In this paper, a novel compact piezoelectric stick-slip actuator integrated with ultrasonic vibrator based on ultrasonic anti-friction effect is proposed. Based on inverse piezoelectric effect, the piezoelectric stack generates the axial vibration under the excitation of asymmetric sawtooth wave, the ultrasonic vibrator is composed of a brass block and four piezoelectric plates, which is used to excite the ultrasonic longitudinal vibration mode in the fast deformation phase of piezoelectric stack. Due to ultrasonic anti-friction effect, the backward displacement of the actuator is effectively suppressed, and the bidirectional comprehensive output performance is improved. The prototype is fabricated and the operating principle of hybrid excitation is introduced, then the frequency of the first-order longitudinal vibration mode is explored by finite element analysis and impedance test, and the systematic experimental test is conducted. The test results show that when the sawtooth frequency is 300 Hz, comparing with the traditional sawtooth excitation mode, the proposed hybrid excitation mode can improve the velocities of the forward and backward directions by 30% and 26.7%, and the bidirectional maximum vertical mass loads are increased by 44.4% and 50%. This work provides a design concept that uses ultrasonic vibrator to improve the bidirectional comprehensive output performance of the piezoelectric stick-slip actuator.
Flexure hinges have been widely applied in driving mechanisms to achieve the high velocity of stick-slip piezoelectric actuators. However, the majority of driving mechanisms are designed with existing flexure hinge forms, and it is difficult for the actuators to realize the optimal velocity performance. Therefore, a systematic method based on the topology optimization to design flexure hinges of driving mechanisms is proposed in this paper for improving the velocity of the actuators. According to the working principle, the velocity can be increased by maximizing displacement of a driving foot along the positive direction of x-axis. The optimization problem of flexure hinges is described utilizing the Solid Isotropic Material with Penalization (SIMP) method. To illustrate the proposed method in detail, a four-bar mechanism with optimized flexure hinges is designed. Among them, three optimization schemes are implemented based on positions of flexure hinge design domains, and then deformations and equivalent stresses of the four-bar mechanism are investigated by simulation to find optimal flexure hinge forms. To prove the feasibility of the proposed method, the characteristic experiments of prototype are conducted. When the driving voltage and driving frequency of prototype are 100 V p-p and 470 Hz, the maximum velocity is 17.50 mm/s, the maximum load is 220 g. And it is interesting to find that the prototype has no backward motion. Compared with the previously reported actuators with four-bar mechanisms, the velocity of prototype is significantly improved. INDEX TERMS stick-slip piezoelectric actuators, flexure hinges, driving mechanisms, SIMP method, velocity performance.
In this paper, the shape design process is briefly discussed emphasizing the use of topology optimization in the conceptual design stage. The basic idea is to view feasible domains for sensitivity region concepts. In this method, the main process consists of two steps: as the design moves further inside the feasible domain using Taguchi method, and thus becoming more successful topology optimization, the sensitivity region becomes larger. In designing a double-eccentric butterfly valve, related to hydrodynamic performance and disc structure, are discussed where the use of topology optimization has proven to dramatically improve an existing design and significantly decrease the development time of a shape design. CFD analysis results demonstrate the validity of this approach.
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