Christian Pape

Bio: Christian Pape is an academic researcher from Leibniz University of Hanover. The author has contributed to research in topics: Image processing & Digital image processing. The author has an hindex of 4, co-authored 28 publications receiving 69 citations.

Optical derotator for scanning vibrometer measurements on rotating objects

Abstract: In this paper we present an optical derotator for scanning vibrometer measurements on rotating objects. The main part of an optical derotator is a rotating prism. Several concepts are known from literature. We have chosen a Dove prism because it can derotate the rotation of the specimen by simply watching through the prism, which rotates with half the speed. The design of our derotator is presented in this paper as well as a discussion of the system performance. In addition we show experimental measurement results on a fan rotating with 3000 rpm.

Hybrid Monocular SLAM Using Double Window Optimization

Abstract: This letter presents a hybrid framework, both in front-end and back-end, for monocular simultaneous localization and mapping (SLAM), capable of utilizing the robustness of feature matching and the accuracy of direct alignment. In the front-end, the feature-based method is first used for coarse pose estimation that is subsequently taken by the direct alignment module as initialization for further refinement. In the back-end, a double window structure is constructed based on the maintained semi-dense map and the sparse feature map, of which the states are optimized via a multi-layer optimization scheme based on the reprojection constraints and the relative pose constraints. Our evaluation on several public datasets demonstrates that this hybrid design retains the superior resilience to scene variations of salient features, and achieves better tracking accuracy due to the integration of the direct modules, leading to a comparable performance with the state-of-the-arts.

Predictor-corrector framework for the sequential assembly of optical systems based on wavefront sensing.

Abstract: Alignment of optical components is crucial for the assembly of optical systems to ensure their full functionality. In this paper we present a novel predictor-corrector framework for the sequential assembly of serial optical systems. Therein, we use a hybrid optical simulation model that comprises virtual and identified component positions. The hybrid model is constantly adapted throughout the assembly process with the help of nonlinear identification techniques and wavefront measurements. This enables prediction of the future wavefront at the detector plane and therefore allows for taking corrective measures accordingly during the assembly process if a user-defined tolerance on the wavefront error is violated. We present a novel notation for the so-called hybrid model and outline the work flow of the presented predictor-corrector framework. A beam expander is assembled as demonstrator for experimental verification of the framework. The optical setup consists of a laser, two bi-convex spherical lenses each mounted to a five degree-of-freedom stage to misalign and correct components, and a Shack-Hartmann sensor for wavefront measurements.

Automated calibration of an optomechanical derotator using 6-axes parallel kinematics and industrial image processing algorithms

Abstract: A concept for an optomechanical derotator is presented. The derotator allows optical measurements of rotating objects during operation. To guarantee a stationary optical image, the optical axis of the derotator needs to be coaxially aligned to the rotational axis of the measured object. The correlation between the movement of the optical image and a miscalibration is explained by a mathematical model. The movement of the optical image is tracked with a high-speed camera. Approximating the tracked path as a Limacon of Pascal, a parameter corresponding to the magnitude of the miscalibration is identified. This parameter is minimized by modifying the position and the orientation of the derotator with a hexapod. The limitations of this procedure are analyzed and further approaches are discussed.

Process-Integrated State Estimation of Optical Systems With Macro–Micro Manipulators Based on Wavefront Filtering

Abstract: To date, the assembly of optical systems is still not fully automated. Automated assembly can be facilitated by having an optical simulation at hand, which, in turn, requires knowledge about the current state of the optical system. Due to the strict demands on the positioning tolerances, the uncertainties of the positioning system play an important role and lead to non-negligible deviations from the nominal poses. Therefore, the actual poses of the optical components need to be estimated in order to correct misaligned components. Furthermore, it is beneficial to develop methods that utilize the dedicated primary sensor and to avoid additional external sensors. In this letter, we employ a macro-micro manipulator for moving optical components and utilize filtering methods for realizing an in-process state estimation. For this, the uncertainty of the positioning system, as well as sensor noise, need to be identified, which lay the groundwork for methods such as the extended Kalman filter, iterated extended Kalman filter, unscented Kalman filter, or particle filter. In this letter, we compare these methods in simulation with current nonlinear approaches from the literature with respect to the estimation error. Experimental verification is carried out by a macro-micro manipulator comprised of a Cartesian piezo-driven 3-DOF positioning system attached to a 6-DOF industrial robot. With the proposed filtering approach and macro-micro manipulator, the pose of a bi-convex lens is estimated via a wavefront sensor.

海外文献紹介 Optical Engineering

Abstract: Optical Engineering Core 28 hours CPE 112 3 Intro To Computer Programming MA 113, MA 115, or Level III placement FSM EE 307 3 Electricity and Magnetism EE 300 FSM EE 313 3 Electrical Circuits II Preor co-requisite: EE 307 FSM EE 447 3 Electromagnetic Waves EE 313 S OPE 453 3 Laser Systems EE 307 F OPE 455 2 Optical Engineering Laboratory PH 113, OPT 342, EE 382 or OPT 442 S OPE 459 3 Optical Engineering Design ISE 321, Senior standing S OPT 341 3 Geometrical Optics PH 113 F OPT 342 3 Physical Optics OPT 341 S OPT 411 2 Geometrical Optics Laboratory PH 116, OPT 341, OPE 441 suggested co-requisite F

Vibration and modal analysis of a rotating disc using high-speed 3D digital image correlation

Abstract: Rotating structures are of interest in many engineering fields, where knowing their dynamic behaviour is important to prevent undesired operating states. However, the experimental measurement of vibrations in rotating structures is still a relatively demanding task that requires the use of special measurement technique or method. The paper deals with the application of high-speed digital image correlation in vibration analysis of rotating structures. The method introduced in this research is based on the elimination of rigid body motion components contained in the primary responses measured by cameras. The process of separation and subsequent elimination of these components is given by numerical post-processing of three-dimensional displacement fields. The basis is to determine rotation matrix and translation vector that optimally describe rigid transformation between two positions of an analysed object. The proposed method is applicable for measuring under both constant and variable speed of rotation. Practical application is presented by three experiments in which vibrations of a flat rotating disc were analysed. The first experiment is focused on determine the operating deflection shapes of the disc rotating at 4700 rpm. The second one is a run-up analysis under variable rotational speed that ranges from 0 to 4700 rpm. The aim of the third measurement is to obtain natural frequencies and modal shapes of the disc rotating at 4800 rpm. The results of the experiments show that the elimination of rigid body motions leads to a higher accuracy of measurement and provides more pronounced frequency response spectra.

Scanning LDV using wedge prisms

Abstract: Recent work on laser vibrometry proposed a mathematical model for the velocity sensed by a laser beam incident in an arbitrary direction on a rotating target undergoing arbitrary vibration. A single arbitrary point along the line of incidence of the laser beam must be known, together with an arbitrary known point along the line of the beam and the main purpose of this paper is to introduce a general procedure to determine both. This new procedure is applied to a novel, scanning LDV arrangement in which rotating wedge prisms are used in order to track a rotating component. Special attention is given to the time-dependent laser beam orientation using a vector description of refraction to enable concise expression. Experimental data are presented for the first time suggesting advantages over the convention dual-mirror system currently used for tracking LDV.

Review of Applications of Generalized Regression Neural Networks in Identification and Control of Dynamic Systems

Abstract: This paper depicts a brief revision of Generalized Regression Neural Networks (GRNN) applications in system identification and control of dynamic systems. In addition, a comparison study between the performance of back-propagation neural networks and GRNN is presented for system identification problems. The results of the comparison confirm that GRNN has shorter training time and higher accuracy than the counterpart back-propagation neural networks.