Journal of System Design and Dynamics Vol. 7(2013) No. 4

In the present study, a target level setting method for the reference signal of operational TPA was considered using the principal component regression method. A principal component having a high contribution to the response signal was selected and target levels of the reference signals were set through principal component sensitivity analysis. In addition, a method that can extract the behavior of a principal component having a high contribution to the response signal was considered for the countermeasure. In order to verify the effectiveness of these methods, operational TPA and the proposed methods were applied to a small model vehicle. In the experiment, floor vibration was set as the response signal and nine measurement points, such as motor attachment points, were used as the reference signals. Here, we set the target reduction level of the response point vibration as 5 dB. Next, the target levels of the reference signal were calculated by principal component sensitive analysis and the countermeasure was considered through the principal component behavior analysis. By referring to the analytical result, a countermeasure to reduce the floor vibration was sought. As a result, the floor vibration level was almost reduced to the target level (5 dB). These considerations and experiments indicate that operational TPA could have additional functionality, whereby the method could set reference signal targets and suggest countermeasure guidelines in addition to performing contribution separation.

It is well known that the asymmetric vane spacing can result in decreased levels of the excitation at specific frequencies. In the previous paper, the resonant response reduction of the mistuned bladed disks due to the asymmetric vane spacing was studied by use of the equivalent spring-mass model. Although the mistuned bladed disk should be analyzed by FEA (Finite Element Analysis) to accurately evaluate the resonant response reduction effect of the asymmetric vane spacing, it is unrealistic due to enormous computational time. Therefore, in this study, the mistuned bladed disk is modeled by use of FMM (Fundamental Mistuning Model) to evaluate the resonant response reduction effect of the asymmetric vane spacing accurately and practically. First, the frequency response analysis of a simple mistuned bladed disk consisting of flat plate blades is carried out for the symmetric and asymmetric vane spacing, using both of FMM and the direct FEA, and the calculated results are compared to confirm the validity of FMM. Second, the frequency response analysis of a realistic bladed disk is carried out for the symmetric and asymmetric vane spacing, using FMM, to examine the effect of the resonant response reduction effect.

When an elevator rope for a high-rise building is forcibly excited by long-period ground motion, rope displacement becomes large even if the ground acceleration is small. Therefore, detecting the rope sway in real time is important to avoid damage during and after earthquakes. In a previous paper, when elevator cage is moving, a simplified calculation method, based on a single-degree-of-freedom (SDOF) system, for estimating rope displacement during an earthquake by using the building acceleration and ground acceleration has been presented. This simplified calculation method is applied to main rope, which resonates only once with building's sway while the elevator is moving. In the case of the main rope, the results of this simplified calculation method agree with those of the conventional finite difference method (FDM), within the 20% error margin. In this paper, a simplified calculation method is applied to compensating rope, which resonates twice with building's sway while the elevator is moving, by considering distribution of the rope tension. Finite difference analyses of rope vibration are also performed to verify the validity of the simplified calculation method. The results of this simplified calculation method agree with those of the conventional finite difference method, within the +20%,-30% error margin.

A force redistribution method for compensating actuator breakdown of vibration-isolation tables is studied. The vibration-isolation table is supported by eight pneumatic actuators and has a redundant number of actuators with respect to the degrees of freedom of table motion. We propose a force redistribution method that utilizes the redundancy of the actuators. In the proposed method, when some of the actuators break down, their output forces are redistributed on the unbroken actuators. We construct a detailed mathematical model in view of the behavior of the vibration-isolation table when some of the actuators break down. A type 1 digital servo system is applied to control the vibration and position of the vibration-isolation table. We perform numerical simulations in which some of the actuators break down at a certain time and the pressure of the broken actuators decreases at a constant rate. The numerical simulations examine the effectiveness of the proposed method.

This paper describes the particle/granular damper design, based on the analytical single mass damper model and experiments with smaller size steel balls. The effects of various system parameters, including filled mass ratio, particle size, enclosure/container dimensions, intensity and frequency of excitation, were investigated using a SDOF structure under harmonic force excitation when the vertical excitation is applied to the structure. The damper design calls for that the damped motions of the structure equipped with steel ball become periodic as well as kept approximately equivalent as predictions with the analytical model. It is shown that the suitable size of steel ball and enclosure/container dimensions were found to be selected for the combinations of filled mass ratio and excitation levels in the vicinity of the optimum range of system. Thus, the particle dampers with steel balls within moderate mass ratio can be very effective in attenuating the response of lightly damped structures.

This paper proposes an evaluation method for operability of pleasure boats in order to develop an electronic control steering system of those boats. Based on the concept of usability as addressed by ISO 9241-11, some evaluation standards such as effectiveness and efficiency are defined for a task of avoiding collision and resuming original course. For safety and repeatability, the simulation with a simplified ship simulator, which is composed a manual hydraulic steering system as hardware in HILS, is performed instead of experiments. As the results of the simulation, it is found that the operability of the manual hydraulic steering system deteriorates in the case of emergency collision avoidance. In particular, the wakes of the course resuming after the emergency collision avoidance are caused to be winding by wrong estimate of the normal pressure and by time delay in the dynamics of the pleasure boat. Therefore, it is found that the electronic control steering system of pleasure boats should have the functions to support estimation of the normal pressure and to compensate the time delay.

In this study, the rebound vibration characteristics of the internal mirror of SLR camera were investigated using experimental models. The mechanism of the mirror rebound phenomena is tested by using six 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 with a stopper and this phenomenon simulate the motion. A laser displacement meter is used to measures the amount of rebound. The result reveals that the rebound amount and the vibration characteristics after the collision depend on the stopper position. Also, the vibration after the collision depends on the collision behavior and when the amount of rebound is small, there is a tendency that the vibration after the collision becomes large.

Automatic transmissions consist of several planetary gear sets that are utilized to change gears. Needle roller bearings are widely employed in planetary gears used under high-load and high-speed conditioins, and thus the torque loss of these bearings is an important issue in designing high-efficiency transmissions. In this paper, a dynamic analysis is conducted using a multibody dynamics model to investigate friction losses in the needle roller bearings that support pinions. This numerical model takes into consideration the detailed conditions of contact and friction between the needle rollers and other parts. A discrete sphere model is used in the contact analysis to simulate the load distribution for the needle rollers. The friction coefficient is defined as a function of sliding velocity, and is used to describe the experimentally determined relationship between the skew angle and thrust force of needle rollers. The measurements obtained for the axial force of a pinion validate the predictions of the numerical model. A numerical analysis is conducted to evaluate the radial and cage pocket clearances of needle roller bearings, and it is found that the cage pocket clearance is a dominant factor affecting the friction loss of pinion. An increase in loss is caused by the thrust force generated by the skew of the needle rollers. Consequently, the cage pocket clearance needs to be small so as to lessen the friction loss of the bearing.

In this study, we applied an independent component analysis (ICA) to separate the contributions of vehicle interior noise by using only response signals. To verify the applicability of ICA, we utilized engine and wind noise and integrated them into a simple simulation with three conditions (synchronous, asynchronous, and asynchronous with frequency characteristic), and identified their separate contributions by applying ICA to these mixed response signals. Results show contributions were calculated accurately while using time-domain ICA for the case in which source signals were synchronously mixed, and it was found that accuracy was low when the signals were asynchronously mixed. Frequency-domain ICA was found to separate the contributions correctly. When the source signals were asynchronously mixed with specific frequency characteristic, permutation problems occurred, in which the matching between calculated independent component by frequency-domain ICA and the actual sound source changed among frequency. Therefore, a permutation solution method using a non-Gaussian characteristic of the calculated contributions was proposed. As a result, the contributions could be calculated accurately.

This paper presents a control scheme of engine-dynamometer system performing real gasoline engine operation in virtual driver-vehicle-road simulation conditions. The focus is on the transient behavior of the dynamometer speed control during engine-in-the-loop simulation, and a control-oriented model of the dynamometer is constructed. Based on the model, the generalized predictive controller is designed as the external control loop of the existing dynamometer controller to improve the response of the engine-dynamometer system, which reduces the synchronizing speed error between actual engine-dynamometer and the virtual driveline-vehicle model. The performance of the proposed control scheme is verified through comparison experiments including using the original control without the external control loop and a conventional proportion-differentiation control in the external control loop. The results indicate that the generalized predictive control yields significant improvement in terms of response ability. Finally, a speed following test using the proposed control scheme is conducted, which demonstrates the fast response of the engine-dynamometer system during a transient simulation process.

The primary aim of this study is to model and identify vibrations in mechanical systems subject to arbitrary external excitations. We propose a method based on infinite impulse response digital filter technology—termed time-frequency analysis—to analyze transient and steady-state vibrations. First, we introduce the time-frequency analysis procedure and the algorithm that implements it. Second, we analyze typical discrete signal inputs, such as impulse, sinusoidal and swept sine signals, and present time-frequency characteristics for transient and steady-state signals. Third, we apply our analysis method to the mechanical vibration behavior of a single-degree-of-freedom system subjected to various types of external excitations. The results of our analysis for steady-state vibration are verified as being equivalent to those from a Fast Fourier Transform (FFT) analysis. Moreover, the proposed analysis has the advantage over FFT analysis that we can also use it to analyze transient vibration phenomena.

A dynamics simulator for Gas Circuit Breaker (GCB) with spring operating mechanism was developed. The spring stores mechanical energy. When opening and closing instructions are entered in the GCB, the solenoid opens the trigger, and mechanisms release the compression force of the spring at a high speed. A compact and light-weight mechanism is required for high-speed operation of the GCB. This means that the high-speed operation must be analytically investigated. We made a mechanical dynamics model of the whole GCB, including an FEM modal analysis. The dynamics simulator incorporates a solenoid electromagnetic field analysis and a gas pressure analysis of puffer chamber in the mechanical dynamics model. The operating characteristics of the GCB were analyzed with the simulator and measured in an operating experiment. The analytical results were in good agreement with the experimental results, and this proved that the simulator can be used to estimate the operating characteristics and appraise the stability of operation. The compact and light-weight GCB can be designed in short time by using the dynamics simulator.

An excretion care support robot, which can reduce the burden of caregivers, has been developed for bedridden persons. Because the excretion care support robot needs to move between its stop position and the caregiving room, which typically requires navigating a narrow and complex route, the robot must precisely follow a predefined path to avoid colliding with obstacles or falling over. However, different floor conditions in different rooms cause a wide range of time-varying friction, which has a serious effect on the motion accuracy of the robot motion system. To address this issue, a digital acceleration controller is designed to enable the excretion care support robot to accurately follow the predefined path. The digital acceleration controller is a special control algorithm that compensates for friction and can be designed without a priori friction information. Simulations and experiments are conducted under different friction conditions and the results demonstrate that this control method can effectively deal with the friction problem. Therefore, the excretion care support robot can safely move to the user's side when needed.

Equipment developed for rehabilitation commonly carries patients in reference movements that are generally based on natural movements of healthy people. This type of movement may not place the lowest load on a patient's body. We propose a selecting process of an index value that quantifies the body load during sit-to-stand (STS) movement to evaluate natural movements of a person and to calculate an optimized movement about a specific part of the body for individualized rehabilitation. The computation starts by collecting kinematic and kinetic data, estimating the forces and moments, and then extracting an index value of the movement that quantifies the body load. The index value strongly correlates with the chair height, and decreasing the value of this index by changing the movement during STS transfer could reduce the impact on the body, which is the same amount of load as that placed on the body while standing up from a higher chair height. A modified STS movement that can minimize the body load is finally computed. The results of this study could be used to help users see how much force and moment are placed on the ankle, knee, and hip joints, and provide a personalized optimum movement for rehabilitation with reduced body load on patients.

This paper presents a method for comparing the input powers and contribution rates from a power source to a structure in machine operation determined by statistical energy analysis (SEA) and transfer path analysis (TPA). Identifying external forces and contribution rates from input power sources during machine operation is important for analyzing machine and equipment, and dynamic designs. SEA is used for systems with many resonant modes, and predicted results are based on spatial averages. In contrast, TPA is based on estimation of a frequency response function between an excitation point and a response point. In this study, a method is proposed for comparing SEA evaluated by the power injection method and TPA evaluated by the matrix inversion method. The proposed method is validated through numerical analyses, using a finite element method of a simple structure consisting of two flat plates connected in an L-shaped configuration and a partial car model consisting of four subsystems. As a result, the SEA input power is spatial averaged over each subsystem quantitatively agrees with the TPA input power expressed as the product of the force and velocity at the excitation point. Contribution rates from a power source, the SEA and TPA results are qualitatively similar without having to consider the phase.

Recently, power assisted nursing care systems have received much attention and those researches have been done actively. In such a control system, an actuator and a control valve are mounted on the human body. Designing the system, the size and weight of the valve become serious concerns. The purpose of our study is to develop a small-sized, lightweight and low-cost servo valve for precise control using wearable pneumatic actuators. In this study, a low-cost wearable servo valve that can control the output flow rate by changing the twisted angle of the buckled tube in the servo valve is proposed and tested. The position control system of a McKibben rubber artificial muscle using tested valve and an embedded controller is also proposed and tested. As a result, we confirmed that the tested servo valve can control the flow rate in both supply and exhaust in an analog way. In addition, the pressure control type wearable servo valve is proposed and tested. As a result, the valve can control the output pressure with a bandwidth frequency of 2.2 Hz. Moreover, the estimated cost of the proposed valve can be reduced about 1/100 (9 US dollars) compared with the typical servo valve.

Extra low-power magnetic suspension system is achieved using solely solar power. Presently, solar cells have become more efficient and cost-saving year by year. In this work, a solar power generation technique is combined with zero-power control magnetic suspension. The zero-power control is achieved by converging the control current to zero in the steady states where the bias force generated by a permanent magnet is balanced with the gravitational force. Therefore, the steady-states power consumption becomes virtually zero in this suspension system. However, peripheral devices including sensors and controllers need power in both transient and steady states. Hence, the power consumed in the peripheral devices becomes dominant. In this work, dedicated power-saving peripheral devices are fabricated. It is observed that the average power consumed by the electromagnet is 20[mW] for suspending a 90-gram mass, and the power consumed by the peripheral devices is 13[mW]. In contrast, a conventional system consumes a few watts to suspend a floator of the same dimensions. The solar cells used in the apparatus has a maximum power capacity of 2[W] under a typical summer sunlight (approximately 120[klx]). The fabricated system can achieve stable suspension even under a illuminance of a fluorescent lamp of 5[klx].

This paper describes a structural optimization method for subsystems which realizes the desired value of coupling loss factors (CLFs) in statistical energy analysis (SEA). We have developed the structural design process on the basis of experimental SEA for the purpose of reducing structure-borne sound in real-world machinery. The process identifies the CLFs which should be changed in order to reduce the noise radiated from the machinery. The optimization method is implemented using the finite element method and optimization algorithms. The finite element model represents a part of a whole system which includes a junction together with their neighboring SEA subsystems, associated with the CLFs which need to be changed. In this paper, the proposed method for the structural optimization is demonstrated. Consequently, taking one CLF as the objective function, an optimization of the thickness of the shell elements is performed showing the efficiency of the structural optimization method.

This paper discusses high speed and non-contact transportation of a steel disk using magnetic levitation and feedforward tilt control. In magnetic levitation systems for handling a thin plate, horizontal slip due to weak horizontal restoring force limits the transportation performance. Tilt control can improve the performance as it can prevent the horizontal slip by compensating inertial force. Previous studies demonstrated the effectiveness of the technique, but their experiments were performed only in a low speed region. This paper applies the tilt control to high-speed transportation in a short distance. In high-speed and short-distance transportation of a disk, angular velocity and acceleration dominate the transportation performance. The paper discusses these factors and proposes a path planning algorithm. Using the algorithm, the paper demonstrates disk transportation for 197 mm within 0.44 seconds. The maximum horizontal acceleration reached 7.9 m/s² with the maximum tilt angle of 39°. The paper also discusses the effect of vertical acceleration on the tilt control performance.

New measuring and training method of muscle power for senior age, that utilizes small 'electric generator' instead of conventional 'spring force', is described in this paper. Our study clarified that this method can measure not only the muscle power, but also the reflection time and the muscle strength without any physical stress on aged senior subject. Meanwhile, another advantage of employing electric generator is that generator can electrically produce regeneration resistance as the load for rehabilitation. This paper also describes whether the developed system can be applied for rehabilitation. With a view of physiotherapist, various investigations were executed. The evidences show the effects of the developed training method and the developed system.

The present paper investigates the effects of a coupling element placed between nonlinear self-excited oscillators on synchronization. A simple nonlinear model is newly developed by modifying the model treated in our previous report. This model consists of two oscillators subjected to Coulomb friction and a block installed in the coupling element. These elements are connected in series by coil springs and dashpots. In this model, stick-slip motion frequently occurs due to Coulomb friction. The synchronized solutions and the stability are analyzed accurately by the improved shooting method. The new model is validated by comparing the calculated results and the experimental results, and the features of the synchronized solutions are investigated. The results reveal that the frequencies and vibratory patterns closely correspond to the natural frequencies and natural modes of a three-degree-of-freedom system without Coulomb friction and that the existence regions of the synchronized solutions depend on the block mass as a parameter of the coupling element. When the parameter is set appropriately, the existence regions expand. The mechanism behind this is examined from the viewpoint of the energy transition between oscillators.

Motion analysis of balancing balls of an auto-balancer is performed in order to reduce the residual positioning error when the device passes the critical speed. The rotation speed profile control method improves the performance of an auto-balancer by providing a variable-speed period in the middle of motor acceleration at a rotation speed that passes through the critical speed. In order to confirm its effect, equations of motion of the auto-balancer mechanism including balancing balls are modeled based on a non-stationary vibration model. Time-variant dynamics of an auto-balancer in accelerating the motor are simulated by using MATLAB and the balls are confirmed to move toward the balancing position. Optimal conditions of the variable-speed period of the rotation speed profile are explored and comprehensively simulated as a parameter of start time, transit time and profile shape. It is shown that residual balancing is eliminated by the driving force of the balls. Furthermore, an experimental study is performed on an optical disc drive with an auto-balancer and vibration amplitude caused by an unbalanced disc is measured to be suppressed by the method.