Research achievements about control theory and control method

Journal Paper about Control (Eng)

[23] Hiroshi Okajima, Kenta Arinaga and Atsuo Hayashida, Design of observer-based feedback controller for multi-rate systems with various sampling periods using cyclic reformulation, IEEE ACCESS (2023) (Open Access)

Outline: Signal sensing periods typically vary depending on the sensor used and may differ even within a single control system that involves multiple sensors. Likewise, input periods can vary based on the actuator used. This paper discusses the design of observer-based feedback controllers for linear, time-invariant, discrete-time systems operating in a multi-rate sensing and actuating environment. The observation and control periods of the sensors and actuators in the plant are assumed to have mutually rational ratios. First, we reduce the multi-rate system to a periodically time-varying system and provide a linear matrix inequality (LMI) condition for analyzing the l 2 performance using cyclic reformulation, which is a type of time-invariant reformulation for periodic systems. Next, we extend the analysis method to design an observer-based feedback controller for the multi-rate system. This allows us to obtain multi-rate observer gains and feedback gains based on the l 2 -induced norm from disturbances to outputs. Finally, we present numerical results to demonstrate the effectiveness of the observer-based feedback system in the multi-rate environment.

[22] Nobutomo Matsunaga, Kazuhi Murata, Robust cooperative transport system with Model Error Compensator using multi-robots which has suction-cups, Journal of Robotics and Mechatronics, Vol. 35, No. 6, pp. 1583-1592 (2023)

Outline:In cooperative transport systems, multiple robots work together to transport objects that are difficult to transport with a single robot. In recent years, multi-robot systems that cooperate to transport objects have been researched. However, during the transfer of objects, misalignment occurs between the ideal and actual grasp positions. In an automatic transport system, a grasping error can cause an error in the trajectory of the object, significantly reducing the transport efficiency. In this paper, a control system that allows robust cooperative transport control using a model error compensator is proposed for a leader–follower system in which the transported object is the virtual leader and the followers are ideally arranged. This system adds robustness to the operation of a conventional cooperative transport system by using the ideal formation of robots. The effectiveness of the proposed method was evaluated through cooperative transport experiments using two ideal formations for passing through a narrow entrance. The cooperative transport system could not pass through the narrow entrance using the conventional method; however, the system using the compensator passed through the narrow entrance smoothly.

[21] Nobutomo Matsunaga, Ikuo Yamamoto, Hiroshi Okajima, Navigation System for Personal Mobility Vehicles Following a Cluster of Pedestrians in a Corridor Using Median of Candidate Vectors Observer, Journal of Robotics and Mechatronics, Vol. 35, No. 6, pp. 1562-1572 (2023)

Outline: In recent years, personal mobility vehicles have been required to operate autonomously in places with numerous pedestrians. A navigation method using a single human-following scheme is used to avoid collision with pedestrians. However, in many cases, a single human-following method cannot be successfully used for guidance. In crowded places, pedestrians do not always keep walking in the desired direction a user wants to go, and the vehicle must change the target pedestrian frequently. Instead of following a single pedestrian, we propose a method for the vehicle to follow a cluster of pedestrians for stable and robust following. First, the pedestrians around the vehicle are detected by multiple RGB-D cameras, and the pedestrians are tracked using YOLO and Deep Sort. Pedestrians are classified according to their walking direction, and the cluster of pedestrians walking toward the goal is selected and followed. However, the position of pedestrian is sometimes lost in occlusions and the accuracy of the walking direction depends on the distance and pose detected by the sensors. A notable problem is that the cluster of pedestrians is unstable in the cluster following; therefore, a median of candidate vectors (MCV) observer is used to remove outliers caused by observation errors. The proposed method is applied to a scenario involving pedestrians walking toward an elevator hall in a building, and its effectiveness is verified through experiments.

[20] Hiroshi Okajima, Yohei Hosoe and Tomomichi Hagiwara, State Observer under Multi-rate Sensing Environment and Its Design using l2 -Induced Norm, IEEE ACCESS (2023) MATLAB code

Outline: The duration of a signal's sensing period typically relies on the sensor being used, and can vary even within a single control system that uses multiple sensors. This paper explores the design challenge of creating state observers for linear, time-invariant, discrete-time systems in a multi-rate sensing environment. We assume that the sensing periods of the plant's sensors have mutually rational ratios. First, we describe a state observer for a system with multi-rate sensing as a periodically time-varying state observer. Next, we examine the l2 performance analysis of state estimation errors using the given periodically changing state observer. A linear matrix inequality (LMI) condition is provided for this analysis. By expanding the LMI condition for analysis, we also offer a condition for multi-rate observer synthesis. We then demonstrate the effectiveness of our proposed multi-rate state observer through numerical examples. Notably, even when all sensors share the same period, sensing timing is not unique. As a result, we numerically investigate whether performance varies when the observation timing differs among multiple sensors.

[19] Nobutomo Matsunaga, Masaki Kuwahara, Hiroshi Okajima and Gou Koutaki, Analysis of Measuring Precision of 3D Model of Ishigaki Stone in Kumamoto Castle Using Automatic CMG Crane System, JRM, Vol.34 No.3 pp. 622-630 doi: 10.20965/jrm.2022.p0622 (2022)

Outline: Kumamoto Castle, which features stone walls known as ''Ishigaki'', suffered significant damage during the 2016 Kumamoto earthquake. Due to the castle's cultural importance in Japan, it is essential to promptly and accurately restore the damaged stone walls. Recently, researchers have been studying the use of 3D stone data to precisely determine the positions of collapsed stones. For efficient stone wall restoration, it is crucial to measure the 3D stone data automatically and quickly. A small control moment gyro (CMG) device was proposed to control the stone's attitude, and a robust controller with a model error compensator was applied to the CMG device. This study analyzed the measurement precision of a 3D stone model using the CMG crane system. The automatic measuring system comprises a CMG device and an elevator for a 3D scanner, which helps reduce the workload on workers. The scanning motion was planned automatically based on the shape and position of stones using depth sensors. The effectiveness of the proposed measuring system was evaluated based on the accuracy and measurement time, including the data correction time for 3D modeling.

[18] Ryuichiro Yoshida, Hiroshi Okajima and Takumi Sato, Model error compensator design for continuous- and discrete-time non-minimum phase systems with polytopic-type uncertainties, SICE Journal of Control, Measurement, and System Integration, Volume 15 Issue 2 pags 141-153 (2022) (T&F, Open Access) MECpage

Outline: This paper introduces a design for a model error compensator combined with a parallel feedforward compensator for continuous- and discrete-time non-minimum phase multiple input multiple output (MIMO) plants. The model error compensator can readily enhance robustness in various control systems. By adding the compensator to the actual plant, the plant's output trajectory can closely follow that of the control system with the intended nominal model. Our previous research proposed a model error compensator design using particle swarm optimization and linear matrix inequalities based on the common Lyapunov function, addressing polytopic-type uncertainties in plants. However, designing the appropriate gain for the model error compensator becomes challenging when dealing with non-minimum phase MIMO systems. In this study, we attach a parallel feedforward compensator to the model error compensator to achieve minimum phase characteristics. With some assumptions, an evaluation system incorporating a parallel feedforward compensator can be derived as a system with polytopic uncertainties. This approach simplifies the gain design of the model error compensator, ensuring robust performance. We demonstrate the effectiveness of our proposed design through numerical examples.

[17] Hiroshi Okajima, Yasuaki Kaneda and Nobutomo Matsunaga, State estimation method using median of multiple candidates for observation signals including outliers, SICE Journal of Control, Measurement, and System Integration, Volume 14 Issue 1 pags 257-267 (2021) (T&F, Open Access) SupportPage

Outline: This paper addresses the state estimation problem for systems with observation outputs that include outliers. The presence of outliers in observation outputs can significantly reduce the accuracy of state estimation. To tackle this issue, we propose a novel observer structure that employs multiple estimated state candidates. First, we generate multiple estimated state candidates, each using the sensing output value from a different detection timing. If outliers are rare, removing candidates affected by outliers helps maintain estimation accuracy. Our proposed observer then selects one estimated state candidate from the group using either a median or weighted median operation. This process ensures that the selected estimated state does not rely on outlier values. Furthermore, we present a method for designing observer gains for these estimated state candidates based on the reachable set of the estimated state error, using Lyapunov-based inequalities. The effectiveness of our proposed observer is demonstrated through numerical examples.

[16] R. Yoshida, Y. Tanigawa, H. Okajima, and N. Matsunaga, A Design Method of Model Error Compensator for Systems with Polytopic-type Uncertainty and Disturbances, SICE Journal of Control, Measurement, and System Integration, Volume 14 Issue 2 Pages 119-127 (2021) (T&F, Open Access) MECpage

Outline: Control systems can achieve desired performance using a model-based controller if the actual plant's dynamic model is provided with sufficient accuracy. However, if there is a difference between the actual plant and its model dynamics, the model-based controller may not work well and may fail to achieve the intended desired performance. In our previous study, we have proposed a model error compensator (MEC) to overcome model errors and disturbances. By attaching the compensator for model errors to the actual plant, the output trajectory of the actual plant is made to closely resemble that of its model. As a result, the apparent difference in dynamics from the controller's perspective is minimized, and performance degradation is significantly reduced. MEC is useful for various control systems, such as nonlinear systems and control systems with delay, among others. In this paper, we propose an original design method for filter parameters in MEC for systems with polytopic-type uncertainties. First, we present an analysis method for the robust performance of MEC in systems with polytopic-type uncertainties based on a linear matrix inequality problem. The gain parameters in MEC are designed using particle swarm optimization and the presented analysis method. The effectiveness of the design method for systems with polytopic-type uncertainty and disturbances is evaluated using numerical examples.

[15] H. Okajima, K. Fujinami, Estimation of Robust Invariant Set for Switched Linear Systems using Recursive State Updating and Robust Invariant Ellipsoid, SICE Journal of Control, Measurement, and System Integration, Volume 14 Issue 1 Pages 97-106 (2021) (T&F, Open Access) YouTube, SupportPage

Outline: This paper presents an analysis method for robust invariant sets in discrete-time linear switched systems with peak-bounded disturbances. Analyzing the robust invariant set in switched linear systems is more challenging than in linear time-invariant systems. We introduce a novel approach to estimate a robust invariant set by combining recursive state updating and an invariant ellipsoid for a common Lyapunov function. The accuracy and effectiveness of our proposed method are demonstrated through numerical examples.

[14] H. Okajima, Y. Nakabayashi and N. Matsunaga, Signal-Limitation Filters to Simultaneously Satisfy Constraints of Velocity and Acceleration Signals, SICE Journal of Control, Measurement, and System Integration, Volume 13 Issue 1 Pages 1-8 (2020) (T&F, Open Access) MECpage

Outline: In this paper, we introduce a novel filter structure designed to ensure that output signals adhere to velocity and acceleration constraints for any given input signals. In the field of factory automation, step signals are occasionally transformed into trapezoidal waves to comply with specified velocity limitations, helping operators avoid overloading industrial robots. By constraining the characteristics of input signals in actual plants, equipment protection, safety, and the ride quality can be maintained. We propose a signal-limitation filter that adjusts input signals to meet the desired signal constraints. In previous research, a signal-limitation filter structure was presented as a simple unit-feedback control incorporating a saturation function. However, this filter structure caused a delay between input and output signals, as designing gains for both saturating and non-saturating cases proved challenging. To address this issue, we propose an innovative filter structure that combines feedforward and feedback components. This structure, which includes saturation within the feedforward terms, allows for the fulfillment of desired limitations for any input signals. We assessed the effectiveness of our proposed filter structure in a signal-limitation filter designed to simultaneously limit velocity and acceleration. Simulation results demonstrate the efficacy of the introduced filter.

[13] H. Okajima, Y. Minami and N. Matsunaga：A Control Structure for Unilateral System with Communication Rate Constraint, SICE Journal of Control, Measurement, and System Integration, Vol. 11, No. 6, pp. 510-516（2018） (T&F, Open Access) QUANTIZERpage

Outline: In this study, we present a design method for unilateral control systems subject to communication rate constraints. When controlling systems under such constraints, it is crucial to minimize the impact of quantization noise using efficient signal quantization techniques. A feedback-type dynamic quantizer is one such effective method. In our previous work, we proposed a design approach for dynamic quantizers that adhered to communication rate constraints. In this paper, we introduce a unilateral control structure aimed at minimizing the effects of quantization errors. The design method for the dynamic quantizer is applied to this proposed structure. We evaluate the effectiveness of the resulting system, featuring the designed quantizer, through a series of numerical examples.

[12] G. Ichimasa, H. Okajima, K. Okumura and N. Matsunaga：Model Error Compensator with Parallel Feed-Forward Filter, SICE Journal of Control, Measurement, and System Integration, Vol.10, No.5, pp.468-475 (2017) (T&F, Open Access) MECpage

Outline: Control system design methods based on plant models have been extensively developed over the years. When a mathematical model accurately captures the input-output relationship of a plant, the designed controller performs effectively in the control system connected to that plant. However, if a significant modeling error exists, the desired control performance may not be achieved. To address this issue, the authors introduced the model error compensator (MEC), designed to minimize the impact of modeling errors between the plant and the model. The MEC has proven successful in various control systems, including unstable and non-linear systems. Nonetheless, applying the MEC to non-minimum-phase plants remains challenging due to their control system structures. Non-minimum-phase plants are notoriously difficult to control. In this paper, we propose a MEC incorporating a parallel feed-forward filter (PFF) to overcome these challenges. The PFF is employed to counteract the non-minimum-phase characteristics of the plant. The effectiveness of the proposed method is demonstrated through numerical examples.

[11] H. Okajima, K. Sawada and N. Matsunaga：Dynamic Quantizer Design Under Communication Rate Constraints, IEEE Transactions on Automatic Control, Vol.61, No.10, pp.3190-3196 (2016) SupportPage

Outline: Feedback-type dynamic quantizers, such as delta-sigma modulators, are often effective for converting high-resolution data into lower-resolution data. These dynamic quantizers consist of a filter and a static quantizer. When controlling under a communication rate constraint, the data rate of the quantizer output should be minimized appropriately through quantization. This technical note presents numerical methods for the comprehensive design of a type of dynamic quantizer, including the selection of all quantizer parameters to minimize a specific performance index while satisfying a communication constraint. We propose a design method for the dynamic quantizer using a particle swarm optimization (PSO) approach. Some initial quantizers in PSO are designed based on an invariant set analysis and an iteration algorithm. The effectiveness of the system employing the proposed quantizer is demonstrated through numerical examples.

[10] G. Koutaki, H. Okajima, N. Matsunaga and K. Uchimura：Color quantization and optimization of luminance for digital mirror device–based projector, IEEE transactions on Consumer Electronics, Vol.62, No.2, pp.103-110 (2016) QUANTIZERpage

Outline: Digital mirror device (DMD)-based projectors are commonly used in consumer electronics. DMDs can toggle between ON and OFF states, reflecting light to project binary images onto a screen. In addtion, full-color images can be displayed by rapidly switching among 24 binary images. To increase the frame rate, DMD switching must be accelerated; however, mechanical constraints limit the switching time. One solution involves reducing the number of binary images needed to represent a full-color image. This paper presents a framework for optimizing color quantization and light-emitting diode (LED) luminance. We evaluated the developed system using a projector and a complementary metal-oxide-semiconductor (CMOS) camera. Experimental results demonstrated that the proposed method enhances the total luminance of projected images by approximately 122% compared to earlier models while maintaining superior image quality.

[9] H. Okajima and T. Asai：Tracking Performance Limitation for 1-DOF Control Systems Using a Set of Attainable Outputs, SICE Journal of Control, Measurement, and System Integration Vol.8, No.5, pp.348-353 (2015) (T&F, Open Access)

Outline: This paper addresses an analytical solution to performance limitations in tracking control problems. The authors have previously provided explicit tracking performance limitations for two-degree-of-freedom systems concerning a class of reference signals, offering a uniform description of these signals. In this study, we extend these results to one-degree-of-freedom systems. For unstable plants, the tracking performance of one-degree-of-freedom systems has not been analyzed except in the context of step references. Our analysis results distinctly isolate the contributions of plant and reference characteristics. Optimal performances are demonstrated through a numerical example using a sinusoidal reference.

[8] H. Okajima, M. Honda, R. Yoshino and N. Matsunaga：A Design Method of Delta-Sigma Data Conversion System with Pre-Filter, SICE Journal of Control, Measurement, and System Integration Vol.8, No.2, pp.154-160 (2015) (T&F, Open Access) QUANTIZERpage

Outline: Analog-to-digital and digital-to-analog (AD/DA) conversion has become critical technology in digital signal processing. Signal compression plays a significant role in AD/DA conversion systems. The delta-sigma modulator (DSM) is a well-known and effective method for encoding analog signals into digital signals. Traditional data conversion systems consist of a post-filter and a DSM, requiring careful design to ensure minimal quantization noise and signal distortion. In this study, the authors propose a novel data conversion system design method that incorporates a pre-filter in addition to the traditional components. To simplify the design process, we introduce an evaluation framework for the data conversion system. Based on this framework, we develop a design algorithm using the particle swarm optimization algorithm. The post and pre-filters are designed to minimize the effects of noise and signal distortion caused by quantization. We evaluate the AD/DA systems with post and pre-filters using a voice signal compression system. The effectiveness of the proposed design method is demonstrated through numerical simulations.

[7] A. T. Zengin, Y. Maruno, H. Okajima, N. Matsunaga：Maneuverability Improvement of Front-Drive-Type Electric Wheelchair STAVi, SICE Journal of Control, Measurement, and System Integration, Vol.6, No.6, pp.419-426 (2013) (T&F, Open Access)

Outline: Electric-powered wheelchairs serve as convenient transportation devices for the elderly and disabled, with riding capability being a crucial feature for users. To enhance user comfort, we developed the front-drive-type electric wheelchair "STAVi." This wheelchair allows easy boarding from a bed or chair, offering convenience to both disabled users and care personnel. Furthermore, STAVi's base plane is lower compared to traditional rear-drive-type wheelchairs, as the motors and electrical components are positioned at the front. However, front-drive-type wheelchairs are more sensitive to disturbances, making it difficult to run straight and maneuver. The dynamics on a slope are particularly complex, as a gravitational force acts as a disturbance. This paper analyzes the dynamics of front-drive-type wheelchairs and proposes a control method that compensates for the differences between the actual wheelchair's dynamics and those of a desired wheelchair model, using yaw rate and velocity feedback. With appropriate compensation, it is expected that users can easily operate STAVi on slopes. The effectiveness of the proposed method is confirmed through driving simulations and experiments.

[6] H. Okajima, H. Umei, N. Matsunaga and T. Asai：A Design Method of Compensator to Minimize Model Error, SICE Journal of Control, Measurement, and System Integration, Vol.6, No.4, pp.267-275 (2013) (T&F, Open Access) MECpage

Outline: Robust control design methods have been widely studied in recent decades. A control system performs well under modeling errors and disturbances when the controller design is based on robust control methods. However, it is well known that control systems typically face a trade-off between control performance and robustness. To address this trade-off problem, an internal model-type compensator structure that minimizes the modeling gap between the nominal model and actual plant dynamics is proposed. By employing the proposed compensator, the dynamics of the compensated system closely match those of the nominal model. Additionally, we introduce a design method for compensator parameters aimed at minimizing a set of plant dynamics. The proposed design method can be reduced to the standard µ design control problem. Using the proposed compensator for control systems instead of the plant itself may lead to improved output performance despite plant uncertainty. As the proposed compensator can be used for controlling not only linear but also nonlinear plants, it allows for the easy achievement of robust control in nonlinear systems. The effectiveness of our proposed method is demonstrated through numerical examples.

[5] H. Okajima and T. Asai：Performance Limitation of Tracking Control Problem for a Class of References, IEEE Transactions on Automatic Control, Vol.56, No.11, pp.2723-2727 (2011) SupportPage PDF

Outline: This technical note focuses on the analysis of fundamental limitations in tracking control problems for single-input single-output (SISO) systems. Existing results analyze these limitations based on specific assumptions of reference signals, such as step, trigonometric signals, and others. In contrast, we define a class of reference signals in a more abstract but general way. For this general class of reference inputs, we provide an analytical solution for tracking performance limitations based on the achievable set of outputs, which are characterized by transfer functions. The analysis results clearly separate the contributions of the plant and the reference signal.

[4] N. Matsunaga, A. T. Zengin, H. Okajima, and S. Kawaji：Emulation of Fast and Slow Pains using Multi-layered Sensor modeled the Layered Structure of Human Skin, Journal of Robotics and mechatronics, Vol.23, No.1, pp.239-247 (2011)

Outline: In human and robot coexistence, human sensory and emotional feelings are aroused in the case of interaction. This causes such an unpleasant feeling called pain. It’s an important feeling in avoiding danger. For more safe interactions between humans and robots, it becomes important for robots to sense pain. To emulate fast and slow pain, we use a pain emulation system consisting of a pain model and a multilayer sensor. After an overview of the superficial pain model, we discuss a multilayer sensor we developed to model the laminated human skin structure. We measure sensor response and emulate fast and slow pain using our proposed system in experiments. Results confirmed that the proposed system responds similarly to both fast and slow pain in the subjects tested.

[3] C. L. Ooi, T. Asai and H. Okajima：Extension of Reference Signals in Iterative Learning Control for Non-Minimum Phase Systems, SICE Journal of Control Measurement and System Integration, Vol.4, No.1, pp.50-54 (2011) (T&F, Open Access)

Outline: This paper proposes to extend given reference signals in the iterative learning control context so that the resultant signals have the same right half-plane zero structure as the given plants. This extension enables preventing control inputs from exponentially increasing. The extending signals can be synthesized by solving a linear equation. The effectiveness of the proposed method is examined by a numerical example.

[2] H. Okajima, N. Matsunaga and S. Kawaji：Design of Dynamic Quantizers for 2-DOF IMC and Its Application to the Temperature Control of a Heat Plate, SICE Journal of Control Measurement and System Integration, Vol.4, No.1, pp.77-82 (2011) (T&F, Open Access)

Outline: Plants with dead time are known to be difficult to control using traditional control methods. Some controllers with dead time, such as Internal Model Control (IMC) and the Smith method, have been proposed for systems with dead time. However, these controllers introduce another challenge, as it is difficult to realize the dead-time component in the controller due to the memory limitations of micro control units (MCUs). When dealing with plants with large dead time, the sampling time must be increased to maintain sufficient data size. Consequently, there is a trade-off between the sampling time and the maximum quantization error imposed by the memory limit. In this paper, we propose a design method for dynamic quantizers to achieve small quantization errors for control systems in MCUs. The effectiveness of the proposed method is demonstrated through numerical examples. Furthermore, the proposed method is applied to the temperature control of a heat plate. As the input-output relation of the temperature control system can be described with dead time, a 2-DOF IMC is introduced for this system. We verify that the output with the proposed quantizer closely approximates the desired output under the memory constraint.

[1] T. Asai, H. Okajima and C. L. Ooi：Pole Constraints of Reference Models in 2-DOF Servo System Design for Non-Minimum Phase Systems, SICE Journal of Control Measurement and System Integration, Vol.1, No.6, pp.429-434 (2008) (T&F, Open Access)

Outline: This paper is concerned with the analysis of pole constraints in servo system design for non-minimum phase (NMP) systems. We first characterize the achievable closed-loop system for a SISO plant. For simplicity, we assume that the plant has only one NMP zero. Based on the characterization and the tracking condition, we show for some combinations of degree and relative degree of the closed-loop system that the admissible location of poles is restricted. For these cases, we provide a quantitative measure for the limitation. We also provide a concrete formula for some specific cases.

International conference paper about control

[65] H. Okajima, Model Error Compensator for adding Robustness toward Existing Control, Preprints of the IFAC World Congress, pp. 3998 - 4005 (2023)

[64]I. Yamamoto, K. Nakamura, N. Matsunaga and H. Okajima: Crowd Tracking of Electric Wheelchair using RGB-D Camera with Median of Candidate Vectors Observer, Proceedings of the SICE Annual Conference 2021 (2021)

[63]K. Fujinami and H. Okajima: Less-Conservative Reachable Set Estimation using Feedforward State Updating and Robust Invariant Set, Proceedings of the SICE Annual Conference 2020 pp. 1156-1158 (2020)

[62]Y. Take, S. Tokunaga, H. Okajima and N. Matsunaga: A Proposal of Collation Method Using Nonlinear SVM for Restoration of Stone Wall in Kumamoto Castle, Proceedings of the SICE Annual Conference 2020, pp. 888-893 (2020)

[61]R. Yoshida, Y. Tanigawa, H. Okajima and N. Matsunaga: A Design Method of Model Error Compensator using Meta-Heuristics and LMIs, Proceedings of the SICE Annual Conference 2020 pp. 1150-1155 (2020) MECpage

[60]Y. Takeuchi, N. Matsunaga and H. Okajima: Driving Instruction and Training of Welfare Vehicle controlled by Virtual Platoon Scheme using Sharing System of AR, 19th International Conference on Control, Automation and Systems, 1438-1443 (2019)

[59]T. Honda, N. Matsunaga and H. Okajima: Hybrid Steering Model depending on Driver's Gazing Point to detect inattentive driving using Machine Learning, 19th International Conference on Control, Automation and Systems, 1344-1349 (2019)

[58]K. Tanaka, S. Fukumoto, N. Matsunaga and H. Okajima:Obstacle Avoidance of Welfare Vehicle with Head Mounted Display using Spatial Mapping of Driving Environment, 19th International Conference on Control, Automation and Systems, 1222-1227 (2019)

[57] Shizuku Kai, Minori Watanabe and Hiroshi Okajima, Dynamics modeling of necessary quantity of relief supplies in large-scale disasters, Proceedings of the SICE Annual Conference 2019, pp.1044-1049 (2019)Finalist of the young author award

[56] Yusuke Take, Hiroshi Okajima, Nobutomo Matsunaga and Gou Koutaki, Restoration of Stone Wall “ISHIGAKI” Using Dropposition Information, Proceedings of the SICE Annual Conference 2019, pp.976-981 (2019)

[55] Hiroshi Okajima, Yohei Hosoe, Tomomichi Hagiwara and Yuki Minami, Basic Idea of Periodically Time-Varying Dynamic Quantizer in Networked Control Systems, Proceedings of the SICE Annual Conference 2019, pp.883-889 (2019)Finalist of the poster presentation award QUANTIZERpage

[54] Hiroshi Okajima, Yasuaki Kaneda and Nobutomo Matsunaga, State Estimation By Observer Using Median Operation for Observed Output with Outliers, Proceedings of the SICE Annual Conference 2019, pp.877-882 (2019)Finalist of the poster presentation award

[53] Nobutomo Matsunaga, Naufal Bayu Fauzan, Hiroshi Okajima and Gou Koutaki, Archive Method of Stone Wall in Kumamoto Castle Lifted by Small CMG Crane using Model Error Compensator, 2019 12th Asian Control Conference , 18849231 (2019)

[52] Nobutomo Matsunaga, Yudai Takeuchi and Hiroshi Okajima, Driver’s Gaze-point Analysis of Virtual Platoon Driving for Welfare Vehicle using Direct Eye Measurement Device with HMD, 2019 12th Asian Control Conference, 18834072 (2019)

[51] Shoichi Sakamoto, Nobutomo Matsunaga and Hiroshi Okajima, Hybrid Steering Model Estimated by Particle Swarm optimization Based on Driver’s Eye Tracking Information, 2018 18th International Conference on Control, Automation and Systems, Paper No.P00160 (2018)

[50] Yuta Nakabayashi, Hiroshi Okajima, Nobutomo Matsunaga, Inter-Vehicle Distance Stabilization in Adaptive Cruise Control Using Signal Limitation Filter, Proceeding of 2018 IEEE International Conference on Systems, Man, and Cybernetics, pp.1985-1990 (2018) MECpage

[49] Nobutomo Matsunaga, Ryota Kimura, Haruya Ishiguro, Hiroshi Okajima, Driving Assistance of Welfare Vehicle with Virtual Platoon Control Method which has Collision Avoidance Function Using Mixed Reality, Proceeding of 2018 IEEE International Conference on Systems, Man, and Cybernetics, pp.1911-1916 (2018)

[48] Shizuku Kai, Hiroshi Okajima, Time series modeling of evacuees for evacuation centers in large-scale disasters, Proceedings of the SICE Annual Conference 2018, pp.1148-1151 (2018)

[47] Yuki Tamura, Hiroshi Okajima, Nobutomo Matsunaga, Yasuaki Kaneda, Construction of new robust state estimation observer for packet loss environment, Proceedings of the SICE Annual Conference 2018, pp.1166-1168 (2018)

[46] Yuki Saigo, Hiroshi Okajima, Nobutomo Matsunaga, Design of networked control for multiple inputs and outputs feedback control system, Proceedings of the SICE Annual Conference 2018, pp.1423-1428 (2018) QUANTIZERpage

[45] S. Kimura, N. Matsunaga, H. Okajima and G. Koutaki：Design of virtual platoon control system using augmented reality to assist welfare vehicle users, Proceedings of ICCAS 2017 (2017) Outstanding Paper Award

[44] S. Sakamoto, T. Tanaka, H. Okajima and N. Matsunaga：Maneuverability evaluation of skid steer welfare vehicle for robust assistance control with model error compensator, Proceedings of ICCAS 2017 (2017)

[43] N. Matsunaga, H. Okajima and Y. Yamamoto：Robust variable stiffness control of McKibben type pneumatic artificial muscle arm by using multiple model error compensators, Proceedings of ICCAS 2017 (2017)

[42] K. Kimura, N. Matsunaga and H. Okajima：Driving Assistance System forWelfare Vehicle using Virtual Platoon Control with Augmented Reality, Proceedings of the SICE Annual Conference 2017

[41] K. Inomoto, H. Okajima, G. Koutaki, N. Matsunaga and K. Uchimura：Method for designing a quantized image for digital micromirror device-based projectors using a weighted evaluation function, Proceedings of the SICE Annual Conference 2017Finalist of the young author award

[40] Y. Nakabayashi, H. Okajima and N. Matsunaga：Signal limitation filter to satisfy velocity and acceleration constraints for arbitrary input signals, Proceedings of the SICE Annual Conference 2017 MECpage

[39] D. Matsuno, N. Matsunaga, Y. Shida and H. Okajima：Evaluation of steering model depending on gazing distance by using driving simulator, Proceedings of ICCAS 2016 (2016) Outstanding Paper Award

[38] T. Tanaka, H. Okajima and N. Matsunaga：Experiment of robust driving assistance control for skid steer welfare vehicle using model error compensator, Proceedings of ICCAS 2016 (2016) Outstanding Paper Award

[37] H. Okajima, Y. Minami and N. Matsunaga：Unilateral Control Structure Under Communication Rate Constraint, Proceedings of NecSys 2016 (6pages) (2016) QUANTIZERpage

[36] G. Ichimasa, K. Okumura, H. Okajima and N. Matsunaga：Extended structure of MEC for thermal process, Proceedings of the SICE Annual Conference 2016, pp.1593-1598 (2016) MECpage

[35] T. Sugano, H. Okajima, S. Samura and N. Matsunaga：Narrow space driving of welfare vehicles using robust platoon control with adaptive way point tracking, Proceedings of the SICE Annual Conference 2016, pp.1436-1441 (2016)

[34] H. Okajima, T. Asai and N. Matsunaga：Disturbance rejection performance limit for a class of disturbance signals, Proc. of the IEEE Conference on Decision and Control 2015, 2015.12

[33] G. Koutaki, H.Okajima, N. Matsunaga and K.Uchimura：Optimization of color quantization with total luminance for DLP projector and its evaluation system, ICIP2015 QUANTIZERpage

[32] T.Sugano, H.Okajima and N.Matsunaga：Robust and precise platoon driving control of welfare vehicles along wheel track by using model error compensator, IECON2015, YF-001503

[31] H. Okajima, T. Asai and N. Matsunaga：Analytical Solutions for Disturbance Rejection Problems using All Achievable Output Set for Stable Plants, SICE International Symposium on Control Systems 2015, 513-2, (2015.3)

[30] H. Okajima, M. Honda, R. Yoshino and N. Matsunaga：A design method of delta-sigma data conversion system with pre-filter, SICE Annual Conference 2014, pp.1388-1394, (2014.9) QUANTIZERpage

[29] R. Yoshino, H. Okajima, N. Matsunaga and Y. Minami：Dynamic quantizers design under data rate constraints by using PSO method, SICE Annual Conference 2014, pp.1041-1046, (2014.9) QUANTIZERpage

[28] T. Sugano, Y. Dan, H. Okajima, N. Matsunaga and Z. Hu：Indoor Platoon Driving of Electric Wheelchair with Model Error Compensator along Wheel Track of Preceding Vehicle, The 5th International Symposium on Advanced Control of Industrial Processes, 2014.5

[27] Y. Dan, H. Okajima, N. Matsunaga, Z. Hu and N. Nakamura：Experiment of Indoor Platoon Driving using Electric Wheelchair STAVi Controlled by Modeling Error Compensation System, ICT-PAMM Workshop on Mobility Assistance and Service Robotics, p26-31, 2013.11.

[26] K. Nabekura, H. Okajima, N. Matunaga and N. Nakamura：On Collision-Avoidance Steering Assistance of Piggyback Type Electric Wheelchair with Inference of Driver’s Intention, ICT-PAMM Workshop on Mobility Assistance and Service Robotics, p20-25, 2013.11.

[25] Y. Maruno, Y. Dan, A. T. Zengin, H. Okajima and N. Matsunaga：Maneuverability Analysis of Front Drive Type Personal Vehicle STAVi using Modeling Error Compensation System, 7th IFAC Symposium on Advanced in Automative Control, 2013.9.

[24] A. T. Zengin, Y. Maruno, H. Okajima and N. Matsunaga：Slope driving experiment of front drive type electric wheelchair with casters using yaw-rate compensation, ICCAS 2012, 2012.10.

[23] Y. Maruno, A. T. Zengin, H. Okajima,N. Matsunaga and N. Nakamura：Driving experiment of front drive type electric wheelchair using yaw-rate control, SICE Annual Conference 2012, WeA11-01 pp.1408-1413, 2012.8.

[22] A. T. Zengin, Y. Maruno, H. Okajima and N. Matsunaga：Improvement in Straight-ahead Stability of Front Drive Type Electric Wheelchair using Yaw-rate Control, VTI 2012, 2012.7.

[21] K. Sawada, H. Okajima, N. Matsunaga and Y. Minami：Dynamic quantizer design for MIMO systems based on communication rate constraint, IECON 2011, 2011.11. QUANTIZERpage

[20] Y. Maruno, H. Okajima, A. T. Zengin and N. Matsunaga：Direct yaw moment control of front drive type electric wheelchair with free-casters, ICCAS 2011, 2011.10. Outstanding Award

[19] A. T. Zengin, H. Okajima and N. Matsunaga：On vibration feedback method for pain emulation and its feedback to human, ICCAS 2011, 2011.10. Finalist of Outstanding Award

[18] H. Umei, H. Okajima, N. Matsunaga and T. Asai：A design method of compensator to minimize model error, SICE Annual Conference 2011, 2011.9. MECpage

[17] H. Okajima, K. Sawada and N. Matsunaga：Integrated Design of Filter and Interval in Dynamic Quantizer under Communication Rate Constraint, The 18th IFAC World Congress, 2011.8. QUANTIZERpage

[16] N. Matsunaga, H. Okajima, T. Yoshida and S. Kawaji：Passivity evaluation of steering action with adjusting reaction torque to the driver, ASCC2011, 2011.5.

[15] H. Okajima, N. Matsunaga and K. Sawada：Optimal quantization interval design of dynamic quantizers which satisfy the communication rate constraints, Proc. of the IEEE Conference on Decision and Control 2010, 2010.12. QUANTIZERpage

[14] N. Matsunaga, K. Sasano and H. Okajima：An implementation of fractional-order PID controller with dynamic quantizer considering the memory constraint, Proc. of the IEEE Multi-conference on Systems and Control 2010, 2010.9. QUANTIZERpage

[13] H. Okajima, S. Yonaha, N. Matsunaga and S. Kawaji：Direct Yaw-moment Control method for electric vehicles to follow the desired path by driver, SICE Annual Conference 2010, 2010.8., Finalist of the young author award

[12] C. L. Ooi, T. Asai and H. Okajima：Extension of reference signal in iterative learning control for non-minimum phase systems, SICE Annual Conference 2010, 2010.8.

[11] A. T. Zengin, N. Matsunaga, H. Okajima and S. Kawaji：Pain perception model of human skin using multiple pain sensors, SICE Annual Conference 2010, 2010.8.

[10] H. Okajima, T. Asai and S. Kawaji：Unified form of performance limitations in reference tracking control problem for discrete time systems, Proc. of the 47th IEEE Conference on Decision and Control/CCC joint, 2009.12.

[9] N. Matsunaga, T. Shiotsuki, H. Okajima, N. Ohmura：Experiment of Measurement and Control using Embedded System for Undergraduate Students, the 8th IFAC Symposium on Advances in Control Education, Kumamoto, ThC01.5, 2009.10.

[8] H. Okajima, T. Umemoto, N. Matsunaga and S. Kawaji：Analysis of dynamic quantizer in 2-DOF Internal Model Control system with dead-time, Proc. of ICROS-SICE International Joint Conference 2009, pp.4380-4383, 2009.8.

[7] M. Nakano, N. Matsunaga, H. Okajima and S. Kawaji：Tuning of feedback type decoupling controller for two-dimensional thermal process based on VRFT method, Proc. of ICCAS-SICE International Joint Conference 2009, pp.925-930, 2009.8.

[6] N. Matsunaga, R. Mera, H. Okajima and S. Kawaji：Stifness Analysis of Crank Motion Task using Six-Muscles Model, Proc. of ICROS-SICE International Joint Conference 2009, pp.4478-4483, 2009.8.

[5] H. Okajima and T. Asai：Performance limitation of tracking control problem for a class of references, Proc. of the 47th IEEE Conference on Decision and Control, pp.3694-3699, 2008.12.

[4] H. Okajima, T. Asai and S. Kawaji：Optimal Velocity Control Method in Path Following Control Problem, Proc. of The 17th IFAC World Congress, pp.90-95, 2008.6.

[3] H. Okajima and T. Asai：Parameterization of Outputs Tracking to Reference Asymptotically and Achievable by Bounded Inputs, Proc. of The 32nd Annual Conference of the IEEE Industrial Electronics Society, pp.682-687, 2006.11.

[2] C. L. Ooi, H. Okajima and T. Asai：Constraints in Servo System Design for Non-Minimum Phase System, Proc. of Sice-Icase International Joint Conference 2006, pp.970-973, 2006.10.

[1] H. Okajima and T. Asai：Path-Following Control based on Trajectory Differences, Proc. of The 10th IFAC/IFORS/IMACS/IFIP Symposium on Large Scale Systems, pp.735-740, 2004.7.

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