Details of a Researcher - Ohnishi, Kouhei

Papers - Ohnishi, Kouhei

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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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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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Mathematical modeling of semicircular linear motor based on vector potential with landen's transformation

Asai H., Shimono T., Fujimoto Y., Mizoguchi T., Ohnishi K.

IEEE Transactions on Industry Applications (IEEE Transactions on Industry Applications) 55 ( 1 ) 437 - 447 2019.01

ISSN 00939994

© 1972-2012 IEEE. A semicircular linear motor that realizes a motion along circumference of the circle has been developed. To settle the optimal design of this motor by mathematical analysis, the theoretical equation of motor performance has to be clarified. In this paper, the mathematical modeling of semicircular linear motor is carried out from the viewpoint of Lorentz force and magnetic flux density derived by vector potential. By comparing calculated, analyzed, and measured magnetic flux density and thrust force, the validity of derived mathematical model is confirmed. In addition, the cause of difference among three results is also discussed.

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Control Structure Determination of Bilateral System based on Reproducibility and Operationality

Tanida K., Okano T., Murakami T., Ohnishi K.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 8 ( 5 ) 767 - 777 2019

ISSN 21871094

© 2019 The Institute of Electrical Engineers of Japan. The 4ch bilateral control is a teleoperation method that transmits the position and force information between the master and slave, and the reproducibility and operationality are often used to evaluate it. Conventionally, the reproducibility and operationality have been utilized only for performance evaluation, although many controllers based on the 4ch bilateral control scheme have been proposed. Therefore, the aim of this paper is to determine the controller structure based on the target reproducibility and operationality in advance. The contribution of this paper is to develop an appropriate controller from the reproducibility and operationality through numerical computations and analyses. The structure of the proposed controller is verified through simulations and experiments.

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Simultaneous bipedal locomotion based on haptics for teleoperation

Prasanga D., Tanida K., Ohnishi K., Murakami T.

Advanced Robotics (Advanced Robotics) 33 ( 15-16 ) 824 - 839 2019

ISSN 01691864

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group and The Robotics Society of Japan. This paper proposes a novel, simultaneous bipedal locomotion method using haptics for remote operation of biped robots. In general, traditional biped walking methods require very high computational power and advanced controllers to perform the required task. However, in this proposed method, a master exoskeleton attached to the human’s lower body is used to obtain the trajectory and haptic information to generate the trajectory of the slave biped robot in real time. Lateral motion of the center of mass of the biped is constrained in this experiment. Also, it is considered that no communication delay is presented in between the two systems in this experiment, and they are not discussed in this paper. Since a direct motion transmission is used in the proposed method, this method is quite straight forward and a simultaneous walking can be realized at the same time with high performance. Also, it does not require an exact dynamic model of the biped or specific method to plan the trajectory. The gait pattern of the biped is directly determined by that of the human. Also, the operator can feel the remote environment through the exoskeleton robot. Results obtained from the experiments validate the proposed method.

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Development of small-diameter haptic flexible gripping forceps robot

Matsunaga T., Ohnishi K., Wada N., Kitagawa Y.

IEEJ Transactions on Industry Applications (IEEJ Transactions on Industry Applications) 139 ( 12 ) 966 - 972 2019

ISSN 09136339

© 2019 The Institute of Electrical Engineers of Japan. Robotic technologies are being increasingly utilized for medical treatments to support surgeons and reduce the burden to patients. Flexible endoscopic surgical systems with an endoscope and flexible forceps robots are state-of-the-art devices that are expected to realize more difficult and less invasive surgery. Surgeons teleoperate these flexible forceps robots as their own hands and conduct various medical tasks. The wire-driven mechanism is applied to many flexible forceps robots to transmit the driving force to the tip of the robots in a narrow space. However, the flexible structure makes it difficult to control the wire-driven robots and implement the haptic technologies to realize safer surgery. In this paper, a force sensor-less, small-diameter flexible forceps robot with the ability to transmit haptic sensation is presented. The driving part at the tip of the flexible part, composed of a small actuator with a reduction mechanism, realizes the miniaturization of the robot. Haptic information is estimated by low resolution position information. The bending of the flexible part with electric wires does not deteriorate the performance of the end effector. The performance of the haptic flexible forceps robot is evaluated through experiments.

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Fiber suspended micro force transmission system using scaling bilateral control

Hangai S., Nozaki T., Ohnishi K.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society) 4575 - 4580 2018.12

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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Development of flexible haptic forceps based on the electrohydraulic transmission system

Ogawa K., Ibrahim M., Ohnishi K.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics) 14 ( 12 ) 5256 - 5267 2018.12

ISSN 15513203

© 2018 IEEE. Minimally invasive surgery (MIS) has many benefits, e.g., unnecessary trauma and blood loss can be minimized by opening tiny surgery scars, recovery process of patients can be lessened, and the possibilities of complications can be decreased. The natural orifice transluminal surgery (NOTES) is one of the MIS surgical methodologies. NOTES surgery is performed using an endoscope. This methodology does not rely on making holes to patients' body to insert the medical instruments. Although some medical robots for NOTES have been proposed, current robots mainly suffer from the absence/limitation of haptic feedback to the surgeon's hands. In order to overcome this problem, this paper proposes electro hydraulic transmission system (EHTS) based forceps. The EHTS is a remote actuation system using fluid energy. By using the EHTS, the classical position and force transmission losses will not be influenced by the tube's shape. The validity of the proposal and its advantages have been experimentally verified and presented in this paper.

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An estimation method of end-point impedance based on bilateral control system

Okano T., Ohnishi K., Murakami T.

Advanced Robotics (Advanced Robotics) 32 ( 21 ) 1151 - 1167 2018.11

ISSN 01691864

© 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group and The Robotics Society of Japan. This paper aims at developing an estimation method of end-point impedance. Human operators are constantly changing their end-point impedance for adapting to the surrounded environment and executing some complicated tasks, and it is highly meaningful to investigate these variations for the further understanding of human motion. Most of the conventional researches, however, have considered non-contact-point impedance or tasks that is only holding the vibrated sticks due to the experimental constraints. This paper proposes the estimation method of end-point impedance by using bilateral control system. The extra signal is added to the force controller for the impedance estimation. In addition, the effect of the bilateral controller is estimated and removed from the impedance estimation process for securing the applicability of moving tasks. The proposed method was validated through simulations and an experiment. The experimental result showed that the end-point stiffness can be estimated properly even if the operator robot was moving and changed its end-point impedance.

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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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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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Comparative study of soft motion for motion copying system with environmental variations

Okano T., Oboe R., Ohnishi K., Murakami T.

IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM (IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM) 2018-July 646 - 651 2018.08

ISSN 9781538618547

© 2018 IEEE. Technologies for the skill succession and machine automation are strongly demanded in some developed countries under the circumstance of declining working population due to the lower birth rate and the aged society. Motion copying system (MCS) is one of the methods for the skill succession and machine automation. MCS is able to play back the saved motion in the case that the environmental conditions between the saving and the loading phases are the same. Conventionally, the pure position controller, the pure force controller, or Hybrid Position and Force Control (HPFC) is applied to MCS. The reproduction performance is, however, degraded when the environmental variations happen. In such case, impedance control is applicable to MCS instead of HPFC. The purpose of this paper is to conduct the comparative study of some control strategies: position control, force control, HPFC, the Position-Based Impedance Control (PBIC), and the Force-Based Impedance Control (FBIC), and clarify which control strategy is appropriate for the tasks. Simulations were conducted for supporting the argument.

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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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Identification method of environmental stiffness using haptic forceps for brain surgery

Aoki M., Shimon T., Matsunaga T., Mizoguchi T., Shibao S., Sasaki H., Ohnishi K.

IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM (IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM) 2018-July 207 - 212 2018.08

ISSN 9781538618547

© 2018 IEEE. In surgical field, a technique of haptic transmission solves various problems such as limitation of visual field in minimally invasive surgery (MIS), operation mistakes, and so on. Generally, haptic transmission is used in large-scale robots whose end-effector is located in the remote side from the operator. In order to naturally utilize the technique of haptic transmission, it should be implemented in the tools which are frequently used by surgeons. This paper proposes a master-slave integrated haptic forceps like a pincet. The identification method of the environmental stiffness that the developed forceps contacts is proposed in order to consider the safety of operation. Assuming neurosurgery, the experiments using imitation models of brain tissue verified that the slight difference of the stiffness between a healthy tissue and a tumor can be recognized. Experimental results showed that the proposed forceps can be operated properly and the environmental stiffness is measured accurately. It also showed that by the scaling method of the bilateral control system, the identifications of the environmental stiffness became clearer.

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Compensation Method for Environmental Variations of Motion Reproduction System Based on the Different Control Impedance

Okano T., Ohnishi K., Murakami T.

IEEE International Symposium on Industrial Electronics (IEEE International Symposium on Industrial Electronics) 2018-June 1045 - 1050 2018.08

ISSN 9781538637050

© 2018 IEEE. Some developed countries will encounter the shortage of working population, and machine automation is considered as one of the promising methods to overcome its issue. This paper considers Motion Reproduction System (MRS) as a method of the machine automation. MRS can be easily repeated the executed motion; however, this system is sensitive to environmental variations. One of simple countermeasures is introducing compensation values that are designed based on the environmental variations, but these values contain errors and degrade the motion reproduction. This paper proposes the modification of control impedance on the basis of the type of environmental variations, and the trustworthy information is much more weighted. The effectiveness of the proposal is verified through simulation and experiments.

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Evaluation of Gait Phase Detection Methods for Walking Assist Robot

Tawaki Y., Okano T., Murakami T., Ohnishi K.

IEEE International Symposium on Industrial Electronics (IEEE International Symposium on Industrial Electronics) 2018-June 1051 - 1056 2018.08

ISSN 9781538637050

© 2018 IEEE. Lower paralysis interrupts the mobility and depresses quality of life. Some incomplete paraplegia have an ability to walk in rehabilitation. However, incomplete paraplegia consumes larger energy for the gait motion than able-bodied people. Therefore, it is difficult for them to walk a long time. To solve this problem, many walking assist exoskeletons have been developed. In the case of walking assist, assist timing is one of the essential factors. The mismatch of assist timing interferes user's motion, thus it is required to adjust the assist timing. To control the assist timing, gait phase detection methods are used. Gait motion is divided into several phases. Many researchers introduce the gait phase detection method to control the assist timing. However, there is a mismatch between assist torque and ideal torque which is required by the user. There are no researches to evaluate the gait phase detection methods based on the analysis of the transition of assist torque required by the user. The purposes of this research are to propose the novel FSBM and evaluate the gait phase detection methods. In the experiment, a subject walks on the treadmill with wearing knee exoskeleton. The motor of the exoskeleton is controlled by the bilateral controller. Therefore, the assist torque can be adjusted to be suited to the user by manipulating master side motor. After the experiment, the assist torque and detected gait phases of proposed FSBM are compared to the conventional methods.

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Time delay compensation for force controller in bilateral teleoperation system under time delay

Tashiro T., Shimono T., Mizoguchi T., Ohnishi K.

Proceedings - 2018 IEEE 15th International Workshop on Advanced Motion Control, AMC 2018 (Proceedings - 2018 IEEE 15th International Workshop on Advanced Motion Control, AMC 2018) 649 - 654 2018.06

ISSN 9781538619469

© 2018 IEEE. Time delay compensation is very important in the teleoperation field because time delay deteriorates the system performance and stability. Therefore, a lot of research about time delay compensation have been proposed and developed. One of the effective methods, communication disturbance observer (CDOB) has realized the time delay compensation for the position tracking in bilateral teleoperation. Thanks to CDOB, the smooth operation has been achieved. However, the precise force matching has not been achieved yet by any methods. To solve this problem, the time delay compensation method for the force control system has been proposed. This method realizes the precise contact force control under time delay. Therefore, the time delay compensation method is extended to bilateral teleoperation in this paper. In other words, the time delay compensation for the force controller in the bilateral teleoperation system is proposed toward the precise force matching. The validity is confirmed by the experiments.

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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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Disturbance observer and kalman filter based motion control realization

Phuong T., Ohishi K., Mitsantisuk C., Yokokura Y., Ohnishi K., Oboe R., Sabanovic A.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 7 ( 1 ) 1 - 14 2018

ISSN 21871094

© 2018 The Institute of Electrical Engineers of Japan. Many effective robot-manipulator control schemes using a disturbance observer have been reported in the literature in the past decades. Besides, the disturbance observer combined with the Kalman filter has attracted the attention of researchers in the field of motion control. The major advantage of a motion control system based on the Kalman filter and disturbance observer is the realization of high robustness against disturbance and parameter variations, effective noise suppression and wideband force sensing. This paper presents a survey of motion control based on the Kalman filter and disturbance observer, which have been previously introduced by the authors. Several control schemes, as well as formulations and applications of the Kalman filter and disturbance observer, are described in the paper. The performance and effectiveness of the control schemes are evaluated to give a useful and comprehensive design of the Kalman filter and disturbance observer in various motion control applications.

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Active motion evaluation by mechanical power factor analysis based on specific frequency component

Osada S., Shimono T., Mizoguchi T., Ohnishi K.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 7 ( 3 ) 244 - 249 2018

ISSN 21871094

© 2018 The Institute of Electrical Engineers of Japan. This paper proposes a new approach of mechanical power factor analysis for evaluating human active motion. The mechanical power factor is affected by the motion trajectory of an evaluation object. Therefore, in active motion, unified evaluation is difficult using the conventional analysis method. In this study, the power factor evaluation of active motion is realized by applying the perturbation from the evaluation system and using its frequency component for power factor calculation.

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