| With the development of natural science and industrial production,precision actuation and operation technology has become the hot topic both in academic and industrial circles nowadays.And this technology has been widely used in the fields of ultra-precision machining,life sciences,aerospace,precision optical systems,etc.In order to promote the further development of related fields,the investigation of precision rotary actuators with large stroke and high resolution is needed urgently.At present,precision rotary actuators based on electromagnetic,electrostatic,electrothermal,and piezoelectric principles are developed by researchers from various countries,but it’s difficult for them to balance large stroke and high resolution.Compared with first three type actuators,the performances in terms of resolution,response speed,driving force and environmental compatibility of the piezoelectric actuator are more outstanding.Thus,the principle of piezoelectric actuation is adopted in this article to develop a precision rotary actuator that can realize both large stroke and high resolution.Piezoelectric actuators can be divided into direct drive type,resonant type,inchworm type and inertial type according to their actuation principles.Among them,the resolution of direct drive piezoelectric actuator can achieve nanometer level but the motion range can only reach micron level,and the inertial piezoelectric actuator can achieve infinite motion range but the resolution can only reach micron level.According to those characters,a rotary piezoelectric actuator with direct drive and inertial drive dual modes is proposed in this work to achieve both large stroke and high resolution.On this basis,combining on the main problems of direct drive and inertial rotary piezoelectric actuators,the basic configuration of longitudinaltorsional conversion(LTC)is proposed.Then,the static analysis about the torsional actuation unit with the LTC element is carried out,the static model of this part is established and the feasibility of the LTC actuation is theoretically verified.After that,based on the Coulomb friction theory,the "stick-slip" working mechanism of the inertial drive actuator is analyzed and the friction coupling dynamic model is established.The static model of the torsional actuation unit is used to optimize the structural dimensions of the key components in this part,and the static and modal analyses are carried out by the finite element analysis software ANSYS to verify the static and dynamic characteristics.Later,according to the analyses of inertial drive principle and the friction coupling dynamic model of the actuator,the structural dimensions of the key components in the inertial drive part of the actuator are determined.And the inertial drive output characteristics of the actuator are evaluated by the simulation of Simulink software.Finally,the structures and dimensions of the actuator are decided and the prototype of cross-scale longitudinaltorsional motion conversion rotary piezoelectric actuator is manufactured.In order to verify the feasibility for achieving both the large stroke and high resolution by the combination of direct drive-inertial drive dual modes,as well as the feasibility of LTC actuation,and to evaluate the mechanical output characteristics of the new rotary piezoelectric actuator,an open-loop experimental test system is built and an indirect measurement scheme of angular displacement is proposed.The mechanical output characteristics of the torsional actuation unit and the actuator are studied in detail by the open-loop experimental test.The experimental results show that the maximum static rotary angle of the torsional actuation unit can reach 4.935 mrad(100 V)with the resolution of 46 nrad,the firstorder resonance frequency of 1361.537 Hz,and the maximum hysteresis rate of19.224%;The actuator can output bidirectional 360° rotary motion under inertial drive mode.Exciting by sawtooth wave signal,the stable working frequency range of the actuator is [0 Hz,400 Hz],the maximum speed can reach 1.854 rad/s(100 V,400 Hz),and the stalling load is 2.8 kg.According to the related experimental results,the proposed actuator can balance both the large stoke and high resolution,and has the wide velocity range as well as sufficient load-carrying capacity.Finally,a closed-loop experimental test system is built.And the control accuracy of point positioning of the actuator is measured based on the inertial-direct drive dual modes switching method.The experimental result shows that the width of positioning errorband is 12.000 μrad under the motion range of 6.666 mrad and the inertial drive frequency of 50 Hz;Aiming at the shortcomings of systematic error,overshoot,oscillation and service life reduction in the inertial drive trajectory tracking method,a direct drive-inertial drive mode fusion trajectory tracking method is proposed,and the feasibility of it is verified through experiments.The experimental results show that the widths of tracking error band are 144.611 μrad and 165.267 μrad for the proposed mode fusion method and inertial drive trajectory tracking method respectively when tracking a sinusoidal target trajectory with a frequency of 0.5 Hz and amplitude of 3.333 mrad;And the widths of tracking errorband of the two methods are 35.000 μrad and 116.155 μrad respectively when tracking a linear reciprocating target trajectory with a rise time of 12.5 s and a motion range of 6.666 mrad.The comparison shows that the proposed mode fusion method can not only compensate the inherent problems of inertial drive trajectory tracking method,but also can obtain higher tracking accuracy when tracking slowly changing and large turning target trajectories. |
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