| With the further study in space exploration engineering domain by various countries,the advanced technologies such as satellite laser communication,antenna pointing adjustment,precision optical tacking,etc.put forward the urgent demand for multi-DOF precision drive technologies.The piezoelectric driving has many advantages including simple structure,fast response,high resolution,strong anti-interference ability,self-locking,etc.by comparing with the traditional electromagnetic driving.Therefore,the multi-DOF precision piezoelectric actuators?PEAs?become a hot research topic.In this work,the two-DOF piezoelectric actuator?PEA?with spherical rotor is studied to meet the actual demand of multi-DOF precision drive in precision pointing and adjusting,in which the critical issues about its mechanical structure,output performance and motion control system are discussed in detail.The exciting signal and actuation process of the PEA are primarily determined by analyzing the inertial stick-slip drive principle.A two-DOF bending-bending hybrid piezoelectric vibrator is proposed,and its static mathematical model is established to derive the relationship among the main structural parameters,material parameters,exciting voltage and the static output displacement;the relationship is verified by finite element simulation with ANSYS software.The critical parameters of the vibrator are determined,and then the experimental prototype of it is developed.The output displacement response of the vibrator is measured by laser displacement sensor.The equivalent static capacitance of the vibrator is tested with precision impedance analyzer.A scheme for supporting the rotor and applying preload on it is proposed,and its structure is also designed.The experimental prototype of the two-DOF PEA with spherical rotor is ultimately developed after designing the whole package.The measuring methods of the angular displacement and output torque are presented.Moreover,the effect from the preload condition to the output characteristics is analyzed.A series of mechanical output performances are separately tested with commercial power amplifier?Model:E01.A4?.Test results indicate:the maximum velocity around X axis and Y axis at the frequency of 460 Hz are obtained to 0.153 rad/s and 0.154 rad/s,respectively;the maximum output load torque exceeds 4.07 mN·m under exciting voltage of 400Vp-p and frequency of 1 Hz;while the rotary motion around X or Y axes are separately excited,the coupling displacements around another axis are 3.09%?5.74%,respectively;the angular displacement resolution rotating around X axis and Y axis are 2.49?rad and 2.52?rad,respectively.These test results fully demonstrate that high resolution moitons of the developed PEA are realized.The basic design indexes of the power amplifier with high voltage output,low frequency and linear amplification ability are determined according to the equivalent static capacitance,mechanical output performances and experimental requirement of the developed PEA.The overall design is accomplished,and the power amplifier are divided into some functional modules.The basic circuit structure of each functional module is determined by means of principle analyses.The parameters of the electronic components are determined by simulating analysis with Multisiom software;the PCBs of each functional module are designed with Altium Designer software,and then the physical circuit boards are fabricated,after that the whole power amplifier is assembled.The input-output performances of the developed power amplifier are tested in sequence.Test results show:the amplification error of the developed power amplifier is less than 0.3470%;the maximum zero input response deviation is 0.6726 V;the peak-to-peak voltage drift within 20 minutes is less than 0.0355%.These results fully indicate the performance characteristics of good linearity,low zero input response deviation and low time drift of the developed power amplifier,and the functional characteristics of multi-chanel output,linear amplification with low frequency and high voltage output.Besides,with comparing between the developed and the commercial power amplifier,there are about 8 times output power of the developed power amplifier than the commercial one under the rated capacitive load of 100 nF.The power on characteristics and driving effect are separately tested with the commercial and the developed power amplifier.Test results indicate:the displacement rollback of the developed PEA around X axis and Y axis can be reduced by 23.63%and 27.82%with the developed power amplifier.It fully presents the significance of improving the output power of the power amplifier to improve the rollback characteristic of inertial PEA for promoting its output performance.The motion control hardware platform of the actuator is built by using the developed power amplifier.Then the closed-loop control program flow is determined.The drive system and closed-loop control system based on the parameter self-tuning PID control algorithm are established with LabVIEW software.After that the closed-loop positioning characteristic and trajectory tracking characteristic are tested,respectively.Test results indicate:the positioning errors of rotating around X axis and Y axis are 23.48?rad and 13.20?rad,respectively,while the target displacement is 30000?rad;while a sinusoidal target displacement with amplitude of 30000?rad and frequency of 0.2 Hz is tracked,the relative tracking errors around X axis and Y axis are about 4.98%and 4.83%,respectively.The test results show:the developed two-DOF PEA and its motion control system have the potential to be used in precision pointing and attitude adjustment mechanisms.The advantage of high moiton resolution of the developed PEA can be obtained by comparing with the exciting multi-DOF PEAs. |
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