In this paper, we show experimental results indicating that tactile mechanoreceptors have non-linear sensitivity to an applied vibration. We focus on the perceptual characteristic of high frequency amplitude-modulated (AM) vibration. It is known that humans can feel AM vibration even when its carrier frequency is higher than the perceivable range. Non-linearity of perception should be taken into consideration for explaining this characteristic. We observed a deformation of the skin when the AM vibration is applied. We found that we can detect an envelope of the applied AM vibration, even when the skin surface deforms as a linear elastic body; whereas harmonic vibratory pairs cannot be perceived. This result indicates that only a squared value of a displacement, which is proportional to strain energy density, cannot explain the non-linearity of mechanoreceptors. These perceptual characteristics should be taken into consideration for designing a tactile display with multi-spectral vibrations. Otherwise, the simultaneous multi-spectral vibrations can affect each other and may change perceptions because of the non-linearity of the perceptual process.

Remote transmission of high quality sense of touch requires the representation of multiple tactile properties and compensation of communication delay. We developed a real-time remote transmission system that can deliver multiple tactile properties using a master-slave robot system. First, we assessed what type of tactile properties should be transmitted and how to connect them in real time. Three tactile properties - roughness, friction, and softness - were transmitted on the basis of the real-time estimated physical properties of three main wavelengths, a kinetic friction coefficient, and spring constants, respectively. Tactile stimulations were generated in synchronization with hand exploration at the master side by using local tactile generation models to compensate for communication time delay. The transmission of multiple tactile properties was achieved by the integration and enhancement of our previously reported methods for vibrotactile displays and tactile sensors. A discrimination experiment using different materials showed the feasibility of the total system involving the three tactile properties.

In this study, a tactile-roughness transmission system applicable to master-slave systems with a communication time delay is developed. The master-side system constructs a local model of target objects placed in the slave-side environment. Tactile feedbacks presented to an operator at the master side are produced by combining the physical properties of target objects in the local model and the kinetic information of the operator. The time delay between the operator's motion and the tactile feedback is cancelled because the stimuli are synchronized with the exploratory motions. The proposed system is applied to the transmission of tactile-roughness. The tactile stimuli presented to the operator are vibratory stimuli whose amplitude and frequency are controlled. These stimuli are locally synthesized by combining the surface wavelength of target objects and the operator's hand velocity. Using the developed tactile-roughness transmission system, an experiment for transmitting the perceived roughness of grating scales was conducted. As a result, the roughness perceived by the operators was found to highly correlate with the roughness of the scales in the slave-side environment with a coefficient of 0.83.

Simple grippers with one or two degrees of freedom are commercially available prosthetic hands; these pinch type devices cannot grasp small cylinders and spheres because of their small degree of freedom. This paper presents the design and prototyping of underactuated five-finger prosthetic hand for grasping various objects in daily life. Underactuated mechanism enables the prosthetic hand to move fifteen compliant joints only by one ultrasonic motor. The innovative design of this prosthetic hand is the underactuated mechanism optimized to distribute grasping force like those of humans who can grasp various objects robustly. Thanks to human like force distribution, the prototype of prosthetic hand could grasp various objects in daily life and heavy objects with the maximum ejection force of 50 N that is greater than other underactuated prosthetic hands.

A small tactile display that can be attached to a mobile terminal device or a handheld game controller will enhance user experience in virtual worlds. This paper proposes an ultrasonic vibrator which has a compact mechanism to produce vibratory stimulation on human skin using a pin array driven by a single piezoelectric actuator. Amplitude modulations of the ultrasonic vibration can generate tactile sensations even if a finger is fixed on the vibrator. To generate enough stimulation to deform the skin, resonance of the piezoelectric actuator was designed. We proposed a new mechanical design method to arrange arbitrary distributions of vibration for the pin array using the principle of a dynamic vibration absorber. Detailed designs were conducted by finite element analysis. We successfully designed a smart vibrator which had a size of 17 times 17 times 3.65 mm and a weight of about 4 g. The vibrator could mount on the joystick of the PlayStation2 controller. Trial experiments of tactile presentation showed that the prototype vibrator could generate vibratory feelings in the range of 30 - 50 Hz and 200 - 300 Hz. In addition, stimulation corresponding to joystick operation generated some rubbing-like sensation.

This Paper presents a hybrid tactile displaying method of realistic texture using ultrasonic vibrator and force display. The aim of this study is to display various realistic tactile senses by controlling multiple factors including roughness, softness and friction sense. First, a tactile displaying system was configured for displaying roughness, softness and friction sense simultaneously by compensating the interference among multiple parameters of ultrasonic vibration and force feedback on multiple tactile senses. Second, by conducting several sensory evaluation experiments, the proposed method for displaying softness and friction senses were verified. The relationship between each control parameter and the tactile senses were quantified as well. Then, material discrimination experiment was conducted. As a result, percentage of questions answered correctly was more than 87.5 in all materials. Finally, the tactile senses of real materials and artificial tactile senses were evaluated using adjectives. As a result, the correlation coefficients between real materials and hybrid artificial tactile senses were quite high at the evaluation items on roughness, softness and friction senses.

Tactile telepresence has been expected to be technology which encourages operators of robotic systems to remotely maneuver objects or recognize materials being touched through robotic arms. In remote environments, temporal disparity in tactile sensations is caused by temporal latency between a touch motion of the operator and a tactile stimulus applied on him. A framework of tactile telepresence systems, which is suitable in remote environments, has been proposed in the present paper. In the framework, a tactile display locally generates the tactile stimulus in synchronization with the touch motion of the operator in order to cancel communication delay. The tactile stimulus is generated by combining the motion and tactile factors, which are sensed by a tactile sensor. The factors are characteristic parameters of objects and effect on tactile sensations. In the present paper, physical parameters of the objects are selected as the factors because the tactile stimuli can be computed using physical models involving the motions and the parameters. Based on the proposed framework, a roughness feeling telepresence system was implemented and successfully transferred a roughness factor to the operator.

This research aims to develop a portable haptic master hand with 20 degrees of freedom (DOF). Master hands are used as haptic interfaces in master-slave systems. A masterslave system consists of a haptic interface that communicates with a virtual world or an end-effector for tele-operation, such as a robot hand. The thumb and fingers are usually modeled as a serial linkage mechanism with 4 DOF. So far, no 20 DOF master hands are developed that can exert perpendicular forces on the finger phalanges during the complete flexion and extension motion. In this paper, the design and development of a portable 4 DOF haptic interface for the index finger is presented. The concept utilizes a mechanical tape brake at the rolling-link mechanism (RLM) for passive force feedback. The systematic Pahl and Beitz design approach is used as an iterative design method. Important design requirements are; perpendicular forces on the finger phalanges, low friction mechanism, easy to control, no backlash, high backdrivability and lightweight

A method is proposed to control human grasping force unconsciously by generating small distributed vibration stimuli on a finger based on a human reflex action against detection of partial slippage of contact. Human beings can increase grasping force before the grasped object slips off the fingers based on afferent signals from tactile receptors that detect the expansion of the partial slippage area. We assumed that vibration stimuli that have an appropriate frequency and distribution generate a virtual sensation of partial slippages and induce a reflective grasping force increase. Grasping experiments with minute distributed vibration stimuli using ICPF (ionic conducting polymer gel film) actuators were performed. Experiments results showed that the effective vibratory frequency was 30 Hz, which is the most sensitive range for Meissner's corpuscles that are closely related to detection of partial slippage. We also found that distribution of vibration stimuli were important to produce human grasping force increase

Carbon micro coil (CMC) tactile sensor, containing CMCs in elastic material, is considered to have LCR circuit. When the sensor is transformed by mechanical force, LCR circuit changes in the sensor. In consequence, the sensor is able to detect various kind of tactile information by measuring impedance. In this paper, we focused on LCR circuit formed by distribution of CMCs. By changing CMC weight percent, we made the sensors in which CMCs are in contact and not in contact. First, we analyzed static characteristics of CMC tactile sensor. When the sensor is under unloaded condition, we measured the relationship between frequency of alternating voltage and impedance. As the result, we found that electrical parameters change with CMC weight percent. When the sensor is under transformed condition, we measured relationship between strain and impedance. As the result, we found that impedance changes by deformation of CMC and change in distance between CMCs. Secondly, we analyzed dynamic characteristics of CMC tactile sensor. We measured relationship between mechanical frequency and impedance by exciting vibration on CMC tactile sensor

This paper discusses the development and control of the master-slave system capable of grasping an object with unknown coefficient of static friction. Partial slip information is known to be essential for conducting stable grasping in teleoperating system. The developed partial slip sensor contains strain gages in several ridges placed on the curvature contact surface of the elastic body. By measuring strain velocity of each ridge with the strain gages, the vibration that occurs due to the partial slip can be detected. We developed the master-slave system with the slave robot uses the developed sensor to detect a partial slip and automatically controls the grasping force. When an operator intentionally decreases the grasping force applied to the master device in order to release an object, the suppressor suppresses grasping force that is automatically increased by the slave robot. Through the grasp manipulation experiment, the validity of the developed system was confirmed

To realize a telepresence system with tactile feedback and force feedback, real-time estimation of various tactile sensation must be conducted. Because several types of tactile sensation consist in touch and human tactile feeling has high time resolution. A man feels active touch extraordinary with time delayed transmission of tactile information. Our proposing human finger mimetic sensor covers three tactile factors, which are roughness, softness and friction of objects to touch. Current tactile telepresence systems represent just one tactile sensation in addition to kinesthetic information. For augmented reality, wider tactile factors must be sensed at a tactile sensor system and transferred to a tactile display system with small time delay. We realized quick estimation of vibrational frequencies of the sensor and softness of objects to regenerate touch feelings to human skin by tactile displays, which usually need time-consuming samples and make it hard to address tactile telepresence system. Quick estimation of vibrational frequency was conducted by emulating impulse emission of Meissner's corpuscles. Quick estimation of Young's modulus of objects was solved by computing strain distribution in a sensor

This paper discusses a novel approach in developing a texture sensor emulating the major features of a human finger. The aim of this study is to realize precise and quantitative texture sensing. Three physical properties, roughness, softness, and friction are known to constitute texture perception of humans. The sensor is designed to measure the three specific types of information by adopting the mechanism of human texture perception. First, four features of the human finger that were focused on in designing the novel sensor are introduced. Each feature is considered to play an important role in texture perception; the existence of nails and bone, the multiple layered structure of soft tissue, the distribution of mechanoreceptors, and the deployment of epidermal ridges. Next, detailed design of the texture sensor based on the design concept is explained, followed by evaluating experiments and analysis of the results. Finally, we conducted texture perceptive experiments of actual material using the developed sensor, thus achieving the information expected. Results show the potential of our approach.

A five-fingered robot hand having almost an equal number of DOF to the human hand is developed. The robot hand is driven by a unique method using ultrasonic motors and elastic elements. The method makes use of restoring force as driving power in grasping objects, which enables the hand to perform stable and compliant grasping motion without power supply. In addition, all the components are placed inside the hand because the ultrasonic motors have characteristics of high torque at low speed and compact size. Applying the driving method to a multi-DOF mechanism, a five-fingered robot hand is designed. The robot hand has twenty joints and DOF. It is almost equal in size to the hand of an average grown-up man. The robot hand is produced, and control experiments are conducted. As a result, the potential of the robot hand is confirmed.

This paper presents a novel type of multi degree-of-freedom ultrasonic motors. Today, in various fields, actuators having multi degrees-of-freedom is needed. In the past, many multi-degree-of-freedom actuators have been developed. However, they are all still large and heavy. Thus, we propose a miniature multi-degree-of-freedom actuator using plural single-phase-driven ultrasonic vibrators. A single-phase-driven ultrasonic motor is known for its miniaturizing facility. On the other hand, it is also known for its lack of output force. Therefore, we proposed to use plural single-phase-driven vibrators and also tried to make one vibrator generate great force. This motor has many small vibrators; each one having four patterns in the thrust direction. By controlling the frequency of each vibrator, we can obtain multiple movements of a movable object. First, we proposed the principles of this motor. Next, we selected vibration modes and designed the size of a vibrator to be 10 /spl times/ 7.5 /spl times/ 0.9 mm/sup 3/ using finite element analysis. Finally, we measured frequency, vibration, and driving characteristics of the vibrators. The maximum thrust was about 3.14 N and the maximum torque was about 6mN-m.

The goal of our study is development of a "tactile mirror" for displaying tactile perception information. A point of distinctive difference between a tactile mirror and conventional tactile displays is that a tactile mirror possesses a feedback mechanism for acquiring the contact state information on the finger pad concerning not force but tactile perception sensation. The primary development concerns human static friction sensation. First, a control method and the structure of a tactile mirror are described. Second, simulation results using FEM for contact analysis and a ANN(artificial neural network) for generating feedback signals are shown. Finally, experiments demonstrating that providing a feedback component accomplish accurate display of static friction sensation with a conventional type of tactile displays.

In this paper, analysis of the dynamics of the ultrasonic motors is introduced. Though static characteristics have in the past been clarified, the dynamic characteristics were still unclear. For the purpose of realizing high speed control of ultrasonic motors, we analyzed the dynamic characteristics through measurement and numerical simulation. Among the different types of ultrasonic motors, we focused on bar-type ultrasonic motors and first measured the step response using a laser Doppler velocimeter (LDV). We measured changing the input parameters and showed the relationship between input parameters and delay, overshoot of the rotational speed of the rotor. Next, we established a mathematical model of the bar-type ultrasonic motor. In our model, we approximated the stator as a rigid disc and torsional spring. We set the discrete spring at the contact area between rotor and stator, and simulated considering stick-slip at the contact area. The results of numerical simulation matched that of the measurements qualitatively and we clarified the dynamics of the contact condition and friction force at the contact area.

In this paper, a mouse-shaped haptic device is proposed. The device solves conventional problems of previously developed devices such as structure and control complexity and operating difficulties. We adopted multiple finger inputs in order to carry out complicated tasks and in order to highly adapt to the environment. To develop the multi-fingered haptic device, we focused on anatomical knowledge and neurophysiology. Since there is a primacy of the visual information over somatic sensation, we believe the movable range of human fingers does not necessarily have to be completely satisfied, i.e. visual information can compensate for the difference between the displacement of the haptic device and that of the slave device in a master-slave system. We applied this feature to miniaturize and simplify the device. To confirm the usefulness of our developed device for a virtual reality system, we carried out three experiments: position control, familiarization and force feedback. The results show the effectiveness of the developed haptic device.

A method is proposed to estimate the friction coefficient between a planar surface and an elastic finger-shaped sensor by only pressing a sensor against the surface of an object. The contact condition between a planar surface and a half-cylindrical finger is considered, using finite-element analysis. The deformation of the elastic finger, contact forces, and strain distribution inside the elastic finger are calculated for various friction coefficients between the finger and the surface. Results show that the shear strain differs when the friction coefficient differs. In addition, in this paper, an elastic finger-shaped sensor made of silicone rubber is designed and constructed. In an experiment using this newly designed sensor, the friction coefficient between the finger and the planar surface is estimated using the strain inside the finger.

In this paper, a method for co-evolving morphology and controller of a real biped walking robot is proposed using evolutionary computation. Although certain control theories exist, such as zero moment point (ZMP) compensation, these theories assume humanoid robot morphology is given in advance. Thus, engineers have to design a control program for a priori designed morphology. If morphology and locomotion are considered simultaneously, we do not have to spend time with trial-and-error. The detailed model of morphology is used for morphology in which the characteristics of the servo module are considered. As the controller, pattern generators are used. The biped walking robot which can walk the longest distance are designed with a two step genetic algorithm. As a result, the detailed model of the robot which can walk the longest distance is generated from limited size of chromosomes.

In this paper, evolutionary designing method of a biped walking robot is proposed and evaluated in comparison with traditional manner. Usually, the structure and control system of robot have been designed separately. Therefore, the structure is given in advance when the control system is developed. This results in a great deal of trial-and-errors. On the other hand, evolutionary designing method carries out these operations simultaneously. Two calculations are conducted of which morphologies are changed (evolutionary designing method) and not changed (traditional manner) during the evolution. As a result, almost the same number of pareto optimal solutions are emerged. However, solutions generated with evolutionary designing method obtain higher fitnesses than the others. This means that evolutionary designing method could be powerful and efficient method for the real robot.

In this paper, we propose a hierarchical control method for manipulation/grasping tasks using multi-fingered robot hands. This method imitates human motion control. Human motion can be divided into two classes, reflex and voluntary movement. Reflex is suppressed by voluntary movement. In the proposed method, a robot hand's grasping control corresponds to human reflex and manipulation control corresponds to voluntary movement. We constructed a controller composed of a manipulation controller, grasping controller and suppresser. The grasping controller has fast feedback but can only execute simple motion. The manipulation controller has slow feedback, and can execute complex motion. Finally, the validity of the hierarchical method is confirmed by computer simulation of various tasks, i.e. grasping, manipulation, and re-grasping motion.

A novel multi-fingered exoskeleton haptic device using passive force feedback has been proposed by the authors. The haptic device solves the conventional problems of previously developed master-slave systems with force feedback, such as oscillations, complex structures and complicated control algorithm. However, some problems still remain in the conventional passive elements. In the present paper, an ultrasonic clutch for multi-fingered exoskeleton haptic device with passive force feedback function is developed. The ultrasonic clutch can solve problems of conventional passive elements, such as time delay, instability, and large size, by using unique characteristics of ultrasonic motor, as fast response, silent motion, and non-magnetic feature. It can also be designed to be smaller than conventional elements due to its simple structure. The clutch locks or releases the rotor by use of ultrasonic levitation phenomenon. First, we have designed the structure of the ultrasonic clutch using an equation of ultrasonic levitation phenomenon, results from structural analysis and finite element (FE) analysis of piezoelectric material of the vibrator. Then we have manufactured the ultrasonic clutch and have conducted a driving experiment. Finally, we have demonstrated that the maximum levitation force is around 20 N and the static friction torque of the ultrasonic clutch is up to 0.14 Nm.

A method is presented to display partial slip in precision grip of humans. Partial slip is important information for precision grip of humans, because the human controls grasping force by detecting expansion of the partial slip area. Therefore, a device that displays partial slip will make it easier for remote controlled mechanical hands to grasp objects, irrespective of the friction coefficient between the mechanical hand and object. To design the device displaying partial slip, we analyzed the deformation of a finger when in contact with a rigid plate using a finite element model. We also analyzed the deformation of the finger section model when in contact with the device that displays partial slip. As a result of the analyses, it is confirmed that there is a possibility in displaying partial slip using a tactile display device, which stimulates the finger through deformation of an elastic body.

This paper describes a new driving mechanism for a miniature robot hand. In developing miniature robot hands for dexterous manipulation, it is necessary to consider miniaturizing and minimizing. The proposed mechanism uses elastic torsion springs and hinges as joints, and the finger is wire-driven from actuators placed outside the robot hand. First, the driving mechanism of a one joint finger is described, and the mechanism is applied to a five-fingered miniature robot hand. The robot hand is one-half the size of the hand of an adult male, and has a total of eighteen degrees of freedom (DOF). The properties of the robot hand are discussed, and are shown to be an effective mechanism for miniature robot hands.

A robot finger is developed for five-fingered robot hand having equal number of DOF to human hand. The robot hand is driven by a new method proposed by authors using ultrasonic motors and elastic elements. The method utilizes restoring force of elastic element as driving power for grasping an object, so that the hand can perform the soft and stable grasping motion with no power supply. In addition, all the components are placed inside the hand thanks to the ultrasonic motors with compact size and high torque at low speed. Applying the driving method to multi-DOF mechanism, a robot index finger is designed and implemented. It has equal number of joints and DOF to human index finger, and it is also equal in size to the finger of average adult male. The performance of the robot finger is confirmed by fundamental driving test.

We present a method for co-evolving structures and a controller of biped walking robots. Currently, biped walking humanoid robots are designed manually on trial-and-error basis. Although a certain control theory exists, such as zero moment point compensation, these theories assume humanoid robot morphology is given in advance. Thus, engineers have to design a control program for a priori designed morphology. It is very time consuming if both morphology and locomotion are considered simultaneously. Therefore, a method useful for designing the robot is proposed. First, simple models for both morphology and controller are used for the dynamic simulation, which are multi-link models as morphology and two kinds of controllers. One is a layered neural network and the other is a neural oscillator. Robots with optimal energy efficiency of walking are designed with the genetic algorithm. As a result, various combinations of morphologies and gaits are generated, and the relationship between the length of each link and moving distance is obtained, which gives an optimal energy efficiency. Moreover, the robots are encoded from the limited size of chromosomes.

A multi-DOF ultrasonic motor has significant potentials for dexterous actuation. The ultrasonic motor provides multi-DOF rotation of a spherical rotor using three natural vibrations of a bar-shaped stator. In this paper, numerical analyses on the multi-DOF ultrasonic motor are conducted. First, a forward model of multi-DOF ultrasonic motor is developed considering the frictional condition between the rotor/stator. Using the forward model, driving state of the multi-DOF ultrasonic motor under arbitrary combination of vibrations is clarified. Second, an inverse model of the multi-DOF ultrasonic motor is also developed. The inverse model is constructed using experienced knowledge about ultrasonic motor and neural network technique. An appropriate input for the multi-DOF ultrasonic motor with regard to arbitrary rotational axis is estimated using the inverse model. The proposed models are available not only for our motor but for all multi-DOF ultrasonic motors.

A new type of master-slave control methodology, which has the merits of both unilateral and bilateral ones, is proposed. The methodology is built on switching the unilateral feedback controls of position and force as required using switching and elastic elements. Proposed methodology not only eliminates the demerits of bilateral control, but also supplies the mechanical force feedback to the operator. It utilizes a feature of human factor that direct displacement feedback is not as important as visual and force feedback. Effectiveness of the proposed method is confirmed by experiments using a developed simple single axis master-slave arm system. Driving test of the experimental devices and sensory evaluations are conducted. As a result, it is confirmed that the methodology successfully provides the sense of touch to the operator of the system.

In this paper, we present a method for co-evolving morphology and controller of bi-ped humanoid robots. Currently, bi-ped walking humanoid robots are designed manually on trial-and-error basis. Thus, engineers have to design control program for apriori designed morphology, neither of them shown to be optimal within a large design space. We propose evolutionary approach that co-evolves the morphology and controller. Two steps of co-evolutions were achieved in a precision dynamics simulator. One is for obtaining the optimal lengths of links using simple multi-link model and the other is for obtaining the optimal geometry of servomotor which is often used for radio control car. Finally, unexpected optimal solutions were discovered. This indicates that a complex design task of biped humanoid can be performed automatically using evolution-based approach, thus varieties of humanoid robots can be designed in speedy manner.

A novel control methodology for master-slave systems using passive force feedback has been proposed by the authors. The methodology solves the conventional problems of previously developed master-slave systems with force feedback, such as oscillations, complex structures and complicated control algorithm. In the present paper a multi-fingered exoskeleton haptic device (master hand) with passive force feedback function is developed. First, the exoskeleton master hand with three fingers (12 degrees of freedom) is designed and implemented. Each finger of the master hand consists of a link mechanism with elastic-shaft joints and clutches. Using link mechanisms, the master hand measures fingertip positions and angles of index finger middle finger and thumb. Furthermore, it also enables passive force feedback to an operator by the same link mechanism used for the geometric measurements. Then, a virtual reality system of human hand is constructed using the master hand and the control methodology. Using the system, sensory evaluations are conducted on human subjects to confirm the usability of the developed master hand and the possibility of the control methodology in the virtual reality system. As a result, the subjects possibly recognize the stiffness of the objects in the virtual environment.

A multi-DOF ultrasonic motor developed by the authors is capable of generating multi-DOF rotation of a spherical rotor using three orthogonal natural vibrations of a bar-shaped stator. The ultrasonic motor is suitable for making small, light weight and simple multi-DOF motion unit. In the present paper, a control methodology for the multi-DOF ultrasonic motor is proposed and a motion control test using the method is conducted. First, an inverse model of the multi-DOF ultrasonic motor is developed using our prior knowledge in ultrasonic motors and neural network technique in order to deal with the redundancy and non-linearity of driving characteristics. Second, a novel control method using the inverse model is proposed. Then, motion control tests are conducted to confirm the ability of the proposed control method. The results confirm that the rotor can be rotated around arbitrary rotational axis using the inverse model, and that the proposed control method does work successfully.

In this paper, morphology of body and neural systems that define the locomotion of multilinked locomotive robots that can adapt to changes in environment are designed using the evolutionary computation. The morphology of the body and neural systems have a close relationship to each other. The model of the robot is designed so that the morphology of the body and neural systems emerge simultaneously. The morphology of the body and neural systems are generated using a genetic programming. The tasks are that the robots move on ground including hills of different heights in the two dimensional lateral simulated world under the effect of gravity. The robots are evaluated based both on a moving distance and an efficiency. As a result, various combinations between the morphology of the body and neural systems of the robots were emerged. The evolved robots were able to go over hills which they had not experienced.

Master-slave active robot hands and endoscopes, which provide dexterous manipulations and wide views like human hands and eyes, are required to be constructed. We have previously developed a multi-DOF ultrasonic motor consisting of a spherical rotor and a bar-shaped stator. The rotor rotates around three perpendicular axes using three natural vibration modes of the stator. In this study, a multi-DOF unilateral master-slave system using the multi-DOF ultrasonic motor is developed. Master and slave arms for the system have similar configurations, so that an operator can easily handle the master-slave system. First, driving characteristics of the multi-DOF ultrasonic motor are clarified experimentally and analytically in order to design the slave arm and its controller. Next, the master-slave arms and the unilateral feedback controller for the master-slave system are developed. Finally, the motion control tests of the system are performed to show the applicability of the master-slave system.

An artificial elastic finger skin for robot fingers was developed for controlling the grasp force when the weight and friction coefficient of the grasped object are unknown. The elastic finger skin has ridges at the surface to divide the stick/slip area. It also has a pair of tactile sensors embedded per one ridge similar to human fingertips. The surface of the whole finger is curved so that the reaction force can be distributed. A finite element (FE) model of the elastic finger skin was developed to perform a dynamic contact analysis using the FE method in order to design the elastic finger skin. The elastic finger skin was then constructed. It was confirmed by calculation and experiment that the incipient slippage of the ridge that occurs near the edge of contact area can be detected. This result is useful for controlling the grasping force when the weight and friction coefficient between the elastic finger skin and grasping object are unknown.

A method for controlling the grasping force when an object is grasped by artificial elastic fingers is proposed. First, the relationship between the stick area and the internal strain distribution of the finger is calculated using FE (finite element) analysis. Based on this relationship, a method is proposed for controlling the grasping force by decreasing the increasing ratio of the tangential force when the stick area is decreasing. Finally, the grasping force is controlled using an actual elastic finger, which is made of silicone rubber and in which strain gages are incorporated. It is confirmed that objects can be grasped using adequate grasping force without complete slippage, even when the weight and the friction coefficient of the objects are unknown.

The authors developed a bar-shaped ultrasonic motor capable of generating a multi-DOF motion. The multi-DOF ultrasonic motor consists of a bar-shaped stator and a spherical rotor. The spherical rotor is rotated around three perpendicular axes by the three natural vibrations excited on the stator. In the present study, the driving and control characteristics around one driving axis, which is perpendicular to the stator's geometric axis, are measured in detail, namely the relationship between the frequency of the input signal and the rotational speed, the relationship between the torque and the rotational speed and the step response of the ultrasonic motor, are measured. The maximum rotational speed and the maximum torque are 183 rpm and 5 mNm, respectively. The rotational speed was controlled successfully.

Humans obtain complex information using different tactile receptors in the skin of the finger. Artificial tactile sensors capable of detecting complex information can be realized by imitating certain characteristics of the human finger, such as the geometry of the finger and the location of the tactile receptors. We analyze the strain distribution that occurs inside an elastic finger having a curved surface when the finger is in contact with an object. Detection of the shear strain distribution pattern is found to be important. In addition a strain distribution sensor is developed, in which strain gages bonded on thin plates are arranged at uniform intervals inside the curved surface of an elastic finger made of silicone rubber. The geometry of the elastic finger is designed by calculating the contact condition between the finger and objects with/without tangential load using FE (finite element) analysis. The fundamental characteristics of the strain distribution sensor are confirmed.