This study aims at a design technique of energy-efficient biped walking robots on level ground with simple mechanisms. To do this, we focus on the passive dynamic walkers which can walk stably down a shallow slope without actuators and controllers. On level ground, active walking should be studied because the mechanical energy is mainly lost through the swing-leg impacts with the ground. In this paper, numerical simulations show that planar biped robots with torso can walk efficiently on level ground over a wide range of speed by only using hip actuators. The hip actuators are used for a torso and swing-leg control based on passive-dynamic walking. The torso is used to generate active power replacing gravity used in the case of the passive walk. The swing-leg control is introduced to walk stably over a wide range of speed.

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In this paper, vibration control of a safe arm with passive compliant joints and visco-elastic covering for a human-friendly service robot is presented. The passive compliant joint (PCJ) is designed to passively attenuate the applied force. The rotary spring gives the arm compliant property, and yet it can be a source of vibration. We use an input-preshaping method which is motivated by the input shaping technique (IST) based on impulse responses. Experiments prove that both of fast motion and force attenuation of the safe arm can be achieved.

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In this paper, a grasp force feedback control method of a robot hand attached to a single-link robot arm is proposed, and the usefulness of the grasp force feedback control method is confirmed theoretically and experimentally. The robot hand consists of two permanent-magnet-type stepping motors, reduction gears and plate springs. In the design of the grasp force feedback control system, the start-stop performance without missing steps concerning stepping motors is effectively utilized. For the shock reduction of the robot hand mechanism using stepping motors, the stepping motors should be stopped at a lower pulse rate. Therefore, the grasp force feedback control system is designed to finish the grasp force feedback control at a lower pulse rate of the stepping motors. For this purpose, the control method of the stepping motors using the angular velocity pattern of trapezoidal shape with a constant-velocity time and an estimated finish-time determined by the grasp force feedback control is devised. Then, numerical simulations using the equations of motion of the robot and the grasp force feedback control law have been carried out, and it is ascertained theoretically that the grasping force can be precisely controlled by the present grasp force feedback control method. Furthermore, experiments have been carried out, and the excellent performance of the grasp force feedback control is confirmed experimentally.

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A surface acoustic wave (SAW) linear motor is a kind of ultrasonic motor. The advantages of the SAW linear motor are thin structure, high thrust force, high velocity and precise positioning. The relationship between applied current and output velocity is, however, unstable in the low velocity range due to the friction drive principle. Therefore the SAW linear motor cannot obtain stable driving without feedback control in the low-velocity region. In this research, to realize low velocity, a pulse width modulation (PWM) control and flexible slider structure are employed. Flexible structure is installed to cancel vibration due to the PWM carrier wave. A lower velocity in the unstable range is realized. Moreover we change the calculation algorithm for the slider velocity measurement. As a result, the SAW linear motor can be driven at an ultra low velocity of 30μm/s. Additionally, driving characteristics are improved using a feedforward controller.

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The density of components on precision devices such as semiconductor processors has been increasing recently. As a consequence, the acceptable vibration level of floors on which manufacturing equipment is installed is decreasing. Conversely, vibrations generated by the manufacturing equipment are increasing because manufactured objects are increasing in size. For these situations, active vibration isolation devices are usually used to isolate equipment from floor vibrations. However, the vibration control forces generated by active vibration isolation devices cause floor vibrations when these devices are used to isolate the large vibrations generated by manufacturing equipment. To solve this problem, a new vibration-canceling system using inertial-force generators is developed in this research. In addition, the effectiveness of the developed vibration-canceling system is confirmed via experiments.

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This study deals with the design of passive suspension system of railway vehicles. The proposed model has six-degree-of-freedom and can be designed via control theory. Since the classical fixed point theory is no longer applicable to the design of passive suspension system of railway vehicle, many methods have been developed to replace it. In this paper, By utilizing feedback control theories the problem is examined from the view of feedback control problem. Consequently, the “feedback gain” is a decentralized matrix composed of the suspension parameters to be optimized. Since minimizing H_∞ norm of the system implies suppressing the peaks of the magnitude of frequency response of the system, parameters optimization of passive suspension systems become a H_∞ static output feedback problems, and it is transformed to Bilinear-Matrix-Inequality (BMI) problem. One of the easiest methods to solve this BMI problem is alternative algorithm, which is derived from iterative schemes of alternation between analysis and synthesis via Linear Matrix Inequalities (LMIs). Finally, numerical simulations for the passive suspension system designed by control theory and fixed point theory will show the comparison of performance of each method.

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A read/write head assembly attached to a spinning disk was modeled and investigated through a different approach, in which the head assembly was represented by a suspension arm with an attached mass and an air spring (film) at its free end. The receptance method was applied to connect the spinning disk and the head assembly. The natural frequencies and mode shapes of the combined spinning disk-fixed head assembly as a whole were then interpreted. Numerical results showed that the head assembly induced extra modes from a single disk. Even for just weak coupling between disk and head, the bifurcations of mode shapes were very obvious, but the changes of natural frequencies were slight. The effects on frequency changes due to head's flexibility, air spring constant, head's location, and spinning speed were examined as well. Disk's spinning speed was found to pull the disk-head frequency loci to pass through the crossings of single disk's frequency loci and induce curve veering phenomenon.

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Elevator ropes in high-rise buildings are forcibly excited by the displacement of the building induced by wind force. An approximate solution to the forced vibration of a rope with time-varying length and having linear damping is presented here. It is assumed that the rope tension and the moving velocity are constant, and that the damping coefficient of the rope is small. Virtual sources of waves which can be assigned to reflecting waves are used for obtaining the approximate solution. Finite difference analyses of rope vibration are also performed to verify the validity of this approximate solution. The calculated results of the finite difference analyses are in fairly good agreement with the calculated results of the approximate solution. The effects of moving velocity and damping factor on the maximum rope deflection are quantitatively made clear.

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This paper describes a self-excited vibration of a Flow Dynamic Conveyor (FDC). The FDC is often used in power plants and in iron works because of superiority in noise control compared with a roller type conveyor. The FDC consists of a trough and a belt, and the air is supplied from many holes provided on the trough. A large vibration suddenly occurs when the flow rate becomes the critical value. In this paper, some measurements were performed in order to clarify the phenomenon. As a result, it was found that the phenomenon was the self-excited vibration based on the interference between two vibration systems such as the load·air-spring system and the trough·supporting system.

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Dynamic behavior of a variable stroke swash plate mechanism is analytically and numerically investigated. Deriving a simple degree of freedom model, we propose a dimensionless arm length to characterize dynamic stabilities of the swash plate angle. We then make a comparison between two types of constraints of the swash plate: one fixating the plate with the swing component and the other linking it with the followers in a frictionless manner. It is numerically shown that the fixed-type constraint improves the stabilities of the mechanism while the frictionless-type constraint makes the mechanism destabilized. An equivalent design technique is also proposed to convert optimal specifications between the different types of the constraints.

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Swirl Braked Grooved Seal (SBGS) is an advanced grooved annular seal for rotordynamic stability improvement. SBGS has circumferential or helical grooves in which several swirl brakes are placed. The swirl brakes can prevent the circumferential flow that might generate unstable dynamic fluid force in the seal. The stability and the unbalance response of a simply supported Jeffcott rotor, having a seal near the disk, are analyzed by FEM in which measured rotordynamic coefficients of seals are used. The rotordynamic analysis is performed for 18 different types of seals, including 13 SBGS, 4 conventional grooved seals (1 circumferential and 3 helical), and a smooth seal. Results show that the SBGS with circumferential grooves have high stability and low sensitivity to unbalance. On the other hand, the swirl brakes did not improve either stability or unbalance response for the helically grooved seals.

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Friction between two relatively sliding surfaces in mechanical structures possibly excites unstable vibration, which emits squeal noise. In this paper, the authors propose an idea to predict the possibility of squeal noise occurrence in actual structures having relative sliding surfaces with friction by means of experimental modal analysis and experimental spatial matrix identification. Using spatial matrices that derived from experimental modal data, unstable mode coupling that causes squeal noise can be predicted. By this method it is possible to calculate the possibility of squeal noise incident and its frequency within the practical realistic range of friction coefficient and contact stiffness. The method is presented with showing an experimental verification study using a simple L shape frame.

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A frog shaped guiro is a wooden percussion instrument with an open-ended cave. By rubbing dorsal fins like saw blades on a back of the guiro with a wooden stick, the guiro generates the sound like a frog's voice. The exciting force, response acceleration and radiating sound pressure were measured with accelerometers on the stick and guiro and a condenser microphone and then the relation between the impulsively exciting force and sound pressure was revealed. A three-dimensional solid model of the guiro was built by use of an X-ray CT scanner device and a finite element model composed of tetrahedral elements was then obtained. The FEM modal analysis revealed that the frog shaped guiro had four dominant modes of vibration which was characterized by motion of mouth of the guiro such as the yawn mode and grinding teeth mode. The frequency spectrum of the sound pressure radiating from the frog shaped guiro excited by sequential impulsive forces moving along the dorsal fins was theoretically estimated. Since the estimated sound pressure agreed well with the measured one, the sound radiating from the guiro like a frog's voice could be reproduced. It was also revealed that the variation of driving point mobility of the dorsal fins and amplitude of the exciting force affected to generate the sound like a frog's voice.

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