Details of a Researcher - NOZAKI, Takahiro

Papers - NOZAKI, Takahiro

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Design of bilateral control based on equivalent circuit model

Akutsu S., Nozaki T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology) 2019-February 1351 - 1356 2019.02

ISSN 9781538663769

© 2019 IEEE. Haptic teleoperation has been studied as an attractive technology for a long time. Although the haptic teleoperation has been already realized by conventional methods, their physical meanings are remained vague and unclear. This paper explains bilateral control for the haptic teleoperation using an equivalent circuit model. Owing to the circuit model, which takes into account characteristics of electrical actuators, a control strategy and its physical meanings are clearly illustrated. Torque (force) control and position (velocity) control for the haptic teleoperation can be designed independently because of mode decomposition. Feedback controller design for each control is based on analyses of sensitivity derived from the equivalent circuit. The control strategy derived from the equivalent circuit have been confirmed by experiments and resulted in the haptic teleoperation.

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Impedance Field Expression of Bilateral Control for Reducing Data Traffic in Haptic Transmission

Nozaki T., Shimizu S., Murakami T., Oboe R.

IEEE Transactions on Industrial Electronics (IEEE Transactions on Industrial Electronics) 66 ( 2 ) 1142 - 1150 2019.02

ISSN 02780046

© 1982-2012 IEEE. It is expected that bilateral control will find broad applications such as mobile robot exploration and operations in extreme environments. However, the transmission of vivid haptic sensation requires a rapid data-transfer rate of haptic data due to the short sampling period and high-frequency communication. The objective of this paper is aimed at the traffic reduction of haptic data by exploiting an impedance field equivalence of a standard bilateral control. The proposed approach theoretically clarifies the equivalence of the standard bilateral control and impedance control in terms of haptic transmission. Based on this equivalence, the same performance of a standard bilateral control can be achieved by only communicating the force information that determines the equilibrium position of the impedance control. The validity of the proposed approach is confirmed through both simulations and experiments. The obtained results show that the proposed approach successfully reduced the amount of communicated haptic data without any disadvantages compared with the standard acceleration-based bilateral system. This paper shows novel interpretation that haptic transmission is realized by controlling the equilibrium force, which contributes reducing data traffic in haptic transmission and understanding motion generation.

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Multilevel inverter topology using current path change for zero current switching

Sugimoto T., Nozaki T., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 8 ( 2 ) 250 - 255 2019

ISSN 21871094

© 2019 The Institute of Electrical Engineers of Japan. In motor drive applications, a high switching frequency is required to mitigate current harmonics, which cause a copper loss. However, the high switching frequency makes the switching loss large. Hence, some switching loss reduction techniques have been studied in the past. These techniques have some problems. This paper proposes a multilevel inverter topology for switching loss reduction. Because of provision of multiple current paths, the proposed inverter realizes the zero current switching. Consequently, a loss of the whole system including an inverter and motor can be reduced with a higher switching frequency. The switching loss of the proposed inverter is smaller than that of the conventional one. It was verified that the proposed inverter has some advantages at high switching frequency, through calculations.

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Haptics-Led Innovation for Coming Society

K. Ohnishi and T. Nozaki and Y. Saito and T. Shimono and T. Mizoguchi

2019 IEEE International Electron Devices Meeting (IEDM) ({IEEE}) 2019

ISSN 2380-9248

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Selective wireless power transfer via magnetic resonant coupling by using variable impedance circuit

Nakagawa T., Sugimoto T., Nozaki T., Murakami T.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society) 4834 - 4839 2018.12

ISSN 9781509066841

© 2018 IEEE. Recently, Wireless Power Transfer (WPT) via Magnetic Resonant Coupling is especially focused around the world. Since a space will have a lot of devices in the future, WPT considering multiple devices will be required. It is important to consider not only power transfer efficiency but also power distribution when power is wirelessly transferred to multiple devices. The amount of received power in a receiver depends on the impedance of the receiver and the ratio of power distribution has the relation to the impedance. Conventional WPT system requires a few controllable repeaters and the large size of the receiver. In this paper, a variable impedance circuit for power distribution is proposed. Using the proposed circuit controllable by DC voltage, the problem for the conventional system is solved. In the future when WPT is popular, the circuit realizes electrically controllable power distribution.

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Position and torque sensorless motion transmission using parameter identification based on least mean squares method

Akutsu S., Nozaki T., Murakami T.

ISSN 9781509066841

© 2018 IEEE. Motion transmission is a technology which is expected to be used for teleoperation systems. Sensorless control can improve fault tolerance of teleoperation robots exposed to harsh environments. However, sensorless control methods are generally sensitive to parameter errors of an actuator. A previously proposed sensorless motion transmission method especially requires the accurate value of resistance. Therefore, this work aims to identify resistance of two direct current motors used as a master slave system. Taking account of the master slave system of which common mode and differential mode correspond respectively to torque transmission and velocity synchronization, a least mean squares method jointly using a voltage injection is newly applied to the differential mode. Simulation results validated the proposed identification method and indicated that the sensorless motion transmission succeeded using the identified resistance value. The proposed novel method will improve the usefulness of sensorless motion transmission by adaptability to parameter errors.

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Multilevel inverter topology for switching loss reduction

Sugimoto T., Nozaki T., Murakami T.

ISSN 9781509066841

© 2018 IEEE. In motor drive application, a high switching frequency is required in order to mitigate current harmonics which cause a copper loss. However, the high switching frequency makes the switching loss large. Hence, some switching loss reduction techniques have been studied before. However, they requires complicated circuits. This paper proposes a multilevel inverter topology for a switching loss reduction. By changing current paths, the proposed inverter realizes the zero current switching. It was experimentally verified that the proposed inverter realizes the zero current switching by a foundation circuit.

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Design of a multi-stage stiffness enhancing unit for a soft robotic finger and its robust motion control

Mutlu R., Sariyildiz E., Nozaki T., Alici G.

ISSN 9781509066841

© 2018 IEEE. Conventional robotics have always pursued methods to bring robots near human. Human robot interaction (HRI) has gained great momentum to realize freeing robots with various control methods to ensure their safe operations with human presence. Soft robotics, alternatively, focuses on building robots mainly made of low elastic moduli materials, which may not be capable of harming humans due to nature of the materials they are made of, nevertheless, requires stiffness augmentation to be able to transmit relatively higher forces. In this study, we designed and fabricated an underactuated soft robotic finger using fused deposition modelling type 3D printing with a thermoplastic elastomer material. Robotic finger is actuated with a tendon-cable attached to a linear servo-actuator while secondary linear servo-actuator is used to control position of a stiffness-enhancement unit made of bistable metal strips. In order to verify stiffness enhancement, we perform precise position control and estimate external disturbances. Experimental results suggest that estimated external disturbances (i.e. stiffness of soft robotic finger) change under the same position conditions (finger flexion) thanks to precise robust motion controller.

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Fiber suspended micro force transmission system using scaling bilateral control

Hangai S., Nozaki T., Ohnishi K.

ISSN 9781509066841

© 2018 IEEE. In this paper, friction-reduced scaling bilateral control system for micro force transmission is proposed. Recently, demand for micro manipulation is drastically increasing in the fields of medical or biological science. In order to support micro manipulation, many researchers are trying to apply force feedback to the manipulation. One of the methods is bilateral control with Reaction Force Observer(RFOB). Bilateral control system is composed of a master robot and slave robot. Slave robot tracks master robot's motion and transmits reaction force to operator at master side. In the conventional bilateral control system, if reaction force is smaller than frictional force of machine structure, operator cannot distinguish the slight reaction force at hand. In this paper, actuator is supported by fiber to reduce the frictional force. Furthermore, disturbance arisen by fiber tension is modeled, and compensated. Experiments are conducted to validate the proposal.

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Design of iterative learning control for force control considering environmental impedance

Fukui M., Akutsu S., Okano T., Nozaki T., Murakami T.

ISSN 9781509066841

© 2018 IEEE. In this paper, a new approach for high-precise force control in repeated tasks is proposed. In the general force control, the feedback control tends to be used for a matching the output force to the desired force safely. However, when the feedback control is used, the input of the plant does not change until the error is observed. The characteristic makes reactivity bad. In the position control, the model-based feedforward control is often used to solve this problem. However, the model-based feedforward control cannot be used in force control due to the difficulty of making the accurate model. The main reason of this problem is the uncertainty of the environmental impedance. Owing to the uncertainty, the model-based feedforward control cannot work properly. To solve this problem, Iterative Learning Control (ILC) is used in this paper. ILC does not require the accurate model, and it is able to match the output force to the desired one through repeated trials. However, the convergence condition in force control has not been analyzed until now. In this paper, by taking account of the environmental impedance of the object, a new convergence restriction is proposed. Under the proposed condition, the force control in repeated tasks becomes more precise. The procedure was demonstrated on simulations.

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Design and Evaluation of a Remote Actuated Finger Exoskeleton Using Motion-Copying System for Tendon Rehabilitation

Lemerle S., Nozaki T., Ohnishi K.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics) 14 ( 11 ) 5167 - 5177 2018.11

ISSN 15513203

© 2017 IEEE. Hand recovery process is a major issue in the rehabilitation field as hands are vital to perform most daily activities. This paper presents the design and evaluation of a one actuated degree-of-freedom exoskeleton finger using flexible actuator to assist patients in rehabilitation process and more specifically in tendon recovery protocols. The control strategy based on the motion-copying system is used to be able to take advantages of the sensation of the patient. The wearability and adaptability of the device are improved, compared to other specific devices, mainly by the use of remote actuation and light-weight materials. Evaluation of the device in terms of wearability, adaptability, repeatability and accuracy of the position estimation are conducted. All these criteria are confirmed. The next step is to test the device in actual recovery protocols to evaluate its efficiency.

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Human motion analysis and its application to walking stabilization with COG and ZMP

Kim S., Hirota K., Nozaki T., Murakami T.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics) 14 ( 11 ) 5178 - 5186 2018.11

ISSN 15513203

© 2005-2012 IEEE. A stability index has been generally used in a gait system of formulaic structure. In this standardized structure, a human model has a center of gravity (COG), while a robot device has a zero moment point (ZMP) with COG as the stability standard in the walking motion. In the gait system of wearable type, the stability of human model is closely related with the robot device, in other words, the COG and ZMP are located in the limited domain of human motion and robot task. In this paper, the human and device are designed individually and the knee joint of human is unconstrained from the device work to allow the human reliance. The stability index that includes the COG and ZMP is defined. The validation of this index is guaranteed through a few tests to describe a correlation between the stability index and the human model condition. Based on the validity of the stability index, the experiment for the walking stabilization is implemented with the ZMP estimation by reaction torque observer.

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A Stability Analysis for the Acceleration-Based Robust Position Control of Robot Manipulators via Disturbance Observer

Sariyildiz E., Sekiguchi H., Nozaki T., Ugurlu B., Ohnishi K.

IEEE/ASME Transactions on Mechatronics (IEEE/ASME Transactions on Mechatronics) 23 ( 5 ) 2369 - 2378 2018.10

ISSN 10834435

© 1996-2012 IEEE. This paper proposes a new nonlinear stability analysis for the acceleration-based robust position control of robot manipulators by using disturbance observer (DOb). It is shown that if the nominal inertia matrix is properly tuned in the design of a DOb, then the position error asymptotically goes to zero in regulation control and is uniformly ultimately bounded in trajectory-tracking control. As the bandwidth of a DOb and the nominal inertia matrix are increased, the bound of error shrinks, i.e., the robust stability and performance of the position control system are improved. However, neither the bandwidth of the DOb nor the nominal inertia matrix can be freely increased due to practical design constraints, e.g., the robust position controller becomes more noise-sensitive when they are increased. The proposed stability analysis provides insights into the dynamic behavior of DOb-based robust motion control systems. It is theoretically and experimentally proved that nondiagonal elements of the nominal inertia matrix are useful in improving the stability and in adjusting the tradeoff between robustness and noise sensitivity. The validity of the proposal is verified by simulation and experimental results.

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Improvement of supporting robot for lower limb and evaluation of output force in vertical direction

Inamura N., Shimono T., Mizoguchi T., Nozaki T., Ishii S., Ohnishi K.

IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM (IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM) 2018-July 1240 - 1245 2018.08

ISSN 9781538618547

© 2018 IEEE. There are many falling accidents of elderly people. The main reason of these accidents is that their muscle of lower limb weaken with aging. The purpose of this research is to provide them an assisting robot that can support their weight. As the robot consists of belt and rotational motor, adjusting to subject and subject's posture is easy. Thanks to the structure, hip and knee joints' extensor torques are generated by the belt pulling up when the motor rotates. We also created an evaluation apparatus that simulates human lower limb with pulleys and links to conduct an experiment. In this paper, we consider when to assist during stance phase of walking, and the experiment was conducted in order to confirm whether the apparatus follows the motion equations. Experimental results show that there are some error between calculated force and measured force. This error may be resulted from friction between belt and pulleys.

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Artificial Replacement of Human Sensation Using Haptic Transplant Technology

Fukushima S., Sekiguchi H., Saito Y., Iida W., Nozaki T., Ohnishi K.

IEEE Transactions on Industrial Electronics (IEEE Transactions on Industrial Electronics) 65 ( 5 ) 3985 - 3994 2018.05

ISSN 02780046

© 2018 IEEE. This study proposes a novel prosthetic hand that can artificially replace human sensation using haptic transplant technology. Conventional motorized prostheses are unable to precisely control the grasping force of the hand due to the lack of force sensation. In this paper, a haptic prosthetic hand is developed that allows for intuitive operation and precise force adjustment. These functions are realized by artificially transplanting the tactile sensation of a healthy part of the user's body to the amputated part of their body. The haptic transplant technology transmits the force sensation of the prosthesis to the master interface attached to the amputee's healthy part of body using bilateral control without a force sensor. Furthermore, variable compliance control is proposed for flexible adaptation to the shape of the object being grasped. The effectiveness of the proposed system was experimentally verified by comparing the controllability of the proposed system with that of a myoelectric prosthesis. In summary, an artificial replacement for human sensation was developed, and the intuitive operability and flexibility of the proposed system were confirmed.

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Translation and inclination control for Intelligent Tension Pole based on mode decoupling method

Hanaoka R., Nozaki T., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 7 ( 2 ) 158 - 165 2018

ISSN 21871094

© 2018 The Institute of Electrical Engineers of Japan. An aging society is a serious problem in many developed countries. Due to this issue, there has been a significant increase in the demand for assist devices that can support human motion. This paper proposes a novel assist device, Intelligent Tension Pole (ITP), to assist in indoor activities of daily living (ADL), and it is expected to provide support for achieving self-reliance, space saving, and stability. The structure and control system of this assist device are presented. This novel assist device is based on a movable handrail, and therefore wheels are added to the lower and upper ends of the tension pole. In addition, a ball screw, which enables the ITP to move while stretching to the floor and ceiling at any time using force control, is added. In order to improve user comfort and reduce the risk of falling down of the ITP, translation and inclination controls of the ITP are applied to the wheel control. These controls are controlled independently by the mode decoupling method. Experiments are conducted to verify the effectiveness of the proposed device and its control system.

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Position and torque sensorless motion transmission using voltage compensation

Akutsu S., Nozaki T., Sekiguchi H., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 7 ( 2 ) 150 - 157 2018

ISSN 21871094

© 2018 The Institute of Electrical Engineers of Japan. This paper aims to realize position and torque sensorless motion transmission between a generator and a motor. The proposed voltage compensation method requires only one current sensor on the generator side. Since the motor side is completely sensorless, this system is suitable for operation under harsh environments. Comparative analyses indicate that the proposed method satisfies the conditions for the transmission of an actual tactile sensation. Simulations and experiments confirmed that motion transmission is realized using the proposed method.

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Telexistence and Real Haptics

Takahiro Nozaki and Satoshi Hangai

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 36 ( 10 ) 668 - 672 2018

ISSN 0289-1824

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