Freestanding low pressure chemical vapor deposition (LPCVD) silicon nitride (SiN) membrane resonators are widely investigated as Nano-Electromechanical System (NEMS) for their outstandingly low mechanical dissipation and high mechanical quality (Q) factor. The high Q-factor brings better sensitivities to force, displacement, and temperature excitations. However, integrated actuation methods are not trivial to implement on this platform and are required to harness their high Q-factor in practical applications. The first goal of this research is to develop a recipe for fabricating large area low stress LPCVD SiN membrane since commercial membranes are relatively expensive and have limited flexibility in terms of geometries. Starting from 4 inches, 500 μm thick, (100) single crystal silicon wafers double-side coated with 100 nm LPCVD SiN, we successfully fabricate five different sizes (i.e., 1 mm, 1.5 mm, 3 mm, 6 mm and 12 mm) of square shape membrane chips. The developed recipe is universally applicable for any size (i.e., under 12 mm) of square shape SiN membrane from the same type of wafer. All recipe parameters are presented in this work, along with experienced challenges and their associated solutions. The second part of this work is to develop an on-chip actuation method for these resonators. We develop a new method for creating acoustic waves in the silicon substrate using metal – silicon nitride – silicon capacitors. Acoustic waves due to the voltage-dependent mechanical stress arising from charge attractions was already observed previously in silicon substrate p-n junction resonators but is observed here for the first time in a capacitively coupled metal-dielectric-semiconductor (MDS) assembly. In the MDS system, we model three main possible actuation regimes, i.e., depletion, accumulation, and thermal expansion. Both depletion and accumulation rely on electrostatic attraction forces in MDS capacitors when an AC electrical current flows through. The same current can also generate thermal expansion forces resulting from resistive dissipation in the silicon. This contribution, however, is found to be negligible. In experimental measurements on 1.5 mm membranes in high vacuum, the accumulation MDS is found to perform better than the depletion one in terms of membrane actuation amplitude. With 2 V drive voltage, the membrane achieves up to 10 nm displacement for fundamental mode (1, 1). The contribution of thermal expansion forces is found to be negligible, with resonator temperature changes smaller than 4 mK. A comparison of energy dissipation between a conventional external piezo actuation method and our approach is also presented, through which we find that both methods have comparable power consumption.

Hybrid actuation is an expanding field in which several systems, such as a mechanical, electrical, hydraulic, pneumatic, and/or thermal, among others, are integrated in order to combine certain aspects of each system, and achieve a better and more efficient performance under certain operating conditions. The concept of piezohydraulic actuation takes advantage of the high force capabilities that piezoceramics have and combines it with the operation at high frequencies, in order to achieve the hydraulic actuation of a system under a specified stroke and force. High frequency rectification translates the low stroke of a piezoelectric stack into a desired amount of stroke per unit time. Thus, the low displacement, oscillatory motion of the piezoelectric device (coupled with a high frequency operation) is translated into a unidirectional motion of a hydraulic cylinder. As part of this research, a benchtop piezohydraulic unit has been developed and the concept of piezohydraulic actuation has been demonstrated. The effective bidirectional displacement of a hydraulic cylinder through the actuation of a piezoelectric stack has been achieved. A lumped parameter model is developed in order to simulate the dynamics of the hydraulic system and of the entire piezohydraulic unit. The model did approximate the response of the piezohydraulic unit under a one-sided operation. Time response analysis is performed through the frequency spectrum comparison of the measured and the simulated data. Then a two-stage cycle simulation is used to model the pumping operation of the unit. Discrepancies were obtained between the model and the actual system for the single-ended piezohydraulic unit, nonetheless, a good approximation has been achieved for the pumping operation of the double-ended unit under certain conditions. Furthermore, several factors have been identified that may limit the operation of the piezohydraulic unit. First, the need of high displacement actuators often comes with the requirement of high voltage operation along with high current consumptions. Thus, the amplifier becomes the first limitation to overcome. Second, is the response of the controlled valves. The highest valve operating frequency and their time response will set the limit on the piezohydraulic unit. And finally, once these limitations are overcome, the unit is eventually limited by the dynamics of the fluid and the hydraulic system itself. Attenuation in the frequency response, or the operation near resonance and the possibility of cavitation, are some of the aspects that eventually will limit the operation of the piezohydraulic unit. A custom made, high displacement stack is used along with a custom made switching amplifier. The current system is being limited by the second factor, the solenoid valves. Nonethelss the analysis performed has addresed the relevant issues required for the design and use of another set of controlled valves. Finally, the eventual limitation from the hydraulic system has been determined through the analysis of the fluid dynamics of the system. The analysis does not account for potential cavitation, and future operations at high frequencies should take it into account. / Master of Science

Grasp stability was studied and researched upon by various research groups, but mainly focused on robotic grippers by devising conditions for a stable grasp. Maintaining grasp stability is important so as to reduce the chances of the object slipping and dropping. But there was little focus on the grasp stability of robotic exoskeleton gloves and most of the research was focused on mechanical design. A robotic exoskeleton glove was developed as well as novel methods to improve the grasp stability. The exoskeleton glove developed is intended for patients who have suffered paralysis of the hand due to stroke or other factors. The robotic glove aids them in grasping objects as part of daily life activities. The glove is constructed with rigidly coupled 4-bar linkages attached to the finger tips. Each linkage mechanism has 1- Degree of Freedom (DOF) and is actuated by a linear Series Elastic Actuator (SEA). Two methods were developed to satisfy two of the conditions required for a stable grasp. These include deformation prevention of soft objects, and maintaining force and moment equilibrium of the objects being grasped. Simulations were performed to validate the performance of the algorithms. A battery of experiments was performed on the integrated prototype in order to validate the performance of the algorithms developed. / Master of Science / An exoskeleton glove is robotic device that can aid people who suffer from paralysis of their hands caused by a stroke or other factors with the primary goal of allowing them to regain the basic ability of grasping objects and thereby improving their quality of life. The exoskeleton glove developed in this research is focused on objects grasping assistance rather than for rehabilitation purposes. Since the exoskeleton glove lacks conscious senses like a human hand typically possesses, it may not be able to apply sufficient grasping force or may apply excessive force than required irrespective of the object being grasped. In order to ensure that the exoskeleton glove applies the proper amount of force, two novel methods were developed which help improve the overall grasping performance of the robotic glove. These methods use sensors that enable the glove to react to the force interaction changes that exists between the hand and the object being grasped through the exoskeleton glove. The first method detects any deformation that may occur while grasping a soft object and applies lesser force accordingly to prevent further damage to the object. The second method uses motion sensor to detect any movement by the user while grasping the object and applies corrective forces so that the object doesn’t slip from the hand. A prototype was designed and integrated and the two methods were tested on the prototype to validate them.

Emergency first responders are the great heroes of our day, having to routinely risk their lives for the safety of others. Developing robotic technologies to aid in such emergencies could greatly reduce the risk these individuals must take, even going so far as to eliminate the need to risk one life for another. In this role, humanoid robots are a strong candidate, being able to take advantage of both the human engineered environment in which it will likely operate, but also make use of human engineered tools and equipment as it deals with a disaster relief effort. The work presented here aims to lessen the hurdles that stand in the way through the research and development of new humanoid robot technologies. To be successful in the role of an emergency first responder requires a fantastic array of skills. One of the most fundamental is the ability to just get to the scene. Unfortunately, it is at this level that humanoid robots currently struggle. This research focuses on the complementary development of physical hardware, digital controllers, and trajectory planning necessary to achieve the research goals of improving the locomotion capabilities of a humanoid robot. To improve the physical performance capabilities of the robot, this research will first focus on the interaction between the hip and knee actuators. It is shown that much like the human body, a biped greatly benefits from the use of biarticular actuation. Improvements in efficiency as much as 30% are possible by simply interconnecting the hip roll and knee pitch joints. Balancing and walking controllers are designed to take advantage of the new hardware capabilities and expand the terrain capabilities of bipedal walking robots to uneven and non-stationary ground. A hybrid position/force control based balancing controller stabilizes the robot's COM regardless of the terrain underfoot. In particular two feedback mechanisms are shown to greatly improve the stability of bipedal systems in response to unmodelled dynamics. The hybrid position/force approach is shown through experiments to greatly extend humanoid capabilities to many types of terrain. With robust balancing ensured, walking trajectories are defined using an improved linear inverted pendulum model that incorporates the swing leg dynamics. The proposed method is shown to significantly reduce the control authority (by 50%) required for satisfactory trajectory following. Three parameters are identified which provide for quick manual or numerical solutions to be found to the trajectory problem. The walking and balance controller were operated on four different terrains successfully, strewn plywood, gravel, and high pile synthetic grass. Furthermore, SAFFiR is believed to be the first bipedal robot to ever walk on sand. The hardware enabled force control architecture was very effective at modulating ground reaction torques no matter the ground conditions. This in combination with highly accurate state estimation provided a very stable balance controller on top of which successful walking was demonstrated. / Ph. D.

After skeletal muscle damage, satellite cells move towards the injured area to assist in regeneration. However, these cells are rare as their numbers depend on the age and composition of the injured muscle. This regeneration method often results in scar tissue formation along with loss of function. Although several treatment methods have been investigated, no muscle replacement treatment currently exists. Tissue engineering attempts to create, repair, and/or replace damaged tissue by combining cells, biomaterials, and tissue-inducing substances such as growth factors. Electrospinning produces a non-woven scaffold out of biomaterials with fiber diameters ranging from nanometers to microns to create an extracellular-like matrix on which cells attach and proliferate. Our focus is on synthetic polymers, specifically poly(D,L-lactide) (PDLA), poly(L-lactide) (PLLA), and poly(ε-caprolactone) (PCL). Skeletal muscle cells grown on electrospun scaffolds tend to elongate and fuse together thus, mimicking natural tissue. Electrical stimulation has been shown to increase the number of cells fused in culture and decreased the time needed in culture for cells to contract. Therefore, a conductive element was added to each scaffold, specifically polyaniline (PANi), gold nanoparticles (Au Nps), and multi-walled carbon nanotubes (MWCNT). Our project goal is to create a polymeric, conductive, and biocompatible scaffold for skeletal muscle regeneration. PANi and PDLA were mixed to form the following solutions 24% (83% PDLA/17% PANi), 24% (80% PDLA/20% PANi), 22% (75%PDLA/25% PANi), 29% (83% PDLA/17% PANi), and 29% (80% PDLA/20% PANi). Only the 75/25 electrospun scaffold was conductive and had a calculated conductivity of 0.0437 S/cm. Scaffolds with larger amounts of PANi were unable to be electrospun. PDLA/PANi scaffolds were biocompatible as primary rat skeletal muscle cells cultured in vitro did attach. However, the scaffolds shrunk, degraded easily, and became brittle. Although PDLA/PANi scaffolds were easily manufactured, our results indicate that this polymer mixture is not appropriate for skeletal muscle scaffolds. PLLA and Au Nps were electrospun together to form three composite scaffolds: 7% Au-PLLA, 13% Au-PLLA, and 21% Au-PLLA. These were compared to PLLA electrospun scaffolds. Measured scaffold conductivities were 0.008 ± 0.015 S/cm for PLLA, 0.053 ± 0.015 S/cm for 7% Au-PLLA, 0.076 ± 0.004 S/cm for 13% Au-PLLA, and 0.094 ± 0.037 S/cm for 21% Au-PLLA. It was determined via SEM with a Bruker energy dispersive x-ray spectrometer (EDS) that the Au Nps were not evenly distributed within the scaffolds as they had agglomerated. Rat primary muscle cells cultured on the three Au-PLLA scaffolds displayed low cellular activity. A second cell study was conducted to determine Au NPs toxicity. The results show that the Au Nps were not toxic to the cells and the low cellular activity may be a marker for myotube fusion. Elastic modulus and yield stress values for the three Au-PLLA scaffolds measured on days 0, 7, 14, 21, and 28 were much larger than skeletal muscle tissue. Due to the larger mechanical properties and Au Nps agglomeration, a third polymer and conductive element scaffold was investigated. PCL was chosen as the new synthetic polymer as it had a lower elastic modulus and high elongation. MWCNT were chosen as the conductive element as they disperse well within PCL when acid functionalized. A third component was added to the scaffold to help it move similar to skeletal muscle. Ionic polymer gels (IPG) are hydrogels that respond to an external stimulus such as temperature, pH, light, and electric field. A poly(acrylic acid)/poly(vinyl alcohol) (PAA/PVA) mixture is one type of IGP that responds to an electric field. The scaffolds were coaxially electrospun so that each fiber had a PCL-MWCNT interior with a PAA/PVA sheath. These scaffolds were compared to electrospun PCL and PCL-MWCNT ones. The addition of MWCNT to the PCL did increase scaffold conductivity. Actuation of the PCL-MWCNT-PAA/PVA scaffold occurred when 15V and 20V were applied. All three scaffolds had rat primary skeletal muscle cells attached but, more multinucleated cells with actin interaction were seen on PCL-MWCNT-PAA/PVA scaffolds. Once again the mechanical properties were greater than muscle, but because of its ability to actuate we believe the PCL-MWCNT-PAA/PVA scaffold has potential as a bioartificial muscle. Further characterization of the PCL-MWCNT-PAA/PVA included varying the ratios of PAA/PVA, smaller crosslinking times, and lower amounts of MWCNT. Four ratios, 83/17, 60/40, 50/50, and 40/60, were successfully coaxially electrospun with PCL and MWCNT. Overall, very few differences were seen between the four ratios in conductivity, cellular biocompatibility, actuation angular speed, and mechanical properties. The 83/17 and 40/60 ratios were chosen for additional investigation into mechanical properties and actuation. As the mechanical properties of the two types of scaffolds did not change significantly through degradation, lower PVA crosslinking times were tested. No significant effects were found and it was hypothesized that the evaporation of the solution played a role in the crosslinking process. The smaller MWCNT amount scaffolds also did not significantly affect the mechanical properties or the actuation angular speeds. More work into lowering the scaffold mechanical properties while increasing the actuation angular speed is necessary. Though the mechanical properties for the 83/17 and 40/60 scaffolds remained high compared to skeletal muscle, we also looked for differences in in vivo biocompatibility. Both scaffolds were implanted into the right vastus lateralis muscle of Sprague-Dawley rats. The left vastus lateralis muscle served as either the PBS injected sham surgery or an unoperated control. Biocompatibility was evaluated using enzymes, creatine kinase (CK) and lactate dehydrogenase (LDH), levels, fibrosis formation, inflammation, scaffold cellular infiltration, and neovascularization on days 7, 14, 21, and 28 post-implantation. Fibrotic tissue formation, inflammation, and elevated CK and LDH levels were observed initially but responses decreased during the four week study. Cells infiltrated the scaffolds and histological staining showed more fibroblasts than myogenic cells initially but over time, the fibroblasts decreased and myogenic cells increased. Neovascularization of both scaffolds was also recorded. PCL-MWCNT-PAA/PVA scaffolds were determined to be biocompatible, but some differences between the two types were noted. The 83/17 scaffolds caused less of a response from the body compared to the 40/60 scaffolds and had more myogenic cells attached. However, the 40/60 scaffolds had a larger number of blood vessels running through the scaffold. In conclusion, we have successfully fabricated a polymeric, conductive, and biocompatible scaffold that can actuate for skeletal muscle tissue engineering. Although our results are promising, more work is necessary to continue developing and refining the scaffold. / Ph. D.

The purpose of this thesis has been to compare and analyse the use of digital hydraulic actuators in place of traditional actuators in aircraft control surface manipulation. Digital hydraulic actuator referring to a hydraulic actuator where the power has been discretized using discrete on/off-valves. For this purpose three simulation models have been used. The first model consists of a benchmark model, designed to represent a digital hydraulic actuator acting on a mass under the influence of an external spring load. The discretization in this case comes from the fact that three separate pressure levels have been used to power a four-chambered tandem piston, resulting in 81 possible force combinations.The second simulation model represents a 6 degrees of freedom aircraft model parametrised to behave like a F16 fighter aircraft. The purpose of this model has been to serve as a means to implement the digital actuator in an aircraft. The third model has been heavily based on the F16 model but re-parametrised such that it represents a delta canard aircraft. The actuators in the aircraft models was initially mounted on the control surface primarily dedicated for the manoeuvre which was simulated, in this case a step in altitude, meaning that the control surface was the elevon.As it would turn out the digital actuator had trouble achieving the precision required in order to adequately fly the aircraft at a low enough energy consumption. As such the idea took form to implement a hybrid design where the digital actuator would be paired with a proportional actuator on a separate control surface, flaperons. The digital actuator would then only require to be positioned in a close enough position and once there lock in place, leaving the proportional actuator to handle the fine tuning and trim of the aircraft. It would appear that by using the hybrid actuator design the energy consumption during the right circumstances could be reduced by as much as 40% for the delta canard configuration and 30% for the F16 case.

In aviation industry, one of the most important aspects is weight savings. This since with a lowered weight, the performance of the aircraft can be increased together with increased fuel savings and thus lowered running costs. One way of saving weight is to reduce energy consumption, since with lowered energy consumption, lowered mass of fuel is required etc. Most aircraft are today maneuvered with hydraulic systems due to its robustness and power density. It is the primary source of power for primary and secondary flight controls. The control of a conventional system which is using proportional valves is done by altering flow by restricting it to the extent where the desired output is achieved, which implies heat losses since the full performance of its supply is wasted through the valve. In previous research, more energy efficient hydraulic systems called digital hydraulics has been investigated. In difference with conventional hydraulics, digital hydraulics uses low cost, high frequency on/off valves, which either are fully opened, or fully closed, instead of proportional valves to achieve the desired output. With this comes the benefit of no energy losses due to leakage and restriction control. The downsides with digital hydraulics is the controlabillity. One way of controlling it is by using several pressure sources which outputs different pressure levels. By using the on/off valves in different combinations, different outputs can be achieved in a discrete manner. In this thesis, the aim was to remove the impact of the discrete force steps which are present in digital hydraulics by creating concepts with hybrid solutions containing both digital hydraulics and restrictive control. Three concepts were developed and investigated using simulation. The energy consumption and performance was analysed and compared with a reference model, the concepts redundancy compared to conventional systems was discussed and finally the concepts were tested with an aircraft simulation model. The concepts were found to reduce the energy consumption with different magnitude depending on the load cycle. The performance was found to be almost as good as the reference model. The redundancy compared with conventional systems should be possible to maintain with slight modifications, but further investigation is needed. It was found that one of the most important aspects regarding energy consumption is which combination of supply pressures is used to supply the system since it influences leakage and flow due to compression.

No description available.

This thesis investigates the role of phonetic biases and systemic effects in the actuation of sound change through computer simulations and experimental methods. Phonetic biases are physiological and psychoacoustic constraints on speech. One example is vowel undershoot: vowels sometimes fail to reach their phonetic targets due to limitations on the speed of the articulators. Phonetic biases are often paralleled by phonological patterns. For instance, many languages exhibit vowel reduction, a phonologised version of undershoot. To account for these parallels, a number of researchers have proposed that phonetic biases are the causal drive behind sound change. Although this proposal seems to solve the problem of actuation, its success is only apparent: while it might be able to explain situations where sound change occurs, it cannot easily explain the lack of sound change, that is, stasis. Since stability in sound systems seems to be the rule rather than the exception, the bias-based approach cannot provide an adequate account of their diachronic development on its own. The problem of bias-based accounts stems from their focus on changes affecting individual sound categories, and their neglect of system-wide interactions. The factors that affect speech production and perception define an adaptive landscape. The development of sound systems follows the topology of this landscape. When only a single category is investigated, it is easy to take an overly simplistic view of this landscape, and assume that phonetic biases are the only relevant factor. It is natural that the predicted outcomes will be simple and deterministic if such an approach is adopted. However, when we look at an entire sound system, other pressures such as contrast maintenance also become relevant, and the range of possible outcomes is much more diverse. Phonetic biases can still skew the adaptive landscape towards themselves, making phonetically natural outcomes more likely. However, their effects will often be countered by other pressures, which means that they will not be satisfied in every case. Sound systems move towards peaks in the adaptive landscape, or local optima, where the different pressures balance each other out. As a result, the system-based approach predicts stability. This stability can be broken by changes in the pressures that define the adaptive landscape. For instance, an increase or a decrease in functional load or a change in lexical distributions can create a situation where the sound system is knocked out of an equilibrium and starts evolving towards a new stable state. In essence, the adaptive landscape can create a moving target for the sound system. This ensures that both stability and change are observed. Therefore, this account makes realistic predictions with respect to the actuation problem. This argument is developed through a series of computer simulations that follow changes in artificial sound systems. All of these simulations are based on four theoretical assumptions: (i) speech production and perception are based on probabilistic category representations; (ii) these category representations are subject to continuous update throughout the lifetime of an individual; (iii) speech production and perception are affected by low-level universal phonetic biases; and (iv) category update is inhibited in cases where too many ambiguous tokens are produced due to category overlap. Special care is taken to anchor each of these assumptions in empirical results from a variety of fields including phonetics, sociolinguistics and psycholinguistics. Moreover, in order to show that the results described above follow directly from these theoretical assumptions and not other aspects of these models, the thesis demonstrates that exemplar and prototype models produce the same dynamics with respect to the observations above, and that the number of speakers in the model also does not have a significant influence on the outcomes. Much of the thesis focuses on rather abstract properties of simulated systems, which are difficult to test in a systematic way. The last chapter complements this by presenting a concrete example, which shows how the simulations can be linked to empirical data. Specifically, I look at the effect of lexical factors on the strength of contextual effects in sound categories, using the example of the voicing effect, whereby vowels are longer before voiced obstruents than they are before voiceless ones. The simulations implemented in this chapter predict a larger effect in cases where a given vowel category occurs equally frequently in voiced and voiceless environments, and a smaller difference where one of the environments dominates the lexical distribution of the vowel. This prediction is borne out in a small cross-linguistic production experiment looking at voicingconditioned vowel length patterns in French, Hungarian and English. Although this is only one of many predictions that fall out of the theory of sound change developed in this thesis, the success of this experiment is a strong indication that the research questions it brings into focus are worth investigating.

This thesis presents a study on the design and analysis of a morphing flap structure integrated with actuation mechanism for potential application to large aircraft. Unlike the conventional rigid flap mounted on the wing trailing edge, the morphing flap is designed as a unitized structural system integrated with three primary components: the upper and lower flexible skins reinforced by stringers, an eccentric beam actuation mechanism (EBAM) with discs fixed on it, and the connection of the discs with the stringers. Based on the EBAM concept proposed by Dr Guo in previous research [1], the current study has been focused on the EBAM design and optimization, kinematic simulation and structural modelling of the morphing flap. Although a lot of efforts have been made to develop the morphing flap in previous research, it is lack of detailed design of the disc-skin linkage and clear view on the mechanism optimization in relation to the shape requirement. The main objective of this research is to meet the morphing shape requirements and calculate the actuation torque for a specified morphing flap. Firstly effort was made to design and optimize the disc shape and locations in the EBAM for the best matching of the specified morphing shape with minimum actuation torque demand. It is found that minimum three discs are required and their locations have little effect on the actuation torque. Secondly attention was focused on designs of the disc and a C-linkage with the stringers. To ensure that the C- linkage works in practice, a twisted stringer flange design was proposed. Thirdly the actuation mechanism was integrated with the stiffened skin to play the role of an active rib in the flap structure. Based on the design, FE modelling and analysis of the morphing flap structure was carried out. The behaviour of the morphing flap under the internal actuation and external aerodynamic load was applied for stress analysis and detailed design of the structures. Finally the kinematics of the integrated morphing flap was simulated by using CATIA to demonstrate the feasibility and the effectiveness of the improved design.