Mechatronics Systems Engineering - Theses, Dissertations, and other Required Graduate Degree Essays

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3D designed cellular solids for the case study of soft robotics

Author: 
Date created: 
2019-04-29
Abstract: 

With the advances in technology, robots have tremendously evolved over the past decades, emerging a new paradigm in robotics, called soft robotics, which is largely inspired by the biological systems in nature, and are primarily composed of materials with mechanical moduli similar to that of soft biological materials. The material properties and morphology of the soft bodies can help in achieving the desired performance for the soft robot, by deforming, adapting, and reacting to interaction forces. Most of the soft robots have bodies made out of intrinsically soft and/or flexible materials (for example, silicone rubbers) that can deform and absorb most of the energy arising from a collision. These robotic bodies built with elastomer materials show lack of structural stiffness that limits their use in many practical applications. The objective of this study is to design specific cellular materials and integrate stiffness into soft robotic gripper bodies, by applying both engineering and architectural principles to form a lightweight and stiff body. An architectured cellular robotic body design is demonstrated, with deformable structures for a soft gripper, which is easy to fabricate, lightweight, mechanically durable, and compliant while maintaining its resilience. This cellular body design not only overcomes the stiffness limitation but also other drawbacks of most common pneumatically actuated soft bodies which includes getting easily damaged from high pressure or impact and exhibiting low gripping force due to their soft, deformable bodies. To form a functional system, artificial cellular finger is equipped together with capacitance based pressure sensors on the fingertip in a single-building process with the advantage of multi-material three-dimensional (3D) printing. The integrated architectured grippers, composed of cellular fingers with repeatably reliable bending profile, demonstrated an average gripping force as 16 N on actuation with gripping capability of various objects. It is highly expected that 3D cellular designs open new possibilities for architectured materials that can be used from robotic grippers to many practical applications.

Document type: 
Thesis
File(s): 
etd20269-manpreet-kaur-Movie S1.Intelligent bending.mp4
etd20269-manpreet-kaur-Movie S2.gripper moving.mp4
Supervisor(s): 
Woo Soo Kim
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Compressive behaviour of thin porous layers with application to PEM fuel cells

Author: 
Date created: 
2019-04-05
Abstract: 

A key factor in Polymer Electrolyte Membrane (PEM) fuel cell performance is the compression due to expansion, swelling, and force exerted by bipolar plates on Membrane Electrode Assembly (MEA) which changes the porous microstructure and transport properties of layers in MEA. During manufacturing and operation of fuel cell, MEA goes through numerous cycles of compression, temperature, and humidity, which introduce hygrothermal stresses and result in change in properties of the layers which leads to adjustment of performance. Transport properties such as thermal conductivity, electrical conductivity, and gas diffusivity are dependent on mechanical properties and microstructure of MEA layers, which necessitate the study of their mechanical properties. The focus of this work is compression of Gas Diffusion Layer (GDL) and Catalyst Layer (CL) which play important role in dictating fuel cell performance. In this thesis, mechanical properties of GDL are measured and modeled analytically. Compression tests are performed on three GDL samples (SGL 34BA, Freudenberg, TGP-H-060). The results suggest a non-linear behaviour for pressure-strain curves which is because of their porous nature. Also, using effective medium theory, a representative geometry is introduced for GDL and the mechanical deformation of the simplified geometry is found analytically and validated by experimental data. Moreover, mechanical deformation of five different CL is measured under cyclic compressive load up to 5 MPa for the first time. Results show that CL behaves elastically below 2 MPa and no plastic deformation is observed; the Young’s modulus is decreased with increase in porosity, which was expected. More than that, cyclic compression tests for higher pressures show a slight change in Young’s modulus at higher pressures (more than 2 MPa) which is because of the change in microstructure at higher pressures. A geometrical platform for CL is developed in this study and a mechanistic compression model is developed based on the simplified geometry. The model is validated by comparing with the experimental results obtained for five different CLs. Using the model, effect of compressive load on porosity and pore size distribution is studied which shows significant change in larger pores and shift in pore size distribution curves.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Ned Djilali
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Development of capillary-assisted low pressure evaporator for adsorption chillers

Date created: 
2018-06-07
Abstract: 

The sales of air conditioners are poised to intensely increase over the next several years as incomes and global temperatures rise around the world. Conventional air conditioning systems use vapor-compression refrigeration (VCR) technology that has been the dominant technology for close to a century. However, the environmental impact of VCR systems, particularly their high energy consumption, around 36% of energy consumed in the US building sector, is contrary to sustainable development. In addition to the residential sector, VCR systems for vehicle air conditioning (A/C) applications can cause a 20% increase in fuel consumption. Moreover, while the commonly used refrigerants in VCR systems, hydrofluorocarbons (HFCs), are ozone-friendly, they still contribute to global warming. Alternative, natural refrigerants, such as water, have no toxicity and significantly lower global warming potential compared to HFCs. Furthermore, water is an ideal refrigerant for systems driven by low-grade thermal energy. Solar-thermal and waste-heat from industrial facilities and data centers are all abundant sources of low-grade thermal energy, with a temperature less than 100°C. Low-grade thermal energy can be used to run adsorption chillers for air conditioning of vehicle cabins and residential units. When using water as an air conditioning refrigerant, evaporation occurs at pressures below an atmosphere. In such a low pressure (LP) environment, the performance of a flooded evaporator is negatively affected by the hydrostatic pressure. This problem can be resolved by using a capillary-assisted low-pressure evaporator (CALPE) that exploits thin film evaporation. The focus of this doctoral research is to develop an effective CALPE for proof-of-concept demonstration of an adsorption chiller for vehicle A/C applications. In this research, a low pressure evaporator testbed is designed and built for the first time at Laboratory for Alternative Energy Conversion (LAEC) to test CALPE. In addition, a mathematical model is developed to understand detailed phenomena in capillary-assisted evaporation and to provide insight to design an effective and compact CALPE. Several commercial tubes with different fin geometries are tested. The results show that the capillary-assisted tubes provide two times greater heat transfer rate compared to a plain tube. To further enhance the performance, the outside surfaces of CALPE are coated with a thin film of porous copper to increase the capillary action and the surface area available for thin film evaporation. The coating increased the overall heat transfer coefficient by 30%. However, a significant amount of the thermal resistance is from the inside of the evaporator tubes. Therefore, a new µCALPE is designed with microchannels on the inside and rough capillary channels on the outside is 3D printed by using direct metal laser sintering process. The internal microchannels and external capillary channels led to enhanced heat transfer both internally and externally. The µCALPE increased the overall heat transfer coefficient by a factor of 2.5 when compared to the CALPE built with commercial Turbo Chil-40 FPI tubes, which had footprint of four times larger than that of µCALPE. The developed µCALPE is expandable to the entire low-grade thermal energy driven A/C systems in vehicles as well as residential units.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Developing a vector light sensor

Author: 
Date created: 
2019-01-10
Abstract: 

Over the past few decades, numerous sensors have been invented for the measurement of light intensity. In most cases, a setup external to the sensor is required to detect the direction of an incoming beam of light. In this work, the design, fabrication, and characterization of a novel light sensor is described. The three-dimensional structure of the sensor allows it to detect both the intensity as well as the direction of the incident light beam, hence becoming a vector light sensor (VLS). The sensor structure is based on creating photodiodes on sidewalls of miniaturized raised or inverted pyramids etched in silicon. Each photodiode was formed by selective doping of the material on each facet of the pyramid, forming a photodiode with the P-type substrate. A set of signal processing algorithms was developed to estimate the direction and the distance of a light source from the sensors. The light sensing devices with both raised and inverted pyramid structures were then fabricated in a cleanroom based on silicon microfabrication technologies. Throughout the process, the lithography step for the textured surface needed to be optimized. An interface circuit was designed and used to amplify and process the signals from the devices. The device operation was verified experimentally to estimate the direction of a light beam. The small size and low power consumption of the individual sensors make them suitable for applications were simple distance and direction estimation is required. The sensors can be arrayed to provide light-field information in the plane of sensor.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Behraad Bahreyni
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

3D architecture electrodes for energy storage applications

Author: 
Date created: 
2018-12-10
Abstract: 

Micro-scale energy storage devices have been developed for the demand of required energy autonomy of the portable and small-scale electronics. One main drawback in realization of micro-scale energy storage devices is limited areal capacitance due to low material loading per unit area on the substrate. 3-D electrodes with high aspect ratio could be promising strategy to overcome this, resulting in higher device performance. Specially, 3D printing technology offers numerous advantages to generate 3D electrodes for energy storage devices, which includes time-saving, cost-effective manufacturing, and realization of tailorable complex electrode designs. In this thesis, novel hierarchical 3D designs were printed by photo-curable 3D printing. Photo-curable resins with conductive fillers were optimized for conductive 3D electrode formation. Finally, energy storage devices with the hierarchical 3D electrodes have been demonstrated for the application of micro-supercapacitors (MSCs). The fabricated 3D hierarchical electrodes demonstrated low electrical resistance to be used as feasible MSCs electrodes. Energy storage from redox reactions was demonstrated in 3D architecture electrodes designed with mechanically durable 3D octet trusses.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Woo Soo Kim
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

MagnetoRheological dampers for mass and energy sensitive applications

Date created: 
2018-12-05
Abstract: 

MagnetoRheological (MR) dampers have been used as reliable electronically adjustable shock and motion control devices in the past few years. Although these dampers have proven their performance in practice and the cost has decreased, their usage has been limited to high-end applications. The main drawback of MR dampers is their relatively large weight and energy consumption when compared to their passive counterparts. In this thesis, we investigate factors affecting weight and energy consumption of MR dampers and devise solutions to achieve energy-efficient and light-weight dampers. To this end, an analytic approach is presented to design and build a low-energy consumption and lightweight MR damper. It is shown that the proposed configuration can decrease the mass of MR damper significantly and reduce the energy consumption when AlNiCo alloys are utilized in the magnetic core. A proof-of-concept MR damper for mountain bike applications is designed, fabricated, characterized, and tested in the field, which meets the requirements in mountain bike industry in terms of energy consumption, compression and rebound forces, mass, size, and on-the-fly adjustability of the damping forces, by the user.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Mehrdad Moallem
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Thermal contact resistance between ceramic and metallic surfaces with applications in power electronics

Date created: 
2018-11-29
Abstract: 

In power electronic systems, aluminum oxide (alumina) is frequently used to electrically isolate high voltage devices mounted onto touch safe heat sinks for cooling. The thermal contact resistance (TCR) developed between the aluminum oxide and the metallic surfaces may significantly increase the thermal resistance between the heat generating device and the heat sink. In this thesis, the thermal contact resistance between ceramics and metals is explored analytically and experimentally. The TCR between polished ceramics and bead-blasted metals was first measured under uniform contact pressures (0.25 – 1.5 MPa) in both atmospheric and vacuum conditions. These results are compared with existing metallic surface TCR models to validate their use with metallic-ceramic surfaces. TCR measurements of as-fired, lapped and polished aluminum oxide in contact with machined, cast and anodized extruded aluminum surfaces with thermal interface materials (TIMs) are also presented.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Heat and electron conduction in microporous catalyst layers of polymer electrolyte membrane fuel cells

Author: 
Date created: 
2018-11-28
Abstract: 

Recent movement toward zero-emission mobility has propelled significant technological advancements in commercialization of polymer electrolyte membrane fuel cells (PEMFCs). PEMFCs provide electricity by reacting hydrogen with oxygen through two half-reactions occurring inside two respective anodic/cathodic microporous catalyst layers (CLs) with thicknesses of ~2-8 µm. Other products of the overall reaction include water and waste heat. All the electricity generation/consumption and most of the heat generation modes occur inside the CLs through a set of highly coupled multi-physics phenomena (a coupling between the electrochemical reactions, transport of species, electron conduction, and heat conduction). This necessitates knowing thermal and electronic conductivities of CLs for optimizing the fuel cell performance in various operating conditions. In this thesis, novel procedures are developed to measure thermal and electronic conductivities of CLs at low error rates. The procedures are based on novel methods to increase the amount of catalyst in the testbeds for enhancing the signal to noise ratio while ensuring complete deconvolution of the CL bulk signal. Further, a comprehensive platform is developed to characterize microstructure of CLs from different aspects, including a complete scheme for characterizing cracks for the first time. Separate measurements of in-plane and through-plane electronic conductivities, for the first time, uncovers anisotropic microstructure of CLs. CL designs with various compositions and structures are made and characterized. Observed trends in the conductivity data are linked to various structural properties of the CLs to understand structure-property correlations. A complete set of closed-form multi-scale structural models are developed for the conductivities in different directions to understand the underlying physics and provide tools for development of CLs with desired conductivities. The developed models agree well with the experimental data and precisely predict the structural trends. The models also explain and predict effects of different operating conditions. Using the developed tools, design guidelines are proposed for fabricating CLs with desired thermal and electronic conductivities, whose proof of concepts were made and successfully tested in the experimental phase of this research. Order of magnitude analyses show significant potentials for enhancing the fuel cell performance by tuning the conductivities through engineering the microstructure.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Gas diffusion in thin porous catalyst layers of PEM fuel cells

Author: 
Date created: 
2018-10-30
Abstract: 

Oxygen molecules reach the reaction sites in the cathode catalyst layer (CL) of PEM fuel cells through diffusion, and the water vapor produced at the cathode leaves the reaction sites through diffusion. Therefore, the gas diffusivity of CL influences fuel cell performance. Uniform oxygen delivery to the Pt particles is one of the primary parameters ensuring high activity level of Pt particles and prolonging the CL lifetime. A sufficient supply of oxygen to the CL is required to achieve high current densities. Therefore, to reach high power outputs with low Pt loading, it is vital to understand the mechanism and improve the oxygen diffusion rate within CL and investigate the effects of different operating conditions on its performance. To investigate the effect of different CL designs and operating conditions on gas diffusivity, a modified Loschmidt cell was used to measure the gas diffusivity of CL. Also, the pore size distribution of CL was measured with N2 adsorption porosimetry. Moreover, the structure of CL was modeled through considering a packed-sphere model for carbon particles within agglomerates, and a network of overlapped spherical agglomerates forming the CL. The gas diffusion problem was solved analytically for the CL structure considering both Knudsen and molecular mechanisms. The results show that decreasing the ionomer content of CL from an ionomer to carbon weight ratio of 1.5 to 0.5 increases the relative diffusivity by 400%. Dry milling the catalyst powders for 48 hours led to 50% drop in the relative diffusivities of CL. Drying the catalyst ink on the support substrate at elevated temperatures improved gas diffusivity in some cases. The CL effective diffusivity is higher in higher operating temperature; however, its relative gas diffusivity is lower. High compressive loads (30 MPa or 50 MPa) reduces the CL diffusivity; however, in range of fuel cell operating condition (<5 MPa) the effect is negligible. The effect of gas relative humidity on the relative diffusivity of CL is negligible. On the other hand, liquid water reduces CL relative diffusivity. For example, a 25 wt. % water content in CL results in a 25% drop in relative diffusivity.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Development of hardware and algorithms for a multi-functional capacitive proximity sensing system

Author: 
Date created: 
2018-11-05
Abstract: 

This thesis focuses on the development of a multi-functional capacitive proximity sensor to improve the worker safety during the industrial human-robot interactions. The sensor is to be mounted on the worker and used to maintain a safe distance between the worker and robot or the parts moved by the robot. The response of a capacitive proximity sensor is a function of the actual distance as well as the geometry of the approaching object. This uncertainty can lead to a wrong estimation of distance or possibly a missed detection. The proposed sensing system in this work aims to solve this issue. Three sensing capabilities, namely distance measurement, surface profile recognition, and parallel motion tracking are implemented in a single platform. These capabilities are achieved by a capacitive sensing element coupled to reprogrammable interface electronics. The sensing element features a 4×4 matrix of electrodes that can be reconfigured to different arrangements at run-time to obtain information on the desired parameters of interest (i.e., distance, shape, and trajectory). The control modules are mapped on a field programmable gate array while the capacitance generated by each configuration of electrodes is measured and quantized by a capacitance-to-digital chipset. Digital filters are used to pre-process the raw capacitive data in order to compensate for random walk and environmental interferences such as temperature and humidity variations. Statistical learning methodologies are applied to classify objects and calculate distance values. Quantitative regression models are built to seek out distance values while classification tools including K nearest neighbors, neural network, and support vector machine are employed to recognize the surface profiles. The performance of the sensing modalities is experimentally assessed with lab equipment as well as on an industrial robot. The system can detect objects and classify their geometries at distances up to about 20 cm with high accuracy. Three different surface profiles can be recognized by all the classifiers. Recognizing the shape of the object improved the regression models and reduced the close-distance measurement error by a factor of five compared to methods that did not take the geometry into account. The capability of tracking the parallel motion is demonstrated by combining the capacitive responses from different electrode connection configurations. The breakthroughs made through this work will make capacitive sensing a viable low-cost alternative to existing technologies for proximity detection in robotics and other fields.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Behraad Bahreyni
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.