Mohebullah Wali - Academia.edu (original) (raw)
Papers by Mohebullah Wali
Positioning stages are widely applied in the precision technology, such as manufacturing process ... more Positioning stages are widely applied in the precision technology, such as manufacturing process of semiconductor devices, scanning probe microscopy (SPM), and etc. Nowadays the manufacturing industries are trying to make the semiconductor conductor devices more compact, in order to reduce the cost. However, to meet these demands ultra-high precise stages with high speed and high resolution are required. These crucial demands inspired researchers to develop ultra-high precision stages. This is the main reason that the control of critical problems of positioning systems is interpreted by many researchers since last three decades. However, a few studies have concerned the effect of reaction force in linear motor driven positioning stages. While this problem along with positioning speed was still not concerned in a pneumatically actuated stages. Therefore, in our works, we focused on the positioning control of a pneumatic positioning stage. The concerned pneumatic stage is composed of the mechanical and pneumatic parts. The mechanical part consists of a single-axis moving stage which provides bidirectional motion towards x-axis, and placed between two parallel needle bearings guideways fixed on the top of a base plate. Whereas the base plate is suspended on four units of coil-type spring isolators which are used instead of anti-vibration isolation tables. The pneumatic part is composed of four double-acting single-rod pneumatic type cylinders, two servo valves, an air regulation and treatment system, and an air compressor. The cylinders are equipped such that two of them are used as the actuator in left side, while the other two are used as the right side actuators. Due to the suspension of stage on the coil-type spring isolator, the mechanical system is modeled as a two degree-of-freedom system, while the pneumatic system is approximated as a first order lag system. Three main issues of pneumatic stage are concerned in this study, i.e., the effect of reaction force, the flow disturbance, and the low positioning speed achieved by the pneumatic actuators. The reaction of the driving force results in the natural vibration of base plate which is conveyed to the stage due to the mutual interference. This problem becomes more critical when the base plate is lightweight as that used in our system. The flow disturbance is mainly caused by the variation of supplied air pressure when the air compressor periodically compresses and decompresses the air during its operation. The s-to z-domain ……………………………………………………………… 3.6.3 A General Description of Experimental Method ………………………….. 88 3.7 References ………………………………………………………………………
2011 8th Asian Control Conference (ASCC), 2011
In this paper, a pneumatic positioning stage is considered. The stage is moved by the driving for... more In this paper, a pneumatic positioning stage is considered. The stage is moved by the driving force and the reaction force leads the base plate to vibrate, resulting in the fluctuation of the stage in the opposite direction. In order to reduce the effect of the reaction force and improve the positioning time, the base plate jerk feedback is proposed. This feedback is firstly realized using an external force exerted to the base plate and then applied for the real condition of positioning. The experimental results show the effectiveness of the proposed method.
Due to several merits, the pneumatic actuation systems are commonly used to drive the positioning... more Due to several merits, the pneumatic actuation systems are commonly used to drive the positioning stages. However, one of the critical demerits of the pneumatic systems is the problem of the compressibility, which results in the flow disturbance. Another problem of the positioning stage can be addressed to the vibration which occurs due to the active condition of the base plate. Therefore, this paper concerns the mentioned two issues in a pneumatic positioning stage. In order to suppress the flow disturbance and reduce the horizontal vibration of the stage due to the reaction force, a combined control scheme is proposed. This scheme is composed of the fusion of flow disturbance observer (FDOB) and base plate jerk feedback (BPJFB) schemes. An enhanced methodology is provided to efficiently implement the combined scheme. The experimental results show the effectiveness of the proposed method.
Metals
Along with industrialization and rapid urbanization, environmental remediation is globally a perp... more Along with industrialization and rapid urbanization, environmental remediation is globally a perpetual concept to deliver a sustainable environment. Various organic and inorganic wastes from industries and domestic homes are released into water systems. These wastes carry contaminants with detrimental effects on the environment. Consequently, there is an urgent need for an appropriate wastewater treatment technology for the effective decontamination of our water systems. One promising approach is employing nanoparticles of metal oxides as photocatalysts for the degradation of these water pollutants. Transition metal oxides and their composites exhibit excellent photocatalytic activities and along show favorable characteristics like non-toxicity and stability that also make them useful in a wide range of applications. This study discusses some characteristics of metal oxides and briefly outlined their various applications. It focuses on the metal oxides TiO2, ZnO, WO3, CuO, and Cu2O,...
Journal of Sustainability Outreach
Currently, Afghanistan imports a high percentage of electric energy from the neighboring coun-tri... more Currently, Afghanistan imports a high percentage of electric energy from the neighboring coun-tries, while less attention has been paid on the utilization of internal domestic energy resources. Recently progress has been made with solar and wind energy, but other sources such as hydro energy remain underappreciated. Originally intended as a short-term solution to fulfill demand, the policy for importing power from neighboring countries is still in effect as energy demand has increased dramatically and exposed vulnerabilities in the existing power system. These issues can be categorized based on different aspects like technical, economic, political, security-related issues, natural disasters and many others that negatively affect the reliability of the energy sector. In this paper, the sustainability of the power system of Afghanistan is analyzed from different aspects. These multi-disciplinary problems are analyzed separately and linked with the weaknesses of the existing power syst...
Applied Sciences
Within the framework of this study, the inductive analysis of voltage stability indices’ theoreti... more Within the framework of this study, the inductive analysis of voltage stability indices’ theoretical formulation, functionality, and overall performances are introduced. The prominence is given to investigate and compare the original indices from three main dimensions (formulation, assessment, and application) standpoints, which have been frequently used and recently attracted. The generalizability of an exhaustive investigation on comparison of voltage stability indices seems problematic due to the multiplicity of the indices, and more importantly, their variety in theoretical foundation and performances. This study purports the first-ever framework for voltage stability indices classification for power system analysis. The test results found that indices in the same category are coherent to their theoretical foundation. The paper highlights the fact that each category of the indices is functional for a particular application irrespective of the drawback ranking, and negated the ap...
The 2012 International Conference on Advanced Mechatronic Systems, 2012
Sice Annual Conference 2011, Sep 1, 2011
Journal of Advanced Mechanical Design, Systems, and Manufacturing, 2012
In this study, a positioning stage is considered, which is actuated by four pneumatic cylinders a... more In this study, a positioning stage is considered, which is actuated by four pneumatic cylinders and vertically supported by four coil-type spring isolators. Previously, we realized the base plate jerk feedback (BPJFB) to be analogues to a Master-Slave system which can synchronize the motion of the stage as a Slave to the motion of the base plate as a Master. However, in the case of real positioning, the stage had slightly self oscillation with higher frequency due to the higher gains set to the outer feedback loop controller besides its oscillation due to the natural vibration of the base plate. The self oscillation of stage was misunderstood to be the natural vibration of base plate due to the reaction force. However, according to the experimental results, the BPJFB scheme was able to control both of the mentioned vibrations. Suppression of the self vibration of stage is an interesting phenomenon, which should be experimentally investigated. Therefore, the current study focuses on the suppression of the self vibration of stage by using the BPJFB scheme. The experimental results show that besides operating as a Master-Slave synchronizing system, the PBJFB scheme is able to increase the damping ratio and stiffness of stage against its self vibration. This newly recognized phenomenon contributes to further increase the proportional gain of the outer feedback loop controller. As a result, the positioning speed and stability can be improved.
IECON 2013 - 39th Annual Conference of the IEEE Industrial Electronics Society, 2013
Journal of Advanced Mechanical Design, Systems, and Manufacturing, 2013
In this paper, a unidirectional positioning stage which is supported by four coil-type spring iso... more In this paper, a unidirectional positioning stage which is supported by four coil-type spring isolators and actuated by four pneumatic cylinders is considered. The stage jerk feedback scheme (SJFB) with positive polarity is proposed to reduce the stage mass, resulting in the improvement of positioning speed. However, reduction of stage mass results in the overshoot that can be controlled by increasing the stage stiffness through the outer feedback loop controller. In addition, to avoid the selfoscillation of stage caused by high gain of SJFB and to improve the repeatability, the conventionally used scheme, namely, base plate jerk feedback (BPJFB) with positive polarity based on its damping role is combined with the SJFB scheme. It is concluded from the experimental results that the proposed control system obeys the related theory and provides high speed positioning with improved repeatability. The amount of the reduced mass through SJFB scheme is also experimentally estimated.
Journal of System Design and Dynamics, 2011
In this paper a pneumatic positioning stage which is mounted on the base plate and supported by t... more In this paper a pneumatic positioning stage which is mounted on the base plate and supported by the coil-type spring isolators is considered. The stage is moved by the driving force during positioning and the reaction force causes vibration of the base plate with its natural frequency, which degrades the performance of the positioning. To reduce the effect of the reaction force and improve the positioning time, the base plate jerk feedback is proposed. An external force is used to realize the principle of the base plate jerk feedback based on the theoretical background. The experimental results confirm that the working principle of the base plate jerk feedback obeys the theoretical concepts. The feedback is then employed for the real positioning. Based on the experimental results including repeatability, the effect of the reaction force was considerably reduced and the settling time of the response was improved, after employing the base plate jerk feedback with approximate optimal gain.
International Journal of Advanced Mechatronic Systems, 2013
Journal of System Design and Dynamics, 2012
Pneumatic actuation systems are commonly used to drive the positioning stage due to several merit... more Pneumatic actuation systems are commonly used to drive the positioning stage due to several merits. However, one of the critical demerits of the pneumatic systems is the problem of the compressibility, which results in the flow disturbance. Another problem of the positioning stage can be addressed to the vibration which occurs due to the active condition of the base plate. This paper concerns the mentioned two issues in a pneumatic positioning stage. In order to suppress the flow disturbance and to reduce the horizontal vibration of the stage due to the reaction force, a combined control scheme is proposed. This scheme is composed of the fusion of flow disturbance observer (FDOB) and base plate jerk feedback (BPJFB) scheme. An enhanced experimental methodology is provided to successfully implement the fusion of the mentioned feedback controllers. The results show the effectiveness of the proposed method.
Positioning stages are widely applied in the precision technology, such as manufacturing process ... more Positioning stages are widely applied in the precision technology, such as manufacturing process of semiconductor devices, scanning probe microscopy (SPM), and etc. Nowadays the manufacturing industries are trying to make the semiconductor conductor devices more compact, in order to reduce the cost. However, to meet these demands ultra-high precise stages with high speed and high resolution are required. These crucial demands inspired researchers to develop ultra-high precision stages. This is the main reason that the control of critical problems of positioning systems is interpreted by many researchers since last three decades. However, a few studies have concerned the effect of reaction force in linear motor driven positioning stages. While this problem along with positioning speed was still not concerned in a pneumatically actuated stages. Therefore, in our works, we focused on the positioning control of a pneumatic positioning stage. The concerned pneumatic stage is composed of the mechanical and pneumatic parts. The mechanical part consists of a single-axis moving stage which provides bidirectional motion towards x-axis, and placed between two parallel needle bearings guideways fixed on the top of a base plate. Whereas the base plate is suspended on four units of coil-type spring isolators which are used instead of anti-vibration isolation tables. The pneumatic part is composed of four double-acting single-rod pneumatic type cylinders, two servo valves, an air regulation and treatment system, and an air compressor. The cylinders are equipped such that two of them are used as the actuator in left side, while the other two are used as the right side actuators. Due to the suspension of stage on the coil-type spring isolator, the mechanical system is modeled as a two degree-of-freedom system, while the pneumatic system is approximated as a first order lag system. Three main issues of pneumatic stage are concerned in this study, i.e., the effect of reaction force, the flow disturbance, and the low positioning speed achieved by the pneumatic actuators. The reaction of the driving force results in the natural vibration of base plate which is conveyed to the stage due to the mutual interference. This problem becomes more critical when the base plate is lightweight as that used in our system. The flow disturbance is mainly caused by the variation of supplied air pressure when the air compressor periodically compresses and decompresses the air during its operation. The s-to z-domain ……………………………………………………………… 3.6.3 A General Description of Experimental Method ………………………….. 88 3.7 References ………………………………………………………………………
2011 8th Asian Control Conference (ASCC), 2011
In this paper, a pneumatic positioning stage is considered. The stage is moved by the driving for... more In this paper, a pneumatic positioning stage is considered. The stage is moved by the driving force and the reaction force leads the base plate to vibrate, resulting in the fluctuation of the stage in the opposite direction. In order to reduce the effect of the reaction force and improve the positioning time, the base plate jerk feedback is proposed. This feedback is firstly realized using an external force exerted to the base plate and then applied for the real condition of positioning. The experimental results show the effectiveness of the proposed method.
Due to several merits, the pneumatic actuation systems are commonly used to drive the positioning... more Due to several merits, the pneumatic actuation systems are commonly used to drive the positioning stages. However, one of the critical demerits of the pneumatic systems is the problem of the compressibility, which results in the flow disturbance. Another problem of the positioning stage can be addressed to the vibration which occurs due to the active condition of the base plate. Therefore, this paper concerns the mentioned two issues in a pneumatic positioning stage. In order to suppress the flow disturbance and reduce the horizontal vibration of the stage due to the reaction force, a combined control scheme is proposed. This scheme is composed of the fusion of flow disturbance observer (FDOB) and base plate jerk feedback (BPJFB) schemes. An enhanced methodology is provided to efficiently implement the combined scheme. The experimental results show the effectiveness of the proposed method.
Metals
Along with industrialization and rapid urbanization, environmental remediation is globally a perp... more Along with industrialization and rapid urbanization, environmental remediation is globally a perpetual concept to deliver a sustainable environment. Various organic and inorganic wastes from industries and domestic homes are released into water systems. These wastes carry contaminants with detrimental effects on the environment. Consequently, there is an urgent need for an appropriate wastewater treatment technology for the effective decontamination of our water systems. One promising approach is employing nanoparticles of metal oxides as photocatalysts for the degradation of these water pollutants. Transition metal oxides and their composites exhibit excellent photocatalytic activities and along show favorable characteristics like non-toxicity and stability that also make them useful in a wide range of applications. This study discusses some characteristics of metal oxides and briefly outlined their various applications. It focuses on the metal oxides TiO2, ZnO, WO3, CuO, and Cu2O,...
Journal of Sustainability Outreach
Currently, Afghanistan imports a high percentage of electric energy from the neighboring coun-tri... more Currently, Afghanistan imports a high percentage of electric energy from the neighboring coun-tries, while less attention has been paid on the utilization of internal domestic energy resources. Recently progress has been made with solar and wind energy, but other sources such as hydro energy remain underappreciated. Originally intended as a short-term solution to fulfill demand, the policy for importing power from neighboring countries is still in effect as energy demand has increased dramatically and exposed vulnerabilities in the existing power system. These issues can be categorized based on different aspects like technical, economic, political, security-related issues, natural disasters and many others that negatively affect the reliability of the energy sector. In this paper, the sustainability of the power system of Afghanistan is analyzed from different aspects. These multi-disciplinary problems are analyzed separately and linked with the weaknesses of the existing power syst...
Applied Sciences
Within the framework of this study, the inductive analysis of voltage stability indices’ theoreti... more Within the framework of this study, the inductive analysis of voltage stability indices’ theoretical formulation, functionality, and overall performances are introduced. The prominence is given to investigate and compare the original indices from three main dimensions (formulation, assessment, and application) standpoints, which have been frequently used and recently attracted. The generalizability of an exhaustive investigation on comparison of voltage stability indices seems problematic due to the multiplicity of the indices, and more importantly, their variety in theoretical foundation and performances. This study purports the first-ever framework for voltage stability indices classification for power system analysis. The test results found that indices in the same category are coherent to their theoretical foundation. The paper highlights the fact that each category of the indices is functional for a particular application irrespective of the drawback ranking, and negated the ap...
The 2012 International Conference on Advanced Mechatronic Systems, 2012
Sice Annual Conference 2011, Sep 1, 2011
Journal of Advanced Mechanical Design, Systems, and Manufacturing, 2012
In this study, a positioning stage is considered, which is actuated by four pneumatic cylinders a... more In this study, a positioning stage is considered, which is actuated by four pneumatic cylinders and vertically supported by four coil-type spring isolators. Previously, we realized the base plate jerk feedback (BPJFB) to be analogues to a Master-Slave system which can synchronize the motion of the stage as a Slave to the motion of the base plate as a Master. However, in the case of real positioning, the stage had slightly self oscillation with higher frequency due to the higher gains set to the outer feedback loop controller besides its oscillation due to the natural vibration of the base plate. The self oscillation of stage was misunderstood to be the natural vibration of base plate due to the reaction force. However, according to the experimental results, the BPJFB scheme was able to control both of the mentioned vibrations. Suppression of the self vibration of stage is an interesting phenomenon, which should be experimentally investigated. Therefore, the current study focuses on the suppression of the self vibration of stage by using the BPJFB scheme. The experimental results show that besides operating as a Master-Slave synchronizing system, the PBJFB scheme is able to increase the damping ratio and stiffness of stage against its self vibration. This newly recognized phenomenon contributes to further increase the proportional gain of the outer feedback loop controller. As a result, the positioning speed and stability can be improved.
IECON 2013 - 39th Annual Conference of the IEEE Industrial Electronics Society, 2013
Journal of Advanced Mechanical Design, Systems, and Manufacturing, 2013
In this paper, a unidirectional positioning stage which is supported by four coil-type spring iso... more In this paper, a unidirectional positioning stage which is supported by four coil-type spring isolators and actuated by four pneumatic cylinders is considered. The stage jerk feedback scheme (SJFB) with positive polarity is proposed to reduce the stage mass, resulting in the improvement of positioning speed. However, reduction of stage mass results in the overshoot that can be controlled by increasing the stage stiffness through the outer feedback loop controller. In addition, to avoid the selfoscillation of stage caused by high gain of SJFB and to improve the repeatability, the conventionally used scheme, namely, base plate jerk feedback (BPJFB) with positive polarity based on its damping role is combined with the SJFB scheme. It is concluded from the experimental results that the proposed control system obeys the related theory and provides high speed positioning with improved repeatability. The amount of the reduced mass through SJFB scheme is also experimentally estimated.
Journal of System Design and Dynamics, 2011
In this paper a pneumatic positioning stage which is mounted on the base plate and supported by t... more In this paper a pneumatic positioning stage which is mounted on the base plate and supported by the coil-type spring isolators is considered. The stage is moved by the driving force during positioning and the reaction force causes vibration of the base plate with its natural frequency, which degrades the performance of the positioning. To reduce the effect of the reaction force and improve the positioning time, the base plate jerk feedback is proposed. An external force is used to realize the principle of the base plate jerk feedback based on the theoretical background. The experimental results confirm that the working principle of the base plate jerk feedback obeys the theoretical concepts. The feedback is then employed for the real positioning. Based on the experimental results including repeatability, the effect of the reaction force was considerably reduced and the settling time of the response was improved, after employing the base plate jerk feedback with approximate optimal gain.
International Journal of Advanced Mechatronic Systems, 2013
Journal of System Design and Dynamics, 2012
Pneumatic actuation systems are commonly used to drive the positioning stage due to several merit... more Pneumatic actuation systems are commonly used to drive the positioning stage due to several merits. However, one of the critical demerits of the pneumatic systems is the problem of the compressibility, which results in the flow disturbance. Another problem of the positioning stage can be addressed to the vibration which occurs due to the active condition of the base plate. This paper concerns the mentioned two issues in a pneumatic positioning stage. In order to suppress the flow disturbance and to reduce the horizontal vibration of the stage due to the reaction force, a combined control scheme is proposed. This scheme is composed of the fusion of flow disturbance observer (FDOB) and base plate jerk feedback (BPJFB) scheme. An enhanced experimental methodology is provided to successfully implement the fusion of the mentioned feedback controllers. The results show the effectiveness of the proposed method.