Study on dynamic friction characteristics in reciprocating friction drive system

The dynamic friction characteristics of a reciprocating friction drive system are investigated under conditions of dry contact using 0·45% carbon steel pair. Three friction modes are found during the operation, i.e. stick-slip, sticking and a transition region. The critical operating conditions in classifying these three modes are examined under various driver speeds, normal loads and spring constants. The critical values of driver speed and normal load increase with increasing spring constant. Generally, in the friction drive system the disappearance of the stick-slip results in smooth rolling. It is also found that the slope at the first period of slip on the traction force–relative slip velocity curve would have a transition from negative to positive value when the friction mode of stick-slip changes into sticking. Moreover, results show that the sticking mode gives the best positioning accuracy with the least wear on the contact surfaces. In addition, a transition from severe wear to mild wear is found when the friction mode is transferred from stick-slip to sticking only.     

基于电流控制的压电陶瓷驱动电源及其试验研究

压电陶瓷致动器在电场驱动下会产生迟滞和蠕变现象,降低了定位精度。根据压电陶瓷致动器的位移与电荷量之间具有线性关系,研制了基于电流控制的压电陶瓷驱动电源。通过控制压电陶瓷的充电电流来控制其运动速度,从而控制其位移量。设计特殊电路和有针对性的控制算法,实现对压电陶瓷的快速驱动与高精度定位的结合。试验结果表明,利用该电源可实现对压电陶瓷的线性驱动和快速精密定位。     

Study on slip displacement and stick-slip characteristics in reciprocating friction drive system

The effects of follower mass, time ratio, driver speed, and normal load on the slip displacement and stick-slip characteristics are experimentally and theoretically investigated in the reciprocating friction drive system under dry contact using a 0.45% carbon steel pair. Results show that the accumulative slip displacement is linearly proportional to the rotating cycle under various operating conditions. The slope for this linear relationship is defined as the slip rate. The slip rate increases with increasing driver speed, the mass of the follower, and |δ−1|, but decreasing normal load. There are three modes of relative motion between the driver ring and the follower in the present study, namely, unstable stick-slip (USS), stable stick-slip (SSS), and sticking (ST) regimes. They are significantly influenced by the driver speed, normal load, time ratio and mass of the follower. The critical operating conditions among unstable stick-slip, stable stick-slip, and sticking regimes were also established. The critical frequency can be theoretically calculated and agrees well with experimental results.     

新型多模式弹性驱动器的弹跳性能研究

基于人体肌肉的仿生驱动机制,提出一种多模式弹性驱动器,采用电动机带动丝杆螺母串联弹簧,结合相应的刹车离合装置,实现驱动器不同模式的运动,并对其运动模式进行分析;建立弹性强驱动器的动力学方程,进行简谐激励下的弹跳运动研究,并进行不同负载、不同弹性系数下的弹跳运动仿真分析;进行弹性驱动器的运动性能试验研究,分别对弹性驱动器的刹车力、连续弹跳及单次跳跃进行试验,结果表明,弹性驱动器能实现有效刹车,在简谐激励下能实现良好的连续弹跳,在输入的双曲正切信号控制下,能实现良好的单次弹跳;多模式弹性驱动器研究对对深入理解仿生驱动器的运动机理提供了重要的理论基础。     

脉冲进给系统的高平稳运动控制

数控系统插补产生的驱动脉冲序列特性直接影响到脉冲进给系统的运动平稳性。通过理论分析、建模仿真和试验验证系统研究脉冲进给系统的运动平稳性问题及其控制对策。在建立插补输出模型的基础上,从时域和频域剖析了其平稳性问题的本质;根据所揭示的精度、效率和平稳性之间的制约关系给出传统模式下实现平稳运动控制的途径;并从改变插补周期及多轴联动方式入手,突破传统数控的插补控制模式,提出全新的高平稳运动控制方案——随机周期独立轴自适应插补控制。大量的时域和频域仿真及实际加工试验验证所提算法的有效性。为改善数控设备的运动平稳性提供了理论依据和全新途径。     

Thermal effect on piezoelectric stick-slip actuator systems

The piezoelectric stick-slip (PZT-SS) actuator is known to achieve motion with a theoretically unlimited range yet high resolution (several nanometers). In this type of actuator, friction plays an active role in producing a meaningful stick-slip motion. However, friction is a source of heat which may cause significant temperature rise, affecting the dynamic performance of the actuator. Our study aimed to measure temperature rise in the stick-slip motion and to understand whether such a rise could significantly affect the displacement of the stick-slip motion. In this study, a temperature measurement system was developed using the off-the-shelf components, with which the temperature rise up to 0.436 degrees C was successfully measured on a proprietary PZT-SS actuator. The experiment further shows that the temperature rise affects the displacement of the actuator when operating voltage is at the low end (approximately 6 V). Therefore, one of the design recommendations for such an actuator system is that the operating voltage should be at the high end (approximately 30 V). The study also measured the temperature rise (approximately 0.263 degrees C after the system worked for 6300 s) at the friction interface due to the piezoelectric element which is a part of the whole PZT-SS actuator. This means that temperature rise is due to both the friction at two interacting surface and the operation of the piezoelectric element.     

Development and characterization of a novel piezoelectric-driven stick-slip actuator with anisotropic-friction surfaces

This paper reports a novel piezoelectric-driven stick-slip (PDSS) actuator with working surfaces of anisotropic friction. Compared to existing PDSS actuators, the new PDSS actuator has the higher efficiency and higher loading capability. The working surfaces of the new actuator were fabricated by employing hot filament chemical vapor deposition and ion beam etching. The surfaces were constructed such that they can provide with different levels of friction dependent on the direction of their relative motion, thereby providing a means to enhance the actuator performance. The performance of the novel actuator was characterized and compared to that of a PDSS actuator with the normal working surfaces, demonstrating its performance improvement.     

A solid-state generator with pulsed excitation of the oscillating circuit

A solid-state high-frequency damping oscillation pulse generator based on a pulsed excitation circuit is designed. The frequency of high-frequency oscillations reaches units of megahertz with a pulse repetition rate in the continuous mode of up to 1 kHz. The frequency of output pulses determines the power consumption from the supply mains that does not exceed 700 W. In this case, the peak power of output pulses reaches hundreds of kilowatts with a generator efficiency of up to 65%, if the optimal resistive load is used. The main area of the generator application is the generation of low-temperature atmospheric-pressure plasma.     

具有偏置结构的非对称惯性压电旋转驱动器

为改善惯性压电驱动器输出性能,提出了一种新型具有偏置结构的非对称惯性压电旋转驱动器。在非对称夹持的基础上,定义了一种偏置结构。为了解偏置结构对驱动器输出性能的影响,建立了机构的力学模型方程,推导并仿真分析了驱动器的动力学特性。设计、制作了试验样机,搭建了试验系统;进行了试验测试并与无偏置结构驱动器进行了性能对比。结果表明:偏置距离为15mm时,驱动器输出步距角速度最大。与无偏置结构驱动器相比,驱动电压为100V、23Hz时,驱动器输出最大角速度从3.48rad/s增加至5.39rad/s,增幅达54.88%,驱动器最大驱动力矩从2.41N·mm增加至3.62N·mm,增幅达50.2%;驱动电压为100V,4Hz时,驱动器稳定运行时的承载量达1 300g。理论与试验结果表明,提出的有偏置结构的驱动器具有输出步距角速度和驱动力矩更大的特点。     

A nanosecond SOS generator with a peak power of 4 GW

A high-current nanosecond generator with a peak power of up to 4 GW, an output voltage of 0.4–1 MV, a pulse duration of 8–10 ns, and pulse repetition rates of 300 Hz in a continuous mode and up to 1 kHz in the burst mode is described. The average output power at a pulse repetition rate of 1 kHz reaches 30 kW. The generator has an all-solid-state energy-switching system. A semiconductor opening switch on SOS diodes forms output pulses. The electric circuit and design of the generator are described, and the experimental results are presented. A device for eliminating prepulses across the load is proposed. The results of its testing and numerical simulation are presented.     

A nanosecond SOS-generator with a 20-kHz pulse repetition rate

A nanosecond SOS-generator with a 20-kHz pulse repetition rate in the continuous operating mode and with a 100-kHz pulse repetition rate in the pulse burst mode is described. The generator contains a low-voltage module with a primary capacitive storage and a transistor switch, and a high-voltage module with a magnetic compressor and a semiconductor opening switch (SOS diode). The generator forms pulses with amplitudes of 40–100 kV with a 20- to 30-MW peak power and a 10- to 14-ns duration across a 50- to 500-Ω external load. The output average power in the continuous operating mode is 5 kW. The electric circuit, principle of operation, and design of the generator’s elements are described. The test results are given.     

Precision tracking of a piezo-driven stage by charge feedback control

This paper presents a novel approach for precisely controlling the motion of a piezo actuator embedded in a mechanical stage without using a displacement sensor. A piezo actuator has a high displacement resolution, but the positioning performance is degraded by hysteresis between the applied voltage and resultant displacement. However, an electromechanical model of a piezo actuator suggests that the charge flowing in the actuator is directly related to the dynamic response of the piezo displacement. Therefore, this study directly measured the charge stored in a piezo actuator, and achieved dynamic reference tracking of the actuator's displacement by regulating the charge flowing through the actuator to follow a predefined trajectory.This novel approach requires neither specially designed charge amplifier circuits nor implementation of an inverse hysteresis model. The complete model identification and the digital controller design procedure for a piezo-driven mechanical stage are presented. The charge feedback controller is designed according to the dynamic characteristics of both the actuator and the stage, so that instability is minimized relative to using a charge amplifier. The experimental results confirm satisfactory tracking performance, and reveal the influence of model uncertainties on the system performance.     

Formation of Short Pulses with a Subnanosecond Rise Time and a Peak Power of Up to 1 GW by a Semiconductor Avalanche Sharpener

The results of experiments on the formation of high-power pulses with a rise time of <1 ns and a duration of 1–2 ns by a solid-state semiconductor sharpener operating in the mode of delayed impact ionization wave are presented. A peak power of 1 GW in a single-pulse operation mode and 750 MW at a pulse repetition rate of 3.5 kHz was obtained across a 50- load. Experiments on the pulse transformation using a forming line with a variable wave impedance and generation of bipolar voltage pulses are described.     

尺蠖式直线微驱动器的设计

针对普通尺蠖式直线微驱动器运动速度低和输出力小等问题,基于柔顺机构设计了一种新型尺蠖式直线微驱动器。微驱动器由箝位机构、驱动机构和输出轴组成,其运动特点是驱动机构驱动箝位机构进行往复直线运动,箝位机构带动输出轴作直线运动。箝位机构和驱动机构均采用柔性杠杆结构,保证了微驱动器所需的箝位力与驱动力,并提高了其运动速度。采用伪刚体方法建立了驱动电压与箝位力、驱动机构输入位移与输出位移之间的关系,根据功能原理建立了输入力与驱动力之间的关系并制作了样机,搭建了实验测试系统进行性能测试,测试结果表明,驱动器最大箝位力为216.43N,最大驱动力为13.5N,在驱动电压120V,频率95Hz时,达到最大速度48.91mm/s。     

基于热力学性能的形状记忆合金驱动器多目标优化

提出了一种可应用于微小型水下机器人摆动关节的形状记忆合金差动驱动方法及其实验装置。分析了形状记忆合金差动驱动的摆动关节运动机理;针对不同结构参数的形状记忆合金驱动器在不同驱动条件和外界环境下的热力学性能,对形状记忆合金驱动器的响应能力、驱动力及能耗展开实验研究和分析;采用多目标优化设计理论和算法,对形状记忆合金差动驱动器的综合热力学性能进行了优化,得到了满足使用条件的形状记忆合金驱动器最优结构参数和与之匹配的控制量。     

A compact semiconductor opening swith-based generator with a 300-kV output voltage and up to 2-kHz pulse repetition rate

A compact generator with a semiconductor opening switch (SOS-diode) shaping across resistive load pulses with an amplitude of up to 300 kV, duration of 30–50 ns, and a 300-Hz pulse repetition under uninterrupted operation and up to 2 kHz in a 30-s burst mode is described. The generator contains a thyristor charging device, magnetic compressor, and inductive storage with a semiconductor opening swith based on SOS-diodes. The average output power at a maximum pulse repetition rate and a 250kV-voltage is 16 kW. The overall dimensions of the generator are 0.85×0.65×0.42 m, the weight is about 115 kg.     

BUEVA: a bi-directional ultrasonic elliptical vibration actuator for micromachining

This paper presents a novel actuator design for vibration-induced micromachining. The bi-directional ultrasonic elliptical vibration actuator (BUEVA) possesses a combination of features that renders it suitable for the machining a wide range of materials over a variety of cutting parameters. The cutting motion is an elliptical tool motion that resembles “spoon feeding”. This cutting action is in contrast to in-plane, horizontal motion utilized by most existing setups. The motion is arrived at through a combination of motions along the tool's axial and transverse directions and by vibrating out of phase and is generated by two stacked ceramic multilayer actuator ring piezo elements. Another distinguishing feature of BUEVA is the use of piezo stacks which ensure high blocking force compared to low force of piezo benders as used in many existing actuators. Furthermore, the amplitude and frequency of vibration of the tool are controlled on-line in order to vary the cutting depth and cutting speed according to the desired cutting parameters. This is a desirable characteristic which allows one to “dial-in” a desirable cutting speed for different workpiece materials. Another attractive BUEVA feature is that the design is very compact and can fit easily into the working space of most milling machining centers without the need for custom motion setups. An off the shelf TiALN-coated carbide turning tool is utilized as the cutting tool. Furthermore, refined versions of previously reported models by other workers in the micromachining field have been developed. Experimental force and surface roughness measurements are compared versus these ideal calculations from the improved models. Compared with these reference models, our refined calculations show improvements in describing chip geometry based on corrected tool motion and which, consequently, resulted in improved estimates of both surface roughness and cutting forces. Verification cutting tests in two different materials (Al2024 and Plexiglas) show good surface integrity and dimensional definition with roughness measurements in reasonable correlation to the refined model calculations.     

时栅角位移传感器自动检定系统

针对时栅角位移传感器产业化过程中产品质量检定环节采用人工检定方式导致工作效率低且容易产生漏记、错记进而影响产品质量检定的问题,研制了时栅角位移传感器自动检定系统。系统采用PMAC作为运动控制单元,以直驱电机作为驱动机构,有效减小传动环节误差,质量检定选用ELCOMAT3000型双轴电子自准直仪,全量程检定误差小于±0.25″。构建了参数化的直线梯形加速运动模型与产品质量检定算法,整个产品质量检定全部自动完成,检定精度高,工作效率得到有效提升,产品质量得到可靠的保证。     

A piezoelectric motor for precision positioning applications

This study presents a novel precise piezoelectric motor capable of operating in either an AC drive mode or DC drive mode. In the AC drive mode, the motor acts as an ultrasonic motor which is driven by two orthogonal mechanical vibration modes to generate elliptical motion at the stator to push the slider into motion. In the DC drive mode, stick-slip friction between the stator and slider is used to drive the motor step-by-step. The experimental results show that the AC drive mode can drive the motor at a high moving speed, while the DC drive mode can simply drive the motor with a nanoscale resolution. In our experiments, a prototype motor is fabricated and its actions are measured. The results demonstrate that in the AC drive mode, the piezoelectric motor can achieve a 106 mm/s speed without a mechanical load and a 34 mm/s speed with 340 g of mechanical load when applying two sine waves with a drive of 11.3 V at 38.5 kHz. Meanwhile, in a DC driving mode, the motor is capable of performing precision positioning with a displacement resolution of 6 nm when driving at 100 Hz.