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Kazuaki YAMADA, Toshiyuki YASUDA, Kazuhiro OHKURA
2018 Volume 84 Issue 862 Pages
17-00288
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 18, 2018
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The field of multi-robot systems (MRSs), which deals with groups of autonomous robots, is recently attracting much research interest from robotics. MRSs are expected to achieve their tasks that are difficult to be accomplished by an individual robot. In MRSs, reinforcement learning (RL) is one of promising approaches for distributed control of each robot. RL allows participating robots to learn mapping from their states to their actions by rewards or payoffs obtained through interacting with their environment. Theoretically, the environment of MRSs is non-stationary, and therefore rewards or payoffs learning robots receive depend not only on their own actions but also on the action of other robots. From this point of view, an RL method which segments state and action spaces simultaneously and autonomously to extend the adaptability to dynamic environment, named Bayesian-discrimination-function-based Reinforcement Learning (BRL) has been proposed. In order to improve the learning performance of BRL, this paper proposes a technique of selecting either of two state spaces: one is parametric model useful for exploration and the other is non-parametric model for exploitation. The proposed technique is evaluated through computer simulations of a cooperative carrying task with six autonomous mobile robots.
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Ichiro TAMURA, Shinichi MATSUURA, Ryuya SHIMAZU, Koji KIMURA
2018 Volume 84 Issue 862 Pages
17-00403
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 16, 2018
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The ductility factors of nonlinear SDOF systems at Service Limits Ds “using elastic analysis design” in JEAC4601 are investigated, and it was confirmed that the ductility factors depend on the natural frequencies of systems, seismic motions and constant loads. Based on the above results, an acceptance criterion of components to prevent ductile failure and plastic collapse is proposed. The criterion is given as a limit of ductility factor for Service Limits Ds “using elastoplastic analysis design”. The proposed limit of ductility factor allows single state for nonlinear systems, and doesn't depend on the natural frequencies of systems, seismic motions and constant loads.
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Eiichi SUGINO, Takahiro KOSAKI, Yuzo TAKAHASHI, Shigang LI
2018 Volume 84 Issue 862 Pages
17-00519
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 17, 2018
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Power assist devices are worn by users, directly transmit actuator power to the users’ bodies, and can deliver assistance in activities of daily living, such as load lifting. In this study, we built a wearable power assist device for lower limbs driven by pneumatic actuators. Pneumatic power assist devices are safe for users, owing to the compressibility of air; however, the weight of the devices and assist torque often have a negative effect on the wearer’s body balance. Here, an assist control strategy is proposed for the pneumatic power assist device. In this strategy, the relationship between the lower-limb joint angles and the center-of-gravity (COG) of a human body is represented based on a simplified human body model during squatting. Assuming that the anterior and posterior movement of the COG follows the knee joint flexion and extension, the desired COG position is calculated from the knee joint angle measured with a sensor. The desired hip and ankle joint angles are found with the desired COG position, and the desired assist torque is obtained with these joint angles based on the human body model. The power assist device based on this principle was worn by research subjects, and its assistive performance was evaluated through experiments from the viewpoint of the COG fluctuation and muscle activity reduction.
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Teruhiko NAKAZAWA, Haruhiro HATTORI, Ichiro TARUTANI, Shinji YASUHARA, ...
2018 Volume 84 Issue 862 Pages
17-00543
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 24, 2018
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CVT chains have become widely used in vehicles because the slip between parts is very small, which enables efficient power transmission. However, the motion caused by the pins of the CVT chain entering and leaving the pulleys one after another during the power transmission process results in periodic motion of the whole chain. This behavior is known to affect noise and other basic performance aspects of CVTs. Therefore, it is important to study the geometrical specifications of the chain that affect periodic motion, such as the shape and dimensions of the parts. This study aimed to (1) identify the periodic motion that affects noise, and (2) formulate a motional theory to derive the ideal specifications of a CVT chain. First, after measuring the acceleration of the pulleys under conditions that generate large CVT noise, it was found that noise was greatly affected by periodic motion caused by the chordal action of the chain. Based on this result, a mathematical model was proposed to describe this chordal action. The pin profile curve was particularly considered in the model since it determines the motion of the chain at both ends of the chord part and has an important effect on the chordal action. Next, the chordal action of the chain was measured using an accelerometer, and the measured results were compared with the results calculated by the model. The results were consistent, which confirmed the validity of the model.
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Naoto YOSHIDA, Masahiro IEZAWA, Kazuhiro NISHIWAKI, Masaki TAKAHASHI
2018 Volume 84 Issue 862 Pages
17-00583
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 24, 2018
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In recent years, an automatic collision avoidance system has been put into practical use by various automotive companies. In this study, we propose an automatic collision avoidance system for a four-wheel independent drive vehicle using the state-dependent Riccati equation. By designing the state-dependent weighting functions, a control gain is automatically determined, based on the relative relationship with a preceding vehicle and the system can properly perform automatic braking and automatic steering. Moreover, by updating the state-dependent linear representation obtained from a nonlinear vehicle model in each control cycle, we design a control system in consideration of a change in vehicle dynamics due to vehicle velocity. Therefore, this study verifies the effectiveness of the automatic collision avoidance system using the state-dependent Riccati equation. We compare the performance of the proposed method with constant weight cases. The simulation results show that the proposed method can automatically adjust the control gain and properly avoid a collision by braking and steering to change the relative relationship with a preceding vehicle.
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Hideyuki KIMURA, Takahiro TSUCHIDA, Koji KIMURA
2018 Volume 84 Issue 862 Pages
17-00586
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 16, 2018
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In this study, vibration characteristics of a single-degree-of-freedom linear oscillator with the fractional order derivative are examined in terms of the critical damping over a wide range of the order of the fractional derivative by using numerical analysis. Two types of the definitions of the critical damping used in the previous studies are considered. It is shown that (i) the critical viscoelastic damping ratio changes according to the order of the fractional derivative and its minimum value for both types of the critical damping is less than 1; (ii) no critical viscoelastic damping ratio is observed in a certain range of the order; (iii) the difference in the existence of the critical damping between the oscillators with the derivative of order 1/3 and 2/3 is caused by the change of the behavior of a component of the response corresponding to one of the roots of the characteristic polynomial for the oscillator. Finally, the impulse response characteristics are classified into three classes depending on the order of the fractional derivative and viscoelastic damping ratio of the oscillator.
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Ko INAGAKI, Yasuhiro BONKOBARA, Takahiro KONDOU, Mie IKE, Takayuki HAM ...
2018 Volume 84 Issue 862 Pages
18-00004
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: June 06, 2018
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In household refrigerators, the rotational speed of a reciprocating compressor can be appropriately adjusted according to the temperature inside of the refrigerator. The lower rotational speed reduces the power consumption of the compressor. However, several natural frequencies of the compressor exist in the low rotation region, and besides, the unbalance force arising from the piston motion acts on the internal drive unit. Thereby the vibrations of the compressor are likely to be larger due to the resonance in the low rotation region. In this study, a method for supporting the drive unit inside the shell, which is called “the self-standing support” is newly proposed in order to reduce the vibration of the compressor drastically. In the proposed method, a spherical support element is utilized instead of coil springs to support the drive unit. And the drive unit can maintain a stable self-standing state by acting restoring moment due to the gravity while it is directly placed on the shell. The natural frequencies of the compressor can be greatly reduced by decreasing the support stiffness for the drive unit in comparison with the support method using coil springs. Furthermore, in designing the drive unit, the application point of the exciting force is matched with the center of percussion to the contact point on the spherical support. As a consequence, the periodic restraining force acting on the contact point can be minimized. By these two features, it is possible to considerably reduce the vibration transmission from the drive unit to the shell. In the present study, a simplified model for a reciprocating compressor is treated, and the effectiveness of the self-standing support is investigated analytically and experimentally.
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Takeshi NAKAHARA, Takashi FUJIMOTO
2018 Volume 84 Issue 862 Pages
18-00017
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 24, 2018
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A semi-active vibration control technique using piezoelectric actuators with switched inductance shunts has been studied. This technique can be used for not only vibration suppression but also energy harvesting. In order to design semi-active vibration control systems and energy harvesters using this technique efficiently, it is necessary to analyze and understand the effects of design parameters on the performance of these systems. Responses of these systems to harmonic disturbance forces can be used for performance evaluation and previous studies analyze periodic responses of semi-active vibration control systems by assuming sinusoidal displacement responses and using method of harmonic balance. However, this control technique induces rectangular control forces and the displacement responses are distorted. Enhancing the control forces leads to stronger distortion of the responses and the validity of the assumption of the previous studies becomes lost. In order to overcome this problem, the authors have proposed to use shooting method which is a numerical method to calculate periodic solutions of non-linear systems without assuming certain forms of responses. This paper presents periodic responses obtained by shooting method with an improved non-dimensional model and the periodic responses are compared with ones obtained by method of harmonic balance. Furthermore, this paper considers not only the periodic responses but also non-periodic chaotic responses obtained by long term simulations with the non-dimensional model.
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Takashi OHHIRA, Akira SHIMADA
2018 Volume 84 Issue 862 Pages
18-00019
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 28, 2018
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This study aims to realize fast disturbance estimation with a Kalman filter (KF). This paper presents a methodology of fast estimation and rejection for some types disturbances. This methodology attempts to estimate the state of mechatronics systems that rejected the influences of disturbance and noise by using KF. Most of known disturbance estimation method is the disturbance observer (DOB). However, the conventional DOB can not estimate the disturbance that is contaminated of noises. Generally, KF is known as state estimation algorithm that can consider influences of various noise. In addition, we had done some previous studies to design a linear KF with disturbance estimation. We obtained a fact that the disturbance estimation speed by the KF is slow from these studies results. Therefore, this paper proposes a new design method of KF with disturbance estimation which includes a design parameter to speed up disturbance estimation, where we have never concerned in this paper with KF design method except linear systems. Finally, we show the design method on the proposed method and usefulness via the simulation results relative to the position control for an simple cart system.
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Nobuaki HIRAOKA, Hiroyuki SOGO, Satoshi YURA, Tomohiro HENMI, Shinichi ...
2018 Volume 84 Issue 862 Pages
18-00031
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 30, 2018
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A motor shaft direct drive is known as a simple and low cost scheme for small toy vehicles, however the mechanism how it produces propelling force has not yet been explained nor discussed in detail. A trivial idea that a small dent is formed on the road surface just under the shaft end due to static weight takes us to the unexpected result. Brief calculus reveals that the propelling force vector of the system directs somewhat forward with respect to sagittal plane which includes motor shaft slant axis. It suggests that the motor alternative cw and/or ccw rotation generates gradual forward movement, i.e. the vehicle moves perpendicular direction with respect to that of right-left swinging motion. The forward motion is confirmed experimentally with single motor shaft direct drive vehicle, and also discussed in details.
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Sanga TAKAGI, Shinji WAKUI
2018 Volume 84 Issue 862 Pages
18-00043
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 25, 2018
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In the field of precision positioning such as semiconductor exposure apparatus, weak disturbance vibration from the floor influences processing accuracy. In recent years, as the precision of the device increases, the vibration allowance value becomes more severe, and performance improvement of the vibration isolator is required. In order to improve the performance, there are researchs reducing natural frequency by the frequency characteristics of the vibration transmissibility from the floor to the vibration isolator. Reducing natural frequency and decreasing stiffness are equivalent, and main target was stiffness generated by compressed air of air spring. In addition, rubber bellows of air spring is also targeted for further performance improvement. We already proposed a method combining the two stiffness separately decreasing method. However, decreasing stiffness simultaneously destabilized the device, then it could not be completely decreased. In this paper, as a new stabilization method, stiffness is completely decreased only in the operation frequency band. Since the low frequency has positive rigidity, the localization is maintained. We demonstrated the reducing natural frequency by the experimental result. When stiffness was completely decreased, the servo stiffness which had not been focused in the past became dominant in determining the natural frequency. Therefore, an appropriate design of the servo stiffness is required for further reducing natural frequency. To satisfy this requirement, we calculated the relationship between natural frequency and servo stiffness and gave an index for appropriate design.
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Yui AOKI, Shinji WAKUI
2018 Volume 84 Issue 862 Pages
18-00052
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 25, 2018
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In this paper, it is confirmed that natural frequency of isolated table is operated and that degeneration, which means that some natural frequencies have the same value, has a bad influence. Pneumatic anti vibration apparatuses (AVAs) support that loaded devices, i.e., XY stages, operate accurately. However, many strict design conditions are imposed on AVAs with six degrees-of-freedom (DOF) which are used on manufacturing floor. There is a risk that the natural frequency of each motion mode approaches, in other words, that isolated table falls into degeneration. This disturbs accurate operations of XY stages. In this paper, AVA with two DOF is used to simplify motion instead of six DOF. First, it is stated that mode control is used to pressure control. Next, position differential feedback (PFB) is proposed. PFB, which is used to the natural frequency control, is applied for each mode. This means that air spring stiffness is considered as each motion mode, and these are deleted or given. It is shown that the natural frequency of each mode can be controlled individually, by calculation, simulation, and experiment. Finally, the degeneration is reproduced to AVA with two DOF by PFB. At this moment, acceleration control which effects to nearby the natural frequency interferes with each other mode. From these results, conclusions are the following: degeneration should be avoided, and mode PFB is effective to control natural frequency of each motion mode. In addition, mode PFB accomplishes not only avoiding degeneration, but also lowering the natural frequency.
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Kenya NEMOTO, Hiroshi YAMAMOTO, Terumasa NARUKAWA
2018 Volume 84 Issue 862 Pages
18-00062
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: June 06, 2018
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One of effective ways to suppress vibration of a mechanical system is using a dynamic vibration absorber. The dynamic vibration absorber consists of a mass, a spring and a damper. The optimal tuning of natural frequency and damping ratio of the dynamic vibration absorber is required to suppress vibration, so adding an adjustable mechanism of stiffness and damping of the dynamic vibration absorber makes tuning easy. This paper proposes a new design concept of an adjustable dynamic vibration absorber consisted of an adjustable mechanism of stiffness and damping. The adjustable mechanism of stiffness consists of an arm, a couple of coil springs and a rotatable spring holder. Stiffness is varied by rotating the spring holder. The adjustable mechanism of stiffness can expand the range of stiffness by increasing spring constant of a couple of coil springs. The adjustable mechanism of damping consisted of a copper plate, a couple of magnets and a linkage mechanism. Damping is varied by driving the linkage. Driving the linkage to tune damping is necessary large torque because of attractive force of magnets. A compensation spring attached to the linkage can reduce the driving torque for tuning the damping. We made the proposed adjustable dynamic vibration absorber and verified whether the proposed adjustable mechanism is valid by experiments.
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Takeshi KAWACHI, Yukihisa KURIYAMA, Katsuyuki SUZUKI
2018 Volume 84 Issue 862 Pages
18-00063
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: June 06, 2018
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In order to clarify the mechanism of the vehicle body hysteresis affecting “rigidity feeling”, one of the driver's sensory evaluation in the driving test, the influence of friction acting on spot welding flanges on hysteresis, which is drawn by the displacement-load diagram of double-hat-shaped parts assembled by spot welding under static or relatively slow deformation, is experimentally and numerically evaluated. The hysteresis of two specimens, one has the contact around R-tangent of flanges and the other has it around edge, are compared and it is confirmed that the former type has larger hysteresis than the latter. The hysteresis is evaluated by the friction loss which is energy dissipation generated only by friction on the surfaces of the spot welding flanges. The loss calculated by the finite-element-method (FEM) with the contact and friction between two flange surfaces opposing each other has good agreement with that measured by the experiment. Additionally, by studying the detail of the relative slip and friction force distribution on the surface of two flanges obtained by the FEM analyses, the difference in hysteresis of two specimens and the cause of the friction loss are discussed.
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Tatsuhiro HIRAMITSU, Hiroyuki NABAE, Koichi SUZUMORI, Gen ENDO
2018 Volume 84 Issue 862 Pages
18-00083
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: May 30, 2018
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Pneumatic artificial muscles have many advantages. They have high force mass ratio, high compliance and simple structures. Especially, the flexibility contributes to compose novel mechanisms. The flexibility of pneumatic artificial muscles releases us from the spatially strict design required for rigid mechanical elements: it could actualize compact mechanisms made of a fewer parts. Our research group developed a thin McKibben actuator. The thin McKibben actuators is more flexible than conventional McKibben actuators. Authors succeeded in manufacturing novel soft mechanisms that are made of only braided artificial muscles. We aim to establish a design method for these novel mechanisms. We already have fabricated a cylindrical mechanism made of helical muscles. In this paper, we report a geometric model for the cylindrical mechanism. We focus on only deformation of a side surface in the coordinate system of muscles to simulate the movements of the cylindrical mechanism. The movement was verified by an experiment, and besides, it was simulated successfully in the geometric model that was created. The deformation of height and radius directions changed according to muscles alignment.
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Kengo KOMORI, Takeshi TOI
2018 Volume 84 Issue 862 Pages
18-00103
Published: 2018
Released on J-STAGE: June 25, 2018
Advance online publication: June 07, 2018
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Numerical simulations, such as the finite element method have been widely used to predict noise and vibration behavior. This allows reducing the development time and production cost of products. However, these results have been calculated based on the governing equations at each physical areas as the idealized conditions. Then, these simulations are not taken into account the fluctuation of response characteristic by the uncertainties of noise factors. Therefore, it is important to restrain the fluctuation of products properties by the uncertainties. In this paper, focusing on the transient analysis, we propose a robust design for minimizing the time history amplitude fluctuation by structure uncertainties. The robust design is implemented based on the combined use of the stochastic finite element method and the structural optimization. Since this method is performed by minimizing the 1st sensitivity, we will formulate the 1st and 2nd sensitivity in the time domain. Then, the proposed method is validated by applying it to the simple mass-damper-spring system whether the fluctuation of the time history response amplitude is restrained.
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Design, Machine Element & Tribology, Information & Intelligent Technology, Manufacturing, and Systems