This study proposes a novel technique to display tactile sensation using electro-rheological fluid (ERF). ERF changes its rheological characteristics according to the electric field applied. The ERF used in this study generates relatively high yield stress and behaves as a solid when subjected to a strong electric field. Using this solid-liquid phase transition, we propose a novel device which provides a tactile sensation, i.e., tactile bump display. Applying electric field at a specific position in an ERF chamber, the corresponding ERF behaves as solid at the position. This solid-state ERF gives tactile sensation like a physical bump to a user. We fabricate in this study a prototype, which may realize the above-mentioned idea, and characterize it. We obtained the following results by experiments. First, the tactile bump display could make the users recognize their finger position on a flat surface by creating a tactile bump. Second, we confirmed that the tactile bump might significantly improve the accuracy and the precision of touch typing.

An electro-conjugate fluid (ECF) is a kind of functional fluid, which produces a jet flow (ECF jet) when subjected to high DC voltage. It is known that a strong ECF jet is generated under nonuniform electric field, for example, the field with a pair of needle and ring electrodes. This study introduces the ECF jet to develop a novel flexible robot hand. First, we characterize the ECF jet generator which could be a micro fluid pressure source of the robot hand, and confirm the effect of the variation of electrode parameters and the number of electrode pairs on its performance. Next, we investigate the characteristics of the robot finger which mainly consists of the ECF jet generator, a flexible rubber finger and an ECF tank. The robot finger is integrated with the pressure source (ECF jet generator) and the tank, and is successfully driven. Finally we developed a five-fingered flexible robot hand and demonstrate that the robot hand can grasp some objects with various shapes without any complex controller. The height, the width and the mass of the robot hand are approximately 60 mm, 40 mm and 15 g, respectively.

We propose a novel liquid rate gyroscope using an electro-conjugate fluid in this study. The electro-conjugate fluid (ECF) is a dielectric fluid that works here as a functional/smart fluid generating a powerful jet flow (ECF jet) when subjected to high DC voltage. Using the ECF jet, we developed a liquid rate gyroscope based on the principle of a conventional gas rate sensor operated by Coriolis force. Because the ECF jet is generated only with a tiny electrode pair, the pumping part of proposed ECF gyroscope needs no mechanically moving parts, resulting in making the ECF gyroscope suitable for micro sensor compared to the gas rate sensor having a pumping mechanism inside. We fabricated a prototype of liquid rate gyroscope (40mm × 60mm × t7mm) and confirmed its characteristics by experiment. The experimental results confirm the effectiveness of the proposed liquid rate gyroscope. The scale factor of −29 mV/(°/s) is obtained with applied voltage of 4.5 kV.

A gyroscope is one of the most important mechanical components, used in wide variety of mechanical systems. Although many kinds of gyroscopes are commercially available, for consumer applications, lately becoming a big market for gyroscopes, a vibration gyroscope is the present standard. Vibration gyroscopes are small in size and low cost, however, they are not robust enough for external impact/vibration because they have vibrating elements inside.

This paper presents a new type of micromotor using electro-conjugate fluid (ECF). An electro-conjugate fluid is a kind of dielectric fluid, which works as a smart fluid. The fluid generates a powerful jet flow, which we call an ECF jet, when subjected to high DC voltage with highly non-uniform electric field, which means, it works as a fluid power source for mechanical components without bulky pumps. We introduce this attractive smart fluid to micromotors in this paper. Inside the motor is filled with the electro-conjugate fluid and a rotor has electrode pairs on the surface. By applying high DC voltage to the electrode pairs, the rotor rotates due to the ECF jet. In this paper, we design several types of electrode pairs and examine each influence on motor performances.

As a man-machine interaction increases its importance in robotics and mechatronics fields, a soft robot inspired from natural systems becomes one of the research trends. There are several research topics related to soft robots such as soft structures or artificial skins, compliance control, soft actuators or artificial muscles, and so on. For the natural muscle potentially has great flexibility, the authors believe the artificial muscle actuator must have a great potential in soft robots. Hence in this study we develop a new type of micro artificial muscle cell, which is an element of an integrated artificial muscle, using electro-conjugate fluid and measure its driving performances. In addition, position control characteristics are also clarified by experiments. As a result, the micro artificial muscle cell using electro-conjugate fluid shows quite good control performances

Soft robots inspired from natural systems are one of the main research topics in the robotic field since the last decade. Accordingly, artificial muscles were widely investigated due to their potentials in soft machines or soft robots. Many types of artificial muscles have been developed, including pneumatic actuators, ion-exchange polymer composite actuators, polymer gels, shape memory alloys, and so on. However, these artificial muscles are not used as practical actuators. In this study, the authors propose a new type of micro artificial muscle actuator (3) utilizing an electro-conjugate fluid (ECF) which generates a powerful jet flow when subjected to a high voltage (~ kV). The actuator basically consists of a fiber-reinforced silicone rubber tube and a micro pressure source using the ECF. The inner pressure of the silicone rubber tube is increased by the jet flow generated at the pressure source. The silicone rubber tube contracts along the actuator axis with the increasing pressure. The driving characteristics of the micro artificial muscle actuator were experimentally investigated. The experimental results show that this new actuation technology yields great potentials for driving soft robots.

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.

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.

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.

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.

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.

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.

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.