Kentaro Hirata

Spectrum of Monodromy Operator for a Time-Delay System With Application to Stability Analysis

This note studies the spectral properties of monodromy operators, which play an important role in stability analysis of linear time-invariant time-delay feedback systems. The note is motivated by the fact that this operator can actually be defined naturally on four spaces, where the difference stems from different choices for the function space on which the infinite-dimensional state of such a time-delay system is assumed to take its value. It is first shown that the spectrum of the monodromy operator is independent of the spaces on which it is defined. This implies that stability of time-delay systems is independent of the underlying function spaces. It is further shown that the operator spectrum is continuous at monodromy operators, which justifies the spectrum computation of the monodromy operator through its approximation by any sort of tractable operators. A numerical study relevant to the theoretical development is provided and a practical implication of our theoretical study is suggested.

Power assisting control for electric bicycles using an adaptive filter

This paper considers controller synthesis problem of power assisting system for periodic motions. Most commercial electric power assisting bicycles are using proportional assist to human pedaling torque. However, human pedaling motion is almost periodic and it can be shown that such a strategy is not optimal in the sense of energy efficiency. In our previous work, we observed that pedaling frequency of human fluctuates to some extent. Thus, an adaptive compensation is introduced here. In particular, we propose a power assisting control with adaptive notch filter to suppress the velocity deviation. The effectiveness of the proposed method is demonstrated through numerical simulations.

Robust controller synthesis for a class of uncertain systems and application to visual feedback control

In this paper, we consider the robust synthesis problem of dynamic output feedback controller for a class of polytopic uncertain systems. The motivation dealing with this special class arises from visual feedback stabilization problems under image distortion. The effectiveness of the proposed matrix inequality condition is verified by the experiments of visual feedback stabilization with a cart and pendulum system.

Energy-efficient power assist control with periodic disturbance observer and frequency estimator

In this paper, energy-efficient power assist control problem for almost-periodic motions is considered. Specifically, we focus on the electric power assisted bicycles. Previously, it was shown that the energy efficiency improves by flattening the pedaling torque pattern. To cope with the frequency fluctuation of our motion, we introduce the periodic disturbance observer and a frequency estimator and suppress the pulsation of the human pedaling torque based on a disturbance observer framework. The effectiveness of the proposed method is demonstrated through experiments with an actual bicycle.

Model Predictive Control of hot-rolled strip cooling process using variable-resolution model

Model Predictive Control is an effective control method for nonlinear plants with constraints. However, application to large-scale systems and/or processes that require high sampling rate is quite challenging because of the heavy computation. Here we consider MPC approach for the cooling process of hot-rolled strip having 3D thermal distribution. To solve this large-scale problem, we propose a method to change the resolution of the model dynamically according to the uniformity of the thermal distributions in the directions of interest. Combined with a hierarchical control strategy to flatten the thermal distribution in a certain direction, one can balance the computational load across the cooling process.

Eigenvalue structure of the predictor feedback for discrete-time LTI systems

The discrete-time predictor feedback system was designed to compensate for constant input delays based on d-step ahead state predictions in discrete-time linear time-invariant systems. The entire spectrum, initially investigated by numerical computation, shows that aside from the eigenvalues of A + BK, there are other eigenvalues located about the origin. Existing literature only focuses on the spectrum coinciding with that of A + BK, but, in this study, we extended previous results by considering the full state of the system to obtain the eigenvalues mathematically. In contrast to the continuous-time case, it is important to note that the discrete-time delay system is finite-dimensional. From this viewpoint, we started our analysis from the state space representation to construct a proof that derives the poles of the closed-loop system. Furthermore, as a preliminary step, we attempt a frequency domain analysis by considering nonzero initial conditions in taking the Z-transform of the system with an example.

Modified state predictive control of continuous-time systems with input delay

The state predictive control is one of the most effective methods to compensate the input delay of linear systems. In the continuous/discrete-time scenario, the corresponding closed-loop poles except for the eigenvalues of A + BF are arranged at −∞/the origin automatically. In the discrete-time setting, a modified state predictive control method has been proposed in which all closed-loop poles including the rest can be assigned arbitrarily. Since the deadbeat nature of the original control is altered, it might be effective in robustness. Motivated by this observation, in this paper, the continuous-time counterpart is derived. The robustness against the delay length mismatch is examined via numerical examples.

State Estimation of Thermal Systems with Multiple Operation Modes

The state estimation of thermal systems with multiple operation modes is considered. Based on a description as hybrid dynamical systems, we reduce it into an observer design problem for switched linear systems. In this design, a tradeoff between fast response and robustness must be taken into account in addition to a guarantee of stability as a switched system. For this purpose, we introduce LMIs with common Lyapunov function to place the closed-loop poles of the observer for each subsystem in the prescribed region in the complex plane. The effectiveness of proposed method is verified through numerical simulations with experimental data set.

Development of Pneumatic Myoelectric Hand with Simple Motion Selection

Of the 82 thousand upper-extremity amputees in our country, the majority use prosthetic hands. Recently, research and development of myoelectric hand have come to the forefront. However, due to the usage of multiple electric actuators, the myoelectric hand is heavy, structurally complicated and expensive. Thus, the authors propose a pneumatically-driven prosthetic hand with bellows incorporated in the joint. This grip force exceeds that of general pneumatically-driven prosthetic hands. Also it is lightweight of 240i¾?g, reducing user fatigue. The hands control performance showed quick response to the reference angle and pressure. Moreover, this prosthetic hand enables grasping, pinching, and typing by simple motion selection although it is not equipped with motion estimation.

Ideal operation model and experimental verification for non-pulsating flow tube pumps

Tube pumps which transfer fluid by squeezing the tube with rollers are used in various fields thanks to their cleanliness and convenience. However, periodical flow fluctuation occurs when the rollers leave the tube because the tube restoring force disrupts the flow speed. In this paper, we contend that the pump can theoretically achieve non-pulsating flow by assuming the rollers can move independently and operating them at a non-constant speed based on an ideal operation model we make. The effectiveness of this model is shown by simulation and experimental verifications using repetitive control theory.