A novel design process of low cost 3D printed ambidextrous finger designed for an ambidextrous robotic hand

This paper presents the novel mechanical design of an ambidextrous finger specifically designed for an ambidextrous anthropomorphic robotic hand actuated by pneumatic artificial muscles. The ambidextrous nature of design allows fingers to perform both left and right hand movements. The aim of our design is to reduce the number of actuators, increase the range of movements with best possible range ideally greater than a common human finger. Four prototypes are discussed in this paper; first prototype is focused on the choice of material and to consider the possible ways to reduce friction. Second prototype is designed to investigate the tendons routing configurations. Aim of third and fourth prototype is to improve the overall performance and to maximize the grasping force. Finally, a unified design (Final design) is presented in great detail. Comparison of all prototypes is done from different angles to evaluate the best design. The kinematic features of intermediate mode have been analysed to optimize both the flexibility and the robustness of the system, as well as to minimize the number of pneumatic muscles. The final design of an ambidextrous finger has developed, tested and 3D printed

Development and Biomechanical Analysis toward a Mechanically Passive Wearable Shoulder Exoskeleton

Shoulder disability is a prevalent health issue associated with various orthopedic and neurological conditions, like rotator cuff tear and peripheral nerve injury. Many individuals with shoulder disability experience mild to moderate impairment and struggle with elevating the shoulder or holding the arm against gravity. To address this clinical need, I have focused my research on developing wearable passive exoskeletons that provide continuous at-home movement assistance. Through a combination of experiments and computational tools, I aim to optimize the design of these exoskeletons. In pursuit of this goal, I have designed, fabricated, and preliminarily evaluated a wearable, passive, cam-driven shoulder exoskeleton prototype. Notably, the exoskeleton features a modular spring-cam-wheel module, allowing customizable assistive force to compensate for different proportions of the shoulder elevation moment due to gravity. The results of my research demonstrated that this exoskeleton, providing modest one-fourth gravity moment compensation at the shoulder, can effectively reduce muscle activity, including deltoid and rotator cuff muscles. One crucial aspect of passive shoulder exoskeleton design is determining the optimal anti-gravity assistance level. I have addressed this challenge using computational tools and found that an assistance level within the range of 20-30% of the maximum gravity torque at the shoulder joint yields superior performance for specific shoulder functional tasks. When facing a new task dynamic, such as wearing a passive shoulder exoskeleton, the human neuro-musculoskeletal system adapts and modulates limb impedance at the end-limb (i.e., hand) to enhance task stability. I have presented development and validation of a realistic neuromusculoskeletal model of the upper limb that can predict stiffness modulation and motor adaptation in response to newly introduced environments and force fields. Future studies will explore the model\u27s applicability in predicting stiffness modulation for 3D movements in novel environments, such as passive assistive devices\u27 force fields

Effect of solar radiation on suspension bridge performance

© 2014 American Society of Civil Engineers.Observations of a U.K. suspension bridge show that thermal expansion and contraction cycles do not follow simple linear relationships with a single temperature value and that time lag and temperature distribution can be significant factors. This investigation explores these effects by simulating the transient thermal and quasistatic response of the Tamar Bridge with separate finite-element models of the bridge and suspension cables. Thermal loads are determined by calculated solar radiation intensities and temperature data from the bridge monitoring system. Because cloud cover plays an important role in the levels of solar radiation, cloud coverage was estimated indirectly using monitored temperature differences between the top and bottom of the suspended structure. The results demonstrate that peak temperatures of the suspended structure and cables occur at different times. The lag is caused by differing material properties and the surfaces' ability to absorb and lose heat. Transient phenomena manifest in the structural responses such as the tower sway.EU FP7 project IRISEngineering and Physical Sciences Research Council (EPSRC

A method of using computer simulation to assess the functional performance of football boots

This thesis details the development of Finite Element Analysis (FEA) techniques to simulate assembly and functional performance of football boots within a virtual environment. With a highly competitive market and seasonal changes in boot design common, the current design process can require numerous iterations, each adding time and cost to the development cycle. Using a reliable model allows evaluation of novel design concepts without the necessity to manufacture physical prototypes, and thus has potential financial benefits as well as reducing development time. A modelling approach was developed to construct a three dimensional boot model using FEA techniques, simulating the assembly of representative boot constituent parts based on manufacturing patterns, geometries and materials. Comparison between the modelled and physical boots demonstrated good agreement. Assessment of physical boot manufacture enabled the validation of the simulated assembly techniques, with digital image correlation hardware and software used to provide experimental measurements of the surface deformation. Good agreement was reported, demonstrating the predictive capabilities of FEA. Extensive review of literature provided applicable loading conditions of the boot during game play, with bending and torsional stiffness identified as important parameters. Boundary conditions associated with the foot during these movements provided a platform from which mechanical tests were used and developed to quantify boot function. Modelling techniques were developed and applied to the assembled FEA boot model, simulating the loading conditions to verify the validity when compared with experimental measurements. Bending and torsional stiffness extracted from the model were compared with the physical equivalent, demonstrating good predictive capabilities. The model was able to represent bending stiffness of the physical equivalent within 5.6% of an accepted boot range up to 20°, with torsional stiffness represented within the accepted range between 10° inversion to 7.5° eversion, corresponding to a large proportion of match play. Two case studies proved the applicability of the FEA techniques to simulate assembly and determine mechanical functionality virtually through a combination of automated modelling methods and a bespoke framework, demonstrating how it could be implemented within the industrial design process

Mechanical modelling of superconducting cables for fusion under cyclic electromagnetic and thermal loads

In Tokamak-type experimental fusion reactors, an ionized gas reaching millions of degrees is confined by high magnetic fields produced by electro-magnets. To reduce the thermal dissipation, modern tokamaks use superconducting materials at cryogenic temperatures that can carry large currents without electrical resistance. However, for advanced superconductors, this current-carrying capability is a function of the mechanical strain state of the material. In the ITER Tokamak the toroidal field magnets cables are composed of hundreds of strain-sensitive composite superconducting wires. During operation, these cables are submitted to cyclic electromagnetic and thermal mechanical loads triggering a gradual but steady decrease of the electrical performance of the cable. Up to now, the exact mechanisms relying this macroscopic loss of electrical performance to the local strain state of the superconducting wires are still partially unknown. This issue is extremely complex because of its multi-scale and multi-physics nature. The Ph.D. goal is to identify and understand the main causes of performance degradation as well as to obtain a predictive tool to assess superconducting cables behavior by developing a solid numerical electromechanical model to simulate the superconducting cables in operation. In parallel, the experimental activities focused on the mechanical characterization of Nb3Sn wires under cyclic compressive and tensile stresses, at both room and cryogenic temperature. Thanks to these test campaigns, specific experimental protocols were developed and behaviors and trends about cyclic loading of superconducting wires were identified. Finally, the modelling of complete cables under representative loading permitted a new interpretation of the mechanisms driving the electrical performance degradation in the ITER TF magnet conductors. Moreover, parametric studies demonstrated the impact of certain design parameters of the cables on their global mechanical behavior. This opened the way to studies of cables from other and new fusion projects, thus demonstrating the versatility of the model developed

Modeling of Force and Motion Transmission in Tendon-Driven Surgical Robots

Tendon-based transmission is a common approach for transferring motion and forces in surgical robots. In spite of design simplicity and compactness that comes with the tendon drives, there exists a number of issues associated with the tendon-based transmission. In particular, the elasticity of the tendons and the frictional interaction between the tendon and the routing result in substantially nonlinear behavior. Also, in surgical applications, the distal joints of the robot and instruments cannot be sensorized in most cases due to technical limitations. Therefore, direct measurement of forces and use of feedback motion/force control for compensation of uncertainties in tendon-based motion and force transmission are not possible. However, force/motion estimation and control in tendon-based robots are important in view of the need for haptic feedback in robotic surgery and growing interest in automatizing common surgical tasks. One possible solution to the above-described problem is the development of mathematical models for tendon-based force and motion transmission that can be used for estimation and control purposes. This thesis provides analysis of force and motion transmission in tendon-pulley based surgical robots and addresses various aspects of the transmission modeling problem. Due to similarities between the quasi-static hysteretic behavior of a tendon-pulley based da Vinci® instrument and that of a typical tendon-sheath mechanism, a distributed friction approach for modeling the force transmission in the instrument is developed. The approach is extended to derive a formula for the apparent stiffness of the instrument. Consequently, a method is developed that uses the formula for apparent stiffness of the instrument to determine the stiffness distribution of the tissue palpated. The force transmission hysteresis is further investigated from a phenomenological point of view. It is shown that a classic Preisach hysteresis model can accurately describe the quasi-static input-output force transmission behavior of the da Vinci® instrument. Also, in order to describe the distributed friction effect in tendon-pulley mechanisms, the creep theory from belt mechanics is adopted for the robotic applications. As a result, a novel motion transmission model is suggested for tendon-pulley mechanisms. The developed model is of pseudo-kinematic type as it relates the output displacement to both the input displacement and the input force. The model is subsequently used for position control of the tip of the instrument. Furthermore, the proposed pseudo-kinematic model is extended to compensate for the coupled-hysteresis effect in a multi-DOF motion. A dynamic transmission model is also suggested that describes system’s response to high frequency inputs. Finally, the proposed motion transmission model was used for modeling of the backlash-like hysteresis in RAVEN II surgical robot

On the Boundary Conditions and Internal Mechanics of Parallel Wire Strands

This dissertation analyzes the internal mechanics of parallel wire strands as found in the main cables of suspension bridges. Parallel wire strands of reduced order (7-wire, 19-wire, and 61-wire strands made of steel and aluminum) are fabricated and subjected to various boundary conditions and external loads (tension, clamping, twist, etc.). Neutron diffraction is used as an elastic strain measurement tool for its ability to penetrate bulk materials and/or layers of a multi-body system without disturbing the sample. Firstly, this thesis aims to quantify the development length – the distance over which a broken wire within a strand regains near-full service strain – as a function of various boundary conditions and failure scenarios. The feasibility of using neutron diffractometers to measure in situ elastic strains on civil-engineering-scale samples under both tensile load and radial confinement is validated using strands fabricated from steel bridge wire. Results from various 7-wire strands indicate that friction and mechanical interference on the microscopic level play a significant role in the load partitioning. Furthermore, wires that have been broken – either pre-cracked or fractured live and in situ during tensile loading – are capable of regaining significant stresses from their neighbors over a distance of tens of centimeters. The contribution of both friction force and mechanical interference on elastic strain redevelopment in broken wires should be included in analytical models designed to simulate failure processes. The second part of this thesis aims to measure the internal mechanics of larger parallel wire strands in response to various confinement (clamping) forces. 19 and 61 aluminum wire strands are fabricated and the internal strains of all constituent wires mapped in three orthogonal directions under various clamping loads. The strain distributions for both 19-wire and 61-wire strands show a surprising degree of heterogeneity. An increase in clamping force homogenizes the distribution to a degree, but only at unfeasibly high clamping forces. The results suggest that microscale variations in wire diameter dominate the internal mechanics of parallel wire strands. The stochastic distribution of wire sizes due to manufacturing tolerances throughout a strand cross-section creates a randomly ordered network of over- and under-sized wires. This imperfectly packed lattice results in large wire-to-wire variations in clamping constraint. The up-scaling in strand size from 19 to 61 wires increases the resolution of the experiment but does not reduce the heterogeneity of the strain distribution. Ergo, the assumption of perfect hexagonal packing in parallel wire strands is weak, and mean field distributions do not accurately describe the internal mechanics of such structures