia. La conclusión principal del estudio numérico ha sido que las propiedades mecánicas y tensiones iniciales de la cápsula del cristalino proporciona la fuerza necesaria para acomodar, es decir, cambiar su curvatura para enfocar de cerca. Especificamente, el ratio de rígidez entre el núcleo y el cristalino gobierna cómo el cristalino cambia de forma. Con la edad, se produce una rigidización del núcleo, y el incremento de la relación entre ambas rigideces (núcleo y corteza) podría ser el principal responsable de la pérdida de la amplitud de acomodación con la edad. En segundo lugar, se ha estudiado la estabilidad biomecánica de diferentes diseños de lentes intraoculares (IOL). Las IOLs sustituyen las funciones del cristalino en pacientes con cataratas, es por ello necesario garantizar su estabilidad en el interior del saco para garantizar una visión adecuada. Entre los aspectos estudiados destaca la caracterización mecánica de los materiales acrílicos con los que se fabrican las lentes. Para ello, se han combinado ensayos uniaxiales con ensayos de indentación. Éstos últimos se han utilizado para caracterizar la respuesta visco-elástica del material. El definir la respuesta del material mediante modelos visco hiperelásticos es necesario para posteriormente analizar la estabilidad de la IOL mediante elementos finitos. Este análisis se ha defino a dos niveles, en un primer nivel se analiza la estabilidad de la IOL simulando el ensayo establecido en la norma ISO 11979-3:2012. Esta norma es de obligado cumplimiento para los fabricantes antes de introducir un nuevo diseño en el mercado. Se ha realizado un estudio estadístico para estudiar el efecto de la geometría de los hápticos tipo C-loop en la estabilidad mecánica de la IOL, obteniendo que el entronque, la unión entre el háptico y la lente, es el parámetro más influyente. Para validar la metodología numérica, se fabricaron varios diseños y se analizaron experimentalmente para comparar los resultados correspondientes con biomarcadores mecánicos (desplazamiento axial, rotación y la inclinación de la IOL) que están relacionados con la calidad visual resultante de la IOL. En un segundo nivel, se ha simulado la respuesta de la IOL en el interior del saco capsular, estudiando la influencia de diferentes parámetros del paciente, como geometría y propiedades mecánicas del saco. También se ha analizado la influencia de parámetros de la cirugía de la catarata, como es el diámetro y posición de la capsulorexis. En este último nivel, se ha estudiado tanto la respuesta instantánea, es decir, tras la cirugía, como a largo plazo, cuando sucede la huella de fusión (fusion footprint) entre la cápsula y la IOL. Para que los modelos computacionales sean de ayuda a los cirujanos o puedan servir en tiempo real, se ha planteado una metodología basada en inteligencia artificial. En este caso la base de datos de partida corresponde a modelos numéricos altamente fiables y con ellos, se genera datos con los que se entrena la red neuronal. En esta tesis, se estudia la estabilidad de la IOL en función del diámetro de compresión del paciente y la edad, que a su vez influye en las propiedades mecánicas del saco. Por último, se ha evaluado experimentalmente la influencia del material de la IOL (hidrófobo o hidrofílico) y su geometría durante la inyección de la IOL en el saco, registrando la fuerza de inyección que debe realizar el cirujano. De cara a evitar complicaciones (se dañe la IOL o el tejido corneal) durante la cirugía, es conveniente que la fuerza a ejercer sea baja. Se ha comprobado que su valor está fuertemente influenciado por el material de la lente.¿Por qué el cristalino es de vital importancia?El cristalino es el responsable tanto del cambio dinámico de la potencia refractiva del ojo a través del mecanismo de acomodación como de la corrección de las aberraciones de la córnea. El cambio óptico dinámico es consecuencia de un cambio geométrico del cristalino. Sin embargo, a medida que el cristalino envejece, disminuye este cambio óptico dinámico y se opacifica, lo que da lugar a las dos patologías comúnmente asociadas al envejecimiento como es, la presbicia y las cataratas. Por este motivo, en esta tesis doctoral se ha profundizado en el estudio mecánico del cristalino y tras su sustitución mediante una lente intraocular artificial durante la cirugía de catarata. La metodología establecida pueden ayudar en un futuro tanto al diseño de nuevos implantes como a los oftalmólogos a seleccionar la IOL adecuada a cada paciente para mejora su calidad visual.This thesis addresses three different case studies related to the crystalline lens. Firstly, the mechanical causes of the loss of accommodation amplitude with age, called presbyopia, were analysed through the finite element method. A high-fidelity simulation of the mechanism of accommodation including the contraction of the ciliary muscle was developed. This allowed us to analyse accommodation in depth, showing that although the lens capsule provides the force to accommodate, the stiffness ratio between the lens cortex and lens nucleus could have a higher effect on how the lens changes its shape. Secondly, the biomechanical stability of intraocular lenses (IOLs) was analysed. IOLs are essential for post-cataract patients as they substitute the functions of the crystalline lens. In this thesis, a wide variety of solutions were addressed: from the visco- and hyper-elasticity characterisation of IOL acrylic materials from depth sensing indentation and uniaxial tests to the simulation of the IOL biomechanical stability inside the capsular bag. We also performed a high-fidelity simulation of the IOL compression standards tests required by the IOLs to be commercialised and the results obtained were compared with clinical data. Lastly, we developed a patient-specific methodology to customise the IOL haptic design. Most of the numerical methology developed is intended to be used in the IOL pre-design phase to avoid costs and time. Thirdly, the IOL delivery during cataract surgery according to haptic and material design and injector characteristics was experimentally studied to avoid any possibility of IOL and eye damage. Apart from the injector size, the IOL material was the most influential parameter in the force exerted in IOL delivery. Why is the crystalline lens of vital importance? The crystalline lens is the responsible for both the dynamic change of the refractive power of the eye through the mechanism of accommodation and the correction of cornea aberrations. The dynamic optical change is consequence of change of the lens shape. However, as the lens ages over time, it decreases this dynamic optical change and becomes cloudy, what leads to the two most common lens-related pathologies, presbyopia and cataracts. Therefore, it is of utmost importance to study the lens mechanics and all issues related to the artificial intraocular lens that substitutes the lens during cataract surgery.<br /

A FEEDBACK-BASED DYNAMIC INSTRUMENT FOR MEASURING THE MECHANICAL PROPERTIES OF SOFT TISSUES

In this paper, a novel feedback-based dynamic instrument integrated into a Minimally- Invasive-Surgery (MIS) tool to evaluate the mechanical impedance of soft tissues is presented. This instrument is capable of measuring viscoelasticity of tissues if specific boundary conditions are known. Some important advantages of the proposed instrument are that it is robust and simple in comparison to other similar instruments as it does not require magnitude information of plant’s displacement output and no force sensor is used. The precision and accuracy of the measurements of the proposed instrument for soft tissues is noticeably higher than similar instruments, which are not optimized to work with soft tissues. The proposed dynamic instrument is designed to detect the frequency shifts caused by contacting a soft tissue using an improved phase-locked loop feedback system (closed loop). These frequency shifts can then be used to evaluate the mechanical properties of the tissue. The closed-loop method works fast (with an approximate resonance-frequency-shift rate of 15 Hz per second), and is capable of measuring dy­ namic mechanical properties of viscoelastic tissues, while previous focus was mostly on static/quasi-static elastic modulus. The instrument is used to evaluate the equivalent stiffness of several springs and cantilever beams, mass of reference samples, and also the frequency shifts of several phantoms with injected tumors, noting that these frequency shifts can be used to measure the viscoelasticity of the tissues. It is also shown that the instrument can be used for tumor localization in these phantoms

Magneto-Rheological Fluid Device as Artificial Feel Force System on Aircraft Control Stick

The conventional feel system in any aircraft occupies large space in the cockpit and has complicated designs. The primary objective of this research is to develop an artificial feel force system that can overcome some drawbacks of the current feel force system. A novel feel system using magneto-rheological (MR) fluid is constructed to precisely control the shear stress under the magnetic field. To validate the functionality of the MR artificial feel system, the final system is fabricated and multiple tests are performed to acquire force-velocity characteristics that are compared to the mathematical model derived. In addition, the reference model of the force feedback control is simulated for the feel force application. Both experimental and simulation results are compared to validate the derived system model. The system response time and the sampling rates are evaluated and compared to the conventional system at the end. It is concluded from the research that the developed artificial feel system can precisely control and acts as a fail proof system when incorporated with a modern fly-by-wire aircraft system

Nonlinear effects in finite elements analysis of colorectal surgical clamping

Minimal Invasive Surgery (MIS) is a procedure that has increased its applications in past few years in different types of surgeries. As number of application fields are increasing day by day, new issues have been arising. In particular, instruments must be inserted through a trocar to access the abdominal cavity without capability of direct manipulation of tissues, so a loss of sensitivity occurs. Generally speaking, the student of medicine or junior surgeons need a lot of practice hours before starting any surgical procedure, since they have to difficulty in acquiring specific skills (hand–eye coordination among others) for this type of surgery. Here is what the surgical simulator present a promising training method using an approach based on Finite Element Method (FEM). The use of continuum mechanics, especially Finite Element Analysis (FEA) has gained an extensive application in medical field in order to simulate soft tissues. In particular, colorectal simulations can be used to understand the interaction between colon and the surrounding tissues and also between colon and instruments. Although several works have been introduced considering small displacements, FEA applied to colorectal surgical procedures with large displacements is a topic that asks for more investigations. This work aims to investigate how FEA can describe non-linear effects induced by material properties and different approximating geometries, focusing as test-case application colorectal surgery. More in detail, it shows a comparison between simulations that are performed using both linear and hyperelastic models. These different mechanical behaviours are applied on different geometrical models (planar, cylindrical, 3D-SS and a real model from digital acquisitions 3D-S) with the aim of evaluating the effects of geometric non-linearity. Final aim of the research is to provide a preliminary contribution to the simulation of the interaction between surgical instrument and colon tissues with multi-purpose FEA in order to help the preliminary set-up of different bioengineering tasks like force-contact evaluation or approximated modelling for virtual reality (surgical simulations). In particular, the contribution of this work is focused on the sensitivity analysis of the nonlinearities by FEA in the tissue-tool interaction through an explicit FEA solver. By doing in this way, we aim to demonstrate that the set-up of FEA computational surgical tools may be simplified in order to provide assistance to non-expert FEA engineers or medicians in more precise way of using FEA tools

A state-of-the-art review on magnetorheological elastomer devices

© 2014 IOP Publishing Ltd. During the last few decades, magnetorheological (MR) elastomers have attracted a significant amount of attention for their enormous potential in engineering applications. Because they are a solid counterpart to MR fluids, MR elastomers exhibit a unique field-dependent material property when exposed to a magnetic field, and they overcome major issues faced in magnetorheological fluids, e.g. the deposition of iron particles, sealing problems and environmental contamination. Such advantages offer great potential for designing intelligent devices to be used in various engineering fields, especially in fields that involve vibration reduction and isolation. This paper presents a state of the art review on the recent progress of MR elastomer technology, with special emphasis on the research and development of MR elastomer devices and their applications. To keep the integrity of the knowledge, this review includes a brief introduction of MR elastomer materials and follows with a discussion of critical issues involved in designing magnetorheological elastomer devices, i.e. operation modes, coil placements and principle fundamentals. A comprehensive review has been presented on the research and development of MR elastomer devices, including vibration absorbers, vibration isolators, base isolators, sensing devices, and so on. A summary of the research on the modeling mechanical behavior for both the material and the devices is presented. Finally, the challenges and the potential facing magnetorheological elastomer technology are discussed, and suggestions have been made based on the authors' knowledge and experience