Okayama Prefectural University

www.oka-pu.ac.jp/en/index.html
Okayama, Japan

Okayama Prefectural University is a public university in Sōja, Okayama, Japan, established in 1993. Wikipedia.


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Xin X.,Okayama Prefectural University
2016 IEEE 55th Conference on Decision and Control, CDC 2016 | Year: 2016

This paper concerns an n-link underactuated revolute planar robot in a vertical plane with two or more actuators and encoders. The linear controllability and observability of such a robot around the upright equilibrium point (UEP), where all the links are in the upright position, are investigated. This paper concerns the problem of the linear controllability and observability of an n-link planar robot around the UEP with only multiple intermediate links being active and the corresponding link angles being measured. When neither the first link nor the last link of the robot is active, and the robot has two or more active intermediate links and the corresponding link angles are measured, this paper proves via a new constructive example that, if there do not exist two active intermediate adjacent links, then there always exists a set of mechanical parameters that renders the robot linearly uncontrollable and unobservable around the UEP. When neither the first link nor the last link of the robot is active, together with an existing result, this paper shows that the robot is linearly controllable and observable, regardless of its mechanical parameters, if and only if there are at least two active adjacent links among the n-2 intermediate links and the corresponding link angles are measured. © 2016 IEEE.


Xin X.,Okayama Prefectural University
2016 IEEE 55th Conference on Decision and Control, CDC 2016 | Year: 2016

This paper considers an n-link underactuated revolute planar robot with all the links moving in the same vertical plane. This paper studies two open problems of the linear controllability and observability of the robot with only an active intermediate joint or only active intermediate joints around the upright equilibrium point (UEP), where all the links are in the upright position. First, when the robot only has a single active intermediate joint or only has multiple active intermediate nonadjacent joints with the corresponding joint angle(s) being measured, this paper shows via an illustrative example that there always exists a set of mechanical parameters that renders the robot linearly uncontrollable and unobservable around the UEP. This, together with an existing result, shows that an n-link planar robot with an actuator and an encoder is linearly controllable and observable around the UEP, regardless of its mechanical parameters, if and only if the first or last link, or the last joint, with the corresponding angle is measured. Second, when the robot only has two intermediate adjacent joints with the corresponding joint angles being measured, this paper proves that the robot is linearly controllable and observable around the UEP regardless of its mechanical parameters. When neither the first nor last joint of the robot is active, this paper shows that the robot is linearly controllable and observable around the UEP if and only if there are at least two active adjacent joints of n - 2 intermediate joints and the corresponding joint angles are measured. © 2016 IEEE.


She J.-H.,Tokyo University of Technology | Xin X.,Okayama Prefectural University | Pan Y.,Ryerson University
IEEE/ASME Transactions on Mechatronics | Year: 2011

This paper deals with the high-precision positioning control of a dual-stage feed drive. The design of the control system is based on the equivalent input-disturbance (EID) approach to improve the disturbance rejection performance. An analysis of the EID approach reveals the mechanism of disturbance rejection. The design procedure is illustrated by a numerical example. Simulation results show that the EID control system not only rejects disturbances, but also suppresses uncertainties and nonlinearities in the plant. Design and simulation results for the example are also employed to compare our method with the disturbance observer method, and to demonstrate the validity of our method. © 2010 IEEE.


Xin X.,Okayama Prefectural University | Liu Y.,Okayama University
Automatica | Year: 2013

This paper concerns reduced-order stable controllers in a unified way for two typical examples of underactuated robots called the Acrobot and the Pendubot, which are two-link planar robots moving in a vertical plane with a single actuator at joints 1 and 2, respectively. The main contributions of this paper are threefold. First, with the aid of properties of the mechanical parameters of two-link planar robots, this paper proves constructively that stable controllers exist for stabilizing the UEP (Upright Equilibrium Point with two links being still in the upright position) of each robot by designing a single output with an adjustable parameter. Second, the paper presents a design method to obtain explicitly a formula of second-order (reduced-order) stable controllers by choosing the adjustable parameter. Third, in terms of strong stabilization, some new features of the Acrobot and the Pendubot are revealed and are compared with those of the cart-pendulum system. Simulation results for the two robots are presented to validate the theoretical results and to demonstrate that the presented stable stabilizing controllers achieve a better control performance than several other controllers. © 2013 Published by Elsevier Ltd.


Taniguchi T.,Okayama Prefectural University
Sangyō eiseigaku zasshi = Journal of occupational health | Year: 2012

The purpose of this study was to describe workplace bullying experienced by professional caregivers at welfare facilities for the elderly in Japan and to confirm its effects on stress reactions. A cross-sectional survey was carried out using self-administered questionnaires in 2009 of all the employees working in rural area of facilities for long-term care. Among the 1,233 respondents who filled out all questionnaires concerning stress reactions the Japanese version of the Negative Acts Questionnaire (NAQ) (response rate: 63.9%), we analyzed 897 professional caregivers. We measured stress reactions by using the stress reaction scores of the Brief Job Stress Questionnaire (29 items) and workplace bullying and harassment by using NAQ. We used the unpaired t-test and analysis of covariance (ANCOVA) to compare crude and adjusted average stress reactions with groups classified on the basis of each subscale of the NAQ or all of them. About 40% of both men and women suffered from "malicious gossip" and over 60% of both men and women experienced "someone withholding necessary information so that their work gets complicated". Among women, scores of the lack of vigor and fatigue were significantly higher in caregivers targeted by person-related bullying than those not targeted (p<0.05). Scores of depression were significantly higher in caregivers targeted by work-related bullying than those not targeted (p<0.05). Scores of anxiety were significantly higher among caregivers targeted by sexual harassment than those not targeted (p<0.05). Among men, scores of the lack of vigor were significantly lower in caregivers targeted by work-related bullying than those not targeted (p<0.05). Among women, workplace bullying or harassment could may aggravate effects on psychological stress responses. While among men, work-related bullying was positively associated with vigor.


Xin X.,Okayama Prefectural University
International Journal of Robust and Nonlinear Control | Year: 2011

Designing and analyzing controllers for mechanical systems with underactuation degree (difference between the number of degrees of freedom and that of inputs) greater than one is a challenging problem. In this paper, for the double pendulum on a cart, which has three degrees of freedom and only one control input, we study an unsolved problem of analyzing the energy-based swing-up control which aims at controlling the total mechanical energy of the cart-double-pendulum system, the velocity and displacement of the cart. Under the energy-based controller, we show that for all initial states of the cart-double-pendulum system, the velocity and displacement of the cart converge to their desired values. Then, by using a property of the mechanical parameters of the double pendulum, we show that if the convergent value of the total mechanical energy is not equal to the potential energy at the up-up equilibrium point, where two links are in the upright position, then the system remains at the up-down, down-up, and down-down equilibrium points, where two links are in the upright-down, down-upright, and down-down positions, respectively. Moreover, we show that each of these three equilibrium points is strictly unstable in the closed-loop system by showing that the Jacobian matrix valued at each equilibrium point has at least one eigenvalue in the open right half plane. This shows that for all initial states with the exception of a set of Lebesgue measure zero, the total mechanical energy converges to the potential energy at the up-up equilibrium point. This paper provides insight into the energy-based control approach to mechanical systems with underactuation degree greater than one. © 2010 John Wiley & Sons, Ltd.


Yamashita H.,Okayama Prefectural University
Critical Reviews in Food Science and Nutrition | Year: 2016

Fatty acids derived from adipose tissue are oxidized by β-oxidation to form ketone bodies as final products under the starving condition. Previously, we found that free acetic acid was formed concomitantly with the production of ketone bodies in isolated rat liver perfusion, and mitochondrial acetyl CoA hydrolase was appeared to be involved with the acetic acid production. It was revealed that acetic acid was formed as a final product of enhanced β-oxidation of fatty acids and utilized as a fuel in extrahepatic tissues under the starving condition. Under the fed condition, β-oxidation is suppressed and acetic acid production is decreased. When acetic acid was taken daily by obesity-linked type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats under the fed condition, it protected OLETF rats against obesity. Furthermore, acetic acid contributed to protect from the accumulation of lipid in the liver as well as abdominal fat in OLETF rats. Transcripts of lipogenic genes in the liver were decreased, while transcripts of myoglobin and Glut4 genes in abdominal muscles were increased in the acetic acid-administered OLETF rats. It is indicated that exogenously administered acetic acid would have effects on lipid metabolism in both the liver and the skeletal muscles, and have function that works against obesity and obesity-linked type 2 diabetes. © Taylor & Francis Group, LLC.


The energy-based control approach aiming to control both the total mechanical energy and actuated variables of underactuated mechanical systems has generated renewed interest in recent years. Different from the reports of successful applications of this approach, we investigate whether there exists an underactuated mechanical system for which we fail to control both the total mechanical energy and actuated variable(s) to some given desired values by studying a CWA (Counter-Weighted Acrobot), which is a modified Acrobot with its first link having a counterweight and only its second link being actuated. By analyzing globally the solution of the closed-loop system consisting of the CWA and the controller designed via the energy-based control approach, we show that unless the CWA is linearly controllable at the up-up equilibrium, where links 1 and 2 are in the upright position, the controller fails to achieve the goal of controlling the energy to the potential energy at the equilibrium and controlling the actuated joint variable to zero. We also provide corresponding results for the up-down, down-up, and down-down equilibriums of the CWA, where up and down denote that the link is in the upright and downward positions, respectively. We present numerical simulation results to validate the theoretical results. © 2013 Taylor & Francis Group, LLC.


Xin X.,Okayama Prefectural University | Yamasaki T.,Okayama Prefectural University
IEEE Transactions on Control Systems Technology | Year: 2012

This brief concerns the energy-based swing-up control for a remotely driven acrobot (RDA) which is a 2-link planar robot with the first link being underactuated and the second link being remotely driven by an actuator mounted at a fixed base through a belt. An energy-based swing-up controller is designed via the Lyapunov stability theory. A global motion analysis of the RDA under the designed controller is provided focusing on the behavior of the closed-loop solution and the stability of the closed-loop equilibrium points. The conditions on control parameters for achieving a successful swing-up control are given. Furthermore, an experimental setup is described and experimental results are given to validate the presented theoretical results. The energy-based swing-up controller for the RDA is shown to be effective both theoretically and practically. © 2011 IEEE.


Xin X.,Okayama Prefectural University
Proceedings of the IEEE Conference on Decision and Control | Year: 2011

This paper concerns the swing-up control problem for a two-link underactuated robot moving in the vertical plane with a single actuator at the base joint and a spring between the two links (flexible elbow joint). First, we present two new properties of such a flexible robot about the linear controllability at the UEP (upright equilibrium point, where two links are in the upright position) and the limitation of the PD control on the angle of the base joint. Second, for the robot which can be not locally stabilized about the UEP by the PD control, we study how to extend the energy-based control approach, which aims to control the total mechanical energy and the angle and angular velocity of the base joint of the robot, to design a swing-up controller. We provide a necessary and sufficient condition for avoiding the singularity in the controller. Third, we analyze the motion of the robot under the presented controller by studying the convergence of the total mechanical energy and clarifying the structure and stability of the closed-loop equilibrium points. We validate the presented theoretical results via numerical investigation. This paper not only unifies some previous results for the Pendubot (a two-link robot with a passive elbow joint), but also provides insight into the control and analysis of the underactuated robots with flexible joints. © 2011 IEEE.

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