Corina Mnerie

Mathematical model of a galvanometer-based scanner: simulations and experiments

The paper presents an insight into our current researches on galvanometer-based scanners (GSs). A brief overview is first performed on the state-of-the-art, as well as on some of our contributions to optimize the scanning and the command functions of this most used scanning device. Considerations on the use of GSs in high-end biomedical imaging applications such as Optical Coherence Tomography (OCT) are made, with a focus towards obtaining the best possible duty cycles and artifact-free OCT images when using GSs for lateral scanning, as studied in our previous works. The scope of our present study is to obtain the mathematical model of a GS system (motor and controller included) in order to optimize the command functions of the device and to support the development of some more advanced control structures. The study is centered on the mathematical and experimental modeling of GSs. Thus, the results of an experimental identification made on a classical multi-parameter mathematical model proposed for such a system are presented. The experiments are carried out in different operating regimes, and the specific characteristic parameters of the GS are determined. Using these parameters obtained experimentally, we carry out simulations in Mathlab Simulink to validate the theoretical model. With the indentified model, an extended control solution is proposed. We point out the match between the theory and the results of the simulations and of the testing for different types of input signals, such as triangular, sinusoidal, and sawtooth with different duty cycles.

Performance enhancement of galvanometer scanners using extended control structures

The galvanometer-based scanners (GS) are optomechatronic devices with a wide range of applications, from industrial to biomedical imaging. They are driven with periodical and time variable signals - especially sawtooth, triangular, sine wave or signals with special variations. We approach in this paper the rejection of the effect of disturbances in order to improve the tracking performances of the GS. The control solution proposed in the paper is based on the extension of the existing control structure with an additional loop, with an additional controller PID-Ll type, which will ensure better speed response and good immunity to constant disturbances which can affect the servo system.

Optimization of Scanning and Command Functions of Galvanometer- based Scanners

We discuss and demonstrate the optimal scanning functions of a galvanometer-based scanner (GS) from an optomechanical point of view. Triangular versus sawtooth and sinusoidal scanning functions are reviewed briefly. From this discussion, we focus on triangular functions with linear active portions and as fast as possible non-linear stop-and-turn portions, necessary to obtain an as high as possible duty cycle. We have studied analytically the performances of these return portions for various sinusoidal, parabolic and higher order polynomial equations. Contrary to what is pointed out in the literature, where linear + sinusoidal scanning function was considered best, we demonstrated that actually the linear + parabolic function provides the highest duty cycle (i.e. time efficiency of the scanning process). The second part of the study approaches the command function, given by the input voltage of the GS that has to provide the optimal scanning function discussed above. This command function is considered in relationship with the active torque that drives the device. This torque is studied with regard to the constructive parameters of the device (moment of inertia, damping coefficient and elastic coefficient of the torsion springs), and to the imposed parameters of the scanning regime (scan frequency, amplitude, velocity and duty cycle). Especially the trade-off that can be done between the various - and contradictory - requirements one has for the device is of interest. The main one is between the duty cycle and the maximum value of the command voltage, in order to minimize the maximum input electrical signal for the device with a minimum loss in what concerns the scan efficiency. Thus, this modeling of the active torque can show the practical limits of the duty cycle, after the study concerning the scanning function has demonstrated its theoretical limitations.

Galvanometer-Based Scanners: Mathematical Model and Alternative Control Structures for Improved Dynamics and Immunity to Disturbances

Galvanometer scanners (GSs) are the most utilized optomechatronic systems for laser scanning. A GS consists of an oscillatory element (which includes the galvomirror) in a motor structure equipped with a positioning servo-system built usually in a closed-loop structure and controlled by different algorithms. Such structures have to provide speed and accuracy in the positioning of the laser beam or for raster scanning. Although tackled by numerous studies, on different aspects, this is still an open problem. The aim of this study is to approach it in a simple way and to provide a low cost solution to increasing accuracy by developing a structure which is more immune to disturbances than the classical one. In order to do this, a basic closed-loop GS which consists of a proportional-derivative (PD-L1) controller and a servo-motor is considered first. The mathematical model and the GS parameters are identified using a theoretical approach followed by experimental identifications. The extended control solution is developed starting from this basic GS structure by introducing a proportional-integrative (PI) controller in series with the PD-L1 controller of the GS; further on, a P-L1 reference filter is added to this new structure. In the absence of disturbances, both the basic and the extended control solutions show good tracking performances, but the basic solution is faster. In the presence of constant disturbances which can affect the servo-system, the latter structure (extended and filtered) has the best dynamical and tracking performances.

Classical PID versus predictive control solutions for a galvanometer-based scanner

The galvanometer-based scanners (GS) are oscillatory optical systems utilized in high-end biomedical technologies. From a control point-of-view the GSs are mechatronic systems (mainly positioning servo-systems) built usually in a close loop structure and controlled by different control algorithms. The paper presents a Model based Predictive Control (MPC) solution for the mobile equipment (moving magnet and galvomirror) of a GS. The development of a high-performance control solution is based to a basic closed loop GS which consists of a PD-L1 controller and a servomotor. The mathematical model (MM) and the parameters of the basic construction are identified using a theoretical approach followed by an experimental identification. The equipment is used in our laboratory for better dynamical performances for biomedical imaging systems. The control solutions proposed are supported by simulations carried out in Matlab/Simulink.

Optomechatronics Applications of the Theory of Mechanisms with Active Student Involvement in Research

The paper presents some of our current investigations in the multi-disciplinary field of optomechatronics, based in part on different applications of the theory of mechanisms. Classical mechanism applications approached mostly with undergraduate students are presented in the first part of the paper. Scanners, choppers and attenuators—optomechatronic devices, in general—are considered in the second part, with both kinematical and dynamical aspects, and some of our relevant results in the field are pointed out. Student involvement (both under and postgraduate) in these researches is presented, as well as some of the implementation of the results and expertise gained through research in the curricula of the Mechanical and Electrical Engineers in our university.

Control architectures of galvanometer-based scanners for an increased precision and a faster response

High-end biomedical applications, such as Optical Coherence Tomography (OCT) or Confocal Microscopy (CM) require both precision and speed. The latter is essential in OCT by example to achieve in vivo, real time imaging – with video rate imaging capability. An essential element of this effort to achieve such speeds in OCT by example is the optomechatronic system used for lateral scanning. It usually consists of a dual axis double galvanometer-based scanner (GS). However, GSs are used in a larger variety of applications in biomedical imaging – not only in lateral scanning. Due to the importance of the topic, we have approached different aspects of GSs technology, including scanning and control functions, duty cycle optimization, and minimization of artifacts. The paper proposes a Model-based Predictive Control (MPC) structure for driving the GSs in order to achieve either an improved precision or a higher speed. The predictive control solution was tested for different types of input signals. Reasons for choosing the objective function and the predictive horizons are discussed. The GS was characterized by a second order mathematical model (MM), with the values of the parameters identified experimentally. Simulations were carried out using Matlab Simulink. The control results achieved are compared with the Proportional Integrative Derivative controller with Lags (PID-L1). The conclusions support the proposed control solution and its implementation in applications.

Towards a research pole in photonics in Western Romania

We present our efforts in establishing a Research Pole in Photonics in the future Arad-Timisoara metropolitan area projected to unite two major cities of Western Romania. Research objectives and related training activities of various institutions and groups that are involved are presented in their evolution during the last decade. The multi-disciplinary consortium consists principally of two universities, UAVA (Aurel Vlaicu University of Arad) and UMF (Victor Babes Medicine and Pharmacy University of Timisoara), but also of the Arad County Emergency University Hospital and several innovative SMEs, such as Bioclinica S.A. (the largest array of medical analysis labs in the region) and Inteliform S.R.L. (a competitive SME focused on mechatronics and mechanical engineering). A brief survey of the individual and joint projects of these institutions is presented, together with their teaching activities at graduate and undergraduate level. The research Pole collaborates in R&D, training and education in biomedical imaging with universities in USA and Europe. Collaborative activities, mainly on Optical Coherence Tomography (OCT) projects are presented in a multidisciplinary approach that includes optomechatronics, precision mechanics and optics, dentistry, medicine, and biology.

Classifier Ensemble Selection Based on mRMR Algorithm and Diversity Measures: An Application of Medical Data Classification

Classifier selection is a significant problem in machine learning to reduce the computational time and the number of ensemble members. Over the past decade, multiple classifier systems (MCS) have been actively exploited to enhance the classification accuracy. Finding a pertinent objective function for measuring the competence of base classifier is a critical issue to select the appropriate subset from a pool of classifiers. Along with the accuracy, diversity measures are designed as objective functions for ensemble selection. This current work proposed a new selection method based on accuracy and diversity in order to achieve better medical data classification performance. The classifiers correlation was calculated using Minimum Redundancy Maximum Relevance (mRMR) method based on relevance and diversity measures. Experiments were carried out on five data sets from UCI Machine Learning Repository and LudmilaKuncheva Collection. The experimental results proved the superiority of the proposed classifiers selection method.

Building an optomechatronics group in a young university in Western Romania

We present our experience regarding the establishing of an interdisciplinary group with Optics as one of its main topic at the Aurel Vlaicu University of Arad (UAVA) – linked with the improvement through research of our educational activities. The 3OM Group (in Opto-Mechatronics, Optical Metrology, and Optics and Mechanics) is described in its evolution from optomechanics to photonics, the latter with a focus on OCT (Optical Coherence Tomography) – with the national and the international collaborations established, with universities from Romania, Europe and USA. While the research directions of the 3OM Group are presented, they are linked with the educational components implemented in the various subjects we teach, for both undergraduate and graduate students, both in Mechanical and in Electrical Engineering. The main effort is to integrate education and research, to move teaching beyond the classical aspects to put the stress on hands-on-experiments, as well as on research-based activities – even with undergraduates. The main goals of this approach are to obtain an early orientation towards innovation and discovery, with a taste for novelties and with a clear focus on international standards. While this account is only one of many, it offers our experience in passing through the difficulties of developing both research and education in Optics in a young university in an emergent economy in Eastern Europe.