Ultra-high precision mechatronics positioning systems are critical devices in current precision e... more Ultra-high precision mechatronics positioning systems are critical devices in current precision engineering and micro- and nano-systems’ technologies, as they allow repeatability and accuracy in the nanometric domain to be achieved. The doctoral thesis deals thoroughly with nonlinear stochastic frictional effects that limit the performances of ultra-high precision devices based on sliding and rolling elements. The state-of-the-art related to the frictional behavior in the pre-sliding and sliding motion regimes is considered and different friction models are validated. Due to its comprehensiveness and simplicity, the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances of a translational axis of an actual multi-degrees-of-freedom point-to-point mechatronics positioning system aimed at handling and positioning of microparts. The parameters of the GMS model are identified via innovative experimental set-ups, separately for the actuator-gearhead assembly and for the linear guideways, and included in the overall MATLAB/SIMULINK model of the used device. With the aim of compensating frictional effects, the modeled responses of the system are compared to experimental results when the system is controlled by means of a conventional proportional-integral-derivative (PID) controller, when the PID controller is complemented with an additional feed-forward model-based friction compensator and, finally, when the system is controlled via a self-tuning adaptive regulator. The adaptive regulator, implemented within the real-time field programmable gate array based control system, is proven to be the most efficient and is hence used in the final repetitive point-to-point positioning tests. Nanometric-range precision and accuracy (better than 250 nm), both in the case of short-range (micrometric) and long-range (millimeter) travels, are achieved. Different sensors, actuators and other design components, along with other control typologies, are experimentally validated in ultra-high precision positioning applications as well.
Presliding and sliding frictional effects, limiting the performances of ultrahigh precision mecha... more Presliding and sliding frictional effects, limiting the performances of ultrahigh precision mechatronics devices, are studied in this work. The state-of-the-art related to frictional behavior in both motion regimes is, hence, considered, and the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances present in a micromanipulation device. All the parameters of the model are identified via experimental set-ups and included in the overall MATLAB/SIMULINK model. With the aim of compensating frictional effects, the modelled response of the system is thus compared to experimental results when using proportional-integral-derivative (PID) control, feed-forward model-based compensation and a self-tuning adaptive regulator. The adaptive regulator proves to be the most efficient and is, hence, used in the final repetitive point-to-point positioning tests allowing to achieve nanometric precision and accuracy.
A need for enabling autonomous powering of wireless sensor network nodes is evident today. Sensor... more A need for enabling autonomous powering of wireless sensor network nodes is evident today. Sensor nodes may be placed in locations hard to access and powered via batteries of limited lifetime. Different energy harvesting principles allow to overcome these limitations. Energy harvesting concepts designed for sensor nodes to be placed in watercourses, are explored in this work: a miniaturized underwater turbine, a ‘piezoelectric eel’ and a hybrid turbine solution coupled with a rigid piezoelectric beam. The foreseen autonomous sensor nodes are to be placed 0.5 m from the bottom of the river and used for measuring pollutants’ concentration in the river flow. The miniaturized underwater hydro-generator, designed in a 3D modelling software, is based on a DC generator enclosed in a watertight enclosure. The electronics used to adapt the voltage levels to the employed sensors is designed and manufactured. Laboratory and river experiments are conducted showing that the achieved power levels are compatible with the foreseen application. The piezoelectric eel is a composite flag-like compliant device made of two layers of piezoelectric polymer PVDF, a substrate layer and electrodes placed on PVDF’s surface layer. A bluff body induces Karman vortexes coercing the eel to move in a flapped motion. A custom software, where fluid flow is modelled using Navier-Stokes equations, while the eel is modelled as a massless beam interacting with the fluid, and a second massive beam, which is connected to the first one via stiff springs, is developed in C++. The eel is prototyped and its performances are experimentally assessed. The third proposed harvesting configuration is a solution based on ‘plucking’ a rigid piezoelectric cantilever by means of fulcrums protruding from propeller’s shaft and then allowing it to vibrate freely thus generating electrical charge. The concept is modelled via a finite element model in a transient analysis routine.
Objective: To determine the unique contribution of geometrical design cha-rac teristics of orthod... more Objective: To determine the unique contribution of geometrical design cha-rac teristics of orthodontic mini-implants on maximum insertion torque while controlling for the influence of cortical bone thickness. Methods: Total num ber of 100 cylindrical orthodontic mini-implants was used. Geo metrical design characteristics of ten specimens of ten types of cylindrical self-drilling orthodontic mini-implants (Ortho Easy®, Aarhus, and Dual Top TM) with diameters ranging from 1.4 to 2.0 mm and lengths of 6 and 8 mm were measured. Maximum insertion torque was recorded during manual insertion of mini-implants into bone samples. Cortical bone thickness was measured. Retrieved data were analyzed in a multiple regression model. Results: Significant predictors for higher maximum insertion torque included larger outer diameter of implant, higher lead angle of thread, and thicker cortical bone, and their unique contribution to maximum insertion torque was 12.3%, 10.7%, and 24.7%, respectively. Conclusions: The maximum insertion torque values are best controlled by choosing an implant diameter and lead angle according to the assessed thickness of cortical bone. [Korean J Orthod 2014;44(4):177-183]
Friction is one of the main disturbances in precision positioning and, in the pre-sliding motion ... more Friction is one of the main disturbances in precision positioning and, in the pre-sliding motion regime, it is characterised by an elasto-plastic nonlinear hysteretic behaviour with a marked variability. Pre-sliding friction, modelled via the state-of-the-art Generalised Maxwell Slip (GMS) and the Hsieh model (HM), is experimentally assessed in this work with the aim of developing suitable control typologies aimed at compensating its effects. The models are hence compared in terms of the complexity of identifying their parameters, simulating their dynamic responses and implementing them in real-time systems. It is thus shown that the GMS model is readily identified and comprises also the sliding motion regime, whereas HM is difficult to implement and requires a separate sliding friction model with a corresponding switching function.
Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain... more Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain. Measurements are performed on nickel-titanium archwires without and with different coatings as well as subjected for four weeks to an artificial saliva solution with different pH values (4.8 and 6.6). Since surface properties can have a meaningful influence on friction, corrosion or plaque accumulation, surface texture of the wires is measured by employing atomic force microscopy. On the other hand, with the aim of determining Young's modulus and the hardness, nanoindentation tests are performed for different peak load values. It is hence established that there is no statistically relevant deterioration of the surfaces after their exposure to saliva. Rh coating leads, in turn, to an increase of surface roughness. Young's moduli and hardness values tend to increase with increasing indentation depths, while they are not meaningfully affected by the coating or the corrosion in saliva.
Networks of underwater sensors are used in watercourses for measuring and wirelessly transmitting... more Networks of underwater sensors are used in watercourses for measuring and wirelessly transmitting, among others, pollution levels. To ensure constant work, each sensor node requires a power source. In this frame, energy harvesting devices based on miniaturized hydro-generators appear a viable autonomous powering option whose concept is described in this work. The harvester is based on a DC generator and a 3D printed propeller driven by the river flow. A suitable energy management electronics is also developed. Measurements on the innovative hydro-generator are carried on in real-life river conditions, as well as in a flow tunnel. The measured generated power levels correspond to values needed to constantly power a sensor node. Wireless autonomous sensor networks, pollution sensor nodes, energy harvesting, miniaturized hydro-generator
Continuous monitoring of pollutants in watercourses requires an uninterrupted sensors' power supp... more Continuous monitoring of pollutants in watercourses requires an uninterrupted sensors' power supply. In the case of large networks, when sensor nodes can be placed in hardly accessible locations, energy harvesting can provide a feasible solution to assure power autonomy. The possibility to use a harvesting concept known as the piezoelectric eel is studied in this work. A custom code that implements the penalty immersed boundary method is developed and used to simulate eel's motion. Based on the results of the calculations, eel's design, consisting of a structural support covered with active piezoelectric polymer layers, is finalised. The respective power conditioning electronics is also been designed and prototyped. The obtained experimental results are finally given.
The nonlinear model of a small-scale ultra-high precision positioning device is developed in this... more The nonlinear model of a small-scale ultra-high precision positioning device is developed in this work in the MATLAB/SIMULINK environment. The conventional Stribeck model is used to describe the DC motor frictional nonlinearities, while the more sophisticated Dahl model is used for the behaviour of the mechanical components of the system. In the experimental setup , a linear incremental encoder is used as a feedback sensor, while a laser interferometric system is employed to validate the obtained precision. The digital PID controller is implemented on the FPGA architecture by using the LabVIEW programming environment. A good matching of simulated and measured dynamic responses is obtained although some friction-induced discrepancies are still present. Ultra-high precision positioning, frictional nonlinear disturbances, experimental validation, FPGA architecture
– A comparison between different DC motor positioning control algorithms is performed in this wor... more – A comparison between different DC motor positioning control algorithms is performed in this work. Transient responses while employing a PID controller, a cascade controller and a state-space controller are considered. LabVIEW programming environment with a suitable acquisition card and a miniature DC motor with an integrated encoder are used for experimental assessment. Calculations and control system simulations are made using Matlab. The PID controller is implemented via the predefined PID block in LabVIEW. In turn, the state-space controller is modelled by using Matlab while the accuracy of the results is confirmed experimentally using LabVIEW. The cascade controller is developed as a series of two Proportional-Integral (PI) controllers, one representing the positioning and the other the velocity loop. The obtained results allow establishing that positioning control via the state-space controller has the fastest response and the lowest settling times.
Measuring of pollutants in rivers is often required. Underwater sensor networks are commonly used... more Measuring of pollutants in rivers is often required. Underwater sensor networks are commonly used for this purpose. The sensors and the respective electronics must have enough power for undisturbed constant work. The possibility of using three energy harvesting principles for powering the sensors is described in this work. The focus is on piezoelectric eels. Alternatively, miniature underwater turbines and a hybrid solution based on " plucking " of piezoelectric beams, are also considered.
High resolutions and positioning accuracies are often required in precision engineering and micro... more High resolutions and positioning accuracies are often required in precision engineering and microsystems' technologies. An experimental ultra-precision mechatronics system with long travel ranges is conceived in this work. The mechanical design of the system is optimized in order to achieve ultra-precision displacements. The control system of the device is integrated into a high-speed FPGA-based module as a virtual instrument (VI), where closed loop feedback is obtained by employing microstepping control. User controls are programmed as an independent Host VI. A linear incremental encoder with a sinusoidal output signal, which is interpolated and converted into a TTL signal, is employed for position feedback. Experimental validation of the achieved results is conducted by using laser interferometry. A set of short and long step point-to-point positioning experiments are performed and true sub-micron positioning repeatability and accuracy are obtained.
– In this paper a micropositioning mechatronics system is conceived and described. Its mechanical... more – In this paper a micropositioning mechatronics system is conceived and described. Its mechanical design is optimized in order to achieve high precision displacements. High speed closed-loop feedback control is obtained by using both PID and ramp control algorithms programmed as virtual instruments (VI) on an FPGA (Field Programmable Gate Array) module. User controls are programmed in an independent Host VI. A Linear Variable Differential Transformer (LVDT) is employed as a position feedback sensor, while positioning accuracy and repeatability are experimentally assessed by using a Michelson-type laser Doppler interferometric system. Different experiments with point-to-point positioning are conducted. In the first set of experiments, positioning with 100 µm steps is performed. In a second step, 10 mm positioning experiments are done. The system shows a marked nonlinearity when longer positioning steps are used; this nonlinearity influences significantly the output error. It is hence found that the main contribution to system's nonlinearity is caused by the LVDT. The error is compensated via system linearization by an experimentally obtained analytical function which is programmed in the LabVIEW Host VI. Positioning accuracy and repeatability are finally assessed experimentally again and true micrometric positioning is achieved.
Ultra-high precision mechatronics positioning systems are critical devices in current precision e... more Ultra-high precision mechatronics positioning systems are critical devices in current precision engineering and micro- and nano-systems’ technologies, as they allow repeatability and accuracy in the nanometric domain to be achieved. The doctoral thesis deals thoroughly with nonlinear stochastic frictional effects that limit the performances of ultra-high precision devices based on sliding and rolling elements. The state-of-the-art related to the frictional behavior in the pre-sliding and sliding motion regimes is considered and different friction models are validated. Due to its comprehensiveness and simplicity, the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances of a translational axis of an actual multi-degrees-of-freedom point-to-point mechatronics positioning system aimed at handling and positioning of microparts. The parameters of the GMS model are identified via innovative experimental set-ups, separately for the actuator-gearhead assembly and for the linear guideways, and included in the overall MATLAB/SIMULINK model of the used device. With the aim of compensating frictional effects, the modeled responses of the system are compared to experimental results when the system is controlled by means of a conventional proportional-integral-derivative (PID) controller, when the PID controller is complemented with an additional feed-forward model-based friction compensator and, finally, when the system is controlled via a self-tuning adaptive regulator. The adaptive regulator, implemented within the real-time field programmable gate array based control system, is proven to be the most efficient and is hence used in the final repetitive point-to-point positioning tests. Nanometric-range precision and accuracy (better than 250 nm), both in the case of short-range (micrometric) and long-range (millimeter) travels, are achieved. Different sensors, actuators and other design components, along with other control typologies, are experimentally validated in ultra-high precision positioning applications as well.
Presliding and sliding frictional effects, limiting the performances of ultrahigh precision mecha... more Presliding and sliding frictional effects, limiting the performances of ultrahigh precision mechatronics devices, are studied in this work. The state-of-the-art related to frictional behavior in both motion regimes is, hence, considered, and the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances present in a micromanipulation device. All the parameters of the model are identified via experimental set-ups and included in the overall MATLAB/SIMULINK model. With the aim of compensating frictional effects, the modelled response of the system is thus compared to experimental results when using proportional-integral-derivative (PID) control, feed-forward model-based compensation and a self-tuning adaptive regulator. The adaptive regulator proves to be the most efficient and is, hence, used in the final repetitive point-to-point positioning tests allowing to achieve nanometric precision and accuracy.
A need for enabling autonomous powering of wireless sensor network nodes is evident today. Sensor... more A need for enabling autonomous powering of wireless sensor network nodes is evident today. Sensor nodes may be placed in locations hard to access and powered via batteries of limited lifetime. Different energy harvesting principles allow to overcome these limitations. Energy harvesting concepts designed for sensor nodes to be placed in watercourses, are explored in this work: a miniaturized underwater turbine, a ‘piezoelectric eel’ and a hybrid turbine solution coupled with a rigid piezoelectric beam. The foreseen autonomous sensor nodes are to be placed 0.5 m from the bottom of the river and used for measuring pollutants’ concentration in the river flow. The miniaturized underwater hydro-generator, designed in a 3D modelling software, is based on a DC generator enclosed in a watertight enclosure. The electronics used to adapt the voltage levels to the employed sensors is designed and manufactured. Laboratory and river experiments are conducted showing that the achieved power levels are compatible with the foreseen application. The piezoelectric eel is a composite flag-like compliant device made of two layers of piezoelectric polymer PVDF, a substrate layer and electrodes placed on PVDF’s surface layer. A bluff body induces Karman vortexes coercing the eel to move in a flapped motion. A custom software, where fluid flow is modelled using Navier-Stokes equations, while the eel is modelled as a massless beam interacting with the fluid, and a second massive beam, which is connected to the first one via stiff springs, is developed in C++. The eel is prototyped and its performances are experimentally assessed. The third proposed harvesting configuration is a solution based on ‘plucking’ a rigid piezoelectric cantilever by means of fulcrums protruding from propeller’s shaft and then allowing it to vibrate freely thus generating electrical charge. The concept is modelled via a finite element model in a transient analysis routine.
Objective: To determine the unique contribution of geometrical design cha-rac teristics of orthod... more Objective: To determine the unique contribution of geometrical design cha-rac teristics of orthodontic mini-implants on maximum insertion torque while controlling for the influence of cortical bone thickness. Methods: Total num ber of 100 cylindrical orthodontic mini-implants was used. Geo metrical design characteristics of ten specimens of ten types of cylindrical self-drilling orthodontic mini-implants (Ortho Easy®, Aarhus, and Dual Top TM) with diameters ranging from 1.4 to 2.0 mm and lengths of 6 and 8 mm were measured. Maximum insertion torque was recorded during manual insertion of mini-implants into bone samples. Cortical bone thickness was measured. Retrieved data were analyzed in a multiple regression model. Results: Significant predictors for higher maximum insertion torque included larger outer diameter of implant, higher lead angle of thread, and thicker cortical bone, and their unique contribution to maximum insertion torque was 12.3%, 10.7%, and 24.7%, respectively. Conclusions: The maximum insertion torque values are best controlled by choosing an implant diameter and lead angle according to the assessed thickness of cortical bone. [Korean J Orthod 2014;44(4):177-183]
Friction is one of the main disturbances in precision positioning and, in the pre-sliding motion ... more Friction is one of the main disturbances in precision positioning and, in the pre-sliding motion regime, it is characterised by an elasto-plastic nonlinear hysteretic behaviour with a marked variability. Pre-sliding friction, modelled via the state-of-the-art Generalised Maxwell Slip (GMS) and the Hsieh model (HM), is experimentally assessed in this work with the aim of developing suitable control typologies aimed at compensating its effects. The models are hence compared in terms of the complexity of identifying their parameters, simulating their dynamic responses and implementing them in real-time systems. It is thus shown that the GMS model is readily identified and comprises also the sliding motion regime, whereas HM is difficult to implement and requires a separate sliding friction model with a corresponding switching function.
Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain... more Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain. Measurements are performed on nickel-titanium archwires without and with different coatings as well as subjected for four weeks to an artificial saliva solution with different pH values (4.8 and 6.6). Since surface properties can have a meaningful influence on friction, corrosion or plaque accumulation, surface texture of the wires is measured by employing atomic force microscopy. On the other hand, with the aim of determining Young's modulus and the hardness, nanoindentation tests are performed for different peak load values. It is hence established that there is no statistically relevant deterioration of the surfaces after their exposure to saliva. Rh coating leads, in turn, to an increase of surface roughness. Young's moduli and hardness values tend to increase with increasing indentation depths, while they are not meaningfully affected by the coating or the corrosion in saliva.
Networks of underwater sensors are used in watercourses for measuring and wirelessly transmitting... more Networks of underwater sensors are used in watercourses for measuring and wirelessly transmitting, among others, pollution levels. To ensure constant work, each sensor node requires a power source. In this frame, energy harvesting devices based on miniaturized hydro-generators appear a viable autonomous powering option whose concept is described in this work. The harvester is based on a DC generator and a 3D printed propeller driven by the river flow. A suitable energy management electronics is also developed. Measurements on the innovative hydro-generator are carried on in real-life river conditions, as well as in a flow tunnel. The measured generated power levels correspond to values needed to constantly power a sensor node. Wireless autonomous sensor networks, pollution sensor nodes, energy harvesting, miniaturized hydro-generator
Continuous monitoring of pollutants in watercourses requires an uninterrupted sensors' power supp... more Continuous monitoring of pollutants in watercourses requires an uninterrupted sensors' power supply. In the case of large networks, when sensor nodes can be placed in hardly accessible locations, energy harvesting can provide a feasible solution to assure power autonomy. The possibility to use a harvesting concept known as the piezoelectric eel is studied in this work. A custom code that implements the penalty immersed boundary method is developed and used to simulate eel's motion. Based on the results of the calculations, eel's design, consisting of a structural support covered with active piezoelectric polymer layers, is finalised. The respective power conditioning electronics is also been designed and prototyped. The obtained experimental results are finally given.
The nonlinear model of a small-scale ultra-high precision positioning device is developed in this... more The nonlinear model of a small-scale ultra-high precision positioning device is developed in this work in the MATLAB/SIMULINK environment. The conventional Stribeck model is used to describe the DC motor frictional nonlinearities, while the more sophisticated Dahl model is used for the behaviour of the mechanical components of the system. In the experimental setup , a linear incremental encoder is used as a feedback sensor, while a laser interferometric system is employed to validate the obtained precision. The digital PID controller is implemented on the FPGA architecture by using the LabVIEW programming environment. A good matching of simulated and measured dynamic responses is obtained although some friction-induced discrepancies are still present. Ultra-high precision positioning, frictional nonlinear disturbances, experimental validation, FPGA architecture
– A comparison between different DC motor positioning control algorithms is performed in this wor... more – A comparison between different DC motor positioning control algorithms is performed in this work. Transient responses while employing a PID controller, a cascade controller and a state-space controller are considered. LabVIEW programming environment with a suitable acquisition card and a miniature DC motor with an integrated encoder are used for experimental assessment. Calculations and control system simulations are made using Matlab. The PID controller is implemented via the predefined PID block in LabVIEW. In turn, the state-space controller is modelled by using Matlab while the accuracy of the results is confirmed experimentally using LabVIEW. The cascade controller is developed as a series of two Proportional-Integral (PI) controllers, one representing the positioning and the other the velocity loop. The obtained results allow establishing that positioning control via the state-space controller has the fastest response and the lowest settling times.
Measuring of pollutants in rivers is often required. Underwater sensor networks are commonly used... more Measuring of pollutants in rivers is often required. Underwater sensor networks are commonly used for this purpose. The sensors and the respective electronics must have enough power for undisturbed constant work. The possibility of using three energy harvesting principles for powering the sensors is described in this work. The focus is on piezoelectric eels. Alternatively, miniature underwater turbines and a hybrid solution based on " plucking " of piezoelectric beams, are also considered.
High resolutions and positioning accuracies are often required in precision engineering and micro... more High resolutions and positioning accuracies are often required in precision engineering and microsystems' technologies. An experimental ultra-precision mechatronics system with long travel ranges is conceived in this work. The mechanical design of the system is optimized in order to achieve ultra-precision displacements. The control system of the device is integrated into a high-speed FPGA-based module as a virtual instrument (VI), where closed loop feedback is obtained by employing microstepping control. User controls are programmed as an independent Host VI. A linear incremental encoder with a sinusoidal output signal, which is interpolated and converted into a TTL signal, is employed for position feedback. Experimental validation of the achieved results is conducted by using laser interferometry. A set of short and long step point-to-point positioning experiments are performed and true sub-micron positioning repeatability and accuracy are obtained.
– In this paper a micropositioning mechatronics system is conceived and described. Its mechanical... more – In this paper a micropositioning mechatronics system is conceived and described. Its mechanical design is optimized in order to achieve high precision displacements. High speed closed-loop feedback control is obtained by using both PID and ramp control algorithms programmed as virtual instruments (VI) on an FPGA (Field Programmable Gate Array) module. User controls are programmed in an independent Host VI. A Linear Variable Differential Transformer (LVDT) is employed as a position feedback sensor, while positioning accuracy and repeatability are experimentally assessed by using a Michelson-type laser Doppler interferometric system. Different experiments with point-to-point positioning are conducted. In the first set of experiments, positioning with 100 µm steps is performed. In a second step, 10 mm positioning experiments are done. The system shows a marked nonlinearity when longer positioning steps are used; this nonlinearity influences significantly the output error. It is hence found that the main contribution to system's nonlinearity is caused by the LVDT. The error is compensated via system linearization by an experimentally obtained analytical function which is programmed in the LabVIEW Host VI. Positioning accuracy and repeatability are finally assessed experimentally again and true micrometric positioning is achieved.
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