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The backward motion is an intrinsic feature of the conventional piezoelectric stick-slip actuator (PSSA), limiting the output speed and applications. Various methods have been proposed for restraining the backward motion. Each method has its pros and cons for the practical application of driving a precision motion stage. A novel method for restraining the backward motion is proposed in this article, in which a passive damping foot is utilized to hold the runner when the active driving foot slips on the runner. An actuator is developed based on this mechanism. The structural dimensions of the actuator are determined with an analytic model and a finite element model. A prototype of the proposed actuator is fabricated and tested by experiments. The experiments validate the operating principle of the actuator for restraining the backward motion, which is eliminated (the backward ratio is less than 1%) when the passive damping foot has an appropriate clamping force. The proposed method is very valuable for designing a PSSA with no backward motion, and it can broaden the applications for precision manipulations. [ABSTRACT FROM AUTHOR]

Microactuators have been playing crucial roles in micromachine technologies because of their small sizes and light weights. The piezoelectric actuation is one of the most important driving methods to perform the motion output with miniature structures. The rotary piezoelectric microactuators are relatively mature, whereas the linear ones need to be further developed. Inspired by the hollowing art, a novel linear piezoelectric microactuator with miniature dimensions of 7.4 mm × 7.4 mm × 10 mm is proposed, which is designed to be an integrated hollow structure without a guide rail and can achieve bidirectional standing-wave drive. The bidirectional motions are achieved by the same first-order bending vibrations of two pairs of thin-walled beams, respectively, which are conducive to the consistency of the forward and backward motions indicate that the maximum velocity, resolution, and maximum thrust force achieved in the forward motion are 19.06 mm/s, 0.3 μm, and 17.45 mN, respectively, whereas those in the backward motion are 16.92 mm/s, 0.45 μm, and 15.28 mN, respectively. The design inspired by the hollowing art has the potential to be an effective and alternative solution for the development of linear piezoelectric microactuators. [ABSTRACT FROM AUTHOR]

Soft actuator is the key component for soft robots to realize flexible motion. But the difficulty of sensing and control of soft actuators seriously restricts their application. Twisted artificial muscles (TAMs) made from together self-coiling of nylon 6,6 fiber and heating wire are potential to address this challenge due to their extremely high actuating stress and self-sensing ability. However, the together coiled twisted artificial muscles (TCTAMs) have a large self-sensing hysteresis because of the small heating area and the self-coiling process restricts their deformation stroke. Besides, the lack of accurate physical models also blocks the development of the TCTAMs. This article presents a new type of tightly wrapped twisted artificial muscles (TWTAMs) to improve the stroke and reduce the hysteresis. Compared with TCTAMs, the hysteresis of TWTAMs is reduced by 76% and the stroke is improved by 35%. Besides, a physical analytical model based on the self-sensing temperature is established and verified by experiments. This article not only provides a new type of TAMs with large stroke and low hysteresis, but also offers an accurate theoretical analysis model for the performance prediction of TWTAM. [ABSTRACT FROM AUTHOR]

A novel ultrasonic burnishing (UB) system with a flat tool using a piezoelectric longitudinal transducer (PLT) is proposed. High-precision no-feeding mark planar burnishing can be achieved by the compact system with a size of only 280 × 224 × 558 mm without the need for machine tools. Above all, the structure of the burnishing system is presented and the operation principle is analyzed in detail. A resonant frequency design method of the PLT with a tool head is discussed. Based on this, the PLT achieves the expected resonant frequency precisely. Subsequently, the test system for the PLT is built and the resonant frequency and vibration amplitude are tested, which are in good agreement with the simulation results. Ultimately, the UB experiments are carried out and the results indicate that the surface roughness of the workpiece is reduced from Ra 1.6 μm to Ra 0.182 μm, which is reduced by 88.31%. Furthermore, the surface topography shows that the surface without the feeding mark is generated, which is beneficial to improve the burnishing accuracy and expand the application in ultra-precision processing. [ABSTRACT FROM AUTHOR]

Lubrication failure of bearing is one of the important factors that limit the service life of the space shafting system. Due to the strict restrictions on the volume and weight, the traditional oil supply devices are difficult to meet the requirements of space active lubrication. In this article, we propose a piezoelectric microjet, which can achieve active lubricating for bearings of space equipment serving in a harsh environment. A constant pressure oil storage system, with a storage capacity of more than 4 g and can achieve vacuum oil storage, is proposed. Control accuracy of 0.012 μL per pulse is obtained and a theoretical service life of more than 20 years can be achieved. The whole active lubricating system is embedded in the bearing system, which has no effect on the normal operating of the original bearing system and almost creates no mass increment of the bearing system. The methods of controlling the characteristics of the ejected oil droplet are proposed to meet different lubrication requirements. Combined with the monitoring of bearing temperature and friction torque, active lubrication on demand can be realized. This work can provide important references for prolonging the service life of space bearing. [ABSTRACT FROM AUTHOR]

Unbalance exists widely in rotating electromechanical systems, resulting in vibrations, instability, and many other negative influences. In this article, a novel method for unbalance diagnosis of the affiliated rotating chamber in 2-DOF precision centrifuge is proposed. Unlike the widely applied sensor-based unbalance diagnosis methods, the proposed one in this article investigates the internal relationships between signals in the control loop, involving the driving current of the permanent magnet synchronous motor, the disturbance signal of the control loop as well as the unbalance signal of the rotating chamber. By using the unbalance kinematic analysis, two kinematic-mechanical-electric driving current models are established, which are based on the 2-DOF precision centrifuge with uniform motion and uniform acceleration, respectively. Based on the models, the valid information of the unbalance is included in the driving current. Furthermore, a signal analysis procedure, which includes domain conversion and ensemble empirical mode decomposition, is presented to calculate the unbalance mass and the phase of the unbalance. Finally, the effectiveness of methods is validated by experiments and simulations. [ABSTRACT FROM AUTHOR]

This work presents a novel constant frequency ultrasonicamplitude control (CFUAC) method based on fuzzy proportional-integral-derivative (FPID) and amplitude direct feedback. The frequency shift and amplitude nonlinearity of the piezoelectric transducer (PT) are measured to determine the optimal constant control frequency of 19.2 kHz. The FPID controller is designed to adapt to the nonlinear changes in different target amplitudes and loads. A direct PT amplitude feedback method is used to improve the signal’s anti-interference ability and accuracy. The 5% settling time and steady-state error of FPID can reach 92.22 ms and $\pm 0.18~\mu \text{m}$ at the step response under 24 $\mu \text{m}$. The 5% settling time and steady-state error of FPID are less than 131.44 ms and $\pm 0.26~\mu \text{m}$ at 10 $\mu \text{m}$ under 150 N. The results confirmthat fast and precise control of the vibration amplitude of an ultrasonic transducer can be realized by the proposed method. The new CFUAC method lays a foundation for revealing the ultrasonic welding and metal processing (UWMP) mechanism and helps to expand the application of ultrasonic vibration in the fields of precision machining and high dynamic ultrasonicmedical equipment. [ABSTRACT FROM AUTHOR]

This paper presents a high-efficiency inverter with the aid of the soft-switching technology, which is accomplished by the resonance of the in-series inductance with the snubber capacitance. The equivalent circuit of the quarter-phase ultrasonic motor is initially deduced, based on which the topology along with the operations of the novel inverter is subsequently presented. The configuration of the new quarter-phase inverter shows its uniqueness in terms of the shared arms and the especially designed snubber capacitance in comparison with the existing inverters. The circuit analysis infers that the dead time of the inverter is the key factor to arrive at the zero-voltage-switching or the zero-current-switching operations. Experimental measurements have demonstrated that the efficiency of the whole drive increases by a factor of 1.25 after replacing the traditional inverter with the proposed one. It should also be noted that the proposed inverter in association with the design method of the dead time not only can work for the quarter-phase ultrasonic motor, but also can be applicable for other kinds of quarter-phase devices. The soft-switching operations are achieved in the quarter-phase inverter for the first time, whose amplitudes of the output voltage and switching frequency are not required to be constant any more. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A piezoelectric microjet, which can achieve lubrication on demand, is designed to realize the trace redundant lubrication for bearings. The volume of the ejected oil droplet can reach 0.0147 μL with the velocity of the droplet as 0.91 m/s. A coupling analysis method is proposed to analyze the influences of excitation and oil properties on the dynamic characteristics of droplets. Based on the theory of central oil film thickness, an oil volume prediction model for the trace redundant lubrication of deep groove ball bearings is given. Experiments are carried out, the proposed coupling analysis method is verified by comparing the analysis results with experimental data, and the relative errors are given. The designed microjet is proved to be effective for redundant lubrication by testing its actual lubricating performance. The numbers of voltage pulses, which are required to achieve trace redundant lubrication under different excitations and operating conditions, are given. The validity of the proposed oil volume prediction model is proved by comparing results obtained from experiments and theoretical calculations, and the relative errors are given. [ABSTRACT FROM AUTHOR]

Generally, the modal degeneration problem existed in the design of ultrasonic motors using composite vibration modes can be overcome by adopting the same-order orthogonal-bending composite vibrations. The conventional excitation and the modified hybrid one of sandwich type orthogonal-bending composite vibrations with the same order are compared and analyzed in this paper. Compared with the conventional one, the modified hybrid excitation favors that two groups of ceramics exciting two orthogonal-bending modes are placed in the optimum excitation position. Moreover, the modified hybrid excitation can achieve larger vibration amplitude than the conventional one, while the amount of the ceramics adopted and the exciting voltages applied are the same. The first-order orthogonal-bending composite vibrations are chosen to analyze the advantage of the modified hybrid excitation. Finite-element method is adopted to compare the amplitudes of the models with the same sizes but different excitations. The prototypes corresponding to two excitations are fabricated and tested to verify the results of the theory and simulation. It is proved that the modified hybrid excitation can improve the performance of the sandwich type ultrasonic motors using bending composite vibrations. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

This paper presents a novel 2-DOF planar linear ultrasonic motor. The stator of the motor can be divided as two transducers and two isosceles triangular beams. The bending vibration modes and longitudinal vibration modes of the stator are superposed as three operation modes and generate elliptical trajectories of the driving foot in two planes to provide the thrust force along two dimensions. The operating principle of the motor and the formation of the elliptical trajectory of the driving foot are analyzed, and the variable mode excitation method is illustrated. A prototype was made and experiment investigation of the motor characteristics is presented. Testing results of the prototype shows that this motor can gain a maximum speed of 211.3 mm/s and its thrust force can reach 3.15 N under an exciting voltage of 400 VP-P. The major feature of the motor is that the 2-DOF driving function can be achieved by using the method of variable mode excitation. [ABSTRACT FROM AUTHOR]

A piezoelectric actuator, which is constructed by bonding six pieces of lead zirconate titanate (PZT) ceramic plates on a step aluminum alloy beam, was proposed and tested for the design of a small-size rotary driving appratus. Two pieces of PZT ceramic plates bonded in the middle part is used to generate the first bending mode, whereas the other four on the two sides are set for the excitation of the second bending mode; their superimposition can produce elliptical movements on the two ends of the beam, which can rotate a disk-shaped rotor. Compared with the traditional ring-shaped traveling-wave piezoelectric actuator, the proposed actuator has a simpler structure and operating principle; it also gives a new mode for rotary driving. The resonance frequencies of the first and second bending modes were designed to be close at about 21.1 kHz. The maximum no-load speed and torque were tested to be 158 r/min and 0.053 \mboxN\cdot\mboxm, respectively. The prototype achieved a power density of 19.0 W/kg under a weight of 15.8 g. The proposed combination plan of the first and second bending modes is very suitable for constructing a small-size piezoelectric actuator, which exhibits merits for application in small systems. [ABSTRACT FROM PUBLISHER]