The Frequency-Variable Rotor-Blade-Based Two-Degree-of-Freedom Actuation Principle for Linear and Rotary Motion.

Piezoelectric accurate actuation plays an important role in industrial applications. The intrinsic frequency of previous actuators is invariable. However, variable frequency can approach the range near the low-intrinsic-frequency and realize a high actuation capability. The frequency-variable linear and rotary motion (FVLRM) principle is proposed for rotor-blade-based two-degree-of-freedom driving. Inertial force is generated by frequency-variable piezoelectric oscillators (FVPO), the base frequency and vibration modes of which are adjustable by the changeable mass and position of the mass block. The variable-frequency principle of FVPO and the FVLRM are recognized and verified by the simulations and experiments, respectively. The experiments show that the FVLRM prototype moves the fastest when the mass block is placed at the farthest position and the prototype is at the second-order intrinsic frequencies of 42 Hz and 43 Hz, achieving a linear motion of 3.52 mm/s and a rotary motion of 286.9 mrad/s. The actuator adopts a lower operating frequency of less than 60 Hz and has the function of adjusting the natural frequency. It can achieve linear and rotational motion with a larger working stroke with 140 mm linear movement and 360° rotation.

A bipedal cooperative drive method for the stick-slip piezoelectric actuator to achieve smooth motion.

Existing kinds of stepping piezoelectric actuators have difficulty in maintaining smooth stepping characteristics in motion, especially with applied loads, because they are limited by their driving principle and structural design. However, non-smooth stepping characteristics not only reduce the output performance of piezoelectric actuators but also greatly limit the applications of piezoelectric actuators. In this paper, a bipedal cooperative drive method for the stick-slip actuator is proposed to improve stepping characteristics and achieve smooth motion under different conditions. Two flexible driving feet alternately push the rotor to rotate clockwise. Experimental results show that the stepping characteristics vary with the driving voltage, and the displacement curve transitions from non-smooth to smooth to sudden jump as the driving voltage rises. Furthermore, the displacement curves can maintain good smoothness within a horizontal load range of 20-30 g. The maximum angular speed of the designed actuator is 1452 mrad/s when the driving voltage and driving frequency are 100 V and 1400 Hz, respectively. These features help broaden the practical application of actuators.

Development of a three-degree-of-freedom piezoelectric actuator.

Multi-degree of freedom piezoelectric actuators are strongly needed for industrial applications, especially when manipulating a large and heavy mirror or lens in an optical system. A novel three-degree-of-freedom piezoelectric actuator, which is driven by two pairs of piezo-stack actuator with spatial compliant mechanisms designed to guide the motion and preload the piezo-stack actuators, is herein proposed. The structure and working principle of the proposed actuator are illustrated and its kinematic characteristic is analyzed. The stiffness of the spatial compliant mechanisms is modeled, and the dynamic characteristics are analyzed, Finite Element method is utilized to validate the correctness of the stiffness modeling and the free vibration analysis of the proposed actuator. A prototype actuator is fabricated and its output performances have been tested. Working space of X ranging from -7.1 to 5.6 µm, Y ranging from -6.2 to 8.2 µm and Z ranging from -2.3 to 2.1 µm, displacement resolutions of 15/16/21 nm along X-/Y-/Z-axis and average velocities of 52.3, 82.8 and 29.5 µm/s along X-axis, Y-axis, and Z-axis with carrying load up to 2 kg and driving frequency of 500 Hz have been achieved by the prototype actuator. The method of waveform generating for the proposed actuator has been developed with the inverse hysteresis compensation, and test results indicate that the positioning accuracy of the prototype actuator in the open loop has been improved from 0.94 to 0.23 µm for a circular trajectory tracking, from 0.48 to 0.29 µmm for an elliptical trajectory tracking, and from 0.61 to 0.32 µm for a rectangular trajectory tracking with the compensated waveform of driving voltage.

A stick-slip piezoelectric actuator with high consistency in forward and reverse motions.

This paper presents a stick-slip piezoelectric actuator with high consistency in performances of forward and reverse motions. It is achieved by developing an integrated stator which bonds two lead zirconate titanate ceramic plates to a symmetrical flexible hinge mechanism. The working principle of the actuator was introduced, and the stator was optimized by finite-element analysis. Experimental results showed that the proposed actuator had an excellent consistency in output performances of forward and reverse motions with or without an external load. The positioning resolution, maximum speed, and maximum loading capacity of the actuator were 0.061 µm, 2195.29 µm/s, and 1.1 N, respectively. This study provides a solution for improving the forward and reverse motion consistency of stick-slip piezoelectric actuators.

Experimental Research on Fluid Coupling Flexible Actuator.

In the field of micromechanics, piezoelectric actuator has attracted great attention for its high-frequency response, high displacement resolution, and high output force. However, its prospect of practical application has been largely limited by the displacement of micrometer. A fluid coupling flexible actuator was proposed, which utilizes resonance to enlarge the output displacement. The actuator uses a piezoelectric oscillator as an excitation source, fluid as the transmission medium and a flexible diaphragm for the displacement output. On the condition that the fluid is inviscid and incompressible, mathematical formulation of the membrane vibration theory has been analyzed. Then, the prototype is made. The displacement is amplified 21 times to 1.106 mm when driving frequency is 127 Hz. The flexible diaphragm appears the largest displacement output when driving frequency is close to one of the system's natural frequency. Then, the points with zero amplitude form a circle on the surface of flexible diaphragm and the movement direction of the flexible diaphragm is opposite on different sides of the circle. In fact, rather than vibrates at the first resonance frequency, the membrane in the essay is vibrating at a certain higher-order resonance frequency. The experimental results are mainly consistent with the theoretical analysis.