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Friction drive and wear control is a tough issue for linear standing-wave ultrasonic motors with intermittent contact and impact friction. For the widely recognized reduction of friction/wear, minimum quantity lubrication was adopted to improve the output performances and services for motors through friction regulation. Given different preload and driving voltages, the mechanical characteristics of motors with minimal quantity lubrication were investigated using a homemade test rig. Results show that output performances and driving efficiency under film lubrication differ from those of dry friction. The optimized driving voltage was reduced by 31.5% and the minimum startup voltage was reduced by 41.67% using film lubrication. Additionally, the output speed increased by 26.29%, and thrust decreased by 41.26% under uniform exciting conditions (e.g., 150 V at 39.14 kHz). The existence of film lubrication broadens the effective frictional contact boundary, and effective friction contribution enhances the driving efficiency (the maximum efficiency of motors increased by 14%). Furthermore, the singularity of the effect of preload is significantly improved after lubrication, and the friction interface of the stator/slider becomes more controllable. Suitable lubrication is critical to the improvement of startup performance and prone to realize low-voltage driving, and the combination of lubrication regulation and wear inhibition is conducive to the durability and reliability of motors. This study provides an additional alternative for performance improvement of linear standing-wave motors apart from frictional materials. [ABSTRACT FROM AUTHOR]

The contact process of stator and slider described by the Coulomb friction model is basically in a pure sliding friction state, and a mechanical model based on the Dahl friction theory was proposed to describe the contact process between stator and slider of V-shape linear ultrasonic motor. With consideration for the tangential compliance of stator and slider, the dynamic contact and friction processes of stator and slider were addressed in stages. The simulation results show that the ratio of the friction positive work decreases with the increase of the preload, and the vibration amplitude of the stator increases the proportion of positive work of the friction force. Improving the contact stiffness of the stator and slider is conducive to improving the output performance of the ultrasonic motor. The asymmetry of the left and right performance of the V-shaped vibrator will cause a difference in the left and right running speeds of the ultrasonic motor. The improved Dahl friction-driving model makes up for the discontinuity of tangential contact force calculated by the Coulomb friction model. This study demonstrates that the friction-driving model based on the Dahl theory is reliable and reasonable for linear ultrasonic motors according to the experimental results. [ABSTRACT FROM AUTHOR]

• Stator textures and rotor flexibility were used to reshare stresses and anti-wear. • Frictional stress homogenization is available after surface texturing. • Stress overloading and subsurface damage are released for textured stator. • Directional microtextures assist low-voltage and high-performance driving. • 158 rpm and 73 N·mm were obtained at 80Vp of drive voltage and 40 N of preload. Traveling-wave ultrasonic motors promise widespread applications in precision engineering, medical, and aerospace field due to their high-power density, but suffer from low efficiency and stress gradient. In this case, the synergy effect of surface-functionalized friction regulation and interface coupling interference of wear loss/debris could effectively eliminate these deficiencies. Herein, we report a low-voltage driving rotational piezoelectric motor (PM30) that proceeds through laser-induced microtextured stators coupling with flexible rotors, which enables working at a rotational speed of 158 rpm and torque of 73 N·mm, respectively, under the condition of low-voltage (80V p) and low-preload (40 N). Such operation parameters are far beyond the current reported results. Furthermore, FEM simulation and SEM observation demonstrated that the low-voltage driving and high-performance output are resulting from the combination of surface microtextured stators for friction enhancement and flexible rotors for displacement amplification with contact expansion, which regulates tangential friction and reshares the stresses distribution during the dynamic contact along with the rotary motion of rotors. This work provides a promising strategy to construct friction-stress regulation and energy-transformation enhancement toward energy-saving and high-efficient friction drive for piezoelectric devices. [ABSTRACT FROM AUTHOR]

Friction behavior and serious wear of the stator/slider pair are critical to restrict the development and commercialization of standing-wave linear ultrasonic motors. Owing to the effective friction regulation of laser surface microtextures, a multi-connected vesicle-like microarray consisting of the micropits and microgrooves was prepared on the slider surface. Finite element analysis at the microscale showed the proposed micro-textures were prone to cause the stator tip to sink, resulting in an increase of horizontal impact effect of ultrasonic vibration and the alternately regulating of static-dynamic friction boundary, which enhances the tangential force and improves the driving effect. The experimental results approved that the composite microtextures combining the pits of 100 μm and the grooves of 50 μm are positive for friction drive and output performance enhancement. Specifically, the output power of the low-voltage driving linear piezoelectric motor with the complex texturing array is 66% higher than that of non-textured ones. This study provides a reliable approach to enhancing the friction-driving performance and operation stability of piezoelectric motors or actuators. [Display omitted] [ABSTRACT FROM AUTHOR]

Classical traveling-wave ultrasonic motors (TWUMs) usually generate the elliptical clusters on the stator surface through the bending vibration of the annular stator on the basis of piezoelectric excitation, and the torque output and power transmission are realized by friction coupling under the rational preload. Stable and reliable working characteristics attracted the focus of various applications. High energy consumption and low efficiency are restricted factors for the service performance of motors. Displacement amplification and stress regulation based on flexible design become a possible approach to improve motor performances. In this study, a TWUM30 prototype was proposed with consideration of (sub) structure optimization, i.e., tooth height and backlash of the stator elastomer. The flexible design of the rotor structure was carried out for consideration of the contact area and stress regulation. After integrated bonding of the stator and PZT4, the electrical and vibration characteristics of the stator prototype are measured by an impedance analyzer and high-precision laser micro-displacement sensor. Results showed that the proposed TWUM30 is capable of operation under low-voltage driving (41.9 kHz @ 80 V p), and the extreme mechanical performances presented the stall toque of 64mN∙m and the no-load speed of 153.8 rpm. With the combination of the flexible design and systematic integrated manufacturing of the stator/rotor, low-voltage driving of the TWUM30 motor under ultra-low preload was realized at low cost and the adverse effects of excessive preload were suppressed. This study is expected to provide support for high reliability design and long-life service of the TWUMs. It also provides a realistic possibility for the flexible design and application of energy-saving and high-efficient traveling-wave piezoelectric drivers. [Display omitted] • TWUM30 prototype was proposed with (sub)structures optimization and integrated manufacturing. • Flexible redesign of rotor was conducted for the contact area and stress regulation. • TWUM30 is capable of operation under low preload and low-voltage driving (40 N, 80 V p @41.9 kHz). • Mechanical performances (toque & speed) of TWUM30 were compared and improved. [ABSTRACT FROM AUTHOR]

The application of the friction drive of carbon-fiber-reinforced composites to a standing-wave ultrasonic motor was investigated. Friction drive tests were conducted on carbon-fiber-reinforced epoxy resins (CF/epoxy) by home-made test rig, which was based on plate-rod vibrator. The effects of fiber orientation and ply thickness on dynamic drive and dynamic normal forces were investigated. Fiber orientation angle and ply thickness affected friction drive. Different dynamic drive forces, which varied both in amplitude and period, were observed for CF/epoxy composites with different winding angles. A CF/epoxy composite with a winding angle of 30° showed the largest dynamic drive force (∼0.45 N) and the shortest contact period (∼26 μs). The period of dynamic normal force was uniform (∼65 μs) for various CF/epoxy composites. Wear traces of different composites exhibited different wear modes, such as scuffing, peeling, and shearing. The anisotropic property of CF/epoxy material affected the drive process of standing-wave ultrasonic motor. The current study taking the carbon-fiber-reinforced epoxy resin as an example of anisotropic materials arise more enough attention on inexpensive, biodegradable, and renewable alternatives for the efficient and durative drive of a standing-wave ultrasonic motor. POLYM. COMPOS., 37:2152-2159, 2016. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Coulomb friction model is modified with considering the preliminary distance of rigid bristles and shear stiffness of the contact surface. The degeneration in friction drive and wear behavior induced by nonlinear contact (i.e., impact, intermittent, and fretting) is outlined. Wear tests of LUSMs with V-shape transducers are conducted by a homemade reciprocating apparatus. Results show that chemical inertness, thermotolerance, elasticity as well as surface topography are critical for the contact interface of LUSMs A systematic approach involving, for instance, dynamic contact, friction model, and wear behavior provides new perspectives in improving service performances and promoting practical applications. [ABSTRACT FROM AUTHOR]

Friction materials with favorable mechanical and tribological characteristics are critical to the drivability and reliability of ultrasonic motors. Preliminary screening at atmospheric conditions suggests that filled polymer composites such as poly-tetrafluoroethylene (PTFE), phenol formaldehyde resins (PF), and poly-p-hydroxybenzoic acid (Ekonol ® ) are potential candidates for use as friction materials ultrasonic motors. The wear behavior of these polymers in contact with duralumin (2A12) stators was examined and compared under various environmental conditions: room temperature (RT) and atmospheric pressure, RT and low vacuum (5 Pa), RT and high vacuum (5×10 −3 Pa), and both low temperature and low vacuum. The wear loss of these various polymers was characterized by tracking changes in their surface roughness parameters ( R a and R v ). Wear tracks on the surfaces of different frictional materials were inspected using scanning electron microscopy. Results show that the wear resistance of Ekonol and PF composites is poorer in vacuum than in ambient conditions, whereas that of PTFE composite is not readily susceptible to ambient conditions. Lastly, wear modes and mechanisms at the various conditions are discussed. [ABSTRACT FROM AUTHOR]

While high friction coefficients and good wear resistance are antagonistic properties of most materials, these properties are expected to promote excellent torque-speed characteristics and extend the life span of ultrasonic motors. Blending is an accepted technique for modifying tribological applications. p-Hydroxybenzoic acid polymer (Ekonol) blends with different compositions, and proportions were prepared through mechanical blending. Poly(tetrafluoroethylene) (PTFE), poly(etheretherketone), and poly(phylenesulfide) (PPS) were selected as dispersed phases. The mechanical properties of the blends were investigated, and their tribological performance was tested using a block-on-ring wear meter. The worn surfaces of Ekonol blends were observed using a scanning electron microscope to elucidate the relevant wear mechanisms. Results showed that the dispersed phases have distinct effects on the impact strength and hardness, as well as friction coefficient and wear rate, of the blends. Curves of hardness and friction coefficient versus the dispersed phase content showed apparent similarities, which indicates that hardness influences the friction of polymer blends in contact with carbon steel. Worn tracks on the surfaces of different polymer materials showed that the dominant wear mechanism transforms from fatigue and abrasion into adhesion with the addition of a dispersed phase; delamination was observed in the transfer films, especially those formed by the Ekonol/PTFE and Ekonol/PPS blends. [ABSTRACT FROM AUTHOR]

• A home-made measured simple system for output performances of linear piezoelectric motors were constructed. • A prototype of SWUMs is manufactured and the mechanical characteristics were tested. • A basic measurement approach for service performances of linear ultrasonic motors was presented. • Static and dynamic performances of linear motor can be measured simultaneously in real time. A prototype of the linear standing-wave ultrasonic motors having arc tip is designed and manufactured, and the output performances and mechanical characteristics were tested and evaluated using a home-made measured simple system in this study. Results show that the flexible design of the driving foot is interesting for the performance improvement and simplification design of standing-wave ultrasonic motors. The measured system is simple and is available to evaluate the output performances (thrust and speed) and mechanical characteristics curves of linear motors. The influence trend of preload and driving voltage on output speed is opposite, while the influence trend of thrust is parabola. The peak value of applied voltage is critical for the mechanical characteristic curve of piezoelectric motor. This study also supports a basic measurement approach for service performances of linear ultrasonic motors and the tribological behaviors of motor and/or actuator devices using piezoelectric vibration. [ABSTRACT FROM AUTHOR]

This study focuses on the wear debris of different friction materials for linear standing-wave ultrasonic motors (SWUMs). Wear debris with different morphology and sizes derive from wear mechanisms and has a critical influence on the contact state. The generation mechanisms of the wear debris are analyzed by using the elastic-plastic indentation mechanics and the typical morphography of the wear debris are discussed by considering of the energy balance. Oxide ceramics with high strength and fracture toughness were used as the friction materials of the driving tips, which are in contact with the carbon steel and oxide ceramic sliders. The wear tests were conducted using a homemade reciprocating apparatus. The worn surfaces and debris of different couples were investigated by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The statistical results of the debris size analysis were consistent with the results of the theoretical analysis of the indentation fracture mechanics. The wear debris was characterized with regard to size parameters, roundness factor, aspect ratio, and fractal dimension using image processing, and the relationships of the parameters and the wear modes are discussed. The generation mechanisms of the wear debris differ for the different friction couples due to the complex states and the differences in the mechanical properties. The plastic factor (E / H) and brittleness factor (H / K IC) are critical to the maximum dimension of the wear debris for given friction couples. Image 1 • Dimensions of wear debris from friction couples for SWUMs were analyzed based on indentation fracture. • Patterns of wear debris were analyzed by using a general theoretical approach. • Relation between debris dimensions and the plastic factor (H / E) and brittle factor (K C / H) were sketched quantitatively. • Clustering of debris was conducted by the morphology parameters of convex hull and bounding circle. [ABSTRACT FROM AUTHOR]

• A measuring system for electromechanical multi-parameters of linear piezoelectric motors was constructed. • Signal conditioning and measurement circuits were designed for physical signals processing, A/D conversion, and transmission. • The principle and structures of the synchronous testing system were demonstrated based on the virtual instrument. • The calculation principle of the transient characteristic of multi-parameters of piezoelectric motors was proposed. Due to the time-dependent correlations, the measurement and characterization of electronic and mechanical parameters are critical for linear piezoelectric ultrasonic motors (USMs) during the running process. This study constructed a homemade system to measure the electromechanical multi-parameters and kinetics performances agilely, transiently, and synchronously. The principles and structures of the test system were demonstrated based on virtual instrument technology. A signal conditioning circuit is designed and used for physical signal processing, A/D conversion, and transmission. The difference in resonant frequencies was discovered for the synchronization acquisition of mechatronic parameters, and the instantaneous characteristics of electromechanical parameters for SWUM (e.g., driving voltage, input current, thrust force, and speed during the start-up and power-off process) were established based on the experimental data. This study is significant for the measurement/evaluation of the dynamic and transient performances of linear piezoelectric motors and actuators. [ABSTRACT FROM AUTHOR]

The wear of a traveling wave ultrasonic motor has certain particularities due to its special drive mechanism. In this investigation, the progression of wear of a brass stator against a PTFE–matrix composite friction material is reported. During 200 h of operation, the performances of an ultrasonic motor and the properties of its friction surfaces were examined. Different wear stages were observed. Surface topography and debris characteristics were analyzed to assess the wear mechanisms that operate in different wear stages. Under the imposed operating conditions the running-in wear stage requires 80 h. In early period of running-in wear stage, adhesive wear is the main wear mechanism of the friction material. The debris forms a multi-layered, agglomerate sheet. In the second part of the running-in period, the main wear mechanisms change to delamination wear and adhesive wear. The debris piles up as small particles. In the steady wear stage, the main wear mechanism is delamination wear result from fatigue. The debris forms small flake-like sheet but they are rare. Abrasive wear exist in all stages of wear. By contrast, the main wear mechanism of the brass stator is abrasive wear. [ABSTRACT FROM AUTHOR]