In the piezoelectric driving field, backward motion commonly exists in output displacement curves of the actuators designed by various driving principles, which deteriorates the output performances and increases difficulty in subsequent control. To suppress the backward motion, a synergic motion principle (SMP) was proposed in this paper, which employed two piezoelectric stacks (PESs), one for driving and the other for lifting. By synergic driving of these two PESs, the contact force during the driving process could be effectively controlled and thus the backward motion could be actively suppressed. To verify the feasibility, an actuator prototype was designed and fabricated, and an experimental system was established to test its output performances. By theoretical analysis and experiments, the relationship of the driving voltages for these two PESs was determined. Under the optimized experimental conditions, it showed that the actuator could output stepping displacement without backward motion when working under the SMP. By comparing the results with those obtained when the actuator worked under the parasitic motion principle (PMP), the feasibility and validity of the proposed SMP for suppressing the backward motion were further confirmed.

Taking advantage of simple structure and control, stick-slip piezoelectric actuators have been widely employed to realize precision positioning in precision machinery and instrument. However, their output characteristics could be significantly affected by the contact status between the driving mechanism and the mover (or rotor). If the contact status changes in the motion process, strong nonlinearity will appear in the displacement-time curve, deteriorating the performances. To achieve a constant contact status, the gravity of the rotor was used in this paper, and accordingly, a novel stick-slip piezoelectric rotary actuator was developed. The structure design, motion principle, as well as output characteristics of the actuator were addressed and discussed in detail. Experimental results indicated that when the driving frequency was below 350 Hz, stable stepping motions with quite small backward motion could be achieved. By changing the driving frequency, voltage and radius, various stepping rotation angles and speeds were easily obtained. The output characteristics changing with the vertical load were further characterized. Furthermore, by simply changing the direction of the driving waveform, forward and reverse rotation motions showing good linearity with time were achieved in a very large motion range, corresponding to a millimeter scale linear displacement. Comparative experiments with a normal stick-slip actuator further confirmed the validity and advancement of the proposed strategy for keeping a constant contact status, which will be beneficial to the subsequent motion control and mass production.

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The rigorous thermal environment brought by long-time high-speed flight is imposed severe requirements on the structural bearing capacity and structural thermal safety of the aircraft. The integrated non-ablative thermal protection system based on continuous fiber-reinforced ceramic matrix composites is becoming a hot spot on the design of aircraft structures. However, the multi-scale, non-linear, non-uniform features of such materials, as well as complex thermal and mechanical characteristics, pose serious challenges to structural design and evaluation. Under the aero heating environment, the non-uniform temperature rising and thermal matching between different components in the continuous fiber-reinforced ceramic matrix composites are extremely complicated, which has a significant influence on the thermal safety performance of the structure. In this paper, based on the commonly used 3D orthogonal weaving process and the thermal characteristics prediction method of fiber bundles considering the effect of PyC interface layer, the fluid-structural strong thermal coupling characteristics of different woven parameters in typical aircraft structure is carried out. Quantitatively characterizing the heat transfer characteristics of this new material under the actual flight condition of the aircraft can further to improve the accuracy of the thermal property parameters obtained based on the ground test. The analysis results show that increasing the proportion of fiber bundles in a certain direction is the most effective method to increase the thermal conductivity in this direction. At the same time, the arrangement of the coupling yarns will also have a greatly influence on the thermal conductivity of the material. These results is of great significance for the design of the materials.

Although the stick-slip principle has been widely employed for designing piezoelectric actuators, there still exits an intrinsic drawback, i.e., the backward motion, which significantly affects its output performances and applications. By analyzing the generation mechanism of backward motion in stick-slip piezoelectric actuators, the elliptical trajectory was employed to design a novel stepping piezoelectric actuator free of backward motion. Accordingly, a prototype of piezoelectric actuator was designed, which utilized a flexure hinge mechanism and two vertically arranged piezoelectric stacks to generate the required elliptical trajectory. The compliance matrix method was used to theoretically analyze the flexure hinge mechanism. The theoretical and measured elliptical trajectories under various phase differences were compared, and the phase difference of 45° was selected accordingly. Under a critical relative gap, output performances of the actuator working under the elliptical trajectory were characterized, and then compared with that obtained under the normal stick-slip driving principle. Experimental results indicated that forward and reverse stepping displacement with completely suppressed backward motion could be achieved when employing the elliptical trajectory, verifying its feasibility. This study provides a new strategy for designing a stepping piezoelectric actuator free of backward motion.