Eccentricity Compensator for Log-Polar Sensor

his paper aims at acquiring robust rotation, scale, and translation-invariant feature from a space-variant image by a fovea sensor. A proposed model of eccentricity compensator corrects deformation that occurs in a log-polar image when the fovea sensor is not centered at a target, that is, when eccentricity exists. An image simulator in discrete space remaps a compensated log-polar image using this model. This paper proposes unreliable feature omission (UFO) that reduces local high frequency noise in the space-variant image using discrete wavelet transform. It discards coefficients when they are regarded as unreliable based on digitized errors of the input image. The first simulation mainly tests geometric performance of the compensator, in case without noise. This result shows the compensator performs well and its root mean square error (RMSE) changes only by up to 2.54 [%] in condition of eccentricity within 34.08[deg]. The second simulation applies UFO to the log-polar image remapped by the compensator, taking its space-variant resolution into account. The result draws a conclusion that UFO performs better in case with more white Gaussian noise (WGN), even if the resolution of the compensated log-polar image is not isotropic

Eccentricity estimator for wide-angle fovea sensor by FMI descriptor approach

This paper proposes a method for estimating eccentricity that corresponds to an incident angle to a fovea sensor. The proposed method applies Fourier-Mellin Invariant descriptor for estimating rotation, scale, and translation, by taking both geometrical distortion and non-uniform resolution of a space-variant image by the fovea sensor into account. The following 2 points are focused in this paper. One is to use multi-resolution images computed by discrete wavelet transform for reducing noise caused by foveation properly. Another is to use a variable window function (although the window function is generally used for reducing DFT leakage caused by both ends of a signal.) for changing an effective field of view (FOV) in order not to sacrifice high accuracy. The simulation compares the root mean square (RMS) of the foveation noise between uniform and non-uniform resolutions, when a resolution level and a FOV level are changed, respectively. Experimental results show that the proposed method is consistent with the wide-angle space-variant image by the fovea sensor, i.e., it does not sacrifice high accuracy in the central FOV

Eccentricity estimator for wide-angle fovea sensor by FMI descriptor approach

This paper proposes a method for estimating eccentricity that corresponds to an incident angle to a fovea sensor. The proposed method applies Fourier-Mellin Invariant descriptor for estimating rotation, scale, and translation, by taking both geometrical distortion and non-uniform resolution of a space-variant image by the fovea sensor into account. The following 2 points are focused in this paper. One is to use multi-resolution images computed by discrete wavelet transform for reducing noise caused by foveation properly. Another is to use a variable window function (although the window function is generally used for reducing DFT leakage caused by both ends of a signal.) for changing an effective field of view (FOV) in order not to sacrifice high accuracy. The simulation compares the root mean square (RMS) of the foveation noise between uniform and non-uniform resolutions, when a resolution level and a FOV level are changed, respectively. Experimental results show that the proposed method is consistent with the wide-angle space-variant image by the fovea sensor, i.e., it does not sacrifice high accuracy in the central FOV

Magnetic Bearings

The term magnetic bearings refers to devices that provide stable suspension of a rotor. Because of the contact-less motion of the rotor, magnetic bearings offer many advantages for various applications. Commercial applications include compressors, centrifuges, high-speed turbines, energy-storage flywheels, high-precision machine tools, etc. Magnetic bearings are a typical mechatronic product. Thus, a great deal of knowledge is necessary for its design, construction and operation. This book is a collection of writings on magnetic bearings, presented in fragments and divided into six chapters. Hopefully, this book will provide not only an introduction but also a number of key aspects of magnetic bearings theory and applications. Last but not least, the presented content is free, which is of great importance, especially for young researcher and engineers in the field

INVESTIGATION INTO SUBMICRON TRACK POSITIONING AND FOLLOWING TECHNOLOGY FOR COMPUTER MAGNETIC DISKS

In the recent past some magnetic heads with submicron trackwidth have been developed in order to increase track density of computer magnetic disks, however a servo control system for a submicron trackwidth head has not been investigated. The main objectives of this work are to investigate and develop a new servo pattern recording model, a new position sensor, actuator, servo controller used for submicron track positioning and following on a computer hard disk with ultrahigh track density, to increase its capacity. In this position sensor study, new modes of reading and writing servo information for longitudinal and perpendicular magnetic recording have been developed. The read/write processes in the model have been studied including the recording trackwidth, the bit length, the length and shape of the transition, the relationship between the length of the MR head and the recording wavelength, and the SIN of readout. lt has also been investigated that the servo patterns are magnetized along the radial direction by a transverse writing head that is aligned at right angles with the normal data head and the servo signals are reproduced by a transverse MR head with its stripe and pole gap tangential to the circumferential direction. lt has been studied how the servo signal amplitude and linearity are affected by the length of the MR sensor and the distance between the shields of the head. Such things as the spacing and length of the servo-pattern elements have been optimised so as to achieve minimum jitter and maximum utilisation of the surface of the disk. The factors (i.e. the skew angle of the head) affecting the SIN of the position sensor have been analysed and demonstrated. As a further development, a buried servo method has been studied which uses a servo layer underneath the data layer, so that a continuous servo signal is obtained. A new piezo-electric bimorph actuator has been demonstrated. This can be used as a fine actuator in hard disk recording. The linearity and delay of its response are improved by designing a circuit and selecting a dimension of the bimorph element. A dual-stage actuator has been developed. A novel integrated fine actuator using a piezo-electric bimorph has also been designed. A new type of construction for a magnetic head and actuator has been studied. A servo controller for a dual-stage actuator has been developed. The wholly digital controller for positioning and following has been designed and its performances have been simulated by the MAL TAB computer program. A submicron servo track writer and a laser system measuring dynamic micro-movement of a magnetic head have been specially developed for this project. Finally, track positioning and following on 0.7 µm tracks with a 7% trackwidth rms runout has been demonstrated using the new servo method when the disk-was rotating at low speed. This is one of the best results in this field in the world

Mathematical Modelling of the Drilling Process for Real-time Applications in Drilling Simulation, Interpretation and Assistance

For the last thirty years, mathematical modelling has been used to develop software solutions that support drilling engineering activities at the planning stage of drilling operations. But it is only for the last decade that mathematical models have been used for the real-time support of drilling operations. Moving from a pure engineering perspective to having models that can respect real-time requirements, necessitates many improvements of the subjacent mathematical modelling of the drilling process. First, it is not anymore possible to ignore transient behaviors that were somewhat irrelevant at the planning stage. Second, there is a need for solutions that should be fast enough to cope with the real-time constraints of the drilling process. With the perspective of creating applications that can support the drilling process in real-time, the following mathematical models have been developed: • Drilling fluid behavior. The properties of drilling fluids depend on their composition and pressure-temperature conditions. For instance, the pressure-temperature dependence of the mass density of drilling fluids, depends on the individual PVT-properties (Pressure-Volume-Temperature) of each of the components and their relative volume fractions. Therefore, the addition of drill-cuttings in the drilling fluid also changes the drilling fluid PVT-behavior. Furthermore, the rheological behavior of drilling fluids depends also on its composition. We have found that the rheological behavior of a KCl/polymer water-based mud is simultaneously modified by the relative proportion of barite and sand. Furthermore, it is known that drilling fluids are thixotropic. Yet, we found that the thixotropic behavior of drilling fluids is different from the one of other thixotropic fluids and we have determined that one of the causes for the discrepancy is related to the presence of solids in the fluid mix. We have developed a method to estimate the rheological behavior and its associated uncertainty, as a function of the modification of the solid proportions. • Drill-string mechanical sub-models coupled with hydraulic effects. Hydraulic pressure has also an impact on drill-string mechanical forces not only because the fluid mass density modifies buoyancy but more generally because viscous pressure gradients generate net forces along the drill-string. These hydraulic related forces are superposed to those engendered by mechanical friction and elastic deformation. • Steady state and transient drill-string mechanical models. Steady state torque and drag models utilizing the above-mentioned drill-string mechanical sub-models can be used to assess some characteristics of the drilling process when constant velocities are prevalent. But, during a drilling operation, there are many moments during which the drill-string displacement is in transient mode. Therefore, it is also important to have access to transient torque and drag models with a fast response time. • Transient cuttings transport model. The transport of cuttings is obviously influenced by hydraulic circulation but also drill-string rotational speed, at least in the deviated parts of a well. On the other hand, the presence of drill-cuttings in suspension or settling on the low-side of the borehole, influences pressure losses and mechanical forces along the drill-string. Therefore, the estimation of the transient displacement of drill-cuttings plays an important role in the overall estimation of the actual drilling conditions during a drilling operation. However, a transient cuttings transport model shall also be sufficiently fast, especially when it is used in real-time applications. Equipped with such models of the drilling process that are compatible with real-time constraints, then it is possible to solve problems that are relevant for the assistance of drilling operations. A first domain of application is related to the estimation, in real-time, of surface and downhole sensor values as a function of external commands like the block position and speed, the top-drive rotational velocity and the pump rates. We will refer to this domain of application as “drilling simulation”. However, comparison of measured values with simulated ones, require the proper modelling of the sensors and the impact of their actual position on the readings. For instance, drilling fluid is retained in the flowline and mud treatment equipment. Therefore, to simulate pit volumes, it is important to model the retention mechanism. Transient hydraulic, mechanical and heat transfer models, associated with precise modelling of sensor measurements, can then be used to interpret the current actual drilling conditions, because if their estimated parameters differ from the measurements, then a possible reason is that something unexpected is happening downhole. However, such drilling symptom detection method necessitates two additional conditions to be fulfilled: • The models shall be calibrated. Regardless of the quality of the drilling models, the inputs to these models are always known with a limited degree of accuracy and therefore their outputs may differ from measurements for that simple reason. However, it is important to distinguish between uncertainties that are related to properties that do not change substantially during a given drilling operation, from those that can change at any time. To avoid influencing the calibration of time invariant properties with possible side effects of the deterioration of the drilling condition, it is important to utilize drilling conditions by which undesirable side effects have no or little influence on the measurements that are used to calibrate the property. • Uncertainty of the modelled outputs shall be estimated. Calibration may reduce the uncertainty on the model outputs, but it does not eliminate it completely. It is therefore important to estimate the uncertainty of the predicted values. To achieve this, it is necessary to capture the precision by which the inputs of the process are known and to propagate that uncertainty throughout the modelling of the outputs. With continuously calibrated models and an estimation of the current downhole conditions, then it is possible to address some preliminary drilling process assistance functions: • Safety triggers. During the execution of automation functions, the situation awareness of the driller is reduced as he does not drive the drilling machines himself. Therefore, it shall not be attempted to automate any functions before a minimum set of protection functions are in place. Such safety triggers shall detect and react to incidents related to the axial and rotational movement of the drill-string and, of course, associated with pressure. Example of such safety triggers are: o Reactions to overpulls and set-down weights. o Reactions to abnormal torques. o Reactions to abnormal pressures. • Safeguards. Any drill-string or drilling fluid movements shall not generate a drilling incident. Therefore, commands to the drilling machines shall be kept within safe operational envelopes. For instance, upward movement of the drill-string shall not decrease the downhole pressure below the pore pressure or the collapse pressure of the open hole formations. Similarly, the applied flowrate combined with a possible downward movement and rotation of the drill-string shall not overpass the fracturing pressure of open hole formation rocks. • Automated procedures. Protected by safety triggers and operating within acceptable safeguards, then it is possible to automate some standard procedures. However, such automatic procedures must continuously be adapted to the current drilling conditions. For instance, the length of a friction must be modified to account for the current drill-string length and mechanical friction, or the flowrate applied during the ream-down sequence of a reciprocation procedure shall be reduced as a function of the current potential surging risk

The Aerostatic Seal: Analysis and Development of a New Dynamic Seal Concept for Steam Turbine Application

This thesis describes the development of a new seal concept for steam turbines called the Aerostatic Seal. The Aerostatic Seal is a dynamic seal, and so can respond to rotor radial movement to maintain a low clearance between the seal and the rotor. As the seal is dynamic, smaller clearances can be achieved without rotor contact compared to conventional static seals such as the labyrinth seal, hence increasing the efficiency of the turbine through reduced leakage. Furthermore, as the seal is dynamic it can tolerate larger radial transients typically found during start up and shut down of the steam turbine, and so also contributes to increasing the flexibility of the turbine plant. In this thesis an analytical design and analysis methodology was developed for the Aerostatic Seal. The methodology was used to generate a number of seal designs which were experimentally tested in a non-rotating test facility using room temperature air. The results confirmed that the seal would operate dynamically, and the experimental campaign provided valuable data on the operation of the seal. The non-rotating rig was also used to test a second generation seal design. The seal was then tested in a rotating test facility, which modelled high speed rotor radial transients with an adjustable eccentric rotor. The Aerostatic Seal demonstrated the ability to respond to high speed transients. A final test campaign was conducted in the high temperature steam rig at TU Braunschweig, Germany, enabling experimental demonstration of the Aerostatic Seal using realistic materials and represented realistic steam turbine conditions. Finally, based on the experimental and analytical work carried out within this thesis, a proposed Aerostatic Seal design for steam turbine implementation is presented

Evaluation and Improvement of Control Vector Iteration Procedures for Optimal Control

An alternate graphical representation of linear, time-invariant, multi-input, multi-output (MIMO) system dynamics is proposed that is highly suited for exploring the influence of closedloop system parameters. The development is based on the adjustment of a scalar forward gain multiplying a cascaded multivariable controller/plant embedded in an output feedback configuration. By tracking the closed-loop eigenvalues as explicit functions of gain, it is possible to visualize the multivariable root loci in a set of "gain plots" consisting of two graphs: (i) magnitude of system eigenvalues versus gain and (ii) argument (angle) of system eigenvalues versus gain. The gain plots offer an alternative perspective of the standard MIMO root locus plot by depicting unambiguously the polar coordinates of each eigenvalue in the complex plane. Two example problems demonstrate the utility of gain plots for interpreting closed-loop multivariable system behavior. Introduction Since their introduction, classical control tools have been popular for analysis and design of single-input, single-output (SISO) systems. These tools may be viewed as specialized versions of more general methods that are applicable to multiinput, multi-output (MIMO) systems. Although modern "statespace" control techniques (relying on dynamic models of internal structure) are generally promoted as the predominant tools for multivariable system analysis, the classical control extensions offer several advantages, including requiring only an input-output map and providing direct insight into stability, performance, and robustness of MIMO systems. The understanding generated by these graphically based methods for the analysis and design of MIMO systems is a prime motivator of this research. An early graphical method for investigating the stability of linear, time-invariant (LTI) SISO systems was developed by ference transfer function matrix ([I + G(s)] where G(s) is the open-loop system transfer function matrix, rather than just 1 + g(s) for the SISO case where g{s) is the system transfer function). Despite the complication, significant research has supported the MIMO Nyquist extension for assessment of multivariable system stability and robustness The Bode plots Although promoted as an SISO tool, Evans root locus method To aid the controls engineer in extracting more information from the multivariable Evans root locus plot, we propose a set of "gain plots" that provide a direct and unique window into the stability, performance, and robustness of LTI MIMO systems. A conceptual framework motivating the gain plots and a discussion of their applicability to SISO systems has been presented previously Multivariable Eigenvalue Description Basic MIMO Concepts. A LTI MIMO plant can be represented in the standard state-space form as where state vector x p is length n, input vector u is length m, and output vector y is length m. Matrices A p , B p , C p , and D p are the system matrix, the control influence matrix, the output matrix, and the feed-forward matrix, respectively, of the plant with appropriate dimensions. The plant input-output dynamics are governed by the transfer function matrix, G p (s), GpW^CplsI-ApV'Bp + Vp (3) The system is embedded in the closed-loop configuration shown in Fig. 1 Ml MO closed-loop negative feedback configuration where A c , B c , C c , and D c are the controller matrices representing its internal structure, in similarity to Eqs. In the MIMO root locus plot, the migration of the eigenvalues of G*(5) in the complex plane is graphed for 0 < k < oo. (By equating the determinant of [I + kG p (s)G c (s)] to zero, the MIMO generalization of the SISO characteristic equation The presence of the determinant is the major challenge in generalizing the SISO root locus sketching rules to MIMO systems and complicates the root locus plot.) The closed-loop system dynamics can alternatively be cast in state-space form in terms of state vector r . The closed-loop system matrix then becomes where The eigenvalues of the closed-loop system,5 = X; = eig(A') (i = 1,2, . . . , «), may be computed numerically from Eq. (6). In the examples, the loci of the eigenvalues are calculated as k is monotonically increased from zero. High Gain Behavior. As the gain is swept from zero to infinity, the closed-loop eigenvalues trace out "root loci" in the complex plane. At zero gain, the poles of the closed-loop system are the open-loop eigenvalues. At infinite gain some of the eigenvalues approach finite transmission zeros, defined to be those values of s that satisfy the generalized eigenvalue problem. In the absence of pole/zero cancellation, the finite transmission zeros are the roots of the determinants of G p (s) and G c (s). Algorithms have been developed for efficient and accurate computation of transmission zeros The eigenvalues can be considered as always migrating from the open-loop poles to their matching transmission zeros MIMO Gain Plots. Just as the Bode plots embellish the information of the Nyquist diagram by exposing frequency explicitly in a set of magnitude versus frequency and angle (phase) versus frequency plots, it follows that a pair of gain plots (Kurfess and Nagurka, 1991) can enhance the standard root locus plot. As the gain-domain analog of the frequencydomain Bode plots, the gain plots explicitly depict the eigenvalue magnitude versus gain in a magnitude gain plot, and the eigenvalue angle versus gain in an angle gain plot. In similarity to the Bode plots, the magnitude gain plot employs a log-log scale whereas the angle gain plot uses a semi-log scale (with the logarithms being base 10). Although gain is selected as the variable of interest in the gain plots, it should be noted that any scalar parameter may be used in the geometric analysis, leading to the more generic idea of parametric plots. Gain plots can be drawn for both SISO and MIMO systems. In MIMO systems it is assumed that a single scalar gain amplifies all controller/plant inputs. For such systems, inspection of the magnitude and angle gain plots enables one to uniquely identify locus branches as a function of gain. As such, gain plots are a natural complement to multivariable root locus plots, where uncharacteristically confusing eigenvalue trajectories can result from being drawn in a single complex plane. Furthermore, it can be shown that the slopes of the lines in the gain plots are proportionally related to the root sensitivity function (Kurfess and Nagurka, 1992). MIMO Examples This section presents two multivariable examples. The first example introduces the concept of the gain plots and demonstrates the insight they offer by "unwrapping" the multivariable root locus and exposing unambiguous behavior. The second example highlights the power of the gain plots in revealing typical multivariable properties, such as high gain Butterworth patterns. Example 1: Coupled MIMO Example. The forward loop dynamics of this example are given by the transfer function matrix (Equation The gain plots presented in The gain plots highlight several other important features. For example, they show that the gains corresponding to the complex conjugate eigenvalue pairs break into the real axis and then proceed toward ± oo. Complex conjugate eigenvalues are shown as symmetric lines about either the 180 or 0 deg line with equal magnitudes. Purely real eigenvalues possess equal angles (180 or 0 deg) but distinct magnitudes. This behavior is demonstrated in The rates at which the eigenvalues increase toward infinite magnitude is seen in the magnitude gain plot of From Conclusions In typical MIMO root locus plots trajectories may be camouflaged as branches may overlap. Gain plots are promoted as a means to "untangle" MIMO eigenvalue trajectories. The major enhancement is the visualization of eigenvalue trajectories as an explicit function of gain, assumed here to be the same static gain applied to all error signals. The perspective presented in this note is intended to complement the many tools available to the controls engineer. In particular, for MIMO systems the gain plots provide: (/) a unique description of eigenvalues and their trajectories as a parameter, such as gain, is varied, (ii) a geometric depiction of the Riemann sheets at high gain, and (Hi) a rich educational tool for conducting parametric analyses of multivariable systems. Research efforts, currently underway, may shed additional light on gain plots for multivariable systems. In addition, work by MacFarlane and'Postlethwaite (1977 and In conclusion, gain plots enrich the multivarible root locus plot in much the same way that singular value frequency plots are an alternate and extended presentation of the multivariable Nyquist diagram. Their use in conjunction with the multivariable root locus provides a valuable geometric perspective on multivariable system behavior. Acknowledgment The authors wish to thank Mr. Ssu-Kuei Wang for his help, and for his earnest enthusiasm of gain plots for studying multivariable and optimal systems

Science yield estimate with the Wide-Field Infrared Survey Telescope coronagraph

The coronagraph instrument (CGI) on the Wide-Field Infrared Survey Telescope will directly image and spectrally characterize planets and circumstellar disks around nearby stars. Here we estimate the expected science yield of the CGI for known radial-velocity (RV) planets and potential circumstellar disks. The science return is estimated for three types of coronagraphs: the hybrid Lyot and shaped pupil are the currently planned designs, and the phase-induced amplitude apodizing complex mask coronagraph is the backup design. We compare the potential performance of each type for imaging as well as spectroscopy. We find that the RV targets can be imaged in sufficient numbers to produce substantial advances in the science of nearby exoplanets. To illustrate the potential for circumstellar disk detections, we estimate the brightness of zodiacal-type disks, which could be detected simultaneously during RV planet observations