Published papers

Purpose: The present study used haptic technology to determine the safe forceps grip force for preventing organ damage when handling the intestinal tract. Material and methods: The small intestines of ten male beagle dogs (weighing 9.5–10 kg) were grasped with the entire forceps for one minute; the small intestines were then pulled out of the forceps and evaluated for damage. The force at which the shaft inside the forceps was pulled to close the tip of the forceps was defined as the grip force. Small intestine damage was classified into macroscopic (serosal defects, hemorrhage, hematomas, grip marks) and microscopic (damage layer to the mucosa, submucosa/muscularis mucosa, inner orbicularis muscle, external longitudinal muscle, serosa/subserosa). Grip marks and damage layer to the serosa/subserosa have been considered as acceptable safety margins when grasping the small intestines of beagle dogs. Results: The macroscopic findings showed that the maximum grip force that produced a 0% incidence of hemorrhage and hematoma was 15 N. At the microscopic level, the maximum grip force that produced a 0% incidence of external longitudinal muscle injury was 15 N, respectively. Conclusions: A grip force of 15 N does not damage the small intestines of beagle dogs.

Teleoperation systems utilizing master-slave systems and video apparatuses are useful for tasks requiring human judgments and skills. Haptic sensation can be transmitted by master-slave systems implementing bilateral control, while visual information is shown to operators by video apparatuses. Furthermore, augmented reality (AR) can be presented to operators by processing visual and haptic information. Operators can move virtual objects in real environment by using teleoperation systems. However, virtual objects cannot interact with real environment, although rendering of virtual objects can be changed according to the positional relation to real environment. The noninteractive characteristics of AR between real and virtual objects restricts application of teleoperation systems. In this paper, a method that enables operators to contact with real environment through a virtual object is proposed. Bilateral control with compliance controller is implemented to a one degree-of-freedom master-slave system as haptic AR. The end effector of the slave robot is hidden by image processing. Instead of the real end effector, a virtual end effector with a virtual object is presented as visual AR. Operators can perform contact motion by the teleoperation system, as if reaction force from real environment is presented through the virtual object. The feasibility of the proposed method is confirmed by an experiment.

© 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.

© 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.

© 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.

© 2019 IEEE. Teleoperation gets a significant attention from the society, and 4ch bilateral control is known as a method to realize the haptics transmission. Its controller is able to achieve the rich haptics transmission, but the performance is degraded under the presence of time-delay due to the interference between the position and force controllers. In particular, its interference becomes larger when position and force scaling are set more than 1 and the mass difference between the master and slave is large. 3ch architecture has proposed to tackle with the performance deterioration when the position and force scaling are set more than 1, but no researches have conducted for considering both the scaling and mass difference. This paper considers the situation that the scaling are set and the mass difference is existed in addition to the time-delay. Oblique coordinate control is utilized, and the superiority of 4ch and 3ch architectures are discussed. The proposal takes the superiority of these two architectures, and its effectiveness was verified through simulations and experiments.

© 2020, Fuji Technology Press. All rights reserved. With the remarkable development of related technologies, the number of robots has been gradually increasing and their presence is becoming much more familiar in our daily lives. The motion copying system (MCS) is utilized as the method for conducting some tasks by robots. This system enables tasks to be reproduced when the environmental conditions are not changed. The task reproduction performance is degraded when environmental variations occur, and human-like adaptable motion is expected to be developed in the MCS. This study reveals the dominant element of motion, and the control strategy is varied at each time in each axis by considering the task realization. The flexibility of motion is learned from both the operator and the task implementation. The task reproduction experiments by MCS are conducted to verify the effectiveness of the proposal.

© 2020, Springer Nature B.V. Reconstructing a pitchfork bifurcation that is destroyed by an exogenous disturbance is important to control it. This paper extends the equivalent-input-disturbance (EID) approach to solve the problem of reconstructing a pitchfork bifurcation when there is an exogenous disturbance for the first time. A nonlinear term and a bifurcation parameter are designed in the system to reconstruct the pitchfork bifurcation. The bifurcation characteristics of the equilibriums of the system are analyzed by exploring the features of the EID-based system. This provides us analytic solutions for a system with a degree higher than four for the first time. Unlike other pitchfork-bifurcation control systems, the EID-based control system only rejects the disturbance and retains the nonlinearity. Numerical examples demonstrate the effectiveness of the presented method and show its superiority over others. The robustness of the reconstruction with respect to measurement noise and control of a pitchfork bifurcation are also shown by the examples.

© 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.

© 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.

© 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.

© 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.

© 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.

© 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.

© 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.

© 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.