| With the development of advanced materials and new high technology,special processing technology has gradually become a key technology for the national industrial,aerospace and military product technologies.Rotary ultrasonic machining(RUM)is an important part of special processing.RUM technology is applied to CNC machining machines for processing hard and brittle materials and advanced composite materials with high processing efficiency and small cutting force.The loosely coupled transformer is a key component of RUM for contactless energy transmission.However,it is found that the method of loosely coupled transformer features difficult modeling of ultrasonic tool holder,equivalent parameters are greatly affected by the environment and high control complexity.It brings great challenges to related research work.The key theoretical and technical problems of ultrasonic driving system design,equivalent impedance modeling of ultrasonic transducer,loosely coupled transformer compensation optimization and vibration amplitude control algorithm are studied in this dissertation.The main work is as follows:Aiming at the high operating power of ultrasonic transducers in rotary ultrasonic machining,a variable frequency ultrasonic driver for the rotary ultrasonic machining is designed to drive different ultrasonic tool holders in multiple frequency bands,intelligently search for the optimal operating frequency of the driving components,realize dynamical phase locking.A control minimum system,a signal generation circuit,an RMS acquisition circuit,and a phase acquisition circuit are included in the self-developed hardware circuit.The rotary ultrasonic machining tool holder consists of a loosely coupled transformer and an ultrasonic transducer.The frequency impedance characteristic of ultrasonic transducer under different voltages is studied based on the developed ultrasonic driving system.The dynamic correspondences of input current and output vibration amplitude are analyzed under different frequencies.It is proved that the input current and output vibration amplitude of the ultrasonic transducer are positively correlated.The problem of resonant frequency and impedance deviation between the ultrasonic tool holder and the ultrasonic transducer is investigated in this dissertation.This deviation problem causes the output voltage and output current both oscillate at the initial moment and attenuate at the steady time when the ultrasonic tool holder is operated at the resonant frequency of ultrasonic transducer.To analyze the equivalent load characteristics of ultrasonic transducers,an equivalent impedance model of ultrasonic transducer is constructed to predict the resonant frequency and impedance characteristics of ultrasonic transducers.The effects of the tightening torque of the clamping nut and the extension length of the machining tool on the resonant frequency and impedance of ultrasonic transducer are analyzed in this dissertation.An equivalent transfer function model of the ultrasonic transducer is established based on the equivalent dynamics model and the electrical equivalent model.The cutting force testing platform is established by a motor motion platform,a force driver and an impedance analyzer.The electrical equivalent parameters of the ultrasonic transducer under different cutting forces are obtained by the testing platform.It is found that the resonant frequency and impedance of the ultrasonic transducer increase as the cutting force increases.The equivalent transfer function model of the ultrasonic transducer varies with the cutting force.Based on the linear parameter fitting method,the dynamic transfer function model of the transducer is established.It is found that the dynamical transfer function model can better describe the current response characteristic of the ultrasonic transducer under different external cutting forces.In order to solve the deviation of the resonant frequency and impedance between the ultrasonic tool holder and the ultrasonic transducer in the RUM system,two compensation topologies are proposed to realize the compensation of wireless power transfer system: bilateral compensation and unilateral compensation.In the bilateral compensation structure,an equivalent leakage inductance model of a loosely coupled transformer based on T-network leakage inductance equivalent circuit is constructed in this dissertation.Based on the zero-phase contour line method,it is found that the bilateral compensation exists multiple solutions problem in four compensation topologies visually.A multi-objective optimization mathematical model is established to eliminate the deviation of resonant frequency and impedance in this dissertation.Based on Pareto frontier method,the optimum distribution of phase difference of ultrasonic tool holder,and impedance difference between ultrasonic tool holder and ultrasonic transducer is obtained in this dissertation.Based on a multi-objective genetic optimization algorithm,the compensation capacitance values are optimized in bilateral compensation topologies.It is found that the optimization capacitance values of series-series compensation topology can solve the problem of resonant frequency and impedance deviation between the ultrasonic tool holder and the ultrasonic transducer.The state space equations of four topologies are constructed to analyze the dynamic response characteristics of ultrasonic tool holder vibration system.Therefore,the output voltage and output current response trends of different topologies are analyzed.The MATLAB simulation platform of the ultrasonic tool holder vibration system is constructed to comprehensively analyze the transient response curves of the input and output voltage,current and phase difference of the ultrasonic tool holder.It is proved that the voltage gain of loosely coupled transformer is improved from 0.333 to 0.920 by the series-series compensation structure in the experiments.Compared with no compensation case,the output active power is increased by 7.634 times,the monitoring sensitivity of the ultrasonic tool holder for the external cutting force is improved,and the rising rate of impedance for monitoring cutting force is improved from 1.151 to 1.823.In the unilateral compensation topology structure,a novel primary side compensation method is proposed to achieve double compensation of the resonant frequency and impedance between the ultrasonic tool holder and the ultrasonic transducer.Based on the T-type network equivalent leakage inductance model of loosely coupled transformer,the coil self-inductance and the equivalent series resistance decrease exponentially,and the leakage inductance linearly rises as the length of air gap increases within a certain range.When the series compensation structure in primary side is used in the ultrasonic tool holder,the output voltage gain of the loosely coupled transformer is increased.The theoretical calculation and experimental verification of the response state of the ultrasonic tool holder driven at the sweeping frequency and the resonant frequency are carried out based on the physical characteristics of the loosely coupled transformer.Compared with the uncompensated case,the voltage gain is increased from 0.267 to 0.90,the output active power is increased by 11.3 times,and the sensitivity of impedance for monitoring cutting force is increased by 1.54 times based on the series compensation in primary side.The deviation of the resonant frequency and impedance of the ultrasonic tool holder and the ultrasonic transducer increases as external cutting force increases based on the primary series compensation topology.The fuzzy PID neural network self-correction algorithm is proposed to track the resonant frequency of ultrasonic transducer under different cutting forces,the feasibility of this algorithm is verified by experiments in this dissertation.In order to solve the vibration amplitude attenuation problem of ultrasonic vibration system under the cutting force,the auto disturbance rejection controller(ADRC)is proposed to realize the constant vibration amplitude output of the ultrasonic tool holder.The MATLAB simulation platform is established to achieve the current response curves of ultrasonic tool holder vibration system under no load and noise interference.The effects of different parameters of tracking differentiator,extended state observer and state error feedback controller of ADRC on the current response curve under no load are verified by experiments,and the effects of ADRC on the current response is verified under different cutting forces in this dissertation.The ultrasonic tool holder vibration system is verified to keep the constant vibration amplitude without attenuation.A machining experimental platform is built to verify the effectiveness of the ultrasonic machining vibration system. |
PDF Full Text Request