As an alternative to bang-bang control, a time optimal control (TOC) algorithm for discrete-time systems was first reported by Han⁽¹⁾. This algorithm not only acts as a noise-tolerant tracking differentiator (TD) to avoid setpoint jumps in control processes, but also has wide applications in the design of controllers and observers. However, determination of the real-time state position on the phase plane involves complex boundary transformations, which renders this algorithm impractical for some engineering applications. This paper proposes a methodology for discrete-time optimal control (DTOC) of double integrators with disturbances. The closed-form solution with lower computational burden can be easily extended to general second-order systems. Further, in consideration of the inevitable disturbances in the systems, a rigorous and full-convergence proof is presented for the proposed algorithm. The results show finite-time and fast convergence as well as provide the ultimate stable attraction regions for the system states. Examples and experiments are also presented to demonstrate the effectiveness of the proposed algorithm for solving a signal processing problem in a maglev train.

Technology in a broad sense is driven by developments in semiconductor technology, particularly with respect to the computational power of devices and systems, as well as sensor technology. The progress of semiconductor technology has demonstrated an exponential curve since the middle of the previous century, representing Moore's Law. Consequently, it is of utmost importance to bridge the gaps between disciplines in the fields of control, automation, and robotics. Moreover, data-driven approaches need to be combined with model-based design. This will lead to new digital twinning and automated design approaches that provide major opportunities. Furthermore, this necessitates the redefinition of our university system.

This paper reports on our work conducted during 2020 in the development of actuation and sensing techniques and devices. In gait rehabilitation, active body weight support systems are often needed to guarantee the safety of patients. These support systems are required to operate at two distinct operation points: a high-force operating mode to hold a patient and prevent falls and, conversely, a “transparent mode” that reduces the mechanical impedance of high-force actuators to enable patients, even those who are weak or paralyzed, to easily express movement. However, the ability to deliver high forces and easily manipulate robots is a key challenge in improving the force-based interaction control. Force feedback is an effective approach to reduce the inertia and friction of robots, but stability is paramount particularly when interacting with humans. By modeling the environment as a second-order spring-mass-damper system and considering the phase response, we derived the control parameter gains required to guarantee a stable human-robot interaction. The design of actuators with intrinsically adjustable mechanical properties is a complementary strategy. For instance, the stiffness of actuators can be modulated by adjusting the unsupported length of a cantilever leaf spring. To model the spring stiffness under deflection, an ideal cantilever support model cannot be assumed for a conventional design of a slider with dual roller pairs, particularly with a soft spring. We proposed a beam deflection model considering the non-zero slopes at the contact points between the rollers and spring. The spring parameters were determined to attain the desired range of stiffness with a short traveling distance of the adjuster. For a single degree-of-freedom (DOF) linear motion, we investigated a macro-mini actuation concept using an electrorheological-fluid brake. Balancing these conflicting requirements between the driving force generated from the non-backdrivable high-force unit and the low-inertia and low-friction unit was achieved by controlling the electrical field affecting the fluid yield stress between the rotor and stator electrodes of the brake. One of the limitations of the feedback control scheme was noisy force sensors. We discuss our novel proximity and force sensor using optical techniques and conclude with a description of low-profile 3-DOF flat motor.

This paper proposes a constrained bilateral control method to maintain a safe force limit in a remote environment in an event where the operator applies excessive force on the master system. The disturbance observer compensates system disturbances, and the reaction force observer (RFOB) estimates the external force exerted on individual. The paper introduces a force regulator called excess force reduced RFOB (EFR RFOB) to reduce the excessive force applied by the operator to the safe force limit. The amount of excess force is determined by adding the master-side RFOB output and the replica-side safe force limit. Acceleration-based bilateral control is implemented in a virtual space with a master virtual force input, virtual position response, and replica real force-position responses. It realizes transparency in the virtual space. This paper derives the relation between master-side real and virtual space variables to facilitate reproducibility between the master operator and replica environment. The restrained master force-position responses in the virtual space realize precise and safe force control on the replica-side in real space. The proposed method is verified using experiments.

Torsion torque control (TTC) has been studied in applications ranging from industrial robots to electric vehicles. However, its performance is severely compromised when there is joint backlash, causing limit cycles and inducing unstable behavior. This study proposes a stable TTC scheme for two-inertia systems with joint backlash based on an analogy between static friction and backlash phenomena. First, a transformation of the joint torsion dynamics into a first-order system is applied, and a proportional torsion torque controller is proposed. Then, an analogy between the transformed joint torsion dynamics with backlash and one-mass systems with static friction is established. Based on this analogy, a combination of a switched disturbance observer and an impact torque suppression controller is proposed, ensuring rapid control over backlash and stable reengagement with reduced gear collision impact. The effectiveness of the proposed method is verified through simulation and experimental results.

A system that is able to measure motions is necessary for preserving the skills of experts. A previously reported study proposed a system that precisely measures and reproduces motions. However, this type of system must physically interact with the subject whose motions are measured. Such interaction can be troublesome when the measured motions require precise control of force or position or even a high degree of freedom. Therefore, this study proposes a novel method for sensing motions without interference and applies the approach to measure the skill of playing the violin. Using the data measured by the proposed system, the skills of an experienced violin player and a novice violin player are compared. This study attempts to visualize the differences between the two types of players by applying wavelet transform on the measured data and analyzing them in the frequency domain.

Manufacturing equipment often require high-speed and high-precision positioning with long strokes. This study aims to utilize pneumatic cylinders for such equipment owing to their several advantages. One of the challenges in pressure and position control is valve nonlinearity, such as a varying dead zone. While the conventional feedforward dead zone compensation method cannot address variations in valve input-output characteristics, the twin-drive system, a feedback compensation method, can address the variations using a fast-response flowmeter. However, the disadvantage of the twin-drive system is that it is likely to cause saturation and windup. To solve this problem, we propose an anti-windup method for the twin-drive system. Experimental results indicate the proposed method avoids windup and enables accurate tracking control in the difference mode (i.e., mass-flow input to the tank). Moreover, the experimental results reveal that the proposed twin-drive system with the anti-windup structure improves the pressure tracking performance and enhances the pressure control system's linearity compared with those of the conventional feedforward compensation method.

Conventional aircraft use mechanical air brakes to adjust their descent paths; however, the lift-drag ratio cannot be continuously controlled, which results in zigzag descent paths. Previous research has shown that the negative thrust produced by the windmilling propeller works as a substitute air brake called the regenerative air brake. This paper proposes a new pitch angle control method using the regenerative air brake. The proposed method includes thrust estimation, negative thrust control, airspeed estimation, and pitch angle control using the pitching-jerk-based disturbance observer. The effectiveness of the proposed method is verified via simulations and experiments in a wind tunnel.

Permanent magnet synchronous motors (PMSMs) have wide applicability owing to their many advantages. For efficient driving of PMSMs, a number of high-efficiency control methods have been developed. However, few studies have discussed the relationship between the tracking characteristics to the current command and driving loss. Here, we propose using the RPTC, which is a digital controller with high tracking performance, as the current controller for reducing the iron loss. The RPTC can suppress the periodic disturbances; therefore, the iron loss caused by the harmonic current in the input current is reduced. Simulations confirmed that the presence or absence of the harmonic current affects the iron loss reduction. Experiments also showed that RPTC reduced the extent of the iron loss in interior permanent magnet synchronous motors (IPMSMs).

This paper proposes a new vibration suppression control based on the coordinate transformation. In the new coordinate system, the vibration components of motor angle and velocity correspond to the horizontal and vertical axes, respectively. Owing to this, similar to the dq Transform in power electronics, the components draws a circle depending on the angle on the coordinate, and the vibration amplitude can be easily obtained. Thus, on this coordinate system, the components synchronized to the motor angle are expressed as a DC component. Hence, by introducing integral control, it is possible to completely suppress the vibration. High vibration suppression performance was confirmed by numerical simulations and experiments with an actual machine.

Disturbance observers are widely used in the industrial field to mitigate the influence of disturbance, and the trial-and-error method is commonly employed in their design. Herein, a fully parameterized bandwidth-maximized disturbance observer problem was formulated into a frequency response data-based convex optimization problem by transforming the original constraints into their convex form. Furthermore, a comparison with the trial-and-error method verified the feasibility of the proposed method.

This paper proposes a novel active power decoupling circuit that is integrated with an interleaved boost converter for isolated DC to single-phase AC conversion applications. The proposed isolated converter consists of two full-bridge inverters with a coupled inductor, a small buffer capacitor for active power decoupling, and a diode rectifier. Further, the proposed isolated converter is controlled for active power decoupling and DC to single-phase AC power conversion independently by the coupling inductor and common-mode operation of the interleaved boost converter, respectively. This paper presents the control method of the proposed converter and design criteria of the passive components. In addition, the performance of the proposed isolated converter is demonstrated by the experimental results in order to confirm the validity of the proposed method. As the experimental results, the second-order harmonic due to the double-line frequency power ripple is reduced by 84.5% owing to the active power decoupling capability. Finally, a maximum efficiency of 94.5% is obtained using the proposed converter.

A control structure for vibration suppression is proposed to improve positioning speed and accuracy. Acceleration feedback is well-known for suppressing residual vibrations and disturbances. In this study, our previously proposed load-side acceleration feedback (LSAFB) and machine stand acceleration feedback (MSAFB) controllers were simultaneously applied to a semi-closed servo system to use dual acceleration feedback for a positioning machine with rocking mode vibration and local resonance. The polarity of the LSAFB controller was negative, whereas that of the MSAFB controller was both positive and negative. Moreover, the MSAFB controller was updated for positioning machines with local resonance, and the LSAFB controller was modified to avoid interference with the MSAFB controller. The effectiveness of the proposed structure and its dual acceleration feedback were evaluated through root locus and frequency response analyses. This dual acceleration feedback was then evaluated through simulations and experiments.

This paper presents output power characteristic of a unidirectional Secondary-Resonant Single-Active-Bridge (SR-SAB) DC-DC converter with isolated high-frequency transformer. In the SR-SAB converter, the secondary H- bridge converter of the Dual-Active-Bridge (DAB) converter is replaced with the diode rectifier circuit, in which each diode has a resonant capacitor in parallel. The voltage and current waveforms of the SR-SAB converter in the rated condition are similar to those of the DAB converter. The authors propose the output power control of the SR-SAB converter that changes the pulse width of the primary voltage. The effectiveness of the proposed output power control is verified by experiments.

Many techniques have been proposed as power supply methods for high-side gate drivers. However, most techniques that do not depend on the topology of the main circuit have drawbacks related to the size and cost. This paper proposes a novel floating power supply based on capacitive isolation. The proposed circuit is designed to operate independently of the main circuit, and it is cheaper and smaller than conventional circuits. The proposed method is applied to a diode-clamped multilevel topology and is validated by experiments.

Permanent magnet synchronous motors (PMSMs) are widely used in various applications as high-power-density and highly efficient drive sources. However, a PMSM generates electromagnetic vibration because of the space and time harmonics. In this paper, we propose a synchronous PWM control method for shifting the carrier wave phase against the modulated wave. As the proposed control matches the ripple frequencies caused by the spatial and time harmonics, the ripple caused by the space harmonics is canceled by that caused by the time harmonics, with the phase shift of the carrier wave. The phase shift of the carrier wave is confirmed experimentally. In addition, it is experimentally verified that the vibration of the proposed method at a specific frequency is reduced by 46%@7,900r/min and 53%@19,500r/min.