We have developed biped robots with a passive dynamic walking mechanism. This study proposes a compass model with a wobbling mass connected to the upper body and oscillating in the horizontal direction to clarify the influence of the horizontal dynamics of the upper body on bipedal walking. The limit cycles of the model were numerically searched, and their stability and energy efficiency was investigated. Several qualitatively different limit cycles were obtained depending mainly on the spring constant that supports the wobbling mass. Specific types of solutions decreased the stability while reducing the risk of accidental falling and improving the energy efficiency. The obtained results were attributed to the wobbling mass moving in the opposite direction to the upper body, thereby preventing large changes in acceleration and deceleration while walking. The relationship between the locomotion of the proposed model and the actual biped robot and human gaits was investigated.

Our research team has been developing biped robots based on the nature of passive dynamics. We aim to both investigate the effect of wobbling mass and apply the findings to biped robots to achieve high-performance running. We used an elastically supported wobbling mass in the trunk of biped robots because humans utilize their elastic organs in the upper body and arms to improve running performance. To investigate the characteristics and mechanisms of passive dynamics of the wobbling mass focusing on the vertical ground reaction force, we used a simple model equipped with an elastically supported wobbling mass and analytically derived periodic solutions. The normal mode analysis of the obtained solutions explained the mechanism under which periodic solutions are achieved, and analytic solutions showed similar vertical locomotion to human running and suggested the mechanism under which high-performance locomotion is achieved from the viewpoint of the ground reaction force and energy efficiency. Based on these solutions, we conducted experiments using a prototype and a biped robot equipped with wobbling mass. Experimental results showed similar characteristics in the vertical movement to the simple model and human running. These findings will help improve our understanding of biped running and contribute to producing human-like running of biped robots.

This paper aims to develop a wearable tactile sensor for measuring skin vibrations using a polyvinylidene fluoride (PVDF) film, which is a polymer piezo material. The sensor is worn on the finger pad where is remote from contact fingertip and detects skin-propagated vibrations when fingertip touches an object. The proposed sensor allows users to touch with bare fingers and to conduct active touch. A transfer function from vibrations applied on the fingertip to the sensor output is expressed by using a finger model, a sensor model, and an electric model of the PVDF film. On the basis of the transfer function, frequency response of the sensor is measured and estimation of vibrations is tested. Furthermore, the sensor output is investigated for three materials with different textures. Results show the validity and availability of the sensor.

We have developed a forceps-type tactile sensor for palpation of a tumor in laparoscopic surgery. The sensor responds to contact position and force at deformable cavity in the sensor probe by using acoustic reflection. The sensor has high applicability for laparoscopic surgery because of its simple structure and disuse of electrical elements within inserted part into patient's body. In this study, we try to measure softness of a contact tissue by using the sensor. Human can estimate softness from contact area and force. Indentation depth is not always required for softness perception. This perception mechanism suggests that our sensor has a possibility for softness measurement because the sensor can respond to contact position and force. Softness measurement contributes to tumor localization and improvement of diseases database. First, the sensor output characteristic is investigated for different soft samples. Then, a method of stiffness measurement using the sensor outputs is proposed. Experimental results show that the sensor has the capability of softness measurement without any additional sensors.

Haptic perception is bidirectionally related to the exploratory movements. This means that exploration influences perception, but also perception influences exploration. We can optimize/change the exploratory movements according to the perception and/or the task, consciously or unconsciously. In this paper, a tactile sensing system including bidirectionality is proposed and its potential and application to laparoscopic surgery are discussed. The proposed system is composed of a tactile sensor and a tactile display. The tactile sensor is mounted on a forceps, and the tactile feedback based on the sensor output is provided by using the tactile display. The user can feel sensor outputs and adjust the forceps manipulation according to the environment and the target. This leads to collect adequate sensor outputs. Implementing the bidirectionality gets the most out of the capability of the tactile sensor. Furthermore, the developed system might have an additional effect due to using the tactile display to the other hand, not to the hand with the forceps. It is an enhancement of haptic perception by tactile feedback to distant part. The developed system is introduced and establishment of the bidirectionality and its effect are discussed. Psychophysical experiments on the enhancing effect are conducted. Experimental results show a potential of the proposed tactile sensing system.

The development of modern technologies, touch and/or tactile sensors have been well-developed, exploring various possible methods of transduction and available in many commercial products. The demand for more friendly and safe products, such as household robots, is growing up day by day. But the issues of tactile sensors such as wiring and robustness still remain. By researching human mechanoreceptors, we got an idea of a novel type of tactile sensor based on tissue engineering, which is expected to provide some solutions for those issues. In this paper, we propose the basic concept of tactile sensor based on tissue engineering and the hypotheses of approaching methods.

In this paper, a compliant parallel mechanism with high precision and a wide working area is presented. A compliant parallel mechanism is a parallel mechanism in which all of the joints are deformable elastic joints. The presented mechanism is composed of circular compliant joints that have been inspired by Drakaea, which is an orchidaceous species. From our analytical and experimental tests, it was revealed that these circular compliant joints have desirable characteristics for composing a compliant parallel mechanism. Based on these primary experimental results, we developed a 3-DOF compliant parallel mechanism for an optic component positioning machine. The prototype evaluation tests revealed the mechanism's advantageous characteristics.

In this paper, we introduce a further optimization of morphology of compliant joint based on FEM analysis for a compliant-parallel mechanism with a wide working area and a high accuracy. Compliant-parallel mechanism is the mechanism that all joints are composed by compliant joints in a parallel structure. In the integration of compliant and parallel mechanism, the motion of compliant joints can be guided by mechanical constraints from the parallel structure; thus the mechanism can be precisely driven. However, since compliant joints generally have a limited working area due to limitation in their structural deformation, the working area is commonly limited in micrometer-scale. Designing the compliant joints within a wide range of working area presents us a new challenge: the joints should be elastic for the desired direction, but also rigid for non-desired direction to be deformed. From these requirements, the morphology of the compliant joint was optimized by FEM analysis, and newly serially layered-flat spring compliant joint was developed. The developed compliant joint was implemented on a parallel mechanism as a high precision micro-assembly system for optical components. The prototype enabled 50×50×5 mm of working area within 0.71 mm of repeatable accuracy. From these results, the effectiveness of the morphological optimization for compliant joint was shown.

Human tactile perception incorporates two important characteristics - self-reference and bidirectionality. Self-reference is an important factor when evaluating tactile sensations. Bidirectionality contributes to sensing capability enhancement. In this paper, a tactile sensor including self-reference and bidirectionality is presented. The sensor with two microphones is mounted on a human finger. Users can apply the sensor while retaining their normal tactile perceptions and simultaneously obtaining sound and skin deformation data based on the mechanical interaction between the finger and the object. Experimental results on roughness evaluations and convexity detections show the validity of the proposed sensing method and its potential for use in various applications.

Passive running robot can run down shallow slope with no energy source without gravity. The robot can generate a stable limit cycle. Dynamics of passive running is very interesting target and important for developing the robot and understanding the human locomotion. By the way, running high jumper can jump very high. The point of jumping is to transfer horizontal velocity into lifting momentum through the hinged-movement. In this paper, we demonstrate the experimental passive running based on the hinged-movement. Moreover, we derive the fixed point of the passive running, and analyze its stability.

The aim of this study is the development of a human-friendly tactile sensor for measuring softness, sliminess, smoothness, and so on. We have proposed active tactile sensing method using balloon expansion. A balloon is contacted with an object and expanded by using fluid. Tactile information is evaluated by measuring the expansion process. In this paper, we developed a sensor system using syringe. It is a compact system and can ensure enough safety for human body tissues in safe contact, using no electric power, and sterilization. Pressure changes and volume changes of the balloon can be measured together in the balloon expansion. First, overview of the developed sensor system is presented. Next, composition of the sensor system and the sensing process are presented. Then, experiments using the developed sensor are conducted on samples with different stiffness and surface conditions. Features extracted from sensor outputs indicate that the sensor can know the difference both the stiffness and surface condition. The results show the validity of the proposed sensor system.

The passive walker with knees can naturally execute the leg motion by the dynamics of legs under the gravity only. Circular arc foot is very important for the leg motion. In this paper, the dynamical effects of the arc foot, which can keep the knee joint of stance leg straight only by the stopper and can enhance the flexion of knee joint of swing leg, are discussed. Also, its geometrical negative effect is examined. Finally, the desired arc foot is designed and the actual effects are confirmed by a walking experiment.

In our earlier work, we showed that high stability of passive walking can be achieved by the global stabilization principle of fixed point. The principle has been established, providing that the state just after heel-strike exists at the next step. However, this condition may not always hold. The passive walker with knees can execute the leg-swing motion with no control, only by gravity effect. Unfortunately, while the walker takes a step forward, the swing leg may strike its toe on the slope at unsuitable point. Therefore, understanding of the mechanism of leg-swing motion is very important for assuring the next step. In this paper, we focus on the leg-swing motion of passive walking, and demonstrate the mechanism of the flexion and extension of knee joint of swing leg.

This paper presents the development of an active tactile sensor using fluid. Measurement of stiffness and surface conditions, such as sliminess, smoothness, and others, of body tissue is discussed. This sensor is made of a silicone balloon catheter. The balloon is contacted with a soft object and expanded by using fluid. In the process of the expansion, the balloon pushes the object and the contact surface of the balloon slips or sticks. These phenomena depend on stiffness and surface conditions of the object. The expansion can be evaluated by measuring the flow of the fluid. The balloon that is a sensing element is very soft and flexible and does not need electricity. This sensor is available as a medical sensor since it provides safety for human. Experiments using the sensor are carried out on soft samples with various stiffness and surface conditions. It is confirmed that the sensor output are different from each sample. Furthermore, some experiments under different conditions on inner pressure and load are conducted. The results show that the sensor has a potential to measure stiffness and surface conditions.

A passive walker with knees can walk down gentle slope in a natural gait and can exhibit a stable limit cycle. Though the passive walker is simple, it is a sort of hybrid system which combines the continuous dynamics of leg-swing motion and the discrete event of leg-exchange. We focus on the mechanisms of generation and stabilization of a fixed point of passive walking. We propose a generation method of fixed point based on its physical structure. We derive the local stabilization control method from a stability mechanism of a fixed point of passive walking.

In this research, a buried suture simulator is developed from attention that there is a most complicated diversity in plastic surgery. Buried suture is one of suture techniques with difficult usage. In comparison with normal suture, buried suture needs more care because it is difficult to handle it. Moreover accuracy of surgical techniques or effect of skill on postoperative deformation are unknown. Furthermore buried suture have two advantages; less mark of wound on cosmetic advantage, and no necessity to thread removal on clinical advantage. Buried suture simulator developed from the two major needs is available in each need. One is manipulation simulator for experience, study and training through manipulation from high difficulty skill. The other is deformation simulator for confirmed postoperative deformation that has an effect on difference of suture pattern from clinical point that is largely-concerned with QOL (quality of life) of a patient. In suture simulator, usually operating time or efficiency and the number of mistakes as typified by failure in gripping an object are the points of the quantitative evaluation. In this research, keeping the evaluation of the postoperative deformation in mind, a suture simulator that can express 3D deformation of wounds and those vicinities is developed. The elemental technologies of the developed simulator are described. Moreover the effect of passing point in suture exerted on the post-operative ligation deformation is considered

Passive walker with knees can walk down shallow slope in a natural gait and can exhibit a stable limit cycle. Though the passive walker is mechanically simple, it is a sort of hybrid system that combines the continuous dynamics of leg-swing motion and the discrete event of leg-exchange. In this paper, we focus on the mechanism of fixed point. We demonstrate a physical principle of gait generation and its stabilization derived from the mechanism of fixed point. Based on the principle, we made a simple improvement on passive walker with knees. The passive walker could have high stability, and could walk on treadmill for 4010 steps

Modeling of friction force is cumbersome because of its discontinuity at zero velocity. This paper presents a set of discrete-time friction models for the purpose of haptic rendering and virtual environment construction. These models allow friction to be treated as an admittance-type or impedance-type element of a virtual environment. They are derived from implicit Euler integration of Coulomb-like discontinuous friction and linear mass-spring-damper dynamics, and have closed-form expressions. They include rate-dependent friction laws, and their extension to multidimensional cases is easy in most practical cases. The validity of the models is demonstrated through numerical examples and implementation experiments

Friction force is cumbersome in numerical simulations due to its discontinuity at zero velocity. Fixed-step simulation techniques are especially desirable for control purposes, such as haptic friction rendering and friction compensation. Previous techniques have difficulties especially in numerical robustness and extensibility to multidimensional cases. This paper proposes two discrete-time friction models that can be used in fixed-step simulations. They can be used in multidimensional space, and can capture arbitrary velocity-dependent friction phenomena. The first one is a discrete-time discontinuous model. This model determines the friction force so that the velocity reaches zero in finite time by using the values of the mass and the timestep size. The second one is a discrete-time continuous model, which is a serial coupling of the discontinuous model and a linear viscoelastic element. This model is useful for haptic rendering because it is formulated as a velocity-input, force-output system. The second model can be extended into a more sophisticated friction model, which exhibits a hysteresis behavior in the presliding regime. Results of numerical simulations and an experiment are presented.

Human-machine cooperative systems have been proposed. Most of them consider carrying, positioning and assembling tasks. Precise tracking tasks are also required in factories. However, an assist system for tracking task has not been studied well. In this paper, we aim to realize the human-machine system that assists a tracking task. In order to achieve the goal, the virtual friction field is proposed. Isotropic and anisotropic friction fields are presented and they are applied to the rotating object which should be tracked. The tracking task experiments are carried out and it is shown that the virtual guide of the friction improves the tracking performance effectively.

This paper introduces a device for enhancing detection of surface undulation through active touch. This device, which we call a “tactile contact lens,” is composed of a sheet and numerous pins arranged on one side of the sheet. Experimental results show that a small bump on a surface can be detected more accurately through this device than by bare finger and than through a flat sheet. A mathematical analysis of this phenomenon suggests two possible explanations for this phenomenon. One lies in the lever-like behavior of the pins. The pins convert the local inclination of the object surface into the tangential displacement of the skin surface. The second is the spatial aliasing effect resulting from the discrete contact. Due to this effect, the temporal change in the skin surface displacement is efficiently transduced into the temporal change in the skin tissue strain. The results of this analysis are then discussed in relation to other sensitivity-enhancing materials, tactile sensing mechanisms, and tactile/haptic display devices.

In the bilateral teleoperator systems, transferring tactile information from a slave to a human operator is very important in order to improve the presence in the master side. The coiled nerve structure of the Meissner corpuscles can separately detect stretch and shear deformation of the skin that is caused by various frictional conditions. Based on this property, a biomimetic coiled tactile sensor involved in the non-uniform elastic skin has been developed in this study. In this paper, it is confirmed that this novel sensor can measure a friction coefficient just after the contact. Furthermore, the lifting of the slippery tapered object by the pinch grip is dealt with as a precision task. In the experiment of teleoperation, the human subject could adequately regulate the coordination between the grip force and the vertical lifting force by utilizing the frictional information from the tactile display.

Passive walking robot can dynamically walk down with natural gait by the interaction between walker's dynamics and environment (slope). This robot exhibits a stable limit cycle and its gait bifurcates for larger slope. Analysis of dynamics of passive walking may be useful for understanding human locomotion and development of walking machine. In this paper, we analyze dynamics of passive walking from the aspect of "storage energy" and "supply rate". We also demonstrate that a stable fixed point becomes unstable when 1-periodic gait turns 2-periodic.

Passive walking robot can dynamically walk down with natural gait by the interaction between walker's dynamics and environment (slope). This robot can exhibit a stable limit cycle and its gait bifurcates for larger slope. Analysis of dynamics of passive walking may be useful for understanding human locomotion and development of walking machine. In this paper, we focus on the mechanism of limit cycle. And, we demonstrate that the leg exchange plays the important role in a stable limit cycle. We also investigate the behavior of stability of fixed point for short and long period gaits from analysis of eigenvalues.

In micro-teleoperation, such as micro telesurgery, a scaling problem is one of the most important problems. The human operator must be able to identify the micro-environment and execute well the micro-teleoperation. In this study, a human-centered scaling is suggested. In the developed micro-teleoperation system, the human operator can choose the optimum scaling parameters in consideration of his ability of perception and motor control.

In this study, a novel teleoperation through a spherical display is discussed in the framework of mixed reality. From the viewpoint of the recognition of environment and the maneuverability of teleoperator, it is desired that one should be able to deal with the teleoperation like the usual operation and get the feeling of directly manipulating objects by the tool. This study accomplishes this goal by reconstructing the slave environment into a compact spherical display at the master side and realizing accurate visual/haptic registration. The validity of proposed system is demonstrated by experiments of teleoperation.

Force-reflection is significantly important in complex teleoperations. This study aims to develop a practical force-reflecting teleoperator through the Internet, and supposes the time delay in the order of several hundred milliseconds. Since the transmission delays existing in network vary rapidly and possibly randomly, it is very difficult to ensure the stability. Accordingly, in this paper, the time-varying controllers, which are adjusted to the round trip time delay observed online are designed based on the framework of the H/sub /spl infin// gain-scheduling. The validity of the proposed method is demonstrated by experiments of the bilateral teleoperation through the Internet.

In this study, the design of controllers for the master-slave system is discussed on the basis of the H/sub /spl infin//-optimal control theory. A few controllers that achieve given performance specifications for the free motion and the constrained motion are designed in order. Especially, by considering a variation of time delay, a time-varying controller incorporates to adjust to the current time delay is designed in the framework of the gain scheduling. This control strategy typically achieves higher performance in the face of large variations in operating conditions. The effectiveness of proposed method is confirmed by the experiments and the simulations.

The purpose of this study is to realize the bounce gait in articular-joint-type quadruped robots. We first develop a new robot which can realize bounce. A simulator is then made for the purpose of analyzing dynamic walking and efficiently developing its control methods. We formulate the leg-support-exchange phenomenon using Lagrangian impulsive equation. The control method is discussed, and the results of computer simulation are shown. Experimental results are also presented.

In biped locomotion systems, the angular momentum of the whole system can be taken as a good index, as seen from the law of conservation of angular momentum. A control method which divides the walking into motions in the sagittal plane and in the lateral plane has been adopted. For motion in the sagittal plane, the angular momentum is placed close to a smooth reference function given in advance by controlling the ankle torque of the supporting leg. For motion in the lateral plane, the motion control is treated as a regulator problem with two equilibrium states. The effectiveness of the proposed control method has been examined by experiments with the BLR-G2 walking robot. The BLR-G2 achieved 3-D walking at a speed of 0.35 m/s.>