**5. Characteristic analysis of the bionic actuators**

The inchworm actuator and the seal actuator are the commonest bionic type piezoelectric actuators, which are also the stepping type actuators. With the stepping driving principles, the piezoelectric actuators are completely free of the micro deformations of the piezoelectric materials and are able to generate the long-range displacements as required step by step. Therefore, the output displacements can reach numerous millimeters, or even without limit. The characteristics of the two types of bionic actuators are presented in **Table 1**.


#### **Table 1.**

*Characteristics of the bionic actuators.*

The inchworm actuator has a complex configuration while the structure of the seal actuator is compact. Thus, if there are requirements for the space and the weight, the seal actuator is preferred. Generally, the resolution of the seal actuator is higher than that of the inchworm. Hence, we use the seal actuator a lot to achieve more precise operation. The inchworm actuator has a larger load capacity than the seal actuator, so we can select the inchworm actuator when we need the large output force. If high speed is required, the seal actuator is more appropriate. Because the seal actuator is able to generate higher velocity than the inchworm actuator. In addition, the seal actuator is easier to control than the inchworm actuator. Because the inchworm actuator has more moving executive components. In application, we can select and use an appropriate type of bionic actuators according to **Table 1**.
