1,721,008 research outputs found
Model-based Feedforward Control for Inkjet Printheads
No full textIn recent years, inkjet technology has emerged as a promising manufacturing tool. This technology has gained its popularity mainly due to the facts that it can handle diverse materials and it is a non-contact and additive process. Moreover, the inkjet technology offers low operational costs, easy scalability, digital control and low material waste. Thus, apart from conventional document printing, the inkjet technology has been successfully applied as a micro-manufacturing tool in the areas of electronics, mechanical engineering, and life sciences. In this thesis, we investigate a piezo-based drop-on-demand (DoD) printhead which is commonly used for industrial and commercial applications due to its ability to handle diverse materials. A typical drop-on-demand (DoD) inkjet printhead consists of several ink channels in parallel. Each ink channel is provided with a piezo-actuator which on the application of an actuation voltage pulse, generates pressure oscillations inside the ink channel. These pressure oscillations push the ink drop out of the nozzle. The print quality delivered by an inkjet printhead depends on the properties of the jetted drop, i.e., the drop velocity, the drop volume and the jetting direction. To meet the challenging performance requirements posed by new applications, these drop properties have to be tightly controlled. The performance of the inkjet printhead is limited by two factors. The first one is the residual pressure oscillations. The actuation pulses are designed to provide an ink drop of a specified volume and velocity under the assumption that the ink channel is in a steady state. Once the ink drop is jetted the pressure oscillations inside the ink channel take several micro-seconds to decay. If the next ink drop is jetted before these residual pressure oscillations have decayed, the resulting drop properties will be different from the ones of the previous drop. The second limiting factor is the cross-talk. The drop properties through an ink channel are affected when the neighboring channels are actuated simultaneously. Generally, the drop consistency is improved by manual tuning of the piezo actuation pulse based on some physical insight or based on exhaustive experimental studies on the printhead. However, these ad-hoc procedures have proved to be insufficient in dealing with the above limitations. In this thesis, a model-based control approach is proposed to improve the performance of a DoD inkjet printhead. It offers a systematic and efficient means to improve the attainable performance of a DoD inkjet printhead by reducing the effect of the residual oscillations and the cross-talk. Furthermore, the models that have been developed for this purpose can also give new insights into the operation of the printhead. In order to achieve this goal, it is required to have a fairly accurate and simple model of an inkjet printhead. It is not easy to obtain a good physical model for an inkjet printhead due to insufficient knowledge of the complex interactions in the printhead. Therefore, in this thesis, we have used system identification, i.e. we use experimental measurements in order to develop a model. For this purpose, it is required that the piezo-actuator is also used as a sensor. Note that the crucial aspect in the model development is to obtain a model of the inkjet system close to its operating conditions. Therefore, we have collected measurements of the piezo sensor signal during the jetting of a series of drops at a given DoD frequency. For the printhead under investigation, we found that the dynamics of the ink channel are dependent on the DoD frequency. This phenomenon is caused by non-linearities in the droplet formation. Consequently, we have modeled the ink channel dynamics for every DoD frequency. In this thesis, it is shown that the set of local inkjet models obtained at different DoD frequencies can be encompassed by a polytopic uncertainty on the parameters of a nominal model. Using the same identification procedure, the cross-talk can also be modeled. In order to improve the printhead performance the actuation pulse was redesigned. The new drive pulse is designed to provide good performance for all models in the area of uncertainty by means of robust feedforward control. The pulse also respects the pulse shape constraints posed by driving electronics (ASICS). Besides the robust actuation pulse, our approach also introduces an optimal delay between actuation of neighboring channels to reduce the cross-talk. The current driving electronics limits the possibilities of reshaping the actuation pulse. Since it is expected that this limitation will be relaxed in the future, we have also developed procedure to design a robust pulse without pulse shape constraints. The performance improvement achieved with this unconstrained pulse has proved to be quite limited. The proposed method is also useful for inkjet practitioners who do not have any insight in the inkjet dynamics. The efficacy of our approach is demonstrated by our experimental results. The proposed method was verified in practice by jetting a series of ink drops at various DoD frequencies and also by jetting a bitmap image. For the printhead under consideration, the drop-consistency is improved by almost four times with the proposed approach when compared to the conventional methods.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Small-Scale Helicopter Automatic Autorotation: Modeling, Guidance, and Control
No full textOur research objective consists in developing a, model-based, automatic safety recovery system, for a small-scale helicopter Unmanned Aerial Vehicle (UAV) in autorotation, i.e. an engine OFF flight condition, that safely flies and lands the helicopter to a pre-specified ground location. In pursuit of this objective, the contributions of this thesis are structured around three major technical avenues. The first one concerns the modeling of the nonlinear dynamics of a small-scale helicopter UAV. We have developed a nonlinear, first-principles based, high-order model, used as a realistic small-scale helicopter simulation environment. This helicopter model is applicable for high bandwidth control specifications, and is valid for a range of flight conditions, including (steep) descent flight and autorotation. This comprehensive model is used as-is for controller validation, whereas for controller design, approximations of this nonlinear model are considered. The second technical avenue addresses the development of a guidance module, or Trajectory Planner (TP), which aims at generating feasible and optimal open-loop autorotative trajectory references, for the helicopter to follow. We investigate two such TP methods. The first one is anchored within the realm of nonlinear optimal control, and allows for an off-line computation of optimal trajectories, given a cost objective, nonlinear system dynamics, and controls and states equality and inequality constraints. The second approach, based upon the concept of differential flatness, aims at retaining a high computational efficiency, e.g. for on-line use in a hard real-time environment. The third technical avenue considers the Trajectory Tracker (TT), which compares current helicopter state values with the reference values produced by the TP, and formulates the control inputs to ensure that the helicopter flies along these optimal trajectories. Since the helicopter dynamics is nonlinear, the design of the TT necessitates an approach that tries to respect the system’s nonlinear structure. Here we have selected the robust control ? paradigm. In particular, our simulations show that the crucial control of helicopter vertical position and velocity exhibit outstanding behavior, in terms of tracking performance. However, the tracking of horizontal position and velocity could potentially be improved by considering some other control methods, such as Linear Parameter-Varying (LPV) ones. To this end, we present an approach that approximates a known complex nonlinear model by an affine LPV model. The practicality of this LPV modeling method is further validated on a point-mass pendulum example, and in the future this method could prove useful when applied to our helicopter application.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Analysis of the Robust Performance of Large-Scale Linear Systems using a Hierarchical Approach: PLL Network Application
No full textLarge-scale systems have become more important in the last years and will probably continue to do so due to the increasing complexity of nowadays problems. One example of such a system is a clock distribution network consisting of several phase locked loop systems deployed in an array. It is possible to obtain a (nominal) linear model describing the dynamical behaviour of a phase locked loop system around an operating point and to design a controller such that desired performance is achieved for this model and the overall linear model of the large-scale system. Although the phase locked loop systems are produced on an industrial scale, they will never be exactly equivalent. These dispersions can be captured by including uncertainty blocks in the model which results in a set of models describing the large-scale system. It is interesting to check if after including uncertainty in the model, certain performance can still be ensured. Analysing performance for such a set of mathematical models is called analysis of the robust performance. A method to perform robust performance analysis called μ-analysis or the direct approach exists though is relatively time consuming. Since the time computation is significant and crucial when applying the direct approach, it is interesting to study another method which can decrease the computation effort. M. Dinh, A. Korniienko and G. Scorletti have, after an idea of M.G. Safonov, developed a frequency dependent method to perform robust performance analysis on a linear large-scale system in several steps which can reduce the computation time needed though can give more conservative results with respect to the direct method. This new method is called the hierarchical approach. In this thesis we will explain the hierarchical approach and compare the robust performance analysis results obtained with the direct approach and with the hierarchical approach. We will also illustrate that the latter approach contains a trade-off between computation time and conservatism. We then introduce the two contributions of this thesis. First, an additional mathematical tool will be presented which can be used in the hierarchical approach to reduce the conservatism in the results. Then we will introduce a method which allows us to perform analysis of the robust performance not only for one specific frequency but also for a range around this frequency.Mechanical, Maritime and Materials EngineeringDelft Center for Systems and ControlSystems and Contro
Identification and Feedforward Control of a Drop-on-demand Inkjet Printhead
No full textDCSCMechanical, Maritime and Materials Engineerin
Identification and Control of a Batch Crystallization Process
No full textCrystallization is a slow chemical process evolving in a reactor called crystallizer. A solution initialized in a high temperature is cooled down such that the dissolved solute is transferred from the solution into pure crystalline phase. The evolution of the process characterizes the properties of the crystals in the end-product. The transient nature of the process together with the stochasticity that governs the chemical kinetic phenomena motivate the development of efficient methods for identification and control. The kinetics of the process are modeled with nonlinear equations which contain a number of parameters to be identified from the measured data. An appropriate model is required such that model-based control techniques can be implemented. Under these conditions, experiment design for open loop control of the crystallization is studied in this thesis where a nonlinear model of the crystallization is used as a model structure in the prediction error identification framework. A temperature cooling profile constitutes the input to the system which must be designed in such a way that the crystals formed at the end of the process admit the desired performance criteria. The first part of the thesis deals with the derivation of the optimal cooling profile using the D-optimality criterion in order to obtain the most informative data about the kinetic parameters. Sequentially, an optimization method is used as an open loop control law for the crystallization process. The selection of the optimal input profile is achieved by minimization of the performance degradation, occurring in the controlled process, from the use of the identified model instead of the true unknown system.Delft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Vector-valued model structure validation test in direct closed-loop identification: On the basis of the cross-correlation function
No full textDelft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Artifact Correction for EEG Alpha Wave Measurements: Real Time Alpha Wave And Relaxation State Detection from EEG
No full textDelft Center for Systems and ControlMechanical, Maritime and Materials Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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