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Control Systems Technology, IEEE Transactions on

Issue 5 • Date Sept. 2009

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Displaying Results 1 - 25 of 26
  • Table of contents

    Page(s): C1 - C4
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    Freely Available from IEEE
  • IEEE Transactions on Control Systems Technology publication information

    Page(s): C2
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    Freely Available from IEEE
  • Nonminimum Phase Dynamic Inversion for Settle Time Applications

    Page(s): 989 - 1005
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1822 KB) |  | HTML iconHTML  

    Single-track hard disk drive (HDD) seek performance is measured by settle time, ts. In this paper, we show the effective use of feedforward dynamic inversion, coupled with reference trajectory yd generation, to achieve high performance ts. Models of HDD dynamics are typically nonminimum phase (NMP), and it is well known that the exact tracking solution for NMP systems requires noncausal preactuation to maintain bounded internal signals. In the specific HDD operating modes of interest, anticipation of a seek command is unrealistic, and thus preactuation adds to the overall computation of settle time. Unlike many dynamic inversion tracking applications, this negative effect of preactuation leads to interesting trade-offs between preactuation delay, yd tracking accuracy, and achievable settle performance. We investigate multiple single-input single-output (SISO) inversion architectures, and we show that the feedforward closed-loop inverse (FFCLI) achieves superior settle performance to the feedforward plant inverse (FFPI) in our application because FFCLI does not excite the closed-loop dynamics. Using the FFCLI architecture, we further investigate numerous NMP inversion algorithms, including both exact inversion schemes with initial condition preloading and stable approximate NMP inverse techniques. We conclude that the settle performance of the zero-order Taylor series stable NMP approximation matches the best performance of the exact inversion techniques in our application, and does so without the high frequency excitation required by the zero magnitude error tracking controller (ZMETC), or the excessive preactuation required by the zero phase error tracking controller (ZPETC). Minimum energy optimal trajectory generation methods show that the system order n is a limiting factor in settle performance. This confirms that the zero-order series method, which is capable of producing settle times in less than n samples, is on par with opti- - mal approaches yet much simpler to implement. Multiple NMP inversion algorithms are experimentally validated on a servo track writer (STW), which reinforces the general trends observed in ideal simulations. View full abstract»

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  • A System-on-a-Chip Implementation for Embedded Real-Time Model Predictive Control

    Page(s): 1006 - 1017
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (814 KB) |  | HTML iconHTML  

    This paper presents a hardware architecture for embedded real-time model predictive control (MPC). The computational cost of an MPC problem, which relies on the solution of an optimization problem at every time step, is dominated by operations on real matrices. In order to design an efficient and low-cost application-specific processor, we analyze the computational cost of MPC, and we propose a limited-resource host processor to be connected with an application-specific matrix coprocessor. The coprocessor uses a 16-b logarithmic number system arithmetic unit, which is designed using cotransformation, to carry out the required arithmetic operations. The proposed architecture is implemented by means of a hardware description language and then prototyped and emulated on a field-programmable gate array. Results on computation time and architecture area are presented and analyzed, and the functionality of the proposed architecture is verified using two case studies: a linear problem of a rotating antenna and a nonlinear glucose-regulation problem. The proposed MPC architecture yields a small-in-size and energy-efficient implementation that is capable of solving the aforementioned problems on the order of milliseconds, and we compare its performance and area requirements with other MPC designs that have appeared in the literature. View full abstract»

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  • Control Strategy for a Low Cost Manipulator to Transport and Align IC Mask-Plates

    Page(s): 1018 - 1027
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (909 KB) |  | HTML iconHTML  

    A 4-DOF manipulator is developed to carry mask-plates of integrated-circuit lithography. Its three translation axes are driven with servo motors, and its rotation axis is driven with a step motor. The manipulator is controlled with a programmable controller to execute two movement categories. One is the transport in large range, which is a feedback system with two loops such as position loop and velocity loop. Another is the alignment in small range, which is a feedback system with three loops including aligning loop, position loop, and velocity loop. The aligning errors are measured with two four-quadrant photodetectors. The property of the detectors is investigated, and a novel control strategy for alignment is proposed. Experiments were well conducted to verify the effectiveness of the proposed control system and algorithms. View full abstract»

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  • Thermoacoustic Instability Suppression by Gain-Delay and {cal H}_{\infty } Controllers Designed for Secondary Fuel Injection

    Page(s): 1028 - 1042
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1880 KB) |  | HTML iconHTML  

    This paper describes the suppression of thermoacoustic instabilities in a swirl-stabilized test rig. To that end, a high-bandwidth secondary fuel injector is installed and commanded with robust H infin and simpler gain-delay controllers. Depending on the operating condition, several distinct flame types occur, which are investigated with OH chemiluminescence. A model of the plant is obtained by means of closed-loop identification experiments. The model-based H infin approach confers more design freedom to the engineer and gives better results. In particular, the sensitivity can be distributed arbitrarily to target specific and separate frequency ranges. The pressure spectrum reductions achieved are compared with the predictions of the design process and are found to agree well. The influence of the injected natural gas on the flame is studied through OH chemiluminescence. Experiments show that the controlled flame assumes a position similar to the one of a flame being in a stable operating condition. View full abstract»

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  • Control of an Overactuated Cable-Driven Parallel Mechanism for a Radio Telescope Application

    Page(s): 1043 - 1054
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1185 KB) |  | HTML iconHTML  

    The large adaptive reflector is a Canadian design concept for a new type of large-scale radio telescope. This new telescope would be composed of a reflector made of individually actuated panels and a multitethered feed platform held aloft by an aerostat. This paper focuses on the position and orientation control of the feed platform. Models of both the cables and the feed platform are first derived. Then, a control strategy adapted to the particular system's dynamics is designed. This control strategy is based on a cascade-control architecture, in which the inner control loop adjusts the tension in each cable. This inner loop controller is synthesized using the H infin optimal-control technique. In addition, gain scheduling is used to adapt the H infin optimal controller to the cable lengths. The outer control loop adjusts the pose of the feed platform, using inverse-dynamics control and PID control. The model derived is coupled to the multiloop controller, and simulations are run to evaluate the performance level of the control strategy. View full abstract»

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  • A Dynamic Semi-Analytic Channel-to-Channel Model of Two-Phase Water Distribution for a Unit Fuel Cell

    Page(s): 1055 - 1068
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1259 KB) |  | HTML iconHTML  

    The critical task of controlling the water accumulation within the gas diffusion layer (GDL) and the channels of a polymer-electrolyte-membrane (PEM) fuel cell is shown to benefit from a partial-differential-equation (PDE) approach. Starting from first principles, a model of a fuel cell is represented as a boundary value problem for a set of three coupled nonlinear second-order PDEs for mass transport across the GDL of each electrode. These three PDEs are approximated, with justification founded in linear systems theory and a time-scale decomposition approach, by a semianalytic model that requires less than one-third the number of states to be numerically integrated. A set of numerical transient, analytic transient, and analytic steady-state solutions for the semianalytic model are presented, and an experimental verification of the cell voltage prediction due to liquid-water accumulation is demonstrated. The semianalytic model derived and the associated analysis represent our main contribution for which future expansion of along-the-channel dynamics and statistical consideration of cell-to-cell variations can be implemented for application to control, estimation, and diagnostic algorithms. View full abstract»

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  • Robust Inversion-Based 2-DOF Control Design for Output Tracking: Piezoelectric-Actuator Example

    Page(s): 1069 - 1082
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1188 KB) |  | HTML iconHTML  

    In this paper, a novel robust inversion-based 2-DOF control approach for output tracking is proposed. Inversion-based feedforward control techniques have been successfully implemented in various applications. Usually, to account for adverse effects such as dynamics variations and disturbances, the inverse feedforward control is applied by augmenting it with a feedback control. However, such effects have not been directly addressed in existing system-inversion methods, and the integration of the feedback control with the inversion-based feedforward control is performed in an ad hoc manner, which may not lead to an optimal complement of the inversion-based feedforward control with the feedback control. The contribution of this paper is the development of the following: 1) a robust system-inversion approach to directly account for and then minimize the dynamics-uncertainty effect when finding the inversion-based feedforward controller, and 2) a systematic integration (of such a feedforward controller) with a robust feedback controller. The proposed robust inversion method achieves a guaranteed tracking performance of the feedforward control for bounded dynamics uncertainties. Then, the quantified bound of the feedforward control tracking error is utilized in designing an H infin robust feedback controller to complement the feedforward control. Based on the concept of Bode's integral, it is shown that the feedback bandwidth can be improved from that obtained by using feedback alone. We illustrated the proposed approach by implementing it in experiments on a piezotube actuator of an atomic force microscope for precision positioning. View full abstract»

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  • Adaptive Sliding-Mode Control of a Charged Particle in an Ion Trap

    Page(s): 1083 - 1095
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1278 KB) |  | HTML iconHTML  

    Currently, commercial ion traps used for mass spectrometry are controlled in an open-loop manner with sinusoidally varying inputs. In this paper, we discuss the possible advantages of adding nonlinear feedback control to this system and demonstrate them through numerical simulations. Using sliding-mode control, we find that we can have a particle fall onto a trapping surface of our choosing, despite the presence of uncertainty in the system. In addition, when used in an open-loop fashion, the sliding-mode input creates stable attractors in the phase space. This shows that nonsinusoidal periodic inputs can effectively trap a group of particles. When an adaptive component is added to the closed-loop sliding-mode controller, we see that a simulated particle of unknown mass and charge can be successfully trapped and driven onto a desired surface. In addition, if that trajectory satisfies the persistent-excitation condition, then the controller can attain perfect estimation of the unknown parameters, thus measuring the particle mass and charge without ejecting it from the trap. These simulation results suggest a number of interesting experiments. View full abstract»

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  • Yaw Stability Control Design Through a Mixed-Sensitivity Approach

    Page(s): 1096 - 1104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    In this paper, a vehicle dynamic control (VDC) system for tracking the desired vehicle behavior is developed. A 2-DOF control structure is proposed to prevent vehicle skidding during critical maneuvers through the application of differential braking between the right and left wheels in order to control yaw motion. The feedforward filter is a reference generator which computes the desired yaw rate on the basis of the steering angle, while the feedback controller is designed to track the reference as close as possible and to satisfy suitable loop robustness requirements. Mixed-sensitivity minimization techniques are exploited in order to design the loop controller. The performance of the control system is evaluated through the hardware-in-the-loop simulation system under both emergency maneuvers and noncritical driving conditions, i.e., when the VDC system is not supposed to intervene. View full abstract»

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  • Real-Time Motion Planning With Applications to Autonomous Urban Driving

    Page(s): 1105 - 1118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1782 KB) |  | HTML iconHTML  

    This paper describes a real-time motion planning algorithm, based on the rapidly-exploring random tree (RRT) approach, applicable to autonomous vehicles operating in an urban environment. Extensions to the standard RRT are predominantly motivated by: 1) the need to generate dynamically feasible plans in real-time; 2) safety requirements; 3) the constraints dictated by the uncertain operating (urban) environment. The primary novelty is in the use of closed-loop prediction in the framework of RRT. The proposed algorithm was at the core of the planning and control software for Team MIT's entry for the 2007 DARPA Urban Challenge, where the vehicle demonstrated the ability to complete a 60 mile simulated military supply mission, while safely interacting with other autonomous and human driven vehicles. View full abstract»

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  • Passivity-Based Attitude Synchronization in SE(3)

    Page(s): 1119 - 1134
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1279 KB) |  | HTML iconHTML  

    This paper addresses passivity-based motion coordination of rigid bodies in the special Euclidean group SE(3) under the assumption that the agents exchange information over strongly connected graphs. In this paper, we especially focus on one of the motion coordination problems on SE(3) called attitude synchronization. We first develop a passivity-based distributed velocity input law to achieve attitude synchronization. Using the notion of algebraic connectivity, we then establish a connection between the speed of convergence and the structure of the interconnection graph. We also prove attitude synchronization in the leader-follower case and in the cases of communication delay and temporary communication failures. Finally, the performance of our developed control laws is demonstrated through both numerical simulation and experiments on a planar (2D) test bed. View full abstract»

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  • Experimental Validation of Nonlinear Control for a Voltage Source Converter

    Page(s): 1135 - 1144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (890 KB) |  | HTML iconHTML  

    In this brief, we consider reactive power and DC voltage tracking control of a three-phase voltage source converter (VSC). This control problem is important in many power system applications including power factor correction for a distribution static synchronous compensator (D-STATCOM). Traditional approaches to this problem are often based on a linearized model of the VSC and proportional-integral (PI) feedback. In order to improve performance, a flatness-based tracking control for the VSC is proposed where the nonlinear model is directly compensated without a linear approximation. Flatness leads to straightforward open-loop control design. A full experimental validation is given as well as a comparison with the industry-standard decoupled vector control. Robustness of the flatness-based control is investigated and setpoint regulation for unbalanced three-phase voltage is considered. View full abstract»

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  • Identification of Bilinear Systems With White Noise Inputs: An Iterative Deterministic-Stochastic Subspace Approach

    Page(s): 1145 - 1153
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (425 KB) |  | HTML iconHTML  

    In this technical brief, a new subspace state space system identification algorithm for multi input multi output bilinear systems driven by white noise inputs is introduced. The new algorithm is based on a uniformly convergent Picard sequence of linear deterministic stochastic state space subsystems which are easily identifiable by any linear deterministic stochastic subspace algorithm such as MOESP, N4SID, CVA, or CCA. The key to the proposed algorithm is the fact that the bilinear term is a second order white noise process. Using a standard linear Kalman filter model, the bilinear term can be estimated and combined with the system inputs at each iteration, thus leading to a linear system with extended inputs of dimension m(n + 1), where n is the system order and m is the dimension of the inputs. It is also shown that the model parameters obtained with the new algorithm converge to those of the true bilinear model. Moreover, the proposed algorithm has the same consistency conditions as the linear subspace identification algorithms when i ?? ??, where i is the number of block rows in the past/future block Hankel data matrices. Typical bilinear subspace identification algorithms available in the literature cannot handle large values of i, thus leading to biased parameter estimates. Unlike existing bilinear subspace identification algorithms whose row dimensions in the data matrices grow exponentially, and hence suffer from the ??curse of dimensionality,?? in the proposed algorithm the dimensions of the data matrices are comparable to those of a linear subspace identification algorithm. A case study is presented with data from a heat exchanger experiment. View full abstract»

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  • Optimal Stabilizing Gain Selection for Networked Control Systems With Time Delays and Packet Losses

    Page(s): 1154 - 1162
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (675 KB) |  | HTML iconHTML  

    This brief addresses the optimal-stabilization problem for networked control systems (NCSs) with time delays and packet losses. The closed-loop NCS is modeled as a discrete-time switched system, and the stability conditions are derived in terms of linear matrix inequality. A controller design method with both system stability and control performance taken into account is proposed, and estimation of distribution algorithm is used to select the optimal stabilizing gain. The proposed method can be easily implemented to various applications, since it has simple structure and has no assumptions on time-delay and packet-loss models. Simulation and experimental results are given to demonstrate the effectiveness of the proposed approach. View full abstract»

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  • Input–Output Decoupling Control by Measurement Feedback in Four-Wheel-Steering Vehicles

    Page(s): 1163 - 1172
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (956 KB) |  | HTML iconHTML  

    The well-known single-track linearized model for four-wheel-steering vehicle dynamics is used to design a second-order dynamic decoupling controller. Yaw rate and lateral speed are the outputs to be decoupled, while the rear steering angle and an additive steering angle with respect to the driver command are the control inputs. It is shown that the lateral speed dynamics and the yaw rate dynamics can be decoupled by feeding back longitudinal speed, yaw rate, and lateral acceleration measurements, while the effect of sensor disturbances on yaw rate is attenuated. Lateral speed measurements or observers are not required. The yaw rate controlled dynamics are independent from lateral speed and are described by a third-order input-output model, depending on the driver steering wheel command and sensor disturbances; the lateral speed dynamics are autonomous and tend exponentially to zero with a vehicle-dependent time constant while the lateral acceleration tends to be proportional to the yaw rate. The nonlinear analysis on a single-track model shows the suppression of the unstable equilibrium points of the uncontrolled system, the generation of new stable equilibrium points as the critical driver step input increases, and the enlargement of the stability regions. Simulations of typical maneuvers and disturbances on a nonlinear third-order single-track model and on a higher order model provided by CarSim show robustness with respect to unmodeled dynamics, vehicle parameter uncertainty, and sensor disturbances; moreover, significant dynamic decoupling, larger bandwidth, overshoot suppression, and improved maneuverability even at high speed are confirmed. View full abstract»

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  • Experiments of Formation Control With Multirobot Systems Using the Null-Space-Based Behavioral Control

    Page(s): 1173 - 1182
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3020 KB) |  | HTML iconHTML  

    In this paper, the experimental validation of a behavior-based technique for multirobot systems (MRSs), namely, the Null-Space-based Behavioral (NSB) control, is presented. The NSB strategy, inherited from the singularity-robust task-priority inverse kinematics for industrial manipulators, has been recently proposed for the execution of different formation-control missions with MRSs. In this paper, focusing on the experimental details, the validation of the approach is achieved by performing different experimental missions, in presence of static and dynamic obstacles, with a team of grounded mobile robots available at the Laboratorio di Automazione Industriale of the Universita degli Studi di Cassino. View full abstract»

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  • Genetic Hybrid Predictive Controller for Optimized Dissolved-Oxygen Tracking at Lower Control Level

    Page(s): 1183 - 1192
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (474 KB) |  | HTML iconHTML  

    A hierarchical two-level controller for dissolved-oxygen reference trajectory tracking in activated sludge processes has been recently developed and successfully validated on a real wastewater treatment plant. The upper level control unit generates trajectories of the desired airflows to be delivered by the aeration system to the aerobic zones of the biological reactor. A nonlinear model predictive control algorithm is applied to design this controller. The aeration system itself is a complicated hybrid nonlinear dynamical system. The lower level controller (LLC) forces the aeration system to follow these set-point trajectories, minimizing a cost of energy due to pumping of the air and accounting for system operational limitations such as the limits on the allowed frequency of switching of the blowers and on their capacity. The predictive control is also applied to design the LLC based on a piecewise-linearized hybrid dynamics of the aeration system. Casting the mixed-integer nonlinear optimization problem under heterogeneous constraints due to the limits on the blower switching frequency into the approximated mixed-integer form is done at a cost of introducing large number of auxiliary variables into the lower level predictive controller optimization task. This paper derives another nonlinear hybrid predictive control algorithm for the LLC. It is directly based on the nonlinear hybrid dynamics and logical formulation of the switching constraint. A genetic algorithm is derived with dedicated operators allowing for efficient handling of the switching constraint and nonlinear hybrid system dynamics. The efficiency of the control algorithm is validated by simulation based on real data records. View full abstract»

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  • Performance Enhancement in High-Speed Contact-Mode Atomic Force Microscopy

    Page(s): 1193 - 1201
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (757 KB) |  | HTML iconHTML  

    Atomic force microscopy is having a substantial impact on nanosciences and technologies. However, the low atomic- force-microscope (AFM) scanning speed continues to be a major obstacle that impedes the widespread adoption of AFM-based systems. This paper presents a controller design approach for constant-force contact-mode AFM operation to enhance the AFM system performance with respect to the scanning speed and the image accuracy. The purpose of the controller is to maintain a constant force between the cantilever tip and the sample surface through suitable displacement of the base end of the cantilever. Given that the sample surface profile is unknown, the difficulty in the controller design lies in attempting to regulate the contact force against an unknown and time-varying signal. To overcome this problem, it is proposed in this paper to use a two-step adaptive regulator design approach. The first step involves the use of the Q parameterization of stabilizing controllers to construct a set of parameterized stabilizing controllers. The second step involves tuning the Q parameter in the expression of stabilizing controllers so that the tuned controller converges to the desired controller needed to achieve regulation. The proposed strategy makes it possible to use small contact forces and high scanning speeds, hence improving the performance of contact-mode AFM systems. View full abstract»

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  • Linear Tracking for a Fixed-Wing UAV Using Nonlinear Model Predictive Control

    Page(s): 1202 - 1210
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1046 KB) |  | HTML iconHTML  

    In this paper, a nonlinear model predictive control (NMPC) is used to design a high-level controller for a fixed-wing unmanned aerial vehicle (UAV). Given the kinematic model of the UAV dynamics, which is used as a model of the UAV with low-level autopilot avionics, the control objective of the NMPC is determined to track a desired line. After the error dynamics are derived, the problem of tracking a desired line is transformed into a problem of regulating the error from the desired line. A stability analysis follows to provide the conditions that can assure the closed-loop stability of the designed high-level NMPC. Furthermore, the control objective is extended to track adjoined multiple line segments. The simulation results demonstrate that the UAV controlled by the NMPC converged rapidly with a small overshoot. The performance of the NMPC was also verified through realistic ??hardware in the loop simulation.?? View full abstract»

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  • Leader–Follower Flocking: Algorithms and Experiments

    Page(s): 1211 - 1219
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB) |  | HTML iconHTML  

    In this paper, we investigate a leader-follower flocking system where few members are group leaders who have global knowledge (a desired trajectory), while majority of the members are group followers who can communicate with neighbors but do not have global knowledge. The followers do not even know who the leaders are in the group. The flocking group is able to track a specific trajectory led by group leaders. In this system, all group members estimate the position of flocking center by using a consensus algorithm via local communication in order to keep the flocking group connected. Based on the estimated position of flocking center, a leader-follower flocking algorithm is proposed, and its stability is proved. A group of real robots ldquowifibotsrdquo are used to test the feasibility of the algorithm. Experiments show that this leader-follower flocking system can track the desired trajectory led by group leaders. View full abstract»

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  • Vision Based Flexible Beam Tip Point Control

    Page(s): 1220 - 1227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (590 KB) |  | HTML iconHTML  

    Because of the light weight and less wear and tear on components, the flexible beam/arm has been and will continue to be an appealing option for civil and military applications, such as space-based flexible manipulators. However, flexibility brings with it unwanted oscillations and severe chattering which may even lead to an unstable system. To tackle these challenges, a two-time scale controller is presented to track a desired tip point signal and at the same time mitigate the tip point vibration using direct vision feedback. In particular, an linear quadratic regulator (LQR) controller in the fast mode stabilizes the oscillations of the beam, and a boundary layer augmented sliding mode controller is proposed to track the desired position. To obtain more precise information of the tip point location and facilitate the easy extension to multiple-flexible-link problems, a camera is used to provide vision feedback in which the delayed vision signal is compensated by the state estimator and predictor. The vision data, which provides a direct measurement of the tip point, proves to be a better substitute for the more traditional strain gauge, which can only provide indirect measurements based on the mathematically derived mode shapes of the beam. The controller is experimentally verified, and shown to exceed the performance of other tested controllers. View full abstract»

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  • A Modified Moving Horizon Estimator for In Situ Sensing of a Chemical Vapor Deposition Process

    Page(s): 1228 - 1235
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB) |  | HTML iconHTML  

    A modified moving horizon estimator (mMHE) was developed to estimate thin film thickness, growth rate, and refractive indices in situ from a dual-wavelength reflectance measurement during chemical vapor deposition. In this application, mMHE combines the advantage of high speed of the recursive least squares estimator (RLS) and the accuracy of the moving horizon estimator (MHE). A simulated deposition process with drifting growth rate was used as a benchmark to compare the performance of RLS, MHE, mMHE, and the extended Kalman filter (EKF). The results indicate that mMHE yields more accurate estimates than RLS by incorporating a priori estimates in the optimization function. Improved accuracy of mMHE over EKF was obtained due to the horizon of data used at each time step. In addition, mMHE provided similar accuracy to MHE for short horizons, and it was much faster than MHE. RLS, MHE, mMHE, and EKF were also compared on an experimental chemical vapor deposition system where a yttrium oxide thin film was deposited on a silicon substrate. The ex situ ellipsometry characterization indicated that a more accurate and robust estimate was obtained by MHE and mMHE, compared to the RLS and EKF estimates. View full abstract»

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  • Quality without compromise [advertisement]

    Page(s): 1236
    Save to Project icon | Request Permissions | PDF file iconPDF (324 KB)  
    Freely Available from IEEE

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