Shigeki Nakaura

Sasebo National College of Technology, Saseho, Nagasaki, Japan

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Publications (60)4.15 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This brief describes a control strategy for the throwing motion of an underactuated two-link planar robot called the Pendubot. The springed Pendubot is built based on the concept of unstable zero dynamics, and our investigation uses it as a dynamic model of superior limbs to imitate human throwing motion. In the proposed control strategy, the zero dynamics is intentionally destabilized when a ball held by the end-effector is constrained on a geometric path in a vertical plane, using output zeroing control for the deviation between the ball and geometric path. The unstable zero dynamics drives the ball along the geometric path to achieve fast and accurate throw in a desired direction. The unstable zero dynamics is analytically derived to guarantee the dynamic acceleration of the ball along the geometric path. Numerical simulations and experimental results confirm the effectiveness of the proposed control strategy.
    No preview · Article · May 2013 · IEEE Transactions on Control Systems Technology
  • Kazuma Sekiguchi · Mitsuji Sampei · Shigeki Nakaura
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    ABSTRACT: The partial feedback linearization is capable of expressing a complicated nonlinear system as a simple form for control. To get a proper linearized subsystem, it is most important to select a proper coordinate transformation. This paper plays a fundamental role in selecting the proper coordinate by revealing the system structure with respect to a relative degree. The relative degree is a key concept to treat the partial feedback linearization, especially, the input-output linearization of an input affine system. Using special functions of the state characterized in the relative degree, all functions are parameterized and classified according to their relative degrees. Applying the proposed parameterization to a coordinate transformation, the system structure with respect to relative degrees is revealed. Moreover using the input-output linearization with parameterized outputs, it is also shown that the internal dynamics of the partially linearized system is parameterized.
    No preview · Article · Jan 2011
  • Yoshihiro Sakayanagi · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: The solvable condition of nonlinear H∞ control problems is given by the Hamilton Jacobi inequality (HJI). The state-dependent Riccati inequality (SDRI) is one of the approaches used to solve the HJI. The SDRI contains the state-dependent coefficient (SDC) form of a nonlinear system. The SDC form is not unique. If a poor SDC form is chosen, then there is no solution for the SDRI. In other words, there exist free parameters of the SDC form that affect the solvability of the SDRI. This study focuses on the free parameters of the SDC form. First, a representation of the free parameters of the SDC form is introduced. The solvability of an SDRI is a sufficient condition for that of the related HJI, and the free parameters affect the conservativeness of the SDRI approach. In addition, a new method for designing the free parameters that reduces the conservativeness of the SDRI approach is introduced. Finally, numerical examples to verify the effect of this method are presented.
    No preview · Article · Jan 2011
  • Kazuma Sekiguchi · Mitsuji Sampei · Shigeki Nakaura
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    ABSTRACT: This paper discusses the exact linearization problem of two-input affine systems via the dynamic extension based on the relative degree structure. A necessary and sufficient condition for two-input systems to be exactly linearizable via 1-degree dynamic extension is derived, and the input transformations of two-input systems with dynamic extension are classified into two forms. Finally, a method to derive the input transformation such that the transformed system is exactly linearizable via the dynamic extension is proposed. The proposed method is applied to a mechanical system.
    No preview · Article · Jan 2011
  • Takuya Shoji · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper describes a control strategy for throwing motion of the springed Pendubot based on the concept of unstable zero dynamics. An underactuated two-link planar robot called the Pendubot is investigated to realize dexterous actions of the superior limb in human throwing motion. A torsion spring is mounted on the passive joint of the Pendubot representing the flexibility of the cubital joint. In the proposed control strategy, the zero dynamics is intentionally destabilized when the end-effector of the springed Pendubot is constrained on a geometric path via output zeroing control for the deviation between the end-effector and the geometric path. The unstable zero dynamics drives the end-effector along the geometric path to achieve a fast and accurate throw in a desired direction when the input is devoted to constrain the end-effector on the geometric path. The unstable zero dynamics is analytically derived to guarantee the divergence of the end-effector along the geometric path. Numerical simulations confirm the effectiveness of the proposed control strategy.
    No preview · Conference Paper · Oct 2010
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    Masao Kanazawa · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: Inverse optimal design for bilinear systems is considered. The main result is that a nonlinear optimal feedback control law which minimizes a new quadratic cost function with nonlinear weight is obtained based on an inverse optimal control problem for bilinear systems. This inverse optimal control design is applied to the problem of the stabilization of the inverted pendulum on the cart which moves not only in the horizontal direction but also in the vertical direction. This inverted pendulum system can be transformed into a bilinear system by using input transformation and coordinate transformation focused on the center of percussion of the pendulum. It is theoretically shown that the proposed nonlinear optimal feedback controller has higher control performance than a conventional linear optimal controller for the linear approximation system. Furthermore, it is shown by numerical simulations that the control performance of the pendulum is improved by utilizing the vertical movement of the pendulum.
    Full-text · Conference Paper · Jan 2010
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    Tsubasa Numata · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper describes fly-casting motion control for a multilinked manipulator named `fly-casting manipulator', which consists of a casting rod, a fly line and a sinker. This manipulator simulates fly-fishing rod and has flexible potential. Flexible structure such as fly-fishing rod has advantages of accumulating energy because of its flexibility. Fly-casting motion has three phases, back-casting motion, collision and forward casting motion. Back-casting motion and forward-casting motion are energy accumulating phases and collision is energy losing phase. Additionally, the number of control inputs is less than the degree of freedom of the fly-casting manipulator. Thus, it is not possible to control all the states. Since this property makes it difficult to handle the casting rod, control problem of fly-casting motion is interesting as a point of view of control theory. Fly-casting manipulator is modeled as a multilinked underactuated manipulator. Only base joint is active joint, while the others are passive and constrained by torsion springs. The springs generate bending force which makes manipulator control easier. The proposed controller for casting motion is based on an input-output linearization and an output zeroing control to constrain the sinker on the desired path. Simulation results show the effectiveness of the proposed controller.
    Preview · Conference Paper · Jan 2010
  • Keisuke Nakamura · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper investigates the running control problem for the 7-link, 6-actuator planar bipedal robot including ankle joints. The control strategy is based on the “synchronization structure” with the angular momentum of the pivot point. The synchronization not only follows the simplified joint angle dynamics of human running but also generates the uniform running speed from wide range of initial speed, which claims that the controller is robust for the error of initial speed. Moreover, it successfully verifies the acceleration of running speed from 0.1[m/s], which is almost zero speed, to a uniform running speed “without” switching controllers. Finally, the controller is applied for the running on an uneven terrain, and it successfully achieves running with the maximum slope angle 6[deg], which is highly steep terrain in the real situation.
    No preview · Conference Paper · Jan 2010
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    Jumpei Nishizaki · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: Hula-hoop is not only one of familiar toys but also interesting system as a nonlinear control system. While humans play hula-hoop, hoop does not slide on the body but rotates around it. Though it is controlled only by the motion of the body, humans can realize enduring rotary motion without dropping hoop. The purpose of this paper is modeling and control of hula-hoop system as a nonlinear control systems. For modeling, hula-hoop system is regarded as the motion of the hoop and the pole in contact constraints. Note that there exist two types of models depending on constraints. For control, hula-hoop system can be divided to two subsystems. One is derived from dynamic equation, and the other is derived from contact constraints. The former subsystem has the motion of the pole and the angle of rotation as input and output, respectively. The latter subsystem has the angle of rotation and the altitude of contact point as input and output, respectively. For the latter subsystem, the angle of rotation to stabilize the altitude of contact point is derived. From the former subsystem, the motion of the pole to realize the angle of rotation is derived by output zeroing control. Finally, the validity of the proposed controller is verified by numerical simulations.
    Preview · Conference Paper · Dec 2009
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    Y Sugahara · A Kazato · R Koganei · M Sampei · S Nakaura
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    ABSTRACT: To improve ride comfort in railway vehicles, the suppression of vertical bending vibration and rigid-body-mode vibration in the car body is essential. In this paper, a system is proposed that aims to reduce bending and rigid-body-mode vibration simultaneously by introducing damping control devices in the primary and secondary suspensions. The technique involves a control system of primary vertical dampers and air springs; the former are used to suppress the first bending mode vibration; the latter, to suppress the rigid-body-mode vibration. The results of both simulations and vehicle running tests on the Sanyo—Shinkansen line demonstrate that this system reduced vertical vibrations in the bogies and the car body using the sky-hook control theory. In the running tests in particular, the system reduced the vertical vibration acceleration PSD peak value in the first bending mode to almost 20 per cent and in the rigid body mode to almost 50 per cent compared with the case when the system was not used. As a result, the ride quality level LT (a widely used index of ride comfort in Japan) decreased by at least 3 dB, indicating greater ride comfort.
    Preview · Article · Nov 2009 · Proceedings of the Institution of Mechanical Engineers Part F Journal of Rail and Rapid Transit
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    ABSTRACT: This paper deals with motion control of throwing generated by dexterous action. Dexterous actions can be seen in many sports. In baseball pitching, dexterous throwing seems to use energy transfer and a physical constraint at the elbow joint. To implement the dexterous throwing, two types of two-link underactuated manipulator are presented. One model has a spring at 2nd joint which represents an arm's stiffness and a constraint at elbow joint, another model has a physical absolute constraint at elbow joint. For these models, throwing motion control method based on output zeroing which specifies the path of the ball held by an end-effector is proposed. The proposed control strategy realizes the energy efficient motion for throwing to the desired direction. Simulation and experimental results show the effectiveness of the proposed control method.
    Preview · Conference Paper · Jul 2009
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    Shimpei Isobe · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper describes the modeling of the Acrobot composed of 2 links with a curved contour and the continuous rolling motion control for this Acrobot. The outer contour of each link is shaped from the arc whose radius is different by the tip and the sidepiece of the link. The model differs according to the contact point between the Acrobot and the ground. Therefore, it is difficult to control the whole motion via common control strategy. From an intuitive analysis based on the Acrobot¿s energy while the Acrobot rolls with a certain constant relative angle, control strategy is constructed in two phases. The phases are when the Acrobot rolls with lowering( downward phase) and raising(upward phase) the center of the gravity. As the control in upward phase needs to lower the COG of the Acrobot, a collision between the Acrobot and the ground becomes unavoidable. Therefore, analysis of this collision phenomenon is also conducted. At last, by selecting the output functions that can achieve the control objective at each phase and applying Output Zeroing control, continuous rolling motion is realized in numerical simulation.
    Preview · Conference Paper · Jan 2009
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    Yoshihiro Sakayanagi · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: Recently, nonlinear H<sub>¿</sub> control theory has been paid attention. The solvable condition of nonlinear H<sub>¿</sub> control problem is given by the Hamilton Jacobi inequality (HJI). State-Dependent Riccati Inequality (SDRI) is one of approaches to solve the HJI. The SDRI contains state-dependent coefficient (SDC) form of a nonlinear system. The SDC form is not unique, so free parameters of it is considered. If bad SDC form is chosen, then there is no solution of SDRI. In this paper, the relationship between free parameters and SDRI is clarified. The free parameters are generated when SDRI is derived from HJI. And they affect the conservativeness of SDRI. Then new method of design free parameters which reduces the conservativeness of SDRI is proposed. Finally, numerical examples to verify the effect of this method is shown.
    Preview · Conference Paper · Jan 2009
  • M. Sampei · S. Nakaura
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    ABSTRACT: An inverted pendulum is one of the most well known control problems: many textbooks on modern control theory treat it and many control courses in university use it as a laboratory experiment. But, usually, only the horizontal input to the cart is considered in those textbooks or benchmark problems. On the other hand, if we carefully analyze how we (human being) stabilize the inverted pendulum, we will find that we use not only the horizontal motion but also the vertical motion of the hand. In this note, we will consider the inverted pendulum on the cart with horizontal and vertical motion. We will show that the pendulum system can exactly be transformed into a bilinear system. We would like to propose to use this system as a benchmark problem of bilinear systems. We will also show one of our control strategy for bilinear systems based on an inverse optimal control, which efficiently uses the vertical motion of the cart.
    No preview · Article · Jan 2009
  • Keisuke Nakamura · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: Devil stick is a type of juggling which uses two sticks, one held by juggler and one to be manipulated. Many varieties of tricks of devil stick have been performed. In this paper, one of the tricks called “propeller” is specifically examined. Previously, the motion of propeller was analysed theoretically, and a controller for stable propeller motion by output zeroing control was proposed, and the validity of the controller was confirmed by numerical simulations. In the analysis of propeller motion, several conditions were assumed for simplifying the control problem. The controller was implemented to a general-purpose manipulator, and several experiments were carried out. However, those experiments could not successfully verify the propeller motion because the assumptions used in theoretical analysis were unfeasible. To correct this problem, an additional compensator is proposed, and the validity of the compensator is confirmed by numerical simulations and experiments. Finally, the enduring rotary motion of 37 rotations was achieved by an experiment.
    No preview · Chapter · Dec 2008
  • Yasuhiro Amagata · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper describes a control structure for planar humanoid runner on uneven terrain utilizing output zeroing. In this paper, the terrain whose inclination changes at random within a certain range is called uneven terrain. First, the change of dynamics by running on uneven terrain is considered, and the change of dynamics by running on uneven terrain is negated by adding the impulse input. The running on uneven terrain whose inclination changes within plusmn7 [deg] is achieved by the simulation. Second, important parameters of the output function is modified online utilizing Q-learning to acquire the running motion which can dynamically cope with the inclination of terrain. As a result, the running on uneven terrain whose inclination changes gradually within plusmn5[deg] is achieved.
    No preview · Conference Paper · Sep 2008
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    ABSTRACT: This paper describes the throwing motion control experiment utilizing a 2 link arm with a passive joint. In throwing, dexterous actions can be seen. Dexterous throwing uses energy transfer from a trunk of the body to a hand and a physical constraint at the elbow joint. However, human throwing is very difficult to analyze all features, because throwing motion performs in three dimensions. Therefore, under-actuated 2 link model is applied in this paper. Proposed model has a spring joint which is represented as an armpsilas stiffness and a constraint at elbow joint. For this model, the control method based on output zeroing which specifies the path of the ball at the end-effector is proposed. By developing an experimental equipment and carrying out experiments of throwing motion control, the effectiveness of the proposed control method is verified.
    No preview · Conference Paper · Sep 2008
  • Shimpei Isobe · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper describes the modeling of the Acrobot composed of 2 links with a curved contour and the rolling motion control for this Acrobot. The outer contour of each link is shaped from the arc whose radius is different at the tip and the sidepiece of the link. As the model changes according to the contact point between the Acrobot and ground, it is difficult to control the whole motion via common control strategy. From an intuitive analysis based on systempsilas energy when the Acrobot rolls with a certain constant relative angle, control strategy is constructed in two phases when the Acrobot rolls with lowering or raising the center of the gravity of itself. But, because the control in upward phase needs to lower the COG of the Acrobot, the collision between robot and ground becomes unavoidable. Therefore analysis at collision is also conducted. At last, by setting the output functions that can achieve the control objective in each phase and applying output zeroing control, continuous rolling motion is realized in numerical simulation.
    No preview · Conference Paper · Aug 2008
  • Kazuma Sekiguchi · Mitsuji Sampei · Shigeki Nakaura
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    ABSTRACT: In this paper, deriving method of a parameterized form of partial feedback linearizing output for a single input nonlinear affine system is discussed. The necessary condition of having a relative degree is derived for all available relative degree. And the output functions of relative degree in certain limit are parameterized using basis function completely. Moreover the sufficient condition for the other relative degree is derived.
    No preview · Article · Aug 2008
  • Kohei Suseki · Shigeki Nakaura · Mitsuji Sampei
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    ABSTRACT: This paper describes a control structure for humanoid runner which is using Q-learning and output zeroing. Based on this structure, the sagittal plane motion control algorithm is formulated using output zeroing. And Q-learning algorithm is used to learn key parameters of output function so that humanoid robot can achieve desired running motion. For the parameters of output function to be learned, the parameters which control the hip trajectory and torso angle of humanoid are selected. For an evaluation of learning, the running speed and stride of humanoid are used. As a result of learning, it is confirmed that key parameters of output function converge on constant value and that humanoid robot can realize continuous running in numerical simulation. Besides it is also verified that humanoid robot can realize continuous running at uneven terrain using similar control structure.
    No preview · Conference Paper · Jan 2008