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Advanced galvanometer-based optical scanner design
Abstract
The closed loop galvanometer-based optical scanners continues to be an advanced technology for the integration and enabling of a broader range of laser system applications and uses. Advances in the technology have provided major improvements in galvo positioning speed, accuracy, size and cost. This paper will introduce the benefits, operating ranges and recent advances in galvanometer technology for scanning applications along with some of the other components and issues related to system design for high performance scanning applications. Several different actuator and position detector technologies and designs will be presented including moving coil actuators, moving magnet actuators and patented capacitive and optical position detector designs that offer positioning speeds as fast as 100 s and positioning repeatability to single microradians. The performance and system design trade-offs that one should consider during the selection of the appropriate galvanometer technology and the optical systems design will be discussed along with a performance comparison of the galvanometer to other optical scanning technologies.
... Laser scanning technology holds great importance in material processing [1][2][3] and optical imaging [4][5][6][7][8][9][10][11][12]. Many high-performance biomedical imaging techniques rely on laser scanning, which include confocal microscopy [5], optical coherence tomography [6,13] and multiphoton microscopy [4,7,8,[14][15][16]. ...
... Many high-performance biomedical imaging techniques rely on laser scanning, which include confocal microscopy [5], optical coherence tomography [6,13] and multiphoton microscopy [4,7,8,[14][15][16]. For high-throughput recording, resonant galvo scanner is particularly important for its speed, robustness, compactness and 100% duty cycle [3,7,8,17]. The data throughput of a scanner is determined by its aperture, angular range, frequency and wavelength [5]. ...
... The position jitter may result from several factors, the accuracy of the galvo's internal position sensor, the temporal accuracy of the data acquisition system, air turbulence and the environmental noise. First, resonant scanners are typically driven by an internal phase locked loop which requires a positon feedback [3,11]. This internal position feedback also provides a trigger signal for synchronizing the application system's data acquisition to the resonant scanning [18]. ...
Laser scanning has been widely used in material processing and optical imaging. Among the established scanners, resonant galvo scanners offer high scanning throughput and 100% duty cycle and have been employed in various laser scanning microscopes. However, the common applications of resonant galvo often suffer from position jitters which could introduce substantial measurement artifacts. In this work, we systematically quantify the impact of position sensor, data acquisition system and air turbulence and provide a simple solution to achieve jitter free high-throughput measurement.
... However, when the number of facets (mirrors) of the polygon increases, the number of straddle mirrors increases. Thus, the portions of the active scanning period are reduced over the full scan period due to the scan discontinuities [38]. In other words, the connection lines among the mirror increases when the number of facet increases. ...
... Typically, there are several types of oscillatory resonant scanners that are commonly found in the literatures. They include galvanometric [38], resonant scanners, and piezoelectrically driven mirror transducers [46]. Although the resonant scanner can be divided into two major groups according to the size of the scanner (MEMS or non-MEMS), the main differences between these oscillatory resonant scanners are the actuation modes used and the compliant structures in actuating the mirror. ...
... The galvanometric actuator makes use of the interaction between a permanent magnet and the magnetic field created by a current in a wire coil. When current is supplied to the wire coil, it results in a rotary torque on the actuator rotor which is suspended on a set of bearings [38]. The galvanometric structure typically consists of three types which are categorized according to the movement of stator and rotor. ...
The design parameters of torsional spring mechanism resonant scanner are the scanning angle, frequency and also power consumption. Generally, high resolution scanning is desired due to the reason of smaller devices are developed. This review covers the linear optical and rotational scanner technologies for both the MEMS and non-MEMS. The overview of scanner technology is discussed accordingly to the recent researches and development performed on the scanning technology. The review is categorized into several sub-topics according to the scanner’s components. The component includes the actuator used, the compliant structure and the control system. Furthermore, damping characteristics are also presented in this review as it affected the scanning angle for the scanner. Finally, the application of the scanner is discussed conferring to the fields. The fields include light detection and ranging systems, medical and also biomedical systems. This review serves as the reference for the mechanical design of the scanning devices. © 2016, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
... Galvanometer based scanning mirrors are the most widely used scanning systems for high-precision in vivo biological imaging systems, such as scanning confocal and two-photon excitation microscopes (Aylward, 2003;Pawley, 2006;Saggau, 2006). In principle, these microscopes record an image by scanning a laser point by point to achieve a high spatial resolution. ...
... For the experiments, a high performance galvanometer scanner (6210 H, Cambridge Technology Inc., Lexington, MA, USA) is used, which is widely installed in commercial laser confocal microscopes (Aylward, 2003;Pawley, 2006). The galvanometer scanner is a moving-magnet type as shown in Fig. 2, i.e. magnets along the shaft are rotated by the Lorentz force created by the current i c through the fixed coils. ...
... A scanning mirror is attached at one end of the shaft for directing a laser beam. At the other end of the shaft an encoder is attached for the precise angle measurement of the mirror by the passed light through the blocking butterfly (Aylward, 2003). The mechanical actuation range θ m of the galvanometer scanner is 710°, corresponding to 720°in optical angle θ o . ...
Iterative learning control (ILC) for a galvanometer scanner is proposed to achieve high speed, linear, and accurate bidirectional scanning for scanning laser microscopy. A galvanometer scanner, as a low stiffness actuator, is first stabilized with a feedback control compensating for disturbances and nonlinearities at low frequencies, and ILC is applied for the control of the fast scanning motion. For stable inversion of the non-minimum phase zeros, a time delay approximation and a zero phase approximation are used for design of ILC, and their attainable bandwidths are analyzed. Experimental results verify the benefits of ILC of its wide control bandwidth, enabling a faster, more linear, and more accurate scanning without a phase lag and a gain mismatch. At the scan rate of 4112 lines per second, the root mean square (RMS) error of the ILC can be reduced by a factor of 73 in comparison with the feedback controlled galvanometer scanner of the commercial system.
... Galvanometers are the most commonly used scanners for biomedical imaging [41][42][43][44] due to their moderate speed (> 1 kHz), low step response times (∼100 µs for 3 mm apertures), and high positional accuracy [45]. Additionally, closed-loop controller feedback of mirror position can be used to optimize galvanometer inputs to improve linearity and minimize positional errors. ...
... Despite the aforementioned advantages of galvanometers, their performance is directly related to response time optimizations specific to mirror size, material stiffness, weight, and alignment [45]. Previously demonstrated methods for scanner optimization include iterative learning control [46,47], Landweber-based deconvolution [48], and optimization of input scan waveform shape, frequency, and amplitude [49][50][51]. ...
Galvanometers are ubiquitous in point-scanning applications in optical imaging, display, ranging, manufacturing, and therapeutic technologies. However, galvanometer performance is constrained by finite response times related to mirror size and material properties. We present a model-driven approach for optimizing galvanometer response characteristics by tuning the parameters of the closed-loop galvanometer controller and demonstrate settling time reduction by over 50%. As an imaging proof-of-concept, we implement scan waveforms that take advantage of the optimized galvanometer frequency response to increase linear field-of-view, signal-to-noise ratio, contrast-to-noise ratio, and speed. The hardware methods presented may be directly implemented on galvanometer controllers without the need for specialized equipment and used in conjunction with customized scan waveforms to further optimize scanning performance.
... The control strategy of the galvanometer motor which drives each axis of the actuator is addressed here. The galvanometer motor is mostly used in a closed-loop control framework [4]. The controller structure is synthetized so as to meet the precision and rapidity requirements of the operation. ...
... The reference [5] proposes a general framework in which the synthesis of the controller can be divided into four main points of interest towards the improvement of the closed-loop dynamics: 'Feedforward/ Command Shaping', 'Feedback Control', 'Modeling/Identification' and 'Optimization/ Auto tuning'. The most-encountered conventional structures in industry are Proportional-Integral-Derivative (PID)-based controllers [4]. State of the art works supply a large panel of advanced controller schemes that tackle specific problems such as residual vibration suppression by initial value compensation techniques [6], disturbance rejection through enhancement of the controller with an observer [7] or online closed-loop dynamics enhancement with adaptive control strategies [8]. ...
SLM (Selective Laser Melting) is the most widespread additive manufacturing technique of metal part. The desired part is elaborated through local melting of a raw metal powder bed by means of laser. In industrial machines, galvanometer motors achieve the laser beam deflection and focus control tasks. This paper proposes a H-infinity controller synthesis which improves the system accuracy and robustness towards physical features. Compared to a conventional control scheme, results obtained with the H-infinity controller implemented in an open architecture test bench consisting of a 2-axis laser deflection system showed improved accuracy performance while operation rapidity is optimized.
... In addition, there are approaches that improve control for fast confocal imaging with a conventional galvanometer based optical scanner. Galvanometer based optical scanners are most popular scanning systems for biological laser scanning confocal microscopes, which are usually provided as a default scanner [10], [11]. A modified bidirectional scanning function is studied for fast and undistorted imaging and applied to optical coherent tomography [12]- [14]. ...
... II. NON-COLLOCATED DYNAMICS OF GALVANOMTER SCANNER Fig. 1 shows a mechanical model of a moving-magnet galvanometer scanner, which is typically used in confocal laser scanning microscopy [10], [11]. A scanning mirror is attached at one end of the shaft for beam positioning. ...
A transformation-based iterative learning control (ILC) approach is proposed to achieve accurate image scanning for the non-collocated dynamics of a galvanometer scanner. The non-collocation between the encoder and beam scanning mirror results in a tracking error of the actual beam position although the encoder measurement matches the reference signal. The proposed ILC is extended from the conventional ILC design by adding a reference transformation filter, which is based on the transfer functions between the measured and the controlled output. An error analysis shows that the proposed method can reduce the error of the actual controlled output, especially for applications of a large tracking reference such as image scanning. Experimental results with the proposed ILC show a better tracking accuracy as compared to conventional ILC design with non-collocated sensing.
... High-spatiotemporal-resolution SIM techniques demand high-speed photoelectric devices such as modulators and detectors, like SLMs [50][51][52] , DMDs [53][54][55] , Galvos [56] , and sensitive detectors such as scientific CMOS cameras or detector arrays [57][58][59][60] . The speed limit of an SIM system is affected by multiple factors, including the illumination modulation, the detection sensitivity, the brightness of the fluorescence sample, and the photobleaching/phototoxicity issue. ...
... Similarly, in point-scanning SIM, the imaging speed is largely limited by the aspect ratio of the excitation PSF and the spatial period of the illumination pattern, that is, the number of raw images that need to be taken, as well as the precise stepping movement of the focal point(s). 30,49 High spatiotemporal resolution SIM techniques demand high-speed photoelectric devices such as modulators and detectors, like spatial light modulators (SLM) 50-52 , digital (x, y, z, t) (x, y, z, t, λ) ± 1 micromirror devices (DMD) [53][54][55] , galvanometers (galvo) 56 , and sensitive detectors such as scientific CMOS camera or detector array 57-60 . The speed limit of a SIM system is affected by multiple factors, including the illumination modulation, the detection sensitivity, the brightness of the fluorescence sample, and the photobleaching/phototoxicity issue, etc.. ...
Among super-resolution microscopy techniques, structured illumination microscopy (SIM) shows great advances of low phototoxicity, high speed, and excellent performance in long-term dynamic observation, making it especially suitable for live cell imaging. This review delves into the principles, instrumentation, and applications of SIM, highlighting its capabilities in achieving high spatiotemporal resolution. Two types of structured illumination mechanics are employed: (1) stripe-based SIM, where the illumination stripes are formed through interference or projection, with extended resolution achieved through Fourier-domain extension; (2) point-scanning based SIM, where illumination pattern are generated through projection of the focal point or focal array, with extended resolution achieved through photon reassignment. We discuss the evolution of SIM from mechanical to high-speed photoelectric devices, such as spatial light modulators, digital micromirror devices, galvanometers, etc., which significantly enhance imaging speed, resolution, and modulation flexibility. The review also explores SIM's applications in biological research, particularly in live-cell imaging and cellular interaction studies, providing insights into disease mechanisms and cellular functions. We conclude by outlining the future directions of SIM in life sciences. With the advancement of imaging techniques and reconstruction algorithms, SIM is poised to bring revolutionary impacts to frontier research fields, offering new avenues for exploring the intricacies of cellular biology.
... Laser positioning in commercial systems is usually controlled using closed-looped galvanometer motors to deliver quick and precise motions Aylward 2003). Hence, scanning speeds are often available over a wide range of 200-1,500 mm/ s . ...
... The galvanometer scanner is another type of light deflection device, which consists of two optical reflection mirrors fixed on their rotation shafts. It features high speed and high accuracy for light deflection [12,13] and has been widely applied in laser scanning for material processing [14,15], medical treatment [16,17], and laser indication [18,19]. The galvanometer scanner was also combined with the camera to enlarge the FOV of the vision system for surveillance [20], large-scale structure inspection [21], high-speed moving object tracking [22], etc. Owing to the ultrafast light defection capability, the galvanometer scanner was also applied in image capturing for motion blur compensation [23,24]. ...
A novel visual 3D reconstruction system, composed of a two-axis galvanometer scanner, a camera with a lens, and a set of control units, is introduced in this paper. By changing the mirror angles of the galvanometer scanner fixed in front of the camera, the boresight of the camera can be quickly adjusted. With the variable boresight, the camera can serve as a virtual multi-ocular system (VMOS), which captures the object at different perspectives. The working mechanism with a definite physical meaning is presented. A simple and efficient method for calibrating the intrinsic and extrinsic parameters of the VMOS is presented. The applicability of the proposed system for 3D reconstruction is investigated. Owing to the multiple virtual poses of the camera, the VMOS can provide stronger constraints in the object pose estimation than an ordinary perspective camera does. The experimental results demonstrate that the proposed VMOS is able to achieve 3D reconstruction performance competitive with that of a conventional stereovision system with a much more concise hardware configuration.
... To measure samples in the xy-direction Galvano scanners are typically used in LSM. 8,9 They have the advantage of a fast scanning rate, but on the other hand, there are drawbacks due to the limited aperture of the used focus lenses. In the case of an F-theta lens the focus point is moving in a plane, but the minimal focus spot size is 3-30 μm, and it is also not constant over the entire scan field. ...
A laser scanning microscope for measuring 3D pyroelectric distributions inside thin vinylidene fluoride-trifluoroethylene copolymer films using the Laser Intensity Modulation Method was developed. The setup consists of a laser unit, a laser driver, an xyz-stepper motor unit, a transimpedance amplifier, and a lock-in amplifier. The focus lens at the laser unit is fixed by magnetic levitation and can correct a defocusing of the system or a tilt of the sample surface. It has been demonstrated in different samples that the system has a lateral resolution of 1 μm for measuring the topological surface structure or the pyroelectric distributions. The self-developed laser driver and transimpedance amplifier combined with a fast lock-in amplifier are able to measure small pyroelectric currents and their variation inside a pyroelectric sample in the range of some 1 pA. The maximum measure frequency of 4 MHz and the fast lock-in make it possible to measure the 3D pyroelectric distributions with high resolution. A 3D scan of 30 different layers with depths of 100 nm-5 μm inside the sample and 100 × 100 points in the xy-direction per layer is performed in 3 days. Published under an exclusive license by AIP Publishing. https://doi.
... To measure samples in the xy-direction Galvano scanners are typically used in LSM. 8,9 They have the advantage of a fast scanning rate, but on the other hand, there are drawbacks due to the limited aperture of the used focus lenses. In the case of an F-theta lens the focus point is moving in a plane, but the minimal focus spot size is 3-30 μm, and it is also not constant over the entire scan field. ...
A laser scanning microscope for measuring 3D pyroelectric distributions inside thin vinylidene fluoride-trifluoroethylene copolymer films using the Laser Intensity Modulation Method was developed. The setup consists of a laser unit, a laser driver, an xyz-stepper motor unit, a transimpedance amplifier, and a lock-in amplifier. The focus lens at the laser unit is fixed by magnetic levitation and can correct a defocusing of the system or a tilt of the sample surface. It has been demonstrated in different samples that the system has a lateral resolution of 1 μm for measuring the topological surface structure or the pyroelectric distributions. The self-developed laser driver and transimpedance amplifier combined with a fast lock-in amplifier are able to measure small pyroelectric currents and their variation inside a pyroelectric sample in the range of some 1 pA. The maximum measure frequency of 4 MHz and the fast lock-in make it possible to measure the 3D pyroelectric distributions with high resolution. A 3D scan of 30 different layers with depths of 100 nm–5 μm inside the sample and 100 × 100 points in the xy-direction per layer is performed in 3 days.
... Parmi les technologies de balayage existantes, nous pouvons citer les systèmes à miroir tels que les miroirs polygonaux, les galvanomètres [98], et les MEMS [99] ainsi que des systèmes plus complexes mais rapides comme les déflecteurs acousto-optiques (AOD) et électro-optiques (EOD) [100]. Les AOD étant peu achromatiques, ils sont peu adaptés à l'incorporation dans un chemin d'excitation comportant plusieurs lasers pour la microscopie, là où des miroirs peuvent couvrir une vaste plage de longueur d'onde via un revêtement optique adapté. ...
La microscopie de fluorescence et la microscopie de localisation de molécules uniques (SMLM) permettent d’imager spécifiquement les entités subcellulaires et sont donc des outils indispensables en Biologie. Cependant ces techniques d’imagerie sont intimement liées aux propriétés de l’illumination, qui possède des limites en termes d’uniformité et de contrôle de l’éclairement.Nous proposons une nouvelle méthode d’illumination nommée ASTER (Adaptable Scanning for Tunable Excitation Regions), capable de délivrer une illumination modulable et uniforme, et compatible avec les méthodes de sectionnement optique classiques. Nous l’appliquons en premier lieu à la microscopie de fluorescence où nous montrons sa compatibilité avec l’imagerie d’échantillons vivants. Ensuite, dans le contexte de l’imagerie SMLM nous démontrons l’obtention de résolutions uniformes, mais également l’impact sur d’autres paramètres et possibilités d’acquisitions. Ainsi ASTER permet de réduire le fond ambiant, d’imager des champs larges de 200x200µm² ou de réaliser une image SMLM sur l’ordre de quelques minutes.Nous présentons ensuite le bénéfice du couplage d’ASTER avec l’imagerie 3D, et une méthode d’imagerie multi-couleur SMLM. Cette méthode quantifiée analytiquement permet d’obtenir des cross talk de l’ordre de 2%, nous montrons sont application à l’imagerie à deux et trois couleurs, ainsi qu’à l’imagerie 3D. Différentes pistes d’amélioration d’ASTER et de l’imagerie multi couleur sont ensuite proposées.
... The primary assembly defects of the laser-scanner system originate from the scanner, laser beam, and working plane [21]. However, as precision devices, the scanner and its supporting optical modules have good manufacturing precision, fine-tuning design [29], and include water cooling, which can avoid assembly defects caused by scanner and laser beam deviations. On the other hand, because of the initial assembly deviation, mechanical vibration, and thermal cycling of the build chamber, it was difficult to maintain the working plane determined by the scraper parallel to the galvo plane, as shown in Fig. 2f. ...
Multi-laser powder bed fusion (ML-PBF) adopts multiple laser-scanner systems to increase the build envelope and build speed, but its calibration is an iterative and time-consuming process. In particular, multiple large-scale scan fields have a complex distortion in the overlap area, challenging the calibration process. In this study, owing to the enormous workload and alignment problems in the calibration of multiple scan fields, a novel calibration system is designed in this study to realize in situ auto-detection of numerous laser spots in the build chamber to ensure high efficiency and accuracy. Moreover, because the detectable area could not cover the entire build area and the detection data still contained errors, a virtual laser-scanner system was established by identifying the assembly defects and galvo nonlinearities of the ML-PBF system from the detection data, which served as the system's controller to improve calibration accuracy. The multi-field alignment error was less than 0.012%, which could avoid the intersection and separation of scan paths in multi-laser scanning and therefore meet the requirements for high-precision ML-PBF. Finally, the reliability of the method was verified theoretically using principal component analysis.
... Essentially, a GS system that works in closed-loop is a DC motor with a mirror mounted on its shaft and equipped with a detector of its current angular position, as well as a servo-ampli¯er. Various types of such characteristic components are presented in the literature, 1,11,19 as well as testing techniques of the GSs. 20 The signal from the position detector is compared to the reference signal and the servo-ampli¯er generates an appropriate control algorithm in order to minimize the steady-state error. ...
... Specifically, the scanning mirror that deflects the laser beam follows a periodic sawtooth or triangular trajectory at a designated high frequency to perform raster scans. Thus, galvanometer scanners are designed for high-speed laser scanning applications, in which the scanning mirror is driven by the galvanometer mechanism (Aylward, 2003). Tracking performance of the galvanometer scanner in terms of scanning bandwidth and positioning error determines the temporal and spatial resolution of the imaging system (Yoo, Ito, & Schitter, 2016). ...
Data-driven repetitive control (RC) is proposed in this work to track online, dynamical raster trajectories in galvanometer-based scanning. To remove the requirement of a plant model in conventional model-based RC, we use model-free iterative learning control (ILC) to synthesize the data-driven repetitive controllers. Specifically, the frequency-domain plant-inversion and loop-shaping methods are both converted into time-domain trajectory tracking problems. The ILC is then applied to solve the trajectory tracking problems and subsequently derive the repetitive controllers from data. The stability conditions of both methods are analyzed and used to guide the data-driven control design. Experimental results on a commercially available galvanometer scanner demonstrate that the proposed methods improve the tracking error of a predefined raster scan by more than 30 times, as the conventional ILC does. Moreover, after applying data-driven RC, users can online assign various center positions and magnitudes of the raster trajectory. Once assigning a new reference in this continuous mode, the tracking error rapidly converges to the steady-state within ten periods.
... [5] Lidar is a laser beam as a new detection signal active modern optical remote sensing system, [6] compared with the traditional radar operating frequency band, optical band of shorter wavelengths, which can greatly improve the radar distance resolution, angular resolution, velocity resolution, [7] and thanks to the laser's high directionality, high monochromatic, and high coherence, have the advantage of achieving high accuracy, anti-interference ability, and small volume. [8,9] Lidar scanning technology is an important development direction in the laser radar application market, [10] and X-Y galvanometer scanning technology has the advantages of small moment of inertia, fast response, small size, highprecision real-time drive control, and non-contact. [11] It can meet the requirements of the laser radar scanning system for the scanner. ...
Aiming at the problem of scanning distortion in X – Y galvanometer light detecting and ranging (Lidar) scanning system, we propose a method of image scanning distortion correction with controllable driving voltage compensation. Firstly, the geometrical optics vectors model is established to explain the principle of pincushion distortion in the galvanometer scanning system, and the simulation result of scanning trajectory is consistent with experiments. The linear relationship between the driving voltage and the scanning angle of the galvanometer is verified. Secondly, the relationship between the deflection angle of the galvanometer and the scanning trajectory and the driving voltage is deduced respectively, and an image scanning correction algorithm with controllable driving voltage compensation is obtained. The simulation experiment results of the proposed method show that the root-mean-square error (RMSE) and the corresponding curve between the scan value and the actual value at different distances, have a good correction effect for the pincushion distortion. Finally, the X – Y galvanometer scanning Lidar system is established to obtain undistorted two-dimensional scanned image and it can be applied to the three-dimensional Lidar scanning system in the actual experiments, which further demonstrates the feasibility and practicability of our method.
... The amount of rotation is determined by the current or voltage applied [6,7]. A galvo-scanner is composed of a small coil of wire wound on an armature that is suspended in the gap of a moving permanent magnetic field by means of pivots and bearings [2,8]. When the coil is flown by a current, it develops a magnetic field that acts against the static field in the gap, causing the coil to rotate [7]. ...
Galvo scanners are popular devices for fast transversal scanning. A triangular signal is usually employed to drive galvo scanners at scanning rates close to the inverse of their response time where scanning deflection becomes a nonlinear function of applied voltage. To address this, the triangular signal is synthesized from several short ramps with different slopes. An optimization algorithm similar to a simulated annealing algorithm is used for finding the optimal signal shape to drive the galvo scanners. As a result, a significant reduction in the nonlinearity of the galvo scanning is obtained.
... In laser-systems, a focused laser beam is guided across the building area. A galvanometer scanner acts as control unit [17]. Depending on the galvanometer mirror-construction or the preliminary lensing de- sign, possible types are a 2D-galvanometer-, a 3D-galvanometer, and a polygon scanner [18]. ...
Lithography-based Additive Manufacturing Technologies (L-AMT) exploit the curing of photosensitive materials upon light exposure. We developed a hybrid exposure concept. This system is able to overcome the challenge of providing good surface qualities and excellent feature resolution as well as a throughput similar to dynamic mask-based L-AMT systems by combining two light sources. A Digital Light Processing (DLP®) Light Engine (LE) with a building area of 144 x 90 mm² offers a pixelsize of 56 μm. In order to further improve the achievable resolution, a continuous laser-exposed contour line (spot size 20 μm) on the outside of the projected envelope can be written with an additional scanning laser-system. The matching of the DLP® projection mask and the laser-contour is crucial for accurate printing. Therefore a calibration tool was developed, which facilitates the alignment of the two light sources. A dichroic coated mirror enables a perpendicular alignment of the DLP® light beam and the laser beam.
... The servo driver demodulates the position detector's signal, compare it with commanded position signal and then drive the actuator to bring the galvo mirrors to the desired position. 15 As stated for best performance in two-axis steered-beam systems, the two mirrors are positioned optically conjugate to each other by using a 4f relay system in between them. 16 A 4f relay system comprising of two lenses of focal length f image the plane P onto the plane P as shown in figure 2(a), so that any ray within the segment MN in plane P enters the segment M N in plane P , irrespective of the direction of the ray inside the relay system. ...
... Compared with the other scanning scanners, galvanometer optical scanner has the larger scan angle, higher efficiency, higher precision, and more compact structure. From the aspects of the existing scanning performance, it is one of the best laser scanning ways by now [1]. In a complex system, because of the controlled object's time-varying, nonlinear and uncertainty performance, the traditional PID control is always difficult to achieve good control effect. ...
A new method based on fuzzy self-adaptive PID for the galvanometer control system is presented. This method overcomes some defects of the traditional PID control, such as lower control precision and worse anti-jamming performance. At first, this paper analyzed the theory of galvanometer control system and established the mathematical model of the moving magnetic galvanometer motor. Then, the paper presented the design method of fuzzy self-adaptive PID controller in detail and using the simulation software to realize the system design. At last, the simulation results of PID control were compared with those of the Fuzzy-PID control method. The results show that the Fuzzy-PID control method has better dynamic and static performance, as well as anti-jamming performance.
... Essentially, a GS system that works in closed-loop is a DC motor with a mirror mounted on its shaft and equipped with a detector of its current angular position, as well as a servo-ampli¯er. Various types of such characteristic components are presented in the literature, 1,11,19 as well as testing techniques of the GSs. 20 The signal from the position detector is compared to the reference signal and the servo-ampli¯er generates an appropriate control algorithm in order to minimize the steady-state error. ...
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.
... Essentially, a GS system that works in closed-loop is a DC motor with a mirror mounted on its shaft and equipped with a detector of its current angular position, as well as a servo-ampli¯er. Various types of such characteristic components are presented in the literature, 1,11,19 as well as testing techniques of the GSs. 20 The signal from the position detector is compared to the reference signal and the servo-ampli¯er generates an appropriate control algorithm in order to minimize the steady-state error. ...
... DIC produces contrast by visually displaying the refractive index gradients of different areas of a specimen. Galvo [5] and resonant [6] scanners are presented on Figure 1. The first one may be used for rectangular area (line-by-line) scanning, line scanning or point scanning and for uncaging some drug (e.g. ...
This work represents the real steps to development and design advanced two-photon microscope by efforts of laboratory staff. Self-developed microscopy system provides possibility to service it and modify the structure of microscope depending on highly specialized experimental design and scientific goals. We are presenting here module-based microscopy system which provides an opportunity to looking for new applications of this setup depending on laboratories needs using with galvo and resonant scanners.
... Various optical actuators have been developed, and control methods suitable for various optical applications have been proposed [1,2]. Particularly, galvanometer mirrors used in such optical actuators offer a good balance of accuracy, speed, mobility, and cost [3][4][5]. In optical applications such as target tracking and drawing, scanning control that takes advantage of the speed and accuracy of galvanometer mirrors has been realized [6][7][8][9][10][11]. Hence, we are in the process of developing a real-time image capturing system [11] based on the motion of a galvanometer mirror including an internal proportional-integral-differential (PID) controller through the use of sine-wave scanning based on position control. ...
We propose a method to achieve precise sine-wave path tracking for real-time motion-blur compensation to extend the corresponding frequency spectrum in proportional-integral-differential (PID) control by using a pre-emphasis technique. We calculate pre-emphasis coefficients in advance to follow a sine wave with a gain of 0 dB and multiply the input signal by these pre-emphasis coefficients. In experiments, we were thus able to extend the greatest frequency from 100 to 500 Hz and achieve gain improvement of approximately 3 dB at 400 and 500 Hz. For the application of inspection, we confirmed that motion blur is significantly reduced when the system operates at high frequency, and we achieved a responsiveness 3.3 times higher than that of our previous system.
... 6 The galvanometric scanner, also known as galvo, is a popular optical scanning device based on permanent magnetic motor principles and a resonant galvo typically has a maximal rotating frequency of 8 KHz. 7 Besides its applications in real-time and in vivo tissue imaging, LSM is also useful in examining ex vivo samples for potential disease biomarkers. To explicitly characterize tissue, cellular morphology needs to be correlated with the underlying chemical composition, which requires spectra (fluorescence and/or Raman) to be acquired by allowing the excitation laser to dwell at focus points for a specified time period. ...
To simplify imaging focusing and calibration tasks, a laser-scanning microscope needs to scan ata moderate frame rate. The inertia of a galvanometric scanner leads to time delays when following external commands, which subsequently introduces image distortions that deteriorate as scan frequency increases. Sinusoidal and triangular waveforms were examined as fast axis driving patterns. The interplay among driving pattern, frequency, sampling rate, phase shift, linear scanning range, and their effect on reconstructed images was discussed. Utilizing position feedback from the linear galvo scanners, the effect of response time could be automatically compensated in real time. Precompensated triangular driving waveform offered the least amount of image distortion.
... Galvoscanners (GSs) are the most used devices nowadays for lateral scanning in biomedical imaging. Their technology is mature [11] in terms of construction, control, and testing [26][27][28][29]. One of their main advantages is the fact that the incoming laser beam can be incident on the mirror in its pivot -which is not the case for the PMs. ...
We review some of the most important scanning systems that are competitive in high-end biomedical imaging applications such as Optical Coherence Tomography (OCT), but also Confocal Microscopy (CM) or multiphoton microscopy. Both 1-D (uni-dimensional) and 2-D (bi-dimensional) scanning systems are considered. The paper discusses different scanners, including polygon mirror, galvanometer-based and Risley prisms. Their configurations and characteristics, as well some of our contributions in the domain are presented. The tendency of applying them into special designs such as handheld scanning probes and endoscopes - the latter with MEMS (Micro-Electro-Mechanical Systems) and micro-systems is pointed out. A discussion on further advancements of scanning technology in biomedical applications in general and in OCT in particular concludes the study.
... Essentially, a GS system that works in closed-loop is a DC motor with a mirror mounted on its shaft and equipped with a detector of its current angular position, as well as a servo-ampli¯er. Various types of such characteristic components are presented in the literature, 1,11,19 as well as testing techniques of the GSs. 20 The signal from the position detector is compared to the reference signal and the servo-ampli¯er generates an appropriate control algorithm in order to minimize the steady-state error. ...
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.
... Essentially, a GS system that works in closed-loop is a DC motor with a mirror mounted on its shaft and equipped with a detector of its current angular position, as well as a servo-ampli¯er. Various types of such characteristic components are presented in the literature, 1,11,19 as well as testing techniques of the GSs. 20 The signal from the position detector is compared to the reference signal and the servo-ampli¯er generates an appropriate control algorithm in order to minimize the steady-state error. ...
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 Matlab Simulink to validate the theoretical model. With the identified 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.
In the last Chapter, we introduced a general configuration for a holographic display system. In holographic display systems, the key technology is how to implement a hologram display with high space-bandwidth-product capability. In this Chapter, we will introduce an efficient approach using a coarse integral hologram display structure (i.e., CIH) to achieve high space bandwidth products. CIH displays aim to overcome the limitations of current SLMs in rendering 3D holographic videos. Various methods, including static and dynamic CIH, as well as full bandwidth CIH, have been proposed to achieve a large FOV. Spatial tiling is utilized to enhance the hologram size in the horizontal direction. Ongoing research focuses on the seamless integration of multiple CIH displays and exploring interactive hologram display methods, optimized rendering algorithms, high-speed data delivery, and large-scale holographic displays.
Galvanometer is a critical component for beam steering in additive manufacturing, profilometry, and medical imaging. In these applications, the quality of the process relies on the precision motion control of the galvanometer to either track or reject narrow-band signals. From the internal model principle, this can be accomplished by incorporating the dynamic model of the reference or disturbance signal in the feedback loop. This paper proposes an innovative internal model principle controller based on numerically robust all-pass filters. The main concept revolves around converting the controller design into a phase response design problem with all-pass filters. For the proposed approach, the targeted frequencies of the internal model can be arbitrarily placed without sacrificing the performance. Further, it produces lower-order controller and is robust against quantization effect. When combining with frequency estimation algorithm and adaptive filter, it can be readily applied to unknown and time-varying disturbance rejection. The advantages of the proposed method are demonstrated by comparing with conventional approaches through analysis, simulation, and experimentation.
Multiphoton lithography inside a mesoporous host can create optical components with continuously tunable refractive indices in three-dimensional (3D) space. However, the process is very sensitive at exposure doses near the photoresist threshold, leading previous work to reliably achieve only a fraction of the available refractive index range for a given material system. Here, we present a method for greatly enhancing the uniformity of the subsurface micro-optics, increasing the reliable index range from 0.12 (in prior work) to 0.37 and decreasing the standard deviation (SD) at threshold from 0.13 to 0.0021. Three modifications to the previous method enable higher uniformity in all three spatial dimensions: (1) calibrating the planar write field of mirror galvanometers using a spatially varying optical transmission function which corrects for large-scale optical aberrations; (2) periodically relocating the piezoelectrically driven stage, termed piezo-galvo dithering, to reduce small-scale errors in writing; and (3) enforcing a constant time between each lateral cross section to reduce variation across all writing depths. With this new method, accurate fabrication of optics of any index between n = 1.20 and 1.57 (SD < 0.012 across the full range) was achieved inside a volume of porous silica. We demonstrate the importance of this increased accuracy and precision by fabricating and characterizing calibrated two-dimensional (2D) line gratings and flat gradient index lenses with significantly better performance than the corresponding control devices. As a visual representation, the University of Illinois logo made with 2D line gratings shows significant improvement in its color uniformity across its width.
One of the main visualization method in neuroscience is two-photon microscopy. However, scientists need to upgrade their microscopy system so regular because they are interested to get more specific data. Also this is due to the fact that this technique allows to obtain 3D images of tissues due to laser focus change, that is possible due to substantially greater penetration depth on the main wavelength into biological tissues. Self-developed microscopy system allow to modify the construction of microscope in not-complicated manner depending on specialized experimental models and scientific tasks. This work is small attempt to help researchers who are interested to build their own two-photon laser scanning microscope for using in neuroscience. The work was performed with financial support of the government represented by the Ministry of Education and Science of the Russian Federation, the unique identifier of the project is RFMEFI57814X0079, the agreement on granting a subsidy №14.578.21.0079 dated 28.11.2014.
In this article, we report on a high-bandwidth large-aperture fast steering mirror (FSM) actuated by piezoelectric actuators (PEAs) for laser beam machining and a control strategy to achieve high bandwidth and precision tracking control. To simultaneously achieve high bandwidth and a large aperture, we used a low-density and high-rigidity 50-mm round mirror to ensure sufficient stiffness and to minimize the moment of inertia. Also, the overall structure of the moving part in the FSM was simplified to further reduce the moment of inertia. Based on modal analysis, and taking into account the conflicting requirements for the natural frequency and the stroke, the thickness of the base plate used to provide the preload force to the PEAs and to transmit motion to the mirror was determined. Moreover, to achieve high bandwidth and precision tracking control, we propose an integrated control solution, in which an inner digital charge control (DCC) loop is used to eliminate hysteresis, an outer displacement loop with a design based on pole-zero cancellation and loop shaping is introduced to eliminate resonance, and feedforward compensation is applied to reduce the phase lag. The feasibility of an FSM with this control solution was validated by experiments. A bandwidth of 10 kHz with a resolution of less than 0.3 μrad can be achieved for the FSM. Moreover, precision tracking with a maximum radius error of less than 2.2 μrad below 2 kHz for a circular trajectory at a radius of 25 μrad can be realized.
This paper presents a scanning system that integrates a chromatic confocal displacement sensor for topography measurement of a surface. To take an advantage of its compactness and reliability, an off-the-shelf chromatic confocal displacement sensor is integrated. Instead of moving the sensor, a galvanometer scanner reflects the optical point to increase the scan speed, and fast and accurate scanning motion is realized by learning without a model. The resulting images are corrected based on a geometric model to compensate for image distortion.
Optical image generation is a very important step in many optical imaging system applications. However, current optical image generation systems (OIGS) produce a fixed simple grid image with a small field of view (FOV) because of the physical limitation of the OIGS itself. Here, we use proposed an optical image generation method using optical scanners to achieve a large FOV and images defined by the user. The combination of two scanners implements the two-dimensional optical scanning for obtaining the improvement of field-of-views (FOV) in two-dimensional (2D) directions. Here, three important findings, including scanning optical configurations, an analog-to-digital-based scanning pattern, and a scanning imaging model, of 2D optical scanning in the image generation with a large field of view are reported. The proposed method can improve the FOV with 20° in the 2D directions. These three results are very valuable references for the application of image generation. The proposed method has potential applications in multiple fields, such as camera calibration, computation imaging, and image compression.
This paper presents the design and evaluation of a high-bandwidth fast steering mirror (FSM) driven by a piezoelectric actuator (PEA) for applications in the scanning systems. To avoid additional dynamics induced by flexure hinges and to simplify the structure of the FSM, a preload force mechanism based on permanent magnets (PMs) is proposed. Actuators and sensors that can satisfy the required flatness and bandwidth are chosen, and the designs of the mirror and the preload force mechanism are completed with the aid of finite element analysis. A simple system model and controller design are achieved by analyzing the voltage transformation and the relationships between different displacements. To verify the feasibility of the design and evaluate the performance of the FSM, a series of experiments was carried out with voltage control, charge control, and charge plus notch filter control. The final experimental results show that the FSM reaches a high bandwidth of 8 kHz with charge plus notch filter control, demonstrating that design of an FSM with a PM preload force mechanism is feasible.
An efficient method to implement the coarse integral holographic (CIH) concept for dynamic CIH displays is to scan the information generated from a spatial light modulator (SLM) of a low space bandwidth product (SBP) but high bandwidth to form the hologram array for the integral optics. Previously, just over half of the SLMs bandwidth was utilized due to the fact that the galvanometer scanner in use could not tile all the holograms that the SLM is capable to produce, resulting in the loss of nearly half of the field of view (FOV). Here, we propose a full bandwidth dynamic CIH display using a large resonant scanner in conjunction with a hybrid raster scanner, which can utilize the full bandwidth of the spatial light modulator and double the horizontal FOV. Experimental results confirm that with the SLM and scanners as used, the FOV can reach 48° when the SLM reaches its full bandwidth. This approach can be used for future scalable and tileable CIH display systems.
Today one of the main areas of application of two-photon microscopy is biology. This is due to the fact that this technique allows to obtain 3D images of tissues due to laser focus change, that is possible due to substantially greater penetration depth on the main wavelength into biological tissues. Self-developed microscopy system provides possibility to service it and modify the structure of microscope depending on highly specialized experimental design and scientific goals. This article may be regarded as a quick reference to laboratory staff who are wishing to develop their own microscopy system for self-service and modernization of the system and in order to save the lab budget.
We present the handheld scanning probes that we have recently developed in our current project for biomedical imaging in general and for Optical Coherence Tomography (OCT) in particular. OCT is an established, but dynamic imagistic technique based on laser interferometry, which offers micrometer resolutions and millimeters penetration depths. With regard to existing devices, the newly developed handheld probes are simple, light and relatively low cost. Their design is described in detail to allow for the reproduction in any lab, including for educational purposes. Two probes are constructed almost entirely from off-the-shelf components, while a third, final variant is constructed with dedicated components, in an ergonomic design. The handheld probes have uni-dimensional (1D) galvanometer scanners therefore they achieve transversal sections through the biological sample investigated - in contrast to handheld probes equipped with bi-dimensional (2D) scanners that can also achieve volumetric (3D) reconstructions of the samples. These latter handheld probes are therefore also discussed, as well as the possibility to equip them with galvanometer 2D scanners or with Risley prisms. For galvanometer scanners the optimal scanning functions studied in a series of previous works are pointed out; these functions offer a higher temporal efficiency/duty cycle of the scanning process, as well as artifact-free OCT images. The testing of the handheld scanning probes in dental applications is presented, for metal ceramic
prosthesis and for teeth.
In ultrashort pulsed (USP) laser micro-processing several optical and optomechanical components are needed to enable the desired process. Besides the USP laser itself, systems to guide and focus the laser beam are mandatory in almost all applications. Furthermore beam profile shaping
, e.g. the creation of top-hat or super-Gaussian beam profiles, results in beneficial effects for many applications, such as increased efficiency and superior quality. In this chapter an overview of both established and up-to-date technologies regarding beam guiding
, focal position shifting
and beam profile shaping will be presented. For beam guidance and focal position shifting comparable key parameters will be stated to enable easy comparability. As an outlook on probable future applications, both temporal and spatial polarization profile shaping will be presented.
A micromirror driven by electrostatic actuation methods requires high actuation voltage supplied by a high voltage amplifier and suffers from the pull-in phenomenon that limits an operation range of a micromirror to 44 % of its maximum angular displacement. To provide practical solutions to this high actuation voltage and a limited operation range, we present complete analytical and numerical models of a micromirror coupled with resonant drive circuits that enable us to actuate a micromirror at much lower supply voltage than that of conventional voltage control circuits. The presented work also facilitates the stability analysis of a micromirror coupled with a resonant drive circuit and provides how a parasitic capacitance of a micromirror and a quality factor of a resonant drive circuit affect an operation range of a micromirror. Furthermore, we present a new method of an angular displacement measurement of a micromirror by sensing the phase delay of an actuation voltage with reference to an input voltage.
A laser light scanning device consisting of an electronically driven mechanically resonant torsional spring-mirror system was developed for display applications. The original design suffers fatigue failure due to the repeated rotation of the torsional spring. The torsional spring design is investigated and analyzed to attain the lowest possible stress level while maintaining a constant reso-nant frequency. The finite element analysis model of the torsional spring was created and the stress was minimized by changing the geometrical parameters of the spring. Spring geometric optimiza-tion resulted in a maximum stress of 0.632 GPa, that is 12% reduction in stress from the original design, which should give an extended life span of 1 month for the intended application.
The control system of scanning motor is studied. The method to control the scanning motor with a single neuron self-adaptive PID controller to counter the disadvantage of analogue PID controller is discussed. The structure of control system and the method about how to implement the single neuron self-adaptive PID controller is designed. The simulation experiment results show that it not only satisfies the requirement of stabilization and accuracy, but also has the characteristic of rapid response, strong anti-jamming and better robustness.
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