Browsing by Author "Tadesse, Yonas"
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Item A Real-Time Solution Enabling Humanoids to Efficiently Identify Faces and Facial Expressions(2018-08) Saxena, Abhishek Girish; Tadesse, Yonas; Bhatia, Dinesh K.Owing to the advantages and effectiveness of using humanoids in the field of therapy and rehabilitation, there is a need for robots to have the capability to recognize a person and understand his/ her emotional state based on facial expressions, thus making the human-robot interaction more natural. In this thesis, an accurate, real-time and power efficient solution for face recognition and facial expression recognition is presented. The solution consists of a combination of a convolutional neural network (CNN) and a Support Vector Machine (SVM), which is deployed on NVIDIA Jetson TX2, a cheap, powerful and small sized hardware processing platform. For efficient deployment, a study on power consumption and performance of standard deep learning networks is drawn to analyze and find out the best hardware configuration of NVIDIA Jetson TX2 for inferring networks. The proposed solution was compared with AlexNet [Krizhevsky, Sutskever, and Hinson, Advances in Neural Information Processing Systems, 1097-1105 (2012)] and was found to be more accurate on facial expression datasets considered. It also has smaller model size, faster inference, lesser number of trainable parameters and consumes lesser power. The performance and functionality of the developed application was tested on videos and humans in a real Human-Robot Interaction scenario. The results were satisfactory, vindicating the fact that the application can be deployed and used in the real world.Item Additive Manufacturing of Heterogeneous Composites for Biomimetic Robots(2019-11-22) Hamidi, Armita; Tadesse, YonasPrinting complex objects from computer-aided design models is a unique capability of additive manufacturing (AM). Developing this ability to print heterogeneous materials with diverse mechanical properties will advance AM beyond the current capabilities, eliminating the need for assembly and post-processing, and promoting the efficient design of multifunctional complex objects with minimum time and cost. Considering this concept, we aim to investigate this technology to fabricate biologically inspired structures, actuators, and robots. In this dissertation, first, an inexpensive 3D printer is developed for a single step fabrication of a novel bioinspired joint system, consisting of dissimilar materials with high strength and high strain. The joint consists of thermoplastic parts reinforced with metal fibers that resemble bones and soft elastomer that mimics soft tissue. An open-source 3D printer is modified to print thermoplastic with continuous fibers (copper and steel), where the metal fibers act as reinforcement within a polymer matrix (PLA and PETG). The influence of different wire materials and polymer matrixes on the tensile modulus and ultimate tensile strength is studied. The properties of the samples are predicted analytically using several models and compared with experimental results. Highly stretchable elastomer is directly 3D printed and simultaneously cured by heating. Moreover, a cost effective multi-material AM (modified FDM and DIW) is developed that maintained high elasticity and sufficient strength for printing components that mimic the musculoskeletal system. In the second part of the study, the main focus is on the highly elastic materials, sacrificial materials, and actuation units to further develop the fabrication of highly elastic soft structures. Silicone thinner is used to tailor the mechanical properties of the soft material, and it is shown that the addition of the thinner to the silicone reduces the tensile modulus and improves the elongation to break. By adding 20% volume thinner to the silicone, the 3D printed silicone samples reached to 1260% elongation without breaking, which is the highest among all the 3D printed elastomers previously reported. However, this strain is not achieved in the cyclic tensile test, instead, the maximum strain was 600 % where the sample failed after 40 cycles. To create hollow channels during 3D printing of silicone, carbohydrate glasses are introduced as sacrificial materials. Few configurations of fluidic actuators that are commonly used in soft robots are developed by forming channels in the silicone elastomer via 3D printed sacrificial carbohydrate structures. The last part is the design and development of biomimetic structures (jellyfish, modular joint and starfish structures) by the existing method of robot manufacturing and proposed AM techniques. The primary focus on this part is on the design, development, and analysis of the heterogeneous structures of biomimetic robots. Therefore, a complete fabrication process for each of the robotic structure is identified and used to make multiple functional prototypes. All the demonstrated biomimetic systems are actuated by embedding twisted and coiled polymer (TCP) muscle during or after the fabrication process or assembled. The flexibility of the TCP enables the soft robot to bend, twist, and change shape while it is embedded in the structure. 6-Ply and 4-Ply silver-coated nylon (TCP) muscle geometries were studied and used for the design and development of the jellyfish and starfish like robots. The capabilities offered by these biomimetic robots are extensively characterized such as: (i) swimming, (ii) multidirectional bending, and (iii) producing morphing shapes. Extensive evaluations of these capabilities with functional prototypes demonstrate that integration TCP with elastomer is viable for creating biomimetic robots.Item Artificial Heart for Humanoid RobotPotnuru, Akshay; Wu, Lianjun; Tadesse, Yonas; BarCohen, Y.A soft robotic device inspired by the pumping action of a biological heart is presented in this study. Developing artificial heart to a humanoid robot enables us to make a better biomedical device for ultimate use in humans. As technology continues to become more advanced, the methods in which we implement high performance and biomimetic artificial organs is getting nearer each day. In this paper, we present the design and development of a soft artificial heart that can be used in a humanoid robot and simulate the functions of a human heart using shape memory alloy technology. The robotic heart is designed to pump a blood-like fluid to parts of the robot such as the face to simulate someone blushing or when someone is angry by the use of elastomeric substrates and certain features for the transport of fluids.Item Characterization and Circuit Design of Soft Bend Sensors for Use in Robotic Hands and Orthotics(2022-05-01T05:00:00.000Z) Mohapatra, Sanjana; Tadesse, Yonas; Kang, Gu Eon; Prasad, ShaliniSmart materials such as shape memory alloy (SMA) and twisted and coiled polymer fishing line (TCPFL) are essential elements for the realization of novel smart robotic hands, orthotic hands, and prosthetic hands. These artificial muscle-actuated robotic hands need to be assessed extensively to understand the properties and efficiency of the designs. Cyclic movement of the fingers must be monitored to characterize the actuation frequency of the artificial muscles and the response due to the amplitude of stimuli. Flex sensors and strain gauges are commonly used to observe the bending action of robotic fingers by attaching them along the finger’s length. Such sensors are piezoresistive in nature and change their resistance due to stresses exerted on them which change the sensor’s dimensions. This piezoresistive property of some standard sensors available in the market is studied in this research to determine the angular position of the robotic finger during flexion or extension when the artificial muscles are triggered. A similar type of strain gauge sensor was designed in-house, which can be 3D printed and directly embedded into an orthotic finger. This sensor was fabricated using conductive and soft filament materials which consist of a composite of thermoplastic polyurethane (TPU) and carbon nanotubes (CNT). The purpose of this thesis is to characterize the sensor and design the optimized signal conditioning circuit of this sensor. A voltage divider circuit was utilized to characterize and understand the properties of the sensors. Various techniques including Wheatstone bridge, differential amplifiers, and active low pass filters have been implemented for designing the signal conditioning circuit of the strain gauge sensor, and several simulations results were obtained. This optimization converts the variable resistance of this strain gauge into a linearized voltage signal that is easier to monitor through common interfaces. In general, soft smart materials, actuators, and sensors can transform the existing robotic hands to achieve more elegant, lightweight, and modular designs.Item Coiled Shape Memory Alloy (CSMA) Actuators and Conductive Filament for the Realization of 3D Printed Robots(2018-08) Potnuru, Akshay; Tadesse, YonasSoft robots and humanoids need actuators with low profile, lightweight, high strain and relatively high frequency. Coiled shape memory alloy (CSMA) actuators satisfy these requirements, as SMAs are high-energy density actuators. There are a number of variables that affect the performance of the CSMA actuators. We present the manufacturing, characterization and simulation of the NiTi based CSMA actuators mainly focusing on the geometry and performance relationships. The manufacturing technique resulted in 80% strain with respect to loaded length and greater than 1000% with respect to original length, when actuated with an input voltage of 3.4 V, 0.66 A, and 6 MPa load. The strain response at different frequency was determined experimentally and these actuators can be used in many soft robots. To improve actuation speed, a novel 2-step hot-cold water-cooling was implemented. One of the requirements of fully functional 3D printed robots is electrical connections in some part of the printed structure. To this effort, we present composite materials consisting of conductive carbon nanoparticles, thermoplastics, and solvents to create filaments for 3D printing. The mechanical and electrical properties of filaments were investigated using a concentration of 0 − 15% weight of carbon nanoparticles (NC) in polylactide (PLA) using dichloromethane (DCM) solvent and subsequently, the DCM is evaporated by drying. The electrical conductivity of the composite filament is compared with commercial and academia counterparts. To demonstrate the application of CSMA, three devices /systems are presented in this study. The first one is the actuation of an artificial musculoskeletal (MS) system that can be used as a building block for bioinspired soft robots. The second one is a soft robotic pump inspired by the pumping action of a biological heart. The soft artificial heart can be used in a humanoid robot with facial expressions and can simulate someone blushing or angry by circulating a blood-like fluid. Different designs and their characterization are presented both experimentally and via simulations. The third application is a coronary artery stent. In this work, we performed a case study on the double helix coiled SMA for use as a stent to overcome the mechanical failure due to stress concentration in existing stents. Simulation and experiments were conducted using hyperelastic silicone rubber that mimics the human coronary arteries.Item Control of a Soft 3D-printed Artificial Finger Actuated by Coiled Shape Memory Alloy Muscles With Thermoelectric Cooling(2022-05-01T05:00:00.000Z) Deng, Eric; Tadesse, Yonas; Koeln, Justin; Park, WooramArtificial hands with many unique designs and capabilities have been presented in the literature; however, most of these hands only have binary finger states, meaning only open or closed states. Position control of fingers for these hands enables more precise manipulation of objects for a wide variety of applications, expanding their usage beyond simple grasping tasks. An additional area of focus, particularly with thermally actuated artificial muscles, is increasing actuation frequency, which is currently limited by heat transfer rates. Improving frequency will allow for faster response of the hands to input stimuli and accelerate their potential usage in robotic and prosthetic applications. The objective of this research is to improve upon existing robotic hand designs that utilize thermally actuated artificial muscles. Such muscles have a high strength-to-weight ratio, low profile and silent actuation, but suffer from low actuation frequency and energy inefficiency. In this thesis, coiled shape memory alloy (SMA) muscles were studied and utilized for the design of a robotic hand using soft 3D-printed thermoplastic polyurethane (TPU). First, discussion on the design of the hand, manufacturing and characterization are presented. Next, finger position control to the hand using embedded flex sensors to create a closed-loop system is presented. This strategy maintains the ease of manufacturing of the TPU hand via 3D-printing, while also introducing new sensing capability. An investigation into improving the actuation frequency of the coiled SMAs using thermoelectric cooling via Peltier plates is also conducted. Holistically, these additions to the 3D-printed hand are projected to increase its overall actuation speed and precision, allowing for greater manipulation capabilities, but also adding additional weight and complexity to the overall system.Item Creating Interactive Social Robots and Multimodal Control of Robotic Hands with Artificial Muscles(2019-11-22) Jafarzadeh, Mohsen; Tadesse, Yonas; Gans, NicholasSocial robots are essential for healthcare applications as assistive devices or behavior-based intervention systems. Social interactions, robotic hands and multimodal control are three core aspects of social robots, which are investigated in this dissertation. First, we present a wearable sensor vest and an open-source software architecture with the Internet of Things (IoT) for social robots. The IoT feature allows the robot to interact with local humans and other humans over the Internet. The designed architecture is demonstrated in a humanoid robot, and it works for any social robot that has general-purpose graphics processing unit (GPGPU), I2C/SPI buses, Internet connection, and Robot Operating System. The modular design of this architecture enables developers to easily add/remove/update complex behaviors. The proposed software architecture provides IoT technology, GPGPU nodes, I2C and SPI bus mangers, audio-visual interaction nodes, and isolation between behavior nodes and other nodes. Second, our humanoid robot uses novel actuators, called twisted and coiled polymer (TCP) actuators/artificial muscles, to move its fingers. Classical controllers and fuzzy-based controllers are examined for force control of these actuators. It was noted that disturbance and noise are major challenges in system identification and control of TCPs. In a short term, the muscles behave like a first-order, linear time-invariant system when the input is voltage square and the output is either force or displacement. However, the behaviors and parameters of the polymer muscles slowly change. An on-policy adaptive controller is designed for regulating force of the muscles that is optimized by stochastic hill-climbing and a novel associated search element. The third part is multimodal control of robotic hands. Recent advancements in GPGPUs enable intelligent devices to run deep neural networks in real-time. Thus, state-of-the-art intelligent systems have rapidly shifted from the paradigm of composite subsystems optimization to the paradigm of end-to-end optimization. By taking advantages of GPGPU, we showed how to control robotic hands with raw electromyography signals and speech 2D features using deep learning and convolutional neural networks. The proposed convolutional neural networks are lightweight, such that it runs in real-time and locally in an embedded GPGPU.Item Deformation Analysis of TPU Structures and Actuation Using SMA Coils for a Prosthetic Finger(December 2022) Okoh, Albert; Tadesse, Yonas; Ruths, Justin; Malik, ArifThis thesis focuses on experimental study on the use of coiled shape memory alloy (SMA) and Peltier plates for robotic finger actuation, their manufacturing and design, and the relationships between input magnitudes and output results such as finger joint angles. A fundamental flexible structure based on cantilever beam that is 3D-printed using thermoplastic polyurethane (TPU) is studied both experimentally and via simulations. The experiments for robotic finger actuation with the use of coiled shape memory alloys and Peltier plates were all based on prior studies. However, here extensive open loop characterization study has been conducted to understand the system. First, we will go into the data that was acquired through characterization experiments for some pre-made cantilever beams. This will help give us a better understanding on the movement and characteristics of the robotic finger that is discussed in this work. Specifically, the bending properties of a robotic finger that is actuated by coiled SMA and its characteristics in response to change in amplitude of current and heating time. Next, TPU cantilever beams were simulated using CAD analysis software package, such as SolidWorks, to determine deflection in response to tip load. Structural analysis and frequency analyses were performed. The simulation results were compared with experimental results and good agreement in terms of the trend of the angles as the loads were varied. Instead of a solid geometry, we used a serrated structure that resembles the 3D printed structure. This modification was made because the advanced 3D printed used for the fabricated structures resulted in irregular surface finish of the structure. Finally, discussion on results and future improvements will be explained.Item Design and Implications of a Robotic Prosthetic Leg with Low-Impedance Actuation(2020-04-08) Elery, Toby Brent; Gregg, Robert D.; Tadesse, YonasRecent developments in the field of powered prostheses have produced several devices that implement a wide variety of actuation schemes, each presenting specific benefits and limitations to prosthetic design and acceptance of robotic prostheses. The work of this dissertation encompasses research focused on the design and implications of an actuation scheme new to robotic prosthetic leg design; low-impedance actuation. Although this style of actuation has shown promise in legged robots, it has potential benefits specifically relating to powered prosthetic legs as well. Such benefits include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, less acoustic noise, and power regeneration. To investigate these potential benefits a custom transfemoral (knee-ankle) robotic prosthetic leg with high-torque, low-impedance actuators was created. Preliminary benchtop testing established that both joints can be backdriven by small torques (~1-3 Nm), confirming the small reflected inertia and low impedance. The reduced joint-level impedance was achieved while maintaining the ability to produce very large torque (~180 Nm). Impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback or lengthy tuning trials. The negligible effect of the actuator’s unmodeled dynamics is further demonstrated through the direct implementation of biological impedances in amputee walking experiments. The regenerative abilities, low friction, and small reflected inertia of the presented actuators also offer practical benefits through reduced power consumption and acoustic noise compared to state-of-art powered legs. Although these benefits are mainly related to the physical device, this dissertation also extends the investigation into potential benefits to the wearer. Additional walking experiments were conducted with three amputee subjects to study how the powered prosthetic leg with low-impedance actuators affected gait compensations, specifically at the residual hip. A walking controller was implemented on the powered prosthesis to exploit the low-impedance actuators’ power density during push-off, impedance control abilities in stance, and trajectory tracking abilities to ensure toe-clearance during swing. Results show that when large push-off power is provided, less work is demanded from the residual hip to progress the limb forward. Moreover, all subjects displayed increased step length and propulsive impulses for the prosthetic side, compared to their passive prostheses. These results reduce demand on the hip to accelerate the body forward and display the ability to improve gait symmetries. Hip circumduction improved for subjects who had previously exhibited this compensation on their passive prosthesis. The improvements made to these compensations lead to reduced residual hip power and work, which can reduce fatigue and overuse injuries.Item Embedded TCP and SMA Actuators for Use in Flexible Structures of Bioinspired Robots and Humanoids(2018-05) Almubarak, Yara; Tadesse, YonasSoft robots consist of elastomeric materials, compliant actuators, and sensors that enable them to be used for numerous applications due to their flexibility, lightweight, and many degrees of freedom. Many actuators such as pneumatic actuators and servomotors introduce many design constraints due to their size, weight, and cost. Moreover, vibration and noise are undesired attributes that preclude the use of the robot. Smart materials play a vital role in the field of soft robotics since they can be used as sensors and actuators. This thesis presents the design and characterization of three robotic structures that are actuated by twisted and coiled polymer (TCP) muscles and shape memory alloys (SMA). First, a soft silicone skin embedded with TCP muscles that shows two unique modes of actuation is presented. The two actuation modes (undulatory and bending) depend on the muscle placement, skin thickness, applied voltage, and actuation time. Second, a humanoid head actuated using fully embedded TCP muscles featuring basic facial expressions, head nodding and jaw movement is presented. Third, an underwater jellyfish-like robot actuated by SMA muscles is developed. Several studies for the bell segment actuation were conducted to determine the influence of power input, bell geometry, and number of spring steels embedded within the elastomer. Studying these different application domains experimentally plays an important role in gaining new knowledge on design, fabrication, and performance of smart materials and soft robots.Item Fabrication of Polylactide Nanocomposite Filament Using Melt Extrusion and Filament Characterization for 3D Printing(2017-05) Jain, Shrenik Kumar; Tadesse, YonasFused deposition modeling (FDM) technology uses thermoplastic filament for layer by layer fabrication of objects. To make functional objects with desired properties, composite filaments are required in the FDM. In this thesis, less expensive mesoporous Nano carbon (NC) and carbon nanotube (CNT) infused in Polylactide (PLA) thermoplastic filaments were fabricated to improve the electrical properties and maintain sufficient strength for 3D printing. Solution blending was used for nanocomposite fabrication and melt extrusion was employed to make cylindrical filaments. Mechanical and electrical properties of 1 to 20 wt% of NC and 1 to 3 wt% of CNT filaments were investigated and significant improvement of conductivity (3.76 S/m) and sufficient yield strength (35MPa) were obtained. Scanning electron microscopy (SEM) images exhibited uniform dispersion of nanoparticles in polymer matrix and differential scanning calorimetry (DSC) results showed no significant changes in the glass transition temperature (Tg) for all the compositions. Perspective uses of this filament are for fabrication of electrical wires in 3D printed robots, drones, prosthetics, orthotics and others.Item Fabrication of Polylactide/Carbon Nanopowder Filament Using Melt Extrusion and Filament Characterization for 3D Printing(World Scientific Publishing Co. Ltd) Jain, Shrenik Kumar; Tadesse, Yonas; Jain, Shrenik Kumar; Tadesse, YonasIn this study, less expensive mesoporous nano carbon (NC) infused in polylactide (PLA) thermoplastic filaments were fabricated to improve the electrical properties and maintaining sufficient strength for 3D printing. Solution blending was used for PLA-NC nanocomposite fabrication and melt extrusion was employed to make cylindrical filaments. Mechanical and electrical properties of 1-20wt.% of NC-filaments were investigated and significant improvement of conductivity (3.76S/m) and sufficient yield strength (35MPa) were obtained. SEM images exhibited uniform dispersion of NC in polymer matrix and DSC results showed no significant changes in the glass transition temperature (Tg) for all the compositions. Perspective uses of this filament are for fabrication of electrical wires in 3D printed robots, drones, prosthetics, orthotics and others.Item Fishing Line Based Twisted and Coiled Polymer (TCP) Muscles and Thermoelectric Coolers for Improved Frequency of Actuation(2022-12-01T06:00:00.000Z) Singh, Rippudaman 1997-; Tadesse, Yonas; Fadda, Dani; Malik, ArifThe combination of muscles, bones, cartilage, and ligaments that are essential for mobility can result in different configurations of a musculoskeletal system design. The most used actuators for robotic movement are tendon driven systems using DC-motor-based. Besides DC motors, pneumatic artificial muscles are of interest for biologically inspired musculoskeletal systems due to pneumatic muscles’ similarity to natural muscles in terms of length-load curves, their compliance, rapid contraction, and the high power/weight ratio. Actuators such as the electric motors and pneumatic artificial muscles used in robotics have their own drawbacks. Although electric motors are energy efficient actuators, they require complex transmission systems, resulting in limitations in terms of size and space. Above all, electric motors do not fit in the bio-inspired design approach. On the other hand, pneumatic artificial muscles require a compressor to force a gas into the actuators to create a pressure difference between the inside and the ambient environment for actuation. This makes pneumatic artificial muscles bulky in an overall system. We investigate twisted and coiled polymer (TCP) artificial muscles for actuation of limb movements using fishing line and a resistive heater nichrome (TCPFL NR). The actuation by these muscles is due to their contraction and expansion while exposed to different temperatures. TCP muscles have been deeply researched in the University of Texas at Dallas and have been implemented on multiple robotic arms. One of the major drawbacks observed after using these muscles is the time it takes to move back to its initial length after actuation. Hence a method of cooling is required to increase the rate of cooling such that the muscles take shorter time to get back to their initial length. This thesis proposes the use of Peltier cooling mechanism that should be employed during the contraction and extension of TCP muscles. The addition of a Peltier module decreases the time it takes for the muscle to expand back to its original length. Currently, for a typical TCP muscle of diameter 3 mm, the muscles are only subjected to natural convection for cooling and takes about 40 seconds to cool down for 10 seconds actuation stimuli. Due to this, the robotic fingers, attached to the TCP muscles, also take 40 seconds to retract back to their initial length. Current research focuses on the improvement of TCP muscles as actuators for use in robots. The primary area of improvement would be the actuation frequency of the artificial muscles to ensure realistic applications of TCPFL.Item Hardware-assisted Malware Detection for Securing Embedded Systems(2021-12-01T06:00:00.000Z) Kuruvila, Abraham Peedikayil; Basu, Kanad; Tadesse, Yonas; Bhatia, Dinesh; Balsara, Poras; Bennett, Terrell RIn the era of Internet of Things (IoT), Malware has been proliferating exponentially over the past decade. Traditional Anti-Virus Software (AVS) is ineffective against modern complex Malware. In order to address this challenge, researchers have proposed hardware-assisted Malware detection using Hardware Performance Counters (HPCs). The HPCs are used to train a set of Machine learning (ML) classifiers, which are deployed as Hardware-assisted Malware Detectors (HMDs), and used to distinguish benign programs from Malware. Recently, adversarial attacks have been designed by introducing perturbations into HPC traces to misclassify a program for specific HPCs. The attacks function by inducing sleep and running dummy benign instructions to bolster the count of incurred HPCs. Furthermore, HPC-based techniques can suffer from a high false positive rate due to the similar executed instructions in both benign and malicious applications. Lastly, HPC-based detection can be infeasible in devices that do not possess HPCs or have limited profiling capabilities. This dissertation extends and explores various improvements to current HPC-based detection schemes in a multi-part operation. First, various different traditional ML classifiers are evaluated for HPC-based detection and this security is extended to automotive vehicles by securing an engine control unit from malicious attacks. Second, a Moving Target Defense (MTD) that dynamically changes the attack surface to jeopardize attackers’ endeavors, as well as Non-Differential HMDs (ND-HMDS), which use gradient free classifiers, is developed. Third, tailor-made HPCs, which sample assembly instructions from an application’s dynamic trace, are introduced as a solution for devices without HPCs in addition to providing better fine-grain precision for reducing false positives. Fourth, to further ameliorate the aforementioned problems, a Sequential Time Series-based Detection (SEQ-TSD) framework for identifying Malware is proposed that utilizes only a single HPC. Finally, an explainable HPC-based Malware technique that furnishes the location of the most malicious instruction is produced for providing human-readable results.Item iGrab Hand Orthosis: Design and Development Using Twisted and Coiled Polymer Muscles(2017-12) Saharan, Lokesh Kumar; Tadesse, YonasFour million Americans are suffering from upper limb malformation due to various neurological disorders. Efforts have been made to develop orthosis and prosthesis to improve the quality of life of those individuals. This work primarily focuses on the design, development and analysis of a hand exoskeleton created using novel actuators called twisted and coiled polymer (TCP) muscles, 3D printed structures, and a garment glove for a rehabilitation of the patients with partial or no motor abilities in the hand. The 3D printed exoskeleton incorporates the TCP muscles (380 mm long and 1.25 mm in diameter) wrapped around pulleys to pull the tendons which in turn facilitate the flexion motion of fingers. Extension motion was done using elastic cords on the dorsal side of the hand. A custom made biomimetic hand was developed using a 3D printed hand skeleton and casting Ecoflex 30 silicone to mimic similar stiffness as the natural hand and to test the orthosis device. Eight different orthotic hands were designed and developed, and we showed precise prehensile and non-prehensile hand movements. Further, we analyzed the motions of the robotic and the orthotic devices using Euler-Lagrangian equations. The modeling included the derivation of equation of motion for the three-link under-actuated serial manipulator suitable for numerical simulations. System identification was used to determine the electro-thermo-mechanical model transfer functions of the TCP muscle. These two transfer functions were integrated with the Euler-Lagrange model in the Simulink®. Then, a measured power and force profile of the TCP muscle was used as input to the Simulink model to determine the motion behavior of all three joints of the robotic finger. Errors in the torque and force profile were determined statistically. Also, sensitivity analysis was conducted using key model parameters. The TCP muscles are the most recent revolutionary development in the field of the smart actuators, with high power to weight ratio 5.4 kW/kg, 16 %- 200 % actuation stroke and stress of 1- 35 MPa presented by Carter Haines in 2014 introductory science paper and in a subsequent study in 2016. In addition, the precursor material for the muscles is inexpensive (~$5/kg) compared to a shape memory alloy ($3000/kg) and the muscle fabrication is easier. Also, the hysteresis is minimal for the TCP muscles but the efficiency is one of the limitations of the actuator which is close to 1%. We have developed an experimental setup to fabricate and characterize the TCP muscles under different loading conditions and determine stress, strain, and power, number of cycle and temperature rise. We used silver coated nylon 6,6 multifilament threads and performed actuation tests, microscopy and tensile tests . Different geometries of the TCPs 1-ply, 2-ply and 3-ply muscles were studied for the effect of speed of the rotation during fabrication and natural frequency. Further, the low efficiency of the muscles is addressed with the design and implementation of two different types of the locking mechanism in the prosthetic and orthotic devices. The locking mechanisms have shown significant improvements in the efficiency of the muscle. The novelty of this work lies in the design, development and modeling of the orthotics device, improving the muscle efficiency along with study and characterization of the TCP muscles.Item Informing Surgical Interventions via Biomechanical Engineering Techniques for Individuals With Lower-limb Loss and Pathology(2021-05-01T05:00:00.000Z) Levy, Emily T; Tadesse, Yonas; Fey, Nicholas; Saquib, Mohammad; Wells, Joel; Majewicz Fey, Ann; Rodrigues, DanieliAmputations (i.e., limb loss) and osteoarthritis are two of the leading causes of long-term disability. Persons within these associated populations suffer from gait abnormalities and pain, which lead to a lower quality of life. Individuals with transfemoral amputation who are ambulatory don prosthetic sockets that often need frequent clinical refitting/reconfiguration and have few realistic alternatives, especially in individuals with obesity and/or vascular disease. To overcome these issues, osseointegration, or direct skeletal attachment of a prosthesis to a limb, has been proposed and shown to greatly improve functional mechanics of the lower-limb. But osseointegration surgery has only be used on patients with traumatic limb loss (representing the minority of the population) and can lead to infection of limb soft tissue and bone that requires additional amputation surgery and loss of limb length. Medial thighplasty, or excision and liposuction of adipose tissue in the residual limb, is a more conservative surgical alternative with higher eligibility than osseointegration and that may also improve prosthetic function. However, this limb “recontouring” procedure is often viewed as a surgery that improves limb cosmesis (i.e., its appearance), as opposed to its function. In fact, most medial thighplasty candidates are non amputees who are obese. This dissertation evaluates the influence of medial thighplasty surgery in the context of transfemoral limb loss and quantifies improvements in lower-limb and center-ofmass kinematics and kinetics during straight-line walking as well as during transient changes of direction. This surgical technique—modifying only the limb adipose tissue—improved biomechanical function and maneuverability characterized by greater path efficiency, faster movement completion times, smoother turning curvatures, tighter coupling between movement velocity and curvature, and increased shear ground reaction forces. This work suggests that confidence and fluidity of movement can be improved if medial thighplasty is applied in individuals with transfemoral limb loss and provides a missing link between the underlying structure of the residual limb and the function of lower-limb prostheses. Osteoarthritis has been shown to be secondary to developmental joint abnormalities, which are often expected to lead to higher contact stress of the articulating joint surfaces. Dysplasia and femoroacetabular impingement are two common hip deformities that lead to premature joint degradation. Yet, diagnosis is complex, and the course of treatment is different depending on the pathology. A robust treatment plan for therapy or surgery is vital to preserving the hip joint before the onset of osteoarthritis. This dissertation evaluated patients with diagnosed dysplasia or impingement prior to hip preservation surgery and uncovered significant differences in their gait biomechanics. The dysplasia cohort exhibited widespread gait deviations throughout the stride, while impingement group showed localized differences in mechanics that primarily occurred during peak hip extension (i.e., last stance phase of the stride). Furthermore, this dissertation investigated the use of dynamic simulation of static medical imaging from these patients. We argue, as an alternative to dynamic imaging modalities, that imposing normative motion of these static joint images in a simulation framework can lead to further insight about the underlying root causes of each deformity and calculate geometric properties of the hip center-of-rotation, as well as inadmissible variations of the relative motion between femur and acetabulum during normative level and sloped walking. Finally, continuous classification schemes were evaluated (linear and nonlinear discriminant analyses) to probe the separation between time-varying features of these multiple pathologies that occur throughout the stride. These final studies pertaining to hip preservation also deepen our understanding of the functional link between lower-limb structure and its function during widely varying ambulation scenarios and provide a potentially powerful tool to improve the diagnosis and treatment of a given patient.Item Laser Processing and Additive Manufacturing of Metallic Alloys: Laser Impact Welding, Laser Shock Peening, and Directed Energy Deposition(August 2022) Sadeh, Sepehr; Malik, Arif S.; Hansen, John H.L.; Qian, Dong; Tadesse, Yonas; Ryu, Ill; Bernal Montoya, RodrigoThe objectives of this work are to develop a more accurate numerical simulation of the laser impact welding (LIW) process, to investigate the effects of the laser shock peening (LSP) process as a post-treatment to LIW, and to examine the effects of interlayer machining (IM) on the microstructure and residual stress (RS) in builds manufactured via the directed energy deposition (DED) additive manufacturing (AM) process. First, a method for capturing the laser-generated plasma pressure load is proposed to increase the accuracy in numerical LIW simulations. LIW is a recently developed technology for the fully-mechanical joining of thin metallic foils. LIW is of great interest as it could be used to join any pair of similar or dissimilar metals without any melting required, thus avoiding the formation of brittle intermetallic compounds. However, the LIW of thin metallic foils is a complex process, and the underlying physical phenomena involved in the mechanical interlocking of the foils are not yet fully understood. Therefore, to benefit from its full potential in the near future, extensive research on experimental implementation and numerical simulation of the LIW process is of paramount importance. Thus far, only a few articles on numerical simulations of the LIW process have been published in the literature. All of these works have made over-simplifying assumptions such as using a pre-defined deformed flyer foil shape with a uniform initial velocity, that diminish the accuracy of the simulation. In contrast, the research in this work proposes the idea that the incorporation of the actual spatial and temporal profiles of the laser beam and modeling of the corresponding pressure pulse based on an LSP approach could provide a more realistic prediction of the LIW process mechanism. In this study, spatial and temporal profiles of an Nd:YAG laser beam pressure pulse are experimentally characterized and fully captured for use in numerical simulations of LIW. Both axisymmetric, arbitrary Lagrangian-Eulerian, and Eulerian dynamic explicit numerical simulations of the collision and deformation of the flyer and target foils are created. The effect of the standoff distance between the foils on impact angle, velocity distribution, springback, the overall shape of the deformed foils, and the weld strength in lap shear tests are investigated. In addition, the jetting phenomenon (separation and ejection of particles at very high velocities due to high-impact collision) and interlocking of the foils along the weld interface are simulated. Preliminary work indicates very similar deformation and impact behaviors in simulation results compared to experiments performed for validation. Next, using the same laser system configuration, an experimental methodology is proposed to investigate the effects of the extremely high strain rates present in the LSP process on the strength and interface geometry of welds obtained from LIW of dissimilar metallic foils. LSP is a processing technology capable of improving fatigue life and performance by inducing plastic deformations and, thus, compressive RS into the near-surface depth of metallic components. Due to this unique ability, in recent years, LSP has been explored as a post- treatment to improve performance in metallic welds fabricated via conventional fusion-based techniques. However, in high-velocity impact welding (HVIW) methods, specifically LIW, LSP has never been explored as a post-welding treatment. Therefore, in this work, LSP’s potential to improve the weld strength and integrity in dissimilar metallic joints fabricated via the LIW technique is investigated for the first time. Single and double LSP shots are applied to LIW foils using three different metallic material combinations. Subsequent lap shear testing show that single-shot LSP increases the average weld strength by 12% to 25%, depending on the flyer and target material combination. In contrast, with double-shot LSP, the average weld strength decreases regardless of the flyer and target materials involved. Scanning electron microscope images reveal wavy weld interfaces and increased interlocking between the foils for the single-shot LSP treatments as compared to the initial “flat” weld interface geometry, thereby leading to greater flyer/target weld strength. In the double-shot LSP treatments, however, separations and melting are observed along the weld interface due to rebounding and excessive plastic heat dissipation of the foils. The findings of this study reveal the first insights and effects regarding the application of LSP as a post-welding treatment beyond conventional fusion-based welding to HVIW methods. Last, an experimental procedure is presented to examine IM’s impact on the microstructure and RS in metallic components manufactured via the powder-based DED AM process. DED is one of the major additive manufacturing processes for producing and repairing large-size and high-value metallic components. At smaller size scales (micro to millimeters), DED could be potentially used in conjunction with LIW to manufacture small devices such as micro/mini robots. However, IM may be necessary to provide a flat surface on the DED build for its successful joining to metal sheets/wires via LIW. Recently, it has been shown that the grain structure of the materials influences the in-situ LIW behavior and likely performance. Therefore, to predict the performance of assemblies manufactured via hybrid processes that combine DED, IM, and LIW, it is important to understand the IM effects on the DED build’s microstructure. Therefore, in this work, for the first time, the influence of IM on the processing-structure-properties relationships in powder-based DED of stainless steel 316L is investigated. Four types of single-track builds are manufactured on stainless steel 316L substrates: single-layer, double-layer, machined single-layer, and double-layer with IM. The effects of IM on the microstructure and residual stress before and after the second layer’s deposition are studied via metallographic imaging and neutron diffraction. In single-layer samples, due to induced plastic strains and heat generated during the machining process, the microstructure undergoes dynamic recrystallization, which results in smaller, more equiaxed grains. In double-layer samples, IM results in greater tensile stresses at the interface of the two deposited layers, where a considerable variation in the microstructure is also observed. This is attributed to the delay caused by IM resulting in the second layer’s deposition onto a cooler first layer and thus a higher temperature gradient. However, the overall build height remains almost unchanged, with a slight reduction in build width. This study’s results show that IM has important and influential effects that should be considered in the design and control of the processing-structure-properties-performance relationships in the DED AM.Item Manufacturing Methods for Medium-Volume Production of Planar Dielectric Elastomer Actuators(2020-05) Little, Ryan Christopher; 0000-0002-0095-8329 (Little, RC); Gregg, Robert D; Tadesse, YonasDielectric elastomer actuators (DEAs) are a class of synthetic muscles which can be used in contexts such as robotics and powered prostheses, with the additional benefits of being lighter, quieter, and requiring fewer components than their mechanical counterparts. Existing research in this field focuses more on actuator design, modeling, and materials development than the method by which they are fabricated. The manufacturing methods used in prior works are inappropriate for a small lab that desires a reasonable degree of uniformity and precision; one-off manufacturing of DEAs does not provide adequate precision, and an automated solution for high-volume manufacturing runs is too expensive and takes up excessive floor space. This thesis presents a manufacturing method which achieves reasonable uniformity at low cost for medium-volume production. We found that by using readily available DEA materials and consumer-grade desktop fabrication tools such as a 3D printer and an automated cutting machine, the issues inherent in existing low and high-volume manufacturing methods are eliminated. Our method produced a medium quantity of actuators at a low cost without the use of dedicated floor space and machinery, and experiments showed that they functioned reliably in isolation and in assembly.Item The Mechanical Design of a Humanoid Robot with Flexible Skin Sensor for use in Psychiatric TherapyBurns, Alec; Tadesse, Yonas; BarCohen, Y.In this paper, a humanoid robot is presented for ultimate use in the rehabilitation of children with mental disorders, such as autism. Creating affordable and efficient humanoids could assist the therapy in psychiatric disability by offering multimodal communication between the humanoid and humans. Yet, the humanoid development needs a seamless integration of artificial muscles, sensors, controllers and structures. We have designed a human-like robot that has 15 DOF, 580 mm tall and 925 mm arm span using a rapid prototyping system. The robot has a human-like appearance and movement. Flexible sensors around the arm and hands for safe human-robot interactions, and a two-wheel mobile platform for maneuverability are incorporated in the design. The robot has facial features for illustrating human-friendly behavior. The mechanical design of the robot and the characterization of the flexible sensors are presented. Comprehensive study on the upper body design, mobile base, actuators selection, electronics, and performance evaluation are included in this paper.Item Numerical Modeling and Simulation of Biomedical Devices and Underwater Biomimetic Robots(2019-05-03) Shah, Shrey; Tadesse, YonasNumerical simulations are essential in different fields of engineering for several types of analysis. They help in solving complex mathematical equations that govern the behavior of physical systems whose analytical solutions might be difficult to obtain. The simulations can be used in conjunction with the experimental results to compare, study and improve physical systems. This thesis focuses on the use of computational tools for three separate systems. The first one is a static structural finite element study of a self-expandable shape memory alloy (SMA) based stent. Different structures such as cantilever and coiled geometry are studied to characterize the SMA material. The SMA material is then applied to different stages of stent deployment. The behavior of a hyper elastic material such as silicone, which is used to mimic the behavior of human tissues and in the study of underwater soft robotics is also characterized and compared through different available models. The second and third parts of this study cover underwater flow simulations for an octopus and a jellyfish-like robots. In the octopus-like robot simulation, emphasis was given to the use of dynamic meshing techniques for underwater rigid motion to capture the flow behavior. Whereas, in the jellyfish simulation, attention was given to the use of fluid-structure interaction analysis, where the flapping movement of the soft jellyfish bell segment is coupled with the surrounding fluid domain to generate the required propulsion for forward motion. The study provides insightful information on the flow behavior of unique bioinspired underwater robots.