A Novel Haptic Simulator for Evaluating and Training Salient Force-Based Skills for Laparoscopic Surgery

Laparoscopic surgery has evolved from an \u27alternative\u27 surgical technique to currently being considered as a mainstream surgical technique. However, learning this complex technique holds unique challenges to novice surgeons due to their \u27distance\u27 from the surgical site. One of the main challenges in acquiring laparoscopic skills is the acquisition of force-based or haptic skills. The neglect of popular training methods (e.g., the Fundamentals of Laparoscopic Surgery, i.e. FLS, curriculum) in addressing this aspect of skills training has led many medical skills professionals to research new, efficient methods for haptic skills training. The overarching goal of this research was to demonstrate that a set of simple, simulator-based haptic exercises can be developed and used to train users for skilled application of forces with surgical tools. A set of salient or core haptic skills that underlie proficient laparoscopic surgery were identified, based on published time-motion studies. Low-cost, computer-based haptic training simulators were prototyped to simulate each of the identified salient haptic skills. All simulators were tested for construct validity by comparing surgeons\u27 performance on the simulators with the performance of novices with no previous laparoscopic experience. An integrated, \u27core haptic skills\u27 simulator capable of rendering the three validated haptic skills was built. To examine the efficacy of this novel salient haptic skills training simulator, novice participants were tested for training improvements in a detailed study. Results from the study demonstrated that simulator training enabled users to significantly improve force application for all three haptic tasks. Research outcomes from this project could greatly influence surgical skills simulator design, resulting in more efficient training

Modulating the Perceived Softness of Real Objects Through Wearable Feel-Through Haptics

In vision, Augmented Reality (AR) allows the superposition of digital content on real-world visual information, relying on the well-established See-through paradigm. In the haptic domain, a putative Feel-through wearable device should allow to modify the tactile sensation without masking the actual cutaneous perception of the physical objects. To the best of our knowledge, a similar technology is still far to be effectively implemented. In this work, we present an approach that allows, for the first time, to modulate the perceived softness of real objects using a Feel-through wearable that uses a thin fabric as interaction surface. During the interaction with real objects, the device can modulate the growth of the contact area over the fingerpad without affecting the force experienced by the user, thus modulating the perceived softness. To this aim, the lifting mechanism of our system warps the fabric around the fingerpad in a way proportional to the force exerted on the specimen under exploration. At the same time, the stretching state of the fabric is controlled to keep a loose contact with the fingerpad. We demonstrated that different softness perceptions for the same specimens can be elicited, by suitably controlling the lifting mechanism of the system

Realistic tool-tissue interaction models for surgical simulation and planning

Surgical simulators present a safe and potentially effective method for surgical training, and can also be used in pre- and intra-operative surgical planning. Realistic modeling of medical interventions involving tool-tissue interactions has been considered to be a key requirement in the development of high-fidelity simulators and planners. The soft-tissue constitutive laws, organ geometry and boundary conditions imposed by the connective tissues surrounding the organ, and the shape of the surgical tool interacting with the organ are some of the factors that govern the accuracy of medical intervention planning.\ud \ud This thesis is divided into three parts. First, we compare the accuracy of linear and nonlinear constitutive laws for tissue. An important consequence of nonlinear models is the Poynting effect, in which shearing of tissue results in normal force; this effect is not seen in a linear elastic model. The magnitude of the normal force for myocardial tissue is shown to be larger than the human contact force discrimination threshold. Further, in order to investigate and quantify the role of the Poynting effect on material discrimination, we perform a multidimensional scaling study. Second, we consider the effects of organ geometry and boundary constraints in needle path planning. Using medical images and tissue mechanical properties, we develop a model of the prostate and surrounding organs. We show that, for needle procedures such as biopsy or brachytherapy, organ geometry and boundary constraints have more impact on target motion than tissue material parameters. Finally, we investigate the effects surgical tool shape on the accuracy of medical intervention planning. We consider the specific case of robotic needle steering, in which asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. We present an analytical and finite element (FE) model for the loads developed at the bevel tip during needle-tissue interaction. The analytical model explains trends observed in the experiments. We incorporated physical parameters (rupture toughness and nonlinear material elasticity) into the FE model that included both contact and cohesive zone models to simulate tissue cleavage. The model shows that the tip forces are sensitive to the rupture toughness. In order to model the mechanics of deflection of the needle, we use an energy-based formulation that incorporates tissue-specific parameters such as rupture toughness, nonlinear material elasticity, and interaction stiffness, and needle geometric and material properties. Simulation results follow similar trends (deflection and radius of curvature) to those observed in macroscopic experimental studies of a robot-driven needle interacting with gels

Developments on Electrodynamic Levitation of Rotors

Magnetic bearings are systems capable of supporting rotors in absence of mechanical contact. Among many advantages with respect to ball and roller bearings are the possibilities of operating at extremely high rotational speeds and free of maintenance. Nevertheless, classical active magnetic bearings (AMB) are costly systems and may suffer from reliability problems. The most common types of passive magnetic bearings (PMB) based on the use of permanent magnet and reluctance forces are robust and relatively cheap but are affected by an intrinsic stability problem related to negative stiffness. The alternative of superconducting bearings has to deal with the difficulties for guaranteeing low temperatures for the superconducting materials to work; this represents a barrier for this technology. In the last decades an alternative for obtaining stable passive magnetic levitation has been searched, leading to the development of electrodynamic bearings. These systems, capable of realizing electrodynamic suspension for rotors using regular materials at room temperature, may be an alternative for the suspension of high rotational speed machines in the near future. The technological solutions proposed are still unable of devising a system capable of demonstrating the feasibility of this concept. Introduced in this context, this doctoral dissertation aims at developing models and design procedures to bring electrodynamic levitation of rotors closer to industrial applications. To this end, a large portion of the work is devoted to develop a unified model for representing the electromechanical interaction between rotor and stator generated by electrodynamic bearings of different types, namely homopolar and heteropolar configurations. The electromechanical model is developed taking advantage of the complex coordinate representation, typical in rotordynamics, in order to enable easy integration of the bearing's model with different rotordynamic models. An experimental validation of the model is carried out for homopolar configurations. The study of the dynamics of rotors on electrodynamic bearings is probably one of the most important aspects that must be dealt with before the bearings can reach the technological development needed to become industrially available. Bearing this in mind, the dynamics of a Jeffcott rotor and that of a four degree of freedom rotor are studied devoting special attention to the study of stability demonstrating the presence of unstable cylindrical and conical modes. The unbalance and frequency responses of the rotor on electrodynamic bearings are used to evidence the advantages and drawbacks between homopolar and heteropolar configurations. The studies are conduced using the state space formalism to obtain easy to manipulate system models. The modelling of the suspension evidences the strong coupling between the subsystems, showing that the influence of each subsystem on the rotordynamic stability is not obvious, thus complicating the design of the whole suspension. Considering an iterative design approach, the design of a test rig is presented. It is designed to test the validity of the models and the feasibility of radial electrodynamic suspension. A the mechanical layout of the test rig is developed to deal with the stability aspects introduced by the use of electrodynamic bearings

Numerical Investigation of Subglottal Stenosis Effects on Human Voice Production

This dissertation aimed to advance knowledge of how subglottal stenosis impacts voice production physiology. An in-house fluid-structure-acoustic interaction approach based on the hydrodynamic/acoustic splitting technique was employed. This technique was rigorously verified for simulating phonation by matching the acoustic behavior to a compressible flow solver for phonation-relevant geometries. Simulations of an idealized 2D vocal tract model demonstrated the effects of supraglottal acoustic resonance on vocal fold kinematics and glottal flow waveform. Results showed that the acoustic coupling between higher harmonics and formats generated pressure oscillations, modifying vocal fold dynamics and glottal flow rate. A major novelty was the incorporation and systematic parametric study of subglottal stenosis effects on voice production in an idealized 3D laryngeal model for the first time. Variation of subglottal stenosis severity revealed changes in vocal fold motion for severities higher than 90%, and flow rate and acoustics for severities higher than 75%. Detailed analysis revealed relative flow resistance and the ratio between glottal and stenosis minimum areas as primary factors determining the degree of influence. This provided new insights relating stenosis severity to physical changes in voice production consistent with clinical intervention guidelines. Highly detailed subject-specific realistic laryngeal and vocal tract geometries were reconstructed from high-resolution imaging to enable developing a coupled flow-acoustics-solid interaction model. Self-sustained vocal fold oscillations and glottal flow rates matching human phonation validated this highfidelity model’s capabilities. Parametric stenosis studies provided confirmation using real geometries and additional insights into underlying physical mechanisms. In summary, this dissertation research verified numerical methods, revealed acoustic resonance effects, systematically quantified stenosis severity thresholds, and elucidated mechanisms relating observations to area ratio and pressure drops. Outcomes significantly advance fundamental knowledge of simulating normal and pathological voice production. This work provides a strong foundation for future translational research on modeling other voice disorders, supporting surgical planning, and guiding interventions

Research reports: 1991 NASA/ASEE Summer Faculty Fellowship Program

The basic objectives of the programs, which are in the 28th year of operation nationally, are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA Centers. The faculty fellows spent 10 weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague. This is a compilation of their research reports for summer 1991

Incidence and transfer behaviors of high-order hot judder in passenger cars

As one of the brake-induced noises and vibrations, hot judder is forced vibration, which is caused by unevenness of the brake disc due to the thermal mechanical interactions in wheel brakes. Brake disc unevenness is normally described and evaluated as the Disc Thickness Variation (DTV) and the disc’ Lateral Run-Out (LRO). DTV and LRO gener-ate Brake Pressure Variation (BPV) and Brake Torque Variation (BTV) in wheel brakes, which are transmitted to the driver and perceived by the driver as the brake pedal pulsa-tion, the steering wheel oscillation, the car body vibrations, and low-frequency drone noises inside a vehicle. Hot judder is characterized by hot spots on the disc surfaces. The frequency of hot judder is dependent on the wheel rotational speed, showing order behaviors. The num-ber of hot spots generally corresponds to the dominant order of hot judder. In the last decades, most of the hot judder tests have been carried out with brake dynamometers, and high numbers (typically around 10) of hot spots were found in the majority of the tests. The generation and development mechanisms of the high dominant order have been almost the exclusive focus of current hot judder researches. However, the influ-ences of the vibrations and noises (with higher frequencies compared with the low-order cold judder) caused by high-order hot judder on the driver’s subjective perception have been still not clarified. That is to say, it is still unknown in which form and under which conditions, the high-order hot judder can be transmitted to and perceived by the driver, and thus causing customer complaints. A top-down approach is used in order to investigate the influences of high-order judder on driver’s perception with respect to two aspects: the incidence of high-order hot jud-der in vehicle tests and the drivers’ perception of high-order hot judder. The first aspect is mainly investigated by studying the transferability of dynamometer tests to vehicle tests and by identifying the incidence of high-order hot judder in production brakes. Specifically, identical brakes from one front brake and one rear brake are separately tested with a brake dynamometer and through vehicle tests by means of road tests and chassis dynamometer tests, and all brakes of four production passengers are identified with accelerometers attached on the brake caliper and the caliper bracket. The perception of high-order hot judder is chiefly studied by investigating its transfer behaviors. Global transfer functions from BPV/BTV to the selected driver interface quantities (brake pedal pulsation, steering wheel oscillation, seat track vibrations, and vehicle interior drone noise) are defined, which establish the links between the hot judder intensity in the wheel brake and the intensity at the driver interface. In order to identify the transfer functions with a high signal-noise-ratio and better reproducibility, a novel testing method is adopted: vehicle tests with brake discs that are artificially modi-fied with the desired surface shapes simulating the high-order DTV/LRO. Altogether three vehicles with seven different modified discs are tested. Two critical levels of drone noise (60 and 80 dB(A)) are selected according to the general vehicle total noise level and the human’s perception characteristics of sound. The perception threshold values of the driver interface vibrations are obtained through regression analysis between their subjective ratings and objective measurements. Based on the critical drone noise levels and the threshold values of vibrations, as well as the global transfer functions, threshold values of BPV and BTV for perceiving the high-order judder are computed. Concerning the incidence of high-order judder, both the dominant order and the thermal increases of BTV and BPV for the dominant order showed great discrepancies in differ-ent test types (e.g. brake dynamometer or vehicle, drag braking application with con-stant velocity and constant pressure/torque or stop braking application with decreasing velocity and constant deceleration/pressure). Hot judder behaviors in the brake dyna-mometer test were not transferable to the vehicle tests. Besides, no evident high-order hot judder has been identified in all the brakes of the four passenger cars. Generally, hot judder seems to be more likely to be excited at the brake dynamometer than in the vehi-cles. Therefore, brake dynamometer test is still appropriate for detecting hot judder in the early phase of brake development, and thus preventing its occurrence in the vehicle. Regarding the driver’s perception, the drone noise is the most probable reason leading to customer complaints, since higher than 100 Hz less than 10 Nm BTV is required to perceive the drone noise and 50 Nm BTV can already result in unacceptable drone noise. The driver is less sensitive to the vibrations caused by high-order judder. Roughly at least 20 Nm BTV or 2.5 bar BPV is needed for perceiving the vibrations, and the perception is most possibly due to the steering wheel oscillation or the vertical vehicle vibration. Moreover, some resonances in the transfer paths play a significant role in the high-order judder transmission. Although the investigations in this work are limited to three vehicles, the practical significance of high-order hot judder on the driver’s percep-tion is revealed for the first time. With these results, the impact of the measured BTV and BPV of hot judder, e.g. in the brake dynamometer tests, can be assessed. Combining these results, the most effective and efficient way to mitigate the high-order hot judder would be reducing its occurrences in the wheel brakes and diminishing the prominent resonances in the transfer paths