Plasma spray for depositing thermal barrier coatings features large distributions of particle sta... more Plasma spray for depositing thermal barrier coatings features large distributions of particle states that result in significant variations in coating quality. These variations arise from distributions of particle sizes, large spatial gradients of plasma thermal-fluid fields, and temporal variations of the arc and jet. This paper describes a simplified approach for studying how particle state distributions are influenced by torch conditions and powder distributions, and the implications for deposition rate monitoring and control. The approach combines a simplified jet model with a more detailed particle model. The important fluid-thermal spatial gradients in the plasma jet are captured using a three zone model: a core region, modeled by growth of a turbulent shear layer around a laminar core, a transition region and a similarity region. Plasma-particle momentum and thermal interactions, particle phase transitions, internal particle temperature gradients, and collapse of in-flight hol...
Thermal Spray 2003: Proceedings from the International Thermal Spray Conference
This paper investigates the advantages that an advanced control system can provide for plasma spr... more This paper investigates the advantages that an advanced control system can provide for plasma spray deposition in terms of variation reduction and greater ability to engineer coating structure. We report our work on implementing a feedback control system that automatically adjusts system inputs to maintain the desired particle states in spite of process variations. The limitations and performance capabilities of both feed forward and real-time control are evaluated. Important system characteristics needed to develop such controllers are discussed including dominant nonlinearalities, dynamics, cross-coupling, distributions, and sensor issues. Performance is evaluated in terms of engineering coating structure and production objectives.
Thermal Spray 2005: Proceedings from the International Thermal Spray Conference
Real-time control offers the potential to reduce plasma spray variations that affect yield and co... more Real-time control offers the potential to reduce plasma spray variations that affect yield and coating quality. Important factors for designing such controllers are discussed including dominant nonlinearities, cross-coupling interactions, and sensor issues. The performance of several alternative strategies to achieve better coating thickness control are evaluated.
This paper analyzes the bending region of non-aqueous hydrophilic PVP/alcohol solutions, using a ... more This paper analyzes the bending region of non-aqueous hydrophilic PVP/alcohol solutions, using a combined experimental and modeling approach. A major focus of this work is modeling the complex mass transport including solvent evaporation and water absorption, which is verified by evaporation experiments. The developed model captures the coupled mass and force balances in the bending region and predicts the final fiber diameter to within 8% of experimental measurements for three different PVP/alcohol solutions with significantly different properties. The model analysis reveals the effect that RH has on alcohol evaporation rate, which affects both net stretching force and jet length in determining the final fiber diameter.
This paper investigates the need to develop an advanced control system for plasma spray depositio... more This paper investigates the need to develop an advanced control system for plasma spray deposition. The limitations and performance capability of both feed forward and real-time control are evaluated. Critical system characteristics for developing such controllers are experimentally identified including dominant nonlinearalities; dynamics, cross-coupling, distributions, and sensor issues.
In order to understand the microstructural evolution in plasma sprayed coatings, the solidificati... more In order to understand the microstructural evolution in plasma sprayed coatings, the solidification process was modeled using a 2-D FEM model based on enthalpy formation. Studies of the surface of the coatings showed surface roughnesses across multiple length scales. The model was used to examine the effects of the substrate and splat temperatures and the surface roughness features on the onset of remelting of the underlying surface on which the splat solidifies. The surface roughness was found to promote remelting, indicating that it was an important parameter that determines splat solidification. The temperatures of the splat and substrate were consolidated into one non-dimensional parameter that captured the onset of remelting with a non-dimensional remelting point.A fully coupled thermo-mechanical finite element model was also run for a single splat case, to provide more insight stress buildup during solidification. An important result was that the relative size of the surface r...
ABSTRACT Electrospinning is a method to produce submicron polymer fibers for a wide range of appl... more ABSTRACT Electrospinning is a method to produce submicron polymer fibers for a wide range of applications. In many applications, the average electrospun fiber size and uniformity are important for the product's performance and process economics. Thus, it is desirable for electrospinning to achieve consistent and controllable fiber diameters. However, the current state-of-the-art electrospinning process can result in variable fiber diameters, both run-to-run and during a run. This paper investigates how the operating regime as well as several important process factors affect fiber diameter using a vision-based system. For aqueous polyethylene oxide (PEO) solutions, it is found that the relative humidity has a strong effect on fiber diameter. Correlations between measurable parameters and fiber diameter are also developed to provide the ability to achieve the desired fiber diameters. The jet dynamics are experimentally identified through step response for development of appropriate control strategies.
Volume 13: Nano-Manufacturing Technology; and Micro and Nano Systems, Parts A and B, 2008
Electrospinning is a method of producing nanometer scale fibers by accelerating a jet of charged ... more Electrospinning is a method of producing nanometer scale fibers by accelerating a jet of charged polymer solution in an electric field. In many emerging, high value electrospinning applications, such as the biomedical area, the diameter distribution of electrospun polymeric nanofibers has important implications for the product’s performance and process economics (in terms of yield and production rate). However, the current state-of-the-art electrospinning process results in unpredictable and time varying diameter distributions, both during a run and run-to-run. Thus, this work is focused on developing an appropriate control system to achieve consistent and controllable fiber diameters. Another goal of this work is to develop a better understanding of the relation between process physics and the resulting fiber diameter characteristics. To address these problems, a well instrumented and computer based actuator control system has been developed. The effects of process parameters on fi...
Volume 10: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B, and C, 2008
Real-time control offers the potential to reduce plasma spray variations that affect yield and co... more Real-time control offers the potential to reduce plasma spray variations that affect yield and coating quality. Important factors for designing such controllers are discussed including sensor issues, dominant nonlinearities, and cross-coupling interactions. The performance of several alternative strategies to achieve better coating thickness control are evaluated.
Volume 10: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B, and C, 2008
Plasma spray for depositing thermal barrier coatings features large distributions of particle sta... more Plasma spray for depositing thermal barrier coatings features large distributions of particle states that result in significant variations in coating quality. These variations arise from distributions of particle sizes, large spatial gradients of plasma thermal-fluid fields, and temporal variations of the arc and jet. This paper describes a simplified approach for studying how particle state distributions are influenced by torch conditions and powder distributions, and the implications for deposition rate monitoring and control. The approach combines a simplified jet model with a more detailed particle model. The important fluid-thermal spatial gradients in the plasma jet are captured using a three zone model: a core region, modeled by growth of a turbulent shear layer around a laminar core, a transition region and a similarity region. Plasma-particle momentum and thermal interactions, particle phase transitions, internal particle temperature gradients, and collapse of in-flight hol...
Volume 1: Active Control of Aerospace Structure; Motion Control; Aerospace Control; Assistive Robotic Systems; Bio-Inspired Systems; Biomedical/Bioengineering Applications; Building Energy Systems; Condition Based Monitoring; Control Design for Drilling Automation; Control of Ground Vehicles, Man..., 2014
Electrospinning produces submicron fibers for a variety of applications using a wide range of pol... more Electrospinning produces submicron fibers for a variety of applications using a wide range of polymers. Achieving the desired fiber diameter, maximizing productivity, and minimizing variation are important production objectives. This paper addresses several important areas needed to develop a general electrospinning control approach including: developing a correlation between measurements, process conditions, and the resulting fiber diameter, developing a method to determine an operating regime that meets manufacturing objectives, and identifying process dynamics for controller design.
The plasma spray process is characterized by variations that occur over multiple time-scales and ... more The plasma spray process is characterized by variations that occur over multiple time-scales and events such as over the life-time of the electrodes, changing of electrode sets, arc instabilities, and torch power cycling. As a result, there can be large variations in coating thickness from part-to-part and even for a large single part. In order to reduce the effects of these sources of process variation, a number of alternative control strategies have been proposed. This paper discusses the requirements for implementing real-time control, and evaluates the performance of several alternative strategies in terms of maintaining desired coating thickness. This paper will also review the sensor requirements for implementing real-time control as well as the performance of several alterative sensing schemes in terms of how well they correlate to specific control objectives.
Plasma spray for depositing thermal barrier coatings features large distributions of particle sta... more Plasma spray for depositing thermal barrier coatings features large distributions of particle states that result in significant variations in coating quality. These variations arise from distributions of particle sizes, large spatial gradients of plasma thermal-fluid fields, and temporal variations of the arc and jet. This paper describes a simplified approach for studying how particle state distributions are influenced by torch conditions and powder distributions, and the implications for deposition rate monitoring and control. The approach combines a simplified jet model with a more detailed particle model. The important fluid-thermal spatial gradients in the plasma jet are captured using a three zone model: a core region, modeled by growth of a turbulent shear layer around a laminar core, a transition region and a similarity region. Plasma-particle momentum and thermal interactions, particle phase transitions, internal particle temperature gradients, and collapse of in-flight hol...
Thermal Spray 2003: Proceedings from the International Thermal Spray Conference
This paper investigates the advantages that an advanced control system can provide for plasma spr... more This paper investigates the advantages that an advanced control system can provide for plasma spray deposition in terms of variation reduction and greater ability to engineer coating structure. We report our work on implementing a feedback control system that automatically adjusts system inputs to maintain the desired particle states in spite of process variations. The limitations and performance capabilities of both feed forward and real-time control are evaluated. Important system characteristics needed to develop such controllers are discussed including dominant nonlinearalities, dynamics, cross-coupling, distributions, and sensor issues. Performance is evaluated in terms of engineering coating structure and production objectives.
Thermal Spray 2005: Proceedings from the International Thermal Spray Conference
Real-time control offers the potential to reduce plasma spray variations that affect yield and co... more Real-time control offers the potential to reduce plasma spray variations that affect yield and coating quality. Important factors for designing such controllers are discussed including dominant nonlinearities, cross-coupling interactions, and sensor issues. The performance of several alternative strategies to achieve better coating thickness control are evaluated.
This paper analyzes the bending region of non-aqueous hydrophilic PVP/alcohol solutions, using a ... more This paper analyzes the bending region of non-aqueous hydrophilic PVP/alcohol solutions, using a combined experimental and modeling approach. A major focus of this work is modeling the complex mass transport including solvent evaporation and water absorption, which is verified by evaporation experiments. The developed model captures the coupled mass and force balances in the bending region and predicts the final fiber diameter to within 8% of experimental measurements for three different PVP/alcohol solutions with significantly different properties. The model analysis reveals the effect that RH has on alcohol evaporation rate, which affects both net stretching force and jet length in determining the final fiber diameter.
This paper investigates the need to develop an advanced control system for plasma spray depositio... more This paper investigates the need to develop an advanced control system for plasma spray deposition. The limitations and performance capability of both feed forward and real-time control are evaluated. Critical system characteristics for developing such controllers are experimentally identified including dominant nonlinearalities; dynamics, cross-coupling, distributions, and sensor issues.
In order to understand the microstructural evolution in plasma sprayed coatings, the solidificati... more In order to understand the microstructural evolution in plasma sprayed coatings, the solidification process was modeled using a 2-D FEM model based on enthalpy formation. Studies of the surface of the coatings showed surface roughnesses across multiple length scales. The model was used to examine the effects of the substrate and splat temperatures and the surface roughness features on the onset of remelting of the underlying surface on which the splat solidifies. The surface roughness was found to promote remelting, indicating that it was an important parameter that determines splat solidification. The temperatures of the splat and substrate were consolidated into one non-dimensional parameter that captured the onset of remelting with a non-dimensional remelting point.A fully coupled thermo-mechanical finite element model was also run for a single splat case, to provide more insight stress buildup during solidification. An important result was that the relative size of the surface r...
ABSTRACT Electrospinning is a method to produce submicron polymer fibers for a wide range of appl... more ABSTRACT Electrospinning is a method to produce submicron polymer fibers for a wide range of applications. In many applications, the average electrospun fiber size and uniformity are important for the product's performance and process economics. Thus, it is desirable for electrospinning to achieve consistent and controllable fiber diameters. However, the current state-of-the-art electrospinning process can result in variable fiber diameters, both run-to-run and during a run. This paper investigates how the operating regime as well as several important process factors affect fiber diameter using a vision-based system. For aqueous polyethylene oxide (PEO) solutions, it is found that the relative humidity has a strong effect on fiber diameter. Correlations between measurable parameters and fiber diameter are also developed to provide the ability to achieve the desired fiber diameters. The jet dynamics are experimentally identified through step response for development of appropriate control strategies.
Volume 13: Nano-Manufacturing Technology; and Micro and Nano Systems, Parts A and B, 2008
Electrospinning is a method of producing nanometer scale fibers by accelerating a jet of charged ... more Electrospinning is a method of producing nanometer scale fibers by accelerating a jet of charged polymer solution in an electric field. In many emerging, high value electrospinning applications, such as the biomedical area, the diameter distribution of electrospun polymeric nanofibers has important implications for the product’s performance and process economics (in terms of yield and production rate). However, the current state-of-the-art electrospinning process results in unpredictable and time varying diameter distributions, both during a run and run-to-run. Thus, this work is focused on developing an appropriate control system to achieve consistent and controllable fiber diameters. Another goal of this work is to develop a better understanding of the relation between process physics and the resulting fiber diameter characteristics. To address these problems, a well instrumented and computer based actuator control system has been developed. The effects of process parameters on fi...
Volume 10: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B, and C, 2008
Real-time control offers the potential to reduce plasma spray variations that affect yield and co... more Real-time control offers the potential to reduce plasma spray variations that affect yield and coating quality. Important factors for designing such controllers are discussed including sensor issues, dominant nonlinearities, and cross-coupling interactions. The performance of several alternative strategies to achieve better coating thickness control are evaluated.
Volume 10: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B, and C, 2008
Plasma spray for depositing thermal barrier coatings features large distributions of particle sta... more Plasma spray for depositing thermal barrier coatings features large distributions of particle states that result in significant variations in coating quality. These variations arise from distributions of particle sizes, large spatial gradients of plasma thermal-fluid fields, and temporal variations of the arc and jet. This paper describes a simplified approach for studying how particle state distributions are influenced by torch conditions and powder distributions, and the implications for deposition rate monitoring and control. The approach combines a simplified jet model with a more detailed particle model. The important fluid-thermal spatial gradients in the plasma jet are captured using a three zone model: a core region, modeled by growth of a turbulent shear layer around a laminar core, a transition region and a similarity region. Plasma-particle momentum and thermal interactions, particle phase transitions, internal particle temperature gradients, and collapse of in-flight hol...
Volume 1: Active Control of Aerospace Structure; Motion Control; Aerospace Control; Assistive Robotic Systems; Bio-Inspired Systems; Biomedical/Bioengineering Applications; Building Energy Systems; Condition Based Monitoring; Control Design for Drilling Automation; Control of Ground Vehicles, Man..., 2014
Electrospinning produces submicron fibers for a variety of applications using a wide range of pol... more Electrospinning produces submicron fibers for a variety of applications using a wide range of polymers. Achieving the desired fiber diameter, maximizing productivity, and minimizing variation are important production objectives. This paper addresses several important areas needed to develop a general electrospinning control approach including: developing a correlation between measurements, process conditions, and the resulting fiber diameter, developing a method to determine an operating regime that meets manufacturing objectives, and identifying process dynamics for controller design.
The plasma spray process is characterized by variations that occur over multiple time-scales and ... more The plasma spray process is characterized by variations that occur over multiple time-scales and events such as over the life-time of the electrodes, changing of electrode sets, arc instabilities, and torch power cycling. As a result, there can be large variations in coating thickness from part-to-part and even for a large single part. In order to reduce the effects of these sources of process variation, a number of alternative control strategies have been proposed. This paper discusses the requirements for implementing real-time control, and evaluates the performance of several alternative strategies in terms of maintaining desired coating thickness. This paper will also review the sensor requirements for implementing real-time control as well as the performance of several alterative sensing schemes in terms of how well they correlate to specific control objectives.
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Papers by Michael Gevelber