This note studies the identification of individual systems operating in a large-scale distributed network by considering the interconnection signals between neighboring systems to be unmeasurable. The unmeasurable interconnections act as unknown system inputs to the individual systems in a network, which poses a challenge for the identification problem. A subspace identification framework is proposed in this note for the consistent identification of individual systems using only local input and output information. The key step of this identification framework is the accurate estimation of the unknown system inputs of individual systems using local observations. Sufficient identifiability conditions are provided for the proposed identification framework and a simulation example is given to demonstrate its performance.","","en","journal article","","","","","","Accepted Author Manuscript","","","","","Numerics for Control & Identification","","","" "uuid:beac87df-e778-4550-b234-e844e0e263a1","http://resolver.tudelft.nl/uuid:beac87df-e778-4550-b234-e844e0e263a1","Rapid identification of coherent pupil functions from multiple intensity measurements","Wilding, D. (TU Delft Numerics for Control & Identification); de Iongh, Gijs (Student TU Delft); Soloviev, O.A. (TU Delft Numerics for Control & Identification; ITMO University; Flexible Optical B.V.); Pozzi, P. (TU Delft Numerics for Control & Identification); Vdovine, G.V. (TU Delft Numerics for Control & Identification; ITMO University; Flexible Optical B.V.); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Wojtkowski, M. (editor); Boppart, S.A. (editor); Oh, W.Y. (editor)","2017","By taking multiple input-output measurements, it is shown how to determine the input to an optical system that corrects unknown phase aberrations without interferometric measurements or online iterative optimization within a couple of seconds. It is shown to work in simulations and experiment. This technique may also be used to acquire the complex field in the pupil, hereby permitting a complex field image to be acquired.

1 constraint can be easily added to the optimization problem as a convex variant of a cardinality constraint, in order to induce sparsity on the controller matrices.","Output feedback control; Relaxations; Robust control; Robust controller synthesis","en","journal article","","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:22de3878-7188-41e2-9642-e0c6332c1ce4","http://resolver.tudelft.nl/uuid:22de3878-7188-41e2-9642-e0c6332c1ce4","Temperature-immune readout of an integrated optical wavelength meter based on microring resonators","Taballione, Caterina (University of Twente); Agbana, T.E. (TU Delft Numerics for Control & Identification); Vdovin, Gleb (TU Delft Numerics for Control & Identification); Hoekman, Marcel (LioniX International BV); Wevers, Lennart (LioniX International BV); Kalkman, J. (TU Delft ImPhys/Quantitative Imaging); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification); van der Slot, Peter J.M. (University of Twente); Boller, Klaus-Jochen (University of Twente)","","2017","Wavelength meters are central for many applications such as in telecommunication systems or laser monitoring. The primary function of a wavelength meter is to provide an output signal that changes sensitively with the wavelength of the input light. Of central importance is the reproducibility of the output signal even in the presence of external perturbations, e.g., temperature changes causing thermal drift. Various different methods are usually applied to improve reproducibility, e.g., thermal stabilization or repeated calibration with an additional reference light source of well-known and stable wavelength.","","en","conference paper","","","","","","","","","","","","","","" "uuid:503ef7de-a2a4-4204-ba7b-288a60348b5e","http://resolver.tudelft.nl/uuid:503ef7de-a2a4-4204-ba7b-288a60348b5e","Adaptive optics in digital micromirror based confocal microscopy","Pozzi, P. (TU Delft Numerics for Control & Identification); Wilding, D. (TU Delft Numerics for Control & Identification); Soloviev, O.A. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Vdovine, G.V. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Bifano, Thomas G. (editor); Kubby, Joel (editor); Gigan, Sylvain (editor)","2016","This proceeding reports early results in the development of a new technique for adaptive optics in confocal microscopy. The term adaptive optics refers to the branch of optics in which an active element in the optical system is used to correct inhomogeneities in the media through which light propagates. In its most classical form, mostly used in astronomical imaging, adaptive optics is achieved through a closed loop in which the actuators of a deformable mirror are driven by a wavefront sensor. This approach is severely limited in fluorescence microscopy, as the use of a wavefront sensor requires the presence of a bright, point like source in the field of view, a condition rarely satisfied in microscopy samples. Previously reported approaches to adaptive optics in fluorescence microscopy are therefore limited to the inclusion of fluorescent microspheres in the sample, to use as bright stars for wavefront sensors, or time consuming sensorless optimization procedures, requiring several seconds of optimization before the acquisition of a single image.

We propose an alternative approach to the problem, implementing sensorless adaptive optics in a Programmable array microscope. A programmable array microscope is a microscope based on a digital micromirror device, in which the single elements of the micromirror act both as point sources and pinholes.","Confocal Microscopy; Digital Micromirror Device; Wavefront Optimization; Fluorescence","en","conference paper","SPIE","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:0ef8bcbc-19e8-441c-834c-ef559d86683b","http://resolver.tudelft.nl/uuid:0ef8bcbc-19e8-441c-834c-ef559d86683b","Sequential convex relaxation for convex optimization with bilinear matrix equalities","Doelman, R. (TU Delft Numerics for Control & Identification); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Rantzer, Anders (editor); Bagterp Jørgensen, John (editor); Stoustrup, Jakob (editor)","2016","We consider the use of the nuclear norm operator, and its tendency to produce low rank results, to provide a convex relaxation of Bilinear Matrix Inequalities (BMIs). The BMI is first written as a Linear Matrix Inequality (LMI) subject to a bi-affine equality constraint and subsequently rewritten into an LMI subject to a rank constraint on a matrix affine in the decision variables. The convex nuclear norm operator is used to relax this rank constraint. We provide an algorithm that iteratively improves on the sum of the objective function and the norm of the equality constraint violation. The algorithm is demonstrated on a controller synthesis example.","optimisation; convex programming; linear matrix inequalities","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","","Numerics for Control & Identification","","","" "uuid:0d3a0695-3eb6-4da3-a341-e022df2c8629","http://resolver.tudelft.nl/uuid:0d3a0695-3eb6-4da3-a341-e022df2c8629","Light-sheet optimization for microscopy","Wilding, D. (TU Delft Numerics for Control & Identification); Pozzi, P. (TU Delft Numerics for Control & Identification); Soloviev, O.A. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Vdovine, G.V. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Bifano, Thomas G. (editor); Kubby, Joel (editor); Gigan, Sylvain (editor)","2016","Aberrations, scattering and absorption degrade the performance light-sheet fluorescence microscopes (LSFM). An adaptive optics system to correct for these artefacts and to optimize the light-sheet illumination is presented. This system allows a higher axial resolution to be recovered over the field-of-view of the detection objective. It is standard selective plane illumination microscope (SPIM) configuration modified with the addition of a spatial light modulator (SLM) and a third objective for the detection of transmitted light. Optimization protocols use this transmission light allowing the extension the depth-of-field and correction of aberrations whilst retaining a thin optical section.","Adaptive optics; imaging; microscopy; light-sheet microscopy; optimization","en","conference paper","SPIE","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:7c7772f6-2fcc-4dca-a9e3-c45e79db6595","http://resolver.tudelft.nl/uuid:7c7772f6-2fcc-4dca-a9e3-c45e79db6595","N2SID: Nuclear norm subspace identification of innovation models","Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification); Hansson, A (Linköping University)","","2016","The identification of multivariable state space models in innovation form is solved in a subspace identification framework using convex nuclear norm optimization. The convex optimization approach allows to include constraints on the unknown matrices in the data-equation characterizing subspace identification methods, such as the lower triangular block-Toeplitz of weighting matrices constructed from the Markov parameters of the unknown observer. The classical use of instrumental variables to remove the influence of the innovation term on the data equation in subspace identification is avoided. The avoidance of the instrumental variable projection step has the potential to improve the accuracy of the estimated model predictions, especially for short data length sequences","Subspace system identification; Optimization; Structural constraints; Innovation state space models","en","journal article","","","","","","Accepted Author Manuscript","","2018-07-19","","","Numerics for Control & Identification","","","" "uuid:df8a117b-f870-4b6a-b79a-8ab090ef7cf5","http://resolver.tudelft.nl/uuid:df8a117b-f870-4b6a-b79a-8ab090ef7cf5","Blind multivariable ARMA subspace identification","Yu, C. (TU Delft Numerics for Control & Identification); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","","2016","In this paper, we study the deterministic blind identification of multiple channel state-space models having a common unknown input using measured output signals that are perturbed by additive white noise sequences. Different from traditional blind identification problems, the considered system is an autoregressive system rather than an FIR system; hence, the concerned identification problem is more challenging but possibly having a wider scope of application. Two blind identification methods are presented for multi-channel autoregressive systems. A cross-relation identification method is developed by exploiting the mutual references among different channels. It requires at least three channel systems with square and stably invertible transfer matrices. Moreover, a general subspace identification method is developed for which two channel systems are sufficient for the blind identification; however, it requires the additive noises to have identical variances and the transfer matrices having no transmission zeros. Finally, numerical simulations are carried out to demonstrate the performance of the proposed identification algorithms.","State-space representation; blind identification; cross-relation equation","en","journal article","","","","","","Accepted Author Manuscript","","2018-01-14","","","Numerics for Control & Identification","","","" "uuid:84f40623-6186-4163-94b4-d90920afcced","http://resolver.tudelft.nl/uuid:84f40623-6186-4163-94b4-d90920afcced","Subspace identification of 1D spatially-varying systems using Sequentially Semi-Separable matrices","Sinquin, B. (TU Delft Numerics for Control & Identification); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Johnson, K (editor); Chiu, G (editor); Abramovitch, D (editor)","2016","We consider the problem of identifying 1D spatially-varying systems that exhibit no temporal dynamics. The spatial dynamics are modeled via a mixed-causal, anti-causal state space model. The methodology is developed for identifying the input-output map of e.g a 1D flexible beam described by the Euler-Bernoulli beam equation and equipped with a large number of actuators and sensors. It is shown that the static input-output map between the lifted inputs and outputs possess a so-called Sequentially Semi-Separable (SSS) matrix structure. This structure is of key importance to derive algorithms with linear computational complexity for controller synthesis of large-scale systems. A nuclear norm subspace identification method of the N2SID class is developed for estimating these state space models from input-output data. To enable the method to deal with a large number of repeated experiments a dedicated Alternating Direction Method of Multipliers (ADMM) algorithm is derived. It is shown in this paper that a nuclear norm relaxation on the SSS structure can be imposed which improves the estimates of the system matrices.","nuclear norm subspace identification; spatially distributed systems; sequentially semi-separable matrices","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","","Numerics for Control & Identification","","","" "uuid:3cdede71-a55d-4fc9-adb5-7b9989e677a5","http://resolver.tudelft.nl/uuid:3cdede71-a55d-4fc9-adb5-7b9989e677a5","Feedforward operation of a lens setup for large defocus and astigmatism correction","Verstraete, H.R.G.W. (TU Delft Numerics for Control & Identification); Almasian, M. (University of Amsterdam); Pozzi, P. (TU Delft Numerics for Control & Identification); Bilderbeek, R (Student TU Delft); Kalkman, J. (TU Delft ImPhys/Quantitative Imaging); Faber, DJ (University of Amsterdam); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Schelkens, Peter (editor); Ebrahimi, Touradj (editor); Cristóbal, Gabriel (editor); Truchetet, Frédéric (editor); Saarikko, Pasi (editor)","2016","In this manuscript, we present a lens setup for large defocus and astigmatism correction. A deformable defocus lens and two rotational cylindrical lenses are used to control the defocus and astigmatism. The setup is calibrated using a simple model that allows the calculation of the lens inputs so that a desired defocus and astigmatism are actuated on the eye. The setup is tested by determining the feedforward prediction error, imaging a resolution target, and removing introduced aberrations.","Active or Adaptive Optics; Imaging","en","conference paper","SPIE","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:9ddaee73-b3ec-496f-b332-f0cb3ae0c2bf","http://resolver.tudelft.nl/uuid:9ddaee73-b3ec-496f-b332-f0cb3ae0c2bf","Adaptive optics for confocal laser scanning microscopy with adjustable pinhole","Yoo, H.W. (Vienna University of Technology); van Royen, M.E. (Erasmus Medical Center); van Cappellen, WA (Erasmus Medical Center); Houtsmuller, AB (Erasmus Medical Center); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification); Schitter, G (Vienna University of Technology)","Popp, Jürgen (editor); Tuchin, Valery V. (editor); Matthews, Dennis L. (editor); Pavone, Francesco S. (editor)","2016","The pinhole plays an important role in confocal laser scanning microscopy (CLSM) for adaptive optics (AO) as well as in imaging, where the size of the pinhole denotes a trade-off between out-of-focus rejection and wavefront distortion. This contribution proposes an AO system for a commercial CLSM with an adjustable square pinhole to cope with such a trade-off. The proposed adjustable pinhole enables to calibrate the AO system and to evaluate the imaging performance. Experimental results with fluorescence beads on the coverslip and at a depth of 40 μm in the human hepatocellular carcinoma cell spheroid demonstrate that the proposed AO system can improve the image quality by the proposed calibration method. The proposed pinhole intensity ratio also indicates the image improvement by the AO correction in intensity as well as resolution.","Adaptive Optics; Square Adjustable Pinhole; Confocal Laser Scanning Microscopy; Pinhole Intensity Ratio","en","conference paper","SPIE","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:bfb510ed-ce4f-49c5-8008-6304b1cbd701","http://resolver.tudelft.nl/uuid:bfb510ed-ce4f-49c5-8008-6304b1cbd701","Phase retrieval from multiple binary masks generated speckle patterns","Gong, H. (TU Delft Numerics for Control & Identification); Pozzi, P. (TU Delft Numerics for Control & Identification); Soloviev, O.A. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification); Vdovine, G.V. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.; ITMO University)","Berghmans, Francis (editor); Mignani, Anna G. (editor)","2016","We present a reference-less and time-multiplexing phase retrieval method by making use of the digital micromirror device (DMD). In this method, the DMD functions not only as a flexible binary mask which modulates the optical field, but also as a sampling mask for measuring corresponding phases, which makes the whole setup simple and robust. The DMD reflection forms a sparse intensity mask in the pupil which produces speckle pattern after propagation. With the recorded intensity on the camera and the binary pattern on the DMD, the phase in all the ‘on’ pixels can be reconstructed at once by solving inverse problems with iterative methods, for instance using Gerchberg-Saxton algorithm. Then the phase of the whole pupil can be reconstructed from a series of binary patterns and speckle patterns. Numerical experiments show the feasibility of this phase retrieval method and the importance of sparse binary masks in the improving of convergence speed.","phase retrieval; adaptive optics; digital micromirror device; inverse problems","en","conference paper","SPIE","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:3be74749-534a-420b-bec3-a087f39d1e90","http://resolver.tudelft.nl/uuid:3be74749-534a-420b-bec3-a087f39d1e90","On distributed wavefront reconstruction for large-scale adaptive optics systems","de Visser, C.C. (TU Delft Control & Simulation); Brunner, A.E. (TU Delft Numerics for Control & Identification); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","","2016","The distributed-spline-based aberration reconstruction (D-SABRE) method is proposed for distributed wavefront reconstruction with applications to large-scale adaptive optics systems. D-SABRE decomposes the wavefront sensor domain into any number of partitions and solves a local wavefront reconstruction problem on each partition using multivariate splines. D-SABRE accuracy is within 1% of a global approach with a speedup that scales quadratically with the number of partitions. The D-SABRE is compared to the distributed cumulative reconstruction (CuRe-D) method in open-loop and closed-loop simulations using the YAO adaptive optics simulation tool. D-SABRE accuracy exceeds CuRe-D for low levels of decomposition, and D-SABRE proved to be more robust to variations in the loop gain.","","en","journal article","","","","","","","","2017-11-01","","","Control & Simulation","","","" "uuid:02a42fdc-ed98-4391-8bc5-a4bc40ffffc9","http://resolver.tudelft.nl/uuid:02a42fdc-ed98-4391-8bc5-a4bc40ffffc9","Sensorless adaptive optics system based on image second moment measurements","Agbana, T.E. (TU Delft Numerics for Control & Identification); Yang, H. (Huaihai Institute of Technology); Soloviev, O.A. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.; ITMO University); Vdovine, G.V. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.; ITMO University); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","Schelkens, Peter (editor); Ebrahimi, Touradj (editor); Cristóbal, Gabriel (editor); Truchetet, Frédéric (editor); Saarikko, Pasi (editor)","2016","This paper presents experimental results of a static aberration control algorithm based on the linear relation be- tween mean square of the aberration gradient and the second moment of point spread function for the generation of control signal input for a deformable mirror (DM). Results presented in the work of Yang et al.1 suggested a good feasibility of the method for correction of static aberration for point and extended sources. However, a practical realisation of the algorithm has not been demonstrated. The goal of this article is to check the method experimentally in the real conditions of the present noise, finite dynamic range of the imaging camera, and system misalignments. The experiments have shown strong dependence of the linearity of the relationship on image noise and overall image intensity, which depends on the aberration level. Also, the restoration capability and the rate of convergence of the AO system for aberrations generated by the deformable mirror are experi- mentally investigated. The presented approach as well as the experimental results finds practical application in compensation of static aberration in adaptive microscopic imaging system.","wavefront sensorless adaptive optics; experimental results; static aberration; microscopic imaging system","en","conference paper","SPIE","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:af5ff77f-8bf5-4106-8ed8-bf33ead02a26","http://resolver.tudelft.nl/uuid:af5ff77f-8bf5-4106-8ed8-bf33ead02a26","Preconditioning optimal in-domain control of navier-stokes equation using multilevel sequentially semiseparable matrix computations","Qiu, Y.; Van Gijzen, M.B.; Van Wingerden, J.W.; Verhaegen, M.H.G.; Vuik, C.","","2015","In this manuscript, we study preconditioning techniques for optimal in-domain control of the Navier-Stokes equation, where the control only acts on a few parts of the domain. Optimization and linearization of the optimal in-domain control problem results in a generalized linear saddle-point system. The Schur complement for the generalized saddle-point system is very difficult or even impossible to approximate. This prohibits satisfactory performance of the standard block preconditioners. We apply the multilevel sequentially semiseparable (MSSS) preconditioner to the underlying system. Compared with standard block preconditioning techniques, the MSSS preconditioner computes an approximate factorization of the global generalized saddle-point matrix up to a prescribed accuracy in linear computational complexity. This in turn gives parameter independent convergence for MSSS preconditioned Krylov solvers. We use a simple wind farm control example to illustrate the performance of the MSSS preconditioner. We also compare with the performance of the state-of-the-art preconditioning techniques. Our results show the superiority of the MSSS preconditioning techniques to standard block preconditioning techniques for optimal in-domain control of the Navier-Stokes equation.","in-domain flow control; MSSS preconditioners; generalized saddle-point system; Navier-Stokes control","en","report","EWI Dept. Applied Mathematics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Applied Mathematics","","","","" "uuid:8436eae7-da40-443e-957b-527851321fa2","http://resolver.tudelft.nl/uuid:8436eae7-da40-443e-957b-527851321fa2","Optical field reconstruction with digital micromirror interferometry","Gong, H. (TU Delft Numerics for Control & Identification); Pozzi, P. (TU Delft Numerics for Control & Identification); Soloviev, O.A. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification); Vdovine, G.V. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.; ITMO University)","Bonora, S (editor)","2015","We investigate the possibility of interferometric optical field sensor with DMD forming a series of sampling interferometers in the pupil of an optical system. Our preliminary experiment validates the feasibility of our approach for the field reconstruction in the case of coherent field. We believe that this approach can be extended to sensing of speckle patterns and even incoherent fields, by analyzing not only the intensity and phase, but also the amplitude and the visibility of the interference patterns. Such analysis would yield the complete complex amplitude and/or coherence function, making the approach directly applicable to a wide range of inverse source problems in optics.","Ditigal Micromirror Device (DMD); wavefront sensing","en","conference paper","Inst. of Photonics and Nanotechnology-Nat. Res. Council of Italy","","","","","","","","","","Numerics for Control & Identification","","","" "uuid:a93f4eb7-5bd0-4850-a4c7-1c85021b745f","http://resolver.tudelft.nl/uuid:a93f4eb7-5bd0-4850-a4c7-1c85021b745f","Local subspace identification of distributed homogeneous systems with general interconnection patterns","Yu, C. (TU Delft Systems and Control); Verhaegen, M.H.G. (TU Delft Systems and Control)","Zhao, Y (editor); Bai, E-W (editor); Zhang, J-F (editor)","2015","This paper studies the local identification of large-scale homogeneous systems

with general network topologies. The considered local system identification problem involves unmeasurable signals between neighboring subsystems. Compared with our previous work in Yu et al. (2014) which solves the local identification of 1D homogeneous systems, the main challenge of this work is how to deal with the general network topology. To overcome this problem, we first decompose the interested local system into separate subsystems using some state, input and output transform, namely the spatially lifted local system has block diagonal system matrices.We subsequently estimate the Markov parameters of the local system by solving a nuclear norm regularized optimization problem. To realize the state-space system model from the estimated Markov parameters, another nuclear norm regularized optimization problem is provided by taking into account of the inherent dependence of a redundant parameter vector. Finally, the overall identification procedure is summarized.","Subspace identification; nuclear norm; networked systems","en","conference paper","IFAC","","","","","Accepted Author Manuscript","","","","","Systems and Control","","","" "uuid:41f8b749-72b7-4646-91d8-bdff06f5e233","http://resolver.tudelft.nl/uuid:41f8b749-72b7-4646-91d8-bdff06f5e233","Lensless coherent imaging by sampling of the optical field with digital micromirror device","Vdovine, G.V. (TU Delft Numerics for Control & Identification); Gong, H. (TU Delft Numerics for Control & Identification); Soloviev, O.A. (TU Delft Numerics for Control & Identification); Pozzi, P. (TU Delft Numerics for Control & Identification); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification)","","2015","We have experimentally demonstrated a lensless coherent microscope based on direct registration of the complex optical field by sampling the pupil with a sequence of two-point interferometers formed by a digital micromirror device. Complete registration of the complex amplitude in the pupil of the imaging system, without any reference beam, provides a convenient link between the experimental and computational optics. Unlike other approaches to digital holography, our method does not require any external reference beam, resulting in a simple and robust registration setup. Computer analysis of the experimentally registered field allows for focusing the image in the whole range from zero to infinity, and for virtual correction of the aberrations present in the real optical system, by applying the adaptive wavefront corrections to its virtual model.","Microscopy; Digital holography; Inverse problems; Phase retrieval; Adaptive optics","en","journal article","","","","","","Accepted Author Manuscript","","","","","Numerics for Control & Identification","","","" "uuid:ee5779f3-dd08-49da-a202-5d2ab5d9d709","http://resolver.tudelft.nl/uuid:ee5779f3-dd08-49da-a202-5d2ab5d9d709","Subspace identification of local 1D homogeneous systems","Yu, C. (TU Delft Systems and Control); Verhaegen, M.H.G. (TU Delft Systems and Control); Hansson, A (Extern)","Zhao, Y (editor); Bai, E-W (editor); Zhang, J-F (editor)","2015","This paper studies the local subspace identification of 1D homogeneous networked systems. The main challenge lies at the unmeasurable interconnection signals between neighboring subsystems. Since there are many unknown inputs to the concerned local system, the corresponding identification problem is semi-blind. To cope with this problem, a nuclear norm optimization based subspace identification is presented, which is carried out for solving the Markov parameters of a locally lifted system, followed by determining the system matrices of a single subsystem. In the step of Markov parameter estimation, we form a nuclear norm regularized optimization problem which can well handle the adverse effects of the unknown system inputs as long as the number of unknown system inputs is relatively small. In the step of system realization, we again derive a nuclear norm regularized optimization formulation which can cope with the under-determinedness of the realization problem. In the end, the overall identification algorithm is summarized.","Markov parameter; system realization; low rank constraint","en","conference paper","IFAC","","","","","Accepted Author Manuscript","","","","","Systems and Control","","","" "uuid:e24ee66b-377b-480b-9d76-b55a4dc5bcaa","http://resolver.tudelft.nl/uuid:e24ee66b-377b-480b-9d76-b55a4dc5bcaa","Identification of structured LTI MIMO state-space models","Yu, C. (TU Delft Applied Mechanics); Verhaegen, M.H.G. (TU Delft Systems and Control); Kovalsky, S (Extern); Basri, R (Extern)","Valcher, ME (editor); Ohta, Y (editor); Sampei, M (editor)","2015","The identification of structured state-space model has been intensively studied for a long time but still has not been adequately addressed. The main challenge is that the involved estimation problem is a non-convex (or bilinear) optimization problem. This paper is devoted to developing an identification

method which aims to find the global optimal solution under mild computational burden. Key to the developed identification algorithm is to transform a bilinear estimation to a rank constrained optimization problem and further a difference of convex programming (DCP) problem. The initial condition

for the DCP problem is obtained by solving its convex part of the optimization problem which happens to be a nuclear norm regularized optimization problem. Since the nuclear norm regularized optimization is the closest convex form of the low-rank constrained estimation problem, the obtained initial

condition is always of high quality which provides the DCP problem a good starting point. The DCP problem is then solved by the sequential convex programming method. Finally, numerical examples are included to show the effectiveness of the developed identification algorithm.","","en","conference paper","IEEE Society","","","","","Accepted Author Manuscript","","","","","Applied Mechanics","","","" "uuid:a9f2fcf3-53c5-4778-a3df-445b90958198","http://resolver.tudelft.nl/uuid:a9f2fcf3-53c5-4778-a3df-445b90958198","Curvature sensing with a Shack-Hartmann sensor","Soloviev, O.A. (TU Delft Numerics for Control & Identification; Flexible Optical B.V.); Verhaegen, M.H.G. (TU Delft Numerics for Control & Identification); Vdovin, Gleb (TU Delft Numerics for Control & Identification; Flexible Optical B.V.; ITMO University)","Bonora, S (editor)","2015","Shack-Hartmann (SH) sensor, based on sampling of wavefront tilts in subapertures, is a simple, reliable, and widely used in adaptive optics wavefront sensor. A wavefront curvature sensor has the advantage of providing the results suitable for direct control of membrane and bimorph deformable mirrors [1], but requires linear registration of intensity in two planes. SH sensor modifications using astigmatic microlens array [2] and three SH sensors [3] provide measurement both in the form of wavefront gradients and Laplacian curvatures. In this work, we consider a simple arrangement that turns a standard SH sensor into a curvature sensor by moving the camera chip of the SH sensor into the optical plane conjugated to a deformable mirror. This establishes a direct geometric correspondence between the coordinates on the DM surface and the sensor chip. Then, change in the local centroid density corresponds to the Laplacian curvature of the mirror, and the phase at the boundary can be found from the centroid displacements along the edge of the pupil. We investigate the feasibility of this approach for direct control of membrane deformable mirror by measuring the dependence of the calculated centroid density on the control signal applied to the mirror actuators. The experimental results demonstrate a good linear dependence.","Adaptive optics; Shack-Hartmann sensor; curvator sensor; membrane deformable mirror","en","conference paper","Inst. of Photonics and Nanotechnology-Nat. Res. Council of Italy","","","","","","","","","","","","","" "uuid:026751c2-14b6-4b19-b3c5-f70ca59e091e","http://resolver.tudelft.nl/uuid:026751c2-14b6-4b19-b3c5-f70ca59e091e","Automated spherical aberration correction in scanning confocal microscopy","Yoo, H.W.; Royen, M.E.; van Cappellen, W.A.; Houtsmuller, A.B.; Verhaegen, M.H.G.; Schitter, G.","","2014","Mismatch between the refractive indexes of immersion media and glass coverslips introduces spherical aberrations in microscopes especially for high numerical aperture objectives. This contribution demonstrates an automated adjustment of the coverslip correction collar in scanning confocal microscopy to compensate for spherical aberrations due to coverslip thickness mismatch. With a motorized coverslip correction collar, the adjustment procedure consists of xz image scans, image processing, correction quality evaluation, the mismatch estimation, and eventually the optimal adjustment of the correction collar. For fast correction with less photodamage, coarse-fine Gaussian fitting algorithms are proposed and evaluated with various specimen for their estimation accuracy. The benefits of the proposed automated correction are demonstrated for various coverslips with biological specimens, showing the optimized resolution of the confocal microscope.","mage sensors; spherical aberrations; medical imaging; confocal microscopes; entropy","en","journal article","American Institute of Physics","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:57f6de4f-b5e7-4203-b67a-f2c3bc07815f","http://resolver.tudelft.nl/uuid:57f6de4f-b5e7-4203-b67a-f2c3bc07815f","Fast & Furious focal-plane wavefront sensing","Korkiakoski, V.A.; Keller, C.U.; Doelman, N.; Kenworthy, M.; Otten, G.; Verhaegen, M.H.G.","","2014","We present two complementary algorithms suitable for using focal-plane measurements to control a wavefront corrector with an extremely high-spatial resolution. The algorithms use linear approximations to iteratively minimize the aberrations seen by the focal-plane camera. The first algorithm, Fast & Furious (FF), uses a weak-aberration assumption and pupil symmetries to achieve fast wavefront reconstruction. The second algorithm, an extension to FF, can deal with an arbitrary pupil shape; it uses a Gerchberg–Saxton (GS)-style error reduction to determine the pupil amplitudes. Simulations and experimental results are shown for a spatial-light modulator controlling the wavefront with a resolution of 170×170??pixels. The algorithms increase the Strehl ratio from ?0.75 to 0.98–0.99, and the intensity of the scattered light is reduced throughout the whole recorded image of 320×320??pixels. The remaining wavefront rms error is estimated to be ?0.15??rad with FF and ?0.10??rad with FF-GS.","active or adaptive optics; phase measurement; optical sensing and sensors","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:9692365e-000d-4828-9fa5-5106a4fd2904","http://resolver.tudelft.nl/uuid:9692365e-000d-4828-9fa5-5106a4fd2904","Distributed system identification with ADMM","Hansson, A (Extern); Verhaegen, M.H.G. (TU Delft Systems and Control)","Jabbari, F (editor); Teel, AR (editor)","2014","","","en","conference paper","IEEE Society","","","","","Accepted Author Manuscript","","","","","Systems and Control","","","" "uuid:a2299252-6249-4755-94ad-b139023aaa4a","http://resolver.tudelft.nl/uuid:a2299252-6249-4755-94ad-b139023aaa4a","A class of efficient preconditioners with multilevel sequentially semiseparable matrix structure","Qiu, Y.; Van Gijzen, M.B.; Van Winderden, J.W.; Verhaegen, M.H.G.","","2013","This paper presents a class of preconditioners for sparse systems arising from discretized partial differential equations (PDEs). In this class of preconditioners, we exploit the multilevel sequentially semiseparable (MSSS) structure of the system matrix. The off-diagonal blocks of MSSS matrices are of low-rank, which enables fast computations of linear complexity. In order to keep the low-rank property of the off-diagonal blocks, model reduction algorithm is necessary. We tested our preconditioners for 2D convection-diffusion equation, the computational results show the excellent performance of this approach.","preconditioners; partial differential equations (PDEs); multilevel; sequentially semiseparable matrices","en","conference paper","American Institute of Physics","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:3386e464-1a6b-42cd-9557-b0a3b2dd24ff","http://resolver.tudelft.nl/uuid:3386e464-1a6b-42cd-9557-b0a3b2dd24ff","Iterative linear focal-plane wavefront correction","Smith, C.S.; Marinica, R.M.; Den Dekker, A.J.; Verhaegen, M.H.G.; Korkiakoski, V.; Keller, C.U.; Doelman, N.","","2013","We propose an efficient approximation to the nonlinear phase diversity (PD) method for wavefront reconstruction and correction from intensity measurements with potential of being used in real-time applications. The new iterative linear phase diversity (ILPD) method assumes that the residual phase aberration is small and makes use of a first-order Taylor expansion of the point spread function (PSF), which allows for arbitrary (large) diversities in order to optimize the phase retrieval. For static disturbances, at each step, the residual phase aberration is estimated based on one defocused image by solving a linear least squares problem, and compensated for with a deformable mirror. Due to the fact that the linear approximation does not have to be updated with each correction step, the computational complexity of the method is reduced to that of a matrix-vector multiplication. The convergence of the ILPD correction steps has been investigated and numerically verified. The comparative study that we make demonstrates the improved performance in computational time with no decrease in accuracy with respect to existing methods that also linearize the PSF.","","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:db99fb26-88c9-4199-907e-87e23b574361","http://resolver.tudelft.nl/uuid:db99fb26-88c9-4199-907e-87e23b574361","Identification of a dynamical model of a thermally actuated deformable mirror","Haber, A.; Polo, A.; Ravensbergen, S.; Urbach, H.P.; Verhaegen, M.H.G.","","2013","Using the subspace identification technique, we identify a finite dimensional, dynamical model of a recently developed prototype of a thermally actuated deformable mirror (TADM). The main advantage of the identified model over the models described by partial differential equations is its low complexity and low dimensionality. Consequently, the identified model can be easily used for high-performance feedback or feed-forward control. The experimental results show good agreement between the dynamical response predicted by the model and the measured response of the TADM.","","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:a080437c-507f-4281-8fac-40fef5b86b3c","http://resolver.tudelft.nl/uuid:a080437c-507f-4281-8fac-40fef5b86b3c","High precision wavelength estimation method for integrated optics","Oldenbeuving, R.M.; Song, H.; Schitter, G.; Verhaegen, M.H.G.; Klein, E.J.; Lee, C.J.; Offerhaus, H.L.; Boller, K.J.","","2013","A novel and simple approach to optical wavelength measurement is presented in this paper. The working principle is demonstrated using a tunable waveguide micro ring resonator and single photodiode. The initial calibration is done with a set of known wavelengths and resonator tunings. The combined spectral sensitivity function of the resonator and photodiode at each tuning voltage was modeled by a neural network. For determining the unknown wavelengths, the resonator was tuned with a set of heating voltages and the corresponding photodiode signals were collected. The unknown wavelength was estimated, based on the collected photodiode signals, the calibrated neural networks, and an optimization algorithm. The wavelength estimate method provides a high spectral precision of about 8 pm (5·10?6 at 1550 nm) in the wavelength range between 1549 nm to 1553 nm. A higher precision of 5 pm (3·10?6) is achieved in the range between 1550.3 nm to 1550.8 nm, which is a factor of five improved compared to a simple lookup of data. The importance of our approach is that it strongly simplifies the optical system and enables optical integration. The approach is also of general importance, because it may be applicable to all wavelength monitoring devices which show an adjustable wavelength response.","","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:30947ca3-e964-4150-b566-d7f8dcb3cd9c","http://resolver.tudelft.nl/uuid:30947ca3-e964-4150-b566-d7f8dcb3cd9c","Modeling the Effect of Wave-front Aberrations in Fiber-based Scanning Optical Microscopy","Verstraete, H.R.G.W.; Verhaegen, M.H.G.; Kalkman, J.","","2013","In scanning microscopy and optical coherence tomography, aberrations of the wave-front cause a loss in intensity and resolution. Intensity and resolution are quantified using Fresnel propagation, Fraunhofer diffraction, and the calculation of overlap integrals.","","en","conference paper","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:75c067d3-ef95-4aab-a6b0-43ff5139b73d","http://resolver.tudelft.nl/uuid:75c067d3-ef95-4aab-a6b0-43ff5139b73d","Wavefront reconstruction in adaptive optics systems using nonlinear multivariate splines","De Visser, C.C.; Verhaegen, M.H.G.","","2012","This paper presents a new method for zonal wavefront reconstruction (WFR) with application to adaptive optics systems. This new method, indicated as Spline based ABerration REconstruction (SABRE), uses bivariate simplex B-spline basis functions to reconstruct the wavefront using local wavefront slope measurements. The SABRE enables WFR on nonrectangular and partly obscured sensor grids and is not subject to the waffle mode. The performance of SABRE is compared to that of the finite difference (FD) method in numerical experiments using data from a simulated Shack Hartmann lenslet array. The results show that SABRE offers superior reconstruction accuracy and noise rejection capabilities compared to the FD method.","","en","journal article","Optical Society of America","","","","","","","","Aerospace Engineering","Control & Operations","","","","" "uuid:4b90e0c5-1407-46b3-ac8c-469e206158af","http://resolver.tudelft.nl/uuid:4b90e0c5-1407-46b3-ac8c-469e206158af","An innovative and efficient method to control the shape of push-pull membrane deformable mirror","Polo, A.; Haber, A.; Pereira, S.F.; Verhaegen, M.H.G.; Urbach, H.P.","","2012","We carry out performance characterisation of a commercial push and pull deformable mirror with 48 actuators (Adaptica Srl). We present a detailed description of the system as well as a statistical approach on the identification of the mirror influence function. A new efficient control algorithm to induce the desired wavefront shape is also developed and comparison with other control algorithms present in literature has been made to prove the efficiency of the new approach.","","en","journal article","Optical Society of America","","","","","","","","Applied Sciences","IST/Imaging Science and Technology","","","","" "uuid:f6ab426a-997d-44e3-90c1-27c841380ec7","http://resolver.tudelft.nl/uuid:f6ab426a-997d-44e3-90c1-27c841380ec7","Semidefinite programming for model-based sensorless adaptive optics","Antonello, J.; Verhaegen, M.H.G.; Fraanje, R.; Van Werkhoven, T.; Gerritsen, H.C.; Keller, C.U.","","2012","Wavefront sensorless adaptive optics methodologies are widely considered in scanning fluorescence microscopy where direct wavefront sensing is challenging. In these methodologies, aberration correction is performed by sequentially changing the settings of the adaptive element until a predetermined image quality metric is optimized. An efficient aberration correction can be achieved by modeling the image quality metric with a quadratic polynomial. We propose a new method to compute the parameters of the polynomial from experimental data. This method guarantees that the quadratic form in the polynomial is semidefinite, resulting in a more robust computation of the parameters with respect to existing methods. In addition, we propose an algorithm to perform aberration correction requiring a minimum of N+1 measurements, where N is the number of considered aberration modes. This algorithm is based on a closed-form expression for the exact optimization of the quadratic polynomial. Our arguments are corroborated by experimental validation in a laboratory environment.","","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:4ffdbcf9-6267-4f74-9255-2d74915e0995","http://resolver.tudelft.nl/uuid:4ffdbcf9-6267-4f74-9255-2d74915e0995","Joint optimization of phase diversity and adaptive optics: Demonstration of potential","Korkiakoski, V.; Keller, C.U.; Doelman, N.; Fraanje, P.R.; Verhaegen, M.H.G.","","2011","We study different possibilities to use adaptive optics (AO) and phase diversity (PD) together in a jointly optimized system. The potential of the joint system is demonstrated through numerical simulations. We find that the most significant benefits are obtained from the improved deconvolution of AO-corrected wavefronts and the additional wavefront sensor (WFS) information that reduces the computational demands of PD algorithms. When applied together, it is seen that the image error can be reduced by 20% compared to traditional PD, working with one focused and one defocused camera image, and the computational load is reduced by a factor of 20 compared to a more reliable PD algorithm requiring more camera images. In addition, we find that the system performance can be optimized by adjusting the magnitude of the applied diversity wavefronts.","active or adaptive optics; deconvolution; image reconstruction techniques; inverse problems","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:ac4caac8-6a37-464e-b46c-79bed2c0016e","http://resolver.tudelft.nl/uuid:ac4caac8-6a37-464e-b46c-79bed2c0016e","Fault tolerant wind turbine production operation and shutdown (Sustainable Control)","Van Engelen, T.; Schuurmans, J.; Kanev, S.; Dong, J.; Verhaegen, M.H.G.; Hayashi, Y.","","2011","Extreme environmental conditions as well as system failure are real-life phenomena. Especially offshore, extreme environmental conditions and system faults are to be dealt with in an effective way. The project Sustainable Control, a new approach to operate wind turbines (Agentschap NL, grant EOSLT02013) pro- vides the concepts for an integrated control platform. This platform accomplishes fault tolerant control in regular and extreme conditions during production operation and shutdown. The platform is built up from methods for the detection of extreme conditions and faults and from methods for operation and shut-down. The detection methods are largely model-based, which implies that event detection is derived from anomalous behaviour of outcomes from an observer, which can be an Kalman fiter. Various types of control approaches are included in the control methods. Often, more scalar feedback loops work together, the validity of which is motivated through frequency separation or orhogonality. The detection and handling of extreme conditions and sensor failures elongates the operation. The application of optimizing techniques during production operation and during shut down can reduce the loads on the turbine significantly. A proof of principle on a multi MW wind turbine for optimzied production operation showed a typical reduction of fatigue damage equivalent loads between 10% and 30%.","fault detection; gust detection; individual pitch control; fault tolerance; NMPC; optimal shutdown control","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:9f5fd3b8-29a8-4313-8650-a71e9e727141","http://resolver.tudelft.nl/uuid:9f5fd3b8-29a8-4313-8650-a71e9e727141","Port-Hamiltonian description and analysis of the LuGre friction model","Koopman, J.; Jeltsema, D.; Verhaegen, M.H.G.","","2010","A port-Hamiltonian formulation of the LuGre friction model is presented that can be used as a building block in the physical modelling of systems with friction. Based on the dissipation structure matrix of this port-Hamiltonian LuGre model, an alternative proof can be given for the passivity conditions that are known in the literature. As a specific example, the interconnection of a mass with the port-Hamiltonian LuGre model is presented. It is shown that the lossless-interconnection structure and dissipation structure of the port-Hamiltonian LuGre model are consistent with those of this interconnection. As an additional example, the port-Hamiltonian formulation of a quarter-car system with a LuGre-based tyre model is presented.","friction; modelling; nonlinear systems; Port-Hamiltonian systems","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","","" "uuid:9d6b2cd6-7936-4afc-ab55-62ca84be31d3","http://resolver.tudelft.nl/uuid:9d6b2cd6-7936-4afc-ab55-62ca84be31d3","Exploiting the spatiotemporal correlation in adaptive optics using data-driven H2-optimal control","Hinnen, K.; Verhaegen, M.H.G.; Doelman, N.","","2007","A recently proposed data-driven H2-optimal control approach is demonstrated on a laboratory setup. Most adaptive optics (AO) systems are based on a control law that neglects the temporal evolution of the wavefront. The proposed control approach is able to exploit the spatiotemporal correlation in the wavefront without assuming any form of decoupling. By analyzing the dynamic behavior of the wavefront sensor (WFS), it is shown that if the wavefront correction device can be considered static, the transfer function from control input to WFS output reduces to a two-tap impulse response and an integer number of samples delay. Considering this model structure, a data-driven identification procedure is developed to estimate the relevant parameters from measurement data. The specific structure allows for an analytical expression of the optimal controller in terms of the system matrices of the minimum-phase spectral factor of the atmospheric disturbance model. The performance of the optimal controller is compared with that of the standard AO control law. An analysis of the dominant error sources shows that optimal control may reduce the temporal error.","active or adaptive optics; atmospheric turbulence","en","journal article","Optical Society of America","","","","","","","","Mechanical, Maritime and Materials Engineering","Delft Center for Systems and Control","","","","" "uuid:f08bae25-62be-4c09-81c8-ecb9a0723460","http://resolver.tudelft.nl/uuid:f08bae25-62be-4c09-81c8-ecb9a0723460","A novel approach on parameter identification for inverter driven induction machines","Koning, R.F.F.; Verhaegen, M.H.G.; Ben Klaassens, J.; Uittenbogaart, J.R.","","2000","","","en","journal article","IEEE","","","","","","","","","","","","",""