Details of a Researcher - NOZAKI, Takahiro

Papers - NOZAKI, Takahiro

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An Approach to Evaluation Index-Based Gain Scheduling for Acceleration-Based Four-Channel Bilateral Control

精密工学会誌 2020.09

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Visualization of important human motion feature using convolutional neural network

Fukui M., Kokubun G., Nozaki T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology) 2020-February 406 - 411 2020.02

ISSN 9781728157542

© 2020 IEEE. Human motion feature extraction is necessary for robot motion generation. In particular, feature extraction methods related to non-periodic motion should be proposed. Recently, the number of the human motion recognition studies utilizing Convolutional Neural Network (CNN) is increasing due to the brilliant ability of extracting and identifying features. CNN has the same or better discrimination ability than humans so that the features extracted by CNN are thought to be useful for human motion understanding. However, since the internal structure of CNN is like a black box, it is difficult to understand the extracted features. In order to understand the features, some visualization methods which are utilized in the image field are applied in this paper. Furthermore, the many conventional studies utilizing the gradient are not preferred for visualizing CNN which recognizes human motion because human motion is sensitive for the object which treated. That is, the gradient method does not work because the value varies greatly depending on the environment even in the same motion. Therefore, new visualizing method without using the gradient is proposed in this paper. The proposed method visualizes CNN focusing part by following the neuron in CNN. Since this method does not require the gradient, the stable and accurate visualization can be performed. The effectiveness is shown by experiments.

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Extended T-type boost inverter for capacitance reduction

Sugimoto T., Nozaki T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology) 2020-February 474 - 479 2020.02

ISSN 9781728157542

© 2020 IEEE. In these days, multilevel inverters are focused thanks to their advantages, such as small voltage stress, low electromagnetic interferences, and harmonics reduction. Generally, renewable energy sources output a low DC voltage. From the viewpoint of efficiency, a single-stage conversion system which can directly change the lower DC-link voltage to higher AC voltage is required. Some single-stage conversion systems have been proposed before. However, these systems have large energy storage such as an inductor and a capacitor. This paper proposes a multilevel boost inverter stepping up the AC output peak voltage at any boost ratio by changing the number of switched capacitors. To reduce the capacitance, the proposed inverter has multiple conduction patterns when the output voltage is boosted. This characteristic distributes the discharging time to multiple capacitors. This inverter can set any maximum boost ratio and apply to the multiphase applications. The operation principle and the boost ability with multiple boost ratios were confirmed by simulations and experiments. The capacitance reduction was also confirmed by simulations.

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Independent Drive of Multiple AC Motors Using Amplitude Modulation

Yamada Y., Nozaki T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology) 2020-February 181 - 186 2020.02

ISSN 9781728157542

© 2020 IEEE. With the recent development of electric drive technology, systems with multiple electric motors are increasingly used in various applications. Among them, methods of driving multiple electric motors by using only one power source is studied. This multi-motor drive system contributes to the reduction of the number of power supplies and electric parts. Because of these characteristics, the system is effective in reducing the weight and the size of whole system. Therefore, this paper proposes a circuit that can control motors by frequency separation using the principle of amplitude modulation. As a result, it is possible to drive a plurality of motors independently and simultaneously with only one power supply. The simulations of multiple motor drives by the proposed circuit was conducted.

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Measurement of joint moments using wearable sensors

Fukutoku K., Nozaki T., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 9 ( 2 ) 125 - 131 2020

ISSN 21871094

© 2020 The Institute of Electrical Engineers of Japan. Advanced rehabilitation requires a measurement system that quantitatively analyzes the actions of each individual. Joint moment is an indice used to quantitatively evaluate an individual's actions. Conventionally, force plates and highspeed cameras have been used to analyze joint moments. However, these devices need to be fixed in a laboratory, which limits the measurable motions and measurement range. Further, these sensors are expensive. Hence, it is difficult to use them in medical or nursing care facilities. Therefore, this study aimed to estimate joint moments using inexpensive and wearable sensors. This paper proposes a practical joint moments estimation system using inertial measurement units, which is a wearable sensor. The proposed method uses wearable sensors to measure continuous motion without limitation. It is also cheaper than conventional systems. The effectiveness of the proposed system was verified by comparison with the method using force sensors.

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Development of a microsurgery-assisted robot for high-precision thread traction and tension control, and confirmation of its applicability

Hangai S., Nozaki T., Soma T., Miyashita H., Asoda S., Yazawa M., Sato K., Kawana H., Ohnishi K., Kobayashi E.

International Journal of Medical Robotics and Computer Assisted Surgery (International Journal of Medical Robotics and Computer Assisted Surgery) 17 ( 2 ) e2205 2020

ISSN 14785951

© 2020 The Authors. The International Journal of Medical Robotics and Computer Assisted Surgery published by John Wiley & Sons Ltd. Background: Microsurgery requires high skills for suturing using fragile threads, often within narrow surgical fields. Precise tension is required for good healing and to avoid the risk of thread breakage. Methods: To meet the demands, we developed a novel assist robot utilizing high-precision sensorless haptic technology. The robot adopts a cable-driven mechanism to maintain a distance from the surgical area and enhances compatibility with surgical equipment such as microscopes. The robot performance was verified through in vitro and in vivo experiments using a rat model. Results: The realization of precise tension control was confirmed in both experiments. In particular, in the in vivo experiments, the developed robot succeeded to produce a knot with an accurate tension of 0.66% error. Conclusions: The developed robot can realize to control traction force precisely. This technology might open up the window for a full assist robot for microsurgery with haptic feeling.

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Impedance Field-based Teleoperation with Data Holders for Reducing Data Traffic in Haptic Transmission and Its Analysis of Performance and Stability

Hangai S., Nozaki T.

IEEE Access (IEEE Access) 9 6334 - 6343 2020

ISSN 2169-3536

CCBY In order to realize a vivid tactile transmission in a teleoperation system, it is necessary to send and receive a lot of motion information such as position, speed, and force with extreme high frequency. In addition, in the actual use, many systems are connected to each other through a network. Against this backdrop, the explosive increase in communication traffic becomes a serious problem. The difficulty of this problem is that there exist complicated exchanges of motion information among the systems and they affect each other. Therefore, this paper proposes a novel configuration of a teleoperation system that consists of the conversion technique of transmitted and received information into a single physical quantity (equilibrium force) and the reconstruction technique of discrete data (ZOH: zero-order hold/FOH: first-order hold). The analyses and experiments revealed that 1) FOH is superior to ZOH in terms of operational force 2) FOH and ZOH are about the same performance in terms of reproducibility 3) FOH tends to be more unstable when the packet transmission period increases.

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A Method to Make a Robot Understand What was a Target Object in Motion Copying System

Sun Xiaobai, Nozaki Takahiro, Murakami Toshiyuki, Ohnishi Kouhei

2020 IEEE 16TH INTERNATIONAL WORKSHOP ON ADVANCED MOTION CONTROL (AMC) 241 - 246 2020

ISSN 1943-6572

Observer Structure Considering Reluctance Torque of IPMSM for Noise Resistance

Yamada Y., Nozaki T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2019-October 461 - 466 2019.10

ISSN 9781728148786

© 2019 IEEE. In this paper, Disturbance OBserver (DOB) and Reaction Torque OBserver (RTOB) considering reluctance torque is proposed. By changing the structure of DOB when performing Maximum Torque Per Amplitude Control (MTPAC), a high torque and a robust control system is designed. Specifically, a control system resistant to noise is designed by considering the reluctance torque in the torque constant part. The proposed method is effective in situations where noise is large, as in position sensorless control. Due to the noise resistance, the vibration of the current or torque is reduced. Also, by considering the reluctance torque, the estimated value of the reaction torque can be estimated accurately. Therefore the performance of the force control is improved. The effectiveness of the proposed method is confirmed by simulation.

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A Controller Design Method of Bilateral Teleoperation for Velocity Control Driver

Saito Y., Shimmyo S., Nozaki T., Ohnishi K.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2019-October 3585 - 3590 2019.10

ISSN 9781728148786

© 2019 IEEE. Bilateral control can realize haptic feedback required for securing safety and diversity in teleoperation by robots. Since conventional approaches are based on a servo controller which has high-performance current control or torque control, there is a barrier for advancing into society. The objective of this paper is to propose a design method of the bilateral controller using velocity control driver to achieve haptic feedback. The velocity control driver such as an inverter is widely used in the industrial fields. In the proposed method, a reaction force observer modified for velocity control driver is used to estimate environmental reaction force. The control system is constructed by applying the concept of hybrid control which controls velocity and force independently, and the concept of modal space which separates motions into functions is also applied. Furthermore, the proposed bilateral controller is designed based on the ideal conditions of operationality and reproducibility. The validity of the proposal is verified through a simulation and an experiment. The obtained results show that the proposed controller successfully achieves the teleoperation with haptic feedback using velocity control driver.

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Extended T-Type Boost Inverter Using Switched Capacitors

Sugimoto T., Nozaki T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2019-October 1756 - 1761 2019.10

ISSN 9781728148786

© 2019 IEEE. Recently, for renewable energy applications, multilevel inverters are an attractive option due to their advantages, such as harmonics reduction, low electromagnetic interferences, and small voltage stress. Additionally, lower DC-link voltage should be converted to higher AC voltage, which needs an inverter and a DC-DC boost converter or a transformer. However, the two-stage conversion reduces efficiency and reliability in renewable energy applications. Hence, a single-stage conversion system which can directly change the lower DC-link voltage to higher AC voltage is required. Some single-stage conversion systems have been proposed before. However, the maximum boost ratio and the level of these systems are constant, which limits applications. This paper proposes a multilevel boost inverter stepping up the AC output peak voltage at any boost ratio by changing the number of switched capacitors. The operation principle and the boost ability with multiple boost ratios are confirmed by simulations.

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Continuously Variable Transmission by High-speed Path Switching of Linear Electro-hydrostatic Actuator

Sugihara K., Nozaki T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2019-October 3603 - 3608 2019.10

ISSN 9781728148786

© 2019 IEEE. In robotic systems, reduction drives are utilized to increase actuators' force. Actuators with a constant reduction ratio can not achieve characteristics of both high velocity driving and high force driving. In order to perform various tasks, high force drive and high velocity drive are required for robotic actuators since required driving characteristics are different among tasks. Therefore, a mechanism which can change a reduction ratio continuously is needed. This paper proposes a mechanism that can change a reduction ratio with a linear electro-hydrostatic actuator (EHA). The proposed mechanism switches between two discrete reduction ratios by switching two oil paths with solenoid valves. Furthermore, this paper realizes a continuously variable reduction ratio by switching the solenoid valves quickly. This paper confirms that the reduction ratio changes continuously and widely by simulations.

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Bandwidth Expansion of Bilateral Teleoperation Based on Synergy of Observer Gain and Velocity Feedback Gain

Shimmyo S., Saito Y., Nozaki T., Ohnishi K.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2019-October 3597 - 3602 2019.10

ISSN 9781728148786

© 2019 IEEE. Bilateral control is getting much attention as a key technology in teleoperation. A reproducibility is one of the performance indices of bilateral teleoperation, and four-channel acceleration-based bilateral control (4ch ABC) which has a high reproducibility with wide bandwidth enables operators to feel environmental impedance, clearly. Both position control and force control are required for the 4ch ABC, and a PD controller and a P controller are often utilized with a disturbance observer (DOB) and a reaction force observer (RFOB). This paper discusses how operators can feel environmental impedance with wide bandwidth in the 4ch ABC. A damping ratio of a PD controller has been, conventionally, set about 1 by imitating a traditional design principle of servo control. This paper theoretically reveals that a velocity feedback gain of a PD controller affects a bandwidth of reproducibility as a synergy with observer gains of a DOB, and a PD controller using a high velocity feedback gain is introduced. The validity of the theoretical analysis is confirmed by simulations and experimental results.

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Power-based restoration of haptic teleoperation from communication blackout

Hangai S., Nozaki T.

IEEE International Conference on Industrial Informatics (INDIN) (IEEE International Conference on Industrial Informatics (INDIN)) 2019-July 583 - 588 2019.07

ISSN 9781728129273

© 2019 IEEE. Recently, network-based control systems attract a lot of attentions. One of the applications of such control systems is haptic transmission using a bilateral control system. In order to construct the bilateral control system over the time delayed-network, many researchers have proposed many methods and succeeded to improve the stability and performance of the system. By assuring the system's passivity, some of conventional methods have succeeded to stabilize the system even when the communication blackout occurs. However, the passivity-based methods are conservative and deteriorate the performance. In this paper, the mode shifting method is proposed to deal with the communication blackout without considering the system's passivity. In the proposed method, the bilateral controller is shifted to a local controller when the communication blackout occurs. By shifting to the local controller, the system is not destabilized by the blackout. Moreover, when the communication recovers, the bilateral controller is gradually restored to regulate the robot's output power. Owing to the power regulation, the robots never damage environmental objects during and after the communication blackout. Therefore, the proposed method realizes stable and safe control even under the blackout. The validity of the proposed method is confirmed by simulations and a experiment.

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Sensorless Bilateral Control Using Hall ICs

Akutsu S., Nozaki T., Murakami T.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019) 243 - 248 2019.05

ISSN 9781538669594

© 2019 IEEE. Sensorless bilateral control has been studied to improve fault-tolerance of teleoperation without using torque sensors, position sensors, and other mechanical sensors. However, sensorless control often has less control accuracy due to model errors, parameter variations, and other unexpected factors. Feedback control with some position sensors is practically required for teleoperation. Therefore, this study aims at sensorless bilateral control using Hall ICs. A proposed bilateral control does not necessarily require disturbance observers unlike a conventional method originally using high-resolution sensors. Owing to this advantage, low-resolution sensors are applicable to the proposed bilateral control. Experiments showed that the proposed method succeeded bilateral control using Hall ICs without mechanical sensors, although the conventional control did not work using the low-resolution sensors. Therefore, the proposed method will be able to enhance fault-tolerance of teleoperation systems.

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Symmetric Operational Force Compensator for Bilateral Teleoperation under Time Delay Based on Power Flow Direction

Shimmyo S., Saito Y., Nozaki T., Ohnishi K.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019) 700 - 705 2019.05

ISSN 9781538669594

© 2019 IEEE. This paper proposes an operational force reduction method for four-channel bilateral teleoperation under time delay. The four-channel bilateral control is an attractive way to realize a remote control with haptic sensation. In general, the haptic sensation deteriorates under the time delay in the four-channel bilateral teleoperation, e.g., operationality of the teleoperation, stability of the system, and other performances. To improve the operationality in free motion, a communication disturbance observer and a three-channel bilateral control have been proposed. Although the operational force in the free motion is reduced by these methods, the system becomes asymmetric. This means that the performance of the remote control from the slave side deteriorates in these methods. To overcome this problem, a novel symmetric compensator by using variable compliance control is proposed. A feedback gain is varied based on a power flow direction. The validity of the proposed method is confirmed by experimental results.

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A Decentralized Force Controller Synthesis for Compliant Robots Driven by Series Elastic Actuators

Sariyildiz E., Mutlu R., Nozaki T., Murakami T.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019) 661 - 666 2019.05

ISSN 9781538669594

© 2019 IEEE. This paper deals with the decentralized force control problem of compliant robots driven by Series Elastic Actuators (SEAs). The decentralized force control problem of a compliant robot manipulator is transformed into the robust position control problem of a servo system by using Hooke's law and lumping the nonlinear dynamics and unknown disturbances of the robot manipulator into a fictitious disturbance variable. In order to precisely follow the reference force trajectories at joint space, i.e., the position trajectories of the servo systems, the robust controller is synthesized by using Disturbance Observer (DOb) and Sliding Mode Control (SMC). Although the robust force controller can be synthesized by using only SMC, the force control signal may suffer from high control signal chattering as the force reference input is increased. In addition to improving the robustness of force control, DOb significantly suppresses the discontinuous control signal chattering by allowing to decrease the SMC gain. When the proposed decentralized robust force controller is implemented, the compliant robot can precisely track desired force trajectories and safely contact to different environments. The validity of the proposed force controller is verified by giving the simulation results of a redundant robot manipulator.

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Grasping Point Estimation Based on Stored Motion and Depth Data in Motion Reproduction System

Sun X., Nozaki T., Murakami T., Ohnishi K.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019) 471 - 476 2019.05

ISSN 9781538669594

© 2019 IEEE. Most countries are running shortage of working force due to the aging population and reduction in the birthrate. Robot manipulators are expected to replace human work. However, it it still difficult for manipulators to do simple tasks such as fruit harvesting, foods cooking or toy assembling. A problem for robotic automation arise in the difficulty in teaching how much force manipulators should use for a task execution. Motion reproduction system, which uses bilateral control to store motion data, is one of a method to teach manipulators motion including position and force. The problem concerning motion reproduction system is that the motion reproducing fails if environment is changed between motion saving phase and motion reproducing phase. Motion reproduction system which can understand and adapt to environment is required. Vision sensor can sense environment. Computer vision is mainly focus on how to classify objects. Vision information is seldom combined with motion control especially force motion. Therefore, I propose a motion reproduction system in which reproduced motion is decided based on several motions and collected depth data. Convolutional Neural Network(CNN) was used to estimate a motion command from a depth image. Saved force data was used to generate labels for training. The label decision is different from conventional Machine learning alzorithm.

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Development of Three-Axis Seating Posture Holding Assist Chair and Proposed Variable Compliance Control

Togashi N., Shimono T., Nozaki T., Shibata T., Aoyama Y., Kitahashi Y.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019) 455 - 460 2019.05

ISSN 9781538669594

© 2019 IEEE. This paper introduces the development of the seating posture holding assist chair and proposes the variable compliance control method. The children with cerebral palsy (CP) cannot control the seating posture themselves. In order to support their life, a wheelchair for holding the seating posture is used. However, the seating posture is holding forcibly. As a result, they get stressed and press their back to wheelchair. From the backgrounds, the seating posture holding assist chair is developed in our research. This chair has three-degrees rotational axis in reclining, twist of hip, and neck. Furthermore, the variable compliance control for holding seating posture is proposed. By experiment of reclining control, the proposed control method is verified.

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Automatically-Tuned Damping Injection for Stable Bilateral Control under Time Delay

Hangai S., Nozaki T.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019) 667 - 672 2019.05

ISSN 9781538669594

© 2019 IEEE. Bilateral control is one of the methods to realize a teleoperation with force feedback. However, communication time delay seriously deteriorates operationality and stability of bilateral control. Although 3-channel bilateral control has been proposed to improve operationality, the system becomes unstable in contact motion. Damping injection is an effective method to stabilize the contact motion by producing viscous force. However, this method produces large operational force and deteriorates operationality. Many researchers tried to inject damping without deteriorating operationality. However, their methods are affected by several situations/factors such as delay time or operator's motion speed. As a result, their methods require a redesigning procedure in order to deal with such situations/factors. In this paper, automatically-tuned damping injection is proposed to stabilize the contact motion in 3-channel bilateral control. In the proposed method, damping gain is automatically determined by monitoring the Lyapunov stability of the force control. The effectiveness of the proposed method is verified by experiments.

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