*3.2.2 Research on direction-guidance hybrid method*

The related work based on the DGHM is as follows [19]. As shown in **Figure 12(a)**, an actuator is fabricated to verify the feasibility of the DGHM. In the first place, the influence of the DG waveform with different amplitudes of the driving foot is analyzed by the FEM. The point *P* is chosen as the reference point, which represents the contact point between the slider and the driving foot, as shown in **Figure 12(c)**. **Figure 12(b)** simulates the equivalent stress of the stator and deformation of the point *P* when the piezoelectric stack inputs different displacements driven by the DG waveform. The displacement of the point *P* increases linearly in the o*x* and o*y* axes directions with the increase of the input displacement, which verifies the effectiveness of the DG waveform. Besides, the equivalent stress of the stator is 202.46 MPa with the input of 10 *μ*m. Afterwards, the modes of the stator are analyzed to make the actuator operate at a resonant frequency. As shown in **Figure 12(c)**, when the frequency of RD waveform is at fourth mode (around 30.57 kHz), the proposed actuator has the potential to achieve higher speed.

The actuator is manufactured and the test system is built, as shown in **Figure 12(d)**. Firstly, the effect of the voltage of DG waveform on the displacement of the driving foot is explored. As shown in **Figure 12(e)**, the driving foot can achieve displacement along

#### **Figure 12.**

*Research on DGHM. (a) Configuration of the proposed design. (b) Simulation of the stator by FEM. (c) Fourth mode of the stator. (d) The experimental system and the prototype. (e) The relationship between the displacement of the reflector and the voltage of DG waveform. (f) The relationship between driving frequency of DGHM and output velocity. (g) The relationship between the velocity and the voltage of RD waveform under the different voltages of DG waveform. (h) The displacement of the prototype at different voltages of DG waveform. (i) The horizontal thrust and the velocity versus at the voltages of DG waveform under the DGHM [19].*

the positive direction of the *ox* and *oy* axes. With the increase of the voltage of the DG waveform, the displacements in both directions have a good linear relationship, which shows that the actuator can produce a pre-deformation by the aid of the proposed excitation method.

Under the condition of an initial preload force of 0.5 N, a series of experiments are carried out to explore the output characteristics of the proposed actuator. As shown in **Figure 12(f)**, the output speed and the frequency of the RD waveform are studied under different voltage of the DG waveform to determine the optimal driving frequency of the RD waveform. At different voltages of the DG waveform, the optimal frequencies of the RD waveform are around 33 kHz, which is close to the frequency simulated by FEM. When the DG waveform is 20 V and the RD waveform is 8 VP-P and 33.1 kHz, the actuator reaches the maximum velocity of 70.26 mm/s.

Under different DG waveform voltages, the velocities of the actuator versus voltages of the RD waveform are measured. It can be seen from **Figure 12(g)** that the velocity increases as the RD waveform voltage. The actuator starts to move as the voltage of RD waveform is about 3 Vp-p. At the voltage of 8 Vp-p, the velocity reaches the maximum and it can be further improved by increasing the voltage of the RD waveform. As shown in **Figure 12(h)**, the displacement curve at different voltages of DG waveform shows that the DGHM can make the actuator move stably. As shown in **Figure 12(i)**, the horizontal thrust and velocity at a different voltage of the DG waveform are explored which shows that the actuator can achieve the large horizontal thrust or the relatively high velocity under the DGHM. Although the initial locking force is 0.5 N, the actuator can achieve the maximum horizontal thrust of 1.36 N when the voltage of DG waveform is 60 V.

## **4. Conclusions**

A comprehensive work of piezoelectric stick–slip actuators was presented to improve their output characteristics. This work divided our team's stick–slip actuators into two categories based on the research ideas, including structural designs and driving methods.

In terms of structural designs, the trapezoid-type actuator increased static friction force in slow extension stage and decreased kinetic friction force in rapid contraction stage by lateral motion, which improved the forward performance. The actuators with asymmetrical flexure hinges widened the structure forms of the actuator and improved the velocity, load and efficiency. The mode conversion actuator could be used in precision positioning platform and ultra-precision machining due to its nanometer resolution. Besides, an actuator with a coupled asymmetrical flexure hinge mechanism realized the bidirectional motion.

In terms of driving methods, a non-resonant mode smooth driving method (SDM) based on ultrasonic friction reduction was proposed, and the backward motion was restrained during the rapid contraction stage. Compared with nonresonant mode SDM, the resonant mode SDM achieved a higher velocity, larger load and smoother displacement. Besides, the proposed SDM achieved better low voltage characteristics and widened the symmetry relative to the traditional driving method. Finally, a direction-guidance hybrid method (DGHM) could achieve superior performance, especially for high speed.

## **Acknowledgements**

This work was financially supported by the Jilin Province Science and Technology Development Plan Item (No. 20150312006ZG), the Postdoctoral *The Asymmetric Flexure Hinge Structures and the Hybrid Excitation Methods for Piezoelectric… DOI: http://dx.doi.org/10.5772/intechopen.95536*

Science Foundation of China (No. 2015 M571356), the Key Projects of Science and Technology Development Plan of Jilin Province (No. 20160204054GX), the Project of Industrial Technology Research and Development of Jilin Province Development and Reform Commission (No. 2019C037-6) and the Science and Technology Development Plan of Jilin Province (Nos. 20190201108JC and 20200201057JC).
