The actuators required for a wearable system need to be flexible so as not to injure the body. The purpose of this study is to develop a flexible and lightweight actuator which can be safe enough to be attached to the human body. In the previous study, a new type of McKibben artificial muscle that had a long stroke of more than 80 % of its original length was proposed and tested. However, the damages on the tube of the actuator were found. They are caused by a large friction between the slide stage and the tube. Therefore, the life time of the actuator becomes shorter. In this paper, the improved McKibben actuator which consists of a McKibben artificial muscle on the market (FESTO Co. Ltd.), steel balls as a cylinder head and two pairs of slide stages is proposed and tested. The slide stage has steel balls set on the inner bore of the stage to decrease the friction. The steel ball in the McKibben actuator is held by two pairs of slide stages from both sides of the ball. As a result, the minimum driving pressure of the improved actuator decreases about 68 % compared with that of the previous one. The actuator can realize both pushing and pulling motion even if it has flexibility. By using these properties of the actuator, the various rehabilitation devices were proposed and tested.

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Recently, force feedback devices in virtual reality and power assisted nursing care systems have received much attention and active research. In such a control system, an actuator and a driving device such as a control valve are mounted on the human body. In this condition, the size and weight of the control valve become serious problems. At the same time, the valve should be operated with lower energy consumption because of using a limited electrical power. The typical electro magnetic solenoid valve drives its spool using a larger solenoid to open the valve. The complex construction of the valve for sealing makes its miniaturization and the fabrication of a low cost valve more difficult. In addition, the solenoid in the valve consumes more electrical power while the valve is kept opening. The purpose of our study is to develop a small-sized, lightweight, lower energy consumption and flexible control valve that can be safe enough to mount on the human body at a lower cost. In our pervious study, we proposed and tested the control valve that can open using a vibration motor. In this study, we propose and test a new type of fluid control valve with a self-holding function. The new valve uses a permanent magnet ball. It has a cylindrical magnet and two solenoids. The self-holding function of the valve is done as follows. When one side of the solenoid is stimulated by the current momentarily, the solenoid gives a repulsive force to the cylindrical magnet. The magnet moves toward the opposite side of the solenoid and is attracted to the iron core. Then, the magnet ball moves toward the cylindrical magnet and opens the orifice. The valve can keep open without electrical energy. As a result, the valve with the extremely lower energy consumption can be developed.

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In the factory, the continuous steel plates subjected to iron and steel processes are supported by a series of rollers during processes such as rolling. However, because roller comes in contact with the steel plates, the problem of surface quality deterioration arises. To solve this problem, we develop a non-contact guide for parts of the steel plate at which its traveling direction changes in high-speed traveling by applying an electromagnetic force from the direction of the edge of the steel plate, and experimentally examine the effectiveness of the system. Moreover, when the position of the plate is controlled, it is extremely difficult to determine the mass of the control target. We confirm the suppressive effect of a sliding mode control theory that has robustness in mass variation. The results indicate that the proposed system can be achieved.

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A repulsive magnetic bearing supports a rotating shaft without contact by utilizing a magnetic repulsive force between the magnets. However, because of the nonlinear characteristic of the magnetic repulsive force, the vibration during passage through the critical speed may increase. This paper investigates a vibration suppression method of the rotating shaft supported by the repulsive magnetic bearing. A vibration suppression method by controlling the axial displacement of the repulsive magnetic bearing is proposed. Its axial displacement control generates the changes of both the linear and the nonlinear coefficients of stiffness. The influence of the parameters of the axial displacement control are investigated, and these results are validated experimentally.

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In this paper, we propose a design method of a dual-mode model predictive control law for linear dynamical systems with input constraints. The proposed control law is composed of a finite horizon open-loop optimal control law and a state-dependent gain-scheduled feedback control law. By using the proposed control law, both high control performance and large region of attraction ca be achieved. We show that, by using the control law, the closed-loop stability can be guaranteed and the tracking error converges to zero in the case where a reference signal to be tracked is generated by a certain linear dynamics. The control algorithm is reduced to a convex optimization problem under linear matrix inequlitity constraints.

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The purpose of this paper is to study the determination of L₂ gain performance index in a design method of anti-windup compensator. Since the purpose of the anti-windup compensation is to control the controller state, we introduce a new L₂ gain performance index that contains both the plant state and the controller state. Local control design technique which is based on the circle criterion is used for anti-windup compensator synthesis, while global control performance analysis is conducted using Popov criterion. Better response is obtained by tuning the two weighting matrices on the states of the performance index, which is demonstrated by simulation and experiment examples.

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Swashplate mechanism is the steering control mechanism used in most helicopters. It is a complex multi-loop closed kinematic chain which controls the angles of attack of the main rotor blades. In most new model helicopters, this mechanism is also equipped with the bell-hiller stabilizer bar (flybar), to improve the stability. This paper aimed at the kinematic analysis of one of the latest architectures of the swashplate mechanism, used for hingeless rotor with the flybar. Hence, the position analysis of each module and whole mechanism, based on parallel manipulators concept with more details involved than other works, was presented here. The kinematic model was further developed to obtain Jacobian matrices, velocity and acceleration analysis in detail. Finally, a particular example was conducted and compared with an ADAMS rigid body dynamic model, to verify the analytical model. In many simulated cases, the results matched.

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Squeal and chatter phenomena are often generated in bicycle disc brakes. The squeal is in-plane unstable vibration along the disc surface caused by dry friction with negative slope with respect to the relative velocity. The squeal is generated in the vibrating system including the brake unit, spokes and hub. According to experiments, the chatter is generated in a certain limited range at high disc temperatures, and is nonlinear frictional vibration in which the out-of-plane unstable vibration of the disc due to Coulomb friction and the squeal are combined through the internal resonance relationship between the out-of-plane and in-plane vibrations caused by the increase in disc temperature during braking. First, we propose a simple nonlinear system with three degrees of freedom which possesses the essential vibration factors included in a bicycle disc brake system to investigate whether or not the coupled nonlinear vibration due to the internal resonance occurs. Then, we numerically confirm the mechanism of the chatter generated in a bicycle disc brake by nonlinear analysis.

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A pressure wave propagating in a tube often changes to a shock wave because of the nonlinear effect of the fluid it is traveling through. The purpose of this study is to establish a practical analytical model to analyze this phenomenon. In previous reports, a concentrated mass model was proposed to analyze nonlinear pressure wave phenomena in a straight cylindrical tube. In this paper, the modeling of a branched junction is proposed. The model of the branched junction consists of masses, nonlinear pressure elements, base support dampers, and nonlinear dampers. The nonlinear damper is derived from the pressure loss at the branched junction. To confirm the validity of the proposed branch model, the numerical results obtained from the concentrated mass model are compared with the theoretical value of the transmission loss of a branch pipe. Additionally, an experiment on a sound tube with a branch pipe is performed and the experimental results are compared with the numerical result. All computational results agree very well with the theoretical value and the experimental results. Therefore, it is concluded that the proposed branch model is valid for the numerical analysis of nonlinear pressure wave problem in a tube with a branch pipe.

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This paper presents experimental results on chaotic vibrations of a thin circular plate with a circular center hole. The plate has an asymmetric curved configuration due to an initial imperfection, an in-plane compressive stress and lateral deformation by the gravity. First, linear natural frequencies and natural modes of vibration are measured. The second and the third modes of vibration have one nodal diameter with different natural frequencies. These nodal diameters are perpendicular to each other. The linear natural frequencies of the lowest and the second modes satisfy the condition of one-to-two internal resonance, closely. Characteristics of restoring force of the plate show the type of a softening-and-hardening spring. Next, the plate is excited with periodic acceleration, laterally. Sweeping the excitation frequency, nonlinear responses of the plate are measured. In a restricted frequency range of the principal resonance of the lowest mode, non-periodic responses with amplitude modulation are generated. The time histories of the response are measured for a long-time interval at four positions, simultaneously. The time histories are inspected by the Fourier spectrum, the Poincaré projection, the maximum Lyapunov exponents and the principal component analysis. The non-periodic response is found to be the chaotic response generated from the one-to-two internal resonance coupled with the lowest and the second modes. The results of the principal component analysis with the time histories of the multiple positions on the plate show that the lowest, second and third modes predominantly contribute to the chaotic response. Applying the calculation with short-time intervals cut out from the time histories, it is found that the nodal patterns of the second and the third modes of vibration are fluctuated along the circumferential direction. Furthermore, the exchange of the contribution ratio is shown between the lowest and the second modes of vibration.

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