Junkao Liu

Bio: Junkao Liu is an academic researcher from Harbin Institute of Technology. The author has contributed to research in topics: Ultrasonic motor & Vibration. The author has an hindex of 22, co-authored 159 publications receiving 1495 citations.

A High-Power Linear Ultrasonic Motor Using Bending Vibration Transducer

Abstract: To overcome the modal degeneration problem that commonly exists in the design of ultrasonic motors (USMs) using composite vibration modes, a high-power linear USM using a bending vibration transducer is proposed in this paper. In this new design, two orthogonal bending vibration modes with the same order are superimposed in the motor and generate elliptical motions at the two driving feet. Square cross-section structure is adopted by the motor to ensure that the two bending modes have the same resonance frequency. After the introduction of the working principle, the motor is analyzed by using finite-element method. A prototype motor is fabricated and measured. Typical output of the prototype is a no-load speed of 1527 mm/s and a maximum thrust force of 50 N at a voltage of 200 Vrms. This study verifies the feasibility of the proposed design and provides a way to improve the output power of USMs.

Development of a Nonresonant Piezoelectric Motor With Nanometer Resolution Driving Ability

Abstract: A nonresonant-type piezoelectric motor with a precise driving ability was proposed. The operating principle of the proposed motor is different from the previous nonresonant piezoelectric motors using either the clamping and feeding mechanism (inchworm mechanism) or the inertia drive mechanism. An oblique linear motion formed by the hybrid of two bending motions of a sandwich transducer was used to push the runner step-by-step. Two square-wave voltages were applied to the horizontal and vertical PZT elements to obtain the desired oblique linear motion. The mechanism of the proposed piezoelectric motor was illustrated in detail. Then, transient analyses were performed by ANSYS software to simulate the motion trajectory and to find the response characteristics of the motor. Finally, a prototype was fabricated to verify the mechanism and to test the mechanical output characteristics of the proposed motor. Under the input square-wave voltages of 500 V $_{\text{p-p}}$ , the prototype achieved a step displacement of 5.96 μm, a maximum no-load velocity of 59.64 μm/s, and a maximum thrust of 30 N. This paper provides a new mechanism for the design of a nonresonant piezoelectric motor with long stroke and precise driving ability.

A Rotary Piezoelectric Actuator Using the Third and Fourth Bending Vibration Modes

Abstract: A piezoelectric actuator using the third and fourth bending vibration modes was proposed, designed, fabricated and tested with the aim of accomplishing rotary driving by boltclamped transducer. By superimposing the third and fourth bending vibrations, elliptical movements are formed on the two leading ends of the actuator. When a ring type rotor is in contact with the two diving tips and the vertical preload is applied, the horizontal movements of the driving tips generated by the third bending vibration will push the rotor into motion by frictional forces while the vertical movements produced by the fourth bending vibration will overcome the preload. A method of tuning the resonance frequency of the third bending mode to the fourth bending one was discussed. The horn shape was adjusted to make the two bending modes have nearly uniform frequencies. The vibration characteristic and mechanical ability of a prototype were tested, and the tested resonance frequencies agreed well with the calculated ones. The prototype achieved maximum speed and torque of 86 r/min and 2.5 Nm, respectively.

A Frog-Shaped Linear Piezoelectric Actuator Using First-Order Longitudinal Vibration Mode

Abstract: A frog-shaped linear piezoelectric actuator was proposed, designed, fabricated, and tested. The proposed actuator only used the first-order longitudinal vibration to generate linear motion, which made the design, optimization, and miniaturization of the actuator more flexible by abbreviating the frequency degeneration. By stimulating the first-order longitudinal vibration, alternate oblique movements are formed on the ends of two driving feet. Meanwhile, an elongating and shortening movement of the whole actuator is generated. When two parallel walls are in contact with the ends of two diving feet and a vertical preload is applied, the vertical components of the alternate oblique movements will overcome the preload, while the horizontal components of the alternate oblique movements and the elongating and shortening movements will together push the actuator into linear motion. Vibration characteristics and alternate oblique movements of the driving feet were investigated by the finite-element method. Experiment tests of vibration characteristics and mechanical output ability were then carried out. The tested resonance frequency and vibration amplitudes agreed well with the calculated ones. The prototype achieved a maximum speed and a thrust of 287 mm/s and 11.8 N, respectively.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fish-inspired robots: design, sensing, actuation, and autonomy--a review of research.

Abstract: Underwater robot designs inspired by the behavior, physiology, and anatomy of fishes can provide enhanced maneuverability, stealth, and energy efficiency. Over the last two decades, robotics researchers have developed and reported a large variety of fish-inspired robot designs. The purpose of this review is to report different types of fish-inspired robot designs based upon their intended locomotion patterns. We present a detailed comparison of various design features like sensing, actuation, autonomy, waterproofing, and morphological structure of fish-inspired robots reported in the past decade. We believe that by studying the existing robots, future designers will be able to create new designs by adopting features from the successful robots. The review also summarizes the open research issues that need to be taken up for the further advancement of the field and also for the deployment of fish-inspired robots in practice.

A Two-DOF Ultrasonic Motor Using a Longitudinal–Bending Hybrid Sandwich Transducer

Abstract: A two-degrees-of-freedom (two-DOF) ultrasonic motor, which could output linear motions with two-DOF by using only one longitudinal–bending hybrid sandwich transducer, is proposed and tested in this paper. The motion in the horizontal ( X ) direction is achieved by the hybrid of the second longitudinal and fifth bending vibrations of the motor, while the motion in the vertical ( Y ) direction is gained by the composition of two orthogonal fifth bending vibrations. The proposed ultrasonic motor is designed and the principles for the two-DOF driving were analyzed. Then, the simulation analyses of the motor are accomplished to verify the described principles. Finally, a prototype is fabricated and its mechanical output characteristics are tested. The results indicate that the maximum no-load velocities of the motor in horizontal and vertical directions are 572 and 543 mm/s under the preload of 100 N and the voltage of 300 Vp-p, respectively. The maximum output forces in horizontal and vertical directions are 24 and 22 N when the preload is 200 N. The simulation and experiment results verify the feasibility of the proposed two-DOF ultrasonic motor.

Computational analysis of vortex dynamics and performance enhancement due to body-fin and fin-fin interactions in fish-like locomotion

Abstract: Numerical simulations are used to investigate the hydrodynamic benefits of body–fin and fin–fin interactions in a fish model in carangiform swimming. The geometry and kinematics of the model are reconstructed in three-dimensions from high-speed videos of a live fish, Crevalle Jack (Caranx hippos), during steady swimming. The simulations employ an immersed-boundary-method-based incompressible Navier–Stokes flow solver that allows us to quantitatively characterize the propulsive performance of the fish median fins (the dorsal and the anal fins) and the caudal fin using three-dimensional full body simulations. This includes a detailed analysis of associated performance enhancement mechanisms and their connection to the vortex dynamics. Comparisons are made using three different models containing different combinations of the fish body and fins to provide insights into the force production. The results indicate that the fish produces high performance propulsion by utilizing complex interactions among the fins and the body. By connecting the vortex dynamics and surface force distribution, it is found that the leading-edge vortices produced by the caudal fin are associated with most of the thrust production in this fish model. These vortices could be strengthened by the vorticity capture from the vortices generated by the posterior body during undulatory motion. Meanwhile, the pressure difference between the two sides of posterior body resulting from the posterior body vortices (PBVs) helps with the alleviation of the body drag. The appearance of the median fins in the posterior region further strengthens the PBVs and caudal-fin wake capture mechanism. This work provides new physical insights into how body–fin and fin–fin interactions enhance thrust production in swimming fishes, and emphasizes that movements of both the body and fins contribute to overall swimming performance in fish locomotion.

On the estimation of swimming and flying forces from wake measurements

Abstract: The transfer of momentum from an animal to fluid in its wake is fundamental to many swimming and flying modes of locomotion. Hence, properties of the wake are commonly studied in experiments to infer the magnitude and direction of locomotive forces. The determination of which wake properties are necessary and sufficient to empirically deduce swimming and flying forces is currently made ad hoc. This paper systematically addresses the question of the minimum number of wake properties whose combination is sufficient to determine swimming and flying forces from wake measurements. In particular, it is confirmed that the spatial velocity distribution (i.e. the velocity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with the fluid pressure distribution. Importantly, it is also shown that the spatial distribution of rotation and shear (i.e. the vorticity field) in the wake is by itself insufficient to determine swimming and flying forces, and must be combined with a parameter that is analogous to the fluid pressure. The measurement of this parameter in the wake is shown to be identical to a calculation of the added-mass contribution from fluid surrounding vortices in the wake, and proceeds identically to a measurement of the added-mass traditionally associated with fluid surrounding solid bodies. It is demonstrated that the velocity/pressure perspective is equivalent to the vorticity/vortex-added-mass approach in the equations of motion. A model is developed to approximate the contribution of wake vortex added-mass to locomotive forces, given a combination of velocity and vorticity field measurements in the wake. A dimensionless parameter, the wake vortex ratio (denoted Wa), is introduced to predict the types of wake flows for which the contribution of forces due to wake vortex added-mass will become non-negligible. Previous wake analyses are re-examined in light of this parameter to infer the existence and importance of wake vortex added-mass in those cases. In the process, it is demonstrated that the commonly used time-averaged force estimates based on wake measurements are not sufficient to prove that an animal is generating the locomotive forces necessary to sustain flight or maintain neutral buoyancy.