Research On An Asymmetrical Piezoelectric Inertial Rotary Actuator With An Adjustable Friction Function

Piezoelectric inertial precise actuator is a device which uses the piezoelectric element to generate inertial impact movement. Based on the domestic and overseas research status of precision actuator, the inertial type of piezoelectric actuator has simple structure, high response, high resolution, lagre stroke, high movement speed and low costing. However, it also bears some disadvantages, such as high control requirements for circuit and friction, the friction influence, small output loads, etc. These shortcomings, to some extent, constrain the further development, application and popularization of the piezoelectric inertial actuator. Facing the current main problems, this paper has made the corresponding research strategies and then an asymmetrical piezoelectric inertial actuator with an adjustable friction function has been put forward and developed. This novel actuator, driven by the cantilever bimorph vibrators, could generate inertial impact rotary movement. Through theoretical analysis, simulation and experimental tests, the cantilever bimorph vibrator and the proposed actuator are studied systematically. One one hand, the fundamental characteristics, static characteristics, dynamic characteristics of the vibrators and their influence factor are analyzed particularly. On the other hand, the main working performace of the new actuator is evaluated briefly.1. The research of cantilever bimorph vibrator with symmetrical clamping sturctureFirstly, this study builds the dynamic model and equation for the piezoelectric cantilever bimorph vibrator with symmetrical clamping sturcture by the proposed method of transforming symmetric electrical signal excitation to equivalent harmonic force. Through the analysis and tests of the system parameters, the full response analytic expression of the vibration system constructed by the vibrator is obtained. The results of simulation and experiments indicate that the correctness of the dynamic model and the validity of the proposed equivalent method. Secondly, the influence factors of the dynamic displacement at the end of the vibrator and the driving force of the vibrator are analyzed in simulation. The results of simulation show that the dynamic displacement at the end of the vibrator increases significantly with the increase of the static displacement input and the length of the bimorph, but is little effected with the stiffness coefficient or the mass of the mass block. However, the driving force of the vibrator grows obviously with the increase of the static displacement input, the length of the bimorph and the the mass of the mass block, but is little influenced with the stiffness coefficient.2. The research of cantilever bimorph vibrator with asymmetrical clamping sturctureThis paper presents two types of clamping way according to the different condition of clamping, respectively called asymmetrical material clamping and asymmetrical structure clamping. Then on the basis of the dynamic equation of the vibrator constructed under the condition of symmetrical clamping, two driving schemes are proposed and analyzed in theory under the condition of asymmetrical clamping. After that, the feasibility of two driving schemes is verified in the simulation and experiments. The results show that the displacement amplitude and acceleration of the vibrator at the short clamping side are both larger than the ones at the long clamping side. In other words, the asymmetrical structure clamping could provide much larger driving force to drive the actuator. So it is selected as the clamping way for the vibrator. On the other hand, the difference of the acceleration between the short and long clamping side reaches the maximum when the clamping size difference is 5mm, which is chosen as working condition for the vibrator.3. Theorecical design and simulation of the asymmetrical piezoelectric inertial rotary actuator with an adjustable friction functionTwo vibrators are symmetrically assembled on the moving body of the actuator. After that, the research strategies of utilizing mechanical control method, frction force control device and magnetic force amplifying structure are presented to solve the main existing problem of the actuator. Based on the inertial impact working principle and research strategies, the mechanical structure is designed and two kinds of working modes are determined. Furthurmore, the motion process of the actuator is introduced in detail. On account of the working principle, the dynamic equation and Simulink simulation system of the actuator are established. What is more, a time series superposition method is proposed to describe the motion state of the asymmetrical clamping vibrator in simulation. At last, the simulation results indicate that the theoretical resolution of the novel actuator could reach 1.20μrad.4. Experimental study on the asymmetrical piezoelectric inertial rotary actuator with an adjustable friction functionThe friction force characteristics, frequency characteristics, voltage characteristics, output stepping angle characteristics, angular velocity and output force characteristics on the property of this actuator are observed and recorded in a series of experiments under A and B working modes. The experimental results show that the minimum resolution and drawback/forward rate of this actuator are respectively 0.85μrad and 24%. The response curve of stepping angle in the tests is coincident well with the one in simulation. The working frequency of the actuator ranges from 1Hz to 7Hz. However, the friction torque which makes the actuator rotates steadily ranges from 1.485N·mm to 2.475N·mm under A working mode, while 0 to 5.445N·mm under B working mode. Within certain limits, the linearity of the output stepping angle curve increases evidently with increasing friction torque. The actuator under B working mode performs much better than it works under A working mode, the maximum angular velocity and output force of which could reach 4.02 rad/s and 980 mN respectively. In general, the proposed actuator not only has the basic advantages like simple structure, high response and speed, lagre stroke, no electromagnetic interference and pollution, but also possesses the features like special’ driving method, simple control circuit and mechanical structure, low friction control requires, low cost of driving element, no creep and hysteresis. Besides, this novel actuator also has some superior characteristics such as stable output stepping angle, high resolution, adjustable friction function, high output stepping angle linearity and controllability, improvable angular velocity and output force.