Showing papers in "Journal of System Design and Dynamics in 2010"

Visual Servoing of Quadrotor Micro-Air Vehicle Using Color-Based Tracking Algorithm

Abstract: This paper describes a vision-based tracking system using an autonomous Quadrotor Unmanned Micro-Aerial Vehicle (MAV). The vision-based control system relies on color target detection and tracking algorithm using integral image, Kalman filters for relative pose estimation, and a nonlinear controller for the MAV stabilization and guidance. The vision algorithm relies on information from a single onboard camera. An arbitrary target can be selected in real-time from the ground control station, thereby outperforming template and learning-based approaches. Experimental results obtained from outdoor flight tests, showed that the vision-control system enabled the MAV to track and hover above the target as long as the battery is available. The target does not need to be pre-learned, or a template for detection. The results from image processing are sent to navigate a non-linear controller designed for the MAV by the researchers in our group.

Autonomous Hovering and Landing of a Quad-rotor Micro Aerial Vehicle by Means of on Ground Stereo Vision System

Abstract: On ground stereo vision system is used for autonomous hovering and landing of a quadrotor Micro Aerial Vehicle (MAV). This kind of system has an advantage to support embedded vision system for autonomous hovering and landing, since an embedded vision system occasionally gives inaccurate distance calculation due to either vibration problem or unknown geometry of the landing target. Color based object tracking by using Continuously Adaptive Mean Shift (CAMSHIFT) algorithm was examined. Nonlinear model of quad-rotor MAV and a PID controller were used for autonomous hovering and landing. The result shows that the Camshift based object tracking algorithm has good performance. Additionally, the comparison between the stereo vision system based and GPS based autonomous hovering of a quad-rotor MAV shows that stereo vision system has better performance. The accuracy of the stereo vision system is about 1 meter in the longitudinal and lateral direction when the quad-rotor flies in 6 meters of altitude. In the same experimental condition, the GPS based system accuracy is about 3 meters. Additionally, experiment on autonomous landing gives a reliable result.

Attitude Control of Quad Rotors QTW-UAV with Tilt Wing Mechanism

Abstract: In this paper, we propose an autonomous attitude control of a quad tilt wing-unmanned aerial vehicle (QTW-UAV). A QTW-UAV can achieve vertical takeoff and landing; further, hovering flight, which are characteristic of rotary-wing aircraft such as helicopter. And high cruising speeds, which is a characteristic of fixed-wing aircraft, can be also achieved by changing the angle of the rotors and wings by a tilt mechanism. First, we construct an attitude model of the QTW-UAV by using the identification method. We then design the attitude control system with a Kalman filter-based linear quadratic integral (LQI) control method; the experiment results show that a model-based control design is very useful for the autonomous control of a QTW-UAV.

Design and Development of Electric Active Stabilizer Suspension System

Abstract: An electric active stabilizer suspension system has been developed as a technology for controlling vehicle roll. The system includes various sensors that detect the vehicle's running state, and active stabilizer actuators that use electric motors and reduction gears to control roll. The electric stabilizer suspension system was compared with hydraulic stabilizer systems, and an investigation demonstrated the superiority of the developed system, which offers outstanding vehicle behavior, improved responsiveness and reduced energy consumption (including energy regeneration).

Experimental Study on the Vehicle Safety by Earthquake Track Excitation with 1/10 Scale Vehicle and Roller Rig

Abstract: A railway is organized by a variety of individual technologies, and functions safely and properly as a system, therefore it is necessary for the system safety to study each potential unsafe case caused due to large earthquakes. Recent reports indicate that railway vehicles could be derailed by earthquake ground motions with no fatal damages of vehicles or tracks. Thus, we should further study the derailment mechanism to pursue to minimize the risk of railway system safety against large earthquakes. Particularly, for more comprehensive understanding on the derailment mechanism of high speed railway vehicle, the derailment process of the case should be directly verified. Therefore, in this study, we arrange an experimental setup with 1/10 scale vehicle and roller rig providing both conditions of high speed wheel/rail rolling contact and large amplitude excitations. Through the experiment, we obtained the outcomes. (1) Two types of vehicle derailment motions are observed; one is rocking derailment and the other is sliding derailment. Derailment motions are similar regardless of vehicle speed. (2) By contrast, the excitation amplitudes for derailment decrease according to the increase of vehicle speed particularly by low frequency excitations. (3) The excitation amplitudes for wheel lift of flange height are relatively independent of vehicle speed. (4) Based on the similarity of fundamental vehicle dynamics between the 1/10 and full scale vehicles, those observed mechanisms in the scaled test should be applicable to that of full scale vehicle.

Consideration of Whirl Frequency Ratio and Effective Damping Coefficient of Seal

Abstract: Seal stability is often evaluated by Whirl frequency ratio (WFR) and Effective damping coefficient (Ceff) calculated on the assumption of synchronous whirl. However, the natural frequency of the rotor system must be used for calculation of WFR and Ceff when determining self-excited vibration. This paper discusses the evaluation of seal stability using WFR and Ceff. First, the stability analysis is performed by FEM for a simply supported Jeffcott rotor model, having a seal near the disk. Next, WFR and Ceff are calculated for the following two frequencies; (1) the natural frequency of the rotor system, (2) rotational frequency. As the reference of stability, the logarithmic decrement is used for comparing with WFR and Ceff. Effective damping coefficient (Ceff) calculated using the natural frequency of the rotor correctly estimates the seal stability. Whirl frequency ratio (WFR) for the natural frequency of the rotor can judge the rotor stability, but cannot evaluate how good the seal is. Both Ceff and WFR calculated by using the rotational frequency cannot give correct criterion for the rotor stability.

Parametric Studies on Static Performance and Nonlinear Instability of Bump-Type Foil Bearings

Abstract: A theoretical analysis model is presented to investigate the nonlinear dynamic behavior of bump-type foil bearings, i.e., the instability and unbalance response. In the developed model, the foil structure of bump-type foil bearings was simulated using the link-spring model, which was presented and validated in a previous study. During the calculation, the Reynolds equation and the foil structure model were coupled though the pressure and film thickness. An iteration solution method with the equation of shaft motion was applied for the shaft orbit. Parametric studies of design parameters, such as the bump number, the length ratio of the segment between two bumps and a bump, the foil thickness, the bump height, and the Young's Modulus, were presented upon the analysis of static performance and the instability of bump-type foil bearings. It is noted that more bumps or lager length ratio lead to larger load capacity. But the bearing load capacity does not change with different bump heights. Moreover, the threshold speed of instability decreases significantly with the rise of the bump number, especially when the number of bumps is low. However, it almost does not affect by other four parameters.

Experimental Study on the Thermal Characteristics of a Colloidal Damper

Abstract: Lately, ecological and intelligent colloidal dampers based on the liquid penetration/exudation in/from lyophobic nanoporous solids were proposed. Although colloidal dampers could be attractive for various applications, they are still under research, since some unexpected findings await satisfactory explanation. For instance, colloidal dampers are able to dissipate large amounts of mechanical energy without significant heating, and such result is surprising since traditional absorbers transform almost integrally the dissipated energy into heat. In this work, using a digital infrared-camera, the temperature distribution on the external surface of a colloidal damper is recorded versus the working time and the positions of the main heat sources are identified. Such experiments allow evaluation of the temperature inside the colloidal damper's working cylinder and the absorber's generated heat. Introducing the colloidal damper inside of an incubator, variation of the hysteresis shape and dissipated energy versus the working temperature can be found. From such experimental results, ratio of the generated heat to the dissipated energy is evaluated.

Interpreting Fuzzy Linguistic Information by Acquiring Robot's Experience Based on Internal Rehearsal

Abstract: This paper proposes a method for interpreting fuzzy linguistic information by acquiring robot's experience on previous movements. The quantitative assessment for a fuzzy linguistic term such as “little” depends on the spatial arrangement of surrounding environment. Robot's experience on previous movements is very useful for understanding such information in a context dependant manner. Therefore, an internal rehearsal system is introduced to acquire the robot's experience on previous movements. Such acquisition enhances the robot's capability to interpret fuzzy linguistic information in fuzzy voice commands (FVCs) according to the current environmental context. The proposed system is used to evaluate the fuzzy linguistic information related to primitive movements of a robot manipulator. Those primitive movements are realized by a behavior evaluation network (BEN) with the guidance of an internal rehearsal system. The end-effector movements and the single joint movements of a robot manipulator are considered as primitive movements. They are activated by fuzzy voice motion commands (FVMCs) and fuzzy voice joint commands (FVJCs) respectively. The proposed idea is demonstrated with a PA-10 robot manipulator by navigating the robot manipulator in the user's working space. The use of the behavior evaluation network and the internal rehearsal system introduced a better way of assessing fuzzy linguistic information by acquiring the robot's experience on the corresponding environment.

Control of Steering-by-Wire System of Electric Vehicle using Bilateral Control Designed by Passivity Approach

Abstract: Steer-by-Wire (SBW) system has a mechanical feature that the conventional mechanical linkages between the steering wheel and the front wheel are removed, and is operated by electric actuators. SBW system suits for active steering control improving vehicle stability, dynamics and maneuverability and so on. With conventional controller for SBW system, it is difficult for driver to feel reaction torque exactly from steering block. In this paper, a new SBW system of electric vehicle based on bilateral control designed by passivity approach is proposed. At first, conventional bilateral control scheme using disturbance observer is reexamined. Secondly, a novel bilateral control with passivity is introduced. We also make clear the performance of the proposed control scheme and compare it with conventional bilateral control scheme. Finally, the effectiveness of the proposed method is demonstrated by experiments with the electric vehicle.

Q-value Evaluation and Rotational Test of Flexible Rotor Supported by AMBs

Abstract: Reducing the weight of industrial rotational machinery equipped with Active Magnetic Bearings (AMBs) has been shown to achieve efficient hydraulic performance at high speed rotation. It also improves space efficiency and gives cost reductions. One of our solutions for increasing rotational speed is to experimentally demonstrate the passing of the 3rd bending critical speed. In this paper, a flexible rotor supported by AMBs is introduced. The controller design for mode separation control is studied and the stability margin is evaluated according to ISO 14839-3. After checking the stability, we successfully perform the rotation test to pass a total of 5 critical speeds, i.e., 2 rigid modes and 3 bending modes, by using a modal balancing technique. This paper proves that stability and balancing are key technologies for achieving high-speed rotation.

Analytical Study on the Safety of High Speed Railway Vehicle on Excited Tracks

Abstract: A railway is organized by a variety of individual technologies, and functions safely and properly as a system, therefore it is necessary for the system safety to study each potential case of disasters caused by earthquakes. Recent reports indicate that railway vehicles could be derailed solely by the ground motions of earthquakes with no fatal damages of vehicles or tracks. Based on the reports and facts, we believe that we should further study the derailment mechanism of a high speed railway vehicle excited by large seismic motions, to pursue to minimize the risk of railway system against large earthquakes. At the start of the study, we developed our original vehicle dynamics simulation and then employed it for numerical analyses. At the present stage, through the analyses, we obtained the following major outcomes. (1) Most of derailments are brought as the result of the rocking motion of a vehicle by track excitations underneath. Interestingly, the derailing motions are observed similarly regardless of vehicle speed. (2) By contrast, the excitation amplitudes for derailment are influenced by vehicle speed particularly in lower input frequencies. This can be explained by the sensitivity of the relative wheel/rail slide due to creepage. (3) The excitation amplitudes for 30mm of wheel lift are relatively independent of vehicle speed. (4) The wheel/rail slide strongly depends on the friction coefficient if a vehicle stationed, being relatively independent of the friction coefficient at higher speeds.

Design and Implementation of a Compact Master-Slave Robotic System with Force Feedback and Energy Recycling*

Abstract: Master-slave control is becoming increasingly popular in the development of robotic systems which can provide rehabilitation training for hemiplegic patients with a unilaterally disabled limb. However, the system structures and control strategies of existent master-slave systems are always complex. An innovative master-slave system implementing force feedback and motion tracking for a rehabilitation robot is presented in this paper. The system consists of two identical motors with a wired connection, and the two motors are located at the master and slave manipulator sites respectively. The slave motor tracks the motion of the master motor directly driven by a patient. As well, the interaction force produced at the slave site is fed back to the patient. Therefore, the impaired limb driven by the slave motor can imitate the motion of the healthy limb controlling the master motor, and the patient can regulate the control force of the healthy limb properly according to the force sensation. The force sensing and motion tracking are achieved simultaneously with neither force sensors nor sophisticated control algorithms. The system is characterized by simple structure, bidirectional controllability, energy recycling, and force feedback without a force sensor. Test experiments on a prototype were conducted, and the results appraise the advantages of the system and demonstrate the feasibility of the proposed control scheme for a rehabilitation robot.

Vibration Suppression of the Rotating Shaft using the Axial Control of the Repulsive Magnetic Bearing

Abstract: A repulsive magnetic bearing supports a rotating shaft without contact by utilizing a magnetic repulsive force between the magnets. However, because of the nonlinear characteristic of the magnetic repulsive force, the vibration during passage through the critical speed may increase. This paper investigates a vibration suppression method of the rotating shaft supported by the repulsive magnetic bearing. A vibration suppression method by controlling the axial displacement of the repulsive magnetic bearing is proposed. Its axial displacement control generates the changes of both the linear and the nonlinear coefficients of stiffness. The influence of the parameters of the axial displacement control are investigated, and these results are validated experimentally.

Numerical and Experimental Studies of Planar Passive Biped Walker with Flat Feet and Ankle Springs

Abstract: Passive biped walkers can walk down a shallow slope without actuators. This study presents a simple planar passive biped walker with flat feet and ankle springs and investigates the effect of torsional spring stiffness on the pitch motion at the ankle joints. Numerical stability studies indicated that the motion of the passive walker is stable. The physical biped walker has four legs, with each of the two legs connected so that they move identically in order to restrict the motion of the walker to the sagittal plane. Experimental results showed that the biped walker can walk in a stable manner.

Bang-bang Type Semi-active Control of Civil Structures: A Prediction-based Approach

Abstract: We propose a semi-active control of civil structures based on a one-step-ahead prediction of the seismic response. The vibration control device (VCD), which has been developed by authors, generates two types of resistance forces, i.e., a damping force proportional to the relative velocity and an inertial force proportional to the relative acceleration between two stories. The damping coefficient of the VCD can be changed with a command signal to an electric circuit connected to the VCD. In the present paper the command signal for changing the damping coefficient of each VCD is assumed to take two values, i.e., the command to take the maximum or minimum damping coefficient. The optimal command signal is selected from all candidates of command signals so that the Euclidean norm of the one-step-ahead predicted seismic response, calculated by a numerical integration, is minimized. As an example a semi-active control of a fifteen-story building with three VCDs is considered. The simulation results show that the proposed semi-active control achieves superior performance on vibration suppression compared with a passive control case where the damping coefficient of each VCD is fixed at its maximum value.

Prediction of Impact Shock Vibrations at Tennis Player's Wrist Joint: Comparison between Conventional Weight Racket and Light Weight Racket with Super Large Head Size

Abstract: The lightweight racket with handle-light configuration and large head size is recent tendency of high-tech tennis rackets, increasing power or post-impact ball velocity with an increasing racket swing speed. This paper investigated the performance of lightweight tennis racket with super-large head size in terms of feel or comfort. It predicted the effect of the mass and mass distribution of super-large sized rackets on the impact shock vibrations of the racket handle and the player's wrist joint when a player hits a flat forehand drive. The prediction is based on the identification of the racket characteristics, the damping of the racket-arm system, equivalent mass of the player's arm system and the approximate nonlinear impact analysis in tennis. A super-light weight balanced racket (mass: 292 g, the center of gravity LG: 363 mm from the butt end) and a conventional weight and weight balanced racket (349 g, LG: 323 mm) are selected as representatives. They are the super-large sized rackets made of carbon graphite with a head size of 120 square inches and the same geometry. The result showed that the shock vibration of the super-light weight balanced racket with super-large sized head is much larger than that of the conventional weight balanced type racket. It also showed that the sweet area of the former in terms of the shock vibration shifts from the center to the topside on the racket face compared to the latter. This is because the location of the grip on the racket handle is further from the location of the node on the handle of the first mode of super-light racket than that of the conventional weight racket.

Improvement of McKibben Artificial Muscle with Long Stroke Motion and Its Application

Abstract: The actuators required for a wearable system need to be flexible so as not to injure the body. The purpose of this study is to develop a flexible and lightweight actuator which can be safe enough to be attached to the human body. In the previous study, a new type of McKibben artificial muscle that had a long stroke of more than 80 % of its original length was proposed and tested. However, the damages on the tube of the actuator were found. They are caused by a large friction between the slide stage and the tube. Therefore, the life time of the actuator becomes shorter. In this paper, the improved McKibben actuator which consists of a McKibben artificial muscle on the market (FESTO Co. Ltd.), steel balls as a cylinder head and two pairs of slide stages is proposed and tested. The slide stage has steel balls set on the inner bore of the stage to decrease the friction. The steel ball in the McKibben actuator is held by two pairs of slide stages from both sides of the ball. As a result, the minimum driving pressure of the improved actuator decreases about 68 % compared with that of the previous one. The actuator can realize both pushing and pulling motion even if it has flexibility. By using these properties of the actuator, the various rehabilitation devices were proposed and tested.

Development of Small-sized Fluid Control Valve with Self-holding Function Using Permanent Magnet

Abstract: Recently, force feedback devices in virtual reality and power assisted nursing care systems have received much attention and active research In such a control system, an actuator and a driving device such as a control valve are mounted on the human body In this condition, the size and weight of the control valve become serious problems At the same time, the valve should be operated with lower energy consumption because of using a limited electrical power The typical electro magnetic solenoid valve drives its spool using a larger solenoid to open the valve The complex construction of the valve for sealing makes its miniaturization and the fabrication of a low cost valve more difficult In addition, the solenoid in the valve consumes more electrical power while the valve is kept opening The purpose of our study is to develop a small-sized, lightweight, lower energy consumption and flexible control valve that can be safe enough to mount on the human body at a lower cost In our pervious study, we proposed and tested the control valve that can open using a vibration motor In this study, we propose and test a new type of fluid control valve with a self-holding function The new valve uses a permanent magnet ball It has a cylindrical magnet and two solenoids The self-holding function of the valve is done as follows When one side of the solenoid is stimulated by the current momentarily, the solenoid gives a repulsive force to the cylindrical magnet The magnet moves toward the opposite side of the solenoid and is attracted to the iron core Then, the magnet ball moves toward the cylindrical magnet and opens the orifice The valve can keep open without electrical energy As a result, the valve with the extremely lower energy consumption can be developed

Analysis of Interaction between Grouser and Soil Using Distinct Element Method (DEM)

Abstract: When signing for tracked vehicles, which are operated on unpaved roads or soft ground, the interaction between machine and soil must be analyzed. In this research, attention was focused on the interaction under front idler, that is, traction soil by a grouser in driving system. To verify the validity of interaction analysis between a grouser and soil by using 3D DEM soil model, traction simulations and experiments were carried out. In addition, the soil model was considered particle roughness to introduce compaction effect by compression. To check the effectiveness of the soil model, compression test and shearing test were conducted. Consequently, soil behavior and porosity change were found on the tests. And comparing the results of traction simulations and experiments, soil behavior and qualitative characteristics of traction resistance were conformed. Therefore, interaction between grouser and soil could be analyzed by using the soil model considering particle roughness.

Integrated Controller Design for Automotive Semi-Active Suspension Considering Vehicle Behavior with Steering Input

Abstract: This study aimed at simultaneously achieving realization of ride comfort and steering stability through controller design for semi-active suspension taking into consideration the most sensitive frequency range of the human body and vehicle behavior when steering. A method that can improve both ride comfort and vehicle stability is proposed by separating the control range in terms of the frequency domain, where the frequency weighting in controlled variables is used. Furthermore, the controller is scheduled in the time domain to attain a positive pitch angle during slaloms. The dynamics of road disturbance is assumed and is accommodated into the controller to make control more effective. Computer simulations were carried out to investigate the effectiveness of the proposed control system by using a full-vehicle model that had a variable stiffness and damping semi-active suspension system. As a result, it was demonstrated that the proposed method can improve ride comfort, reduce vehicle motion, and synchronize the roll and pitch motions caused by steering.

Performance Prediction of Active Piezo Fiber Rackets in Terms of Tennis Power

Abstract: Several former top players sent a letter to the International Tennis Federation (ITF) encouraging the governing body to revisit the question of rackets. In the letter, the players wrote that racket technology has led to major changes in how the game is played at the top level. This paper investigated the physical properties of a new type of racket with active piezoelectric fibers appeared recently in the market, and predicted the various factors associated with the frontal impact, such as impact force, contact time, deformation of ball and strings, and also estimated the racket performance such as the coefficient of restitution, the rebound power coefficient, the post-impact ball velocity and the sweet areas relevant to the power in tennis. It is based on the experimental identification of the dynamics of the ball-racket-arm system and the approximate nonlinear impact analysis with a simple swing model. The predicted results with forehand stroke model can explain the difference in mechanism of performance between the new type racket with active piezoelectric fibers and the conventional passive representative rackets. It showed that this new type racket provides higher coefficient of restitution on the whole area of string face and also gives larger rebound power coefficients particularly at the topside and bigger powers on the whole area of string face but the difference was not so large. It seems that the racket-related improvements in play are relatively small and the players themselves continue to improve, accordingly there is a gap between a perception and reality.

Influence of Brake Pad Thickness on Disk Brake Squeal

Abstract: A squeal test using a pad with a different thickness demonstrated that a squeal with a higher frequency can be generated if a thin pad is used. The factors that changed as a result of pad thickness were termed 'difference of pad rigidity' and 'dimension difference in the thickness direction of the pad,' and the influence each factor exerted on the squeal was clarified. First, the dynamic stiffness of the pads used for the squeal tests were measured by adding a vibration that imitated the frequency and amplitude of the squeal. The measurement showed that the pad rigidity becomes hard when the pad thickness becomes thin. In addition, the pad vibrated with the same amplitude and the same phase from the frictional contact surface to the back plate in the thickness direction. The pad rigidity is in inverse proportion to the pad thickness because the pad can be viewed as springs in series in the thickness direction. Next, the influence that pad thickness exerted on squeal was analyzed by using a surface-contact-analysis model that reproduced the pad rigidity with a distributed spring and the dimension difference in the thickness direction of the pad with distance from the contact surface to the rotational center of the pad. Results showed that the squeal frequency becomes high when the pad rigidity becomes hard. If the dimension in the thickness direction of the pad becomes small, the squeal is not generated easily; however, the dimension does not influence the squeal frequency.

FEM Modeling and Experimental Verification of a Rotor System with an Open Crack

Abstract: Continuous operation of rotating machinery with a rotor crack is a risk condition since the rotor crack grows rapidly and may fail causing a catastrophic accident. This paper develops the finite element model of the rotating shaft with an open crack. The analytical method for the calculation of the natural frequencies of such a rotor system with an open crack is investigated, and the modeling of the open crack element is discussed. The natural frequency of the experimental system is measured for various cases of positions and depths of the open crack. By comparing both the theoretical and experimental results of the natural frequencies, the accuracy of the developed finite element model of the rotating shaft with an open crack is clarified.

Analysis of a Swashplate Mechanism of the Hingeless Rotor Hub with the Flybar in a Model Helicopter, Part I: Kinematics

Abstract: Swashplate mechanism is the steering control mechanism used in most helicopters. It is a complex multi-loop closed kinematic chain which controls the angles of attack of the main rotor blades. In most new model helicopters, this mechanism is also equipped with the bell-hiller stabilizer bar (flybar), to improve the stability. This paper aimed at the kinematic analysis of one of the latest architectures of the swashplate mechanism, used for hingeless rotor with the flybar. Hence, the position analysis of each module and whole mechanism, based on parallel manipulators concept with more details involved than other works, was presented here. The kinematic model was further developed to obtain Jacobian matrices, velocity and acceleration analysis in detail. Finally, a particular example was conducted and compared with an ADAMS rigid body dynamic model, to verify the analytical model. In many simulated cases, the results matched.

Effect of Structural Dimensions on Dynamic Stability of Elastic Beam Subjected to Axial Flow in Confined Narrow Passage

Abstract: The evaluation methodologies for the flow-induced vibration of an elastic beam subjected to an axial flow in confined narrow passage are reported. One of authors has already proposed an analytical method using the Navier-Stokes equation for the dynamic stability of an elastic beam subjected to an axial flow confined in a narrow passage. In this paper, by using the proposed analytical methods, the numerical studies are performed taking three kinds of support conditions as parameters, that is, a cantilever fixed at the upstream side, a cantilever fixed at the downstream side, and a simple support beam at the both sides, respectively. Moreover, the parameter-studies are also performed concerning with a width of annular gap, viscosity of a fluid, and structural damping. And the effects of support conditions of a structure, structural damping, and fluid characteristics on the dynamic stability of an elastic beam due to an axial flow confined in a narrow passage are clarified for proposing a safety dynamic design guideline concerning axial flow-induced vibrations in industries.

The Parameterization of All Robust Stabilizing Simple Repetitive Controllers

Abstract: The modified repetitive control system is a type of servomechanism for the periodic reference input. That is, the modified repetitive control system follows the periodic reference input with small steady state error, even if a periodic disturbance or an uncertainty exists in the plant. Using previously proposed modified repetitive controllers, even if the plant does not include time-delay, transfer functions from the periodic reference input to the output and from the disturbance to the output have infinite numbers of poles. When transfer functions from the periodic reference input to the output and from the disturbance to the output have infinite numbers of poles, it is difficult to specify the input-output characteristic and the disturbance attenuation characteristic. From the practical point of view, it is desirable that the input-output characteristic and the disturbance attenuation characteristic are easily specified. In order to specify the input-output characteristic and the disturbance attenuation characteristic easily, transfer functions from the periodic reference input to the output and from the disturbance to the output are desirable to have finite numbers of poles. From this viewpoint, Yamada et al. proposed the concept of simple repetitive control systems such that the controller works as a modified repetitive controller and transfer functions from the periodic reference input to the output and from the disturbance to the output have finite numbers of poles. In addition, Yamada et al. clarified the parameterization of all stabilizing simple repetitive controllers. However, the method by Yamada et al. cannot be applied for the plant with uncertainty. The purpose of this paper is to propose the parameterization of all robust stabilizing simple repetitive controllers for the plant with uncertainty.