830 research outputs found
Gaussian Process Repetitive Control With Application to an Industrial Substrate Carrier System With Spatial Disturbances
No full textRepetitive control (RC) can perfectly attenuate disturbances that are periodic in the time domain. The aim of this article is to develop an RC approach that compensates for disturbances that are time-domain nonperiodic but are repeating in the position domain. The developed position-domain buffer consists of a Gaussian process (GP), which is learned using appropriate dynamic filters and nonequidistant data. This approach estimates position-domain disturbances resulting in perfect compensation. The method is successfully applied to a substrate carrier system, demonstrating performance robustness against time-domain nonperiodic disturbances that are amplified by traditional RC. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Jan-Willem van Wingerde
Feedback control and injection locking of the sawtooth oscillation in fusion plasmas
No full textIn this thesis various different control strategies have been developed to control the period of the sawtooth oscillation inside a tokamak. This sawtooth instability arises at the q = 1 surface in nuclear fusion plasmas and manifests itself as a repetitive slow rise and sudden crash of the plasma core temperature and pressure. The mixing effect of the sawtooth crash can regulate the exhaust of helium ash from and the fuelling of deuterium and tritium to the plasma core. At the same time, the crash can trigger other instabilities, such as neoclassical tearing modes, which is generally undesirable. These processes are affected by the periodicity of the sawtooth oscillation, hence, control over the sawtooth period is essential to enable optimization of the plasma performance. Based on the dominant dynamics of the underlying magnetics of the sawtooth, a control-relevant sawtooth model has been developed and numerically implemented. This model is actuated via an electron cyclotron current drive (ECCD) term, characterized by two inputs: the amount of driven current and its deposition location. The output of the model is the sawtooth period. This sawtooth model mimics the static input–output behaviour observed on tokamaks, and has therefore been used as a casestudy for the controller designs. Two different control strategies have been investigated: feedback control (closed loop) and injection locking (open loop). Feedback control In the closed loop approach, first the sawtooth period dynamics has been determined. Via dedicated step response simulations and the application of approximate realization techniques, the dynamic behaviour around various operating points has been identified and represented in the frequency domain. Next, three different feedback control approaches have been based upon these identified systems: Low complexity - First, a standard linear controller has been designed, considering only the deposition location as a control variable. The parameters of the chosen controller structure (PII) have been optimized based on frequency domain specifications. The resulting closed loop is relatively robust, but its performance can sometimes be unsatisfactory whenever the ECCD mirror launcher, i.e. the actuator for the deposition location, is slow compared to the sawtooth period. High performance - In a second approach the closed-loop performance has been improved by the employment of gain-scheduling, feedforward and anti-windup techniques. Alternatively, the amount of driven current has been used as a control variable, which yields a closed-loop performance improvement as well. Moreover, a multivariable controller design has been proposed to combine fast settling times of the sawtooth period with power efficiency. These high-performance control designs are particularly interesting for future fusion reactors. High robustness - On experimental devices plasma uncertainties and disturbances are relatively large. For such applications a very robust feedback controller has been designed, based on extremum seeking. This adaptive controller makes online estimations of the sawtooth input–output behaviour via an external perturbation, based upon which the deposition location is adjusted to steer towards a desired sawtooth period. Various simulations have demonstrated the large robustness of the approach. Injection locking In addition, open-loop injection locking has been presented as an alternative sawtooth period control strategy. In this strategy, the deposition location is kept constant while the driven current (or gyrotron power) is modulated with a certain period and duty cycle. Extensive simulations have revealed that the sawtooth period can lock to the modulation period. All combinations of modulation period and duty cycle for which locking occurs define the locking range, which is particularly large for depositions close to the q = 1 surface. Similar sawtooth periods as with continuous wave ECCD can be achieved, while consuming time-averaged less power. Sawtooth period locking can be both fast and robust; simulations have demonstrated convergence speeds within only a handful of crashes, while locking is maintained even in the presence of plasma variations or disturbances. These predictions have been validated by experimental results; injection locking of the sawtooth period has been demonstrated on TCV plasmas. The experimentally obtained time responses and locking range show strong resemblances with the predictive simulations. Based on the identified locking range, an open-loop controller has been designed and implemented. Successful application to a TCV discharge has demonstrated that this controller can force a desired sawtooth period unto the plasma, even if this setpoint is slowly changing over time. The results in this thesis form a basis for further research on sawtooth control. Future work includes the application of the feedback control strategies in tokamak experiments, and further investigation of the locking phenomenon
Primary mirror control for large segmented telescopes: combining high performance with robustness
No full textFuture large telescopes, such as E-ELT and TMT, will need feedback control of the thousands of actuators underneath their segmented primary mirrors (M1). Differences in actuator dynamics and spatially and temporally changing disturbances make it extremely diffcult to formulate classical controllers which are both suffciently robust and highly performing. Therefore, TNO has developed and tested a control approach, in which the actual system response is quickly measured, disturbances are continuously estimated and the controller is adapted in real-Time. The algorithm is tested on an actual M1-relevant setup, in which it converges to a sub-nm optimum within a few minutes, keeps track of changing disturbances and shows its reliability over multiple days
On‐line instrumental variable‐based feedforward tuning for non‐resetting motion tasks
No full textData-driven feedforward control for tracking of varying and non-resetting point-to-point references requires continuous updating of feedforward parameters instead of task-by-task updating. The aim of this paper is to develop an adaptive feedforward controller for non-resetting point-to-point motion tasks by a data-driven feedforward controller. An approximate optimal instrumental variable (IV) estimator with real-time bootstrapping is employed in a closed-loop setting to update the feedforward parameters. A case study on a wafer-stage and experimental validation on a benchmark motion system show the performance benefit.Team Jan-Willem van Wingerde
Gaussian process repetitive control: Beyond periodic internal models through kernels
No full textRepetitive control enables the exact compensation of periodic disturbances if the internal model is appropriately selected. The aim of this paper is to develop a novel synthesis technique for repetitive control (RC) based on a new more general internal model. By employing a Gaussian process internal model, asymptotic rejection is obtained for a wide range of disturbances through an appropriate selection of a kernel. The implementation is a simple linear time-invariant (LTI) filter that is automatically synthesized through this kernel. The result is a user-friendly design approach based on a limited number of intuitive design variables, such as smoothness and periodicity. The approach naturally extends to reject multi-period and non-periodic disturbances, exiting approaches are recovered as special cases, and a case study shows that it outperforms traditional RC in both convergence speed and steady-state error.Team Jan-Willem van Wingerde
Unearthing the Real Process Behind the Event Data The Case for Increased Process Realism
No full textThis book is a revised version of the PhD dissertation written by the author at Hasselt University in Belgium.This dissertation introduces the concept of process realism. Process realism is approached from two perspectives in this dissertation. First, quality dimensions and measures for process discovery are analyzed on a large scale and compared with each other on the basis of empirical experiments. It is shown that there are important differences between the different quality measures in terms of feasibility, validity and sensitivity. Moreover, the role and meaning of the generalization dimension is unclear. Second, process realism is also tackled from a data point of view. By developing a transparent and extensible tool-set, a framework is offered to analyze process data from different perspectives. From both perspectives, recommendations are made for future research, and a call is made to give the process realism mindset a central place within process mining analyses.
In 2020, the PhD dissertation won the “BPM Dissertation Award”, granted to outstanding PhD theses in the field of Business Process Management
Dynamic testing of primary mirror segment supports for the Extremely Large Telescope
No full text\u3cp\u3eThe preparations for the design and construction of the Extremely Large Telescope (ELT) are in full swing. One of the most critical components of this enormous telescope is its segmented primary mirror (M1), for which Netherlands Organisation for Applied Scientific Research (TNO), in collaboration with VDL, has designed the mechanical segment support (M1SS) in the period 2015-2016.\u3csup\u3e1\u3c/sup\u3e This new M1SS design is based on the previous M1SS prototypes developed in 2009-2010,\u3csup\u3e2\u3c/sup\u3e but includes several enhancements to further improve its performance. Specific design drivers were, among others, the serviceability of the M1SS, the introduced surface form error at the segment, and the increased target values for the structural eigenfrequencies. The latter defines the dynamic performance of the structure (including the ∼178 kg segment), which needed to be validated experimentally. From the latest M1SS design one engineering model (EM) and six qualification models (QMs) have been manufactured recently, which have tested intensively to verify their performance. This work will present the test procedure employed to validate the dynamic behavior, describe these dynamic tests and present their results in detail. During these tests a QM, including a dummy segment, has been placed on a heavy rigid structure and three accelerometers have been mounted across the assembly. The structure has then been excited on several strategic locations using a roving hammer technique,\u3csup\u3e3\u3c/sup\u3e resulting in a large collection of frequency responses. From these, the eigenfrequencies and accompanying mode shapes have been estimated, resulting in accurate determination of the clocking, lateral, piston and tip/tilt modes of the structure. This allows for correct assessment of the dynamic performance and comparison to the design objectives and finite element model (FEM) predictions. This procedure has been applied to two different QMs, but since each M1SS consists of a fixed frame (FF) and a removable segment assembly (SA), four different configurations have been tested. The results demonstrate compliance with the challenging design objectives for all QMs, and they show only small variations among the configurations, demonstrating that the dynamic performance of the M1SS design is very reproducible.\u3c/p\u3
Authorship as cultural performance: new perspectives in authorship studies
No full textThis article proposes a performative model of authorship, based on the historical alternation between predominantly 'weak' and 'strong' author concepts and related practices of writing, publication and reading. Based on this model, we give a brief overview of the historical development of such author concepts in English literature from the Middle Ages to the twentieth century. We argue for a more holistic approach to authorship within a cultural topography, comprising social contexts, technological and media factors, and other cultural developments, such as the distinction between privacy and the public sphere
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