The Research Of Constant Voltage Control Stratage On Power Ultrasonic Transducer

The study of power ultrasonic have been improved,and a various types of ultrasonic equipment that based on this theory be used wildly.Compared with the traditional chemical adhesive,hot melt adhesive and other methods,ultrasonic welding is a new welding process with great advantages and it avoids the pollution on the environment.As the key equipment of ultrasonic welding machine,the power adjustment ability and the stability of output amplitude of ultrasonic power will directly affect the quality of welding.Based on control theory,this paper researched ultrasonic power of constant amplitude oriented thermoplastic material welding control strategy and simulation,the main studies are as follows:(1)Due to the nonlinear characteristics of the piezoelectric transducer,the core component of vibration equipment,and the change of characteristics between the small signal with large power,and on the base of equivalent circuit analyze the mechanism.The relationship between the output amplitude and the ambient temperature,the frequency of input signal and the voltage of the load transducer are obtained by experiment.That provides the realistic basis for the transducer mechanism modeling.(2)In view of that the nonlinear characteristics of the piezoelectric transducer in the presence of the hysteresis,creep and so on,make the electrical parameters of the transducer as change values that be affected by the variation of the interference.According to the progress of electrical power-mechanical energy conversion,established the equivalent circuit model of piezoelectric transducer and the transducer energy transfer mechanism,and transformed it into differential equation.Then the state space equation of the energy transfer mechanism is obtained according to the input and output relations of the inverter,rectifier and power adjustment module in ultrasonic power supply.(3)Based on the established state space model of piezoelectric transducer,a feedforward control algorithm based on the robust control theory is proposed.The control law is designed according to the uncertain information of the system model,which makes the system stable effectively under the parameters with bounded perturbation.PID algorithm based on integral separation and DFS-PI control algorithm is proposed.The former avoids the problem of the computational expensiveness which is caused by the accumulation of input deviation in model input.The latter using the direct inverse model control and the iterative learning control theory to identify the parameters of the controlled object,to adaptively control nonlinear systems via fuzzy identification.Finally,the paper test the digital ultrasonic spot welding in the condition of slowly changing load and suddenly changing load,the result is the amplitude stable performance of the ultrasonic power achieved the desired effect.And the verified the effectiveness of the control strategy.