This paper summarises the content of the associated keynote presentation, one objective of which is to outline the development of the Advanced Control and Test Laboratory (ACTLab) at the University of Bristol, since its original inception in 1999, together with an appraisal of the research that is conducted in the laboratory. Hence, aspects of our work on adaptive control, dynamically substructured systems, data fusion and associated experimentation will be included in the talk. The other objective of the presentation is to place due emphasis on ACTLab links with Japanese researchers, since they have had (and continue to have) a very significant impact on the laboratory - both in terms of fundamental concepts and the associated application and implementation of the ideas.

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Passive vibration control measures typically involve either introducing separately or in a combination changes to a system, such as adding damping or dissipation, stiffness and mass. This presentation will explore two particular application areas namely isolation and the use of a vibration absorber. For isolation the typical passive system has limitations, so research has been conducted into introducing nonlinear characteristics which include friction, nonlinear viscous damping and switchable stiffness changes. In some scenarios these provide additional benefits, albeit that the systems now become nonlinear, and the philosophy behind their consideration will be presented. The analysis of these configurations will then be accompanied with numerical simulations and experimental validation to clarify how and why things are different. More recently there has been some interest in the use of a nonlinear vibration absorber. A summary of some progress to date in this field, including theoretical and experimental work, will be given. Suggestions and guidelines for its potential will be explored as will issues that might make its general adoption difficult.

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The nonlinear oscillating wing stroke of diptera has been attributed to a pre-compressed flight motor anatomy. To date, biological evidence has demonstrated the nonlinearity and mathematical evaluations of simplified mechanical wing motor models link empirical observations to characteristic bistable oscillator dynamics. It was concluded that the fast switching between two stable wing orientations leads to high velocity movements, capable of large aerodynamic force generation which is more efficient than sinusoidal motions. While interesting and informative, the investigations have yet to address why the pre-compressed motor anatomy is well-suited to produce flapping aerodynamic forces for various flight conditions. This research seeks to explore the benefits of the dipteran wing motor through a representative structural model to uncover motor components and configurations important for flapping force generation. With such a study, improved design solutions for flapping mechanisms may be proposed that could find application in micro air vehicles. Analytical and experimental investigations suggest that the combination of adjustable axial suspension of the motor and its degree of pre-compression critically regulate the wing motor motions. While bistable motor configurations are shown to produce the most energetic dynamics, the vast range of velocity amplitudes obtained from a variably pre-compressed and stiffened motor exemplify a substantial versatility of flapping force generation is available for advanced flight control. The results suggest that micro air vehicles adopting a pre- compressed wing motor with axial flexure may greatly benefit in incorporating control over axial pre-load and suspension characteristics to enhance the range of flapping forces achievable.

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The paper presents a non-interference measurement and diagnostic method for the parametric identification of vibrations in rotating engine blades, based on blade tip-timing (BTT) measured by optical sensors. Because of the inherent under-sampling nature associated with BTT measurement, effective algorithms are needed to extract key vibration parameters such as frequency and amplitude from the measurement. In this paper, an enhanced estimation of signal parameters via rotational invariance technique (ESPRIT) is proposed. The main advantage of this technique is its ability to analyze both single and multi-mode blade vibrations spreading across a wide dynamic range, while accommodating the effect of varying rotational speeds and sensor installation errors. Analysis and numerical simulation have shown that the method can effectively improve the accuracy and robustness of vibration frequency and amplitude estimation compared to the traditional ESPRIT.

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Real structures are inevitably subject various uncertainties due to manufacturing tolerance, assemblage error, and in-service degradation, etc. As a result, structural vibratory responses may exhibit significant variation with respect to the nominal one under ideal situation. Excessive response variation is detrimental to the safe and reliable operation of structures. This research explores the possibility of mitigating structural vibratory response variation by modifying the mean surface geometry design. That is, we assume the uncertainties remain unchanged, and attempt to reduce response variation by perturbing the nominal geometry. Essentially, this is equivalent to identifying necessary change of parameters defining the structural surface geometry towards robust optimization. Mathematically, such a problem is intrinsically challenging, because 1) a very large number of elements are necessary to describe subtle change of surface geometry when conventional finite element method is employed; and 2) inverse identification under uncertainty is typically carried out using Monte Carlo simulation type analysis which is computationally prohibitive. In this paper, we present a novel, efficient way of robust geometry optimization towards reducing response variation. We adopt the NURBS finite element, i.e., the non-uniform rational B-spline finite element method, which can directly describe complex surface geometry as well as its modification smoothly. To improve the analysis efficiency, we develop a sensitivity-based approach to directly extract the response variation, and then use such prediction to identify optimal modification of the geometry that yield the minimized response variation. This new methodology is illustrated by case analyses on wind turbine structures.

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A rotating beam subjected to a torsional excitation is studied in this paper. Both quadratic and cubic geometric stiffening nonlinearities are retained in the equation of motion, and the reduced model is obtained via the Galerkin method. Saddle-node bifurcations and Hopf bifurcations of the Period-1 motions of the model were obtained via the high order harmonic balance method. The period-2 solutions, which are emanated from the period-1, are obtained by the combined implementation of the harmonic balance method, Floquet theory, and Discrete Fourier transform (DFT). The analytical periodic solutions and their stabilities are verified through numerical simulation.

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Piezoelectric wafer active sensors (PWAS) have been developed for structure health monitoring (SHM) for years, however, SHM at extreme environments has rarely been attempted due to the low phase transition temperature of common piezoelectric materials. In this paper, new piezoelectric materials-Langasite (LGS) has been selected for a pilot study for structure health monitoring applications. A preliminary study is performed to verify the possibility of developing the LGS high temperature piezoelectric waver active sensors. The E/M impedance method is applied to detect the frequency behavior of the PWAS. Experiments that verify the basic frequency behavior of the LGS PWAS in high temperature environments have been carried out. Further validations are conducted by testing structures attached by LGS PWAS at elevated temperatures. The results, at the first time, show that LGS is ideal to make piezoelectric wafer active sensors for high temperature structure health monitoring applications.

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Among various types of Tuned Mass Dampers(TMDs) for the civil structures (such as tall buildings, slender towers and long bridges), dual-functional electromagnetic TMDs have received a lot of attentions due to its enhanced effectiveness in mitigating the vibration of the primary structures and harvest the energy at the same time. This paper quantitatively investigates the effectiveness of dual-functional electromagnetic TMDs to the building performance regarding to building safety, human comfort and energy harvesting when the primary structure is being disturbed by the wind excitation regularly and seismic excitation in an extreme situation. Six corresponding individual Performance Indexes (PIs) are defined and optimized using H_2 optimization criterion so as to determine the optimal parameters of dual-functional electromagnetic TMDs, resulting in the best performances of building safety, human comfort and energy harvesting respectively. Moreover, a combinational PI is defined and optimized to evaluate the overall effectiveness of dual-functional electromagnetic TMDs including the priority concerned Pis and the energy harvesting performance. A case study is then performed based on the parameters a real building to verify the effectiveness of the optimized dual-functional electromagnetic TMD. Simulation results of dual electromagnetic TMD are presented in comparison with classic TMD and without TMD case.

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This study employed a resettable variable stiffness TMD (RVS-TMD) to alleviate detuning effect. The RVS-TMD is composed of a TMD and a resettable variable stiffness device (RVSD), which consists of a resettable element and a controllable stiffness element. By varying the stiffness element of RVSD, the detuning effect can be mitigated. While, by actuating the resettable element, the hysteresis loop of the RVSD can cover all four quadrants in the force-deformation diagram and thus result in more energy dissipation. However, to adjust the stiffness of the TMD system, the problem of time-delay is inevitable. For an active control system, time is consumed in data acquisition, data processing, on-line calculation, and control force execution. There is always a delay between the time at which the control force is assumed to be applied and actually applied, which may cause degradation in control efficiency. Therefore, the control design of a RVS-TMD system should take into account the effect of time delay. This study applied delayed control gains to alleviate the time delay effect based on the LQR optimal output feedback control algorithm. A parametric study was conducted to demonstrate the relationships of delayed gains with intentionally-added delay time. The results of numerical simulation show the application of optimally-delayed gains significantly alleviates the time delay effect and assure the desired control efficacy.

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This paper introduces a method of on-line estimation of the wheel cylinder pressure, which can improve the regulation accuracy of the wheel cylinder pressure and reduce the actuation time of the solenoid valves, thus, bring the advantages of improving the quality of pressure control, the longevity of the solenoid valves and the comfortableness of vehicle. Firstly, a mathematical model is established to estimate the wheel cylinder pressure using lumped-parameter bond graph technique. The discrete system difference equation can be derived from the proposed model to estimate the real wheel cylinder pressure using the data from pressure sensors in real time. Secondly, a proper digital filter is applied to post process the estimated wheel cylinder pressure to make it suitable for pressure controller, for certain fluctuation exists at the brake transmission line with high frequency, which is undesirable for the controller. The pressure lag introduced by the filter is compensated by data processing. Finally, a device is introduced to improve the transient characteristics of the braking system, which would improve the quality of pressure control. Test has been made on the test bench, and the accuracy of the on-line estimation of wheel cylinder pressure is proved to be satisfactory by test result.

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We report the scaling analysis of levitation-induced vibration energy (LIVE) harvesters. The analysis was conducted on the double-repulsion configuration in the moving magnet composite. This configuration has been shown to reduce the electrical damping from the coils, improve the dynamics, and increase the power output response of the harvester. The scaling analysis covered a broad length scale from micro to macro scale based on the distance between the stationary magnets (d = 0.36mm to 360mm) and a wide range of applied base accelerations from 0.01g to 10g. The magnetic flux calculations showed similar flux densities across all the length scales. However, the magnetic force field exhibited a linear response to scaling. The linear stiffness increased with increasing size while the nonlinear stiffness decreased with increasing size. The resonance frequency decreased with increasing scale regardless of the applied base acceleration while the peak velocity also decreased with increasing scale due to the decreased spacing. The resonance frequencies and bandwidth however increased as the applied acceleration increased. Also, the voltage and power response of the harvesters for any given acceleration scaled by 2-4 orders of magnitude as the distance between the stationary magnets was scaled by one order of magnitude. The model was compared with the experimental harvester and the results were in close agreement.

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An axisymmetric two-body wave energy converter is studied here. Previous results show that the cross couple terms of the added mass and damping can be neglected when the distance between the two buoys is far enough. A linear dynamic model of this two-body system is established and analyzed based on linear wave theory. The optimal power takeoff stiffness and damping were obtained. The numerical results show that large bottom body will result in a large output power. However, it is also constrained by the power takeoff stiffness. The viscous damping will always have bad influence on energy harvesting. The performance of a two-body point in irregular wave was also investigated.

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This paper reports a new approach to improving the electro-mechanical coupling by stiffness compensation through negative force based on magnetic effects. Two sheets of permanent magnet are placed in the vicinity of a piezoelectric composite cantilever, and another permanent magnet bar is attached onto the beam with one end located between two sheets to form a monopole-like proof-mass. Analyses and experiments are carried out to demonstrate that a linear magnetic field yielding linear, negative force can be produced as beam vibrates, which results in the reduction of the effective stiffness of the piezoelectric cantilever and therefore the enhancement of its electro-mechanical coupling effect.

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The energy delivery from piezoelectric harvester to resistive load is investigated in this paper. Two types of piezoelectric harvesters are studied, i.e., 33-mode multilayer piezoelectric stack, and the same stack with force amplification frame. Theoretical modeling of generated voltage, electrical power, and power delivery ratio from piezoelectric harvester to resistive load is established. Experiment verification of the theoretical modeling is also carried out. A precise force controllable piezoelectric harvesting measurement method with 1 nm resolution of displacement monitoring was developed to make the experimental results more accurate. Experiment results match well with theoretical modeling, including (1) the voltage cross various resistors, (2) the electrical power delivered to those resistors, and (3) the ratios of the electrical power delivered to resistive loads over the generated electrical power. Moreover, it is proven that 70% of generated electrical power can be directly delivered to a matched resistive load for a real material based piezoelectric energy harvester and √2/2% of generated electrical power can be directly delivered to a matching resistive load for ideal material based piezoelectric energy harvester.

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This work reports the energy harvesting performance of a piezoelectric curved energy generator (THUNDER) under harmonic vibration excitation. Most piezoelectric energy harvesting literatures study monolithic piezoceramic (PZT) thin beam sheet. Compared to the less flexible PZT, although THUNDER is more difficult to model, THUNDER has better vibration absorption capacity and higher energy recovery efficiency. The electromechanical model is developed based on linear constitutive law of the piezoelectric material and the substrate. The AC current and AC power generated by this model is obtained. This article also investigates the AC-DC power output with the THUNDER connected to a bridge rectifier and a capacitor. The analytical solution of the AC-DC power is derived in terms of the vibration amplitude and frequency, energy harvesting circuit, and the THUNDER'S geometric dimensions, which include the excitation frequency, the damping ratio, the natural frequency of the THUNDER, the electrical load, and the radius of curvature of the THUNDER. The effect of all above factors on the power output is investigated.

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This paper presents design of a vehicle stability control system for a micro electric vehicle with four in-wheel motors by driving/braking torque control considering both vehicle handling and stability and energy consumption efficiency of in-wheel motors. To obtain a vehicle dynamical model for design of the vehicle stability control system, the subspace system identification method is applied using the input/output signals obtained from simulations of the full vehicle model. The full vehicle model constructed by a simulation software based on the Modelica modeling language have been provided by the benchmark problem No.3 of the Society of Automotive Engineers of Japan and the Society of Instrument and Control Engineers. After analyzing frequency responses for the identified vehicle model, an H-infmity controller is designed to meet the requirement in terms of vehicle handling and stability and energy consumption efficiency of in-wheel motors. By carrying out simulations under the crossing side wind test and the double lane change test for the vehicle model, it is demonstrated that the proposed control system satisfies the performance requirements.

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Drive/brake-by-wire technology is a driving/braking control technology designed to improve the maneuverability and stability of an automobile. With using drive/brake-by-wire technology, driving/braking control can be actively performed against changes in the road surface and physical parameter errors. It can be used to construct a system that is independent of the driving ability of the driver and that reduces the driver ' s load by performing corrections based on changes in the driving situation. In conventional studies, driving/brake-by-wire technology has been considered for vehicle velocity tracking control, where the vehicle velocity was tracked to the reference model velocity in order to develop a control method for switching the velocity controller and slip-ratio controller to prevent wheel slip based on changes in the driving situation. However, one problem was that only braking was considered without driving. In addition, the systems were not robust against physical parameter errors and changes in the driving situation. In this paper, we propose a vehicle velocity tracking control method that considers both driving and braking and is robust against physical parameter errors and changes in the driving situation. Similar to the conventional studies, we realize vehicle velocity tracking control by switching between a vehicle velocity controller and slip-ratio controller according to changes in the driving situation.

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In this paper, a controllable colloidal damper designed to work as a vehicle suspension is experimentally investigated. In order to control the damping properties (dissipated energy and damping coefficient) as well as the elastic characteristic (spring constant) of a colloidal damper, the pressurization level inside the cylinder has to be dynamically adjusted by using a pressure controlling device. Concretely, a pumping device in communication with the cylinder, able to force the working liquid to flow into and to flow out from the cylinder is employed. In this way, a controllable parameter, called initial pressure, is adjusted to achieve ideal comfort conditions for the vehicle's passengers. First, the working principle, the main components, the model of vibration and the control system of a controllable colloidal damper are explained. Using some illustrative hysteresis change diagrams, variation of the dissipated energy, damping coefficient and spring constant versus the initial pressure is phenomenologically interpreted. Experimentally obtained results are used to validate the phenomenological model, and then to evaluate the sensitivity of the proposed system. Since the experimentally obtained damping ratio fluctuation (up to 153%), is larger than the required change of damping ratio for Kelvin-Voigt and Maxwell suspensions (133% and 100%, respectively), one concludes that the proposed controllable colloidal damper has the ability to accommodate real applications.

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Road noise is one of the main interior noises in passenger cars. This phenomenon is caused by road roughness, and tire vibration characteristics play a major role. Recent research showed that not only radial vibration but also lateral vibration of a tire has an impact on road noise. This paper describes the modeling of tire lateral vibration and one idea for control of natural frequency against tire lateral vibration. First, experimental modal analysis was performed to reveal the mode shape exciting lateral vibration. Accelerometers were put on three positions of the tread lateral direction, two positions of each sidewall, and 12 positions of the circumferential direction every 30 degrees. Mode shape and natural frequency were confirmed. Second, we built the tire vibration model based on thin cylindrical shell theory. This model has a tread ring as a continuous body and springs expressing the sidewall stiffness. It is assumed that tire vibration follows non-elongation deformation. Kinetic and potential energy were derived, and natural frequencies were predicted by Rayleigh's method. The theoretical value of lateral bending mode closely corresponded to the experimental data. Focusing on unknown parameters regarding tread, sidewall stiffness and tension, only the latter two have influence on natural frequency. Finally, sensitivity analysis was performed using a natural frequency formula. Changing tension, sidewall stiffness, and change ratio of natural frequency were confirmed.

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This paper proposes extension of the path-generating regulator (PGR) to a tracking problem along a straight pas- sage for car-like robots. The PGR is a control method for a vehicle so as to orient its heading toward a tangent to one of the curves belonging to a family of path functions. Originally, it applies to the navigation problem so that the vehicle moves and stops at the origin in the direction of horizontal axis in a Cartesian coordinate system. First, we extend it to the tracking problem along a straight passage. This is accomplished by modifying the family of path functions and taking the horizontal axis on the center line of the straight passage. Next, we discuss the convergent property using Lyapunov's method and derive the condition that the vehicle speed should satisfy. To avoid collision with the boundary of the passage, such as a wall, the PGR automatically produces the motion so that the vehicle goes backward and then performs a Y-turn. Numerical simulations show that the proposed PGR has not only convergence properties, but also robustness against these disturbances. It is also pointed out that the steering angle limitation degrades the performance of the PGR.

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For high-speed trains, active control of the pantograph is crucial technology to collect electrical current from the overhead contact wire. In this paper, a mathematical model of the pantograph-catenary system is developed to design a controller, and then a sliding mode controller is proposed to regulate the contact force in the presence of variation in the equivalent stiffness of the catenary system. Although the proposed controller is based on the standard sliding mode control theory, some modifications are made from a practical point of view, in particular necessary sensors for its implementation.

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This paper introduces mathematical models of three degree-of-freedom (3-DOF) half car model of railway vehicle suspension. The governing equations of railway vehicle model are developed based on Second Newton's Law. The development of controller techniques applied to reduce unwanted body response of railway vehicle is presented. The controllers used in this study are PID and limited state feedback (LSF) controller. Genetic algorithm is used to optimize the PID controller by minimizing the mean square error of the railway vehicle body acceleration, and sensitivity analysis (SA) method is used to find an optimal value of LSF controller. The results show that the proposed control schemes are able to improve the vehicle body response effectively.

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In generally, a suspension system needs to be soft to insulate against road disturbances and hard to insulate against load disturbances. It cannot achieve with a traditional passive suspension that only considered to the stiffness and damper. On other hands, the formula cars need high tire grip on racing challenge by reducing rolling displacement at corner or double change lands with the simplest suspension dynamics system. In this study, the paper clarifies some issues related to suspension system with inerter to reduce displacement and rolling angle under impact from road disturbance on Formula SAE Car. In this paper, we integrate some kinds of suspension system with inerter on quarter-car and half-car models. We propose some new designs, which have some advantages for suspension system by improving dynamics. We optimize design of model based on the minimization of cost functions for roll dynamics, by reducing the displacement transfer and the energy consumed by the inerter. The base model is a passive suspension model then we carried out quarter-car and half-car model with different parameters; they show the benefit of the inerter in proposal suspension system. The advantage of research is integration a new mechanism, the inerter; this system can improve the vehicle oscillation.

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This paper proposes a method to guarantee robust stability for anti-lock braking system (ABS). The objective of ABS is to maintain slip rate at the optimal value in any road condition. The dynamics of ABS depends rationally on uncertain parameters, which are car velocity and friction coefficient between tire and road. We design a method to consider variation of these parameters. Since the friction coefficient cannot be estimated in real time, robust control is applied for any friction coefficient in the prescribed range. On the other hand, the car velocity can be estimated in real time. Gain scheduling control whose scheduling parameter is the car velocity is applied for ABS. Control law is designed to minimize the quadratic cost function, which is model of LQ control. The polytopic representation for the system with uncertain parameters is provided. By using descriptor representation and linear fractional transformation (LFT), we show that the system which is affine with respect to car velocity and friction coefficient can be obtained.Then, the problem is formulated as solving a finite set of Linear Matrix Inequalities(LMI). Finally, the robust stability and the robust performance are guaranteed theoretically. The effectiveness of the proposed method is illustrated by simulation and experiment.

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We experimentally investigated the maneuverability and comfort of an inverted-pendulum vehicle when operated with handle roll rotation and handle yaw rotation. Our experimental vehicle can switch between handle modes and is equipped with a Bluetooth communication function for measurement of the state of the vehicle. We thus investigated the two handle operations at high, intermediate and low gains. The experimental course was a slalom course with two cones placed at an interval of 1.8 m. The research participants made one round trip. The trajectory of the vehicle was measured by a three-dimensional motion analysis device called VICON. Maneuverability for the two types of handle operartios and for various control gains was determined from data of the trajectory of the vehicle, revolutions of the wheel, the steering angle, and a questionnaire.

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In this paper, a commercial active hood lift system (AHLS) is optimally designed and evaluated. After introducing the working principle of AHLS operated by a gunpowder actuator, the mathematical model of the AHLS is formulated. The dominant factors that are sensitive to performance index are defined by mathematical equations. Structural constraint conditions of system such as limited space are defined in details. Since the response time system is the most important factor for reducing the damage of the pedestrian, the kinematic structure of AHLS is optimally designed to decrease the response time under the constraint conditions on the basis of trial and error method. In order to evaluate the proposed method, the performances of the optimally designed model including the deformed distance and the response time are compared with the conventional AHLS model.

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To reduce the collision shock and injury risk to an infant in a child car bed (or child safety bed or in-car crib) during a car crash, it is necessary to keep the force acting on the bed constant and below a certain allowable value. To this end, we propose a semi-active child car bed with joint application of regular and inverted pendulum mechanisms. The bed is supported like a pendulum by arms, and the pendulum system is supported like an inverted pendulum by arms. This system not only reduces the impulsive force but also transfers the force to the infant's back using a spin control system, i.e., the force acts perpendicularly on the bed. The spin control system was developed previously. In the present study, an acceleration control system is developed. One of the characteristics is that this system has the merits of both a regular pendulum-style child car bed and an inverted pendulum-style child car bed. The regular pendulum-style one is suitable when moderate impulsive forces are involved because the bed moves smoothly soon after the force begins to affect the bed. The inverted pendulum-style one is suitable when large impulsive forces are involved because the arm that is initially tilted backward, which constitutes the inverted pendulum, is difficult to move under weak forces. Therefore, the proposed child car bed is able to increase the acceleration of the bed gradually and maintain it around the target value. This paper focuses on the control system. The control law is introduced, and the robustness is examined using numerical simulation.

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The paper presents the benchmark of control algorithm for flywheel energy storage system (FESS) with active magnetic bearing (AMB) on electric vehicle (EV). EV (especially, battery EV) cannot run long distance than gasoline vehicles. One of the solutions of this problem is using AMB FESS. If AMB FESS is useful for charger and discharger, EV can run long distance. But, because AMB FESS is unstable system, it must be controlled. Moreover, applying AMB FESS to EV, it will be complex system. So, it is necessary to benchmark controllers which are applied to AMB FESS on EV. Because of satisfying requirements of design which were given by motor companies, robust adaptive controllers were selected for AMB FESS controllers. The controllers were benchmarked by some evaluate items in simulation. The evaluate items are difficulty of design, disturbance suppression, and power consumption. Difficulty of design was quantitatively evaluated by the number of tuning parameters. Disturbance suppression was quantitatively evaluated by 2 norm and infinity norm of the displacement of flywheel rotor. Power consumption was quantitatively evaluated by the original function. Simulation was done on the assumption that normal driving by the flywheel-car (which was made by our group). Through the benchmark, interesting results and tendency are found. The most interesting result or tendency is that the controllers which have high rigidity and appropriate bias input can suppress power consumption of course disturbance. So, the first challengeable controller - Simple Adaptive Controller with epsilonl-modification and variable gamma approach (using bias control method) is proposed and verified the best robust adaptive control algorithm for AMB FESS on EV. The controller has high rigidity and appropriate bias input and can design easily. The controller has not so many tuning parameters.

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For these three decades, active suspension systems for vehicle have been studied and various control theories have been applied. One of those control theories is sliding mode control theory, which is extremely systematized in the nonlinear robust control theories. The most useful feature of sliding mode control is to theoretically show the invariant performance against uncertainty of satisfying the matching condition. Sliding mode control seems to be suitable for control of the active suspension for vehicles, since high robustness to uncertainty of masses or actuators is needed. In practice, however, response delay of actuators might cause deterioration of suspension performance especially in high frequency bands. Therefore, we propose a design method of sliding mode controller to lead continuous control inputs with the describing function method.

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Advanced traffic systems, for instance automatic platooning control, are required to solve environmental problems and traffic problems. The vehicles under the automatic platooning control can travel automatically with maintaining short distances between vehicles and following preceding vehicles. However, precise control is necessary to ensure driving safety because vehicles controlled by automatic platooning maintain short distances between vehicles. Accurate parameters are important to conduct high performance of automatic control because control system is affected by a change of vehicle parameters. Especially parameters of trucks are changed widely according to the loaded condition. Performance of the automatic platooning control is affected by changing of vehicle parameters. Therefore the accurate parameters is required in real-time. Among the vehicle parameters, the yaw moment of inertia is an important parameter for the vehicle steering control, cornering or lane change. A method is proposed using Dual Kalman filter algorithm, which estimates state of vehicle and parameters of vehicle simultaneously, to identify the yaw moment of inertia of vehicle on travelling. Performance to estimate the yaw moment of inertia was evaluated through the experiment using the GPS sensor. The yaw moment of inertia was estimated by the proposed method. The results of the experiment show the proposed method is effective for the identification of the yaw moment of inertia. Validity of the proposed method is confirmed through the examination.

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This paper demonstrates an amazing ability of a developed seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. Since the measuring range of the displacement sensor is higher than the natural frequency of itself, it is difficult to detect a low frequency vibration below 1 Hz using conventional seismic-type displacement sensors. Therefore, for detecting earthquake waves with a long period, acceleration sensors are used commonly. However for obtaining absolute displacements by the acceleration sensor, it is necessary to integrate twice of the acceleration signal. Then the drift problem guided to signal saturation will be happen essentially in the acceleration process by unknown signals. This seismometer-type absolute displacement sensor is consisted of a sensor body with a moving mass and its supporting springs, feedback control circuits and a third order phase lag compensator. The natural frequency of the sensor body located at 6.8Hz originally is reduced to 0.23 Hz using by acceleration feedback mainly and then moving stroke of the moving mass is compressed to 1mm to 1/630mm. Moreover the new natural frequency of 0.23Hz developed by feedback control is sifted to 0.065Hz by the third order phase lag compensator. Therefore the sensor has a measuring range from 0.08Hz to 10Hz, in addition to no drift problems by the use of feedback control way. In this way, the seismometer-type absolute displacement sensor with the amazing ability has been realized to measure the long period over 10 second of earthquake waves. In addition, the large magnitude to measure 630mm is expected, nevertheless a small size with moving stroke of 1mm. So far as we know, such a sensor for measuring absolute displacement is very novel in the world. In this paper the ability of the sensor will be shown by simulation and experiment.

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In this paper, the tracking control of mobile harbor (MH) crane is proposed for dynamic positioning of containers to moving container ship. During operation of MH exposed to external disturbances, the MH and container ship have 6 degree of freedom motions. In such cases, a container position becomes difficult to control accurately due to the unwanted swing motion of pay load and variation of target position. It is the most significant technology in the MH system. The MH crane model in 3D space with roll, pitch and heave motion caused by disturbances is derived. Then, this model is linearized and the parameters of the linear model is identified by experiments of 1/20 scale model. In the proposed tracking control, a preview control method is applied including feed-back and feed-forward control with predicted reference information in near future. Through numerical simulations and experiments of small scaled model, the performances of the proposed position control method are verified when roll and pitch motion is generated as disturbances.

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A new control design framework for vibration control, the hybrid control of active and semi-active control, is proposed in the paper. In the hybrid control framework, structural systems having both of an actuator for active vibration control and a semi-active control device, e.g., MR damper etc., is defined as the control object. In the proposed control approach, the higher control performance is aimed with the hybrid manner between the actuator and the semi-active control device. A design method to determine the active control law and the command signal of the semi-active control device based on the one-step prediction of the control output is proposed. A design example of the vibration control for a base-isolated building is presented to show the effectiveness of the proposed control framework.

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This study proposes a new semi-active base-isolation system using harmonically varying damping (parametric excitation of damping) and having a filter consisting of the neural oscillators. The harmonically varying damping is the oscillation of the damping coefficient by using a variable damper and can shifts the frequency of the damping force by the frequency modulation. The new semi-active vibration control method using this parametric excitation of damping induces interference among structural vibration components by the controlled parametric excitation of damping, and the effect of the interference can reduce the vibration amplitude of structure excited by multiple frequency input. The key technology is extracting the designated frequency components from external input or structural vibration to modulate the frequency of the damping force to an appropriate frequency for the parametric excitation of damping. In this study, we use neural oscillators, called FitzHugh oscillators, as the filter to extract the frequency component, because such nonlinear oscillators have synchronization property with periodic external input in a frequency region close to the natural frequency of the oscillator. We show the special configuration of the neural oscillators for frequency modulation in this paper. The viability of the proposed system is tested in numerical simulation.

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Reducing collapse damages of buildings and constructions by earthquakes is an important issue for human lives. Hydraulic active vibration suppression is made by mobilizing cylinders with the most suitable command signals through servo valves after computing data. These data are collected by various measuring instruments. However unforeseeable contingency takes place in natural disasters such as electric power failure or disconnection by sharp vibration. If any of such disaster should occurs, the system does not function. The excess power would rather cause out of control. The system itself contains potential for harm. This study is to propose the simple and reliable control system for hydraulic cylinder using robust mechanical structure instead of electronic measurement and control. The results of model experiments and simulations presented in our previous works show good results. But it is necessary to raise the precision of simulation to put it into practical use. For the purpose of improving accuracy, we made experiments and simulations for various parameters such as inertial load mass, link ratio for control sensibility, and coefficient of oil switching flow and so on. Then, the control performance is evaluated.

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In this paper we propose a novel design of a hexarotor helicopter called "Non-planar Hexarotor Helicopter." The purpose of this study is to perform autonomous flight control of the proposed helicopter and put it into practical use. First, we present the characteristics and application examples. Six rotors are divided into three pairs and placed on three orthogonal planes. This configuration allows for decoupling of translational and attitude motions and realize absolutely free flight in three dimensional space that has never been achieved by any other aircraft. Variable thrust can be generated via variable-pitch rotors. Additionally, by enclosing all mechanical parts within a frame, it is possible to protect it from collisions, fly in narrow space, and roll on the ground. Unless it is needed to hover, it can move to the destination using rolling motion, thereby reducing energy consumption. The proposed helicopter is suitable for a number of flight missions, such as the scene of an accident and the inspection of the sewer. Other applications imaginable are shown in this paper. Second, We performed mechanical design of the proposed helicopter in detail towards flight testing. Its hardware specification and CAD drawings are described. Third, static and dynamic models are derived from geometrical relations and simple aerodynamic models. We also designed control systems using modern control theory and backstepping. Finally, we simulated the designed system to examine whether the performance meets requirements.

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A flying cargo system based on multi-copter is presented in this study. This system is designed for transporting at irregular ground. Two types of specialized "Direct Touch Operation" method for flying cargo system were tested. The first flight mode is "Direct push operation", and second flight mode is "Touch / Auto Operation". We report the results of both flight modes. These are intuitive operation method by which any one can operate flying cargo system. Flying cargo can do transportation in horizontal and vertical directions without topographically effect.

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This paper presents a heliport for industrial multi rotor helicopter which is possible to exchange battery automatically. Recent years, study of multi rotor helicopter is active in all over the world and it develops for practical use is in progress. In our group, we develop multi rotor helicopter named Mini-Surveyor, and we are trying various studies. However, flight time of multi rotor helicopter is as short as 10 to 15 minutes because most of them are drive by lithium polymer battery. So, in order to extend the flight time of the multi rotor helicopter, we develop autonomous battery exchange system. We have developed an automatic battery exchange system than before. But it is directed to small multi-rotor helicopter, so payload is too small to operate using some device and there was a problem in landing system. So now, we develop new automatic battery exchanger. This new system is developed based on old system, but when the multi rotor helicopter take off and land, it performs accurate take off and land at battery exchanger using by the Vicon system which is high accuracy positioning system. In addition, we develop transportable heliport system which is consisting of autonomous battery exchanger, Vicon system, generator and others. It is designed to be able to operate multi rotor helicopter and battery exchanger in long time at dangerous place such as disaster cannot stay a person and it is possible to operate the multi rotor helicopter only the heliport system. Here we report design of heliport system including autonomous battery exchanger and discuss autonomous takeoff and landing from the heliport.

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In this paper, collision-free guidance control of multiple small unmanned helicopters is designed. Collision avoidance of the helicopters should be considered in the control system design for safe operation. Therefore, a guidance control system using a distributed nonlinear model predictive control (DNMPC) is proposed to realize the collision avoidance. A constraint for the relative position vector between the each helicopter is considered in the design for efficient avoidance. Small single rotor helicopter is considered as controlled object, and the guidance control system is designed for the nonlinear translational model treated a helicopter as an ellipsoid. DNMPC is designed with three constraints, an input constraint, a state constraint, and a relative position vector constraint. An input constraint and a state constraint realize collision avoidance in input within the constant limits. If the moving path of the one helicopter is significantly affected by the moving path of other helicopter, the relative position vector constraint makes the helicopters exchange their relative position each other. By using these constraints, smooth collision avoidance is realized. The helicopters exchange information about current state and optimal input sequence each other for calculating the predictive trajectory of others. Based on the calculated trajectories, each helicopter solves its local optimization problem. Here, sharing the velocity information is difficult because calculation processing capability of the small sensor and communication capability between UAVs are restricted. Therefore, a dynamic compensator for velocity compensation is introduced. By introducing the dynamic compensator, collision avoidance using only exchange on the position and the input sequence information is accomplished without exchanging velocity information. The effectiveness of the proposed control system is verified by numerical simulations.

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The ground-based experiment of a tethered satellite system becomes increasingly important in order to get an insight into its dynamics and control. With the accurate modeling for a ground tethered satellite, however, it necessary to deal with the undetermined parameters in dynamics model. The vast majority of the physical parameters are to be identified by experiment. This paper presents a parameter identification method for ground experiment of an in-plane tethered satellite with attitude motion, according to the acquired responses of system states. The 2D micro-gravity motion of the tethered satellite is simulated by using a simulator floating on air-floating platform. The kinematics and dynamics similarity between the ground-based experiments and the on-orbit system is studied first. Then, the Model Reference Adaptive Control (MRAC) method is employed to identify some uncertain or immeasurable parameters in dynamics model of the tethered satellite system with attitude control, due to air bearing and micro-gravity deviation caused by the slight inclination of the platform. The design of experimental system for dynamics simulation is illustrated, including its components, operating mechanism and calibration results. Finally, the ground-based tests are conducted to verify the proposed identification scheme.

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This paper presents a new navigation system consisting of a resource-constrained rover and landers for planetary long-range exploration. During the exploration, they communicate with each other using radio and the rover receives signals from the landers which contain Angle of Arrival (AOA) data. The rover estimates its position using AOA data. Although obtaining AOA data generally requires a complex device and is difficult to apply to navigation for small rovers. In this study, we implement AOA-based navigation for a resource-constrained rover by rotating a directional antenna such as the high-gain antenna of the landers. In this case, since the rover obtains signals containing AOA data intermittently, we employ an event-driven extended Kalman filter to implement real-time navigation. Our proposed method has the advantage that the rover does not need navigation cameras or sun sensors, and it is therefore suitable for resource-constrained rovers. We developed a small rover and several landers, and conducted experiments in a wide range of Black Rock Desert in America, using the small rover and the landers to obtain the experimental data of AOA which is difficult to simulate. The experimental data are used in numerical simulation. We also validate some cases where there is one lander. These results show the effectiveness of our proposed navigation system using AOA data from the landers in long-range exploration.

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Vibration isolation is traditional technique for mitigating structural vibrations, and has been successfully applied to whole-spacecraft vibration isolation. Transmissibility across the isolator, which derived from the single degree-of-freedom vibration isolation system, is usually used to evaluate the performance of the isolator. However, it is not sufficient to evaluate the performance of multi degree-of-freedom system, such as whole-spacecraft vibration isolation. Considering the flexibility of the original payload attachment fitting, the ratio of transmissibility with the isolator to transmissibility with the payload attachment fitting should be used. In order to take into account the flexibility of the spacecraft, transmissibility ratio of more observation nodes in the spacecraft have to be calculated. Furthermore, in order to consider the flexibility of launch vehicle, the response ratio or power flow ratio, which overcomes the limitation of transmissibility, is used to quantify the vibration isolation performance. The method presented here can be applied to other complicated flexible vibration isolation systems.

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A large number of small-size helicopters are widely used for some industrial works. This study deals with a problem of a transportation system of the helicopters which carry a load by suspending a load. Dynamics of the small-size helicopters is fast and sensitive in comparison with normal large-scale helicopters and tends to be unstable to disturbances. The transportation system needs a vibration control of the slung load. The purpose of our study is to suppress the vibration of the slung load during hovering. To simplify the control system, we assume that it is possible to measure only the angle of the slung load by potentiometer. Since the helicopter with slung load system is nonlinear and constrained system in three dimensional space, it is difficult to design a state estimator. Therefore we adopt output delayed feedback control to suppress the vibration of the slung load. A limitation of the delayed feedback control is that the theoretically control design method is not established. We tried to determine the delayed feedback control parameters theoretically by using a linearized model and system parameters identified by the frequency response test. To verify the effectiveness of the present vibration control method, we implemented flight tests with a small-size helicopter with slung load system. Consequently, the control parameters are nearly identical to the parameter determined by trial-and-error in the experiments.

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In this study, the optimal mechanical design method for fixed-pitch coaxial-rotor helicopter is proposed. The fixed-pitch coaxial-rotor helicopter has several advantages compared with any single-rotor type or variable-pitch rotor type helicopters. For example, it has great simplicity of the mechanisms, well maintainability, and well energy conversion efficiency, and so on. However, fixed-pitch coaxial-rotor helicopter has a drawback in forward flight named pitch-up phenomenon. The pitch-up phenomenon causes a little cruise speed of the helicopter, and it is fatal problem in the practical operations. To overcome such a problem, optimal mechanical design of the fixed-pitch coaxial-rotor helicopter is proposed. The optimal design is based on the precise mathematical model of the helicopter and numerical optimization method. The mechanical parameters are examined to maximize the cruise speed of the helicopter. First, the dynamics of a fixed-pitch coaxial-rotor helicopter is modeled by using multi-body dynamics technique and aerodynamics theory. In the modeling, the helicopter is considered as a rigid body system consist of multiple rigid bodies, mission and frame unit, and rotors. Additionally, the aerodynamic interaction between upper and lower rotor is considered in the model. Second, mechanical parameter optimization based on derived mathematical model and Particle Swarm Optimization (PSO) method is proposed. Finally, the fundamental optimization of mechanical parameter is performed to show the validity of proposed optimal design method. In the simulation, the position of the universal joint is optimized to maximize the cruise speed of the helicopter.

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For the purpose of simulating a flight of a flapping vehicle a test device with a circular flight has been developed. The device provides us a flight speed, the trimmed pitch angle and the generated lift force which can be derived from the angle of a vertical arm. Thanks to this device, the appropriate parameters to achieve a stable flight can be set in advance without damaging a vehicle, such as the flapping frequency, the feathering angle and the elevator angle. In the present paper the deriviation of the lift and pitching moment generated by a flapping motion is described.

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The aim of this study is to make stable adaptive control system without model generation, even if the helicopter's dynamics changes. Our research group has been studying the autonomous control of multi-rotor helicopter, and it was successfully demonstrated in outdoor experiments. The control system design is based on optimal control theory using gray-box modeling, and it requires much time and effort of modeling and control. In addition, changing helicopter's dynamics leads to deterioration of the control performance. Therefore, it is necessary to design new controller in order to shorten the hours of control system design and adapt to changing dynamics. In this study, we applied adaptive control method to solve the problems that have been presented. As a first step, we verified an adaptive controller for altitude control of multi-rotor helicopter in the simulation and experiments. The experiments were conducted indoor-outdoor. In indoor experiments, VICON motion capture system was used as altitude information. In outdoor experiments, a pressure sensor was used as its. It was found from experimental result that adaptive control is effective for altitude control of multi-rotor helicopter. Moreover, it made a success to shorten the time required controller design. In this paper, we present its adaptive control system and experimental results.

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This study describes online mass estimation and adaptive control of a multi-rotor helicopter. The altitude model is calculated in order to learn the relationship between the altitude and the mass. Here, motor dynamics and air resistance, and the approximation of the rotor frequency and the thrust power relationship are considered. The estimation approach is a nonlinear filtering problem for a augmented state space. The mass of a helicopter is augmented to the state vector, and the augmented state vector forms a nonlinear system. As a filter for a nonlinear system, EKF (Extended kalman Filter) and UKF (Unscented Kalman Filter) are compared. A simulation and offline data processing are done to verify the efficiency of the estimations. Furthermore, Self-Tuning PID Controller is designed. Once PID gains are tuned, Self-Tuning PID Controller tunes these gains automatically in response to the mass variation. This tuning algorithm is based on a characteristic equation of the feedback system. Altitude control simulation is done to verify the controller performance. In this simulation, mass of a UAV varies sharply. The controlled altitude and automatically tuned gains are shown.

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Many different kinds of artificial arms have been developed for people who have been injured in traffic or industrial accidents. A motor drive is mainly used as an artificial arm for realizing highly precise position and force control. However, when the artificial arm of a motor drive is given a strong external force, it may cause injuries. In this research, we adopt a pneumatic actuator because it is a safe drive source. The five fingers of its artificial arm move like those of humans, and the finger joints are manipulated by a control model whose structure is difficult. Previous work, which failed to consider the influence of gravity, had to be offset in real time, and so controlling the model structure was difficult. In this basic research on developing an artificial arm, we manufactured a two-link manipulator of a pneumatic actuator drive source. We propose a model that consists of a pair of two-link manipulators that was mutually opposed to hold and manipulate objects. Our experiments and simulations verified that an object can be moved to a certain initial position by a desired value. We showed comparatively identical behavior and verified the holding and manipulation validity of our model based on gravity.

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In this study, we propose a system to reduce the displacement of the tuned mass damper (TMD) with lever and pendulum mechanism that was placed in the roof for seismic response control of high-rise buildings. This is a displacement magnifying mechanism attaching the weight and lever in the horizontal direction in the space between the roof and TMD. In particular, in thig paper, the optimal tuning method of the dynamic mass(D.M.) is examined, and by applying this control system to the single degree of freedom (SDOF) building and the multi-degree of freedom (MDOF) buildings as shown in Figs.l and 2 subjected long-period earthquake motions for response control, its effectiveness is examined

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This paper introduces a tilt-controlling axial self-bearing motor with a single stator. The motor consists of a stator and a disc rotor and is capable of controlling motor torque, axial position and tilt angle. The stator has six coils, which are driven by separate amplifiers. The rotor has two or four magnetic poles. By adding two types of currents (a motor current, which has the same poles as the rotor, and a tilt control current, which has plus two or minus two poles of the rotor) four degrees of freedom of the rotor can be actively controlled. The motor torque, axial force and tilt moment are theoretically analysed and a control method is shown. A prototype using a superconducting radial magnetic bearing is fabricated and tested to study the feasibility of the proposed motor. Results show that the motor can levitate and rotate, but the radial force produced by the tilt control current, and tilt moments coupled with the motor control current, cause stability problems.

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