Papers - NOZAKI, Takahiro

Motion Generation Based on Physical Property Estimation in Motion Copy System

T Kitamura, X Sun, Y Saito, H Asai, T Nozaki, K Ohnishi

2022 IEEE 17th International Conference on Advanced Motion Control (AMC), 62-67    62 - 67 2022

ISSN  1943-6572

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Model-Free Detection of Penetration and Automatic Stop Control in Dental Implant Surgery Based on Differential Value of Torque

Y Kido, H Kawana, S Asoda, T Nozaki, T Murakami

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    144 - 149 2022

ISSN  1943-6572

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Improvement and Analysis of Position and Speed Estimator in Low Speed Range for IPMSM Based on Disturbance Observer

R Nakatsuka, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    225 - 230 2022

ISSN  1943-6572

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Force Control at Arbitrary Position of Manipulator Based on Estimated Contact State by Force/Torque Sensor Installed at Base Frame

H Handa, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    420 - 425 2022

ISSN  1943-6572

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Experimental Verification of a Novel Continuously Variable Transmission with Electro-Hydrostatic Actuator

H Asai, K Sugihara, T Kitamura, Y Saito, K Ohnishi, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC), 30-35    30 - 35 2022

ISSN  1943-6572

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Delay Time of Human Motion Generation in Response to Changing Periods in Force Tracking Task

K Yane, HI Krebs, T Nozaki

2022 9th IEEE RAS/EMBS International Conference for Biomedical Robotics and … 2022-August 2022

ISSN  21551774

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It is important to understand how humans gen-erate tracking forces when considering the increase of human- robot interactions. Previous research has mostly focused on po-sitional target tasks. A recent study was conducted to investigate the basic characteristics of the force tracking task. That study suggested predictive compensatory behavior in humans during fast rhythmic movements. In this paper, we investigated the relationship between the frequency of rhythmic force generation and predictive compensation in humans. Here we conducted experiments using four square waves with different periods as target values with four healthy young subjects. Subjects were instructed to control the force exerted at the tip of their fingers during a force pursuit tracking task. The results suggest the following: the faster the tracking period, the faster the delay time converges to a steady value; the relationship between the motion period and the rate of convergence is not linear; individual differences in delay time are large when the force generation is transitioning from slow to very fast, which corresponds to the rhythmic task; when the period is extremely short (the period is 1 sec), the ascent and descent force characteristics are different.

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Position/force controller, and position/force control method and storage medium

K Ohnishi, T Nozaki, T Mizoguchi

US Patent App. 17/429,240  2022

Position and Speed Estimation in Low Speed Range for IPMSM Based on Disturbance Observer

R Nakatsuka, T Nozaki

IECON 2021–47th Annual Conference of the IEEE Industrial Electronics Society … (IECON Proceedings (Industrial Electronics Conference))  2021-October 2021.10

ISSN  1553-572X

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Interior Permanent Magnet Synchronous Motors (IPMSM) are an important component for a robotic application because of its high torque property. In order to drive IPMSM with high efficiency, feedback control with rotor position sensors is utilized. However, since those sensors make the instrument size large and the cost high, many researches on sensorless control which is feedback control without position sensors have been conducted. Especially for low-speed range, sensorless control with the use of additional high-frequency signals to detect rotor position has been proposed although these signals might cause rotor vibration or low efficiency. This paper proposes a novel position estimation method based on disturbance observer which detect position estimation error. The estimation method achieves detection of rotor position at low speed since rotor saliency and current derivative are utilized. This method differs from conventional observer-based methods in that the disturbance observer not only estimates the phase, but also estimates the term proportional to the axial error and applies a compensation voltage for it. This method also avoids to use any additional signals such as high-frequency voltage for the estimation. The effectiveness of the proposal was confirmed by simulations.

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Stability and Robustness of the Disturbance Observer-Based Motion Control Systems in Discrete-Time Domain

Sariyildiz E., Hangai S., Uzunovic T., Nozaki T., Ohnishi K.

IEEE/ASME Transactions on Mechatronics (IEEE/ASME Transactions on Mechatronics)  26 ( 4 ) 2139 - 2150 2021.08

ISSN  10834435

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This article analyses the robust stability and performance of the disturbance observer (DOb) based digital motion control systems in the discrete-time domain. It is shown that the phase margin and the robustness of the digital motion controller can be directly adjusted by tuning the nominal plant model and the bandwidth of the observer. However, they have the upper and lower bounds due to robust stability and performance constraints as well as the noise sensitivity. The constraints on the design parameters of the DOb change when the digital motion controller is synthesized by measuring different states of a servosystem. For example, the bandwidth of the DOb is limited by the noise sensitivity and waterbed effect when the velocity and position measurements are employed in the digital robust motion controller synthesis. The robustness constraint due to the waterbed effect is removed when the DOb is implemented by acceleration measurement. The design constraints on the nominal plant model and the bandwidth of the observer are analytically derived by employing the generalized Bode integral theorem in discrete time. The proposed design constraints allow one to systematically synthesize a high-performance DOb-based digital robust motion controller. The experimental results are given to verify the proposed analysis and synthesis methods.

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Identification of contact position and force estimation on manipulator using force sensor implemented on base frame

H Handa, T Nozaki, T Murakami

IEEJ Journal of Industry Applications 10 (3), 324-330 (IEEJ Journal of Industry Applications)  10 ( 3 ) 324 - 330 2021.05

ISSN  21871094

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Sensing is essential in human cooperative robots to realize safe and powerful operations against contact with the surrounding environment. Contact sensing has been studied for manipulators to avoid accidents caused by collisions between humans and robots. Conventional research has demonstrated that contact sensing requires many sensors or has a limited measurable range. In the conventional research without sensors, modeling systems, such as frictional force and plant parameters, have been used to estimate the contact force. However, a high reduction ratio mechanism for achieving powerful operations hinders accurate force estimation. This study proposes a method to estimate the contact force and contact position on a manipulator with a high reduction ratio mechanism by installing only one force/torque sensor on the base frame of the manipulator. By using the proposed method, the contact force and contact position can be detected regardless of the location where the contact force is applied. Furthermore, when the contact force is applied in a location where the contact position cannot be accurately estimated, an estimated disturbance or a link motion is used to determine the contact position. The effectiveness of the proposed method is validated through experiments.

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Haptic Data Prediction and Extrapolation for Communication Traffic Reduction of Four-Channel Bilateral Control System

Hangai S., Nozaki T.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics)  17 ( 4 ) 2611 - 2620 2021.04

ISSN  15513203

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© 2005-2012 IEEE. Robotic teleoperation with a bilateral control system has attracted attention owing to its haptic transmission performance. However, conventional bilateral control systems require broadband communication to transmit the vivid haptic sensation. This problem limits the application range of the bilateral control systems. The communication traffic can be reduced by predicting and extrapolating the incoming data. However, in the conventional prediction-based methods, only one type (e.g., position, velocity, or force) of data is transmitted per one direction because of the difficulty of predicting multiple independent data. The novelty of this article is the realization of the prediction-based traffic reduction in the four-channel bilateral control system that transmits accurate haptic sensation by communicating both position and force data. By equivalently transforming this control scheme in the structure of impedance control, the transmit data are summed up to one data, equilibrium force. The equilibrium force is not only transmitted but extrapolated on the receiver side. As a result, the communication frequency becomes low without degrading haptic transmission performance. The validity of the proposed method was confirmed through experiments and succeeded to reduce the communication data size to less than 3.0%. The proposed method helps to realize a high-performance bilateral control system on band-limited networks.

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Association of periodontal disease with atherosclerosis in 70-year-old Japanese older adults

Kitamura Masahiro, Ikebe Kazunori, Kamide Kei, Gondo Yasuyuki, Yamashita Motozo, Takedachi Masahide, Nozaki Takenori, Fujihara Chiharu, Yamada Satoru, Kashiwagi Yoichiro, Miki Koji, Iwayama Tomoaki, Hatta Kodai, Mihara Yusuke, Kurushima Yuko, Takeshita Hajime, Kabayama Mai, Oguro Ryousuke, Kawai Tatsuo, Akasaka Hiroshi, Takeya Yasushi, Yamamoto Koichi, Sugimoto Ken, Ishizaki Tatsuro, Arai Yasumichi, Masui Yukie, Takahashi Ryutaro, Rakugi Hiromi, Maeda Yoshinobu, Murakami Shinya

ODONTOLOGY 109 ( 2 ) 506 - 513 2021.04

ISSN  1618-1247

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Admittance control-based bilateral control system considering position error

S Kimura, T Nozaki, T Murakami

2021 IEEE International Conference on Mechatronics (ICM), 1-6 (2021 IEEE International Conference on Mechatronics, ICM 2021)   2021.03

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This paper proposes a bilateral control system implementing an admittance control system. Bilateral control system realizes teleoperation of a remote robot with a sense of touch. We focus on an admittance-based bilateral control system, which needs only two communication channels and has almost the same control performance as an acceleration-based bilateral control system, which is one of the highest transparent teleoperation systems. However, the conventional admittance-based system assumes an ideal communication situation where there is no communication time delay and no packet loss and has possible to increase position error as time goes on in practical use. The proposed admittance-based system achieves the same control performance as the conventional structure without increasing position error even if there is a communication delay. The validity of the proposed system is confirmed through simulations and experiments.

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Development of neural network-based explicit force control with disturbance observer

T Okano, T Nozaki, T Murakami

IEEJ Journal of Industry Applications 10 (2), 153-164 (IEEJ Journal of Industry Applications)  10 ( 2 ) 153 - 164 2021.03

ISSN  21871094

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Human support robots are in high demand and the performance enhancement through force control has been extensively studied. However, the design of the force controller and selection of appropriate gains are sometimes difficult because they are affected by the conditions of motion such as environmental impedance or model uncertainties. This study discusses force control with a disturbance observer and applies a neural network (NN) into its controller; the NN works as both the feedback and feedforward components. The contribution of this study is to show the development method of force control using disturbance observer and a NN, which enhances the performance of force control from the perspective of both feedback and feedforward components. The structure of the controller and composition of the NN were selected through simulation results; moreover, the compensator based on NN was designed in a frequency range higher than the cutoff frequency of the observer with a small number of hidden layers. Moreover, this study discusses a training method of weights in real time. Simulations and experiments were performed for showing the effectiveness of the proposal.

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Discrete-time analysis and synthesis of disturbance observer-based robust force control systems

E Sariyildiz, S Hangai, T Uzunovic, T Nozaki

IEEE Access 9, 148911-148924 (IEEE Access)  9   148911 - 148924 2021

ISSN  2169-3536

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This paper analyses Disturbance Observer- (DOb-) based robust force control systems in the discrete-time domain. The robust force controller is implemented using velocity and acceleration measurements. A DOb is employed in an inner-loop to achieve robustness, and another DOb, viz. Reaction Force Observer (RFOb), is employed in an outer-loop to estimate interaction forces and improve the performance of force control. First, the inner-loop is analysed. It is shown that the DOb works as a phaselead/lag compensator tuned by the nominal design parameters in the inner-loop. The phase margin of the inner-loop controller and the bandwidth of the velocity-based (i.e., conventional) DOb are constrained not only by noise-sensitivity but also by the waterbed effect. This explains why we observe unstable responses as the bandwidth of the conventional DOb increases in practice. To eliminate the design constraint due to the waterbed effect, this paper proposes an acceleration-based DOb. Then, the robust force controller is analysed. It is shown that the design parameters of the RFOb have a notable effect on the stability of the robust force control system. For example, the robust force controller has a non-minimum phase zero (zeros) when the RFOb is not properly tuned. This may cause severe stability and performance problems when conducting force control applications. By using the stability and robustness analyses, this paper proposes new design tools which enable one to synthesize a high-performance robust force control system. Simulations and experiments are presented to validate the proposed analysis and synthesis methods.

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

S Hangai, T Nozaki, T Soma, H Miyashita, S Asoda, M Yazawa, K Sato, ...

The International Journal of Medical Robotics and Computer Assisted Surgery …  2021

Perception of Approaching Objects in Bilateral Control Using Proximity Sensor

T Nozaki, T Karato, T Murakami, HI Krebs

The Proceedings of The 9th IIAE International Conference on Industrial …  2021

Development of a Novel Hydrostatic Continuously Variable Transmission with Fast Path Switching

K Sugihara, T Nozaki, T Murakami

Proceedings of the 9th IIAE International Conference on Industrial …  2021

Characteristics of Human Behavior in Force Modulation while Performing Force Tracking Tasks

Nozaki T., Krebs H.I.

Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics (Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics)  2020-November   240 - 245 2020.11

ISSN  9781728159072

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© 2020 IEEE. In designing a human-computer interface, it is vital to understand the principle behind motion generation in humans. Previous research has mostly focused on kinematics and not kinetics. In this paper, we present the characteristics of human behavior while performing force tracking tasks. Here we present a preliminary study in which three type of measurements were conducted with three healthy young adult male subjects to characterize force modulation (discrete, rhythmic, and target transition). Subjects were instructed to control the force exerted to the load cell during a force pursuit tracking task. The visually-guided discrete attempt investigated human behavior when the target changed discretely (every 5 seconds). The rhythmic attempt investigated human behavior when the target changed continuously and periodically (every 1 second). The target transition required subjects to alter the behavior of the input force. The results suggest the following: the differential value of the force generated by a human is sufficiently large, while the response speed is based on visual information; humans can predict future reference to a small degree and attempt to improve or correct their force; and the rule of superimposition comes into effect with regard to the differential value of force.

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Online Motion Modification by Operator in Motion Reproduction System

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

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2020-October   668 - 673 2020.10

ISSN  9781728154145

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© 2020 IEEE. This paper proposes a novel online motion modification method in motion reproduction system. Motion reproduction is used to reproduce human motion saved through bilateral control. Bilateral control is a teleoperation which can transmit both position and force. Human judgement is needed for compensating the saved motion when the environment is different. However, conventional motion reproduction system only relies on saved motion or environment in slave side. Therefore operators in master side cannot modify the motion after motion has been saved. Instead of just reproducing the motion data, the proposed method adds master system at motion reproduction phase so that an operator can modify the motion. If the master system is simply added to motion reproduction system, the operator's motion and saved motion will interfere each other. Therefore, we propose to use weightings to suppress the interference. Simulated results validates the effectiveness of the proposal.

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