Synergistic approaches to ultra-precision high performance cutting

Diamond milling allows for the flexible production of optical and high precision parts, but suffers from poor setup and production speeds. This paper presents recent advances that aim towards achieving high performance (HPC) and high speed cutting (HSC) in ultra-precision machining. After a short introduction, the benefits of high speed cutting for both metals and brittle-hard materials are shown. Thereafter, novel mechatronic devices are presented that enable an automated balancing of the applied air bearing spindles and the application of multiple diamond tools on one tool holder and by thus, contribute to HPC. These developments are supplemented by a novel linear guiding system based on electromagnatic levitation that, along with a dedicated model-based control system, enables fast and precise movements of the machine tool. After presenting the recent developments in detail, their synergistic performance is assessed and an outlook to future developments is given. © 2020 The Author

ULTRAPRECISION MACHINING OF HYBRID FREEFORM SURFACES USING MULTIPLE-AXIS DIAMOND TURNING

Ph.DDOCTOR OF PHILOSOPH

Control Methods for Improving Tracking Accuracy and Disturbance Rejection in Ball Screw Feed Drives

This thesis studies in detail the dynamics of ball screw feed drives and expands understanding of the factors that impose limitations on their performance. This knowledge is then used for developing control strategies that provide adequate command following and disturbance rejection. High performance control strategies proposed in this thesis are designed for, and implemented on, a custom-made ball screw drive. A hybrid Finite Element (FE) model for the ball screw drive is developed and coded in Matlab programming language. This FE model is employed for prediction of natural frequencies, mode shapes, and Frequency Response Functions (FRFs) of the ball screw setup. The accuracy of FRFs predicted for the ball screw mechanism alone is validated against the experimental measurements obtained through impact hammer testing. Next, the FE model for the entire test setup is validated. The dynamic characteristics of the actuator current controller are also modeled. In addition, the modal parameters of the mechanical structure are extracted from measured FRFs, which include the effects of current loop dynamics. To ensure adequate command following and disturbance rejection, three motion controllers with active vibration damping capability are developed. The first is based on the sensor averaging concept which facilitates position control of the rigid body dynamics. Active damping is added to suppress vibrations. To achieve satisfactory steady state response, integral action over the tracking error is included. The stability analysis and tuning procedure for this controller is presented together with experimental results that prove the effectiveness of this method in high-speed tracking and cutting applications. The second design uses the pole placement technique to move the real component of two of the oscillatory poles further to the left along the real axis. This yields a faster rigid body response with less vibration. However, the time delay from the current loop dynamics imposes a limitation on how much the poles can be shifted to the left without jeopardizing the system’s stability. To overcome this issue, a lead filter is designed to recover the system phase at the crossover frequency. When designing the Pole Placement Controller (PPC) and the lead filter concurrently, the objective is to minimize the load side disturbance response against the disturbances. This controller is also tested in high-speed tracking and cutting experiments. The third control method is developed around the idea of using the pole placement technique for active damping of not only the first mode of vibration, but also the second and third modes as well. A Kalman filter is designed to estimate a state vector for the system, from the control input and the position measurements obtained from the rotary and linear encoders. The state estimates are then fed back to the PPC controller. Although for this control design, promising results in terms of disturbance rejection are obtained in simulations, the Nyquist stability analysis shows that the closed loop system has poor stability margins. To improve the stability margins, the McFarlane-Glover robustness optimization method is attempted, and as a result, the stability margins are improved, but at the cost of degraded performance. The practical implementation of the third controller, was, unfortunately, not successful. This thesis concludes by addressing the problem of harmonic disturbance rejection in ball screw drives. It is shown that for cases where a ball screw drive is subject to high-frequency disturbances, the dynamic positioning accuracy of the ball screw drive can be improved significantly by adopting an additional control scheme known as Adaptive Feedforward Cancellation (AFC). Details of parameter tuning and stability analysis for AFC are presented. At the end, successful implementation and effectiveness of AFC is demonstrated in applications involving time periodic or space periodic disturbances. The conclusions drawn about the effectiveness of the AFC are based on results obtained from the high-speed tracking and end-milling experiments

Mehatronički pristup pozicioniranju ultravisokih preciznosti i točnosti

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.Mehatronički sustavi ultra-visokih (nanometarskih) preciznosti i točnosti pozicioniranja su u današnje vrijeme vrlo važni u preciznom inženjerstvu i tehnologiji mikro- i nano-sustava. U disertaciji se temeljito analiziraju nelinearni stohastički učinci trenja koji vrlo često ograničavaju radna svojstva sustava za precizno pozicioniranje temeljenih na kliznim i valjnim elementima. Analizira se stanje tehnike za pomake pri silama manjim od sile statičkog trenja, kao i u režimu klizanja, te se vrednuju postojeći matematički modeli trenja. U razmatranom slučaju mehatroničkog sustava ultra-visokih preciznosti i točnosti pozicioniranja, namijenjenog montaži i manipulaciji mikrostruktura, trenje koje se javlja kod linearnih jednoosnih pomaka se, zbog jednostavnosti i sveobuhvatnosti toga pristupa, modelira generaliziranim Maxwell-slip (GMS) modelom trenja. Parametri GMS modela se identificiraju na inovativnim eksperimentalnim postavima, i to posebno za pokretački dio analiziranog sustava, koji se sastoji od istosmjernog motora s reduktorom, te posebno za linearni translator. Rezultirajući modeli trenja se zatim integriraju u cjeloviti model sustava implementiran u MATLAB/SIMULINK okruženju. S ciljem minimizacije utjecaja trenja, modelirani odziv sustava uspoređuje se potom s eksperimentalnim rezultatima dobivenim na sustavu reguliranom pomoću često korištenog proporcionalno-integralno-diferencijalnog (PID) regulatora, kada se sustav regulira po načelu unaprijedne veze, te kada se regulira prilagodljivim upravljačkim algoritmom. Regulator s prilagodljivim vođenjem, implementiran unutar stvarno-vremenskog sustava temeljenog na programibilnim logičkim vratima, pokazao se kao najbolje rješenje te se stoga koristi u uzastopnim eksperimentima pozicioniranja iz točke u točku, koji predstavljaju željenu funkcionalnost razmatranog sustava. Postignute su tako nanometarska preciznost i točnost (bolje od 250 nm) i to kako kod kraćih (mikrometarskih), tako i duljih (milimetarskih) pomaka. U završnom se dijelu disertacije eksperimentalno analizira i mogućnost korištenja drugih pokretača, osjetnika i strojnih elemenata kao i različitih upravljačkih pristupa pogodnih za ostvarivanje ultra-visokih preciznosti i točnosti pozicioniranja

Mehatronički pristup pozicioniranju ultravisokih preciznosti i točnosti

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.Mehatronički sustavi ultra-visokih (nanometarskih) preciznosti i točnosti pozicioniranja su u današnje vrijeme vrlo važni u preciznom inženjerstvu i tehnologiji mikro- i nano-sustava. U disertaciji se temeljito analiziraju nelinearni stohastički učinci trenja koji vrlo često ograničavaju radna svojstva sustava za precizno pozicioniranje temeljenih na kliznim i valjnim elementima. Analizira se stanje tehnike za pomake pri silama manjim od sile statičkog trenja, kao i u režimu klizanja, te se vrednuju postojeći matematički modeli trenja. U razmatranom slučaju mehatroničkog sustava ultra-visokih preciznosti i točnosti pozicioniranja, namijenjenog montaži i manipulaciji mikrostruktura, trenje koje se javlja kod linearnih jednoosnih pomaka se, zbog jednostavnosti i sveobuhvatnosti toga pristupa, modelira generaliziranim Maxwell-slip (GMS) modelom trenja. Parametri GMS modela se identificiraju na inovativnim eksperimentalnim postavima, i to posebno za pokretački dio analiziranog sustava, koji se sastoji od istosmjernog motora s reduktorom, te posebno za linearni translator. Rezultirajući modeli trenja se zatim integriraju u cjeloviti model sustava implementiran u MATLAB/SIMULINK okruženju. S ciljem minimizacije utjecaja trenja, modelirani odziv sustava uspoređuje se potom s eksperimentalnim rezultatima dobivenim na sustavu reguliranom pomoću često korištenog proporcionalno-integralno-diferencijalnog (PID) regulatora, kada se sustav regulira po načelu unaprijedne veze, te kada se regulira prilagodljivim upravljačkim algoritmom. Regulator s prilagodljivim vođenjem, implementiran unutar stvarno-vremenskog sustava temeljenog na programibilnim logičkim vratima, pokazao se kao najbolje rješenje te se stoga koristi u uzastopnim eksperimentima pozicioniranja iz točke u točku, koji predstavljaju željenu funkcionalnost razmatranog sustava. Postignute su tako nanometarska preciznost i točnost (bolje od 250 nm) i to kako kod kraćih (mikrometarskih), tako i duljih (milimetarskih) pomaka. U završnom se dijelu disertacije eksperimentalno analizira i mogućnost korištenja drugih pokretača, osjetnika i strojnih elemenata kao i različitih upravljačkih pristupa pogodnih za ostvarivanje ultra-visokih preciznosti i točnosti pozicioniranja

Conceptual design and analysis of a large antenna utilizing electrostatic membrane management

Conceptual designs and associated technologies for deployment 100 m class radiometer antennas were developed. An electrostatically suspended and controlled membrane mirror and the supporting structure are discussed. The integrated spacecraft including STS cargo bay stowage and development were analyzed. An antenna performance evaluation was performed as a measure of the quality of the membrane/spacecraft when used as a radiometer in the 1 GHz to 5 GHz region. Several related LSS structural dynamic models differing by their stiffness property (and therefore, lowest modal frequencies) are reported. Control system whose complexity varies inversely with increasing modal frequency regimes are also reported. Interactive computer-aided-design software is discussed

Design, control, and application of piezoelectric actuator: External-sensing and self-sensing actuator

Ph.DDOCTOR OF PHILOSOPH

Cumulative Index to NASA Tech Briefs, 1963 - 1966

Cumulative index of NASA Tech Briefs dealing with electrical and electronic, physical science and energy sources, materials and chemistry, life science, and mechanical innovation

Characterization of Periodic Disturbances In Rolling Element Bearings

The objective of this research is to observe and characterize periodic fluctuations in friction force of ball-element bearings that occur during velocity tracking motion. It is proposed that this periodic fluctuation in friction force is caused by the motion of the balls. We hope to show this relation by demonstrating that the frequency of the periodic fluctuation is equal to the frequency of the balls passing a position in the race. To illustrate the relation between the fluctuating friction force and the motion of the balls, a testbed has been built to measure friction force, ball passage rate, and velocity error during velocity tracking motion. The velocity error will be calculated from the measurement of position, and may show how the periodic fluctuations in friction force act like a periodic disturbance to the velocity. This paper will discuss the design and fabrication of the testbed, and the resulting measured signals that will be processed to determine their periodic content and to show how they are correlated. However, before inspecting the test results, some qualitative analysis of the system and models of the measured signals will be discussed to give insight into what we may expect from the results of the velocity tracking tests. An optical sensor has been designed and built to detect the motion of the balls in the race. The optical sensor measures the light reflected off the surface of a ball as it passes the sensing fiber. It was necessary to make some adjustments to the initial design of the sensor to correct for an instability in the signal. These adjustments, and the cause of the instability, will be discussed in this paper. Some ball bearings display an odd sticking behavior, where the friction force greatly increases beyond the approximated static friction force. This sticking behavior will be discussed, and how it relates to the motion of the balls in the race will be illustrated. It will also be discussed how the spectral density of friction force can be used to evaluate the performance of a bearing

Cumulative index to NASA Tech Briefs, 1963-1967

Cumulative index to NASA survey on technology utilization of aerospace research outpu