Kenjiro Takemura

Design and control of an ultrasonic motor capable of generating multi-DOF motion

A multi-degree-of-freedom (DOF) ultrasonic motor consisting of a bar-shaped stator and a spherical rotor was developed. It can generate 3-DOF rotation of the rotor around perpendicular axes using the bending vibration and longitudinal vibration of the stator, which is designed using the finite element analysis. From the simulated driving characteristics, a control method for the ultrasonic motor is proposed. Following this, the driving characteristics of the motor under both open-loop and closed-loop controls were measured experimentally. The multi-DOF position control of the rotor was achieved successfully using the proposed control method.

Multi-fingered exoskeleton haptic device using passive force feedback for dexterous teleoperation

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.

Development of a robot finger for five-fingered hand using ultrasonic motors

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.

Characteristics of an ultrasonic motor capable of generating a multi-degrees of freedom motion

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 stators 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.

Design of a plate type multi-DOF ultrasonic motor and its self-oscillation driving circuit

Multi-degrees-of-freedom (DOF) actuators have become more useful in the field of robotics, as a result of the increasing number of DOFs of systems. The general features of ultrasonic motors are suitable for constructing a direct-drive multi-DOF actuator. However, previously developed ultrasonic motors do not have advantages in volume and weight in contrast to multi-DOF motion units composed of plural electromagnetic motors. In the present study, authors developed a novel multi-DOF ultrasonic motor with a compact plate stator and spherical rotor. First, a new driving principle of the motor is proposed. Next, the stator geometry is designed in detail using the finite element method, and a prototype of the multi-DOF ultrasonic motor is produced. Then, vibration characteristics of the stator and driving characteristics of the motor have been measured, respectively. The results confirm that the motor successfully provides the desired multi-DOF motion of the rotor around orthogonal axes driven by a single plate stator. Finally, a novel self-oscillation driving circuit for the motor is proposed and driving tests using the circuit are conducted.

A Micro Artificial Muscle Actuator using Electro-conjugate Fluid

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 (< 1 cm3) 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.

Development of an ultrasonic clutch for multi-fingered exoskeleton haptic device using passive force feedback for dexterous teleoperation

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 multi-degree-of-freedom ultrasonic motor using single-phase-driven vibrators

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.

Method for controlling master-slave robots using switching and elastic elements

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.

Electro-Conjugate Fluid Jet-Driven Micro Artificial Antagonistic Muscle Actuators and their Integration

An electro-conjugate fluid (ECF) is a type of dielectric and functional fluid that generates a powerful jet flow when subjected to high DC voltage. Although a high voltage is needed to generate the jet flow, the current is quite low at several microamperes, resulting in a total power consumption of several milliwatts. Using this smart fluid, we can develop micro fluid-driven mechanical components without any bulky pumps. Also, it is clarified that the power density of the ECF jet is higher when the electrode pair is miniaturized; therefore, it is suitable for micro actuators. Here, we propose and fabricate three types of soft actuators with an antagonistic configuration: (i) micro artificial muscle cells, (ii) a McKibben-type micro artificial muscle actuator using the ECF effect and (iii) a micro finger actuator with two chambers to bend. The actuators basically consist of a silicone rubber tube covered with a fiber sleeve and a micro pressure source using the ECF effect. Next, we apply and integrate these actuators into a micro robot hand, driven with ECF jets. The driving characteristics of the micro artificial muscle actuator and the integrated micro ECF hand with ECF fingers were fabricated and experimentally investigated. The experimental results show that this ECF jet actuation is effective for driving soft micro hands.