Elevation Axis Research Articles

Analysis and design of PI-based controllers for the axes of European Solar Telescope

European Solar Telescope (EST) represents the largest European research infrastructure projected in the field of solar astrophysics. It is a 4-meter class solar telescope currently in the design phase. Within this phase, an essential objective is to analyze the control strategy of the telescope axes to achieve an accurate sun trajectory tracking. This paper presents a cascade control scheme based on proportional-integral (PI) controllers specifically designed for the elevation and azimuth axes of EST. The control strategy, which employs nested position-velocity loops, is devised to adeptly track the sun’s trajectory while mitigating wind impact. The controller tuning adheres to criteria of relative stability margins and bandwidth constraints using the state-space representation derived from Finite Element Model of the EST structure. An end-to-end dynamics model has been proposed to evaluate the performance of the control strategy during a ten-minute simulation. Results evidenced the convenience of the proposed controllers, highlighting wind as the main source of the control error (0.78 arcsec and 0.14 arcsec in azimuth and elevation axes, respectively) compared to the sun tracking error. Future control strategy enhancements should target the reduction of wind-induced effects to meet stringent image stability requirements.

2–Bit Programmable Metasurface for Low Radar Cross Section Antenna and Beam Steering Applications

AbstractIn this paper, a 2‐bit water‐based programmable digital metasurface for beam steering and backscatter field reduction applications is presented, a reflective and transmissive type water based programmable metasurface (WPMS) for RCS reduction and the antenna's beam steering is suggested, respectively. It has been demonstrated that a 2‐bit water‐based programmable unit cell can reduce RCS by changing its state (0/1). If the unit cell channel is empty, the state is “0,” if the channel is filled, the state is “1.” So at different resonance frequencies, the four phase and reflection coefficient responses are achieved as "00"01"10"11". This functionality enables beam steering in both the elevation and azimuth axis and also backscattering reduction of the antenna. Furthermore, the impacts of the number of unit cells and reflection phase states on the far‐field pattern are examined. Beam steering of ±45° in the elevation is attained with 10‐dB impedance bandwidth of 4.25–4.40 GHz, radiation gain of more than 7.1 dBi is maintained. With the present antenna, it is possible to achieve volumetric beamsteering performance directly. The patterns of far‐field radiation that are predicted theoretically coincide well with full waves simulations. As such, the proposed prototype can be a good option for applications that require a low RCS platform including beam steering in radars, 5G/6G, etc.

Multi-Elevations Upward Continuation Method to Depth Detection of the Main Crustal Layers in Western Desert of Iraq

The upward continuation technique was applied to the gravity and RTP magnetic data to obtain the residual anomalies maps in the western part of Iraq. Twelve upward elevation residual gravity maps and another twelve upward elevation residual RTP magnetic were determined using the same twelve upward continuation elevations. The applied upward elevations range from 1000 to 55000 m. The total range of the residual anomalies maps (Color Bar range) of gravity and RTP magnetic were plotted against the upward elevations. Five segments and four intersection points were obtained for the gravity and magnetic data. The trace of these intersection points on the upward elevation axis approximately indicate the following values 4.4-5, 12.8-13.5, 27-24, and 39-39.6 km. These values may indicate the depth of the following layer boundaries, the Burj Formation ( Mid-Cambrian), basement, mid layer in the basement rocks, and the Moho depth. The authors believe it is possible to apply the upward continuation to find the main layers which show abrupt change in the physical properties

SAT273 Characterizing The Diurnal Rhythm And Duration Of Adrenal Suppression Following Weeklong Corticosterone Treatment And Withdrawal

Abstract Disclosure: C.N. Snyder: None. J.L. Spencer-Segal: None. Exogenous or endogenous glucocorticoid can create a dependence on glucocorticoid excess that manifests as a withdrawal syndrome during attempted taper. The etiology of this syndrome is unclear, and mechanistic understanding is hampered by the lack of a suitable mouse model. Here we present results from one attempt to define a suitable mouse model of chronic glucocorticoid excess and withdrawal. Male mice were treated with corticosterone (45μg/mL) in 1% ethanol in the drinking water for one week prior to withdrawal to a lower dose (10μg/mL) or complete withdrawal (vehicle). Control groups received vehicle or corticosterone 45μg/mL without withdrawal. Tail vein blood samples were collected from mice numerous times during the withdrawal and plasma levels of corticosterone were measured using an Enzyme Immunoassay (Arbor Assays) to determine circulating levels of corticosterone achieved at the diurnal peak and trough during treatment and withdrawal. There were three main goals of this study: (1) measure the circulating levels of corticosterone achieved at the peak and trough using this treatment paradigm (2) determine if 10μg/mL was a physiologic dose during the withdrawal period, and (3) to determine the duration of HPA axis suppression. Results showed that the diurnal rhythm of corticosterone in the treated mice was the opposite of control such that corticosterone levels were high in the morning and low in the evening. Corticosterone levels returned to control levels within 24 hours of withdrawal to 10μg/mL. When withdrawn completely, corticosterone levels decrease below control levels twenty-four hours into the withdrawal but begin to return to baseline by seventy-two hours post-withdrawal indicating rapid recovery of the endogenous HPA axis. This shows that providing corticosterone to mice in the drinking water alters the diurnal peak and trough of circulating corticosterone without continuous corticosterone elevation or prolonged HPA axis suppression. This disruption of the diurnal peak and trough should be considered in the interpretation of studies using chronic corticosterone in the drinking water. Further, this model may not be suitable for studying glucocorticoid withdrawal from chronic excess as the level of corticosterone drops below control at time points in this treatment model. Presentation: Saturday, June 17, 2023

Influences of tracking and installation errors on the optical performance of a parabolic trough collector with heat pipe evacuated tube

In this study, the parabolic trough collector with heat pipe evacuated tube is used as the research object. Using the ray tracing method, this study analyzes the effect of tracking error of azimuth-elevation axis and receiver installation error on the optical performance of the collector. A test bench for the azimuth-elevation axis manual tracking device of the parabolic trough concentrator was designed and built, and the heat flux distribution at the focal plane was measured. The optical simulation results were compared with the test results to verify their accuracy, and the maximum relative error was 2.69%. The simulation results were compared with those calculated in the literature, and the maximum error was 16.23%. Simulation results show that the circumferential heat flux of the receiver is still symmetrically distributed when longitudinal incidence angles and vertical installation errors were found. The symmetry disappeared when transverse incidence angles and horizontal installation errors were found. As the tracking error of the elevation axis increases, the optical efficiency of the collector decreases, and the length of the end loss increases. For the collector in this study, the azimuth axis tracking error is less than 1.5° and the elevation axis tracking error is less than 6°, which can ensure high optical efficiency. The vertical installation error of the receiver was |Δz| <17 mm, the horizontal installation error was |Δx| < 20 mm, and the optical efficiency of the collector remained unchanged. The calculation method and results in this study can provide theoretical support for selecting an automatic tracking system with reasonable tracking accuracy and determining the allowable installation errors for the parabolic trough collector with heat pipe evacuated tube, and can also provide detailed thermal boundary conditions for the subsequent research of heat transfer performance of the receiver, which has great theoretical value.

L 1 Minimization with Perturbation for Off-grid Tomographic SAR Imaging

Synthetic Aperture Radar (SAR) Tomography (TomoSAR) is a novel technique that enables three-Dimensional (3-D) imaging using multi-baseline two-Dimensional (2-D) data. The essence of TomoSAR is actually to solve a one-dimensional spectral estimation problem. Compressed Sensing-based (CS) algorithm can retrieve solutions with only a few non-uniform acquisitions and has gradually become the main imaging method. In the conventional processing flow of CS algorithms, the continuous elevation direction is divided into a pre-set grid, and the targets are assumed to be exactly on the grid. \begin{document}$ {{L}}_{1} $\end{document} minimization has been proven to be effective in TomoSAR imaging. In the conventional processing flow, the continuous elevation axis is divided into fixed grids, and scatters are assumed to be exactly on the pre-set grid. However, this hypothesis is generally untenable, and will lead to a problem called “Basis Mismatch”, which is rarely discussed in TomoSAR. In this letter, we first discuss the model of Off-grid TomoSAR, and then propose an addictive perturbation model to compensate for the errors caused by the grid effect. We utilize the local optimization thresholding algorithm to solve the complex-valued \begin{document}$ {{L}}_{1} $\end{document} minimization problem of TomoSAR. We conducted experiments both on simulation data and actual airborne flight data. Our simulation results indicate that the proposed method can estimate a more accurate position of scatters, which leads to better original signal recovery. The reconstruction results of actual data verify that the impact of grid mismatch can be mostly eliminated.

Clinical Outcomes of Laser Asymmetric Keratectomy to Manage Postoperative Adverse Effects–A Retrospective Clinical Trial

Background: Laser asymmetric keratectomy reduces the regional asymmetry of corneal thickness. Objective: We aimed to describe the clinical outcomes of laser asymmetric keratectomy keratectomy with laser refractive surgery performed to resolve the adverse effects following ophthalmic surgeries. Methods: We compared the preoperative and postoperative outcomes and complaints of blurring after performing laser asymmetric keratectomy with laser refractive surgery in 24 eyes of 16 patients with a deviation sum in corneal thickness in four directions &gt;80 µm. Laser asymmetric keratectomy with laser refractive surgery, with full integration of the Vision Up software, was used to analyze the corneal thickness deviation, employed selective laser ablation to create central symmetry on the thicker cornea to reduce regional asymmetry of corneal thickness, simultaneously correcting the refractive power and myopic shift. The pre-and postoperative clinical and topographic findings were analyzed. Results: The patients’ age was 37.57±22.30 (range, 23–65) years. The follow-up period was 16.56±3.23 months. The spherical equivalent (p=0.026), sphere (p=0.022), uncorrected distance visual acuity (LogMAR, p=0.045), blurring score (p=0.000), central corneal thickness (p=0.024), sum of deviations in corneal thickness in four directions (p=0.02), distance between the maximum posterior elevation and visual axis (p=0.04), and kappa angle (p=0.031), significantly decreased postoperatively. The efficiency and safety indices were 0.96±0.11 and 1.00, respectively. There was no myopic regression or blurred vision postoperatively. Conclusion: Performing laser asymmetric keratectomy with laser refractive surgery improved corneal symmetry and visual acuity and reduced blurring.

Feedback-linearization based robust relatively optimal trajectory tracking controller for 3-DOF helicopter

This paper proposes a feedback linearization-based robust trajectory tracking controller for the elevation and pitch axes of three degrees of freedom (3-DOF) helicopter. The 3-DOF helicopter is a benchmark system that operates on the same principle of operation as that of a tandem-rotor helicopter. Accurate control of this laboratory set up in the presence of external disturbances is a sophisticated problem as it is easily affected by external disturbances due to its low weight. Hence, to ensure efficient trajectory tracking performance in the presence of uncertainties and disturbances a nonlinear disturbance observer is integrated with a feedback linearization (FL) based relatively optimal trajectory tracking controller (ROTTC). Feedback linearization of the nonlinear model results in a decoupled linear error dynamics for each axis, which is used for the design of the ROTTC. The stability of the 3-DOF helicopter in the presence of estimation error and parameter uncertainties is analyzed using the Lyapunov method. A comparison study with an FL-based robust linear quadratic regulator (RLQR) method illustrates the superiority of the proposed method in terms of tracking error and disturbance estimation. The efficacy of the proposed controller to accommodate external disturbances is demonstrated with real-time implementation on the 3-DOF helicopter with a strong wind disturbance as well as an impulse disturbance.

Effect of the shafting nonorthogonal error on the tracking performance of solar dish concentrator system

A solar dish concentrator (SDC) system accurately tracks the sun using a dual-axis tracking device to achieve efficient heat utilization. However, the tracking performance and optical performance of an SDC system are significantly reduced by shafting nonorthogonal errors between the elevation axis and azimuth axis of the double-axis tracking device and the focal axis of the parabolic dish concentrator occurring during installation. In this paper, a tracking performance model of an SDC system is established based on the rigid body motion theory; the model considers the nonorthogonal errors between the elevation axis, azimuth axis, and focal axis. The radial angle and tangential angle are used to describe the deviation error of each axis from its ideal position. A virtual motion model of the SDC system with the nonorthogonal errors is established in the Solidworks 2014 software to verify the accuracy of the mathematical model. The influences of the nonorthogonal errors (single-factor error and overall error) on the tracking accuracy and comprehensive tracking performance of the SDC system are analyzed in detail. The results show that the tracking errors (single-factor error and overall error) of the SDC system increase and the tracking performance decreases as the radial angle error increases. When the radial angle error is the same and the axis vector changes (ie, the size of the tangential angle), the tracking performance of the SDC system improves. The focal axis error has the largest influence on the tracking performance of the system, followed by the azimuth axis error and the elevation axis error. The tracking performance of the SDC system is better when the azimuth axis is biased toward the south and north than toward the east and west and for elevation axis errors in the horizontal plane than the vertical plane. This work can provide a theoretical basis for the installation, debugging, and error control of solar concentrating systems with a double-axis drive.

Influence of Spawning Ground Dynamics on the Long-Term Abundance of Japanese Flying Squid (Todarodes pacificus) Winter Cohort

Japanese flying squid (Todarodes pacificus) is one of the most commercially important resources in the Pacific Ocean and its abundance is largely affected by environmental conditions. We examined the influence of environmental factors in potential spawning grounds of the winter cohort, approximated from Japanese and South Korean catch and catch per unit effort (CPUE) data of Japanese flying squid. Annual spawning ground dynamics were constructed using sea surface temperature (SST), submarine elevation and mean Kuroshio axis data from 1979 to 2018. Based on these information, we generated a suite of spawning ground indices including suitability SST-weighted area of potential spawning ground (SSWA), mean values (January–April) of suitable SST (MVSS), and the meridional position (MP) of SST isolines (18–24°C). Comparable interannual-decadal variability patterns were detected between the squid abundance and spawning ground indices, with abrupt shifts around 1990/1991 and in recent decades. In particular, the Pacific Decadal Oscillation is negatively correlated with spawning ground indices, suggesting its role in regulating the environmental dynamics in the area. Further, the gradient forest model underpinned the importance of SSWA, SSWA_Lag1 and MVSS_Lag1 on squid abundance. The CPUE is also shown to be a better abundance index than the annual catch in modeling the species’ response to environmental variability in its spawning grounds. Our findings suggest that it is imperative to pay more and timely attention to the relationship between the abundance of Japanese flying squid and environmental changes, especially under adverse environmental conditions.

Development of a low-cost six-axis alignment instrument for flexible 2D and 3D ultrasonic probes.

BACKGROUND: The pulse-echo test is used to evaluate the performance of ultrasonic probes before manufacturing ultrasonic systems. However, commercial alignment instruments are very large and use complex programs with long operation times.OBJECTIVE: To develop a low-cost alignment instrument used in the pulse-echo test for evaluating the performance of various 2D and 3D ultrasonic probes.METHODS: The developed alignment instrument can be aligned with the X, Y, Z, azimuth, elevation, and tilt axes with manual structure to support mounting fixtures that hold 2D and 3D ultrasonic probes. Each axis has a manual lever and is designed to have no movement when fixed. In particular, tilt and azimuth directions are designed to move more than 5 left and right.RESULTS: The probe mounted in the X, Y, and Z axes can move at above 50 mm. The probe mounted in the azimuth, elevation, and tilt axes can move more than 5 in the left and right directions. The pulse-echo test using commercial ultrasonic probes showed maximum error rate of less than 5%.CONCLUSIONS: Our developed alignment instrument can reduce costs by eliminating the need for shortening inspection times for probe manufacturers.

Detection of DG-islanding employing decision boundary of polarization ellipse parameters

This article presents a mathematical equations-based approach for islanding detection of distributed generations (DGs). To develop the proposed method, first, a set of mathematical expressions, characterizing the dynamics of electrical quantities during islanding situations, are selected; the quantities are: deviation of rotor angle, frequency and rate-of-change-of-frequency (RoCoF). Second, these electrical quantities are transformed into three-dimensional (3D) Polarization Ellipse (PE) domain, which yields five parameters, namely, azimuth, elevation, tilt angles, semi-minor and semi-major axes. Finally, an equation of decision boundary (DB) is developed to classify between the islanding events and non-islanding incidents. An extensive assessment of the proposed method is carried out considering the critical test cases which include surplus or shortage of real/reactive power mismatch situations that may exist during islanding. The presence of different load-types, with various quality factors, is also accounted for the test. A large number of islanding events and non-islanding disturbances, such as, capacitor switching, load switching, temporary faults, etc., are simulated in real-time using the model of a practical distribution network developed in Opal-RT digital platform. The proposed approach is critically assessed using F-measure technique and the assessment emphasize the selection of the method as a potential tool for detection of DG-islanding.

Comparison between Surgical Outcomes of LASIK with and without Laser Asymmetric Keratectomy to Avoid Conventional Laser Refractive Surgery Adverse Effects

This study compared one-year postoperative outcomes of laser refractive surgery combined with laser asymmetric keratectomy (LAK) and laser in situ keratomileusis (LASIK)for myopia correction in middle-aged patients (aged 40–49 years) with a total corneal thickness deviation (summed across four directions) ≥ 80 microns. The control group (n = 26; 52 eyes) underwent LASIK; the comparison group (n = 26; 52 eyes) underwent combined laser refractive surgery and LAK. Age, spherical equivalence, uncorrected visual acuity (near and far), corneal irregularity on the Orbscan map, sum of corneal thickness deviations in four directions, corneal thickness distribution, distance between the maximum posterior elevation (best-fit sphere; BFS) and visual axis, and postoperative blurring scores were analysed retrospectively between the groups. Both groups had similar preoperative findings. Postoperatively, the sum of corneal thickness deviations in four directions (p = 0.000), distance between maximum posterior elevation (BFS) and visual axis (p = 0.003),blurring score (p = 0.001), and corneal irregularity in the 3.0 and 5.0 mm zones on the Orbscan map (p = 0.033 and p < 0.0001, respectively) were significantly lower in the comparison group (p = 0.000). LAK reduced total corneal thickness deviation, improved corneal symmetry, and reduced blurring scores significantly, one-year postoperatively. LAK could resolve shortcomings of LASIK, producing better surgical outcomes.

The Seimei telescope project and technical developments

ABSTRACT An overview of the Seimei telescope, a 3.8 m optical infrared telescope located on Mt. Chikurinji in the Okayama prefecture of Japan, is presented. Seimei is a segmented-mirror telescope whose primary mirror consists of 18 petal-shaped segments. The telescope tube supporting the thin segmented mirrors is structurally incorporated within large arc-rails providing the elevation axis. The tube has a light-weight homologous structure designed with a genetic algorithm. The total weight of the telescope tube, including 1.4-ton optics, is only 8 tons. By virtue of its light weight, the telescope is able to point at an object anywhere in the observable sky within one minute. The telescope is operated by Kyoto University in collaboration with the National Astronomical Observatory of Japan (NAOJ). Half of the telescope time is used by Kyoto University. The remaining time is open to the Japanese astronomical community. NAOJ is responsible for the management of the open-use time, including handling of the observation proposals. The telescope is now regularly performing scientific observations on the basis of a variety of proposals.

Conformal antenna array radiation pattern synthesis by tilt correction to improve Direction-of-Arrival estimation accuracy

ABSTRACT This paper, considering the tilt effect, presents a hemispherical antenna structure modeled by an improved conformal antenna array with the maximum angular coverage of the elevation axis to increase the Direction-of-Arrival (DOA) estimation accuracy. For this purpose, a multiface conformal structure with 3 different tilts and 13 directive circular patch antennas is designed in the Full Wave Simulation Software (HFSS). By optimizing the angles α and β as two key parameters in this design, nine different structures are constructed and their impacts on the DOA performance are carefully studied. The Cramer–Rao Lower Bound (CRLB), Multiple Signal Classification (MUSIC), and Root Mean Square Error (RMSE) algorithms are utilized to evaluate all constructed structures and chose the most improved structure for DOA estimation. At the end, it is shown that the proposed hemispherical antenna structure has a better performance than previous conformal designs for DOA applications and spatial resource positioning in which the maximum elevation angle coverage by the antenna is highly required. It is noted that the tilt optimization method proposed in this paper can lead to design a near optimal conformal antenna array structure for DOA estimation for a wide elevation angle coverage which can be considered for next works.

Elevation, pitch and travel axis stabilization of 3DOF helicopter with hybrid control system by GA-LQR based PID controller

This research work presents an efficient hybrid control methodology through combining the traditional proportional-integral-derivative (PID) controller and linear quadratic regulator (LQR) optimal controlher. The proposed hybrid control approach is adopted to design three degree of freedom (3DOF) stabilizing system for helicopter. The gain parameters of the classic PID controller are determined using the elements of the LQR feedback gain matrix. The dynamic behaviour of the LQR based PID controller, is modeled and the formulated in state space form to enable utlizing state feedback controller technique. The performance of the proposed LQR based LQR controller is improved by using Genetic Algorithm optimization method which are adopted to obtain optimum values for LQR controller gain parameters. The LQR-PID hybrid controller is simulated using Matlab environment and its performance is evaluated based on rise time, settling time, overshoot and steady state error parameters to validate the proposed 3DOF helicopter balancing system. Based on GA tuning approach, the simulation results suggest that the hybrid LQR-PID controller can be effectively adopted to stabilize the 3DOF helicopter system.

Hinge and overturning moments due to unsteady heliostat pressure distributions in a turbulent atmospheric boundary layer

Non-uniform pressure distributions on the heliostat surface due to turbulence in the atmospheric boundary layer (ABL) have a significant impact on the maximum bending moments about the hinge of and pedestal base of a conventional pedestal-mounted heliostat. This paper correlates the movement of the centre of pressure due to the mean and peak pressure distributions with the hinge and overturning moment coefficients using high-frequency pressure and force measurements on a scale-model heliostat within two simulated ABLs generated in a wind tunnel. The positions of the centre of pressure were calculated for a range of heliostat elevation-azimuth configurations using a similar analogy to those in ASCE 7-02 for monoslope-roof buildings, ASCE 7-16 for rooftop solar panels, and in the literature on flat plates. It was found that the maximum hinge moment is strongly correlated to the centre of pressure movement from the heliostat central elevation axis. Application of stow and operating load coefficients to a full-scale 36 m2 heliostat showed that the maximum hinge moment remains below the stow hinge moment at maximum operating design gust wind speeds of 29 m/s in a suburban terrain and 33 m/s in a desert terrain. The operating hinge moments at elevation angles above 45° are less than 60% of the stow loads with a constant 40 m/s design wind speed. The results in the current study can be used to determine heliostat configurations and appropriate design wind speeds in different terrains leading to the maximum design wind loads on the elevation drive and foundation.

An update algorithm design using moving Region of Attraction for SDRE based control law

State Dependent Riccati Equation (SDRE) methods have the considerable advantages over other nonlinear control methods. However, stability issues can be arisen in SDRE based control system due to the lack of the global asymptotic stability property. Therefore, the previous studies have usually shown that local asymptotic stability can be ensured by estimating a Region of Attraction (ROA) around the equilibrium point. These estimated regions for stability may become narrow or the condition to keep the states in this region may be very conservative. To resolve these issues, this paper proposes a novel SDRE method employing an update algorithm to re-estimate the ROA when the states tend to move out of the stable region. The tendency is checked using a condition which is developed based on a new theorem. The theorem proves that it is possible to redesign the previous ROA with respect to the current states lying close to its boundary for ensuring the “non-local” stability along the trajectory without the need of solving SDRE at each time instant, unlike the standard SDRE approach. Therefore, the new theorem is now able to enhance the stability of the SDRE based closed-loop control system. The feasibility of the proposed SDRE control method is tested in both simulations and experiments. A validated 3-DOF laboratory helicopter is used for experiments and the control objective for the helicopter is to realise a preplanned movement in both elevation and travel axes. The results reveal that the proposed SDRE approach enables the controlled plant to track the desired trajectory as satisfactorily as the standard SDRE approach, while only solving SDRE when needed. The proposed SDRE method reduces the computational load for practical implementation of the control algorithm whilst ensuring the stability over the operational region.

Training a model-free reinforcement learning controller for a 3-degree-of-freedom helicopter under multiple constraints

The purpose of the article is to design data-driven attitude controllers for a 3-degree-of-freedom experimental helicopter under multiple constraints. Controllers were updated by utilizing the reinforcement learning technique. The 3-degree-of-freedom helicopter platform is an approximation to a practical helicopter attitude control system, which includes realistic features such as complicated dynamics, coupling and uncertainties. The method in this paper first describes the training environment, which consists of user-defined constraints and performance expectations by using a reward function module. Then, actor–critic-based controllers were designed for helicopter elevation and pitch axis. Next, the policy gradient method, which is an important branch of the reinforcement learning algorithms, is utilized to train the networks and optimize controllers. Finally, from experimental results acquired by the 3-degree-of-freedom helicopter platform, the advantages of the proposed method are illustrated by satisfying multiple control constraints.

A New Precision Goniometer Mechanism for Direct Angle Measurement by a Rotary Encoder

In order to perform optical tests of an optical device such as a camera, a collimator system is needed which is aligned to a precision two axes rotary system (gimbal) where the optical device (Unit Under Test, UUT) is mounted. By the help of gimbal system, precision positioning of the UUT can be achieved and optical tests can be performed with a high accuracy. However, it is hard to position elevation axis accurately for relatively heavier UUT because of direct moment applied by UUT to the elevation axis of the gimbal system. Therefore, directly driven elevation axis is replaced by a goniometer system. Due to gear coupling clearance in goniometer systems, precision positioning is not achievable. In order to overcome this problem, a new mechanism, which is driven by a power screw, is used for the goniometer and virtual center of rotation is moved within the goniometer for direct angle measurement by a rotary encoder. Validation test is performed by autocollimator and precise mirror calibrators to check the accuracy of the new goniometer system.