Published papers

© 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.

© 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.

© 2019 IEEE. This paper proposes a new multi-layered axial motor. It is designed as a core-less motor. A core-less motor does not generate cogging torque but generates less torque than a motor including core. In the proposed motor, the multi-layered structure is applied in order to improve torque. Multi permanent magnet layers and multi coil layers are arranged alternatively in the axial direction. Because flux density reaching coil layers is improved by the multi-layered structure, torque is improved. By 3D finite element method analysis, the relationship between torque and the ratio of permanent magnet to coil is analyzed. The relationship between torque and the number of layers is analyzed. Moreover the relationship of the outside diameter between the permanent magnet layer and the coil layer is analyzed. Based on the analysis, the experimental model of the multi-layered axial motor is designed.

© 2019 IEEE. This paper examines relationship between haptic sense transmission versus wireless network communication. Network communication is a big issue in haptics research area. It is well studied that time-delay, jitter, and packet-loss deteriorates the performance of haptic sense transmission. Transparency is well known evaluation criteria to examine the performance of haptic transmission. The uniqueness of this paper is that the evaluation is examined in real wireless communication environment. The throughput in the system depends on several different disturbances in wireless communication. The paper examines the performance of haptic system from the aspects of transparency. Series of experimental results supports the paper.

© 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.

© 2019 IEEE. Reduction of burden on patients and surgeons is an issue in the medical field. Robotic surgery utilizing teleoperation robots is a method to realize minimally invasive surgery and support surgeons. Structure of surgical robots can be divided into robotic surgical tools and robotic platforms. Robotic platforms have multi degree of freedom (DoF) arms to mount robotic surgical tools and functions to change workspace of the end effector of robotic surgical tools by its large movable range. Therefore, large output to support robotic surgical tools, precise motion, and enough movable range are necessary for the robotic platforms. In this paper, a novel multi DoF robotic platform with two arms and a robotic surgical tool are presented. The robotic platform consists of large circular linear motors which can generate large output force and realize remote center of motion. As the robotic surgical tool, a master-slave three DoF forceps robot which has ability to transmit haptic sensation to operators is developed. In an experiment, the robotic platform with the slave of the three DoF forceps robot is teleoperated to validate the performance of the robots.

© 1982-2012 IEEE. Human haptic perception system is complex, involving both cutaneous and kinesthetic receptors. These receptors work together and enable human to perceive the external world. To simulate immersive interaction with virtual objects in virtual reality scenarios haptic devices are desired to reproduce multiproperties of virtual objects, support multigestures of human hands to perform fine manipulation, produce haptic stimuli for simultaneously stimulating multireceptors (including cutaneous and kinesthetic receptors) of human haptic channel, and thus invoke realistic compound haptic sensations. In recent years, such multimodal haptic devices have emerged. In this paper, we survey the latest progress on multimodal haptic devices, identify the gaps, and put forward future research directions on the topic.

© 1982-2012 IEEE. Disturbance observer (DOB) has been one of the most widely used robust control tools since it was proposed by Ohnishi in 1983. This paper introduces the origins of DOB and presents a survey of the major results on DOB-based robust control in the last 35 years. Furthermore, it explains DOB's analysis and synthesis techniques for linear and nonlinear systems by using a unified framework. In final section, this paper presents concluding remarks on DOB-based robust control and its engineering applications.

© 2020 Japan Society for Precision Engineering. All rights reserved. For non-deconstructive generator inspection, robots which can crawl in a gap of a rotor and a stator have been developed. Since the robot should be enough thin to crawl in the gap, the inspection devices also need to be compact. Percussion is a method to detect the stator wedge looseness. Since echo vibration excited by striking the target is analyzed in this method, the device requires two functions: A striking function and a sensing function. Basically, two devices such as a hammer and a microphone are utilized to achieve the functions. In this paper, a percussion device with the force control technique and the inspection method to detect the stator wedge looseness are proposed. Since the proposed device can not only control the striking force but also sense the reaction force by itself, it is expected that the device can be compact. Moreover, in the proposed method, inner stator slot model parameters are estimated by analyzing the gain characteristics of the proposed device. Then, the amount of the stator wedge looseness is evaluated based on the model parameters. The validity of the proposed percussion device and the inspection method are evaluated through the experiments.

© 2020 IEEE. There exist many dental surgery such as orthognathic surgery and an implant operation. Jaw deformity is one of the dental diseases such as an abnormality of occlusion and facial distortion in the shape. To treat jaw deformity, the osteotomy is carried out by human hands. However, drilling a jawbone accurately by oral surgeons is difficult. Recently, surgical robots are attracting attention in the medical field. The researches of surgery supporting systems have been carried out. They have possibilities to avoid unexpected accidents in the surgery, a hands shake and so on. The improvement of the minimally invasive surgery can be expected, thanks to robotic technology. The purpose of this research is the design and development of master-slave dentistry and oral surgery assisting robot. By implementing acceleration based bilateral control, haptic information can be communicated. Moreover, the proposed robot has the serial-parallel hybrid mechanism that can obtain the advantages of a serial mechanism and a parallel mechanism. In this paper, the mechanism of the proposed robot is explained and the performance of the proposed robot is validated by experiments.

© 2019 IEEE. Utilization of haptic sensation for robots has advantages in various fields. Haptic rendering which is a technology to contact with virtual objects will be useful for virtual reality and simulation devices in medical and industrial fields. To realize these applications, technologies to extract environmental information and reconstruct virtual environments have been studied. In this paper, a force sensorless probe to obtain environmental information for a haptic rendering system is presented. Environmental information such as shape and stiffness is automatically recorded by the haptic probe driven by linear motors. By utilizing a large circular linear motor which has circular motion, haptic information of environments which have a two dimensional shape can be extracted by the device with simple structure. In experiments, the haptic probe contacts with an environment which has two kinds of stiffness. The recored environmental information is processed and rendered to an operator by a XY table composed of two linear motors. Experimental results show that the system can capture environmental information and it can be used for haptic rendering.

© 2019 IEEE. Contact task by artifact has been an unsolved problem since its starting in 1940's. After many RDs including the early works in US and the other countries, bilateral control is a strong solution for this issue. Quality of tactile sensation heavily depends on transparency between master and slave. The Hadamard transformation designed in acceleration space gives the high transparency. The real haptics based on this transformation brings not only the vivid sensation of contact task but also two important applications into the coming society. One is a high-quality tele-operation and the other is a playback of skilled motion by human. The real haptics is a key concept in 21st century where QOL should be the fundamental basis of the society. The paper shows some examples of experiments.

© 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.

© 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.

In orthopedic surgery, tasks to cut the vertebra by surgical drills involve the risk of the spinal cord injury. Since the spinal cord injury causes motor and sensory disorder to patients, orthopedists who perform spine surgery must have skills to achieve tasks using surgical drills. Although robotic technologies is being applied to orthopedic surgical operations, support for surgeons in delicate tasks requiring surgeon's skills is insufficient. In this study, a multi functional drill available for both a surgical instrument and a simulator is presented. A linear motor incorporated in the proposed device used as a surgical instrument provides support for operators, while measuring position information and estimating force information. Furthermore, environmental information can be abstracted by haptic information such as position and force information. Virtual environment reproduced by the environmental information is presented by the proposed device used as a simulator. The feasibility of the multi functional drill is confirmed by utilizing functions as a surgical instrument and a simulator.

© 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.

© 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.

© 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.

© 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.

© 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.