Master of Science / Department of Mechanical and Nuclear Engineering / Warren N. White / As energy efficient devices become more necessary, it is desired to increase the efficiency of air conditioning systems. Current systems use on/off control, where the unit primarily operates in the long lasting start up transients. A proposed solution is an air conditioning unit that runs continuously with active computer control implemented to maximize efficiency. The objective of this thesis is to develop a mathematical model for a specific air conditioning unit and to compare this model to measurements made on the specific unit. This model can then be used to develop a multi-input multi-output control law in the future. In this thesis, a linearized moving interface lumped parameter model is presented, and the derivation verified with great detail. The model predicts transient perturbations from a steady state operating point. The air conditioner tested in this work required several modifications including the addition of sensors and controllers. A description of the system is provided. Methods used to determine all of the parameters for the model are given with explanation. The model is simulated with computer software and compared with experimental data. Simulations predict the final value of superheat and pressures in the evaporator and condenser well for step changes in the compressor speed and expansion valve opening.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Kirby S. Chapman / The increasingly strict air emission regulations may require implementing Non-Selective Catalytic Reduction (NSCR) systems as a promising emission control technology for stationary rich burn spark ignition engines. Many recent experimental investigations that used NSCR systems for stationary natural gas fueled engines showed that NSCR systems were unable to consistently control the exhaust emissions level below the compliance limits. Part of this thesis is devoted to show the results from the field testing of three engines working in natural gas gathering stations located in the “Four Corners” area. These three engines are retrofitted with NSCR systems. Emissions and engine operating data were monitored for more than one year. Data collected from October 2007 through December 2008 shows significant variation in emissions levels over hours, days, and longer periods of time, as well as seasonal variations. As a result of these variations, simultaneous control of NOx and CO below the compliance limit was achieved less than fifty percent of the monitored time. Modeling of NSCR components to better understand, and then exploit, the underlying physical processes that occur in the lambda sensor and the catalyst media is now considered an essential step toward improving NSCR system performance. The second portion of this thesis focuses on modeling the lambda sensor that provides feedback to the air-to-fuel ratio controller. Correct interpretation of the sensor output signal is necessary to achieve consistently low emissions level. The goal of this modeling study is to improve the understanding of the physical processes that occur within the sensor, investigate the cross-sensitivity of various exhaust gas species on the sensor performance, and finally this model serves as a tool to improve NSCR control strategies. This model simulates the output from a planar switch type lambda sensor. The model consists of three modules. The first module models the multi-component mass transport through the sensor protective layer. Diffusion fluxes are calculated using the Maxwell-Stefan equation. The second module includes all the surface catalytic reactions that take place on the sensor platinum electrodes. All kinetic reactions are modeled based on the Langmuir-Hinshelwood kinetic mechanism. The third module is responsible for simulating the reactions that occur on the electrolyte material and determine the sensor output voltage. The details of these three modules as well as a parametric study that investigates the sensitivity of the output voltage signal to various exhaust gas parameters is provided in the thesis.

Master of Science / Department of Mechanical Engineering / Warren N. White / The subject of linear control is a mature subject that has many proven powerful techniques. Recent research generally falls into the area of non-linear control. A subsection of non-linear control that has garnered a lot of research recently has been in underactuated dynamic systems. Many applications of the subject exist in robotics, aerospace, marine, constrained systems, walking systems, and non-holonomic systems. This thesis proposes a sliding mode control law for the tracking control of an underactuated dynamic system. A candidate Lyapunov function is used to build the desired tracking control. The proposed control method does not require the integration of feedback as does its predecessor. The proposed control can work on a variety of underactuated systems. Its predecessor only worked on those dynamic systems that are simply underactuated (torques acting on some joints, no torques acting on others). For dynamic systems that contain a roll without slip constraint, often a desired trajectory to follow is related to dynamic coordinates through a non-holonomic constraint. A navigational control is shown to work in conjunction with the sliding mode control to allow tracking of these desired trajectories. The methodology is applied through simulations to a holonomic case of the Segbot, an inverted cart-pole, a non-holonomic case of Segbot, and a rolling wheel. The methodology is implemented on an actual Segbot and shown to provide more favorable tracking results than linear feedback gains.

The introduction of microassembly technologies has opened up new venues for the fabrication of sophisticated, three-dimensional Microelectromechanical System (MEMS) devices. This thesis presents the development of a robotic micromanipulation system and its controller algorithms for conventional pick-and-place microassembly processes. This work incorporated the approach of parallel assembly and automation to improve overall productivity and reduce operating costs of the process. A parallel set of three microgrippers was designed and implemented for the grasping and assembly of three microparts simultaneously. The complete microassembly process was automated through a vision-based control approach. Visual images from two vision systems were adopted for precise position evaluation and alignment. Precise alignment between the micropart and microgripper is critical to the microassembly process. Due to the limited field of view of the vision systems, the micropart could displace away from the microscope field of view during the re-orientation process. In this work, a tracking algorithm was developed to constrain the micropart within the camera view. The unwanted translational motions of the micropart were estimated. The algorithm then continuously manipulated and repositioned the micropart for the vision-based assembly. In addition, the limited fields of view of the vision systems are not sufficient to concurrently monitor the assembly operation for all three individual grippers. This work presents a strategy to use visual information from only one gripper set for all the necessary alignment and positioning processes. Through proper system calibration and the alignment algorithms developed, grippers that were not visually monitored could also perform the assembly operations. When using visual images from a single vision camera for 3D positioning, the extra dimension between the 2D image and 3D workspace results in errors in position evaluation. Hence, a novel approach is presented to utilize image reflection of the micropart for online evaluation of the Jacobian matrix. The relative 3D position between the slot and micropart was evaluated with high precision. The developed algorithms were integrated onto the micromanipulation system. Automated parallel microassemblies were conducted successfully.

This thesis presents the theoretical analysis and experiment results of MEMS sensors designed for the application of low frequency vibration sensing. Each sensor consists of a proof mass connected to a folded beam micro-flexure, with an attached capacitive comb drive for displacement sensing. Three comb drive arrangements are evaluated, the transverse, lateral, and tri-plate differential. The sensors are fabricated using the well developed foundry processes of PolyMUMPS and SoiMUMPS. In addition, a capacitance to voltage readout circuit is fabricated using discrete components. Static tests, evaluating the capacitance to displacement relation, are conducted on a six degree of freedom robotic manipulator, and dynamic tests evaluating the sensor response to sinusoidal excitations are conducted on a vibrating beam. The end use of the sensor involves real-time vibration monitoring of automobile mechanical systems, such as power seats, windshield wipers, mirrors, trunks, and windows, allowing for early detection of mechanical faults before catastrophic failure.

This thesis deals with the fabrication of MEMS air quality sensors for automotive applications. The goal of this project is to design, fabricate and test an integrated sensor that measures three important air quality components inside the automotive cabin, which are temperature, relative humidity and carbon monoxide (CO) concentration. The sensors are fabricated on silicon substrate covered with thermal oxide and LPCVD nitride. Various deposition and etching techniques were utilized to fabricate these sensors including E-beam evaporation, thermal oxide growth, PECVD, LPCVD, RIE, KOH and HF etching. The temperature and humidity sensor use nickel as the sensitive material while the CO sensor was designed to use SnO2 although it was not fabricated to completion. A chamber was created where the temperature and humidity are controlled and the sensors were tested. Curves of sensor resistance vs. temperature and sensor resistance vs. humidity were created and the two sensor’s sensitivity was calculated.

The introduction of microassembly technologies has opened up new venues for the fabrication of sophisticated, three-dimensional Microelectromechanical System (MEMS) devices. This thesis presents the development of a robotic micromanipulation system and its controller algorithms for conventional pick-and-place microassembly processes. This work incorporated the approach of parallel assembly and automation to improve overall productivity and reduce operating costs of the process. A parallel set of three microgrippers was designed and implemented for the grasping and assembly of three microparts simultaneously. The complete microassembly process was automated through a vision-based control approach. Visual images from two vision systems were adopted for precise position evaluation and alignment. Precise alignment between the micropart and microgripper is critical to the microassembly process. Due to the limited field of view of the vision systems, the micropart could displace away from the microscope field of view during the re-orientation process. In this work, a tracking algorithm was developed to constrain the micropart within the camera view. The unwanted translational motions of the micropart were estimated. The algorithm then continuously manipulated and repositioned the micropart for the vision-based assembly. In addition, the limited fields of view of the vision systems are not sufficient to concurrently monitor the assembly operation for all three individual grippers. This work presents a strategy to use visual information from only one gripper set for all the necessary alignment and positioning processes. Through proper system calibration and the alignment algorithms developed, grippers that were not visually monitored could also perform the assembly operations. When using visual images from a single vision camera for 3D positioning, the extra dimension between the 2D image and 3D workspace results in errors in position evaluation. Hence, a novel approach is presented to utilize image reflection of the micropart for online evaluation of the Jacobian matrix. The relative 3D position between the slot and micropart was evaluated with high precision. The developed algorithms were integrated onto the micromanipulation system. Automated parallel microassemblies were conducted successfully.

This thesis presents the theoretical analysis and experiment results of MEMS sensors designed for the application of low frequency vibration sensing. Each sensor consists of a proof mass connected to a folded beam micro-flexure, with an attached capacitive comb drive for displacement sensing. Three comb drive arrangements are evaluated, the transverse, lateral, and tri-plate differential. The sensors are fabricated using the well developed foundry processes of PolyMUMPS and SoiMUMPS. In addition, a capacitance to voltage readout circuit is fabricated using discrete components. Static tests, evaluating the capacitance to displacement relation, are conducted on a six degree of freedom robotic manipulator, and dynamic tests evaluating the sensor response to sinusoidal excitations are conducted on a vibrating beam. The end use of the sensor involves real-time vibration monitoring of automobile mechanical systems, such as power seats, windshield wipers, mirrors, trunks, and windows, allowing for early detection of mechanical faults before catastrophic failure.

This thesis deals with the fabrication of MEMS air quality sensors for automotive applications. The goal of this project is to design, fabricate and test an integrated sensor that measures three important air quality components inside the automotive cabin, which are temperature, relative humidity and carbon monoxide (CO) concentration. The sensors are fabricated on silicon substrate covered with thermal oxide and LPCVD nitride. Various deposition and etching techniques were utilized to fabricate these sensors including E-beam evaporation, thermal oxide growth, PECVD, LPCVD, RIE, KOH and HF etching. The temperature and humidity sensor use nickel as the sensitive material while the CO sensor was designed to use SnO2 although it was not fabricated to completion. A chamber was created where the temperature and humidity are controlled and the sensors were tested. Curves of sensor resistance vs. temperature and sensor resistance vs. humidity were created and the two sensor’s sensitivity was calculated.

While tissue-engineering approaches of heart valves have made great strides towards creating functional tissues in vitro, the instruments used, named bioreactors, cannot efficiently integrate multiple stimuli to accurately emulate the physiological microenvironment. To address this, we conceptually designed and built a bioreactor system that applied a range of mechanical tension conditions, modulated matrix stiffness, and introduced biochemical signals in a combinatorial and high-throughput manner. Proof-of-concept experiments on PAVIC-seeded hydrogels were performed to assess the independent and combined effects of tensile strain, matrix stiffness and TGF-β1 on myofibroblast differentiation by measuring α-SMA expression, a marker that indicates a disease-associated phenotype. We found that matrix stiffness and TGF-β1 significantly increased α-SMA levels (p < 0.001), while the effect of mechanical strain was only significant on soft gels (~12 kPa) without TGF-β1. This study therefore demonstrated independent and integrated effects of multiple stimuli in regulating key cellular events in the aortic valve.