Takashi Maeno

Finite-element analysis of the rotor/stator contact in a ring-type ultrasonic motor

A way to understand mechanical characteristics of an ultrasonic motor is presented. First, the vibration mode of a stator is calculated using a finite-element method (FEM) code. The path of the elliptic motion of the stators teeth is obtained. The computed vibration mode at the surface of the stator is compared with that measured by an electrooptical displacement transducer. Next, the contact condition of the rotor/stator is calculated. The displacement and velocity of the rotor/stator, the distortion of the stick/slip area, the rotational speed of the rotor, and the friction loss of the motor are obtained. The calculated rotor displacement and torque-rotational speed curve correspond closely to the experimentally measured ones. The internal loss of the rotor/stator and the loss of the supporting felt are measured. The total loss of these losses and the calculated friction loss agree with the measured total loss. The calculated and the measured efficiency of the motor also agree.<<ETX>>

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.

Development of a Texture Sensor Emulating the Tissue Structure and Perceptual Mechanism of Human Fingers

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.

Five-fingered Robot Hand using Ultrasonic Motors and Elastic Elements

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.

Control of grasping force by detecting stick/slip distribution at the curved surface of an elastic finger

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.

Development of artificial finger skin to detect incipient slip for realization of static friction sensation

The goal of our study is the realization of static friction sensation using a piece of artificial finger skin for robot hand manipulation. In order to realize the sensation, we recall the importance of incipient slip detection. First, artificial finger skin is designed which has characteristics similar to those of a human finger with respect to the shape and sensing functions which enable incipient slip detection: the finger skin has ridges on the surface in which a pair of artificial FAI receptors are embedded. The design process of artificial finger skin is also shown that includes three phases. Design phase 1 involves designing the characteristics of a FAI receptor, which has a transducer for which we chose PVDF film sheets, which have a dynamic stress rate characteristic. Design phase 2 involves determination of the shape and size of the artificial finger skin, and the location of the transducer is analyzed to find its best position. Design phase 3 involves manufacturing artificial finger skin. Experimental results show that incipient slip occurs at the surface of artificial finger skin and reveal that the differential output voltage signal from a pair of artificial FAI receptors embedded in a ridge captures not only low-frequency vibration to generate a predictive signal which warns of incipient slip of the ridge, but also a high frequency vibratory signal which indicates slip of the ridge. In order to judge automatically that incipient slip occurs, we use a multi-layered ANN (artificial neural network). Judging incipient slip using an ANN shows that the system is robust to noise and can detect incipient slip.

Underactuated five-finger prosthetic hand inspired by grasping force distribution of humans

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.

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.

Friction estimation by pressing an elastic finger-shaped sensor against a surface

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.

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.