Tomoaki Mashimo

Development of spherical ultrasonic motor as a camera actuator for pipe inspection robot

We present a pipe inspection robot using a newly developed spherical ultrasonic motor (SUSM) as a camera actuator. The novel SUSM has improved the range of movement compared to previous SUSMs, and the robot can point a camera in any direction. In this study, we determined a method for controlling the rotational direction and strategic control from the kinematics and characteristics of ultrasonic motors. The rotational directions were defined by the phase differences of the applied voltages, and the rotational speeds were changed with the frequencies. Additionally, we developed a very small position sensing system using rotary potentiometers. In the control experiment performed using the sensing system, the SUSM showed the returnability to the default position from several specified points, within an accuracy of 1°.

Design and implementation of spherical ultrasonic motor

We present a mechanical design and implementation of spherical ultrasonic motor (SUSM) that is an actuator with multiple rotational degrees of freedom (multi-DOF). The motor is constructed of 3 annular stators and a spherical rotor and is much smaller and simpler than conventional multi-DOF mechanisms such as gimbals using servomotors. We designed a novel SUSM using experimental data from a single annular stator and a finite element method. The SUSM using a spherical rotor of diameter 20 mm without any reduction gear has demonstrated advantages of high responsiveness, good accuracy, and high torque at low speed. The dynamic implementation of SUSM was consistent with the driving model of SUSM based on a friction drive.

Development of a Spherical Ultrasonic Motor with an Attitude Sensing System using Optical Fibers

We present a spherical ultrasonic motor (SUSM) and an attitude sensing system using optical fibers for the SUSM. The SUSM is constructed from three ring-shaped stators and a spherical rotor, and has three degrees of freedom (DOF). It has good responsiveness, high positioning accuracy, and strong magnetic field compatibility. In the attitude sensing system, a flat mirror is built in the spherical rotor. Light is emitted to the mirror, and the reflection is caught by optical fibers. The light intensities captured by the optical fibers are processed by a neural network and are converted to attitude information for the spherical rotor. We describe a system comprising the SUSM and the attitude sensing system with its design derived from mechanics and optics. The prototype SUSM is 26mm in diameter and was actuated by the attitude sensing system. Position errors with respect to x and y axes are less than 0.5deg.

Rotary-linear piezoelectric microactuator with a cubic stator of side length 3.5 mm

We report a miniature rotary-linear piezoelectric actuator with a single cubic stator of side length 3.5 mm which can generate rotary motion around the center axis and linear motion in the axial direction. The stator is fabricated as a single metallic cube of side length 3.5 mm with a 2.5-mm diameter through-hole and four piezoelectric elements bonded to the sides of the stator. The simplicity makes the actuator compact without any special manufacturing. In the design for miniaturization, the modal analysis using the finite element method indicates the natural frequency of the stator from the side length 14 mm to 3.5 mm. In the experiments, rotary motion of 24 rad/s and 2.5 μNm were obtained at a resonant frequency of 280 kHz, and linear motion of 80 mm/s and 2.6 mN was observed at 305 kHz by driving the system at an applied voltage of 42 Vrms.

Rotary-linear piezoelectric actuator using a single stator

We report a piezoelectric actuator having a single stator with rotary and linear motions (RLPA). The stator is fabricated as a single metallic cube with a through-hole. The surface of the inner circle of the hole generates elliptical motions at each natural frequency, transferring the energy to an output shaft, when AC voltages at the appropriate resonant frequency are applied to the piezoelectric elements. This study clarifies the principle of rotary and linear motions and uses finite element methods (FEM) to show how the elliptical motions are generated. Modal analysis illustrated the shapes of the vibration modes and the natural frequencies, and the shape of the stator was designed accordingly. A dynamic analysis of the stator showed the generation of elliptical motion in the directions of the rotary and linear motions. The prototype RLPA was successfully actuated at the resonant frequencies, consistent with the dynamic analysis. The speed of the rotary and linear motions was obtained.

Micro rotary-linear ultrasonic motor for endovascular diagnosis and surgery

We present a micro ultrasonic motor having rotary and linear motions (rotary-linear motor) suitable for endovascular diagnosis and surgery. The rotary-linear motor is miniaturized to the size needed to function in a blood vessel. The stator prototype is a cube of side 3.5 mm, and the main body is fabricated as a single metallic cube with a through-hole. Four piezoelectric elements are bonded to the sides of the stator. When AC voltage at each resonant frequency is applied to the piezoelectric elements, the circumference of the stator generates elliptical motions at each natural frequency. We can obtain the output from a shaft inserted through the hole. We developed the first prototype of the stator using the finite element method (FEM), and experimentally determined the output of the rotary-linear motor. In the rotary sense, approximately 260 rpm and 0.1 mNm were attained at a resonant frequency of 270 kHz, and in the linear sense about 50 mm/s and 0.01 mN was attained at 306 kHz by driving the system at applied voltages of 42 Vrms.

Optimal placement of a two-link manipulator for door opening

This paper presents a study on the optimal base location and arm motion of a mobile manipulator for door opening task. Numerical simulation results show that the base location where the manipulability of the two-link arm is almost degenerated at the start and end points of door opening is optimal.We show by analysis that the location has an advantage in supplying kinetic energy to the door by using torques at the joints of arm. In order to represent properly the arm motion near a singular point of manipulability, the rotational motion of the door is parameterized by piecewise fifth order polynomials of time, and the parameters of polynomials are optimized to minimize the joint torques.

Experimental Verification of Elliptical Motion Model in Traveling Wave Ultrasonic Motors

We propose a model of a traveling wave ultrasonic motor that includes the elliptical motion amplitudes of the stator and verify this model experimentally using a high-speed camera with a high-power lens (i.e., a high-speed microscope). This approach makes it easy to estimate the motor characteristics, such as the rotational speed and torque. In this paper, we build a mechanical model of the stator and rotor that incorporates the elliptical motion amplitudes. The elliptical motion of a few microns at ultrasonic frequencies is captured and measured by the high-speed microscope. When modeling parameters are determined from the observed vibration amplitudes, the model can predict the motor characteristics. We study how the observed elliptical motion is related to the motor output by varying the frequency of applied voltages, and verify the proposed model by comparison with the experimental results.

Micro Ultrasonic Motor Using a Cube With a Side Length of 0.5 mm

Actuator miniaturization to submillimeter scales encounters difficult fabrication and serious torque dissipation caused by adhesion forces. This study presents a design for micro ultrasonic motors that enables microfabrication and motor actuation. The stator prototype, which is the smallest ultrasonic motor reported to date, comprises a metallic cube with a side length of 0.5 mm and a through-hole of 0.33-mm diameter at its center, and two piezoelectric elements adhered to its sides. Under two different applied voltages, the stator generates a driving force and transfers it to the rotor inserted in the through-hole. Performance assessments show that this micromotor generates an average angular velocity of 123 rad/s and a peak torque of 0.2 μN·m. This torque value exceeds that of the existing micromotors.

Spherical ultrasonic motor drive system for camera orientation in pipe inspection

We propose a camera actuating system using a spherical ultrasonic motor for inspection of the inside wall of a small pipe. The spherical ultrasonic motor has advantages that include three degrees of freedom, high responsiveness and high accuracy all within a compact body. We describe here the development of an outer rotor spherical ultrasonic motor (OR-SUSM) that enables a camera to rotate by more than 360° along the side of the pipe. All components, including the OR-SUSM, the sensing system, and the electric circuits, are designed to be assembled in the pipe inspection device with outer diameter of 52 mm. To control the system, the phase difference and frequency of the applied voltages are used. The rotational direction is determined by the phase difference and the angular velocity is controlled by the frequency. The completed system can be controlled to within 2° in an experimental pipe inspection test.