This paper firstly proposes a kind of virtual reference feedback tuning (VRFT) method with a performance index which is obtained by modifying that of the standard VRFT. Then, analysis results on optimality conditions for the modified VRFT method are presented. Next, a VRFT method under hysteresis compensation is proposed, in which the modified VRFT method and the hysteresis compensation technique proposed in the previous work are combined. The proposed VRFT method with hysteresis compensation is applied to an experimental shape memory alloy actuator system, and its effectiveness is verified.
This paper presents a high-speed CMOS operational amplifier (OP Amp) with a dynamic switching bias circuit, capable of processing video signals of over 2 MHz with decreased dissipated power. The OP Amp was designed to operate at a 10 MHz dynamic switching rate, and was shown in simulations to have a dissipated power of 66 % of conventional continuous operation. This OP Amp was applied to a switched capacitor (SC) non-inverting amplifier with a gain of 2, and its high-speed 10 MHz dynamic switching operation, capable of processing video signals, was demonstrated. By increasing the switching duty ratio to 70 %, its power dissipation decreased to 56 % of normal operation. Some inaccuracy in the SC amplifier performance resulted mainly from the limited open loop gain of the OP Amp. This circuit configuration should be extremely useful in realizing low-power wide-band signal processing ICs.
The Hyper H∞ Filter is an adaptive filtering algorithm, where a forgetting factor ρ is built into the H∞ optimization framework as a function of the robustness parameter γf and determined through the process of γ-iteration. This paper examines how the choice of γf affects the resultant steady-state mean-square error of this algorithm. For moderately large γf, a theoretical expression of the excess mean-square error is derived, which turns out to coincide with that of RLS. Based on this expression and numerical simulations, it is shown that there is a trade-off between the robustness and the mean-square performance at steady-state. For balancing this trade-off, preferable values of γf are also considered.
This paper proposes the use of the inverse linear quadratic (ILQ) regulator design method for the efficient tuning of the performance index in nonlinear model predictive control (NMPC). First, a linear quadratic regulator is designed for the linearized model using the ILQ regulator design approach and then the inverse optimality conditions are applied to the designed regulator to tune the quadratic weights in the performance index of NMPC. After that, the NMPC algorithm is applied to the nonlinear model. This approach provides some tuning parameters that give a trade-off between the speed of the system's response and the magnitude of the control input. Moreover, this tuning methodology provides a free parameter that can be utilized to adjust the transient response as well as to obtain a balance between the magnitudes of the control inputs.
The transition time of a hopping machine (HM) as a piecewise linear (PWL) system is estimated by using a wavelet analysis method proposed in previous papers. The HM is a nonlinear system because its equation of motion has a nonlinear drag coefficient term owing to air resistance. The effectiveness of the proposed method for real (nonlinear) systems is verified through instrumental experiments performed on the HM. First, the effect of nonlinearity on the estimation of a transition time is examined. The HM has a discrete transition caused by the nonlinearity in a real system. In addition, two types of discrete transitions are detected from the output data: one caused by the change between discrete free-fall and spring-mass states and the other caused by inversion of the sign of the nonlinear term owing to a change in the velocity of the mass. These transition times are estimated using the proposed method. Finally, the proposed method is compared with a conventional method based on a clustering technique.
Instead of conventional signaling systems (fixed-block signaling systems), moving-block signaling systems are in use to increase transport capacity by reducing headways on railway lines. A moving-block is considered as the sum of the length of the train and the safe following distance between trains. Communication Based Train Control (CBTC) systems and European Rail Traffic Management System (ERTMS) application level 3 are examples of moving-block signaling systems. In this study, speed control of two consecutive trains as moving-block is realized in two levels: the modeling level and the control level. To cope with both discrete and continuous behavior of the moving-block signaling system, a Generalized Batches Petri Net (GBPN) approach is used for modeling the system whereas a fuzzy logic control method is proposed at the control level. Simulation results are shown in order to demonstrate the accuracy of the proposed approach.
The present paper proposes an efficient design method for a multiple-input multiple-output (MIMO) integral preceded by a proportional and derivative (I-PD) controller, which is a type of PID controller. In the proposed method, a given plant model is first reduced to a lower-order model using fractional balanced reduction, and an integral-type or robust optimal servomechanism is then designed for the reduced plant, which is expressed in a peculiar state-space form, where the state vector is composed of outputs, their derivatives, and control inputs. The resultant optimal feedback control law is immediately transformed into a MIMO I-PD control law. The optimal servomechanism, which is based on a linear quadratic regulator, provides a controller with desirable control performance, adequate stability margins, and easy trade-off between the control performance and stability margins attained through weight selection of the quadratic cost function. Although these features are not perfectly guaranteed in the resulting control system due to the model reduction, if the properties are adequately preserved, they make the controller design very simple and efficient. A design example illustrates the effectiveness of the proposed design method as well as its limitations.
Electric-powered wheelchairs have been used as a convenient transport device for the elderly and disabled. The riding capability of a wheelchair is one of the most important functionality for wheelchair users. Therefore, the authors developed a new front-drive-type electric wheelchair “STAVi” to achieve a comfortable ride for wheelchair users. It is easy for a disabled person to climb into this wheelchair from a bed because they can do so by piggybacking from a bed or chair. Moreover, the base plane of STAVi is very low compared with traditional rear-drive-type wheelchairs because the motors and all electric devices are placed in the front. Such functions are very useful not only for the disabled but also for care personnel, because the riding task is very difficult with rear-drive-type wheelchairs. However, front-drive-type wheelchairs are hard to run straight and difficult to operate because their sensitivity to disturbances is higher than that of rear-drive-type wheelchairs. In particular, the dynamics on a slope are complex to allow for easy driving because the gravitational force acts as a disturbance. This paper analyzes the dynamics of front-drive-type wheelchairs and propose a wheelchair control method that compensates for the difference between the dynamics of the actual wheelchair and that of a desired wheelchair model by using yaw rate and velocity feedback. It is expected that the user can easily operate STAVi on a slope easily via appropriate compensation. The effectiveness of the proposed method is confirmed by driving simulations and experiments.