Research On Vibration Filter Utilized In Piezoelectric Motors

Piezoelectric motors utilize the inverse piezoelectric effect of piezoelectric materials,which possess the advantages of compact structure,being apt to miniaturization,high motion accuracy,self-locking,etc.Piezoelectric motors have been widely employed in the fields of aerospace,biomedical instruments,and optics.As a sort of typical electromechanical coupling device,the motion characteristic of piezoelectric motors is influenced by their mass and stiffness distribution.This dissertation studies the mechanism of the influence in-depth and proposes the idea of vibration mass isolation in the field of piezoelectric motors for the first time.By introducing a vibration filter,the mass and stiffness distribution of piezoelectric motors can be controllably adjusted to improve the motion characteristic.Considering that there are varieties of piezoelectric motors and their different working mechanisms,this dissertation has discussed four representative piezoelectric motors from a theoretical or experimental point of view and expounds on the working mechanism of the vibration mass isolation method based on the vibration filter.The main research contents are summarized as follows:From a theoretical point of view,the application of the vibration mass isolation method to standing wave piezoelectric motors(standing wave motors for short)is studied.Traditional standing wave motors have severe friction and wear,resulting in short service life.Based on the vibration mass isolation method,we propose a slider with a separated structure,that is,the traditional slider is divided into two parts,which are connected through a vibration filter.The small part has an extremely wide frequency response range,and can quickly follow the vibrator's movement without relative slippage during contact.The movement of the small part is transmitted to the large part through the vibration filter,and the high-frequency harmonic components contained therein are effectively suppressed.Therefore,the mass of the large part will not affect the movement of the small part.The driving process based on the vibration mass isolation method theoretically has no friction loss.Thus,the operating efficiency and service life of standing wave motors can be improved.We established the kinematic model of a general standing wave motor to verify the above analysis.The results prove that the friction loss power of the standing wave motor based on the vibration filter is reduced by about 6 times compared with the traditional situation.From a theoretical point of view,the application of the vibration mass isolation method to traveling wave piezoelectric motors(traveling wave motors for short)is studied.When traveling wave motors are in a static state,the initial preload force makes the vibrator and the slider completely coupled.The slider strengthens the vibrator,forcing the modal frequency of the latter to increase.As a result,traveling wave motors may encounter problems such as difficulty in startup or sudden stop.The vibration mass isolation method can provide a new way of solving the problem.We constructed the vibration filter with two degrees of freedom by using a flexure hinge.The filter has a high cut-off frequency in the longitudinal direction and a low cut-off frequency in the tangential direction.Using the above characteristic,the modal frequency of the coupling body of the vibrator and the slider can be appropriately reduced by controllably increasing its modal quality without affecting its modal stiffness.The analytical model is established based on Hamilton's principle,and the finite element method is used for verification.In order to avoid the interference of irrelevant vibration modes,we verified the feasibility of the equivalence between the out-of-plane bending mode of a ring-shaped vibrator and the bending mode of a simply supported beam,thereby transforming the sophisticated three-dimensional issue into a more concise two-dimensional one.The results prove that the modal frequency of the coupling body can be adjusted to the corresponding modal frequency of the free vibrator without affecting the mode shape,thereby improving the startup characteristic of traveling wave motors.For the first time,the vibration mass isolation method is applied to impact drive piezoelectric motors(impact motors for short).The step distance of impact motors is inversely proportional to the load mass.When the load is large,the moving efficiency will be seriously reduced.The main reason is the huge inertial force generated on the load by the high-frequency harmonic components contained in the movement of impact motors.The low-pass characteristic of a vibration filter can effectively suppress the transmission of the high-frequency harmonic components to the load,thereby weakening the influence of the load on the movement of impact motors.As a result,the moving efficiency of impact motors can be improved.Based on Newton's second law,we established the kinematic model of an impact motor,which is analyzed by MATLAB/Simulink.We designed and assembled two impact motors for control experiments,to one of which the vibration mass isolation method is applied and the other represents the traditional situation.The experimental results are consistent with the theoretical calculation.According to the results,it can be concluded that the impact motor based on the vibration filter mainly has the following two characteristics:1)It still maintains a high moving efficiency while dragging a heavy load,which proves that it has a considerable heavy load capability;2)Since the vibration mass isolation method weakens the influence of the load,the step distance and moving efficiency of the impact motor basically does not change with the variation of load mass.For the first time,the vibration mass isolation method is applied to a precision moving stage driven by a piezoelectric actuator.The structure design and working principle of the precision moving stage are described in detail.A flexure hinge is used as the core part of the vibration filter to improve the response speed of the local structure.Two design rules are proposed,and the size of the flexure hinge is optimized by the finite element method.We assembled two precision moving stages for control experiments,to one of which the vibration mass isolation method is applied and the other acts as the referenced object.Experimental results prove that the modified precision moving stage not only inherits the advantages of the referenced stage,such as low cost of driving circuit,compact structure,positioning accuracy of nanometer's order,etc.,but also has largely improved the speed and heavy-load capability.According to the motion characteristic of the precision moving stage,we established the kinematic model and explored the motion behavior of the precision moving stage under different frictional forces and signals of different waveforms.