**1. Introduction**

With the rapid development of science and engineering, ultra-precision positioning technology has been gradually becoming a common supporting technology in many fields such as integrated circuit, optical engineering, high-end manufacturing, biomedicine, and MEMS [1–3]. The actuator, which plays a big role, is one of the key parts in the ultra-precision positioning system. The stable output with millimeter-scale stroke and nanometer-scale resolution is the basic capacity for the actuator. Besides, other characteristics, such as quick response, wide speed range, and large loading capacity, are also important [4, 5]. The traditional actuators, such as stepping motors, hydraulics, and pneumatics equipment, have lots of advantages, including adequate positioning range, high stiffness, and large load capacity. Nevertheless, some performance defects, such as cumulative positioning error, wind up, and lost motion, cannot be eliminated [6, 7].

In order to acquire better performance of the actuators, some smart functional materials are developed as the actuating materials, such as piezoelectric materials [8], shape memory alloys [9], magnetostrictive materials [10], electrostrictive materials [11], and photostrictive materials [12]. Compared with other ones, piezoelectric materials possess many structural and functional advantages, such as large stiffness, compact size, quick response, high resolution, powerful output, and easy control. Therefore, they have been utilized in ultra-precision positioning systems more widely [13, 14]. Piezoelectric materials are crystals that have no inversion symmetry structures. Under external electric field, they can generate deformations because of the rotation of the internal electric domain by the inverse piezoelectric effect. All dielectric materials generate

an electrostriction effect, but only crystal structures with no inversion symmetry can produce piezoelectric effect [12]. For electrostrictive materials, the relationship between the deformation and the electric field is parabolic, while for piezoelectric materials, it is linear [12]. Moreover, under different signal voltages, the piezoelectric materials can generate reversible expanding, contracting, and rotating deformations in one component [15]. Although the piezoelectric materials possess so many excellent characteristics, it is difficult to overcome a defect that the deformation of the piezoelectric materials is small [4, 5]. Due to the above defect, it is difficult to make use of the strain of the piezoelectric materials under the external electric field in the engineering world [16, 17]. Therefore, it has become a hot issue to develop piezoelectric actuators with a long work range and other excellent performance.

To make the piezoelectric actuator produce a long work range, researchers from all over the world propose a great many principles. The first principle is that a number of single layer piezoelectric components are stacked to form one multilayer piezoelectric actuator which can be called piezo-stack actuator. Using this method, many small deformations from the single-layer piezoelectric components can be concatenated to produce a long displacement of the multilayer piezoelectric actuator [18, 19]. The working range of a piezo-stack actuator can reach 0.1% to 0.15% of its dimension [20, 21]. The second principle is to utilize some designed mechanisms to enlarge the small deformation of the piezoelectric materials, such as lever mechanisms and polygon mechanisms. Using these enlarging mechanisms, we can obtain the submillimeter scale work range of the piezoelectric actuator [22, 23]. The third principle is the stepping principle which imitates some animals' movement behavior to repeat and accumulate numerous small displacements of the piezoelectric materials until an adequate stroke is achieved [24–27]. Many stepping-type piezoelectric actuators are bionic type piezoelectric actuators. The fourth principle is the ultrasonic driving principle which uses the high-frequency vibrations of the piezoelectric materials to drive the output component to produce large displacements [28–30].

This chapter introduces the working principle of the piezoelectric actuators with a long work range, especially the bionic type piezoelectric actuators. The actuators can

**Figure 1.** *The chapter organization.*

*Bionic Type Piezoelectric Actuators DOI: http://dx.doi.org/10.5772/intechopen.103765*

be classified as linear ones and rotary ones. This chapter is mainly elaborated from the linear actuators. But the theories in this chapter are also suitable for the rotary actuators. The organization of the chapter is shown in **Figure 1**. The chapter is designed as follows: In Section 2, the piezoelectric materials and the piezoelectric effects are introduced briefly. In Section 3, the inchworm type actuators are elaborated, which are classified into the walker type, the pusher type, and the mixed type. In Section 4, we describe the seal type actuators including the walker type, the pusher type, and the mixed type. In Section 5, the characteristics of the bionic actuators are analyzed. In the last section, the conclusions of the chapter are given.
