**3. Inchworm actuators**

The inchworm is a kind of insect in nature, which moves by wriggle. The researchers found that the inchworm has special body structures including a flexible body and numerous feet. The flexible body can be bent and the feet are on the head end and the tail end of the body. When the inchworm moves, it grips the tree trunk firstly with its forefeet on the head end of the body. Next, the inchworm bends its flexible body and pulls forward the hindfeet on the tail end of the body. Then, it grips the tree trunk with its hindfeet. Afterward, the inchworm releases the forefeet from the tree trunk. Then, it straightens the flexible body and pushes forward the forefeet. Finally, the inchworm grips the tree trunk again with its forefeet and releases the hindfeet from the tree trunk. After the above actions, the inchworm has moved forward with one step and reverts to the initial status. If the above process is repeated continuously, the inchworm can move forward continuously on the tree trunk.

Inspired by the wriggle mode of the inchworm, the researchers develop the inchworm type actuators driven by the piezoelectric materials. Similarity with the body structures of the inchworm, the inchworm type piezoelectric actuator is composed of a feeding component and two clamping components, which imitate the flexible body, forefeet, and hindfeet of the inchworm respectively. As shown in **Figure 3**, according to the relative position relationship of the feeding component and two clamping components, the inchworm actuator is classified as walker type, pusher type, and mixed type. As shown in **Figure 3(a)**, the walker type actuator is whose feeding component and two clamping components are all designed on the mover. During the process of the walker type actuator running, all of the feeding component and two clamping components are pushed with the mover. As shown in **Figure 3(b)**, the pusher type actuator is whose feeding component and two clamping components are all designed on the stator. During the process of the pusher type actuator running, none of the feeding component and two clamping components is pushed with the mover. As shown in **Figure 3(c)**, the mixed type actuator combines the structural features of the walker and pusher piezoelectric actuators. Either the feeding component or the two clamping components is designed on the mover and the other component is designed on the stator. During the process of the pusher type actuator running, Either the feeding component or the two clamping components is pushed with the mover and the other component is fixed on the stator.

The operating principles for the three types of inchworm actuators are shown in **Figure 3** and introduced as follows:

a.The operating principle of the walker type actuator:

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

**Figure 3.**

*Operating principles of inchworm actuators [32]. (a) Walker type; (b) pusher type; (c) mixed type.*


After the above actions, the mover of the walker actuator has moved rightwards with one step. If steps (1) to (7) are repeated continuously, the walker inchworm

actuator can move rightwards to output long-range displacement step by step. The backward motion can be generated if the operating sequences of feeding component and the clamping components are changed.

b.The operating principle of the pusher type actuator:


After the above actions, the mover of the pusher actuator has moved rightwards with one step. If steps (1) to (7) are repeated continuously, the pusher inchworm actuator can move rightwards to output long-range displacement step by step. The backward motion can be generated if the operating sequences of feeding component and the clamping components are changed.

	- 1.The initial status of the mixed actuator;
	- 2.The left clamping component operates and clamps the left end of the mover;
	- 3.The feeding component functions and pushes the right end of the mover rightwards;
	- 4.The right clamping component operates and clamps the right end of the mover;
	- 5.The left clamping component resets and releases the left end of the mover;
	- 6.The feeding component resets and pulls the left end of the mover rightwards;
	- 7.The left clamping component operates and clamps the left end of the mover again;
	- 8.The right clamping component resets and releases the right end of the mover. The actuator reverts to step (1).

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

After the above actions, the mover of the mixed actuator has moved rightwards with one step. If steps (1) to (7) are repeated continuously, the mixed inchworm actuator can move rightwards to output long-range displacement step by step. The backward motion can be generated if the operating sequences of feeding component and the clamping components are changed. Generally, the electric signals to drive the inchworm actuator are usually the rectangular wave signal or trapezoidal wave signal.
