Understanding the stability inherent in limit cycle walking with constraint on impact posture without numerical integral is one of the fundamental goals in the area of robotic legged locomotion. The two major methods to analyze the stability of generated dynamic gaits have ever been proposed. One is the method for deriving the transition function of the state error using linearization of motion, and the other is that for describing the convergence of the kinetic energy based on mechanical energy balance. In both methods, however, numerical integral was necessary. In this paper, we theoretically show that it is possible to achieve stability analysis without numerical integral by integrating the two methods. First, we analytically derive the transition functions of the state error without including unknown variables for a 1-DOF semipassive walker and evaluate the solution accuracy through numerical simulations. Second, we consider a 2-DOF underactuated walker and show that the stability of the generated level gait can be analyzed in the same manner as the 1-DOF walker.

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This paper describes a data center energy management system which reduces power consumption of cooling and a novel method for semi-optimal workload placement and cooling. The energy management is formulated as an optimization problem and the optimal workload and cooling are calculated using mathematical programming such as mixed integer programming (MIP), which needs long computation time for large data centers. The computation of cooling control has to be completed within its control interval. Therefore, the semi-optimal solution is used for actual data centers. In this paper, an algorithm for semi-optimal solution is introduced. First, semi-optimal workload placement is calculated based on an equation of cooling power consumption and workload placement. This includes only matrix calculations and sorting. Then, optimal cooling is calculated using the resultant workload placement and liner programming, which is faster than MIP. Simulation results indicate that its computation is fast and accurate enough to apply it to large data centers.

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In this paper, a new method to estimate model prediction error using process database for the purpose of improvement in model prediction accuracy for the steel plant was investigated. The basic concept of the proposed method is to compensate prediction error of physical model by using local regression modeling method, such as Model-On-Demand technique or Just-In-Time modeling. In this method, several local models are obtained using several datasets and then the estimation value of prediction error is calculated by applying ensemble learning method. In addition, the effectiveness of proposed method has been confirmed for the temperature prediction model of plate cooling by numerical simulations and actual online tests.

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In this paper, the problem to find the minimum control efforts trajectory of constant speed vehicle is reduced by non-dimensionalization and is formulated as a two point boundary value problem (TPBVP). Optimal input is given as a function of states and unknown parameters; the parameters are determined by solving the TPBVP using shooting method. The method for providing the initial guess of the shooting method is also proposed. The number of iterations in shooting method shows the validity of our method for initial guess.

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Our research group has worked on an ultrasound-based noncontact tactile display. It utilizes a nonlinear effect of ultrasound to produce a force in midair. It is known that an object in the ultrasound field suffers a force (acoustic radiation pressure) in the direction of the ultrasound propagation. The position of the force is controlled three-dimensionally based on the phased array focusing technique: A focal point of ultrasound is generated by setting the phases of hundreds of ultrasound transducers adequately. After the presentations and the demonstrations of this tactile display, it gradually came out that some researchers working on research fields other than tactile display liked to use this device for their own issues. But the previous prototype device had a bulky body and complicated wires, and so it took time and labor to carry, setup, and install it. These drawbacks limited the situations in which it could be used and prevented us from giving it a try to use it in other application areas. In order to break through this difficulty, we newly developed a compact device which generates a noncontact force up to 16mN. It was carried out by integrating driving circuits and cutting out the expandability of the device. This small-sized and light-weighted device is easy to use and so useful for exploring new application areas. In this paper, firstly, the principles of the device are explained. Secondly, the design concept and the specifications of the device are provided. Thirdly, the experiments show that the ultrasound is focused as the theory predicted, the intensity of the output force is surely controlled by PWM, and the frequency characteristics covers up to 1kHz. Finally, the collaborative researches based on the developed ultrasound device are reported as the evidence of application exploration.

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This paper presents a feedforward control technique for the suppression of residual vibrations in mechanical systems with parameter variations. We deal with the Point-To-Point (PTP) motion of the pendulum system consisting of an unactuated pendulum attached to the end of a horizontal rotating arm, and demonstrate the effectiveness of the proposed method through numerical simulations and experiments.

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In this paper, we give an algebraic characterization of solutions to infinite-horizon nonlinear discrete-time optimal control problems. We define an algebraic function solution to the equation, which is obtained by solving algebraic equations, and derive a necessary and sufficient condition for the existence of an algebraic function solution in terms of commutative algebra. According to our main theorem, obtaining an algebraic solution reduces to finding a specific polynomial ideal.

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