**1. Introduction**

Micro/nano-positioning system with micro-/nano-accuracy is a key technology in industry and science fields such as precision machining and measurement, optical engineering, modern medical treatment, biological genetic engineering, and aerospace science and technology [1–4]. The so-called actuators refer to a functional device that can output specific motion, such as linear and rotary motion, for micro-/ nano-positioning systems. Traditional actuators, such as electrical motors, hydraulic motors, and pneumatic motors, can realize the large stroke and large load; however, their positioning accuracy is low and the size is large. They are still facing the problem of high-positioning resolution and compact size. In recent decades, researchers

**Figure 1.** *Classification of piezoelectric actuators.*

devote themselves to the research of new actuators with better performance to realize micro-/nano-accuracy with a compact size. Piezoelectric actuator is one novel actuator that uses the inverse piezoelectric effect of piezoelectric materials to convert electrical energy into mechanical energy to realize controllable positioning accuracy [5, 6]. Piezoelectric actuators have the characteristics of compact size, light weight, high precision, fast response, good control characteristics, high energy density, low energy consumption, and free from magnetic field interference. Researchers have developed a variety of piezoelectric actuators and applied them to biological cell micromanipulation, atomic manipulation, micro-/nano-indentation and other systems, and achieved good application results. According to different driving principles, generally, the piezoelectric actuators can be divided into two categories: direct-driving piezoelectric actuators and stepping piezoelectric actuators. The direct-driving piezoelectric actuators mainly apply piezoelectric elements to directly drive the output mechanism, and its working stroke is usually small; the stepping piezoelectric actuators adopt the stepping motion mode to realize large working displacement, which can be further subdivided into ultrasonic piezoelectric actuator, friction-inertia piezoelectric actuator, bionic piezoelectric actuator, etc., as shown in **Figure 1**.
