This paper analyzed the suppression method of the nonlinear vibration called subharmonic vibration of order 1/2 in the car powertrain by using a dynamic absorber. In the car powertrain, the torsional forced vibration caused by engine explosions leads to inhibition of the ride quality. Thus, in the torque converter of an automatic transmission car, a piecewise-linear spring called damper is used to reduce the transmission of the forced vibration. However, the subharmonic vibration occurred in the actual vehicle, when the spring restoring characteristics is around the switching point. The fundamental vibration frequency of the subharmonic vibration is half to the engine forced vibration frequency. Although the design of the dynamic absorber to suppress the forced vibration has been established for the linear systems, the optimum design to suppress the subharmonic vibration of order 1/2 has not yet been investigated. The powertrain is modeled by multi degree-of-freedom system as an actual vehicle, including engine, torque converter, transmission gears and wheels. Equation of motion is developed with also considering spring restoring force of piecewise-linear spring. The numerical result shows subharmonic vibration occurs when the engine excitation frequency is almost twice of the second mode of natural frequency, and the result shows a good agreement with the experimental data. Then, the dynamic absorber is introduced to suppress the occurrence of subharmonic vibration theoretically. In this paper, the optimum design of the dynamic absorber to suppress the subharmonic vibration is discussed. The numerical result shows the optimally designed dynamic absorber in the natural frequency and the damping ratio is capable of suppressing the occurrence of the subharmonic vibration.
This paper describes a controllable damper with high reliability and wide dynamic range using magnetorheological (MR) grease and semi-active vibration control using the damper. Some types of cylindrical controllable dampers based on pressure difference between chambers in the dampers using “MR fluid”, whose rheological properties can be varied by applying a magnetic field, have been reported as a semi-active device. However, there are some challenging issues of them. One is to improve dispersion stability. The particles dispersed in MR fluid would make sedimentation after a period due to density difference between the particles and the carrier fluid. Another is to expand dynamic range. Since cylindrical dampers require sealing elements because of pressure difference in the dampers, the dynamic range between the maximum and minimum damping force according to a magnetic field is reduced not making the best use of MR effect. In this study, a controllable damper using MR effect was proposed and its performance was experimentally verified to improve the dispersion stability by using “MR grease”, which uses grease as the carrier of magnetic particles, and to expand the dynamic range by adopting a shear type structure not requiring sealing elements. As a result, it was confirmed that MR grease had the high dispersion stability and that the dynamic range of the present damper was seventy times, which was more than five times as high as the conventional dampers using MR effect. Furthermore, the MR grease damper was applied to a semi-active vibration control system of a one degree-of-freedom model structure using a simple on-off algorithm and its performance was experimentally verified. The results indicated that the vibration response was successfully reduced by using the on-off algorithm. It was shown that the MR grease damper effectively worked for the semi-active vibration control system.
For the purpose of developing a vibration-isolation table with flexibility and/or scalability (which means “with adaptability to desired load specification”), this study investigates a self-identification method with regard to positions or arrangement and effective pressure areas of pneumatic actuators which support a vibration-isolation table. The proposed identification method is a fundamental technique necessary to construct a scalable vibration-isolation table in which the actuators supporting the table can be added or removed flexibly according to the load demand, easily, and in a short period of time. First, this study constructs a mathematical model for a vibration-isolation table supported by a redundant number of actuators and a type 1 digital servo controller to control the position and inclination angles of the table. Next, we derive the identification method for obtaining the position of the added pneumatic actuator and the effective pressure areas of the pneumatic actuators. We then demonstrate the proposed identification method by numerical simulations using our detailed mathematical model. Finally, this study shows an example of the application of the proposed identification method coupled with a force redistribution technique by addition of an actuator into the vibration-isolation table system during continuous operation. The validation and success of our method was confirmed by the displacement and pressure responses of the vibration-isolation table.
This paper presents a non-contact measurement and diagnostic method for the parametric identification of vibrations of rotating engine blades, based on blade tip-timing (BTT) measured by optical sensors. Because of the inherent under-sampling nature of BTT measurements, 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 (E2SPRIT) 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 traditional ESPRIT.
In this paper, the characteristics and the effectiveness of a nonlinear passive vibration isolator based on a post-buckled beam is investigated experimentally. The intended application is specifically isolation in the vertical direction where the isolator is required to be sufficiently stiff statically to bear the weight of the isolated mass. The isolator consists of two beams joined to form an inverted L-shape and the weight of the isolated mass is taken to act at the vertex. If the weight of isolated mass is larger than the buckling load of the L-shaped beam then the beam buckles in one of two modes, one of which is unstable. In this paper, the static restoring force of the unstable mode is measured and an appropriately selected coil spring is added to counteract the negative stiffness of the beam. The resulting system presents a dramatically lower stiffness to small excursions about its equilibrium position in its buckled state but maintains its static load bearing capability. Free vibration measurements are presented which show some amplitude dependency of the natural frequency for large amplitude motion. Low amplitude harmonic base excitation measurements are also conducted from which transmissibility measurements are obtained and compared with corresponding results from a Finite Element model. The fundamental resonance is about 80% lower than that achievable by a comparable linear isolator. However the potential improvement in isolation performance has not been fully realised in the prototype design due to the presence of higher frequency internal resonances of the isolator, mitigation of which is the focus of ongoing work.
Vibration manipulation function (VMF) is applied as a linear-piecewise feedforward function to suppress residual vibration of a hoisting load in a one-dimensional overhead travelling crane. The system is modeled as a pendulum of a one-degree-of-freedom (1DOF) oscillator with enforced acceleration of a trolley. When an initial swing angle of the wire of the crane is small, residual vibration of the load can be vanished by this method in one natural period of the oscillator. On the contrary, in case of a large initial angle, certain amount of residual vibration remains because of the nonlinearity of the pendulum. However, it can be eliminated with repeated enforce accelerations of the trolley under VMF in every natural period. Moreover, in case of the existence of external noises and errors, the intermittent repeated accelerations can remove residual vibration with sampled-data feedback control in every natural period. Some examples of numerical simulations and experimental results are shown to validate the abilities of VMF in the crane operation. Residual vibration of the load can be suppressed in any time of the crane work, as far as the trolley travels in constant speed including static position, i.e. in any inertial frame, at the beginning of each operation. This feedforward function could be used for an automatic crane machine with or without the sampled-data feedback control. Since the function is an analytic solution of an intrinsic repowering operations, it can also be used in tutoring software for operator's training.
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 application.
This paper proposes a design method of sliding mode controller with the robustness against actuator uncertainty for active suspension systems of half-vehicle model. The features of the proposed sliding mode controller are not to require any force sensors to constitute local force feedback loop and to avoid chattering, which will be often a problem in sliding mode control. Based on the concept of the second order sliding mode control, the switching control input is redesigned by the describing function method in order to occur limit cycles of the switching function. Occurring the limit cycles instead of perfect sliding mode can lead continuous control inputs to suppress deterioration in high frequency band. The describing function method shows the existing condition of the limit cycles for the design parameters of the redesigned switching input. From numerical simulations, it can be checked that the proposed sliding mode controller can occur almost desired limit cycles of the switching function. Also, it can be seen that the proposed sliding mode controller shows high robustness against actuator uncertainty while it can suppress chattering in high frequency band.
A flexible biomimetic fish-like robot for use in a flow in narrow passage was developed. Downsizing of the moving body was achieved using shape memory alloy (SMA) actuators. However, overheating an SMA actuator causes phase-transition saturation, and may cause a decrease in the fin vibration amplitude. In order to avoid this problem, a new driving method that utilized a self-excited oscillator was introduced. This proposed method is suited for generating oscillation with keeping temperature in SMA constant by using self-sensing, and needs to adjust only one parameter. We confirmed the effectiveness of the proposed driving method against overheating based on experiments and numerical simulations. Simulation proved that this method can keep thrust force of the moving body constant. For the fish-like moving body, multiple actuators are needed to realize higher degree of freedom behavior, and the phases of these actuator outputs also are needed to be synchronized to generate fish-like behavior, i.e., traveling wave. On the other hand, in the proposed driving method, the actuator system simulates a self-excited vibration system. Therefore, it was necessary to design the coupled inputs for oscillators composed by actuators to synchronize the oscillator outputs. To achieve this, a phase model was obtained from an actuator model, which consists of a thermal conductivity model and hysteresis model using a phase reduction analysis. Coupled inputs for proposed connecting method were designed based on this phase model, and the relationship between the phase difference of the coupled actuators and the connection gains was examined. Finally, we realized phase control using this.
To reduce the collision shock and injury risk to an infant in an in-car crib (or in a child safety bed) during a car crash, it is necessary to keep the force acting on the crib constant and below a certain allowable value. To this end, we propose a semi-active in-car crib with joint application of regular and inverted pendulum mechanisms. The crib 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 crib. 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 in-car crib and an inverted pendulum-style in-car crib. The regular pendulum-style one is suitable when moderate impulsive forces are involved because the crib moves smoothly soon after the force begins to affect the crib. 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 in-car crib is able to increase the acceleration of the crib 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.
This paper focuses on a real-time obstacle avoidance control method for vehicles using model predictive control (MPC). MPC can optimize the motion of the vehicle over a finite time horizon while satisfying various constraints such as vehicle dynamics, the road width and the steering range. However, the computational cost is too large for conducting real-time control. In this paper, a collision avoidance is realized by MPC with constraints for avoiding prohibited regions represented as circles. We approximate this region into a half plane separated by the tangent of the prohibited region. By handling approximated regions as constraints of the road width of MPC, we can implement the collision avoidance algorithm into the controller without increasing the computational cost. Moreover, in order to reduce the computational effort, we transform the nonlinear vehicle dynamics into reduced order and linearizable subsystems called time-state control form (TSCF). The effectiveness of the proposed method is proved by comparative simulations with conventional method where artificial potential method is applied to MPC. In addition, we conduct two experiments using a 1/10 scale vehicle which is equipped with a laser range finder to execute obstacle detection and localization. We show that real-time control can be realized even if we use an on-board embedded CPU which runs at the frequency of 500MHz.
Superconducting technique is applied to the levitation system. Persistent current in superconducting coil and control current in copper coil are used for levitating object and controlling object, respectively. The system is composed of a superconducting coil, a copper coil, a levitated object, a photo sensor, a PID controller, and power amplifiers. In this paper, basic study on superconducting coil and solenoid coil, and the dynamic characteristics of levitated object are performed. As a result, it is found that the levitated object continues to levitate at a distance 9.0 mm for ≈ 15 s. This may be the first trial that superconducting coil is used for magnetic levitation.
The completely passive levitation of a column-shaped graphite object is achieved. Graphite is a typical diamagnetic material. Diamagnetic materials have a property of generating repulsive force in magnetic field. Most diamagnetic levitation systems use high-oriented pyrolytic graphite (PG) sheets because sufficient force for levitation is easily obtained. In contrast, column-shaped graphites are proposed as the target of levitation in this work. Experimental apparatus for diamagnetic levitation is fabricated. The apparatus uses a two-dimensional Halbach array made of cubic neodymium magnets. The magnetic fields in the apparatus are analyzed numerically and experimentally. It is shown that the stable diamagnetic levitation of a column-shaped graphite can be achieved. The floator is fabricated by combining the pencil leads made from graphite. Then the diamagnetic forces acting on the floator are measured. In addition, the effects of anisotropy of graphite on the levitation characteristics are discussed.
Hydraulic pumps are positive displacement machines and the primary components of fluid power systems that transform energy from mechanical sources to pressurized oils. The reliability and efficiency of pump components are highly dependent on the tribological characteristics of the sliding parts, which perform bearing and sealing functions. Higher pressurization and increased compactness result in higher contact pressure and oil temperature, which can cause catastrophic damage to the components and severe deterioration of the oils. Three representative hydraulic pumps—including a swash plate axial piston pump, a pressure-balance vane pump, and an external gear pump—were tested under real operating conditions to determine their thermal effects. Discharge pressures up to 21 MPa and rotational speeds up to 50 s-1 were tested. Hydraulic oils with viscosity grades of 22, 32, and 46 were used at 30°C-50°C. The thermocouples were embedded in the cylinder block, swash plate, and valve plate of the piston pump, cam ring and side plate of the vane pump, and the side plate of the gear pump. Platinum resistance thermometers were placed in the conduits close to the suction and discharge ports of the pumps. The temperatures of the sliding parts and working oils were measured simultaneously. Results indicated that for all pump tests, temperatures increased almost monotonically as the discharge pressure increased. The temperatures of the sliding parts were always higher than those of the discharge oils. With the piston pump, the temperatures at the locations corresponding to the discharge port of the swash plate and valve plate were higher. In contrast, with the vane pump, the temperature at the location on the cam ring closest to the suction port was highest.
In this study, the rebound vibration characteristics of the internal mirror of an SLR camera are investigated using experimental models. The mechanism of the mirror rebound phenomena is tested by using four types of rectangular metal plate models. The mirror (plates) model is supported by fixing its longitudinal edge on a horizontal rotatable shaft. The mirror plate swings down freely around a horizontal axis and hits a stopper. A laser displacement meter is used to measures the amount of rebound and the mirror model vibration behavior. It is clear that the contact time with the stopper is determined by the first mode of vibration in contact with the stopper. The higher mode effects to the rebound angle. The rebound angle depends on the mode of the mirror model. The predictions for the rebound angle agreed qualitatively well with the experimental results.
This paper considers position and attitude control of large flexible space structures composed of a number of subsystems(substructures) which are interconnected by flexible links modeled by springs and dampers. It is assumed that sensors and actuators are collocated in each subsystem. The purpose of the paper is to propose a decentralized control scheme by local proper controllers using only displacement output, which makes both each closed-loop subsystem and an overall closed-loop system not only robustly stable against uncertainty of characteristic parameters such as mass, damping, and stiffness, but also optimal for quadratic cost functions. First, we introduce a second order low-pass filter of which relative degree is 1, at each input channel of each subsystem. Then, we temporarily feed back displacement and velocity output of the substructure and output of the filter to input of the filter locally, so that we obtain a local proper controller using displacement output. By choosing parameters of each local proper controller as it becomes a phase lead compensator, the closed-loop subsystems and the overall closed-loop system become robustly stable. Furthermore, it can be shown the closed-loop subsystems and the overall closed-loop system also become optimal for quadratic cost functions by making two feedback gains in each local proper controller sufficiently large. Finally, numerical examples are presented to show effectiveness of the proposed method.
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 for output regulation problems, a design parameter is introduced to guarantee the existence of sliding mode from a practical point of view. Furthermore, the physical interpretation of the dynamics during sliding mode is given by analysis.
Simple adaptive control (SAC) is a control method that maintains control performance despite perturbations of a plant. However, there is a problem in that the vibratory output occurs in the transient response when SAC is applied to a vibration system which includes anti-resonance modes. The occurrence of the output depends on the structure of SAC and the output is caused by the vibratory input corresponding to the anti-resonance frequency. In order to overcome the problem, a method using an appropriate parallel feedforward compensator (PFC) is proposed. In the proposed method, an effective PFC is designed such that the gain of an augmented system is matched to that of a desired model under the ASPR condition of the augmented system. A design problem is described by LMI/BMI conditions. The problem using LMI/BMI conditions is solved by an iterative procedure. However, the leading coefficient of the PFC must be given a priori in order to guarantee the ASPR property, which provides some restrictions for applications of the proposed method. In the present paper, an improved method to overcome the abovementioned restrictions is proposed using the stability theorem of the descriptor system. The effectiveness of the proposed method is verified through numerical simulations and experiments.
Nonlinear defect interactions between the 180° domain wall and oxygen-vacancies (O-vacancies) in PbTiO3, and the characteristic ferroelectricity due to the interactions are investigated using first-principles calculations based on the hybrid Hartree-Fock (HF) density functionals, which correctly reproduce the band gap and provide the accurate defect electronic structures. We show that an oxygen vacancy is likely to form at 180° domain walls than inside the bulk and the vacancy behaves as a double shallow donor that contributes to partial conductivity preferentially than that inside the bulk. The defect interactions between 180° domain walls and oxygen vacancies have a significant influence on the polarization distribution in PbTiO3, and the effect differs depending on the location of O-vacancies with respect to the domain wall. An oxygen vacancy that is located in the polar  direction relative to the Ti atom suppresses ferroelectricity around the vacancy in front of a domain wall, and enhances ferroelectricity only an the center of domain wall, which leads to a shift of the domain wall towards the vacancy and pinning of the domain wall. On the other hand, an O-vacancy that is located in the non-polar  and  directions relative to the Ti atom induces polarization perpendicular to the  axis and outward from the vacancy. Furthermore, the magnitude of polarization change around the O-vacancy inside the 180° domain wall is larger than inside the bulk, which originates from the strong interaction between the 180° domain wall and O-vacancy. These results will provide significant fundamental insight for the design of ferroelectrics.
This study aimed to apply magnetic resonance elastography (MRE) using micro-magnetic resonance imaging (micro-MRI) system for the measurements of viscoelastic modulus in soft matters. The rectangular specimens of 90 × 70 × 50 mm were made of agarose gel with five kinds of stiffness by changing concentrations. The specimens were oscillated with longitudinal waves transmitted by an elastic-bar from a vibration generator in a micro-MRI system. Since the viscoelastic properties depend on the excitation frequency and amplitude, the experimental conditions were selected in the range of 50-250 Hz and 0.1-0.5 mm. The viscoelastic modulus was expressed as storage shear modulus G´ and loss shear modulus G˝. As a result, G´ increased with the frequency and amplitude, and the difference of G´ between hard and soft gels was obtained. The viscoelastic modulus of agarose gels was measured using the MRE system under the excitation conditions. Furthermore, double-layer specimens composed of 0.6 and 2.0 wt% gels were examined as an application of the MRE system. The difference of wave pattern between the hard and soft parts was observed. The values of G´ in the soft parts of the double-layer specimens corresponded to the value of the single-layer specimen, but the values of G´ in the hard parts were varied.
The silica-agglomerate electret could be obtained after spraying negatively charged solution of colloidal silica on a fluororesin film using an electrostatic spraying technique. The surface electric potential was measured after spraying to investigate which method was suitable for preparing the electret. As a result, the method in which a spray gun was installed to a conventional corona-charging setup delivered the electret with the amplitude of the electric surface potential over 0.8 kV. The silica agglomerates using an electrostatic spraying technique (ES electret) showed larger diameter D and lower point density N than those using conventional technique (corona-charging after spraying, CC electret). Furthermore, the prepared electrets were heated to examine the improvement of the heat resistivity by the electrostatic spraying. Then, the obtained silica-agglomerate electret showed better heat resistivity than the conventional silica-agglomerate electret. Then, the charge retention at 250°C R250 of ES electrets prepared in this study was higher than 57 % when the electrets suffered high temperature from 200 to 250 °C for 12.5 min at the heating test. Consequently, it can be concluded that the electrostatic spraying was excellent technique to obtain the silica-agglomerates electret with high heat resistance.
In continuous metal strip processing lines, such as pickling, annealing and surface treatment lines, lateral instability of strips is a common problem. Strip lateral movement has a bad influence on productivity of the processing lines. A simple and effective device to control a lateral position of a strip is required because conventional preventions such as a steering roll and crown roll are not effective. In this study, a method of controlling a strip lateral position using electromagnets was investigated. First, theoretical equations were derived to predict capability to control a strip. Next, the derived theory was verified compared with lab experiments. The results obtained can be summarized as follows: (1) The theoretical equations of velocity of lateral movement are derived from inclination when the strip is attracted by electromagnet(s). The inclination is calculable from geometric relation. (2) It is found that the theoretical equations are valid by lab experiments in the conditions of changing attracting displacement and line speed. Controlling lateral movement using electromagnets is possible, and the control capability can be estimated by the derived theory. (3) The velocity of lateral movement in the case of attracting the half of strip width is three times as fast in the case of attracting the edge of the strip.
This paper presents a controller design of a robotic manipulator for soft catching of a falling object. If a robotic system is able to catch a falling object softly, there will be many applications expected in human activities such as industry, welfare, nursing, housework and office work, because this ability allows a human operator or another robot system to move an object to the catching robot without any transportation systems such as an conveyor or a mobile structure. First, this paper considers a nonlinear decoupling control of a robotic manipulator. Next, a controller design is presented for catching a falling object with a small impact force. This controller consists of two parts: a position tracking controller that tracks a desired trajectory before contact between the object and the robot end-effector, and a force controller that is triggered after the contact. We employ a position-based impedance controller so that the entire control system can be constructed as a position-based controller. In order to achieve the soft catching, precise motion control is required to achieve the same velocity of the robot end-effector with a falling object when they are in contact. Hence, we employ an adaptive controller that consists of a feedback controller to compensate for disturbance such as friction and a feed forward controller to improve the tracking performance to the desired trajectory by adjusting controller parameters in real time. Experimental results with a falling raw egg demonstrate the effectiveness of the proposed approach.
In this study, we applied a modified Kobayashi-Warren-Carter (KWC) phase-field model to the neurite growth process. To confirm the applicability of this model, we observed axonal extension of PC-12D cells cultured with nerve growth factor (NGF). Based on our observations, we defined three stages of nerve cell axonal extension: neurite generation, neurite contraction, and axon extension. We further determined the parameters in the phase-field equations to express the three extension stages. Finally, our results show that the modified KWC phase-field model reasonably expresses the morphologies of nerve cells and predicts the three stages of nerve cell axonal extension. Although, we employed the binary alloy solidification model as a sample model in the present phase-field simulations, this work will be extensible to relatively more realistic models for nerve cell growth.
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